Nitrate Removal From Aqueous Solution Using Activated Carbon Modified By Conducting Polypyrrole (PPy-AC)

In recent years,contamination of water by nitrate has raised serious concerns globally.Owing to the extensive use of nitrogen fertilizers and improper treatment of wastewater from industrial sites,a significant increase in the nitrate level in the surface water and groundwater in many areas has been found.A high nitrate concentration in drinking water can cause serious threat to human health.Therefore,it is of great significance to develop a highly efficient technique for the removal of nitrate from drinking water.Biological denitrification and electrochemical reduction were the two widely used treatment methods.Electrochemical reduction has some limitations such as ammonium production and the pH control requirement.Biological denitrification needs addition of carbon source and temperature control.Comparatively,adsorption processes seems to be superior to other techniques for the removal of nitrate in terms of ease of operation,simplicity of design,and low economic costs.In this study,an activated carbon composite modified by polypyrrole(PPy-AC)as a novel adsorbent for nitrate adsorption was developed via in situ chemical oxidative polarization.The optimum polymerization conditions of PPy-AC composite were designed by Response Surface Methodology.SEM,FTIR,XPS,and BET specific surface area analysis methods were performed to characterize the PPy-AC composite.The effect of adsorbent dosage,initial nitrate concentration,pH and co-existing ions on nitrate adsorption was investigated.Morphology,chemical structure and element analysis showed that the AC was successfully decorated with flocculent PPy.Over 90% removal efficiency was achieved with a wide pH range of 3.0-9.0.The pHzpc was obtained at pH 9.05.Nitrate adsorption was most independent of pH and temperature and was a spontaneous exothermic process.The experimental data followed the pseudo-second-order kinetic model and fitted well to the Redlich–Peterson isotherm model.The maximum adsorption capacity for nitrate on the PPy-AC composite was 13.36 mg NO3--N/g.The mass and charge balances were calculated,and about 8.4% of the nitrogen in the polypyrrole functionality was active for capturing nitrate.The mechanism of nitrate removal by the PPy-AC composite was electrostatic attraction and ion exchange process,accompanying with the intraparticle diffusion.Overall,in this study,the activated carbon modified by polypyrrole caneffectively adsorb nitrate from aqueous,which is a low cost,simple and efficient water treatment method.