Nano sized ZnS particles: Optical properties and preparation by coupling of biological reduction and chemical precipitation mediated with EDTA

High-purity nano ZnS particles were synthesized using a coupling reaction of biological reduction and chemical precipitation mediated with EDTA(CRBRCP-EDTA process). The results showed that the addition of EDTA with equal molar concentration to Zn²⁺ eliminated the toxicity of Zn ²⁺ to sulfate reducing bacteria (SRB), leading to growth of SRB, reduction of SO₄² and ZnS production. The characterization by XRD, EDS, SEM and TEM demonstrated that the obtained ZnS particles were highly pure and well-distributed solid spheres with diameter about 10-15 nm for primary particles and around 400 nm for secondary particles. When polyacrylamide (PAM)was incorporated in CRBRCP-EDTA process, the secondary particles diameter was reduced to less than 100 nm. PL studies further proved that the nanoparticles with smaller size exhibited strong quantum size effect and highly intense PL characteristics compared to that without EDTA-mediated ones. The FTIR studies confirmed the ZnS nanoparticles had no IR absorption.