Investigating Catalytic Selectivity of Nanoparticles encapsulated in MOFs:

Thesis advisor: Chia-kuang TsungThesis advisor: Dunwei WangCoating porous materials is a potential pathway to improve Catalytic performance of heterogeneous catalysts. The unique properties of Metal organic frameworks (MOFs) like huge surface area, long range order and high tenability make them promising coating materials. However, two traditional MOF encapsulation methods have their own issues. Herein, we synthesized Pt/Pd metal nanoparticles @UiO-66-NH2 via a one-pot in situ method which has good control of nanoparticles size while avoids the introduction of capping agent. The catalytic performance of synthesized Pt@UiO-66-NH2 is tested via selective hydrogenation of Crotonaldehyde. And the selectivity of our desired product achieves 70.42% which is much higher than merchant Pt catalysts. A step further, we used linker exchange to replace the original NH2-BDC linker of which amine group plays an important role in the coating process. After linker exchanging, the significant decreasing in selectivity of our target product demonstrates that the interaction between Pt and amine group does have some positive impacts on their catalytic performance. We hope our research could provide some insights of the MOFs and nanoparticles interface and help rational design of catalysts with high performance.Thesis (MS) — Boston College, 2021.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Chemistry

Response and Simulation of Vegetation in Desert Scenic Spot to Tourists’ Trampling Disturbance

A large number of tourists had a devastating effect to the scenic area. Shapotou and Huangshagudu scenic spots in Ningxia were selected as the research areas. The fait accompli method was used to investigate the response of footpath in the above scenic spots to tourists’ stampede interference. Three different angles and different vegetation types of quadrats were set up to simulate tourists’ stampede mode and observe the vegetation recovery after stampede. The results showed that: (1) The tourist trampling disturbance mainly were limited 0-4 meters distance from the tourist trails, but there was difference for different tourist trails. (2) The index of land cover impact (ILCI) of the investigating sections indicated the 1 meter distance from tourist trail is seriously disturbed; Because of the palisade on both sides of the plank road, the average value of ILCI in north of Shapotou (investigating section 4) is less than 44.9%.(3)With the increase of tourist activity,the coverage of vegetation decline, the height of plant reduce, the quantity and kinds decrease,soil crust fragmentation increase.(4)Because of different angle of sand dune, the impact of tourist activity to vegetation and soil is different.Vegetation and biological crust of sample C which is the biggest angle suffer from the devastation.(5)Based on limits of acceptable change (LAC) visitor questionnaires, the limit of acceptable change in ground coverage was 16.4%. The vegetation coverage should be below this level at desert scenic spots. It shows that there is natural incompatible relationship between tourist demand to the empty and desolate desert and desert ecological management. The results also indicated that the current tourism disturbance had some negative effect on the tourist experience and ecosystem.

Two-Stage Submodular Optimization of Dynamic Thermal Rating for Risk Mitigation Considering Placement and Operation Schedule

Cascading failure causes a major risk to society currently. To effectively mitigate the risk, dynamic thermal rating (DTR) technique can be applied as a cost-effective strategy to exploit potential transmission capability. From the perspectives of service life and Braess paradox, it is important and challenging to jointly optimize the DTR placement and operation schedule for changing system state, which is a two-stage combinatorial problem with only discrete variables, suffering from no approximation guarantee and dimension curse only based on traditional models. Thus, the present work proposes a novel two-stage submodular optimization (TSSO) of DTR for risk mitigation considering placement and operation schedule. Specifically, it optimizes DTR placement with proper redundancy in first stage, and then determines the corresponding DTR operation for each system state in second stage. Under the condition of the Markov and submodular features in sub-function of risk mitigation, the submodularity of total objective function of TSSO can be proven for the first time. Based on this, a state-of-the-art efficient solving algorithm is developed that can provide a better approximation guarantee than previous studies by coordinating the separate curvature and error form. The performance of the proposed algorithms is verified by case results

An achromatic metafiber for focusing and imaging across the entire telecommunication range

Dispersion engineering is essential to the performance of most modern optical systems including fiber-optic devices. Even though the chromatic dispersion of a meter-scale single-mode fiber used for endoscopic applications is negligible, optical lenses located on the fiber end face for optical focusing and imaging suffer from strong chromatic aberration. Here we present the design and nanoprinting of a 3D achromatic diffractive metalens on the end face of a single-mode fiber, capable of performing achromatic and polarization-insensitive focusing across the entire near-infrared telecommunication wavelength band ranging from 1.25 to 1.65 um. This represents the whole single-mode domain of commercially used fibers. The unlocked height degree of freedom in a 3D nanopillar meta-atom largely increases the upper bound of the time-bandwidth product of an achromatic metalens up to 21.34, leading to a wide group delay modulation range spanning from -8 to 14 fs. Furthermore, we demonstrate the use of our compact and flexible achromatic metafiber for fiber-optic confocal imaging, capable of creating in-focus sharp images under broadband light illumination. These results may unleash the full potential of fiber meta-optics for widespread applications including hyperspectral endoscopic imaging, femtosecond laser-assisted treatment, deep tissue imaging, wavelength-multiplexing fiber-optic communications, fiber sensing, and fiber lasers

Metafiber transforming arbitrarily structured light

Structured light has proven useful for numerous photonic applications. However, the current use of structured light in optical fiber science and technology is severely limited by mode mixing or by the lack of optical elements that can be integrated onto fiber end-faces for complex wavefront control, and hence generation of structured light is still handled outside the fiber via bulky optics in free space. We report a metafiber platform capable of creating arbitrarily structured light on the hybrid-order Poincar\'e sphere. Polymeric metasurfaces, with unleashed height degree of freedom and a greatly expanded 3D meta-atom library, were laser nanoprinted and interfaced with polarization-maintaining single-mode fibers. Multiple metasurfaces were interfaced on the fiber end-faces, transforming the fiber output into different structured-light fields, including cylindrical vector beams, circularly polarized vortex beams, and an arbitrary vector field. Our work provides a new paradigm for advancing optical fiber science and technology towards fiber-integrated light shaping, which may find important applications in fiber communications, fiber lasers and sensors, endoscopic imaging, fiber lithography, and lab-on-fiber technology