Eco-friendly synthesis of size-controlled silver nanoparticles by using Areca catechu nut aqueous extract and investigation of their potent antioxidant and anti-bacterial activities

Silver nanoparticles (AgNPs) have attracted considerable attention owing to their unique biological applications. AgNPs synthesized by plant extract is considered as a convenient, efficient and eco-friendly material. In this work, the aqueous extract of Areca catechu L. nut (ACN) was used as the reducing and capping agents for one-pot synthesis of AgNPs, and their antioxidant and antibacterial activities were investigated. UV (Ultra Violet)-visible spectrum and dynamic light scattering (DLS) analysis revealed that the size of AgNPs was sensitive to the synthesis conditions. The synthesized AgNPs were composed of well-dispersed particles with an small size of about 10 nm under the optimal conditions (pH value of extract was 12.0; AgNO₃ concentration was 1.0 mM; reaction time was 90 min). In addition, scanning electron microscope with energy dispersive X-ray (SEM-EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD) results further verified that the synthesized AgNPs had a stable and well-dispersed form (Zeta potential value of ?30.50 mV and polydispersity index of 0.328) and a regular spherical shape (average size of 15–20 nm). In addition, Fourier transform infrared spectrometry (FTIR) results revealed that phytochemical constituents in ACN aqueous extract accounted for Ag⁺ ion reduction, capping and stabilization of AgNPs. The possible reductants in the aqueous extract of Areca catechu L. nut were identified by high-performance liquid chromatography-electrospray ionization-quadrupole-time of flight-mass spectrometry (HPLC-ESI-qTOF/MS) method. More importantly, the synthesized AgNPs indicated excellent free radical scavenging activity of 1,1-diphenyl-2-picrylhydrazyl (DPPH, IC₅₀ = 11.75 ± 0.29 μg/mL) and 2,2-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS⁺, IC₅₀ = 44.85 ± 0.37 μg/mL), which were significant higher than that of ascorbic acid. Moreover, AgNPs exhibited an enhanced antibacterial activity against six selected common pathogens (especially Escherichia coli and Staphylococcus aureus) compared with AgNO₃ solution. In a short, this study showed that the Areca catechu L. nut aqueous extract could be applied for eco-friendly synthesis of AgNPs.     

Novel organic magnet derived from pyrazine-fused furazans

The first organic magnet based on a high-nitrogen framework of pyrazine-fused furazans Na(L⁻)(H₂O)₃ was found. A quantum-chemical study of M(L⁻)(H₂O)_n, where M = Li, Na, K, Rb, NH₄, revealed that exchange coupling energy between the neighboring radical anions proved highly sensitive to the motion of one L⁻ relative to another.     

Covalent organic frameworks functionalized carbon fiber paper for the capture and detection of hydroxyl radical in the atmosphere

Developing a fast, sensitive and convenient method for the detection of hydroxyl radicals (OH) in the atmosphere could help us know the precursor levels of atmospheric species and control air pollution. In this work, the carbon fiber paper (CFP) functionalizing with a kind of covalent organic frameworks (COFs), formed from 1,3,5-triformylphloroglucinol (Tp) and benzidine (BD) (COF(TpBD)), was firstly used a new platform for OH trapping and detection. The COF(TpBD) modified CFP was acted as a filter to impregnate salicylic acid (SA) and a detector to detect 2,5-dihydroxybenzoic acid (2,5-DHBA) which was produced from the reaction between the impregnated SA and OH in the atmosphere. This method provided a linearity for 2,5-DHBA from 5.0 × 10⁻¹⁴ mol/L 1.0 × 10⁻⁹ mol/L with a detection limit of 6.9 × 10⁻¹⁵ mol/L, which is corresponding to the amount of OH from 3.0 × 10⁷ to 6.0 × 10¹¹ molecules/cm³ with the detection limit of 4.1 × 10⁶ molecules/cm³. This COF(TpBD)-CFP platform has been successfully applied for the detection of OH concentration under different conditions of Yangzhou when the sampling time was shortened to 30 min. This work has provided a new method for atmospheric OH detection with excellent sensitivity, simplicity, and high speed.     

