Efficient Nanoclay-Based Composite Photocatalyst: The Role of Nanoclay in Photogenerated Charge Separation

Abstract

Natural clay mineral is a low-cost support for photocatalytic materials, but it exhibits insulating properties determined by intrinsic compositions of aluminosilicate, which normally makes it difficult to participate in the charge carrier separation and transfer of the photocatalytic system. Herein, natural iron-rich kaolinite clay with photoresponse is used as a multifunctional support to construct a CdS composite photocatalyst, and we find that the natural kaolinite nanosheets exhibit strong oxygen adsorption capacity by hydroxyl groups and could enhance the charge carrier separation. Density functional theory calculations show that the hydroxyl groups of kaolinite could effectively adsorb oxygen via hydrogen bonding, and the absorbed water further promotes the adsorption of oxygen. Because of these special properties, the kaolinite nanosheets not only directly improved photogenerated charge separation efficiency by a type II staggered band structure of heterostructures but also promoted the production of superoxide radicals via providing an oxygen-rich microenvironment, which resulted in the greatly enhanced photocatalytic performance of CdS nanoparticles. This work could provide a deeper understanding of the role of the iron-rich natural clay mineral as a photocatalytic support and shed light on the design of clay-based composite photocatalysts.

Interfacial Chemical-Bond-Modulated Charge Transfer of Heterostructures for Improving Photocatalytic Performance

“…This is because the OH-oriented Kaol surface possesses a large number of −OH groups with electron-donating properties (Figure S18c). 31,49 When the interfacial Al−O−Ti bonds formed, the electrons of the Kaol surface were injected into TiO 2 and thus increased the electron density of TiO 2 space charge regions, while the electron density of the Kaol surface decreased, which is supported by the XPS data of the Kaol/P25 HCs. Therefore, the Al−O−Ti bonds intensified the energy band bending of the space charge regions near the interfacial bonds 7 (Figure S18d), which explains the observed enhancements of photocatalytic ability caused by Al 2 O 3 in our Al 2 O 3 /P25 samples and reported literature.…”

“…The calculations of DFT were employed to further confirm the interfacial chemical bonds of the Kaol/P25 HCs. Kaol has two types of surface termination, either an OH-terminated Al− OH surface or an O-terminated Si−O surface, 31 thus allowing for the formation of OH-or O-oriented Kaol/TiO 2 HCs (Figure 2). The (101) surface of anatase was the most stable and was chosen as the model surface of TiO 2 .…”

“…The photocurrent measurement was performed using the previous method. 31 To keep the same amount of P25 (7.3 mg) in the working electrodes with different photocatalysts, different quantities of samples were added to a Nafion ethanol solution (1%).…”

“…Raw Kaol NSs were purchased from Suzhou, China, and were used without further purification. The major compositions can be referred to previous reports. , P25-TiO 2 was obtained from Degussa Company. In a typical synthesis, 0.252 g of Kaol and 0.680 g of P25 were uniformly mixed by grinding for 10 min.…”

“…As an important photocatalyst, TiO 2 and its heterojunctions have been widely studied. − The hydrophilicity of TiO 2 facilitates the interactions of its surface and components with hydroxyl groups. Natural clay materials with abundant surface hydroxyl groups, such as halloysite and kaolinite, have been usually employed as multifunctional supports of catalysts for environmental applications. − Owing to the isomorphous substitution of Fe or Ti in the aluminosilicate lattice, natural clay materials exhibit an obvious photoresponse like semiconductors and effectively transfer and separate photogenerated charges of supported photocatalysts. − Hence, the construction of HCs using TiO 2 and nanoclay should form controllable interfacial chemical bonds, which would be an effective platform for identifying the effect of interfacial chemical bonding on photogenerated charge transfer. Although many nanoclay/TiO 2 HCs have been investigated, , reports about interfacial chemical bonds for modulating charge transfer are rare, and its essential roles remain unclear.…”