Browsing by Author "Mtavangu, Stanslaus"

Now showing 1 - 9 of 9

Cockle (Anadara granosa) shells-based hydroxyapatite and its potential for defluoridation of drinking water
(Elsevier, 2022-03-03) Mtavangu, Stanslaus; Mahene, Wilson; Machunda, Revocatus; Bruggen, Bart; Njau, Karoli
The present study describes the synthesis and characterization of a hydroxyapatite (HAp)-based adsorbent derived from biogenic cockle (Anadara granosa) shells for the defluoridation of drinking water. The raw cockle shells and synthesized HAp were characterized by X-ray fluorescence spectroscopy (XRF), attenuated total reflection-Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), Field emission scanning electron microscopes-energy dispersive X-ray (FESEM-EDX) and Brunauer-Emmett-Teller (BET) surface area analysis. As demonstrated by FTIR, cockle shells were found to be composed of calcium carbonate (97.4%), an aragonite polymorphous type of carbonate mineral. XRD and SEM analysis supported the formation of a nanocrystalline HAp with an average crystal size of 19.08 nm and 57.1 nm, respectively, with a surface area of 105.8 m2/g and a pore size of 5.6 nm, as depicted by BET. Batch adsorption experiments were conducted using the Box-Behnken design (BBD) with five input parameters: adsorbent dose (2–10 g/L), initial fluoride concentration (10–80 mg/L), contact time (0.5–24 h), reaction temperature (303–333 K), and pH. (3–11). BBD revealed the following optimum conditions: adsorbent dose (6 g/L), initial fluoride concentration (45 mg/L), contact period 12.25 h, reaction temperature (303 K), and pH 3. Experimentally, the adsorption of fluoride on HAp fitted well with the non-linear Langmuir isotherm and linear pseudo-second order kinetics, signifying the chemisorption process. A maximum adsorption capacity (qm) of 15.374 mg/g, which is closer to the experimental value of 14.053 mg/g, was presented by the Langmuir isotherm. Thermodynamically, the adsorption process was spontaneous, endothermic, and stable in nature. The defluoridation mechanism was through electrostatic attraction, ion exchange, hydrogen bonding, and precipitation. Furthermore, the synthesized HAp and bone char were used to examine their efficacy in defluoridating field water: HAp performed better at natural pH, where the treated water met WHO and TBS standards, whereas bone char had insufficient fluoride removal, especially at high fluoride levels. As a result, this study suggests that HAp derived from Anadara granosa shells could be a viable adsorbent for the defluoridation of drinking water.
Cockle (Anadara granosa) shells-based hydroxyapatite and its potential for defluoridation of drinking water
(Elsevier, 2022-02-27) Mtavangu, Stanslaus; Mahene, Wilson; Machunda, Revocatus; Bruggen, Bart; Njau, Karoli
The present study describes the synthesis and characterization of a hydroxyapatite (HAp)-based adsorbent derived from biogenic cockle (Anadara granosa) shells for the defluoridation of drinking water. The raw cockle shells and synthesized HAp were characterized by X-ray fluorescence spectroscopy (XRF), attenuated total reflection-Fourier transform infrared (ATR-FTIR), X-ray diffraction (XRD), Field emission scanning electron microscopes-energy dispersive X-ray (FESEM-EDX) and Brunauer-Emmett-Teller (BET) surface area analysis. As demonstrated by FTIR, cockle shells were found to be composed of calcium carbonate (97.4%), an aragonite polymorphous type of carbonate mineral. XRD and SEM analysis supported the formation of a nanocrystalline HAp with an average crystal size of 19.08 nm and 57.1 nm, respectively, with a surface area of 105.8 m2/g and a pore size of 5.6 nm, as depicted by BET. Batch adsorption experiments were conducted using the Box-Behnken design (BBD) with five input parameters: adsorbent dose (2–10 g/L), initial fluoride concentration (10–80 mg/L), contact time (0.5–24 h), reaction temperature (303–333 K), and pH. (3–11). BBD revealed the following opti- mum conditions: adsorbent dose (6 g/L), initial fluoride concentration (45 mg/L), contact period 12.25 h, re- action temperature (303 K), and pH 3. Experimentally, the adsorption of fluoride on HAp fitted well with the non-linear Langmuir isotherm and linear pseudo-second order kinetics, signifying the chemisorption process. A maximum adsorption capacity (qm) of 15.374 mg/g, which is closer to the experimental value of 14.053 mg/g, was presented by the Langmuir isotherm. Thermodynamically, the adsorption process was spontaneous, endo- thermic, and stable in nature. The defluoridation mechanism was through electrostatic attraction, ion exchange, hydrogen bonding, and precipitation. Furthermore, the synthesized HAp and bone char were used to examine their efficacy in defluoridating field water: HAp performed better at natural pH, where the treated water met WHO and TBS standards, whereas bone char had insufficient fluoride removal, especially at high fluoride levels. As a result, this study suggests that HAp derived from Anadara granosa shells could be a viable adsorbent for the defluoridation of drinking water.
