A nanoreactor based on SrTiO3 coupled TiO2 nanotubes confined Au nanoparticles for photocatalytic hydrogen evolution

A TiO₂ nanotube-based nanoreactor was designed and fabricated by facile two steps synthesis: firstly, hydrothermal synthesized SrTiO₃ was deposited on TiO₂ nanotubes (TiO₂NTs). Secondly, the Au nanoparticles (NPs) were encapsulated inside the TiO₂NTs followed by vacuum-assisted impregnation. The as-synthesized composites were characterized using Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and Ultraviolet–visible absorption spectroscopy (UV–vis). The photocatalytic performance was evaluated by the hydrogen evolution reaction. The results revealed that the SrTiO₃ modified TiO₂NTs confined Au NPs (STO-TiO₂NTs@Au) achieved an enhanced hydrogen evolution rate at 7200 μmol h⁻¹ g⁻¹, which was 2.2 times higher than that of bald TiO₂NTs@Au at 3300 μmol h⁻¹ g⁻¹. The improved photocatalytic activity could be attributed to the synergistic effect of the electron-donating of SrTiO₃ and TiO₂NTs confinement. The as-designed nanoreactor structure provides an example of efficient carriers' separation photocatalyst.     

Deposition of CdS and Au nanoparticles on TiO2(B) spheres towards superior photocatalytic performance

TiO₂(B)/CdS/Au and TiO₂(B)/Au/CdS heterostructures were synthesized to investigate the effect of the selected deposition of CdS and Au nanoparticles (NPs) on H₂ generation. TiO₂(B) spheres (phase B) consisted of nanosheets were synthesized via a hydrothermal reaction. The deposition of CdS and Au NPs were carried out using wet-chemical method and a reduction reaction, respectively. The size and amount of Au and CdS NPs were adjusted to optimize the resulting properties and discuss the change of band gap. Two kinds of heterogeneous revealed different photocatalytic hydrogen generation which indicated the position of Au NPs affect the transfer of photogenerated carriers. The hydrogen production rate of TiO₂(B)/CdS/Au heterostructures reached up to 12100 μmol g⁻¹ h⁻¹, which is about 3.8 times of that of pure TiO₂(B) spheres. This is ascribed to the structure of heterostructures. CdS NPs increase the separation of photogenerated electrons and Au NPs accelerated the transfer of the electrons. The result provided a utilizable strategy for efficient photocatalysis H₂ generation.     

Ionothermal synthesis of TiO2 nanoparticles for enhanced photocatalytic H2 generation

Photocatalytic hydrogen generation is one of the most promising solutions to convert light energy into green chemical energy. In the present work, methoxy ethyl methyl imidazolium methyl sulphonate ionic liquid is used for the synthesis of i-TiO₂ nanoparticles via ionothermal method at 120 °C. The obtained products were characterized by various spectroscopic techniques like XRD, FTIR, Raman, UV–visible, DRS, TEM and TG-DSC analysis. XRD pattern confirmed the anatase phase with minor rutile phase having average crystallite size of 5 nm. From the FTIR spectrum, the band appeared at ～547 cm^?1 confirmed the Ti–O–Ti stretching and also few bands of ionic liquid. UV–vis spectrum clearly reveals the blue shift due to size effect of TiO₂. The spherical surface structure and particle size (15–30 nm) have been studied in detail using TEM images. Finally, the practical applicability of the as synthesized i-TiO₂ nanoparticles is shown by using it as a photocatalyst towards the generation of H₂ through water splitting reaction and it is found to be 462 μmol h^?1g^?1.     

