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Abstract: In this work, several operational parameters affecting the photocatalytic degradation of mixtures of two azo dyes – Acid Yellow (AY) monoazo dye and Acid Black (AB) diazo dye – including types of dye, initial dye concentration, photocatalyst dosage, dissolved oxygen, initial solution pH, and water hardness concentration, were investigated by using a mesoporous-assembled TiO2 nanocrystal photocatalyst. The experimental results showed that the initial concentration of both azo dyes in the dye mixture greatly affected the degradation efficiency. It was interestingly found that the degradation efficiency of one azo dye could be improved by the presence of the other with suitable concentrations. At AY and AB concentrations of 2.5 and 5mg/l, the optimum conditions for the highest degradation efficiency of both azo dyes were a photocatalyst dosage of 10g/l, a dissolved oxygen of 7.5mg/l, and an initial solution pH of 4.5. Moreover, even though water hardness negatively affected the degradation efficiency, the pH adjustment could be applied for enhancing the degradation of the dyes present in the extremely hard solution. [Copyright &y& Elsevier]

Abstract: In this work, novel mesoporous-assembled SrTi x Zr1−x O3 nanocrystal photocatalysts were successfully synthesized by a sol–gel process with the aid of a structure-directing surfactant under mild conditions. The photocatalytic activity of the synthesized photocatalysts for degradation of Acid Black (AB) diazo dye used as a model contaminant in textile wastewater was investigated by varying Ti-to-Zr molar fraction, calcination conditions, and Pt loading. The synthesized photocatalysts were systematically characterized by TG–DTA, N2 adsorption–desorption analysis, XRD, UV–visible spectroscopy, SEM–EDX, TEM–EDX, TPR, and H2 chemisorption. The photocatalytic activity results showed that without Pt loading, the mesoporous-assembled SrTi x Zr1−x O3 photocatalyst with a Ti-to-Zr molar fraction of 0.9:0.1 (i.e. SrTi0.9Zr0.1O3) calcined at 700°C for 4h provided a maximum degradation rate constant as compared to the other SrTi x Zr1−x O3 photocatalysts. The optimum Pt loading of 1wt.% by a single-step sol–gel method on the mesoporous-assembled SrTi0.9Zr0.1O3 photocatalyst was found to greatly increase the degradation rate constant of the AB dye. Furthermore, the calcination temperature was found to significantly affect the degradation rate constant of the Pt-loaded mesoporous-assembled SrTi0.9Zr0.1O3 photocatalyst. [Copyright &y& Elsevier]

Abstract: Hydrogen production from the photocatalytic water splitting reaction is very attractive because it is an environmentally friendly process, where hydrogen is produced from two abundantly renewable sources, i.e. water and solar energy, with the aid of photocatalysts. TiO2 is the most widely investigated photocatalyst; however, it alone still exhibits low performance to photocatalytically produce hydrogen. Hence, the aim of this work focused on the enhanced photocatalytic hydrogen production over Ag-loaded mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystal photocatalysts under UV light irradiation. The TiO2–ZrO2 mixed oxides with various TiO2-to-ZrO2 molar ratios were synthesized by a sol–gel process with the aid of a structure-directing surfactant, followed by Ag loading via a photochemical deposition method. The influences of photocatalyst preparation parameters, i.e. calcination temperature, phase composition, and Ag loading, were studied. The results revealed that the mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystal photocatalyst with a TiO2-to-ZrO2 molar ratio of 93:7 calcined at 500 °C exhibited the highest photocatalytic hydrogen production activity, and the Ag loading of 0.5 wt.% further greatly enhanced the photocatalytic activity of such TiO2–ZrO2 mixed oxide photocatalyst. [Copyright &y& Elsevier]

