Adsorption Of Carboxylic Acids Research Articles

Evaluation of the tribological performance and oxidative stability of a bi-functional lubricating oil additive prepared from corn cob extract

To meet the requirements of a circular economy, a class of sulfur- and phosphorus-free green bifunctional lubricating oil additives was developed based on corn cob extract as a naturally renewable biomass material. These additives can significantly enhance the friction-reducing, anti-wear properties, and oxidative stability of base oils. Results indicate that at an addition level of 4000 ppm, ternary polymer additive reduced the wear volume and surface roughness of steel friction pairs by 98.17 % and 97.63 %, respectively, and increased the oxidation induction period by 40.52 %. The improvement in tribological performance is attributed to the rigid ring structure preventing direct contact between friction pairs, and the chemical adsorption of carboxylic acid and anhydride groups with the metal, forming a dense friction film.

A fatty acid photodecarboxylase-mimicking photonanozyme with defect-induced enzymatic substrate-binding pockets

Hydrocarbon synthesis hints at the significance of in-depth investigations and detailed explanations of mimicking fatty acid photodecarboxylase (FAP). Considering the importance of photodecarboxylases in hydrocarbon synthesis, we present the potential of defective semiconductor nanomaterials as a novel type of photonanozymes (PNZs) that mimic enzyme-like performance, serving as alternatives to FAP. Ferrum-doped titanium dioxide (Fe-TiO2) was synthesized to introduce appropriate amounts of surface defects including reduced Ti3+ sites and oxygen vacancies, which reduce the band gap of TiO2 and enhance the visible-light absorption, thereby facilitating efficient charge trapping. Notably, the surface defects of Fe-TiO2 PNZs singularly act as enzymatic substrate-binding pockets that enable efficient carboxylic acid adsorption during the dark process, conversely facilitating the formation of more defects and boosting the FAP-like activity for photocatalytic decarboxylation reactions. This work provides a creative strategy for designing substrate-dependent higher-concentration defects as enzyme-like binding sites on promising PNZs that mimic natural photoenzymes.

Analytical solutions for the injection of wettability modifiers in carbonate reservoirs based on a reduced surface complexation model

The potential of tuned-composition waterflooding to enhance oil recovery from carbonate reservoirs has been widely investigated, where wettability alteration is the dominant mechanism. It is hypothesized that the sulfate in seawater adsorbs on the rock surface, removing acidic hydrocarbon species adsorbed thereon. Glycine, the simplest amino acid, has also been investigated as a wettability modifier for carbonates that acts similarly to sulfate.Wettability alteration by the adsorption of sulfate ion and glycine anion has been satisfactorily modeled by extending calcite's surface complexation model (SCM) based on zeta potential measurements. However, determining the relevance of the individual geochemical reactions is obscured by the complexity of the SCM. Moreover, the large number of equilibrium constants and their associated uncertainty result in many degrees of freedom when matching corefloods and spontaneous imbibition experiments.This research determines the chemical reactions in the calcite's SCM that govern wettability alteration and the incremental oil recovery by glycine-enhanced waterflooding in carbonate reservoirs. We found that the wettability alteration by SCM can be approximated by two anion exchange reactions between the wettability modifiers, sulfate and glycine anions, and the carboxylic acids adsorbed on the rock surface. Moreover, the wettability of the system described by the adsorption of carboxylic acids and the incremental oil recovery by waterflooding are linearly correlated with the K value of the reaction of carboxylic acids with the carbonate surface and the concentration of carboxylic acids in the system, which is a function of the total acid number.We present analytical solutions for the two-phase, multicomponent reactive-transport model coupled with anion exchange reactions. To the best of our knowledge, this is the first time the presented analytical solutions are applied to describe enhanced waterflooding in carbonate reservoirs where more than one wettability modifier is injected. The analytical solutions showed that glycine injection enhances oil recovery over waterflooding by the formation of two wettability alteration waves. The number of waves and their types (rarefaction or shock) depend on glycine's and sulfate's concentration at the injection. The improvement in oil recovery by wettability alteration mainly occurs because the more favorable mobility ratio increases the displacement efficiency with no reduction in residual oil saturation. A synergy was found between glycine and sulfate, where the presence of glycine promotes the formation of a wettability-alteration shock by sulfate that improves the displacement efficiency.

