Ag-Bridged Z-Scheme 2D/2D Bi5FeTi3O15/g-C3N4 Heterojunction for Enhanced Photocatalysis: Mediator-Induced Interfacial Charge Transfer and Mechanism Insights

Verifying the Unique Charge Migration Pathway in Polymeric Homojunctions for Artificial Photosynthesis of Hydrogen Peroxide

Artificial photosynthesis for producing high-value hydrogen peroxide (H2O2) using carbon nitride-based systems holds immense potential. However, understanding the charge transfer dynamics in homojunction photocatalysts remains a significant challenge owing to the limitations of current characterization techniques. Here, a polymeric C3N5/C3N4 homojunction (CNHJ) is employed as a model system to probe interfacial electron transfer. Bimetallic cocatalysts serve as sensitive probes, enabling in situ tracking of the S-scheme electron transfer between C3N5 and C3N4 via X-ray photoelectron spectroscopy. Leveraging the unique advantages of this S-scheme, the CNHJ demonstrates substantially enhanced performance in the two-electron oxygen reduction reaction, achieving an impressive H2O2 production rate of 8.78 mmol g-1 h-1 under visible light irradiation. Furthermore, the system demonstrates robust performance in continuous-flow setups, under natural sunlight, and in photocatalytic disinfection tests, highlighting its practical potential. This approach offers new insights into dynamic electron transfer mechanisms and paves the way for advancing artificial photosynthesis technologies.

Efficient photocatalytic degradation of microplastics by constructing a novel Z-scheme Fe-doped BiO2-x/BiOI heterojunction with full-spectrum response: Mechanistic insights and theory calculations

Recently, microplastics (MPs) have garnered significant attention as a challenging emerging pollutant to address. Here, a full-spectrum light-driven Fe-doping BiO2-x/BiOI (FBI) Z-scheme heterojunction was constructed for efficiently degrading MPs in waters. Compared with BiO2-x, Fe doping BiO2-x, and BiOI, the optimal photocatalyst (40-FBI) can cause deep cracks in the polyethylene terephthalate (PET) within 10 h under the irradiation of full-spectrum light. Meanwhile, FT-IR characterization revealed that the absorption peak intensities of the C-O group, CO group, -CH stretching vibration, and -OH group on the MPs surface gradually increased with degradation time. A series of experiments and theory calculations revealed that the introduction of Fe creates impurity levels, accelerating the separation of photo-generated carriers and reducing the work function of BiO2-x, thereby enhancing the transport of photo-generated carriers between Z-scheme heterojunctions. This study offers a valuable idea for designing an efficient photocatalyst by simultaneously introducing ion doping and constructing heterojunctions for enhancing MPs degradation.

Support based metal incorporated layered nanomaterials for photocatalytic degradation of organic pollutants

An effective approach to producing sophisticated miniaturized and nanoscale materials involves arranging nanomaterials into layered hierarchical frameworks. Nanostructured layered materials are constructed to possess isolated propagation assets, massive surface areas, and envisioned amenities, making them suitable for a variety of established and novel applications. The utilization of various techniques to create nanostructures adorned with metal nanoparticles provides a secure alternative or reinforcement for the existing physicochemical methods. Supported metal nanoparticles are preferred due to their ease of recovery and usage. Researchers have extensively studied the catalytic properties of noble metal nanoparticles using various selective oxidation and hydrogenation procedures. Despite the numerous advantages of metal-based nanoparticles (NPs), their catalytic potential remains incompletely explored. This article examines metal-based nanomaterials that are supported by layers, and provides an analysis of their manufacturing, procedures, and synthesis. This study incorporates both 2D and 3D layered nanomaterials because of their distinctive layered architectures. This review focuses on the most common metal-supported nanocomposites and methodologies used for photocatalytic degradation of organic dyes employing layered nanomaterials. The comprehensive examination of biological and ecological cleaning and treatment techniques discussed in this article has paved the way for the exploration of cutting-edge technologies that can contribute to the establishment of a sustainable future.

Z-Scheme Ag2S-Ag-In2O3 Heterostructure with Efficient Antibiotics Removal under Natural Sunlight

The widespread distribution of antibiotics in natural waters is a great threat to human health. Photocatalytic degradation is an environmentally friendly technology to remediate antibiotic-polluted waters, driven by endless solar energy. Herein, a Z-scheme Ag2S-Ag-In2O3 heterostructure photocatalyst is prepared to remove antibiotics under environmental conditions. Under natural sunlight (light intensity: ∼78 mW/cm2) irradiation, the optimal Ag2S-Ag-In2O3 (10-ASAIO) exhibits considerable performance for decomposing diverse antibiotics, including norfloxacin (NOR), tetracycline hydrochloride, sulfisoxazole, ciprofloxacin, chlortetracycline hydrochloride, and ofloxacin. The NOR photodegradation rate constant of 10-ASAIO reaches 0.025 min-1, which is 12.50, 5.00, and 6.25 times higher than that of In2O3 (0.002 min-1), Ag-In2O3 (0.005 min-1), and Ag2S-In2O3 (0.004 min-1), respectively. This performance of the 10-ASAIO photocatalyst for decomposing NOR under natural sunlight exceeds most of the previously reported photocatalysts under a xenon lamp. Particularly, due to the intermittency of natural sunlight, a light-emitting diode (LED) lamp (light intensity: 5.1 mW/cm2) is also used as a light source, and 72.20% of NOR can be degraded with irradiation for 12 h. The effects of many water characteristics (water bodies, coexisting inorganic anions, pH, and humic acid) on the degradation performance of 10-ASAIO have been investigated, which exhibits stable degradation efficiency in variable aquatic environments. A 10-ASAIO catalyst-coated frosted glass sheet is fabricated to settle the problem of recovery of powder photocatalysts, and the immobilized catalyst shows outstanding activity and stability to decompose NOR. The photocatalytic mechanism and pathway of degrading NOR over 10-ASAIO have also been systemically investigated and proposed. The ecotoxicity (phytotoxicity and biotoxicity) of the 10-ASAIO photocatalyst and treated NOR solution have been tested by their toxic effects on cabbage seeds and Staphylococcus aureus (S. aureus). This work provides a feasible photocatalytic system for environmental pollutant remediation under natural sunlight or an LED lamp.

