Enhanced photocatalytic activity of sulfated silica-titania composites prepared by impregnation using ammonium persulfate solution

Sulfate (SO₄²⁻) modified silica–titania (SiO₂–TiO₂) composite photocatalysts with different loadings of SO₄²⁻ were prepared by a facile pore impregnating method using ammonium persulfate (NH₄)₂S₂O₈ solution. The surface parameters, structure, morphology, the adsorption ability of light, the binding energy of Ti2p and O1s, and the formation rate of OH radicals produced during the photocatalytic reaction process were characterized by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS) and terephthalic acid photoluminescence probing technique (TA-PL), respectively. The results reveal that sulfating of SiO₂–TiO₂ induces the shift of Ti2p and O1s, and increases the adsorption of rhodamine B on the sulfated photocatalysts and the formation rate of OH radicals produced during the photocatalytic reaction process. The photocatalytic activity of SO₄²⁻/SiO₂–TiO₂ for de-colorization of rhodamine B aqueous solution was evaluated. The result shows that when wt% of SO₄²⁻ is 8.6%, SO₄²⁻/SiO₂−TiO₂ exhibits the best photocatalytic activity under ultraviolet light irradiation and the possible reason is discussed.     

Enhanced photo-induced charge separation and solar-driven photocatalytic activity of g-C3N4 decorated by SO42−

SO₄²⁻ decorated g-C₃N₄ with enhanced photocatalytic performance was prepared by a facile pore impregnating method using (NH₄)₂S₂O₈ solution. The photocatalysts were characterized by the Brunauer–Emmett–Teller (BET) method, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and surface photovoltage (SPV) spectroscopy, respectively. The separation efficiency of photo-generated charge was investigated using benzoquinone as scavenger. The results demonstrate that sulfating of g-C₃N₄ increases the adsorption of rhodamine B on g-C₃N₄, the hydroxyl content and the separation efficiency of photo-generated charge. The photocatalytic activity of SO₄²⁻/g-C₃N₄ for decolorization of rhodamine B and methyl orange (MO) aqueous solution was evaluated. The result shows that loading of 6.0 wt% SO₄²⁻ results in the best photocatalytic activity under simulated solar irradiation and SO₄²⁻ play an important role in boosting the photocatalytic activity.     

Additive-free hydrothermal synthesis of novel bismuth vanadium oxide dendritic structures as highly efficient visible-light photocatalysts

A novel bismuth vanadium oxide (BiVO₄) dendritic structure was successfully synthesized via an additive-free hydrothermal route. The crystal structures, morphologies and photophysical properties of the as-obtained BiVO₄ samples were characterized. The photocatalytic activities of the as-synthesized BiVO₄ samples were evaluated by the degradation of rhodamine B (RhB) under visible-light irradiation. BiVO₄ sample synthesized at 140 °C showed the highest photocatalytic degradation efficiency, up to 99.3%, due to its relatively high surface area and high crystallinity.     

Mesoporous TiO2 nano-spheres: Electrospray combined sol-gel fabrication and application to organic phosphorus degradation

In this work, electrospray technique combined sol-gel method was used to prepare porous TiO2 film. X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), and Scanning Electron Microscope (SEM) analyses were conducted to examine the chemical composition, phase structure, and surface morphology of the sprayed TiO2 film. After calcined at 450℃ in air atmosphere for 2 h, mesoporous TiO2 nano-spheres clusters were formed on the surface of silicon wafer and the average size of nano-spheres was 250 nm. Ti presented as Ti 4+ oxidation state in TiO2 film, and the TiO2 film exhibited the anatase phase. The sprayed porous TiO2 films were employed as photocatalyst to degrade organic phosphorus in water samples. Compared with the TiO2 film prepared by Sol-Gel spin-coating method, the porous TiO2 film deposited by electrospray combined sol-gel method showed higher photocatalytic activity.     

