Thiadiazole-Based Covalent Organic Frameworks with a Donor-Acceptor Structure: Modulating Intermolecular Charge Transfer for Efficient Photocatalytic Degradation of Typical Emerging Contaminants

Applications of COFs and Their Derivatives in Photocatalysis for Energy Production and Harmful Substance Degradation

Photocatalytic technology has attracted considerable attention in recent years due to its significant potential in environmental protection and energy conversion. Covalent organic frameworks (COFs), a novel class of porous materials, demonstrate remarkable photocatalytic performance owing to their high surface areas, tunable pore sizes, permanent porosities, and customizable functionalities. This review provides a comprehensive overview of the application of COFs in photocatalysis. In energy-related applications, COFs effectively catalyze hydrogen (H2) and hydrogen peroxide (H2O2) generation, and uranium (U(VI)) extraction from seawater, thereby offering new avenues for sustainable energy generation. In environmental remediation, COFs exploit photocatalytic properties to reduce carbon dioxide (CO2) emissions and degrade antibiotics in wastewater, thereby contributing to greenhouse gas mitigation and the enhancement of water quality. The review further explores the underlying mechanisms of COFs in photocatalytic H2 and H2O2 generation, U(VI) reduction, CO2 reduction, and antibiotic degradation, emphasizing the pivotal role of the COF structure in governing photocatalytic performance. Nevertheless, challenges persist concerning the stability, catalytic efficiency, and scalability of COFs. Future research should prioritize optimizing synthesis methods, tuning structural features, and enhancing the stability and performance of COFs to facilitate their practical applications. These advancements are crucial for promoting the widespread adoption of photocatalytic technologies in the energy and environmental sectors.

Enhancing Spin-Orbit coupling in covalent organic polymers to facilitate intersystem crossing for uranium (VI) photoreduction

Photocatalytic removal and recovery of uranium from wastewater by heightening reactive oxygen species, especially superoxide radical (O2•-), is of great significance for radioactive contamination remediation. However, limited by the sluggish intersystem crossing (ISC) rates, the generation of triplet excited states is inefficient in polymeric semiconductors, thereby lower the level of O2•-. Herein, we first furnish a heteroatomic nitrogen-embedded strategy to enhance spin-orbit coupling (SOC) capacity of covalent organic polymers (COPs) by decorating benzo[c][1,2,5]thiadiazole-based COPs with the benzene, triazine, and tris([1,2,4]triazolo)[4,3-a:4',3'-c:4'',3''-e][1,3,5]triazine (TTT) cores, resulting in SOC value of 0.03, 0.10 and 0.41 cm-1, respectively. Thus, the TTT-functionalized COPs exhibited the highest ISC rates and the longest triplet excited state with a lifetime of 30.5 μs, dramatically facilitating the photoreduction of U(VI) (95.0 %, 1.5 h). This work validates that enhancing SOC ability is an effective strategy to improve ISC rate, which contributed to the rational design of polymeric semiconductors with intersystem crossing behaviors.

Manipulating Charge Dynamics in Carbon Nitride by Carbon Dot Doping for Efficient Photocatalysis

Graphitic carbon nitride (g-C3N4), a prominent metal-free semiconductor photocatalyst, faces limitations due to its high exciton binding energy. While significant efforts have been focused on optimizing charge-carrier processes, the interplay of exciton and free carrier in this system have received less attention. Herein, this density-functional theory (DFT) and time-dependent DFT calculations demonstrate that carbon dot-functionalized g-C3N4 (g-C3N4/CD), synthesized via a facile thermal polymerization, shifts the excited state from localized to charge transfer characteristics. The g-C3N4/CD exhibits reduced exciton binding energy from 41.0 to 24.6 meV, as shown by temperature-dependent photoluminescence spectroscopy. Particularly, g-C3N4/CD-10 (10 wt.% CD solution in precursors) achieves a 3-fold increase in the photodegradation rate (k = 0.020 min⁻¹) of an emerging environmental pollutant, levofloxacin (LEV), under 10 W LED light. Enhanced photocatalytic performances correlate with optimized band structure and efficient charge transport, as confirmed by photophysical and photoelectrochemical analyses. Although the excited state lifetime in g-C3N4/CD is slightly reduced compared to pristine g-C3N4, photocatalytic activity remains unaffected, underscoring the critical role of charge excited state in enhancing photocatalytic efficiency. This work offers insights onto the potential of manipulating charge transfer excited state dynamics for improved g-C3N4-based photocatalysis in environmental applications.

Regulating the Combinations of Donor and Acceptor Units via DFT Calculations for Photocatalysts with Efficient Electron-Hole Separation and Transfer Dynamics

