Development of Graphene-Based Adsorbents for Removal of Heavy Metals from Tannery Effluents

Abstract

Water, an essential part of the life cycle, is seriously affected during industrial, domestic and agricultural activities. Tannery effluents contain a huge amount of toxic metal ions, organic and inorganic pollutants that pose high risks to the environmental ecosystem and human beings. Heavy metals, which are non-biodegradable and frequently accumulate in the environment, need special consideration among the numerous pollutants found in water since they can cause harm even at low concentrations. Adsorption has outperformed other technologies in terms of efficiency and economic viability, particularly when it comes to removing contaminants from diluted solutions. In this regard, substantial research is being conducted on novel graphene-based adsorbents. In this framework, the feasibility of using graphene-based adsorbents graphene oxide (GO) and calcium alginate-graphene oxide (CA-GO) composite beads for the removal of chromium(III), copper(ii) and cadmium(II) for the aqueous solution and tannery effluents has been studied. This thesis is divided into five chapters, such as Chapter 1 (Introduction), Chapter 2 (Literature Review), Chapter 3 (Materials and Method), Chapter 4 (Results and Discussion) and Chapter 5 (Conclusions). Chapter 1 describes the background, problem statement, objectives, conceptual framework and thesis outlines of the study. Chapter 2 reviews the literature on water pollution and pollutants, tannery effluents, physicochemical parameters of tannery effluents, heavy metals occurrence in the environment, metal pollutants, different technologies of heavy metal removal and graphene-based adsorbents. Chapter 3 represents information on the materials which were used in this research. This chapter also represents different methods, equations and models used for the research. Chapter 4 is related to the main research work and is divided into two parts. Part 1 narrates the synthesis of graphene oxide (GO), its characterization and its application for the removal of chromium(III), copper(II) and cadmium(II) from aqueous solutions. Here graphite powder was used to prepare GO by modified Hummer’s method. The prepared GO was characterized by FTIR, Raman spectroscopy, SEM, XRD, XPS and BET analysis. The adsorption capacity of GO was found to be 366.3 mg/g for Cr(III) at pH 4.0, 193.05 mg/g for Cu(II) at pH 6.0 and 231.48 mg/g for Cd(II) at pH 7.0.

Part 2 describes the preparation, characterization and application of calcium alginategraphene oxide (CA-GO) composite beads for heavy metals like chromium(III), copper(II)

and

cadmium(II) removal form an aqueous solution. The CA-GO composite beads were prepared using the ratio of sodium alginate and GO (10:1) and 6% CaCl w/w solution. Characterization of CA-GO was carried out by FTIR, SEM, XRD and spectrum analysis. The adsorption capacity of CA-GO is 90.58 mg/g for Cr(III) at pH 4.5, 108.57 mg for Cu(II) at pH 6.0 and 134.77 mg/g for Cd(II) at pH 7.0. Finally, the conclusion and further scope of work are presented in chapter 5. From these results, it is realized that the prepared adsorbents showed significant adsorption capacity for heavy metal removal from aqueous solution and tannery effluents. The distribution of adsorbate (heavy metals) on the adsorbent (GO, CA-GO) surface was explained by Langmuir and Freundlich isotherm models. It was observed that the adsorption was followed both the models, preferably the Langmuir model. The pseudo-first-order and pseudo-second-order reaction kinetic models were used to analyze the experimental data. Analyzing the kinetic parameters, it was observed that the pseudo-second-order kinetic models contributed better correlation for most of the metals and adsorbents. The thermodynamic analyses were also carried out for all adsorbents. It was observed that the adsorptions were physical and spontaneous at lower temperatures in most cases. The regeneration of the used GO and CA-GO composite beads was studied and found that the used adsorbents can be regenerated. The regenerated adsorbents showed significant adsorption capacity for removing heavy metals such as chromium, copper and cadmium from aqueous solution.