title: Surface Properties and Photocatalytic Activities of the Colloidal ZnS:Mn Nanocrystals Prepared at Various pH Conditions.
abstract: Water-dispersible ZnS:Mn nanocrystals (NC) were synthesized by capping the surface with mercaptoacetic acid (MAA) molecules at three different pH conditions. The obtained ZnS:Mn-MAA NC products were physically and optically characterized by corresponding spectroscopic methods. The UV-Visible absorption spectra and PL emission spectra showed broad peaks at 310 and 590 nm, respectively. The average particle sizes measured from the HR-TEM images were 5 nm, which were also supported by the Debye-Scherrer calculations using the X-ray diffraction (XRD) data. Moreover, the surface charges and the degrees of aggregation of the ZnS:Mn-MAA NCs were determined by electrophoretic and hydrodynamic light scattering methods, indicating formation of agglomerates in water with various sizes (50-440 nm) and different surface charge values accordingly the preparation conditions of the NCs (-7.59 to -24.98 mV). Finally, the relative photocatalytic activities of the ZnS:Mn-MAA NCs were evaluated by measuring the degradation rate of methylene blue (MB) molecule in a pseudo first-order reaction condition under the UV-visible light irradiation. As a result, the ZnS:Mn-MAA NC prepared at the pH 7 showed the best photo-degradation efficiency of the MB molecule with the first-order rate constant (kobs) of 2.0 × 10-3·min-1.
authors.affiliation: Department of Chemistry, Institute of Nanosensor and Biotechnology, Center for Photofunctional Energy Materials (GRRC), Dankook University, 152 Yongin-si, Suji-ku, Jukjeon-ro, Gyunggi-do 448-701, South Korea. cshwang86@hotmail.com.
authors.forename: Jungho
authors.initials: J
authors.lastname: Heo
authors.affiliation: Department of Chemistry, Institute of Nanosensor and Biotechnology, Center for Photofunctional Energy Materials (GRRC), Dankook University, 152 Yongin-si, Suji-ku, Jukjeon-ro, Gyunggi-do 448-701, South Korea. cshwang@dankook.ac.kr.
authors.forename: Cheong-Soo
authors.initials: CS
authors.lastname: Hwang
keywords: MAA capping; ZnS:Mn; aggregations; methylene blue degradation; photocatalytic activities; water-dispersible