New Concepts and Advances in Photocatalytic Materials for Energy and Environmental Applications
Session I-1 - Design Elements and Advanced Concepts for Photo-functional Materials
I-1:IL01 Nanostructured Materials for Photocatalytic Energy Conversion Applications
E. SELLI, G.L. CHIARELLO, M.V. DOZZI, Dipartimento di Chimica, Università degli Studi di Milano, Milano, Italy
The main challenge in the field photocatalytic fuels production consists in the electronic structure engineering of photocatalytic materials able to harvest solar radiation producing electron-hole couples and ensure efficient charge separation for solar energy driven thermodynamically up-hill processes. In recent years we focused on the development of innovative photocatalytic materials, based on the engineering of their electronic structure, on solid solutions and heterojunctions produced by different techniques, on the modification of the surface properties by noble metals or co-catalysts to achieve increased charge separation. Innovative technologies, including RF magnetron sputtering and flame spray pyrolysis, together with electrochemical growth of nanotube (NT) arrays to obtain photoactive electrodes, have been explored with the final aim of producing photocatalytic systems in integrated form to be employed within devices for pure hydrogen production. In particular, recent results showed that the ordered 2D structure of the NT array confers them the photonic crystal properties with the formation of a photonic bandgap, the shift of which leads to a red shift of the activity threshold that allows harvesting and converting a larger portion of the solar spectrum.
I-1:IL04 Z-scheme over all Water Splitting on Rh/K4Nb6O17 Nanosheet Photocatalyst
HSIN-YU LIN, YU-LIN YE, Department of Materials Science and Engineering, National Dong Hwa University, Hualien, Taiwan
Developing a photocatalysis system to generate hydrogen from water is a topic of great interest for fundamental and practical importance. In this study, hydrogen production by a new Z-scheme photocatalysis water splitting system was examined over Rh modified K4Nb6O17 nanosheet and Pt/WO3 photocatalysts for H2 evolution and O2 evolution with I-/IO3- electron mediator under UV light irradiation. The H2 evolution photocatalyst, Rh/K4Nb6O17 nanosheet with a slit like framework, was prepared by exfoliation of and proton exchange reaction. Pt/WO3 prepared by incipient-wetness impregnation method was used as O2 evolution photocatalyst. The catalysts were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy analysis (XPS), and ultraviolet-visible spectroscopy (UV-vis). These catalysts characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible spectroscopy (UV-Vis). In this study, we developed a facile method of preparing K4Nb6O17 nanosheet containing Rh nanoparticles. Our results show that I- concentration and pH of reaction solution significantly influenced the photocatalytic activity. The combination of Rh modified K4Nb6O17 nanosheet with Pt/WO3 achieves a very high photoactivity (H2: 4240 μmol g-1 h-1 and O2: 1622 μmol g-1 h-1).
I-1:L05 Iron Oxide-based Electrocatalysts for Water Oxidation at Neutral pH
HIROSHI IRIE, K. ISHIKAWA, T. TAKASHIMA, Clean Energy Research Center, University of Yamanashi, Kofu, Yamanashi, Japan
Various photocatalytic materials aiming at water splitting have been reported because produced hydrogen (H2) is attractive as a clean and renewable fuel. As for the water-splitting reaction, oxygen (O2) evolution reaction (OER) usually requires a large overpotential because it is intrinsically difficult to control the multielectron transfer process. Then the decreasing in the overpotential has been regarded as the critical issue and thus the development of an active and effective OER catalyst is required to enhance the water-splitting reaction. So far, iridium- or ruthenium-based catalysts have been enthusiastically investigated as OER catalysts. In place of them, we have tried to find the OER catalysts among earth-abundant metal oxides, such as iron oxides. We have found that the stabilization of Fe4+ was responsible for the enhancement of OER activity. Base on the finding, we have investigated the OER activity of strontium ferrite (Sr3Fe2O7) and lanthanum-substituted Sr3Fe2O7 (Sr2.6La0.4Fe2O7) to confirm the important role of Fe4+ stability in the OER activity.
I-1:L07 Bismuth Vanadate-based Heterojunction Photoelectrodes for Photoelectrochemical Water Splitting: Synthesis and Characterisation
CHONG SIANG YAW1, MENG NAN CHONG1,2, AI KAH SOH3, 1School of Engineering, Chemical Engineering Discipline, Monash University Malaysia, Bandar Sunway, Selangor, Malaysia; 2Sustainable Water Alliance, Advanced Engineering Platform, Monash University Malaysia, Bandar Sunway, Selangor, Malaysia; 3School of Engineering, Mechanical Engineering Discipline, Monash University Malaysia, Bandar Sunway, Selangor, Malaysia
The main aim of this study was to electrochemically synthesize and characterise bismuth vanadate (BiVO4) photoelectrodes for water splitting. The influence of electrodeposition duration and annealing temperature on the BiVO4 nanocrystals structure were systematically studied. These were followed by advanced characterisation of the BiVO4 photoelectrodes by using FE-SEM, EDX, XRD, UV-visible spectroscopy, PEC measurements and EIS analysis. Though this study, it was found that the electrodeposition duration of 4500s under air condition and heat treatment at 400℃ were able to yield the highest photocurrent density of 1.02 mA/cm2. When the electrodeposited BiVO4 thin films wereis subjected to different annealing temperatures, phase transitions will occuroccurred for tetragonal (528 K) and monoclinic (670 K). Through this study, it was found that the electrodeposition duration of 4500 s under air condition and annealing treatment at 400 ℃ were able to yield the highest photocurrent density of 1.02 mA/cm2. Finally, other BiVO4-based heterojunction photoelectrodes with various n-type semiconductors were coupled and formed in order to reduce the rapid recombination rate of electron-hole pairs.
I-1:IL08 Reflections on Rust: Iron Oxide Photoelectrodes for Solar Energy Conversion and Storage
A. ROTHSCHILD, Department of Materials Science and Engineering, Technion – Israel Institute of Technology, Haifa, Israel
Large scale utilization of solar power requires affordable energy storage technology. Likewise, there is a need for renewable fuels to replace fossil fuels. These challenges can be achieved by splitting water into hydrogen and oxygen using solar power. The first and foremost challenge toward this goal is the development of stable, efficient and affordable photoelectrodes. Photoelectrodes for solar water splitting must employ a semiconductor material with exceptional stability against corrosion and visible-light absorption. On top of that, it should also be abundant, inexpensive and non-toxic. Iron oxide (hematite) is one of few materials meeting these criteria, but its poor transport properties and ultrafast charge carrier recombination present a challenge for efficient charge carrier generation, separation and collection. We explore an innovative solution to this challenge using ultrathin (20-30 nm) films on specular back reflector substrates. This simple design traps the light in otherwise nearly translucent ultrathin films, amplifying the intensity close to the surface wherein photogenerated charge carriers can reach the surface and split water before recombination takes place. This is the enabling key towards the development of high efficiency photoelectrodes.
I-1:IL09 Hybrid Organic/Inorganic Assemblies with Tailored Photoelectro-chemical Activity: from Synthetic Aspects to Energy Applications
C. JANAKY, A. VARGA, A. KORMANYOS, G. SAMU, University of Szeged, Hungary, K. RAJESHWAR, The University of Texas at Arlington, TX, USA
To efficiently harness the possible synergies, stemming from the combination of organic conducting polymers and inorganic semiconductors, sophisticated assembling methods are required to control the composition and morphology at the nanoscale. This talk focuses on how to use light-assisted methods in the synthesis of such hybrid materials. First, I will show examples on the photoelectrochemical deposition of conducting polymers (e.g., polypyrrole, polyaniline, PEDOT) on nanostructured inorganic semiconductor matrices, such as TiO2 nanotube arrays and nanoporous WO3. In the second part of my talk, I will present our proof-of-concept study, demonstrating the in situ photocatalytic deposition of CdS nanoparticles on poly(3-hexylthiophene) (P3HT) nanofibers, exploiting the semiconducting nature of this polymer. We confirmed that both the particle size and the loading can be tuned by the deposition time. Photoelectrochemical studies revealed the facile transfer of photogenerated electrons from P3HT to CdS, as well as that of the holes from CdS to P3HT. It is believed that ensuring intimate contact between the components in these nanohybrids will open new avenues in various application schemes, e.g., solar energy conversion.
