Study On Adsorption Of Lopamidol By NaHCO₃ Activated Buckwheat Biochar

Iodinated X-ray constrast media(ICM)is mainly used to strengthen the imaging of blood vessels,caverns and human organs.which cannot be completely metabolized in human body because of its strong stability,and can easily enter into the municipal sewage system.Moreover,conventional wastewater treatment process can not remove ICM effectively,resulting the residual of ICM in water environment,with the residue concentration even up to thousands of μg/L.So it is of great necessity to strengthen the removal study of ICM.In this paper,buckwheat bark was used as raw material to prepare biochar activated by NaHCO3.The physicochemical properties and functional group changes of the activated biochar were analyzed,its adsorption performance on the non ionic ICM—Iopamidol(IPM)was further investigated as well.The main contents are as follows:(1)Single factor experiment was used to explore different activation modes(one-and twostep activation),pyrolysis temperatures(500℃,600℃ and 700℃),different types of alkali[KOH,Na2CO3,NaHCO3,KHCO3 and Ca(HCO3)2]and alkali-carbon ratio[m(NaHCO3):m(buckwheat bark)=:x:1,x=0,0,1,0,25,0.5,1,2]on the adsorption of IPM by biochar.And the preparation process was optimized as:pyrolysis temperature 700℃,one-step activatation mode,m(NaHCO3):m(buckwheat bark)=0.25:1(0.25N-BC),under which 98.24%of IPM was adsorbed in 30 min.(2)Thermogravimetric analysis,SEM-EDS,elemental composition,BET,XRD,XPS,FTIR and Raman were used to analyze the effects of NaHCO3 activation on the physicochemical properties of biochar.The results showed that compared with buckwheat bark biochar(BC),NaHCO3-activated biochar had higher structural defects(surface area and pore volume increased from 480.40 m2/g and 0.29 cm3/g to 572.83 m2/g and 0.40 cm3/g,respectively,and ID/IG was 1.22 times that of BC).The number of carbon-containing and oxygen-containing functional groups on the 0.25N-BC surface changed significantly,the polarity enhanced[(N+O)/C increased from 0.15 to 0.24],which would be more beneficial for the adsorption of IPM.The maximum adsorption capacity of 0.25N-BC for IPM reached 74.94 mg/g,9.51 times than that of BC(7.88 mg/g).The pseudo-second-order adsorption kinetics and Langmuir and Freundlich isotherm models can well fit the adsorption process.The IPM adsorption processes are mainly a chemical and monolayer,heterogeneous multilayer adsorption.The electrostatic potential distribution on the surface of 0.25N-BC indicates that π electrons and lone-pair electrons in functional groups(—COOH,—OH and O—C=O)in aromatic rings are the main sites for IPM adsorption.Pore filling,hydrogen bonding,π-π and n-π interaction are the main mechanisms for IPM adsorption.(3)The properties of other biochars activated by NaHCO3 and 0.25N-BC adsorption on other organic pollutants were investigated.Compared with the original biochar,the removal rates of IPM from corn stalk,coffee grounds and buckwheat bark biochar after NaHCO3 activation were increased from 43.61%,36.56%and 84.61%to 82.52%,95.90%and 98.61%,respectively.NaHCO3 is a fine activator.The removal rates of 0.25N-BC for ornidazole,tinidazole,metronidazole,methyl orange,methylene blue and Rhodamine B reached above 95%in 180 min.Compared with other adsorbents,the adsorption of 0.25N-BC was higher,After three times of adsorption-desorption,the removal rate of IPM remained at 74.91%,which showed good cyclic performance.0.25N-BC can also effectively remove IPM residues in actual water bodies(secondary sedimentation tank effluent and lake water),and the removal rates of 180 min are 97.60%and 97.30%,respectively.The results show that NaHCO3 activated buckwheat bark biochar is a green,effective and sustainable adsorbent for removing organic pollutants.