Visible light induced dye-sensitized photocatalytic hydrogen production over platinized TiO2 derived from decomposition of platinum complex precursor

Pt/TiO₂ derived from complete decomposition of the surface-anchored Pt(dcbpy)Cl₂ (dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) precursor (denoted as C-Pt/TiO₂) was prepared to serve as photocatalyst in visible light region. For dye-sensitized hydrogen production experiments, the photocatalyst was sensitized by Ru(2,2′-bipyridine-4,4′-dicarboxylic)₂(NCS)₂ (the N3 dye) and Ru(2,2′bipyridyl-4,4′-dicarboxylic) (4,4′- dinonyl-2,2′bipyridine) (NCS)₂ (the Z907 dye) to induce hydrogen evolution in the presence of sacrificial electron donor, triethanolamine (TEA). The hydrogen generation results showed that C-Pt/TiO₂ was found to be a much more active photocatalyst when compared to P-Pt/TiO₂, prepared by conventional method of photochemical deposition of H₂PtCl₆ (denoted as P-Pt/TiO₂). For further investigation, the photodegradation experiments in visible region were also confirmed the better photocatalytic activity of C-Pt/TiO₂. The enhanced catalytic activity is due to efficient interparticle electron transfer with the small-size and high-disperse platinum particles generated from photodeposition of Pt(dcbpy)Cl₂, which was verified by the transmission electron microscopy (TEM) measurement.     

Facile preparation of amorphous SrTiO3- crystalline PbS heterojunction for efficient photocatalytic hydrogen production

The amorphous SrTiO₃- crystalline PbS heterojunctions were prepared through different weight percentages of PbS (5 and 10%) to promote the photocatalytic water splitting. The amorphous SrTiO₃ exhibits the combination of the hexagonal cone and nanoparticle like morphology. Similarly, the crystalline PbS shows nanoparticle like morphology. The XRD and TEM results further confirm the amorphous SrTiO₃-crystalline PbS heterojunction formation. The EDS and XPS analysis confirm the presence of SrTiO₃–PbS heterojunction. The SrTiO₃–PbS heterojunction inhibits the self-trapped excitons recombination. The formation of amorphous-crystalline heterojunction suppress the electron transfer resistance which effectively reduces the charge carrier recombination. The SrTiO₃–PbS (5%) shows efficient photocatalytic hydrogen production of 5.9 mmol g^?1h^?1 under ultraviolet irradiation.     

Harnessing of low-energy IR photons via oxygen-vacancies in SrTiO3 nanocrystals for photocatalytic hydrogen production

The surface-oxygen vacancies were generated to enhance the near-IR light response of the SrTiO₃ photocatalyst by heating SrTiO₃ in a highly reducing environment. The UV–visible diffuse reflectance spectra of SrTiO₃-Ov revealed strong absorption between 400 and 800 nm, while IPCE response was extended beyond 800 nm, confirming the near-IR light response of SrTiO₃-Ov. The hydrogen production rates for SrTiO₃-Ov at pH 3.0 under full solar spectrum, visible and IR radiation were 100, 25 and 10 μlg⁻¹h⁻¹, respectively. The respective normalized hydrogen with respect to light intensity were found to be 100, 50 and 33 μlg⁻¹h⁻¹ while hydrogen production of pristine SrTiO₃ was less than 2 μlg⁻¹h⁻¹ under full solar spectrum. The mid-gap O_v and Ti³⁺ states in SrTiO₃-Ov are key factors in the origin of the near-IR responses of the catalyst and the feasibility of using low-photonic-energy IR light to produce hydrogen by water splitting was demonstrated.     