I-1:L10 Flexible Transparent Conductive Electrodes and Photocatalytic Conversion of CO2 to CO Gas Sensor using Single Crystal Cu Thin Film
SE-YOUNG JEONG1,2, I.H. PARK1, W.K. KIM3, S. LEE4, H.Y. PARK1, Y.J. LEE1, G.W. LEE5, 1Department of Cogno-Mechatronics Engineering, Pusan National University, Miryang, Rep.of Korea; 2Department of optics and mechatronics engineering, Pusan National University, Miryang, Rep.of Korea; 3R&D Center, LG Display Co., Ltd., Paju, Rep.of Korea; 4Materials and Science Engineering, University of Maryland, College Park, Maryland, USA; 5Korea Research Institute of Standards and Science & Department of Science of Measurement, University of Science and Technology, Daejeon, Rep.of Korea
(Cu) thin films have been widely used as electrodes and interconnection wires in integrated electronic circuits, and more recently as substrates for the synthesis of graphene. However, the ultra-high vacuum processes required for high-quality Cu film fabrication, such as molecular beam epitaxy (MBE), restricts mass production with low cost. In this work, we demonstrated high-quality Cu thin films using a single-crystal Cu target and sputtering technique; the resulting film quality was comparable to that produced using MBE, even under unfavorable conditions for pure Cu film growth. The Cu thin film was epitaxially grown on an Al2O3 (0001) substrate, and had high crystalline orientation along the (111) direction. Despite the 10-3 Pa vacuum conditions, the resulting thin film was oxygen free due to the high chemical stability of the sputtered specimen from a single-crystal target; moreover, the deposited film had > 5 X higher adhesion force than that produced using a polycrystalline target. We applied the technique fabricating the single crystal thin film to the flexible transparent conducting electrodes, where a micromesh/nanomesh structure was fabricated on a polyimide substrate using UV lithography and wet etching. Hybrid Cu mesh electrodes were fabricated by adding a capping layer of either ZnO or Al-doped ZnO. The sheet resistance and the transmittance of the electrode with an Al-doped ZnO capping layer were 6.197 ohm/sq and 90.657 %, respectively, and the figure of merit was 60.502 × 10-3 /ohm, which remained relatively unchanged after thermal annealing at 200 °C and 1,000 cycles of bending. We succeeded to fabricate Cu single crystal nanowire by the patterning of the single crystal Cu thin film grown on sapphire substrate, which shows less resistivity than bulk Cu even in nano scale and can be located where we want. We also applied Cu single crystal film to photo-catalystic conversion of CO2 to CO by making homogeneous CuO film by oxidation.
1. W. K. Kim, et al., and Se-Young Jeong, Scientific Reports 5, 10715 (2015). 2. J. Y. Kim et al., and Se-Young Jeong, Scientific Reports 4, 05450 (2014). 3. S. Lee et al., Cheol Seong Hwang, and Se-Young Jeong, Scientific Reports 4, 6230 (2014). 4. Y. C. Cho et al., G. W. Lee, and Se-Young Jeong, CrystEngComm, 16 7575 (2014)
I-1:IL12 Electron Trapping in Semiconductor Photocatalysis
BUNSHO OHTANI1,2, AKIO NITTA2, NAOYA MURAKAMI3, MAI TAKASE4, 1Institute for Catalysis, Hokkaido University, Sapporo, Japan; 2Graduate School of Environmental Science, Hokkaido University, Sapporo, Japan; 3Graduate School of Engineering, Kyushu Institute of Technology, Kitakyushu, Fukuoka, Japan; 4Graduate School of Engineering, Muroran Institute of Technology, Muroran, Japan
A hypothesis proposed is that electron traps (ETs) in photocatalyst particles govern electron transfer and electron-hole recombination, i.e., photocatalytic activity: the higher the density of shallow ETs and the lower the density of deep ETs are, the higher the photocatalytic activity is. Although their structure is not clear, it is sure that appreciable ETs are there in metal oxides. It has been well known that metal oxides turn gray when reduced. Here, newly developed reversed double-beam photoacoustic spectroscopy (RDB-PAS) is reported as a powerful tool for ERDT (energy-resolved density of ETs) measurement. A brief explanation of the principle of RDB-PAS is (i) photoacoustic detection, using modulated LED light (first beam), of accumulation of electrons, i.e., ETs filling, from deeper to shallower level, using scanning continuous monochromatic light (second beam) to excite valence-band electrons directly to ETs, (ii) differentiating the resultant spectra from the longer wavelength side and conversion to absolute density of ETs with reference to results of the photochemical methods and (iii) plotting ERDT as a function of energy difference from the bottom of CB which is determined by ordinary PAS measurement of anatase titania samples.
I-1:IL13 Doped Lanthanum Ferrite Perovskites: Promising Materials for Photocatalytic Applications
F. PARRINO1, E. GARCÍA-LÓPEZ1, G. MARCÌ1, L. PALMISANO1, V. FELICE2, I. NATALI SORA2, L. ARMELAO3, 1“Schiavello-Grillone” Photocatalysis Group, Dipartimento di Energia, Ingegneria dell’informazione e Modelli matematici (DEIM), University of Palermo, Palermo, Italy; 2INSTM R.U. Bergamo and Dipartimento di Ingegneria, University of Bergamo, Dalmine, Bergamo, Italy; 3IENI-CNR and INSTM, Dipartimento di Scienze Chimiche, Università di Padova, Padova, Italy
Perovskite-type transition metal oxides (TMOs) are semiconductors with a band gap narrow enough for efficient absorption of visible light. Therefore, they offer the possibility of using solar radiation or visible-light lamps for their activation, thus allowing the development of low cost photocatalytic applications. This is a strong advantage over the most used photocatalyst for environmental remediation, i.e. titanium dioxide, which instead absorbs UV light. One of the most used TMOs is lanthanum ferrite (LaFeO3). Generally, the functional properties of LaFeO3 can be controlled either by modulating structure and defectivity or by substitution of the metals into the crystal structure. Although modification is a quite simple task due to the versatility of this material, understanding the consequences of doping on the physico-chemical properties and on the photocatalytic activity still remains a challenging issue. In this work the effects of Sr and Cu doping on the physico-chemical and photoelectrochemical properties of LaFeO3 are presented along with their influence on the photocatalytic activity in gas and liquid phases. In particular, the photocatalytic oxidation of 2-propanol and of 4-nitrophenol were investigated as model reactions in gas and liquid phases, respectively.
I-1:L14 Enhancing Photocatalytic Activity of TiO2 by a Synergistic Effect between Plasmon Resonance in Ag Nanoparticles and Optical Interference
G. CACCIATO1,2, M. ZIMBONE2, M. BAYLE3, C. BONAFOS3, V. PRIVITERA2, M.G. GRIMALDI1,2, R. CARLES3, 1Dipartimento di Fisica ed Astronomia-Università di Catania, Catania, Italy; 2IMM-CNR, Catania, Italy; 3CEMES-CNRS Université de Toulouse, Toulouse Cedex, France
Development of plasmo-electronic-based nanostructures, such as photocatalysis, strongly depends on the understanding of carrier generation enhancement in an active semiconductor layer. We present original results obtained from assemblies of silver nanoparticles (Ag NPs) buried at few nm deep underneath the free surface of a thin titania (TiO2) layer. By using a properly sample architecture, we have taken simultaneous benefit of spectrally and spatially localized surface plasmon resonance, and optical amplification in order to enhance photon capture in the visible range. TEM and optical reflectance are used control the optical design. Plasmon-resonant Raman spectroscopy is originally used to analyze confinement of vibrations and electronic excitations in Ag NPs, the latter through the so-called “background” in SERS that gives here the signature of confined electron-hole excitations in the NPs. Moreover, the observation of mixed LO-plasmon modes in TiO2 gives proof of coupling between injected carriers in the active semiconductor layer and its polar phonons. These substrates optimized so as to maximize the electromagnetic energy harvesting and carriers generation, show a high increase of the photocalyst activity, but also appear promising for other plasmo-electronics based devices.
I-1:L15 Ternary TiO2-CuxS-Fly Ash System: Synthesis, Characterisation and Application in Adsorption and Photocatalysis
L. ANDRONIC, M. VISA, A. DUTA, Transilvania University of Brasov, R&D Centre of Renewable Energy Systems and Recycling, Brasov, Romania
The wastewater from industrial processes has a multi-pollutants composition, thus their treatment (e.g. for re-use) often requires simultaneous/combined advanced processes as adsorption and photocatalysis. Therefore, the paper proposes a new approach based on the simultaneous photocatalysis and adsorption to remove a wide range of pollutants. This study aimed at developing an adsorption–photocatalysis system to treat industrial wastewater; additionally, as this industrial process is acceptable, photocatalysis exceeds the technical and economic main barrier: the use of UV radiation as activating agent and replace it with the VIS radiation or sunlight. A range of visible active composite photocatalyst based on the tandem TiO2-CuxS-Fly ash composites were prepared by hydrothermal synthesis and photochemical precipitation. SEM, AFM, XRD, FT-IR, and UV–vis diffuse reflectance spectroscopy were used to characterise materials. Methylene blue, SDBS and Cd2+ were selected as pollutants to evaluate the photocatalytic and adsorption ability of the composites. The pollutants degradation and adsorption mechanisms on the ternary composites were discusses based on experimental results.
