Low Temperature Synthesis of Needle‐like α‐FeOOH and Their Conversion into α‐Fe₂O₃ Nanorods for Humidity Sensing Application

Abstract

In this study, we report template and surfactant‐free, low temperature (70°C) synthesis of needle‐like α‐FeOOH and its conversion at 400°C into α‐Fe2O3 nanorods using Fe(+2) and Fe(+3) chlorides and urea as a hydrolysis‐controlling agent. The isolated needle‐like α‐FeOOH indicates asparagus‐type growth pattern having length ca. 600 nm with 80 nm diameter at base and apex diameter of around 10 nm. The sample on heating (α‐Fe2O3) shows nanorod‐like morphology. The samples were characterized using various physicochemical characterization techniques such as XRD, Raman spectroscopy, UV‐Vis spectroscopy, particle size distribution analysis, Field Emission Scanning Electron Microscopy (FE‐SEM), and humidity sensing performance. The humidity sensing behavior of both α‐FeOOH and α‐Fe2O3 was studied. The α‐FeOOH shows quicker (10 s) and higher response toward change in humidity from 20%RH to 90%RH as compared with α‐Fe2O3 (60 s). Their typical morphology and crystalline structure plays an important role in humidity sensing behavior.

Goethite (α-FeOOH) nanopowders synthesized via a surfactant-assisted hydrothermal method: morphology, magnetic properties and conversion to rice-like α-Fe2O3 after annealing

“…As is well-known, α-FeOOH can be converted to α-Fe 2 O 3 at high temperature [4,6,20]. In order to confirm the phase transition temperature, Fig.7 gives the TG-DTA curves of acicular α-FeOOH powder hydrothermally synthesized with 0.2 g CTAB at 180ºC.…”

Fabrication of magnetic nanorods and their applications in medicine

“…In Figure (a), two strip broad absorption band of α-FeOOH nanorods mainly located in an area away from UV. One of these bands located at wavelengths of 280-300 nm and the other of 360-380 nm which is similar to the absorption band of α-FeOOH nanoneedles [72]. There was no specific absorption in the visible regime but according to Sherman and colleagues [73] we can say that the intensity of α-Fe 2 O 3 nanorods is greater than α-FeOOH nanorods.…”

A novel structure for enhancing the sensitivity of gas sensors – α-Fe2O3 nanoropes containing a large amount of grain boundaries and their excellent ethanol sensing performance

“…It results in the coalescence of adjacent small particles into a larger one. 34 The optical absorption properties of the a-Fe 2 O 3 nanostrings and nanoropes were investigated to study the effect of size on their band structures as shown in Fig. When the temperature reaches 600 C, the size of these particles is large enough that equals the ber diameter, resulting in the appearance of the string-of-bead morphology.…”