Ethylenediaminetetraacetic Acid Molecules Research Articles

Lewis-base ligand-reshaped interfacial hydrogen-bond network boosts CO2 electrolysis.

Both the catalyst and electrolyte strongly impact the performance of CO2 electrolysis. Despite substantial progress in catalysts, it remains highly challenging to tailor electrolyte compositions and understand their functions at the catalyst interface. Here, we report that the ethylenediaminetetraacetic acid (EDTA) and its analogs, featuring strong Lewis acid-base interaction with metal cations, are selected as electrolyte additives to reshape the catalyst-electrolyte interface for promoting CO2 electrolysis. Mechanistic studies reveal that EDTA molecules are dynamically assembled toward interface regions in response to bias potential due to strong Lewis acid-base interaction of EDTA4--K+. As a result, the original hydrogen-bond network among interfacial H2O is disrupted, and a hydrogen-bond gap layer at the electrified interface is established. The EDTA-reshaped K+ solvation structure promotes the protonation of *CO2 to *COOH and suppressing *H2O dissociation to *H, thereby boosting the co-electrolysis of CO2 and H2O toward carbon-based products. In particular, when 5mM of EDTA is added into the electrolytes, the Faradaic efficiency of CO on the commercial Ag nanoparticle catalyst is increased from 57.0% to 90.0% at an industry-relevant current density of 500mA cm-2. More importantly, the Lewis-base ligand-reshaped interface allows a range of catalysts (Ag, Zn, Pd, Bi, Sn, and Cu) to deliver substantially increased selectivity of carbon-based products in both H-type and flow-type electrolysis cells.

Hydrothermally Stimulated Molecular Interfaces for Augmented Electron Delocalization in Wet-Chemical Phosphorus Recovery from Incineration Ash of Sewage Sludge.

Wet-chemically recovering phosphorus (P) from sewage sludge incineration ash (SSIA) has already become a global initiative to address P deficit, but effectively isolating P from these accompanying metals (AMs) through adsorption in a SSIA-derived extract remains elusive. Here, we devised a hydrothermal stimulus-motivated thermodynamic and kinetic enhancement to gain anionic ethylenediaminetetraacetic acid (EDTA) molecular interfaces for AM enclosure to resolve this conundrum. A new dosage rule based on the EDTA coordination ratio with AMs was established for the first time. Upon hydrothermal extraction at 140 °C for 1 h, the P extraction efficiency reached 96.7% or higher for these obtained SSIA samples, and then exceptional P sequestration from these EDTA-chelated AMs was realized by the peculiar lanthanum (La)-based nanoadsorbent (having 188.86 mg P/g adsorbent at pH ∼ 3.0). Relevant theoretical calculations unraveled that these delocalized electrons of tetravalent EDTA molecules boosted the enclosure of liberated AMs, thereby entailing a substantially increased negative adsorption energy (-408.7 kcal/mol) of P in the form of H2PO4- through intruding lattice-edged carbonates to coordinate La with monodentate mononuclear over LaCO5(1 0 1). This work highlights the prospect of molecular adaptation of these common extractants in wet-chemical P recovery from various P-included wastes, further sustaining global P circularity.

Taming Active‐Ion Crosstalk by Targeted Ion Sifter Toward High‐Voltage Lithium Metal Batteries

AbstractLithium metal batteries (LMBs), based on high‐voltage (HV) LiNixCoyMnzO2 (NCM, x+y+z = 1) materials, exhibit great potential for next‐generation electric vehicle (EV) cells. Nevertheless, the inevitable dissolution and shuttle of transition metal (TM) ions from NCM cathodes poses a threat to the electrochemical sustainability of LMBs, especially at high voltage and high temperatures. Herein, ethylene diamine tetraacetic acid (EDTA)‐grafted MOF‐808 is proposed to serve as a multifunctional ion‐selective separator coating, in which EDTA molecules play a targeted ion sifter role in restricting active‐ion crosstalk. Judicious characterizations and theoretical calculations reveal that the separator coating effectively captures the TM‐ions in the electrolyte and thus ensures stable Li deposition without dendrites. As a result, the 4.5 V NCM622//Li cell with the ion‐selective separator achieves a high‐capacity retention over 1000 cycles with a high Coulombic efficiency of 99.68%, and its cycling stability at 55 °C is also upgraded. This crosstalk‐taming strategy offers fresh insight into constructing long‐life HV‐LMBs.

