Carboxyl-Engineered Silicon Quantum Dots (CSiQDs) as an Efficient Scale Inhibitor: Formulation Inhibition Mechanism

Multiple recent initiatives have focused on developing environmentally friendly antiscalants/scale inhibitors; however, most of the investigated green antiscalants have demonstrated low scaling ion tolerance and concealed scale inhibitor-mineral crystal interaction. New fluorescent green antiscalants, due to their fluorescence properties, appear to be among the best solutions, since they both solve critical environmental issues and offer insights into the inhibition mechanism. In this work, the surface of synthesized SiQDs was engineered by introducing carboxyl moieties. The functionalized/surface engineered Carboxyl Silicon Quantum Dots (CSiQDs) were characterized in terms of FTIR, XPS, HRTEM, DLS, zeta-potential, and fluorescence properties. The characterization results confirmed successful functional tailoring through the introduction of carboxyl groups while retaining the excitation and emission properties. The performance of the engineered CSiQDs was evaluated, for the first time, using calcium sulfate scale at different brine stresses, temperatures, and pHs. The results revealed the exceptional high efficiency of the CSiQDs, reaching 100% at a 20-ppm dosage in a brine containing 6,600 ppm of calcium and sulfate ions at 70 °C. The calcium sulfate, formed in the gypsum phase, scale inhibition mechanism was investigated using fluorescence images and morphology analysis by means of XRD and SEM in the presence and absence of CSiQDs. The inhibitor is believed to affect gypsum crystal nucleation and growth. This work may lay a foundation for the rational design of next-generation nanophotonic antiscalants.