Shining light on panchromatic ruthenium sensitizers towards dye-sensitized photocatalytic hydrogen evolution

Five new photocatalysts have been synthesized in order to extend the photo response upto visible range, by adsorbing MC113-MC117 ruthenium complexes on TiO₂-Pt composites. Highlight harvesting properties of these ruthenium complexes instigated us to evaluate for photocatalytic activity. The absorption curves of the synthesized photocatalysts extended up to 750 nm. Morphological studies of photocatalysts have been carried out using SEM and powder X-ray crystallography. Among all photocatalysts, MC113PC showed high photocatalytic activity i.e. 9474 TONs. IPCE and fluorescence quenching studies of the catalysts revealed the light harvesting nature and electron injection efficiency. The photocatalytic activity of MC photocatalysts were systematically screened at different pH and employing different sacrificial electron donors (SED) in order to obtain optimal photocatalytic performance.     

Near-infrared absorption carboxylated chlorophyll-a derivatives for biocompatible dye-sensitized hydrogen evolution

Chlorophylls (Chls) are naturally occurring photosensitizers having an excellent visible and near-infrared light absorption property. Herein, we employ three Chl a derivatives as sensitizers in a TiO₂-based photocatalytic system for H₂ evolution with ascorbic acid as the sacrificial reagent under visible light (λ > 400 nm). The H₂-evolution activity of these Chl a derivatives depends on a carboxy group in the C3- and/or C17-substituent(s). The concentration of 1 mg/ml dye/Pt/TiO₂ powder suspended in an aqueous solution with ascorbic acid as the sacrificial reagent gives the highest H₂-evolution rate. The fact that Chl-2 with a carboxy group on the C3 position of the chlorin macrocycle gives the highest H₂-evolution rate of 0.79 μmol h^?1 is ascribed to the lowest charge recombination rate between Chl-2 and TiO₂ among all Chls investigated. This work provides us with important information in synthesizing more favorable molecular structure of Chl derivatives for the highly efficient photocatalytic H₂ evolution from water splitting.     

Nanostructured Bi2O3@TiO2 photocatalyst for enhanced hydrogen production

Here we report on Bi₂O₃ clusters immobilized on anatase TiO₂ nanostructures for an enhanced rate of photocatalytic H₂ evolution. Structural, morphological, and optical properties of the Bi₂O₃@TiO₂ nanocomposite (BT) were characterized by a series of techniques including X-ray diffraction, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, diffuse reflectance spectroscopy and electrochemical impedance spectroscopy. The catalytic H₂ evolution experiments were carried out under different light sources: natural solar light, LED UV (365 ± 5 nm) and LED visible (420 ± 5 nm) light source. Under the solar light a pristine anatase TiO₂ nanostructured (TNS) catalyst generated 4.20 mmol h^?1 g^?1, whereas in the presence of Bi₂O₃@TNS showed much higher H₂ production 26.02 mmol h^?1 g^?1. The photocatalytic activity of the BT and its reproducible performance for five recycles is ascribed to an efficient separation of photogenerated charge carriers. A plausible reaction mechanism for the H₂ generation is proposed.     

Self-sacrificing template synthesis of CdS quantum dots/Cd-Hap composite photocatalysts for excellent H2 production under visible light

Well dispersive CdS quantum dots (QDs) were successfully in-situ grown on cadmium hydroxyapatite (Cd₅(PO₄)₃OH, Cd-Hap) assembled rods through a self-sacrificing hydrothermal method. No any nocuous organic ligands were used in such self-sacrificing route, allowing for a green approach to prepare CdS QDs with clean surfaces and enough active sites. The deposition of CdS QDs onto Cd-Hap surfaces led to a dramatically enhanced performance in H₂ production under visible light irradiation as compared to bulk CdS nanoparticles. The optimal CdS QDs/Cd-Hap composite displayed a H₂ evolution rate of 14.1 μmol h^?1 without using any noble metal cocatalyst, which was about 4.2 times higher than that of pristine CdS. The apparent quantum efficiency for CdS QDs/Cd-Hap composite was up to 18%. It was also found that CdS QDs/Cd-Hap composite can continuously generate H₂ from water in the presence of electron donors for more than 125 h. The enhanced photocatalytic performance of CdS QDs/Cd-Hap composites could be attributed to the high charge separation efficiency resulting from the efficient capture of photoinduced electrons by oxygen vacancies in Cd-Hap rods and the quantum confinement effect of CdS QDs with strong redox capacity as well as the increased active sites.     

