Abstract
A bio-based Silica/Calcium Carbonate (CS–SiO2/CaCO3) nanocomposite was synthesized in this study using waste eggshells (ES) and rice husks (RH). The adsorbents (ESCaCO3, RHSiO2and, CS-SiO2/CaCO3) characterized using XRD show crystallinity associated with the calcite and quartz phase. The FTIR of ESCaCO3shows the CO−23group of CaCO3,while the spectra of RHSiO2 majorly show the siloxane bonds (Si–O–Si) in addition to the asymmetric and symmetric bending mode of SiO2. The spectra for Chitosan (CS) show peaks corresponding to the C=O vibration mode of amides, C–N stretching, and C–O stretching. The CS–SiO2/CaCO3nanocomposite shows the spectra pattern associated with ESCaCO3and RHSiO2.The FESEM micrograph shows a near monodispersed and spherical CS–SiO2/CaCO3nanocomposite morphology, with an average size distribution of 32.15 ± 6.20 nm. The corresponding EDX showed the representative peaks for Ca, C, Si, and O. The highest removal efficiency of phenol over the adsorbents was observed over CS–SiO2/CaCO3nanocomposite compared to other adsorbents. Adsorbing 84–89% of phenol in 60–90 min at a pH of 5.4, and a dose of 0.15 g in 20 ml of 25 mg/L phenol concentration. The result of the kinetic model shows the adsorption processes to be best described by pseudo-second-order. The highest correlation coefficient (R2) of 0.99 was observed in CS-SiO2/CaCO3nanocomposite, followed by RHSiO2and ESCaCO3. The result shows the equilibrium data for all the adsorbents fitting well to the Langmuir isotherm model, and follow the trend CS-SiO2/CaCO3> ESCaCO3> RHSiO2. The Langmuir equation and Freundlich model in this study show a higher correlation coefficient (R2= 0.9912 and 0.9905) for phenol adsorption onto the CS–SiO2/CaCO3nanocomposite with a maximum adsorption capacity (qm) of 14.06 mg/g compared to RHSiO2(10.64 mg/g) and ESCaCO3(10.33 mg/g). The results suggest good monolayer coverage on the adsorbent’s surface (Langmuir) and heterogeneous surfaces with available binding sites (Freundlich).
Highlights
The synthesis of adsorbents with adequate adsorption capacity and functionality underscores the need to efficiently remove emerging pollutants in water sources for humanHow to cite this article Bwatanglang IB, Magili ST, Kaigamma I. 2021
The peaks at 3,285–3,629 cm−1, 1,651 cm−1, 1,056 cm−1, and 796 cm−1 in the spectra of RHSiO2 are from the silanol OH groups of water, the H–O–H bending vibration, siloxane asymmetric bending vibrations bands (Si–O–Si), and the symmetric bending mode of silanol (Si–O)
The broadband around 3,312–3,618 cm−1 and the peak centered at 1,643 cm−1 are fingerprints from O–H bond and H–O–H bending vibrations of ESCaCO3, and RHSiO2, in the CS-SiO2/CaCO3 nanocomposite
Summary
The synthesis of adsorbents with adequate adsorption capacity and functionality underscores the need to efficiently remove emerging pollutants in water sources for humanHow to cite this article Bwatanglang IB, Magili ST, Kaigamma I. 2021. The synthesis of adsorbents with adequate adsorption capacity and functionality underscores the need to efficiently remove emerging pollutants in water sources for human. These emerging pollutants, if not removed in water sources for human consumption, could, in the long run, interfere and mimic physiological processes that regulate the metabolic functions of enzymes, hormones, and several biochemical indices (Ali, AL-Othman & Alwarthan, 2016). One of the emerging chemicals classified as a priority pollutant is phenol (United States Environmental Protection Agency (USEPA), 1985), with a recommended permissible limit of 1.0 μg/L allowed in drinking water (Khare & Kumar, 2012). The fingerprint of phenolic compounds is manifested in humans through several exposure pathways, exerting their toxicity by inducing protoplasmic poison, denaturing proteins, and creating an acid-base imbalance amongst many (Agency for Toxic Substances & Disease Registry, 2014)
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