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This review presents one dimensional (1D) TiO2 nanostructured photoanodes for next generation solar cells such as dye-sensitised solar cells (DSCs) and perovskite solar cells (PSCs). Due to the unique morphological properties, 1D TiO2 nanostructures can act as express electron channels as well as light scattering layer, leading to improved charge transport properties, such as charge separation, electron injection, and electron lifetime, and light harvesting efficiency. As 1D TiO2 nanostructures are applied to solar cells, 1D TiO2 nanostructures should be further modified to overcome some drawbacks. In this review, we have described some solutions by introducing various 1D TiO2 synthetic methods and device fabrication processes for solar cell applications, where we have described some important surface engineering and hierarchical device design strategies that facilitate charge transport and light utilisation in 1D TiO2 nanostructured photoanode system. [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]

Tungsten trioxide (WO3) has been demonstrated to possess visible light photoactivity and presents a means of overcoming the UV-light dependence of photocatalysts, such as titanium dioxide. In this study, WO3 nanostructures have been synthesised by a hydrothermal method using sodium tungstate (Na2WO4∙2H2O), sulphate precursors and pH as structure-directing agents and parameters, respectively. By altering the concentration of the sulphate precursors and pH, it was shown that different morphologies and phases of WO3 can be achieved. The effect of the morphology of the final WO3 product on the visible light photoactivity of ethylene degradation in the gas phase was investigated. In addition, platinum (Pt) was photodeposited on the WO3 structures with various morphologies to enhance the photocatalytic properties. It was found that the photocatalytic properties of the WO3 samples greatly depend on their morphology, chemical composition and surface modification. WO3 with a cuboid morphology exhibited the highest visible light photoactivity compared to other morphologies, while adding Pt to the surface improved the performance of certain WO3 structures. [ABSTRACT FROM AUTHOR]

Abstract: This work demonstrated the absence of surface terminal hydroxyl groups plays a key role in the photocatalytic oxidation of low concentration volatile organic compounds. Probed by 1H MAS NMR spectroscopy, we showed the synthesis of bare and F-TiO2 nanoparticles with undetectably low content of terminal hydroxyl groups (TiOH) on the surface of TiO2 could be obtained through a sol–gel process. The characterization results by N2 adsorption, XRD, HRTEM, Raman, and XPS show that the bare TiO2 and F-TiO2 have almost identical bulk and surface structural properties. The photocatalytic activity was evaluated by photocatalytic oxidation of acetaldehyde and ethanol. Due to the absence of terminal TiOH in the bare TiO2 and F-TiO2, both materials exhibit 100% photodegradation of acetaldehyde and ethanol. No deactivation was observed during the experimental period of 8 days. The activities surpassed the photodegradation performance of the benchmarking Aeroxide P25 TiO2 under similar conditions (93%). On the bare TiO2, only stoichiometric CO2 production was observed and no detectable by-product existed in the product stream, resulting in no expanded off-odor problems. On the contrary, ethanol photodegradation on F-TiO2 produced minor acetaldehyde as a by-product, but the amount of acetaldehyde produced was still lower than that produced on Aeroxide P25. [Copyright &y& Elsevier]

The effect of NaOH-etching and UVC-irradiation on the mechanical stability of TiO2 nanoparticles on polycarbonate (PC) slides was investigated. TiO2 nanoparticles were found to adhere more strongly on UVC-treated PC than NaOH-etched PC, caused by the increase in the hydroxyl and carboxyl groups on the UVC-treated PC. Although a mechanically strong TiO2 film was developed on UVC-treated PC, the sheet-like wetting effect and antifogging behaviour were only observed with the film coated on NaOH-etched PC. It was also detected that the film coated onto NaOH-etched PC exhibited a more superior performance in degrading methylene blue than that in the UVC-treated PC system. Evidences from the FTIR and AFM analyses indicated that the performance of TiO2 films was strongly depended on the leaching rate of PEG. [ABSTRACT FROM AUTHOR]

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]

