The RHs used in this research were obtained from Guangdong
Academy of Agricultural Science. Analytical reagent grade hydrochloride
acid (37 wt %) and KNO3 were ordered from Alfa Aesar, both
of which were used as received.
The raw RHs were boiled in 10 wt % HCl solution for 2 h, rinsed
with deionized water, and then dried at 100 °C for 24 h. The dried
RHs were then pyrolyzed in a muffle furnace, which was preheated to
700 °C, for 2 h to prepare silica nanoparticles. A control sample was
prepared via the same pyrolysis condition but using water rinsed RHs
instead of HCl treatment. The silica nanoparticles synthesized from
the pyrolysis were then ultrasonicated in 0.20 and 0.50 M KNO3
solution, respectively, followed by 1 h of stirring. The samples were
then filtered and dried at 105 °C for 4 h. The dried samples were
subsequently pyrolyzed at 800 °C for 2, 4, and 8 h to form
semicrystalline porous silica framework.