Study on deactivation and reaction mechanism of Co thiolate complexes in photocatalytic hydrogen production system

Hydrogen is an environment‐friendly source with high efficiency, which is also an important alternative to traditional energy sources. In this paper, noble‐metal‐free photocatalyst Co thiolate complexes Co(bpy)(pyS)₂ (M1) and Co(phen)(pyS)₂ (M2) were synthesized and used in photocatalytic decomposition of water to generate hydrogen. The deactivation and reaction mechanism of Co thiolate complexes in photocatalytic hydrogen generation system were studied. The results of photocatalytic hydrogen generation with regeneration of system by re‐addition of catalyst and fluorescein exhibited that the main reasons for the deactivation of system were probably the deactivation of catalyst and small part of decomposition of photosensitizer. The results of UV‐vis spectra of the system after irradiation revealed that the electron transfer mode between fluorescein, catalyst, and triethylamine was favorable for the stability and life of fluorescein. Furthermore, the electron transfer rates from fluorescein to M1 and M2 were 2.1 × 10¹²M^?1 S^?1 and 1.5 × 10¹²M^?1 S^?1. This investigation may lay the theories foundation for further research on hydrogen evolution of noble‐metal‐free catalysts and also may provide a novel approach for building a feasible and more environmental‐friendly photocatalytic hydrogen production system.     

A coordinatively saturated cobalt complex as a new kind catalyst for efficient electro- and photo-catalytic hydrogen production in purely aqueous media

It has been shown that coordinatively unsaturated complexes can catalyze hydrogen production via an unstable hydride intermediate. Herein we present a new kind of water soluble catalyst based on a coordinatively saturated cobalt complex, [(phen)₂Co(CN)₂]?ClO₄1 that is formed by the reaction of 1,10-phenanthroline (phen), Co(ClO₄)₂·6H₂O and tetracyanoethylene (TCNE). Under photoirradiation with blue light (λ_max = 469 nm) in air, together with [Ru(bpy)₃]Cl₂ and ascorbic acid in a pH 5.5 aqueous solution, 1 possesses photocatalytic activity for water reduction to hydrogen with an initial turnover number (TON) of 1232H₂ per mol of catalyst at first 10 h, and this activity is sustained for at least 70 h. This can be attributed to that oxidative quenching by 1 (k_q = 1.69 × 10¹⁰ M^?1 s^?1) dominates over reductive quenching to [Ru(bpy)₃]Cl₂ by ascorbic acid (k_q = 1.55 × 10¹⁰ M^?1 s^?1). Additionally, 1 electrocatalyze hydrogen generation from a neutral water with a turnover frequency (TOF) of 1113.1 mol of hydrogen per mole of catalyst per hour (mol H₂/mol catalysts/h) at an overpotential (OP) of 838 mV. We hope this can afford a new method in proton or water reduction catalysis using coordinatively saturated complexes in purely aqueous media.     

Hydrogen generation by aluminum‐water reaction in acidic and alkaline media and its reaction dynamics

The additives AlCl₃, CoCl₂, Al(OH)₃, Ca(OH)₂, and NaAlO₂ are added to water to regulate its pH value (pH = 2‐13) in this study. The effects of media on the aluminum‐water reaction are investigated. Up to an increase in temperature, the hydrogen generation rate in different media increases. H⁺, OH^?, Cl^?, or Co produced from the additive favors the initial removal of the oxide film and aluminum corrosion. Therefore, the initial hydrogen generation rate increases in acidic and alkaline media. The synergistic effect of the formed fresh Co and Cl^? catalyzes aluminum‐water reactions. However, the amount of hydrogen decreases with increasing mass of CoCl₂ because of agglomeration of the catalyst Co. The higher concentration of OH^? ions aids hydrogen generation. However, the reaction rate became slow after the rapid consumption of OH^?, when the concentration of OH^? was relatively small. Hydrogen is quickly generated and Al is completely reacted upon following additions of Al due to the cooperation between H⁺, Cl^?, OH^? ions, and the formed Al(OH)₃.     

