Photocatalytic H 2 and Added‐Value By‐Products – The Role of Metal Oxide Systems in Their Synthesis from Oxygenates

Increasing Profitability of Ethanol Photoreforming by Simultaneous Production of H2 and Acetal

Often, H2 is produced photocatalytically at the expense of sacrificial agents. When a sacrificial agent is selectively oxidized, this allows coupling of H2 production with synthesis of value-added organic compounds. Herein, it is argued that the conversion of bioethanol into 1,1-diethoxyethane with simultaneous H2 production increases the economic viability of photocatalysis and suggests a semiconductor material that is the most relevant for this purpose.

Multisite Cocatalysis: Single atomic Pt2+/Pt0 active sites synergistically improve the simulated sunlight driven H2O-to-H2 conversion performance of Sb2S3 nanorods

Single atomic metal (SAM) cocatalysis is a potential strategy to improve the performance of photocatalytic materials. However, the cocatalytic mechanism of SAM sites in different valence states is rarely reported. Herein, single atomic Pt2+/Pt0 active sites were anchored on Sb2S3 nanorods to synergistically improve the photoactivity for hydrogen production under simulated sunlight. Experimental results and density functional theory calculations indicated that the coexistence of single atomic Pt2+/Pt0 sites synergistically improves the broadband light harvesting and promotes the Sb2S3-to-Pt electron transfer following inhibited photoexciton recombination kinetics and enhanced H proton adsorption capacity, resulting higher and more durable photoactivity for hydrogen production. Therefore, the optimal Sb2S3-Pt0.9‰ composite catalyst achieved remarkably enhanced hydrogen evolution rate of 1.37 mmol∙g-1∙h-1 (about 105-fold greater of that of Sb2S3 NRs) under faintly alkaline condition, and about 5.41 % of apparent quantum yield (AQY700 nm) was achieved, which shows obvious superiority in hydrogen production by contrasting with the reported Sb2S3-based photocatalysts and conventional semiconductor photocatalytic materials modified with noble metals. This study elucidate a well-defined mechanism of multisite cocatalysis for photoactivity improvement.

Antifouling CuO@TiO2 coating on plasma-grafted PAA/PES membrane based on photocatalysis and hydrogen peroxide activation

Because of the small size effect leading to the high bandgap of TiO₂ P25, the photocatalytic membrane using this photocatalyst has low antifouling efficiency. This study prepared CuO@TiO₂ composite photocatalyst with a lower bandgap than TiO₂ P25 and used it as antifouling coatings on the PES membrane with PAA intermediate adhesive layer. PAA was grafted onto the surface of the PES membranes through free radicals generated by the cold plasma treatment of the PES membrane. The composite photocatalysts were characterized by FTIR, SEM-EDS, TEM-EDS, XRD, BET, UV-Vis DRS, XPS, and ESR methods demonstrating high surface area (51.0 m²/g), decreased bandgap, and the formation of active free radicals under UV light irradiation. Under photocatalysis and hydrogen peroxide activation, the degradation of AB260 (acid blue 260) catalyzed by 10%CuO@TiO₂ reached about 92% after 60 min. Besides, the photocatalytic and antifouling activities of CuO@TiO₂/PAA/PES membranes are high and stable over five continuous cycles. The water flux of the modified membrane was not significantly influenced and only decreased about 10% compared to the pristine membrane. In addition, the flux recovery ratios (FRR) of fouled membranes treated by photocatalysis were almost 100%.

