Introduction Of Oxygen-containing Functional Groups Research Articles

Polyethylene, whose surface has been modified by UV irradiation, induces cytotoxicity: A comparison with microplastics found in beaches

Microplastics, plastic particles 5 mm or less in size, are abundant in the environment; hence, the exposure of humans to microplastics is a great concern. Usually, the surface of microplastics found in the environment has undergone degradation by external factors such as ultraviolet rays and water waves. One of the characteristics of changes caused by surface degradation of microplastics is the introduction of oxygen-containing functional groups. Surface degradation alters the physicochemical properties of plastics, suggesting that the biological effects of environmentally degraded plastics may differ from those of pure plastics. However, the biological effects of plastics introduced with oxygen-containing functional groups through degradation are poorly elucidated owing to the lack of a plastic sample that imitates the degradation state of plastics found in the environment. In this study, we investigated the degradation state of microplastics collected from a beach. Next, we degraded a commercially available polyethylene (PE) particles via vacuum ultraviolet (VUV) irradiation and showed that chemical surface state of PE imitates that of microplastics in the environment. We evaluated the cytotoxic effects of degraded PE samples on immune and epithelial cell lines. We found that VUV irradiation was effective in degrading PE within a short period, and concentration-dependent cytotoxicity was induced by degraded PE in all cell lines. Our results indicate that the cytotoxic effect of PE on different cell types depends on the degree of microplastic degradation, which contributes to our understanding of the effects of PE microplastics on humans.

Selective oxygen-doping in self-supportive carbon electrode by electrochemical oxidation for electrocatalytic synthesis of hydrogen peroxide

We report the selective introduction of oxygen-containing functional groups for two-electron oxygen reduction reaction (2e-ORR) in self-supportive carbon electrode using electrochemical oxidation method. The optimal electrode shows hydrogen peroxide (H2O2) selectivity up to 95 %. CO is found active to control 2e-ORR selectivity and mechanism of oxygen species variation is elucidated by in situ infrared reflection absorption spectroscopy. We further improve mass transfer by introducing highly interconnected macropores in electrode, which shows H2O2 yield of 144 mmol cm−2 h−1 and Faradaic efficiency of nearly 100 %. These may inspire advanced active electrode creation for applications through selective electrochemical doping and structural design.

Significant Increase in the Dipole Moment of Graphene on Functionalization: DFT Calculations and Molecular Dynamics Simulations.

The limited solubility of graphene in water can be attributed to the existence of π-π bonds connecting its layers. Functionalized graphene or graphene oxide (GO) is frequently produced in order to overcome the shortcomings of graphene. Using density functional theory (DFT) calculation, functionalized graphene with various combinations of hydroxyl, epoxy, and carboxylic functional groups were investigated computationally. The study focused on the effects of functional group combinations on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, giving information about the chemical reactivity and stability of the molecules under investigation. Global chemical reactivity descriptors, including chemical hardness, softness, electronegativity, chemical potential, and electrophilicity index, were calculated to further elucidate the overall stability and reactivity of the molecules. The results demonstrated that the introduction of oxygen-containing functional groups on graphene significantly influenced its electronic properties, leading to variations in the chemical reactivity and stability. Molecular electrostatic potential (MEP) maps highlighted the susceptibility of specific regions to electrophilic and nucleophilic attacks. The flexibility and stability of functionalized graphene through root mean square fluctuation (RMSF) and root mean square deviation (RMSD) analyses indicate the stability of functionalized graphene in water. This comprehensive computational investigation provides valuable insights into the design and understanding of functionalized graphene for potential applications in drug delivery.

Study on the performance of MnOx modified graphite felts as electrodes for iron-chromium redox flow battery obtained by permanganic acid etching

In order to improve the electrochemical performance of graphite felt electrodes, this paper utilizes the strong oxidizing and corrosive properties of potassium permanganate under acidic conditions to modify graphite felt, and investigates the degree of permanganic-acid's modification of graphite felt at different temperatures as well as the performance of modified graphite felt as an electrode for iron-chromium redox flow batteries. The cyclic voltammetry and electrochemical impedance of the electrodes were tested by a three-electrode system, and the results showed that the introduction of oxygen-containing functional groups reduced the conductivity of the graphite felt, but also the charge transfer impedance. The single-cell test results show that the graphite felt corroded by permanganic-acid at 60 °C has the best performance after assembling the battery, and the discharge capacity and energy efficiency at a current density of 60 mAcm−2 are 41 % and 21 % higher than those of the battery assembled with GF as the electrode. DFT calculations show that the introduction of MnOx can adsorb the active substances in the solution, thus improving the battery efficiency. This method of introducing the number of oxygen-containing functional groups on the surface of graphite felt by temperature modulation and thus obtaining good electrochemical performance of the electrode can provide new ideas for industrial applications.

