Self-assembly hybridization of COFs and g-C3N4: Decipher the charge transfer channel for enhanced photocatalytic activity

Unlocking enhanced photocatalytic power: Donor-acceptor synergy in non-metallic g-C3N4 hollow nanospheres

Selecting safe, non-toxic, and non-metallic semiconductor materials that facilitate the degradation of pollutants in water stands out as an optimal approach to combat environmental pollution. Herein, graphitic carbon nitride (g-C3N4)-based hollow nanospheres nonmetallic photocatalyst modified with covalent organic framework materials named TpMA, based on 1, 3, 5-trimethylchloroglucuronide (Tp) and melamine (MA), was successfully synthesized (abbreviated as CNTP). The ordered electron donor-acceptor structure inherent in TpMA contributed to enhancing the transport efficiency of photogenerated carriers in CNTP. The CNTP photocatalysts exhibited excellent performance in degrading rhodamine B and tetracycline in visible light, with optimal degradation rates reached more than 90% in 60 and 80 min, respectively, which were 5.3 and 3.0 times higher than those of pure CNNS. The increased photocatalytic efficiency observed in CNTP composites could be traced back to the covalently connection between the two molecules, forming a π-conjugated system that facilitated the separative efficiency of photogenerated electron-hole pairs and intensified the utilization of visible light. This study provided a new means to design and fabricate highly efficient and environmentally friendly non-metallic photocatalytic materials.

Self-standing perylene diimide covalent organic framework membranes for trace TMA sensing at room temperature

The unprecedented demand for highly selective, real-time monitoring and low-power gas sensors used in food quality control has been driven by the increasing popularity of the Internet of Things (IoT). Herein, the self-standing perylene diimide based covalent organic framework membranes (COFMPDI-THSTZ) were prepared via liquid-liquid interfacial synthesis method. By incorporating the perylene diimide monomer into the COFM through molecular engineering, COFMPDI-THSTZ based sensor demonstrated an outstanding trimethylamine (TMA)-sensing performance at room temperature. Benefited from the TMA-accessible self-standing membrane morphology, π-electron delocalization effect, and extensive surface area with continuous nanochannels, the specific and highly sensitive TMA measurement has been achieved within the range of 0.03-400 ppm, with an exceptional theoretical detection limit as low as 10 ppb. Moreover, the primary internal mechanism of COFMPDI-THSTZ for this efficient TMA detection was investigated through in-situ FT-IR spectra, thereby directly elucidating that the chemisorption interaction of oxygen modulated the depletion layers on sensing material surface, resulting in alterations in sensor resistance upon exposure to the target gas. For practical usage, COFMPDI-THSTZ based sensor exhibited exceptional real-time in-situ sensing capabilities, further confirmed their potential for application in dynamic prediction evaluation of marine fish products and quality monitoring in IoT.

Recent progress in the synthesis and applications of covalent organic framework-based composites

Covalent organic frameworks (COFs) have historically been of interest to researchers in different areas due to their distinctive characteristics, including well-ordered pores, large specific surface area, and structural tunability. In the past few years, as COF synthesis techniques developed, COF-based composites fabricated by integrating COFs and other functional materials including various kinds of metal or metal oxide nanoparticles, ionic liquids, metal-organic frameworks, silica, polymers, enzymes and carbon nanomaterials have emerged as a novel kind of porous hybrid material. Herein, we first provide a thorough summary of advanced strategies for preparing COF-based composites; then, the emerging applications of COF-based composites in diverse fields due to their synergistic effects are systematically highlighted, including analytical chemistry (sensing, extraction, membrane separation, and chromatographic separation) and catalysis. Finally, the current challenges associated with future perspectives of COF-based composites are also briefly discussed to inspire the advancement of more COF-based composites with excellent properties.