Modulation of Electronic Availability in g-C3N4 Using Nickel (II), Manganese (II), and Copper (II) to Enhance the Disinfection and Photocatalytic Properties

Carbon nitrides can form coordination compounds or metallic oxides in the presence of transition metals, depending on the reaction conditions. By adjusting the pH to basic levels for mild synthesis with metals, composites like g-C3N4-M(OH)x (where M represents metals) were obtained for nickel (II) and manganese (II), while copper (II) yielded coordination compounds such as Cu-g-C3N4. These materials underwent spectroscopic and electrochemical characterization, revealing their photocatalytic potential to generate superoxide anion radicals-a feature consistent across all metals. Notably, the copper coordination compound also produced significant hydroxyl radicals. Leveraging this catalytic advantage, with band gap energy in the visible region, all compounds were activated to disinfect E. coli bacteria, achieving total disinfection with Cu-g-C3N4. The textural properties influence the catalytic performance, with copper's stabilization as a coordination compound enabling more efficient activity compared to the other metals. Additionally, the determination of radicals generated under light in the presence of dicloxacillin supported the proposed mechanism and highlighted the potential for degrading organic molecules with this new material, alongside its disinfectant properties.

In Situ Synthesis of Exfoliated Ni(OH)2 Nanosheets and AgNPs-Embedded Functionalized Polyindole-Based Trinary Hybrid Microspheres: A Z-Scheme Photocatalyst for the Sunlight-Driven Degradation of Organic Pollutants with Enhanced Antibacterial Efficacy

Advancing a facile one-pot synthetic approach for the fabrication of a hybrid heterojunction photocatalyst remains a significant challenge in research pursuits. Herein, a microsphere-like trinary hybrid nanocomposite has been synthesized (NH/PIn/MAA/Ag). It comprises exfoliated single- and a few-layered Ni(OH)2 (NH nanosheets), mercaptoacetate-functionalized polyindole (PIn/MAA), and Ag nanoparticles (AgNPs) through an in situ approach. The formation mechanism is based on the exfoliation of stacked Ni(OH)2 multilayers [i.e., Ni(OH)2 microflowers] and stabilization of NH nanosheets through host-guest formation of PIn/MAA, followed by the adsorption-reduction of Ag+ ions in a one-pot reaction at low temperature. Surface morphological analyses of hybrid nanocomposite microspheres have exhibited that highly dense Ni(OH)2 microflowers have been transformed into low-density layered forms (NH nanosheets) within the polymeric platform (PIn/MAA) with deposited AgNPs. An interfacial heterojunction has been developed between the components in the depletion region, leading to an improvement in photocatalytic efficiency through a synergistic effect over the components for charge separation and transfer through the heterojunction interface via solid-state mediator Ag-based Z-scheme charge transfer dynamics. The superior photocatalytic degradation of tetracycline (98.2%) by trinary hybrid microspheres can be attributed to the deteriorated recombination rate of electron-hole pairs with reduced charge transfer resistance of the heterojunction in the photocatalyst, as obvious from photoluminescence, electrochemical impedance spectroscopy, chronoamperometry, and time-resolved photoluminescence (TRPL) analyses. Moreover, the antibacterial properties of microspheres against Bacillus pumilus (Gram-positive) and Escherichia coli (Gram-negative) bacteria have validated their potential as promising materials for the overall purification of aquatic systems.

Molecular modulation of interfaces in a Z-scheme van der Waals heterojunction for highly efficient photocatalytic CO2 reduction

The construction of van der Waals (vdW) heterojunctions is a key approach for efficient and stable photocatalysts, attracting marvellous attention due to their capacity to enhance interfacial charge separation/transfer and offer reactive sites. However, when a vdW heterojunction is made through an ex-situ assembly, electron transmission faces notable obstacles at the components interface due to the substantial spacing and potential barrier. Herein, we present a novel strategy to address this challenge via wet chemistry by synthesizing a functionalized graphene-modulated Z-scheme vdW heterojunction of zinc phthalocyanine/tungsten trioxide (xZnPc/yG-WO3). The functionalized G-modulation forms an electron "bridge" across the ZnPc/WO3 interface to improve electron transfer, get rid of barriers, and ultimately facilitating the optimal transfer of excited photoelectrons from WO3 to ZnPc. The Zn2+ in ZnPc picks up these excited photoelectrons, turning CO2 into CO/CH4 (42/22 μmol.g-1.h-1) to deliver 17-times better efficiency than pure WO3. Therefore, the introduction of a molecular "bridge" as a means to establish an electron transfer conduit represents an innovative approach to fabricate efficient photocatalysts designed for the conversion of CO2 into valued yields.