Photoreduction/removal of cadmium was studied at pH 7 using TiO2 Degussa as photocatalyst, and either formate or methanol as hole scavengers. In the absence of organic additives, approximately 60% of 30 ppm cadmium was found to be removed from the solution by adsorption. Addition of formate resulted in the photoreduction of cadmium to its metallic form. No cadmium reduction was observed when methanol was added as the hole scavenger. Zeta potential measurements of the catalyst suspensions and studies on the extent of organic additive adsorption and mineralisation were used to prove the photoreduction process. It was found that the adsorption of both cadmium and the organic hole scavenger is crucial for the photoreduction of cadmium. It is postulated that to be an effective hole scavenger the organic additive needs to be easily photooxidised under an anoxic environment. In addition, the presence of formate radicals could be responsible for the Cd photoreduction. [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]

The CuInS2(CIS) nanoparticles were wrapped uniformly throughout the inner and outer walls of TNTs (TNT) by using square wave pulsed-electrodeposition. This structure enables the CuInS2–TiO2(CIS–TNT) to exhibit p–n junction diode behavior and enhanced photoelectrochemical properties. [ABSTRACT FROM AUTHOR]

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]

Titanium dioxide-supported nickel (Ni/TiO 2 ) catalyst was studied for the low temperature steam reforming of methane (SRM). While studies have frequently reported deactivation/inactivity of TiO 2 -supported metal catalysts under conventional high temperature methane reforming conditions, it is shown here that by applying activation treatments at a milder temperature of 400 °C, Ni/TiO 2 is able to maintain stable and effective hydrogen production at 500 °C even at a low steam to methane input ratio of 1:1. Temperature programmed reduction studies showed that the presence of nickel species with stronger support interaction is crucial for the low temperature activation of methane while more weakly interacting nickel species contributed to hydrogen production via the water gas shift reaction. This observation was further confirmed when an identical reaction was performed with nickel supported on an inert oxide (silica) whereby the nickel species predominantly possessed a weaker metal–support interaction. When the amount of steam fed into the SRM system was increased, an enhancement in methane conversion by Ni/TiO 2 was observed with up to 45% methane conversion achieved at 500 °C for a H 2 O/CH 4 feed ratio of 3. The Ni/TiO 2 catalyst was shown to be capable of maintaining stable conversions and product selectivities for at least 96 h, depending on the H 2 O/CH 4 feed ratio. [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: 1,4-Dioxane, is a synthetic organic compound used widely throughout industry as a solvent. 1,4-Dioxane causes liver damage and kidney failure and has been shown to be carcinogenic to animals, and is a potential carcinogen to humans. Its recalcitrant nature means that conventional water treatment methods are ineffective in removing it from water. A class of technologies called advanced oxidation technologies has been shown to completely mineralise 1,4-dioxane. In this study the effects of pH on TiO2 photocatalysis reactor systems were investigated. pH was found to significantly affect the efficiencies of these processes with neutral pH conditions the most effective. [ABSTRACT FROM AUTHOR]

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: A serial thin-layer photoelectrocatalysis system was developed to study the relationships between the photoelectrocatalytic activity and the structural characteristics of the mesoporous TiO2 film electrodes prepared by an evaporation-induced self-assembly method. The structural characteristics of the mesoporous film electrodes were altered by using Pluronic F127 as the structural directing agent and by controlling the relative humidity and the temperature during coating and thermal treatment processes. Key structural characteristics of the resultant mesoporous TiO2 thin film electrodes were measured. For the mesoporous TiO2 film, the crystallinity can be introduced at a low thermal treatment temperature of 350°C while at lest 450°C thermal treatment temperature will be required to introduce the same degree of crystallinity to a TiO2 film prepared via a conventional sol–gel process. The effect of key structural parameters on the photoelectrocatalytic activity was investigated using glucose and succinic acid as the model organic compounds to represent weak and strong adsorbents, respectively. The reported key structural properties, such as porosity, surface area and crystallinity, that affect the photocatalytic activity were found to also critically affect the photoelectrocatalytic activity but in a different manner. This is because, for a photocatalysis application, the performance of a catalyst is mainly determined by the characteristics of individual catalyst particles, while for a photoelectrocatalysis application the performance of a catalyst also depends on the photoelectron transport process within the photocatalyst layer this in turn relies strongly on attributes such as photocatalyst particles’ interconnectivity and the contact to the conducting substrate. [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]

