Augmentation of magnetic properties and antimicrobial activities of band gap modified Ho3+ and Sm3+ doped ZnO nanoparticles: A comparative experimental study

Abstract

ZnO nanoparticles (NPs) and rare-earth elements i.e., Ho and Sm, doped ZnO NPs were synthesized adopting the modified sol-gel route. Structural and morphological modifications leading to alternation of magneto-optical properties as well as antimicrobial activities of doped ZnO NPs were investigated. Crystalline wurtzite structure of the NPs along with phase purity was confirmed by XRD and rietveld analysis. Densely dispersed smaller-sized NPs, compared to pristine ones, were found from SEM and TEM analysis for Zn0.97Ho0.03O and Zn0.97Sm0.03O. HRTEM and SAED patterns confirmed highly polycrystalline nature of the NPs. The existence of Ho3+ and Sm3+ on the surface of doped NPs was corroborated by XPS. The deconvolution of the O 1s peak validated the variation in oxygen vacancies in lattice amongst NPs. Doping significantly reduced the band gap, most effectively for Zn0.97Ho0.03O NPs, leading to an increase in doped NPs' visible light absorbability. PPMS revealed the existence of RTFM in all the samples, along with diamagnetic and paramagnetic ordering in pure ZnO and Ho3+ doped ZnO, respectively. Coercivity decreased with doping in both instances, while saturation magnetization increased significantly with Sm3+ doping, reaching 0.1009 emu/g from 0.028 emu/g for pure ZnO NPs. Increase of oxygen vacancies on doping plays a key role in enhancing magnetic properties by mediating impurity ions leading to significant spin alignment. BMP model was fitted precisely with experimental magnetic data validating the involvement of the oxygen vacancies in the onset of ferromagnetism. Superior antimicrobial activities of Ho3+ and Sm3+ doped ZnO NPs compared to ZnO NPs were also observed against several gram-positive, gram-negative bacteria and fungi. The intriguing findings of magnetism along with enhanced antimicrobial activities widen the scope of implementing rare earth-doped ZnO NPs in applications like soft magnetic devices, magnetic switches, food packaging, medicine and drug delivery, coating on walls and fabrics for inhibiting bacterial spread and so forth.