High-Performance Ultrafine Bubble Aeration on Janus Aluminum Foil Prepared by Laser Microfabrication

A solar-driven nanocellulose Janus aerogel with excellent floating stability and dual functions of oil-water separation and photocatalytic degradation of organic pollutants

Effective and practical cleanup of viscous crude oil spills is extremely important in real harsh marine environments. Herein, we designed a solar-driven, nanocellulose-based Janus aerogel (Janus-A) with excellent floating stability and dual function of oil-water separation and degradation of aqueous organic pollutants. Janus-A, with its amphiprotic nature, was prepared through polypyrrole (PPy) deposition, freeze-drying, octyltrichlorosilane (OTS) impregnation, TiO2 spraying on the bottom surface, and UV irradiation treatment. The photothermal conversion effect of PPy coating raised the surface temperature of aerogel to 75.8 °C within 6 min under one simulated solar irradiation, which greatly reduced the viscosity of the crude oil and increased the absorption capacity of the aerogel to 36.7 g/g. Benefiting from the balance between the buoyancy generated by the hydrophobic part and water absorption of the hydrophilic part, Janus-A showed excellent floating stability under simulated winds and waves. In addition, Janus-A exhibited high degradation efficiency for organic pollutants in water owing to the synergistic photocatalytic properties of TiO2 and PPy. These excellent performances make Janus-A ideal for integrated water-oil separation and water remediation.

Passive Automatic Switch Relying on Laplace Pressure for Efficient Underwater Low-Gas-Flux Bubble Energy Harvesting

The buoyancy potential energy contained in bubbles released by subsea geological and biological activities represents a possible in situ energy source for underwater sensing and detection equipment. However, the low gas flux of the bubble seepages that exist widely on the seabed introduces severe challenges. Herein, a passive automatic switch relying on Laplace pressure is proposed for efficient energy harvesting from low-gas-flux bubbles. This switch has no moving mechanical parts; it uses the Laplace-pressure difference across a curved gas-liquid interface in a biconical channel as an invisible "microvalve". If there is mechanical equilibrium between the Laplace-pressure difference and the liquid-pressure difference, the microvalve will remain closed and prevent the release of bubbles as they continue to accumulate. After the accumulated gas reaches a threshold value, the microvalve will open automatically, and the gas will be released rapidly, relying on the positive feedback of interface mechanics. Using this device, the gas buoyancy potential energy entering the energy harvesting system per unit time can be increased by a factor of more than 30. Compared with a traditional bubble energy harvesting system without a switch, this system achieves a 19.55-fold increase in output power and a 5.16-fold enhancement in electrical energy production. The potential energy of ultralow flow rate bubbles (as low as 3.97 mL/min) is effectively collected. This work provides a new design philosophy for passive automatic-switching control of gas-liquid two-phase fluids, presenting an effective approach for harvesting of buoyancy potential energy from low-gas-flux bubble seepages. This opens a promising avenue for in situ energy supply for subsea scientific observation networks.

Influence of Surface Wettability on Bubble Formation and Motion

Bubble dynamics plays an important role in boiling heat transfer, and surface wettability affects bubble behaviors. In the present work, the effects of surface superhydrophilicity (SHI) and superhydrophobicity (SHO) on bubble dynamics are experimentally studied by observing the formation and motion behaviors of air bubbles and vapor bubbles on varied surfaces. For air bubbles to better mimic vapor bubbles, the air bubbles are introduced in a water pool by injecting airflow from a through hole of the surface. Air bubble tests are first conducted on homogeneous SHO and SHI surfaces, respectively. It is observed that surface wettability significantly affects the bubble size and departure frequency. To discover the dynamic behaviors of a bubble under both SHI and SHO, a biphilic surface with SHI and SHO areas is fabricated, and air bubbles are injected right on the biphilic border between the two areas. It is observed the wettability contrast significantly displaces the air bubbles, which spread only onto the SHO area. The biphilic surface is fabricated for the pool boiling test. Vapor bubbles are observed at different stages of the nucleate boiling, showing surface effects similar to the observations of air bubbles. Not only does this study present the influence of surface wettability on air and vapor bubble behaviors but also it provides useful implications for understanding and optimizing the biphilic surface design for enhancing boiling heat transfer.