N, S-carbon quantum dots as inhibitor in pickling process of heat exchangers for enhanced performance in multi-stage flash seawater desalination

The heat exchanger in multi-stage flash seawater desalination needs to be pickled during long-term service to remove oxidation products on the copper surface. In this paper, we introduce a method for preparing carbon quantum dots from biowaste, and explore their ability to inhibit the corrosion of copper in sulfuric acid and its corrosion inhibition mechanism. Firstly, the UV–vis spectra, microstructure, tissue composition of N, S-CDs were tested by Ultraviolet-visible spectrophotometer, TEM and Fourier transform infrared. Secondly, the effectiveness of N, S-CDs in preventing corrosion was analyzed by electrochemical testing. The electrochemical test results showed that the impedance value of the solution of 200 mg/L N, S-CDs was 94,440 Ω cm2 at 298 K, with corrosion inhibition efficiencies (η) of 99.89 %, 99.77 % and 99.72 % at 298 K, 308 K, and 318 K, respectively. Moreover, SEM, XPS and AFM were used to characterize the micro-morphology and composition both before and after corrosion. It is worth noting that we used the fluorescence properties of carbon quantum dots as fluorescent probes to deeply verify the corrosion inhibition mechanism of N, S-CDs on copper.