Efficient photocatalytic H2 production using visible‐light irradiation and (CuAg)xIn2xZn2(1 − 2x)S2 photocatalysts with tunable band gaps

The band structures of semiconductor photocatalysts fundamentally determine the photocatalytic activity and the H₂ production from the visible‐light‐driven water‐splitting reaction. We synthesize a suite of multicomponent sulfide photocatalysts, (CuAg)_xIn_2xZn_{2(1 ? 2x)}S₂ (0 ≤ x ≤ 0.5), with tunable band gaps and small crystallite sizes to produce H₂ using visible‐light irradiation. The band gap of the photocatalysts decreases from 3.47 eV to 1.51 eV with the increasing x value. The (CuAg)_0.15In_0.3Zn_1.4S₂ (x = 0.15) photocatalyst yielded the highest photocatalytic activity for H₂ production owing to the broad visible‐light absorption range and suitable conduction band potential. Under the optimized reaction conditions, the highest H₂ production rate is 230 µmol m^?2 h^?1 with a visible‐light irradiation of 2.7 × 10^?5 einstein cm^?2 s^?1, and the quantum yield reaches 12.8% at 420 ± 5 nm within 24 h. Furthermore, the photocatalytic H₂ production is shown to strongly depend on their band structures, which vary with the elemental ratios and could be analyzed by the Nernst relation. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrogen generation from photocatalytic hydrolysis of alkali‐metal borohydrides

The controllable photocatalytic hydrolysis of alkali‐metal borohydrides is studied for hydrogen generation in this work. The results indicate that the photocatalysis of P25 TiO₂ controllably promotes the hydrogen generation rates from alkali‐metal borohydride hydrolysis. Its apparent activation energy is calculated to be reduced from 57.20 to 53.86 kJ mol^?1. This is due to the mechanism of photocatalytic hydrolysis: holes (h⁺) react with BH₄‐ and OH^? to form H₂ and B(OH)₄‐, meanwhile electrons (e^?) react with H⁺ to from H₂. In addition, Ti³⁺‐doped TiO₂ with a crystalline‐disordered core‐shell structure can be generated during the photocatalytic hydrolysis process. The consumption of e^? is identified as the rate‐limiting step in photocatalytic hydrolysis process. Copyright © 2017 John Wiley & Sons, Ltd.     

Stability and kinetic studies of MOF‐derived carbon‐confined ultrafine Co catalyst for sodium borohydride hydrolysis

A mesoporous carbon‐confined cobalt (Co@C) catalyst was fabricated by pyrolysis of macroscale Co‐metal–organic framework (MOF) crystals and used to catalyze NaBH₄ hydrolysis for hydrogen production. To reveal the structural changes of cobalt nanoparticles, we characterized the fresh and used Co@C catalysts using X‐ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and N₂ adsorption. This MOF‐derived Co@C exhibits high and stable activity toward NaBH₄ hydrolysis. No obvious agglomeration of Co nanoparticles occurred after five consecutive runs, implying good resistance of Co@C composite to metal aggregation. The kinetics of NaBH₄ hydrolysis was experimentally studied by changing initial NaBH₄ concentration, NaOH concentration, and catalyst dosage, respectively. It was found that the hydrogen generation rate follows a power law: r = A exp (?45.0/RT)[NaBH₄]^0.985[cat]^1.169[NaOH]^?0.451 .     

Catalytic effect of EG and MoS2 on hydrolysis hydrogen generation behavior of high‐energy ball‐milled Mg‐10wt.%Ni alloys in NaCl solution—A powerful strategy for superior hydrogen generation performance

In this study, the metallurgical melting Mg‐10wt.%Ni (Mg10Ni) alloy is firstly modified by high‐energy ball milling (HEBM) and then surface catalysts expanded graphite (EG) or MoS₂ or EG‐MoS₂ are introduced to prepare Mg10Ni‐M (M = EG, MoS₂, and EG‐MoS₂) composites. The effects of surface catalysts on hydrolysis hydrogen generation of HEBM Mg10Ni alloy are comprehensively investigated. Their kinetics, rate‐limiting steps, and apparent activation energies are investigated by fitting the hydrolysis curves at different temperatures. The results indicate that the total hydrogen generation capacities of prepared Mg10Ni‐M (M = EG, MoS₂, and EG‐MoS₂) composites are 200, 170, 674, and 720 mL·g^?1 within 1 minute at 291 K. The capacity and yield of Mg10Ni are 500 mL·g^?1 and 56% within 15 minutes. The surface catalysts EG or MoS₂ or EG‐MoS₂ can distinctly elevate the initial H₂ produce rate and promote the complete hydrolysis process. The highest capacity and generation yield within 15 minutes are 740.8 mL·g^?1 and 91% obtained by HEBM Mg10Ni‐EG‐MoS₂ composite at 291 K. The surface catalysis can promote high generation yield of Mg10Ni alloy in a short time.     

