Simultaneous removal of heavy metals and antibiotics from anaerobically digested swine wastewater via functionalized...

The removal of heavy metal ions and antibiotics from livestock and poultry wastewater has gained significant attention. Developing dual-functional materials capable of simultaneously removing heavy metal ions and antibiotics from wastewater is a promising strategy. In this study, a functionalization approach was proposed to enhance active sites in covalent organic frameworks (COFs), thereby improving their adsorption performance and maintaining photocatalytic activity. Vinyl-functionalized covalent organic frameworks (COFs-V) were first synthesized in a room-temperature solution. Subsequently, 4-mercaptobenzoic acid was introduced into COFs-V via grafting and chelation to prepare COF@COOH, aiming to modify surface active sites. Fourier transform infrared spectroscopy (FTIR) and in-situ X-ray photoelectron spectroscopy (XPS) confirmed the successful introduction of carboxyl groups into COF@COOH, significantly increasing the number of active sites. The performance and mechanism of COF@COOH in the removal of Cu²⁺, Zn²⁺, and tetracycline hydrochloride (TC) from swine wastewater were systematically studied. The results revealed that the adsorption capacities of COF@COOH for Cu²⁺ and Zn²⁺ reached 19.27 mg/g and 12.95 mg/g, respectively, which were 58 and 29 times higher than those of the unmodified COFs. Additionally, COF@COOH completely degraded TC within 5 min, with 100% photocatalytic degradation efficiency and an apparent rate constant of 1.13 min^-1. After five cycles, the adsorption capacities for Cu²⁺ and Zn²⁺ and the degradation efficiency of TC remained nearly unchanged, demonstrating the stability of the composite material. This study provides an effective approach for the simultaneous removal of heavy metal ions and antibiotics from swine wastewater.