Application of Wasted Oolong Tea as a Biosorbent for the Adsorption of Methylene Blue

Hindawi Journal of Chemistry Volume 2019, Article ID 4980965, 10 pages https://doi.org/10.1155/2019/4980965 Research Article Application of Wasted Oolong Tea as a Biosorbent for the Adsorption of Methylene Blue Yunfei Hu, Yue Zhang, Yuqun Hu, Chen-Yao Chu , Jinke Lin , Shuilian Gao, Dongyi Lin, Jing Lu, Ping Xiang, and Tzu-Hsing Ko Anxi College of Tea Science, Fujian Agricultural and Forestry University, Fuzhou, Fujian, China Correspondence should be addressed to Tzu-Hsing Ko; Yunfei Hu and Yue Zhang contributed equally to this work. Received 25 September 2018; Revised 13 November 2018; Accepted 6 December 2018; Published 16 January 2019 Academic Editor: Mostafa Khajeh Copyright © 2019 Yunfei Hu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tea powder, a biosorbent prepared from wasted oolong tea, was collected as a prospective adsorbent for the adsorption of methylene blue (MB) from aqueous solution. The effect of factors on adsorption efficiency, isotherms, kinetics, and potential mechanism was carried out. Adsorption capacity of MB onto wasted tea powder increased with the MB concentration and contact time, whereas the increase in pH value and ion strength appeared to have a negative effect for the adsorption process. The adsorption efficiency increased rapidly and reached a stable state within 120 min. The optimal tea powder loading weight is suggested to be at 0.1 to 0.2 g, and the highest efficiency of 94.8% is achieved at 333 K. There were no significant changes in adsorption efficiency when the effect of temperature is considered. The Langmuir isotherm model was found to be the best isotherm models to elucidate the adsorption mechanism in this study. The maximum adsorption capacities calculated at different temperatures by the Langmuir model ranging from 312.5 to 333.3 mg·g−1 were much close to the experimental results. From the kinetic analysis, the pseudo--second-order model was found to be the best model to describe the adsorption behavior. The calculated adsorption capacities at different initial MB concentrations by the pseudo-second-order model ranging from 92.34 to 400 mg·g−1 were well close to the experimental data. The fitting results obtained from the intraparticle diffusion model suggested that the intraparticle diffusion was not the only rate-controlling step and some other mechanisms along with the intraparticle diffusion were probably involved. The intraparticle diffusion of MB molecules into pore structures of wasted tea powder is the ratelimiting step for the adsorption process in this study. The repetitive cycle experiments indicated that the wasted oolong tea powder was efficiently regenerated using NaOH and thus be used for many times. 1. Introduction Dyeing is one of the important raw materials for many industries such as dyeing, textile, printing, cosmetic, and papermaking [1, 2]. In addition to obvious color in appearance, dyeing wastewater poses a serious toxicity to the ecosystem because of its high concentration, complex organic components, and lower biodegradability. It has been estimated that about 2% of the produced dyes are directly emitted into water resources, which causes a severe environmental and health problems [3, 4]. Therefore, the removal of dyeing wastewater from aqueous solution is of great importance and crucial. Many techniques have been developed to treat dyeing wastewater including biological treatment, chemical degradation, membrane separation, and catalytic oxidation [5–8]. Among these treatments, adsorption has been considered as one of the effective and lowcost processes for dyeing removing from wastewater. Biosorbent is the material which is a byproduct of wastes from the agricultural waste material. The major advantages of biosorbent are the relative low cost, high efficiency, and no additional nutrient requirement [9]. Therefore, it has been become a popular material for environmental pollutant remediation. In the past, many agricultural waste products including grass waste, rice husk, and peel have been used for the removal of pollutants [10–13]. Thousand tones of wasted tea are produced and disposed unutilized every day in China. The main constituents of tea leaves are cellulose, 2 Journal of Chemistry hemicelluloses, lignin, tannins, and proteins. The functional groups in these compounds are mainly hydroxyl, aromatic carboxylate, amino, sulfonic, and phenolic groups, which promote the physicochemical interactions for adsorption of heavy metals and other pollutants [14]. China is the largest tea-producing country, and the production in 2010 amounted to 1475 kilotons and 35.4% of the total world production [15]. It is undoubtedly that the huge amount of wasted tea was produced in China, leading to the severe environmental problem. The main objective of this study was to evaluate the potential of wasted oolong tea powder as an alternative biosorbent for the removal of MB from aqueous. A series of operative factors, including contact time, initial MB concentration, wasted tea powder loading weight, temperature, pH value, and ionic strength on the adsorption efficiency and capacity, were experimentally investigated. The equilibrium isotherms were determined by several models to understand the mechanism of MB. Furthermore, the kinetics involved in the adsorption process was evaluated at different initial MB concentrations. was adjusted to a range of 3–11 with 0.1 N NaOH and 0.1 N HCl to investigate the effect of pH on adsorption. The concentrations of MB with different pH values were measured at a wavelength of 664 nm. Results indicated that there are no appreciable changes in spectra of MB in the used pH range. The pH value at different concentrations of MB was measured between 4.7 and 4.8, showing a stable pH range for adsorption experiment. All adsorption experiments were carried out in a conical flask with a 50 mL of MB solution and were placed on a thermocontrolled shaker with a shaking rate of 200 rpm. After the adsorption experiment, the solution was centrifuged at 5000 rpm for 10 minutes and then the supernatant solution was analyzed to determine the concentration of MB by the UV-visible spectrophotometer. The adsorption efficiency and adsorption capacity were calculated using the following equation: C − Ct adsorption efficiency(%) � 0 × 100, C0 (1) C0 − Ct adsorption capacity � × V, C0 2. Materials and Experimental Procedure where C0 (mg·L−1) is the initial concentration of MB and Ct (mg·L−1) is the concentration of MB at any time t. M (g) is the wasted tea powder loading weight. Duplicate measurements were conducted for each sample, and mean values were used for the adsorption calculation. 2.1. Tea Sample Preparation. Tea samples used in this study were collected from a tea factory located at Anxi County, Fujian Province, and was classified to the oolo (...truncated)