Visible light photocatalytic activity enhancement for water purification in Cu(II)-grafted WO3 thin films grown by photoreaction of nanoparticles

We have developed a simple process for improving the visible light photocatalytic activity in Cu(II)-grafted WO3 thin films, called ‘the photoreaction of nanoparticles’ (PRNP). The films prepared by PRNP showed an enhanced photodegradation rate for an organic dye. Glass substrates were coated with WO3 nanoparticles (5–30 nm) obtained by wet ball milling, and a post-treatment of either conventional heating or PRNP using KrF laser irradiation was carried out. Compared with the conventional heat treatment at 500 °C, PRNP significantly enhanced surface crystallite growth; pulsed photothermal gradient heating and photochemical stimulation increased the formation of new bonds between nanoparticles. The crystallite size near the surface of the WO3 film after 7500 pulses of laser irradiation increased to 70 nm, while it was largely-unchanged in the sample prepared by heat treatment at 500 °C. The photocatalytic dye degradation under visible light irradiation was measured for the samples after Cu(II)-grafting, and showed that the degradation rate of the sample prepared by the PRNP process was 2.8-fold higher than that of the sample prepared by heating at 500 °C. We propose that the improved surface crystallinity of WO3 thin films after the PRNP process stimulates the photoexcited electron/hole transfer at the film surface, resulting in the enhancement of photocatalytic activity.

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► WO3 nanoparticles with 5–30 nm size are obtained by ball milling as catalyst precursors.
► KrF laser irradiation of the films enhances anomalous crystallite growth.
► Laser-induced photothermal and photochemical effects are the key factors for crystal growth.
► Very high photocatalytic dye degradation activity in the film prepared by KrF laser irradiation.