Modulation Of Electron Transfer Research Articles

Fine-Tuning Electron Transfer for Nanozyme Design.

Nanozymes, with their versatile composition and structural adaptability, present distinct advantages over natural enzymes including heightened stability, customizable catalytic activity, cost-effectiveness, and simplified synthesis process, making them as promising alternatives in various applications. Recent advancements in nanozyme research have shifted focus from serendipitous discovery toward a more systematic approach, leveraging machine learning, theoretical calculations, and mechanistic explorations to engineer nanomaterial structures with tailored catalytic functions. Despite its pivotal role, electron transfer, a fundamental process in catalysis, has often been overlooked in previous reviews. This review comprehensively summarizes recent strategies for modulating electron transfer processes to fine-tune the catalytic activity and specificity of nanozymes, including electron-hole separation and carrier transfer. Furthermore, the bioapplications of these engineered nanozymes, including antimicrobial treatments, cancer therapy, and biosensing are also introduced. Ultimately, this review aims to offer invaluable insights for the design and synthesis of nanozymes with enhanced performance, thereby advancing the field of nanozyme research.

Synthesis of iron-manganese bimetallic materials supported by activated carbon and application of activated persulfate in the degradation of soil contaminated by crude oil

Heterogeneous catalytic processes based on zero-valent iron (ZVI) have been developed to treat soil and wastewater pollutants. However, the agglomeration of ZVI reduces its ability to activate persulfate (PS). In this study, a new Fe-Mn@AC activated material was prepared to activated PS to treat oil-contaminated soil, and using the microscopic characterization of Fe-Mn@AC materials, the electron transfer mode during the Fe-Mn@AC activation of PS was clarified. Firstly, the petroluem degradation rate was optimized. When the PS addition amount was 8%, Fe-Mn@AC addition amount was 3% and the water to soil ratio was 3:1, the petroluem degradation rate in the soil reached to the maximum of 85.69% after 96 hours of reaction. Then it was illustrated that sulfate and hydroxyl radicals played major roles in crude oil degradation, while singlet oxygen contributed slightly. Finally, the indigenous microbial community structures remaining after restoring the Fe-Mn@AC/PS systems were analyzed. The proportion of petroleum degrading bacteria in soil increased by 23% after oxidation by Fe-Mn@AC/PS system. Similarly, the germination rate of wheat seeds revealed that soil toxicity was greatly reduced after applying the Fe-Mn@AC/PS system. After the treatment with Fe-Mn@AC/PS system, the germination rate, root length and bud length of wheat seed were increased by 54.05%, 7.98 mm and 6.84 mm, respectively, compared with the polluted soil group. These results showed that the advanced oxidation system of Fe-Mn@AC activates PS and can be used in crude oil-contaminated soil remediation.

Combustion Growth of NiFe Layered Double Hydroxide for Efficient and Durable Oxygen Evolution Reaction.

NiFe layered double hydroxide (LDH) with abundant heterostructures represents a state-of-the-art electrocatalyst for the alkaline oxygen evolution reaction (OER). Herein, NiFe LDH/Fe2O3 nanosheet arrays have been fabricated by facile combustion of corrosion-engineered NiFe foam (NFF). The in situ grown, self-supported electrocatalyst exhibited a low overpotential of 248 mV for the OER at 50 mA cm-2, a small Tafel slope of 31 mV dec-1, and excellent durability over 100 h under the industrial benchmarking 500 mA cm-2 current density. A balanced Ni and Fe composition under optimal corrosion and combustion contributed to the desirable electrochemical properties. Comprehensive ex-situ analyses and operando characterizations including Fourier-transformed alternating current voltammetry (FTACV) and in situ Raman demonstrate the beneficial role of modulated interfacial electron transfer, dynamic atomic structural transformation to NiOOH, and the high-valence active metal sites. This study provides a low-cost and easy-to-expand way to synthesize efficient and durable electrocatalysts.

