Silica-supported $$\hbox {Ni}_{{x}}\hbox {O}_{{y}}$$, $$\hbox {Z n}_{{x}}\hbox {O}_{{y}}$$Z nxOy a nd $$\hbox {M n}_{{x}}\hbox {O}_{{y}}$$M nxOy na nocomposites: physicochemical characteristics a nd i nteractio ns with water a nd n-deca ne

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.