(585j) Fluorescent Carboxyl Silicon Quantum Dots (CSiQDs) As an Efficient Scale Inhibitor and the Scale Inhibition Mechanism.

The formation of sparingly soluble salts and the simultaneous adhesion to process units, known as scaling, is one of the top operational challenges in water-based industries. Scaling is a major concern in various water-based industries due to increased resistance of mass, heat and momentum transfer, limiting process efficiency and effectiveness. Although phosphorous and sulfur-based antiscalants have long been used as the gold standard owing to their adequate inhibition performance, their potential negative environmental impacts render them less desirable. Despite recent efforts in developing green antiscalants, there has been no promising green solution since most developed green antiscalants have low calcium tolerance and unknown underlying scale inhibition mechanism. Therefore, exploitation of novel fluorescent green antiscalants might be the best solution since it doesn’t only solve environmental issues but also gives insights on scale inhibition mechanism thanks to their fluorescence properties. In this work, SiQDs were synthesized in one step from APTES using ascorbic acid as the reducing agent. The surface of the resulting product was engineered and modified by the introduction of carboxyl groups (CSiQDs) to improve water solubility and inhibition efficiency. Both modified (CSiQDs) and non-modified (SiQDs) were characterized in terms of FTIR, XPS, HRTEM, and fluorescence properties. The characterization results confirmed the successful synthesis and modification through the introduction of carboxyl groups while retaining the excitation and emission properties. The modified product was evaluated towards calcium sulfate scale at different brine stresses, temperature, and pH. The results revealed the high efficiency of the CSiQDs reaching 100% inhibition efficiency at 20 ppm dosage in a brine containing 6800 ppm of calcium and sulfate ions at 70 °C. The inhibition mechanism was investigated by fluorescence images as well as morphology analysis, by means of SEM and XRD, of scale crystals in the presence and absence of CSiQDs. The inhibitor is believed to have effect on both nucleation and crystal growth of the scale crystals. This work may help in setting the foundations for rational design of next generation of nanostructure based antiscalants.