Search

Over 79 % of 6.3 billion tonnes of plastics produced from 1950 to 2015 have been disposed in landfills or found their way to the oceans, where they will reside for up to hundreds of years before being decomposed bringing upon significant dangers to our health and ecosystems. Plastic photoreforming offers an appealing alternative by using solar energy and water to transform plastic waste into value‐added chemical commodities, while simultaneously producing green hydrogen via the hydrogen evolution reaction. This review aims to provide an overview of the underlying principles of emerging plastic photoreforming technologies, highlight the challenges associated with experimental protocols and performance assessments, discuss recent global breakthroughs on the photoreforming of plastics, and propose perspectives for future research. A critical assessment of current plastic photoreforming studies shows a lack of standardised conditions, hindering comparison amongst photocatalyst performance. Guidelines to establish a more accurate evaluation of materials and systems are proposed, with the aim to facilitate the translation of promising fundamental discovery in photocatalysts design. [ABSTRACT FROM AUTHOR]

As a fascinating visible‐light‐responsive photocatalyst, zinc indium sulfide (ZnIn2S4) has attracted extensive interdisciplinary interest and is expected to become a new research hotspot in the near future, due to its nontoxicity, suitable band gap, high physicochemical stability and durability, ease of synthesis, and appealing catalytic activity. This review provides an overview on the recent advances in ZnIn2S4‐based photocatalysts. First, the crystal structures and band structures of ZnIn2S4 are briefly introduced. Then, various modulation strategies of ZnIn2S4 are outlined for better photocatalytic performance, which includes morphology and structure engineering, vacancy engineering, doping engineering, hydrogenation engineering, and the construction of ZnIn2S4‐based composites. Thereafter, the potential applications in the energy and environmental area of ZnIn2S4‐based photocatalysts are summarized. Finally, some personal perspectives about the promises and prospects of this emerging material are provided. [ABSTRACT FROM AUTHOR]

Crystal facet engineering of semiconductor photocatalysts is regarded as an emerging strategy to tune their physicochemical properties and optimize the photoreactivity of the materials. In this work, two plate‐like Bi2MoO6 samples were prepared, dominant in either the distinctly different {100} or {010} facets. As a consequence of the electronic structure effects induced by the facets, the {100}‐dominant Bi2MoO6 (100‐BMO) possessed a smaller band gap and delivered a much higher photocatalytic water oxidation activity than {010}‐dominant Bi2MoO6 (010‐BMO). A greater charge carrier density in 100‐BMO was found to promote electron accumulation on the {100} surfaces, leading to the narrower band gap, as supported by Mott‐Schottky measurements. Efficient intrinsic electron‐hole separation and longer charge carrier lifetimes in 100‐BMO were also observed. Further, a higher photocurrent density and smaller Nyquist plot arc radius presented by 100‐BMO imply a higher charge transfer capacity. EPR analysis indicated that the 100‐BMO boasted a higher oxygen vacancy density, whereby the vacancies could serve as shallow donors to trap electrons and suppress photogenerated electron‐hole pair recombination. Overall, the {100} facet in Bi2MoO6 delivered a mix of distinctly advantageous characteristics relative to the {010} facet with the findings clearly illustrating the value of crystal facet engineering in boosting photocatalytic performance. [ABSTRACT FROM AUTHOR]

Redox catalysis, including photocatalysis and (photo)electrocatalysis, may alleviate global warming and energy crises by removing excess CO2 from the atmosphere and converting it to value-added resources. Nano-to-atomic two-dimensional (2D) materials, clusters and single atoms are superior catalysts because of their engineerable ultrathin/small dimensions and large surface areas and have attracted worldwide research interest. Given the current gap between research and applications in CO2 reduction, our review systematically and constructively discusses nano-to-atomic surface strategies for catalysts reported to date. This work is expected to drive and benefit future research to rationally design surface strategies with multi-parameter synergistic impacts on the selectivity, activity and stability of next-generation CO2 reduction catalysts, thus opening new avenues for sustainable solutions to climate change, energy and environmental issues, and the potential industrial economy. [ABSTRACT FROM AUTHOR]

Abstract: Cuprous Oxide (Cu2O) is a photocatalyst with severe photocorrosion issues. Theoretically, it can undergo both self‐oxidation (to form copper oxide (CuO)) and self‐reduction (to form metallic copper (Cu)) upon illumination with the aid of photoexcited charges. There is, however, limited experimental understanding of the “dominant” photocorrosion pathway. Both photocorrosion modes can be regulated by tailoring the conditions of the photocatalytic reactions. Photooxidation of Cu2O (in the form of a suspension system), accompanied by corroded morphology, is kinetically favourable and is the prevailing deactivation pathway. With knowledge of the dominant deactivation mode of Cu2O, suppression of self‐photooxidation together with enhancement in its overall photocatalytic performance can be achieved after a careful selection of sacrificial hole (h+) scavenger. In this way, stable hydrogen (H2) production can be attained without the need for deposition of secondary components. [ABSTRACT FROM AUTHOR]

