Simultaneous preparation of nano silica and iron oxide from palm oil fuel ash and thermokinetics of template removal

Abstract

Nanomaterials have potential applications in the fields of catalysis, drug delivery, nanocomposites, and nanofluids. This study suggests a method for simultaneous preparation of nano silica and iron oxide from palm oil fuel ash (POFA). First, POFA was leached out with H₂SO₄ followed by alkali (NaOH) leaching. Basification (pH = 14) of the filtrate of the first leaching process produced iron oxide, while acidification of the alkali leachate produced nano silica. Addition of polymeric surfactant polyethylene glycol (PEG MW 20 000) resulted in deagglomeration of the silica nanoparticles. Silica nanoparticles with sizes in the range of 20–80 nm, surface area of 326 m² g⁻¹, and pore diameter of 8.2 nm were obtained. Thermokinetic and thermodynamic studies of template (PEG) removal from the silica matrix were performed using the Kissinger and Ozawa methods based on model-free kinetics. The activation energy of PEG decreased from 330 kJ mol⁻¹ to 140 kJ mol⁻¹ when it was used as a template; this result demonstrates the lack of chemical bonding between the surfactant and silica. The findings are supported by the Fourier-transform infrared spectra of the PEG–silica composites.