Monoclinic Bi2O3 Research Articles

Fabrication of a hyphenated S-scheme and Schottky-junction photocatalyst based on a ternary TiNbCTx@α-Bi2O3/ZnSe heterostructure with enhanced optical and photoelectrochemical properties

Environmental pollution by pharmaceuticals poses a serious threat to humans and animals. Hence there is a need for a low-cost, environmentally friendly, and sustainable treatment technology for environmental remediation. Herein, we report the synthesis of a novel TiNbCTx@α-Bi2O3/ZnSe ternary photocatalytic nanocomposite, characterised using spectroscopic and microscopic techniques. Moreover, the optical and photoelectrochemical properties of the photocatalysts were assessed using spectroscopic tools such as UV–Vis DRS, EIS and PL. The synthesised pristine, cubic ZnSe, monoclinic Bi2O3, α-Bi2O3/ZnSe and the ternary composites’ crystallinity were all confirmed by the co-existence of their crystal planes and bands in XRD, SAED, and Raman spectroscopy, correspondingly. SEM and TEM analysis confirmed the anticipated characteristic morphologies and the interfaces. Improved optical properties deduced from UV–Vis DRS measurements revealed α-Bi2O3 and ZnSe to have band gaps of 2.7 eV and 2.41 eV, respectively. Upon creating an α-Bi2O3/ZnSe heterostructure and TiNbCTx@α-Bi2O3/ZnSe ternary system, a red shift was observed in their band gaps, indicating improved optical properties. The electrochemical properties of the materials were determined using EIS. These were used to deduce the charge transfer kinetics of the heterostructure and ternary system, which showed TiNbCTx@α-Bi2O3/ZnSe to be an outstanding photocatalyst over the synthesised pristine materials and α-Bi2O3/ZnSe heterostructure. The photocurrent response of the TBZ-7 % exhibited enhanced generation and separation of photoexcited charge carriers 4 folds higher than those of pristine materials. The PL spectra of the TBZ-7 % showed low intensity due to the suppression of charge recombination rates. Moreover, the Nyquist and LSV plots of TBZ-7 % presented improved charge transfer ability and a prolonged lifetime of photoinduced charge carriers (280 ms), respectively. With these enhanced properties, TiNbCTx@α-Bi2O3/ZnSe ternary photocatalytic nanocomposite demonstrates the extraordinary potential for environmental remediation in degrading ARVs from water.

Boosted visible light dye-decontamination and colossal dielectric constant features of Bi2O3: Role of In, Cu and Li-dopants

This study focused on improving the optical, dielectric properties, and photocatalytic efficiency of Bi2O3, a prominent photocatalyst with challenges like limited visible light absorption and rapid electron-hole pair recombination. Using an adapted sol-gel technique, pure Bi2O3, In, Cu and Li-doped Bi2O3 visible-light-driven photocatalyst were synthesized. X-ray diffraction (XRD) confirmed monoclinic Bi2O3 formation. The inclusion of In, Cu, and Li ions into the Bi2O3 lattice was evidenced by alterations in diffraction peak intensities, lattice parameters, and changes in average crystallite size. Vibrational spectra corroborated the formation of pure α-Bi2O3 with slight shifts in transmittance bands, aligning with the XRD findings. Morphological investigation via scanning electron microscopy (FE-SEM-EDX) confirmed the purity of the synthesized nanocompositions and unveiled that the doping induces distinct morphological changes in Bi2O3 nanoparticles, resulting in increased porosity and formation of round and needle-like shapes (In-doped), coalescence of particles (Cu-doped), and fused agglomerates with altered particle size distribution (Li-doped). Optical analysis demonstrated a red shift in the band gap energy of α-Bi2O3 (initially 2.90 eV), with In, Cu, and Li doping, resulting in band gaps of 2.77 eV, 2.78 eV, and 2.88 eV, respectively, accompanied by high refractive indices exceeding 2.0, rendering them suitable for optical applications. Both Cu and Li doping led to enhanced relative permittivity (εʹ) values, with the Li-doped sample displaying remarkable εʹ values at low frequencies (up to 1000 Hz). The In, Cu and Li doping has the effect of reducing PL (photoluminescence) emission intensity while simultaneously diminishing radiative recombination and promoting the separation of photogenerated charge carriers. The doped samples demonstrated superior degradation performance, with In-doped and Cu-doped samples achieving degradation efficiencies of 99% and 91%, respectively, within 180 min. This remarkable performance can be attributed to their visible-light-responsive band gaps, increased electron-hole trapping sites, and distinct morphological features.

