Photocatalytic hydrogen evolution and antibiotic degradation by S-scheme ZnCo2S4/TiO2

In this study, ZnCo₂S₄ (ZCS) nanoparticles were coupled on the surface of TiO₂ by simple solvothermal method to form S-scheme heterojunction. Compared with ZCS and TiO₂, the photocatalytic performance of ZCS/TiO₂ under simulated sunlight is significantly improved, and its hydrogen evolution efficiency reaches 5580 μmol·g^?1·h^?1 with the apparent quantum efficiency (AQY) up to 11.5% at 420 nm, which is 88.3 times and 54.3 times that of TiO₂ and ZCS, respectively. Moreover, ZCS/TiO₂ also has excellent performance in the photocatalytic degradation of tetracycline (TC). The enhancement of photocatalytic performance of ZCS/TiO₂ is mainly due to S-scheme heterojunction. On the one hand, the S-scheme electron transfer path not only improves the electron-hole separation efficiency, but also improves the charge transfer efficiency. On the other hand, ZCS significantly enhances the visible light absorption of ZCS/TiO₂. The photocatalytic mechanism and S-scheme heterojunction structure is confirmed by XPS, EPR, ultraviolet photoelectron spectroscopy (UPS) and energy band structure. This work provides a new idea for designing and constructing S-scheme heterojunction to improve the performance of photocatalytic hydrogen evolution and TC degradation.     

An anthraquinone-integrated S-scheme-based NiTiO3-g-C3N4 composite with enhanced hydrogen production activity

A novel anthraquinone (AQ) integrated and S-scheme-based NiTiO₃-gC₃N₄ (NT-gCN) photocatalytic system is synthesized with an improved electron transfer rate for hydrogen production. Materials characterization using spectroscopic techniques reveal the intimate heterojunction interface between NT and gCN as well as integration of AQ with the binary composite. The synthesized AQ-NT-gCN photocatalyst exhibits a significantly enhanced H₂ evolution rate (576 μmol g^?1 h^?1), which is ～22 and 33% higher than that of NT-gCN and gCN, respectively, attributed to the spatial separation of charge carriers expedited by AQ. The radical trapping test data provide evidence for the S-scheme charge transfer mechanism in AQ-NT-gCN. The present study opens a new avenue for developing an S-scheme heterojunction by integrating binary composite with an organic molecule to improve the solar to energy conversion efficiency.     

Efficient photocatalytic H2 evolution over Cu and Cu3P co-modified TiO2 nanosheet

Schottky junction and p-n heterojunction are widely employed to enhance the charge transfer during the photocatalysis process. Herein, Cu and Cu₃P co-modified TiO₂ nanosheet hybrid (Cu–Cu₃P/TiO₂) was fabricated using an in situ hydrothermal method. The ternary composite achieved the superior H₂ evolution rate of 6915.7 μmol g^?1 h^?1 under simulated sunlight, which was higher than that of Cu/TiO₂ (4643.4 μmol g^?1 h^?1) and Cu₃P/TiO₂ (6315.8 μmol g^?1 h^?1) and pure TiO₂ (415.7 μmol g^?1 h^?1). The enhanced activity can be attributed to the collaboration effect of Schottky junction and p-n heterojunction among Cu/TiO₂ and Cu₃P/TiO₂, which can harvest the visible light, reduce the recombination of charge carriers and lower the overpotential of H₂ evolution, leading to a fast H₂ evolution kinetics. This work develops a feasible method for the exploration of H₂ evolution photocatalyst with outstanding charge separation properties.     

Porous g-C3N4/TiO2 S-scheme heterojunction photocatalyst for visible-light driven H2-production and simultaneous wastewater purification

In this work, photocatalysts with a novel S-scheme heterojunction were fabricated by coupling MOF-derived TiO₂ with porous g-C₃N₄ (MTO/PCN). The S-scheme heterojunction with matching band gap possesses different advantageous properties, which can not only inhibit photo-generated charge recombination, but also reserve outstanding redox ability. As expected, superior hydrogen evolution efficiency of 40-MTO/PCN was obtained in a TEOA-containing aqueous solution and pure water, which were 5252.9 and 974.6 μmol h⁻¹ g⁻¹, respectively. Meanwhile, the hybrid can also serve as a bifunctional catalyst for H₂ generation (2137.3 μmol h⁻¹ g⁻¹) and organic contaminant removal (the RhB purification efficiency: 35.24%). This work furnishes a feasible method for devising bifunctional photocatalysts that can simultaneously produce hydrogen and purify wastewater to provide both energy-saving and environmental restoration functions.     