Chemical storage of solar energy: hydrogen generation by visible light with Cr(Ox)33H2O−3 containing ferrous sulphate in acidic solution

Hydrogen gas is generated continuously by visible light irradiation of aqueous H₂SO₄ solution at pH 2–4 containing (5 × 10^?3M) K₃Cr(Ox)₃ · 3H₂O and (10^?2 M) FeSO₄.The rate of formation of hydrogen has been recorded. Hydrogen is about 21% of the total gases evolved. The reaction is markedly pH dependent. The chromium is the photoactive species and the chromium or the iron forms the storage system for electrons and protons. It appears that the generation of hydrogen is taking place by indirect photodecomposition of water.Hydrogen was generated when Fe(CN)₆^?4 was substituted for FeSO₄. Control experiments have been performed and the mechanism and proposed cycle for the processes are discussed.     

Hydrogen evolution under visible light over the heterojunction p‐CuO/n‐ZnO prepared by impregnation method

The semiconducting properties of the heterojunction CuO/ZnO, synthesized by impregnation method from nitrates, are studied for the first time to assess its feasibility for the hydrogen production under visible light, an issue of energy concern. CuO exhibits a direct optical transition at 1.33 eV, due to Cu²⁺: 3d orbital splitting in octahedral site, and possesses a chemical stability in the pH range (4–14). The Mott–Schottky plot in (Na₂SO₄, 0.1 M) medium indicates p‐type conduction with a flat band potential of 0.70 V_SCE and a holes density of 1.35 × 10¹⁷ cm^?3. As application, hydrogen evolution upon visible light is demonstrated on the heterojunction ×%CuO/ZnO (x = 5, 10 and 20 wt.%). The best performance occurs at pH ~12 with an evolution rate of 4.8 cm³ min^?1 (g catalyst)^?1 and a quantum yield of 0.12%. The improved activity is attributed to the potential of the conduction band of CuO (?1.34 V_SCE), more negative than that of ZnO, the latter acts as electrons bridge to water molecules. The presence of SO₃^2? reduces the recombination process, thus resulting in more H₂ evolution. Copyright © 2015 John Wiley & Sons, Ltd.     

Design and preparation of CdS/H-3D-TiO2/Pt-wire photocatalysis system with enhanced visible-light driven H2 evolution

In recent years, tremendous efforts have been devoted to develop new photocatalyst with wide spectrum response for H₂ generation from water or aqueous solution. In this work, CdS nanoparticles (NPs) have been immobilized on hydrogenated three-dimensional (3D) branched TiO₂ nanorod arrays, resulting in a highly efficient photocatalyst, i.e, CdS/H-3D-TiO₂. In addition, electrochemical reduction of H⁺ ion is identified as a limiting step in the photocatalytic generation of H₂ at this catalyst, while here a Pt wired photocatalysis system (CdS/H-3D-TiO₂/Pt-wire) is designed to overcome this barrier. Without the application of potential bias, visible light photocatalytic hydrogen production rate of CdS/H-3D-TiO₂/Pt-wire is 18.42 μmol cm^?2 h^?1, which is 11.2 times that of CdS/H-3D-TiO₂ without Pt (1.64 μmol cm^?2 h^?1). The Pt wire acts as an electron super highway between the FTO substrate and H⁺ ions to evacuate the generated electrons to H⁺ ions and catalyze the reduction reaction and consequently generate H₂ gas. This work successfully offers a novel direction for dramatic improvement in H₂ generation efficiency in photocatalysis field.     

A BiOCl/β‐FeOOH heterojunction for HER photocatalytic performance under visible‐light illumination

β‐iron oxide hydroxide (β‐FeOOH) had been proven to be an effective co‐catalyst during H₂ evolution reaction (HER) process. In this research, a BiOCl/β‐FeOOH heterojunction was successfully synthesized by a solid‐state doping method. Then, the structure, composition, and photo‐electrochemical properties of the prepared photocatalysts were studied. For the superior HER photocatalytic activity of ultrasmall β‐FeOOH nanoparticles (NPs) and the formation of the BiOCl/β‐FeOOH heterojunction, this heterojunction photocatalyst exhibited very superior photocatalytic performance in the HER process. Especially, when the amount of incorporated β‐FeOOH NPs was appropriate, the BFOH‐2 possessed the highest photocatalytic activity in HER process, and the HER rate was about 16.64 mmol·g^?1·h^?1 during illuminated time of 6 hours under visible light. When appropriate, ultrasmall β‐FeOOH NPs were implanted into the structure of BiOCl, the BiOCl/β‐FeOOH heterojunction interfaces would form for the existence of interfacial interactions. Therefore, this BiOCl/β‐FeOOH heterojunction exhibited superior visible‐light response, fast photo‐carrier migration, and high‐efficient separation of photo‐carriers, so that the BFOH‐2 heterojunction possessed high‐efficient hydrogen evolution reaction (HER) photocatalytic activity.     

