科研论文

2022
Ding P, Ji H, Li P, Liu Q, Wu Y, Guo M, Zhou Z, Gao S, Xu W, Liu W, et al. Visible-light degradation of antibiotics catalyzed by titania/zirconia/graphitic carbon nitride ternary nanocomposites: a combined experimental and theoretical study. Applied Catalysis B: Environmental [Internet]. 2022;300:120633. 访问链接Abstract
Development of low-cost, high-performance photocatalysts for the effective degradation of antibiotics in wastewater is critical for environmental remediation. In this work, titanium dioxide/zirconium dioxide/graphitic carbon nitride (TiO2/ZrO2/g-C3N4) ternary composites are fabricated via a facile hydrothermal procedure, and photocatalytically active towards the degradation of berberine hydrochloride under visible light illumination. The performance is found to increase with the Ti:Zr atomic ratio in the nanocomposites, and obviously enhanced in comparison to that of the binary TiO2/g-C3N4 counterpart, due to the formation of type I/II heterojunctions that help separate the photogenerated electron-hole pairs and produce superoxide and hydroxy radicals. The mechanistic pathways are unraveled by a deliberate integration of liquid chromatography-mass spectrometry measurements with theoretical calculations of the condensed Fukui index. Furthermore, the ecotoxicity of the reaction intermediates is examined by utilizing the Toxicity Estimation Software Tool (TEST) and quantitative structure activity relationship calculations (QSAR).
Wu Y, Ji H, Liu Q, Sun Z, Li P, Ding P, Guo M, Yi X, Xu W, Wang C-C, et al. Visible light photocatalytic degradation of sulfanilamide enhanced by Mo doping of BiOBr nanoflowers. Journal of Hazardous Materials [Internet]. 2022;424:127563. 访问链接Abstract
Design of high-efficiency visible light photocatalysts is critical in the degradation of antibiotic pollutants in water, a key step towards environmental remediation. In the present study, Mo-doped BiOBr nanocomposites are prepared hydrothermally at different feed ratios, and display remarkable visible light photocatalytic activity towards the degradation of sulfanilamide, a common antibacterial drug. Among the series, the sample with 2% Mo dopants exhibits the best photocatalytic activity, with a performance 2.3 times better that of undoped BiOBr. This is attributed to Mo doping that narrows the band gap of BiOBr and enhances absorption in the visible region. Additional contributions arise from the unique materials morphology, where the highly exposed (102) crystal planes enrich the photocatalytic active sites, and facilitate the adsorption of sulfanilamide molecules and their eventual attack by free radicals. The reaction mechanism and pathways are then unraveled based on theoretical calculations of the Fukui index and liquid chromatography/mass spectrometry measurements of the reaction intermediates and products. Results from this study indicate that deliberate structural engineering based on heteroatom doping and morphological control may serve as an effective strategy in the design of highly active photocatalysts towards antibiotic degradation.
Dang C, Jiang H, Zheng M, Li Z, Liu W, Fu J. Chapter 17 The Different Toxicity and Mechanism of Titanium Dioxide (TiO2) and Titanate Nanotubes (TNTs) on Escherichia coli. In: Emerging Nanotechnologies for Water Treatment. The Royal Society of Chemistry; 2022. pp. 507-522. 访问链接Abstract
As typical titanium nanomaterials, TiO2 and titanate nanotubes (TNTs) are extensively used. Although the toxicity of nano-TiO2 under solar light has been investigated, it is not enough to evaluate its environmental toxicity because the dark environment is also important in the natural environment. In addition, little is known about the environmental toxicity and mechanism of the emerging TNTs. In this study, we investigated the toxicity of nano-TiO2 and TNTs based on the inactivation performance on Escherichia coli cells under simulated solar light and in a dark chamber, and their toxicity mechanisms were explored on a subcellular level. The inactivation performance was: nano-TiO2-solar (100.0%) > TNTs-solar (62.7%) > TNTs-dark (36.6%) > TiO2-dark (0.5%). The excellent inactivation performance of nano-TiO2 under solar light is caused by the large amount of active free radicals attacking cell organelles until peroxidation and death, which is due to the strong photocatalytic properties. The lower inactivation ability of nano-TiO2 in the dark was due to the absence of radicals and its accessible physical morphology. For TNTs, the inactivation ability under solar light is derived from a combination of its weak photocatalytic performance and morphological effects, and TNTs in a dark environment can only attack cells via physical piercing.