Efficient interfacial charge transfer of 2D/2D CoP/CdS heterojunction for extremely boosted photocatalytic H2 evolution performance

Constructing 2D/2D heterojunction photocatalysts has attracted great attentions due to their inherent advantages such as larger interfacial contact areas, short transfer distance of charges and abundant reaction active sites. Herein, 2D/2D CoP/CdS heterojunctions were successfully fabricated and employed in photocatalytic H₂ evolution using lactic acid as sacrificial reagents. The multiple characteristic techniques were adopted to investigate the crystalline phases, morphologies, optical properties and textual structures of heterojunctions. It was found that integrating 2D CoP nanosheets as cocatalysts with 2D CdS nanosheets by Co–S chemical bonds would significantly boost the photocatalytic H₂ evolution performances, and the 7 wt% 2D/2D CoP/CdS heterojunction possessed the maximal H₂ evolution rate of 92.54 mmol g^?1 h^?1, approximately 31 times higher than that of bare 2D CdS nanosheets. Photoelectrochemical, steady photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements indicated that there existed an effective charge separation and migration over 2D/2D CoP/CdS heterojunction, which then markedly lengthened the photoinduced electrons average lifetimes, retarded the recombination of charge carriers, and caused the dramatically boosted photocatalytic H₂ evolution activity. Moreover, the density functional theory (DFT) calculation further corroborated that the efficient charge transfer occurred at the interfaces of CoP/CdS heterojunction. This present research puts forward a promising strategy to engineer the 2D/2D heterojunction photocatalysts endowed with an appealing photocatalytic H₂ evolution performance.     

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).     

Amorphous sulfur-rich CoSx nanodots as highly efficient cocatalyst to promote photocatalytic hydrogen evolution over TiO2

In this work, amorphous cobalt sulfide with a sulfur-rich structure (sr-CoS_x) is developed as the cocatalyst for photocatalytic hydrogen evolution. Through a facile hydrothermal reaction, sr-CoS_x nanodots are in situ grown on TiO₂ to obtain a heterojunction photocatalyst (sr-CoS_x/TiO₂). The as-prepared photocatalyst exhibits remarkable improved hydrogen evolution performance compared with TiO₂. Under the irradiation of xenon lamp, the hydrogen evolution rate of sr-CoS_x/TiO₂ can reach 507 μmol h^?1 g^?1, which is about 121 times that of pristine TiO₂, indicating that sr-CoS_x is a highly efficient cocatalyst to promote hydrogen evolution on TiO₂. Moreover, sr-CoS_x/TiO₂ exhibits better performance than crystalline CoS₂ or amorphous CoS modified TiO₂, suggesting the important role of sulfur-rich structure and amorphous state in promoting the cocatalytic effect. Electrochemical and photoluminescence measurements show the most efficient carrier separation between sr-CoS_x and TiO₂, which also contributes to its high photocatalytic hydrogen evolution performance.     

Active-center-enriched Ni0.85Se/g-C3N4 S-scheme heterojunction for efficient photocatalytic H2 generation

Photocatalysts with abundant active sites are essential for photocatalytic H₂ evolution from water. Herein, Ni_0.85Se-deposited g-C₃N₄ was obtained by a physical solvent evaporation method. The investigation shows that Ni_0.85Se with unsaturated active Se atoms can significantly improve the photocatalytic activity of g-C₃N₄, and the H₂ production rate of Ni_0.85Se/g-C₃N₄ can reach 8780.3 μmol g^?1 h^?1, which is 3.5 and 92.9 times higher than that of Ni_0.85+xSe/g-C₃N₄ (2497.9 μmol g^?1 h^?1) and pure g-C₃N₄ (94.5 μmol g^?1 h^?1), respectively. This improvement can be attributed to the quick charge transfer between Ni_0.85Se and g-C₃N₄ with S-scheme heterojunction feature based on a series of trapping experiments and photoelectrochemical analysis. Moreover, abundant unsaturated Se atoms could provide more H₂ evolution active sites. This work sheds light on the construction of heterojunctions with abundant active sites for H₂ production.     

