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.     

二氧化钛光催化分解水制氢技术进展

简单介绍了二氧化钛光催化分解水制氢的基本原理。综述了加入牺牲剂、碳酸钠、贵金属负载化、金属离子掺杂、阴离子掺杂、染料光敏化、半导体复合以及离子注入等提高二氧化钛光催化制氢的方法,讨论了这几种改性技术的机理以及对提高二氧化钛在可见光下的制氢效率的作用。重点讨论了阴离子掺杂和离子注入技术的机理和研究进展,指出离子注入是目前扩展二氧化钛光响应的最为有效的技术。最后讨论了光催化分解水制氢的氢氧分离问题,并通过与其他制氢技术的对比分析,指出光催化制氢将是通往氢经济的非常有潜力的制氢技术。     

光催化制氢用纳米结构光催化剂的研究进展

纳米结构光催化剂由于其独特的性能优势已成为催化剂领域未来发展的必然趋势。综述了各种光解水制氢用纳米光催化剂的研究进展,如金属氧化物、金属硫化物、金属氮化及其复合物等,指出TiO2已经也将会是光催化制氢中所用光催化剂最重要的一种,其它类型氧化物根据其性能特点在实际的光催化制氢系统中也能被有效应用,如何对纳米半导体材料进行合理裁剪和复合是纳米复合材料的研究重点。根据目前研究现状指出,结合不同的技术和方法,实现多技术集成将是今后光催化制氢纳米材料研究的主要方向。     

Black ZrO2 synthesized by molten lithium reduction strategy for photocatalytic hydrogen generation

To promote the performance of metal oxides, introducing oxygen vacancies is an effective strategy. Oxygen vacancies can tailor the atomic arrangement and band structure, thus optimizing the physical and chemical properties of metal oxides. Herein, we prepared oxygen-deficient black ZrO₂ nanoparticles via molten lithium (Li) reduction. Massive oxygen vacancies were introduced into ZrO₂ nanoparticles as well as defective disorder domains formed in ZrO₂ lattice during the molten lithium treatment process. Benefitting from the defective structure, black ZrO₂ with enhanced light absorption demonstrated increased photocatalytic hydrogen generation rate, which was ~5 times higher than that of pristine ZrO₂. Moreover, molten lithium reduction provides a powerful way to not only implant oxygen vacancies to metal oxides but also extend their applications.     

CTAB assisted microwave synthesis of ordered mesoporous carbon supported Pt nanoparticles for hydrogen electro-oxidation

Mesoporous carbon with ordered hexagonal structure derived from the co-assembly of triblock copolymer F127 and resol was employed as the carbon support of Pt catalysts for hydrogen electro-oxidation. Structural characterizations revealed that the mesoporous carbon exhibited large surface area and uniform mesopores. The Pt nanoparticles supported on the novel mesoporous carbon were fabricated by a facile CTAB assisted microwave synthesis process, wherein CTAB was expected to improve the wettability of carbon support as well as the dispersion of Pt nanoparticles. X-ray diffraction and transmission electron microscopy were applied to characterize the Pt catalysts. It was found that the Pt nanoparticles were uniform in size and highly dispersed on the mesoporous carbon supports. The cyclic voltammograms in sulfuric acid demonstrated that the electrochemical active surface area of Pt catalysts prepared with CTAB was two times than that without CTAB.     

TiO_2/C复合光催化剂的制备及降解染料性能的研究

以钛酸四丁酯为前驱体,棉织物纤维为载体,通过水热处理和煅烧制备了TiO_2/C复合光催化剂。通过扫描电镜、傅里叶变换红外光谱仪和X射线衍射对制备的催化剂的形貌和结构进行了表征,考察了辐照时间和催化剂用量对亚甲基蓝降解率的影响。结果表明,煅烧后,棉织物被炭化,炭化后的棉纤维转变为棒状炭材料,在其上分布着具有良好分散性的锐钛矿型纳米二氧化钛。在催化剂用量为1.82 g/L,紫外光照射6 h,MB溶液初始浓度为10 mg/L的条件下,对亚甲基蓝溶液的降解率可达97.5%。     