Improvement of photocatalytic hydrogen generation from CdSe/CdS/TiO2 nanotube-array coaxial heterogeneous structure

The fabrication and characterization of CdSe/CdS/TiO₂ nanotube-array coaxial heterogeneous structure that has potential applications in photocatalytic water splitting and toxic pollutants degradation are investigated. CdSe(top)/CdS(under) double-layer is conformally deposited onto TiO₂ nanotubes by successive ionic layer adsorption and reaction (SILAR) and electrochemical atomic layer deposition (ECALD), respectively, for the CdS under layer and the CdSe top layer. Such double sensitized TiO₂ nanotubular photoelectrode exhibits significant enhancements in photoconversion efficiency, visible light response, and efficient hydrogen generation. The detailed synthesis process and the surface morphology, phase structure, elemental analysis, and photoelectrochemical properties of the resulting films with the CdSe/CdS/TiO₂ nanotube-array coaxial heterogeneous structure are discussed. The photoconversion efficiency of 9.47% and hydrogen generation rate of 10.24 ml h⁻¹ cm⁻² were observed. Both values are a 7-fold enhancement compared with that of the pure TiO₂ nanotube. The as-prepared photoelectrode presents potential application for industrialized photocatalytic hydrogen generation in the future.     

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.     

A promising synergistic effect of nickel ferrite loaded on the layered double hydroxide-derived carrier for enhanced photocatalytic hydrogen evolution

In this study, an attempt was made to modify the photocatalytic properties of an ion-exchangeable semiconductor material to enhance the efficiency of hydrogen production. Visible-light active NiFe₂O₄ was loaded onto NiZn/Cr layered double hydroxide (LDH) (Ni/Zn molar ratio = 75/25) with the Fe/Cr molar ratio of 0.005, 0.010, and 0.015 as cocatalyst through a simple solvothermal process and subsequently subjected to calcination at temperature of 500 °C. The results revealed that the presence of the loaded cocatalyst significantly facilitated the photocatalytic activity and the mixed oxide with Fe/Cr = 0.010 displayed the highest photocatalytic activity for visible light-induced H₂ generation. The optimal amount of hydrogen evolution reached to 269.44 μmolh^?1 under visible light (λ > 420 nm), which is far superior to that of the pristine NiZn/Cr LDH-derived oxides material (130.85 μmolh^?1), indicating the important catalytic role of NiFe₂O₄. The significant enhancement in photoactivity was attributed to the synergistic effect of nickel ferrite attached on the external surface of the calcined brucite-like sheets of the LDH. The cocatalyst NiFe₂O₄ nanoparticles increase the donor or acceptor levels in comparison with the pristine NiZn/Cr LDH-derived semiconductor oxide. Moreover, the existence of sheet-like LDH-derived carrier could inhibit the rapid recombination of photogenerated electrons and holes.     

Multifunctional MoS2 ultrathin nanoflakes loaded by Cd0.5Zn0.5S QDs for enhanced photocatalytic H2 production

Two‐dimensional MoS₂ has been widely used as hydrogen evolution reaction (HER) cocatalyst to load onto nanostructured semiconductors for visible light‐response photocatalytic hydrogen production. However, its another important role as light harvester because of the band‐gap tunable property and beneficial band position has been rarely exploited. Herein, few layer‐thick MoS₂ nanoflakes with extended light absorption over the range of 400 to 680 nm and a photocatalytic HER rate of 0.98 mmol/h/g have been obtained. Then 7‐nm‐sized Cd_0.5Zn_0.5S quantum dots (QDs) are selectively grown upon ultrathin MoS₂ nanoflakes for enhanced photocatalytic H₂ generation. Upon the photocatalytic, light absorption, and charge transfer properties of the MoS₂‐Cd_0.5Zn_0.5S composites evolved with the amount of MoS₂ from 0 to 3 wt%, the multiple roles of MoS₂ as long‐wavelength light absorber, in‐plane carrier mediator, and edge site‐active HER catalyst have been revealed. An optimum H₂ generation rate of 8863 μmol/h/g and a solar to hydrogen (STH) efficiency of 2.15% have been achieved for 2 wt% MoS₂‐Cd_0.5Zn_0.5S flakes. Such a strategy can be applied to other cocatalysts with both the light response and HER activity for efficient photocatalytic property.     