Stimuli-Responsive 3D Printable Conductive Hydrogel: A Step toward Regulating Macrophage Polarization and Wound Healing

Conductive hydrogels (CHs) are promising alternatives for electrical stimulation of cells and tissues in biomedical engineering. Wound healing and immunomodulation are complex processes that involve multiple cell types and signaling pathways. 3D printable conductive hydrogels have emerged as an innovative approach to promote wound healing and modulate immune responses. CHs can facilitate electrical and mechanical stimuli, which can be beneficial for altering cellular metabolism and enhancing the efficiency of the delivery of therapeutic molecules. This review summarizes the recent advances in 3D printable conductive hydrogels for wound healing and their effect on macrophage polarization. This report also discusses the properties of various conductive materials that can be used to fabricate hydrogels to stimulate immune responses. Furthermore, this review highlights the challenges and limitations of using 3D printable CHs for future material discovery. Overall, 3D printable conductive hydrogels hold excellent potential for accelerating wound healing and immune responses, which can lead to the development of new therapeutic strategies for skin and immune-related diseases.

Visible Light-Driven Photocatalytic Degradation of Methylene Blue Dye Using a Highly Efficient Mg-Al LDH@g-C3N4@Ag3PO4 Nanocomposite

The issue of water resource pollution resulting from the discharge of dyes is a matter of great concern for the environment. In this investigation, a new ternary heterogeneous Mg-Al LDH@g-C3N4X@Ag3PO4Y (X = wt % of g-C3N4 with respect to Mg-Al layered double hydroxide (LDH) and Y = wt % of Ag3PO4 loaded on Mg-Al LDH@g-C3N430) nanocomposite was prepared with the aim of increasing charge carrier separation and enhancement of photocatalytic performance to degrade methylene blue (MB) dye. The prepared samples were subjected to characterization via Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray, transmission electron microscopy, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, photoluminescence, and photoelectrochemical analysis. It was observed that in the presence of the composite of Mg-Al LDH and g-C3N4, the photocatalytic decomposition of MB under 150 W mercury lamp illumination increases significantly as opposed to Mg-Al LDH alone, and the Mg-Al LDH@g-C3N4 level with Ag3PO4 coating causes the complete degradation of MB to occur in less time. The outcomes show that the Mg-Al LDH@g-C3N430@Ag3PO45 nanocomposite demonstrated the highest photodegradation activity (99%). Scavenger tests showed that the two most effective agents in the photodegradation of MB are holes and hydroxyl radicals, respectively. Finally, a type II heterojunction photocatalytic degradation mechanism for MB by Mg-Al LDH@g-C3N430@Ag3PO45 was proposed.

Ag-loaded BiFeO3/CuS heterostructured based composite: an efficient photocatalyst for removal of antibiotics and antibacterial activities

The performance of advanced materials in environmental applications using green energy is the tremendous interest among researchers. The visible light responsive BiFeO3 (BFO), BiFeO3/CuS (BFOC), and Ag-loaded BiFeO3/CuS (Ag-BFOC) heterostructures have been synthesized by reflux method followed by hydrothermal and wetness impregnation method. These synthesized composites are well characterized through X-ray diffraction, UV diffuse reflectance spectroscopy, scanning electron microscope, and Fourier transfer infrared spectroscopy techniques. Compared with BFO and BFOC, Ag-BFOC exhibits the highest photocatalytic performance towards the degradation of antibiotics ciprofloxacin (76%) within 120-min time and also showed better antibacterial performance towards gram-negative (Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii) bacteria. Moreover, the novelty of the present work is the addition of CuS on the surface of BiFeO3 from heterojunction type II and facilitates the electron-hole channelization at the interfaces between BiFeO3 and CuS. Again, the loading of Ag on BiFeO3/CuS helps in shifting the absorption band towards the red end, is eligible to absorb more sunlight due to surface plasmon resonance effect, improves the separation efficiency of photo-generated charge carriers, and enhances the photocatalytic degradation of ciprofloxacin. The antibacterial property of Ag gives a best result towards antimicrobial activity. The prepared composites have proved their durability and stability by four successive cycles and prove the versatility of the composite.

Gold nanoparticle-decorated earth-abundant clay nanotubes as catalyst for the degradation of phenothiazine dyes and reduction of 4-(4-nitrophenyl)morpholine

In the present work, halloysite nanotubes modified with gold nanoparticles (AuNPs-HNT) are successfully prepared by wet chemical method for the catalytic degradation of phenothiazine dyes (azure B (AZB) and toluidine blue O (TBO)) and also cleaner reduction of 4-(4-nitrophenyl)morpholine (4NM) in the sodium borohydride (NaBH4) media. The catalyst is formulated by modifying the HNT support with a 0.964% metal loading using the HNT supports modified with 3-aminopropyl-trimethoxysilane (APTMS) coupling agent to facilitate the anchoring sites to trap the AuNPs and to prevent their agglomeration/aggregation. The AuNPs-HNT catalyst is investigated for structural and morphological characterization to get insights about the formation of the catalyst for the effective catalytic reduction of dyes and 4NM. The microscopic studies demonstrate that AuNPs (2.75 nm) are decorated on the outer surface of HNT. The as-prepared AuNPs-HNT catalyst demonstrates AZB and TBO dye degradation efficiency up to 96% in 10 and 11 min, respectively, and catalytic reduction of 4NM to 4-morpholinoaniline (MAN) is achieved up to 97% in 11 min, in the presence of NaBH4 without the formation of any by-products. The pseudo-first-order rate constant (K1) value of the AuNPs-HNT catalyst for AZB, TBO, and 4NM were calculated to be 0.0078, 0.0055, and 0.0066 s-1, respectively. Moreover, the synthesized catalyst shows an excellent reusability with stable catalytic reduction for 7 successive cycles for both the dyes and 4NM. A plausible mechanism for the catalytic dye degradation and reduction of 4NM by AuNPs-HNT catalyst is proposed as well. The obtained results clearly indicate the potential of AuNPs-HNT as an efficient catalyst for the removal of dye contaminants from the aquatic environments and cleaner reduction of 4NM to MAN, insinuating future pharmaceutical applications.

