Research Articles (Chemistry)

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Elucidating the effects of covid-19 lockdowns in the UK on the o3-nox-voc relationship
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Shallcross, Dudley; Holland, Rayne; Seifert, Katya
The unprecedented reductions in anthropogenic emissions over the COVID-19 lockdowns were utilised to investigate the response of ozone (O3) concentrations to changes in its precursors across various UK sites. Ozone, volatile organic compounds (VOCs) and NOx (NO+NO2) data were obtained for a 3-year period encompassing the pandemic period (January 2019–December 2021), as well as a pre-pandemic year (2017), to better understand the contribution of precursor emissions to O3 fluctuations. Compared with pre-lockdown levels, NO and NO2 declined by up to 63% and 42%, respectively, over the lockdown periods, with the most significant changes in pollutant concentrations recorded across the urban traffic sites. O3 levels correspondingly increased by up to 30%, consistent with decreases in the [NO]/[NO2] ratio for O3 concentration response. Analysis of the response of O3 concentrations to the NOx reductions suggested that urban traffic, suburban background and suburban industrial sites operate under VOC-limited regimes, while urban background, urban industrial and rural background sites are NOx-limited. This was in agreement with the [VOC]/[NOx] ratios determined for the London Marylebone Road (LMR; urban traffic) site and the Chilbolton Observatory (CO; rural background) site, which produced values below and above 8, respectively. Conversely, [VOC]/[NOx] ratios for the London Eltham (LE; suburban background) site indicated NOx-sensitivity, which may suggest the [VOC]/[NOx] ratio for O3 concentration response may have had a slight NOx-sensitive bias. Furthermore, O3 concentration response with [NO]/[NO2] and [VOC]/[NOx] were also investigated to determine their relevance and accuracy in identifying O3-NOx-VOC relationships across UK sites. While the results obtained via utilisation of these metrics would suggest a shift in photochemical regime, it is likely that variation in O3 during this period was primarily driven by shifts in oxidant (OX; NO2 + O3) equilibrium as a result of decreasing NO2, with increased O3 transported from Europe likely having some influence.
Particle number concentration measurements on public transport in Bangkok, Thailand
(Multidisciplinary Digital Publishing Institute (MDPI), 2023) Shallcross, Dudley E; Matthews, James C; Chalida, Chompoobut; Navasumrit, Panida
Traffic is a major source of particulate pollution in large cities, and particulate matter (PM) level in Bangkok often exceeds the World Health Organisation limits. While PM2.5 and PM10 are both measured in Bangkok regularly, the sub-micron range of PM, of specific interest in regard to possible adverse health effects, is very limited. In the study, particle number concentration (PNC) was measured on public transport in Bangkok. A travel route through Bangkok using the state railway, the mass rapid transport underground system, the Bangkok Mass Transit System (BTS) Skytrain and public buses on the road network, with walking routes between, was taken whilst measuring particle levels with a hand-held concentration particle counter. The route was repeated 19 times covering different seasons during either morning or evening rush hours.
Wood-derived, monolithic chainmail electrocatalyst for biomass-assisted hydrogen production
(Wiley, 2023) Iwuoha, Emmanuel I; Li, Di; Li, Zengyong
The chainmail catalyst by encapsulating an active species within the carbon support is a well-established concept to endorse extraordinary stability for catalytic reactions under harsh conditions. Conventional chainmail catalysts inevitably suffer from poor accessibility to active sites, leading to extra voltage to compensate the sluggish diffusion kinetics in electrocatalysis. Herein, the naturally abundant wood material is converted into a monolithic chainmail electrocatalyst by encapsulating cobalt nanoparticles within N-doped carbonized wood. Such a monolithic chainmail catalyst is employed directly as electrode for hydrogen evolution (HER), oxygen evolution (OER), and monosaccharide oxidation reactions (MOR) with benchmark performance. By coupling the HER with MOR, the electrolyzer equipped with the monolithic chainmail catalyst allows hydrogen production at a current density of 100 mA cm−2 with a full cell voltage of only 1.36 V. Such design of wood-derived chainmail catalyst provides a promising way to fabricate robust electrocatalysts for future production of hydrogen and value-added chemicals.
