Nano spinel NiAl₂O₄: structure, optical and photocatalytic performance evaluation and optimization

Four kinds of spinel NiAl₂O₄were synthesized by the polyacrylamide gel method using Al₂(SO₄)₃·18H₂O and Al(NO₃)₃·9H₂O as aluminum salts and anhydrous NiSO₄and NiSO₄·6H₂O as nickel salts. The effects of different aluminum salts and nickel salts on the structure, optical and photocatalytic activity of spinel NiAl₂O₄were confirmed by various characterizations. There is no NiO impurity in the spinel NiAl₂O₄synthesized with Al₂(SO₄)₃·18H₂O as aluminum salt, while NiAl₂O₄, NiO and C-O functional group coexist in the target product with Al(NO₃)₃·9H₂O as aluminum salt, and C-O functional group and NiO inhibits the photocatalytic activity of the system. Based on photocatalytic experiment, response surface methodology and free radical verification experiment, the influence of experimental parameters including synthesis pathway, initial drug concentration, initialpHand catalyst content on the photocatalytic activity of spinel NiAl₂O₄and the main active species involved in the reaction were investigated. The degradation percentage of spinel NiAl₂O₄synthesized with Al₂(SO₄)₃·18H₂O as aluminum salt and NiSO₄·6H₂O as nickel salt was 86.3% at the initial concentration of 50 mg l^-1,pH= 5.33 and catalyst content of 1 g l^-1. The mechanism investigation confirmed that the C-O functional group plays the dual role of impurity level and electron transfer in the degradation of tetracycline hydrochloride by spinel NiAl₂O₄.