Precursor foam based Co incorporated α-Fe 2O 3 (AFC) was successfully synthesized at 600 ℃ calcination temperature by simple solution method using PVA. The formation of α-Fe 2O 3 nanoparticles was confirmed by X-ray diffraction measurement and reduction in crystallite size was found after cobalt incorporation. Field emission scanning electron microscopy revealed the existence of pyramidal shaped iron oxide in AFC. FTIR and Raman spectra also confirmed the presence of α-Fe 2O 3. Photocatalytic activity study showed that the cobalt incorporated α-Fe 2O 3 was better photocatalyst than pure α-Fe 2O 3. The cobalt incorporated iron oxide nanoparticles could be used for drug delivery application and this simple preparation method could be adopted for the synthesis of other transition metal oxides.
Nanomaterials (NMs) have received a great deal of interest because of their size dependent amazing properties and versatile applications [
Therefore, in the present work, we report cobalt incorporated α-Fe2O3 nanoparticles mostly in pyramidal shape by simple solution route from a foam-like precursor having Fe(NO3)3∙9H2O and CoCl2∙6H2O salts as the sources of iron oxide and cobalt, respectively in presence of PVA as an organic binder and in water as solvent respectively. To obtain the final product, the precursor was calcined at 600˚C in air atmosphere. The structural property of samples was characterized by X-ray diffraction and field emission scanning electron microscope whereas the spectral properties were measured by using UV-Vis, FTIR and Raman spectral studies. Finally, photocatalytic activity of the samples towards degradation of rhodamine B dye was checked under visible light irradiation.
Ferric nitrate (Fe(NO3)3∙9H20) (Merck, purity 98%), cobaltous chloride (CoCl2∙6H2O, Merck; purity, ³98%) as the sources of iron and cobalt, respectively and polyvinyl alcohol (PVA, BDH, molecular weight ~22,000; purity, 98%) as organic binder were purchased and used without their further purifications. Double distilled water was used as a solvent to prepare the precursor solution.
Pure and 10% Co incorporated α-Fe2O3 were prepared by a simple and cost effective solution method. In this work, the preparation strategy of iron oxide from foam-based precursor is reported for the first time. In a typical synthesis, 2.88 g iron nitrate and 0.19 g cobalt chloride was dissolved (Fe:Co, 90:10; atomic ratio) in double distilled water and heated the solution at 70˚C to obtain a gel like material. The gel was formed after 2 h with continuous stirring of the precursor solution. On the other hand, a clear solution containing 4 wt% PVA was made by stirring and warming the solution at 40˚C. After that an appropriate amount PVA solution (7 ml) was added slowly to the gel with vigorous stirring. The solution was found to transform into a gel after stirring and warming at 70˚C for an hour. The gel was kept at 100˚C in an air oven and obtained a foam-like material. In the next, the foam was heat-treated under air atmosphere at 600˚C for 60 min to remove the organics and the product of cobalt incorporated α-Fe2O3 (AFC) was obtained. Similar procedure was also adopted for preparation of undoped α-Fe2O3 (AF) without the addition of hydrated cobaltous chloride in the precursor solution. A flowchart of the overall synthesis process is shown in
X-ray diffraction (XRD) study of the samples was performed by X-ray diffractometer (Bruker D8 Advance with DAVINCI design X-ray diffraction unit) with nickel filtered CuKα radiation source (λ = 1.5418 Å) in the 2θ range, 20˚ - 80˚. Morphological property of the samples were measured by adopting field emission scanning electron microscope (FESEM and FESEM-EDS, ZEISS, SUPRATM 35VP). Raman spectra were recorded using micro-Raman (Renishaw in Via Raman microscope). An argon ion laser with an incident wavelength of 514 nm was used as an excitation source for the Raman measurement. FTIR spectral study was carried out by using Thermo Electron Corporation, USA make FTIR spectrometer (Nicolet 5700). For each experiment, the number
of scans was fixed at 100 (wavenumber resolution, 4 cm−1). A Netzsch STA 409 C/CD thermoanalyzer was used for thermogravimetric analysis (TG-DTA) of the composite using Al2O3 as a reference maintaining the heating rate of 10 K/min in air. For the TG-DTA run, a maximum temperature was chosen up to 800˚C. The UV-Vis spectra were obtained by UV-Vis-NIR spectrophotometer (UV3600, Shimadzu, Japan) by the diffuse reflectance mode with ISR 3600 attachment.
