Contribution of organic carotenoid and carbonaceous biomass of Tagetes erecta flowers for enhanced solar hydrogen generation†

Waste Tagetes erecta (Marigold) yellow-coloured flowers comprising carbonaceous biomass and organic pigment carotenoids are utilised for enhanced solar hydrogen generation through water splitting. The carbonaceous moiety of floral biomass, acting as a substrate is oxidised, makes uphill water splitting thermodynamically easier and improves the hydrogen production rate. Carotenoid, having visible light absorption and charge separation capability, acts as a photosensitizer when hybridised with semiconductors. A carotenoid–CdS nanohybrid photocatalyst exhibits an enhanced photocatalytic activity of 15 mmol g⁻¹ h⁻¹, almost three times that of pristine CdS (5 mmol g⁻¹ h⁻¹), when tested for hydrogen generation via water splitting under the full-band solar spectrum. The activity is further enhanced to 35 mmol g⁻¹ h⁻¹ (∼7 times that of pristine CdS) when the Tagetes erecta–CdS photocatalytic system is used for water splitting. An AQE of ∼17% is achieved using 420 nm of visible light.