Polyaspartic acid modified by fluorescent carbon quantum dots as an environmentally friendly scale inhibitor for calcium sulphate

Polysuccinimide (PSI), as the precursor of polyaspartic acid (PASP), can easily react with amino (-NH2) groups under mild conditions. A novel scale inhibitor, designed as PASP/N-CDs, is synthesised through the ring-opening reaction of PSI with nitrogen-doped carbon quantum dots (N-CDs). XPS, TEM, FT-IR and Raman spectroscopy are used to analyse the micro structure and spectral characteristics of synthesised inhibitors. The efficiency of PASP/ N-CDs in inhibiting calcium sulphate (CaSO4) scale is tested through static scale inhibition experiments. The comparative analysis reveals a significant enhancement in the scaling resistance of PASP/N-CDs over PASP, particularly noticeable at reduced concentrations. The scale inhibition efficiency of PASP/N-CDs reaches nearly 100 % at 5 mg/L. The underlying mechanism of scale inhibition in PASP/N-CDs is investigated using SEM and XRD. It indicates that the PASP/N-CDs inhibits the formation of CaSO4 scale via a combination of chelation, adsorption, and lattice distortion.