Successive
surface reactions on hydrophilic silica substrates were
designed and performed to immobilize ethanolamine-modified magnetic
ferrite-based nanoparticle (NP) for surface characterization. The
various surfaces were monitored using sum-frequency generation (SFG)
spectroscopy. The surface of the hydrophilic quartz substrate was
first converted to a vinyl-terminated surface by utilizing a silanization
reaction, and then, the surface functional groups were converted to
carboxylic-terminated groups via a thiol–ene reaction. The
appearance and disappearance of the vinyl (CH2)
peak at ∼2990 cm–1 in the SFG spectra were
examined to confirm the success of the silanization and thiol–ene
reactions, respectively. Acyl chloride (−COCl) formation from
carboxy (−COOH) functional group was then performed for further
attachment of magnetic amine-functionalized magnesium ferrite nanoparticles
(NPs) via amide bond formation. The scattered NPs attached on the
modified silica substrate was then used to study the changes in the
spectral profile of the ethanolamine modifier of the NPs for in situ lead(II) (Pb2+) adsorption at the solid–liquid
interface using SFG spectroscopy. However, due to the limited number
of NPs attached and sensitivity of SFG spectroscopy toward expected
change in the modifier spectroscopically, no significant change was
observed in the SFG spectrum of the modified silica with magnetic
NPs during exposure to Pb2+ solution. Nevertheless, SFG
spectroscopy as a surface technique successfully monitored the modifications
from a clean fused substrate to −COCl formation that was used
to immobilize the decorated magnetic nanoparticles. The method developed
in this study can provide a reference for many surface or interfacial
studies important for selective attachment of adsorbed organic or
inorganic materials or particles.