Nickel oxide/Au porous nanobelts: Synthesis and visible light-driven photocatalytic hydrogen production

Nickel oxide/Au porous nanobelts were synthesized by hydrolysis of nickel (II) sulfate in the presence of Au nanoparticles under hydrothermal condition and subsequent calcination of Ni(OH)₂/Au precursor in air. XPS measurement indicated the existence of both NiO and Ni₂O₃ in nickel oxide/Au porous nanobelts. Heterojunctions between NiO and Ni₂O₃, as well as between NiO and Au, were observed in HRTEM images. Under visible light irradiation (λ > 420 nm), nickel oxide/Au porous nanobelts effectively produced hydrogen from water in the presence of Na₂S and Na₂SO₃ as sacrificial electron donor. The highest rate of hydrogen production over nickel oxide/Au porous nanobelt was 38.5 times higher than that of commercial NiO loaded with the same amount of Au. The photoluminescence spectra and transient photocurrent responses of nickel oxide/Au nanobelts reveal that the improved photocatalytic activity is due to the increased electron–hole separation at NiONi₂O₃ and NiOAu interfaces. This work shows that low-cost nickel oxide could be used as visible light-active photocatalyst for hydrogen production.     

Photocatalytic hydrogen production using bench-scale trapezoidal photocatalytic reactor

Hydrogen is the future fuel and energy carrier, which has numerous applications. During combustion, produces only water vapour instead of greenhouse gas emissions. Photocatalytic production of hydrogen as a clean fuel from sulphide wastewater arises as a necessary option that must be considered. Here we report the performance of CNT added CdZnS/Fe₂O₃ for hydrogen recovery from highly toxic sulphide containing wastewater. The prepared photocatalysts were characterised for XRD (structure), UV-DRS (band gap), HRTEM (particle size), XPS (binding energy), SEM (morphology) and ICP (elemental composition). The photocatalytic hydrogen recovery was performed using novel trapezoidal photocatalytic reactor. The synthesized novel CNT - CdZnS/Fe₂O₃ nano-photocatalyst has highest production of hydrogen (2679 μmol/h) than plain CdZnS/Fe₂O₃ (2009 μmol/h).The feasibility studies were conducted to optimize the operating variables viz., S^2- (sulphide ion) concentrations, SO₃^2- (sulphite ion) concentrations, catalyst amount, light irradiation and volume of wastewater. Reusability studies under natural solar irradiation were performed and the CNT deposited CdZnS/Fe₂O₃ photocatalyst was found to be stable upto seven runs.     

Visible light-driven photothermal Au/Ag/TiO2 trihybrid plasmonic nanomaterial for synthetic fuel production

In the present article, a new numerical investigation is conducted to quantify the fluidic flow-photothermal performance of a trihybrid nano-catalyst for biomethane reforming inside a 1 μm micro-reactor on gold-silver nanoparticles coated on titanium oxide (TiO₂). The model generates a two-way coupling between heat, mass, fluid flow and electromagnetic profiles to simulate the plasmonic effect for the plasmonic photocatalyst in a micro-boundary layer adjacent to the catalyst. The effect of light wavelength on operating parameters and system performance was investigated and discussed. This included chemical conversion, the lower heating value of the syngas, mole fractions of species in the gaseous product, and the spatiotemporal velocity profiles. It was found that light absorptance by the nanoparticles is highest when visible light wavelength within 570 nm < λ < 590 nm is used to stimulate the plasmonic nanostructure. Also, the chemical conversion reached 81% at an exposure time of 1 μs of visible light. At λ = 570 nm, the produced syngas had a lower heating value of 311 kJ/mol and syngas quality of 0.16, which is suitable for ethanol production. Also, a maximum temperature elevation of 998 K was achieved which is above the minimum temperature required for reforming methane (823 K). The spatiotemporal velocity and chemical conversion profiles across the micro-reactor showed that at exposure times > 5 μs, both profiles become fully developed resulting in the suppression of chemical conversion.     

Performance of gas-phase photocatalytic reactors on hydrogen production

Three types of high-performance photocatalytic reactors were developed for gas-phase photocatalytic hydrogen (H₂) production from hydrogen sulphide (H₂S) and effective photocatalytic decomposition of gaseous H₂S at a very low concentration is investigated. In this paper, three lab-scale photocatalytic reactors viz., packed bed photocatalytic reactor, catalyst coated fixed bed photocatalytic reactor and catalyst dispersed photocatalytic reactors were developed to study the performance of reactors on hydrogen production. The novel photocatalyst (CdS + ZnS)/Fe₂O₃ and the optimized catalyst dosage, H₂S gas flow rate, pollutant concentration, light irradiations were used. The experimental result indicates that packed bed photocatalytic reactor can effectively splits the H₂S into hydrogen (i.e. 98%) and rapidly decompose H₂S toward zero concentration than the other two reactors. Hence the bench-scale photocatalytic reactor was fabricated in packed bed reactor and the maximum hydrogen conversion achieved from hydrogen sulphide was found to be 98%.     

