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Wastewater is a multicomponent and multiphase mixture. Gas bubbles and solid particles in the dispersed phase influence sonochemical efficiency during ultrasonic treatment of wastewater, sometimes unfavorably; however, the influencing factors and mechanisms remain unclear. In this paper, the influence of argon gas bubbles (1.2 mm) and monodisperse silica particles (0.1 mm) on sonochemical effects in an aqueous system using a horn-type reactor (20 kHz) is reported. Triiodide formation decreased with an increase in the volume fraction of either or both phases. The two phases started inhibiting sonoreactions as the total volume fraction approached 3.0-4.0 vol% compared to pure water. The effect of the gas-to-solid ratio is also considered. We propose an acoustic attenuation model, which incorporates the scattering effect of solid particles and the thermal effect of gas bubbles. The agreement between the modeling and experimental results demonstrates that the two phases are jointly responsible for sonochemical inhibition by increasing ultrasound attenuation. This enhances the understanding of sonochemistry in gas-solid-liquid systems and helps regulate gases and solids in sonochemical reactors.

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High-efficiency electrocatalytic water splitting requires high intrinsic activity of catalysts and even more importantly favorable mass transfer. However, gas bubbles adhering to the surface of catalysts limit the re-expose of catalytic active sites to the electrolyte and reduce the catalytic activities. The efficient desorption of bubbles can be facilitated by a hierarchical multiscale structure of the electrode surface. Herein, we report an opened periodic three-dimensional electrode composed of iron (Fe)-cobalt (Co)-nickel (Ni) (oxy)hydroxide nanorods (NRs) grown in situ on a high aspect ratio nickel microcolumn array (NCA) for electrocatalytic water splitting. Compared with the flat nickel plate, the NCA not only increases the surface area for catalyst loading but also improves the wettability of the electrolyte on the electrode surface, exhibiting superhydrophilicity/superaerophobicity (the electrolyte and the bubble contact angles were about ∼0 and 163°, respectively), which accelerates the bubble evolution and desorption process. The X-ray photoelectron spectroscopy indicates that the synergy of Fe-Co-Ni could enhance the ratio of Co3+/Co2+ and Ni3+/Ni2+ and promote the electrocatalytic activity. Benefiting from the microstructure design and synergistic effects, the Co4Fe0.5Ni0.5OOH-NR@NCA electrode achieves a superior OER performance with an overpotential of 199 mV at 10 mA·cm-2.

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Freeze-thaw-induced embolism, a key limiting factor for perennial plants results from the formation of gas bubbles during freezing and their expansion during thawing. However, the ice volumetric increase generates local pressures, which can affect the formation of bubbles. To characterize local dynamics of pressure tension and the physical state of the sap during freeze-thaw cycles, we simultaneously used ultrasonic acoustic emission analysis and synchrotron-based high-resolution computed tomography on the diffuse-porous species Betula pendula. Visualization of individual air-filled vessels and the distribution of gas bubbles in frozen xylem were performed.. Ultrasonic emissions occurred after ice formation, together with bubble formation, whereas the development of embolism took place after thawing. The pictures of frozen tissues indicated that the positive pressure induced by the volumetric increase of ice can provoke inward flow from the cell wall toward the lumen of the vessels. We found no evidence that wider vessels within a tissue were more prone to embolism, although the occurrence of gas bubbles in larger conduits would make them prone to earlier embolism. These results highlight the need to monitor local pressure as well as ice and air distribution during xylem freezing to understand the mechanism leading to frost-induced embolism.

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Sea ice is heavily contaminated with microplastics (MPs), with the repeatedly confirmed increased number of larger-sized particles, deficit of fibers, and prevalence of materials denser than the surrounding water. To get insight into the drivers behind such a specific pattern, sets of laboratory experiments were performed on the formation of ice by cooling from the surface of fresh and salty (NaCl, 34 g/L) water, with particles of different sizes from heavy plastics (HPP) distributed initially over the bottom of the experimental volume. After freezing, about 50-60 % of HPP were trapped in ice in all the runs. Vertical distribution of HPP, plastic mass distribution, ice salinity (in saltwater experiments), and bubble concentration (in freshwater experiments) were recorded. Formation of bubbles on hydrophobic surfaces was the main cause of the entrapment of HPP into ice, with convection playing a secondary role. Supplementary bubble formation experiments with the same particles in water demonstrated that at larger fragments and fibers, several bubbles grow at the same time, so particle rising and residing at the surface is stable. Smaller HPP experience rising/sinking cycles with minimum time spent at the surface: one bubble is enough to cause a particle rising, but it is most often lost when colliding with the water surface. Application of the results to oceanic conditions is discussed. Oversaturation with gases due to various physical/biological/chemical processes and liberation of bubbles from methane seeps and melting permafrost are common in Arctic waters. Convective water motions are able to relocate HPP in vertical. Based on applied research, the bubble nucleation and growth, the hydrophobicity of weathered surfaces, the effectiveness of flotation methods for plastic particles are discussed. Interaction of plastic particles with bubbles is an important feature, still completely overlooked in the context of MPs behavior in marine environment.