Effects of surfactants on microstructure and photocatalytic activity of TiO2 nanoparticles prepared by the hydrothermal method

TiO₂ nanoparticles were prepared using a surfactant (linoletic acid (LA) or polyethylene glycol-400 (PEG-400)) at various hydrolysis ratios (R=H₂O/C₂H₅OH) by the hydrothermal method and studied for photocatalytic degradation of rhodamine B (RhB) under visible light irradiation. Special shapes of TiO₂ nanoparticles, such as cubic, hexagon, bipyramid, and bullet, were found from the use of PEG-400 during the preparation. The cause for the formation of these special shapes is also discussed here. Interestingly, the hydrolysis ratios affected the Brunauer–Emmett–Teller (BET) special surface areas of the TiO₂ nanoparticles. Owing to the effects of the surfactant PEG-400 on the microstructures, the resulting materials exhibited relatively higher photocatalytic activity than conventional TiO₂ nanoparticles in the presence of LA. Furthermore, P-TiO₂-8/10 (P is PEG-400 and 8/10 is H₂O/C₂H₅OH molar ratio) nanoparticles had a similar photocatalytic activity to P25 and TiO₂-10/10.     

Visible light photocatalytic performance of hierarchical BiOBr microspheres synthesized via a reactable ionic liquid

Hierarchical BiOBr microspheres were synthesized via a one-pot solvothermal process in the presence of ethylene glycol and 1-butyl-3-methylimidazolium bromide ([BMIM]Br) as a reactable ionic liquid. The products were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance absorption spectra, nitrogen adsorption–desorption measurements, and photoluminescence spectroscopy. The photocatalytic activity of BiOBr microspheres was evaluated in terms of the degradation of Rhodamine B (RhB), methyl orange (MO), and 4-chlorophenol (4-CP) under visible light irradiation. We found that the solvothermal temperature had important effects on the crystallinity, crystallite size, optical property, adsorptive performance, and photocatalytic activity of BiOBr microspheres. BiOBr microspheres with a specific surface area of 15.7 m² g⁻¹ prepared at 160 °C exhibited the best adsorption and photocatalytic performance for RhB degradation in aqueous solution. However, this sample showed hardly any activity for photodegradation of 4-CP. Tests using radical scavengers confirmed that h⁺ and O₂⁻ were the main reactive species during RhB degradation. A possible mechanism for photocatalysis by BiOBr microspheres is proposed.     

Temperature‐Induced Stacking to Create Cu2O Concave Sphere for Light Trapping Capable of Ultrasensitive Single‐Particle Surface‐Enhanced Raman Scattering

The fabrication of bowl or concave particles with “asymmetric centers” has drawn considerable attentions, in which multiple scattering occurs inside the particles and the ability of light scattering is distinctly enhanced. However, the limited variety of templates, the uncontrollable dimensions such as the size of concavity and the complex growth process have posed serious limitations to the reproducible construction of concave particles with desired geometries and their light‐trapping properties. Herein, a “temperature‐induced stacking” strategy is proposed to create controllable concavity Cu₂O spheres for the first time. Different sizes of F68 micelles can be formed through aggregation under different reaction temperatures, which can serve as soft template to tailor concave geometries of Cu₂O spheres. The as‐prepared Cu₂O concave sphere (CS) can serve as single‐particle (SP) surface‐enhanced Raman scattering (SERS) substrate for highly repeatable and consistent Raman spectra. The unique cavity of Cu₂O CS entraps light effectively, which also enhances the scattering length owing to multiple light scattering. Combined with slightly increased surface area and charge‐transfer process, Cu₂O CS exhibits remarkable single‐particle SERS performance, with an ultralow low detection limit (2 × 10^?8 mol L^?1) and metal comparable enhancement factor (2.8 × 10⁵).     