Elucidation of the Roles of Water on the Reactivity of Surface Intermediates in Carboxylic Acid Ketonization on TiO2.

The effects of water on the carboxylic acid ketonization reaction over solid Lewis-acid catalysts were examined by nuclear magnetic resonance (NMR) spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature-programmed desorption (TPD), and kinetic measurements. Acetic acid and propanoic acid were used as model compounds, and P25 TiO2 was used as a model catalyst to represent the anatase TiO2 since the rutile phase only contributes to <2.5% of the overall ketonization activity of P25 TiO2. The kinetic measurement showed that introducing H2O vapor in gaseous feed decreases the ketonization reaction rate by increasing the intrinsic activation barrier of gas-phase acetic acid on anatase TiO2. Quantitative TPD of acetic acid indicated that H2O does not compete with acetic acid for Lewis sites. Instead, as indicated by combined approaches of NMR and DRIFTS, H2O associates with the adsorbed acetate or acetic acid intermediates on the catalyst surface and alters their reactivities for the ketonization reaction. There are multiple species present on the anatase TiO2 surface upon carboxylic acid adsorption, including molecular carboxylic acid, monodentate carboxylate, and chelating/bridging bidentate carboxylates. The presence of H2O vapor increases the coverage of the less reactive bridging bidentate carboxylate associated with adsorbed H2O, leading to lower ketonization activity on hydrated anatase TiO2. Surface hydroxyl groups, which are consumed by interaction with carboxylic acid upon the formation of surface acetate species, do not impact the ketonization reaction.

Adsorption of Low-Molecular-Weight Carboxylic Acids to Anion Exchange Resins with Various Properties and the Mechanisms of Interaction

Anion exchange resin (AER) is often used to produce ultrapure water by removing low-molecular-weight (LMW) carboxylic acids (CAs). However, the adsorption performance of resins requires improvement, and the adsorption mechanisms are not fully clear. In this study, eight AERs with different polymer matrices, porosity types, and ammonium group properties were used to investigate the adsorption of common LMW CAs. The adsorption efficiency of strongly basic AERs (80–100%) was much higher than that of weekly basic AERs (2–56%). The adsorption kinetics were limited by intraparticle diffusion. In particular, for CAs with a molecular volume of > 83.5 Å, the gellular AERs showed an obvious size exclusion effect that was not as apparent for the macroporous AERs. The adsorption capacity and affinity were highly related to the polymer matrix. The polystyrene AERs showed 1.60–3.00 times higher maximum adsorption and 2.00–3.80 times greater adsorption affinity than their polyacrylic counterparts. Adsorption also depended on the CA structure. The carbon and carboxyl number of the CA affect the total negative atomic charge density, which in turn affects the CA–AER electrostatic interaction. Besides, hydrogen bonds between the carboxyl group and the AER matrix increased CA adsorption; this effect was especially prominent for diprotic CAs.

First-principles calculations of carboxylic acid adsorption on carbonate surfaces: Chain size and aqueous interface effects

In enhanced oil recovery (EOR), low salinity water (LSW) is an essential condition to change wettability in carbonate reservoirs for organic compound desorption. However, the nature of the water–oil–carbonate interactions remains challenging. Accordingly, we performed first-principles calculations to determine the adsorption energies of the propanoic and octanoic acids on the calcite and dolomite surfaces with water interface and implicit solvation medium. Our results confirm that the Mg sites are less selective for adsorption of both acidic oil components, whereas the Ca sites keep retaining the acid molecules. The differentiated influence from the carbonate surfaces is enhanced through the aqueous environment. In presence of Mg, the aqueous environment may act mainly on the unoccupied electronic levels of the dolomite carbonate sites instead of the Ca sites in calcite, which in turn has a stronger interaction with the acid molecules. The effect of the acid chain size is less pronounced. The acid desorption process could be then reached from the carbonate sites as the surface hydrophilicity is mainly increased in dolomite, which has a favourable ionic exchange and water adsorption. Therefore, our simulation models help to shed light on some important interaction properties in complex water–oil–carbonate interfaces under LSW conditions for EOR.