CA and/or EDTA functionalized magnetic iron oxide nanoparticles by oxidative precipitation from FeCl2 solution: structural and magnetic study

Four samples containing magnetic iron oxide nanoparticles (MIONs) of various sizes are prepared employing a simple low-temperature method of oxidative precipitation from FeCl2∙4H2O–NaOH–NaNO3 aqueous solution. For the preparation of two samples, the usual oxidation-precipitation synthesis protocol is modified by using ethylenediaminetetraacetic acid (EDTA) chelating agent as a stabilizer of the Fe2+ ions in a solution, which results in the partial capping of the prepared MIONs with EDTA molecules. Three out of four samples are subjected to citric acid (CA) functionalization in the post synthesis protocol. Structural and magnetic properties of the synthesized MIONs are assessed using various experimental techniques (XRD, TEM, Fourier transform infrared, dynamic light scattering, Mössbauer, and SQUID). The average size of spherical-like MIONs is tuned from 7 nm to 38 nm by changing the synthesis protocol. Their room temperature saturation magnetization, M s, is in the range of 43 to 91 emu g−1. Magnetic heating ability, expressed via specific absorption rate value, which ranges from 139 to 390 W/gFe, is discussed in relation to their structural and magnetic properties and the possible energy dissipation mechanisms involved. The best heating performance is exhibited by the sample decorated with EDTA and with a bimodal size distribution with average particle sizes of 14 and 37 nm and M s = 87 emu g−1. Though this sample contains particles prone to form aggregates, capping with EDTA provides good colloidal stability of this sample, thus preserving the magnetic heating ability. It is demonstrated that two samples, consisting of 7 nm-sized CA- or 14 nm-sized EDTA/CA-functionalized superparamagnetic MIONs, with a similar hydrodynamic radius, heat in a very similar way in the relatively fast oscillating alternating current magnetic field, f = 577 kHz.

Two-dimensional MXene membranes with biomimetic sub-nanochannels for enhanced cation sieving

Membranes with high ion permeability and selectivity are of considerable interest for sustainable water treatment, resource extraction and energy storage. Herein, inspired by K+ channel of streptomyces A (KcsA K+), we have constructed cation sieving membranes using MXene nanosheets and Ethylenediaminetetraacetic acid (EDTA) molecules as building blocks. Numerous negatively charged oxygen atoms of EDTA molecules and 6.0 Å two-dimensional (2D) sub-nanochannel of MXene nanosheets enable biomimetic channel size, chemical groups and tunable charge density for the resulting membranes. The membranes show the capability to recognize monovalent/divalent cations, achieving excellent K+/Mg2+ selectivity of 121.2 using mixed salt solution as the feed, which outperforms other reported membranes under similar testing conditions and transcends the current upper limit. Characterization and simulations indicate that the cation recognition effect of EDTA and partial dehydration effects play critical roles in cations selective sieving and increasing the local charge density within the sub-nanochannel significantly improves cation selectivity. Our findings provide a theoretical basis for ions transport in sub-nanochannels and an alternative strategy for design ions separation membranes.

Inhibition of Strontium Adsorption and Desorption by Ethylenediaminetetraacetic Acid at the Barite (001)–Water Interface

