Z-scheme Charge Transfer Mechanism Research Articles

Fabrication of a Novel Co/CoO@Fe2 V4 O13 Composite Catalyst as a Photoanode for Enhanced Photoelectrochemical Water Oxidation.

Herein, the synthesis of a novel composite photocatalyst, Co/CoO@Fe2 V4 O13 , is reported by the deposition of CoO metal oxide nanoparticles on the surface of Fe2 V4 O13 bimetallic oxide. The synthesised photocatalyst exhibited a band gap of roughly 1.8 eV, rendering it responsive to the complete visible light spectrum of the sun, thereby enabling optimal absorption of solar radiation. The Co/CoO@Fe2 V4 O13 composites demonstrated an enhanced photoelectrochemical water oxidation capacity compared to pristine Fe2 V4 O13 when exposed to visible light. The enhanced performance is attributed primarily to the creation of a p-n junction at the interface of Fe2 V4 O13 and Co/CoO, as well as the Z-scheme charge transfer mechanism, which aids in the separation and transfer of photogenerated charge carriers. Light absorption by Co nanoparticles via plasmonic excitation and intra- and inter-band transitions in the composite structure is also likely, resulting in increased composite efficiency. Our findings indicate that Co/CoO@Fe2 V4 O13 composites show promising performance for solar water splitting applications and offer new perspectives for designing effective photocatalysts.

Dual Z-scheme heterojunction NH2-UiO-66/BiOBr/AgI with enhanced performance on visible light driven elimination of tetracycline and Cr(VI)

To tackle the challenges for photocatalysts efficacy enhancement, a novel dual Z-scheme NH2-UiO-66/BiOBr/AgI (NUBA) ternary composite photocatalyst was constructed and systematically characterized. NUBA displayed much higher visible light photocatalytic efficacies in tetracycline (TC) degradation and Cr(VI) reduction than the corresponding single components and binary composites. With employment of NUBA and visible light irradiation, 97% of TC was removed in 40 min whereas 96% of Cr(VI) was reduced in 30 min for the individual TC and Cr(VI) solution. Furthermore, NUBA manifested superior efficacy in simultaneously and synergistically removing TC/Cr(VI) mixture than for corresponding single pollutant. A dual Z-scheme charge transfer mechanism was established which confirmed that •O2− and h+ dominated TC degradation, whereas photo-induced electrons implemented Cr(VI) reduction. The promoted activity of NUBA was attributed to the synergism through incorporating the advantages furnished by individual components with rich charge transfer channels, larger specific surface areas, and strengthen visible light harvest, thus preeminently reinforced the production, separation and transportation of photogenerated charge carriers. NUBA demonstrated good anti-interfering ability and wide applicability for organic pollutants degradation, along with exceptional stability and durability for cyclic use. This work may supply an inspiration for the construction of efficacious dual Z-scheme photocatalytic systems for wastewater remediation.

Novel Z-scheme MgFe2O4/Bi2WO6 heterojunction for efficient photocatalytic degradation of tetracycline hydrochloride: Mechanistic insight, degradation pathways and density functional theory calculations

In this study, a new Z-scheme MgFe2O4/Bi2WO6 heterojunction was successfully prepared by hydrothermal and wet ball milling process. The results of the study showed that after 90 min of visible light exposure, the photocatalytic degradation of tetracycline hydrochloride (TCH) by 25%-MgFe2O4/Bi2WO6 heterojunction was as high as 95.82%, and the highest photocatalytic rate (0.0281 min−1) was 4.61 and 3.43 times higher than that of pure Bi2WO6 (0.0061 min−1) and MgFe2O4 (0.0082 min−1), respectively. Furthermore, spin-polarized density functional theory (DFT) calculations were performed to provide additional evidence of the presence of a Z-scheme charge transfer mechanism between MgFe2O4 and Bi2WO6. We investigated the effects of initial TCH concentration, pH, coexisting ions and different water sources on the efficiency of photocatalytic degradation of TCH in composite samples. The recovery experiments demonstrated that the MgFe2O4/Bi2WO6 composites had good stability and repeatability. A series of experimental results showed that 25%-MgFe2O4/Bi2WO6 had a larger specific surface area, better ultraviolet and visible absorbance, superior charge transfer and higher efficiency of photogenerated electron-hole pair separation. This paper provides new ideas for the design and preparation of new Z-scheme heterojunctions and has great prospects for practical applications in the field of wastewater treatment.