Oxygen vacancies mediated in-situ growth of noble-metal (Ag,Au, Pt) nanoparticles on 3D TiO2 hierarchical spheres for efficient photocatalytic hydrogen evolution from water splitting

Defect engineering is effective to extend the light absorption range of TiO₂. However, the oxygen vacancy defects in TiO₂ may serve as recombination centers, hampering the separation and transfer of photo-generated charges. Here, we present a strategy of in-situ depositing noble-metal (M = Ag, Au or Pt) nanoparticles (NPs) on defective 3D TiO₂ hierarchical spheres (THS) with large surface area through the redox reaction between metal ions in solution and the electrons trapped at oxygen vacancies in THS. The oxygen vacancies at the THS surface are consumed, resulting in direct contact between TiO₂ and noble-metal NPs, while the other oxygen vacancies in the bulk are retained to promote visible light absorption. The noble-metal NPs with well-controlled size and distribution throughout the porous hierarchical structure not only facilitate the generation of electron-hole pairs in THS due to the effect of surface plasmon-induced resonance energy transfer (SPRET) from noble-metal NPs to TiO₂, but also expediate the electron transfer from TiO₂ to noble-metal NPs due to the Schottky junction at the TiO₂/M interface. Therefore, THS-M shows improved photocatalytic performance in water splitting compared to THS. The optimum performance is achieved on THS-Pt (13.16 mmol h⁻¹g⁻¹) under full-spectrum (UV–Vis) irradiation but on THS-Au (1.49 mmol h⁻¹g⁻¹) under visible-light irradiation. The underlying mechanisms are proposed from the surface plasmon resonance of noble-metal NPs as well as the Schottky junction at the TiO₂/M interface.     

TiO2 hollow spheres with separated Au and RuO2 co-catalysts for efficient photocatalytic water splitting

Hollow mesoporous TiO₂ photocatalysts with dual co-catalysts, located at specific positions, were prepared using Polystyrene (PS) as sacrificial templates. Au nanoparticles (NPs) were in situ loaded on the surface of PS spheres and the resulting nanocomposites were coated with TiO₂ shell using sol-gel reaction. The outer surface of core-shell spheres was impregnated with Ru and the subsequent calcination produced hollow anatase spheres with Au and RuO₂ dual co-catalysts. The hollow mesoporous spheres of Au@TiO₂@RuO₂ were proved by various techniques such as TEM, EDX, and SEM images. Photocatalysts were applied for hydrogen generation from water splitting and that with dual co-catalysts showed efficient catalytic activity under simulated solar light. The catalytic activity of photocatalysts with both oxidation and reduction co-catalysts (Au@TiO₂@RuO₂) showed hydrogen evolution (3165 μmol g⁻¹) almost two times more than that Au@TiO₂ and TiO₂@RuO₂ with single co-catalysts. And the hydrogen evolved is more than three times as compared to TiO₂ (935 μmol g⁻¹) without any co-catalyst. Hollow mesoporous morphology with different co-catalysts on inner and outer surfaces is believed to enhance photocatalytic activity which is due to better separation of photo-generated charges.     

Structural properties of CuO/TiO2 nanorod in relation to their catalytic activity for simultaneous hydrogen production under solar light

CuO was introduced into porous TiO₂ nanorod through impregnation method. Before the impregnation step, TiO₂ nanorod was hydrothermally synthesized from TiO₂ powder in aqueous NaOH solution and followed by thermal treatment at 450 °C. The structures and properties of impregnated samples were characterized using various techniques, including XRD, BET, XAS, TEM, and UV-DRS. Their photocatalytic performance on simultaneous hydrogen production from pure water and aqueous methanol solution was also investigated under solar light. It was found that CuO/TiO₂ nanorod possessed a high surface area, good photocatalytic property and excellent hydrogen generation activity. Incorporation of Cu ions into the lattice framework of anatase TiO₂ nanorod enhanced the efficiency in visible region at 438–730 nm. Moreover, the XAS results showed that some Cu ions formed solid solution in the TiO₂ nanorod (Cu_xT_1−xO₂). However, the excessive incorporation of Cu ions did not improve any ability of anatase TiO₂ nanorod for production of hydrogen from pure water splitting. This could be due to the excessive CuO agglomeration at outside-pores which blocked the sensitization of TiO₂ nanorod. Only 1% Cu/TiO₂ nanorod was found to be a remarkable and an efficient photocatalyst for hydrogen production under solar light from both pure water and sacrificial methanol splitting. The highest rate of hydrogen production of 139.03 μmol h⁻¹ g_catalyst⁻¹ was found in sacrificial methanol which was 3.24% higher than in pure water.     

