Mesoporous Na+SiO2 spheres for efficient removal of Cr3+ from aqueous solution
Mesoporous Na + SiO 2 spheres with large surface areas, high porosities and tunable Na + contents have been synthesized by the Stöber method followed by the “polyvinylpyrrolidone (PVP)-protected NaOH etching” process. With the surface protection of PVP, the NaOH etching preferentially occurs inside the SiO 2 spheres results in the increase of the surface areas and porosities of the SiO 2 spheres while keeping the sphere size unchanged at the etching degree less than 50%. The surface area and pore volume of the selected Na + SiO 2 spheres with etching degree of 50% are 302.9 m 2 /g and 0.946 cm 3 /g, respectively, which are 31 times and 59 times higher than that of the SiO 2 spheres without NaOH etching. The Na + SiO 2 spheres with etching degree of 10% calcined at 400 °C shows high adsorption activity for Cr 3+ removal from different natural waters such as tap water, lake water and river water. The adsorption kinetic of Cr 3+ by the Na + SiO 2 spheres fits well with the pseudo-second-order model, and the adsorption isotherm can be fitted by the Langmuir adsorption isotherm. The maximum adsorption capacity of 10% Na + SiO 2 400 for Cr 3+ is 33.18 mg/g. Finally, it has been confirmed that the ion-exchange between Na + and Cr 3+ plays the leading role in the adsorption process while the contribution from static adsorption is relatively weak.
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