Boosting Exciton Dissociation and Charge Transfer in Triazole-Based Covalent Organic Frameworks by Increasing the Donor Unit from One to Two for the Efficient Photocatalytic Elimination of Emerging Contaminants

Abstract

As novel photocatalysts, covalent organic frameworks (COFs) have potential for water purification. Insufficient exciton dissociation and low charge mobility in COFs yet restricted their photocatalytic activity. Excitonic dissociation and charge transfer in COFs could be optimized via regulating the donor−acceptor (D−A) interactions through adjusting the number of donor units within COFs, yet relevant research is lacking. By integrating the 1,2,4-triazole or bis-1,2,4-triazole unit with quinone, we fabricated COF-DT (with a single donor unit) and COF-DBT (with double donor units) via a facile sonochemical method and used to decontaminate emerging contaminants. Due to the stronger D−A interactions than COF-DT, the exciton binding energy was lower for COF-DBT, facilitating the intermolecular charge transfer process. The degradation kinetics of tetracycline (model contaminant) by COF-DBT (k = (12.21 ± 1.29) × 10 −2 min −1 ) was higher than that by COF-DT (k = (5.11 ± 0.59) × 10 −2 min −1 ) under visible-light irradiation. COF-DBT could efficiently photodegrade tetracycline under complex water chemistry conditions and four real water samples. Moreover, six other emerging contaminants, both Gram-negative and Gram-positive strains, could also be effectively eliminated by COF-DBT. High tetracycline degradation performance achieved in a continuous-flow system and in five reused cycles in both laboratory and outdoor experiments with sunlight irradiation showed the stability and the potential for the practical application of COF-DBT.

Floatable Cu2(OH)PO4/rGO Aerogel for Full Spectrum Driven Photocatalytic Degradation of Organic Pollutants

“…This is because the S atoms of MB molecules exhibit a positive state which is prone to be electrophilic or attacked by radicals. 49 According to the radical detection results, DFT calculation, and degradation pathway analysis, the degradation mechanism of the CHP/rGO aerogels was raised as illustrated in Figure 7. The 0D CHP can be activated by the solar light to produce electron−hole pairs.…”

“…At the same time, the CS and CN bonds in the center ring of MB break due to the electron rearrangement, leading to the product P3 with m / z = 316. This is because the S atoms of MB molecules exhibit a positive state which is prone to be electrophilic or attacked by radicals . Similarly, the electron rearrangement transformation to break the CS and CN bonds occurs when the deaminated MB ( P2 ) transform to the product P4 ( m / z = 200).…”

Ionization-triggered low exciton binding energy in covalent organic frameworks for efficient photocatalytic synthesis of benzimidazole

“…One popular strategy is to integrate the strong electron donor (D) and acceptor (A) units into COFs. 25–30 This design philosophy is rooted on the principle that the disparity in electron affinities between D and A units can create a strong dipole moment, which helps to construct a built-in electric field and promote the dissociation of excitons. 31–33 In a recent report, Wang et al put forward another strategy that involves introducing ionic moieties into the skeleton of COFs.…”

Thiolation-Annulation-Assisted Synthesis of Fully Conjugated Benzothiophene-Linked Covalent Organic Framework toward Strongly Enhanced Photoelectrocatalytic Uranium Extraction

“…The DFT calculation showed the U atoms that coordinated to N atoms from the triazine exhibited the highest binding energy of −2.07 eV, with a bond distance of 2.45 Å (Figure b). In the molecular orbital distribution, for 2DCOF-S, the HOMO was located on the thiophene unit, whereas the LUMO was mainly delocalized across the triazine nucleus; , however, the delocalization of electrons in v-2DCOF-Br is not significant (Figure c). Meanwhile, the calculated HOMO–LUMO energy gaps are consistent with the experimental data.…”