Graphdiyne as a novel nonactive anode for wastewater treatment: A theoretical study

Electrochemical oxidation of water to produce highly reactive hydroxyl radicals (OH) is the dominant factor that accounts for the organic compounds removal efficiency in water treatment. As an emerging carbon-based material, the investigation of electrocatalytic of water to produce OH on Graphdiyne (GDY) anode is firstly evaluated by using first-principles calculations. The theoretical calculation results demonstrated that the GDY anode owns a large oxygen evolution reaction (OER) overpotential (η^OER = 1.95 V) and a weak sorptive ability towards oxygen evolution intermediates (HO*, not OH). The high Gibbs energy change of HO* (3.18 eV) on GDY anode makes the selective production of OH (ΔG = 2.4 eV) thermodynamically favorable. The investigation comprises the understanding of the relationship between OER to electrochemical advanced oxidation process (EAOP), and give a proof-of-concept of finding the novel and robust environmental EAOP anode at quantum chemistry level.     

Enhanced visible light photocatalytic activity of CeO2@Zn0.5Cd0.5S by facile Ce(IV)/Ce(III) cycle

In this study, CeO₂@Zn_0.5Cd_0.5S heterostructure (Ce@ZCS) is synthesized via a simple two-step hydrothermal method. The effect of CeO₂ loading on the visible-light photoactivity of Zn_0.5Cd_0.5S is mainly investigated. It is found that Ce@ZCS shows a 1.9 times activity as high as ZCS for the MB degradation. The improved activity mainly results from the significant enhanced charge separation by CeO₂, in which the electron transfer is obviously promoted by the facile Ce(IV)/Ce(III) cycle. The excited electrons of ZCS is easy to transfer to CeO₂, thus obviously increasing the charge separation of ZCS. The accepted electrons by CeO₂ may easily be captured by the adsorbed O₂ to form O₂⁻, and then O₂⁻ could combine with H⁺/H₂O to form HO₂, and OH. Finally, O₂⁻, h⁺ and OH are confirmed as the major oxidative species in photocatalytic reaction for Ce@ZCS, and a possible photocatalytic mechanism is proposed. The cheap, efficient Ce@ZCS photocatalyst could be applied for practical waste water treatment.     

Pretreatment of polyvinyl alcohol by electrocoagulation coupling with catalytic oxidation: Performance,mechanism and pathway

In this study, various conditions for the removal of polyvinyl alcohol (PVA) by electrocoagulation (EC) coupled catalytic oxidation are systematically studied. The direct oxidation of the anode, the reduction of the cathode, the oxidation of OH and Cl, and the synergistic effect of flocculation on the degradation of polyvinyl alcohol are investigated. It is observed that the optimum experimental conditions obtained are as follows: Cell voltage 9 V, natural pH 7, NaCl concentration 0.02 mol/L, and interelectrode distance 3.0 cm. The evolution of iron ions is also discussed in the EC process. By contrast, EC had made an outstanding contribution to the removal of PVA, which removes 71.29% of PVA. Free radicals, especially OH and Cl, are equivalent to the contribution of the electrodes in the degradation of PVA. And the contribution of PVA degradation by anode oxidation and cathode reduction are 12.76% and 8.02%, respectively. Characterization of solution and floc, such as Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), thermogravimetric analysis (TGA), GC–MS and molecular weight, showed that PVA is effectively removed by the EC process, and a possible degradation pathway is proposed     

InP quantum dots on g-C3N4 nanosheets to promote molecular oxygen activation under visible light

Largely limited by the high dissociation energy of the OO bond, the photocatalytic molecular oxygen activation is highly challenged, which restrains the application of photocatalytic oxidation technology for atmospheric pollutants removal. Herein, we design and fabricate the InP QDs/g-C₃N₄ compounds. The introduction of InP QDs promotes the charge transfer within the interface resulting in the effective separation of photo-generated carriers. Furthermore, InP QDs greatly facilitates the activation of molecular oxygen and promote the formation of O₂⁻ under visible-light illumination. These conclusions are identified by experimental and calculation results. Hence, NO can be combined with the O₂⁻ to form OONO intermediate to direct conversion into NO₃⁻. As a result, the NO removal ratio of g-C₃N₄ has a onefold increase after InP QDs loaded and the generation of NO₂ is effectively inhibited. This work may provide a strategy to design highly efficient materials for molecular oxygen activation.     

