Ultraviolet-visible Diffuse Reflectance Spectra Research Articles

Systematic studies on Ca19M2(PO4)14:Eu3+ (M = Mg, Zn) phosphors: Effects of M cation on photoluminescence

Ca19(1-x)M2(PO4)14:19xEu3+ (M = Mg, Zn) (x = 0.05, 0.07, 0.09, 0.10, 0.11 and 0.12) red phosphors were successfully synthesized by the high-temperature solid-phase reaction method. The phase composition, morphology and characteristic photoluminescence properties of Ca19Mg2(PO4)14 (CMPO):Eu3+ and Ca19Zn2(PO4)14 (CZPO):Eu3+ were analyzed by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and photoluminescence spectroscopy. The photoluminescence excitation (PLE) and emission (PL) spectra of both samples indicate that the phosphors can be effectively excited by ultraviolet (UV) and blue light, and also it is shown that the electric-dipole transition of Eu3+ is dominant. The typical concentration quenching occurs when Eu3+-doping concentrations of both phosphors exceed 10 mol%, and the PL intensity of CZPO:0.10Eu3+ sample is 1.65 times that of CMPO:0.10Eu3+. Furthermore, the infrared spectra (IR), differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) curves, ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS), thermal stability, chromaticity coordinates (CIE) and correlated color temperature (CCT) of Ca19M2(PO4)14:Eu3+ phosphors were evaluated in detail. The band gaps of CMPO and CZPO hosts were equal to 6.46 and 6.39 eV, respectively. The I423K/I298K values of CMPO:Eu3+ and CZPO:Eu3+ phosphors are as high as 73.89% and 88.29%. The chromaticity coordinates of Ca19(1-x)M2(PO4)14:19xEu3+ (M = Mg, Zn) phosphors locate in red region, and the color purity values of CMPO:Eu3+ and CZPO:Eu3+ are determined to be 99.82% and 99.61%, respectively. To sum up, the phosphors are considered as the potential luminescence materials for use in white light emitting diodes (w-LEDs).

Novel stable enhanced visible light photocatalytic system based on a Ag3PO4@polypyrrole core-shell Z-scheme with in-situ generated metallic Ag ohmic contacts

Maintaining the high photocatalytic activity and stability of Ag3PO4 in practical applications is a still a major challenge. In this study, a series of Ag3PO4@polypyrrole (PPy) core-shell structure photocatalysts were prepared successfully by facile in-situ oxidative polymerization. A transmission electron microscopy image of the composite showed that the PPy shell with a thickness of 5–10 nm was coated tightly on the surface of the Ag3PO4 particle core. X-ray diffractometer and X-ray photoelectron spectroscopy analyses demonstrated that the silver ions were reduced to metallic Ag during polymerization. Ultraviolet–visible diffuse reflectance spectra indicated that the light response range of PA-5 broadened from 300 to 630 nm. Compared with pure Ag3PO4, the composites exhibited higher photocatalytic activities and better photostability, especially Ag3PO4@PPy with a PPy content of 5 wt% (PA-5). The degradation rate of PA-5 with organic dyes exceeded 98% within 15 min under visible light irradiation. Even after five repeated reactions, PA-5 still maintained a high degradation rate of 94.98%. The degradation rate of the pure Ag3PO4 decreased significantly from 94.53% to 60.33% after five cycles. Based on the experimental results, a reasonable mechanism is proposed for the Z-scheme electron-transfer photocatalytic system with metallic Ag as an ohmic contact.

