The nitrogen adsorption–desorption isotherm of the MgHAp/Fe3O4
(Fig. 1(c)) belonged to types I (BDDT classification). Condensation and
evaporation occurred at an intermediate relative pressure range.
Adsorbent with this type of hysteresis loop had a typical cylinder
shape [43]. At the same time, the plot of the pore size distribution
(Fig. 1(c)) was determined using the Barrett–Joyner–Halenda (BJH)
method from the desorption branch of the isotherm. The average pore
size of the MgHAp/Fe3O4 nanosphere was 13 nm. The high surface
area (52 m2
/g) and nano-scale size were beneficial to ion-exchange
and diffusion specially.
The FTIR patterns of MgHAp/Fe3O4 were shown in Fig. 1(d). The
peak around 3434 cm−1 represented the vibration of –OH groups
[44]. The peaks at 1013 cm−1 and 557 cm−1 were characteristic of the
PO4
3− stretching vibration [45]. In addition, it was noted that a band at
581 cm−1 appeared in the FTIR spectrum was attributed to Fe3O4
(Fe-O stretching vibration) [44]. These peaks confirmed the successful
composite of MgHAp and Fe3O4.
The magnetic separation process of MgHAp/Fe3O4 is shown in
Fig. 1(f). With the strong magnet, it just needed 50 seconds to achieve
the separation between the MgHAp/Fe3O4 and the Cu2+ solution.
MgHAp/Fe3O4 has a very good magnetic property. It is easy to realize
the solid–liquid separation