Hydrotalcite-like compounds, being anti-types of clay minerals, are potential sorbents for polar and anionic molecules. This work summarizes the experimental results of adsorption—desorption of two ...phenols (trichlorophenol, TCP, and trinitrophenol, TNP) on an hydrotalcite (HT) and its calcined product (HT500). Both phenols are adsorbed on HT by anion exchange, but TNP adsorption was much higher than that of TCP due to their different p
K
a. The adsorption of both phenols on HT500 occurs by the reconstruction of the layered structure, TNP being also adsorbed at more than TCP. These adsorption mechanisms were confirmed by X-ray diffraction, IR spectroscopy and TG-DTA analysis of the HT-TCP and HT-TNP products. Results presented here indicate HT500 as potential sorbent for phenols from waters, and that its recyclability is possible.
Layered double hydroxides (LDH) which are one type of layered materials and are also known as anionic clays, are promising layered materials due to some of their interesting properties, such as ease ...of synthesis, unique structure, uniform distribution of different metal cations in the brucite layer, surface hydroxyl groups, flexible tunability, intercalated anions with interlayer spaces, swelling properties, oxo-bridged linkage, and high chemical and thermal stability, ability to intercalate different type of anions (inorganic, organic, biomolecules, and even genes), delivery of intercalated anions in a sustained manner and also high biocompatibility. Considering the previous work on LDH as novel biomaterials, research on this particular materials has become one of the most interesting topic of today's research. LDH has become an important class of layered materials having prospects in the field of biomaterials, wherein great attention has been paid to the biocompatibility nature, exchange of the existing anion with the target anion, holding of guest species in between the interlayer space and its controlled release of the anion in a particular medium. This article, after deliberating the recent significant evolution in the structure and different methods of synthesis of different LDH materials and its applications in various extents especially its biological applications through their structural and functional properties, considers many typical examples. In particular, recent progress on the emerging strategies of LDH to improve their antimicrobial activity is also presented.
•Synthesis methods of layered double hydroxide•Structural analysis layered double hydroxide•Applications of layered double hydroxides
Removal of Methylene Blue (MB) from aqueous solutions is studied using a raw Algerian kaolin sample as a low-cost adsorbent. The effects of pH, contact time, dye concentration and temperature are all ...taken into consideration. The adsorption kinetics results are adjusted to best fit the pseudo-second order model. The experimental data are analyzed by Langmuir isotherms, revealing that the maximum adsorption capacity of MB on this kaolin sample equals 52.76mg/g at T=25°C and pH=6.0. The calculated thermodynamic data demonstrates that adsorption is spontaneous and enhanced at higher temperatures. Desorption studies with water indicate that the adsorbent could successfully retain MB, even after four cycles. From these results, it can be considered that the raw Algerian kaolin sample tested herein is effective in the removal of MB from aqueous solutions and moreover may be used as an alternative to high-cost commercial adsorbents.
•Raw kaolin from Algeria was characterized as an adsorbent for methylene blue.•This raw kaolin sample showed high methylene blue removal efficiency.•High concentrations of methylene blue can be quickly removed by adsorption.•The adsorption data follow both a Langmuir isotherm and a pseudo-second order kinetic model.
Exfoliating montmorillonite (Mt) to nanolayers is a crucial step during producing clay/polymer nanocomposites(CPN). Only well-exfoliated and well-dispersed Mt. nanolayers in the polymer matrix can ...significantly improve the properties of the nanocomposites. This review examines the latest scientific advances in the exfoliation methods of Mt., the insights into the exfoliation mechanisms, and the peculiar functionalities of the resultant CPN. The direct exfoliation of Mt. dispersed in water or organic solvents is often intensified by ultrasonication. Grinding of Mt. in the form of solid in a high-energy ball mill can directly exfoliate Mt. to some extent. Exfoliating Mt. for producing CPN is mainly achieved through so-called in situ exfoliation, solution exfoliation and melt exfoliation. The Mt./polymer nanocomposites exhibit typically improved barrier properties, mechanical strength, thermal stability, and fire retardancy. The literature survey suggests that future work should place emphases on developing green and effective exfoliation methods, and deepening understanding of exfoliation mechanisms and the interfacial interactions between the inorganic Mt. nanolayers and organic monomers/polymers. Future research is suggested to assembling exfoliated Mt. nanolayers with functional polymeric molecules or other nano-scale building blocks to produce functional hierarchical nanomaterials with practical applications.
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•Literature survey and opinions on exfoliating montmorillonite (Mt) into nanolayers.•Organic modification of Mt for exfoliating Mt in polymer matrix.•Exfoliation of Mt by in situ polymerization, in polymer solution, and melt exfoliation•Exfoliated Mt for improving barrier, mechanical and thermal properties, and flame retardancy.•Remarks on challenges and opportunities in exfoliation of Mt for nanocomposites.
