<![CDATA[The acidification step in silica extraction from rice husks typically uses strong mineral acids, such as sulfuric acid, which pose safety risks and environmental concerns. Citric acid, a weak organic acid, is a safer and more environmentally friendly alternative for this process. This study aimed to produce green amorphous silica (GAS) from rice husk waste using the sol-gel method and to compare the effects of sulfuric acid and citric acid during the acidifying step. Rice husks were calcined at 700°C, acid-pretreated to pH 1, extracted with 1 M NaOH, and neutralized with either 1 M H₂SO₄ or 1 M C₆H₈O₇. The resulting silica powders were characterized using XRF, XRD, SEM-EDX, and FTIR. The SiO₂ content reached 95.22 % by mass with sulfuric acid and 93.59 % with citric acid. XRD revealed that sulfuric acid produced a poorly crystalline phase, whereas citric acid maintained a fully amorphous structure. SEM images showed uniform nanoparticles (~50–80 nm) for the sulfuric acid route, whereas citric acid produced more agglomerated clusters. FTIR spectra confirmed the presence of siloxane bonds in both samples; however, citric acid-derived silica exhibited residual carboxylate bands and less extensive condensation. Overall, sulfuric acid produced purer, more uniform silica suitable for high-performance applications. In contrast, citric acid proved a viable, greener alternative for preserving the amorphous state, suggesting that further process optimization could enhance its competitiveness in sustainable silica synthesis.]]>
