Browsing by Author "Makauki, Elizabeth"

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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.
Hydrogen sulfide and ammonia removal from biogas using water hyacinth-derived carbon nanomaterials
(Academic Journals, 2017-07-31) Makauki, Elizabeth; King’ondu, Cecil; Kibona, Talam
The presence of hydrogen sulfide (H2S) and ammonia (NH3) in biogas pose serious human health and environmental challenges. In this study, H2S and NH3 were successfully removed from biogas using water hyacinth-derived carbon (WHC) nanomaterials. Carbonization temperature, biogas flow rate, mass of the adsorbent and activating agent (KOH/water hyacinth (WH)) ratio were found to greatly influence the efficiency of the H2S and NH3 removal. The adsorption capacity of both H2S and NH3 was found to increase with the carbonization temperature as carbon materials prepared at 450, 550, and 650°C afforded removal efficiencies of 22, 30, and 51% for H2S and 42, 50, and 74% for NH3, respectively, after contact time of 2 h. Similarly, the KOH/WHC ratio showed huge impact on the adsorptive removal of the two species. WH materials carbonized at 650°C and activated at 700°C using 1:4, 1:2, and 1:1 KOH/WHC ratios showed removal efficiencies of 80, 84, and 93% for H2S and 100, 100, and 100% for NH3, correspondingly after 2 h contact time. The adsorption capacity of NH3 increased with the decrease in flow rate from 83 to 100% at flow rates of 0.11 and 0.024 m3 /h, respectively, while that of H2S increased from 22 to 93% with flow rate 0.11 and 0.024 m3 /h, respectively. The removal of H2S and NH3 increased with adsorbent mass loading. With the 0.05, 0.1, 0.2, and 0.3 g of the adsorbent, the adsorption of H2S after 1.5 h contact time was 63, 93, 93, and 95%, respectively while that of NH3 was 100% for all the adsorbent masses.
Investigation of the Potential of Wild Lettuce for the Biosynthesis of Silver-Zinc Oxide Nanocomposites as Antimicrobial Agents for Water Treatment
(NM-AIST, 2025-05) Makauki, Elizabeth
Silver-zinc oxide nanocomposites (Ag-ZnO NCs) are highly effective antimicrobial agents for point-of-use water treatment. However, chemically synthesized Ag-ZnO NCs pose potential health risks due to the use of toxic and carcinogenic chemicals as reducing and stabilizing agents raising a concern for the use of safe, non-toxic, readily available, and non-carcinogenic biochemicals. This study explored the potential of wild lettuce as a natural source of biochemicals that can serve as safe and eco-friendly reducing and stabilizing agents for the biosynthesis of Ag-ZnO NCs. The study further investigated the use of water hyacinth activated carbon (AC) as a potential impregnation precursor for the biosynthesized Ag-ZnO NCs and evaluated their antimicrobial efficacy. The biochemicals were extracted using 0, 50 and 100% ethanolic solvents (EtOH) in different extraction circles and volumes. The wild lettuce leaf extracts were used to biosynthesize Ag-ZnO NCs and eventually were impregnated in the AC. The antimicrobial activity was performed using ager plate and the water treatment was analysed using synthetic and natural water in a batch reaction. The FTIR results confirmed the presence of alkaloids, flavonoids, tannins, saponins, and proteins which are essential for the biosynthesis process. Phytochemical analysis confirmed the presence of high amounts of biochemicals in wild lettuce leaves. Total phenolic and antioxidant contents of the leaf extract followed the trend 100<0<50% EtOH with the highest yield of about 11 044 ± 63 and 44 112 ± 894 µg/g, respectively (p<0.05). The XRD analysis of Ag-ZnO NCs confirmed their crystalline nature with an average particle size of 21.51 nm. The SEM and TEM images confirmed formation of spherical shaped nanocomposites with a successful doping of Ag into ZnO. It further confirmed a successful impregnation of Ag-ZnO into AC. The BET results of Ag-ZnO-AC indicated an increase of surface area with activation creating more surface for the Ag-ZnO