Photodegradation of methyl orange by BiOI-sensitized TiO2

BiOI-sensitized titanium dioxide (TiO2) photocatalysts were prepared by a deposition method at room temperature and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller surface area measurements. The photocatalytic activities of the catalysts were evaluated for the degradation of methyl orange (MO) solution under UV and visible light irradiation. The effects of catalyst amount, initial pH value, initial concentration of MO, as well as KI amount were investigated. ...     

Cu/Co/Cr Nanocomposites Obtained from Hydrotalcite Precursors as Catalysts for Thermal Decomposition of Ammonium Perchlorate

A series of Cu/Co/Cr nanocomposites with different Cu/Co/Cr molar ratios were obtained by calcination of Cu/Co/Cr hydrotalcites precursors,which were prepared by a co-precipitation reaction.X-ray diffraction,inductively coupled plasma analysis,and transmission electron microscopy were used to characterize the structure,composition,and morphology of Cu/Co/Cr nanocomposites.The results show that Cu/Co/Cr nanocomposites have both CuCr2O4and CoCr2O4spinel phase.The particle size of Cu/Co/Cr nanocomposites is 15–20 nm and the specific surface area is 95–115 m2/g.Cu/Co/Cr nanocomposites were used as new catalysts for improving thermal decomposition of ammonium perchlorate(AP).Their catalytic activities were investigated using differential thermal analysis and thermal gravimetric analyzer coupled with an online mass spectrometer.The results show that the decomposition temperature of AP lowered 132–146 °C by adding 4 wt% Cu/Co/Cr nanocomposites.Catalytic activities of the prepared nanocomposites depend on the calcinations temperature and addition amount of corresponding nanocomposites.The possible catalytic mechanism of Cu/Co/Cr nanocomposites was also studied and discussed.     

Preparation of nitrogen-doped titania and its photocatalytic activity

Yellowish nitrogen-doped titania was produced through sol-gel method in mild condition, with the elemental ni- trogen derived from aqua ammonia. The titania catalysts were characterized using XRD, BET, TEM, XPS, and UV-Vis diffuse reflectance spectrophotometer, and their photocatalytic activities were evaluated under UV and visible light, respec- tively. The XRD results showed that all titania catalysts were anatase. More significantly, the crystallite size of nitro- gen-doped titania increased with an increase in N/Ti proportion, and the doping of nitrogen could extend the absorption shoulder into the visible-light region, thus it possessed a higher visible-light activity illustrated by decolorization of methyl orange (65.3%) under the irradiation of visible light, whereas pure titania showed little of such kind of visible light activity. The UV-light activity of nitrogen-doped titania catalysts was worse than that of pure titania and Degussa P25. In the range of N/Ti proportion of 4-10 mol%, the activity of nitrogen-doped titania weakened appreciably in the visible-light region as the N/Ti proportion increased, whereas a reverse relationship existed under the irradiation of UV light.     

Hierarchically 1D CdS decorated on 2D perovskite-type La_2Ti_2O_7 nanosheet hybrids with enhanced photocatalytic performance

In this paper,a heterojunction of hierarchically one-dimensional(1 D) cadmium sulfide(CdS) nanowires decorated on the two-dimensional(2 D) La_2 Ti_2 O_7(LTO)has been fabricated by a simple two-step hydrothermal process.The structure,morphology and surface chemical composition of CdS/LTO were studied by a variety of characterizations,in which the X-ray photoelectron spectroscopy(XPS) results showed a strong interaction between CdS and LTO through S-O bonds.The type Ⅱ band alignment of CdS/LTO for favorable electron transfer from CdS to LTO and hole transfer from LTO to CdS was clarified by ultraviolet-visible(UV-Vis) diffuse reflectance spectroscopy and Mott-Schottky(M-S) plot measurements.In the absence of any co-catalyst,H_2 production from water splitting and Rhodamine B(RhB) decomposition in aqueous solution were carried out to evaluate the photocatalytic activities,showing that the photocatalytic performance of CdS/LTO was superior to that of pure LTO and CdS under visible light and simulated sunlight.The optimal CdS content in the CdS/LTO system was determined to be 7.5 wt%.The present results show an effective pathway to design a 1 D/2 D heterojunction photocatalyst in the face of overwhelming problems of energy crisis and environmental pollution.     