Isotherm and kinetic studies for the adsorption of methylene blue onto a novel Mn3O4-Bi2O3 composite and their antifungal performance

Metal oxide-based adsorbents are quite in for wastewater treatment because of their selectivity, stable structure and very low solubility in aqueous systems. To explore the adsorption of methylene blue (MB), Mn3O4-Bi2O3 adsorbents were made using a wet-impregnation technique with various concentrations of Mn3O4. The presence of Mn3O4 contents on the surface of monoclinic Bi2O3 was confirmed through representative scanning electron micrographs. The diffractions pertaining to cubic Mn3O4 and monoclinic Bi2O3 were noticed in the XRD pattern of 5% Mn3O4-Bi2O3 which confirm the composite nature of the adsorbent. XPS analysis revealed the existance of Bi 4f, Bi 4d, Bi 4p, Bi4s, and Mn 2p core levels in Mn3O4-Bi2O3. The adsorption study divulged highest efficiency (∼95% and qe = ∼1.4 mgg-1) of 5% Mn3O4-Bi2O3 composite among other contestants in removing 30 ppm MB at 28 ° C, pH 7 and 250 rpm. In addition to the determination of adsorption ability, the effect of preliminary dye concentration (5, 10, 20, and 30 ppm) and contact time (0.5–6 h) on the removal efficiency of prepared adsorbents were also monitored. The adsorption data from the batch experiments were evaluated using the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich-Kaganer (DRK) adsorption isotherms and pseudo 1st and 2nd-order kinetic models. The fitting of adsorption isotherms and kinetic models revealed the formation of adsorbate’s monolayer on the surface of adsorbents through the process of chemisorption. Through FTIR measurement, the MB adsorption onto the effective adsorbent (5% Mn3O4-Bi2O3) was also confirmed. Moreover, TGA analysis showed ∼1.5% weight loss by 5% Mn3O4-Bi2O3 before MB adsorption whereas ∼2.6% weight loss was noticed after dye adsorption onto the adsorbent. The antifungal activity was evaluated against the fungi A. solani and M. fructicola using the agar well diffusion technique. The 5% Mn3O4-Bi2O3 composites have exceptional antifungal characteristics compared to Bi2O3 and Mn3O4, with zone inhibition values of 58.6 and 53.9 mm, respectively.

Mechanistic insights for electroreduction of CO2 on pristine monoclinic α-Bi2O3 (120) surface

To date, the electrochemical reduction of CO2 (CO2RR) into valuable chemicals is a promising method for combating global warming. However, finding a suitable electrocatalyst for CO2RR is critical to reducing CO2 emissions. Herein, the CO2RR mechanism on a pristine monoclinic Bi2O3 (120) surface was thoroughly investigated using density-functional theory (DFT) calculations. The CO2 adsorption modes of side-on, end-on, and chemisorbed were compared, with the chemisorbed species outperforming for CO2 activation. Furthermore, analyses of the Bader charge, the density of states, and electron density difference strongly suggest that the Bi2O3 (120) surface has excellent activation for CO2 molecules. More importantly, the DFT calculations revealed that the electrochemical CO2RR over the Bi2O3 surface favors both formic acid and methanol in the limiting-potential step of *CO2→ *COOH with the free energy barriers of 0.86 eV and 0.87 eV with and without solvent, respectively. The microkinetic simulation also supports the DFT result, showing the possibility of more selective production by predicting desorption temperatures. This research suggests a promising way for CO2RR mechanisms on pristine monoclinic Bi2O3 surfaces to produce formic acid (HCOOH) and methanol (CH3OH).

