Photocatalytic hydrogen production from aqueous methanol solution with CuO/Al2O3/TiO2 nanocomposite

The photocatalytic hydrogen production from aqueous methanol solution was investigated with ZnO/TiO₂, SnO/TiO₂, CuO/TiO₂, Al₂O₃/TiO₂ and CuO/Al₂O₃/TiO₂ nanocomposites. A mechanical mixing method, followed by the solid-state reaction at elevated temperature, was used for the preparation of nanocomposite photocatalyst. Among these nanocomposite photocatalysts, the maximal photocatalytic hydrogen production was observed with CuO/Al₂O₃/TiO₂ nanocomposites. A variety of components of CuO/Al₂O₃/TiO₂ photocatalysts were tested for the enhancement of H₂ formation. The optimal component was 0.2 wt% CuO/0.3 wt% Al₂O₃/TiO₂. The activity exhibited approximately tenfold enhancement at the optimum loading, compared with that with pure P-25 TiO₂. Nano-sized TiO₂ photocatalytic hydrogen technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy.     

Research on photocatalytic H2 production from acetic acid solution by Pt/TiO2 nanoparticles under UV irradiation

The Pt/TiO₂ particles have been prepared by the photodeposition of Pt on TiO₂ surface and characterized by X-ray diffraction. Photocatalytic H₂ production from acetic acid (HAc) over Pt/TiO₂ in aqueous solution has been studied at ambient temperature under UV irradiation. The effects of operational variables such as Pt loading, photocatalyst concentration, HAc concentration, and solution pH, have been systematically investigated. The optimum conditions for H₂ production from HAc by Pt/TiO₂ were Pt loading 1.0 wt.%, Pt/TiO₂ concentration 0.22 g/L, HAc concentration 6.52 g/L and pH 1.0. The H₂ yield is 0.27 mol-H₂/mol-HAc obtained under prolonged time irradiation. Experimental results showed that the photocatalytic H₂ production activity could be enhanced remarkably by depositing a suitable amount Pt on TiO₂ surface. Based on our results, a new process for H₂ production from biomass can be achieved by coupling fermentative H₂ production with photocatalytic H₂ production. The process also provides a method for degradation of organic pollutants with simultaneous H₂ production. A possible mechanism for photocatalytic decomposition of HAc over Pt/TiO₂ was also proposed.     

CuCr2O4/TiO2 heterojunction for photocatalytic H2 evolution under simulated sunlight irradiation

CuCr₂O₄/TiO₂ heterojunction has been successfully synthesized via a facile citric acid (CA)-assisted sol-gel method. Techniques of X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV-vis diffuse reflectance spectrum (UV-vis DRS) have been employed to characterize the as-synthesized nanocomposites. Furthermore, photocatalytic activities of the as-obtained nanocomposites have been evaluated based on the H₂ evolution from oxalic acid solution under simulated sunlight irradiation. Factors such as CuCr₂O₄ to TiO₂ molar ratio in the composites, calcination temperature, photocatalyst mass concentration, and initial oxalic acid concentration affecting the photocatalytic hydrogen producing have been studied in detail. The results showed that the nanocomposite of CuCr₂O₄/TiO₂ is more efficient than their single part of CuCr₂O₄ or TiO₂ in producing hydrogen. The optimized composition of the nanocomposites has been found to be CuCr₂O₄·0.7TiO₂. And the optimized calcination temperature and photocatalyst mass concentration are 500 °C and 0.8 g l⁻¹, respectively. The influence of initial oxalic acid concentration is consistent with the Langmuir model.     

Photocatalytic hydrogen production over CuO and TiO2 nanoparticles mixture

Cheap and efficient photocatalysts were fabricated by simply mixing TiO₂ nanoparticles (NPs) and CuO NPs. The two NPs combined with each other to form TiO₂/CuO mixture in an aqueous solution due to the opposite surface charge. The TiO₂/CuO mixture exhibited photocatalytic hydrogen production rate of up to 8.23 mmol h⁻¹ g⁻¹ under Xe lamp irradiation when the weight ratio of P25 to CuO was optimized to 10. Although the conduction band edge position of CuO NPs is more positive than normal hydrogen electrode, the TiO₂/CuO mixture exhibited good photocatalytic hydrogen production performance because of the inter-particle charge transfer between the two NPs. The detailed mechanism of the photocatalytic hydrogen production is discussed. This mixing method does not require a complicated chemical process and allows mass production of the photocatalysts.     

