Gui-Fang Huang

Novel Ag3PO4/CeO2 composite with high efficiency and stability for photocatalytic applications

A novel Ag3PO4/CeO2 composite was fabricated by in situ wrapping CeO2 nanoparticles with Ag3PO4 through a facile precipitation method. The photocatalytic properties of Ag3PO4/CeO2 were evaluated by the photocatalytic degradation of MB and phenol under visible light and UV light irradiation. The photocatalytic activity of the composite is much higher than that of pure Ag3PO4 or CeO2. The rate constant of MB degradation over Ag3PO4/CeO2 is more than 2 times and 20 times than those of pure Ag3PO4 and CeO2 under visible light irradiation, respectively. The Ag3PO4/CeO2 composite photocatalyst also shows higher photocatalytic activity for the colorless phenol degradation compared to pure Ag3PO4. Moreover, the Ag3PO4/CeO2 sample has almost no loss of photocatalytic activity after five recycles under the irradiation of visible light and UV light, indicating that the composite has good photocatalytic stability. The excellent photocatalytic activity of the Ag3PO4/CeO2 composite is closely related to the fast transfer and efficient separation of electron–hole pairs at the interfaces of the two semiconductors derived from the matching band positions between CeO2 and Ag3PO4. This newly constructed Ag3PO4/CeO2 composite, with promising and fascinating visible light-driven photocatalytic activity as well as good stability, could find potential applications in environmental purification and solar energy conversion.

Ag 3 PO 4 semiconductor photocatalyst: possibilities and challenges

Ag3PO4 as a photocatalyst has attracted enormous attention in recent years due to its great potential in harvesting solar energy for environmental purification and fuel production. The photocatalytic performance of Ag3PO4 strongly depends on its morphology, exposed facets, and particle size. The effects of morphology and orientation of Ag3PO4 on the catalytic performance and the efforts on the stability improvement of Ag3PO4 are reviewed here. This paper also discusses the current theoretical understanding of photocatalytic mechanism of Ag3PO4, together with the recent progress towards developing Ag3PO4 composite photocatalysts. The crucial issues that should be addressed in future research activities are finally highlighted.

Interfacial Interactions of Semiconductor with Graphene and Reduced Graphene Oxide: CeO2 as a Case Study

The pursuit of superb building blocks of light harvesting systems has stimulated increasing efforts to develop graphene (GR)-based semiconductor composites for solar cells and photocatalysts. One critical issue for GR-based composites is understanding the interaction between their components, a problem that remains unresolved after intense experimental investigation. Here, we use cerium dioxide (CeO2) as a model semiconductor to systematically explore the interaction of semiconductor with GR and reduced graphene oxide (RGO) with large-scale ab initio calculations. The amount of charge transferred at the interfaces increases with the concentration of O atoms, demonstrating that the interaction between CeO2 and RGO is much stronger than that between CeO2 and GR due to the decrease of the average equilibrium distance between the interfaces. The stronger interaction between semiconductor and RGO is expected to be general, as evidenced by the results of two paradigms of TiO2 and Ag3PO4 coupled with RGO. The interfacial interaction can tune the band structure: the CeO2(111)/GR interface is a type-I heterojunction, while a type-II staggered band alignment exists between the CeO2(111) surface and RGO. The smaller band gap, type-II heterojunction, and negatively charged O atoms on the RGO as active sites are responsible for the enhanced photoactivity of CeO2/RGO composite. These findings can rationalize the available experimental reports and enrich our understanding of the interaction of GR-based composites for developing high-performance photocatalysts and solar cells.

Dual role of monolayer MoS2 in enhanced photocatalytic performance of hybrid MoS2/SnO2 nanocomposite

The enhanced photocatalytic performance of various MoS2-based nanomaterials has recently been observed, but the role of monolayer MoS2 is still not well elucidated at the electronic level. Herein, focusing on a model system, hybrid MoS2/SnO2 nanocomposite, we first present a theoretical elucidation of the dual role of monolayer MoS2 as a sensitizer and a co-catalyst by performing density functional theory calculations. It is demonstrated that a type-II, staggered, band alignment of ∼0.49 eV exists between monolayer MoS2 and SnO2 with the latter possessing the higher electron affinity, or work function, leading to the robust separation of photoexcited charge carriers between the two constituents. Under irradiation, the electrons are excited from Mo 4d orbitals to SnO2, thus enhancing the reduction activity of latter, indicating that the monolayer MoS2 is an effective sensitizer. Moreover, the Mo atoms, which are catalytically inert in isolated monolayer MoS2, turn into catalytic active sites, making the mo...

Facile ion-exchange synthesis of mesoporous Bi2S3/ZnS nanoplate with high adsorption capability and photocatalytic activity.

Novel Bi2S3/ZnS nanoplates have been successfully prepared by simple reflux and cation exchange reaction between the preformed ZnS spheres and Bi(NO3)3·5H2O. The synthesized Bi2S3/ZnS nanoplates are mesoporous structures, possess a high specific surface area of 101.30m(2)/g and exhibit high adsorption capability and photocatalytic activity for methylene blue (MB) degradation under UV light irradiation. The high adsorption capability and photocatalytic activity can be ascribed to the fact that the formation of Bi2S3/ZnS nanoplates with large specific surface area provides more reactive sites and facilitates the separation of photogenerated electron-hole pairs. The possible formation mechanism of Bi2S3/ZnS nanoplates is proposed based on the time-dependent observation. Moreover, a tentative mechanism for degradation of MB over Bi2S3/ZnS has been proposed involving OH radical and photoinduced holes as the active species, which is confirmed by using methanol or ammonium oxalate as scavengers. This work provides a cost-effective method for large-scale synthesis of composite with controlled architectural morphology and highly promising applications in photocatalysis.