Significant improvement of photocatalytic activity of porous graphitic-carbon nitride/bismuth oxybromide microspheres synthesized in an ionic liquid by microwave-assisted processing

Graphitic-carbon nitride/bismuth oxybromide (g-C₃N₄/BiOBr) porous microspheres have been successfully synthesized by a one-pot ethylene glycol (EG) assisted microwave process in the presence of 1-hexadecyl-3-methylimidazolium bromine ([C₁₆mim]Br). The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and UV–vis diffuse reflectance spectroscopy (DRS). During the reaction process, the ionic liquid acts not only as solvent and Br source but also as a template for fabrication of g-C₃N₄/BiOBr porous microspheres. In addition, the photocatalytic activity of the g-C₃N₄/BiOBr is evaluated by degrading Rhodamine B (RhB) and ciprofloxacin (CIP) under visible-light irradiation. It is found that 12.75 wt% g-C₃N₄/BiOBr microspheres exhibit higher photocatalytic activity than that of the as-prepared BiOBr. A possible photocatalytic mechanism based on the relative band positions of g-C₃N₄/BiOBr has been proposed.     

Enhanced photo-degradation methyl orange by N–F co-doped BiVO4 synthesized by sol–gel method

Using ammonium fluoride (NH₄F) as the source of nitrogen (N) and fluorine (F), N–F co-doped bismuth vanadate (BiVO₄) visible-light-driven photocatalysts have been synthesized via a sol–gel method. The resulting materials were characterized by a series of techniques: X-ray photoelectron spectroscopy, X-ray diffractometry, scanning electron microscopy, Brunauer–Emmett–Teller (BET) surface analysis, and UV–vis diffuse reflectance spectroscopy. Compared with BiVO₄, the N–F co-doped BiVO₄ photocatalysts exhibited much higher photocatalytic activity for methyl orange (MO) degradation under visible light irradiation. It was revealed that N and F atoms were doped into the lattice of BiVO₄. The doped N atoms existed as O–N or V–O–N bonding, and the F atoms replaced some O atoms to form the O–V–F structure, which can be attributed to the appearance of more active species V⁴⁺ and oxygen vacancies. The doped N and F atoms resulted in a red shift in the absorption edge. However, the N and F doping only slightly changed the morphologies and BET special surface areas of the samples. The photocatalytic activity of BiVO₄ significantly depended on the N–F doping content and the calcination temperature. The maximum activity was observed for the catalyst obtained with calcination at 500 °C, a molar ratio of NH₄F to Bi(NO₃)₃ was 6%.     

An oil-in-water self-assembly synthesis,characterization and photocatalytic properties of nano Ag@AgBr sensitized K2Ti4O9

Nano-sized plasmonic Ag@AgBr sensitized K₂Ti₄O₉ composite photocatalysts (hereafter designated as Ag@AgBr/K₂Ti₄O₉) was synthesized via a facile oil-in-water self-assembly method. The photocatalytic activity of the prepared materials for methylene blue (MB) degradation was examined under visible light irradiation. The results reveal that the size of Ag@AgBr, which evenly dispersed on the surface of K₂Ti₄O₉, distributes about 20 nm. The UV–vis diffuse reflectance spectra indicate that Ag@AgBr/K₂Ti₄O₉ samples have a significantly enhanced optical absorption in 420–800 nm. The photocatalytic activities of the Ag@AgBr/K₂Ti₄O₉ samples increase first and then decrease with increasing amount of loading Ag@AgBr and the Ag@AgBr(10 wt%)/K₂Ti₄O₉ sample exhibits the best photocatalytic activity and 95.75% MB was degraded after irradiation for 90 min. Additionally, studies performed using radical scavengers indicated that h⁺, ·OH and Br⁰ acted as the main reactive species.     

