A facile yet versatile modification method was adopted as template by functioning homoionic-vermiculites with 1, 2-bis (hexadecyldimethylammonio) ethane dibromide (16-2-16), which fulfilled the gap in the modification of vermiculite with gemini surfactant. The cation exchange capacity (CEC) values of the precursors were clearly determined by the improved BaCl2 measurement particular for vermiculite. The resultant organo-vermiculites (OVTs) were characterized by X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and Thermogravimetric analysis (TG-DTG). Batch experiments were performed to evaluate the effects that metallization and organic modification have on the adsorption process of OVTs for a typical anionic dye, methyl orange (MO). The removal efficiencies of OVTs towards MO followed the order of OVT-Li > OVT-Na > OVT-K > OVT. Adsorption performances of OVTs were all susceptible to pH and contact time, with the adsorption processes reached equilibrium at 40–60 min for OVT-Li, OVT-Na and OVT-K, while extended as long as 150 min for OVT, which verified the necessity of metallization. The adsorption processes of OVTs towards MO were all fitted well with pseudo-second-order, Freundlich isotherm and endothermic processes in nature. Results obtained from this study would not only bring new lights into the high-efficiency and cost-effective adsorbent, especially OVT-Li and OVT-Na, but also provide theoretical guidance for the modification of vermiculite with gemini surfactant.Scheme 1 Organo-vermiculite prepared by two-steps.Download high-res image (312KB)Download full-size image

•Organoclays modified by the novel trimeric quaternary ammonium surfactant were prepared.•16-2-16-2-16-Mt presented highest adsorption capacity at the lower modifier dosage for 2,4,6-TCP.•2,4,6-TCP adsorption is related to the number of alkyl chain and loaded amount of surfactant.•Hydrophobic interactions are responsible for 2,4,6-TCP adsorption.Understanding the structures and characteristics of surfactants used to modify montmorillonites is crucial to predict the adsorption capacity of the resultant organo-montmorillonites in the aquatic environment. Herein, organo-montmorillonites modified by surfactants containing various amounts of head groups and hexadecyl chains were prepared. A general comparison was conducted of organo-montmorillonites modified by methyl hexadecyl bis[3-(dimethylhexadecylammonio)ethyl] ammonium tribromide (16-2-16-2-16), dimeric surfactants (1, 2-bis (hexadecyldimethylammonio) ethane dibromide, 16-2-16) and cetyl trimethyl ammonium bromide (CTAB) for their adsorption performance on 2,4,6-trichlorophenol (2,4,6-TCP) from aqueous solution. The resultant organo-montmorillonites were characterized by XRD, TGA and FT-IR spectroscopy. Batch studies were performed to evaluate the influences of various parameters like the amount of modifiers, the number of alkyl chain, contact time and solution pH on the removal of 2,4,6-TCP. Results indicated that the removal efficiency follows the order of CTAB-Mt <16-2-16-Mt < 16-2-16-2-16-Mt from 0.4 CEC to 1.2 CEC, which may be due to increasing hydrophobicity with the increase in hexadecyl chain number. However, the adsorption capacity is on the rise in the order 16-2-16-Mt > 16-2-16-2-16-Mt > CTAB-Mt beyond 1.2 CEC. This might be interpreted in terms of the combined contribution of packing density of hexadecyl chains in the interlayer of montmorillonites and ion–dipole interaction between the head group of intercalated surfactants and 2,4,6-TCP. Full kinetics, equilibrium and thermodynamics were also undertaken. Moreover, the maximum adsorption capacities of 2,4,6-TCP were 328.9 mg/g at 1.6 CEC for CTAB-Mt and 306.7 mg/g at 0.8 CEC for 16-2-16-Mt, respectively, whereas as high as 322.6 mg/g for 16-2-16-2-16-Mt even at the modifier amount as low as 0.6 CEC. This study suggests that 16-2-16-2-16-Mt with three head groups and hexadecyl chains can serve as a more high-efficiency and cost-effective adsorbent for removal of 2,4,6-TCP from aqueous solution.Download high-res image (93KB)Download full-size image

A novel adsorbent (DHAPS-Mt) was prepared with Na montmorillonite (Na-Mt) and a zwitterionic surfactant (3-(N,N-dimethylhexadecylammonio)propanesulfonate, DHAPS). Then DHAPS-Mt was characterized by a series of characterization techniques and applied in herbicide adsorption. Two representative herbicides in agriculture, paraquat (PQ, 1,1′-dimethyl-4,4′-dipyridinium dichloride) and amitrole (AMT, 3-amino-1,2,4-triazole), were removed by DHAPS-Mt varying with different experimental conditions. The adsorption mechanisms, obtained from a comparison of adsorption capacities of DHAPS-Mt and two other kinds of organomontmorillonite (CTAB-Mt and SDS-Mt), suggested that the surface electrostatic adsorption and electrostatic attraction between herbicide cations and negatively charged group of DHAPS were the main interaction in PQ and AMT removal. The results of anionic dye (methyl orange) removal onto these three kinds of clay indicated that DHAPS-Mt might be applied in the treatment of mixed-ion wastewater. The kinetic study indicated that the adsorption of herbicides onto DHAPS-Mt followed the pseudo-second-order model, and the Langmuir isotherm model agreed well with the experimental data. Furthermore, thermodynamic parameters illustrated that PQ removal by DHAPS-Mt was more spontaneous at higher temperature, and the process was endothermic and randomness increasing in nature, while the AMT removal presented an opposite tendency.

