Doped BiVO4 Research Articles

Band Diagram Insights into the Kinetic and Thermodynamic Engineering of Tandem Photocatalytic Cells.

In this work, we theoretically investigate the impact of kinetic and thermodynamic properties on the performance of photocatalytic cells operating in an unassisted tandem configuration, including electron affinity and ionization energies, recombination rates, and reaction rates. To this end, we present general rules and metrics for identifying and isolating the origin of an observed shift in the onset potential at either the photoanode or the photocathode of these devices. The correlation between kinetic and thermodynamic shifts in the onset potential is demonstrated through the use of band diagrams and key comparable features within readily accessible characterization tools: current-voltage plots are taken both under illumination and in the dark and further coupled with Mott-Schottky plots. To illustrate this conceptual framework, a model system comprised of a p-type doped BiVO4 photocathode and an n-type doped BiVO4 photoanode is employed. By varying each of the aforementioned kinetic and thermodynamic parameters in isolation, the manner in which these various mechanisms shift the onset potential is demonstrated. This work intends to showcase how kinetic and thermodynamic effects are distinctly manifested in these commonly used characterization tools and further proposes thermodynamic band-edge engineering as a potentially useful and largely unexplored avenue for possibly improving tandem cell performance, in addition to the conventional approach of optimizing kinetics.

Tungsten-doped BiVO4 and its composite with g-C3N4 for enhanced photocatalytic applications

In this study, BiVO4, W–BiVO4, and W–BiVO4@g-C3N4 composite were successfully synthesized by hydrothermal and ultra-sonication approach respectively. The physiochemical characterizations of BiVO4, W–BiVO4, and W–BiVO4@g-C3N4 were performed by XRD and FTIR techniques. Band gap values of BiVO4 and W–BiVO4 were found to be 2.42 eV and 2.50 eV, respectively. The photocatalytic degradation of pendimethalin (PM) and Aspirin was done in the presence of BiVO4, W–BiVO4, and W–BiVO4@g-C3N4 under visible light irradiation. When used for photocatalytic application, W–BiVO4@g-C3N4 composite showed ∼86% removal of aspirin while W–BiVO4 and pure BiVO4 showed 78% and 63% degradation of aspirin respectively. Furthermore, the nanocomposite (W–BiVO4@g-C3N4) exhibited remarkable degradation activity of ∼91% against PM as compared to BiVO4 (60%) and W–BiVO4 (66%). The higher degradation activity of W–BiVO4@g-C3N4 composite for both aspirin and PM as compared to pure and doped BiVO4 is accredited to its large surface area provided by gCN sheets, and effective separation of photo reactive species because of its Z scheme electron transfer mechanism.

Preparation of nanofiber Co–BiVO4/Bi2O3 p-n heterojunction for high efficiency photocatalytic degradation of organic pollutants

In recent years, water pollution caused by organic pollutants and antibiotic residues has become increasingly serious, posing a serious threat to human health and ecosystems. In this paper, Co–BiVO4/Bi2O3 heterojunction was successfully prepared by electrospinning of Co3+ doped monoclinic BiVO4 nanofibers and Bi2O3. The photocatalytic degradation of chlortetracycline hydrochloride (CTC·HCl) and 2-mercaptobenzothiazole (MBT) in water was tested by simulating visible light conditions. The degradation efficiency of CTC·HCl by 3Co–BiVO4/Bi2O3-0.8 reached 90.5 % within 30 min, and the degradation rates were 3.93 and 7.06 times that of BiVO4 and Bi2O3, respectively. At the same time, the degradation efficiency of MBT by 3Co–BiVO4/Bi2O3-0.8 reached 97.7 % within 40 min, and the degradation rates were 8.93 and 41.80 times that of BiVO4 and Bi2O3, respectively. In addition, the photocatalytic performance of the catalyst and potassium persulfate (PS) co-system on pollutants was investigated. When 0.5 mM PS and a small amount of 3Co–BiVO4/Bi2O3-0.8 catalyst were added, the degradation efficiency of CTC·HCl and MBT could reach 87.6 % and 92.8 % in a short time. Furthermore, the work function and difference of the material were calculated by density functional theory (DFT), and the charge transfer mechanism of the p-n heterojunction was further determined. Finally, the intermediate products, degradation pathways and reaction mechanisms of MBT degradation were analyzed in detail by high performance liquid chromatography-mass spectrometry (HPLC-MS). Therefore, this study provides a potential effective way for the treatment of water pollution.

