Phase Characterizations and Photocatalytic Applications of CuO-K2M04013 Composites

A series of CuO-K₂Mo₄O₁₃composite materials have been prepared by mixing appropriates quantities,in solid state,of CuO and pure K₂Mo₄O₁₃ according to the molar ratios CuO/K₂Mo₄O₁₃ = 0.05,0.1,0.2,0.5,and 1.The prepared samples were characterized using techniques such as X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IR）,differential thermal analysis（DTA）,nitrogen adsorption measurements,and UV spectroscopy.According to XRD results,the phase composition of the CuO-K₂Mo₄O₁₃ systems has significantly changed by increasing the molar ratio CuO/K₂Mo₄O₁₃ where new phases,identified as K₂Mo₃O₁₀ and CuMoO₄,have been detected.The formation of these new phases has been tracked through FT-IR and DTA measurements.The nitrogen adsorption-desorption measurements also reveal a change in the pore type of me studied materials due to the presence of these new phases.The photocatalytic activities of K₂Mo₄O₁₃ and CuO-K₂Mo₄O₁₃ composites were studied by means of monitoring the ability of these materials to the degradation,under UV irradiation,of methyl red in liquid media.It was found that the phase composition of the used samples significantly controls their photocatalytic activities.     

Novel photocatalyst-based colourimetric indicator for oxygen: Use of a platinum catalyst for controlling response times

The preparation and characterisation of a novel, UV-activated, solvent-based, colourimetric indicator for oxygen is described, comprising a redox dye (methylene blue, MB), semiconductor photocatalyst (Pt-TiO₂), and a sacrificial electron donor (SED = glycerol), all dispersed/dissolved in a polymer medium (sulfonated polystyrene, SPS). Upon exposure to UVA light, the Pt-TiO₂/MB/glycerol/SPS oxygen indicator is readily photobleached as the MB is converted into its oxygen-sensitive, leuco form, LMB. In contrast to its non-platinised TiO₂ counterpart (TiO₂/MB/glycerol/SPS oxygen indicator), the recovery of the original colour is faster (ca. 1.5 days cf. 5 days at 21 °C). This is due to the catalytic action of the 0.38 wt% platinum loaded onto the semiconductor photocatalyst, TiO₂, on the oxidation of the photogenerated LMB by ambient O₂. Furthermore, by increasing the level of platinum loading, recovery times can be decreased further; e.g. a Pt-TiO₂/MB/glycerol/SPS oxygen indicator with platinum level of 1.52 wt% recovers fully within 12 h. A study of the kinetics of recovery as a function of film thickness revealed the recovery step is not controlled by the diffusion of O₂ through the film, but instead dependent upon the slow rate of oxidation of LMB to MB by O₂ in the low dielectric polymer encapsulation medium. Other work showed this recovery is only moderately dependant upon temperatures above −10 °C and very sensitive to relative humidity above 30% RH. Potential uses of this UV light activated indicator are discussed briefly.     

Spectrophotometric evaluation of the photocatalytic degradation of formaldehyde by Fe2O3–TiO2 nano hybrid

Photocatalytic capabilities of sol–gel synthesized Fe₂O₃–TiO₂ nano hybrid was investigated in degradation of formaldehyde in presence of ultra violet and visible irradiation. The reaction stream was evaluated by UV–vis spectrophotometry at 330–500 nm spectral region, using Fluoral-P (4-amino-3-penten-2-one) as a complexing agent. Obtained results confirmed the effective role of Fe₂O₃ phase in nano hybrid for degradation of formaldehyde according to Baeyer–Villiger reaction. On the other hand TiO₂ would play the role of photocatalyst in presence of UV ray. Nano hybrid assisted process was monitored by spectrophotometry, utilizing multivariate curve resolution chemometric technique.     