Sustainable fuels: Lower alcohols perspective
(Wiley, 2023) Anekwe, Ifeanyi Michael Smarte; Nyembe, Nhlanhla; Nqakala, Loyiso Clemence
In the coming years, energy sources will play a vital role in global development. Biofuels made from sustainable sources are essential for the global economy's long-term viability and the reduction of greenhouse gas emissions. Clean, renewable, and sustainable must be the watchwords for future energy strategy. Alcohol fuels are again becoming a popular term in the context of green fuel usage in relation to climate change mitigation and clean fuel technology. In this review, low alcohol synthesis, applications and limitations as fuel and its catalytic conversion to fuel and petrochemicals were discussed, in addition to the techno-economic evaluation, environmental implications and prospects for practical application of low alcohols as fuels and petrochemicals.
Multi-objective optimization of a metal hydride reactor coupled with phase change materials for fast hydrogen sorption time
(Journal of Energy Storage, 2023) Pasupathi, Sivakumar; Nyamsi, Serge Nyallang; Tolj, Ivan
Recently, the utilization of phase change materials (PCM) for the heat storage/recovery of the metal hydride's reaction heat has received increasing attention. However, the poor heat management process makes hydrogen sorption very slow during heat recycling. In this work, the H2 charging/discharging performance of a metal hydride tank (MHT) filled with LaNi5 and equipped with a paraffin-based (RT35) PCM finned jacket as a passive heat management medium is numerically investigated. Using a two-dimensional mathematical model validated with our in-house experiments, the effects of design parameters such as PCM thermophysical properties and the fin size on hydrogen charging/discharging times of the MHT are investigated systematically. The results showed that the PCM's melting point and apparent heat capacity have a conflicting impact on the hydrogen sorption times, i.e., the low melting point and high specific heat capacity reduce the H2 charging time
Eliminating micro-porous layer from gas diffusion electrode for use in high temperature polymer electrolyte membrane fuel cell
(Elsevier, 2017) Su, Huaneng; Xu, Qian; Chong, Junjie
In this work, we report a simple strategy to improve the performance of high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) by eliminating the micro-porous layer (MPL) from its gas diffusion electrodes (GDEs). Due to the absence of liquid water and the general use of high amount of catalyst, the MPL in a HT-PEMFC system works limitedly. Contrarily, the elimination of the MPL leads to an interlaced micropore/macropore composited structure in the catalyst layer (CL), which favors gas transport and catalyst utilization, resulting in a greatly improved single cell performance. At the normal working voltage (0.6 V), the current density of the GDE eliminated MPL reaches 0.29 A cm2 , and a maximum power density of 0.54 W cm2 at 0.36 V is obtained, which are comparable to the best results yet reported for the HT-PEMFCs with similar Pt loading and operated using air. Furthermore, the MPLfree GDE maintains an excellent durability during a preliminary 1400 h HT-PEMFC operation, owing to its structure advantages, indicating the feasibility of this electrode for practical applications.
Silver–zinc oxide nanocomposite antiseptic from the extract of Bidens pilosa
(Springer, 2019) Kyomuhimbo, Hilda Dinah; Michira, Immaculate Nyambura; Iwuoha, Emmanuel I.
Silver nanoparticles (Ag-NPs), zinc oxide (ZnO-NPs) and zinc oxide–silver (ZnO–Ag-NPs) were biosynthesized based on the rich matrix of alkaloids, flavones, tannins capping/stabilizing agents present in Bidens pilosa extract. Different plant parts-root, leaf and seed ware used to prepare the plant extract for synthesis. Also, zinc and silver nitrate salts were used as precursor materials. The surface plasmon peaks (SPR) based on the UV–Vis results for the Ag-NPs, ZnO-NPs were located between 408–411 and 365–450 nm respectively. The SPR peaks for the Ag–ZnO-NPs occurred at 300–450 nm indicating both blue and red shifts. The Ag–ZnO-NPs SPR shifts were associated with possible nanoparticle size reduction and change in dielectric constant of the synthesis medium. Raman measurement peaks at 356, 484, 1350, 1578, 2435 cm−1 associated with OH, –C==C–, –C–O, S=O, =C–H moieties indicated successful capping. Nanoparticle yield was temperature dependent and optimal yield could not be tied to a particular plant part as source of extract. Tunneling electron microscope results showed Ag-NPs and ZnO-NPs were globular/spherical with a diameter range of 2–20 nm. Interestingly, ZnO-NPs TEM displayed isolated miniaturized globular nanoparticles (< 2 nm) which then joined up to form a large donut shaped structure indicating different formation mechanisms for the nanoparticles. XRD results showed the Ag-NPs, ZnO-NPs and the Ag–ZnO-NPs particles were crystalline in nature.
