Montmorillonite Surface Research Articles

Wettability of different clay mineral surfaces in shale: Implications from molecular dynamics simulations

Shale contains a lot of clay minerals. Clay minerals mainly exist in nano- and micro-meter sized particles, and the pore structure is complex, which leads to its extremely complex wettability. The surface wettability of clay minerals significantly affects the oil and gas-bearing capacity of shale reservoirs. Therefore, studying the wettability of common clay minerals in shale at the nanoscale is of great significance for shale hydrocarbon exploration and development. In this study, the wetting behavior of water in n-hexane and toluene on different clay mineral surfaces at the nanoscale was systematically studied using Molecular dynamics (MD) simulation. And the influencing factors of wettability were analyzed. Through the analysis of the morphological changes of water, relative concentration of water, RDF and interaction energy, it is concluded that the following order of water wettability on the surfaces of clay minerals: montmorillonite > chlorite > kaolinite > illite. Through the analysis of interaction energy, it is concluded that the hydrophilicity of four clay minerals is stronger than that of lipophilicity. And the main interactions between water and oil and the mineral surfaces were van der Waals force and electrostatic force. In addition, the temperature, liquid hydrocarbon type, and mineralization of water affected the wettability of clay minerals. The concentration of water on the surfaces of montmorillonite, kaolinite, and illite decreased with increasing temperature, and the water wettability decreased. At 298 K, the hydrophilicity of the surfaces of the clay minerals in toluene follows the order montmorillonite > chlorite > kaolinite > illite. The higher the NaHCO3 concentration in water, the weaker the wettability of the clay mineral surfaces to water. By comparing the previous experimental results with the MD simulation results, similar wetting characteristics were obtained, and the reliability of the simulation results was verified. MD simulation was used to explore the water wetting of the surfaces of four clay minerals in a shale reservoir from the micro level. This makes up for the lack of experimental means for clarifying the flow and production mechanisms of shale oil and gas and effectively improves the evaluation technology of shale.

Steered photogenerated carrier separation via mixed-crystal-homojunction-mediated permanent negative charge electric field

The chelation between heavy metal ions and small organic molecules limits the prospects of traditional adsorption methods in dealing with the complex water environment, annihilating the non-negligible reutilization value of heavy metal ions. Photocatalysis enables the reduction of heavy metal ions and the mineralization of small molecule pollutants to be accomplished simultaneously, but the enhancement of photogenerated carrier separation efficiency is a technical challenge to be overcome. Herein, a photocatalyst loaded with mixed-crystal titanium dioxide (TiO2) on the surface of montmorillonite (MMT) was prepared, which is reported for the exceptional performance in the recovery of heavy metals Cr(VI) and the mineralization of organic pollutants Rh-B (10 ppm chelate in total) within 60 min. Scientific characterization and theoretical calculations demonstrate that the generation of oxygen vacancies in mixed-crystal homojunctions driven by a permanent negative charge electric field will maximize the adsorption capacity for H2O and O2. The MMT surface is converted into a reduction platform for Cr(VI), and anatase-TiO2 acts as an active site for Rh-B mineralization, under the synergistic effect of permanent negative charge electric field and mixed-crystal homojunctions. The Cr(III) obtained by photocatalytic reduction is collected by cation exchange between the interlayers of MMT with corresponding selective adsorption. This novel structural design concept provides a highly innovative orientation for the application of photocatalytic technology to the remediation of complex aqueous environments.

Preparation of Laser-Ablated Ag Nanoparticle-MMT Clay-Based Beeswax Antibiofilm Coating.