A new photosensitive coordination compound [RuL(bpy)2](PF6)2 and its application in photocatalytic H2 production under the irradiation of visible light

A new organic–inorganic photosensitive coordination compound [RuL(bpy)₂](PF₆)₂ (to represent by TM1) had been synthesized by reaction of L (L = 2-hydroxyl-5-(imidazo-[4,5-f]-1,10-phenanthrolin) benzoic acid) with bipyridyl ruthenium, and further characterized by UV–vis, IR, NMR MS and CV. The target photocatalyst 6 wt% TM1-0.5 wt% Pt-TiO₂ (Ⅰ) was obtained by sensitization of Pt-loaded TiO₂ with TM1. The H₂ production activity of target photocatalyst Ⅰ was systematically evaluated by the reaction of photocatalytic H₂ production from water under visible light irradiation. The maximum H₂ evolution of 386.7 μmol in irradiation 3 h and H₂ production rate of 2578 μmol · h⁻¹ · g⁻¹ was detected under the optimal conditions with pH 5, target photocatalyst Ⅰ 50 mg and 5% sacrificial reagent TEOA (v/v).     

TiO2 nanosheets loaded with Cu: A low-cost efficient photocatalytic system for hydrogen evolution from water

Rutile TiO₂ nanosheets were prepared by a simple solvothermal process, and Cu was loaded on the surface of TiO₂ nanosheets using the in situ photo-deposition method. Meanwhile, photocatalytic H₂ evolution from water over the as-prepared TiO₂ nanosheets loaded with Cu was explored using methanol as a sacrificial reagent. The results indicate that the TiO₂ nanosheets loaded with Cu is an efficient photocatalyst under UV irradiation. During the first 5 h, a rate of H₂ evolution of approximately 22.1 mmol g⁻¹ h⁻¹ was achieved under optimal conditions. Furthermore, for practical purposes, the photocatalytic hydrogen evolution was studied as a function of content of Cu, pH of solution, concentration of methanol and dosage of photocatalyst, respectively. At last, the photocatalytic mechanism was preliminarily discussed.     

Synergetic catalysis of CuO and graphene additives on TiO2 for photocatalytic water splitting

A highly efficient and visible-light-responsive CuO/TiO₂-GR photocatalyst had been synthesized by a two-step process. The as-prepared CuO/TiO₂-GR composites were characterized by X-ray diffraction, N₂-physisorption, transmission electron microscope, X-ray photoelectron spectroscopy, Raman spectra, UV–vis diffuse reflectance spectra and Photoluminescence spectra. The results indicated that a chemical bond formed between GR and TiO₂ in CuO/TiO₂-GR composites. CuO/TiO₂-GR composites had a higher photocatalytic activity for hydrogen production due to a synergistic effect between CuO and GR. The synergistic effect could efficiently suppress charge recombination, improve interfacial charge transfer, enhance visible-light adsorption and provide plentiful phtotocatalytic reaction active sites. The maximum hydrogen evolution rate of CuO/TiO₂-GR-0.5 was 2905.60 μmol/(h·g), which was 20.20 times larger than pure P25.     

Photocatalytic hydrogen evolution with simultaneous degradation of organics over (CuIn)0.2Zn1.6S2 solid solution

Using various organics as electron donor, (CuIn)_0.2Zn_1.6S₂ microsphere solid solution prepared via hydrothermal method as photocatalyst, hydrogen production by anaerobic photocatalytic reforming organics were researched. The photocatalytic hydrogen production activity was notably enhanced in the presence of the organic electron donors. Formic acid was found to be the most efficient sacrificial agent among methanol, glucose, triethanolamine and formic acid. The effects of initial formic acid concentration on hydrogen generation were investigated. When the initial formic acid concentration was 10 vol%, the photocatalytic activity reached the highest. The average activity in initial 10 h can amount to 144 μmol h⁻¹. The possible mechanism of photocatalytic reaction for hydrogen production with simultaneous formic acid degradation was discussed preliminary.     

The influence of the electrodeposition potential on the morphology of Cu2O/TiO2 nanotube arrays and their visible-light-driven photocatalytic activity for hydrogen evolution

The influence of the electrodeposition potential on the morphology of Cu₂O/TiO₂ nanotube arrays (Cu₂O/TNA) and their visible-light-driven photocatalytic activity for hydrogen evolution have been investigated for the first time in this work. The photocatalytic hydrogen evolution rate of the as-prepared Cu₂O/TNA at the deposition potential of −0.8 V was about 42.4 times that of the pure TNA under visible light irradiation. This work demonstrated a feasible and simple electrodeposition method to fabricate an effective and recyclable visible-light-driven photocatalyst for hydrogen evolution.     

Photocatalytic H2 production from water splitting under visible light irradiation using Eosin Y-sensitized mesoporous-assembled Pt/TiO2 nanocrystal photocatalyst

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 30 vol.% diethanolamine aqueous solution with dissolved 2 mM Eosin Y. Moreover, the optimum photocatalyst dosage and initial solution pH for the maximum photocatalytic activity for hydrogen production are 3.33 g dm⁻³ and 11.5, respectively.     