Inhibition of HIV-1 enzymes, antioxidant and anti-inflammatory activities of Plectranthus barbatus
(Elsevier, 213) Kapewangolo, Petrina; Hussein, Ahmed A.; Meyer, Debra
Ethnopharmacological relevance: Plectranthus barbatus is widely used in African countries as an herbal remedy to manage HIV/AIDS and related conditions. Aim of the study: To investigate the HIV-1 inhibitory, anti-inflammatory and antioxidant properties of P. barbatus and thereby provide empirical evidence for the apparent anecdotal success of the extracts. Materials and methods: Ethanolic extract of P. barbatus's leaves was screened against two HIV-1 enzymes: protease (PR) and reverse transcriptase (RT). Cytotoxicity of the extract was determined through measuring tetrazolium dye uptake of peripheral blood mononuclear cells (PBMCs) and the TZM-bl cell line. Confirmatory assays for cytotoxicity were performed using flow cytometry and real-time cell electronic sensing (RT-CES). The free radical scavenging activity of the extract was investigated with 2,2- diphenyl-1-picrylhydrazyl while the anti-inflammatory properties of the plant extract were investigated using a Th1/Th2/Th17 cytometric bead array technique.
Underpotential deposition of SnBi thin films for sodium ion batteries: The effect of deposition potential and Sn concentration
(Elsevier, 2019) Xaba, Nqobile; Modibedi, Remegia M.; Khotseng, Lindiwe E.
Bimetallic SnBi film was deposited on a Cu foil substrate via the electrochemical atomic layer deposition (E-ALD) technique. The deposition attainment of Sn and Bi were investigated using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The deposition potential of Bi was varied in the underpotential deposition (UPD) region and the concentration of Sn was varied in the SnBi bimetallic material. The materials were characterised using field emission scanning electron microscopy coupled with energy dispersive spectroscopy (FE-SEM/EDS) for morphology and elemental distribution, focused ion beam scanning electron microscopy (FIBSEM) for thickness, X-ray diffraction (XRD) for crystallinity and inductively coupled plasma mass spectroscopy (ICP-MS) for composition measurements. Bi deposited at different UPD regions was structurally different. The deposits were crystalline SnBi materials containing Sn, Bi and other phases of Cu and Sn. Bi was concentrated on the surface, while Sn was distributed evenly across the film. The SnBi electrodes were tested as anode materials in Na-ion batteries using galvanostatic cycling (GC), CV and electrochemical impedance spectroscopy (EIS). Initial discharge capacities of 1900 mAh g 1 for SnBi (1:1) and 341 mAh g 1 for SnBi (3:1) electrodes at 38.5 mA g 1 were obtained, while the electrodes suffered capacity loss after 10 cycles.
Enhanced photovoltaic effects of microwave-assisted polyolsynthesized Cu2(Pd/Zn)SnS4 kesterite nanoparticles
(Elsevier, 2023) Nwambaekwe, Kelechi C.; Ramoroka, Morongwa E.; Iwuoha, Emmanuel I.
Kesterite materials show excellent optical and semiconductive properties for use as petype absorber layer in photovoltaic (PV) applications, but they have a high open circuit voltage deficit (Voc,def) due to high antisite defect and secondary phase formation, resulting in poor device performance. This work reports a PV cell composed of Cu2PdSnS4 (CPTS) nanoparticles as an absorber layer yielding highly improved Voc of 900 mV, which is two times that of fabricated pristine Cu2ZnSnS4 (CZTS) PV cell. Improved PV cell parameters such as fillefactor (FF) of 83.4% and power conversion efficiency (PCE) of 1.01% were obtained for CPTS devices which are 3efold that of pristine CZTS devices. Optical studies revealed enhanced redshift absorption for CPTS nanoparticles. Electrochemical studies show improved current production, high electron mobility and low charge resistance for CPTS nanoparticles. This study shows that the improved photovoltaic properties can be attributed to enhancement in the bulk properties when Zn atoms are replaced by Pd atoms in kesterite nanomaterials as absorber layer material for PV applications.
