Hydrophobic Modification of ZrO2-SiO2 Xerogel and Its Adsorption Properties to Rhodamine B

Abstract

Zirconium nitrate pentahydrate (Zr(NO3)4·5H2O) and tetraethyl orthosilicate (TEOS) are used as the zirconium source and silicon source, respectively, and methyltriethoxysilane (MTES) as the hydrophobic modifier; the hydrophilic and hydrophobic ZrO2-SiO2 xerogels were prepared successfully. The xerogels were characterized using Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption–desorption measurement. The adsorption mechanism of hydrophobic ZrO2-SiO2 xerogels to RhB was described by the kinetic and adsorption isotherms. The results showed that the introduction of Si-CH3 groups can make the average pore size, BET surface area, and total pore volume of ZrO2-SiO2 xerogel increase. The hydrophobic ZrO2-SiO2 xerogel displays an adsorption capacity of 169.23 mg·g−1 for RhB dye at 25 °C and pH = 3. The adsorption process of hydrophobic ZrO2-SiO2 xerogel to RhB followed a pseudo–second-order kinetic model. Fitting results from the D–R model of adsorption indicate that the adsorption of RhB onto the hydrophobic ZrO2-SiO2 xerogels is mainly physical, accompanied by a spontaneous heat absorption process. The regeneration and recycling properties of hydrophobic xerogels were investigated, and their recoverability and reusability were demonstrated.