Large-Area Nanoporous Iron Oxide Thin Films with an Interconnected Worm-like Architecture Fabricated by Lyotropic Liquid Crystal Templating

Abstract Large-area nanoporous metal oxide thin films with controlled morphology and high structural uniformity are of significant interest for applications in sensing, optoelectronics, catalysis, and energy conversion. Herein, we report, for the first time, a simple and scalable lyotropic liquid crystal (LLC)-templating strategy for the fabrication of large-area, uniform nanoporous Fe2O3 thin films with an interconnected worm-like nanostructure. The LLC precursor solutions were prepared from iron nitrate (Fe(NO3)3) as the iron source and the nonionic surfactant 10-lauryl ether (C12E10) as the structure-directing agent in a water–alcohol solvent mixture. Spin coating of the Fe(NO3)3–C12E10 LLC precursor solution onto solid substrates produced ordered Fe(NO3)3–C12E10 LLC films in which Fe3+ ions were confined within the hydrophilic domains of the mesophase. The structural evolution of the LLC films was systematically investigated as a function of the Fe(NO3)3/C12E10 molar ratio using low-angle X-ray diffraction and polarized optical microscopy. The results revealed the formation of well-ordered liquid-crystalline mesophases at optimized compositions, particularly at a Fe(NO3)3/C12E10 molar ratio of 3. Subsequent calcination at 450 °C removed the organic template and converted the hybrid films into crack-free, large-area (several cm2) nanoporous hematite phase of iron oxide (α-Fe2O3). The nanoporous films exhibit an interconnected worm-like morphology with structural features below 25 nm, consistent with their mesoporous nature. The films possess an indirect optical band gap of approximately 2.0 eV and a direct optical band gap of approximately 2.45 eV, consistent with the semiconducting behavior of hematite. Furthermore, the nanoporous iron oxide films are fully compatible with conventional photolithographic processing, enabling the direct fabrication of patterned microelectrodes and their integration into photodetector devices. The nanoporous iron oxide photodetectors exhibit a fast, reversible photoresponse with a responsivity of 26 nA/W under 488 nm illumination. This work establishes a versatile and scalable route for high-quality nanoporous hematite thin films and demonstrates their potential applications in optoelectronics, photocatalysis, sensing, flexible electronics, and electrochemical energy storage.