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[en] In this paper, we report degradation of methyl orange, an azo dye through silver nanoparticles, with the help of UV-Visible spectroscopy. These silver nanoparticles have been found to act as a potential catalyst for the degradation of methyl orange in the presence of sodium borohydride. Rate constants for the catalyzed and uncatalyzed reaction have been determined. The catalyzed reaction spectrum shows a sudden fall in absorbance value confirming catalytic effect of Ag nanoparticles. No significant change in absorbance in case of uncatalyzed reaction is observed, indicating very slow reduction rate of methyl orange. (author)
[en] Highlights: • Multi-walled carbon nanotubes were functionalized with cysteamine groups. • The adsorption of methylene blue and orange dyes was investigated on these surfaces. • The effect of temperature, contact time and initial concentration was considered. • The optimal contact time was found to be about 60 min. • Kinetic of the adsorption process was explored. Multi-walled carbon nanotubes (MWCNTs) were functionalized with cysteamine groups by several percentage of mass as adsorbents, then kinetics adsorption capacity was investigated for methylene blue (MB) and methyl orange (MO) as anionic and cationic dyes adsorbate molecules, respectively. The effect of temperature (from 283 to 303 K), contact time and initial concentration of the MB and MO dyes in a solution (10 to 40 ppm) was considered. The optimal contact time was found to be about 60 min. Some kinetics model such as pseudo-first-order, pseudo-second-order, intra-particle diffusion and the Elovich were tested. The adsorptions of MB dye on the pristine and functionalized MWCNT surfaces were found to be the intra-particle diffusion and the pseudo-second-order kinetic model, respectively and for adsorption of MO dye by the pristine and low functionalized MWCNTs and highly functionalized tubes, found to be the pseudo-second-order and intra-particle diffusion kinetic model, respectively, based on the chi-square statistic (X2) and also high correlation coefficient (R2) values.
[en] Highlights: • ZnO/SnO2 nanocomposites as photocatalysts were synthesized by co-precipitation. • The ZnO/SnO2 nanocomposites showed enhanced photocatalytic activities. • The enhanced photo-degradation of MO was corresponded to better charge separation. • Super oxide radicals and photo-generated holes were involved in photo-degradation of MO.
[en] Highlights: • Largely enhanced photocatalytic properties in the visible light region. • The shape-controlled Cu2O crystals are obtained by adjusting the reaction condition. • A plausible growth mechanism of Cu2O nanostructures was proposed. An interesting evolution to prepare shape-controlled Cu2O nanocrystals was realized by a convenient one pot synthesis. The Cu2O nanocrystals with different shapes can be obtained simply by adjusting the composition of reaction system. And, a plausible mechanism was also proposed to explain the nanostructures formation. The surface of Cu2O spheres with thorn exhibited high photocatalytic activity on the degradation of methyl orange (MO) solution under visible light irradiation. The photodegradation efficiency of MO solution reach up to 99.67% at the first 10 min. It is still as high as 98% even at the end of the fourth cycle.
[en] Naturally abundant bentonite clay minerals have high cation exchange capacity (80–120 meq/g), greater surface area, enhanced swelling properties with micro and meso-porosity. However, their hydrophilic surface limits their adsorption ability. In the present study, bentonite clay (BT) was modified with a cationic surfactant by using cation exchange reaction to modify its surface from hydrophilic to hydrophobic; thus making it a better adsorbent for the removal of pollutants from contaminated water. The modified clay was characterized through fourier transform infrared spectroscopy, and thermo gravimetric analysis. It was used as an adsorbent for the removal of methyl orange and deltamethrin from aqueous solutions. The results showed that modified bentonite has strong tendency to remove organic pollutants from water. About 97% removal of methyl orange was observed with surfactant modified bentonite in contrast to only 56% removal with unmodified bentonite. Similarly, modified bentonite removed up to 98% deltamethrin as compared to only 47% removal with unmodified bentonite. Kinetic study of both experiments showed that the absorption process follows a pseudo second order equation. (author)
[en] Degradation of hazardous organic dyes utilizing multifunctional catalytic materials is supposed to be an efficient and promising method. Here, homogeneous Cu-Fe3O4 nanocomposites are synthesized through a facile and versatile one-pot hydrothermal method. The prepared Cu-Fe3O4 possesses spherical structure with rough surface and average diameter of 230 nm. High catalytic activity and structure stability make Cu-Fe3O4 nanocomposites effectively degrade rhodamine B, methylene blue, methyl orange, and congo red. The existence of magnetic Fe3O4 leads the nanocomposites to separate from the solution through external magnet and reuse for cycle degradation. And during the cyclic utilization, Cu-Fe3O4 nanocomposites keep high catalytic activity and, thus, could be used as an efficient degradation catalyst for the application of organic dyes. .
[en] CdS–TiO2–Au composites were synthesized via microwave-assisted reaction of CdS precursor and chloroaurate solution with TiO2 suspension using a microwave system. The photocatalytic performance of CdS–TiO2–Au composites in degradation of methyl orange was investigated. The results show that CdS–TiO2–Au composites exhibit an enhanced photocatalytic performance with maximum degradation rate of 98% under visible light irradiation as compared with pure TiO2 (43%) and CdS–TiO2 (80%) composite due to the increased light absorption intensity and the reduction of electron–hole pair recombination with the introduction of Au.
[en] A static and dynamic investigation was performed on liquid crystal cells containing pure nematics and nematics doped with an azo-dye (Methyl Orange). It was found that the critical field for magnetic Freedericksz transition was decreased in samples containing the 'trans' isomer and increased in those containing the 'cis' isomer. Changes in the relaxation time τA, τB intervening when switching on/off the magnetic field were also noticed. A theoretical model was elaborated to explain these phenomena
[en] Highlights: • TiO2/Ag binary nanocomposites were prepared via graft copolymerization. • TiO2/Ag binary nanocomposite showed enhanced photocatalytic performance under visible light. • The improvement of the photocatalytic performance was due to the plasmonic effect. We report the synthesis of a TiO2/Ag binary nanocomposite with high activity for visible-light-driven photocatalysts using graft copolymerization: (1) conversion of terminal OH groups on the surface of TiO2 nanoparticles to Cl groups, (2) graft polymerization from TiO2–Cl via ATRP with ionically charged poly(styrene sulfonic acid), (3) ion exchange process with an AgNO3 solution following sintering. TiO2/Ag binary nanocomposite showed enhanced photocatalytic performance for the degradation of methyl orange under visible light illumination. The improved photocatalytic performance of the TiO2/Ag binary nanocomposite was due to the plasmonic effect, recombination rate of electron–hole pairs that was suppressed by Ag nanoparticles.