•g-C3N4 quantum dots (CN QDs) were first reported to modified rutile TiO2 (rTiO2).•CN QDs-rTiO2 hybrid was prepared by a simple mixed-calcination process.•CN QDs were formed in-situ during calcination of melamine.•CN QDs-rTiO2 shows enhanced photocatalytic activity in degradation of RhB and NO.•A Z-scheme degradation mechanism was proposed for CN QDs-rTiO2 hybrid.To make full use of solar light, fabrication of g-C3N4 quantum dots (CN QDs) modified rutile TiO2 (rTiO2) hybrid (CN QDs-rTiO2), using both visible light responsive semiconductors as components, was successfully achieved by calcination the mixture of P25 TiO2 and melamine at 500 °C for 4 h. It was found that CN QDs were in-situ formed during calcination, which were homogeneously deposited on the surface of rTiO2. Modification of rTiO2 by CN QDs not only improved the visible-light harvesting ability, but also retarded the recombination of photo-generated electron-hole pairs. CN QDs-rTiO2 hybrid (S15) with nominal 15 at.% CN QDs loading showed the highest photocatalytic activity among all the photocatalysts, whatever for degradation of RhB or photocatalytic decomposition of NO, under visible light irradiation. The increased formation of OH radicals in CN QDs modified rTiO2 suspensions supports a Z-Scheme degradation mechanism instead of the formation of CN QDs-rTiO2 heterojunctions.An efficient visible-light driven Z-scheme hybridized photocatalyst was fabricated by modification of rutile TiO2 with g-C3N4 quantum dots (CN QDs-rTiO2).Download high-res image (272KB)Download full-size image

TiO2 nanocrystals with exposed high-energy (001) facets have been reported to show higher photocatalytic activity than those with exposed traditional (101) facets. However, they can only be excited by UV light. In this paper, visible-light responsive Ti3+-doped TiO2 nanosheets with exposed (001) facets were one-pot fabricated by hydrothermal treatment of a mixture solution of tetrabutyl titanate (80 mmol) and hydrofluoric acid (80 mmol) in the presence of Ti powder (0–12 mmol) at 200 °C for 24 h. The prepared Ti3+-doped TiO2 nanosheet photocatalyst was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption–desorption isotherms. The photocatalytic activity was evaluated by a photoluminescence (PL) technique using coumarin as a probe molecule under visible-light irradiation. The experimental results show that the visible-light photocatalytic activity of the prepared photocatalyst increases first and then decreases with increasing amount of Ti powder. Ti3+–TiO2 nanosheets prepared in the presence of 4 mmol Ti powder show the highest visible-light photoactivity.

Hierarchical nanostructures have attracted increasing interest due to their exceptional properties and widespread potential applications. In this paper, anatase TiO2 hollow nanoboxes (TiO2–HNBs) are formed by assembly of nanosheets with exposed {001} facets by solvothermal treatment of TiOF2 cubes in alcohols (tert-butanol and ethanol) at 180 °C. It was found that phase transformation of TiOF2 to anatase TiO2 begins at corners and edges of TiOF2 cubes due to in situ hydrolysis of TiOF2, where water was produced by dehydration of alcohol molecules. With extension the reaction time, TiO2–HNB assemblies from nanosheets with exposed high-energy {001} facets were formed due to the steady inside–outside dissolution-recrystallization process. However, the resulting hierarchical TiO2–HNBs are unstable, which can decompose to discrete high-energy TiO2 nanosheets if the reaction time is further extended. The hierarchical TiO2–HNBs show higher photocatalytic activity than discrete high-energy TiO2 nanosheets and P25 TiO2 due to the unique structures of TiO2–HNBs.Keywords: hierarchical structure; hollow nanobox; photocatalytic activity; titanium dioxide; titanium oxidifluoride;

A new kind of carbonic electrode material (ACF@OMC), activated carbon fibers (ACF) grafted by ordered mesoporous carbon (OMC), was prepared by developing a lay of OMC on the walls of ACF. The function of ACF@OMC cathode material was evaluated by E-Fenton degradation of brilliant red X3B (X3B), an anionic dye. The results suggest the overwhelmingly better performance of ACF@OMC than that of ACF. The structural properties of the mesoporous ACF@OMC composite are strongly related to its excellent performance.Highlights► Cable-like novel oxygen-fed gas diffusion cathode material (ACF@OMC) was prepared. ► Overwhelmingly better performance of ACF@OMC was found in E-Fenton system. ► The excellent performance of ACF@OMC is due to its ordered mesoporous structure. ► The stability makes ACF@OMC promising in sorption, energy storage and catalysis.