Facile Synthesis of gC3N4-Exfoliated BiFeO3 Nanocomposite: A Versatile and Efficient S-Scheme Photocatalyst for the Degradation of Various Textile Dyes and Antibiotics in Water

Water pollution engendered from textile dyes and antibiotics is a globally identified precarious concern that is causing dreadful risks to human health as well as aquatic lives. This predicament is escalating the quest to develop competent photocatalysts that can degrade these water pollutants under solar light irradiation. Herein, we report an efficient photocatalyst comprising a hierarchical structure by integrating the layered graphitic carbon nitride (gC3N4) with nanoflakes of exfoliated BiFeO3. The coexistence of these two semiconducting nanomaterials leads to the formation of an S-scheme heterojunction. This nanocomposite demonstrated its excellent photocatalytic activity toward the degradation of several textile dyes (Yel CL2R, Levasol Yellow-CE, Levasol Red-GN, Navy Sol-R, Terq-CL5B) and various antibiotics (such as tetracycline hydrochloride (TCH), ciprofloxacin (CPX), sulfamethoxazole (SMX), and amoxicillin (AMX)) under the simulated solar light irradiation. As this photocatalyst exhibits its versatile activity toward the degradation of several commercial dyes as well as antibiotics, this work paves the path to develop a reasonable, eco-benign, and highly efficient photocatalyst that can be used in the practical approach to remediate environmental pollution.

In situ fabrication of Z-scheme C3N4/Ti3C2/CdS for efficient photocatalytic hydrogen peroxide production

Photocatalysis is a potential technology to produce hydrogen peroxide with low energy consumption and no pollution. However, when using traditional photocatalysts it is hard to meet the requirements of wide visible light absorption, high carrier separation rate and sufficient active sites. Graphitic carbon nitride (g-C3N4) has great potential in the photocatalytic production of hydrogen peroxide, but its photocatalytic performance is limited by a high carrier recombination ratio. Here, we fabricated the Z-Scheme heterojunction of C3N4/Ti3C2/CdS in situ. The large specific surface area of C3N4 can provide plenty of reactive sites, and the absorption efficiency under visible light is improved with the addition of Ti3C2 and CdS. The better conductivity of Ti3C2 reduces the charge transfer resistance. With the increase of surface charge carriers, the width of the space charge region decreases and the photocurrent density increases significantly. Under visible light irradiation, the H2O2 yield of the ternary photocatalyst reaches 256 μM L-1 h-1, which is about 6 times that of pristine C3N4. After three cycles, the high photocatalytic efficiency can still be maintained. In this paper, the reaction mechanism of photocatalytic hydrogen peroxide production by the C3N4/Ti3C2/CdS composite material is proposed through an in-depth study of energy band theory, which provides a new reference for the design and preparation of high-performance materials for photocatalytic hydrogen peroxide production.

Photoelectron "Bridge" in Van Der Waals Heterojunction for Enhanced Photocatalytic CO2 Conversion Under Visible Light

Constructing Van der Waals heterojunction is a crucial strategy to achieve excellent photocatalytic activity. However, in most Van der Waals heterojunctions synthesized by ex situ assembly, electron transfer encounters huge hindrances at the interface between the two components due to the large spacing and potential barrier. Herein, a phosphate-bridged Van der Waals heterojunction of cobalt phthalocyanine (CoPc)/tungsten disulfide (WS2 ) bridged by phosphate (xCoPc-nPO4 - -WS2 ) is designed and prepared by the traditional wet chemistry method. By introducing a small phosphate molecule into the interface of CoPc and WS2 , creates an electron "bridge", resulting in a compact combination and eliminating the space barrier. Therefore, the phosphate (PO4 - ) bridge can serve as an efficient electron transfer channel in heterojunction and can efficiently transmit photoelectrons from WS2 to CoPc under excited states. These excited photoelectrons are captured by the catalytic central Co2+ in CoPc and subsequently convert CO2 molecules into CO and CH4 products, achieving 17-fold enhancement on the 3CoPc-0.6PO4 - -WS2 sample compared to that of pure WS2 . Introducing a small molecule "bridge" to create an electron transfer channel provides a new perspective in designing efficient photocatalysts for photocatalytic CO2 reduction into valuable products.

A review on plasmonic-based heterojunction photocatalysts for degradation of organic pollutants in wastewater

Organic pollutants in wastewater are the biggest problem facing the world today due to population growth, rapid increase in industrialization, urbanization, and technological advancement. There have been numerous attempts to use conventional wastewater treatment techniques to address the issue of worldwide water contamination. However, conventional wastewater treatment has a number of shortcomings, including high operating costs, low efficiency, difficult preparation, fast recombination of charge carriers, generation of secondary waste, and limited light absorption. Therefore, plasmonic-based heterojunction photocatalysts have attracted much attention as a promising method to reduce organic pollutant problems in water due to their excellent efficiency, low operating cost, ease of fabrication, and environmental friendliness. In addition, plasmonic-based heterojunction photocatalysts contain a local surface plasmon resonance that enhances the performance of photocatalysts by improving light absorption and separation of photoexcited charge carriers. This review summarizes the major plasmonic effects in photocatalysts, including hot electron, local field effect, and photothermal effect, and explains the plasmonic-based heterojunction photocatalysts with five junction systems for the degradation of pollutants. Recent work on the development of plasmonic-based heterojunction photocatalysts for the degradation of various organic pollutants in wastewater is also discussed. Lastly, the conclusions and challenges are briefly described and the direction of future development of heterojunction photocatalysts with plasmonic materials is explored. This review could serve as a guide for the understanding, investigation, and construction of plasmonic-based heterojunction photocatalysts for various organic pollutants degradation.