Reinforced photocatalytic reduction of CO2 to fuel by efficient S-TiO2: Significance of sulfur doping

The photocatalytic reduction of CO₂ to valuable chemicals and fuels is an efficient approach to control the ever-rising CO₂ level in the atmosphere. The present paper describes a significant improvement in photoreduction of carbon dioxide (CO₂) using sulfur (S) doped titania (S-TiO₂) nanoparticles as a photocatalyst under UV-A and visible light irradiation. The sulfur doping was done by following a simple sonothermal method, and a series of photocatalysts were synthesized with the varied amount of S doping. Various characterization techniques were employed for the photocatalysts such as XRD, surface area, UV–Visible, SEM, TEM, and XPS. The XPS reveals that S is predominantly present as S⁴⁺ in S-TiO₂. The electronic structure for S-TiO₂ anatase was calculated with the Vienna ab initio simulation package (VASP) code in the framework of spin-polarized density functional theory. Additional states closer to the valence band are produced inside the band gap as a result of doping. In situ reductive reaction conditions can partially reduce the catalyst, and results in the shift of Fermi level into the conduction band. It is suggested that S-doping increases catalyst surface conductivity, improves the charge transfer rate and the rate of photocatalytic reactions. The prepared series of catalysts have shown excellent activity under UV-A and visible light for photocatalytic reduction of CO₂. The effect of the different base including K₂CO₃, Na₂CO₃, NaOH and KOH; catalyst amount; sulfur doping amount; and light wavelength were monitored. Methane, ethylene, propylene, and propane were observed as reaction products. In 24 h, S-TiO₂ exhibited the highest photoactivity in KOH aqueous solution with a maximum yield of 6.25 μmol g^?1 methane, 2.74 μmol g^?1 of ethylene, 0.074 μmol g^?1 of propylene and 0.030 μmol g^?1 of propane under UV-A irradiation. The catalysts were active in visible light and able to generate methane and methanol in acetonitrile-H₂O mixture with/without TEOA as sacrificial donor producing 846.5 μmol g^?1 of methane and 4030 μmol g^?1 of methanol for the former and 167.6 μmol g^?1 of methane and 12828.4 μmol g^?1 of methanol for the latter case. An estimate demonstrates that mass transfer does not limit the CO₂ reaction.     

Enhancing hydrogen evolution of water splitting under solar spectra using Au/TiO2 heterojunction photocatalysts

An effective improvement of hydrogen evolution from water splitting under solar light irradiation was investigated using quantum dots (QDs) compounds loaded onto a Au/TiO₂ photocatalyst. First, Au/TiO₂ was prepared by the deposition-precipitation method, and then sulfide QDs were loaded onto the as-prepared Au/TiO₂ by a hydrothermal method. QDs were loaded onto Au/TiO₂ to enhance the energy capture of visible light and near-infrared light of the solar spectrum. The results indicated that the as-prepared heterojunction photocatalysts absorbed the energy from the range of ultraviolet light to the near-infrared light region and effectively reduced the electron-hole pair recombination during the photocatalytic reaction. Using a hydrothermal temperature of 120 °C, the as-prepared (ZnS–PbS)/Au/TiO₂ photocatalyst had a PbS QDs particle size of 5 nm, exhibited an energy gap of 0.92 eV, and demonstrated the best hydrogen production rate. Additionally, after adding 20 wt % methanol as a sacrificial reagent to photocatalyze for 5 h, the hydrogen production rate reached 5011 μmol g⁻¹ h⁻¹.     

Designing and fabrication of phenothiazine and carbazole based sensitizers for photocatalytic water splitting application

In the present work, we have designed and synthesized two carbazole and phenothiazine donor moieties based metal-free organic sensitizers and their codes are WCBZ2 and WPTZ2 respectively. These sensitizers have been used for photocatalytic hydrogen (H₂) evaluation application. The sensitizers exhibit good light absorption capability and electrochemical properties as well. For increasing water splitting capacity, incorporate platinum salt on TiO₂ semiconductor photoanode was performed and compared hydrogen evolution with pure TiO₂ photoanode. We have also studied the influence of the sensitizer's concentration and the effect of pH of the medium was explored. Using a theoretical measurement optimized both the synthesized dimer dyes structure geometry and the calculated their HOMO-LUMO energy level. Here also reported optimized pH and concentration of sensitizers in the reaction medium and found that the high hydrogen generation efficiency from water splitting is 138.3 μmol (348 TONs) by the WPTZ2 dye.     

