Facile fabrication of mesoporous biochar/ZnFe2O4 composite with enhanced visible-light photocatalytic hydrogen evolution

A promising biochar/ZnFe₂O₄ (BZF) composite has been synthesized to improve the efficiency of visible-light-driven H₂ evolution via a simple microwave hydrothermal method. The materials were investigated through diverse characterization means including XRD, FTIR, SEM, BET, XPS, VSM, UV–vis/DRS, PL, EIS. Different ratios of BZF composites expressed enhanced photocatalytic H₂ evolution performance over pure ZnFe₂O₄. Especially, biochar/ZnFe₂O₄ catalysts with 5:1 mass ratio (BZF-5) attained the optimal H₂ evolution rate, which is around 6 times higher than that of pure ZnFe₂O₄. Biochar acts as an electron mediator can effectively promote the separation of electron-hole pairs to enhance the rate of photocatalytic hydrogen evolution. Moreover, Eosin Y, photocatalyst and TEOA have synergistic effects accounted for enhanced photocatalytic performance in reaction system. Three cyclic runs for the photocatalytic H₂ evolution on BZF-5 sample illustrated its good stability and sustainable reusability.     

Facile fabrication of Bi2O3/TiO2-xNx nanocomposites for excellent visible light driven photocatalytic hydrogen evolution

Mesoporous Bi₂O₃/TiO_2−xN_x nanocomposites (BiNT) were synthesized by soft chemical template free homogeneous co-precipitation technique. XRD, XPS, TEM, UV-Vis DRS and photoluminescence studies were adapted to determine the structural, electronic and optical properties. The photocatalytic activities of the catalysts were evaluated for water splitting to generate clean hydrogen fuel under visible light irradiation (λ ≥ 400 nm). BiNT-400 catalyst showed highest results towards hydrogen production (198.4 μmol/h) with an apparent quantum efficiency of 4.3%. The pronounced activity of BiNT-400 sample towards hydrogen production was well consistent with high crystallinity, large surface area, proper excitation by N doping and Bi₂O₃ sensitization.     

Facile fabrication of CdSe/CuInS2 microflowers with efficient photocatalytic hydrogen production activity

Photocatalytic water splitting to produce hydrogen has attracted extensive attention and exhibited broad development prospects. In this work, CuInS₂ microflowers were fabricated through the solvothermal method, and decorated with CdSe quantum dots on the surface. As-prepared CdSe/CuInS₂ microflowers exhibited high photocatalytic hydrogen production activity (10610.37 μmol g^?1 h^?1) and high AQE of 48.97% at 420 nm. The enhanced photocatalytic hydrogen production activity owing to the construction of p-n heterostructure improved light absorption ability, increased electrons transfer efficiency and reduced recombination of photo-induced electrons and holes. Moreover, high stability and cyclic utilization of CdSe/CuInS₂ microflowers were beneficial to photocatalytic hydrogen production application.     

Direct Z-scheme ZnIn2S4/LaNiO3 nanohybrid with enhanced photocatalytic performance for H2 evolution

The direct Z-scheme ZnIn₂S₄/LaNiO₃ nanohybrid based on ZnIn₂S₄ nanosheets and LaNiO₃ cubes was synthesized by a facile hydrothermal method. The ZnIn₂S₄/LaNiO₃ nanohybrid showed improved photocatalytic H₂ evolution and stability. The photocatalytic H₂ evolution activity of ZnIn₂S₄/LaNiO₃ nanohybrid is 3-fold enhanced than that of bare ZnIn₂S₄. The enhanced performance of ZnIn₂S₄/LaNiO₃ nanohybrid is mainly ascribed to the formation of heterojunction between LaNiO₃ and ZnIn₂S₄. The heterojunction can facilitate charge transport on the interface between LaNiO₃ and ZnIn₂S₄ and suppress the recombination of photo-generated charge carriers over ZnIn₂S₄/LaNiO₃ nanohybrid, which were well demonstrated by photoelectrochemical tests. Moreover, the direct Z-scheme photocatalytic reaction mechanism was proposed to elucidate the improved performance of ZnIn₂S₄/LaNiO₃ nanohybrid photocatalyst. This study may provide some guidance on the construction of direct Z-scheme photocatalytic system for photocatalytic H₂ evolution.     

