Hydrogen evolution by water splitting using novel composite zeolite-based photocatalyst

Novel zeolite-based material showing photocatalytic properties in the visible light have been synthesized by incorporating TiO₂, heteropolyacid (HPA) and transition metal, namely cobalt. This material shows high efficiency for water splitting under visible light irradiation. Hydrogen generation to the tune of 2171 μmol/h/g of TiO₂ has been achieved for the composite photocatalyst synthesized as compared to H₂ evolution rate to the tune of 131.6 μmol/h/g of TiO₂ for Degussa P25. This suggests that the TiO₂ which gets effectively dispersed and stabilized on the surface of zeolite works synergistically with cobalt and heteropolyacid to make the material active in visible light for evolution of hydrogen from water. TiO₂ is the photocatalyst, HPA functions as the dye sensitiser as well as redox system; zeolite functions as support matrix and as electron acceptor in synergy with cobalt. The probable mechanism for improved hydrogen evolution rate using such composite photocatalyst has been discussed.     

Photocatalytic Decomposition of Organic Contaminants by Bi2WO6 Under Visible Light Irradiation

An oxide photocatalyst Bi₂WO₆ with corner-shared WO₆ octahedral layered structure was synthesized. Its band gap was determined to be 2.69 eV from UV–vis diffuse reflectance spectra. The photocatalyst showed not only the activity for photocatalytic O₂ evolution with the initial evolution rate of 2.0 μmol/h but also the activity of mineralizing both CHCl₃ and CH₃CHO contaminants under visible light irradiation. Meanwhile, wavelength dependence of CH₃CHO decomposition was observed, which indicated that the photocatalytic activity of the photocatalyst was in good agreement with its light-absorption ability.     

Photocatalytic reduction of water by TaON under visible light irradiation

Some noble metals have been studied as H₂ evolution promoters for TaON, a visible light driven oxynitride photocatalyst. H₂ evolution on TaON photocatalyst under visible light irradiation (420 nm≤λ≤500 nm) in an aqueous methanol solution was found to be remarkably enhanced by adding Ru as a noble metal co-catalyst.     

Room-temperature synthesis of Zn(0.80)Cd(0.20)S solid solution with a high visible-light photocatalytic activity for hydrogen evolution

Visible light photocatalytic H(2) production from water splitting is of great significance for its potential applications in converting solar energy into chemical energy. In this study, a series of Zn(1-x)Cd(x)S solid solutions with a nanoporous structure were successfully synthesized via a facile template-free method at room temperature. The obtained solid solutions were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS) and N(2) adsorption-desorption analysis. The solid solutions show efficient photocatalytic activity for H(2) evolution from aqueous solutions containing sacrificial reagents S(2-) and SO(3)(2-) under visible-light irradiation without a Pt cocatalyst, and loading of the Pt cocatalyst further improves the visible-light photocatalytic activity. The optimal photocatalyst with x = 0.20 prepared at pH = 7.3 displays the highest activity for H(2) evolution. The bare and 0.25 wt% Pt loaded Zn(0.80)Cd(0.20)S nanoparticles exhibit a high H(2) evolution rate of 193 μmol h(-1) and 458 μmol h(-1) under visible-light irradiation (λ ≥ 420 nm), respectively. In addition, the bare and 0.25 wt% Pt loaded Zn(0.80)Cd(0.20)S catalysts show a high H(2) evolution rate of 252 and 640 μmol h(-1) under simulated solar light irradiation, respectively. Moreover, the Zn(0.80)Cd(0.20)S catalyst displays a high photocatalytic stability for H(2) evolution under long-term light irradiation. The incorporation of Cd in the solid solution leads to the visible light absorption, and the high content of Zn in the solid solution results in a relatively negative conduction band, a modulated band gap and a rather wide valence bandwidth, which are responsible for the excellent photocatalytic performance of H(2) production and for the high photostability.     

