An efficient photocatalytic system containing Eosin Y, 3D mesoporous graphene assembly and CuO for visible-light-driven H2 evolution from water

In the present work, 3D mesoporous graphene assembly was fabricated in a hydrothermal process using triethylenetetramine molecules as cross-linkers. And CuO nanoparticles were introduced in the graphene assembly via in-situ photodeposition. Then, a photocatalytic system containing Eosin Y as a sensitizer, graphene assembly as a supporter material and electron transfer channel, and CuO nanoparticles as an active center of H₂ evolution from water was prepared. Meanwhile, photocatalytic hydrogen evolution from water over the as-prepared photocatalytic system was explored under visible irradiation. Furthermore, for practical purposes, the durability of the photocatalytic system was also studied. And the photocatalytic mechanism was preliminarily discussed. The experimental results indicate that the as-prepared photocatalytic system is an efficient photocatalyst for visible-light-driven H₂ evolution from water. The rate of H₂ evolution over the photocatalytic system is up to 5.85 mmol g^?1 h^?1 under optimal conditions, which is 2.3 times higher than that over reduced graphene oxide loaded with CuO. The 3D porous graphene assembly plays an important role in the photocatalytic process. It can not only efficiently enhance the electron transfer in the photocatalytic system, but also result in fast diffusion of sacrificial reagent and timely release of H₂ bubbles. This work provides us with new possibility for designing an efficient Pt-free visible photocatalyst for H₂ evolution from water.     

A latest overview on photocatalytic application of g-C3N4 based nanostructured materials for hydrogen production

Photocatalytic H₂ production is a hopeful technology to solving the environment problems and global energy. Consequently, it is essential to develop high efficient, nonprecious and stable photocatalysts. Graphitic carbon nitride (g-C₃N₄) was fascinated much concentration owed to this metal free n-type semiconductor possesses appropriate bandgap, unique two dimensional (2D) layered structures, low toxicity, high thermal and chemical stability, lowcost, facile preparation and visible light response. Moreover, the g-C₃N₄ composites are having huge promise on photocatalytic H₂ production but, the efficiency of pure g-C₃N₄ is at present limited by its poor visible light absorption and suffers from high recombination rate of g-C₃N₄ photogenerated electron/hole pairs resulting in low photocatalytic performance. Furthermore, the g-C₃N₄ has unique electronic structure, therefore renowned candidates have been coupled with different functional components to improve photocatalytic activity. In this contribution, we review the recent research progresses of transition metals, non metals, noble metals, semiconductor compounds, graphene, carbon nanotubes (CNTs), carbon dots and quantum dots, supported on g-C₃N₄ nanosheets, which were applied to photocatalytic H₂ production. In addition, different techniques used to synthesis the g-C₃N₄ based photocatalyst including with their corresponding examples have been described. We hope that this review will encourage the readers to extend the applications of g-C₃N₄ based heterostructure in the field of H₂ production in a green manner.     

Current trends in structural development and modification strategies for metal-organic frameworks (MOFs) towards photocatalytic H2 production: A review

Photocatalytic H₂ generation using semiconductor photocatalysts is considered as a cost-effective and eco-friendly technology for solar to energy conversion; however, the present photocatalysts have been recognized to depict low efficiency. Currently, porous coordination polymers known as metal-organic frameworks (MOFs) constituting flexible and modifiable porous structure and having excess active sites are considered to be appropriate for photocatalytic H₂ production. This review highlights current progress in structural development of MOF materials along with modification strategies for enhanced photoactivity. Initially, the review discusses the photocatalytic H₂ production mechanism with the concepts of thermodynamics and mass transfer with particular focus on MOFs. Elaboration of the structural categories of MOFs into Type I, Type II, Type III and classification of MOFs for H₂ generation into transition metal based, post-transition metal based, noble-metal based and hetero-metal based has been systematically discussed. The review also critically deliberate various modification approaches of band engineering, improvement of charge separation, efficient irradiation utilization and overall efficiency of MOFs including metal modification, heterojunction formation, Z-scheme formation, by introducing electron mediator, and dye based composites. Also, the MOF synthesized derivatives for photocatalytic H₂ generation are elaborated. Finally, future perspectives of MOFs for H₂ generation and approaches for efficiency improvement have been suggested.     

