Z-scheme Heterojunction Photocatalyst Research Articles

0D/2D/0D heterostructure of SrTiO3/BiOBr/Cu2O double Z-scheme for elimination sulfadiazine: Insight into performance, mechanism, and toxicity assessment

Z-scheme heterojunction photocatalysts, notable for their efficient generated charge separation performance, have attracted significant attention for solving environmental pollution. Herein, novel 0D/2D/0D SrTiO3/BiOBr/Cu2O double Z-scheme ternary heterojunction are fabricated via a simple synthetic strategy. The double Z-scheme heterojunction facilitates the separation and migration of photogenerated charges, as confirmed by the photoluminescence (PL), transient photocurrent response (I–T), and electrochemical impedance spectrum (EIS). The catalyst presented in this work exhibits excellent photocatalytic performance under visible light, degrading 94.3% of sulfadiazine (SDZ) in 30 min. Moreover, it has a rate constant that is 1.95 and 2.0 times greater than that of SrTiO3/BiOBr and BiOBr, respectively. The X-ray photoelectron spectroscopy valence band (VB–XPS) and Mott–Schottky (M–S) measurement results provide further insights into the double Z-scheme heterojunction charge-transfer mechanism of SrTiO3/BiOBr/Cu2O. According to density functional theory (DFT) calculations, free radical capture tests, and identification based on liquid chromatography-mass spectrometry (LC–MS), the reaction species (h+, •OH, and •O2–) are crucial in the photocatalytic degradation of SDZ and its intermediates. Furthermore, the toxicity of the intermediates was analyzed using mung bean sprouting experiment and Toxicity Estimation Software Tool (T.E.S.T) software.

A triazine-based covalent organic framework decorated with cadmium sulfide for efficient photocatalytic hydrogen evolution from water

Construction of inorganic/organic heterostructures has been proven to be a very promising strategy to design highly efficient photocatalysts for solar driven hydrogen evolution from water. Herein, we report the preparation of a direct Z-scheme heterojunction photocatalyst by in situ growth of cadmium sulfide on a triazine-based covalent organic framework (COF). The triazine based-COF was synthesized by condensation reaction of precursors 1,3,5-tris-(4-formyl-phenyl) triazine (TFPT) and 2,5-bis-(3-hydroxypropoxy) terephthalohydrazide (DHTH), termed as TFPT-DHTH-COF. Widely distributed nitrogen atoms throughout TFPT-DHTH-COF skeletons serve as anchoring sites for strong interfacial interactions with CdS. The CdS/TFPT-DHTH-COF composite showed a hydrogen evolution rate of 15.75 mmol h−1 g−1, which is about 75 times higher than that of TFPT-DHTH-COF (0.21 mmol h−1 g−1) and 3.4 times higher than that of CdS (4.57 mmol h−1 g−1). With the properly staggered band alignment and strong interfacial interaction between TFPT-DHTH-COF and CdS, a Z-scheme charge transfer pathway is achieved. The mechanism has been systematically analyzed by steady state and time-resolved photoluminescence measurements as well as in situ irradiated X-ray photoelectron spectroscopy.

Z-scheme heterojunction photocatalyst formed by MOF-derived C-TiO2 and Bi2WO6 for enhancing degradation of oxytetracycline: Mechanistic insights and toxicity evaluation in the presence of a single active species

