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This study undertook the testing of Cu2+ and Ni2+ adsorption using synthesized oxalic acid-crosslinked chitosan (CTS)-modified montmorillonite (MMT), as well as a kinetic analysis and equilibrium analysis. We believe that our study makes a significant contribution to the literature because we showed that the interlayer distance of untreated MMT was increased from 1.23 to 2.05–2.21 nm, and thus verified the intercalation of CTS into the MMT interlayer. The maximum adsorption of Cu2+, as calculated using the Langmuir equation, was significantly higher for oxalic acid-crosslinked CTS-modified MMT, relative to untreated MMT or the non-crosslinked CTS-modified-MMT. The oxalic acid-crosslinked CTS-modified MMT could also take up more Cu2+ than Ni2+ from a solution containing a mixture of Cu2+-Ni2+. The selective adsorption of oxalic acid-crosslinked CTS-modified-MMT (i.e. Ni2+ < Cu2+) is governed by the selective adsorption of CTS and the oxalic acid. This reveals the effect of the complex formation with CTS and oxalic acid. [ABSTRACT FROM AUTHOR]

Owing to the low atmospheric concentration of CO 2 (400 ppm), direct air capture technologies require adsorbents that offer high CO 2 adsorption capacities at low CO 2 concentrations. In this study, we investigated the potential of CO 3 ·Mg–Al layered double hydroxides (LDHs; Mg/Al molar ratio = 2, 3, and 4) as CO 2 adsorbents. The CO 2 adsorption and desorption behavior was studied at various molar ratios, adsorption/desorption temperatures, and linear speeds. CO 2 adsorption by CO 3 ·Mg–Al LDH followed the Langmuir model, indicating that monolayer adsorption occurs. The maximum CO 2 adsorption quantity calculated using the Langmuir equation was 0.794 mmol/g for CO 3 ·Mg–Al LDH with a Mg/Al molar ratio of 3. In dry CO 2 adsorption experiments, a maximum CO 2 adsorption quantity of 0.319 mmol/g was recorded with a Mg/Al molar ratio of 3 and temperature of 60 °C. In dry CO 2 desorption experiments, the CO 2 concentration and desorption quantity reached maximum values at 300 °C and a linear speed of 0.250 m/min. Notably, the maximum CO 2 concentration was 6232 ppm, showing a 15.6-fold increase in comparison with the initial concentration of 400 ppm. Overall, our results demonstrate that CO 3 ·Mg–Al LDH has high potential as a CO 2 adsorbent. The study findings have significant implications for the development of new CO 2 adsorbents for the direct air capture and storage of CO 2. • We have developed new CO 2 adsorbents for the direct air capture and storage of CO 2. • Our results demonstrate that CO 3 ·Mg–Al LDH has high potential as a CO 2 adsorbent. • CO 2 adsorption followed the Langmuir model, indicating that monolayer adsorption occurs. [ABSTRACT FROM AUTHOR]

The adsorption of Cu2+ and Ni2+ on synthesized tripolyphosphate-crosslinked-chitosan-modified montmorillonite (TPP-crosslinked-CTS-modified MMT) was examined by kinetic and equilibrium studies. The adsorption followed a pseudo-second order kinetics. Based on the activation energies, chemisorption due to electron transfer between TPP-crosslinked-CTS-modified MMT and the Cu2+ and Ni2+ cations was concluded to be the rate-determining step. Equilibrium analysis for the adsorption of each cation shows a good fit to the Langmuir equation. The adsorption of metal cations onto TPP-crosslinked-CTS-modified MMT proceeds because of the cation adsorption capacity of MMT, complexation with CTS, and complexation with the crosslinking agent (TPP). The selectivity toward Cu2+ was high because of the selective adsorption of this cation by CTS. Comparison of maximum adsorption amount of heavy metal ions by both adsorbents. Image 1 • Montmorillonite modified by crosslinked tripolyphosphate was prepared. • Kinetics and equilibrium of the adsorption of Cu2+ and Ni2 ions have been analyzed. • We were able to achieve selective adsorption of Cu2+ over Ni2+. [ABSTRACT FROM AUTHOR]

