Ultraviolet-visible Diffuse Reflectance Spectra Research Articles

In-situ synthesis of CdS/g-C3N4 hybrid nanocomposites with enhanced visible photocatalytic activity

A novel and simple in situ synthetic strategy was used to fabricate CdS/g-C3N4 hybrid nanocomposite catalysts with visible-light-driven photocatalytic activity from cadmium-containing carbon nitride compounds. X-ray diffraction measurements, high-resolution transmission electron microscopy images, and Fourier transform infrared spectra showed heterojunctions with a close interface between the g-C3N4 and the CdS nanoparticles and nanorods in the composite. Ultraviolet visible diffuse reflectance spectra exhibited a red shift that further presented the CdS in the polymer g-C3N4 skeleton, which allowed the efficient utilization of the solar spectrum for creating photogenerated electrons and holes. The photoluminescence spectra of the nanocomposites suggested charge transfer from g-C3N4 to CdS. The photocurrent intensity of hybrid nanocomposites was 2.3 times than that of pure g-C3N4 sample, and photocatalytic activity for the photodegradation of methyl orange was 2.5 times, and hydrogen evolution reaction was 2.8 times. Enhanced photocatalytic activity and photocurrent for the CdS/g-C3N4 hybrid nanocomposites were achieved.

Carbonylation of cyclohexene to 2-cyclohexene-1-one by montmorillonite-supported Co(II) catalysts

AbstractA novel environmentally-friendly catalytic system for the carbonylation of cyclohexene with molecular oxygen under conditions of mild temperature, and under an atmospheric oxygen pressure is presented. In this system, a series of readily-prepared cobalt complexes of 2-aminophenol and its derivatives immobilised onto montmorillonite were used as catalysts. The catalysts were characterised by FT-IR, elemental analysis, thermogravimetric analysis, powder X-ray diffraction, diffuse reflectance ultraviolet visible spectra, scanning electron microscopic measurements, transmission electron microscopic measurements and the Brunauer-Emmett-Teller method. The effects of various reaction conditions such as catalyst dosage, temperature and time were optimised, obtaining an 88.7 % conversion with 72.0 % selectivity of 2-cyclohexene-1-one in 6 h. The results show that the catalytic activity of the cobalt complexes encapsulated in montmorillonite is higher than those of the free complexes. In addition, the heterogeneous catalysts were stable and can be recycled up to five times without any noticeable change in the catalytic activity.

Photocatalytic activity of LaTaON<sub>2</sub> powders prepared using an oxide precursor derived from a hydrothermal reaction

Plate-like LaTaON2 was prepared by the nitridation of plate-like LaTaO4 precursor synthesized by hydrothermal method to improve the photocatalytic activity for H2 evolution from an aqueous methanol solution under visible light irradiation. LaTaON2 samples derived from hydrothermal method consisted of only slightly aggregated particles 5–10 μm in size. In contrast, LaTaON2 samples derived from solid-state reaction method consisted of irregular-shaped and aggregated primary particles 0.5–1.5 μm in size. For photocatalytic H2 evolution using Pt as a co-catalyst, plate-like LaTaON2 exhibited higher photocatalytic activity than irregular-shaped LaTaON2. In addition, ultraviolet-visible diffuse reflectance spectra suggested that plate-like LaTaON2 had a lower density of defects due to the presence of anion vacancies or reduced Ta5+ species than irregular-shaped LaTaON2, as demonstrated by the reduced intensity of absorption at longer wavelengths (λ ＞ 660 nm). Therefore, using a LaTaO4 precursor synthesized by hydrothermal method, we obtained LaTaON2 with reducing the density of defects that act as recombination centers for photogenerated carriers.