A new strategy to the NaY(MoO4)2:Eu3+ phosphors modified by tetraethyl orthosilicate for LEDs: Photoludminescence properties and morphology

NaY(MoO4)2:Eu3+ microcrystals with different morphologies have been successfully synthesized via a hydrothermal method by varying the molar ratios of tetraethyl orthosilicate (TEOS). The structure and photoluminescence properties of phosphors are investigated by the X-ray powder diffraction (XRD), transmission electron microscope (TEM), the ultraviolet-visible diffuse reflectance spectra (UV–vis DRS), photoluminescence excitation (PLE) and emission (PL) spectra as well as the decay curves. There are two intense PLE peaks at 395 and 465 nm in the PLE spectra, which well matched with the near ultraviolet (NUV) and blue GaN-based light-emitting diodes (LEDs). In the PL spectra, the strongest PL peak is caused by 5D0 → 7F2 electric dipole transition. In addition, the amount of TEOS has an important impact on the morphologies and PL intensity of samples. With the increase of the amount of TEOS, the morphologies of the samples vary from double shuttle-like architectures, truncated rhombic polyhedrons, to quasi-cubes. It is found that the International Commission on Illumination (CIE) chromaticity coordinates of phosphors are located in red region, and the color purity is 99.70 % for S2 sample. Besides, the correlated color temperature (CCT) values of S1−3 samples are in the range of “warm appearance”. Therefore, the above obtained results suggest that the samples possess potential application value in the field of optical display systems, photoelectric devices and LEDs.

Zinc-substituted Ag2CrO4: A material with enhanced photocatalytic and biological activity

Abstract In the past years, new environmentally-friendly photocatalysts have been reported, but the realization of efficient visible-light driven photocatalyst with highly active bactericidal and fungicidal activity is still challenging. This work is a joint experimental and theoretical study on the structural, electronic, and optical properties of Ag2CrO4:Zn2+ (ACOxZn, x = 1%, 2%, and 4%) solid solutions for photocatalytic, bactericidal, and fungicidal activity. For the first time, synthesis of these innovative and multifunctional materials were performed through the cation exchange of zinc and silver using a simple, fast, and cheap co-precipitation method. Powder X-ray diffraction measurements revealed the long range order of the materials. X-ray photoelectron spectroscopy provided information about the surface of the samples demonstrating that they were pure. The materials showed short-range order as verified by FT-Raman spectroscopy. Additionally, ultraviolet-visible diffuse reflectance spectra and photoluminescence spectroscopy were used to examine the electronic properties which corroborated with the increasing photocatalytic activity for the degradation of Rhodamine B and bactericidal activity against Staphylococcus aureus and Candida albicans. Field emission scanning electron microscopy images showed different types of particles with different facets and sizes. Theoretical results based on density functional theory calculations complement the experimental results to rationalize the effects of the incorporation of Zn cations in the ACO host lattice.

In situ synthesis of ultrafine TiO2 nanoparticles modified g-C3N4 heterojunction photocatalyst with enhanced photocatalytic activity

To improve the redox performance and light absorption property, the 2D/0D g-C3N4/TiO2 heterojunction photocatalyst were successfully fabricated by co-annealing process based on melamine powder and ultrafine TiO2 nanoparticles (about 9.87 nm) obtained from electrochemical etching technology. The surface micromorphology, crystal structure, basic element composition, chemical structure, specific surface and optical performance were analyzed by SEM-EDS, TEM, HR-TEM, XRD, XPS, FTIR and Ultraviolet–visible diffuse reflection spectra (UV–vis DRS). The photocatalytic performance of g-C3N4/TiO2 photocatalyst was assessed by the degradation of tetracycline hydrochloride (TC) under simulated sunlight irradiation. The results showed that the obtained TiO2 powder had extremely smaller particle size and higher photocatalytic activity than commercial P25. The coupling of 0D TiO2 nanoparticles and 2D g-C3N4 nanosheet further promoted the visible light absorption performance of TiO2. The unique g-C3N4/TiO2 heterojunction photocatalyst exhibited remarkable photocatalytic performance for the degradation of TC, whose degradation rate could reach to 99.40% under 120 min irradiation. The kinetic constant of the g-C3N4/TiO2 photocatalyst was 1.48 times of that of TiO2. The ESR results confirmed ·OH and ·O2– radicals produced in the photocatalytic process. This work could provide an effective reference for the fabrication of ultrafine TiO2 powder and binary heterojunction photocatalyst with excellent photocatalytic activity for organic pollutants degradation in water purification.

