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

Designing and synthesis of perovskite nanocrystals: a promising wide-spectrum solar light-responsive photocatalyst and lead ion sensor

Perovskites are an emerging material with a variety of applications, ranging from their solar light conversion capability to their sensing efficiency. In current study, perovskite nanocrystals (PNCs) were designed using theoretical density functional theory (DFT) analysis. Moreover, the theoretically designed PNCs were fabricated and confirmed by various characterization techniques. The calculated optical bandgap from UV-Vis and fluorescence spectra were 2.15 and 2.05 eV, respectively. The average crystallite size of PNCs calculated from Scherrer equation was 15.18 nm, and point of zero charge (PZC) was obtained at pH 8. The maximum eosin B (EB) removal efficiency by PNCs was 99.56% at optimized conditions following first-order kinetics with 0.98 R2 value. The goodness of the response surface methodology (RSM) model was confirmed from analysis of variance (ANOVA), with the experimental F value (named after Ronald Fisher) of 194.66 being greater than the critical F value F0.05, 14, 14 = 2.48 and a lack of fit value of 0.0587. The Stern-Volmer equation with a larger Ksv value of 1.303710 × 10 6 for Pb2+ suggests its greater sensitivity for Pb2+ among the different metals tested.

Photocatalytic activity in graded off-valent cations substituted NaNbO3

This study investigates the impact of off-valent doping on the photocatalytic properties of NaNbO3 concerning the degradation of Methylene Blue. Compositions with x values of 0.00 (representing pure NaNbO3, denoted as NBO) and 0.05 within the material system Na1-xAxNbO3 (where A is K1+, Ba2+, La3+, abbreviated as K-NBO, Ba-NBO, and La-NBO respectively) were synthesized using the conventional solid-state reaction method. The UV-visible analysis revealed a decrease in the band gap for samples K-NBO and Ba-NBO, while an increase was observed for sample La-NBO. Raman modes of lower wave numbers merged and shifted towards the higher wave number side. The determination of valence band edge and conduction band edge involved computational analysis based on XPS survey scans, and the band gap energy values were derived from UV-Visible spectroscopy results. Examining the band diagram of the samples (NBO, K-NBO, Ba-NBO, and La-NBO) in conjunction with the highest occupied molecular orbital and lowest unoccupied molecular orbital levels of MB dye provided insights into potential degradation mechanisms. Photocatalytic dye degradation experiments for Methylene Blue demonstrated that doping increased the degradation efficiency of samples K-NBO, Ba-NBO, and La-NBO compared to NBO. Among all NaNbO3 based prepared samples, Ba-NBO exhibited the highest degradation efficiency of 96%, however slightly less than the reference sample P25 TiO2.

Dopant-driven recombination delay and ROS enhancement in nanoporous Cd1-xCuxS heterogeneous photocatalyst for the degradation of DR-23 dye under visible light irradiation

Developing an efficient heterogeneous photocatalyst for environmental remediation and treatment strategies using visible light harvesting processes is promising but challenging. Herein, Cd1-xCuxS materials have been synthesized and characterized by precise analytical tools. Cd1-xCuxS materials exhibited excellent photocatalytic activity for direct Red 23 (DR-23) dye degradation in visible light irradiation. The operational parameters, like dopant concentration, photocatalyst dose, pH, and initial concentration of dye were investigated during the process. The photocatalytic degradation process follows pseudo-first-order kinetics. As compared to other tested materials, 5% Cu doped CdS material revealed superior photocatalytic performance for the degradation of DR-23 (k = 13.96 × 10-3 min-1). Transient absorption spectroscopy, EIS, PL, and transient photocurrent indicated that adding copper to the CdS matrix improved the separation of photo-generated charge carriers by lowering the recombination rate. Spin-trapping experiments recognized the photodegradation primarily based on secondary redox products, i.e., hydroxyl and superoxide radicals. According to by Mott-Schottky curves, photocatalytic mechanism and photo-generated charge carrier density were elucidated regarding dopant-induced valence and conduction bands shifting. Thermodynamic probability of radical formation in line with the altered redox potentials by Cu doping has been discussed in the mechanism. The identification of intermediates by mass spectrometry study also showed a plausible breakdown mechanism for DR-23. Moreover, samples treated with nanophotocatalyst displayed excellent results when tested for water quality metrics such as DO, TDS, BOD, and COD. Developed nanophotocatalyst shows high recyclability with superior heterogeneous nature. 5% Cu-doped CdS also exhibit strong photocatalytic activity for the degradation of colourless pollutant bisphenol A (BPA) under visible light (k = 8.45 × 10-3 min-1). The results of this study offer exciting opportunities to alter semiconductors' electronic band structures for visible-light-induced photocatalytic activity for wastewater treatment.

