Simple fabrication of thermally stable apertured N-doped TiO2 microtubes as a highly efficient photocatalyst under visible light irradiation

Apertured N-doped TiO₂ microtubes have been fabricated by simple hydrolysis of titania tetrachloride using ammonia without any external templates. The morphology and microstucture characteristics of apertured N-doped TiO₂ microtubes were characterized by means of the specific surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FT-IR), UV–visible diffuse reflectance spectra (DRS) and X-ray powder diffraction (XRD). The unique morphology of microtubes and mesoporous microstructure were maintained after a heat treatment at 723 K for 3 h, exhibiting significantly thermal stability. The catalysts exhibited high ultraviolet and visible light photocatalytic activity in degrading phenol and methyl orange.     

Fabrication of ternary p-n heterostructures AgCl/Ag2O/NaTaO3 photocatalysts: Enhanced charge separation and photocatalytic properties under visible light irradiation

Ternary p-n heterostructures photocatalysts of AgCl/Ag₂O/NaTaO₃ were synthesized via a simple method and the crystal structure characterized by X-ray diffraction (XRD). The morphology of the photocatalysts were characterized by scanning electron microscopy and transmission electron microscopy. The composition of the photocatalysts was studied by X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscope. The photocatalytic activity of the AgCl/Ag₂O/NaTaO₃ photocatalysts was evaluated using the degradation of Rhodamine B. The AgCl/Ag₂O/NaTaO₃ photocatalysts showed higher visible light activity than the pure NaTaO₃ and Ag₂O/NaTaO₃ photocatalysts. Additionally, the photocatalytic mechanism was that the rapidly separation of photoinduced electrons and holes resulted the enhancement of photocatalytic activity.     

Environmental remediation of aqueous nitrate solutions by photocatalytic reduction using Pd/NaTaO3 nanoparticles

NaTaO₃ nanoparticles were prepared by an ultrasonic method, and Pd was deposited onto the surface of NaTaO₃ via photoassisted deposition. The resulting samples were characterised by X-ray diffraction, ultraviolet and visible spectroscopy, photoluminescence emission spectroscopy, transmission electron microscopy, extended X-ray absorption fine structure analysis, and surface area measurements. The catalytic performance of the samples in the photoreduction of nitrate under visible light was determined. The UV–vis analysis indicated that a red shift occurred after Pd was loaded onto NaTaO₃. The maximum reduction efficiency was 100%, which was obtained using 0.6 wt% Pd/NaTaO₃ after a reaction time of 50 min.     

Hydrothermal synthesis and characterization of Lanthanum-doped NaTaO3 with high photocatalytic activity

Lanthanum-doped NaTaO₃ (NaTaO₃:La) nanocrystals have been synthesized by a hydrothermal method. X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microcopy (TEM), inductive coupled plasma atomic absorption spectrometric analysis, volumetric adsorption method (BET) and UV–vis spectroscopy were used to characterize the samples. The NaTaO₃:La nanocubes show a higher photocatalytic activity than that of the pure NaTaO₃ in the degradation of the safranine T dye under UV irradiation. The highest photocatalytic activity was achieved when 2 mol% lanthanum was doped.     

N-doped anodic titania nanotube arrays for hydrogen production

Titanium dioxide (TiO₂) nanotube arrays are grown in a mixed electrolyte by anodizing process. The anodic nanotubes for N-doping were calcinated at 773 K in a tube furnace with a mixture of NH₃ and Ar gas. The photocatalytic activity of N-doped TiO₂ nanotubes was carried out in a water-splitting reaction under UV and visible light irradiation. Various characterization techniques (Scanning electron microscopy, X-ray diffractometry, X-ray photo-electron spectroscopy, etc.) are used to study the surface morphology, phase of structure, and binding energy.     

