Density Functional Theoretical Calculations Research Articles

Active Electrochemical Catalysts for Ammonia and Hydrogen Evolution Reaction

An environmentally friendly alternative synthesis process is desired to produce NH3 with no CO2 emissions and low energy demand in a sustainable and ecological way in the future. The electrochemical method assisted by earth-abundant materials has been widely utilized for the chemical energy conversion. We have developed new earth-abundant layered structure metal sulfide based materials as active catalysts for electrochemically nitrogen reduction reaction. From electrochemical analysis, the Faraday efficiency of MoS2 and FeS2 for NRR can be achieve to~27% and 14% with good catalytic stability, respectively. The energy profile of the NRR reaction pathway on the catalysts will be performed by the density functional theoretical (DFT) calculation. Besides, there have been lots of studies on hydrogen evolution reaction (HER) catalytic activity using ultralow loading of Pt catalysts or even Pt single atom catalysts as well. However, Pt single atom deposited on the surface of the carbon or metal oxide material showed some drawbacks, such as high possibility of Pt desorption from the supported material in the electrolyte. Our work demonstrated that gold nanodendrites (Au NDs) with high facet surface was chosen as the supported materials for studying the relation between the low loading amount of Pt atoms and reaction mechanism of HER activity. Overall results provides a feasible approach to morphological control of metal sulfide and atomic deposition of Pt element on the specific substrate as active catalysts for NRR and HER applications, respectively.

In Situ Laser-Induced Breakdown Spectroscopy for Chromium Speciation Analysis Based on the Interactions of Oxygen-Containing Groups with Functionalized Co3O4-rGO: Evidence from Advanced Optical Techniques and Density Functional Theoretical Calculations under Electric Field.

Achieving accurate detection of different speciations of heavy metal ions (HMIs) in an aqueous solution is an urgent problem due to the different bioavailabilities and physiological toxicity. Herein, we nominated a novel strategy to detect HCrO4- and Cr(OH)2+ at a trace level via the electrochemical sensitive surface constructed by Co3O4-rGO modified with amino and carboxyl groups, which revealed that the interactions between distinct functional groups and different oxygen-containing groups of target ions are conducive to the susceptible and anti-interference detection. The detection sensitivities of 19.46 counts μg-1 L for HCrO4- and 13.44 counts μg-1 L for Cr(OH)2+ were obtained under optimal conditions, while the limits of detection were 0.10 and 0.12 μg L-1, respectively. Satisfactory anti-interference and actual water sample analysis results were obtained. A series of advanced optical techniques like X-ray photoelectron spectroscopy, X-ray absorption near-edge structure technology, and density functional theory calculations under an electric field demonstrated that chemical interactions between groups contribute more to the fixation of target ions than electrical attraction alone. The presence of oxygen-containing groups distinct from simple ionic forms was a critical factor in the selectivity and anti-interference detection. Furthermore, the valence cycle of Co(II)/(III) synergistically boosted the detection performance. This research provides a promising tactic from the microscopic perspective of groups' interactions to accomplish the precise speciation analysis of HMIs in the water environment.

Simple and rapid ionic liquid-based one-, two-, three-phase transition microextraction for efficient extraction of trace organic pollutants and elimination of lipid co-extractives from fatty food matrices

Extraction of trace contaminants from fatty food matrices is challenging in food analysis. Herein, a new ionic liquid-based one-, two-, three-phase transition microextraction (IL-OTTPTME) was proposed to efficiently extract trace targets while simultaneously eliminating lipid co-extractives. The method performance was illustrated through the determination of chrysoidine in fatty soybean products using high-performance liquid chromatography-ultraviolet/visible detection. The strong interactions and infinite contact between IL and chrysoidine in the one-phase system ensured ultra-high extraction efficiency (∼100 %). Density functional theoretical calculations confirmed the presence of strong hydrogen bonding and π-π interactions. The formation of the three-phase system during extraction could completely eliminate lipid co-extractives. The IL-OTTPTME integrated extraction, enrichment and cleanup steps into one step, making it rapid and extremely easy to operate. The method had a wide linear range of 0.5–5000 μg/kg and low limit of detection (0.15 μg/kg). It also had satisfactory relative recoveries (95.1 %-104.0 %) and low RSDs (≤5.0 %, n = 5).

