Abstract
Waste black tea powder was used as a potential adsorbent to remove methylene blue (MB) from aqueous solution. Several operating factors in adsorption of MB onto waste black tea powder were investigated, including contact time, initial MB concentration, solution pH, adsorption temperature, and dosage of waste black tea powder. Experimental results revealed that the adsorption efficiency increased with contact time and solution pH values and decreased with initial MB concentration and adsorption temperature. The equilibrium time was estimated to be around 60 min. The maximum adsorption capacity and the highest adsorption efficiency were 302.63 mg·g−1 and 100%, respectively. In kinetic study, pseudo-first-order and pseudo-second-order kinetic models, intraparticle diffusion model, and Boyd and Elovich models were employed to analyze the adsorption behavior and the adsorption mechanism. It was found that the pseudo-second-order kinetic model was suitable to describe the adsorption process, and the calculated equilibrium adsorption capacity was well close to the experimental data for different initial MB concentrations. The internal diffusion was not the only rate-controlling step, and the existence of boundary effect was observed in this study. From isotherm analysis, the equilibrium data were well represented by the Langmuir model, rather than Freundlich, Dubinin–Redushckevich, or Temkin models. The nonlinear fitting for various isotherm models implied that the adsorption behavior between MB and waste black tea powder was complication. Thermodynamic parameters including changes in Gibb’s free energy, enthalpy, and entropy suggested that adsorption of MB onto waste black tea powder was a spontaneous and exothermic process. The multiple regeneration/adsorption experiments indicated that the used black tea powder efficiently remained more than 75% after five cycles using NaOH as a regenerative reagent and thus be used for many times. Therefore, as a low-cost and easily available material, waste black tea powder could be applied in wastewater treatment.
Highlights
Synthetic dyes are extensively used in various fields such as textile, printing, and decoration [1]
Methylene blue (MB) was obtained from Tianjin Zhiyuan Chemical Reagents Factory (Tianjin, China). e pH value of the MB solution was adjusted with HCl (Sinopharm Chemical Reagent Company) and NaOH (Sinopharm Chemical Reagent Company)
No sharp peaks were detected in the XRD pattern, indicating the major species present in black tea are in form of amorphous texture. e FTIR spectrum of waste black tea powder before and after adsorption of MB revealed that the major signal features of adsorbed black tea sample corresponded to the standard MB, indicating that the MB is significantly adsorbed on the surface of black tea and resulted in the disappearance of some functional groups for fresh black tea
Summary
Synthetic dyes are extensively used in various fields such as textile, printing, and decoration [1]. Stability, high chroma, and high concentration, synthetic dyes detrimentally affect aquatic lives and human beings [2]. Studies have proven that textile wastewater can reduce the level of dissolved oxygen and inhibit the reproduction of aquatic organisms if it enters a water body [3, 4]. Synthesis of dyes results in increased incidence of noncommunicable diseases, such as hormone disruptions, asthma and allergies, and chronic lung diseases, and contributes to occupational diseases, such as chronic kidney disease of multifactorial origins [5]. Methylene blue (MB) can be used in several applications, such as a vital component in the textile industry, an adjuvant in clinical practice or a disinfectant in fishery [6,7,8].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