A facile route to construct NiTiO3/Bi4NbO8Cl heterostructures for enhanced photocatalytic water purification

NiTiO3/Bi4NbO8Cl heterostructure photocatalysts were successfully synthesized by a mechanical mixing method. The crystal structure, morphology, optical properties and energy band structures of all samples were determined by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, ultraviolet–visible diffuse reflection spectra (UV–Vis DRS), and Mott–Schottky tests. The NiTiO3/Bi4NbO8Cl composites were observed to possess an improved activity in the photocatalytic degradation of organic dye rhodamine B (RhB) under irradiation. In particular, Bi4NbO8Cl modified with NiTiO3 (10% in weight) exhibits the best photocatalytic performance. The enhanced photocatalytic performance can be ascribed to the formation of intimate interfacial contact and type-II band alignment between NiTiO3 and Bi4NbO8Cl. From the results of photoluminescence spectra (PL), time-resolved decay spectra (TR-PL), photocurrent and electrochemical impedance spectroscopy, the rapid separation and transportation of photoinduced charge carriers were proved. In addition, the proposed mechanism for the enhanced photocatalytic activities is proposed in this paper.

Luminescence properties and energy transfer in Ce3+ and Tb3+ co-doped Sr5(PO4)2SiO4 phosphor

A novel blue-emitting apatite structure phosphate phosphor Sr5(PO4)2SiO4: Ce3+, Tb3+ has been synthesized by a high-temperature solid-state reaction. X-ray diffraction (XRD), scanning electric microscopy (SEM), ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS), photoluminescence excitation (PLE) and emission (PL) spectra were utilized to characterize the samples. The results showed that the Sr5(PO4)2SiO4: Ce3+, Tb3+ samples exhibit a wide and strong emission band located at 405 nm. In addition, the process of energy transfer (ET) from Ce3+ to Tb3+ has been proved to be a dipole-dipole interaction. Importantly, the color of the phosphor emission can be changed by proper tuning of the Ce3+/Tb3+ ratio. Therefore, the prepared phosphors exhibit great potential for applications in the fields of luminescence and display.

Boosted Ag/g-C3N4 prepared under microwave irradiation for photocatalytic activity of RhB under visible light

The effluent of Rhodamine B (RhB) from industries causes a high impact toward contamination of the environment. Photocatalytic degradation has become a promising destructive technique to remove those dye from industrial. In this study, Silver/graphitic carbon nitride (Ag/g-C3N4) prepared using simplistic preparation using microwave irradiation in its place of normal calcination under furnace as heating media. The prepared photocatalyst was characterized by using Fourier transform infrared (FTIR), N2 adsorption-desorption, ultraviolet-visible diffuse reflectance spectra (UV-VIS/DRS). The deposited of Ag on g-C3N4 surface photocatalyst enhanced capability to extend the adsorption of visible light region. The texture of g-C3N4 affected after deposited with Ag and the bandgap energy of Ag/g-C3N4 narrowed from 2.7 eV to 2.31 eV significantly boosting and improved the efficiency of degradation RhB under visible light irradiation. The additional Ag on g-C3N4 revealed highest performance (98%) using RhB solution after exposed under visible light for 180 min. As a result, this works can give benefit to purify the effluent of toxic dyes as wastewater treatment.

Novel Ag–TiO2/ZnFe2O4 Nanocomposites for Effective Photocatalytic, Electrocatalytic and Cytotoxicity Applications