Designing of covalent organic framework/2D g-C3N4 heterostructure using a simple method for enhanced photocatalytic hydrogen production

Designing heterostructure photocatalysts is a promising approach for developing highly efficient photocatalysts for hydrogen energy production. In this work, we synthesized a series of a covalent organic framework (COF)/g-C3N4 (CN) heterojunction photocatalysts, denoted as x % COF/CN (in which x indicates the weight % of COF and x  = 5, 10, 20, 30, 40, 50, 90, 95, 100), for hydrogen production. The COF, which is a key component of the photocatalyst, was prepared by assembling benzothiadiazole (BT) and pyrene (Py) derivatives as building blocks. Integrating COF rods into the two-dimensional (2D) layered g-C3N4 structure significantly improved photocatalytic H2 production. The hybrid system (30 % COF/CN) displayed an outstanding hydrogen evolution rate (HER) of 27540 ± 805 μmol g-1h-1, outperforming most known COFs and g-C3N4-based photocatalysts, besides exhibiting stable photocatalytic performance. Moreover, the apparent quantum yield (AQY) was 15.5 ± 0.8 % at 420 nm. Experimental techniques and density functional theory (DFT) calculations demonstrated that the 30 % COF/CN heterostructure has broad visible-light absorption, adequate band energy levels, and the best chemical reactivity descriptors compared to the individual components, resulting in effective carrier separation and excellent performance. Our findings offer a valuable strategy for developing highly efficient and stable heterojunction photocatalysts for visible-light-driven H2 evolution.

Solar-to-H2 O2 Catalyzed by Covalent Organic Frameworks

Benefiting from the excellent structural tunability, robust framework, ultrahigh porosity, and rich active sites, covalent organic frameworks (COFs) are widely recognized as promising photocatalysts in chemical conversions, and emerged in the hydrogen peroxide (H2 O2 ) photosynthesis in 2020. H2 O2 , serving as an environmental-friendly oxidant and a promising liquid fuel, has attracted increasing researchers to explore its potential. Over the past few years, numerous COFs-based photocatalysts are developed with encouraging achievements in H2 O2 production, whereas no comprehensive review articles exist to summarize this specific and significant area. Herein we provide a systematic overview of the advances and challenges of COFs in photocatalytic H2 O2 production. We first introduce the priorities of COFs in H2 O2 photosynthesis. Then, various strategies to improve COFs photocatalytic efficiency are discussed. The perspective and outlook for future advances of COFs in this emerging field are finally offered. This timely review will pave the way for the development of highly efficient COFs photocatalysts for practical production of value-added chemicals not limited to H2 O2 .

Composite materials based on covalent organic frameworks for multiple advanced applications

Covalent organic frameworks (COFs) stand for a class of emerging crystalline porous organic materials, which are ingeniously constructed with organic units through strong covalent bonds. Their excellent design capabilities, and uniform and tunable pore structure make them potential materials for various applications. With the continuous development of synthesis technique and nanoscience, COFs have been successfully combined with a variety of functional materials to form COFs-based composites with superior performance than individual components. This paper offers an overview of the development of different types of COFs-based composites reported so far, with particular focus on the applications of COFs-based composites. Moreover, the challenges and future development prospects of COFs-based composites are presented. We anticipate that the review will provide some inspiration for the further development of COFs-based composites.

Covalent Organic Framework-Semiconductor-Based Heterostructures for Photocatalytic Applications

Photocatalysis is a promising and sustainable technology in the fields of energy conversion/storage and environment purification; however, the utilization of individual component as photocatalyst is generally restricted due to the low catalytic activity deriving from the rapid recombination of photogenerated electrons/holes. Covalent organic framework (COF)-semiconductor-based composite photocatalysts with synergistic effects provide a feasible route to achieve high-performance photocatalytic reactions with more active sites, strong light utilization ability, and high stability. In recent years, significant progress has been made in the rational design and preparation of the COF-semiconductors-based heterostructures for photocatalytic water splitting, carbon dioxide (CO₂ ) reduction, and dye/pollutant degradation. In this Review, the synthetic strategies of COF-semiconductor-based heterostructures are first introduced, which includes the rational design of the morphology, connection modes, and type of heterojunctions. The performance of COF-semiconductor-based heterostructures in different photocatalytic reactions are comprehensively reviewed. The structure-activity relationship and the synergistic effects within the heterostructures are discussed, and the photocatalytic mechanism and the role of COFs during the photocatalytic process are also presented. Finally, an outlook and challenges of realizing COF-semiconductor-based heterostructures with simple synthesis methods, diverse functions, high performance, and well-defined reaction mechanisms are provided.

