Carbon nanotubes (CNTs)/two-dimensional transition metal dichalcogenides (MX2) hybrids have shown unique physical properties, making them promising materials for various applications ranging from photocatalysis to solar energy conversion. Understanding the interfacial interactions is highly desirable for designing these hybrids having excellent performance. Here, we systematically study the interfacial interaction in single-walled CNT/monolayer MoS2 hybrids and its effects on electronic and optical properties by first-principles calculations. It is found that the CNT is interacted noncovalently with monolayer MoS2, forming van der Waals heterostructures, and their interfacial interaction is closely related to tube diameter. In these hybrids, interestingly, MoS2 gaining or losing electrons depends also on tube diameter: (3,0)CNT would gain some electrons from MoS2, whereas other CNTs lose some electrons. The small band gap makes these hybrids have a strong optical absorption in the visible-light region. The type-II, staggered, band alignment in CNT/MoS2 hybrids can facilitate the separation of photoexcited electrons and holes, improving the photocatalytic activity. Moreover, the CNTs are not only an effective sensitizer but also a highly active cocatalyst in hybrids. These results have revealed the mechanism of enhanced photocatalytic performance of CNT/MoS2 hybrids observed in experiments, and help for developing highly efficient carbon nanomaterial-based nanophotocatalysts.

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 and band gaps of each layer and trilayer can be readily tuned by the external electric field, verifying multilayer vdW heterostructures with unique optoelectronic properties found by experiments. These results suggest that tuning the vdW interaction, as a new design parameter, would be an effective strategy for devising particular 2D multilayer vdW heterostructures to meet demands in various applications.

Perfect light absorbers have attracted much attention because of their potential applications in solar cells, thermal imaging, material detection, bio-sensing, and others. However, it is extremely difficult to obtain the ultra-narrow bandwidth of a perfect light absorber in the terahertz region. Herein, an ultra-narrow terahertz perfect light absorber based on the surface lattice resonance of three stacking layers, namely a square resonator, a dielectric spacer, and a metallic film, is reported. A resonance absorption peak with bandwidth of 0.0200 THz and absorption rate of 98.86% is realized. The absorption performance of the device can be controlled by employing different sized (unit) periods and dielectric spacer thicknesses. Particularly, the device bandwidth can be decreased by reducing the dielectric layer thickness. At a certain thickness, a resonance peak with a bandwidth of only 0.0067 THz is achieved. This peak is very sensitive to the surrounding refractive index. The large sensitivity (2.58 THz per refractive index) and simultaneous ultra-narrow bandwidth lead to an ultra-high figure of merit (385.07), making this a promising light device in terahertz detection and sensing.

Understanding the interfacial interaction is of paramount importance for rationally designing carbon nanomaterial-based hybrids with optimal performance for electronics, optoelectronics, sensing, advanced energy conversion and storage. Here, we firstly reveal that both covalent and noncovalent interactions simultaneously exist in carbon nanotube (CNT)/Ag3PO4 hybrids by studying systematically the electronic and optical properties to elucidate the mechanism of their enhanced photocatalytic performance. Metallic CNT(9,0) may chemically or physically interact with the Ag3PO4(100) surface depending on its relative orientations, whereas semiconducting CNT(10,0) can only noncovalently functionalize Ag3PO4. The C–Ag bond in the covalently bonded hybrid and type-II, staggered, band alignment in noncovalent hybrids lead to a robust separation of photoexcited charge carriers between two constituents, thus enhancing the photocatalytic activity. The small band gap makes the CNT/Ag3PO4 hybrids absorb sunlight from the ultraviolet to infrared region. Moreover, CNTs are not only effective sensitizers, but also highly active co-catalysts in hybrids. The results can be rationalized by the available experiments, thereby partly resolving a debate on the interpretation of the experimental results, and paving the way for developing highly efficient carbon-based nanophotocatalysts.

