Effect Of Oxygen-containing Functional Groups Research Articles

Adsorption Mechanism of Hexavalent Chromium on Electron Beam-Irradiated Aged Microplastics: Novel Aging Processes and Environmental Factors

Microplastics are widely present in the natural environment and exhibit a strong affinity for heavy metals in water, resulting in the formation of microplastics composite heavy metal pollutants. This study investigated the adsorption of heavy metals by electron beam-aged microplastics. For the first time, electron beam irradiation was employed to degrade polypropylene, demonstrating its ability to rapidly age microplastics and generate a substantial number of oxygen-containing functional groups on aged microplastics surface. Adsorption experiments revealed that the maximum adsorption equilibrium capacity of hexavalent chromium by aged microplastics reached 9.3 mg g-1. The adsorption process followed second-order kinetic model and Freundlich model, indicating that the main processes of heavy metal adsorption by aged microplastics are chemical adsorption and multilayer adsorption. The adsorption of heavy metals on aged microplastics primarily relies on the electrostatic and chelation effects of oxygen-containing functional groups. The study results demonstrate that environmental factors, such as pH, salinity, coexisting metal ions, humic acid, and water matrix, exert inhibitory effects on the adsorption of heavy metals by microplastics. Theoretical calculations confirm that the aging process of microplastics primarily relies on hydroxyl radicals breaking carbon chains and forming oxygen-containing functional groups on the surface. The results indicate that electron beam irradiation can simultaneously oxidize and degrade microplastics while reducing hexavalent chromium levels by approximately 90%, proposing a novel method for treating microplastics composite pollutants. Gas chromatography-mass spectrometry analysis reveals that electron beam irradiation can oxidatively degrade microplastics into esters, alcohols, and other small molecules. This study proposes an innovative and efficient approach to treat both microplastics composite heavy metal pollutants while elucidating the impact of environmental factors on the adsorption of heavy metals by electron beam-aged microplastics. The aim is to provide a theoretical basis and guidance for controlling microplastics composite pollution.

Formation of Fe2(SO4)3-Fe2O3 interface induced by OCFGs electrostatic anchoring on AC surface: High efficiency NH3-SCR performance at low temperatures

Low-temperature activity and SO2 poisoning were the key factors limiting the application of NH3-SCR catalysts. In this study, Fe2(SO4)3/AC and Fe2(SO4)3/OAC catalysts were prepared by oxidation function modification and incipient wetness impregnation. In the temperature range of 100–250 ℃, the catalytic performance and SO2 resistance of Fe2(SO4)3/AC and Fe2(SO4)3/OAC catalysts were investigated, the denitrification efficiency increased from 28 % (Fe2(SO4)3/AC) to 80 % at 100 °C and reached 100 % at 170 °C, and 100 ppm SO2 was introduced at 250 ℃ for 24 h, the denitrification efficiency remains 100 % unchanged. The mechanism of activity enhancement was further explored by BET, XRD, ICP, TG, XPS, FT-IR, H2-TPR and NH3-TPD. The results showed that (NH4)2S2O8 modification enhanced the surface acidity, and the increase of surface oxygen-containing functional groups improved the redox performance. At the same time, due to electrostatic anchoring effects of oxygen-containing functional groups, Fe3+ and SO42- were adsorbed at different sites and promoted the binding of S to the carbon skeleton to form −C-S-C-. Thus, the interaction between OAC and Fe2(SO4)3 caused part of Fe2(SO4)3 to decompose into Fe2O3, and the formation of Fe2(SO4)3-Fe2O3 interface further enhanced the acidity and redox properties. More importantly, the decomposition temperature of NH4HSO4 was lower and the decomposition was more thorough on the Fe2(SO4)3/OAC than that of Fe2(SO4)3/AC. Finally, the possible mechanism of (NH4)2S2O8-modified Fe2(SO4)3/OAC catalyst to improve NH3-SCR performance was proposed, which is of great significance for the development of NH3-SCR catalyst with sulfur resistance at low temperatures.

