Article
A Molecular Dynamics Simulation Study of Fe-Containing Palygorskite
- Zhijun Lu, Jinhong Zhou, Xiancai Lu
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 399-405
-
- Article
- Export citation
-
Fe is a common substituent in palygorskites (Plg), but its effect on the microscopic properties is unclear. In the current study, molecular dynamics (MD) simulations were carried out to investigate the effect of Fe on the properties of the nano-pores in Plg. The structures and dynamics of water and Na+ ions in the pores were computed by analyzing the MD trajectories. The results revealed that for both Fe-containing and ordinary Plg, zeolitic water molecules can diffuse into the pores with very low mobility whereas Mg-coordinated water fails to escape. Na+ ions show no obvious diffusivity because they are fixed above the Si–Osix-membered rings. Detailed comparison indicates that Fe-substitution has no significant influence on the pore properties of Plg.
Montmorillonite-Hydrochar Nanocomposites as Examples of Clay–Organic Interactions Delivering Ecosystem Services
- Guodong Yuan, Jing Wei, Benny K. G. Theng
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 406-415
-
- Article
- Export citation
-
Clay–organic interaction is an important natural process that underpins soil ecosystem services. This process can also be tailored to produce clay–organic nanocomposites for industrial and environmental applications. The organic moiety of the nanocomposites, typically represented by a toxic surfactant, could be replaced by hydrochar formed from biomolecules (e.g. glucose) via hydrothermal carbonization. The effect of montmorillonite (Mnt) and glucose dosage on hydrochar formation, however, has not been clarified. In addition, the mechanisms by which Mnt-hydrochar nanocomposites (CMnt) can detoxify and remove carcinogenic Cr(VI) from aqueous solution are not well understood. In the current study, research milestones in terms of clay–organic interactions are summarized, following which the synthesis and characterization of CMnt for Cr(VI) adsorption are outlined. Briefly, 1 g of Mnt was reacted with 75 mL of glucose solution (0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mol L−1) by hydrothermal carbonization at 200°C for 16 h. The resultant CMnt samples were analyzed for chemical composition, functional groups, morphological features, and Cr(VI) adsorptive properties. Mnt promoted the conversion of glucose to hydrochars, the particle size of which (~80 nm) was appreciably smaller than that formed in the absence of Mnt (control). Furthermore, the hydrochars in CMnt had an aromatic structure with low hydrogen substitution and high stability (C/H atomic ratio 0.34–0.99). The weakened OH (from hydrochar) and Si–O–Si stretching peaks in the Fourier-transform infrared (FTIR) spectra of CMnt are indicative of chemical bonding between Mnt and hydrochar. The CMnt samples were effective at removing toxic Cr(VI) from acidic aqueous solutions. Several processes were involved, including direct reduction of Cr(VI) to Cr(III), complexation of Cr(III) with carboxyl and phenolic groups of hydrochar, electrostatic attraction between Cr(VI) and positively charged CMnt at pH 2 followed by indirect reduction of Cr(VI) to Cr(III), and Cr(III) precipitation.
Efficient Concentration of PB From Water by Reactions With Layered Alkali Silicates, Magadiite and Octosilicate
- Donhatai Sruamsiri, Thipwipa Sirinakorn, Makoto Ogawa
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 416-424
-
- Article
- Export citation
-
Human health problems are often related to contamination of the aqueous environment by toxic metal ions. In the present study, two layered alkali silicates (magadiite and octosilicate) were examined to assess removal of Pb2+ from aqueous solutions in terms of quantity and kinetics. The ion-exchange reaction between the silicates and aqueous solutions of lead(II) acetate at various concentrations was examined at room temperature for 24 h. The adsorption isotherms were H-type, showing the strong interactions between Pb2+ and the silicates. The amounts of Pb2+ adsorbed were as much as 1.23 mmol Pb/g magadiite and 2.32 mmol Pb/g octosilicate, which are larger than the reported values for various ion exchangers. They were larger than the theoretical cation exchange capacities (2.2 and 3.7 meq/g for magadiite and octosilicate, respectively), suggesting that the collection of Pb2+ included the precipitation as basic lead salts in addition to the ion exchange. The adsorption isotherms for magadiite and octosilicate fitted the Langmuir equation with correlation coefficients, R2, of 0.9991 and 0.9972, respectively. The adsorption of Pb2+ onto the layered alkali silicates from acidic aqueous solution was examined to obtain smaller amounts of adsorbed Pb2+ (0.32 mmol Pb/g magadiite and 0.34 mmol Pb/g octosilicate), confirming the important role of pH on the surface charge of the layered silicates in terms of ion exchange. The adsorption of Pb2+ reached equilibrium within 5 min for magadiite while it took 60 min for octosilicate. The difference was in the particle morphology; smoother diffusion of Pb2+ was possible through flower-shaped aggregates of particles of magadiite.
