Hydrophobic Modification of ZrO-SiO Xerogel and Its Adsorption Properties to Rhodamine B.

Zirconium nitrate pentahydrate (Zr(NO)·5HO) 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 ZrO-SiO xerogels were prepared successfully. The xerogels were characterized using Fourier transform infrared spectra (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and N adsorption-desorption measurement. The adsorption mechanism of hydrophobic ZrO-SiO xerogels to RhB was described by the kinetic and adsorption isotherms. The results showed that the introduction of Si-CH groups can make the average pore size, BET surface area, and total pore volume of ZrO-SiO xerogel increase. The hydrophobic ZrO-SiO xerogel displays an adsorption capacity of 169.23 mg·g for RhB dye at 25 °C and pH = 3. The adsorption process of hydrophobic ZrO-SiO 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 ZrO-SiO 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.