Modulating Electron Transfer between Pt and MOF Support through Pd Doping Promotes Nanozyme Catalytic Efficiency.

Electron transfer is considered to be a typical parameter that affects the catalytic activity of nanozymes. However, there is still controversy regarding whether higher or lower electron transfer numbers are beneficial for improving the catalytic activity of nanozymes. To address this issue, we propose the introduction of Pd doping as an important electron regulation strategy to tune electron transfer between Pt and ZIF-8 carriers (PtxPd1@ZIF-8). We observe a volcano-shaped relationship between the electron transfer number and catalytic activity, reaching its peak at Pt4Pd1@ZIF-8. Mechanism studies indicate that as the electron transfer number from Pt to ZIF-8 carriers increases, the d-band center of the active site Pt increases, reducing the occupancy of antibonding states and enhancing the adsorption capacity of the key intermediate (*O). However, a further increase in the adsorption of *O energy makes it difficult to desorb and participate in the next reaction, thus exhibiting volcanic activity. The optimized Pt4Pd1@ZIF-8 nanozyme is applied to develop an immunoassay for the detection of zearalenone, achieving a detection limit of 0.01 μg/L, which is 6 times higher than that of the traditional enzyme-linked immunosorbent assay. This work not only reveals the potential regulatory mechanism of electron transfer on the catalytic activity of nanozymes but also improves the performance of nanozyme-based biosensors.

Anti-oxidative reactivity and mechanism of formic hydrazide, acethydrazide and butyrohydrazide towards reduction of single electron oxidant iridium(IV)

Reduction of a well-known single electron oxidant [IrCl6]2– by aliphatic hydrazides, viz. formic hydrazide, acethydrazide and butyrohydrazide, was investigated by use of several techniques including 1H NMR and rapid scan spectroscopies. It was demonstrated that the redox reactions exclusively follow second-order kinetics over a wide pH range; the observed second-order rate constants k' versus pH profiles have been established. When the features revealed by the rapid scan spectra, the reaction stoichiometry and the oxidation products were considered together, a reaction mechanism was proposed involving three parallel rate-determining steps in which [IrCl6]2– reacted with all the three protolytic forms of the hydrazides. Rate constants of the rate-determining steps and the dissociation constants of hydrazides at 25.0 °C and 1.0 M ionic strength were derived from the kinetic data. Activation parameters were determined for the reactions of [IrCl6]2– with the neutral forms of the hydrazides, and an outer-sphere electron transfer mode was implied. The reactivity of each protolytic form of the hydrazides was elucidated and its distribution versus pH was calculated. The reactivity of the protolytic forms was compared with that of the corresponding forms of aryl hydrazides, revealing that both the neutral and enolate forms of aliphatic hydrazides are less reactive than those of the aryl hydrazides towards reduction of [IrCl6]2–. It was concluded that aryl hydrazides are more important than aliphatic ones in the development of new hydrazide-based antioxidants in the future. Additionally, the protolysis equilibria of these aliphatic hydrazides in aqueous solution and their redox properties have been characterized and the dissociation constants in the case of butyrohydrazide are reported for the first time.

Halogen-powered static conversion chemistry.

Halogen-powered static conversion batteries (HSCBs) thrive in energy storage applications. They fall into the category of secondary non-flow batteries and operate by reversibly changing the chemical valence of halogens in the electrodes or/and electrolytes to transfer electrons, distinguishing them from the classic rocking-chair batteries. The active halide chemicals developed for these purposes include organic halides, halide salts, halogenated inorganics, organic-inorganic halides and the most widely studied elemental halogens. Aside from this, various redox mechanisms have been discovered based on multi-electron transfer and effective reaction pathways, contributing to improved electrochemical performances and stabilities of HSCBs. In this Review, we discuss the status of HSCBs and their electrochemical mechanism-performance correlations. We first provide a detailed exposition of the fundamental redox mechanisms, thermodynamics, conversion and catalysis chemistry, and mass or electron transfer modes involved in HSCBs. We conclude with a perspective on the challenges faced by the community and opportunities towards practical applications of high-energy halogen cathodes in energy-storage devices.

