Ardhendu Sekhar Giri

Ciprofloxacin degradation from aqueous solution by Fenton oxidation: reaction kinetics and degradation mechanisms

Pharmaceutical wastewater from a large number of manufacturing units is extremely contaminated by ciprofloxacin (CIP), an antibiotic drug. In this work, aqueous CIP solution was treated by Fenton oxidation (FO). The effects of typical process parameters on drug mineralization have been reported. The optimal Fe2+/H2O2 molar ratio of 0.125 and pH of 3.5 were determined with 15 mg L−1 initial CIP at 25 °C temperature. Maximum CIP, COD and TOC removal of 74.4, 47.1 and 37.9% were obtained under the optimal conditions. The mean oxidation number of carbon determined in terms of COD and TOC values was in accordance with that from the oxidation number of individual carbon atom. The concentration of hydroxyl radicals was measured using the N,N-dimethyl phenyl hydrazine method using dimethyl sulphoxide as a probe. Thirteen fragments appeared in the mass spectra and the proposed mechanism explored the routes of daughter ion formation. The cleavage of the piperazine ring was more effective in CIP oxidation due to high nucleophilic character of lone pair of electrons present on the nitrogen atom. A simple 2nd order kinetic model was proposed for the oxidation of CIP and degradation products (DPs) with respect to OH˙ concentration. The rate constants of 3.13 × 103, 4.89 × 103 M−1 s−1 were estimated for CIP and DPs. The initial concentration of OH˙ was found to be 11.67 μM.

Decomposition of drug mixture in Fenton and photo-Fenton processes: Comparison to singly treatment, evolution of inorganic ions and toxicity assay

The degradation of three pharmaceutical compounds i.e. chloramphenicol (CHPL), ciprofloxacin (CIP) and dipyrone (DIPY) singly and from equimolar (CCD) mixture has been investigated in Fenton and photo-Fenton processes. Drug mineralization was slightly less when present singly than their mixture. The degradation efficiency was likely hindered due to formation of common ions like Cl(-), F(-), NH4(+) and NO3(-). Addition of the same ions i.e. Cl(-) and F(-) in drug solution released upon cleavage of CHPL and CIP in CCD mixture suppressed the decomposition efficiency remarkably in both the oxidation processes. The major intermediates appeared in the mass spectra in combination of ion chromatograph were used to validate the routes of CCD decomposition and evolution inorganic ions. Furthermore, the bacterial toxicity assay was investigated using Escherichia coli (E. coli). The average reduction in cell death was about 38% in CCD system compared to 52%, 42% and 47% for CHPL, CIP and DIPY, respectively.

Bio-mediated silver nanoparticle synthesis: mechanism and microbial inactivation

ABSTRACT Even though plenty of literature is available on the biosynthesis of metal nanoparticles, there are serious lacunae on the mechanisms of their formation. In the present study, the mechanism of formation of mono-crystalline silver nanoparticles using a fruit extract of the ornamental tree Thevetia peruviana is emphasized, i.e. how the pH of the reaction mixture affected reaction kinetics and size of the nanoparticles. The facilitation of formation of Ag2O at higher pH resulted in a faster rate of particle formation. The diameter of the bare particles at neutral pH determined by field emission scanning electron microscopy and the hydrodynamic diameter determined by dynamic light scattering were 53 and 104 nm, respectively. The silver nanoparticles exhibited good inactivation of Escherichia coli due to participation of free radicals as evidenced by electron spin resonance spectroscopy.