Synthesis and photocatalytic performance of P-doped three-dimensional g-C3N4 from supramolecular precursors
P-doped three-dimensional graphitic phase carbon nitride(g-C3N4)MNP-x(x denotes additive mass of ammonium phosphate when melamine is 0.01 mol,the same below)was prepared by supramolecular self-assembly and chemical precipitation method using melamine and cyanuric acid as raw materials and ammonium phosphate as P dopant,characterized by XRD,FTIR,XPS,SEM,UV-Vis and photoluminescence(PL),and evaluated for its photocatalytic performance on Rhodamine B(RhB)degradation.The active groups responsible for the photocatalysis were validated via free radical trapping agents,while the reaction mechanism was explored.The results showed that the morphology of MNP-0.08 prepared under the optimal conditions changed from one-dimensional tubular shape of g-C3N4(MN)to three-dimensional bouquet,with P atoms replacing some C atoms and doping into g-C3N4 structural unit.MNP-0.08 improved the electron-hole pair(e--h+)separation and changed the energy band structure,with the valence band(VB)increasing from 1.96 eV of pure g-C3N4 prepared by melamine(CN,the same below)to 2.00 eV,the conduction band(CB)from-0.70 eV(CN)to-0.75 eV,and the energy band gap(Eg)from 2.66 eV to 2.75 eV.The MNP-0.08 photocatalytic degradation of RhB was enhanced by·O2-,the main reactive group,with a reaction rate constant(k)of 0.02816 min-1,2.95 times higher than that of MN(k=0.00955 min-1).The synergistic effects of band structure change,P as an electron-rich centre to promote carrier separation,and P doping to induce high charge transfer and localization of excited electrons enabled MNP to display much improved photocatalytic performance than MN.
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