| China is the Country with the largest amount of paper products in the world.Every year,millions of tons of papermaking black liquor are produced.As the main organic component in papermaking back liquor,lignin is also the second largest natural polymer material in nature,only after cellulose.Because its structure is very complex and it is difficult to decompose,recycling and reuse of lignin are limited.At present,most of the lignin have to be discharged together with the papermaking black liquor,causing both environmental pollution and waste of resources.Exploring the simple and highly efficient use of lignin to make it to turn waste into treasure for the benefit of the people is of great significance.Lignin has a high carbon content and is an ideal precursor for the formation of activated carbon materials.The use of lignin to prepare activated carbon reduces the production cost of activated carbon so as to realize the resource utilization of lignin.Furthermore,the activated carbon produced can absorb pollutants,thus to create a win-win result with important practical significance.In this study,the lignin used in the black liquor ex-traction process after alkali extraction and pretreatment and purification was used as raw material.Different activating agents were selected.The preparation,characterization and adsorption applications of ligniii-based activated carbon were discussed in detail.The research mainLy includes the following aspects.(1)Activated carbons were prepared by physical activation with steam as the activating agent.The preparation process was divided into two parts;the carbonization process and the activation process.The effects of carbonization temperature,activation temperature and activation time on the BET surface areas and pore volumes of activated carbons were investigated by the single factor experimental method.The optimized preparation process of activated carbon was selected by the BET surface area as the target.The results showed that the increase of the BET surface area was higher by increasing the carbonization temperature from 400 to 450?,and the maximum was obtained at 450 ?.The BET surface area of activated carbon firstly increased,then decreased and then increased and decreased with the increase of the activation temperature,and reached the maximum when the activation temperature was 725 ?.The BET surface area of activated ca:rbon increased first and then decreased by increasing the activation time,and reached the maximum at 40 min.In conclusion,the optimized preparation conditions for the preparation of lignin-based activated carbon from papermaking black liquor by physical activation with steam were as follows:the carbonization temperature was 450 ?,the activation temperature was 725 ?,and the activation time was 40 min.The BET surface area of the activated carbon(SLAC)prepared under this condition reached 310 m2/g.SLAC was characterized by scanning surface electron microscope(SEM).Fourier infrared spectrometer(FTIR)and Bohem titration.The results showed that showed that the content of the acidic functional group was higher than that of the basic functional group.SLAC was acted as the adsorbent for the adsorption of Methylene Blue(MB)and the influences of pH,the adsorption time and the initial concentration on the adsorption of MB were explored.The experimental results showed that the adsorption of methylene blue gradually increased with the increase of pH,and increased greatly in the pH range of 8.08-11.97;In comparison with the pseudo-first-order model,the pseudo-second-order kinetic model can provided a better description for the adsorption of MB onto SLAC.The fitted results of the intra-particle diffusion model demonstrated that the diffusion of the particle was not the only step for controlling the adsorption rate;The adsorption of MB was more consistent with the Langmuir isotherm model,indicating that the adsorption of MB onto SLAC was a homogeneous and single-molecular-layer adsorption.The adsorption mechanisms were mainly the hydrogen bonding,electrostatic interaction and the effect of ?-?electron-donor-acceptor interaction.(2)The lignin-based activated carbon from papermaking black liquor were prepared by employing potassium acetate as activating agent.The effects of two important preparation parameters,the activation temperature and impregnation ratio of the activating agent to the precursor on the BET surface area and pore structure parameters of activated carbons were investigated by N2 adsorption/desorption isotherms,and the preparation process of activated carbon was optimized.The activated carbon prepared under the optimal preparation conditions was characterized by SEM,FTIR,Bohem titration and the determination of the point of zero charge.The adsorption of Congo red was also studied.The experimental results show that the BET surface area increased first and then decreased with the increase of the activation temperature.The maximum was obtained at the activation temperature of 800 ?.The variation of the micropore surface area and pore volume also revealed the same trend,whereas the average pore size decreased first and then increased.The BET surface area,micropore surface area and micropore volume also increased first and then