Liu W, Ji H, Chen L, Duan J. Chapter 7 Application of Titanate Nanotubes for Water Treatment. In: Emerging Nanotechnologies for Water Treatment. The Royal Society of Chemistry; 2022. pp. 185-227. 访问链接Abstract
Titanate nanotubes (TNTs), derived from TiO2 nanoparticles through hydrothermal treatment, have been attracting intensive research interests in recent years. Unlike the precursor TiO2 nanoparticles that have high photocatalytic activity under ultraviolet light, TNTs exhibit multi-layered and tubular structures. In addition, TNTs are composed of corrugated ribbons of edge-sharing [TiO6] octahedrons as the skeleton and H+/Na+ are located in the interlayers. Thus, TNTs usually have uniform tubular microstructures, large specific surface area, abundant functional groups (–ONa/–OH), good ion-exchange properties, high solution stability and high photoelectric quantum conversion effects. The specific physicochemical properties of TNTs indicate their great application potential in water and wastewater treatment. This chapter provides an overview of the latest research on the environmental applications and implications of TNTs. Conventional methods for the synthesis and characterization of TNTs are also summarized. TNTs and modified TNTs used as adsorbents, photocatalysts and catalysts for peroxymonosulfate/peroxydisulfate activation are systematically discussed. The environmental behaviors of aggregation and sedimentation of TNTs in water are also described.
Liu Y, Wang C-C, Liu W. Emerging Nanotechnologies for Water Treatment. (Liu Y, Wang C-C, Liu W). The Royal Society of Chemistry; 2022 pp. P001-542. 访问链接
Cai Z, Huang Y, Ji H, Liu W, Fu J, Sun X. Type-II surface heterojunction of bismuth-rich Bi4O5Br2 on nitrogen-rich g-C3N5 nanosheets for efficient photocatalytic degradation of antibiotics. Separation and Purification Technology [Internet]. 2022;280:119772. 访问链接Abstract
A novel g-C3N5/Bi4O5Br2 surface heterojunction was developed via in-situ growth of Bi-rich Bi4O5Br2 on g-C3N5 nanosheets. The optimal composite achieved 3.6- and 16.0- times of sulfathiazole (STZ) degradation activity when compared with pristine Bi4O5Br2 and g-C3N5. The interlayer stacking morphology and extra nitrogen in triazine units significantly narrowed the conduction band of g-C3N5, which greatly promoted its visible utilization; while the bismuth-rich property of Bi4O5Br2 prolonged the excited charge carrier lifetime. Both photoluminescence and electrochemical impedance spectroscopy analysis demonstrated that the type-II surface heterojunction (g-C3N5/Bi4O5Br2) offered remarkable charge transfer and separation due to the matched energy band structure. The STZ degradation mechanism and pathways were proposed based on experiments and density functional theory calculation, and the contribution of reactive species for STZ degradation followed the order of O2∙- > h+ > OH. Moreover, the toxicity evolution of STZ was evaluated, suggesting that sufficient mineralization is required to ensure safe discharge. The Box-Behnken experimental design methodology study revealed that g-C3N5/Bi4O5Br2 exhibited high reactivity for antibiotics degradation under different water matrix. This study suggested that g-C3N5/Bi4O5Br2 has great application potential for cost-effective remediation of persistent organic contaminants by using solar light.
Zong Y, Zhang H, Zhang X, Liu W, Xu L, Wu D. High-valent cobalt-oxo species triggers hydroxyl radical for collaborative environmental decontamination. Applied Catalysis B: Environmental [Internet]. 2022;300:120722. 访问链接Abstract
The overlooked role of high-valent cobalt-oxo species (Co(IV)) in the Co(II)/peroxymonosulfate (PMS) process was uncovered recently using methyl phenyl sulfoxide (PMSO) as the probe. Herein, we further interestingly found that Co(IV) could trigger hydroxyl radical (•OH) formation, resulting in the oxidized products distribution of PMSO heavily relied on the relative concentration of PMSO. More significantly, the generation of a series of 18O-labeled hydroxylated products (i.e., hydroxylated methyl phenyl sulfone, nitrobenzene and 4-nitrobenzoic acid) in H218O conclusively verified that •OH was triggered by Co(IV) species. Density functional theory calculation demonstrated that Co(IV) initiated •OH formation via oxo ligand protonation-induced valence tautomerization. Moreover, the oxidative contribution of Co(IV) and •OH on organic degradation was specifically dependent on the type and concentration of the substrate. This study provided deeper insights into the evolution pathway of •OH mediated by Co(IV) species and enriched the understandings on the collaborative oxidation mechanism in Co(IV)-involved processes.
