Simple Synthesis of Magnetic Nickel Ferrite Nano Composites Containing Luminescence Material Applicable to Identify Heavy Metal Ions

INTRODUCTION
Luminescence emission happens after a suitable material has absorbed energy from a source such as electron beams, ultraviolet or X-ray, chemical reactions, and heat [1]. The energy leads the atoms into an excited state, and then, because excited states are unstable, the atom undergoes next transition, back to its ground state, and the diffused energy is released in the form of either heat or light or both [2,3]. Photoluminescence, which occurs by virtue of electromagnetic radiation, may range from visible light through ultraviolet and X-ray. It has been demonstrated that, in photoluminescence, the wavelength of emitted light is equal to or longer than that of the exciting light. This distinction in wavelength is caused, to non-radiating vibration energy of atoms or ions [4, 5]. The sulfides of zinc (z) and of cadmium (Cd) are the most main basic materials of sulfide-type phosphors [6]. II-IV semiconductor nanocrystals are a significant group of materials owing to the direct connection of their electronic and optical attributes with the size of the nano-particles. In special the photoluminescence spectrum of nano-particles develops from the UV to the IR spectral region owing to the size dependence of the energy band gap.
The use of nano-scale photoluminescence development the photoluminescence efficiency, but ultrafine materials can cause irrecoverable environmental danger. Also, reuse of materials saves raw materials. Due to of the nano-material size, separating this particles after end of the reaction by ordinary filtration are impractical. An efficient way to separate of nano-particle is use of the magnetic nano-particles as one part at nanocomposites that containing photoluminescence nano-material. Magnetic nano-particles can remove the problem of photoluminescence separating by using exterior magnetic field [7-10].
Magnetic material such as the ferrites, in addition to the separation of nanoparticles, can develop the photoluminescence performance. Magnetic nanoparticles show superior properties than the bulk state because they demonstrate the effect of quantum restriction. These unique features emerge when the particle size is less critical size [11, 12].
Ferrite, a ceramic material with magnetic attributes those are useful in many types of electronic system. The most important attributes of ferrites include high electrical resistance and high magnetic permeability. Spinel ferrites of general formula AFe2O4 are a large group of materials, they are composed of iron oxide and one (or more other) metals in chemical combination. Recently ferrite has receiving great attention due to their wide range of technological applications in various fields such as ferro-fluids, drug delivery, sensors, catalyst and magnetic resonance imaging (MRI) enhancement. Powder of nano sized NiFe2O4 a beneficial material owing to its high electromagnetic performance, mechanical hardness, highcoercivity, and great chemical stability [12-17].
Toxic heavy metals in industrial effluents include iron, copper, nickel, mercury, cadmium, lead and chromium. Heavy metal pollution is an important problem, as wide heavy metals produce environmental pollution, and their accumulation in the environment a major danger to Organisms health. There is a necessary requirement for a rapid, sensitive and effective method for finding heavy metal in the environment. Among the common systems for detecting heavy metal ions, induction of plasma / atomic or mass emission spectroscopy by atomic absorption spectroscopy are very prevalent. Light adsorption is a very simple and fast method for making sensors. Metal nanoparticles have very strong and desirable adsorption properties in the ultraviolet-visible region of the electromagnetic spectrum. The most important feature of nano-sensors is their very high sensitivity and detection power [18-20].
Escherichia coli are Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus E. coli that is generally found in the lower intestine of warm-blooded organisms. Most ways to detect bacteria take a long time; detection by sensors with a photoluminescence mechanism can be a suitable way to shorten the detection time [21,22].
This research goal to presentation a method for detects bacteria and heavy material by ultraviolet light radiation. In this work, CdS-NiFe2O4 nanocomposite was used to detect heavy metal. The nanocomposite prepared in this study can be frequently used to detect. 