Hydrogen production from water splitting under UV light irradiation over Ag-loaded mesoporous-assembled TiO2-ZrO2 mixed oxide nanocrystal photocatalysts

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.     

The role of CuO in promoting photocatalytic hydrogen production over TiO2

Low cost semiconductor photocatalysts that can efficiently harvest solar energy to generate H₂ from water or biofuels will be critical to future hydrogen economies. In this study, low cost CuO/TiO₂ photocatalysts (CuO loadings 0–15 wt.%) were prepared, characterized and evaluated for H₂ production from ethanol–water mixtures (80 vol.% ethanol, 20 vol.% H₂O) under UV excitation. TEM, XRF, EDAX, EPR, Raman, TGA, XPS and Cu L-edge NEXAFS data showed that at CuO loadings <5 wt.%, Cu(II) was highly dispersed over the TiO₂ support, possibly as a sub-monolayer CuO species. At higher loadings, CuO crystallites of diameter 1–2 nm were identified. The photocatalytic activity of CuO/TiO₂ photocatalysts was highly dependent on the CuO loading, with 1.25 wt.% CuO being optimal (H₂ production rate = 20.3 mmol g⁻¹ h⁻¹). Results suggest that sub-monolayer coverages of Cu(II) or CuO on TiO₂ are highly beneficial for H₂ generation from ethanol–water mixtures and support the development of a sustainable H₂ economy.     

Photocatalytic H2 evolution on a novel CaIn2S4 photocatalyst under visible light irradiation

A novel visible-light-driven photocatalyst CaIn₂S₄ was synthesized using a facile hydrothermal method followed by a post-calcination process. The influence of the calcination temperature and time on the activities of the photocatalyst was investigated. CaIn₂S₄ exhibits optical absorption predominantly in visible region with an optical band gap of 1.76 eV. Considerable activity for hydrogen evolution from pure water was observed without any sacrificial agents or cocatalysts under visible light irradiation. The maximum hydrogen evolution rate achieved was 30.92 μmol g⁻¹ h⁻¹ without obvious deactivation of the photocatalytic activity for four consecutive runs of 32 h.     

Photocatalytic splitting of seawater and degradation of methylene blue on CuO/nano TiO2

The main objective of this study was to prepare effective photocatalysts for splitting of seawater for solar fuel – H₂ and degradation of seawater organic pollutants such as dyes. To enhance photocatalytic activities, CuO is supported on nano TiO₂ (CuO/nano TiO₂). By X-ray absorption near edge structure (XANES) spectroscopy, CuO clusters are found on nano TiO₂. The 2.5% CuO/nano TiO₂ has greater activities in photocatalytic splitting of water and seawater than nano TiO₂ by 9.9 and 7.8 times, respectively. Interestingly, the 2.5% CuO/nano TiO₂ is also very active for photocatalytic splitting of water and seawater contaminated with dyes such as methylene blue (MB) (10 ppm). Under a 5-h irradiation of the UV–Vis light, about 99% of MB is degraded while 3.1 μmol/h g cat of H₂ are generated from seawater in the photocatalysis process.     

Stability of an H2-producing photocatalyst (Ru/(CuAg)0.15In0.3Zn1.4S2) in aqueous solution under visible light irradiation

Efficient photocatalytic water-splitting systems require stable photocatalysts that have photocatalytic activity with repeated consecutive use. This study investigated H₂ production under visible light irradiation with an Ru/(CuAg)_0.15In_0.3Zn_1.4S₂ photocatalyst and KI as an electron donor. In addition, the stability and reusability of the catalyst were evaluated over multiple cycles of H₂ production and catalyst regeneration. The results show that sintering temperature influenced the crystallinity and photocatalytic activity, as indicated by the X-ray diffraction analyses and H₂ production rates. In particular, the catalyst sintered at 873 K yielded the highest quantum yield of 4.6% at 420 ± 5 nm of wavelength. After seven consecutive reaction cycles, the quantum yield decreased from 4.6% to 3.0% at the end of the seventh cycle. The decrease probably occurred because (1) particles of the catalyst underwent pronounced aggregation, which led to the increase in particle size; and (2) a release of significant metal ions was observed during H₂ production, which led to a loss of the catalyst mass and potential changes in the photocatalytic activity. This study will help facilitate a search of stable photocatalysts for water splitting.     

Cu(OH)2-modified TiO2 nanotube arrays for efficient photocatalytic hydrogen production

Cu(OH)₂/TNAs photocatalyst was prepared by loading Cu(OH)₂ nanoparticles on TiO₂ nanotube arrays (TNAs) using a chemical bath deposition method. The amount of Cu(OH)₂ loaded on the arrays was controlled by the repeated deposition times. The prepared catalyst was used to generate hydrogen under simulated solar light irradiation, and the results demonstrated that the hydrogen yield of Cu(OH)₂/TNAs was 20.3 times that of the pure TNAs. Furthermore, the photocatalytic efficiency for hydrogen production decreased only 5.8% after five cycles, indicating that Cu(OH)₂/TNAs photocatalyst showed excellent stability and reusability. This work presents an applicable and facile method to fabricate a highly active and stable photocatalyst for hydrogen production.     

