Trapping Melamine with Pristine and Functionalized Graphene Quantum Dots: DFT and SERS Studies

Abstract

Present study reports structural, electronic, and surface-enhanced Raman spectroscopy (SERS) investigation of melamine on pristine and functionalized graphene quantum dots (f-GQD) using density functional theory. Structural analysis reveals that melamine is strongly adsorbed over f-GQD than pristine GQD through hydroxyl group. Adsorption energy of −0.530 eV shows the physisorption of melamine on f-GQD. HOMO–LUMO gap for pristine melamine is 5.595 eV which reduces to 1.184 eV after adsorption over f-GQD depicting the charge transfer between melamine and f-GQD. The f-GQD plays a vital role in detecting melamine through surface-enhanced Raman spectroscopy (SERS). Three peaks at 584 cm⁻¹, 680 cm⁻¹, and 736 cm⁻¹ are denoted as the characteristic Raman peaks for melamine. A significant shift in Raman spectra of ~10 cm⁻¹ is found after the adsorption of melamine over f-GQD. Interaction between melamine and f-GQD results in the enhancement of Raman intensities of melamine which leads to melamine detection. To evaluate SERS effect, enhancement factor (EF) is evaluated with highly intensified peak at 736 cm⁻¹. The characteristic peak of melamine at 584 cm⁻¹ is increased by 396% when adsorbed over f-GQD. Our study suggests that the f-GQD is an efficient substrate for SERS effect and makes them a potential candidate for detection and sensing of melamine.