The α-Fe2O3 (AF), and Co incorporated α-Fe2O3 (AFC) samples were dispersed separately in 50 ml 10−6 M of aqueous rhodamine B (RhB) solution for measurement of photocatalytic activity of the samples. The suspension was stirred in a dark for 1 h to establish adsorption-desorption equilibrium. The amount of samples in the dye solution was kept fixed (1.0 mg/ml). The photocatalytic activity (PA) of samples under visible light (Philips India make tungsten bulb, 200 Watt) towards the degradation of RhB (10−6 M solution) was monitored by measuring the concentration change of the RhB dye at ~555 nm. The details of PA measurement under visible light were given in our previous report [
Thermogravimetric and differential thermal analyses (TG-DTA) (
The crystal phase and crystallite size present in the samples were determined by X-ray diffraction (XRD) study.
The XRD patterns of pure iron oxide (AF) as well as cobalt incorporated iron oxide (AFC) samples are shown in
where k is proportionality constant (~0.9), λ is wavelength of X-ray (1.5406 Å), β is FWHM (full width at half maximum) for maximum intensity peak in radians, θ is diffraction angle and D is the crystallite size.
FESEM images of AF and AFC are shown in
FTIR analysis of pure α-Fe2O3 (AF) and Co incorporated α-Fe2O3 (AFC) was done in the spectral range, 4000 - 400 cm−1 (
UV-visible spectra of the samples, measured by diffused reflectance spectroscopy are shown in
the absorption peak is found to shift slightly in the blue wavelength region (520 nm, ~2.4 eV). The decrease of crystallite size in the cobalt incorporated iron oxide as measured from XRD study (
Micro-Raman spectral study (
The Raman peaks appeared at 229, 294, and 413 cm−1, could be assigned to A1g mode (229 cm−1) and Eg mode (294 and 413 cm−1) [
Photocatalytic activity (PA) of samples towards degradation of RhB under visible light irradiation was investigated after adsorption-desorption process in the dark environment. Time dependent absorption spectra (remnant dye concentration vs. irradiation time) of aqueous RhB dye solution using AF and AFC as photocatalysts are shown in
where, k is the reaction constant and t is the time.
The calculated degradation rate constants, k (×10−3 min−1) of AF and AFC samples were found to be 2.5 and 5.3 (
Nanocrystalline pure and Co incorporated α-Fe2O3 (AFC) were successfully synthesized at 600˚C calcination temperature from precursor foam by simple solution method using PVA as gelling and stabilizing agent. The formation of α-Fe2O3 nanoparticles was confirmed by XRD measurement and reduction in crystallite size was found after cobalt incorporation. Field emission scanning electron microscopy revealed the existence of pyramidal shaped iron oxide in AFC. FTIR and Raman spectra also confirmed the presence of α-Fe2O3. Photocatalytic activity study showed that the cobalt incorporated α-Fe2O3 was better photocatalyst than pure α-Fe2O3. The cobalt incorporated iron oxide nanoparticles could be used for drug delivery application and this simple method could be adopted for synthesis of other transition metal oxides.
Authors are grateful to the Director, CSIR-CGCRI, Kolkata for his kind support and encouragement for this work. The authors AN and SB thankfully acknowledge UGC-RGNF and CSIR, respectively, Govt. of India for providing their Ph.D. research fellowships. The authors also acknowledge the help rendered by Materials Characterization Division for several measurements of the samples. The work has been done as an associated research work of 12th Five Year Plan project of CSIR (No. ESC0202).
AtanuNaskar,SusantaBera,Awadesh KumarMallik,SunirmalJana, (2016) Cobalt Incorporated Pyramidal Shaped α-Fe2O3 Nanoparticles from Poly-vinyl Alcohol Based Precursor. Advances in Nanoparticles,05,9-17. doi: 10.4236/anp.2016.51002