Unlike other antimicrobial agents, Ag-based composites are stable and currently widely used as broad spectral additives, fighting microbial biofilms and other biological threats. The goal of the present study is to develop a green, multifunctional, and robust antibiofilm water-insoluble coating, inhibiting histamine-producing Lentilactobacillus parabuchneri biofilms. Herein, laser-ablated Ag NPs (L-Ag NPs) were incorporated into and onto a montmorillonite (MMT) surface layer with a simple wet chemical method, provided that the electrostatic interaction between L-Ag NPs and MMT clay led to the formation of L-Ag/MMT nanoantimicrobials (NAMs). The use of MMT support can facilitate handling Ag NPs in industrial applications. The Ag/MMT composite was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM), which confirmed the entrapment of L-Ag NPs into MMT clay. The surface chemical composition was assessed with X-ray photoelectron spectroscopy, proving that Ag NPs were in contact with and deposited onto the surface of MMT. The characteristic L-Ag/MMT band was investigated with UV-vis spectroscopy. Following that, the L-Ag/MMT composite was embedded into a biosafe water-insoluble beeswax agent with a spin coating technique. The antimicrobial ion release kinetic profile of the L-Ag/MMT/beeswax coating through an electrothermal atomic absorption spectroscopy (ETAAS) study supported the controlled release of Ag ions, reaching a plateau at 420 ± 80 nM, which is safe from the point of view of Ag toxicity. Microbial biofilm growth inhibition was assessed with real-time in situ Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) in a flow cell assembly over 32 h. The study was further supported by optical density (OD) measurements and SEM on bacteria incubated in the presence of the L-Ag/MMT/beeswax coating.

Acid-Base Properties of Cis-Vacant Montmorillonite Edge Surfaces: A Combined First-Principles Molecular Dynamics and Surface Complexation Modeling Approach.

Montmorillonite layer edge surfaces have pH-dependent properties, which arises from the acid-base reactivity of their surface functional groups. Edge surface acidity (with intrinsic reaction equilibrium constant, pKa) is a chemical property that is affected by crystal structure. While a cis-vacant structure predominates in natural montmorillonites, prior molecular-level studies assume a centrosymmetric trans-vacant configuration, which potentially leads to an incorrect prediction of montmorillonite acid-base surface properties. We computed intrinsic acidity constants of the surface sites of a montmorillonite layer with a cis-vacant structure using the first-principles molecular dynamics-based vertical energy gap method. We evaluated pKa values for both non-substituted and Mg-substituted layers on common edge surfaces (i.e., surfaces perpendicular to [010], [01̅0], [110], and [1̅1̅0] crystallographic directions). The functional groups ≡Si(OH), ≡Al(OH2)2/≡Al(OH)(OH2), and ≡SiO(OH)Al sites on surfaces perpendicular to [010] and [01̅0] and ≡Si(OH)U, ≡Si(OH)L, ≡Al(OH2), and ≡Al(OH2)2 on surfaces perpendicular to [110] and [1̅1̅0] determine the proton reactivity of non-substituted cis-vacant edge surfaces. Moreover, the structural OH sites on edge surfaces had extremely high pKa values, which do not show reactivity at a common pH. Meanwhile, Mg2+ substitution results in an increase in pKa values at local or adjacent sites, in which the effect is limited by the distance between the sites. A surface complexation model was built with predicted pKa values, which enabled us to predict surface properties as a function of pH and ionic strength. Edge surface charge of both trans- and cis-vacant models has little dependence on Mg2+ substitutions, but the dependence on the crystal plane orientation is strong. In particular, at pH below 7, edge surfaces are positively or negatively charged depending on their orientation. Implications of these findings on contaminant adsorption by smectites are discussed.