Well-aligned, high aspect-ratio and open-ended TiO2 nanotube arrays secured within a Ti foil (TiO2 nanotubes cartridge) were successfully prepared through the double-sided anodization method. With ∼210 µm of nanotube length, the anodic growth of TiO2 was accelerated and stabilized by the lactic acid-containing ethylene glycol electrolyte. In the absence of lactic acid, the anodization led to detachment of nanotubes from the Ti foil after 5-6 h of high voltage (80 V) anodization. Transmission electron microscope image and Raman spectrum revealed that the as-anodized TiO2 nanotube arrays without annealing treatment were partially crystalline anatase and demonstrated photocatalytic activity in the mineralization of formic acid. © 2015 American Institute of Chemical Engineers AIChE J, 62: 415-420, 2016 [ABSTRACT FROM AUTHOR]

A TiO2-based photocatalytic reaction is demonstrated to synthesize water miscible reduced graphene oxide (RGO) sheets with conductivity comparable to that of bulk graphite. Unlike the conventional chemical/thermal reduction pathways which effectively deoxygenated the oxidized graphite, the photocatalytic method removes oxygen functional groups selectively to afford excellent conductivity restoration yet maintaining its water miscibility. The controlled redox capabilities of the photocatalyst serve as an effective modulation tool to tune the conductivity restoration and suppression of hydrophobicity. Moreover, the evolution of defect minimization/generation in a two-step pattern is monitored throughout the photocatalytic process and its association with the conductivity of RGO is established. The insights of defect engineering at the initial stage of graphene oxide (GO) to RGO transformation provides useful information in developing optimum chemical methods to produce large domain and small defect density graphene. [ABSTRACT FROM AUTHOR]

The mineral ilmenite is one of the most abundant ores in the Earth′s crust and it is the main source for the industrial production of bulk titanium oxide. At the same time, methods to convert ilmenite into nanostructures of TiO2 (which are required for new advanced applications, such as solar cells, batteries, and photocatalysts) have not been explored to any significant extent. Herein, we describe a simple and effective method for the preparation of rutile TiO2 nanorods from ball-milled ilmenite. These nanorods have small dimensions (width: 5-20 nm, length: 50-100 nm, thickness: 2-5 nm) and possess large specific surface areas (up to 97 m2 g−1). Dissolution/hydrolysis/precipitation is proposed as a growth mechanism. The nanorods were found to have attractive photocatalytic properties in the degradation of oxalic acid. Their photocatalytic activity is close to that of the benchmark Degussa P25 material and better than that of a commercial high-surface-area rutile powder. [ABSTRACT FROM AUTHOR]

A comparative photocatalytic analysis was carried out on TiO2 made in a Flame Spray Pyrolysis (FSP) process and flame-made Degussa P25. Both have similar crystallinity, phase composition, phase segregation and a non-porous surface. Hence comparison was made based on their difference in specific surface area, organic adsorption and the amount of OH• generated upon illumination. The photocatalytic activity tests were carried out using the following series of organic compounds: sucrose, glucose, fructose, maleic acid, glyoxylic acid, oxalic acid, isobutyric acid, phenol and methanol. FSP-made TiO2 outperformed P25 for saccharides mineralisation, while for phenol and methanol mineralisation P25 was better than FSP-made TiO2. Similar mineralisation rates were observed for both FSP-made and P25 TiO2 for the mineralisation of carboxylic acids. This shows that the relative performance of the photocatalysts depends on the type of organic compounds to be degraded. The high surface area and possibly a more efficient interfacial charge transfer of FSP-made TiO2 provided an efficient pathway for saccharides mineralisation. As for phenol and methanol, the mineralisation rates were higher when using P25 due to the greater amount of OH• radicals generated by this photocatalyst. The fast mineralisation rates of carboxylic acids made degradation of these organic compounds to be less affected by the TiO2 photocatalyst properties and conditions tested in this work. [ABSTRACT FROM AUTHOR]

This article first indicates the various types of temperature-induced oxygen isotopic exchange (OIE) that can occur between labeled gaseous O2 and solid oxides. Earlier main results of light-induced OIE with semiconductor oxides are then briefly reviewed. The core of the article reports new results about the use of light-induced OIE to assess (i) the lability of TiO2 surface O atoms, as altered by calcination or Se deposits, via the comparison of OIE with the photocatalytic removal of methanol in air and (ii) the accessibility of TiO2 affixed on a fiberglass material by means of a silica binder. Both this overview and these novel results illustrate the interest of OIE in heterogeneous photocatalysis. [ABSTRACT FROM AUTHOR]

Abstract: Visible light-active Fe-doped TiO2 was prepared by a one-step flame spray pyrolysis (FSP) technique. The properties of the photocatalysts were characterised by UV–vis diffuse-reflectance spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption (BET), transmission electron microscope (TEM) and zeta potential techniques. Being a bottom-up approach, the short residence time coupled with rapid quenching during FSP resulted in homogeneous Fe-doped TiO2 for Fe/Ti ratios approximately up to 0.05. This is five times higher than that reported for particles synthesised by conventional wet techniques followed by high temperature annealing. Under visible light irradiation (λ >400nm), the rate of oxalic acid mineralisation by Fe-doped TiO2 (Fe/Ti=0.05) was 6.4 times higher than that of similarly prepared bare TiO2 and Degussa P25. A unique Fe-leaching and re-adsorption properties were observed during the reaction. Unlike the system of bare TiO2 spiked with dissolved Fe(III) ions, the FSP Fe-doped TiO2 photocatalyst was found to be stable and reusable after each run with minimal loss of Fe from the surface. [Copyright &y& Elsevier]