Constructing novel inorganic-organic α-Fe2O3/SNW-1 Z-scheme heterojunction for Methylene Blue photodegradation

A novel organic/inorganic heterostructured photocatalyst binary nanocomposite was typically prepared by the solvothermal method. The overwhelming superiority of this composite has been confirmed by spectroscopic and characterization methods, where the addition of α-Fe2O3 reduced the agglomeration of the Schiff-based covalent organic framework SNW-1 and significantly increased the specific surface area. The effects of operating parameters such as catalyst dosage, initial solution concentration, and pH on photocatalytic degradation of methylene blue (MB) dye were carefully investigated. Among them, a UV irradiation time of 80 min, a powder dose of 0.6 g/L, and pH=2 were the best choice. Under these favorable conditions, the α-Fe2O3/SNW-1 system exhibited excellent photocatalytic performance, and the degradation rate of MB reached more than 95%. In addition, the photocatalytic degradation efficiency of the pollutants acid orange 7 (AO7), rhodamine-B (RhB), and acid red (ArB) comfortably reached 92%, 92%, and 91%, respectively. After five cycles of testing, the prepared photocatalyst showed good stability and reusability. Through energy band calculation, free radical quenching experiment, and electron paramagnetic resonance (ESR) study, it was discovered that the main active substances were ·O2- and ·OH, and the photogenerated holes and electrons also participated in the photocatalytic reaction. The Z-scheme charge transfer mechanism of α-Fe2O3/SNW-1 was proposed. Photoelectric chemical tests further demonstrated the extraordinary photocatalytic activity, low internal resistance, and high carrier separation capability of the binary nanocomposites. This study presents the potential application of high-performance photocatalysts for the removal of organic dyes in water purification.

Ag/Ag2S–TiO2 composite film formed using dual phase Ag/Ag2O layer as a sulfurized layer for enhanced photocatalytic activity

The Ag/Ag2S–TiO2 composite films were synthesized through vulcanizing sputtering Ag/Ag2O dural-phase template capping layer on the TiO2 film. After hydrothermal vulcanization using thiourea as a sulfur precursor, the initially decorated Ag2O layer transformed into the Ag2S. The surface morphology of the continuous block structure of the Ag/Ag2S composite layer gradually shrinks to form irregular island grains dispersed on the surface of the composite film, with vulcanization reaction duration increased from one to 3 h. The light absorption ability of the Ag/Ag2S–TiO2 composite film was enhanced substantially compared to the TiO2 film because of the surface plasmon resonance effect from the Ag particles and the narrow energy band of the Ag2S. Among various surface morphologies of the Ag/Ag2S–TiO2 composite films, the irregular island Ag/Ag2S grains-decorated TiO2 composite film presents superior photoelectrochemical and photocatalytic degradation performances than the composite films consisting of continuous block and spider-web structure of the Ag/Ag2S decorated layers. The synergistic effects of surface plasmon resonance, Ag pathway between the semiconductors, and Z-scheme charge transfer mechanism explain the high-efficiency photocatalytic activity of the Ag/Ag2S–TiO2 composite films.