Dominant role of in defect on carrier distribution and photocatalytic activity for BiVO4

The bismuth vanadate samples (In-BiVO4) have been synthesized through sol-gel method. The typical XRD patterns of samples have revealed that the doped In ions could enter the lattice of BiVO4. The results indicate that doped In ions improve the photocatalytic properties of the BiVO4 for the degradation of methyl orange. The as-prepared In doped BiVO4 photocatalysts exhibit strong visible light absorption capacity than that of bare crystalline BiVO4. Density functional theory calculations show that doped indium ions can effectively promote the separation of photogenerated holes.

Optimization of Z-Scheme Photocatalytic Reactors for Solar Water Splitting

The U.S. Department of Energy recently announced its first Energy Earthshot on Clean Hydrogen, with a cost target of $1/kg-H2 by 2031. Assuming future utility-scale grid electricity prices from photovoltaics ($0.02/kWh), 80% of the cost of H2 would come from performing low-temperature water electrolysis at its thermoneutral voltage, with zero additional overpotential. This fact motivates alternative, less-expensive means of using light to generate mobile charge carriers than photovoltaics, and reactor designs with exceedingly low capital costs, like those we recently invented. Systems using low capital cost reactors benefit from low-voltage operation, which represents a paradigm shift from current state-of-the-art electrolyzers that aim to operate at high current densities. Analytical models predict that solar photocatalytic water splitting inherently operates at low voltages through use of an ensemble of optically thin photoabsorbers each operating at a low rate. Collectively the ensemble exhibits larger overall solar-to-hydrogen conversion efficiencies in comparison to optically thick designs. In efforts to attain these predicted higher efficiencies, we are performing detailed studies on the properties of state-of-the-art doped SrTiO3 and BiVO4 photocatalyst particles. During my talk, I will share our recent efforts in atomic-layer deposited ultrathin oxide coatings to impart redox selectivity and materials stability, single-photocatalyst-particle current–potential behavior and mobile charge carrier properties, and atomic-level information on dopant distributions and materials interfaces obtained from electron microscopies and X-ray spectroscopies. Collectively, our discoveries provide new design guidelines and additional research pathways for the development of effective composite materials to serve as active components in techno-economically viable artificial photosynthetic devices.

Defect assisted enhanced nonlinear optical performance and optical limiting of pure and doped BiVO4 powders and nanocomposite films

The linear and nonlinear absorption properties, photoluminescence and optical limiting properties of bismuth vanadate (BiVO4) powders and films were presented in this work. The structural, morphological and optical effects of different doping elements (M: Mo,W and Ni) were investigated (M: BiVO4). XRD and Raman results proved that BiVO4 and M: BiVO4 powders were synthesized in the monoclinic scheelite structure. Twhe powder morphology as found to be changed by Ni and W doping. The nonlinear optical responses of pure and M: BiVO4 were studied using the open aperture Z-scan experiment and a theoretical model was used to determine the nonlinear optical absorption performance. The nonlinear absorption coefficient (βeff) values were found to be 6.59 × 104, 8.86 × 104, 2.26 × 105 and 1.62 × 106 cm/GW for BiVO4, Mo: BiVO4, W: BiVO4 and Ni: BiVO4 nanocomposite films, respectively. The highest nonlinear absorption coefficients (βeff) and saturation intensity thresholds (ISAT) were obtained for Ni:BiVO4 film. Experimental results showed that the βeff value and band gap can be controlled by the dopant element, making doped BiVO4 a good candidate for nonlinear optical applications such as optical limiters, optical switches and modulators in integrated photonic devices.

