Pore-scale physics of ice melting within unconsolidated porous media revealed by non-destructive magnetic resonance characterization.

Melting of ice in porous media widely exists in energy and environment applications as well as extraterrestrial water resource utilization. In order to characterize the ice-water phase transition within complicated opaque porous media, we employ the nuclear magnetic resonance (NMR) and imaging (MRI) approaches. Transient distributions of transverse relaxation time T2 from NMR enable us to reveal the substantial role of inherent throat and pore confinements in ice melting among porous media. More importantly, the increase in minimum T2 provides new findings on how the confinement between ice crystal and particle surface evolves inside the pore. For porous media with negligible gravity effect, both the changes in NMR-determined melting rate and our theoretical analysis of melting front confirm that conduction is the dominant heat transfer mode. The evolution of mushy melting front and 3D spatial distribution of water content are directly visualized by a stack of temporal cross-section images from MRI, in consistency with the corresponding NMR results. For heterogeneous porous media like lunar regolith simulant, the T2 distribution shows two distinct pore size distributions with different pore-scale melting dynamics, and its maximum T2 keeps increasing till the end of melting process instead of reaching steady in homogeneous porous media.

Solar-driven surface-heating membrane distillation using Ti3C2Tx MXene-coated spacers.

The emergence of two-dimensional (2D) MXenes as efficient light-to-heat conversion materials offers significant potential for solar-based desalination, particularly in photothermal interfacial evaporation, enabling cost-effective solar-powered membrane distillation (MD). This study investigates solar-powered MD afforded by a photothermally functionalized spacer, which is built by spray-coating Ti3C2Tx MXene sheets on metallic spacers. 2D Ti3C2Tx MXene gives an ultrahigh photothermal conversion efficiency; thereby, by Ti3C2Tx MXene-coated metallic spacer, this rationally designed spacer allows for a localized photothermal conversion and interfacial feed heating effect on the membrane surface, especially for MD operation. As a feed spacer and a photothermal element, Ti3C2Tx MXene-coated metallic spacer exhibited stable enhanced water flux of up to 0.36 kg·m-2h-1 under one sun illumination for a feed salinity of 35 g·L-1, corresponding energy conversion efficiency of 28.3 %. Overall, the developed photothermal Ti3C2Tx MXene-coated spacers displayed great potential in enhancing the performance, scalability, and feasibility of solar-driven MD process, paving the way for further development of photothermal elements that can be implemented in solar MD applications.

Sustainable biomimetic solar distillation with edge crystallization for passive salt collection and zero brine discharge.

The urgency of addressing water scarcity and exponential population rise has necessitated the use of sustainable desalination for clean water production, while conventional thermal desalination processes consume fossil fuel with brine rejection. As a promising solution to sustainable solar thermal distillation, we report a scalable mangrove-mimicked device for direct solar vapor generation and passive salt collection without brine discharge. Capillarity-driven salty water supply and continuous vapor generation are ensured by anti-corrosion porous wicking stem and multi-layer leaves, which are made of low-cost superhydrophilic nanostructured titanium meshes. Precipitated salt at the leaf edge forms porous patch during daytime evaporation and get peeled by gravity during night when saline water rewets the leaves, and these salt patches can enhance vaporization by 1.6 times as indicated by our findings. The proposed solar vapor generator achieves a stable photothermal efficiency around 94% under one sun when treating synthetic seawater with a salinity of 3.5 wt.%. Under outdoor conditions, it can produce 2.2 L m-2 of freshwater per day from real seawater, which is sufficient for individual drinking needs. This kind of biomimetic solar distillation devices have demonstrated great capability in clean water production and passive salt collection to tackle global water and environmental challenges.

Electrothermal interfacial evaporation through carbon-nanostructured composite membranes.

High energy demand required in membrane distillation (MD) process to heat feed water and maintain the necessary temperature gradient across the membrane presents a challenge to widespread adoption of MD. In response to this challenge, surface heating membrane distillation (SHMD) has emerged as a promising solution. SHMD can employ solar or electrical energy to directly heat the membrane and feed, eliminating the need for an external heat source to heat feed water. In this study, we explore electrothermally-driven interfacial evaporation using a multi-walled carbon nanotube (MWCNT)-based composite membrane and further envision its utilization for high-efficient SHMD. Upon application of voltage, the resistance of the MWCNT leads to the conversion of electrical energy into heat, which is then uniformly transferred to feeds. The MWCNT-based composite membrane exhibited an evaporative water flux of up to 2.34 kg m-2h-1 with an associated energy efficiency of 61% and demonstrated outstanding localized surface heating performance. The employed membranes exhibited no significant variations in either resistance or surface temperature, regardless of the direction of the applied electric field. Energy parameters from the electrothermal membranes showed quantitative agreement with values reported for various electrothermal MD systems, suggesting the potential of the composite membranes in energy-efficient and cost-effective localized heating MD applications.

