Johnson Kwame Efavi

The growing focus on green chemistry and its application in nanomaterials has sparked a desire to explore more efficient and environmentally friendly synthesis methods. In this work, Citrus sinensis peel extract was used to synthesize silver‐titanium dioxide, and the photocatalytic properties were evaluated in comparison with pristine titanium dioxide for wastewater purification and the antimicrobial efficacy tested. Titanium dioxide was coated with silver nanoparticles using weighted amounts of silver nitrate, with C. sinensis peel extract serving as the reducing agent. Characterization via X‐ray diffraction, Fourier‐transform infrared spectroscopy, scanning electron microscopy‐energy dispersive spectroscopy, and ultraviolet‐visible spectrophotometry confirmed silver‐titanium dioxide formation. The maximum photodegradation rate was observed with a 1.5 wt.% silver‐titanium dioxide composite using rhodamine B, proving it to be the most effective for organic molecule photodegradation. Subsequently, silver nanoparticles and silver‐titanium dioxide demonstrated growth inhibition against strains of Staphylococcus aureus and Escherichia coli, highlighting their potential for wastewater treatment and microbial control.

For the first time, acrylonitrilebutadiene rubber (NBR)graphene oxide (GO) and reduced graphene oxide (rGO) composites were prepared without cure activators: zinc oxide/stearic acid (ZnO/SA) and studied. The vulcanization characteristics of the compounds were systematically studied at 160190C, with the aid of rheometer and differential scanning calorimetry (DSC) techniques. NBR revealed rapid curing time (t₉₀) with greater cure rate index compared with NBRGO/rGO composites for the rheometer measurement. This results were in correspondence with the activation energies E_a (kJ/mol) calculated by Ozawa and Kissinger models of vulcanization kinetics. NBRrGO obtained reduced t₉₀ and E_a (kJ/mol) than NBRGO, perhaps due to lower oxygenated groups: epoxide (COC), carboxyl (OC=O), and hydroxyl (OH) present. Although, the composites delayed in curing, they significantly recorded high tensile properties with high reinforcing factors than NBR. The order of increasing mechanical properties: NBRNBRrGONBRGO followed the same order of increasing crosslinking density. In terms of tensile strength, NBRGO-1 obtained 62.5 and 18.2 increment than NBR and NBRrGO-1, respectively. The findings from this study indicate that the absence of ZnO/SA in rubber compounds may slow down curing of rubberGO/rGO composites and lower networks compared with those containing activators ZnO/SA. However, optimization of ZnO/SA and with desired functional groups on graphene and derivative graphene sheets (GDS) including other proposed factors may enhance the curing speed of rubberGDS based systems, without compromising their mechanical integrity for advanced applications.

The synergy between photogenerated reactive oxygen species and the anticancer potency of curcumin was examined by exposing HeLa cancer cells to irradiated curcumin loaded halloysite nanotubes-Ag–TiO ₂ nanomaterial. 0% cell viability was obtained.

The use of noble metal loading such as Ag to improve the photocatalytic performance of TiO₂ has been well studied. Though different synthesis methods have been used to synthesize Ag-TiO₂ nano-composite, the effect of the different synthesis routes on the photocatalytic performance has not been studied and compared. This study focusses not only on the enhancement of photocatalytic performance by the addition of Ag, but also on the influence of the synthesis process on photocatalytic performance. Two different routes: photodeposition (PD) and formaldehyde assisted microwave (MW) synthesis of Ag-TiO₂ nano-composite and their photocatalytic performance were evaluated using model pollutants. The Ag-TiO₂ were synthesized using different wt% (0.5, 1.0, 1.5 and 2.0 wt%) of Ag. The synthesized Ag-TiO₂ were characterized with x-ray diffractometer, scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX) and UV–vis spectrophotometry. The Ag-TiO₂ photocatalyst showed superior photocatalytic performance towards rhodamine b dye as compared to raw TiO₂. 0.5 wt% Ag-TiO₂-PD recorded the highest rate constant and degradation percent among the composites synthesized using photodeposition (PD) method. On the other hand, 1.0 wt% Ag-TiO₂-MW performed better among the composites synthesized using microwave and formaldehyde assisted synthesis. The potential of these best performing composites; 0.5 wt% Ag-TiO₂ and 1.0 wt% Ag-TiO₂ to photocatalytically degrade pharmaceutical (Naproxen Sodium and Flurbiprofen) and pesticide (Atrazine and Pyrimethanil) pollutants were examined. These composites degraded the pollutants exceptionally well with 0.5 wt% Ag-TiO₂-PD outperforming the 1.0 wt% Ag-TiO₂-MW. 1H NMR and 13C NMR analysis revealed that the synthesized Ag-TiO₂ were effective in degrading the model pollutants.