In situ fabrication of CDs/g-C3N4 hybrids with enhanced interface connection via calcination of the precursors for photocatalytic H2 evolution

Novel carbon dots (CDs)/graphitic carbon nitride (g-C₃N₄) hybrids were fabricated via an in situ thermal polymerization of the precursors, urea and glucose. This heterojunction catalyst exhibited enhanced photocatalytic H₂ evolution activity under visible-light (λ > 420). A sample of CDs/g-C₃N₄ hybrids, CN/G0.5, which was prepared from 0.5 mg of glucose in 6.0 g of urea (8.3 × 10^?3 wt% glucose), exhibited the best photocatalytic performance for hydrogen production from water under visible light irradiation, which is about 4.55 times of that of the bulk g-C₃N₄ (BCN). The improvement of photocatalytic activity was mainly attributed to the construction of built-in electric field at the interface of CDs and g-C₃N₄, which could improve the separation of photogenerated electron-hole pair. Moreover, the tight connection of CDs with g-C₃N₄ would serve as a well electron transport channel, which could promote the photocatalytic H₂ evolution ability.     

Photocatalytic system with water soluble nickel complex of S,S′-bis(2-pyridylmethyl)-1,2-thioethane over CdS nanorods for hydrogen evolution from water under visible light

In this paper, we report a new nickel complex, [(bpte)NiCl₂] (bpte = S,S′-bis(2-pyridylmethyl)-1,2-thioethane) that can serve as a catalyst both for electrochemical and photochemical driven hydrogen production from water. As an electrocatalyst, [(bpte)NiCl₂] can electrocatalyze hydrogen generation from a neutral buffer with a turnover frequency (TOF) of 555.78 mol of hydrogen per mole of catalyst per hour (mol H₂/mol catalyst/h) at an overpotential (OP) of 837.6 mV. Together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H₂A) as a sacrificial electron donor, the nickel complex also can photocatalyze hydrogen evolution in heterogeneous environments and can work for 107 h. Under an optimal condition, the photocatalytic system can afford 24900 mol of H₂ per mole of catalyst during 83 h irradiation, with a TOF of 300H₂ per catalyst per hour. The average value of apparent quantum yield (AQY) is ～24% at 420 nm.     

The effects of micellar media on the photocatalytic H2 production from water

The photocatalytic H₂ production efficiency of a multi-component system, containing [Ir(ppy)₂(bpy)]⁺ as photosensitizer, [Co(bpy)₃]²⁺ as H₂-evolving catalyst, and triethanolamine (TEOA) as sacrificial electron donor, was investigated in water/acetonitrile (8:2, v/v) solution in the presence of different kinds of surfactants, such as cetyl trimethyl ammonium bromide (CTAB), Triton X-100, and sodium lauryl sulfonate (NaLS). The H₂ evolution rate is found to follow the order of cationic micellar media > nonionic micellar media > anionic micellar media > water/acetonitrile solution. The underlying mechanism was discussed.     

Usage of natural leaf as a bio-template to inorganic leaf: Leaf structure black TiO2/CdS heterostructure for efficient photocatalytic hydrogen evolution

Herein, first time we report that highly efficient sheet like leaf structure black TiO₂ (LBT)/CdS hetero-structure (LBT/CdS). Photocatalytic hydrogen generation was tested for different material in the presence of visible light (λ ≥ 420 nm) irradiation. 10 wt% of LBT loaded CdS (10LBT/CdS) exhibit maximum photocatalytic H₂ generation rate about ~10 mmol h^?1 g^?1, which is higher than the H₂ production results of pristine CdS (6 mmol h^?1 g^?1) and leaf black-TiO₂ 5.1 mmol h^?1 g^?1) respectively. Detailed characterization revealed that higher photocatalytic activity was mainly attributed to enormous spatial transfer efficiency of photo-excited charge carriers at the hetero-junction between LBT and CdS in LBT/CdS. Additionally, introduction of 2D black leaf-TiO₂ to CdS act as a mat and enhances the mobility of charge carriers. In addition, presence of anatase-rutile surface-phase junction in leaf TiO₂ (synthesized at 750 °C) and more edges, steps and corners on the CdS synergistically increased the photocatalytic H₂ generation and photocurrent response of LBT/CdS.     

