Comparative investigation of hydrogen production over Ag-, Ni-, and Cu-loaded mesoporous-assembled TiO2–ZrO2 mixed oxide nanocrystal photocatalysts (original) (raw)
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Materials Science in Semiconductor Processing, 2013
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 TiO 2-ZrO 2 mixed oxide nanocrystal photocatalysts. The mesoporous-assembled TiO 2-ZrO 2 mixed oxide nanocrystals, with various TiO 2-to-ZrO 2 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, N 2 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 ZrO 2 with suitable contents could preserve the mesoporous-assembled structure of TiO 2 at high calcination temperatures and enhance its thermal stability significantly. Results of the photocatalytic-sensitized hydrogen production revealed that the TiO 2-ZrO 2 mixed oxide photocatalyst, with a TiO 2to-ZrO 2 molar ratio of 95:5, calcined at 800 1C for 4 h, provided maximum photocatalytic hydrogen production activity. The optimized TiO 2-ZrO 2 mixed oxide photocatalyst can be considered as a potential photocatalyst for hydrogen production under solar light irradiation.
Mesoporous coupled ZnO/TiO2 photocatalyst nanocomposites for hydrogen generation
The present work investigates mesoporous coupled ZnO-TiO 2 based nanocomposites towards photocatalytic hydrogen generation. The effect of Zn 2þ loadings was examined on the photocatalytic activities of the sol-gel derived ZnO-TiO 2 nanocomposites employing a structure-directing template. ZnO-TiO 2 nanocomposites were characterized by powder X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, nitrogen isotherm, Raman, and electrochemical impedance spectroscopy (EIS) methods. The photocatalytic H 2 evolution of the ZnO-TiO 2 suspensions was evaluated in an aqueous methanol medium under UV illumination. The Zn 2þ concentrations utilized to prepare ZnO-TiO 2 nanocomposites were found to have significant effect on the specific surface area, pore volume, and photocatalytic activity. The H 2 evolution results obtained with ZnO-TiO 2 nanocomposites were compared with H 2 generation using commercial TiO 2 P25 and individual ZnO nanoparticles. The photocatalytic activity of ZnO-TiO 2 composite enhanced significantly as compared to P25 or ZnO nanoparticles. With respect to an increment in Zn 2þ loading, the photocatalytic activity of the composite increased and reaching an optimal H 2 production of 17.3 ml/g of catalyst for the ZnO-TiO 2 composite containing 30 wt. % ZnO (30ZnO). The specific surface area of the samples increased from 19 (single ZnO) to 122 m 2 /g for ZnO-TiO 2 composite containing 50 wt. % ZnO (50ZnO). With an appropriate Zn 2þ presence in ZnO-TiO 2 nanocomposites, the specific surface area, total pore volume, charge transfer, and photocatalytic activity were significantly improved. Particularly, the samples containing 30 and 50 wt. % (30ZnO and 50ZnO) showed higher photocatalytic activity towards hydrogen generation, which attributed to higher specific surface areas, larger pore volumes, and lower interface resistance as confirmed by adsorption-desorption isotherms and EIS measurements, respectively. Hence, ZnO-TiO 2 composites with higher than 50 wt. % ZnO were found to be not favorable to attain reasonable photocatalytic activity toward hydrogen generation as specific surface area and pore volume were drastically decreased. V
Photoelectrochemical characterization and photocatalytic properties of mesoporous TiO2/ZrO2 films
International Journal of Photoenergy, 2006
Optically transparent, crack-free mesoporous titania and zirconia-doped titania thin film photocatalysts were fabricated by sol-gel technique, using nonionic amphiphilic block copolymer Pluronic P123 as template. The structural and optical properties of these films were characterized using SEM, low-angle XRD, and UV/Vis spectroscopy, hexane adsorption investigation. Band gap energy and the position of flatband potentials were estimated by photoelectrochemical measurements. Enhancing of photocatalytic activity of zirconia-doped films relative to pureTiO2originates from an anodic shift of the valence band edge potential. Catalytic activity of mesoporousTiO2andTiO2/ZrO2(5–50% ofZrO2) films in the processes ofCrVItoCrIIIphotoreduction and 2,4-dinitroaniline photooxidation correlates with crystalline size and growth with increasing of specific surface area of the samples.