Wang Y, Song Y, Li N, Liu W, Yan B, Yu Y, Liang L, Chen G, Hou L’an, Wang S. Tunable active sites on biogas digestate derived biochar for sulfanilamide degradation by peroxymonosulfate activation. Journal of Hazardous Materials [Internet]. 2022;421:126794. 访问链接Abstract
Conversion of digestate into biochar-based catalysts is an effective strategy for disposal and resource utilization. The active sites on biochar correlated with reactive species formation in peroxymonosulfate (PMS) system directly. Clarifying the structure-performance relationship of digestate derived biochar in PMS system was essential for decomposition of contaminants. Herein, dairy manure digestate derived biochar (DMDB) was prepared for PMS activation and sulfamethoxazole (SMX) degradation. The higher pyrolysis temperature could promote effective sites generation. Especially, the DMDB-800 catalyst exhibited excellent performance for PMS activation, achieving 90.2% degradation of SMX within 60 min. Based on the correlation analysis between log (k) values and active sites, defects, graphite N and CO were identified as dominant sites for PMS activation. The 1O2 oxidation and surface electron transfer were critical routes for SMX degradation. Besides, the degradation pathways of SMX were proposed according to DFT calculations and intermediates determination. The cleavage of the sulfonamide bond, hydroxylation of the benzene ring and oxidation of the amino group mainly occurred during SMX degradation. Overall, this study provides deep insights into the enhanced mechanism of tunable active sites on DMDBs for PMS activation, boosting the application of digestate biochar for water treatment in advanced oxidation systems.
2021
Li N, Li R, Duan X, Yan B, Liu W, Cheng Z, Chen G, Hou L’an, Wang S. Correlation of Active Sites to Generated Reactive Species and Degradation Routes of Organics in Peroxymonosulfate Activation by Co-Loaded Carbon. Environmental Science & Technology [Internet]. 2021;55:16163-16174. 访问链接Abstract
Peroxymonosulfate (PMS)-based advanced oxidation processes (PMS-AOPs) as an efficient strategy for organic degradation are highly dependent on catalyst design and structured active sites. However, the identification of the active sites and their relationship with reaction mechanisms for organic degradation are not fully understood for a composite catalyst due to the complex structure. Herein, we developed a family of Co encapsulated in N-doped carbons (Co-PCN) with tailored types and contents of active sites via manipulated pyrolysis for PMS activation and ciprofloxacin (CIP) degradation, focusing on the correlation of active sites to generated reactive species and degradation routes of organics. The structure–function relationships between the different active sites in Co-PCN catalysts and reactive oxygen species (ROS), as well as bond breaking position of CIP, were revealed through regression analysis and density functional theory calculation. Co–Nx, O–C═O, C═O, graphitic N, and defects in Co-PCN stimulate the generation of 1O2 for oxidizing the C–C bond in the piperazine ring of CIP into C═O. The substitution of F by OH and hydroxylation of the piperazine ring might be induced by SO4•– and •OH, whose formation was affected by C–O, Co(0), Co–Nx, graphitic N, and defects. The findings provided new insights into reaction mechanisms in PMS-AOP systems and rational design of catalysts for ROS-oriented degradation of pollutants.
Zhao D, Liu W, Li F, Xu T, Zhu Y, Duan J, Wei Z.; 2021. Compositions and methods for removal of per- and polyfluoroalkyl substances (pfas). United States of America patent US US20210206670A1. 访问链接Abstract
The invention relates to composite compositions including a carbonaceous material and a photocatalyst. The invention includes compositions and various methods, including methods for removing one or more contaminants from a substance such as air, soil, and water.
