Hydrothermal Synthesis Of Carbon Nanomaterials For Removal Of Cadmium And Lead Ions In Water

Heavy metal pollutants in wastewaters are non-biodegradable, and can beaccumulated in the food chain and cause severe damage to the environment and humanbeings. In the existing treatment methods, adsorption is widely used due to goodselectivity, adaptability to low concentration heavy metals and easy operation. In recentyears, environmental friendly adsorbents synthesized from biomass have causedwidespread concern for their large output, carbon fixation and sustainability.To obtain carbon-based absorbent with high capacity and excellent separabilitytoward adsorption of heavy metals in water, in the first part of this paper, magneticcarbon microspheres （MCMS） were obtained by hydrothermal carbonization of glucose,followed by immobilization of magnetic iron oxide nanoparticles via chemicalco precipitation method. The MCMS were characterized by scanning electronmicroscope （SEM）, transmission electron microscope （TEM）, Fourier transforminfrared （FT IR） spectroscopy and X ray photoelectron spectroscopy （XPS）, specificsurface analyzer and Zeta potential analyzer, and used in Cd²⁺and Pb²⁺ion adsorption.The results showed that the hydrothermal method could yield high qualityhomogeneous microspheres （0.20.6μm in diameter） with abundant oxygen containingfunctional groups and magnetic Fe3O4nanoparticles （40150nm） on surface. MCMSexhibited effective adsorption of Cd²⁺ions in water, which was endothermicspontaneous reaction and well consistent with the pseudo second order kinetics andLangmuir isotherms. In individually adsorption, the maximum adsorption capacity ofPb²⁺was higher than that of Cd²⁺. In competitive adsorption, Pb²⁺ions adsorption waspreferential, and when concentration was higher, advantage of Pb²⁺ions was moreobvious. When adsorption wass done, the MCMS could be separated from the liquidphase instantly by magnet.To further improve the separation performance of the adsorbent, in the second partof this paper, carbon nanowire membrane （CNM） was obtained by hydrothermalsynthesis. First, carbon nanowires were prepared using ultrafine tellurium nanowires asa template, and glucose as raw material, and then CNM was made via solventevaporation self-assembly process. The CNM was characterized by SEM, FT IR,specific surface analyzer, contact angle meter and Zeta potential analyzer, and used inCd²⁺and Pb²⁺ion adsorption. The results showed that CNM was porous networkstructure formed by lots of nanowires which were at least ten microns long and hadaverage diameter of220nm. CNM had a hydrophilic surface with abundantoxygen containing functional groups on it. Adsorption of Cd²⁺ions on CNM wasendothermic spontaneous reaction and well consistent with the pseudo second orderkinetics and Langmuir isotherms. BET specific surface area was28.8m2·g-1, and maximum membrane water flux was1300L·m-2·h-1.Studies have shown that compared with conventional adsorbent, MCMS andCNM both have excellent separability and higher capacity for heavy metal removal, andthe use of CNM is more convenient, and easy to regenerated.