Nayak Susanginee, Parida K M
Centre for Nano Science and Nano Technology, Siksha 'O' Anusandhan Deemed to be University, Bhubaneswar 751030, Odisha, India.
ACS Omega. 2018 Jul 4;3(7):7324-7343. doi: 10.1021/acsomega.8b00847. eCollection 2018 Jul 31.
In this work, a series of heterostructure Ag@AgPO/g-CN/NiFe layered double hydroxide (LDH) nanocomposites were prepared by a combination of an electrostatic self-assembly and in situ photoreduction method. In this method, positively charged p-type AgPO was electrostatically bonded to the self-assembled negatively charged surface of the n-n-type g-CN/NiFe (CNLDH) LDH hybrid material with partial reduction of Ag to metallic Ag nanoparticles (NPs) by the photogenerated electrons and available surface -OH groups of LDH under visible light irradiation. The presence of AgPO as a p-type semiconductor, the surface plasmon resonance (SPR) effect of metallic Ag NPs, and oxygen vacancies as O-type defects in NiFe LDH could greatly achieve the quasi-type-II p-n/n-n dual heterojunctions, which was revealed by the shifted conduction band and valence band potentials in Mott-Schottky (M-S) analysis. Among all the optimized heterostructures, CNLDHAgP4 could achieve the highest photocatalytic Cr(VI) reduction rate of 97% and phenol oxidation rate of 90% in 2 h. The heterostructure CNLDHAgP4 photocatalyst possesses a unique morphology consisting of cubic phases of both Ag NPs and AgPO, which adhered to the thin and curvy layers of the CNLDH hybrid for smooth electronic and ionic charge transport. Furthermore, the intimate Schottky barriers formed at the interface of quasi-type-II p-n/n-n dual heterojunctions were verified by the photoluminescence, linear sweep voltammetry, M-S, electrochemical impedance study, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy studies. The SPR effect of Ag NPs and oxygen vacancies as O-type defect in NiFe LDH can effectively accelerate the threshold of charge separation and be the main reason for the enhanced activity achieved by the as-fabricated heterostructure photocatalyst.
在本工作中，通过静电自组装和原位光还原法相结合制备了一系列异质结构的Ag@AgPO/g-CN/NiFe层状双氢氧化物（LDH）纳米复合材料。在该方法中，带正电的p型AgPO通过静电作用与n-n型g-CN/NiFe（CNLDH）LDH杂化材料自组装的带负电表面结合，同时在可见光照射下，光生电子和LDH的表面-OH基团将部分Ag还原为金属Ag纳米颗粒（NPs）。作为p型半导体的AgPO的存在、金属Ag NPs的表面等离子体共振（SPR）效应以及NiFe LDH中作为O型缺陷的氧空位，能够极大地实现准II型p-n/n-n双异质结，这在Mott-Schottky（M-S）分析中通过导带和价带电位的移动得以揭示。在所有优化的异质结构中，CNLDHAgP4在2小时内可实现最高的光催化Cr(VI)还原率97%和苯酚氧化率90%。异质结构CNLDHAgP4光催化剂具有独特的形貌，由Ag NPs和AgPO的立方相组成，它们附着在CNLDH杂化材料的薄而弯曲的层上，以实现平滑的电子和离子电荷传输。此外，通过光致发光、线性扫描伏安法、M-S、电化学阻抗研究、高分辨率透射电子显微镜和X射线光电子能谱研究，验证了在准II型p-n/n-n双异质结界面形成的紧密肖特基势垒。Ag NPs的SPR效应和NiFe LDH中作为O型缺陷的氧空位能够有效加速电荷分离阈值，这是所制备的异质结构光催化剂活性增强的主要原因。
