Sticking with the formation of ZnWO4 nanoparticles on more time. This tungstate has been used for the photocatalytic generation of hydrogen from water and mineralization of organic pollutants under UV irradiation. Now that we understand the importance of the application, let’s head back — there haven’t been too many publications on the ways in which clean, high-photocatalytic ZnWO4 particles have been made. The shortcomings of traditional methods include too high a temperature, long reaction cycles and complex reaction set-ups, but largely because conventional approaches do not provide volumetric heating. Unlike the the last approach (MW solvothermal) at 160C for 1 and 3 h, this group reports studies at multiple temperatures and ultimately settling 5,10 and 15 minutes at 180C following a look at the XRD patterns at lower temperature. Na2WO4·2H2O (0.14  g), ZnCl2 (0.13 g), H2O (10.0 mL), and poly(ethylene glycol) (0.12 g) were placedin a closed microwave vessel (multi-mode reactor) and heated to 180C at a rate of 50C/min for several minutes, cooled and washed, dried and characterized. Certainly this is an improvement in time (and a movement to water over solvent) and significant details of crystallinity are better defined in their relationship to photocatalytic activity.

Phase composition of samples prepared at different temperatures indicate a lack of phase formation at 140C and 160C.

XRD with 5 min MW

XRD with 5 min MW

Further study with multiple time points at 180C provide additional information when pure wolframite structures form under MW irradiation.

XRPD ZnWO4 at 180C

XRPD ZnWO4 at 180C

Surface area, crystallinity and particle dispersion are all included in the discussion of what leads to the best photocatalytic activty. Control of particle size and crystallinity under MW conditions allow tuning of particles designed for specific applications.

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