Donor-acceptor (D-A)-type conjugated microporous polymers (CMPs) are considered promising photocatalytic materials due to their easily tunable structures and optical properties. However, the rational combination of D and A units to design D-A-type CMPs with efficient electron-hole separation and transfer dynamics remains an ongoing challenge. Herein, we employed Density Functional Theory (DFT) calculations to evaluate 16 potential D-A pair combinations and their respective electron-hole separation and transfer dynamics. These combinations consisted of M-salens (M = Zn, Cu, Co, and Ni) as bromine-containing monomers and four alkyne-based monomers: 2,4,6-tris(4-ethynylphenyl)-1,3,5-triazine (TEPT), 4,4″-diethyl-5'-(4-ethynylphenyl)-1, 1':3',1″-terphenyl (TEPB), tris(4-ethynylphenyl) amine (TEPA), and 3,7-diethyl-10-(4-ethynylphenyl)-10H-phenothiazine (TEPP). Eight D-A pair combinations were obtained via DFT calculation, with their electron-hole separation and transfer dynamics ranking as follows: Zn-salen-TEPA > Zn-salen-TEPP > Zn-salen-TEPT > Cu-salen-TEPP > Cu-salen-TEPA > Cu-salen-TEPT > Ni-salen-TEPT > Co-salen-TEPT. Based on these results, three D-A pairs exhibiting the highest electron-hole separation and transfer dynamics were selected for the synthesis of corresponding CMPs and subsequent photoelectric characterization. Experimental enhancements aligned closely with the DFT predictions. Notably, the photocatalytic aerobic oxidative amidation of diverse aldehydes and amines catalyzed by Zn-salen-TEPA under blue LED irradiation achieved a yield of up to 97%, which surpassed the performance of most reported works. This work offers novel perspectives on the rational design of D-A-type CMPs endowed with highly efficient photocatalytic activity.

Advances in the development of N-glycopeptide enrichment materials based on hydrophilic interaction chromatography

Protein glycosylation is one of the most important post-translational modifications, implicated in the development of various diseases, including neurodegenerative diseases, diabetes, and cancers. However, the low content of glycoproteins in biological samples, the diversity and heterogeneity of glycan structures, and insensitive detection methods make glycosylation analysis challenging. As a result, efficient enrichment of glycopeptides from complex samples is a critical step. Efficient enrichment technology can increase the abundance of intact N-glycopeptides in complex biological samples, thereby improving the sensitivity and coverage of glycosylation analysis, which is of great significance for the accurate identification of biomarkers and the development of glycopeptide-based drugs. Among various separation methods for N-glycopeptides, hydrophilic interaction chromatography has received increasing attention, and a variety of enrichment materials have been developed. This article classifies and describes the relevant hydrophilic interaction chromatography materials and provides a comprehensive review of their applications in N-glycopeptide enrichment regarding selectivity, sensitivity, and enrichment performance. Future development trends of ideal glycopeptide enrichment materials are also discussed.

In-Situ Growth of Metallocluster Inside Heterometal-Organic Cage to Switch Electron Transfer for Targeted CO2 Photoreduction

Construction of metal-organic cages (MOCs) with internal modifications is a promising avenue to build enzyme-like cavities and unlocking the mystery of highly catalytic activity and selectivity of enzymes. However, current interests are mainly focused on single-metal-node cages, little achievement has been expended to metallocluster-based architectures, and the in situ endogenous generation of metal clusters. Herein, based on the hard-soft-acids-bases (HSAB), the metallocluster-based heterometallic MOC (Cu3VMOP) constructed of [Cu3OPz3]+ and [V6O6(OCH3)9(SO4)(CO2)3]2- clusters was obtained by one-pot method. In addition, Cu4I4 was generated in situ in the cage to form Cu4I4@Cu3VMOP by the coordination-driven hierarchical self-assembly strategy. As catalysts for CO2 reduction, Cu3VMOP produces HCOOH and CH3COOH as the main reduction product with yield of CH3COOH up to 0.9 mmol g-1, ranking among the highest value of reported materials, whereas Cu4I4@Cu3VMOP exhibited targeted CO2-to-HCOOH conversion with 100 % formic acid selectivity and the yield outperforms that of Cu3VMOP by 5 fold. Theoretical calculations and femtosecond time-resolved transient absorption reveal that endogenous Cu4I4 not only regulates orbital arrangements and enhances localized electron states to generate a long-lived charge-separated state, but also raises *CO coupling energy barrier, resulting in the targeted conversion of CO2 to formic acid.

In situ self-cleaning removal of emerging organic contaminants with covalent organic framework armed with arylbiguanide

An in situ self-cleaning covalent organic framework featuring arylbiguanide arms (Aryl-BIG-COF) was first developed to remove emerging organic pollutants such as propranolol (PRO) from water. The main breakthroughs addressed the scarcity of functional active sites, the impracticality of ex situ regeneration, and the rapid recombination of electronhole pairs in the application of COFs. Owing to the directional capture ability and electronic structure regulation of the arylbiguanide arms, the adsorption capacity and photocatalytic degradation rate of the newly synthesized COF increased by nearly four and seven times, respectively. Its self-cleaning ability, driven by the photocatalytic regeneration of active sites, enabled in situ removal of PRO and sustained over 90 % removal efficiency after six cycles. Moreover, it demonstrated broad applicability for removing PRO and other emerging pollutants, such as bisphenol A (BPA), tetracycline (TC), and norfloxacin (NOR), across various water matrices with less residual toxicity. The coexisting organic matter and ions in natural water promoted the removal of PRO. The enhancement mechanism involved arylbiguanide arms narrowing the band gap and inducing local charge polarization, thereby increasing the separation efficiency of electronhole pairs. This work provides significant insights into the structural design and practical applications of COFs for purifying water.