Layered Double Hydroxide-Based MRI/CT Dual Modal Contrasting Agent With Homogeneous Particle Size
- Sang-Yong Jung, Jin Kuen Park, Jae-Min Oh
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 425-433
-
- Article
- Export citation
-
The development of nanoparticles incorporating Gd3+ has attracted interest in the field of contrasting nanomedicine for magnetic resonance (MR) and computed tomography (CT). In order to achieve an effective contrasting performance, the amount and stability of Gd incorporated as well as particle-size control of the nanoparticles should be considered simultaneously. In the current study, Gd-diethylenetriaminepentaacetate(Gd-DTPA) was incorporated into layered double hydroxide (LDH) to meet the physicochemical properties required for MR-CT dual contrasting nanomedicine. Strategically, the particle size and nanometer incorporation of Gd-DTPA into LDH (GL-R hybrid) were controlled homogeneously using the reverse micelle method. X-ray diffraction showed that the hybrid obtained possessed a hydrotalcite phase. Dynamic light scattering and electron microscopic analyses showed that the hybrid had a controlled size of <200 nm with significant homogeneity. Fast Fourier-transform of transmission electron microscopy confirmed that the platelets of the GL-R hybrids were oriented randomly to form inter-particle space, enabling the Gd-DTPA moiety to be encapsulated stably. The encapsulation efficiency of Gd-DTPA was 20.8%, which was sufficiently high compared with other Gd-DTPA-incorporatedLDH. According to X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy, Gd-DTPA incorporated in the hybrid preserved its structure intact. Its potential as a dual modal contrast agent was demonstrated by measuring the concentration-dependent Hounsfield unit and magnetic resonance relaxivity, which were determined to be 230 at 2 mg/mL and 5.8 in the range ~0.2–1 mM-Gd, respectively.
Construction and Characterization of a Nanostructured Biocatalyst Consisting of Immobilized Lipase on Mg-Amino-Clay
- Mingzhu Zhang, Shiyong Sun, Rui Lv, Yevgeny Aleksandrovich Golubev, Ke Wang, Faqin Dong, Olga Borisovna Kotova, Elena Leonidovna Kotova
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 434-442
-
- Article
- Export citation
-
Lipase is an industrial enzyme, the catalytic efficiency of which is restricted by various environmental factors. To improve this efficiency, immobilization technology has been utilized in the past to improve the stability of lipase in harsh conditions. Immobilization technology can be divided into physical methods and chemical methods. Some unsolved problems remain in current immobilization technology. The interaction between enzyme and immobilization support is weak and reversible during physical adsorption, resulting in poor stability of the immobilized enzyme and the contamination of substrate solution by leached enzymes. In chemical methods, enzyme-active sites might be inactivated due to the chemical reactions between enzyme molecules and support, resulting in a decrease in the enzymes’ catalytic activity (Liu et al., 2018a). The objective of the current study was to construct a nanostructured lipase via Mg-amino-clay as a carrier and improve the catalytic activity and stability of lipase by immobilization. Lipase produced by Aspergillus oryzae was immobilized on aminopropyl functionalized magnesium phyllosilicate (a 2:1 trioctahedral talc-like silicate Mg-amino-clay) via a 1-(3-Dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride (EDC) coupling agent. The physical and chemical properties of the Mg-amino-clay and Mg-amino-clay-based nanostructured biocatalyst (Mg-clay-lipase) were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Optimal immobilization conditions were determined by taking into account the following variables: amount of initial lipase, EDC concentration, and reaction time. The results revealed that the optimum temperature, pH, and thermal stability of Mg-clay-lipase were greater than equivalent values for free lipase under optimal conditions (described below – Process for Immobilization of Lipase on Mg-amino-clay). The Michaelis-Menten constant (Km) values were 5.25 mM and 7.42 mM while the maximum reaction rates (vmax) were 30.58 mM/(L·min) and 55.87 mM/(L·min) for free lipase and Mg-clay-lipase, respectively. The present study provided a new nanostructured biocatalyst and demonstrated that the enzyme activity and stability of Mg-clay-lipase were superior to those of free lipase due to the mechanism of 'interface activation'.
