Na^(+)/g-C_(3)N_(4)材料的制备及光催化降解亚甲基蓝机理

Preparation of Na^(+)/g-C_(3)N_(4) Materials and Their Photocatalytic Degradation Mechanism on Methylene Blue

制备碱金属掺杂的g-C_(3)N_(4)在g-C_(3)N_(4)半导体光催化材料研究中属于一个重要分支。本研究采用溶液合成、煅烧和溶剂热反应方法制备了Na^(+)掺杂的g-C_(3)N_(4)样品(Na^(+)/g-C_(3)N_(4)),通过不同检测手段确定了Na^(+)在g-C_(3)N_(4)中的负载位置和光电性能,考察了样品的形貌、比表面积及孔径随溶剂热反应时间延长的变化规律。结果表明:Na^(+)负载位置和表面生成的C-O-基团增强了g-C_(3)N_(4)材料的物理和化学吸附性能,Na^(+)/g-C_(3)N_(4)对亚甲基蓝(MB)的吸附率最高可达到93.25%;Na^(+)负载位置对g-C_(3)N_(4)的π共轭体系的电子分布产生影响,进而改变了材料的禁带宽度(Eg)、导(价)带位置和光生载流子分离效率及传输速率;在可见光降解过程中,由于MB的自身光敏性和在Na^(+)/g-C_(3)N_(4)样品表面的强吸附性,MB和Na^(+)/g-C_(3)N_(4)样品构建了独特的光敏-光催化降解体系,MB不仅通过光敏自降解,还在Na^(+)/g-C_(3)N_(4)协同下进行了光催化降解。在pH 6.0条件下,MB和Na^(+)/g-C_(3)N_(4)光催化体系对MB的最高降解率可达96.40%。

Preparation of alkali metal doped g-C_(3)N_(4) materials is an important branch in the research of g-C_(3)N_(4) semiconductor photocatalytic materials.However,there is still lack of study on g-C_(3)N_(4) materials revealing mechanisms in photosensitizer-assisted photocatalytic degradation.In this study,Na^(+)doped g-C_(3)N_(4) photocatalysts(Na^(+)/g-C_(3)N_(4))were prepared using solution synthesis,calcination,and solvothermal reaction methods.The doped position of Na^(+)in g-C_(3)N_(4) and photoelectric performance were determined.The changes of morphological,specific surface area,and pore size of Na^(+)/g-C_(3)N_(4) materials were analyzed by scanning electron microscopy,N2 adsorption and desorption experiments.In Na^(+)/g-C_(3)N_(4) materials,the Na^(+)loaded in a cyclic structure composed of three heptazine structural units,coordinating with N atoms.Na^(+)/g-C_(3)N_(4) changed the adsorption performance of g-C_(3)N_(4),altered its bandgap width and position of conduction(valence)band,and increased its separation rate of photogenerated electrons and holes and charge transport rate of the material by affecting theπ-conjugated system of g-C_(3)N_(4).During the solvothermal reaction process for synthesis of Na^(+)/g-C_(3)N_(4),strong hydrolysis caused decomposition of unstable structures of g-C_(3)N_(4) while the C-O-bonds were formed at the edge of g-C_(3)N_(4).The physical and chemical adsorption sites for methylene blue(MB)of Na^(+)/g-C_(3)N_(4) materials are confirmed byπ-conjugated system and C-O-bonds of Na^(+)/g-C_(3)N_(4),by which Na^(+)/g-C_(3)N_(4) materials can adsorb MB up to 93.25%,in contrast to the g-C_(3)N_(4) materials’adsorbtion only up to 24.50%.Under visible light irradiation,due to their strong adsorption capacity and photosensitivity to MB,Na^(+)/g-C_(3)N_(4) materials have constructed a unique photosensitive-photocatalytic degradation system with MB.MB not only acts as the photosensitizer for self degradation but also collaborates with Na^(+)/g-C_(3)N_(4) materials for photocatalytic degradation.At pH 6.0,the maximum degradation rate of MB is up to 96.40%in the photosensitive-photocatalytic system constructed with MB and Na^(+)/g-C_(3)N_(4) samples.