Urea/Thiourea Imine Linkages Provide Accessible Holes in Flexible Covalent Organic Frameworks and Dominates Self-Adaptivity and Exciton Dissociation

Unraveling the robust self-adaptivity and minimal energy-dissipation of soft reticular materials for environmental catalysis presents a compelling yet unexplored avenue. Herein, a top-down strategy, tailoring from the unique linkage basis, flexibility degree, skeleton electronics to trace-guest adaptability, is proposed to fill the understanding gap between micro-soft covalent organic frameworks (COFs) and photocatalytic performance. The thio(urea)-basis-dominated linkage within benzotrithiophene-based COFs induce the framework contraction/swelling (intralayer micro-flexibility) in response to tetrahydrofuran or water. Adaptability of micro-flexible thiourea-COF with pore hydrophilicity not only contributes to the favorable mass transfer, but also enhances the accessible redox active sites, culminating in nearly 100 % removal of micropollutant with low-energy dissipation in wastewater. The incorporating urea/thiourea into imine linkage facilitates polarization reduction and exciton dissociation within skeleton wall, inducing strong localization for holes. This transformation facilitates interchain charge transport and unbalanced distribution conducive to oxidative holes-mediated micropollutant decomposition.

H2O2 Triggering Electron-Directed Transfer of Emerging Contaminants over Asymmetric Nano Zinc Oxide Surfaces for Water Self-Purification Expansion

Slow mass transfer processes between inert emerging contaminants (ECs) and dissolved oxygen (DO) limit natural water self-purification; thus, excessive energy consumption is necessary to achieve ECs removal, which has become a longstanding global challenge. Here, we propose an innovative water self-purification expansion strategy by constructing asymmetric surfaces that could modulate trace H2O2 as trigger rather than oxidant to bridge a channel between inert ECs and natural dissolved oxygen, achieved through a dual-reaction-center (DRC) catalyst consisting of Cu/Co lattice-substituted ZnO nanorods in situ (CCZO-NRs). During water purification, the bond lengths of emerging contaminants (ECs) adsorbed on the asymmetric surface were stretched, and this stretching was further enhanced by H2O2 mediation, resulting in a significant reduction of bond-breaking energy barriers. As a result, the consumption rate of H2O2 was reduced by two-thirds in the presence of ECs. In contrast, the removal of ECs was increased approximately 95-fold mediated by trace H2O2. It exhibits the highest catalytic performance with the lowest dosage of H2O2 among numerous similarly reported systems. This discovery is significant for the development of water self-purification expansion technologies.

Precise control of photogenerated carrier behavior of zinc oxide through band reconstruction to enhance photocatalytic treatment of dye wastewater

In the field of photocatalytic treatment of dye wastewater, zinc oxide (ZnO) is a typical semiconductor photocatalyst, but it has some disadvantages such as wide band gap, low carrier yield and easy recombination. In this study, Cr-ZnO/N-CQDs catalyst was synthesised using the strategy of p-type doping and construction of Z-scheme heterojunction. The results showed that the removal rate of Cr-ZnO/N-CQDs for MB dye was 97.42 %, which was 70.56 % higher than that of ZnO, and was still 92.16 % after 5 cycles, and the TOC removal rate of methylene blue wastewater was 88.60 %. The reason for the enhanced photocatalytic activity of Cr-ZnO/N-CQDs is that the π* electron (e-) in the N-CQDs interact with the 3d orbitals of Cr-ZnO, so that e- is more easily transferred from the valence band of Cr-ZnO to the conduction band of N-CQDs. The band gap of p-type Cr-ZnO is narrowed, which makes its photogenerated carrier yield increase, hole concentration raise, and the adsorption capacity of H2O molecules reduce by 1.04 eV. The density functional theory calculation shows that the maximum Gibbs free energy of Cr-ZnO for the production of hydroxyl radical is 0.05 eV lower than that of ZnO. This study lays theoretical and practical foundation for the photocatalytic treatment of dye wastewater with ZnO.

Nickel single atoms anchored on a bipyridine-based covalent organic framework: boosting active sites for photodegradation of acetaminophen

It remains crucial but challenging to construct single-atom photocatalysts based on covalent organic framework (COF) materials in a simple, fast, and controllable manner and to clarify their structure-efficacy relationship. Here, a single-atom photocatalyst (Ni-TpBpy) featuring atomically dispersed Ni sites with a high loading content and a specific tetra-coordinated N2-Ni-Cl2 environment in a bipyridine-based COF was for the first time rapidly synthesized using dielectric barrier discharge (DBD) plasma and a wet chemical method. Visible light-driven Ni-TpBpy can achieve 97.8% photodegradation efficiency of acetaminophen at 0.177 min-1 in 30 min, outperforming other advanced photocatalysts. Experimental studies and density-functional theory (DFT) calculation clarified the role of well-dispersed Ni active sites in enhanced photodegradation, which not only narrowed the bandgap, facilitating carrier separation and migration, but also promoted the generation of reactive superoxide radicals. This study represents the first use of single-atom Ni-TpBpy in the efficient photocatalytic degradation of emerging pollutants with remarkable stability and universality, bringing new insights into the application of COF-based single-atom materials in environmental remediation.

Photocatalytic applications of covalent organic frameworks: synthesis, characterization, and utility

Photocatalysis has emerged as an energy efficient and safe method to perform organic transformations, and many semiconductors have been studied for use as photocatalysts. Covalent organic frameworks (COFs) are an established class of crystalline, porous materials constructed from organic units that are easily tunable. COFs importantly display semiconductor properties and respectable photoelectric behaviour, making them a strong prospect as photocatalysts. In this review, we summarize the design, synthetic methods, and characterization techniques for COFs. Strategies to boost photocatalytic performance are also discussed. Then the applications of COFs as photocatalysts in a variety of reactions are detailed. Finally, a summary, challenges, and future opportunities for the development of COFs as efficient photocatalysts are entailed.

