Preparation And Adsorption Properties Of Cellulose-based Composites

Cellulose,the most abundant natural organic polymer material in the world,has excellent characteristics such as biodegradability and regeneration.Making full use of cellulose resources are of great significance for solving the resource and environmental problems in the world.In this paper,two type of celluloses,carboxymethyl cellulose(CMC)and cellulose acetate(CA),were selected as raw materials and modified with physical composites or chemical reagents to decrease the solubility of cellulose in water and enhance its adsorption capacity by organic or inorganic cross-linking methods,followed by the introduction of reactive functional groups.Based on these considerations,three kinds of cellulose-based adsorbents with different morphologies and amphoteric adsorption properties were prepared ingeniously by various techniques.The influence factors on adsorption performance and the possible adsorption mechanism of the adsorption process were systematically studied.The main research contents and results are as follows:(1)In the first part,to decrease the solubility of CMC in water and its stability,with carboxymethyl cellulose(CMC)as the raw material,the epichlorohydrin(ECH)as the organic cross-linking agent,ethylenediamine as the modifier,a novel amphoteric adsorbent,carboxymethyl cellulose(EDA-CMC_x)with various CMC amounts,was prepared by the method of organic cross-linking to eliminate toxic methylene blue(MB)and orange Ⅱ(ORII)dyes from wastewater.At 293 K,the maximum adsorption capacities of 82.06 and 63.72 mg·g-1 for 250 mg·L-1 MB and ORII,respectively,were obtained at pH 11(MB)and pH 3(ORII)within 30 min.Various Zeta potentials were obtained(+10 mV at pH3 and-30 mV at pH1l)and pH-sensitive properties of EDA-CMC1 were exhibited during the adsorption process.The results showed that the adsorption process was influenced by the protonization and deprotonization of functional groups on adsorbent surface.The adsorption of ORII followed the Langmuir isotherm,while MB adsorption could be described better by Freundlich model.For adsorption kinetics,both of them followed the pseudo-second-order kinetics equation,which confirmed the adsorption mechanism:hydrogen bond and electrostatic interaction existed between MB and CR dye molecules and the functional groups of adsorbent surface dominate the adsorption precess.These results indicated that EDA-CMC1 could serve as a potential material for textile wastewater treatment.However,the type of powder adsorbent was not conducive to the recovery and easy to be consumed in the adsorption process.(2)In the second part,aluminum nitrate(Al(NO3)3)was used as the inorganic crosslinking agent,CMC-based microbead adsorbents(HAx/CMC-yAl)were prepared by inorganic cross-linking method and modified with various amount of humic acid(HA)under mild conditions to improve the stability and recycling performance of CMC in adsorption process.Its adsorption properties toward representative cationic and anionic dyes were studied.The HA1.0/CMC-3Al showed pH-sensitive and the maximum adsorption capacities toward MB and ORII were 76.92 and 71.43 mg·g-1,respectively,within 300 min at pH 3 and 295 K.The pseudo-second-order kinetic model and Langmuir isotherm provided better correlation with the experimental data for the adsorption of dyes onto HA1.0/CMC-3Al,indicating that the adsorption rate-limiting step of MB and ORII adsorption was governed by the surface reaction of dyes and HA1.0/CMC-3Al.In coexisting inorganic salts and surfactants systems,NaCl inhibited dyes adsorption,while SDBS promoted MB adsorption and inhibited ORII adsorption.In addition,the main interaction between the dyes and HA1.0/CMC-3Al involved in the adsorption process was hydrogen bonding and electrostatic interaction.(3)In the third part,cellulose acetate(CA)nano fiber membrane was prepared by one-step electrospinning method with appropriated solvent system to improve the efficiency of the adsorption and separation of cellulose materials.To simultaneously and effectively remove both cationic and anionic dyes,a novel cost-effective multifunctional cellulose acetate(CA)fibers membrane was prepared by electrospinning followed by deacetylation,carboxymethylation and polydopamine coating(PDA@DCA-COOH).The maximum adsorption capacities of 69.89 and 67.31 mg·g-1 for MB and CR,respectively,in the individual systems.The effect of co-existed dyes,inorganic salts and surfactants in the simulated real complex system exhibited the uptake of MB and CR were strongly depended on the initial pH and ionic strength of the solution.The excellent adsorption capacities of the composite membrane were due to strong electrostatic attraction through the abundant functional groups on PDA@DCA-COOH surface.Based on its excellent recycling performance and adsorption property,PDA@DCA-COOH has a promising potential as an effective adsorbent in water treatment.