Shi J, Zhang B, Wang W, Zhang W, Du P, Liu W, Xing X, Ding D, Lv G, Lv Q, et al. In situ produced hydrogen peroxide by biosynthesized Palladium nanoparticles and natural clay mineral for Highly-efficient Carbamazepine degradation. Chemical Engineering Journal [Internet]. 2021;426:131567. 访问链接Abstract
Fenton reaction is an effective method to remove refractory organics such as carbamazepine (CBZ) from water streams. Nevertheless, its application is greatly compromised by extra hydrogen peroxide (H2O2) addition and iron mud accumulation. Herein, Fenton-like process with in situ produced H2O2 by biosynthesized palladium nanoparticles (bioPd-NPs) and natural iron-bearing clay minerals is proposed for CBZ degradation. The bioPd-NPs prepared by Shewanella loihica PV-4 were in the size range of 5–20 nm, which catalyzed the in situ production of H2O2 from formic acid (FA) and oxygen. Then the in situ generated H2O2 underwent Fenton-like reactions with nontronite for CBZ degradation. With bioPd-NPs and nontronite dosage of 1 g/L and FA concentration of 20 mM, the complete CBZ (10 mg/L) degradation was achieved within 60 min. Oxidative radicals such as HO· and H2O2 generated in our constructed system played key roles in CBZ degradation. Intermediates/products identification and theoretical calculation revealed that hydroxylation was the main CBZ degradation pathway. This work provides a promising Fenton-like technology for elimination of CBZ from environment with prevention of additional H2O2 supplementation and excessive iron mud production.
Luo M, Zhou H, Zhou P, Lai L, Liu W, Ao Z, Yao G, Zhang H, Lai B. Insights into the role of in-situ and ex-situ hydrogen peroxide for enhanced ferrate(VI) towards oxidation of organic contaminants. Water Research [Internet]. 2021;203:117548. 访问链接Abstract
Recently, several studies have been conscious of the promotion effect of hydrogen peroxide (H2O2), a self-decay product of ferrate (Fe(VI)), on Fe(VI) to oxidize contaminations, but the pivotal activation mechanism has not been thoroughly evaluated. This work aims to compare and reveal the promoting mechanism of H2O2 in Fe(VI) and Fe(VI)−H2O2 processes, and to illustrate the practical use potential of Fe(VI)−H2O2 system. Many lines of evidence verified the involvement of •OH and O2•− in pollutant degradation were excluded in Fe(VI) and Fe(VI)−H2O2 systems, meaning that high dosage of H2O2 cannot trigger an activation pathway different from in-situ H2O2. The better oxidation performance of the Fe(VI)−H2O2 system than Fe(VI) alone was ascribed to the catalytic role of in-situ and ex-situ H2O2, which can directly and/ or indirectly facilitate the formation of Fe(IV) and Fe(V). Considering the structural similarity of peroxymonosulfate (PMS) and peroxydisulfate (PDS) with H2O2 as well as their universality in water pollutant remediation, the oxidation properties and reactive oxidants of Fe(VI)−PMS and Fe(VI)−PDS processes were also examined. Besides, the Fe(VI)−H2O2 system suffered from less restriction by inorganic ions and natural organic matter, and exhibited satisfactory pollutant removal effects in real water. Overall, this work provides a further and comprehensive cognition about the role of H2O2 in Fe(VI) and Fe(VI)−H2O2 systems.
Chen J, Wu ZJ, Zhao X, Wang YJ, Chen JC, Qiu YT, Zong TM, Chen HX, Wang BB, Lin P, et al. Atmospheric Humic-Like Substances (HULIS) Act as Ice Active Entities. Geophysical Research Letters [Internet]. 2021;48:e2021GL092443. 访问链接Abstract
Abstract We investigated the ice nucleation activities of humic-like substances (HULIS), an important component of organic aerosol (OA), derived from atmospheric and biomass burning aerosols, and produced from aqueous-phase chemical reactions. Respective HULIS can effectively trigger heterogeneous IN under mixed-phase cloud conditions. HULIS ice active entities (IAE) were aggregates in size between 0.02 and 0.10 μm. At −20°C, the IAE numbers per unit HULIS mass varied from 213 to 8.7 × 104 mg−1. Such results were different than those detected in aquatic humic substances (HS) from previous studies, implying using HS as surrogates may not robustly estimate the IAE concentrations in the real atmosphere. Combining the abundance of atmospheric HULIS with the present results suggests that HULIS could be an important IAE contributor in the atmosphere where other ice nucleating particle species, such as dust and biological particles, are either low in concentration or absent.