Effect of oxygen-containing groups in functionalized graphene on its gas sensing properties

The creation of active material for chemiresistive gas sensors with high selectivity and sensitivity will allow a step towards miniaturization and reduction of power consumption of portable gas sensors. Graphene is a promising platform for the synthesis of two-dimensional active materials with high sensitivity. In this work, applying density functional theory (DFT) calculations, the effect of oxygen-containing functional groups (O, OH, O, COOH) on the adsorption of small gas molecules (NH3, CO2, CO, H2S, NO2, SO2) was rigorously studied. Based on the adsorption energies and partial charges from DFT calculations, the sensitivity and selectivity of graphene with different functionalizations were predicted. It was found that hydroxyl and carboxyl groups demonstrate increased selectivity and sensitivity of gas sensors, and the edge of graphene with hydroxyl groups shows the highest enhancement. Graphene with a carbonyl group was found to undergo irreversible chemisorption of NO2, which can potentially cause active material degradation, limiting the recyclability of gas sensors. Most of the molecules show both donor and acceptor behavior, which highlights the importance of a thorough selection of specific functional group types. The obtained results are useful for the rational design of graphene-based active material with oxygen-containing functional groups for chemiresistive gas sensors.

Quantum chemical study of the effect of oxygen-containing functional groups on N2O adsorption on char

This work aims to investigate the effect of oxygen-containing functional groups (OFGs) on nitrous oxide (N2O) adsorption on char based on density-functional theory (DFT) at M06-2X/6-311G(d) level using pristine and defective zigzag char models. The char model configurations were geometrically optimized and single-point energy was calculated. The adsorption energy, bond length, Mayer bond order (MBO), atomic dipole moment corrected Hirshfeld (ADCH) charges, electrostatic potential (ESP), partial density of states (PDOS) and interaction region indicator (IRI) were analyzed. Results show that the presence of OFGs has little influence on the structure of char model but increases its activity. In addition, it was found that the effect of OFGs on N2O adsorption on char surface is related to char model and adsorption configurations. Further char configurations analysis after adsorbing N2O molecules suggests that the OFGs addition can significantly affect adsorption energies by changing chemical bond length and MBO. Moreover, the ESP analysis indicates that the OFGs addition increases the overall level of ESP on char surface, leading to the formation of orbital hybridization and electrons transfer and further promoting N2O adsorption on char surface. ADCH analysis indicates that OFGs affect the active site charge and facilitate N2O adsorption. IRI analysis reveals a variety of weak interactions in the structure after the incorporation of OFGs. Therefore, this study provides a theoretical foundation for a better understanding of the heterogenous adsorption of N2O on char.

Effect of oxygen-containing functional groups on the micromechanical behavior of biodegradable plastics and their formation of microplastics during aging

Biodegradable plastics (BPs) are more prone to generate harmful microplastics (MPs) in a short time, which have always been ignored. Oxygenated functional group formation is considered to be a key indicator for assessing microplastic formation, while it is difficult to characterize at a very early stage. The micromechanical properties of the aging plastic during the formation of the MPs are highly influenced by the evolution of oxygen-containing functional groups, however, their relationship has rarely been revealed. Herein, we compared changes in the physicochemical properties of BPs and non-degradable plastic bags during aging in artificial seawater, soil, and air. The results showed that the oxidation of plastics in the air was the most significant, with the most prominent oxidation in BPs. The accumulation of carbonyl groups leads to a significant increase in the micromechanical properties and surface brittleness of the plastic, further exacerbating the formation of MPs. It was also verified by the FTIR, 2D-COS, AFM, and Raman spectroscopy analyses. Furthermore, the increased adhesion and roughness caused by oxygen-containing functional groups suggest that the environmental risks of BPs cannot be ignored. Our findings suggest that the testing of micromechanical properties can predicate the formation of the MPs at an early stage.

Penetration resistance of graphene oxide/epoxy resin coating-A molecular dynamics investigation.

