Mesoporous hybrid Zn-silicate derived from red palygorskite clay as a high-efficient adsorbent for antibiotics

Abstract

A hierarchical mesoporous hybrid Zn-silicate adsorbent with superior adsorption performance for aureomycin (AMC) and tetracycline (TC) has been successfully synthesized by employing an “all-into-one” strategy and one-pot hydrothermal reaction, using naturally abundant, low-cost red palygorskite clay (RPAL), sodium silicate and zinc salts as raw materials. The morphologies and crystal forms of the Zn-silicates can be tuned by altering the dosage of Zn2+ ions. Low-crystalline sheet-like Zn-silicates were formed at the Si/Zn ratio of 3:1 and 2:1, and zinc orthosilicates were obtained at the Si/Zn ratio of 1:1 and 1:2. A systematic study on their adsorption abilities for the antibiotics AMC and TC indicates that the sheet-like Zn-silicate has higher adsorption capacity for AMC and TC than zinc orthosilicate, and the Zn-silicate with Si/Zn ratio of 3:1 has the best adsorption capacity of 384 mg/g for AMC and 337 mg/g for TC, which is obviously higher than that of RPAL (154 mg/g for AMC and 140 mg/g for TC). The adsorption properties are dependent on the pore size and surface charges, instead of specific surface area. The average pore sizes of 10.62–11.50 nm and the negative surface charge (−42.54 mV) resulting from the –Si(M)O− groups are beneficial to the adsorption for both AMC and TC. The adsorption process mainly involves with monolayer coverage, and chemo-adsorption plays a key role for the enhanced adsorption capacity. The results suggest that the Zn-silicates derived from natural abundant clay mineral have superior performance, and could be candidates to remove AMC and TC from the wastewater with high amounts of AMC and TC.