GRAPHICAL ABSTRACT

Herein, the plasmonic effects in photocatalysts, such as hot electrons, local field effect, and photothermal effect, as well as the plasmonic-based heterojunction photocatalysts with five junction systems for the degradation of pollutants are explained. Recent work on plasmonic-based heterojunction photocatalysts for the degradation of various organic pollutants in wastewater such as dyes, pesticides, phenols, and antibiotics is discussed. Challenges and future developments are also described.

Oxygen-Defect-Mediated ZnCr2O4/ZnIn2S4 Z-Scheme Heterojunction as Photocatalyst for Hydrogen Production and Wastewater Remediation

Photocatalysis has long been considered a promising technology in green energy and environmental remediation. Since the poor performance of single components greatly limits the practical applications, the construction of heterostructures has become one of the most important technical means to improve the photocatalytic activity. In this work, based on the synthesis of oxygen-vacancy-rich ZnCr₂O₄ nanocrystals, ZnCr₂O₄/ZnIn₂S₄ composites are prepared via a low-temperature in situ growth, and the oxygen-vacancy-induced Z-scheme heterojunction is successfully constructed. The unique core-shell structure offers a tight interfacial contact, increases the specific surface area, and promotes the rapid charge transfer. Meanwhile, the oxygen-vacancy defect level not only enables wide-bandgap ZnCr₂O₄ to be excited by visible light enhancing the light absorption, but also provides necessary conditions for the construction of Z-scheme heterojunctions promoting charge separation and migration and allowing more reactive charges. The reaction rates of visible-light-driven photocatalytic hydrogen production (3.421 mmol g^-1 h^-1), hexavalent chromium reduction (0.124 min^-1), and methyl orange degradation (0.067 min^-1) of the composite reach 3.6, 6.5, and 8.4 times those of pure ZnIn₂S₄, and 15.8, 41.3, and 67.0 times those of pure ZnCr₂O₄, respectively. This work presents a novel option for constructing high-performance photocatalysts.

Interface Engineering in 2D/2D Heterogeneous Photocatalysts

Assembling different 2D nanomaterials into heterostructures with strong interfacial interactions presents a promising approach for novel artificial photocatalytic materials. Chemically implementing the 2D nanomaterials' construction/stacking modes to regulate different interfaces can extend their functionalities and achieve good performance. Herein, based on different fundamental principles and photochemical processes, multiple construction modes (e.g., face-to-face, edge-to-face, interface-to-face, edge-to-edge) are overviewed systematically with emphasis on the relationships between their interfacial characteristics (e.g., point, linear, planar), synthetic strategies (e.g., in situ growth, ex situ assembly), and enhanced applications to achieve precise regulation. Meanwhile, recent efforts for enhancing photocatalytic performances of 2D/2D heterostructures are summarized from the critical factors of enhancing visible light absorption, accelerating charge transfer/separation, and introducing novel active sites. Notably, the crucial roles of surface defects, cocatalysts, and surface modification for photocatalytic performance optimization of 2D/2D heterostructures are also discussed based on the synergistic effect of optimization engineering and heterogeneous interfaces. Finally, perspectives and challenges are proposed to emphasize future opportunities for expanding 2D/2D heterostructures for photocatalysis.

Ag-enhanced CeF3-O: highly enhanced photocatalytic performance under NIR light irradiation

CeF₃-O with intermediate band showed improved synergic photodegradation activity toward HCl-TC and RhB under NIR light irradiation when enhanced by Ag as a cocatalyst. Ag⁺ ions take electrons from the second transition in CeF₃-O's intermediate band, which are then reduced to Ag as cocatalyst. The photodegradation efficiencies of HCl-TC by various Ag/CeF₃-O nanoparticles in 180-min increase from 26.5 to 73.1%. The optimal Ag/CeF₃-O-100 is about 2.76 times that of pure CeF₃-O. Ag/CeF₃-O-100 has an apparent rate constant of 4.5 × 10^-3 min^-1, which is 3.0 times that of pure CeF₃-O. Similarly, Ag/CeF₃-O-10 achieves a superior photodegradation efficiency of RhB at 96.7% under NIR light within 120 min. Its apparent rate constant of 27.7 × 10^-3 min^-1 is 12.0 times that of pure CeF₃-O (2.3 × 10^-3 min^-1). Further, the turnover frequencies of Ag/CeF₃-O nanoparticles are greatly higher than that of the corresponding pure CeF₃-O nanoparticles. Ag-enhanced CeF₃-O has a unique metal-semiconductor interface where Ag acts as a bridge for facilitating charge transfer and the separation efficiency of photogenerated carries. The synergic effect between CeF₃-O and Ag provides a practical technique for enhancing the wastewater treatment with NIR light irradiation.

Photocatalytic Applications of g-C3N4 Based on Bibliometric Analysis

To further understand the application of g-C3N4 in the field of photocatalysis, this study focuses on the visualization and analysis of articles in this field using VOSviewer and Citespace. These articles were analyzed in terms of number of articles, journals, authors, countries and keywords, respectively. The results show that there is little collaboration among the core authors in this field and insufficient cross-directional communication; the current applications of g-C3N4 are concentrated on hydrogen evolution, CO2 reduction and water treatment. The developing trend is in the direction of constructing Z-scheme structures, regulating the separation of photogenerated carriers and reducing the recombination rate, to which more and more attention is being paid. In the future, cross-directional communication among scholars can be strengthened to promote faster development of the field of photocatalytic applications of g-C3N4.

