Effects of Mn Doping on Surface Chemistry, Phase Stability, and Physical Properties of NiO Synthesized via Green Methods

Abstract

ABSTRACT This study investigates the effect of manganese (Mn) doping (1–5 wt. %) on the phase transition of nickel hydroxide (Ni(OH) 2 ) to nickel oxide nanoparticles (NiO NPs) synthesized via a green route. Phase transition, structural, optical, and magnetic properties of Mn‐doped NiO are thoroughly investigated. Thermogravimetric analysis (TGA) reveals the influence of Mn on the thermal decomposition and the stability of Ni(OH) 2 and the organic compounds from olive leaf extract under inert calcination conditions. X‐ray photoelectron spectroscopy (XPS) provides insights into surface chemistry modifications before and after calcination, as well as in the presence of Mn. X‐ray diffraction (XRD) confirms Mn incorporation and lattice distortion within the NiO structure. HRTEM and BET analyses show that 2 wt. % Mn is a critical concentration, yielding the smallest spherical particle size (6 nm) and the highest surface area. The calculated work function from ultraviolet photoelectron spectroscopy (UPS) reveals a decrease from 6.0 eV (0 wt. % Mn) to 5.4 eV (5 wt. % Mn). Analysis of the valence band maximum (VBM) region further indicates a bandgap widening with Mn incorporation. Raman spectra reveal the appearance of the two magnon (2M) vibrational mode, suggesting modified magnetic behavior. Vibrating sample magnetometry (VSM) indicates a ferromagnetic response, with the appearance of a Néel temperature at 5 wt. % Mn, indicating an antiferromagnetic to paramagnetic transition. This study offers key insights into the design of stable, high‐performance materials for photovoltaic and magnetic applications.