Ultraviolet-visible Diffuse Reflectance Spectra Research Articles

Photocatalytic Active Titania Thin Films through Oxidation of Metallic Ti in Aqueous H2O2 Solutions Containing Various Block Copolymers

Abstract Various nanostructured titania thin films were fabricated by direct oxidation of metallic Ti substrates in hydrogen peroxide solutions with the additives of nitric acid and block copolymers of P123 or F127. X-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS) were utilized to analyze the morphology and structure of the titania films. Photocatalytic properties of the thin films were evaluated by the degradation of rhodamine B in water under the illumination of a high-pressure mercury lamp. The film only with the block copolymer additive consists of rod-like titania; while flower-like titania aggregates are achieved when both block copolymers and nitric acid are added to the hydrogen peroxide solution. After a subsequent calcination at 450 °C, all the titania films are crystallized further to a mixture of anatase and rutile with a similar average grain size. An indirect bandgap of 2.65–2.85 eV is estimated for the present films, which is significantly lower that of the bulk titania. The titania film derived with the P123 additive shows higher photocatalytic activity than that with the F127 additive, either with or without the additive of nitric acid.

Synthesis and Characterization of the N-Doped TiO<SUB>2</SUB> Photocatalyst for the Photodegradation of Methylene Blue and Phenol

To extend the light absorption of TiO2-based photocatalysts towards the visible-light range and to eliminate the rapid recombination of excited electrons/holes during photoreaction, a new type of photocatalyst (N-doped TiO2) powder was prepared through a simple sol-gel process. The crystal phase composition, structure, and light absorption of the new photocatalyst were comprehensively examined via X-ray diffraction, ultraviolet-visible (UV-Vis) absorption spectroscopy, and atomic-absorption spectroscopy. The photo-oxidation efficiency of the photocatalyst was also evaluated in the photodegradation of methylene blue (MB) and of phenol in aqueous solutions under visible-light irradiation from a neon lamp (lambda > 400 nm). The results of the analyses that were performed in this study indicated that the N-doped TiO2 could eliminate the electron/holes recombination and could increase the light absorption in the visible range. The results of the analysis of the UV-Vis diffuse reflection and optical-absorption spectra indicated that a new energy level below 3.2 eV generated in the N-doped TiO2 promoted the optical absorption in the visible-light region and made visible-light excitation possible (E < 3.2 eV). The experiment demonstrated that the photo-oxidation efficiency of MB when N-doped TiO2 powder was used was significantly higher than that when the conventional TiO2 powders were used. The development of such photocatalyst may be considered a breakthrough in the large-scale utilization of solar energy to address the current and future environmental needs.

Preparation and formation mechanism of three-dimensionally ordered macroporous (3DOM) MgO, MgSO 4, CaCO 3, and SrCO 3, and photonic stop band properties of 3DOM CaCO 3

Three-dimensionally ordered macroporous (3DOM) magnesium (Mg) oxide (MgO), MgSO 4, calcium (Ca) carbonate (CaCO 3), and strontium (Sr) carbonate (SrCO 3) were prepared using a colloidal crystal of polymer spheres as a template. Ethanol or ethanol–water solution of metal salts (acetate or nitrate) and citric acid was infiltrated into the void of the colloidal crystal template of a monodispersed poly(methyl methacrylate) (PMMA) sphere. Heating of this PMMA–metal salt–citric acid composite produced the desired well-ordered 3DOM materials with a high pore fraction, which was confirmed by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet-visible (UV–vis) diffuse reflectance spectra. The presence of citric acid is crucial for production of the 3DOM structures. Reaction of citric acid with metal salt produces metal citrate solid in the void of PMMA spheres, which is necessary to maintain the 3DOM structure during the calcination process. 3DOM CaCO 3 shows opalescent colors because of it's photonic stop band properties.

