Nanocrystalline NiWO4 wolframite structure has been prepared by a simple salt solution addition
(NiW1SS), co-precipitation (NiW4Cop) and sol–gel (NiW4SG) techniques via employing polymeric templates
particularly polyethylene glycol (PEG) and triblock copolymer, respectively. The synthesis method
as well as the metal molar ratio (W/Ni) influenced the phases, morphology, optical and surface properties
of synthesized samples as configured by X-ray diffraction, transmission electron microscopy, UV–vis
diffuse reflectance spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy and N2 sorptiometry
techniques. Accordingly, the NiW1SS material that exposed only NiWO4 of nano-plate shape
at a molar ratio (W/Ni) 1 indicates higher surface texturing values (SBET = 52.6 m2/g, Vp = 0.2061 cm3/g
and r = 15.7 nm) exceeding those of NiW4Cop (SBET = 15.07 m2/g, Vp = 0.0491 cm3/g and r = 13.0 nm) of
anisotropic shapes (hexagonal and tetragonal); synthesized at a ratio of 4 and by the same template (PEG).
The NiW1SS material indicated Eg value of 2.23 eV whereas that of NiW4Cop revealed a value of 2.92 eV.
On the other hand, NiW4SG that exposed well crystallized WO3 beside NiWO4 of nano-flakes shape and
an average diameter of 25 nm indicates Eg value of 2.56 eV and in addition evokes the formation of narrow
pore size distribution in mesopores range (2–12 nm) as well as in macropores (60 nm) exploring the
effect of template type on the pore texturing. Photodegradation of methylene blue (MB) dye was used
to evaluate the photoactivity of NiWO4 catalysts under UV irradiations. The NiW4SG catalyst exhibited
the best degradation performance (92.5% for MB after 5 h). The results showed that the feasibility of MB
degradation was not only due to morphological properties but also to the NiWO4/WO3 heterojunction.
Significantly, WO3 facilitates effective charge separation as traced by the photoluminescence emission |
