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Abstract
Samples of water based commercial acrylic resin paints were spread in a film form on slides, dried at room temperature and exposed to solar radiation for up to eight months. The characterization and quantification of resins and charges in the white paint emulsion were carried out for the thermal decomposition. Besides this, X-ray diffractometry was used to identify CaCO3 as charge and TiO2 (rutile phase) as pigment. It was observed through thermal techniques similar behavior to the samples even though with varied exposure time. Kinetic studies of the samples allowed to obtain the activation energy (E a) and Arrhenius parameters (A) to the thermal decomposition of acrylic resin to three different commercial emulsion (called P1, P2, P3) through non-isothermal procedures. The values of E a varied regarding the exposition time (eight months) and solar radiation from 173 to 197 kJ mol−1 (P1 sample), from 175 to 226 kJ mol−1 (P2 sample) and 206 to 197 kJ mol−1 (P3 sample). Kinetic Compensation Effect (KCE) observed for samples P2 and P3 indicate acrylic resin s present in these may be similar in nature. This aspect could be observed by a small difference in the thermal behavior of the TG curves from P1 to P2 and P3 sample. The simulated kinetic model to all the samples was the autocatalytic Šesták-Berggreen.
Abstract
Nanostructures of β-Ga2O3 were prepared by solution combustion route using urea as the fuel. Transmission electron microscopic measurements and powder X-ray diffraction measurements confirmed the crystalline nature of β-Ga2O3 with particle size in the range of 10–15 nm. Surface area measurements indicated that the synthesized semiconductor catalyst had a specific surface area of 30 m2/g. In this work, photocatalytic degradation studies of tri-n-butyl phosphate using nano sized β-Ga2O3 is presented. A cylindrical photoreactor was used for the degradation studies and gas chromatographic estimation was adopted to follow the extent of degradation. Complete degradation of tributyl phosphate could be achieved in less than 40 min using 10 mg of photocatalyst and 0.5 mL of H2O2 for 1000 mL of 400 ppm TBP. Degradation of TBP was found to follow pseudo first order kinetics and the rate of TBP degradation was found to be superior for β-Ga2O3 photocatalyst compared to P-25 TiO2.
Abstract
The atom economy concept is one of the earliest recognition for green and sustainable aspects of organic synthesis. Over the years, novel technologies emerged that made this important feature of reactions into practice. Continuous-flow devices increased the efficiency of the chemical transformations with novel process windows (high T, high p and heterogeneous packed catalysts etc.) and increased safety which turned the attention to reexamine old, industrial processes. Oxidation can be performed under flow catalytic conditions with molecular oxygen; alcohols can be oxidized to carbonyl compounds with high atom economy (AE = 87 %). Using O2 and 1 % Au/TiO2, alcohol oxidation in flow was achieved with complete conversion and >90 % yield. N-alkylation is another good example for achieving high atom economy. Under flow catalytic conditions (Raney Ni), amines were successfully reacted with alcohols directly (AE = 91 %) with >90 % conversion and selectivity. In both examples, the effective residence time was less than 1 min. These two examples demonstrate the significant contribution of flow technology to the realization of key principles in green and sustainable chemistry.
Abstract
The photocatalytic properties of MoS2 samples including nano-ball, nano-slice and bulk 2H-MoS2 were evaluated and compared with that of the anatase TiO2 using the degradation reaction of methyl orange under visible light. The catalytic behaviors of the samples were also characterized using transmission electron microscopy, Brunauer-Emmett-Teller (BET) surface area, ultraviolet-visible spectroscopy, and FTIR spectroscopy. The results show that the bulk MoS2 and the anatase TiO2 were almost inactive under visible light. The nano-slice presented the most positive catalytic effect because it has a wide absorption at 400–700 nm and a high BET surface area. Though the BET surface area of the nano-ball was lower than that of the nano-slice, it has an active curved basal surface and presented a catalytic activity close to that of the nano-slice. Moreover, the MoS2 nano-slice catalyst could be conveniently regenerated after filtration and drying.
Abstract
Ruthenium catalysts have been prepared by incipient wetness impregnation of ruthenium(III) nitrosylnitrate, Ru(NO)(NO3)3 onto high surface area titanate supports obtained by hydrothermal treatment of TiO2 P25 in concentrated alkaline solutions. These Ru-containing catalysts were evaluated in the catalytic wet air oxidation of p-hydroxybenzoic acid (p-HBZ), a model compound representative of phenolic pollutants present in olive mills wastewaters, at 413 K and 50 bars of air. Two different titanates morphologies were tested as supports for this reaction: hydrogenotitanate nanotubes (HNT) obtained with concentrated NaOH and hydrogenotitanate nanowires (HNW) formed in the presence of highly concentrated KOH solution. The HNT and HNW supports and their corresponding supported Ru catalysts were characterized by means of N2 adsorption–desorption, XRD, UV and TEM analyses. Results showed that the use of high surface area titanate supports led to catalysts much more active than similar Ru catalysts supported on conventional TiO2 supports.
