Study on photocatalytic-adsorption properties of hollow ZrFe 2 O 4 cauliflowers for removal of organic pollutants

Hollow zirconium ferrite cauliflowers were synthesized by a facile solvothermal method using ultrasonic waves. The prepared nanoparticles were employed for the removal of methylene blue (MB) in the wastewater treatment. X-ray diffraction (XRD) pattern of the ferrite sample is well in agreement with the standard pattern of the ZrFe2O4 structure. Scanning electron microscopy (SEM) image reveals that the resultant ferrite is nanoporous structurally and the average sizes of cauliflowers and holes diameter were measured at 150 and 20 nm, respectively. UV-visible absorption spectroscopy was used to record the adsorption and photocatalytic behaviors of prepared ferrite.

Various methods to eliminate pollutants compounds from wastewater have been reported in the previous published articles among them, the advanced oxidation processes, in which the photo-degradation processes are included.These processes consist in the decomposition of organic molecules interacting with both, an UV or visible light as well as the interaction with a photo-catalyst material [6].Methylene Blue (MB), which is commonly applied to cotton, wood, and silk [7], can cause various symptoms including difficulty in breathing, nausea, and vomiting [8,9], and can impair photosynthetic processes in aquatic ecosystems [10][11][12].
Furthermore, dye substances typically exhibit long term chemical stability [13][14][15], and their complex aromatic structure is not conducive to biological degradation [16][17].Therefore, it is of environmental importance to develop efficient methods to remove MB from wastewater effluents [18].
Utilization of a combination with magnetite is more economical, due to the ease of separation and recovery of the catalyst after the elimination of the pollutant Naturally a catalyst that has the ability to remove contaminants in visible light is more desired [19].
In this work, for the first time, synthesis of ZrFe2O4 cauliflowers with nanopores, the catalyst was used for photocatalytic degradation of methylene blue under visible light LED lamp.The nanoscale pores in addition to the photocatalytic degradation process, causing part of the contaminants to be removed from the environment by adsorption.

2-2-Preparation of ZrFe2O4 cauliflowers
A mixture of 70 mL ethylene glycol, iron (ІІІ) chloride and zinc chloride was stirred in a mechanic stirrer to achieve a clean solution.Then, the above solution was added during stirring 2.312 g NH4Ac.With continued practice of mixing, the color turns to dark yellow and palms appeared.This solution for 40 min was sonicated.The solution is then placed in an oven at 215 ºC for 24 h to obtain a black precipitate.

2-3-Characterization of ZrFe2O4 cauliflowers
The particle morphologies of the ZrFe2O4 powder were observed by an AIS2100 (Seron Technology) scanning electron microscopy (SEM) and a JEOL 2010F transmission electron spectrophotometer using a KBr pellet for sample preparation.Furthermore, the structure of particles was analyzed by powder X-ray diffractometer (XRD).

2-4-Photocatalytic experiments
Photocatalytic activity studies of the ZrFe2O4 were evaluated by the degradation MB solution.
In a typical process, the catalytic reaction was carried out in a 100 mL photoreactor, which contains 50 mL of MB dye (10 mgL -1 ) solution and 0.05 g of catalyst.Before irradiation, the solution was stirred in the dark (15 min) for obtaining an equilibrium point of initial physical adsorption of MB over the surface of samples.Irradiation was carried out using a 5 W LED visible light (with emission wavelength about 460-490 nm).All photocatalytic experiments were accomplished at the same conditions.For determination of MB decolorization at specified periods, the lamps were turned off and 3 mL of each sample was collected and indirectly monitored by relating the optical absorbance to the MB degradation amount using a double beam UV-Vis spectrophotometer at a wavelength of 664 nm.

Fig. 2. SEM image and XRD pattern of ZrFe2O4
The EDX analysis and SEM image of ZrFe2O4 are shown in Fig. 3. EDX analysis show the presence of Zr in prepared ferrite.The SEM image shows that the morphology of prepared ferrite is clearly similar with spheres and cauliflowers.

3-3-Photocatalytic degradation of methylene blue
The photocatalytic activities of pure ZrFe2O4 cauliflowers catalysts were evaluated by the degradation of MB in aqueous solution under LED visible light irradiation.The photocalytic activity and adsorption property of ZrFe2O4 was compared in Fig. 4A.Removal of MB was carried out about 50% by adsorption on ZrFe2O4, but MB was degraded in the presence of ZrFe2O4 under LED light irradiation about 78%.This figure show that photolysis degraded only 12% of MB.Concerning the initial MB concentration, it can be concluded that there was a decrease in the photodegradation of MB with increasing initial MB concentration (Fig. 4B).Fig. 4C show the images of MB solution before and after photocatalytic degradation process.

4-Conclusions
Magnetically ZrFe2O4 nanohallow cauliflowers as visible-light-driven photocatalysts was prepared by hydrothermal method.Visible light photocatalytic activity of the nanohallow cauliflowers was investigated by degradation of MB.After visible light irradiation for 3 h, about 78% of MB molecules were degraded on ZrFe2O4.