Effective Electron-hole Separation Research Articles

The performance and mechanism of persulfate activation boosted MoO2@LDHs Z-scheme heterojunction for efficient photocatalytic degradation of tetracycline

Photocatalytic activation of persulfate for the synergistic degradation of pollutants has become a major research hotspot, but the activation effect is poor due to the problems of low catalyst carrier separation efficiency and insufficient active sites. In this study, direct Z-Scheme heterojunctions of MoO2@CoFe LDHs were prepared by a simple hydrothermal method and a Co and Fe dual active site system was constructed to activate Na2S2O8 (PS) for the synergistic degradation of tetracycline under visible light. The results showed that the synergistic degradation of tetracycline was 3.7 times and 2.7 times more efficient than the original heterojunction and PS, respectively. Combining material characterisation, photovoltaic performance tests and theoretical calculations revealed that the high efficiency is attributed to the formation of an internal electric field under the Z-Scheme heterostructure type generating effective electron-hole separation, with more photo-generated electrons converted into radicals acting together with holes to degrade the TC and activate the PS. More importantly, Co(II) and Fe(II) provide electrons to synergistically activate PS, and a portion of the photogenerated electrons and PS activation intermediates can facilitate cycling between Co(II)/Co(III) and Fe(II)/Fe(III) to accelerate PS activation. This paper's work on activating PS-assisted Z-Scheme heterojunctions for the efficient degradation of TC provides a reference for the study of high-performance photocatalytic catalysts for the degradation of organic pollutants.

Study on Method and Mechanism of Noble Metals Photoelectric Deposition by Directly Utilizing Solar Energy

The recovery of noble metals is crucial in terms of resource utilization and ecological environment. Herein, a green strategy for the recovery of three noble metals, Au, Ag, and Pt, by photoelectric deposition at the cathode without external voltage is described. The realizability and mechanism of noble metals deposition are investigated and analyzed in terms of the band structure and the reduction potential of metal ions using the special heterostructure ZnO/ZnS composites derived from metal–organic frameworks, as well as ZnO and Fe2O3 semiconductors. It is found that ZnO/ZnS has preferable photoelectrochemical performance than pure ZnO due to their effective electron–hole separation and appropriate band matching structure. To deposit metals Au, Ag, and Pt, the potential of electrons in the conduction band of ZnO/ZnS should be more negative than the reduction potential of these metals, allowing for the deposition of these metals while simultaneously undergoing an oxygen evolution reaction, mediated by the photogenerated holes on the surface of the photoanode, and the collection of conduction band electrons by the back electrode.

Enhanced photocatalytic activity of cubic ZnSn(OH)6 by in-situ partial phase transformation via rapid thermal annealing

In this study, a mixed phase ZnSn(OH)6/ZnSnO3 photocatalyst was synthesized by calcining ZHS nanostructures via rapid thermal annealing (RTA) process. The composition ratio of ZnSn(OH)6/ZnSnO3 was controlled by changing the duration of the RTA process. The obtained mixed-phase photocatalyst was characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectroscopy, ultraviolet photoelectron spectroscopy, photoluminescence, and physisorption analysis. Results showed that ZnSn(OH)6/ZnSnO3 photocatalyst obtained by calcining ZHS at 300 °C for 20 sec displayed the best photocatalytic performance under UVC light illumination. Under optimized reaction conditions, ZHS-20 (0.125 g) demonstrated nearly complete removal (>99%) of MO dye in 150 min. Scavenger study revealed the predominant role of OH• in photocatalysis. The enhanced photocatalytic activity of the ZnSn(OH)6/ZnSnO3 composites was mainly ascribed to the photosensitization of ZHS by ZTO and effective electron-hole separation at the ZnSn(OH)6/ZnSnO3 heterojunction interface. It is expected that this study will provide new research input for the development of photocatalyst through thermal annealing-induced partial phase transformation.