Abstract
This contribution is concerned with the investigation of the removal efficiency of the pyridine-based insecticide imidacloprid from aqueous solution irradiated with UV or visible light in the presence of AlFe-pillared clay and Fe-ZSM-5 as catalysts. The obtained results were compared with those achieved using the photo-Fenton reaction as well as TiO2 Degussa P25. A stability study under natural conditions and direct photolysis in the presence of both light sources were also performed.
Abstract
The sorption of hafnium on hydrous titanium oxide (TiO2·1.94 H2O) has been studied in detail. Maximum sorption of hafnium can be achieved from a pH 7 buffer solution containing boric acid and sodium hydroxide using 50 mg of the oxide after 30 minutes shaking. The value ofk
d, the rate constant of intraparticle transport for hafnium sorption, from 0.01M hydrochloric and perchloric acid and pH 7 buffer solutions has been found to be 17 mmole·g–1·min–2. The kinetics of hafnium sorption follows Lagergren equation in 0.01M HCl solution only. The values of the overall rate constantK
=6.33·10–2 min–1 and of the rate constant for sorptionk
1=6.32·10–2 min–1 and desorptionk
2=2.28·10–5 min–1 have been evaluated using linear regression analysis. The value of correlation factor(
) is 0.9824. The influence of hafnium concentration on its sorption has been examined from 4.55·10–5 to 9.01·10–4 M from pH 7 buffer solution. The sorption data followed only the Langmuir sorption isotherm. The saturation capacity of 9.52 mmole·g–1 and of a constant related to sorption energy have been estimated to be 2917 dm3·mole–1. Among all the additional anions and cations tested only citrate ions reduce the sorption significantly. Under optimal experimental conditions selected for hafnium sorption, As(III), Sn(V), Co(II), Se(IV) and Eu(III) have shown higher sorption whereas Mn(II), Ag(I) and Sc(III) are sorbed to a lesser extent. It can be concluded that a titanium oxide bed can be used for the preconcentration and removal of hafnium and other metal ions showing higher sorption from their very dilute solutions. The oxide can also be employed for the decontamination of radioactive liquid waste and for pollution abatement studies.
Abstract
Behavior of cadmium(II) in aqueous solutions irradiated by accelerated electrons was studied. A concentration of 8.8 × 10−4 mol L−1 of cadmium dissolved from Cd(NO3)2 requires dose of 15 kGy to be effectively removed from the system containing 1 × 10−2 mol L−1 of HCOOK as a scavenger of OH radicals. The positive effect of deaeration with N2O or N2 was observed in the range of lower doses. The addition of solid modifiers (bentonite, active carbon, zeolite, Cu2O, NiO, TiO2 and CuO) reduced the effectivity of radiation removal of cadmium. Product of irradiation is CdCO3. On the contrary, in the system with cadmium dissolved from CdCl2 radiation reduction takes place. Systems contained organic complexants (ethylene diamine tetraacetic acid–EDTA, citric acid) were also studied. The solutions of Cd(NO3)2 containing initial concentration 2.37 × 10−4 mol L−1 of CdII were mixed with 3 × 10−4 mol L−1 EDTA. In this system the efficient degradation proceeds up to 90% at a dose of 45 kGy with addition of 5 × 10−3 mol L−1 carbonate (pH 10.5). The product of irradiation is CdCO3. The presence of 1 × 10−2 mol L−1 of HCOOK in the solution is necessary for radiation removal of cadmium complexed with citric acid (1 × 10−3 mol L−1) at pH 8. With increasing concentration of HCOOK (up to 5 × 10−2 mol L−1) decreases the pH value necessary for the radiation induced precipitation of cadmium. The best result was obtained in the system containing zeolite as a solid modifier.
Studies of the thermal behaviour of binary oxide mixtures containing vanadium(V) oxide (V2O5-TiO2, V2,O5- MoO3, V2,O5-ZrO2 and V2O5-ZnO) have shown that the evolution of gaseous oxygen at fairly low temperatures is characteristic of those systems which are eflective catalysts for the oxidation of hydrocarbons. No weight changes were observed with V2, O5-ZnO mixtures under these conditions and, in accordance with this, zinc(II) oxide does not enhance the catalytic activity of vanadium(V) oxide. In V2O5-containing systems, evolution of oxygen occurs during the reduction of V2O5 to V2O4. This process is accelerated in the presence of certain metal oxides and such acceleration may be caused by structural interactions at the interface of the oxides. Among the systems studied, the formation of compounds such as Mo6V9O40 is thought to be of little significance from the catalytic point of view.
2 has excellent photocatalytic properties for the degradation of unwanted organic compounds in aqueous solution. However, the absorption edge of TiO 2 falls in the UV region, in which only ∼3% of the solar spectrum is [ 13 ]. Alternatively, to deal