Controllable synthesis of BiPr composite oxide nanowires electrocatalyst for sensitive L-cysteine sensing properties

BiPr composite oxide nanowires with rhombodedral Bi1.35Pr0.65O3, monoclinic Bi2O3 and monoclinic Pr5O9 phases were synthesized via a facile sodium dodecyl sulfate (SDS) assisted hydrothermal route. The obtained nanowires were characterized by x-ray diffraction, electron microscopy, x-ray photoelectron spectroscopy and electrochemical measurements. The BiPr composite oxide nanowires possess poly-crystalline structure, semi-circular tips, diameter and length of 20–100 nm and several micrometers, respectively. SDS is essential for the formation of the BiPr composite oxide nanowires which can be explained by a SDS assisted hydrothermal growth process. Electrochemical impedance spectroscopy shows that the electrons are easier to transfer by the surface of the BiPr composite oxide nanowires modified glassy carbon electrode (GCE) than bare GCE. The BiPr composite oxide nanowires modified GCE possesses good electro-catalytic activity for L-cysteine detection with a pair of quasi-reversible cyclic voltammetry peaks at +0.04 V and –0.72 V for the oxidation and reduction of L-cysteine, respectively. The roles of the scan rate, electrolyte species and L-cysteine concentration on the electrochemical responses of L-cysteine at the nanowires modified GCE were systematically analyzed. The BiPr composite oxide nanowires modified GCE presents a linear response range from 0.001 to 2 mM and detection limit of 0.27 μM, good reproducibility and stability.

Sodium Ligninsulfonate-assisted Synthesis of Lithium Bismuthate/bismuth Oxide Microspheres and Solar Light Photocatalytic Performance

Background: Great attention has been paid to the environmental pollution by organic dyes, which are difficult to be degraded in the natural environment and have been an unavoidable and urgent global problem. It is essential to develop green wastewater treatment technology with high removal efficiency and low-cost for protecting the surrounding and human health. Objective: The aim of the research is to synthesize lithium bismuthate/bismuth oxide microspheres with good photocatalytic performance for the removal of gentian violet (GV). Methods: Lithium bismuthate/bismuth oxide microspheres were successfully prepared by a sodium ligninsulfonate-assisted hydrothermal synthesis route. The lithium bismuthate/bismuth oxide microspheres were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform infrared spectroscopy (FTIR), and solid UV-vis diffuse reflectance spectrum. Results: XRD pattern and SEM observation show that the lithium bismuthate/bismuth oxide microspheres are composed of cubic LiBi12O18.50 and monoclinic Bi2O3 with a diameter of 250 nm-1 μm. Irregular microscale and nanoscale particles are formed under low hydrothermal temperature, low sodium ligninsulfonate concentration, and short duration time. By increasing the sodium ligninsulfonate concentration, hydrothermal temperature, and duration time, irregular particles are transferred into microspheres. Lithium bismuthate/bismuth oxide microspheres possess a band gap energy of 1.85 eV, suggesting good visible light absorption ability. The photocatalytic removal ability for GV is enhanced by prolonging light irradiation time and microspheres dosage. GV solution with the concentration of 10 mg•L-1 is able to be totally degraded by 10 mg lithium bismuthate/bismuth oxide microspheres in 10 mL GV solution under solar light irradiation for 6 h. Conclusion: The lithium bismuthate/bismuth oxide microspheres show good photocatalytic removal ability toward GV in wastewater under solar light irradiation.

Investigation of electrical and aging properties of Bi-modified (Zn0.4Ni0.6)1-xNaxO ceramic thermistors

Bi-modified (Zn0.4Ni0.6)1-xNaxO (denoted as xZNN, x < 0.1) ceramics were prepared by conventional solid-state reaction process. The xZNN ceramics have rock-salt type structure. Besides the rock-salt phase, there is a monoclinic Bi2O3 secondary phase coexisting in the Bi-modified xZNN ceramics. These ceramics exhibit typical characteristic of negative temperature coefficient (NTC) of resistivity. The NTC material constants (B values) of all prepared ceramics are higher than 4000 K. The room temperature resistivity and B values can be adjusted in a large range by altering either or both content of Na-ions and Bi-ions. The effect of Bi2O3 addition is remarkable in term of enhancing sinter ability to reduce sintering temperature from 1350 °C to 1150 °C, and improving aging stability to drop resistance drift rate from 237 % to 1.8 %. Aging characteristic was discussed based on models of space charge distribution and interfacial barriers.

