There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Metal-organic frameworks (MOFs) are an emerging class of porous materials with potential applications in gas storage, separations, catalysis, and chemical sensing. Despite numerous advantages, applications of many MOFs are ultimately limited by their stability under harsh conditions. Herein, the recent advances in the field of stable MOFs, covering the fundamental mechanisms of MOF stability, design, and synthesis of stable MOF architectures, and their latest applications are reviewed. First, key factors that affect MOF stability under certain chemical environments are introduced to guide the design of robust structures. This is followed by a short review of synthetic strategies of stable MOFs including modulated synthesis and postsynthetic modifications. Based on the fundamentals of MOF stability, stable MOFs are classified into two categories: high-valency metal-carboxylate frameworks and low-valency metal-azolate frameworks. Along this line, some representative stable MOFs are introduced, their structures are described, and their properties are briefly discussed. The expanded applications of stable MOFs in Lewis/Bronsted acid catalysis, redox catalysis, photocatalysis, electrocatalysis, gas storage, and sensing are highlighted. Overall, this review is expected to guide the design of stable MOFs by providing insights into existing structures, which could lead to the discovery and development of more advanced functional materials.

Stable Metal-Organic Frameworks: Design, Synthesis, and Applications.

http://csmres.co.uk/cs.public.upd/article-downloads/lynch.pdf

Protein-nanoparticle interactions

Atmospheric water is a resource equivalent to ~10% of all fresh water in lakes on Earth. However, an efficient process for capturing and delivering water from air, especially at low humidity levels (down to 20%), has not been developed. We report the design and demonstration of a device based on a porous metal-organic framework {MOF-801, [Zr6O4(OH)4(fumarate)6]} that captures water from the atmosphere at ambient conditions by using low-grade heat from natural sunlight at a flux of less than 1 sun (1 kilowatt per square meter). This device is capable of harvesting 2.8 liters of water per kilogram of MOF daily at relative humidity levels as low as 20% and requires no additional input of energy.

https://science.sciencemag.org/content/sci/early/2017/04/12/science.aam8743.full.pdf

Water harvesting from air with metal-organic frameworks powered by natural sunlight

A theoretical model has been developed to predict the behavior of a buoyancy-driven upward co-current two-phase flow in an annular channel with uniform gap size that forms between a hemispherical vessel and its surrounding structure. The vessel is fully submerged in water and is heated from within, leading to downward facing boiling on its outer surface. The problem under consideration is relevant to the so-called in-vessel retention (IVR) of core melt, which is a key severe accident management strategy for some advanced pressurized water reactors (APWRs). One available means for IVR is the method of external reactor vessel cooling by flooding of the reactor cavity with water during a severe accident. Design features of most APWRs have the provision for substantial water accumulation in the reactor cavity during numerous postulated accident sequences. With water covering the lower external surfaces of the reactor pressure vessel, significant energy (i.e., decay heat) could be removed from the core melt through the vessel wall by downward facing boiling on the vessel's outer surface. As boiling of water takes place on the vessel outer surface, the vapor generated on the surface would flow upward through the annular channel under the influence of gravity. The vapor motions would entrain liquid water, thus resulting in a buoyancy-driven upward co-current two-phase flow in the channel. While the flow is induced entirely by the boiling process, the rate of boiling, in turn, can be significantly affected by the resulting two-phase flow. As long as the heat flux from the core melt to the vessel wall does not exceed the critical heat flux limit for downward facing boiling, nucleate boiling is the prevailing regime and the vessel wall can be maintained at relatively low temperatures to prevent failure of the lower head. With this scenario in mind, the problem is formulated by considering the conservation of mass, momentum, and energy in the two-phase mixture, along with the use of available information on two-phase frictional drop and void fraction. The resulting governing system is solved numerically to predict the total mass flow rate that would be induced in the channel by the boiling process. Based on the numerical results, the optimal gap size that would maximize the steam venting rate and the rate of downward facing boiling over a range of wall heat fluxes is determined. The effects of system pressure and liquid level in the reactor cavity on the induced mass flow rate have also been identified.

Optimal Gap Size for Downward Facing Boiling and Steam Venting in a Hemispherical Annular Channel

Monolithically integrated heat pump. The heat pump includes an adsorbent/absorbent condenser forming a hot terminal integrated with a phase change heat exchanger forming a cold terminal. The adsorbent/absorbent condenser and the phase change heat exchanger are integrated into a single pressure vessel.

