Thermal stability of metakaolin -based geopolymer blended with rice husk ash with replacement levels of 5–20% by weight of MK was investigated. The phase composition, thermal stability and ...microstructure of geopolymer before and after high-temperature exposure were explored by using X-ray diffraction(XRD), Thermogravimetric analysis (TGA), Fourier Transform Infrared Spectrometer (FTIR), BET specific surface area test (BET) and Scanning electron microscope (SEM). The optimum chemical activity of rice husk ash can be obtained when calcined at 600 °C for 4 h. The addition of rice husk ash increases the compressive strength of geopolymer by accelerating the alkali-activated reaction process. The compressive strength at 28 days of curing increases by 24% with 15 wt% rice husk ash. The porous rice husk ash accelerates the discharge of water vapor from geopolymer and protects geopolymer from cracking caused by air pressure. The high chemical activity of rice husk ash accelerates the high-temperature geopolymerization process and contributes to the healing of microcracks. Rice husk ash reduces the melting sintering temperature of geopolymer from 870 °C to 780 °C, improves the formation of compact ceramic protective layer and prevents the high temperature spalling of geopolymer.
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•Rice hull ash calcined at 600 °C for 4 h has excellent chemical reactivity.•The compressive strength at 28 days of curing increases by 24% with 15 wt% RHA.•Rice husk ash improves the thermal stability of geopolymer.•15 wt% rice husk ash reduces the sintering temperature from 870 °C to 780 °C.
Halloysite nanotubes (HNTs) showed natural nanotubular structures with similar chemical composition to kaolin. This paper reviewed the exciting applications of HNTs due to their abundantly deposit, ...nanoscale lumens, high length-to-diameter ratios, and relatively low surface hydroxyl group density. HNTs have been used as ideal templates for conveniently immobilizing nanoparticles, which could enable the construction of designed nano-architectures that are extremely attractive as supports for heterogeneous catalysts and for use in the fuel cells and related technologies that exploited the inherent ‘smallness’ and hollow characteristics of the nanoparticles. The recent developments in this area by exploring the various techniques with which HNTs could be functionalized with metal nanoparticles, and the diverse applications of the resulting materials overviewed in detail. The corresponding interfacial characteristics of the nanocomposites were emphasized.
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•Halloysite nanotubes (HNTs) have notubular structures with low surface group density.•The wide applications of HNTs-metal composites were in detail summarized.•The techniques for functionalizing HNTs with metal nanoparticles were reviewed.•The interfacial characteristics between metal nanoparticles and HNTs were analyzed.
Natural waters are prone to pollution with organic contaminants, waste pharmaceuticals being an example. Pharmaceutical compounds are widely detected in different surface waters, such as lakes and ...rivers. Removal of such contaminants from water is therefore imperative. Different strategies are commonly followed such as adsorption, chlorination, ozonation, peroxidation and others. Each method has its shortcomings. Photodegradation of water organic contaminants by semiconductors is a safe and non-costly method. In photodegradation, the organic contaminant is completely mineralized with radiation and oxygen using stable semiconductor nanoparticles as photocatalysts. ZnO nanopowder is widely described for photodegradation processes. Due to its wide band gap (~3.2 eV) ZnO excitation is limited to UV radiation. Moreover, the nano-particle nature for the ZnO catalyst makes it difficult to recover and re-use after process completion. Supporting the ZnO nanoparticles onto stable solid material surfaces is one possible way out, and is studied here. Raw clay (kaolin) is described to support ZnO particles in photodegradation of a widely encountered pharmaceutical contaminant, tetracycline (TC). The results show the possibility of annealed ZnO/Kaolin to remove TC from water, firstly by adsorbing the contaminant then by photodegrading it into mineral species. The study shows that TC molecules pre-adsorbed onto ZnO/Kaolin were mineralized during photodegradation experiments. Complete mineralization of reacted contaminant molecules was confirmed by spectrophotometry, high performance liquid chromatography (HPLC) and total organic carbon (TOC) study. Control experiments with a cut-off filter (400 nm and shorter) confirmed the ability of the catalyst to function in the visible region, where contaminant molecules behave as sensitizers in the photodegradation process. Optimizing the efficiency of the ZnO catalyst in TC photodegradation processes by studying the effect of pH using the point of zero charge (pHPZC) concepts is achieved. Collectively, the results show the possibility to prepare an efficient recoverable ZnO/Kaolin catalyst, which can be sensitized with TC molecules themselves with optimal working pH range 6–9.