Copper-catalyzed synthesis of oxime ethers from iminoxy radical (CN–O) and maleimides via radical addition

An efficient Cu(II)-catalyzed radical addition of maleimides has been achieved. The identified copper catalyst enables the formation of oxime radicals (N–O) by cleaving the O–H bond in ketoximes, followed by the radical addition to N-substituted maleimides. The oxime radicals (N–O) were detected and confirmed by EPR spectroscopy and variable-temperature ¹H NMR. The simple one-pot reaction realizes the facile preparation of a variety of oxime ether adduct products in moderate to good yields.     

HPLC–DAD–MS identification of polyphenols from Passiflora leschenaultii and determination of their antioxidant,analgesic, anti-inflammatory and antipyretic properties

Passion fruit (Passiflora leschenaultii DC), an endemic species to peninsular India, is traditionally used to treat various ailments such as dysentery, urinary stone disease and wounds. The present study aimed to investigate the antioxidant, analgesic, anti-inflammatory, antipyretic activities and chemical composition of leaf extracts of P. leschenaultii. Bioactive secondary metabolites such as total phenolics, tannins and flavonoids were quantified. Antioxidant activities were determined by DPPH, ABTS⁺, FRAP, metal chelating and phosphomolybdenum assays. Hot plate, acetic acid and formalin induced pain models were used to evaluate the analgesic activity. In order to study the acute and chronic anti-inflammatory activities, carrageenan and cotton pellet induced models were used in rats. Brewer’s yeast induced pyrexia method was applied for the antipyretic test. Functional compounds from the plant were identified and quantified through HPLC–DAD–MS analysis. The obtained results revealed that the acetone extract of leaves exhibited higher phenolic (440.24 mg GAE/g extract) and flavonoid (253.33 mg RE/g extract) contents and scavenged the DPPH (IC₅₀ 29.14 μg/mL), ABTS⁺ (10509.69 μM TEAC/g extract) effectively. On investigating the analgesic, anti-inflammatory and antipyretic activities, the acetone extracts of leaves, at a dose of 400 mg/kg (p.o.) reduced significantly (p < 0.001) the pain, inflammation and fever responses in vivo. Bioactive compounds such as hyperin, chlorogenic acid, rutin and caffeic acids were identified in the leaves of P. leschenaultii employing HPLC–DAD–MS analysis. These findings illustrate the excellent potential of this species as valuable source of natural phytochemicals with pharmacological properties.     

High active amorphous Co(OH)2 nanocages as peroxymonosulfate activator for boosting acetaminophen degradation and DFT calculation

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.     

Oxygen dependent oxidation of trimethoprim by sulfate radical: Kinetic and mechanistic investigations

Trimethoprim (TMP) is a typical antibiotic to treat infectious disease, which is among the most commonly detected antibacterial agents in natural waters and municipal wastewaters. In the present study, the impacts of dissolved oxygen (DO) on the oxidation efficiency and pathways of TMP by reaction with sulfate radicals (SO₄⁻) were investigated. Our results revealed that the presence of DO was favourable for TMP degradation. Specifically, TMP would react initially with SO₄⁻ via electron-transfer process to form a carbon-centered radical. In the absence of oxygen, the carbon-centered radical could undergo hydrolysis to produce α-hydroxytrimethoprim (TMP−OH), followed by the further oxidation which generated α-ketotrimethoprim (TMP=O). However, in the presence of oxygen, the carbon-centered radical would alternatively combine with oxygen, leading to a sequential reaction in which peroxyl radical and a tetroxide were formed, and finally generated TMP−OH and TMP=O simultaneously. The proposed pathways were further confirmed by density functional theory (DFT) calculations. The results obtained in this study would emphasize the significance of DO on the oxidation of organic micro-pollutants by SO₄⁻.     

