Yang-Hsin Shih

The development and application of nanomaterials to remove environmental organic pollutants

Yang-hsin Shih

Department of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan

Abstract:

Petroleum organic chemicals, persistent organic pollutants (POPs), and emerging organic contaminants (EOCs) such as toluene, diesel, pentachlorophenol (PCP), hexachlorobenzene (HCB), bisphenol A (BPA), polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA), and hexabromocyclododecane (HBCD) have gained a lot of attention. Sorption of organic contaminants in soils plays an important role in their environmental fate, especially rebound issue. By synchrotron XRD, we observed that toluene penetrates into clay interlayers under a dry condition ¹. However, only few resides after desorption of organic compounds from soil components indicated that soil ingredients which do not mainly contribute the slow desorption. For the environmental technology, we developed several nanomaterials to effectively degrade these POPs and some emerging organic contaminants. Nanoscale zerovalent iron (NZVI) can quickly remove PBDEs by debromination and adsorption ². The presence of reduced forms of iron were observed on NZVIs before and after reactions by XAS analysis. Pd/Fe NPs can degrade PCP effectively. For common cations, the enhancement of Cu²⁺ and Ni²⁺ ions result from the presence of reduced forms of copper and nickel on Pd/Fe surfaces by XANES analysis ³. Furthermore, a more effective removal of PCP with Pd/Fe NPs in oxic than anoxic by concurrent oxidation and reduction. We developed Ni/Fe NPs since Ni doping enhanced PCP removal and it is cheaper than Pd. Among several surfactants, cetyl trimethylammonium bromide (CTAB) markedly enhanced the removal of PCP by Ni/Fe ⁴. From removal kinetics, sorption of PCP onto Ni/Fe surfaces with CTAB increased when compared to that without CTAB. The small particle size of Ni/Fe-CTAB and the electrostatic interaction between an electronegative phenolate group of PCP and the electropositive Ni/Fe-CTAB increased sorption of PCP onto Ni/Fe surfaces by CTAB and then accelerated the reduction of PCP. In addition, with CTAB, the observed bulky and soft surface of Ni/Fe NPs allows enhanced electron transfer from the zerovalent iron core. The removal mechanism of PCP is dechlorination for Ni/Fe-CTAB but, for bare Ni/Fe, adsorption is mainly responsible for the removal. Carboxymethylcellulose (CMC) coating can stabilize Ni/Fe NPs, increase their adsorption of HBCD, provide buffer pH capacity, and overcome common inhibition effects of anions ⁵.To avoid the metal use, short-chain organic acids were evaluated on the degradation of PCP by NZVI. oxalic acid (OA) enhanced the PCP degradation by NZVI ⁶. The formation of oxalate-iron complexes out of NZVI particles was observed, indicating that OA could strongly complex with ferrous ions produced during PCP dechlorination and decrease the formation of ferrous (hydro)oxides, which would precipitate on the NZVI surface. OA led to the highest efficiency of PCP dechlorination by NZVI due to its strong complexating and pH buffering properties. This green treatment strategy, without doping secondary metals, can facilitate the decontamination of POPs. We also synthesized TiO₂ nanotubes to effectively degrade antibiotic sulfamethoxazole by photoelectrocatalysis ⁷. Recently, graphitic carbon nitride (g-C₃N₄) with Fe/Cu NPs, graphene quantum dots (GQDs)/g-C₃N₄ nanocomposites we synthesized provide greener materials to degrade organic pollutants ⁸. On the other hand, microbial degradation of HBCD was studied through some strains and in soil through genomics, transcriptomics, and metagenomics ⁹. Some possible functional enzymes and pathways are reported. These functional enzymes which can degrade EOCs well in the environment should be studied by some synchrotron tools in the future.

Keywords - nanoscale zerovalent iron (NZVI); carboxymethylcellulose (CMC); cetyl trimethylammonium bromide (CTAB); oxalic acid (OA); graphitic carbon nitride (g-C₃N₄).

References:

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