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•Nano-size ZnO particles are supported onto raw clay particles.•Supported ZnO/Clay effectively catalyses aqueous tetracycline mineralization.•Tetracycline molecules self-sensitize ZnO/Clay catalyst in the visible light.•Photo-degraded tetracycline molecules are completely mineralized.•ZnO/Clay particles retain photo-catalytic efficiency on multi-recovery and reuse.
Using alkali activation, un-calcined soils have potential as precursors for low carbon, low cost, geopolymer-stabilised construction materials. This technology has been recently promoted as a lower ...impact alternative to cement stabilisation for walling materials in construction around the world. There is a lack of fundamental understanding around the alkali activation of un-calcined montmorillonite and illite, which, along with kaolinite, are clay minerals commonly found in soils. Kaolinite, as a 1:1 clay mineral, has been shown to form crystalline hydrosodalite when alkali-activated, but 2:1 montmorillonite and illite could form stronger geopolymer structures due to the higher Si:Al ratio in the precursor mineral. The lack of understanding of the underlying mechanisms at work with 2:1 clay minerals is a barrier to knowing how viable un-calcined geopolymer stabilised soil materials are for the range of soil types found in nature. In this study, montmorillonite and illite precursors were activated with a range of sodium hydroxide concentrations, compacted, and then cured at 80 °C for 24 h. The cured samples were characterised using a variety of advanced analytical techniques, including powder XRD, SEM, TGA, 27Al and 29Si-MAS-NMR, and FTIR. For the first time it was confirmed that alkali activation of uncalcined montmorillonite forms a NASH or (N,C)ASH geopolymer as the major product phase, which increases in quantity with increasing Na:Al molar ratio of the system. Although it has a similar Si:Al ratio, alkali activation of illite seems to result in structural alteration and increased porosity for Na:Al ≥ 0.5. The behaviour of these individual clay minerals suggests that the alkali activation of un-calcined 2:1 clay minerals is complex. Although alkali activation of montmorillonite can form a geopolymer, alkali activation of soils containing illite may lead to poor quality materials. This research has shown that the focus of future development work should be around montmorillonite-based clays.
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•First direct comparative study on alkali activation of montmorillonite and illite.•Montmorillonite forms N-A-S-H or (N,C)-A-S-H geopolymer.•Si:Al ratio of geopolymer gel influenced by Na:Al ratio of system.•Illite undergoes structural alteration.
In this study, cross-linked activated organo-bentonite (AOBent)/sodium alginate (SA) composite was prepared by the intercalation of sodium alginate in activated organo-bentonite and the cross-linking ...reaction between sodium alginate and chlorhydric acid to produce interesting new low cost material for the removal of cationic and anionic dyes (methylene blue (MB) and methyl orange (MO)) from aqueous solutions. Adsorbents were characterized by using X-ray diffraction (XRD), thermal gravimetric analyses (TGA) and Fourier transform infrared spectroscopy (FTIR). Batch adsorption studies were carried out to evaluate the effect of pH solution, the kinetic and the isotherm on the adsorption capacity of the adsorbents. The kinetic of MB and MO adsorption was found to follow a pseudo-second-order kinetic model meanwhile the isotherm was well described by the Langmuir model for all samples. Results obtained from this study suggest the potential of prepared composites for cationic and anionic dyes removal which can also be used easily for clean and ecofriendly processes.