Construction of ternary Z-scheme covalent triazine framework@Au@TiO2 for enhanced visible-light-driven hydrogen evolution activity

One key challenge in photocatalytic hydrogen production is how to construct high-performance photocatalyst. Covalent triazine framework (CTF) based polymers as photocatalysts show great application potential because of their good photocatalytic activity, high chemical stability, tunable electronic and optical properties, and easy synthesis process. In this paper, we designed the ternary Z-scheme heterojunction Au@TiO₂-X%TrTh based on CTF polymer TrTh, TiO₂ and Au nanoparticle, which exhibit higher photocatalytic hydrogen production rate compared with the corresponding binary heterojunction Au@TiO₂ and TiO₂-12%TrTh. The results of photocatalytic hydrogen production show that the optimized Au@TiO₂-12%TrTh has a remarkable hydrogen production rate of 4288.54 μmol g^?1 h^?1, which is about 312.3 times of Au@TiO₂ and 9.1 times of the TiO₂-12%TrTh. The enhanced hydrogen production activity of the ternary heterojunction comes from the local surface plasmonic resonance effect of Au nanoparticle, lower recombination efficiency of photogenerated electron-holes pairs and Z-scheme electron transfer pathway of Au@TiO₂-12%TrTh. The work provides a new strategy for designing efficient and practical photocatalyst.     

Hierarchical TiO2 spheroids decorated g-C3N4 nanocomposite for solar driven hydrogen production and water depollution

A novel hierarchical TiO₂ spheroids embellished with g-C₃N₄ nanosheets has been successfully developed via thermal condensation process for efficient solar-driven hydrogen evolution and water depollution photocatalyst. The photocatalytic behaviour of the as-prepared nanocomposite is experimented in water splitting and organic pollutant degradation under solar light irradiation. The optimal ratio of TiO₂ spheroids with g-C₃N₄ in the nanocomposite was found to be 1:10 and the resulting composite exhibits excellent photocatalytic hydrogen production of about 286 μmol h^?1g^?1, which is a factor of 3.4 and 2.3 times higher than that of pure TiO₂ and g-C₃N₄, respectively. The outstanding photocatalytic performance in this composite could be ascribed as an efficient electron-hole pair's separation and interfacial contact between TiO₂ spheroids with g-C₃N₄ nanosheets in the formed TiO₂/g-C₃N₄ nanocomposite. This work provide new insight for constructing an efficient Z-scheme TiO₂/g-C₃N₄ nanocomposites for solar light photocatlyst towards solar energy conversion, solar fuels and other environmental applications.     

Synergetic effect of carbon self-doping and TiO2 deposition on boosting the visible-light photocatalytic hydrogen production efficiency of carbon nitride

To improve the visible light utilization and photogenerated carriers separation, carbon self-doped carbon nitride (C-CN) supported TiO₂ photocatalysts were synthesized via a designed two-step strategy. After carbon self-doping, the colloid TiO₂ were in-situ deposited on C-CN surface and crystalized by calcination. Simultaneously, the bulk C-CN structure was thermally exfoliated to nanosheet morphology. This strategy ensured the saturated deposition of colloid TiO₂ nanoparticles on C-CN nanosheets to form well-constructed heterostructure with sufficient interfacial contact. The as-prepared TiO₂/C-CN (TCN) heterojunction photocatalysts showed enhanced visible light absorption capability, resulting in impressively high hydrogen production efficiency as 212.7 μmol h⁻¹, which was 10.8 times higher than that of CN. The remarkably enhanced photocatalytic performance may be mainly ascribed to synergetic effect of carbon self-doping and TiO₂ deposition on the improved visible light utilization and photogenerated carriers separation. The probable mechanism in such well-constructed heterojunction photocatalysts was proposed based on the structural analysis, electrical and photoelectrical properties, and photocatalytic process. The proposed strategy may be extended to the preparation of diverse heterojunction photocatalysts with excellent performance for solar energy conversion.     

Enhanced photocatalytic hydrogen evolution over 0D/3D NiTiO3 nanoparticles/CdIn2S4 microspheres heterostructure photocatalyst

Constructing S-scheme heterojunction is regarded as an effective mode to motivate excellent photocatalytic performance for hydrogen generation. This paper prepares NiTiO₃/CdIn₂S₄ S-scheme heterostructure photocatalyst by hydrothermal method successfully. In the experiments, 20 wt% NiTiO₃/CdIn₂S₄ has the supreme photocatalytic activity with the H₂ generation rate of 5168.6 μmol g⁻¹ h⁻¹ and the apparent quantum yield (AQY) of 5.14% at 420 nm, approximately 7.7 times of pure CdIn₂S₄. Through the phase characterization analyses, NiTiO₃ and CdIn₂S₄ successfully compounded, with NiTiO₃ nanoparticles wrapping around CdIn₂S₄ microspheres to form the irregular clumps. Further analyses of performance reveal the larger specific surface area, wider absorption region, faster charge transfer rate, outstanding photostability and recyclability for 20 wt% NiTiO₃/CdIn₂S₄, all of which play the significant role in photocatalytic hydrogen evolution activity. Finally, a plausible S-scheme photocatalytic mechanism for NiTiO₃/CdIn₂S₄ is proposed. This study provides a novel and effective S-scheme photocatalyst for hydrogen generation from water splitting.     