In-situ implantation of oxygen-containing reaction site in heterogeneous carbon–nitrogen in-plane polymer heterojunction with donor–acceptor feature for enhanced CO2 photoconversion

Herein, a heterogeneous carbon–nitrogen heterojunction g-C3N4-C2N (CC) is constructed by embedding electrophilic hexaazatriphenylene (HAT) into the heptazine framework of graphitic carbon nitride (g-C3N4) through in-plane fusing. The similar chemical compositions and molecular structures between g-C3N4 and C2N derived from HAT allow for great compatibility in co-planarly grafting. Electrochemical tests and theoretical calculations show that after co-planar grafting with C2N, g-C3N4 forms a typical donor–acceptor relationship with it. The photoinduced electrons generated by the excitation of the composite would converge to C2N, effectively enhancing the separation of electron-hole pairs. Moreover, oxygen-doped g-C3N4-C2N (CC-O) is obtained by the introduction of oxygen-containing functional groups, and the CO2 adsorption performance is further optimized. In the absence of any co-catalyst, photosensitizer or organic sacrificial agent, the photocatalytic reduction of CO2 to CO on the oxygen-doped polymer CC-O0.2 exceeded a yield of 28.64 μmol g-1h−1 with a selectivity of 99 %. Furthermore, the reaction site for photoconversion and the reason for different photocatalytic efficiency are revealed. The strategy of synergizing the two modification methods in this work offers more possibilities for the rational design of organic polymers for light-driven carbon neutralization.

Effects of Dissolved Organic Matter on the Release of Soluble Phosphorus and Fluoride Ion from Phosphate Ore

Unreasonable storage of phosphate ore is becoming an important pathway causing phosphate pollution in the surrounding aquatic environment. However, there is little research on the influence of dissolved organic matter (DOM) in water on the fate of phosphate ore. Here, we collected phosphate ores from two phosphate mines along the coast of Tanglang River and studied the effects of DOM concentrations and pH on the release of soluble active phosphorus (SRP) and fluoride ion (F−) from phosphate ores using humic acid (HA) as the representative of DOM. Based on the analysis of ZP, FTIR, XPS, and SEM, the influence mechanism of HA was revealed. The results showed that HA efficiently promoted the release of SRP and F− from phosphate ore. With decreasing pH, the P release increased in both water and HA solutions in general. The beneficial influence of HA on the release of SRP and F− from phosphate ore was ascribed to the introduction of oxygen-containing functional groups by HA, which altered the surface properties and enhanced the dispersion stability of phosphate ore. These findings provided new insights into the dispersion behavior of phosphate ore, which is helpful in promoting the pollution control and management strategy of phosphate ore.

Oxygen-modified graphitic carbon nitride with nitrogen-defect for metal-free visible light photocatalytic H2O2 evolution

Photocatalytic oxygen reduction is regarded as the cleanest approach for the production of hydrogen peroxide (H2O2). Herein, oxygen-modified graphite carbon nitride (g-C3N4) with nitrogen-defect (namely g-C3N4-ND4-OM3) was synthesized by a feasible method. Owing to the existence of nitrogen vacancy and oxygen-containing functional group, the absorption bands derived from n → π* and π → π* electronic transitions were enhanced, thereby enlarging the visible light response range of catalysts. Interestingly, nitrogen-defect can capture electron and effectively suppress the recombination of photoinduced electrons and holes. More importantly, the introduction of oxygen-containing functional groups can improve the hydrophilicity of g-C3N4, which was beneficial for the adsorption of dissolved oxygen. The electrostatic potential distributions of g-C3N4-based photocatalyst structural unit were also changed after introducing nitrogen vacancy and oxygen-containing functional group, and the electron-donating ability of g-C3N4 was improved. As a result, the evolution rate of H2O2 catalyzed by g-C3N4-ND4-OM3 was as high as 146.96 μmol/g/L under visible light irradiation. The photocatalytic H2O2 generation was completed through the direct 2-e− oxygen reduction. In short, current work will share novel insights into photocatalytic H2O2 generation over g-C3N4-based catalyst.