Flexible Hybrid Membrane with Synergistic Exciton Dynamics for Excessive 280 h of Durably Piezo-Photocatalytic H2O-to-H2 Conversion

Solar-driven H2O-to-H2 conversion is a feasible artificial photoconversion technology for clean energy production. However, low photon utilization efficiency has become a major obstacle limiting the practical application of this technology. Herein, a metal atomic replacement (Sb→Ni) is conducted to disintegrate bulk Sb2S3 nanorods and synchronously grow the NiS nanolayers, and a flower-like Sb2S3-NiS nanocomposite with high BET specific surface area and synergistic exciton dynamics is constructed for simulated solar (SSL)-driven H2O-to-H2 conversion. The optimal Sb2S3-NiS nanocomposite is compounded with polyvinylidene fluoride (PVDF) to prepare a flexible PVDF/Sb2S3-NiS (PSN) hybrid membrane with stable structure and excellent recyclability via an electrospinning method. Due to the synergistically interacted organic-inorganic interface and high porosity, it is conducive to the exposure of effective active sites, exciton conduction and mass transfer and exchange, thereby an outstanding alkaline (Ph = 13.0) H2O-to-H2 conversion activity with a 0.06% of solar-to-hydrogen efficiency and over 280 h (70 cycles) of durable recycling is achieved under the collaborative drives of SSL and weak ultrasound (40 Hz). This study raises a state-of-the-art membrane material for solar-driven panel reaction technology.

Donor-acceptor type COFs with multiple fluorine groups as electron storage units to promote antimicrobial performance

The novel donor-acceptor (D-A) type covalent organic frameworks TATF-COF and TATP-COF, with multiple fluorine groups as electron storage units, were successfully constructed to achieve efficient charge transfer and photocatalytic activity for antibacterial photocatalytic therapy. Fluorine, the most electronegative element, was utilized as an electron-withdrawing substituent for the acceptor, which could unite the donor unit together and efficiently improve the charge transfer from the donor to acceptor. The unique D-A structures of TATF-COF and TATP-COF ensure that they have narrow band gaps, strong photocurrent responses, long fluorescence lifetimes, and good capacity to generate reactive oxygen species (ROS) to realize good antibacterial activity. Meanwhile, the inclusion of multiple hydrophilic fluorine groups means that TATF-COF and TATP-COF are highly water dispersible, which is also beneficial in terms of promoting the generation of adequate quantities of ROS. Hence, in view of their excellent photoelectric properties and good water dispersibility, further investigations were performed, and excellent antibacterial activities in vitro against both gram-negative and gram-positive bacteria were demonstrated for TATF-COF and TATP-COF. In addition, we also showed that they can function as effective antibacterial dental materials.

Interlayer synergistic reaction of radical precursors for ultraefficient 1O2 generation via quinone-based covalent organic framework

Singlet oxygen (1O2) is important in the environmental remediation field, however, its efficient production has been severely hindered by the ultrafast self-quenching of the as-generated radical precursors in the Fenton-like reactions. Herein, we elaborately designed lamellar anthraquinone-based covalent organic frameworks (DAQ-COF) with sequential localization of the active sites (C═O) at molecular levels for visible-light-assisted peroxymonosulfate (PMS) activation. Theoretical and experimental results revealed that the radical precursors (SO5·-) were formed in the nearby layers with the migration distance less than 0.34 nm, via PMS donating electrons to the photogenerated holes. This interlayer synergistic effect eventually led to ultraefficient 1O2 production (14.8 μM s-1), which is 12 times that of the highest reported catalyst. As an outcome, DAQ-COF enabled the complete degradation of bisphenol A in 5 min with PMS under natural sunlight irradiation. This interlayer synergistic concept represents an innovative and effective strategy to increase the utilization efficiency of ultrashort-lived radical precursors, providing inspirations for subtle structural construction of Fenton-like catalysts.

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.

Cyano-deficient g-C3N4 for round-the-clock photocatalytic degradation of tetracycline: Mechanism and application prospect evaluation

Without light at night, the system for photocatalytic degradation of refractory organic pollutants in aquatic environments based on free radicals will fall into a dormant state. Hence, a round-the-clock photocatalyst (CCN@SMSED) was prepared by in situ growth of cyanide-deficient g-C3N4 on the surface of Sr2MgSi2O7:Eu2+,Dy3+ through a simple calcination method. The CCN@SMSED exhibits an outstanding oxidative degradation ability for refractory tetracycline (TC) in water under both light and dark conditions, which is attributed to the synergistic effect of free radical (•O2- and •OH) and non-radical (h+ and 1O2). Electrochemical analyses further indicate that direct electron transfer (DET) is also one of the reasons for the efficient degradation of TC. Remarkably, the continuous working time of the round-the-clock photocatalyst in a dark environment was estimated for the first time (about 2.5 h in this system). The degradation pathways of TC mainly include demethylation, ring opening, deamination and dehydration, and the growth of Staphylococcus aureus shows that the process is biosafe. More importantly, CCN@SMSED holds significant promise for practical application due to its low energy consumption and suitability for removing TC from a variety of complex water bodies. This work provides an energy consumption reference for the practical application of round-the-clock photocatalytic degradation of organic pollutants.