The current status, challenges and prospects of using biomass energy in Ethiopia

Despite enormous challenges in accessing sustainable energy supplies and advanced energy technologies, Ethiopia has one of the world's fastest growing economies. The development of renewable energy technology and the building of a green legacy in the country are being prioritized. The total installed capacity for electricity generation in Ethiopia is 4324.3 MW as on October, 2018. Renewable energy accounts for 96.5% of total generation; however, despite the county's enormous biomass energy potential, only 0.58% of power is generated using biomass. Ethiopia has surplus woody biomass, crop residue and animal dung resources which comprise about 141.8 million metric tons of biomass availability per year. At present the exploited potential is about 71.9 million metric tons per year. This review paper provides an in-depth assessment of Ethiopia's biomass energy availability, potential, challenges, and prospects. The findings show that, despite Ethiopia's vast biomass resource potential, the current use of modern energy from biomass is still limited. As a result, this study supports the use of biomass-based alternative energy sources without having a negative impact on the socioeconomic system or jeopardizing food security or the environment. This finding also shows the challenges, opportunities and possible solutions to tackle the problem to expand alternative energy sources. The most effective techniques for producing and utilizing alternate energy sources were also explored. Moreover, some perspectives are given based on the challenges of using efficient energy production and sustainable uses of biomass energy in Ethiopia as it could be also implemented in other developing countries. We believe that the information in this review will shed light on the current and future prospects of biomass energy deployment in Ethiopia.

Photocatalytic Hydrogen Production from Urine Using Sr-Doped TiO2 Photocatalyst with Subsequent Phosphorus Recovery via Struvite Crystallization

Currently, the discharge of wastewater and utilization of phosphorus (P) in human activities cause some environmental problems, such as high organic pollutants in aquatic environments which results in dirty water sources, and a shortage of phosphate rock reserves due to the high demand of P. Therefore, fuel energy and struvite crystallization from waste sources can be considered interesting alternatives. In this work, the modified catalyst for hydrogen production, along with solving environmental problems, was examined. The strontium (Sr) doped-titanium dioxide (TiO2) nanoparticles were synthesized by wetness impregnation method. The synthesized catalyst was characterized using UV-vis spectroscopy (UV-vis), photoluminescence (PL), X-ray diffraction (XRD), photoluminescence (PL), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). The Sr-doped TiO2 catalysts had been utilized as the photocatalyst for the hydrogen production from synthetic human urine (a representative of waste source). The doping content of Sr in TiO2 varied from 0.5, 1, 2, and 4%, and the photocatalytic performances were compared with pristine TiO2 nanoparticles. The results showed that 1% Sr-doped TiO2 had the highest photocatalytic activity for hydrogen production and decreased the amount of chemical oxygen demand (COD) in the synthetic human urine. Subsequently, P could be recovered from the treated human urine in the form of struvite.

Current developments and future trends in photocatalytic glycerol valorization: process analysis

Challenges and opportunities in photocatalytic glycerol valorization to hydrogen and value-added liquid products: process analysis and parametric study.

Regulating Photochemical Selectivity with Temperature: Isobutanol on TiO2(110)

Selective photocatalytic transformations of chemicals derived from biomass, such as isobutanol, have been long envisioned for a sustainable chemical production. A strong temperature dependence in the reaction selectivity is found for isobutanol photo-oxidation on rutile TiO₂(110). The strong temperature dependence is attributed to competition between thermal desorption of the primary photoproduct and secondary photochemical steps. The aldehyde, isobutanal, is the primary photoproduct of isobutanol. At room temperature, isobutanal is obtained selectively from photo-oxidation because of rapid thermal desorption. In contrast, secondary photo-oxidation of isobutanal to propane dominates at lower temperature (240 K) due to the persistence of isobutanal on the surface after it is formed. The byproduct of isobutanal photo-oxidation is CO, which is evolved at higher temperature as a consequence of thermal decomposition of an intermediate, such as formate. The photo-oxidation to isobutanal proceeds after thermally induced isobutoxy formation. These results have strong implications for controlling the selectivity of photochemical processes more generally, in that, selectivity is governed by competition of desorption vs secondary photoreaction of products. This competition can be exploited to design photocatalytic processes to favor specific chemical transformations of organic molecules.

Metal-free photocatalysts for hydrogen evolution

This article provides a comprehensive review of the latest progress, challenges and recommended future research related to metal-free photocatalysts for hydrogen productionviawater-splitting.