Promotional effect of Ce on Cu-SAPO-34 monolith catalyst for selective catalytic reduction of NOx with ammonia

The activity and hydrothermal stability of Cu-SAPO-34 and CuCe-SAPO-34 for selective catalytic reduction of NOx with ammonia (NH3-SCR) were investigated systematically. The catalysts were prepared by wet-impregnation method, and characterized by N2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), Ultraviolet-visible diffuse reflectance spectrum (UV–vis-DRS), H2-temperature programmed reduction (H2-TPR) and NH3-temperature programmed desorption (NH3-TPD). The experimental results of fresh catalysts suggested that Ce mainly existed on the surface of the catalyst and was well dispersed in the form of Ce3+, and its interaction with copper could improve the dispersion of copper species and increase the amount of isolated Cu2+ ions, so that CuCe-SAPO-34 performed better NH3-SCR activity than Cu-SAPO-34. After hydrothermal aging at 800°C for 12h, the characterization results indicated that the introduction of cerium effectively improved the textural and structural stability of SAPO-34 since more cations at the exchange site of SAPO-34 could decrease the concentration of SiO(H)Al bond which was closely related to the damage of the SAPO-34 framework. Moreover, the addition of Ce could prevent the decrease of acid densities, promote the redistribution of CuO during hydrothermal aging and provide higher amount of isolated Cu2+ ions, leading to superior hydrothermal stability of CuCe-SAPO-34 catalyst.

Propene oligomerization to high-quality liquid fuels over Ni/HZSM-5

Ni/HZSM-5 catalysts with different Ni contents ranging from 0.76 to 5.05wt.% were prepared by wet impregnation method. The catalysts were characterized by X-ray diffraction (XRD) and N2 adsorption, diffuse reflectance ultraviolet–visible spectra (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of ammonia (NH3-TPD) and the Fourier transform infrared spectra for pyridine adsorption (Py-IR), followed by the evaluation for the propene oligomerization to high-quality liquid fuels. It was demonstrated that the chemical state of the nickel in the final catalyst was affected by the NiSO4 concentration. And also the catalyst acidity was modified by the addition of NiSO4, both of the number of Lewis and Brønsted acid sites and the strength of acid sites increase with the increasing of the NiSO4 content. Compared with the parent HZSM-5, the addition of NiSO4 to HZSM-5 promotes the high molecular weight oligomers formation, with high selectivity to diesel. The catalytic performance seems to be relevant to the ratio of Ni2+/acid sites. The 2.21wt.% Ni/HZSM-5 catalyst exhibits high stability for the propene oligomerization with propene conversion of about 70% and diesel selectivity of about 80% during the 72h time on stream.

NOVEL HIERARCHICAL NANORODS OF SILICON-DOPED Bi2O2CO3 AND ITS PHOTOCATALYTIC ACTIVITY

The silicon-doped Bi 2 O 2 CO 3 nanorods with the interesting hierarchical structure are synthesized by a simple hydrothermal method. The samples are characterized by XRD, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), Ultraviolet-visible diffuse reflectance spectra (UV-DRS) and nitrogen sorption isotherms. It is found that with the increase of silicon content, the XRD peak of the sample significantly shifts toward a low diffraction angle and the particle morphologies change from nanosheets, nanoflowers to hierarchical nanorods. Moreover, the silicon-doped Bi 2 O 2 CO 3 hierarchical nanorods exhibit improved photocatalytic degradation activities for different types of dyes under simulated solar light irradiation. The improved activity has been mainly attributed to the unique hierarchical nanorods structure and the formation of Si – O – Bi bonds.

Synthesis and Characterization of Isobutyl-Chitosan-Ca(II) Complexes

Through an alkylation reaction under alkaline conditions, isobutyl was introduced to chitosan to form isobutyl-chitosan. Isobutyl-chitosan-Ca (II) complex was synthesized at pH 6.0 by a reaction of isobutyl-chitosan and calcium chloride. The structure of isobutyl-chitosan-Ca (II) complexes was characterized by ultraviolet-visible diffuse reflectance spectrum (UV-Vis) and FT-IR spectrum, and the content of calcium was measured by inductively coupled plasma-optical emission spectrometry (ICP-OES). The FT-IR spectra of isobutyl-chitosan and chitosan showed that structure of isobutyl-chitosan-Ca (II) complexes was obviously different with isobutyl-chitosan. Results of UV spectra showed that the maximum absorption of isobutyl-chitosan and isobutyl-chitosan-Ca (II) were at 310 nm and 324 nm, respectively. The content of calcium was 1.6026%, measured by ICP-OES.