Effects of annealing temperature on the photocatalytic activity of N-doped TiO2 thin films

The effects of annealing temperature on the photocatalytic activity of nitrogen-doped (N-doped) titanium oxide (TiO₂) thin films deposited on soda-lime-silica slide glass by radio frequency (RF) magnetron sputtering have been studied. Glancing incident X-ray diffraction (GIAXRD), Raman spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectra were utilized to characterize the N-doped TiO₂ thin films with and without annealing treatment. GIAXRD and Raman results show as-deposited N-doped TiO₂ thin films to be nearly amorphous and that the rutile and anatase phases coexisted when the N-doped TiO₂ thin films were annealed at 623 and 823 K for 1 h, respectively. SEM microstructure shows uniformly close packed and nearly round particles with a size of about 10 nm which are on the slide glass surface for TiO₂ thin films annealed at 623 K for 1 h. AFM image shows the lowest surface roughness for the N-doped TiO₂ thin films annealed at 623 K for 1 h. The N-doped TiO₂ thin films annealed at 623 K for 1 h exhibit the best photocatalytic activity, with a rate constant (k_a) of about 0.0034 h⁻¹.     

Photoelectrocatalytic properties of Ag nanoparticles loaded TiO2 nanotube arrays prepared by pulse current deposition

A pulse current deposition technique was adopted to construct highly dispersed Ag nanoparticles on TiO₂ nanotube arrays which were prepared by the electrochemical anodization. The morphology, crystallinity, elemental composition, and UV-vis absorption of Ag/TiO₂ nanotube arrays were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). In particular, the photoelectrochemical properties and photoelectrocatalytic activity under UV light irradiation and the photocatalytic activity under visible light irradiation for newly synthesized Ag/TiO₂ nanotube arrays were investigated. The maximum incident photon to charge carrier efficiency (IPCE) value of Ag/TiO₂ nanotube arrays was 51%, much higher than that of pure TiO₂ nanotube arrays. Ag/TiO₂ nanotube arrays exhibited higher photocatalytic activities than the pure TiO₂ nanotube arrays under both UV and visible light irradiation. The photoelectrocatalytic activity of Ag/TiO₂ nanotube arrays under UV light irradiation was 1.6-fold enhancement compared with pure TiO₂ nanotube arrays. This approach can be used in synthesizing various metal-loaded nanotube arrays materials.     

Property Characterization and Photocatalytic Activity Evaluation of BiGdO3 Nanoparticles under Visible Light Irradiation

BiGdO₃ nanoparticles were prepared by a solid-state reaction method and applied in photocatalytic degradation of dyes in this study. BiGdO₃ was characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, UV-Vis diffuse reflectance spectroscopy and transmission electron microscopy. The results showed that BiGdO₃ crystallized well with the fluorite-type structure, a face-centered cubic crystal system and a space group Fm3m 225. The lattice parameter of BiGdO₃ was 5.465 angstrom. The band gap of BiGdO₃ was estimated to be 2.25 eV. BiGdO₃ showed a strong optical absorption during the visible light region. Moreover, the photocatalytic activity of BiGdO₃ was evaluated by photocatalytic degradation of direct dyes in aqueous solution under visible light irradiation. BiGdO₃ demonstrated excellent photocatalytic activity in degrading Direct Orange 26 (DO-26) or Direct Red 23 (DR-23) under visible light irradiation. The photocatalytic degradation of DO-26 or DR-23 followed the first-order reaction kinetics, and the first-order rate constant was 0.0046 or 0.0023 min⁻¹ with BiGdO₃ as catalyst. The degradation intermediates of DO-26 were observed and the possible photocatalytic degradation pathway of DO-26 under visible light irradiation was provided. The effect of various operational parameters on the photocatalytic activity and the stability of BiGdO₃ particles were also discussed in detail. BiGdO₃/(visible light) photocatalysis system was confirmed to be suitable for textile industry wastewater treatment.     

