Determination of photoluminescence quantum yields in dilute solution using non-monochromatic excitation light.

The photoluminescence (PL) quantum yields (QYs) of fluorophores in dilute solutions can be determined fluorimetrically according to the comparative method employing standards of known PLQY. This method has recently been demonstrated to become more robust when the absorption of the excitation light and the PL emission are measured simultaneously using a transmitted light detector integrated in the fluorimeter. Herein, aided by fiber-coupled spectroscopic equipment and computerized data processing, we elaborate on this method by measuring the full corrected intensity spectrum of the excitation light transmitted through the sample. This further releases constraints on the monochromatic character of the excitation light and enables the use of broad-band excitation sources such as light-emitting diodes (LEDs). Furthermore, the protocol includes measurements at increasing dye concentration, rigorously verifying the required proportionality between absorbed and emitted light intensities. The PLQYs of solutions of fluorophores determined using the new method are in close agreement with published values.

Immobilisation of bacteria onto magnetic nanoparticles for the decolorisation and degradation of azo dyes.

Azo dyes are widely used in industries and their release in the environment contributes to the pollution of effluents. The authors aim to develop a new eco-friendly water treatment method for the degradation of azo dyes based on in situ magnetic separation and immobilisation of bacterial cells. The immobilisation was achieved using superparamagnetic Fe3O4 nanoparticles and offers the possibility of reusing bacteria by magnetic separation for several degradation cycles. The iron-oxide nanoparticles were synthesised by reverse co-precipitation. The Gram-positive bacteria Bacillus subtilis were immobilised using iron-oxide nanoparticles by adsorption and then separated with an external magnetic field. Transmission electron microscopy observation showed that the particles' diameter was ∼20 nm with a narrow size distribution. Moreover, the iron-oxide nanoparticles were adsorbed onto the surface in order to coat the cells. B. subtilis has proved its ability to decolorise and degrade several azo dyes at different values of pH, with the highest decolorisation rate for Congo red. Furthermore, immobilised cells have a degradation activity similar to that of free cells. The system provided a degradation rate up to 80% and could be reused for seven batch cycles.