Abstract: The photodeposition of cadmium selenide (CdSe) using Se-TiO2 photocatalysts was studied at pH 3.5 and 7 in the presence of formic acid. The Se-TiO2 photocatalysts were obtained by Se ion photoreduction using selenite (Se(IV)) and selenate (Se(VI)) as precursors. The formation of cadmium selenide was attributed to the reaction between cadmium ions and selenide ions (Se2−) released from the Se deposited on TiO2 particles under illumination. The release of the Se2− ions from the Se–TiO2 is believed to be the determining step for the formation of the CdSe particles, hence controlling their morphology as either rod-shaped or spherical. Metallic cadmium was also detected on the surface of TiO2 particles as a product of the photocatalytic reduction at pH 7. Its formation was attributed to the photoreduction of cadmium by the photogenerated electrons in the TiO2 and/or the Se semiconductors. [Copyright &y& Elsevier]

Abstract: Comparative performance studies between different photocatalysts for reduction reactions are scarce. Here, Millennium PC500 and PC50 photoreactivities were investigated for selenite (Se(IV)) and selenate (Se(VI)) reduction to their elemental form (Se(0)) and compared with that of Degussa P25 TiO2. Millennium PC500, with the highest surface area demonstrated the fastest photoreduction of Se(IV) and Se(VI), compared to P25 and Millennium PC50. Millennium PC50 and P25, which have comparable surface areas, showed similar photoreactivities. UV–Vis reflectance measurements and XRD characterisation revealed that the Se(0) deposits underwent phase transformation from amorphous to stable crystalline Se(0) during the drying and ageing process. Overall, the Millennium PCs appear to be promising photocatalysts for the photoreduction process. [Copyright &y& Elsevier]

Magnetic iron oxide–titania photocatalysts (Fe3O4–TiO2) were prepared using a coating technique in which the photoactive titanium dioxide was deposited onto the surface of a magnetic iron oxide core. These particles had a core–shell structure. The prepared particles were heat treated at high temperature in order to transform the amorphous titanium dioxide into a photoactive crystalline phase. The heat treatment temperature and duration were varied, and the correlation between the heat treatment and the observed photoactivities was investigated. An increase in the applied heat treatment, either by increasing the temperature or increasing the heat treatment duration, led to a decrease in the activities of the catalyst particles. A decrease in surface area due to sintering, along with the diffusion of Fe ions into the titanium dioxide coating are seen as contributing factors to the decline in photoactivity which accompanied an increase in the heat treatment. Differential scanning calorimetry analysis (DSC) results confirmed that the presence of the iron oxide core did not have an effect on the phase transformation of titania under the experimental conditions investigated. In this study we also present surface charge measurements which show that the surface of the particles became more positive as the heat treatment was increased. This is an indication of changing surface properties as heat treatment is applied. For single-phase TiO2 powders, this is postulated to be due to a decrease in the surface hydroxyl (OH) groups and/or residual organics (OR) groups. For the Fe3O4–TiO2 powders, in addition to the loss of OH and OR groups, the diffusion of the Fe into the titania shell is postulated to also play a role in the changing surface properties with applied heat treatment. Experiments aimed at reducing the duration of the heat treatment revealed that a heat treatment duration of 20 min at 450 °C was sufficient to transform amorphous titanium dioxide into a photoactive crystalline phase. This does not only minimise loss of surface hydroxyl groups but it also has the potential to limit the oxidation of the magnetic core, which occurs due to the porosity of the coating. This has practical implications in terms of separating the magnetic particles from the treated waste waters under the application of an external magnetic field. It also presents an opportunity to produce photoactive composite particles while limiting the interactions between the core and the shell during the heat treatment. [Copyright &y& Elsevier]

The simultaneous photocatalytic degradation of organic compounds and reduction of silver ions in titanium dioxide suspensions at pH 3.0–3.5 has been studied. The organic compounds of interest were sucrose and salicylic acid.The presence of silver ions in TiO2 suspensions was found to enhance the photooxidation of high loadings (2000 μg C) of sucrose. However, for low sucrose loadings (100 μg C), pure TiO2 particles performed as well as modified TiO2 particles. An optimum silver ion loading of 2.0 at.% Ag+ was observed for the mineralisation of 2000 μg C sucrose. At this silver ion loading, the mineralisation of 2000 μg C sucrose was enhanced by a factor of approximately 4.0 (based on 90% overall oxidation rates). In contrast, the addition of silver ions to TiO2 suspensions did not have any significant effect on the photocatalytic mineralisation of salicylic acid to carbon dioxide, for both low and high loadings of salicylic acid in the suspension. It was also observed that pure TiO2 particles performed as well as silver-modified TiO2 particles for the degradation of 2000 μg C salicylic acid.The higher activity of silver ion-modified titanium dioxide suspensions for sucrose mineralisation is predominantly due to the presence of small silver particles on the titania surface, rather than due to the trapping of electrons during the reduction of silver ions. Approximately 50% of the initial mass of silver ions added to TiO2 suspensions were reduced to metallic silver deposits in the presence of sucrose and salicylic acid mineralisation at the 2.0 at.% Ag+ loading.Nanosize silver deposits on TiO2 particles act as sites of electron accumulation where the reduction of adsorbed species such as oxygen occur. The enhanced reduction of oxygen through better electron–hole separation in Ag/TiO2 particles compared to pure TiO2 particles increases the rate of sucrose mineralisation. Therefore, it is proposed that the rate-limiting step in the sucrose photooxidation reaction is the transfer of electrons to dissolved oxygen molecules, whereas in the case of salicylic acid degradation and mineralisation, the rate-limiting step is the attack of salicylic acid molecules and its degradation intermediate products by holes and hydroxyl radicals. Hence silver deposits on TiO2 particles are not beneficial for the photocatalytic degradation and mineralisation of salicylic acid but are advantageous for the mineralisation of sucrose. [Copyright &y& Elsevier]

