Preparation of amine-functionalized fibrous silica nanosphere from rice husk ash for lead removal / Rosalyza Hasan

Faculty of Chemical and Natural Resources Engineering

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2019

Includes bibliographical references

Lead (Pb(II)) is one of the most toxic metals found in water bodies through industrial activities which can cause severe hazardous impacts to living organisms even at trace levels. Therefore, several methods for lead removal have been investigated, including the adsorption process. Regarding the selection of adsorbent, fibrous silica nanosphere (KCC-1) has attracted considerable attention owing to its high surface area and fibrous silica morphology. However, owing to the high cost of the commercial silica precursor, utilization of rice husk ash (RHA) (SiO2 = 95.44%) as alternative silica source seems to be a promising approach and the application of amine functionalization will enhance its adsorption capacity. The main objective of this study is to synthesize and characterize KCC-1(RHA) and 3-aminopropyltriethoxysilane modified KCC-1(RHA) (NH2/KCC-1(RHA)) for Pb(II) removal. The experimental started with the extraction of Na2SiO3-RHA from RHA using alkaline fusion method before being used as alternative silica source in synthesizing KCC-1(RHA) and NH2/KCC-1(RHA). The synthesized KCC-1(RHA) and NH2/KCC-1(RHA) were characterized using Transmission Electron Microscopy (TEM), Surface Area Analyzer, X-Ray Diffraction (XRD), and Fourier Transformation Infra-Red (FTIR). The characterization analyses showed that the synthesized KCC-1 consists of fibrous silica morphology with high surface area (SBET, KCC-1(RHA) = 220 m2/g, SBET, NH₂/KCC-1(RHA) = 274 m2/g) comparable with KCC-1 synthesized from commercial silica source, indicating the successful formation of KCC-1 structure from RHA. The adsorption study revealed the positive role of amine modification in adsorption efficiency with 6% enhancement in percentage removal owing to the improvement in surface area and functional groups that responsible in the adsorption process. The experimental data were analyzed using Langmuir, Freundlich, Temkin, and Dubinin-Redushkevich isotherm models, and were found to follow Langmuir isotherm model with maximum adsorption capacity of 28.169 mg/g and high correlation coefficient (R2 = 0.9927), implying monolayer adsorption occurred on the homogenous surface of the adsorbent. Pseudo-first order, Pseudo-second order, and Elovich kinetic models were tested with the experimental data, and Pseudo-second order kinetic model was best fitted the adsorption process, indicating that the adsorption process most likely controlled by the chemisorption process and the rate of reaction is directly proportional to the number of active sites on the surface of adsorbent. The reusability studies revealed that NH2/KCC-1(RHA) performs good adsorption-desorption for five cycles with a moderate reduction (42.70%) in the percentage of Pb(II) removal. The influences of prominent parameters (initial concentration (X1), adsorbent dosage (X2) and time (X3)) on Pb(II) removal was evaluated by RSM, and the optimal conditions were achieved at X1 = 306.88 mg/L, X2 = 2.43 g/L and X3 = 114 min, with 91.2% of Pb(II) removal from aqueous solution. Additionally, NH2/KCC-1(RHA) showed an excellent performance in petrochemical wastewater treatment with excellent Pb(II) removal (90.3%), and acceptable COD (106 mg/L) and BOD (34 mg/L) values, thus affirmed a great potential of NH2/KCC-1(RHA) as an excellent adsorbent for Pb(II) removal.