A green and facile synthesis of TiO 2/graphene nanocomposites and their photocatalytic activity for hydrogen evolution

This work reports a green and facile approach to synthesize chemically bonded TiO 2/graphene sheets (GS) nanocomposites using a one-step hydrothermal method. The as-prepared composites were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and ultraviolet visible (UV-Vis) diffuse reflectance spectra. The photocatalytic activity was evaluated by hydrogen evolution from water splitting under UV–Vis light illumination. An enhancement of photocatalytic hydrogen evolution was observed over the TiO 2/GS composite photocatalysts, as 1.6 times larger for TiO 2/2.0 wt%GS than that of Degussa P25. This fabrication process features the reduction of graphene oxide and formation of TiO 2 simultaneously leading to the well dispersion of generated TiO 2 nanoparticles on the surface of GS.

Metathesis of butene to propene on WO3 supported on MTS-9 titanium-silica: effect of loading on selectivity of product and yield of propene

An advanced heterogeneous catalyst for olefin disproportion was prepared by supporting WO3 on titanium-silica sieve (MTS-9). The nature of the surface tungsten oxide species present in these catalysts was determined as a function of tungsten oxide loading by X-ray diffraction (XRD), ultraviolet–visible diffuse reflectance spectra (UV–DRS) and ultraviolet–visible Raman (UV-Raman). The catalyst showed high activity for the metathesis of butene to propene. The active centers are not crystallites of WO3 but rather surface tungsten oxide species. The conversion of butene varies with the degree of catalyst loading.

Synthesis and Visible Light Photocatalytic Activity of Cross-Linked Sodium Rectorite/Cu&lt;sub&gt;2&lt;/sub&gt;O Nanocomposites

CN-REC/Cu2O nanocomposites were synthesized with Cu(CH3COO)2·H2O as a copper source and cross-linked sodium rectorite (CN-REC) as a carrier and template. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet visible diffuse reflectance spectrum (UV-Vis DRS). The results indicate that the regulatory effects of CN-REC on Cu2O are significant. Cu2O is dispersed in the interlayer and on the surface of the lamellar structure of CN-REC. A Si―O―Cu bond was formed between the cuprous oxide crystal and the CN-REC crystal, which established a bridge for the transfer of photogenerated charge. The energy band gap of the nanocomposites became wider and the photoresponse properties of the nanocomposites became stronger. To study the visible light photocatalytic activity of the nanocomposites, reactive brilliant red (X-3B) was selected as a target contaminant. The photocatalytic degradation rate of X-3B with the nanocomposites is more than 80%, which is better than that with Cu2O. The degradation progress accorded with the L-H kinetics equations.

Deactivation of Au/TiO 2 catalyst in the hydrogenation of o-chloronitrobenzene in the presence of CO 2

The hydrogenation of o-chloronitrobenzene over Au/TiO 2 was investigated in supercritical carbon dioxide (scCO 2), ethanol, H 2O, and H 2O/CO 2 at 140 °C. The reaction rate followed the order of H 2O > H 2O/CO 2 > ethanol > scCO 2. Au/TiO 2 was deactivated in the systems containing CO 2. Changes of Au/TiO 2 catalysts were investigated by means of transmission electron microscopy (TEM), in situ infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance ultraviolet-visible spectra (DR-UV/Vis). Aggregation of Au particles was excluded from origins of deactivation by TEM. Carbonate-like species formed on gold in the presence of CO 2 and H 2 were detected by in situ IR spectroscopy. The results of XPS and DR-UV/Vis reveal that the active species of Au 0 was oxidized in the presence of CO 2. The possible formation of CO and its influence on the activity of Au/TiO 2 were also discussed. Accordingly, the formation of carbonates, the oxidation of surface Au 0 by CO 2, and the CO formation are proposed to be the possible factors for the deactivation of Au/TiO 2.

Influence of mechanical milling on photocatalytic activity of g-C3N4 prepared by heating melamine

Using X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area measurement, ultraviolet-visible diffuse reflection spectra, and photoluminescence spectroscopy, the effect of mechanical milling on the photocatalytic activity of g-C3N4 photocatalyst was investigated. The rhodamine B, as a photodegrading goal, was used to evaluate the photocatalytic activity of g-C3N4. The experimental results indicate that the milling treatment is an effective method to improve the photocatalytic activity of g-C3N4. The enhanced photocatalytic activity was attributed to the improvement in catalyst’s surface area and dye adsorption on catalyst surface. Moreover, checking the luminescence properties of g-C3N4, it is found that the photocatalytic active sites on g-C3N4 are likely the same as luminescence sites.