Effect of triethylamine treatment of titanium silicalite-1 on propylene epoxidation

Titanium silicalite-1(TS-1) treated with triethylamine (TEA) solution under different conditions was characterized by X-ray powder diffraction (XRD), Fourier-transform infrared spectrum (FTIR), ultraviolet-visible diffuse reflectance spectrum (UV-Vis), nitrogen physical adsorption and desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The characterization results show that many irregular hollows are generated in the TS-1 crystals due to the random dissolution of framework silicon and the volume of the hollow cavities increase with increasing the TEA concentration, and the treatment temperature and time. The modified TS-1 samples improved in varying degrees the catalyst life for the epoxidation of propylene in a fixed-bed reactor probably due to the generation of the hollows to make it easy for the reactants and products to diffuse out of the channels.

Synthesis of magnetic photocatalyst and sensitization properties of polypyrrole

Abstract In order to solve the difficulty of separation and recycling of TiO2 and its lower utilization of solar radiation, a new type of TiO2 photocatalyst, which was sensitized by polypyrrole (PPy) and carried by self-made modified Fe3O4, named PPy-TiO2/M-Fe3O4, was fabricated successfully by combining suspension dispersion and in situ polymerization. The structure of photocatalyst and Fe3O4 was characterized using X-ray diffraction, the Fourier transmission infrared spectrometer, and scanning electron microscopy. Light response property was tested by ultraviolet-visible diffuse reflectance spectra. Photocatalytic activity was evaluated with methyl orange as the degradation substance under different light radiation. Magnetic recovery property was investigated by using vibrating sample magnetometer and gravimetric analysis methods. The results showed that due to sensitization of PPy, the light response scope of PPy-TiO2/M-Fe3O4 was broadened to 451 nm and the degradation rate of methyl orange had been increased by 32.5% under the same conditions. Meanwhile, the recovery rate of PPy-TiO2/M-Fe3O4 remained above 97.9% after five cycles.

PbS sensitized TiO2nanotube arrays with different sizes and filling degrees for enhancing photoelectrochemical properties

PbS nanoparticles (PbS NPs), an efficient sensitizer for TiO2 nanotube arrays (TiO2 NAs), were fabricated by the method of sonication-assisted successive ionic layer adsorption and reaction (SILAR). The filling degree and size of PbS NPs can be tuned by changing the repeated cycles (N) of the SILAR process. TiO2 NAs can be fully covered with PbS NPs with a size ranging from less than 4 nm to 25 nm and large aggregates inside and outside the nanotubes when N reaches 15. The growth mechanism of PbS NPs in TiO2 NAs was expounded in great detail in this work. Ultraviolet-visible diffuse-reflectance spectra and surface photovoltage spectroscopy were used to investigate the light absorption properties and the transfer behavior of photogenerated charges in PbS-modified TiO2 NA heterostructures. Results show that the absorption range of TiO2 NAs is extended from the ultraviolet to the visible region by PbS NPs modification. A heterojunction is formed between PbS NPs and TiO2 NAs, facilitating the separation of photogenerated charge carriers. This PbS NPs fully-covered TiO2 NA electrode exhibits the best photoelectrochemical performance in all PbS-sensitized TiO2 NA electrodes, due to a larger number of small PbS NPs (<4 nm). With AM 1.5G illumination at 100 mW cm(-2), its short-circuit current density, open-circuit voltage and photoelectric conversion efficiency are 9.55 mA cm(-2), 0.95 V and 2.83%, respectively.

