Comparison between Asymmetric and Symmetric Gemini Surfactant-Modified Novel Organo-vermiculites for Removal of Phenols

Organo-Montmorillonite Modified by Gemini Quaternary Ammonium Surfactants with Different Counterions for Adsorption toward Phenol

The discharge of industrial phenol pollutants causes great harm to the natural environment and human health. In this study, phenol removal from water was studied via the adsorption of Na-montmorillonite (Na-Mt) modified by a series of Gemini quaternary ammonium surfactants with different counterions [(C₁₁H₂₃CONH(CH₂)₂N⁺ (CH₃)₂(CH₂)₂ N⁺(CH₃)₂ (CH₂)₂NHCOC₁₁H₂₃·2Y^-, Y = CH₃CO₃^-, C₆H₅COO^- and Br^-, 12-2-12·2Y^-]. The results of the phenol adsorption indicated that MMt-12-2-12·2Br^-, MMt-12-2-12·2CH₃CO₃^- and MMt-12-2-12·2C₆H₅COO^- reached the optimum adsorption capacity, which was 115.110 mg/g, 100.834 mg/g and 99.985 mg/g, respectively, under the conditions of the saturated intercalation concentration at 2.0 times that of the cation exchange capacity (CEC) of the original Na-Mt, 0.04 g of adsorbent and a pH = 10. The adsorption kinetics of all adsorption processes were in good agreement with the pseudo-second-order kinetics model, and the adsorption isotherm was better modeled by Freundlich isotherm. Thermodynamic parameters revealed that the adsorption of phenol was a physical, spontaneous and exothermic process. The results also showed that the counterions of the surfactant had a certain influence on the adsorption performance of MMt for phenol, especially the rigid structure, hydrophobicity, and hydration of the counterions.

Organo-Vermiculites Modified by Aza-Containing Gemini Surfactants: Efficient Uptake of 2-Naphthol and Bromophenol Blue

To explore the effect of spacer structure on the adsorption capability of organo-vermiculites (organo-Vts), a series of aza-containing gemini surfactants (5N, 7N and 8N) are applied to modify Na-vermiculite (Na-Vt). Large interlayer spacing, strong binding strength and high modifier availability are observed in organo-Vts, which endow them with superiority for the adsorption of 2-naphthol (2-NP) and bromophenol blue (BPB). The maximum adsorption capacities of 5N-Vt, 7N-Vt and 8N-Vt toward 2-NP/BPB are 142.08/364.49, 156.61/372.65 and 146.50/287.90 mg/g, respectively, with the adsorption processes well fit by the PSO model and Freundlich isotherm. The quicker adsorption equilibrium of 2-NP than BPB is due to the easier diffusion of smaller 2-NP molecules into the interlayer space of organo-Vts. Moreover, stable regeneration of 7N-Vt is verified, with feasibility in the binary-component system that is demonstrated. A combination of theoretical simulation and characterization is conducted to reveal the adsorption mechanism; the adsorption processes are mainly through partition processes, electrostatic interaction and functional interactions, in which the spacer structure affects the interlayer environment and adsorptive site distribution, whereas the adsorbate structure plays a role in the diffusion process and secondary intermolecular interactions. The results of this study demonstrate the versatile applicability of aza-based organo-Vts targeted at the removal of phenols and dyes as well as provide theoretical guidance for the structural optimization and mechanistic exploration of organo-Vt adsorbents.

Mechanistic evaluation of metformin drug confiscation from liquid phase on itaconic acid/kaolin hydrogel nanocomposite

Herein, kaolin (K) was amended by a novel gemini surfactant to attain nano-kaolin (nK), which was subsequently employed as a cross-linker in the preparation of itaconic acid/kaolin hydrogel nanocomposite (IA/nK) via free radical polymerization route employing the sonochemical technique, which has been used for the first time to extract metformin (MF) from water solution. The aspects which affect sorption behavior of IA/nK on metformin (MF) were systematically investigated via batch experiments, in harmony with effect of sorbent dosage, contact time, pH, MF concentration, equilibrium curves, kinetic behavior, and thermodynamic parameters. BET studies of IA/nK exhibited S_BET of 106.42 m²g^-1, pore volume 0.281 cm³ g^-1, and a pore radius of 16.627 Å. Kinetic and isotherm modelling portrayed that pseudo-second order and Freundlich model appropriated adsorption data with maximum sorption capacity of 278.35 mg g^-1. Thermodynamic parameters ΔH^O (13.67 kJmol^-1) and ΔG^O (-7.648 kJmol^-1) revealed that sequestration of MF on IA/nK was endothermic, spontaneous, and dominated by physisorption. Molecular docking study along with X-ray photoelectron spectroscopy inferred electrostatic interaction and hydrogen bonding as main mechanism of MF removal. IA/nK demonstrated dose-reliant inhibition of both gram-positive and gram-negative bacterial strains. IA/nK demonstrated good regeneration properties, up to four cycles without considerable decrease in its efficacy. The admirable sorption capacity coupled with good reusability, and low toxicity substantiates IA/nK as promising adsorbent for MF confiscation.

Pore wettability for enhanced oil recovery, contaminant adsorption and oil/water separation: A review

Wettability, a fundamental property of porous surface, occupies a pivotal position in the fields of enhanced oil recovery, organic contaminant adsorption and oil/water separation. In this review, wettability and the related applications are systematically expounded from the perspectives of hydrophilicity, hydrophobicity and super-wettability. Four common measurement methods are generalized and categorized into contact angle method and ratio method, and influencing factors (temperature, the type and layer charge of matrix, the species and structure of modifier) as well as their corresponding altering methods (inorganic, organic and thermal modification etc.) of wettability are overviewed. Different roles of wettability alteration in enhanced oil recovery, organic contaminant adsorption as well as oil/water separation are summarized. Among these applications, firstly, the hydrophilic alteration plays a key role in recovery of the oil production process; secondly, hydrophobic circumstance of surface drives the organic pollutant adsorption more effectually; finally, super-wetting property of matrix ensures the high-efficient separation of oil from water. This review also identifies importance, challenges and future prospects of wettability alteration, and as a result, furnishes the essential guidance for selection and design inspiration of the wettability modification, and supports the further development of pore wettability application.