The uptake of ethylsulfate (ES − ), hexylsulfate (HS − ), and dodecylsulfate (DS − ) anions by Mg–Al oxide in aqueous solution was examined through adsorption equilibrium and kinetic modelling. The removal of ES − , HS − , and DS − by Mg–Al oxide proceeded as diffusion-controlled reactions exhibiting Langmuir-type adsorption isotherms. The maximum amounts of adsorption are ordered as DS − > HS − > ES − . Mg–Al oxide preferentially reacts with the organic anion with lower charge density, because the effect of hydrophobic interactions in these cases is stronger than that of electrostatic interactions. In the first stage of reaction, Mg–Al oxide, which is prepared by the thermal decomposition of Mg–Al layered double hydroxides (LDHs) intercalated with CO 3 2− (CO 3 ·Mg–Al LDH), rehydrates and combines with alkylsulfate to reconstruct the LDH structure. Then the alkylsulfate anions intercalated in the interlayer of the LDH attracted other anions in the solution via hydrophobic interactions, thereby promoting their removal by Mg–Al oxide. DS − was removed with the highest efficiency followed by HS − , because the hydrophobic attraction between DS − anions is stronger than that between HS − , which is stronger than that between ES − . At low initial concentrations (C 0 ), the intercalated alkylsulfates are likely oriented parallel to the brucite-like host layers of Mg–Al LDH. With increasing C 0 , pairs of alkyl chains in DS − and HS − may overlap due to the hydrophobic interaction, while the alkyl chains in DS − are likely arranged perpendicular to the host layers to form bilayers. [ABSTRACT FROM AUTHOR]

[Display omitted] • The adsorption follows a pseudo-second-order kinetic equation. • The Δ G values for adsorption systems ranged from − 20 to 0 kJ/mol. • It indicates that adsorption could be classified as physical adsorption. • NP was adsorbed on OS•Cu-Al LDH by hydrophobic interaction. • AP was adsorbed on SCD•Cu-Al LDH by CH/π interactions. Our previous study revealed that Cu-Al layered double hydroxides (LDHs) intercalated with 1-octanesulfonate and sulfonated β-cyclodextrin showed good adsorption selectivity toward m -nitrophenol (NP) and m -aminophenol (AP), respectively. We also found that the adsorption behaviors of these LDHs fit the Freundlich equation. Herein, we performed a kinetic analysis to elucidate the adsorption mechanism of the LDHs for phenols in greater detail. The adsorption results were fitted to a pseudo-first-order kinetic equation, a pseudo-second-order kinetic equation, and an intraparticle diffusion model. The correlation coefficients of the pseudo-second-order kinetic equation for each adsorption process were fairly high, and the measured and calculated equilibrium adsorption amounts were relatively close. Thus, the adsorption of NP and AP by OS•Cu-Al LDH and SCD•Cu-Al LDH, respectively, fits the pseudo-second-order kinetic equation. Because the ΔG values for each system ranged from − 20 to 0 kJ/mol, the adsorption processes in these systems may be classified as physical adsorption. Specifically, NP was adsorbed on OS•Cu-Al LDH by hydrophobic interactions, whereas AP was adsorbed on SCD•Cu-Al LDH by CH/π interactions. Our findings provide new insights into the adsorption of phenols onto modified Cu-Al LDHs and could serve as a foundation for future studies on the adsorption properties of LDHs intercalated with anions as guest layers. [ABSTRACT FROM AUTHOR]

• The NO 3 ⋅Mg-Al LDH and the nanosheets could adsorb the SeO 4 2− in an aqueous solution. • The adsorption capacity was greater for the delaminated NO 3 ⋅Mg-Al LDH nanosheets. • This is because the specific surface area of the NO 3 ⋅Mg-Al LDH nanosheets is larger. • The nanosheets are layered after the anion exchange on the surface of the host layer. Layered double hydroxides (LDHs) are excellent anion-exchange materials, and are useful in adsorbing hazardous anions. The LDHs form nanosheets upon delamination, which improves their efficiency. In this study, we investigated the SeO 4 2− adsorption properties of the nanosheets obtained by the delamination of NO 3 ⋅Mg-Al LDH in an aqueous solution and compared them with those of the NO 3 ⋅Mg-Al LDH. The SeO 4 2− adsorption by both substances was a "pseudo-second-order rate reaction". The reaction-rate constant during the early stage was greater for the nanosheets as their surface area was larger than the NO 3 ⋅Mg-Al LDH. The amorphous nanosheets reverted to an ordered LDH structure after the anion exchange. Atomic force microscopy (AFM) imaging and the corresponding height profile analysis of the samples confirmed the nanosheets stacking post SeO 4 2− adsorption. We propose a mechanism of the SeO 4 2− adsorption by the NO 3 ⋅Mg-Al LDH nanosheets. These findings may improve the understanding of the anion exchange by the LDHs, which may lead to the development of high-efficiency materials that extract metals such as Se from wastewater. [ABSTRACT FROM AUTHOR]