Design of Organic-Free Superhydrophobic TiO2 with Ultraviolet Stability or Ultraviolet-Induced Switchable Wettability.

Superhydrophobic TiO2 with great application potential is mainly obtained by surface modification with low surface energy organics, which is easily degraded under sunlight irradiation, which results in the loss of superhydrophobic properties. Herein, we developed a room-temperature pulsed chemical vapor deposition (pulsed CVD) method to develop amorphous TiO2-deposited TiO2 nanoparticles. The ultraviolet stability/ultraviolet-induced reversible wettability switch had been simultaneously realized by different and controllable deposition cycles of amorphous TiO2. The superhydrophobic properties of the organic-free TiO2 were determined by the micrometer-nanometer-sub-nanometer multiscale structure, the multiscale pore structure, and the large Young's contact angle resulting from carboxylic acid adsorption. Also, we found that the adsorption rate and adsorption stability of oxygen and water at the surface oxygen vacancies were the key to facilitate the reversible switching between superhydrophilic and superhydrophobic states, which was well demonstrated by experimental characterization and theoretical simulation. In addition, we also found that the resistance of dense amorphous TiO2 films on the TiO2 surface to the migration of photogenerated electrons and holes was the key to maintain the stable superhydrophobic properties of superhydrophobic TiO2 under ultraviolet illumination. The powders were strongly ground and the coating surface was rubbed on the surface of the sandpaper, which still maintained superhydrophobic properties, providing favorable conditions for the application of superhydrophobic TiO2. This work modulates the ultraviolet stability and dark/ultraviolet-induced switchable superhydrophobicity/superhydrophilicity of coated TiO2 by simply adjusting the number of deposition times in a pulsed CVD process for the first time, thus contributing to the development of organic-free superhydrophobic TiO2.

First-Principles Calculations of Carboxylic Acid Adsorption on Carbonate Surfaces: Chain Size and Aqueous Interface Effects

First-Principles Calculations of Carboxylic Acid Adsorption on Carbonate Surfaces: Chain Size and Aqueous Interface Effects

Predicting the electrokinetic properties on an outcrop and reservoir composite carbonate surfaces in modified salinity brines using extended surface complexation models

Surface complexation models (SCM), based mainly on the diffuse double layer (DDL) theory, have been used to predict zeta potential at the crude oil-brine-rock (COBR) interface with limited success. However, DDL is inherently limited in accurately predicting zeta potential by the assumptions that all the brine ions interact with the rock surface at the same plane and by the double layer collapse at higher brine ionic strength (>1M). In this work, a TLM-based SCM captured zeta potential trends at the calcite-brine interface with ionic strength up to 3 M. An extended DDL and TLM-based SCMs were used to predict the electrokinetic properties of a composite carbonate rock showing a different mineralogical composition. The extended TLM-based SCM captured the zeta potential prediction trends and magnitude, highlighting the contribution of the inorganic minerals and organic impurities on the composite carbonate surface. In contrast, the extended DDL-based SCM captured the zeta potential trends but failed to capture the magnitude of the measured zeta potential. Interestingly, the TLM-based SCM predicted a positive SP for the rock-brine interface, which could explain the oil-wet nature of composite carbonate rocks due to electrostatic adsorption of negatively charged carboxylic acids. Conversely, the DDL-based SCM predicted a negative SP, leading to an inaccurate interpretation of the electrokinetic properties at the rock-brine interface. Thus, the use of extended TLM-based SCM was required to accurately predict the zeta potential and account for the adsorption of carboxylic acids on the reservoir composite carbonate surface.

