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Carbon nitride (C3N4) has attracted widespread attention in the photocatalysis field for its stability, facile preparation from low-cost materials, and outstanding visible-light activity. Exploring novel synthesis or modification approaches of C3N4 with excellent photocatalytic property is still a research hotspot in this area. Herein we report a high-yield synthesis of C3N4 and boron-doped C3N4 using the mixed salts KCl-NaCl-LiCl as solvent. Compared with C3N4 sample prepared by the traditional solid-state reaction method, the sample by the molten-salt process showed much better photocatalytic activity for the degradation of methyl orange solution under visible light, which should be originated from high crystallinity and large surface areas as demonstrated by XRD, TEM and BET results. Furthermore, the photocatalytic activity of the molten-salt prepared C3N4 samples was regulated by boron doping, and the best photocatalytic performance was found at the boron content of 0.5%. Moreover, the photoluminescence properties of the samples were also investigated. The relationship between the photoluminescent and photocatalytic performances of the samples were compared and discussed. We believe the synthetic approach reported here provides a new strategy toward the homogeneous doped C3N4-based materials.

The bismuth layered-structure Sr 1-x Ca x Bi 2 Ta 2 O 9 (SCBT) and Eu 3+ doped Sr 1-x Ca x Bi 2 Ta 2 O 9 solid solutions (0 ≤ x ≤ 1) have been synthesized by molten salt synthesis (MSS). X-Ray diffraction (XRD) characterizations showed that an unlimited solid solution with orthorhombic structure was formed in the x range from 0 to 1.0. Scanning electron microscopy (SEM) showed that the prepared samples presented regular nanosheets with a thickness of 100 nm. The structure evolutions of the solid solution were investigated by Fourier transform infrared spectra (FT-IR), UV–Vis spectrum and transmission electron microscopy (TEM) images. X-ray photoelectron spectroscopy (XPS) result showed that only Eu 3+ was present in the Eu-doped SCBT solutions. Influences of the chemical composition on the photoluminescent and photocatalytic performance have been performed and discussed: In the composition range x = 0 to 0.6, intensities of emission exhibited increased values and x = 0.6 shows the best photoluminescent performance under both 397 and 464 nm excitation at room temperature. All the as-prepared nanosheets showed a long lifetime in the range from 1.30 to 1.60 ms, depending on chemical composition. The photocatalytic activity for the degradation of methylene blue (MB) under UV-light was also varied with the chemical composition.

BiPO4 microspheres with three kinds of crystal phase (h-BiPO4, m-BiPO4 and n-BiPO4) were prepared by a facile hydrothermal-calcination process. The crystalline phase, microstructures and photoelectrochemical properties were studied by various techniques. The results indicated that h-BiPO4 could transform into m-BiPO4 at 600 °C. Interestingly, h-BiPO4 accompanied with a little bit of n-BiPO4 would transform into n-BiPO4. After UV irradiation for 2 h, conversion of 94.6% and a mineralization rate of 76.8% could be achieved on n-BiPO4 for photocatalytic degradation of bisphenol A, which is almost 1.33 times as high as that of m-BiPO4 and 3.14 times that of h-BiPO4. Moreover, the n-BiPO4 also displayed the highest photocatalytic activity for degradation of other phenols (phenol and p-chlorophenol) in water and gaseous benzene. The enhancement of activity could be attributed to the improvement of the photogenerated electron–hole separation efficiency, which would be conducive to the formation of active species (hydroxyl radicals (˙OH) and superoxide radicals (˙O2−)). The results suggest that n-BiPO4 shows potential applications as an efficient and stable photocatalyst for the photocatalytic decomposition of persistent organic pollutants in water and in the gas phase.

