High added value functionalized carbon quantum dots synthetized from orange peels by assisted microwave solvothermal method and their performance as photosensitizer of mesoporous TiO2 photoelectrodes

A direct pathway to convert orange peels waste to useful co-functionalized carbon quantum dots (CQDs) was performed through a friendly and efficient “greener method” consisting of a one-step microwave assisted solvothermal synthesis. The reaction proceeds in a mixture of powder of orange peels as precursor and water. The biomass was characterized by ICP-OES and CHONS analysis together with Fiber's analysis and FT-IR spectroscopy. The prepared CQDs presented a photoluminescent of brightness blue, high aqueous dispersion, chemical stability, an average particle size of 1.16 nm ± 0.1 nm and surface carboxylic and amine groups together with some dopants from the bio-precursor. The Fluorescence study revealed their potential emission in the electromagnetic spectrum of visible light. The bare mesoporous TiO2 semiconductor was impregnated with CQDs and the resultant composites presented a red-shift in the energy band gap with values from 2.3 eV to 2.08 eV, clearly lower than those on bare semiconductor and depending on the amount of CQDs. The CQDs/TiO2 photoelectrodes increased their photocurrent when they were exposed to the UV–Vis light, a decrease of photoelectrochemical band gap energy and an increase of the charge transfer constant in contrast with bare TiO2. These CQDs/TiO2 photoanodes were evaluated in carbon quantum dots-sensitized solar cells (CQDSSC) where there was an increase in the performance of the photovoltaic parameters compared with the bare semiconductor.