Preparation of photoactive chitosan–niobium (V) oxide composites for dye degradation

From an environmental standpoint, heterogeneous photocatalysis is a significant cutting-edge technology for application in water purification. Moreover, immobilising an appropriate catalyst onto the surface of a natural organic polymer presents a number of additional advantages including low-cost, high catalytic activity and extensive potential for reuse. In the present work, composites of niobium (V) oxide and chitosan (Chit/Nb) were prepared with semiconductor loadings in the range 0–13.9% attached to the polymer surface. Scanning electron microscopy (SEM) and niobium mapping with X-ray energy dispersive spectrometry showed that the niobium (V) oxide was homogeneously dispersed over the surface of the composites. Lewis and Bronsted acid sites were present on the biopolymer surfaces, the acidic character of which increased with the amount of semiconductor attached. The Chit/Nb composites were used to photocatalyse the degradation of indigo carmine dye in aqueous solution by UV irradiation. The kinetic constants were obtained by application of the Langmuir–Hinshelwood equation and determined to be 5.32, 5.90 and 9.10 μmol L−1 h−1, respectively, for Chit/Nb composites with semiconductor loadings of 3.9, 9.3 and 13.9%, respectively. Whilst the thermal stabilities of the Chit/Nb composites were slightly lower than that of the pure biopolymer, the materials presented high catalytic efficiencies that remained unaltered after 15 cycles of reuse.