Hydrazine-induced synthesis of CdS nanorings for the application in photodegradation

In this paper, CdS nanorings synthesized by a facile hydrazine-induced microwave method for the photodegradation of pollutants were reported for the first time. Different reaction method, microwave power, the category and dosage of pH regulating reagent, reaction temperature and reaction time were investigated. The formation of CdS nanorings from the self-assembly of nanoparticles was attributed to the coordination of hydrazine producing the dipole–dipole interaction among the uniform nanoparticles prepared by microwave method. The crystal phase, composition, morphology and surface property of CdS nanorings were characterized. The results showed that 100 nm-sized wurtzite CdS nanorings generated with the self-assembly of 5–8 nm nanoparticles, which presented mesoporous structures. To study the influence of ring-like structures on the photocatalysis, the photodegradation of rhodamine B (RhB) with CdS nanorings and nanoparticles was compared. The results showed that, CdS nanorings displayed higher photodegradation efficiency, which were originated from more favorable band edge potential and effective electron–hole separation producing more superoxide radical and holes as active specifies. The photodegradation path of RhB contained the process of the demethylation, the decarboxylation process, the chromophore cleavage and ring-open reactions. Finally, the available photodegradation of multiple pollutants and reusability of CdS nanorings were carried out.

Strong interface interaction and internal electric field promote electron transfer of Bi2O2S/NiFe2O4 heterojunction for photocatalytic antibiotic degradation

Heterojunction photocatalysts have shown considerable activities for organic pollutants degradation. However, the faint connection interface and inferior charge shift efficiency critically block the property of heterojunction photocatalysis. Herein, Bi2O2S/NiFe2O4 nanosheets heterojunction with ultrastrong interface interaction and high internal electric field are designed by an in-situ growth method. Tentative and theoretical consequences prove that the interfacial interaction and internal electric field not only act as the electron flow bridge but also decrease the electrons shift energy obstacle, thus speeding up electrons transfer and achieving effective spatial electron-hole separation. Therefore, a large amount of ·O2– and holes as active species were generated. Remarkably, Bi2O2S/NiFe2O4 establishes a considerably boosted photocatalytic performance for tetracycline degradation (0.032 min–1), which is about 14.2-fold and 7.8-fold of the pristine BOS and NFO, respectively. This work provides a promising motivation for modulating charge transfer by interface control and internal electric field to boost photocatalytic performance.

Titanium-based metal-organic framework capsulated with magnetic nanoparticles: Antimicrobial and photocatalytic degradation of pesticides

Pesticide residues create an ecological ecosystem that is incredibly dangerous and presents major risks to human health. To solve this issue, scientists are concentrating on creating extremely effective composites with superior photocatalytic performance. Even if several efforts have been made to remove pesticides and dangerous compounds using adsorption, the development of novel adsorbents with large adsorption capabilities is still very desirable. Here, the photocatalytic of carbamate pesticides in aqueous solution under simulated sunlight irradiation in the existence of Fe3O4, CuO/Cu2O, MIL-125-NH2, Fe3O4@MIL-125-NH2 and CuO/Cu2O@MIL-125-NH2 were investigated. The photocatalytic process may be credited with the effective electron-hole separation and wider area of light response. Moreover, the mechanism of pesticide photocatalytic process was discovered as mineralization of pesticides to carbon dioxide, water, sulphate, and ammonia. Total organic carbon (TOC) analysis was used to quantify the mineralization of pesticides while UV spectroscopy was used to measure the rates of pesticides photocatalytic activity. CuO/Cu2O@MIL-125-NH2 and Fe3O4@MIL-125-NH2 composite demonstrated the maximum pesticide photocatalytic efficiency and outstanding cycle stability. The antimicrobial potency was increased and the inhibition zone was minimised when treated by a parent MIL-125-NH2 and its composites, which is surprising data when employing CuO/Cu2O@MIL-125-NH2 and Fe3O4@MIL-125-NH2 nanocomposite as an anti-bacterial material.