Fabrication of the SnS2/ZnIn2S4 heterojunction for highly efficient visible light photocatalytic H2 evolution

A series of SnS₂/ZnIn₂S₄ (x-SS/ZIS) photocatalysts with different mass ratios of SnS₂ were prepared by a hydrothermal method. The resulted composites were used for photocatalytic hydrogen evolution under visible light excitation. All the SS/ZIS composites exhibited significantly enhanced photocatalytic activity for H₂ evolution. Obviously, the highest H₂ evolution rate of 769 μmol g^?1 h^?1 was observed over 2.5-SS/ZIS, which was approximately 10.5 times that of the ZnIn₂S₄ (73 μmol g^?1 h^?1). The enhanced photocatalytic performance was attributed to the successful construction of SnS₂/ZnIn₂S₄ heterojunctions, leading to rapid charge separation and fast transfer of the photo-generated electrons and holes under light irradiation. On the basis of PL, electrochemical impedance spectroscopy (EIS), photocurrent measurements and the H₂ evolution tests, a plausible photocatalytic mechanism was proposed.     

Realizing efficient exciton dissociation in an all-organic heterojunction photocatalyst for highly improved photocatalytic H2 evolution

Although graphitic carbon nitride is a promising photocatalyst in the field of energy conversion and environmental purification, the intrinsic properties like excitonic effects and sluggish charge transfer restrict further photocatalytic applications. To circumvent these limitations, the novel all-organic heterojunction photocatalysts were constructed by anchoring organic carbon dots (O-dots) on porous graphitic carbon nitride nanosheets (O-dots/CNS). Results demonstrated that excitons can be e?ectively dissociated into electrons and holes at the interface of O-dots/CNS heterojunction, followed by holes injected to O-dots and electrons accumulated in CNS to realize efficient charge separation. Consequently, the O-dots/CNS with the optimized hydrogen (H₂) evolution performance could be reached 1564.5 μmol h^?1g^?1 under the visible light irradiation. This work not only presents new ideas for rational design photocatalytic reaction system from exciton and charge carrier, but also broaden the applications of this new kind of organic dots in the field of energy conversion.     

TiO2 nanosheets loaded with Cu: A low-cost efficient photocatalytic system for hydrogen evolution from water

Rutile TiO₂ nanosheets were prepared by a simple solvothermal process, and Cu was loaded on the surface of TiO₂ nanosheets using the in situ photo-deposition method. Meanwhile, photocatalytic H₂ evolution from water over the as-prepared TiO₂ nanosheets loaded with Cu was explored using methanol as a sacrificial reagent. The results indicate that the TiO₂ nanosheets loaded with Cu is an efficient photocatalyst under UV irradiation. During the first 5 h, a rate of H₂ evolution of approximately 22.1 mmol g⁻¹ h⁻¹ was achieved under optimal conditions. Furthermore, for practical purposes, the photocatalytic hydrogen evolution was studied as a function of content of Cu, pH of solution, concentration of methanol and dosage of photocatalyst, respectively. At last, the photocatalytic mechanism was preliminarily discussed.     

V2O5 nanoribbons/N-deficient g-C3N4 heterostructure for enhanced visible-light photocatalytic performance

Visible-light-induced heterostructure photocatalysts have been regarded as promising candidates in clean energy production and environmental treatment of organic pollutants. In this study, we have prepared nanocomposites of V₂O₅/N-deficient g-C₃N₄ (VO/Ndef-CN), which have been characterized by a variety of techniques. The as-synthesized nanocomposites show efficient bifunctional photocatalytic properties toward hydrogen generation and pollutants degradation (dye and antibiotic). The optimized 5VO/Ndef-CN photocatalyst exhibits improved photoactivity for H₂ production (5892 μmol g^?1 h^?1), with a high quantum yield of 6.5%, and fast degradation of organic pollutants, as well as high photocatalytic stability under visible light irradiation. The high photocatalytic efficiency is due to the presence of N defects and S-scheme heterojunction formation, which leads to rapid charge separation, enhanced visible-light absorption, and increased active sites. Furthermore, the possible activity-enhanced mechanism and the photodegradation pathway are proposed based on the experimental and density functional theory (DFT) investigations.     