Evidence for new enantiospecific interaction force in chiral biomolecules

Evidence for new enantiospecific interaction force in chiral biomolecules

Incorporation of Activated Biomasses in Fe-N-C Catalysts for Oxygen Reduction Reaction with Enhanced Stability in Acidic Media

Fe-N-C materials are promising oxygen reduction reaction (ORR) catalysts for replacing expensive platinum-based catalysts (Pt/C) in proton exchange membrane fuel cells. However, they still show low volumetric activity and stability compared to Pt/C catalysts, with carbon corrosion being one of the main factors for the loss of active Fe-Nx sites. Within this study, phosphoric acid-activated rye straw and coconut shells are revealed as a promising matrix for Fe-Nx sites with advanced stability against electrochemical carbon corrosion (5000 cycles, 1.0–1.5 VRHE, and 0.1 M HClO4) compared to a common Fe-N-C catalyst based on carbon black. Electrochemical characterization of the two biomass-based catalysts (Fe-N-CBio) shows on the one hand 50% higher stability in terms of mass activity as well as comparable activity and active site density but on the other hand a lower selectivity toward the four-electron ORR than the common Fe-N-C catalyst. Nitrite stripping experiments in acetate buffer as an electrolyte display a 1.5-fold stronger effect of carboxylic acid adsorption than on a common Fe-N-C catalyst, revealing differences to the electronic structure of the Fe-N-CBio catalyst. This difference is mainly attributed to the presence of phosphor species and higher amounts of nitrogen functionalities in the Fe-N-CBio catalysts. The presence of P is assumed to stabilize the carbon against carbon corrosion by inhibiting electron withdrawal from the C. This study points out the impact factors on Fe-N-C stability and further shows the promising application of activated biomasses in more stable and sustainable Fe-N-C catalysts for ORR.

Identification of organic species with “double-sided tape” characteristics on the surface of carbonate reservoir rock

Carbonate reservoir rocks are normally mixed-wet or oil-wet, leading to low oil recovery efficiency using water-based oil recovery methods. It is critical to understand the molecular composition of the organic material coating the surface of carbonate reservoir rock in order to design better enhanced oil recovery (EOR) methods. Herein, we extracted organic compounds from a carbonate reservoir rock and characterized their composition using high resolution mass spectrometry (HRMS). In contrast to conventional interpretation that the mixed-wet or oil-wet nature of carbonate reservoir rocks arises from the adsorption of carboxylic acids, our results demonstrated that the organic species strongly bound to carbonate reservoir rock surface are dominated by N-containing species, including a group of “sticky molecules”. Each of these molecules can form multiple hydrogen-bonds, therefore they might act as a “double-sided tape” which binds crude oil strongly to the carbonate rock surface. Furthermore, we applied atomic force microscopy (AFM) techniques to a model mineral surface with regions of positive change and negative charge which was contacted with the crude oil produced from the formation where the rock was sampled. It was found that only the organic molecules with positive charge in the oil were adsorbed onto the mineral. This supports HRMS results which suggest that the organic materials strongly bound to the carbonate reservoir rock surface are dominated by basic N-containing molecules. Overall, these findings suggest that, beside fatty acids, these “sticky molecules” might also play an important role in controlling the wetting state of carbonate reservoir rock.

First-Principles Study of the Adsorption of Carboxylic Acid on Cu(111)

The geometric structure and electronic properties of the adsorption of organic carboxylic acids on the closed-packed Cu(111) surface have been addressed by periodic density functional theory (DFT) calculations. We also have taken into account van der Waals (vdW) interaction by the VdW-DF method. The optimized structures show that formic and acetic acids have stable structures of molecular adsorption in clean copper surfaces. We find that the adsorption energies at 1/16 ML coverage are -0.27, -0.30 and -0.10 eV for formic, acetic, and propionic acid, respectively. On the other hand, in the case of vdW-DF, their adsorption energies increased to -0.63, -0.70 and -0.73 eV.

Adsorption of aromatic carboxylic acids on carbon nanotubes: impact of surface functionalization, molecular size and structure.

A large quantity of emerging contaminants are ionizable, and the ionized compounds display different adsorption behaviors than their neutral counterparts. In particular, a strong intermolecular force, negative charge assisted hydrogen bonding ((-)CAHB), was recently identified, which explains the unusually strong adsorption of negatively charged compounds on carbon nanotubes with oxygen-containing functional groups. However, most previous studies only probed molecules with one benzene ring. The adsorption of ionizable compounds with more than one benzene ring and additional functional groups has not been examined. This study investigated the effect of surface functionalization, molecular size and structure of six aromatic carboxylic acids on their adsorption on multi-walled carbon nanotubes (MWNTs) in batch reactors. In addition, the short-range interactions of the neutral acids with MWNTs were calculated to evaluate the effect of aromaticity and bulkiness. Hydrophobicity and electrostatic interactions dominate the intermolecular forces between ionized contaminants and MWNT surfaces. pH dependent octanol/water partitioning coefficient (Dow) is a more precise indicator of the adsorption of ionizable compounds on MWNTs. (-)CAHB is a significant force only for compounds with one benzene ring. Hydroxyl and carboxyl functional groups displayed similar capacity to form (-)CAHB, as indicated by the release of hydroxide ions.

