Thin films of uniform hematite nanoparticles: control of surface hydrophobicity and self-assembly

Abstract

In this study we show that uniform hematite (α-Fe₂O₃) nanoparticle thin films with controlled layer thickness can be formed by Langmuir–Blodgett (LB) monolayer deposition on surface areas of several square centimeters. The technique involves synthesis of uniform hematite nanoparticles by forced hydrolysis and surface modifications for increased hydrophobicity to bring the particles to the air–water interface. Methods of thermal treatment, stepped solvent exchange, and oleate surfactant coating were studied for their effectiveness in increasing hydrophobicity by removing surface adsorbed water and –OH groups and were subsequently validated by Fourier-transform infrared (FTIR) spectroscopic analysis. Surface pressure–area (π–A) and surface pressure–time (π–t) isotherms indicate that the stability of the particle monolayer at the air–water interface depends on the method of surface modification. Thermal evaporation treatment was found to produce thin films of hematite nanoparticles with the greatest uniformity and surface coverage as characterized by UV-visible spectroscopic, scanning electron microscopic (SEM) and atomic force microscopic (AFM) analyses.