Influence of lanthanum-doping on photocatalytic properties of BiFeO 3 for phenol degradation

Construction of La1-xSrxNiO3/g-C3N4 type-Z heterojunctions with enhanced visible-light photocatalytic degradation of organic pollutants

Lanthanum nickelate (LaNiO3), known for its high visible-light absorption, is a promising photocatalyst for water purification. However, the low conduction band position and high photogenerated carrier complexation rate of pure LaNiO3 limit its photocatalytic activity. To address this issue, we investigated the synergistic effects of doping and constructing heterojunctions. A La0.9Sr0.1NiO3 (20%)/g-C3N4 (L2CN8) heterojunction was successfully created. In addition, various characterisation techniques were then employed to analyse the structure-performance relationships of these heterojunction photocatalysts in degrading organic dyes. Results revealed that at a 10% Sr doping level, the oxygen vacancy content was 0.68, which is significantly higher than that of LaNiO3 (0.05). The increased number of oxygen vacancies enhanced the electron capture ability and improved the separation efficiency of photogenerated carriers. Furthermore, the optimised L2CN8 (20 mg) achieved 81.2% and 73.8% removal of methylene blue (50.0 mL, 10 mg L-1) and tetracycline (50.0 mL, 10 mg L-1) under simulated visible-light irradiation (λ > 420 nm). Furthermore, an active species capture experiment confirmed the significant role of superoxide radicals (·O2-) in the degradation process. Based on these experimental findings, we proposed a rational Z-type charge transfer mechanism. This study holds great importance for water pollution control and environmental protection.

Efficient Visible-Light-Driven Tetracycline Degradation and Cr(VI) Reduction over a LaNi1-xFexO3 (0 ≤ x ≤ 1)/g-C3N4 Type-II Heterojunction Photocatalyst

The development of efficient, stable, and visible-light-responsive photocatalysts is crucial to address the pollution of water bodies by toxic heavy metal ions and organic antibiotics. Herein, a series of LaNi_1-xFe_xO₃/g-C₃N₄ heterojunction photocatalysts are prepared by a simple wet chemical method. Moreover, LaNi_0.8Fe_0.2O₃/g-C₃N₄ composites are characterized by various methods, including structure, morphology, optical, and electrochemical methods and tetracycline degradation and photocatalytic reduction of Cr(VI) under visible light irradiation. Then, the photocatalytic performance of as-prepared LaNi_0.8Fe_0.2O₃/g-C₃N₄ composites is evaluated. Compared with pure LaNi_0.8Fe_0.2O₃ and g-C₃N₄, the LaNi_0.8Fe_0.2O₃/g-C₃N₄ composite photocatalysts exhibit excellent photocatalytic performance due to synergy of doping and constructing heterojunctions. The results show that the doping of Fe ions can increase the concentration of oxygen vacancies, which is ultimately beneficial to the formation of electron traps. Moreover, the type-II heterojunction formed between LaNi_0.8Fe_0.2O₃ and g-C₃N₄ effectively strengthens the separation and transfer of photoinduced carriers, thereby promoting photocatalytic activity. Furthermore, the photocatalytic activity of the LaNi_0.8Fe_0.2O₃/g-C₃N₄ photocatalyst remains almost unchanged after three cycles, indicating long-term stability. Ultimately, the photocatalytic mechanism of the LaNi_0.8Fe_0.2O₃/g-C₃N₄ composites is proposed.

Research progresses on the application of perovskite in adsorption and photocatalytic removal of water pollutants

The problem of global water pollution and scarcity of water resources is becoming increasingly serious. Multifunctional perovskites can well drive adsorption and photocatalytic reactions to remove water pollutants. There are many advantages of perovskites, such as abundant oxygen vacancies, easily tunable structural morphology, stable crystal state, highly active metal sites, and a wide photo response range. However, there are few reviews on the simultaneous application of perovskite to adsorption and photocatalytic removal of water pollutants. Thus, this paper discusses the preparation methods of perovskite, the factors affecting the adsorption of water environmental pollutants by perovskite, and the factors affecting perovskite photocatalytic water pollutants. The particle size, specific surface area, oxygen vacancies, electron-hole trapping agents, potentials of the valence band, and conduction band in perovskites are significant influencing factors for adsorption and photocatalysis. Strategies for improving the performance of perovskites in the fields of adsorption and photocatalysis are discussed. The adsorption behaviors and catalytic mechanisms are also investigated, including adsorption kinetics and thermodynamics, electrostatic interaction, ion exchange, chemical bonding, and photocatalytic mechanism. It summarizes the removal of water pollutants by using perovskites. It provides the design of perovskites as high-efficiency adsorbents and catalysts for developing new technologies.

