Bi-functional hydrogen tungsten bronze/carbon composite catalysts towards biomass conversion and solar water purification

We presented a novel bi-functional catalyst composed of H_xWO₃ and carbon composites, which exhibits excellent catalytic activity in biomass conversion and can effectively purify water via a wide range of wavelengths in the light spectrum. The H_xWO₃/carbon composites were effectively produced from commercially available monoclinic tungsten trioxide (WO₃) and polypropylene (PP) powders to a single-step mechanochemical reaction employing high-energy ball milling. We systemically investigated how different synthesis parameters, such as rotation speed, processing duration, and ball diameter, affect the mechanochemically-induced phase transformation to either tetragonal or cubic H_xWO₃ during planetary ball milling. The crystal phase of H_xWO₃ was controllable by altering the total impact energy in the ball milling. In addition, real-time monitoring of the pressure increment inside the pot and evaluation of the evolved gas revealed the degassing behavior through the oxidative degradation of PP assisted by WO₃. The CV and Rietveld analysis proved that H_xWO₃ exhibited significant enhancement by two orders of magnitude in the rate of H⁺ diffusion compared to monoclinic WO₃. This enhancement would be attributed to the expansion of a mechanically-formed tunnel along the a-axis, which facilitates the migration of H⁺ ions. The H_xWO₃/carbon composites performed approximately 12-fold higher efficiency in generating soluble solids (glucose and furfural derivatives) compared to untreated WO₃ through the catalytic hydrolysis of cellulose, owing to the enhanced Brønsted acidity. Moreover, the composite particles showed broad light absorption in the UV–Vis–NIR range and demonstrated a considerable enhancement of over three orders of magnitude in the photocatalytic degradation of methyl orange pollutants when exposed to NIR and visible light.