Multiple Effects Induced by Mo6+ Doping in BiVO4 Photoanodes

Mo6+ doping increases the photoelectrochemical performance of BiVO4 photoanodes in water oxidation. Herein, the underlying mechanisms is elucidated through a systematic structural, morphological, and photoelectrochemical investigation on photoelectrodes of pure and Mo6+ doped BiVO4 prepared by a novel multistep spin‐coating deposition approach, leading to multilayer flat films with high optical transparency. Transient absorption spectroscopy in the nano‐ to microsecond time scale reveals a longer lifetime of photogenerated holes in the doped films. Besides confirming that Mo6+ ions improve the electron transport in the material bulk, impedance spectroscopy also reveals the crucial role of the dopant on the surface properties of BiVO4 photoanodes. The presence of intra‐bandgap states, acting as traps of photogenerated charge carriers in pure BiVO4, is detected through the build‐up of the interfacial surface state capacitance. The limited activity of pure BiVO4 in water oxidation is largely improved upon 3 at% Mo6+ incorporation, ensuring a more efficient charge carrier transport with respect to pure BiVO4, together with the beneficial passivation of its trap surface states.

Synthesis of Sn and Zr‐Doped BiVO4 Nanocatalyst with Enhanced Photocatalytic and Photoelectrochemical Activity

AbstractHerein, a facile microwave route to synthesized of Tin (Sn) and Zirconium (Zr) doped BiVO4 with enhanced photocatalytic and photoelectrochemical performance are demonstrated. X‐ray diffraction (XRD) studies confirmed the monoclinic‐tetragonal structure of metal doped BiVO4. Field Emission Scanning Electron Microscopy (FE‐SEM) images confirmed the sphere like morphology while bare is in floral structure. The Raman (RS) and Fourier Transform Infra‐Red (FT‐IR) Spectroscopy indicate the functional group of composition. Photoluminance (PL) spectroscopy revealed that the doped BiVO4 showed better excitation then the bare BiVO4. The UV‐Visible diffused reflectance (UV‐vis‐DRS) spectroscopy exposed improved visible light driven by narrow band gap of metal doped BiVO4. Further Electrochemical impedance spectroscopy (EIS) and Linear Sweep voltammetry characterization (LSV) report that the metal doped BiVO4 established better photoelectrochemical activity in water splitting. The impact of metal doping in the crystallinity, optical properties, electrical properties and photocatalytic activity were evaluated using model pollutant of azo dyes and gaseous acetaldehyde under visible light irradiation. The Zr doped BiVO4 exhibit better performance for degradation of dyes, acetaldehyde decomposition and water splitting properties then the Sn doped BiVO4 and bare BiVO4. This work founds that the metal doping with semiconductor is effective in creating heterostructured nanomaterials, which result in reduce the recombination processes, leading to improved photocatalytic and photoelectrochemical performance.

New insights into the structural, optical, electronic and photocatalytic properties of sulfur doped bulk BiVO4 and surface BiVO4 on {0 1 0} and {1 1 0} via a collective theoretical and experimental investigation

In this paper, we have reported as a comparative study a theoretical and experimental approach to photocatalytic efficiency of S-doped BiVO4 at bulk and surface {010} and {110} crystal facets on BiVO4. It is observed that the well-defined BiVO4 crystal with unique configurations of {010} and {011} has enhanced photocatalytic activity compared to bulk BiVO4 owing to the morphology tuning and the obtained crystalline facets. A systematic investigation on the theoretical and experimental results confirm that the S 3p energy level is induced by the added oxygen vacancy and sulphur (S) doped on the bulk and surface BiVO4, resulting in a reduced band gap value leading to charge separation and a comprehensible change in optical absorption to the lower wavelength region. This paper brings a strong understanding of the effect of S 3p energy level in BiVO4 in the computational and experimental analysis of S-doped BiVO4 and {010} and {110} crystal facets on BiVO4.