Nanoflower-like CdS and SnS2 loaded TiO2 nanotube arrays for photocatalytic wastewater treatment and hydrogen production

In this work, nanoflower-like CdS/SnS₂/TiO₂ NTs ternary heterojunction photocatalysts were synthesized by a hydrothermal method, the relationship between the morphology, microscopic morphology, crystallinity, elemental presence state and hydrogen production performance of the ternary photocatalysts were investigated by SEM, TEM, XRD and XPS, respectively. The photocatalytic performance, electrochemical property and hydrogen production capacity of CdS/SnS₂/TiO₂ NTs were compared with pure TiO₂ NTs, CdS/TiO₂ NTs and SnS₂/TiO₂ NTs. After 2 h of photocatalytic reaction, the removal efficiency of MB wastewater reached 100%, and the photocatalytic efficiencies toward RhB and Cr(VI) removal reached 86.08% and 80.93% after 3 h, respectively. The electron spin resonance (ESR) technique certified the active radical groups that played a role in the catalytic process and further investigated the possible photocatalytic mechanism. Hydrogen production per unit time achieved 97.14 μmol h^?1 cm^?2, this work provides the new technique to achieve solar energy conversion for hydrogen generation.     

TiO_2/C复合光催化剂的制备及降解染料性能的研究

以钛酸四丁酯为前驱体,棉织物纤维为载体,通过水热处理和煅烧制备了TiO_2/C复合光催化剂。通过扫描电镜、傅里叶变换红外光谱仪和X射线衍射对制备的催化剂的形貌和结构进行了表征,考察了辐照时间和催化剂用量对亚甲基蓝降解率的影响。结果表明,煅烧后,棉织物被炭化,炭化后的棉纤维转变为棒状炭材料,在其上分布着具有良好分散性的锐钛矿型纳米二氧化钛。在催化剂用量为1.82 g/L,紫外光照射6 h,MB溶液初始浓度为10 mg/L的条件下,对亚甲基蓝溶液的降解率可达97.5%。     

Synthesis,structure, and photocatalytic hydrogen of three environmentally friendly titanium oxo-clusters

In this paper, three environmentally friendly titanium oxo-clusters, Ti₆O₄(OEt)₄(OPrⁱ)₄(OOCC₆H₅)₈ (1), Ti₆O₄(OEt)₈[OOC(CH₃)₃]₈ (2) and Ti₆O₄(OCH₃)₈[OOC(CH₃)₃]₈ (3), were obtained under three similar solvent-thermal reactions of titanium(IV) isopropoxide, alcohols and carboxylic acids, and structurally characterized by single-crystal X-ray diffraction, TGA and IR analysis. All the compounds were crystallized in the space group P2₁/c and the arrangements of the titanium atoms are similar. In addition, the UV-light photocatalytic hydrogen evolution activities have been observed for them, which showed good photocatalytic activity for hydrogen production from water.     

In situ hydrogen generation from cycloalkanes using a Pt/CNF catalyst

Pt catalyst supported on carbon nanofibers (CNFs) has been prepared via ion-exchange and it was characterized by XRD, TEM, N₂ physisorption and CO chemisorption. The Pt/CNF catalyst has a small Pt crystallite size in the range of 2–3 nm. This catalyst has been tested in the dehydrogenation of decalin, which is a cycloalkane proposed in the literature as H₂ storage media for vehicles and portable devices. The objective is finding a Pt catalyst suitable for in situ generation of H₂ from chemical storage in decalin. The results revealed that Pt supported on CNF outperforms a Pt catalyst supported on micro–mesoporous activated carbon. Finally, we propose a reactor configuration aiming at the intensification of H₂ production in continuous.     