Construction of CdS@ZnO core–shell nanorod arrays by atomic layer deposition for efficient photoelectrochemical H2 evolution

Photoelectrochemical (PEC) water splitting provides a promising strategy for the production of clean hydrogen fuel. Herein, a new CdS@ZnO core–shell nanorod arrays (NRAs) is successfully constructed by atomic layer deposition (ALD) for H2 evolution from PEC water splitting. The CdS@ZnO200 obtained after 200 ALD cycles presents a significantly enhanced PEC H2 evolution rate of 21.64 μmol·h−1·cm−2, which is about 9.4 times of pristine CdS NRAs (2.31 μmol·h−1·cm−2). The reasons for the improved PEC H2 evolution performance can be ascribed to several aspects: firstly, the Z-scheme charge transfer mechanism formed between CdS core and ZnO shell promotes the effective spatial separation of photo-induced electrons and holes; secondly, the close contact between the two semiconductors resulted from ALD process helps to reduce the transfer resistance of charge carriers. In addition, the CdS core is tightly wrapped by ZnO shell, which helps to prevent the photo-corrosion of CdS core. This work provides a new type of photoanode material suitable for PEC H2 evolution from water splitting, and provides an efficient anti-corrosion method for the use of photocorrosive semiconductor materials.

SnC/PtS2 heterostructure: A promising direct Z-scheme photocatalyst with tunable electronic optical properties and high solar-to-hydrogen efficiency

Due to their excellent ability of hydrogen evolution, the direct Z-scheme heterostructures are promising to be candidates for next-generation photocatalysts. In this article, the structure, electronic and photocatalytic properties of SnC/PtS2 heterojunction have been investigated by first-principles. The data suggest that SnC/PtS2 heterostructure possesses a Type-Ⅱ band alignment with an indirect bandgap of 1.27 eV which is considerably lower than the bandgap of the SnC (1.79 eV) and PtS2 monolayers (2.67 eV). The built-in electric field directed towards PtS2 from SnC gives rise to a Z-scheme charge transfer mechanism. A maximum bandgap value of 1.32 eV is expressed by the heterojunction at 2% compressive strain. More importantly, the redox potential of water under biaxial strain of −8%–4% is fully satisfied. Light absorption coefficients of 3.81 × 105 cm−1 and the solar-to-hydrogen efficiency of 13.50% proves that the energy of photons is able to be utilized adequately by the heterostructure. Additionally, the absorption peak of the heterojunction at 650 nm is as high as 2.47 × 105 cm−1 under 4% tensile strain. We are therefore convinced that SnC/PtS2 heterojunction have great possibilities for applications in the field of photocatalytic water decomposition.

Interface designing of efficient Z-scheme Ti-ZnFe2O4/In2O3 photoanode toward boosting photoelectrochemical water oxidation

Ti-ZnFe2O4 photoanode has attracted extensive attention in photoelectrochemical (PEC) water oxidation due to its narrow band gap and good photostability. However, its low efficiency limits its development. Herein, we designed and constructed direct Z-scheme Ti-ZnFe2O4/In2O3 (Ti-ZFO/In2O3) photoanode. Under the interface electric field, photogenerated holes with stronger oxidation capacity on In2O3 are retained to participate in the water oxidation reaction, and the photocurrent density of Ti-ZFO/In2O3 is much higher than that of pure Ti-ZFO, reaching 2.2 mA/cm2 at 1.23 V vs. RHE. Kelvin Probe, steady-state photovoltage spectroscopy (SPV), transient photovoltage spectroscopy (TPV) and in-situ double beam strategy were used to demonstrate the Z-scheme charge transfer mechanism of Ti-ZFO/In2O3 photoanode. Our work provides an effective scheme and technical means for further understanding the mechanism of interfacial charge transfer.

Visible light-driven photocatalytic degradation of fluoroquinolone drugs in water over plasmonic Ag/ZnNb2O6@SC3N4 indirect Z-scheme nanostructures