ZrO2-Modified Mesoporous Nanocrystalline TiO2-xNx as Efficient Visible Light Photocatalysts
Environmental Science & Technology, 2006
Mesoporous nanocrystalline TiO 2-x N x and TiO 2-x N x /ZrO 2 visible-light photocatalysts have been prepared by a solgel method. The photocatalysts were characterized by XRD, N 2 adsorption-desorption, TEM, XPS, UV/Vis, and IR spectroscopy. The photocatalytic activity of the samples was evaluated by the decomposition of ethylene in air under visible light (λ > 450 nm) illumination. Results revealed that nitrogen was doped into the lattice of TiO 2 by the thermal treatment of NH 3-adsorbed TiO 2 hydrous gels, converting the TiO 2 into a visible-light responsive catalyst. The introduction of ZrO 2 into TiO 2-x N x considerably inhibits the undesirable crystal growth during calcination. Consequently, the ZrO 2modified TiO 2-x N x displays higher porosity, higher specific surface area, and an improved thermal stability over the corresponding unmodified TiO 2-x N x samples.
International Journal of Hydrogen Energy, 2010
Mesoporous-assembled SrTiO 3 photocatalysts with different loaded metal co-catalysts (Au, Pt, Ag, Ni, Ce, and Fe) synthesized by the single-step solegel 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 SrTiO 3-based photocatalyst and its visible light harvesting enhancement. A 1 wt.% Au-loaded SrTiO 3 photocatalyst exhibited the highest photocatalytic hydrogen production activity with a hydrogen production rate of 337 and 200 mmol h À1 g cat À1 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.
Structural and photocatalytic properties of co-doped hybrid ZrO2 -TiO2 photocatalysts
SN Applied Sciences, 2019
In this study, pure TiO 2 , ZrO 2 , and hybrid ZrO 2-TiO 2 photocatalysts were synthesized through solgel process and cal-cined at three different temperatures. The synthesized photocatalysts were characterized using powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FESEM), Brunauer-Emmet-Teller (BET), ultraviolet-visible (UV-Vis) spectrometer, and photoluminescence (PL) spectrometer. The PXRD patterns show that the rutile phase of TiO 2 was suppressed through co-doping with ZrO 2 and produced small crystallite size. The hybrid photocatalysts with small crystallite size recorded the highest surface area of 114.7 m 2 /g compared to pure TiO 2 and ZrO 2 photocatalysts as confirmed by BET analysis. Irregular size and shape was observed in the hybrid photocatalysts compared to spherical shape and size in TiO 2 and flaky shape in ZrO 2 as shown by the FESEM images. The optical properties of the photocatalysts investigated using UV-Vis spectroscopy showed a decrease in band gap energy of pure TiO 2 through linear extrapolation from the Tauc's plot despite the slightly higher band gap energy of the hybrid photocatalysts. However, PL analysis showed that doping of ZrO 2 into TiO 2 increased the separation efficiency of the electron-hole pairs and enhanced the photocatalytic activity. The phenol degradation of the hybrid ZrO 2-TiO 2 photocatalysts was higher compared to those of the pure TiO 2 and ZrO 2 .
Photocatalytic hydrogen evolution over mesoporous TiO 2/metal nanocomposites
Journal of Photochemistry and Photobiology A-chemistry, 2008
Na+ complex with the dibenzo-18-crown-6 ester was used as a template to synthesize mesoporous titanium dioxide with the specific surface area 130–140 m2/g, pore diameter 5–9 nm and anatase content 70–90%. The mesoporous TiO2 samples prepared were found to have photocatalytic activity in CuII, NiII and AgI reduction by aliphatic alcohols. The resulting metal–semiconductor nanostructures have remarkable photocatalytic activity in hydrogen evolution from water–alcohol mixtures, their efficiency being 50–60% greater than that of the metal-containing nano-composites based on TiO2 Degussa P25.The effects of the thermal treatment of mesoporous TiO2 upon its photocatalytic activity in hydrogen production were studied. The anatase content and pore size were found to be the basic parameters determining the photoreaction rate. The growth of the quantum yield of hydrogen evolution from TiO2/Ag0 to TiO2/Ni0 to TiO2/Cu0 was interpreted in terms of differences in the electronic interaction between metal nanoparticles and the semiconductor surface. It was found that there is an optimal metal concentration range where the quantum yield of hydrogen production is maximal. A decrease in the photoreaction rate at further increment in the metal content was supposed to be connected with the enlargement of metal nanoparticles and deterioration of the intimate electron interaction between the components of the metal–semiconductor nanocomposites.
