Rice husk-derived photothermal materials for membrane distillation

This study aimed to develop innovative photothermal materials derived from agricultural by-products (rice husk), with a primary focus on assessing the potential of both rice husk ash (RHA) and rice husk char (RHC) powders as effective photothermal for localised heating. A comparative analysis of their feasibility for membrane integration and photothermal performance was conducted through comprehensive physical, chemical, and optical characterisations. The RHC powder demonstrated superior qualities for utilisation in comparison with RHA. This superiority is attributed to several key factors: a notably high production yield (40.3 %), a smaller particle size of z-average (0.65 μm), a significantly larger effective BET surface area (301.78 m² g⁻¹), smaller pore size (2.78 nm) and an elevated total pore volume (0.21 cm³.g⁻¹). Dominated by a significant carbon content of 38.5 %, RHC powder showcased minimal light reflection (<5 %) and excellent light absorption across the entire spectrum, while RHA exhibited reflectance of more than 40 %, with light absorption occurring solely in the UV region. Moreover, RHC powder displaced superior light-to-thermal conversion, evident in a 20.9 °C temperature rise (83.6 %) from a 90-min exposure to a 0.4 kW m⁻² full spectrum light source. The findings of this study firmly established RHC powder as the preferred alternative option for sustainable photothermal materials, given its physical properties compatible with membrane integration and exceptional photothermal conversion ability.