Highly stable and durable ZnIn2S4 nanosheets wrapped oxygen deficient blue TiO2(B) catalyst for selective CO2 photoreduction into CO and CH4

Developing new and highly stable efficient photocatalysts is crucial for achieving high performance and selective photocatalytic CO2 conversion. In this paper, we designed a one-dimensional oxygen-deficient blue TiO2(B) (BT) catalyst for improved electron mobility and visible light accessibility. In addition, hexagonal ZnIn2S4 (ZIS) nanosheets with a low bandgap and great visible light accessibility are employed to produce effective heterostructures with BT. The synthesized materials are tested for photocatalytic conversion of CO2 into solar fuels (H2, CO and CH4). The optimized composite yields 71.6 and 10.3 μmol g-1h-1 of CO and CH4, three and ten times greater than ZIS, respectively. When ZIS nanosheets are combined with a one-dimensional oxygen-deficient BT catalyst, improved electron mobility and visible light accessibility are achieved, charge carriers are effectively segregated, and the transfer process is accelerated, resulting in efficient CO2 reduction. The photocatalytic CO2 conversion activity of the constructed BT/ZIS heterostructures is very stable over a 10-day (240-hour) period, and CO and CH4 production rates increase linearly with time; however, as time goes on, the rates of H2 production decrease. Further, a five-time recycling test confirmed this, revealing essentially equal activity and selectivity throughout the experiment. As a result, CO2 to CO and CH4 conversion has high selectivity and longer durability. The band structure of the BT/ZIS composite is determined using Mott-Schottky measurement, diffuse reflectance spectroscopy, and valence band X-ray photoelectron spectroscopy. This research demonstrates a novel approach to investigating effective, stable, and selective photocatalytic CO2 reduction systems for solar-to-chemical energy conversion.

Lattice Distortion in a Confined Structured ZnS/ZnO Heterojunction for Efficient Photocatalytic CO2 Reduction

It is a promising strategy to effectively promote "carbon neutrality" by reducing CO₂ to small energy molecules through photocatalysis technology. However, due to low light utilization and recombination of photogenerated carriers, photocatalysts usually have low activity and low selectivity for products. Herein, a hollow spherical ZnS/ZnO heterojunction with a spatial confinement effect photocatalyst was synthesized toward CO₂ photoreduction through preciously controlling the nano-/microstructure. The local lattice distortions were introduced into the surface of the hollow ZnS/ZnO microsphere, which activated lattice oxygen and provided additional active reaction sites. Furthermore, the heterojunction constructed between ZnS and ZnO interfaces facilitated the separation of photoinduced charge carriers. Combined with the natural advantage of enhanced light capture and absorption for a hollow confined structure, as a result, the systemic design in the electronic and confined structures for the photocatalyst has brought an excellent CO₂ reduction performance with a CO yield rate as high as 35.85 μmol g^-1h^-1 and durability under a 300 W Xe lamp irradiation without any sacrificial agent and cocatalyst.

Photocatalytic hydrogen evolution from glycerol-water mixture under visible light over zinc indium sulfide (ZnIn2S4) nanosheets grown on bismuth oxychloride (BiOCl) microplates

ZnIn₂S₄ (ZIS) is one of the widely studied photocatalyst for photocatalytic hydrogen evolution applications due to its prominent visible light response and strong reduction ability. However, its photocatalytic glycerol reforming performance for hydrogen evolution has never been reported. Herein, the visible light driven BiOCl@ZnIn₂S₄ (BiOCl@ZIS) composite was synthesized by growth of ZIS nanosheets on a template-like hydrothermally pre-prepared wide-band-gap BiOCl microplates using simple oil-bath method to be used for the first time for photocatalytic glycerol reforming for photocatalytic hydrogen evolution (PHE) under visible light irradiation (λ > 420 nm). The optimum amount of BiOCl microplates in the composite was found 4 wt% (4% BiOCl@ZIS) in the presence of in-situ 1 wt% Pt deposition. Then, the in-situ Pt photodeposition optimization studies over 4% BiOCl@ZIS composite showed the highest PHE rate of 674 μmol g^-1h^-1 with the ultra-low platinum amount (0.0625 wt%). The possible mechanisms behind this improvement can be ascribed to the formation of Bi₂S₃ low-band-gap semiconductor during BiOCl@ZIS composite synthesis resulting in Z-scheme charge transfer mechanism between ZIS and Bi₂S₃ upon visible light irradiation. This work expresses not only the photocatalytic glycerol reforming over ZIS photocatalyst but also a solid proof of the contribution of wide-band-gap BiOCl photocatalysts to enhancement of ZIS PHE performance under visible light.

