Study On The Preparation And Adsorption Property Of Lignocellulose/layered Silicate Nanocomposite

With the rapid development of modern industrial economy,many industries are discharging lots of heavy metal ions,such as metallurgy,mining,chemical,electroplating,battery manufacturing units,pharmaceutical and so on.Because heavy metal pollutants are difficult to be biodecomposed and destroyed,once discharged into the environment,they will enter the plants and animals through the food chain,and ultimately cause great harm to human health.Therefore,the treatment of heavy metal wastewater has been widely recognized by researchers at home and abroad.People are very cautious and important to deal with heavy metal pollutants,and actively explore various effective treatment methods.At present,the adsorption method of removing heavy metal ions from wastewater by using cheap biomaterials is widespread application,for the reasons of its low cost,highly efficiency,strongly operability and environmental protection.As a kind of renewable bioresources polymer and also a kind of natural porous materials,lignocellulose?LCS?has a three-dimensional structure,its molecule contains a large number of active phenolic,hydroxyl,carboxyl,and other active groups that can be used in electrostatic interaction and in coordination sites for heavy metal ions.However,its weak polydispersity properties,poor reactivity,and low specific gravity has made it difficult to apply extensively.Montmorillonite?MTN?is a typical representative of the layered silicate clay minerals with a wide range of sources,cheap and easy to access,strong ion exchange ability,and its lamellaes can be stripped into thinner single crystals with a larger specific surface area,has a higher adsorption capacity of heavy metal ions,but it has a very limited adsorption capacity toward heavy metal ions owing to low affinity,swelling and dispersion in water.Taking into account the rational and adequate use of biomass resources,in order to optimize the performance of biological materials at the molecular level to maximize their added value,organic polymer/inorganic layered silicate clay mineral nanocomposites have the characteristics of both organic and inorganic materials,and also has excellent properties of nanocomposites,therefore,it has become one of the current hot spots in the field of materials science.In this paper,two novel types of nanocomposite were successfully prepared by using LCS and the thiol modified SH@LCS as the matrix,and intercalation modification reaction with MTN,the adsorption properties of heavy metal ions were optimized and the adsorption mechanisms were detailed studied.The conclusions were summarized as below:1.LCS/MTN nanocomposite were successfully prepared in a alkaline solution through intercalation method,and the effects of the mass ratio of LCS to MTN,mass concentration of NaOH,reaction temperature and reaction time of preparation process optimum conditions were analyzed.The specific surface areas,pore volumes,pore sizes,appearance morphology and functional group types of LCS/MTN nanocomposite were characterized by the means of N₂ adsorption/desorption curves,FTIR,XRD,SEM and TEM.Results show that LCS/MTN nanocomposites is a mesoporous adsorbent,the lamellar structure of MTN was opened and destroyed,LCS interspersed uniformly between MTN nanoscale lamellae,forming a new intercalated-exfoliated nanocomposite.2.The synthesized LCS/MTN nanocomposite was used as adsorbent to remove six kinds of heavy metal ions Cu?II?,Mn?II?,Zn?II?,Cd?II?,Fe?III?and Co?II?from aqueous solution.Batch experiments were conducted to optimize adsorption parameters such as LCS/MTN nanocomposite dosage,the initial concentration of metal ions,solution pH,adsorption temperature,and adsorption time.The optimal adsorption conditions of six heavy metal ions were obtained respectively,and the order of maximum saturation adsorption was determined in the order of Fe?III??452.06 mg/g?>Zn?II??324.02mg/g?>Cu?II??322.60 mg/g?>Cd?II??118.45 mg/g?>Co?II??93.02 mg/g?>Mn?II??55.23mg/g?.Adsorption kinetics experiments show that the pseudo-second order kinetic model could describe the whole adsorption process well,the correlation coefficient R² were all greater than 0.9800.The results of adsorption isotherm model indicate that the adsorption equilibrium conformed to the Langmuir model,the correlation coefficient R² are greater than 0.9800,too.The desorption capacity of LCS/MTN was dependent on desorption parameters such as the eluent types,concentration,desorption temperature,and ultrasonic desorption time.The satisfactory desorption capacity and desorption efficiency were obtained by using HNO₃ and HCl as eluents,respectively.It was determined that the maximum desorption amount order was followed by Fe?III??350.62 mg/g?