Heterogeneous photocatalytic reduction of hexavalent chromium by modified Ag, Cu co-doped tungsten oxide nanoparticles

A highly efficient photocatalyst of Ag, Cu co-doped tungsten oxide nanoparticles (WO3) with 5.0 mol% Ag and 0.5 mol% Cu contents was synthesised by using a simple co-precipitation method at a low temperature. The nanoparticles had a large specific surface area, a rectangular shape and a controlled size. The Ag metal ions acted as loading on the surface, and the Cu metal ions disappeared as decorated into the WO3 structure to enhance electron trapping and reduce the bandgap energies. This enhanced the photocatalytic reduction, a Cr6+ solution. The intense and narrow peak of XRD patterns corresponded to strong crystallinity of monoclinic WO3 with rectangular particles of 30-40 nm. In addition, the high value of the specific surface area of co-doped WO3 (34.0 m(2)/g) was key to enabling Cr6+ ions to adsorb to the large active sites of the catalyst. A TEM micrograph of the modified WO3 confirmed that the Ag hemisphere particles deposited on the surface of the WO3 and Cu2+ also might be incorporated into the WO3 microstructure. Results from the X-ray photoelectron spectroscope (XPS) showed a drastic shift of binding energy for all oxidation states. This was consistent with EDX and the results of spontaneous element mapping. DRS-UV-vis spectrum of Ag, Cu-WO3 annealed the red-shift to the wavelength of ca. 475 nm, and it revealed bandgap energy of 2.61 eV that helped to increase the rate of electron generation. The photoreduction activities of Cr6+ over the optimum catalyst showed extremely fast decay: 82.38% in only 15 min under low-energy visible light radiation. Eventually, the optimum sample decayed the percentage of C6+ around 8 times as much as pure WO3.

Automated summary

Ag, Cu co-doped tungsten oxide nanoparticles were successfully synthesized using a simple co-precipitation method at low temperature. These nanoparticles exhibited high photocatalytic efficiency for Cr6+ reduction, attributed to their large specific surface area, controlled size, and modified structure with Ag and Cu ions. The optimized catalyst showed a significant 82.38% reduction of Cr6+ in just 15 minutes under low-energy visible light, highlighting the potential for enhanced photocatalytic performance compared to pure WO3.