We report the preparation and characterization of a new heterostructured Ag-TiO₂/ZnFe₂O₄ (ATZ) nanocomposite. X-ray diffraction (XRD) reveals the presence of spinel type ZnFe₂O₄ and anatase TiO₂. Scanning electron microscope (SEM) images of ATZ nanocomposites show that Ag nanoparticles are successfully loaded on the composite Ag-TiO₂ and is uniformly distributed on surface of ZnFe₂O₄ forming a nanocomposite with an approximate particle size of 44.8 nm. High-resolution transmission electron microscope (HR-TEM) analysis clearly indicates the particles with spherical and hexagonal structure and sizes of most of the particles are below 50 nm. Ultra violet-visible diffuse reflectance spectra (UV-vis-DRS) show that Ag-TiO₂/ZnFe₂O₄ has increased visible absorption than TiO₂. Photoluminescence (PL) spectra shows that the intensity of ATZ is low relative to prepared TiO₂. The photocatalytic degradation of Reactive Yellow 86 (RY 86) dye was studied. Based on the band gap energies of TiO₂ and ZnFe₂O₄, a mechanism of degradation is given. Photocatalytic activity results suggest that as-prepared ATZ shows higher photodegradation efficiency than pure TiO₂. The main reactive oxidative species involved in the degradation and stability of photocatalyst were also investigated. ATZ shows higher electrocatalytic activity than TiO₂ for methanol electrooxidation. The cytotoxicity of ATZ was analysed. Multifunctionality of ATZ makes it useful for environmental and biomedical applications.

Bleachability improvement of eucalypt mechanical pulps using hydrogen peroxide in ethanol-water media

Alkaline darkening has a negative effect on chemimechanical pulps produced from various eucalypt chips. For instance, the pulp’s brightness has been found to drop rapidly when alkali addition exceeds its optimum amount. Therefore, to compare the effects of different media on brightness gain, eucalypt mechanical pulps were bleached using a typical peroxide bleaching sequence in a water medium and in an ethanol-water (E/W) medium. Various pulp brightness levels and changes of residue chemicals in the spent bleaching liquors were investigated. Compared to water medium, the net brightness gain notably increased when using the E/W medium at the same chemical dosages. The rate of pulp brightness loss caused by increasing alkali dosage dropped in the E/W medium. Analyses based on ultraviolet-visible diffuse reflectance spectra of bleached pulps, as well as gel permeation chromatography and pyrolysis-gas chromatography-mass spectrometry spectra of the residues in the spent bleaching liquors, indicated that the contributions to brightness improvement from ethanol-water media could be explained by the selective dissolution and removal of phenolic- or guaiacyl-structured lignin fragments that result in the formation of chromophoric groups under alkaline conditions.

Microstructures, Optical Properties and Degradation Efficiency of Nitrogen-doped Titanium Dioxide to Automobile Exhaust

To understand the influence of nitrogen (N) dopant on phase structure, morphology, optical property, photocatalytic degradation of TiO2 to automobile exhaust (AE) under visible light irradiation, the N-doped TiO2 was first prepared, and then X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS) and photocatalytic degradation tests were conducted. Results indicated that only anatase phase was found in both pure TiO2 and N-doped TiO2, and the N doping improved the dispersity of TiO2. Also, the N doping increased the absorbance of TiO2 under UV and visible light, respectively. An obvious red shift was observed on UV-Vis DRS of pure and N-doped TiO2 samples, indicating that the spectral response range of TiO2 was expanded to visible light region, and the utilization efficiency of solar irradiance was increased. The prepared N-doped TiO2 nanoparticles with an N dopant content of 3.0% showed better optical properties. Finally, the N doping improved the photocatalytic activity of TiO2 to AE in the visible light region. Furthermore, the N-doped TiO2 presented lower degradation efficiency to CO than that to CO2 under visible light radiation. Thus, it is found that the degradation efficiency of TiO2 to AE can be increased by the N doping under visible light radiation.