Visible light-driven hydrogen evolution by using mesoporous carbon nitride-metal ferrite (MFe2O4/mpg-CN; M: Mn,Fe, Co and Ni) nanocomposites as catalysts

Four different earth-abundant ferrite nanoparticles (MFe₂O₄, M: Mn, Fe, Co, Ni) with spinel structure were synthesized by using the surfactant-assisted high temperature thermal decomposition methods and then assembled on mesoporous graphitic carbon nitride (mpg-CN) to study their comparative catalysis for the photocatalytic hydrogen evolution reaction (HER) in the presence of Eosin-Y (EY) as a visible-light sensitizer. The yielded monodisperse ferrite nanoparticles and the MFe₂O₄/mpg-CN nanocomposites were characterized by using advanced analytical techniques including TEM, XPS, XRD, ICP-MS, and UV–Vis DRS. All the tested MFe₂O₄/mpg-CN nanocomposites provided the better catalytic performance than that of pristine mpg-CN in the photocatalytic HER and their photocatalytic HER rates are in the order of NiFe₂O₄/mpg-CN > CoFe₂O₄/mpg-CN > MnFe₂O₄/mpg-CN > Fe₃O₄/mpg-CN > mpg-CN. Among the tested MFe₂O₄/mpg-CN nanocomposites, NiFe₂O₄/mpg-CN nanocomposite provided the highest hydrogen generation of 14.56 mmol g⁻¹, which is 6.75 times greater than that of pristine mpg-CN and, using EY as a visible light sensitizer and triethanolamine (TEOA) as a sacrificial reagent. According to the optical properties and energy band positions of the nanocomposites, a plausible mechanism for the NiFe₂O₄/mpg-CN catalyzed HER is proposed to give insights on the highest activity of NiFe₂O₄/mpg-CN nanocomposites among others.     

Co3O4/CeO2 p-n heterojunction construction and application for efficient photocatalytic hydrogen evolution

The construction of p-n type heterojunction is an effective way to enhance the efficiency of photocatalytic hydrogen evolution. In this work, Co₃O₄/CeO₂ p-n heterojunction was construct by a simple hydrothermal method. This heterojunction mainly uses the internal electric field formed and accelerate the separation of electrons and holes in the opposite direction. In addition, according to SEM and TEM characterization, it was found that the granular cobalt oxide nanoparticles prepared by in-situ hydrothermal method were firmly and uniformly dispersed in cerium oxide, which effectively increased the active sites of hydrogen evolution. And combined with the BET results, it shows that the growth of cobalt oxide effectively increases the specific surface area and increases the active sites for hydrogen evolution. By exploring the hydrogen evolution capacity of different ratios of the complex, the test results showed that in all different ratios of the catalyst, CC-0.16 showed the best performance, and the hydrogen production efficiency reached 2298.52 μmol g⁻¹h⁻¹, which was 71 times that of nanobelt CeO₂ and 2.72 times that of Co₃O₄. According to the characterization results, the photocatalytic water splitting mechanism of the p-n heterojunction was proposed, and the charge transfer mechanism in the process was discussed in depth.     

Preparation of Ag/Ga2O3 nanofibers via electrospinning and enhanced photocatalytic hydrogen evolution

In this paper, gallium oxide (Ga₂O₃) was modified by in situ silver (Ag) to improve the photocatalytic activity for hydrogen (H₂) evolution. The photocatalysts Ga₂O₃ and Ag/Ga₂O₃ were synthesized via electrospinning and calcination, and characterized by X-ray diffraction patterns (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscope (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS). It is observed that the 1% Ag/Ga₂O₃ had higher activity than that of the pure Ga₂O₃ for photocatalytic H₂ evolution. Photoluminescence spectra (PL) and transient photocurrent analysis indicated that the high separation efficiency of photo-generated carriers of Ag/Ga₂O₃ resulted in the high photocatalytic H₂ evolution.     

Highly efficient Bi2O3/MoS2 p-n heterojunction photocatalyst for H2 evolution from water splitting

The design of p-n heterojunction photocatalysts to overcome the drawbacks of low photocatalytic activity that results from the recombination of charge carriers and narrow photo-response range is promising technique for future energy. Here, we demonstrate the facile hydrothermal synthesis for the preparation of Bi₂O₃/MoS₂ p-n heterojunction photocatalysts with tunable loading amount of Bi₂O₃ (0–15 wt%). The structure, surface morphology, composition and optical properties of heterostructures were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–visible absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL), electrochemical impedance spectroscopy (EIS). Compare to pure Bi₂O₃ and MoS_2, the Bi₂O₃/MoS₂ heterostructures displayed significantly superior performance for photocatalytic hydrogen (H₂) production using visible photo-irradiation. The maximum performance for hydrogen evolution was achieved over Bi₂O₃/MoS₂ photocatalyst (10 μmol h⁻¹g⁻¹) with Bi₂O₃ content of 11 wt%, which was approximately ten times higher than pure Bi₂O₃ (1.1 μmol h⁻¹g⁻¹) and MoS₂ (1.2 μmol h⁻¹g⁻¹) photocatalyst. The superior performance was attributed to the robust light harvesting ability, enhanced charge carrier separation via gradual charge transferred pathway. Moreover, the increased efficiency of Bi₂O₃/MoS₂ heterostructure photocatalyst is discussed through proposed mechanism based on observed performance, band gap and band position calculations, PL and EIS data.     

