Effect Of Oxygen-containing Groups Research Articles

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.

Study on mercury adsorption mechanism of iron-modified biomass char in coal-fired flue gas based on density functional theory

As a new type of porous adsorbent, iron-modified biomass char (Fe10%-BC) may efficiently remove Hg0 from flue gas. However, the lack of in-depth research on the mercury adsorption mechanism of biomass char limits the development of this technology. The reaction path of mercury adsorption was quantitatively revealed by DFT (Density Functional Theory). The effects of oxygen-containing groups and adsorption atmosphere on Hg0 adsorption were analyzed. The results show that Hg0 adsorption by Fe10%-BC includes two stages, that is adsorption and oxidation. The modified biochar utilized the strong oxygen release/storage capacity of iron oxides, reacting with Hg0 by Lewis acid-base reaction. Oxygen-containing groups regulated molecular orbital energy level and surface charge distribution of iron-modified biomass char, affecting the adsorption capacity of Fe10%-BC. Aldehyde, ketone and carboxyl group promoted Hg0 adsorption performance of Fe10%-BC, and the effect from strong to weak was aldehyde group > ketone group > carboxyl group. Hydroxyl group inhibited mercury adsorption by Fe%10-BC. The adsorption atmosphere CO2，O2 and HCl promoted the mercury adsorption performance of the iron-based modified biomass char by forming new adsorption sites with the modified biomass char. SO2 consumed the high valence metal and lattice oxygen, forming competitive adsorption with Hg0. Hg0 adsorption efficiency of the modified biomass char decreased to 58%.

Effect of Oxygen-Containing Groups on Electrochemical and Marine Electric Field Response Properties of Carbon Fiber Electrode

Electric field response of carbon fiber sensor in sea water can be tuned up through modification of molecules or groups on its surface, which plays an important role in its high sensitivity and stability. Herein, high performance carbon fiber electrodes with different oxygen-containing functional groups were prepared by electrochemical oxidation coupled with electrochemical reduction, and their electric field response and electrochemical performances of electrodes are investigated. The results show that the electrochemical oxidation and reduction obviously alter the dominant contents of carbonyl, hydroxyl and carboxyl groups. Among them, carbonyl group has positive effects for paired carbon fiber electrode on its electrode potential stability and its distortion rate of electric field response curves, hydroxyl group makes the paired carbon fiber electrode more sensitive to weak electric field. Carboxyl group has negative effects on the electrode potential stability due to its high activity, but its larger specific capacitance and smaller charge transfer resistance are simultaneously obtained. The detailed relationship between the dominant oxygen-containing carbon fiber electrode and its electric field response is first reported systematically, and it will shed some light on the design of fast-stable and highly sensitive marine electric field electrodes.

Molecular Insight into the Adsorption Thermodynamics and Interfacial Behavior of GOs at the Liquid-Liquid Interface.

The adsorption of two-dimensional (2-D) graphene oxide (GO) nanosheets at liquid-liquid interfaces has broad technological implications from functional material preparations to oil-water emulsification. Molecular-level understanding of the adsorption thermodynamics and the interfacial behavior is of great significance. Here, the adsorption free energy of GO nanosheets at the water-cyclohexane system was simulated, in which the effect of oxygen-containing groups and deprotonation has been investigated. It was observed that the neutral GO (GO-COOH) has obvious interfacial activity with a reduction of interfacial tension, while the deprotonated GO (GO-COO-) shows a weak interface affinity. There exists an optimal oxidization degree that could cause the best interfacial stability, which is attributed to the balance of interfacial hydrophilic-hydrophobic interactions. The interaction arising from water is the main factor determining interfacial activity. The interfacial morphology and dynamics of GO nanosheets have also been simulated, in which an anisotropic 2-D translation and rotation along the interface were revealed. Our simulation results provide new insight into the adsorption mechanism and dynamics behavior of GO at the oil-water interface.