In English

The development of novel materials ensuring the use of solar radiation as an inexhaustible source of renewable and environmentally friendly energy is one of the actual problems of materials science. Scientific research towards of solving this important task showed the expediency of using photocatalytic processes with the participation of semiconductor systems. One of the most well-known catalyst titanium dioxide TiO 2 has photoactivity only in the ultraviolet region of the spectrum that significantly restricts its use. The application of based on undoped graphite-like carbon nitride g-C 3 N 4 or g-C 3 N 4 /TiO 2 composite catalysts allows using only part of the visible spectrum of solar radiation (with a wavelength of less than 460 nm). It is found that the doping of carbon nitride by oxygen significantly improves its photocatalytic properties to enhancing solar energy utilization. Therefore, to improve the photocatalytic activity of semiconductor photocatalyst, the coupling O-doped g-C 3 N 4 (O-g-C 3 N 4 ) with rutile TiO 2 is a good strategy. Novel composite material O-g-C 3 N 4 /TiO 2 was synthesized by gas phase method of deposition of O-doped g-C 3 N 4 on particles of rutile powder under the special reactionary conditions of the pyrolysis of melamine. Obtaining O-g-C 3 N 4 /TiO 2 binary composite was confirmed through various analytical techniques including X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and ultraviolet-visible diffuse reflectance spectra (UV-Vis-DRS) methods. It is found that the absorption spectra of the O-g-C 3 N 4 /TiO 2 powders show a bathochromic shift of the long-wavelength edge of the fundamental absorption band (to 600 nm) relative to the absorption band of g-C 3 N 4 /TiO 2 (~ 460 nm). As a result, O-g-C 3 N 4 /TiO 2 photosensitivity is observed in the significant part of the visible region and the band gap of synthesized product is determined to be less than 2.4 eV versus 2.7 eV for undoped g-C 3 N 4 or g-C 3 N 4 /TiO 2 . One stage constructing heterojunction structure of O-g-C 3 N 4 /TiO 2 composite may be used as a low-cost way to avoid the limitations of each component and realize a synergic effect in promoting the efficient generation and separation of charge carriers, thus boosting the photocatalytic activity to enhancing solar energy utilization.

BiOCl-Bi12O17Cl2 nanocomposite with high visible-light photocatalytic activity prepared by an ultrasonic hydrothermal method for removing dye and pharmaceutical

A BiOCl-Bi12O17Cl2 nanocomposite with a high visible-light response and a low photoinduced electron-hole pair recombination rate was successfully synthesized using an ultrasonic-hydrothermal method. The texture, structure, optical, and photocatalytic properties of the composite were characterized. The results showed that the composite had a sheet flower-like structure with a large specific surface area. Ultraviolet-visible diffuse reflection spectra and photoluminescence spectra showed that the composite had an excellent visible-light response and a low recombination rate of photoinduced electron hole pairs. The photocatalytic property of the composite was evaluated by the removal efficiency of rhodamine B and ciprofloxacin under visible-light illumination. The composite's reaction rate constant of removing rhodamine B (/ciprofloxacin) was approximately 8.14 (/4.94), 42.63 (/11.91) and 64.66 (/36.07) times that of Bi12O17Cl2, P25, and BiOCl, respectively. Furthermore, the composite showed a wide applicable pH range and excellent reusability. Mechanism analysis showed that photogenerated holes played a dominant role and ·O2− also contributed to photocatalytic degradation. In summary, this study presents a high-efficiency photocatalyst for wastewater treatment.

Dye-sensitized TiO2@SBA-15 composites: Preparation and their application in photocatalytic desulfurization

Photocatalytic oxidation desulfurization has become a research hotspot in recent years because of mild reaction conditions, less energy consumption and high selectivity. In this paper, TiO2 was loaded onto SBA-15 molecular sieves and sensitized with organic dyes (2, 9-dichloroquinacridone, DCQ) to extend its spectral response range from ultraviolet light to visible light. The catalyst DCQ-X%TiO2@SBA-15 was characterized by BET measurements, X-ray diffraction, Fourier transform infrared spectroscopy and Ultraviolet–visible diffuse reflection spectra, and then it was applied for photocatalytic oxidation desulfurization of gasoline. The effects of different catalytic systems, TiO2 concentration, catalyst dosage, and different model sulfur compounds on catalytic desulfurization performance were investigated. Experimental results show that DCQ-TiO2@SBA-15 has a better performance than the unsensitized TiO2@SBA-15, and the desulfurization rate can reach up to 96.1% in a reaction time of 90 min.