A signal amplifying photoelectrochemical immunosensor based on the synergism of Au@CoFe2O4 and CdS/NiCo2O4 for the sensitive detection of neuron-specific enolases

Neuron-specific enolase (NSE), a marker of small cell lung cancer, is over-expressed in patient serum. To reduce the threat of lung cancer to human health and life, a rapid and effective method for the sensitive detection of NSE is necessary. In this study, a sandwich-type photoelectrochemical (PEC) immunosensor for the rapid and sensitive detection of NSE was constructed. To provide a powerful and stable photocurrent signal, the bandgap-matched CdS/NiCo2O4 was used as the substrate material. In addition, Au@CoFe2O4, which can form a step electron transfer mode with NiCo2O4, was proposed for the first time as a second antibody (Ab2) marker to amplify photoelectric signals. The constructed signal-amplified PEC immunosensor showed good linearity in the range of 1 pg/mL − 100 ng/mL with a detection limit as low as 0.24 pg/mL (S/N=3). The constructed PEC immunosensor has shown excellent stability, selectivity, reproducibility, and repeatability. It showed recoveries in the range of 98% − 105% and relative standard deviations (RSD) within 5% in sample analysis. The method proposed in this study is expected to be more widely used in the future for the detection of other disease markers as well as environmental pollutants.

TEMPO radically expedites the conversion of sulfides to sulfoxides by pyrene-based metal-organic framework photocatalysis

Metal-organic frameworks (MOFs) are well-documented for visible light photocatalysis because of their tailorable structures and tunable absorptions through organic linkers. By employing a highly conjugated linker, 4,4’,4’’,4’’’-(pyrene-1,3,6,8-tetrayltetrakis(ethyne-2,1-diyl))tetrabenzoic acid, the optical absorption of the MOF NU-1100 is effectively tuned to visible light below 600 nm region. Under green light irradiation, NU-1100 triggers charge separation and modulates electron transfer from the linkers to the Zr6O4(OH)412+ clusters, driving the oxidation of sulfides to sulfoxides. Notably, adding a redox mediator radically expedites the oxidation of sulfides by NU-1100 photocatalysis, TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl) and 4-carboxy-TEMPO. At least 2.7 and 5.2 times of conversions of phenyl methyl sulfide are achieved by NU-1100 photocatalysis with TEMPO and 4-carboxy-TEMPO, respectively. A series of characterizations illustrate that 4-carboxy-TEMPO is adsorbed onto the exterior surface of Zr6O4(OH)412+ clusters of NU-1100 to mediate hole transfer and achieve higher charge transfer efficiency. Mechanistic studies indicate that superoxide is the essential reactive oxygen species and that the oxidation of sulfides is driven by an electron transfer pathway. This study demonstrates the integration of redox mediators with MOFs can drive more efficient visible light photocatalytic reactions.

Reactivity of tris(3-hydroxypropyl)phosphine species towards reduction of hexachloroiridate(IV): a comparison with tris(2-carboxyethyl)phosphine

Tris(3-hydroxypropyl)phosphine (THPP) was shown to be a more powerful reductant than tris(2-carboxyethyl)phosphine (TCEP), but its oxidation kinetics and mechanisms were scarcely investigated. The reduction of single electron oxidant [IrCl6]2− by THPP was thus investigated comparatively and shown to follow overall second-order kinetics. The established logk′ versus pH profiles for THPP and TCEP were different, where k′ is the observed second-order rate constant. THPP was oxidized to (HOCH2CH2CH2)3PO, confirmed by 1H NMR spectroscopy, which is in line with the determined stoichiometry. On the other hand, the proposed reaction mechanism is similar to that suggested for the TCEP reaction. The reactivity of THPP was derived, enabling a reactivity comparison with TCEP at physiological pH. Surprisingly, the measured activation parameters for the reduction of [IrCl6]2− by P(CH2CH2CH2OH)3 and P(CH2CH2CO2 −)3 were essentially identical, providing information on the transition state and on the electron transfer mode. This work also defines the pK a value of THPP under well-defined conditions (pK a = 6.97 ± 0.05 at 25.0 °C and 1.0 M ionic strength) as derived by the kinetic approach.