Lamellar WO3/AgI S-scheme heterojunction for superior visible light driven photocatalytic degradation of ciprofloxacin

A unique lamellar WO3/AgI S-scheme heterojunction is constructed via integrated hydrothermal and coprecipitation methods. Optimized WO3/AgI composite shows significantly enhanced photocatalytic ciprofloxacin (CIP) degradation under visible light irradiation, achieving a removal rate of 53.4 % within 3 h, which is about 7.63 and 1.56 times superior than those of pristine WO3 and AgI, respectively. The characterizations, experiment results and Density Functional Theoretical (DFT) calculation results confirm the enhanced light absorption, well-aligned straddling band structures and reasonable formation of S-scheme heterojunction with efficient photogenerated carriers transfer between WO3 and AgI. Moreover, O2− and h+ are identified as the main active species, with O2− plays a dominant role in WO3/AgI during the photocatalytic degradation of CIP. This work elucidates a possible approach to develop photocatalysts with a high antibiotic removal efficiency through a higher reducing ability and stronger oxidizing ability of S-scheme heterojunction by reasonable structure configuration.

Combined Surface-Enhanced Raman and Infrared Absorption Spectroscopies for Streamlined Chemical Detection of Polycyclic Aromatic Hydrocarbon-Derived Compounds.

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of universally prevalent carcinogenic environmental contaminants. It is increasingly recognized, however, that PAHs derivatized with oxygen, sulfur, or nitrogen functional groups are frequently more dangerous than their unfunctionalized counterparts. This much larger family of chemicals─polycyclic aromatic compounds─PACs─is far less well characterized than PAHs. Using surface-enhanced Raman and IR Absorption spectroscopies (SERS + SEIRA) combined on a single substrate, along with density functional theoretical (DFT) calculations, we show that direct chemical detection and identification of PACs at sub-parts-per-billion concentration can be achieved. Focusing our studies on 9,10-anthraquinone, 5,12-tetracenequinone, 9-nitroanthracene, and 1-nitropyrene as model PAC contaminants, detection is made possible by incorporating a hydroxy-functionalized self-assembled monolayer that facilitates hydrogen bonding between analytes and the SERS + SEIRA substrate. 5,12-Tetracenequinone was detected at 0.3 ppb, and the limit of detection was determined to be 0.1 ppb using SEIRA alone. This approach is straightforwardly extendable to other families of analytes and will ultimately facilitate fieldable chemical detection of these dangerous yet largely overlooked environmental contaminants.

Supramolecular Aggregation of Carbon Nanodots.

Supramolecular aggregation has provided the archetype concept to understand the variants in an emerging systems property. Herein, we have achieved the supramolecular assembly of carbon nanodots (CDs) for the first time and employ supramolecular aggregation to understand their alteration in photophysical properties. In detail, we have employed the CDs as a block to construct the supramolecular assembly of aggregates in the CDs' antisolvent of ethanol. The CD-based aggregates exhibit complex and organized morphologies with another long-wavelength excitation-dependent emission band. The experimental results and density functional theoretical calculations reveal that the supramolecular assembly of CDs can decrease the energy gap between the ground and excited states, contributing to the new long-wavelength excitation-dependent emission. The supramolecular aggregation can be employed as one universal strategy to manipulate and understand the luminescence of CDs. These findings cast new light to build the emerging systems and understand the light emission of CDs through supramolecular chemistry.

Unveiling the electronic structure and optical properties of two-dimensional TMDCs: first-principles study

Transition metal dichalcogenide (TMDC) materials are considered extremely efficient materials with significant applications in photovoltaics and optoelectronics. Here, the electronic structure and optoelectronic features of new transition metal-containing dichalcogenides are studied using state-of-the-art density functional theoretical calculations. For the analysis of the electronic band structures, we employed a modified Becke-Johnson potential. According to the band structure analysis, Platinum-based dichalcogenides possess an indirect band profile, having the valence band maximum and the conduction band minimum situated at discrete symmetry regions. At the same time, the zirconium-based materials have a direct type band structure at the same Γ-point. We calculated cohesive energies and formation energies to assess the stability of these materials. The substantial optical parameters such as the two parts of the dielectric constant, absorption coefficients, energy loss functions, reflectivity spectra, refractive index, real optical conductivity spectra, spectra, and the extinction coefficients, are calculated. These findings provide insight into potential applications in optoelectronic devices. The calculated band gaps and refractive index revealed an inverse relationship. This research aims to make a significant contribution to the advancement of various and possibly gainful semiconducting technologies, as well as their practical applications.

