In recent years, the production and consumption of antibiotics have been increased all over the world, while their potential adverse effects on ecology and human health have attracted more attention. A literature research showed that 110 antibiotics have been detected in China’s environment, most of these were in aquatic environments (Huang et al. 2020). Through cluster analysis, seven dominant antibiotics, including norfloxacin, can be discovered in almost all environmental compartments with concentrations up to several micrograms per liter. In some bodies of water in European countries, such as wastewater, surface water, groundwater and drinking water, quinolones were the most frequently detected antibiotics (Carvalho and Santos 2016). These phenomena indicated that quinolone antibiotics were more likely to accumulate in the environment and had strong persistence (Xi et al. 2019). Norfloxacin is a kind of fluoroquinolones drug with stable chemical structure and poor biodegradability. However, traditional sewage treatment technologies are not enough to remove norfloxacin effectively because of its special properties such as low concentration and high bio-toxicity (de Souza Santos et al. 2014). The main migration pathways of norfloxacin are the discharge of livestock wastewater, effluent and sludge into surface water, groundwater and soil, respectively (Huang et al. 2020). Therefore, it is urgent to develop the effective technology for norfloxacin removal from drinking water and wastewater.
Although antibiotics such as norfloxacin are ubiquitous in the environment, their concentration is lower than that of other conventional organics. Molecularly imprinted polymers (MIP) can selectively adsorb trace pollutants in water environment (BelBruno 2019), which is extremely beneficial for the removal of norfloxacin with low concentration and high toxicity. Tan et al. (2013) synthesized ofloxacin imprinted polymers on the surface of mesoporous carbon nanoparticles to prove the feasibility of MIP to remove fluoroquinolone antibiotics from seawater. MIP had high selectivity and affinity for template molecules, for they contained a large number of “tailor-made” binding sites (Shen et al. 2012). Similarly, fluoroquinolone imprinted polymers had also been developed for the extraction and detection of relevant antibiotics in actual water samples (Barahona et al. 2019). However, such imprinted materials cannot degrade the adsorbed pollutants, resulting in poor regeneration performance of the polymers, while elution may well cause environmental pollution.
Photocatalysis reaction can effectively degrade organic pollutants (Dong et al. 2015). The use of photocatalysis to remove pollutants adsorbed on MIP is a new technology (Sajini et al. 2019). The degradation of the target adsorbent on the MIP surface allows the materials to be reused. Due to the selective adsorption of MIP, they exhibit better photocatalytic activity to the target material. Some representative estrogenic chemicals could be selectively and rapidly removed from secondary effluents of municipal wastewater treatment plants using photocatalyst prepared by surface molecularly imprinted TiO2 nanotubes (Zhang et al. 2013). Compared with organic imprinting, the synthetic method of inorganic imprinting nano TiO2 layer on microspheres was demonstrated higher catalytic efficiency for the degradation of bisphenol A under ultraviolet light (Ye et al. 2019). A TiO2-based imprinted material showed outstanding photocatalytic in-situ regeneration performance, after eleven regeneration cycles, the adsorption and degradation removal efficiency of MIP to norfloxacin did not decrease significantly (Wei et al. 2018). In addition, some imprinted polymers that can degrade template molecules in visible light had also been prepared (Du et al. 2020), but their degradation efficiency was not as outstanding as that under ultraviolet light. However, the imprinted photocatalytic materials listed above are difficult to separate from the solution. The material must be centrifuged from the decontaminated water to achieve reuse, whereas the recovery ratio is low.
Nowadays, there have been many researches to fix powdered materials on various substrates (Shan et al. 2010). For photocatalytic materials, the most common is the glass substrate (Pestana et al. 2015). However, material immobilization would reduce the exposure area of the catalyst, and the loaded materials might be lost due to the continuous scouring and friction of the water flow (Jiang et al. 2019). Magnetic separation technology is different from immobilization technology, which has the characteristics of environmental protection and high efficiency. The synthesized material has its own magnetism, which can separate from the solution by applying an external magnetic field (Wang et al. 2015). The magnetic molecularly imprinted composite material prepared by cross-linking chitosan and γ-Fe2O3 particles showed effective norfloxacin adsorption performance when mixing with other organic matter in the effluent of the actual sewage treatment plant (Wu et al. 2016). Heterojunction of magnetic core CuFe2O4 and photocatalyst g-C3N4 improved the separation efficiency of photoinduced electron-hole pairs (Yao et al. 2015). More experiments showed the degradation mechanism of magnetic nano-photocatalyst was similar to that of single photocatalyst (Kumar et al. 2019). It can be seen that magnetic separation technology combined with molecular imprinting and photocatalysis technology has good development prospects.
In this paper, we synthesized magnetic molecularly imprinted polymers with specific recognition ability for norfloxacin and photocatalytic in-situ regeneration. Magnetic cores, TiO2 coating and surface molecular imprinting modification were adopted to realize the photocatalytic regeneration and magnetic separation recovery. Based on previous research about the adsorption performance, we have reported the characterization and selective adsorption properties of the materials towards norfloxacin (Fang et al. 2021). However, the degradation efficiency of target pollutants and the regeneration of MMIP still need to be investigated. Here, the kinetics of photocatalytic degradation was studied, and the influences of different environmental media factors on the photocatalytic degradation performance of the material were systematically explored. Besides, the products, pathways and mineralization of photocatalytic reactions were further analyzed to evaluate the security and sustainability of the materials.