Preparation Of Composite Materials Of CoS₂/GO And Its Properties For Treatment Of Heavy Metals Hg???and Cr??? In Water

Graphene oxide is a kind of typical two-dimensional laminar carbon materials with a large specific surface area on which contains a large number of oxygen containing functional groups.Some small molecules or functional groups can be used to modify its surface to obtain functional GO,which can be used to remove some heavy metal ions in wastewater.Besides,GO can also be an excellent substrate on which to load suitable semiconductors and can be used as a photocatalyst with excellent properties.The transition metal sulfide CoS₂ has a wide light response range and can utilize ultraviolet,visible and near-infrared light in sunlight,making it an ideal material for photocatalytic materials.However,due to its narrow band gap,the separation efficiency of photogenerated carriers is low,which leads to its low photocatalytic efficiency.When heterogeneous junction is formed with other semiconductors,the separation efficiency of photogenerated carriers can be improved.Therefore,in this paper,GO was used as a substrate to prepare adsorbent and photocatalyst with high adsorption capacity by hydrothermal method respectively for removal of Hg?II?and Cr?VI?in wastewater.Specific research results are as follows:As an adsorbent,the CoS₂/GO composites were synthesized by hydrothermal method for selective removal of Hg?II?in wastewater.The changes of elements,morphology of adsorbent before and after Hg?II?adsorption and the changes of chemical structure were studied by SEM,TEM,XRD and FT-IR.It can be seen that the CoS₂ is uniformly loaded on GO with granular morphology.In addition,we studied the influence of pH,temperature and the adsorption capacity of adsorbent in the adsorption process.The results show that the adsorption process matches well with the Langmuir Isothermal adsorption model and the maximum adsorption capacity is 1267 mg/g indicating that the adsorption process of CG-3 to Hg?II?is a single monolayer adsorption.Further,CG-3 has a good selectivity to the heavy metal Hg?II?contained in wastewater,and the common metal ions,such as Na⁺,Fe³⁺and Ni²⁺,in water have less effect on the adsorption of Hg?II?.In addition,we used the adsorbent for 5 cycles,and the removal rate of Hg?II?was all above 95%,indicating that the CG-3 prepared with high stability.A series of CoS₂/g-C₃N₄-GO composite materials with different GO contents were synthesized by solvent-thermal method and used as a photocatalyst to reduce highly toxic heavy metal Cr?VI?to low-toxic Cr?III?under visible light,which was proved to have good photocatalytic performance.The composite photocatalyst was characterized by various analytical methods.It is found that when CoS₂ is combined with g-C₃N₄ and GO,the optical response range is extended to visible and near-infrared regions,solving the problem of narrow optical response range of photocatalyst.In addition,g-C₃N₄ and CoS₂form heterogeneous junction,which reduces the recombination rate of photogenerated electrons and holes which overcome the high recombination rate of photogenerated carriers.It was found that high GO content and low solution pH value were significantly conducive to the reduction of Cr?VI?,and the GO content was 20%,and its photocatalytic efficiency was 12.3 times and 2.5 times higher than that of pure CoS₂ and g-C₃N₄,respectively.Finally,it is found that the superoxide radical is the main active species during the photocatalytic process through the study of photocatalytic mechanism.