Microwave fabrication of Cu2ZnSnS4 nanoparticle and its visible light photocatalytic properties

Cu₂ZnSnS₄ nanoparticle with an average diameter of approximately 31 nm has been successfully synthesized by a time effective microwave fabrication method. The crystal structure, surface morphology, and microstructure of the Cu₂ZnSnS₄ nanoparticle were characterized. Moreover, the visible light photocatalytic ability of the Cu₂ZnSnS₄ nanoparticle toward degradation of methylene blue (MB) was also studied. About 30% of MB was degraded after 240 min irradiation when employing Cu₂ZnSnS₄ nanoparticle as a photocatalyst. However, almost all MB was decomposed after 90 min irradiation when introducing a small amount of H₂O₂ as a co-photocatalyst. The enhancement of the photocatalytic performance was attributed to the synergetic effect between the Cu₂ZnSnS₄ nanoparticle and H₂O₂. The detailed photocatalytic degradation mechanism of MB by the Cu₂ZnSnS₄ was further proposed.     

A facile solid-state heating method for preparation of poly(3,4-ethelenedioxythiophene)/ZnO nanocomposite and photocatalytic activity

Poly(3,4-ethylenedioxythiophene)/zinc oxide (PEDOT/ZnO) nanocomposites were prepared by a simple solid-state heating method, in which the content of ZnO was varied from 10 to 20 wt%. The structure and morphology of the composites were characterized by Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) absorption spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The photocatalytic activities of the composites were investigated by the degradation of methylene blue (MB) dye in aqueous medium under UV light and natural sunlight irradiation. The FTIR, UV-vis, and XRD results showed that the composites were successfully synthesized, and there was a strong interaction between PEDOT and nano-ZnO. The TEM results suggested that the composites were a mixture of shale-like PEDOT and less aggregated nano-ZnO. The photocatalytic activity results indicated that the incorporation of ZnO nanoparticles in composites can enhance the photocatalytic efficiency of the composites under both UV light and natural sunlight irradiation, and the highest photocatalytic efficiency under UV light (98.7%) and natural sunlight (96.6%) after 5 h occurred in the PEDOT/15wt%ZnO nanocomposite.     

Recent progress in the development of visible light-driven powdered photocatalysts for water splitting

Many photocatalyst materials for water splitting have been developed, particularly since the second half of the 1990s. Highly efficient water splitting on tantalate photocatalysts under UV irradiation has been achieved. Moreover, band engineering by doping, valence band formation, and synthesis of solid solutions, has led to the development of a large number of visible light-driven photocatalysts for _H2${\mathrm{H}}_2$ or _O2${\mathrm{O}}_2$ evolution from aqueous solutions containing electron donors or acceptors. Z-scheme photocatalyst systems for water splitting to _H2${\mathrm{H}}_2$ and _O2${\mathrm{O}}_2$ under visible light irradiation have been developed. This progress in the development of visible light-driven photocatalysts for water splitting is reviewed.     

Solar photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) using TiO2/SiO2 aerogel composite photocatalysts

Silica aerogels and TiO₂/silica aerogel composite photocatalysts were synthesized by sol–gel technique at ambient pressure using orthosilioate and tetra-n-butyl titanate as precursors, respectively. The prepared composite photocatalysts were characterized by XRD, TEM, BET surface area, FT-IR and UV–vis absorption spectra. The results showed that the TiO₂/silica aerogel composite photocatalysts possess high surface area. The addition of silica aerogels inhibited the grain growth and phase transformation of anatase to rutile during calcination. The TiO₂/silica aerogel composite sample calcined at 500 °C with an optimal silica aerogel content of 7 wt.% afforded the highest photocatalytic activity. The photocatalytic degradation of 2-sec-butyl-4,6-dinitrophenol (DNBP) was investigated by using this novel TiO₂/silica aerogel composite photocatalyst under solar light irradiation. The effects of irradiation time, pH, catalyst concentration, temperature and initial DNBP concentration were examined as operational parameters. The optimal operational parameters were found as follows: pH as solution pH 4.82, 8 g L⁻¹ catalyst concentration, 20 °C, and 240 min irradiation time. The kinetics of DNBP degradation by TiO₂/silica aerogel composite fit well a pseudo-first-order kinetic model. The repeatability of photocatalytic activity was also tested. This study showed the feasible and potential use of TiO₂/silica aerogel composite photocatalysts in degradation of toxic organic contaminants.     