Electron flux at the Schottky junction of Bi NPs and WO3-supported g-C3N4: an efficient ternary S-scheme catalyst for removal of fluoroquinolone-type antibiotics from water

Recently, global-scale attempts have been conducted to develop clean technologies and affordable materials to remediate pharmaceutical contaminants of water resources that are resistant to the biodegradation. In line with global efforts, this study reports a facile method to fabricate Bi nanocrystals in situ decorated on WO₃ nanoplates and its composite with graphitic carbon nitride (WO₃/Bi/g-C₃N₄) for photocatalytic degradation of fluoroquinolone-type antibiotics (ciprofloxacin and ofloxacin). The designed ternary S-scheme WO₃/Bi/g-C₃N₄ composite material was fully characterized by physicochemical and electrochemical analysis. Depositing the cost-effective and earth-abundant Bi nanocrystals onto WO₃ via a facile reduction route has been shown to increase the boosting of electron flux at their interface (Schottky junction). The S-scheme separation is confirmed by the calculation of band positions and the analysis of photogenerated hydroxyl radicals and holes. The complete removal of contaminants was obtained over the WO₃/Bi/g-C₃N₄ photocatalyst after 90 min under visible light irradiation. The present work would provide a rational route for developing Bi NP-based photocatalysis to replace metallic Au, Pt, and Ag NPs.

Constructing novel graphitic carbon nitride-based nanocomposites - From the perspective of material dimensions and interfacial characteristics

Two-dimensional (2D) graphitic carbon nitride (g-C₃N₄), a fascinating metal-free conjugated polymer, has garnered immense interest in the fields of solar power generation and environmental remediation. The construction of g-C₃N₄-based nanocomposites with materials of various dimensions can further improve their photocatalytic activities by surface area enlargement, bandgap tuning, heterojunction formation, etc. In this paper, we comprehensively reviewed the design, synthesis, and functionalities of g-C₃N₄-based nanocomposites based on their applications in hydrogen evolution, CO₂ reduction, and pollutants removal. We provided detailed analyses on the integration of 2D g-C₃N₄ with zero-, one-, two-, and three-dimensional materials with a focus on their interfacial characteristics and functional improvement. This review aims to stimulate fresh ideas on the interfacial engineering of g-C₃N₄-based nanocomposites to broaden their future applications.

Template-based textural modifications of polymeric graphitic carbon nitrides towards waste water treatment

The composite materials based on graphitic carbon nitrides (g-C₃N₄) are remarkably better semiconductors, but the inherent photocatalytic performance in its generic synthesis form is not up to the mark. Eminence efforts have been made to improve its performance and photocatalytic efficiencies. Recently, extensive investigations have been performed to develop their texturally modified and highly porous structures to get around the big flaws of bulk g-C₃N₄. One significant disadvantage is the increase in the polycondensation while preparation at 550 °C results in g-C₃N₄ materials with restricted specific surface area (SSA) (<10 m²/g) and no textured pores. Textural modification has emerged as an efficient and progressive way to improve optical and electronic characteristics. The final texture and shape of CN are influenced by the precursor's interaction with the template. Researchers are interested in developing CN materials with high SSA and changeable textural properties (pore volume and pore size). Based on the literature review it is concluded that the soft templating approach is relatively simple, and straightforward to induce textural changes in the g-CN type materials. This review focused on improving the textural properties of bulk g-C₃N₄ via templating method, and the major advances in the modified g-C₃N₄ materials for the treatment of wastewater. The procedures and mechanisms of numerous approaches with varying morphologies are thoroughly explained.

Ternary photocatalysts based on MOF-derived TiO2 co-decorated with ZnIn2S4 nanosheets and CdS nanoparticles for effective visible light degradation of organic pollutants

A high-efficiency visible-light-responsive CdS/ZnIn2S4/TiO2 photocatalyst was prepared for the first time by the self-sacrificing template method followed by a two-step chemical bath process.

Facile synthesis of porous 3D honeycomb-like ZnIn2S4 microspheres with improved photocatalytic activity for hydrogen evolution

The synthesized 3D honeycomb-like ZnIn2S4 microspheres exhibited good hydrogen production performance under simulated sunlight.

