Efficient Light Harvesting and Water Retention Realized by Soybean Protein-Based Microgels Embedded in Hybrid Sodium Alginate Hydrogels Containing Photocatalyst for Hydrogen Evolution

The hydrogen evolution and water retention are enhanced by introducing soybean protein-based microgels into the hybrid sodium alginate (SA) hydrogels containing photocatalyst g-C₃N₄/Pt nanosheets. The soybean protein-based microgels are prepared from a mixture of soybean protein nanofibers (SPN) and SA. Due to the different refractive indices of SPN and SA, multi-scattering of incident light on the transparent SPN/SA microgels significantly improves the light-harvesting capability. The hydrogen evolution rate (HER) significantly rises to 4830 µmol h⁻¹ g⁻¹, 57% higher than that without SPN/SA microgels. In addition, the ─COOH and ─NH₂ groups in soybean protein also trigger the formation of additional hydrogen bonding and electrostatic interaction. It prominently reduces the water evaporation rate. After exposure to infrared illumination for 3 h, the weight loss of hybrid SA hydrogels embedded with SPN/SA microgels (mass ratio of SPN to SA = 2:1) is only 5.7%, which is 27% slower than that without SPN/SA microgels. Thus, the embedded SPN/SA microgels not only improve the light-harvesting but also prolong the lifetime of the hybrid SA hydrogels. They are very suitable for hydrogen production in areas rich in sunlight but poor in water, such as prairies and deserts.