Graphene (GR) and its derivatives are generally assumed to be electron shuttles in order to explain the improved photocatalytic activity of their nanocomposites (such as TiO2/GR). However, it fails to account for the experimental results, which demonstrate that the photocatalytic activity of TiO2/reduced graphene oxide (RGO) is higher than that of TiO2/GR. Herein, we explore the underlying mechanism for the enhanced photocatalytic activity of TiO2/RGO (GR) by comparing several influential factors: band gap, band alignment near the gap, optical absorption, and active sites, via first-principles calculations. The results show that the small band gap, the type-II staggered band alignment, and the negatively charged O atoms as active sites in photocatalytic reactions are likely to be key factors for the photocatalytic activity of TiO2/RGO being better than that of TiO2/GR, partly offering a physical interpretation for related experimental results. Interestingly, the enhanced photocatalytic activity of TiO2/graphane (GRH) is also predicted. These results suggest that functionalized GR is most likely better than pristine graphene at improving the photocatalytic activity of TiO2/GR-based semiconductor photocatalysts.

•We have investigated the mechanism of enhanced photocatalytic activity of SnO through fullerene modification.•Composites of C60 coupled with SnO2 firstly provide theoretical evidence supporting the experimental reports.•We have revealed whether other fullerene/SnO2 composites also have superior photocatalytic properties.Carbon nanomaterials are prominent building blocks in the synthetic van der Waals (vdW) heterostructures with desired properties. Scientific understanding of their interfacial interactions is the premise to design this kind of vdW heterostructures with optimal performance. We here study the mechanism of enhanced photocatalytic activity of SnO2 by fullerene modification at electronic level, to explore the interfacial interaction and its correlation with photocatalytic activity. The results show that the interfacial interaction increases with the number of C atom of fullerene, and leads to some of C atoms be positively/negatively charged, making the fullerene a highly active co-catalyst in heterostructures. Compared to pristine SnO2, the band gap of the heterostructures is much smaller, leading to their absorption wavelength extending the entire visible region. Interestingly, a staggered type-II band alignment in the C20 (C60)/SnO2 (101) heterostructures results into the robust separation of photoexcited charge carriers between the two constituents, indicating that the fullerene is an effective sensitizer, and thus enhanced photocatalytic activity. These findings can rationalize the available experiment and will be of broad interest in developing the highly efficient semiconductor photocatalysts via fullerene modification.

•g-C3N4/CeO2/ZnO ternary nanocomposites with multi-heterointerfaces have been synthesized.•Robust separation of photoexcited charge carriers in g-C3N4/CeO2/ZnO composites is verified.•The resulting ternary nanocomposites show appreciably increased photocatalytic activity.•The enhanced photocatalytic activity stems from novel shape and efficient charge separation.Promoting the spatial separation of photoexcited charge carriers is of paramount significance for photocatalysis. In this work, binary g-C3N4/CeO2 nanosheets are first prepared by pyrolysis and subsequent exfoliation method, then decorated with ZnO nanoparticles to construct g-C3N4/CeO2/ZnO ternary nanocomposites with multi-heterointerfaces. Notably, the type-II staggered band alignments existing between any two of the constituents, as well as the efficient three-level transfer of electron-holes in unique g-C3N4/CeO2/ZnO ternary composites, leads to the robust separation of photoexcited charge carriers, as verified by its photocurrent increased by 8 times under visible light irradiation. The resulting g-C3N4/CeO2/ZnO ternary nanocomposites unveil appreciably increased photocatalytic activity, faster than that of pure g-C3N4, ZnO and g-C3N4/CeO2 by a factor of 11, 4.6 and 3.7, respectively, and good stability toward methylene blue (MB) degradation. The remarkably enhanced photocatalytic activity of g-C3N4/CeO2/ZnO ternary heterostructures can be interpreted in terms of lots of active sites of nanosheet shapes and the efficient charge separation owing to the resulting type-II band alignment with more than one heterointerface and the efficient three-level electron-hole transfer. A plausible mechanism is also elucidated via active species trapping experiments with various scavengers, which indicating that the photogenerated holes and •OH radicals play a crucial role in photodegradation reaction under visible light irradiation. This work suggest that the rational design and construction of type II multi-heterostructures is powerful for developing highly efficient and reusable visible-light photocatalysts for environmental purification and energy conversion.The ternary heterostructures fabricated by decorating g-C3N4/CeO2 nanosheets with ZnO nanoparticles show efficient photocatalytic activity and excellent photostability owing to lots of active sites and the efficient charge separation.Download high-res image (226KB)Download full-size image