Noble metal-free NiCo nanoparticles supported on montmorillonite/MoS2 heterostructure as an efficient UV–visible light-driven photocatalyst for hydrogen evolution

In this study, a noble-metal-free photocatalyst, based on NiCo nanoparticles supported on montmorillonite/MoS₂ heterostructure (MMT/MoS₂/NiCo), was successfully synthesized and applied for photocatalytic water reduction to produce H₂. Under UV–visible light irradiation, the composite showed improved photocatalytic performance for H₂ evolution compared to MMT/MoS₂, MMT/MoS₂/Ni, MMT/NiCo, and MoS₂/NiCo. The as-synthesized MMT/0.79MoS₂/Ni_8.14Co_6.4 (0.79, 8.14 and 6.4 denote the weight ratios % of MoS₂, Ni and Co in the catalyst) photocatalyst exhibited a high H₂ production rate of 8.7 mmol g^?1 h^?1, 26.5 and 2.3 times higher than for MMT/0.79MoS₂ and MMT/Ni_8.14Co_6.4, respectively. The enhanced photocatalytic performance was attributed to the loaded MoS₂ and NiCo nanoparticles, introducing active sites, increasing the light-absorbing capacity and accelerating the charge transfer from the Eosin Y dye owing to their appropriate Fermi level energy alignment. This work presents a cost-effective method combining the 2D sheets of MMT and MoS₂, and NiCo nanoparticles to form a quaternary photocatalytic system showing highly efficient hydrogen evolution from water without using noble metals.     

Zn‐Al hydrotalcite‐derived CoxZnyAlOz catalysts for hydrogen generation by auto‐thermal reforming of acetic acid

Auto‐thermal reforming (ATR) of acetic acid (HAc) is considered as a promising route for hydrogen generation from renewable resources, while oxidation, coking, and sintering need to be addressed for durable catalysts in ATR. In the current work, Zn‐Al hydrotalcite‐derived Co_xZn_yAlO_z catalysts were prepared by co‐precipitation and evaluated in a fixed‐bed tubular quartz continuous‐flow reactor. The Co_0.70Zn_3.30AlO_{5.5 ± δ} catalyst presented a HAc conversation near 100% and a stable hydrogen yield near 3.01 mol‐H₂/mol‐HAc. The characterization results of XRD, H₂‐TPR, BET, SEM, XPS, and TG indicated that the hydrotalcite structure was obtained via co‐precipitation method; over the hydrotalcite‐derived mixed oxides, (a) the specific surface area was increased with high dispersion of Co, (b) the phases of ZnO with spinel of ZnAl₂O₄,CoAl₂O₄, Co₃O₄, and ZnCo₂O₄ were beneficial to improve resistance to coking and oxidation, and (c) the relative stability of Co species over ZnO and spinel phases helps to suppress sintering. Meanwhile, ratio of O/C and temperatures near 0.28 and 650 °C, respectively, were also evaluated and proposed as optimized conditions for hydrogen generation, and the durable Co_0.70Zn_3.30AlO_{5.5 ± δ} catalyst produced a rate of 114.9 mmol‐H₂/s/g‐catalyst in a 15‐hour ATR test, showing promising potential for hydrogen generation.     

An infinite chain, {[Ni(tn)2]3[Fe(CN)4(μ-CN)2]2}n,a new catalyst for electrochemical-driven water splitting and photochemical-driven hydrogen evolution from water under blue light

