Catalytic Reduction Of Hexavalent Chromium By A Novel Nitrogen-functionalized Magnetic Ordered Mesoporous Carbon Doped With Pd Nanoparticles

Hexavalent chromium (Cr (?)) is a commonly used metal in the process of industrial production such as steel industry, auto preserving, clothing making and so on. Serious chromium pollution has occurred due to the leaking and improper use in technological production. As is known to all, Cr(?) is regarded as a major toxic pollutants of the world and has been proved to increase risk of DNA mutation and has carcinogenicity and acute toxicity as well. Cr(?), is relatively nontoxic, inert and less mobile, as a well-known nutrient of lipid and sugar metabolism for human and animal. It is also a serious water pollution which can cause highly toxic influence to the health of the human and animals. Therefore, developing new methods to remove hexavalent chromium in water attracts great attention of scholars.Recently, a few in situ chemical reduction technologies which need addition of reductants into the subsurface, wherein Cr(?) can be subsequently removed at acidic condition, have been mentioned to remediate the pollution in the groundwater in recent years. For example, nanosized iron particles have stimulated wide attention on successfully reductive precipitation of Cr(?) in wastewater purification and groundwater due to their low cost. However, it was proposed that chromium ions and Fe oxide formed the precipitate on Fe0 surface, which hindered the reduction reaction due to the aggregation. While redox manipulation that decreases the chromium compound concentrations by the addition of dithionite is proven an effective method, but the amount of reactive iron has always been limited. Consequently, it is of great importance to develop new recovery process which possesses a sustainable capacity to reduce Cr(?) efficiently.In our research, we successfully synthesized a new type of magnetic mesoporous carbon hybrid nitrogen (Fe-NMC) loaded with catalyst Pd nanoparticles (NPs), which performed excellent reduction efficiency towards Cr(VI). The characterization of Pd/Fe-NMC composites was investigated in detail using scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR), and nitrogen adsorption-desorption measurements. According to the experimental results, we dealt with in-depth discussion and studied on the mechanism of hexavalent chromium removed by Pd/Fe-NMC composites. Batch experiments were conducted to investigate the reduction of composites. It was found that the chromium reduction process conforms to first order reaction kinetics model when the concentrations of chromium and sodium formate were low. It took only 20 min for the Pd/Fe-NMC composites to reach 99.8% reduction of Cr(VI) (50 mg/L). The results suggested that the Pd/Fe-NMC composites may exhibit significantly improved catalytic activity for the hexavalent chromium reduction at industrial waste water.