This research was supported by a grant of the Romanian National ANCS UEFISCDI project PNII-PT-PCCA-2013-4-0726
I-1:IL16 Novel Functional Materials Applied to Photocatalysis
YEN-TING CHEN1, KAO-SHUO CHANG1,2, 1Department of Materials Science & Engineering, National Cheng Kung University, Tainan City, Taiwan; 2Promotion Center for Global Materials Research (PCGMR), National Cheng Kung University
We would like to report the efficient study of Y2O3 enhanced photocatalysis using novel Y2O3-TiO2 nanorod composite composition spreads. The highlights of this research are 1) successful fabrication of the sample using a combinatorial sputtering system without involving any special treatments, 2) systematic investigation of the coupling effect between Y2O3 and TiO2 to achieve synergistic photocatalysis, and 3) opening an alternative novel application in photocatalysis for high-k materials. The composition variation and phase evolution across the sample were achieved through the well-controlled shutter moving strategy, which were verified using electron probe energy dispersive spectroscopy (XPS) and x-ray diffraction, respectively. XPS and UV-vis spectrometry measurements also complemented the composition variation results. The sample #6 (4 at% Y2O3-96 at% TiO2) was observed to exhibit the best photocatalytic efficiencies among all the samples under study, approximately 3.4 and 1.4 times higher than that of P25 and pure TiO2 nanorods, respectively, suggesting the effectiveness of Y2O3 incorporation. With the aid of PL analyses and the simple Y2O3-TiO2 energy band diagram, the charge carrier transport in the system was elucidated. The predominant factor to achieve synergistic photocatalysis for the sample #6 was justified to be electron migration along defective Y2O3 nanorods to the sample surface. In addition, the photoelectrochemical stability and reusability of the sample #6 was also demonstrated. All the features suggested the sample #6 promising for the photocatalytic applications.
I-1:L17 Micro-TiO2 as Photocatalyst for New Ceramic Surfaces Activated via Digital Printing
M. STUCCHI, C.L. BIANCHI, C. PIROLA, Università degli studi di Milano, Milano, Italy; G. CERRATO, Università degli studi di Torino, Torino, Italy; A. DIMICHELE, Università degli studi di Perugia, Perugia, Italy; V. CAPUCCI, GranitiFiandre SpA, Fiorano M.se, Italy
Nowadays pollution is one of the biggest concerns of both the public and different governments because it is risky for the safety of the every habitat. Among the AOPs, photocatalysis is one of the most promising and TiO2 is the best semiconductor able to oxidize pollutants; especially, it can be applied on materials: TiO2-photocatalytic surfaces might play a major role in cleaning environments. Industrial photocatalytic tiles are commercially available but the classical preparation consists in the deposition of TiO2 by airless spray, sometimes without a good powder’s distribution. The digital printing was exploited as a new tool to manufacture photocatalytic tiles even of very large size, in order to solve this issue. Crucial is the use of micro-TiO2 instead of nano: some tests on the animals have reported that NPs are dangerous and the high difficulty of handling is not convenient in industrial uses. The surface of the photoactive slabs was analyzed by HR-SEM showing an excellent uniformity. Photocatalytic degradation tests performed in air using both NOx and VOCs molecules confirm the good performances of the tiles to tackle the environment pollution.
I-1:L18 Designing Bimetallic Reduction Co-catalysts – Correlating Atomic Structure with Properties
M. BAR SADAN, Department of chemistry, Ben Gurion University of the Negev, Israel
Correlating structure and function is fundamental for the design of functional materials. Specifically, the atomic rearrangement within a nanoparticle has a direct effect on its properties and overall performance as a building block. While synthetic efforts have succeeded in producing diverse complex materials, the rational design of new materials is still a challenge. Our approach is using atomic resolution transmission electron microscopy to unravel the atomic structure of the particle, therefore allowing the understanding of the growth process and the origin of the functionality of the structures. We believe that by doing so, design rules can be offered to optimize the available nanoparticles for their designated role as functional units.The above-mentioned rationale was used for understanding the enhanced activity of Au-Pd metal tips on seeded rods of CdSe@CdS, by studying the effects of structure both on efficiency and stability. I will show that a structure of Au@alloy is the most efficient photocatalyst and also more stable in longer illumination times (50 hours). The degradation mechanisms will be unraveled and potential strategies to prevent them will be suggested. In addition, I will present the evolution of the structures through the synthesis stages, showing how that atomic re-construction of the particles during the initial synthesis of the structures might have detrimental consequence on their stability.
I-1:L19 Nanoplasmonics-assisted Degradation of Pollutants and Oxidation of Glycerol under Visible Light
Z. CHEHADI1,2, S. ZAID3,4, J.-S. GIRARDON3,4, J. TOUFAILY2, M. CAPRON3,4, F. DUMEIGNIL3,4, T. HAMIEH2, R. BACHELOT1, S. JRADI1, 1Laboratoire de Nanotechnologie et d’Instrumentation Optique, Institut Charles Delaunay, UMR 6281 CNRS, Université de Technologie de Troyes, Troyes Cedex, France; 2Laboratory of Materials, Catalysis, Environment and Analytical Methods, Faculty of Sciences I, Doctorate School of Science and Technology, Lebanese University, Beirut, Lebanon; 3Université Lille Nord de France, Lille, France; 4Unité de Catalyse et de Chimie du Solide, UCCS (UMR CNRS 8181), Villeneuve d’Ascq, France
Many approaches were used for new solar energy harvesting. An especially attractive approach is based on the use of sunlight to drive chemical reaction (1). In this context Plasmonic nanostructures of noble metals have been attracting significant attention due to their ability to interact with light from visible to near IR range through the creation of resonant surface plasmon (2). Recent studies have shown that plasmonic nanostructures can be used to drive chemical model reaction with visible light where nanoparticles (NPs) act as the light absorber and the catalytic active site (3). This behavior is attributed to the plasmonic effect of gold nanoparticles (GNPs) which can concentrate the energy of visible light and convert it into heat (5). Consequently, photoexcited GNPs can act as efficient nanosources of light, heat and energetic electrons (4). The recent advances in the comprehension of local properties of GNPs have led to development of the plasmonic assisted catalysis approach which has been applied to a large variety of reactions (4, 6). Here we report the feasibility of this “nanoplasmonic” catalysis on an industrial and environmental application reaction. First, we studied the photocatalytic degradation of Bisphenol A (BPA) under visible irradiation (laser source and LED). We investigate the coupling between Plasmonic GNPs and catalyst supports such as TiO2, ZnO and Al2O3 on the photodegradation reaction of BPA. The experimental investigations have shown extremely fast and complete photodegradation of organic pollutants in water (7). Secondly, the oxidation of glycerol (co-product of biodiesel production) in the presence of supported GNPs under visible irradiation and atmospheric pressure at room temperature was demonstrated. The conversion of glycerol was 89% after 2 h of reaction at ambient temperature. Experimental results indicate that oxidation was induced by excited gold nanoparticles and that organic acids such as glyceric acid and tartronic acid are appropriate as essential products in the oxidation reaction. The reaction does not occur in the absence of laser irradiation. In comparison to previous experiments our approach is characterized by many aspects: (a) Coupling nanothermal effect and catalytic effect of nanoparticles offers the potential of studying the oxidation of glycerol under sunlight (b) Coupling hot electrons effect of MNPs and catalyst support offers the potential of studying the degradation of BPA under sunlight (c) The oxidation of glycerol was carried out in the absence of macroscopic heating and atmospheric pressure (d) The photodegradation of BPA is complete after 12 min using visible source of light.
(1) Akihiko Kudo, Yugo Miseki, Heterogeneous photocatalyst materials for water splitting , Chem. Soc. Rev. 2009, 38, 253−278. (2) Matthew E. Stewart, Christopher R. Anderton, Lucas B. Thompson, Joana Maria, Stephen K. Gray, John A. Rogers, and Ralph G. Nuzzo, Nanostructured plasmonic sensors, Chem. Rev 108 (2008) 494. (3) Peng Wang et al., Plasmonic photocatalysts: harvesting visible light with noble metal nanoparticles, Phys.chem. 14 (2012) 9813-9825. (4) Guillaume Baffou and Romain Quidant, Nanoplasmonics for chemistry, Chem soc rev, 2014 (43), 3898—3907. (5) Guillaume Baffou, Romain Quidant, and F. Javier Garcia de Abajo, Nanoscale Control of Optical Heating in complex plasmonic systems, American Chemical Society (4), 709-716. (6) Saji Thomas Kochuveedu, Yoon Hee Jang and Dong Ha Kim, A study on the mechanism for the interaction of light with noble metal-metal oxide semiconductor nanostructures for various photophysical applications, Chem. Soc .Rev, 2013, 42, 8467-8493. (7) Z. Chehadi, et al., Plasmonic enhanced photocatalytic activity of semiconductors for the degradation of organic pollutants under visible light Materials Science in Semiconductor Processing (2015), http://dx.doi.org/10.1016/j. mssp.2015.08.044i.