0D/3D heterostructure of perovskite Cs2CuBr4 quantum dots/Bi2O3 microflower as a step-scheme photocatalyst for enhanced CO2 reduction

Exploring highly-efficient photocatalytic materials to convert CO2 into clean energy fuels is of great significance. Herein, lead-free perovskite Cs2CuBr4 quantum dots (QDs) were loaded onto Bi2O3 microflower to construct a 0D/3D heterostructure of Cs2CuBr4/Bi2O3 (CCB/Bi2O3) for photocatalytic CO2 reduction reaction (CO2 RR). The developed 0D/3D CCB/Bi2O3 heterostructure exhibited dramatically enhanced CO2 RR activity, with an electron consumption rate (Relectron) up to 322.12 μmol g−1h−1, which was 3.16 folds that of pure Cs2CuBr4 QDs. The improvement of CO2 RR activity was originated from the promoted carrier separation and transfer, as well as retainment of strongly reducing electrons induced by the step-scheme electron transfer mode, as authenticated by in-situ X-ray photoelectron spectra (XPS), electron paramagnetic resonance (EPR), and density function theory (DFT) calculation. The CO2 RR pathway was unveiled by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The innovation of perovskite QDs-based step-scheme heterostructures can throw inspiration on designing high-performance photocatalysts applied in artificial photosynthesis.

Hybridization of PPy/C toward high capacity and stability for sodium-ion batteries

Hybrid composites are widely regarded as the most promising choice for anode material in sodium-ion batteries. However, integrating high capacity and excellent cyclic stability into composites remains challenging. This work demonstrates a thin-liquid-layer polymerization approach to fabricate an integrated porous polypyrrole/carbon composite (PPy/C) for a high-performance sodium storage anode. By adjusting the monomer concentration reasonably and combining with heterostructure engineering, the optimized PPy/C was used as the anode for sodium-ion batteries, achieving rapid electrochemical kinetics and satisfactory reversible capacity. The reaction mechanism between PPy and Na+ in the Faraday reaction was revealed by ex-situ electrochemical impedance spectroscopy (EIS). DFT calculations illustrate that the synergistic effect between porous carbon and PPy can regulate the electron transfer mode around Na atoms, which contributes to anchoring Na in the PPy/C composite structure. Moreover, the PPy/C offers an ultrahigh capacity of 552 mA h g−1 at 0.1 A g−1 and a capacity retention rate of 86.5 % after 200 cycles. A full cell assembled with PPy/C and Na3V2(PO4)3 demonstrates a high energy density of 243.1 W h kg–1 at 125 W kg−1 power density. This work would offer valuable thought for advancing the practical application of conductive polymer/carbon composites.

Defect and interface/surface engineering synergistically modulated electron transfer and nonlinear absorption properties in MoX2 (X = Se, S, Te)@ZnO heterojunction.

