Multi-dimensional micro-/nano-reactor spheres for sustainable water treatment

Abstract

We report multi-dimensional hierarchical hollow heterojunctioned carbonaceous copper oxide (CuO)/titanium dioxide (TiO₂) spheres (HHHS) synthesized using carbonaceous spheres as the template, with Cu ions penetrating the spheres through diffusion, followed by encapsulating with a hierarchical TiO₂ shell by a solvothermal approach. This method elucidates a green synthesis pathway, applying minimal additives, to design hierarchical structured carbonaceous TiO₂ and a micro/nanostructured mesoporous hollow shell assembled from CuO/CuTi₃O₈/TiO₂ heterojunctions of 20 to 30 nm. The microreactor design allowed the photocatalyst to facilitate wider light absorption wavelengths and pollutant pathways through the HHHS. Pollutants pass through channels of hierarchical thorn-like structures with enhanced charge transfer due to the compaction of 20 nm nanoparticulates, generating reactive oxygen species which initiate pollutant degradation. The pollutants/intermediates will then be filtered and adsorbed onto the heterojunction shell, featuring a mesoporous bimodal pore distribution of 4 nm to 30 nm with an enlarged effective surface area of 30.6 m² g⁻¹. Degradation occurs due to the enhanced charge separation of heterojunctions and the concentrated reactive oxygen species (ROS) region which maintains the porosity of the shell structure. The inner hollow sphere minimizes the internal volume of the sphere and narrows the transverse distance for ROS or intermediates, thereby maximizing their interaction. This micro-/nano-reactor design optimizes pollutant degradation, adsorption and transfer to produce clean water and shows high potential for scalability and practical engineering applications for water treatment facilities to address global water scarcity.