Schottky Plots Research Articles

Enhanced electrocatalytic OER activity following electrochemical pre-cathodic treatment of Mn-substituted nickel ferrite

In this study, the electronic engineering of a high-valent active site for enhanced oxygen evolution reaction (OER) was achieved through the electrochemical pre-cathodic treatment method (EPCTM). This method involves applying a cathodic potential to the drop-cast working electrode of Mn-substituted nickel ferrite (Ni1−xMnxFe2O4; where x = 0.0, 0.2, and 0.4) electrocatalysts. X-ray photoelectron spectroscopy analysis revealed an increase in the ratios of Ni3+/Ni2+ and Mn3+/Mn2+ in Ni1−xMnxFe2O4 after EPCTM followed by OER, leading to an enhancement in electrochemical OER current density at 600 mV overpotential by 3.65 times for x = 0.0, 5.56 times for x = 0.20, and 4.72 times for x = 0.40. This enhancement was further supported by a decrease in the slope of the anodic Tafel equation after EPCTM, indicating improved efficiency of the interaction between the working electrode and electrolyte, as a lower Tafel slope suggests better charge exchange at the electrode–electrolyte interface. The positive slope in the Mott–Schottky (MS) plot for all Ni1−xMnxFe2O4 samples confirmed the p-type nature of the electrocatalysts. Additionally, the significant decrease in the slope of the linear portion of the MS plot indicated an increase in carrier concentration after electrochemical pre-cathodic treatment in all Ni1−xMnxFe2O4 samples. This increase in p-type carrier concentration supports the observed increase in the Ni3+/Ni2+ ratio for OER after EPCTM.

Ag3PO4 anchored SnWO4 Z-scheme heterojunction for reactive blue 21 degradation: Performance analysis and mechanism insights

The Ag3PO4–SnWO4 heterostructured nanocomposites have been prepared by the chemical precipitation process. The prepared nanocomposites were examined through XRD, TEM, UV–visible NIR, PL, BET, Mott Schottky, EIS, and ESR measurements. The diffraction peaks of Ag3PO4–SnWO4 nanocomposite showed the peaks of SnWO4 nanoparticles that are orthorhombic in the Ag3PO4 tetragonal structure, which suggested that they are present in the mixed phase of the composite. Photoluminescence spectra displayed efficiency in charge separation of e−-h+ pairs in Ag3PO4–SnWO4-1 nanocomposite. The Ag3PO4–SnWO4 nanocomposites have been examined for degrading the aqueous solution of reactive blue (RB 21) under natural sunlight irradiation. The superior photoactivity of Ag3PO4–SnWO4-1 could be ascribed to the existence of a heterostructure between Ag3PO4 and SnWO4 nanoparticles that improved the light absorption ability of the heterostructure. Also, a low rate of recombination of electron and hole pairs between Ag3PO4 and SnWO4 nanoparticles was observed. The Mott–Schottky plot revealed both Ag3PO4 and SnWO4 as n type semiconductor with flat-band potential values as 0.34 and −0.54 eV respectively. The photocatalytic rate reached the fastest on the incorporation of 100 mg SnWO4 compared to pristine Ag3PO4 and SnWO4 particles with 91.4% degradation efficiency and a rate constant of 0.257 min−1. The photogenerated O2∙−, h+ and ∙OH radicals indicated by the radical trapping experiment were mainly liable for the RB 21 degradation.

Role of oxidants in the anodic oxidation of 2024 aluminum alloy by dominating anodic and cathodic processes

The addition of oxidants into the electrolyte of Al anodic oxidation can alter the anodic and cathodic reactions, further affects the quality of the oxide film. In this paper, the role of two typical oxidants of H2O2 and Na2MoO4 in the microstructure and corrosion resistance of the oxide film on 2024 aluminum alloy was investigated by the scanning electron microscopy (SEM), Mott Schottky plots and electrochemical impedance spectroscopy (EIS). The addition of H2O2 increases the oxygen evolution amount on the anode Al and more oxygen can participate in the oxide film formation to improve the compactness. The addition of Na2MoO4 results in the deposit of MoO2 on the cathode plate to accelerate the hydrogen evolution reaction by the catalytic action of the MoO2, which further accelerates the anodic reaction to form a thick oxide film. As a result, the corrosion resistance of the oxide film is significantly improved by adding H2O2 or Na2MoO4 due to the promotion of film thickness and compactness.