Iron single atoms anchored on ultrathin carbon nitride photocatalyst for visible light-driven water decontamination

Graphitic carbon nitride has gained considerable attention as a visible-light photocatalyst. However, its photocatalytic efficiency is restricted by its limited capacity for absorbing visible light and swift recombination of charge carriers. To overcome this bottleneck, we fabricated an atomic Fe-dispersed ultrathin carbon nitride (Fe-UTCN) photocatalyst via one-step thermal polymerization. Fe-UTCN showed high efficiency in the photodegradation of acetaminophen (APAP), achieving > 90 % elimination within 60-min visible light irradiation. The anchoring of Fe atoms improved the photocatalytic activity of UTCN by narrowing the bandgap from 2.50 eV to 2.33 eV and suppressing radiative recombination. Calculations by density functional theory revealed that the Fe-N4 sites (adsorption energy of - 3.10 eV) were preferred over the UTCN sites (adsorption energy of - 0.18 eV) for the adsorption of oxygen and the subsequent formation of O2•-, the dominant reactive species in the degradation of APAP. Notably, the Fe-UTCN catalyst exhibited good stability after five successive runs and was applicable to complex water matrices. Therefore, Fe-UTCN, a noble-metal-free photocatalyst, is a promising candidate for visible light-driven water decontamination.

Synthesis of borocarbonitride nanosheets from biomass for enhanced charge separation and hydrogen production

Borocarbonitride (BCN) materials have shown significant potential as photocatalysts for hydrogen production. However, traditional bulk BCN exhibits only moderate photocatalytic activity. In this study, we introduce an environmentally conscious and sustainable strategy utilizing biomass-derived carbon sources to synthesize BCN nanosheets. The hydrogen evolution efficiency of BCN-A nanosheets (110 μmol h-1 g-1) exceeds that of bulk BCN photocatalysts (12 μmol h-1 g-1) by 9.1 times, mainly due to the increased surface area (205 m2g-1) and the presence of numerous active sites with enhanced charge separation capabilities. Notably, the biomass-derived BCN nanosheets offer key advantages such as sustainability, cost-effectiveness, and reduced carbon footprint during hydrogen production. These findings highlight the potential of biomass-based BCN nanomaterials to facilitate a greener and more efficient route to hydrogen energy, contributing to the global transition towards renewable energy solutions.

New breakthrough in rapid degradation of lignin derivative compounds · A novel high stable and reusable green organic photocatalyst

The pulp and paper sectors are thriving yet pose significant environmental threats to water bodies, mainly due to the substantial release of pollutants. Lignin-derived compounds are among the most problematic of these contaminants. To address this issue, we present our initial results on utilizing organic semiconductor photocatalysis under visible light for treating lignin-derived compounds. Our investigation has been centered around creating a green and cost-effective organic semiconductor photocatalyst. This catalyst is designed using a structure of bagasse cellulose spheres to support PM6 (poly[(2,6-(4,8-bis(5-(2-ethylhexyl)-4-fluorothiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene))-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c']dithiophene-4,8-dione))]: MeIC (3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-cyclopentane-1,3-dione[c]-1-methyl-thiophe))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']-dithiophene)). This photocatalyst demonstrates remarkable efficiency, achieving over 91 % degradation of lignin-derived compounds. The superior photocatalytic performance is attributed to three main factors: (1) The ability of PM6 to broaden MeIC's absorption range from 300 to 800 nm, allowing for effective utilization of visible light; (2) the synergistic interaction between PM6 and MeIC, which ensures compatible energy levels and a vast, evenly spread surface area, promoting charge mobility and extensive donor/acceptor interfaces. This synergy significantly enhances the generation and transport of carriers, resulting in a high production of free radicals that accelerate the decomposition of organic materials; (3) The deployment of PM6:MeIC on biomass-based carriers increases the interaction surface with the organic substances. Notably, PM6: MeIC showcases outstanding durability, with its degradation efficiency remaining between 84 % and 91 % across 100 cycles. This study presents a promising approach for designing advanced photocatalysts aimed at degrading common pollutants in papermaking wastewater.

Phenanthroline-functionalized donor-acceptor covalent organic frameworks as photo-responsive nanozymes for visual colorimetric detection of isoniazid

Development of metal-free nanozymes has raised concern for their extensive applications in photocatalysis and sensing fields. As novel metal-free nanomaterials, covalent organic frameworks (COFs) have engendered intense interest in the construction of nanozymes due to their structural controllability and molecular functionality. The formation of the molecular arrangement by embedding orderly donor-acceptors (D-A) linked in the framework topology to modulate material properties for highly efficient enzyme mimicking activity is of importance but challenging. Here, a strong D-A type of COF was designed and synthesized by integrating electron donor units (pyrene) and electron acceptor units (phenanthroline), named Py-PD COF. Using experiments and theoretical calculations, the introduction of a phenanthroline ring endowed the Py-PD COF with a narrowed band gap, and efficient charge transfer and separation. Further, the Py-PD COF exhibited a superior light-responsive oxidase-mimicking characteristic under visible light irradiation, which could catalyze the oxidation of 3,3',5,5-tetramethylbenzidine (TMB) and give the corresponding evolution of color. The nanoenzymatic activity of the Py-PD COF was light-regulated, which offers a fascinating advantage because of its high efficiency and spatial controllability. Based on previously mentioned characteristics, an "on-off" sensing platform for the colorimetric analysis of isoniazid (INH) could be constructed with a good linear relationship (2-100 μM) and a low limit of detection (1.26 μM). This research shows that not only is Py-PD COF an environmentally friendly compound for the colorimetric detection of INH, but it is also capable of providing the interesting D-A type COF-based material for designing an excellent nanozyme.

