Raman reporter‐based surface‐enhanced Raman scattering (SERS) has been used to investigate the detection of one member of a class of the cationic surfactant quaternary ammonium compounds, alkyl dimethyl benzyl ammonium chloride, also known as benzalkonium chloride (BAC). For this study, SERS was performed using silver nanoparticles (AgNPs). Density functional theory (DFT) of BAC on Ag6 clusters was introduced to estimate binding at the level of the B3LYP/LANL2DZ basis sets. As the chain length increased from n = 8 to 18, the binding energies were expected to increase by 2.1 kcal/mol. Methylene blue (MB) Raman reporter molecules were subsequently treated on BAC thin‐film‐covered glass surfaces. Atomic force microscopy (AFM) images were used to determine the coverage of BAC on the glass, and field‐emission electron microscope (FE‐SEM) images revealed the surface morphologies of the SERS substrates. A standard calibration curve was prepared to quantify BAC within a concentration range of 0.0036805 to 36 805 ppm (r2 ≥ 0.99), according to the BAC‐correlated SERS intensities of MB Raman peaks at ~1620 cm−1 adsorbed on AgNPs. A molecular dynamics (MD) simulation supported strong adsorption of BAC on glass surfaces.
Carboxymethyl jackfruit seed starch (CMS) was synthesized under different reaction conditions. The influence of sodium hydroxide concentration, monochloroacetic acid (MCA) concentration, IPA-water ratio, solvent-starch ratio, reaction time, and temperature were evaluated for degree of substitution (DS). Results have shown that the optimal DS of 0.68 was obtained at 50 °C, 90 minutes in solvent-starch ratio and isopropanol-water were 8:1 and 10:0. The ratio of sodium hydroxide and monochloroacetate acid moles to anhydroglucose unit (AGU) moles for the optimal DS were 1 and 1. Scanning electron microscope (SEM) of CMS particles showed the starch grain structure remains the same but the surface appeared many alveolar holes and no longer smooth as MS. Fourier transform infrared spectra (FTIR) of CMS and MS confirmed that carboxymethylation takes place on native starch molecules when the absorption band appears at a wavenumber of 1643 cm−1 corresponding to the vibrations of featured functional C=O group in CMS structure.
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