In the work, Bi2WO6/C-TiO2 photocatalyst was successfully synthesized for the first time by loading narrow bandgap semiconductor Bi2WO6 on MOF-derived carboxyl modified TiO2. The phase structure, morphology, photoelectric properties, surface chemical states and photocatalytic performance of the prepared photocatalysts were systematically investigated using various characterization tools. The degradation efficiency of oxytetracycline by 6BT Z-scheme heterojunction photocatalyst under visible light could reach 93.6 % within 100 min, which was related to the high light harvesting and effective separation and transfer of photo-generated carriers. Furthermore, the effects of various environmental factors in actual wastewater were further investigated, and the results showed that 6BT exhibited good adaptability, durability and resistance to interference. Unlike most works, the degradation system with a different single active species were designed and constructed based on their formation mechanism. In addition, for the first time, a positive study was conducted on the priority attack sites, intermediate products, and degradation pathways for the photocatalytic degradation of oxytetracycline by a single active species through HPLC-MS and Fukui index calculations. The toxicity changes of intermediate products produced in three different single active species oxidation systems were evaluated using toxicity assessment software tools (T.E.S.T.), Escherichia coli growth experiments, and wheat growth experiments. Among them, the intermediate products formed through O2– oxidation had the lowest toxicity and the main active sites it attacked were the 20C, 38O, 18C, 41O, and 55O atoms with high f+ values in the oxytetracycline molecular structure. This work provided the insight into the role of each active species in the degradation of antibiotics and offered new ideas for the design and synthesis of efficient and eco-friendly photocatalysts.

Internal electric field promoted NCDs/BiOBr/AgBr Z-scheme heterojunction with rich oxygen vacancies for efficient photocatalytic degradation of tetracycline and reduction of Cr (VI)

It is important to prepare efficient photocatalysts for the degradation of antibiotics and heavy metals. In this study, NCDs/BiOBr/AgBr Z-scheme heterojunction photocatalysts with excellent performance were constructed. NCDs/BiOBr/AgBr form a Z-type heterojunction system with pyrrole nitrogen-doped carbon quantum dots (NCDs) as charge transfer channels. The internal electric field formed in NCDs/BiOBr/AgBr greatly facilitated electron transfer. The more easily broken Bi-O bonds were utilized in the synthesis to introduce rich oxygen vacancies (OVs) into NCDs/BiOBr/AgBr to promote molecular oxygen activation. Meanwhile, silver nanorods were reduced in the synthesis to enhance the photodegradation performance. The photocatalytic degradation of tetracycline (TC) and reduction of Cr (VI) were enhanced by about 4 and 6 times. The factors affecting the removal effects of TC and Cr (VI) were analyzed. The catalysts were also tested to have good stability and potential for application in real wastewater. The reactive oxygen species (ROS), which play a dominant role in the photodegradation of TC and Cr (VI) by NCDs/BiOBr/AgBr, were tested, and a possible photocatalytic mechanism was proposed.

Bismuth-Based Z-Scheme Heterojunction Photocatalysts for Remediation of Contaminated Water.

Agricultural runoff, fuel spillages, urbanization, hospitalization, and industrialization are some of the serious problems currently facing the world. In particular, byproducts that are hazardous to the ecosystem have the potential to mix with water used for drinking. Over the last three decades, various techniques, including biodegradation, advanced oxidation processes (AOPs), (e.g., photocatalysis, photo-Fenton oxidation, Fenton-like oxidation, and electrochemical oxidation process adsorption), filtration, and adsorption techniques, have been developed to remove hazardous byproducts. Among those, AOPs, photocatalysis has received special attention from the scientific community because of its unusual properties at the nanoscale and its layered structure. Recently, bismuth based semiconductor (BBSc) photocatalysts have played an important role in solving global energy demand and environmental pollution problems. In particular, bismuth-based Z-scheme heterojunction (BBZSH) is considered the best alternative route to overhaul the limitations of single-component BBSc photocatalysts. This work aims to review recent studies on a new type of BBZSH photocatalysts for the treatment of contaminated water. The general overview of the synthesis methods, efficiency-enhancing strategies, classifications of BBSc and Z-scheme heterojunctions, the degradation mechanisms of Z- and S-schemes, and the application of BBZSH photocatalysts for the degradation of organic dyes, antibiotics, aromatics compounds, endocrine-disrupting compounds, and volatile organic compounds are reviewed. Finally, challenges and the future perspective of BBZSH photocatalysts are discussed.