Fast Degradation of Green Pollutants Through Nanonets and Nanofibers of the Al-Doped Zinc Oxide

In this study, series of nanolayered structures of Zn–Al LDHs were prepared by urea hydrolysis. Nanofibers and nanonets of the Al-doped ZnO were formed via the decomposition of the nanolayers under high pressure and temperature. Nanospheres were also prepared for comparison. The different morphologies of the prepared nanomaterials were confirmed by several techniques. An improvement for the optical properties of the doped zinc oxides was observed through narrowing of their band gap energies because of transforming the nanolayers to nanonets and nanofibers. The photocatalytic activities of the prepared nanomaterials were studied through photocatalytic degradation of the pollutants of acid green dyes. Complete decolorization and mineralization of green dyes happened in the presence of the nanolayers and nanospheres within 4–6 h,while the nanonets and the nanofibers achieved the complete decolorization and degradation of the dyes at shorter time 1.3 h. These results could be explained though the kinetic study of the photocatalytic degradation of dyes. It was concluded that the nanonets and the nanofibers were very effective for the photocatalytic degradation of pollutants.     

Eu^2＋/Gd^3＋-codoped nanocrystalline titania catalyst and its photocatalytic activity under natural light

Eu^2＋/Gd^3＋-codoped nanocrystalline titania catalysts were prepared by a modified sol-gel method. Powder X-ray diffraction, Transmission electron microscopy and UV-Vis spectra analyse were carried out to characterize the catalysts with different Eu^2＋/Gd^3＋contents.The photocatalytic efficiency was evaluated by the photodegradation of methyl orange in an aqueous solution under natural light irradiation. It has been confirmed that Eu^2＋/Gd^3＋-codoped titania could be excited by natural light. The higher natural light activity is due to the codoping of Eu^2＋/Gd^3＋. An optimum synergetic effect was found for a mass ratio of Eu/TiO2 equal to 1.0% and Gd/TiO2 equal to 0.5%. The effects induced by Eu^2＋/Gd^3＋-codoped on the titania catalysts may be explained in terms of Eu^2＋/Gd^3＋ energy transfer to affect the photocatalysis activity of the titania catalysts.     

Photocatalysis of Cd-doped ZnO synthesized with precipitation method

ZnO particles doped with 0 mol%-5 mol% Cd dopant were successfully synthesized by a precipitation method.The as-synthesized products were characterized by thermogravimetric analysis(TGA),differential scanning calorimetry(DSC),X-ray diffraction(XRD),photoluminescence(PL) spectroscopy,Raman spectroscopy,scanning electron microscopy(SEM) coupled with an energydispersive X-ray(EDX) spectroscopy and transmission electron microscopy(TEM).The precursors showed weight loss at 35-700℃ caused by phase transformation and evaporation processes.The as-synthesized products were specified as hexagonal wurtzite ZnO.The crystallite size of ZnO samples doped with 0 mol%-5 mol% Cd gradually increased with the increase in Cd content.The photocatalytic activities of 0 mol%-5 mol% Cd-doped ZnO samples were evaluated through photodecolorization of methylene blue(MB) under ultraviolet(UV) radiation.In this research,ZnO doped with 3 mol% Cd shows the best photocatalytic activity in degrading of MB molecules as much as 89% within 240 min.     