Reactive oxygen species, electrode potential and pH affect CoCrMo alloy corrosion and semiconducting behavior in simulated inflammatory environments

Crevice corrosion in modular taper junctions of hip or knee replacements using cobalt-chrome-molybdenum (CoCrMo) alloys remains a clinical concern. Non-mechanically-driven corrosion has been less explored compared to mechanically assisted crevice corrosion. This study hypothesized that solution chemistry within crevices, inflammation, and cathodic electrode potential shifts during fretting result in low pH and generate reactive oxygen species (ROS), affecting oxide film behavior. This study investigated how resistance and capacitance of the CoCrMo oxide film (i.e., corrosion resistance) are modified in simulated in vivo crevice environments of modular taper junctions. Six solutions were evaluated (two pH levels: 1 and 7.4 and four hydrogen peroxide (H2O2) concentrations: 0, 0.001, 0.01 and 0.1 M). Rp versus voltage and Mott–Schottky plots were created from symmetry-based electrochemical impedance spectroscopy (sbEIS). At pH 1, the semiconductor transition to p-type occurs at more anodic potentials and higher flat band potentials were found. H2O2 decreased the flat band potential and slope in the Mott–Schottky plot. Higher H2O2 in pH 7.4 solution significantly modified the oxide film, leading to increased donor density (p = 0.0004) and a 150-fold reduction in Rp in the cathodic potential range at -1 V (p = 0.0005). The most unfavorable condition (0.1 M H2O2 pH 1) resulted in a 250-fold lower resistance compared to phosphate buffered saline (PBS) pH 7.4 at -1 V (p = 0.0013). This study highlights the corrosion susceptibility of CoCrMo under adverse chemical and potential conditions, identifying increased defects in the oxide film due to ROS, hydrogen ions and electrode potential. Statement of significanceCorrosion of cobalt chrome molybdenum alloy caused by direct chemical attack in the crevice region of hip replacements, such as modular taper junctions, remains a clinical concern. The junction environment contains adverse chemical compositions, including high acidity and reactive oxygen species (ROS) due to inflammatory responses against the corrosion products. We simulate inflammatory environments with different pH levels and hydrogen peroxide, representative of ROS. We employ electrochemical impedance spectroscopy and apply stepwise voltage over the range induced by tribocorrosion processes. We relate the effect of adverse chemical components on corrosion and semiconducting behavior of the oxide film using Mott–Schottky analysis. This study shows how pH and ROS concentration compromises the oxide film potentially leading to non-mechanically induced corrosion.

An innovative Zn3In2S6/ZnIn2S4 homojunction photocatalyst with enhanced interfacial charge transfer for the highly efficient degradation of tetracycline under visible radiation

The interfacial charge transfer ability is a decisive factor influencing the photocatalytic performance of composite photocatalysts. Compared with heterojunctions that combine two or more semiconductors with different properties, homojunctions that combine two semiconductors with similar properties can accelerate the interfacial charge shift and achieve higher photocatalyticability. In this study, a Zn3In2S6/ZnIn2S4 homojunction photocatalyst (ZIS-5) with a Zn3In2S6 to ZnIn2S4 molar ratio of 5:1 was synthesized by selecting Zn3In2S6 nano-microspheres as the substrate material and growing ZnIn2S4 flocs on the nano-microspheres. The photocatalytic performance of the ZIS-5 homojunction was assessed by using tetracycline (TC) as a typical pollutant. The photocatalytic performance and mineralization rate of the ZIS-5 homojunction were significantly improved compared with those of Zn3In2S6 and ZnIn2S4, and its photocatalytic performance was increased by 10.2% and 20.9%, compared with Zn3In2S6 and ZnIn2S4, respectively, while the mineralization rate was enhanced by 22.78% and 43.28%, respectively. The results of the comparison experiment revealed that the interfacial electron transfer ability of the ZIS-5 homojunction is 1.6 times that of the g-C3N4/ZnIn2S4-5 heterojunction. The density functional theory (DFT) computation and Mott–Schottky plots verified the formation of an internal electric field. The toxicity analysis showed that the ZIS-5 homojunction system effectively reduced the toxicity of TC. This work supplies a valuable route for inventing catalysts with efficient photocatalytic performances.