Humic substances mediated superior photochemical pollutant conversion on defective TiO2 in environmentally relevant matrices: The key roles of oxygen vacancy in surface interactions, oxidant activation and radical generation

Ubiquitous humic substances usually exhibit strong interfering effects on target pollutant removal in advanced water purification. This work aims to develop a photochemical conversion system on the nonstoichiometric TiO2 for pollutant removal in environmentally relevant matrices. In this synergistic reaction system, the redox-reactive humic substances and defective oxygen vacancies can serve as the organic electron transfer mediator and the key surface reactive sites, respectively. This system achieves a superior pollutant degradation in real surface water at low oxidant concentrations. Reactive oxygen vacancies on the TiO2 surface and sub-surface are of considerable interest for this photochemical reaction system. By engineering defective oxygen vacancies on high-energy {001} polar facet, the surface and electronic interactions between tailored TiO2 and humic substances are greatly strengthened for the promoted electron transfer and oxidant activation. Rendered by the strong surface affinity and molecular activation, defective oxygen vacancies thermodynamically and dynamically promote reactive chain reactions for free radical formation, including the selective O2 reduction to ·O2- and the H2O2 activation to ·OH. Our findings take new insights into environmental geochemistry, and provide an effective strategy to in-situ boost the humic substances-mediated water purification without secondary pollution. ENVIRONMENTAL IMPLICATION: Humic substances are widely distributed in aquatic environment, thus playing important roles in environmental geochemistry. For example, humic substances can achieve good surface adsorption through electrostatic adsorption, ligand exchange and electronic interactions with typical TiO2 to form reactive ligand-metal charge transfer complexes for pollutant degradation. Inspired by the unique properties of surface and sub-surface oxygen vacancies, the defective TiO2 was designed to refine the humic substances-mediated photochemical reactions. A superior reactivity was measured for pollutant degradation. Our findings provide an effective strategy to boost naturally photochemical decontamination in environmentally relevant matrices.

Organic Donor-Acceptor Systems for Photocatalysis

Organic semiconductor materials are considered to be promising photocatalysts due to their excellent light absorption by chromophores, easy molecular structure tuning, and solution-processable properties. In particular, donor-acceptor (D-A) type organic photocatalytic materials synthesized by introducing D and A units intra- or intermolecularly, have made great progress in photocatalytic studies. More and more studies have demonstrated that the D-A type organic photocatalytic materials combine effective carrier separation, tunable bandgap, and sensitive optoelectronic response, and are considered to be an effective strategy for enhancing light absorption, improving exciton dissociation, and optimizing carrier transport. This review provides a thorough overview of D-A strategies aimed at optimizing the photocatalytic performance of organic semiconductors. Initially, essential methods for modifying organic photocatalytic materials, such as interface engineering, crystal engineering, and interaction modulation, are briefly discussed. Subsequently, the review delves into various organic photocatalytic materials based on intramolecular and intermolecular D-A interactions, encompassing small molecules, conjugated polymers, crystalline polymers, supramolecules, and organic heterojunctions. Meanwhile, the energy band structures, exciton dynamics, and redox-active sites of D-A type organic photocatalytic materials under different bonding modes are discussed. Finally, the review highlights the advanced applications of organic photocatalystsand outlines prospective challenges and opportunities.

Construction of Thiadiazole-Bridged sp2-Carbon-Conjugated Covalent Organic Frameworks with Diminished Excitation Binding Energy Toward Superior Photocatalysis

Sp2-carbon-conjugated covalent organic frameworks (sp2c-COFs) have emerged as promising platforms for phototo-chemical energy conversion due to their tailorable optoelectronic properties, in-plane π-conjugations, and robust structures. However, the development of sp2c-COFs in photocatalysis is still highly hindered by their limited linkage chemistry. Herein, we report a novel thiadiazole-bridged sp2c-COF (sp2c-COF-ST) synthesized by thiadiazole-mediated aldol-type polycondensation. The resultant sp2c-COF-ST demonstrates high chemical stability under strong acids and bases (12 M HCl or 12 M NaOH). The electro-deficient thiadiazole together with fully conjugated and planar skeleton endows sp2c-COF-ST with superior photoelectrochemical performance and charge-carrier separation and migration ability. As a result, when employed as a photocathode, sp2c-COF-ST exhibits a significant photocurrent up to ∼14.5 μA cm-2 at 0.3 V vs reversible hydrogen electrode (RHE) under visible-light irradiation (>420 nm), which is much higher than those analogous COFs with partial imine linkages (mix-COF-SNT ∼ 9.5 μA cm-2) and full imine linkages (imi-COF-SNNT ∼ 4.9 μA cm-2), emphasizing the importance of the structure-property relationships. Further temperature-dependent photoluminescence spectra and density functional theory calculations demonstrate that the sp2c-COF-ST has smaller exciton binding energy as well as effective mass in comparison to mix-COF-SNT and imi-COF-SNNT, which suggests that the sp2c-conjugated skeleton enhances the exciton dissociation and carrier migration under light irradiation. This work highlights the design and preparation of thiadiazole-bridged sp2c-COFs with promising photocatalytic performance.