Mesoporous Anatase Titania Hollow Nanostructures though Silica‐Protected Calcination

The crystallization of nanometer‐scale materials during high‐temperature calcination can be controlled by a thin layer of surface coating. Here, a novel silica‐protected calcination process for preparing mesoporous hollow TiO₂ nanostructures with a high surface area and a controllable crystallinity is presented. This method involves the preparation of uniform silica colloidal templates, sequential deposition of TiO₂ and then SiO₂ layers through sol–gel processes, calcination to transform amorphous TiO₂ to crystalline anatase, and finally etching of the inner and outer silica to produce mesoporous anatase TiO₂ shells. The silica‐protected calcination step allows crystallization of the amorphous TiO₂ layer into anatase nanocrystals, while simultaneously limiting the growth of anatase grains to within several nanometers, eventually producing mesoporous anatase shells with a high surface area (～311 m² g^?1) and good water dispersibility upon chemical etching of the silica. When used as photocatalysts for the degradation of Rhodamine B under UV irradiation, the as‐synthesized mesoporous anatase shells show significantly enhanced photocatalytic activity with greater enhancement for samples calcined at higher temperatures thanks to their improved crystallinity.     

Enhanced photocatalytic decolorization of methyl orange by gallium-doped α-Fe2O3

Gallium (Ga)-doped hematite (α-Fe₂O₃) with different molar ratios of Ga/Fe (1%, 2%, 3% and 4%) was prepared by a facile parallel flow co-precipitation method. The photocatalysts prepared were characterized by the Brunauer–Emmett–Teller method, X-ray diffraction, UV/vis diffuse reflectance spectroscopy, and scanning electron microscope. The photo-generated charges separation efficiency of different photocatalysts was investigated using benzoquinone as scavenger. The formation rate of OH radicals produced during the photocatalytic reaction process was studied by a terephthalic acid photoluminescence probing technique. Doping Ga³⁺ into α-Fe₂O₃ increases the specific surface area and the separation efficiency of photo-induced charges. The catalytic activity of the photocatalysts for decolorization of methyl orange aqueous solution was investigated. The results show that α-Fe₂O₃ doped with 3% Ga possesses the best photocatalytic activity. The underlying mechanism is suggested.     

Synthesis of Self‐Supported Ordered Mesoporous Cobalt and Chromium Nitrides

Herein, we demonstrate an ammonia nitridation approach to synthesize self‐supported ordered mesoporous metal nitrides (CoN and CrN) from mesostructured metal oxide replicas (Co₃O₄ and Cr₂O₃), which were nanocastly prepared by using mesoporous silica SBA‐15 as a hard template. Two synthetic routes are adopted. One route is the direct nitridation of mesoporous metal oxide nanowire replicas templated from SBA‐15 to metal nitrides. By this method, highly ordered mesoporous cobalt nitrides (CoN) can be obtained by the transformation of Co₃O₄ nanowire replica under ammonia atmosphere from 275 to 350 °C, without a distinct lose of the mesostructural regularity. Treating the samples above 375 °C leads to the formation of metallic cobalt and the collapse of the mesostructure due to large volume shrinkage. The other route is to transform mesostructured metal oxides/silica composites to nitrides/silica composites at 750–1000 °C under ammonia. Ordered mesoporous CrN nanowire arrays can be obtained after the silica template removal by NaOH erosion. A slowly temperature‐program‐decrease process can reduce the influence of silica nitridation and improve the purity of final CrN product. Small‐angle XRD patterns and TEM images showed the 2‐D ordered hexagonal structure of the obtained mesoporous CoN and CrN nanowires. Wide‐angle XRD patterns, HRTEM images, and SAED patterns revealed the formation of crystallized metal nitrides. Nitrogen sorption analyses showed that the obtained materials possessed high surface areas (70–90 m² g^?1) and large pore volumes (about 0.2 cm³ g^?1).     

Facile synthesis of Cu/tetrapod-like ZnO whisker compounds with enhanced photocatalytic properties