Environmental performance of a photovoltaic brackish water reverse osmosis for a cleaner desalination process: A case study.

Reverse osmosis (RO) membrane-based desalination system with various configurations has emerged as a critical option for reclaiming brackish water. This study aims to evaluate the environmental performance of the combination of photovoltaic-reverse osmosis (PVRO) membrane treatment system via life cycle assessment (LCA). The LCA was calculated using SimaPro v9 software with ReCiPe 2016 methodology and EcoInvent 3.8 database following the ISO 14040/44 series. The findings identified the chemical and electricity consumption at both the midpoint and endpoint level across all impact categories with terrestrial ecotoxicity (27.59 kg 1,4-DCB), human non-carcinogenic toxicity potential (8.06 kg 1,4-DCB) and GWP (4.33 kg CO2 eq) as the highest impacts for the PVRO treatment. As for the endpoint level, the desalination system affected human health, ecosystems and resources at 1.39 × 10-5 DALY, 1.49 × 10-7 species·year and 0.25 USD2013 respectively. The construction phase for the overall PVRO treatment plant was also assessed and impacted less significantly compared to the operational phase. Three different scenarios (i.e. S1: Grid input (Baseline); S2: Photovoltaic (PV)/Battery; S3: PV/Grid) based on different sources of electricity used were also compared as electricity consumption is one of the significant impacts in the operational phase. The study found that S2 had the lowest environmental impact, while S1 contributed the highest when both midpoint and endpoint approaches are considered.

Photothermal Surface Heating Membrane Distillation Using 3D-Printed Ti3C2Tx MXene-Based Nanocomposite Spacers.

To address the growing global need for freshwater, it has become essential to use nonpotable saline water. Solar membrane distillation is a potential desalination method that does not need conventional electricity and may cut water production costs. In this study, we develop a photothermal surface heating membrane distillation using a new class of photothermal spacers constructed with Ti3C2Tx MXene-based nanocomposites. In contrast to traditional membrane distillation, which utilizes energy-intensive bulk feed heating, solar-powered surface heating membrane distillation removes the external thermal energy input requirements, hence reducing operating costs significantly. In particular, three-dimensional (3D)-printing technology was used to fabricate the functional spacer, which allowed the design and materials to be fine-tuned per the needs of the process. Under solar illumination, the printed spacer can exhibit a localized photothermal conversion-driven heating effect near the surface of distillation membranes, which generates vapor pressure strong enough to operate distillation across membranes. Importantly, a two-dimensional Ti3C2Tx MXene with outstanding photothermal conversion efficiency and stability in hypersaline ionic solutions was incorporated into the 3D-printed spacers as the crucial nanofiller for imparting a local heating effect of feed. The fabricated nanocomposite spacers showed superior photothermal heating response under sunlight with an average permeate flux and energy conversion efficiency of 0.49 kg·m-2·h-1 and 30.6%, respectively. An enhancement in both photothermal efficiency and permeate flux was noticed as the amount of MXene nanosheets increased in the 3D-printed spacers. This study demonstrates the feasibility of using 3D-printed photothermal spacers for high-performance and sustainable surface heating membrane distillation, providing a promising avenue for further improvement with other photothermal nanofillers or spacer modifications.

Insights into capillary-driven motion of micro-particles interacting with advancing meniscus on a substrate.

Liquid-particle interactions at the micro-scale are quite different from the corresponding macro-scale interactions due to the substantial role of capillary forces. Herein, we explore the interaction of a single micro-particle with an air-liquid-substrate contact line. The interaction features ballistic-like motion of micro-particles toward the interacting three-phase contact line with velocities as high as 0.46 m s-1. Through high-speed optical imaging, we elucidate the interaction mechanism and associated intertwined dynamics, including evolution and backward dragging of the transient air-liquid-particle contact line, capillary-inertial launch of micro-particles and its subsequent trapping at the air-liquid-substrate contact line. Based on the force analysis, we build a model to predict the particle velocity profile during the interaction. Our experimental results show that both hydrophilic and hydrophobic micro-particles exhibit capillary-driven motion. The maximum velocity of the hydrophobic particle, as well as its total displacement, is smaller than that of the hydrophilic one with the same particle size. Micro-particle lifting, like dust removal from self-cleaning surfaces, is observed when the dynamic contact angle of the air-liquid-substrate contact line is sufficiently high (i.e. >100°). We also develop criteria for the capillary-driven motion of particles and predict the critical size for particle motion. These findings are valuable to various applications including capillary-driven self-cleaning, pickering emulsions, micro-scale fluid structure interactions and capillary dynamics in porous media.

