Research on the differential side-chain design of amino acid-modified carbon quantum dots and scale inhibition mechanism toward CaCO 3

To address the scaling issues encountered during the oilfield water injection process, citric acid was employed as the carbon source, and three amino acids with distinct side chain structures glutamic acid, glutamine, and methionine, were individually introduced to synthesize Glu-CQDs, Gln-CQDs, and Met-CQDs via a one-pot hot-melt polycondensation method. At a concentration of 50 mg/L, the scale inhibition efficiency of Glu-CQDs and GIn-CQDs were 89.91% and 57.78%, respectively, while that of Met-CQDs was only 22.15%. This suggests that the -S-CH3 group in methionine’s side chain exhibits negligible chelating or solubilizing effects on Ca2+. FT-IR, XPS, TEM, Uv-vis, and Fluorescence spectrophotometer are used to analyze the micro structure and optical properties of AA-CQDs. The delaying effect of AA-CQDs on scale formation was evaluated through laser turbidimetry, while their regulatory influence on scale crystal morphology was investigated via SEM and XRD. This indicates that AA-CQDs inhibit the formation of calcium carbonate scale through combined mechanisms such as chelation and lattice distortion. Quantum chemical calculations were conducted to assess the coordination and binding affinity between AA-CQDs and Ca2+, that the ΔE value of Glu-CQDs is 3.36907. This indicates that Glu-CQDs exhibit more outstanding nucleophilic and electrophilic properties, stronger electron transfer ability, and a stronger binding affinity to the calcite crystal surface. This comprehensive study elucidates the impact of functional side chain groups, such as -COOH, -CONH2, and -S-CH3 on the scale inhibition performance and crystallization behavior of carbon dots.