Interaction between low molecular weight carboxylic acids and muscovite: Molecular dynamic simulation and experiment study

Interface phenomena between low molecular weight (LMW) carboxylic acids and muscovite was investigated through molecular dynamic simulation and experiment, where the typical monocarboxylic acids including formic acid (C1), acetic acid (C2), propionic acid (C3) and butyric acid (C4) were used as models. Density distribution, adsorption energy, root mean square dynamic (RMSD) of carboxylic acids on water-muscovite interface were calculated through molecular dynamic simulation, and the advanced characterization methods, such as ATR-FTIR spectra, AFM images and contact angle were performed to test and verify the relative simulation findings. The molecular simulation showed that carboxylic acids adsorbed on surface of muscovite through hydrogen bond between H atom of COOH functional group of carboxylic acid and O atom of muscovite, belong to outer sphere adsorption, and ATR-FTIR spectra and AFM images confirmed this finding. Adsorption energy for long carbon chain carboxylic acid (C4) was higher than that for short carbon chain carboxylic acid (C1, C2 and C3) due to the effect of carboxylic acid diffusion on water-muscovite interface. The hydrophilic functional group COOH of carboxylic acids preferably adsorbed on muscovite surface, while the hydrophobic functional groups CH3 and CH2 of carboxylic acids were far from the muscovite surface. So, the hydrophobicity on muscovite surface increased due to the adsorption of carboxylic acids, which resulted in the increase of contact angle of water on muscovite surface.

Carboxylic acids as efficient corrosion inhibitors of aluminium alloys in alkaline media

The efficiency of AA5754 aluminium alloy corrosion inhibition achieved with maleic, malic, succinic, tartaric, citric, tricarballylic acids and serine in alkaline environment (pH 11) was examined. Selected corrosion inhibitors are characterized by different numbers and distribution of carbonyl and hydroxyl groups within their molecules. We have proposed and verified a novel approach for determining the adsorption isotherms based on the impedance measurements in galvanostatic mode (g-DEIS), allowing to distinguish subtle changes in the adsorption dynamics. It was shown that g-DEIS precisely determines the inhibitor concentration required for the full coverage of aluminium surface with the adsorbed inhibitor monolayer. Our approach was then cross-verified with the ellipsometry, cyclic polarization and classic EIS measurements, while the SEM and XPS analyses served to determine changes in the surface topography and chemistry. We have demonstrated that the investigated compounds significantly decelerate the corrosion rate of AA5754 at low inhibitor concentrations. Inhibition efficiency exceeds 99% at 6.9 mM for tricarballylic, 8.1 mM for citric and 12.0 mM for tartaric acid. The inhibition efficiency was primarily dependent on the high number of carbonyl groups in the molecule, while the inhibition provided by monocarboxylic amino acid (serine) was negligible, reaching 60% at 20 mM. The plotted isotherms fitted the Langmuir adsorption model, with similar values of Gibbs free energy for each studied inhibitor. The adsorption of carboxylic acids onto the surface of aluminium occurred via ligand exchange mechanism. On the basis of electrochemical and XPS studies, we claim that the role played by hydroxyl groups is secondary, while their presence slightly worsens the corrosion resistance of aluminium.

