Stage-wise characterization and adsorption selectivity test of magnetized and functionalized rice husk nanosilica in simulated mixture of ternary heavy metal and binary dye solutions

The transformation of agricultural solid waste into sustainable products to attain zero-waste society via design innovation and advanced waste recycling techniques is imperative. In this study, a local adsorbent (MNS@MBT) was synthesized via chemical modification and thermal treatment of nanosilica from rice husk and subsequent functionalization with 2-mercaptobenzothiazole. Comparative study of the stage-wise characterization results of adsorbents synthesized via calcination of rice husk (CRH), chemical modification of CRH to form nanosilica (NS) and magnetization of NS to form (MNS) was conducted with MNS@MBT using Brunauer-Emmett-Teller (BET) method, Fourier transform infrared (FTIR) spectrophotometer, scanning electron microscope (SEM)/energy dispersive spectroscopy (EDX), powder X-ray diffractometer (XRD), Thermogravimetric analysis (TGA) and vibrating sample magnetometer (VSM) analysis. Adsorption selectivity test of all adsorbents in simulated heterogeneous mixture of Cu 2+ , Hg 2+ , Pb 2+ , methyl orange (MO) and methylene blue (MB) was conducted. Total pore volume and surface area of 0.248 cm 3 /g and 157.06 m 2 /g were recorded by BET. EDX revealed wt% of Si, O, Fe, N, S and C to be 74.02wt%, 12.44 wt%, 3.98 wt%, 3.65 wt%, 3.47 wt% and 1.12 wt% respectively. Large pore openings with formation of agglomerated composite nanomagnetic materials were noticed on the adsorbent surface. TGA revealed adsorbent to be thermally stable with no weight loss above 600 o C. Active –OH, O-Si-O, Fe–O, C-S, C=N and C-H functional groups were found on adsorbent surface. XRD revealed adsorbent to be crystalline in nature. MNS@MBT recorded highest adsorption capacities of 8.77 mg/g, 9.89 mg/g, 9.42 mg/g, 8.09 mg/g and 8.31 mg/g; and distribution coefficients of 17.98, 1.43, 3.25, 0.85 and 0.98 for Cu 2+ , Hg 2+ , Pb 2+ , MO and MB respectively. The order of adsorption capacity was CRH < NS < MNS < MNS@MBT. All the adsorbents revealed preferential affinity for Hg 2+ ions in solution over other pollutants. In conclusion, MNS@MBT proved to be the best among the examined adsorbents and was found suitable as potential adsorbent for pollutants removal from solution.