Systematic interface and defect engineering strategies have been demonstrated to be an effective way to modulate the electron transfer and nonlinear absorption properties in semiconductor heterojunctions. However, the role played by defects and interfacial strain in electron transfer at the interface of the MoX2 (X = Se, S, Te)@ZnO heterojunction remains poorly understood. Herein, using the MoX2@ZnO heterojunction, we reveal that vacancies play a critical role in the interfacial electron transfer of heterojunctions. Specifically, we present the defect and interface engineering of the MoX2@ZnO heterojunction for controlled charge transfer and electron excitation-relaxation. The experimental characterization combined with first-principles calculations showed that the presence of defects promoted the transport of photogenerated carriers at the heterojunction interface, thereby inhibiting their rapid recombination. The DFT calculation confirmed that the electron band structure, density of states and charge density distribution in the system changed after the formation of Mo-O bonds. On the basis of defects and interfacial stress and the effective charge transfer, the MoX2@ZnO heterojunction exhibited excellent excitation and emission behaviors. The nonlinear optical regulation behavior of TMDs is expected to be realized with the help of the defects and interface/surface synergistically modulated effect of ZnO nanoparticles. The local strain generation on the MoX2@ZnO heterojunction boundary provides a new method for the design of new heterogeneous materials and will be of great significance to investigate the contact physical behavior and application of metals and two-dimensional (2D) semiconductors. This work provides some inspiration for the construction of heterojunctions with rich defects and surface/interface charge transfer channels to promote tunable electron transfer dynamics, thereby achieving a good nonlinear optical conversion efficiency and efficient charge separation in optoelectronic functional materials.

Self-indicating polymers: a pathway to intelligent materials.

Self-indicating polymers have emerged as a promising class of smart materials that possess the unique ability to undergo detectable variations in their physical or chemical properties in response to various stimuli. This article presents an overview of the most important mechanisms through which these materials exhibit self-indication, including aggregation, phase transition, covalent and non-covalent bond cleavage, isomerization, charge transfer, and energy transfer. Aggregation is a prevalent mechanism observed in self-indicating polymers, where changes in the degree of molecular organization result in variations in optical or electrical properties. Phase transition-induced self-indication relies on the transformation between different phases, such as liquid-to-solid or crystalline-to-amorphous transitions, leading to observable changes in color or conductivity. Covalent bond cleavage-based self-indicating polymers undergo controlled degradation or fragmentation upon exposure to specific triggers, resulting in noticeable variations in their structural or mechanical properties. Isomerization is another crucial mechanism exploited in self-indicating polymers, where the reversible transformation between the different isomeric forms induces detectable changes in fluorescence or absorption spectra. Charge transfer-based self-indicating polymers rely on the modulation of electron or hole transfer within the polymer backbone, manifesting as changes in electrical conductivity or redox properties. Energy transfer is an essential mechanism utilized by certain self-indicating polymers, where energy transfer between chromophores or fluorophores leads to variations in the emission characteristics. Furthermore, this review article highlights the diverse range of applications for self-indicating polymers. These materials find particular use in sensing and monitoring applications, where their responsive nature enables them to act as sensors for specific analytes, environmental parameters, or mechanical stress. Self-indicating polymers have also been used in the development of smart materials, including stimuli-responsive coatings, drug delivery systems, food sensors, wearable devices, and molecular switches. The unique combination of tunable properties and responsiveness makes self-indicating polymers highly promising for future advancements in the fields of biotechnology, materials science, and electronics.

Electron transfer rate modulation with mid-IR in butadiyne-bridged donor-bridge-acceptor compounds.