A critical review in strategies to improve photocatalytic water splitting towards hydrogen production

Water splitting for hydrogen production under light irradiation is an ideal system to provide renewable energy sources and to reduce global warming effects. Even though significant efforts have been devoted to fabricate advanced nanocomposite materials, the main challenge persists, which is lower efficiency and selectivity towards H₂ evolution under solar energy. In this review, recent developments in photo-catalysts, fabrication of novel heterojunction constructions and factors influencing the photocatalytic process for dynamic H₂ production have been discussed. In the mainstream, recent developments in TiO₂ and g-C₃N₄ based photo-catalysts and their potential for H₂ production are extensively studied. The improvements have been classified as strategies to improve different factors of photocatalytic water splitting such as Z-scheme systems and influence of operating parameters such as band gap, morphology, temperature, light intensity, oxygen vacancies, pH, and sacrificial reagents. Moreover, thermodynamics for selective photocatalytic H₂ production are critically discussed. The advances in photo-reactors and their role to provide more light distribution and surface area contact between catalyst and light were systematically described. By applying the optimum operating parameters and new engineering approach on photoreactor, the efficiency of semiconductor photocatalysts for H₂ production can be enhanced. The future research and perspectives for photocatalytic water splitting were also suggested.     

2D CoP supported 0D WO3 constructed S-scheme for efficient photocatalytic hydrogen evolution

For heterojunction composite photocatalyst, intimate contact interface is the key to the carrier transfer separation conditions. Due to the interface contact, the electron transfer rate between catalysts can be increased during photocatalytic hydrogen production, therefore, we design the close contact of 0D/2D heterojunction, which greatly enhanced the photocatalytic hydrogen production activity of the composite catalyst. The composite catalyst WO₃/CoP was obtained by simple high temperature in situ synthesis. Moreover, it was proved by photoelectric chemistry and fluorescence tests that appropriate conduction band and valence band locations of WO₃ and CoP provided a favorable way for thermodynamic electron transfer. In addition, fluorescence results showed that WO₃ load effectively promoted photoelectron-hole transfer and increased electron lifetime. The formation of S-scheme heterojunctions can make more efficient use of useful photogenerated electrons and prevent the photogenerated electron-hole recombination of CoP itself, further promote the liveness of photocatalytic H₂ evolution. Meanwhile, the study of Metal-organic frameworks (MOFs) materials further promoted the application of MOFs derivatives in the field of photocatalytic hydrogen evolution, and provided a reference for the rational design of composite catalysts for transition metal phosphide photocatalysts.     

Engineering bimetallic PtX (X=Sn,Cu) immobilized on graphene as efficient catalysts: Boosted charge migration and hydrogen evolution

In this work, bimetallic PtX (X = Sn, Cu) decorated graphene nanohybrids (PtX/G) were developed, which showed enhanced photocatalytic hydrogen evolution performance than that of Pt/G in Eosin Y sensitized H₂ production system. The presence of Sn or Cu in PtX/G nanohybrids can remarkably improve the photogenerated charge separation efficiency and contribute to promoting the reduction of protons to molecular hydrogen in comparison to with noble metal Pt. Meanwhile, graphene acted as a more suitable electronic support to accelerate the migration of electrons from sensitizer to catalysts, owing to its higher electron mobility and larger surface area than other supports (such as carbon sphere, Al₂O₃ and SiO₂). The optimal H₂ evolution rate PtSn/G and PtCu/G was about 2.2 and 2.0 times higher than that of Pt/G. The apparent quantum efficiency (AQE) of PtSn/G and PtCu/G reached up to 12.46% and 11.06% under visible light irradiation (λ ≥ 420 nm), respectively.     

Exploration of waste-generated nanocomposites as energy-driven systems for various methods of hydrogen production; A review

Recently, waste-generated nanomaterials have received a surge in consideration for energy production due to their excellent properties and eco-friendly effects. A plethora of literature has reported on the growing interest for the production of hydrogen (H₂) by utilizing sunlight through water splitting and the recycling of bio-waste into organic catalysts. To the best of our knowledge, there has been no review on waste-derived nanocomposites for the production of H₂. Herein, potential methods, modes of fabrication, and the efficacy of synthesized nanocomposites for H₂ production have been highlighted. Distinct attention has been given to waste-generated nanocomposites, including a variety of graphene nanomaterials. Remarkable efforts have been made to fabricate biomass-derived nanomaterials and to optimize their reaction conditions and efficient use in energy production. Finally, future prospects and challenges in improving photocatalytic H₂ production are also summarized.     

