Preparation Of Mesoporous Carbon And Its Adsorption Prosperies Of Combined Pollutions Of Antibiotics And Heavy Metals

With the quick development of livestock,poultry,aquaculture and other industries,antibiotics or heavy metals are frequently detected in the water,which pose a growing potential threat to the aquatic ecological environment and human health.The coexistence of antibiotics and heavy metals in aquatic environment is one of the typical contaminant for water treatment.Developing a new technology to remove antibiotics from aqueous solution has become a hot research area in the control of emerging pollutants.Meanwhile,it is also a difficulty for that studying a removal technique for multi-pollutants from wastewater containing with both antibiotics and heavy metals.Comprehensive analysis of antibiotics and heavy metals removing techniques,adsorption is a popular method for both two contaminants.Previous studies reported that enlarging the pore size of adsorbent could improve the adsorption performance of antibiotics,and enhancing the functional groups on adsorbent could enhance the adsorption capacity of heavy metals.Therefore,in this study,mesoporous carbon(MC)was prepared using hard template method with plenty of organic functional groups,large mesoporous pores and ordered structures.The adsorption performance and mechanism by MC of three kinds of antibiotics(tetracycline(TC),ciprofloxacin(CIP)and sulfadiazine(SDZ))or two kinds of heavy metals(Cu(?)and Pb(?))were investigated.In addition,the removal characteristics and mechanisms of multi-contaminants of antibiotics and heavy metals onto MC adsorbent have been studied systematically and thoroughly,which could provide a theoretical guidance for the removal of multi-contaminants of antibiotics and heavy metals.The main contents and conclusions are shown as follows:The MC adsorbent is prepared using mesoporous silica as hard template that synthesized with Pluronic F127 as structure-directing agent and tetraethoxysilane(TEOS)as silica resource.The influence factors including the ratios of TEOS and F127,carbonization temperatures,carbon precursors on the pore size,specific surface area and organic functional groups of MC adsorbents were investigated.The characteristic data depicted that with the increase of the TEOS:F127 value and carbonization temperature,the pore diameter and specific surface area of MC adsorbent increase firstly and then decrease.Combined with the adsorption efficiency of antibiotics and heavy metals,the optimum conditions of MC preparation are the values of TEOS:F127 at 2.2,glucose used as carbon precursors and its dosage(m _{mesoporous silicon}:m_{carbon source} at 1:1.25)and carbonization temperature at 900°C.The specific surface area,pore diameter and mesoporous volume of MC adsorbent were 1126.46 m²/g,7.27 nm and 1.86 cm³/g,respectively.The MC adsorbent also has many organic functional groups including carboxyl,hydroxyl,etc.,some ordered mesoporous structures and a good thermal stability.The adsorption experiments of TC,CIP and SDZ using MC adsorbent were conducted in single and multiple antibiotic(s).And the effects of p H,temperature,initial concentration,ionic strength,natural organic compounds,etc.,on antibiotics adsorption were also investigated.The results showed that the adsorption efficiencies of TC,CIP and SDZ using MC adsorbents increased firstly and then decreased as the increase of p H.The optimal p H values of TC,CIP and SDZ were 6,6 and 4 respectively due to the difference of p Ka values,and their removal efficiencies were>94%under their optimal p H values.Ionic strength(Na⁺and Ca²⁺)and oxalic acid have a little effect on the adsorption efficiencies of antibiotics,while humic acid has a certain inhibitory effect,which may be attributed to its blocking to the pores and channels of MC.Under experimental conditions,the adsorption efficiencies of target antibiotics at different temperatures within 5 min were up to 82.46?96.95%.The adsorption process of antibiotics could be described using the pseudo second order model and Langmuir isothermal adsorption model.At 308K,the maximum adsorption amount of TC,CIP and SDZ were 297.91,369.85 and 246.73 mg/g,respectively.Temperature can promote the antibiotics adsorption.The adsorption process of antibiotics is spontaneous and endothermic.The adsorption mechanisms of target antibiotics mainly include electrostatic action,hydrophobic action and?-?electron receptor interaction.After 5cycles of adsorption and desorption,the MC still had a high removal efficiency for the three target antibiotics(>80%),suggesting that the MC had a good regeneration and economic prosperity for the elimination of antibiotics from wastewater.In multiple antibiotics existing systems,the removal rates of the co-existing systems of TC,CIP and SDZ were 94.49,75.45 and 78.93%,respectively.In co-existing systems,there was no competitive relationship between TC and SDZ,while there was adsorption site competition between TC or SDZ and CIP,respectively.In adsorption of Pb(?)and Cu(?)by MC,the adsorption performance are also affected by factors including intial p H values,MC adsorbent dosage,coexisting ions and natural organic matter.The optimum p H for Pb(?)and Cu(?)adsorption were 4 and5,respectively.Ionic strength and natural organic matter have a certain inhibition on the adsorption amount.Both divalent cation of Ca²⁺and Mg²⁺have more significant effect on adsorption amount than that of monovalent Na⁺.The models of pseudo second order and Langmuir isothermal fit well with the adsorption process of Pb(?)and Cu(?).The maximum adsorption amount of Pb(?)and Cu(?)were 78.06 and 67.90mg/g,respectively.Combined with characteristics and fitting models,the adsorption mechanisms of Pb(?)and Cu(?)on MC adsorbent may have electrostatic adsorption,surface precipitation,ion exchange,surface complexation,physical adsorption and chemical adsorption.Among of them,chemical adsorption is the main adsorption mechanism.The MC adsorbed Pb(?)and Cu(?)also have a good reusability after desorbed using by dilute nitric acid solution.In binary systems,Pb(?)and Cu(?)have a competitive relationship for adsorption sites on the surface of MC adsorbent.Compared with a single system,the removal percentages of Pb(?)and Cu(?)in binary systems were decreased by 30.55%and 13.94%,respectively.The values of the distribution coefficient(R²)and selectivity coefficient(?)showed that Cu(?)had a high competitive ability on active site on the surface of MC adsorbent.Based on the composite contamination characteristics of antibiotics and heavy metals in aquatic environment,the adsorption performance of them using MC adsorbent in multi-contaminants of antibiotics and heavy metals and the interaction mechanism between them were studied.The results indicated that the co-adsorption between TC and the target heavy metals(Pb(?)and Cu(?))could be achieved through complexation due to the abundant functional groups in TC molecule.Co-adsorption only occurred between CIP and Cu(?)with a high complexation ability.But SDZ has a competive adsorption for the sites on MC with both Pb(?)and Cu(?).In adsorption experiment of multi-contaminants of antibiotics and heavy metals by MC adsorbent in stimulated wastewater spiked with two contaminants including lake,well and effluent from swine wastewater treatment process.MC adsorbent was used to adsorb The data presented that MC adsorbent had good adsorption efficiencies for 5 kinds of target composite pollutants in real wastewater.The adsorption efficiencies of target antibiotics from wastewater using MC were relatively stable.The adsorption efficiency of Pb(?)and Cu(?)from well water decreased slightly compared with that from simulated wastewater in lab,while these values in effluent from pig farm wastewater treatment process increased significantly.The adsorption mechanism of MC adsorbent to the target pollutants in the multi-contaminants system mainly includes complexation,competitive effect and the adsorption effect promoted by the enhancement of negative charge on the adsorbent surface.