F. Prinetto et al., Synthesis and characterization of sol-gel Mg/Al and Ni/Al layered double hydroxides and comparison with co-precipitated samples, MICROP M M, 39(1-2), 2000, pp. 229-247
Mg/Al and Ni/Al layered double hydroxides (LDI-Is) were prepared by a sol-g
el(sg) route performing hydrolysis of alkoxide or acetylacetonate precursor
s with HCl or HNO3. For comparison, other samples were prepared from nitrat
e salts by the classical co-precipitation (cp) method at constant pH. Pure
sg Mg/Al LDHs with a Mg2+/Al3+ ratio in the range 2.47-4.29 were obtained,
as shown by XRD. Almost pure sg Ni/Al LDHs resulted when using HCl for the
precursor hydrolysis, while unsuccessful trials were done with HNO3. The mi
xed oxides, obtained by calcination of sg materials, exhibited alcogel like
texture and specific surface areas, at least 10% higher than those of the
cp ones, as evidenced by N-2 volumetric measurements. Furthermore, TEM anal
ysis revealed different morphologic features of the sg and co-precipitated
materials, both as-prepared and calcined. TG-DSC analysis and IR spectrosco
py evidenced the presence of organic species remaining as compensating anio
ns in the interlayer space, inducing a rather different decomposition proce
ss for the sg than for the co-precipitated samples. IR spectroscopy also in
dicated the higher basicity of the Mg-compared to the Ni-containing LDHs. F
urthermore, it evidenced that Al3+ was more easily segregated from Ni(Al)O
than from Mg(AI)O mixed oxides. (C) 2000 Elsevier Science B.V. All rights r
eserved.