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

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.

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.