Several papers have shown that CuWO 4 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 2 on the irradiated CuWO 4 is a multielectron transfer process with the formation of H 2 O 2 . More importantly, the surface modification of CuWO 4 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 3 ) 2 and Na 2 WO 4 , followed by thermal treatment at 773 K. High-resolution transmission electron microscopy revealed that triclinic CuWO 4 (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 4 and an interfacial hole transfer from CuWO 4 to CuO.
Various
methods that aim to improve the photocatalytic activity
of TiO2 have been reported in the literature. Herein, we
report that addition of CuWO4 into the aqueous suspension
of TiO2 can result in significant enhancement in the rate
of phenol degradation. As the amount of CuWO4 increased,
the rate of phenol degradation increased and then decreased. A maximum
rate of phenol degradation observed with 2 wt % CuWO4 was
about 2.83 times that in the absence of CuWO4. A similar
result was also observed with CuO. However, six consecutive tests
showed that CuWO4/TiO2 was much more stable
than CuO/TiO2, due to the very high stability of CuWO4 against photocorrosion. The improved activity of TiO2 is not due to CuWO4 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 H2O2 in aqueous solution, CuWO4/TiO2 was also more active than TiO2. Through a (photo)
electrochemical measurement, a possible mechanism is proposed, involving
electron transfer from the irradiated TiO2 to CuWO4 that facilitates the charge separation of TiO2 and consequently accelerates reactions at interfaces.
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