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Aminopropyltrimethoxysilane- and aminopropyltrimethoxysilane-silver-modified montmorillonite for the removal of nitrate ions

ABSTRACT A natural clay (Mn) modified with γ-aminopropyltrimethoxysilane (Mn–S) and silver (Mn–S–Ag) were evaluated as a potential adsorption media for nitrate removal from water. These materials were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, zeta-potential, thermogravimetric analysis, scanning electron microscopy and elemental analyses. First, the adsorption capacity of the Mn–S clay for Ag+ was studied. The cation adsorption capacity was almost three times greater for Mn–S than for Mn because a metal-amino group complex is favored. Second, the nitrate adsorption on Mn–S and Mn–S–Ag was studied as a function of contact time, pH, temperature and adsorbent dosage using batch techniques. In the absence of Ag+, adsorption was high at low pH and the amount of adsorbed nitrate decreased as the pH increased. For the Mn–S, the following monolayer adsorption capacities were obtained: Qmax = 0.80, 0.72 and 0.68 mmol /g at pH 3, 5 and 7, respectively, whereas for the Mn–S–Ag the values obtained were: Qmax = 0.77, 0.74 and 0.42 mmol /g at pH 3, 5 and 7, respectively. From the results obtained, adsorption occurs over surface groups without involving the Ag+ cation in the adsorption process.