Carbonated hydroxyapatite (CHAp) adsorbent material was prepared from Achatina achatina snail shells and phosphate-containing solution using a wet chemical deposition method. The CHAp adsorbent material was investigated to adsorb aqua Fe(II) complex; [Fe(H₂O)₆]²⁺ from simulated iron contaminated water for potential iron remediation application. The CHAp was characterized before and after adsorption using infrared (IR) and Raman spectroscopy. The IR and the Raman data revealed that the carbonate functional groups of the CHAp adsorbent material through asymmetric orientation in water bonded strongly to the aqua Fe(II) complex adsorbate. The adsorption behaviour of the adsorbate onto the CHAp adsorbent correlated well to pseudo-second-order kinetics model, non-linear Langmuir and Freundlich model at room temperature of a concentration (20–100 mg L⁻¹) and contact time of 180 min. The Langmuir model estimated the maximum adsorption capacity to be 45.87 mg g⁻¹ whereas Freundlich model indicated an S-type isotherm curvature which supported the spectroscopy revelation.

Silver nanoparticles (AgNPs) have been synthesized from the more chemically rich and diverse cocoa pod; the synthesis of silver nanoparticles from cocoa leaves, which are less rich and have low diversity in bioactive molecules, is yet to be achieved. In this work, AgNPs produced using the extracts of the cocoa leaf (CL) and cocoa pods (CP) have been investigated and their antimicrobial activity against E. coli was evaluated. UV-visible absorption spectroscopy was used to examine the reduction of silver ions in solution and the surface plasmon resonance of AgNPs. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to further characterize the nanoparticles. The crystalline nature of AgNPs was confirmed by XRD, and the purity and presence of elemental silver were determined by EDX. CL-AgNPs were observed to have a surface plasmon resonance of 425nm, while CP-AgNPs had a surface plasmon resonance of 440nm. CL-AgNPs had a significantly higher purity than CP-AgNPs. With a shorter nucleation time, the intensity of the UV-Vis spectrum was always higher in the case of CL-AgNPs, indicating a larger population of bioactive molecules available for CL-AgNPs synthesis. FTIR confirmed the presence of phenolic compounds in the leaf and pod extract, implying that water-soluble polyphenolic and flavonoid chemicals are responsible for nanoparticle reduction, capping, and stability. AgNPs generated from CL and CP extracts are polydispersed, with particle sizes of 10110nm and 20680nm, respectively, according to DLS. The corresponding zeta potentials measured are 2.7mV for CL-AgNPs and 0.93mV for CP-AgNPs. The zeta potential values suggest that the particles have long-term stability. Furthermore, CL-AgNPs outperformed CP-AgNPs in terms of antibacterial activity against Escherichia coli. CL-AgNPs were found to have a maximal inhibitory zone of 21mm.

Synthesis scheme of the Ag ₃ PO ₄ –TiO ₂ nanocomposite.

Characterization and Inhibitory Effects of Magnetic Iron Oxide Nanoparticles Synthesized from Plant Extracts on HeLa Cells: Magnetic Fe₃O₄ nanoparticles were synthesized from maize leaves and plantain peels extract mediators. Particles were characterized, and the inhibitory effects were studied on HeLa cells in vitro using cyclic voltammetry (CV). Voltammograms from the CV show that Fe₃O₄ NPs interaction with HeLa cells affected their electrochemical behavior. The nanoparticles formed with higher Fe³⁺/Fe²⁺ molar ratio (2.8:1) resulted in smaller crystallite sizes compared to those formed with lower Fe³⁺/Fe²⁺ molar ratio (1.4:1). The particles with the smallest crystallite size showed higher anodic peak currents, whereas the larger crystallite sizes resulted in lower anodic peak currents. The peak currents relate to cell inhibition and are confirmed by the half-maximum inhibitory concentration (IC₅₀). The findings show that the particles have a different inhibitory mechanism on HeLa cells ion transfer and are promising to be further exploited for cancer treatment.

In this work, the potential application of TiO₂-Fe-HNT photocatalyst-adsorbent composite in water treatment technologies was confirmed. The photocatalyst-adsorbent composite (TiO₂-Fe-HNTs) was synthesized by the hydrothermal method and characterized by X-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and diffuse reflectance spectroscopy. The adsorption and photocatalysis mechanism by the TiO₂-Fe-HNT composite were examined on methylene blue dye, rhodamine blue dye, naproxen sodium (pharmaceutical drug waste), and imidacloprid (pesticide). The TiO₂-Fe-HNT composite was active in UV and visible regions of the electromagnetic spectrum. The adsorption and photocatalytic efficiency increased with increasing amount of HNTs. The photocatalyst-adsorbent composite exhibited excellent removal efficiency for pharmaceutical waste (naproxen sodium) and pesticides (imidacloprid). An adsorption equilibrium data fitted well with the pseudo-second-order kinetics for both methylene blue and rhodamine blue dyes with the intraparticle model describing its rate-controlling steps. The Langmuir and Freundlich isotherm models further described the adsorption of methylene blue and rhodamine blue molecules, respectively.