Amine-Functionalized TiO2 Nanoparticles Covalently Loaded into Epoxy Networks via Thermal and Microwave Curing Processes

TiO2 nanoparticles were surface modified by NH2-functionalized organic moieties, and then chemically loaded into diglycidyl ether of bisphenol A-derived epoxy networks. Amine functionalization of these organically modified nanoparticles allowed them to have an efficient participation in the curing processes. Alongside the main amine hardener, i.e., 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane, the aminated TiO2 played the role of a new inorganic co-hardener. Thermal and microwave-assisted curing processes resulted in epoxy-based composites incorporated by uniformly dispersed TiO2 nanoparticles. Diffuse reflectance ultraviolet-visible spectra showed that unlike the neat synthesized counterparts, TiO2-loaded epoxy composites have significant absorption in the visible range of 400–700 nm. According to the results obtained from atomic force microscopy technique, it was found that the microwave-assisted curing process results in a smoother surface in comparison with the thermal one. Transmission electron microscopy obviously demonstrated that the average size of the loaded particles is below 50 nm. Thermogravimetric analysis of the TiO2-containing epoxy networks revealed that the resulted composites are thermally decomposed through a simple one-step process at about 360 °C. Dynamic mechanical thermal analysis profiles indicated that no agglomeration of the nanoparticles occurs during the curing processes of the epoxy resin, and the incorporated nanoparticles somewhat limit the segmental motions of the polymer chains.

Highly sensitive detection of chromium (VI) by photoelectrochemical sensor under visible light based on Bi SPR-promoted BiPO4/BiOI heterojunction

In this work, Bi surface plasmon resonance (SPR)-promoted BiPO4/BiOI heterostructures (Bi-BPI) are synthesized through a one-step hydrothermal method. The structure and morphology have been measured by a series of physical characterizations. Furthermore, the photoelectrochemical (PEC) experiments show that the PEC properties of BiPO4/BiOI are higher than those of pure BiPO4 and BiOI, while BiPO4/BiOI-6 % has the best PEC performance. At the same time, it is found that Bi metal could improve the PEC properties of BiPO4/BiOI-6 %, and that 0.05-Bi-BiPO4/BiOI-6 % has the highest performance among all materials. Ultraviolet-visible diffuse reflection spectra (DRS) and photoluminescence (PL) also prove that 0.05-Bi-BiPO4/BiOI-6 % features excellent visible light absorption and a lower electron recombination rate than the other composites. Therefore, PEC sensors based on 0.05-Bi-BiPO4/BiOI-6 % have been fabricated for the detection of hexavalent chromium (Cr (VI)). They exhibit a wide linear range from 0.5–180 μM with high stability for sensing Cr (VI). Thus, the PEC sensor has a great potential application in Cr (VI) detection.

Tunable micro-morphology and visible-light response property of worm-like monoclinic BiVO4

Using sol-gel auto-combustion method, monoclinic bismuth vanadate (m-BiVO4) nano-powder was successfully prepared and the influence of sol precursor’s pH value on performances of m-BiVO4 was thoroughly investigated. X-ray diffractions (XRD), scanning electron microscope (SEM), and ultraviolet-visible diffuse reflection spectrum (UV-vis) analytic methods were used to characterize phases, microstructure and visible-light response properties of samples in order to understand the influence of pH value. The study results show that precursor’s pH value obviously influences the microstructure and visible-light response performance of m-BiVO4 nano-powder, i.e., the morphology of m-BiVO4 can be controlled by adjusting the precursor’s pH value. When the pH value equals 9, the appearance of nano-powder is worm-like shape which disperses well and has great visible-light response performance.