Ultrafast Hot Electron Transfer and Trap-State Mediated Charge Carrier Separation toward Enhanced Photocatalytic Activity in g-C3N4/ZnIn2S4 Heterostructure

Comprehensive understanding of charge carrier dynamics in the heterostructure based photocatalytic materials will strengthen their candidature as future solar energy harvesting resources. Here, in this work, the g-C₃N₄(CN)/ZnIn₂S₄ (ZIS) heterostructure was successfully synthesized and a direct spectroscopic correlation was established between excited-state charge carrier dynamics and enhanced photocatalytic activity using ultrafast transient absorption (TA) spectroscopy. TA analysis demonstrated the dominance of hot electron transfer over the band edge one. The photogenerated hot electrons migrated from the high-energy excitonic states of CN toward ZIS in the subpicosecond time scale. Broad-band (UV to NIR) ultrafast transient pump-probe spectroscopy revealed the collective effect of hot electron transfer as well as trap-state mediated electron delocalization in the enhanced photocatalytic H₂ evolution. This work reveals the role of photogenerated carriers in the photocatalytic performance of the CN/ZIS heterostructure and would create a new avenue toward the advancement of CN based heterostructure in photocatalytic devices.

Structure modulation of g-C3N4 in TiO2{001}/g-C3N4 hetero-structures for boosting photocatalytic hydrogen evolution

Structure design of photocatalysts is highly desirable for taking full advantage of their abilities for H₂ evolution. Herein, the highly-efficient TiO₂{001}/g-C₃N₄ (TCN) heterostructures have been fabricated successfully via an in situ ethanol-thermal method. And the structure of g-C₃N₄ in the TCN heterostructures could be exfoliated from bulk g-C₃N₄ to nanosheets, nanocrystals and quantum dots with the increase of the synthetic temperature. Through detailed characterization, the structural evolution of g-C₃N₄ could be attributed to the enhanced temperature of the ethanol-thermal treatment with the shear effects of HF acid. As expected, the optimal TCN-2 heterostructure shows excellent photocatalytic H₂ evolution efficiency (1.78 mmol h⁻¹ g⁻¹) under visible-light irradiation. Except for the formed built-in electric field, the significantly enhanced photocatalytic activity of TCN-2 could be ascribed to the enhanced crystallinity of TiO₂{001} nanosheets and the formed g-C₃N₄ nanocrystals with large surface area, which could extend the visible light absorption, and expedite the transfer of photo-generated charge carriers further. Our work could provide guidance on designing TCN heterostructures with the desired structure for highly-efficient photocatalytic water splitting.

The structure of g-C₃N₄ in the prepared TiO₂{001}/g-C₃N₄ hetero-structures could be modulated from BCN to CN-NS, CN-NC or CN-QD by tuning the synthetic temperature.

ZnIn2 S4 -Based Photocatalysts for Energy and Environmental Applications

As a fascinating visible-light-responsive photocatalyst, zinc indium sulfide (ZnIn₂ S₄ ) has attracted extensive interdisciplinary interest and is expected to become a new research hotspot in the near future, due to its nontoxicity, suitable band gap, high physicochemical stability and durability, ease of synthesis, and appealing catalytic activity. This review provides an overview on the recent advances in ZnIn₂ S₄ -based photocatalysts. First, the crystal structures and band structures of ZnIn₂ S₄ are briefly introduced. Then, various modulation strategies of ZnIn₂ S₄ are outlined for better photocatalytic performance, which includes morphology and structure engineering, vacancy engineering, doping engineering, hydrogenation engineering, and the construction of ZnIn₂ S₄ -based composites. Thereafter, the potential applications in the energy and environmental area of ZnIn₂ S₄ -based photocatalysts are summarized. Finally, some personal perspectives about the promises and prospects of this emerging material are provided.

Porous organic polymer enriched in Re functional units and Lewis base sites for efficient CO2 photoreduction

A porous organic polymer, BTN-Re, which contains two functional units, exhibits outstanding ability for CO2 photoreduction.

Photocatalytic CO2 reduction to CH4 on iron porphyrin supported on atomically thin defective titanium dioxide

The synergistic effect of OVs and FeTPP on 2D TiO2 improves the efficiency and selectivity of CO2 photoreduction to CH4.