Date of Award

Fall 11-15-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular Science and Nanotechnology

First Advisor

David Mills

Abstract

This dissertation presents an integrated research framework that bridges nanotechnology, green chemistry, and sustainable agriculture, aiming to address two critical global challenges: enhancing plant growth under resource-limited conditions and valorizing agricultural waste for bioactive compound extraction. The study is divided into three major projects that together highlight the innovative application of magnesium oxide-coated halloysite nanotubes (MgO-HNTs) and the development of environmentally conscious extraction methods for high-value phytochemicals. The first component of this work investigates the design, fabrication, and functional evaluation of MgO-HNTs as advanced nanocarriers for promoting seed germination and early root development in tomato plants. MgO-HNTs were synthesized via an electrodeposition technique and structurally characterized using scanning electron microscopy (SEM), confirming successful surface modification. Growth experiments were conducted under hydroponic and soil-based conditions using Heirloom Cherry Tomato and Golden Tomato seeds, and further extended to simulated extraterrestrial environments. A Response Surface Methodology (RSM) approach, based on a Box–Behnken Design, was applied to assess the interaction of three independent variables—temperature, MgO-HNT concentration, and light duration—on multiple physiological responses. Among eight growth indicators evaluated, seedling length and root length stress tolerance index (RLSI) emerged as key response variables for optimization. Optimal conditions (25 °C, 12-hour light exposure, 100 mg/L MgO-HNTs) led to maximum root and shoot elongation in Earth soil simulants. These optimized conditions were validated using lunar and Martian regolith simulants to explore applications in space agriculture. The MgO-HNTs treatment substantially improved root penetration, seedling vigor, and germination rates even under nutrient-deficient, high-stress soil analogs. Notably, lunar regolith supported peak root development at 100 mg/L, while Martian regolith showed optimal results at lower concentrations (10 mg/L), reflecting the distinct mineralogical and oxidative properties of the soils. These results underscore the potential of MgO-HNTs to support in-situ resource utilization (ISRU) strategies for sustainable extraterrestrial crop production. The second component of the dissertation focuses on developing a sequential microwave–ultrasound-assisted extraction (MUAE) method to recover lycopene—a potent antioxidant and natural pigment—from tomato pomace waste. A one-factor-at-a-time (OFAT) experimental design was employed to individually investigate the effects of particle size, solvent composition, solvent-to-solid ratio, microwave time, and ultrasound conditions on extraction efficiency. Ethanol–water mixtures were chosen as a green solvent system, with 60% ethanol providing the best compromise between extraction power and environmental safety. Optimal extraction conditions included microwave irradiation at 180 W for 60 seconds followed by ultrasound treatment at 70 °C for 30 minutes, using a solvent-to-solid ratio of 40:1 (mL/g) and a particle size of 180 μm. Under these conditions, the lycopene yield reached 8.56 ± 0.30%, the highest among all tested methods. Visual and spectrophotometric analyses confirmed that the MUAE approach not only improved pigment release but also minimized thermal degradation due to its synergistic thermal-mechanical mechanism. The third component builds on the findings of the OFAT study and applies RSM to statistically optimize the simultaneous extraction of lycopene and total carotenoids. A Box–Behnken Design was used to model the effects of five variables: microwave time, ultrasound time, ultrasound temperature, ethanol concentration, and solvent-to-solid ratio. A total of 46 experimental runs were performed to develop predictive quadratic models. Statistical analysis (ANOVA) revealed that several linear and interaction terms significantly influenced extraction outcomes. The optimal extraction conditions predicted by the models were validated experimentally, yielding 8.25% lycopene and 10.50% total carotenoids. The reliability of the models was supported by high R² values, low residual errors, and good agreement between predicted and observed responses. Comparative evaluation of extraction strategies—MAE, UAE, UMAE, MUAE (single-factor), and MUAE (RSM-optimized)—confirmed that the optimized MUAE method offered the highest extraction efficiency and reproducibility. Furthermore, UV–Vis spectrophotometric calibration curves and High-Performance Liquid Chromatography (HPLC) were employed to quantify and verify the composition of the extracts. HPLC analysis identified eleven carotenoids, with lycopene as the major compound (5.43 μg/g DW), followed by β-carotene, lutein, rubixanthin, phytoene, and phytofluene, reflecting a diverse antioxidant profile suitable for nutraceutical and pharmaceutical applications. Together, these three research threads establish a cohesive narrative that merges space-inspired agricultural innovation with sustainable waste valorization. The novel use of MgO-HNTs for plant growth enhancement presents a feasible strategy for improving agricultural productivity in extreme or extraterrestrial environments, while the green extraction techniques developed for lycopene and carotenoid recovery offer scalable approaches for transforming food waste into high-value functional compounds. This work contributes to the advancement of molecular science and nanotechnology by offering practical solutions for two of the 21st century’s pressing needs: food security and sustainable resource utilization—on Earth and beyond.

Download

Share

COinS