Design and fabrication of NPI/γ-Fe2O3 composite films and investigation of the synergistic mechanism for enhanced photothermal conversion efficiency

Abstract

In response to the demand for high-performance photothermal conversion materials in applications such as emergency rescue and passive de-icing, this study investigated the potential of polyimide (PI) materials with conjugated aromatic heterocyclic structures. We used density functional theory (DFT) calculations to determine the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and the energy gaps of various PI structural units. Based on these calculations, pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) were selected as the core structures, with 1,4,5,8-naphthalenetetracarboxylic dianhydride (1,4,5,8-NTDA) incorporated to tailor the energy gap. A series of polynaphthalimide (NPI) photothermal conversion films were synthesized, and the impact of NTDA content on their photothermal conversion performance was evaluated. The incorporation of NTDA led to an efficiency increase from 6.1% to 21.9%. Furthermore, a series of NPI/γ-Fe2O3 composite films were designed and prepared via in situ polymerization. The complexation transformation pathway of Fe3+ and its synergistic effect with NPI on photothermal conversion was systematically investigated. The NPI-3-0.9% film achieved a maximum photothermal conversion efficiency of 36.8%, a six-fold increase compared to pure PI films, while maintaining a tensile strength of 109 MPa, demonstrating excellent photothermal conversion and mechanical properties. The application of the composite films in emergency rescue blankets was assessed, exhibiting excellent photothermal heating and de-icing functionalities. These films hold significant potential for applications in polar scientific research, emergency rescue, solar de-icing, and desalination.