Performance and mechanisms for Cd(II) and As(III) simultaneous adsorption by goethite-loaded montmorillonite in aqueous solution and soil

A series of goethite-modified montmorillonite (GMt) materials was synthesized for the amelioration of cationic cadmium (Cd) and anionic arsenic (As) complex contaminants in soil and water bodies. The results showed that goethite (Gt) was successfully loaded onto the surface of montmorillonite (Mt), which possessed more functional groups (such as Fe–O, and Fe–OH) and a larger specific surface area. GMt-0.5 (Mt loaded with Gt at a ratio of 0.5:1) showed the highest adsorption capacity for Cd(II) and As(III) with the maximum of 50.61 mg/g and 57.58 mg/g, respectively. The removal rate of Cd(II) was highly pH dependent, while the removal rate of As(III) showed little dependence on pH. The goethite on montmorillonite might contribute to the formation of surface complexes with As(III) and oxidation of As(III) to As(V). In the binary system, both, synergistic and competitive adsorption existed simultaneously. Importantly, in the binary system, the removal of As(III) was more favorable because of the electrostatic interaction, formation of a ternary complex, and co-precipitation. In addition, the amendment of GMt-0.5 significantly reduced the availability of Cd and As in the soil. This study suggests that GMt-0.5 is a promising candidate for the simultaneous immobilization of metal (loid)s in both, aqueous solution and mine soil.

Використання відпрацьованих глинистих сорбційних матеріалів у технологіях виробництва шкіри та хутра

The work is devoted to solving the current problem of increasing the level of environmental safety of treatment industrial wastewater of leather production from chromium ions (III) through the use of natural and modified bentonite. The most promising way of wastewater purification is the sorption technology, which is widely used in many countries to prevent pollution of the environment by wastewater from industrial enterprises. Studies of the use of natural and modified bentonite in the adsorption of Cr3 + ions have been carried out. The purpose of the research was to study the use of clay sorbents previously applied for the purification of wastewater from heavy metal ions in technological processes of leather and fur production. The possibility and modes of application of spent bentonite dispersions for the processing of leather semi-finished products to increase resource conservation and environmental friendliness of leather production were also established. The influence of the process duration on the sorption efficiency of chromium ions has been studied. Studies have been conducted to use spent bentonite in tanning and filling processes. The efficiency of modification of montmorillonite has been proved and the expediency of using mineral dispersion for qualitative formation of the structure and properties of the leather during tanning has been established.The efficiency of adsorption of anionic dyes on spent montmorillonite is investigated. Was identified a high level of adsorption of anionic dyes at pH 5-6.5. The role of the dye structure, the level of the critical concentration of micelle formation on the dye adsorption on the surface of montmorillonite is provided. Utilization of spent bentonite by using it as part of multifunctional materials for the processing of leather semi-finished products contributes to a considerable increase in resource conservation and environmental friendliness of leather production.

53 - Changes in surface and structure of montmorillonite by acid activation

53 - Changes in surface and structure of montmorillonite by acid activation

THE APPLICATION OF HYBRID PIGMENTS IN THE FORMATION OF A POLYMER-MINERAL COATING FOR LEATHER FINISHING

The paper is focused to the study of the physical and mechanical properties of a polymer-mineral coating based on hybrid pigments for leather finishing. The aim of this research is to study the effect of hybrid pigments based on montmorillonite on the formation of a polymer-mineral coating for leather finishing. Hybrid pigments obtained by complex modification of native montmorillonite with sodium carbonate and basic chromium (III) sulfate with further subsequent adsorption of anionic dyes on the cationic surface of the mineral particles were used for this research. A ready-made mixture of various structures film-formers, intended for the finishing of facial and polished leather was used as a film-former. For the leather finishing, coating paints were prepared in the form of polymer-mineral compositions by mixing hybrid pigments with a film-forming agent in the ratio, wt. part 1: 5. In this study it was calculated that montmorillonite consumption at the level of 1.5-2.0% in terms of the mass of montmorillonite from the mass of dry polymer residue was optimal for obtaining high physical and mechanical properties of polymer films for finishing leather. A mechanism for structuring the polymer matrix with a hybrid pigment was proposed. According to this mechanism the highly developed sorption surface of montmorillonite provided adsorption of the polymer and stabilized its structure with the formation of a mixed polymer-mineral composite. It was shown that the use of montmorillonite in the composition of hybrid pigment allowed to adjust the physical and mechanical properties of the polymer-mineral composition for leather finishing, provided an increase in strength and regulated the level of elasticity of the covering film, which ensured an increase in the operational properties of the leather coating.