WO3/g-C3N4 two-dimensional composites for visible-light driven photocatalytic hydrogen production

WO₃/g-C₃N₄ two-dimensional (2D) composite photocatalysts were prepared through a simple hydrothermal method followed by a post thermal treatment. The H₂ generation activity of these photocatalysts in the visible light was evaluated. The photocatalysts were characterized by X-ray powder diffraction, Fourier transform infrared spectra, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy et al. These results show that the orthorhombic-phase WO₃ nanoparticles with a grain size from 5 to 80 nm were successfully anchored on g-C₃N₄ nanosheets surface with intimate contact. Furthermore, the charge separation mechanisms of photo-generated charge carriers of the 2D WO₃/g-C₃N₄ photocatalysts were further studied by photoelectrochemical response and electrochemical impedance spectroscopy. The result shows that the 2D WO₃/g-C₃N₄ photocatalyst with 10 wt% WO₃ possesses the maximum photocatalytic performance for H₂ generation, as high as of 1853 μmol h^?1 g^?1, which is about 6.5 times higher than that of bare g-C₃N₄, indicating the fast injection of interface interaction between 2D g-C₃N₄ and WO₃. The increased photocatalytic performance of the composite photocatalyst can be attributed to the enhanced absorption of visible light, the higher photo-generated electrons and holes separation efficiency and low recombination rate of electrons and holes generated by photoexcitation.     

Hierarchical spheres assembled from large ultrathin anatase TiO2 nanosheets for photocatalytic hydrogen evolution from water splitting

We report the synthesis of TiO₂ hierarchical spheres (THS) with large specific surface area via a facile one-pot solvothermal method. The as-prepared THS are self-assembled by ultrathin TiO₂ nanosheets with thickness of several nanometers and they show a uniform spherical morphology with an average size of 500–700 nm. However, the as-prepared light yellow THS exhibit inferior photocatalytic activity for hydrogen evolution from water splitting due to the poor crystallization of TiO₂ and the existence of oxygen vacancies. Significantly, a subsequent thermal treatment improves the crystallinity of THS, reduces the oxygen vacancies, and thereby enhances the photocatalytic performance. It demonstrates that the sample annealed at 550 °C (THS550) exhibits the highest photocatalytic activity, about 5 times higher than that of commercial TiO₂ nanoparticles (CTiO₂). Moreover, the THS550 sample loaded with 1 wt% Pt exhibits an hydrogen evolution rate as high as 17.9 mmol h^?1g^?1, and the corresponding apparent quantum efficiency has been determined to be 28.46% under 350 nm light irradiation.     

Effectively extending visible light absorption with a broad spectrum sensitizer for improving the H2 evolution of in-situ Cu/g-C3N4 nanocomponents

Photocatalysts with broad spectrum absorption have been desired for a long time due to their ability to absorb more visible light. Herein, we developed an in-situ approach to specifically fabricate Cu nanoparticles onto the exterior surface of g-C₃N₄, followed by sensitization with Erythrosin B, to improve the photocatalytic H₂ evolution of g-C₃N₄ and extend the spectrum absorption. The photocatalytic H₂ evolution rate was significantly promoted, to more than 26 times that of pure g-C₃N₄, and the photocatalytic ability was maintained until reaching a wavelength of 700 nm. The origin of the improved activity was attributed to an in-situ Cu nanoparticle modification, which acts as an electron reservoir, and dye sensitization, which could extend the range of the visible light absorption, preventing charge recombination and enhancing the visible light utilization efficiency. In addition, the photocatalytic stability was investigated, and no significant attenuation was detected after six recycles.     

