Ag-iodide nano-scaled materials as seed nano-compounds for cloud seeding

Abstract

Water can be considered as one of the vital necessities of human life which is sustaining the human life as well as all other creatures like plants and animals. Due to global warming issue and other environmental problems at recent decades, water scarcity and potable water shortage is one of the main and critical world wild problems. This study focuses on improving artificial rainfall techniques which can be considered as one of the practical solutions for water scarcity and drought. This study focuses on enhancing cloud seeding and artificial rainfall techniques by using nanosized silver iodide (AgI) particles instead of micro-sized ones to in cloud seeding application and investigating new eco-friendly particles to be used in cloud seeding to address the health-care and environmental concern of using silver iodide as seed for ice nucleation and cloud seeding processes. Exploring efficient approaches to enhance rainfall and address water shortage has become extremely important recently because of growing concerns about water shortages, especially in dry areas. In natural conditions, ice nucleation in clouds typically starts at around –38 °C. However, by introducing ice-nucleating agents such as silver iodide (AgI), this process can be triggered at much warmer temperatures, sometimes as high as –5 °C. This significantly enhances the likelihood of ice formation and precipitation. AgI is a well-known and effective material for ice nucleation. One of the main reasons for efficiency of the AgI in cloud seeding applications is its crystal parameters and hexagonal crystal structure which is very similar to that of hexagonal ice. In this project explores how to fabricate AgI and reduce its particle size to the nanoscale since the nanoscale particles improve the rate of ice nucleation in the clouds due to high surface to volume ratio of nano-sized particles. In the first step AgI nanoparticles were produced using solution-based and hydrothermal methods and in the next step the novel, eco-friendly, and clean method of pulsed laser ablation in liquid (PLAL) were used for fabrication of nanoparticles. PLAL is a novel and clean synthesis method that avoids chemical contaminants which is very important in cloud seeding and environmental-related applications. It is for the first time that PLAL was used in cloud seeding application to prepare nano colloidal AgI to enhance ice nucleation process. After synthesis process, different analysis including SEM, TEM, XRD, UV-Vis, Raman and etc. were used to examine the particles structural and morphological properties. Based on the characterizations the synthesized AgI NPs predominantly shows a hexagonal crystal structure (β-phase), which is known for its strong ice nucleation activity. AgI nanoparticles were synthesized using two different PLAL approaches. In the first method, a silver (Ag) target was ablated in an iodine-deionized water (I-DW) solution, while in the second, an AgI target was ablated in deionized water. The average sizes of the AgI nanoparticles obtained from the two methods were 23 nm and 25 nm, respectively. In another phase, this research was followed by the development MgCO3 nanoparticles as an eco-friendly material (carbonate-based material) for cloud seeding which can be efficient, healthier, less toxic and more environment friendly to be used in cloud seeding applications. Magnesium carbonate NPs synthesized, characterized and investigated for the first time as a non-toxic ice nucleating particles to be used in eco-friendly cloud seeding application. The PLAL method was also used to synthesize MgCO₃ nanoparticles, with an average size of 6 nm. Laboratory experiments were run to observe the ice-forming ability of the prepared AgI and MgCO3 nanoparticles using droplets cooling system. The growth and freezing behavior of droplets was monitored using a time-resolved imaging system, allowing for dynamic observation of the nucleation process over time. For AgI nanoparticles synthesized by the two PLAL methods, droplet growth increased by 7% and 12%, respectively, compared to deionized water. For the first method, the ice nucleation rate was calculated as j(T) = 867.31 cm−2s−1 and Log (j(T)) = 2.94 at 269.65 K. For MgCO₃ nanoparticles synthesized via PLAL, the increase was measured to be 5.1%. Ice nucleation experiments were conducted at -3.5 °C for AgI nanoparticles and at -5 °C for MgCO₃ nanoparticles. Moreover, the dendrite freezing pattern was observed during the experiment which is related to ice growing pattern above -5 °C. The time dynamic observation of freezing for NPs loaded droplets showed the efficiency of synthesized NPs in ice forming experiments even in very low concentration of NPs. The outcome of the thesis may offer practical solutions for regions facing serious water stress. The findings are especially relevant for potential cloud seeding programs in the coastal parts of different countries including South Africa.