Study On Preparation And Adsorption Property Of Activated Carbon From Windmill Palm Sheath Fiber

Environment degradation, resources lack and energy crisis make human beings realized the importance and urgency of protecting the environment, as well as seeking and developing the natural resource. Palm sheath fiber(palm fiber), as a natural polymer material, is a typical kind of renewable biomass resources and widespread in nature. It is a important topic of sustainable development to deeply explore and make full use of the potential properties of palm fiber and its products. As a wood fiber, palm fiber itself has porous structure and is a ideal material for preparation of activated carbon, which will have important research significance for environmental treatment and broadening its application. From the perspective of development and application of new natural fiber, the main work of this paper is to prepare activated carbon from palm fiber by KOH activation, study on its activation technology and the adsorption performance and mechanism of palm fiber-based activated carbon. This research aims at broadening application fields of this natural polymers, providing valuable reference and new ways for the application of palm fiber-based activated carbon in waste liquid and gas treatment and environment protection, contributing to solve the problem of resources lack and energy crisis, which is of great practical significance.In this study, chemical activation with KOH was used to prepare activated carbon from palm fiber for full utilization of the bioresource. Palm fiber was first powdered.Next, single-factor experiment analysis and orthogonal experiment design were used to determine the optional activation parameters for preparation of palm fiber powder(PFD)-based activation carbon(PFAC), in which activation mass ratio, activation temperature and time were chosen as the factors, and adsorbed amount of methylene blue(MB) as the evaluation index. The pyrolysis process of PFD and activation process of KOH were investigated by thermogravimetric analysis(TGA). PFAC were then prepared under the optimized activation condition and characterized by SEM, FTIR,XRD, and nitrogen adsorption techniques. MB was chosen as the adsorbate. The adsorption characteristics of MB on PFAC were evaluated. The adsorption effects of various parameters such as contact time, initial MB concentration(50-600 mg/L),solution pH(2-12), and temperature(30-50 °C) were investigated. Equilibrium data of the adsorption experiment were fitted to Langmuir, Freundlich, and Dubinin–Radushkevich isotherms to study the adsorption isotherm and evaluate the adsorption property of PFAC. Pseudo-first-order kinetics, pseudo-second-order kinetic and Weber and Morris intra-particle diffusion model were used to study the adsorption kinetics. The adsorption thermodynamics were studied by formula computing. The results show that:(1) Results show that the optimal process for preparing an excellent adsorbent from palm fiber employs an impregnation ratio of 4:1 at 850 °C for 2.5 h, which can result in a good adsorption property for methylene blue. The effect factors on adsorption capacity of PFAC for MB follow the sequence: impregnation ratio ﹥activation temperature﹥activation time.(2) TG analysis indicates that the reaction mechanisms were deduced in two phases.The reaction mechanisms in the first carbonization process were mainly related to substitution, scission, and oxidization reactions of methylene. In the second activation process, KOH and carbon began to react at 350 °C, producing potassium compounds,which further reacted with carbon.(3) PFAC activated with KOH exhibits abundant well-developed and well-distributed pores on its surface seeing from the SEM images. The details of FTIR spectrum indicates that PFAC contained many functional groups, which could interact with the cationic groups of MB or other adsorbates. The isotherm of PFAC for nitrogen adsorption suggests a combination of type I and type IV isotherm based on the International Union of Pure and Applied Chemistry(IUPAC) classification, which indicates the presence of microporous and mesoporous structures. The BET surface area,total pore volume and average pore size of PFAC are 1734.34 m2/g, 0.96cm3/g and 2.28 nm, respectively. XRD suggests a strong crystallized structure of cellulose and a carbonaceous crystalline structure.(4) The factors including initial MB concentration, contact time, solutiontemperature and pH are all have effects on the adsorption capacity of PFAC for MB. The adsorption capacity increased with an increase in the four parameters studied.(5) The adsorption equilibrium data of MB on PFAC are best represented by theLangmuir isotherm, with a maximum monolayer adsorption capacity of 384.68mg/g50℃. The adsorption kinetics follows the pseudo-second-order kinetic model, which indicates a chemical adsorption process of the PFAC for MB. The values of thermodynamic parameters, including standard enthalpy changes(ΔH), entropy changes(ΔS), and free energy changes(ΔG) demonstrate that the adsorption process of MB on PFAC is spontaneous in nature and endothermic.