Photocatalytic degradation of acid orange 7 in aqueous solution with La^3＋-doped TiO2 photocatalysts

Nanocrystalline La^3＋-doped TiO2 of 20-30 nm in size was prepared by a sol-gel technique. The photocatalytic activities of the samples were evaluated by the degradation of harmful acid orange 7（AO7） azo-dye in aqueous solution. The effects of La^3＋ ion implantation on the photocatalytic activity of TiO2 were also discussed. The results show that the La^3＋ content plays an essential role in affecting the photocatalytic activity of the La^3＋-doped TiO2 and the optimum content of La^3＋-doped is 1.0 wt.%. The photocatalytic activity of the samples with La^3＋-doped TiO2 is higher than that of pure TiO2 in the treatment of AO7 wastewater. The photodegradation effect of AO7 effluent is the best by means of La^3＋-doped TiO2 with 1.0% La^3＋.     

Regulation of morphology and visible light-driven photocatalysis of WO_3 nanostructures by changing pH

The controlled preparation of hexagonal tungsten trioxide(h-WO_3) nanostructures was achieved by adjusting the pH of the precursor solution. The effect of the pH on the morphology, elemental composition, and photocatalytic performance of the samples was characterized via X-ray diffraction(XRD), scanning electron microscopy, energy dispersive X-ray spectroscopy, and Raman spectroscopy. Ultraviolet–visible(UV–Vis) spectra were used to evaluate the absorbance and the photocatalytic performance of methylene blue. Photoluminescence(PL),electrochemical impedance spectroscopy, photocurrent response and Brunauer–Emmett–Teller(BET) were used to study the optical properties, electrical performance, and specific surface area of the WO_3-nanostructures, respectively. The results indicate that the WO_3 nanorods prepared at pH = 1.0 exhibit the highest photocatalytic performance(87.4% in 1 h), whereas the WO_3 nanoblocks prepared at p H = 3.0 show the lowest. The photocatalytic performance of the one dimensional(1 D)-nanorods can be attributed to their high specific surface area and charge transfer ability.The h-WO_3 nanostructures were synthesized via a simple method and without a capping agent. They show an excellent photocatalytic performance, which is promising for their application in environment purification.     

Enhanced photocatalytic properties of ultra-long nanofiber synthesized from pure titanium powders

Using Ti powder as reagent,ultra-long TiO2 nanofibers were prepared via hydrothermal method in NaOH solution.The samples were char-acterized respectively by means of field emission scanning electron microscopy (FESEM),transmission electron microscopy (TEM) with selected area electron diffraction (SAED),and X-ray diffraction (XRD).The diameter and the length of the ultra-long TiO2 nanofiber were ～100 nm and >200μm,respectively.The ultra-long TiO2 nanofibers were anatase after heat treatment at 450 ?C for 1 h.Moreover,the optical properties of the products were investigated by UV-visible light absorption spectrum.Furthermore,methyl orange was used as a target molecule to estimate the photocatalytic activity of the specimens.Under the same testing conditions,the photocatalytic activity of the ultra-long TiO2 nanofibers was higher than that of P25.Direct electrical pathway and improved light-harvesting efficiency were crucial for the superior photocatalytic activity of the ultra-long TiO2 nanofibers.     

Fast fabrication of Co3O4 and CuO/BiVO4 composite photocatalysts with high crystallinity and enhanced photocatalytic activity via ultrasound irradiation

A facile and efficient approach for the fabrication of Co₃O₄ and CuO/BiVO₄ composite photocatalysts was developed by intense ultrasound irradiation at room temperature. The as-synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy, UV-vis diffuse reflectance spectra (UV-vis DRS), and Brunauer-Emmett-Teller (BET) surface areas. The photocatalytic activity of the composite catalysts was evaluated by photocatalytic degradation of acid orange II under visible light (λ > 420 nm) irradiation. Results showed that under intense ultrasonic irradiation, the precursors of copper acetate and cobaltous acetate could transform into CuO and Co₃O₄, respectively and the amorphous BiVO₄ can easily crystallize to highly crystalline BiVO₄. The composite photocatalysts exhibited much higher photocatalytic activity than that of pure BiVO₄. The enhanced photocatalytic performance could be attributed to the high crystallinity of BiVO₄ and the formed p-n heterojunction of Co₃O₄/BiVO₄ or CuO/BiVO₄. These two factors can effectively suppress the recombination of photogenerated hole-electron pairs.     