Understanding the sorption behavior of ions at the mineral–water interface is important to determine the fate of elements in the environment. Here, we used barite to understand metal and organic molecule interactions with ionic crystals as organic molecules are used to remove scale that can form during oil recovery in sulfate-rich settings. The sorption behavior of strontium (Sr) on the (001) surface in the presence of ethylenediaminetetraacetic acid (EDTA) was measured using in situ specular X-ray reflectivity (XR) and resonant anomalous X-ray reflectivity (RAXR). Based on the XR results, the presence of EDTA disrupts the barite surface structure, particularly that of the top two monolayers. A maximum of 0.7 (±0.2) EDTA molecules per surface unit cell are adsorbed, though the exact amount cannot be distinguished from that of other adsorbed species, such as Ba2+ and H2O. Based on the RAXR results, the presence of EDTA inhibits Sr incorporation into the barite surface and binds with Sr in solution to limit the amount of Sr2+ in solution. The Sr-EDTA2– complex then binds with barium ions at the barite surface, presumably in a bi-nuclear, bi-dentate state. Desorption of the Sr was also measured in the presence of EDTA. The desorption experiments show that ∼75% of the sorbed strontium was removed following extended reactions with EDTA and deionized water. There were minimal changes in the surface structure following desorption measurements implying that changes following Sr sorption in the presence of EDTA may be irreversible.

Fabrication and performance study of a superhydrophobic anti-scaling and anti-corrosion coating

In this work, we designed and fabricated an anti-scaling and anti-corrosion superhydrophobic 1H,1H,2H,2H-perfluorodecyl triethoxysilane (PFDS)/ethylenediamine tetraacetic acid (EDTA)/anodized copper oxide (ACO) coating at the surface of a copper alloy. The water contact angle of PFDS/EDTA/ACO coating reaches 164.53°, showing superhydrophobicity, which will reduce the contact between scale crystals, corrosive medium and substrates, and help to inhibit scaling deposition and corrosion. Results show during the CaCO3 deposition test, EDTA molecules, EDTA-Zn2+ and EDTA-Cu2+ chelates stored in the micro-structure of superhydrophobic PFDS/EDTA/ACO coating are released to the interface and help to improve scaling prevention. After soaking for 48 h, the CaCO3 scaling mass of PFDS/EDTA/ACO coating was only 27.0 % that of ACO coating, and the corrosive protection efficiency of the superhydrophobic PFDS/EDTA/ACO coating was improved by 3.4 times that of ACO coating. Studies indicated that the anti-scaling and anti-corrosion of the superhydrophobic PFDS/EDTA/ACO coating contributes to the cooperation of superhydrophobic air film and the potential storage and dynamic release of EDTA, as well as the passivation layer formed on the substrate.

Improved Electrochemical Performance of Zinc Anodes by EDTA in Near‐Neutral Zinc−Air Batteries

AbstractThe influence of ethylenediaminetetraacetic acid (EDTA) electrolyte additive on the performance of Zn−air batteries with near‐neutral chloride‐based electrolytes was examined for primary and secondary batteries. The electrochemical measurements indicated that Zn is not completely active in neat 2 M NaCl, but still could be discharged up to 1 mA cm−2 around −1.0 VAg/AgCl. The characterization of the Zn surfaces revealed the existence of a passive film consisting of Simonkolleite, Zn(OH)2, and/or ZnO. The EDTA additive enhanced the discharge voltages by 200 mV to −1.2 VAg/AgCl indicating an active Zn surface. The effect of EDTA is explained by its chelation abilities with Zn2+ before formation of hydroxide or oxide species. The Zn−air cells with EDTA were operated up to 930 h with specific energies up to 840 Wh kgZn−1. The cells could also be cycled up to 70 cycles while providing enhanced discharge voltages at 1.15 V over 50 cycles. The positive effect of EDTA is dependent on the amount of free EDTA molecules. Nevertheless, the Zn−air cells showed better performance in terms of higher discharge voltage, discharge energies, and lower overpotentials in presence of EDTA.

Tumor Cell Dissociation Removes Malignant Bladder Tumors

Summary Surgery and subsequent chemotherapy are still the most adopted clinical modalities for bladder cancer treatments with the inevitable operation risks, chemotherapy toxicity, and high recurrence rate. Here, we report an unprecedented tumor cell dissociation strategy for malignant bladder tumor removal without the needs of conventional surgery and chemotherapy. A common metal ion chelator, ethylene diamine tetraacetic acid (EDTA), has been loaded into the interlayers of neurotensin (NT)-modified Zn-Al layered double hydroxide (LDH). Under the targeting by NT, such a nano-platform shows high affinity to bladder tumor cells, leading to the highly selective and efficient accumulation at the bladder tumor site. The released EDTA molecules deprive Ca2+ from the intercellular calcium-dependent connexin by EDTA-Ca2+ chelation, resulting in the tumor disaggregation that is then safely excreted out of body rather than killed using toxic chemodrugs, thus, ensuring excellent biosafety and extraordinarily high effectiveness.