Development of Z-scheme bimetallic tungstate-supported nitrogen deficient g-C3N4 heterojunction for the treatment of refractory pharmaceutical pollutants

The binary BMT/ND-GCN-based heterostructure photocatalyst for pharmaceutical industry wastewater treatment.

Enhanced visible light photo-Fenton catalysis by lanthanum-doping BiFeO3 for norfloxacin degradation

Efficient photo-Fenton removal of antibiotic effluent is a widely followed and significant attempt to deal with the growing environmental pollution. In this study, BiFeO₃ and lanthanum doped BiFeO₃ catalysts were synthesized via one-step hydrothermal method as hydrogen peroxide activator for mineralization of norfloxacin (NOR). Various characterization measurements were used to verify La was successfully doped into the lattice of perovskite and investigated the effect of La doping molar ratio on BiFeO₃ through the characterization of the morphology and physicochemical properties. The degradation experiment and reaction rate constants showed that the La-doped BiFeO₃ particle exhibited superior photo-Fenton catalytic performance to undoped BiFeO₃. Especially, the degradation efficiency of 15% La-doped BiFeO₃ could reach up to 84.94%. And the first order kinetic constant of optimized conditions was 0.01638 min^-1, which was about 6.9 times than that of undoped BiFeO₃.The influence of pH, oxidizer content and catalyst dosage in photo-Fenton reaction were investigated detailedly. Besides, the synthetic catalyst possessed favorable stability and reusability with little metal leaching after many cycles of use. Radical scavenger experiments and electron spin resonance tests were carried out to conclude that the ·OH and holes were regarded as the dominate active species in the catalytic process. The narrow band gap and excellent electron transfer efficiency were the key factors for La-doped BiFeO₃ to have high catalytic efficiency in the photo-Fenton system. Current works demonstrated the great promise of La-doped BiFeO₃ in the elimination of antibiotic organics.

Application of perovskite oxides and their composites for degrading organic pollutants from wastewater using advanced oxidation processes: Review of the recent progress

In the recent years, perovskite oxides are gaining an increasing amount of attention owing to their unique traits such as tunable electronic structures, flexible composition, and eco-friendly properties. In contrast, their catalytic performance is not satisfactory, which hinders real wastewater remediation. To overcome this shortcoming, various strategies are developed to design new perovskite oxide-based materials to enhance their catalytic activities in advanced oxidation process (AOPs). This review article is to provide overview of basic principle and different methods of AOPs, while the strategies to design novel perovskite oxide-based composites for enhancing the catalytic activities in AOPs have been highlighted. Moreover, the recent progress of their synthesis and applications in wastewater remediation (pertaining to the period 2016-2022) was described, and the related mechanisms were thoroughly discussed. This review article helps scientists to have a clear outlook on the selection and design of new effective perovskite oxide-based materials for the application of AOPs. At the end of the review, perspective on the challenges and future research directions are discussed.

Novel pure α-, β-, and mixed-phase α/β-Bi2O3 photocatalysts for enhanced organic dye degradation under both visible light and solar irradiation

Combining the pure α- and β-phases of bismuth oxide enhances its photocatalytic activity under both visible and solar irradiation. α-Bi₂O₃, β-Bi₂O_3, and α/β-Bi₂O₃ were synthesized by a solvothermal calcination method. The structural, optical, and morphological properties of the as-synthesized catalysts were analyzed using XRD, UV-DRS, XPS, SEM, TEM, and PL. The bandgaps of α/β-Bi₂O₃, α-Bi₂O₃, and β-Bi₂O₃ were calculated to be 2.59, 2.73, and 2.34 eV, respectively. The photocatalytic activities of the catalysts under visible and solar irradiation were examined by the degradation of carcinogenic reactive blue 198 and reactive black 5 dyes. The kinetic plots of the degradation reactions followed pseudo-first-order kinetics. α/β-Bi₂O₃ exhibited higher photocatalytic activity (∼99%) than α-Bi₂O₃ and β-Bi₂O₃ under visible and solar irradiation. The TOC and COD results confirmed the maximum degradation ability of α/β-Bi₂O₃, and the decolorization percentage remained above 90%, even after five cycles under visible irradiation. The photocatalytic dye degradation mechanism employed by α/β-Bi₂O₃ was proposed based on active species trapping experiments.

Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Photoelectrochemical Degradation of Organic Pollutants on a La3+ Doped BiFeO3 Perovskite

Towards nonconventional wastewater treatment methods for the degradation of organic pollutants in wastewater, a perovskite-based photoelectrochemical system was developed. Bismuth ferrite doped with lanthanum (La-BiFeO3, La-BFO) perovskite was synthesised through a hydrothermal method with low calcination temperature for the photoelectrochemical degradation of orange II dye and other cocktails of dyes. Photoanodes were prepared by the deposition of the perovskites on a fluorine-doped tin oxide (FTO) substrate. The photoanodes were characterised using XRD, FESEM, FTIR and UV-vis diffuse reflectance. The photoelectrochemical properties of the synthesised photoanodes were investigated with chronoamperometry and electrochemical impedance spectroscopy (including Mott–Schottky analysis). The results show that all La3+-doped BFO photoanodes exhibited a higher absorption edge in the visible light region than the undoped BFO. The photocurrent response of 10% La-BFO (the best performing electrode) exhibited a three times higher current response than the pure BFO. In addition, the electrode exhibited a good degradation efficiency of 84.2% within 120 min with applied bias potential of 2 V at a pH of 7. EIS studies showed a significant enhancement of the interfacial electron transfer of the charge carriers. The enhancements in electrode performances were attributed to the synergistic effect of the applied bias potential and the introduction of La3+ into the BFO matrix. This study therefore shows that the photoelectrocatalytic performance of BFO for water treatment can be improved by the introduction of perovskites-doping ions such as La3+.

Lanthanum-Zinc Binary Oxide Nanocomposite with Promising Heterogeneous Catalysis Performance for the Active Conversion of 4-Nitrophenol into 4-Aminophenol

This work intended to enhance the unique and outstanding properties of lanthanum by synthesizing its nanocomposite. A lanthanum-based nanocomposite was prepared by a simple and cost-effective “co-precipitation” method. Lanthanum nitrate (La (NO3)3) and zinc nitrate (Zn (NO3)2) were used as precursors. The lanthanum/zinc oxide nano composite formed was then calcined at 450 °C for 4 h in order to obtain a fine powder with size in the nano range of 1–100 nm. Characterization of the prepared catalyst was done by ultraviolet/visible spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence. Crystallinity and morphology were found by X-ray diffraction and scanning electron microscopy. The synthesized nanocomposite material was also tested for heterogeneous catalytic applications of 4-nitrophenol (4-NP) reduction into 4-aminophenol (4-AP). It was found to be successful in complete reduction of 4-NP with enhanced catalytic performance.

Perovskite Oxide-Based Materials for Photocatalytic and Photoelectrocatalytic Treatment of Water

Meeting the global challenge of water availability necessitates diversification from traditional water treatment methods to other complementary methods, such as photocatalysis and photoelectrocatalysis (PEC), for a more robust solution. Materials play very important roles in the development of these newer methods. Thus, the quest and applications of a myriad of materials are ongoing areas of water research. Perovskite and perovskite-related materials, which have been largely explored in the energy sectors, are potential materials in water treatment technologies. In this review, attention is paid to the recent progress in the application of perovskite materials in photocatalytic and photoelectrocatalytic degradation of organic pollutants in water. Water treatment applications of lanthanum, ferrite, titanate, and tantalum (and others)-based perovskites are discussed. The chemical nature and different synthetic routes of perovskites or perovskite composites are presented as fundamental to applications.

One-Pot Hydrothermal Synthesis of La-Doped ZnIn2S4 Microspheres with Improved Visible-Light Photocatalytic Performance

Impurity element doping is extensively taken as one of the most efficient strategies to regulate the electronic structure as well as the rate of photogenerated charge separation of photocatalysts. Herein, a one-pot hydrothermal synthesis process was exploited to obtain La-doped ZnIn₂S₄ microspheres, aiming at gaining insight into the role that doping ions played in the improvement of pollutant photodegradation. Systematical characterization means, comprising of X–ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–vis) diffuse reflection spectroscopy and Raman spectra, combination with high-resolution transmission electron microscopy (HRTEM), were employed to in depth reveal the concomitancy of La ions and ZnIn₂S₄ crystal lattice. The results showed that the La-doped ZnIn₂S₄ samples exhibited a slightly wider and stronger spectral absorption than pristine ZnIn₂S₄; and the specific surface area of doped ZnIn₂S₄ samples was a bit larger. The La-doped ZnIn₂S₄ electrodes showed improved photocurrent response, and the photocurrent density reached a maximum value at La content of 1.5 wt%. As expected, La-doped ZnIn₂S₄ samples exhibited a remarkable enhancement of photocatalytic behaviour toward the photodegradation of tetracycline hydrochloride (TCH) and methyl orange (MO). The prominently enhanced photoactivity of doped ZnIn₂S₄ samples was due to the synergistic effect of the elevated visible-light absorption ability and effective photogenerated charge carriers’ separation.

