Efficient adsorption of tetracycline by carbon-silicon composites with abundant Si-OH active groups: Experimental and density functional theory calculations

The massive accumulation of fly ash poses serious threats to the environment and land resources, making its effective utilization urgently needed. Although fly ash can be used to prepare silicon-carbon composites, the formation pathways of Si-OH/Si-O-C groups, the construction of Si-C bonds, and the regulation of microstructure remain unclear. In this study, a series of novel silicon-carbon composites (FAKXNY-Z) with unique microstructures were synthesized via high-temperature activation combined with hydrothermal crystallization, using fly ash and chitosan as raw materials. Among them, FAK2N2–150 exhibits a high specific surface area (1511.7 m 2 /g) and abundant active functional groups (Si-OH). This material achieves an adsorption capacity of 550.55 mg g −1 for tetracycline at room temperature. Density functional theory (DFT) calculations based on the experimental structure confirm its distinctive amorphous silica layer derived from sodalite collapse and reveal the adsorption mechanism toward tetracycline (TC), clarifying the strong affinity between Si-OH groups and TC molecules. This work not only provides a feasible strategy for the resource utilization of fly ash, but also offers theoretical support for the design of solid-waste-based functional adsorbents.