In vitro cytotoxicity study of virgin, ethylenediaminetetraacetic acid- and hexamethylenetetramine-capped silica particles synthesized by precipitation method

Silica particles synthesized by precipitation method were in situ capped with Ethylenediaminetetraacetic acid (EDTA) and Hexamethylenetetramine (HMTA) compounds aiming to increase their biocompatibility. XRD, FTIR, TG/DSC, DLS and SEM analyses were performed to determine the crystalline structure, attached functional groups, thermal behaviour, size and morphology of silica particles. XRD analysis showed the amorphous structure of synthesized particles. FTIR results confirmed the formation of SiO2 particles and pointed about the functional groups (−CN, −CO,−OH etc.) attached on surface. Thermal analysis results showed that weight loss was due to removal of water and gradual degradation of EDTA molecules with rise of temperature, i.e. above 220 °C. The dynamic laser scattering measurements (zeta potential) depicted the strongest electrophoretic stability (− 30 mV) of EDTA-capped silica than virgin (− 13 mV) and particles capped with HMTA(− 24 mV). The SEM results revealed that virgin and silica particles capped with EDTA ligand exhibited spherical morphology with an average particle size of 210 nm and 280 nm, respectively. Whereas, HMTA-capped silica partilces showed hexagonal morphology with an average particle size of 240 nm. The in vitro cytotoxicity analysis was also carried out using human HepG2w, ATCC® HB-8065™ cell culture of 100 µg/ml concentration in Dulbecco’s Modified Eagle Medium (DMEM) solution maintained at 37 °C in the presence of CO2 environment. The results revealed that silica particles capped with EDTA (0.07 g) have shown remarkable biocompatibility (~ 96%) than virgin silica (~ 69%) due to bearing better hydrophobic characteristics. However, HMTA decomposed during synthesis which induced toxicity and agglomeration among silica particles. As a result, poor biocompatibility (~ 65%) was observed.

Investigation of Spectral Characteristics of Pulsed Xenon Lamps for Combined Photochemical Degradation of Organometallic Compounds in Liquid Radioactive Waste

The paper considers the composition of liquid radioactive wastes from the nuclear plants. Using traditional ways to extract organometallic compounds formed, when using the deactivation solutions to clean the surfaces of nuclear plant rooms, are complicated. The paper studies the edge-cutting methods of solving this problem. Its proposal is to use a combined ultraviolet treatment for organometallic compounds degradation based on ethylenediaminetetraacetic acid (EDTA) via pulsed xenon lamps. A potential use of the tubular and spherical geometry lamps is examined and advantages, disadvantages and features of these lamps are described. Instead of the pure EDTA the experiments used its disodium salt ( Na 2 -EDTA). The hydrogen peroxide was used as an extra oxidizer. Absorption spectrums of solutions with various Na 2 -EDTA - hydrogen peroxide ratio were measured. It is found that the absorbance curve maximum is in the shortwave spectrum region (λ < 210 nm). The use of amalgam lamps of monochromatic radiation at wavelength λ = 254 nm will result only in formation of hydroxyl radicals but direct destruction processes of EDTA molecules due to radiation will be rare, and this decreases efficiency of their use. The spectral radiation characteristics of various continuum spectrum pulsed xenon lamps was measured. The experimental data expressed in relative units were compared with the emission spectrum of an absolutely black body. The paper shows that in spherical lamps high brightness temperature can be reached. Thus, in spherical lamps it is possible to obtain a spectrum, which is in maximum correlation with the absorption spectrum of the solutions under study, thereby making them a prospective radiation source for photo-degradation of EDTA compounds. For drawing a final conclusion it is necessary to conduct researches in order to compare Na 2 -EDTA degradation via tubular and spherical xenon lamps.