Session I-2 - Understanding Fundaments of Photoinduced Processes and Charge Transport
I-2:IL01 Understanding Charge Transfer Processes on Metal Oxide Surfaces through Laser Flash Photolysis Analysis
J. SCHNEIDER1, I. KRETSCHMER1, D. BAHNEMANN1,2, 1Institut für Technische Chemie, Leibniz Universität Hannover, Germany; 2St. Petersburg State University, St. Petersburg, Russia
During the last decade great attention has been paid to the synthesis of different semiconductors possessing high photocatalytic activities, whereas fundamental studies concerning the underlying photocatalytic processes have rarely been executed. The knowledge of these processes is, however, of utmost importance for the understanding of the photocatalytic reaction mechanism and thus for a better design of photocatalytic systems. In the present study, the dynamics of charge carriers photogenerated in TiO2, Fe2O3, NaTaO3, and in Ba5Ta4O15 nanoparticles have been investigated using diffuse reflectance laser flash photolysis. Upon laser excitation of TiO2 nanoparticles (anatase, rutile, brookite) at 351 nm in air the transient absorption of the trapped holes was observed, while the trapped electrons could only be detected in the presence of electron donors indicating that holes are trapped faster than electrons. Due to the higher driving force the conduction band electrons subsequently rather undergo recombinations with these trapped holes instead of forming less stable Ti3+ centers. Following laser excitation of hematite trapped holes and trapped electrons could be observed simultaneously with the former exhibiting shorter lifetimes due to bimolecular disproportionation processes.
I-2:IL02 Charge-carrier Dynamics in Photocatalytic Processes
C. COLBEAU-JUSTIN1, A. HERISSAN1, S. PIGEOT-RÉMY2, O. DURUPTHY2, S CASSAIGNON2, C. FERRONATO3, R. HAZIME3, C. GUILLARD3, 1Laboratoire de Chimie Physique, CNRS UMR 8000, Université Paris-Sud, Orsay, France; 2Chimie de la Matière Condensée de Paris, Collège de France, CNRS UMR 7574, UPMC, Paris, France; 3IRCELYON, CNRS UMR 5256, Université Lyon 1, Villeurbanne, France
The photocatalytic activity of TiO2 compounds is related to the creation and the evolution of charge-carriers in the photocatalyst. Thus, the knowledge of the relation existing between charge-carrier lifetimes and material structural parameters can help to understand the mechanisms leading to the photoactivity. To follow the charge-carrier dynamics in TiO2, Time Resolved Microwave Conductivity (TRMC) may be used. It is a contactless method, based on the measurement of the change of the microwave power reflected by a sample induced by laser pulsed illumination. In this work, monophasic and biphasic TiO2 powders (anatase, rutile and brookite) with numerous morphologies have been synthetized using various methods (hydrolysis, thermohydrolysis, hydrothermal, microwave), with different precursors and additives. The photocatalytic activity of TiO2 samples has been studied by photodegradation of phenol and formic acid in water. The electronic properties have been followed by TRMC. In each case, the relation between titania modification, charge-carrier dynamics (electronic properties) and photocatalytic activity has been investigated. It has been shown that a strong influence of structural parameters and morphology on photoconductivity and photoactivity is observed.
I-2:IL03 Role of Reduced Graphene Oxide in Promoting the Photoelectro-chemical Responses of 1D Oxide-0D Chalcogenide Nanocomposites
R. SUBRAMANIAN, University of Nevada, Reno Pawan Pathak, University of Nevada, Reno, USA
A fundamental driver that determines the performance of photoactive inorganic materials in a solar-driven process, is charge transport. Carbon additives have been examined extensively as a candidate materials to perform such a process. However the integration of these materials with the photoactive materials can be tricky, especially when the photoactive components show dimensionality and aspect ratios. This work outlines a strategy that can be implemented to assemble a 1D oxide – 0D chalcogenide and a carbon-based charge transporting agent to demonstrate multifunctional applications. As a case study, the focus here will be on 1D large bandgap oxides such as TiO2 and ZnO along with 0D CdX (X=S,Se) using reduced graphene oxide as the charge transporting agent. Select physical, surface, and optical properties of these compounds will be presented. It will be shown that the photoinduced charges generated in the chalcogenides are transported effectively by the reduced graphene oxide. These interesting heterostructures can find applications in photoelectrochemical processes and photocatalysis.
This work is supported by the National Science foundation of the United States of America.
I-2:L04 Mimicking in Photocatalysis the Photosynthesis Z Scheme with one Monophasic Material
J.C. CONESA, R. LUCENA, Inst. de Catálisis y Petroleoquímica, CSIC, Madrid, Spain; P. PALACIOS, P. WAHNON, Inst. de Energía Solar, Univ. Politécnica de Madrid, Spain
Based on ours DFT results we have proposed in recent years, intermediate band (IB) single-phase materials which may couple two low energy photons to achieve a higher energy excitation (like in nature’s Z-scheme), providing wider spectral response and higher efficiency in photovoltaic or photocatalytic systems. We have realized the concept in some of these cases with transition metal-substituted main group sulfides. Thus substituting In by V in In2S3 (having gap=2.0 eV) extends its photon absorption to <1.6 eV, and its spectral response in an aqueous HCOOH photo-oxidation test is extended equally. This is not due to band gap narrowing: this material has photoluminescence (PL) of emitted 2.0 eV photons not only if irradiated with E>2.0 eV photons (as for In2S3), but also with the same <1.6 eV photon range, i.e. upconversion occurs. Also, the thus induced PL intensity grows linearly, not quadratically, with incident light intensity, which is explained by IB partial filling. Same principle should be utilizable in H2 photogeneration.
I-2:IL05 Molecular Electrets: Effects of Localized Fields on Photo-induced Charge Transfer
J.M. LARSEN, E.M. ESPINOZA, V.I. VULLEV, Department of Bioengineering and Department of Chemistry, University of California, Riverside, CA, USA
Controlling charge transfer at a nanoscale and molecular level is fundamental for electronic and energy applications. Electrets, materials that possess ordered electric dipoles, present an excellent choice for a source of fields that could guide flows of charges. Electrets, however, are dielectrics, unable to efficiently mediate long-range charge transduction. To overcome this challenge, we undertake bioinspired approaches. Adopting principles from bioenergetics and combinatorial proteomics, we design macromolecular electrets comprising de novo non-native aromatic amino acids that are capable of holding charges. While the electrets still possess large intrinsic dipoles originating from ordered amide and hydrogen bonds, the aromatic moieties along the electret backbones provide pathways for efficient long-range charge transfer. The bioinspired electrets rectify charge transfer. The dipoles play a key role in the charge-transfer rectification. For charge recombination, however, the spin-density distribution of the radical-ion forms of the non-native residues prevails the rectification and opposes the dipole effects. This somewhat surprising finding presents unexplored venues for controlling charge transfer that could proof essential for multiscale design of electronic materials.
I-2:IL06 Interfacing Light Absorbers with Catalysts for Enhanced Photo(electro)catalysis
R. BERANEK, Institute of Electrochemistry, Universität Ulm, Germany
The development of photochemical systems capable of mimicking the natural photosynthesis by driving useful chemical transformations has attracted significant interest motivated by the need to secure the future supply of clean and sustainable energy. The activity of such systems is typically determined by efficient separation of photogenerated charges at well-designed interfaces introducing gradients of electrochemical potential. Assembling different materials in form of hybrid or composite architectures can therefore lead to highly enhanced photoconversion efficiencies. The talk will focus on our recent research on fabrication of hybrid photoanodes for water splitting and their interfacing with metal oxide-based co-catalysts (IrOx, CoOx) for oxygen evolution. The high quality of coupling between the light absorber and the electrocatalysts is crucial for both activity and stability of the hybrid photoanodes. Visible light-induced photooxidation of water to dioxygen at moderate bias potentials has been demonstrated. In particular, the advantages and drawbacks of different co-catalyst deposition routes and the role of photoelectrochemical and advanced spectroscopic techniques for elucidation of the mechanism of the photo(electro)catalytic action will be discussed in detail.
I-2:L08 Kinetics of Photocatalytic, Self-cleaning Surfaces: Connecting Contaminant Removal to Contact Angle Evolution
D. OLLIS, Chemical Engineering Department, North Carolina State University, USA
The ISO test method for photocatalyst activity of self-cleaning surfaces involves measurement of the air-water-solid contact angle (CA) (1) to determine when a contaminated, hydrophobic surface is clean, as determined by achieving a sufficiently small CA value. The contact angle for a flat surface is related to the solid-vapor (SV), solid-liquid (SL) and vapor-solid (VS) interfacial energies, ßSV, ßSK, and ßVS, respectively, by the Young-Dupre equation (2):
ßSG – ßSL – ßVG cos ( ø ) = 0
The vapor(air)-liquid energy is known, and the solid-gas and solid-liquid interfacial energies depend on the solid surface composition . Hydrocarbon deposits on flat TiO2 surfaces may involve configurations of monolayers (3), ridges (4), or multi-layer islands (5). This paper extends our earlier models of reaction kinetics for self-cleaning, photocatalytic surfaces (6) to predict contact angle (Ø) evolution vs. time.
