Investigating photocatalytic and antimicrobial activity of synthesised nitrogen and erbium co doped zinc oxide nanoparticles

Abstract

In this thesis, pristine, p-block element nitrogen (N) doped, and rare earth element erbium (Er) co-doped ZnO nanoparticles (NPs) were successfully prepared using chemical co-precipitation technique. Synthesized pure, doped, and co-doped ZnO NPs were analyzed by different techniques. XRD and XPS was used to investigate the structural, elemental and phase properties of the nanoparticles. SEM with EDX was utilized for morphological and elemental analyses. Diffuse reflectance spectra of ZnO obtained from UV-visible spectroscopy were utilized to measure the direct band gap for optical analysis. Photocatalytic activities of synthesized nanoparticles were studied using Rhodamine B solution as organic dye and antimicrobial activities were investigated against gram-positive, gram negative bacteria as well as against fungi.

Prior to doping and co-doping, the synthesis conditions and annealing temperatures were optimized to produce pristine ZnO NPs as potential photocatalysts. ZnO NPs were then doped with p-block element (N) at various concentration (0.5 mol.%, 1 mol.%, and 2 mol.%). XRD and XPS analyses confirmed complete incorporation of N into the ZnO lattice. SEM images revealed that particle shape was changed from spherical to nanorod by doping ZnO with nitrogen. It was observed that photocatalytic and antimicrobial activities of N doped ZnO NPs both were increased compared to pure ZnO NPs by band gap narrowing. After structural, morphological, optical, and photocatalytic analysis, 1 mol.% N doped ZnO NPs were carefully chosen for co-doping with erbium as 1 mol.% N doped ZnO NPs showed highest degradation of 88% after 6 hours irradiation under UV-light compared to 59% degradation for pure ZnO NPs. Further, rare earth element (Er) was co-doped with optimized (1 mol.%) N doped ZnO at various concentration (1 mol.%, 2 mol.%, and 3 mol.%). XRD and XPS analyses confirmed complete incorporation of Er and N into the ZnO lattice. SEM images revealed that nanorod diameter and length both were increases due to Er and N co-doping. It was also observed that photocatalytic and antimicrobial activities of Er and N co-doped ZnO NPs were increased compared to pure and N doped ZnO NPs by delaying electron-hole recombination. Direct band gap value was decreased from 3.243 eV for pure ZnO to 3.215 eV for 3 mol.% Er and 1 mol.% N co-doping. Degradation efficiency was increased from 88% for 1 mol.% N doped ZnO to 96% for 3 mol.% Er and 1 mol.% N co-doped ZnO NPs. Rare earth element (Er) mainly generate impurity levels in the forbidden energy gap especially near the band edges to reduce electron-hole recombination rate by acting as active trapping sites of the charge carriers, which increased photocatalytic and antimicrobial activities of nanoparticles.