La-modified TiO2/carbon nanotubes assembly nanocomposite for efficient photocatalytic hydrogen evolution from glycerol-water mixture

Lanthanum (La) modified TiO₂ embedded over carbon nanotubes (CNTs) to develop nanocomposite for enhanced photocatalytic hydrogen evolution from glycerol-water mixture has been investigated. The samples, synthesized by sol-gel assisted hydrothermal method, were characterized by XRD, FESEM, HRTEM, FTIR, BET, UV–Visible, Raman and PL spectroscopy. La/TiO₂ anchored CNTs has larger surface area with uniform distribution of La³⁺ ions. The performance of hybrid assembly was evaluated in a continuous flow slurry photoreactor system under UV–visible light irradiations. The highest H₂ evolution rate of 17265 ppm g-cat⁻¹ h⁻¹ was obtained over 5% La-5% CNTs/TiO₂ NRs, 1.14 folds the amount produced over 5% La-5% CNTs/TiO₂ NPs, 1.53 time than 5% La/TiO₂ and 4.10 folds than using pure TiO₂ NPs. This significant improvement in the photo-activity was obviously due to synergistic effect between La and CNTs, larger BET surface area, cleavage of glycerol by La, appropriate band structure, and hindered charges recombination rate. Among the sacrificial reagents, highest H₂ evolution was obtained using glycerol due to the presence of α-hydrogen atoms attached to carbon atoms. A correlation between BET surface area and photonic flux in terms of photocatalytic H₂ production rate was established to understand the performance of hybrid nanostructures. It was observed that BET surface area and photo-flux utilization for the generation of charge carriers with their efficient separation has significant contribution towards improved H₂ production rate. More interestingly, catalyst persisted prolonged stability with a steady H₂ production in cyclic runs. This study provides promising pathway for constructing composite of La/TiO₂ coupled CNTs for efficient H₂ production under visible light.     

Hydrogen production from sulphide wastewater using Ce3+–TiO2 photocatalysis

Cerium (Ce³⁺) doped TiO₂ powder was synthesized by a sol-gel method and characterized by Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), UV–Vis Diffuse Reflectance Spectroscopy (UV-DRS), Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The Ce³⁺ doping strongly reduced the band gap of the TiO₂ from 3.2 eV (UV) to 2.7 eV (visible region). The photocatalytic activity of Ce³⁺ doped TiO₂ catalysts was evaluated by hydrogen production from sulphide wastewater under visible light illumination. The photocatalytic production of H₂ was studied in a batch recycle tubular photocatalytic reactor. The results show that 0.4% Ce³⁺–TiO₂ suspended in 500 mL of simulated sulphide wastewater irradiated at 150 W visible lamp produced maximum H₂ of 6789 μmol h^?1. It was noticed that the Ce³⁺ doped TiO₂ performs well than Nano TiO₂ and P25 TiO₂ photocatalysts.     

Exploration of 1D-2D LaFeO3/RGO S-scheme heterojunction for photocatalytic water splitting