Combination of covalent-organic framework and Bi2O2S by covalent bonds to form p-n heterojunction for enhanced photocatalytic CO2 conversion

The objective of current photocatalysis research is to increase the separation efficiency of photogenerated carriers and convert CO2 into useful resources for human beings. In the present study, TpPa-2-COF was successfully grown in situ on Bi2O2S nanosheets by hydrothermal and thermal solvent two-step experimental method, and a typical p-n heterojunction was constructed by covalent-bond between TpPa-2-COF and Bi2O2S, which significantly improved the photocatalytic activity of CO2. When Bi2O2S@TpPa-2-COF-15 heterojunction was illuminated with 300 W xenon lamp for 3 h, the CO yield reached 19.5 μmol·g−1·h−1, while the CH4 yield reached 6.2 μmol·g−1·h−1. Compared with pure TpPa-2-COF and Bi2O2S, the photocatalytic activity of the Bi2O2S@TpPa-2-COF-15 increased 66.8 and 3.96 times, respectively. Meanwhile, the Bi2O2S@TpPa-2-COF-15 composite showed good stability under multiple cycles. Furthermore, the mechanism of Bi2O2S@TpPa-2-COF heterojunction enhanced photocatalytic reduction of CO2 was also proposed. The experimental and characterization findings have shown that the transit of photo-generated electron-hole pairs via TpPa-2-COF to Bi2O2S may be greatly promoted to achieve the effect of electron hole separation under visible-light irradiation.

Modular calcination strategy to construct defect-rich nitrogen-doped Nb2O5 for boosting photocatalytic oxidation of cyclohexane to cyclohexanone in solvent-free conditions

The partial oxidation of cyclohexane (CHA) with oxygen to cyclohexanone (CHA-one) is one of the most transformation in the chemical industry in view that CHA-one is an irreplaceable raw material in the production of nylon. Herein, hydrogen, vacuum and air modules combined with ammonia module, respectively, were used to construct defect-rich nitrogen-doped Nb2O5. And, the calcination order and temperature were also considered to establish a modular calcination strategy. A series of modified N-doped Nb2O5 were prepared by the proposed strategy, which were used to catalyze the photo-oxidation of CHA in solvent-free and room temperature conditions. Among these modified N-doped Nb2O5 samples, the HN-Nb2O5 possessed abundant chemical defects of oxygen vacancies and Nb4+, and achieved the best photocatalytic performance. Surprisingly, HN-Nb2O5 achieved an amount of 130.35 μmol for CHA-one, which was approximately 2.2 and 26 times that of the pure Nb2O5 and commercial Nb2O5, respectively, with up to 96.68% selectivity to CHA-one. The outstanding photocatalytic performance of the HN-Nb2O5 can be ascribed to the presence of chemical defect-rich and the NOx species, enhanced light absorption and effective electron-hole separation. DFT calculations explained the promotion of the chemical defects and N doping on Nb2O5 photocatalytic activity in terms of the band electron and band-gap level. The results of EPR analysis and scavenger tests found that e− is the main active species resulted in photocatalytic activity, while O2− is the dominant active species for producing CHA-one in the photo-oxidation of CHA. The present work developed an efficient strategy to construct the defect-rich N-doped metal oxide for the improved photocatalytic oxidation of hydrocarbon.

Mg-doped TiO2 nanorods-SrTiO3 heterojunction composites for efficient visible-light photocatalytic degradation of basic yellow 28

In this study, a series of Mg-doped TiO2/SrTiO3 heterojunctions were constructed using SrTiO3 nanoparticles anchored onto the surface of TiO2 nanorod arrays. Titanium dioxide (TiO2) nanorods and SrTiO3 nanoparticles were synthesized using the liquid phase deposition (LPD) and sol-gel methods, respectively. The photocatalytic activity of obtained photocatalysts was investigated towards the degradation of basic yellow 28 (BY28) dye under visible-light irradiation compared to the pristine TiO2 nanorods and SrTiO3 nanoparticles. The obtained samples were carefully characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron (XPS), UV–Vis, and photoluminescence spectroscopy. 1.5 Mg–TiO2/SrTiO3 nanocomposite demonstrated the highest photocatalytic activity and the corresponding apparent rate constants of 0.0255 min−1 which is that is 2.9, 9.4, and 2.3 times higher than TiO2 nanorods, SrTiO3 nanoparticles, and TiO2/SrTiO3 nanocomposite, respectively. This enhanced photocatalytic performance can be attributed to the improved charge transfer, more effective electron-hole separation, and a red-shift in light absorption derived from the Mg doping and coupling effect of TiO2 nanorods and SrTiO3 nanoparticles.