Peroxymonosulfate conversion to singlet oxygen over π-electron delocalized carbon nitride for selective degradation of emerging contaminants

Graphitic carbon nitride is a promising catalyst for peroxymonosulfate (PMS) activation towards removal of emerging contaminants in water environment. However, the dependence on light and the non-selectivity of PMS activation pathway limit its practical applications. In this work, a two-step thermal treatment process was developed to modulate the π-electron delocalization degree of carbon nitride. The obtained modified carbon nitride (TCN) showed excellent capability on PMS activation without light, and simultaneously achieved high selectivity on the generation of non-radical species 1O2. Based on the results of quenching and probe experiments, isotopic solvent effect, as well as in-situ capture technique, the dominant contribution of 1O2 to the degradation of pollutants was clarified. The TCN/PMS system showed highly selective degradation of electron-donating pollutants, further demonstrating the dominant role of 1O2. Combining the control experimental results, PMS was speculated to be catalytically activated mainly through the spontaneous decomposition pathway. Further, according to the characterizations results and density functional theoretical calculations, it was the delocalized π-electrons at modified C-N heterocycles that accelerated the self-decomposition reactions of PMS. The high selectivity towards 1O2 endowed good resistance of TCN/PMS system in complex water matrices, achieving efficient removal of a number of emerging contaminants.

Evolution of molecular structure of TATB under shock loading from transient Raman spectroscopic technique

By combination of the transient Raman spectroscopic measurement and the density functional theoretical calculations, the structural evolution and stability of TATB under shock compression was investigated. Due to the improvement in synchronization control between two-stage light gas gun and the transient Raman spectra acquisition, as well as the sample preparation, the Raman peak of the N–O mode of TATB was firstly observed under shock pressure up to 13.6 GPa, noticeably higher than the upper limit of 8.5 GPa reported in available literatures. By taking into account of the continuous shift of the main peak and other observed Raman peaks, we did not distinguish any structural transition or any new species. Moreover, both the present Raman spectra and the time-resolved radiation of TATB during shock loading showed that TATB exhibits higher chemical stability than previous declaration. To reveal the detailed structural response and evolution of TATB under compression, the density functional theoretical calculations were conducted, and it was found that the pressure make N–O bond lengths shorter, nitro bond angles larger, and intermolecular and intra-molecular hydrogen bond interactions enhanced. The observed red shift of Raman peak was ascribed to the abnormal enhancement of H-bound effect on the scissor vibration mode of the nitro group.

Enhanced removal of phenolic compounds by ferrate(VI): Unveiling the Bi(III)-Bi(V) valence cycle with in situ formed bismuth hydroxide as catalyst

The use of 2-hydroxybenzophenone (2-HBP) in personal care products is of great concern due to its potential negative effects on the ecosystem and public health. This paper presents the degradation of 2-HBP by bismuth(III) (Bi3+)-ferrate(VI) (FeVIO42−, Fe(VI)) (Bi3+-Fe(VI) system). Experimental studies at different pH and dosages of Bi3+ and Fe(VI) showed that the Bi3+-Fe(VI) system increased the degradation rate and removal efficiency of 2-HBP compared to Fe(VI) alone. The in situ formed flake-like white flocculent precipitate of Bi(OH)3 showed catalytic performance through the Bi(III)-Bi(V)-Bi(III) valence cycle which was demonstrated through spectroscopic measurements. The hydrogen transfer-mediated reactions between Fe(VI) and Bi(OH)3 as well as subsequent formation of Bi(V) were supported by performing density functional theoretical (DFT) calculations. Seventeen identified transformation products of 2-HBP by Fe(VI) with and without Bi3+ revealed hydroxylation, bond breaking, carboxylation, and polymerization reaction pathways. Significantly, Bi3+ facilitated the polymerization reaction and the dioxygen transfer-mediated hydroxylation reaction pathways. The ions (anions and cations) and humic acids (HA) present in the Bi3+-Fe(VI) system had minimal influence on the removal efficiency of 2-HBP. Reusability tests and use of real water samples as well as toxicity assessments of transformation products unveiled the practical application aspect of the Bi3+-Fe(VI) system. Finally, the results showed that the system exhibits good removal efficiency for all 12 phenolic compounds, indicating theuniversality. The Bi3+-Fe(VI) system may be an easy-to-implement cost-effective method for the catalytic degradation of benzophenones by Fe(VI).