This study investigates the influence of CO 2 gas on the treatment of single acidic gases (HCl, SO 2 , and NO 2) using Mg Al layered double hydroxide intercalated with CO 3 2− (CO 3 ·Mg-Al LDH) as the adsorbent. The gas-removal kinetics is analyzed, and the reaction mechanisms are discussed. The coexisting CO 2 gas decreased the removal rate of all three acidic gases. This is likely due to the exchange reaction between intercalated CO 3 2− and gas-phase CO 2 , which inhibits the exchange between intercalated CO 3 2− and HCl, SO 2 , or NO 2. The HCl removal by CO 3 ·Mg-Al LDH follows pseudo first order kinetics, suggesting that the main removal mechanism is chemisorption (chemical reaction between CO 3 ·Mg-Al LDH and HCl). Meanwhile, the removal of SO 2 and NO 2 by CO 3 ·Mg-Al LDH also follows pseudo first order kinetics. However, the corresponding adsorption mechanisms are classified as physisorption onto the Mg Al LDH. • 10% coexisting CO 2 reduced the acidic gases absorption ratio by CO 3 ·Mg-Al LDH. • This is attributed to the exchange reaction between CO 2 gas and pre-intercalated CO 3 2−. • All the kinetic data were well fitted to pseudo-first order models. [ABSTRACT FROM AUTHOR]

Modern regenerative medicine and pharmaceutical manufacturing require a large-scale culture of cells. Consequently, cells must be suspension-cultured at high densities, which is challenging because more metabolites, especially ammonia, are produced that inhibit cell proliferation. To address this problem, we tested four zeolites (L-type zeolite, ferrierite, mordenite, and Y-type zeolite) and Prussian blue for their ability to adsorb NH 4 + (the predominant form of ammonia in a culture-solution pH) from an aqueous solution and a culture solution. The L-type zeolite and Prussian blue effectively adsorbed NH 4 + from aqueous solutions, while the other absorbents were ineffective. Notably, neither adsorbent removed glucose, a representative nutrient, from the aqueous solution. Kinetics and equilibrium studies revealed that both adsorbents (L-type zeolite and Prussian blue) obey pseudo-second-order kinetics and are well fitted by the Langmuir isotherm model. The L-type zeolite also exhibited a high NH 4 +-adsorption in the culture solution. Further, while the L-type zeolite exhibited minimal cytotoxicity, Prussian blue was cytotoxic. Using the L-type zeolite for adsorption is simple and cost-effective, thus making it a suitable NH 4 + adsorbent for culture solutions. Furthermore, reusing an expensive culture solution on a large scale can effectively lower costs of producing cell cultures intended for pharmaceutical manufacturing and regenerative medicine purposes. Thus, it is expected that this method will be used to regenerate culture solutions on a large-scale. Proposed mechanism for the adsorption of NH4+by Prussian blue. [Display omitted] ● L-type zeolite and Prussian blue exhibit high NH4+-adsorption rates. ● The L-type zeolite was not cytotoxicity, while Prussian blue was highly cytotoxicity. ● L-type zeolite is a suitable NH 4 + adsorbent for use in culture solutions. [ABSTRACT FROM AUTHOR]

Proposed molecular orientation of HEPES intercalated in the Mg–Al LDH interlayers. • Various LDH and LDO can selectively remove lactate from aqueous solution and cell culture medium. • NO 3 •Mg-Al LDH showed reasonable performance including moderately low cell toxicity. • HEPES•Mg-Al LDH is excellent adsorbent for regenerating cell culture medium by removing lactate. When cells proliferate in a culture medium, metabolites such as lactic acid gradually accumulate and eventually hinder cell growth. Herein, we considered various layered double hydroxides (LDH) and layered double oxides (LDO) for the selective removal of lactate in aqueous solution and a culture medium by anion exchange. NO 3 •Mg-Al LDH showed high lactate adsorption, low adsorption of glucose (a nutrient in culture medium), appropriate pH stability, and low cytotoxicity within a limited contact time. In contrast, NO 3 •Ni-Al LDH, NO 3 •Ca-Al LDH, Mg-Al LDO, and Cl•Mg-Al LDH had a lower performance than NO 3 •Mg-Al LDH. To further improve the performance, the anion of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES, a common pH buffer in culture media) was tested as the intercalated anion in Mg-Al LDH. HEPES•Mg-Al LDH (Mg/Al = 2) was found to be the most promising adsorbent for culture medium regeneration because its adsorption behavior was similar to that of NO 3 •Mg-Al LDH, while it had a much lower cytotoxicity. The traditional methods for regenerating a culture medium by removing accumulated lactate to increase the cell density in large-scale cell culture and lower the costs, including electrolysis, cell modification, and modification of the culture medium's composition, are complicated to operate and expensive. The adsorption method using HEPES•Mg-Al LDH presented in this study, instead, can be easily operated and has low costs. Thus, it is expected to be applied in actual cases for regenerating culture media. [ABSTRACT FROM AUTHOR]