The Preparation Of Organic-Modified Bentonite And Mesoporous Carbon And The Study Of Their Adsorption Properties And Mechanism For Phenolic Compounds In Wastewater

With the global water pollution becoming increasingly severe,it is imminent to deal with the phenolic compounds.The adsorption method is considered to be one of the most effective technical methods in the treatment of phenolic wastewater because of its easy operation,high adsorption capacity and low cost.However,it is still urgent to search for an efficient,economical and environment-friendly adsorbent.In this paper,the low cost organic-modified bentonite and the mesoporous carbon with rich functional groups were choosed as adsorbents for the removal of phenolic compounds in wastewater.Firstly,the organic-modified bentonite and the mesoporous carbon were successfully prepared.Secondly,the structure and morphology of the organic-modified bentonite and mesoporous carbon were analyzed by various characterization methods.Then,the adsorption performance and mechanism of the organic-modified bentonite and mesoporous carbon on phenol,4-chlorophenol?4-CP?and 2,4-dichlorophenol?2,4-DCP?in wastewater were studied.Finally,the more suitable adsorbent for the treatment of phenolic compounds in wastewater was choosed,which provides a solid theoretical basis for the practical treatment of phenolic wastewater.The main contents of this paper contain the following three parts:1.The organic-modified bentonite?CTAB-Bent?was successfully prepared by the hexadecyltrimethyl ammonium bromide as the modifier.The microstructure and surface chemical characteristics of the organic-modified bentonite were characterized by XRD,SEM,N₂ adsorption-desorption,FT-IR and Zeta.The Effects of dosage of the adsorbent,pH,contact time,initial concentration and temperature on the adsorption performance and mechanism for phenol,4-CP and 2,4-DCP onto the CTAB-Bent were comprehensively investigated,and the kinetic characteristics,isotherm characteristics and the thermodynamics characteristics in adsorption process were also studied.The results show that CTAB is successfully intercalated Na-bentonite,and the layer spacing increases from 1.05 nm to 2.04 nm.Besides,the organic-modified bentonite belongs to the typical mesoporous materials;its specific surface area and total pore volume can reach 32.735 m²/g and 0.785 cm³/g,respectively,and the pore size distribution is around 3.865 nm.Moreover,the organic-modified bentonite exhibits obvious lamellar structure and rich surface hydrophobic functional group.Experimental conditions are as follows:the adsorbent dosage of0.20 g,phenol,4-CP and 2,4-DCP solution at the pH values of 6.80,6.70 and6.65,respectively,the initial concentration of 100 mg/L,the adsorption time of 40min and the adsorption temperature of 25?.The removal rates of phenol,4-CP and 2,4-DCP onto the CTAB-Bent are up to 30.26%,77.28%and 93.61%,respectively,and the adsorption quantity are 7.57 mg/g,19.32 mg/g and 23.40mg/g,respectively.Furthermore,the adsorption of phenolic compounds onto CTAB-Bent follows the pseudo-second-order kinetic model,and the Freundlich isotherm model could describe well the adsorption of phenolic compounds onto CTAB-Bent.By further exploring the thermodynamic study,the adsorption of phenol onto the CTAB-Bent is nonspontaneous endothermic reaction.However,the adsorption of 4-CP and 2,4-DCP onto the CTAB-Bent is spontaneous.The disorder and chaos of the adsorption system increase during the adsorption process.As for the adsorption mechanism,the adsorption of phenolic compounds onto CTAB-Bent is dominated by the interlayer distribution function,during which the surface adsorption is complementary.2.The mesoporous carbon was synthesized through nano-casting approach using sucrose as the carbon precursor,KIT-6 as the template,and subsequently carbonized at the temperature of 900?.The structure and property of the obtained mesoporous carbon were systematically