Triazine-based two dimensional porous materials for visible light-mediated oxidation of sulfides to sulfoxides with O2

Donor-acceptor conjugated porous polymers from truxene and triazine: Effect of connecting units on photocatalytic activity for selective oxidation of amines and sulfides

Donor-acceptor (D-A) conjugated polymers have been widely reported as promising photocatalysts for organic conversion. However, achieving excellent photocatalytic performance still relies on the rational design of molecular structures and the careful selection of appropriate building blocks. In this study, we designed two D-A type conjugated porous polymers (CPPs) using 2,7,12-tribromo-5,5,10,10,15,15-hexamethyl-10,15-dihydro-5H-diindeno[1,2-a:1',2'-c]fluorene (Tx) as the donor unit and two 1,3,5-triazine-based derivatives, namely 2,4,6-tri(thiophen-2-yl)-1,3,5-triazine (TTT) and 2,4,6-triphenyl-1,3,5-triazine (TPT), as the acceptor units. The resulting CPPs are named ThTx-CPP and PhTx-CPP, respectively. The research findings emphasize the profound impact of minute structural changes in the triazine peripheral groups on the photocatalytic activity of the polymers. Compared to PhTx-CPP, ThTx-CPP exhibits superior light-harvesting capabilities, narrower bandgaps, and improved efficiency in charge separation. Specifically, ThTx-CPP demonstrates outstanding activity and selectivity in both amine coupling and sulfide oxidation reactions, surpassing PhTx-CPP by a significant margin. Furthermore, the catalyst retains its consistent activity even after five cycles of reuse, showcasing its high stability and excellent reusability.

Donor polarization engineering of conjugated microporous polymers to boost exciton dissociation for photocatalytic degradation of tetracycline

The misuse and inevitable release of antibiotics can cause significant harm to both human health and the environment, and the use of polymeric semiconductors for photodegradation of antibiotics in aqueous environments is one of the most effective strategies to alleviate the current dilemma. Nevertheless, the inherently high exciton binding energy (Eb) and low photogenerated carrier transfer efficiency for most photocatalysts results in unsatisfactory photodegradation performance. Hence, this work proposes a donor polarization strategy to regulate the exciton dissociation of conjugated microporous polymers (CMPs) by minimizing their Eb. Results exhibited that the introduction of the strong donor unit 3,4-ethylenedioxythiophene (EDOT) not only reduces the Eb and effectively promotes exciton dissociation, but also broadens the visible light absorption of CMP. Among them, EdtTz-CMP with the lowest Eb (99 meV) delivered an efficiency of 94.6% in photocatalytic degradation of tetracycline (TC) with in 90 min, significantly higher than those of its analogues. This work provides a viable approach to design CMPs by tuning the intrinsic dipole of the donor for efficient environmental purification.

A triazine-based covalent organic framework decorated with cadmium sulfide for efficient photocatalytic hydrogen evolution from water

Construction of inorganic/organic heterostructures has been proven to be a very promising strategy to design highly efficient photocatalysts for solar driven hydrogen evolution from water. Herein, we report the preparation of a direct Z-scheme heterojunction photocatalyst by in situ growth of cadmium sulfide on a triazine-based covalent organic framework (COF). The triazine based-COF was synthesized by condensation reaction of precursors 1,3,5-tris-(4-formyl-phenyl) triazine (TFPT) and 2,5-bis-(3-hydroxypropoxy) terephthalohydrazide (DHTH), termed as TFPT-DHTH-COF. Widely distributed nitrogen atoms throughout TFPT-DHTH-COF skeletons serve as anchoring sites for strong interfacial interactions with CdS. The CdS/TFPT-DHTH-COF composite showed a hydrogen evolution rate of 15.75 mmol h-1 g-1, which is about 75 times higher than that of TFPT-DHTH-COF (0.21 mmol h-1 g-1) and 3.4 times higher than that of CdS (4.57 mmol h-1 g-1). With the properly staggered band alignment and strong interfacial interaction between TFPT-DHTH-COF and CdS, a Z-scheme charge transfer pathway is achieved. The mechanism has been systematically analyzed by steady state and time-resolved photoluminescence measurements as well as in situ irradiated X-ray photoelectron spectroscopy.