Photoelectrochemical properties of self-powered corundum-structured Ga2O3 nanorod array/fluorine-doped SnO2 photodetectors modulated by precursor concentrations

Herein, corundum-structured Ga2O3 (α-Ga2O3) nanorod array/fluorine-doped SnO2 (FTO) structures have been fabricated by hydrothermal and thermal annealing processes with different precursor concentrations from 0.01 to 0.06 M. The diameter and length of the nanorod arrays are much larger with increasing precursor concentrations due to more nucleation sites and precursor ions participating in the reaction procedures. The optical bandgap decreases from 4.75 to 4.47 eV because of the tensile stress relieving with increasing the precursor concentrations. Based on self-powered photoelectrochemical (PEC) photodetectors, the peak responsivity is improved from ∼0.33 mA W−1 for 0.06 M to ∼1.51 mA W−1 for 0.02 M. Schottky junctions can be formed in PEC cells. More photogenerated carriers can be produced in wider depletion region. From Mott–Schottky plots, the depletion regions become much wider with decreasing the precursor concentrations. Therefore, the enhance responsivity is owing to the wider depletion regions. Due to the reduced possibility of photogenerated holes captured by traps ascribed from fewer green and yellow luminescence defects, smaller charge transfer resistance, and shorter transportation route, the decay time becomes much faster through decreasing the precursor concentrations. Compared with the other self-powered α-Ga2O3-nanorod-array-based PEC photodetectors, it shows the fastest response time (decay time of 0.005 s/0.026 s) simply modulated by precursor concentrations for the first time without employing complex precursors, seed layers or special device designs. Compared with other high-responsivity monoclinic Ga2O3 (β-Ga2O3) self-powered photodetectors, our devices also show comparable response speed with simple control and design. This work provides the realization of fast-speed self-powered Ga2O3 based solar-blind ultraviolet photodetectors by simple modulation processes and design, which is a significant guidance for their applications in warnings, imaging, computing, communication and logic circuit, in the future.

Role of Semiconductive Property on Selective Cementation Mechanism of Iron Oxides to Gold in Galvanic Interaction with Zero-Valent Aluminum from Gold–Copper Ammoniacal Thiosulfate Solutions

Iron oxides (hematite, Fe2O3, and magnetite, Fe3O4), previously used as electron mediators in the galvanic system with zero-valent aluminum (ZVAl), have been shown to recover Au upon cementation in Au–Cu ammoniacal thiosulfate media selectively, and this warrants further investigation. This research is focused on investigating the role of the semiconductive properties of metal oxides by performing a cementation experiment by mixing 0.15 g of electron mediators (Fe3O4, Fe2O3, TiO2 (anatase and rutile)) and 0.15 g of zero-valent aluminum powder as an electron donor in various electrochemical experiments. The results revealed that upon the cementation experiment, synthetic Fe2O3 and Fe3O4 were consistently able to selectively recover Au at around 90% and Cu at around 20%. Compared to activated carbon (AC), TiO2, in anatase and rutile forms, obtained selective recovery of gold, but the recovery was utterly insignificant compared to that of iron oxides, obtaining an average of 93% Au and 63% Cu recovery. The electrochemical and surface analysis supports the results obtained upon the cementation process, where TiO2, upon cyclic voltammetry (CV), obtained two reduction peaks centered at −1.0 V and −0.5 V assigned to reducing Au and Cu ions, respectively. Furthermore, various electrochemical impedance spectroscopic analyses revealed that the flat band potential obtained in the Mott–Schottky plot is around −1.0 V and −0.2 V for iron oxides and titanium oxides, respectively, suggesting that the electrons travel from semiconductor interface to electrolyte interface, and electrons are accessible only to Au ions in the electrolyte interface (reduction band edge around −1.0 V). The determination of this selective cementation mechanism is one of a kind. It has been proposed that the semiconductive properties of Fe2O3, Fe3O4, and, by configuring their relative energy band diagram, the travel of electrons from the iron oxide–electrolyte interface facilitate the selective cementation towards Au(S2O3)23+ ions in gold–copper ammoniacal thiosulfate solutions.