Controlling electron transfer (ET) processes in donor-bridge-acceptor (DBA) compounds by mid-IR excitation can enhance our understanding of the ET dynamics and may find practical applications in molecular sensing and molecular-scale electronics. Alkyne moieties are attractive to serve as ET bridges, as they offer the possibility of fast ET and present convenient vibrational modes to perturb the ET dynamics. Yet, these bridges introduce complexity because of the strong torsion angle dependence of the ET rates and transition dipoles among electronic states and a shallow torsion barrier. In this study, we implemented ultrafast 3-pulse laser spectroscopy to investigate how the ET from the dimethyl aniline (D) electron donor to the N-isopropyl-1,8-napthalimide (NAP) electron acceptor can be altered by exciting the CC stretching mode (νCC) of the butadiyne bridge linking the donor and acceptor. The electron transfer was initiated by electronically exciting the acceptor moiety at 400 nm, followed by vibrational excitation of the alkyne, νCC, and detecting the changes in the absorption spectrum in the visible spectral region. The experiments were performed at different delay times t1 and t2, which are the delays between UV-mid-IR and mid-IR-Vis pulses, respectively. Two sets of torsion-angle conformers were identified, one featuring a very fast mean ET time of 0.63 ps (group A) and another featuring a slower mean ET time of 4.3 ps (group B), in the absence of the mid-IR excitation. TD-DFT calculations were performed to determine key torsion angle dependent molecular parameters, including the electronic and vibrational transition dipoles, transition frequencies, and electronic couplings. To describe the 3-pulse data, we developed a kinetic model that includes a locally excited, acceptor-based S2 state, a charge separated S1 state, and their vibrationally excited counterparts, with either excited νCC (denoted as S1Atr, S1Btr, S2Atr, and S2Btr, where tr stands for the excited triplet bond, νCC) or excited daughter modes of the νCC relaxation (S1Ah, S1Bh, S2Ah, and S2Bh, where h stands for vibrationally hot species). The kinetic model was solved analytically, and the species-associated spectra (SAS) were determined numerically using a matrix approach, treating first the experiments with longer t1 delays and then using the already determined SAS for modeling the experiments with shorter t1 delays. Strong vibronic coupling of νCC and of vibrationally hot states makes the analysis complicated. Nevertheless, the SAS were identified and the ET rates of the vibrationally excited species, S2Atr, S2Btr and S2Bh, were determined. The results show that the ET rate for the S2A species is ca. 1.2-fold slower when the νCC mode is excited. The ET rate for species S2B is slower by ca. 1.3-fold if the compound is vibrationally hot and is essentially unchanged when the νCC mode is excited. The SAS determined for the tr and h species resemble the SAS for their respective precursor species in the 2-pulse transient absorption experiments, which validates the procedure used and the results.

Self-assembly-integrated tumor targeting and electron transfer programming towards boosting tumor type I photodynamic therapy.

Type I photodynamic therapy (PDT) is attracting increasing interest as an effective solution to the poor prognosis of patients with hypoxic tumors. The development of functional type I photosensitizers is limited by a lack of feasible strategies to systematically modulate electron transfer (ET) in photosensitization. Herein, we present an easily accessible approach for the preparation of nanophotosensitizers with self-assembly-integrated tumor-targeting and ET programming towards boosting tumor type I PDT. Specifically, a dual functional amphiphile PS-02 was designed with a ligand (6-NS) that had the ability to not only target tumor cell marker carbonic anhydrase IX (CAIX) but also regulate the ET process for type I PDT. The amphiphile PS-02 tended to self-assemble into PS-02 nanoparticles (NPs), which exhibited a local "ET-cage effect" due to the electron-deficient nature of 6-NS. It is noteworthy that when PS-02 NPs selectively targeted the tumor cells, the CAIX binding enabled the uncaging of the inhibited ET process owing to the electron-rich characteristic of CAIX. Therefore, PS-02 NPs integrated tumor targeting and CAIX activation towards boosting type I PDT. As a proof of concept, the improved PDT performance of PS-02 NPs was demonstrated with tumor cells under hypoxic conditions and solid tumor tissue in mouse in vivo experiments. This work provides a practical paradigm to develop versatile type I PDT nano-photosensitizers by simply manipulating ET and easy self-assembling.

Ab initio investigation of hot electron transfer in CO2 plasmonic photocatalysis in the presence of hydroxyl adsorbate.

