Experimental and computational studies of metals doped α/β-PbO nanoparticles and lead oxide thin films for photocatalytic application

Abstract

Photocatalysts are promising materials to suppress the environmental pollution and energy crisis encountered in the world. In this research, undoped and different metals (Sn, Co, Cu, Ni, and Li) doped α-PbO and β-PbO phases nanoparticles were successfully synthesized by a facile chemical precipitations method and utilized for the degradation of Methylene blue dye under visible light irradiation. The synthesized nanoparticles were further studied by using different characterization techniques. The XRD results confirmed that the prepared nanoparticles were pure α-PbO and β-PbO phases that are free of the mixture of the two and other PbO phases. The obtained optical band gaps from UV-Vis DRS analysis were 2.03 eV, 2.68 eV, 1.61 eV, 1.78 eV, 1.67 eV, and 2.00 eV for pristine α-PbO, Sn, Co, Cu, Ni, and Li doped α-PbO respectively. For pristine β-PbO, Co, Cu, Ni, Li, and Sn doped β-PbO, the obtained band gap was 2.68 eV, 1.88 eV, 2.01 eV, 2.65 eV, 2.64 eV, and 2.70 eV respectively. The results from the PL emission reveals that, the lowest PL intensity of the doped samples indicated the low recombination of the electron-hole pairs that improved the photocatalytic performance of pristine α-PbO and β-PbO nanoparticles. The SEM and EDX were used to analyze the surface morphology and composition of the synthesized nanoparticles, respectively. The photocatalytic activities of the prepared nanoparticles were assessed through the degradation of the Methylene Blue (MB) dye under visible light irradiation. The UV-Visible spectrophotometer analysis showed that the MB dye concentration decreased as the irradiation time varied from 0 to 100 min for α-PbO and from 0 to 80 min for β-PbO. The results show that within 100 minutes, the Sn-doped α-PbO nanoparticles possessed the maximum degradation efficiency compared to other metal-doped α PbO nanoparticles, with 100% MB dye degradation compared to 94.76 % by pristine α-PbO. This is attributed to the broader light harvesting in the visible region to facilitate in photocatalytic degradation of MB dye. All doped β-PbO nanoparticles exhibit enhanced photocatalytic activity compared to pristine β-PbO towards the degradation of MB dye under visible light irradiation. In particular, Cu and Co-doped β-PbO exhibit 99.45% and 99.39% degradation rates of MB dye after 80 min of irradiation, respectively, whereas pristine β-PbO exhibit only 75.13%. After doping, the band gap narrowing, formation of impurity states, enhanced specific surface area, higher carrier concentration, reduced carriers recombination, surface roughness, the action of dopant ions, and microstructural changes in the catalyst aspects are enhanced the photocatalytic activity of pristine β-PbO. Additionally, PbO thin films with nanorods, nanosheets, and cauliflower-shaped were produced using a one-step chemical synthesis approach by just varying the cation concentrations to identify PbO phases. Density functional theory (DFT) is also used to characterize the material's properties for photocatalysis applications. The obtained indirect bandgap, the impurity level induces the bandgap narrowing, enhanced optical properties, and the decrease of effective masses of photogenerated carriers in the DFT study of different metal doped α-PbO and β-PbO shows the trends of improvement of photocatalytic performance. The indirect bandgap property is indicated by the calculation of electronic band structure, with spin-up bandgap values of 2.28 eV, 0.68 eV, 1.01 eV, 1.57 eV, 1.79 eV, and 1.76 eV for pristine, Co, Ni, Cu, Li, and Sn doped β-PbO, respectively by using PBE exchange functional. The bandgap values of 1.75 eV, 1.14 eV, 1.36 eV, 1.30 eV, 1.57 eV, and 1.53 eV were also obtained for pristine, Co, Ni, Cu, Li, and Sn-doped α-PbO, respectively using the same method. The DFT result provides in-depth functional characteristics for guiding laboratory working experiments and the applications of the materials in various fields such as photocatalysis, energy storage, and solar cells.