Author: Saleque, Ahmed Mortuza
Title: Natural porous and two-dimensional materials for efficient solar energy conversion
Advisors: Tsang, Yuen Hong Peter (AP)
Degree: Ph.D.
Year: 2022
Subject: Solar cells -- Materials
Nanostructured materials
Hong Kong Polytechnic University -- Dissertations
Department: Department of Applied Physics
Pages: xxvii, 209 pages : color illustrations
Language: English
Abstract: Water, energy, and the environment are the three most crucial and intricately intertwined components of a sustainable human civilization. The rising global demand for energy, the declining reserve of fossil fuel, and its adverse effects are adding sail wind to the renewable energy conversion technology research. Among all the renewable energy resources, solar energy is considered the most abundant and limitless source. Therefore, the future of renewable energy penetration to meet the global energy demand is most likely dependent on solar energy conversion technologies. The deployment of the photothermal energy conversion technique is becoming increasingly popular to generate interfacial solar steam for many applications, including water distillation, seawater desalination, and sterilizing. As a result, the primary objective of this thesis is to investigate prospective solar energy conversion technology for effective photothermal energy conversion utilizing natural porous and two-dimensional (2D) materials and demonstrate its applicability in water desalination and sterilization applications. Furthermore, the possibility of using squandered heat to generate electricity using a thermoelectric module while electrolyzing seawater to produce hydrogen gas with zero carbon emissions has been investigated in this thesis.
As an excellent solar photothermal conversion material for water purification applications, a chemically treated luffa sponge (LS) obtained from the mature fruit of the Luffa cylindrica (LC) plant was examined for the first time in this research. Dopamine treatment and candle soot surface coating have been applied to improve the hydrophilicity and solar absorption capability of the luffa sponge. As much as five times higher water evaporation rate has been achieved for the surface modified luffa sponge than the freshwater evaporation under one sun illumination. The outdoor experiment demonstrated an improved solar evaporation efficiency of 79.98%, much greater than that of other low-cost materials. For seawater desalination, surface modified LS can generate up to 7.5-8 liters of freshwater per day for a 1 m² area. It is thus possible to use the proposed system in isolated locations and refugee camps.
The second part of this thesis investigates the superior thermal properties of 2D transition metal dichalcogenides (TMDs) materials to design an efficient solar photothermal absorber. A van der Waals heterostructure composed of 1D-2D metallic multiwall carbon nanotubes and hafnium telluride (HfTe₂) TMDs have been investigated to achieve broadband solar absorption of 92% weighted by the standard air mass 1.5 global solar spectrum across 250 - 2000 nm. As provided by the heterostructure, the surface plasmonic resonance enhances the surface temperature and the steam temperature significantly. Evaporation efficiency increased to 87.34% under one sun illumination, resulting in a steam temperature rise to 132°C in about 20 mins. There is a significant reduction in sterilizing costs due to the simple construction technique and minimalist design. A proof-of-concept sterilizing demonstration reduces E. coli bacteria by 99.04 %, surpassing World Health Organization requirements. By replacing a standard autoclave with a capacity of 10 liters, this sterilizing device might save 2.45 tons of CO₂ each year. With its excellent sterilizing performance, dramatic capital and operating cost reduction capability, ease of maintenance, and significant reduction in carbon footprint, the MWCNT-HfTe₂@Cu foam surgical equipment sterilization system could be a promising and low-cost solution for sterilization in off-grid and resource-constrained areas.
In the final part of the thesis, the quantum confinement effect of TMDs-based quantum dots has been investigated to increase heat confinement at the nanoscale and achieve higher photothermal conversion efficiency. A novel TiTe₂ quantum dots decorated with reduced graphene oxide (rGO) based hierarchical structure is coated on a recycled surgical facemask to produce freshwater from seawater with an evaporation efficiency of 87.79%. Concurrently, squander heat from the steam generation system generates 339.26 mW of electricity using thermoelectric generator modules made of bismuth telluride (Bi₂Te₃). Finally, an electrolysis system driven by the thermoelectric generator modules produces hydrogen gas at 0.52 mmol/h while producing zero carbon emissions. Likewise, novel TaTe₂ quantum dots decorated rGO-based bio-hydrogel with light-trapping structure have been demonstrated for seawater desalination with an efficiency of 91.17%. The equally distributed proposed micro-size light trapping texture helps to progressively convert incident solar irradiance to heat by the process of numerous times reflections within the texture hole. Therefore, only a small amount of incident light can escape the hole, resulting in improved photothermal energy conversion efficiency compared to a flat texture. The anti-biofouling properties of the telluride presence in TaTe₂ quantum dots improve the broadband solar absorption but also helps to eradicate microbes in wastewater at an acceptable level that exceeds the WHO requirement.
Rights: All rights reserved
Access: open access

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