Pulse electrodeposition of CuSbS2 thin films: Role of Cu/Sb precursor ratio on the phase formation and its performance as photocathode for hydrogen evolution§

In this paper, we outline the development of stoichiometric chalcostibite, CuSbS2 thin films, from a single bath by pulse electrodeposition for its application as a photocathode in photoelectrochemical cells (PEC). The Cu/Sb precursor molar ratio of the deposition bath was varied to obtain stoichiometric CuSbS2 thin films. The optimized deposition and dissolution potentials were −0.72 V and −0.1 V vs saturated calomel electrode, respectively. The formation of CuSbS2 was analyzed using different characterization tools. X-ray diffraction and Raman results showed the formation of the pure chalcostibite phase from a precursor bath with molar ratio Cu/Sb = 0.41. The heterostructure CuSbS2/CdS/Pt was tested as a photocathode in the PEC. The energy positions of the conduction and valence bands were estimated from the Mott Schottky plots. The conduction band and valence band offset of CuSbS2/CdS heterojunction were 0.1 eV and 1.04 eV, respectively. The electric field created in the junction reduced the recombination of the electron/hole pairs and improved charge transfer in the interface. The heterostructure CuSbS2/CdS/Pt demonstrated an improved photocurrent density of 3.4 mA cm−2 at 0 V vs reversible hydrogen electrode. The PEC efficiency obtained from the CuSbS2/CdS heterojunction was 0.56 %. Therefore, we demonstrated the feasibility of an inexpensive technique like electrodeposition for the development of an efficient earth-abundant photocathode.

A novel carbon doped CeO2/g-C3N4 heterostructure for disinfection of microorganisms and degradation of Malachite green and Amoxicillin under sunlight

The fabrication of semiconductor heterojunction with defect engineering is an efficient technique to boost photocatalytic activity. In this study, a novel step-scheme heterojunction C-CeO2/g-C3N4 nanocomposite was developed via the hydrothermal method for the degradation of aqueous dye and antibiotics in sunlight. The photocatalytic experiment of the CeO2/g-C3N4 heterojunction nanocomposite reveals superior photocatalytic activity and significant reusability. Further, 91.9 % of Malachite green (MG) and 87.5 % of Amoxicillin(AMX) were degraded by C-CeO2/g-C3N4 nanocomposite under 150 mins of sunlight irradiation, which is ∼ 1.78 folds of the photodegradation performance of C-CeO2. The decomposition of MG and AMX into non-toxic secondary compounds was verified by total organic carbon and high-performance liquid chromatography analysis. Further, the migration and separation of charge carriers due to photons were confirmed through electrochemical analysis and, photoluminescence spectroscopy. The potential S-Scheme charge transfer pathway for improved photocatalytic activity was postulated via the quenching experiment, Mott Schottky (M-S) plot, and XPS Valance band spectroscopy (VB-XPS). In addition, the C-CeO2/g-C3N4 nanocomposite displays excellent bactericidal and fungicidal activity against pathogenic microorganisms S. aureus, E. coli, and C. albican. Hence, the synthesized S-Scheme heterojunction C-CeO2/g-C3N4 nanocomposite is an ideal catalyst for the detoxification of industrial wastewater.

