Adsorptive Removal of Iron Using SiO₂ Nanoparticles Extracted from Rice Husk Ash

In this work, SiO₂ nanoparticles were prepared by the sol-gel method after sodium silicate was extracted from rice husk ash (RHA) under various experimental conditions such as types of acids, NaOH concentration, dissolved time, and temperature and used for removal of Fe²⁺ ions from aqueous solutions. The extracted SiO₂ was morphologically and chemically characterized and showed a surface area of 78 m²/g and uniform pores of 2.71 nm, offering high adsorption capacity for Fe²⁺ ions. The influence of pH, contact time, and amount of adsorbent was studied in order to establish the best conditions for the Fe²⁺ adsorption and removal. Furthermore, the adsorption data were fitted with an exponential shape curve for all the three variable parameters that affect the adsorption process. The best results were obtained for pH 5, 20 min contact time, and 0.5 g adsorbent dose. The loading adsorption capacity was 9 mg of Fe²⁺ ions/g SiO₂ in the concentration range 0.1-1.0 mgL^-1. In addition, the synthesized SiO₂ with the size of around 50 nm can be used for specific heavy metal removal and drug delivery, after modification of the SiO₂ surface with various functional groups.