Enhanced photocatalytic performance of NiFe2O4 nanoparticle spinel for hydrogen production

The spinel NiFe₂O₄, prepared from nitrates precursors, was characterized by thermal analyses, X-Ray Diffraction, UV-Vis diffuse reflectance, Scanning electron microscopy, X-Ray Fluorescence spectrometry, X-ray photoelectron spectroscopy and photo-electrochemistry measurements. The X-ray diffrcation analysis of the powder indicates a cubic phase with a lattice constant of 8.327(8) Å and crystallite size of 19 nm. The X-Ray Fluorescence spectrometry indicates a stoichiometry, very close to NiFe₂O₄ catalyst calcined at 900 °C The X-ray photoelectron spectroscopy analysis confirmed the valences and crystallographic sites of the transition elements. The direct optical gap of NiFe₂O₄ (1.78 eV), due to the crystal field splitting of the 3d orbital in the octahedral site, is well suited for the solar spectrum and attractive for photo-electrochemical H₂ production. The flat band potential (E_fb = 0.47 V_SCE) was obtained from the capacitance-potential (C^?2 - E) characteristic in NaOH (0.1 M) electrolyte. A conduction band of ?1.11 V_SCE, more cathodic than the H₂ level (?0.8 V_SCE), enabled the use of NiFe₂O₄ for the water reduction into hydrogen. The H₂ evolution rate of 46.5 μmol g^?1 min^?1 was obtained under optimal conditions (1 mg of catalyst/mL, NaOH and 50 °C) in the presence of SO₃^2? (10^?3 M) as hole scavenger under visible light flux of 23 mW cm^?2. A deactivation effect of only 1% was obtained.     

Cl-doped carbon nitride nanostrips for remarkably improving visible-light photocatalytic hydrogen production

Visible-light-driven photocatalysts for hydrogen production have been made great progress in recent years, there yet remain grand spaces to be improved further for implementing practical feasibility. We herein report a chlorine doped carbon nitride (Cl-p-C₃N₄) with ultrathin nanostrips morphology, which displays excellent photocatalytic hydrogen generation performance (5976 μmol h⁻¹ g⁻¹, 16.5 times higher than that of bulk C₃N₄) under visible light irradiation, with an apparent quantum yield of 8.91% at 420 nm. Experimental results and DFT calculations show that the ultrathin Cl-p-C₃N₄ nanostrips with heteroatom doping are greatly conducive to reduce the band gap, increase the surface area, and promote the separation efficiency of the photogenerated charge carrier, leading to the improvement of the charge carrier migration to the material surface or co-catalyst during the photocatalytic reaction. This work sheds light on the effective strategy to construct excellent photocatalyst by reasonably regulating the band structure and morphology.     

Enhanced photocatalytic performance of CdO-WO3 composite for hydrogen production

Considering the renewability and cleanness of hydrogen generation system, the photocatalytic H₂ evolution through water splitting with assistance of Earth abundant co-catalysts has become a scientific hotspot. Efficient and visible light driven CdO-WO₃ composites with versatile properties have been fabricated through hydrothermal approach for H₂ evolution. X-ray diffractometer, scanning electron microscope, UV-Vis absorption spectroscopy, photoluminescence emission spectroscopy and photocatalytic activity test were employed to investigate different properties like crystallography, morphology, optical and photocatalytic properties. The effect of CdO concentration on the grain size indicated the reduction of bad gap energy of the WO₃. The concentration of CdO nanoparticles in WO₃ directly effect on the morphology of the particles that are in the form of nanorods. The atoms of CdO makes the WO₃ nanoparticles more effective and efficient up to 4% of CdO but when coupling amount increases then the CdO-WO₃ nanoparticles exhibited less photocatalytic performance to evolve H₂ energy. Results shown that 4% content in WO₃ had exceptional photocatalytic activity for water splitting when compared to other samples. The improved hydrogen production was allied with formation of active Cd species during the photocatalysis process, which has the ability to promote the interfacial charge-separation and concurrently may cause to reduce the over potential of hydrogen evolution, thus boosting the photocatalytic activity over the hybrid sample. The improved photocatalytic activity of composites could be accredited to extended absorption region of visible light, efficient separation of charge carrier's and suppress recombination of electron-hole pairs. The current work not only shows a prospect for the utilization of low cost CdO as a co-catalyst in photocatalytic hydrogen generation but also shows a substantial enhancement in H₂ evolution, first time, using CdO-WO₃ hybrid photocatalyst.     

