Polyoxometalates Embedded into Covalent Triazine Frameworks Regulating Charge Transfer for Visible-Light-Driven Synthesis of Functionalized Sulfoxides and Detoxification of Mustard Gas Simulants

For environmentally friendly and sustainable development demands, visible-light-driven oxidation of sulfides has become one of the most popular strategies to synthesize functionalized sulfoxides and degrade mustard gas simulants. Herein, three novel polyoxometalate-based covalent triazine frameworks, SiW12-CTF (1), PW12-CTF (2) and PMo12-CTF (3) (CTF = covalent triazine framework), were synthesized via hydrothermal reaction and characterized by infrared spectroscopy, powder X-ray diffraction, XPS spectroscopy and UV-vis DRS, etc. These compounds are excellent photocatalysts for visible-light-driven selective synthesis of various sulfoxides as well as degradation of 2-chloroethyl ethyl sulfide (CEES) illuminated by a 10 W 425 nm LED in an O-2 atmosphere. Oxygen-rich POMs with strong electronegativity modulate the electronic structure and create a built-in electric field in POM-CTFs, which promotes the separation and migration of photogenerated carriers. Meanwhile, encapsulation of various POM guests into the CTF induces different electron transfer behaviors, resulting in different photocatalytic activities. Specifically, SiW12-CTF and PW12-CTF, in visible-light-induced oxidation of methyl phenyl sulfide, obtain sulfoxide yields of 96% and 88% within 2 h, respectively, which is higher than the CTF (68%) and SiW12 (5%). However, PMo12-CTF exhibits inferior photocatalytic properties, and the sulfoxide yield is 35% under the same conditions. The in-depth mechanism reveals that the electron transfer process dominated by the O-2(center dot-) and the energy transfer process induced O-1(2) exist in the photocatalytic system. In addition, SiW12-CTF can be used to catalyze various sulfur-containing compounds and maintains boosted structural stability and catalytic activity after the reaction.