Hydrothermal Preparation Of The Corncob-derived Adsorbent Materials And Its Performance And Mechanism Of Adsorption

Corn is one of the biggest food crops in our country.Corncob is a kind of widely existed biomass,as well as a renewable,biodegradable and environmentally friendly natural resource.While,most of the corncobs are not fully utilized,it not only caused a waste of resources,but also polluted the environment.Corncob itself has a good hydrophilic specific structure,which contains the natural cellulose of the active group.So it can effectively adsorb the organic dyes and heavy metal ions.In this paper,this method uses the hydrolyzed product of agricultural waste material corncobs as carbon source to prepare carbon microspheres in the presence of hydrochloric acid under ambient pressure.Because of the complex preparation of glucose,higher manufacturing cost,waste liquid corrodes strongly in posttreatment,badly environment pollution,not suitable for large-scale industrialized production and so on.Therefore,agricultural waste material corncobs were chosen as the carbonized precursor,by hydrothermal method in the presence of phosphoric acid.Samples were characterized by using FTIR,SEM and XRD techniques,the principles of kinetics,isotherms and thermodynamics about the adsorption of methylene blue(MB),Cu(II)and Pb(II)ions on the prepared samples were studied.The influence of several operating parameters on the adsorption capacity was also investigated.Hydrochar can be used in dealing with environmental pollutants as a new environmentally friendly carbon material.The main conclusions of this study are as follows:(1)This method uses the hydrolyzed product of agricultural waste material corncobs as carbon source to prepare carbon microspheres in the presence of hydrochloric acid under ambient pressure.The optimal conditions for the production of carbon microspheres were: 2.0 mol/L hydrochloric acid solution molar concentration,95 ? hydrothermal reaction temperature,6 h hydrothermal reaction time.Samples were characterized by using FTIR,Raman,SEM and XRD techniques,suggesting the possible presence of an amorphous carbon phase within the carbon materials were rich in surface oxygen containing functional groups,such as hydroxyl,carbonyl and carboxyl groups.(2)This method uses the agricultural waste material corncobs as carbon source to prepare hydrochar in the presence of phosphoric acid.The optimal conditions for the production of hydrochar was: 1.5 mol/L phosphoric acid solution molar concentration,160 ? hydrothermal reaction temperature,6 h hydrothermal reaction time.Samples were characterized by using FTIR,Raman,SEM and XRD techniques,suggesting the possible presence of an amorphous carbon phase within the carbon materials were rich in surface oxygen containing functional groups,such as hydroxyl,carbonyl and carboxyl groups.(3)Adsorption of MB onto hydrochar prepared was investigated in a batch system.The results show that it takes 2 hours to reach the equilibrium.The MB removal is pH dependent,which was affected over pH range of 2.0~12.0 and found to be maximum at pH 12.Langmuir isotherm model fitted the data well.The maximum monolayer adsorption capacity of MB onto hydrochar prepared was calculated as 120.25 mg/g.Pseudo-second-order kinetics equation was better than pseudo-first-order kinetics equation to describe the adsorption process of MB.Thermodynamic parameters for the adsorption system were determinated,?G=-1.94 kJ/mol~-0.34 kJ/mol.The negative value of of ?G showed spontaneous nature of adsorption.As the temperature rise,the adsorption proceeded faster.Possible adsorption mechanism was proposed as follows: hydrogen bonding formation,electrostatic interactions and electron donor-acceptor interaction,hydrogen bonding formation and electron donor-acceptor interaction played important role for the adsorption mechanism.(4)Adsorption of Pb(II)onto hydrochar prepared was investigated in a batch system.The results show that it takes 4 hours to reach the equilibrium.The Pb(II)removal is pH dependent,which was affected over pH range of 2.0~7.0 and found to be maximum at pH 6.Langmuir isotherm model fitted the data well.The maximum monolayer adsorption capacity of Pb(II)onto hydrochar prepared was calculated as 49.58 mg/g.Pseudo-second-order kinetics equation was better than pseudo-first-order kinetics equation to describe the adsorption process of Pb(II).Thermodynamic parameters for the adsorption system were determinated,?G=-1.45 kJ/mol~-0.99 kJ/mol.The negative value of of ?G showed spontaneous nature of adsorption.The adsorption process of Pb(II)onto hydrochar prepared was an endothermic and spontaneous process.It was indicated that adsorption of Pb(II)onto hydrochar prepared was controlled by chemical adsorption.The involved adsorption mechanisms for Pb(II)included the electrostatic interactions,ion exchange and surface complexation.(5)Adsorption of Cu(II)onto hydrochar prepared was investigated in a batch system.The results show that it takes 4 hours to reach the equilibrium.The Cu(II)removal is pH dependent,which was affected over pH range of 2.0~7.0 and found to be maximum at pH 6.Langmuir isotherm model fitted the data well.The maximum monolayer adsorption capacity of Cu(II)onto hydrochar prepared was calculated as 34.72 mg/g.Pseudo-second-order kinetics equation was better than pseudo-first-order kinetics equation to describe the adsorption process of Cu(II).Thermodynamic parameters for the adsorption system were determinated,?G=-1.67 kJ/mol~-0.57 kJ/mol.The negative value of of ?G showed spontaneous nature of adsorption.The adsorption process of Cu(II)onto hydrochar prepared was an endothermic and spontaneous process.