Carbon nitride-based Z-scheme heterojunctions for solar-driven advanced oxidation processes

Solar-driven advanced oxidation processes (AOPs) via direct photodegradation or indirect photocatalytic activation of typical oxidants, such as hydrogen peroxide (H₂O₂), peroxymonosulfate (PMS), and peroxydisulfate (PDS), have been deemed to be an efficient technology for wastewater remediation. Artificial Z-scheme structured materials represent a promising class of photocatalysts due to their spatially separated charge carriers and strong redox abilities. Herein, we summarize the development of metal-free graphitic carbon nitride (g-C₃N₄, CN)-based direct and indirect Z-scheme photocatalysts for solar-driven AOPs in removing organic pollutants from water. In the work, the classification of AOPs, definition and validation of Z-schemes are summarized firstly. The innovative engineering strategies (e.g., morphology and dimensionality control, element doping, defect engineering, cocatalyst loading, and tandem Z-scheme construction) over CN-based direct Z-scheme structure are then examined. Rational design of indirect CN-based Z-scheme systems using different charge mediators, such as solid conductive materials and soluble ion pairs, is further discussed. Through examining the relationship between the Z-scheme structure and activity (charge transfer and separation, light absorption, and reaction kinetics), we aim to provide more insights into the construction strategies and structure modification on CN-based Z-schemes towards improving their catalytic performances in AOPs. Lastly, limitations, challenges, and perspectives on future development in this emerging field are proposed.

Recent Advances in g-C3 N4 -Based Photocatalysts for Pollutant Degradation and Bacterial Disinfection: Design Strategies, Mechanisms, and Applications

Emerging photocatalytic technology promises to provide an effective solution to the global energy crisis and environmental pollution. Graphite carbon nitride (g-C₃ N₄ ) has gained extensive attention in the scientific community due to its excellent physical and chemical properties, attractive electronic band structure, and low cost. In this paper, research progress in design strategies for g-C₃ N₄ -based photocatalysts in the past five years is reviewed from the perspectives of nanostructure construction, element doping, and heterostructure construction. To clarify the relationship between application requirements and structural design, variations in the morphology, electronic energy band structure, light absorption capacity, as well as interfacial charge transfer caused by various modification strategies are discussed in detail. The recent applications of g-C₃ N₄ -based photocatalysts for pollutant degradation and bacterial disinfection are reviewed, as well as the antimicrobial activity and degradation mechanisms. Finally, current challenges and future development directions for the practical application of g-C₃ N₄ -based photocatalysts are tentatively discussed.

MXenes based nano-heterojunctions and composites for advanced photocatalytic environmental detoxification and energy conversion: A review

Extensive research is being done to develop multifunctional advanced new materials for high performance photocatalytic applications in the field of energy production and environmental detoxification, MXenes have emerged as promising materials for enhancing photocatalytic performance owing to their excellent mechanical properties, appropriate Fermi levels, and adjustability of chemical composition. Numerous experimental and theoretical research works implied that the dimensions of MXenes have a significant impact on their performance. For photocatalysis to thrive in the future, we must understand the current state of the art for MXene in different dimensions. Using MXene co-catalysts in widely used in photocatalytic applications such as CO2 reduction, hydrogen production and organic pollutant oxidation, this study focuses on the most recent developments in MXenes based materials, structural modifications, innovations in reaction and material engineering. It has been reported that using 5 mg of CdS-MoS2-MXene researchers were able to generate as high as 9679 μmol/g/h hydrogen under visible light. The MXenes based heterojunction photocatalyst Co3O4/MXene was utilized to degrade 95% bisphenol A micro-pollutant in just 7 min. Numerous novel materials, their preparations and performances have been discussed. Depending upon the nature of MXene-based materials, the synthesis techniques and photocatalytic mechanism of MXenes as co-catalyst are also summarized. Finally, some final thoughts and prospects for developing highly efficient MXene-based photocatalysts are provided which will indeed motivate researchers to design novel hybrid materials based on MXenes for sustainable solutions to energy and pollution issues.

Visible-NIR light-responsive 0D/2D CQDs/Sb2WO6 nanosheets with enhanced photocatalytic degradation performance of RhB: Unveiling the dual roles of CQDs and mechanism study

Environmental pollution caused by dye wastewater discharge has attracted much attention in the past decades. Developing photocatalysts with high solar energy utilization efficiency for the treatment of dye wastewater is one of the most promising methods to address afore-mentioned environmental problem. Herein, novel Vis-NIR (visible to near-infrared) light-responsive carbon quantum dots modified Sb₂WO₆ (CQDs/Sb₂WO₆) nanosheets with remarkably enhanced photocatalytic degradation performance of Rhodamine B (RhB) aqueous solution were successfully synthesized. Under the irradiation of Vis light, the photocatalytic degradation efficiency reaches 83% over the optimal composite, which is nearly seven times higher than that of pristine Sb₂WO₆. Meanwhile, under NIR light irradiation, the optimal composite also keeps a stable degradation performance, while pristine Sb₂WO₆ exhibits sluggish performance. Besides, a detailed photocatalytic degradation pathway was proposed via the analyses of corresponding intermediates in the photocatalytic degradation process. On the basis of electron spin resonance spectrometry, quenching experiment and density functional theory (DFT) calculation, hydroxyl radicals (•OH) play a dominating role in the photocatalytic reactions and a possible photocatalytic degradation mechanism was unearthed. This work provides new insights for constructing novel Vis-NIR responsive photocatalysts to purify dye wastewater for environmental remediation.

