Browsing by Author "Rahman, Ateeq"

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    An efficient method for the synthesis of dihydropyridine by hantzsch reaction with Fe/SiO2 nano heterogeneous catalysts
    (2020) Rahman, Ateeq; Nehemia, P.N.; Nyambe, Moola M.
    An efficient method for the synthesis of dihydropyridines (DHPs) by Hantzsch reaction with Fe/SiO2 heterogeneous catalysts was developed. The Fe/SiO2 catalysts was prepared by impregnation method. The catalysts were characterized by IR and SEM instruments. The SEM results indicated that Fe/SiO2 nano spheres were formed. The reaction procedure involved reaction of aldehyde, ethyl acetoacetate (EAA), ammonium acetate (NH4OAc) and ethanol under reflux. The study was focused on optimizing reactions conditions: Standardization of catalyst, substrate of study and solvent study. In order to iden-tify the best active catalysts, five different ratios of catalyst were synthesized and evaluated for the ti-tle reaction under similar conditions. To standardize the active catalysts, different temperature condi-tions (i.e. room temperature, 60 ºC and 80 ºC) as well as catalysts amounts were evaluated. Under these established conditions, 2.5% Fe/SiO2 was the best active catalysts that resulted. Benzaldehyde and p-anisaldehyde were used to study the effect of having various substrates on the conversion and reaction time, especially the substituted aldehydes. The best results were obtained by reacting p-anisaldehyde with EAA, NH4OAc, and ethanol at 60 ºC with 0.3 grams of 2.5% Fe/SiO2 heterogeneous catalysts. Thin Layer Chromatography (TLC) monitoring of the reaction mixture showed no selectivity at high temperatures (80 ºC) with 15% Fe/SiO2. Standardization of solvent study was executed with two solvents, ethanol and acetonitrile. The product dihydropyridines were analyzed using gas chroma-tography-mass spectrometry (GC-MS). The melting points of the products were compared with authen-tic samples reported in the literature. Hence, the Fe/SiO2 catalysts is eco-friendly and economically de-veloped for the title reaction.
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    The photon‐electrical conversion efficiency of dye‐sensitivesolar cells fabricated using a highly conductive silver‐nanoparticle/titania photocathode
    (Wiley‐VCH GmbH, 2023) Daniel, Likius S.; Kaffer, Rocha T.; Kalipi, Loini M.; Rahman, Ateeq; Kalengay, Mbela; Uahengo, Veikko
    The TiO2 thin film, Ag NP and three Ag‐NP/TiO2 composite thin films (COMP‐Agn; n = 20, 50, and 75 Ag mol%) were successfully fabricated on quartz glass. The optical properties of the composite electrodes were investigated, and the results indicate a surface plasmonic resonance peak at 410 nm while the electrical resistivity of the composite thin films improved up to 6.9 × 10−5 Ω cm. The photo‐response threshold of the Ag‐NP/TiO2 composite thin films was enhanced and shifted into the visible and near‐infrared when the chlorophyll dye was adsorbed onto them. The hall effect was performed on the fabricated thin films and the charge carrier concentrate value confirmed that the Ag/TiO2 with Ag concentrate >45% are found to be p‐type. The n‐types were observed till the Ag content in TiO2 was increased up to 45 mol%. COMP‐Ag75 has a charge carrier concentration of 1.3 × 10−19 cm−3 as a p‐type electrode was then employed to construct a p‐DSSC. Such enhancement on photovoltaic activity can be attributed to the generated Z‐scheme system in the anatase/rutile phase‐junction Ag/TiO2 photocathode enhances the separation, diffusion, and transformation of electron/hole pairs inside the structure. This p‐DSSC exhibits a photon‐electrical conversion efficiency (PCE) of 0.37%. The PCE recorded is equal to or greater than those of traditional high‐efficiency n‐DSSCs. This allows the creation of a new generation of photocathodic p‐DSSCs with previously unheard‐of unprecedentedly high concentrations of Ag (up to 80 mol%) evenly scattered in a TiO2 matrix, and this efficacy is the highest ever reported for a p‐type working Ag/TiO2/chlorophyll/iodine electrode. This may enable the use of this electrode as a component of photosensitizer tandem devices.
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    Photophysical, electrochemical, and DFT studies of the novel azacrownbridged dinuclear ruthenium dye sensitizers for solar cells
    (University of Namibia, 2019) Uahengo, Veikko; Cai, Ping; Naimhwaka, Johannes; Rahman, Ateeq; Daniel, Likius S.; Bhakhoa, Hanusha; Rhyman, Lydia; Ramasani, Ponnadurai
    A dinuclear ruthenium bipyridyl complex with 1,10-diaza-18-crown-6 bridging ligand was synthesized and characterized. Its photophysical and electrochemical properties were also studied. DFT computations were performed to complement the experimental investigations. Analysis of the results indicates that the path in which charges move from one metal center to the other is significant for effective electronic coupling. However, electron transfer between the two ruthenium centers is hindered by the azacrown bridging ligand, compared to the smooth electronic transfer reported for a related dye involving an azo bridging ligand.
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    The production of activated carbon from Acacia erioloba seedpods via phosphoric acid activation method for the removal of methylene blue from water.
    (Elsevier, 2023) Rahman, Ateeq; Hamushembe, Mirjam N.; Kapolo, Paulus; Daniel, Likius S.; Uahengo, Veikko; Jonnalagadda, Sreekantha B.
    Wastewater treatment requires a lot of granular activated carbon to absorb the dissolved organic components. This article describes a low-cost process for making highly active adsorption activated carbons from biomass, which could be used for wastewater treatment. A one-step carbonization and chemical activation with phosphoric acid at 500 ◦C produced low-cost acacia-derived porous activated carbons. The activated carbons’ moisture, ash, volatile matter, and fixed carbon content were determined using proximate analysis. The activated carbon’s adsorption qualities were also determined by studying its bulk density, surface morphology, power of hydrogen, iodine number, and methylene blue number index. To test the produced activated carbons for water treatment, batch adsorption dynamics were performed at room temperature for the removal of methylene blue from aqueous solution. Compared to activation using H2SO4, H3PO4 proves superior in generating welldeveloped pores, leading to a mesoporosity and microporosity structure with a larger surface area and high adsorption capacity. Brunauer–Emmett–Teller determined the sample’s specific surface area, which was found to be 387 m2 /g. The iodine number for 50, 100, and 200 μm activated carbon particles size was 620, 592, and 632 mg/g, respectively. The adsorption of MB on AC material better fits with Langmuir’s adsorption isotherm; hence, particles are adsorbed on well-pronounced heterogeneous surfaces. The sips model is found to best represent the equilibrium data with R2 values of 0.994, suggesting the heterogeneous surface adsorption of MB on AC. Therefore, the adsorption of AC by MB involves physical and chemical processes. The produced AC hence appears to remove dissolved organic contaminants from raw water.