Friction Mechanisms by Carboxylic Acids in Aqueous Lubricants

Carboxylic acids are well known for their friction-reducing abilities driven by the formation of low-shear-strength films on the steel surface. However, understanding of the adsorption mechanisms especially in polar solvents is yet not well explored. In this work, atomic force microscopy was used to visualise the adsorption behaviour of various carboxylic acids in both polar and less-polar solvents. The work was continued with a tribological study of the lubricants additivated with carboxylic acids in a laboratory scale ball-on-disc tribometer. During this study, the effect of concentration and carboxylic acid chain length was studied in polar media (water-based lubricants) and compared with commonly used synthetic non-polar lubricant (poly-α-olefin, PAO). It was observed that for both polar and less-polar lubricants, surface coverage of carboxylic acids increased with increasing length of hydrocarbon tail. In less-polar lubricants, carboxylic acids adsorbed to the surface by spreading on it evenly, whereas in polar lubricants, very dense multi-layered formation was promoted. Friction reduction achieved with the use of carboxylic acids in the non-polar lubricant was not as efficient as in the case of the polar lubricant. This was associated with the more pronounced multilayer formation of carboxylic acids in the polar lubricants, facilitating higher friction reduction as compared to the adsorption of carboxylic acids in a dense monolayer form seen in the less-polar lubricant.

Comparative study of carboxylic acid adsorption on calcite: l-malic acid, d-malic acid and succinic acid

Succinic acid and l-malic acid are known to affect calcite dissolution/crystallization due to their tendency to adsorb on calcite’s surface. Taking into account the structural similarity among succinic acid, l-malic acid, and d-malic acid, a comparative study of their adsorption behavior on calcite was investigated for clarifying their adsorption mechanism. Kinetic results showed that l-malic acid adsorption reached equilibrium within 12 h, while succinic acid required 48 h. Results from the pH effect study showed that the strength of surface complex of succinic acid on calcite was weaker, even compared to its aqueous complex with Ca2+ ion. Alternately, l-malic acid exhibited a much stronger surface complex strength, even compared to its aqueous complex with Ca2+ ion. The adsorption isotherm results indicated that the saturated adsorption amount of l-malic acid was twice that of succinic acid, suggesting the surface complex of succinic acid may occupy a larger space on calcite surface compared to that of l-malic acid. Based on these results and those from previous studies, we proposed that succinic acid adsorption is through its two carboxyl groups binding to two adjacent surface sites (> Ca+), and not only one. Also, l-malic acid adsorption occurs through one carboxyl group and one hydroxyl, which forms a “claw” on calcite surface. The similar adsorption behavior between l-malic acid and d-malic acid reinforces this proposition for l-malic acid adsorption mechanism. Our study will serve as good reference information to provide better understanding into the adsorption of other carboxylic acids on calcite.

Formic Acid Dissociative Adsorption on NiO(111): Energetics and Structure of Adsorbed Formate

The dissociative adsorption of carboxylic acids on oxide surfaces is important for understanding adsorbed carboxylates, which are important as intermediates in catalytic reactions, for the organo-functionalization of oxide surfaces, and in many other aspects of oxide surface chemistry. We present here the first direct experimental measurement of the heat of dissociative adsorption of any carboxylic acid on any single-crystal oxide surface. The enthalpy of the dissociative adsorption of formic acid, the simplest carboxylic acid, to produce adsorbed formate and hydrogen (as a surface hydroxyl) on a (2 × 2)-NiO(111) surface is measured by single crystal adsorption calorimetry. The differential heat of adsorption decreases with formic acid coverage from 202 to 99 kJ/mol at saturation (0.25 ML). The structure of the adsorbed products is clarified by density functional theory (DFT) calculations, which provide energies in reasonable agreement with the calorimetry. These calculations show that formic acid readily...

Collectability and Selectivity of Physical Adsorption of Carboxylic Acids in Flotation

The collecting ability of desorbable species (DS-species) of carboxylic acids is analyzed. The spreading velocity and surface pressure of some fat acids are correlated with their collectability. It is found that increase in the hydrocarbon chain length to a certain limit results in the higher collectability of carboxylic aids, which correlates with the high spreading velocity of acid derivants on water surface. The cause of reduction in the collecting ability of short-chain collectors is discovered. It is shown that an adequate criterion of fat acid collectability can be a surface flow thickness of the agent’s DS-species film. The flotation performance with the compound chemisorption and physisorption coat and with the solely chemical adsorption coat is estimated. The causes of the decrease in the valuable component recovery and in the concentrate quality without the physical form of reagent adsorption at a mineral surface are revealed.