Band structure engineering of monolayer MoS2: a charge compensated codoping strategy

The monolayer MoS2, possessing an advantage over graphene in that it exhibits a band gap whose magnitude is appropriate for solar applications, has attracted increasing attention because of its possible use as a photocatalyst. Herein, we propose a codoping strategy to tune the band structure of monolayer MoS2 aimed at enhancing its photocatalytic activity using first-principles calculation. The monodoping (halogen element, Nd) introduces impurity states in the gap, thus decreasing the photocatalytic activity of MoS2. Interestingly, the NbMoFS codoping reduces the energy cost of doping as a consequence of the charge compensation between the niobium (p-dopant) and the fluorine (n-dopant) impurities, which eliminates the isolated levels (induced by monodopant) in the band gap. Most importantly, the NbMoFS codoped MoS2 has more active sites for photocatalysis. These results show the proposed NbMoFS codoped monolayer MoS2 is a promising photocatalyst or photosensitizer for visible light in the heterogeneous semiconductor systems.

A facile and rapid route for synthesis of g-C3N4 nanosheets with high adsorption capacity and photocatalytic activity

A graphitic carbon nitride (g-C3N4) nanosheet and its nanocomposites have recently attracted increasing interest due to their massive potentials in applications ranging from fluorescence imaging to solar energy conversion. An economical mass-production method for the synthesis of g-C3N4 nanosheets is urgently needed for the application of these intriguing nanomaterials. Here we develop a facile and rapid route to synthesize g-C3N4 nanosheets by using chemical exfoliation followed by extraction and thermal treatment. The feature of this approach lies in its rapid speed with exfoliation time of only about one minute and facile operation free of long-time ultrasonication or stirring, filtration and repeated washing processes to remove the residual acid. Moreover, the method is high-yield and easily upscalable. Meanwhile, the exfoliated g-C3N4 nanosheets exhibit high adsorption capability and photocatalytic activity due to the synergistic effects of large surface area, decreased recombination probability of photoinduced electron–hole pairs and enlarged band gap. This simple and rapid route enables the possibility of large-scale synthesis of g-C3N4 nanosheets with high yield, thus promoting their application in environmental purification and solar energy conversion.

Tuning near-gap electronic structure, interface charge transfer and visible light response of hybrid doped graphene and Ag3PO4 composite: Dopant effects.

The enhanced photocatalytic performance of doped graphene (GR)/semiconductor nanocomposites have recently been widely observed, but an understanding of the underlying mechanisms behind it is still out of reach. As a model system to study the dopant effects, we investigate the electronic structures and optical properties of doped GR/Ag3PO4 nanocomposites using the first-principles calculations, demonstrating that the band gap, near-gap electronic structure and interface charge transfer of the doped GR/Ag3PO4(100) composite can be tuned by the dopants. Interestingly, the doping atom and C atoms bonded to dopant become active sites for photocatalysis because they are positively or negatively charged due to the charge redistribution caused by interaction. The dopants can enhance the visible light absorption and photoinduced electron transfer. We propose that the N atom may be one of the most appropriate dopants for the GR/Ag3PO4 photocatalyst. This work can rationalize the available experimental results about N-doped GR-semiconductor composites, and enriches our understanding on the dopant effects in the doped GR-based composites for developing high-performance photocatalysts.

Electronic properties and photoactivity of monolayer MoS2/fullerene van der Waals heterostructures

van der Waals (vdW) heterostructures have attracted immense interest recently due to their unusual properties and new phenomena. Atomically thin two-dimensional MoS2 heterostructures are particularly exciting for novel photovoltaic applications, because monolayer MoS2 has a band gap in the visible spectral range and exhibit extremely strong light–matter interactions. Herein, first-principles calculations based on density functional theory is used to investigate the effects of vdW interactions on changes in the electronic structure, charge transfer and photoactivity in three typical monolayer MoS2/fullerene (C60, C26, and C20) heterostructures. Compared to monolayer MoS2, the band gap of the heterostructures is smaller, which can enhance the visible light absorption and photoinduced electrons transfer. The amount of charge transfer at interface induced by vdW interaction depends on the size of fullerenes. Most importantly, a type-II, staggered band alignment can be obtained in the MoS2/C20 heterostructure, leading to significantly reduced charge recombination and thus enhanced photocatalytic activity. These results reveal that fullerene modification would be an effective strategy to improve the photocatalytic performance of semiconductor photocatalysts.

Two-Dimensional MoS2-Graphene-Based Multilayer van der Waals Heterostructures: Enhanced Charge Transfer and Optical Absorption, and Electric-Field Tunable Dirac Point and Band Gap

Multilayer van der Waals (vdW) heterostructures assembled by diverse atomically thin layers have demonstrated a wide range of fascinating phenomena and novel applications. Understanding the interlayer coupling and its correlation effect is paramount for designing novel vdW heterostructures with desirable physical properties. Using a detailed theoretical study of two-dimensional (2D) MoS2-graphene (GR)-based heterostructures based on state-of-the-art hybrid density functional theory, we reveal that for 2D few-layer heterostructures, vdW forces between neighboring layers depend on the number of layers. Compared to that in the bilayer, the interlayer coupling in trilayer vdW heterostructures can significantly be enhanced by stacking the third layer, directly supported by short interlayer separations and more interfacial charge transfer. The trilayer shows strong light absorption over a wide range (<700 nm), making it great potential for solar energy harvesting and conversion. Moreover, the Dirac point of GR ...