Study On The Selective Adsorption Of Tobacco Specific Nitrosamines By Activated Carbon And Zeolite

To control tobacco specific nitrosamines(TSNA)pollution at source,this research was focused on the selective liquid adsorption of TSNA by the modified active carbon and H? zeolite.The adsorption performance of regenerated sorbents were also examined,extenting the industrial applications of efficient sorbents as well as offering new clues in researches of more efficient porous sorbents.The main research content is as follows:1.Modification of coconut shell-made activated carbon with loading ferric oxides considerably elevated the adsorption capability of TSNA in tobacco extract solution.The undispersed ferric species and carbon particles roughened the spore wall and adjusted the most probable pore size to0.7-0.8nm.Meanwhile,the ferric species improved the Zeta potential of the sorbent from-18.3mV to-8.3mV These changes were beneficial for capturing TSNA by sorbent-TSNA electrostatic interaction as well as to distinguish TSNA and parental alkaloids in tobacco solution,contributing to two kinds of adsorptive selectivity,TSNA over alkaloids and 4-methylnitrosamino-l-3-pyridyl-l-butanone(NNK)over other TSNA molecules.Especially,10Fe*AC-g sample trapped over60%of TSNA in the tobacco solution containing TSNA of 1796ng mL-1,achieving the adsorption capability of 222?g g-1.2.Considering the three restricting factor of liquid adsorption by zeolites,hydrophobicity,pore size and cations,H? zeolite with a Si/Al ratio of 14 was used to study the adsorption of NNK in aqueous solution,aiming at finding a'top sieve'for TSNA liquid adsorption.High Si/Al ratio,proper pore size and protons endowed HP zeolite with a good TSNA adsorptive capacity.The saturated adsorptive quantity for NNK in aqueous solution exceeded 70 mg g-1;and the adsorption data was fitted to Temkin model,where the isosteric heat of adsorption decreased linearly with the increasing surface coverage,indicating an energetically heterogeneous adsorption surface.In the tobacco solution with TSNA concentration of1900?3602?g L-1,H?zeolite reached a TSNA capacity of 58?347?g g-1while it kept the selectivity of NNK by removing 75%?90%NNK.3.In order to further discuss the effect of zeolite pore size on TSNA liquid adsorption,zeolite H?,MCM-22 and NTY were selected for comparison.Zeolite H?with the pore size of 0.6-0.7nm showed the protuberant adsorptive capacity for TSNA in both laboratory formulated solution and tobacco solution,with an obvious selectivity of NNK.Calcination at 873K efficiently regenerated the zeolite HP adsorbed TSNA and no secondary pollution of nitrosamines occurred.A kind of self-activation was observed on the regenerated H? sorbents that captured slightly more TSNA in succeeding adsorption,achieving an adsorptive quantity of 225.8 ?g g-1.The pore size of MCM-22 zeolite was only 0.6nm,which was inappropriate for adsorbing TSNA in viscous tobacco solution.Yet it exerted the adsorptive advantage of super-cage cavity in the simpler solution.With larger pore size,zeolite NTY captured considerable TSNA in tobacco solution with the selectivity of NAT,which might be a promising replacement of H? zeolite in liquid adsorption.