The fabrication of visible light responsive heterojunction photocatalyst with efficient charge separation and transfer is an important quest in the exploitation of photocatalysis for environmental remediation. In this work, a ternary heterostructure comprising of zinc niobate (ZnNb2O6) coupled with sulphur-doped graphitic carbon nitride (SC3N4) and decorated with varying loadings of silver nanoparticles (Ag NPs) was obtained using ultrasonic synthesis. The photocatalysts were characterized extensively using various microscopic, spectroscopic, and electrochemical analytical techniques. The 5 wt%Ag/ZnNb2O6 @SC3N4 heterojunction showed the highest degradation efficiencies towards the antibiotic drugs; levofloxacin (LVF, 94.6 % removal) and ofloxacin (OFX, 98.0 % removal) in just 60 min of visible light irradiation. This activity is nearly 5 times and 3.5 times higher than that over ZnNb2O6 @SC3N4 for LVF and OFX, respectively, which indicates the importance of incorporating the Ag NPs towards better visible utilization, improved charge separation efficiency and lower charge transfer resistance. The influence of pH, photocatalyst dose and initial concentration of pollutant were investigated. Finally, a typical Ag NPs mediated indirect Z-Scheme charge transfer mechanism was proposed to describe the formation of the reactive species and subsequent degradation of the pollutants. This work demonstrates a systematic design of simple but efficient photocatalytic nanocomposites with the capability to ameliorate a wide variety of fluoroquinolone drugs, which is significant towards pharmaceutical pollution mitigation.

Construction of electron donor–acceptor Z-scheme heterojunction for boosting photocatalytic H2 production

Enhancing the solar energy conversion of metal-free graphitic carbon nitride (g-C3N4) based photocatalyst remains a great challenge. Herein, a novel Z-scheme heterojunction photocatalyst is constructed by in-situ anchoring Pt6 NCs on carbon self-doping g-C3N4 (CCN/Pt6 NCs) for boosting photocatalytic H2 evolution activity. Remarkably, the optimized CCN/Pt6 NCs photocatalyst exhibits high H2 evolution rate of 6.32 mmol·h−1·g−1 and 36.25 mmol·h−1·g−1, which is ≈150.5 and ≈412 times than that of pristine CN under visible light (λ > 420 nm) and full solar spectrum irradiation, respectively, outperforming majority of the reported g-C3N4-based photocatalysts. Systematic characterizations have revealed that CCN with delocalized electrons and larger the work function is deemed to be a preferable electron-acceptor. Meanwhile, Pt6 NCs with appropriate HOMO-LUMO level is regarded as an electron-donor. Theoretical and experimental works reveal that the favorable photocatalytic performance of CCN/Pt6 NCs heterojunction is mainly attributed to the giant internal electric field induced donor–acceptor interaction, which achieves Z-scheme charge transfer mechanism. This work opens up new insights for rational fabrication of metal-free g-C3N4 based photocatalysts to boost the solar energy conversion.

Janus Z-scheme heterostructure of ZnIn2S4/MoSe2/In2Se3 for efficient photocatalytic hydrogen evolution

Artificial manipulation of charge separation and transfer are central issues dominating hydrogen evolution reaction triggered via photocatalysis. Herein, through elaborate designing on the architecture, band alignment, and interface bonding mode, a sulfur vacancy-rich ZnIn2S4-based (Vs-ZIS) multivariate heterostructure ZnIn2S4/MoSe2/In2Se3 (Vs-ZIS/MoSe2/In2Se3) with specific Janus Z-scheme charge transfer mechanism is constructed through a two-step hydrothermal process. Steering by the Janus Z-scheme charge transfer mechanism, photogenerated electrons in the conduction band of MoSe2 transfer synchronously to the valence band of Vs-ZIS and In2Se3, resulting in abundant highly-active photogenerated electrons reserved in the conduction band of Vs-ZIS and In2Se3, therefore significantly enhancing the photocatalytic activity of hydrogen evolution. Under visible light irradiation, the optimized Vs-ZIS/MoSe2/In2Se3 with the mass ratio of MoSe2 and In2Se3 to ZnIn2S4 at 3 % and 30 %, respectively, performs a high hydrogen evolution rate of 124.42 mmol·g−1·h−1, about 43.5-folds of the original ZIS photocatalyst. Besides, an apparent quantum efficiency (AQE) of 22.5 % at 420 nm and favorable durability are also achieved over Vs-ZIS/MoSe2/In2Se3 photocatalyst. This work represents an important development in efficient photocatalysts and donates a sound foundation for the design of regulating charge transfer pathways.