Comparative antiradical activity and molecular Docking/Dynamics analysis of octopamine and norepinephrine: the role of OH groups

Octopamine is a neurotransmitter in invertebrates and a phenol analog of norepinephrine. The crystallographic and spectral (UV–visUV, and NMR) characteristics of octopamine were investigated experimentally and theoretically by applying appropriate level of theory, B3LYP-D3BJ/6-311++G(d,p), which reproduced well the experimental bond lengths and angles. The intramolecular interactions governing the stability of conformers were described by NBO and QTAIM analyses. The antiradical potencies of octopamine and norepinephrine towards DPPH and ABTS⁺ were examined with special emphasis on the preferred mechanism and effect of catechol moiety. Several techniques were used to distinguish Hydrogen Atom Transfer (HAT) and Proton Coupled Electron Transfer (PCET) mechanisms for reaction with DPPH. The calculated rate constants of the reactions with both radicals showed that Sequential Proton Loss Electron Transfer (SPLET) mechanism was dominant both thermodynamically and kinetically, with values of thermodynamic functions and rate constants clearly proving the importance of the second hydroxyl group in structure. The Molecular Docking and afterward Molecular Dynamics calculations of formed complexes between octopamine/norepinephrine with β1- and β2- adrenergic receptors examined in details the interactions that lead to the formation of stable complexes. The number of strong interactions of amino acids with norepinephrine was higher, but the absence of hydroxyl group in octopamine did not lead to a significant change in the type of interactions and stability. The formed complexes showed higher flexibility of amino acids, similar compactness of structure as proteins and increased interatomic distances of the backbone when compared to pure proteins.     

New insight in the O2 activation by nano Fe/Cu bimetals: The synergistic role of Cu(0) and Fe(II)

This study demonstrated that as-synthesized nano Fe/Cu bimetals could achieve significant enhancement in the degradation of diclofenac (DCF), as compared to much slow removal of DCF by Cu(II) or zero valent iron nanoparticles (nZVI), respectively. Further observations on the evolution of O₂ activation process by nano Fe/Cu bimetals was conducted stretching to the preparation phase (started by nZVI/Cu²⁺). Interesting breakpoints were observed with obvious sudden increase in the DCF degradation efficiency and decrease in solution pH, as the original nZVI just consumed up to Fe(II) and Cu(II) appeared again. It suggested that the four-electrons reaction of O₂ and Cu-deposited nZVI would occur to generate water prior to the breakpoints, while Cu(0) and Fe(II) would play most important role in activation of O₂ afterwards. Through the electron spin resonance (ESR) analysis and quenching experiments, OH was identified as the responsible reactive species. Further time-dependent quantifications in the cases of Cu(0)/Fe(II) systems were carried out. It was found that the OH accumulation was positively and linearly correlated with nCu dose, Fe(II) consumption, and Fe(II) dose, respectively. Since either Cu(0) or Fe(II) would be inefficient in activating oxygen to produce OH, a stage-evolution mechanism of O₂ activated by nano Fe/Cu bimetals was proposed involving: (a) Rapid consumption of Fe(0) and release of Fe(II) based on the Cu-Fe galvanic corrosion, (b) adsorption and transformation of O₂ to O₂²⁻ at the nCu surface, and (c) Fe(II)-catalyzed activation of the adsorbed O₂²⁻ to OH.     

Reaction pathway change on plasmonic Au nanoparticles studied by surface-enhanced Raman spectroscopy

Gold nanoparticles (Au NPs) are nanoscale sources of light and electrons, which are highly relevant for their extensive applications in the field of photocatalysis. Although a number of research works have been carried out on chemical reactions accelerated by the energetic hot electrons/holes, the possibility of reaction pathway change on the plasmonic Au surfaces has not been reported so far. In this proof-of-concept study, we find that Au NPs change the reaction pathway in photooxidation of alkyne under visible light irradiation. This reaction produces benzil (COCO) without the presence of Au NPs. In contrast, as indicated by surface-enhanced Raman spectroscopic (SERS) results, the CC triple bonds (CC) adsorbed on Au NPs are converted into carboxyl (COOH) and acyl chloride (COCl) groups. The plasmonic Au NPs not only provide energetic charge carriers but also activate the reactant molecules as conventional heterogeneous catalysts. This study discloses the second role of plasmonic NPs in photocatalysis and bridges the gap between plasmon-driven and conventional heterogeneous catalysis.     