Influences of Substrate Temperatures and Oxygen Partial Pressures on the Crystal Structure, Morphology and Luminescence Properties of Pulsed Laser Deposited Bi2O3:Ho3+ Thin Films

Monoclinic Bi2O3:Ho3+ powder was synthesized using a co-precipitation method, followed by the deposition of Bi2O3:Ho3+ thin films on Si (100) substrates at various substrate temperatures (room temperature–600 °C) and oxygen partial pressures (5–200 mT) using pulsed-laser deposition. X-ray diffraction analysis showed a single α-Bi2O3 phase at temperatures of 400 and 500 °C, while a mixed α- and β-Bi2O3 phase was obtained at 600 °C. The films deposited at the different oxygen partial pressures showed an α-Bi2O3 and non-stoichiometric phase. The influences of different substrate temperatures and oxygen partial pressures on the morphology and the thickness of the films were analyzed using a scanning electron microscope. The root mean square roughnesses of the films were determined by using an atomic force microscope. The surface components, oxidation states and oxygen vacancies in all the deposited thin films were identified by X-ray photoelectron spectroscopy. The optical band gap of the Bi2O3:Ho3+ thin films was calculated using diffused reflectance spectra and was found to vary between 2.89 and 2.18 eV for the deposited films at the different temperatures, whereas the different oxygen partial pressures showed a band gap variation between 2.97 and 2.47 eV. Photoluminescence revealed that Ho3+ was the emitting centre in the isolated thin films with the 5F4/5S2 → 5I8 transition as the most intense emission in the green region.

Atmospheric Pressure Plasma Coating of Bismuth Oxide Circular Droplets

In this study, bismuth oxide powder (Bi2O3) was deposited by an atmospheric pressure plasma jet onto borosilicate glass. The layer produced through this method is to be used as a photo catalyst in later applications. The deposited coating was analyzed by X-ray diffraction (XRD) to determine the crystal structure, and X-ray photoelectron spectroscopy (XPS) to analyze the chemical state. The results showed a change in crystal and chemical structure during the deposition process. The morphological properties of the layer were examined with scanning electron microscopy (SEM) and laser scanning microscopy (LSM). The band gap structure of the coating was investigated by UV-Vis spectroscopy. The layer produced by the plasma spraying process consisted of circular multi-phase bismuth oxide droplets (monoclinic Bi2O3 and tetragonal Bi2O2.33), showing a direct band gap of Eg = 2.72 eV, which allows their use as a photocatalyst.

Synthesis and Characterisation of Bismuth Oxide Nanoparticles using Hydrothermal Method: The Effect of Reactant Concentrations and application in radiotherapy

High atomic number (Z) of bismuth oxide nanoparticles (Bi2O3 NPs) has more cell penetration and less adverse effects than conventional radiosensitisers. In this work, 60 nm and 90 nm of Bi2O3 NPs were successfully synthesised using the hydrothermal method by varying the bismuth nitrate, Bi(NO3)3 concentration. The properties of Bi2O3 NPs were characterised to determine the phase presence, crystallinity, morphology, elements presence and size of nanoparticles. The as-synthesised Bi2O3 NPs was in monoclinic Bi2O3 phase (ICDD 98-008-5622). As the Bi(NO3)3 concentration increased, the particle size of Bi2O3 NPs decreased due to less ions diffusion per nuclei. The morphology observation showed that Bi2O3 NPs were in rods form. The produced Bi2O3 NPs were subjected to cytotoxicity analysis and radiotherapy. Bi2O3 NPs did not induce cytotoxicity in breast cancer (mcf-7) cell lines at concentration from 0.05 µM. The radiotherapy performance of the as-prepared Bi2O3 NPs was obtained by calculating the sensitisation enhancement ratio (SER). The optimum result was found for 60 nm Bi2O3 NPs with SER of 3.45.

