| Recently, as a new environmental functional material, biochars has attracted wide attention. In addition to the potential function of carbon sequestration, reducing greenhouse gas emissions. Biochars are more and more applied in soil amendment, contaminated soil remediation and other fields, and show some potential.Five kinds of biomasses, including eucalyptus globulus, corncob, silkworm excrement, pomelo peel and banana stem, were selected as raw materials. These biomasses were pyrolyzed at4different temperatures (200-500℃) with limited oxygen supply. Elemental analysis, BET-N2surface characteristics analysis, Fourier transform infrared spectroscopy and X-ray diffraction techniques were employed to characterize the physicochemical properties of these biochars. Bisphenol A (BPA) and sulfamethoxazole (SMX) were chosen as the target pollutants to study the sorption of polar and ionic synthetic organic pollutants by the biochars in water. This study was aimed at understanding the sorption characteristics of biochars without acid treatment and their impacts on the environmental behaviors and risks of organic pollutants after applied in soils.The results showed that:1) For all biochars, with increasing pyrolytic temperature, carbon content increased, hydrogen content and oxygen content decreased; stability and aromaticity increased, polarity and cation exchange capacity decreased. These property changes implied that "soft-carbon" gradually turned to be high aromaticity "hard-carbon"; The application of Eucalyptus globulus-derived biochars and silkworm excrement-derived biochars can improve the N fertilizer of soil, but corncob-derived biochars can make N fixed, reduce nitrogen oxide emissions; ash content of biochars derived from herbaceous biomass is larger than biochars derived from herbaceous-xyloid biomass, and this ash may interfere the results of elemental analysis.2) Pore structure of biochars derived from biomass rich in lignin is more developed.3)Oxalate is mainly generated at low temperature and carbonate is mainly generated at high temperature, carbonate content increased with the increasing pyrolytic temperature; During carbonization process, cellulose crystal disappeared when300℃, then gradually formed the graphene layer crystallization.5) The pH values of biochars suspension in water increased with the increasing pyrolytic temperature.With the increasing pyrolytic temperature, nonlinear sorption of BPA and SMX on differents biochars were enhanced.There is electrostatic repulsion effect between SMX and biochars surface due to they are negatively charged, thus SMX can’t fully contact with the biochars surface, which leads to its nonlinear and sorption capacity weaker than BPA.The sorption of BPA and SMX on biochars are conducted by the partition effects and adsorption effects. With the increasing pyrolytic temperature, due to the reduction of aliphatic and alicyclic of biochars, the partition coeffients of BPA on biochars declined, but the partition coeffients of SMX showed various regulations due to electrostatic repulsion effect. The adsoption of BPA with biochars conduct via the π-π electron donor-acceptor interaction, hydrogen bonding interaction and π-π bond adsorption interaction, by which the adsorption capacity decreased with increasing pyrolytic temperature, surface adsorption saturation adsorption quantity Qmax values declined due to π-π electron donor-acceptor interaction which is the major driving forse. The adsoption of SMX with biochars conduct via the π-π electron donor-acceptor interaction, hydrogen bonding interaction and cation bridging effect. Since the electrostatic repulsion effect, there are various regulations between SMX and biochars.Generally biochars prepared under200℃and500℃take the least surface negative charge, so the electrostatic repulsion effect is the weakest,which leads to the increase of partition coeffients and Qmax between SMX and biochars.Therefore, the electrostatic interaction is the major driving forse in adsorption behavior of SMX on the biochars.Final conclusion, the sorption of polar compounds on biochars prepared at low temperature are stronger than biochars prepared at high temperature. To biochars without acid treating, the sorption of ionic compounds negatively charged on biochars prepared at lower and higher temperature are stronger than biochars prepared at middle temperature. Otherwise, This study will provide theory evidence for the practical application of biochar without acid treating, and to lay the foundation for the popularization of them. |
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