Study On The Removal Of Pb(?) And U(?) By Sulfur-and Oxygen-modified Graphitic Carbon Nitride Nanosheets

Heavy metals and radionuclides pollution is extremely harmful to nature,and the negative effects are long-lasting and difficult to recover.Therefore,environmental researchers have always attached great importance to these pollutions.Oxide carbon nitride(OCN)and sulfur-doped carbon nitride(S-g-C3N4)materials were synthesized by improving graphite phase carbon nitride(g-C3N4)materials through oxidation and sulfuration.The mechanism of OCN adsorption of UO22+and S-g-C3N4 adsorption of Pb(?)was studied respectively,and the microscopic morphology,spectroscopic properties,surface charge and specific surface area of the material were systematically and comprehensively analyzed by advanced characterization methods.The specific research contents and conclusions are as follows:(1)Increasing active site and specific surface area are two key methods to enhance the adsorption capacity of adsorbent.Herein,oxide carbon nitride(OCN)nanoparticles were manufactured by oxidizing the g-C3N4.The synthesized OCN exhibited excellent adsorption capacities for UO22+(94.1 mg g-1)and the rapid adsorption efficiency with reaching equilibrium within 10 minutes.Based on the batch experiment results,the adsorption isotherms could follow the Langmuir models.Combined with the X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD)and Fourier transform infrared spectrometry(FT-IR)analyses,the results indicated that the original triazine structure was destroyed and a large number of oxygen-containing functional groups were introduced.Herein,more conbining sites were introduced to form a stable inner complex with UO22+.To sum up,OCN nanoparticles are easy to prepare,possess high adsorption capacity and could aviod secondary pollution.Hererin,the material could have broad application prospects in repairing the water of uranyl high-emission waste solution.(2)Two-dimensional(2D)layered adsorbents for environmental decontamination possess high affinity for target contaminations and rich active groups.In this work,we synthesized a heteroatom S-g-C3N4 nanosheet by pyrolysis for S-and N-rich supramolecular polymer precursor.A hierarchically porous structure with multimodal pore size distribution can facilitate the Pb(?)ions diffusion from the wastewater to S-g-C3N4 surface.Batch adsorption experiments shown that the as-prepared S-doped conjugated system of g-C3N4 displayed higher adsorption capacity(52.63 mg g-1)as compared with that of bulk g-O3N4(31.25 mg g-1).The higher adsorption capacity of S-g-C3N4 was owing to the more binding sites(i.e.soft S ligand),coordination with Pb(?).Thermodynamic parameters established that the adsorption process w2s spontaneous and endothermic.And the kinetic experiments shown that the adsorption experiment was dominated by chemisorption.Futhermore,all geometries of(S-g-C3N4)-Pb(?)systems were constructed to search the optimized structure.According to the Density Functional Theory(DFT),the improvement of S-g-O3N4 adsorption for Pb(?)was favored in C3N4-S-N3—the mono-substituted system,in which the chemical binding of N-Pb and S-Pb was further demonstrated by X-ray photoelectron spectroscopy(XPS)analysis.The results established a environmentally friendly and facile strategy to manufacture S-g-C3N4 with desirable adsorption ability.Meanwhile,the study revealed the adsorption mechanism by theory simulation and experiments.