Solvent-free fabrication of broadband WS<sub>2</sub> photodetectors on paper

Paper-based devices have attracted extensive attention due to the growing demand for disposable flexible electronics. Herein, we integrate semiconducting devices on cellulose paper substrate through a simple abrasion technique that yields high-performance photodetectors. A solvent-free WS₂ film deposited on paper favors an effective electron-hole separation and hampers recombination. The as-prepared paper-based WS₂ photodetectors exhibit a sensitive photoresponse over a wide spectral range spanning from ultraviolet (365 nm) to near-infrared (940 nm). Their responsivity value reaches up to ~270 mA W⁻¹ at 35 V under a power density of 35 mW cm⁻². A high performance photodetector was achieved by controlling the environmental exposure as the ambient oxygen molecules were found to decrease the photoresponse and stability of the WS₂ photodetector. Furthermore, we have built a spectrometer using such a paper-based WS₂ device as the photodetecting component to illustrate its potential application. The present work could promote the development of cost-effective disposable photodetection devices.

Visible-light-driven organic oxidation over CdS-doped metal-organic frameworks.

In this research, we synthesized CdS nanoparticle-doped metal-organic frameworks (CdS@DUT-52) with different contents using a solvothermal method. CdS@DUT-52 possesses strong light absorption ability and effective electron-hole separation properties, which was proved by performing UV-vis spectroscopy and photoelectrochemical testing. It was used to trigger the photooxidation of amines, sulfides, and alcohols to produce the corresponding imines, sulfoxides, and aldehydes in the presence of air or oxygen, exhibiting considerable yields of products under visible light irradiation compared with a single component.

Multifunctional porous nanofibrous membranes with superior antifouling properties for oil-water separation and photocatalytic degradation

The oily wastewater composed of complicated organic pollutants and bacteria showed a huge threat on the environment and humans. Currently, the membrane used to treat oily wastewater have the problems of cumbersome preparation, weak adhesion and metal leaching, and membrane pollution is also the focus of urgent problems. In this study, the metal-free chlorine-sulphur double-doped graphitic carbon nitride (Cl/S-g-C3N4) photocatalyst was incorporated into polyacrylonitrile (PAN) nanofibrous membrane via an electrospun method. The resultant porous nanofibrous membrane possessed the superior superhydrophilicity and superoleophobicity under water, ensuring a high separation efficiency (>98.0%) for various oil-in-water emulsions. Specially, the membrane achieved a superior self-cleaning property after visible light irradiation for crude oil/water mixture and actual oily wastewater with FRR up to 95%, which was related to the enhanced light absorption ability and the effective electron hole separation ability of Cl/S-g-C3N4. Moreover, the porous structure increased the possibility of contact between contaminants/bacteria and reactive species, beneficial to the photodegradation and antibacterial properties, achieving extremely high resistance to contamination. Overall, the multifunctionality of the porous anti-fouling nanofibrous membrane exhibited a huge potential in practical oily wastewater treatment.

Facile Preparation of a Bispherical Silver-Carbon Photocatalyst and Its Enhanced Degradation Efficiency of Methylene Blue, Rhodamine B, and Methyl Orange under UV Light.

