| Biochar is considered to be a carbon-rich material produced from thermal treatment of naturally abundant biomass such as agricultural waste under oxygen-limited conditions. Biochar is often applied to soil as soil conditioner and fertilizer due to its excellent environmental properties. Due to multifunctional properties, two different types of biochars was prepared from pine sawdust and rice straw biomass to study the effects of different pyrolysis temperatures on composition and structure of biochar in combination with different analytical tools namely thermogravimetric analysis, CHN elemental analysis, Fourier Transformed Infrared Spectroscopy and specific surface area analysis. Five different organic pollutants parachlorophenol,phenol, chloramphenicol, ethinylestradiol and sulfadiazine were selected as typical antibiotic contaminants while being smaller in size to study the adsorption mechanism and structuralactivity between organic pollutants and different structures of biochar(rice straw RS and pine sawdust PS biochar with different pyrolysis temperature).Based on the adsorption isotherm, parachlorophenol was chosen as the model pollutant to explore the adsorption-transformation interface process and micro-mechanism on biochar structure by kinetic models. In order to enhance the adsorption-conversion of biochar to pollutants, biochar structural properties was optimized and modified by using metal modification and solvent cleaning methods to study the enhancement of the adsorption -transformation ability. In order to simulate the effect of biochar added to the soil on the migration and transformation of pollutants under natural conditions, the method of soil column experiment was selected to study the potential application of biochar in practical soil remediation. The thesis systematically investigate the effects of pyrolysis temperature on biochar structure, and mechanism of pollutants adsorption-transformation, with structural-activity relationship, thereby providing a theoretical base for more efficient and safe application of biochar during remediation of contaminated soils. The main conclusions and recommendations are as follows:(1) The relationships of biochar preparation temperature and surface functional groups, pore structure and persistent free radicals were proved. The result showed that with the increase of the pyrolysis temperature, polar functional groups of biochar decreased gradually, and degree of aromatization deepened gradually, with gradual increase of micropores, whilethe persistent free radicals on the surface increased initially and then finally decreased.(2) The adsorption mechanism and structure-activity relationship different pyrolysis temperature biochar (pine sawdust and rice straw, PS and RS) on ionizable organic pollutants (parachlorophenol, phenol, chloraphenicol, ethinyoestradiol,sulfadiazine) were discussed deeply. The result showed that the adsorption of parachlorophenol, phenol on biochar mainly depended on π-π electron transfer reaction,whereas chloraphenicol, ethinyoestradiol, sulfadiazine mainly depended on the electrical effect. The adsorption effect of PS biochar to organic pollutants is stronger than RS biochar for that PS biochar has more abundant voids structure and specific surface area with less mineral components.(3) The adsorption-transformation performance and influencing factors of different structures biochar on parachlorophenol were investigated. In non-free radical pathway, high-temperature PS biochar can destroy C-Cl bond by chlorine reaction.However, compared with PS biochar, RS biochar had a better adsorption-transformation performance for parachlorophenol under the action of mineral components.(4) The effects of metal ion modification (Fe3+, Al3+, Mn2+) and solvent washing(water-washing and methanol-washing) on the biochar strcture and adsorption-transformation performance were studied. The results showed that the iron-based modification significantly enhanced the PS biochar adsorption capacity and conversion capacity of organic pollutants (phenol,parachlorophenol, ethinylestradiol). However,more active sites of biochar structure exposed by removing excess ash with solvent cleaning treatment, and significantly enhanced RS biochar adsorption-transformation to contaminants. |
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