Introduction Of Oxygen Functional Groups Research Articles

Insight into roles of carbon anodes for removal of refractory organic contaminants in electro-peroxone system: Mechanism, performance and stability

Electro-peroxone (EP) is a novel technique for the removal of refractory organic contaminants (ROCs), while the role of anode in this system is neglected. In this work, the EP system with graphite felt anode (EP-GF) and activated carbon fiber anode (EP-ACF) was developed to enhance ibuprofen (IBP) removal. The results showed that 91.2% and 98.6% of IBP was removed within 20 min in EP-GF and EP-ACF, respectively. Hydroxy radical (O⋅H) was identified as the dominant reactive species, contributing 80.9% and 54.0% of IBP removal in EP-ACF and EP-GF systems, respectively. The roles of adsorption in EP-ACF and direct electron transfer in EP-GF cannot be ignored. Due to the differences in mechanism, EP-GF and EP-ACF systems were suitable for the removal of O⋅H-resistant ROCs (e.g., oxalic acid and pyruvic acid) and non-O⋅H-resistant ROCs (e.g., IBP and nitrobenzene), respectively. Both systems had excellent stability relying on the introduction of oxygen functional groups on the anode, and their electrolysis energy consumption was significantly lower than that of EP-Pt system. The three degradation pathways of IBP were proposed, and the toxicity of intermediates were evaluated. In general, carbon anodes have a good application prospect in the removal of ROCs in EP systems.

An efficient and general oxidative magnetization for preparation of versatile magnetic porous biochar at low temperature

Oxidative magnetization is an emerging method for manufacturing versatile magnetic biochar at comparatively low pyrolysis temperature, benefiting to reducing functional groups decomposition with low energy consume. A magnetic porous biochar was manufactured by a novel oxidative magnetization [KMnO4/Fe2(SO4)3 accelerated pyrolysis of kelp at 300 °C] for removing three kinds of contaminants from aqueous solution. Spherical nanoscale Fe3O4 was massively doped with introduction of oxygen functional groups simultaneously. Remarkable increase of surface area and pore volume was also observed. Benefiting from these factors, remarkably increased adsorption capability and saturation magnetization were achieved. The magnetic biochar possessed 145.71, 72.58, and 322.48 mg/g maximum adsorption amounts for Cr6+, methylene blue, and tetracycline with 17.11 emu/g saturation magnetization, respectively, in which nanoscale iron oxides and oxygen functional groups made significant contributions. Furthermore, KMnO4/Fe2(SO4)3 accelerated pyrolysis showed superior generality for fabricating high-performance magnetic biochars using diverse bio-wastes at low temperature.

Effective Surface Structure Changes and Characteristics of Activated Carbon with the Simple Introduction of Oxygen Functional Groups by Using Radiation Energy

In recent years, research has aimed to enhance the environmental friendliness of activated carbon by modifying its surface properties to effectively capture specific harmful gases. This study’s primary goal is to swiftly introduce oxygen functional groups to activated carbon surfaces using microwave and plasma techniques and evaluate their characteristics. In the microwave method, we varied nitric acid concentrations and treatment durations for surface modification. Additionally, plasma treatment was used to introduce oxygen functional groups for comparative purposes. Surface characteristics were assessed through SEM, BET, XPS, and FT-IR analyses. The results indicate that in the microwave method, the quantity of oxygen functional groups increased with longer reaction times. Specifically, the sample treated for 20 min with 8 moles of nitric acid displayed an oxygen content of 14.11 at%, and higher nitric acid concentrations led to a reduced specific surface area. In the case of plasma treatment, higher oxygen flow rates resulted in an O1s content of 17.1 at%, and an increase in oxygen flow rate introduced more oxygen functional groups but decreased the specific surface area.

Surface functionalization of vertical graphene significantly enhances the energy storage capability for symmetric supercapacitors

Vertical graphene (VG) sheets, which consist of few-layer graphene vertically aligned on the substrate with three-dimensionally interconnected porous network, make them become one of the most promising energy storage electrodes, especially for SCs. Nevertheless, the intrinsic hydrophobic nature of pristine VG sheets severely limited its application in aqueous SCs. Here, electrochemical oxidation strategy is adopted to increase the hydrophilicity of VG sheets by introducing oxygen functional groups so that the aqueous electrolyte can fully be in contact with the VG sheets to improve charge storage performance. Our work demonstrated that the introduction of oxygen functional groups not only greatly improved the hydrophilicity but also generated a pseudocapacitance to increase the specific capacitance. The resulting capacitance of electrochemically oxidized VG for 7 min (denoted as EOVG-7) exhibited three orders of magnitude higher (1605 mF/cm2) compared to pristine VG sheets. Through assembled two EOVG-7 electrodes, a symmetric supercapacitor demonstrated high specific capacitance of 307.5 mF/cm2, high energy density of 138.3 μWh/cm2 as well as excellent cyclic stability (84% capacitance retention after 10000 cycles). This strategy provides a promising way for designing and engineering carbon-based aqueous supercapacitors with high performance.

