Hydrogels with immobilized enzymes are increasingly applied in biocatalytic industrial processes. Here, polymer hydrogels containing 2-hydroxyethyl methacrylate (HEMA), itaconic acid (ITA), (2-((2-(ethoxycarbonyl)prop-2-en-1-yl)oxy)ethyl) phosphonic acid (ECPPA), and N,N′-diethyl-1,3-bis(acrylamido)propane (BAAP) as the cross-linker are synthesized by UV-initiated radical polymerization. Laccase from Trametes versicolor (LAC) is modified by reaction with itaconic anhydride (ITAn) yielding the LAC-immobilized monomer ITA-LAC with enhanced enzyme activity. ITA-LAC paves the way to an in situ method for enzyme immobilization. Hydrogels with HEMA, ECPPA, and BAAP with stepwise varied chemical composition and functionalization are prepared. The influence of the composition on the morphology, the swelling behavior, the mechanical stability, and the enzymatic activity is studied. The polymerization is monitored by the conversion of double bonds with in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The polymerization of HEMA is complete after 10 min of UV exposure, whereas hydrogels of HEMA/ITA/ECPPA (85/5/10) with 5 mol % cross-linker require 30 min. These hydrogels are compared with those containing ITA-LAC instead of ITA. The covalent binding of LAC is proven by ATR-FTIR spectroscopy and results in an enhanced enzyme activity. The incorporation of ECPPA induces pH-dependent swelling with an equilibrium degree of swelling of up to 6 at pH 8. Only a weak influence of temperature on the degree of swelling is found. The morphology strongly depends on the hydrogel composition. LAC-ITA hydrogels are characterized by an open morphology providing access to catalytic centers. The enzyme-immobilized hydrogels are used as granules as well as coatings on porous Al2O3 ceramic substrates as biocatalysts to convert models for organic trace compounds [bisphenol A (BPA), diclofenac, p-chlorophenol (pCP), 17α-ethinylestradiol (EED), triclosan, paracetamol, and 4-tert-octylphenol]. The highest conversion after 24 h in water is achieved for triclosan (>90%), while pCP, BPA, and EED reach a conversion between 60% and 70%. The conversions are even higher in citrate buffer.
Abstract:For the first time, commercial macroporous melamine formaldehyde foam Basotect ® (BT) was used as a basic carrier material for both adsorptive and covalent enzyme immobilization. In order to access inherent amino groups, the Basotect ® surface was pretreated with hydrochloric acid. The resulting material revealed 6 nmol of superficial amino groups per milligram Basotect ® . Different optimized strategies for tethering the laccase from Trametes versicolor and the lipase from Thermomyces lanuginosus onto the pre-treated Basotect ® surface were studied. Particularly, for covalent immobilization, two different strategies were pursued: lipase was tethered via a cross-linking method using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, and laccase was bound after functionalizing Basotect ® with hydrophilic copolymer poly(ethylene-alt-maleic anhydride) (PEMA). Prior to laccase immobilization, the PEMA coating of Basotect ® was verified by ATR-FTIR analysis. Subsequent quantification of available high-reactive PEMA anhydride moieties revealed an amount of 1028 ± 73 nmol per mg Basotect ® . The surface-bound enzyme amounts were quantified as 4.1-5.8 µg per mg Basotect ® . A theoretical surface-covered enzyme mass for the ideal case that an enzyme monolayer was immobilized onto the Basotect ® surface was calculated and compared to the amount of adsorptive and covalently bound enzymes before and after treatment with SDS. Furthermore, the enzyme activities were determined for the different immobilization approaches, and the stability during storage over time and against sodium dodecyl sulfate treatment was monitored. Additionally, PEMA-BT-bound laccase was tested for the elimination of anthropogenic micropollutant bisphenol A from contaminated water in a cost-effective and environmentally-friendly way and resulted in a degradation rate higher than 80%.
Advanced oxidation processes are the main way to remove persistent organic trace compounds from water. For these processes, heterogeneous Fenton catalysts with low iron leaching and high catalytic activity are required. Here, the preparation of such catalysts consisting of silica-supported iron oxide (Fe2O3/SiOx) embedded in thermoplastic polymers is presented. The iron oxide catalysts are prepared by a facile sol–gel procedure followed by thermal annealing (calcination). These materials are mixed in a melt compounding process with modified polypropylenes to stabilize the Fe2O3 catalytic centers and to further reduce the iron leaching. The catalytic activity of the composites is analyzed by means of the Reactive Black 5 (RB5) assay, as well as by the conversion of phenol which is used as an example of an organic trace compound. It is demonstrated that embedding of silica-supported iron oxide in modified polypropylene turns the reaction order from pseudo-first order (found for Fe2O3/SiOx catalysts), which represents a mainly homogeneous Fenton reaction, to pseudo-zeroth order in the polymer composites, indicating a mainly heterogeneous, surface-diffusion-controlled process.
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