microscope (TEM) operating at 120 kV. A JEM-2100F operating at 210
kV was also used for some samples. The hydrodynamic radius and zeta
potential were measured with a Zetasizer from Malvern via dynamic
light scattering (DLS). The N2 adsorption–desorption
isotherms at 77 K were measured on a Micrometitics ASAP 2020 system.
FT-IR spectrum was performed on a Spectrum Two spectrometer from PerkinElmer.
The nitrogen in the OSNP was analyzed using a PerkinElmer CHN analyzer.
Solid-state 29Si NMR spectra were recorded using a Bruker
AMX-600 spectrometer. X-ray photoelectron spectroscopy (XPS) analysis
was performed using a Kratos Axis Ultra DLD instrument with monochromatic
Al (Ka) radiation. The data were analyzed using Casa-XPS software,
and two different components were fit to the N 1s signals. The energy
difference between these components was fixed at 1.8 eV.42 (link) An inductively coupled plasma optical emission
spectrometer (ICP-OES, Optima 3000DV, PerkinElmer) was used to quantify
the loss of OSNP during desorption. The pH was measured with a Milwaukee
MW 102 pH/Temp Meter. All absorbance measurements used a SpectraMax
M5 spectrophotometer from Molecular Devices.