Composition and Structure Evolution of Bi2O3 Coatings as Efficient Photocatalysts

To overcome the recovery disadvantages of Bi2O3 photocatalyst in the form of powder, Bi2O3 photocatalyst coatings were developed via a ball milling, followed by the calcination method. The composition and structure evolution rules of the as-synthesized samples were analyzed based on XRD (X-ray powder diffraction) patterns and SEM (scanning electron microscope) observations. XPS (X-ray photoelectron spectroscopy) and UV-Vis (Ultraviolet-visible) spectra were also employed to characterize the samples. The results showed that monoclinic Bi2O3 coatings were obtained after sintering Bi coatings at 673 or 773 K for 2 h, while calcination at a higher temperature and for a longer time resulted in monoclinic and triclinic mixed-phase Bi2O3 coatings. Bi2O3 coatings with a radial growth structure assembled by nanosheets could be realized at a lower temperature lasting for a longer time, while sintering at a higher temperature with relatively short oxidation time led to tangential growth structure. Photodegradation of malachite green solution under simulated solar irradiation for 180 min showed that the largest degradation efficiency of 91.49% was achieved over the photocatalyst coatings calcined at 873 K for 5 h. Additionally, the degradation efficiency was maintained above 80% even after three cycles.

Structure and conductivity characterization of new type ionic conductor stabilized bismuth oxide ternary systems

In this study, the new type electrolyte (Yb2O3)x(Dy2O3)y(Bi2O3)1-x-y ternary compounds were synthesized with different stoichiometric ratios by the solid-state reaction method at different annealing treatment and also their microstructural and electrical properties were analysed. X-ray powder diffraction results showed that the high temperature δ-phase of pure monoclinic Bi2O3 has been synthesized by doping of Yb2O3. Grain size and grain form of pellet formed samples was compared from their surface images taken by the scanning electron microscopy. The grain size has been varying between ∼17–37 µm, and degrading with the increasing dopant concentrations. The relationships between the structural parameters (e.g. lattice parameters, crystallite size and the lattice microstrain) and structural properties (e.g. ionic radii of dopant cations and heat treatment procedure) were particularly discussed. Total conductivity values were calculated by Nyquistic complex impedance plot. Impedance measurement revelaed that total conductivity values of the samples increase with the increasing Yb dopant ratio. The activation energies calculated by the Arrhenius approach are measured at around 1 eV. In addition, activation energies and pre-exponential terms decrease with the increasing Yb cation dopant rate for the same ambient temperature.

Easily recycled Bi2O3 photocatalyst coatings prepared via ball milling followed by calcination

Bi2O3 photocatalyst coatings derived from Bi coatings were first prepared by a two-step method, namely ball milling followed by the calcination process. The as-prepared samples were characterized by XRD, SEM, XPS and UV–Vis spectra, respectively. The results showed that monoclinic Bi2O3 coatings were obtained after sintering Bi coatings at 673 or 773 K, while monoclinic and triclinic mixed phase Bi2O3 coatings were obtained at 873 or 973 K. The topographies of the samples were observably different, which varied from flower-like, irregular, polygonal to nanosized particles with the increase in calcination temperature. Photodegradation of malachite green under simulated solar irradiation for 180 min showed that the largest degradation efficiency of 86.2% was achieved over Bi2O3 photocatalyst coatings sintered at 873 K. The Bi2O3 photocatalyst coatings, encapsulated with Al2O3 ball with an average diameter around 1 mm, are quite easily recycled, which provides an alternative visible light-driven photocatalyst suitable for practical water treatment application.

Synthesis and room-temperature NO2 sensing properties of Sb2O5 nanowires

The sensing properties of Sb2O5 nanowires are reported for the first time. By varying the heating temperature of a mixture of Sb and Bi powders, we have successfully prepared Sb2O5 nanowires. For nanowires grown at 600°C, the stem is mainly comprised of a monoclinic Sb2O5 phase, with a trace amount of a monoclinic Bi2O3 phase. The existence of Au nanoparticles at the tips suggests that the 600°C-synthesized nanowires are mainly grown via a vapor-liquid-solid process. The 500°C-grown products comprise a small amount of 1D nanostructures, whereas the 700°C-grown product does not exhibit sufficiently thin 1D nanostructures. A representative A survey XPS spectrum exhibits several peaks, including Sb 3p, Sb 3d, O 1s, C 1s, Bi 4f, and Sb 4d. At room temeperature, the sensor response, response time, and recovery time of the nanowires were measured to be 1.20, 2104 s, and 6579 s, respectively. Sensor measurements employing NO2 gas indicate that the Sb2O5 nanowires synthesized in this work have potential for use as a room-temperature NO2 chemical gas sensors.