1. ISO 27488: Fine Ceramics, Contact Angle Measurement. 2. A. Adamson, Physical Chemistry of Surfaces, 2nd ed., John Wiley, New York, 1967, pp. 352-353. 3. X. Zhang, A. Fujishima et al, J. Phys. Chem B, 110 (2006) 25142-25148. 4. A. Zaleska et al, App. Catal. B, 88 (2005) 407. 5. M. Ghazzal et al, App. Catal. B, 103 (2011). 6. D. Ollis, App. Catal. B, 99 (2010) 478.
I-2:IL09 Charge Transport and Recombination in Nanostructured Materials for Photoelectrochemical and Solar Cells
G. OSKAM1, J. VILLANUEVA-CAB2, J.A. ANTA3, 1Department of Applied Physics, CINVESTAV-IPN, Mérida, Yucatán, México; 2Instituto de Física, Benemérita Universidad Autónoma de Puebla, Puebla, Pue., México; 3Area de Química Física, Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Sevilla, Spain
The electronic properties of nanostructured photoelectrodes determine the performance of a variety of devices, including several types of third generation solar cells. We report here on the commonly unaccounted for effect of recombination under short-circuit conditions on the charge transport and recombination dynamics in nanostructured photoelectrodes. It is observed that when recombination occurs under short circuit conditions the charge-collection efficiency determined from small-perturbation methods is overestimated, and this effect becomes more pronounced with increasing recombination losses under short circuit conditions. We propose a simple method to detect whether recombination losses at short-circuit are important. ZnO is an interesting material for application in the dye-sensitized solar cell (DCS) related to the large variety of low-temperature synthesis methods that allow for easy manipulation of the morphology and texture of the material, which may affect the dye bonding, dye coverage, and injection efficiency, the electron transfer kinetics to the solution, and the trap state distribution. Using these materials, we have compared the electron transport and recombination properties using small-signal perturbation techniques.
I-2:IL11 Photocatalytic Activation of Biomaterials
K.H. CHEUNG, P. KOSHY, M.B. PABBRUWE, C.S. SORRELL, School of Materials Science and Engineering, UNSW Australia, Sydney, NSW, Australia
Photocatalytic materials generally are activated by ultraviolet radiation. However, it is less well known that clinical doses of X-radiation are adequate to activate biocompatible and photocatalytic oxides, such at TiO2, when implanted in the body in the form of bulk materials or coatings. Anodised coatings of TiO2 on Ti and biomedical-grade Ti alloy have been produced as a function of voltage and time and characterised in terms of chemistry, mineralogy, and microstructure. They have been subjected to varying doses X-radiation and the photocatalytic activity has been assessed in terms of the decomposition of different organic materials.
I-2:IL12 Analysis of the Dynamics in Composition of Pt and Ni/NiO promoted SrTiO3 in Overall Water Splitting
G. MUL, Mesa+ Insitute for Nanotechnology, University of Twente, Enschede, The Netherlands
In this presentation I will show that various co-catalysts, frequently reported to be active in the overall water splitting reaction, change their chemical composition in the first hours after initiation of illumination. When SrTiO3 is equipped with a Pt co-catalyst prepared by photo-deposition in oxidative conditions, a strong O2 evolution transient occurs before hydrogen production is observed, assigned to in situ reduction of PtOx to metallic Pt. Interestingly, doping of SrTiO3 with Rh cations, results in a significantly lower O2 evolution transient, and higher average steady state oxidation state of Pt co-catalyst particles, which negatively affects the efficacy in water splitting. Another frequently studied co-catalyst for SrTiO3 is Ni/NiO. In particular the structure performance relation of the active Ni species has been frequently discussed in the literature. I will provide novel insight on the basis of transient productivity, this time in hydrogen evolution, and will propose an important role of in situ formation of NiOOH in stimulating hydrogen formation. Implications of these findings are that structure activity correlations reported in the literature on the basis of characterization of as-prepared catalysts should be considered preliminary.
I-2:IL13 Metal Oxides for Photoelectrochemical Water Splitting and Environmental Remediation
S. CARAMORI, V. CRISTINO, N. DALLE CARBONARE, F. RONCONI, C.A. BIGNOZZI, G. LONGOBUCCO, L. PASTI, A. MOLINARI, Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy; R. ARGAZZI, CNR/ISOF c/o Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Ferrara, Italy
Metal oxide semiconductors play a central role as photoanodes for the photooxidation of water, thanks to the fulfillment of some fundamental requirements which include the absorption of near UV-Visible photons, the favorable position of their valence band edge with respect to the O2/H2O potential and stability in aqueous electrolytes under oxidizing conditions within appropriate pH intervals. The photoelectrochemical properties and the charge transfer dynamics of materials based on WO3 (both anodized and sol-gel), BiVO4 and Fe2O3 will be described in photoelectrochemical water splitting processes and in the OH radical mediated degradation of impervious emerging contaminants. The molecular sensitization of WO3 and SnO2 by cationic perylenes characterized by strongly oxidizing ground state redox potentials, aimed at the realization of molecular driven solar fuel production will also be considered.
I-2:IL14 Organic Photoelectrochemical Cells for Selective Redox Reactions
A. GUERRERO, Institute of Advanced Materials (INAM), Universitat Jaume I, Castelló, Spain
Organic photoactive materials are promising candidates for generation of solar fuels in terms of efficiency and cost. However, their low stability in aqueous media constitutes a serious problem for technological deployment. Here, we present organic photocathodes for generation of hydrogen in aqueous media with outstanding stability. The device relies on the use of water resistant selective contacts, which protect the photoactive layer. An insoluble cross-linked PEDOT:PSS hole selective layer avoids delamination of the film and an electron selective TiOx layer in contact with the aqueous solution electrically communicates the organic layer with the hydrogen evolving catalyst (Pt). Tuning the thickness of the TiOx/Pt layer leads to a trade-off between the highest photocurrent reported for this system (~1 mAcm-2) and stable hydrogen generation of 6 μmol h-1cm-2. The high photocurrent limit approaches to our recently demonstrated results in non-aqueous solvents where obtained photocurrents are close to the theoretical maximum.
1. M. Haro, C. Solis, G. Molina, L. Otero, J. Bisquert, S. Gimenez and A. Guerrero, The Journal of Physical Chemistry C, 2015, 119, 6488-6494. 2. A. Guerrero, M. Haro, S. Bellani, M. R. Antognazza, L. Meda, S. Gimenez and J. Bisquert, Energy & Environmental Science, 2014, 7, 3666.
I-2:L15 Band Engineering of Titanium Dioxide Relevant to Solar Cells and Photocatalysis
L. KAVAN, J. Heyrovsky Institute of Physical Chemistry, Prague, Czech Republic
The electronic band engineering of TiO2 is fundamental for photocatalysis, solar cells and solar fuel generation. The position of conduction band (CB) edge controls the driving force for photocatalytic hydrogen evolution from water, potential of dye-sensitized solar cell (DSC) and recombination blocking in perovskite solar cells. The staggered alignment in mixed anatase/rutile phases is assumed to enhance photocatalytic activity, but it is unclear whether the CB of rutile or that of anatase is higher. XPS and most DFT simulations support the former, but the flat-band potential measurements provide just opposite results. The controversy can be explained by taking into account the adsorption of OH– and H+ from the electrolyte solution on the electrode surface. XPS indicates that the CB edge of (001)-anatase is upshifted by 0.1 eV referenced to (101)-anatase in agreement with the DFT calculation  and with the electrochemical flatband potentials (upshift of CB by 60 meV).
This work was supported by by the Grant Agency of the Czech Republic (contract No. 13-07724S).
Session I-3 - Design Approaches for Advanced Applications
I-3:IL01 Efficient Solar Driven Water Splitting using a Bipolar Membrane to enable pH-gradients
D.A. VERMAAS, W.A. SMITH, Delft University of Technology, Department of Chemical Engineering, Materials for Energy Conversion and Storage (MECS). Delft, The Netherlands
The conversion of solar energy into a chemical fuel, such as hydrogen, is a promising route to enable a sustainable and clean energy future. Multiple designs for this conversion have been proposed, ranging from separate photovoltaic and electrolysis cells (PV-EC) to direct photo-electrochemical (PEC) fuel production technologies. However, efficient operation of (photo-)electrodes and catalysts depends on the electrolyte’s pH. Differences in optimal pH conditions for each element seriously challenges the practical applicability of a solar fuel device. To ease the combination of suitable electrodes and catalysts, a solar-assisted design with a bipolar membrane (BPM) was demonstrated . This BPM dissociates water into H+ and OH-, which maintains an acidic cathodic compartment and an alkaline anodic compartment. We demonstrate the practical operation of a BPM for direct photo-assisted hydrogen production, as well as for photovoltaic driven electrolysis. Our experimental results show a voltage over the BPM very close to its thermodynamic minimum, a stable pH difference for several days and a solar-to-hydrogen efficiency of >10%, showing the efficacy of bipolar membranes in developing a practical solar fuel device.
