Melamine functionalized mesoporous silica SBA-15 for separation of chromium (VI) from wastewater

In this study, a Melamine-functionalized mesoporous silica-SBA-15 (Melamine-MS-SBA-15) adsorbent was syn-thesized to remove Cr(VI) from wastewater. The mesoporous silica-SBA-15 adsorbent was first synthesized using the hydrothermal method and post-synthesis under toluene reflux. Then, 3-aminopropyl trimethoxy silane was added to the adsorbent surface and it was further modified by melamine to obtain the final product. SBA-15 well -performed after Melamine functionalization against the Cr(VI) removal due to the conversion of physisorption to chemisorption adsorption. The adsorption of Cr(VI) using the Melamine-MS-SBA-15 was studied. XRD, BET, SEM, FTIR, TGA, and zeta potential analyses were used to characterize the adsorbent. Parameters affecting adsorption including pH (3-9), initial concentration (20-200 ppm), contact time (1-24 h), adsorbent dose (1.5-15 mg L-1), and temperature (18-30 degrees C). Optimal results were pH = 3, an initial concentration of 20 ppm, an adsorbent dose of 4 mg L-1, a contact time of 6 h, and a temperature of 18 degrees C. The results of isotherm and kinetics model studies were consistent with Temkin and pseudo-second-order models, respectively. The ther-modynamics parameters confirmed the spontaneous reaction. Experimental results showed that functionalization of the adsorbent surface of MS-SBA-15 with melamine increased the adsorption efficiency and adsorption ca-pacity. The highest adsorption capacity for Cr(VI) was about 50 mg/g. The maximum adsorption efficiency for solutions containing Cr(VI) was about 84%. Increasing the adsorption concentration in a fixed value of the heavy metal concentration increased the adsorption capacity and increasing the heavy metal concentration, increased the adsorption capacity.