AgVO3/Ag6Si2O7 nanocomposites with enhancing visible-light driven photocatalysis performance

The AgVO3/Ag6Si2O7 nanocomposite was developed via the coprecipitation method. After being composited, these two nanostructures developed a heterojunction form. The DRS spectra suggested that these nanocomposites with different ratios possessed suitable bandgap, therefore could strongly absorb visible light. The EIS and Mott−Schottky plot curves show that the AgVO3 structure was n-type conductivity semiconductor, while the Ag6Si2O7 structure was p-type conductivity, and these two semiconductors could form the p-n heterojunction nanostructure. The AgVO3/Ag6Si2O7 nanocomposite possess higher photogenerated carrier transfer efficiency and stability of the photogenerated carriers. The organic dye photodegradation activity studies suggested that the AgSV-12 exhibited the best photocatalysis effectivity, and showed good photodegradation activity to other organic dyes. The ESR and reactive species quenchers study suggested that the reactive species that oxidized the organic dyes were photogenerated holes, •O2− and •OH, and the photogenerated holes played the essential factor. Finally, the photocatalysis mechanism and process were presumed as the p-n heterojunction mechanism.

Interphase corrosion inhibition mechanism of sodium borate on carbon steel rebars in simulated concrete pore solution

Sodium borate (Na2B4O7) corrosion inhibition mechanism was studied on carbon steel rebars in 0.6 mol/L Cl– simulated concrete pore solution (SCPS) at different temperatures and concentrations. Electrochemical testing including cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and Mott–Schottky plots were utilized to understand the influence of inhibitor concentration and temperature on the thermodynamics of the adsorption and activation processes. It was found Na2B4O7 imparts corrosion protection due to the formation of a 3D Fe–B–O stable interphase passive film, achieving an inhibition efficiency up to 86%. This can be attributed to the film having a lower donor current density and less vacancies, according to the Mott–Schottky tests. The formed interphase passive film was more stable and compact with less point defects compared to the blank due to Na2B4O7 adsorption, this phenomenon was substantiated using the atomic packing factor, film thickness, and Mott–Schottky plots. It was revealed, using adsorption isotherms, that Na2B4O7 interacted with the surface via physiochemical adsorption, creating a thinner/compact passive film composed of a rhombohedral calcite-type structure. SEM, XRD, and XPS were used to illustrate that Na2B4O7 aides in the formation of a stable double-layered net structure Fe2O3/FeBO3 passive oxide film. Finally, an interphase corrosion inhibition mechanism of Na2B4O7 was proposed.

Enhanced photocatalytic degradation of reactive blue 21 dye and textile dyeing effluent by synthesized SmFeO3-rGO photocatalyst in combination with ultrasonication: Characterization and performance evaluation

This research aimed to synthesize SmFeO3 and SmFeO3-rGO photocatalysts via an ultrasound-assisted sol-gel technique. The synthesized photocatalysts were characterized through various analytical technique including XPS, XRD, FESEM with EDX, FTIR, PL, UV-DRS LC-MS, Mott Schottky Plot, and BET analysis. The study evaluated the photocatalytic degradation efficiency of Reactive Blue 21 (RB21) using these synthesized photocatalysts, and the influence of operating factors such as solution pH, catalyst dose, and initial dye concentration. In order to enhance the activity of the photocatalyst, a combination of ultrasonication (US) and ultraviolet (UV) irradiation, were used, and their respective results have been reported in the present study. The RB21 degradation followed first-order kinetics, achieving a rate constant of 8.7 × 10−3 min−1. Over 68.82 % degradation was noted under optimal conditions, utilizing 20 mg/L SmFeO3 catalyst at a pH of 7.1. Using SmFeO3-rGO with an optimal molar ratio of rGO to SmFeO3 (1:1) achieved over 92.37 % degradation in 120 min. However, the sonophotocatalytic approach resulted in 99.41 % degradation within 30 min. The mineralization of textile dyeing effluents using sonophotocatalytic method observed significant COD and TOC reductions of 78.3 % and 75.9 % respectively in 30 min treatment. The SmFeO3-rGO nanophotocatalyst exhibited reliable degradation performance across five cycles. The LC-MS analysis provides a detailed view into the degradation pathway of RB21 through sonophotocatalysis. The combined ultrasonication and photocatalytic oxidation strategy yielded superior energy efficiency (4.45 × 10−6 mg/J) as compared to UV, US, and UV + SmFeO3-rGO methods.

