A rational approach for the synthesis of near-infrared absorbing porous hypercrosslinked polymers for solar steam generation

Abstract

Hypercrosslinked polymers (HCPs) are an important class of porous organic polymers (POPs) owing to their ease of synthesis with a wide range of applications. Unlike other POPs, such as conjugated microporous polymers and covalent organic frameworks, HCPs are typically not suitable for applications where near-infrared absorption is essential. This is because most of the HCPs absorb in the Ultraviolet-Visible (UV-Vis) region. In the present work, we present a strategy to synthesise near-infrared (NIR)-absorbing HCPs by crosslinking tetraphenyldibenzoperiflanthene (DBP) with formaldehyde dimethyl acetal (FDA) using FeCl₃. The resultant HCP, DBP-HCP, exhibits a surface area of 645 m² g⁻¹ with a pore volume of 0.46 cc g⁻¹. Importantly, it shows broad light absorption covering from the Vis to NIR region (400–1600 nm). Due to the porous nature and NIR light absorption, we explored DBP-HCP as a photothermal material in solar steam generation (SSG). It shows an evaporation rate of 2.29 kg m⁻² h⁻¹ with an energy conversion efficiency of 74.3% under 1 sun illumination. This evaporation also helps to recover pure water from dye-contaminated water and desalination of seawater. The results presented here provide a rational design strategy for synthesising NIR-HCPs with good porosity for various photothermal applications.