H2O2 and/or photocatalysis under UV-C irradiation for the removal of EDTA, a chelating agent present in nuclear waste waters

In this study, we compare the efficiency of photocatalytic processes based on TiO2 (Degussa P-25) and UV/H2O2 as a means of degrading and mineralizing ethylenediaminetetraacetic acid (EDTA) under UV-C irradiation. EDTA was the molecule studied here because it is present in high proportions at nuclear facilities, where it is used for cleaning and decontamination purposes because of its chelating properties. The photonic power of the UV-C lamps used (13 and 15W) was established using actinometric and Keitz's methods. The adsorption of EDTA on TiO2 Degussa P-25 corresponds to a Langmuir isotherm, and the photocatalytic degradation process is consistent with the Langmuir–Hinshelwood model. During the photocatalytic process, an increase in the initial EDTA concentration favors the formation of large quantities of intermediates, which occupy the active sites, thus delaying the production of detectable quantities of oxalic acid. The results obtained here also show that nitrogen originating from EDTA molecules is mainly converted into ammonium and nitrate ions with a conversion rate of 67%. In addition, the amount of oxalic acid formed increases with the pH. The efficiency of the UV/TiO2 and UV/H2O2 processes as a means of EDTA degradation was found to be similar, provided H2O2 was added continuously during the UV/H2O2 process. The quantum efficiency was calculated and found to be equal to 0.9% in the case of photocatalysis and 1.4% in that of UV/H2O2.

Degradation of a cobalt(II)–EDTA complex by photocatalysis and H2O2/UV-C. Application to nuclear wastes containing 60Co

The 60Co present in some low-level effluents forms complexes with organic ligands such as ethylenediaminetetraacetic acid (EDTA). These complexes make it difficult to remove the 60Co using conventional filtration methods. The aim of this study was to test the use of titanium-based photocatalysis (TiO2/UV) and photochemical methods involving the use of oxidation agents (H2O2/UV-C) (both of which are advanced oxidation processes) to degrade EDTA and recover 60Co once it has been released from the complex. In preliminary experiments on the 59Co-EDTA complex, we tested the efficiency of the TiO2/UV and H2O2/UV-C processes as means of degrading EDTA molecules and releasing cobalt in its cationic forms Co2+ and Co3+. These cations can be trapped by either precipitating and/or adsorbing them on TiO2 depending on the pH. When this treatment was applied experimentally to radioactive wastes, it turned out to be highly effective since it improved the decontamination factor (DF: initial volumic activity/final volumic activity) twofold.

Influence of rare-earth-functionalized carbon nanotubes on thermal and mechanical properties of polytetrafluoroethylene nanocomposites

Mixed acid and rare-earth (RE) solution were used as the surface modifiers to functionalize multi-walled carbon nanotubes (CNTs). Fourier transform infrared spectra reveal that the carboxylic groups were induced on the surface of acid-functionalized and RE-functionalized CNTs, and the presence of C–N bond suggests that the ethylenediamine tetraacetic acid molecules were successfully grafted on the surface of RE-functionalized CNTs. Raman analysis indicates that acid-treatment and RE-treatment did not significantly change the structure of pristine CNTs. X-ray photoelectron spectroscopy analysis shows that both acid-treatment and RE-treatment improved the number of carboxylic groups on treated CNTs surfaces compared to pristine CNTs, and RE-treatment is superior to acid-treatment to improve the oxygen to carbon ratio on the CNTs surfaces. Transmission electron microscope and scanning electron microscope observations indicate that RE-functionalized CNTs have better dispersion in solvent and in polytetrafluoroethylene (PTFE) matrix than acid-functionalized CNTs, respectively. Thermal stability analysis and mechanical tests display that RE-functionalized CNTs/PTFE nanocomposite has the highest thermal stability and mechanical properties than acid-functionalized CNTs/PTFE nanocomposite and pristine CNTs/PTFE nanocomposite.