Sustainable energy innovation is spearheading the way to achieve decarbonisation through commercially viable and highly competitive renewable technologies for green hydrogen. Photocatalytic water splitting has received global attention, as it promotes the direct conversion of solar energy to chemical energy and hydrogen production. Lanthanum orthoferrite (LaFeO₃) has been selected due to its narrow bandgap perovskite-oxides (ABO₃) type nature, low cost and high chemical stability but it is limited with fast charge recombination. To circumvent its constraint of fast charge recombination, an efficient graphene-based nanocomposite has been prepared by employing reduced graphene oxide (RGO) nanosheets as charge separators for visible light driven photocatalytic water splitting. Here, we present a thorough physical and spectroscopic characterization of the Lanthanum orthoferrite/Reduced Graphene oxide (LaFeO₃/RGO) nanocomposites, and investigate its photocatalytic and photoelectrochemical performance. The photocurrent density of the nanocomposites demonstrated ∼21 times higher in comparison to pure LaFeO₃. The as-prepared nanocomposites have been successfully used as photocatalysts for H₂ generation through water reduction under visible light. A significant enhancement in H₂ generation has been recorded for nanocomposites (∼82 mmol g⁻¹ h⁻¹) as compared to that of bare LaFeO₃ (∼9 mmol g⁻¹ h⁻¹) which is among the highest values obtained using noble-metal-free graphene-based photocatalytic nanocomposites. This work offers a facile approach for fabricating highly efficient 1D-2D heterostructure for photocatalysis application.     

Electrospun Pt/TiO2 hybrid nanofibers for visible-light-driven H2 evolution

One-dimensional (1D) Pt/TiO₂ hybrid nanofibers (HNFs) with different concentrations of Pt were fabricated by a facile two-step synthesis route combining an electrospinning technique and calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) results showed that the Pt nanoparticles (NPs) with the size of 5–10 nm were well dispersed in the TiO₂ nanofibers (NFs). Further investigations from the UV–Vis diffuse reflectance (DR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that some Pt ions were incorporated into the TiO₂ lattice as Pt⁴⁺ state, which contributed to the visible light absorption of TiO₂ NFs. Meanwhile, the Pt²⁺ ions existing on the surface of Pt NPs resulted in the formation of Pt–O–Ti bond at Pt NPs/TiO₂ NFs interfaces that might serve as an effective channel for improving the charge transfer. The as-electrospun Pt/TiO₂ HNFs exhibited remarkable activities for photocatalytic H₂ evolution under visible light irradiation in the presence of l-ascorbic acid as the sacrificial agent. In particular, the optimal HNFs containing 1.0 at% Pt showed the H₂ evolution rate of 2.91 μmol h⁻¹ and apparent quantum efficiency of 0.04% at 420 nm by using only 5 mg of photocatalysts. The higher photocatalytic activity could be ascribed to the appropriate amount of Pt ions doping and excellent electron-sink effect of Pt NPs co-catalysts.     

Photocatalytic hydrogen production over CuO and TiO2 nanoparticles mixture

Cheap and efficient photocatalysts were fabricated by simply mixing TiO₂ nanoparticles (NPs) and CuO NPs. The two NPs combined with each other to form TiO₂/CuO mixture in an aqueous solution due to the opposite surface charge. The TiO₂/CuO mixture exhibited photocatalytic hydrogen production rate of up to 8.23 mmol h⁻¹ g⁻¹ under Xe lamp irradiation when the weight ratio of P25 to CuO was optimized to 10. Although the conduction band edge position of CuO NPs is more positive than normal hydrogen electrode, the TiO₂/CuO mixture exhibited good photocatalytic hydrogen production performance because of the inter-particle charge transfer between the two NPs. The detailed mechanism of the photocatalytic hydrogen production is discussed. This mixing method does not require a complicated chemical process and allows mass production of the photocatalysts.     

Green synthesis of well dispersed TiO2/Pt nanoparticles photocatalysts and enhanced photocatalytic activity towards hydrogen production

Deposition of Pt NPs with preferred dispersion and morphologies on TiO₂ have been the focus of studies in photocatalytic and photoelectrochemical hydrogen production. Green synthesis of TiO₂/Pt NPs nanocomposites with narrow size distribution of Pt NPs still remain a challenge. Herein, we report that sucrose is highly efficient for the preparation of well-dispersed TiO₂/Pt NPs photocatalysts. Moreover, the sucrose could act as an electron donor, showing higher hydrogen production activity under simulated sunlight than pure water. The as-synthesized photocatalysts have been characterized by techniques of transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX), and diffuse reflectance spectroscopy (DRS). Compared with TiO₂/Pt NPs photocatalysts prepared through conventional photodeposition, the photocatalysts as prepared showed higher photocatalytic efficiency. Moreover, the catalyst could be reused easily without apparent degradation of their original photocatalytic activities. This approach presents a promising and low-cost strategy to improve the photocatalytic performance of TiO₂ from biomass.     

