Charge-Switchable Integrated Nanocatalysts for Substrate-Selective Degradation in Advanced Oxidation Processes

Substrate-selective catalysis is highly desirable in pharmaceutical and petrochemical industries. To pursue the goal, basically, catalysts should have the ability to recognize and screen their substrates by shape, size, charge, or hydrophobicity/hydrophilicity matching. In this contribution, we design a new type of integrated nanocatalyst, which shows selective catalytic activities toward substrates carrying different charges. More significantly, such “smart” catalysts possess switchable surface charges under different pH environments, and thus, the catalytic performance with controllable substrate selectivity can be achieved. These integrated nanocatalysts encompass three basic components: (i) metal nanoparticles serving as catalytically active centers for chemical reactions (i.e., 4 nm Pt); (ii) charge-switchable polymer shell (i.e., polydopamine layer, PDA) working as dual-function membrane (i.e., screening substrates and protecting metal catalysts underneath); and (iii) carrier material providing large reaction area/space (i.e., hollow mesoporous support, such as Mn, Fe, Co, Ni silicates) for immobilization of metal catalysts. Importantly, in a typical advanced oxidation process (AOP), the exemplary nanocatalyst Pt/MnSi@PDA shows selective degradation of cationic dyes (e.g., rhodamine 6G, methylene blue) at pH values higher than the isoelectric point (IEP = 3.1), whereas anionic dyes (e.g., Congo red, methyl orange, thymol blue) were degraded preferably at pH values lower than the IEP.