The coupling of carbon nanomaterials with semiconductor photocatalysts is a promising route to improve their photocatalytic performance. Herein, density functional theory was used to investigate the electronic structure, charge transfer, photocatalytic activity, and stability in a series of hybrid fullerene (C20, Li@C20, C26, Li@C26)/Ag3PO4(100) composites. When a Li atom is incorporated in fullerene, the adsorption energies significantly increase, although the change of interface distance is negligibly small due to the weak interface interaction. The charge transfer between constituents decreases with the C atom number of fullerene. Compared to pure Ag3PO4, the band gap of the composites is smaller, which enhances the visible-light absorption and photoinduced electron transfer. Most importantly, a type-II, staggered band alignment could be obtained in the C26–Ag3PO4(Li@C26–Ag3PO4) interface, 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 Ag3PO4 semiconductor photocatalysts.

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 101.30 m2/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.

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.

•ZnO with various morphologies are synthesized by a facile solution combustion method.•ZnO annealed at 600 °C exhibits superior photocatalytic activity.•ZnO-600 is composed of some irregularly nanocubes with reactive {002} facets exposed.•The mechanism for the excellent performance of ZnO nanocubes is proposed.ZnO nanoparticles with various morphologies are successfully synthesized via a facile solution combustion method without using any templates or surfactants. The prepared ZnO nanoparticles possess good-crystallinity and wurtzite hexagonal phase. Interestingly, the morphology of ZnO can be adjusted by changing the annealing temperature. ZnO nanocubes annealed at 600 °C exhibit superior photocatalytic activity for photodegradation of methyleneblue (MB) under UV-light irradiation. The enhanced photocatalytic activity can be attributed to the highly reactive {002} facets exposed, which facilitate the adsorption of organic molecules and degradation reactions with more catalytically active sites. This work provides simple strategy for the development of efficient photocatalysts for solar energy conversion applications in solving energy crisis and environmental pollution problems.

The reduced graphene oxide (RGO)-based composites have attracted intensive attention in research due to its superior performance as photocatalysts, but still lacking is the theoretical understanding on the interactions between constituents, as well as the connection between such interaction and the enhanced photoactivity. Herein, the interaction between the g-C3N4 and RGO sheets is systematically explored by using state-of-the-art hybrid density functional theory. We demonstrate that the O atom plays a crucial role in the RGO-based composites. Compared to the isolated g-C3N4 monolayer, the band gap of composites obviously decreases, and at higher O concentration, the levels in the vicinity of Fermi level are much more dispersive, indicating the smaller effective mass of the carrier. These changes are nonlinear on the O concentration. Interestingly, appropriate O concentration alters the direct-gap composite to indirect-gap one. Most importantly, at a higher O concentration, a type-II, staggered band alignment can be obtained in the g-C3N4-RGO interface, and negatively charged O atoms in the RGO are active sites, leading to the high hydrogen-evolution activity. Furthermore, the calculated absorption spectra which vary with the O concentration shed light on different experimental results. The findings pave the way for developing RGO-based composites for photocatalytic applications.

The pursuit of semiconductor photocatalysts with outstanding performance has stimulated increasing efforts to explore novel materials to address problems in environmental remediation and energy utilization. Herein, we first report the synthesis of CeF3 nanoparticles by a facile low-temperature solution combustion method and its performance for photocatalytic degradation of methylene blue (MB) under UV light irradiation. Interestingly, only by adjusting the molar ratios of ammonium fluoride to cerium chloride, pure CeF3 nanoparticles, its mixture with CeO2 and/or Ce2O3, and pure CeO2 nanoparticles can be easily obtained, respectively. The synthesized CeF3 nanoparticles can effectively decompose organic contaminants in aqueous solution and show enhanced photocatalytic activity than CeO2 nanoparticles. Moreover, CeF3 exhibits high stability. The density functional theory (DFT) calculation has been performed to understand the photocatalysis mechanism of CeF3 nanoparticles. This research might provide some new insights for the synthesis of novel photocatalyst with high photocatalytic performance.

