Fig. 1 shows that the as-prepared sample, MK-NaOH-4 M-6 h-HCl, is
X-ray amorphous. Tables 2 and S1 (shown in Supporting Information)
show that it is dominant in silica. The N2 adsorption–desorption isotherm
(Fig. 3) could be defined as typical Langmuir IV curve with a H2
hysteresis loop, evidencing it to be mesoporous with uniform inkbottle
or cage-like pores (Kruk and Jaroniec, 2001). Its sponge-like mesoporous structure is also confirmed by the TEM observation
(shown in Fig. 4). In detail, it possesses a SBET as high as 751.5 m2
/g
and a pore size of about 4.0 nm at the maximum probability (DBJH)
(shown in Fig. 3 and Table 3), both of which are much superior to the
properties of the kaolin-based nanoporous silica reported in literatures
(shown in Table 1). This material benefits from the process novelty,
i.e., pre-alkali-treating the metakaolin before the acid-treatment. In
the study, two major aspects of the alkali-treatment (c mol/L, NaOH
concentration and t h, reaction time) were investigated to reveal the
processing mechanism. The detailed results are shown and discussed
as follows.