Sol- Gel Synthesis of Hematite Nanoparticles and Photo Degradation of Cibacron Red FN-R Dye

This paper describes the synthesis of αFe2O3 nanoparticles by sol-gel route using carboxylic acid(2-hydroxy benzoic acid) as gelatin media and its photo activity for degradation of cibacron red dye . Hematite samples are synthesized at different temperatures: 400, 500, 600, 700, 800 and 900 OC at 700 OC the α-Fe2O3 nanoparticles are formed with particle size 71.93 nm. The nanoparticles are characterized by XRD , SEM, AFM and FTIR . The 0.046 g /l of the catalyst sample shows high photo activity at 3x10 -5 M dye concentration in acidic medium at pH 3.


Introduction:
Azo dyes are the largest group of dyes with -N= N-, as a chromophore in an aromatic system and have wide application in textile industries due to their ease of synthesis, versatility and cost effectiveness [1,2].However, due to the strong toxicity and the high solubility of these dyes ,different methods are proposed for their removal such as adsorption, filtration, flocculation and catalytic action [3]. Semiconductor photo catalysis is a quickly organizing multidisciplinary research field with potential applications in mineralization of organic pollutants. The advanced oxidation processes (AOP) have been considered as an effective technology in treating organic chemicals containing dyes in wastewater [4]. Iron oxides exist in nature in many forms such as hematite (α -Fe 2 O 3 ) , maghemite (γ -Fe 2 O 3 ) and magnetite (Fe 3 O 4 ). Among those phases hematite is one of the most attractive and significant metal oxide [5]. Many methods on the synthesis of iron oxide NPs by solgel are developed [6,7]. Tang and his co-workers report the synthesis of α-Fe 2 O 3 nanorods through the calcination of Fe OOH nanorods precursor [8] , Zhang et al. [9] use the solgel route to prepare hematite nanoparticles at various temperatures (423 -800 K) . The present work describes the synthesis of hematite (α-Fe 2 O 3 ) NPs by sol-gel route using 2-

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hydroxy benzoic acid as a gelatin agent and its use in photo degradation of cibacron red dye. The SEM, XRD, AFM, &FTIR technique is used to characterize the hematite nanoparticles.

Materials and Methods:
Material Preparation : Iron oxide nanoparticles are synthesized by sol-gel route using ferric chloride as iron source from SDFCL (97%) analytical grad and 2-hydroxy benzoic acid as a gelatin agent . In a typical synthesis (1.6 g,9.87mmole) of ferric chloride is dissolved in distilled water (100 cm 3 ) with stirring for 30 min. to complete dissolution in the same way as we check the pH On the other hand, (2.7g,19.5 mmole) of gelatin is dissolved in a small amount of absolute ethanol (10 cm 3 )to complete dissolution and then 100 cm 3 of distilled water is added with stirring for 30 min. and the mixture is heated at 60 ºC for one hour at pH 8 by adding drops of (30%)ammonium hydroxide. The color of solution changes to purple and the solution turns to gel followed by drying in oven at 80 ᴼC for four hours. The obtained compound is calcined at different temperatures for 2 hours using muffle furnance to obtain the product. Characterizations : The identification phase ,particle size and crystalline structure analysis are determined by XRD using shimadzu -6000 model with a Cu radiation ( λ= 1.54 Aᴼ) ,voltage 40 Kv and current 30 mA with speed 5ᴼ / min. The Atomic force microscopy (AFM)CAPM type AA3000 is used to investigate the particle size and morphology of the derived nanoparticles. Catalytic Activity Test:The photolysis of dyes have been performed using a tengusten Lamp (600W   [10,11,12].Also, the atomic force microscope (AFM) is used to determine nanoparticles size [13,14,15].The analysis of the roughness leads to an average dimension of 71.93 nm . So it can be concluded that it is possible to measure the size distribution of NPs with AFM too but this technique is bounded because it is very complex with respect to DLS. .  (1) shows the decreasing of the particle size with increasing temperature until 700 ºC, where particle size increases with increasing temperature.