The mechanism study of enhanced antioxidant capacity: Intermolecular hydrogen bonds between epigallocatechin gallate and theanine in tea

The interactions between various substances in foods have significant implications for their nutritional values. The antioxidant capacity of polyphenols in tea can also be modulated by interactions with other substances. In this study, the intermolecular hydrogen bonds between epigallocatechin gallate (EGCG) and theanine, as well as the antioxidant capacity, were both analyzed and demonstrated. The results showed that the antiradical activity against DPPH• increased by approximate 2.4 %, and the relative cellular activity of PC12 cells in hydrogen peroxide increased by approximate 3.4 %, when appropriate theanine was added to EGCG. This phenomenon could be interpreted by the intermolecular hydrogen bonds between EGCG and theanine, which activated the phenol hydroxyl group of EGCG, inducing the departure of proton and electron. Therefore, the antioxidant capacity was enhanced. The proposed mechanism was verified by electrochemical methods and density functional theoretical calculations. Electrochemical methods confirmed the interactions between EGCG and theanine, and exhibited the shift of the redox peaks before and after the formation of hydrogen bonds. The HOMO-LUMO energy gap of EGCG obtained by density functional theoretical calculation was reduced after hydrogen bonding with theanine.

A semiconducting hybrid of RhOx/GaN@InGaN for simultaneous activation of methane and water toward syngas by photocatalysis.

Prior to the eventual arrival of carbon neutrality, solar-driven syngas production from methane steam reforming presents a promising approach to produce transportation fuels and chemicals. Simultaneous activation of the two reactants, i.e. methane and water, with notable geometric and polar discrepancy is at the crux of this important subject yet greatly challenging. This work explores an exceptional semiconducting hybrid of RhOx/GaN@InGaN nanowires for overcoming this critical challenge to achieve efficient syngas generation from methane steam reforming by photocatalysis. By coordinating density functional theoretical calculations and microscopic characterizations, with in situ spectroscopic measurements, it is found that the multifunctional RhOx/GaN interface is effective for simultaneously activating both CH4 and H2O by stretching the C-H and O-H bonds because of its unique Lewis acid/base attribute. With the aid of energetic charge carriers, the stretched C-H and O-H bonds of reactants are favorably cleaved, resulting in the key intermediates, i.e. *CH3, *OH, and *H, to sit on Rh sites, Rh sites, and N sites, respectively. Syngas is subsequently produced via energetically favored pathway without additional energy inputs except for light. As a result, a benchmarking syngas formation rate of 8.1 mol·gcat-1·h-1 is achieved with varied H2/CO ratios from 2.4 to 0.8 under concentrated light illumination of 6.3 W·cm-2, enabling the achievement of a superior turnover number of 10,493 mol syngas per mol Rh species over 300 min of long-term operation. This work presents a promising strategy for green syngas production from methane steam reforming by utilizing unlimited solar energy.

Spectrofluorometric detection of mercury ions in aqueous medium and cellular milieu using MoS2 nanoflakes

