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1. Introduction
In recent years, pharmaceuticals and personal care products (PPCPs) have been frequently detected in the environment, and they have attracted scrutiny as a new type of pollutant that threatens the biosphere and human health [1,2]. Antibiotics are one of the main PPCPs. Since penicillin was discovered in 1929, antibiotics have been used extensively to improve the health of animals and humans, and antibiotics have also been used as growth promoters for livestock, bees, aquatic products and other aquaculture industries [3,4]. Globally, the average total annual use of antibiotics is approximately 200,000 tons [4,5]. At present, the most widely used antibiotics are the sulfonamides (SAs) [6], quinolones (QNs) [7], macrolides (MALs) [7], and tetracyclines (TCs) [8], among which TCs are some of the most frequently detected antibiotics in water [9]. In the process of biological metabolism, the vast majority of TCs is discharged through feces and urine directly from the body and, ultimately, into the water environment [10]. This damages the aquatic ecosystem and induces the generation of resistant genes in the environment, resulting in continuous pollution [11]. Thus, there is an urgent need to develop a low-cost, high-efficiency and productive removal technology.
TC removal technologies mainly include biological, adsorption, photolysis and advanced oxidation methods [11]. Because of its high efficiency, lack of byproducts and other characteristics, adsorption methods have been widely used in the removal of TCs from water [8,12,13,14]. Adsorbent materials currently being studied include graphene oxide (GO) [15], magnetite [9,12,13], goethite [16], birnessite [17], and chitosan [18]. GO is a two-dimensional material consisting of a single layer of carbon atoms arranged in six-membered rings and is one of the thinnest known 2-D materials [19]. GO has unique physical and chemical properties and has become a major research focus. The oxygen-containing groups on the surface of GO can be used as an adsorbent for the adsorption, extraction and separation of antibiotics, thus rendering GO of great significance for environmental protection [20].
Because of the small particle size and hydrophilic groups on the surface, GO-based adsorbent materials can be easily dispersed in water [19]. After completing the adsorption process, the material needs to be separated from the aqueous solution by filtration or centrifugation [21]. These separation methods have a high cost, require complex...