CdS Quantum Dots in Hierarchical Mesoporous Silica Templated on Clay Nanotubes: Implications for Photocatalytic Hydrogen Production

A scalable and efficient photocatalyst is a key factor for sustainable hydrogen production. For the first time, clay nanotube-templated mesoporous silica of MCM-41 type was used as an efficient carrier for photocatalytic nanoparticles. 4–5 nm CdS quantum dots (QDs) were synthesized in situ on the surface of this hierarchical aluminosilicate. The influence of the QD composition on the structural, spectral, and photocatalytic properties was investigated. A series of photocatalysts with various QD sizes (3.2–4.8 nm) and band gaps (2.46–2.66 eV) were obtained. Optimization of the CdS and cocatalyst (Ru) concentration resulted in an efficient visible light photocatalyst for hydrogen production. The photocatalytic activity was tested in an aqueous solution of Na2S/Na2SO3 under 30 W 450 nm diode illumination. The hydrogen evolution rate reached 2600 μmol/gcat·h (apparent quantum efficiency of 15%) for the system with 15.0 wt % of CdS doped with 0.2 wt % of Ru, which corresponds to the rate of hydrogen production of 17.1 mmol per hour counting on the active phase. The material demonstrated almost 100% efficiency of the catalytically active phase. It showed better catalytic activity in comparison to MCM-41 due to the hierarchical structure and presence of Al that stimulated electron transfer during the photocatalytic reaction.