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

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(+), [Formula: see text] 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 [Formula: see text]/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 [Formula: see text]/g at pH 3, 5 and 7, respectively. From the results obtained, [Formula: see text] adsorption occurs over [Formula: see text] surface groups without involving the Ag(+) cation in the adsorption process.