Regular octahedron Cu-MOFs modifies Mn0.05Cd0.95S nanoparticles to form a S-scheme heterojunction for photocatalytic hydrogen evolution

Structured efficient and effective photocatalysts was crucial to improve photocatalytic efficiency. In this work, regular octahedron Cu-MOFs and Mn_0.05Cd_0.95S nanoparticles were adopted to constitute a S-scheme heterojunction. The Cu-MOFs/Mn_0.05Cd_0.95S (5 wt%) composite exhibited powerful photocatalytic hydrogen evolution activity of 547.5 μmol after 5 h under visible light irradiation (λ > 420 nm), which was ascribed to structure a S-scheme heterojunction brought great redox capacity and efficient separation and transfer of electrons and holes. The SEM and HRTEM results presented close contact of the Cu-MOFs and Mn_0.05Cd_0.95S. The PL, TRPL, and electrochemical properties further indicated that the composite photocatalysts had competent photocatalytic performance. The UV–vis DRS indicated that the composite catalyst had excellent light absorption capacity. It was confirmed that the composite photocatalysts owned excellent chemical stability by the XPS, FT-TR, and XRD. The S-scheme process can eliminate useless electrons and holes and provide more electrons to participate H₂ evolution reduction. This work contributed new strategy to rational structure heterojunction photocatalysts for hydrogen evolution.     

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.     

Controllable fabrication of 3D porous carbon nitride with ultra-thin nanosheets templated by ionic liquid for highly efficient water splitting

Modifying the texture of carbon nitride to adjust its physicochemical performance is a fascinating method for achieving high photocatalytic activity. Herein, we synthesized 3D porous carbon nitride with ultra-thin nanosheets by using cyanuric acid-melamine supramolecular and ionic liquid as precursor and template, respectively. The ionic liquid adjusts the morphology of materials and induces the carbon residue into the porous channels owing to its incomplete degradation. The 3D porous framework makes carbon nitride reflect the enhanced surface area, exposes adequate reaction sites, and offers a pathway for charge transport. And carbon residue and ultra-thin nanosheets further promote the photogenerated carriers transport and reduce the recombination rate of charge carriers. Consequently, 3D porous carbon nitride with ultra-thin nanosheets exhibit outstanding and stable hydrogen evolution under visible light irradiation. Significantly, as-fabricated sample CN-100 reflects an improved H₂ generation rate, up to 17,028 μmol h^?1 g^?1, which is 12 times higher than that of CN (1412 μmol h^?1 g^?1). The present work offers a unique synthesis strategy to develop the novel photocatalyst with efficient photocatalytic performance.     

Fully-depleted dual P–N heterojunction with type-II band alignment and matched build-in electric field for high-efficient photocatalytic hydrogen production

In this work, a dual p-n heterojunction of Cu₂O/Ni(OH)₂/TiO₂ with type-II band alignment and matched build-in electric field was fabricated. This dual p-n heterojunction promoted the separation and transfer of charge carriers, which is much more efficient than individual p-n heterojunction. Photocatalytic hydrogen evolution under the simulated sunlight shows a high rate of 6145 μmol g⁻¹ h⁻¹ for Cu₂O/Ni(OH)₂/TiO₂, which is 1.9 and 2.7 times that of Ni(OH)₂/TiO₂ and Cu₂O/TiO₂, respectively. The apparent quantum yield of Cu₂O/Ni(OH)₂/TiO₂ is about 20.2% under the irradiation of monochromatic light (λ = 420 nm). The recycling test of hydrogen evolution also verified a high stability for this dual heterojunction. The type-II band alignment and matched build-in electric field was confirmed, which accelerate the migration of charge carriers. The width of space-charge layer was calculated and proved that the p-n junctions in Cu₂O/Ni(OH)₂/TiO₂ are fully-depleted, which largely reduced the bulk recombination of charge carriers. The synergistic effect of the improved visible-light response, type-II band alignment, matched build-in electric field, and fully-depleted space-charge layer contributes to the enhanced photocatalytic hydrogen evolution.