Preparation Of Cellulose-based Adsorbents And Study On Their Adsorption Performance

In industrial wastewater treatment,adsorption method is simple,and adsorbent is easy to be recycled and reused,so adsorption method are widely used in wastewater treatment.Cellulose is one of the most abundant renewable and degradable materials in nature,and it is safe and non-toxic.Therefore,the development and application of cellulose-based adsorbents have attracted wide attention.In this paper,cotton fibers,bagasse and kapok fibers were used as substrates,and hydroxyl groups in cellulose were chemically modified to introduce specific functional groups to remove heavy metal ions,dyes and oil pollutants in water by adsorption.The purpose of this paper is to study the chemical modification of various cellulose substrates and their adsorption properties for water-soluble pollutants,such as metal ions and dyes,as well as oil pollutants insoluble in water,so as to provide reference for the application of cellulose materials in wastewater treatment.The research work of this paper includes three parts:(1)Preparation and properties of adsorbent based on cotton fiber(NC-cotton)A kind of adsorbent NC-cotton based on cotton fiber containing cyclodextrin and polyamines was prepared using p-CD and polyamines hyperbranched polymer(HPA).The adsorbent is rich in amino functional groups which can chelate with metal ions.The cavity of cyclodextrin can form inclusion with some dye molecules.The amino functional groups can also form electrostatic or hydrogen bond adsorption with dyes.The adsorption properties of NC-cotton for heavy metal ions(Pb2+,Ag+,Cu2+),anionic dyes Congo Red(CR)and cationic dyes(MB)were studied.Compared with raw cotton fibers,the adsorption capacity of NC-cotton increased by 8-20 times for Pb2+,Ag+and Cu2+,and 7-18 times for CR and MB.NC-cotton showed excellent adsorption capacity for CR.The pH value affects the interaction between adsorbent and adsorbate,and has a significant effect on the adsorption capacity.With the increase of pH value(3-12),the adsorption capacity for CR increased first and then decreased,reaching a maximum of 247.1mg/g at pH=5,while the adsorption capacity for MB continued to increase,reaching 94.6mg/g at pH=12.The adsorption capacity of Pb2+,Ag+ and Cu2+ increased with the increase of pH value(2-6),reaching 88.7 mg/g,48.6 mg/g and 38.5 mg/g,respectively.The adsorption behavior for Pb2+,Ag+,Cu2+ conforms to Langmuir isotherm model,and the adsorption for CR and MB conforms to Frendlich isotherm model.The adsorption kinetics experiments show that the adsorption process for metal ions and dyes conforms to Lagergren quasi-second-order kinetics equation,and is a composite adsorption process with both chemical and physical adsorption.(2)Preparation and properties of modified bagasse adsorbent(HPA-SA-SB)Sugar bagasse is a kind of residual product.On the basis of cotton fiber-based adsorbent,bagasse was modified chemically with succinic anhydride(SA)and amino-terminated hyperbranched polymer(HPA).Carboxyl and amino functional groups were introduced onto bagasse substrate to achieve effective adsorption for heavy metal ions(Pb2+,Cu2+)and dyes(CR,MB).The effect of pH value on adsorption capacity is significant for Pb2+,Cu2+,CR and MB.With the increase of pH value(2-13),the adsorption capacity for CR first increases and then decreases,reaching the maximum of 227.6mg/g at pH=6,while the adsorption capacity for MB increases with the increase of pH value,reaching 208.7mg/g at pH=13.With the increase of pH value of adsorbate solution(2-6),the adsorptive capacity of adsorbent for Pb2+ and Cu2+ increased continuously,reaching 110.3mg/g and 90.6mg/g,respectively.The adsorption behavior for CR,MB,Pb2+ and Cu2+ conforms to Langmuir isotherm model.The maximum adsorption capacity of Langmuir is 233.6mg/g,177.8mg/g,144.3mg/g and 106.6mg/g,respectively.The adsorption process for metal ions and dyes conforms to Lagergren quasi-second-order kinetic equation.(3)Preparation and Oil absorption properties of modified kapok fiberIn order to remove oil pollutants from water surface,kapok fiber was used to prepare oil absorption material.Kapok fiber is a kind of good buoyancy material,which has advantages in removing oil caontanminants from water surface.Kapok fiber was modified with oleic acid and dodecyl trimethoxysilane to improve adsorption capacity for oil pollutants in the oil-water system.The contact angle test showed that the water contact angle of kapok fiber modified with silane-oleic acid increased from 113.2° to 162.7°,and the contact angle to diesel oil was 0°.The modified kapok fiber showedexcellent hydrophobicity and hydrophobility.The oil absorption ratio for diesel oil by modified kapok fiber is 52.5 g/g,which is about 2.5 times of that of unmodified kapok fiber.The oil retention rate of modified kapok is 86.4%after adsorbing diesel oil for 120 minutes,which is slightly lower than that of raw kapok.The increase of adsorption temperature is not conducive to the adsorption of oil products.After five times of adsorption and desorption,the oil absorption ratio of raw kapok and modified kapok fiber for diesel oil decreased from 20.3g/g,52.5g/g to 8.6g/g and 38.5g/g,respectively.After five times of reuse,the oil absorption of modified kapok fiber was still higher than that of raw kapok.The comparison for diesel oil,soybean oil and lubricating oil shows that oil with high density and viscosity is easier to be absorbed.