Review on the interface engineering in the carbonaceous titania for the improved photocatalytic hydrogen production

Hydrogen is the prime source of energy with enormous attention in the current research development process as it is safe, clean, eco-friendly, and can be produced from renewable resources through simple catalytic reactions. Scalable production of hydrogen through photocatalysis has been achieved using carbon-modified semiconductors since 2009. In this direction, this review delivers comprehensive understandings into the interface and structural interactions between TiO₂ and carbonaceous materials such as carbon, carbon nanotubes, graphene, activated carbon, graphitic carbon nitride, carbon quantum dots, etc., and their influences toward improving the hydrogen generation activity of these systems. Besides, recently developed carbonaceous materials such as 3-D graphene, carbon nanohorns, and carbon nanocones have also been discussed on their character in the photocatalytic water splitting procedure. In general, the observed improvements in this carbon-modified TiO₂ attributed to the synergetic effects, which offer the active migration of charge carriers and reduced recombination rates in the photocatalyst. Finally, highlighting the future perspectives of the carbonaceous materials in photocatalytic applications are concluded.     

Investigation of Photo(electro)catalytic water splitting to evolve H2 on Pt-g-C3N4 nanosheets

g-C₃N₄ has shown great potentials in photocatalytic water splitting to produce hydrogen. Herein, we successfully synthesized g-C₃N₄ nanosheets via exfoliating bulk g-C₃N₄. And different metal nanoparticles were photo-deposited onto the surface of g-C₃N₄ nanosheets. The photocatalytic H₂ production activity of g-C₃N₄ nanosheets increased from 0 to 11.2 μmol/h/g_cat. The Pt loaded g-C₃N₄ nanosheets manifested the highest H₂ production activity with a rate of 589.4 μmol/h/g_cat. In addition, the hydrogen evolution rate was further enhanced with addition of external bias to fabricate a photoelectrocatalytic (PEC) system. And the maximum hydrogen production rate (23.1 mmol/h/m²) was obtained at a voltage of 0.6 V (vs. Ag/AgCl). The enhancement in H₂ production may be due to the following reasons: (1) Two-dimensional atomic flakes is beneficial to increase the specific surface area of g-C₃N₄, enhance the mobility of carriers, and improve the energy band structure, (2) Pt nanoparticles play an important role in g-C₃N₄ electron transport, (3) the g-C₃N₄ nanosheets loaded with Pt nanoparticles exhibited significant enhancement in photoelectrocatalytic performance, which may be attributed to its enhanced electronic conductivity and photoelectrochemical surface area, (4) Pt inhibited the recombination of photogenerated carriers and significantly improved the photocatalytic performance. The enhancement mechanism was deeply discussed and explained in this work.     

Boosting the performance of visible light‐driven WO3/g‐C3N4 anchored with BiVO4 nanoparticles for photocatalytic hydrogen evolution

In this article, a ternary WO₃/g‐C₃N₄@ BiVO₄ composites were prepared using eco‐friendly hydrothermal method to produce efficient hydrogen energy through water in the presence of sacrificial agents. The prepared samples were characterized by scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), ultraviolet‐visible (UV‐vis), Brunauer‐Emmett‐Teller (BET) surface area, and photoluminescence spectroscopy (PL) emission spectroscopy. The experimental study envisages the formation of 2‐D nanostructures and observed that such kinds of nanostructures could provide more active sites for photocatalytic reduction of water and their inherent reactive‐species mechanism. The results showed the excellent photocatalytic performance (432 μmol h^?1 g^?1) for 1.5% BiVO₄ nanoparticles in WO₃/g‐C₃N₄ composite when compared with pure WO₃ and BiVO₄. The optical properties and photocatalytic activity measurement confirmed that BiVO₄ nanoparticles in WO₃/g‐C₃N₄ photocatalyst inhibited the recombination of photogenerated electron and holes and enhanced the reduction reactions for H₂ production. The enhanced photocatalytic efficiency of the composite nanostructures may be attributed to wide absorption region of visible light, large surface area, and efficient separation of electrons/holes pairs owing to synergistic effects between BiVO₄ and WO₃/g‐C₃N₄. The prepared samples would be a precise optimal photocatalyst to increase their suppliers for worldwide applications especially in energy harvesting.     