Introducing catalysis in photocatalysis: What can be understood from surface science studies of alcohol photoreforming on TiO2

Mechanisms in heterogeneous photocatalysis have traditionally been interpreted by the band-structure model and analogously to electrochemistry. This has led to the establishment of 'band-engineering' as a leading principle for the discovery of more efficient photocatalysts. In such a picture, mainly thermodynamic aspects are taken into account, while kinetics are often ignored. This holds in particular for chemical kinetics, which are, other than those for charge carrier dynamics, often not at all considered for the interpretation of the catalysts' photocatalytic performance. However, while being usually neglected in photocatalyis, they are a traditional and powerful tool in thermal catalysis and are still applied with great success in this field. While surface science studies made substantial contributes to thermal catalysis, analogous studies in heterogeneous photocatalysis still play only a minor role. In this review, the authors show that the photo-physics of defined materials in well-defined environments can be correlated with photochemical events on a surface, highlighting the importance of well-characterized semiconductors for the interpretation of mechanisms in heterogeneous photochemistry. The work focuses on contributions from surface science, which were obtained for the model system of a titania single crystal and alcohol photo-reforming. It is demonstrated that only surface science studies have so far enabled the elucidation of molecularly precise reaction mechanisms, the determination of reaction intermediates and assignment of reactive sites. As the identification of these properties remain major prerequisites for a breakthrough in photocatalysis research, the work also discusses the implications of the findings for applied systems. In general, the results from surface science demonstrate that photocatalytic systems shall also be approached by a perspective originating from heterogeneous catalysis rather than solely from an electrochemical point of view.

Insights into a rutile/brookite homojunction of titanium dioxide: separated reactive sites and boosted photocatalytic activity

Benefiting from studies into Degussa TiO2, forming junctions via combining different phases of a semiconductor may provide new insights into the design of efficient photocatalysts, which are a key element in current solar-driven fuel production and environmental remediation. In this work, we aimed at creating a highly efficient rutile/brookite homojunction through precise crystal phase control. Characterization of the morphology and structure revealed that the ultrafine brookite phase TiO2 particles were uniformly attached to the surfaces of the rod-like rutile phase, not only readily forming a homojunction but also stabilizing the brookite phase. Surprisingly, the rutile/brookite-TiO2 homojunction exhibited a synergetic effect, improving the photocatalytic activity for both hydrogen generation and organic dye degradation. This was attributed to the well-matched band alignment and separated reaction sites, effectively promoting the charge separation efficiency. These results highlight the potential for bifunctional photocatalyst design with separated reactive sites for simultaneous redox reactions.

Hydrogen and Propane Production From Butyric Acid Photoreforming Over Pt-TiO2

Photocatalysis is a promising technology from economic, energetic, and ecological points of view because it takes advantage of solar light. Hence, it is one of the investigated green routes to produce hydrogen from renewable energy resources. Butyric acid (BA) is largely present in wastewater and as an intermediate product in anaerobic digestion and therefore it is an inexpensive resource, which can be converted to valuable chemicals. In this work, photoreforming of butyric acid (BAPR) under UV light in aqueous suspensions of platinum-modified titanium dioxide-based catalysts is reported for the first time. Titania nanotubes (TNT) synthesized and calcined at different temperatures (300, 400, 500°C) and commercial TiO₂ (P25), decorated with platinum nanoparticles, have been tested and characterized through different techniques including X-ray powder diffraction, UV-vis diffuse reflectance and photoluminescence spectroscopy, transmission electron microscopy, BET and porosimetry analysis. The main identified products of the BAPR were H₂, propane, CO₂ and several organic acids (e.g., pentanoic and 3-methylhexanoic acid). It has been found that the morphology and crystallinity of the photocatalysts affected dramatically their optical properties and, consequently, the reaction rate and the product distribution. Specifically, the highest conversion of BA (X_BA) and selectivity toward H₂ (S_H2) was recorded with P25-Pt (X_BA = 26.9%, S_H2 = 47.2% after 8 h of irradiation). TNT-400-Pt showed the highest selectivity toward propane (S_C3H8 = 16.1%) with X_BA = 23.4% and S_H2 = 36.2%. The activity results in conjunction with the characterization of the catalysts highlighted that the main factor affecting the activity in terms of X_BA and generation of H₂ was the crystallinity, and in particular the presence of rutile phase in TiO₂, whereas S_C3H8 appears to increase when the electron-holes recombination is lower.

