Synthesis Of Functionalized Ultra-thin Carbon Nitride Nanosheets And Its Application In Heavy Metal Analysis

Ultra-trace heavy metal ion pollution has attracted worldwide attention,it's very important to develop efficient methods for detecting and separating metal ions in the environment samples.Graphite-like carbon nitride materials have the advantages of easy-to-prepare and non-toxic,which can be widely used in sensors and adsorbents.This paper systematically studied the preparation of oxygenous functionalized carbon nitride and new method to control the oxygen content on the surface of carbon nitride.The main contents are listed as follows:(1)Ultrathin graphene-like carbon nitride nanosheets have shown promising prospect in photocatalysis,whereas no preparation strategy for adjusting their bandgap in a wide range has ever been reported.Herein,high yield-rate synthesis of ultrathin two-dimensional carbon nitride nanosheets with controllable oxygenous functionalization(the mass ratio of oxygen ranges from 0.523 to 19.9%)was firstly achieved by an improved hummer's method combining concentrated sulfuric acid protonation and potassium permanganate assisted exfoliation,and reduction employing hydrazine hydrate.Protonation and intercalation behavior of different acids in the treatment of bulk-g-C3N4 was elaborated at molecule level for the first time.Our strategy may open a new vista for design and construction of various carbon nitride nanocomposites and give detailed instructions in bandgap engineering of other two-dimensional functional materials for wider applications.(2)Enhancing the sensitivity of sensors is one of the most critical targets for the progress of analytical chemistry.Herein,an ultrasensitive voltammetric sensor for determination of Cu(?)was firstly prepared based on carbon nitride materials.Ultrathin carbon nitride nanosheets with large amount of oxygenous groups(?o= 19.9%,SBET =360.2 m2/g)was synthesized for the electrode modification via an improved Hummer's method for the first time.The accumulation mechanism of the large amount of oxygenous groups on ultrathin carbon nitride nanosheets towards Cu(?)was also firstly verified employing cyclic voltammetry and X-ray photoelectron spectroscopy.The as-prepared electrode showed extremely high sensitivity and wide linear ranges in Cu(?)determination employing differential pulse stripping voltammetry with acceptable anti-contamination ability,repeatability,fabrication reproducibility,storage stability and anti-interference ability,whose limit of detection(S/N = 3)is 2.3 × 10-15 mol/L with two linear relationships in 2.3 × 10-14?5.5 × 10-9 and 5.5 × 10-9?3.2 × 10-6 mol/L.The determination of Cu(?)in environmental water samples showed satisfactory precision and accuracy employing the as-presented method.The simultaneous determination for Hg(?),Pb(?)and Cu(?)was also achieved by the as-prepared electrode.(3)A voltammetric sensor for selective determination of ultra-trace Pb(?)was prepared by EDTA-immobilized Graphene-like Carbon Nitride Nano Sheets(EDTA-CN-NS),which has been designed to improve the accumulation performance for Pb(?)onto the electrode surface.The EDTA-CN-NS was prepared through pre-oxidation by K2S2O8 and silanization by N-(trimethoxysilylpropyl)ethylene-diamine triacetic acid sodium salt.The crystalline structure,morphology and the added functional groups of EDTA-CN-NS were characterized by XRD,SAED,TEM,STEM mapping and FT-IR,which is quite in accord with the catalysis action in CV test generated by improved accumulation performance of the immobilized EDTA for Pb(?).The detection limit of EDTA-CN-NS/Nafion modified sensor reached 5.7 × 10-13 mol/L with two linear ranges from 2.1 × 10-12?5.7 × 10-10 mol/L and 1.3 × 10-9?1.7 × 10-6 mol/L.The sensor showed acceptable selectivity for Pb(?)in the presence of common potential interferences and was successfully applied to analysis the concentration of Pb(?)in different water samples.This work gives new instructions for the design of ultra-sensitive sensors in determination of heavy metal ions using 2D functional materials.(4)Developing an available analysis platform for simultaneous heavy metal ion flux measurement at trace level is urgent for understanding the mechanisms of phytoremediation.Herein,oxygenous functionalized carbon nitride nanosheets assembled porous films on multi-walled carbon nanotube formed nano frameworks was firstly prepared on a carbon fiber disk microelectrode by an advanced drop-casting method.The as-prepared electrode shows low detection limit(1.0 × 10-13 mol/L for Cu2+,1.8 × 10-11 mol/L for Pb2+ and 8.0 × 10-12 mol/L for Hg2+),acceptable linear ranges(6.6 × 10-12?8.5 × 10-6 mol/L for Cu2+,8.1 × 10-10?8,5 ×10-6 mol/L for Pb2+ and 2.2 x 10-11?8.5 × 10-6 mol/L for Hg2+)and fine selectivity in simultaneous determination.The improved accumulation ability of modifier is attributed to improved conductivity and the porous morphology of the film,which may improve useful rate of the chelation groups.Based on the as-prepared electrode and a stepper motor,the voltammetric platform for simultaneous heavy metal ion flux measurement at trace level is fabricated for the first time.This platform can be utilized for mechanism investigation of simultaneous metal uptake on the surface of rice roots at trace level.(5)Superparamagnetic thiol functionalized oxygenous carbon nitride nanocomposites(CNO/Fe3O4-SH)with multifunctional groups such as-NH2,-OH,-SH and-COOH were fabricated by a simple and eco-friendly method for removal Pb(?),As(?)and Cd(?).CNO/Fe3O4-SH nanocomposites were characterized by scanning electron microscopy(SEM),power X-ray diffraction(XRD),Infrared spectrometry(FI-IR)and X-ray photoelectron spectroscopy(XPS).The maximum adsorption capacities of Pb(?),As(?)and Cd(?)on CNO/Fe3O4-SH at pH = 6 are 80.79,71.78 and 66.19 mg/g respectively when the equilibrium concentration was 20 mg/L.Furthermore,the adsorption capacity of CNO/Fe3O4-SH at low equilibrium concentration of metal ions were higher than other work.The competitive adsorption experiments presented the affinity in the order of Pb(?)>As(?)>Cd(?).Adsorption kinetic and isotherms studies indicated that sorption of Pb(?),As(?)and Cd(lI)on CNO/Fe3O4-SH nanocomposites was monolayer adsorption and the adsorption process were controlled by chemical adsorption.The thermodynamic studies demonstrated that adsorption processes were endothermic and spontaneous.The CNO/Fe3O4-SH nanocomposites still maintain their primary morphology and can be repeatedly used for more than six cycles without obvious degradation after the initial HCl and subsequent KOH treatment.Chemical adsorption was confirmed by XPS(binding energy and shape of N 1s,O 1s and S 2p peaks)of CNO/Fe3O4-SH with adsorbed Pb(?),As(?)and Cd(?).CNO/Fe3O4-SH nanocomposites have remarkably potential application in decontamination of trace heavy metal ions with fast adsorption kinetics,high adsorption efficiency,good regeneration,and ease of separation operation.