Biopolymer Based Hydrogel for Adsorption of Heavy Metal Ions from Aqueous Solution: Experimental and Theoretical Investigation
| dc.contributor.advisor | Zebene Kiflie (Prof.) | |
| dc.contributor.author | Leta Lemma | |
| dc.date.accessioned | 2024-07-31T08:29:31Z | |
| dc.date.available | 2024-07-31T08:29:31Z | |
| dc.date.issued | 2024-04 | |
| dc.description.abstract | Contamination of water by heavy metal ions, in particular, hexavalent chromium (Cr6+) ion, lead (Pb2+) ion and cadmium (Cd2+) ion, has become one of the most serious issues threatening human health and thus remedial measure have to be taken. Adsorption–based research toward biodegradable polymers for heavy metal ions remediation has received much attention in recent years due to environmental concerns. Polysaccharides in this domain are interesting starting materials for the preparation of novel adsorbents. In this work, novel type of biopolymer–based hybrid hydrogel such as PPSgCG, PCCFG, and CZVI–CS–PVA were designed for removal of Cr6+, Pb2+, and Cd2+ ions from aqueous solution. Polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), acrylamide–grafted native starch (Coccinia abyssinica) (S–g–AAm), chitosan (CS), and graphene oxide (GO) were used to prepare PVA–PVP–S–g–AAm–CS–GO (PPSgCG) hydrogel. L-cysteine–functionalized graphene oxide (CFG), chitosan, and polyvinyl alcohol were used to synthesis polyvinyl alcohol–chitosan–cysteine–functionalized graphene oxide (PCCFG) hydrogel. L–cysteine stabilized zero–valent iron (CZVI), chitosan, and polyvinyl alcohol were used to prepare L–cysteine–zero–valent iron–chitosan–polyvinyl alcohol (CZVI–CS–PVA) hydrogel. Physiochemical properties of freeze–dried hydrogel were characterized by Fourier transform infrared spectroscopy (FTIR; Spectrum 65, PerkinElmer), zetasizer (3000HS), scanning electron microscopy (SEM; JCM-6000 Plus, Japan), energy dispersive X–ray spectroscopy (EDX; JSM–IT 100, JEOL), X-Ray Diffractometer (XRD; XRD–7000, Shimadzu, Japan), and thermogravimetric analysis (TGA/DTA; HCT–1, China). Adsorptions of Cr6+ ion onto PPSgCG and CZVI–CS–PVA hydrogel, and Pb2+ and Cd2+ ions onto PCCFG hydrogel as functions of initial heavy metal ion concentration, pH, time, hydrogel dose, and temperature have been studied by following a one–factor–at–a–time approach. The Cr6+ ions concentration in solution was determined by UV–vis spectrophotometer (Human, X–ma 1200). The Pb2+, Cd2+, and Cu2+ ions concentration in the solution after adsorption was determined by atomic adsorption spectroscopy (AAS; ZEEnit 700p, Analytikajena). The adsorption of Cr6+ onto PPSgCG hydrogel, at optimum conditions: 2, 100 mg l-1, 120 minutes, 3 g l-1, and 25oC of pH, initial Cr6+ ion concentration, hydrogel dose and temperature, respectively; were obtained considering both adsorption capacity and removal efficiency. The adsorption data agree with Langmuir (R2 = 0.99) isotherm at 25°C and follow pseudo–second–order kinetic model (R2 = 0.999) at pH of 2. The maximum adsorption capacity of the PPSgCG hydrogel towards to Cr6+ was 93 mg g−1. The obtained negative standard Gibb‟s free energy (ΔG°= – 1.120 kJ mol−1) and negative enthalpy (ΔH°= – 2.360 kJ mol−1) reveal the spontaneity and exothermic nature of Cr6+ ion adsorption onto the hydrogel. Moreover, the adsorption thermodynamics shows enthalpically favoring host–guest complexion along with decrease in entropy. Furthermore, the effect of common competing ions such as sulfate (SO32-), phosphate (PO43-), nitrate (NO3−), and chloride (Cal−) ions on adsorption efficiency and selectivity of Cr6+ ion on the hydrogel were investigated and the result shows that sulfate ion has a significant effect on the Cr6+ ion adsorption, which might be related to identical chemical properties and geometrical configuration. The adsorption of Cr6+ onto CZVI–CS–PVA hydrogel, at optimum conditions: 3, 45 mg l-1, 90 minutes, 4 g l-1, and 25oC of pH, initial Cr6+ ion