Abstract
The thesis aims to create sustainable photocatalysts for self-cleaning applications by doping TiO2 with other metals and compounds. Photocatalytic degradation can be used to protect solar panel surfaces, cementitious material surfaces, biomedical and textile materials surfaces, reduce environmental impact, and remove pollutants from water and wastewater, making it a popular self-cleaning technique. Electricity producers concentrate on researching and developing renewable energy sources, such as solar energy collected using photovoltaic panels, in response to the growing global interest in creating sustainable energy sources that do not negatively impact human habitation. One of the solutions under investigation to assist keep solar surfaces clean and lower the expense and risks involved with alternative cleaning techniques is self-cleaning. This has led to the development of sustainable photocatalytic materials that may be used as overlays to facilitate the removal of deposited pollutants and preserve or improve the solar energy absorption efficiency and light transmission of the surfaces. In photocatalytic settings, TiO2 is the most commonly utilized material because it is inexpensive, nontoxic, chemically stable, and inert. However, its large band gap of 3.2 eV limits its practical applications. TiO2 can only absorb approximately 5% of sunlight in the ultraviolet spectrum. To expand this absorption limit, TiO2 needs to be doped with other elements or compounds to lower its bandgap and enhance its photocatalytic activity to get over this restriction.
In this work, urea, which is a high source of nitrogen, previously reported to create defects within TiO2 structures to retard its charge recombination rate and improve photocatalytic activity desired for self-cleaning, was used to dope TiO2. Since using simple synthesis methods such as the sol-gel to produce its results in particle clustering, the study considered the effect of post-synthesis heat treatment on its self-cleaning functionality. Secondly, because zeolites like Silicoaluminophosphate (SAPO-34) offer large surface area, regular pore size, distinctive structural features, superior adsorption, and superior thermal stability, which affords them to be effective photocatalyst support materials, this study developed a novel nanocomposite (Cu@TiO2@SAPO-34), photocatalyst that by doping TiO2 with SAPO-34 and copper, using a modified hydrothermal synthesis method. The developed photocatalysts were characterized for structure, morphology, and optical and electrochemical properties using X-ray diffraction (XRD), Fourier Transformed Infrared Spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) analysis, and X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM), UV-vis and photoluminescence spectroscopy, AUTOLAB ORIEL LCS-100 electrochemical workstation and subsequently
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subjected to a series of self-cleaning application tests including methylene blue degradation, Rhodamine dye degradation, waste water treatment, thin film cleaning and wettability analysis.
The morphological analysis of Urea-TiO2 nanoparticles showed that when the temperature of calcination rose from 300 to 700 °C, the particles became loose and powder-like, with varying sizes. The nanoparticles were crystalline, tetragonal, and had enlarged cell volume. Optical properties showed a drop in bandgap from 2.80 eV at 300 °C to 2.70 eV at 700 ⁰C, increased absorption capability in visible light, and higher photocatalytic activities. The study found that higher calcination temperatures enhance self-cleaning functionality in urea-doped TiO2 samples, with faster degradation rates observed at 700 ⁰C.
The novel composite, Cu@TiO2@SAPO-34, was found to have enhanced structural properties, with aa average crystallite size of 17.56 nm compared to 13.11 nm for the pristine TiO2. The composite also showed a narrow pore size distribution, resulting in a gain in surface area. Optical properties showed that the composite showed weak adsorption in both UV and visible regions, with early absorption in the infrared region. This was accompanied by a concomitant decrease in band gap energy from 3.09 eV (TiO2) to 2.61eV for the new Cu@TiO2@SAPO-34 composite. The electrochemical analysis showed that the novel Cu@TiO2@SAPO-34 composite had a lower charge transfer resistance (2007 Ω) than TiO2( 3931Ω) and a higher photocurrent density of 46μA/cm2, approximately five times that of TiO2 which stood at 9μA/cm2 indicating more excellent conductivity and more effective charge migration for the novel Cu@TiO2@SAPO-34. The novel Cu@TiO2@SAPO-34 morphology prevents the recombination of photogenerated electron-hole pairs, resulting in better photoelectrochemical efficiency. Its superhydrophobicity, with a water contact angle of 7.70° compared to 54.18° for pristine TiO2, makes it super suitable for self-cleaning, anti-fouling, anti-fogging, and photocatalytic applications. The self-cleaning application tests confirmed the Cu@TiO2@sapo-34 nanoparticle to be highly photocatalytic, superhydrophilic, and capable of degrading 98.06% of methylene blue dye within 30 minutes, compared to 35.09 for TiO2. It also removes higher percentages of contaminants from wastewater and coated film surfaces than TiO2, and its performance is not dependent on initial dye concentration, as it could effectively degrade higher concentrations of methylene blue contaminants within 30 minutes of reaction time. This makes it very suitable for a variety of self-cleaning applications.
This research will broaden our corpus of knowledge in promoting a green economy by improving solar cell development, power conversion efficiency, hydrogen production, and general development of self-cleaning materials for building surfaces, automotive paints, concrete, fabrics, and wastewater treatment.