Silver nanoparticles from Tabernaemontana divaricate leaf extract: mechanism of action and bio-application for photo degradation of 4-aminopyridine.

Silver nanoparticles (Ag NPs) were synthesised by the reduction of Ag+ to Ag0 in the presence of enol form of flavonoids present in plant extract of Tabernaemontana divaricate (T. divaricate). Prepared Ag NPs were characterised using UV-Vis, XRD, HR-TEM with EDX and XPS techniques. XPS spectra exhibited peaks at 366 eV and 373 eV, which specified spin orbits for Ag 3d3/2, and Ag 3d5/2 that confirmed the formation of Ag NPs. Ag NPs were spherical in shape with an average size of 30 nm as revealed by HR-TEM and FE-SEM techniques. EDX studies verified the high purity of Ag NPs with silver 46.96%, carbon 16.35%, oxygen 16.22%, nitrogen 20.25% and sulphur 0.21%. LC-MS analysis of plant extract confirmed the qualitative presence of alkaloids, tannins, flavonoids, phenols, and carbohydrates. Prepared Ag NPs showed good photocatalytic activity towards degradation of 4-Amniopyridine with 61% degradation efficiency at optimum conditions in 2 h of reaction time under visible light. The ten intermediates were found within the mass number of 0-450. Ag NPs synthesised using bio-extract have also shown good inactivation against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis) bacteria due to the availability of free radicals.

Kinetics, degradation mechanisms and antibiotic activity reduction of chloramphenicol in aqueous solution by UV/H2O2 process.

In this study, the aim was to explore the effectiveness of the UV/H2O2 photolysis (UVP) process in terms of antimicrobial activity reduction and increasing the mean oxidation number of carbon (MONC) under the degradation of chloramphenicol (CHPL) drug. CHPL degradation kinetics and the effects of foreign anions on CHPL degradation were explored in this study. The order of the inhibition effect was found as Cl- > NO3- > HCO3- due to their different in HO• radical scavenging capacity. A pseudo-first-order model for CHPL degradation was well established, and the rate constant (kobs) was 2.93 × 10-2 min-1 (R2 = 0.98) in UVP. Thirteen intermediate products were detected in MS-chromatogram and were identified through different proposed degradation pathways. The cleavage of the amide side chain in CHPL was more effective in CHPL degradation due to an electrophilic attacks by HO. radicals on it. The inactivation rates of E. coli were decreased due to the reduction of -NO2 group into -NH2 functional group in CHPL that leads to the production of low toxic compounds on CHPL degradation.

Ciprofloxacin degradation in photo-Fenton and photo-catalytic processes: Degradation mechanisms and iron chelation.

Ciprofloxacin (CIP) is a broad spectrum synthetic antibiotic drug of fluoroquinolones class. CIP can act as a bidentate ligand forming iron complexes during its degradation in the photo-Fenton process (PFP). This work investigates on PFP for the degradation of CIP to understand the formation mechanism and stability of iron complexes under ultraviolet (UV)-light illumination. A comparison was made with the UV-photocatalysis (UV/TiO2) process where CIP doesn't form a complex. In PFP, the optimal dose of Fe2+ and H2O2 were found to be 1.25 and 10 mmol/L with pH of 3.5. An optimal TiO2 dose of 1.25 g/L was determined in the UV/TiO2 process. Maximum CIP removal and mineralization efficiency of 93.1% and 47.3% were obtained in PFP against 69.7% and 27.6% in the UV/TiO2 process. The mass spectra could identify seventeen intermediate products including iron-CIP complexes in PFP, and only seven intermediate products were found in the UV/TiO2 process with a majority of common products in both the processes. The proposed mechanism supported by the mass spectra bridged the routes of CIP cleavage in the PFP and UV/TiO2 process, and the decomposition pathway of Fe3+-CIP chelate complexes in PFP was also elucidated. Both in PFP and UV/TiO2 processes, the target site of HO• radical attack was the secondary-N atom present in the piperazine ring of the CIP molecule. The death of Escherichia coli bacteria was 55.7% and 66.8% in comparison to the control media after 45 min of treatment in PFP and UV/TiO2 process, respectively.

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.