High photocatalytic hydrogen production from methanol aqueous solution using the photocatalysts CuS/TiO2

Photocatalysts CuS/TiO₂ for hydrogen production were synthesized by hydrothermal method at high temperature and characterized by XRD, UV–visible DRS, XPS, EDX, SEM and TEM. When TiO₂ was loaded with CuS, it showed photocatalytic activities for water decomposition to hydrogen in methanol aqueous solution under 500 W Xe lamp. Among the photocatalysts with various compositions, the one with 1 wt% CuS-loaded TiO₂ showed the maximum photocatalytic activity for water splitting, which indicated CuS could improve the separation ratio of photoexcited electrons and holes. What's more, the amounts of the produced hydrogen was about 570 μmol h⁻¹, which had exceeded pure titania (P25) 32 times. In the present paper, it is proven that CuS can act as an effective co-catalyst to enhance the photocatalytic H₂ production activity of TiO₂.     

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).     

Preparation and photocatalytic activities of two new Zn-doped SrTiO3 and BaTiO3 photocatalysts for hydrogen production from water without cocatalysts loading

Sr_2/3Zn_1/3TiO₃ (1) and Ba_5/6Zn_1/6TiO₃ (2) with perovskite structure have been prepared by a facile sol–gel method, among which the A sites (Sr and Ba for 1 and 2, respectively) were partially replaced by zinc ions. The photocatalysts were characterized by powder X-ray diffraction, UV–vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The results of photocatalysis experiment showed that both 1 and 2 exhibited good activity for water reduction to form H₂ without cocatalysts loading under ultraviolet light irradiation. Compared with pure SrTiO₃ and BaTiO₃, 1 and 2 showed remarkable improvement in H₂ production efficiency, respectively. And the photocatalytic mechanisms of them were investigated by the theoretical method. This study demonstrated that the substitutional doping of appropriate ions could change the crystal and band structures and significantly promote electron transport in catalysts, which result in their good photocatalytic activities.     

Gas and vapor adsorption in octacyanometallate-based frameworks Mn2[M(CN)8] (M = W,Mo) with exposed Mn sites

Dehydration of the isostructural three-dimensional (3D) octacyanometallate-based materials Mn₂M(CN)₈·7H₂O (M = Mo, 1·7H₂O; W, 2·7H₂O) generates robust porous frameworks (1 and 2). In the structure, the [M(CN)₈]⁴⁻ units are linked via octahedral Mn²⁺ centers to form an open 3D framework with 1D channels, in which the non-coordinated and coordinated water molecules are involved. The permanent porosities have been confirmed by thermogravimetric analysis, variable-temperature X-ray diffraction and Raman spectra, and adsorption (H₂O, N₂ and H₂) measurements. H₂ adsorption at 1.1 bar and 77 K was 0.60 wt% for 1 and 0.49 wt% for 2. At initial loading ΔH_ads has the value of ca. 10.0 kJ mol⁻¹ for both materials, which represents the highest value reported for any cyanide-based assemblies. The high enthalpy can be attributed to the presence of coordinatively-unsaturated Mn²⁺ sites left exposed by the removal of coordinated water molecules in the structure.     

A molecular Keggin polyoxometalate catalyst with high efficiency for visible-light driven hydrogen evolution

A molecular Keggin polyoxometalate catalyst K₇[Co^IIICo^II(H₂O)W₁₁O₃₉](1) was successfully synthesized and efficiently catalyzed the hydrogen evolution. To the best of our knowledge, the molecular Keggin polyoxometalate catalyst 1 is the first reported polyoxometalate containing cobalt with efficient hydrogen production activity under the visible light irradiation. Under the optimal photocatalytic condition (photoirradiation at λ ≥ 420 nm, Eosin-Y as the photosensitizer, triethanolamine as the electron donor and Pt produced in situ photoreduction as co-catalyst), the turnover number (TON/based on catalyst) reached as high as 100; the initial quantum yield and the initial turnover frequency (TOF) at the first 10 min were 29% and 0.025 s⁻¹, respectively. The hydrogen evolution average rate of 1 achieved 13,395 μmol h⁻¹ g⁻¹, as far as we are concerned, which is the highest among all the polyoxometalates photocatalytic systems reported so far. A possible mechanism of the hydrogen evolution reaction was proposed on the basis of steady-state fluorescence decay studies.     

