Investigation On Carbon Nanotubes/graphene Oxide Modified Cigarette Filter For The Removal Of Cadmium And Chromium From Mainstream Smoke

The issue of cigarette smoking and health has always been paid widespread attention.More than 4000 chemicals have been found in tobacco smoke and most of them are toxic and harmful to human health.Among them,heavy metals from tobacco smoke are directly associated with cancer risk.Arsenic,chromium,beryllium,cadmium and nickel have been defined as Group I carcinogens by International Agency for Research on Cancer(IARC).Considering the fact that various heavy metals in cigarette smoke can enter into human body directly,it is thus important to remove heavy metals from cigarette smoke for protecting human health.In the present work,a novel cigarette filter is prepared by immersing of the commercial cigarette filter into a mixture solution of oxidized multi-wall carbon nanotubes(o-MWNTs)and graphene oxide(GO),followed by lyophilization.It has been applied for the removal of heavy metals from mainstream cigarette smoke.Chapter 1 gives a brief introduction to several common harmful substances in mainstream cigarette smoke and their quantitative analysis,modified materials of cigarette filter and their applications for the removal of harmful substances from cigarette smoke.Chapter 2 conducts the determination of cadmium and chromium contents in various parts of cigarette by inductively coupled plasma-mass spectrometry(ICP-MS).Microwave digestion is employed for the sample pretreatment of tabacco leaves,and its related factors are investigated to fix the optimal conditions,including the amount of HNO3 and H2O2,time and temperature of digestion,etc.By the comparisons of two trapping approaches for heavy metal from mainstream smoke,i,e.,Cambridge filter and solution absorption,it is found that the trapping effectiveness of Cambridge filter is better than that of solution absorption,with a simple operation.Cigarette filter after smoking is pretreated by an ultrasonic-assisted extraction.After investigation on the HNO3 extract volume and the ultrasonic extraction times,it is found that cadmium and chromium in the cigarette fiter could be virtually extracted by 50 mL 5%HNO3.Finally,the effects of puff volume and puff interval time on the contents of cadmium and chromium in mainstream smoke are investigated.It seems that the lower puff volume and the longer puff interval time are beneficial to decrease the contents of cadmium and chromium in mainstream smoke.Chapter 3 preapares a novel and specific cigarette filter for the improvement of heavy metal removal from mainstream smoke.The modification includes immersing of the commercial cellulose acetate cigarette filter into a mixture solution of o-MWNTs/GO,followed by lyophilization.The o-MWNTs/GO modified cigarette filter is characterized by scanning electronic microscope,thermogravimetric analysis,Fourier-transform infrared spectra and Raman spectroscopy.The results indicate that the o-MWNTs/GO composite has been successfully coated on the surface of cellulose acetate of cigarette filter.Meanwhile,the original porous and spongy structure in the interior of the cigarette filter is mostly maintained,giving rise to the less variation of draw resistance.In addition,the o-MWNTs/GO modified cigarette filter is superior to chitosan,active carbon,o-MWNTs,GO modified cigarette filters and original cigarette filter for heavy metal removal from mainstream smoke.4 mg o-MWNTs/GO modified cigarette filter at a length of 25 mm is further applied to five brands of cigarettes,giving rise to the removal efficiencies of 64-79%for cadmium and chromium from mainstream smoke.