Synthesis of Mesoporous Eu³⁺-Doped Zinc/Silicate Phosphors for Highly Selective and Sensitive Detection of Sulfide Ions

A mesoporous Eu³⁺-doped zinc/silicate phosphor with a large surface area (>100 m²g^-1) and amorphous structure was prepared in an aqueous solution without using any organic template. The residual concentration of the Zn²⁺ ion in the filtrate is lower than the standard of effluent 3.5 ppm under a pH 8-11 preparation condition. When a sulfide ion (S^2-) is present in aqueous solution, the phosphor can react with the sulfide ion to transform from the amorphous structure to the crystalline ZnS, which causes structural transformation and a subsequent decrease in luminescent intensity. This distinct phosphor with a high surface area and amorphous structure can be applied through the structure transformation mechanism for highly selective and sensitive detection of the sulfide ions at low concentrations. In addition, the luminescent efficiency was obtained from adjustments in the pH value, calcination temperature, and Eu³⁺ ion concentration. The quenching efficiency, the limit of detection (C_LOD), S^2- ion selectivity, and phosphor regeneration ability were systematically explored in sulfide ion detection tests. Due to the novel S^2- ion-induced structural transformation, we found that the amorphous Eu³⁺-doped zinc/silicate phosphors demonstrate a C_LOD sensitivity as low as 1.8 × 10^-7 M and a high Stern-Volmer constant (K_SV) of 3.1 × 10⁴ M^-1. Furthermore, the phosphors were easily regenerated through simple calcination at 500 °C and showed a K_SV value of 1.4 × 10⁴ M^-1. Overall, the Eu³⁺-doped zinc/silicates showed many advantageous properties for detecting sulfide ions, including low toxicity, green synthesis, good selectivity, high sensitivity, and good renewability.