1. Vermaas, Sassenburg and Smith, J.Mat.Chem.A, 2015,3, 19556-62
I-3:IL02 Development of Photocatalyst Sheet for Unassisted Sunlight-driven Water Splitting
T. HISATOMI, K. DOMEN, The University of Tokyo, Tokyo, Japan; Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem)
Photocatalytic water splitting has been studied as a means of renewable solar hydrogen production . It is necessary to activate narrow band gap semiconductors to achieve a sufficient solar-to-hydrogen energy conversion efficiency (STH) with reasonable quantum efficiencies. Z-scheme water splitting based on two-step excitation is suited to utilizing long-wavelength photons because the energy required to drive each photocatalyst can be lowered than overall water splitting on single photocatalytic materials. The authors’ group recently developed photocatalyst sheets consisting of a hydrogen evolution photocatalyst and an oxygen evolution photocatalyst embedded into a conductive layer . The photocatalyst sheets exhibited significantly higher activity in Z-scheme water splitting than the corresponding photocatalyst powder suspensions owing to the presence of the conductive layer that facilitated the electron transport between the photocatalysts. In this talk, the factors controlling the activity of the photocatalyst sheets will be discussed. Our recent effort in the development of photocatalyst sheets using photocatalysts with narrow band gap energies will also be presented.
 Hisatomi et al., Chem. Soc. Rev. 2014, 43, 7520.  Wang et al., J. Catal. 2015, 328, 308.
I-3:L03 Quasi-1D Black Titanium Oxide Nanostructures for Water Splitting Applications
L. MASCARETTI, S. FERRULLI, P. MAZZOLINI, C.S. CASARI, V. RUSSO, A. LI BASSI, Micro and Nanostructured Materials Laboratory, Politecnico di Milano, Milano, Italy; R. MATARRESE, I. NOVA, Laboratory of Catalysis and Catalytic Processes, Politecnico di Milano, Milano, Italy
Quasi-1D titanium oxide nanostructures synthetized by Pulsed Laser Deposition (PLD) were developed and studied as photoanodes for photoelectrochemical water splitting. An explorative combined approach to improve TiO2 performance was investigated, i.e. extension of the photoresponse to the visible range as well as optimization of morphology and structure to increase light harvesting and quantum efficiency. This was pursued by varying the deposition atmosphere (from pure O2 to Ar/O2 or Ar/H2), and by substituting/combining the air annealing process (necessary to induce crystallization to the anatase phase) with Ar/H2 annealing, to induce reduction/hydrogenation (the so-called black titania). SEM, Raman spectroscopy and UV-vis-IR spectroscopy were employed to understand the material morphology, structure and optical properties. A photoluminescence background and a tail absorption towards the visible emerged for hydrogen-treated samples. Photocurrent measurements under solar simulator illumination showed a noteworthy increase of photocatalytic response for the Ar/O2 deposited samples followed by a double air+Ar/H2 thermal treatment. These findings could be ascribed to the combination between an optimized nanoscale morphology and oxygen vacancy-related tail states in the bandgap.
I-3:IL04 A Stand Alone Artificial Photosynthesis of Formate from Carbon Dioxide and Water
HYUNWOONG PARK, School of Energy Engineering, Kyungpook National University, Daegu, Korea
There is renewed interest in the photocatalytic and photoelectrochemical conversion of CO2 into value-added chemicals using various semiconductor particles and electrodes. Common CO2 reduction products are C1 chemicals (CO, HCOOH, CH3OH, and CH4) in aqueous media, while the production of C2-C4 hydrocarbons (e.g., C2H6 and C3H8) has also been reported. A number of solar-active materials have been reported, but they still suffer from low selectivity, poor energy efficiency, and instability, while failing to drive simultaneous water oxidation. This talk presents our recent studies on the solar CO2 conversion to value-added chemicals while using water as an electron donor in various photo-systems [1-4].
 S.K. Choi, U. Kang, S. Lee, D.J. Ham, S.M. Ji, and H. Park, Advanced Energy Materials 4 (2014) 1301614.  H. Park, H.-H. Ou, A.J. Colussi, and M.R. Hoffmann, Journal of Physical Chemistry A 119 (2015) 4658.  U. Kang, S.K. Choi, D.J. Ham, S.M. Ji, W. Choi, D.S. Han, A. Abdel-Wahab, and H. Park, Energy & Environmental Science 8 (2015) 2638.  H. Park, H.-H. Ou, U. Kang, J. Choi, and M.R. Hoffmann, Catalysis Today, accepted.
I-3:L05 Sculpting Photocatalysts on the Nano Scale
L. AMIRAV, Schulich Faculty of Chemistry, Technion - Israel Institute of Technology, Haifa, Israel
The solar-driven photocatalytic splitting of water into hydrogen and oxygen is a potential source of clean and renewable fuels. However, four decades of global research have proven this multi-step reaction to be highly challenging. The design of effective artificial photocatalytic systems will depend on our ability to correlate the photocatalyst structure, composition, and morphology with its activity. Here, I will present our strategies, and most recent results, in taking photocatalyst production to new and unexplored frontiers. I will focus on unique design of innovative nano scale particles, which harness nano phenomena for improved activity, and methodologies for the construction of sophisticated heterostructures. I will demonstrate how vital is the ability to characterize our hybrid nanostructures on the atomic level, and how we can benefit from information on the structure-properties relationship for the future design of an efficient photocatalyst for solar-to-fuel energy conversion.
I-3:IL07 Bioinspired Photoelectrode Designs for Solar Fuel Generation
K. RAJESHWAR, University of Texas, Dept of Chemistry & Biochemistry, Arlington, TX, USA
In this talk, the synergies between electrocatalysis, photocatalysis, and photoelectrosynthesis will be underlined with the dioxygen reduction, hydrocarbon oxidation, and dinitrogen reduction as representative examples. Approaches based on the use of electrodes and photoelectrodes as well as those based on the use of colloidal suspensions will be compared and contrasted. Ideas on how we can learn from the intricate self-assembled architectures that Nature has evolved over millions of years, will be discussed with specific examples The talk will then turn toward a discussion of work in the author’s laboratory on the use of carbon and oxide semiconductor nanocomposites for driving catalytic processes of interest both in the dark and under irradiation of the oxide semiconductor component. Incorporation of bioinspired components such as flavins in these assemblies will be described. The reactions of interest here include dioxygen reduction and the reduction of carbon dioxide to fuels such as methanol. The role of the nanocomposite components and their complementary functionality within the material architecture will be discussed within the context of systems that Nature has evolved.
I-3:IL08 Reduction of Small Molecules in Photocatalytic Systems
W. MACYK, Faculty of Chemistry, Jagiellonian University, Kraków, Poland
Photocatalytic reduction of small molecules is very often a key step of a photocatalytic reaction. Reduction of water or carbon dioxide can be used to convert solar energy into fuels, however, also in processes of pollutants photodegradation reduction of a small molecule (O2) influences the overall efficiency of photocatalysis. During the presentation selected examples of photocatalytic reduction of small molecules will be presented. Factors influencing these reactions will be discussed. Among them redox properties of photocatalysts are particularly important. Recently, a new method of determination of the density of states was developed in our group. Its application enabled understanding the differences between rutile-TiO2 and anatase-TiO2. The results revealed significantly better reduction properties of rutile than anatase. Therefore the reduction of oxygen is more efficient at rutile than at anatase. On the other hand, holes generated within anatase particles are stronger oxidants than holes from the valence band of rutile, so oxidation of water to hydroxyl radicals proceeds efficiently at anatase-TiO2, but not at rutile-TiO2. These properties explain the differences in photocatalytic activities of both crystalline forms of titanium dioxide.
I-3:L10 Superhydrophilic and Photocatalytic Active Ceramic Glazes for Sanitary Ware
F. KNIES1,2, K. SCHRANTZ1, C. ANEZIRIS1,2, T. GRAULE1,2, 1EMPA-Swiss Federal Labs for Materials Science and Technology, Laboratory for High Performance Ceramics, Duebendorf, Switzerland; 2TU Bergakademie Freiberg, Institute for Ceramics, Glass and Building Materials, Freiberg, Germany
Self-cleaning, superhydrophilic surfaces are of high relevance both for public places like hospitals and as well for households applications. In the present work the aim is to transfer the knowledge for photocatalytic active, but little mechanically utilised surfaces to more mechanically utilised surfaces. By everyday use sanitary ceramics in households get confronted with strong cleaning agents, abrasive brushes and sponges. Due to this sol-gel-coatings are not stable for longer time periods. To avoid this problem of surface degradation, we incorporate photocatalytic active oxides in the bulk of the glaze. The properties are now not influenced by scratches originating from extensive cleaning procedures. To generate both photocatalytically active as well as superhydrophilic surfaces we were incorporating TiO2, ZnO and CeO2 in an industrial standard glaze. The glazes were analysed for optical appearance, surface roughness, wetting and cleaning behaviour and results compared with a standard ZrSiO4-whitened glaze with a medium roughness of 60 nm and a water wetting angle of 45°. Samples are irradiated with 365 nm UV light and tested for Methylene Blue degradation and wetting angle. Promising results were achieved with both zinc oxide and rare earth metal oxide incorporation.