Microscopic spreading characteristics of non-polar oil droplet on low rank coal surface: Effects of surfactant pretreatment and oxygen-containing groups

Numerous oxygen-containing groups present on the low rank coal (LRC) surface makes a poor flotation performance of LRC only using common oily collector. Increasing the spreading strength of oily collector on the LRC surface is of great significance for improving its flotation behavior. In this study, molecular dynamics simulation (MDS) was employed to investigate the microscopic spreading characteristics of non-polar oil droplet on the LRC surface. For this purpose, the configurations of non-polar oil droplet, spreading area, and interaction energy were calculated. It was found that on the raw LRC surface, the non-polar oil droplet remained spherical with a small spreading area and weak interaction strength. Besides, a non-ionic surfactant, dodecyl nonaethoxyl ether (C12EO9) was used to modify the surface wettability of LRC to enhance the non-polar oil droplet spreading. After surfactant pretreatment, a pancake-like oil film was formed on the LRC surface with a larger spreading area and more negative interaction energy compared with the case of the raw LRC surface. Based on these observations, the microscopic insights were provided about the spreading of non-polar oil droplet on the surface of LRC, as well as the role of surfactant enhancing its spreading intensity. In addition, the effect of the oxygen-containing groups on the spreading behaviors of non-polar oil droplet was also explored. The results suggested that carboxyl and hydroxyl are the main groups that hinder the spreading of the non-polar oil droplet on LRC surface. The simulation results are in accordance with the available experimental data.

Investigation of interactions between oxygen-containing groups and water molecules on coal surfaces using density functional theory

The oxygen-containing group is a crucial factor that affects the water wettability of a coal surface. An investigation of the interaction between the oxygen-containing group and water molecule is conducive for understanding the water wettability of the coal surface. In this study, water contact angle measurements and X-ray photoelectron spectroscopy were used to explore the surface wettability and oxygen-containing groups for different rank coals respectively. The adsorption behavior of water molecules on the coal surface was investigated using the density functional theory. The results indicated that the oxygen-containing group enhances the hydrophilicity of the coal surface. In oxygen-containing groups, oxygen atoms possess strong nucleophilicity, and enhance the electrophilicity of hydrogen atoms attached to them. The oxygen atom in the water molecule prefers to form strong hydrogen bonds with the hydrogen atom that is attached to the oxygen atom in the oxygen-containing group. The hydrogen atom in the water molecule prefers to face down, thereby generating a strong van der Waals force on the carbon rings. Based on the combined action of hydrogen bonds and van der Waals force, the effect of oxygen-containing groups on water adsorption capability follows the order –OOH > –OH > –CHO > –OCH3.

Chitosan/graphene oxide composite as an effective removal of Ni, Cu, As, Cd and Pb from wastewater

The possible interactions between some divalent heavy metals and chitosan/graphene oxide (Cs/GO) were studied by density functional theory (DFT) at B3LYP level with LANL2DZ basis set. Ni, Cu, As, Cd and Pb have been selected as the heavy metals to be studied because of their high impact in industrial wastewater. The interactions between Cs and these heavy metals have been considered and compared to Cs/GO composite. The proposed model was applied to study the interaction between Cs and the heavy metals in compare to both the effect of oxygen-containing groups on the surface of GO and the effect of the nitrogen-containing groups on the surface of Cs. The interaction between the composite Cs/GO and hydrated metal showed more selectivity for the metals than Cs alone. These new results can be applied in the field of environmental pollution by removing the heavy metals from industrial wastewater.

The interaction of perrhenate and acidic/basic oxygen-containing groups on biochar surface: A DFT study

Biochar has a good adsorption ability for perrhenate (ReO4−), which can be attributed to its abundant oxygen-containing groups, yet the effects of oxygen-containing groups on ReO4− adsorption are still unclear. Here, the interaction of ReO4− and acidic/basic oxygen-containing groups (hydroxyl, carboxyl, pyrone and chromene) on biochar were investigated by density functional theory (DFT) calculation with conductor-like screening model (COSMO). According to the calculated results, it was evidenced that the adsorption of oxygen-containing group functionalized BC towards ReO4− was gradually strengthened as decreased pH, and the protonated positively charged oxygen-containing groups presented stronger chemisorption to ReO4− mainly through electrostatic interaction, complexation and atomic orbital hybridization. The protonated hydroxyl and carboxyl and the protonated etheric oxygen of pyrone and chromene can offer favorable binding sites to ReO4−. Compared with the acidic oxygen-containing groups, the higher adsorption energy values, and the larger Mayer bond order indexes of interacting atoms identified that the basic oxygen-containing groups have stronger affinity with ReO4−. Pyrone had the strongest adsorption stability toward ReO4−. Our results can provide new ideas into the design and preparation of separation materials for ReO4− or the other anions capture from the aqueous solution.

