Dendritic Fibrous Nano Silica–Titania for High-Performance Photocatalytic Hydrogen Evolution

Abstract

A crucial factor for the success of hydrogen (H₂) as the backbone of energy transformation is the efficient production of green H₂, especially through the solar-to-hydrogen process. The key to greatly improving photocatalytic H₂ evolution lies in the design of catalyst materials, where nanostructure engineering plays a pivotal role in driving these advancements. Engineering the nanostructure of TiO₂ as a photocatalyst can significantly drive up its H₂ evolution performance by benefiting from the created large surface area and the suppressed charge recombination. Here we show the synthesis of dendritic fibrous nano silica–titania (DFNST) using in situ seed-microemulsion crystallization which demonstrate high performance H₂ evolution even without the addition of any cocatalyst. The impact of different TiO₂ crystalline phases on the formation of the DFNST composites and their H₂ photogeneration performance under visible light is thoroughly investigated. Synthesizing the composites using a low-temperature reflux method enhances the textural properties of the TiO₂. Significant influence of the inclusion of anatase, rutile, and mixed rutile–anatase TiO₂ phases on the morphology, optical, and catalytic characteristics of the DFNST is revealed. The formation of Si–O–Ti bonds acting as electron transfer bridges between TiO₂ and the SiO₂ framework boosts the photocatalytic activity. On the other hand, the increased hydrophilicity in DFNST_a and DFNST_m enhanced water molecule uptake, contributing to efficient H₂ ion generation and interaction with electrons to produce H₂. Based on our current finding, the surface area plays a key role in enhancing the photocatalytic H₂ evolution by providing the surface active sites, which supports other conditions, such as mesoporosity, band gap, and hydrophilicity, and is combined with defect control for facilitating effective charge carrier transfer and separation in the homojunction system, as observed in the mixed-phase DFNST_m that exhibit the highest H₂ photogeneration rate.