I-3:IL12 Mechanistic Studies of Charge Carriers in Materials for Artificial Photosynthesis
A.J. COWAN, M. FORSTER, University of Liverpool, Department of Chemistry, Liverpool, UK
The utilization of solar energy conversion technologies on a TW scale will require the development of storage technologies to overcome the intermittent nature of sunlight at ground level. An extremely attractive approach is to develop “artificial leaf” materials that use solar energy for either water splitting to produce hydrogen or combined water oxidation and carbon dioxide reduction to potentially produce a range of fuels including, CH3OH, CO, CH4. To enable the rational development and design of new more efficient artificial leaf materials we carry out a range of transient spectroscopic measurements on state of the art photoelectrodes to identify the key design rules to be fed into both our own and collaborators synthetic research programmes. Here I will present an overview of our recent synthetic and mechanistic work including studies on both (i) semiconductor materials for water oxidation, concentrating on the study of mechanism of activity of oxygen deficient metal oxides (ii) the development of novel semiconductor/molecular catalyst photoelectrodes for the reduction of protons and/or CO2 to fuels.
I-3:L13 Artificial Photosynthesis Device Development for CO2 Photoelectrocatalytic Conversion
J.F. THOMPSON, BIN CHEN, J. MINUZZO, N. LONDONO, NASA Ames Research Centre, Mountain View, CA, USA; G. WHITING, Palo Alto Research Center (PARC)
We present development of a 3D photocatalytic device with a nanostructured photoelectrocatalyst. Containing TiO2 and transition metal co-catalysts allowing the reaction of CO2 and H2O to produce oxygen and hydrocarbons at a rate of at least 622μL per hour for every gram of catalyst. The novel composite catalyst significantly improves upon current published literature. In addition to the high rate of methane production, the composition can also be tuned to produce other hydrocarbons. Operating at ambient pressure and concentration and using sunlight as an energy source, the device enables placement of devices in environments where electrical power is limited. The device has broad applications in heavy CO2 emitters, from power plants to vehicles, as well as in life support for space travel. The catalyst is processed through thin film deposition onto the device and uses acrylic waveguide material with origami structures to deliver solar radiation to the available surface area of the catalyst, allowing maximized catalyst efficiency. Furthermore, 3D printing techniques accomplish a catalytic ink coating upon the waveguide substrate. The printing strategies enable a high tortuosity design for efficient mass transport of CO2, as well as high reaction surface areas.
I-3:L14 Photocatalytic Ag/AgCl Polymer Composites
E.W. TATE, J.H. JOHNSTON, School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington, New Zealand
In our recent work, photocatalytic Ag/AgCl composite materials were produced using the support materials of polyurethane paint and nylon. This was achieved through the development of a simple aqueous synthesis method, utilising the substrate to control the formation of the AgCl nanoparticles and their stabilisation. These were then exposed to UV light to generate Ag nanodomains and hence form plasmonic Ag/AgCl photocatalysts, successfully incorporating the plasmonic photocatalyst nanoparticles within the support. UV Vis, XRD, SEM and EDS were used to characterise the Ag/AgCl nanoparticles and their distribution within the composites. The photocatalytic activity of the Ag/AgCl composites was evaluated by the photodegradation of methylene blue, showing them to be effective photocatalysts. Due to the inherent antimicrobial properties of the Ag/AgCl nanoparticles, the composites were also seen to display significant antimicrobial action against E. Coli. These novel composite materials have promising applications in water treatment, where the photocatalytic mechanism is effective in the reduction of organic contaminants, whilst the Ag+ simultaneously imparts antimicrobial action. This then lead to the design and incorporation of these composites into a laboratory scale reactor system.
I:P04 Hybrid DFT Study of the Fe:NiOOH OER Catalyst and its Interface to BiVO4
J.C. CONESA, Inst. de Catálisis y Petroleoquímica, CSIC, Madrid, Spain
Fe-doped NiOOH is one of the best inexpensive catalysts for O2 evolution in photo/electrocatalytic water splitting, but its atomic and electronic features are not well understood, as its structure, made of H bond-linked sheets, is normally highly disordered. Here its bulk electronic structure, Fe-doped or not, is modeled with a hybrid DFT method able to give accurate bandgaps. Different sheet stackings and proton orderings are studied. Several of them having different stackings and Ni coordinations and redox states have close lowest energies, explaining the said disorder. Bandgaps, with edges made of Ni 3d levels, are in the ~1.0-1.4 eV range. Substituting Ni by Fe gives filled Fe 3d levels near the valence band edge; in some cases a Ni(3+) + Fe(3+) -> Ni(2+) + Fe(4+) process occurs, eventually with proton jump from Fe to Ni coordination spheres. This suggests a high electronic and protonic conductivity, which probably helps the electrocatalytic activity of the material. The band alignment of NiOOH with photocatalyst BiVO4 is modeled also using hybrid DFT and a method taking electrostatic potential as reference; the results imply that the NiOOH valence band lies closely above that of BiVO4, facilitating the transfer of photo-holes to the former as desired to drive O2 evolution.
I:P06 ZnO2 Thin Films for Polymer Solar Cells
MYUNG-SEOK JEON, DO-HEYOUNG KIM, School of Chemical Engineering, Chonnam National University, GwangJu, Korea
Polymer solar cell (PSC) is considered as one of the promising candidates for the partial replacement of Si-based solar cell due to its advantages of low cost, easy fabrication, and moderate power conversion efficiency compared Si-based solar cells. However, poor stability of a conventional PSC in ambient condition should be resolved for commercialization. To improve the stability, there has been great attention in the alternative architecture, inverted structures where indium tin oxide (ITO) acts as electron collecting layer by lowering its work function with thin layer of inorganic metal oxides. ZnO2 is considered as a promising material to improve charge extraction for electrons in PSC. Here, we compare two processes for the formation of the ZnO2 films and sol-gel based ZnO2 films. The effect on interface properties, surface morphology, and solar cell parameters with the films prepared by the sol-gel and CVD TiO2 will be discussed.
I:P08 Grafting of TiO2 on PMMA Film and Reusability in Photodegradation of Organic Dye under UV and Visible Light Irradiation
R. KLAYSRI1, S. WICHAIDIT1, O. MEKASUWANDUMRONG2, P. PRASERTHDAM1, 1Center of Excellence on Catalysis and Catalytic Reaction Engineering, Department of Chemical Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, Thailand; 2Department of Chemical Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakorn Pathom, Thailand
Grafting TiO2 on PMMA was studied by atom-transfer radical-polymerization (ATRP). Each step in grafting process was monitored by fourier transform infrared spectroscopy (FT-IR), 1H NMR and 13C NMR spectra. The glass temperature of grafted-PMMA film was determined by using differential scanning calorimetry (DSC). The morphology and bulk composition were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX). The surface composition was characterized by X-ray photoelectron spectroscopy (XPS). As results, a novel method of grafting TiO2 on PMMA was successfully grafted and confirmed in various techniques. The photocatlytic activity was evaluated under UV and visible light irradiation. The reusability of TiO2-g-PMMA films was studied in details.
I:HP10 Ni and Ni-M Nanoparticles Supported on Hierarchical Oxides for Methane Dry Reforming Catalysis
PENG ZHANG, LIAN GAO, QING ZHANG, XUEFENG SONG, School of Materials Science & Engineering, Shanghai Jiao Tong University, Shanghai, China
Methane dry reforming (DRM) catalysts with hierarchical nanostructures based on non-precious metal/alloys have been prepared using conventional hydrothermal methods. The hierarchical catalysts are resulted from hydrothermal treatment of SiO2 nanospheres or Al3+ salt with the presence of Ni2+ and the alloy precursor ions. The metal nanoparticles resulted from high temperature decomposition of hierarchical phyllosilicates or aluminates in hydrogen show a strong metal-support interaction, which corresponds to a superior catalytic performance and a high resistance to sintering and coking of the catalysts during high temperature DRM catalysis. The synthetic mechanisms for the synthetic routes are proposed and discussed.
I:HP11 Photocatalytic Semihydrogenation of Triple Bond of Organosilanes without Use of H2
Y. KOJIMA, K. HASHIMOTO, H. KOMINAMI, A. TANAKA, Department of Applied Chemistry, Kindai University, Higashiosaka, Japan
Photocatalysis of titanium(IV) oxide (TiO2) has been promised to apply to synthesis of organic compounds. Since photocatalysis of TiO2 occurs at room temperature and atmosphere, photocatalytic reactions are environmentally friendly processes. We have shown various types of conversion of organic compounds over TiO2 photocatalyst; for example, hydrogenation of nitrile group and deoxygenation of epoxide group. However, most of the papers report conversion of CHONS compounds whereas we focused on organosilanes in this study. Organosilanes having the C=C bond are useful compounds as surface modification agents and they are synthesized by semihydrogenation of organosilanes having the C≡C triple bond. However, a reducing reagents such as hydrogen (H2) gas and undesirable chemicals are necessary for the semihydrogenation. In this study, we examined photocatalytic hydrogenation of organosilanes having the C≡C triple bond to explore the possibility of photocatalysis and found that photocatalytic semihydrogenation of organosilanes occurred without the use of H2.