配合法制备InNbO_4及其光催化活性的研究

以配合法制备InNbO4催化剂,研究了在甲醇为电子给体,Pt为助催化剂的条件下,InNbO4光催化分解水的产氢活性。并与固相合成法制备的InNbO4光催化活性进行对比。通过X-射线衍射和比表面分析对两种方法制备的催化剂进行表征。研究发现,在焙烧温度为900℃、时间为12 h时,配合法制备的InNbO4光催化产氢活性最高(87.27μmol),为固相合成法的2倍。     

温和条件下CoPc/TiO2光催化还原CO2

采用浸渍法制备的TiO2负载钴酞菁(CoPc/TiO2)为光催化剂,在碱性水溶液中、可见光照下,CO2可被光催化还原为产物HCOOH、CO、CH4。对催化剂的制备条件进行了考察,在m(CoPc)∶m(TiO2)=1∶100、催化剂浸渍时间12 h、浸渍溶剂为甲苯、催化剂焙烧温度200℃的条件下,还原总产物量最高可达1 075.38μmol/g-cat,其中甲酸为主产物,最高可达708.54μmol/g-cat。对催化剂进行了XRD、DRS表征,证实了CoPc在TiO2表面的负载。结果表明:用该催化剂在可见光照及常温常压下,于水溶液中就可将CO2还原。其次,实验还发现光照下可产生电子转移,实现了电荷的重新分配,以降低电子-空穴的重新结合;TiO2表面应有一定的空隙率,有利于CO2在其表面获得电子被还原。     

Enhanced visible light response of heterostructured Cr2O3 incorporated two-dimensional mesoporous TiO2 framework for H2 evolution

Mesoporous TiO₂ frameworks incorporated with diverse percentages of Cr₂O₃ nanoparticles (NPs) were achieved through the one-step sol-gel approach for photocatalytic H₂ evolution under visible-light exposure. The obtained isotherms could be classified as type IV, indicating mesopore 2D-hexagonal symmetry. The H₂ evolution rate over mesoporous Cr₂O₃/TiO₂ photocatalyst was observably promoted employing glycerol as a sacrificial agent, providing a comparatively high H₂ yield of 14300 μmolg^?1. The highest photocatalytic efficiency was achieved with an optimal 4% Cr₂O₃/TiO₂ photocatalyst, and the evolution rate was enhanced 1430-fold compared to pristine TiO₂. The eminent photocatalytic performance of mesoporous Cr₂O₃/TiO₂ was ascribable to different key factors such as the narrow bandgap, wide visible light photoresponse, Cr₂O₃ as photosensitizer, synergistic effect and high surface area. The recycle tests for five times over synthesized photocatalyst revealed excellent durability and stability without loss in H₂ evolution. The photocatalytic mechanisms for H₂ evolution over Cr₂O₃/TiO₂ photocatalyst were proposed according to the photocurrent transient and photoluminescence measurements and photocatalytic H₂ evolution results.     

可见光分解水制氢催化剂研究进展

可见光分解水制氢研究主要集中在新型光催化剂的研制以及对传统光催化剂的改性。本文概述了近年来可见光分解水制氢技术的重要进展及最新研究成果,深入研究和分析了拓展光催化剂响应范围、提高其反应活性的几种技术路线,主要包括阴阳离子掺杂技术、固溶体技术、半导体复合技术以及加入助催化剂等;总结出了传统光催化剂存在可见光利用率低、光化学转化效率低等问题,提出了开发新型高效光催化剂并加强机理研究的必要性和可行性。     

A novel noble metal-free ZnS–WS2/CdS composite photocatalyst for H2 evolution under visible light irradiation

A novel ZnS–WS₂/CdS composite photocatalyst for H₂ evolution under visible light irradiation has been successfully synthesized. The loading amounts of WS₂ and ZnS on the CdS surface were optimized. A H₂ evolution rate up to 1224 μmol·h^− 1 has been achieved for the 9.6 mol% ZnS–1 mol% WS₂/CdS photocatalyst. The enhancement of the photocatalytic activity is attributed to the synergistic effect of WS₂ as co-catalyst and ZnS as passivation layer.     

Solar hydrogen generation from organic substance using earth abundant CuS–NiO heterojunction semiconductor photocatalyst

