Impact of functional groups on cellulose nanofibers on the state of water molecules, photocatalytic water splitting, and photothermal water evaporation

Abstract

Cellulose nanofibers (CNFs) have emerged as promising candidates for renewable energy and fresh water applications. A comprehensive comprehension of the intricate interplay between various functional groups of CNFs and water molecules is deemed essential to harness their potential fully. This study delves into the profound implications of functional groups adorning CNFs on multifaceted processes, including photocatalytic water splitting (PWS) and photothermal water evaporation (PWE). Three distinct types of modified CNFs, including 3-chloro-2-hydroxypropyltrimethylammonium chloride modified CNFs (chCNF), oxidative sulfonated CNFs (soCNF₁), and directly sulfonated CNFs (soCNF₂), were prepared. A comprehensive analysis involving evaporation efficiency assessments, Raman spectroscopy, and molecular dynamics simulations demonstrates that the type and content of functional groups on CNFs significantly influence the state of water molecules. CNFs featuring anionic sulfonic acid groups exhibit superior abilities to regulate the water molecules' hydrogen bonding network structure. Furthermore, bismuth oxychloride nanosheets (BNs) were employed as a photoabsorbent. CNFs were inserted into lamellar membranes to delve deeper into the relationship between functional groups of CNFs and PWS or PWE properties. Notably, the lamellar membrane prepared using soCNF_2–2 and BNs achieved a remarkable hydrogen production rate of 13.97 μmol g⁻¹ h⁻¹, and the PWE rate reached 1.06 kg m⁻² h⁻¹ under 1.0 sun irradiation. These findings highlight the potential of CNF functionalization to optimize PWS or PWE processes and provide valuable insights into the interplay between the functional groups of cellulose and water molecules, spanning from molecular interactions to sustainable energy generation and fresh water production.