pH-responsive and partially reversible adsorption of Rice husk-derived silica nanoparticles on muscovite: Nanoscale insight using atomic force microscopy

Silica nanoparticles derived from rice husk (RH-SNP) offer a sustainable approach to enhancing oil recovery by modifying reservoir wettability through strongly adsorbing to mineral surfaces. However, this strong adsorption may also cause unintended reservoir damage and permeability loss. In this study, we demonstrate that RH-SNP can be reversibly desorbed from chemically modified muscovite surfaces that mimic reservoir minerals by adjusting pH. Atomic force microscopy (AFM), zeta potential analysis, and surface coverage quantification reveal that maximum adsorption (46%) occurs at near-neutral pH (pH 6) due to a balance between moderate electrostatic repulsion and optimal calcium-ion bridging. At low pH (pH 2), limited silanol deprotonation restricts bridging (21%), while at high pH (pH 11), strong electrostatic repulsion reduces nanoparticle adsorption (5%). These findings provide mechanistic insight relevant to the design of pH-responsive interfacial systems and offer conceptual guidance for understanding RH-SNP retention behavior in applications such as enhanced oil recovery. • pH-controlled adsorption of RH-SNPs enables partial reversible nanoparticle binding • AFM revealed up to 46% coverage at pH 6, decreasing to 4% at pH 11 • Adsorption partially restored by re-immersion in pH 6 after pH 2 or pH 11 • Study enables design of smart, partialy reversible nanofluids for subsurface applications