Ultrafast O2 activation by copper oxide for 2,4-dichlorophenol degradation: The size-dependent surface reactivity

This study demonstrated interesting ultrafast activation of molecular O₂ by copper oxide (CuO) particles and very rapid elimination of aqueous 2,4-dichlorophenol (2,4-DCP) within reaction time of 30 s. Electron paramagnetic resonance (EPR) characterization indicated that OH, Cu³⁺, ¹O₂ and O₂⁻ were generated in the CuO/O₂ systems, wherein O₂⁻ would be the main reactive species responsible for 2,4-DCP degradation. It was further found that the catalytic ability of CuO for O₂ activation was highly size dependent and nano-CuO was far reactive than micro-CuO. H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM) analyses revealed that both the quantity and the reactivity of the surface reaction sites (surface Cu⁺ and O₂) could determine the catalytic ability of CuO affecting efficient Cu⁺-based molecular oxygen activation. Moreover, the O₂ activation ability of CuO would depend on not only the dimension, but also crystalline factors, for example, the exposed facets.     

Effective removal of chlorinated organic pollutants by bimetallic iron-nickel sulfide activation of peroxydisulfate

Chlorinated organic pollutants(COPs) have caused serious contaminants in soil and groundwater,hence developing methods to remove these pollutants is necessary and urgent.By a simple hydrothermal method,we synthesized the bimetallic iron-nickel sulfide(FeNiS) particles which exhibited excellent catalytic property of COPs removal.FeNiS was chosen as the peroxydisulfate(PDS) activator to removal COPs including 4-chlorophenol(4-CP),1,4-dichlorophenol(1,4-DCP) and 2,4,6-trichlorophenol(2,4,6-TCP).The results show that FeNiS can efficiently activate PDS to produce sulfate radical(SO_4~(·-)) which plays major role in the oxidative dechlorination and degradation due to its strong oxidizing property and the ability of producing hydroxyl radicals(~·OH) in the alkaline condition.Meanwhile,the Cl-abscised from COPs during the dechlorination can turn into the chlorine radicals and enhance the degradation and cause further mineralization of intermediate products.This bimetallic FeNiS catalyst is a promising PDS activator for removal of chlorinated organics.     

Chitosan capped silver nanoparticles: Adsorption and photochemical activities

Chitosan capped silver nanoparticles (Chi-Ag) were prepared using AgNO₃ and sodium borohydride. Chitosan was detected by using ninhydrin test, thermal gravimetric analysis and measurement of relative viscosity. Chi-Ag was used for removal of cadmium (Cd²⁺) at room temperature. The maximum monolayer adsorption capacity, and sorption intensity were estimated to be 119.04 mg/g and 1.6, respectively, from Langmuir and Freundlich adsorption isotherm models. The kinetics of Cd²⁺ adsorption onto Chi-Ag was proceeds through the pseudo-second-order kinetic model. Boyd and Elovich models suggest the adsorption and/or coordination of Cd²⁺ with the NH₂ and OH groups of chitosan along with AgNPs proceeds through the film diffusion and chemisorption process. The average viscosity molecular weight of chitosan and Chi-Ag decreased with increased potassium persulfate (K₂S₂O₈) and hydrogen peroxide (H₂O₂) concentration. The presence of H₂O₂ and K₂S₂O₈ promoted the hydrolysis of chitosan due to the cleavage of glycosidic bond by generated HO and SO₄^? radicals.     

Visible light induced efficient activation of persulfate by a carbon quantum dots (CQDs) modified γ-Fe2O3 catalyst

