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Start date: 2021Subject: search.filters.subject.Titanium dioxide

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    Ion doped metal oxide and its power conversion efficiency influence on Perovskite solar cells
    (2024-09) Reddy, Dwayne Jensen; Lazarus, Ian Joseph
    ABSTRACT Ion Doped Metal Oxide and its Influence on the Power Conversion Efficiency of Perovskite Solar Cells Dwayne Jensen Reddy Doctor of Applied Sciences This study focuses on the fabrication and characterization of Zinc-doped Titanium dioxide (ZnTiO2) as an Electron Transport Layer (ETL) in CH3NH3PbI3-based perovskite solar cells (PSCs). A one-step spin coating technique under controlled ambient conditions (relative humidity < 65%, room temperature ∼ 20oC ) for the development of PSC was applied to investigate the effects of Zn-ion doping on the structural, morphological, optical, and photovoltaic properties. Numerical simulations using SCAPS 1D were additionally performed to further investigate the influence of ion doping on the power conversion efficiency (PCE) of PSCs. Zn-doped TiO2 was successfully incorporated into the TiO2 crystal structure using the solgel technique. Characterization through X-ray diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDX) confirmed the incorporation of Zn ions. The crystallite size ranged from 19.99 to 7.1 nm, depending on the Zn ion doping concentration. XRD results also indicate the formation of a highly crystalline tetragonal perovskite (CH3NH3PbI3) phase. Fourier Transform Infrared (FTIR) spectroscopy verified the presence of the anatase phase of Zn-doped TiO2, while the formation of the adduct of Pb2 with dimethyl sulfoxide (DMSO) and methylammonium iodide (MAI) was confirmed at 1015 cm-1. Scanning Electron Microscope (SEM) images exhibited fairly smooth and uniform surface coverage for the Zn-doped TiO2 layers. The Root Mean Square (Rq) values for surface roughness showed a decrease from 26.85 nm for undoped TiO2 to 23.4 nm for the 5 mol% Zn-doped TiO2 layer. UV-Vis spectroscopy demonstrated low light transmission loss characteristics from 300 to 790 nm, with the 2 mol% Zn-doped TiO2 showing slightly improved light transmission between 550 and 800 nm. The bandgap energy of undoped and Zn-doped TiO2 ranged from 3.53 to 3.38 eV, while the perovskite layer exhibited a bandgap energy of 2.06 eV. Experimentally, an optimum PCE of 5.67% was achieved with a 2 mol% dopant concentration. However, increasing the Zn dopant to 5 mol% led to a slight deterioration in the PCE. Numerical simulations revealed that increasing the donor doping concentration in the ETL improved the conduction band alignment at the ETL and perovskite interface, resulting in a PCE of 6.17%. Optimizing the absorber acceptor doping concentration and band gap improved the PCE to 10.79%, however, created a pronounced conduction band offset at the ETL/perovskite interface. This was mitigated by introducing an interfacial layer of Cubic Silicon Carbide (3C-SiC) between the absorber and ETL to minimize the conduction band offset, ultimately achieving a PCE of 12.09%.