In situ construction of oxygen deficient MoO3-x nanosheets/porous graphitic carbon nitride for enhanced photothermal-photocatalytic hydrogen evolution

In this work, the photocatalysts containing oxygen-deficient molybdenum oxide and macroscopic three-dimensional porous graphitic carbon nitride phase composite (MoO3-x/PCN) were prepared by in situ self-assembly method. The crystal phase and structure were characterized by XRD, XPS, FT-IR, SEM, and TEM measurements. Hydrogen production results showed that introducing of MoO3-x resulted in a higher hydrogen production rate of MoO3-x/PCN composite catalyst than that of PCN. Among them, the highest hydrogen production rate of 2336.15 μmol g−1 h−1 was achieved for MoO3-x-10/PCN, which was 2.23 times higher than PCN (1048.00 μmol g−1 h−1). When the reaction system temperature was 100 °C, the photothermal hydrogen production rate of MoO3-x-10/PCN was 8902.00 μmol g−1 h−1, which was 3.81 times higher than that at room temperature. PL spectra, UV–vis spectra and photoelectrochemical measurements showed that the localized surface plasmon resonance (LSPR) effect of MoO3-x effectively enhanced the photo response range and increased the temperature of the reaction system. ESR measurements showed that he composites should follow the Z-scheme charge transfer mechanism, the electrons in the CB of MoO3-x further migrate to the VB of PCN, which hinders the charge complexation in MoO3-x and PCN, improving the hydrogen production activity. This study provides a new idea for constructing a plasma-based photothermal synergistic catalytic hydrogen production strategy.

Constructing NiWO4/In2S3 hetero-junction to promote photo-generated carriers separation for enhancing photo-catalytic performance

Semiconductor photo-catalysis is a reliable solution in settling environmental pollution and energy shortage, but the single-phased semiconductors generally have low catalytic efficiency due to the ultra-fast recombination of photo-generated electron-hole pairs. The construction of hetero-junction is a popular and effective strategy to enhance photo-catalytic performance. Herein, the NiWO4/In2S3 hetero-junction was successfully prepared through chemical precipitation and hydrothermal two-step method. The structure and morphology of samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Meanwhile, not only the X-ray photoelectron spectroscopy (XPS) was used to confirm the formation of hetero-junctions, but also the diffuse reflectance spectroscopy (DRS) and photo-electrochemical tests were used to characterize the capacity of optical absorption and the photo-generated carrier separation. The photo-catalytic performances of all samples were assessed by rhodamine B (RhB) degradation, potassium dichromate (Cr6+) reduction and hydrogen production. Results indicated that NiWO4/In2S3 hetero-junction exhibited better photo-catalytic performance than those of NiWO4 and In2S3. Z-scheme charge transfer mechanism of NiWO4/In2S3 hetero-junction was suggested based on the results of trapping and electrochemical experiments.

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.

An Unprecedented Strategy to Fabricate Inside/Surface Homojunction in Bismuth Oxychloride for Efficient Photocatalysis

The design of an efficient homojunction in bismuth oxychloride via simple means is still challenging. Herein, an inside/surface homojunction of bismuth oxychloride via fabricating surface-layer oxygen vacancies from a sulfur dopant and surface-layer hydroxyl from an alkali modification (BOCSO) in a one-pot hydrothermal process is successfully prepared. BOCSO exhibits enlarged specific surface area, improved adsorption of substrate, and enhanced photogenerated charge separation and transfer efficiencies. Extensive characterizations and density functional theory (DFT) calculations demonstrate BOCSO can form a defect level via surface oxygen vacancies and S doping to narrow the energy gap and capture the photogenerated electrons and holes. Meanwhile, both oxygen vacancies and hydroxyls on the BOCSO surface can also form an inside/surface homojunction containing an interfacial electric field (IEF) to induce a direct Z-scheme charge transfer mechanism. Taking advantage of the above, the photocatalytic degradation activity is remarkably elevated compared to that of pristine BiOCl (BOC). This work provides a new strategy for the fabrication of an inside/surface homojunction in bismuth oxychloride via novel surface modification engineering.