Inhibition mechanism of cationic polyacrylamide on montmorillonite surface hydration: A molecular dynamics simulation study

Cationic polyacrylamide (CPAM), a typical drilling fluid shale inhibitor can prevent the clay swelling and maintain the wellbore stable. Understanding the adsorption behavior of CPAM on montmorillonite (MMT) surfaces is of great significance in explaining the excellent performance of cationic inhibitors. In this work, molecular dynamic simulations (MD) are applied to investigate the adsorption mechanism of CPAM on the Na-MMT surface. The simulation results show that there are two main adsorption configurations of CPAM: 1) trimethylamine group adsorption; 2) the co-adsorption of trimethylamine group and amide group, the latter has stronger interaction energy, also trimethylamine group accounted for a large proportion of the interaction energy. The CPAM coating will decrease the H-bond number, neutralize the negative charge of Na-MMT surface and weaken the surface hydration ability of Na-MMT. Due to the existence of the CPAM coating, the diffusion and transport ability of water molecules on Na-MMT surface are greatly reduced. This study provides a theoretical explanation for the coating-forming mechanism and adsorption characteristics of CPAM inhibitors on Na-MMT surfaces and may shed light on the design of high-performance water-based drilling fluid systems.

Advanced materials based on montmorillonite modified with poly(ethylenimine) and poly(2-methyl-2-oxazoline): Experimental and DFT study

This work reports for the first time the ability of inorganic matrix Na-montmorillonite (Mt) to interact with two structurally similar but in term of charge different polymers: linear cationic poly(ethylenimine) (PEI) and non-ionic poly(2-methyl-2-oxazoline) (PMeOx). The effect of various polymer loadings on the interlayer structure and physico-chemical characteristics of composite materials was examined using experimental (XRD, IR, TA analysis) and ab initio Density Functional Theory (DFT) methods. The different charge characteristics of the polymers affected their intercalation into Mt. For PEI-Mt, almost complete exchange of Na+ with PEI cations was found, implying that the PEI chains interacted with the Mt interlayer surface electrostatically. In PMeOx-Mt, the content of Na+ remained the same as in Na-Mt, indicating that PMeOx chains adhered to the Mt surface by hydrogen bonds and/or van der Waals forces. The results showed that PEI could only be intercalated into Mt interlayers up to 100% of the cation exchange capacity (CEC) of Na-Mt; the resulting chains were adsorbed on the Mt outer surface. In contrast, unexpected and very high adsorption of PMeOx on Mt interlayer and outer surfaces, markedly exceeding the CEC of Na-Mt, was discovered for the first time. DFT calculations indicated that both polymers are anchored onto the basal surface of montmorillonite through moderate to weak Cp–Hp∙∙∙ Ob hydrogen bonds. Additional Np–Hp∙∙∙Ob hydrogen bonds in the PEI-Mt structure support the stability of this hybrid structure. Both the PMeOx-Mt and PEI-Mt models showed high stability.

Interactions between CTAB and montmorillonite by atomic force microscopy and molecular dynamics simulation

