Wood-inspired polypyrrole/cellulose aerogels with vertically aligned channels prepared by facile freeze-casting for efficient interfacial solar evaporation

Abstract

Interfacial solar evaporation has drawn increasing attention in recent years due to its high efficiency, clean energy source and adaptability to a wide range of water sources. Herein, a solar evaporator was fabricated using a cellulose aerogel (CA) as the support by facile freeze-casting and polypyrrole (PPy) as the solar-thermal-conversion material by in situ growth. The cellulose aerogel showed unique morphology of a porous honeycomb-like structure at cross-section and vertically aligned channels, not only benefiting fast water delivery to the evaporator surface, but also alleviating the salt precipitation problem. With the growth of PPy nanoplates, the composite aerogel exhibited a high evaporation rate (∼3.16 kg m⁻² h⁻¹) and energy conversion efficiency (∼90.25%) under one sun illumination and great stability indicated by continuous long-term evaporation in saline water. The interaction between composite aerogels and water molecules could decrease water vaporization enthalpy to around 1400 kJ kg⁻¹ after stabilization, which plays an important role in enhancing evaporation performance. The impact of the cellulose concentration and PPy coverage percentage during preparation, saline concentration, and exposure height of the solar evaporator on evaporation performance was also investigated. Finally, the purified water was collected using a purpose-made collector with a collecting rate of 1.27 ± 0.08 kg m⁻² h⁻¹ and the condensed water showed high purity from various water sources. Attributed to its excellent light-harvesting ability, unique structure for fast and sufficient water transport and decreased water vaporization enthalpy, this cellulose-based aerogel shows great potential in clean water production.