Modified microwave method for the synthesis of visible light-responsive TiO2/MWCNTs nanocatalysts

Recently, TiO₂/multi-walled carbon nanotube (MWCNT) hybrid nanocatalysts have been a subject of high interest due to their excellent structures, large surface areas and peculiar optical properties, which enhance their photocatalytic performance. In this work, a modified microwave technique was used to rapidly synthesise a TiO₂/MWCNT nanocatalyst with a large surface area. X-ray powder diffraction, field-emission scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller measurements were used to characterise the structure, morphology and the surface area of the sample. The photocatalytic activity of the hybrid nanocatalysts was evaluated through a comparison of the degradation of methylene blue dye under irradiation with ultraviolet and visible light. The results showed that the TiO₂/MWCNT hybrid nanocatalysts degraded 34.9% of the methylene blue (MB) under irradiation with ultraviolet light, whereas 96.3% of the MB was degraded under irradiation with visible light.     

Synthesis and photocatalytic behavior of BiVO4 with decahedral structure

Decahedral BiVO₄ was successfully synthesized with Tween-80 as a template by the microwave hydrothermal method. The effects of hydrothermal temperature and Tween-80 on crystal phase and morphology of the obtained BiVO₄ were investigated. The crystal phase and morphology were characterized by X-ray diffraction, field emission scanning electron microscopy and UV–vis diffuse reflectance spectroscopy. The results indicated that the as-prepared decahedral BiVO₄ was monoclinic. The photocatalytic behavior for methylene blue (MB) degradation was enhanced with the assistance of an appropriate amount of hydrogen peroxide (H₂O₂) under visible light irradiation. The photocatalytic tests indicated that the photocatalytic efficiency of decahedral BiVO₄ synthesized at 180 °C was 63.5%. However, BiVO₄ sample synthesized at 160 °C showed the highest photocatalytic degradation rate, up to 81.6%, due to its small size and crystal defects.     

Visible light-induced photocatalytic activity of delafossite AgMO2 (M = Al, Ga, In) prepared via a hydrothermal method

Delafossite-structured oxides AgMO₂ (M = Al, Ga, In) were successfully synthesized using fluoro(ethylene-propylene) (FEP) pouch via a facile hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared samples was evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. All three samples showed photocatalytic activity for RhB and MO degradation under visible light irradiations and their photocatalytic activity followed the order of AgInO₂ > AgGaO₂ > AgAlO₂. The relative high photocatalytic activity of AgInO₂ can be attributed to its high quantity of the surface hydroxyl groups. The photocatalytic mechanism of AgInO₂ was proposed and its stability was also investigated.     

Visible-Light-Driven Antimicrobial Activity and Mechanism of Polydopamine-Reduced Graphene Oxide/BiVO4 Composite

In this study, a photocatalytic antibacterial composite of polydopamine-reduced graphene oxide (PDA-rGO)/BiVO₄ is prepared by a hydrothermal self-polymerization reduction method. Its morphology and physicochemical properties are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared (FT-IR), and X-ray diffraction (XRD). The results indicate that BiVO₄ particles are evenly distributed on the rGO surface. Escherichia coli (E. coli) MG1655 is selected as the model bacteria, and its antibacterial performance is tested by flat colony counting and the MTT method under light irradiation. PDA-rGO/BiVO₄ inhibits the growth of E. coli under both light and dark conditions, and light significantly enhances the bacteriostasis of PDA-rGO/BiVO₄. A combination of BiVO₄ with PDA-rGO is confirmed by the above characterization methods as improving the photothermal performance under visible light irradiation. The composite possesses enhanced photocatalytic antibacterial activity. Additionally, the photocatalytic antibacterial mechanism is investigated via the morphology changes in the SEM images of MG1655 bacteria, 2′,7′-dichlorofluorescein diacetate (DCFH-DA), the fluorescence detection of the reactive oxygen species (ROS), and gene expression. These results show that PDA-rGO/BiVO₄ can produce more ROS and lead to bacterial death. Subsequently, the q-PCR results show that the transmembrane transport of bacteria is blocked and the respiratory chain is inhibited. This study may provide an important strategy for expanding the application of BiVO₄ in biomedicine and studying the photocatalytic antibacterial mechanism.     