decreased,whereas the average pore size increased with the increase of the impregnation ratio.The maximum was obtained at the impregnation ratio of 2:1.The BET surface area of the activated carbon(PALAC)prepared under the optimized activation temperature of 800 ? and impregnation ratio of 2:1 was up to 2043 m2/g,indicating that the activated carbon with high BET surface area can be prepared from papermaking black liquor by potassium acetate activation.Based on the Bohem titration analysis,the content of the basic surface functional group of PALAC was higher than that of the acidic surface functional group,and the content of the carboxyl group was the highest among the surface acidic functional group.From the Congo Red(CR)adsorption experiment,it was found that the adsorption capacity of PALAC for CR decreased basically with the increase of pH,and the change of pH just had a little effect on the CR adsorption capacity,indicating that the electrostatic interaction was not the main adsorption mechanism.The adsorption of CR was more consistent with the pseudo-second-order kinetic model.The adsorption speed was controlled by the intra-particle diffusion and extra-particle diffusion.The adsorption of CR onto PALAC can be better described by the Langmuir isotherm model,and the maxium monolayer adsorption capacity was 195.51 mg/g.(3)The preparation of lignin-based activated carbon from papermaking black liquor was conducted by using potassium oxalate as activating agent.The single factor experimental method was carried out by choosing the activation temperature and impregnation ratio of the activating agent to the precursor as the main preparation parameters.The effects of the activation temperature and impregnation ratio on the BET surface area and pore structure parameters of the activated carbon were investigated by using the N2 adsorption/desorption method.In addition,the preparation process for potassium oxalate activation was optimized and the optimized activated carbon POLAC was selected.SEM,TEM,FTIR,Bohem titration and the determination of the point of zero charge were used to characterize PLAC.The experimental results showed that the BET surface area and total pore volume of activated carbon increased first and then decreased with the increase of the activation temperature or the impregnation ratio.The BET surface area and pore volume of the activated carbon also showed the same trend.The BET surface area reacheed the maximum value of 1817 under the activation temperature of 800 ? and the impregnation ratio of 2:1.POLAC was used as an adsorbent for the antibiotic cephalexin(CEX)treatment.The results showed that the amount of CEX firstly increased and then decreased with the increase of pH,and reached the maximum at the pH of about 4.4.The adsorption of CEX onto POLAC almost reached equilibrium at 1600 min.The pseudo-second-order kinetic model was more suitable for the CEX adsorption,suggesting that the adsorption process was chemisorption.In comparison with the Langmuir isotherm model,the Freundlich isothem model was more proper for the adsorption of CEX onto POLAC.indicating that the adsorption process was dominated by the multimolecular layer adsorption.(4)Potassium citrate was chosen as the activating agent for the preparation of lignin-based activated carbon from papermaking black liquor.The effects of different activation temperature and impregnation ratio of the activating agent to the precursor on BET surface area and pore structure parameters of activated carbon were explored by the N2 adsorption/desorption isotherms obtained from the BET surface area analyzer.The optimized preparation process and the optimal activated carbon were also figured out.The physical and chemical properties of the optimal activated carbon were characterized by SEM,TEM and Bohem titration.Moreover,the surface functional groups of the activated carbons obtained under the other preparation conditions were measured by FTIR,and the changes in the surface functional groups were also compared.In this study,norfloxacin(NOR)was chosen as the target pollutant,and the adsorption capacity of NOR toward the optimal activated carbon was preliminarily evaluated.The results showed that the BET surface area and pore volume of activated carbon increased first and then decreased with the increase of the activation temperature.The effect of the impregnation ratio on BET surface area,micropore surface area and micropore volume was also the same The prepared activated carbon reached the highest BET surface area of 2219 m2/g under the activation temperature was 850 ? and the impregnation ratio was 2.5:1,and simultaneously the micropore surface area,the micropore pore volume and the total pore volume were 1599 m2/g,0.820 cm3/g and 1.667 cm3/g respectively.The surface functional groups of activated carbons prepared under different conditions were the same,however,the content decreased with the increase of the activation temperature and impregnation ratio.The highest adsorption capacity of NOR toward the optimal activated carbon reached 378.55 mg/g.The adsorption was more consistent with the Langmuir isotherm model,which suggested a monolayer adsorption process. |
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