A stable magnetic photocatalyst was prepared by coating a magnetic core with a layer of photoactive titanium dioxide. A direct deposition of titanium dioxide onto the surface of magnetic iron oxide particles proved ineffective in producing a stable magnetic photocatalyst, with high levels of photodissolution being observed with these samples. This observed photodissolution is believed to be due to the dissolution of the iron oxide phase, induced by the photoactive the titanium dioxide layer due to electronic interactions at the phase junction in these magnetic photocatalysts. The introduction of an intermediate passive SiO2 layer between the titanium dioxide phase and the iron oxide phase inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase. The magnetic photocatalyst is for use in slurry-type reactors from which the catalyst can be easily recovered by the application of an external magnetic field. [Copyright &y& Elsevier]

We demonstrate a general strategy to prepare Bi2WO6/Ag/N–TiO2film with double visible-light-active components bridged by Ag nanoparticles as an electron shuttle, which exhibits enhanced photocatalytic activity and photoelectrochemical performance under visible light. [ABSTRACT FROM AUTHOR]

The nascent field of nanotechnology-enabled metallurgy has great potential. However, the role of eutectic alloys and the nature of alloy solidification in this field are still largely unknown. To demonstrate one of the promises of liquid metals in the field, we explore a model system of catalytically active Bi-Sn nano-alloys produced using a liquid-phase ultrasonication technique and investigate their phase separation, surface oxidation, and nucleation. The Bi-Sn ratio determines the grain boundary properties and the emergence of dislocations within the nano-alloys. The eutectic system gives rise to the smallest grain dimensions among all Bi-Sn ratios along with more pronounced dislocation formation within the nano-alloys. Using electrochemical CO2 reduction and photocatalysis, we demonstrate that the structural peculiarity of the eutectic nano-alloys offers the highest catalytic activity in comparison with their non-eutectic counterparts. The fundamentals of nano-alloy formation revealed here may establish the groundwork for creating bimetallic and multimetallic nano-alloys. The combination of metallurgy concepts and nanotechnology with liquid metal processing has been largely unexplored. Here the authors use liquid-phase ultrasonication to produce a model system of catalytically active nano-alloys, demonstrating electrocatalysis and photocatalysis. [ABSTRACT FROM AUTHOR]

The photocatalytic water‐splitting system ideally consists of just photocatalyst powder and water without any additives. Herein, improvement of water‐splitting activity under neutral conditions is achieved by applying Mo‐doping and cocatalyst‐loading to BiVO4 of an O2‐evolving photocatalyst in a Z‐scheme system with Ru‐loaded SrTiO3 doped with Rh as a H2‐evolving photocatalyst and a reduced graphene oxide as an electron mediator. The strategies are based on the idea that the Z‐schematic electron migration process in the powdered Z‐scheme system with reduced graphene oxide is similar to that in the photoelectrochemical system. Although the reaction condition becomes out of the ideal states, adding Ca(NO3)2 and CaCl2 into the reactant solution further improves the water‐splitting activity due to the formation of aggregated photocatalyst particles to boost the electron transfer from Mo‐doped BiVO4 to Ru‐loaded SrTiO3 doped with Rh through the reduced graphene oxide. [ABSTRACT FROM AUTHOR]