Enhanced Z-scheme visible light photocatalytic hydrogen production over α-Bi2O3/CZS heterostructure

Depletion of fossil fuels and associated environmental issues has drawn attention of researchers to renewable energy resources and photocatalytic hydrogen production is considered to be safe and applicable method to meet future energy demand. Herein, we have used α-Bi₂O₃ nanorods for loading CZS (Cd_0.5Zn_0.5S) to form a heterostructure for photocatalytic H₂ production. The α-Bi₂O₃/CZS heterostructure was characterized through TEM, Elemental Mapping, XRD and XPS analysis. The α-Bi₂O₃/CZS heterostructure shows photocatalytic H₂ production rate of 254.1 μmol h^?1 with apparent quantum yield of 6.8% (λ = 420 nm). The enhanced photocatalytic performance was supported by transient photocurrent response curves and electrochemical impedance spectroscopy (EIS) results which suggest the efficient charge separation and electron mobility in α-Bi₂O₃/CZS heterostructure. The intimate contact formed between α-Bi₂O₃ nanorods and CZS nanoparticles responsible for the efficient flow of electrons following a Z-scheme pattern resulting in higher photocatalytic H₂ production. Moreover, the as-synthesized α-Bi₂O₃/CZS heterostructure shows negligible loss of activity after 4 consecutive recycling cycles. Our findings open new possibilities for the design of heterostructure based photocatalysts.     

Fabrication of MgTiO3 nanofibers by electrospinning and their photocatalytic water splitting activity

The photocatalytic H₂ evolution from water splitting is a promising process for generating renewable energy. In regard of the fascinating properties of the one-dimensional (1D) nanostructure, when used as photocatalyst, we report the synthesis of MgTiO₃ 1D nanofibers by the electrospinning technique and the investigations of their photocatalytic performance. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) corporately confirmed the successful fabrication of pure MgTiO₃ nanofibers. By contrast, the MgTiO₃ nanoparticles obtained via sol-gel method still contains impurities because of the inhomogeneous crystallization. The MgTiO₃ nanofibers exhibited enhanced efficiency and stability in photocatalytic H₂ generation under ultraviolet light, compared with the MgTiO₃ nanoparticles and P25. The photoelectrochemical measurements further revealed that MgTiO₃ nanofibers facilitated the transport and separation of the photoinduced charge carriers, mainly resulting from their special 1D structure, unique mesh morphology, large specific surface area and pure phase.     

Enhanced photocatalytic H2 production activity of Ag-doped Bi2WO6-graphene based photocatalysts

Ag-doped Bi₂WO₆-graphene based photocatalysts were found to exhibit hydrogen production activity. The performance of Bi₂WO₆-graphene based photocatalysts were investigated and optimized in this study. The activity can be further improved by Ag-doping. The morphology, surface chemistry, and phase structure of the photocatalysts were investigated by Field emission scanning electron microscopy, Transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectra, and X-ray diffraction. UV–vis diffuse reflectance spectroscopy and zeta potential were measured to study the optical properties, bandgap and dispersion stability of the photocatalysts. The effects of forming Bi₂WO₆-graphene contact and Ag doping on the light absorption, band gap, dispersion stability, and photocatalytic H₂ production performance of the composite photocatalysts were evaluated. The improved photocatalytic performance is mainly owing to the Ag doping and high electrical conductivity of graphene.     

