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

Abstract

Lanthanum phosphate (LaPO 4 ) 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 N 2 adsorption-desorption isotherm analyses were employed to examine the synthesized products. Results revealed that Bi 3+ effectively incorporates into the LaPO 4 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 LaPO 4 network, underscoring the positive correlation between Bi content and photocatalytic efficiency. As a result, La 0.96 Bi 0.04 PO 4 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.