Construction of hierarchical core-shell Z-scheme heterojunction FeVO4@ZnIn2S4 for boosted photocatalytic degradation of tetracycline

Constructing core-shell heterojunction and designing hierarchical structures have been considered as efficient strategies for enhancing the activity and stability of photocatalysts. Herein, a novel hierarchical core-shell Z-scheme heterojunction FeOV4@ZnIn2S4 was prepared via the in-situ growth of ZnIn2S4 on the surface of FeVO4 submicron bar with a facile solvothermal method. The formation of the hierarchical core-shell heterostructure between FeVO4 and ZnIn2S4 improved light-harvesting ability and promoted the separation of photoinduced electron-hole pairs. The prepared FeOV4@ZnIn2S4 exhibited superior photocatalytic activity toward tetracycline. The removal efficiency of tetracycline reached up to 90.8% within 120 min. The degradation rate were 5.75 and 2.06 times that of FeVO4 and ZnIn2S4, respectively. Furthermore, Z-Scheme charge transfer mechanism at the interface between FeVO4 and ZnIn2S4 was proposed based on the results obtained from radical trapping test and electron spin resonance (ESR), which revealed that •O2−, •OH and h+ all act as active species in photocatalytic reaction. This work can bring a strategy for the preparing highly efficient heterojunction photocatalysts.

Visible light and iodate/iodide mediated degradation of bisphenol A by self-assembly 3D hierarchical BiOIO3/Bi5O7I Z-scheme heterojunction: Intermediates identification, radical mechanism and DFT calculation

Broadening the light absorption and inhibiting carrier's recombination are vital to the improvement of photocatalytic performance. Herein, self-assembly 3D hierarchical microsphere BiOIO3/Bi5O7I Z-scheme heterojunction with carrier transfer channel was firstly fabricated by in-situ solvothermal method. The degradation efficiency for bisphenol A (BPA) reached 98.9 % within 60 min visible light irradiation. The enhanced photocatalytic activity was benefited from the Z-scheme system assisted by iodate/iodide (IO3-/I-) as carrier transfer channel that not only accelerated the interfacial charge separation, but also provided massive reactive centers for obtaining high redox capacity. The vulnerable sites and the degradation pathways of BPA were identified by density functional theory calculations and liquid chromatography-mass spectrometry analyses. The toxicity of BPA and its intermediates were predicted by ECOlogical Structure Activity Relationship (ECOSAR) and the results demonstrated that BPA was eventually mineralized to harmless products. The Z-scheme charge transfer mechanism was deeply elucidated based on the role of active species (·O2-, ·OH and h+), band structure and carrier separation efficiency. This study provides a promising strategy for the photoactivity enhancement of bismuth based heterojunction in environment purification.

Interfacial chemical bond modulated Z-scheme mechanism in In2−xS3/Cd1+xIn2−xS4 heterojunction for enhanced photocatalytic CO2 reduction and wastewater treatment

An interfacial CdS bond modulated hierarchical Z-scheme heterostructure composed by indium vacancies-rich In2-xS3 and Cd-rich Cd1+xIn2-xS4 (In2-xS3/Cd1+xIn2-xS4) is rationally designed and fabricated by using MIL-68 (In) as precursor and template, and used for efficient photocatalytic wastewater treatment and CO2 reduction. The in-situ ion-exchange derived CdS bond at the heterointerface induced the Z-scheme charge transfer mechanism in hierarchical In2-xS3/Cd1+xIn2-xS4 photocatalyst, which is verified by the X-ray photoelectron spectroscopy, electron paramagnetic resonance and density functional theory calculations. Moreover, the hierarchical ultrathin and loose two-dimensional nanosheet structure is conducive to expose more active sites and adsorb more reactants. By integrating the efficient adsorption capacity and Z-scheme mechanism, the In2-xS3/Cd1+xIn2-xS4 photocatalyst shows superior photocatalytic CO2 reduction activity and high removal efficiency of dyes and heavy metal. For example, under visible light illumination, it removed almost 100 % of various dyes within 10 min operation, and reduced 100 % Cr(VI) within 1 h, and it also manifested state-of-the-art production rates of 132.5 and 392.1 μmol h−1 g−1 for CH4 and CO, respectively, in reducing CO2 without co-catalyst. A useful inspiration on purposive modulating Z-scheme charge transfer by atomic-level interface engineering was proposed to significantly promote the photocatalytic performance.

