A robust phenazine-containing organic polymer as catalyst for amine oxidative coupling reactions

Novel phenazine-based microporous organic network for selective and sensitive determination of trace sulfonamides in milk samples

BACKGROUND

Sulfonamide (SA) residues in food of animal origin possess a potential threat to human health and environment. However, due to the polar and ionic characteristics and trace level of SAs and the complexity of food matrices, direct measurement of SAs in these samples is still very difficult. Development of efficient sample pretreatment method for sensitive and selective extraction of trace SAs is of great significance and urgently desired. Therefore, rational design and synthesizing advanced and selective extractants is quite important.

RESULTS

In this work, a novel phenazine-based microporous organic network (MON) named TEPM-DP is reasonably synthesized and employed as a packing material for selective solid phase extraction (SPE) and sensitive determination of four typical SAs in milk samples. Phenazine-based monomer with aromatic and heteroaromatic ring and numerous N atoms is chosen to construct TEPM-DP adsorbent to provide π-π, hydrogen bonding, hydrophobic, and electrostatic extraction sites for SAs. The proposed method owns wide linear ranges, low limits of detection, high enrichment factors, and good precisions and recoveries for SAs in complex milk samples. The recoveries of SAs on TEPM-DP are much higher than those of commercial C18 and activated carbon. The extraction mechanisms are also elucidated via FT-IR, XPS, and comparative experiments.

SIGNIFICANCE

This work reports the first example of design and synthesizing phenazine-based MON in SPE via a simple and rapid solvothermal method. The results reveal the great prospects of TEPM-DP for enriching polar and ionic SAs in complex samples and uncover the potency of phenazine-based MON in sample pretreatment, which will promote the development of MON.

Structural Conjugation Tuning in Covalent Organic Frameworks Boosts Charge Transfer and Photocatalysis Performances

Structural conjugation greatly affects the optical and electronic properties of the COF photocatalyst. Herein, we show that 2D hydrazone COFs with either π-extended biphenyl (BPh-COF) or acetylene (AC-COF) frameworks demonstrated distinct charge transfer and photocatalytic performances. The two COFs show good crystallinity and decent porosity as their frameworks are enforced by intra/interlayers hydrogen bonding. However, computational and experimental data reveal that AC-COF managed broader visible-light absorption and narrower optical bandgaps and performed efficient photoinduced charge separation and transfer in comparison with BPh-COF, meaning that the ethynyl skeleton with enhanced planarity better improves the π-conjugation of the whole structure. As a result, AC-COF exhibited an ideal bandgap for rapid oxidative coupling of amines under visible-light irradiation. Furthermore, taking advantage of its better charge transfer properties, AC-COF demonstrated considerable enhanced product conversion and notable functional tolerance for metallaphotocatalytic C-O cross-coupling of a wide range of both aryl bromides and chlorides with alcohols. More importantly, besides being recoverable, AC-COF showcased the previously inaccessible etherification of dihaloarene. This report shows a facile approach for manipulating the structure-activity relationship and paves the way for the development of a COF photocatalyst for solar-to-chemical energy conversion.

3-D nitrogen-doped carbon cage encapsulated ultrasmall MoC nanoparticles for promoting simultaneous ZnIn2S4 photocatalytic hydrogen generation and organic wastewater degradation

Simultaneous redox reactions on photocatalysts make it possible to use wastewater for hydrogen production. The controlled synthesis of ultrasmall metal carbides effectively enhances the photocatalytic efficiency under this system. Here, we report a new type of cocatalyst in which a three-dimensional (3-D) nitrogen-doped carbon cage (NGC) of metal-organic framework derivatives encapsulates ultrasmall MoC nanoparticles (MoC@NGC), promoting simultaneous degradation of organic pollutants and hydrogen production by ZnIn₂S₄ (ZIS). Characterization analyses showed that MoC accelerated the separation of the photogenerated carrier and effectively reduced the overpotential of hydrogen evolution, while NGC promoted the good dispersion of MoC particles and provided sufficient sites. The MoC@NGC/ZIS composite exhibited a high hydrogen (H₂) evolution rate of 1012 µmol g^-1h^-1, which exceed that of ZIS loaded with platinum. In the coupled system, where the electron donor was replaced with rhodamine B (RhB), the mechanism analysis showed that RhB and the as-generated intermediates consumed holes and facilitated hydrogen evolution. In addition, we designed a combined photocatalytic anoxic and oxic sequence process to achieve the recovery of hydrogen energy during the treatment of dye wastewater. This study provides a new way for cooperation between energy development and environmental protection.

Post-Synthetic Modification of Metal-Organic Frameworks Bearing Phenazine Radical Cations for aza-Diels-Alder Reactions

Metal-organic frameworks (MOFs) consisting of organic radicals are of great interest because they have exhibited unique and intriguing optical, electronic, magnetic, and chemo-catalytic properties, and thus have demonstrated great potential applications in optical, electronic, and magnetic devices, and as catalysts. However, the preparation of MOFs bearing stable organic radicals is very challenging because most organic radicals are highly reactive and difficult to incorporate into the framework of MOFs. Herein we reported a post-synthetic modification strategy to prepare a novel MOF containing phenazine radical cations, which was used as heterogeneous catalyst for aza-Diels-Alder reaction. The zinc-based metal-organic framework Zn₂ (PHZ)₂ (dabco) (N) was successfully synthesized from 5,10-di(4-benzoic acid)-5,10-dihydrophenazine (PHZ), triethylene diamine (dabco) with Zn(NO₃ )₂  ⋅ 6H₂ O by solvothermal method. The as-synthesized MOF N was partially oxidized by AgSbF₆ to form MOF R containing ∼10% phenazine radical cation species. The resultant MOF R was found to keep the original crystal type of N and very persistent under ambient conditions. Consequently, MOF R was successfully employed in radical cation-catalyzed aza-Diels-Alder reactions with various imine substrates at room temperature with high reaction conversion. Moreover, heterogeneous catalyst MOF R was reusable up to five times without much loss of catalytic activity, demonstrating its excellent stability and recyclability. Therefore, the post-synthetic modification developed in this work is expected to become a versatile strategy to prepare radical-based MOFs for the application of heterogeneous catalysts in organic synthesis.

β-Diketone boron difluoride dye-functionalized conjugated microporous polymers for efficient aerobic oxidative photocatalysis

Two new conjugated microporous polymers, TPB-B-CMP and TPA-B-CMP, with β-diketone-boron difluoride dye as the key building block were designed and successfully prepared. They were further employed as efficient metal-free heterogeneous photocatalysts.