Gemini surfactants and polyoxometalates hybrid assemblies: Spacer controlled oxidative desulfurization activity

Highly efficient, deep desulfurization of model oil containing benzothiophene, dibenzothiophene, or 4,6-dimethyldibenzothiophene has been achieved under mild conditions through the use of gemini surfactant-encapsulated H₃AsMo₁₂O₄₀ complexes (SEPGn: n = 2, 4, 6, 8, 10) as catalysts and H₂O₂ as an oxidant. The unique structure of gemini surfactant provides a delicate chemical environment to facilitate the formation of active peroxo-polyoxometalates species and the penetration of apolar sulfides. The rationally designed amphiphilic structures exhibit enhanced catalytic efficiency in the oxidation of sulfides compared to conventional surfactant-encapsulated POMs utilizing single positively charged surfactants with one or two tails because of the optimal interfacial pathway for both sulfides and H₂O₂. Dibenzothiophene can be completely oxidized to its corresponding sulfone in 25 min under mild conditions. SEPG2 catalyst could be recycled ten times without obvious loss of activity due to its enhanced stability. Therefore, present work paves a new way to design the amphiphilic polyoxometalates via the introduction of unique surfactants through the molecular design concept.