The combination of organic and inorganic materials is attracting attention as a photocatalyst that promotes the decomposition of organic dyes. A facile thermal procedure has been proposed to produce spherical silver nanoparticles (AgNPs), carbon nanospheres (CNSs), and a bispherical AgNP-CNS nanocomposite. The AgNPs and CNSs were each synthesized from silver acetate and glucose via single- and two-step annealing processes under sealed conditions, respectively. The AgNP-CNS nanocomposite was synthesized by the thermolysis of a mixture of silver acetate and a mesophase, where the mesophase was formed by annealing glucose in a sealed vessel at 190 °C. The physicochemical features of the as-prepared nanoparticles and composite were evaluated using several analytical techniques, revealing (i) increased light absorption, (ii) a reduced bandgap, (iii) the presence of chemical interfacial heterojunctions, (iv) an increased specific surface area, and (v) favorable band-edge positions of the AgNP-CNS nanocomposite compared with those of the individual AgNP and CNS components. These characteristics led to the excellent photocatalytic efficacy of the AgNP-CNS nanocomposite for the decomposition of three pollutant dyes under ultraviolet (UV) radiation. In the AgNP-CNS nanocomposite, the light absorption and UV utilization capacity increased at more active sites. In addition, effective electron-hole separation at the heterojunction between the AgNPs and CNSs was possible under favorable band-edge conditions, resulting in the creation of reactive oxygen species. The decomposition rates of methylene blue were 95.2, 80.2, and 73.2% after 60 min in the presence of the AgNP-CNS nanocomposite, AgNPs, and CNSs, respectively. We also evaluated the photocatalytic degradation efficiency at various pH values and loadings (catalysts and dyes) with the AgNP-CNS nanocomposite. The AgNP-CNS nanocomposite was structurally rigid, resulting in 93.2% degradation of MB after five cycles of photocatalytic degradation.

Reduced Graphene Oxides Modified Bi2Te3 Nanosheets for Rapid Photo‐Thermoelectric Catalytic Therapy of Bacteria‐Infected Wounds

AbstractTemperature variation‐induced thermoelectric catalytic efficiency of thermoelectric material is simultaneously restricted by its electrical conductivity, Seebeck coefficient, and thermal conductivity. Herein, Bi2Te3 nanosheets are in situ grown on reduced graphene oxides (rGO) to generate an efficient photo‐thermoelectric catalyst (rGO‐Bi2Te3). This system exhibits phonon scattering effect and extra carrier transport channels induced by the formed heterointerface between rGO and Bi2Te3, which improves the power factor value and reduces thermal conductivity, thus enhancing the thermoelectric performance of 2.13 times than single Bi2Te3. The photo‐thermoelectric catalysis of rGO‐Bi2Te3 significantly improves the reactive oxygen species yields, resulting from the effective electron–hole separation caused by the unique thermoelectric field and heterointerfaces of rGO‐Bi2Te3. Correspondingly, the electrospinning membranes containing rGO‐Bi2Te3 nanosheets exhibit high antibacterial efficiency in vivo (99.35 ± 0.29%), accelerated tissue repair ability, and excellent biosafety. This study provides an insight into heterointerface design in photo‐thermoelectric catalysis.

Enhanced photocatalytic and photoelectrochemical performance of KBiFe2O5/g-C3N4 heterojunction photocatalyst under visible light

Here we report the synthesis of graphitic carbon nitride (g-C3N4)/brownmillerite KBiFe2O5 (KBFO) based heterojunction photocatalyst. The heterojunction composite revealed rod shaped KBFO embedded on the surface of g-C3N4. The distinct phases of individual compounds are revealed through X-ray diffraction. An effective reduction in bandgap energy of KBFO/g-C3N4 (KCN) composite in comparison to pristine g-C3N4 confirmed the formation of heterojunction. Photocatalytic performance of as developed heterostructures is tested and compared by degrading common organic effluent methylene blue (MB). 25 wt% of g-C3N4 content in KBFO sample shows a remarkable improvement (92% degradation efficiency) over pure KBFO (77%) and g-C3N4 (54%). The electrode composed of 25 wt% g-C3N4 content in KBFO also reveals significant photoelectrochemical response (0.3 mA/cm2) over KBFO (1.5 μA/cm2). The improvement was attributed to an effective electron-hole separation in the heterojunction. These stable and reusable KBFO/g–C3N4 heterostructures hold promising future materials for energy and environmental applications.