Calix[4]arene-Derived 2D Covalent Organic Framework with an Electron Donor-Acceptor Structure: A Visible-Light-Driven Photocatalyst

The calixarenes are ideal building blocks for constructing photocatalytic covalent organic frameworks (COFs), owing to their electron-rich and bowl-shaped π cavities that endow them with electron-donating and adsorption properties. However, the synthesis and structural confirmation of COFs based on calixarenes are still challenging due to their structural flexibility and conformational diversity. In this study, a calix[4]arene-derived 2D COF is synthesized using 5,11,17,23-tetrakis(p-formyl)-25,26,27,28-tetrahydroxycalix[4]arene (CHO-C4A) as the electron donor and 4,7-bis(4-aminophenyl)-2,1,3-benzothiadiazole (BTD) as the acceptor. The powder X-ray diffraction data and theoretical simulation of crystal structure indicate that COF-C4A-BTD exhibits high crystallinity and features a non-interpenetrating undulating 2D layered structure with AA-stacking. The density functional theory theoretical calculation, transient-state photocurrent tests, and electrochemical impedance spectroscopy confirm the intramolecular charge transfer behavior of COF-C4A-BTD with a donor-acceptor structure, leading to its superior visible-light-driven photocatalytic activity. COF-C4A-BTD exhibits a narrow band gap of 1.99 eV and a conduction band energy of -0.37 V versus normal hydrogen electrode. The appropriate energy band structure can facilitate the participation of ·O2- and h+ . COF-C4A-BTD demonstrates high efficacy in removing organic pollutants, such as bisphenol A, rhodamine B, and methylene blue, with removal rates of 66%, 85%, and 99% respectively.

Novel heterogeneous Fenton catalysts for promoting carbon iron electron transfer by one-step hydrothermal synthesization

Carbon materials play a crucial role in promoting the Fe(III)/Fe(II) redox cycle in heterogeneous Fenton reactions. However, the electron transfer efficiency between carbon and iron is typically low. In this study, we prepared a novel heterogeneous Fenton catalyst, humboldtine/hydrothermal carbon (Hum/HTC), using a one-step hydrothermal method and achieved about 100 % reduction in Fe(III) during synthesis. Moreover, the HTC continuously provided electrons to promote Fe(II) regeneration during the Fenton reaction. Electron paramagnetic resonance (EPR) and quenching experiments showed that Hum/HTC completely oxidized As(III) to As(V) via free radical and non-free radical pathways. Attenuated total reflectance Fourier-transform infrared (ATR-FTIR) and two-dimensional correlation spectroscopy (2D-COS) analyses revealed that monodentate mononuclear (MM) and bidentate binuclear (BB) structures were the dominant bonding methods for As(V) immobilization. 40 %Hum/HTC exhibited a maximum As(III) adsorption capacity of 167 mg/g, which was higher than that of most reported adsorbents. This study provides a novel strategy for the efficient reduction of Fe(III) during catalyst synthesis and demonstrates that HTC can continuously accelerate Fe(II) regeneration in heterogeneous Fenton reactions.

Exploration of the Performance and Mechanism of Uranium Adsorption by a Covalent Organic Framework Possessing the Thiazole Structure

This study prepared an active 2-D covalent organic skeleton (HDU-27) with a network structure, high crystallinity, considerable specific surface area, excellent pore structure, and excellent stability. Kinetic studies manifested that HDU-27 could effectively capture uranium as monolayer chemisorption within a very short kinetic equilibrium time (10 min). In particular, the temperature significantly and positively impacted the uranium adsorption performance of HDU-27. At 298, 313, and 328 K, the adsorption capacity reached 269.2, 488.8, and 576.2 mg g-1, respectively, suggesting the potential to treat high-temperature industrial wastewater containing uranium. HDU-27 had high stability and recoverability with an adsorption efficiency of 98.5% after five adsorption-desorption cycles. According to X-ray photoelectron spectroscopy, the mechanism of interaction between U(VI) and HDU-27 was mainly the chelation of UO22+ by the N atom in the thiazole structure and the strong coordination of the O atom in the keto structure with UO22+. More excitingly, HDU-27 could chemically reduce soluble U(VI) to insoluble U(IV) and release binding sites for the adsorption of additional U(VI). In conclusion, HDU-27 has outstanding potential for uranium adsorption from industrial wastewater containing uranium.

Twistedly hydrophobic basis with suitable aromatic metrics in covalent organic networks govern micropollutant decontamination

The pre-designable structure and unique architectures of covalent organic frameworks (COFs) render them attractive as active and porous medium for water crisis. However, the effect of functional basis with different metrics on the regulation of interfacial behavior in advanced oxidation decontamination remains a significant challenge. In this study, we pre-design and fabricate different molecular interfaces by creating ordered π skeletons, incorporating different pore sizes, and engineering hydrophilic or hydrophobic channels. These synergically break through the adsorption energy barrier and promote inner-surface renewal, achieving a high removal rate for typical antibiotic contaminants (like levofloxacin) by BTT-DATP-COF, compared with BTT-DADP-COF and BTT-DAB-COF. The experimental and theoretical calculations reveal that such functional basis engineering enable the hole-driven levofloxacin oxidation at the interface of BTT fragments to occur, accompanying with electron-mediated oxygen reduction on terphenyl motif to active radicals, endowing it facilitate the balanced extraction of holes and electrons.

