Preparation Of Pyrrole-based Biomass Composites And Its Comprehensive Treatment Of Hexavalent Chromium Ions In Water

With the advantage of low-cost,wide-ranging,environmentally friendly and easily degradable,biomass materials can be used not only in energy but also as a water pollutant adsorbent.In this paper,three kinds of biomass-based polypyrrole nanocomposites were prepared by using biomass materials?filter paper,straw,gelatin?as raw materials,and polypyrrole as modifier.The obtained nanocomposites show excellent adsorption effect on hexavalent chromium ions.Moreover,photothermal properties and electrical conductivity of polypyrrole were used,so that the material can be used for desorption process by the light and electrical assistant.As a result,the adsorbent can reduce reliance on high concentrations of eluent,reduce secondary environmental pollution.Furthermore,the transition between the oxidation state and the reduced state of polypyrrole enable polypyrrole-based nanomaterials not only adsorb hexavalent chromium ions,but also reduce hexavalent chromium ions to trivalent chromium ions.Then the comprehensive treatment of hexavalent chromium ions in water can be achieved.The main research contents are as follows:1.Filter paper was decorated with polyethylene glycol?PEG?and polypyrrole?PPy?to fabricate a FP/PEG/PPy nanocomposite,which could be used as an adsorbent for Cr???with a high adsorption capacity.The FP/PEG/PPy nanocomposite adsorbent can reach the adsorption equilibrium within 3 hours and exhibits good adsorption performance to hexavalent chromium ion.According to the conductivity and endothermic properties of polypyrrole,electrical-assisted desorption and photo-assisted desorption were designed.The results show that the Cr???release with applying the-1.0 V reduction voltage is about 6 times than that of the Cr???release without applying potential.Under the light condition,the concentration of Cr???released from the composite in the desorption solution gradually increased from 0.31 mg/L to0.84 mg/L.The results show that it could enhance the desorption process by electro-assisted or photo-assisted.2.Using ammonium persulfate as oxidant,pyrrole is polymerized onto the surface of the straw to prepare three kind of composites,named polypyrrole/straw composite material,polypyrrole/acidolysis straw composite material,and polypyrrole/enzymatically hydrolyzed straw composite material.The experimental results show that the three polypyrrole/straw complexes have good adsorption properties for hexavalent chromium ions.Among them,polypyrrole/enzymatically hydrolyzed straw has the best adsorption efficiency and its adsorption capacity was 10.5 mg/g.According to the quasi-first-order kinetic equation and quasi-second-order kinetic equation fitted from the adsorption data,it was found that the correlation coefficients of the quasi-second-order kinetic equation were all greater than those of the quasi-first-order kinetic equation when the adsorption equilibrium was reached for the three composites.It can be confirmed that the adsorption mechanism of the hexavalent chromium ion on the composite material is chemical adsorption caused by mutual attraction of static electricity.3.Using chromic acid as oxidizing agent,the PPy was introduced in Gel/CS,Gel/SA,Gel/CMC hydrogel network respectively.Three ion imprinted materials were prepared and named as Gel/CS/PPy,Gel/SA/PPy,Gel/CMC/PPy.The effects of additives?CMC,CS,SA?,pyrrole concentrations?0.1M,0.2M,0.3M?and gelatin additive ratios?4:0,4:1,4:2?in preparation process of hexavalent chromium imprinted materials were investigated respectively.The result shows that the prepared Gel/CS/PPy_0.2 had the best adsorption efficiency to hexavalent chromium when CS used as additive,the concentration of pyrrole was 0.2M,and the ratio of gelatin to additive was 4:2.The adsorption capacity of Gel/CS/PPy_0.2 could reach14.98 mg/g.In addition,the imprinted materials have excellent selectivity for hexavalent chromium and the electro-assistant can improve the desorption efficiency by 140%,while photo-assistant can improve the desorption efficiency by 19.8%.Three types of polypyrrole-based biomass composites were prepared for the adsorption of hexavalent chromium ion.The obtained PPy-based composites not only improve the adsorption/desorption performance of heavy metal ions,but also achieve the green economic utilization of biomass materials.