Photoreduction of carbon dioxide (CO2) on plasmonic structures is of great interest in photocatalysis to aid selectivity. While species commonly found in reaction environments and associated intermediates can steer the reaction down different pathways by altering the potential energy landscape of the system, they are often not addressed when designing efficient plasmonic catalysts. Here, we perform an atomistic study of the effect of the hydroxyl group (OH) on CO2 activation and hot electron generation and transfer using first-principles calculations. We show that the presence of OH is essential in breaking the linear symmetry of CO2, which leads to a charge redistribution and a decrease in the OCO angle to 134°, thereby activating CO2. Analysis of the partial density of states (pDOS) demonstrates that the OH group mediates the orbital hybridization between Au and CO2 resulting in more accessible states, thus facilitating charge transfer. By employing time-dependent density functional theory (TDDFT), we quantify the fraction of hot electrons directly generated into hybridized molecular states at resonance, demonstrating a broader energy distribution and an 11% increase in charge-transfer in the presence of OH groups. We further show that the spectral overlap between excitation energy and plasmon resonance plays a critical role in efficiently modulating electron transfer processes. These findings contribute to the mechanistic understanding of plasmon-mediated reactions and demonstrate the importance of co-adsorbed species in tailoring the electron transfer processes, opening new avenues for enhancing selectivity.

Photocatalytic degradation of benzotriazole through synergy of electron donor–acceptor units and Au clusters in covalent organic frameworks

Covalent organic frameworks (COFs) have attracted great attention in photocatalysis, but the high recombination rate of photo-induced electron − hole pairs limits their photocatalytic performance. We report a synergy strategy based on the donor − acceptor (D-A) effect and Au clusters to enable the effective transfer and separation of photogenerated electrons to rationally fabricate visible light driven photocatalyst (MT-COF-Au) for the degradation of benzotriazole (BTA). MT-COF-Au displayed superior photocatalytic activity. The degradation efficiency of BTA was 93 % within 110 min, which was significantly improved 6.7 times than COF. For BTA degradation, O2− played a prominent role based on reactive species trapping experiments. The products of the last stage of the reaction were ketone, imidazole, acetamide, and nitrogen, which were formed via ring opening and isomerization reactions. MT-COF-Au could be reused for at least 5 cycles without significantly deteriorating its catalytic activity. Experiments and theory calculations confirmed the electron transfer mode and photocatalytic mechanism. This work provides new prospects for the design and synthesis of high-efficiency photocatalyst photocatalysts.

Electrochemical surface-enhanced Raman spectroscopy analysis of malachite green on gold substrates

The pH-sensitivity and electroactivity of malachite green (MG), a cationic dye, can potentially affect the surface-enhanced Raman spectroscopy (SERS) profile during electrochemical SERS (EC-SERS) analysis. An EC-SERS investigation was performed by acquiring dynamic SERS profiles of MG on Au SERS substrates at various applied potentials to elucidate the electrochemistry of MG at the molecular level. The appropriate EC-SERS potential window of MG, mass and electron transfer modes, and the number of electrons and protons in the redox process were determined by cyclic voltammetry. The EC-SERS parameters (pH and type of supporting electrolyte) were optimized. The highest SERS signal was achieved by chronoamperometry SERS (CA-SERS) and CV-SERS at an applied potential of 0.6 V (vs. Ag/AgCl) using 0.1 M phosphate buffer at pH 4 as the supporting electrolyte. Plausible mechanisms for electrooxidation and SERS signal enhancement were proposed. The oxidized form of MG, conformational changes, and evolution of the adsorption orientation were successfully elucidated using CV-SERS. This study provides molecular-level insight into the adsorption orientation of MG and its oxidized form, which involves aromatic rings with a tilted upright orientation at positive applied potentials. The mechanism of SERS signal enhancement is expounded, which is valuable for developing EC-SERS-based MG sensing.