Photocatalytic hydrogen production with aid of simultaneous metal deposition using titanium dioxide from aqueous glucose solution

The photocatalytic hydrogen production with aid of simultaneous metal deposition using TiO₂ was investigated in biomass glucose solution. Because the hydrogen production was very trace with pure TiO₂, the simultaneous metal deposition was applied into the glucose solution. The photocatalytic H₂ production activity with TiO₂ was significantly enhanced by simultaneous metal deposition for Au and Pd. The experimental factors such as glucose concentration, metal ion concentration and reaction temperature were investigated. The photocatalytic hydrogen production increased with increasing the concentration of glucose, and it followed Langmuir–Hinshelwood mechanism. Under the optimal conditions, the photocatalytic hydrogen generations from aqueous glucose solution with in-situ Au and Pd deposited TiO₂ were about 203 and 362 times larger compared with those observed with pure TiO₂. The enhanced photocatalytic activity could be explained in terms of reduced electron hole recombination via electron transfer from conductance band of TiO₂ to metal.     

Bimetallic PtNi alloy modified 2D g-C3N4 nanosheets as an efficient cocatalyst for enhancing photocatalytic hydrogen evolution

Platinum-based alloy materials as effective cocatalysts in improving the performance of photocatalytic H₂ production have raised great interest. Herein, a facile strategy of chemical reduction is established to synthesize bimetallic PtNi nanoparticles on 2D g-C₃N₄ nanosheets with excellent photocatalytic activity. The addition of PtNi nanoparticles can provide new H⁺ reduction sites and increase more active sites of the material. The synergistic effect between PtNi alloy nanoparticles and 2D g-C₃N₄ nanosheets can regulate electronic structure, narrow the band, accelerate charge transfer efficiency and inhabit the recombination of photo-induced electron (e⁻) and hole pairs (h⁺), contributing to the improvement of hydrogen evolution activity. The optimal hydrogen evolution rate of Pt_0.6Ni_0.4/CN shows higher hydrogen evolution rate (9528 μmol·g⁻¹·h⁻¹), which is 13.1 times than that of pure g-C₃N₄ nanosheets. Besides, a possible mechanism of photocatalytic hydrogen generation has been brought up according to a series of physical and chemical characterization. This work also provides a potential idea of developing cocatalysts integrating metal alloys with 2D g-C₃N₄ nanosheets for promoting photocatalytic hydrogen evolution.     

Eosin Y functionalized graphene for photocatalytic hydrogen production from water

Chemically reduced graphene oxide (RGO) can be functionalized by eosin Y (EY). The formation of the stable aqueous EY functionalized graphene (EY-RGO) suspension is due to the non-covalent interaction between EY and RGO surface via hydrogen bonding and π-π stacking. EY-RGO was characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Spectral and photoelectrochemical studies indicate that photoinduced electron transfer occurs from EY to RGO. The EY-RGO is photocatalytic active for water reduction to produce hydrogen. The average production rate of H₂ for the photocatalyst (w_EY/w_RGO = 1) in a 10 vol% triethanolamine aqueous solution can reach 3.35 mmol g⁻¹ h⁻¹ and 0.40 mmol g⁻¹ h⁻¹ under 30 h UV-vis and 10 h visible light irradiation, respectively. The photocatalytic activity of EY-RGO is superior to that of RGO, graphene oxide (GO), and EY-GO. Modification EY-RGO with Pt nanoparticles can further improve photocatalytic activity. All these features demonstrated that organic sensitizers functionalized graphene provided a nice candidate as a photocatalyst for H₂ generation from water under solar light irradiation.     

Boosting photocatalytic hydrogen evolution of g-C3N4 via enhancing its interfacial redox activity and charge separation with Mo-doped CoSx

To achieve low-cost photocatalytic hydrogen (H₂) production, it is necessary to develop low-priced transition metal co-catalysts to replace the roles of noble metals for photocatalytic H₂ evolution. Herein, a co-catalyst of Mo-doped CoS_x (Mo-CoS_x) was synthesized by using the hydrothermal procedure, then attached to g-C₃N₄ to construct a composite photocatalyst. As a co-catalyst, Mo-CoS_x can work as an electron acceptor, it is utilized to receive electrons generated by g-C₃N₄ photocatalyst on the surface of the catalyst, and inhibit the recombination of those electrons, thus showing enhanced charge transfer ability as well as reduction ability. The optimized Mo-CoS_x/g-C₃N₄ delivered a prominent photocatalytic H₂ evolution rate of 2062.4 μmol h^?1 g^?1, which was ～193 times higher than g-C₃N₄. Its AQE at 400 nm and 420 nm were 11.05% and 6.83%, respectively. This work provides a novel non-precious metal co-catalyst/g-C₃N₄ photocatalyst that is expected to be an acceptable cost route to solar energy conversion.     