Nickel sulfide as co-catalyst on nanostructured TiO2 for photocatalytic hydrogen evolution

In this study, TiO₂ photocatalysts with nickel sulfide cocatalyst are prepared by loading nickel sulfide on TiO₂ with solvothermal synthesis approach. The materials were prepared by glycol solvothermal method using anatase, nickel nitrate, thiourea as precursor. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), and X-ray photoelectron spectroscopy (XPS). This is the first time to report that NiS is used as a cocatalyst with TiO₂ for the photocatalytic production of H₂. The results revealed that the structure and the amount of the cocatalyst loaded on TiO₂ play important roles in the photocatalytic activity of NiS/TiO₂ composite. The maximum evolution of H₂ was obtained when NiS had hexagonal structure with content in the composite of 7 at% in relation to TiO₂. The rate of H₂ evolution was increased up to about 30 times than that of TiO₂ alone.     

Photocatalytic hydrogen production with CuS/ZnO from aqueous Na2S + Na2SO3 solution

The photocatalytic hydrogen production in the sacrificial S²⁻–SO₃²⁻ anions was investigated with ZnO in the addition of metal sulfides containing Ag₂S, CuS, Fe₂S₃, and NiS. In the absence of metal sulfides, the photocatalytic H₂ evolution using ZnO was observed with 255 μmol g⁻¹. The CuS amount and the concentrations of S²⁻ and SO₃²⁻ ions were optimized. It was found that ternary component semiconductor CuS/ZnS/ZnO was formed during the photocatalytic hydrogen production in the aqueous Na₂S + Na₂SO₃ solution. The photocatalytic hydrogen evolution with CuS/ZnS/ZnO in the 0.4 M Na₂S–0.4 M Na₂SO₃ solution was more than about 8.5 times better compared with those obtained with only ZnO. The CuS clusters on the surface of ZnS/ZnO seem to play an important role on the separation for electron–hole pair and the enhancement of H₂ production. Nano-sized ZnS/ZnO photocatalytic hydrogen technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy.     

A copper based metal-organic framework as single source for the synthesis of electrode materials for high-performance supercapacitors and glucose sensing applications

The article describes the conversion of MOF-199 to Cu–Cu₂O–CuO/C 700 (1) and Cu–Cu₂O–CuO/C 800 (2) nanostructures by simple pyrolysis at 700 and 800 °C under inert atmosphere. The X-ray photoelectron spectroscopy analysis reveals that the nanostructures Cu–Cu₂O–CuO/C consist of graphitic carbon functionalized with carboxylic, carbonyl and hydroxyl functional groups with copper/copper oxide particles on surfaces. The electrochemical properties of 1 and 2 are evaluated as electrode material for supercapacitors using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results for the capacitive performance from cyclic voltammetry and galvanostatic charge/discharge reveal that both the samples have gravimetric capacitance greater than 750 F g⁻¹ at a scan rate of 2 mV s⁻¹ and current density of 2 mA cm⁻². The samples retain about 43% of their initial capacitance even at high scan rate of 75 mV s⁻¹. The cycling performance of the nanostructures illustrate that there is 5.5% capacitance loss after 3000 cycles. The sample 1 and 2 are washed with 1 mol L⁻¹ HCl solution to obtain copper oxide free materials Cu/C 700 (3) and Cu/C 800 (4). Samples 3 and 4 are tested as electrocatalysts for glucose sensing and the cyclic voltammetry measurement shows enhanced current densities compared to the literature values.     

A new insight for photocatalytic hydrogen production by a Cu/Ni based cyanide bridged polymer as a co-catalyst on titania support in glycerol water mixture

A two dimensional Cu/Ni based coordination polymer [{Cu^II(4,4ʹ-dipy)₂}{Ni(CN)₄}]_n·0.7(C₂H₆O₂)·1.6(H₂O) (CP-1) (4,4ʹ-dipy = 1,3-di (4-pyridyl)propane) has been demonstrated as a potential co-catalyst on TiO₂ support for hydrogen evolution under UV light. CP-1/TiO₂ composite exhibits considerable hydrogen production in comparison with the pristine CP-1 and TiO₂ (P25), highlighting that the photocatalytic performance is significantly related with the good separation of photo generated e⁻/h⁺ pairs. Different wt. % (2.5, 5 and 7.5%) of CP-1 in CP-1/TiO₂ composites were tested for photocatalytic hydrogen production in 5 vol % glycerol/water mixture. The 5 wt % CP-1/TiO₂ composite displayed the greatest hydrogen production of 9.2 mmolh⁻¹g⁻¹. The concealed mechanism is divulged on the behalf of results obtained by cyclic voltammetry, photoluminescence and diffused reflectance/UV-visible studies which demonstrate that upon irradiation of UV light, electrons transfer from TiO₂ conduction band to CP-1. CP-1 not only grabs the conduction band electrons of titania but also performes as a co-catalyst to reduce the protons into hydrogen. These results are anticipated to direct the forthcoming advancement in creating proficient, cheap semiconductor photocatalysts for solar hydrogen production.     

