Covalent Triazine Frameworks (CTFs) are a class of Porous Organic Polymers which attracts continuously growing interest because of their outstanding chemical and physical properties. However, the control of extended porous organic frameworks' structures at the molecular scale for a precise adjustment of their properties has hardly been achieved so far.Here, we present a series of bipyridine-based CTFs synthesized through polycondensation, in which the sequence of specific building blocks is well controlled. The reported synthetic strategy allows to tailor the physicochemical features of the CTF materials, including nitrogen content, apparent specific surface area and opto-electronic properties. Based on a comprehensive analytic investigation, we demonstrate a direct correlation of the CTF bipyridine content with the material features such as specific surface area, bandgap, charge separation and surface wettability with water. The entirety of those parameters dictates the catalytic activity as demonstrated for the photocatalytic hydrogen evolution reaction (HER).The material with the necessary balance between opto-electronic properties and highest hydrophilicity enables HER production rates of up to 7.2 mmol•h -1 •g -1 under visible light irradiation and in the presence of a platinum co-catalyst.Supporting Information. Detailed experimental procedures, materials and instruments used as well as addition material characterization and overview are provided in the Supporting Information.
Photocatalytic selective oxidation of aromatic alcohols by covalent organic frameworks (COFs) is a sustainable strategy to replace present metal‐based heterogeneous catalytic oxidation systems. Covalent triazine‐based frameworks (CTFs), a subgroup of COFs, possess promising properties as efficient catalysts for photocatalytic oxidation. Sulfur‐containing metal‐free CTFs exhibit a good performance in photocatalysis due to their narrowed band gap, and the fast generated photoelectrons/holes separation and transfer. Here, we report the synthesis of thiophene‐based CTFs under mild conditions for photocatalytic oxidation of aromatic alcohols to the corresponding benzaldehydes using pure oxygen as the oxidant. Full conversion and a selectivity as high as 90 % to benzaldehyde were obtained paving the way for a potential application of these metal‐free photocatalysts in fine chemicals synthesis.
The ability to molecularly engineer materials is a powerful tool toward increasingly performing heterogeneous catalysts. Porous organic polymers stand out as photocatalysts due to their high chemical stability, outstanding optoelectronic properties and their easy and tunable syntheses. In photocatalysis, the insertion of photosensitizing π-extended molecules into molecularly well-defined donor-acceptor junctions is supposed to increase the catalytic activity, but yet remain experimentally underdeveloped. This study presents a pyrene-based Covalent Triazine Framework (CTF) synthesized through a polycondensation approach, which was designed to contain a molecularlydefined pyrene-triazine-bipyridine donor-acceptor-acceptor triad as the repetition unit of the CTF. The CTF is an efficient photocatalyst for hydrogen evolution from water reaching a significant production rate of 61.5 mmol H2 /h/g cat . Moreover, the same CTF can easily be used as porous macroligand for an organometallic Rh complex to efficiently catalyze the carbon dioxide photoreduction into formic acid under visible light.
The immobilization and structural analysis of platinum nanoparticles on a nitrogen‐rich, bipyridine‐containing covalent triazine framework (bpyCTF) having structural defects are disclosed by taking advantage of 15N solid‐state nuclear magnetic resonance measurements at natural 15N isotope abundance and X‐ray photoelectron spectroscopic analyses. The photocatalyst (Pt@bpyCTF) with structural defects reduces CO2 to formic acid (FA) at a rate of 152 µmol h−1g−1 and a selectivity higher than 95% over CO and H2 in water under simulated solar light. The presence of amine defects and the immobilization of Pt cause improvement in the photocurrent density and CO2 capture capacity (≈8% by weight) despite the moderate surface area (0.54 cm3 g−1)of the photocatalyst. Theoretical models and density functional theory calculations are employed to investigate the possible CO2 reduction reaction (CO2RR) mechanisms. Considering the exceptional CO2 capture capacity and high FA production using only CO2‐bubbled water, this work highlights the great potential of nitrogen‐rich CTFs for photocatalyzed CO2RRs under green conditions.
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