Novel sodium and potassium carbon quantum dots as forward osmosis draw solutes: Synthesis, characterization and performance testing

Abstract

Novel draw solutes based on potassium- and modified sodium-functionalized carbon quantum dots (K-CQDs and Na-CQDs) were prepared for seawater desalination. The characteristics of draw solutes were determined using Fourier Transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, and thermal gravimetric analysis (TGA). The results of the FO system with K-CQDs and deionized water (DI) as a feed revealed a high water flux of 10.94–13.924 L/m2.h (LMH), very low reverse solute flux of 0.0161–0.0253 g/m2.h (gMH), and specific reverse solute flux of 0.0015–0.0018 at a concentration of 0.3–0.5 g/mL. The water flux of K-CQDs at a concentration of (0.3–0.5) g/mL for seawater and 0.5 g/mL for Real Persian Gulf (RPG) water (Arabian Gulf) was (3.779–5.371) LMH and 6.1662 LMH, respectively. For Na-CQDs with DI, the obtained water flux, reverse solute flux, and specific reverse solute flux were 10.3433–11.935 LMH, 0.0414–0.0621 gMH of 0.004–0.0052, respectively at a concentration of 0.3–0.5 g/mL at 29 °C. The fluxes of synthetic seawater and RPG with K-CQDs and Na-CQDs were 5.37 and 6.16 LMH and 2.78 and 3.78 LMH, respectively, at CQDs concentration of 0.5 g/mL. The stability test showed that there was only a slight decrease in the flux of 2 % after three-cycle of FO operations with K-CQDs.