Sorption Of Organic Contaminants To Typical Environmental Micro-interfaces And Their Mechanisms

Soil is a solid-liquid-gas-organism complex with a heterogeneous composition and has many nanoparticles, micropores, voids, or channels. Natural nanoparticles have a very powerful sorption capacity and catalytic functionality. It can produce a nano-effect by formation of "nano-reaction field", and a number of very important chemical reactions in soil take place at this kind of interface. Environmental interface, especially the mobility and transformation of organic contaminants taking place at the environmental micro-interface, is one of the most active researches in micro-environment field and has aroused great concerns of researchers from home and abroad. There are a lot of environmental micro-interfaces in soil, such as clay minerals, soil organic matter and black carbon (soot and charcoal). They all play a key role in the mobility, transformation, degradation and ecological effects of organic pollutants in the environment.The sources, structural characteristics and characterization methods of two natural nanoparticles, i.e., clay minerals and soot, were introduced. Sorption of organic pollutants to typical environmental micro-interface and their mechanisms were reviewed. In this dissertation, several typical environmental micro-interfaces, including clay minerals, black carbon (soot and charcoal) and carbon nanotubes (CNTs) were choosen. The nano-structure of bentonite interlayer in solutions with different cations were characterized using transmission electron microscopy (TEM) and in-situ X-ray diffraction (XRD) analysis. The structures and morphology of two kinds of black carbon were characterized using thermal gravimetric (TG) analysis, elemental analysis, specific surface area and pore size distribution analysis, scanning electron microscopy (SEM) and TEM. Sorption of polar and non-polar organic pollutants to different micro-interfaces and their mechanisms were investigated using batch equilibrium method. The relationship between the structure-activity effects and changes of structural characteristics of environmental micro-interfaces were discussed. The sorption capacity of the natural environmental micro-interfaces and the man-made nano-materials were compared to reveal the sorption behavior of typical environmental micro-interface. These observations will provide an important evidence and support for predicting transport and fate of organic pollutants in the environment, and give a theoretical reference to control and remediate organic polluted soil. Some innovative results were obtained as follows:(1) The structure-activity relationship for sorption of nitroaromatic compounds (NACs) to nano-interlayer of bentonite was revealed. Cetyltrimethylammonium (CTMAB) can enhance the sorption of naphthalene (nonpolar) and nitroaromatic compounds (NACs, polar) to bentonite. The sorption isotherms are practically linear (N> 0.9). This is because CTMA⁺ can transfer the hydrophilic interlayer of bentonite into hydrophobic, and form a new partition phase of CTMA⁺ in the interlayer of bentonite. Weakly hydrated cations, such as potassium and ammonium cations, can enhance the sorption of NACs to bentonite (as high as 430 times), but the sorption isotherm shapes vary for different NACs. This is because weakly hydrated cations can cause the interlayer of bentonite to dehydrate (interlayer spacing decreased from 1.88 nm to about 1.5 nm); Electron-withdrawing group (-NO₂) of NACs can complex with potassium cations or ammonium cations in the interlayer, and promote the sorption to bentonite. For m-dinitrobenzene, it can further dehydrate the interlayer of bentonite (interlayer spacing decreased to about 1.25 nm) by direct complexation with potassium cations or ammonium cations in the interlayer, while enhanced sorption of nitrobenzene to bentonite by potassium cations is achieved by indirect complexation of nitryl on nitrobenzene and potassium cation (interlayer spacing of about 1.5 nm).(2) Soot is a combustion continuum rather than one homogeneous black carbon entity, and the change of nano-structure of soot can have a great impact on sorption of organic pollutants. Sorption isotherms of organic pollutants to original soot are generally linear (N > 0.86), indicating the sorption mechanism is mainly partition. Sorption of ash-purified soot increases due to the increase of organic carbon content and surface area. Removal of native extractable organic matter (EOM) from soot enhanced adsorption and reduced partition, indicating that EOM served as a partitioning phase and simultaneously masked the adsorptive sites. Oxidative acid treatment can enhance the aromaticity of soot samples (H/C from 0.97 to 0.5), and promote the additionalÏ€-Ï€interaction of organic pollutants, especially phenanthrene with soot.(3) Sorption of organic pollutants to CNTs and various environmental micro-interfaces were compared. Sorption to CNTs follow the order of SWCNT >> 1020MWCNT > 4060MWCNT, in line with their distinct specific surface areas. Sorption mechanism for sorption of naphthalene is mainly hydrophobic interaction, while for NACs the mechanism is mainlyÏ€-Ï€interactions between NACs and CNTs. CNTs, especially SWCNT, can be a supersorbent for organic pollutants. Sorption mechanisms for soot and charcoal vary a lot, though they are both derived from burned straws. For soot, the mechanism is mainly partitioning, while adsorption dominated sorption of charcoal. Sorption of naphthalene to organobentonite 100CTMAB is greater than that of m-dinitrobenzene, while sorption of m-dinitrobenzene to "0.5 mol/L KCl+original bentonite" is greater than that of naphthalene.