Abstract: In this work, photocatalytic degradation of 4-chlorophenol (4-CP) was investigated using TiO2, Au/TiO2, Ag/TiO2, and Au–Ag/TiO2 photocatalysts prepared by a sol–gel method. Experiments were carried out in a batch reactor with a photocatalyst suspended in a reaction solution under irradiation from an 11-W low-pressure mercury lamp emitting UV light in the wavelength range of 200–280nm. Qualitative analysis of the reaction solution was performed by means of both a high performance liquid chromatograph (HPLC) and a total organic carbon (TOC) analyzer. The amounts of intermediates obtained from the 4-CP degradation were also determined. The results showed that the loading of a small amount (0.1%) of either Au or Ag onto the TiO2 significantly improved the photocatalytic activity, but the loading of 0.1% Au onto the 0.1% Ag/TiO2 slightly affected the photocatalytic activity, exhibiting almost the same photocatalytic activity as the host 0.1% Ag/TiO2. However, both the 0.1% Ag/TiO2 and 0.1% Au–0.1% Ag/TiO2 provided the highest photocatalytic activity in terms of TOC reduction. [Copyright &y& Elsevier]

Abstract: The hydrogen production via the photocatalytic water splitting under UV irradiation using different compounds as hole scavengers (including methanol, formic acid, acetic acid, propanoic acid, hydrochloric acid, and sulfuric acid) under a low concentration range (<8vol.%) was investigated over the 1wt.% Au-loaded mesoporous-assembled SrTiO3 nanocrystal photocatalyst. The results indicated that the hydrogen production efficiency greatly depended on the molecular structure, chemical properties, and concentration of the hole scavengers. Formic acid, which is the smallest and completely-dissociated water-soluble carboxylic acid, exhibited the highest hydrogen production enhancement ability. The 2.5vol.% aqueous formic acid solution system provided the highest photocatalytic hydrogen production rate. [Copyright &y& Elsevier]

Abstract: A modified sol–gel technique with the aid of a structure-directing surfactant was employed to synthesize highly crystalline mesoporous-assembled V2O5 nanosheet under mild conditions. The synthesized V2O5 nanosheet was systematically characterized by TG-DTA, XRD, N2 adsorption–desorption, high resolution TEM, and UV–visible spectroscopy analyses. The characterization results revealed that the synthesized V2O5 nanosheet exhibited not only high crystallinity but also narrow pore size distribution in the mesoporous range. The photocatalytic H2 production activity of the synthesized mesoporous-assembled V2O5 nanosheet from both self photoexcitation and dye photosensitization systems under visible light irradiation was also found to be higher than that of a commercially available V2O5 powder. [Copyright &y& Elsevier]

Abstract: The photocatalytic degradation of 2-propanol was studied by using platinum, titania, and platinum loaded on titania as photocatalysts. In this study, the catalysts were prepared by microemulsion technique, which gives ultrafine particles in the range of 3–5nm. Each synthesized photocatalyst was suspended in an aqueous solution of 2-propanol, and the solution was photoirradiated by an 11W low pressure mercury lamp. The results showed a negligible activity of platinum and a relatively low activity of titania in the degradation of 2-propanol, but a significantly high activity of platinum loaded on titania was observed. The effects of the influencing factors, including initial concentration of 2-propanol, catalyst dosage, initial pH, and dissolved oxygen, were studied. The results revealed that the most efficient degradation of 2-propanol was achieved in a highly acidic region, and the degradation rate increased with both catalyst dosage and initial concentration of 2-propanol. The dissolved oxygen was found to have a significant influence affecting the photocatalytic degradation of 2-propanol since it acts as an electron scavenger and is responsible for producing hydroxyl radical. Acetone was detected as an intermediate during the photocatalytic reaction of 2-propanol. [Copyright &y& Elsevier]

The utilization of mesoporous-assembled nano-titania (TiO 2 ) thin films immobilized on glass plates for the photocatalytic degradation of Acid Black (AB) azo dye under UV light irradiation is investigated. The mesoporous-assembled TiO 2 nanoparticle photocatalyst is synthesized by a sol–gel process with the aid of laurylamine hydrochloride (LAHC) surfactant as an effective mesopore-forming agent. The effects of calcination temperature and number of TiO 2 coatings on the photocatalytic AB dye degradation performance are investigated. The experimental results reveal that an increase in calcination temperature in the range of 400–500 °C can improve the photocatalytic activity of the mesoporous-assembled TiO 2 films, but thick multilayer TiO 2 films cannot be prepared at a higher calcination temperature. In addition, an increase in number of TiO 2 coatings significantly enhances the photocatalytic activity to reach maximum and optimum three coatings. [ABSTRACT FROM AUTHOR]

