Phosphotungstic acid ionic liquid for efficient photocatalytic desulfurization: Synthesis, application and mechanism

Abstract

Efficient mass transfer process is a critical factor for regulating catalytic activity in a photocatalytic desulfurization system. Herein, phosphotungstic acid (HPW) active center is successfully composited with a quaternary ammonium phosphotungstate based hexadecyltrimethylammonium chloride ionic liquid (CTAC-HPW) by the ion exchange method for the photocatalytic oxidative desulfurization of dibenzothiophene sulfide. The keggin structure of HPW and highly mass transfer performance organic cations synergistically enhanced the photocatalytic activity towards the effectively convertion of dibenzothiophene (DBT) with the excitation of visible light. The deep desulfurization (<10 mg·kg−1) is attained within 30 min and well stability is demonstrated within 25 cycles. Moreover, the CTAC-HPW photocatalyst projects well selectivity to interference from coexisting compounds such as olefins and aromatic hydrocarbons and universality of dibenzothiophenes, for example, 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). Ultimately, a possible photocatalytic desulfurization mechanism is proposed according to the GC-MS, proving that the final product is the corresponding sulfone. The trapping experiment and ESR analysis confirmed that h+ and •COOH played critical roles in oxidation process. The work offers a practicable strategy for efficiently converting DBT to DBTO2 with added value.