Role Of Oxygen-containing Functional Groups Research Articles

Evolution of Oxygen Content of Graphene Oxide for Humidity Sensing.

Graphene oxide (GO) has shown significant potential in humidity sensing. It is well accepted that the oxygen-containing functional groups in GO significantly influence its humidity sensing performance. However, the relationship between the content of these groups and the humidity sensing capability of GO-based sensors remains unclear. In the present work, we investigate the role of oxygen-containing functional groups in the humidity sensing performance by oxidizing graphite with mesh numbers 80-120, 325, and 8000 using the Hummers method, resulting in GO-80, GO-325, and GO-8000. Infrared spectroscopy (IR) and X-ray photoelectron spectroscopy (XPS) were used to identify the types and quantification of oxygen-containing functional groups. Molecular dynamics simulation is used to simulate the adsorption energy, intercalation dynamics, and hydrogen bonding of water molecules. Electrochemical tests were used to compare the adsorption/desorption time and response sensitivity of graphene oxide to humidity. It is proposed that hydroxyl and carboxyl groups are the main contributing groups to humidity sensing. GO-8000 shows a relatively fast response time, but the large number of carboxyl groups will hinder intercalation of water molecules, thus exhibiting lower sensitivity. This research provides a reference for the future development of graphene-based sensors, catalysts, and environmental materials.

Insights into the role of oxygen-containing functional groups on carbon surface in water–electricity generation

Insights into the role of oxygen-containing functional groups on carbon surface in water–electricity generation

Transition of Carbon Nanotube Sheets from Hydrophobicity to Hydrophilicity by Facile Electrochemical Wetting

The present study delves into the transformative effects of electrochemical oxidation on the hydrophobic-to-hydrophilic transition of carbon nanotube (CNT) sheets. The paper elucidates the inherent advantages of CNT sheets, such as high electrical conductivity and mechanical strength, and contrasts them with the limitations posed by their hydrophobic nature. A comprehensive investigation is conducted to demonstrate the efficacy of electrochemical oxidation treatment in modifying the surface properties of CNT sheets, thereby making them hydrophilic. The study reveals that the treatment not only is cost-effective and time-efficient compared to traditional plasma treatment methods but also results in a significant decrease in water contact angle. Mechanistic insights into the hydrophilic transition are provided, emphasizing the role of oxygen-containing functional groups introduced during the electrochemical oxidation process.

Enhanced dehydrogenation kinetics for ascorbic acid electrooxidation with ultra-low cell voltage and large current density

Dehydroascorbic acid (DHA) production from ascorbic acid electrochemical oxidation (AAOR) can be used to upgrade biomass derivatives and hydrogen production with low energy consumption. Carbon materials are a promising class of nonmetal AAOR electrocatalysts; however, their performance does not meet the requirements for practical applications. In this study, an oxygen-containing group (OCG)-modified carbon electrocatalyst was prepared via oxygen plasma treatment. It could drive a current density of 100 mA cm−2 at only 0.65 VRHE and realize a Faradaic efficiency of over 90% for DHA production with long-term stability of 20 h. A proton exchange membrane-type electrolyzer integrating the anodic AAOR and the cathodic hydrogen evolution reaction (HER) was assessed. It only requires a cell voltage input of 0.98 V to deliver a current density of 1000 mA cm−2, which is superior to most reported organic upgrading reactions. Moreover, it only needs 1.54 kWh to produce normal cubic H2, which is one-third of that of traditional water electrolysis. Importantly, the contribution of each type of OCG was investigated by combining electrochemical measurements and theoretical calculations. It was revealed that the OCGs, especially the carboxyl groups (–COOH) of carbon materials, could enhance the dehydrogenation kinetics of the AAOR, thereby boosting the electrocatalytic activity. This study presents a low-energy and eco-friendly strategy for electrochemical biomass upgrading and hydrogen production, provides an in-depth understanding of the role of oxygen-containing functional groups in the AAOR, and guides the design of carbon-based electrocatalysts for AAOR.

Hydrogen Peroxide/Phosphoric Acid Modification of Hydrochars for Sulfamethoxazole and Carbamazepine Adsorption: The Role of Oxygen-Containing Functional Groups.