>Cu?II??283.15mg/g?>Zn?II??296.11 mg/g?>Co?II??87.34 mg/g?>Cd?II?(76.22 mg/g?II?>Mn?37.95mg/g?.The regeneration studies showed that the adsorption capacity of LCS/MTN was consistent for 3-4 consecutive adsorption/desorption cycles without any appreciable loss and confirmed that the LCS/MTN was reusable.The adsorption mechanism of LCS/MTN was characterized and analyzed by means of FTIR,SEM and EDS.3.SH@LCS was prepared by the modification with thioglycolic acid.By means of indirect iodometric method and FTIR characterization analysis,it was proved that LCS has been modified by sulfhydryl group,and then a novel SH@LCS/MTN nanocomposite adsorbent was successfully synthesized using a chemical solution intercalation reaction,and the content of-SH in SH@LCS//MTN is 4.102%.Adsorption of Fe?III?ions from aqueous solution onto SH@LCS//MTN was detailed studied.Single factor experiment methods were used to investigate the adsorption effects of the mass ratio of SH@LCS to MTN,mass concentration of NaOH,reaction time and reaction temperature on the removal of Fe?III?,and the optimal processing parameters of SH@LCS/MTN was determined.The structure of SH@LCS/MTN was characterized by N₂ adsorption desorption,FTIR,XRD,SEM and TEM.The results show that SH@LCS molecules had successfully intercalates into MTN interlayer via destroying the crystalline structure of MTN,and the intercalated-exfoliated structure is formed in SH@LCS/MTN nanocomposite,moreover,its surface structure was rich in a variety of active functional groups,such as sulfhydryl,hydroxyl,carbonyl,carboxyl and so on.4.The ability of SH@LCS/MTN as an adsorbent was investigated for the removal of six kinds of heavy metal ions Cu?II?,Mn?II?,Zn?II?,Cd?II?,Fe?III?and Co?II?from aqueous solution.Optimum adsorption parameters were determined based on the initial concentrations of the heavy metal ions,pH,adsorption temperature,and adsorption time according to single factor adsorption experiment studies.The order of maximum monolayer adsorption capacities were as follows:Fe?III??631.13 mg/g?>Cd?II??458.32mg/g?>Zn?II??357.29 mg/g?>Cu?II??342.38?>Co?II??191.54 mg/g?>Mn?II??109.22 mg/g?.Adsorption kinetics and isotherms showed that the adsorption process best fitted the nonlinear pseudo-second order equation,and the correlation coefficients R² were all greater than 0.9800.The isotherm adsorption equilibrium of Cu?II?,Mn?II?,Zn?II?,Cd?II?and Fe?III?were consistent with the Langmuir models,which attribute to the monolayer chemisorption process;the adsorption isotherm of Co?II?ion conforms to the Freundlich isotherm model,its R² is 0.9969,which assigned to multilayered ion-exchange chemisorption process.The desorption capacity of the SH@LCS/MTN nanocomposite depended on parameters such as the types and the concentrations of eluent,desorption temperature,and desorption time by using ultrasonic desorption and recycling performance testing methods.The satisfactory desorption efficiency were obtained using HNO₃ and HCl as elunet,respectively.The maximum desorption followed by Fe?III??407.29mg/g?>Cu?II??209.81mg/g?>Zn?II??140.30mg/g?>Co?II??118.51mg/g?>Cd?II??83.44 mg/g?>Mn?II??46.83 mg/g?.The regeneration studies showed that the adsorption capacity of the SH@LCS/MTN were consistent for 2-4adsorption/desorption cycles without any appreciable loss in the batch process and confirmed that the SH@LCS/MTN nanocomposite was reusable.In addition,the toxicity test of sulfhydryl group was successfully carried out for the recycled SH@LCS/MTN.Whereas the adsorption mechanism was discussed in combination with the results obtained from FTIR,SEM and EDS analyses.The results show that the SH@LCS/MTN nanocomposite material contain multiple types of functional groups,the adsorption process of six heavy metal ions including physical adsorption and chemical adsorption,such as chemical bonding,electrostatic attraction,polydentate chelation,coordination complexation,ion-exchange,and various kinds of chemical adsorption reactions.Dramatically,the introduction of sulfhydryl achieves the increased activated functional groups content of SH@LCS/MTN,leading to remarkably higher adsorption amount on heavy metal ions,compared to pristine LCS/MTN and the conventional spent adsorbents.The overall study revealed that the SH@LCS/MTN nanocomposite functioned as an effective adsorbent in the detoxification of heavy metal ions-contaminated wastewater.