Synthesis of a novel N[sbnd]H[sbnd]TiO2 photocatalyst by annealing in NH3 and H2 for complete decomposition of high concentration benzene under visible light irradiation

A novel NHTiO2 photocatalyst was prepared via hydrothermal synthesis followed by a thermal treatment in NH3 and H2 atmospheres. The results showed that benzene with the initial concentration of 150ppm (±5ppm) could be thoroughly removed by NHTiO2 under visible light irradiation. The influences of doping and hydrogenation on properties of TiO2 samples were investigated. It is suggested that the disordered surface layer introduced by hydrogenation contributes to the excellent photocatalytic activity of NHTiO2. The synergistic effect of N doping and surface oxygen vacancies was also confirmed by ultraviolet–visible diffuse reflectance spectra and photoluminescence. Moreover, the diverse role of oxygen vacancies in different positions of TiO2 has been focused on.

Synthesis of Praseodymium-Doped TiO2Nanocatalysts by Sol-Microwave and Their Photocatalytic Activity Study

The praseodymium-doped <TEX>$TiO_2$</TEX> photocatalyst samples, which could degrade methyl orange under UV irradiation, were prepared by sol-microwave method for improving the photocatalytic activity of <TEX>$TiO_2$</TEX>. The resulting materials were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectra, Fourier transform infrared spectra (FTIR) and Ultraviolet-visible diffuse reflectance spectra (UV-vis DRS). It was found Pr doping retarded the growth of crystalline size and the phase transformation from anatase to rutile, and narrowed the band gap energy. Praseodymium doping brought about remarkable improvement in the photoactivity. The optimal dopant amount of Pr was 2% by molar of cement and the calcination temperature was <TEX>$500^{\circ}C$</TEX> for the best photocatalytic activity. The improvement of photocatalytic activity was ascribed to the occurrence of lattice distortion and the effective containment of the recombination of the electron-hole by <TEX>$Pr^{3+}$</TEX>.

Surfactant-assisted sol–gel synthesis of zirconia supported phosphotungstates or Ti-substituted phosphotungstates for catalytic oxidation of cyclohexene

The Keggin-type polyoxometalates (POMs) including phosphotungstate and Ti-substituted phosphotungstates were supported on zirconia (ZrO2) matrix by a surfactant-assisted sol–gel copolymerization technique. The resultant ZrO2 supported POMs composite materials (ZrO2–POMs) were characterized by X-ray power diffraction, transmission electron microscopy, Fourier transform infrared spectra, diffuse reflectance ultraviolet–visible spectra, thermogravimetry-differential scanning calorimetry analysis, and 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) analysis. The results showed that the ZrO2–POMs materials have worm-like disordered mesoporous, and the primary structure of POMs is preserved after the formation of the composite materials. All the ZrO2–POMs materials are catalytically active for the H2O2-mediated oxidation of cyclohexene with relatively high selectivity to allylic oxidation products. Moreover, these materials exhibit high stability against leaching of active species, and can be easily recycled without obvious loss of activity and selectivity. The existence of relatively strong interaction between the POM units and the ZrO2 framework should play important role in fabricating the stable heterogeneous ZrO2–POMs catalysts.

Ln(IO3)3 (Ln = Ce, Nd, Eu, Gd, Er, Yb) polycrystals as novel photocatalysts for efficient decontamination under ultraviolet light irradiation.

Ln(IO3)3 (Ln = Ce, Nd, Eu, Gd, Er, Yb) polycrystals were hydrothermally synthesized using lanthanide nitrate or lanthanide oxide and iodic acid as precursors. X-ray diffraction was used to characterize the crystal structures of the Ln(IO3)3 products. Scanning electron microscopy was carried out to observe the microscopic morphologies. The lattice spacings were studied by high-resolution transmission electron microscopy and selected area electron diffraction. We evaluated the photocatalytic efficiency by decomposing methyl orange dye under ultraviolet light irradiation, and the Ln(IO3)3 products show excellent photocatalytic properties. To rule out the effect of photosensitization, 2,4-dichlorophenol was also photodegraded. As one of the key factors of photocatalysis, ultraviolet-visible diffuse reflectance spectra of the Ln(IO3)3 samples were also studied, and all products have strong absorption in the ultraviolet region.

