Xiaoyang Pan

Bio: Xiaoyang Pan is an academic researcher from Fuzhou University. The author has contributed to research in topics: Graphene & Materials science. The author has an hindex of 11, co-authored 11 publications receiving 2722 citations.

Defective TiO2 with oxygen vacancies: synthesis, properties and photocatalytic applications

Abstract: Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theoretical calculations and experimental characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties of TiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO2. In particular, photocatalytic applications with regard to defective TiO2 are outlined. In addition, we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial minireview would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.

Assembly of CdS Nanoparticles on the Two-Dimensional Graphene Scaffold as Visible-Light-Driven Photocatalyst for Selective Organic Transformation under Ambient Conditions

Abstract: A series of cadmium sulfide–graphene (CdS–GR) nanocomposites with different weight addition ratios of graphene (GR) have been synthesized via a facile one-step hydrothermal approach, during which the formation of CdS nanoparticles and the reduction of graphene oxide (GO) occur simultaneously. X-ray diffraction (XRD), UV–vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), nitrogen adsorption–desorption, photoluminescence spectra (PL), and electron spin resonance spectra (ESR) are employed to determine the properties of the samples. It is found that the CdS nanoparticles evenly overspread on the graphene scaffold, and the properties of the samples, including morphology, pore structure, optical, and electronic nature, are able to be tuned by the addition of GR as compared with blank-CdS prepared in the absence of GR. The photocatalytic activities of the as-prepared CdS–GR nano...

Constructing Ternary CdS–Graphene–TiO2 Hybrids on the Flatland of Graphene Oxide with Enhanced Visible-Light Photoactivity for Selective Transformation

Abstract: The ternary CdS–graphene–TiO2 hybrids (CdS–GR–TiO2) have been prepared through an in situ strategy on the flatland of graphene oxide (GO). The structure and properties have been characterized by a series of techniques, including X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission scanning electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), UV–vis diffuse reflectance spectra (DRS), electrochemical analysis, photoluminescence spectra (PL), nitrogen adsorption–desorption, and electron spin resonance spectra (ESR). Combined with our previous results, it is found that the introduction of the third-component TiO2 can maintain the morphology and porosity of the samples, whereas it is able to tune the energy band, increase the surface area, and facilitate the electron transfer, thus prolonging the lifetime of photogenerated carriers. Taking photocatalytic selective oxidation of various alcohols to their corresponding aldehydes as model reactions, the tern...

Defect-Mediated Growth of Noble-Metal (Ag, Pt, and Pd) Nanoparticles on TiO2 with Oxygen Vacancies for Photocatalytic Redox Reactions under Visible Light

Abstract: A synergistic strategy involving oxygen-vacancy generation and noble-metal deposition is developed to improve the photocatalytic performance of TiO2 under visible-light irradiation. Through a redox reaction between the reductive TiO2 with oxygen vacancies (TiO2-OV) and metal salt precursors, noble-metal nanoparticles (Ag, Pt, and Pd) are uniformly deposited on the defective TiO2-OV surface in the absence of any reducing agents or stabilizing ligands. The resulting M-TiO2-OV (M = Ag, Pt, and Pd) nanocomposites are used as visible-light-driven photocatalysts for selective oxidation of benzyl alcohol and reduction of heavy metal ions Cr(VI). The results show that the oxygen vacancy creation obviously enhances the visible-light absorption of semiconductor TiO2. Meanwhile, the noble-metal deposition can effectively improve charge-separation efficiency of TiO2-OV under visible-light irradiation, thereby enhancing the photoactivity. In particular, Pd-TiO2-OV, having the average Pd particle size of 2 nm, shows th...

A facile one-step way to anchor noble metal (Au, Ag, Pd) nanoparticles on a reduced graphene oxide mat with catalytic activity for selective reduction of nitroaromatic compounds

Abstract: A facile, one-step clean strategy has been utilized for anchoring noble metal (Au, Ag, Pd) nanoparticles onto the flat surface of two-dimensional (2D) graphene oxide (GO) nanosheets. Without using any additional reductants, surfactants or protecting ligands, the deposition of metallic noble metal (Au, Ag, Pd) nanoparticles on the partially reduced graphene oxide (PRGO) mat has been realized by a simple redox reaction between the noble metal precursors and GO in an aqueous solution. The main size distributions of the Au, Ag and Pd particles are centered on 1–20 nm, 3–10 nm and 0.5–3 nm, respectively. The as-obtained Au, Ag and Pd–PRGO nanocomposites display superb catalytic activities for the selective reduction of nitroaromatic compounds into the corresponding amino compounds under ambient conditions. The rates of reduction follow the sequence, Pd–PRGO > Ag–PRGO > Au–PRGO, suggesting that the smallest noble metal particles size affords the highest catalytic activity. In addition, considering that the Au, Ag and Pd–PRGO nanocomposites still hold the abundant functional groups of the original GO, these noble metal–PRGO composites maintain the excellent hydrophilic nature of GO, which provides a flexible platform for the further fabrication of PRGO–metal-based multicomponent functional materials by a wet-chemistry approach.