Effect of Nitrogen Atom Introduction on the Photocatalytic Hydrogen Evolution Activity of Covalent Triazine Frameworks: Experimental and Theoretical Study

The construction of high-performance photocatalyst has always been explored. Covalent organic frameworks (COFs), especially keto-amine-linked COFs, have many advantages, such as adjustable bandgaps, π-π stacking structure, excellent response ability to visible light, high specific surface area, high mobility of carrier carriers, good physical and chemical stability, and so on, showing strong potential applications in photocatalytic solar energy conversion and hydrogen production. Two analogous covalent triazine frameworks (CTFs), T3H-CTF and T3N-CTF, have been synthesized via Schiff-base condensation reactions between 2,4,6-trihydroxybenzene-1,3,5-tricarbalehyde (MOP) and the corresponding triazine-based aromatic amines under solvothermal condition. For T3N-CTF, the peripheral aromatic linker to the central triazine unit was the pyridine unit, instead of the benzene unit in the T3H-CTF unit. T3N-CTF had a hydrogen production rate (HPR) of 6485.05 μmol g^-1  h^-1 , much higher than that of T3H-CTF (2028.06 μmol g^-1  h^-1 ). Accordingly, T3N-CTF had a much higher apparent quantum yield (AQY) of 12.2 % than that of T3H-CTF (4.12 %) at 405 nm. The experimental and theoretical results showed that the extended light absorption range, enlarged surface area, and enhanced separation and transportation efficiencies of charge carriers of T3N-CTF compared with T3H-CTF were uniformly induced by the introduction of peripheral nitrogen atoms into the skeleton of former CTF, which eventually boosted the visible-light induced hydrogen evolution reaction (HER). The work suggests a new method for enhancing the intrinsic HER activity by modulating the electronic features of the conjugated COFs by the introduction of pyridinic N atoms.

Metal-organic frameworks as a good platform for the fabrication of multi-metal nanomaterials: design strategies, electrocatalytic applications and prospective

MOF-derived multi-metal nanomaterials are attracting numerous attentions in widespread applications such as catalysis, sensors, energy storage and conversion, and environmental remediation. Compared to the monometallic counterparts, the presence of foreign metal is expected to bring new physicochemical properties, thus exhibiting synergistic effect for enhanced performance. MOFs have been proved as a good platform for the fabrication of polymetallic nanomaterials with requisite features. Herein, various design strategies related to constructing multi-metallic nanomaterials from MOFs are summarized for the first time, involving metal nodal substitution, seed epitaxial growth, ion-exchange strategy, guest species encapsulation, solution impregnation and combination with extraneous substrate. Afterwards, the recent advances of multi-metallic nanomaterials for electrocatalytic applications, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), are systematically discussed. Finally, a personal outlook on the future trends and challenges are also presented with hope to enlighten deeper understanding and new thoughts for the development of multi-metal nanomaterials from MOFs.

Degradation and detoxification of broad-spectrum antibiotics by small molecular intercalated BiOCl under visible light

In view of the increasing threat of overuse of broad-spectrum antibiotics to water environment, here, a series of small molecular intercalated bismuth oxychloride (SBC-X) composite photocatalysts were successfully constructed by a simple stirring synthesis at room temperature. Among them, SBC-0.5 showed excellent photocatalytic performance against the three target broad-spectrum antibiotics in visible light, which was 3.06 times, 5.93 times and 11.64 times higher than that of monomer for degrading tetracycline, norfloxacin and ciprofloxacin, respectively. Through analysis, it was found that the excellent photocatalytic degradation performance of SBC-0.5 was mainly attributed to the greatly improved specific surface area, which increased to 14 times of monomer, providing a large number of reaction sites for the subsequent photocatalytic degradation. Besides, intercalated molecules as charge transfer bridges between nanosheets greatly accelerated the efficiency of photogenerated charge transfer between layers. Free radical trapping experiments and electron spin resonance indicated that superoxide anion radicals played a major role in the photocatalytic degradation, followed by singlet oxygen. Furthermore, nine potential degradation intermediates were identified, and the toxicity was greatly reduced confirmed by ECOSAR software prediction and soybean seed germination and seeding growth experiment. Our work will provide useful information for the purification of wastewater containing antibiotics.