Highly efficient electro-peroxone enhanced by oxygen-doped carbon nanotubes with triple role of in-situ H2O2 generation, activation and catalytic ozonation

The oxygen-doped carbon nanotubes coated on the carbon felt acted as cathode to enhance the electro-peroxone (OCNT-EP) process. Owing to the introduction of oxygen-containing functional groups and defect sites, the OCNT modified cathode could achieve in-situ H2O2 generation, activation, and catalytic ozonation in the EP process. The OCNT-EP showed a 2.3-folds apparent first-order rate constant (k) compared with the EP process using CNT cathode (CNT-EP) for atrazine (ATZ) degradation. According to the processes comparison, quenching experiments, electron paramagnetic resonance (EPR) analysis and determination of hydroxyl radical, it was proved that more.OH and 1O2 were generated by the in-situ H2O2 activation and catalytic ozonation in the OCNT-EP process. Especially, this process improved pollutants degradation under acidic condition for the in-situ H2O2 activation and catalytic ozonation, expanding the pH application range of the EP process with a lower energy consumption (0.10 kWh/g ATZ). What’ more, the OCNT modified cathode performed excellent stability with 20 cycle tests, and demonstrated all improved degradation rate (21.7%−78.0%) for various pollutants (carbamazepine, sulfamethazine, phenol and 2,4-dichlorophenol). Therefore, the OCNT-EP process could be considered as a promising and enhanced EP process for wastewater treatment.

Highly sensitive graphene ammonia sensor enhanced by concentrated nitric acid treatment

The ammonia (NH3)-sensing performance of graphene gas sensor treated with concentrated nitric acid (HNO3) was systematically studied in this paper. The performance of graphene gas sensor has been significantly improved after simple immersion in concentrated HNO3 (65 wt%) at a certain temperature (52 °C). In the test concentration range (20 ∼ 100 ppm), the NH3-response of the treated graphene gas sensor is increased by 3.02 ∼ 3.358 times, and the theoretical limit of detection (LOD) is 0.027 ppm (27 ppb). The treated sensor also shows good repeatability, stability and ultra-high selectivity. In the same concentration test, the response of NH3 is dozens of times higher than others. XPS, FTIR and Raman spectra analysis revealed that the nondestructive introduction of oxygen-containing functional groups (NO2–) onto graphene surface by concentrated HNO3 treatment is considered to be the key to improve the NH3-sensing performance of graphene gas sensors. NO2– groups are supposed to provide abundant O atoms as effective adsorption sites to assist graphene to adsorb NH3, thus improving the NH3-response of graphene. A simple, effective and low-cost method is proposed to improve the NH3-sensing performance of graphene in this work, which is of great significance to promote the practical application of graphene gas sensor.

Facile preparation of an oxygen-functionalized carbon felt electrode to improve VO2+/VO2+ redox chemistry in vanadium redox flow batteries

Herein, a new method for the facile introduction of oxygen-containing functional groups on a carbon felt electrode in a short treatment time has been proposed for application in a vanadium redox flow batteries (VRFBs). Benzoyl peroxide (BPO) can produce free radicals by attacking the CC bonds or CH bonds of the carbon felt. The generated unstable free radicals allow further reactions with oxygen to yield oxygen-containing functional groups on the surface of the carbon felt electrode. The electrochemical performance of the BPO-treated carbon felt electrode toward the VO2+/VO2+ redox reaction was superior to that of the pristine carbon felt electrode. Therefore, the VRFB cell employing the BPO-treated carbon felt electrode showed an outstanding energy efficiency of 75% at a current density of 100mAcm−2. This improvement is attributed to the well-known electrocatalytic effects of the oxygen-functionalized surface properties of the BPO-treated carbon felt electrode.