The induced synthesis of mixed phase niobate by Cu doping and its photocatalytic property

Cu-doped KNb₃O₈ photocatalysts were prepared using a simple solid-state method. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectrum. XRD and SEM analyses suggest that Cu doping can induce the formation of the compound K₆Nb_10.8O₃₀ with tungsten-bronze structure and the relative content of K₆Nb_10.8O₃₀ in the Cu-doped samples increased with increasing Cu doping amount. When the Cu doping amount reaches 2 wt.%, the as-prepared sample is mainly composed of K₆Nb_10.8O₃₀. The photocatalytic properties of the catalysts were evaluated using the degradation of acid red G. The results showed that Cu-doping significantly increased the photocatalytic activity of the KNb₃O₈ catalyst. The optimum dopant concentration range of Cu was found to be 0.3-1 wt.%. The synergistic effect of Cu doping and mixed phase niobate compounds is responsible for the enhanced photocatalytic activity.     

Nano-sized Fe-metal catalyst on ZnO-SiO2: (photo-assisted deposition and impregnation) Synthesis routes and nanostructure characterization

A nano-sized Fe metal on ZnO-SiO₂ was synthesized using the photo-assisted deposition (PAD) and impregnation routes. The obtained samples were characterized by a series of techniques including X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy, N₂ adsorption, extended X-ray absorption fine structure (EXAFS), and transmission electron microscopy (TEM). Photocatalytic reactivity using Fe-ZnO-SiO₂ catalysts under visible-light condition on the degradation of methylene blue dye was evaluated. The results of characterization reveal, a notable photocatalytic activity of PAD:Fe-ZnO-SiO₂ which was about 9 and 12 times higher than that of Img:Fe-ZnO-SiO₂ and ZnO-SiO₂, respectively.     

水热合成单分散球状ZnxCd1-xS及其光催化性质

采用简单的水热合成路线制备高产量单分散球状ZnxCd1-xS,通过X射线衍射、扫描电镜以及紫外-可见漫反射对所得的产物进行表征。结果表明,所得产物呈现六方相纤锌矿结构,并且ZnxCd1-xS产物呈现出很好的均匀性与规则性。采用光催化降解罗丹明B反应来评价ZnxCd1-xS的光催化活性。其中,Zn0.4Cd0.6S具有最高的催化活性,并且在降解反应过程中表现出很高的稳定性。     

Characterization of Cr（Ⅵ） resistance and reduction by Pseudomonas aeruginosa

The experiments were conducted to evaluate the Cr(VI) resistance and reduction by Pseudomonas aeruginosa. After this bacterium tolerated 40 mg/L Cr(VI), the growth of cells was observed. The bacterial growth was obviously lower than the controls over 24 h and the binary cell fission was observed in cell morphology by scanning electron microscope. P.aeruginosa was found to be able to reduce Cr(VI) although Cr(VI) had toxic effects on the cells. The results demonstrate that Cr(VI) is reduced from 40 mg/L to about 18 mg /L in 72 h. The value of pH drops from 7.02 to around 5.65 after 72 h. A significant increase in the value of redox potential occurs during Cr(VI) reduction and Cr(VI) reduction can be observed over a range of redox potential from +3 mV to +91 mV. Both of SO₄²⁻ and NO₃⁻ have no effect on Cr(VI) reduction. The presence of Zn²⁺ has a notable inhibitory effect on Cr(VI) reduction while Cu²⁺ substantially stimulates Cr(VI) reduction. In the presence of Zn²⁺, Cr(VI) decreases from 40 mg/L to only 26–27 mg/L, whereas Cr(VI) drops to 1–2 mg/L after 48 h in the presence of Cu²⁺.     

