Ultra-trace analysis of chromium ions (Cr3+/Cr6+) in water sample using selective fluorescence turn-off sensor with natural carbon dots mixed graphene quantum dots nanohybrid composite synthesis by pyrolysis

Abstract

This study was aimed to implement the one-pot pyrolysis for hybrid nanomaterial synthesis consisting of graphene quantum dots (GQDs) from solid citric acid and carbon dots (CDs) which was hydrothermally derived from the herbal plant extract of “Houttuynia cordata”, denoted as Carbon Dots mixed Graphene Quantum Dots (CDs@GQDs). The nanohybrid were structurally characterized by XPS, FT-IR, Fluorescence, and UV–Visible absorption spectroscopy, and their morphological images were also analyzed by HR-TEM and FE-SEM/EDX. The quantum yield was found to be 15 %, higher than that of intact CDs or GQDs. Upon excitation at a maximum wavelength of 355 nm, and emission in the 450 nm. In this case, it was observed that the nanohybrid exhibit a high degree of selectivity towards Cr6+ ion when employed as a fluorescence quenching sensor from screening test with different metal ions. Therefore, the optimization conditions of solution pH, concentration of nanohybrid, H2O2 concentration as an oxidizing agent, reaction duration time with the aid of ultrasonication were carried out in details and the permissible limit of Cr3+ presence in the target analyte was all undertaken in order to enhance the detection of Cr6+ species. Its linear calibration curve was such y = 0.37x + 55.7, with a coefficient of determination (r2) value of 0.9816. The limit of detection (LOD) and limit of quantification (LOQ) was found to be 17.2 nM, and 52.2 nM. Consequently, the nanohybrid as a green chelating agent in the selective assessment of ultra-trace amount of Cr6+ in spiked water sample model was also done with good recoveries in both bottled drinking water and tap water samples ranging from 102.86 to 114.23 %.

Keywords

• Herbal plant extract
• Graphene quantum dots (GQDs)
• Carbon dots (CDs)
• Biosensor
• Chromium ion