Synthèse de points quantiques de carbone photoluminescents biosourcés : application à la détection d'ions métalliques

Abstract

Brewery waste is formed in large quantities during beer fermentation. Its biodegradability property creates several alternatives for its valorization. We propose here an alternative method to reduce waste and add value to beer production by exploiting this rich carbon source and use it as a raw material for producing carbon quantum dots (CQD). Carbon quantum dots have excellent fluorescence characteristics and high water dispersibility. The fluorescence property is of great interest as a new generation of high performance, low cost electronic and optoelectronic devices emanate from advances in the development of fluorescent carbon quantum dots. Their different properties, in particular their strong photoluminescence and their low toxicity, give them a certain notoriety within multiple quantum dots. Quantum dots (QDs) are nanocrystals of similar size to proteins (2-10 nm) whose emission wavelength depends on their size and composition. Also, characterizing quantum dots involves measuring the optical properties of these particles. Two main measures are highlighted: The absorbance measurement whose principle deals with the transitions between the fundamental state and the excited state of the samples, and the fluorescence measurements that involve transitions from the excited state to the fundamental state. Several studies have also highlighted the synthesis of CQDs from biological sources, such as milk, lemon juice and orange peels. Various synthetic methods have also been explored, including: hydrothermal, laser ablation. However, very few studies show that CQDs can be synthesized using a simple microwave reactor using brewery waste as a precursor, hence the interest of focusing on the issue. Our research is therefore mainly to develop an alternative method to valorize this industrial waste produced in large quantities by the breweries. Specifically, this thesis examines the potential of brewery waste CQDs made to serve as sensors for the detection of metal ions that represent a real source of pollution beyond a certain threshold. The methodology developed consists of a complete synthesis method, including the carbonization of the starting carbon source, the addition to the carbonized mass a volume of water acting as a solvent, which facilitates the extraction of CQDs and finally the extraction of CQDs using microwave radiation. To characterize the CQDs produced, we evaluate the absorbance of the CQD obtained with a UV spectrophotometer to determine the optimal absorbance range of our particles. Fluorescence spectrophotometry tests allow a comparative evaluation of the effects on the emission of the different samples as a function of the variations made to the reagents. The distribution and size of the particles generated according to the same initial parameters of the reaction are determined by an electron-transmitting microscope. An elemental analysis is made with XPS spectroscopy. With a Fourier transform infrared spectroscope, the different functional groups present in the structure of the CQDs are determined. Thus, measuring the photoluminescence intensity of the CQDs makes it possible to better understand the variations of this intensity and the limits of absorbance and emission when the CQDs are subjected to certain conditions (change of quantity of reagents, reaction time, and nature of the reagents). The application potential of CQDs as a sensor for the detection of metal ions by measuring the fluorescence intensity variation of the CQDs as a function of the variation of the concentration of copper, iron and aluminum ions by the fluorescence quenching principle. The results obtained show that the CQDs formed are sensitive to the variation of the concentration of the different metals tested with correlation coefficients varying for each type of metals. In general, the interaction of carbon quantum dots (CQDs) with metal ions causes quenching of CQD fluorescence, which is likely due to the energy transfer process between CQDs as donors and metal ions as receivers.

Date	16 Sept 2019
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Claudiane Ouellet-Plamondon (Supervisor)