Study On Preparation Of Corncob-based Activated Carbon And Its Adsorption Performance Of Methylene Blue

Activated carbon is a kind of carbon material with porous structure,which is characterized by great specific surface area,developed pore structure,its unique surface functional groups and so on.It is widely used in the pharmaceutical industry,materials for energy storage,adsorption and other fields.As a kind of typical renewable and biodegradable biomass,corn cob is widely distributed and rich in reserves.It has a broad application prospect to develop effective chemical transformation of biomass waste from corn cob to environmentally friendly materials with excellent properties.In this study,corn cob is used as raw materials to prepare hydrochars precursor by hydrothermal carbonization(HTC)method.The effects of different dosage of acrylic acid,citric acid and zinc chloride respectively as additive agent on hydrothermal carbonization process were studied.Activated carbon was prepared by microwave-assisted heating with hydrochars obtained by HTC.X-ray diffraction analysis(XRD),infrared spectroscopy analysis(FT-IR),scanning electron microscopy(SEM),and other technical means were used to characterize both the obtained hydrochars and the activated carbon samples.Methylene blue(MB)test adsorption was carried out to study the adsorption capacity of different hydrochars and activated carbon,and the effects of dosage for the adsorbent,initial concentration and residence time on adsorption capacity for MB were studied.In addition,the adsorption kinetic and isothermal fitting of methylene blue on the activated carbon were established.The relative results we have got as following:(1)The results showed that acrylic acid,citric acid,zinc chloride as additive agents can promote the HTC process of biomass.The calorific value and carbon content of the obtained hydrochars were increased compared to direct HTC of corn cob.Use of addictive agent led to enhanced formation of oxygen-containing functional groups in hydrochars,especially,there is a large number of carboxyl group formation on the surface of the hydrochars with presence of 5%wt acrylic acid and it showed adsorption capacity for MB up to 221.2mg/g.The adsorption kinetics of hydrochar to MB can better fit the second-order kinetic model,which fitting degree reaches 0.9999.(2)Secondly,one of the hydrochars which has the best adsorption were selected from hydrochars using different addictive agents respectively for the microwave heating activation.KOH was used as the activated agent in this study.The obtained activated carbon materials possessed higher carbon content and more developed pore structure.The activated carbon from which prepared with acrylic acid had the largest specific surface area,reaching to 857.59m2/g,and its pore structure was dominated by mesoporous,with a certain amount of macropores and a small number of micropores.In spite of the specific surface area of activated carbon from hydrochars prepared using citric acid was 511.80 m2g,but its adsorption for MB reached to 451.75mg/g,which had the best performance on adsorption of MB.(3)Research for the factors in the adsorption of MB process showed the optimal conditions for activated carbon from hydrochar using citric acid were as follows:the dosage of adsorbents were 6-8mg,the initial concentration for MB was 80-100mg/L,and the reaction time was at least over 12h.The fitting results of adsorption kinetics showed that the adsorption process of activated carbon based corn cob still conformed to the second-order kinetic model,which is related to chemical adsorption.The results of isothermal adsorption fitting showed that the Langmuir model could better describe the relationship between the adsorption amount of activated carbon and the adsorption concentration of MB.The fitting degree reached to 0.99021,indicating that the adsorption process of the obtained activated carbon for MB was a monomolecular adsorption process.