| dc.description.abstract | The current remediation technologies are not effective for the simultaneous removal of both organic and inorganic contaminants from the contaminated sites due to their different characteristics. In two decades ago, we had used a high molecular organic compound (HDTMA) to modify soil to enhance the SOM content, which increases the ability of organic compounds partitioning to the soil.
One of the studies highlighted the preparation of adsorbents for both organic and inorganic pollutants by modifying sodium montmorillonite using different functionalized modifiers. The effects of different functional groups, including –SH，–S，–NH2，–COOH, of the modifier on the sorption are discussed. Since the long hydrocarbon chains, the water solubility of modifiers is restricted, the materials are prepared by cation exchanging with alkylammonium ions, and protonated of amine group in alkyl polyamine halide to increases water solubility. In addition, we were exploring the influence of different processing methods, via cation exchange and grafting, on the structure, physical and chemical characteristics and adsorption ability of modified montmorillonites. The adsorption behavior of the modified montmorillonites for both inorganic and organic pollutants was also discussed based on the structural and surface properties. The successful grafting of modifiers onto the interlayer was confirmed by spectral analysis. However, adsorption was mainly controlled not only by surface area but also by the nature and surface charge of the modifiers. Based on the experimental results, the soil modifier significant improved the sorption characteristics and, among two metal ions, Cu2+ showed enhanced adsorption. The uptake phenomenon was influenced by various combined factors such as the nature, surface charge and surface area of the modified soils.
Due to small interlamellar spacing of the hydrophilic layered silicate surface of montmorillonite, the intercalated species are capable of increasing the interlayer spacing as pillars. According to the above principle, we present another method to modify soil using the specific modifier. The modified pillared soil could adsorb both the organic contaminants and the heavy metals simultaneously. The effect of different modifiers with different chain lengths on the d-spacing of montmorillonite was studied and discussed in detail. XRD experiments were carried out and it was found that the modifier with a longer carbon chain comparatively enhanced the interlamellar spacing than that of other modifiers. The influence of HCl, the amount of modifiers and temperature on the interlayer structure was also discussed. In addition, the alkyl chain on the soil surface can be regarded as a partition medium.
Although, quaternary ammonium salt can effectively improve the organic matter content of the soil and recent researches on amine modified soil showed that under certain conditions, they can be used as dual adsorbents for the removal of both organic and inorganic pollutants, but the removal of nonionic organic compounds (NOCs) is not effective. Thus the final study was to propose a new concept to use clay composite materials in which polymers are intercalated into interlayer of clay. Such clay composite can possess positive and negative charges and thus can act as versatile adsorbents for both organic and inorganic pollutants (cation and anion).
Finally, this study chooses a methyl methacylate (M), methacrylic acid (A) and dimethylaminoethyl methacrylate (D) to synthesize triblock polymers. The triblock copolymers successfully synthesized by RAFT polymerization method were confirmed by nuclear magnetic resonance (NMR) spectral analysis. In acidic conditions, the dimethylaminoethyl methacrylate is protonated (positively charged) which can be used for anionic pollutants, and in alkaline solution, methacrylic acid can possess negative charge which can adsorb inorganic heavy metal pollutants. Furthermore, methyl methacylate is considered to greatly enhance the distribution of NOCs in the hydrophobic environment. Not only sorption of different pollutants was carried out using these clay synthesized composite materials, but also the effect of pH and other parameters were studied. A systematic study was carried out in depth in order to understand the mechanism and various factors that can affect the adsorption phenomenon. Uptake of both organic (benzene; toluene; ethylbenzene; and xylene; in brief BTEX) and inorganic (Cu2+, Zn2+ and Cr2O7 2-) pollutants were explored and highlighted in the final study. The observed log Koc values for the distribution of organic pollutants onto clay are significantly high in this study. In all cases the adsorption of Cu2+ was comparatively larger than that of Zn2+. The affinity of modified clay for Cr2O72- is increased owing to the occurrence of pH value decreased. The obtained log Koc and log Kom values of BTEX in this study for modified montmorillonite are comparatively larger than those of unmodified montmorillonite or natural soil. The self-synthesized triblock copolymers were embedded in the pillared layered clays, that displayed enhanced adsorption of both organic and inorganic pollutants and hence it was concluded as a great potential candidate.
| en_US |