Kinetic, isotherm, and thermodynamic studies of Cr(VI) removal from aqueous solution using mesoporous silica materials prepared by fly ash

A series of mesoporous silica materials (FMD, FMT, and FMC were synthesized with DTAB, TTAB, and CTAB as template, respectively) have been prepared using fly ash as a silica resource. The as-synthesized materials were characterized by BET, XRF, FTIR, and XPS. The results confirmed the mesoporous structure and nitrogen content to act as potential adsorbents. The adsorption properties of these materials were also investigated by batch adsorption experiments. The FMC exhibited the highest effective removal of Cr(VI) (99%). The Cr(VI) adsorption process over FMC follows the pseudo-second-order kinetic and Langmuir model. Thermodynamic studies revealed that the Cr(VI) adsorption by FMC was spontaneous and endothermic. The study of the adsorption mechanism showed that the removal of Cr (VI) by FMC is through electrostatic attraction and chemical reduction. The coexisting ions experiment showed that FMC had high selectivity for Cr(VI). After three regeneration cycles, the Cr(VI) removal rate of FMC adsorbent still remained about 80%. Thus, this inexpensive adsorbent (FMC) is suitable for removing Cr(VI) from discharged industrial water.