Effect of Heteroatom Doped Graphite Electrode Prepared By Ultrasonication on Energy Efficiency of Vanadium Redox Flow Battery

The vanadium redox flow battery (VRFB) is considered a promising candidate for large-scale energy storage because of their advantages such as long lifetime, flexible design, and safety against explosion. However, the high overpotential induced by high polarization and inferior reversibility of its electrode remain challenges to its application. Therefore, several groups have studied methods of electrode surface modification aimed at increasing the number of active sites. There are two widely used approaches to modify the electrode surface, namely, (i) introduction of oxygen-containing functional groups, such as C–OH or C=O, as active sites through thermal treatment, acid treatment, or electrochemical oxidation, and (ii) introduction of an electrocatalyst such as a noble metal, metal oxide, heteroatom, or carbon-based material. Recently, some studies reported effect of dual functionalization onto electrode surface, thus manifesting synergistic effect and improving energy efficiency of VRFB. Representative examples include dual functionalization of nitrogen and metal oxide (WO3 and Mn3O4) or nitrogen and another heteroatom (oxygen and boron).In this study, we report a simple and easy method for nitrogen-sulfur dual functionalization on the graphite felt surface to enhance the energy efficiency of VRFB via self-polymerization and graft method. In addition, surface properties were investigated using various analytical techniques, and effect of dual functionalization was examined through comparison with the nitrogen functionalized graphite felt

Modeling the Oxidative Aging Kinetics and Pathways of Asphalt: A ReaxFF Molecular Dynamics Study

The ReaxFF molecular dynamics simulations, which can predict chemical reactions, were performed on integral asphalt and individual asphalt molecules at different temperatures and oxygen levels to investigate the oxidation mechanism of asphalt and develop a molecular model suitable for aged asphalt. The simulation of integral asphalt suggests that the main oxidation products of asphalt are C–O, H–O, and S–O bonds. The oxygen level has the greatest influence on the yield of C–O bonds, and the temperature has the greatest influence on the H–O bonds. The simulation of individual asphalt molecules indicated that the oxidation of asphalt is accompanied by the decomposition of the aromatic rings, and thus, the aromaticity of the oxidized asphalt is decreased. Oxidation of asphaltenes starts with the oxygen molecules attacking the aromatic ring and generating a ketone, while the initial reactions of the other components are diverse. In addition, the simulation results were validated with Fourier transform infrared spectroscopy and nuclear magnetic resonance tests and were used to study the effects of oxidation on the characteristics of asphalt. The results suggested that the introduction of oxygen-containing functional groups decreases the component compatibility of asphalt and causes the aged asphalt to be harder and more viscous.

Three-dimensional carbon fiber-graphene network for improved thermal conductive properties of polyamide-imide composites

Thermal conductive polymer matrix composites are becoming more widely used in modern electronic devices. However, the dispersion of the filler in the composite material limits the improvement of its heat dissipation performance. In order to solve the problem, we prepared polyamide-imide composites with three-dimensional (3D) carbon fiber-graphene network. The network is built by braided frame of carbon fiber felt and the hydrogen bonding between carbon fiber and graphene oxide. When the amount of filler is 4.25 wt%, the vertical thermal conductivity (TC) of composites reaches 0.53 W m−1 K−1, which is 165% higher than that of pure PAI. The improvement of TC is mainly attributed to the following factors, for example, 1) the 3D carbon fiber-graphene network structure was established to construct the heat conduction path in the composite material; 2) the interaction between fillers reduced contact thermal resistance; 3) the introduction of oxygen-containing functional groups adversely affected the TC of the composite. Meanwhile, the tensile strength of the composites reaches 34.1 MPa and the Young's modulus is 1.2 GPa. The composites can be used as a heat sink for next-generation electronic devices.

