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 synthesized 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 °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 °C. The results of isotherm and kinetics model studies were consistent with Temkin and pseudo-second-order models, respectively. The thermodynamics 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 capacity. 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.