Surface effect of nanocrystals doped with rare-earth ions enriched on surface and its application in upconversion luminescence

By employing a certain proportion of hydrogen peroxide, ammonia, ammonium fluoride, and ethylene diamine tetraacetic acid (EDTA) as precipitator, well-crystallized LaOF:Eu3+ and LaOF:Yb3+, Er3+ nanocrystals are synthesized by using the chemical co-precipitation method. The structural properties of these samples are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR) spectra. The results show that all the samples have an average size below 70 nm, which decreases gradually with the increase of the EDTA content, and a certain number of EDTA molecules are coupled with doped ions on the surfaces of nanocrystals. Most of the doped ions are proved to be enriched on the surfaces of nanocrystals and surrounded by the high energy vibration groups and bonds in EDTA molecules. The observed differences in upconversion emission spectrum among the different LaOF:Yb3+, Er3+ nanocrystals are explained by the different two-photon upconversion mechanisms. Especially, in the LaOF:Yb3+, Er3+ nanocrystals with EDTA, the two-photon processes that contain several special cross-relaxation processes are introduced to analyse the corresponding upconversion mechanisms.

The release and extraction of lanthanide ions from metal-encoded poly (styrene-co-methacrylic acid) microspheres

This article describes a systematic study of ion release, carried out on lanthanide-encoded polystyrene-co-methacrylic acid (P(S-MAA)) and polystyrene-co-acrylic acid (P(S-AA)) copolymer particles, which were synthesized by two-stage or three-stage dispersion polymerizations. These particles with different levels of lanthanide (Ln) ion content and containing several different types of Ln ions were dispersed in normal buffer media, namely 2-(N-morpholino)ethanesulfonic acid (MES), phosphate buffered saline solution (PBS), ammonium acetate (AmAc) and buffers containing strong chelating molecules like ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA). Traditional inductively coupled plasma mass spectrometry (ICP-MS) was employed to follow the loss of ions into the aqueous medium as a function of time. The release behavior of the Ln ions were compared. In MES and PBS buffers at neutral pH, and AmAc at pH 9.0, there was essentially no significant loss of Ln ions from the particles to the buffer. When the chelating agents EDTA or DTPA were present in the buffer, the loss of Ln ions was more prominent, but less than 15% after 8 weeks under stirring. The differences among the different samples were small. Considering the ability of EDTA and DTPA to remove Ln ions from the particles and the fact of minimal ion release in the presence of PBS buffer, we infer that the ion loss is a more active process involving the EDTA or DTPA molecules. The main conclusion is that in the absence of strong chelating agents, these particles are stable against ion leakage, even upon prolonged storage and stirring. This is of great importance for their application in bead-array biological assays based on mass cytometry detection.

Effects of TEMED and EDTA on the structural and mechanical properties of NIPAAm/Na+ MMT composite hydrogels

N-isopropyl acrylamide (NIPAAm) hydrogels are known as thermosensitive crosslinked polymer networks. In this work, the network parameters of their composites, i.e., NIPAAm/sodium montmorillonite (NIPAAm/Na+MMT) hydrogels synthesized by free radical solution polymerization in the presence of two different types of accelerator (tetramethyl ethylenediamine (TEMED) and ethylenediamine tetraacetic acid (EDTA)) and initiator (potassium persulphate (K2S2O8) and cerium ammonium nitrate ((NH4)2Ce(NO3)6), Ce(IV)) using five different clay content (in the range of 1.0–5.0 wt % of total monomer concentration) at 25 °C were presented and discussed. FTIR spectra, XRD patterns, SEM photographs, and network parameters of the samples indicated that the presence of COOH groups on EDTA molecules was resulted in the formation of exfoliated structures and the activity of EDTA/KPS redox pair was higher than those of TEMED/KPS and EDTA/Ce (IV) pairs. The compression moduli (G) of the hydrogels initiated with EDTA/Ce(IV) redox pair showed smooth and continual changings with increase in Na+MMT content (for swelling equilibrium at 25 °C) on the contrary of EDTA/KPS and TEMED/KPS pairs. It might be related to low initiator efficiency of cerium ammonium nitrate than KPS molecules, having higher effective crosslinking density with increasing clay content. On the other hand, the G moduli of NIPAAm/Na+MMT hydrogels (above their phase transition temperature) initiated with TEMED/KPS redox pair were higher than the others because of the more hydrophobic nature of TEMED molecules. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1256–1264, 2010

