SYNTHESIS AND CHARACTERIZATION OF MGO NANOPARTICLES FOR PHOTOCATALYTIC APPLICATIONS M. Kandiban, P. Vigneshwaran and I. Vetha Potheher* Department of Physics, Bharathidasan Institute of Technology (BIT) Campus, Anna University, Tiruchirappalli, Tamilnadu, India *Corresponding author Email:
[email protected] Abstract MgO nanoparticles were prepared by using wet chemical methods such as co-precipitation and hydrothermal method. The synthesized MgO nanoparicles were characterized by X – ray diffraction analysis. PXRD result reveals that the nanoparticles are in crystalline form with cubic phase and the crystalline size was calculated using Debye Scherrer formula. UV results shows that absoprtion peak at wavelength of 295 nm and 297 nm were obtained for coprecipitation method and hydrothermal method respectively and their band gap values were also calculated and reported. The characteristic vibrational frequency of Mg=O at 548 cm-1agrees well with the literature. The morphology of the synthesized nanoparticles was studied by using Scanning Electron Microscopy (SEM). The photocatalytic property was analyzed by the absorption of methylene blue dye by developed nanoparticles. Keywords:Co-precipitation, Hydrothermal, Dye Degradation.
1. INTRODUCTION MgO is an exceptionally important wide band gap insulator and attracted both fundamental and application studies for use in catalysis, toxic waste remediation, refractory, paint, translucent ceramics, absorbent for many pollutants and superconductor products. Further, it has homomorphous compound with rock salt structure (FCC), the magnesium ions occupying octahedral sites within the anion closed packed structure and its ionic constituents comprise a relatively small number of electrons. Due to their simple crystal structure and perfect ionicity, MgO appears to form outstanding building blocks for the construction of functional nanostructures, or to serve as a suitable model compound for the investigation of surface reactivity on oxides. Its nanostructures are expected to have novel properties superior to their bulk counterparts due to the quantum confinement effect. Thus, many extensive studies have been carried out to synthesize nanoscale. MgO powders using various novel wet chemical methods, like sol–gel, solid state, co-precipitation, and spray pyrolysis and also on their optical, electrical and luminescence properties. In this study, MgOnanoparticles with cubic phase were discussed.
2. EXPERIMENTAL PROCEDURE 2.1 Co-precipitation method MgO nanoparticles were prepared via co-precipitation route using MgNO3, NaHCO3, and NaOH. PVA used as a surfactant under room temperature.1M solution of base [NaHCO3 & NaOH] was prepared by dissolving suitable quantity in distilled water. Similarly MgNO3 solution was prepared by dissolving MgNO3 in distilled water and also PVA Solution was prepared by using distilled water.50 ml of 0.5 M MgNO3and PVA Solution was taken in a 250 ml three necked round bottom flask and kept above in the magnetic stirrer & allowed to stir for 5-10 minutes, at room temperature.Then 50 ml of 1M solution of NaHCO3 was slowly added to it using addition funnel drop by drop under constant stirring condition. Then 50 ml of 1M NaOH solution was slowly added into the above resulting solution under stirring. In this whole process was carried out under constant vigorous stirring condition (130 RPM). After addition of surfactant & precipitating agent the constituent mixture was allowed to stir for 3hrs without altering any parameters. After completion of this whole reaction process, very finely powdered white precipitate MgO was settled at the bottom of RB flask. Then the fine powder was separated carefully using Buckner funnel. The whole precipitation was washed thoroughly with the help of doubly distilled water to make the precipitate free from tracer of foreign elements. The resulting substrate (Mg(OH)2 precursor) was kept in air oven for proper drying for 1 hour at 80 °C for complete drying. Then the MgO nanoparticle was obtained via controlled calcination process using muffle furnace for 5hrs at 350 ºC.
2.2 Hydrothermal method The starting materials used for the synthesis were magnesium nitrate[(MgNO3.6H2O] and sodium hydroxide [NaOH].0.5 M of Magnesium Nitrate(MgNO3.6H2O) was added to 50 ml of DD water and stir well in 30 minutes. 2 g of Sodium Hydroxide (NaOH) and 4.3 g of PVA was directly added to the above solution and after stirring for a few minutes, a white precipitate was obtained and transferred to 60 ml autoclave. The closed autoclave was then placed inside a preheated hot-air oven maintained at 350 ˚C for 14 hours, after that it was cooled to Room Temperature.
