scholarly journals Interactions between Cationic Dye Toluidine Blue and Fibrous Clay Minerals

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 708
Author(s):  
Qingfeng Wu ◽  
Kristen Carlson ◽  
Qi Cheng ◽  
Xisen Wang ◽  
Zhaohui Li
Keyword(s):  
Cation Exchange ◽  
Toluidine Blue ◽  
Electrostatic Interactions ◽  
Cationic Dyes ◽  
Strong Interactions ◽  
Cationic Dye ◽  
Mineral Surfaces ◽  
Dynamic Simulations ◽  
Experimental Conditions ◽  
Maya Blue

Interactions between cationic dyes and negatively charged mineral surfaces have long attracted great attention from clay mineralogists, environmental scientists, and chemical engineers. In this study, the interactions between a cationic dye toluidine blue (TB) and palygorskite and sepiolite were investigated under different experimental conditions. The results showed that in addition to cation exchange, the specific surface area (SSA) of the minerals, particularly the formation of dimer molecules on the surface of both minerals, also accounted for the much higher TB uptake in comparison to their cation exchange capacities (CEC). The TB molecules were sorbed to the external surfaces, as no d-spacing expansion was observed in X-ray diffraction analyses. FTIR analyses showed strong interactions between the C=N or N-(CH3)2 group and the mineral surfaces, suggesting net electrostatic interactions if either of these functional groups bears a positive charge. Results from molecular dynamic simulations suggested dense monolayer TB formation on palygorskite because of its limited SSA and large CEC values. In comparison, a loosely dimeric formation was revealed on sepiolite for its large SSA and limited CEC values. Therefore, palygorskite is a better carrier for the sorption of cationic dyes, as evidenced by Maya blue paintings.

scholarly journals High Purity/Recovery Separation of Propylene from Propyne Using Anion Pillared Metal-Organic Framework: Application of Vacuum Swing Adsorption (VSA)

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 609
Author(s):  
Majeda Khraisheh ◽  
Fares AlMomani ◽  
Gavin Walker
Keyword(s):  
High Purity ◽  
Gas Adsorption ◽  
Metal Organic Framework ◽  
Raw Material ◽  
Strong Interactions ◽  
Step Cycle ◽  
Experimental Conditions ◽  
High Purity Grade ◽  
Trade Off ◽  
Vacuum Swing Adsorption

Propylene is one of the world’s most important basic olefin raw material used in the production of a vast array of polymers and other chemicals. The need for high purity grade of propylene is essential and traditionally achieved by the very energy-intensive cryogenic separation. In this study, a pillared inorganic anion SIF62− was used as a highly selective C3H4 due to the square grid pyrazine-based structure. Single gas adsorption revealed a very high C3H4 uptake value (3.32, 3.12, 2.97 and 2.43 mmol·g−1 at 300, 320, 340 and 360 K, respectively). The values for propylene for the same temperatures were 2.73, 2.64, 2.31 and 1.84 mmol·g−1, respectively. Experimental results were obtained for the two gases fitted using Langmuir and Toth models. The former had a varied degree of representation of the system with a better presentation of the adsorption of the propylene compared to the propyne system. The Toth model regression offered a better fit of the experimental data over the entire range of pressures. The representation and fitting of the models are important to estimate the energy in the form of the isosteric heats of adsorption (Qst), which were found to be 45 and 30 kJ·Kmol−1 for propyne and propylene, respectively. A Higher Qst value reveals strong interactions between the solid and the gas. The dynamic breakthrough for binary mixtures of C3H4/C3H6 (30:70 v/v)) were established. Heavier propylene molecules were eluted first from the column compared to the lighter propyne. Vacuum swing adsorption was best suited for the application of strongly bound materials in adsorbents. A six-step cycle was used for the recovery of high purity C3H4 and C3H6. The VSA system was tested with respect to changing blowdown time and purge time as well as energy requirements. It was found that the increase in purge time had an appositive effect on C3H6 recovery but reduced productivity and recovery. Accordingly, under the experimental conditions used in this study for VSA, the purge time of 600 s was considered a suitable trade-off time for purging. Recovery up to 99%, purity of 98.5% were achieved at a purge time of 600 s. Maximum achieved purity and recovery were 97.4% and 98.5% at 100 s blowdown time. Energy and power consumption varied between 63–70 kWh/ton at the range of purge and blowdown time used. The VSA offers a trade-off and cost-effective technology for the recovery and separation of olefins and paraffin at low pressure and high purity.

