Degradation of naproxen by combination of Fenton reagent and ultrasound irradiation: optimization using response surface methodology.

A central composite factorial design methodology was employed to optimize the degradation of naproxen (NPX) by the combination of Fenton reagent and ultrasound (US) irradiation. In this study, the variables considered for the process optimization were the hydrogen peroxide, ferrous ion and NPX initial concentrations, while ultrasonic power amplitude was adjusted at 90% and initial pH was 3. An appropriate quadratic model was developed in order to plot the response surface and contour curves. Optimum dosage of Fenton reagent for NPX removal was found to be hydrogen peroxide concentration = 9.98 mmol L⁻¹, ferrous ion concentration = 4.83 mg L⁻¹ while NPX concentration was equal to 20 mg L⁻¹. A degradation efficiency of 100% was achieved within 10 min under US.

[Resonance light scattering of 4-(2-pyridylazo)-resorcinol (PAR)].

Mechanism and influence factors of resonance light scattering (RLS) spectra of 4-(2-pyridylazo)-resorcinol (PAR) aqueous solution were studied. In weak acidic solutions, strong RLS of PAR can be observed. The spectral feature of RLS is related to the absorption spectra of PAR. Acidity of the solutions influenced the acid-base equilibrium of PAR and its existing state, thereby influenced the RLS intensity. At pH 3.1 to pH 6.2, PAR exists as neutral molecule, which may assemble into molecular aggregates by hydrophobic force giving a light scattering enhancement. By a light polarization experiment, the RLS of PAR was demonstrated to be complete polarized light. The relationship between RLS intensity and PAR concentration was examined to be linear at a given set of experimental conditions.

[Resonance light scattering of rhodamine B].

The characteristic and mechanism of resonance light scattering (RLS) of Rhodamine B (RhB) were studied. In acidic solutions with pH from -0.38 to 4.10, the intensity of RLS increases with an increase in pH and reaches a maximum at nearly neutral pH. The change in RLS intensity with the wavelength was not accordant with Rayleigh scattering law. The fluorescence excitation and emission spectra of RhB overlap partly, and the RLS peak lies between the fluorescence excitation and emission peaks. In the three-dimensional fluorescence contour spectra of RhB, Rayleigh scattering line intersects fluorescence contour. In light polarization experiment, the polarization of RLS was measured to be P approximately = 0.1. All the above experimental facts reveal that the RLS of RhB is mainly resonance fluorescence. The mechanism of RLS enhancement by the increase in pH is that the formation of fluorescence species occurs in acid-base equilibrium. The RLS peak of RhB appears within the envelope of absorption, and light scattering is affected by light absorption, so, the relationship between RLS intensity and RhB concentration is not strictly linear.