Effective soap removal from biodiesel using NiO ‐doped ZnO nanoparticle adsorbent

Abstract The production of biodiesel generates soap impurities that hinder biodiesel performance and complicate its purification. This study presents a novel approach for soap removal from biodiesel using NiO–doped ZnO nanoparticle (NP) adsorbent. The NPs are synthesized using a gliding arc discharge (GAD) method as a non‐thermal plasma source (NTP). NiO doping reduced the bandgap energy by 74%, reduced the crystallite size, and increased the surface area by 78%, entailing lattice strain and structural modifications. Soap removal efficiency was 99.7% for NiO–doped ZnO within 16 min, compared with 95.5% for ZnO. Soap uptake as high as 2320 mg/g NiO–doped ZnO was reported, which could be equally fitted by Langmuir and Freundlich isotherms suggesting effective physicochemical interactions. Adsorption kinetics followed a pseudo‐first‐order model with k 1 = 0.172 min −1 . NiO–doped ZnO retained 94% of its efficiency after five cycles, whereas the efficiency of ZnO NPs decreased to 90.4%. Molecular docking study revealed a binding energy of between the soap molecules and NiO–doped ZnO, compared with eV for ZnO NPs. These results highlight NiO‐doped ZnO NPs as a highly efficient, cost‐effective, and sustainable material for biodiesel purification with significant implications for clean energy technologies.