A synthesis review of vitamins involved in the fight against Covid-19
(Wiley, 2022) Mciteka, Lulama P.
Although literature studies on earlier viruses such as the Severe Acute Respiratory Syndrome (SARS), the Middle East Respiratory Syndrome (MERS), and other similar viruses, in terms of treatment of coronavirus suggested the repurposing of some antiviral drugs, some Covid-19 specific treatments, general forms of treatments, the use of convalescent plasma, as well as nutritional interventions in the form of vitamins, it is imperative to interrogate the nutritional status, age, and comorbidities of each infected patient before receiving any form of treatment. In the absence of any conclusive treatment so far, the study encourages the use of all likely interventions that could help arrest the spread of the disease.
Effects of film thickness of ald-deposited al2o3, zro2 and hfo2 nano-layers on the corrosion resistance of ti(n,o)-coated stainless steel
(MDPI, 2023) Dinu, Mihaela; Wang, Kaiying; Petrik, Leslie Felicia
The goal of this stydy was to explore the potential of the enhanced corrosion resistance of Ti(N,O) cathodic arc evaporation-coated 304L stainless steel using oxide nano-layers deposited by atomic layer deposition (ALD). In this study, we deposited Al2O3, ZrO2, and HfO2 nanolayers of two different thicknesses by ALD onto Ti(N,O)-coated 304L stainless steel surfaces. XRD, EDS, SEM, surface profilometry, and voltammetry investigations of the anticorrosion properties of the coated samples are reported. The amorphous oxide nanolayers homogeneously deposited on the sample surfaces exhibited lower roughness after corrosion attack compared to the Ti(N,O)-coated stainless steel. The best corrosion resistance was obtained for the thickest oxide layers. All samples coated with thicker oxide nanolayers augmented the corrosion resistance of the Ti(N,O)-coated stainless steel in a saline, acidic, and oxidising environment (0.9% NaCl + 6% H2O2, pH = 4), which is of interest for building corrosion-resistant housings for advanced oxidation systems such as cavitation and plasma-related electrochemical dielectric barrier discharge for breaking down persistent organic pollutants in water.
Antibacterial and anti-inflammatory effects of Syzygium jambos L. (Alston) and isolated compounds on acne vulgaris
(BioMed Central, 2013) Sharma, Richa; Kishore, Navneet; Hussein, Ahmed
Acne vulgaris is a chronic skin disorder leading to inflammation as a result of the production of reactive oxygen species due to the active involvement of Propionibacterium acnes (P. acnes) in the infection site of the skin. The current study was designed to assess the potential of the leaf extract of Syzygium jambos L. (Alston) and its compounds for antibacterial and anti-inflammatory activity against the pathogenic P. acnes. The broth dilution method was used to assess the antibacterial activity. The cytotoxicity investigation on mouse melanocyte (B16-F10) and human leukemic monocyte lymphoma (U937) cells was done using sodium 3’-[1-(phenyl amino-carbonyl)-3,4-tetrazolium]-bis-[4-methoxy-6-nitrobenzene sulfonic acid hydrate (XTT) reagent. The non-toxic concentrations of the samples was investigated for the suppression of cytokines interleukin 8 (IL 8) and tumour necrosis factor (TNF α) by testing the supernatants in the co-culture of the human U937 cells and heat killed P. acnes using enzyme immunoassay kits (ELISA). The statistical analysis was done using the Graph Pad Prism 4 program.
