Photo-degradation of Acid Violet, Acid Blue and Methyl Orange: Photo-catalyst and Magnetic CoFe2O4–ZnS Nanocomposite Preparation of Ni , Co, Cu or Ag-doped ZnS Nanoparticles

INTRODUCTION
At present, understanding the scientific properties of environmental pollution from different perspectives is economically very valuable. Much research has been done to find a method using photocatalysis to decompose toxic and organic pollutants [1-3]. The use of photocatalyst has attracted attention as an affective way to segregate, remove, and purify several contaminants. Centralized research on heterogeneous photocatalysts have been made to develop photocatalyst technology with high performance and low cost for treating pollutants present in toxic wastewater and organic waste with many unique properties [4-6]. Nanosubstances such as  ZnO and metal sulfides are known to have excellent photocatalytic activity in the decomposition and purification of various contaminating components [7-10]. Zinc sulfide (ZnS), one of metal sulfides, has thermodynamic optimum conditions for photocatalytic oxidation–reduction reactions. It has been used to produce a highly efficient photocatalyst with an appropriate band potential of electricity. [11-13]. Among these, ZnS (bandgap energy: 3.6–3.8 eV) has served as one of the most efficient photocatalysts for wastewater treatment. It is a very significant transition metal sulfide that can be used in a number of practical application fields such as electrocatalysts and photocatalysts [14-15] Ferrite nanoparticles have a strong magnetic property, which can be easily used for magnetic separation after degradation. in this work, CoFe2O4, a typical ferromagnetic oxide with a spinel structure with a Curie temperature around 793 K [16] is chosen as the magnetic material. Besides its large magnetic anisotropy and moderate saturation magnetization,CoFe2O4has remarkable chemical stability and mechanical hardness. Nanocomposites with properties of photocatalysis, magnetism, based on ZnS and CoFe2O4 have been reported. Therefore, the combination of CoFe2O4 and ZnS to form coreshell structure nanocomposites will make them have multiple properties. nanocomposites with ZnS nanoparticles can be fabricated to have a variety of physical, thermal, and other unique properties with many advantages. It has superior properties than existing microscale composite materials. In addition, it can be synthesized using simple and inexpensive technology [17–19]. They have excellent mechanical, chemical, and thermal properties with water resistant function [20–24].  This study describes the synthesis and characterization of nanosized Cofe2O4 particles using precipitation method. investigated the formation of monodispersed nanoparticles in transition metal ion (Ni, Co, Cu, Ag)-doped ZnS .The prepared ion-doped ZnS nanoparticles were compared in the same environment in terms of morphology  and structure properties. Finally metal doped CoFe2O4-ZnS-Ag nanocomposites were prepared by a fast chemical procedure.

MATERIALS AND METHODS
NiSO4 6H2O, Zn(CH3COO)2 2H2O, FeCl3 6H2O,Cu(CH3COO)2 2H2O,Co(CH3COO)2 4H2O, AgNO3 , COSO4 ,NaOH, , thiourea were purchased from Merck or Aldrich and all the chemicals were used as received without further purifications. A multiwave ultrasonic generator (Bandeline MS 73), equipped with a converter/transducer and titanium oscillator, operating at 20 kHz with a maximum power output of 150 W was used for the ultrasonic irradiation. Room temperature magnetic properties were investigated using an alternating gradient force magnetometer (V) device made by Meghnatis Kavir Kashan Company (Iran) in an applied magnetic field sweeping between ±10000 Oe. XRD patterns were recorded by a Philips, X-ray diffractometer using Ni-filtered CuKα radiation. SEM images were obtained using a LEO instrument model 1455VP. Prior to taking images, the samples were coated by a very thin layer of Pt (using a BAL-TEC SCD 005 sputter coater) to make the sample surface conductor and prevent charge accumulation, and obtaining a better contrast.  

Synthesis of CoFe2O4 nanoparticles
0.2 g of CoSO4 and 0.4 g of FeCl3 6H2O were dissolved in 200 ml of deionized water. Then 45 ml of NaOH solution (1M) was then slowly added to the solution until reaching pH to 10. A brown precipitate was then centrifuged and rinsed with distilled water. Finally obtained precipitate was calcinated at 85ºC and its colour goes from brown to black.

Synthesis of ZnS-metal-doped (weight percent: 90%:10%) nanocomposite
0.9 g (90%) of Zn(CH3COO)2 2H2O and 0.1g (10%) of metal doping agents Cu(CH3COO)2 2H2O Co(CH3COO)2 4H2O, NiSO4 6H2O and AgNO3 were dissolved in 100 ml of deionized water and 30 minutes stirring, then 0.13 g of thiourea dissolved in 100 ml water and it was added to the solution. NaOH solution (1M) was added to the solution (pH:10) and it was stirred for 20 minutes.

Synthesis of CoFe2O4-ZnS-metal-doped (100:90:10 %) nanocomposite
0.1 g (100%) of CoFe2O4 was dispersed in 100 ml of deionized water by ultrasonic waves for 60 min. Then 0.18 g Yield of ZnS (90%) of Zn(CH3COO)2 2H2O and 0.02g (10%) of metal doping agents AgNO3, Cu(CH3COO)2 2H2O, (Co(CH3COO)24H2O, NiSO4 6H2O were dissolved in 100 ml of deionized water and added to the mixture containing CoFe2O4. After 30 minutes the mixture of 0.13 g of thiourea (dissolved in 100 ml of deionized water) was transferred into the mixture. NaOH solution was slowly added to the aqueous (pH:10) solution and was stirred for 20 minutes.

