Microwave assistant rapid synthesis MCM-41-NH₂ from fly ash and Cr(VI) removal performance

Synthesis of silicon materials from fly ash is an ecologically justified process aimed at the transformation of energy sector waste-fly ash into mesoporous silicon material of broad possible application field. In this study, the MCM-41-NH₂ was successfully synthesized from industrial solid waste fly ash via a facile and fast process of alkali fusion method under the assistant of microwave. Due to the employ of microwave, the aging time was controlled within 30 min, which was significantly shorter than that of traditional hydrothermal method (48-72 h). And, the obtained MCM-41-NH₂ was shown an excellent performance to remove Cr(VI) from solution under the investigation of fixed-bed column. The maximum adsorption capacity for Cr(VI) was 53.77 mg/g. Additionally, the effect of initial concentration, flow rate, bed height, and pH on Cr(VI) removal were investigated, and the models of Thomas and Adams-Bohart were applied to predict the experiment data; the correlation coefficients (R²) of Thomas model under the investigated conditions were all close to 1. Furthermore, the adsorbent was characterized by N₂ adsorption-desorption isotherm, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential, ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), and NH₃-Temperature Programmed Desorption (NH₃-TPD). The results showed that amino groups play an important role in the adsorption process. Cr(VI) was firstly adsorbed on the surface of the MCM-41-NH₂, and then some of the adsorbed Cr(VI) were reduced to Cr(III) by the release of the protons of the ammonium. The information showed that MCM-41-NH₂ could be an effective and low-cost sorbent for removing Cr(VI) from wastewater. Furthermore, recycling experiments showed that the spent adsorbent had high catalytic performance for methyl mercaptan (CH₃SH). Graphical abstract .