scholarly journals Adsorption of pharmaceuticals from aqueous solutions using biochar derived from cotton gin waste and guayule bagasse

Biochar ◽  
2020 ◽  
Author(s):  
Marlene C. Ndoun ◽  
Herschel A. Elliott ◽  
Heather E. Preisendanz ◽  
Clinton F. Williams ◽  
Allan Knopf ◽  
...  
Keyword(s):  
Specific Surface ◽  
Surface Area ◽  
Functional Groups ◽  
Specific Surface Area ◽  
High Surface ◽  
Strong Interactions ◽  
Solution Ph ◽  
Experimental Conditions ◽  
Cotton Gin Waste ◽  
Cotton Gin

Abstract Biochars produced from cotton gin waste (CG) and guayule bagasse (GB) were characterized and explored as potential adsorbents for the removal of pharmaceuticals (sulfapyridine-SPY, docusate-DCT and erythromycin-ETM) from aqueous solution. An increase in biochar pyrolysis temperature from 350 οC to 700 οC led to an increase in pH, specific surface area, and surface hydrophobicity. The electronegative surface of all tested biochars indicated that non-Coulombic mechanisms were involved in adsorption of the anionic or uncharged pharmaceuticals under experimental conditions. The adsorption capacities of Sulfapyridine (SPY), Docusate (DCT) and Erythromycin (ETM) on biochar were influenced by the contact time and solution pH, as well as biochar specific surface area and functional groups. Adsorption of these pharmaceutical compounds was dominated by a complex interplay of three mechanisms: hydrophobic partitioning, hydrogen bonding and π–π electron donor–acceptor (EDA) interactions. Despite weaker π–π EDA interactions, reduced hydrophobicity of SPY− and increased electrostatic repulsion between anionic SPY− and the electronegative CG biochar surface at higher pH, the adsorption of SPY unexpectedly increased from 40% to 70% with an increase in pH from 7 to 10. Under alkaline conditions, adsorption was dominated by the formation of strong negative charge-assisted H-bonding between the sulfonamide moiety of SPY and surface carboxylic groups. There seemed to be no appreciable and consistent differences in the extent of DCT and ETM adsorption as the pH changed. Results suggest the CG and GB biochars could act as effective adsorbents for the removal of pharmaceuticals from reclaimed water prior to irrigation. High surface area biochars with physico-chemical properties (e.g., presence of functional groups, high cation and anion exchange capacities) conducive to strong interactions with polar-nonpolar functionality of pharmaceuticals could be used to achieve significant contaminant removal from water. Graphic Abstract

scholarly journals Coarse-grained dynamic RNA titration simulations

2019 ◽  
Vol 9 (3) ◽  
pp. 20180066 ◽  
Author(s):  
S. Pasquali ◽  
E. Frezza ◽  
F. L. Barroso da Silva
Keyword(s):  
Electrostatic Interactions ◽  
Molecular Organization ◽  
Coarse Grained ◽  
Solution Ph ◽  
Dynamic Simulations ◽  
Rna Molecules ◽  
Coarse Grained Model ◽  
Constant Ph ◽  
Conformational Plasticity ◽  
And Function

Electrostatic interactions play a pivotal role in many biomolecular processes. The molecular organization and function in biological systems are largely determined by these interactions. Owing to the highly negative charge of RNA, the effect is expected to be more pronounced in this system. Moreover, RNA base pairing is dependent on the charge of the base, giving rise to alternative secondary and tertiary structures. The equilibrium between uncharged and charged bases is regulated by the solution pH, which is therefore a key environmental condition influencing the molecule’s structure and behaviour. By means of constant-pH Monte Carlo simulations based on a fast proton titration scheme, coupled with the coarse-grained model HiRE-RNA, molecular dynamic simulations of RNA molecules at constant pH enable us to explore the RNA conformational plasticity at different pH values as well as to compute electrostatic properties as local p K a values for each nucleotide.

scholarly journals Changes in Geochemical Composition of Groundwater Due to CO2 Leakage in Various Geological Media