Ternary noble-metal-free heterostructured NiS–CuS–C3N4 with near-infrared response for enhanced photocatalytic hydrogen evolution

Fast charge recombination and limited visible-light absorption often hinder the practical applications of graphitic carbon nitride (g-C₃N₄) for photocatalytic hydrogen evolution. In this work, we report the synthesis of ternary heterostructured noble-metal-free NiS–CuS–C₃N₄ with near-infrared (NIR) response for enhanced solar light hydrogen evolution from water. At an optimal 7% NiS-3% CuS–C₃N₄ composition, a H₂-evolution rate of 1602 μmol g⁻¹ h⁻¹ can be achieved. The apparent quantum efficiency at 400 nm and 940 nm was measured to be 9.7% and 0.44%, respectively. Based on detailed analysis, the reasonable mechanism is proposed and the significantly enhanced photocatalytic performance should be attributed to dramatically improved charge transfer through type-II heterojunction and NiS cocatalyst. Additionally, the computational study is employed to help explain the promotion of NiS. In this case, this work might provide a platform for the construction of efficient noble-metal-free C₃N₄-based ternary heterostructured photocatalysts in the future.     

Noble-metal-free CuS/CdS composites for photocatalytic H2 evolution and its photogenerated charge transfer properties

CuS/CdS composites have been successfully prepared by a simple hydrothermal and cation exchange method. Even without noble-metal cocatalyst, the prepared CuS/CdS composites exhibited enhanced photocatalytic H₂ evolution activity. CuS content had a great influence on photocatalytic activity and an optimum amount of CuS was determined to be ca. 3 mol%, at which the CuS/CdS displayed the highest photocatalytic activity, giving an H₂ evolution rate of 332 μmol g⁻¹ h⁻¹, exceeding that of pure CdS by 3.5 times. The results of SPV (surface photovoltage) and SPC (surface photocurrent) revealed that photogenerated electrons were captured by CuS loaded. TPV (transient photovoltage techniques) indicated that photogenerated charges lifetime in CdS, was prolonged with CuS loaded. Those are the main reasons for the improvement of photocatalytic H₂ evolution.     

The structural characterization of (NH4)2B10H10 and thermal decomposition studies of (NH4)2B10H10 and (NH4)2B12H12

The structure of (NH₄)₂B₁₀H₁₀ (1) was determined through powder XRD analysis. The thermal decomposition of 1 and (NH₄)₂B₁₂H₁₂ (2) was examined between 20 and 1000 °C using STMBMS methods. Between 200 and 400 °C a mixture of NH₃ and H₂ evolves from both compounds; above 400 °C only H₂ evolves. The dihydrogen bonding interaction in 1 is much stronger than that in 2. The stronger dihydrogen bond in 1 resulted in a significant reduction by up to 60 °C, but with a corresponding 25% decrease in the yield of H₂ in the lower temperature region and a doubling of the yield of NH₃. The decomposition of 1 follows a lower temperature exothermic reaction pathway that yields substantially more NH₃ than the higher temperature endothermic pathway of 2. Heating of 1 at 250 °C resulted in partial conversion of B₁₀H₁₀²⁻ to B₁₂H₁₂²⁻. Both 1 and 2 form an insoluble polymeric material after decomposition. The elements of the reaction network that control the release of H₂ from the B₁₀H₁₀²⁻ can be altered by conducting the experiment under conditions in which pressures of NH₃ and H₂ are either near, or away from, their equilibrium values.     

Iron–iron hydrogenase active subunit covalently linking to organic chromophore for light-driven hydrogen evolution

The first photocatalytic [FeFe]-hydrogenase ([FeFe]-H₂ase) mimic 3 with noble-metal-free benzothiazole as donating photosensitizer had been successfully constructed via an easily accessible approach, and fully characterized by various spectroscopic and X-ray crystallographic techniques. Steady-state spectroscopy and electrochemistry revealed the evidences indicating that the photo-induced electron transfer occurred in 3. The reduced [Fe^IFe⁰] species was further confirmed by laser flash photolysis and considered to be responsible for the light-driven H₂ evolution. As a result, the photocatalytic system consisting of the photocatalyst 3 and the sacrificial electron donor in the presence of proton source indeed produced H₂ with a turnover number (TON) of 24.2 under light irradiation. The TON indicated a remarkably photocatalytic efficiency for an [FeFe]-H₂ase mimic assembled by the covalent combination of a photosensitizer to the catalytic center. The results demonstrated the tremendous potential of present synthetic strategy for the construction of compact, inexpensive, easily accessible [FeFe]-H₂ase model complexes as photocatalysts.     