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    Electrochemical and molecular modelling studies to assess the photoreactive properties of Efavirenz
    (2022-09) Mthiyane, Thethiwe Promise; Bisetty, Krishna; Jordaan, M. A.; Uwaya, Gloria Ebube
    Efavirenz (EFV) is commonly used as an antiretroviral drug to treat HIV/AIDS and is known to undergo photoreactions that could be exploited for photodegradation applications. In addition, there is limited information on the photoreactivity of EFV. This work focuses on two case studies to assess the photocatalytic properties of EFV supported by experimental and molecular modelling (commonly referred to as computational chemistry). The first case study deals with the design of an innovative electrochemical sensor for the detection of EFV, using titanium dioxide nanoparticles (TiO2-NPs) doped on glassy carbon electrode (GCE) with nafion as an anchor agent (GCE/TiO2-NPs-nafion). TiO2-NPs were synthesized using Eucalyptus globulus leaf extract and characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). The electrochemical and sensing properties of the developed sensor for EFV were assessed using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV) and chronoamperometry. The oxidation peak current response for EFV on the GCE/TiO2-NPs-nafion electrode was greater compared to the bare and modified GCE/TiO2-NPs electrodes. A linear dynamic range of 4.5 to 18.7 µM with a 0.01 µM limit of detection was recorded on the electrode using DPV. The electrochemical sensor demonstrated good selectivity as well as practicability for the detection of EFV drugs with excellent recoveries ranging from 92.0-103.9%. The density functional theory (DFT)-based quantum chemical modelling was used to establish the chemical reactivity for EFV, suggesting the benzoxazine ring as the active site. Monte Carlo (MC) simulations revealed a strong electrostatic interaction on the GCE/TiO2-NPs-nafion-EFV (substrate-adsorbate) system. The results showed good agreement between the MC computed adsorption energies and the experimental CV results for EFV. The stronger adsorption energy of nafion onto the GCE/TiO2-NPs substrate contributed to the catalytic role in the signal amplification sensing of EFV. The second case study deals with the assessment of the photocatalytic degradation of EFV in combination with green synthesized TiO2-NPs. The photocatalytic activity of TiO2-NPs was examined by the degradation of EFV in an aqueous medium and a maximum degradation efficiency of 91.77% was observed at a reaction time of 5 h. In addition, the electronic spectra of the EFV complex bound to single TiO2-NPs in a gas- and solution-phase were investigated using time-dependent density functional theory (TD-DFT) calculations. The calculated spectra obtained in this work were benchmarked against the gas-phase photodecomposition of the EFV- TiO2-NPs complex using UV-vis spectrophotometry. Overall, the results show that the biosynthesized TiO2-NPs have the potential for sensing pharmaceutical applications and their degradation. The results provide an effective way to explore the design of new 2D materials for the sensing of EFV, which is highly significant in the field of medicinal and materials chemistry.
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    The efficiency of phytoremediation using Panicum maximum and TiO2 nanoparticles
    (2021) Cibane, Nozipho Sinenhlanhla; Mdluli, Phumlani Selby; Moodley, K.G.; Arthur, G.D.
    This study focused on the application of Panicum maximum (guinea grass) for evaluating the phytoremediation of titanium dioxide nanoparticles (nTiO2). This study was done to explore the ability of Panicum maximum Jacq as a hyperaccumulator for phytoremediation of nTiO2. Titanium dioxide has steadily become more abundant in our environment over the years due to human activities, and this could potentially harm the environment. Panicum maximum (guinea grass) is a non-vascular plant with a short life cycle. It is well adapted to a wide variety of conditions. It originated from Africa but is presently found and cultivated in almost all parts of the world with tropical climates. It is loosely to densely tufted, with short rhizomous rooting at the lower nodes. Leaf blades are linear to narrowly lanceolate. Plant to metal oxide nanoparticle interaction was investigated by germination of seeds in the presence of titanium dioxide nanoparticles (nTiO2). The uptake of nTiO2 by Panicum maximum Jacq was evaluated after treatment of the seedlings with nTiO2. The synthesized nTiO2 was characterized, using Transmission Electron Microscope, Scanning Electron Microscope. Energy Dispersive Spectroscopy (EDX), and X-ray Diffraction (XRD). The average mean particle distribution was analyzed using Image J. The Image J analysis showed that the average particle distribution of nTiO2 was 9 nm. The TEM and SEM results revealed that the particles in the nTiO2 were spherical in shape. The XRD analysis revealed that the nTiO2 was predominantly 67.1% and 32.9% of anatase and rutile forms, respectively. Metal uptake was analyzed using the Inductively Coupled Plasma – Optical Emission Spectrometer method (ICP-OES) after the plants were digested using the wet digestion and microwave digestion methods. The ability of the plants to translocate the metals to the aerial parts of the plants (Translocation Factor - TF) was evaluated for the metal using concentration ranging from 5 ppm to 50 ppm. It was observed that the root had the highest concentration of nTiO2 while the lowest uptake was found in the leaf. The TF was highest for the 5 ppm sample. The roots with the shortest length, which indicated stress/toxicity were that of the plants which were treated with 50 ppm of nTiO2. These also had the highest accumulated nanoparticles which suggested that these plants were negatively impacted by a higher concentration of nTiO2. The standard with 5 ppm treatment showed the highest value of the translocation factor which suggested that at this concentration the nanomaterial aided and catalyzed the movement of nanoparticles to the aerial parts of the plant. The results suggested that seed treated with nanoparticles before planting for phytoremediation purposes could increase the metal uptake selectivity.