Magnetic Graphene Composites for Preconcentration and Removal of Phenolic Compounds

Abstract

A large amount of waste generated by various chemical industries, including phenolic compounds is continuously discharged into water bodies. Owing to its toxicity, phenolic compounds are ranked as priority pollutants by US Environmental Protection Agency and are also included in European community Directive-76/464/EEC for hazardous pollutants added to aquatic system. They are simultaneously harmful to man and animals. They harm various organs of body, such as liver, lungs and kidneys and may lead to cyanosis, coma and death. In order to get rid of these phenolic compounds, efforts have been made for its removal from water bodies. The objectives of the present work were to prepare modified and unmodified magnetic graphene composite for the pre- concentration and removal of selected phenolic compounds from water through solid phase extraction methods. First chapter of the dissertation consist of introduction to nanomaterials, magnetic nanomaterials, modified magnetic nanomaterials, advantages of magnetic nanoparticles over conventional nanomaterials, phenolic compounds and their sources, environmental and biological aspects of phenolic compounds. The second chapter comprises of reported literature, which is related to the preconcentration and removal of phenolic compounds from water samples using various surface modified and unmodified nanomaterials. The third chapter consists of experimental work. It includes preparation of magnetic nanoparticles (Fe3O4), magnetic graphene nanocomposite (Fe3O4-GN), silica coated magnetic nanoparticles (Fe3O4/SiO2), polyaniline coated magnetic/silica nanocomposite (Fe3O4/SiO2/PANI) and magnetic/silica/polyaniline graphene composite (Fe3O4/SiO2/PANI-GO) (MSPGC). This chapter also includes preparation of various phenolic compounds as working standards as well as brief description of various Instruments and methodology used for analysis and characterization purposes. Fourth chapter consists of results and discussions of the experimental work which is mainly divided into two parts. Part one includes characterization of various nanomaterials prepared using various techniques like FTIR, XRD, EDX, SEM and TG analysis. The details of solid phase extraction of 2,4-DCP and 4-NP from aqueous solution using Fe3O4-GN while part 2 is consist of solid phase extraction of 2,4-DCP, 4-NP and BP-A from aqueous solution using MSPGC. It also includes detail study about optimization of various factors effecting removal efficiency, such as temperature, pH, weight of nanocomposite, adsorbate concentration and contact time. Kinetic, isotherm and thermodynamic study is also included in this chapter. In this aspect, common kinetic models such as pseudo-first-order, pseudo-second–order and intraparticle diffusion kinetic model, common isotherm models such as Langmuir and Freundlich isotherms and thermodynamic parameters like ΔH, ΔG and ΔS have been studied. To check the matrix effect on adsorption efficiency and the applicability of the proposed method, it was applied to real environmental water samples. Solid phase extraction of 2,4-DCP on Fe3O4-GN shows that the maximum efficiency for the removal of 2,4-DCP was at pH 3 while with increase in pH removal efficiency decreased. Kinetic study shows that the adsorption process follow pseudo-second-order kinetic model in the concentration range of 30 - 120 mg L-1. The adsorption data better fit to Freundlich isotherm which indicates that the Fe3O4-GN surface is heterogeneous in nature. Thermodynamic data shows that the adsorption process is endothermic and spontaneous. The high activation energy value confirms that the adsorption process is chemically controlled one. Desorption study shows higher recoveries (94%) by using methanolic NaOH (0.1 M) solution. The applicability of the proposed adsorbent, Fe3O4-GN was studied for the real environmental water samples. The results indicates that the proposed magnetic solid phase extraction method could be used for the preconcentration and removal of 2,4-DCP from water samples. Solid phase extraction of 4-NP by Fe3O4-GN shows that the removal efficiency was maximum at pH 3 while minimum at higher pH. Kinetic study shows that adsorption follow pseudo-second-order kinetic model. The sorption data obtained follow Langmuir isotherm, which suggest that adsorption of 4-NP on Fe3O4-GN is monolayer. Thermodynamic data showed that adsorption of 4-NP was exothermic and spontaneous. The activation energy calculated by using Arrhenius equation reveal that adsorption process is physically controlled one. Desorption study shows higher recoveries, which indicates that Fe3O4-GN could be used for the removal and preconcentration of 4-NP from water samples. The applicability of the Fe3O4-GN as an adsorbent was also studied for real environmental water samples analysis. The results indicate that the proposed method can be used for the preconcentration and removal of 4-NP from water samples and it’s a simple, cheap, sensitive, effective and environment friendly. Solid phase extraction of 2,4-DCP onto MSPGC shows that the removal efficiency was maximum at pH 3 while with increase in pH removal efficiency decreased. Kinetic study shows that the adsorption process follow pseudo-second-order kinetic. The adsorption data better fit to Freundlich isotherm which indicates that the MSPGC surface is heterogeneous in nature. Thermodynamic data shows that the adsorption process is endothermic and nonspontaneous. The applicability of the proposed adsorbent MSPGC was studied for the analysis of real environmental water samples. Higher recoveries and low LOD and LOQ shows that the proposed method is a promising tool for the removal and preconcentration of 2,4-DCP from water samples. Solid phase extraction of 4-NP on MSPGC shows that the removal efficiency was maximum at pH 3 while minimum at higher pH. Kinetic study shows that adsorption follow pseudo-second-order kinetic model. The sorption data obtained follow Freundlich isotherm, which suggest adsorption of 4-NP on heterogeneous surfaces through multilayer adsorption mechanism. Thermodynamic data showed that adsorption of 4-NP was exothermic and spontaneous. The activation energy calculated by using Arrhenius equation reveals that adsorption process is physically controlled. Desorption study shows that MSPGC could be used for the removal and preconcentration of 4-NP from water samples. The applicability of the MSPGC as an adsorbent was also applied for the analysis of real water samples. Higher recoveries and low LOD and LOQ show that the MSPGC can efficiently be used for the preconcentration and removal of 4-NP from water samples. Solid phase extraction of BP-A on MSPGC shows that the removal efficiency was maximum at pH 7. Kinetic study shows that adsorption follow pseudo-second-order kinetic model. The sorption data obtained follow Freundlich isotherm. Thermodynamic data shows that adsorption of BP-A was physical in nature, exothermic and spontaneous. The negative value of ΔS confirms the stability of adsorption process. Desorption study shows that MSPGC could be reused for the preconcentration and removal of BP-A from water samples. Low LOD and LOQ shows that the proposed magnetic solid phase extraction method using MSPGC is a promising tool for the removal and preconcentration of BP-A from water samples. The proposed method is simple, cost effective, sensitive, effective and environment friendly.