Abstract
One-dimensional (1D) nanowire black titania heterojunctioned with multi-wall carbon nanotube (bTiO2 NW/MWCNT) structures were successfully synthesized via a facile single-step hydrothermal procedure, coupled with succeeding surface treatments and a solid-state physiochemical mode of reduction. Paramagnetic SiO2-coated Fe3O4 microspheres were fabricated and used as cores for the seeding and growth of the bTiO2 NW/MWCNT photocatalyst. The as-prepared photocatalysts were characterized via X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoemission spectroscopy, Fourier transform infrared spectroscopy, and UV-vis diffuse reflectance spectroscopy. The results of materials characterization confirmed formation of 1D bTiO2 NW structure with chemically bound MWCNT atop the reduced Ti3+ propagated lattice of the predominantly (101) exposed facets of anatase TiO2. Controlling the surface treatment process and NW growth time to maintain the anatase phase and stability of surface morphology upon reduction allowed for superior visible light-driven photoactivity. The visible light-driven photocatalytic degradation of 10 mg/L methylene orange was recorded at 97.4% in 20 min of 0.7 Sun intensity. The apparent reaction rate constant (k) of the as-prepared photocatalyst (0.1439 min−1) is ~ 18 times higher than that of pristine TiO2. Utilization of paramagnetic cores for in situ photocatalyst collection upon water treatment is highly recommended for newly developed materials. Further, performing surface treatment procedures of prepared titania-based photocatalysts has been proven to have a notable advantageous effect on photoactivity and is thus suggested for similar materials.
Highlights
One of the recent emerging areas of contaminant degradation is heterogeneous photocatalysis, which has seen a markedly swell of interest due to abundance and relative cost-effectiveness of semi-conductor materials employed and ability to degrade contaminants in situ
The reduction procedure optimized to yield the most stable and photoactive black titania-based sample showed that a significant phase transformation is not to be expected during reduction, maintaining a 90% anatase phase for the bTNW/multiwalled carbon nanotubes (MWCNTs) sample
X-ray diffraction (XRD) peaks of the final reduced paramagnetic nanocomposite—bTNW/ MWCNT@SiO2@Fe3O4—show a slight absence or reduction in characteristic anatase titania peaks, indicating that the nanocrystalline titania structures are well dispersed in the overall composite mesh
Summary
One of the recent emerging areas of contaminant degradation is heterogeneous photocatalysis, which has seen a markedly swell of interest due to abundance and relative cost-effectiveness of semi-conductor materials employed and ability to degrade contaminants in situ. A photocatalytic process involves a reaction that is preliminarily activated by the absorption of a photon with ample energy to overcome the bandgap energy of the photoactive material used. TiO2 has a bandgap energy of approximately 3.2 eV for anatase and 3.0 eV for rutile [3] This is a fairly high bandgap energy which amounts to only 3–5% of solar photons having enough energy to initiate a photoexcitation event. Separating the active photocatalyst composite from the treated water and retaining them in the photoreactor for further use is of paramount importance to the feasibility of the process, and to ensure the cyclability of the TiO2-based photocatalyst is being utilized appropriately and sustainably. Some work has been done with photocatalysts being coated upon a paramagnetic iron core which can be collected when passed through a magnetic field [4,5,6]
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