The Role of Surface Texture on the Photocatalytic H2 Production on TiO2

It has been often reported that an efficient and green photocatalytic dissociation of water under irradiated semiconductors likely represents the most important goal for modern chemistry. Despite decades of intensive work on this topic, the efficiency of the water photolytic process under irradiated semiconductors is far from reaching significant photocatalytic efficiency. The use of a sacrificial agent as hole scavenger dramatically increases the hydrogen production rate and might represent the classic “kill two birds with one stone”: on the one hand, the production of hydrogen, then usable as energy carrier, on the other, the treatment of water for the abatement of pollutants used as sacrificial agents. Among metal oxides, TiO2 has a central role due to its versatility and inexpensiveness that allows an extended applicability in several scientific and technological fields. In this review we focus on the hydrogen production on irradiated TiO2 and its fundamental and environmental implications.

Supported Mn3O4 Nanosystems for Hydrogen Production through Ethanol Photoreforming

Photoreforming promoted by metal oxide nanophotocatalysts is an attractive route for clean and sustainable hydrogen generation. In the present work, we propose for the first time the use of supported Mn₃O₄ nanosystems, both pure and functionalized with Au nanoparticles (NPs), for hydrogen generation by photoreforming. The target oxide systems, prepared by chemical vapor deposition (CVD) and decorated with gold NPs by radio frequency (RF) sputtering, were subjected to a thorough chemico-physical characterization and utilized for a proof-of-concept H₂ generation in aqueous ethanolic solutions under simulated solar illumination. Pure Mn₃O₄ nanosystems yielded a constant hydrogen production rate of 10 mmol h^-1 m^-2 even for irradiation times up to 20 h. The introduction of Au NPs yielded a significant enhancement in photocatalytic activity, which decreased as a function of irradiation time. The main phenomena causing the Au-containing photocatalyst deactivation have been investigated by morphological and compositional analysis, providing important insights for the design of Mn₃O₄-based photocatalysts with improved performances.

0D-2D Quantum Dot: Metal Dichalcogenide Nanocomposite Photocatalyst Achieves Efficient Hydrogen Generation

Hydrogen generation via photocatalysis-driven water splitting provides a convenient approach to turn solar energy into chemical fuel. The development of photocatalysis system that can effectively harvest visible light for hydrogen generation is an essential task in order to utilize this technology. Herein, a kind of cadmium free Zn-Ag-In-S (ZAIS) colloidal quantum dots (CQDs) that shows remarkably photocatalytic efficiency in the visible region is developed. More importantly, a nanocomposite based on the combination of 0D ZAIS CQDs and 2D MoS₂ nanosheet is developed. This can leverage the strong light harvesting capability of CQDs and catalytic performance of MoS₂ simultaneously. As a result, an excellent external quantum efficiency of 40.8% at 400 nm is achieved for CQD-based hydrogen generation catalyst. This work presents a new platform for the development of high-efficiency photocatalyst based on 0D-2D nanocomposite.

Ga-Promoted Photocatalytic H2 Production over Pt/ZnO Nanostructures

Photocatalytic H2 generation is investigated over a series of Ga-modified ZnO photocatalysts that were prepared by hydrothermal methods. It is found that the structural, textural, and optoelectronic properties remarkably depend on the Ga content. The photocatalytic activity is higher in samples with Ga content equal to or lower than 5.4 wt %, which are constituted by Zn1-xGaxO phases. Structural, textural, and optoelectronic characterization, combined with theoretical calculations, reveals the effect of Ga in the doped ZnO structures. Higher Ga incorporation leads to the formation of an additional ZnGa2O4 phase with spinel structure. The presence of such a phase is detrimental for the textural and optoelectronic properties of the photocatalysts, leading to a decrease in H2 production. When Pt is used as the cocatalyst, there is an increase of 1 order of magnitude in the activity with respect to the bare photocatalysts. This is a result of Pt acting as an electron scavenger, decreasing the electron-hole recombination rate and boosting the H2 evolution reaction.

