Enhanced removal of p-nitrophenol from aqueous media by montmorillonite clay modified with a cationic surfactant

Montmorillonite clay (MC) yields after modification of the interlamellar spacing and the chemical character of its surface by treatment with cetyltrimethylammonium bromide (CTAB) a solid product (MCCTA). This has been used as an adsorbent for the removal of p-nitrophenol (PNP) from aqueous solutions. The MCCTA samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analysis (TG/DTA), FT-IR spectroscopy, zeta potential measurements, X-ray diffraction (XRD), and specific surface area. Investigations were also carried out to assess how the adsorption of PNP was affected by factors such as contact time, initial PNP concentration, adsorbent dosage and temperature. Of the two models tried the Freundlich isotherm gave a better account of the equilibrium data than did the Langmuir one. The kinetics could be successfully replicated by a pseudo-second order model with an activation energy of 55.0 kJ mol^-1, while the thermodynamic parameters indicated an exothermic (Δ_adsH^o = -15.8 kJ mol^-1), non-spontaneous (Δ_adsG^o = + 3.9-5.9 kJ mol^-1) adsorption process. The experimental results showed MCCTA, unlike natural MC, to have a significant adsorption capacity for PNP removal from aqueous media.