Fluorescence sensing and adsorption kinetics of Gd-doped AgInS2 I-III-VI quantum dots - A case study of Ag+ ions interactions

Bambesiwe M May; Olayemi J Fakayode; Mokae F Bambo; Ajay K Mishra; Edward N Nxumalo

doi:10.1016/j.heliyon.2023.e19020

Fluorescence sensing and adsorption kinetics of Gd-doped AgInS₂ I-III-VI quantum dots - A case study of Ag⁺ ions interactions

Heliyon. 2023 Aug 7;9(8):e19020. doi: 10.1016/j.heliyon.2023.e19020. eCollection 2023 Aug.

Authors

Bambesiwe M May^{1

2}, Olayemi J Fakayode¹, Mokae F Bambo², Ajay K Mishra^{3

4}, Edward N Nxumalo¹

Affiliations

¹ Institute for Nanotechnology and Water Sustainability (iNanoWS), College of Science, Engineering, and Technology, University of South Africa, Florida Campus, 28 Pioneer Avenue, Roodepoort, 1709, Johannesburg, South Africa.
² DSI/Mintek Nanotechnology Innovation Centre, Advanced Materials Division, Mintek, 200 Malibongwe Drive, Randburg, Johannesburg, South Africa.
³ Department of Chemistry, Durban University of Technology, Steve Biko Road, Durban, 400, South Africa.
⁴ Department of Chemical and Metallurgical, Vanderbijlpark Campus, Vaal University of Technology, Private Bag X021, Vanderbijlpark, South Africa.

Abstract

The poor fluorescence properties of magneto-fluorescent paramagnetic-ion (Gd, Mn, or Co) doped I-III-VI quantum dots (QDs) at higher paramagnetic-ion doping concentrations have limited their use in magnetic-driven water-based applications. This work presents, for the first time, the use of stable magneto-fluorescent Gd-doped AgInS₂ QDs at high Gd mole ratios of 16, 20, and 30 for the fluorescence detection and adsorption of Ag⁺ ions in water environments. The effect of pH, initial concentration, contact time, and adsorbent dosage were systematically evaluated. The AgInS₂ QDs with the least Gd mole ratio (16) exhibited the best fluorescence characteristics (LOD = 0.88, R² = 0.9549) while all materials showed good adsorption properties under optimized conditions (pH of 2, initial concentration of 30 ppm, contact time of 10 min and adsorbent dosage of 0.02 g) and a pseudo 2nd order reaction was followed. The adsorption mechanism was proposed to be a combination of ion-exchange, electrostatic interaction, complexation, and diffusion processes. Application in environmental wastewater samples revealed complete removal of Ag ⁺ ions alongside Ti²⁺ Pb²⁺, Ni²⁺, Cr³⁺, and Zn²⁺ ions.

Keywords: Adsorption; Magneto-fluorescent; Quantum dots; Sensing.