Facile preparation of porous LaFeO 3 nanomaterial by self-combustion of ionic liquids

A simple self-combustion of ionic liquid (IL) synthesis method has been developed for the porous LaFeO 3 nanocrystals with a perovskite structure. The ILs were synthesized by Fe(NO 3) 3, La(NO 3) 3, and (C 2H 5) 3NHCl. (C 2H 5) 3N·HCl are not only the source of cation in IL, but also the fuels. The electrospray ionization tandem mass (ESI-MS) spectra verify the ionic liquid structure. LaFeO 3 powders have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) surface area, and ultraviolet–visible diffuse reflection spectrum (UV–Vis DRS). The results show that the nanomaterials have porous structure, large specific surface area (36.9 to 84.5 m 2 g −1), and excellent visible light absorption ability.

Synthesis and Photocatalytic Activity of ZnO/H3PW12O40-Supported Mordenite Composite

12-tungstophosphoric acid (H3PW12O40) and Zinc oxide (ZnO) particles were encapsulated into mordenite by salt melting procedure. The material was characterized by X-ray diffraction (XRD), Ultraviolet-visible diffuse reflectance spectra (UV-Vis-DRS), High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive Spectrometer (EDS), and Brunauer, Emmett and Teller surface area (BET). The characterization of ZnO/H3PW12O40-supported mordenite composite (ZnO/PW12/mordenite) clearly shows that some of ZnO and H3PW12O40 particles were encapsulated within the cavities and frameworks of mordenite, which effectively increases the photocatalytic activity on degradation of methyl orange. The ZnO/PW12/mordenite composite showed 1.7-fold increase amplitude of the photodegradation rate versus that of ZnO-supported mordenite composite (ZnO/mordenite) without H3PW12O40.

Molecular design and photophysical properties of acylamido side functionalized polysiloxanes with lanthanide ions as luminescent centers

Two series of acylamido side functionalized polysiloxanes were designed and synthesized from the modifications of amino silane with different acylating agents. They were complexed with lanthanide ions (Tb 3+, Eu 3+, Dy 3+ and Sm 3+) to obtain functionalized polysiloxane–lanthanide ions composite materials and exhibit the molecular assembly behaviors. The structures of products were characterized by Fourier transform infrared (FT-IR), 1H-NMR spectra and diffuse reflectance ultraviolet–visible spectra (DRUVS). Thermal stability was investigated by thermogravimetric analysis (TGA). Narrow-width red and green emissions of the functionalized polysiloxane–lanthanide ions complexes were recorded under the exposure to ultraviolet light. The results show that four kinds of lanthanide ions were all cooperated successfully with the functionalized polysiloxanes and an intra-molecular energy transfer process took place in these systems. Further investigations into the luminescence properties of the functionalized polysiloxane–lanthanide ions composite materials show that the triplet state energy of the benzoylamido side functionalized polysiloxane is more suitable for the emissive energy level of lanthanide ions than that of acetamido side functionalized polysiloxane. According to the rules between photophysical properties and diverse chromophoric conjugate groups, we could design and control the properties of the polysiloxane–lanthanide ion assembly complexes.

Synthesis and photophysical properties of rare earth-containing luminescent silicone resin from cooperative molecular design and assembly

Two series of rare earth-containing luminescent silicone resins have been achieved by sol–gel method. The precursors which were modified via acylamidation reactions behave as structural molecular bridges. The silanol groups were used to form the host of silicone resin and the chromophore groups were used to exhibit the luminescence by the cooperative assembly courses with rare earth ions (Eu 3+, Tb 3+, and Dy 3+). The modifications were determined by Fourier transform infrared (FTIR), 1H-NMR spectra and diffuse reflectance ultraviolet–visible spectra (DRUVS). Scanning electronic microscopy (SEM, micrometric scale) and X-ray diffraction studies (XRD, nanometric scale) were employed to evaluate the frameworks of silicone resin materials. Narrow-width red emission was observed in Eu (III) resin materials and green emissions were obtained in Tb (III) resin materials and Dy (III) resin materials, indicating that an efficient intramolecular energy transfer took place in these resins. Further investigations into the luminescent properties of these materials show that the luminescence in these materials is quite operative by means of the design of molecular structure.