Promoted photoinduced charge separation and directional electron transfer over dispersible xanthene dyes sensitized graphene sheets for efficient solar H2 evolution

Directional electron transfer and effective charge separation facilitated by graphene sheets have provided an inspiring approach to enhance the efficiencies of photoelectric conversion and photocatalysis. Herein, we demonstrated the feasibility of constructing a high-performance of the dye-sensitized H₂ evolution system using dispersible graphene sheets as both efficient electron transfer carrier and catalyst scaffold. Among the xanthene dyes sensitized H₂ evolution catalysts in this study, photocatalyst of Rose Bengal (RB) sensitized graphene decorated with Pt is the most active one and exhibits the highest apparent quantum efficiency (AQE) of 18.5% at wavelength of 550 nm and rather long-term stability for H₂ evolution. Dispersible graphene sheets can not only capture electrons from the excited dye and then transfer them to the decorated catalysts efficiently for improving charge separation with a small energy loss, but also afford large interfaces for highly dispersing catalyst nanoparticles with more active sites, thereby significantly enhancing the H₂ evolution efficiency than graphite oxide (GO) and multiwall carbon nanotubes (MWCNTs). This work proposes a potential strategy to develop efficient photocatalytic systems for solar-energy-conversion and provides a new insight into mechanistic study of photoinduced electron transfer by effective synergetic combination of dispersible graphene sheets with an efficient dye and a H₂ evolution catalyst.     

Dye-cosensitized graphene/Pt photocatalyst for high efficient visible light hydrogen evolution

In this work, a highly efficient and stable photocatalytic H₂ evolution catalyst was constructed on Pt deposited graphene sheets cosensitized by Eosin Y (EY) and Rose Bengal (RB). Under two-beam monochromic light irradiation (520 and 550 nm), a high quantum yield (QY) up to 37.3% has been achieved owing to maximum utilization of incident visible light. As a result of the excellent electron transport properties of graphene, it can greatly facilitate the forward electron transfer from photoexcited dye molecules to Pt catalyst and suppress back electron transfer, which significantly enhances photocatalytic efficiency for H₂ evolution. This efficient cosensitization strategy is also effective in enhancing H₂ evolution efficiencies of dye sensitized TiO₂ and multiwall carbon nanotubes (MWCNTs).     

Insighting role of reduced graphene oxide in BiVO4 nanoparticles for improved photocatalytic hydrogen evolution and dyes degradation

Hydrogen energy production and dyes degradation have been considered the need of modern age of technology in globe irrespective of the level of science and research in that country. Hydrogen gas is a green energy fule for the future application and abunduntly available in environment. Various techniques are reported for the production of hydrogen energy among which photocatalysis method is envirnmental friendly, cost‐efficient method using water that also decontaminated from dyes, which is a main problem nowadays because of increase in industrial applications according to the living standards. The composite of Bismuth vanadate (BiVO₄) with the coupling of the rduced graphene oxide (rGO) were synthezied by the facial hydrothermal technique by using a bismuth nitrate penta hydrate and amonium metavanadate as main precour and graphene oxide solution for reduced graphene oxide incorporation. X‐ray diffraction (XRD), Scanning Electron Microscope (SEM), ultraviolet adsorption spectroscopy (UV‐vis), and Brunauer‐Emmett‐Teller (BET) characterization tools investigate the role of concentration of the coupling material rGO in BiVO₄. All characterization techniques confirms that 1.5% rGO/BiVO₄ shows transformation of tetragonal to monoclinic phase with altration of the particles size (25‐40 nm), with high‐surface area, having irregular spherical porous clusters degradation of methelene blue (97%), production of green energy in the form of hydrogen gas fuel, and enhancement of the absorption of light that is clear intimation of the high photocatalytic efficiency towards the decontamination of the wastewater and production of hydrogen gas. Prepared nanostructured composite in current work reveals effective photocatalytic activity for decontamination of the wastewater and evolution of hydrogen energy would be the precise idea to utilize them in near future with various promising applications.