Thickness-controlled porous NiO films by Ni(OH)2/alginate layer-by-layer assembly

Ni(OH)2/alginate multilayer thin films were prepared directly by dip-coating using Layer-by-Layer assembly method. β-Ni(OH)2 nanoplatelets were first synthetized by chemical precipitation from nickel nitrate in ammonia under ultrasound. These particles, stabilized at pH ≈ 8, present an equivalent diameter of ≈ 250 nm and a zeta potential of ≈ + 35 mV. Sodium alginate was used as a negatively charged polyelectrolyte. In this work, the multilayer growth was first investigated in situ using optical fixed-angle reflectometry showing that particles/polyelectrolyte multilayer film can be successfully carried out. Ni(OH)2/alginate multilayer thin films were elaborated using several parameters: number of adsorbed bilayers, alginate and Ni(OH)2 particles concentrations, showing that multilayer films thickness can be mainly controlled by the number of adsorbed bilayers. The elaborated films were then heated at 325 °C in air for 1 h to calcinate the incorporated polyelectrolyte and to form NiO films. Thermal treatment experiments show an alginate content-dependent film adhesion. Indeed, multilayer films are more adherent and homogeneous with low alginate concentration (< 0.2 g.L−1). Finally, the specific surface area (SSA) of the NiO films was determined by adsorption-desorption of nitrogen gas using BET method.