Confined synthesis of conjugated microporous polymers for selective photocatalytic oxidation of amines

Photocatalytic oxidative coupling of amines is considered a mild, efficient, and sustainable strategy for the synthesis of imines. As a versatile organic semiconductor, conjugated microporous polymers (CMPs) are attractive in photocatalysis areas due to the diversity of their polymeric monomers. Herein, we report that in addition to the design of monomers, size-confined polymerization is also a feasible strategy to modulate the structure and photocatalysis properties of CMPs. We adopted dibromopyrazine as polymeric units to prepare pyrazine-involved hollow spherical CMPs (H-PyB) using a template method and successfully performed size-confined polymerization of hollow samples by resizing the templates. Interestingly, the small confinement space induced the formation of CMPs with better conjugate extensibility, resulting in enhanced conductivity, narrowed bandgaps, improved photoelectric performance, etc. As a result, small-sized H-PyB CMPs had superior activity for the photocatalytic oxidation of amines. Particularly, the smallest H-PyB CMPs that we designed in the present work exhibited excellent performance for the photocatalytic coupling oxidation of amines. When using benzylamine as a model substrate, the yield of the corresponding imine reached ∼ 113 mmol·g-1·h-1, accompanied by almost 100 % selectivity. Furthermore, the as-designed confined samples exhibited stable photocatalytic activity as well as good applicability for oxidative coupling of different amines. This work not merely reports a kind of CMP photocatalysts with excellent performance for the imine coupling oxidation but also proposes an alternative strategy for constructing high-performance organic photocatalysts by size-confined synthesis.

Construction of Bimetallic-Anchored Two-Dimensional Nanosheets on COF for Rechargeable Zinc-Air Batteries

The preparation of carbon materials by doping bimetallic oxides into triazine frameworks (COFs) is a promising electrocatalyst with the potential to replace precious metals in energy storage systems. In this experiment, a covalent triazine framework (COF) was synthesized by 1,4-dicyanobenzene (DCB) and zinc chloride, in which the COF and transition metals were used as carbon, nitrogen, cobalt, and iron sources. According to the properties of this COF, the destruction of the catalyst during pyrolysis can be prevented. The enhanced catalytic performance of the catalysts can be seen by testing all of the samples of catalysts in an alkaline medium. The high half-wave potential (E1/2) of 0.86 V is comparable to Pt/C and also shows excellent durability by testing. Zinc-air batteries were assembled using the prepared catalysts, and the batteries were tested for specific capacity (548 mAh g-1) and power density (189 mW cm-2). This work provides a new direction for COF-derived catalysts for carbon materials.

Engineering of Phenylpyridine- and Bipyridine-Based Covalent Organic Frameworks for Photocatalytic Tandem Aerobic Oxidation/Povarov Cyclization

Covalent organic frameworks (COFs) are emerging as a new class of photoactive organic semiconductors, which possess crystalline ordered structures and high surface areas. COFs can be tailor-made toward specific (photocatalytic) applications, and the size and position of their band gaps can be tuned by the choice of building blocks and linkages. However, many types of building blocks are still unexplored as photocatalytic moieties and the scope of reactions photocatalyzed by COFs remains quite limited. In this work, we report the synthesis and application of two bipyridine- or phenylpyridine-based COFs: TpBpyCOF and TpPpyCOF. Due to their good photocatalytic properties, both materials were applied as metal-free photocatalysts for the tandem aerobic oxidation/Povarov cyclization and α-oxidation of N-aryl glycine derivatives, with the bipyridine-based TpBpyCOF exhibiting the highest activity. By expanding the range of reactions that can be photocatalyzed by COFs, this work paves the way toward the more widespread application of COFs as metal-free heterogeneous photocatalysts as a convenient alternative for commonly used homogeneous (metal-based) photocatalysts.