Photocatalytic degradation of formic acid with simultaneous production of hydrogen over Pt and Ru-loaded CdS/Al-HMS photocatalysts

The CdS/Al-HMS, Pt- and Ru-loaded CdS/Al-HMS photocatalysts were prepared by template, ion exchange and precipitation reaction, and were characterized by N₂ adsorption/desorption measurements, X-ray diffraction (XRD), UV-Visible diffuse reflectance spectra (UVDRS), X-ray fluorescence (XRF), transmission electron microscopy (TEM) and fluorescence emission spectra (FES). The result showed that CdS in the form of clusters was highly dispersed inside the channels of Al-HMS. The reaction activities of photocatalysts were examined by photocatalytic degradation of formic acid under visible light irradiation (λ ≥ 420 nm). The photocatalyst, CdS/Al-HMS loaded 0.34 wt.% Pt, showed the highest H₂ evolution at a rate of 7.63 mL h^− 1 with an apparent quantum yield of 2%.     

Synthesis,Characterization and Photocatalytic Activity of New Photocatalyst ZnBiSbO4 under Visible Light Irradiation

In this paper, ZnBiSbO₄ was synthesized by a solid-state reaction method for the first time. The structural and photocatalytic properties of ZnBiSbO₄ had been characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, transmission electron microscope and UV-visible spectrometer. ZnBiSbO₄ crystallized with a pyrochlore-type structure and a tetragonal crystal system. The band gap of ZnBiSbO₄ was estimated to be 2.49 eV. The photocatalytic degradation of indigo carmine was realized under visible light irradiation with ZnBiSbO₄ as a catalyst compared with nitrogen-doped TiO₂ (N-TiO₂) and CdBiYO₄. The results showed that ZnBiSbO₄ owned higher photocatalytic activity compared with N-TiO₂ or CdBiYO₄ for the photocatalytic degradation of indigo carmine under visible light irradiation. The reduction of the total organic carbon, the formation of inorganic products, SO₄²⁻ and NO₃⁻, and the evolution of CO₂ revealed the continuous mineralization of indigo carmine during the photocatalytic process. One possible photocatalytic degradation pathway of indigo carmine was obtained. The phytotoxicity of the photocatalytic-treated indigo carmine (IC) wastewater was detected by examining its effect on seed germination and growth.     

Low Temperature Preparation and Characterization of N-doped and N-S-codoped TiO2 by Sol–gel Route

This paper reports a new method to prepare the N-doped and N-S-codoped anatase TiO₂ photocatalysts at 100 °C. The as-prepared photocatalysts were characterized by means of XRD, Raman spectra, TEM, BET, UV–Vis diffuse reflectance spectra (DRS) and XPS. The results showed that the N-doping and N-S-codoping extended the absorbance spectra of TiO₂ into visible region with different extent. The BET surface area of the N-S-codoped TiO₂ photocatalysts was high up to 245 m²g⁻¹. The results of degradation of methyl orange (MO) solution showed that the N-doped and N-S-codoped TiO₂ photocatalysts exhibited higher photocatalytic activity than that of Degussa P-25 and the as-prepared pure TiO₂ under visible irradiation. This property can be attributed to the results of synergetic effects of absorption in the visible light region, red shift in adsorption edge, good crystallization and large surface area of the as-prepared N-doped or N-S-codoped TiO₂.     

Preparation of Ag@AgI-intercalated K4Nb6O17 composite and enhanced photocatalytic degradation of Rhodamine B under visible light

In this study, a novel plasmonic photocatalyst, Ag@AgI intercalated layered niobate, was synthesized via a microwave-assisted ion-exchange method. The composite materials prepared were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray fluorescence spectrometry (XRF), Brunauer–Emmett–Teller (BET) and ultraviolet–visible diffuse reflection spectra (UV–vis). The as-prepared plasmonic photocatalyst exhibited an enhanced and stable photocatalytic performance for the degradation of Rhodamine B (RhB) and up to 83% of RhB was degraded in 40 min under visible light irradiation. The mechanism of separation of the photo-generated electrons and holes at the K₄Nb₆O₁₇/Ag@AgI composite was discussed.     