Peng J, Zhou P, Zhou H, Liu W, Zhang H, Zhou C, Lai L, Ao Z, Su S, Lai B. Insights into the Electron-Transfer Mechanism of Permanganate Activation by Graphite for Enhanced Oxidation of Sulfamethoxazole. Environmental Science & Technology [Internet]. 2021;55:9189-9198. 访问链接
Ma J, Chen L, Liu Y, Xu T, Ji H, Duan J, Sun F, Liu W. Oxygen defective titanate nanotubes induced by iron deposition for enhanced peroxymonosulfate activation and acetaminophen degradation: Mechanisms, water chemistry effects, and theoretical calculation. Journal of Hazardous Materials [Internet]. 2021;418:126180. 访问链接Abstract
The large consumption of acetaminophen (APAP) worldwide and unsatisfactory treatment efficiencies by conventional wastewater treatment processes give rise to the seeking of new technology for its effective removal. Herein, we proposed a facile one-step hydrothermal method to synthesize defective iron deposited titanate nanotubes (Fe/TNTs) for peroxymonosulfate (PMS) activation and APAP degradation. The retarded first-order reaction rate of APAP degradation by Fe/TNTs was 5.1 times higher than that of neat TNTs. Characterizations indicated iron deposition effectively induced oxygen vacancies and Ti3+, facilitating the electrical conductivity and PMS binding affinity of Fe/TNTs. Besides, oxygen vacancies could act as an electron mediator through PMS activation by iron. Moreover, the formation of Fe–O–Ti bond facilitated the synergistic redox coupling between Fe and Ti, further enhancing the PMS activation. SO4•− was the major radical, causing C–N bond cleavage and decreasing the overall toxicity. In contrast, APAP degradation by neat TNTs-PMS system mainly works through nonradical reaction. The Fe/TNTs activated PMS showed desired APAP removal under mild water chemistry conditions and good reusability. This work is expected to expand the potential application of titanate nanomaterials for PMS activation, and shed light on facile synthesis of oxygen defective materials for sulfate-radical-based advanced oxidation processes.
Zong Y, Shao Y, Zeng Y, Shao B, Xu L, Zhao Z, Liu W, Wu D. Enhanced Oxidation of Organic Contaminants by Iron(II)-Activated Periodate: The Significance of High-Valent Iron–Oxo Species. Environmental Science & Technology [Internet]. 2021;55:7634-7642. 访问链接Abstract
Potassium periodate (PI, KIO4) was readily activated by Fe(II) under acidic conditions, resulting in the enhanced abatement of organic contaminants in 2 min, with the decay ratios of the selected pollutants even outnumbered those in the Fe(II)/peroxymonosulfate and Fe(II)/peroxydisulfate processes under identical conditions. Both 18O isotope labeling techniques using methyl phenyl sulfoxide (PMSO) as the substrate and X-ray absorption near-edge structure spectroscopy provided conclusive evidences for the generation of high-valent iron–oxo species (Fe(IV)) in the Fe(II)/PI process. Density functional theory calculations determined that the reaction of Fe(II) with PI followed the formation of a hydrogen bonding complex between Fe(H2O)62+ and IO4(H2O)−, ligand exchange, and oxygen atom transfer, consequently generating Fe(IV) species. More interestingly, the unexpected detection of 18O-labeled hydroxylated PMSO not only favored the simultaneous generation of ·OH but also demonstrated that ·OH was indirectly produced through the self-decay of Fe(IV) to form H2O2 and the subsequent Fenton reaction. In addition, IO4– was not transformed into the undesired iodine species (i.e., HOI, I2, and I3–) but was converted to nontoxic iodate (IO3–). This study proposed an efficient and environmental friendly process for the rapid removal of emerging contaminants and enriched the understandings on the evolution mechanism of ·OH in Fe(IV)-mediated processes.
Li P, Gao S, Liu Q, Ding P, Wu Y, Wang C, Yu S, Liu W, Wang Q, Chen S. Recent Progress of the Design and Engineering of Bismuth Oxyhalides for Photocatalytic Nitrogen Fixation. Advanced Energy and Sustainability Research [Internet]. 2021;2:2000097. 访问链接Abstract
Photocatalytic nitrogen fixation represents an effective technology for the artificial production of ammonia from atmospheric nitrogen, a critical step toward a sustainable economy. Bismuth oxyhalides (BiOX, X = Cl, Br, and I) have emerged as viable catalysts for photocatalytic reduction of nitrogen into ammonia, due to their unique electronic structures and optical properties. Herein, the recent progress of BiOX-based photocatalysts for nitrogen fixation, with a focus on the reaction mechanism and pathways, materials preparation, and strategies of structural engineering for enhanced performance, is summarized. The article is concluded with a perspective where the promises and challenges of bismuth-based photocatalysts for nitrogen reduction to ammonia are highlighted, along with possible future research directions.