Abstract: This work focused on the enhancement of photocatalytic hydrogen production activity under UV light irradiation of mesoporous-assembled 0.93TiO2–0.07ZrO2 mixed oxide nanocrystal photocatalysts (having the TiO2-to-ZrO2 molar ratio of 93:7) by non-precious metal (Ag, Ni, and Cu) loadings via a photochemical deposition method. The mesoporous-assembled 0.93TiO2–0.07ZrO2 mixed oxide was synthesized by a sol–gel process with the aid of a structure-directing surfactant prior to the metal loadings. The prepared photocatalysts were characterized by N2 adsorption–desorption, scanning electron microscopy, transmission electron microscopy, X-ray energy dispersive analysis, X-ray diffraction, UV–visible spectroscopy, and H2 chemisorption. The most efficient loaded metal was found to be Cu due to its suitable physical, chemical, and electrochemical properties with the 0.93TiO2–0.07ZrO2 mixed oxide-based photocatalyst. The 0.15wt.% Cu-loaded 0.93TiO2–0.07ZrO2 mixed oxide photocatalyst exhibited the highest photocatalytic hydrogen production activity with a hydrogen production rate of 12.8cm3 h−1 gcat −1. [Copyright &y& Elsevier]

Abstract: The photocatalytic water splitting is a promising process for producing H2 from two abundant renewable sources of water and solar light, with the aid of a suitable photocatalyst. In this work, a combination of sensitizer addition and noble metal loading was employed to modify perovskite photocatalysts in order to achieve the enhancement of photocatalytic H2 production under visible light irradiation. The dependence of the H2 production on type of mesoporous-assembled perovskite titanate nanocrystal photocatalysts (MgTiO3, CaTiO3, and SrTiO3), calcination temperature of photocatalyst, Pt loading, type and concentration of electron donor (diethanolamine, DEA; and triethanolamine, TEA), concentration of sensitizer (Eosin Y, E.Y.), photocatalyst dosage, and initial solution pH, was systematically studied. The experimental results showed that the 0.5 wt.% Pt-loaded mesoporous-assembled SrTiO3 nanocrystal synthesized by a single-step sol-gel method and calcined at 650 °C exhibited the highest photocatalytic H2 production activity from a 15 vol% DEA aqueous solution with dissolved 0.5 mM E.Y. Moreover, the optimum photocatalyst dosage and initial solution pH for the maximum photocatalytic H2 production activity were found to be 6 g/l and 11.6, respectively. [Copyright &y& Elsevier]

Abstract: Mesoporous-assembled SrTiO3 photocatalysts with different loaded metal co-catalysts (Au,Pt, Ag, Ni, Ce, and Fe) synthesized by the single-step sol–gel method with the aid of a structure-directing surfactant were tested for the photocatalytic activity of hydrogen production from a methanol aqueous solution under both UV and visible light irradiation. The Au, Pt, Ag, and Ni loadings had a positive effect on the photocatalytic activity enhancement, whereas the Ce and Fe loadings did not. The best loaded metal was found to be Au due to its electrochemical properties compatible with the SrTiO3-based photocatalyst and its visible light harvesting enhancement. A 1 wt.% Au-loaded SrTiO3 photocatalyst exhibited the highest photocatalytic hydrogen production activity with a hydrogen production rate of 337 and 200 μmol h−1 gcat −1 under UV and visible light irradiation, respectively. The hydrogen diffusivity from the liquid phase to the gas phase also significantly affected the photocatalytic hydrogen production efficiency. An increase in the hydrogen diffusability led to an increase in the photocatalytic hydrogen production efficiency. [Copyright &y& Elsevier]

Abstract: In this work, nanocrystalline mesoporous-assembled TiO2 photocatalyst was synthesized by a sol–gel process with the aid of a structure-directing surfactant and employed for the photocatalytic degradation of methyl orange azo dye (monoazo dye), as compared to various commercially available non-mesoporous-assembled TiO2 powders. The experimental results showed that the synthesized mesoporous-assembled TiO2 nanocrystal calcined at 500°C provided superior decolorization and degradation performance to the non-mesoporous-assembled commercial TiO2 powders. In addition, several operational parameters affecting the decolorization and degradation of methyl orange, namely photocatalyst dosage, initial dye concentration, H2O2 concentration, and initial solution pH, were systematically investigated, using the mesoporous-assembled TiO2 nanocrystal. The optimum conditions were a photocatalyst dosage of 7g/l, an initial dye concentration of 5mg/l, a H2O2 concentration of 0.5M, and an initial solution pH of 4.7, exhibiting the highest decolorization rate of methyl orange. [Copyright &y& Elsevier]

