Author ORCID Identifier

https://orcid.org/0009-0003-3545-1581

Date of Award

17-8-2025

Document Type

Thesis

School

School of Civil Engineering

Programme

Ph.D.-Doctoral of Philosophy

First Advisor

Dr.M.Mahalakshmi

Keywords

Adsorption, Prosopis Juliflora, Biochar, Ionic Liquid, Wastewater Treatment

Abstract

Water resources are increasingly contaminated by toxic pollutants, particularly industrial effluents, posing significant environmental concerns. Addressing the toxicity of these pollutants, especially those released from textile industries, presents challenges due to their harmful effects on living organisms. Various treatment methods are employed to mitigate this issue, including coagulation, flocculation, membrane filtration, photocatalytic degradation, adsorption, anaerobic processes, and chemical oxidation. Among these, adsorption emerges as an effective and economical method due to its minimal secondary contamination, negligible sludge production, and the use of inexpensive agricultural and marine waste materials.

This study examines the ability of Prosopis juliflora treated with imidazolium-based ionic liquid (ILPJS) and untreated Prosopis juliflora (PJS) to adsorb the hazardous dye Malachite green (MG) from aqueous solutions. It also evaluates Prosopis juliflora biochar (PJB) and ionic liquid-treated biochar (ILPJB) for removing Cr(VI) from water. Additionally, hybrid biochar prepared from crab shell waste and Prosopis juliflora (RCB), along with its ionic liquid-treated counterpart (ILCB), is explored for removing Congo red dye (CRD).  The first objective of this study is to utilize ILPJS and PJS for MG removal through batch experiments. Optimal biosorption parameters for ILPJS were determined as pH 9.0, a contact time of 30 minutes, and a biosorbent dosage of 0.2 g. The maximum adsorption capacities for PJS and ILPJS were recorded as 6.91 mg/g and 13.64 mg/g, respectively. Adsorption isotherms were best described by the Langmuir model, while kinetic data fitted the PSO model. Thermodynamic analysis confirmed that MG adsorption was endothermic and spontaneous. Cost analysis estimated preparation costs at INR 58 and INR 718 per kg for PJS and ILPJS, respectively. Both materials demonstrated excellent reusability, maintaining effectiveness for up to five cycles.

Further, the second objective deals with biochar derived from Prosopis juliflora (PJB), which was chemically treated with ionic liquid (ILPJB) to enhance Cr(VI) removal. The adsorption process was optimized with a pH of 2.0 and a dosage of 0.18 g for ILPJB, which performed better than untreated PJB. According to data modeling, multilayer adsorption was implied by the Freundlich isotherm model, which explains the adsorption process. PJB and ILPJB had respective adsorption capabilities of 19.27 and 36.63 mg/g. While thermodynamic investigations showed that Cr(VI) adsorption was endothermic and spontaneous, kinetic modeling validated the PSO mechanism. Cost analysis estimated preparation costs at INR 96 and INR 756 per kg for PJB and ILPJB, respectively, highlighting the efficacy of ionic liquid-treated biochar as an adsorbent for Cr(VI).

This study's third objective is to prepare hybrid biochar (RCB) by combining Prosopis juliflora and crab shell waste, followed by treatment with 1-butyl-3-methylimidazolium chloride ionic liquid (ILCB). RCB and ILCB were tested as adsorbents for removing Congo red dye (CRD) from wastewater. Parameters like the solution's pH, CRD initial concentration, dosage of adsorbent, contact time, kinetics, isotherm, and thermodynamics were used to assess the adsorption performance. Optimal conditions included pH 6 for RCB and pH 2 for ILCB, contact time (120 min), and adsorbent dosage (0.16 g). The Langmuir model described the adsorption process, indicating monolayer adsorption. ILCB and RCB had maximum adsorption capabilities of 126.58 and 91.74 mg/g, respectively. Kinetic studies indicated a chemisorption mechanism, as supported by the PSO model. The CRD adsorption was endothermic, spontaneous, and feasible by thermodynamic analysis. Cost analysis estimated preparation costs at INR 96 and INR 756 per kg for RCB and ILCB, respectively, establishing hybrid biochar as a promising adsorbent for wastewater treatment. In conclusion, this study demonstrates the potential of ionic liquid-treated and untreated adsorbents derived from agricultural and marine waste as efficient and cost-effective adsorbents for removing toxic dyes (MG and CRD) and heavy metal chromium from aqueous solutions.

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