Chiang Mai Journal of Science

 In this study, solid silica nanoparticles (sSiO₂ NPs) were chemically etched using sodium hydroxide solution as an etchant to synthesize porous silica nanoparticles (pSiO₂ NPs). Etchant dosage and etching time were optimized to obtain the optimum etching condition providing the effective removal of paraquat (PQ). High removal efficiency of PQ by the synthesized pSiO₂ NPs was obtained over 90% using 11.1 mL of 1.25 M NaOH and 12 h for the etching process. SEM and TEM images showed that the porosity of pSiO₂ NPs increased with increase of the etchant dosage and etching time. The increment of porosity of pSiO₂ NPs enhanced the PQ removal efficiency. FTIR result indicated that the characteristic functionalities of silica remain after the etching process. After optimum condition of etching obtained, the adsorption behavior of PQ was investigated. Several key factors influencing the adsorption efficiency, i.e., initial solution pH, initial concentration, and adsorption time were optimized. The maximum removal efficiency of PQ (~98%) by the pSiO₂ nanoadsorbent was obtained using 100 mg L^-1 of PQ solution at pH ~7 within 5 minutes. The maximum adsorption capacity (q_max) of the pSiO₂ NPs for the PQ removal was 65.7 mg g^-1. The pSiO₂ nanoadsorbent is effective adsorbent for the PQ removal due to the development of a facile synthetic method for adsorbent preparation, rapid adsorption process, and comparable q_max value with other PQ adsorbents.