Browsing by Author "Yegon, Andrew"

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Fluoride Sorption Using Zirconium ion-impregnated Macadamia Nutshell-Derived Biochar from Aqueous Solution: Adsorption Isotherms and Kinetic Modeling
(Research Article, 2022-11-26) Yegon, Andrew; Mtavangu, Stanslaus; Rwiza, Mwemezi; Machunda, Revocatus
Zirconium ion-impregnated macadamia nutshell biochar (ZMNB) was synthesized and tested for its fluoride sorption capacity by exploiting batch experiments. Four temperatures (300, 400, 500, and 600 ℃) were used to pyrolyze the macadamia nutshells to yield macadamia nutshell biochar (MNB) which was separately impregnated with Zr (IV) aqueous solution. Both non-modified and chemically modified MNB were assessed by X-ray diffraction (XRD), attenuated total reflection Fourier Transform Infra-red (ATR-FTIR), field emission scanning electron microscope-energy dispersive X-ray (FESEM-EDS), thermogravimetric analysis, and Brunauer-Emmett-Teller (BET) surface area analyzer. The sequence of F− adsorption capacities for the synthesized biosorbents was ZMNB 300 > ZMNB 400 > ZMNB 500 > ZMNB 600, which revealed the influence of pyrolysis temperature on sorption process. ZMNB 300 had a maximum percentage fluoride removal effectiveness of 99.05% using 1.0 g L− 1 adsorbent lot, at neutral pH for an interaction period of 1 h. The adsorption studies suited perfectly with the pseudo-second-order kinetic model and the linear Langmuir isotherm, affirming a chemisorption process. Thermodynamic studies revealed that the calculated ΔG° value (-5.593 kJ mol− 1) ascribed the rapidity and spontaneity of the sorption action, ΔH° value (30.102 kJ mol− 1) elucidated the endothermic, irreversible and chemisorption process whereas the ΔS° value (118.55 J mol− 1 K− 1) signified the F− adsorption’s random trait on the solid or liquid interface of the ZMNB 300. Results from the sorption experiments using fluoride-contaminated natural water removed the F− ions below the curbed WHO standard (1.5 mg L− 1) for drinking water and therefore, a potential material for practical applications.
Green synthesis of silver silver chloride (Ag/AgCl) nanoparticles using macadamia nutshell xylan extract, characterization and evaluation of its antibacterial activity
(Discover Nano, 2025-07-26) Yegon, Andrew; Oyetade, Joshua; Mtavangu, Stanslaus; Rwiza, Mwemezi; Machunda, Revocatus
Currently, there is unprecedented emergence of antimicrobial resistant (AMR) bacteria which demand urgent development of novel strategies to combat bacterial infections in humans. In this study, we report on a facile and eco-friendly green synthesis of silver-silver chloride nanoparticles (Ag/AgCl-NPs) using macadamia (Macadamia integrifolia) nut-shell (MNS) agro-waste. The effects of physicochemical parameters including pH, Ag ion precursor concentration, time, and temperature were investigated. The biosynthesized Ag/AgCl-NPs sample was characterized using ultraviolet visible spectroscopy (UV–Vis), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) spectroscopy, field emission scanning spectroscopy (FE-SEM), Transmission electron microscopy (TEM), and energy dispersive X-ray (EDX). UV–Vis spectroscopy exhibited surface plasmon resonance (SPR) between 420 and 446 nm typical for silver nanoparticles (AgNPs). FT-IR spectroscopy provided an insight of the phytochemicals responsible for the reduction of Ag+ into Ago and capping/stabilizing the formed Ag/AgCl-NPs. XRD spectroscopy revealed the formation of crystalline Ag/AgCl-NPs with characteristic peaks at around 38.3°, 44.1°, 64.6°, and 77.5° for AgNPs, and 28.9°, 31.9°, 45.4°, 56.3°, and 66.1° for AgCl NPs. FE-SEM spectroscopy exhibited spherical and block like morphologies of agglomerated Ag/AgCl-NPs. TEM illustrated polydisperse spherical shapes of Ag/AgCl-NPs with average particle sizes of 31.11 nm. EDX confirmed the presence of Ag and Cl elements confirming the formation of Ag/AgCl-NPs. The antibacterial activity of the green synthesized Ag/AgCl-NPs was performed using disc diffusion method and the zone inhibition (ZOI) evaluation showed their effectiveness against Gram negative (E. coli) and Gram positive (S. aureus).
Optimization, Characterization and Modeling of Functionalized Macadamia Nutshell Derived-Biochar for Drinking Water Defluoridation
(Springer International Publishing, 2025-02-25) Yegon, Andrew; Mtavangu, Stanslaus; Rwiza, Mwemezi; Machunda, Revocatus
Fluoride contamination in drinking water is a serious global environmental concern owing to its irreversible health effects. This study synthesized Zr(IV)-impregnated macadamia nutshell biochar (Zr-MNSB) by the surface modification of macadamia nutshell biochar (MNSB) and investigated its fluoride removal efficiency and biosorption capacity. Surface modification significantly enhanced the specific surface area and pore size. FE-SEM results exhibited increased porosity with Zr(IV)-impregnation and EDX confirmed Zr(IV) existence on the MNSB surface which enhanced fluoride removal performance. The effect of pH, co-existing ions, biosorbent dosage, contact time, and initial fluoride concentration were investigated using batch experiments. Zr-MNSB showed stable and excellent fluoride removal efficiency (78–99%) with initial fluoride concentration of 10 mg L–1 at a pH range of 2–8 compared to MNSB with 77.78% removal efficiency at pH 2 which declined significantly with pH increase. Zr-MNSB defluorinated naturally contaminated water below the WHO standard (1.5 mg L–1). The Langmuir isotherm fitted well the experimental results with high R2 (0.98) compared to the investigated isotherms and it exhibited maximum fluoride biosorption capacity of 11.97 mg g–1. The pseudo-second-order kinetic model best suited the experimental results with high R2 (≈1.0). The thermodynamic parameters viz., ΔH°, ΔS° and ΔG° revealed that the fluoride removal process was endothermic, irreversible, random, spontaneous, rapid, and chemisorption in nature. Regenerated Zr-MNSB exhibited stable removal efficiency of 72–89% for three cycles but dropped significantly to 47% after the 4th cycle. Thus, this study developed a simple, affordable and efficient biosorbent that’s potential for drinking water treatment.