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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]