Sorption of naphthalene and phosphate to the CTMAB-Al13 intercalated bentonites

Facile synthesis and physicochemical characterization of κ-Carrageenan-silver-bentonite based nanocatalytic platform for efficient degradation of anionic azo dyes

Water pollution due to textile industry effluents is a global concern that warrants versatile research solutions for degrading them, and for a sustainable environment. In the present work, by using the imperative role of nanotechnology, a facile one-pot synthesis has been devised to generate κ-carrageenan capped silver nanocatalyst (CSNC), and was immobilized on 2D bentonite (BT) sheets to generate nanocatalytic platform (BTCSNC) for the degradation of anionic azo dyes. The nanocomposite(s) were physicochemically characterized using UV-Vis, DLS, TEM, FESEM, PXRD, ATR-FTIR, TGA, BET and XPS etc., to obtain insights into the nanocomposite composition, structure, stability, morphology and mechanism of interaction. The obtained CNSC are monodispersed, spherical with a size of 4 ± 2 nm, and were stabilized by the functional groups (-OH, COO‾, and SO3‾) of κ-Crg. The broadening of peak corresponding to basal plane (001) of BT montmorillonite in PXRD spectra established its exfoliation upon addition of CSNC. XPS and ATR-FTIR data evidenced the absence of covalent interactions between CSNC and BT. The catalytic efficiency of CSNC and BTCSNC composites were compared for the degradation of methyl orange (MO) and congo red (CR). The reaction followed a pseudo first order kinetics, and immobilization of CSNC on BT resulted in a 3-4 fold enhancement in degradation rates. The rates achieved for the degradation kinetics are: MO degradation within 14 s (Ka 9.86 ± 2.00 min-1), and CR degradation within 120 s (Ka of 1.24 ± 0.13 min-1). Further, a degradation mechanism has been proposed by analyzing the products identified through LC-MS. The reusability studies of the BTCSNC evidenced the complete activity of the nanocatalytic platform for six cycles, and gravitational separation method for catalyst recycling. In a nutshell, the current study provided an environmentally friendly, sizable, and sustainable nano catalytic platform" for the remediation of industrial wastewater contaminated with hazardous azo dyes".

Effect of double carbon chains on enhanced removal of phenol from wastewater by amphoteric-gemini complex-modified bentonite

A novle amphoteric-gemini complex-modified bentonite was prepared with a gemini surfactant ethylene bis (tetradecyl dimethyl ammonium chloride) (EB) on the basis of the bentonite modified by amphoteric modifier dodecyldimethyl betaine (BS). The surface and structural characteristics of modified bentonite were characterized by X-ray diffraction (XRD), specific surface area (S_BET), scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), total carbon (TC) and total nitrogen (TN). In addition to studying the enhanced effect of gemini surfactants on phenol adsorption by kinetics and equilibrium adsorption, the influences of modification ratio, pH, temperature and ionic strength were investigated. Results showed that BS + EB complex modification increased the interlayer spacing (IS), TC and TN of bentonite (BT), and S_BET decreased with the increase in its total modification ratio. The adsorption of phenol on modified bentonite reached equilibrium in 20 min, and the adsorption capacities were in the order of BS+50 EB (BS+50% CEC EB)>BS+100 EB > BS+150 EB > BS+25 EB > BS > BT. The adsorption capacities of phenol on BS + EB complex modified bentonite (CMB) increased by 9.98-15.96 and 1.19-3.35 times compared with those on BT and BS single modified bentonite (SMB), respectively. The phenol adsorption capacities decreased with the increases in temperature and pH, while it increased with the augment in ionic strength. This study revealed that double carbon chains increased the organic carbon content more effectively than single carbon chains at low complex modification ratios, thus promoting the adsorption of phenol by hydrophobic partitioning on the bentonite surface.