This communication reports the facile hydrothermal synthesis of fluorescent two-dimensional layered MoS2 nanoflakes using a biomolecule (l-cysteine) for efficient and sensitive detection of mercury ions (Hg2+) in aqueous solution by monitoring the fluorescence quenching of MoS2 in a ratiometric approach. This fluorescence quenching of MoS2 was successfully utilized to detect Hg2+ ions in both normal (H9c2 cell line) and cancer (A549 cell line) cells as well via fluorescence imaging microscopy. The as-synthesized MoS2 nanostructured sample was characterized using UV–vis absorption, steady-state fluorescence emission, X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The strong fluorescence emission of nanostructured MoS2 was heavily quenched by Hg2+ ions in aqueous medium as confirmed by fluorescence spectroscopic results. The binding of Hg2+ with MoS2 nanoflakes and the resulting fluorescence quenching were also supported by Stern–Volmer analysis. The selectivity and sensitivity of the interaction of Hg2+ ions with the as-prepared MoS2 nanoflakes among all other interfering metal ions were analyzed. The selective interaction of Hg2+ with MoS2 was also accompanied by a distinct color change from bluish-green to flaxen or pale yellowish-gray in aqueous medium. The limit of detection of Hg2+ ions in aqueous medium was 0.63 nM. The possible interactions between Hg2+ and MoS2 were confirmed by Fourier transform infrared spectroscopy, time-resolved fluorescence, and cyclic voltammetry studies. Density functional theoretical calculations provided useful information to correlate the electronic structure and energy band distributions with the spectroscopic results for the interaction of Hg2+ with MoS2 nanoflakes. The MoS2 nanoflakes showed no significant cytotoxicity during their interaction with Hg2+ ions in the intracellular medium, as confirmed by MTT assay, thereby ensuring possible future biomedical applications.

A novel intelligent hybrid nano-sensor (IHNS) for detection and clearance of Al(Ⅲ) prepared via “click chemistry”

Intelligent materials are functional material systems with intelligent responses to external stimulation. With the continuous advances in science and technology, intelligent materials have surfaced as a research trend in material science and are providing a new direction for the systematic application of nanocomposite materials. In this study, an intelligent organic-inorganic nano-hybrid sensor or intelligent nanorobot, POSS-RHB-PEG, was developed by employing density functional theoretic calculations (DFT) under the Gaussian 03 program by a “Click Chemistry” based preparation strategy, in which RHB group can act as a recognizing ion in the cell under the action of intense coordination field and then as a function of coordinating ions. A low-chain PEG with good cell permeability functions as a machine wheel on account of the principle of osmotic pressure. The POSS-based nanorobotic molecular analytical device, with appropriate bio-compatibility, was designed and developed for the semiquantitative, intuitive, and sensitive detection and morphological analysis of Al3+ ions in a real sample with a detection limit of 1.0×10−8 M. Significant color evolutions from colorless to red were observed by the naked eye under the ultraviolet lamp, resulting in a semiquantitative visual detection. Compared to the organic sensing material RHB-Ac, the intelligent nanorobot POSS-RHB-PEG has high stability, selectivity (sulfhydryl group can self-screen Fe3+ ions), and good biocompatibility. Furthermore, the nanohybrid nanorobot sensor successfully targeted HeLa cells, monitored cellular endogenous Al3+, and assessed cell stress in living cells. The nanohybrid nanorobot sensor POSS-RHB-PEG was also able to detect and image Al3+ in living nude mice, indicating its exceptional detection potential in biological systems, it mainly involves the detection of metal ions in blood and the detection and treatment of heavy metal ions caused by clinical bone and joint replacement.

Insights into the mechanism in electrochemical CO2 reduction over single-atom copper alloy catalysts: A DFT study

Copper single-atom alloy catalysts (M@Cu SAAs) have shown great promise for electrochemical CO2 reduction reaction (CO2RR). However, a clear understanding of the CO2RR process on M@Cu SAAs is still lacking. This study uses density functional theoretical (DFT) calculations to obtain a comprehensive mechanism and the origin of activity of M@Cu SAAs. The importance of the adsorption mode of M@Cu is revealed: key intermediates either adsorbed in the adjacent hollow site around Cu atoms (AD mode) or adsorbed directly on the top site of M (SE mode). AD mode generally exhibits finely tuned binding strengths of key intermediates, which significantly enhances the activity of the catalysts. Increasing the coverage of ∗CO on the M@Cu with SE mode leads to relocation of the active site, resulting in improved activity of C2 products. The insights gained in this work have significant implications for rational design strategy toward efficient CO2RR electrocatalysts.

Fluorescence detection of hydrazine in an aqueous environment by a corrole derivative.