O2-Involved Electro-activation of Persulfate on Oxidized Carbon Black for Effective Sulfamethoxazole Degradation: Key Role of Side-Reactive Oxygen Reduction

The oxygen reduction reaction (ORR) was an unavoidable side reaction in the electro-activating persulfate (PS) process, especially on the ORR-active carbon materials, which has usually been ignored in previous reports. In this work, the O2/N2-involved electro-activation of the PS system was constructed to confirm the role of side-reactive ORR on oxidized carbon black (OCB) for sulfamethoxazole (SMX) degradation. With O2 involvement, 820.8 μM •OH was produced by PDS electro-activation, over 7 times more than 115.8 μM under N2 aeration, leading to a high SMX removal of 90.6% (only 67.8% under N2 aeration). Such a huge difference in •OH yield and SMX removal performance was mainly attributed to side-reactive 2e– ORR, in which as-generated H2O2 was electro-activated to produce abundant •OH and form an advanced homogeneous •OH/SO4•– oxidation system via mutual transformation with gradual acidification. Meanwhile, the introduction of oxygen functional groups and defects on the surface of carbon black calcined at 600 °C (CB600) also contributed to the improvement of SMX removal performance, attributing to their enhancing effects on SMX electro-adsorption, PDS electro-activation, and O2 electro-reduction. Thus, side-reactive oxygen reduction played the spontaneous and synergistic oxidation roles in the O2-involved electro-activating PS process, helping to design highly effective advanced oxidation systems in the future.

Electrodeposition of manganese dioxide coatings onto graphene foam substrates for electrochemical capacitors

Optimisation of electrodeposition routes of birnessite manganese dioxide (MnO2) coatings onto 3D graphene foam substrates enabled greater attainable capacitances. Current pulse deposition method resulted in highest achievable areal capacitance of 530 mF/cm2 under a 10 mA/cm2 current rate, cycling performance with 91% retention after 9000 cycles, as well as improved rate capability when compared to the cyclic voltammetry or galvanostatic deposition. Introduction of oxygen functional groups to the graphene foam added initial pseudocapacitance and accelerated the rate for nucleation and growth of the MnO2 crystal grains, resulting in an areal capacitance of 410 mF/cm2 under a 10 mA/cm2 current rate. However, in this case the increase in specific capacitance was accompanied by sluggish kinetics for charge storage seen via impedance spectroscopy. The charge storage mechanism of the deposited MnO2 films was investigated using in situ Raman microscopy and analysis of peak shifts revealed expansion and contraction of birnessite MnO2, relating to exchange of Na+ and H2O at the MnO2 interface.

Surface-Specific Modification of Graphitic Carbon Nitride by Plasma for Enhanced Durability and Selectivity of Photocatalytic CO2 Reduction with a Supramolecular Photocatalyst.

Photocatalytic CO2 reduction is in high demand for sustainable energy management. Hybrid photocatalysts combining semiconductors with supramolecular photocatalysts represent a powerful strategy for constructing visible-light-driven CO2 reduction systems with strong oxidation power. Here, we demonstrate the novel effects of plasma surface modification of graphitic carbon nitride (C3N4), which is an organic semiconductor, to achieve better affinity and electron transfer at the interface of a hybrid photocatalyst consisting of C3N4 and a Ru(II)-Ru(II) binuclear complex (RuRu'). This plasma treatment enabled the "surface-specific" introduction of oxygen functional groups via the formation of a carbon layer, which worked as active sites for adsorbing metal-complex molecules with methyl phosphonic-acid anchoring groups onto the plasma-modified surface of C3N4. Upon photocatalytic CO2 reduction with the hybrid under visible-light irradiation, the plasma-surface-modified C3N4 with RuRu' enhanced the durability of HCOOH production by three times compared to that achieved when using a nonmodified system. The high selectivity of HCOOH production against byproduct evolution (H2 and CO) was improved, and the turnover number of HCOOH production based on the RuRu' used reached 50 000, which is the highest among the metal-complex/semiconductor hybrid systems reported thus far. The improved activity is mainly attributed to the promotion of electron transfer from C3N4 to RuRu' under light irradiation via the accumulation of electrons trapped in deep defect sites on the plasma-modified surface of C3N4.