Separation of polyvinyl chloride from waste plastic mixtures by froth flotation after surface modification with sodium persulfate

A new method of surface treatment based on advanced persulfate oxidation technology is proposed for separation of plastics by froth flotation. By means of sodium persulfate treatment, waste plastic mixtures, including polyvinyl chloride (PVC), polycarbonate (PC) and polystyrene (PS), were selectively modified to achieve effective flotation separation. After sodium persulfate treatment, flotation percentage of PS and PC decreased significantly, while flotation percentage of PVC was not affected. The mechanism of sodium persulfate treatment was examined by contact angle, Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The flotability reduction of PS and PC was in virtue of the increase of surface hydrophily. FT-IR analysis and XPS analysis demonstrated the introduction of oxygen-containing functional groups on the surface of PS and PC. The optimum conditions for separating PVC from plastic mixtures were sodium persulfate (Na2S2O8) concentration 0.1 M, temperature 70 °C, pH 10.5, treatment time 30 min, frother concentration 15.8 mg/L and flotation time 4 min. The impacts of particle size, mass ratio and reusability of Na2S2O8 solution were also studied. The results demonstrated that under optimum conditions, PVC was efficiently separated from plastic mixtures. The purity and the recovery of PVC were up to 99.77% and 100%. The proposed method is a simple, environmentally friendly and efficient way to promote the separation of PVC from waste plastic mixtures.

Excellent adsorption performance of dibenzothiophene on functionalized low-cost activated carbons with different oxidation methods

ABSTRACTLow-cost activated carbon (KAC) was functionalized by HNO3, (NH4)2S2O8 and air oxidation, respectively, to remove dibenzothiophene (DBT) from model fuel. The changes in physical and chemical properties of these activated carbons were characterized by thermal analysis, elemental analysis, nitrogen adsorption apparatus, Raman spectra, scanning electron microscope and Boehm’s titration method. HNO3 and (NH4)2S2O8 oxidation result in a significant decrease in pore structure, while air oxidation only causes slight pore reduction due to the re-activation by O2. The oxygen-containing functional groups (OFGs) increase markedly after oxidative modification, in which (NH4)2S2O8 oxidation is considered as the most efficient method with respect to the introduction of OFGs. HNO3 and (NH4)2S2O8 oxidation are more selective to generate carboxyls and lactones, whereas air oxidation creates more phenols, carbonyls and ethers. The DBT adsorption capacity follows the order: NAC (HNO3-oxidized KAC) > OAC (air-oxidized KAC) > KAC > SAC ((NH4)2S2O8-oxidized KAC), implying the introduction of OFGs is beneficial for the DBT adsorption process, especially for selectivity, but excessive OFGs have a negative effect on the removal of DBT. Thus, to achieve high DBT adsorption performance, there should be a trade-off between the micropore volume and the OFGs amount.

Modifying optical properties of reduced/graphene oxide with controlled ozone and thermal treatment in aqueous suspensions

Graphene possesses a number of advantageous properties, however, does not exhibit optical emission, which limits its use in optoelectronics. Unlike graphene, its functional derivative, graphene oxide (GO) exhibits fluorescence emission throughout the visible. Here, we focus on controlled methods for tuning the optical properties of GO. We introduce ozone treatment of reduced graphene oxide (RGO) in order to controllably transform it from non-emissive graphene-like material into GO with a specific fluorescence emission response. Solution-based treatment of RGO for 5–45 min with ∼1.2 g l−1 ozone/oxygen gas mixture yields a drastic color change, bleaching of the absorption in the visible and the stepwise increase in fluorescence intensity and lifetime. This is attributed to the introduction of oxygen-containing functional groups to RGO graphitic platform as detected by the infrared spectroscopy. A reverse process: controllable quenching of this fluorescence is achieved by the thermal treatment of GO in aqueous suspension up to 90 °C. This methodology allows for the wide range alteration of GO optical properties starting from the dark-colored non-emissive RGO material up to nearly transparent highly ozone-oxidized GO showing substantial fluorescence emission. The size of the GO flakes is concomitantly altered by oxidation-induced scission. Semi-empirical PM3 theoretical calculations on HyperChem models are utilized to explore the origins of optical response from GO. Two models are considered, attributing the induced emission either to the localized states produced by oxygen-containing addends or the islands of graphitic carbon enclosed by such addends. Band gap values calculated from the models are in the agreement with experimentally observed transition peak maxima. The controllable variation of GO optical properties in aqueous suspension by ozone and thermal treatments shown in this work provides a route to tune its optical response for particular optoelectronics or biomedical applications.