Effect of TiO2 calcination temperature on the photocatalytic oxidation of gaseous NH3

Carbon-modified titanium dioxide (TiO2) was prepared by a sol-gel method using tetrabutyl titanate as precursor, with calcination at various temperatures, and tested for the photocatalytic oxidation (PCO) of gaseous NH3 under visible and UV light. The test results showed that no samples had visible light activity, while the TiO2 calcined at 400°C had the best UV light activity among the series of catalysts, and was even much better than the commercial catalyst P25. The catalysts were then characterized by X-ray diffractometry, Brunauer-Emmett-Teller adsorption analysis, Raman spectroscopy, thermogravimetry/differential scanning calorimetry coupled with mass spectrometry, ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy. It was shown that the carbon species residuals on the catalyst surfaces induced the visible light adsorption of the samples calcined in the low temperature range (< 300°C). However, the surface acid sites played a determining role in the PCO of NH3 under visible and UV light over the series of catalysts. Although the samples calcined at low temperatures had very high SSA, good crystallinity, strong visible light absorption and also low PL emission intensity, they showed very low PCO activity due to their very low number of acid sites for NH3 adsorption and activation. The TiO2 sample calcined at 400°C contained the highest number of acid sites among the series of catalysts, therefore showing the highest performance for the PCO of NH3 under UV light.

Template free fabrication of porous g-C3N4/graphene hybrid with enhanced photocatalytic capability under visible light

Graphene modified porous g-C3N4 (porous g-C3N4/graphene) with efficient photocatalytic capability under visible light irradiation was fabricated by means of calcinations without extra templates. We expected that the photocatalytic capability of this hybrid photocatalyst could be enhanced by the efficient visible light absorption owing to the porous structure and efficient photogenerated charge separation owing to the heterojunction built between porous g-C3N4 and graphene. Scanning electron microscopy images demonstrated that the as prepared photocatalyst is composed of graphene and porous g-C3N4. The ultraviolet–visible diffuse reflectance spectrum shows that optical absorption for porous g-C3N4/graphene is more intensive than for pristine g-C3N4/g-C3N4/graphene/porous g-C3N4. The enhanced generation of photocurrent under visible light irradiation (λ>400 nm) is observed using the porous g-C3N4/graphene. The results of photocatalytic experiments under visible light irradiation reveal that the pseudo first order kinetic constant of photocatalytic degradation of methylene blue using the porous g-C3N4/graphene is six times as great as that in pristine g-C3N4, showing the advantage of the unique structure in the porous g-C3N4/graphene for efficient photocatalysis.

Selective catalytic reduction of nitric oxide with ammonia over zirconium-doped copper/ZSM-5 catalysts

Selective catalytic reduction (SCR) of NO by NH3 over a series of Cu-Zr/ZSM-5 catalysts with different zirconium loadings was studied to evaluate the correlation between structural characteristics and performance of the catalysts. The Cu-Zr/ZSM-5 catalysts exhibited nearly 100% NO conversion over a wide temperature range (167–452°C), which is markedly superior to those of Cu/ZSM-5 (197–404°C) and conventional V-W/TiO2 catalyst (320–450°C) and within the range of exhaust temperatures of diesel engines. Moreover, the zirconium enhances the sulfur tolerance of the catalysts. The effects of zirconium addition were investigated in detail by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of NH3 (NH3-TPD), temperature-programmed reduction by hydrogen (H2-TPR), oxygen storage capacity (OSC), electron paramagnetic resonance (EPR), ultraviolet–visible diffuse reflectance spectra (UV–vis DR) and in situ diffuse reflectance Fourier transform (DRIFT) spectroscopy. The TEM, XRD and UV–vis DR results showed that addition of zirconium increased the dispersion of copper and prevented its crystallization. The XPS results demonstrated that the introduction of zirconium enhanced the enrichment of copper species on the surfaces of ZSM-5 grains. Addition of zirconium improved the redox properties of the Cu-Zr/ZSM-5 catalysts, which arose from the higher valence of copper and mobility of lattice oxygen than those of Cu/ZSM-5 catalyst. The DRIFT results confirmed that the SCR reaction over Cu-Zr/ZSM-5 catalysts mainly followed the Langmuir–Hinshelwood mechanism; i.e., reaction of activated NOx species with activated NH3 species. The Cu-Zr/ZSM-5 catalysts were able to accelerate the oxidation of NO to NO2 in the presence of oxygen. Compared with Cu/ZSM-5 catalyst, the Cu-Zr/ZSM-5 catalysts caused the amount of –NO2 species after NO+O2 adsorption to increase, resulting in the temperature range for optimum NOx reduction (>95%) extending to lower temperature.