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.     

Photo-induced CO2 reduction by hydrogen for selective CO evolution in a dynamic monolith photoreactor loaded with Ag-modified TiO2 nanocatalyst

Ag-promoted TiO₂ nanoparticles immobilized over the cordierite monolithic support for dynamic and selective photo-reduction of CO₂ to CO by the use of hydrogen has been investigated. Ag-loaded TiO₂ NPs synthesized by a facile sol–gel method were coated over the monolith channels by dip-coating method. The samples were characterized by XRD, Raman, FTIR, SEM, TEM, XPS, N₂ adsorption–desorption, UV–Vis and PL spectroscopy. The photo-activity test of Ag-modified TiO₂ NPs was conducted for dynamic photocatalytic CO₂ reduction with H₂ as a reductant via a reverse water gas shift (RWGS) reaction in a cell type and monolith photo-reactors. Using 5 wt. % Ag/TO₂ NPs, CO₂ was energetically converted to CO with a yield rate 1335 μmole g-catal.^?1 h^?1, a 111 fold-higher than the amount of CO produced over the pure TiO₂ catalyst. More importantly, photo-activity of Ag/TiO₂ catalyst for CO evolution can be improved by 209 fold using monolith photo-reactor than the cell type reactor under the same operating conditions. This enactment was evidently due to the efficient light harvesting with larger illuminated surface area inside monolith micro-channels and efficient charges separation in the presence of Ag-metal. The reusability of Ag/TiO₂ NPs loaded over the monolithic support showed favorable recycling capability than the catalyst dispersed in a cell reactor. A possible reaction mechanism for this observation has been discussed in detail.     

The rational design of gCN/a-WOx/Pt heterostructured nanophotocatalysts for boosting the hydrogen generation from the hydrolysis of ammonia borane under visible light

In-situ generation of platinum nanoparticles (Pt NPs) supported on graphitic carbon nitride/amorphous tungsten oxide (gCN/a-WO_x) binary heterojunctions under white-light irradiation was performed during the hydrolysis of ammonia borane (HAB). The gCN/a-WO_x/Pt(IV) nanocomposites including different amount of W were prepared to study their comparative photocatalysis for the photocatalytic HAB. The yielded gCN/a-WO_x/Pt nanocatalysts provided a maximum turnover frequency (TOF) value of 419.2 mol H₂ mol Pt⁻¹ min⁻¹, which is higher than that of gCN/Pt nanocatalysts (287.7 mol H₂ mol Pt⁻¹ min⁻¹). Many advanced analytical techniques comprising ICP-MS, TEM, HAADF-STEM, XRD, XPS, EDX, and BET were used to determine the elemental composition, morphology, elemental distribution, crystal structure, chemical/oxidation state of the surface elements and the textural properties of the nanocatalysts. The characterization results support the formation of wrinkled paper-like amorphous phase WO_x (a-WO_x) materials in multiple oxidation states over the gCN nanosheets. The photophysical properties of gCN/a-WO_x nanocomposites were also analyzed by using UV–Vis DRS, PL, and TRES techniques to clarify the contribution of the heterojunction formation between gCN and a-WO_x semiconductors to the photocatalytic activity. Owing to the enhanced visible light absorption, suppressed charge recombination, and promoted charge carrier transfer, gCN/a-WO_x/Pt nanocatalysts boosted the hydrogen production from the HAB under white-light irradiation by providing 419.2 mol H₂ mol Pt⁻¹ min⁻¹ TOF, which is 4.8 times higher compared to the one obtained in dark. A plausible photocatalytic mechanism for the photocatalytic HAB reaction in the presence of gCN/a-WO_x/Pt nanocatalysts was suggested based on the results of performed scavenger experiments. The rate law and the activation parameters for the of gCN/a-WO_x/Pt catalyzed HAB were also reported along with kinetic studies. Additionally, a reusability test was performed to understand the stability of gCN/a-WO_x/Pt nanocatalysts in the HAB such that the significance of a-WO_x species in the enhancement of photocatalytic activity became more pronounced. This study reports for the first time that gCN/a-WO_x heterojunctions are favorable support materials for the in-situ generation of Pt NPs and promoting the photocatalytic activity of Pt NPs in the hydrogen generation from the HAB under white-light illumination.     