Review on 2D Molybdenum Diselenide (MoSe2) and Its Hybrids for Green Hydrogen (H2) Generation Applications.

Hydrogen (H2) is a green and economical substitute to traditional fossil fuels due to zero carbon emissions. Water splitting technology is developing at a rapid speed to sustainably generate H2 through electro- and photolysis of water without the harmful emissions associated with steam methane reforming. Development of efficient catalysts for the hydrogen evolution reaction (HER) is pertinent for economical green H2 generation. In this regard, 2D transition metal dichalcogenides (TMDCs) are considered to be excellent alternatives to noble metal catalysts. Among other TMDCs, 2D MoSe2 is preferred due to the low Gibbs free energy for hydrogen adsorption, good electrical conductivity, and more metallic nature. Moreover, the physicochemical and electronic properties of MoSe2 can be easily tailored to suit HER application by simple synthetic strategies. Herein, we comprehensively review the application of 2D MoSe2 in the electrocatalytic HER, focusing on recent advancements in the modulation of the MoSe2 properties through nanostructure design, phase transformation, defect engineering, doping, and formation of heterostructures. We also discuss the role of 2D MoSe2 as a cocatalyst in the photocatalytic HER. The article concludes with a synopsis of current progress and prospective future trends.

Biomimetic on-chip filtration enabled by direct micro-3D printing on membrane.

Membrane-on-chip is of growing interest in a wide variety of high-throughput environmental and water research. Advances in membrane technology continuously provide novel materials and multi-functional structures. Yet, the incorporation of membrane into microfluidic devices remains challenging, thus limiting its versatile utilization. Herein, via micro-stereolithography 3D printing, we propose and fabricate a "fish gill" structure-integrated on-chip membrane device, which has the self-sealing attribute at structure-membrane interface without extra assembling. As a demonstration, metallic micromesh and polymeric membrane can also be easily embedded in 3D printed on-chip device to achieve anti-fouling and anti-clogging functionality for wastewater filtration. As evidenced from in-situ visualization of structure-fluid-foulant interactions during filtration process, the proposed approach successfully adopts the fish feeding mechanism, being able to "ricochet" foulant particles or droplets through hydrodynamic manipulation. When benchmarked with two common wastewater treatment scenarios, such as plastic micro-particles and emulsified oil droplets, our biomimetic filtration devices exhibit 2 ~ 3 times longer durability for high-flux filtration than devices with commercial membrane. This proposed 3D printing-on-membrane approach, elegantly bridging the fields of microfluidics and membrane science, is instrumental to many other applications in energy, sensing, analytical chemistry and biomedical engineering.

Nanoscopic and Macro-Porous Carbon Nano-foam Electrodes with Improved Mass Transport for Vanadium Redox Flow Batteries.

Although free-standing sheets of multiwalled carbon nanotubes (MWCNT) can provide interesting electrochemical and physical properties as electrodes for redox flow batteries, the full potential of this class of materials has not been accessible as of yet. The conventional fabrication methods produce sheets with micro-porous and meso-porous structures, which significantly resist mass transport of the electrolyte during high-current flow-cell operation. Herein, we developed a method to fabricate high performance macro-porous carbon nano-foam free standing sheets (Puffy Fibers, PF), by implementing a freeze-drying step into our low cost and scalable surface-engineered tape-casting (SETC) fabrication method, and we show the improvement in the performance attained as compared with a MWCNT sheet lacking any macro pores (Tape-cast, TC). We attribute the higher performance attained by our in-lab fabricated PF papers to the presence of macro pores which provided channels that acted as pathways for electrolytic transport within the bulk of the electrode. Moreover, we propose an electrolytic transport mechanism to relate ion diffusivity to different pore sizes to explain the different modes of charge transfer in the negative and the positive electrolytes. Overall, the PF papers had a high wettability, high porosity, and a large surface area, resulting in improved electrochemical and flow-cell performances.