The potential of leucosidea sericea against propionibacterium acnes
(Elsevier, 2014) Sharma, Richa; Kishore, Navneet; Hussein, Ahmed
The present study reports on the potential of Leucosidea sericea addressing acne vulgaris. Four known compounds namely phytol acetate, triacontanol, phytol and alpha kosin and one new compound namely, (E)-3,7,11,15-tetramethylheptadec-2-ene-1,17-diol have been isolated for the first time from this plant. The ethanol extract of leaves and one of the isolated compounds, alpha kosin exhibited significant minimum inhibitory concentration (with MIC values 15.7 μg/mL and 1.9 μg/mL, respectively) against acne inducing bacteria, Propionibacterium acnes. Moreover, the transmission electron micrographs showed the efflux of intracellular content of the cells of P. acnes caused by plant extract and alpha kosin. The ethanol extract of L. sericea exhibited significant anti-inflammatory activity by suppressing interleukin 8 (IL 8) and tumour necrosis factor (TNF α) in coculture of human U937 cells and heat killed P. acnes at concentrations of 25.0, 12.5 and 6.2 μg/mL.
Electrocatalytic sensor devices: (I) cyclopentadienylnickel(II) thiolato Schiff base monolayer self-assembled on gold
(Elsevier, 2004) Morrin, Aoife; Moutloali, Richard M.; Killard, Anthony J.
The fabrication of a self-assembled monolayer (SAM) of a cyclopentadienylnickel(II) thiolato Schiff base compound, [Ni(SC6H4NC(H)C6H4 OCH2CH2SMe)( 5-C5H5)]2 on a gold electrode is described. Effective electronic communication between the Ni(II) centres and the gold surface was established by electrochemically cycling the Schiff base-doped Au electrode in 0.1 M NaOH from −200 mV to +600 mV. The SAM-modified electrode exhibited quasi-reversible electrochemistry. The integrity of this electrocatalytic SAM, with respect to its ability to block and electro-catalyse certain Faradaic processes, was interrogated using cyclic voltammetric experiments. The formal potential, E◦ , varied with pH to give a slope of about −30 mV pH−1. The surface concentration, G, of the nickel redox centres was found to be 1.548 × 10−11 mol cm−2. By electrostatically doping the SAM using an applied potential of +700 mV versus Ag/AgCl, in the presence of horseradish peroxidase (HRP), it was fine-tuned for amperometric determination of H2O2. The electrocatalytic-type biosensor displayed typical Michaelis–Menten kinetics and the limit of detection was found to be 6.25 mM. © 2004 Elsevier B.V. All rights reserved.
Quantum dot nanotoxicity investigations using human lung cells and toxor electrochemical enzyme assay methodology
(American Chemical Society, 2017) O’Hara, Tony; Seddon, Brian; Iwuoha, Emmanuel
Recent studies have suggested that certain nanomaterials can interfere with optically based cytotoxicity assays resulting in underestimations of nanomaterial toxicity. As a result there has been growing interest in the use of whole cell electrochemical biosensors for nanotoxicity applications. Herein we report application of an electrochemical cytotoxicity assay developed in house (TOXOR) in the evaluation of toxic effects of mercaptosuccinic acid capped cadmium telluride quantum dots (MSA capped CdTe QDs), toward mammalian cells. MSA capped CdTe QDs were synthesized, characterized, and their cytotoxicity toward A549 human lung epithelial cells investigated. The internalization of QDs within cells was scrutinized via confocal microscopy.
Progress on perovskite materials for energy application
(Elsevier, 2021) Monama, Gobeng R.; Ramohlola, Kabelo E.; Iwuoha, Emmanuel Iheanyichukwu
Energy underlies the human development and welfare. Today energy depends on combustion of fossil fuels (coal, natural gas, oil) sources. These sources have not only led to severe environmental issues because it emits greenhouse gases, they are rapidly depleted due to their enormous consumption. For several years’ numerous technologies have been developed to address the fossil fuel depletion and greenhouse gases emission from the non-renewable in order to constantly supply energy to the people and industries. However, the challenge of being able to store energy generated and utilize it later is a matter of importance when resolving energy problems persists. New materials, particularly perovskites offer a great advantage to be utilized as a possible host or carriers for energy applications. The impact of defect on the material properties and influence of defects as material for energy application is described. The use of perovskites oxides for effective electrocatalysis in hydrogen evolution reactions, photocataysis, photovoltaic solar cells, electrocatalysis, solid oxide fuel cells, supercapacitors and metal-air batteries, are also included. This review covers the latest progress on perovskite oxides as electrochemical energy materials.
