Sonochemical synthesis of mesoporous ZnyCd1-yS quantum dots: Composition-dependent optical, electrical, dielectric, and hydrogen-generation characteristics

Mesoporous Zn_yCd_1-yS quantum dots (QDs) with mixed cubic–hexagonal phases prepared by sonochemical technique at varying Zn content. Incorporating Zn ions in the CdS lattice reduced the crystalline size and enhanced the corresponding surface areas at increasing Zn contents. The increase of Zn content in Zn_yCd_1-yS QDs increased the bandgap from 2.52 eV to 3.83 eV and enhanced the corresponding Urbach energy from 72 meV to 279 meV. Zn_yCd_1-yS QDs exhibited small electrical activation energies ranging from 249 mV to 361 mV. The effect of Zn content on the catalytic activity of Zn_yCd_1-yS QDs toward hydrogen production through NaBH₄ hydrolysis was investigated at different temperatures. Ternary alloys ZnCdS QDs exhibited higher catalytic activity than pure ZnS and CdS QDs, with Zn_0·5Cd_0·5S QDs displaying the highest hydrogen generation rate of 96 mL∙min⁻¹ g⁻¹. The increase of reaction temperature from 30 °C to 60 °C enhanced the rate constant of hydrogen production from 0.071 to 0.36 min⁻¹. Based on the pseudo-first-order equation, the estimated apparent activation energy of Zn_0·5Cd_0·5S QDs was 45.3 kJ mol⁻¹. Overall, the obtained results underscored the potential of Zn_yCd_1-yS QDs as promising catalysts for hydrogen generation.