Hydrogen production performance of active Ce/N co-doped SrTiO3 for photocatalytic water splitting

An efficient visible light responsive photocatalyst Ce/N co-doped SrTiO₃ was prepared via a hydrothermal method for hydrogen production. The phase structure, morphology, contents and valence states of the dopant elements, specific surface area, optical properties, and photocatalytic activity of the samples were characterized. The transient photocurrent response and electrochemical impedance spectra under visible light illumination indicated that Ce/N co-doped SrTiO₃ possessed a more intense photo-current response and lower surface resistance than N–SrTiO₃ and Ce–SrTiO₃. The water splitting rate of Ce/N-co-doped SrTiO₃ is 4.28 mmol/g/h, which is 84.49 times higher than that of pure SrTiO₃. The enhanced photocatalytic performance is due to the narrowing of the band gap of SrTiO₃ by Ce ion and N ion impurities.     

Triazine-free polyimide for photocatalytic hydrogen production

Polyimide (PI) has received considerable attention as a promising donor-acceptor polymer for photocatalytic hydrogen production, yet the previous studies entirely focused on the exploration of triazine-based PI. Herein, we report for the first time triazine-free PI for photocatalytic hydrogen evolution. The triazine-free PI was synthesized by thermal condensation of urea and pyromellitic dianhydride. The resultant PI photocatalyst yielded a stable hydrogen evolution activity and an appreciable photocurrent response. This work manifests that triazine is not an indispensable unit for the photocatalytic hydrogen evolution activity of PI, which expands the chemical library of PI photocatalysts and opens up new opportunities for designing efficient polymeric photocatalysts.     

Thermodynamic analysis of solar-based photocatalytic hydrogen sulphide dissociation for hydrogen production

The dissociation of gaseous hydrogen sulphide (H₂S) into its components is an energy intensive process. The process is studied in this paper with respect to the thermodynamic limits. The band gap of the catalyst and the nature of the solar radiation limit the proportion of incoming radiation that may be used for the reaction. The intensity of the incoming radiation and the reactor temperature are varied and the performance is studied. The exergy efficiency is determined as a function of the quantum efficiency of the photochemical process, and the catalyst band gap. It is shown that an optimum case exergy efficiency of up to 28% can be achieved for the process. With the current status of technology, an exergy efficiency value in the region of 0.4–1% is calculated, with a short-term improvement potential of up to 10%. Hydrogen sulfide has high energy content, but is not widely used due to its impact on environmental pollution. The proposed process in this paper is attractive as it allows that energy to be utilized, while degrading the highly toxic gas into less harmful products.     

High photocatalytic performance for hydrogen production under visible light on the hetero-junction Pani-ZnO nanoparticles

The present work is devoted to the preparation of the hetero-junction of Polyaniline-Zinc oxide nanoparticles (Pani-ZnO_Nps) and its photo-electrochemistry to assess its photocatalytic properties for the water reduction into hydrogen. The semiconducting characterization of the Pani-ZnO_Nps synthetized by in situ chemical oxidative polymerization was studied for the hydrogen evolution reaction (HER) upon visible light illumination. The forbidden bands E_g (= 1.64 eV, Pani) and (3.20 eV, ZnO_NPS) were extracted from the UV–Visible diffuse reflectance data. The Electrochemical Impedance Spectroscopy (EIS) showed the predominance of the intrinsic material with a bulk impedance of 71 kΩ cm². The semi conductivity was demonstrated by the capacitance measurements with flat band potentials (E_fb = - 0.7 and - 0.3 V_SCE) and carriers concentrations (N_A = 1.77 × 10¹⁹ and N_D = 4.80 × 10²⁰ cm^?3) respectively for Pani and ZnO_NPS. The energetic diagram of the hetero-junction Pani-ZnO_Nps predicts electrons injection from Pani to ZnO_NPS in KOH electrolyte. An improvement of 78% for the evolved hydrogen was obtained, compared to Pani alone; a liberation rate of 61.16 μmol g^?1 min^?1 and a quantum yield of 1.15% were obtained. More interestingly, the photoactivity was fully restored after three consecutive cycles with a zero-deactivation effect, indicating clearly the reusability of the catalyst over several cycles.     

