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Synthesis and Characterization of CuBi2O4/Electro-reduced Graphene Oxide Nanocomposites using A New Electrochemical Technique
Abstract
Bu çalışmada, bakır bizmutat (CuBi2O4) ve elektro-indirgenmiş grafen oksitten (ERGO) oluşan nanokompozit (CuBi2O4/ERGO) materyal tek kapta yeni bir elektrokimyasal teknik kullanılarak nikel (Ni) köpük elektrot yüzeyinde başarıyla sentezlenmiştir. Çözelti ortamı olarak Cu+2, Bi+3 ve grafen oksit (GO) ihtiva eden çözelti karışımı kullanılmıştır. Öncelikle oksijen gazı geçirilen çözelti ortamında Ni köpük elektrot yüzeyinde hidroksit türleri depozit edilmiştir. Sonrasında termal tavlama yapılarak oksit formuna dönüşüm sağlanmıştır. Elektrokimyasal olarak sentezlenen CuBi2O4/ERGO modifiye elektrotlar X-ışını kırınımı (XRD), X-ışını fotoelektron spektroskopisi (XPS), Raman, alan emisyonlu taramalı elektron mikroskobu (FE-SEM) ve enerji dağılım spektroskopisi (EDS) teknikleri kullanılarak karakterize edilmiştir. Yapılan karakterizasyon işlemleri nanokompozitin hem CuBi2O4 hem de ERGO yapısını bir arada içerdiğini göstermiştir.
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Microbial infections are considered one of the most dangerous infections in humans due to their resistance to most antimicrobial agents. In this study, nanocomposites based on reduced graphene oxide (RGO) and metal oxides (NiO, AgO, and ZnO) were fabricated. The graphite precursor and RGO were characterized by XRD, Raman spectroscopy, SEM, and HRTEM, while SEM, XRD, and EDX mapping analysis validated the synthesized nanocomposites. In addition, ZOI and MIC were employed to test the antimicrobial potential, while their antibiofilm activity and the effect of UV illumination were also investigated. Finally, reaction mechanism determination was performed using SEM analysis. The results revealed that all the synthesized nanocomposites (RGO-NiO, RGO-AgO, and RGO-ZnO) had outstanding antimicrobial activity against Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), unicellular fungi (Candida albicans and Cryptococcus neoformans) and multicellular fungi (Aspergillus niger, A. terreus, A. flavus and A. fumigatus). Moreover, the synthesized RGO-NiO nanocomposite exhibited antibiofilm activity (following 10.0 µg mL−1 RGO-NiO), with an inhibition percentage of 94.60% for B. subtilis, 91.74% for P. aeruginosa, and 98.03% for C. neoformans. The maximum percentage inhibition under UV illumination toward P. aeruginosa, B. subtilis and C. neoformans at the end of the experiment using RGO-NiO were 83.21%, 88.54%, and 91.15%, respectively, while the values of RGO-AgO were 64.85%, 68.0%, and 80.15%, respectively, and those of RGO-ZnO were 72.95%, 82.15%, and 79.25%, respectively. The SEM analysis of C. neoformans in the absence of the RGO-NiO nanocomposite showed the development of unicellular fungal cells by regular budding. In contrast, after RGO-NiO treatment, noticeable morphological differences were identified in C. neoformans, including the lysis of the outer surface with deformations of the fungal cells. In conclusion, the prepared nanocomposites are promising antimicrobial and antibiofilm agents and can be used to treat the pathogenic microbes at low concentrations and represent a new strategy for managing infectious diseases caused by pathogenic microorganisms.
CuBi2O4 synthesized by thermolysis of a new Bi(III)-Cu(II) oxalate coordination compound, namely Bi2Cu(C2O4)4·0.25H2O, was tested through its integration within carbon nanofiber paste electrode, namely CuBi/carbon nanofiber (CNF), for the electrochemical detection of amoxicillin (AMX) in the aqueous solution. Thermal analysis and IR spectroscopy were used to characterize a CuBi2O4 precursor to optimize the synthesis conditions. The copper bismuth oxide obtained after a heating treatment of the precursor at 700 °C/1 h was investigated by an X-ray diffraction and scanning electron microscopy. The electrochemical behavior of CuBi/CNF in comparison with CNF paste electrode showed the electrocatalytic activity of CuBi2O4 toward amoxicillin detection. Two potential detections, with one at the potential value of +0.540 V/saturated calomel electrode (SCE) and the other at the potential value of −1.000 V/SCE, were identified by cyclic voltammetry, which were exploited to develop the enhanced voltammetric and/or amperometric detection protocols. Better electroanalytical performance for AMX detection was achieved for CuBi/CNF using differential-pulsed and square-wave voltammetries than others reported in the literature. Very nice results obtained through anodic and cathodic currents recorded at +0.750 V/SCE and −1.000 V/SCE in the same time period using a pseudo multiple-pulsed amperometry technique showed the great potential of the CuBi/CNF paste electrode for practical applications in amoxicillin detection in aqueous solutions.