A Paper-Based Photoelectrochemical Sensing Platform Based on In Situ Grown ZnO/ZnIn2S4 Heterojunctions onto Paper Fibers for Sensitively Detecting AFP.

Nowadays, developing a cost-effective, easy-to-operate, and efficient signal amplification platform is of important to microfluidic paper-based analytical devices (μPAD) for end-use markets of point-of-care (POC) assay applications. Herein, an ultrasensitive, paper-based photoelectrochemical (PEC) bioassay platform is constructed by in situ grown ZnO/ZnIn2S4 heterojunctions onto paper fibers, which acted as photoactive signal amplification probes for enhancing the sensitivity of antibodies-based diagnostic assays, for the sensitive detection of alpha-fetoprotein (AFP) targets. The crystalline flake-like ZnIn2S4 composited with hexagonal nanorods (NRs) morphology of ZnO is an in situ grown, at the first time, onto cellulose fibers surface supported with Au nanoparticle (Au NP) modification to improve conductivity of the device working zone. The obtained composites on paper fibers are implemented as a flexible paper-based photoelectrode to realize remarkable performance of the fabricated μPAD, resulting from the enhanced PEC activity of heterojunctions with effective electron-hole pair separation for accelerating photoelectric conversion efficiency of the sensing process under light irradiation. Once the target AFP was introduced into the biosensing interface assistant, with a specific recognition interaction of AFP antibody, a drastically photocurrent response was generated, in view of the apparent steric effects. With the concentration increase of AFP targets, more immune conjugates could be confined onto the biosensing interface, eventually leading to the quantitative decrease of photocurrent intensity. Combined with an ingenious origami design and permitting the hydrophobic/hydrophilic conversion procedure in the bioassay process, the ultrasensitive PEC detection of AFP targets was realized. Under the optimized conditions, the level of AFP could be sensitively tracked by the prepared μPAD with a liner range from 0.1 to 100 ng mL−1 and limit of detection of 0.03 ng mL−1. This work provides a great potential application for highly selective and sensitive POC testing of AFP, and finally, developments for clinical disease diagnosis.

Application of Copper(II)-Organic Frameworks Bearing Dilophine Derivatives in Photocatalysis and Guest Separation.

The functionalized design of metal-organic frameworks (MOFs) has been rapidly developed in the last 20 years, and its broad applicability has been demonstrated in many fields. MOFs with desired functions can be assembled using predesigned organic linkers with specific metal nodes, which possess the ordered functional sites and open structures. Although a large number of carboxylic acid junctions have been used to construct MOFs, it is still a great challenge to realize their multifunctionality. In particular, there is a relative lack of research on MOFs as direct photocatalysts, which require not only abundant active sites and open structures but also adsorption groups and effective electron-hole separation performance. To this end, MOFs constructed from the carboxylic acid ligands derived from lophine-based derivatives and copper ions were deliberately used as a photocatalyst, and then, their application in dye degradation and aromatic alcohol conversion was investigated. In addition, in combination with the abundant Lewis sites of copper ions and imidazole sites, the material shows not only the adsorption and separation of C2 series and dyes but also the application of dye degradation and conversion of aromatic alcohols under illumination conditions. The corresponding results fully illustrate that the MOF constructed by using lophine derivatives can be an effective way to prepare photocatalysts. The subsequent research ideas will focus on designing a series of MOFs constructed with multilinked moieties of lophine groups and exploring their application strategies in the field of photocatalysis.