A novel hierarchical anatase TiO2 hollow microsphere (TiO2-HMS) assembly synthesised from TiO2 hollow nanoparticles (TiO2-HNP), denoted TiO2-HMS-HNP, was rapidly fabricated by a simple hydrothermal route in a Ti(SO4)2–NH4F–H2O2 mixed solution at 180 °C for only 3 h. The influence of NH4F and H2O2 on the formation of TiO2-HMS-HNP was studied. A novel mechanism for the formation of TiO2-HMS-HNP based on a H2O2-assisted fluoride-induced self-transformation (FIST) process is proposed. The prepared TiO2-HMS-HNP showed much higher photocatalytic activity than TiO2-HMS, when the activity was evaluated both by the photocatalytic degradation rate of brilliant red X-3B (an anionic azo dye) and by the rate of formation of photo-induced hydroxyl radicals (˙OH) under UV irradiation.

Photocatalytic degradation of organic pollutants in TiO2/UV/O3 system has been ascribed to the hydroxyl radicals mediated oxidation process. In this paper, TiO2 nanotubes (TNTs) were prepared by hydrothermal treatment of P25 TiO2 in NaOH solution, which was characterized by TEM, XRD and nitrogen adsorption–desorption isotherms. Adsorption and photocatalytic degradation of Brilliant Red X-3B (X3B), an anionic azo dye, in TiO2 suspensions using O2 and O3 as oxidants, TNTs and P25 TiO2 as photocatalysts, respectively. The maximum adsorption of X3B on the surface of TNTs is 3 times higher than that of P25 TiO2, and TNTs showed superior photocatalytic activity than P25 TiO2 under identical conditions. Ozonation and photocatalytic oxidation are involved in the degradation of X3B in TiO2/UV/O3 system. However, only photocatalytic oxidation is responsible for the degradation of X3B in TiO2/UV/O2 system. Compared with O2, O3 is a more efficient oxidant in degradation of X3B in TiO2/UV system. Quenching experiments showed that photocatalytic degradation of X3B, whatever in TiO2/UV/O3 or TiO2/UV/O2 system, is through direct holes oxidation, reflecting the importance of adsorption on the degradation of organic pollutant. It is the first example showing the direct hole oxidation of organic pollutant in TiO2/UV/O3 system.Graphical abstractHighlights► The first example showing the direct hole oxidation of organic pollutant in TiO2/UV/O3 system. ► Adsorption is important on the degradation pathway of organic pollutant in TiO2. ► Ozonation and photocatalytic oxidation are involved in TiO2/UV/O3 system. ► Compared with P25 TiO2, TiO2 nanotubes showed higher photocatalytic activity.

Preparation of visible-light responsive TiO2 photocatalyst for recycling and repeated use is of great importance in practical application, such as water purification. In this paper, anatase TiO2 hollow microspheres were prepared using Ti(SO4)2 and NH4F as the starting materials, which were then mixed with cysteine, a biomolecule, followed by calcination at 300 °C for 2 h. The cysteine modified TiO2 hollow microspheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption isotherms, UV–vis diffuse reflectance spectra, X-ray photoelectron spectroscopy, photoluminescence and photocurrent. The photocatalytic activity of cysteine modified TiO2 hollow microspheres was evaluated using Brilliant Red X3B, an anionic azo dye, as the target organic molecule under visible light irradiation (λ ≥ 400 nm). The experimental results showed that C, N and S elements were doped into the lattices of TiO2 hollow microspheres, resulting in an obvious increase in visible-light harvesting ability. With increase in the molar ratio of cysteine to titania (R) from 0 to 2.0, the visible-light photocatalytic activity of the samples increase first, and then decrease. The photocatalyst with R = 1.0 shows the highest photocatalytic activity, which is 6 and 4 times higher than that of pristine TiO2 counterpart and commercial P25 photocatalyst, respectively. The enhanced photocatalytic activity of cysteine modified TiO2 hollow microspheres is attributed to the synergistic effects of improved visible-light harvesting ability, enhanced adsorption to organic pollutant and increased efficiency in separation of the photo-generated electron and hole.Graphical abstractHighlights► Visible-light-driven TiO2 hollow microspheres were prepared by cysteine modification. ► C, N and S elements were doped into the lattices of TiO2 hollow microspheres. ► Reasons for the enhanced visible-light-driven photocatalytic activity are discussed. ► This method is simple, cost-effective, and environmental friendly.