Ag/α-Fe2O3/g-C3N4 nanocomposites as Z-scheme heterojunction photocatalysts for degradation of RhB

In this study, Ag/α-Fe2O3/g-C3N4 composites with varying α-Fe2O3 and Ag contents were synthesized by loading α-Fe2O3 and Ag nanoparticles onto the g-C3N4 with a high specific surface area via acid annealing. These composites were then utilized for the photocatalytic degradation of RhB under the irradiation of visible light. For α-Fe2O3/g-C3N4 composites with 5 wt% content of α-Fe2O3, the degradation efficiency reached a peak of 97.57% within 55 min, which was much higher than that of α-Fe2O3 and acid-annealed g-C3N4 with 45.92% and 83.61%, respectively. Furthermore, the photocatalytic degradation efficiency of Ag/α-Fe2O3/g-C3N4 composites reached its maximum of 99.61% with 1% content of Ag. It was demonstrated that the ternary Z-scheme heterojunction construction leaded to a significant enhancement of carrier separation and transfer effects, while the incorporation of Ag serves as electron reservoirs and photoinduced electrons capturers, thereby significantly enhancing the Fenton reaction and photocatalytic performance. This work is significant to drive the widespread application of g-C3N4 based heterojunctions in photocatalytic water purification.

Perovskite-based Z-scheme photocatalytic system for hydrogen production

Photocatalytic hydrogen production is recognized as a promising approach to produce greener hydrogen. The development of next-generation photocatalytic materials aims to enhance photocatalysis efficiency. Perovskite, a third-generation photocatalytic material, has gained interest in photocatalytic water splitting due to its optical stability, structural flexibility, bandgap tunability, and charge transfer efficiency. However, the perovskites are not able to achieve the targeted efficiency. Perovskite-based Z-scheme heterojunction photocatalysts can enhance efficiency. This review gives special attention to types and the formation of Z-schemes. In particular, photocatalysts involved in all-solid-state and direct Z-scheme for photocatalytic hydrogen production have been discussed.

Visible-light-driven tetracycline hydrochloride degradation via ZnTi-LDHs/Ce2S3 Z-scheme heterojunctions: Performance and mechanistic analysis

The refractory and hard-to-dispose tetracycline hydrochloride (TC) poses an enormous threat to human health and the water environment. Herein, a novel Z-scheme ZnTi-LDHs/Ce2S3 heterojunction photocatalyst was successfully developed for TC degradation under visible light conditions. This sophisticated material demonstrated a remarkable degradation rate of 0.0124 min−1, marking a noteworthy advancement compared to ZnTi-LDHs, Ce2S3, and the commonly reported LDHs/LDHs-based composites, with an approximate one-order-of-magnitude improvement. The inherent synergy between Ce2S3 and LDHs manifested as a Z-scheme charge transfer channel, augmenting visible-light absorption, and fostering carrier separation. Both O2·- and h+ played critical roles in the TC degradation process, mediating reductive and oxidative pathways, respectively. ZnTi-LDHs/Ce2S3 demonstrated robust reusability and broad applicability for degrading diverse dyes and antibiotics. This work demonstrated a promising protocol for crafting efficient Z-scheme heterojunction photocatalysts based on LDHs and expanded our understanding and potential applications of photocatalytic degradation mechanisms for antibiotics.

Fabrication of MoSe2/Bi3O4Br Z-scheme heterojunction with enhanced photocatalytic performance

Exploring a Z-scheme heterojunction photocatalyst with efficient charge separation and outstanding redox ability is necessary but very challenging. MoSe2 has received much attention as a co-catalyst due to its excellent optical properties. Herein, First-principles density functional theory (DFT) was employed for theoretical calculations of the energy band structure of Bi3O4Br, revealing crossed energy band structures with MoSe2, indicating favorable conditions for heterojunction formation. A solvothermal method was then used to synthesize MoSe2/Bi3O4Br heterostructure photocatalysts with a 2D/2D layered configuration. Characterization via SEM, TEM, DRS, XPS, BET, EIS, and PL confirmed that the MoSe2/Bi3O4Br heterostructure exhibited a larger specific surface area, more active sites, lower impedance, and reduced carrier recombination rate compared to pure Bi3O4Br and MoSe2. These features are advantageous for photocatalytic reactions. The optimized 2.5% MoSe2/Bi3O4Br photocatalyst demonstrated superior performance, achieving nearly 100% photodegradation of RhB under 90 min of simulated sunlight, with an apparent rate constant k value 7.57 times higher than that of Bi3O4Br. The composite photocatalyst exhibited excellent cycling stability over five experiments without significant reactivity attenuation. Finally, a plausible Z-scheme photocatalytic mechanism for MoSe2/Bi3O4Br heterojunctions is proposed based on experimental findings. This study provides new insights for exploring the construction of wide-band semiconductor heterojunctions.