The unique physical and chemical properties of spinels have made them highly suitable electrocatalysts in oxygen evolution reaction and oxygen reduction reaction (OER & ORR). Zinc–air batteries (ZABs), which are safer and more cost-effective power sources than commercial lithium-ion batteries, hinge on ORR and OER. The slow kinetics of the air electrode reduce its high theoretical energy density and specific capacity, which limits its practical applications. Thus, tuning the performance of the electrocatalyst and cathode architecture is vital for improving the performance of ZABs, which calls for exploring spinel, a material that delivers improved performance. However, the structure–activity relationship of spinel is still unclear because there is a lack of extensive information about it. This study was performed to address the promising potential of spinel as the bifunctional electrocatalyst in ZABs based on an in-depth understanding of spinel structure and active sites at the atomic level.
Electrochemical synthesis methods were developed to produce CuBi2O4, a promising p-type oxide for use in solar water splitting, as high surface area electrodes with uniform coverage. These methods involved electrodepositing nanoporous Cu/Bi films with a Cu:Bi ratio of 1:2 from dimethyl sulfoxide or ethylene glycol solutions, and thermally oxidizing them to CuBi2O4 at 450 °C in air. Ag-doped CuBi2O4 electrodes were also prepared by adding a trace amount of Ag+ in the plating medium and codepositing Ag with the Cu/Bi films. In the Ag-doped CuBi2O4, Ag+ ions substitutionally replaced Bi3+ ions and increased the hole concentration in CuBi2O4. As a result, photocurrent enhancements for both O2 reduction and water reduction were achieved. Furthermore, while undoped CuBi2O4 electrodes suffered from anodic photocorrosion during O2 reduction due to poor hole transport, Ag-doped CuBiO4 effectively suppressed anodic photocorrosion. The flat-band potentials of CuBi2O4 and Ag-doped CuBi2O4 electrodes prepared in this study were found to be more positive than 1.3 V vs RHE in a 0.1 M NaOH solution (pH 12.8), which make these photocathodes highly attractive for use in solar hydrogen production. The optimized CuBi2O4/Ag-doped CuBi2O4 photocathode showed a photocurrent onset for water reduction at 1.1 V vs RHE, achieving a photovoltage higher than 1 V for water reduction. The thermodynamic feasibility of photoexcited electrons in the conduction band of CuBi2O4 to reduce water was also confirmed by detection of H2 during photocurrent generation. This study provides new understanding for constructing improved CuBi2O4 photocathodes by systematically investigating photocorrosion as well as photoelectrochemical properties of high-quality CuBi2O4 and Ag-doped CuBi2O4 photoelectrodes for photoreduction of both O2 and water.
CuBi2O4 is a multinary p-type semiconductor that has recently been identified as a promising photocathode material for photoelectrochemical (PEC) water splitting. It has an optimal bandgap energy (~ 1.8 eV) and an exceptionally positive photocurrent onset potential (> 1 V vs. RHE) making it an ideal candidate for the top absorber in a dual absorber PEC device. However, photocathodes made from CuBi2O4 have not yet demonstrated high photo-conversion efficiencies and the factors that limit the efficiency have not yet been fully identified. In this work we characterize CuBi2O4 photocathodes synthesized by a straightforward drop-casting procedure and for the first time report many of the quintessential material properties that are relevant to PEC water splitting. Our results provide important insights into the limitations of CuBi2O4 in regards to optical absorption, charge carrier transport, reaction kinetics, and stability. This information will be valuable in future work to optimize CuBi2O4 as a PEC material. In addition, we report new benchmark photocurrent density and IPCE values for CuBi2O4 photocathodes.