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.

The large intrinsic band gap of GeO2 hinders its potential application as a photocatalyst under visible-light irradiation. Here, we perform first-principles calculations to investigate the origin of the experimentally observed visible-light photocatalytic activity of GeO2 induced by N doping. Four possible defects (N-doping, N+H codoping, Ge vacancy and O vacancy) for the redshift of N-doped GeO2 are tentatively put forward. The lowest formation energy indicates that N+H codoped GeO2 is the most stable and easiest to form. N-doping at an oxygen site induces gap states, which are made up primarily of N 2p-derived states with some O 2p contributions, and the lowest-energy empty states is in the middle of the gap. For Ge vacancy model, O 2p states form the intermediate band, while Ge 4s orbitals localized in the gap contribute to the impurity level in O vacancy model. These gap levels lead to a reduced effective band gap, which is one of the potential interest for photocatalytic applications. Electronic transitions from these localized states induce a redshift to the visible region of the optical absorption edge. The calculated optical properties for N-doped GeO2 show a significant visible light absorption at about 400–600 nm, in close agreement with the experimental result. This work indicates that N-doped GeO2 would be a promising photocatalyst with favorable photocatalytic activity in the visible region.

The enhanced photocatalytic activity of SrTiO3(STO), a promising photocatalyst for decomposing organic compounds and overall water splitting for H2/O2 evolution, has been experimentally demonstrated by coupling the graphene (GR) sheet. Here, we reveal the mechanism of the enhanced photocatalytic activity of STO/GR composites using ab initio calculations. Due to C 2p states forming the bottom of the conduction band or the top of the valence band, the band gap is reduced to about 0.6 eV, resulting in a strong absorption in the visible region. The composites of STO coupled with reduced graphene oxide (RGO) and graphane (GRH) are also explored to investigate their potential photocatalytic activity. We demonstrate that the surface termination layer of the STO(100) surface plays an important role in determining the formation energy, interfacial distance, band gap, and optical absorption of these composites. Moreover, the GR sheet is a sensitizer for STO with a termination layer of TiO2; on the contrary, it is an electron shuttle carrying excited electrons from the STO with a termination layer of SrO. Interestingly, a type II, staggered band alignment is formed in the interface, thus improving photoexcited charge separation. The negatively charged O atoms in the RGO are considered to be active sites in photocatalytic reactions, leading to enhanced photocatalytic activity. The calculated results can rationalize the available experimental reports and provide design principles for optimizing the photocatalytic performance of the STO-based composites.

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.

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.Keywords: density functional theory; electronic structure; graphene and reduced graphene oxide; interfacial interaction; photocatalytic properties; semiconductor

•Ag3PO4 crystals with different shapes were fabricated via adjusting the amount of PVP.•PVP plays important roles in both determining the geometric shape and size of Ag3PO4.•Cubic Ag3PO4 exhibits superior photocatalytic activity for MB photodegradation.Ag3PO4 crystals with various morphologies are synthesized using a facile chemical precipitation method. An interesting shape evolution from agglomeration, to cubes, then to mixture of cubes and spheres, and finally to spherical Ag3PO4 can be realized only by tuning the molar ratio of poly (vinyl pyrrolidone) (PVP) to silver nitrate. During the growth process, PVP acts as not only a stabilizer to prevent the aggregation of the products, but also a shape-controller by selective interacting with the facets of Ag3PO4. The cubic Ag3PO4 exhibits superior photocatalytic activity for the photodegradation of methylene blue (MB) under visible light irradiation due to its larger surface area and easier separation of electron–hole pairs.

•A novel reduction method has been developed to enhance the photocatalytic activity of TiO2.•Abundant Ti3+ is detected on the surface of the reduced TiO2.•Ti3+ self-doped TiO2 photocatalyst exhibits enhanced photocatalytic activity.A novel reduction method has been developed as an effective strategy to improve the photocatalytic activity and the surface photovoltage spectroscopy (SPS) response of TiO2 nanoparticles. As-prepared TiO2 nanoparticles are synthesized through hydrolysis of tetrabutyl titanate, which are subsequently reduced by NH2OH·HCl in NH3·H2O media. Abundant Ti3+ is detected on the surface of the reduced TiO2. The Ti3+ self-doped TiO2 photocatalyst exhibits enhanced photocatalytic degradation efficiency with respect to methyl orange (MO) under UV and visible light irradiation. The enhanced photocatalytic degradation efficiency of Ti3+ self-doped TiO2 can be attributed to the presence of active Ti3+ sites, which is favorable for the separation of photoinduced electron–hole pairs. This work provides a feasible method for the improvement of photocatalytic activity and surface photovoltage response of semiconductors.

