Smart Covalent Organic Framework with Proton-Initiated Switchable Photocatalytic Aerobic Oxidation

Abstract

To conveniently regulate photocatalytic reactions, the design and development of smart photocatalysts, which can realize a series of controllable regulation of their structure, physicochemical properties, photocatalytic activity, and selectivity by simple external stimuli, such as chemical substances, pH, light, electric field, and heat, has aroused keen interest. However, the relevant research is still in its infancy. Herein, a smart imine covalent-organic-framework (COF) photocatalyst HP-n (n represents the pH of COF pretreatment, n = 1∼7) with proton-initiated switchable photocatalytic aerobic oxidation has been prepared. In the structure, the imine units can be reversibly protonated, which leads to the COF skeleton rearrangement from the phenolic to its quinone structure. The corresponding absorption band edge is expanded from 463 nm (HP-7) to 630 nm (HP-1). Meanwhile, the excitation energy transfer, oxygen adsorption, and activation change significantly, endowing HP-n with smartly switchable 1O2 production and interesting proton-initiated efficiency photocatalytic sulfide oxidation with both conversion and sulfoxide selectivity >99%. This work demonstrates a smart imine-COF photocatalyst, which paves the way for the development of smart photocatalysts and reveals the critical roles of protons in the structure–property–activity relationship of COF photocatalysts.

The tail of imidazole regulated the assembly of two robust sandwich-type polyoxotungstate-based open frameworks with efficient visible-white-light-driven catalytic oxidation of sulfides

“…49 Subsequently, O 2 ˙ − combined with the radical cation to further form the methyl phenyl persulfoxide intermediate. 5 Ultimately, the requested MPSO was achieved with the participation of protons derived from the MeOH solvent, and H 2 O was simultaneously generated. 8…”

“…4 Among these photocatalytic organic transformations, the selective aerobic oxidation of sulfides is one of the paramount methods to produce high value-added sulfoxides. 5–8 The traditional methods for the preparation of sulfoxides usually require heavy metal ions or harsh oxidants, which inevitably cause environmental pollution. 9,10 Photocatalytic oxidation of sulfides features the advantages of simple operation, mild reaction conditions, low cost, and environmental friendliness, providing an alternative strategy.…”

Ligand regulation strategy of COF-based photocatalyst for ROS-mediated RAFT polymerization

“…S5a †). 34 In addition, the high transient photocurrent response also illustrates that TAPT-DMTA-COF can achieve effective migration and separation of photogenerated electrons under light irradiation (Fig. S5b †).…”

A critical review on emerging photoactive porous materials for sulfide oxidation and sulfur mustard decontamination

“…12). 36 On the other hand, for the very first time, a chiral metalfree COF (S-DTP-COF-QA) was developed by Dong and his team for the visible-light-assisted enantioselective aerobic oxidation of sulfides in water to produce less toxic sulfoxides with higher enantioselectivity up to 99% (R) of (R)-methylphenyl sulfoxide. Introducing a specific chiral centre in the COF framework promotes the formation of one R-enantiomer of the product compared with the S-enantiomer under photooxidation.…”

“…The minimum energy gap for the PS systems must be greater than 1.61 eV to favour the 3 O 2 → 1 O 2 transformation from the thermodynamic point of view. 36 It has already been noted that, among all other ROS, 1 O 2 is mainly responsible for the decontamination of HDs, 37,38 and the generation of 1 O 2 , particularly with higher concentrations in the reaction medium, is challenging because of its high energy requirement. To address this issue, extensive research is going into the development of porous photocatalysts such as porous organic polymers (POPs), 7 metal-organic frameworks (MOFs), 9 covalent organic frameworks (COFs), 39 covalent triazene frameworks (CTFs), titanium dioxide (TiO 2 ) 40 and graphitic carbon nitride (g-C 3 N 4 ) 41 derived materials for the in situ formation of 1 O 2 followed by HD decontamination.…”