Sustained Antibacterial Effect of Levofloxacin Drug in a Polymer Matrix by Hybridization With A Layered Double Hydroxide
- Su-Joung Ko, Jin-Song Jung, Gyeong-Hyeon Gwak, Hyoung-Jun Kim, Fabrice Salles, Jae-Min Oh
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 443-452
-
- Article
- Export citation
-
The immobilization of antimicrobial drugs can be used to expand the application of antibacterial properties to consumer products. The purpose of this study was to stabilize an antimicrobial agent, levofloxacin (LVX), for sustained antibacterial activity by immobilizing the drug molecules in a layered double hydroxide (LDH) and embedded in a polyurethane substrate. As-prepared MgAl-LDH was calcined at 400°C and reconstructed with LVX for intercalation. The X-ray diffraction patterns and cross-sectional transmission electron microscopy images showed lattice expansion along the crystallographic c axis upon LVX intercalation, suggesting successful loading of the drug. Fourier-transform infrared spectra revealed that the structure of LVX was well preserved between LDH layers. Elemental analysis indicated that the loading capacity of LVX in the hybrid was 41.7%. Bacterial-colony forming inhibitory assay on Bacillus subtilis exhibited ~100% antibacterial activity of both LVX alone and LVX-LDH hybrid (LL). To determine sustainability of antibacterial activity by the hybrid, either LVX alone or LL hybrid was loaded in the polyurethane (PU) substrate for which antibacterial activity was evaluated before and after immersion in a phosphate-buffered saline for 3 days. The LVX-composited PU showed a dramatic decrease in antibacterial activity, down to 0% after buffer treatment; LL-composited PU still contained antibacterial activity (~34% of colony suppression) after phosphate-buffered saline immersion.
Release of Mg and Fe From the Octahedral Sheets During the Transformation of Montmorillonite Into Kaolinite
- Shangying Li, Qi Tao, Lingya Ma, Chaoqun Zhang, Yixuan Yang, Peixin Du, Jiacheng Liu, Jianxi Zhu
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 453-462
-
- Article
- Export citation
-
Isomorphous substitutions of Mg and Fe for Al generally appear in the octahedral sheets of montmorillonite, whereas they are infrequent in kaolinite. Therefore, the release of Mg and Fe from the octahedral sheets probably happens during the transformation of montmorillonite into kaolinite, which could affect the migration of Mg and Fe from clay minerals into surrounding environments. The objective of the current study was to investigate the relationship between Mg and Fe release during the transformation of montmorillonite into kaolinite. The results showed that the d060 value of clay minerals decreased slightly, and the intensities of both the AlMg–OH and AlFe–OH bending vibrations also decreased gradually. In addition, the (Mg+Fe)/Al (major octahedral ions) atomic ratio of kaolinite was lower than that of montmorillonite, especially in identical hydrothermal products. These results indicated that Mg and Fe ions were released progressively from the octahedral sheets during the transformation of montmorillonite into kaolinite. Moreover, the changed relative concentrations of Mg and Fe ions in the supernatant solutions after hydrothermal reactions suggested a random distribution of Mg and/or Fe in the octahedral sheets of the montmorillonite. These results improve understanding of the release relationship between Mg and Fe during clay mineral evolution and of the distribution of these two ions in the octahedral sheets, as well as the chemical composition of clay minerals as an indicator of geological environments.
Zirconia-Intercalated Kaolinite: Synthesis, Characterization, and Evaluation of Metal-Ion Removal Activity
- Khaled S. Abou-El-Sherbini, Mohammed A. Wahba, Elsayed A. Drweesh, Adel I. M. Akarish, Seham A. Shaban, Eman A. M. Elzahany
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 463-476
-
- Article
- Export citation
-
The intercalation of kaolinite through the insertion of ions or molecules amongst the structural aluminosilicate layers is a vital process in numerous clay-based applications and products. Layer neutrality and hydrogen bonding limits direct intercalation into kaolinite, other than for small molecules. Synthesizing zirconia-intercalated kaolinite is not a straightforward matter. To overcome this barrier, raw Egyptian kaolin (UnK) or its acid-activated product (HK) was sonicated and impregnated in aqueous ZrOCl2·8H2O solution followed by thermal treatment at various temperatures (100, 200, 300, and 500°C). The intercalation process was confirmed using various spectroscopic and analytical techniques. The direct intercalation of ZrO2 into the kaolinite layers was observed even through a mild thermal treatment (100, 200, and 300°C). The mechanism of intercalation was suggested to occur by binding ZrO2 to the Si/AlO groups with a preference for the acid-activated HK, causing variable enlargements of the basal spacing and producing very perturbed layers. Interestingly, the surface area increased by 250% as a result of zirconia intercalation. Scanning electron microscopy (SEM) images showed a remarkable improvement in the stacking order of the kaolinite particles. The impact of ZrO2 intercalation into kaolinite also enhanced its adsorption efficiency for Pb2+, Cu2+, and Cd2+ ions. Preliminary investigations showed that the zirconia-intercalated HK demonstrated a removal efficiency, which is three times greater than that of pristine HK. The adsorption tendency toward Pb2+ ions was greater than those of Cu2+ and Cd2+ and followed the order: Pb2+ >> Cu2+ > Cd2+. The study suggests that the chemical modification of kaolin by zirconia via a direct intercalation technique, which greatly improves its functionality as demonstrated by the selective sorption of heavy metal ions, is worthy of further study.