A comprehensive first-principle investigation, based on hybrid density functional theory, produces strong evidence that the Cu2O band-edges do satisfy the requirements of the H+/H2 and O2/H2O redox levels, demonstrating that it has enough driving force for photocatalytic overall water splitting. The calculated band gap of Cu2O is 2.184 eV, which is consistent with the experimental value of 2.17 eV. The highly dispersive s–s hybrid states at the conduction band bottom result in a small effective mass of the electron, which is favorable to carrier separation and the carrier transfer to surface, and thus facilitate the reduction of H+ to H2. The strong optical absorption of Cu2O is beneficial to overall water splitting under visible light irradiation. Possible reasons for no observation of H2 in some experiments are also discussed. The results address the ongoing controversy associated with photocatalytic overall water splitting of Cu2O.

•Highly uniform Ag3PO4 microspheres with novel 3D flower-like morphology were fabricated.•3D flower-like Ag3PO4 exhibits highly efficient photocatalytic activity.•PEG facilitates the formation of flower-like Ag3PO4 architecture.•The mechanism for the excellent performance of flower-like Ag3PO4 microstructures is proposed.Highly uniform Ag3PO4 microspheres with novel 3D flower-like morphology were fabricated through a facile aqueous solution route in the presence of polyethylene glycol (PEG). The formation of flower-like architecture can be attributed to the presence of PEG, which provides nucleation sites for the growth of nanosheets due to strong interactions between activated oxygen in PEG and Ag+ ions. The prepared 3D flower-like Ag3PO4 exhibits highly efficient photocatalytic activity for the photodegradation of methylene blue (MB) under visible light irradiation. The average photocatalytic rate of flower-like Ag3PO4 is more than 2 and 30 times of that of pure Ag3PO4 and commercial TiO2 (Degussa P25), respectively. The possible mechanism for the excellent performance of flower-like Ag3PO4 microstructures is proposed.

•La doping and sensitization of TiO2 photocatalyst have been jointly exploited.•La doping can decrease crystallite size and increase specific surface area of TiO2.•Porphyrin sensitization facilitates the radical generation in photocatalysis process.•Coupling effects of doping and sensitization improve the photoactivity of TiO2.Metal doping and sensitization of photocatalyst have been jointly exploited as a novel strategy to improve photocatalytic activity under visible light irradiation. 5, 10, 15, 20-tetrakis (4-chlorophenyl) porphyrin-Cu (II) (CuPp) is chosen to sensitize La-doped TiO2 (La–TiO2) nanocrystalline. La doping results in smaller crystallite and larger specific surface area. La doping or sensitization of TiO2 exhibits higher absorption in visible-light region and photocatalytic degradation efficiency of methyl orange (MO) than pristine TiO2. Coupling effect of La doping and CuPp sensitization leads to the excellent photocatalytic activity under visible light irradiation. A tentative mechanism for the enhancment of photocatalytic activity under visible light irradiation is proposed.

Size-controllable porous ZnS nanospheres consisting of nanoparticles have been successfully synthesized using an economical and simple chemical bath deposition. The results show that all the prepared nanospheres exhibit good size uniformity and regularity and are cubic ZnS structure. Moreover, the nanosphere surface is relatively rough and porous. It is interesting that the size and its distribution of ZnS nanospheres can be easily tuned by adjusting pH value. The photocatalytic activity of the ZnS nanospheres was evaluated by photodegradation reaction of methylene blue. The as-prepared ZnS nanospheres with smaller diameter exhibit enhanced photocatalytic activity, which is associated with the larger specific surface area and favorable dispersibility.Highlights► Size-controllable porous ZnS nanospheres have been successfully synthesized. ► The prepared ZnS nanospheres exhibit good size uniformity and regularity. ► The ZnS nanospheres with smaller diameter exhibit enhanced photocatalytic activity.

