Sorption kinetics of 1,3,5-trinitrobenzene to biochars produced at various temperatures

Sorption kinetics of organic compounds on biochars is important for understanding the retardation of mobility and bioavailability of organic compounds.Herein,sorption kinetics of 1,3,5-trinitrobenzene on biochars prepared from 200 to 700℃was investigated to explore the sorption process.Loose partition matrix and condensed partition matrix were formed at relatively low and moderate temperatures,respectively.However,biochars produced at relatively high temperatures formed rich pore structures.Therefore,sorption equilibrium time of 1,3,5-trinitrobenzene increased with increasing preparation temperature from 200 to 350℃due to the slower diffusion rate in the more condensed matrix,and then decreased when preparation temperature was higher than 400℃because of the faster adsorption rate in the greater number of pores.Linear positive relationship between matrix diffusion rates of 1,3,5-trinitrobenzene on biochars prepared at 200,250,300,350℃and H/C ratios of biochars was observed,suggesting that the inhibition of partition process was caused by the condensed matrix in biochars.Linear positive relationships between adsorption rates(i.e.,fast outer diffusion rate and slow pore diffusion rate)of 1,3,5-trinitrobenzene on biochars prepared at 400,450,550,700℃and graphite defects of biochars were observed,because the increase of graphite defects of biochars could promote the adsorption by increasing the quantity of fast diffusion channels and sorption sites.This study reveals the underlying mechanisms of sorption kinetics for organic compounds with relatively large size on biochars,which has potential guidance for the application of biochars and prediction of the environmental risks of organic compounds.

Sorption mechanism of naphthalene by diesel soot: Insight from displacement with phenanthrene/p-nitrophenol

The nonlinear sorption of hydrophobic organic contaminants(HOCs)could be changed to linear sorption by the suppression of coexisting solutes in natural system,resulting in the enhancement of mobility,bioavailability and risks of HOCs in the environment.In previous study,inspired from the competitive adsorption on activated carbon(AC),the displaceable fraction of HOCs sorption to soot by competitor was attributed to the adsorption on elemental carbon fraction of soot(EC-Soot),while the linear and nondisplaceable fraction was attributed to the partition in authigenic organic matter of soot(OM-Soot).In this study,however,we observed that the linear and nondisplaceable fraction of HOC(naphthalene)to a diesel soot(D-Soot)by competitor(phenanthrene or p-nitrophenol)should be attributed to not only the linear partition in OM-Soot,but also the residual linear adsorption on EC-Soot.We also observed that the competition on the surface of soot dominated by external surface was different from that of AC dominated by micropore surface,i.e.,complete displacement of HOCs by p-nitrophenol could occur for the micropore surface of AC,but not for the external surface of soot.These observations were obtained through the separation of EC-Soot and OM-Soot from D-Soot with organic-solvent extraction and the sorption comparisons of D-Soot with an AC(ACF300)and a multiwalled carbon nanotube(MWCNT30).The obtained results would give new insights to the sorption mechanisms of HOCs by soot and help to assess their environmental risks.