H2 Generation from a homogeneous photocatalytic system containing noble‐metal‐free Co(II) complex under the irradiation of visible light

A noble‐metal‐free molecular catalyst, [Co(dmbp)₃]Cl₂ (dmbp = 4,4^’‐dimethyl‐2,2^’‐bipyridyl) was prepared for photocatalytic H₂ generation. A three‐component photocatalytic system was constructed by combination of [Co(dmbp)₃]Cl₂ as catalyst, Eosin Y as photosensitizer and triethylamine as sacrificial electron donor to give an efficient H₂ generation system under visible‐light irradiation (λ > 420 nm). The maximum H₂ yield was up to 249.2 turnover number (vs. catalyst) over 2 h irradiation under the conditions with catalyst of 4.0 × 10^?4 M, 10% TEA (v/v), EY^2? of 4.0 × 10^?4 M and pH 10 in MeCN/H₂O (1 : 1,v/v). Furthermore, the dynamics behaviors of the photolysis system were also briefly discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural dependence of photocatalytic hydrogen production over La/Cr co-doped perovskite compound ATiO3 (A = Ca,Sr and Ba)

The crystal structure of a photocatalyst generally plays a pivotal role in its electronic structure and catalytic properties. In this work, we synthesized a series of La/Cr co-doped perovskite compounds ATiO₃ (M = Ca, Sr and Ba) via a hydrothermal method. Their optical properties and photocatalytic activities were systematically explored from the viewpoint of their dependence on structural variations, i.e. impact of bond length and bond angles. Our results show that although La/Cr co-doping helps to improve the visible light absorption and photocatalytic activity of these wide band gap semiconductors, their light absorbance and catalytic performance are strongly governed by the TiO bond length and TiOTi bond angle. A long TiO bond and deviation of TiOTi bond angle away from 180° deteriorate the visible light absorption and photocatalytic activity. The best photocatalytic activity belongs to Sr_0.9La_0.1Ti_0.9Cr_0.1O₃ with an average hydrogen production rate ～2.88 μmol/h under visible light illumination (λ ≥ 400 nm), corresponding to apparent quantum efficiency ～ 0.07%. This study highlights an effective way in tailoring the light absorption and photocatalytic properties of perovskite compounds by modifying cations in the A site.     

Bimetallic PtNi/g-C3N4 nanotubes with enhanced photocatalytic activity for H2 evolution under visible light irradiation

Bimetallic PtNi-decorated graphitic carbon nitride (g-C₃N₄) nanotubes were prepared through calcining the mixture of urea and thiourea in the presence of Pluronic F127, followed by deposition of bimetallic PtNi nanoparticles (NPs) via chemical reduction. It is found that the photocatalytic activity of PtNi/g-C₃N₄ nanotubes is strongly dependent on the molar ratio of Pt/Ni and the highest activity is observed for Pt₁Ni₁/g-C₃N₄. Under visible light (λ > 420 nm) irradiation, the H₂ generation rate over Pt₁Ni₁/g-C₃N₄ nanotubes is 104.7 μmol h^?1 from a triethanolamine (10 vol%) aqueous solution, which is higher than that of Pt/g-C₃N₄ nanotubes (98.6 μmol h^?1) and is about 47.6 times higher than that of pure g-C₃N₄ nanotubes. The cyclic photocatalytic reaction indicates that our Pt₁Ni₁/g-C₃N₄ nanotubes function as a stable photocatalyst for visible light-driven H₂ production. The effect of bimetallic PtNi NPs in the transfer and separation of photogenerated charge carriers occurring in the excited g-C₃N₄ nanotubes was investigated by performing photo-electrochemical and photoluminescence measurements. Our results reveal that bimetallic PtNi could replace Pt as a promising cocatalyst for photocatalytic H₂ evolution with better performance and lower cost.     

Enhanced photocatalytic hydrogen evolution from reduced graphene oxide-defect rich TiO2-x nanocomposites

Solar-driven photocatalytic hydrogen generation by splitting water molecules requires an efficient visible light active photocatalyst. This work reports an improved hydrogen evolution activity of visible light active TiO_2-x photocatalyst by introducing reduced graphene oxide via an eco-friendly and cost-effective hydrothermal method. This process facilitates graphene oxide reduction and incorporates intrinsic defects in TiO₂ lattice at a one-pot reaction process. The characteristic studies reveal that RGO/TiO_2-x nanocomposites were sufficiently durable and efficient for photocatalytic hydrogen generation under the visible light spectrum. The altered band gap of TiO_2-x rationally promotes the visible light absorption, and the RGO sheets present in the composites suppresses the electron-hole recombination, which accelerates the charge transfer. Hence, the noble metal-free RGO/TiO_2-x photocatalyst exhibited hydrogen production with a rate of 13.6 mmol h^?1g^?1_cat. under solar illumination. The appreciable photocatalytic hydrogen generation activity of 947.2 μmol h^?1g^?1_cat with 117 μAcm^?2 photocurrent density was observed under visible light (>450 nm).     