The size and valence state effect of Pt on photocatalytic H2 evolution over platinized TiO2 photocatalyst

Photocatalytic hydrogen production from water or organic compounds is a promising way to resolve our energy crisis and environmental problems in the near future. Over the past decades, many photocatalysts have been developed for solar water splitting. However, most of these photocatalysts require cocatalyst to facilitate H₂ evolution reaction and noble metals as key cocatalysts are widely used. Consequently, the condition of noble metal cocatalyst including the size and valence state etc plays the key role in such photocatalytic system. Here, the size and valence state effect of Pt on photocatalytic H₂ evolution over platinized TiO₂ photocatalyst were studied for the first time. Surprisingly, it was found that Pt particle size does not affect the photoreaction rate with the size range of several nanometers in this work, while it is mainly depended on the valence state of Pt particles. Typically, TOFs of TiO₂ photodeposited with 0.1–0.2 wt% Pt can exceed 3000 h⁻¹.     

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.     

Well-designed NiS/CdS nanoparticles heterojunction for efficient visible-light photocatalytic H2 evolution

Heterojunction photocatalysts based on semiconducting nanoparticles show excellent performance in many photocatalytic reactions. In this study, 0D/0D heterojunction photocatalysts containing CdS and NiS nanoparticles (NPs) were successfully synthesized by a chemical precipitation method. The NiS NPs were grown in situ on CdS NPs, ensuring intimate contact between the semiconductors and improving the separation efficiency of hole-electron pairs. The obtained NiS/CdS composite delivered a photocatalytic H₂ evolution rate (7.49 mmol h^?1 g^?1), which was 39.42 times as high as that of pure CdS (0.19 mmol h^?1 g^?1). This study demonstrates the advantages of 0D/0D heterojunction photocatalysts for visible light-driven photocatalytic hydrogen production.     

Electrochemical and chemical enrichment methods of a sodic–saline inoculum for microbial fuel cells

In microbial fuel cells (MFCs) efficient extracellular electron transfer microbes, also known as anode-respiring bacteria, play an important role on cell performance. This type of microbes can be developed by application of enrichment procedures. The objective of this study was to compare a chemical (only C, final terminal electron acceptor Fe(III)), an electrochemical (only E), and a hybrid method (H, i.e., E followed by 3 serial transfers in iron (III) citrate medium) enrichment methods departing from a saline–sodic soil inoculum. In the electrochemical enrichment procedure in an electrolysis cell, the inoculum was subjected to a continuous electrical stress continually by posing the cell at −150 mV/SCE (+94 mV/SHE). The only C enrichment method delivered powers superior to the only E one (higher values of P_An,max = 49 mW m⁻² and P_V,max = 558 mW m⁻³ of C compared to 33 and 379 of only E). Interestingly, overall resistance as determined by EIS was lower for only E (1240 Ω) than for only C (1632 Ω). Yet, the hybrid H method, showed electrochemical characteristics consistently superior to both only C and only E methods (higher P_An,max and P_V,max, lower internal resistance). Further detailed electrochemical studies of only E-method showed that the anodic resistance decreased with the time of operation of the electrolysis cell that would be consistent with the adaptability/enrichment purpose of the method. Also, Cyclic voltammetry peaks with values close to those reported for bacterial cytochromes appeared with time of cell operation.     

Synthesis of CdS/CNTs photocatalysts and study of hydrogen production by photocatalytic water splitting

A series of CdS and CdS/CNTs photocatalysts were successfully prepared by hydrothermal method and they were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV–visible optical absorption spectra (UV–Vis), etc. By studying their photocatalytic properties, it is found that, for CdS, photocatalysts prepared in appropriate alkaline environment presented higher hydrogen production activity, reaching 794.6 μmol h⁻¹ g⁻¹; the photocatalytic activity of CdS was obviously enhanced by combining it with CNTs via a special two-step hydrothermal method, and the corresponding hydrogen production rate reached 1.771 mmol h⁻¹ g⁻¹; the photocatalytic activity was further improved by loading co-catalyst NiS, achieving 12.13 mmol h⁻¹ g⁻¹.     

A porous 3d-4f heterometallic metal–organic framework for hydrogen storage

A heterometallic metal–organic framework, {[Ce(oda)₃Zn_1.5(H₂O)₃]·0.75H₂O}_n (1, H₂oda = oxydiacetic acid), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction analysis reveals that compound 1 belongs to hexagonal crystal system with space group P6/mcc and exhibits 3D porous framework. The hydrogen adsorption experiments suggest that 1 possesses reversible hydrogen storage capacity, up to 1.34 wt.% at 77 K and 0.86 wt.% at 298 K, respectively.