Impact of bismuth doping on the structural, optical, and photocatalytic characteristics of hydrothermally synthesized LaPO4 nanoparticles

Abstract

Lanthanum phosphate (LaPO4) doped with varied amounts of bismuth (Bi) were hydrothermally synthesized and were used as photocatalysts, as no prior research has delved into their application in the photocatalysis domain. A comprehensive suite of characterization techniques, including X-ray diffraction, scanning electron microscopy, UV-Vis diffuse reflectance spectra, Fourier transform infra-red spectroscopy, Raman spectroscopy, and N2 adsorption-desorption isotherm analyses were employed to examine the synthesized products. Results revealed that Bi3+ effectively incorporates into the LaPO4 lattice, preserving its monoclinic structure (Monazite) with slight distortions. This substitution significantly influences the specific surface area (SSA) of the photocatalyst, demonstrating a decrease with escalating concentrations of the doped ion. Simultaneously, the band gap undergoes a reduction from 5.86 to 4.49 eV. Additionally, the Rietveld method revealed that all materials possess a crystalline phase in the monoclinic system without any impurities. The photocatalytic efficiency of the synthesized materials was assessed using methylene blue (MB) as the target compound under UV-C irradiation. Remarkably, the catalysts exhibited enhanced performance with an elevated proportion of Bi within the LaPO4 network, underscoring the positive correlation between Bi content and photocatalytic efficiency. As a result, La0.96Bi0.04PO4 had achieved 99.71 % MB degradation within 2 h under UV-C radiation. Furthermore, kinetic analysis indicated that the degradation reaction using this oxide followed pseudo-first-order kinetics.