This work explores the critical role of NiO co-catalyst assembled on the surface of a CuS primary photocatalyst which effectively improves interface properties and enhances solar-to-hydrogen production by prolonging lifetime of photo-excitons generated at the CuS surface. The nanoscale CuS/NiO heterojunction is formulated using hydrothermal and wet impregnation methods. The resultant CuS/NiO composite shows optical absorbance between 380 and 780 nm region. The type-II energetic structure formed at CuS/NiO heterojunction facilitates rapid charge separation and as a result, the CuS/NiO composite exhibits 13 folds higher photocatalytic water splitting performance than CuO and NiO. The champion CuO/NiO photocatalyst is first identified by screening the catalysts using a preliminary water splitting test reaction under natural Sunlight irradiation. After the optimization of the catalyst, it was further explored for enhanced photocatalytic hydrogen production using different organic substances dispersed in water (alcohols, amine and organic acids). The champion CuS/NiO catalyst (CPN-2) exhibited the photocatalytic hydrogen production rate of 52.3 mmol h^?1.g^?1_cat in the presence of lactic acid-based aqueous electrolyte and, it is superior than hydrogen production rate obtained in the presence of other organic substances (triethanolamine, glycerol, ethylene glycol, methanol) tested under identical experimental conditions. These results indicate that the energetic structure of CuS/NiO photocatalyst is favorable for photocatalytic oxidation or reforming of lactic acid. The oxidation of lactic acid contributes both protons and electrons for enhanced hydrogen generation as well as protects CuS from photocorrosion. The modification of surface property and energetic structure of CuS photocatalyst by the NiO co-catalyst improves photogenerated charge carrier separation and in turn enhances the solar-to-hydrogen generation efficiency. The recyclability tests showed the potential of CPN-2 photocatalyst for prolonged photocatalytic hydrogen production while continuous supply of lactic acid feedstock is available.     

Inclusion of low cost activated carbon for improving hydrogen production performance of TiO2 nanoparticles under natural solar light irradiation

Photocatalytic studies are primarily focused on the low cost and sustainable materials with suitable bandgap and high surface area. The ultra-fast electron-hole pair recombination and limited light absorptions affect the efficiency of photocatalyst in an adverse manner, which can be unravelled by choosing an efficient combination of photocatalysts and suitable co-catalyst/support materials. The present work explores the combination of low-cost and high potential activated carbon and TiO₂ as a nanocomposite, prepared through a one-pot hydrothermal process for hydrogen production under natural solar light irradiation. Among the synthesized photocatalysts, the one calcined at 400 °C for 2 h was found to be the best catalyst, which exhibited 3.5 times higher hydrogen production rate than the pristine TiO₂ while tested with water containing 5 vol.% glycerol. Importantly, the optimized nanocomposite was also tested for hydrogen production from simulated seawater under same conditions and it showed a hydrogen production rate of 20,383 μmol g^?1 h^?1, which is 2.4 times higher than the glycerol water solution. The enhanced hydrogen production rate is due to the reduced bandgap of AC-TiO₂ nanocomposite which offered more light absorption in the visible region compared to the pristine TiO₂. The XRD, Raman spectroscopy, TEM, and PL analysis were also examined to investigate the crystallinity, purity, morphology, and charge carrier recombination life time of the synthesized catalysts.     

Iron-based composite nanomaterials for eco-friendly photocatalytic hydrogen generation

This study deals with different proton sources for the enhancement of hydrogen generation by a powder-type complex photocatalytic system. This article reports on the undesirable role of external influences for eco-friendly hydrogen generation using low-cost iron-based nanomaterials. The synthesized material using a metal-organic framework template strategy was confirmed by in-situ characterizations. The bandgap of Fe₂O₃–TiO₂ has been tuned by the formation of a Fe₃O₄@Fe₂O₃–TiO₂ complex oxide. The hydrogen production rate has been enhanced by tuning pH, different sacrificial reagents and proton donors. The optimized condition along with the addition of 0.1 g of aniline hydrochloride as a proton source, enhanced the hydrogen evolution rate to 2.366 mmol/0.5 g/h which resulted in high quantum efficiency. Methanol played a crucial role as a sacrificial agent along with the addition of aniline hydrochloride as a proton source for this outstanding hydrogen evolution activity, which is explained by proposing a mechanism. The ultra-pure production of hydrogen gas (98.30%), apparent quantum efficiency of almost 74% under sunlight, and reusability of the proposed photocatalyst have been studied in detail. The presence system has many other advantages such as low cost, easy preparation, high stability and nontoxicity.     

The influence of different zeolitic supports on hydrogen production and waste degradation

The photocatalyst composition affects the chemical–physical properties and directly impacts photocatalytic activity, both in the hydrogen production and degradation of organic contaminants. In this work, the influence of zeolitic structures NaA, NaY, and ZSM-5 combined with a 10% active phase, TiO₂ catalyst doped with 1% copper, and cobalt cocatalysts was tested to mineralize the reactive blue dye (CI250) and to produce hydrogen by photocatalysis under ultraviolet radiation. The band gap energy was affected mainly by the cocatalyst, while the Brunauer-Emmett-Teller method (BET) area was affected by the zeolite structure as well as the X-ray diffraction (XRD). The most active catalyst was the Cu@TiO₂/NaY, which promoted a hydrogen production rate of 240 μmolH₂gcat⁻¹ using 10% ethanol (v/v) aqueous solution as a sacrificial agent and mineralization of 53% of the organic dye, followed by the catalysts impregnated on ZSM-5 zeolites, which had discolouration up to 50% and hydrogen evolution of 92.6 and 109.7 μmolH₂gcat⁻¹ for the catalyst doped with Cu and Co, respectively.     

