Study On Preparation Of Molecular Imprinted Particles And Their Performance For Norfloxacin Removal In Water

Norfloxacin is one kind of typical Pharmaceutical and Personal Care Products (PPCPs), which has been detected frequently in wastewater and surface water. Because of its antibacterial property, norfloxacin, which is even in a low concentration, can raise potential but also great threat to the non-target creatures including humans. The removal performances of the common-used water and wastewater treatment technologies tend to be influenced by natural organic matters in waterbody, and thus have poor and unstable effectiveness for norfloxacin removal. In our research, molecularly imprinted technology was adopted to prepare the molecularly imprinted adsorbent. The adsorption performance for norfloxacin and reusability of this adsorbent were evaluated and analyzed. We hope that it could offer us a novel idea and solution for norfloxacin removal from aquatic environment.In our work, orthogonal experiment was adopted to determine the optimum preparation condition and the molecularly imprinted particles (MIPs) were prepared under optimal condition. The physicochemical characteristics of the materials have been characterized. It has been found that the MIPs owned a greater surface area, average particles size, hole volume and same crystal form compared with P25, which make them own preferable adsorption performance as well as photocatalytic ability.Furthermore, the optimal absorbent dosage, adsorption kinetics, adsorption isotherm, thermodynamic parameters, the effect of humic acid, pH values and inorganic ions on adsorption performance were analyzed and the results were compared between the MIPs, the non-imprinted particles (NIPs) and P25nanoparticles. Moreover, the performances of the MIP, the NIPs and P25were evaluated in single, binary, ternary, quaternary and quinary adsorption system. It has been found that the adsorption of norfloxacin onto the MIPs, the NIPs and P25followed pseudo-second-order and Langmuir model. The adsorption rate constant, the maximum adsorption capacity, Langmuir constant were0.49g·mg-1·min-1,2.99mg·g-1and2.4L·mg-1, respectively. The existence of humic acid had positive effect on adsorption by MIPs, while it had adverse effect when using the NIPs and P25as the adsorbents. The adsorption performance of the adsorbents were better in the neutral conditions than in acidic and alkaline conditions. The existence of inorganic ions had certain influences on the adsorption performance. The plus two and plus three charged ions had obvious negative effect on adsorption while anion had no significant impact on adsorption performance. The functional group might be the main factor that influenced the adsorption selectivity. Molecules, which had same functional group with norfloxacin could be adsorbed onto the adsorbents via hydrogen bond.Besides, the reuse reliability of the MIPs by photodegradation regeneration was studied. The degradation kinetics, products and the effect of pH value, dosage of MIPs, humic acid, water quality, and concentration of norfloxacin on regeneration process were tested. The MIPs were proved to be effectively regenerated by photodegradation. During the photodegradation reaction, some norfloxacin molecules were firstly oxidized and be added by aldehydes or hydroxide radicals, and some were degraded into smaller molecules. The reaction was influenced by pH value, dosage of the MIPs, humic acid, water quality and concentration of norfloxacin. However, these influences were not strong under some certain ranges, which means norfloxacin could be totally degraded and the MIPs could be consequently regenerated in100min, when the pH value of the solution was in neutral range. The MIPs could be regenerated under UV-irradiation at least11times without reducing the removal efficiency.In addition, molecular simulation was adopted to demonstrate and explain the adsorption selectivity of the MIPs towards target molecules. The binding mechanisms and characters of the MIPs towards norfloxacin were studied through molecular simulation method. It was found that there were two kinds of binding sites, namely the hydrogen bond between the oxygen atom of MIPs and hydroxide radical or carboxyl of norfloxacin. The energy changes during the adsorption reaction of norfloxacin and ciprofloxacin onto the MIPs were less than those of bisphenol A, tonalid, carbamazepine and phenol, which led to a better adsorption performance of the MIPs towards norfloxacin and ciprofloxacin. The adsorption selectivity could be explained from this perspective.