Research On Graphene-Like Materials For Fluorescence Detection And Adsorption Of Heavy Metal Ions In Wastewater

With the rapid development of industrial science and technology,the pollution of the heavy metals has become more and more serious.Therefore,accurate detection and treatment of heavy metals are very important to alleviate the pressure on the water environment.Graphite carbon nitride（g-C₃N₄）has a planar two-dimensional sheet structure like graphene.Due to its unique structure and excellent properties,it has been extensively studied on fluorescent detection and pollutants removal.In this experiment,g-C₃N₄ was used as raw material to detect heavy metal ions in sewage,and by modifying g-C₃N₄,S-doped g-C₃N₄/graphene oxide（GO）aerogel material（SGA）was prepared.g-C₃N₄derived materials were explored on detection and removal of mercury ions.The microstructures of the above two materials were observed by scanning electron microscope and transmission electron microscope,and the characterization methods such as element analysis,ultraviolet-visible absorption spectroscopy and infrared spectroscopy were used to analyze the materials before and after modification to elucidate the materials structure.Fluorescence detection has the characteristics of high sensitivity and strong selectivity.g-C₃N₄ is synthesized by calcining melamine at high temperature,and thiocyanuric acid（TCA）and Hg²⁺are detected by selective fluorescence quenching and enhancement.Both theoretical and experimental results prove that g-C₃N₄ has high sensitivity and specificity in response to TCA and Hg²⁺.Due to theπ-πinteraction between g-C₃N₄ and TCA,the fluorescence intensity decreases with the increase of TCA concentration.When the TCA concentration reaches 45μM,the fluorescence spectrum of g-C₃N₄ is basically quenched at the wavelength of 436 nm.After adding Hg²⁺,the fluorescence increases owing to the coordination between TCA and Hg²⁺.When Hg²⁺concentration reaches 70μM,the fluorescence recovers to 50%of the initial fluorescence intensity,achieving fluorescence-enhanced detection of Hg²⁺.In addition,S-doped g-C₃N₄ nanotubes and large sheets of graphene oxide（LGO）were synthesized to prepare a three-dimensional aerogel adsorbent to study the adsorption of mercury ions.Theoretical calculations and experimental results show that this three-dimensional structure can be achieved excellent Hg²⁺adsorption through physical adsorption（electrostatic force generated by the tubular structure of S-doped g-C₃N₄ nanotubes）and chemical adsorption（through S-doping/coordination of S-containing sites）.The optimal adsorption conditions are investigated through parallel experiments.When the p H of the adsorption system is 5,the adsorption reaches equilibrium within 2 hours,and the optimum adsorption temperature is 45℃.When the initial concentration of Hg²⁺is 1000 ppm,the maximum adsorption capacity is 161.55 mg/g.The fitting results of the adsorption data indicate that the adsorption of the adsorbent conforms to the quasi-second-order kinetic model and Langmuir monolayer adsorption model.In addition,the MTT proliferation test in this study shows that the adsorbent has good biocompatibility.Finally,the adsorbent is further applied to the mercury ion treatment in the actual ammonia desulfurization slurry to prevent it from being reduced to zero-valent mercury and then reemission.Therefore,the system is expected to be applied to actual industrial wastewater treatment.