3.2 Improved adsorption performance
The adsorption performance of membrane adsorber with CR and MB, as well
as its kinetic parameters are shown in Figure 6 . The specific
details of the kinetic model parameters are illustrated in Table
S1 . It can be seen that compared with the HKUST-1 powder, the
adsorption capacity and the adsorption rate of the HP-HKUST-1 powder for
CR and MB can be increased obviously. Specifically, for the HP-HKUST-1
powder, the adsorption capacity (qt ) for CR with
458 mg g-1 and for MB with 227 mg
g-1 can be achieved within 70 min. However, for the
HKUST-1 powder, the adsorption capacity for CR with only 155 mg
g-1 and for MB with only 90 mg g-1can be achieved within 70 min. Compared with the HKUST-1 powder , the
equilibrium adsorption capacity (qe ) for both CR
and MB can be increased about three times by the HP-HKUST-1 powder. In
term of the adsorption rate constant (k2 ), the
value can be increased about twice for both CR and MB adsorption. The
increase of the adsorption capacity can be attributed to the increase of
the adsorption active sites after the mesopores introduced into HKUST-1.
The adsorption by HKUST-1 for CR and MB is mainly based on the formation
of hydrogen bonds between the open oxygen active sites and the
adsorbate, the superposition of van der Waals forces, electrostatic
forces, π-π bonds, as well as the coordination bonds between the
unsaturated metal copper ion active sites of HKUST-1 and the adsorbates,
as shown in Figure 7 28. The surface area of
the HKUST-1 can be increased after the introduce of the mesopores in
HKUST-1, leading to the increase of adsorption amount for CR and MB
owing to van der Waals forces and electrostatic forces. More unsaturated
metal active sites and oxygen active sites can be exposed as mesopores
introduced into HKUST-1, leading to an additional adsorption amount
owing to hydrogen bonds and coordination bonds as shown inFigure 7 . Specifically, for CR adsorption, more unsaturated
Cu2+ are appeared as lattice vacancies generated in
the topological structure of HP-HKUST-1, leading an additional
adsorption interaction produced by coordination bond between
Cu2+ and the N and O atoms of CR set off. Besides, the
interaction of electrostatic forces between Cu2+ and
the -SO3- of CR can be enhanced as a
lager surface area of HP-HKUST-1. Moreover, the interaction of π-π bonds
can be also enhanced since volume-filling adsorption can occur during
the adsorption of HP-HKUST-1 in addition to monolayer and multilayer
adsorption with the introduce of mesopores29. For MB
adsorption, coordination bond between Cu2+ and the N
atoms of MB will occur with the introduce of mesopores. In addition, the
interaction of π-π bonds can be enhanced for the reason of
volume-filling adsorption.