Catalytic Reforming of Oxygenates: State of the Art and Future Prospects

This Review describes recent advances in the design, synthesis, reactivity, selectivity, structural, and electronic properties of the catalysts for reforming of a variety of oxygenates (e.g., from simple monoalcohols to higher polyols, then to sugars, phenols, and finally complicated mixtures like bio-oil). A comprehensive exploration of the structure-activity relationship in catalytic reforming of oxygenates is carried out, assisted by state-of-the-art characterization techniques and computational tools. Critical emphasis has been given on the mechanisms of these heterogeneous-catalyzed reactions and especially on the nature of the active catalytic sites and reaction pathways. Similarities and differences (reaction mechanisms, design and synthesis of catalysts, as well as catalytic systems) in the reforming process of these oxygenates will also be discussed. A critical overview is then provided regarding the challenges and opportunities for research in this area with a focus on the roles that systems of heterogeneous catalysis, reaction engineering, and materials science can play in the near future. This Review aims to present insights into the intrinsic mechanism involved in catalytic reforming and provides guidance to the development of novel catalysts and processes for the efficient utilization of oxygenates for energy and environmental purposes.

Engineering titania nanostructure to tune and improve its photocatalytic activity

Photocatalytic pathways could prove crucial to the sustainable production of fuels and chemicals required for a carbon-neutral society. Electron-hole recombination is a critical problem that has, so far, limited the efficiency of the most promising photocatalytic materials. Here, we show the efficacy of anisotropy in improving charge separation and thereby boosting the activity of a titania (TiO2) photocatalytic system. Specifically, we show that H2 production in uniform, one-dimensional brookite titania nanorods is highly enhanced by engineering their length. By using complimentary characterization techniques to separately probe excited electrons and holes, we link the high observed reaction rates to the anisotropic structure, which favors efficient carrier utilization. Quantum yield values for hydrogen production from ethanol, glycerol, and glucose as high as 65%, 35%, and 6%, respectively, demonstrate the promise and generality of this approach for improving the photoactivity of semiconducting nanostructures for a wide range of reacting systems.

Dye-sensitized photocatalytic hydrogen production: distinct activity in a glucose derivative of a phenothiazine dye

A glucose-functionalized phenothiazine dye gave efficient activities compared to the common hydrophilic triethylene glycol derivative as a consequence of improved wettability and peculiar features of the sugar functionality.

Highly efficient hydrogen production through ethanol photoreforming by a carbon nanocone/Pd@TiO2 hybrid catalyst

Production of molecular hydrogen (H₂) is becoming an increasingly prominent process, due to the high expectations as a new green energy carrier and key reagent for many industrial processes.

Tuning Thiophene-Based Phenothiazines for Stable Photocatalytic Hydrogen Production

Dibranched donor-(π-acceptor)2 dyes, where phenothiazine is the donor core, cyanoacrylic acid is the acceptor/anchoring group, and π is represented by mono- and poly-cyclic simple and fused thiophene derivatives, were tested as photosensitizers in the photocatalytic production of H2 , in combination with a Pt/TiO2 catalyst. The optical and electrochemical properties of the dyes were investigated, showing that careful design of the thiophene-based π spacer afforded enhanced optical properties. In the H2 production over 20 h, the new thiophene-based sensitizers revealed improved stability after longer irradiation times and enhanced performances, in terms of H2 production rates and light-to-fuel efficiencies, after an initial activation period, which were for the first time associated with enhanced stability under photocatalytic production of H2 and the absence of critical dye degradation.