Simple fabrication of rod-like N-doped TiO2/Ag with enhanced visible-light photocatalytic activity

Rod-like N-doped TiO₂/Ag composites were successfully synthesized by a modified sol–gel method, without adding any surfactants. The entire preparation differs from the traditional sol–gel synthesis of TiO₂ that the reaction can get controlled by adjusting the flow speed of water vapor and NH₃. Characterization results show that as-prepared samples were uniform nanorods with an average length of ca. 3 µm and a cross section diameter of ca. 150 nm. The rod-like structure was formed during the annealing process. A possible mechanism was proposed to illustrate the formation of rod-like Ag–N–TiO₂. The degradation of methylene blue performed under visible light with the prepared nanorods as the photocatalyst demonstrated the photocatalytic activities of TiO₂ can be improved by the synergistic effect of N doping and Ag modification. In addition, as-prepared TiO₂-based photocatalyst exhibits a significantly enhanced photo-chemical stability after 5 catalytic cycles mainly due to the rod-like morphology. This indicated that they have some potential value in practical application.     

N-doped TiO2 nanoparticles obtained by a facile coprecipitation method at low temperature

N-doped TiO₂ nanoparticles (NPs) were synthesized using a facile synthesis route by coprecipitation method. The effect of the HNO₃ volume and calcination temperature on the structural, morphological, optical and surface properties of the N-doped TiO₂ NPs was studied. X-ray diffraction analysis showed particles of nanometric size (< 16 nm), which are consistent with HR-TEM micrographs. A slight shift of the absorption edge to higher wavelengths is observed as the HNO₃ volume and calcination temperature increases. Both X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) show the presence and stability of nitrogen in the N-doped TiO₂ structure. The photocatalytic activity of the N-doped TiO₂ NPs was assessed by testing the degradation of rhodamine B (RhB) under ultraviolet (UV) and visible light.     

Microwave-hydrothermal synthesis of extremely high specific surface area anatase for decomposing NOx

Apparently C-doped and undoped or pure nanoparticles of anatase were synthesized using a microwave hydrothermal process in the temperature range of 140–180 °C for 1 h from several Ti precursors, such as Ti ethoxide, Ti isopropoxide and Ti oxysulfate. Nanoparticles of anatase samples were characterized by powder X-ray diffraction, transmission electron microscopy (TEM) and photocatalytic activity measurements. Results showed that nanoparticles in the size range of 4–17 nm of anatase were obtained in all cases with surface areas in the range of 151–267 m²/g. The photocatalytic activity of the prepared titanias was measured using methylene blue (MB) and NO_x molecules. Because MB has very strong adsorption on the samples, photocatalytic degradation under either solar light or black light irradiation was found to be very limited. However, the DeNO_x abilities of carbon-doped titanias were higher than those of Degussa P25 commercial titania sample and undoped or pure titanias especially under irradiation by long wavelength or visible light (>500 nm).     

Photocatalytic reduction of carbon dioxide on NiO/InTaO4 under visible light irradiation

Developing a photocatalyst system for the conversion of solar energy to electric energy or chemical energy is a topic of great interest with fundamental and practical importance. The semiconductor catalysts, such as InTaO₄, have been extensively used for water splitting under visible light irradiation. However, it has not been used for photoreduction of carbon dioxide with water. InTaO₄ was synthesized by solid-state reaction. NiO was added by incipient-wetness impregnation method as the cocatalysts. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible spectroscopy (UV–Vis) and X-ray photoelectron spectroscopy (XPS). The photocatalytic reduction was carried out in a Pyrex reactor under visible light illumination using 500 W halogen light as the light source. The band gap of InTaO₄ was estimated, from UV–Vis spectrum, to be 2.6 eV, showing that these catalysts have ability to reduce CO₂ into methanol. The effects of the NiO cocatalyst and pretreatment process on the photocatalytic reduction of the catalyst to methanol were investigated. The methanol yield increased with the amount of NiO cocatalyst. The reduction–oxidation pretreatment had a positive effect on the catalyst.