Facile biosynthesis of Ag–ZnO nanocomposites using Launaea cornuta leaf extract and their antimicrobial activity
(NM-AIST, 2013-11-14) Makauki, Elizabeth; Mtavangu, Stanslaus; Onita, Basu; Rwiza, Mwemezi; Machunda, Revocatus
The quest to synthesize safe, non-hazardous Ag–ZnO nanoomposites (NCs) with improved physical and chemical prop- erties has necessitated green synthesis approaches. In this research, Launaea cornuta leaf extract was proposed for the green synthesis of Ag–ZnO NCs, wherein the leaf extract was used as a reducing and capping agent. The antibacterial activity of the prepared nanoomposites was investigated against Escherichia coli and Staphylococcus aureus through the disc diffusion method. The influence of the synthesis temperature, pH, and precursor concentration on the synthesis of the Ag–ZnO NCs and antimicrobial efficacy were investigated. The nanoparticles were characterized by ATR-FTIR, XRD, UV–Vis, FESEM, and TEM. The FTIR results indicated the presence of secondary metabolites in Launaea cornuta which assisted the green synthesis of the nanoparticles. The XRD results confirmed the successful synthesis of crystalline Ag– ZnO NCs with an average particle size of 21.51 nm. The SEM and TEM images indicated the synthesized nanoparticles to be spherical in shape. The optimum synthesis conditions for Ag–ZnO NCs were at 70 °C, pH of 7, and 8% silver. Antibac- terial activity results show Ag–ZnO NCs to have higher microbial inhibition on E. coli than on S. aureus with the zones of inhibition of 21 ± 1.08 and 19.67 ± 0.47 mm, respectively. Therefore, the results suggest that Launaea cornuta leaf extract can be used for the synthesis of Ag–ZnO NCs
Facile biosynthesis of Ag–ZnO nanocomposites using Launaea cornuta leaf extract and their antimicrobial activity
(Springer Nature, 2023-11-17) Makauki, Elizabeth; Mtavangu, Stanslaus; Basu, Onita; Rwiza, Mwemezi; Machunda, Revocatus
The quest to synthesize safe, non-hazardous Ag–ZnO nanoomposites (NCs) with improved physical and chemical properties has necessitated green synthesis approaches. In this research, Launaea cornuta leaf extract was proposed for the green synthesis of Ag–ZnO NCs, wherein the leaf extract was used as a reducing and capping agent. The antibacterial activity of the prepared nanoomposites was investigated against Escherichia coli and Staphylococcus aureus through the disc diffusion method. The influence of the synthesis temperature, pH, and precursor concentration on the synthesis of the Ag–ZnO NCs and antimicrobial efficacy were investigated. The nanoparticles were characterized by ATR-FTIR, XRD, UV–Vis, FESEM, and TEM. The FTIR results indicated the presence of secondary metabolites in Launaea cornuta which assisted the green synthesis of the nanoparticles. The XRD results confirmed the successful synthesis of crystalline Ag–ZnO NCs with an average particle size of 21.51 nm. The SEM and TEM images indicated the synthesized nanoparticles to be spherical in shape. The optimum synthesis conditions for Ag–ZnO NCs were at 70 °C, pH of 7, and 8% silver. Antibacterial activity results show Ag–ZnO NCs to have higher microbial inhibition on E. coli than on S. aureus with the zones of inhibition of 21 ± 1.08 and 19.67 ± 0.47 mm, respectively. Therefore, the results suggest that Launaea cornuta leaf extract can be used for the synthesis of Ag–ZnO NCs.
