Tajmeri Selima Akhter Islam

Photocatalytic decolorization of crystal violet in aqueous nano-ZnO suspension under visible light irradiation

Nanosized ZnO was prepared through hydrothermal process and characterized by scanning electron microscopy, X-ray diffraction and laser-induced breakdown spectra measurement techniques. The as-prepared nanosized ZnO was used to investigate the decolorization/degradation of crystal violet, a cationic dye which is extensively used in dyeing/textile industries, under visible light through adsorption studies of the dye solution with ZnO in the dark. The results show that the adsorption of CV on ZnO takes about 200 min to reach equilibrium, and the equilibrium time at a certain concentration of the dye seems to be independent of temperatures that are used for the preparation of ZnO samples. The adsorption data follow the pseudo-first-order kinetic model (Lagergren), and the adsorption pattern follows the Langmuir model.Prepared ZnO (300°C) was found to be a more efficient photocatalyst among others including pristine ZnO, to decolorize/degrade the dye. The decolorization rate is increased with the decreasing of the initial dye concentration and reached at a limiting value. The catalyst loading also influences the decolorization/degradation of the dye, and decolorization rate is increased with increasing the catalyst loading and reached at a limiting value. ZnO was found to be stable under visible light irradiation at solution pH = 6. The photocatalytic degradation of the dye followed zero-order kinetics, and the Langmuir-Hinshelwood mechanism was found to be valid.

Zinc oxide-mediated photocatalytic decolorization of Ponceau S in aqueous suspension by visible light

ZnO, comprising nanosize particles (approximately 40 nm) has been prepared by heating (300°C) ZnCO3, which was obtained as precipitate by mixing ZnSO4 and (NH4)2CO3 solutions. The prepared ZnO was characterized by X-ray diffraction, scanning electron microscopy (SEM), laser-induced breakdown spectroscopy, and adsorption studies. It has been used to catalyze the decolorization of Ponceau S (PS), a model diazo dye, in an aqueous suspension under visible light (I ≈ 1.8 × 10−4 W cm−2). This ZnO was found to be more efficient as a photocatalyst compared to pristine ZnO. ZnO samples with higher temperatures (500°C and 700°C) show less catalytic activity. SEM images show that the particle size of ZnO increases with the increase in calcined temperature of ZnO through agglomeration, resulting in a decrease in surface area. Photodecolorization of PS is affected by its and ZnO concentrations, but unaffected by the initial pH of the solutions in the range of 4 to 7. Illumination for a sufficiently long time completely mineralizes the dye, but no Zn2+ can be detected in the clear solution.Photodegradation kinetics in the ZnO suspension obeys the Langmuir-Hinshelwood equation, and some activation of the ZnO surface by light is indicated.

Comparative Adsorption of Methylene Blue on Different Low Cost Adsorbents by Continuous Column Process

