Urchin-like LaPO₄ hollow spheres were successfully synthesized by a facile solution route using citric acid (CA) as a structure-directing agent. The size of the three-dimensional (3D) hollow spheres was tuned by changing the concentration of CA. The formation mechanism of the 3D LaPO₄ hollow spheres was revealed by studying the time-dependent morphology evolution process. Importantly, compared with monodispersed one-dimensional (1D) LaPO₄ nanorods, the 3D LaPO₄ hollow spheres self-assembled from nanorods showed a 6.8-fold enhancement in photocatalytic activity for CO₂ reduction, which is attributed to the synergistic effect of their hierarchical hollow structure, higher light-harvesting capacity, and faster electron transfer. Our findings provide not only a simple, facile method for the synthesis of hierarchical hollow micro/nanoarchitectures but also an efficient route for enhancing the photocatalytic performance.

A facile approach for the heterogenization of transition metal catalysts using non-covalent interactions in hollow click-based porous organic polymers (H-CPPs) is presented. A catalytically active cationic species, [Ru(bpy)₃]²⁺ (bpy = 2, 2'-bipyridyl), was immobilized in H-CPPs via electrostatic interactions. The intrinsic properties of [Ru(bpy)₃]²⁺ were well retained. The resulting Rucontaining hollow polymers exhibited excellent catalytic activity, enhanced stability, and good recyclability when used for the oxidative hydroxylation of 4-methoxyphenylboronic acid to 4-methoxyphenol under visible-light irradiation. The attractive catalytic performance mainly resulted from efficient mass transfer and the maintenance of the chemical properties of the cationic Ru complex in the H-CPPs.