Anatase TiO2 nanocrystals with tunable percentage of reactive {0 0 1} facets were rapidly synthesized by a microwave-assisted hydrothermal treatment of the mixed solution of tetrabutyl titanate (20 g), HF solution (3 ml) and additional water (0–21 g) at 200 °C for 30 min. The resulted sample is denoted as Wx, where x represents the volumes of additional water. The photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, nitrogen adsorption–desorption isotherms and X-ray photoelectron spectroscopy. The photocatalytic activity of the photocatalyst was evaluated by degradation of brilliant red X3B (X3B), an anionic dye, and by a photoluminescence technique using coumarin as a probe molecule. With increasing the amount of additional water from 0 to 21 ml, the shapes of TiO2 nanocrystals evolve from nanosheets to truncated octahedral bipyramids, resulting in a steady decrease in the percentage of exposed {0 0 1} facets (from 71% to 23%). The photocatalytic activity of the resulted surface fluorinated TiO2 nanocrystals increases first and then decrease with increase in the amount of water, and W3 sample with exposed 60% of {0 0 1} facets shows the highest photocatalytic activity. However, for the surface clean TiO2 samples by washing with NaOH solution, W9 with 51% of {0 0 1} facets shows the highest photocatalytic activity. Our experimental results reflect that both crystal planes and surface chemistry play very important roles on the photocatalytic activity of anatase TiO2 nanocrystals.Graphical abstractHighlights► High-energy TiO2 nanocrystals were rapidly synthesized at 200 °C for only 30 min. ► The percentage of exposed {0 0 1} facets is tunable. ► Crystal planes and surface chemistry are important on photo-activity of TiO2.

To study the relationship between the morphology and the photoreactivity of the catalyst, hollow spheres of two semiconductors of ZnO and TiO2 were synthesized by using sulfonated polystyrene (PS) as template. The catalyst samples were then characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), diffuse reflectance spectra (DRS), transmission electron microscopy (TEM) and N2 sorption. Reactive brilliant red X3B, an anionic organic dye, was used in this study as a model chemical with the aim of organic pollutants control. The results show that, whatever the catalyst was, both the adsorptive ability and photoreactivity of the hollow spheres were much higher than that of nanoparticles. The adsorption and photoreactivity of ZnO hollow spheres increased by a factor of 7.36 and 4.66, respectively compared with ZnO nanoparticles, while 3.74 times increased in adsorption and 3.41 times increased in photoreactivity for TiO2 hollow spheres compared with TiO2 nanoparticles. Correlations between adsorption and photoreactivity reflected the importance of adsorption in the enhanced photoreactivity of ZnO and TiO2 hollow spheres.

•mpg-C3N4 was first reported to be used as support for Co3O4.•Tritron X-100 soft template prevents the polymerization of dicyandiamide.•High reactivity of Co3O4/mpg-C3N4 is due to enlarged BET surface area and smaller Co3O4 particle size.Mesoporous graphitic carbon nitride (mpg-CN) was synthesized using Triton X-100, a surfactant containing a hydrophilic polyethylene oxide group and a tert-octyl-phenyl hydrophobic moiety, as a soft template. The obtained mpg-CN was used as a support for Co3O4, and this supported catalyst was used for CO oxidation. The effects of the amount of Triton X-100, weight ratio of Co3O4 to mpg-CN and calcination temperature on the catalytic performances for CO oxidation of Co3O4/mpg-CN composites were systematically studied. It was found that the presence of Triton X-100 not only retarded the polymerization of dicyandiamide, but also affected the microstructure of Co3O4. Bubbles formed because of the hydrophobic group of the surfactant Triton X-100 can be act as a soft template for the synthesis of mesoporous g-C3N4. The enhanced catalytic activity of Co3O4/mpg-CN was attributed to a synergistic effect, enlarged BET surface areas, increased Co3+ and lattice oxygen contents, and the porous structure of mpg-CN support. The high stability of 12.5% Co3O4/mpg-CN(1.0) makes it a promising catalyst for practical applications.Loading Co3O4 over mesoporous g-C3N4 results in the enhanced activity and improved stability of the catalyst for CO oxidation.