Synthesis And Characteristics Of Clay Mineral-Biochar Composites And Their Applications In Organic Contaminants Removal From Water

Various anthropogenic activities like urbanization and industrialization have caused increasingly serious soil and water contamination,especially the release of wastewater containing inorganic and organic contaminants,has posed a serious threat to soil,water,and the environment.Hence,it is crucial to develop technologies that can efficiently remediate toxic contaminants from wastewater.At present,among a number of physical,chemical,and biological remediation techniques,adsorption through biochar（BC）is considered as an effective technique for the removal of organic contaminants such as antibiotics and azodyes from water.Therefore,it is of great significance to study the interaction mechanisms of BC and its composites in environmental remediation.To improve the removal efficiencies of BC,various physical and chemical modification methods like adding clay and clay minerals during biomass pyrolysis can be useful in enhancing char surface area,adsorption active site,and adsorption efficiency.In the thesis,different types of clay minerals were applied to produce BC clay mineral composites.The chemistry involved in the preparation process and the physiochemical properties of the composites were investigated.In addition,the adsorption mechanisms of BC clay mineral composites in the removal process of organic contaminants including antibiotics and azodyes were revealed.In this thesis,BC clay mineral composites were produced from various feedstocks and clay minerals with different activation methods.X-ray diffraction（XRD）,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDS）,BrunelEmmett Taylor（BET）,electron paramagnetic resonance（EPR）,Raman spectroscopy（Raman）,X-ray photoelectron spectroscopy（XPS）,Fourier Transform infrared spectroscopy（FTIR）and other characterization techniques were used to characterize the physicochemical properties of modified BC clay mineral composites.As a result,the production chemistry and activation mechanisms during the process of composites production were elucidated.And the removal efficiency of antibiotics and azodyes by BC-clay mineral composites was experimentally studied,with the explanation of the removal mechanisms.The main results of this study are as follows:1.Pristine rice husk BC,CO₂-activated rice husk BC,rice husk BC modified with montmorillonite（MMT）and CO₂-activated rice husk BC-MMT were prepared at two different pyrolysis temperatures（350 and 650℃）,and the removal effects of ciprofloxacin（CPX）in wastewater of the eight composites were compared.The results showed the maximum adsorption(50.32 mg g^-1)of CPX was obtained by CO₂-activated BC-MMT composite prepared at 350℃,which was almost two times higher than the pristine BC at neutral pH and 40℃.The study revealed that the mechanisms involved for the removal of CPX were electrostatic attraction,cation exchange,pore-filling effect,and π-π interactions.2.Pristine rice husk BC,CO₂-activated rice husk BC,rice husk BC-MMT and CO₂-activated rice husk BC-MMT were prepared at the pyrolysis temperature of 500℃,and the removal effect of the four carbon composites on azithromycin（AZT）were compared.The results showed that the surface functional groups,surface area and porosity of CO₂-activated BC-MMT composite were significantly improved,with the maximum adsorption capacity for AZT removal.The study indicated that the mechanisms involved for the removal of AZT by CO₂-activated BC-MMT composite were the electrostatic interaction,hydrogen bonding and electron donor-acceptor interactions.3.At three different temperatures（350,500 and 650℃）,kaolin,bentonite,and alkali activating agent potassium carbonate（K2CO3）was separately co-pyrolyzed with sewage sludge feedstock,nine types of composites（kaolin BC composites,bentonite composites and potassium carbonate modified composites）and three kinds of sludge BCs were prepared.The removal properties and mechanisms of the twelve materials for anionic dye reactive black-5（RB-5）were compared and studied.It was found that all the prepared materials were of advanced surface structure and removal efficiency for RB-5,but the K2CO3 modified BC（650℃）possessed the best adsorption capacity for RB-5,with the maximum adsorption capacity of 30.33 mg g^-1.