Present work focuses on the surface composition disorder, its origin and relevance to photoluminescent and photocatalytic properties of ZnWO 4 nanocrystals. ZnWO 4 nanoparticles were synthesized under solvothermal conditions, in which formic acid was employed for both the nonstoichiometry and kinetic size control. Nonstoichiometry ranging from 1.05 to 1.18 was originated from the surface Zn-rich disorder layer, as reflected by an excess of cation Zn 2+ in the X-ray photoelectron spectroscopy and a new Raman vibration mode at about 930 cm −1 and HR-TEM images. Surface Zn-rich disorder layer has shown a great impact on the structure and properties, including lattice expansion, band-gap narrowing, luminescence enhancement, as well as photocatalytic weakening effect. The investigation on surface composition disorder of multi-component oxides is helpful to deeply understand their formation process and further to find a new functionality optimizing approach.

Ion doping is one of the most effective ways to develop photocatalysts by creating impurity levels in the energy band structure. In this paper, novel Bi 3+ doped SrMoO 4 (SrMoO 4 :Bi 3+ ) nanocrystals were prepared by a simple hydrothermal method. By systematic characterizations using x-ray diffraction, infrared spectra, UV–vis spectra, X-ray photoelectron spectroscopy and transmission electron microscopy, it is demonstrated that all the samples crystallized in a single phase of scheelite structure, and particle sizes of SrMoO 4 :Bi 3+ gradually decreased. The Bi 3+ doped nanoparticles showed lattice contraction, and band-gap narrowing. The photocatalytic activity of the samples was measured by monitoring the degradation of methylene blue dye in an aqueous solution under UV-radiation exposure. It is found that SrMoO 4 :Bi 3+ showed excellent activity toward photodegradation of methylene blue solution under UV light irradiation compared to the pure SrMoO 4 . These observations are interpreted in terms of the Bi 3+ doping effects and the increased the surface active sites, which results in the improved the ratio of surface charge carrier transfer rate and reduced the electron–hole recombination rate. These results illustrate the potential of particle size and surface defect regulation for the construction of novel semiconductor oxide photocatalysts by ion doping.

In this paper, we constructed a novel Pt/Bi 12 O 17 Cl 2 composite through loading tiny amount of Pt quantum dots on the surface of Bi 12 O 17 Cl 2 by using photoreduction method at room temperature. The phase structures, morphologies, optical properties and elemental contents of the obtained samples were studied by XRD, EDS, ICP-OES, SEM, HRTEM, BET, UV–vis DRS and XPS technologies. The photocatalytic activity of novel Pt/Bi 12 O 17 Cl 2 was evaluated by degrading methyl orange (MO) and phenol under visible light (λ > 400 nm). It shows that Pt/Bi 12 O 17 Cl 2 exhibited largely enhanced activity in comparison with the pure Bi 12 O 17 Cl 2 , among which 15% Pt/Bi 12 O 17 Cl 2 sample displayed the fastest degrading rate for MO ( k app = 1.13 h −1 ) and phenol ( k app = 0.18 h −1 ). The excellent photocatalytic activity of Pt/Bi 12 O 17 Cl 2 resulted from the enhanced separation efficiency of photocharges, which is exactly ensured by the transient photocurrent and surface photovoltage investigation. The surface loaded Pt quantum dots acted as trappers to efficiently capture the photoinduced electrons originating from the Bi 12 O 17 Cl 2 substrate under visible light, which intensively avoids the recombination of electrons and holes. This study provides a potential way to boost the activity of bismuth oxyhalide with non stoichiometric ratios via utilizing the intense electron trapping effect of noble metal quantum dots.

A novel BiOI/Bi 12 O 17 Cl 2 heterojunction composite was fabricated via a facile deposition–precipitation method. The surface loading of a portion of BiOI strongly broadened the visible light absorption of Bi 12 O 17 Cl 2 from 500–600 nm. The photoelectric performance measurements show that the tightly contacted BiOI/Bi 12 O 17 Cl 2 heterojunction largely strengthened the spatial separation efficiency of photocharges under visible light. Furthermore, BiOI/Bi 12 O 17 Cl 2 applying to degrade two contaminant models, methyl orange (MO) and phenol, displayed much higher photocatalytic activity than the single Bi 12 O 17 Cl 2 and BiOI under visible light ( λ >400 nm). This is a successful Bi-based semiconductor composite photocatalytic system that can efficiently remove the organic contaminants in wastewater.

