수환경에서 중금속 및 비스페놀 A 제거를 위한 생물 기반 소재의 응용

Abstract

Various kinds of toxic pollutants are being discharged into water environment with rapid development of society. The heavy metals and endocrine disrupters among them are representative pollutants causing severe concerns to human health. Biological methods to handle those issues have widely been investigated due to its low capital and operation cost, non-toxicity of materials, availability to materials, relatively simple equipment and operation required, and so on. Various biological materials and processes have been developed until now but, are still challenged for its weaknesses such as operational variability, non-selective removal to specific target component, and low efficiency under harsh condition. In this study, two kinds of bio-based materials are applied for the removal of target pollutants (heavy metals and bisphenol A (BPA)). The first material is the enzymatically-synthesized polymeric one for the removal of heavy metals in non-selective adsorptive way. The other material is the peptide fused with magnetic core and is applied for the removal of lead and BPA in selective adsorptive way. Unlike chemical reactions, enzymatic reactions require no toxic oxidants for the polymerizations and do not produce harmful by-products. The enzymatic reaction replacing corresponding chemical reaction was applied to synthesize the polymer via environmentally friendly synthetic route. The polymer of m-phenylenediamine (poly(m-PDA)), synthesized by mild laccase-catalysis in an aqueous buffer, was investigated for the adsorption of several heavy metal ions including Pb2+, Cu2+, Co2+, and Cr3+. The adsorption isotherms of the four heavy metal ions on poly(m-PDA) were well described by Langmuir equation. Poly(m-PDA) shows high maximum adsorption capacities (qmax) for Cu2+, Pb2+, and Cr3+,with the values of 556, 526, and 476 μmol·g-1, respectively. Thus, the synthesis of polymeric absorbents to remove heavy metals can be accomplished through simple and environmentally friendly enzymatic methods. A 7-mer lead-binding peptide (TNTLSNN) was covalently bonded onto the surface of magnetic bead which is a reusable adsorbent to remove Pb2+ from water. Compared to the bare bead without the linked peptides (29.82 μmol·g-1), the peptide-linked adsorbent showed 9 times higher removal capacity of lead (246.05 μmol·g-1). The sequence (TNTLSNN or NNSLTNT) of 7-mer peptide linked to the surface of bead did not significantly influence on whole adsorption capacity of lead. To examine the reusability of bead, the adsorbed lead was desorbed from the bead by using EDTA and then the recovered bead could be repeatedly used several times (6 cycles tested) without significant loss of adsorption capacity. A selective adsorption of lead in the presence of interfering other metals is verified with individual or combinatory use of four metal ions such as Pb2+, Ni2+, Co2+ and Cu2+, where the amount of bound Pb2+ was remarkably higher than the other metal ions. The adsorption isotherm followed Langmuir fitting well with the maximum adsorption loading (qmax) of 308.86 μmol·g-1 adsorbent. A heptapeptide with specific affinity to BPA, LysSerLeuGluAsnSerTyr (KSLENSY) was covalently bonded onto the surface of magnetic bead. Compared to the bare bead without the linked peptides (8.6 μmol·g-1), the peptide-linked adsorbent showed 9 times higher removal capacity of BPA (37.6 μmol·g-1). BPA-binding peptide had higher selectivity toward BPA compared with structural analogs of BPA such as bisphenol F and bisphenol S. Around neutral pH, the adsorption capacity was maximum since the neutral form of BPA was favourable for the adsorption onto peptide. The magnetic-core bead was used in this study to separate the bead after use and reuse for the next round of adsorption. Various chemicals was tested to regenerate the bead used and almost 100% of regeneration efficiency was achieved by using methanol/acetic acid mixture. The adsorption capacities of BPA after sixth cycle maintained more than 87% of initial capacity Finally, the degradation of BPA was investigated by using peptide-mineralized photocatalytic TiO2 particle. Environmentally benign mineralization of TiO2 particle was induced by using the polystyrene (PS) bead fused with mineralization-inducing peptide. The peptide (CHKKPSKSC) with specific affinity to TiO2 was used in this studied. The synthesized TiO2 showed a BPA degradation rate of 86.3%.