Defective TiO2 with oxygen vacancies: synthesis, properties and photocatalytic applications

Abstract: Titanium dioxide (TiO2), as an important semiconductor metal oxide, has been widely investigated in the field of photocatalysis. The properties of TiO2, including its light absorption, charge transport and surface adsorption, are closely related to its defect disorder, which in turn plays a significant role in the photocatalytic performance of TiO2. Among all the defects identified in TiO2, oxygen vacancy is one of the most important and is supposed to be the prevalent defect in many metal oxides, which has been widely investigated both by theoretical calculations and experimental characterizations. Here, we give a short review on the existing strategies for the synthesis of defective TiO2 with oxygen vacancies, and the defect related properties of TiO2 including structural, electronic, optical, dissociative adsorption and reductive properties, which are intimately related to the photocatalytic performance of TiO2. In particular, photocatalytic applications with regard to defective TiO2 are outlined. In addition, we offer some perspectives on the challenge and new direction for future research in this field. We hope that this tutorial minireview would provide some useful contribution to the future design and fabrication of defective semiconductor-based nanomaterials for diverse photocatalytic applications.

Engineering heterogeneous semiconductors for solar water splitting

Abstract: There is a growing interest in the conversion of water and solar energy into clean and renewable H2 fuels using earth-abundant materials due to the depletion of fossil fuel and its serious environmental impact. This critical review highlights some key factors influencing the efficiency of heterogeneous semiconductors for solar water splitting (i.e. improved charge separation and transfer, promoted optical absorption, optimized band gap position, lowered cost and toxicity, and enhanced stability and water splitting kinetics). Moreover, different engineering strategies, such as band structure engineering, micro/nano engineering, bionic engineering, co-catalyst engineering, surface/interface engineering of heterogeneous semiconductors are summarized and discussed thoroughly. The synergistic effects of the different engineering strategies, especially for the combination of co-catalyst loading and other strategies seem to be more promising for the development of highly efficient photocatalysts. A thorough understanding of electron and hole transfer thermodynamics and kinetics at the fundamental level is also important for elucidating the key efficiency-limiting step and designing highly efficient solar-to-fuel conversion systems. In this review, we provide not only a summary of the recent progress in the different engineering strategies of heterogeneous semiconductors for solar water splitting, but also some potential opportunities for designing and optimizing solar cells, photocatalysts for the reduction of CO2 and pollutant degradation, and electrocatalysts for water splitting.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

Abstract: Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Why is anatase a better photocatalyst than rutile?--Model studies on epitaxial TiO2 films.

Abstract: The prototypical photocatalyst TiO2 exists in different polymorphs, the most common forms are the anatase- and rutile-crystal structures. Generally, anatase is more active than rutile, but no consensus exists to explain this difference. Here we demonstrate that it is the bulk transport of excitons to the surface that contributes to the difference. Utilizing high –quality epitaxial TiO2 films of the two polymorphs we evaluate the photocatalytic activity as a function of TiO2-film thickness. For anatase the activity increases for films up to ~5 nm thick, while rutile films reach their maximum activity for ~2.5 nm films already. This shows that charge carriers excited deeper in the bulk contribute to surface reactions in anatase than in rutile. Furthermore, we measure surface orientation dependent activity on rutile single crystals. The pronounced orientation-dependent activity can also be correlated to anisotropic bulk charge carrier mobility, suggesting general importance of bulk charge diffusion for explaining photocatalytic anisotropies.

Black titanium dioxide (TiO2) nanomaterials

Abstract: In the past few decades, there has been a wide research interest in titanium dioxide (TiO2) nanomaterials due to their applications in photocatalytic hydrogen generation and environmental pollution removal. Improving the optical absorption properties of TiO2 nanomaterials has been successfully demonstrated to enhance their photocatalytic activities, especially in the report of black TiO2 nanoparticles. The recent progress in the investigation of black TiO2 nanomaterials has been reviewed here, and special emphasis has been given on their fabrication methods along with their various chemical/physical properties and applications.