Cu/tetrapod-like ZnO whisker (T-ZnOw) compounds were successfully synthesized using N₂H₄·H₂O as a reducing agent by a simple reduction method without any insert gas at room temperature. The crystal phase composition and morphology of the as-prepared samples were investigated by XRD, SEM and FESEM tests. The photocatalytic property of the as-prepared samples was detected by the degradation of methyl orange (MO) aqueous solution under UV irradiation. It can be found that Cu nanoparticles (CuNPs) dispersed on the surface of T-ZnOw increased with the increasing of Cu/Zn molar ratios (Cu/Zn MRs), and an octahedral structure of CuNPs was obtained when the sample was prepared with less than and equal to 7.30% Cu/Zn MR, but tended to a spherical or nanorod structure of CuNPs densely arranged on the surface of T-ZnOw, which is prepared by Cu/Zn MRs up to 22.00%. All the compounds exhibited excellent photocatalytic activity in decomposing of MO than T-ZnOw, the photocatalytic property of the samples increased with the increasing of Cu/Zn MRs up to 7.30%, while it decreases when further increasing the Cu/Zn MRs. The Schottky barrier of the Cu/T-ZnOw compound can effectively capture photoinduced electrons from the interface and enhanced the photocatalytic property of T-ZnOw.     

Synthesis,characterization and photocatalytic behavior of mesoporous ZnS nanoparticles prepared by hybrid salt extraction and structure directing agent method

Mesoporous ZnS nanoparticles have been synthesized using hybrid salt extraction and surfactant assisted approach. Synthesis procedures were conducted in ethanol media under ultrasonic irradiation. As a by-product of the synthesis reaction, NaNO₃, has a very low solubility in ethanol and acts as a template for porosity formation in the final solid structure. In addition, various structure directing agents, namely, CTAB, DDA, F127 and SDS have been used as soft templates for further porosity formation. Characterization of the synthesized specimens was performed using Transmission Electron Microscopy (TEM), X-ray diffraction (XRD), N₂-physisorption, Furrier Transformation Infrared Spectroscopy (FTIR) and Diffuse Reflectance Spectroscopy (DRS). Results show that the by-product has the major contribution on the specific surface area of the obtained samples. It was found that MP-ZnS synthesized by DDA surfactant has the highest values of surface area (261 m² g⁻¹), pore volume (0.43 cm³ g⁻¹) and average pore diameter amongst all of the samples under study. Studies on adsorption efficiency and photocatalytic behavior of the synthesized specimens were conducted for methylene blue removal from aqueous solution. Results revealed that the MP-ZnS sample synthesized using CTAB surfactant has the best total degradation efficiency amongst the samples under study. Findings were explained using optical band gap energy values (deduced from DRS spectra), the intensity of C-H bond vibrations in FTIR spectra, water droplet contact angle, average pore volume and diameter and also specific surface area from N₂-physisorption data. At the end a simple mechanism was proposed in order to explain the main phenomena leading to photocatalytic removal of MB from aqueous solutions.     

Synthesis and characterization of g-C3N4/BiFeO3 composites with an enhanced visible light photocatalytic activity

The novel visible light-induced g-C₃N₄/BiFeO₃ composites were successfully synthesized by introducing BiFeO₃ into polymeric g-C₃N₄. The structures and optical properties of composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), field-emission transmission electron microscope (TEM), UV–vis diffuse reflection spectroscopy (DRS), respectively. For the degradation of Rhodamine B (RhB), the g-C₃N₄/BiFeO₃ composites exhibited significantly higher visible light photocatalytic activity than that of a single semiconductor. The optimal percentage of doped g-C₃N₄ was 50%. Both photooxidation and photoreduction processes follow first order kinetics. In addition, the stability of the prepared photocatalyst in the photocatalytic process was also investigated. The enhanced photocatalytic performance could be due to the high separation efficiency of the photogenerated electron–holes pairs. The possible photocatalytic mechanism of g-C₃N₄/BiFeO₃ was proposed to guide the further improvement of their photocatalytic activity.     

g-C3N4/Ag3PO4 composites with synergistic effect for increased photocatalytic activity under the visible light irradiation

The g-C₃N₄ was synthesized by a hydrothermal method and the g-C₃N₄/Ag₃PO₄ composites were prepared by a ordinary precipitation method. Microstructures, morphologies and optical properties of the as-prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). The results showed that the Ag₃PO₄ nanoparticles were dispersed on the surface of the flake-like g-C₃N₄, and the heterojunction was formed on the interface. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst presented the highest photocatalytic activity for organic dye methylene blue (MB) degradation, and its photocurrent intensity was approximately 2 times than that of the pure Ag₃PO₄. The g-C₃N₄/Ag₃PO₄ (2 wt%) photocatalyst also exhibited photocatalytic performance in the decomposition of colorless antibiotic ciprofloxacin (CIP). The capture experiment confirmed that holes acted as the main active species during the photocatalytic reaction.     