Photo-Fenton assisted AgCl and P-doped g-C3N4 Z-scheme photocatalyst coupled with Fe3O4/H2O2 system for 2, 4-dimethylphenol degradation

In this study graphitic carbon nitride (g-C3N4 or GCN) and phosphorus doped graphitic carbon nitride (p-g-C3N4 or PCN) were prepared using facile thermal polycondensation method. Phosphorus doping was employed to preserve the non-metallic nature of GCN. The AgCl/PCN/Fe3O4 heterojunction was synthesized using a simple in-situ route. The photocatalytic performance of the GCN, PCN, Fe3O4 and AgCl/PCN/Fe3O4 was tested towards 2, 4-dimethylphenol (DMP) pollutant. The work explored improvement in physiochemical properties and reduction of band gap of GCN after P doping (through Tauc's plot method). Coupling with AgCl (silver halide) also enhanced photoinduced charge carriers' separation and migration ability due to apt band alignment among both AgCl and PCN photocatalysts which resulted in formation of direct Z-scheme charge transfer mechanism. Similarly, the incorporation of ferrimagnetic material i.e. Fe3O4 enhanced the generation of hydroxyl (•OH) radicals via photo-Fenton process and facilitated photocatalysts easy separation from the aqueous medium. Through PL and EIS analysis the enhanced charge separation and migration ability in AgCl/PCN/Fe3O4 nanocomposite was validated. The attained DMP degradation efficiency of photo-Fenton assisted AgCl/PCN/Fe3O4/H2O2 Z-scheme nanocomposite was much higher i.e. 99% compared to other photocatalysts within 60 min of visible light irradiation following pseudo-first-order kinetics. Electron paramagnetic resonance (EPR) and scavenging tests confirmed the substantial role of •OH and •O2− radicals in the photo-Fenton reaction. Furthermore, liquid chromatography-mass spectrometry (LC-MS) analysis detected the generated oxidative products and mineralization pathways associated with DMP degradation. The proposed direct Z-scheme charge transfer route presented efficient charge separation and migration ability in AgCl/PCN/Fe3O4 nanocomposite. Recycle ability of the fabricated AgCl/PCN/Fe3O4 photocatalyst was tested up to 5 cycles with 90% removal efficacy, confirming the excellent reusability and stability of AgCl/PCN/Fe3O4 photocatalyst.

Fabrication of CdS/ZnCr-LDH heterojunctions with enhanced of tetracycline hydrochloride photocatalytic degradation under visible light

Water pollution caused by antibiotics is one of the main problems facing mankind. Photocatalytic degradation is a green, thorough and effective method to remove antibiotics from wastewater, which has broad application prospects. In this study, a Z-scheme photocatalyst constructed by cadmium sulfide (CdS) and ZnCr-layered double hydroxide (ZnCr-LDH) was prepared by hydrothermal method. The properties of the photocatalysts were fully characterized and the photocatalytic performance were evaluated via degradation tetracycline hydrochloride (TCH) under visible light irradiation. The CdS/ZnCr-LDH-5 photocatalyst was very effective for the removal of TCH (84.9%), which is 4.7 times and 2.5 times than that of its precursor ZnCr-LDH and CdS, respectively. The enhanced degradation efficiency of CdS/ZnCr-LDH-5 photocatalyst can be attributed to the high redox ability and charge separation efficiency. Finally, possible degradation pathway and a Z-scheme degradation mechanism was proposed according to the liquid chromatography-mass spectrometry (LC-MS), radial trapping experiments and band energy structure, respectively. This work provides new sights for the design heterojunctions with a Z-scheme charge transfer mechanism for effective photocatalytic degradation antibiotics.