XRD Analysis
The XRD patterns for α -Fe 2 O 3 nanoparticles (calcined at 700ºC for 2 hr. ) synthesized by sol-gel method using gelatin as a media and it is explained in Figure (2) .The XRD peaks in the whole angle range of 2 θ from 10º to 70º with Cu radiation (λ= 1.54Aº) voltage 40Kv and current 30 mA with speed 5º/min. It can be found from

FTIR Analysis
FTIR spectra are recorded in the ranges (400 -4000 cm -1 ) for the formed complex compound by reacting 2hydroxy benzoic acid with metals which can be identified by more excellence of their carboxylic and alcoholic (oxy) groups. Figure (3) shows the FTIR spectra of the α-Fe 2 O 3 synthesized by sol-gel method assisted by carboxylic acids: 2-hydroxy benzoic acid. It is observed that the bands from the C-O stretching vibrations of the free carboxyl groups are absent. The strong band at 536 and 569 cm -1 emerging in IR spectrum of calcined (700ºC) compound shows the presence of stretching and bending vibration of the intercalated M-O species .No peak at the presence of the two intense bands around 1647 and 1436 cm -1 indicates the complete replacement of H atoms on the carboxyl groups during the course of the process of complex formation between the carboxylic acid and the ferric ion [18].The characteristic peak at (455&536 cm -1 ) for2-benzoic acid becomes very strong, indicating the formation of stretching mode of α-Fe 2 O 3 ,this specifies the occurrence of hematite nanoparticles in calcined compound.

Fig. (3 ) FTIR Spectra of α-Fe 2 O 3 Prepared by Sol-Gel Method using 2-Hydroxy Benzoic Acid after Calcination at 700ºC.
Samira Bagheri and co-workers [19] have found strong band at 586 cm -1 of calcined 600ºC compound showing the presence of stretching and bending vibrations of the intercalated M -O species.
Oxidative Degradation Activity Test: Figure (4) shows the Uv-Visible spectra evolution and degradation efficiency of cibacron red dye (C.B) catalyzed by the-Fe 2 O 3 NPs, with the catalytic reaction processing, the intensity of the characteristic peak of C.B decreased gradually after 3 hrs. indicating that 77.81%C.B has been degraded. The high catalytic activity might be attributed to the high specific surface area and the active absorbed oxygen species .The effect of dye concentration on photo degradation of C.B dye is studied as shown in Figure 5 and Table 2 .The rate of photo degradation is found to increase with increasing dye concentration up to (3x10 -5 M) due to the availability of more dye molecules for degradation at further increasing in dye concentration,(above 3x10 -5 M),the rate of photo degradation decreases, An explanation to this behavior is at high dye concentration the path length of incident light which entering the solution decreases which retards the photo on the catalyst surface [20,21]. Abdullah, R. M. [22] studied the effect of titanium dioxide on some gram negative bacteria and study their effects on some virulence factors and chromosomal DNA.    Figure .6 shows the effect of α -Fe 2 O 3 loading (mass) varies in the range of (0.015, 0.031, 0.046 and 0.062 g / l) on the reaction. Kinetics under visible light have been studied. The rate of photo degradation immediately increases with increasing the catalyst concentration from 0.01 to 0.06 g/l. Minimum degradation has been observed, because transmittance of incident visible light at low catalyst concentration [23]. The highest rate of photo degradation of dye has been observed at the catalyst concentration of 0.04 g/l with increasing the concentration above 0.04 g/l, the photo activity decreases. The reason for this decrease in rate of photo degradation of dye due to the decrease in number of surface active sites.

Effect of Medium pH :
The effect of variation of pH from 3 to 11 prepared with (0.1N) HCl and (0.1N) NaOH solutions (loading of α-Fe 2 O 3 0.46 g/ L and initial concentration of dye 3 x 10 -5 M ) is studied by the photo catalytic degradation of dye . Figure (7) shows increasing of the rate of degradation of dye in acidic medium and decreases in alkaline medium .This may be due to anionic dye particles which get adsorbed on a catalyst surface by exchanging hydroxyl ions from the surface at acidic medium (pH 3) as the concentration of hydrogen ions in dye solution increases. The rate of adsorption and hence the degradation increases.

Conclusion:
The hematite nanoparticles are prepared from metal chloride by the sol gel method followed by calcination at different temperatures. In AFM analysis, the particle size of produced α-Fe 2 O 3 is approximately 71.93 nm and considerably high photo activity about 77.81% of the cibacron red dye decomposed in 3 hr. at catalyst α-Fe 2 O 3 loading of 0.046 g / l.
Sol-gel synthesized magnetic MnFe2O4 spinel ferrite NPs as novel catalyst for oxidative degradation of