Tribocatalytic activity on Ba(Ti0.95Zr0.05)O3 surfaces: The role of oxygen vacancies and the aging effect

This study explores the potential of tribocatalysis, a resource-efficient degradation technique, using ferroelectric perovskite-type Ba(Ti0.95Zr0.05)O3 (BZT) with oxygen vacancies as a catalyst. The catalysts, synthesized via a standard solid-state method, were analyzed using XPS and EPR to confirm the presence of oxygen vacancies. Their electrical properties were evaluated through UV–vis diffuse reflectance spectra and Mott–Schottky plots. Freshly prepared BZT catalysts demonstrated a 92% degradation of Rhodamine B (RhB) within 20 h, achieving a reaction rate constant (K) of 0.114 h−1. However, aging significantly reduced RhB degradation, with de-aging failing to restore initial activity. The study attributes the catalyst's catalytic activity and aging issues to the oxygen vacancies, acting as shallow donor states. It also highlights the benefits of tribocatalysis due to electron accumulation at the surface from friction-generated contact, emphasizing the critical role of oxygen vacancies in catalytic degradation and long-term catalyst stability.

Visible light photo-Fenton catalytic properties of starch functionalized α-FeOOH/β-FeOOH/Cu2O p-n-p heterojunction nanostructures

Photocatalysts with p-n-p heterojunctions can result in efficient charge separation. This idea motivated the synthesis of starch functionalized α-FeOOH/β-FeOOH/Cu2O heterojunction nanocomposites. All components in the composite have visible range band gaps. In a step-wise procedure, Cu2O nanostructures were precipitated on starch functionalized α-FeOOH/β-FeOOH nanocomposites. Mott Schottky plots confirmed p-n-p heterojunction formation. It enhanced charge separation and slowed down recombination resulting in efficient visible-light photocatalytic activity. The activity of this photocatalyst was evaluated for the photo-Fenton degradation of p-nitrophenol (PNP) and methyl orange (MO). Both degradation reactions follow zero-order kinetics. The photocatalyst remained stable during the organic pollutant degradation process even after repeated use.

Novel ZnO/BiOI nanorod photoanode with interface p-n heterojunction and excellent photoelectric conversion efficiency for photocathodic protection of stainless steel

Bismuth oxyhalide nanoheterojunctions with high photovoltaic conversion efficiency by constructing internal electric field have received extensive attention for photocathode protection (PCP) applications. In this work, BiOI/ZnO nanorod composites (BiOI/ZnO NRs) were synthesized by spin coating and hydrothermal method. The BiOI nanoparticles were found uniformly anchored on the surface of hexagonal wurtzite ZnO nanorods. Morphology and Mott Schottky plots analysis confirm the structure of the p-n heterojunctions at the interface of BiOI and ZnO. Loading of BiOI on the ZnO surface results in the negative shift of the Fermi level of ZnO. The BiOI/ZnO NRs expanded the absorption region of solar light and constructed an internal electric field in p-n heterojunction, which more efficiently accelerated the migration of electrons, inhibited the carrier’s recombination and improved the photoelectric conversion efficiency of BiOI/ZnO. The Open circuit potential (OCP) of BiOI/ZnO NRs photoanode coupled with the 304 stainless steel negatively shifted to −0.757 mV (vs.SCE), and it could protect stainless steel steadily in 4000 s intermittent illumination, showing the high stability of BiOI/ZnO photoanode. The synergistic effects of p-n heterojunction enable BiOI/ZnO NRs photoanode to exhibit an excellent photocathode protection performance.