Self-doped Ti3+ mediated TiO2/In2O3/SWCNTs heterojunction composite under acidic/basic heat medium for boosting visible light induced H2 evolution

Well-designed Ti³⁺/In³⁺ mediated TiO₂/SWCNTs heterojunction composite for photocatalytic H₂ evolution under visible light has been investigated. The samples, fabricated through one-step sol-gel approach with controlled acidic/basic heat treatment environment, were characterized by XRD, Raman, FE-SEM, TEM, XPS, UV–Vis and PL techniques. The maximum H₂ of 1244 ppm h⁻¹ was evolved over In/SWCNTs/TiO₂, a 4.69, 1.54 and 1.53 times higher than using TiO₂, In/TiO₂ and SWCNTs/TiO₂ samples, respectively. This enhancement was due to faster charges separation and higher visible light absorption by synergistic effect of In/SWCNTs. Using catalyst prepared under basic (H₂) treatment, Ti³⁺ was successfully embedded into In⁺³@TiO₂@SWCNTs, exhibited H₂ production of 1446 ppm h⁻¹ which was 12.49% and 15.02% higher compared to catalysts prepared under CO₂ and N₂ atmospheres, respectively. Thus, surface defects like Ti³⁺ inhibits charges recombination and enables visible light responsive. The quantum yield over Ti³⁺/In³⁺ mediated TiO₂/SWCNTs composite was 0.251%, a 1.13 and 1.2 folds higher compared to CO₂ and N₂ atmospheres, respectively. Besides, excellent stability for H₂ generation was observed in cyclic runs. A possible mechanism is proposed to understand synergistic effects between Ti⁺³/In⁺³ in TiO₂/SWCNTs composite catalyst and has great potential as a green photocatalyst in environmental and energy applications.     

Preparation of direct Z-scheme Bi2WO6/TiO2 heterojunction by one-step solvothermal method and enhancement mechanism of photocatalytic H2 production

Direct Z-scheme Bi₂WO₆/TiO₂ heterojunction photocatalyst was prepared by one-step solvothermal method. The catalyst was characterized by XRD, TEM, XPS, UV–Vis DRS, photoluminescence spectroscopy and photoelectrochemical studies. The photocatalytic hydrogen production experiments show that Bi₂WO₆ did not generate H₂ and the H₂-production rate of TiO₂ is only 0.1 mmol⋅g⁻¹h⁻¹. The hydrogen production rate of the Bi₂WO₆/TiO₂ heterojunction photocatalyst reaches 12.9 mmol⋅g⁻¹h⁻¹, which is 129 times that of TiO₂. Compared with TiO₂, the enhanced H₂-production activity of the heterojunction catalyst can be attributed to the wider light absorption range and the efficient separation and migration of carriers at the close contact interface between Bi₂WO₆ and TiO₂. Based on the work functions of Bi₂WO₆, TiO₂ and their heterojunctions, combined with the results of electron paramagnetic resonance spectroscopy and Mott-Schottky measurements, the photocatalytic H₂ production mechanism of Z-scheme heterojunction Bi₂WO₆/TiO₂ was proposed. This work provides an easy and simple way to design a binary Z-scheme photocatalyst with efficient catalytic H₂-production activity without electron mediators.     

