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In this article, a simple and mild preparation of secondary pores are reported, for the first time, with uniform and tunable sizes (in a wide range of 0.9-4.8 nm) in the walls highly connecting the primary mesochannels in 3D mesopore networks. The uniform secondary pores are obtained by using ordered 2D hexagonal mesoporous anatase TiO2-SiO2 nanocomposites as precursors, NaOH as an etchant via an 'extracting SiO2' approach. The strategy here adopts diluted NaOH solution, appropriate extraction temperature, and solid/liquid ratio. The photocatalytic degradation rates of Rhodamine B (0.347 min-1), Acid Red 1 (0.0487 min-1), microcystin-LR (1.66 min-1) on the representative resultant nanocomposite are very high, which are 4.63, 11.7, 1.84 times that of the precursor without secondary mesopores; even up to 18.9, 8.21, 4.66 times that of P25, respectively. These results clearly demonstrate that the secondary mesopores play an overwhelming role to the increments of activities. The mesoporous anatase-silica nanocomposites with secondary mesopores present unprecedented-high degradation activities to various organic pollutants in the mesoporous metal-oxides-based materials reported up to now and are considerably stable and reusable. It is believed that the fundamentals in this study will provide new insights for rational design and preparation of 3D highly interconnected mesoporous metal-oxides-based materials with super-high performances. [ABSTRACT FROM AUTHOR]

• Mesoporous anatase titania with 3D large secondary mesopores was prepared. • The preparation approach is mild, simple and facilely reproducible. • The photocatalyst with 3D large secondary pores displays quite excellent activities. • The activities are far higher than that of P25 photocatalyst and the parent sample. • The photocatalyst with 3D large secondary mesopores is rather stable and reusable. A mesoporous titania (SN2) with three-dimensional (3D) large secondary mesopores (6.2 nm) highly connecting the mesochannels was prepared employing the method of first synthesizing an ordered 2D hexagonal mesoporous titania-silica nanocomposite (SN1) via "synchronous-assembly" of inorganic precursors with surfactant molecules, then "extracting silica". Our tactic adopts a large amount of silica, a high crystallization temperature and mild silica extraction. The 3D interconnectivities of the resultant mesochannels are quite high, but the mesostructures are retained intact. Titania is fully anatase crystalline with uniform nanocrystals size (11.2 nm) and a high specific surface area (∼ 174 m2 g−1). This strategy is gentle, simple and easily reproducible. SN2 presents extremely-high photocatalytic degradation activities to anionic azo dyes like acid red 1 and reactive brilliant red X3B, which reach 55.9 and 51.1 times that of commercial P25 photocatalyst, even up to 87.0 and 84.7 times that of SN1, respectively; and far higher than that of the contrast sample (CS) possessing 3D small secondary mesopores (2.7 nm). Additionally, SN2 also displays a very high activity to microcystin-LR, which is much higher than that of P25 and CS, respectively. Our results clearly indicate that the large secondary mesopores play a key role in the great increases of activities. Moreover, our photocatalyst is considerably stable and reusable. Such results have hitherto not been seen in the literature. Furthermore, this method would pave the way for the rational design and preparation of ordered mesoporous other metal-oxides with large secondary mesopores and unexpected performances. [ABSTRACT FROM AUTHOR]