Z-scheme Fe2(MoO4)3/Ag/Ag3PO4 heterojunction with enhanced degradation rate by in-situ generated H2O2: Turning waste (H2O2) into wealth (•OH)

Ag₃PO₄-based photocatalysts have been deeply studied in environmental remediation; however, two problems limited their further application: photocorrosion and quenching effect by in-situ generated H₂O₂. To addressed these two questions simultaneously, Fe₂(MoO₄)₃ was coupled with Ag₃PO₄ to construct Z-scheme Fe₂(MoO₄)₃/Ag/Ag₃PO₄ heterojunction driven by internal-electric-field. The rhodamine B degradation rate of heterojunction was 254 and 7.0 times higher than those of Fe₂(MoO₄)₃ and Ag₃PO₄, respectively. The outstanding photoactivity was due to the high visible-light harvest, low interface resistance, high separation efficiency of charge carriers, long lifetime of hole (h⁺) and electron (e^-), well-preserved oxidation potential of h⁺, and especially photocatalytic produced H₂O₂ inside the system. The in-situ generated H₂O₂ was fully activated to be ^•OH on the Fe₂(MoO₄)₃ surface via a Fenton reaction, leading to the elimination of quenching effect on h⁺ and e^-, and generation of more ^•OH. Additionally, in Z-scheme heterojunction, e^- transferred from Ag₃PO₄ to Fe₂(MoO₄)₃, avoiding the accumulation on Ag₃PO₄ surface, and hence suppressing the photocorrosion. As a result, 91.2% of degradation efficiency remained after 5 cycles. This paper provides a new method to simultaneously increase the degradation rate by utilizing the in-situ generated H₂O₂ and improve the stability of Ag₃PO₄ via constructing a Z-scheme heterojunction.

Fabrication of 1D/2D BiPO4/g-C3N4 heterostructured photocatalyst with enhanced photocatalytic efficiency for NO removal

The visible light photocatalytic removal of NO in air is a promising way. BiPO₄ is restricted by its wide band gap and can only be responded to ultraviolet light. Herein, 1D BiPO₄ nanorod/2D g-C₃N₄ heterostructured photocatalyst was successfully synthesized via a facile one-step hydrothermal process for efficient visible light photocatalytic removal of NO. With simulated sunlight irradiation, the photocatalytic NO removal activity of the BiPO₄/g-C₃N₄ (64%) is much higher than that of the pure BiPO₄ (7.2%) and g-C₃N₄ (50%). Its excellent photocatalytic performance was ascribed to broadening the light response range to visible light and boosting the separation and transfer of photogenerated electrons and holes. The NO photocatalytic removal mechanism was proposed by the free radical trapping experiment and in situ DRIFTS research. The present study might induce a new means to design BiPO₄-based heterostructured photocatalysts for the removal of NO from air pollution under simulated solar light irradiation.

Reactive species specific RhB assisted collective photocatalytic degradation of tetracycline antibiotics with triple-layer Aurivillius perovskites

Triple-layer Aurivillius perovskites degrade tetracycline antibiotic and rhodamine B together in acidic aqueous solution. Primarily the superoxide radical generated via a semiconductor assisted dye sensitization process degrades the tetracycline.

Facile preparation of bismuth vanadate-sheet/carbon nitride rod-like interface photocatalyst for efficient degradation of model organic pollutant under direct sunlight irradiation

The photocatalytic performance of a semiconducting catalytic system is strongly influenced by charge-carrier separation rate, charge transport properties, surface area, utilization of light energy, and interface bonding. Herein, a series of bismuth vanadate (BiVO₄) samples were prepared via hydrothermal method by changing the volume ratios of ethelene glycol and ethanol as a solvent mixture for bismuth precursors. Further, the optimized BiVO₄ sheets with hierarchical morphology were used to construct an interface with rod-like g-C₃N₄ materials, which was confirmed by HRSEM and HRTEM. Due to the formation of an effective interface bonding between BiVO₄/g-C₃N₄, the photoinduced charge carrier's recombination rate was suppressed as confirmed by the PL analysis. The prepared BiVO₄/g-C₃N₄ sample were used to assess the photodegradation efficiency of Rhodamine B (RhB) under direct sunlight irradiation and the photocatalysts degraded ~92.8% of RhB within 2 h. The TOC measurements revealed a 66.4% mineralization efficiency for RhB. In addition, the radical trapping experiments demonstrated that superoxide and hydroxyl radicals are the main reactive species for the degradation. Based on the experimental evidences, a plausible charge transfer mechanism has been proposed. The enhanced photocatalytic activity has been mainly attributed to the inhibition of the recombination rate, enhanced charge carrier transfer efficiency, and high rate of production of reactive species.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Interfacial engineering in 3D/2D and 1D/2D bismuth ferrite (BiFeO3)/Graphene oxide nanocomposites for the enhanced photocatalytic activities under sunlight

3D-particulate and 1D-fiber structures of multiferroic bismuth ferrite (BiFeO₃/BFO) and their composites with 2D-graphene oxide (GO) have been developed to exploit the different scheme of interfacial engineering as 3D/2D and 1D/2D systems. Particulates and fibers of BFO were developed via sol-gel and electrospinning fabrication approaches respectively and their integration with GO was performed via the ultrasonic-assisted chemical reduction process. The crystalline and phase formation of BiFeO₃ and GO was confirmed from the XRD patterns obtained. The electron microscopic images revealed the characteristic integration of 3D particulates (with average size of 100 nm) and 1D fibers (with diameter of ~150 nm and few μm length) onto the 2D GO layers (thickness of ~27 nm). XPS analysis revealed that the BFO nanostructures have been integrated onto the GO through chemisorptions process, where it indicated that the ultrasonic process engineers the interface through the chemical modification of the surface of these 3D/2D and 1D/2D nanostructures. The photophysical studies such as the impedance and photocurrent measurements showed that the charge separation and recombination resistance is significantly enhanced in the system, which can directly be attributed to the effective interfacial engineering in the developed hetero-morphological composites. The degradation studies against a model pollutant Rhodamine B revealed that the developed nanocomposites exhibit superior photocatalytic activity via the effective generation of OH radicals as confirmed by the radical analysis studies (100% degradation in 150 and 90 min for 15% GO/BFO particulate and fiber composites, respectively). The developed system also demonstrated excellent photocatalytic recyclability, indicated their enhanced stability.