The functionalization of graphene is the best way to improve its interfacial compatibility and dispersibility in polymer matrix to obtain high-performance composites. In this study, three nanocomposite models with different salt layer thicknesses were established and simulated by molecular dynamics method to understand the effect of oxygen-containing functional groups on the impermeability of epoxy coatings. Molecular dynamics (MD) simulation results show that the nanocomposites have better impermeability than pure epoxy resin. The thickness of salt solution affects the permeation rate of salt solution and the interfacial properties of nanocomposites. The salt solution molecules trapped in the coating are mainly concentrated at the interface between graphene and epoxy resin, which is the main reason for the decrease in interface properties of epoxy coating. In this paper, Material Studio 8.0 was used to construct nanocomposite models with different salt layer thicknesses (GO/SW7Å, GO/SW10Å, and GO/SW13Å), and MD simulations were performed using a large-scale atomic and molecular parallel simulator (LAMMPS).

Understanding the boron rejection of cation intercalated multilayered graphene oxide (GO) membrane in reverse osmosis (RO) process: A molecular dynamics study

Cation-intercalated graphene oxide (GO) membrane has emerged as a promising candidate for desalination applications as reverse osmosis (RO) membrane. This study constructs GO membranes with different cations (K+ or Mg2+) and investigates the potential of these membranes in boron removal via nonequilibrium molecular dynamics simulations. In the aquatic environment, boron can exist in the form of boric acid or borate ion, depending on the pH of the solution. As a result, this study considers two forms of boron. This study reveals that the GO membranes effectively reject negatively charged borate ions due to their bigger hydration shell and stronger electrostatic repulsion with the membrane than neutral boric acid molecules. Moreover, K+ ion intercalated GO membranes showed higher boron rejection than Mg2+ ion intercalated GO membranes owing to weaker electrostatic attraction of K+ ions with the boric acid (or borate ions). Additionally, a summary of the effects of oxygen-containing functional groups of the GO membrane on boron rejection is provided. Since the hydroxyl and epoxy functional groups interact with boric acid molecules more strongly, these molecules are prevented from permeating through the membrane. On the other hand, the permeation rate of borate ions declines because of their stronger interactions with the carboxyl functional groups. Furthermore, Mg2+ ion intercalated GO membranes exhibited higher water permeance, excellent Na+ rejection, and poor Cl− rejection compared to K+ ion intercalated GO membranes.

The enhancement in toxic potency of oxidized functionalized polyethylene-microplastics in mice gut and Caco-2 cells

Microplastics (MPs) are inevitably oxidized in the environment, however, to date, no studies have discussed the biological toxicity of oxidized polyethylene (Ox-PE) MPs. In this study, oxidized low-density polyethylene (Ox-LDPE), a representative Ox-PE, was prepared using a selective oxidation method. The difference in toxicity between LDPE-MPs and Ox-LDPE-MPs were evaluated in C57BL/6 mice and Caco-2 cells. The proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy analyses revealed that some hydrocarbon-containing groups were transformed into carboxyl and ketone groups during selective oxidation. In vivo experiment results showed that LDPE-MPs and Ox-LDPE-MPs exists in the intestinal (duodenum and colon) of mice, and Ox-LDPE-MPs caused more severe intestinal histological changes, oxidative stress, and inflammatory response. The gut microbiota data showed that the relative abundance of Lactobacillus decreased significantly in the LDPE-MP- and Ox-LDPE-MP-exposed groups (P < 0.05). The predicted Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathway suggested that exposure to LDPE-MPs or Ox-LDPE-MPs inhibited glycan biosynthesis and metabolism in the flora (P < 0.05). In vitro experiment results showed that selective oxidation to LDPE promoted its uptake by cells and aggravated adverse effects on cells, including reduced cell viability, damaged cell membrane, oxidative stress, and mitochondrial depolarization. The major mechanism of the increased toxicity of Ox-LDPE-MPs may be its easier accumulation and the ionic effect of oxygen-containing functional groups. Overall, these findings provide insights on the differences in toxicity between LDPE-MPs and Ox-LDPE-MPs. They also provide new perspectives for understanding the biohazards of MPs, which are necessary to accurately assess the potential environmental and health risks of these plastic pollutants.