Preparation and properties of CuO/ZnxCd1−xS photocatalysts

CuO/Zn_0.384Cd_0.616S was prepared by an impregnation method, and its structure and optical properties were characterized using X-ray diffraction, scanning electron microscopy, ultraviolet–visible diffuse-reflectance spectroscopy and X-ray photoelectron spectroscopy and their photocatalytic activity were evaluated based on photocatalytic degradation of methyl orange (MO) solution under visible light. The effects on photocatalytic degradation of the catalyst amount, MO concentration and pH were investigated. And the mechanism for enhancing the photocatalytic activity was also discussed. The results indicated that 0.5 wt% CuO/Zn_0.384Cd_0.616S showed the highest photocatalytic activity among the prepared samples. The mechanism for the degradation of MO occurring on the CuO/Zn_0.384Cd_0.616S surface differs from that on Zn_xCd_1−xS surfaces. The catalytic reaction under visible-light irradiation followed pseudo-first-order kinetics.     

Heterostructured dysprosium vanadate – ZnO for photo-electrocatalytic and self-cleaning applications

In this article, we report fabrication of 5 wt% of Dy as DyVO₄ supported ZnO by template-free hydrothermal-thermal decomposition method and its photocatalytic activity towards degradation of azo dyes Rhodamine-B (Rh-B) and Trypan Blue (TB) in solar light, Electrocatalytic activity in methanol oxidation and Self-cleaning properties. The as prepared DyVO₄-ZnO was characterized by surface analytical and spectroscopic techniques. The results suggested that Dysprosium vanadate doping on ZnO has increased its photocatalytic efficiency with high reusability. DyVO₄-ZnO exhibits higher electrocatalytic activity than prepared ZnO for methanol electrooxidation in alkaline medium, revealing its promising potential as the anode in direct methanol fuel cells. Hydrophobicity of ZnO increases by doping of DyVO_4.     

A Novel Multifunctional Photocatalytic Separation Membrane Based on Single-Component Seaweed-Like g-C3N4

Multifunctional separation membrane is usually realized by multi-component collaborative construction, which makes the membrane preparation method complicated and uncontrollable. Herein, a novel multifunctional photocatalytic separation membrane is prepared by vacuum self-assembly of single seaweed-like g-C₃N₄ photocatalyst. The seaweed-like g-C₃N₄ gives membrane certain roughness, large specific surface area, excellent hydrophilicity and abundant transport channels. Through a systematic study, the membrane exhibits excellent separation of five oil-in-water emulsions with a maximum flux of 3114.0 ± 113.0 L m⁻² h⁻¹ bar⁻¹ for 1, 2-dichloroethane-in-water (Dc/W) emulsion and a maximum efficiency of 97.4 ± 0.1% for chloroform-in-water (C/W) emulsion. In addition, the seaweed-like g-C₃N₄ with large specific surface area and narrow bandgap render excellent visible light absorption characteristics and accelerate e⁻-h⁺ pairs transport rate, giving the membrane excellent photocatalytic degradation and antibacterial properties. The membrane shows good degradation for eight different pollutants, among which the degradation effect for rhodamine B (RhB), methylene blue (MB), and crystal violet (CV) were ≈100%. The antibacterial efficiency against E. coli and S. aureus is also close to 100%. After 35 consecutive separations of C/W emulsion and 10 consecutive degradations of RhB, the membrane still maintains excellent separation performance. This long-lasting multifunctional separation membrane exhibits broad application prospects in complex wastewater purification.