Synthesis and characterization of Bi2O3/NaBiO3 composite visible light-driven photocatalyst

Monoclinic Bi2O3 and Bi2O3/NaBiO3 composite visible light-driven photocatalysts were synthesized through simple processes. X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray Spectroscopy (EDX), UV–vis Spectrometer and Photoluminescence spectra (PL) were used to characterize the samples. Their photocatalytic activity was evaluated by using malachite green as the model pollutant. The peanut-like composite showed larger band gap energy and smaller absorbance edge than Bi2O3, but its photocatalytic activity was higher than Bi2O3, which may be attributed to its smaller grain size, less agglomeration and better charge carrier separation.

Oxide ionic conductivity and crystallographic properties of tetragonal type Bi2O3-based solid electrolyte doped with Ho2O3

In the present work, the authors have investigated the binary system of (Bi2O3)1–x(Ho2O3)x. For the stabilisation of the tetragonal type solid solution, small amounts of Ho2O3 were doped into the monoclinic Bi2O3 via solid state reactions in the stoichiometric range 0·01≤x≤0·1. The crystal formula of the formed solid solution was determined as Bi(III)4–4xHo(II)4xO6–2xVo(2+2x) (where Vo is the oxide ion vacancy) according to the XRD and SEM microprobe results. In the crystal formula, stoichiometric values of x were 0·04≤x≤0·08, 0·03≤x≤0·09, 0·02≤x≤0·09 and 0·04≤x≤0·09 for annealing temperatures at 750, 800, 805 (quench) and 760°C (quench) respectively. The four probe electrical conductivity measurements showed that the studied system had an oxide ionic type electrical conductivity behaviour, which is increased with increasing dopant concentration and temperature. The obtained solid electrolyte system has an oxygen non-stoichiometry characteristic, and it contains O2– vacancies, which have disordered arrangements in its tetragonal crystal structure. The increase in the amount of Ho2O3 doping and temperature causes an increasing degree of the disordering of oxygen vacancies and a decrease in the activation energy Ea.

Ferroelectric Properties of Bi1.1Fe1-xCoxO3 Thin Films Prepared by Chemical Solution Deposition Using Iterative Rapid Thermal Annealing in N2 and O2

Ferroelectric Bi1.1Fe1-xCoxO3 (BFCO) thin films with x = 0–0.3 have been prepared on Pt/Ti/SiO2/Si substrates by chemical solution deposition (CSD) using iterative rapid thermal annealing (RTA) in nitrogen and oxygen. The crystallization of the rhombohedral structure of BiFeO3 (BFO) is observed clearly in all thin films, and a monoclinic Bi2O3 phase is also observed and is markedly larger in Co-doped BFO thin films than in BFO thin films. An electric field of 2 MV/cm is applied to the Bi1.1Fe0.9Co0.1O3 thin film annealed in nitrogen at 520 °C without dielectric breakdown, but its polarization versus electric field (P–E) hysteresis loops are not saturated owing to its high leakage current density. The Bi1.1Fe0.8Co0.2O3 thin film prepared at 520 °C in oxygen shows a very good saturation of P–E hysteresis loops at room temperature (RT) at the low leakage current of about 8.7 ×10-3 A/cm2 under a high electric field of 1.5 MV/cm. The leakage current at a low electric field may be Ohmic emission at any temperature; however at a high electric field, it may be attributed to tunnel emission at 80 K and Schottky emission at RT.

Bismuth oxide thin films prepared by chemical bath deposition (CBD) method: annealing effect

Bismuth oxide thin films have been deposited by room temperature chemical bath deposition (CBD) method and annealed at 623K in air. They were characterized for structural, surface morphological, optical and electrical properties. From the X-ray diffraction patterns, it was found that after annealing a non-stoichiometric phase, Bi2O2.33, was removed and phase pure monoclinic Bi2O3 was obtained. Surface morphology of Bi2O3 film at lower magnification SEM showed rod-like structure, however, higher magnification showed a rectangular slice-like structure perpendicular to substrate, giving rise to microrods on the surface. The optical studies showed the decrease in band gap by 0.3eV after annealing. The electrical resistivity variation showed semiconductor behavior and from thermoemf measurements, the electrical conductivity was found to be of n-type.