•Organo-RCMs were successfully prepared by modifying RCMs with QASs.•RCMs singly modified by QASs showed different wettability characteristics.•Compounding of different QASs had a synergistic effect on the wettability.•Simultaneous control of the QASs and layer charge can regulate wettability.A series of montmorillonites with systematically reduced layer charge were prepared by a standard method of different fractions of Li+-fixation in montmorillonite, which could be used to mimic an oil reservoir. Three kinds of quaternary ammonium salts (QASs) with different cationic charges and structure sizes were used singularly or in compound form to modify the reduced-charge montmorillonites (RCMs). The wettability alterations of the organo-RCMs for deionized water and cyclohexane were studied based on capillary rise method and were compared using the Lipophilic to Hydrophilic Ratio (LHR). The results indicate that RCMs singularly modified by three kinds of QASs show different wettability characteristics, whereas compound modified by QASs have a synergistic effect on the wettability. Moreover, the compound type of the QASs plays a more important role on LHR values than the mix proportion. The results of this work also indicate that it is possible to regulate the wettability of the organo-RCMs by simultaneous control of the type, the compound ratio of QASs and the layer charge characteristics, which is helpful in providing theoretical guidance for the oil production.

Capillary rise tests were performed to investigate the influences that the structure of the modifier and layer charge of clay had on wetting properties of organoclays, which were prepared by ion exchange using bispyridinium dibromides (BPs) with different spacer length and the reduced-charge montmorillonites (RCMs). Their structures were examined by Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), and nitrogen adsorption–desorption isotherms. The results indicated that BPs had been successfully intercalated into interlayers and lay in the monolayer. The d001 basal spacing of organo-RCMs increased with the spacer length of BPs increasing, whereas it decreased gradually as the layer charge of the RCMs was decreased, independent of the type of BPs. Whether the organic modification made the Brunauer–Emmett–Teller (BET) surface area increase or decrease depended upon the size of the organic cations and the layer charge of the clays. The wettability alterations of the organo-RCMs for deionized water and cyclohexane were also compared. Both the spacer length of BPs and the layer charge of RCMs had important effects on the relative wettability of organo-RCMs. The hydrophilicity of organo-RCMs was increased with the spacer length of BPs increasing, namely, in the order as follows: C2-2Py-RCMs < C6-2Py-RCMs < C10-2Py-RCMs. In addition, the hydrophobicity was increased with a decrease in the layer charge. The results of this work were supposed to provide some reference information for regulating the wettability of the organo-RCMs by simultaneously controlling the type of modifiers along with the layer charge characteristics, to provide theoretical guidance for the favorable change in reservoir wettability.

•HEMBP-B was firstly prepared and applied in the treatment of aniline wastewater.•π–π polar interaction played a significant role in aniline adsorption on HEMBP-B.•It provided an idea for the removal of aromatic contaminants from aqueous solution.Aniline removal is of great importance for water treatment, and adsorption is an efficient treatment method. Hexamethylene bis-pyridinium dibromide modified bentonite (HEMBP-B) was firstly prepared and characterized by XRD, FT-IR, BET, SEM, TEM and TG–DTG analysis. Adsorptive experiments of aniline on the organo-bentonite were carried out using batch method as a function of the length of linking carbon chain (n), concentration of HEMBP (C), contact time (t), temperature (T) and pH. The optimal conditions for aniline removal on HEMBP-B were as follows: n of 5 or 6, C of 1.0 CEC, t of 120 min, T of 298 K, and natural pH of 6.6. The π–π polar interaction existed between the aromatic rings of aniline and HEMBP has successfully explained the main adsorption mechanism. The equilibrium data of aniline removal on HEMBP-B followed Freundlich and D-R isothermal models precisely, which indicated a less favorable and physical process of aniline adsorption. The kinetic data could be best described by the pseudo-second-order model. Besides, the thermodynamic study revealed that aniline adsorption on HEMBP-B was non-spontaneous, exothermic and physical.The main mechanisms and removal rate (R) of aniline adsorption on HEMBP-B, Na-B and HM-B. *Concentration of adsorption = 0.5 g/50 mL, C0 = 50 mg L−1, t = 120 min, T = 298 K, pH = 6.6.