Dyes are commonly found in the effluents of many industries. The effectiveness of adsorption for the removal of dye from wastewaters has been made it an ideal alternative to other expensive treatment methods. Continuous column adsorption is more affective than batch adsorption. A comparative column adsorption study was performed using three different low cost adsorbents for the removal of methylene blue from synthetic wastewater. Sand was collected from Cox’s Bazar, and sugarcane bagasse and used black tea leaves were locally prepared in laboratory. Three columns were designed for different adsorbents maintaining all conditions were to be approximately similar. UV-vis spectroscopic method was used for analysis of methylene blue in solution. Column adsorption experiments were performed to investigate the comparison of breakthrough curves and exhaust capacity of three different adsorbents. Column study shows that the adsorption capacity of used black tea leaves is highest. The adsorption capacity of bagasse is lower than tea leaves but higher than sand. Introduction There is an ever-increasing demand of fabrics and food in the whole world for the rapid expanding population. The wastewaters discharged from dying and printing processes contain high amounts of dissolved colored materials [1]. The disposal of colored wastes such as dyes and pigments into receiving waters damages the environment, as they are carcinogenic and toxic to humans and aquatic life [2, 3]. Besides the problem of color, some dyes impart non-visibility and can be modified biologically to toxic or carcinogenic compounds. Now a day’s concern has increased about the long-term toxic effect of water containing these dissolved pollutants. Methylene blue is commonly used in textile and printing industries. It is moderately to highly toxic by oral and intravenous routes. Eye contact can cause staining of the eye. Inhalations may cause dryness of mouth, flushed skin, rapid pulse, blurred vision, dizziness, etc. [4]. Therefore, proper treatment of wastewater containing methylene blue is essential before its discharge in aquatic system. Different methods are available for the removal of dyes like methylene blue from wastewater but most of them are expensive. Adsorption has received considerable attention for color removal from wastewaters as it offers the most economical and effective treatment methods. Due to high cost of activated carbon, adsorption on natural materials such as sand [5-7], saw dust [8-11], rice husk [10-11], used tea leaves [13-14], coconut coir [15], bagasse [16-17], banana pith [11], fly ash [10-11], orange peel [18] and modified biomaterials [19-21] have received considerable interest because of their local availability and their practically low cost. Use of above biomass materials [821] in batch adsorption process has been found to be highly effective, cheap and eco-friendly. But their proper process of application is very important. This study investigates the potential use of some low cost adsorbents for the removal of methylene blue using column method as a model test. The aim of the study was to compare the adsorption capacity of different low cost adsorbents such as sand, sugarcan bagasse and used black tea leaves, in column adsorption process by constructing breakthrough curves for different column materials using ideal operational conditions and determining their column exhaustive capacity. International Letters of Chemistry, Physics and Astronomy Submitted: 2017-04-04 ISSN: 2299-3843, Vol. 77, pp 26-34 Revised: 2017-12-20 doi:10.18052/www.scipress.com/ILCPA.77.26 Accepted: 2018-01-19 2018 SciPress Ltd, Switzerland Online: 2018-01-25 SciPress applies the CC-BY 4.0 license to works we publish: https://creativecommons.org/licenses/by/4.0/ Materials and Methods Preparation of adsorbent Sand. Sand is cheap and easily available in nature. In this study the sand was collected from Cox’s Bazar, Bangladesh. Figure 1(a) shows the optical view of the collected sand. It was dried well in an oven (NDO-450, EYELA, Japan) at 105 C for 4 hours, crushed and sieved through metallic sieve of mesh size 0.140 mm and screened out. Sugarcane baggase. Sugarcane bagasse (or bagasse) was collected from local market of Dhaka city and washed with boil water to remove the sweet materials. Then it was dried in an oven (NDO-450, EYELA, Japan) at 105 C for 5 hours, crushed and sieved through metallic sieve of mesh size 0.140 mm and screened out. Figure 1(b) shows the optical view of the collected bagasse. Used black tea leaves. Fresh black tea leaves were collected from departmental store in Dhaka city, Bangladesh. Figure 1(c) shows the optical view of the collected Fresh black tea leaves. About 50 g of fresh black tea leaves were boiled in 500 mL of distilled water for 2 hours. Boiled tea leaves were washed 3-4 times with hot distilled water followed by cold distilled water in several times until the tea liquor was completely disappeared. After washing, tea leaves were dried in an oven (NDO-450, EYELA, Japan) at 105 C for 10 hours. Dried used black tea leaves (UBTL) were sieved through the metallic sieve of mesh size 0.140 mm and screened out. Figure 1. Raw materials of adsorbants: (a) sand, (b) sugarcane bagasse and (c) Fresh black tea leaves. Methylene blue and its analysis Methylene blue (MB) is a heterocyclic aromatic compound, also known as methylthioninium chloride. It’s IUPAC name is 3,7-bis(Dimethylamino)-phenothiazin-5-ium chloride, CAS number is 61-73-4, molecular formula C16H18ClN3S and molar mass is 319.85 g∙mol. Synonyms of Methylene blue are Basic blue 9, Swiss blue, Chromosmon, Methylthionine chloride and Urolene blue. Methylene blue is a compound consisting of dark green crystals or crystalline powder, having a bronze-like luster. Solutions in water or alcohol have a deep blue color. Methylene blue is a potent cationic and basic dye with maximum absorption of light around 670 nm. The specificity of absorption depends on a number of factors, including protonation, adsorption to other materials, and metachromasy the formation of dimers and higher-order aggregates depending on concentration and other interactions [22]. Methylene blue can exist as MB, MBH2, (MB)2 and (MB)3 in aqueous solution. Three different forms of structural formula of methylene blue are presented in Fig. 2 [22]. Analytical grade Methylene blue (MB) was collected from Merck Germany. Required amount of dried methylene blue was taken to prepare 10×10 M of stock solution by dissolved in distilled water. Further dilution was made whenever necessary. To construct a calibration curve, the absorbance of different concentrated solutions of MB within the range of 1.0×10 to 4.0×10 M was measured at pH 6.5 by a double beam UV-vis spectrophotometer (UV-160A, Shimadzu, Japan) using λmax = 665 nm. Measured absorbance was plotted against the respective concentration of MB in different solutions to receive the calibration curve. (a) (b) (c) International Letters of Chemistry, Physics and Astronomy Vol. 77 27