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2597
Author(s):  
Jisu Jeong ◽  
Sung-Wook Jeen ◽  
Hyoun-Tae Hwang ◽  
Kang-Kun Lee
Keyword(s):  
Cation Exchange ◽  
Exchange Capacity ◽  
Co2 Leakage ◽  
Experimental Conditions ◽  
Geochemical Composition ◽  
Ph Buffering ◽  
Physico Chemical ◽  
High Concentrations ◽  
Set Up ◽  
One Year

This study evaluated the effects of CO2 leakage on the geochemical composition of groundwater in various geological media through long-term column experiments. Four columns were set up with soil representing a silicate aquifer; clean sand; a sand and limestone mixture; and alluvium soil, respectively. The experiments were conducted under the same experimental conditions for approximately one year. As the CO2-saturated synthetic groundwater was introduced into the columns, a decrease in pH and increases in electrical conductivity (EC), alkalinity, and concentrations of cations and trace elements were observed in all geological media. However, different patterns of changes were also observed depending on the mineralogical and physico-chemical characteristics of each material. As the column operation continued, while the pH decreased and low alkalinity values were more evident in the silicate soil and clean sand columns, the carbonate column continued to show high alkalinity and EC values in addition to high concentrations of most cations. The alluvium soil showed distinctive cation-exchange behaviors during the initial introduction of CO2. The results indicate that changes in the geochemical composition of groundwater will depend on the characteristic of the geological medium such as pH buffering capacity and cation exchange capacity. This study can be useful for monitoring and managing the impacts of CO2 leakage in various aquifer environments.

scholarly journals Uptake of Cationic Dyes from Aqueous Solution by Biosorption onto GranularMuntingia calabura

2009 ◽  
Vol 6 (3) ◽  
pp. 737-742 ◽  
Author(s):  
T. Santhi ◽  
S. Manonmani ◽  
S. Ravi
Keyword(s):  
Aqueous Solution ◽  
Low Cost ◽  
Freundlich Isotherm ◽  
Cationic Dyes ◽  
Isotherm Models ◽  
Experimental Conditions ◽  
Experimental Parameters ◽  
Initial Ph ◽  
Rate Kinetics ◽  
Muntingia Calabura

A new, low cost, locally available biomaterial was tested for its ability to remove cationic dyes from aqueous solution. A granule prepared from a mixture of leafs, fruits and twigs ofMuntingia calaburahad been utilized as a sorbent for uptake of three cationic dyes, methylene blue (MB), methylene red (MR) and malachite green (MG). The effects of various experimental parameters (e.g.,contact time, dye concentration, adsorbent dose and pH) were investigated and optimal experimental conditions were ascertained. Above the value of initial pH 6, three dyes studied could be removed effectively. The isothermal data fitted the Langmuir and Freundlich isotherm models for all three dyes sorption. The biosorption processes followed the pseudo-first order rate kinetics. The results in this study indicated thatMuntingia calaburawas an attractive candidate for removing cationic dyes from the dye wastewater.

Molecular Interactions Alter Clay and Polymer Structure in Polymer Clay Nanocomposites

2008 ◽  
Vol 8 (4) ◽  
pp. 1638-1657 ◽  
Author(s):  
Debashis Sikdar ◽  
Kalpana S. Katti ◽  
Dinesh R. Katti
Keyword(s):  
Crystal Structure ◽  
Electrostatic Interactions ◽  
Structural Distortion ◽  
Strong Interactions ◽  
Clay Nanocomposites ◽  
Organic Modifiers ◽  
Scanning Calorimetry ◽  
Nonbonded Interactions ◽  
Structural Orientation ◽  
Modes Of Vibration