Photo-catalytic degradation process
20 ml of the dye solution (10 ppm) was used as a model pollutant to determine the photocatalytic activity. 0.02 g catalyst was applied for degradation of 20 ml solution. The solution was mixed by a magnet stirrer for 1 hour in darkness to determine the adsorption of the dye by catalyst and better availability of the surface. The solution was irradiated by a 40 W UV lamp which was placed in a quartz pipe in the middle of reactor. It was turned on after 1 hour stirring the solution and sampling (about 10 ml) was done every 20 min [25-30]. The samples were filtered, centrifuged and their concentration was determined by UV-Visible spectrometry.

RESULTS AND DISCUSSION
The Powder XRD measurement was done for the CoFe2O4-ZnS-Ag to characterize the phase and crystallization. Fig. 1 shows the composition of the CoFe2O4-ZnS-Ag nanocomposite was also investigated. Presence of both cubic phase was confirmed and are illustrated. The crystalline sizes from Scherrer equation, Dc=Kλ/βCosθ, was calculated, where β is the width of the observed diffraction peak at its half maximum intensity (FWHM), K is the shape factor, which takes a value of about 0.9, and λ is the X-ray wavelength (CuKα radiation, equals to 0.154 nm).The average crystalline size for CoFe2O4ZnS-Ag nanoparticles were found to be about 20 respectively. Scanning electron microscopy was employed for estimation of morphology and particle size of the products. SEM image of CoFe2O4 nanoparticle are show in Fig. 2. surfactant-free CoFe2O4 nanoparticles obtained at 85◦C in 200 ml of solvent. The particle size and magnetic properties can be easily controlled by changing in precursors. SEM images of the Ag-doped Zinc sulphide nanoparticles are show in Fig. 3. According to scanning electron microscopy images the average particle size is found to be around 59 nm .Figs.4 shows SEM images of the Ni-doped Zinc sulphide nanoparticles. results confirm bigger product was prepared. Fig. 5 illustrate SEM images of the Co-doped cadmium sulphide nanoparticles. SEM images of the Cu-doped cadmium sulphide nanoparticles are shown in Figs.6. Images approve formation of nanoparticles with a little agglomeration. Figs.7 illustrate SEM images of the as-synthesized CoFe2O4-ZnS-Ag obtained at 80◦C in 200ml of solvent. That result confirms nanocomposites with average size around 29 nm were obtained. The FT-IR spectra of Ag-doped ZnS nanoparticles were obtained at wavelengths ranging from 4000 cm−1 to 500 cm−1 (Fig. 8). Bands of 664 and 1043 cm−1 in sample are characteristic peaks of the Zn-S bond. The spectrum exhibits broad absorption peak around 3414cm−1, corresponding to the stretching mode of O-H group of hydroxyl group and the band of 1617 cm−1 are associated with the functional C=O groups .Fig.  9 shows magnetic property of sample was studied using AGFM instrument and the obtained . Magnetization curve of CoFe2O4-ZnS-Ag that also exhibits also ferromagnetic behaviour with a coercivity of about 350 Oe and saturation magnetization of  43 emu/g .The magnetic property of the prepared nanocomposites is an essential characteristic of a heterogeneous nanocomposite since materials with this magnetic behaviour have low tendency in inter-particles agglomeration caused by dipole-dipole interaction in comparison with ferromagnetic nanocomposites. The photo-catalytic activity of the nanocomposite was evaluated by monitoring the degradation of organic dyes in an aqueous solution, under UV irradiation )Fig. 10.( Acid violet, acid blue and methyl orange were degraded at 60 min respectively by CoFe2O4-ZnS-Ag nanocomposite. As time increase, more and more dyes are adsorbed on the nanoparticles catalyst, until the absorption peaks (λmax) of acid violet, acid blue and methyl orange decrease and vanish around 120 min (Fig. 11).The dyes concentration decreased rapidly with increasing UV-irradiation time organic dyes decompose to carbon dioxide, water and other less toxic or nontoxic residuals[25–26].UV–visible spectro photometer was applied and it confirms in the presence of photo-catalyst under the UV-irradiation,the landa maximum of all azo dyes were disappeared as it is shown in Fig. 12.

CONCLUSIONS
In conclusion, synthesis, characterization, and photocatalytic activity of CoFe2O4, ZnS and CoFe2O4-ZnS-Ag nanocomposite were reported. AGFM confirmed that nanoparticles and nanocomposite exhibit either ferromagnetic or super-paramagnetic behaviour. The photocatalytic behaviour of CoFe2O4-ZnS-Ag nanocomposite was evaluated using the degradation of three various azo dyes under UV light irradiation. The results show that precipitation method is a suitable method for preparation of CoFe2O4-ZnS-Ag and other metal doped (Ni, Co, Cu) nanocomposites as a candidate for photocatalytic applications. 

ACKNOWLEDGEMENTS
This work has been supported financially by Technical and Vocational University Lorestan Branch, under the Grant Number of 221/98/400/25.

CONFLICT OF INTEREST
The authors declare that there are no conflicts of interest regarding the publication of this manuscript.