http://chemgroups.ucdavis.edu/%7Eosterloh/pubs/ref_85.pdf As a visible light active p-type semiconductor, CuBi2O4 is of interest as a photocatalyst for the generation of hydrogen fuel from water. Here we present the first photovoltage and photocatalytic measurements on this material and DFT results on its band structure. Single crystalline CuBi2O4 nanoparticles (25.7 ± 4.7 nm) were synthesized from bismuth and cupric nitrate in water under hydrothermal conditions. Powder X-ray diffraction (XRD) confirms the CuBi2O4 structure type and UV-Vis spectroscopy observes a 1.75 eV optical band gap. Surface photovoltage (SPV) measurements on CuBi2O4 nanoparticle films on fluorine doped tin oxide yield 0.225 V positive photovoltage at >1.75 eV photon energy confirming holes as majority carriers. The photovoltage is reversible and limited by light absorption. When dispersed in 0.075 M aqueous potassium iodide solution, the CuBi2O4 particles support photochemical hydrogen evolution of up to 16 μmol h-1 under ultraviolet but not under visible light. Based on electrochemical scans, CuBi2O4 is unstable towards reduction at -0.2 V, but pH-dependent photocurrents of 6.45 microA cm-2 with an onset potential of +0.75 V vs. NHE can be obtained with 0.01 M Na2S2O8 as a sacrificial electron acceptor. The photoelectrochemical properties of CuBi2O4 can be explained on the basis of the band structure of the material. DFT calculations show the valence and conduction band edges to arise primarily from the combination of O 2p and Cu 3d orbitals, respectively, with additional contributions from Cu 3d and Bi 6s orbitals just below the Fermi level. Trapping of photoelectrons in the Cu 3d band is the cause for reductive photocorrosion of the material, while the p-type conductivity arises from copper vacancy states near the VB edge. These findings provide an improved understanding of the photophysical properties of p-CuBi2O4 and its limitations as a proton reduction photocatalyst.
The synthesis of copper bismuth oxide (CuBi2O4) nanorods with single crystal structure by hydrothermal method is first reported here. The prepared CuBi2O4 nanorods are characterized by X-ray diffractometer, scanning electron microscopy, transmission electron microscopy (TEM) and high resolution TEM. It is found that the concentration of reagent cupric acetate has strong effect on the purity and microstructure of the prepared samples. The growth process is investigated in detail. It is proposed that the nanorods are evolved from spherical particles with oriented attachment mechanism followed by dissolution-splitting process. The optical properties of the samples are detected by UV–vis spectrometer and photoluminescence spectrometer and exhibit strong dependence on surface defect states and microstructure feature, which is mainly determined by preparation conditions.
CuBi2O4 and CuWO4 films (2 × 2 cm) on an FTO substrate have been fabricated to construct an all-copper-based oxide tandem cell for solar-driven photoelectrochemical (PEC) water splitting. CuBi2O4 and CuWO4 films are of opposite semiconductivity, and exhibit a large difference in the onset potentials and matched light absorption, making them ideal for a tandem configuration for solar energy conversion. Under optimal conditions, the tandem cell (4 cm2) exhibits a water splitting photocurrent of 0.3 mA without an external bias under simulated solar insolation. The low cost, non-toxicity, good stability and easy manufacture of this copper-based oxide tandem cell warrant promising applications in the field of solar energy conversion. This journal is
The narrow optical band gap, higher electrical conductivity, and wider-absorption range are three key features that a good photocatalyst must possess. Herein we fabricate Cu-doped MnO2 (Mn1-xCuxO2) nanostructure by facile wet chemical approach and form its nanocomposite with r-GO (Mn1-xCuxO2/r-GO) via ultra-sonication approach. The successful replacement of host metal ions (Mn4+) with the dopant metal ions (Cu2+) was supported with the PXRD, FT-IR, and EDX characterizations. The effect of Cu-doping on the band gap and r-GO matrix on the conductivity of the fabricated nanocomposite was also evaluated via Tauc plots and I–V tests, respectively. The photocatalytic efficiency of the fabricated photocatalysts was tested and compared against the methylene blue (MB) under visible light irradiation. The photocatalytic experiments revealed that Mn1-xCuxO2/r-GO photocatalyst exhibit superior photocatalytic aptitude than that of pristine MnO2 and Mn1-xCuxO2 photocatalysts. More precisely, the Mn1-xCuxO2 photocatalysts degrade 86.89% MB dye at the rate of 0.021 min−1 after a 90-min exposure to the visible light. Observed superior catalytic activity of the nanocomposite can be attributed to the synergistic effects between the Cu doped MnO2 and r-GO nanosheets that result in its narrow band-gap (2.19 eV) and excellent conductivity (2.217 × 10−2 Scm−1).