Gd3+ doped BiVO4 and visible light-emitting diodes (LED) for photocatalytic decomposition of bisphenol A, bisphenol S and bisphenol AF in water

The photocatalytic efficiency of BiVO4 was enhanced through rare-earth doping (Gd3+). The effect of different concentrations of Gd3+ was evaluated through the decomposition of bisphenol A in water. To better understand the photocatalytic properties of the synthesized photocatalysts, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) method were applied. It was found that 4% of Gd3+ in molar mass showed the best photocatalytic efficiency. Decomposition of bisphenol A, bisphenol S, and bisphenol AF was studied using the photocatalyst with the optimal concentration of Gd3+, reaching decomposition percentages up to 77.02% ± 2.16, 44.36% ± 2.74%, and 74.11% ± 5.09, respectively after three hours reaction. Reactive species were identified by scavenging tests and additionally, kinetic studies were performed. A decomposition pathway was proposed for the three studied pollutants. The synthesized Gd3+ doped BiVO4 photocatalysts demonstrated to be a promising alternative for the efficient degradation of disrupting endocrine compounds such as bisphenol A analogs present in water using LED visible light as an eco-friendly irradiation source.

A versatile synthesis strategy and band insights of monoclinic clinobisvanite BiVO4 thin films for enhanced photoelectrochemical water splitting activity

Monoclinic clinobisvanite BiVO4 is one of the promising and extensively researched material for photoelectrochemical (PEC) water splitting. However, no substantial progress has been made to tune the morphology and to explore a wide range of dopants to BiVO4 and heterojunction systems that could affect its PEC activity. Given this, here we propose a versatile BiVO4 thin film synthesis strategy that allows morphology tunability, the feasibility of doping, and heterojunction formation in a single step. The presence of the monoclinic phase was confirmed, and detailed PEC and spectroscopic properties were evaluated to explore water splitting activity and band edge insights. The strategy was extended to fabricate different nanostructures by changing the capping agents and demonstrated the feasibility of Al doping and heterojunction formation with WO3 nanostructure for enhanced PEC activity. Importantly, the proposed strategy could be exploited using new capping agents and dopants for simultaneously obtaining doped BiVO4 in heterojunction systems having unique morphology.

Removal of pharmaceutically active compounds (PhACs) and bacteria inactivation from urban wastewater effluents by UVA-LED photocatalysis with Gd3+ doped BiVO4

In this study, gadolinium doped bismuth vanadate powders were synthesized, characterized, and tested as a potential photocatalyst for the removal of pharmaceutically active compounds (PhACs) and bacterial inactivation in a real wastewater effluent using UVA as irradiation source. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed that the bismuth vanadate system was successfully doped with 4% of gadolinium in molar mass leading to the formation of a heterostructured photocatalyst.Up to 98.3 % of diclofenac was removed from pure water after 120 min through photocatalysis. However, the photocatalytic performance of the photocatalyst on wastewater effluent was rather variable due to the complexity of the matrix where 22 different PhACs were detected by means of Ultra Performance Liquid Chromatography-Triple Quadrupole Mass Spectrometry (UPLC-QqQ-MS/MS). High photocatalytic removal efficiency (80–100%) was observed for some of the studied PhACs (e.g. naproxen and furosemide) whereas moderate efficiency (40–70%) was observed for others (e.g. acetaminophen and azithromycin) after 180 min (UVA dose = 139.5 Wh m−2, t30W = 279 min-1). Some of the studied PhACs like clarithromycin and Ibuprofen showed poor removal efficiency (< 30 %). In disinfection tests, Total coliforms, Escherichia coli, Enterococci, and Klebsiella pneumoniae showed inactivation after direct UVA LED photolysis. Nevertheless, higher inactivation was achieved for Enterococci in the presence of the synthesized photocatalyst showing an increase of 41.1 % in kmax.

Manipulating Luminescence and Photocatalytic Activities of BiVO4 by Eu3+ Ions Incorporation

BiVO4 was selected as a model to manipulate the luminescence and photocatalysis by Eu3+ ions incorporation. Eu3+-uniformly doped and surface-localized BiVO4 was prepared by a coprecipitation route ...