Emerging pollutants, such as sulfonamide antibiotics and pharmaceuticals, have been widely detected in water and soils, posing serious environmental and human health concerns. Thus, it is urgent and necessary to develop a technology for removing them. In this work, a hydrothermal carbonization method was used to prepare the hydrochars (HCs) by pine sawdust with different temperatures. To improve the physicochemical properties of HCs, phosphoric acid (H3PO4) and hydrogen peroxide (H2O2) were used to modify these HCs, and they were referred to as PHCs and HHCs, respectively. The adsorption of sulfamethoxazole (SMX) and carbamazepine (CBZ) by pristine and modified HCs was investigated systematically. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results indicated that the H2O2/H3PO4 modification led to the formation of a disordered carbon structure and abundant pores. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy results suggested that carboxyl (-COOH) and hydroxyl (-OH) functional groups of HCs increased after modification, which is the main reason for the higher sorption of SMX and CBZ on H3PO4/H2O2-modified HCs when compared with pristine HCs. In addition, the positive correlation between -COOH/C=O and logKd of these two chemicals also suggested that oxygen-containing functional groups played a crucial role in the sorption of SMX and CBZ. The strong hydrophobic interaction and π-π interaction between CBZ and pristine/modified HCs resulted in its higher adsorption when compared with SMX. The results of this study provide a novel perspective on the investigation of adsorption mechanisms and environmental behaviors for organic contaminants by pristine and modified HCs.

Revealing the role of oxygen-containing functional groups on graphene oxide for the highly efficient adsorption of thorium ions

Oxygen-containing functional groups on the surface of carbon materials can promote the adsorption capacity of radioactive thorium ions (Th(IV)), but their effect on the adsorption of Th(IV) has not been systematically revealed. Herein, to elucidate the nature of oxygen-containing group-mediated Th(IV) adsorption, a series of graphene oxide nanoflakes (GONFs) with different contents of oxygen-containing groups on the surface were prepared. The experimental results showed that the high adsorption of Th(IV) not only resulted from the oxygen content, but also was related to the type of oxygen-containing functional groups on GONFs. Subsequent density functional theory (DFT) calculations revealed that the high adsorption capacity for Th(IV) originated from the oxygen-containing groups and their adjacent activated sp2 carbon atoms. More importantly, the coordination of Th(IV) with oxygen functional groups induced the aggregation of GONFs, leading to the sedimentation of GONFs, which facilitated the separation of adsorbents and enabled the GONFs to be a more practical adsorbent for Th(IV). This work deepens our understanding of the role of oxygen-containing groups on Th(IV) adsorption and provides a new strategy for the design and synthesis of high-performance surface oxygen-containing carbon-based adsorbents with practical application potential.

Revealing the Role of Oxygen-Containing Functional Groups on Graphene Oxide for the Highly Efficient Adsorption of Thorium Ions

Revealing the Role of Oxygen-Containing Functional Groups on Graphene Oxide for the Highly Efficient Adsorption of Thorium Ions

Construction of all-carbon micro/nanoscale interconnected sulfur host for high-rate and ultra-stable lithium-sulfur batteries: Role of oxygen-containing functional groups

Carbon nanotubes (CNTs) are often used to settle down the sluggish reaction kinetics in lithium–sulfur batteries (LSBs). However, the self-aggregation of CNTs often makes them fail to effectively inhibit the shuttling effect of soluble lithium polysulfide (LiPS) intermediates. Herein, a type of ultra-stable carbon micro/nano-scale interconnected “carbon cages” has been designed by incorporating polar acid-treated carbon fibers (ACF) into three-dimensional (3D) CNT frameworks during vacuum filtration processes. Results show that the ACF-CNT composite frameworks possess a reinforced-concrete-like structure, in which the ACFs can well work as the main mechanical supporting frames for the composite electrodes, and the oxygen-containing functional groups (OFGs) formed on them as cross linker between ACFs and CNTs. Benefitted from this design, the ACF-CNT/S cathodes deliver an excellent rate capability (retain 72.6% at 4C). More impressively, the ACF-CNT/S cathodes also show an ultrahigh cycling stability (capacity decay rate of 0.001% per cycle over 350 cycles at 2C). And further optimization suggests that the suitable treatment on CFs could balance the chemical adsorption (OFGs) and physical confinement (carbon cages), leading to fast and durable electrochemical reaction dynamics. In addition, the assembled soft-pack LSBs further show a high dynamic bending stability.

A molecular dynamics study on the role of oxygen-containing functional groups on the adhesion of polymeric films to the aluminum surface

Polymers with carbonyl groups are widely used in metal binding. It is believed that oxygen-containing functional groups have an essential role in the adhesion of polymers to metal surfaces. Here, molecular dynamics simulation has been employed to study oxygen atoms in the vinyl acetate and maleic acid functional groups that have a main role in the adhesion of poly (vinyl chloride-co-vinyl acetate-co-maleic acid) lacquer to aluminum. Based on the results, carbonyl groups had various neighboring bonds that resulted in different positioning and performances of oxygen atoms in the bonding strength. While oxygen atoms of carbonyl bonds in vinyl acetate had a higher tendency for the aluminum surface, oxygen atoms of maleic acid were closer to the aluminum surface, due to the smaller special hindrance of neighboring hydrogen atoms. It led to a difference in the surface concentrations of oxygen among different comonomers. Analyzing the orientation function revealed that the carbonyl bonds of vinyl acetate and maleic acid were oriented near the aluminum surface, as had been previously observed by Kim et al. [1]. The bond orientation and distance from the aluminum surface were found to be the main reasons behind the more effective role of maleic acid in the adhesion to aluminum, compared to vinyl acetate.

