Abstract
A molecularly imprinted polymer (MIP) that is selective to ketoprofen was synthesized and applied in the adsorption of the target compound from water. The MIP was synthesized using a bulk polymerization method at high temperatures (60–80°C), where ketoprofen, 2-vinylpyridine, ethylene glycol dimethacrylate, toluene and 1,1´-azobis(cyclohexanecarbonitrile) were used as template, functional monomer, cross-linker, porogen and initiator, respectively. Non-imprinted polymer (NIP) was synthesized similarly to the MIP but in the absence of ketoprofen. From molecular dynamics simulation, the nature of interactions that occurred between the template and the functional monomer were found to be based on hydrogen bonding. This was confirmed experimentally, where a high extraction efficiency of ≥ 90% was obtained at acidic conditions (pH 5) due to the protonation of ketoprofen. A contact time of 45 min was sufficient for the maximum adsorption of ketoprofen from 10 mL spiked water using 8 mg of the adsorbent. MIP showed greater selectivity than NIP by achieving a relative selectivity coefficient of 7.7 towards ketoprofen in the presence of structurally related pharmaceuticals. Furthermore, the order of sorption onto the MIPs from water was ketoprofen > fenoprofen > gemfibrozil. From a modelling perspective, the Langmuir adsorption isotherm and pseudo-second-order kinetic model gave the best fit, with maximum adsorption capacity of 8.24 mg·g−1 and sorption rate constant of 0.25 mg·g−1·min−1 for MIP. This was translated to chemisorption of ketoprofen onto the homogeneous MIP binding sites. This work demonstrated the great potential of MIP in selective recognition of ketoprofen from wastewater relative to closely related compounds.
Highlights
The presence of pharmaceutical compounds in surface water and wastewater has been known since the 1960s (Stumm-Zollinger and Fair, 1965)
(K’) of 7.7 for the molecularly imprinted polymer (MIP) was observed. This indicated that the selectivity is 8 and 2 times greater for ketoprofen in the presence of fenoprofen and gemfibrozil, respectively, compared to the Non-imprinted polymer (NIP). These results indicated that the MIP was highly selective for ketoprofen recognition, relative to the NIP, in aqueous samples which resulted in a low selectivity coefficient (Mata et al, 2014)
Linear plots were obtained for both Langmuir and Freundlich isotherms (Fig. A3); the larger R2 for MIP (Table 4) in the Langmuir model indicates that the monolayer adsorption of ketoprofen at homogeneous binding sites was dominant
Summary
The presence of pharmaceutical compounds in surface water and wastewater has been known since the 1960s (Stumm-Zollinger and Fair, 1965). The sources of pharmaceuticals in surface water include wastewater treatment plants (WWTPs), households, effluent from pharmaceutical industries, and health service centres (Bayen et al, 2013; Félix–Cañedo et al, Kyzas et al, 2015; Santos et al, 2005). Pharmaceuticals such as ketoprofen are transported from wastewater to other water matrices. This is due to water being a good carrying medium for polar and semi-polar compounds (Pavlović et al, 2007). Ketoprofen is a well-known pollutant in water matrices
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