Bio-adsorbents based on mesoporous silica produced from rice husks with tunable architecture and surface area for remediation of industrial effluents

The search for efficient and more sustainable treatments of wastewater has become increasingly challenging in recent years. Aiming to contribute with this demand, the current study focused on the synthesis of mesoporous silica (MS) bio-adsorbents (MS1, MS2, MS3 and MS4) based on Santa Barbara Amorphous-15 (SBA-15) by a relatively simple and sustainable process using sodium silicate (SS) extracted from rice husk ashes (RHA) and Pluronic P123. Subtle and careful changes in the synthesis conditions resulted in MS samples with ordered pores and high specific surface area (S_BET), that is, 712 m² g⁻¹ (MS1), 838 m² g⁻¹ (MS2), 905 m² g⁻¹ (MS3) and 806 m² g⁻¹ (MS4), which are higher than other silicas also produced from RHA, indicating that our bio-adsorbents may exhibit superior pollutant adsorption capabilities. In that regard, various research reports the potential of MS to adsorb dyes, heavy metals, bacteria, pharmaceuticals and other pollutants in model systems. However, our proposal advanced in testing the adsorbent potential of these materials for two independent systems: (i) removal of methylene blue (MB) model dye from aqueous solutions and (ii) treatment of an industrial denim laundry effluent. Indeed, all MS bio-adsorbents were potentially efficient and reusable, but MS1 and MS2 exhibited higher adsorption capacities for MB dye (q_e = 327.29 and 365.78 mg g⁻¹, respectively) at pH 12.0. The investigation of the effect of ions and DFT calculations contributed to elucidating the interactions between MB dye and MS bio-adsorbents. In addition, our bio-adsorbents stand out by their excellent efficiency (~ 75%) in the remediation of an industrial effluent exclusively by adsorption. Among the produced bio-adsorbents, MS2 has shown a higher degree of mesoscopic order, well-ordered and open-ended pores with oval architecture and interconnected hollow channels, but both MS1 and MS2 displayed similar adsorption capacities normalized by total surface area, demonstrating to be promising and eco-friendly adsorbents for use in environmental remediation.