A symbiotic hetero-nanocomposite that stabilizes unprecedented CaCl(2)-type TiO(2) for enhanced solar-driven hydrogen evolution reaction

Symbiotic hetero-nanocomposites prevail in many classes of minerals, functional substances and/or devices. However, design and development of a symbiotic hetero-nanocomposite that contains unachievable phases remain a significant challenge owing to the tedious formation conditions and the need for precise control over atomic nucleation in synthetic chemistry. Herein, we report a solution chemistry approach for a symbiotic hetero-nanocomposite that contains an unprecedented CaCl(2)-type titania phase inter-grown with rutile TiO(2). CaCl(2) structured TiO(2), usually occurring when bulk rutile-TiO(2) is compressed at an extreme pressure of several GPa, is identified to be a distorted structure with a tilt of adjacent ribbons of the c-axis of rutile. The structural specificity of the symbiotic CaCl(2)/rutile TiO(2) hetero-nanocomposite was confirmed by Rietveld refinement, HRTEM, EXAFS, and Raman spectra, and the formation region (TiCl(4) concentration vs. reaction temperature) was obtained by mapping the phase diagram. Due to the symbiotic relationship, this CaCl(2)-type TiO(2) maintained a high stability via tight connection by edge dislocations with rutile TiO(2), thus forming a CaCl(2)/rutile TiO(2) heterojunction with a higher reduction capacity and enhanced charge separation efficiency. These merits endow symbiotic CaCl(2)/rutile TiO(2) with a water splitting activity far superior to that of the commercial benchmark photocatalyst, P25 under simulated sunlight without the assistance of a cocatalyst. Our findings reported here may offer several useful understandings of the mechanical intergrowth process in functional symbiotic hetero-nanocomposites for super interfacial charge separation, where interfacial dislocation appears to be a universal cause.