摘要
以硫脲和碘化钾为原料,采用热聚合法合成了K掺杂g-C_3N_4光催化剂(CN-K),通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线能谱(XPS)、比表面积(BET)、紫外-可见漫反射(UV-vis DRS)和荧光光谱(PL)等对样品进行微结构表征分析,并在优化晶体结构模型基础上,采用第一性原理计算模拟并解析能带结构和态密度分布.结果表明,掺杂K离子与N形成K–N键,并存在于g-C_3N_4层间.在可见光照射下对ppb级NO表现出了显著增强的可见光催化活性和良好的光化学稳定性.CN-K优异的活性可归因于K掺杂作用对g-C_3N_4电子结构的调变.K掺杂作用调节禁带位置,价带与导带的位置均下移,其中导带下移幅度高于价带,使催化剂禁带宽度减小,因此拓宽了光响应范围,使其可见光区域吸光能力增强;K掺杂使光生载流子的分离效率增加;K掺杂g-C_3N_4比纯g-C_3N_4的价带位置更正,K的掺杂作用使其光生空穴的氧化能力增强.本文阐明了K掺杂g-C_3N_4改性作用机理以及其可见光催化净化NO的机理.本文为光催化剂碱金属改性降解污染物提供了新的认识.
For the past few years, air quality has surged to worldwide attention. For NOx purification, semiconductor photocatlysis as a green technology that could use sunlight to purify air pollutants, provides an attractive alternative to decrease pollution. Recently, polymeric graphitic carbon nitride（g-C3N4） materials have drawn intensive attention because of its metal-free and high-hardness features, reliable chemical inertness, thermal stability, as well as its versatile optical, electrochemical, and efficient photocatalytic properties. But pure g-C3N4 suffers from rapid recombination of photogenerated electron-hole pairs resulting in low photocatalytic activity. Thus, several coping modifying methods were employed to improve the photocatalytic performance of g-C3N4. The present work developed a facile in situ method to construct novel k-doped g-C3N4（CN-K） structure with molecular composite precursors. In this work, the samples were prepared via pyrolysis of thiourea and a certain amount of KI as the potassium source in a muffle furnace. Different mass ratio（1%, 3%, 5%, 10%） of K-doping g-C3N4 samples were prepared by changing the amount of KI. The as-prepared samples were systematically characterized by XRD, SEM, TEM, XPS, BET, UV-vis DRS and PL. Material studio was used to simulated the crystalline structure of potassium doped g-C3N4. The bond structure of as-prepared samples can be theoretical calculation by DFT theoretical calculation. Both the experimental and theoretical calculation results indicated that potassium ion which were formed chemical bond with nitrogen existed in the interlayer of g-C3N4. The modified catalyst exhibited outstanding photocatalytic activity and photochemical stability towards degradation of NO at ppb-level under visible light irradiation. The superior activity can be ascribed to the significant function of potassium ion worked on morphological structure, band gap and electronic-hole recombination of as prepared samples. Firstly, evidenced by valence band XPS and DFT theoretical calculation, potassium doping has the function of modifying band-gap, making for down-shift both conduction band and valence band, however, The extent of the conduction band down shifting more than the valence band, shortening down the optical band gap more while making a significant enhancement of the solar light response range, thus the absorption capacity of as prepared samples strengthen significantly. Secondly, the separation efficiency of photon-generated carriers increased with potassium doped in the interlayer of g-C3N4 verified by room temperature PL spectra. Thirdly, the in situ K-doped g-C3N4 showed higher oxidation capacity of photo-induced holes for degradating NO, ascribed to a more positive valence band. Integrated three factors, purification efficiency of NO has been significantly improved. This work could provide a new perspective for modification of photocatalyst with alkali metals and mechanism understanding of NO degradation.
出处
《科学通报》
EI
CAS
CSCD
北大核心
2016年第24期2707-2716,共10页
Chinese Science Bulletin
基金
国家自然科学基金(51478070
51508356
21501016)资助
关键词
g-C3N4
K掺杂
可见光催化
禁带结构
NO净化
g-C3N4 K
doping
visible light photocatalysis
density functional theory
NO purification