The preparation of high-purity brookite TiO2 with a unique morphology is rare and difficult. Herein, high-purity brookite TiO2 hollow spheres were hydrothermally synthesized by employing titanium sulfate as the titanium source and chloroacetic acid and sodium hydroxide as the pH regulator. The structure, morphology, and optical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). The results showed that the as-prepared brookite TiO2 exhibited a hollow-sphere morphology with a size of about 1.0 micrometer and showed a direct band gap of 3.13 eV. Additionally, thermal analysis in combination with infrared spectroscopy showed that the as-prepared brookite TiO2 was surface capped by water and organic molecules. Finally, the photocatalytic and photoluminescent properties of brookite TiO2 were studied.

A series of I−-doped BiOBr (I-BiOBr) photocatalysts were prepared through adjusting the synthesis pH values of the reaction solution. The crystalline structure, light absorption, morphology and element component were measured by XRD, DRS, SEM, TEM, EDS, ICP-OES and XPS technologies. The doping of I− ions strongly broadened the visible light absorption range and improved the activity of I-BiOBr. More importantly, the photocatalytic activity of I-BiOBr dramatically depended on the synthesis pH values, in which I-BiOBr (0.5) displayed the best performance for removing methyl orange and phenol under visible light. The photoelectric property measurement revealed that I-BiOBr had stronger electron–hole separation efficiency than the corresponding BiOBr reference samples. With increase in the pH values, the I− ion doping contents varied a little but the surface charge state changed regularly. The decrease in the surface adsorbed negative Br− ions reduced the formation efficiency of active Br0 and resulted in low activity of I-BiOBr. This study provides a facile and efficient way to control the photocatalytic and photoelectric behaviors of novel I−-doped BiOX photocatalysts via changing the pH values of the reaction solution during synthesis.

AgI/Ag 3 PO 4 was successfully synthesized via a simple physical mixing process in the medium of water by using AgI microparticles and Ag 3 PO 4 nanospheres as precursors on the basis of a novel dissolution–precipitation strategy. The as-prepared AgI/Ag 3 PO 4 composite exhibited much higher activity than the pure AgI and Ag 3 PO 4 for eliminating methyl orange under visible light ( λ > 420 nm). The pseudo-first-order rate constant of methyl orange degradation over 75% AgI/Ag 3 PO 4 was 0.056 min −1 , which is 18.6 and 1.36 times higher than those over pure AgI and Ag 3 PO 4 . AgI/Ag 3 PO 4 heterostructure interface efficiently separated the photoinduced carriers and acquired excellent photocatalytic activity and stability. It provides a facile, fast and universal tactic to construct inorganic salts semiconductor composite photocatalysts based on the novel dissolution–precipitation strategy.

Ag/BiOI and Ag/AgI/BiOI composites were successfully in-situ synthesized via the same facile photoreduction strategy through adjusting the Ag + amount. The scanning electron microscopy shows that Ag and Ag/AgI nanoparticles were loaded on the surface of BiOI microplates. The formation of Ag originated from the surface adsorbed Ag + for Ag/BiOI while from the first-step cation-exchange generated AgI for Ag/AgI/BiOI. Under visible light ( λ >420 nm), both Ag/BiOI and Ag/AgI/BiOI displayed higher photocatalytic activities than pure BiOI for degradation of rhodamine B. It provides a universal way to obtain Ag/BiOX and Ag/AgX/BiOX photocatalysts using photoreduction strategy for their potential application in water purification.

