The Synthesis Of Carboxylate-rich Carbon Composites And Their Application In Heavy Metal Wastewater Treatment

In recent years,due to the rapid development of industry and agriculture,with the growing environmental pollution problems,including heavy metals are one of the most significant group of pollutants.All these reasons derived intension of the researchers to focus and find ways to cope with the problem.Carbon-based materials is very suitable for removing heavy metals,because of its excellent physical and chemical properties.In this paper,three carboxylate-rich carbon-based materials including Fe₃O₄/carboxylate-rich carbon sheets、TiO₂/carboxylate-rich carbon、Fe₃O₄/carboxylate-rich carbon were prepared and used in the photocatalytic reduction of Cr（Ⅵ）in chromium-containing wastewater and the adsorption of copper ions in copper-containing wastewater respectively.In addition,NiFe₂O₄ electrode material was prepared by pickling iron-containing wastewater and electroplating nickel-containing wastewater as raw materials,and assembled into a symmetrical battery for battery performance research.The detailed content summarized as following:（1）Fe₃O₄/carboxylate-rich carbon sheets were synthesized by using FeSO₄·7H₂O,glucose and EDTA as raw materials via a low temperature carbonization process.Carbon sheets of Fe₃O₄/carboxylate-rich carbon sheets acts as a supporter.Fe₃O₄ nanoparticles are homogeneously dispersed into the carbon sheets and coordinate strongly with carboxylate groups of EDTA to form the ferricarboxylate complexes,Fe^Ⅱ（R-COO）_n^2-n and Fe^Ⅲ（R-COO）_n^3-n.Ferricarboxylate complexes endow the Fe₃O₄/carboxylate-rich carbon sheets with marked visible light absorption property.Fe（Ⅱ）/Fe（Ⅲ）photoredox cycle based on ferricarboxylate complexes of Fe₃O₄/carboxylate-rich carbon sheets exhibit excellent photocatalytic reduction of Cr（Ⅵ）activities under visible light irradiation.After photocatalytic reduction reaction,Fe₃O₄/carboxylate-rich carbon sheets can be easily retrieved by using an applied magnetic field.（2）TiO₂/carboxylate-rich carbon have been successfully synthesized via a low temperature carbonization process using tetrabutyl titanate,glucose and EDTA as raw materials.The optical,chemical and physical properties of TiO₂/carboxylate-rich carbon were explored with different techniques,such as SEM,TEM,Raman,EDS,XPS and FIR.Carbon sheet of TiO₂/carboxylate-rich carbon acts as a supporter,TiO₂ nanoparticles and EDTA can homogeneously disperse into the carbon sheet supporter and form the TiO₂-EDTA complexes.TiO₂/carboxylate-rich carbon exhibits marked absorption of visible light and excellent photoreduction of Cr（Ⅵ）activity.Via the LMCT sensitization mechanism,TiO₂/carboxylate-rich carbon possess significantly absorption of visible light and enhanced photoreduction of Cr（Ⅵ）activity.（3）Fe₃O₄/carboxylate-rich carbon have been synthesized via a facile one-step low temperature carbonization method from simple precursors,the single iron source FeSO₄·7H₂O and sodium gluconate.Carboxylate groups from sodium gluconate can coordinate with Fe（Ⅱ）and form ferricarboxylate complexes.During the low temperature carbonization process,Fe₃O₄ can be obtained through the thermal decomposition of ferricarboxylate complexes.Abundant carboxylate groups can enhance the adsorption affinity between the adsorbent and Cu（Ⅱ）.In addition,some of the theoretical simulation on the Cu（Ⅱ）adsorption model also been conducted.Among the various kinetics models,the pseudo-second-order model gives the most suitable kinetics model for adsorption of Cu（Ⅱ）onto Fe₃O₄/carboxylate-rich carbon composite.Adsorption of the heavy metals to Fe₃O₄/carboxylate-rich carbon agreed well to the Langmuir adsorption model with a maximum adsorption capacity of 66.67 mg/g.After completion of the adsorption or desorption,the metal loaded Fe₃O₄/carboxylate-rich carbon could be recovered readily from an aqueous solution by magnetic separation and regenerated easily by an acid treatment.The adsorption–desorption studies indicated that Fe₃O₄/carboxylate-rich carbon possesses good stability and good reusability.（4）Two different industrial effluents,spent pickle liquor and Ni-containing wastewater,were simultaneously treated via chemical precipitation and hydrothermal reaction to generate heavy metal sludge based on Ni Fe2O4.Subsequently,the NiFe₂O₄ was used to construct a NiFe₂O₄// NiFe₂O₄ symmetric battery.The NiFe₂O₄// NiFe₂O₄ symmetric battery was able to deliver specific capacity 23.1 mAh/g based on the total mass of the active materials at discharging current densities 0.5 A/g.The NiFe₂O₄// NiFe₂O₄ symmetric battery exhibits good cycling performance and the capacitance retention was found to be 90% after the 500 charge-discharges cycles.After 500 charge-discharges cycles,NiFe₂O₄ still exhibit good stability demonstrated by XRD analysis and TCLP test,which means that the NiFe₂O₄ can be disposed as a general industrial waste.