Different Surfactants-Assisted Hydrothermal Fabrication and Photocatalytic Properties of Bi2MoO6for Methylene Blue Degradation under Simulated Sunlight Irradiation

Bi2MoO6single-crystallites were synthesized by a simple hydrothermal method in the presence of surfactant sodium dodecyl sulfate (SDS), polyvinyl pyrrolidone (PVP), or cetyl trimethyl ammonium bromide (CTAB). The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) techniques. The photocatalytic activities of the as-fabricated Bi2MoO6samples were measured for the degradation of methylene blue (MB) under the Xe light illumination. It is shown that the introduction of surfactant have a crucial influence on the size and morphology of the Bi2MoO6product. Among the as-fabricated Bi2MoO6samples, the ones derived hydrothermally with CTAB showed outstanding photocatalytic activities for the addressed reaction under simulated sunlight irradiation, attributed to the ultrafine nanocrystals and the higher surface areas.

A Facile and Waste-Free Strategy to Fabricate Pt-C/TiO2Microspheres: Enhanced Photocatalytic Performance for Hydrogen Evolution

A facile and waste-free flame thermal synthesis method was developed for preparing Pt modified C/TiO2microspheres (Pt-C/TiO2). The photocatalysts were characterized with X-ray diffraction, field emission scanning electron microscopy, transmission electron microscope, ultraviolet-visible (UV-vis) diffuse reflectance spectra, X-ray photoelectron spectroscopy, and thermogravimetry analysis. The photocatalytic activity was evaluated by hydrogen evolution from water splitting under UV-vis light illumination. Benefitting from the electron-hole separation behavior and reduced overpotential of H+/H2, remarkably enhanced hydrogen production was demonstrated and the photocatalytic hydrogen generation from 0.4 wt% Pt-C/TiO2increased by 22 times. This study also demonstrates that the novel and facile method is highly attractive, due to its easy operation, requiring no post treatment and energy-saving features.

Photocatalytic Reduction of CO2to Methane on Pt/TiO2Nanosheet Porous Film

Anatase TiO2nanosheet porous films were prepared by calcination of the orthorhombic titanic acid films at 400°C. They showed an excellent photocatalytic activity for CO2photoreduction to methane, which should be related to their special porous structure and large Brunauer-Emmett-Teller (BET) surface area. In order to further improve the photocatalytic activity, Pt nanoparticles were loaded uniformly with the average size of 3-4 nm on TiO2porous films by the photoreduction method. It was found that the loading of Pt expanded the light absorption ability of the porous film and improved the transformation efficiency of CO2to methane. The conversion yield of CO2to methane on Pt/TiO2film reached 20.51 ppm/h·cm2. The Pt/TiO2nanosheet porous film was characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and ultraviolet-visible light diffuse reflectance spectra (UV-vis DRS). Moreover, the transient photocurrent-time curves showed that the Pt/TiO2nanosheet porous film exhibited higher photocurrent, indicating that the higher separation efficiency of the photogenerated charge carriers was achieved.