Effect of Mo doping and NiFe-LDH cocatalyst on PEC water oxidation efficiency

The NiFe-layered double hydroxide (LDH) nanosheets were decorated on the surface of doped BiVO4 to structure an integrating photoanode for improving solar photoelectrochemical (PEC) water splitting efficiency, which is a dynamic research topic to solve the energy crisis and remit environmental pollution caused by fossil fuel combustion. The fabricated photoanode exhibits rapid response to visible light, enhances photocurrent density and shows significant cathodic shift compared to BiVO4. Moreover, the measured incident photon-to-current efficiency (IPCE) of the photoanode is comparable to that reported in the literature. The amount of evolution oxygen was measured and the faradaic efficiency produced oxygen was also obtained by comparing the theoretical calculation value. The enhancement is attributed to the increase of the carrier density, the effective separation of photogenerated electron-hole and consuming of the photogenerated holes accumulated at the electrode surface, which has been confirmed by electrochemical impedance spectra (EIS) and the intensity modulated photocurrent spectra (IMPS). The work may offer a promising method for designing a high efficiency and low-cost photoanode.

Single-Source Bismuth (Transition Metal) Polyoxovanadate Precursors for the Scalable Synthesis of Doped BiVO4 Photoanodes.

Single-source precursors are used to produce nanostructured BiVO4 photoanodes for water oxidation in a straightforward and scalable drop-casting synthetic process. Polyoxometallate precursors, which contain both Bi and V, are produced in a one-step reaction from commercially available starting materials. Simple annealing of the molecular precursor produces nanocrystalline BiVO4 films. The precursor can be designed to incorporate a third metal (Co, Ni, Cu, or Zn), enabling the direct formation of doped BiVO4 films. In particular, the Co- and Zn-doped photoanodes show promise for photoelectrochemical water oxidation, with photocurrent densities >1 mA cm-2 at 1.23 V vs reversible hydrogen electrode (RHE). Using this simple synthetic process, a 300 cm2 Co-BiVO4 photoanode is produced, which generates a photocurrent of up to 67 mA at 1.23 V vs RHE and demonstrates the scalability of this approach.

Dip-coating synthesis of P-doped BiVO4 photoanodes with enhanced photoelectrochemical performance

Abstract The application of bismuth vanadate for photoelectrochemical water splitting is limited by the insufficient charge separation and transport characteristics. In this work, phosphorus doped BiVO4 (P-BiVO4) photoanodes were fabricated through dip-coating method and subsequent thermal treatment process. The optimized 2% P-BiVO4 exhibited a photocurrent density up to 0.28 mA/cm2 at 1.23 V versus reversible hydrogen electrode in 0.5 M Na2SO4 electrolyte (AM 1.5 G, 100 mW/cm2). The incident photon-to-current efficiency of 2% P-BiVO4 was boosted to 33%, which was significantly higher than the pristine BiVO4 photoanode. The X-ray photoelectron spectra indicate that the P-BiVO4 possessed abundant oxygen vacancies, which can account for enhancing PEC performance of P-BiVO4. The electrochemical impedance spectroscopy and Mott–Schottky results further show that P-BiVO4 possess less interface obstruction and high carrier concentration, which were beneficial for the improvement of photoelectrochemical performance. This work provides a useful guidance for the design of non-metal doped BiVO4 photoanodes for energy conversion.

Mo6+ Doped BiVO4 with improved Charge Separation and Oxidation Kinetics for Photoelectrochemical Water Splitting

Monoclinic bismuth vanadate (BiVO4) has been widely applied as a promising n-type semiconductor for photoelectrochemical (PEC) water splitting because of its low cost, environmentally friendly, and relatively narrow band gap of ∼2.4eV. Here, we developed a facile fabrication of Mo doped BiVO4 photoanode on the fluorine-doped tin oxide substrate by electrodeposition method and used these samples to better understand the doping effect for charge separation and charge oxidation kinetics. Compared with the undoped BiVO4 photoanode, the optimized Mo doped BiVO4 (3AMo:BV) produced a much higher photocurrent of 1.91mA/cm2 at 1.23V vs. RHE under AM 1.5G illumination for water oxidation. The results of the photoelectric conversion kinetics for various samples revealed that the charge separation and oxidation kinetics efficiencies for 3AMo:BV sample are 74.42% and 49.25% at 1.23V vs. RHE, while the values for undoped BiVO4 are 48.04% and 32.98%, respectively. The improved PEC performance for Mo doped BiVO4 is mainly ascribed to the crystal deformation caused by larger tetrahedral ionic VO4 and higher photovoltage generated by the interface of photoanode and electrolyte.

