Hemoglobin immobilized within mesoporous TiO2–SiO2 material with high loading and enhanced catalytic activity

Hemoglobin (Hb) is immobilized within the channels of mesoporous TiO2–SiO2 materials. It was found that mesoporous TiO2–SiO2 material can immobilize more Hb than mesoporous SiO2 and the greatest loading is achieved on the sample with an optimized Ti/Si molar ratio of 4 : 6. The high loading of Hb in mesoporous TiO2–SiO2 material is attributed to the increased electrostatic interaction between Hb and the pore wall which possesses enhanced electron donating capacity after the lower electronegative Ti substitutes Si in the framework of mesoporous SiO2. Unlike its easy leaching from the pore of mesoporous SiO2, Hb can hardly be released once immobilized within mesoporous TiO2–SiO2 material. The immobilized Hb retains not only its structure like that of the native one in the aqueous solution, but also the catalytic activity. Specifically, Hb has a higher catalytic activity when immobilized within mesoporous TiO2–SiO2 material than that when immobilized within mesoporous SiO2. Furthermore, the catalytic activity of Hb increases when the Ti/Si molar ratio of mesoporous TiO2–SiO2 material changes from 2 : 4 to 4 : 6, which stems from the increasing Hb density in the pore of mesoporous TiO2–SiO2 material. However, the catalytic activity decreased when the Ti/Si molar ratio became 6 : 4 due to the low occupational volume of Hb.