Highly efficient photocatalytic conversion of gas phase CO2 by TiO2 nanotube array sensitized with CdS/ZnS quantum dots under visible light

With the massive consumption of fossil fuels, energy crisis and effectively reducing CO₂ to curb global warming have become urgent and severe problems in the world. Photocatalytic conversion of CO₂ technology which can convert CO₂ into combustible compounds by using solar energy can solve both of the problems mentioned above. However, the photocatalytic conversion of CO₂ exhibits too low efficiency, especially under visible light. So, in order to improve the photocatalytic efficiency, the composite photocatalysts of TiO₂ nanotube array (TNTA) sensitized by CdS/ZnS quantum dots (QDs) were successfully prepared by anodization method and successive ionic layer adsorption and reaction (SILAR) method in this work. And the composite photocatalysts exhibited a high performance for photocatalytic conversion of gas-phase CO₂ to methanol under visible light. X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscope (TEM), and X-ray photoelectric spectroscopy (XPS) were employed to characterize the ingredients and morphologies of the synthesized photocatalysts. And, UV–vis diffuse reflectance spectra (UV–Vis DRS) revealed that CdS/ZnS QDs enhanced the photo-absorption of composite photocatalyst in the visible light region. The main product methanol yield of CdS/ZnS-TNTA under visible light was 2.73 times that of bare TNTA when TNTA was treated by 10 SILAR cycles. Meanwhile, the product yield first increased before decreasing with the increase of the CO₂ flow rate. And the greatest product yield reached up to 255.49 nmol/(cm²-cat·h) with the increase of light intensity. The reaction mechanism was discussed in this paper. This high performance for photocatalytic reduction of CO₂ was primarily attributed to the CdS/ZnS QDs sensitization, which widens the response wavelength range of the catalyst to include visible light and partly inhibits the recombination of electron-hole pairs.     

Rationally designed ternary CdSe/WS2/g-C3N4 hybrid photocatalysts with significantly enhanced hydrogen evolution activity and mechanism insight

Excellent light harvest, efficient charge separation and sufficiently exposed surface active sites are crucial for a given photocatalyst to obtain excellent photocatalytic performances. The construction of two-dimensional/two-dimensional (2D/2D) or zero-dimensional/2D (0D/2D) binary heterojunctions is one of the effective ways to address these crucial issues. Herein, a ternary CdSe/WS₂/g-C₃N₄ composite photocatalyst through decorating WS₂/g-C₃N₄ 2D/2D nanosheets (NSs) with CdSe quantum dots (QDs) was developed to further increase the light harvest and accelerate the separation and migration of photogenerated electron-hole pairs and thus enhance the solar to hydrogen conversion efficiency. As expected, a remarkably enhanced photocatalytic hydrogen evolution rate of 1.29 mmol g⁻¹ h⁻¹ was obtained for such a specially designed CdSe/WS₂/g-C₃N₄ composite photocatalyst, which was about 3.0, 1.7 and 1.3 times greater than those of the pristine g-C₃N₄ NSs (0.43 mmol g⁻¹ h⁻¹), WS₂/g-C₃N₄ 2D/2D NSs (0.74 mmol g⁻¹ h⁻¹) and CdSe/g-C₃N₄ 0D/2D composites (0.96 mmol g⁻¹ h⁻¹), respectively. The superior photocatalytic performance of the prepared ternary CdSe/WS₂/g-C₃N₄ composite could be mainly attributed to the effective charge separation and migration as well as the suppressed photogenerated charge recombination induced by the constructed type-II/type-II heterojunction at the interfaces between g-C₃N₄ NSs, CdSe QDs and WS₂ NSs. Thus, the developed 0D/2D/2D ternary type-II/type-II heterojunction in this work opens up a new insight in designing novel heterogeneous photocatalysts for highly efficient photocatalytic hydrogen evolution.