posted on 2021-01-20, 21:13authored byRikhotso
V. Xikhongelo, Fanyana M. Mtunzi, Paul N. Diagboya, Bamidele I. Olu-Owolabi, Rolf-Alexander Düring
Polyamidoamine functionalized graphene
oxide–SBA-15 mesoporous
composite (PGOSBA) was synthesized, characterized, and examined for
aqueous adsorption of metals (As(III) and Cd(II)) and emerging pollutants
(ciprofloxacin, ivermectin, and tetracycline). The adsorption data
were explained with kinetics and adsorption isotherm models. PGOSBA
is mesoporous, but has lower Brunauer–Emmett–Teller
(BET) surface area and pore dimensions in comparison to the amine-functionalized
SBA-15 (SBA-15-NH2). Infrared spectra peaks peculiar to
the individual constituents were observed in the PGOSBA, which exhibited
thermal stability in-between those of its SBA-15-NH2 and
graphene oxide (GO) constituents. The basic structural lattices of
individual constituents were unaffected in the PGOSBA morphology,
which was covered by GO sheet-like structures. The adsorption of Cd(II),
As(III), ciprofloxacin, and ivermectin attained equilibrium at 240,
20, 180, and 720 min, respectively. The adsorption rate data for Cd(II)
fitted the pseudo-second-order kinetics model, while As(III), ciprofloxacin,
and ivermectin adsorption fitted the fractal pseudo-second-order kinetics
model better. PGOSBA exhibited one optimum adsorption pH for Cd(II)
(pH 5), while two pH points were recorded for ivermectin (a lower
peak at pH 3 and a higher one at pH 9). The Cd(II) and ivermectin
adsorption processes were spontaneous and endothermic; an increase
in temperature up to ≈30 °C slightly enhanced Cd(II) adsorption
(≤5%), as well as ivermectin (≥15%), but to an extent;
a higher temperature increase (≈40 °C) may result in lower
adsorption (≤2%) than at ≈30 °C. Multiple sorption
phenomena including electrostatic interactions, multilayer adsorption
due to π–π interactions, as well as pore filling
were involved in the pollutants removal processes. The PGOSBA adsorption
capacities for Cd(II), As(III), tetracycline, and ciprofloxacin are
92.4, 22.3, 29.2, and 24.6 mg/g, respectively, while it is 291.8 μg/g
for ivermectin. The adsorbent could lower ivermectin in low-concentration
ivermectin solutions (<80 μg/L) to less than 8.5 μg/L.
The PGOSBA reusability for ivermectin adsorption over three consecutive
cycles of adsorption, desorption, and reuse was ≥95%. These
results imply that the PGOSBA adsorbent would be economically viable
for potential use in water treatment processes.