Three kinds of crystal phase BiPO4(HP, LTBP, and HTBP) were selectively synthesized by controlling the preparation conditions. Structures of the three samples are all constructed by PO4 and BiO8 polyhedra but with different geometric structures. Detailed characterization was carried out by X-ray diffraction(XRD), scanning eletron microscopy(SEM) and Raman, UV-Vis, and luminescence spectrometries. Three samples exhibit huge distinctions in their photoluminescence(PL) lifetime: 0.68, 162 and 160 μs for HP, LTBP, and HTBP, respectively. More interesting, an outstanding photocatalytic activity is observed for as-prepared LTBP nanorod, which shows even higher activity for the degradation of MB solution than P25. In addition, experiments were carried out to clarify the role of hydroxyl (·OH) and superoxide radicals(O2 ·) played in photocatalytic process and it was found O2 · was the main active species in BiPO4 photocatalysts. Further comparison of structural and photocatalytic properties of the three samples finds that structure distortion is contributed to their property difference. A correlation was found between photocatalytic performance and the distortion of BiO8 dodecahedra. The internal field generated by the distortion of BiO8 dodecahedra was believed advantageous for the separation of electron and hole, which was in favor of the improvement of photocatalytic activity. This correlation may help to design other photocatalysts with high activity.

This work explored the selective synthesis of polymorphs of CdWO{sub 4} in either tetragonal or monoclinic phase by optimizing the experimental parameters. Systematic characterization indicated that both polymorphs possessed similar spherical morphologies but different structural building blocks. Electronic structures calculations for both polymorphs demonstrated the same constructions of conduction band or valence band, while the conduction band widths of both polymorphs were quite different. Both CdWO{sub 4} polymorphs exhibited good photocatalytic activity for degradation of methyl orange under UV light irradiation. When comparing to some other well-known tungstate oxide materials, the photocatalytic activity was found to follow such a consequence, monoclinic CdWO{sub 4{approx}}monoclinic ZnWO{sub 4}>tetragonal CdWO{sub 4}>tetragonal CaWO{sub 4}. The specific photocatalytic activity of monoclinic CdWO{sub 4} was even higher than that of commercial TiO{sub 2} photocatalyst (Degussa P25). The increased activity from the tetragonal CdWO{sub 4} to the monoclinic was consistent with the trend of the decreased symmetry, and this could be explained in terms of the geometric structures and electronic structures for both polymorphs. -- Graphical abstract: Monoclinic CdWO{sub 4} exhibited a much higher photocatalytic activity than the tetragonal form owing to the lower symmetry, more distorted geometric structure, and the dispersive band configuration. Display Omitted Research highlights:more » > Polymorphs of CdWO{sub 4} in either tetragonal or monoclinic phase were selectively synthesized. > Both polymorphs possessed similar spherical morphologies, while the relevant structural building blocks were different. > Photocatalytic activities of CdWO{sub 4} polymorphs depended strongly on the symmetry, geometric structure, as well as band configuration.« less

CdWO4 polymorphs are solvothermally synthesized from mixtures of Cd2Cl2 and Na2WO4 using water as solvent to prepare monoclinic CdWO4, and propylene glycol for tetragonal CdWO4 (autoclave, 200 °C, 10 h).

Developing new approaches to polymorphic control is significantly important for function and property design of inorganic materials. In this paper, we proposed a novel solvothermal (hydrothermal) approach for polymorphic control of CdWO4 nanocrystals. By tuning the synthetic parameters such as solvent, reaction temperature, and reaction time, both phase structure and crystallite size of CdWO4 nanocrystals were effectively controlled. As a result, two different crystalline phases of CdWO4 in monoclinic and tetragonal structures were successfully obtained. The photocatalytic performances of CdWO4 polymorphs were investigated by both degradation of MO under UV light irradiation and water splitting under visible light, which clearly demonstrates that the monoclinic structured CdWO4 nanocrystals exhibited a catalytic activity higher than that of tetragonal structured counterpart.