Photoreforming ethanol to simultaneously produce hydrogen and value-added organic products was realized over defected TiO 2. Chemically induced defects in TiO 2 promoted light absorption and charge separation, enhancing overall photoactivity. The induced defects also regulated product selectivity, leading to greater hydrogen purity and liquid to gaseous carbon ratio. The optimal catalyst generated 0.08 mmol/hr of hydrogen with a purity greater than 99 % and 0.08 mmol/hr of liquid acetaldehyde over a 6 hr timeframe. This was three times greater than the untreated TiO 2. Active species trapping revealed that the preferred ethanol oxidation pathway was direct hole transfer, indicating the selectivity relies on surface chemisorption. Surface defects decreased the acetaldehyde adsorption energy, instigating its prompt desorption and suppressing overoxidation into CO 2 , thus improving the selectivity towards hydrogen and liquid hydrocarbon products. The work offers an alternative approach towards sustainable energy by coupling photocatalysis with waste organic utilization. [Display omitted] • Defected TiO 2 prepared via a facile chemical reduction delivered improved product selectivity over ethanol photoreforming. • Enhanced light absorption and charge carrier separation by the TiO 2 defects elevated photoreforming activity. • The defected TiO 2 gave higher H 2 and acetaldehyde selectivity by suppressing CO 2 generation from ethanol over-oxidation. • Surface defects contributed to selectivity enhancement by altering intermediate chemisorption. [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]

Herein, we investigate the mechanisms involved in the selective oxidation of ethanol to acetaldehyde by localised surface plasmon resonance (LSPR) enhanced Au-Cu alloys. Temperature programmed oxidation results in tandem with quantitative in-situ DRIFTS of the surface species under different illumination conditions revealed that the cleaving of C C bonds at the Au-TiO 2 interface were inhibited in the presence of Cu at temperatures <175 °C. HAADF-STEM and XPS analysis of the spent catalysts demonstrated that the suppression of C C cleavage was due to selective electron transfer between the atomically ordered Cu and Au arrays. Thus, the selectivity of Au-Cu/TiO 2 towards the formation of acetaldehyde could be enhanced by over 800% at 100 °C under visible light illumination compared to standard thermal catalysis. Nonetheless, the selective electron charge transfer was disrupted at temperature >175 °C, lowering acetaldehyde selectivity. The work suggests that LSPR photo-enhancement is defined by the inherent electronic interactions within the bimetallic alloy and is facilitated by atomically ordering of the Au-Cu arrays. As such, in addition to performance enhancement, LSPR photo-enhancement can be used in combination with other characterisation techniques to ascertain the selective electronic pathways in bimetallic catalysts. [ABSTRACT FROM AUTHOR]

Mixed oxides of titanium with cerium were examined for the impact of their reducible oxide properties as a support for nickel-catalysed low temperature steam reforming of methane. Modifications to characteristics of the mixed oxide supports were obtained by varying the relative cerium/titanium composition and utilising different synthesis routes. Sol-gel and flame spray pyrolysis synthesis techniques were employed to achieve this purpose. The sol-gel-prepared supports exhibited improved methane conversion rates with an increased presence of cerium within the support while the catalysts with flame-made supports demonstrated poor stability upon incorporation of cerium at certain ratios. Despite the consistent high surface area and fine nickel dispersion across all flame-synthesised supports, the findings revealed that while these attributes are beneficial for steam reforming catalysis, they do not necessarily assure effective conversions. In addition to the above qualities, the sol-gel-synthesised materials demonstrated that crystalline features of the support also play a vital role in maintaining stable conversions at 500 °C. [ABSTRACT FROM AUTHOR]

In-depth characteristic studies with H 2 activity and theoretical calculations were used to reveal the copper oxidation states most effective for photocatalytic hydrogen production when loaded on TiO 2 . When the copper was originally present as CuO, photogenerated electrons initially reduced the Cu 2+ to Cu + in preference to proton reduction. The resulting Cu 2 O then behaved as a secondary photocatalyst on the TiO 2 surface acting to improve the hydrogen production rate (1.4 times greater than neat TiO 2 ). When the copper was originally present as Cu 0 , an improved hydrogen generation rate was also evident (2.4 times greater than Cu 2 O/TiO 2 ) and the metallic state was retained over the course of the reaction. In this case, the Cu 0 deposits function as a co-catalyst for proton reduction. The findings reconcile past disagreements associated with this system, demonstrating both Cu + (following reduction from Cu 2+ ) and Cu 0 are able to photocatalytically generate hydrogen, albeit by distinctly different mechanisms. [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]

