A study on removal characteristics of o-, m-, and p-nitrophenol from aqueous solutions by organically modified diatomaceous earth

The natural diatomaceous earth (DAT) was modified with surfactant of hexadecyltrimethylammonium bromide (HDTMABr) to form organic-modified diatomaceous earth (DAT-HDTMABr). The DAT and DAT-HDTMABr were characterized by X-ray fluorescence, X-ray diffraction, FT-IR and DTA-TG. The surface area was determined using Brunauer, Emmett, and Teller adsorption method. Cation exchange capacity was estimated using an ethylenediamine complex of copper method, and the modifier loading was calculated from the total carbon analysis. The ability of raw and organomodified diatomaceous earth to remove o-nitrophenol (ONP), m-nitrophenol (MNP), and p-nitrophenol (PNP) from aqueous solutions has been carried out at predetermined equilibration time, adsorbent amount, pH, and temperatures using a batch technique. The removal of ONP, MNP, and PNP from aqueous solutions by modified clay seems to be more effective than unmodified sample. The experimental equilibrium adsorption data were analyzed by four widely used two parameters, Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich (D–R) isotherm equations. Kinetic studies showed that pseudo-second-order described the adsorption experimental data better than the pseudo-first-order kinetic model. Based on the calculated thermodynamic parameters, such as enthalpy (ΔH), entropy (ΔS), and Gibb’s free energy changes (ΔG), it is noticeable that the adsorption of ONP, MNP, and PNP by DAT and DAT-HDTMABr adsorbents was carried out spontaneously, and the process was exothermic in nature.