Copper bismuth oxide (CuBi2O4 or Bi2CuO4) thin films have been elaborated for the first time by radio-frequency magnetron sputtering using a homemade CuBi2O4 ceramic target. X-ray diffraction characterizations revealed an amourphous phase for as-deposited films. After air annealing at 450 °C for 12 h, a pure polycristalline CuBi2O4 phase can been obtained. Raman spectroscopy confirmed the film phase purity. The influence of the thickness on the structural properties of the films have been studied and we observed that all films treated above 450 °C are crystallized. The thinner films show preferred orientation while there are less crystal defects for the thickest films (∼700 nm). Atomic force microscopy shows a homogeneous polycristalline microstructure at the surface of the film. Optical measurements performed by UV–vis-IR spectrophotometry indicate that these films have one of their optical band gaps in the visible region (Eg∼1.5 eV) which makes them suitable as thin films solar absorption materials.
Global energy crisis escalates the emphasis on ways to find green and sustainable solutions. Photoelectrochemical (PEC) conversion is one of the key technologies to fulfill the energy demand by converting solar energy into chemical fuels. Binary copper oxides suffer from severe photocorrosion and ternary copper oxides such as copper bismuth oxide (CuBi2O4) exhibit poor charge separation and transfer. In this work, a composite consisting of CuO annealed at 450 ⁰C and CBO electrodeposited for 5 min on top of it (CuO-450/CBO-5) showed the best performance with a positive shift of 0.2 V in onset potential, a high current density of -0.9 mA cm⁻² at 0.1 V vs RHE and high stability over pure CuO. The systematic deposition of CBO on CuO leads to intimate contact between the two semiconductors wherein, CuO acts as a hole carrier and CBO accommodates the hydrogen evolution reaction (HER).
In this work, an electrocatalyst, consisting of Pd nanoparticles in an electrochemically-reduced graphene oxide (Pd/ERGO) nanocomposite, was synthesized by the one-pot simultaneous electrochemical deposition technique, on a Ni foam (NiF) electrode. The structural and morphological characterization of the Pd/ERGO nanocomposite was analyzed using several techniques, such as X-ray diffraction (XRD), XPS, EDS, and scanning electron microscopy (SEM). XPS results for the Pd/ERGO composites showed the successful electrochemical reduction of graphite oxide (GO) to ERGO and the presence of metallic Pd in the nanocomposite structure. The electro-oxidation of ethanol on a Pd/ERGO/NiF electrode was then studied using cyclic voltammetry. Electrochemical measurements of the Pd/ERGO composite electrode demonstrated higher electrocatalytic activity (with current density of ~130 mA cm⁻²) for ethanol electro-oxidation in an alkaline medium, at room temperature, than for either naked NiF or ERGO-modified NiF (ERGO/NiF) under the same conditions. Further, Pd/ERGO nanocomposite had greater chronoamperometric stability for ethanol electro-oxidation compared to both naked NiF and ERGO/NiF electrodes. The results showed that a nanocomposite modified electrode can be preferred as a potential electrode material for energy storage and conversion applications.
Photoelectrochemical water splitting (PEC) is considered to be one of the proficient approaches for harvesting perpetual solar energy into chemical energy. Finding newer materials which are earth-abundant and economical, are crucial in commercializing this technology in future. Herein, we have proposed a noble metal free, p-type CuBi2O4 directly fabricated over FTO, overlaid with reduced graphene oxide (RGO). CuBi2O4 with an optimized number of RGO deposition cycles, displayed highest current density, which is ~2-fold higher than that of the bare CuBi2O4 photocathode. An average Faradaic efficiency of 91.7% was achieved, indicating that the photocurrent generated in RGO modified CuBi2O4 photocathode attributes solely to the water reduction. With RGO modification over CuBi2O4, charge carrier density increases from 3.76 x 10²⁰ cm⁻³ to 7.92 x 10²⁰ cm⁻³. A significant increase in carrier density advocates enhanced charge injection as well as separation owing to an efficient charge transfer from CuBi2O4 to RGO through favourable band alignment. Further, open circuit potential decay measurments (OCPD) indicate enhanced charge seperation with the introduction of graphene oxide into the CuBi2O4.