Ab initio characterization and experimental validation on the roles of oxygen-containing groups in graphene based formaldehyde sensors.

The development of formaldehyde (HCHO) sensors employing reduced graphene oxide (rGO) as sensing materials calls for a profound, atomic level understanding on the roles of oxygen-containing groups. In this work, the performances of rGO-based HCHO sensors were investigated using ab initio calculations and experimental validation. Density functional theory (DFT) simulations were performed to calculate the adsorption energy (Eads) and charge transfer (ΔQ) for the adsorption of HCHO on pristine graphene, rGO with epoxides, rGO with hydroxyl groups, and rGO with carboxyl groups. The results show that the incorporation of oxygen-containing groups leads to an obvious increase of Eads and ΔQ values, with an order of carboxyl group > hydroxyl group > epoxides > pristine graphene. The increase of Eads and ΔQ values could increase the variation in the concentration of charge carriers, the change of conductance of the sensing materials, and hence the sensor response. The experimental measurements indicate that with a decrease in the C/O atomic ratio from 16.2 to 6.6, the sensor response to 1 ppm HCHO increases from 0.10% to 0.73%, confirming the DFT calculation results. Moreover, even with a certain C/O atomic ratio of ∼6.6, rGO with 6.80% carboxyl groups exhibits a distinctly larger response to 0.2-3 ppm HCHO, compared with the counterpart with 3.09% carboxyl groups. The as-obtained insights into the effects of oxygen-containing groups on the response of rGO to HCHO could be instructive for preparing rGO-based HCHO sensors for advanced performances.

Adsorption characteristics of Congo red on carbonized leonardite

In this study, a low-rank coal (leonardite) was used as adsorbent for the removal of Congo red (CR) aqueous solution, a model compound representing an anionic azo dye. The effects of oxygen-containing groups, particularly carboxylic, lactonic, and phenolic groups, on the adsorption of CR on leonardite after carbonization at various temperatures were studied. It was determined that the surface chemistry change of carbonized leonardite greatly influenced its adsorption characteristics. Solution pH affects not only the surface charge of the adsorbents but also the ionization of the CR dyes. Based on the experimental data, a mechanism of interaction between CR anionic dye and carbonized leonardite was proposed. A comparison of kinetic and isothermal models demonstrated that the CR adsorption process was best described by a pseudo-second-order kinetic model and Redlich–Peterson model. Further thermodynamic investigations indicated that the adsorption was an endothermic and spontaneous process.

Effects of Oxygen-Containing Groups on Interfacial Electrochemistry of sp2-Hybridized Carbon Materials

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Effects of carbon surface oxides on the dispersion of Pt/C catalysts prepared via adsorption of hexachloroplatinic acid: a new insight

A new concept is advanced to explain some effects of oxygen-containing groups of the carbon surfaces on the dispersion of Pt/C catalysts prepared through the adsorption of H2PtCl6 onto porous carbon powders followed by the reduction with H2. These groups alter the electrochemical properties of the support and, therefore, influence the nature and amount of the adsorbed catalyst precursors formed during a redox reaction between the carbon surface and H2PtCl6, that reflects on the dispersion of Pt/C. A way to account for their impact on platinum dispersion is offered. It allows revising and uniting many literature data related to this problem.

Effect of chemical surface heterogeneity on the adsorption mechanism of dissolved aromatics on activated carbon

The effects of oxygen-containing groups, particularly carboxylic and carbonyl groups, on the adsorption of dissolved aromatics on ash-free activated carbon have been studied. Adsorption isotherms for phenol, aniline, nitrobenzene, and benzoic acid were generated in both aqueous and cyclohexane media, using carbons with different amounts of surface oxygen groups. It was found that water adsorption, dispersive/repulsive interactions, and hydrogen-bonding were the main mechanisms by which surface oxygen groups influence the adsorption capacity, while donor–acceptor interactions were found not to be significant. The adsorption mechanism was also found to be influenced by the properties of the functional group on the aromatic adsorbate, especially its ability to hydrogen-bond and through its activating/deactivating influence on the aromatic ring.