Highly visible light responsive metal loaded N/TiO2 nanoparticles for photocatalytic conversion of CO2 into methane

Photocatalytic reduction of carbon dioxide (CO₂) into valuable hydrocarbon such as methane (CH₄) using water as reducing agent is a good strategy for environment and energy applications. In this study, a facile and simple sol-gel method was employed for the synthesis of metal (Cu and Ag) loaded nanosized N/TiO₂ photocatalyst. The prepared photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, BET Surface area analyzer, X-ray photoelectron spectroscopy and UV–vis diffuses reflectance spectroscopy. The photocatalytic conversion of CO₂ into methane was carried out under visible light irradiation (λ≥420 nm) by prepared photocatalysts in order to evaluate the photocatalytic efficiency. The results demonstrate that Ag loaded N/TiO₂ showed enhanced photocatalytic performance for methane production from CO₂ compared to other Cu–N/TiO₂, N/TiO₂ and TiO₂ photocatalysts. The improvement in the photocatalytic activity could be attributed to high specific surface area, extended visible light absorption and suppressed recombination of electron – hole pair due to synergistic effects of silver and nitrogen in the Ag–N/TiO₂ photocatalyst. This study demonstrates that Ag–N/TiO₂ is a promising photocatalytic material for photocatalytic reduction of CO₂ into hydrocarbons under visible light irradiation.     

A cobalt complex of a pentadentate aminopyridine ligand as an efficient catalyst for photocatalytic hydrogen generation

A linear pentadentate aminopyridine ligand 2,6-bis[(methyl(pyrid-2-ylmethyl)amino)-N-methyl]pyridine (Py^Mepam) has been prepared and characterized. This ligand readily coordinates with Co(II) or Zn(II) ions, and the resulting complexes of general formula [M(Py^Mepam)](BF₄)₂ (M = Co (1) and M = Zn (2)) have been thoroughly characterized and investigated for electro- and photocatalytic water reduction in acetonitrile. Electrochemical studies reveal that the complex 1 is active for electrocatalytic water reduction in acetonitrile. Under visible-light irradiation (λ > 400 nm), the complex 1 displays hydrogen evolution activity when in presence of [Ir(ppy)₂(bpy)]PF₆ as photosensitizer and triethylamine (TEA) as electron donor, whereas 2 shows negligible catalytic activity under the same conditions. Highest turnover numbers (TONs) of 290 for H₂ evolution are achieved from an optimized system containing 1 (0.1 mM), [Ir(ppy)₂(bpy)](PF₆) (0.5 mM), and 10 vol% TEA in CH₃CN-H₂O (1/1, v/v) mixed solvents at pH 10.     

Preparation of Ag nanoparticles loaded TiO2 nanoplate arrays on activated carbon fibers with enhanced photocatalytic activity

Ag loaded TiO₂ nanoplate array which grew on activated carbon fiber (ACF) was prepared in the present work. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectra (DRS). The photocatalytic degradation of methylene blue (MB) was used to investigate the activity of the synthesized samples. Under both UV and visible light irradiation, the Ag loaded samples showed enhanced photocatalytic activity. Besides, the effect of the deposition dosage of Ag nanoparticles on the photocatalytic activity was also investigated. Under UV light irradiation, the Ag nanoparticles acted as electron traps, which enhanced electron–hole separation efficiency of TiO₂. Under visible light irradiation, the Ag nanoparticles showed surface plasmon resonance, which induced the visible light responsive photocatalytic activity for the obtained samples.     

One-pot synthesis of PdAu bimetallic composite nanoparticles and their catalytic activities for hydrogen peroxide generation

We report a facile one-pot aqueous-phase synthesis of PdAu bimetallic nanoparticles with different Pd/Au ratio. The synthesis was conducted by co-reduction of Pd and Au precursor using ascorbic acid as a reducing agent and in the presence of polyallylamine hydrochloride (PAH). By high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and energy-dispersive X-ray spectrometry (EDS) analyses, we found that the synthesized nanoparticles had an onion-like core/shell/shell/shell structure with Au-rich core, Pd-rich shell, Au-rich shell, and Pd shell, respectively. We also investigated the catalytic performance of the synthesized PdAu nanoparticles toward hydrogen peroxide generation reaction.     

