Synthesis of ultra-low density nanosilica with extended Si-O-Si molecular network for Cr(VI) ions capture integrating monoazoic dye-surface interactions by molecular docking study

Nanosilica gels were synthesized by sol-gel route from Rice husk and Beach Sand, and characterized by XRD, FTIR, SEM, XRF, TEM, SAED and pHpzc techniques for batch adsorption of Cr(VI) ions, integrating molecular docking study of AY dye onto the adsorbents. The XRD spectra, and SAED images confirmed that the gels were polycrystalline, while TEM images revealed varying nanometric particle with diameters of 14.70 and 13.3 nm for Rice Husk Aerogel (RHA) nad Beach Sand Aerogel (BSA) adsorbents respectively. The optimum adsorption capacities of 24.02, and 15.62 mg/g of Cr (VI) ions onto RHA and BSA adsorbents were obtained, while 3.20 and 2.39 mg/g of AY dye were obtained for RHA and BSA adsorbents respectively. The Langmuir model gave the best fit to adsorption of AY dye onto RHA adsorbent suggesting monolayer and homogenous adsorption, while Cr(VI) ions adsorption better fit to the Freundlich and Temkin models. All ∆H and ∆S values for adsorption of Cr(VI) ions and AY dye onto RHA and BSA adsorbents show endothermic and random processes respectively, while ∆G and Ea values showed spontaneous processes. The molecular docking experiment showed that the interaction mechanisms between Si-O-Si surface and AY dye, revealed electrostatic attractions and hydrogen bonding. A value of -6.30 kcalmol− 1 was obtained as the best binding pose with an average hydrogen bond lengths of 2.20 Å. This reveals the potential of the adsorbents for complex wastewater systems, as they offer both experimental evidence and atomic-scale insights into surface-contaminant interactions.