Green synthesis of fluorescent carbon quantum dots from bagasse: inhibition of calcium sulphate scales

The conversion of biomass waste generated in large amounts to value-added materials and energy can reduce environmental pollution, atmospheric CO2 emissions and waste disposal costs in a circular economy. Chemicals, such as strong acids and organophosphates, commonly used for industrial water treatment, are harmful and cause environmental pollution. Therefore, safe and eco-friendly water treatment agents must be developed. In this study, carbon quantum dots (CQDs) were successfully synthesised to be used as scale inhibitors via a green and simple one-step hydrothermal method using bagasse (an agricultural waste) as the carbon source. The structure of the CQDs was characterised via TEM, XRD and Raman analysis. FTIR and XPS results demonstrated that the CQDs surface contained abundant oxygen-containing groups. Fluorescence spectra confirmed that the CQDs have excellent stability and are promising for online monitoring of self-dose. The scale inhibition efficiency of CaSO4 scale at CQDs dosage of 17.5 mg L−1 measured using the static scale inhibition method reached 100%, which is better than that obtained in the case of traditional scale inhibitors. Moreover, the CQDs exhibited an outstanding scale inhibition effect at higher temperatures and in strongly alkaline environments. The scale inhibition effect of CQDs was further verified using XRD and SEM. In summary, the CQDs obtained from bagasse are fluorescent and environmentally friendly scale inhibitors, with promising applications in industrial water treatment.