Arm length dependency of Pt-decorated CdSe tetrapods on the performance of photocatalytic hydrogen generation

Pt-decorated CdSe tetrapods with different arm lengths were tested for the photocatalytic hydrogen generation reaction. Well-defined CdSe tetrapods with controlled wurtzite arm lengths were synthesized by the continuous precursor injection (CPI) approach. Pt nanocrystals with an extremely small size of ～1 nm were directly decorated on the overall surfaces of CdSe tetrapods. Ligand-exchanged Pt-decorated CdSe tetrapods with different arm lengths were employed as photocatalysts for photocatalytic hydrogen generation reaction in the presence of hole scavengers. Pt-decorated CdSe tetrapods with shorter arm length showed the highest photocatalytic efficiency, which is due to higher probability of charge separation.     

Effect of Pt loading and calcination temperature on the photocatalytic hydrogen production activity of TiO2 microspheres

TiO₂ microspheres were synthesized by hydrothermal reaction using Ti(OBu)₄ as the precursor. In order to enhance the efficiency of water splitting by the TiO₂ microspheres, Pt-modified TiO₂ microspheres were prepared by the impregnation-reduction method. The diameter of TiO₂ microspheres is around 5–10 μm. The photocatalytic performances of the catalysts were measured by hydrogen generation from a mixture of water and methanol under UV light irradiation. The photocatalytic activity of the TiO₂ microspheres was remarkably enhanced by loading Pt. The optimal Pt loading is 1.2 wt%. Pt/TiO₂ microspheres exhibit about 125 times greater H₂ production rate than the unmodified TiO₂ microspheres. The effect of calcination temperature on photocatalytic activity of the TiO₂ microspheres was also investigated.     

Impact of quenching process on the surface defect of titanium dioxide for hydrogen production from photocatalytic decomposition of water

Nanocrystalline titania was prepared by solvothermal reaction of titanium butoxide in toluene at 300 °C for 2 h. Thus obtained-powder was calcined at 300 °C in box furnace for 1 h and then quenched in various media at different temperature. The physiochemical properties of samples were investigated by using X-ray diffraction (XRD), nitrogen adsorption, CO₂-Temperature Programmed Desorption (CO₂-TPD), UV–visible scanning spectrophotometer, Transmission electron microscopy (TEM) and electron spin resonance spectroscopy (ESR) techniques. All physical properties such as phase, BET surface area and crystal size were not changed after quenching processes. While the CO₂-TPD and ESR results indicate the changing of Ti³⁺ contents on the surface of TiO₂ after quenching process. The amounts of Ti³⁺ increased as the quenching temperature decreased. Photocatalytic decomposition of water was carried out to evaluate the catalytic activity of quenched TiO₂. The activity of quenched-powder increased corresponding to the increasing of Ti³⁺ contents increased by following order: air at 77 K > air at RT > air at 373 K > 30 wt% H₂O₂ at RT = 30 wt% H₂O₂ at 373 K > H₂O at RT > H₂O at 373 K.     

Selective deposition of Pt on Au nanoparticles using hydrogen presorbed into Au nanoparticles during NaBH4 treatment

A facile chemical method to prepare a Pt layer selectively on Au nanoparticles is developed. The hydrogen presorbed into Au nanoparticles during NaBH₄ treatment leads to the formation of a thin Pt layer on Au nanoparticles. The Pt-coated Au nanoparticles exhibit significantly improved electrocatalytic activity for the electrooxidation of formic acid.     

Lanthanum-molybdenum coating for hydrogen evolution on titanium

There is practical interest in the use of titanium as a cathode material in brine electrolysis processes. The overvoltage of hydrogen evolution on titanium is, however, very high and, at the same time, hydrogen penetrates the bulk of the metal. Here, a new type of catalytically active coating has been applied on the surface of titanium in order to overcome these problems. The coating consists of a mixture of the thermal decomposition products of lanthanum chloride and sodium molybdate. The coating has been tested for 18 months of continuous operation. No change in the overvoltage gain (of 0.4 V at 3 kA m^–2, as compared with pure titanium) nor change in the properties of the bulk metal have been noticed during this period.