Well-defined core–shell nanoparticles (NPs) containing concave cubic Au cores and TiO 2 shells (CA@T) were synthesized in colloidal suspension. These CA@T NPs exhibit Localized Surface Plasmon Resonance (LSPR) absorption in the NIR region, which provides a unique property for utilizing the low energy range of the solar spectrum. In order to evaluate the plasmonic enhancement effect, a variety of CA@T NPs were incorporated into working electrodes of dye-sensitized solar cells (DSSCs). By adjusting the shell thickness of CA@T NPs, the plasmonic property can be tuned to achieve maximum photovoltaic improvement. Furthermore, the DSSC cells fabricated with the CA@T NPs exhibit a remarkably plasmonic assisted conversion efficiency enhancement (23.3%), compared to that (14.8%) of the reference cells assembled with spherical Au@TiO 2 core–shell (SA@T) NPs under similar conditions. Various characterizations reveal that this performance improvement is attributed to the much stronger electromagnetic field generated at the hot spots of CA@T NPs, resulting in significantly higher light harvesting and more efficient charge separation. This study also provides new insights into maximizing the plasmonic enhancement, offering great potential in other applications including light–matter interaction, photocatalytic energy conversion and new-generation solar cells. [ABSTRACT FROM AUTHOR]

The role of UV light pre-treatment in enhancing Pt/TiO 2 activity for the catalytic oxidation of formic acid in an aqueous environment and under ambient conditions has been examined. The impact of light pre-treatment, relaxation time (the period between light pre-treatment and formic acid addition) and re-illumination on the oxidation rate were considered. Pre-illuminating Pt/TiO 2 provided an almost seven-fold increase in the formic acid oxidation rate compared with the untreated case. The oxidation rate decreased with increasing relaxation time, whereby after 16 h of relaxation it had stabilised at a value still around three times greater than the untreated sample. Re-illuminating the Pt/TiO 2 led to a complete recovery of the transient element of the activity. The Pt deposits were observed to undergo partial oxidation over the course of the reaction and, when coupled with a lower activity being observed upon purging the system with N 2 , imply the participation of dissolved oxygen in the overall oxidation mechanism. The findings suggest the platinum deposits can inject electrons into adsorbed molecular oxygen where the oxygen remains in an active state ready for oxidising the formic acid. Pre-treating the catalyst with light accentuates this effect as additional photogenerated electrons are drawn into the Pt deposits from the TiO 2 and transferred to and held by the adsorbed oxygen. Striking features of this particular system is the light pre-treatment effect prevails for an unexpectedly long period (in the order of hours) and is completely recoverable with re-illumination. [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]

Highlights: [•] Capable of rapid (within 5min) and efficient removal of NOM (up to 60% removal). [•] Fe3O4@SiO2@TiO2 particles re-usability through regeneration using UV or solar light. [•] Effective NOM removal after repeated adsorption–regeneration cycles. [•] Sustained THMFPs level throughout 5 adsorption–regeneration cycles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Uptake of TiO2 solids by C. reinhardtii generates ROS as an early stress response. [•] Submicron and nanoTiO2 exhibit benign effect on cell proliferation. [•] Uptake of ZnO solids and leached zinc by C. reinhardtii inhibit the alga growth. [•] No cellular oxidative stress is detected with submicron and nano ZnO exposure. [•] The toxicity of particles is not necessarily mediated by cellular oxidative stress. [Copyright &y& Elsevier]

Abstract: Thin mesoporous coatings of TiO2 nanoparticles were developed for in-house and commercial PES membranes of varying pore sizes using a low temperature hydrothermal (LTH) approach. Titania sol–gel particles were dip-coated onto membrane substrates, followed by heat and UV treatments to extract the residual organic templates. Dip-coating parameters such as drying and holding time, dipping and withdrawal velocities, and the number of coating cycles were varied to optimise the microstructure and surface properties of the coating. Coated membranes exhibit a dual level hierarchical roughness and hydrophilicity which was maintained without continuous UV illumination. The organic templating agent (Pluronics F127) enhanced adhesion of the particles; however the heat treatment collapsed some pores in the tighter ultrafiltration membranes. Results showed that the coatings were mechanically robust and photoactive. Passive protein adsorption was reduced significantly on the TiO2 coated surfaces. Filtration performance of coated and uncoated 500kDa membranes was also investigated with humic acid as a model foulant, and an increase in flux recovery was observed during multiple fouling and cleaning cycles with the titania coated membrane. The LTH approach provides a platform for further surface functionalization of polymeric membranes to generate photoactive coatings, tuneable hydrophilicity, low fouling surfaces and novel surface architecture. [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]