Boosted photocatalytic accomplishment of 3D/2D hierarchical structured Bi4O5I2/g-C3N4 p-n type direct Z-scheme heterojunction towards synchronous elimination of Cr(VI) and tetracycline

The threats posed by heavy metal ions and antibiotics present in natural aqueous environments have been a serious cause of concern across the globe. The synchronous elimination of these contaminants through visible light responsive semiconductor mediated photocatalysis is a suitable strategy to solve this problem. However, designing proficient photocatalysts for the said purpose is a crucial task. Herein, hierarchical 3D/2D architectures of Bi4O5I2/g-C3N4 p-n type direct Z-scheme heterojunction photocatalysts (BOCNs) were fabricated by a two-step solvothermal-calcination approach. The characterisation of BOCNs by XRD, FTIR, XPS, SEM, TEM, HRTEM, LSV and MS techniques corroborated the robust heterojunction formation between Bi4O5I2 and g-C3N4. The presence of g-C3N4 and application of high treatment temperature (400 °C) assisted the formation of BiOC bond which is responsible for the development of an intimate interfacial interaction in BOCN. The heterostructured photocatalyst (BOCN3) demonstrated higher rate constant (kCr(VI)/synchronous) of 0.068 min−1 for Cr(VI) detoxification and that (kTCH/synchronous) of 0.075 min−1 for TCH degradation synchronously with respect to the reported values. The determined rate constants are about 1.8 folds greater than those were observed in isolated systems. The expedited photocatalytic activity can be ascribed to its wide visible light response, minimum charge recombination rate and increased redox ability. These are resulted from the synergistic effect of hierarchical 3D/2D architecture construction, existence of strong BiOC interfacial bond, p-n heterojunction formation and prevalence of direct Z-scheme charge transfer principle. The synchronous elimination of Cr(VI) and TCH over BOCN3 up to the fifth consecutive cycle without any appreciable change in photoactivity signified its enhanced stability and reusability. The plausible mechanism for the spectacular photocatalytic performance of BOCN3 was proposed.

A novel Z-scheme heterojunction photocatalyst CeO2@WO3 nanocomposite with enhanced visible-light photocatalytic performance for wastewater treatment by cephalexin antibiotic degradation: Process optimization

Considering growing global environmental concerns, there is a heightened focus on expediting the synthesis of highly efficient catalytic materials to address these challenges effectively. Herein, a novel CeO2@WO3 heterojunction photocatalyst was synthesized using an ultrasonic-assisted method for the environmentally friendly degradation of cephalexin (CPX) under visible light. The optimized photocatalyst synthesis condition was achieved by assessing the influence of effective parameters, including the CeO2 content (5–25 wt%) and calcination temperature (300–600 °C), employing the RSM method. The synthesized photocatalysts were comprehensively characterized through XRD, SEM, TEM, EDS-mapping, BET, FTIR, and UV–Vis band gap analysis. Using optimal photocatalyst (CeO2 content: 15.78 %, calcination temperature: 440.59 °C, and ultrasonic power: 80 W), the influence of four critical variables on CPX degradation was thoroughly investigated via RSM-CCD. The maximum CPX degradation efficiency of 98.8 % was attained under the following optimal conditions: CPX concentration: 20.00 mg/L, solution pH: 6.79, photocatalyst dosage: 0.019 g/L, and visible light time: 94.82 min. Statistical analysis confirmed the accuracy of the regression model based on empirical data. The CeO2@WO3 heterojunction demonstrated substantial Chemical Oxygen Demand (COD) removal, reaching 73.26 % during the mineralization of CPX, surpassing the outcomes of previous studies. Trapping experiments and EPR analysis indicated the crucial involvement of hydroxyl radicals and superoxide radicals as highly active species due to their non-selective oxidation capabilities. Furthermore, a Z-scheme charge transfer mechanism was proposed to elucidate the enhanced photocatalytic activity. Identifying degradation intermediates was accomplished through HPLC-MS analysis, leading to a plausible pathway for CPX degradation. Overall, CeO2@WO3 exhibited excellent stability and could endure five cycles with minimal cerium leaching, highlighting its effectiveness in decomposing organic contaminants.

