Thesis

Response surface methodology for chemical activation of peanut shells : synthesis and application of activated carbon for wastewater treatment

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Awarding institution
  • University of Strathclyde
Date of award
  • 2024
Thesis identifier
  • T16996
Person Identifier (Local)
  • 202080929
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Abstract
  • Modern society has undergone rapid industrialization, which has led to various environmental and health challenges on a global level. Some of the main contributors to these challenges are the industrial discharge of organic dyes, oils, solvents, metal ions etc. and this situation constitutes a serious global concern. Industrial and agricultural effluents are abundant and feasible sources of water; however, these require treatment to protect the ecosystem and enable their reuse. Among various methods employed in the treatment of wastewater, adsorption is one of the most feasible and effective methods. Adsorption processes employ solid materials, known as adsorbents, to facilitate the removal of contaminants from water. Activated carbon (AC) is a widely used adsorbent that has high porosity and adsorption capacity for various contaminants. However, the production of commercial AC faces the challenges of high cost and scarcity of raw materials, due to the high demand of commercial ACs for multiple purposes. Therefore, there is a need to develop low-cost and alternative AC materials by exploring the use of renewable and abundant resources, such as biomass. This work aims to synthesise AC materials from peanut shells, which are an agricultural by-product with high carbon content and potential as a low-cost and renewable precursor for AC production, and to optimise the activation variables (temperature, hold-time, and impregnation ratio, i.e., activating agent weight / precursor weight), to obtain AC materials with high surface areas and yields. Previous studies on peanut shells have lacked a focus in identifying the controlling activation variables to enhance the properties of peanut derived carbon materials. To bridge this gap, the current work employs a single stage chemical activation process, using ZnCl2 as an activating agent, and investigates the effects of activation variables on the properties of AC derived from peanut shells. A design of experiment (DoE) is used to generate a set of experimental design points and obtain a response surface of the results, to visualise the relationship between the responses (surface area and yield) and the independent variables, demonstrating how to model the synthesis of AC from biomass. The work characterises the AC materials synthesised from peanut shells using various techniques, such as Brunauer-Emmett-Teller (BET) analysis of nitrogen adsorption data, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Textural analysis revealed that the synthesised AC materials have relatively high surface areas and porosities, indicating the effectiveness of the chemical activation method, using ZnCl2 as an activating agent. Response surface analysis revealed that temperature and impregnation ratio were the most significant variables in determining the characteristics of the AC materials derived from peanut shells. As revealed, by both textural and surface chemistry analyses, the synthesised AC materials show heterogeneous characteristics. Furthermore, the work provided a screening analysis to select the most effective candidate among the synthesised AC materials, allowing its performance for the removal of ionic dyes (methyl orange, MO and methylene blue, MB) from water to be evaluated. The most effective candidate, denoted as PNTS2-600-15, was obtained under the following activated conditions: temperature of 600 °C, hold time of 15 min and an impregnation ratio of 2. PNTS2-600-15 showed low moisture and ash contents, indicating the high quality of the sample. The adsorption performance of PNTS2-600-15 for MO and MB dyes was investigated by varying the contact time, solution pH, and initial dye concentration. The experimental data were fitted using a number of kinetic and isotherm models to elucidate the adsorption mechanism, and capacity of the carbon material. The results indicate that a pseudo-second-order kinetic model, and the Freundlich and Sips isotherm models, provided the best fit for the adsorption data of both dyes. The Sips model estimated the maximum adsorption capacities of PNTS2-600-15 for MO and MB to be 4584 mg g-1 and 1769 mg g-1 , respectively. These show outstanding capacities in comparison with other AC materials reported in the literature. Finally, the mechanism of adsorption involved in the adsorption processes for MO and MB dyes on PNTS2-600-15 was further investigated, using several experimental techniques, such as post-adsorption characterisation of the textural and surface properties of the carbon material, and desorption studies of the adsorbed dyes. The adsorption mechanism was mainly attributed to π–π interactions, n–π electron donor-acceptor (EDA) interactions, and pore filling. The AC material exhibited good reusability and stability, achieving over 90% dye removal, after five cycles of regeneration. This work demonstrates that peanut shells can be used as a low-cost and effective precursor for AC production, and that the properties and performance of the AC materials can be tuned and tailored by manipulating the activation variables. The work contributes to the development of sustainable and alternative AC materials for water remediation applications.
Advisor / supervisor
  • Somorin, Tosin
  • Fletcher, Ashleigh J.
Resource Type
DOI
Date Created
  • 2023

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