Site Engineering of Covalent Organic Frameworks for Regulating Peroxymonosulfate Activation to Generate Singlet Oxygen with 100 % Selectivity

Singlet oxygen (1 O2 ) is an excellent reactive oxygen species (ROSs) for the selective conversion of organic matter, especially in advanced oxidation processes (AOPs). However, due to the huge dilemma in synthesizing single-site type catalysts, the control and regulation of 1 O2 generation in AOPs is still challenging and the underlying mechanism remains largely obscure. Here, taking advantage of the well-defined and flexibly tunable sites of covalent organic frameworks (COFs), we report the first achievement in precisely regulating ROSs generation in peroxymonosulfate (PMS)-based AOPs by site engineering of COFs. Remarkably, COFs with bipyridine units (BPY-COFs) facilitate PMS activation via a nonradical pathway with 100 % 1 O2 , whereas biphenyl-based COFs (BPD-COFs) with almost identical structures activate PMS to produce radicals (⋅OH and SO4 .- ). The BPY-COFs/PMS system delivers boosted performance for selective degradation of target pollutants from water, which is ca. 9.4 times that of its BPD-COFs counterpart, surpassing most reported PMS-based AOPs systems. Mechanism analysis indicated that highly electronegative pyridine-N atoms on BPY-COFs provide extra sites to adsorb the terminal H atoms of PMS, resulting in simultaneous adsorption of O and H atoms of PMS on one pyridine ring, which facilitates the cleavage of its S-O bond to generate 1 O2 .

Enhanced and synergistic catalytic activation by photoexcitation driven S-scheme heterojunction hydrogel interface electric field

The regulation of heterogeneous material properties to enhance the peroxymonosulfate (PMS) activation to degrade emerging organic pollutants remains a challenge. To solve this problem, we synthesize S-scheme heterojunction PBA/MoS2@chitosan hydrogel to achieve photoexcitation synergistic PMS activation. The constructed heterojunction photoexcited carriers undergo redox conversion with PMS through S-scheme transfer pathway driven by the directional interface electric field. Multiple synergistic pathways greatly enhance the reactive oxygen species generation, leading to a significant increase in doxycycline degradation rate. Meanwhile, the 3D polymer chain spatial structure of chitosan hydrogel is conducive to rapid PMS capture and electron transport in advanced oxidation process, reducing the use of transition metal activator and limiting the leaching of metal ions. There is reason to believe that the synergistic activation of PMS by S-scheme heterojunction regulated by photoexcitation will provide a new perspective for future material design and research on enhancing heterologous catalysis oxidation process.

Porous cyclopentadiene unit-incorporated graphitic carbon nitride nanosheets for efficient photocatalytic oxidation of recalcitrant organic micropollutants in wastewater

For the purpose of searching for efficient photocatalysts to deal with recalcitrant organic micropollutants in wastewater, here an in-situ supramolecule self-assembly-thermal polymerization strategy is developed to prepare a series of porous cyclopentadiene (CPD) unit-incorporated g-C3N4 ultrathin nanosheets (CCPD-g-C3N4). The CCPD-g-C3N4 demonstrate CPD unit doping level-dependent and remarkably enhanced visible-light photocatalytic oxidation efficiency towards two organic micropollutants, acetaminophen and methylparaben, in which the optimized CCPD-g-C3N4-2 shows 6.1 and 3.5 times higher acetaminophen and methylparaben degradation rate than bulk g-C3N4; moreover, CCPD-g-C3N4-2 is still robust and efficient in the treatment of five mixed organic micropollutants in pharmaceutical wastewater, and the satisfactory micropollutant removal efficiency is obtained in a wide pH window and the presence of high concentrations of inorganic anions and cations as well as dissolved organic matters. Theoretical calculation combined with experimental test reveal that CCPD-g-C3N4 can significantly reduce ecological risk of the target pollutant after the photocatalytic degradation reaction. Such enhanced photocatalytic oxidation efficiency is dominated by the accelerated charge carrier separation dynamics and extended visible-light response region due to the incorporation of CPD units, which finally lead to the generation of abundant reactive oxygen species to degrade and mineralize target micropollutants efficiently.

Dissolved organic matter promotes photocatalytic degradation of refractory organic pollutants in water by forming hydrogen bonding with photocatalyst

Removing refractory organic pollutants in real water using photocatalysis is a great challenge because coexisting dissolved organic matter (DOM) can quench photogenerated holes and thus prevent generation of reactive oxygen species (ROS). Herein, for the first time, we develop a hydrogen bonding strategy to avoid the scavenging of photoexcited holes, by which DOM even promotes photocatalytic degradation of refractory organic pollutants. Theoretical calculations combined with experimental studies reveal the formation of hydrogen bonding between DOM and a hydroxylated S-scheme heterojunction photocatalyst (Mo-Se/OHNT) consisting of hydroxylated nitrogen doped TiO2 (OHNT) and molybdenum doped selenium (Mo-Se). The hydrogen bonding is demonstrated to change the interaction between DOM and Mo-Se/OHNT from DOM-Ti (IV) to a hydrogen bonded complexation through the hydroxyl/amine groups of DOM and the OHNT in Mo-Se/OHNT. The formed hydrogen network can stabilize excited-state of DOM and inject its electron to the conduction band rather than the valence band of the OHNT upon light irradiation, realizing the key to preventing hole quenching. The electron-hole separation in Mo-Se/OHNT is consequently improved for generating more ROS to be involved in removing refractory organic pollutants. Moreover, this hydrogen bonding strategy is generalized to nitrogen doped zinc oxide and graphitic carbon nitride and applies to real water. Our findings provide a new insight into handling the DOM problem for photocatalytic technology towards water and wastewater treatment.

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

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.