Effect of oxygen-containing functional groups and pore structure characteristics of coal on the slurryability of coal wastewater slurry

The physical and chemical characteristic of coal have an important influence on the slurryability of coal wastewater slurry. In this paper, eight different coals are used to make coal wastewater slurry, and the effects of oxygen containing functional groups and pore structure characteristics of different coal samples on the slurryability are analyzed. Results show that (a) Coal with more oxygen-containing functional groups on surface have stronger hydrophilicity, higher surface activity and have stronger adsorption capacity for water molecules, this will lead to the reduction of free water and the increase of viscosity of the slurry. (b) Coal with larger BET specific surface area and pore volume and smaller average pore diameter have the stronger ability to adsorb and store water in coal wastewater slurry, thus the concentration of coal wastewater slurry prepared from these coal is low. The conclusion of this paper can provide reference for coal selection in the preparation of coal wastewater slurry.

Effect of oxygen-containing functional groups at SWCNT on the formation of sodium and lithium dendrites

To realize high-performance and safe metal anodes for rechargeable Na/Li metal batteries, it is necessary to explore how various oxygen-containing groups on carbon nanotubes surface affect Na and Li (Na/Li) dendrites growth. Hence, the adsorption behavior of the Na/Li atom and Na/Li dendrites formation on various oxygen-containing groups (-COOH, -OH, -CO, -COO, -O-) decorated SWCNTs (O-SWCNTs) were investigated by density functional theory (DFT) calculations. Compared with intrinsic SWCNT, the groups on SWCNT promote the adsorption of Na/Li because O is more electronegative than C. The adsorption strength of Na/Li and Na2/Li2 on different O-SWCNTs depends on the electron-accepting ability of the active O atom of the groups. The result shows that only OH-SWCNT can serve as a promising current collector for the development of dendrite-free Na/Li metal batteries due to its relatively weak attraction for the second Na/Li. On the other O-SWCNTs, Na and Li dendrites can be formed through NaO and LiO bond respectively. Therefore, dendrite-free carbon tubes collector can be achieved by regulating the oxygen-containing groups on its surface. Overall, this work brings new inspiration to the preparation of collectors to avoid dendrite growth.

Enhanced oriented oxidation of all alkanes through redistributing hydroxy radical by inactivating oxygen-containing functional groups in soil organic matter

To explore the effect of oxygen-containing functional groups in SOM on the oriented oxidation of all n-alkanes (OX-A) (C10 - C30), different proportions of NaOH (NaOH: protein I = 1:1 and 2:1) were used to pretreat two soils (S1 and S2). Then the crude oil (S1: 18,173 mg/kg; S2: 9853 mg/kg) was added to carry six groups of Fenton oxidation treatments. The results showed that when the content of C-O, O-H of phenol or alcohol, and O-H of carboxyl in the soil decreased, the two soils realized oriented oxidation of all n-alkanes under the low intensity of hydroxyl radical (•OH) (1.02 a.u.). The oriented oxidation of all n-alkanes group was as high as 4477.00 mg/kg (S1) and 2685.00 mg/kg (S2), respectively, which was 0.53–2.33 times of the other groups. In addition, after 1:1 regulation, the ability of •OH to capture oxygen-containing functional groups in SOM decreased, then the relative reactivity coefficient k of •OH to total petroleum hydrocarbons (TPH) increased to 2.01 and 1.81 (k > 1), which was 1.02–1.47 and 0.93–1.32 higher than the other five groups. The competition of SOM for oxidants was decreased by improving the reactivity of •OH with TPH. Thus, more •OH (S1: 48%, S2: 46%) transferred to efficiently oxidize TPH (S1: 310.60 mg/mmol, S2: 220.20 mg/mmol). In general, this study reduced the ineffective consumption of oxidants after developing inactivation, thereby the utilization efficiency of H2O2 was improved and the stability of petroleum-contaminated soil remediation was enhanced.

The Key Effect of Carboxyl Group and CuN2 O2 Coordinate Structure for Cu, N Co-Doped Carbon Dots with Peroxidase-Like Property.