Adsorption of XSD-296 resin for Cr（Ⅵ）

The adsorption properties of XSD-296 for Cr（Ⅵ） were studied by using chemical analysis and infrared spectrometry. Experimental results show that XSD-296 resin has a good adsorption ability for Cr（Ⅵ） at pH=2.6 in the HAc-NaAc medium. The statically saturated adsorption capacity is 235 mg/g resin. The apparent activation energy of adsorption reaction, Ea, is 16.73 kJ/mol, and the thermodynamic parameters are △H=11.62 kJ/mol, △G298 K=-4.13 kJ/mol. The adsorption behavior of resin for Cr（Ⅵ） is in accordance with Freundlich adsorption isotherm. Cr（Ⅵ ） adsorbed on resin can be eluted by 5%NaCl-5%NaOH or 5%NH4Cl-5%NH3-H2O quantitatively. Infrared spectra and adsorption mechanism show that the functional group of resin coordinates with Cr（Ⅵ） to form co-ordination compound. The coordination molar ratio of the functional group of resin to Cr（Ⅵ） is 1：1.     

Effect of acidic surface functional groups on Cr（VI） removal by activated carbon from aqueous solution

The activated carbon with high surface area was prepared by KOH activation. It was further modified by H2SO4 and HNO3 to introduce more surface functional groups. The pore structure of the activated carbons before and after modification was analyzed based on the nitrogen ad-sorption isotherms. The morphology of those activated carbons was characterized using scanning electronic microscopy (SEM). The surface functional groups were determined by Fourier transform infrared spectroscopy (FTIR). The quantity of those groups was measured by the Boehm titration method. Cr(Ⅵ) removal by the activated carbons from aqueous solution was investigated at different pH values. The results show that compared with H2SO4, HNO3 destructs the original pore of the activated carbon more seriously and induces more acidic surface functional groups on the activated carbon. The pH value of the solution plays a key role in the Cr(Ⅵ) removal. The ability of reducing Cr(Ⅵ) to Cr(Ⅲ) by the activated carbons is relative to the acidic surface functional groups. At higher pH values, the Cr(Ⅵ) removal ratio is im-proved by increasing the acidic surface functional groups of the activated carbons. At lower pH values, however, the acidic surface functional groups almost have no effect on the Cr(Ⅵ) removal by the activated carbon from aqueous solution.     

Characteristics of N-doped TiO2 nanotube arrays by N2-plasma for visible light-driven photocatalysis

N-doped TiO₂ nanotube arrays were prepared by electrochemical anode oxidation of Ti foil followed by treatment with N₂-plasma and subsequent annealed under Ar atmosphere. The morphologies, composition and optical properties of N-doped TiO₂ nanotube arrays were characterized using field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectrometer (XRD), Photoluminescence (PL) and UV-vis diffusion reflection spectroscopy (UV-vis DRS). Methylene blue (MB) solution was utilized as the degradation model to evaluate the photocatalytic activity of the samples under visible light irradiation. The results suggested N₂-plasma treatment created doping of nitrogen onto the surface of photoelectrodes successfully and the N-doped TiO₂ nanotube arrays display a significantly enhancement of the photocatalytic activity comparing with the pure TiO₂ nanotube arrays under the visible light irradiation.     

Corrosion behavior of Cr electrodeposited from Cr(VI) and Cr(III)-baths using direct (DCD) and pulse electrodeposition (PED) techniques

A comparison was made between the electrochemical corrosion behaviors of chromium deposited from hexavalent [Cr(VI)] and trivalent [Cr(III)] chromium baths using direct current (DCD) and pulse electro deposited (PED) techniques. Chromium coatings were deposited on mild-steel (MS) substrate. The corrosion behavior of both DCD and PED chromium from Cr(VI) and Cr(III)-baths in 3.5%NaCl solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results indicated that PED chromium from Cr(VI) and Cr(III)-baths have higher charge-transfer resistance R_ct and very low I_corr than that of DCD chromium on mild-steel substrate.