3 research outputs found

    Cooperative Effect between Cation and Anion of Copper Phosphate on the Photocatalytic Activity of TiO<sub>2</sub> for Phenol Degradation in Aqueous Suspension

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    Surface modification of TiO<sub>2</sub> with CuO or calcium phosphate (CaP) can result in enhancement in the photocatalytic activity for organic degradation. In this work, we report on a synergism between the cation and anion of copper phosphate (CuP) on the photocatalytic activity of TiO<sub>2</sub>, for phenol degradation in aerated aqueous suspension under UV light at wavelengths longer than 320 nm. Photocatalysts were prepared by mixing TiO<sub>2</sub> and CuP powders in isopropyl alcohol, followed by drying at 90 °C. As CuP loading increased, the activity of the modified TiO<sub>2</sub> first increased and then decreased. The maximum activity was observed with the catalyst containing 0.1 wt % CuP, which was about 1.9–3.4 times that of bare TiO<sub>2</sub> (anatase, rutile, and their mixture) and also exceeded that of the modified TiO<sub>2</sub> with CuO or CaP. During five repeated tests, the catalyst activity was stable, without detectable leaching of cupric and phosphate ions into aqueous solution. Solid characterization with several techniques including electron paramagnetic resonance (EPR) spectroscopy revealed that CuP particles at low loading were highly dispersed onto TiO<sub>2</sub> as a kind of clusters, whereas the TiO<sub>2</sub> phase in different samples remained nearly unchanged in terms of the crystal structure, surface area, and crystallinity. Upon exposure to UV light, the EPR signal of Cu­(II) in CuP or CuO-modifed TiO<sub>2</sub> was unchanged in air but slightly decreased in N<sub>2</sub>. Moreover, CuP-modified TiO<sub>2</sub> showed a higher capacity than bare TiO<sub>2</sub> and CuO- or CaP-modified TiO<sub>2</sub> for the uptake of 2,4-dichlorophenol from water. It is proposed that cupric and phosphate ions act as an electron scavenger and organic sorbent, which facilitate electron and hole transfer, respectively. Their co-operation would significantly improve the efficiency of charge separation, and thus increase the rate of phenol degradation

    Improved Photocatalytic Activity of TiO<sub>2</sub> on the Addition of CuWO<sub>4</sub>

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    Various methods that aim to improve the photocatalytic activity of TiO<sub>2</sub> have been reported in the literature. Herein, we report that addition of CuWO<sub>4</sub> into the aqueous suspension of TiO<sub>2</sub> can result in significant enhancement in the rate of phenol degradation. As the amount of CuWO<sub>4</sub> increased, the rate of phenol degradation increased and then decreased. A maximum rate of phenol degradation observed with 2 wt % CuWO<sub>4</sub> was about 2.83 times that in the absence of CuWO<sub>4</sub>. A similar result was also observed with CuO. However, six consecutive tests showed that CuWO<sub>4</sub>/TiO<sub>2</sub> was much more stable than CuO/TiO<sub>2</sub>, due to the very high stability of CuWO<sub>4</sub> against photocorrosion. The improved activity of TiO<sub>2</sub> is not due to CuWO<sub>4</sub> and CuO themselves and also does not match their solubility in aqueous solution. Moreover, for the generation of OH radicals, and for the decomposition of H<sub>2</sub>O<sub>2</sub> in aqueous solution, CuWO<sub>4</sub>/TiO<sub>2</sub> was also more active than TiO<sub>2</sub>. Through a (photo) electrochemical measurement, a possible mechanism is proposed, involving electron transfer from the irradiated TiO<sub>2</sub> to CuWO<sub>4</sub> that facilitates the charge separation of TiO<sub>2</sub> and consequently accelerates reactions at interfaces

    Enhanced Visible-Light Photoactivity of CuWO<sub>4</sub> through a Surface-Deposited CuO

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    Several papers have shown that CuWO<sub>4</sub> is active under visible light for water oxidation at an applied potential bias and for organic degradation in an aerated aqueous suspension. In this work, we report that the observed reduction of O<sub>2</sub> on the irradiated CuWO<sub>4</sub> is a multielectron transfer process with the formation of H<sub>2</sub>O<sub>2</sub>. More importantly, the surface modification of CuWO<sub>4</sub> with 1.8 wt % of CuO can increase the activity by approximately 9 times under UV light and by 5 times under visible light, for phenol degradation in aerated aqueous suspension. The catalyst was prepared by a hydrothermal reaction between Cu­(NO<sub>3</sub>)<sub>2</sub> and Na<sub>2</sub>WO<sub>4</sub>, followed by thermal treatment at 773 K. High-resolution transmission electron microscopy revealed that triclinic CuWO<sub>4</sub> (40 nm) was covered by monoclinic CuO (4 nm). Through a combination of photo- and electrochemical measurement, a plausible mechanism responsible for the activity enhancement is proposed, involving an interfacial electron transfer from CuO to CuWO<sub>4</sub> and an interfacial hole transfer from CuWO<sub>4</sub> to CuO