Adsorption isotherm mechanism of amino organic compounds as mild steel corrosion inhibitors by electrochemical measurement method

The inhibition ability of 4-amino-5-phenyl-4H-1, 2, 4-trizole-3-thiol (APTT), ethylenediaminetetra-acetic acid (EDTA) and thiourea (TU) for mild steel corrosion in 1.0 mol/L HCl solution at 30 ℃ was investigated. Tafel polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the influence of these organic compounds as corrosion inhibitors of mild steel in 1.0 mol/L HCl solution at 30 ℃. The inhibition mechanism was discussed in terms of Langmuir isotherm model. Results obtained from Tafel polarization and impedance measurements are in a good agreement. The inhibition efficiency increases with the increase of the inhibitor concentration. The adsorption of the inhibitors on the mild steel surface follows Langmuir adsorption isotherm and the free energy of adsorption ∆Gads indicates that the adsorption of APTT, EDTA, and TU molecules is a spontaneous process and a typical chemisorption.

Zeta Potential and Langmuir Films of Asphaltene Polar Fractions

In this work, we study the surface and electrokinetic properties of asphaltenes and some of their polar fractions. Using different mixtures of pentane/methylene chloride as a precipitant, we obtain four fractions (F1−F4), which contain different proportions of iron, nickel, copper, cobalt, aluminum, and vanadium. Modifications of asphaltenes and fractions F1 and F2 are performed by treatment with the salt form of ethylenediamine tetraacetic acid (EDTA) and, after this, with aqueous solutions of copper sulfate. The results indicate differences in the metal content between fractions before and after the treatments. Besides these differences, we observed differences in the zeta potential measurements and differences in the isotherms at the air/water interface. Our results show that, after the EDTA treatment, asphaltenes and fractions F1 and F2 can retain copper (>200% of the original copper content of the samples). This high copper content of the treated asphaltenes and the F1 and F2 samples is reflected in a change of the electrical charge from a negative charge to a positive charge. The hydrophobic behavior of the samples was analyzed with a Langmuir balance. The results show that the asphaltenes and the F1 fractions are more hydrophilic, with a smaller molecular area, and the F4 fractions are more hydrophobic, with a larger molecular area, before and after EDTA and copper sulfate treatments. Both the zeta potential measurements and Langmuir films of the samples indicate the possibility that EDTA molecules remain attached to the asphaltene molecules.

Scanning Force Microscopy Study of Etch Pits Formed during Dissolution of a Barite (001) Surface in CDTA and EDTA Solutions

Dissolution of the barite (001) surface in aqueous solutions of 0.18 M CDTA (trans-1,2-cyclohexylenediaminetetraacetic acid) and 0.18 M EDTA (ethylenediaminetetraacetic acid) at pH 12 was investigated using ex situ scanning force microscopy. In both solutions, triangular and trapezoidal etch pits developed on the (001) surface and became deeper and longer with increasing dissolution time. The orientation of the etch pits in CDTA and EDTA solutions was elongated along the crystallographic b axis. Furthermore, dissolution of the (001) surface in a layer-by-layer fashion was observed. This resulted in the formation of “alternating” etch pits with heights of one half-unit cell (about 3.6 Å), with the orientations of any two consecutive etch pits pointing oppositely to each other. In CDTA, etch pits within the half-unit cell were frequently bounded along the 〈120〉 and 〈010〉 directions. However, in EDTA, etch pits within the half-unit cell were bounded along the 〈110〉 and 〈010〉 directions. The dissolution behavior of barite in these two solutions is different based on the observed differences in the etch pits geometries as an assay for specific interactions between the crystal surface and organic molecules. Thus, we suggest that CDTA molecules bind to one Ba2+ cation along the 〈120〉 and/or 〈010〉 directions and EDTA molecules bind along the 〈110〉 directions to two Ba2+ cations exposed on the (001) surface.