Preparation of Si–Mn/biochar composite and discussions about characterizations, advances in application and adsorption mechanisms

Abstract

A novel Si–Mn binary modified biochar composite material (SMBC) was prepared after being sintered 450 °C for 2 h. The crystal structure, surface functional groups, surface morphology and element composition, specific surface area and pore structure were characterized by XRD, FTIR, XPS, SEM + EDS and BET etc. The results showed that the surface of SMBC was rough and loose, and the specific surface area increased to 35.4284 m2/g. Si and Mn were uniformly attached to the surface of biochar in the form of SiO2, MnOx, MnSiO3. Batch adsorption experiments showed that SMBC had a higher removal efficiency (139.06 mg/g, above 98%) for Cu(II) when the dosage was 2 g/L and pH = 6. The cycle experiments showed that SMBC had good reusability, and its regeneration efficiency still reached 80.24%. The leaching amount of Mn (0.65 mg/L) was greatly reduced and avoid second-pollution resulted from ion exchange, which was attributed to the existence of Si–O–Mn bonds, and they could help Mn adhere to the surface of biochar more stable. The adsorption process was dominated by single-layer chemical adsorption and mainly occurred in the membrane diffusion stage. Cu(II) mainly formed -COOCu, -OCu, Cu(OH)2, Cu(OH)2CO3, Si–O–Cu, Mn–O–Cu by the mechanisms such as precipitation (4.74%), ion exchange (13.81%), complexation and physical adsorption (total 81.45% of the two mechanisms). Among them, complexation was dominant in the adsorption process.