Insights on applications of bentonite clays for the removal of dyes and heavy metals from wastewater: a review

In recent decades, increased industrial, agricultural, and domestic activities have resulted in the release of various pollutants into the aquatic systems, which require a reliable and environmentally friendly method to remove them. Adsorption is one of the most cost-effective and sustainable wastewater treatment techniques. A plethora of low-cost bio-based adsorbents have been developed worldwide so far to supplant activated carbon and its high processing costs. Bentonite clays (BCs), whether in natural or modified form, have gained enormous potential in wastewater treatment and have been used successfully as a novel and cost-effective bio-sorbent for removing organic and inorganic pollutants from the liquid suspension. It has become a sustainable solution for wastewater treatment due to its variety of surface and structural properties, superior chemical stability, high capacity for cation exchange, elevated surface area due to its layered structure, non-toxicity, abundance, low cost, and high adsorption capacity compared to other clays. This review encompasses comprehensive literature about various modification techniques and adsorption mechanisms of BCs concerning dyes and heavy metal removal from wastewater. A critical overview of different parameters for optimizing adsorption capacity and regeneration via the desorption technique has also been presented here. Finally, a conclusion has been drawn with some future research recommendations based on technological challenges encountered in industrializing these materials.

Modification of bentonite clay & its applications: a review

Bentonite clay is one of the oldest clays that humankind has been using from ancient times as traditional habits and remedies. In recent years researchers have found many applications of bentonite clay due to its various physio-chemical properties. In the present work, various physical and chemical properties of bentonite such as surface area, adsorption, swelling properties, cation exchange properties, etc. have been studied. This study also includes various procedures of modification of bentonite clay into Chitosan/Ag-bentonite composite, Fe-Modified bentonite, Hydroxyl-Fe-pillared-bentonite, Organo Bentonite, Organophilic clay, Arenesulfonic Acid-Functionalized Bentonite, Bentonite clay modified with Nb2O5. The study reveals that bentonite clay has large surface area due to similar structure with montmorillonite and it is found that the functionality of bentonite can be increased by increasing total surface area of the clay. Due to high cation exchangeability of bentonite, various cations can be incorporated into it. After purification and modification, the absorbent aluminum phyllosilicate bentonite clay can be used as an efficient catalyst in various types of catalytic reactions. Moreover, bentonite clay can be applied in various field like drilling, civil engineering, agriculture and water treatment.

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 polybrominated diphenyl ethers on sand-bentonite liner material

Polybrominated diphenyl ethers (PBDEs) are present in biosolids and other solid wastes, as well as being detected in landfill leachates. As sand-bentonite mixtures are extensively used as basal liner materials for landfills, a sand-bentonite mixture was investigated by swelling tests and leaching column tests to determine whether it can effectively contain and/or immobilize PBDEs in landfill leachate. Leaching column tests were conducted with permeants consisting of biosolids' leachates diluted to 50% by volume and spiked with 50 μg/mL of a pentaBDE mixture solution. The results showed that the sand-bentonite retained up to 45-66% of the total PBDEs in the permeant; however, the concentration of PBDEs in the effluent increased continuously and reached a significant level during a 3-week period. PBDEs probably sorbed onto both fine and ultra-fine organic particles. During leaching, a compacted sand-bentonite admix could stop fine particles from passing, but at the same time, ultra-fine organic particles carried PBDEs through the barrier materials. The hydraulic conductivity, k, of the sand-bentonite was negatively affected by shrinkage of the clay interlayer caused by the permeant hydrophobicity. However, the hydraulic conductivity changed only to a limited extent, remaining at a magnitude of 10^-9 cm/s, probably because the PBDE concentrations were low. Therefore, caution is needed when sand-bentonite is applied to landfill liners as a barrier for PBDEs.