Carbon dots (CDs) with good water solubility and biocompatibility have become a research hotspot in the nano-enzyme and biomedical field. However, the problems of low catalytic activity and ambiguous catalytic site of CDs as nanozymes still need to be addressed. In this work, CDs loaded with Cu single atoms are obtained through pyrolysis, and the coordination structure and surface functional groups are regulated by adjusting the pyrolysis temperature. CDs obtained at 300°C (named Cu-CDs-300) have the most carboxyl content and Cu is coordinated in the form of CuN2 O2 , which can better decompose H2 O2 to produce free radical and is beneficial to catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). The vmax is 6.56*10-7 ms-1 , 6.56 times higher than that of horseradish peroxidase (HRP). Moreover, Cu-CDs-300 can effectively lead to CT26 apoptosis by generating much free radicals. This work demonstrates the synergistic effect of oxygen-containing functional groups and metal coordination structures on peroxide-like activity of CDs and provides new ideas for the design of clear active structure and high efficiency peroxide-like single atom CDs catalyst.

Co-pyrolysis with pine sawdust reduces the environmental risks of copper and zinc in dredged sediment and improves its adsorption capacity for cadmium

Proper treatment of heavy metal-contaminated dredged sediment (DS) is crucial to avoid secondary pollution. Effective and sustainable technologies are desired for the treatment of Zn- and Cu-contaminated DS. Due to the advantages of low energy consumption and time saving, co-pyrolysis technology was innovatively applied to treat Cu- and Zn-polluted DS in this study, and the effects of the co-pyrolysis conditions on Cu and Zn stabilization efficiencies, potential stabilization mechanisms, and the possibility for resource utilization of co-pyrolysis product were also investigated. The results showed that pine sawdust is an appropriate co-pyrolysis biomass for the stabilization of Cu and Zn based on the leaching toxicity analysis. The ecological risks of Cu and Zn in DS were reduced after co-pyrolysis treatment. The total concentrations of Zn and Cu in co-pyrolysis products were decreased by 5.87%–53.45% and 8.61%–57.45% of that in DS before co-pyrolysis. However, the total concentrations of Zn and Cu in DS remained basically unchanged after co-pyrolysis, which indicating the decreases in total concentrations of Zn and Cu in co-pyrolysis products were mainly related to dilution effect. Fraction analysis indicated that co-pyrolysis treatment contributed to transforming weakly bound Cu and Zn into stable fractions. The co-pyrolysis temperature and mass ratio of pine sawdust/DS had a greater influence than co-pyrolysis time on the fraction transformation of Cu and Zn. The leaching toxicity of Zn and Cu from the co-pyrolysis products was eliminated when the co-pyrolysis temperature reached 600 and 800 °C, respectively. Analysis of the X-ray photoelectron spectroscopy and X-ray diffraction results demonstrated that co-pyrolysis treatment could transform mobile Cu and Zn in DS into metal oxides, metal sulfides, phosphate compounds, etc. Batch adsorption procedures suggested that the co-pyrolysis product possessed a high adsorption capacity for Cd (95.70 mg/g at 318 K). The formation of CdCO3 precipitates and the complexation effects of oxygen-containing functional groups were the principal adsorption mechanisms of the co-pyrolysis product. Overall, this study provides new insights into sustainable disposal and resource utilization for heavy metal-contaminated DS.

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.

Effects of Oxygen-Containing Functional Groups on the Electrochemical Performance of Activated Carbon for EDLCs

Activated carbon (AC) is used in commercial electric double-layer capacitors (EDLC) as electrode active material owing to its favorable properties. However, oxygen functional groups (OFGs) present in AC reduce the lifespan of EDLCs. Thus, we investigated the correlation between the OFGs in AC and their electrochemical characteristics. Samples were prepared by heat-treating commercial AC at 300 °C-900 °C for 1 h under two gas atmospheres (N2 and 4% H2/N2 mixed gas). The textural properties were studied, and the reduction characteristics of AC under Ar and H2/Ar mixed gas atmospheres were investigated. Additionally, changes in the OFGs with respect to the heat-treatment conditions were examined via X-ray photoelectron spectroscopy. The specific surface areas of AC-N and AC-H were 2220-2040 and 2220-2090 m2/g, respectively. Importantly, the samples treated in hydrogen gas exhibited a higher yield than those treated in nitrogen while maintaining their pore characteristics. Additionally, the electrochemical performance of the AC was significantly enhanced after the reduction process; the specific capacitance increased from 62.1 F/g to 81.6 F/g (at 0.1 A/g). Thus, heat treatment in hydrogen gas improves the electrochemical performance of EDLCs without destroying the pore characteristics of AC.