• Cuprous oxide has great potential in photocatalysis but suffering from photocorrosion. • Photocorrosion can be induced by photo-reduction or photo-oxidation, respectively. • Strategies can be formulated for photocorrosion suppression but understandings of the charge dynamics are also important. The emergence of cuprous oxide (Cu 2 O) as a visible light active semiconductor for photocatalytic and photoelectrochemical applications has elevated significantly over the past decade. With photocorrosion identified as a severe issue for Cu 2 O, its photoactivity has been greatly restricted. Given that Cu 2 O redox potentials are located in between its band gap, the possible occurrence of self-photoreduction or self-oxidation upon illumination is inevitable. Various efforts have been directed to implement effective strategies in enhancing the photostability of Cu 2 O. In particular, most of the studies focused on improving the charge transfer from Cu 2 O to reactants or co-catalyst to avoid accumulation of charge within the particles. This review presents recent research progresses for the development of strategies to suppress Cu 2 O photocorrosion in regards to its intrinsic properties and charge kinetics. It is shown that effective transport of electrons or holes out of Cu 2 O photocatalyst by engineering its crystal structure, tuning its reaction environment or depositing secondary elements could effectively inhibit Cu 2 O from experiencing self-photodecomposition. Understanding of the charge dynamics with respect to its photocorrosion is pivotal to optimize the design of Cu 2 O photocatalyst for enhanced performance in the future. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Nitrogen doping in graphene improves the size distribution of platinum nanoparticles. • Platinum loading has correlation with the nitrogen dopant level. • Photocatalytic hydrogen generation is improved in nitrogen-doped graphene samples. Abstract Nitrogen doping of graphene with systematically controlled dopant content and distribution of nitrogen species is demonstrated to improve the size distribution of the deposited platinum (Pt) nanoparticles. While the dopant content can be tuned by varying the urea dosage, the doped nitrogen species (namely pyridinic N, pyrrolic N, and graphitic N) can be controlled through the annealing temperature. Chemically reduced Pt nanoparticles were found to be evenly distributed on the nitrogen-doped graphene sheets (NRGO) with particle size centred at 2.7 nm. In comparison, the decoration of Pt on the non-doped graphene (RGO) yielded a composite material with larger Pt (7.8 nm) and poorer size distribution. The loading of Pt nanoparticles is shown to correlate with the concentration of the nitrogen dopant, in particular that of the graphitic N species. Owing to the smaller and better distributed Pt nanoparticles which facilitated more active sites for reaction, the Pt-loaded NRGO photocatalytically generated H 2 gas ten times higher than that of Pt-loaded RGO when coupled with photoactive graphitic carbon nitride (g-C 3 N 4). [ABSTRACT FROM AUTHOR]

An abstract of the article "Photocatalytic Overall Water Splitting over ALi2Ti6O14 (A: 2Na and Sr) with Tunneling Structure," by Akihide Iwase and colleagues is presented.

Efficient hydrogen production from water by photocatalysis under sunlight requires a significant improvement in light-harvesting capability. Zinc sulfide is a promising, inexpensive hydrogen generation photocatalyst, but in its pure, bulk form it is only active under ultra-violet light. Here, we show clear evidence of photoelectrochemical activity of ZnS thin films under visible-light irradiation without any co-catalysts, achieved through defect engineering. Fabrication of nanostructured ZnS under controlled conditions introduces defects, and hence intermediate electronic states within the band gap, which allow significant absorption of light at energies below the band gap energy of pure, bulk ZnS. The measured band gap of the ZnS thin films is ~2.4 eV, while the photocurrent density exceeds 1.5 mA/cm 2 under visible-light irradiation ( λ ≥435 nm). This is the first measurement of such high photocurrents for undoped ZnS under visible light. [ABSTRACT FROM AUTHOR]

Abstract: Natural zeolite coated with titanium dioxide (TiO2) was used as an adsorbent to rapidly remove humic acid (HA) from an aqueous solution. Coating TiO2 onto zeolite markedly improved its efficiency in adsorbing HA: most of the bulk organic matter (80%) could be removed within 5min of adsorption by the zeolite/TiO2 particles at neutral pH, whereas less than 20% was removed by bare zeolite alone. In addition, immobilisation of TiO2 onto zeolite permitted easier separation of the adsorbent from the treated water. Photocatalytic properties of TiO2 were exploited for the regeneration of the adsorbent. The adsorbent was shown to be readily regenerated by photocatalytic oxidation and was still effective in removing HA after 5 adsorption/regeneration cycles. These results indicate that TiO2-coated zeolite can be a very attractive adsorbent for the rapid removal of HA from aqueous solutions. [Copyright &y& Elsevier]

Abstract: Bare titanium dioxides (TiO2) and doped with metal (Cu) or non-metal ion (F) were synthesized by a single-step flame spray pyrolysis (FSP) method. According to the BET, XRD, and TEM results, the Cu- and F-doped TiO2 nanoparticles synthesized by FSP possess comparable features in terms of surface area, crystallite size and phase composition, and morphology. However, the F-doped TiO2 exhibited the highest photocatalytic activity for the complete oxidation of acetaldehyde (ACE) even surpassing benchmarking Aeroxide TiO2 (P25). In contrast, Cu-doped TiO2 had a detrimental effect on the ACE photocatalytic oxidation. The proportion of native terminal hydroxyl groups, evaluated using high-field 1H MAS NMR, on the particle surface was varied by doping the TiO2 with either Cu or F ions during FSP synthesis. A relationship, whereby decreased terminal hydroxyl group content corresponded to elevated acetaldehyde photodegradation, was subsequently uncovered. The findings were reinforced by studying the XPS O 1s photopeaks in the region attributed to surface hydroxyl groups. [Copyright &y& Elsevier]