Synthesis of Al-substituted mesoporous silica coupled with CdS nanoparticles for photocatalytic generation of hydrogen

Aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS nanoparticles (CdS/Al-HMS) were prepared by template assembly, ion-exchange and sulfuration routes. The XRD and TEM results indicated that the assembly of less than 2 wt% CdS nanoparticles in the porous channels of Al-HMS didn't significantly affect the wormhole-like mesoporous framework structure of Al-HMS, whereas the porous channels of Al-HMS were filled up by CdS nanoparticles after loading of 21 wt% CdS. The diffuse reflectance UV–visible spectra exhibited that the absorption edge was gradually blue-shifted with decrease in CdS content due to the quantum confinement effect. The CdS/Al-HMS sample loaded 0.99 wt% Ru showed the highest H₂ evolution at a rate of 13.23 mL h⁻¹ with an apparent quantum yield of 5.92% at 420 nm by photocatalytic degradation of formic acid under visible light irradiation.     

Synergistic effects of multiple heterojunctions significantly enhance the photocatalytic H2 evolution rate CdS/La2Ti2O7/NiS2 ternary composites

Novel CdS/La₂Ti₂O₇/NiS₂ ternary composite photocatalysts without noble metal were successfully constructed by a simple hydrothermal method. Under visible light irradiation (λ > 400 nm), the optimal CdS/La₂Ti₂O₇/NiS₂ composite produced H₂ at a rate of about 12.77 mmol g⁻¹ h⁻¹, which was 84 times as high as that of pure CdS. This performance enhancement can be attributed to the formation of multiple heterojunctions (including CdS/NiS₂, CdS/La₂Ti₂O₇ and CdS/La₂Ti₂O₇/NiS₂ interface structures) between the three components in the as-prepared CdS/La₂Ti₂O₇/NiS₂ composites. The formed multiple heterojunctions help to separate electron-hole pairs more quickly and efficiently, thus greatly increasing the photocatalytic activity of the CdS/La₂Ti₂O₇/NiS₂ composites. This is very important for the utlization of solar energy for water splitting.     

Facile preparing composite of CoSe2 wrapping N-doped mesoporous carbon with highly electrocatalytic activity for hydrogen evolution reaction

The composites of cobalt selenide (CoSe₂) wrapping nitrogen self-doped mesoporous graphitic carbon were facilely prepared by hydrothermally wrapping CoSe₂ on the carbon material derived from pyrolysis of N-containing zeolitic imidazolate framework. The composites exhibit excellent catalytic activities and durability for electrochemical hydrogen evolution reaction (HER) in 0.5 M H₂SO₄. The optimum composite catalyst needs only low overpotential of 159 mV to approach 10 mA/cm² and as low as 83 mV/dec of Tafel slope can be obtained. The results are among the most active for HER based on non-noble materials in acidic solution.     

Facile synthesis of AuPd/g-C3N4 nanocomposite: An effective strategy to enhance photocatalytic hydrogen evolution activity

AuPd bimetallic nanoparticle (NP) modified ultra-thin graphitic carbon nitride nanosheet photocatalysts were synthesized via photochemical deposition-precipitation followed by hydrogen reduction. The crystal structure, chemical properties, and charge carrier behavior of these photocatalysts were characterized by X-ray diffraction (XRD), surface photovoltage spectroscopy (SPS), transient photovoltage spectroscopy (TPV), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and UV-Vis diffuse-reflectance spectroscopy (DRS). Photocatalytic H₂ evolution experiments indicate that the hydrogen treated AuPd nanoparticles can effectively promote the separation efficiency of electron-hole pairs photo-excited in the g-C₃N₄ photocatalyst, which consequently promotes photocatalytic H₂ evolution. The 1.0 wt% AuPd/g-C₃N₄ (H₂) composite photocatalyst showed the best performance with a corresponding photocatalytic H₂ evolution rate of 107 μmol h^?1. The photocatalyst can maintain most of its photocatalytic activity after four photocatalytic experiment cycles. These results demonstrate that the synergistic effect of light reduction and hydrogen reduction of AuPd and g-C₃N₄ help to greatly improve the photocatalytic activity of the composite photocatalyst.     