concentration, hydrogel dose and temperature, respectively; were obtained considering both adsorption capacity and removal efficiency. The adsorption data agree with Langmuir isotherm (R2 = 0.99) at 25°C and follow pseudo–second order (R2 = 0.999) model at pH of 3. The maximum adsorption capacity of the PPSgCG hydrogel towards to Cr6+ was 15.86 mg g−1. The adsorption of Pb2+ and Cd2+ onto PCCFG hydrogel, at optimum conditions: 5, 225 mg l-1, 50 minutes, 2 g l-1, and 25oC of pH, initial Pb2+ and Cd2+ ion concentration, hydrogel dose and temperature, respectively; were obtained considering both adsorption capacity and removal efficiency. The experimental data well described by a pseudo–second–order kinetic model (R2 = 0.99 for Pb2+ and R2 = 0.98 for Cd2+) and Langmuir isotherm (R2 = 0.980 for Pb2+ & R2 = 0.978) with maximum adsorption capacities of 250 and 192 mg g−1 at 25°C for Pb2+ and Cd2+, respectively. The adsorption capacity of the PCCFG hydrogel increased with the increase in temperature. The value of ΔG° was negative, which shows the spontaneity of the reaction (electron exchange or ion exchange) between the metal ion and electron–rich atoms (–N, –S, –O). The positive ΔH° shows that the adsorption reaction consumes energy and the positive ΔS° shows the strong affinity of PCCFG toward the Pb2+ and Cd2+ ions. Pb2+ had better affinity and less spontaneity than Cd2+. The effect of competing ions was studied in batch adsorption experiments in the solution containing the three metal ions (Pb2+, Cd2+, and Cu2+) and the result shows that the coexistence of metal ions in the solution inhibits the adsorption capacity of the hydrogel compared to solutions containing a single metal ion.Theoretical investigation of adsorption mechanism of Cr6+ and Pb2+: Gauss View 6.0.16 interface were employed to construct the modeled system. The ground state geometry optimization of modeled system were first optimized by Molecular Mechanics (MM) method with aid of Universal Force Field (UFF) followed by Hartree fock (HF) and Density Functional Theory (DFT) method, using Gaussian 09 software package. Moreover, frequency, Natural Bond Orbital (NBO), and energy calculation were done by DFT method with aid of Gaussian 09. Hybrid–generalized gradient approximation (hybrid–GGA), B3PW91–D3 level of theory, where D3 denotes the third–generation dispersion correction by Grimme and basis set, the Stuttgart–Dresden–Boon (SDD) basis set was employed for heavy metal ions, and the 6–31G(d) basis were used for C, N, O, S, and H atoms during geometry optimization, frequency and NBO calculation. Single–point energy calculations were performed using the ωB97XD functional where basis set 6-311+G (d, p) was employed for C, N, O, S, and H atoms, and SDD basis set was employed for heavy metal ions. Solvation effect (H2O) was evaluated with polarizable continuum model (PCM) to mimic the real aqueous solution. The Gaussian simulation result shows that mainly the –N and –O atoms of amine (–NH2), amide (–CONH2), and carboxyl (–COOH) functional group of the hydrogel were responsible for binding of heavy metal ions via electron sharing/covalent bonding. | |
| dc.identifier.uri | https://etd.aau.edu.et/handle/123456789/3356 | |
| dc.language.iso | en_US | |
| dc.publisher | Addis Ababa University | |
| dc.subject | Acrylamide | |
| dc.subject | Adsorbent | |
| dc.subject | Adsorption | |
| dc.subject | Cd2+ ions removal | |
| dc.subject | Chitosan | |
| dc.subject | Cr6+ ions removal | |
| dc.subject | DFT | |
| dc.subject | Graphene oxide | |
| dc.subject | Hybrid hydrogel | |
| dc.subject | L–cysteine | |
| dc.subject | Pb2+ ions removal | |
| dc.subject | PVA | |
| dc.subject | PVP | |
| dc.subject | Starch | |
| dc.subject | Starch grafting | |
| dc.subject | Zero–valent iron | |
| dc.title | Biopolymer Based Hydrogel for Adsorption of Heavy Metal Ions from Aqueous Solution: Experimental and Theoretical Investigation | |
| dc.type | Dissertation |