Mechanisms For Adsorption Of Typical Organic Pollutants On Modified Carbonaceous Materials

Along with the development of modern industry,and the improvement of living standards,the type and distribution of synthetic organic contaminants are both increasing in enviroment.To remove the organic contaminants in water,adsorption has been practiced as a highly effective technology without by-products.The carbonaceous materials are widely applied in aqueous phase adsorption.The superior adsorption capacities of carbonaceous materials for of synthetic organic contaminants are mainly attributed to their relatively high surface area and strong surface hydrophobicity.To upgrade their adsorption performance,the carbonaceous materials needed to be modified such as introducing functional groups in to the adsorbents to improve their physicochemical properties.In this thesis,two representative carbonaceous adsorbents,including a traditional activated carbon and a new emerging carbon nanotube,were selected for investigation.Both of them were modified,and the effect of the pore properties and surface chemistry on their adsroption of aromatic organic compounds and antibiotics were explored respectively.The results will supplement and refine mechanism for the adsorption of synthetic organic contaminants on carbonaceous materials.The main findings are shown as follows:For the adsorption on activated carbon,the pore structure of adsorbents were activated.A highly porous activated carbon was prepared by KOH activation of an anthracite coal(Anth-KOH).To examine its adsorption property,we selected two sulfonamides(sulfamethoxazole and sulfapyridine)and three smaller-sized monoaromatics(phenol,4-nitrophenol and 1,3-dinitrobenzene).In addition,we also chose a commercial powder microporous activated carbon(PAC)and a commercial mesoporous carbon(CMK-3)possessing distinct pore properties as comparative adsorbents.The three porous carbon adsorbents were studied in both batch and fixedbed adsorption experiments to probe the interplay between adsorbate molecular size and adsorbent pore structure.After being normalized by the adsorbent surface area,the batch adsorption isotherms of sulfonamides on PAC and Anth-KOH were displaced upward relative to the isotherms on CMK-3,likely due to the micropore-filling effect facilitated by the microporosity of adsorbents.In the fixed-bed mode,the surface areanormalized adsorption capacities of Anth-KOH for sulfonamides were close to that of CMK-3,and higher than that of PAC.The irregular,closed micropores of PAC might impede the diffusion of the relatively large-sized sulfonamide molecules and in turn led to lowered fixed-bed adsorption capacities.Anth-KOH had large specific surface area(2514 m2/g),high pore volume(1.23 cm2/g)and large micropore sizes(centered at 2.0 nm).Therefore,Anth-KOH exhibited the largest adsorption capacities for all test adsorbates(especially the two sulfonamides)in both batch mode and fixed-bed mode,it is a promising adsorbent in wastewater treatment.In the carbon nanotube portion,numerous studies are trying to develop the tunable surface chemistry of carbon nanotube and improve their adsorption affinity and selectivity toward target organic contaminants,but few studies examine the effect of introduing heteroatom nitrogen atom into the framework of carbon nanotube on adsorption.Hence,heteroatom N-doped multiwall carbon nanotubes(N-MCNT)were synthesized by chemical vapor deposition of pyridine.Compared with commercial nondoped multiwall carbon nanotubes(MCNT),N-MCNT had similar specific surface area,morphology,and pore-size distribution but more hydrophilic surfaces and more surface defects due to the doping of graphitic and pyridinic N atoms.By conducting the batch adsorptin experiment,pH effect experiment and molecular simulation,it is confirmed that the electronegative N atoms will withdraw electrons from the neighboring carbon atoms on the graphitic surface,the N-containing heterocyclic site has higher π-electron acceptance ability.There is favored π-π electron-donor-acceptor(EDA)interaction between N-MCNT and π-donor chemicals(2-naphthol,1naphthalmine),N-MCNT exhibited higher adsorptions(2-10 folds)for 2-naphthol and 1-naphthalmine than MCNT,while similar or lower adsoptions for weak π donor chemical(naphthalene)and π-acceptor chemical(1,3-dinitrobenzene).The selective enhanced adsorption of N-MCNT for specific type compounds promised that N-MCNT may be an efficient adsorbent in water treatment.The antibiotics are widely existed in water and soil.To further examine the adsorption performance of N-doped carbon nanotube,three typical antibiotics,including sulfapyridine,tetracycline and tylosin,were selected.The batch adsorption was adopted,the the effects of various aqueous chemistry conditions(pH,Cu2+)were also examined.It is found that the hydrogen bond between the hydroxyl group of tetracycline or tylosin and N-MCNT will enhance their adsorption on N-MCNT.The presence of Cu2+ can form a ternary composite with antibiotics(sulfapyridine,tetracycline and tylosin)and MCNT,which will increase the antibiotics adsorption on MCNT.However,Cu2+can also complex with the N atom doped in N-MCNT,which will reduce the adsorption of tetracycline and tylosin on NMCNT.