The Critical Role of Oxygen-Containing Functional Groups in the Etching Behavior of Activators to Carbon Materials

Fully activating the carbon matrix to obtain a high specific surface area (SSA) has been a practical approach to enhance the electrochemical performance of carbon materials. Much research mentioned that the activation has a large influence on the oxygen-containing functional groups (OCFGs) of the porous carbon. However, the potential impact of OCFGs ubiquitous in carbon precursors on the etching behavior of activators is rarely studied. Herein, a pitaya peel with a high oxygen content is employed as the carbon matrix and then a series of porous carbon materials are synthesized by a one-step pyrolysis strategy using different activators. We found that the existence of OCFGs in the carbon materials is conducive to enhancing the etching behavior. Theoretical calculations reveal that OCFGs in the carbon matrix could induce the local charge redistributions, thereby improving the binding affinity between the activators and the carbon atoms near OCFGs. Consequently, activators tend to etch carbon atoms around the OCFGs in the carbon precursors. Based on this, the optimized sample exhibits an ultrahigh SSA of 3699 m2 g–1, superior capacitance (373 F g–1 at 1 A g–1), and excellent rate performance. This work contributes to understanding the role of OCFGs in the etching behavior of activators to carbon materials.

Influence of Oxygen-Containing Functional Groups on the Environmental Properties, Transformations, and Toxicity of Carbon Nanotubes.

Carbon nanotubes (CNTs) have unique physical and chemical properties that drive their use in a variety of commercial and industrial applications. CNTs are commonly oxidized prior to their use to enhance dispersion in polar solvents by deliberately grafting oxygen-containing functional groups onto CNT surfaces. In addition, CNT surface oxides can be unintentionally formed or modified after CNTs are released into the environment through exposure to reactive oxygen species and/or ultraviolet irradiation. Consequently, it is important to understand the impact of CNT surface oxidation on the environmental fate, transport, and toxicity of CNTs. In this review, we describe the specific role of oxygen-containing functional groups on the important environmental behaviors of CNTs in aqueous media (e.g., colloidal stability, adsorption, and photochemistry) as well as their biological impact. We place special emphasis on the value of systematically varying and quantifying surface oxides as a route to identifying quantitative structure-property relationships. The role of oxygen-containing functional groups in regulating the efficacy of CNT-enabled water treatment technologies and the influence of surface oxides on other carbon-based nanomaterials are also evaluated and discussed.

Fabrication of reduced graphene oxide membranes for water desalination

Reduced graphene oxide (rGO) has huge potential for membrane applications owing to its appropriate interlayer spacing (0.34–0.37 nm) that enables it to block salt ions as small as Na+ with high precision. However, fabrication of uniform rGO membranes is a great challenge because of the loss of its polar functional groups during preparation from graphene oxide (GO). Although there have been several studies on GO membranes and a few on rGO for water purification, very few attempts to understand the role of oxygen-containing functional groups in successful rGO membrane formation. The present work deals with the investigation of the key factors and functional groups that govern membrane formation. This work also utilizes the facile approach of synthesizing reduced GO by environmentally viable hydrothermal reduction. Further characterizations show that the hydroxyl and carboxyl groups are principally responsible for the formation of uniform rGO membranes. The rGO (treated at 160°C for 2 h) membrane with a small amount of unreduced GO presented shows the lowest Na+/Cl- ion permeation with the highest membrane flux, which is suggested to be a potential candidate for water desalination.