The development of high-efficiency ZnS photocatalyst is of great importance from scientific and practical viewpoints. We investigate the effects of annealing on the photocatalytic activity of ZnS films prepared using chemical bath deposition. The increasing of annealing temperature and heating rate increases the crystallinity and the mean grain size of ZnS films, and significantly enhances the absorption in the visible region. The annealed ZnS films exhibit considerable visible light photocatalytic activity, which is associated with the presence of sulfur vacancies, the larger size grain, and the higher crystallinity.Highlights► ZnS thin films have been prepared by chemical bath deposition. ► The effects of annealing on the optical properties of ZnS films were investigated. ► The adsorption band wavelength of ZnS films red-shifts with increasing annealing temperature or heating rate. ► Heat treatment can effectively enhance the photoactivity of ZnS films.

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.

Graphene (GR) and its derivatives are generally assumed to be electron shuttles in order to explain the improved photocatalytic activity of their nanocomposites (such as TiO2/GR). However, it fails to account for the experimental results, which demonstrate that the photocatalytic activity of TiO2/reduced graphene oxide (RGO) is higher than that of TiO2/GR. Herein, we explore the underlying mechanism for the enhanced photocatalytic activity of TiO2/RGO (GR) by comparing several influential factors: band gap, band alignment near the gap, optical absorption, and active sites, via first-principles calculations. The results show that the small band gap, the type-II staggered band alignment, and the negatively charged O atoms as active sites in photocatalytic reactions are likely to be key factors for the photocatalytic activity of TiO2/RGO being better than that of TiO2/GR, partly offering a physical interpretation for related experimental results. Interestingly, the enhanced photocatalytic activity of TiO2/graphane (GRH) is also predicted. These results suggest that functionalized GR is most likely better than pristine graphene at improving the photocatalytic activity of TiO2/GR-based semiconductor photocatalysts.

The coupling of carbon nanomaterials with semiconductor photocatalysts is a promising route to improve their photocatalytic performance. Herein, density functional theory was used to investigate the electronic structure, charge transfer, photocatalytic activity, and stability in a series of hybrid fullerene (C20, Li@C20, C26, Li@C26)/Ag3PO4(100) composites. When a Li atom is incorporated in fullerene, the adsorption energies significantly increase, although the change of interface distance is negligibly small due to the weak interface interaction. The charge transfer between constituents decreases with the C atom number of fullerene. Compared to pure Ag3PO4, the band gap of the composites is smaller, which enhances the visible-light absorption and photoinduced electron transfer. Most importantly, a type-II, staggered band alignment could be obtained in the C26–Ag3PO4(Li@C26–Ag3PO4) interface, 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 Ag3PO4 semiconductor photocatalysts.

Understanding the interfacial interaction is of paramount importance for rationally designing carbon nanomaterial-based hybrids with optimal performance for electronics, optoelectronics, sensing, advanced energy conversion and storage. Here, we firstly reveal that both covalent and noncovalent interactions simultaneously exist in carbon nanotube (CNT)/Ag3PO4 hybrids by studying systematically the electronic and optical properties to elucidate the mechanism of their enhanced photocatalytic performance. Metallic CNT(9,0) may chemically or physically interact with the Ag3PO4(100) surface depending on its relative orientations, whereas semiconducting CNT(10,0) can only noncovalently functionalize Ag3PO4. The C–Ag bond in the covalently bonded hybrid and type-II, staggered, band alignment in noncovalent hybrids lead to a robust separation of photoexcited charge carriers between two constituents, thus enhancing the photocatalytic activity. The small band gap makes the CNT/Ag3PO4 hybrids absorb sunlight from the ultraviolet to infrared region. Moreover, CNTs are not only effective sensitizers, but also highly active co-catalysts in hybrids. The results can be rationalized by the available experiments, thereby partly resolving a debate on the interpretation of the experimental results, and paving the way for developing highly efficient carbon-based nanophotocatalysts.