A number of organobentonites were synthesized by exchanging the metal ions in bentonite with the cationic surfactant, cetyltrimethylammonium bromide. Samples of natural bentonite and organobentonites were analyzed for their organic carbon contents, examined by X-ray diffraction (XRD) for interlayer spacings, and viewed using a scanning electron microscope (SEM) for surface morphology. The sorption isotherm of benzene vapor from ambient air (relative humidity (RH) = 45 ± 5%) on natural bentonite was nonlinear; however, the isotherms of benzene from ambient air onto organobentonites were virtually linear over a large range of relative vapor concentrations. The sorption capacities of air-dried organobentonites were far greater than that of the natural bentonite. For air-dried organobentonites, the sorption coefficients correlated positively with the sample organic carbon contents and negatively with the sample BET-N2 surface areas. The heats of benzene vapor sorption onto air-dried organobentonites were less exothermic than the heat of benzene-vapor condensation. These findings suggest that benzene vapor sorption by air-dried organobentonites occurs essentially by vapor partition into the sample organic-matter fractions. This offers a potential application of organobentonites for the removal of organic vapors from flue gases and for assessing the efficiency of vapor removal.

Model spent cetyltrimethylammonium bromide (CTMAB)-bentonite, and cetyl pyridinium chloride (CPC)-bentonite used for sorbing p-nitrophenol (PNP) from wastewater, as well as virgin CTMAB-bentonite and CPC-bentonite, were employed as the starting materials to prepare porous clay heterostructures (PCHs). The BET surface areas and total pore volumes of the PCHs based on these spent and virgin organobentonites (PNP-CTMAB-PCH, CTMAB-PCH, PNP-CPC-PCH and CPC-PCH) are 661.5 m2/g and 0.25 cm3/g, 690.4 m2/g and 0.27 cm3/g, 506.3 m2/g and 0.30 cm3/g, and 525.4 m2/g and 0.30 cm3/g, respectively. These values approximate those of activated carbon (AC), at 731.4 m2/g and 0.23 cm3/g, and are much larger than those of bentonite and CTMAB-bentonite, at 60.9 m2/g and 0.12 cm3/g, and 3.7 m2/g and 0.0055 m2/g, respectively. The PCHs have slightly higher adsorption capacities for benzene and CC14 than AC at higher relative pressures despite their comparatively lower benzene and CC14 adsorption capacity at lower relative pressures. The existence of PNP in organobentonites also enhances the volatile organic compounds (VOCs) adsorption capacity of PCHs at lower adsorbate concentrations, although some adsorption capacity is lost at higher concentrations. The hydrophobicity order of the adsorbents is: CTMAB-bentonite > AC > PCHs > bentonite. The micro- to mesoporous pore sizes, superior VOC adsorption properties, thermal stability to 750°C and hydrophobicity and negligible influences of PNP on PCHs make spent PNP-containing organobentonites ideal starting materials for synthesis of PCHs and especially attractive adsorbents for VOC sorption control.

Toxic pollutants such as diclofenac (DCF) and cadmium(II) have been detected together in various water sources; these compounds have adverse effects on human health. The objective of the present study was to investigate the sorption of DCF and Cd(II) from aqueous solutions on an organobentonite. The organobentonite was synthesized by adsorbing the surfactant hexadecyltrimethylammonium (HDTMA) on bentonite; this was designated OBHDTMA. The sorption of DCF and Cd(II) on OBHDTMA and of Cd(II) on OBHDTMA saturated with DCF (OBHDTMA-DCF) were then studied. The bentonite, OBHDTMA, and OBHDTMA-DCF were characterized by X-ray diffraction, thermogravimetric analysis, and Fourier-transform infrared spectroscopy. The capacity of OBHDTMA for adsorbing DCF depended on the solution pH, ionic strength, and temperature. The effect of pH on the adsorption capacity of OBHDTMA was anomalous because, depending on the concentration of DCF at equilibrium, the adsorption capacity increased or decreased by raising the pH. The capacity of OBHDTMA was enhanced by increasing the temperature from 15 to 35°C and by reducing the ionic strength from 1 to 0.01 N. The dependence of the adsorption capacity on the operating conditions was explained by considering the interactions between the DCF in solution and the surface of OBHDTMA. The maximum sorption capacity of the OBHDTMA for DCF was 388 mg/g at T = 25°C and at pH = 7 and was comparable to those of carbon materials. The adsorption of DCF on OBHDTMA was scarcely reversible, but the desorption percentage increased with pH. The adsorption of DCF on OBHDTMA was due to partition and electrostatic attraction. More Cd(II) was adsorbed on OBHDTMA-DCF than on OBHDTMA and this was influenced by the loading of DCF on the OBHDTMA-DCF. The OBHDTMA-DCF may be used to remove Cd(II) from water solution.

In this study, natural bentonite was modified with hexadecyltrimethylammonium (HDTMA) bromide to obtain organobentonite (HDTMA-bentonite). Bentonite and HDTMA-bentonite were then characterized using XRD, XRF, SEM, FT-IR, thermogravimetric (TG) analysis, elemental analysis and Brunauer-Emmett-Teller (BET) surface area techniques. The HDTMA+ cation was found to be located on the surface and enters the interlayer spaces of smectite according to the XRD and SEM results. FT-IR spectra indicated the existence of HDTMA functional groups on the bentonite surface. The BET surface area significantly decreased after the modification due to the coverage of the pores of natural bentonite. After the characterization, the adsorption of a textile dye, Reactive Blue 19 (RB19), onto bentonite and HDTMA-bentonite was investigated. The maximum adsorption capacity of HDTMA-bentonite for RB19 was 502 mg g-1 at 20°C. The adsorption process followed a pseudo-second-order kinetic model and it was exothermic and physical in nature.