Enhancing the removal of phospholipids and trace metals from non-edible oils using surface-modified nanosilica for greener biofuel pretreatment

Phospholipids and trace metal ions in crude non-edible oils hinder energy conversion efficiency and increase pollutant emissions in biofuel applications. This study presented a green pretreatment method using nanosilica synthesized from rice husk waste, evaluated in unmodified (nSi) and surface-modified forms: alkali-activated (nSi–NaOH) and amine-functionalized (nSi–NH₂). Adsorbents were first tested on Ceiba pentandra (CKO) oil, with best performing conditions applied to Jatropha curcas (CJO) and Calophyllum inophyllum (CTO). Molecular simulations using hydratable (DLPC) and non-hydratable (DOPA) phospholipids revealed high affinity toward anionic non-hydratable phospholipids, indicating their potential as a green alternative to acid degumming. Adsorption behavior was further examined via kinetic (pseudo-first order, pseudo-second order, and intraparticle diffusion) and thermodynamic (ΔG, ΔH, ΔS) modeling. All nanosilicas showed high removal efficiencies, with nSi–NH₂ achieving up to 99.86% phospholipids removal at 1 wt%. Interestingly, at 2.5 wt%, unmodified nSi outperformed nSi–NaOH, offering comparable removal at lower cost. All adsorbents effectively reduced Mg²⁺ and Ca²⁺ concentrations to levels compliant with biodiesel EN 14538 standards. The adsorption process was confirmed to be dominated by chemisorption, supported by both modeling and material characterization. These results highlight rice husk-derived nanosilicas as sustainable, high-performance adsorbents for biofuel pretreatment.