Utilization Of Fe³⁺ Doped G-C₃N₄ In Different Photocatalytic Systems

Graphitic carbon nitride(g-C3N4)show intrinsic visible light response and high stability but low photocatalytic performance in practical applications due to defects such as high recombination rate of photo-generated electron-hole pairs.In order to enhance the photocatalytic degradation of organic pollutants by g-C3N4,the Fe3+doped g-C3N4 photocatalyst(Fe-C3N4)was prepared using ferric nitrate and melamine as precursors,and then characterized by Scanning electron microscope(SEM),X-ray diffraction(XRD),Fourier-transform infrared spectrocopy(FT-IR),X-ray photoelectron spectroscopy(XPS),UV-vis diffuse reflectance spectroscopy(UV-vis)and photoluminescence(PL),respectively.It was found from the characterization that the doping of Fe could change the energy band structure and visible light absorption range of g-C3N4 as well as inhabit electrons-holes recombination rate.Meanwhile,Fe-C3N4 was used in Oxalate-modified photocatalytic,heterogeneous-photo-Fenton and persulfate-photo-Fenton-like systems respectively for methylene blue(MB)degradation under simulated solar irradiation.The experimental results showed that in these three system 97.76%,97.91%,94.66%of MB was decolorized within 90 min,respectively.The effects of Fe doped amount,catalyst dosage,Oxalate/H2O2/Persulfate concentration and pH value on MB degradation were systematically investigated in order to explore the parameters effect and system optimum.The results indicated that the three systems had good degradation effects on MB at pH from 3 to 9.It was showed that the Fe-C3N4 can be recollected and employed again for next use.After three cycles reuse,the degradation efficiency of MB degradation had little change and from the results of XRD,the composition of Fe-C3N4 was not changed obviously,illustrating the good stability of Fe-C3N4.The quenching experiment demonstrated that photogenerated holes and·OH played major role in the photocatalytic degradation of MB in the Fe-C3N4/Oxalate system and heterogeneous photo-Fenton system while the high degradation efficiency of MB in the Fe-C3N4/PS syste:m can be firstly attributed to·OH and 02·-,then SO4·-,as well as the photogenerated holes.Besides,the transformation products of the three systems were identified and compared by means of HPLC-MS analysis.Finally,the effect of common inorganic ions in water on the degradation of MB by three systems was studied.The results showed that inorganic ions had an inhibitory effect on the degradation of methylene blue in Fe-C3N4/oxalic acid and Fe-C3N4/PS system.In the Fe-C3N4 heterogeneous photo-Fenton system,HCO3'showed a dual effect on the degradation of MB.However,Cl-,NO3-,Al?,Mg2+ and Ca2+ showed an inhibitory effect on the degradation of MB.