One-step synthesis of magnetic–layered double hydroxide and its application for oxytetracycline removal from water

Abstract

Layer double hydroxide (LDH) is abundantly available for water treatment as its large surface area and large porosity satisfy the important requisite properties of adsorption. However, it is still intricate to integrate LDH with magnetic particles to enable magnetic separation from water after treatment. Therefore, we aimed to demonstrate one-step solvothermal method integrating iron reduction for preparing magnetic layered double hydroxide (MLDH) and optimize it for the oxytetracycline (OTC) adsorption by applying four different Fe:Mg ratios. The results confirmed that the synthesized MLDH by the one-step method (1S-MLDH) had typical structure of LDH and sufficient magnetic property. The adsorption efficiency of 1S-MLDH is higher than MLDH provided by two-step method (2S-MLDH). Among the four different Fe:Mg ratios of 1S-MLDH, the ratio of 1:3 showed maximum adsorption efficiency of OTC (217 mg g−1) under pH 7, which was characterized by monolayer chemisorption. This maximum efficiency was also higher than that of other materials reported in the literature, possibly because the d-spacing of 1S-MLDH1:3 is close to size of OTC molecule, thereby allowing well intercalation and adsorption in interlayers. Under environmentally relevant conditions, anions showed weak interference in OTC adsorption, and the adsorption capacities of 1S-MLDH1:3 decreased by 2.0–14.5%. Furthermore, 1S-MLDH exhibited the photo-assisted regeneration ability for adsorbent recovery and the adsorption efficiency remained over 80% after five cycles of adsorption and regeneration. Besides the higher adsorption performance, the preparation of 1S-MLDH is more convenient and less time-consuming than 2S-MLDH synthesis, and thus applicable for organic pollutants treatment with economic benefit.