In this work, using photoacoustic Fourier transform infrared spectroscopy (FTIR) we have studied the structural distortion of clay crystal structure in organically modified montmorillonite (OMMT) and polymer clay nanocomposites (PCN). To study the effect of organic modifiers on the distortion of crystal structure of clay, we have synthesized OMMTs and PCNs containing same polymer and clay but with three different organic modifiers (12-aminolauric acid, n-dodecylamine, and 1,12-diaminododecane), and conducted the FTIR study on these PCNs. Our previous molecular dynamics (MD) study on these PCNs reveals that significant nonbonded interactions (van der Waals, electrostatic interactions) exist between the different constituents (polymer, organic modifier, and clay) of nanocomposites. Previous work based on X-ray diffraction (XRD) and differential scanning calorimetry (DSC) on the same set of PCNs shows that crystallinity of polymer in PCNs have changed significantly in comparison to those in pristine polymer; and, the nonbonded interactions between different constituents of PCN are responsible for the change in crystal structure of polymer in PCN. In this work to evaluate the structural distortion of crystal structure of clay in OMMTs and PCNs, the positions of bands corresponding to different modes of vibration of Si—O bonds are determined from the deconvolution of broad Si—O bands in OMMTs and PCNs obtained from FTIR spectra. Intensity and area under the Si—O bands are indicative of orientation of clay crystal structures in OMMTs and PCNs. Significant changes in the Si—O bands are observed from each vibration mode in OMMTs and PCNs containing three different organic modifiers indicating that organic modifiers influence the structural orientation of silica tetrahedra in OMMTs and PCNs. Deconvolution of Si—O bands in OMMTs indicate a band at ∼1200 cm−1 that is orientation-dependent Si—O band. The specific changes in intensity and area under this band for OMMTs with three different organic modifiers further confirm the change in structural orientation of silica tetrahedra of OMMTs by organic modifiers. Thus, from our work it is evident that organic modifiers have significant influence on the structure of polymer and clay in PCNs. It appears that in nanocomposites, in addition to strong interactions at interfaces between constituents, the structure of different phases (clay and polymer) of PCN are also altered, which does not occur in conventional composite materials. Thus, the mechanisms governing composite action in nanocomposites are quite different from that of conventional macro composites.

Removal of cationic dye methyl violet 2B from water by cation exchange membranes

2008 ◽  
Vol 309 (1-2) ◽  
pp. 239-245 ◽  
Author(s):  
Jeng-Shiou Wu ◽  
Chia-Hung Liu ◽  
Khim Hoong Chu ◽  
Shing-Yi Suen
Keyword(s):  
Cation Exchange ◽  
Methyl Violet ◽  
Cationic Dye ◽  
Methyl Violet 2B

scholarly journals Narrow equilibrium window for complex coacervation of tau and RNA under cellular conditions

2018 ◽  
Author(s):  
Yanxian Lin ◽  
James McCarty ◽  
Jennifer N. Rauch ◽  
Kris T. Delaney ◽  
Kenneth S. Kosik ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Electrostatic Interactions ◽  
Driving Forces ◽  
Polymer Concentration ◽  
Equilibrium Phase ◽  
Charge Ratio ◽  
Solution Temperature ◽  
Complex Coacervation ◽  
Experimental Conditions ◽  
Form Complex

AbstractThe conditions that lead to the liquid-liquid phase separation (LLPS) of the tau protein, a microtubule associated protein whose pathological aggregation has been implicated in neurodegenerative disorders, are not well understood. Establishing a phase diagram that delineates the boundaries of phase co-existence is key to understanding its LLPS. Using a combination of EPR, turbidity measurements, and microscopy, we show that tau and RNA form complex coacervates with lower critical solution temperature (LCST) behavior. The coacervates are reversible, and the biopolymers can be driven to the supernatant phase or coacervate phase by varying the experimental conditions (temperature, salt concentration, tau:RNA charge ratio, total polymer concentration and osmotic stress). Furthermore, the coacervates can be driven to a fibrillar state through the addition of heparin. The equilibrium phase diagram of the tau/RNA complex coacervate system can be described by a Flory-Huggins model, augmented by an approximate Voorn Overbeek electrostatic term (FH-VO), after fitting the experimental data to an empirical Flory interaction parameter divided into an entropic and enthalpic term. However, a more advanced model in which tau and RNA are treated as discrete bead-spring chains with a temperature-dependent excluded volume interaction and electrostatic interactions between charged residues, investigated through field theoretic simulations (FTS), provided direct and unique insight into the thermodynamic driving forces of tau/RNA complexation. FTS corroborated the experimental finding that the complex coacervation of tau and RNA is has an entropy-driven contribution, with a transition temperature around the physiological temperature of 37 °C and salt concentrations around 100-150 mM. Together, experiment and simulation show that LLPS of tau can occur under physiological cellular conditions, but has a narrow equilibrium window over experimentally tunable parameters including temperature, salt and tau concentrations. Guided by our phase diagram, we show that tau can be driven towards LLPS under live cell coculturing conditions with rationally chosen experimental parameters.

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