Two step synthesis and activation of hydrothermally pre-treated lignocellulosic residues for removal of heavy metals from single solute system / Shobana Sinniah

Shobana , Sinniah (2024) Two step synthesis and activation of hydrothermally pre-treated lignocellulosic residues for removal of heavy metals from single solute system / Shobana Sinniah. Masters thesis, Universiti Malaya.

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Abstract

Application of commercial activated carbon derived from nonrenewable fossil fuel sources as adsorbent materials is restricted due to its’ high cost involved in preparation process. This constraint has thus prompted the development of highly cost-effective activated carbons (ACs), resulting in the utilization of Lignocellulosic biomass residues (LSM). These resources are not only renewable, but also abundantly available. The utilization of Lignocellulosic biomass waste residues (LSM) will not only contribute to the resolution of difficulties related with the dumping of such components into the environment but will also aid in the conversion of these materials into value added products; like char and activated carbons (ACs), bio-oil and bio-gas. Synthesized activated carbon (ACs) can be used as versatile low-cost adsorbent materials for water treatment for purifying the heavy metals from wastewater. In this study, surface-engineered activated carbon (ACs) was synthesized from the lingo-cellulosic waste of Durio zibethinus (durian wood) sawdust (DWS) and Adansonia kilima (Baobab) seed powder (BSP) using hydrothermal carbonization (HTC) followed by pyrolysis in the presence of a mild activating agent of K2CO3 for activation in the second step. The first step of carbonization was carried out in presence of water at a lower temperature of 80°C to yield hydrochar. Water is considered as a green catalyst for carbonization, and the resulting hydrochar can be used to produce functional activated carbon (ACs). It was determined that the process input variables of pyrolysis temperature (A1), residence time (B1), and ratio (C1) had the greatest influence on the production of superior quality carbon with the highest removal efficiencies (β1) for Copper (II) cations from waste effluents, carbon yield percentages (β2) and fixed carbon percentages (β3). The analysis of variance (ANOVA) was utilized to generate appropriate mathematical models, which were then subjected to proper statistical analysis to determine their accuracy. Response Surface Methodology (RSM) relying on the Box Behnken design (BBD) was implemented for experimental design. The surface area of the carbonized hydrochar sample (DSWC and BSPC) and the optimized carbon sample (DSWAC and BSPAC) with porous texture were estimated using Brunauer, Emmett, and Teller (BET) adsorption/desorption curves based on the nitrogen (N2) isotherm. With the help of Field Emission Scanning Electron Microscopy (FESEM), it was possible to observe the surface morphological structure. Thermogravimetric analysis (TGA) was performed to ascertain the thermal stability of the synthesized samples. The ultimate method was used to determine the change in carbon content of the samples. Surface functional groups were determined using FTIR analysis. The BET isotherm showed an increase in the sorption capacity of DSWAC and BSPAC for pollutants in a liquid phase system. Hydrochar (BSPC and DSWC) samples were microporous with relatively lower surface area. BET analysis of DSWAC and BSPAC showed that micropores with a specified fraction of mesopores were present in the activated carbon. Increased fixed carbon retention combined with lower levels of moisture and ash residues results in the adsorbent activated carbons (ACs) of (DSWAC and BSPAC) has made them a better adsorbent material for copper (II) cations removal from lab-based waste synthetic water.

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