Study On The Synthesis And Properties Of High Surface Area-activated Carbon Derived From Enteromorpha Prolifera

Enteromorpha prolifera?EP?,one kind of marine green alga,is becoming more widespread due to the water eutrophication and the corresponding outbreak of green tides in recent years,which has a serious impact on local ocean transportation,marine ecosystem,coast fishery and tourism.EP is mainly composed of carbohydrate,protein,lignin as well as some mineral salts.The high content of carbon endows this waste with good potential for the preparation of activated carbons?ACs?.Hence,EP was used as a precursor to synthesize high-quality ACs via chemical activation method and response surface method.The applications of EP not only reduce the cost of coal source but also offer a approach for the treatment of this marine biomass.This approach can provide environmental,economical and social benefit,simultaneously realize good utilization of EP for recycling,commercialization and high value.The surface area instrument,scanning electron microscope?SEM?,X-ray diffraction?XRD?,Fourier-transform infrared spectroscopy?FTIR?,Boehm titration and X-ray photoelectron spectroscopy?XPS?were used to compare the porous structure,surface morphology and surface chemical property of the prepare ACs.The effects of contact time,solution concentration and solution temperature on the adsorption behavior towards acid brilliant scarlet by the EP based ACs were investigated systematacially.The electrochemical properties of the electrodes derived from EP-based ACs were characterized by cyclic voltammetry,galvanostatic charge-discharge and electrochemical impedance spectroscopy.The main studies in this paper will be foucused on the following steps:?1?The comparasions of all kinds of solid wastes as raw materials for the preparation of ACs are described as follows.Low-cost ACs were prepared from four kinds of solid wastes at the same parameters,including petroleum coke,Enteromorpha prolifera,lignin from papermaking black liquid and hair,by pyrophosphoric acid?H4P2O7?and potassium hydroxide?KOH?activation.The N2 adsorption/desorption isotherms,scanning electron microscope?SEM?and Fourier-transform infrared spectroscopy?FTIR?were applied to compare the different porous structure and chemical properties of four-type ACs.The results show that the surface area of the obtained ACs were in a order of ACs derived from EP and KOH?3471 m2 g-?>ACs derived from lignin from papermaking black liquid and KOH(3119 m2 g^-1)>ACs derived from hair and KOH(2521 m2 g^-1)>ACs derived from petroleum coke and KOH(1344 m2 g^-1)>ACs derived from EP and H4P2O7(1094 m2 g^-1)>ACs derived from hair and H4P2O7(723 m2 g^-1)>ACs derived from petroleum coke and H4P2O7(117 m2 g^-1)>ACs derived from lignin from papermaking black liquid and H4P2O7(104 m2 g^-1).EP is more suitable for the preparation of high surface area-activated carbon in the comparison of the other three.?2?The optimal experiment about H4P2O7 is descriped as follows.EP was used as a low cost precursor to prepare ACs using pyrophosphoric acid,H4P2O7,as a chemical activating agent.The influences of impregnation ratio,activation temperature,activation time and their interaction on the specific surface area of ACs were investigated through response surface methodology.The influence of each variable on the specific surface area was in a order of impregnation ratio>activation time>activation temperature.The optimum preparation conditions were predicted as follows:impregnation ratio of 1.26:1,activation temperature of 455? and activation time of 48 min.The total pore volume and specific surface area of the obtained ACs under the optimum conditions were identified as 1.365 cm3 g^-1 and 1147 m2 g^-1.Additionally,the obtained ACs possessed high mesopore volume,which was more sutiable for the adsorption of large molecule pollutants.?3?The optimal experiment about KOH is recorded in the following part.High surface area activated carbons were prepared from EP using few KOH as activating agent.The influences of pyrolysis conditions,including activating agent/char ratio,activation temperature and activation time,on the porous structure of the obtained ACs were investigated by response surface methodology.The influences of each variable on the specific surface area,micropore ratio and mean pore size was in a order of activation temperature>activating agent/char ratio>activation time.The results of three-dimensional response surface plots,contour plots and the analysis of variance indicated that the effects of each variable on the specific surface area were tiny,but the the effects of each variable on the micropore ratio and mean pore size were significant.The optimized parameters were activating agent/char ratio of 1.1:1,activation temperature of 850?and activation time of 60 min.Activated carbons prepared under optimum conditions possessed high surface area of 3038 m2 g^-1 and large total pore volume of 2.285 cm3 g^-1 The obtained carbons were used as electrode materials.The carbon electrodes exhibited a high specific capacitance of 230 F g^-1 at a current density of 0.5 A g^-1 with a good capacitance retention of 86.96%at a high current density of 5.0 A g^-1.The equivalent series resistance is 0.1765 ? for the electrode,implying that the carbon electrodes possessed high power density and rate performance.?4?The comparision experiment is descripted as follows.EP based-ACs were prepared using chemical activation by H4P2O7?PAC?and KOH?KAC?.The specific surface area of KAC was 3500 m2 g^-1,which was two times higher than that of PAC(926 m2 g^-1).The total pore volume of KAC was 2.872 cm3 g^-1,which was twice higher than that of PAC(1.452 cm3 g^-1).Abundant of acidic functional groups were presented on the surface of both AGs.Furthermore,the KAC owned more functional groups that PAC.The pseudo-second-order model and Langmuir isotherm model were well fitted with the adsorption data towards acid brilliant scarlet by these two carbons.The maximum adsorption capacities of GR onto KAC and PAC were 2500 mg g^-1 and 454 mg g^-1.The physical adsorption and ion-exchange were the dominating adsorption mechanism.?5?The exploration for new activating agents has been performed as follows.Potassium carbonate?K2CO3?,sodium carbonate?Na2CO3?,potassium metasilicate?K2SiO3?,sodium silicate?Na2SiO3?,potassium borate?K2B4O7?and sodium aluminate?Na2Al2O4?were used to prepare activated carbons.The ACs prepared by K2CO3,K2SiO3 and Na2Al2O4 presented large specific surface area of 2395 m2 g^-1,1770 m2 g^-1,1329 m2 g^-1,respectively.The single factor experiment was employed to prepare ACs by sodium aluminate?Na2Al2O4?activation.The effects of impregnation ratio,activation temperature and activation time on the properties of produced ACs were investigated.The BET surface area and pore volume of the produced ACs could reach as high as 1374 m2 g^-1 and 1.150 cm3 g^-1 under the optimum conditions?impregnation ratio of 3:1,activation temperature of 800? and activation time of 0.5 h?.The maximum monolayer adsorption capacity towards acid brilliant scarlet onto the ACs was 1000 mg g^-1.