Core Shell Iron Oxide-Zinc Sulfide (ZnS/α-Fe2O3) Synthesis

Synthesis And Photocatalytic Behavior of ZnS/α-Fe2O3 core shell Prepared by Two-Step Chemical method
Patij Shah, K. S. Siddhapara, D. V. Shah,
Key words: Photo reactive, Two step method, core shell.
Abstract. Core shell iron oxide-Zinc sulfide (ZnS/α-Fe2O3) was fabricated by two-step method: in the first one step uniform α-Fe2O3 particles were synthesized through a hydrolysis process of ferric chloride at 80°C. In the second step, the ZnS particles were admitted in the α-Fe2O3 particles by a zinc acetate (Zn(Ac)2·2H2O) And Sodium sulfide attended hydrothermal method at low temperature (90°C±C). The α-Fe2O3 and ZnS phases were identified by XRD, energy dispersive X-ray analysis (EDX). The photoreactivities of ZnS/α-Fe2O3Core Shall nanoparticles under UV irradiation were quantified by the degradation of formaldehyde.

INTRODUCTION

Recently, photocatalytic oxidation of organic and inorganic pollutants in water using coupled
semiconductor nanopowders has been extensively investigated.[1,2] An effective charge separation can be achieved by coupling two semiconductor materials with different energy band gaps and wellmatched chemical potentials. For example, network structured SnO2/ZnO nanocatalysts,[3] TiO2/Fe2O3 mixed oxides, [4] NiO/ZnO nanocomposites[5]and Cu2O/TiO2 heterojunction [6] have been successfully synthesized, which have high photocatalytic activity. Currently, the coupled semiconductor photocatalytic materials are mainly nanopowders. Nevertheless, it is well known that the photocatalytic nano powder has difficulty in recovering. [7,8] In this regard, immobilization of photocatalytic materials is necessary for actual applications.

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Although noble metals can significantly speed up the photocatalytic reaction rate, the higher cost greatly limits their practical applications in large scale. The practical applications of photocatalysis are limited because of at least two obvious problems arising from using fine photocatalytic powders: (1) separation of fine particles used after the treatment process and the recycling of the photocatalyst; (2) low photoefficiency. Many techniques were proposed for the preparation of fixed photocatalytic systems to eliminate the first problem [9, 10]. In order to improve the Photocatalytic activity of fine (ZnS) powders, many attempts were reported [11, 12]. Compared with other reports, the prime novelties of this work are (1) coating photoactive ZnS on to magnetic Fe2O3 core to prepare a magnetic photocatalysts (after photodegradation, the magnetic composites can be separated from the medium by a simple magnetic process), and (2) the photocatalyst can be reused easily
Zinc sulfide (ZnS) is one of the first semiconductors discovered [13] and it has chronicle shown noticeable fundamental properties versatility and a promise for novel diverse applications, including light-emitting diodes (LEDs), electroluminescence, flat panel displays, infrared windows, sensors, lasers, and biodevices, etc. Its atomic structure and chemical properties are comparable to more popular and widely known ZnO. However, certain properties pertaining to ZnS are unique and advantageous compared to ZnO. To name a few, ZnS has a larger bandgap of 3.72 eV and 3.77 eV (for cubic zinc blende (ZB) and hexagonal wurtzite (WZ) ZnS, respectively) than ZnO (3.4 eV) and therefore it is more suitable for visible-blind ultraviolet (UV)-light based devices such as sensors/photodetectors. On the other hand, ZnS is traditionally the most suitable candidate for electroluminescence devices. However, the nanostructures of ZnS have not been investigated in much detail relative to ZnO nanostructures. In this article, we will provide a comprehensive review of the state-of-the-art research activities related to ZnS nanostructures, including their synthesis, novel properties studies and potential application.

EXPERIMENTAL METHOD:

2.1. Synthesis of Zinc Sulfide nano particles Zinc Sulfide nano particles was prepared by adding sodium sulfide solution drop by drop to zinc acetate solutions mixed in 500 mL distilled water. The solution was kept under stirring condition. After 1 h, a white precipitate was formed for zinc sulfide solutions. After 24 h the solution was removed from stirring condition and washed with isopropyl alcohol and water to avoid agglomeration of particles. The precipitate was allowed to settle and dried in an oven for 12 h at 90â-¦C.
2.2. Synthesis of Fe2O3 nano particles
Uniform Fe2O3 particles were prepared through a hydrolysis process of ferric chloride at 80â-¦C as literature described. Stock solution of 3M FeCl3 and 0.2M HCl was mixed in 1:3 ratio, and deionized water was added until final concentration become of Fe3+ 0.01M. This mixture was preserved in water bath at 96°C for 24 h. Resultant solution was filter for further reaction. It was dried on a hot plate at 125 °C, a dark brown colored fluffy precursor obtained
2.3. Synthesis of ZnS/α-Fe2O3 nano particles.
50 mg of the synthesized Fe2O3 were dissolved in 40 mL of distilled water with the assistance of ultra-sonication for 30min.The sonicated Fe2O3 particles were added to the 500mL distilled water and then appropriate quantities of NaOH (0.1M) solution were added to adjust the pH value to 11.0. Then few drops of Zinc acetate were added to that distilled water containing Fe2O3 nano particles. Then mixed solution was continuously stirred and sodium sulfide solution was added drop by drop. After 24 h, the as-prepared products were washed repeatedly with distilled water and isopropyl alcohol for several times and then dried in an oven at 60°C for 6 h.
3: Result and discussion.
3.1. XRD X-Ray diffraction technique.
To obtain information on the crystal structure of the iron oxide core shell nano particles, X-ray diffraction patterns were measured. Fig. 1 shows the XRD patterns of prepared iron oxide core shell nano particles. Fig. 1(g) shows XRD pattern of the Fe2O3 core shell nano particles, presenting the characteristic peaks. It can also be seen from Fig. 1(a, b and c), where the Fe2O3 was completely coated by ZnS nano particles. The particle size of the core shell particles ZnS, ZnS/Fe2O3 and Fe2O3 were 20, 14, and 17.8 respectively. The core shell particles ZnS/Fe2O3was found to be smaller than the other coreless ZnS and Fe2O3 nano particles. Similarly, Shi et al. [14], coated Ce doped TiO2 in Fe2O3 nano particles. Formation of core shell is verified by the complete absence of reflections due to Fe2O3 in all the other spectra. The spectra of ZnS/ Fe2O3 showed reflections same as that of ZnS. In addition absence of any interaction between core and shell is also verified from the spectra. There might be dipoleedipole forces, but they might not be significant enough to alter the spectral characteristics. Except the spectrum of Fe2O3 in all the others peaks were broadened confirming their nano dim

3.2. EDAX:
Fig. 2 for ZnS/Fe2O3 core shell nano particles. The added elemental composition (during the preparation of the photocatalysts) was matching with the composition of elements analyzed. The EDS spectrum image taken from the sulfide coated iron oxide core shell particles region showing the presence of Zinc, sulfide iron and oxygen.

Element

Weight%

Atomic%

O K

38.41

70.04

Fe K

14.33

7.15

S K

13.44

7.05

Zn K

34.01

15.00

Totals

100.00

 

3.3. UV-Vis Spectroscopy:
Fig. 3 shows the UV-Vis absorption emissions. Spectra, it depicts the influence of ZnS combination of coated in Fe2O3 on the UV-Vis absorption. It is noticeable that a light absorption in the visible region is higher than that of ZnS and the light absorption was found to be increased when the individual nano particles were coated in. Fe2O3 (viz., ZnS/ Fe2O3). Since Fe2O3 has maximum absorbance in visible region [15]. As a result, the ZnS coated nano particles surrounding the Fe2O3grains can absorb a larger range of light radiation and increase the visible light absorption ability of the photocatalysts.

3.4. Photo catalytic behavior.
In Fig. 4, a comparison of photoactivity among ZnS, ZnS /Fe2O3 and Fe2O3catalysts at the same experimental conditions is shown. Previously, in the vacancy of illumination or without catalyst, there was no conversion of Formaldehyde. As it is explained in Fig. 4, the conversion of Formaldehyde after 90min of illumination followed the reduced order: ZnS /Fe2O3 > ZnS > Fe2O3. However, The photoactivity of ZnS, Fe2O3 and ZnS /Fe2O3 remained constant after 90min of irradiation time,

Although many authors have observed that the surface adsorbed water and hydroxyl groups are essential for photocatalytic reactions [16], it should be found that among other factors, the kind of phase, surface area, the adsorption capability, and the surface acid–base properties [17] strongly influence the photoactivity. On the other hand, the experimental conditions such as mass of the catalyst, wavelength, temperature, radiant flux, initial concentration of the reactants and oxygen pressure [18] could manipulate importantly the photoactivity of the catalysts. All these parameters will be studied in a future work with ZnS, ZnS /Fe2O3 and Fe2O3 catalysts in addition to the main benefit of having no need for filtration after the photoactivity test.
4. Conclusions.
The ZnS, Fe2O3 nano particles and ZnS/Fe2O3 core shell nano particles were significantly prepared by hydrolysis process, and characterized by XRD, UV–Vis, tested in Formaldehyde photodegradation. The results indicates a synergism between ZnS and Fe2O3, resulting in slightly more active ZnS/ Fe2O3 catalyst than ZnO and Fe2O3. The photoactivity of ZnS, Fe2O3 and ZnS/ Fe2O3 remained consist after 90min of irradiation time, which was interpreted in terms of the large amount of sub products attached to the surface of the catalysts and prohibit the Formaldehyde adsorption. The reduced order of photoactivity was as follows ZnS /Fe2O3 > ZnS > Fe2O3. Future work is in progress in order to study the experimental conditions of a higher photodegradation of Formaldehyde. The results obtained in this research impart to the understanding of formation of ZnS/ Fe2O3 core shell nano particles, and might lend information to the attempts of enhancing their environmental application.
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