Silica-supported $\hbox {Ni}_{{x}}\hbox {O}_{{y}}$, $\hbox {Zn}_{{x}}\hbox {O}_{{y}}$ and $\hbox {Mn}_{{x}}\hbox {O}_{{y}}$ nanocomposites: physicochemical characteristics and interactions with water and n-decane

Abstract

A series of $\hbox {M}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}$ (where M = Ni, Zn and Mn) nanocomposites were synthesized at different $\hbox {M}_{{x}}\hbox {O}_{{y}}$ contents (0.2, 1 and 3 mmol per 1 g $\hbox {SiO}_{2})$ using a deposition method. The samples were characterized using nitrogen adsorption–desorption, X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy and photon correlation spectroscopy. The heat of immersion in water ($Q_{\mathrm{w}})$ and n-decane ($Q_{\mathrm{d}})$ were measured using a microcalorimetry method, and the corresponding values of the hydrophilicity index $K_{\mathrm{h}}=Q_{\mathrm{w}}/Q_{\mathrm{d}}$ were analysed. The formation of $\hbox {M}_{{x}}\hbox {O}_{{y}}$ on a silica surface leads to diminishing of the $Q_{\mathrm{w}}$ and $Q_{\mathrm{d}}$ values (calculated per 1 g of nanocomposites) because of the specific surface area reduction. However, the $Q_{\mathrm{w}}$ values calculated per 1 $\hbox {m}^{2}$ increase for $\hbox {Zn}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}$ and $\hbox {Mn}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}$ in comparison with the unmodified silica, and it remains unchanged for $\hbox {Ni}_{{x}}\hbox {O}_{{y}}/\hbox {SiO}_{{2}}$. Silica modification with $\hbox {M}_{{x}}\hbox {O}_{{y}}$ significantly changes the pH dependence of zeta potential and affects the surface charge density. A shift of the isoelectric point $(\hbox {pH}_{\mathrm{IEP}})$ and a character of the zeta potential $\zeta$(pH) curve are affected by the $\hbox {M}_{{x}}\hbox {O}_{{y}}$ phase, and $\hbox {pH}_{{\mathrm{IEP}}}$ shifts toward higher values as follows Mn < Zn < Ni.