In this study, a carbon quantum dots modified maghemite catalyst (CQDs@γ-Fe₂O₃) has been synthesized by a one-step solvothermal method for efficient persulfate (PDS) activation under visible light irradiation. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) characterization indicated that the formation of heterojunction structure between CQDs and γ-Fe₂O₃ effectively reduced the catalyst band gap (E_g), favoring the separation rate of electrons and holes, leading to remarkable efficient sulfamethoxazole (SMX) degradation as compared to the dark-CQDs@γ-Fe₂O₃/PDS and vis-γ-Fe₂O₃/PDS systems. The evolution of dissolved irons also demonstrated that CQDs could accelerate the in-situ reduction of surface-bounded Fe³⁺. Electron paramagnetic resonance (EPR) and radical scavenging experiments demonstrated that both OH and SO₄⁻ were generated in the reaction system, while OH was relatively more dominant than SO₄⁻ for SMX degradation. Finally, the reaction mechanism in the vis-CQDs@γ-Fe₂O₃/PDS system was proposed involving an effective and accelerated heterogeneous-homogeneous iron cycle. CQDs would enrich the photo-generated electrons from γ-Fe₂O₃, causing efficient interfacial generation of surface-bond Fe²⁺ and reduction of adsorbed Fe³⁺. This visible light induced iron cycle would eventually lead to effective activation of PDS as well as the efficient degradation of SMX.     

Ultra-fast sustainable synthesis,optimization and characterization of guava phenolic extract functionalized nanosilver with enhanced biomimetic attributes

There had been some reports demonstrating the green synthesis of silver nanoparticles using guava (Psidium guajava (L.) extract); however, detailed and in-depth interrogation of the vital synthesis parameters for rapid, facile, efficacious synthesis at room temperature, and robust characterization of the as-prepared nanoparticle is currently lacking. This study presents a comprehensive delineation of the sustainable phyto-fabrication of biogenic guava phenolic extract functionalized silver nanoparticles (GVE-SNP) based on guava phenolic extract as the sole reductant/stabilizer, as well as the synthesis optimization, thorough physicochemical characterization and potential biological applications of the as-prepared nanosilver. The results revealed that successful synthesis of GVE-SNP was instantaneous and maximum intensity of the plasmonic peak at 425 nm was achieved in less than 10 min. GVE-SNP was found to present stable, well-dispersed, round, uniform, and crystalline nanoparticles of about 5.88 nm. The FTIR and RAMAN spectra indicated that GVE-SNP surface was properly capped by bioactives from GVE. The nanoparticles displayed potent radical scavenging activity against ABTS⁺ and DPPH. Also, GVE-SNP exhibited a significant and dose–response inhibitory effect against tyrosinase. Furthermore, the nanoparticles displayed good cytotoxicity against L929 fibroblast and were found to possess strong antimicrobial properties, inhibiting the growth of S. aureus and S. epidermidis.     

Effect of oxygen-containing functional groups on the wettability of coal through DFT and MD simulation

To investigate the wettability of different oxygen-containing functional group (OFG) surfaces, graphite substrates were used as a model for coal adsorbents. The substrates were modified with COOH, OH, CO, and OCH₃. The adsorption-diffusion behavior of H₂O molecules/water droplets on different OFG surfaces was investigated using molecular dynamics (MD) simulations with frontier orbital energy difference as a metric for different surface wettability degrees in quantum chemical analysis. The results indicated that the frontier orbital energy difference of the H₂O molecule was 3.480, 3.491, 3.631, and 3.680 eV for PhCOOH, PhOH, PhCO, and PhOCH₃, respectively. In addition, the equilibrium contact angle, interaction energy, and number of hydrogen bonds after the adsorption equilibrium of water droplets for COOH, OH, CO, and OCH₃ surfaces were 22.34°, ?5.03 kcal/mol, and 652; –23.72°, ?4.19 kcal/mol, and 450; 68.01°, ?0.79 kcal/ mol, and 61; 90.51°, ?0.50 kcal/mol, and 28, respectively. The smaller the energy difference between the frontier orbitals of the H₂O molecule and the OFG, the smaller the equilibrium contact angle between the water droplet and the OFG surface, the more hydrogen bonds were formed, and the larger the absolute value of the interaction energy, the better the wettability of the surface of the OFG. The order of wettability of the different OFG surfaces was COOH > OH > CO > OCH₃, which is consistent with the radial distribution function and the analysis results for the extended area, etc. The results of density functional theory (DFT) calculations and MD simulations exhibited identical patterns, indicating the reasonableness of the simulations. This study may serve as a reference for the suppression of hydrophilicity in low-order coal and the enhancement of the flotation effect.