Surface modification of carbon-fiber-reinforced plastic by using photo-activated chlorine dioxide radicals as pretreatment of electroless plating

Carbon fiber reinforced plastic (CFRP) plays an important role in industrial fields of automobiles, aerospace transportations and astronautics on account of its high stiffness and light weight. To further expand its utilizations, coating with metals can provide with metallic appearance while improving water-resistance, durability and electric conductivity. In general, the composites of CFRP are hydrophobic and have low affinities to metals. Therefore, it requires the surface pretreatments to increase the wettability and surface energy for stronger adhesive properties with metals via enhancing both mechanical and chemical bonding. In this study, photo-oxidized chlorine dioxide radicals were used to introduce oxygen–containing functional groups on CFRP surface. The hydrophilicity and adhesion strength to metals were successfully improved by the introduction of oxygen functional groups via eco-friendly photo-oxidation by photo-activated ClO2• radicals. The improvement of hydrophilicity was determined by water contact angle measurement, and the incorporation of oxygen was confirmed by infrared (IR) and X-ray photoelectron spectroscopy (XPS) analysis. Scanning electron microscopy (SEM) observations revealed that the surface smoothness and structure of CFRP were maintained after pretreatment. Electroless plating of nickel and copper was then performed on both untreated and oxidized CFRP, demonstrating the enhanced adhesion properties of CFRP to both metals.

Mechanistic effects of graphitization degrees and surface oxygen heteroatoms on VOCs adsorptive separation: Experimental and theoretical perspective

The porous carbon is considered to be one of the most suitable materials for volatile organic compounds (VOCs) adsorption and separation. Revealing the adsorption behavior and molecular interaction mechanism is of great significance for the preparation and synthesis of porous carbon adsorbents. Herein, we investigated detailed mechanistic effects of graphitization degrees and surface oxygen heteroatoms of porous carbon on their benzene and ethanol adsorptive separation performance by combining experiments and theoretical calculations. The results show that graphitized carbon surface has a stronger van der Waals interaction with benzene molecules compared to the disordered carbon surface, and thus exhibit a higher benzene adsorption performance and benzene/ethanol selectivity. While the introduction of oxygen functional groups enhances electrostatic affinity of porous carbon surface, resulting in higher ethanol adsorption capacity and ethanol/benzene selectivity under the entire pressure range. Subsequent theoretical calculations studied the adsorption behaviors of benzene and ethanol molecules in porous carbon models (with different graphitization degrees and oxygen contents) from the perspective of the weak interactions, and found the different molecular configurations of benzene and ethanol is the main leading cause of their different adsorption preferences. This study provided mechanistic insights on how the graphitization degrees and oxygen heteroatoms affected the capture and separation properties of porous carbon, which would further provide a rational alternative strategy in the preparation and synthesis of porous carbons for the effective gas mixture capture and separation.

Evolution of Heterogeneity and Chemical Functionality during the Oxidation of Graphite

A kinetic study of graphite oxidation provided several insights into the mechanism of graphite oxide (GO) synthesis. The oxidation was observed to occur in two distinct stages, with the first stage lasting for 20 to 30 min and including a rapid disruption of the graphene sp2 network, the introduction of oxygen functional groups, and an increase in the spacing between the sheets. The second stage saw a marked decrease in the rate of change in spacing, a significant increase in the homogeneity of the GO, little to no further disruption of the sp2 network, and continuing evolution of the oxygen functionality. The study was based on the analysis by Raman spectroscopy, XRD, FTIR, SEM, and TGA of material taken at various times from a modified Hummers oxidation reaction following work up.

Enhanced catalytic performance of the carbon-supported Ru ammonia synthesis catalyst by an introduction of oxygen functional groups via gas-phase oxidation

Carbon-supported ruthenium catalysts are very promising application in ammonia synthesis. Here we show that the oxygen functional groups can be introduced into carbon preloaded with Ru species by HNO3 gas-phase oxidation treatment. The results reveal that the presence of oxygen functional groups facilitates the desorption of hydrogen species. Moreover, the decomposition of barium nitrate is accelerated, and the ill effects of carbon methanation and hydrogen poisoning are effectively alleviated. The combination of the change in the existing form of Ba promoter, the acceleration in the desorption and exchange of hydrogen species accounts for the superior ammonia synthesis activity of Ru catalyst with HNO3 gas-phase treatment. Understanding the role of oxygen functional groups provides design rules for the rational design of carbon-supported Ru catalyst with highly activity and stability for ammonia synthesis or other hydrogen-involved reactions.