A strategy for constructing the compact carbon structure with high volumetric performance for supercapacitors from porous carbons

In this paper, we present an approach to construct the compact carbon structure with high volumetric capacitive performance by means of the porous carbon structural collapse and the introduction of oxygen-containing functional groups, which is exemplarily realized by oxidizing the porous titanium carbide-derived carbon (CDC) via a modified Hummers method. Electrochemical investigations demonstrate that the oxidized CDC exhibits simultaneously outstanding volumetric capacitance (216.6 F cm−3) and high gravimetric capacitance (228 F g−1) in 6 M KOH aqueous electrolyte, almost 23 and 16 times improvement in comparison to those of the pristine CDC (9.4 F cm−3 and 14 F g−1), respectively. Furthermore, the oxidized CDC also exhibits an excellent cycling stability (almost 92% specific capacitance being retained even after 10,000 cycles). The results of this work suggests that the strategy for constructing the compact carbon structure from the porous carbon by means of the structural collapse and the introduction of oxygen-containing functional groups will be promising for the development of the electrode material with high volumetric performance for supercapacitors.

Enhanced electrochemical performance of graphitized carbide-derived carbon in alkaline electrolyte

A graphitized carbide-derived carbon (CDC), synthesized by chlorination of TiC at 1000°C, has high specific surface area (SSA), hierarchical micro- and meso-pores, and excellent electrical conductivity. However, the low hydrophilicity leads to poor supercapacitive in alkaline electrolyte. A strategy that introducing oxygen-containing functional groups onto the graphitized CDC by nitrate acid treatment is presented to improve its surface wettability. The treated CDC exhibits a great increase in specific capacitance (from 11.3 to 146Fg−1) and, most interestingly, an enhanced power capability, a rectangular shape being maintained in CV curves even at the scan rate of 500mVs−1. The superiority of the treated CDC is caused by the improved wettability, maintained mesopores and high accessible SSA. Moreover, the introduction of oxygen-containing functional groups contributes the pseudocapacitance of graphitized CDC. Therefore, HNO3 treatment is a promising way to improve the supercapacitive performance of graphitized carbon materials with mesopores and high specific surface area.

Sorption mechanisms of organic compounds by carbonaceous materials: site energy distribution consideration.

Sorption of naphthalene, lindane, and atrazine on 10 kinds of carbonaceous materials which included four kinds of graphene, three kinds of graphite, two kinds of carbon nanotubes and one kind of mesoporous carbon was investigated. The approximate sorption site energy distributions were calculated based on Dubinin-Ashtakhov (DA) model. The average sorption site energy and standard deviation of the site energy distribution were deduced and applied to analyze the interaction between sorbents and sorbates, and the sorption site heterogeneity. The introduction of oxygen-containing functional groups to the sorbents caused a decrease in their average sorption energy for the studied compounds. However, relative to the decrease in average site energy, the reduction in number of sorption sites as indicated by surface area more strongly reduced their sorption capacity to the tested carbonaceous materials based on the result of the linear regression analysis. Sorption site heterogeneity of the sorbents decreased as their oxygen contents increased, which is attributed to the better dispersion of the oxygen-containing materials as indicated by their TEM images. The method proposed in this study to quantify the average sorption site energy and heterogeneity is helpful for a better understanding of the sorption mechanisms of organic pollutants to carbonaceous materials.

Determination of the Mechanical Properties of a Poly(methyl methacrylate) Nanocomposite with Functionalized Graphene Sheets through Detailed Atomistic Simulations

Recent experimental studies have demonstrated that the introduction of oxygen-containing functional groups in graphene sheets can greatly enhance the mechanical properties of their nanocomposites with polar polymers even at extremely low loadings. Motivated by these reports, we determine here the elastic constants of syndiotactic poly(methyl methacrylate) (sPMMA) at small wt % loadings of graphene sheets through atomistic modeling. To carry out a comparative study of the effect of graphene functionalization on the degree of mechanical reinforcement, we address both pure (i.e., unfunctionalized) and functionalized graphene sheets bearing epoxy and hydroxyl groups randomly bound on both sides of their surface in the host sPMMA matrix. The calculation of elastic constants (which involves no adjustable parameters) follows the methodology originally proposed by Theodorou and Suter [Macromolecules 1986, 19, 139], and has been based on the use of the Dreiding all-atom force-field. Our predictions for the elastic...