Double Z-scheme in SnO2/SnS2/Cu2SnS3 heterojunction for photocatalytic reduction of CO2 to ethanol

Photocatalytic reduction of CO2 to chemical fuels enables a sustainable way of reducing carbon emissions but faces a high reduction potential due to the high stability of CO2 molecules. Here, we prepared a SnO2/SnS2/Cu2SnS3 double Z-scheme heterojunction photocatalyst, in which SnO2, SnS2, and Cu2SnS3 absorb ultraviolet, visible, and near-infrared light, respectively. Based on the comprehensive analysis of in-situ X-ray photoelectron spectroscopy and photo(chemical) characterizations, we find that the photogenerated electrons would transfer from SnO2 to SnS2 to Cu2SnS3. The optimized SnO2/SnS2/Cu2SnS3–0.3 double Z-scheme heterojunction could achieve 28.44 µmol g–1 h–1 ethanol yield and 92% selectivity, which is roughly 3 folds higher than SnO2/SnS2 single Z-scheme heterojunction. By using in-situ diffuse reflectance infrared Fourier-transform spectroscopy, we observe that ethanol is produced through a *COCOH pathway, in which Cu2SnS3 would decrease the activation energy barrier from *COOH to *CO.

Covalently linked MOF@COF direct Z-scheme heterojunction for visible light-driven photocatalytic degradation of flotation agents

It is necessary to find a green, highly efficient and cost-effective way to treat the water pollution caused by flotation agents that are widely used in mineral processing, coal desulfurization and water treatment. Herein, by wrapping an amino group-containing MOF core with a visible light active triazine COF through imine bonds, a covalently linked MOF@COF composite was prepared and found to work as a direct Z-scheme heterojunction photocatalyst for highly efficient visible light-driven degradation of flotation agents. As prepared MOF@COF not only inherits the merits of parent MOF and COF such as large specific surface area, porous framework, good crystallinity, and strong visible light-harvesting capability, but also shows other attractive advantages including robust stability, highly efficient photogenerated electron-hole pair separation and enhanced redox ability due to its covalently linking mode. After carefully selecting the COF content in the composite and optimizing reaction conditions, the resultant MOF@COF composite was successfully used for the photocatalytic degradation and mineralization of flotation agent pollutes in a wide concentration range, giving an apparent rate constant that was 3.2 and 3.5 times higher than those of parent MOF and COF, respectively. In view of systematical characterization and experimental analysis, the underlying reaction mechanism concerning Z-scheme heterojunction was proposed. This work provides a promising way to prepare high-performance photocatalytic materials for the degradation and removal of flotation agent pollutants using inexhaustible solar energy, and to broaden the applications of MOF and COF-based materials.