Effect of structural optimization of magnetic MnFe2O4@Bi24O31Br10/Bi5O7I with core-shell structure on its enhanced photocatalytic activity to remove pharmaceuticals

Pharmaceutical contamination spreading across the aquatic environment has resulted in great disturbance to ecosystem and severe menace to human health. Magnetic photocatalysts have achieved great attention due to their magnetic separation capacity, recycling usage and low risk for secondary pollution. However, their practical applications to solve pollution problem are limited due to the insufficient photocatalytic activity, which is caused by their low valence band potentials and fast recombination of photo-generated carriers. In our research, by involvements of layer-structured bismuth-rich oxyhalides (BixOyXz, X = Cl, Br, I), optimizations for the microstructure and band structure of magnetic MnFe2O4 were applied to improve its photocatalytic activity for effectively removing pharmaceuticals residues. With the assistance of Bi24O31Br10 and Bi5O7I, MnFe2O4 nanoparticles (NPs) was gradually optimized to core-discontinuous shell structure of MnFe2O4@Bi24O31Br10 (M@B) and multi-layer entire core-shell structure of MnFe2O4@Bi24O31Br10/Bi5O7I (M@B/B). The optimized microstructures of M@B and M@B/B provide tight contact between components and promote the separation and utilization rates of carriers in photocatalytic process. For ternary M@B/B, tight contact between the components permits the working of optimized band structure, where double-Z scheme is formed and a favorable electron transfer mode is allowed. The production rates of active radicals from CB of Bi5O7I and VB of MnFe2O4 and Bi24O31Br10 are promoted and their redox abilities are strengthened. The synergy of improved utilization rate of carriers and their strengthened redox ability endows M@B/B with superior photocatalytic performance for removing pharmaceuticals with high concentrations. The removal efficiencies of M@B/B are determined to be 93.2%, 95.0% and 87.8% in 100 min for levofloxacin (LVFX, 20 mg L−1), tetracycline (TC, 50 mg L−1) and triclosan (TCS, 100 mg L−1), respectively. Our research provides a novel and effective channel to improve the photocatalytic activity of magnetic materials by involvements of BixOyXz compounds. According to its enhanced photocatalytic performance, suitable magnetic separation capacity and recycling usage, the practical applications of MnFe2O4 magnetic composites to treat real pharmaceuticals wastewater are reasonable and realistic.

The significantly boosted photodegradation of tetracycline over a novel hierarchical 0D/3D S-scheme heterojunction ZnSnO3/CdIn2S4

In recent years, constructing S-scheme heterostructure, as a novel and desirable strategy for the improvement of the photocatalytic performance, has attracted extensive interest. Herein, a novel hierarchical 0D/3D S-scheme heterostructure ZnSnO3/CdIn2S4 was constructed. The synthesized ZnSnO3/CdIn2S4 was characterized by various measures. The photodegradation of tetracycline (TC) was conducted under visible light to investigate the photocatalytic activity and stability of ZnSnO3/CdIn2S4. The impacts of pH and typical environmental factors on TC degradation were also explored. The S-scheme electron transfer mode in ZnSnO3/CdIn2S4 heterostructure was proposed based on Fermi level, in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS), and identification of the active species. The ZnSnO3/CdIn2S4 heterojunction exhibits outstanding photocatalytic activity and stability. The degradation efficiency and mineralization rate of TC reach 87% and 33.5%, respectively. After five reuses of ZnSnO3/CdIn2S4, degradation efficiency of TC decreases by only 6.5%. The rate constant (0.0140 min−1) of TC degradation over ZnSnO3/CdIn2S4 is 2.41 and 43.75 times as high as those over CdIn2S4 and ZnSnO3. The dramatically boosted activity of ZnSnO3/CdIn2S4 is owing to the superior visible-light response and the significantly accelerated separation and migration of the photoproduced charge carriers due to the construction of the hierarchical S-scheme heterojunction. Moreover, the photodegradation of TC is enhanced marginally with the rising pH and is slightly inhibited by the typical ions and natural organic matters (NOM). This work brings a new strategy to design highly efficient photocatalysts applied in environmental restoration.