Photocatalytic Degradation of Methylene Blue on RuO₂–CNT

Abstract

Photodegradation of organic pollutants by oxide-based photocatalysts has gained increasing attention as a solution to environmental problems. Generally, the degradation of pollutants proceeds by reaction with reactive hydroxyl radicals, which are generated by the reaction of water molecules adsorbed onto the photocatalyst with photogenerated charge carriers on the surface of the photocatalyst. 1,2 However, the fast recombination rate of photogenerated charge carriers limits the ability to enhance the photocatalytic efficiency of oxide-based photocatalysts. The difficulty of separating and recycling these catalysts also hinders their practical application.Ruthenium dioxide (RuO 2 ) has been used in a variety of applications, including energy storage devices, transparent electrodes, gas sensors, catalysts, and thin film resistors, due to its excellent electrical conductivity, good chemical stability, and high specific capacitance. [3][4][5] In photocatalysis, RuO 2 has generally served as a component of a composite photocatalyst such as RuO 2 /TiO 2 , RuO 2 /ZnO, and RuO 2 / Ag 3 PO 4, due to its good electron conductivity, which can significantly promote the separation efficiency of photogenerated charge carriers. 6-8 However, there are few reports of RuO 2 nanoparticles as a photocatalyst, which may be attributed to their tendency to aggregate in reaction systems, due to their high surface energy. 9,10 Several recent studies have demonstrated that the deposition of nanoparticles onto carbon supports offers great potential for decreasing the recombination rate of charge carriers and preventing the aggregation of nanoparticles. 11-13 Therefore, we report herein on the preparation and photocatalytic properties of a RuO 2 -carbon nanotube (RuO 2 -CNT) nanocomposite, comprised of RuO 2 nanoparticles deposited onto a thiolated CNT substrate by wet chemical methods. The RuO 2 -CNT nanocomposite was characterized by means of transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity was investigated by photodegradation of methylene blue (MB). Figure 1(a) displays a typical TEM image of the RuO 2 -CNT nanocomposite and the corresponding size distribution histogram of the deposited nanoparticles. The TEM image clearly shows the presence of nanoparticles on the surface of the CNTs. No free nanoparticles are observed in the TEM image. The deposited nanoparticles have an average diameter of approximately 1 nm, with a narrow size distribution. As depicted in Figure 1(b), size-similar and quasi-spherical nanoparticles are uniformly dispersed along the CNT surfaces. The nanoparticles attached to CNTs could not be separated from them even after exhaustive washing and prolonged sonication. Figure 2(a) shows the XRD patterns for the thiolated CNTs and RuO 2 -CNT. The simulated pattern of RuO 2 (JCPDS card No. 43-1027) is shown for comparison with the experimental data. In RuO 2 -CNT, the two peaks at 26.0 and 43.2 can be indexed to the...

Shedding light on the use of graphene oxide-thiosemicarbazone hybrids towards the rapid immobilisation of methylene blue and functional coumarins

“…This approach was consistent with previous work on MB decontamination in aqueous media, and, additionally, as a reliable test since MB dye was also commonly used to test photocatalytic ability of nanohybrids. [68][69][70][71][72] Colorimetric observations showed that upon oxidation, this common dye and notorious pollutant, MB turns from blue to colourless, thus providing a qualitative response on its annihilation and removal from solution phase. We observed a similar feature in the presence of GO or ZnBTSC2@GO even in the absence of violet light irradiation (Fig.…”