Solution combustion synthesis of metal oxide nanomaterials for energy storage and conversion

The design and synthesis of metal oxide nanomaterials is one of the key steps for achieving highly efficient energy conversion and storage on an industrial scale. Solution combustion synthesis (SCS) is a time- and energy-saving method as compared with other routes, especially for the preparation of complex oxides which can be easily adapted for scale-up applications. This review summarizes the synthesis of various metal oxide nanomaterials and their applications for energy conversion and storage, including lithium-ion batteries, supercapacitors, hydrogen and methane production, fuel cells and solar cells. In particular, some novel concepts such as reverse support combustion, self-combustion of ionic liquids, and creation of oxygen vacancies are presented. SCS has some unique advantages such as its capability for in situ doping of oxides and construction of heterojunctions. The well-developed porosity and large specific surface area caused by gas evolution during the combustion process endow the resulting materials with exceptional properties. The relationship between the structural properties of the metal oxides studied and their performance is discussed. Finally, the conclusions and perspectives are briefly presented.

Surface Activation of Faceted Photocatalyst: When Metal Cocatalyst Determines the Nature of the Facets

Pt nanoparticles with tunable size are prepared on the entire surface of facet-engineered Cu2WS4 decahedral photocatalyst via a kinetic-controlled chemical reduction process. The {101} facets of the photocatalyst which featured photo-oxidation, are successfully activated for photoreduction by Pt. The resulting photocatalyst shows an activity nine times higher compared to that of the only {001}-facets activated catalyst obtained by a conventional in situ photodeposition route.

Solution based CVD of main group materials

This critical review focuses on the solution based chemical vapour deposition (CVD) of main group materials with particular emphasis on their current and potential applications. Deposition of thin films of main group materials, such as metal oxides, sulfides and arsenides, have been researched owing to the array of applications which utilise them including solar cells, transparent conducting oxides (TCOs) and window coatings. Solution based CVD processes, such as aerosol-assisted (AA)CVD have been developed due to their scalability and to overcome the requirement of suitably volatile precursors as the technique relies on the solubility rather than volatility of precursors which vastly extends the range of potentially applicable compounds. An introduction into the applications and precursor requirements of main group materials will be presented first followed by a detailed discussion of their deposition reviewed according to this application. The challenges and prospects for further enabling research in terms of emerging main group materials will be discussed.

Advances and recent trends in heterogeneous photo(electro)-catalysis for solar fuels and chemicals

In the context of a future renewable energy system based on hydrogen storage as energy-dense liquid alcohols co-synthesized from recycled CO2, this article reviews advances in photocatalysis and photoelectrocatalysis that exploit solar (photonic) primary energy in relevant endergonic processes, viz., H2 generation by water splitting, bio-oxygenate photoreforming, and artificial photosynthesis (CO2 reduction). Attainment of the efficiency (>10%) mandated for viable techno-economics (USD 2.00-4.00 per kg H2) and implementation on a global scale hinges on the development of photo(electro)catalysts and co-catalysts composed of earth-abundant elements offering visible-light-driven charge separation and surface redox chemistry in high quantum yield, while retaining the chemical and photo-stability typical of titanium dioxide, a ubiquitous oxide semiconductor and performance "benchmark". The dye-sensitized TiO2 solar cell and multi-junction Si are key "voltage-biasing" components in hybrid photovoltaic/photoelectrochemical (PV/PEC) devices that currently lead the field in performance. Prospects and limitations of visible-absorbing particulates, e.g., nanotextured crystalline α-Fe2O3, g-C3N4, and TiO2 sensitized by C/N-based dopants, multilayer composites, and plasmonic metals, are also considered. An interesting trend in water splitting is towards hydrogen peroxide as a solar fuel and value-added green reagent. Fundamental and technical hurdles impeding the advance towards pre-commercial solar fuels demonstration units are considered.

