Structural and thermal properties of inorganic–organic montmorillonite: Implications for their potential environmental applications

The highly efficient simultaneous removal of Pb2+ and methylene blue induced by the release of endogenous active sites of montmorillonite

The inherent periodic structure of montmorillonite limits the adsorption capacity of its endogenous active units such as Si-O tetrahedron and Al-O octahedron for pollutants. The high-intensity ultrasound method was used to release these active units and the layer-by-layer assembly was adopted to prepare carbon@chitosan@montmorillointe microsphere adsorbent (C@CS@Mt) to give full play to the adsorption capacity of montmorillonite. The montmorillonite nanosheet exhibited good hole-making ability, resulting in high surface area, pore volume and pore diameter of microspheres. Benefitting from the release of active sites in Si-O tetrahedron and Al-O octahedron of montmorillonite nanosheets, the adsorption capacity of C@CS@Mt was significantly improved. The maximum adsorption capacities of Pb²⁺ and methylene blue (MB) reached 884.19 mg·g^-1 and 326.21 mg·g^-1, respectively. The simultaneous adsorption experiments indicated that the occupation of active sites by Pb²⁺ caused the observed decrease of MB adsorption capacity. The theoretical calculations indicated that Pb was preferentially adsorbed by active adsorption units due to strong electron donating ability in comparison to MB. As an active unit, Si-O tetrahedron exhibited stronger adsorption capacity for cationic dyes than Al-O octahedron due to both the large electronegativity and lower adsorption binding energy.

Enhanced Adsorption of Methyl Orange by Mongolian Montmorillonite after Aluminum Pillaring

This article studies the enhancement of methyl orange (MO) adsorption by Mongolian montmorillonite (MMt) modified by the intercalation of the Keggin Al13 complex, followed by calcination during the pillaring process. The properties of MMt, Al-intercalated MMt (P-MMt), and Al-pillared MMt (P-MMt-C) were determined using X-ray diffraction (XRD), thermogravimetric analysis (TGA), surface-area analysis, and a field emission scanning electron microscope (FE-SEM). The MO adsorption by modified MMt was subsequently evaluated. The XRD basal distance (d001) and the specific surface area (SSA) increased after the modification of MMt. The TGA results revealed that P-MMt and P-MMt-C had better thermal stability than MMt. The Al-pillared MMt obtained after calcination (e.g., P-MMt-C400) showed a larger basal distance and surface area than that without pillaring. The MO adsorption process of P-MMt-C400 was supposed to be dominated by chemisorption and heterogeneous multilayer adsorption, according to the kinetic and isotherm studies. The maximum adsorption capacity of P-MMt-C400 is 6.23 mg/g. The MO adsorption ability of Al-pillared MMt was contributed by the Keggin Al13 complex attracting MO and the increase in the surface area of macro-, meso- and micro-pores (>1.2 nm). The Al-pillared MMt in this study could be applied as an adsorbent in a water purification system to remove MO or other dye elements.

Development of novel multifunctional adsorbent by effectively hosting both zwitterionic surfactant and hydrated ferric oxides in montmorillonite

Intercalating various functional species into the interlayer space is an effective strategy to multi-functionalize 2D materials (e.g., montmorillonite, Mnt), but general limitations have emerged therefrom: (1) various intercalated species compete for the limited interlayer space, and (2) the neighboring intercalated species probably inhibit each other's reactivity. Herein, we have synthesized a novel Mnt-based multifunctional adsorbent (HFO-AZ16Mnt) via intercalation of zwitterionic surfactant (Z16), acid activation by chloric acid, and introduction of hydrated ferric oxides (HFOs). The acid activation can lead to formation of porous nanosilica, which serves as the new active sites for supporting HFO nanoparticles. Employing tetrachloroferrate (FeCl₄^-) as an anionic precursor of HFOs can help preserve the sulfonyl group (SO₃^-) of Z16 from being electrostatically occupied during the HFO introduction. As a result, HFO-AZ16Mnt can separately and effectively host Z16 and HFOs. The unique structure endows HFO-AZ16Mnt with the efficiency on simultaneous removal of hydrophobic organic contaminants, oxyanions, and heavy metal cations (nitrobenzene, phosphate, and Cd(II), respectively in this study) from water. Particularly, HFO-AZ16Mnt exhibits impressive capacity towards Cd(II) in both the single- (26.1 mg/g) and the multi-contaminant system (30.6 mg/g). This work has demonstrated a new strategy to multi-functionalize Mnt, and provided a promising novel Mnt-based multifunctional adsorbent for simultaneous and effective removal of organic and inorganic contaminants from water.