A facile approach for the synthesis of ZnxCd1-xS/C nanocomposite to enhance photocatalytic activity

A series of ZnxCd1-xS/C nanocomposites with different molar ratios of Zn/Cd were successfully synthesized through a facile solid phase thermal decomposition method. The structures and properties of these nanocomposites were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscope (XPS), transmission electron microscopy (TEM), ultraviolet visible diffuse reflectance spectrum, electrochemical workstation and photocatalytic degradation test. The experimental results demonstrated that the photocurrent density of the Zn0.9Cd0.1S/C sample was the highest, which was 15 times that of the Zn0.1Cd0.9S/C sample. Among all the samples, Zn0.5Cd0.5S/C nanocomposite has the best photocatalytic activity. The degradation efficiencies of rhodamine B reached 98.4% under UV irradiation for 90 min. Carbon in ZnxCd1-xS/C nanocomposites improved the separation efficiency of photogenerated electrons and holes, enhancing the photocatalytic activity of ZnxCd1-xS/C nanocomposites.

Microstructures and optical properties of TiO2/ZrO2 nanotube/nanoporous heterofilm prepared by anodizing of Ti/Zr/Ti multilayer films

This paper reports a novel method for preparing TiO2/ZrO2 nanotube/nanoporous (TiO2 NTs/ZrO2 NPs) heterofilm by directly anodizing Ti/Zr/Ti multilayer films deposited on silicon substrates. The as-deposited multilayer and anodized films were characterized by scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction to further investigate the microstructures. The whole upper Ti and partial lower Ti layers were transformed into highly ordered TiO2 nanotubes under an optimized anodizing condition, in contrast the middle Zr layer was transformed into ZrO2 with nanoporous structure. Photo-absorption performance of the P25, TiO2 nanotubes (TiO2 NTs) array and TiO2 NTs/ZrO2 NPs heterofilm were investigated by ultraviolet-visible diffuse reflection spectra. The TiO2 NTs/ZrO2 NPs heterofilm has strong absorption in the ultraviolet region and extends the absorption range to the visible light. Compared with TiO2 NTs, the TiO2 NTs/ZrO2 NPs heterofilm exhibited stronger absorbance in the range of 300-475 nm due to the synergistic effect produced by the nanoscale interaction of two metal oxide semiconductors with different structures. The energy band gap values are 2.98 and 3.01 eV for TiO2 NTs and TiO2 NTs/ZrO2 NPs heterofilm, respectively. These results are of great significance in the preparation of metal oxide with designable heterostructure on desired substrates.

Facile green synthesis of zinc oxide nanoparticles using Thymus vulgaris extract, characterization, and mechanism of chromium photocatalytic reduction

Zinc oxide nanoparticles (ZnO NPs) were synthesized via a green and simple method using extract of Thymus vulgaris (TV). The green synthesized zinc oxide nanoparticles (GZnO NPs) were characterized by field emission scanning electron microscope (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), Ultra violet-visible diffuse reflectance spectra (UV–vis-DRS), and Fourier Transform Infra-Red )FTIR( spectrophotometer.The results of various analyses confirmed the formation of GZnO NPs. UV–vis spectrum exhibited a blue shift absorption peak at 368 nm and the band gap energy was calculated 3.4 eV. FTIR study suggested that polyphenols and other bio-chemicals were responsible for reduction and stabilization of synthesized ZnO NPs. FE-SEM and TEM images showed particles with spherical shape and less than 40 nm diameter in size. In the photocatalytic reduction study, effect of some important variables such as catalyst dosage, methanol hole scavenger, contact time, and Cr(VI) concentration was investigated. To study photocatalytic activity of GZnO NPs, the adsorption control (AP) and photolysis (PP) experiments were conducted in same condition of photocatalytic process (PCP). Synergistic effect of PCP showed the high activity of GZnO NPs as catalyst for Cr(VI) reduction in the photocatalytic reactor (about 83% at 15 min, 0.5 mg l−1 of Cr(VI) and 0.015 g l−1 of GZnO NPs concentration). EDS analysis confirmed the presence of chromium on GZnO after adsorption control and photocatalytic processes. Kinetic constant for Cr(VI) reduction by PCP and PP obtained 0.154 and 0.008, which confirmed the increasing removal efficiency of chromium in the present of GZnO in photo-reactor as catalyst under UV light.