•An activated organo-bentonite–alginate (AOB/SA) composite was prepared facilely.•Pseudo-second-order kinetics was the most suitable adsorption model.•The isotherm model is in good agreement with Langmuir model.•The maximum monolayer adsorption capacity was 769mg/g for MB onto composite.•AOB/SA is an efficient adsorbent for the removal of anionic and cationic dyes.
This study aimed at comparative examining of the interactions between conventionally used clay and carbon nanomaterials and human lung adenocarcinoma cells (A549 cells). The following platy and ...tubular nanomaterials were tested: carbon nanoparticles, i.e. multi-walled carbon nanotubes (MWCNTs) and graphene oxide nanosheets (GO) as well as nanoclays, i.e. halloysite nanotubes (HNTs) and kaolinite nanosheets (Kaol). Nanoparticle physicochemical properties and their internalization into cells were examined using dynamic light scattering as well as atomic force, 3D laser scanning confocal and darkfield hyperspectral microscopies. Biological aspects of the nanomaterial-cell interaction included assessment of cellular toxicity, DNA damage, metabolic activity, and physical parameters of the cells. Regardless of a shape, carbon nanomaterials demonstrated cell surface adsorption, but negligible penetration into cells compared to nanoclays. However, carbon nanomaterials were found to be the most toxic for cells as probed by the MTS assay. They also turned out to be the most genotoxic for cells compared to nanoclays as revealed by the DNA-Comet assay. GO significantly increased the fraction of apoptotic cells and was the most cytotoxic and genotoxic nanomaterial. Comparison of flow cytometry and MTS data indicated that a cytotoxic effect of MWCNTs was not associated with increased cell death, but was rather due to a decrease in cell metabolic activity and/or proliferation. Finally, no significant effect of the shape of the tested nanomaterials on their internalization and cytotoxicity was revealed.
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•Both tubular and platy clay nanoparticles were less toxic than carbon nanomaterials.•Graphene oxide was the most cytotoxic and genotoxic to A549 cells.•Lower toxicity makes clay nanoparticles more appropriate for biomedical applications.
In this study, an acid-treated palygorskite (PAL-O) with negatively charged layers has been used as an adsorbent for the removal of various types of ionic dyes including cationic crystal violet (CV), ...cationic light yellow (7GL), and methylene blue (MB) and anionic methyl orange (MO) and acid green 25 (AG25) ones from water. PAL-O showed efficient performance in the adsorption of all three cationic dyes because of electrostatic interactions. As regards the two anionic dyes, PAL-O also exhibited good adsorption efficiency for MO but had almost no effect on AG25. For detailed investigation of the adsorption mechanisms, PAL-O has been further treated by soxhlet extraction, using distilled water as solvent, to remove water-soluble matter such as metal ions. The efficiencies of the purified palygorskite (PAL-P) for adsorption of cationic dyes were slightly increased, but that of MO adsorption decreased evidently. This result indicated that the metal ions on the palygorskite played an important bridging effect for adsorption of anionic dyes. However, minimal AG25 uptake may occur because this bridging effect was too weak to be bonded for much stronger electrostatic repulsions between AG25 and palygorskite. In general, the charge properties and molecular structures of dyes play important roles in their adsorption behaviors.
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•Palygorskite (PAL) shows efficient adsorption of cationic dyes for electrostatic interaction.•The metal ions on PAL act as bridges for efficient adsorption of anionic dyes.•Various dyes have different bonded manners with PAL for their distinct structures.•Charge property and molecular structure of dye play important roles in adsorption.