Abstract: A dopant-free aerosol synthesis of highly crystalline TiO2 nanoparticles (20–35nm) with tunable polymorphic content is demonstrated by rapid flame spray pyrolysis. By controlling precisely the total ambient oxygen partial pressure of the combustion in a quartz tube enclosure, anatase content as high as 96wt% (4wt% rutile) was obtained at high oxic flame conditions, while rutile content as high as 94wt% (6wt% anatase) was obtained under anoxic flames. The polymorphic variability lies within a narrow range of combustion equivalence ratios, that is, 1.0<Φ<1.5. Unlike any other flame aerosol syntheses, the anatase and rutile crystallite sizes were similar within each sample. Under highly oxic flame conditions (Φ<1.0), twinnings between anatase {011} planes could be observed, inferring oriented attachment taking place. Such mechanism could not, however, be seen under anoxic flame (Φ>1.0) possibly due to physical hindrance by surface carbonaceous content (typically <2wt%). The carbon content can be easily removed by short calcination without significantly affecting the surface areas and crystallite properties of the original TiO2 nanocrystals, preserving hence its pristine state. [Copyright &y& Elsevier]

Abstract: The photocatalytic degradation of malic acid was studied under ambient conditions in an aqueous TiO2 suspension. The results demonstrated the presence of four distinct mineralization rate variations over the course of its degradation. Differences in the mineralization rate were governed by the dominant intermediate present in the solution at that time. Initial mineralization was rapid (∼175μgC/min) resulting from the swift extraction of a carbon from strongly adsorbed malic acid via the photo-Kolbe mechanism. The mineralization rate then slowed down (∼50–70μgC/min) with the continued formation of an intermediate product (believed to be malonaldehydic acid), malonic acid and acetic acid in the solution. The findings provide greater insight into the photocatalytic degradation mechanism, illustrating the importance of intermediates and their attributes in relation to the overall rate of organic removal. [ABSTRACT FROM AUTHOR]

Abstract: A computational fluid dynamics model, coupled with a discrete ordinate radiation model, was developed for a channelled optical fibre reactor (COFR) and used to optimise its channel configuration. Air channels were grouped according to their location in the COFR into: inner arc, intermediate arc and outer arc. The flow field in the COFR was laminar with similar velocity vector distributions in all channels irrespective of their location in the COFR cross-section. The computational results demonstrated TiO2 coatings on the channel walls received light increasingly in the order: outer arc>intermediate arc>inner arc. The radiation distribution on the TiO2-coated channel walls was governed by the spatial distance. The ethylene conversion distribution corresponded well with the radiation distribution with channels in the inner and the outer arcs showing the lowest and the highest conversion, respectively. The simulation results agreed well with the experimental data possessing Pearson correlation coefficients of 0.995, 0.997 and 0.997 for variations in the incident radiant power, gas flow rate and initial ethylene concentration, respectively. Six alternate channel configurations were considered for optimising overall ethylene conversion in the COFR with an improvement of up to 33% being achieved. [Copyright &y& Elsevier]

Photocatalytic and filtration technologies were integrated to develop a hybrid system capable of removing and oxidizing organic pollutants from an air stream. A fluidized bed aerosol generator (FBAG) was adapted to prepare TiO2-loaded ventilation filters for the photodegradation of gas phase ethanol. Compared to a manually loaded filter, the ethanol photodegradation rate constant for the FBAG coated filter increased by 361%. Additionally, the presence of the photogenerated intermediate product, acetaldehyde, was reduced and the time for mineralization to CO2 was accelerated. These improvements were attributed to the FBAG system providing a more uniform distribution of TiO2 particles across the filter surface leading to greater accessibility by the UV light. A dual-UV-lamp system, as opposed to a single-lamp system, enhanced photocatalytic filter performance demonstrating the importance of high light irradiance and light distribution across the filter surface. Substituting the blacklight blue lamps with a UV-light-emitting-diode (UV-LED) array led to further improvement as well as suppressed the electrical energy per order (EE/O) by a factor of 6. These improvements derived from the more uniform distribution of light irradiance as well as the higher efficiency of UV-LEDs in converting electrical energy to photons. [ABSTRACT FROM AUTHOR]