复合微量NCQDs对提高Ag_2CO_3半导体降解苯酚的光催化性能研究(英文)

半导体光催化具有无毒、无污染、低能耗等优点,广泛应用于水溶液中染料、药物分子的降解等.其中Ag_2CO_3半导体因其较窄的带隙能和显著的可见光吸收性能而引起广泛关注.但是Ag_2CO_3在光照下极不稳定.目前,主要是通过引入其它半导体等材料与其进行复合来提其催化活性与稳定性.本文以一种具有良好的水溶性以及能够加快电子转移能力的碳量子点(CQDs)和氮掺杂的碳量子点(NCQDs)作为复合材料,利用简单的沉淀法制备出了CQDs/Ag_2CO_3、NCQDs/Ag_2CO_3等复合材料.结果表明,CQDs和NCQDs的存在能够很好的提升光催化性能.而且发现NCQDs除了具有碳量子点的特性外,还能够诱导电荷离域,更加有效的促进电子的转移.利用X射线衍射、扫描电镜、透射电镜、N_2物理吸附、元素成像、紫外-可见光漫反射吸收光谱、红外光谱以及光电流和交流阻抗测试等手段对所制备的CQDs/Ag_2CO_3和NCQDs/Ag_2CO_3进行了表征.结果表明,量子点的存在能够有效增大Ag_2CO_3的比表面积.紫外-可见漫反射吸收结果说明,量子点的存在还能够在一定程度上增大样品的可见光吸收性能.而光电流和交流阻抗测试结果证明,量子点的存在能显著降低载流子的迁移阻力,提高光生电子与空穴的分离效率.在量子点相同含量下,NCQDs能够更加有效的转移载流子.以350 W氙灯加可见光滤光片(λ≥420 nm)作为光源进行光催化降解苯酚的性能测试.结果表明,NCQDs/Ag_2CO_3比CQDs/Ag_2CO_3表现出更高的活性,其对苯酚的降解率约为后者的2倍;同时NCQDs/Ag_2CO_3还具有更佳的稳定性能.自由基捕获试验说明,在光催化过程中,主要的活性物种为?OH与?O_2~-.NCQDs能够提高Ag_2CO_3活性与稳定性的原因在于,NCQDs能够提高了催化剂的比表面积,增强光催化剂的光吸收性能.另外NCQDs能够比CQDs更有效的转移电子,提高光生e~-和h~+的分离效率,产生更多的光催化降解活性物种.

Boosting the photocatalytic performance of Ag2CO3 crystals in phenol degradation via coupling with trace N-CQDs

A series of N-CQDs/Ag2CO3 composite crystals (where N-CQDs = Nitrogen doped carbon quantum dots) were prepared by adding different volumes of a solution of N-CQDs during Ag2CO3 crystal growth. Under irradiation from a 350-W Xe lamp light (with optical filter, λ ≥ 420 nm), the perfor-mance of N-CQDs/Ag2CO3 inphotocatalytic degradation of phenol was evaluated. The as-prepared samples were analyzed by XRD, SEM, TEM, BET, element mapping, UV-vis DRS, FT-IR, XPS, transient photocurrent response and EIS testing. The results showed that after coupling with trace amounts of N-CQDs, both the photocatalytic activity and stability of Ag2CO3 were greatly boosted. The addi-tion of N-CQDs solution influenced the crystallization of Ag2CO3, resulting in a distinct decrease in Ag2CO3 crystal size and an obvious increase in surface area. Moreover, the charge transfer resistance was greatly reduced, and the separation efficiency of photogenerated electrons and holes was strongly promoted. The presence of NCQDs on the surface of the catalysts facilitates the transfer of photogenerated electrons, slowing the photocorrosion rate of Ag2CO3, and then resulting in higher stability than bare Ag2CO3 in degradation. The synergistic effect of the improvement of morphology and charge transfer rate thus accounted for the superior photocatalytic performance of N-CQDs/Ag2CO3.