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, ΔwetHmθ, 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 cm3 of 8.0×10−3 or 0.127 mol dm−3 solutions of Co2+, Ni2+ or Cu2+. The measurements were also performed using 50.0/50.0 cm3 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 8.0×10−3 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 silica 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.