Performance and mechanisms of thermally treated bentonite for enhanced phosphate removal from wastewater

Optimization of clays as adsorbent for low concentration phosphorus removal from wastewater has received increasing attention in recent years. This study explored the feasibility of using bentonite as an adsorbent for phosphate (P) removal from synthetic wastewater, by assessing the performance of thermally treated bentonite for P removal and elucidating the mechanisms of P adsorption. Natural bentonite (B25) was thermally treated at 100-1000 °C (B100-B1000) for 2 h. Physical and chemical properties were measured by the SEM, XRD, pore size distribution, EDX, and cation exchange capacity (CEC) methods. Thermal treatment increased P sorption capacity of bentonite and that B800 had a higher P sorption capacity (6.94 mg/g) than B25 (0.237 mg/g) and B400 (0.483 mg/g) using the Langmuir isotherm equation. Study of sorption kinetics indicated that B800 rapidly removed 94% of P from a 10 mg P/L solution and the pseudo-second-order equation fitted the data well. The Ca²⁺ release capacity of B800 (1.31 mg/g) was significantly higher than that of B25 (0.29 mg/g) and B400 (0.40 mg/g) (p < 0.05). The initial pH level had a smaller impact on P removal efficiency for B800 than that of B25 and B400. Ca-P was the main fraction of P adsorbed onto B800, and Ca₁₀-P was the main species (41.4%). The main factors affecting the phosphorous adsorption capacity of B800 were changed crystal structure, strong calcium release capacity, and improved stability in different pH solutions. The results demonstrated that thermally treated bentonite (B800) has the potential to be an efficient adsorbent for removal of low-concentration phosphorus from wastewater.

Bentonite modification with hexadecylpyridinium and aluminum polyoxy cations and its effectiveness in Se(IV) removal

Usage of bentonite as a buffer material is suggested in radioactive waste repositories. Although bentonites have higher sorption ability to cations, they cannot adsorp anions due to negative surface charge. Nowadays, ongoing researches focus on increasing anion adsorption ability of the bentonites with modification. Organic-pillared bentonite (OPBent) was produced by modification of sodium bentonite with aluminum polyoxy and hexadecylpyridinium cations in this study. Variation in structure after modification was demonstrated by using different characterization techniques. Se removal efficiency of OPBent is investigated by using (75)Se, since selenium (Se) is one of the important long lived fission products found in radioactive waste and has toxic anionic species in an aqueous environment. The effect of reaction time, solid/liquid ratio, pH and concentration on the adsorption performance were examined. Se speciation and its effect onto adsorption were also investigated by measuring Eh-pH values under certain experimental conditions. Additionally, importance of the amount of Al-polyoxy cations used in modification was investigated by comparing these results with the results of other organic-pillared bentonite produced in our previous research. Experimental results confirmed that both cations were successfully placed into the bentonite interlayer and significant change in the host structure leads to increase Se adsorption. Consequently, bentonite modification improves its Se adsorption ability and further investigations are needed related to the usage of this adsorbent in other remediation studies especially in sorption of other anionic pollutants.

Simultaneous adsorption of Cd(ii) and phosphate on Al13 pillared montmorillonite

Al₁₃ pillared montmorillonites (AlPMts) prepared with different Al/clay ratios were used to remove Cd(ii) and phosphate from aqueous solution.

Adsorption of phosphate from aqueous solution by hydroxy-aluminum, hydroxy-iron and hydroxy-iron-aluminum pillared bentonites

Phosphorus removal is important for the control of eutrophication, and adsorption is an efficient treatment process. In this study, three modified inorganic-bentonites: hydroxy-aluminum pillared bentonite (Al-Bent), hydroxy-iron pillared bentonite (Fe-Bent), and mixed hydroxy-iron-aluminum pillared bentonite (Fe-Al-Bent), were prepared and characterized, and their phosphate adsorption capabilities were evaluated in batch experiments. The results showed a significant increase of interlayer spacing, BET surface area and total pore volume which were all beneficial to phosphate adsorption. Phosphate adsorption capacity followed the order: Al-Bent>Fe-Bent>Fe-Al-Bent. The adsorption rate of phosphate on the adsorbents fits pseudo-second-order kinetic models (R(2)=1.00, 0.99, 1.00, respectively). The Freundlich and Langmuir models both described the adsorption isotherm data well. Thermodynamic studies illustrated that the adsorption process was endothermic and spontaneous in nature. Finally, phosphate adsorption on the inorganic pillared bentonites significantly raised the pH, indicating an anion/OH(-) exchange reaction.