Structural evolution of hexagonal boron nitride powder by Bead-milling

The structural evolution of h-BN powder by bead-milling is investigated. A unique initial stage in h-BN milling is discovered in which the x-ray diffraction (XRD) out-of-plane (0 0 2) and (0 0 4) peak intensities increase distinctly up to 3 and 4.8 times respectively, corresponding to an effective c-axis ordering of the h-BN particles. The structural evolution of h-BN due to milling is correlated to the change in the dominant milling mechanism from out-of-plane cleaving to in-plane cutting. An abnormal contraction of out-of-plane (0 0 2) interplanar spacing up to 0.044 Å due to bead-milling is reported, which could be attributed to the introduction of oxygen functional groups (B-O and N-O) on the h-BN powder.

Role of oxygen functional groups in Pb2+ adsorption from aqueous solution on carbonaceous surface: A density functional theory study

The adsorption mechanism of Pb2+ from aqueous solution on carbonaceous surface modified with oxygen functional groups was investigated by using density functional theory method. The zigzag model with seven benzene rings and armchair model with four benzene rings were used to simulate the different structures of carbonaceous surfaces. It was found that the adsorption of Pb2+ on the pure zigzag surface was chemisorption with the adsorption energy of − 306.26 to − 322.36 kJ/mol, while that on the armchair surface was physisorption with the adsorption energy of − 32.39 kJ/mol. The introduction of oxygen functional groups significantly enhanced the Pb2+ adsorption on the armchair surface. The physisorption changed to chemisorption after adding carboxyl, phenolic hydroxyl, or carbonyl functional group, indicating the stronger adsorption ability of the carbonaceous surfaces after modification. On the zigzag surface, however, the studied functional groups cannot benefit the Pb2+ adsorption. The results showed that the Pb2+ tended to adsorb on the carbon atoms instead of moving to the oxygen atoms from the introduced functional groups for adsorption, which suggests that the oxygen functional groups promoted the Pb2+ adsorption by increasing the activity of their neighboring carbon atoms.

Underlying mechanism of CO2 uptake onto biomass-based porous carbons: Do adsorbents capture CO2 chiefly through narrow micropores?

Biomass-based porous carbon materials, as promising CO2 adsorbents, have demonstrated their superiority and inherent potential. However, most of the previous reports simply attributed the unprecedented CO2 capture of porous carbon to the presence of abundant narrow micropores of less than 0.7 nm. Here, we have successfully prepared microporous carbons with analogous textural properties and oxygen functional groups by KOH activated from hydrothermally treated biomass. Based on the experimental results and theoretical calculations, we have found that the oxygen-containing functional groups on porous carbons are critically sensitive to CO2 uptake, especially with carboxyl and hydroxyl groups. We can roughly estimate that oxygen groups and pore structure of OC700 contribute 37% and 63% respectively to the CO2 capture, which can be elucidated by grand canonical Monte Carlo (GCMC) simulations. The introduction of oxygen functional groups into porous carbon materials firmly grasps CO2 through electrostatic interactions by density function theory (DFT) calculations. These oxygen groups provide new adsorption sites for the efficient CO2 capture. The OC700 achieves an extremely high CO2 adsorption capacity of 8.0 mmol g−1 and 4.8 mmol g−1 at 0° C and 25 °C (1 bar), respectively.

The adsorptive properties of oxidized activated carbons and their applications as carbon paste electrode modifiers

The adsorptive properties of the Organosorb-10 activated carbons treated with different ozone doses (15 and 45 min) and their applications as carbon paste electrode (CPE) modifiers have been studied. As a target organic contaminant the 4-chlorophenol (4-CP) has been selected. Both the physical and chemical properties of the activated carbon surface were characterized and the results show only low changes in porous structure of the oxidized activated carbons but significant changes in their surface chemistry. The adsorption isotherms of 4-CP on the activated carbons were analyzed using the Langmuir, Freundlich and Sips isotherm models. The equilibrium data followed the Langmuir isotherm. The activated carbons prepared by ozonation presented lower 4-CP adsorption than the unmodified adsorbent. Introduction of oxygen functional groups decreased their adsorption properties. The modified CPEs were prepared by mixing graphite powder with the unmodified and oxidized activated carbons (2.5%, 5% and 10% wt. content) and used for cyclic voltammetry measurements in 4-CP solutions of different concentrations. The measured peak currents were strongly dependent on oxidation of activated carbons and correlated with the 4-CP adsorption efficiency.