Halloysite is a natural nanosized tubular clay mineral that has many potentially important uses in different industrial fields. In this paper, the key structural characteristics and properties of ...halloysite and their related applications are comprehensively reviewed. Research advances on halloysite, especially those from the past 20years, are summarized with some critical comments. Attention is mainly paid to the structure and morphology of halloysite and their changes, the formation of tubular structures, the physicochemical properties, the surface chemical modifications, and the halloysite-based advanced materials and some related applications. Additionally, future prospects and key problems to be solved in halloysite studies are discussed. This review shed new light on both fundamental and applied studies that focused on halloysite.
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•Structural characteristics and properties of halloysite have been reviewed.•Surface chemical modifications of halloysite have been reviewed.•Halloysite-based advanced materials and its applications have been reviewed.
Eco-friendly adsorbent of chitosan–montmorillonite/polyaniline (CH–Mt/PANI) nanocomposite was synthesized by the intercalation of CH into Mt through ion-exchange process followed by the impregnation ...of aniline. Then in-situ polymerization of aniline using ammonium peroxydisulfate as an oxidant yielded a conducting polymer, polyaniline, as an additional component. The composite with polyaniline salt was also converted to corresponding CH–Mt/PANI base nanocomposite. The composites were characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, thermal gravimetric analysis and electron microscopy and subsequently used for the removal of methylene blue from aqueous solutions. The composite with polyaniline base proved to be better dye adsorbent than that with polyaniline salt and was therefore investigated in detail. The adsorption of the dye onto CH–Mt/PANI base nanocomposite follows the pseudo second-order kinetics and it is well described by Temkin isotherm model. Moreover, the intraparticle diffusion was found to play a significant role in the adsorption mechanism. The maximum adsorption capacity was estimated to be 111 mg g−1, exceeded the adsorption capacities of the individual precursors.
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•Chitosan and polyaniline were intercalated into montmorillonite interlayers.•Adsorption of methylene blue onto chitosan–montmorillonite/polyaniline nanocomposite.•Eco-friendly candidate for the remediation of organic dyes in industrial effluents.
This research presented six natural clay minerals (NCM) evaluated for the effectiveness of NH4+ adsorption from aqueous solution. For the first time, the NH4+ adsorption capacities of kaolinite, ...halloysite, montmorillonite, vermiculite, palygorskite, and sepiolite were examined and compared in the same study. All the NCM were fully characterized by XRD, SEM/EDS, XRF,FTIR, CEC, zeta potential and nitrogen adsorption-desorption isotherms to better understand the adsorption mechanism-property relationship. Adsorption kinetics showed that the adsorption behavior followed the pseudo-second-order kinetic model. The adsorption isotherms fitted by the Langmuir model illustrated that among all the NCM studied, vermiculite (50.06mg/g) and montmorillonite (40.84mg/g) showed the highest ammonium adsorption capacities. Our results revealed that the cation exchange is the main mechanism for the NH4+ adsorption. Additionally, negatively charged surface, water absorption process and surface morphology of NCM might also contribute to the high adsorption capacity for the NH4+. The maximum adsorption capacities for all NCM were rapidly obtained within 30min with a dosage of 0.3g/25mL at pH of 7. The results illustrated that the NCM have significant potential as economic, safe and effective adsorbent materials for the NH4+ adsorption from the aqueous solution.
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•Vermiculite and montmorillonite showed the highest ammonium adsorption capacities.•Cation exchange was the main mechanism onto NCM.•The structure and surface properties of NCM are the key for the highest adsorption.•Parameters such as contact time, dosage and pH affecting NH4+ adsorption•The adsorption isotherms and kinetic models were investigated.
Clay minerals and their modified derivatives have composed a large family of adsorbents which can be used for the adsorption of most of the chemical contaminants from aqueous solution. Among this ...family of adsorbents, those based on montmorillonite (Mt), a typical 2:1 type clay mineral, have been most extensively studied. This article intends to give a general overview of the microstructure, adsorptive characteristics, and environmental applications of the Mt based adsorbents. A comprehensive survey of the numerous literatures shows that Mt based adsorbents have rather complicated structural and adsorptive characteristics. They may have porous or nonporous structure and contain various functional groups; their interlayer structure may be evidently affected by the incorporation of water molecules in aqueous medium. With the complicated structural characteristics, these adsorbents can be used for a wide variety of contaminants, including hydrophobic organic contaminants, cationic/anionic dyes, heavy metal cations, oxyanions, radioactive nuclides, etc. Accordingly, a wide variety of mechanisms are involved for the uptake of these contaminants, such as surface adsorption, partition, ion exchange, surface precipitation, and structural incorporation. Finally, the approaches for proper disposal/reutilization of the spent adsorbents after contaminant adsorption will be briefly discussed. This review on one hand can help the readers in choosing proper and developing novel clay mineral based adsorbents for target contaminants, and on the other hand can give a proper example to systematically show the various mechanisms for the uptake of contaminants on adsorbents.
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•A diversity of adsorbents can be synthesized using Mt.•Mt based adsorbents can uptake most chemical contaminants.•Adsorption of contaminants on Mt based sorbents involves various mechanisms.•The spent adsorbents after application can be recycled or reutilized.
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