超分子前驱体制备磷掺杂三维g-C_(3)N_(4)及其光催化性能

Synthesis and photocatalytic performance of P-doped threedimensional g-C_3N_(4) from supramolecular precursors

以三聚氰胺、三聚氰酸为原料,磷酸铵为P掺杂剂,采用超分子自组装法和化学沉淀法制备了P掺杂三维石墨相氮化碳(g-C_(3)N_(4))MNP-x[x为三聚氰胺用量0.01 mol时磷酸铵的添加质量(g),下同]。通过XRD、FTIR、XPS、SEM、UV-Vis和光致发光(PL)对MNP-x进行了表征,评价了其对罗丹明B(Rh B)的光催化降解性能,使用自由基捕获剂验证了光催化反应中起作用的活性基团,并推测了反应机理。结果表明,最佳条件下制备的MNP-0.08形貌由g-C_(3)N_(4)(MN)的一维管状变为三维花束状;P原子取代部分C原子掺杂到g-C_(3)N_(4)结构单元;MNP-0.08提高了电子-空穴对(e^(–)-h^(+))的分离能力,改变了能带结构,价带(VB)从1.96 eV(三聚氰胺制备的纯g-C_(3)N_(4)记作CN,下同)升至2.00 eV,导带(CB)从–0.70 eV(CN)降至–0.75 eV,能带间隙(E_(g))从2.66eV(CN)升至2.75eV。·O_(2)^(–)作为主要的活性基团使MNP-0.08光催化降解Rh B能力得到提高,反应速率常数(k)为0.02816 min^(–1),是MN(k=0.00955 min^(–1))的2.95倍。能带结构改变、P作为富电子中心促进载流子分离和P掺杂诱导高电荷转移并使受激电子局部化的协同效应使MNP比MN具备更高的光催化性能。

P-doped three-dimensional graphitic phase carbon nitride(g-C_(3)N_(4)) 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-0.08prepared under the optimal conditions changed from one-dimensional tubular shape of g-C_(3)N_(4)(MN) to three-dimensional bouquet,with P atoms replacing some C atoms and doping into g-C_(3)N_(4) 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-C_(3)N_(4) 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 ·O_(2)^(–),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.