Adsorption of Cu(II) and Pb(II) using silica@mercapto (hs@m) hybrid adsorbent synthesized from silica of Takari sand: Optimization of parameters and kinetics

The silica@mercapto (HS@M) hybrid adsorbent was successfully synthesized from Takari sand and modified with mercapto. The HS@M was synthesized using the sol-gel method. FTIR results showed that HS@M had been successfully prepared by showing the presence of groups of hydroxyl (-OH), silanol (Si-OH), siloxane (Si-O-Si), methylene (-CH₂), and thiol (-SH) with the peak of 3426.33 cm^-1, 2936.62 cm^-1 and 2553.39 respectively. It also showed the interaction in HS@M-Cu(II) and HS@M-Pb(II), indicated by the disappearance of silanol, siloxane, and thiol groups. There was also a new absorption band at 797.2 cm^-1. XRF results showed that there were two major substances in HS@M, which were Si and S with each percentage of 31.7% and 59.6%. The surface morphology imaged by SEM showed there were amorphous granules on the surface of HS@M, The mapping analysis showed there was a homogenous distribution of granules on the surface of HS@M. Optimum acidity for Cu(II) and Pb(II) adsorption was at pH 5. The optimum contact time of Cu(II) was 50 min and that of Pb(II) was 80 min. The optimum concentration of Cu(II) was 80 mg/L and that of Pb(II) was 20 mg/L. Finally, the adsorption kinetics of both ions followed pseudo-second-order.