Synthesis of oxides-on-oxides interfaced spheres with suppressed photoexcited electron-hole recombination

Oxide-on-oxide interfaces are formed by peculiar chemical bonds that give rise to intriguing phenomena such as superconductivity, magneto-electric coupling, and quantum Hall effect, making them promising in a variety of technological applications. However, the conventional design of oxide-on-oxide particle systems results in a non-ideal spatial distribution of isomorphic epitaxial structures, leading to poor interface stability and catalytic activity. This study demonstrates a rational synthesis strategy for developing NiO/TiO₂ contiguous interfaces in which NiO is highly-dispersed and forms rich interfacial polymorphism with TiO₂ in concentrated spheres. The process involves the self-assembly of NiO using cationic dodecyltrimethylammonium bromide (DTAB), followed by the use of NiO_DTAB as a core to grow the thick carbon layer with abundant C[dbnd]O and OH⁻ to host Ti⁴⁺ ions, and finally calcination in air to produce NiO/TiO₂ spheres. SEM, X-ray diffraction and electron microscopy are primarily utilized to reveal material formation mechanisms. The resulting NiO/TiO₂ p-n heterojunction spheres outperformed commercial TiO₂ or conventional NiO/TiO₂ nanoparticles in solar hydrogen evolution. It is anticipated that this work will contribute to the rational synthesis of various inorganic oxide-on-oxide spheres and study of contiguous interfacial chemical bonding organizations both inside and outside of complex spheres.