A new catalyst for both water reduction and oxidation, based on an infinite chain, {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n, is formed by the reaction of NiCl₂, 1,3-propanediamine (tn) and K₃ [Fe(CN)₆]. {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n can electro-catalyze hydrogen evolution from a neutral aqueous buffer (pH 7.0) with a turnover frequency (TOF) of 1561 mol of hydrogen per mole of catalyst per hour (H₂/mol catalyst/h) at an overpotential (OP) of 837 mV {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n also can electro-catalyze O₂ production from water with a TOF of ～45 mol O₂ (mol cat)^?1s^?1 at an OP of 591 mV. Under blue light (λ = 469 nm), together with CdS nanorods (CdS NRs) as a photosensitizer, and ascorbic acid (H₂A) as a sacrificial electron donor, {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n can photo-catalyze hydrogen generation from an aqueous buffer (pH 4.0) with a turnover number (TON) of 11,450 mol H₂ per mole of catalyst (mol of H₂ (mol of cat)^?1) during 10 h irradiation. The average of apparent quantum yield (AQY) is as high as 40.96% during 10 h irradiation. Studies indicate that {[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n exists in two forms: a cyano-bridged chain ({[Ni(tn)₂]₃ [Fe(CN)₄ (μ-CN)₂]₂}_n) in solid, and a salt ([Ni(tn)₂]₃ [Fe(CN)₆]₂) in aqueous media; Catalytic reaction occurs on the nickel center of [Ni(tn)₂]²⁺, and the introduction of [Fe(CN)₆]^3- can improve the catalytic efficiency of [Ni(tn)₂]²⁺ for H₂ or O₂ generation. We hope these findings can afford a new method for the design of catalysts for both water reduction and oxidation.     

Enhanced photooxidative desulphurization of dibenzothiophene over fibrous silica tantalum: Influence of metal-disturbance electronic band structure

Fibrous silica tantalum (FSTa) and a series of metal oxides (silver oxide (AgO), copper oxide (CuO) and zinc oxide (ZnO)) supported on FSTa were prepared by hydrothermal and electrochemical method, respectively. X-ray diffraction, nitrogen adsorption-desorption analyses, Fourier-transform infrared, ultraviolet–visible diffuse reflectance spectroscopy, and photoluminescence were used to characterize the catalysts. The catalyst activity towards on photocatalytic oxidative desulfurization (PODS) of 100 mg L^?1 dibenzothiophene (DBT) was ranked in the following order: FSTa (3.03 × 10^?3 mM min^?1) > Zn/FSTa (2.65 × 10^?3 mM min^?1) > Cu/FSTa (2.33 × 10^?3 mM min^?1) > Ag/FSTa (1.46 × 10^?3 mM min^?1) under visible light irradiation for 150 min. This result demonstrated that the addition of metal oxides lowered the efficiency of PODS of DBT, most probably due to the unfit energy level of the photocatalyst towards redox potentials of superoxide anion radical (?O₂^?) and hydroxyl radical (?OH). Nevertheless, among the metal oxides loaded FSTa, Zn/FSTa showed a higher desulfurization rate, which likely due to its higher valence band energy (E_VB = 3.12 eV) than the redox potential of the H₂O/?OH (+2.4 eV vs. NHE), which allowed the production of ·OH for oxidation of DBT into dibenzothiophene sulfone (DBTO₂). In parallel, the hole at the VB of ZnO can also directly oxidize DBT to DBTO_2, as confirmed by the scavenger experiment. A kinetics study using Langmuir–Hinshelwood model illustrated that the photodegradation over Zn/FSTa followed the pseudo-first-order, and adsorption was the rate-limiting step. These findings are believed to aid in the rational design of high-performance photocatalysts for various photocatalytic applications, especially the removal of sulphur-containing compounds from fuel oils.     

Cocatalyst free nickel sulphide nanostructure for enhanced photocatalytic hydrogen evolution

Metal chalcogenides are highly active, inexpensive, and earth-abundant materials for photocatalytic hydrogen evolution. This work presents cocatalyst-free Nickel Sulphides (α and β phases) nanostructures for photocatalytic hydrogen generation. NiS nanostructures are synthesized by the solvothermal method by varying the water to ethanol ratio. The synthesized sample has shown an optical bandgap of 1.83 eV, which is favorable for H₂ generation. X-ray diffractometer (XRD) patterns confirm the formation of hexagonal and rhombohedral crystal structures with high phase purity for both NiS-α and NiS-β nanostructures. The multifaceted regular-shaped morphology with 50 nm sized particles was confirmed by high-resolution transmission electron microscopy (HR-TEM). The photocatalytic H₂ generation studies reveal that the NiS-α phase exhibited better H₂ generation activity of 13.413 m mol h^?1g^?1 than the NiS-β phase of 12.713 m mol h^?1g^?1 under UV–Vis light irradiation without any cocatalyst.