Abstract: This study compares the photocatalytic (PC) and photoelectrocatalytic (PEC) oxidation of glucose by Pt–TiO2 films under similar conditions. The overall oxidation efficiency of the PEC process was better than the PC process, for both TiO2 and Pt–TiO2 films. The Pt deposits enhanced the PEC oxidation efficiency of glucose at low cathodic (−0.1V) and low anodic potential bias (+0.1V). As the applied anodic bias was increased to >+0.5V, the undoped-TiO2 films outperformed their Pt–TiO2 counterparts. This suggests that in the studied systems, at an anodic bias of >+0.5V, more holes were available for the oxidation of glucose on the surface of TiO2 compared to Pt–TiO2 films. In the PEC systems, above a certain applied bias, Pt deposits may have a detrimental effect on the performance of a PEC system because the Pt deposits could merely block the surface of TiO2 (particularly at the highest Pt loadings). Lower measured photocurrents from Pt–TiO2 films compared to undoped-TiO2 and a decrease in the photocurrent as the Pt loading increased corroborate this postulation. [Copyright &y& Elsevier]

Abstract: The inter-relationship between Pt oxidation state dynamics and the TiO2 photocatalysis of three groups of organic compounds (carboxylic acid, alcohol and phenolics) was investigated. Repetitive photocatalytic mineralisation of formic acid over the as-prepared Pt(II)/TiO2 produced free formate radicals which partially reduced Pt(II) to Pt(0, II)/TiO2. Further repetitive dark mineralisation of formic acid over this pretreated catalyst was as effective as the as-prepared sample under UV-A illumination. As for the photocatalytic mineralisation of methanol, the usually reported current doubling effect which would result in the reduction of Pt was not observed under the studied air-equilibrated condition and low organic concentration. However, the photocatalytic mineralisation of methanol was enhanced over formic acid-pretreated catalyst compared to the as-prepared and phenol-pretreated samples, highlighting the beneficial and detrimental effects of Pt(0) and Pt(IV), respectively. The enhancement was partially attributed to the favourable intimate dark catalytic interaction between Pt(0) and methanol. The photocatalytic mineralisation rates of phenol over as-prepared and formic acid-pretreated catalysts were found to be limited by the benzoquinone/hydroquinone short-circuit equilibrium. The photocatalytic mineralisation of trihydroxybenzene, the immediate product after the short-circuit equilibrium, over as-prepared Pt/TiO2 was faster relative to phenol and more so over the formic acid-pretreated sample. This corroborates the rate-limiting equilibrium while also demonstrates the beneficial effect of Pt(0). The enhancement effects on these phenolic compounds were in qualitative agreement with the observed dark catalytic mineralisation. [Copyright &y& Elsevier]

Abstract: The fate of selenite (Se(IV)) and selenate (Se(VI)) ions in illuminated TiO2 suspensions was studied. In the presence of formic acid as a hole scavenger, both Se(IV) and Se(VI) were photoreduced to Se(0). The Se(0) deposited as either separate particles or a film on the TiO2 particles. UV–vis reflectance measurements showed that the Se–TiO2 powders were red-shifted relative to pure TiO2 with an additional absorbance band at around 680nm, attributed to Se(0). The photocatalytic reduction mechanism of selenium ions, with focus on selenite photoreduction, is discussed. It is proposed that direct reduction of Se(IV) by the electrons photogenerated in TiO2 resulted in the formation of a Se(0) film while the formation of Se(0) particles was due to a chemical reaction between Se(IV) and Se(2−). The Se(2−) is believed to have been generated from the six electron photoreduction of Se(IV) and/or further photoreduction of Se(0) deposits. [Copyright &y& Elsevier]

[Display omitted] • Crystallinity and specific surface area of photocatalyst are two important factors. • In Bi 2 WO 6 , crystallinity effect is more dominant than surface area. • Higher crystallinity leads to improved transportation of photoexcited charges. Crystallinity and specific surface area of a photocatalyst are two important factors in determining the ultimate photocatalytic performances. In this work, hierarchical bismuth tungstate (Bi 2 WO 6) microspheres with modulations in crystallinity and surface area were carefully synthesised using hydrothermal method with a subsequent calcination treatment. Comparison of activities in photocatalytic water splitting was performed systematically to understand the role of each factor. While larger surface area is in general perceived to provide more active sites for reactions, it was found in this work that crystallinity which governs the photoexcited charge transportation has a more profound impact in influencing the photocatalytic water oxidation. These findings should be applicable to other powder type photocatalytic materials. [ABSTRACT FROM AUTHOR]

In this study, two different crystallographic phases of bismuth molybdate, α-Bi 2 Mo 3 O 12 and γ-Bi 2 MoO 6 were synthesized hydrothermally. A series of Bi 2 Mo 3 O 12 /Bi 2 MoO 6 heterostructures with different phase ratios were readily prepared by tuning the concentration of the molybdenum precursor while retaining the same bismuth precursor concentration. The Bi 2 Mo 3 O 12 /Bi 2 MoO 6 heterojunction was found to substantially enhance the photocatalytic water oxidation capability relative to neat Bi 2 Mo 3 O 12 and Bi 2 MoO 6 . The Bi 2 MoO 6 and Bi 2 Mo 3 O 12 were found to possess a complementary band alignment between which enabled the charge transfer process across the heterojunction interface. Ag and MnO x photodeposition was conducted on the heterostructures to affirm the charge transfer direction between the two crystal phases. Under visible light irradiation, photogenerated holes transfer from the active Bi 2 MoO 6 phase to the inactive Bi 2 Mo 3 O 12 , suggesting efficient charge separation occurs between the two components, explaining the better photocatalytic performance. [ABSTRACT FROM AUTHOR]