TiO2–CdS supported CuNi nanoparticles as a highly efficient catalyst for hydrolysis of ammonia borane under visible-light irradiation

TiO₂–CdS nanotubes (NTs) were used for the first time as a support to load metal nanoparticles (NPs) for the hydrolysis of ammonia borane (AB) which is a new strategy. The TiO₂–CdS NTs support was first synthesized using a hydrothermal method, and then the CuNi NPs were loaded using a liquid-phase reduction method. The synthesized samples were characterized by XRD, SEM-EDS, TEM, XPS, ICP, UV–Vis, and PL analyses. The characterization results show that the CuNi NPs existed in the form of an alloy with a size of ~1.2 nm and uniformly dispersed on the support. Compared with their single metal counterparts, the bimetallic CuNi-supported catalysts showed a higher catalytic activity in the hydrolysis of AB under visible-light irradiation: Cu_0·45Ni_0·55/TiO₂–CdS catalyst had the fastest hydrogen evolution rate with a high conversion frequency (TOF) of 25.9 mol_H2·mol_cat⁻¹ min⁻¹ at 25 °C and low activation energy of 32.8 kJ mol⁻¹. Cu_0.45Ni_0.55/TiO₂–CdS catalyst showed good recycle performance, maintaining 99.3% and 85.6% of the original hydrogen evolution rate even after five and ten recycles, respectively. Strong absorption of visible light, improved electron–hole separation efficiency, and metal synergy between Cu and Ni elements played a crucial role in improving the catalytic hydrolysis performance of AB. The catalyst prepared in this study provides a new strategy for the application of photocatalysts.     

Concentrated solar photocatalysis for hydrogen generation from water by titania-containing gold nanoparticles

Photocatalysis is an effective way to utilize solar energy to produce hydrogen from water. Au/TiO₂ nanoparticles (NPs) have a better performance in photocatalytic hydrogen generation because of the localized surface plasmon resonance (LSPR) effect of Au/TiO₂ NPs. In the photocatalytic hydrogen generation experiments, it was found that light intensity plays a key role in the photocatalytic reaction rate of Au/TiO₂ NPs. At a light intensity of 0–7 kW/m², the reaction rate has a super-linear law dependence on the light intensity (Rate ∝ Intensityⁿ, with n > 1). However, at a light intensity of 7–9 kW/m², the dependency becomes sub-linear (n < 1). This means that the increase rate of photocatalytic rate is smaller than that of light intensity when the light intensity exceeds 7 kW/m². In addition, the finite element method (FEM) was utilized to further elucidate the role of light intensity by calculating the absorption power and nearfield intensity mapping of a Au/TiO₂ nanoparticle. The variation trend of the calculated total absorption power agrees with the photocatalytic experimental results for different light intensities. These results shed light on the utilization of concentrated solar photocatalysis to increase the solar-to-hydrogen performance of Au/TiO₂ NPs.     

Enhanced photocatalytic water splitting activity of carbon-modified TiO2 composite materials synthesized by a green synthetic approach

We report a green and facile approach for the preparation of carbon-modified (C-modified) TiO₂ composite materials by hydrothermal synthesis followed by pyrolytic treatment. The resultant materials were characterized by powder X-ray diffraction (XRD), nitrogen physisorption studies, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). The photocatalytic performances of these materials were evaluated by calculating the amount of hydrogen evolved from the decomposition of water under solar simulated irradiation conditions. An improvement was achieved from no H₂ evolution at all with the bare TiO₂, to an evolution of 0.21 mL g⁻¹ h⁻¹ from a composite material modified with an optimum carbon loading of 3.62%. These results suggested that the interaction of carbon with predominantly rutile form of TiO₂ can promote shallow trapping of photogenerated electrons in the oxygen vacancies. This phenomenon consequently enhances the photocatalytic activity by minimizing charge carrier recombination, a characteristic demonstrated by fluorescence quenching of the TiO₂ emission.