3. RESULTS AND DISSCUSSIONS 3.1 UV-visible spectroscopy analysis The UV-Vis absorption spectrum for MgO nanoparticles were analyzed from 200 to 800 nm and shown in Figure 1. The broad absorption peaks for MgO nanoparticles prepared by co-precipitation and hydrothermal method is given by 295 nm and 297 nm respectively. The band gap for the nanoparticles is calculated by the formula Eg=hυ= hc/λ, where h is Planck's constant, c is velocity of light and λ is wavelength. The calculated band gap values are shown in Figure 1.
Co-Precipitation Method
Hydrothermal Method
Figure 1 UV Visible spectra absorption for co-precipitation method and hydrothermal method 3.2 XRD analysis XRD pattern of MgO nanoparticles are compared to the standard JCPDS data (JCPDS No.01-089-7746 and JCPDS No.01-079-0612) for co-precipitation method and hydrothermal methodrespectively and the crystalline size was estimated by Scherer’s formula. The results confirm that there is no impurity phase in the MgO nanoparticles. The obtained powder X-ray diffraction pattern is shown in Figure 2. comparative analysis of XRD analysis is shown below. Both values show that the particles are in cubic phase with average crystalline size of about 60 nm.
(i)
(ii)
Figure 2 XRD results for (i) co-precipitation and (ii) hydrothermal method
3.3 FTIR Analysis IR spectra for the annealed sample obtained from co-precipitation method are shown in Figure 3. A broad band at around 433–769 cm−1 is assigned to the metal–oxygen bending vibration. A broad band at around 3461 cm−1 is attributed to stretching frequency of H–O–H. The broad band near 1381 cm-1is due to C=O stretching frequency shows the presence of aromatic ring.
Figure 3 FTIR spectra of MgO nanoparticles
3.4 SEM The morphologies of synthesized MgO nanoparticles were analyzed by SEM with different magnification and the images are shown in Figure 4. From the Figure, it is confirmed that the micrograph for MgO depicted in Figure 4 have non-uniform distribution of spherical particles and they consist of either some single particle or cluster of particles, in which the magnesium oxide nanoparticles is in aggregated form. It reveals that the powder particles are slightly agglomerated and the closed view of spherical nanoparticles has showed (Figure 4). Heat treatment resulted in agglomeration of the powder due to the interaction between nanoparticles and the sizes of them were around 60–100 nm. The surface of MgO nanoparticles was analyzed and the aggregated structures possess considerable surface roughness.
Figure 4 SEM images of MgO nanoparticles
3.5 Dye degradation The efficiency of MgO nanoparticle was investigated for removal of methylene blue (MB) from liquid solutions under UV radiation and shown in Figure 5. The dye degradation was carried out for different time intervals t1 (5minutes), t2 (10minutes), t3 (15minutes), t4 (30 minutes) under the presence of sunlight. At time interval t4 (after 30 min in sunlight) MB dye degrades completely due to absorption of MB with MgO in the presence of sunlight.
Figure 5 Dye degradation of MB monitored by using UV
4. CONCLUSION MgO nanoparticles were successfully synthesized using co-precipitation and hydrothermal methods. The synthesized nanoparticles were confirmed by powder X-ray diffraction analysis. The obtained nanoparticles exhibits crystalline nature with cubic structure and the size was found to be around 60 nm. The presence of Mg=O bond was confirmed by FT-IR analysis. Surface analysis reveals the cluster form of the synthesized nanoparticles. Photocatalytic study confirms the dye degradation property of the MgO nanoparticles.
REFERENCES [1].NirattisaiRakmaka, WisitsreeWiyaratnb, CharunBunyakana, JuntimaChungsiriporna,∗ “Synthesis of Fe/MgO nano-crystal catalysts by sol–gel method for hydrogen sulfide removal in Chemical Engineering Journal (2010). [2].AsadollahSamodi ,AlimoradRashidi , KatayounMarjani , SakinehKetab.“Effects of surfactants, solvents and time on the morphology of MgO nanoparticles prepared by the wet chemical method” in Materials Letters (2013). [3]. P.B. Devaraja , D.N. Avadhani , S.C. Prashantha , H. Nagabhushana , S.C. Sharma , B.M. Nagabhushana , H.P. Nagaswarupa “Synthesis, structural and luminescence studies of magnesium oxide nanopowder” in SpectrochimicaActa Part A: Molecular and Biomolecular Spectroscopy (2014). [4]. Aniruddha B. Patil, Bhalchandra M. Bhanage “Novel and green approach for the nanocrystalline magnesium oxide synthesis and its catalytic performance in Claisen–Schmidt condensation”in Catalysis Communications (2013). [5]. Z. Robert Kennedy G. Brindha S. Devi Meenakshi, M. Rajarajan and SusaiRajendran “Synthesis and characterization of magnesium oxide nanoparticles”in nanotechnology (2012).