The role of key oxidative species in formic acid oxidation using neat and platinum-loaded TiO 2 , CeO 2 and SiO 2 was investigated. The catalytic reactions under three different illumination conditions; dark catalysis (i.e. no illumination), dark catalysis with UV light pre-treatment (denoted as pre-30) and photocatalysis (i.e. continuous UV illumination), were studied. The activities of neat TiO 2 , CeO 2 and SiO 2 were low under dark and pre-30 conditions while under illumination (photocatalysis) the semiconductor metal oxides, TiO 2 and CeO 2 showed much higher oxidation rates. For the Pt-loaded catalysts, the key active species were surface active oxygen (PtO ads and O − ads ) under the dark catalytic condition with and without light pre-treatment while under photocatalytic condition, photogenerated holes and electrons are believed to form hydroxyl radicals ( OH) and superoxide radicals ( O 2 − ), respectively, for CeO 2 , TiO 2 , Pt/TiO 2 and Pt/CeO 2 . Unexpectedly, Pt/SiO 2 showed the highest activity under the dark catalytic condition. The cuboctahedral shape of the Pt deposits on the SiO 2 surface, which promote a greater number of sharp edges/corners at the interface, is believed to have been advantageous for dissociating and activating adsorbed oxygen species compared to the Pt deposits on TiO 2 and CeO 2 . The Pt deposit shape is thought to be responsible for the observed high activity of Pt/SiO 2 for the dark catalytic oxidation of formic acid. [ABSTRACT FROM AUTHOR]

This article reviews two interrelated areas of research: the first is the use of TiO 2 -supported adsorbent materials as enhanced heterogeneous photocatalysts and their application to various reactions for organic pollutant removal from air and water; the second is the combination of adsorbent materials with TiO 2 photocatalysts which aims to efficiently regenerate adsorbent materials using illumination. By reviewing both areas of research, the following topics are covered; (i) photocatalytic activation of TiO 2; (ii) related properties of photocatalytic TiO 2; (iii) shortcomings of photocatalytic processes; (iv) preparation methods of composite TiO 2 /adsorbent materials and their photocatalytic performance; (v) properties of common adsorbents and their applications for pollutant removal from air and water; (vi) adsorbent regeneration methods and their economic and operational issues; (vii) conclusions and future outlooks. This topic has not been previously reviewed to such an extent, and considerable knowledge can be gained from assembling the large number of studies on adsorption-photocatalysis combinations. As such, this review provides guidance for researchers working in the fields of environmental and chemical engineering focussing on organic pollutant removal and the engineering of new high performance photocatalytic TiO 2 -supported porous adsorbent materials. [ABSTRACT FROM AUTHOR]

Thermal annealing of metal oxides in oxygen-deficient atmosphere, particularly reducing hydrogen gas, has been demonstrated to induce oxygen vacancy formation for enhanced photoactivity of the materials. Here, it is demonstrated that argon annealing (another prevalently used oxygen-deficient gas) in the temperature range of 300-700 °C greatly affects the activity of dual-faceted BiVO4 microcrystals for photocatalytic O2 generation and photocurrent generation. While treatment at 300 °C has little to no effect, higher temperatures of 500 and 700 °C significantly improve the crystallinity, alter the local structure distortion, and reduce the bandgap energy of the treated BiVO4. The higher temperature treatment also favors formation of new subgap states attributed to oxygen vacancies, as supported by surface photovoltage and electron paramagnetic resonance spectroscopies. Despite the most profound improvements in structural, optical, and electronic properties displayed by the 700 °C-treated BiVO4, the sample annealed at 500 °C exhibits the highest photoactivity. The lower activity of the 700 °C-treated BiVO4 is ascribed to the creation of bismuth vacancies and the loss of well-defined crystal facets, contributing to impeded electron transport and poor charge separation. [ABSTRACT FROM AUTHOR]

Hydrogen production by the photoreforming of a glycerol solution using a 0.08 mol% bimetallic Cu–Pt/TiO 2 photocatalyst was investigated. CuO x –PtO 2 deposits were loaded onto TiO 2 particles by impregnation followed by heat-treatment in air. XPS and H 2 -TPR studies indicated an increased electron density in the Pt component of the deposits, attributed to an interaction between the Cu and Pt, which left it in a more reducible state. H 2 generation by the Cu–Pt deposits was found to outperform deposits of the single metals at equivalent metal loadings (i.e. 0.08 mol%), as well as the sum of the single metals (0.04 mol% loading each). The CuO x –PtO 2 was reduced to alloyed metallic Cu–Pt deposits, in preference to proton reduction, during the initial reaction period, after which H 2 production was accelerated. Theoretical calculations reinforced the experimental studies, predicting an increased electron density on the Pt in the bimetallic Cu–Pt deposits compared with single metal Pt deposits. The Cu–Pt deposits favoured charge carrier separation which further enhanced the photocatalytic H 2 production process. [ABSTRACT FROM AUTHOR]

