Beyond C3N4 π-conjugated metal-free polymeric semiconductors for photocatalytic chemical transformations

Post-synthetic modifications (PSM) on metal-organic frameworks (MOFs) for visible-light-initiated photocatalysis

The utilization of green and sustainable solar energy via photocatalysis is regarded as a promising strategy to tackle the ever-increasing energy shortage and environmental deterioration. In addition to traditional semiconductor-based photocatalysts, metal-organic frameworks (MOFs), a class of crystalline micro-mesoporous hybrid materials constructed from metal or metal nodes interconnected with multi-dentate organic linkers, are emerging as a new type of photocatalytic material. Post-synthetic modifications (PSM) on MOFs, in which chemical transformations or exchanges are made on pre-synthesized MOF materials, are found to be a powerful strategy for fabricating photoactive MOFs based on already existing MOFs. In this frontier article, different PSM strategies for the development of photoactive MOFs, including coordination on unsaturated metal sites, metalation on open coordinated sites, covalent modifications on ligands, ligand exchange, metal exchange and cavity encapsulation, have been summarized. Our views on the challenges and the direction in developing photocatalytic MOFs by PSM are also addressed. We hope that this frontier article can provide some guidance for rational designing of highly efficient MOF-based photocatalysts via PSM strategies and to stimulate more research interest to be devoted to this promising yet largely unexplored field.

Charge Transfer from Donor to Acceptor in Conjugated Microporous Polymer for Enhanced Photosensitization

Photosensitization associated with light absorption and energy/electron-transfer represents the central processes for photosynthesis. However, it's still a challenge to develop a heavy-atom-free (HAF) strategy to improve the sensitizing ability of polymeric photosensitizers. Herein, we propose a new protocol to significantly improve the photosensitization by decorating mother conjugated microporous polymer (CMP-1) with polycyclic aromatic hydrocarbons (PAHs), resulting in a series of CMPs (CMP-2-4). Systematic study reveals that covalent modification with PAHs can transfer charge to Bodipy in CMP to further facilitate both intersystem crossing and electron-hole separation, which can dramatically boost energy-/electron-transfer reactions. Remarkably, CMP-2 as a representative CMP can efficiently drive the photosynthesis of methyl phenyl sulfoxide with 92 % yield, substantially higher than that of CMP-1 (32 %). Experiments and theory calculations demonstrate the structure-property-activity relationship of these CMPs, opening a new horizon for developing HAF heterogeneous photosensitizers with highly efficient sensitizing activity by rational structure regulation at a molecular level.

Visible-light-driven photocatalysis of carbon dioxide and organic pollutants by MFeO2 (M = Li, Na, or K)

In recent years, lithium-containing ceramic materials have attracted considerable research attention as high-temperature adsorbents of carbon dioxide. The recycling of electrode materials from spent lithium-ion batteries for use as photocatalysts in recovering CO₂ and degrading organic pollutants is worthy of exploration. Solid, magnetic ferrite-containing photocatalysts are easily separated from reaction solutions by using magnetic devices. Solid catalysts (e.g., LiFeO₂, LiFe₅O₈, NaFeO₂, and K₂Fe₂O₄) were prepared through the calcination of Fe₂O₃ and M₂CO₃. CO₂ was photoreduced and crystal violet (CV) and 2-hydroxybenzoic acid (2-HBA) were photodegraded under visible light irradiation. The optimized K₂Fe₂O₄ photocatalyst increased the rate of photocatalytic conversion from CO₂ to methane at 20.9 µmol g^-1 h^-1. The catalytic efficiency indicated that the optimized reaction rate constants of CV with LiFeO₂, NaFeO₂, and K₂Fe₂O₄ were 2.98 × 10^-1, 5.32 × 10^-1, and 4.36 × 10^-1 h^-1, respectively. The quenching effect achieved through the use of various scavengers and the electron paramagnetic resonance in CV degradation revealed the substantial contribution of the reactive superoxide anion radical O₂^- and the minor roles of h⁺ and the OH radical. Its usefulness in the synthesis of solid-base catalyst MFeO₂ is promising for environmental control and relevant applications, particularly in solar energy manufacturing.

Polyimide with enhanced π stacking for efficient visible-light-driven photocatalysis

Polyimide photocatalysts with enhanced π stacking are prepared through the solvothermal condensation of pyromellitic dianhydride and N,N-dialkylmelamine, exhibiting extended light absorption ranges and efficient visible-light-driven photocatalysis.