Preparation And Performance Of Polyaniline/Cellulose Fiber Composite Materials Using Hydrogen Peroxide As Oxidant

In-situ chemical polymerization is the most common method for preparation of the polyaniline/cellulose fiber composite materials. However, this method brings serious environmental pollution because the reduction product of traditional oxidants such as ammonium persulfate affects the recycling of waste liquor. To solve the above-mentioned problems, the polyaniline/cellulose fiber composites (PAn/CF①and PAn/CF②) were prepared by in-situ FeCl3/H2O2catalytic oxidative polymerization of aniline instead of using relatively costly chemicals such as persulfate salts as oxidants in the presence of cellulose fibers. Using the conductivity and reducibility of polyaniline (PAn) deposited on the cellulose fiber, the composite materials were applied to:1) antistatic packaging material and2) hexavalent chromium sorbing material. The optimal preparation conditions of the polyaniline/cellulose fiber composite materials (PAn/CF) for different purposes were identified, and the factors affecting the process of hexavalent chromium removal from the wastewater were investigated. The experimental data were fitted to various isothermal adsorption and kinetic models, and the thermodynamic parameters of reaction process were determined. Meanwhile, the performance of this fiber composite was compared with the polyaniline/cellulose fiber composite material (PAn/CF③) which was prepared by using ammonium persulfate as oxidant.The main contents/findings of this research are:1. The polyaniline-deposited conductive paper was prepared via in-situ chemical catalytic oxidative polymerization of aniline in pulp suspension by using ferric trichloride as catalyst and hydrogen peroxide as oxidant and hydrochloric acid as dopant. This method solved the problem of weak oxidizability of hydrogen peroxide in the acidic medium. The optimal conditions for the preparation of polyaniline/cellulose fiber composite (PAn/CF①) were: hydrogen peroxide/aniline molar ratio of1mol/mol, hydrogen chloride concentration of1mol/L, reaction time of2h, ferric chloride dosage of0.15mmol/L, aniline dosage of6g/L, reaction temperature of25℃, and nitrogen gas protection. The surface resistance and bulk resistivity of the conductive paper prepared under the optimal conditions were320KQ and25KΩ, respectively, and they could meet the standard of antistatic packaging materials.2. The application of polyaniline/cellulose fiber compositeas a new type of highly efficient adsorbent was investigated. The optimal conditions of FeCl3/H2O2catalytic oxidative in-situ polymerization were:reaction temperature of40℃, hydrogen peroxide/aniline molar ratio of2mol/mol, hydrogen chloride concentration of1mol/L, reaction time of1.5h, ferric chloride dosage of0.15mmol/L, aniline dosage of4g/L, and pulp consistency of1%. For the purpose of comparing with polyaniline/cellulose fiber composite material prepared by using ammonium persulfate as oxidant, the optimum process conditions related to the use of ammonium persulfate as oxidant were also determined:reaction temperature of25℃, ammonium persulfate/aniline molar ratio of0.8mol/mol, hydrogen chloride concentration of1mol/L, reaction time of2h, aniline dosage of4g/L, and pulp consistency of1%. It was found that the two types of cellulose fiber composite materials maintained a good storage stability after48hours storage in water, and the removalof Cr(VI) from contaminated water was still able to maintain more than93%. The removal of Cr(VI) from contaminated water by the two types of cellulose fiber composites after35hours storage in air was maintained at84.32%and91.26%, respectively, and the decreased prcentages were11.6%and6.7%, respectively.3. The removal of Cr(VI) from contaminated water was a reduction-adsorption process. This process was determined by pH, initial concentration of Cr(VI), dosage of fiber composite materials and reaction time. The reduction-adsorption process only required a very short time; within10minutes, all of the Cr(VI) in contaminated water could be removed by the polyaniline/cellulose fiber composites, and the adsorption of Cr(III) by cellulose fiber composite was the key step in the whole process. When the initial concentration of Cr(VI) was400mg/L, the adsorption amounts of Cr(VI) by two types of polyaniline/cellulose fiber composites (PAn/CF②and PAn/CF③) reached the saturation values, i.e.,15.66mg/g and19.11mg/g, respectively.4. The experimental data on the two types of composite materials (PAn/CF②and PAn/CF③) were fitted by various isothermal adsorption models and adsorption kinetic models. The adsorption process followed the Langmuir isotherm model better in comparison to other isotherms, and the calculated saturated adsorption amounts obtained from this model were16.44mg/g and19.85mg/g, respectively, and were more approximate to the experimental values. The kinetic studies showed that pseudo-second-order model was able to provide a realistic description of the biosorption kinetics of the polyaniline/cellulose fiber composites. According to the fitting results, it was found that the reaction rate decreased with the increase of temperature and initial concentration of Cr(VI), but increased with the increase of dosage of fiber composite materials. The thermodynamic analysis indicated that the removal of Cr(VI) by PAn/CF②followed an exothermic reaction (△H=-2.30KJ/mol), i.e., the lower temperature, the better Cr(VI) removal. Conversely, the removal of Cr(VI) by PAn/CF③followed an endothermic reaction (AH=3.62KJ/mol), i.e., the higher temperature, the better Cr(VI) removal. According to the fitting results of intra-particle kinetic model, it was found that the reduction-adsorption process of Cr(VI) by polyaniline/cellulose fiber composite materials was controlled by both liquid film diffusion and intra-particle diffusion.To conclude, the polyaniline/cellulose fiber composite prepared by using hydrogen peroxide as green oxidant may be used as antistatic packaging material and highly effective adsorbent for Cr(VI) and the performance was equivalent to that of polyaniline/cellulose fiber compositeprepared by using the traditional ammonium persulfate as oxidant. This polyaniline/cellulose fiber composite showed a very promising potential for future applications.