A polyacrylamide gel method has been used to synthesize
spinel
type nano-CuB2O4 with cubic phase (B = Al) and
tetragonal phase (B = Cr and Fe). The phase structure, functional
group information, and charge state characterization confirm that
the CuAl2O4 oxides contain no impurities, while
CuCr2O4 and CuFe2O4 contain
CuO impurities. The CuAl2O4 oxides exhibit a
small particle size of 25 nm, high optical band gap (E
g) value, high adsorption capacity for the adsorption
of Congo red dye, and high photocatalytic activity for the photocatalytic
degradation of tetracycline hydrochloride (TCH), which are much better
than those of the CuCr2O4 and CuFe2O4 oxides. The high adsorption capacity for the CuAl2O4 oxides can be ascribed to the larger zero charge
point (pHPZC) values, unique crystal structure, pore filling,
electrostatic interaction, and hydrogen bond force. Photocatalytic
degradation of antibiotics by CuB2O4 (B = Al,
Cr, and Fe) shows high selectivity and B ion and crystal structure
dependencies. The CuAl2O4 oxides exhibit high
photocatalytic activity for the photocatalytic degradation of TCH
and oxycline hydrochloride (OCH) and poor photocatalytic activity
for the photocatalytic degradation of metformin hydrochloride (MFH)
and naproxen sodium (NPS). Cyclic stability tests and XRD results
further confirm that CuAl2O4 oxide is recyclable
and stable. The high photocatalytic activity of CuAl2O4 oxides was explained in terms of the synergetic effects of
the optical absorption coefficient, specific surface area, crystal
structure, adsorbed oxygen concentration, chemical structure of the
antibiotic, and conduction band and valence band potentials. The trapping
experiments confirmed that TCH photodegradation in this reaction system
occurs via photogenerated holes (hVB
+) and superoxide
radicals (•O2
–).