Aqueous Synthesis of Covalent Organic Frameworks as Photocatalysts for Hydrogen Peroxide Production

Abstract

Covalent organic frameworks (COFs) are crystalline porous polymers with designable structures and properties. Their crystallization typically relies on trial-and-error involving harsh conditions including organic solvents, presenting significant obstacles for rational design and large-scale production. Here, we present a liquid crystal directed synthesis methodology and its implementation for up to gram-scale production of highly crystalline COFs in water and air. It is compatible to monomers with different structures, shape, size, length of side chains, and electron-donating, electron-accepting and heterocyclic substitutions near reactive sites. 17 types of donor-acceptor two-dimensional COFs including 4 types of new ones and a three-Page 1 of 24 https://mc03.manuscriptcentral.com/ccsc CCS Chemistry dimensional COF with a yield of up to 94% were demonstrated, showing great generality of the method. The as-synthesized donor-acceptor COFs are organic semiconductors and contain macropores besides intrinsic mesopores which make them as attractive catalysts. The production of H 2 O 2 under visible light in water was studied and the structure-property relationships were revealed. The production rate reached 4347 μmol h -1 g cat -1 , which is about 467% better than that of the benchmark photocatalyst g-C 3 N 4 . This study will inspire the mild synthesis and scale-up of a wide spectrum of COFs and organic semiconductors as efficient catalysts, promote their structure-property investigation, and boost their applications.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

“…Of note, the metallophthalocyanine-COFs with 5th and 6th period metals (e.g., Pt, Rh, Ag, W, Ta, Mo, Os, and Re) have been predicted based on first-principles density functional theory calculations, 223 but their synthesis still remains blank. 3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyanines under alkaline conditions (Fig. 6).…”

“…218 In addition to the pyrazine-linked COFs, the piperazinelinked phthalocyanine-COF has also been reported by Huang and co-workers. By Buchwald-Hartwig cross-coupling reaction of nickel(II) 2,3,9,10,16,17,23,24-octaaminophthalocyanine and cobalt(II) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluorophthalocyanine under solvothermal conditions (dioxane, triethylamine, 120 1C), the piperazine-linked heterometallic NiPc-NH-CoPcF 8 COF was generated. 219 NiPc-NH-CoPcF 8 crystallized in the tetragonal P4/mmm space group, with AA stacking mode, a pore size of 1.1 nm, and an interlayer spacing of 3.6 Å.…”

“…5 As shown, the boroxinelinked COF-1 features a 2D structure with staggered AB stacking mode, whereas the boronate ester-linked 2D COF-5 adopts an eclipsed AA stacking structure. Since then, COFs with different linkages and topologies have been synthesized one after another by various approaches including solvothermal, [6][7][8][9] ionothermal, 10,11 microwave, 12,13 atmospheric solution, [14][15][16][17][18] mechanochemical, [19][20][21] electrochemical, 22,23 photochemical, 24,25 and other methods. [26][27][28][29] The CURATED-COFs database 30 showed that the query string TITLE-ABS-KEY (''Covalent Organic Framework'') retrieved over 4300 research papers and close to 1000 patents, covering various subject areas such as chemistry, materials science, chemical engineering, and environmental science.…”

Rational design of covalent organic frameworks for efficient photocatalytic hydrogen peroxide production

“…4.6 μmol h −1 ) 26 (Table S2 †). 27 The high photocatalytic activity of N 0 -COF mainly arises from the promoted light-harvesting ability, increased charge carrier dissociation efficiency, and faster charge transfer, closely related to the D-A structure. To unravel the H 2 O 2 production pathway during photocatalysis, we further conducted the reaction in different atmospheres.…”

“…In order to produce H 2 O 2 on scale, new photocatalysts have to be developed that fulfil a range of requirements: namely, light absorption profiles that match the solar spectrum, 18 efficient separation of the photogenerated charge carriers, 19 excellent charge transport to the surface and active sites, and high selectivity for surface reactions. 20 Recent studies have shown that metal-free photocatalysts can be superior to the traditional inorganic materials for this aspect, and typical examples include polymeric carbon nitride, [21][22][23][24] covalent heptazine frameworks, 25 covalent organic frameworks (COFs), 26,27 and others. [28][29][30] With respect to inorganic materials, light absorption of meta-free photocatalyst can be readily optimized by rational design of the molecular structure.…”