The tailing dewatering process meets significant challenges due to the contained clay minerals. The clays often have great hydrophilicity and high electronegativity, which improve slurry stability and prevent particle aggregation. Hydrophobic aggregation of chemical additives such as surfactants is an efficient way to enhance dewatering of clay-rich tailings. This work aims to investigate the interactions between CTAB, a cationic surfactant, and montmorillonite by experiments and molecular simulation. In macroscopic dewatering experiments, the results show that, after the treatment with 0.3 mol/L CTAB, the contact angle of montmorillonite cake and the zeta potential increased from 13.0° to 34.1° and from –21.5 mV to 0.22 mV, respectively. The addition of CTAB resulted in improved clay-rich tailings dewatering due to reduced surface tension of the filtrate, increased particle hydrophobicity, and charge neutralization. Then, the interaction forces between montmorillonite particles at various CTAB concentrations were directly measured. AFM results indicated that the interaction forces between montmorillonite particles in water were always repulsive during the approaching process. As the concentration of CTAB increased, the interaction force changed from repulsive to attractive. The adhesion force between montmorillonites increased to approximately 6.46 nN at 0.3 mmol/L CTAB. These adhesion forces help the montmorillonites readily adhere to each other. Finally, molecular simulation results indicated that the interactions between montmorillonite and water molecules were weakened by CTAB. The thickness of the water film was dramatically reduced by CTAB adsorption, enhancing the hydrophobicity of the montmorillonite surface.

Adsorption of Hydrated Pr3+ and NH4+/Mg2+ Ions onto the (001) Surface of Montmorillonite: A DFT Analysis with Experimental Verification

Montmorillonite is a major mineral present in ion-adsorption rare earth ores, and the microscopic adsorption states of rare earth ions on its surface are of a great significance for the efficient exploitation of ion-adsorption rare earth ores. In this article, density functional theory calculations were used to investigate the adsorption mechanisms and bonding characteristics of hydrated Pr, Mg and NH4 ions on the (001) surface of montmorillonite. Pr3+ exhibited a directed tendency geometry with Pr(H2O)103+, which was adsorbed onto montmorillonite by hydrogen bonding with an adsorption energy of −1182 kJ/mol, and one coordinated H2O ligand was separated from the first hydration layer of Pr. Both hydrated Mg and NH4 ions were adsorbed onto the montmorillonite surface through hydrogen bonds, and the adsorption energies were −206 and −188 kJ/mol, respectively, indicating that the adsorption stability of the hydrated Mg ion was slightly higher than that of the hydrated NH4 ion, but both were lower than that of hydrated Pr (−1182 kJ/mol). Hence, higher concentrations of Mg and NH4 ions than rare earth ions would be necessary in the leaching process of ion-adsorption rare earth ores. Additionally, desorption experiments revealed that the recovery of Pr3+ by Mg2+ with a concentration of 38 mmol/L is 80%, while it is only 65% with the same concentration of NH4+, and the concentrations of Mg2+ and NH4+ were much higher than that of Pr3+ in lixivium, which is consistent with the DFT calculations.

Interfacial Interaction of Clay and Saturates in Petroleum-Contaminated Soil: Effect of Clay Surface Heterogeneity.

Petroleum-contaminated soil (PCS) exhibits a variety of oil-soil interfacial properties. Surface heterogeneity of soil particles is one of the most critical influencing aspects. The interaction energies of the heterogeneous surfaces of montmorillonite (Mnt) and kaolinite (Kln) for saturates adsorption were determined by molecular simulation to be -1698.88 ± 0.67 (001 surface of Mnt), -73.81 ± 0.51 (010 edge of Mnt), -3086.33 ± 0.46 (001 surface of Kln), and -850.17 ± 0.74 (010 edge of Kln) kJ/mol, respectively. The adsorption of both clays with saturates relied on van der Waals forces, and the edges of Mnt were hardly adsorbed with saturates. According to adhesive force measurements, the oil-clay interaction forces of Mnt and Kln were 111.18 ± 0.01 and 122.65 ± 0.03 μN, respectively. In agreement with the simulations, Kln adsorbed saturates more strongly. Dynamic interfacial rheology and liquid viscoelasticity also revealed differences in adsorption behaviors between Mnt-saturates and Kln-saturates. It demonstrated that in the case of relatively low clay concentrations, the impact of particle surface heterogeneity on the adsorption process was stronger than that of structure even though Mnt had multilayer structures. Moreover, in thermodynamic adsorption experiments, it was evident that Kln adsorbed more oil than Mnt at the adsorption equilibrium states even though both were multilayer adsorptions and the adsorption amounts declined with increasing temperature. Simultaneously, the characteristics of the thermal adsorption of clay and saturates with different proportions were consistent with clay dispersion in saturates, and Kln released more heat being combined with oil. Overall, the heterogeneity of clay particles strongly affects the oil-clay interfacial chemical behaviors, causing more difficulty in treating PCS containing Kln than those containing Mnt. These results provide a theoretical basis for PCS treatment technology.