Abstract: Sensitized photocatalytic production of hydrogen from water splitting is investigated under visible light irradiation over mesoporous-assembled titanium dioxide (TiO2) nanocrystal photocatalysts, without and with Pt loading. The photocatalysts are synthesized by a sol–gel process with the aid of a structure-directing surfactant and are characterized by N2 adsorption–desorption analysis, X-ray diffraction, UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray analysis. The dependence of hydrogen production on the type of TiO2 photocatalyst (synthesized mesoporous-assembled and commercial non-mesoporous-assembled TiO2 without and with Pt loading), the calcination temperature of the synthesized photocatalyst, the sensitizer (Eosin Y) concentration, the electron donor (diethanolamine) concentration, the photocatalyst dosage and the initial solution pH is systematically studied. The results show that in the presence of the Eosin Y sensitizer, the Pt-loaded mesoporous-assembled TiO2 synthesized by a single-step sol–gel process and calcined at 500°C exhibits the highest photocatalytic activity for hydrogen production from a 30vol.% diethanolamine aqueous solution with dissolved 2mM Eosin Y. Moreover, the optimum photocatalyst dosage and initial solution pH for the maximum photocatalytic activity for hydrogen production are 3.33gdm−3 and 11.5, respectively. [Copyright &y& Elsevier]

Abstract: In this paper, N-doped mesoporous-assembled TiO2 and N-doped non-mesoporous-assembled commercial TiO2 (Degussa P-25) nanocrystals were comparatively investigated for photocatalytic H2 production from water splitting under visible light irradiation. The mesoporous-assembled TiO2 photocatalyst with nanocrystalline and narrow monomodal pore size distribution characteristics was synthesized by a sol–gel process with the aid of structure-directing surfactant under mild conditions. The N-doping technique was directly performed by calcining the mixture of the TiO2 photocatalysts and urea, as a N source, at different N contents and calcination temperatures. All prepared photocatalysts were systematically characterized by N2 adsorption–desorption, Brunauer–Emmett–Teller (BET) surface area analysis, Barrett–Joyner–Halenda (BJH) pore size distribution analysis, UV–visible spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS). From the experimental results, it was found that N-doped mesoporous-assembled TiO2 prepared at a urea:TiO2 molar ratio of 1:1 and a calcination temperature of 250°C exhibited relatively high photocatalytic activity toward hydrogen production. For the N-doped commercial TiO2, the preparation conditions of a molar ratio of 0.5:1 and a temperature of 250°C showed the best photocatalytic activity, but was still less photocatalytically active than N-doped mesoporous-assembled TiO2 prepared at the optimum conditions. The results indicated the importance of the mesoporous characteristic of the photocatalyst in enhancing the photocatalytic activity by increasing the specific surface area and N-doping capability. [Copyright &y& Elsevier]

Abstract: The photocatalytic evolution of hydrogen from water was investigated under various conditions over 0.6wt% Pt-loaded nanocrystalline mesoporous TiO2 photocatalyst prepared by a single-step sol–gel process with a surfactant template. The highly crystalline photocatalyst possessed a mesoporous characteristic with high surface area and narrow monomodal pore size distribution. More specifically, the influence of the following operational parameters, namely sacrificial reagent type, initial solution pH, photocatalyst concentration, initial sacrificial reagent concentration (of the best sacrificial reagent studied), and irradiation time, was the main focus. The hydrogen evolution was experimentally found to be strongly affected by all of the above parameters. The optimum values of initial solution pH, photocatalyst concentration, and sacrificial reagent concentration, as well as the appropriate type of sacrificial reagent, were obtained. The results showed that the utilization of the photocatalyst with the proper selection of optimum operational conditions could lead to considerably high photocatalytic hydrogen evolution activity. [Copyright &y& Elsevier]