of main observation and conclusion
Electrocatalytic carbon dioxide reduction holds great promise for reducing the atmospheric CO2 level and alleviating the energy crisis. High‐performance electrocatalysts are often required in order to lower the high overpotential and expedite the sluggish reaction kinetics of CO2 electroreduction. Copper is a promising candidate metal. However, it usually suffers from the issues of poor stability and low product selectivity. In this work, bimetallic Cu‐Bi is obtained by reducing the microspherical copper bismuthate (CuBi2O4) for selectively catalyzing the CO2 reduction to formate (HCOO‐). The bimetallic Cu‐Bi electrocatalyst exhibits high activity and selectivity with the Faradic efficiency over 90% in a wide potential window. A maximum Faradaic efficiency of ~95% is obtained at ‐0.93 V versus reversible hydrogen electrode. Furthermore, the catalyst shows high stability over 6 h with Faradaic efficiency of ~95%. This study provides an important clue in designing new functional materials for CO2 electroreduction with high activity and selectivity.
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Cu monolayer/electrochemically reduced graphene oxide (ML/ERGO) layered nanocomposites are grown on Au substrates by sequential underpotential deposition of Cu(ML)s and electrochemical reduction of graphene oxide for the electrocatalytic oxidation of ethanol. Characterization of the Au-Cu(ML)/ERGO layered composites by scanning electron microscopy and scanning tunneling microscopy reveal that the smooth Cu(ML) on the Au surface is transformed into parallel aligned nanoparticles after modification by the ERGO layer. X-ray photoelectron spectroscopy and Raman spectroscopy results for the Au-Cu(ML)/ERGO composites show the successful electrochemical reduction of GO to ERGO and the presence of metallic Cu in the nanocomposite structure. Electrochemical measurements of the as-prepared Au-(Cu(ML)/ERGO)1 electrodes exhibit excellent electrocatalytic performance (15 mA cm⁻²), which was 5.7 and 1.6 times higher than those from the naked Au and Au-Cu(ML) electrodes, respectively, toward ethanol electro-oxidation in alkaline condition.
A new strategy of using forward gradient self-doping to improve the charge separation efficiency in metal oxide photoelectrodes is proposed. Gradient self-doped CuBi2O4 photocathodes are prepared with forward and reverse gradients in copper vacancies using a two-step, diffusion-assisted spray pyrolysis process. Decreasing the Cu/Bi ratio of the CuBi2O4 photocathodes introduces Cu vacancies that increase the carrier (hole) concentration and lowers the Fermi level, as evidenced by a shift in the flat-band toward more positive potentials. Thus a gradient in Cu vacancies leads to an internal electric-field within CuBi2O4, which can facilitate charge separation. Compared to homogeneous CuBi2O4 photocathodes, CuBi2O4 photocathodes with a forward gradient show highly improved charge separation efficiency and enhanced photoelectrochemical performance for reduction reactions, while CuBi2O4 photocathodes with a reverse gradient show significantly reduced charge separation efficiency and photoelectrochemical performance. The CuBi2O4 photocathodes with a forward gradient produce record AM 1.5 photocurrent densities for CuBi2O4 up to -2.5 mA/cm2 at 0.6 V vs. RHE with H2O2 as an electron scavenger and they show a charge separation efficiency of 34 % for 550 nm light. The gradient self-doping accomplishes this without the introduction of external dopants and therefore the tetragonal crystal structure and carrier mobility of CuBi2O4 are maintained. Lastly, forward gradient self-doped CuBi2O4 photocathodes are protected with a CdS/TiO2 heterojunction and coated with Pt as an electrocatalyst. These photocathodes demonstrate photocurrent densities on the order of -1.0 mA/cm2 at 0.0 V vs. RHE and evolve hydrogen with a faradaic efficiency of ~91 %.
Dense, homogeneous CuBi2O4 thin films are prepared, for the first time, by spray pyrolysis. Major challenges related to the chemical stability of the precursor solution and spreading behavior of the sprayed droplets are revealed and addressed. Triethyl orthoformate (TEOF) is added as a water scavenger to avoid fast hydrolysis and polycondensation of bismuth ions in the precursor solution, thereby reducing powder formation during the spray deposition process. Polyethylene glycol (PEG) is used to improve the spreading behavior of sprayed droplets over the entire CuBi2O4 film surface, which prevents powder formation completely and allows for the deposition of dense, homogeneous films with thicknesses over 420 nm. These highly uniform CuBi2O4 thin films are well-suited for fundamental studies on the optical and photoelectrochemical properties. Additionally, they produce record photocurrent densities for CuBi2O4 up to 2.0 mA/cm2 under AM 1.5 simulated sunlight along with incident photon-to-current efficiency (IPCE) and absorbed photon-to-current efficiency (APCE) values up to 14 % and 23 %, respectively (for 550 nm light at 0.6 VRHE with H2O2 as an electron scavenger).