Facile fabrication of Z-scheme ZnO/MoO3 heterojunction as an excellent visible-light responsive photocatalyst for the degradation of rhodamine B and alizarin yellow dyes

xZnO-(1-x) MoO3(x = 0.0,0.1,0.3,0.5,0.7) nanocomposite materials have been efficiently fabricated by the facile hydrothermal method to enhance the photocatalytic activities for the environmental applications. The fabricated samples were characterized via XRD, SEM, EDX, XPS, UV–Visible spectroscopy, PL and FTIR analysis. The 5% ZnO-M nanocomposite material exhibits reduced band gab energy and superior photocatalytic activity for rhodamine B (RhB) and alizarin yellow (AY) dyes degradation of 94% and 81% within 120 min under visible light irradiance. Our reported study reveals that the 5% ZnO-M photocatalyst is extremely stable and reusable for more than five reaction of cycles. The photocatalytic enactment of the 5% ZnO-M composite was mostly endorsed due to Z-scheme photocatalysts, higher visible light adsorption on the surface morphology, improved charge separation/transfer, and decreased recombination rate. This study may provide new ideas for developing effective, innovative Z-scheme heterojunction photocatalysts and encouraging their extensive application for the degradation of dyes from wastewater.

Facile construction of iron-based MIL-101@MIL-53 Z-scheme heterojunction for efficient removal of tetracycline hydrochloride

A novel microporous iron-based MIL-101@MIL-53 Z-scheme heterojunction photocatalysts was synthesized via one-pot solvothermal strategy. The composition, structure, morphology and optical properties of the prepared photocatalysts were characterized by XRD, SEM,...

Strain-induced excellent photocatalytic performance in Z-scheme BlueP/γ-SnS heterostructures for water splitting.

Constructing Z-scheme heterojunction photocatalysts with high solar-to-hydrogen (STH) efficiency is a practical alternative to produce clean and recyclable hydrogen energy on a large scale. This paper presents the design of stable Z-scheme blue phosphorene (BlueP)/γ-SnS heterostructures with excellent photocatalytic activities by applying strains. The first-principles calculations show that the BlueP/γ-SnS heterobilayer is a type-I heterojunction with an indirect bandgap of 1.41 eV and strong visible-light absorption up to 105 cm-1. Interestingly, biaxial strains (ε) can effectively regulate its bandgap width (semiconductor-metal) and induce the band alignment transition (type-I-type-II). Compressive and tensile strains can significantly enhance the interfacial interaction and visible-light absorption, respectively. More intriguingly, compressive strains can not only modulate the heterojunction types but also make the band edges meet the requirements for overall water splitting. In particular, the Z-scheme (type-I) BlueP/γ-SnS bilayer at -8% (-2%) strain exhibits a relatively high STH efficiency of 18% (17%), and the strained Z-scheme system (-8% ≤ ε ≤ -6%) also exhibits high and anisotropic carrier mobilities (158-2327 cm2 V-1 s-1). These strain-induced outstanding properties make BlueP/γ-SnS heterostructures promising candidates for constructing economically feasible photocatalysts and flexible nanodevices.

Selective Hydrogenation of Cinnamaldehyde, Furanic, and Aromatic Aldehydes over a Z-Scheme Heterojunction Photocatalyst Constituted of Pd NPs Supported on g-C3N4/ZnO Nanocomposite

Selective Hydrogenation of Cinnamaldehyde, Furanic, and Aromatic Aldehydes over a Z-Scheme Heterojunction Photocatalyst Constituted of Pd NPs Supported on g-C₃N₄/ZnO Nanocomposite

Direct Z-scheme In2S3@BiYWO6 heterojunction photocatalysts for highly efficient environmental remediation

Novel In2S3@BiYWO6 heterojunction photocatalysts were designed and synthesized by a simple two-step hydrothermal method, which exhibit extremely excellent photocatalytic activity for degrading the residual antibiotics in wastewater. Especially, In2S3@BiYWO6 composite with mass ratio of 10:1 shows the highest photo-degradation efficiency towards Tetracycline Hydrochloride, which is about 2.46 and 7.55 times than that of pristine In2S3 and BiYWO6, respectively. A direct Z-scheme charge transfer mechanism was demonstrated in these heterojunctions through the XPS analysis, radical species trapping experiments and fluorescence detection. Within the framework of this mechanism, the critical built-in electric field (Ei) formed at the contact interface between In2S3 and BiYWO6 spatially separates reduction or oxidation sites and thus preserves the photogenerated carriers with stronger redox ability on reaction sites, which ultimately enhances the photocatalytic activity of the heterojunction catalysts. It is commendable that such Z-scheme heterostructures between In2S3 and BiYWO6 exist in a wide span of component ratios (from 5:1 to 30:1), which is beneficial for the environmental remediation applications. It is believed that this work provides new ideas for design and synthesis of novel Z-scheme heterojunction photocatalysts.