Photocatalytic effects for the TiO2-coated phosphor materials

This study investigated the photocatalytic behavior of the coupling of TiO₂ with phosphorescent materials. A TiO₂ thin film was deposited on CaAl₂O₄:Eu²⁺,Nd³⁺ phosphor particles by using atomic layer deposition (ALD), and its photocatalytic reaction was investigated by the photobleaching of an aqueous solution of methylene-blue (MB) under visible light irradiation. To clarify the mechanism of the TiO₂-phosphorescent materials, two different samples of TiO₂-coated phosphor and TiO₂–Al₂O₃-coated phosphor particles were prepared. The photocatalytic mechanisms of the ALD TiO₂-coated phosphor powders were different from those of the pure TiO₂ and TiO₂–Al₂O₃-coated phosphor. The absorbance in a solution of the ALD TiO₂-coated phosphor decreased much faster than that of pure TiO₂ under visible irradiation. In addition, the ALD TiO₂-coated phosphor showed moderately higher photocatalytic degradation of MB solution than the TiO₂–Al₂O₃-coated phosphor did. The TiO₂-coated phosphorescent materials were characterized by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photon spectroscopy (XPS).     

Synergy between surface adsorption and photocatalysis during degradation of humic acid on TiO2/activated carbon composites

A photocatalyst comprising nano-sized TiO(2) particles on granular activated carbon (GAC) was prepared by a sol-dipping-gel process. The TiO(2)/GAC composite was characterized by scanning electron microscopy (SEM), X-ray diffractiometry (XRD) and nitrogen sorptometry, and its photocatalytic activity was studied through the degradation of humic acid (HA) in a quartz glass reactor. The factors influencing photocatalysis were investigated and the GAC was found to be an ideal substrate for nano-sized TiO(2) immobilization. A 99.5% removal efficiency for HA from solution was achieved at an initial concentration of 15 mg/L in a period of 3h. It was found that degradation of HA on the TiO(2)/GAC composite was facilitated by the synergistic relationship between surface adsorption characteristics and photocatalytic potential. The fitting of experimental results with the Langmuir-Hinshelwood (L-H) model showed that the reaction rate constant and the adsorption constant values were 0.1124 mg/(L min) and 0.3402 L/mg. The latter is 1.7 times of the calculated value by fitting the adsorption equilibrium data into the Langmuir equation.     

Titanate quantum dots-sensitized Cu2S nanocomposites for superficial H2 production via photocatalytic water splitting

TiO₂ quantum dots-sensitized Cu₂S (Cu₂S/TiO₂) nanocomposites with varying concentration of TiO₂ QDs are synthesized via a facile two-stage hydrothermal-wet impregnation method. X-ray diffraction analysis confirms the formation of Cu₂S and TiO₂with chalcocite and anatase phases, respectively. The observed shoulder-like absorption peaks indicate the UV–visible light-driven properties of the composite. Morphological analysis reveals that the fabricated Cu₂S/TiO₂ composite consists of Cu₂S with a nano rod-like shape (average length and width of ～856 and ～213 nm, respectively) and nanosheets-like structures (average length and width of ～283 and ～289 nm, respectively), whereas the TiO₂ is formed as quantum dots with a size range of 8.2 ± 0.4 nm. Chemical state analysis shows the presence of Cu⁺, S^2?, Ni²⁺, and O^2? in the nanocomposite. The H₂ evolution rate over the optimized photocatalyst is found to be ～45.6 mmol h^?1g^?1_cat under simulated solar irradiation, which is around 5 and 2.4-fold higher than that of the pristine TiO₂ and Cu₂S, respectively. Continuous H₂ production for 30 h is achieved during time-on-stream experiments, demonstrating the excellent stability and durability of the Cu₂S/TiO₂ photocatalyst for large-scale applications.