Constructing V2O5/CdS/CuS multi-level heterojunction for efficient photocatalytic hydrogen evolution

Multi-level heterojunction can effectively promote charge separation and transfer to improve photocatalytic hydrogen evolution activity. Based on the successful preparation of CdS/CuS heterojunction by one-pot hydrothermal method, V₂O₅ is introduced through the thermal decomposition of NH₄VO₃ for constructing V₂O₅/CdS/CuS(VCU) multi-level heterojunction. In this heterostructure, CdS and CuS are closely combined as mixed nanoparticles, which can boost the electron transfer (ET) process between them, and the introduction of V₂O₅ can increase the light absorption of the whole catalyst system. The hydrogen evolution test shows that VCU has the optimal performance with the hydrogen production rate of 1475 μmol/g/h, which is 16.4 times higher than pure CdS. According to the analysis of the binary composite structures (V₂O₅/CuS and V₂O₅/CdS), the probable ET process of VCU has been given, unraveling the internal catalytic mechanism. The present work expands the approaches for photocatalyst mechanism analysis and demonstrates the dramatic improvement in photocatalytic hydrogen production by the multi-level heterostructure.     

Ta2O5 hollow fiber composed of internal interconnected mesoporous nanotubes and its enhanced photochemical H2 evolution

Ta₂O₅ hollow fibers composed of interconnected mesoporous nanotubes were fabricated by sol-gel method using polysulfone hollow fibers and P123 as the templates. Numerous mesopores were formed on the wall of the nanotubes after thermal treatment at 700 °C, and the shape of the polysulfone fiber was preserved. It exhibited larger specific surface area and produced higher photocatalytic hydrogen than other forms of Ta₂O₅ samples. In addition, although the specific surface area of the porous Ta₂O₅ hollow fiber was smaller than that of TiO₂-P25, its hydrogen generation rate was 2.1 times higher, which might be ascribed to its higher conduction band minimum.     

Facile fabrication of mesoporous carbon nanofibers with unique hierarchical nanoarchitecture for electrochemical hydrogen storage

A colloidal silica incorporated porous anodic aluminum oxide (AAO) was utilized as a dual-template to prepare mesoporous carbon nanofibers (MCNFs). Such a strategy is simple because it takes advantage of commercially available materials (i.e., colloidal silica and AAO) and the templates can be removed in one step. The as-prepared MCNF shows a hierarchical nanostructure consisting of open macroporous channel connected with large mesopores and micropores. As a result of the large surface area and unique hierarchical nanoarchitecture which facilitates fast mass and electron transport, the MCNF reveals a discharge capacity of 679 mA h g⁻¹ at 25 mA g⁻¹. This value is significantly greater than that (i.e., 394 mA h g⁻¹) observed for an ordered mesoporous carbon (OMC) with a similar specific surface area. Furthermore, at 3000 mA g⁻¹, the MCNF demonstrates a discharge capacity of 585 mA h g⁻¹, which is about twice that (i.e., 256 mA h g⁻¹) of the OMC.     

Facile synthesis of CeO2/g-C3N4 nanocomposites with significantly improved visible-light photocatalytic activity for hydrogen evolution

Ceria dioxide supported on graphitic carbon nitride (CeO₂/g-C₃N₄) composites were facilely synthesized to be application for photocatalytic hydrogen (H₂) generation in this present work. The physical and chemical properties of CeO₂/g-C₃N₄ nanocomposites were determined via a series of characterizations. The CeO₂/g-C₃N₄ composites prepared by facile thermal annealing and rotation-evaporation method exhibit excellent photocatalytic H₂ evolution with visible-light illumination. The best hydrogen generation rate of CeO₂/g-C₃N₄ composite with 1.5 wt% Pt is 0.83 mmol h⁻¹ g⁻¹, which is almost same as that of composite with 3 wt% Pt prepared by simple physical mixing method. The significantly developed photocatalytic activity of CeO₂/g-C₃N₄ composite is majorly ascribed to the stronger interfacial effects with the more visible-light absorbance and faster electron transfer. This work reveals that construction of the CeO₂/g-C₃N₄ composite with high disperse and close knit by the facile thermal annealing and rotation-evaporation method could be an effective method to achieve excellent photocatalytic hydrogen evolution performance.     