Photocatalytic degradation of 4-chlorophenol (4-CP) was studied using TiO2, Pt/TiO2, Ag/TiO2 prepared by the sol–gel methods and Degussa P25 as photocatalysts. The influence of dissolved oxygen on the reaction rate and amounts of intermediate products were determined. In the experiments, a photocatalyst was suspended in the 4-CP solution, which was then irradiated with an 11 W low pressure mercury lamp emitting UV light in 200–280 nm window. The results show that, with TiO2 (sol–gel), the decrease of 4-CP concentration was much faster than that with Degussa P25. In contrast, the reduction rate of total organic carbon (TOC) with Degussa P25 was much higher than that with TiO2 (sol–gel). The addition of a small amount of either Pt or Ag into TiO2 (sol–gel) improved the catalyst activity significantly, the highest activity being obtained with 1.0% Pt/TiO2 and 0.5% Ag/TiO2. 0.5% Ag/TiO2 showed the highest activity in terms of both 4-CP and TOC removals. Hydroquinone (HQ) and hydroxyhydroquinone were identified experimentally as the main intermediate products in the presence of dissolved oxygen. The availability of dissolved oxygen played a significant role in enhancing the photocatalytic degradation of 4-CP for all the catalysts. [Copyright &y& Elsevier]

Abstract: The purpose of this work was to investigate, in the first study of its kind, hydrogen production by photocatalytic water splitting under visible light irradiation using Eosin Y-sensitized mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystal photocatalysts. The mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystals, with various TiO2-to-ZrO2 molar ratios, were synthesized by a sol–gel method with the aid of a structure-directing surfactant. The synthesized nanocrystals were characterized by thermogravimetric and derivative thermogravimetric analyzer, N2 adsorption–desorption, X-ray diffraction, UV–visible spectroscopy, scanning electron microscope–energy-dispersive X-ray analyzer, and transmission electron microscope analyses. Parameters affecting the photocatalytic activity, including calcination conditions and phase composition, were mainly discussed. Experimental results showed that the incorporation of ZrO2 with suitable contents could preserve the mesoporous-assembled structure of TiO2 at high calcination temperatures and enhance its thermal stability significantly. Results of the photocatalytic-sensitized hydrogen production revealed that the TiO2–ZrO2 mixed oxide photocatalyst, with a TiO2-to-ZrO2 molar ratio of 95:5, calcined at 800°C for 4h, provided maximum photocatalytic hydrogen production activity. The optimized TiO2–ZrO2 mixed oxide photocatalyst can be considered as a potential photocatalyst for hydrogen production under solar light irradiation. [Copyright &y& Elsevier]

Abstract: Mesoporous-assembled SrTiO3 nanocrystal-based photocatalysts were synthesized via the sol–gel method with the aid of a structure-directing surfactant. The photocatalytic water splitting activity for hydrogen production over the mesoporous-assembled SrTiO3 nanocrystal-based photocatalysts with various hole scavengers: methanol, ethanol, 2-propanol, d-glucose, and Na2SO3, was investigated. The pristine mesoporous-assembled SrTiO3 photocatalysts exhibited much higher photocatalytic activity in hydrogen production via the photocatalytic water splitting using methanol as the hole scavenger than both non-mesoporous-assembled commercial photocatalysts: commercial SrTiO3 and commercial TiO2 (Degussa P-25), even if their specific surface areas were lower than those of both commercial photocatalysts. These results point out that the mesoporous assembly of nanocrystals with high pore uniformity plays a significant role, affecting the photocatalytic hydrogen production activity of the SrTiO3 photocatalysts. The Pt co-catalyst enhances the visible light harvesting ability of the mesoporous-assembled SrTiO3 photocatalyst and behaves as the active site for proton reduction, leading to photocatalytic activity enhancement under both UV and visible light irradiation. Methanol provided the highest photocatalytic hydrogen production enhancement. An optimum Pt loading of 0.5wt.% on the mesoporous-assembled SrTiO3 photocatalyst provided the highest photocatalytic activity, with hydrogen production rates (from 50vol.% methanol aqueous solution systems) of 276 and 188μmolh−1 gcat −1 and quantum efficiencies of 1.9 and 0.9% under UV and visible light irradiation, respectively. [Copyright &y& Elsevier]