I:HP12 Chemoselective and Diastereoselective Hydrogenation of Alkynes to Alkenes in an Alcoholic Suspension of a Cu-TiO2 Photocatalyst without Use of Additives and Reducing Gas
H. KOMINAMI, M. HIGA, T. NOJIMA, T. ITO, K. NAKANISHI, K. HASHIMOTO, K. IMAMURA, Department of Applied Chemistry, Kindai University, Higashiosaka, Japan
Selective hydrogenation (semihydrogenation) of alkynes to corresponding alkenes is important and one of most difficult reactions. This reaction is regarded as a chemoselective reaction because, during the hydrogenation, only the C≡C triple bond should be hydrogenated in the presence of the C=C double bond formed thereof. Lindlar's catalyst, i.e., lead (Pb)-promoted palladium (Pd) supported on calcium carbonate, has been used for selective hydrogenation of alkynes to corresponding alkenes; however, this catalyst system requires undesirable additives, Pb salts and organic bases such as quinoline, to reduce the activity of Pd and increase the selectivity of alkenes and it gives a large amount of undesirable waste. In this study, we examined a new photocatalytic reaction system, i.e., hydrogenation of alkynes in alcoholic suspensions of metal-loaded TiO2 photocatalysts at room temperature without the use of reducing gas. We found that alkynes were chemoselectively converted to corresponding alkenes over copper (Cu)-loaded TiO2 without consecutive hydrogenation of the C=C double bond. Notably, internal alkynes were diastereoselectively hydrogenated to cis-alkenes, and alkynes with functional groups were converted to corresponding alkenes, the functional groups being preserved.
I:HP13 Photocatalytic Chemoselective Reduction of Aromatic Aldehydes in an Ethanol Suspension of TiO2
M. FUKUI, K. HASHIMOTO, A. TANAKA, H. KOMINAMI, Department of Applied Chemistry, Kindai University, Higashiosaka, Japan
When titanium(IV) oxide (TiO2) is irradiated by UV light, charge separation occurs and thus-formed electron in conduction band and holes in valence band causes reduction and oxidation, respectively. This redox reaction proceeds at room temperature and under atmospheric pressure. Therefore, photocatalytic reaction is a “green” redox system. We reported photocatalytic chemoselective reduction of nitro aromatics having other reducible groups over TiO2 using organic acid or alcohol as a hole scavenger. Aromatic alcohols having other reducible groups are produced by chemoselective reduction of corresponding aromatic aldehydes using appropriate reducing agents. However, it is difficult to reduce only the aldehyde group without reducing other reducible groups. Moreover, a conventional reduction of aldehydes by metal hydrides produces waste liquid containing undesirable elements. In this study, we examined the photocatalytic reduction of aromatic aldehydes having other reducible groups using TiO2 in the presence of ethanol as a hole scavenger under irradiation of UV light, and we found that only the aldehyde group was chemoselectively reduced to a hydroxyl group and that aromatic alcohols having other reducible groups were obtained in high yields without using metal hydrides.
I:HP14 Synthesis and Evaluation of Plasmonic Photocatalyst Working under Irradiation of Red Light
R. NISHIJIMA, A. TANAKA, K. HASHIMOTO, H. KOMINAMI, Department of Applied Chemistry, Kindai University, Higashiosaka, Japan
Titanium(IV) oxide (TiO2) is a wide band gap photocatalyst (band gap = 3.2 eV) that can induce H2 formation, decomposition of organic compounds and organic synthesis under ultraviolet (UV) light irradiation. However, UV light accounts for only ∼5% of the total solar energy, whereas visible light accounts for ∼50% of total solar energy. Therefore, the development of photocatalysts using visible light is an important topic from a practical point of view. In the previous studies, we found that colloidal gold (Au) nanoparticles loaded on TiO2 (Au/TiO2) showed strong photoabsorption at around 550 nm due to surface plasmon resonance (SPR) of Au particles and induced various oxidation-reduction reactions under irradiation of visible light. The development of photocatalysts, which work under irradiation of light with wavelengths longer than λ = 550 nm is important in order to utilize solar energy efficiently. In this study, we examined post-calcination of Au/TiO2 sample at 1023 K, and found that photoabsorption due to SPR was shifted to longer wavelength (λ = 620 nm). Herein, we report mineralization of oxalic acid to CO2 under irradiation of red light.
I:HP15 Decoration of Ultra-long Carbon Nanotubes with Cu2O Nanocrystals: A Hybrid Platform for Enhanced Photoelectrochemical CO2 Reduction
E. KECSENOVITY, B. ENDRODI, K. HERNADI, C. JANAKY, University of Szeged, Hungary; K. RAJESHWAR, University of Texas at Arlington, TX, USA
Photoelectrochemical (PEC) reduction of CO2 to form useful chemicals is an increasingly studied avenue for harnessing and storing solar energy. In the quest for efficient and stable photocathodes, nanostructured hybrid assemblies are eminently attractive candidates, because they exhibit multiple favorable properties that cannot be expected from a single material alone. One possible direction is to combine p-type inorganic semiconductors with highly-conductive large surface area supporting electrodes. In this work the controlled synthesis and PEC behavior of carbon nanotube (CNT)/Cu2O films for CO2 reduction is presented. A carefully designed, multiple-step electrodeposition protocol was developed that ensured homogeneous coating of the CNT film (created from mm high CNT forest) with the Cu2O nanocrystals. The hybrid films had five-times higher electrical conductivity compared to their pure Cu2O counterparts, which drastically increased the measured photocurrents for CO2 reduction. Long term photoelectrolysis measurements proved that the hybrids were more stable than the oxide alone. The results presented in the poster, together with the established structure/property relationships, may contribute to the rational design of nanocarbon/inorganic semiconductor hybrids for PEC cells.
I:HP16 Solution Combustion Synthesis of Bi2Ti2O7 and Parallel Bandgap Engineering through Foreign Ion Incorporation
G.F. SAMU, C. JANAKY, University of Szeged, Hungary; K. RAJESHWAR, University of Texas at Arlington, TX, USA
Bandgap engineering is an effective strategy to expand the light harvesting capability of different semiconductor photocatalysts. This can be achieved via either doping or stoichiometric metal ion incorporation. Solution Combustion Synthesis (SCS) is an attractive alternative avenue to prepare such complex materials, compared to other high-cost procedures. This method employs metal salts (mostly nitrates) as oxidants and organic compounds (urea, hexamethylenetetramine) as fuels. The combustion reaction occurring between the reactants is highly exothermic and involves the release of copious amount of gaseous products. Thus the inherent feature of this versatile synthesis technique is its ability to produce crystalline metal oxide nanomaterials in a few minutes of reaction time. Here we specifically present the SCS synthesis of ternary metal titanate (Bi2Ti2O7) and the alloying of the parent structure with different foreign metal ions (Fe(III) and Mn(II)). The effect of increasing metal ion incorporation on the structure and optical properties of the resulting materials was studied. Overall, we found that SCS is indeed a lucrative method in terms of fine tuning the optical properties of Bi2Ti2O7 -based semiconductor oxides.
I:HP17 Solution Combustion Synthesis, Characterization, and Photoelectrochemistry of CuNb2O6 and ZnNb2O6 Nanoparticles
A. KORMANYOS, C. JANAKY, University of Szeged, Hungary; A. THOMAS, K. RAJESHWAR, University of Texas at Arlington, TX, USA
One of the most critical challenges of the 21st century is the shift in energy use from fossil fuels to renewable sources. Utilizing sunlight via solar fuels is unambiguously an effective strategy for attacking supply and environmental concerns. The use of photoelectrochemical (PEC) techniques can be suitable for this purpose. Currently, the most important examples of solar fuels are: H2, obtained via water-splitting, and high-energy chemicals, such as CO, CH4, HCOOH, CH3OH, etc., produced by the photochemical or PEC conversion of CO2. Thus, our main goal is to find n-, and p-type semiconductor materials or assemble nanocomposites which can efficiently catalyze these processes. In my poster presentation I am showing the PEC behavior of copper-, and zinc niobate thin films, fabricated on ITO electrodes using spray coating technique. The nanoparticles were synthesized by the time-, and energy-efficient solution combustion technique. The nanoparticles and films were characterized by several techniques, such as: photovoltammetry, stationary measurements (chronoamperometry), TG/DSC, XRD, SEM, HR-TEM, DR-UV-vis and Raman spectroscopy. Along with these measurements, the applicability of the materials in water splitting-, and carbon dioxide reduction reactions was also investigated.