Multiple‐Oxidation‐State Tungsten‐Oxide Clusters on a Carbon Surface as an Intersection between Molecular and Bulk Oxides

Abstract

Bulk tungsten oxides exhibit a wide range of oxidation states, whereas the oxidation states available in molecular oxides such as polyoxometalates (POMs) is limited. In this paper, tungsten oxide clusters with diameters of 1.2 � 0.4 (W 60 O x /C), 1.1 � 0.4 (W 28 O x /C), and 0.9 � 0.3 nm (W 12 O x /C) were produced in a sizeselective manner on graphitic carbon by using a phenylazomethine-type dendrimer as a template and applying hydrogen reduction after fixing the dendrimers on a support. X-ray photoelectron spectroscopy revealed that the W atoms in the clusters exhibited multiple oxidation states, i. e., W δ + , W 4 + , W 5 + , and W 6 +. Moreover, X-ray absorption fine structure measurements indicated the WÀ W bond length of 2.84-2.85 � 0.01 Å in these clusters. Auto-oxidation with adventitious oxygen after hydrogen reduction is proposed as a reasonable mechanism for the formation of these clusters on the carbon surface.

Enhanced photoluminescence of potassium-doped tungsten oxide by acetone exposure

“…It has several different oxidation states including tungsten( iii ) oxide, tungsten( iv ) dioxide, tungsten( vi ) trioxide, and tungsten pentoxide. 1,2 They can form various heterogeneous nanocrystals, which have found applications in photoelectrochemistry, 3,4 photocatalysis, 5,6 photoelectrodes, 7,8 gas and humid sensing, 9,10 etc . Particularly, tungsten trioxide (WO 3 ) has multiple crystal phases, which are generated in different synthesis conditions and lead to various properties such as the ferroelectric effect, 11 electrochromic effect, 12,13 chemiresistive effect, 14 and so on.…”