Cobalt oxide on mesoporous carbon nitride for improved photocatalytic hydrogen production under visible light irradiation

Cobalt oxide (Co₃O₄) nanoparticles decorated on mesoporous carbon nitride (Co₃O₄/MCN) nanocomposites for photocatalytic hydrogen evolution were investigated in this work. MCN was prepared using 3-amino-1,2,4-triazole, high nitrogen content, as a single molecular carbon and nitrogen precursor and SiO₂ nanoparticles as the hard template. Complementary characterization techniques were employed to understand the textural and chemical properties of the nanocomposites. The bare MCN showed high photocatalytic activity under visible light irradiation without using any co-catalyst. The photocatalytic activity of Co₃O₄/MCN with a Co₃O₄ mass content of 5 wt % presented two times higher than the bare MCN, which is attributed to the enhanced visible-light harvesting and more efficient charge separation. Mechanistic study shows lower electron-hole recombination rate, higher charge separation efficiency occurs after the formation of p-n type heterojunction.     

CuO@NiO core-shell nanoparticles decorated anatase TiO2 nanospheres for enhanced photocatalytic hydrogen production

Core-shell structured co-catalyst has been created much attention in photocatalytic hydrogen production due to their efficient electron-hole pair separation, suppression of surface back reaction and long term stability. Here, we report the preparation of CuO@NiO hierarchical nanostructures as a co-catalyst deposited on TiO₂ nanospheres for enhanced photocatalytic hydrogen generation. The formation of ultrathin NiO shell over the CuO core was confirmed by TEM analysis. Fabricated core-shell nanostructured CuO@NiO over TiO₂ nanospheres was studied for hydrogen evolution under the direct solar light and it showed a high rate of H₂ production of 26.1 mmol. h⁻¹. g⁻¹_cat. It was scrutinized that the rate of hydrogen production was improved with shell thickness and co-catalyst loading. Systematic investigation on CuO@NiO co-catalyst loading, pH of the medium and glycerol concentration for augmented H₂ production. The recorded rate of hydrogen production is almost six folds greater than that of pristine TiO₂. In the view of largescale synthesis for alternative energy storage applications, the composited photocatalyst was made of by simple mixing method, which could be scaled up without any loss in photocatalytic activity. Further, the stability test of photocatalyst for continuous use found that 82% of initial photocatalytic activity is retained even after three days.     

Artificial water-soluble systems inspired by [FeFe]-hydrogenases for electro- and photocatalytic hydrogen production

[FeFe]-hydrogenases efficiently catalyze the hydrogen evolution reactions (HERs) at rates of up to 10⁴ s⁻¹ with low overpotentials in aqueous media. Although the small-molecule diiron mimetics of the active site of [FeFe]-hydrogenases have been studied for years, most of the synthetic models mediate the catalysis in organic solvents, seriously limiting the application of bioinspired catalytic systems in large-scale H₂ production. Herein, we systematically present the state-of-the-art artificial water-soluble systems inspired by [FeFe]-hydrogenases for potentially electro- and photocatalytic HERs utilizing either electrical or solar energy inputs. The engineering motifs and catalytic properties of these water-soluble mimetic systems have been surveyed and discussed. We hope the present review will shed light on some helpful aspects for designing artificial assembling catalysts for HERs in aqueous milieu and provide mechanistic insights into a broad array of natural oxidoreductases.     