Adsorption of Carvone and Limonene from Caraway essential oil onto Tunisian montmorillonite clay for pharmaceutical application

To explore a novel kind of green composite material having excellent antibacterial, antifungal ability and specific-targeting capability for pharmaceutical uses, a novel kind of bio-composite was prepared using sodium purified clay as carrier of Caraway essential oil (CEO). Gas chromatography-mass spectroscopy (GC–MS) analyses of CEO reveals that Carvone (68.30%) and Limonene (22.54%) are the two major components with a minimum inhibitory concentration (MIC) value equal to 125 mg/mL against Staphylococcus (S) aureus bacteria and Candida albicans fungi. Clay from Zaghouan was purified and characterized by X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR) and N2 adsorption–desorption (BET method). Results obtained by chromatograph equipped with a flame ionization detector (GC-FID) show that the concentration of 130 mg/mL of essential oil and 5 h of contact with the purified clay are the optimal conditions for the bio-hybrid formation. The pseudo-second-order model can describe the kinetic study of the adsorption of Carvone and Limonene on sodium montmorillonite, and the adsorption isotherms have been established to the Langmuir type. Limonene registers a maximum adsorption value equal to 3.05 mg/g of clay however Carvone register the higher amount of adsorption (19.98 mg/g) according to its polarity and the abundance of this compound in the crude CEO. X-ray diffraction, Fourier transformed infrared spectroscopy, elemental analyses (CHN) and X-ray fluorescence characterization valid the success adsorption of CEO in sodium montmorillonite surface. The purified clay/CEO hybrid (purified clay/CEO) combined the advantages of both the clay and the essential oil used in exerting the antibacterial and antifungal activity, and thus, the composite has a double antibacterial and antifungal activity compared to the separately uses of inactive clay and CEO, suggesting the great potential application in pharmaceutical treatments.

Straightforward preparation of Ca-bentonite/polymer nanocomposite by confining salt-resistant copolymers into montmorillonite interlayers

Calcium bentonites (CaB), rich in European and Asian countries, are potential barrier materials for landfill leachate containment. However, CaB has to be converted into sodium bentonite (NaB) by Na-activation so as to facilitate intercalation modification. In this study, salt-resistant poly(acrylic acid-N, N-diethyl acrylamide) [P(AA-DEA)] was designed to intercalate and graft CaB by in situ polymerization without prior Na-activation. By this design, acrylic acid monomers were first adsorbed into interlayers of Ca-montmorillonite (Ca-MT) through the electrostatic complexation with Ca2+, dislodging Ca2+ from montmorillonite surfaces. Then, ammonium ions of N, N-diethyl acrylamide were adsorbed into Ca-MT interlayers. Swelling index of the obtained CaB/P(AA-DEA) nanocomposite in aggressive coal combustion product (CCP) leachate is 15.8 mL/2g, which is as high as 3.4 times that of CaB. CaB/P(AA-DEA)-based geosynthetic clay liners (GCLs) exhibit very low hydraulic conductivity (1.6✕10−12 m/s) to CCP leachate, which is as low as 3.3% that of the U.S. standard requirement and ∼4 orders of magnitude lower than that of CaB-based GCL. Polymer elution of CaB/P(AA-DEA)-8% in CCP leachate is as low as 1.9% that of the dry mixed samples.