Heterogeneous catalysis benefits from some merits such as facile catalyst separation and recyclability. In this context, use of halloysite that is a naturally occurring clay with tubular morphology ...received growing attention and in recent decade many halloysite –based heterogeneous catalysts have been developed. Halloysite is a promising candidate for the formation of composites and hybrids. Mostly, halloysite preserved its structure in the course of hybridization and the properties of the resulting hybrids/composites depend on some factors such as the content of halloysite, preparation procedure and the hybrid/composite components. To date, halloysite based hybrids/composites have been applied for promoting various chemical and photochemical transformations. Mostly, this class of compounds exhibited promising catalytic performances that were superior to their individual components, suggesting the synergism between halloysite and the composite/hybrid component(s). Considering the outstanding catalytic performance of these composites/hybrids as catalysts or catalyst supports, this review article targets disclosing the catalytic utility of the halloysite nanocomposites/hybrids. The classification presented in this review is based on the types of the components that were hybridized with halloysite. In each section, it is tried to discuss the catalytic performance of the hybrid/composite and the effects of incorporation of halloysite on the catalysis.
We report a simple and highly efficient preparation of nanocomposite of halloysite (Hal) nanotubes/multi-walled carbon nanotubes (Hal-MWCNTs) and its electrochemical sensor application for the ...determination of methyl parathion (MP). The phase structure and surface morphology of the Hal-MWCNTs nanocomposite were confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectra. According to the electrochemical tests, the fabricated glassy carbon electrode (GCE) sensor with Hal and multi-walled carbon nanotubes showed excellent MP determination performance because of the synergistic effect of Hal and multi-walled carbon nanotubes. The Hal-MWCNTs/GCE sensor exhibited a relatively low detection limit of 0.034 μM in the linear range of 0.5–11 μM. When used for the determination of MP in real samples, the Hal-MWCNTs/GCE sensor showed good detection effect with satisfactory relative standard deviation (RSD) of 2.46 to 3.08% and recoveries of 98.8 of 101.8%. This work indicated that the nanocomposite of Hal-MWCNTs when coated on GCE is useful for the fabrication of high-performance MP electrochemical sensor.
•Prepared halloysite (Hal)/multi-walled carbon nanotubes (MWCNTs) as a composite.•New sensor was fabricated for the determination of methyl parathion (MP).•New sensor exhibited low detection limit and wide linear range for MP.•New sensor showed good MP detection performance in real samples.
Hazardous materials are very harmful to the environment and their removal is quite challenging, and methylene blue is one of them. In the present study, we have successfully designed a bentonite ...encapsulated alginate bead system for the effective removal of methylene blue, extensively used in chemical industries. Synthesized beads were characterized using Field Emission Scanning Electron Microscope, Energy Dispersive X-Ray Spectroscopy (EDX), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer Emmett Teller Surface Analyser, and Dynamic Light Scattering. Bentonite/alginate beads system was optimized at physiological pH 7, and 25 °C and fitted well to pseudo-second-order kinetic model. The maximum adsorption capacity of system as calculated by Langmuir isotherm was found to be 2024 mg g−1 or 6.33 mmol g−1, which is many folds higher as compared to the reported clay-related and other adsorbents. Adsorption process was found be combination of surface adsorption and intra-particle diffusion (IPD) with dominancy during initial phase (30 min) and later phase, respectively. The designed beads enhanced the rates of both surface adsorption and IPD as compared to only bentonite powder as adsorbent. The thermodynamic studies confirmed the spontaneous and exothermic nature of adsorption process. FTIR, and EDX analyses of the removal data confirmed the possibility of both chemisorption and physiosorption. The designed beads imparted recyclability to bentonite powder and exhibited excellent removal efficiency (85%) after four consecutive adsorption-desorption cycles.
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•Bentonite encapsulated alginate beads were designed by crosslinking with calcium.•Optimized adsorption conditions for removal of MB were physiological pH 7 and 25 °C.•Designed beads enhanced rates of surface adsorption and IPD as compared to bentonite.•qm was found to be 2041 mg g−1 many folds higher as compared to related adsorbents.•The designed system was found to be highly effective and reusable for MB removal.
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