Preparation of La3+/Zn2+-doped BiVO4 nanoparticles and its enhanced visible photocatalytic activity

BiVO4 samples doped with different amounts of La3+ or Zn2+ ions have been synthesized successfully by a hydrothermal method, and their composition, microstructure and photocatalytic activity were characterized by means of modern analytical techniques. The results illustrated that these doped BiVO4 samples presented a better photocatalytic performance than the undoped BiVO4 sample, among which Bi0.92La0.08VO4 and Bi0.92Zn0.08VO4 exhibited the highest degradation efficiency. Under visible light illumination, their photocatalytic degradation on RhB was up to 95.4 and 98.56% in 60 min, respectively. In particular, the Bi0.92La0.08VO4 and Bi0.92Zn0.08VO4 had a good stability and still retained the photocatalytic activity of 93.7 and 94% after five cycling test. These results confirmed that the La3+/Zn2+ -doped BiVO4 samples were a kind of efficient and stable visible-light-driven photocatalysts and had a promising application for the degradation of organic contaminant.

Structural analysis and enhanced photoluminescence via host sensitization from a lanthanide doped BiVO4 nano-phosphor

This paper reports the enhanced red photoluminescence from a Eu3+ doped BiVO4 nano-phosphor synthesized through solution combustion method. The XRD and TEM measurements reveal nano-crystalline nature of the sample. The SEM and TEM micrographs show an increase in the particles size on annealing. The EDS measurement confirms the presence of Eu, Bi, V and O elements in the sample. The sample emits red photoluminescence at 615 nm due to 5D0 → 7F2 transition of Eu3+ upon 266 and 355 nm excitations. The emission intensity increases with the increase in the concentration of Eu3+ ion and it is maximum at 1.0 mol%. When the as-synthesized sample is annealed at higher temperature; the emission intensity of the sample enhances upto eight times. The enhancement in the emission intensity is due to an increase in crystallinity and significant reduction in the multi-phonon relaxation of the ions in the excited state, which has been verified by lifetime measurements. The emission intensity is larger for 266 nm excitation (upto two times), which is due to energy transfer from the host (1P1 and 3P1 levels of Bi3+ and CTS of VO43+ ions) to Eu3+ ion. Therefore, the Eu3+ doped BiVO4 nano-phosphor may be a suitable candidate for displays devices.

Enhanced Photoelectrochemical Behavior of Undoped and Doped BiVO4 inverse Opal Photoelectrode for Photoelectrochemical Water Splitting

Semiconductor metal oxides are one of the most interesting materials for photoelectrochemical (PEC) applications because of inexpensive, robust and strong photocorrosion as well as the possibility of easily morphological control. Among the most investigated metal oxides, BiVO4 metal oxides have attracted considerable interest due to their unique optical and electrical properties with a band gap of 2.4 eV. In this work, the introduction of new photoelectrode architectures to improve the light-harvesting and charge-collection properties was performed using the polystyrene opal template with a size of approximately 380 nm. Upon this template, undoped BiVO4 inverse opal (IO) film was developed via sandwich like infiltration method. Furthermore, to enhance the electric conductivity of undoped BiVO4 material regarded as one of weak points to retard the high efficient PEC performance, the doping process of undoped BiVO4IOs was done to facilitate the various candidates such as- Nb, Ag, Ce and so on.., Related results and discussion would be presented. Keywords: BiVO4, polystyrene opal template, Photoelectrochemical water splitting, Doped BiVO4