Utilization of floral waste for hydrogen generation via photocatalytic water splitting

Abstract

Enhanced solar hydrogen generation through photocatalytic water splitting utilizing floral waste biomass of yellow colored Tagetes erecta (Marigold) is reported in this thesis. Tagetes erecta is chosen due to the its higher content of organic dye carotenoid. Presence of carbonaceous moiety of biomass acting as a substrate, reduces the thermodynamic barrier of uphill water splitting reaction and increases the rate of hydrogen generation. Organic pigment, carotenoids of Tagetes erecta acting as the photosensitizer, absorbs visible light and transfer electron to the semiconductor photocatalyst CdS.. Experimentally, fine powder of Tagetes erecta is extracted from waste flower and hybridized with the synthesized nano-rods of CdS, by hydrothermal method to form a nanohybrid Tagetes erecta-CdS. Also, for comparison purpose, only carotenoid part extracted from Tagetes erecta floral biomass is hybridized with CdS to synthesize carotenoid-CdS nanohybrid. Structural and morphological (XRD, FTIR, TGA, FE-SEM, EDS), optical (UV-Vis, and PL), and photo-electrochemical (CV, LSV, and Transient photocurrent analysis) characterization of Tagetes-erecta-CdS photocatalytic system are performed and it is tested for hydrogen generation in presence of water, sacrificial agent Na2S and solar irradiation (full band) using solar simulator of 1 sun intensity. The results show the successful synthesis of photocatalytic material with a larger surface area, lower recombination rate of holes and electrons and better redox reaction. Tagetes erecta–CdS photocatalyst shows high-performance hydrogen generation due to the presence of organic carotenoid and carbonaceous moiety. The Tagetes erecta-CdS photocatalytic system exhibits almost seven times higher hydrogen generation of ~ 35 mmol.g-1.hr-1 compared to pristine CdS ~5 mmol.g-1.hr-1 under full band irradiation. Using a 420 nm band pass filter, ~17% apparent quantum efficiency (AQY %) is attained. A probable mechanism of enhanced hydrogen generation through water splitting in presence of biomass containing organic pigment, is proposed. The work has significance in context of solar hydrogen generation on a commercial scale and floral waste management.