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Graphical abstract Highlights • Ag NPs confined in shell-in-shell hollow TiO 2 photocatalyst was constructed. • The photocatalyst exhibited a complete degradation of tetracycline. • The excellent recyclability even after acid treatment was obtained. • TC degradation mechanism and pathway was proposed. • This work opened a new pathway for exploring other photocatalysts with two shells. Abstract The complete degradation of tetracycline still is a challenge for TiO 2 -based photocatalysts under simulated solar light irradiation. To tackle this challenge, we devise Ag nanoparticles (Ag NPs) confined in shell-in-shell hollow TiO 2 photocatalyst (HTAT). This strategy mainly involves the construction of CPS@TiO 2 core-shell composites, the form of TiO 2 inner shell, AgNPs loading by photo-deposition, the assembly of TiO 2 outer shell, and phase transition of anatase TiO 2 by calcination at 450℃. All characterizations including TEM, STEM Mapping, BET, and XPS confirm the unique structure of the as-synthesized HTAT photocatalyst. As expected, the complete degradation of tetracycline (TC and TCH) can be realized by using HTAT photocatalyst under simulated solar light irradiation because its TiO 2 two shells simultaneously take part in the photodegrading reaction of TC or TCH. The transformation intermediates and degradation pathway were analyzed by LC/MS. Our work effectively overcomes the disadvantages of many previously reported TiO 2 -based photocatalysts for the incomplete degradation of tetracycline. [ABSTRACT FROM AUTHOR]