Waste Nelumbo nucifera (lotus) stem-floral biomass-assisted enhanced and sustainable photocatalytic hydrogen generation

Abstract

Herein, waste Nelumbo nucifera (NN) stem-floral biomass-assisted photocatalytic hydrogen generation through water splitting is explored. A novel, recyclable, cost-effective, environment-friendly dual-functioning nano-hybrid (NN–ZnO), integrating the porous carbonaceous framework of NN with ZnO nanoparticles at different compositions, is synthesized via one-step carbonization–activation and tested for sustainable hydrogen generation using a laboratory-scale H₂ reactor. The oxidation of the carbonaceous moiety of the NN-biomass acting as a substrate makes the uphill water-splitting thermodynamics easy and enhances generation; the synergistic coupling of the defect-mediated charge separation and porous carbon enhances the photocatalytic activity. Under full-spectrum irradiation, the NN–ZnO nanohybrid exhibits a dual-functional role, as experimentally verified. When NN-biomass and ZnO are introduced as a mixture, the photocatalytic activity reaches 20.46 mmol g⁻¹ h⁻¹ of H₂, primarily attributed to biomass oxidation. However, upon nanohybrid formation between NN and ZnO, it produces a maximum hydrogen evolution rate of ∼27.34 mmol g⁻¹ h⁻¹ (∼4 times more than pristine ZnO, i.e., 6.99 mmol g⁻¹ h⁻¹), confirming the synergistic effect of the nanohybrid structure. Remarkable values (∼71% and ∼50%) of the apparent quantum efficiency (AQE) are achieved (using 420 and 350 nm wavelength band-pass filters, respectively). The NN–ZnO nanohybrid preserves 82.58% of the initial activity after 4 cycles and 1 month, proving its recyclability and robust infrastructure.