Adsorption of Dyes on Hierarchical Mesoporous TiO₂ Fibers and Its Enhanced Photocatalytic Properties

In this Article, the surface characteristics of acid-modified continuous TiO2 fibers, the adsorption of dyes, and the photocatalytic degradation of dye pollutants under UV and visible light irradiation were investigated. After HF extraction of silicon, a hierarchical mesoporous structure is produced. The −OH groups located on the surface were more resistant to exchange with F− because of the inductive effect on surface Ti4+ centers originating from adjoining electronegative F− ions. After protonation of the HF-modified fibers by HNO3 treatment, the photodegradation percentage of X-3B on the TiO2 fibers reached 98% in 45 min under visible light irradiation, and the first-order rate constant increased by a factor of 163.4. The high visible light activity was mainly attributed to a synergetic effect of the hierarchical mesoporous structure and the strong adsorption of X-3B upon the protonated surface. The adsorption isotherms showed that the adsorption of X-3B on acid-modified TiO2 followed the Langmuir model with a maximum adsorption capacity of 19.03 mg/g, 6-fold higher than the unmodified TiO2. The nature of the X-3B sorption was spontaneous and thermodynamically favorable. The sorption kinetics was best described by the pseudo-second-order model.