Photochemical oxidation of water and reduction of polyoxometalate anions at interfaces of water with ionic liquids or diethylether

Abstract

DEAP ¼ diethanolamine hydrogen phosphate). Photochemical formation of reduced POMs at both thermodynamically stable and unstable water-IL interfaces led to their initial diffusion into the aqueous phase and subsequent extraction into the IL phase. The mass transport was monitored visually by color change and by steady-state voltammetry at microelectrodes placed near the interface and in the bulk solution phases. However, no diffusion into the organic phase was observed when ½P 2 W 18 O 62 6− was photo-reduced at the water-diethylether interface. In all cases, water acted as the electron donor to give the overall process:However, more highly reduced POM species are likely to be generated as intermediates. The rate of diffusion of photo-generated POM − was dependent on the initial concentration of oxidized POM and the viscosity of the IL (or mixed phase system produced in cases in which the interface is thermodynamically unstable). In the water-DEAS system, the evolution of dioxygen was monitored in situ in the aqueous phase by using a Clark-type oxygen sensor. Differences in the structures of bulk and interfacial water are implicated in the activation of water. An analogous series of reactions occurred upon irradiation of solid POM salts in the presence of water vapor.electrochemistry | water oxidation I t has been known for some time that photochemical reduction of polyoxometalate anions (POMs) in molecular solvents may occur in the presence of an efficient electron donor such as 2-propanol or benzyl alcohol (1-6). In recent studies, we have found that photoreduction of tetracyanoquinodimethane (TCNQ) to TCNQ − and ½P 2 W 18 O 62 6− to ½P 2 W 18 O 62 7− or more extensively reduced POMs occurs in "wet" ionic liquids (ILs) where water acts as an electron donor and is photo-oxidized to dioxygen (7,8). Intriguingly, these processes do not occur in wet molecular organic solvents or in neat water itself. The net reactions that describe the photo-irradiation of ½P 2 W 18 O 62 6− in wet 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF 4 ] (Fig. S1) are summarized in Eqs. 1 and 2:However, while ½P 2 W 18 O 62 7− is the detected product it is probable that more extensively reduced POMs are generated (8) as intermediates in the overall water oxidation reaction [Eq. 3]:[3]

Electrochemistry of Polyoxometalates: From Fundamental Aspects to Applications

“…Ionic liquids exhibit specific chemical properties, such as nonvolatility, high conductivity, and chemical interactions, which lead to high yields and/or high selectivities for many chemical reactions. Wells‐Dawson‐type [P 2 W 18 O 62 ] 6− , [S 2 Mo 18 O 62 ] 4− , and [S 2 W 18 O 62 ] 4− did not produce O 2 in water or water‐organic mixed media but did generate O 2 at water‐ionic liquid and water‐diethylether interfaces under irradiation by white light (275–750 nm) or sunlight ,. The ionic liquids (ILs) employed were aprotic ([Bmim]X; Bmim 1‐butyl‐3‐methylimidazolium, X=BF 4 , PF 6 ) and protic (DEAS =diethanolaminehydrogen sulfate; DEAP=diethanolamine hydrogen phosphate).…”

Redox Chemistry of Heteropolyacid Microemulsions

“…Such dual attributes make them particularly attractive as materials for catalytic and sensing functions, wherein the organization of the organic moieties attached to as well as encapsulating the POMs impacts their redox behavior in manners that remain to be completely understood. [1d, 8] This is despite long-standing and contemporary methods to manipulate POMs for electrochemical [9] and photochemical [10] processes and directed syntheses, [11] including the formation of nanoparticles [2b, 12] and nanosheets. [13] The formation of metal-loaded organic phases known as "third phases" is common in the liquid-liquid extraction of metal ions [14] and inorganic acids, [15] including POMs.…”

Removal of Multiple Contaminants from Water by Polyoxometalate Supported Ionic Liquid Phases (POM‐SILPs)

“…[7][8][9] In SILPs,asolid porous or non-porous substrate,for example,silica is used to adsorb an ionic liquid (IL), giving as olid composite whose properties can be tuned by chemical modification of each component. [21] Pioneering studies have used POM-ILs as self-separating epoxidation catalysts, [23] industrial catalysts for large-scale petrochemical processes, [24] catalysts for solar energy conversion, [25] or selfrepairing corrosion protection coatings. Further,SILPs allow the heterogenization of molecular species within as upported IL, giving composites for advanced synthesis, [15,16] catalysis, [10,17] energy storage, [18] and green chemistry.…”