Total Synthesis of (-)-Cardiopetaline.

The total synthesis of (-)-cardiopetaline, an aconitine-type natural product, has been accomplished. Our synthesis involved a Wagner-Meerwein rearrangement of a sulfonyloxirane that enabled, in a single step, the construction of the bicyclo[3.2.1] system in the aconitine skeleton and effective introduction of oxygen functional groups at the appropriate positions.

Tailoring interactions of carbon and sulfur in Li–S battery cathodes: significant effects of carbon–heteroatom bonds

In this study, effects of carbon–heteroatom bonds on sulfur cathodes were investigated. A series of carbon black substrates were prepared using various treatments to introduce nitrogen or oxygen surface species. Our results indicated that nitrogen-doped carbon black significantly improved the electrochemical performance of sulfur cathode materials. Synchrotron-based XPS revealed that the defect sites of nitrogen-doped carbon are favorable for the discharge product deposition, leading to a high utilization and reversibility of sulfur cathodes. Our studies also found that the introduction of oxygen functional groups results in deteriorated performance of Li–sulfur batteries due to the reduced conductivity and unwanted side reactions occurring between sulfur and surface oxygen species.

Electrical resistance behavior of oxyfluorinated graphene under oxidizing and reducing gas exposure.

The electrical resistance behavior of graphene was studied under oxidizing and reducing gas exposure. The graphene surface was modified via oxyfluorination to obtain a specific surface area and oxygen functional groups. Fluorine radicals provided improved pore structure and introduction of an oxygen functional group. A high-performance gas sensor was obtained based on enlarged target gas adsorption sites and an enhanced electron charge transfer between the target gas and carbon surface via improved pore structure and the introduction of oxygen functional groups, respectively.

Enzyme biosensor based on an N-doped activated carbon fiber electrode prepared by a thermal solid-state reaction

The sensitivity of a biosensor electrode was increased by introducing hydrophilic N-groups onto the surface of a polyacrylonitrile (PAN) based activated carbon fiber. The electrospun carbon fiber was activated using KOH to improve the adsorption of glucose oxidase (GOx) enzymes through pore production and the introduction of oxygen functional groups. The activated carbon fibers (ACFs) were then reacted with urea to increase their hydrophilicity by doping their nitrogen groups. The sensor sensitivity and the Michaelis-Menten constant, Km, were altered by varying the percentages of functional groups on the electrode surfaces. Whereas the value of Km was affected by the kind of functional groups, the sensitivity of the biosensor electrode was chiefly affected by the amount of functional groups introduced urea modification because the enzyme was better immobilized onto urea-modified activated carbon fibers. Quantitatively, the sensitivity was two- to three-fold higher for the biosensors based on urea-treated ACFs than those based on untreated ones. This increased sensitivity is attributed to the nitrogen and oxygen functional groups on the urea-modified ACFs.

Influence of H2O2 treatment on electrochemical activity of mesoporous carbon-supported Pt–Ru catalysts

In this report, we describe the preparation of OMC (ordered mesoporous carbon) via a conventional templating method using mesoporous silica (SBA-15) as a Pt–Ru catalyst support for use in fuel cells. The influence of surface treatment of the carbon supports on the electrochemical properties of Pt–Ru/OMC was investigated by exposing the surface to hydrogen peroxide at concentrations of 0, 15, 30, 40, and 50 wt%. X-ray photoelectron spectroscopy (XPS) revealed that surface treatment changed the surface chemistry of the OMC samples considerably and introduced surface oxygen functional groups including C–O, CO, OC–O–H, and CO32−. The numbers of these functional groups increased with increasing concentration of H2O2 used in the surface treatment, while the average Pt–Ru nanoparticle size decreased owing to their improved dispersibility. Using CV (cyclic voltammetry), we determined that the electrochemical activity of the Pt–Ru catalyst increased with increasing H2O2 concentration used for surface treatment, up to 40 wt%, due to the introduction of oxygen functional groups. Based on these results, we have established that surface treatment influences the surface properties of OMC materials, resulting in improved electrochemical activity of catalysts for fuel cells.