太阳能光解水制氢的核心催化剂及多场耦合研究进展

太阳能光解水制氢可从根本上解决能源需求及碳排放造成的环境污染问题,是各国关注的热点之一。利用太阳能全光谱光催化制氢是目前研究的主要方式,但存在催化效率较低,难以实际应用的问题。造成光催化剂催化效率低的主要因素在于比表面积小、光吸收能力弱、禁带宽度较宽、载流子迁移能力弱。对光催化机理和催化剂的优化策略进行了总结,通过敏化材料掺杂、元素掺杂、异质结构建、助催化剂负载、高导电性石墨烯掺杂等策略来有效提高光催化剂对可见光的吸收、降低光生载流子的复合、增加活性位点、加速表面反应。此外,对光电、光热及光热电催化等近年发展起来的多场耦合催化制氢做了系统的介绍,对太阳能制氢催化剂理论和实践的未来发展做出了展望。     

Construction of ternary rGO/1D TiO2 nanotubes/3D ZnIn2S4 microsphere heterostructure and mutually-reinforcing synergy for high-efficiency H2 production photoactivity under visible light

The novel ternary reduced graphene oxide/1D TiO₂ nanotubes/3D ZnIn₂S₄ microspheres (rGO/TiO₂/ZIS) heterostructured photocatalyst with high-efficiency H₂ production capacity under visible light illumination is designed and prepared in this work. In rGO/TiO₂/ZIS system, the 1D TiO₂ nanotubes are tightly inserted in the interspace of flower-like ZnIn₂S₄ microspheres, which are further covered by rGO, leading to an intimate contact among ZnIn₂S₄, TiO₂ and rGO. The exquisite design of rGO/TiO₂/ZIS makes it possess remarkable superiority in photocatalysis. Firstly, the unique 3D microsphere structure of ZIS increases the surface area and visible light absorption ability caused by their unique hollow structure. More importantly, the matched CB and VB positions between ZIS and TiO₂ contribute to separate photogenerated holes and electrons of ZIS efficiently under visible light; then, the separated electrons on TiO₂ are further transferred to rGO due to the superior-strong electron-attracting ability of rGO. At last, the thoroughly suppressing recombination of photogenerated holes and electrons is achieved by the mutually-reinforcing synergy among ZIS, TiO₂ and rGO, and thus the hydrogen generation capacity of ZIS is significantly enhanced. The H₂ production amount and rate of rGO/TiO₂/ZIS (2.0 wt% rGO and 50 wt% ZIS) after 10 h are 4623 μmol/g and 462.3 μmol/g/h, respectively, which is 71.1 times of pristine TiO₂ and 1.6 times of ZIS under the same condition. The apparent quantum yield of rGO/TiO₂/ZIS (2.0 wt% rGO and 50 wt% ZIS) in 10 h is about 0.6888%. This excellent photocatalytic performance is ascribed to the mutually-reinforcing synergy among ZIS, TiO₂ and rGO, which can be confirmed by X-ray photoelectron spectroscopy, photoelectrochemical measurements and photoluminescence spectrum. Based on the photocatalytic and characterization results, the corresponding mechanism is proposed.     

Noble-metal-free carbon nanotube-Cd0.1Zn0.9S composites for high visible-light photocatalytic H2-production performance