Broadly, the industrial applications of hydrazine cause environmental pollution and damage to living organisms because of the high toxicity of hydrazine. Therefore, monitoring hydrazine in the environmental system is of great significance to human health. Here, a new fluorescent probe PC-N2 H4 based on corrole dye was developed for the detection of hydrazine that had excellent specificity, low limit of detection (LOD: 88 nM), and a wide pH range (6-12). Upon addition of hydrazine into the probe solution, the strong red fluorescence was 'turned on' centred at 653 nm with a 127-fold fluorescence intensity enhancement. The detection mechanism was proved using ESI-MS, 1 H NMR, and density functional theoretical calculations. Importantly, the probe was utilized to fabricate a ready-to-use test strip to realize the visual inspection of hydrazine. Furthermore, PC-N2 H4 was successfully applied for practical detection of hydrazine in water samples with satisfactory recoveries ranging from 96.2% to 105.0%, and indicating that the designed PC-N2 H4 is highly promising for hydrazine detection in an aqueous environment. Considering the diverse toxicological functions of hydrazine, PC-N2 H4 was also successfully used to image exogenous hydrazine in HeLa cells and zebrafish.

Strong and Ultratough Ionogel Enabled by Ingenious Combined Ionic Liquids Induced Microphase Separation

AbstractIonogels have become a popular material in flexible electronics and soft robotics based on their excellent ionic conductivity, environmental tolerance, and electrochemical stability. However, it remains a challenge to develop an ionogel integrated with high strength, toughness, self‐healing, and adhesion. Herein, a novel strategy is established to design a high‐strength (0.97 MPa) and tensile (980%), excellent crack insensitivity, self‐healing ionogel based on the cosolvent method. By virtue of differential interactions between the specific polymer and various ionic liquids with gradient polarity, cosolvent systems are employed to achieve high‐performance ionogels by a simple one‐step polymerization. Gel permeation chromatography, atomic force microscopy, time‐domain nuclear magnetism, and density functional theoretical calculation are used to analyze the reasons. Microphase separation can be induced by hydrone or stretching to enhance strength of the ionogel. Therefore, ionogels can be assembled as strain and temperature sensors to monitor human movement and person's body temperature with a low detection threshold (0.1 °C) in extreme environments. This concept creates a new path to achieve soft materials with high performance, and provide a prospective strategy to regulate the in situ microphase change and performance of the resulting ionogel via the one‐step polymerization.

Enhancing chemical stability and performance in proton-conducting solid oxide fuel cells through novel composite cathode design

Thermal and chemical compatibility between the cathode and electrolyte is crucial for the development of proton-conducting solid oxide fuel cells (H–SOFCs). To tackle this challenge, composite cathodes are often prepared by mixing traditional cathode materials with BaZr0.1Ce0.7Y0.2O3+δ (BZCY) electrolyte material. However, it should be noted that BZCY has a propensity to react with water generated during cell operation. Thus, this article presents the recent findings on performance enhancement of H–SOFCs through the utilization of a novel composite cathode, consisting of La0.6Sr0.4Co0.2Fe0.8O3+δ (LSCF) and La2-xNixCe2O7-δ (LNCOx) (x = 0.1, 0.2, 0.3, 0.4). The novel composite LSCF-LNCO0.3 cathode has shown significant improvements in the catalytic activity and durability, achieving a maximum power density of 1283 mW cm−2 at 700 °C. Density functional theoretical calculation (DFT) results reveal that the Ni doping in La2Ce2O7+δ (LCO) can effectively reduce the proton migration energy and enhance hydration ability, thereby obtaining high cathode performance. Compared traditional cathode design strategy, a novel design strategy involving the adjustment of the electrolyte component shows great potential for further advancement in cell performance.

Combined Experimental and Theoretical Insights on Selectivity of Rare Earth Elements with Tetra‐2‐ethylhexyl Diglycolamide

AbstractA diglycolamide based extractant namely tetra‐2‐ethylhexyl diglycolamide [TEHDGA] has been synthesized and characterized for extraction of rare earths from coal fly ash (CFA). The formation rare earth‐TEHDGA complex in the organic phase was determined from slope analysis method. The same structure was further corroborated by the density functional theoretical calculation. Furthermore, DFT approach was adopted to explain the relative stability of rare earth complex with TEHDGA over other matrix elements like Fe, Ca, Al, Mg of CFA by determining their free energy of extraction. The calculated selectivity trend from the free energy of extraction is obtained after consideration of 1 : 3 stoichiometry for Europium – the representative of all rare earth elements. Thus the correct selectivity order was established from a combined experimental and density functional theoretical studies.

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 1.99eV and a conduction band energy of -0.37V 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.