Melvin M Mashingaidze - Academia.edu (original) (raw)

Uploads

Papers by Melvin M Mashingaidze

Bismuth-based lead-free perovskite solar cells (PSCs) are a non-toxic alternative to lead-based o... more Bismuth-based lead-free perovskite solar cells (PSCs) are a non-toxic alternative to lead-based organic-inorganic hybrid PSCs. However, bismuth-based halides PSCs exhibit low power conversion efficiency (PCE) due to the grain boundaries and interfacial defects in the crystalline perovskite film. This discouragingly poor PCE has limited the continued development of bismuth-based PSCs. Herein, for the first time on record, this work fabricated blended, heterojunction, all-inorganic bismuth-based PSCs consisting of Cs3Bi2I9 and Ag2BiI5 perovskite absorber layer components with potassium iodide (KI) incorporation and carbon electrodes. Scanning Electron Microscopy (SEM) and X-ray diffraction spectroscopy (XRD) techniques confirmed that the addition of KI enhances the perovskite’s surface morphology, leading to larger grains and a more uniform distribution of contact potential along the grain boundaries. The Cs3Bi2I9/Ag2BiI5 PSC device with KI incorporation (K-C-ABI) achieved a record PC...

Nanomaterials

Lead-free, bismuth-based perovskite solar cells (PSCs) are promising, non-toxic, and stable alter... more Lead-free, bismuth-based perovskite solar cells (PSCs) are promising, non-toxic, and stable alternatives to lead-based PSCs, which are environmentally harmful and highly unstable under deprived air conditions. However, bismuth-based PSCs still suffer from low-power-conversion efficiency (PCE) due to their large bandgap and poor film morphology. Their poor film-forming ability is the greatest obstacle to Cs₃Bi₂I₉ progress in thin-film solar cell technology. This study synthesizes novel, lead-free perovskites with a small bandgap, excellent stability, and highly improved photovoltaic performance by integrating different amounts of potassium iodide (KI) into a perovskite precursor solution. KI incorporation improves the crystallinity of the perovskite, increases the grain size, and decreases the potential contact distribution, which is demonstrated by X-ray diffraction, electronic scanning microscopy, atomic force microscopy, and ultraviolet-visible spectroscopy. The Cs₃Bi₂I₉ PSC devic...

Advanced Composites and Hybrid Materials

International Journal of Biomaterials

Nanoparticle production and functionalization for various biomedical uses are still challenging. ... more Nanoparticle production and functionalization for various biomedical uses are still challenging. Polymer composites constituted of poly(amidoamine) (PAMAM), polyallylamine hydrochloride (PAH), and calcium carbonate (CaCO3) nanoparticles have good biocompatibility with physiological tissue and fluids, making them excellent candidates for biomedical applications. This study investigated the characteristics of polymeric/nano-CaCO3 composite films based on a PAH/PAMAM matrix, which were fabricated through layer-by-layer synthesis on quartz glass substrates. It was found that the as-prepared elastic moduli of the resultant (PAH/PAMAM)n-CaCO3 (where n represents the number of bilayers) composite films varied from 1.40 to 23.70 GPa for different degrees of cross-linking when 0.1 M nano-CaCO3 particles were incorporated into the polymer matrix. The highly cross-linked (PAH/PAMAM)15-CaCO3 composite film had the highest recorded elastic modulus of 23.70 GPa, while it was observed that for all...

Coatings, 2022

The recent rapid development in perovskite solar cells (PSCs) has led to significant research int... more The recent rapid development in perovskite solar cells (PSCs) has led to significant research interest due to their notable photovoltaic performance, currently exceeding 25% power conversion efficiency for small-area PSCs. The materials used to fabricate PSCs dominate the current photovoltaic market, especially with the rapid increase in efficiency and performance. The present work reviews recent developments in PSCs’ preparation and fabrication methods, the associated advantages and disadvantages, and methods for improving the efficiency of large-area perovskite films for commercial application. The work is structured in three parts. First is a brief overview of large-area PSCs, followed by a discussion of the preparation methods and methods to improve PSC efficiency, quality, and stability. Envisioned future perspectives on the synthesis and commercialization of large-area PSCs are discussed last. Most of the growth in commercial PSC applications is likely to be in building integr...

Coatings

Gypsum is a waste product of the iron precipitation stage of cobalt purification in many cobalt e... more Gypsum is a waste product of the iron precipitation stage of cobalt purification in many cobalt extraction plants. Most cobalt producers either landfill the gypsum or sell it cheaply to cement manufacturers. The gypsum contains residual cobalt which can be extracted through sulphuric acid leaching but the cost of the sulphuric acid is prohibitive. Leaching using recycled acidic liquors like nickel eluate offers an economical alternative. This study investigated the technical feasibility of leaching gypsum with nickel eluate, which is an acidic waste stream from the nickel ion exchange plant at the specific cobalt producer. This study also established the optimum pH and solids concentration for nickel eluate leaching. Nickel eluate leaching tests and sulphuric acid leaching tests were conducted on a one-factor-at-a-time experimental design basis. pH and pulp densities were varied while temperature, time and agitation speed were kept constant. Cobalt recoveries from the two sets of te...