Qi J, Liu J, Sun F, Huang T, Duan J, Liu W. High active amorphous Co(OH)2 nanocages as peroxymonosulfate activator for boosting acetaminophen degradation and DFT calculation. Chinese Chemical Letters [Internet]. 2021;32:1814-1818. 访问链接Abstract
Acetaminophen (ACE) is commonly used in analgesic and antipyretic drug, which is hardly removed by traditional wastewater treatment processes. Herein, amorphous Co(OH)2 nanocages were explored as peroxymonosulfate (PMS) activator for efficient degradation of ACE. In the presence of amorphous Co(OH)2 nanocages, 100% of ACE removal was reached within 2 min with a reaction rate constant k1 = 3.68 min−1 at optimum pH 5, which was much better than that of crystalline β-Co(OH)2 and Co3O4. Amorphous materials (disorder atom arrangement) with hollow structures possess large specific surface area, more reactive sites, and abundant vacancies structures, which could efficiently facilitate the catalytic redox reactions. The radicals quenching experiment demonstrated that SO4− radicals dominated the ACE degradation rather than OH radicals. The mechanism of ACE degradation was elucidated by the analysis of degradation intermediates and theoretical calculation, indicating that the electrophilic SO4− and OH tend to attack the atoms of ACE with high Fukui index (f −). Our finding highlights the remarkable advantages of amorphous materials as heterogeneous catalysts in sulfate radicals-based AOPs and sheds new lights on water treatment for the degradation of emerging organic contaminants.
Liang J, Zhang W, Zhao Z, Liu W, Ye J, Tong M, Li Y. Different degradation mechanisms of carbamazepine and diclofenac by single-atom Barium embedded g-C3N4: the role of photosensitation-like mechanism. Journal of Hazardous Materials [Internet]. 2021;416:125936. 访问链接Abstract
This study reports the different degradation mechanisms of carbamazepine (CBZ) and diclofenac (DCF) by single-atom Barium (Ba) embedded g-C3N4. Single-atom Ba is anchored onto g-C3N4 by forming ionic bond with triazine ring, thus greatly enhances the photocatalytic activity with an atom ratio of 1.78%. CBZ undergoes a typical photocatalysis mechanism, while DCF is degraded via a photosensitization-like process, which does not need band gap excitation of photocatalyst. By means of Density Functional Theory (DFT) calculation, the selectivity is found to be related with the different valence excitation modes of CBZ and DCF. Specifically, CBZ undergoes a local excitation, which does not obviously affect molecular configuration. In contrast, DCF undergoes a charge transfer excitation, which significantly changes the reactive sites distribution and facilitates photosensitization-like degradation. Due to the different degradation mechanism, the effects of pH, co-existed anions, and water matrix are also different. Since photosensitization-like mechanism does not rely on photo-generated holes mediated oxidation, the degradation efficient of DCF shows higher anti-interference capacity in real water.
Liu F, Ma Z, Deng Y, Wang M, Zhou P, Liu W, Guo S, Tong M, Ma D. Tunable Covalent Organic Frameworks with Different Heterocyclic Nitrogen Locations for Efficient Cr(VI) Reduction, Escherichia coli Disinfection, and Paracetamol Degradation under Visible-Light Irradiation. Environmental Science & Technology [Internet]. 2021;55:5371-5381. 访问链接Abstract
Covalent organic frameworks (COFs) have great application potentials in photocatalytic water treatment. By using p-phenylenediamine with different numbers and locations of heterocyclic nitrogen atoms as a precursor, five types of COFs with different nitrogen positions were synthesized. We found that Cr(VI) photoreduction,Escherichia coli inactivation, and paracetamol degradation by COFs were heterocyclic nitrogen location-dependent. Particularly, the photocatalytic performance for all three tested pollutants by five types of COFs followed the order of the best performance for COF-PDZ with two ortho position heterocyclic N atoms, medium for COF-PMD with two meta position heterocyclic N atoms, and COF-PZ with two para position heterocyclic N atoms, and COF-PD with a single heterocyclic N atom, the worst performance for COF-1 without a heterocyclic N atom. Compared to the other COFs, COF-PDZ contained improved quantum efficiency and thus enhanced generation of electrons. The lower energy barriers and larger energy gaps of COF-PDZ contributed to its improved quantum efficiencies. The stronger affinity to Cr(VI) with lower adsorption energy of COF-PDZ also contributed to its excellent Cr(VI) reduction performance. By transferring into a more stable keto form, COF-PDZ showed great stability through five regeneration and reuse cycles. Overall, this study provided an insight into the synthesis of high-performance structure-dependent COF-based photocatalysts.

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