Monolithically integrated bi-directional heat pump

Electric vehicle (EV) technology faces a substantial challenge in terms of driving range, especially when the vehicle’s climate control system relies entirely on the onboard electric battery. Therefore, we are developing an advanced adsorption-based thermal battery (ATB) capable of delivering both heating and cooling for electric vehicles with minimal use of the electric battery bank. While adsorption based climate control systems offer the advantage of direct usage of primary thermal energy sources for operation, they typically have low COP values, and are often bulky and heavy. A compact and lightweight ATB is necessary to replace existing climate control systems in EVs that use electric battery for operation. In this paper, we present a detailed computational analysis of adsorption kinetics taking place within an adsorption bed that is capable of delivering large cooling and heating capacities by making use of novel adsorbents. The overall design of the adsorption bed, which is a critical element in achieving a high performance thermal battery, is also discussed. To make performance predictions, we characterized the adsorbents to obtain their thermophysical and transport properties as well as adsorption characteristics. The model consequently incorporates these measured properties to predict the performance variation as a function of time. This work provides the critical parameters affecting heating and cooling rates, and identifies avenues for further improvement in the overall performance of the thermal battery. NOMENCLATURE

Design and Optimization of High Performance Adsorption-Based Thermal Battery

Microbial fuel cells (MFC) can generate electric energy from wastewater which can be enhanced further by anode catalysts. The recovery of electrons produced by oxidation of organics catalyzed by bacteria in the anode was enhanced when carbon dots(CDs) were added into the MFC. In this present study, a novel strategy for designing anode material and the fabrication of a high-efficient and environmentally friendly anode for energy generation from wastewater was reported. The CDs were synthesized by the pyrolysis of a peanut shell at the temperature of 250 °C for 2 h with a heating rate of 10 °C min−1. Thus synthesized CDs were characterized by transmission electron microscopy (TEM), UV/Vis spectroscopy, and fluorescence spectroscopy. The TEM analysis showed morphology with an average size of 1.62 nm. The UV/Vis absorbance of the CDs shows a wide absorption band without a characteristic peak. The excitation spectrum of CDs recorded at the emission wavelength of 440 nm exhibits a peak around 320 nm. CDs were investigated as an anode material in a MFC utilizing acetate as the organic substrate. The average chemical oxygen demand (COD) removal in closed circuit operation mode was 89%. The maximum power density production (7.2 W/m3) was observed in MFC containing 1 mg/cm2 CD-impregnated anode (CDsIA). The CDsIA provides the ability to promote efficient biofilm formation. These results emphasize the application of CD-based electrodes in MFCs for the simultaneous treatment of wastewater and electricity generation while also providing additional benefits.

https://www.mdpi.com/2073-4344/12/12/1580/pdf?version=1670332164

Application of Low-Cost Plant-Derived Carbon Dots as a Sustainable Anode Catalyst in Microbial Fuel Cells for Improved Wastewater Treatment and Power Output

A novel cooling scheme utilizing evaporative cooling for an ultra-thin, spatially confined liquid film is described for meeting the challenge of hot spot thermal management aiming at locally removing heat fluxes in excess of 200 W/cm2 . This work presents the conceptual system design and results of performance calculations supporting the feasibility of the proposed cooling scheme. The phase change heat transfer is one of the most efficient means of heat transfer due to an advantage offered by the significant latent heat of vaporization of liquids. Fundamentally, evaporation could be a much more efficient method of heat removal as compared to boiling if certain conditions are met. Theoretically, we demonstrate that if a stable monolayer of liquid can be maintained on the surface and fully dry sweeping gas (e.g., air) is blown at high velocity above this liquid monolayer one can dissipate heat fluxes of the order of several hundreds of Watts per cm2 . We also show that a more volatile FC-72 can outperform water in evaporative cooling using stable liquid microfilms.© 2007 ASME

Shankar Narayanan

Papers

Optimal Gap Size for Downward Facing Boiling and Steam Venting in a Hemispherical Annular Channel

Monolithically integrated bi-directional heat pump

Design and Optimization of High Performance Adsorption-Based Thermal Battery

Application of Low-Cost Plant-Derived Carbon Dots as a Sustainable Anode Catalyst in Microbial Fuel Cells for Improved Wastewater Treatment and Power Output

Perspiration Nano-Patch for Hot Spot Thermal Management