Citric-acid-assisted sol-gel synthesis of mesoporous silicon-magnesium oxide ceramic fibers and their adsorption characteristics

Abstract

This work reports a novel citric-acid-assisted sol-gel method that does not contain any template or hazardous chemicals for the electrospinning of mesoporous silicon-magnesium oxide (MgO–SiO2) ceramic fibers. Citric acid was fully utilized in the preparation of a precursor solution to catalyze tetraethyl orthosilicate (TEOS) hydrolysis, chelate with magnesium ions and cause pore formation during calcination. Moreover, H2O2 addition resulted in fiber decoloration, hydrophilicity, surface area reduction and surface basicity enhancement. The studied mesoporous MgO–SiO2 ceramic fibers (Si:Mg = 1.5:1 atomic ratio) exhibited good morphologies with diameters of 1.23 ± 0.34 μm and a BET surface area of 142.61 m2‧g−1 after heat-treatment at 600 °C. The adsorption characteristics of the ceramic fiber toward Pb(II), Cu(II), methylene blue (MB) and fulvic acid (FA) were studied. The ceramic fibers showed high adsorption capacities of 753.1/481.0 mg‧g−1 for Pb(II)/Cu(II), which obeyed the pseudo-second-order kinetics and the Langmuir isotherm model. The Freundlich model provided a better fit for the MB and FA adsorption isotherms, and the pseudo-first-order model could describe the kinetics data of FA adsorption. The abnormal kinetics of MB adsorption were observed to follow a pseudo-second-order model at the early phase but then followed a pseudo-first-order model. The innovative strategy of synthesizing MSCFs could contribute to the development of composite oxide ceramic fibers that are relevant to a variety of applications.