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

Abstract Four kinds of spinel NiAl 2 O 4 were synthesized by the polyacrylamide gel method using Al 2 (SO 4 ) 3 ·18H 2 O and Al(NO 3 ) 3 ·9H 2 O as aluminum salts and anhydrous NiSO 4 and NiSO 4 ·6H 2 O as nickel salts. The effects of different aluminum salts and nickel salts on the structure, optical and photocatalytic activity of spinel NiAl 2 O 4 were confirmed by various characterizations. There is no NiO impurity in the spinel NiAl 2 O 4 synthesized with Al 2 (SO 4 ) 3 ·18H 2 O as aluminum salt, while NiAl 2 O 4 , NiO and C–O functional group coexist in the target product with Al(NO 3 ) 3 ·9H 2 O 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, initial pH and catalyst content on the photocatalytic activity of spinel NiAl 2 O 4 and the main active species involved in the reaction were investigated. The degradation percentage of spinel NiAl 2 O 4 synthesized with Al 2 (SO 4 ) 3 ·18H 2 O as aluminum salt and NiSO 4 ·6H 2 O 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 NiAl 2 O 4 .