Effect of oxygen functional groups on competitive adsorption of benzene and water on carbon materials: Density functional theory study

It is important to study the effect of oxygen-containing functional groups on the competitive adsorption mechanism of benzene and water on the surface of carbon materials, and to directional modification of activated carbon to improve its selective adsorption of benzene in air. In this study, the adsorption characteristics of benzene and water on original and linked ester, carboxyl, hydroxyl, carbon materials linked by ether groups were calculated by quantum chemical simulation based on density functional theory. The types and proportions of weak interactions in the adsorption process were calculated by energy decomposition analysis, and the adsorption mechanism of carbon materials for water and benzene was described. The influence and contribution of oxygen-containing functional groups on the adsorption of benzene and water were further analyzed by van der Waals potential and electrostatic potential, respectively, so as to determine the difference in the adsorption effect of different types of oxygen-containing functional groups on the two molecules. It was found that the carboxyl group has a great influence on the hydrophilicity of carbon materials, and the electrostatic potential distribution before and after linking the carboxyl group changed significantly. Therefore, they can attract each other with water through hydrogen bonds and occupy the surface adsorption sites of carbon materials, thereby inhibiting the adsorption of benzene on carbon materials. On the contrary, due to its hydrophobic properties, the ether group will free up adsorption space for the adsorption of benzene on the surface of the carbon material, which is beneficial to the adsorption of benzene. The adsorption experiments were carried out, and the results were consistent with the simulation. This study provides an idea for preparing efficient carbonaceous adsorbent of benzene and reducing benzene pollution in industry.

Study on the effect of SDBS and SDS on deep coal seam water injection

Coal seam water injection, as an important disaster prevention means in the process of coal mining, can effectively suppress coal dust, add water injection additives, can effectively improve the wettability of coal body, improve the permeability of coal body, so as to achieve the prevention of rock burst. To improve the wettability of coal in coal seam water injection, the surfactant is often added to water, but sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfate (SDS) have limitations in improving wettability of deep coal seam by injecting water. Therefore, it is very important to determine the influencing factors of SDBS and SDS to improve the wettability of coal. In this paper, the effects of oxygen-containing functional groups and minerals in coal on the wettability of coal are revealed, and the wettability mechanism of SDBS and SDS is expounded from the microscopic point of view. SEM was used to characterize the interaction between coal surface and surfactant, and the contact angle experiment was used to verify the influence of minerals in coal on wettability. Inductively coupled plasma atomic emission spectroscopy (ICP) and dynamic light scattering (DLS) tests were used to characterize the interaction of SDBS, SDS with minerals and the size of precipitation generated by the interaction of SDBS, SDS and mineral ions. The results showed that SDBS and SDS interact with Ca2+ to produce precipitation and block the flow of water in coal, which is not conducive to improving the wettability of deep coal seam to a certain extent. The significant chelating effect of chelating agent and Ca2+ provides a feasible solution to this problem.

Simulation study on the adsorption characteristics of CO2 and CH4 by oxygen-containing functional groups on coal surface