Evidence of oxygen evolution over sputtered zinc ferrite (ZnFe2O4) thin film by enhanced lattice oxygen participation

We report evidence of oxygen evolution over zinc ferrite (ZnFe2O4) thin films grown on indium tin oxide and quartz substrates using the RF sputtering. The thin films are deposited at ambient temperature with different argon/oxygen gas ratios, specifically 1:0 (Z–Ar), 1:1 (Z–Ar:O), and 0:1 (Z–O). Structural characterization using grazing incidence x-ray diffraction at a 0.400° grazing angle confirmed the polycrystalline nature of the films. X-ray photoelectron spectroscopy scans of Zn 2p, Fe 2p, and O1s were conducted to investigate the lattice oxygen vacancies. The lattice oxygen vacancies in the Z–Ar film resulted in a lower bandgap of 2.05 eV than the Z–O film of 2.36 eV. The oxygen evolution reaction (OER) performances of the thin films are investigated to understand the effect of oxygen vacancies on electrochemical activity and observed that the Z–Ar film, with oxygen vacancies, exhibits a decrease in overpotential by ∼12.5% at 10 mA cm−2, eightfold increase in current density at 520 mV overpotential deduced from linear sweep voltammetry, and a 71.9% increase in donor density inferred from the Mott–Schottky plot, as compared to the Z–O film. The findings suggest that the Z–Ar film follows a “lattice oxygen participation mechanism” for the OER, instead of an “adsorbate evolution mechanism” observed in the Z–O film. The results highlight the significant impact of argon/oxygen gas ratios on the structural, optical, and electrochemical properties of zinc ferrite thin films and provide insight into the role of oxygen vacancies in modulating the OER performance for potential applications.

Photoelectrochemical aptasensing of tetracycline enabled by efficient photoanode: Integrating high visible light-harvesting Bi2S3 and metal-free g-C3N4 into Z-scheme heterojunction

The development of a reliable method for detecting tetracycline (TC) in fish is essential to ensure the safety of aquatic products and human health. Herein, a photoelectrochemical (PEC) aptasensor was fabricated for the efficient detection of TC based on a designed efficient photoanode with a novel high light-harvesting heterojunction of bismuth sulfide/graphitic carbon nitride (Bi2S3/g-C3N4) as a photoactive material. The Bi2S3/g-C3N4 exhibited enhanced photocurrent due to its increased light capture capability, high carrier density and especially low electron-hole recombination efficiency enabled by the Z-scheme electron transfer, which was verified by the UV–vis diffuse reflectance spectrum, Mott–Schottky plot, and electron spin resonance spectroscopy. Under optimal experimental conditions, the fabricated aptasensor had the advantages of a wide linear range of 0.01–10 nM, a low detection limit of 3 pM and good selectivity and reproducibility. When the aptasensor was applied to determine TC in fish, the results were in good agreement with the UPLC-MS/MS method, indicating the reliability of the PEC aptasensing method for detecting TC in real samples.

Study on the photoelectrocatalytic activity of reduced TiO2 nanotube films for removal of methyl orange