Hydrogen evolution from visible light by CdS nanocrystals made of 0D quantum dots on 1D nanorods

The photocatalytic hydrogen evolution (PHE) activity of CdS photocatalysts is restricted by their inherent defects such as photocorrosion and rapid recombination of charge carriers. In this study, a hydrothermal approach was developed for the synthesis of one-dimensional (1D) CdS nanorods (CSNRs) coated with zero-dimensional (0D) CdS quantum dots (CSQDs) with the objective of enhancing photogenerated charge separation and transfer, and ultimately improve PHE. HRTEM images confirmed that CSQDs had intimate contact with CSNRs and were well distributed on the surface of CSNRs. A surface and porosity analysis showed that optimal CSQDs/CSNRs exhibited an augmented specific surface area compared to unmodified CSNRs, which facilitates charge transport and surface reactions. PHE experiments carried out under visible light demonstrated that CSQDs loaded on the surface of CSNRs enhanced PHE 1.51 times. Transient photocurrent, electrochemical impedance spectroscopy, and photoluminescence analyses indicated that the improved PHE was mainly due to more effective electron-hole separation due to charge transfer between CSQDs and CSNRs.

Unveiling charge dynamics of Co3S4 nanowalls/CdS nanospheres n-n heterojunction for efficient photoelectrochemical Cr(VI) detoxification and N2 fixation

Photoelectrochemical (PEC) conversion of solar energy is a sustainable and ecological approach as it offers green energy carriers, renewable fuels as well as environmental remediation. Herein, a polyaniline-coated anodized stainless-steel mesh (PANI-ASSM) was supported n-n heterojunction of CdS nanosphere (NSs)-Co3S4 nanowalls (NWs) by a simple step by step electrochemical deposition method. The PEC performance of the developed photoanode was then assessed toward Cr(VI) detoxification and N2 fixation. The PL, UV-Vis, electrochemical impedance spectroscopy (EIS), intensity-modulated photocurrent spectroscopy (IMPS), cyclic voltammetry (CV), transient photocurrent (TPC), chronopotentiometry, and Bode phase tests also proved the excellent PEC performance and significant stability of this catalyst. UV–vis, Urbach energy (UE), Mott-Schottky (M-S), and linear sweep voltammetry (LSV) results coupled to the Robert Mulliken method confirmed the formation of robust n-n CdS-NSs-Co3S4-NWs heterojunction with viable band edge potential for Cr(VI) detoxification and N2 fixation; while PANI only acted as a powerful bridge to transfer the photo-generated electrons to ASSM support. The possible mechanism was investigated by experimental and electrochemical analysis which suggested a 3-electron-coupled Cr(VI) and 6-electron-coupled N2 reduction pathway. Such a PEC exhibited considerable electrocatalytic performance due to effective electron-hole separation with an ammonia yield and Cr(VI) reduction of 12.33 µg/mol.h NH3 and 90.61%, respectively. This work presented a new paradigm for the illustrative design of promising photoanodes for renewable fuel production and detoxification performance.

The First-Principle Study on Tuning Optical Properties of MA2Z4 by Cr Replacement of Mo Atoms in MoSi2N4.

Recently, with the successful preparation of MoSi2N4, an emerging family of two-dimensional (2D) layered materials has been predicted with a general formula of MA2Z4 (M: an early transition metal, A: Si or Ge and Z: N, P, or As). In terms of this new type of 2D material, how to effectively tune its light absorption properties is unclear. We systematically discuss the effects of replacing Mo with Cr atoms on the lattice structure, energy bands, and light absorption properties of 2D monolayer MoSi2N4 using density functional theory (DFT) and the Vienna Ab initio Simulation Package (VASP). Additionally, the results show that the single replacement of the atom Cr has no significant effect on the lattice structure of the outermost and sub-outer layers but plays a major role in the accumulation of electrons. In addition, the 2D MoSi2N4, Mo0.5Cr0.5Si2N4, and CrSi2N4 all have effective electron–hole separation properties. In the visible region, as the excited state increases, the required excitation energy is higher and the corresponding wavelength of light is shorter. It was found that the ultraviolet (UV)–visible spectra are red-shifted when Cr atoms replace Mo atoms in MoSi2N4; when Cr atoms and Mo atoms coexist, the coupling between Cr atoms and Mo atoms achieves modulation of the ultraviolet (UV)–visible spectra. Finally, we reveal that doping M-site atoms can effectively tune the light absorption properties of MA2Z4 materials. These results provide a strategy for the design of new 2D materials with high absorption properties.