Enhanced inhibition of calcium phosphate scale by polyaspartic acid modified with sulfur-nitrogen co-doped carbon quantum dots

Abstract

In this study, a novel hybrid scale inhibitor, sulfur‑nitrogen co-doped carbon quantum dots modified polyaspartic acid (SN-CDs/PASP), was developed to mitigate calcium phosphate (CaP), an area that remains largely underexplored. The synthesis and properties of the SN-CDs/PASP composite were characterized using Raman, FTIR, XPS, and TEM. Static scale inhibition experiments and electrochemical tests revealed that the composite significantly outperforms pure PASP, achieving a maximum inhibition rate of 98 % at 10 mg/L with an optimized Polysuccinimide (PSI):SN-CDs ratio of 10:1. Unlike traditional scale inhibitors such as phosphonates or ordinary PASP, which lack multifunctionality and exhibit limited specific surface area, the SN-CDs/PASP composite offers increased surface area due to the nanoscale SN-CDs, enhancing ion chelation. Compared to other nanomaterial-based inhibitors, such as common carbon quantum dots, the sulfonic and amino groups from SN-CDs further improve chelation and electrostatic repulsion, disrupting CaP crystal formation. Additionally, its fluorescence intensity correlates linearly with concentration, enabling real-time dosage monitoring—a feature absent in conventional inhibitors. This environmentally friendly composite provides new insights into advanced, high-efficiency scale inhibition for industrial applications.