In this study, a chemically modified electrode, consisting of CuO nanoparticles decorated nano-dendrite-structured CuBi2O4 (nanoCuBi2O4|CuO), was fabricated and its application as an electrocatalyst in catalyzing the oxidation of glucose was investigated. nanoCuBi2O4|CuO was fabricated by firstly electrodepositing BiOI nanosheet array (nanoBiOI) on the flourine-doped tin oxide coated glass substrate, followed by its conversion into nanoCuBi2O4|CuO via drop-casting a ethanolic Cu²⁺ solution and follow-up thermal treatment. The degree of conversion of nanoBiOI into nanoCuBi2O4|CuO and electrocatalytic activites of resultant nanoCuBi2O4|CuO were controlled by adjusting the dosage of the ethanolic Cu²⁺ precursor solution. Surface morphology, structure, crystal phase, chemical composition, and electrocatalytic properties of the nanoCuBi2O4|CuO were characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. It was found that both CuO and CuBi2O4 are active in electrocatalyzing the oxidation of glucose, but the porous structure of nanoCuBi2O4|CuO along with the synergistic catalytic enhancement, exerted by CuBi2O4 and CuO, renders nanoCuBi2O4|CuO superior electrocatalytic activity than CuO or CuBi2O4 alone. The mechanism of electrocatalytic oxidation of glucose on nanoCuBi2O4|CuO is proposed. Finally, the sensing characteristics of nanoCuBi2O4|CuO was evaluated, and the results indicate nanoCuBi2O4|CuO is a promising sensing material for the electrochemical detection of glucose.
CuBi2O4 hierarchical microspheres are synthesized via a coprecipitation method, where the effect of the NaOH concentration in precursor solution on the product morphology is investigated. At n(NaOH) = 1 M, irregular microspheres of 0.5–1 μm are produced. With increase in the concentration of NaOH, the microspheres grow bigger in size and more regular in morphology. When the NaOH concentration is increased up to 6 M, regular microspheres of 4–6 μm in diameter are obtained. These microspheres are constructed from nanorods with 30–60 nm in diameter and 200–400 nm in length via the hierarchical self-assembly process. The electrochemical performances of the as-prepared samples are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge. It is demonstrated that the sample composed of 0.5–1 μm microspheres exhibits the highest specific capacity, reaching about 1895 F g−1 in a 2 M KOH electrolyte at a measured current density of 1 A g−1. This value is larger than the specific capacity for most transition metal oxides. Due to its excellent electrochemical performance, CuBi2O4 could find a promising application as the supercapacitor electrode material.
In this work, copper-bismuth oxide (CuBi2O4) nanoparticles were supported on nanoporous stainless steel by a simple electrochemical deposition method and then was employed as a binder-free electrode for supercapacitor application. The structure and surface morphologies of the nanoparticles-supported on nanoporous stainless steel were investigated using X-ray diffraction spectroscopy, energy dispersive X-ray spectroscopy and scanning electron microscopy. The electrochemical properties of the proposed electrode were examined using cyclic voltammetry and galvanostatic charge–discharge techniques in different electrolytes. The results showed that the proposed electrode exhibited a maximum specific capacitance of 144 mA h g−1 or 647 F g−1 at a current density of 1.0 A g−1 in 6.0 mol L−1 KOH with excellent long-term cycling stability (80% capacitance remained after 500 charge–discharge cycles). The proposed nanostructure is a suitable candidate for electrode material in energy storage devices.
Reduced graphene oxide (RGO)/ CuBi2O4 (GCB) composites were synthesized, through a novel single step solvothermal process. Properties of the synthesized composites such as functionality, morphology, composition and optical properties were characterized by FT-IR, Raman, XRD, FE-SEM, EDAX, HR-TEM, UV-DRS and PL analysis. Spinel structured CuBi2O4 (CB) was incorporated into RGO at various percentages. Among the developed composites, 2 wt % GO incorporated GCB2 composite shows 95% and 87% degradation efficiency for methylene blue and methyl orange, respectively in comparison to pure CB and other composites. In addition, the enhanced photocatalytic activity of CuBi2O4 has been explained and the mechanism attributing to the excellent performance of GCB has been proposed.