Fabrication of polyoxometalate-modified palladium–nickel/reduced graphene oxide alloy catalysts for enhanced oxygen reduction reaction activity
(Royal Society of Chemistry, 2021) Sanij, Fereshteh Dehghani; Balakrishnan, Prabhuraj; Khotseng, Lindiwe
Designing advanced nanocatalysts for effectively catalyzing the oxygen reduction reaction (ORR) is of great importance for practical applications of direct methanol fuel cells (DMFCs). In this work, the reduced graphene oxide (rGO)-supported palladium–nickel (Pd–Ni/rGO) alloy modified by the novel polyoxometalate (POM) with Keggin structure (Pd–Ni/rGO-POM) is efficiently fabricated via an impregnation technique. The physical characterizations such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), field emission scanning electron microscopy coupled with energy dispersive Xray spectroscopy (FESEM-EDX), and transmission electron microscopy (TEM) are utilized to confirm the structure, morphology, and chemical composition of the fabricated samples. The XRD results verify the formation of the POM-modified Pd8Ni2/rGO alloy electro-catalyst with the face-centered-cubic (fcc) structure and average crystallite size of 5.54 nm.
A quarter century of marine biodiscovery in Algoa bay, South Africa
(Journal of Natural Products, 2023) Davies-Coleman, Michael T; McPhail, Kerry L; Parker-Nance, Shirley
Algoa Bay, the largest crenulate bay on the south-eastern coast of South Africa, is currently one of the most well-studied marine ecosystems in southern Africa. A plethora of endemic marine invertebrates inhabits the benthic reefs on the western edge of the Bay in close proximity to South Africa’s sixth largest city. Over the past 25 years, South African marine natural products chemists, together with international collaborators from the US National Cancer Institute and other US institutions, have focused their attention on Algoa Bay’s benthic marine invertebrates as a potential source of new anticancer compounds. This review commemorates a quarter of a century of marine biodiscovery in Algoa Bay and presents the structures and bioactivities of 49 new and 36 known specialized metabolites isolated from two molluscs, eight ascidians, and six sponges. Thirty-nine of these compounds were cytotoxic to cancer cells in vitro with 20 exhibiting moderate to potent cytotoxicity. Six other compounds exhibited antimicrobial activity. Foremost among the potential anticancer compounds is mandelalide A (38) from the Algoa Bay ascidian Lissoclinum species.
Zinc(ii) complex of (Z)-4-((4-Nitrophenyl)Amino)Pent-3-en-2-one, a potential antimicrobial agent: synthesis, characterization, antimicrobial screening, DFT calculation and docking study
(Chemical Society of Ethiopia, 2023) Waziri, I; Wahab, O.O; Mala, G.A; Oselusi, S.O; Egieyeh, S.A; Nasir, H
Herein, the synthesis and characterizations of (Z)-4-((4-nitrophenyl)amino)pent-3-en-2-one (HL) ligand and its Zn(II) complex are reported. The compounds were characterized using elemental and thermogravimetric (TGA) analysis, electrochemical studies, FTIR, UV-Vis, 1H and 13C{H}NMR, HRMS, and PXRD techniques. Antimicrobial activity was screened on some Gram-positive and Gram-negative bacteria. DFT predictions were achieved using B3LYP, ωB97XD and M06-2X functional with 6-31+G(d,p) and LANL2DZ basis sets for nonmetallic and metallic atoms, respectively. The therapeutic potentials of the compounds were evaluated based on protein binding affinity, ADME/T and drug-likeness properties. The experimental results revealed the formation of a complex in which two ligands coordinated to the zinc ion in a tetrahedral arrangement through their carbonyl and amino groups. The antimicrobial study showed that the complex possesses higher antimicrobial activity than free ligand and the control (Streptomycin). B3LYP emerged as the best performing functional having yielded the best IR spectra and geometrical parameters relative to the experimental data. The density functional theory (DFT) predictions revealed that the complex is more active than the ligand, and its formation is thermodynamically feasible and exothermic. The docking results revealed that the binding affinities of the compounds are in agreement with the in-vitro data, and they possess drug-like properties.

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