Biochar Sorption To Carbamazepine And Bisphenol A Through Micropores As Affected By Chemical Modification

Biochar is a solid carbon-rich material that is produced by the pyrolysis of biomass in limited or no oxygen condition.Biochar has widely attracted attention due to its effective application as a soil amendment for carbon sequestration,fertility improvement,as well as contamination immobilization.However,few attentions have been paid on the micropore development of biochars through different preparation technique or modification methods,and the role of micropores as well as carbon components(noncondensed aromatic moieties)in sorption of organic contaminants.Therefore,biochars from various techniques and modified biochars from various chemicals methods were prepared at different temperatures.These biochars and modified biochars were characterized to understand the relationship between their properties and pyrolysis mechanism,to investigate the sorption for carbamazepine(CBZ)and bisphenol A(BPA)in environment.The main contents of this dissertation are as following:(1)Microwave irradiation(MW)is an effective preparation technique in pyrolysis.This study compared the properties of biochars produced using MW and electrothermal pyrolysis(FN).At the same pyrolysis temperature,MW biochars preserved more biomass(as indicated by their higher yields and higher abundance of functional groups)and possessed larger the specific surface area(SSA)due to the high abundance of micropores.MW biochars generally exhibited higher sorption of CBZ and BPA than FN biochars.However,their SSA-normalized sorption was lower,suggesting that the inner pores may not be fully available to CBZ and BPA sorption.MW biochar sorption may be further improved if micropore accessibility can be enhanced.Although CBZ and BPA did not degrade in the biochar sorption systems,the potential role of stronger free radical signals in MW biochars for organic contaminant control may not be overlooked in studies with other chemicals.(2)To enhance the micropore structure of biochars,phosphoric acid(H3PO4)pretreatment is an available method for chemical modification of biochars,but the mechanism is not yet fully understood.In this work,biochars and the raw biomass were treated by H3PO4 prior to pyrolysis.Due to an acid catalysis and crosslink,the micropores of the pretreated particles were much more than those without H3PO4 pretreatment,leading to the dramatical enhancement in the SSA of the pretreated particales.Crystalline cellulose(CL)exhibited a greater advantage in the formation of micropores than of amorphous lignin(LG)with H3PO4 modification.The formation mechanisms of micropores were:(a)H+ from H3PO4 contributes to micropores generation via H+ catalysis process;(b)the organic phosphate bridge protected the carbon skeleton from micropore collapse via the crosslinking of phosphate radical.The sorption capacites to CBZ and BPA increased after H3PO4 modification,which is ascribed to the large hydrophobic surface areas and more abundant micropores.Overall,H3PO4 pretreatment produced biochars with large surface area and high abundance of porous structures.Furthermore,the H3PO4 modified biochars can be applied as high adsorbing material as well as P-rich fertilizer.(3)To investigate the role of noncondensed aromatic moieties in sorption of organic contaminants,an approach by combing bleaching treatment and different techniques(eg.13 C NMR,Raman)was used to distinguish noncondensed aromatic component and other carbon structure components in biochars at different temperatures.The noncondensed aromatic component in biochars was selectively removed through bleaching.Different techniques were applied to characterize biochar compositions and thus the role of different carbon structures in relation to organic contaminant sorption was discussed.The aromatic carbon structures in biochars were developed during pyrolysis and evolved from noncondensed to condensed aromatic structure with the increased pyrolytic temperatures from 300 to 700 °C.The micropore development of biochars was positively related to the formation of condensed aromatic moieties.After the surface area-normalized apparent sorption,both CBZ and BPA showed increased sorption on bleached biochars produced at 500 °C,but not observed on bleached biochars produced at 300 and 700 °C.Bleaching removed noncondensed aromatic structures and enriched condensed aromatics,which resulted in increased sorption.However,bleaching also resulted in the blockage of micropores,especially for biochars with abundant condensed aromatics,which resulted in decreased sorption.The apparent sorption change was determined by the balancing of these two opposite impacts.