Ti3C2-MXene/Bismuth Ferrite Nanohybrids for Efficient Degradation of Organic Dyes and Colorless Pollutants

The current environmental and potable water crisis requires technological advancement to tackle the issues caused by different organic pollutants. Herein, we report the degradation of organic pollutants such as Congo Red and acetophenone from aqueous media using visible light irradiation. To harvest the solar energy for photocatalysis, we fabricated a nanohybrid system composed of bismuth ferrite nanoparticles with two-dimensional (2D) MXene sheets, namely, the BiFeO3 (BFO)/Ti3C2 (MXene) nanohybrid, for enhanced photocatalytic activity. The hybrid BFO/MXene is fabricated using a simple and low-cost double-solvent solvothermal method. The SEM and TEM images showed that the BFO nanoparticles are attached onto the surface of 2D MXene sheets. The photocatalytic degradation achieved by the hybrid is found to be 100% in 42 min for the organic dye (Congo Red) and 100% for the colorless aqueous pollutant (acetophenone) in 150 min. The BFO/MXene hybrid system exhibited a large surface area of 147 m2 g-1 measured via the Brunauer-Emmett-Teller sorption-desorption technique, which is found to be the largest among all BFO nanoparticles and derivatives. The photoluminescence spectra indicate a low electron-hole recombination rate. Fast and efficient degradation of organic molecules is caused by two factors: larger surface area and lower electron-hole recombination rate, which makes the BFO/MXene nanohybrid a highly efficient photocatalyst and a promising candidate for many future applications.

Effect of Graphene Oxide Nano-Sheets on Structural, Morphological and Photocatalytic Activity of BiFeO3-Based Nanostructures

Photocatalysts are widely used for the elimination of organic contaminants from waste-water and H2 evaluation by water-splitting. Herein, the nanohybrids of lanthanum (La) and selenium (Se) co-doped bismuth ferrites with graphene oxide were synthesized. A structural analysis from X-ray diffraction confirmed the transition of phases from rhombohedral to the distorted orthorhombic. Scanning electron microscopy (SEM) revealed that the graphene nano-sheets homogenously covered La-Se co-doped bismuth ferrites nanoparticles, particularly the (Bi0.92La0.08Fe0.50Se0.50O3-graphene oxide) LBFSe50-G sample. Moreover, the band-gap nanohybrids of La-Se co-doped bismuth ferrites were estimated from diffuse reflectance spectra (DRS), which showed a variation from 1.84 to 2.09 eV, because the lowering of the band-gap can enhance photocatalytic degradation efficiency. Additionally, the photo-degradation efficiencies increased after the incorporation of graphene nano-sheets onto the La-Se co-doped bismuth ferrite. The maximum degradation efficiency of the LBFSe50-G sample was up to 80%, which may have been due to reduced band-gap and availability of enhanced surface area for incoming photons at the surface of the photocatalyst. Furthermore, photoluminescence spectra confirmed that the graphene oxide provided more electron-capturing sites, which decreased the recombination time of the photo-generated charge carriers. Thus, we can propose that the use of nanohybrids of La-Se co-doped bismuth ferrite with graphene oxide nano-sheets is a promising approach for both water-treatment and water-splitting, with better efficiencies of BiFeO3.