MATERIALS AND METHODS
Materials
Fe (NO3)3 9H2O, NiSO4 6H2O, Sodium hydroxide (NaOH), Cd (NO3)2, Thiourea (CH4N2S), distilled water, Grapefruit extract, Cetrimonium bromide (CTAB), Escherichia coli.

Synthesis of NiFe2O4 nanoparticles
First 1.54 g of Fe (NO3)3.9H2O and 0.5 g of NiSO4.6H2O were dissolved in 200 ml of distilled water, and it was mixed on magnetic stirrer for 5 min. Then 18 ml of 1 M aqueous solution of sodium hydroxide was added as precipitator the pH of solution and was fixed to 10. Resultant solution was then transferred to a Teflon-lined stainless steel autoclave and was heated at 180 °C for 8 h. 
In synthesis by microwave, NaOH solution (1 M) was then slowly added to the solution under microwave radiations (510 W, 5 min). In both ways obtained precipitate was washed twice with de-ionized water (After each wash, pH checked) and then was dried in oven for 48h.

Synthesis of CdS nanoparticles
First 0.3 g of Cd(NO3)2 and 0.1 g of Thiourea were dissolved in 200 ml of distilled water, One time without using surfactant and next times using a surfactant (CTAB and again grapefruit as a natural surfactant). Then it was mixed on magnetic stirrer for 20 min. The resultant solution was then transferred to a Teflon-lined stainless steel autoclave and was heated at 200 °C for 12 h. The obtained light yellow precipitate was washed twice with distilled water.  The product then was dried in oven for 20h. CdS nanoparticles were prepared without precipitator using hydrothermal method.

Synthesis of NiFe2O4-CdS nanocomposites
Firstly 0.1 g of synthesized nickel ferrite was dissolved in 200 ml of distilled water, and it was mixed on magnetic stirrer for 5 min. Then 0.9 g of Cd(NO3)2 and 0.1 g of Thiourea was added to the solution and was mixed for 10 min and dispersed by  mechanical stirrer for 3h. Then transferred to a Teflon-lined stainless steel autoclave and was heated at 200 °C for 12 h. The obtained precipitate was washed. Then product was dried in oven for 20h. Fig. 1 shown the schematic diagram of the preparation steps used in this work.  

Methodologies for heavy metal and bacteria detection 
First, we examined the photoluminescence (PL) of the cadmium sulfidesolution and CdS-NiFe2O4 nanocomposites. Next, different concentrations of mercury, lead and bacteria were added to the same solution. Photoluminescence property was examined by luminescence spectrometer.