Ternary Ni2P/reduced graphene oxide/g-C3N4 nanotubes for visible light-driven photocatalytic H2 production

Developing low cost co-catalysts is crucial for both fundamental research and practical application of g-C₃N₄. In this work, we prepared ternary Ni₂P/rGO/g-C₃N₄ nanotubes with different Ni₂P contents for visible-light-driven photocatalytic H₂ generation from triethanolamine aqueous solution. The optimal Ni₂P/rGO/g-C₃N₄ produced H₂ at a rate of 2921.9 μmol h⁻¹ g⁻¹, which is about 35, 16 and 9 times as large as that of g-C₃N₄, binary rGO/g-C₃N₄ and Ni₂P/g-C₃N₄, respectively. The apparent quantum efficiency of optimal Ni₂P/rGO/g-C₃N₄ was 5.6% at λ = 420 nm. We believe that the improved photocatalytic performance of Ni₂P/rGO/g-C₃N₄ originates from the synergistic effect of rGO as electron transfer medium and Ni₂P as reaction site, which is supported by photoelectrochemical and photoluminescence measurements. Cyclic experiment demonstrated an excellent stability of Ni₂P/rGO/g-C₃N₄. Moreover, we further studied the effect of other nickel-based compounds by replacing Ni₂P with NiS, Ni₃C, and Ni₃N, respectively. The order of the H₂-generation rate is Ni₂P/rGO/CNNT > NiS/rGO/CNNT > Ni₃C/rGO/CNNT > Ni₃N/rGO/CNNT, which could be reasonably explained based on Mott–Schottky plots. Our work reveals that Ni₂P can be used as a promising cocatalyst for photocatalytic H₂ evolution.     

Synthesis of g-C3N4/WO3-carbon microsphere composites for photocatalytic hydrogen production

In this paper, a g-C₃N₄/WO₃-carbon microsphere composite-based photocatalyst was successfully prepared by a one-pot thermal synthesis method for sunlight driven decomposition of water to produce hydrogen. The results show that the g-C₃N₄/WO₃-carbon microspheres had better photocatalytic properties and stability. Under visible light and sunlight irradiation, the hydrogen production efficiency of the photocatalytic decomposition of water was 107.75 times and 70.54 times greater than that of pure g-C₃N₄, respectively. The experimental and characterization results show that g-C₃N₄ and WO₃ formed a Z-scheme heterojunction on the surface of the g-C₃N₄/WO₃-carbon microsphere composite-based photocatalyst. Carbon microspheres modified on g-C₃N₄ nanosheets and WO₃ had good conductivity and promoted the transfer of photogenerated electrons in g-C₃N₄ nanosheets. The addition of carbon microspheres increased the specific surface area of the composite photocatalyst. The g-C₃N₄/WO₃-carbon microsphere composite-based photocatalyst showed strong adaptability to the fluctuating light intensity, providing feasibility for industrialized mass production.     

Prickly Ni3S2 nanowires modified CdS nanoparticles for highly enhanced visible-light photocatalytic H2 production

The photocatalytic water splitting strategy is one of the most promising ways to achieve clean and renewable solar-to-hydrogen energy conversion. In this study, a highly enhanced photocatalytic H₂ production system has been achieved, using CdS nanoparticles (NPs) decorated on prickly Ni₃S₂ nanowires (NWs) as the light-driven photocatalyst. The photocatalyst was prepared by a co-precipitated method in which spiky Ni NWs were employed as starting material for prickly Ni₃S₂ NWs. Characterization analysis (XRD, TEM, XPS, etc.) show the high purity of Ni₃S₂/CdS hybrid structures and the well deposition of CdS NPs on prickly Ni₃S₂ NWs. Besides, the as synthesized Ni₃S₂/CdS photocatalyst exhibit reduced photoluminescence peak intensity, which means the Ni₃S₂ NWs functions as electron collector and transporter to quench the photoluminescence of CdS. This prickly Ni₃S₂/CdS nanocomposite demonstrates a 70 times higher H₂ production rate than that of pure CdS and a quantum efficiency of 12.3% at the wavelength of 400 nm in the absence of noble metals. This enhanced H₂ production activity is better than the one of CdS loaded with 0.5 wt% Pt. Our findings highlight the potential application of Ni₃S₂/CdS hybrid structures for visible light photocatalytic hydrogen yielding in the energy conversion field.