ABSTRACT To investigate the adsorption mechanism of CO2 and CH4 with oxygen-containing functional groups in coal, the structural models of coal with different functional groups of carboxyl, hydroxyl, carbonyl, and ether bonds were constructed using Materials Studio software, and the adsorption isotherms, heat of adsorption, adsorption energy, energy distribution, and adsorption configurations of CO2 and CH4 adsorbed by different functional group structures were analyzed using the giant regular GCMC method. The results showed that the presence of carboxyl, hydroxyl, and carbonyl functional groups will promote the adsorption of CO2 by coal, and the intermolecular interaction energies of the model with the addition of carboxyl, hydroxyl, and carbonyl groups, and CO2 increased by 70.37%, 33.67%, and 14.26%, respectively. The order of the adsorption strength of the five structures is: AC-COOH > AC-OH > AC-O > AC > AC-OCH3, which indicates that the influence of oxygen-containing functional groups on the adsorption performance of CO2 by coal mainly depends on polarity. The presence of carboxyl, hydroxyl, and carbonyl functional groups weakens the adsorption of CH4 on coal, and the interaction energy between the model and gas molecules with the addition of carboxyl, hydroxyl, carbonyl, and ether bonds reduced by 41.83%, 36.14%, 26.22%, and 80.21%, respectively. The order of the adsorption strength of the five structures is: AC > AC-O > AC-OH > AC-COOH > AC-OCH3, which indicates that the effect of oxygen-containing functional groups on the adsorption of CH4 on coal mainly depends on hydrophobicity; the introduction of ether-bonded functional groups does not favor the adsorption of CO2 and CH4 molecules on coal. It indicates that the ether bond has a certain repulsive effect on CO2 and CH4 molecules. In different functionalized coal structures with the same carbon atom skeleton, there are different adsorption capacities for CH4 as well as CO2, but in the same functionalized structure, the adsorption magnitude relationship is CO2 > CH4, indicating that the coal body structure interacts with CO2 more than CH4.

Experimental and molecular perspective on VOCs adsorption and separation: Study of the surface heterogeneity and oxygen functionalizing

Heteroatoms doping brings a burgeoning class of adsorbents for the removal of volatile organic compounds (VOCs). It is of great importance to reveal the molecular interaction and adsorption mechanism on account of the nanoscale nature of adsorption. Herein, we combined adsorption experiments and theoretical calculations (using porous carbon as adsorbent and graphene as computational model) to reveal the influence of doping oxygen atoms on the surface heterogeneity and the VOCs adsorption performance, and to investigate the synergistic effect of oxygen-containing functional groups. The results show that oxygen doping can significantly change the charge distribution and improve the adsorption and separation of methanol and acetone (the selected representative of VOCs). Among various oxygen-containing functional groups, the carboxyl doped surface displays the largest theoretical adsorption capacity of methanol (36.74 mmol/g) and acetone (18.35 mmol/g) and the highest selectivity (16.11 at 0.1 kPa). Specifically, the doped oxygen containing groups significantly changed the charge distribution on the carbon surface (e.g., –0.50 to 0.43 e for carboxyl group), and enhanced the electrostatic interaction between the surface and VOCs molecules, thereby increasing the adsorption capacity. Moreover, the stronger binding energy between the oxygen-functionalized surface and methanol contributed to the preferential adsorption of methanol on the oxygen active sites, leading to the aggregation of methanol molecules, which is responsible for the high selectivity. Meanwhile, no obvious synergistic effect between oxygen functional groups was found. This study provides fundamental understanding of the role of oxygen-containing groups toward VOCs adsorption.

Effect of oxygen-containing functional groups of layered graphene oxide membrane on the removal of amoxicillin: a molecular dynamics study

ABSTRACT The removal of amoxicillin (AMX) from the pharmaceutical industrial wastewater with a non-lamellar graphene oxide (GO) membrane has been investigated using non-equilibrium molecular dynamics (MD) simulations. The influence of oxygen-containing functional groups of the GO nanosheets on the separation of AMX molecules is investigated by considering three different membranes. These membranes are GO, reduced GO, and extended reduced GO which differ in the number of oxygen-containing functional groups on the GO nanosheets. AMX solution is used as the feed solution, and a mixture of and solution is used as a draw solution. This study reveals that the water and ion permeance depend on the number of oxygen-containing functional groups and pore sizes of the membranes. Reducing the number of oxygen-containing functional groups of the membranes leads to smaller pore sizes and lower water permeance. The retention and dynamics of AMX molecules reveal that the AMX molecules are likely to be retained on the basal plane of the membrane. This can be attributed to a strong interaction between hydroxyl and epoxy functional groups of the GO nanosheets with AMX molecules.