Photocatalytic properties of mesoporous TiO2/ZrO2 films in gas-phase oxidation of alcohols
Theoretical and Experimental Chemistry, 2005
The photocatalytic activity of mesoporous TiO 2 modified by the addition of carbon nanotubes (CNTs) and Cu is reported. Nanocomposites of carbon nanotubes (CNTs) containing varying amounts of Cu were formed by treatment with Cu 2 þ then reduced to Cu 0 using NaBH 4 as the reducing agent. The mesoporous TiO 2 , synthesized by a sol-gel method from titanium isopropoxide, was combined with the CNT/Cu nanocomposites to form the photocatalysts which were characterized by XRD, SEM, TEM, FTIR, XPS and BET surface area analysis. The photocatalytic properties of the mesoporous TiO 2 composites were studied by measuring the degradation of methyl orange (MO) which was optimal in the sample containing 20 wt% of the Cu-CNT nanocomposite. The degradation efficiency for MO was a synergistic effect of photo-degradation of TiO 2 and may be due to improvement of the electrical conductivity of the system by the presence of the CNT/Cu networks, since the photodegradation of MO and the photocatalytic activity of the photoactive systems increased with increasing copper content.
Brazilian Journal of Chemical Engineering, 2024
Photocatalysts are promising materials for removing organic dyes from the environment. TiO2 is one of the most extensively studied photocatalysts; however, its application in the photocatalytic industry has yet to be realized. We contend that fundamental research and the quest for synergy are essential in this field. One approach to enhancing the efficiency of TiO2 is deposition onto porous inert substrates. In this work, we introduce a novel approach by applying TiO2 onto the surfaces of porous nanosized Al 2 O 3 and ZrO2. Employing two soft chemistry methods-the glycol-citrate route for creating a porous and inert substrate and the peroxide route for depositing a TiO2 layer-we have created a technology that allows us to vary the TiO2 concentration on the inert matrix. The developed composite photocatalysts demonstrate competitive efficacy in disintegrating the model dye methylene blue. The most effective photocatalyst was Al2O3 @Ti 2 (0.26 wt.%) at 1200 °C. This material degrades approximately 98.2% of the methylene blue in 5 h, while nanosized TiO2 degrades only 33.5% of the dye under the same conditions. The photocatalytic activity of the material is affected by the concentration of TiO2 in the material due to the dilution of the peroxide solution. Notably, a decrease in the TiO2 concentration enhances the photocatalytic activity of the composite. We assumed that titanium dioxide was distributed in thinner layers at lower concentrations, which increased the area of effective contact and photocatalytic activity. The most efficient aluminum and zirconium oxides decorated with titanium dioxide had surface areas of 12.7 and 16.9 m 2 /g, respectively, while Al2 O3 and ZrO2 had surface areas of 31.7 and 34.3 m 2 /g, respectively. Therefore, the decrease in methylene blue concentration was caused by photocatalysis but not by the sorption mechanism. The decomposition of methylene blue in all the samples is consistent with a pseudo-second-order photocatalysis model. The findings of this work lie in the precise application of TiO2 onto the surfaces of inert matrices, which is valuable for developing photocatalytic materials.
NATO Science for Peace and Security Series C: Environmental Security, 2008
TiO2 and TiOzlZnO films with silver nanoparticles (Ag NP's) distributed in the matrix and on the surface were characterized by TEM, AFM and UV-Vis spectroscopy. Direct photoelectrochemical investigations of the TiO2l Ag and TiOzlZnOlAg heterojunctions showed the cathodic shift of the flat-band potential position and the increase of photocurrent quantum yield in comparison with unmodified TiO2 electrodes. Photocatalytic activity of Ag/TiC.2 and Agl TiOzlZnO films estimated in the process of Rhodamine B dye degradation is coincides with photoelectrochemical data.