Loading insoluble sulfides in mesoporous oxide films from precursors in solution

Abstract

E-waste from the electric and electronics industry is an emerging threat due to the pollution caused by hazardous cations. Immobilization and confinement of these cations as nanoparticles (NPs) in porous materials provide a strategy for the recovery and recycling of hazardous cations. Therefore, we propose the use of mesoporous oxides (MPO) films where the pores act as nanoreactors for the precipitation of metal sulfides (MS) to achieve a process in which dissolved cations are removed and at the same time form a nanostructure to serve as a basis for future designs. In this work, we present a detailed study of the formation of metal sulfides (MS - M = Cd, Zn, Co, Ni) NPs controlling the NP growth in the pores of the MPO by a successive ionic layer adsorption and reaction (SILAR) process. By varying diverse variables of interest such as pH, matrix composition (SiO2, TiO2, ZrO2), isoelectric point (IP) of the inorganic pore surface by organic functionalizers, we show that precipitation is comparable for the different metal sulfides where transport in the mesoporosity and the electrical charge of the surface, as well as the solvent, control the physicochemical response of the system. Understanding the role of each variable allows the limitations of loading MPOs to be identified and the pore filling to be optimized, although ion transport limitations in aqueous solutions lead to inhomogeneous distributions. Through a thorough characterization study (SEM, TEM, UVVIS, EEP, XRR, XPS), it was concluded that MPO thin films are useful platforms for the efficient removal of cations dissolved in water and even in alcohols.