Biochar Hydrogel Shines in Solar Water Purification
Researchers at Harbin Institute of Technology (Shenzhen) embedded sorghum straw biochar into a polyzwitterionic hydrogel and achieved a solar evaporation rate of 3.57 kg m⁻² h⁻¹ under one-sun irradiation, roughly 1.87 times higher than the biochar-free hydrogel. The study demonstrates that low-cost biomass-derived biochar can simultaneously enhance photothermal conversion, heat localization, and water molecule activation in hydrogel evaporators, offering a viable pathway for biochar use in solar-driven desalination materials.
Biochar-doped hydrogels are showing promise in solar water purification, according to a study published in the journal Biochar. Researchers from Harbin Institute of Technology (Shenzhen) have developed a hybrid solar evaporator that efficiently converts sunlight into vapor while enhancing water transport and minimizing heat loss. This innovation utilizes a polyzwitterionic hydrogel integrated with sorghum straw biochar.
The hybrid hydrogel, characterized by its soft and porous structure, absorbs sunlight and localizes heat at the evaporation surface. It continuously supplies water to this surface, facilitating rapid evaporation. Dr. Wenzong Liu, the corresponding author, highlighted that biochar enhances the hydrogel's ability to absorb light, manage heat, transport water, and activate water molecules.
Hydrogels are known for their water-retaining networks, but they often lack efficient photothermal conversion. Biochar, a carbon-rich material derived from biomass, offers strong light absorption and chemical stability. In this study, biochar was prepared through pyrolysis and other processes, then embedded into the hydrogel. This addition turned the hydrogel black, significantly improving its optical performance with over 95% light absorption across a broad solar spectrum.
The incorporation of biochar altered the hydrogel's structure, creating a denser and rougher pore network. This structure increased internal light scattering and extended the light path, capturing more solar energy. The pore network also supported capillary-driven water transport. Under one-sun irradiation, the hybrid hydrogel achieved a surface temperature of 41.1°C, concentrating heat at the evaporation interface.
The study also identified a non-photothermal mechanism where biochar surface groups interacted with water molecules, altering the hydrogen-bond structure. This interaction increased the amount of 'intermediate water,' which requires less energy to evaporate. Consequently, the hybrid hydrogel reduced the evaporation enthalpy to 877.79 J g⁻¹, lower than the control hydrogel.
In saline water, the hybrid hydrogel demonstrated improved swelling and water transport, achieving a saturated water content of 520%. This supports sustained water supply during evaporation. Dr. Liu emphasized that biochar not only serves as a solar absorber but also regulates the hydrogel's pore structure and water molecule state, enhancing evaporation performance.
These findings suggest that low-cost biomass-derived materials can advance solar evaporator design. The biochar-hydrogel strategy could benefit desalination and water purification technologies, particularly in saline or resource-limited environments.
Source: Biochar Feed