Tuning the surface hydrophilicity of a C3N4 nanosheet for efficient photocatalytic H2 evolution coupled with microplastic degradation

Simultaneously realizing highly-efficient degradation of microplastics coupled with H₂ evolution is urgently demanded to solve the white pollution and energy shortage issues. Herein, we fabricate a series of fragmented hydrophilic homogeneous carbon nitride (TP-PCN) by terminating the polymerization of carbon nitride using iodide ions (I⁻), which acts as an invisible inhibitor by breaking the π-π bond to reduce the accumulation of ultra-thin layers in PCN to inhibit the polymerization. The H₂ evolution rate of resultant photocatalyst could reach 600.3 μmol g⁻¹ h⁻¹ in alkaline polyethylene terephthalate (PET) solution, exhibiting outstanding photocatalytic activity. Meanwhile, the PET was also degraded into small molecules, which were used in agricultural production, food processing and pharmaceuticals. The high photocatalytic activity of the TP-PCN photocatalyst can be ascribed to the promoted hydrophilicity and charge separation ability. This work supplies new insights for the design of functional photocatalysts and developing green technologies to solve environment pollution.     

Mesoporous carbon/graphitic carbon nitride spheres for photocatalytic H2 evolution under solar light irradiation

Herein, two different photocatalytic composites based on ordered (OCS) and disordered (DCS) mesoporous hollow carbon spheres and graphitic carbon nitride (gCN) have been successfully fabricated through facile acid treatment. The influence of carbon shell morphology of the spheres on gCN loading and photocatalytic H₂ production under simulated solar light irradiation has been revealed. The amount of evolved H₂ was ~6.2 (OCS/gCN) and ~5.3 (DCS/gCN) times higher in comparison to pristine gCN. It was found that graphitic carbon nitride was much more homogenously supported onto ordered mesoporous carbon spheres than disordered ones. The deposition of gCN onto ordered carbon spheres was found to be more efficient to increase carrier concentration, enhance photogenerated charge carrier transport and separation. It is assigned to the formation of the graphitic carbon nitride/carbon heterojunction facilitating the contact surface between the two phases of hybrid. Therefore, via tuning of the morphology of carbon shell being a host for gCN it was possible to find more promising candidate as a photocatalyst in H₂ production under solar light irradiation.     

Design and fabrication of hollow structured Cu2MoS4/ZnIn2S4 nanocubes with significant enhanced photocatalytic hydrogen evolution performance

The unique architecture is very significant for photocatalysts to achieve high photocatalytic efficiency. Herein, hollow Cu₂MoS₄/ZnIn₂S₄ heterostructural nanocubes with intimate-contact interface have been prepared for the first time via a self-template way, which can promote the photocatalysis hydrogen evolution. First, novel hollow structured Cu₂MoS₄ nanocubes were successfully synthesized using Cu₂O as a precursor, then the ZnIn₂S₄ nanosheets were in-situ grew on the surface of hollow Cu₂MoS₄ nanocubes. The unique hollow heterostructures have markedly enhanced photocatalytic efficiency, and 15 wt% Cu₂MoS₄/ZnIn₂S₄ sample exhibits the highest hydrogen production rate of 8103 μmol·h⁻¹·g⁻¹, which is approximately four times higher than pure ZnIn₂S₄. The improved photocatalytic performance is mainly attributed to the following two points: (1) the hollow nanocube structure can provide rich active sites and increase light absorption; (2) forming a built-in electric field is conducive to transfer the holes generated by ZnIn₂S₄ to Cu₂MoS₄, which can effectively promote charge separation. This work may provide insights for the design of hollow architecture cage materials for high photocatalytic performance.     

High-efficient C3N4-viologen charge transfer systems for promoting photocatalytic H2 evolution through band engineering

Accelerating the charge transfer (CT) capability of photocatalysts is an efficient way to improve the overall photocatalytic performance, yet the precise regulation of CT in photocatalyst systems is still lacking. In this paper, a series of hybrid photocatalysts composed of graphitic carbon nitride (CN) and various viologens (V) were prepared for the photocatalytic hydrogen evolution (PHE) from water splitting under visible-light irradiation. Considering the fixed energy structure of CN, the different electron-withdrawing substituents were introduced to engineer the band structure of V delicately and modulate the CT process between CN and V. It was shown that all the hybrid photocatalysts CN-x%V_y exhibited higher photocatalytic performance, of which CN–1%V₃, possessing the strongest electron withdrawing group (-NO₂), demonstrated the best PHE performance (3572.3 μmol g⁻¹ h⁻¹), exceeding 29 times over the unmodified CN. It was proposed that the introduction of V can optimize the interfacial photogenerated electron transfer (CN→V→Pt) of the whole photocatalytic system effectively. We highlighted the V as an efficient chemical segment to modify semiconductors toward enhanced activity due to the following unique characteristics: (i) the unique redox ability, (ii) the easy synthetic methods for controlling the band structures precisely, and (iii) the inherent positively charged feature. This work provides a deep understanding of CT for the rational design of high-performance photocatalysts through band engineering.