Abstract
A scalable solvothermal technique is reported for the synthesis of a photocatalytic composite material consisting of orthorhombic Ta3N5 nanoparticles and WOx≤3 nanowires. Through X-ray diffraction and X-ray photoelectron spectroscopy, the as-grown tungsten(VI) sub-oxide was identified as monoclinic W18O49. The composite material catalysed the degradation of Rhodamine B at over double the rate of the Ta3N5 nanoparticles alone under illumination by white light, and continued to exhibit superior catalytic properties following recycling of the catalysts. Moreover, strong molecular adsorption of the dye to the W18O49 component of the composite resulted in near-complete decolourisation of the solution prior to light exposure. The radical species involved within the photocatalytic mechanisms were also explored through use of scavenger reagents. Our research demonstrates the exciting potential of this novel photocatalyst for the degradation of organic contaminants, and to the authors’ knowledge the material has not been investigated previously. In addition, the simplicity of the synthesis process indicates that the material is a viable candidate for the scale-up and removal of dye pollutants on a wider scale.
Highlights
With almost 300,000 tonnes of synthetic dye released into the world’s water each year[1], the environmental damage resulting from such pollutants is a matter of utmost concern
By employing Transmission electron microscopy (TEM) to image the Ta3N5 nanoparticles at atomic resolution, an example of which is displayed in Fig. 1c, the high crystallinity of the nanoparticles became evident; the TEM image shows that the nanoparticles consisted of well-ordered atomic planes, and the measured lattice spacing of 0.356 nm is consistent with the spacing of {110} planes in Ta3N5, as indexed by JCPDS card number 79–1533
Lattice planes of W18O49 were much harder to identify, this may be attributable to the practical difficulty of locating the W18O49 nanowires due to the abundance of Ta3N5 nanoparticles
Summary
With almost 300,000 tonnes of synthetic dye released into the world’s water each year[1], the environmental damage resulting from such pollutants is a matter of utmost concern. In many studies TiO2 is used in conjunction with a semiconductor of narrower band gap to yield a composite capable of utilising a much wider range of light wavelengths[20,21,22,23,24,25], or alternatively the material may be doped[25,26,27,28,29,30,31,32] or employed in different phases[31, 33,34,35] in an effort to expand the usable portion of the electromagnetic spectrum Both TaON and Ta3N5 have been shown to degrade organic dyes such as Rhodamine B and methylene blue[36,37,38] under exposure to white light, recent work on photocatalysis by Ta3N5 in the literature suggests that higher degradation rates might be achieved by combining the material with a second, strategically-chosen photocatalyst[39, 40]. As in these previous works, it is demonstrated that charge transfer between the two materials successfully enhances the photocatalytic degradation of Rhodamine B relative to the original nanoparticle precursor, both by augmenting the formation of superoxide and hydroxyl radicals and by increasing the rate of direct oxidation of the dye molecules through interaction with valence band holes
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