An overview on visible light responsive metal oxide based photocatalysts for hydrogen energy production

The present review summarizes the recent development and challenges in visible light responsive metal oxide based photocatalysts for water splitting.

Photocatalytic hydrogen evolution from glycerol and water over nickel-hybrid cadmium sulfide quantum dots under visible-light irradiation

Natural photosynthesis offers the concept of storing sunlight in chemical form as hydrogen (H2), using biomass and water. Herein we describe a robust artificial photocatalyst, nickel-hybrid CdS quantum dots (Nih-CdS QDs) made in situ from nickel salts and CdS QDs stabilized by 3-mercaptopropionic acid, for visible-light-driven H2 evolution from glycerol and water. With visible light irradiation for 20 h, 403.2 μmol of H2 was obtained with a high H2 evolution rate of approximately 74.6 μmol h(-1)  mg(-1) and a high turnover number of 38 405 compared to MPA-CdS QDs (mercaptopropionic-acid-stabilized CdS quantum dots). Compared to CdTe QDs and CdSe QDs, the modified CdS QDs show the greatest affinity toward Ni(2+) ions and the highest activity for H2 evolution. X-ray photoelectron spectroscopy (XPS), inductively-coupled plasma atomic emission spectrometry (ICP-AES), and photophysical studies reveal the chemical nature of the Nih-CdS QDs. Electron paramagnetic resonance (EPR) and terephthalate fluorescence measurements clearly demonstrate water splitting to generate ⋅OH radicals. The detection of DMPO-H and DMPO-C radicals adduct in EPR also indicate that ⋅H radicals and ⋅C radicals are the active species in the catalytic cycle.

Tailoring photocatalytic nanostructures for sustainable hydrogen production

Photocatalysis is an important component for achieving sustainability in chemical transformations. It requires light absorption by a semiconductor and efficient extraction of the photogenerated electron-hole pairs to chemically active sites. One of the main problems in photocatalytic materials is to avoid electron-hole recombination following excitation. Tailored nanostructures offer a new way for achieving this goal by facilitating electron-hole separation. Nanoscaling of materials offers additional opportunities to generate unique photocatalysts that demonstrated novel light absorption, thermodynamic and kinetic properties. In this feature article we highlight some recent approaches towards the preparation of materials and nanostructures that showed improved activity for the sustainable production of hydrogen. This reaction has received much attention for the supply of future demand both for chemical industry and energy-related applications.

Sunlight-promoted photocatalytic hydrogen gas evolution from water-suspended cellulose: a systematic study

Photocatalytic H₂ evolution from water in the presence of cellulose as the sacrificial agent is studied. The photoreaction proceeds under sunlight also using waste cellulosic biomass, i.e. rice husk.

Photoelectrochemical hydrogen production on α-Fe2O3 (0001): insights from theory and experiments

The photoelectrochemical (PEC) decomposition of organic compounds in wastewater is investigated by using quantum chemical (DFT) methods to evaluate alternatives to water splitting for the production of renewable and sustainable hydrogen. Methanol is used as a model organic species for the theoretical evaluations of electrolysis on the surface of the widely available semiconductor hematite, α-Fe2 O3 , a widely studied photocatalyst. Three different α-Fe2 O3 surface terminations were investigated, including the predominant surface found in aqueous electrolytes, (OH)3 R. The PEC oxidation of methanol is energetically downhill, producing CO2 and protons. The protons are reduced to hydrogen on the cathode. Experimental PEC measurements were also performed for several polyalcoholic compounds, glycerol, erythritol, and xylitol, on α-Fe2 O3 as the photocatalyst and showed high incident-photon-to-current-efficiencies (IPCE) that were much greater than those of water splitting. Interestingly, high IPCEs were observed for hydrogen production from polyalcohols in the absence of any applied bias, which was not thought to be possible on hematite. These results support the potential application of PEC for hydrogen production by using widely available hematite for the PEC oxidation of selected components of organic wastewater present in large quantities from anthropogenic and industrial sources.