Impregnation of smectite with layered double hydroxides of different chemistry for simultaneous removal of Cr(III) and acid blue dye

Bifunctional adsorbents obtained by co-precipitation of anionic layered double hydroxides (LDH) on the surface of cationic montmorillonite (MMT) are considered to be more effective than the physical mixtures of the mentioned materials. This is due to high degree of dispersion of the materials and their mutual interactions which improve the rheological properties. Such hybrid composite enables a simultaneous removal of both cationic and anionic pollutants from aqueous solutions. This includes wastewaters from the tanning industry, which often contain chromium(III) from tanning processes and various dyes. In this work, an in-situ synthesis method at room temperature was developed. Four materials were obtained by LDH co-precipitation – Mg/Fe, Mg/Al, Ni/Al and Ni/Fe – in the presence of a smectite-rich sample from Wyoming (SWy). The mass ratio of smectite/LDH was 1:1. For comparison, four analogous physical mixtures of MMT/LDH, raw SWy and LDHs were used in the experiments. The materials were analyzed by XRD, FTIR, SEM/EDS analysis, thermal and textural analysis based on N2 adsorption/desorption. The effectiveness of removing pollutants was determined in adsorption experiments using Cr(III) cations and anionic dye Acid Blue 129. The conducted experiments showed a high removal capacity of both pollutants by the Mg/Al and Mg/Fe LDH-smectite composites, in single- (up to 100% for AB129 and 97% for Cr(III)), two- (up to 94% for AB129 and 91% for Cr(III)) and multi-component systems (over 62% for AB129 and 99.9% for Cr(III)). The synthesized materials show promising properties in terms of their use as adsorbents for treatment of complex industrial wastewaters.

Investigation of adsorption of Basic Orange 2 dye on montmorillonite and error analysis

ABSTRACT. In this study, isotherm studies were investigated for the removal of basic orange 2 (BO2) dye on the montmorillonite surface. Two-parameter isotherm models such as Langmir, Freundlich, and Temkin isotherms and Three-parameter isotherm models such as Sips, Toth, and Khan isotherms were calculated by non-linear analysis method. The adsorption capacity at equilibrium was calculated by adding 0.035 g of adsorbent at 10-300 mg/L concentrations to 100 mL of synthetic dyestuff solution at room temperature. According to the results obtained, it was determined that the isotherm data matched the Langmuir isotherm with a regression coefficient of 0.995 from the Two-parameter models, and the Sips isotherm with a regression coefficient of 0.998 from the Three-parameter isotherm models. In addition, according to the results of error analysis, it was determined that the lowest error value fit the HYBRID model. SNE values support the HYBRID model.
 
 KEY WORDS: Adsorption, Basic orange 2, Isotherm models; Error analyses, Hybrid
 Bull. Chem. Soc. Ethiop. 2023, 37(1), 47-58. 
 DOI: https://dx.doi.org/10.4314/bcse.v37i1.5

Flocculation performance and mechanism of P (DMDAAC-AM) on clay mineral layer: Insights from DFT calculation and experiment

In order to investigate the flocculation performance and mechanism of quaternary ammonium cationic polyacrylamide (CPAM) on clay mineral particles. Dimethyl diallyl ammonium chloride (DMDAAC) and acrylamide (AM) were used as the monomers to synthesize the polymer P (DMDAAC-AM), referred to as PDA. The flocculation and sedimentation effects of PDA on the kaolinite and montmorillonite suspensions were studied. Furthermore, the PDA structural unit was constructed, and the adsorption mechanism on the kaolinite and montmorillonite layers was explored using the density functional theory calculation method. Experimental results reveal that PDA exerts a better flocculation and sedimentation effect than the commercially polyacrylamide (PAM) on kaolinite and montmorillonite suspensions, and the effect exerted by PDA on the kaolinite suspension is stronger than that on montmorillonite. Simulation results show that the PDA structural unit can be stably adsorbed on the surface of mineral particles: kaolinite (001¯) surface (−279.46 kJ/mol) > montmorillonite (001) surface (−226.09 kJ/mol) > kaolinite (001) surface (−220.76 kJ/mol). The difference in PDA adsorption on each surface is influenced by the various quantum chemical properties of the structural unit AM and DMDAAC molecules. During flocculation, PDA is adsorbed on the surface of the mineral particles exploiting hydrogen bonds and electrostatic attraction forces. During the adsorption process, electrostatic attraction plays the leading role. The polymer chains establish a bridge between the particles, and these bridging flocs settle down under the influence of gravity.