Effect of Microwave Radiation on Regeneration of a Granulated Micelle–Clay Complex after Adsorption of Bacteria

Granulated micelle–clay complexes including the organic cation octadecyltrimethylammonium (ODTMA) were shown to be efficient in removal of total bacteria count (TBC) from water. Microwave (MW) heating of granules to restore bacterial removal was investigated. Drying of granules by MW required 20-fold less energy than by conventional heating. When water content of granules approached 10%, or less, their heating period by MW had to be below 1 min, e.g., 30 s, and less, in order to avoid ignition and irreversible structural changes. Structural and thermal properties of MW heated samples were studied by FT-IR spectra and thermo gravimetric analyses (TGA). Inactivation of bacteria in water was more efficient by MW than by conventional oven, or by electric plate. For elimination of bacteria from water, MW heating was at least five-fold more efficient than by conventional heating. The results have established an adequate regeneration procedure by MW heating at durations depending on the remaining percentage of water associated with the granules. Tests of first and second regenerations by MW heating, and HCl washing of columns, were carried out. It was concluded that MW treatment may be chosen for optimal regeneration of the granulated micelle–clay complex as an efficient and low-cost procedure.

The preparation of novel mineral-based mesoporous microsphere by microencapsulation technology and its application in the adsorption of dye contaminants

Microencapsulation technology was adopted to prepare the novel mineral-based mesoporous microsphere (MBMM) for the removal of dye contaminants from water. Field emission scanning electron microscopy, energy dispersive spectrometry, Brunauer-Emmett-Teller zeta potential analysis, and Fourier transform infrared spectrometry were used to investigate the microstructure characteristics of MBMM and its changes in the functional groups before and after adsorption. Batch experiments were carried out to investigate the effect of calcination temperature, initial concentration, pH, contact temperature, and time on the adsorption behavior of rhodamine B and methylene blue onto MBMM. The results indicated that the prepared MBMM had a hollow structure and mesoporous surface, which was beneficial to improving its adsorption capacity. The maximum adsorption capacities of rhodamine B and methylene blue onto MBMM prepared at calcination temperature 500 °C were 57.79 mg g^-1 and 55.94 mg g^-1 under the conditions of initial concentration 300 mg L^-1, dosage 0.1 g, pH 7.0, adsorption temperature 55 °C, and adsorption time 7 h. The results showed that the calcining treatment was beneficial to the formation of mesoporous microspheres, improving their adsorption capacities. The adsorption process was endothermic reaction, and electrostatic attraction and hydrogen bonding were the driving forces of the reaction.

Polyamine-Based Organo-Clays for Polluted Water Treatment: Effect of Polyamine Structure and Content

Hybrid materials based on clays and polyamines are supposed to be efficient heavy metals sorbents due to the well-known adsorption behaviour of the clay matrix and to the coordination properties of un-protonated amino groups. For this purpose, a montmorillonite clay was modified with three different aliphatic polyamines: L6 and L10 have a linear structure with six and ten amino groups, respectively, while B14 is a branched polyamine with fourteen amino groups. Initial amine concentration was the main parameter investigated and data were fitted with Langmuir and Freundlich models. Interaction mechanisms between clay and amines were deeply investigated by different experimental techniques such as X-ray powder diffraction (XRD), thermal analysis measurements (DTG), Fourier Transform Infrared Spectroscopy (FT-IR) and diffuse reflectance (NIR) spectroscopy. Experimental results showed that the amount of amines efficiently immobilized in the solid phase can be increased by increasing the initial concentration of polyamines in the clay modification process. These data were best fitted by Freundlich model, indicating a presence of surface sites of different nature. In the resulting hybrid materials, neither the accessibility of the NH/NH₂ groups of the amines, nor the accessibility of the structural OH of the clay was hindered. Several preliminary tests in La ions’ uptake and release from aqueous solution were also carried out. In the conditions used for this study, total metal ion removal was achieved at sufficiently low linear amine loadings (i.e., 0.45 mmol/g_clay for the small L6 amine), suggesting that these hybrid materials are promising for the proposed application in environmental remediation.

Synthesis and Characterization of a Dual-Cation Organomontmorillonite Nanocomposite

In this study, a novel dual-cation organomontmorillonites (OMt) nanocomposite was synthesized by two kinds of modifiers cetyltrimethylammonium chloride and cysteamine hydrochloride, and the adsorption behavior of modifiers into montmorillonite (Mt) has been investigated. The OMt were characterized by techniques, such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, and thermogravimetric and differential thermal (TG-DTA) analyses. The effects of temperature, contact time, the order of addition and the concentration of organic modifiers on the amounts of organics adsorbed were investigated. The adsorption amount of cetyltrimethylammonium chloride (CTAC) and cysteamine hydrochloride (CSH) increased with the increase of the added CTAC amount and contact time, while the addition order of modifiers and modification temperature had no significant effect on the actual adsorption amount of CTAC and CSH on Mt, as confirmed by the XRD patterns. The experimentally determined isotherms showed a good fit with the Langmuir adsorption models. The adsorption kinetics demonstrated that the adsorption of CTAC and CSH by Mt followed the pseudo-second-order model, and CTAC adsorption rate on Mt was faster than that of CSH. FTIR spectrum clearly revealed the incorporation of surfactant ions into the interlayer region. The TG-DTA analyses showed that the total mass losses of OMt strongly depended on the molecular volume of modifiers.