Polymers for separation and adsorption
Polymers can be used as sorbents in various separation processes (chromatography, solid-phase extraction, membrane separations), as well as wastewater treatement. Amongst them, superabsorbent polymers and molecularly imprinted polymers (MIPs) stand out.
-
Molecularly imprinted polymers (MIPs) are synthetic materials with predetermined selectivity for a particular analyte or group of structure-linked chemicals which make them an ideal separation component [1].
-
Superabsorbent polymer materials (SAPs) are cross-linked polymer networks constituted by water-soluble building blocks. SAPs are generally composed of ionic monomers and are characterized by a low cross-linking density, which results in a large fluid uptake capacity (up to 1000 times their own weight) [2].
​
BikiarisLab started working on polymers for adsorption in collaboration with Assoc. Professor George Kyzas and Prof. Nikolaos Lazaridis, with focus on chitosan and its derivatives for removal of toxic metals and dyes from wastewater. This long and fruitful collaboration yielded numerous publications [3][4][5][6] and allowed the expansion of the types of polymers used and their applications. Various MIPs [7] were synthesized and studied for the selective separation of dyes [8][9].
​
​
​
Carbohydrate Polymers Volume 91, Issue 1, 2013, Pages 198-208
​
Two types of novel molecularly imprinted polymers (MIPs) were prepared, for toxic and carcinogenic dyes adsorption. Substrates of the polymeric matrix of the two MIPs were β-cyclodextrin and chitosan. The conditions in the polymerization/imprinting stage and in the rebinding/adsorption step were optimized. The effect of a range of parameters (polymer, cross-linker, and initiator concentrations, reaction time and pH) on the selectivity and adsorption capacity of the dye-MIPs were investigated. Their dye rebinding properties were demonstrated by equilibrium batch experiments (fitting with Freundlich model) and their kinetic rates were exported by the pseudo-first order model. Additionally, a thermodynamic evaluation was carried out through the determination of enthalpy, entropy, and free energy. The selectivity of MIPs was elucidated by their different rebinding capabilities in a trichromatic mixture (composed of related structurally dyes). Regeneration/reuse of the dye-loaded polymers was evaluated via sequential adsorption–desorption cycles.
As the interest for polymer adsorbents in wastewater treatment expanded in pharmaceutical contaminants, BikiarisLab started their close collaboration with Dr. Dimitra Lambropoulou, Assoc. Professor on Environmental Chemistry in the Environmental Pollution Control Laboratory, Department of Chemistry, Aristotle University of Thessaloniki (AUTH), one of the pioneers in the development of microextraction techniques and among the first scientists in Greece in the development of solid phase microextraction (SPME). Different adsorbents were tested for removing pharmaceuticals from polluted water matrices, including modified chitosan [10][11][12], modified carrageenan [13][14], and MIPs for SPME applications [15][16]. Part of this work was co-financed by the European Union (European Social Fund — ESF) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework (NSRF) — Research Funding Program “Excellence II (Aristeia II)”, Research Grant No 4199 with the title "Advanced Microextraction Approaches Based on Novel nano- Polymers to Measure Pharmaceuticals, Personal Care Products (PPCPs) and their Transformation Products (TPs) in the Aquatic Environment", which was completed in 2015.
Analytica Chimica Acta Volume 913, 2016, Pages 63-75
​
​
​
In this study, a molecularly imprinted solid-phase microextraction fiber (MIP-SPMEf) was synthesized and applied for the selective removal and extraction of the antiviral drug, abacavir (ABA). Morphology and structure characterization of fibers were performed by scanning electron microscopy and Fourier transform infrared spectra, respectively. The effects on the adsorption behavior of the process parameters were studied and the equilibrium data were fitted by the Langmuir, Freundlich and Langmuir-Freundlich models. The maximum adsorption capability (Qmax) was determined by Langmuir- Freundlich model and was 149 mg/g for MIP-SPMEf. In the next step, SPME methodology followed by liquid desorption and liquid chromatography with mass spectrometry (LC/MS) has been developed and evaluated for the determination of the target compound in environmental and biological matrices (surface waters, wastewaters and urine). Parameters that could influence SPME efficiency were investigated. Then, optimization of stirring speed, extraction time and salt content was carried out by using a central composite design (CCD) and response surface methodology (RSM). A quadratic model between dependent and independent variables was built. Under the optimum conditions (extraction time 40 min, stirring rate 650 rpm and salt content 0.3% NaCl w/v) the validated method presented a high sensitivity and selectivity with LODs and LOQs in the range of 10.1–13.6 and 33.3–43.9 ng/L, respectively. The developed method was successfully applied to the analysis of ABA in real samples. The percentage extraction efficiency ranged from 88 to 99% revealing good accuracy and absence of matrix effects.
The removal of pharmaceutic pollutants from wastewater is also being explored with photocatalysis. Titanium dioxide has been reported as one of the most efficient photocatalysts, mostly because of its low cost, the high chemical, photo, and biological stability and high catalytic activity. However, when applied to wastewater in the form of powder, it suffers from the following drawbacks: Low light utilization efficiency of suspended photocatalyst, due to the attenuation loss suffered by light rays; requirement of post-treatment recovery, that is both time and money consuming, and also leads to the loss of catalyst and possible cause of un-favorable human health problems associated with the mobility of the powder form. In order to overcome all the aforementioned drawbacks, continuous efforts are being made to support TiO2 on various substrates. Polymer support appears to be highly suitable for TiO2 due to a series of advantages. Firstly, polymers are innoxious materials, chemically inert and mechanically stable with high durability. BikiarisLab has developed polymer-supported TiO2 photocatalysts for the removal of antibiotics [17] and Anti-inflammatory/Analgesic Drugs [18].
​
Currently, BikiarisLab participates in the research project "Development of Monitoring and Removal strategies of Emerging Micropollutants in wastewater - MOREM" (PI Asoc Prof Dimitra Lambropoulou). The ultimate goal of the project is to develop an integration methodology framework combining novel sampling, monitoring and removal strategies in order to manage and remove emerging micropollutants such as Pharmaceuticals, Personal Care Products (PPCPs) and microplastics in wastewaters. The project is divided into three phases; the first phase is the monitoring of the PPCPs in a municipal wastewater treatment plant by using novel Super-Adsorbent Materials (SAMs) and Molecularly Imprinted Polymers (MIPs) with remarkable properties, the second will focus on removal approaches of PPCPs by using AOPs and the third is focused on sampling and monitoring of microplastics in wastewaters.