Spinel MBi2O4(M = Cu, Zn) were synthesized by a special sol–gel method, and we report the photocatalytic activity of novel photocatalyst MBi2O4 under visible light irradiation. The prepared samples were characterized by X-ray diffraction and scanning electron microscope. The chemical composition of these photocatalysts was confirmed by SEM–EDS spectrum and X-ray photoelectron spectroscopy. The results indicated that the chemical formulas of the samples are CuBi2O4 and ZnBi2O4, which was no report before. All of them exhibited high photocatalytic activity for the degradation of industrial dyes, the 2 h degradation values of ZnBi2O4 and CuBi2O4 for brilliant red K-2G are 91.5 and 72.6 %, and the 2 h degradation values for acid red B are 99.8 and 89.8 %, respectively. These characteristics make the photocatalysts to be promising candidates for the photocatalytic degradation of dyes.
We report the synthesis of visible-light-active thin films of p-CuBi2O4 utilizing electrodeposition for the first time. Bimetallic films of Cu and Bi were deposited from a single bath onto fluorine-doped tin oxide (FTO) substrates and thermally oxidized in air. The effects of deposition parameters such as potential, time, and bath concentration were investigated. In general, the films consisted of interconnected particles roughly 250 nm in diameter and showed an onset of light absorption at 680 nm (1.8 eV). The films were characterized by photoelectrochemical (PEC) techniques in order to provide insight into the critical PEC properties of CuBi2O4 such as flat-band potential, photocurrent stability, and incident photon-to-current efficiency (IPCE). Despite the narrow band gap and quite suitable band edge positions for PEC H2 generation, the films’ stable calculated AM1.5G photocurrents in N2 degassed Na2SO4 were relatively small (44–55 μA/cm2 at −0.2 V vs Ag/AgCl) due to maximum UV quantum yields of 1–2% that decreased significantly throughout the visible range, becoming negligible near 700 nm. Film stability tests under constant illumination revealed that the films were unstable in acidic electrolyte (pH 3.5) due to the reduction and dissolution of Cu but were stable in basic electrolyte (pH 10.8) after an initial 50% decrease in performance.
Copper bismuth oxide (CuBi2O4) film electrodes were fabricated by anodic co-electrodeposition of Bi2O3 and CuO, followed by heat treatment in air at 500 ℃. The compositions of the electrolyte solution, such as concentrations of Cu2+, Bi3+, and tartaric acid, alkaline strength, and temperature, were optimized to fabricate pure CuBi2O4 films on FTO substrates. XRD and optical absorption were employed to confirm the formation of CuBi2O4, and SEM observation showed the fabrication of a closed packed film with good contact to the FTO substrate. Mott-Schottky plots based on Nyquist plots at various potentials gave the flat band potential of 0.62 V (vs. Ag/AgCl) at pH 6.0. Since the band gap energy measured was 1.80 eV, the conduction band bottom locates at -0.98 V (vs. NHE). At the potential more negative than 0 V (vs. Ag/AgCl), the photo cathodic current for hydrogen production was observed under visible light irradiation in a deoxygenated 0.1M Na2SO4 solution. The film electrode sustained the photo electrochemical activity in the electrolyte solution at -0.3 V (vs. Ag/AgCl), at least, for 100 min.
Copper bismuth complex oxides with various novel morphologies were successfully prepared via a hydrothermal process at 120 °C for 3 to 24 h. The structure, morphology, composition and light absorption properties were characterized with XRD, SEM, TEM, HRTEM, EDX and UV–vis diffuse reflectance. The photocatalytic properties under visible light irradiation were evaluated using a degradation experiment. The results showed that some prepared samples exhibited a novel leaf-like nanosheet morphology with a uniform spinel CuBi2O4 structure, and their excellent visible light absorption characteristics, the photocatalytic properties exhibited a strong dependence on nanocrystal microstructure, morphology and lattice orientation.
Emerging electrosynthetic techniques such as electrogeneration of base, anodic oxidation, and ac (alternating current) synthesis provide simple and inexpensive alternative routes to the synthesis of ceramic thin films and coatings, nanoparticulate materials, and metastable phases. In this review, we survey illustrative examples to highlight the potential application of these techniques in meeting the goals of inorganic solid-state synthesis.
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