Luminescence property of Ca3(VO4)2:Eu3+ dependence on molar ratio of Ca/V and solution combustion synthesis temperature

Red emitting phosphor Ca3(VO4)2:Eu3+ was prepared by citric acid-assisted solution combustion method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and fluorescence spectrophotometer. The influences of Ca to V molar ratio and synthesis temperature on phase composition, morphology, grain size, photofluorescence properties, and ultraviolet–visible diffuse reflectance spectra (UV–Vis DRS) of as-synthesized samples were investigated. The results indicate that Ca to V molar ratio play a key role for the changing of phase composition, excitation spectrum, and luminescence intensity. The sample prepared at 900 °C, keeping Ca/V = 3:2.2, has the highest photoluminescence intensity. The possible causes of the effects on photoluminescence mechanism were also discussed in this work.

Controlling the electronic structure of SnO2 nanowires by Mo-doping

Mo-doped SnO2 (MTO) nanowires are synthesized by an in-situ doping chemical vapour deposition method. Raman scattering spectra indicate that the lattice symmetry of MTO nanowires lowers with the increase of Mo doping, which implies that Mo ions do enter into the lattice of SnO2 nanowire. Ultraviolet-visible diffuse reflectance spectra show that the band gap of MTO nanowires decreases with the increase of Mo concentration. The photoluminescence emission of SnO2 nanowires around 580 nm at room temperature can also be controlled accurately by Mo-doping, and it is extremely sensitive to Mo ions and will disappear when the atomic ratio reaches 0.46%.

Enhancement of photocatalytic degradation of methylene blue in surfactant/ceriurm(III)-titanium dioxide/float pearls aqueous dispersions

Ceriurm(III)-titanium dioxide/float pearls photocatalyst mixed with Sodium Lauryl Sulphate (SLS) were used to degrade methylene blue under visible light illumination. The photocatalyst of Ce3+-TiO2/float pearls was prepared by sol-gel method and characterised by Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Ultraviolet-visible Diffuse Reflection Spectrum (UV-vis DRS) and Energy Dispersive Spectrometer (EDS). The influence of pH value and dosage of SLS on the photocatalytic activity was studied. The result indicated that the presence of SLS cut down the surface tension of dye liquor, leading to obviously increased degradation rate. The photocatalytic degradation rate reached 93.49% under visible light radiation in 240 min, improved by 10.30% in the non-neutral aqueous.

Synthesis, crystal structure, and photocatalytic activity of the new three-layer aurivillius phases, Bi 2ASrTi 2TaO 12 ( A=Bi, La)

Two new three-layer Aurivillius phases Bi 2 ASrTi 2TaO 12 ( A=Bi, La) have been synthesized. The detailed structure determination of Bi 2 ASrTi 2TaO 12 ( A=Bi, La) performed by powder X-ray diffraction (XRD) and selected area electron microscopy (SAED) shows that they all crystallize in the space group I/4 mmm. UV–visible diffuse reflection spectrum of the prepared Bi 2 ASrTi 2TaO 12 ( A=Bi, La) indicates that it had absorption in the ultraviolet (UV) region. The photocatalytic activity of the Bi 2 ASrTi 2TaO 12 ( A=Bi, La) powders was evaluated by degradation of rhodamine B (RB) molecules in water under UV light irradiation. The results showed that Bi 2 ASrTi 2TaO 12 ( A=Bi, La) has high photocatalytic activity at room temperature. Therefore, the preparation and properties studies of Bi 2 ASrTi 2TaO 12 ( A=Bi, La) with a three-layer Aurivillius structure suggest potential future applications in photocatalysis.