RESULTS AND DISCUSSION
The crystal structure of the NiFe2O4-CdS nanocomposites was investigated by XRD pattern and it is depicted in Fig. 2. The pattern illustrates the existence of only single phase of cubic spinel ferrite, which is accordant to JCPDS No 00-003-0875, with Fd-3m space group for nickel ferrite. XRD pattern of CdS that approves suitable agreement with cubic of pure CdS nano-crystal) JCPDS No 00-010-0454). It confirms presence of both phases of NiFe2O4, and CdS in the pattern. The peak intensities related to each counterpart is relatively similar which is representative of rather equal portion of the shared compounds in the composite.
Fig. 3 and 4 illustrate SEM images of NiFe2O4 product by hydrothermal and microwave method respectively. The images indicate that the nanoparticles with average diameter size of less than 50 nm were prepared. In the microwave method, the particle size is smaller in comparison to the hydrothermal method.  
Effect of surfactant on the morphology and particle size of products under hydrothermal method was investigated. Fig. 5 shows SEM images of cadmium sulfide nanoparticles without the use of surfactants .The average particle size of nanoparticles in this sample is less than 50 nm and with a small variation around this value. Fig. 6 shows cadmium sulfide nanoparticles prepared by adding CTAB surfactant and Fig. 7 illustrate SEM images of CdS nanoparticles in the presence of Grapefruit extract.
In both cases, nanotubes with dimensions of less than 50nm are formed; however, nanostructures synthesized using grapefruit juices have fewer dimensions of the proportion of particles synthesized by using CTAB.
SEM images of NiFe2O4-CdS nanocomposite are shown in Figs. 8 at two magnifications. The images approve formation of mono-disperse structures with average particle size of around 55 nm.
FT-IR analysis was used to study the type of bond and the purity of the synthesized nanocomposites of nickel ferrite -cadmium sulfide. The results of this analysis can be seen in Fig. 9. According to the FT-IR pattern, the absorption peaks in the 590 cm-1 range indicate the metal bond (nickel and iron) - oxygen in the ferrite composition. Also, the absorption peak in the range 47cm-1 indexes the CdS bond. A peak in the range 3500 cm-1 is due to the O-H bond remaining on the surface of the ferrite nanoparticles.
Nickel ferrite is an inverse type of spinel; it shows high magneto crystalline anisotropy, high saturation magnetization, and unique magnetic structure. Room temperature magnetic properties of nickel ferrite samples were studied using VSM instrument. Hysteresis loops of magnetic NiFe2O4 nanoparticles and nanocomposite of NiFe2O4-CdS   are shown in Figs. 10 and 11. As-synthesized magnetite nanoparticles with saturation magnetization of 35 emu/g and coercivity is 150 Oe.
Mr/Ms=0.21, the difference scale of this quantity with the number 1 represents the soft magnetism of the material. Also, the corresponding analysis of the ferri-magnetic property of the nickel ferrite nanoparticles is confirmed. 
Our result also shows that prepared nanocomposite show magnetic behaviour with a saturation magnetization of 7 emu/g and coercivity is 90 Oe. As you can see, the magnetization property has dropped in comparison nickel ferrite, which can be due to the presence of cadmium sulfide in the desired nanocomposite and the coating of nickel ferrite nanoparticles by this non-magnetic material.
The energy gap of cadmium sulfide nanoparticles was calculated using ultraviolet-visible spectroscopy. According Fig. 12a an intense absorption of cadmium sulfide nanoparticles was obtained at 513.754 nm. In Fig. 12b, the energy gap was specified by the Tauc formula and Beer-Lambert law, which is as follows:

                                                                                                                                
α is coefficient of absorption, c is constant coefficient, A is the light absorption by a solution containing nanostructure, b is the size of the cuvette (cell) containing the desired solution, C is concentration of sample (with molar unit) and n for semiconductor an indirect energy gap is 1/2. From the extrapolation of this region on the longitudinal axis, the nanostructure band gap value is specified. Fig. 12b shows energy of 2.413 eV with well precision. Fig. 13 show schematic of the photoluminescence mechanism of CdS-NiFe2O4 nanostructure.

Photoluminescence property of products 
The photoluminescence property of the cadmium sulfide nanoparticles synthesized by the hydrothermal method was performed using PL The cadmium sulfide nanoparticles have a significant deformity over the specified wavelength. There was no change in the wavelength, but the peak intensity increased that can owing to due to transitions between the nanoparticles conduction band with each other. Photo-luminescence of CdS prepared and reacted with Pb (II) and Hg (II), decreasing in PL peak by enhancing in Pb2+ and Hg2+ ions concentration was observed. These nanostructures introduce suitable sensor for harmful heavy metal ions detection. Orbital of Pb2+ and Hg2+ can take electron from CdS that has excitation. By junction of Pb2+ and Hg2+ ions, the fluorescence of the CdS was reduced due to electron transfer in complex compounds. By increasing the concentration of heavy metals PL peak is reduced further. (Fig. 14)

CONCLUSIONS
First nickel ferrite nanoparticles were synthesized via microwave-assisted and hydrothermal method. CdS nanostructure and NiFe2O4–CdS nanocomposites were then prepared via a hydrothermal method. The photoluminescence treatment of CdS nanostructure was measured using the detected of heavy metal ions. The photoluminescence activity measurements show that the CdS nanostructure result a highly active for detect of toxic ions and bacteria. 

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.