attachment. The antibacterial activity of Ag-ZnO NCs indicated high microbial inhibition on E. coli (21 ± 1.08 mm) and S. aureus (19.67 ± 0.47 mm). The Ag-ZnO-AC had significant antimicrobial activities against E. coli (14.00 ± 0.37 mm) and S. aureus (17.33 ± 0.36 mm). The water treatment analysis of Ag-ZnO-AC indicated complete microbial elimination on synthetic (2 h) and natural water (1 h). These results confirm wild lettuce as a potential natural source of biochemicals for the biosynthesis of Ag-ZnO NCs and water hyacinth as a potential impregnation material due to its high porosity and high surface area
Launaea cornuta (wild lettuce) leaf extract: phytochemical analysis and synthesis of silver-zinc oxide nanocomposite
(IOP Science, 2024-10-11) Makauki, Elizabeth; Rwiza, Mwemezi; Basu, Onita
Access to quality drinking water is an essential human right and a fundamental aspect of human dignity, yet a challenge to many in developing countries. Over 2 billion people worldwide lack access to quality drinking water due to microbial contamination, among other factors. Silver-doped zinc oxide impregnated activated carbon nanocomposites, Ag-ZnO-AC NCs, a strong antimicrobial agent have been used at point-of-use to treat water treatment. Green synthesis of Ag-ZnO-AC NCs has played a vital role since it leads to the acquisition of non-toxic nanocomposites compared to chemical synthesis. In this study, Ag-ZnO-AC NCs were green-synthesized using Launaea cornuta leaf extract as a source of reducing and capping agents in place of synthetic chemicals. Antioxidants from Launaea cornuta (Wild Lettuce) leaves were extracted using 0, 50, and 100% EtOH solvents with different volumes and extraction circles. The highest phenolic (11044 ± 63 μg) and antioxidant (44112 ± 894 μg) contents were extracted using 50% EtOH and 20 ml of extract solvent with p < 0.05. The SEM and TEM images of the synthesized Ag-ZnO-AC NCs show the formation of highly porous AC with sheet-like structures and successful Ag-ZnO NCs impregnation within the pores and on the surface of the AC. Based on the inhibition zone, the antimicrobial activity of the Ag-ZnO AC NCs had significant results with 14.00 ± 0.37 for E. coli and 17.33 ± 0.36 mm for S. aureus, p < 0.05. These results confirm the significance of Launaea cornuta (Wild Lettuce) as a source of antioxidants that can be used as reducing and capping agents to synthesize Ag-ZnO-AC NCs.
Synergistic antimicrobial mechanisms of silver-doped zinc oxide for water treatment: a systematic review
(IWA Publishing, 2025-03-10) Makauki, Elizabeth; Machunda, Revocatus; Basu, Onita; Rwiza, Mwemezi
This systematic review provides an overview of the existing research on antimicrobial mechanisms of silver-doped zinc oxide nanocomposites (Ag/ZnO NCs). It reports the existing knowledge on the synergistic effect (relationship) between silver (Ag) and zinc oxide (ZnO) for its optimum application. The doping of Ag into the ZnO has been used to enhance its photocatalysis and antimicrobial performance by improving the generation of reactive oxygen species (ROS). The Ag/ZnO NCs’ microbial elimination can be done through generated ROS, metallic (Ag+ and Zn2+) ions, and direct attack by the nanoparticles (NPs). Unlike the summation of individual use outcomes, the antimicrobial results of Ag/ZnO create a synergetic effect. This brings the sustainable use of the materials by increasing their efficiency while lowering the amounts used. This article systematically reviews the antimicrobial mechanisms of Ag/ZnO against gram-negative and gram-positive bacteria. It further analyses the quantitative and qualitative synergism between Ag and ZnO when applied together as antimicrobial materials. This systematic review found Ag/ZnO as a potential microbial elimination agent. Many studies reported the chemical synthesis of Ag/ZnO, which might cause a yield of toxic nanomaterials. Further studies on biosynthesis are pivotal for the sustainable supply of safe, non-toxic materials aimed at drinking water treatment.