Abstract The reduced TiO2 film on which a photoelectrocatalytic (PEC) process had occurred was created from TiO2 nanotube film electrodes by the electrochemical reduction method. The obtained samples’ structure and morphology were characterized using UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, photoluminescence, and X-ray diffraction. Cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, chronoamperometry, UV-Vis absorbance spectroscopy, and Mott–Schottky plots were employed to examine the electrochemical and photoelectrochemical activities of the prepared electrodes. The results showed that the optimal conditions of cathodic polarization were a potential of −1.4 V for 60 min. The reduced TiO2 nanotube film electrode had better photoelectrochemical activities than pristine TiO2 under UV light due to the higher photocurrent density (13.7 mA‧cm−2) at 1.5 V (vs Ag/AgCl, sat. KCl reference electrode) compared to pristine TiO2 achieving 7.3 mA‧cm−2, indicating more effective charge separation and transport. The degradation of methyl orange (MO) on pristine TiO2 and reduced TiO2 electrodes was carried out in electrocatalytic (EC) and PEC conditions. The PEC process on the reduced TiO2 electrode had the highest MO processing efficiency (98.4%), and the EC process for MO removal on reduced TiO2 had higher efficiency (95.1%) than the PEC process on pristine TiO2 (89.2%).

Cocatalyst loaded Al-SrTiO3 cubes for Congo red dye photo-degradation under wide range of light

The continued pollution, waste, and unequal distribution of the limited amount of fresh water on earth are pushing the world into water scarcity crisis. Consequently, development of revolutionary, cost-effective, and efficient techniques for water purification is essential. Herein, molten flux method was used for the preparation of micro-sized Al-doped SrTiO3 photocatalyst loaded with RhCr2O3 and CoOOH cocatalysts via simple impregnation method for the photo-assisted degradation of Congo red dye under UV and visible irradiation compared with P25 standard photocatalyst. In addition, photoelectrochemical analysis was conducted to reveal the separation and transfer efficiency of the photogenerated e−/h+ pairs playing the key role in photocatalysis. SEM and TEM analyses revealed that both P25 and the pristine SrTiO3 have spherical shapes, while Al-doped SrTiO3 and the sample loaded with cocatalysts have cubic shapes with a relatively higher particle size reaching 145 nm. In addition, the lowest bandgap is due to Al+3 ion doping and excessive surface oxygen vacancies, as confirmed by both UV–Vis diffuse-reflectance and XPS analyses. The loading of the cocatalysts resulted in a change in the bandgap from n-type (pristine SrTiO3 and Al-SrTiO3) into p-type (cocatalyst loaded sample) as exhibited by Mott–Schottky plots. Besides, the cocatalyst-loaded sample exhibited good performance stability after 5 cycles of the photocatalytic removal of Congo red dye. OH· radical was the primary species responsible for CR degradation as confirmed by experiments with radical scavengers. The observed performance of the prepared samples under both UV and visible light could foster the ongoing efforts towards more efficient photocatalysts for water purification.

Electrochemical Fabrication and Characterization of Cu2ZnSnS4 (CZTS) Thin Film Deposits on Gold Substrate for Hydrogen Production

In this paper, room temperature one-step electrodeposition of chalcogenide CZTS followed by annealing at different temperatures was studied. The scanning electron microscopy images of the deposits confirmed the presence of agglomerated particles in the deposits. The deposits annealed at [Formula: see text]C did not show the presence of voids whereas deposits annealed at [Formula: see text]C showed severe sulfur loss and were off-stoichiometric. Annealing at [Formula: see text]C resulted in the deposits of compositions closer to the required ratio. Good absorbance over the entire visible range makes both the annealed deposits suitable absorber materials for thin-film photovoltaic cells. Current–voltage characteristics resulted in Ohmic trend and the slope of the plot increased with annealing temperature. The deposits showed good photosensitive behavior where resistance decreased upon shining the light source. The Mott–Schottky plot showed that the deposits were made of positively charged particles. CZTS thin film annealed at [Formula: see text]C provided higher H2 production rate (68.68 [Formula: see text]mol ⋅ [Formula: see text] ⋅ [Formula: see text], which was 32 times higher than that of CZTS annealed at [Formula: see text]C (2.08 [Formula: see text]mol ⋅ [Formula: see text] ⋅ [Formula: see text]. What’s more, photocatalytic activity of CZTS thin film remained 94% after 48 h which confirmed the good stability and reusability of CZTS thin film. CZTS thin film is a potential and durable candidate for photocatalysis.