2D/2D Heterojunction systems for the removal of organic pollutants: A review

Photocatalysis is considered to be an effective way to remove organic pollutants, but the key to photocatalysis is finding a high-efficiency and stable photocatalyst. 2D materials-based heterojunction has aroused widespread concerns in photocatalysis because of its merits in more active sites, adjustable band gaps and shorter charge transfer distance. Among various 2D heterojunction systems, 2D/2D heterojunction with a face-to-face contact interface is regarded as a highly promising photocatalyst. Due to the strong coupling interface in 2D/2D heterojunction, the separation and migration of photoexcited electron-hole pairs are facilitated, which enhances the photocatalytic performance. Thus, the design of 2D/2D heterojunction can become a potential model for expanding the application of photocatalysis in the removal of organic pollutants. Herein, in this review, we first summarize the fundamental principles, classification, and strategies for elevating photocatalytic performance. Then, the synthesis and application of the 2D/2D heterojunction system for the removal of organic pollutants are discussed. Finally, the challenges and perspectives in 2D/2D heterojunction photocatalysts and their application for removing organic pollutants are presented.

Plasmonic Bi-enhanced ammoniated α-MnS/Bi2MoO6 S-scheme heterostructure for visible-light-driven CO2 reduction

Low redox ability and severe photocorrosion limit the photocatalytic activity of metal sulfides. Herein, step-scheme (S-scheme) heterojunction composited by diethylenetriamine (DETA) ammoniated MnS (α-MnS) and Bi₂MoO₆ with Bi surface plasmon resonance (SPR) was successfully fabricated (Bi-5 %M/BMO). This special electron transport structure effectively suppresses the photocorrosion of α-MnS and makes photocatalysts with high redox ability. DETA was protonated to form positively charged ammonium ions and they are easy to combine with acid gas CO₂, reducing the activation energy of CO₂, building an efficient catalytic reaction system, and improving CO₂ reduction efficiency. The CO evolution rate of Bi-5 %M/BMO (61.11 μmol g^-1h^-1) is 2.42, 7.89 and 5.01 times greater than that of 5 %M/BMO, pure α-MnS hollow spheres and Bi₂MoO₆, respectively. This indicates that Bi SPR effect can promote the separation of photon-generated electron-hole pairs dramatically. The ammoniated S-scheme heterostructure decorated with the SPR effect may provide a new perspective to design heterojunction.

Novel AgI/BiSbO4 heterojunction for efficient photocatalytic degradation of organic pollutants under visible light: Interfacial electron transfer pathway, DFT calculation and degradation mechanism study

Herein, we constructed a novel AgI/BiSbO₄ heterojunction via a hydrothermal-precipitation method. The heterojunction structure boosts the generation of hydroxyl and superoxide radicals for efficient degradation of organic pollutants. The photocatalytic activities of the optimal sample for ARG and TC degradation are 10 and 1.6 times higher than those of bare AgI, respectively. Characterizations and theoretical calculations together confirm a strong interfacial charge transfer exists between the interlayer in AgI and BiSbO₄ by the formation of Ag‒O bond, making O atoms obtain rich free electrons from Ag atoms of AgI, thus forming an ultrahigh electron transfer tunnel, and ultimately accelerating the separation of photoinduced electrons. More interestingly, low amounts of Ag⁰ NPs formed during the photocatalytic process, enhancing the visible light absorption because of its SPR (surface plasmon resonance) effect and further promoting the separation of photoinduced carriers. Furthermore, photocatalytic degradation pathways were proposed in detail by analyzing intermediates and a reasonable photocatalytic mechanism was unearthed. This work extends the development of AgI-based heterojunction photocatalysts.

A visible light active, carbon-nitrogen-sulfur co-doped TiO2/g-C3N4 Z-scheme heterojunction as an effective photocatalyst to remove dye pollutants

Heterojunction formation and heteroatom doping could be viewed as promising strategies for constructing composite photocatalysts with high visible light catalytic activity. In this work, we fabricated a carbon, nitrogen and sulfur co-doped TiO2/g-C3N4 (CNS-TiO2/g-C3N4) Z-scheme heterojunction photocatalyst composite via one-step hydrothermal and calcination methods. Compared with pure TiO2 and g-C3N4, the CNS-TiO2/g-C3N4 Z-scheme heterojunction photocatalyst possessed excellent degradation performance under visible light irradiation. Due to the formation of the Z-scheme heterostructure, the utilization rate of the photogenerated electrons-holes generated by the catalyst was increased, which enhanced the catalytic activity. Moreover, the heteroatom doping (C, N and S) could efficiently tailor the band gap of TiO2 and facilitate electron transition, contributing to enhancing the degradation ability under visible light. The CNS-TiO2/g-C3N4-2 exhibited a superior photocatalytic degradation efficiency (k = 0.069 min-1) for methyl orange dye (MO), which is higher than those of pure TiO2 (k = 0.001 min-1) and g-C3N4 (k = 0.012 min-1), showing excellent photocatalytic activity against organic pollutants.