Beatriz Chiyin Ma

Molecular Engineering of Conjugated Polybenzothiadiazoles for Enhanced Hydrogen Production by Photosynthesis

The search for metal-free organic photocatalysts for H2 production from water using visible light remains a key challenge. Reported herein is a molecular structural design of pure organic photocatalysts, derived from conjugated polybenzothiadiazoles, for photocatalytic H2 evolution using visible light. By alternating the substitution position of the electron-withdrawing benzothiadizole unit on the phenyl unit as a comonomer, various polymers with either one- or three-dimensional structures were synthesized and the effect of the molecular structure on their catalytic activity was investigated. Photocatalytic H2 evolution efficiencies up to 116 μmol h(-1) were observed by employing the linear polymer based on a phenyl-benzothiadiazole alternating main chain, with an apparent quantum yield (AQY) of 4.01 % at 420 nm using triethanolamine as the sacrificial agent.

Hollow nanoporous covalent triazine frameworks via acid vapor-assisted solid phase synthesis for enhanced visible light photoactivity

Herein, we report a novel trifluoromethanesulfonic acid vapor-assisted solid phase synthetic method to construct nanoporous covalent triazine frameworks with highly ordered hollow interconnected pores under mild reaction conditions. This unique solid state synthetic route allows not only the avoidance of undesired side reactions caused by traditional high temperature synthesis, but also the maintaining of defined and precise optical and electronic properties of the nonporous triazine frameworks. Promising photocatalytic activity of the polytriazine networks was demonstrated in the photoreduction reaction of 4-nitrophenol into 4-aminophenol under visible light irradiation.

A fixed-bed photoreactor using conjugated nanoporous polymer-coated glass fibers for visible light-promoted continuous photoredox reactions

Here, we report on a fixed-bed photoreactor containing conjugated nanoporous polymer-coated glass fibers for visible light-promoted, heterogeneous photoredox reactions in a continuous flow system. A thin film of nanoporous polybenzothiadiazole with a thickness of ca. 80 nm was fabricated directly on the glass fiber with an effective catalyst content of ca. 3.2 wt%. The photocatalytic dehalogenation reaction of α-bromoacetophenones and the enantioselective α-alkylation of aldehydes were carried out in the fixed-bed photoreactor with comparable efficiencies to the state-of-art transition metal-based photocatalysts.

Enhanced visible light promoted antibacterial efficiency of conjugated microporous polymer nanoparticles via molecular doping

The increase in the resistance of bacteria to antibiotics is one of the main concerns of public health and holds a great demand in the development of new disinfection methods. Photodynamic therapy (PDT) has been considered as a promising alternative approach towards the eradication of bacteria and great attention has been dedicated to the use of non-toxic and pure organic PDT agents. Herein we report the structural design method of a series of conjugated microporous polymer nanoparticles (CMP NPs) as a new class of highly effective photoactive materials for the inactivation of bacteria in water upon visible light exposure. Through molecular doping of electron-withdrawing moieties into electron-donating polymer backbones, enhanced antibacterial properties are demonstrated upon the inactivation of Escherichia coli K-12 and Bacillus subtilis mainly by means of photogeneration of singlet oxygen as the main photogenerated active species. Additionally, the high stability, reusability and disinfection mechanism of the CMP NPs are also described.

Visible light active nanofibrous membrane for antibacterial wound dressing

Chronic wound infections, especially due to the emergence of multidrug resistance in bacteria, require the urgent development of alternative antibacterial therapies. Here, we developed a new class of hydrogel nanofibrous membranes that show visible light-induced disinfection. The presented photocatalytic disinfection is based on the generation of reactive singlet oxygen from a conjugated microporous polymer upon visible light irradiation. Therefore, sustained protection of the wound area can be provided in the presence of visible light. Fabrication of the photoactive wound dressing consists of first synthesizing photoactive conjugated microporous polymer nanoparticles by miniemulsion polymerization and subsequently embedding the nanoparticles in polyvinyl alcohol hydrogel nanofibers by colloid-electrospinning. The fibers were then crosslinked in glutaraldehyde/HCl vapor to be water-insoluble. This nanoparticle-in-nanofiber structure allows for a flexible combination of the properties of the nanoparticles and supporting nanofibers. The disinfecting properties of the membranes were evaluated with the inactivation of Escherichia coli K-12 and Bacillus subtilis as model systems of Gram-negative and Gram-positive bacteria, as well as the inhibition of biofilm growth under irradiation of visible light. Cytotoxicity tests on fibroblast cells revealed a high cytocompatibility of the membranes. Furthermore, the good mechanical properties of the membranes allow for their facile removal after use and prevent the leakage of the embedded nanoparticles into the wound, making the photoactive hydrogel membranes a promising candidate for active wound dressing materials.

Nanostructured Porous Polymers for Metal-Free Photocatalysis

The direct utilization of sunlight, especially the visible light part of solar spectrum as a clean and abundant energy source to activate organic reactions is a great challenge in organic chemistry and materials science. Beside the well-developed metal-based photocatalysts such as inorganic semiconductors or transition metal complexes, pure organic photocatalytic systems have gained much attention currently. Among metal-free photocatalysts, nanostructured and highly porous conjugated polymers are of particular interest due to their flexible tunability of optical and electronic properties. In this chapter, an overview on the development of this new class of functional materials is given. Various structural design methods such as donor–acceptor combination on the molecular level, band positions modification, and p/n character variation are shown, and porosity, morphology control and their impact on the photocatalytic efficiency are also described.