Study on the heterogeneous degradation of chitosan with H 2O 2 catalyzed by a new supermolecular assembly crystal: [C 6H 8N 2] 6H 3[PW 12O 40]·2H 2O

A new supermolecular assembly crystal, [C 6H 8N 2] 6H 3[PW 12O 40]·2H 2O (DMB–PWA), was synthesized with phosphotungstic acid (PWA) and 1,2-diaminobenzene (DMB) under hydrothermal conditions and was characterized by Fourier-transform infrared spectra (FTIR) and single-crystal X-ray diffraction analysis. DMB–PWA could effectively catalyze oxidative degradation of chitosan with H 2O 2 in the heterogeneous phase. The optimum degradation conditions were determined by orthogonal tests as follows: amount of chitosan 1.00 g, 30% (wt %); H 2O 2, 3.0 mL; dosage of catalyst, 0.06 g; reaction temperature, 85 °C; and reaction time, 30 min. The water-soluble chitosan with a viscosity-average molecular weight ( M v) of 4900 was obtained under the optimum degradation conditions and was characterized by FTIR, ultraviolet–visible diffuse reflection spectra (UV–vis DRS), and X-ray powder diffraction analysis.

Enhanced photocatalytic activity for degrading Rhodamine B solution of commercial Degussa P25 TiO 2 and its mechanisms

In this paper, the Degussa P25 TiO 2 (P-TiO 2) is modified by the post-treatment with the phosphorous acid, and the resulting samples are also characterized by X-ray Powder Diffraction (XRD), Raman spectra (Raman), Brunauer–Emmett–Teller (BET) surface area analyzer, Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectra (FT-IR), X-ray Photoelectron Spectroscopy (XPS), Ultraviolet–Visible Diffuse Reflectance Spectra (UV–vis DRS) and Surface Photovoltage Spectroscopy (SPS). The effects of surface-modification on the thermal stability and photocatalytic activity of the P-TiO 2 are investigated in detail. The results show that the surface-modification enhances the thermal stability of P-TiO 2, even still with a main anatase phase after thermal treatment at 900 °C, which is close related to the inhibition effects of the PO 4 3− groups on the surface mass diffusion as well as the directing connections of P-TiO 2 nanoparticles. Interestingly, the modified P-TiO 2 by thermal treatment at 700 and 800 °C can exhibit much higher photocatalytic activity than un-modified ones. The reasons for the activity enhancement are involved with the enhanced anatase thermal stability, consequently improving photoinduced charge separation rate, and still keeping large surface area and a certain amount of surface hydroxyl groups.

Epoxidation of Cyclohexene with Air over the Composite Catalysts of Mn-mont Coordinated with Ligands

The catalytic activity of the composite catalysts of Mn-mont (where mont represents montmorillonite) coordinated with ligands for the epoxidation of cyclohexene by air under Mukaiyama conditions was studied. The composite catalysts were characterized by atomic absorption spectroscopic analysis, elemental analysis, fourier transform infrared spectra, diffuse reflectance ultraviolet visible spectra, X-ray photoelectron spectroscopy, powder-X-ray-diffraction, and scanning electron microscopy measurements. The effects of various reaction conditions on the catalytic reaction were studied. Experimental results indicated that the catalysts performed excellent activity for the epoxidation of cyclohexene by air. Repeated runs indicate that the catalyst is stable for 3 cycles. The composite catalysts of Mn-mont coordinated with ligands are economical and environmentally friendly for the epoxidation of cyclohexene.

Effects of carbon on the sulfidation and hydrodesulfurization of CoMo hydrating catalysts

The effects of carbon addition on CoMo catalyst performance for sulfidation and hydrodesulfurization (HDS) were investigated. The carbon-containing catalyst was prepared by impregnation of γ-Al2O3 support with NH3 aqueous solution containing Co(NO3)2·6H2O, (NH4)6Mo7O24·4H2O and ethylenediamine. The results indicated that the incorporation of proper carbon on CoMo catalyst can improve its HDS performance. The carbon species on the catalyst were characterized by temperature-programmed oxidation and reduction, temperature-programmed desorption of ammonia and ultraviolet-visible diffuse reflectance spectra. Two forms of carbon species were differentiated: one is spread over the catalyst surface, similar to coke formed from reaction; the other interacts with active phase as an intermediate support. The carbon species acting as intermediate support may decrease the interaction of active metals with support, which enhances the sulfidation and HDS activities of CoMo catalyst.