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).
In situ facile green synthesis of Ag–ZnO nanocomposites using Tetradenia riperia leaf extract and its antimicrobial efficacy on water disinfection
(Springer Nature Limited, 2022-09-13) Mtavangu, Stanslaus; Machunda, Revocatus; Bruggen, Bart; Njau, Karoli
In this work, Ag–ZnO nanocomposites were prepared by a green synthesis route using aqueous leaf extract of Tetradenia riperia and investigated for antibacterial activity against Escherichia coli and Staphylococcus aureus. To optimize the synthesis of the Ag–ZnO, the effects of precursor concentrations, pH, and temperatures were studied. The Ag–ZnO nanocomposites were characterized by XRD, ATR-FTIR, FESEM, and TEM. Results show that the concentration of 8% Ag, the temperature of 80 °C, and a pH of 7–8 were optimal for the synthesis of Ag–ZnO nanocomposites. The XRD analysis showed the decrease in particle size of Ag–ZnO from 23.6 to 14.8 nm with an increase in Ag concentrations, which was further supported by FESEM analysis. TEM image of 8% Ag provides more information on the coexistence of Ag on ZnO where an average particle size of 14.8 nm was determined. The ATR-FTIR analysis confirmed the presence of phenolic compounds, which work as reducing and stabilizing agents. The antimicrobial activity results show that Ag–ZnO nanocomposite demonstrated a higher antimicrobial potency on E. coli than on S. aureus. Therefore, Tetradenia riperia leaf extract is a viable route for the synthesis of Ag–ZnO nanocomposites to be used for various applications, including water disinfection.
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.
Performance of constructed wetland integrated with sand filters for treating high turbid water for drinking
(IWA Publishing, 2017-03) Mtavangu, Stanslaus; Rugaika, Anita; Hilonga, Askwar; Njau, Karoli
The feasibility of constructed wetland integrated with sand filters (CW-SFs) for treating high turbid water for drinking was investigated. Turbid water of .1,000 NTU from Nadosaito dam in Monduli District, Tanzania was used. Along with turbidity; faecal coliform (FC), chemical oxygen demand (COD), total suspended solids (TSS) and nitrate removal were investigated. Furthermore, determination of optimal retention time for pollutants removal to acceptable levels was assessed at retention times of 0.5 to 5 days. Horizontal subsurface flow constructed wetland (HSSFCW) was used as pretreatment stage prior to biosand or slow sand filters. Results showed that HSSFCW produced effluent turbidity of ,10–50 NTU at retention time of 3 days. Moreover, integrated CW-BSF needed a total retention time of 5 days to produce effluent of turbidity (0 NTU), FC (0 CFU/100 ml), COD (6.25 mg/L), TSS (0.5 mg/L) and nitrate (4.2 mg/L) whereas, CW-SSF needed 7 days to produce effluent of turbidity (0.6 NTU), FC (0 CFU/100 ml), COD (6.5 mg/L), TSS (1 mg/L) and nitrate (1.79 mg/L), which met drinking water standards of Tanzania Bureau of Standards (TBS) and World Health Organization (WHO). CW-BSF showed better performance than CW-SSF therefore, its application can enhance the availability of potable water in Tanzania rural communities.