characterized by XRD,TEM and N₂ adsorption/desorption isotherm.The effects of adsorbent dosage,pH,contact time,initial concentration and the contact temperature on phenol,4-CP and 2,4-DCP onto the mesoporous carbon were comprehensively investigated,respectively.The adsorption kinetic,adsorption isotherm and the adsorption thermodynamics were also studied.The results demonstrate that the mesoporous carbon is an amorphous carbon of cubic la3d structure,and exhibits the worm-like morphology with high specific surface area?398.767 m²/g?,large pore volume?0.078 cm³/g?and uniform pore size?3.8 nm?.The experimental condition are as follows:the adsorbent dosage of 0.10 g,phenol,4-CP and 2,4-DCP solution at the p H values of 6.80,6.70 and 6.65,respectively,initial concentration of 100mg/L,adsorption time of 120 min and the adsorption temperature of 25?.The removal rate of phenol,4-CP and 2,4-DCP onto the mesoporous carbon are70.15%,81.66%and 85.57%,respectively,and the adsorption quantity are 35.07mg/g,40.83 mg/g and 42.78 mg/g,respectively.Moreover,their kinetic experimental data is described by the pseudo-second-order model,and their adsorption data fits the Langmuir isotherm model well.The thermodynamic study also shows that the adsorption of phenol,4-CP and 2,4-DCP onto the mesoporous carbon is spontaneous and endothermic.As far as the adsorption mechanism,with the increase of the number of substituted radicals on phenol benzene ring,the hydrophobic and the electron effect of the phenolic compounds are also enhanced,which result in the stronger hydrophobic interaction and?-?interaction between the mesoporous carbon and phenolic compounds.3.By comparing the adsorption effect of CTAB-Bent with the mesoporous carbon for the same phenolic compound?phenol,4-CP and 2,4-DCP?,the more suitable adsorbent was selected to remove the phenolic compounds.The results are as follows:for the treatment of the phenol,the removal rate by mesoporous carbon is 70.15%,which is much higher than that of CTAB-Bent?30.26%?under the optimal reaction condition.Considering the actual treatment of phenolic wastewater,the mesoporous carbon has more development prospect than CTAB-Bent.CTAB-Bent shows unique advantages from the aspects of the dosage of adsorbent,reaction time and adsorption temperature when dealing with the 4-CP.From the aspect of pH,the removal rate of the mesoporous carbon is over 81.66%,superior to the removal rate of CTAB-Bent's when the pH of 4-CP varies from 2.0to 6.0.At the neutral pH range,the removal effect of CTAB-Bent is 80%,no less than that of the mesoporous carbon.And the CTAB-Bent exhibits worse removal efficiency than the mesoporous carbon in the alkaline condition.As for the concentration,the adsorption capacity by the mesoporous carbon is 85.56 mg/g,which shows great efficiency compared with CTAB-Bent's at the 4-CP concentration of 0 mg/L-400 mg/L.However,with the increasing of 4-CP concentration,the adsorption of 4-CP onto the mesoporous carbon has been basically saturated,while CTAB-Bent shows the excellent adsorption capacity of148.56 mg/g.Therefore,in the practical application,flexible measures should be taken according to the wastewater quality.In the treatment of 2,4-DCP,the removal rate of CTAB-Bent is up to 93.61%,which is higher than the removal rate of the mesoporous carbon?85.57%?.And CTAB-Bent displays a better application prospect from the aspects of dosage of adsorbent,pH,reaction time and the adsorption temperature.Specifically,from the aspect of concentration,the adsorption capacity of mesoporous carbon is 101.60 mg/g,greater than that of the CTAB-Bent?92.37 mg/g?at the 2,4-DCP concentration of 0 mg/L-400 mg/g.But with the increase of 2,4-DCP concentration,CTAB-Bent exhibits excellent adsorption capacity of 206.83 mg/g while adsorption of the 2,4-DCP onto the mesoporous carbon has been saturated.In summary,CTAB-Bent has more advantages in the actual treatment of 2,4-DCP wastewater.