Visible-light-driven photocatalytic disinfection mechanism of Pb-BiFeO3/rGO photocatalyst

While the visible-light-driven photocatalytic disinfection techniques for drinking water have recently attracted tremendous attentions, it is necessary to further improve the solar energy utilization efficiency. In this study, we synthesized Pb-BiFeO₃ photocatalysts doped with different amounts of reduced graphene oxide (Pb-BiFeO₃/rGO). The photocatalytic disinfection efficiencies toward gram-negative Escherichia coli (E. coli) and gram-positive Staphylococcus aureus (S. aureus) were evaluated under visible-light irradiation (λ ≥ 400 nm). The results indicated that Pb-BiFeO₃ with 0.5 wt% rGO (Pb-BiFeO₃/0.5% rGO) exhibited the highest disinfection efficiency. Complete inactivation was reached within 30 min and 90 min for E. coli and S. aureus, respectively. The transcriptomic analysis results indicated that Pb-BiFeO₃/0.5% rGO deregulates the genes in E. coli cells that are involved in the cell membrane damage and oxidative stress responses. This was validated by the cell leakage of nucleic acids or proteins, transmission electron microscopy images of the bacteria, and the disinfection efficiency decrease caused by the introduction of scavenger of hydroxyl radical (HO•). Metal ions (Pb²⁺, Bi²⁺, and Fe³⁺) released from the photocatalysts did not contribute to the disinfection process. For the first time, our results elucidated that the photocatalytic disinfection mechanism of Pb-BiFeO₃/rGO toward E. coli was mainly associated with oxidative stress due to HO• generation and the loss of membrane integrity from direct contact with the photocatalyst. After four consecutive cycles, the Pb-BiFeO₃/0.5% rGO photocatalyst exhibited a strong antibacterial efficiency. The excellent disinfection efficiency and stability of Pb-BiFeO₃/0.5% rGO suggests that this photocatalyst shows great potential for drinking water disinfection.

La- and Mn-Codoped Bismuth Ferrite/Ti3C2 MXene Composites for Efficient Photocatalytic Degradation of Congo Red Dye

Over the years, scarcity of fresh potable water has increased the demand for clean water. Meanwhile, with the advent of nanotechnology, the use of nanomaterials for photocatalytic degradation of pollutants in wastewaters has increased. Herein, a new type of nanohybrids of La- and Mn-codoped bismuth ferrite (BFO) nanoparticles embedded into transition-metal carbide sheets (MXene-Ti₃C₂) were prepared by a low-cost double-solvent sol-gel method and investigated for their catalytic activity in dark and photoinduced conditions. The photoluminescence results showed that pure BFO has the highest electron hole recombination rate as compared to all the codoped BFO/Ti₃C₂ nanohybrids. The higher electron-hole pair generation rate of the nanohybrids provides a suitable environment for fast degradation of organic dye molecules. The band gap of the prepared nanohybrid was tuned to 1.73 eV. Moreover, the BLFO/Ti₃C₂ and BLFMO-5/Ti₃C₂ degraded 92 and 93% of the organic pollutant, respectively, from water in dark and remaining in the light spectrum. Therefore, these synthesized nanohybrids could be a promising candidate for catalytic and photocatalytic applications in future.

Rationally designed La and Se co-doped bismuth ferrites with controlled bandgap for visible light photocatalysis

Development of efficient visible light photocatalysts for water purification and hydrogen production by water splitting has been quite challenging. The activities of visible light photocatalysts are generally controlled by the extent of absorption of incident light, band gap, exposure of catalyst surface to incident light and adsorbing species. Here, we have synthesized nanostructured, La and Se co-doped bismuth ferrite (BLFSO) nanosheets using double solvent sol–gel and co-precipitation methods. Structural analysis revealed that the La and Se co-doped BFO i.e. Bi_0.92La_0.08Fe_1−xSe_xO₃ (BLFSO) transformed from perovskite rhombohedral to orthorhombic phase. As a result of co-doping and phase transition, a significant decrease in the band gap from 2.04 eV to 1.76 eV was observed for BLFSO-50% (having Se doping of 50%) which requires less energy during transfer of electrons from the valence to the conduction band and ultimately enhances the photocatalytic activity. Moreover, upon increase in Se doping, the BLFSO morphology gradually changed from particles to nanosheets. Among various products, BLFSO-50% exhibited the highest photocatalytic activities under visible light owing to homogenous phase distribution, regular sheet type morphology and larger contact with dye containing solutions. In summary, La, Se co-doping is an effective approach to tune the electronic structure of photocatalysts for visible light photocatalysis.

Development of efficient visible light photocatalysts for water purification and hydrogen production by water splitting has been quite challenging.

Review on nanoscale Bi-based photocatalysts

Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

The high photocatalytic activity and reduced band gap energy of La and Mn co-doped BiFeO3/graphene nanoplatelet (GNP) nanohybrids

This article details a comparison of the photocatalytic activity of La, Mn co-doped BiFeO₃/GNP nanohybrids prepared by co-precipitation and hydrothermal methods.