capillaries (internal diameter (i.d.) 0.53 and 0.32 mm, length 100
mm) were purchased from Dalian Zhonghuida Scientific Instrument Corporation.
The chemical reagents included tetrapropylammonium hydroxide solution
(TPAOH, ∼50 wt % in water), tetraethyl orthosilicate (TEOS,
wt % ≥99.5%), sodium aluminate (NaAlO2, wt % ≥99.0%),
sodium hydroxide (NaOH, wt % ≥96.0%), anhydrous alcohol (EtOH,
wt % ≥99.7%), ammonium acetate (NH4Ac, wt % ≥98.0%),
sodium sulfate (Na2SO4, wt % ≥99.0%),
acetone (marked as ACT, wt % ≥99.5%), glycerol (marked as GCR,
wt % ≥99.0%), and N,N-dimethylformamidel
(DMF, wt % ≥99.5%) were purchased from Sinopharm Chemical Reagents
Co., Ltd. (Shanghai, China). The used chemical coupling agent of (3-aminopropyl)
trimethoxysilane (APTMS, ∼97 wt %) was purchased from Aladdin
Industrial Corporation (Shanghai, China). All the above used chemical
reagents were analytical reagent (AR) and used as received without
further purification. The used deionized water (DI water, 18.2 MΩ)
was home-made.