Photoelectrocatalytic Degradation of Methylene Blue on Electrodeposited Bismuth Ferrite Perovskite Films

Electrodeposited bismuth ferrite (BiFeO₃) thin films on fluorine-doped tin oxide (FTO) substrate were employed as photoanodes in the photoelectrocatalytic degradation of methylene blue. The BiFeO₃ thin films electrodeposited for 300 s, 600 s, 1200 s, 1800 s and 3600 s were characterised with XRD, field emission scanning electron microscopy (FESEM) and UV-vis diffuse reflectance spectroscopy. SEM images displayed different morphology at different electrodeposition times which affects the photoelectrocatalytic (PEC) performances. The FESEM cross-sectional area was used to measure the thickness of the film. The optical properties showed that the band gaps of the photoanodes were increasing as the electrodeposition time increased. The photocurrent response obtained showed that all thin film photoanodes responded to visible light and lower charge transfer resistance (from electrochemical impedance spectroscopy studies) was observed with photoanodes electrodeposited at a shorter time compared to those at a longer time. The PEC application of the photoanode for the removal of methylene blue (MB) dye in water showed that the percentage degradation decreased with an increase in electrodeposition time with removal rates of 97.6% and 70% observed in 300 s and 3600 s electrodeposition time, respectively. The extent of mineralisation was measured by total organic carbon and reusability studies were carried out. Control experiments such as adsorption, photolysis, photocatalysis and electrocatalysis processes were also investigated in comparison with PEC. The electrodeposition approach with citric acid exhibited improved electrode stability while mitigating the problem of catalyst leaching or peeling off during the PEC process.

Norfloxacin mineralization under light exposure using Sb-SnO2 ceramic anodes coated with BiFeO3 photocatalyst

Advanced Oxidation Processes have been proven to be an efficient way to remove organic pollutants from wastewaters. In this work, a ceramic electrode of Sb-SnO₂ (BCE) with a layer of the photocatalytic material BiFeO₃ (BFO-BCE), has been characterized electrochemically and further tested for norfloxacin photo-electrooxidation in the presence and absence of light. The electrode photoactivity was highly enhanced thanks to the presence of BiFeO₃, as confirmed by Linear Sweep Voltammetry, chronoamperometry and potentiometry, and Electrochemical Impedance Spectroscopy. Additionally, working in galvanostatic mode, a high mineralization of norfloxacin was achieved after 240 min, reaching 62% at 25 mA cm^-2 under light conditions. This value is comparatively higher than the 40% achieved with the BCE. The oxidation byproducts were followed by ionic chromatography and HPLC analysis, which also allowed us to propose an oxidation pathway of the norfloxacin molecule. Finally, some indicators of the reactor performance such as the Mineralization Current Efficiency and the specific energy consumption were analyzed, revealing that lower current densities (8.3 mA cm^-2) led to higher current efficiencies, and that light improved both the current efficiency and energy consumption.

Experimental and Theoretical Investigations of Low-Dimensional BiFeO3 System for Photocatalytic Applications

We report on the fabrication of sub-20 nm BiFeO3 (BFO) nanoparticles using a solid-state approach and preferential leching process. The nanoparticles were subsequently used to deposit, through spray pyrolysis, BFO thin films in a rhombohedral (R3c) crystallographic structure. Then, systematic investigations of the optical and the photocatalytic properties were conducted to determine the effects of the particles size, the microstructure and the increased surface area on their catalytic performances. Especially, improved optical properties were observed, with an optical bandgap energy of 2.20 eV compared to reported 2.7 eV for the bulk system. In addition, high optical absorption was obtained in the UV–visible light region reaching up to 90% at 400 nm. The photoelectrochemical measurements revealed a high photocurrent density under visible light irradiation. Besides, density functional theory calculations were performed on both bulk and thin film BFO structures, revealing an interesting comparison of the electronic, magnetic, ferroelectric and optical properties for bulk and thin film BFO systems. Both theoretical and experimental findings show that the alignment of the band edges of BFO thin film is coherent with good photocatalytic water splitting potential, making them desirable photoanode materials.