Orange II removal by a horseradish peroxidase immobilized onto chemically modified diatomites is a combination of adsorption and oxidation processes

In this work, a horseradish peroxidase (HRP) was immobilized onto diatomites by covalent bonding. Results indicated that the enzyme loading increased when diatomites were modified with (3-Aminopropyl)triethoxysilane (APTES) and glutaraldehyde. The immobilization was confirmed by SEM/EDX, XRD, DRIFT, and TGA analysis. Higher HRP concentrations of the immobilization solution and immobilization time had also a positive effect on the enzyme loading. Orange II (OII) adsorption onto diatomites and oxidative catalytic activity was evaluated. Results demonstrated that diatomites had a low OII adsorption capacity. However, under the presence of hydrogen peroxide, the dye removal was highly increased due to the catalytic activity of the immobilized HRP. A mathematical model that adequately describes the simultaneous adsorption and enzymatic oxidation of OII in batch tests was developed. Finally, immobilized diatomites were tested in the decolourization reaction of Orange II in a fixed-bed column reactor. Column results demonstrated that the immobilized HRP remained active for at least 12 h during three sequential OII removal tests.