Graphitic Carbon Nitride:From Chemical Functionazation To Photoelectric Property Investigation

Recently,graphitic carbon nitride（g-C₃N₄）has been considered to be a promising inorganic semiconductor photoelectric conversion material because of its two dimensional planar structure as similar to graphene sheet,the suitable energy bandgap for photocatalytic and good enough chemical stability.However,bulk g-C₃N₄materials prepared from direct thermal-induced self-polymerization of organic precursors at high temperature generally have low surface area,narrow range of visible-light absorption,serious charge carriers recombination and poor dispersibility in common solvents,which limit its large-scale applications.This work foucs on the chemical functionalization of g-C₃N₄ and photoelectric property investigation.In particular,noncovalent modification and mixed-solvents assisted sonication dispersion approaches are applied to prepare g-C₃N₄ based hybrid materials with larger specific surface area,good dispersibility in solvents as well as high photocurrent response ability.In this wrok,the morphology,structure,optical and electrical properties of the prepared materials are fully characterized,and the photoelectric property,such as the photocurrent response performance is carefully measured and optimazied.Besides,the application of g-C₃N₄ composites in photocatalytic degradation is further investigated.The main contents of this paper are as follows:（1）Experimental design:alcian blue 8GX（a copper（II）phthalocyanine derivative,noted as AB）,was employed to functionalize graphitic carbon nitride（g-C₃N₄）in the manner of mixed-solvent liquid-phase exfoliation and noncovalent functionalization.The AB compound used inwork is because of it possesses suitable band gap energy（3.03 eV）,wide range of UV-Visible absorption scope（250 to400 nm and 550 to 800 nm）and excellent solubility.Meanwhile,the Zeta potential of AB is measured to bepositive,while the g-C₃N₄ shows negative Zeta potential,both of them can form stable composite material through Van Der Waals interaction and electrostatic adsorption force.First UV-Visible absorption and photoluminescence（PL）spectroscopy are applied to optimize the volume ratio of water and ethanol,and to deterime the mass ratio of g-C₃N₄ and AB.Experimental results show that the optimazed water and ethanol volume ratio is 3/2,and the mass fraction of AB in the g-C₃N₄/AB complex up to 10.6%.Second,SEM,TEM and AFM are empolyed to characterize the construction structure and morphologyof the hybrid materials.Characterization results demonstrate that the carbon nitride based hybrid composite with large surface area,excellent solution dispersibility and wide light absorption range was successfully prepared.Moreover,the photocurrent response,performance,alternating-current impedance and Mott Schottky photoelectric properties of the g-C₃N₄/AB composite are investigated,which showed that g-C₃N₄ and AB can form p-n heterostructure,and the prepared g-C₃N₄/AB composite has higher charge transfer efficiency than that of individual g-C₃N₄ and AB.Finally,application of g-C₃N₄/AB composites in photocatalytic degradation of organic dyes,with rhodamine 6G（R6G）as the representative of organic dye is also studied.Under the visible light irradiation and in the absence of sacrificial agent,the g-C₃N₄/AB hybrid reveals the highest photodegradation effficiency of R6G and the C/C₀ value of R6G decreases 99.1%under light irradiation for 80 min,while the decomposition of R6G was about 58.0%and 71.9%for the bulk g-C₃N₄ and induvidual g-C₃N_4,respectively.This work provides a novel approach for the preparation of functionalized g-C₃N₄ composites.（2）Experimental design:β-cyclodextrin（β-CD）was employed to functionalize graphitic carbon nitride（g-C₃N₄）with the help of mixed-solvent liquid-phase exfoliation,in order to preparedβ-CD/g-C₃N₄ hybrid with high dispersion concentration in solution and large specific surface area.β-cyclodextrin can be selectively the organic pollutants forming inclusion complexes in solutiondue to it has hydrophilic external cavity and hydrophobic lumen,which achieve to make water purification and sewage treatment.The particular work is as follows:FTIR and TGA are empolyed to characterize the composite components,which shows that theβ-CD was successfully modified on the surface of g-C₃N₄,and the mass ratio ofβ-CD is23.8%.Meanwhile,the microstructure and morphology of the composites are characterized by TEM and AFM.The experimental results show that the g-C₃N₄sheets with thickness of 3⁴ nm are facilely prepared in our work.Morepver,theβ-CD/g-C₃N₄ composite exhibits excellent performance in the adsorption and photodegradation of organic dyes.In terms of adsorption,the thermodynamic performance parameter of theβ-CD/g-C₃N₄ composite are calculated to be 47.62mg/g and 17355 L/mol,which is much larger than those of the pre-exfoliated g-C₃N₄(q_max.e=15.87 mg/g and K=2801 L/mol).The reaction kinetics performance parameter of K_obs(mg·g^-1·min^-1)reveals that the K_obs ofβ-CD/g-C₃N₄ is 0.216 mg·g^-1·min^-1,which is 5 times as much as the pre-exfoliated g-C₃N₄(0.041 mg·g^-1·min^-1).The above mentioned results clearly illustrate that theβ-CD/g-C₃N₄ hybrid possesses high efficiency for removing organic pollutants.In terms of photodegradation,theβ-CD/g-C₃N₄ hybrid reveals the highest photodegradation effficiency of MB and the C/C₀ value of MB decreases 98.5%under light irradiation for 180 min,while the decomposition of R6G was about 37.9%and 76.5%for the two control groups using bulk g-C₃N₄ and g-C₃N₄ alone as the catalyst,respectively.Meanwhile,the relationship between the scavengers and the photodegradation efficiency ofβ-CD/g-C₃N_4,and the photocatalytic mechanism are also investigated.（3）Experimental design:for the first time,a new small organic fluorescent compound（short for MAP）with highly green light emitting was synthesized from small molecule organic alkali and organic acids under a mild condition.The details as follows:the molecular structure was characterized by ¹H-NMR,¹³C-NMR,HLPC-MS and FTIR spectrum.UV-Vis absorption and PL spectrum are applied to characterized optical property of the MAP,the experimental results show that the emission wavelength and quantum yield of MAP were highly dependent on the solvent polarity.On this basis,we inspected the biocompatibility and cellular imaging of MAP,which show that the MAP had extremely weak toxicity to cells under the relatively high concentrations of 250μg/mL.Moreover,a very good cellular uptake with bright green fluorescence was observed in the cells from the confocal laser scanning microscope（CLSM）images.These results presented here show that these the prepared bright fluorescent compound is a novel and efficient material for cellular imaging and biotechnology.