High Performance Magnetically Separable TiO2-CN Nanocomposite with Enhanced Photocatalytic Activity towards the Cefixime Trihydrate Degradation under Visible Light Irradiation

Abstract

Antibiotics considered as growing pollutants that required special attention owing to their continuous consumption in human and veterinary medicine. These materials come into the environment from different sources comprising hospitals sewage, pharmaceutical industries wastewater, human domestic effluents and so on. Since most of the antibiotics have low biodegradability and are difficult to be removed by conventional wastewater treatments, their residual even at very low concentrations is a serious risk for the human health and aquatic organisms in the coming years [1]. Therefore, the development of effectual techniques for the mineralization of these pollutants has become a mandatory issue. Various physical and chemical methodologies have been reported for the elimination of antibiotics from wastewater, comprising the ion exchange processes, reverse osmosis, coagulation-flotation, adsorption, membrane filtration, different advanced oxidation processes (AOPs), etc. [2]. Among these methods, AOPs are the most superior due to the capability of complete degradation of contaminants compared with the other mentioned techniques in which the pollutants just transferred from one phase to another and the entire elimination of them does not occur. As one of the novels AOPs, the heterogeneous photocatalysis which was developed in the 1970s, has attracted a great deal of attention in recent years [3]. In this line, semiconductor-based heterogeneous photocatalysis is the most promising method for the green and facile elimination of antibiotics from wastewater. The principal mechanism of this technique relies on releasing free hydroxyl radicals that are capable to convert most of the water pollutants to biodegradable minerals. Cefixime, which is a third-generation cephalosporin, belongs to the class of β-lactam antibiotics. The low bioavailability (40-50%) of this antibiotic limited its adsorption by the gastrointestinal tract, leads to serious environmental damages. It is effective against both gram-positive and gram-negative aerobic bacteria. This antibiotic can be used in the treatment of a wide range of bacterial infectious diseases such as respiratory, skin, bone or joint and urinary tract infections [4]. It may also be utilized to prevent infection in people undergoing severe surgical operations. To the best of our knowledge, the photocatalytic degradation of cefixime trihydrate is limited to only a few methods [4]. These procedures suffer from one or more of the following difficulties such as using large amounts of photocatalyst, loss of the photocatalyst during recycling, long periods of time, low degradation efficiency, and most importantly the employment of detrimental light sources and complex photoreactors. Thus, the necessity of promoting more proficient and durable photocatalytic systems for the degradation of cefixime trihydrate is evident. In this study, a high performance magnetically separable TiO2-CN nanocomposite is fabricated. After its full characterization, the photocatalyst was effectually utilized towards the cefixime trihydrate degradation under visible light illumination. Moreover, the central composite design (CCD) along with response surface methodology (RSM) was carried out for modeling and optimizing the photo-degradation protocol. The influence of the operational parameters comprising the initial cefixime trihydrate amount (15–25 mg/L), photocatalyst concentration (0.02–0.06 g/L), pH (3–8), light intensity (6-12 W/m2) and the contact time (60–120 min) on the cefixime trihydrate degradation efficiency is investigated. The photocatalyst was separated simply by the aid of an external magnet and reused for seven times without noticeable loss of efficiency. Also, the first-order kinetics derived from the Langmuir–Hinshelwood (L-H) model well fits the experimental data.