Functionality Modulation Toward Thianthrene-based Metal-Free Electrocatalysts for Water Splitting.

The development of metal-free bifunctional electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) is significant but rarely demonstrated. Porous organic polymers (POPs) with well-defined electroactive functionalities show superior performance in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Precise control of the active sites' local environment requires careful modulation of linkers through the judicious selection of building units. Here, a systematic strategy is introduced for modulating functionality to design and synthesize a series of thianthrene-based bifunctional sp2 C═C bonded POPs with hollow spherical morphologies exhibiting superior electrocatalytic activity. This precise structural tuning allowed to gain insight into the effects of heteroatom incorporation, hydrophilicity, and variations in linker length on electrocatalytic activity. The most efficient bifunctional electrocatalyst THT-PyDAN achieves a current density of 10 mA cm─2 at an overpotential (η10) of ≈65 mV (in 0.5 m H2SO4) and ≈283 mV (in 1 m KOH) for HER and OER, respectively. THT-PyDAN exhibits superior activity to all previously reported metal-free bifunctional electrocatalysts in the literature. Furthermore, these investigations demonstrate that THT-PyDAN maintains its performance even after 36 h of chronoamperometry and 1000 CV cycling. Post-catalytic characterization using FT-IR, XPS, and microscopic imaging techniques underscores the long-term durability of THT-PyDAN.

Morphology Tuning via Linker Modulation: Metal-Free Covalent Organic Nanostructures with Exceptional Chemical Stability for Electrocatalytic Water Splitting.

The development of synthetic routes for the formation of robust porous organic polymers (POPs) with well-defined nanoscale morphology is fundamentally significant for their practical applications. The thermodynamic characteristics that arise from reversible covalent bonding impart intrinsic chemical instability in the polymers, thereby impeding their overall potential. Herein, a unique strategy is reported to overcome the stability issue by designing robust imidazole-linked POPs via tandem reversible/irreversible bond formation. Incorporating inherent rigidity into the secondary building units leads to robust microporous polymeric nanostructures with hollow-spherical morphologies. An in-depth analysis by extensive solid-state NMR (1D and 2D) study on 1H, 13C, and 14N nuclei elucidates the bonding and reveals the high purity of the newly designed imidazole-based POPs. The nitrogen-rich polymeric nanostructures are further used as metal-free electrocatalysts for water splitting. In particular, the rigid POPs show excellent catalytic activity toward the oxygen evolution reaction (OER) with long-term durability. Among them, the most efficient OER electrocatalyst (TAT-TFBE) requires 314 mV of overpotential to drive 10 mA cm-2 current density, demonstrating its superiority over state-of-the-art catalysts (RuO2 and IrO2).

Covalent Organic Frameworks for the Purification of Recombinant Enzymes and Heterogeneous Biocatalysis.

Recombinant enzymes have gained prominence due to their diverse functionalities and specificity and are often a greener alternative in biocatalysis. This context makes purifying recombinant enzymes from host cells and other impurities crucial. The primary goal is to isolate the pure enzyme of interest and ensure its stability under ambient conditions. Covalent organic frameworks (COFs), renowned for their well-ordered structure and permeability, offer a promising approach for purifying histidine-tagged (His-tagged) enzymes. Furthermore, immobilizing enzymes within COFs represents a growing field in heterogeneous biocatalysis. In this study, we have developed a flow-based technology utilizing a nickel-infused covalent organic framework (Ni-TpBpy COF) to combine two distinct processes: the purification of His-tagged enzymes and the immobilization of enzymes simultaneously. Our work primarily focuses on the purification of three His-tagged enzymes ß-glucosidase, cellobiohydrolase, and endoglucanase as well as two proteins with varying molecular weights, namely, green fluorescent protein (27 kDa) and BG Rho (88 kDa). We employed Ni-TpBpy as a column matrix to showcase the versatility of our system. Additionally, we successfully obtained a Ni-TpBpy COF immobilized with enzymes, which can serve as a heterogeneous catalyst for the hydrolysis of p-nitrophenyl-ß-d-glucopyranoside and carboxymethylcellulose. These immobilized enzymes demonstrated catalytic activity comparable to that of their free counterparts, with the added advantages of recyclability and enhanced stability under ambient conditions for an extended period, ranging from 60 to 90 days. This contrasts with the free enzymes, which do not maintain their activity as effectively over time.

Porous covalent organic nanotubes and their assembly in loops and toroids.

Carbon nanotubes, and synthetic organic nanotubes more generally, have in recent decades been widely explored for application in electronic devices, energy storage, catalysis and biosensors. Despite noteworthy progress made in the synthesis of nanotubular architectures with well-defined lengths and diameters, purely covalently bonded organic nanotubes have remained somewhat challenging to prepare. Here we report the synthesis of covalently bonded porous organic nanotubes (CONTs) by Schiff base reaction between a tetratopic amine-functionalized triptycene and a linear dialdehyde. The spatial orientation of the functional groups promotes the growth of the framework in one dimension, and the strong covalent bonds between carbon, nitrogen and oxygen impart the resulting CONTs with high thermal and chemical stability. Upon ultrasonication, the CONTs form intertwined structures that go on to coil and form toroidal superstructures. Computational studies give some insight into the effect of the solvent in this assembly process.