Surface Modified Silicon Dioxide Based Functional Adsorbents Derived From Waste Sand for the Removal of Toxic Pollutants From Water

Waste foundry sand (WFS), an industrial waste mainly comprising silicon dioxide was used to generate low-cost and efficient adsorbents for the expulsion of toxic pollutants from water through adsorption. The WFS was converted into particles by top–down approach followed by subsequent activation and functionalization. Activated sand particles (ASPs) with –OH groups and amino-functionalized sand particles (AFSPs) with –NH 2 groups were synthesized and fully characterized using FESEM, EDX, ATR-FTIR, XRD, TGA, and BET analyses. The adsorption capacities at experimental conditions for cationic dyes namely methylene blue(MB), malachite green(MG), methyl violet (MV), rhodamine B(Rh B) were 38.16, 26.31, 55.24 and 35.84 mg g −1 while for anionic dyes namely methyl orange (MO), patent blue VF(PB VF), quinoline yellow(QY), reactive Red 2(RR 2) were 7.28, 4.63, 7.84 and 6.91 mg g −1 as well as for metal ions namely Cd(II)), Ni(II)), Co(II)), and Cr(VI)were 23.81, 43.06, 17.03 and 3.47 mg g −1 respectively. The adsorption equilibrium isotherms optimally fit the Langmuir isotherm model, indicating homogeneous surfaces and monolayer adsorption. A pseudo-second-order model showed a strong agreement with the experimental data, thus identifying chemisorption as the rate-limiting step. Additionally, these particles were verified to be reusable for a minimum five adsorption–desorption cycles without loss of efficiency.