MHC synthesis and characterization
The MHC synthesis steps and structure are shown in Figure 2. Briefly,
the organic-inorganic covalently bound MHC was synthesized in one step
by mixing Fe3+, Fe2+, and silane
coupling agents in proportion, slowly titrating alkalinity, and ageing.
The TEM image (Figure 3a) shows that MHC has an irregular shape.
Comparing to the Fe3O4 TEM image (Figure
3b), it can be seen that the black component in MHC is
Fe3O4. The periphery of
Fe3O4 is the highly-crosslinked polymer
of the organic silane coupling agent. It shows that MHC is a
cross-linked integral structure consisting of magnetic components and
organic compounds.
The presence of silane coupling agents will form Si-O-Si bonds.
Generally, the asymmetric stretching peak of Si-O-Si is at 1046
cm-1.18 Shown in the infrared
absorption spectrum of MHC (Figure 3c), there is a clear absorption peak
at 1028 cm-1. It may be related to red shift of the
Si-O characteristic peak induced by Fe replacing Si in
Si-O-Si.19 This indicates that the inorganic Fe
components in MHC are coupled to organic components through covalent
bonds of Si-O-Fe, which is different from MSC that simply physically
mixes magnetic seeds and coagulants. Other absorption wavenumbers are
listed in Table S1. In addition, MHC has a high zeta potential
(>25 mV) over a wide pH range of 3–11 (Figure S1), which
can be attributed to the introduction of positively-charged quaternary
ammonium groups.