Facile synthesis of direct Z-scheme PPy/NH2-UiO-66 heterojunction for enhanced photocatalytic Cr(VI) reduction, industrial electroplating wastewater treatment, and tetracycline degradation

Z-scheme heterojunction photocatalysts generally have excellent redox ability and robust removal efficiency for contaminants in water. Herein, we combined p-type PPy and n-type NH2-UiO-66 by ball milling to prepare a direct Z-scheme PPy/NH2-UiO-66 photocatalyst with ultra-high redox potential. Notably, the optimized efficiency of PPy/NH2-UiO-66 (the mass ratio of PPy to NH2-UiO-66 is 1 wt%, named PPy/NU-1) rapidly reduced Cr(VI) (>95%, 60 min) and TC degradation (>90%, 180 min) at 100 W LED light. Moreover, the PPy/NU-1 has high stability and good anti-interference ability, which can effectively remove Cr(VI) from industrial electroplating wastewater, and the Cr(VI) removal rate is 99%, which meets the industrial wastewater standard and has the potential attraction of actual wastewater treatment. In addition, the techniques of UV-Vis diffuse reflection, electron spin resonance (ESR), photoluminescence (PL), and photoelectrochemical measurement showed that PPy/NH2-UiO-66 composites improved the light capture ability, thereby improving the photocatalytic efficiency. The PPy/NU-1 has a very high redox potential by constructing a Z-scheme heterojunction, enhances the interfacial charge transfer ability, and improves the separation efficiency of photogenerated carriers. Finally, the mechanism of the Z-scheme was systematically by nitroblue tetrazolium (NBT) and p-phthalic acid (TA) transformation, ESR experiments, and density functional theory (DFT) calculations. This work provides a strategy for the preparation of visible photocatalysts with excellent photocatalytic activity and provides new insights for interfacial charge transfer and molecular oxygen activation.

Engineering direct Z-scheme GCN/ bimetallic-MOF heterojunctions as efficient and recyclable photocatalysts for enhancing degradation of RR 195 under visible light

Direct Z-scheme heterojunction photocatalyst GCN/M-FeBTC (M: Ni, Co, Cu, Zn, Mn; BTC: 1,3,5-benzenetricarboxylate, GCN: graphitic carbon nitrides) were synthesized by in-situ hydrothermal method assisted using microwave. GCN/M-FeBTC materials exhibit excellent photocatalytic performance with nearly 100 % of reactive red 195 (RR-195) being removed after 30 min under direct sunlight irradiation. Tests for reactive radicals have shown that holes (h+) and superoxide radicals (•O2–) close a major function in the removal of RR-195. Based on the band structure (BS) of the material, a direct Z-scheme heterojunction photocatalyst mechanism has been proposed. The effects of catalyst mass, pH and RY-145 concentration on the photocatalytic activity of GCN/Mn-FeBTC materials were also researched. The innovation of the photocatalytic activity of the GCN/Mn-FeBTC materials may be due to the synergistic combination of factors such as: (i) the high surface area; (ii) visible light absorption and efficient splitting of electron (e–) and h+; (iii) increased oxygen vacancies and defects; (iv) shortening of charge transport distances. The decomposition pathway of RR-195 was determined based on liquid chromatography mass spectrometry (LC-MS) analysis. Chemical oxygen demand (COD), biological oxygen demand (BOD) and total organic carbon (TOC) show high mineralization potential for the degradation of RR-195 on direct Z-scheme photocatalysts GCN/M-FeBTC.