Novel synthesis of cyano-functionalized mesoporous silica nanospheres (MSN) from coal fly ash for removal of toxic metals from wastewater

Trace amounts of toxic metals are usually difficult to be purified by conventional chemical precipitation or physical adsorption in wastewater. In this study, in order to realize high-value utilization of coal fly ash for wastewater purification, a novel method was applied to prepare high-performance mesoporous silica materials from coal fly ash. In comparison with a commonly used method, characterizations revealed that the new method obtained mesoporous silica nanospheres with uniformly distributed cyano groups (denoted by MSN), while the common method only obtained irregular sponge-like microstructure (denoted by ISM). Besides, MSN showed better hydrothermal stability, higher specific surface area (693 m2/g) and more ordered mesopores from the comparison. Moreover, the sorption experiments of simulated wastewater suggested that MSN was better in removing toxic metals (Ni2+ and Cd2+) than ISM. For the practical wastewater from a battery plant, 2 g/L dosage of MSN showed excellent performance for purification of trace amounts of various toxic metals (Ni, Cd, Mn, Zn, Hg and Pb), the concentration of which reduced to ppb level after MSN treated. The results suggested that MSN can be an effective and low-cost sorbent for removing various toxic metals from wastewater.