Continuous Aspect‐Ratio Tuning and Fine Shape Control of Monodisperse α‐Fe2O3 Nanocrystals by a Programmed Microwave–Hydrothermal Method

Abstract

A rapid and economical route based on an efficient microwave–hydrothermal process has been developed to synthesize monodisperse α‐Fe 2 O 3 nanocrystals with continuous aspect‐ratio tuning and fine shape control, which takes advantage of microwave irradiation and hydrothermal effects. This method easily programs the experimental conditions (e.g., temperature and time) and significantly shortens the synthesis time to minutes. It allows the creation of numerous recipes for optimizing and scaling up production. The effects of experimental conditions including reaction temperature and reactant concentration on the morphology of α‐Fe 2 O 3 have been investigated systematically. Results reveal that the initial molar ratio of Fe 3+ to PO plays a crucial role in the final morphology of the α‐Fe 2 O 3 products. Several morphologies, which include ellipsoids/spindles with aspect ratios that range from 1.1 to 6.3, nanosheets, nanorings, and spheres can be obtained. The as‐formed α‐Fe 2 O 3 exhibits shape‐dependent infrared optical properties. The growth process of colloidal α‐Fe 2 O 3 crystals in the presence of phosphate ions is discussed. The products have been characterized by using X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared spectroscopy. This work presents an efficient and cost‐effective approach that is potentially competitive for scaling‐up industrial production. The as‐formed α‐Fe 2 O 3 crystals with controllable morphologies not only provide flexible building blocks for advanced functional devices, but are also ideal candidates for studying their nanoarchitecture‐dependent performance in optical, catalytic, and magnetic applications.