A Novel Process for Intercalating Alkylammonium Ions in a Thai Bentonite and its Effect on Adsorption Performance
- Sonchai Intachai, Chomponoot Suppaso, Nithima Khaorapapong
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 477-488
-
- Article
- Export citation
-
The organization of organic species on the ordered structures of clays and clay minerals is one way to produce inorganic-organic hybrids with controlled microstructures and properties. The reactions of the adsorbed species and their arrangement on the clay surfaces can be guided by the choice of clay and of adsorbed species. The purpose of the present study was to intercalate alkylammonium ions into a Thai bentonite and to study the effect on dye-adsorption efficiency. A series of alkylammonium ions, CnH2n+1NH3+ (n = 8, 10, 12, or 18), was incorporated into the interlayer spaces of a natural bentonite by mixing an aqueous dispersion of bentonite with an aqueous solution of protonated alkylamines at room temperature. The basal spacings of the intercalation compounds varied depending on the alkyl chain lengths and the amount of alkylammonium ions. The alkylammonium ions adsorbed formed lateral monolayer, bilayer, pseudo-trimolecular layer, paraffin-type monolayer, and/or paraffin-type bilayer structures. The adsorption efficiency of alkylammonium-bentonites was determined using batch adsorption experiments of rhodamine 6G from a water-ethanol solution; the greatest efficiency was 87% while that of the bare bentonite was 47%. The loading amount and the arrangement of the intercalated alkylammonium ions in the interlayer spaces, as well as the specific surface area and pore volume, played important roles in the adsorption efficiency of alkylammonium-bentonite. The adsorption equilibrium data for rhodamine 6G on the best adsorbent were interpreted using the Langmuir isotherm model and a pseudo-second order kinetics model. The adsorption efficiency of the adsorbent decreased by only 17% after five runs.
Reduction of Clay Hydration by Addition of an Organic Stabilizer
- Wei Huang, Yunlong Zhang, Zequan Luo, Xiang Wei, Huanran Fu
-
- Published online by Cambridge University Press:
- 01 January 2024, pp. 489-499
-
- Article
- Export citation
-
Organic, ionic soil stabilizers (OISS) are designed to regulate directly the hydration properties of clay minerals to improve their engineering behavior. The steps involved in this regulation by OISS are unclear and this might limit their application in the current construction environment in China. The purpose of the present study was to reveal the origin of changes in hydration properties of four typical clay samples (with clay mineral contents of >90 wt.%: Na-bentonite, Ca-bentonite, illite, and kaolinite) as affected by OISS. The water-retention capacity of each clay was measured first through liquid limit and water-vapor adsorption tests. Then, the changes in hydration sites, such as exchangeable cations and the surfaces of minerals, were investigated by a series of microscopic measuring and testing techniques. Finally, infrared spectroscopy (IR) and thermal analysis were performed to verify the regulation of hydration properties by OISS. The results suggested that the exchangeable cation and surface changes controlled the regulation of hydration properties. OISS could cause some of the exchangeable cations to become free ions and disrupt the interaction between some cations and water molecules by its long organic chains; thus, the amount of hydrated cations decreased. In addition, the long organic chains covered the mineral surface and weakened its adsorption capacity. Furthermore, the long chains had cementitious qualities, connecting them to the crystalline layer and resulting in more aggregated clay particles and a smaller specific surface area (SSA). With the decrease in the number of cations and in the SSA by OISS, the hydration of the four clay samples decreased, especially in the case of bentonite.