Removal of Malachite Green from Waste Waters by Bentonite Based Photocatalyst Technology

Polat K, Yurdakoc M. JOTCSA. 2019; 6(2): 261-270. RESEARCH ARTICLE Removal of Malachite Green from Wastewaters by Bentonite-Based Photocatalytic Technology Kinyas Polat* and Muruvvet Yurdakoc Dokuz Eylul University, Faculty of Sciences, Department of Chemistry, Tinaztepe, 35390, Izmir, Turkey. Abstract: MgFe2O4-B/Ag 3VO4 visible light active photocatalyst was successfully synthesized for the photocatalytic decolorization of organic pollutants. Malachite green (MG) was selected as a model dye representing those pollutant chemicals. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). Malachite green (MG) decolorization was carried out by visible light irradiation of a 105 W tungsten light source. Decolorization yield and kinetic studies were traced by the help of a UV-Vis spectrophotometer. Kinetic model of decolorization was derived from Langmuir–Hinshelwood (L–H) model and found coherent to first order kinetics. Catalysis reaction showed high dependency on pH especially out of 5-7 range which gave high decolorization. Photocatalytic activity also depended on concentration with dual character in which high concentration hindered the light coming to catalyst surface but on the other hand it supported the activity by boosting the dark adsorption resulting in a decolorization time changing fro m 40 to 100 min. After the reaction was completed, powders of catalyst were effortlessly removed from the medium by a magnet bar. It was shown that MgFe 2O4-B/Ag3VO4 photocatalyst has a potential to be simple and efficient alternative material for the removal pollution resources from wastewaters. Keywords: Malachite green, photocatalyst, visible light active catalyst, decolorization, wastewater. Submitted: February 13, 2019. Accepted: May 22, 2019. Cite this: Polat K, Yurdakoc M. Removal of Malachite Green from Wastewaters by Bentonite -Based Photocatalytic Technology. JOTCSA. 2019;6(2):261–70. DOI: https://dx.doi.org/10.18596/jotcsa.526822. *Corresponding author. E-mail: . INTRODUCTION advancements have been made recently using photocatalytic technology that is being one of the most efficient means operating at mild conditions. Photocatalytic oxidation degrades the toxic molecules into nontoxic mineralized forms (7-10). Industrial wastewaters containing hazardous dye molecules have detrimental consequences to human and animal life (1). Malachite green (MG) is one of those toxic dyes and is consist of Nmethylated diaminotriphenylmethane. MG is heavily utilized for dying fabrics in textile industry and also used as a fungicide and a bactericide in aquatic industry. It is known that MG is responsible for hepatic toxicity, cancer, anemia, and thyroid tumors (2,3) and several studies were made to remove the MG from the wastewaters with photocatalytic technology (4,5,6) In finding effective ways to prevent the contamination of water effluents by these chemicals, important Photocatalyst materials are usually made from transition metal oxides such as TiO 2, ZnO, BiPO4. TiO2 is still the most widely investigated photocatalytic material up to now due to good performance, photostability, and low cost, but only active at UV region of the spectrum which is roughly 4% of the solar spectrum. This situation limits its effective usage (11,12,13). In order to utilize natural sunlight efficiently, it is necessary to design visible light sensitive photocatalysts. 261 Polat K, Yurdakoc M. JOTCSA. 2019; 6(2): 261-270. Since Ag3VO4 emerged as a photocatalyst having activity towards visible light, it has attracted a lot of interest (14). Ag3VO4 has a narrowed band gap (15) suitable for efficient absorption of sunlight but charge carriers formed during excitation has small life-time. Therefore, produced electrons are captured by holes before the reduction reaction completely finished. Another drawback of Ag3VO4 is the low adsorptive capacity (16). RESEARCH ARTICLE 𝑉2 𝑂5 + 6𝑂𝐻 − → 2𝑉𝑂4 3− + 3 𝐻2 𝑂 3𝐴𝑔+ +𝑉𝑂4 3− → 𝐴𝑔3 𝑉𝑂4 The precipitate was left at room temperature for 24 h, cleaned thoroughly with deionized water and dried at 70 °C. Precipitate dying was done at 300 °C for 4 h (24). For MgFe2O4-Bentonite (MgFe2O4B) nanoparticles, a definite amount of bentonite was added to the mixture of FeCl 2.4H2O and FeCl3.6H2O in deionized water under nitrogen atmosphere. After 10 min,10 mL of NH4OH (25%) was added and mixed giving Fe3O4. Coprecipitation was achieved by drop by drop mixing of Mg(OAc)2.4H2O to the suspension. Mg(OH) 2 was the resulting compound with the reaction 1 M aqueous NaOH. The powder was washed with deionized water, filtered, dried and calcined at 550 °C for 6.5 h (25). Finally, 0.5 g Ag 3VO4 was mixed with 0.5 % MgFe 2O4-B in an agate mortar for 30 min and calcined at 300 °C for 2 hours (26). The material was characterized by XRD for crystal structure analysis. The size and surface morphology examined by SEM. There are several efforts to increase the photocatalytic activity by making composites with mediators such as graphene oxide, Co 3O4, and Gd2O3. These materials act in two ways, one is increasing the life time of charge carriers to suppress the recombination of electron and hole pairs, the other way is to create adsorption sides close to the catalyst active surface (17-21). In addition to activity enhancement issue, taking out of the catalyst from the aqueous solution without employing conventional expensive techniques is another important concept. For this purpose, magnetic MgFe 2O4 nanoparticles are recently used for easy and fast separation (22,23). Photocatalytic performance MG solution containing catalyst powders were irradiated by visible light produced from 105 W tungsten light source. MG content and the volume of the solution were 1×10 -5 M and 50 mL. Continuously stirred beaker was used to homogenize the solution during reaction. Samples were taken from the beaker at regular intervals and absorbance values were recorded at (615) nm wavelength by using a UV-visible spectrophotometer. Here, bentonite nanoparticles were incorporated to the Ag3VO4 photocatalyst to increase the photocatalytic performance. To the best of our knowledge this is the first study using bentonite as an adsorbent with Ag 3VO4 formulations. Furthermore, magnetic MgFe 2O4 nanoparticles were used for efficient removal of the catalyst by external magnetic field. MATERIALS AND METHODS Materials AgNO3 and V2O5 were purchased from Sigma Aldrich. FeCl 3.6H2O, FeCl2.4H2O, Mg(OAc)2.4H2O, NH4OH (25 %) and sodium hydroxide were taken from Merck. Bentonite was brought from EdirneEnez / Turkey region. Simulated wastewater was prepared with a mixture of sodium dodecyl sulfate (SDS), NH4NO3, NaCl, NaHCO3, and grease at 100 ppm of each. All chemicals in the simulated wastewater were purchased from Merck. Mechanism of Photocatalytic process Formation of reactive species, caused by visible light as .OH, HOO . is the main reas (...truncated)