Reactivity, characterization of reaction products and immobilization of lead in water and sediments using quercetin pentaphosphate.

Lead is currently ranked the number one heavy metal pollutant with a maximum contaminant level (MCL) of 0.015 mg L(-1). The use of organic solvent-free methods to immobilize lead from the environment is attracting the attention of scientists and environmental engineers. This study reports the application of water soluble quercetin pentaphosphate (QPP), a derivative of quercetin, for the detection and immobilization of Pb(2+) from water and soil samples. The techniques employed include UV-visible, fluorescence, atomic absorption; inductively coupled plasma optical emission and Fourier transform infrared (FTIR) techniques. Results indicated the formation of a QPP-Pb complex that inhibits the fluorescence intensity of the parent molecule. The fluorimetric limit of detection was found to be 3.46 × 10(-4) M. The QPP-Pb complex exhibited a corresponding stoichiometry with the predominant complex PX2. A Scatchard plot of y = -4 × 10(6)x + 2916.3 was observed with a negative slope giving an equilibrium constant of 4 × 10(6) M(-1) and 5.4 × 10(5) M(-1) in acidic and alkaline conditions respectively. Results show 90.4% and 91.5% lead(ii) immobilization from BRS and BU soil samples respectively. On the other hand, 91% lead immobilization efficiency from a water sample was achieved at room temperature and is in compliance with the MCL level of 15 ppm at ∼3.82% error margin. This approach does not require the use of organic solvents or the disposal of large amounts of sludge. Once complexed with lead, QPP may not release phosphate to cause any secondary pollution.

Reduction of hexavalent chromium using naturally-derived flavonoids.

Quercetin is a naturally occurring flavonoid that is known to form complexes with metals; a process that reduces the environmental availability of toxic metals such as chromium. We hereby report the first evidence of the removal of Cr(VI) from environmental samples using quercetin (QCR) and two synthetic derivatives: namely quercetin pentaphosphate (QPP) and quercetin sulfonic acid (QSA). We successfully synthesized both QPP and QSA using simple procedures while characterizing them with UV-vis spectroscopy, H(1)-NMR, (13)C NMR, (31)P-NMR, and LC-MS techniques. The solubility of QPP was found to be 840 mg/mL and aqueous solutions of both QPP and QSA were stable for over a period of 1 year. Quercetin and these derivatives were subsequently utilized for the reduction of Cr(VI) and QCR was found to have a higher reduction efficiency of 99.8% (30 min), followed by QPP/palladium nanoparticles mixture (PdNPs) at 96.5% (60 min), and finally QSA/PdNPs mixtures at 91.7% (60 min). PdNPs catalyst increased the efficiency by ∼36.5% while a change in operating temperature from 25 to 45 °C improved the efficiency by ∼46.8%. Electron paramagnetic resonance spectroscopy was used to confirm the presence of Cr (III) in the reaction products. This reduction approach was validated in environmental (Binghamton University) BU and standard reference material (BRS) soil samples. Results showed that the analysis could be completed within one hour and the efficiency was higher in BU soil than in BRS soil by 16.1%. QPP registered the highest % atom economy of 94.6%. This indicates enhanced performance compared to bioremediation approach that requires several months to achieve about 90% reduction efficiency.