| Activated carbons(ACs)has been widely used as adsorbent for removal of organic contaminants from wastewater due to their large specific surface area,developed porous structure and strong adsorption capacity.The specific surface area of common ACs is normally less than 1500 m2/g,while that of KOH-activated carbons(KOH-ACs)can more than 3000 m2/g,thus KOH-ACs are expected as alternates of common ACs as adsorbents.Biomass has been widely used as precursor for ACs due to their abundant sources,low cost and renewable.Knowledge of the influence of biomass species and components on porous properties and adsorption behaviors of KOH-ACs are benefit to their preparation.Knowledge of adsorption behavior and mechanism of organic compounds by KOH-ACs from water is crucial to the environmental applications of KOH-ACs as adsorbent.In this dissertation,the influence of biomass species and components on porous properties and adsorption behavior of KOH-ACs were studied.Moreover,the adsorption behaviors of 25 organic compounds on KOH-AC were studied,and correlations of adsorption capacity and adsorption affinity of KOH-ACs with physiochemical properties of organic compounds were established,in oreder to study the adsorption mechnisms.Main conclusions of this study are as follows:(1)Predictive models for BET surface area of KOH-ACs prepared from four natural biomass(bamboo,sawdust,straw and coconut shell)and three biomass components(cellulose,xylan and lignin)were established and the optimum experimental conditions were obtained.The optimum experimental conditions were focused on 500℃-600℃ of carbonization temperature,4.5-6 of weight ratio,and 800℃-900℃ of activation temperature.The porous properties,adsorption capacity(Q0c)and adsorption affinity(E and b)of KOH-ACs at optimum experimental conditions were similar,the carbon-normalized properties even can be regarded as constants.The specific surface area(SBET-c)and total pore volume(Vtot-c)of KOH-ACs were 4121(± 242)m2/g and 2.43(± 0.26)cm~3/g,respectively.The Q0c,E and b of 4-nitrophenol on KOH-AC was 2436(±206)mg/g,23.89(±1.95)KJ/mol and 0.93(±0.11)respectively,while that for nitrobenzene was 2509(±326)mg/g,12.15(±1.74)KJ/mol and 1.64(±0.21)respectively.Thus,the influence of biomass species and components on porous properties and adsorption behavior of KOH-ACs is insignificant.(2)The adsorption behaviors of 25 organic compounds on KOH-AC were studied.A negative relationship of adsorption capacity(Q0)of organic compounds with melting point of organic compounds was observed,suggesting that adsorption is dependent on stacking density of molecules on KOH-AC.While the negative relationship of adsorption capacity with molecule size of organic compounds was not observed,indicating that the molecular sieving effect on adsorption was insignificant.A multiple linear relationship of adsorption affinity(E)with solute solvatochromic parameters(π*,am)was established,indicating that π-π,EDA interaction,hydrogen bonding interaction and hydrophobic effect derived from Van der Waals force are the domain attractive forces responsible for the adsorption on KOH-AC.The multiple linear relationship can be used to quantify the contributions of π-π EDA interaction,hydrogen-bonding interaction and hydrophobic effect to the adsorption of a given compound on KOH-AC.Combined with the reported results of adsorption of organic compounds on carbon nanotubes and biochar,it was observed that external surface area of adsorbents could affect adsorption capacity of organic compounds,while micropore surface area and the fraction of micropores could affect adsorption affinity of organic compounds. |
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