Proceedings of the 4th TWAS ROSSA Young Scientists Conference, Nairobi, Kenya, 2009.,Economic gro... more Proceedings of the 4th TWAS ROSSA Young Scientists Conference, Nairobi, Kenya, 2009.,Economic growth is a result of value addition that creates wealth for nations. Nations utilise the gifts of nature which are the raw materials to manufacturing. Africa has abundancy of these natural resources but lacks appropriate economic development due to lack of Science and Technology. In the worst case, raw materials are extracted from Africa and exported in their raw state at very low prices. Value addition or processing is done outside the countries of origin and the finished goods or processed materials imported as finished products that attract more money. The importation at high prices opens the gap between poverty and wealthy nations. This paper highlights the plight of Zimbabwe due to lack of appropriate technologies to engage in complete value addition to the raw materials that are abundant in their nations. This unavailability of such technologies is quickly capitalized by rich nations...

Journal of Energy in Southern Africa

Coal-fired power plants utilising fluidised bed technologies emit copious amounts of fly-ash, whi... more Coal-fired power plants utilising fluidised bed technologies emit copious amounts of fly-ash, which is harmful to people owing to its particulate nature. A planned 300 MW power plant will have an electrostatic precipitator (ESP) for fly-ash emissions control, in line with power generation industry best practices. This ESP should meet a fly-ash emission limit value ≤ 50 mg/Nm3. This paper details the design process and resultant technical specifications of a cold-side, single-stage, and plate-wire dry ESP designed for the power plant. The ESP will consist of twin-chambers with quadruple-fields (2 4 315 m3) and octonary bus-sections independently energised by individual high-frequency three-phase switched integrated rectifiers (70 kV, 800 mA) to maximise ionisation. Dynamically balanced, single-impact, tumbling hammer rappers (857.5 rpm) will dislodge fly-ash from the collector plates into mass-flow wedge-shaped hoppers. A specific collection area (≥ 56.9 m2/m3/s) and an ESP index (≥ ...

International Journal of Engineering & Technology

This study examined the feasibility of recovering copper from a sulphuric acid leach solution of ... more This study examined the feasibility of recovering copper from a sulphuric acid leach solution of chalcopyrite flotation plant tailings assaying 0.18 % copper and 0.19 % zinc using DOWTM XUS 43578.00 ion exchange resin. Zn2+cations are counter ionsto Cu2+cations during the ion exchange process. Adsorption and desorption tests were conducted on the resin with a leach solution containing26 mg Cu/L and 225 mg Zn/L,under various conditions of pH, DOWTM XUS 43578.00resin dosage, agitation time and eluant(ammonium hydroxide solution) concentration. The DOWTM XUS 43578.00resindemonstrated a high selectivity for copper over zinc, with a separation factor of 30.26 mg/g. The highcopper distribution coefficient of65L2/g2suggeststhe resin can effectively concentrate copper in leach solutions of these particular tailings.A 4M ammonium hydroxide solution yielded the highest copper recoveryat pH 3and0.6gresin dosageafter3hours of agitation. These results can be improved by a pre-treatment step to r...

Conference Presentations by Melvin M Mashingaidze

The 8th International Conference of the African Materials Research Society (December 7 - 10, 2015, Accra Ghana, 2015

Aluminium alloy AA6082 is easy to machine, heat-treatable and optimized to be the strongest alloy... more Aluminium alloy AA6082 is easy to machine, heat-treatable and optimized to be the strongest alloy in the 6000 aluminium alloy series. These properties have seen it replace AA6061 in many applications of skin sheet or structural sheet materials. Aluminium alloy AA6082 is a relatively new alloy hence several studies are being done to evaluate the formability. However, little information is available on formability characteristics of aluminium alloy AA6082-O sheet metal. The main objective of this study was to determine the deep drawability of AA6082-O sheet metal. The deep drawability was experimentally investigated by carrying out Erichsen Cupping tests carrying on 60 mm x 60 mm flat sheet specimens of two different gauge thicknesses (1.0 mm and 2.0 mm), using a WP 300 Universal Material Tester with a loading capacity of 20 kN. The resultant forming limit curve (FLC) level of the forming limit diagrams (FLDs) from the Erichsen Cupping test was found to be higher for 2.0 mm thick sheet than 1.0 mm thick sheet. Based on the FLDs it was concluded that the alloy formability is largely affected by the sheet thickness and the rolling direction. The formability increases with increasing sheet thickness, but the alloy exhibits planar anisotropy (Δr < 0) as evidenced by some test samples earing. The alloy fractures with little or no observable necking, but the general stress-strain behaviour is typical of that of the aluminium 6000 alloy series.