Nanostructured CuOx/TiO2 (a mixture of Cu/Cu2O/CuO) was prepared by impregnation for enhancing photocatalytic hydrogen generation from an aqueous solution containing 10 v/v% methanol. At an optimum Cu loading of 0.5 wt% and a calcination temperature of 500 °C, the CuOx was present as relatively highly dispersed (0.90), fine deposits. At Cu loadings beyond 0.5 wt% a bimodal distribution of CuOx deposits appeared with the prevalence of larger Cu deposits increasing with increasing Cu content. A corresponding decrease in H2 generation was observed as Cu loading increased which was attributed to the increasing presence of the larger CuOx deposits. The particle calcination temperature (in air) was also found to affect CuOx/TiO2 activity with an optimum performance achieved at a temperature of 300 °C. Calcining the CuOx/TiO2 at 500 °C led to greater oxidation of the CuOx deposits (∼40%) to form more Cu2+ which corresponded to an almost proportional (42%) decrease in H2 generation. The findings demonstrate the importance of Cu dispersion and oxidation state in governing photocatalytic H2 generation by CuOx/TiO2. [ABSTRACT FROM AUTHOR]

Abstract: The photocatalytic activity of sodium titanate (Na1.48H0.52Ti3O7), sodium hexatitanate (Na2Ti6O13), and hydrogen titanate (H2Ti3O7) nanoribbons and anatase TiO2 nanorods were compared for water splitting, oxalic acid photodegradation and H2 and O2 generation using sacrificial agents. The intrinsic properties of the materials were found to affect their performance depending on the particular reaction system. The Na2Ti6O13 nanoribbons, in the presence of RuO2 co-catalyst, outperformed the anatase nanorods, for the water splitting reaction, generating over 10 times more H2/O2. This was thought to derive from their tunnel-like structure which provided better electron/hole separation when compared with TiO2. However, the efficient holes and electrons scavenging in the presence of sacrificial agents, methanol or AgNO3, to generate H2 or O2, respectively, overwhelmed the tunnel-like structure effect. In this case photoactivity was governed by the crystal structure, with observed decreasing activity in the order TiO2>Na2Ti6O13>H2Ti3O7∼Na1.48H0.52Ti3O7, and by the band gap of the semiconductor which determined its capacity to absorb photons in producing electron/hole pairs. [Copyright &y& Elsevier]

Abstract: The photocatalytic degradation of butanedioic acid (BDA), hydroxybutanedioic acid (OH-BDA) and 2,3-dihydroxybutanedioic acid (diOH-BDA) (succinic acid, malic acid and tartaric acid, respectively) in a TiO2 aqueous suspension at pH 3 was investigated to determine the effects of hydroxyl substitution. Temporal variations in the concentrations of the main intermediate products are reported. The use of a set of reactions involving decarboxylation and formation of alkylperoxy and alkoxy radicals has allowed us to account for the occurrence of these products, and to suggest the preferential decarboxylation of the COOH/COO− group adjacent to the OH group in OH-BDA. The adsorbed amounts in the dark increased with the number of OH groups, while the irradiation time necessary for total disappearance of the initial diacid, decreased. However, the evolution rate of CO2, which was initially the same for the three acids, was then lower for the hydroxylated diacids for a significant period of irradiation time. This difference is tentatively attributed predominantly to the effect of hydroxyl substitution on the adsorption mode. One of the carboxyl groups would remain away from the surface (and hence not be available for direct electron transfer) due to the restricted mobility of the adsorbed diacid caused by hydrogen-bonding of TiO2 with the alcohol group adjacent to the other carboxyl group. This hypothesis is also effective to qualitatively interpret how the zeta potential varied in the course of the degradation of each diacid. The present study further illustrates the essential role of distinct adsorption modes in photocatalytic events. [Copyright &y& Elsevier]

Abstract: A photoreactor comprising a bundle of TiO2-coated quartz tubes was studied by varying its tube wall thickness and tube configuration as well as introducing a mesoporous SiO2 intermediate layer between the TiO2 coating and quartz tube. The bundled tube photoreactor (BTP) performance was assessed based on tube light propagation and photocatalytic degradation rate of ethylene. Increasing the tube wall thickness improved the tube light propagation and the degradation rate of ethylene. An array of eight 6-mm tubes was found to be the best BTP configuration in this work. The findings from varying the tube configuration suggested an effectively illuminated surface area as a second important parameter to consider when comparing different BTP performances. Introducing a mesoporous SiO2 intermediate layer with a thickness between 210 and 400nm between the TiO2 coating and quartz tube improved not only the tube light propagation but also the ethylene photocatalytic degradation rate by up to 70%. This improvement was attributed to controlled light refraction from the quartz tube, which can be achieved under the conditions of frustrated total internal reflection. [Copyright &y& Elsevier]

The effectiveness of reduced graphene oxide as a solid electron mediator for water splitting in the Z-scheme photocatalysis system is demonstrated. We show that a tailor-made, photoreduced graphene oxide can shuttle photogenerated electrons from an O2-evolving photocatalyst (BiVO4) to a H2-evolving photocatalyst (Ru/SrTiO3:Rh), tripling the consumption of electron-hole pairs in the water splitting reaction under visible-light irradiation. [ABSTRACT FROM AUTHOR]