Visible light photocatalytic H(2) production from water splitting using solar light is of great importance from the viewpoint of solar energy conversion and storage. In this study, a novel visible-light-driven photocatalyst multiwalled carbon nanotube modified Cd(0.1)Zn(0.9)S solid solution (CNT/Cd(0.1)Zn(0.9)S) was prepared by a simple hydrothermal method. The prepared samples exhibited enhanced photocatalytic H(2)-production activity under visible light. CNT content had a great influence on photocatalytic activity and an optimum amount of CNT was determined to be ca. 0.25 wt%, at which the CNT/Cd(0.1)Zn(0.9)S displayed the highest photocatalytic activity under visible light, giving an H(2)-production rate of 78.2 μmol h(-1) with an apparent quantum efficiency (QE) of 7.9% at 420 nm, even without any noble metal cocatalysts, exceeding that of pure Cd(0.1)Zn(0.9)S by more than 3.3 times. The enhanced photocatalytic activity was due to CNT as an excellent electron acceptor and transporter, thus reducing the recombination of charge carriers and enhancing the photocatalytic activity. Furthermore, the prepared sample was photostable and no photocorrosion was observed after photocatalytic recycling. Our findings demonstrated that CNT/Cd(0.1)Zn(0.9)S composites were a promising candidate for the development of high-performance photocatalysts in photocatalytic H(2) production. This work not only shows a possibility for the utilization of low cost CNT as a substitute for noble metals (such as Pt) in the photocatalytic H(2)-production but also for the first time shows a significant enhancement in the H(2)-production activity by using metal-free carbon materials as effective co-catalysts.     

Ag＋改性SO4^2-/TiO2的制备及其光催化性能研究

本文用溶胶凝胶法制备了纳米Ag＋-SO42-/TiO2固体超强酸（AST）,采用XRD、FT-IR等方法对AST的结构进行表征,研究AST在紫外光和可见光下降解罗丹明B的光催化活性。结果表明,适宜的制备条件为：Ag＋掺杂量为0.5%,硫酸浓度为0.5mol/L,焙烧温度为450℃制备的AST具有较好的光催化活性,且在模拟可见光下AST也具有光催化活性,2h能将罗丹明B几乎完全降解。     

三维WO3/rGO复合物的制备及光解水制氢性能研究

通过水热法制备出WO₃/rGO复合物用于可见光下光解水制氢。采用XRD和SEM表征手段对复合物组成、形貌进行研究,同时进行光解水制氢性能测试并对其机理进行探讨。研究结果表明,WO₃样品呈海草状,具有丰富的空隙,可以更大程度上提升光解水制氢性能,WO₃/rGO复合物与未复合石墨烯的WO₃样品比较,其形貌没有明显变化。并且还原氧化石墨烯(rGO)的导电性在提高光感应电荷载流子分离效率中也起着关键作用。WO₃/rGO复合物产氢速率为236μmol/h,而WO₃样品的产氢速率为212μmol/h,氧化石墨与WO₃复合后样品对光解水制氢性能得到提升。增强的光解水制氢性能归因于rGO的优异电导率和WO₃/rGO复合物纳米结构的协同作用。     

Purification of textile wastewater by using coated Sr/S/N doped TiO<Subscript>2</Subscript> nanolayers on glass orbs

Simultaneous doping of TiO₂ nanoparticles with three elements including Sr, S, and N is reported. The resulting material shows superior photocatalytic performance toward degradation of textile waste under visible and sunlight. The pure and doped TiO₂ nanolayers were prepared by sol-gel method and were fixed on a bed of glass orbs. The immobilized TiO₂ were characterized by a variety of techniques: X-ray diffraction (XRD), scanning electron microscopy (SEM), spectroscopy diffusion reflection (DRS), energy dispersive X-ray spectrometry (EDS) and elemental analysis (CHNS). The photocatalytic activity of the prepared fixed-bed materials toward degradation of the textile wastes was determined by using ultraviolet-visible spectroscopy (UV-Vis) and measurement of the chemical oxygen demand testing (COD). The best photocatalytic activity was observed with the use of Sr/S/N-TiO₂ nano-layers. Afterwards, the experimental conditions were optimized by tuning reaction parameters, including amount of doped metal ion on photocatalyst structure, sample solution pH and photoreactor output flow rate. The results confirmed that at natural pH 5.9 of sample solution, maximum decomposition of 91-99% of azo dyes was obtained in 8 h under visible irradiation. Finally, the experiments were repeated under 1.5 AM sunlight with high volume of reactants in order to confirm the cost-effectiveness of the designed photocatalyst.     

CdS/Fe7S8复合光催化剂的制备及光催化性能研究

随着环境和能源问题越来越凸显,开发价格低廉、性能优异的新型光催化剂越来越有实际意义。将直径为5nm的CdS量子点与廉价铁硫化合物结合,制备出新型的能够在可见光下分解水的复合光催化剂,其最优化产氢速率高达519.55μmol h~(-1),高于同条件下CdS/Pt催化剂。