Role of oxygen-containing functional groups in forest fire-generated and pyrolytic chars for immobilization of copper and nickel

Char as a carbon-rich material, can be produced under pyrolytic conditions, wildfires or prescribed burn offs for fire management. The objective of this study was to elucidate mechanistic interactions of copper (Cu2+) and nickel (Ni2+) with different chars produced by pyrolysis (green waste, GW; blue-Mallee, BM) and forest fires (fresh-burnt by prescribed fire, FC; aged char produced by wild fire, AC). The pyrolytic chars were more effective sorbents of Cu2+ (∼11 times) and Ni2+ (∼5 times) compared with the forest fire chars. Both cross-polarization (CPMAS-NMR) and Bloch decay (BDMAS-NMR) 13C NMR spectroscopies showed that forest fire chars have higher woody components (aromatic functional groups) and lower polar groups (e.g. O-alkyl C) compared with the pyrolytic chars. The polarity index was greater in the pyrolytic chars (0.99–1.34) than in the fire-generated chars (0.98–1.15), while aromaticity was lower in the former than in the latter. Fourier transform infrared (FTIR) and Raman spectroscopies indicated the binding of carbonate and phosphate with both Cu2+ and Ni2+ in all chars, but with a greater extent in pyrolytic than forest fire-generated chars. These findings have demonstrated the key role of char's oxygen-containing functional groups in determining their sorption capacity for the Cu2+ and Ni2+ in contaminated lands.

Activation of peroxymonosulfate by carbonaceous oxygen groups: experimental and density functional theory calculations

The active sites for metal-free carbocatalysis in environmental remediation are intricate compared to those for traditional metal-based catalysis. In this study, we report a facile fabrication of amorphous carbon spheres with varying oxygen functional groups by hydrothermal treatment of glucose solutions. With air/N2 annealing and regeneration in the glucose solution of the as-synthesized carbon spheres, the concentrations of oxygen-containing groups were tailored on the amorphous carbon spheres in an Excess-On-Off-On manner. Accordingly, an Off-On-Off-On catalytic behavior in peroxymonosulfate (PMS) activation using these amorphous carbon spheres was observed. To uncover the mechanism of catalytic activity, electron spin resonance (EPR) spectra were recorded to investigate the variation of the generated OH and SO4−radicals. Moreover, density functional theory (DFT) studies were employed to identify the role of oxygen-containing groups on the amorphous carbon spheres in adsorptive OO bond activation of PMS. Results revealed that ketone groups (CO) are the dominant active sites for PMS activation among oxygen-containing functional groups. In order to simulate real wastewater treatment, influences of chloride anions and humic acid on PMS activation for phenol degradation were further evaluated. This study provides an in-depth insight to discovering the role of oxygen-containing functional groups as the active sites in metal-free carbocatalysis.

Flame treatment of low-density polyethylene: Surface chemistry across the length scales

The relationship between surface chemistry and morphology of flame treated low-density polyethylene (LDPE) was studied by various characterization techniques across different length scales. The chemical composition of the surface was determined on the micrometer scale by X-ray photoelectron spectroscopy (XPS) as well as with time of flight secondary ion mass spectrometry (ToF-SIMS), while surface wettability was obtained through contact angle (CA) measurements on the millimeter scale. The surface concentration of hydroxyl, carbonyl and carboxyl groups, as a function of the “number” of the flame treatment passes (which is proportional to the treatment time) was obtained. Moreover, a correlation was found with chemical composition and polarity, emphasizing the role of oxygen-containing functional groups introduced during the treatment. Carboxyl functional groups were specifically identified by fluorescent labeling and the results were compared with the ToF-SIMS data. In addition, atomic force microscopy (AFM) was used to evaluate changes in surface topography and roughness on the nanometer to micrometer length scales. After flame treatment, water-soluble low molecular weight oxidized materials (LMWOM), which were generated as products of oxidation and chain scission of the LDPE surface, agglomerated into small topographical mounds that were visible in the AFM micrographs. After rinsing the flame treated samples with water and ethanol, bead-like nodular surface structures were observed. The ionization state of flame treated LDPE surfaces was monitored by chemical force microscopy (CFM). The effective surface p K a values of carboxylic acid (–COOH) obtained by AFM were revealed by chemical force titration curves and the effective surface p K a values were found to be around 6.

Modeling Water Adsorption in Carbon Micropores: Study of Water in Carbon Molecular Sieves

Measurements of water adsorption equilibrium in a carbon molecular sieve are undertaken in order to gain insight into the nature of water adsorption in carbon micropores. The measurements are taken at low concentrations to emphasize the role of oxygen-containing functional groups in the adsorption of water. Comparisons are made with previously published water adsorption data at higher concentrations to provide a data set spanning a wide range of loading. The assembled data set provides an opportunity for comparison of various theories for prediction of water adsorption in carbon micropores. Shortcomings of current theories are outlined, and an analytical theory that is free of these deficiencies is proposed in this investigation. With the consideration of micropore volume and pore size distribution, the experimental data and proposed isotherm model are consistent with previous studies of Takeda carbon molecular sieves. Also investigated is the uptake kinetics of water, which is characterized by a Fickian diffusion mechanism. The Maxwell-Stefan formulation is applied to characterize the dependence of the diffusional mobility upon loading.