Thermochemical features of lamellar silica, copper, nickel and cobalt-doped forms synthesized from neutral amine route

Lamellar silica prepared from sol-gel process through neutral amine route, was doped with cobalt, nickel or copper. X-ray diffraction pattern, thermogravimetry, and differential scanning calorimetry and reaction-solution calorimetry characterized these synthesized hybrids. The wetting enthalpy, Delta(wet)H(m)(theta), for lamellar matrix doped with 10.0 and 15.0 mmol of CuCl2 gave 41.81 +/- 0.02 and 40.54 +/- 0.02 J g(-1), respectively. The enthalpy of cation adsorption was carried out by using 100.0 cm(3) of 8.0 x 10(-3) or 0.127 mol dm(-3) solutions of Co2+ , Ni2+ or Cu2+. The measurements were also performed using 50.0/50.0 cm(3) mixture of Co2+ and Cu2+ solutions. The results gave 20.73 +/- 0.07; - 69.22 +/- 0.03; 10.91 +/- 0.06 and - 34.44 +/- 0.06 J g(-1) for nickel, copper, cobalt and copper-cobalt solutions, for a concentration of 8.0 x 10(-3) mol dm(-3). The same sequence of cations gave the enthalpic values - 97.12 +/- 0.06, - 106.90 +/- 0.01, 42.56 +/- 0.06, 34.97 +/- 0.12 J g(-1) for 0.127 mol dm(-3) solution. The results showed that the lamellar sirica matrix can be used as a sequestrating agent for these cations with a capacity of adsorption established as Ni2+ > Cu2+ > Co2+. The wetting enthalpic values as well as the thermal stability of these matrices are associated to the crystallinity of the samples. (C) 2000 Elsevier Science B.V. All rights reserved.