Improving hydrogen production via water splitting over Pt/TiO2/activated carbon nanocomposite

Mesoporous TiO₂/AC, Pt/TiO₂ and Pt/TiO₂/AC (AC = activated carbon) nanocomposites were synthesized by functionalizing the activated carbon using acid treatment and sol–gel method. Photochemical deposition method was used for Pt loading. The nano-photocatalysts were characterized using XRD, SEM, DRS, BET, FTIR, XPS, CHN and ICP methods. The hydrogen production, under UV light irradiation in an aqueous suspension containing methanol has been studied. The effect of Pt, methanol and activated carbon were investigated. The results show that the activated carbon and Pt together improve the hydrogen production via water splitting. Also methanol acts as a good hole scavenger. Mesoporous Pt/TiO₂/AC nanocomposite is the most efficient photocatalyst for hydrogen production compared to TiO₂/AC, Pt/TiO₂ and the commercial photocatalyst P25 under the same photoreaction conditions. Using Pt/TiO₂/AC, the rate of hydrogen production is 7490 μmol (h g catal.)⁻¹ that is about 75 times higher than that of the P25 photocatalyst.     

The pH effects on H2 evolution kinetics for visible light water splitting over the Ru/(CuAg)0.15In0.3Zn1.4S2 photocatalyst

Much progress has been made in the development of novel visible light photocatalysts that split water into hydrogen (H₂) and oxygen (O₂). In this study, we examine the impact of initial solution pH on H₂ production using an Ru/(CuAg)_0.15In_0.3Zn_1.4S₂ photocatalyst under visible light irradiation. In addition, the reaction mechanism was analyzed by examining the oxidation products of the electron donor (I‾) at different solution pH values. The results show that the initial pH significantly influenced the rate of H₂ production and quantum yield (QY). In particular, the photocatalyst yielded the highest apparent QY (∼12.8%) at 420 ± 5 nm and highest H₂ production rate (∼525 μmol h⁻¹) at pH 2; with increasing pH, the H₂ production and QY decreased significantly. The oxidation product of I‾ at pH < 6 was mainly I₃‾, whereas at pH > 6 water splitting did not occur at all, so no IO₃‾ or I₂ were observed.     

Significant improvement of photocatalytic hydrogen generation rate over TiO2 with deposited CuO

TiO₂ photocatalyst with deposited CuO (CuO-TiO₂) was synthesized by the impregnation method using P25 (Degussa) as support, and exhibited high photocatalytic hydrogen generation activity from methanol/water solution. A substantial hydrogen evolution rate of 10.2 ml min⁻¹ (18,500 μmol h⁻¹ g⁻¹_catalyst) was observed over this efficient CuO-TiO₂ with optimal Cu content of 9.1 mol% from an aqueous solution containing 10 vol% methanol; this improved hydrogen generation rate is significantly higher than the reported Cu-containing TiO₂, including some Pt and Pd loaded TiO₂. Optimal Cu content of 9.1 mol% provided maximum active sites and allowed good light penetration in TiO₂. Over this efficient CuO-TiO₂, the hydrogen generation rate was accelerated by increasing the methanol concentration according to Freundlich adsorption isotherm. However, the photocatalytic hydrogen generation rate was suppressed under long time irradiation mainly due to accumulation of by-products, reduction of CuO and copper leaching, which requires further investigation.     

Hydrogenated CdS nanorods arrays/FTO film: A highly stable photocatalyst for photocatalytic H2 production

To improve the photocorrosion of CdS nanorod arrays (CdS NRAs), we have designed a simple and facile treatment method of in-situ hydrogenation to fabricate CdS@SnS/SnO₂ heterostructure on fluorine-doped tin oxide glass, which is a highly photostable hydrogenated CdS-based film photocatalyst (CdS NRAs-H₂). Over a 25-h long time irradiation, the total photocatalytic hydrogen production of hydrogenated CdS NRAs is almost 2.0 times higher than that of un-hydrogenated CdS NRAs. Moreover, the average hydrogen production rate of CdS NRAs-H₂ can steadily maintain at 23.75 μmol cm^?2 h^?1 with 102% of retention rate after 5 reaction cycles, while they are only 6.13 μmol cm^?2 h^?1 with 30% of retention rate for un-hydrogenated common CdS NRAs. The photocatalytic mechanism on enhanced activity and stability for hydrogenated CdS NRAs photocatalyst is also investigated and discussed in detail.