Study on competitive adhesion of coal dust on water droplet

Using the molecular dynamics simulation, we explored the interaction of water and montmorillonite/graphite at a microcosmic level. Due to the interaction between the oxygen atom at the montmorillonite (001) surface with the hydrogen atom in the water molecule, the distance between the water molecule with the montmorillonite surface was calculated to be 3.05 Å while that with the graphite surface was 3.57 Å, indicating that montmorillonite was more easily wetted than graphite. We studied the wetting behavior of coal dust particles and the adhesion behavior between dust powder with water droplets via a high-speed motion acquisition system. The coal dust powder was found to be slowly wetted until a gangue proportion of 40% above which the dust powder was wetted so rapidly. Furthermore, the wrap angle of dust powder at the droplet surface decreased as the gangue proportion increased. The competitive adhesion behavior was revealed that the pre-adhered hydrophobic particles prevented the later particles while the pre-adhered hydrophilic particles did not. The smaller experimental wrap angle as compared to the calculated values proved that the competitive behavior did occur during the coal dust adhesion process. Our results could provide valuable insight into the development of technology for coal dust removal.

Adsorption of cytosine on prebiotic siliceous clay surface induced with metal dications: Relevance to origin of life

Adsorption of protobiomolecules on primigenial mineral surfaces transacts a very specific and selective role in prebiotic chemical evolution. Cytosine (CYN) is a core constituent of genetic macromolecules i.e., DNA and RNA. A prebiotic simulation experiment following adsorption behaviour of a nucleic acid base CYN, as a function of pH, concentration, time and temperature on the surface of Montmorillonite (MMT), a prominent siliceous clay of smectite group having specific surface area, was studied systematically and methodically using UV, FTIR, SEM and XRD. Biologically significant metal dication [M2+ = Mg2+, Ca2+, Fe2+ and Cu2+] embeded surfaces of MMT (MMT-M2+) were prepared separately by cation-exchange approach. Results observed through UV spectral data reveal a very significant role of metal ions on the quantity of CYN adsorbed on different solid surfaces. The adsorption behaviour fitted well with Langmuir isotherm model and the adsorption isotherm shows monolayer formation of CYN (as adsorbate) on the surface of MMT and MMT-M2+(as adsorbent) showing Langmuir type adsorption. The calculated Langmuir adsorption parameters (KL& Xm) delineate appreciable interaction of CYN on MMT-Fe2+ surface following MMT-Cu2+ as compared to MMT alone and to other metal induced MMTs.In terms of % binding and Xm data, the effectiveness of various adsorbents in adsorption of CYN on MMT/MMT-M2+ at pH 6.6 and temperature 298K was found in the order; MMT-Fe2+> MMT-Cu2+> MMT > MMT-Ca2+> MMT-Mg2+. The results were further confirmed by SEM, XRD and FTIR which also support the outcomes. The present work throws light on the affinity of MMT clay (having multifarious applications in biological systems) with and without biogenic metal diions towards the surface interaction of nucleic acid base mimicking primeval sea shore/sea bed or hydrothermal vent conditions deciphering the phenomena that how biomonomers could have been protected from extreme hazardous conditions of primitive Earth and stabilized during chemical evolution and availed them for consecutive molecular evolution. Results further embark better adsorption capability of transition metal ion incorporated MMTs than the clay without metal ion and exchanged with alkaline Earth dications.