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AIM: To evaluate the efficacy of a novel ultrasonic irrigation device, remotely-generated irrigation with a non-invasive sound field enhancement (RINSE) system, in removing biofilm-mimicking hydrogel from a simulated isthmus model and compare it with sonically- and ultrasonically-activated irrigation systems. METHODOLOGY: A polycarbonate root canal model containing two standardized root canals (apical diameter of 0.20 mm, 4% taper, 18 mm long with a coronal reservoir) connected by three isthmuses (0.40 mm deep, 2 mm high, 4 mm long) was used as the test model. The isthmuses were filled with a hydroxyapatite powder-containing hydrogel. The canals were filled with irrigant, and the models were randomly assigned to the following activation groups (n = 15): EndoActivator (EA), ultrasonically activated irrigation (UAI), and RINSE system (RS). Syringe irrigation (SI) with a 30G needle served as the control. Standardized images of the isthmuses were taken before and after irrigation, and the amount of hydrogel removed was determined using image analysis software and compared across groups using anova (p < .05). RESULTS: Hydrogel removal was significantly higher with the RS (83.7%) than with UAI, EA, or SI (p ≤ .01). UAI (69.2%) removed significantly more hydrogel than SI and EA (p < .05), while there was no significant difference between SI (24.3%) and EA (25.7%) (p = .978). CONCLUSIONS: RINSE system resulted in the most hydrogel removal, performing better than UAI or EA. The effect of RS was also not reliant on the insert or tip entering the pulp chamber or root canal, making it particularly useful in conservative endodontics.

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HYPOTHESIS: The dynamics of gas-liquid interfaces differs between aqueous surfactant and nanoparticle mixtures in rectangular cross-section capillaries. EXPERIMENTS: We designed and fabricated a new microfluidic device with a meter-long channel and a noncircular cross section (35 µm by 100 µm by 1 m) to study the flow behavior of long bubbles in capillaries wetted by water as well as surfactant and nanoparticle solutions. Flow in the novel symmetric loop device maintains essentially straight and inertialess conditions over a wide range of flow rates. FINDINGS: The pressure-drop versus velocity relationship of long bubbles in capillaries with noncircular cross sections has been studied theoretically but not extensively validated. The measured pressure drop (normalized with respect to interfacial properties) experienced by bubbles varies as Ca2/3 over the range 10-7

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This paper investigated the improved leaching of Cu, Sn, Pb, Zn, and Al from waste printed circuit boards (WPCBs) by electro-generated Cl2 in HCl solution through multiple leaching cells in series, double intake pipes, and bubble stone for leaching. The leaching agents in the leaching cell include Cl2(aq), HCl, HClO, and Cl3-. The leaching rate and leaching speed of Zn, Sn, Al, and Pb exceeded that of Cu. Leaching time and HCl concentration have a strong impact on the dissolution of Cu, whereas the effect of the electrolytic current and the leaching temperature is comparably weak. The series of leaching cells improved the effective utilization of Cl2 and increased the treatment capacity of the WPCBs. Bubble stones significantly enhanced the efficiency and rate of leaching. Reduction of the size of the Cl2 gas bubbles improved the leaching kinetics. The leaching rate of Cu reached 87.22%, whereas the leaching rate of Zn, Sn, Al, and Pb exceeded 90% after 100 min. Our experimental data provide a reference for electrolytic leaching recovery of metals from WPCBs, and our method improves the metal leaching and electrolytic efficiency in practice.

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Alkaline water electrolysis, a promising technology for clean energy storage, is constrained by extrinsic factors in addition to intrinsic electrocatalytic activity. To begin to compare between catalytic materials for electrolysis applications, these extrinsic factors must first be understood and controlled. Here, we modify extrinsic electrode properties and study the effects of bubble release to examine how the electrode and surface design impact the performance of water electrolysis. We fabricate robust and cost-effective electrodes through a sequential three-dimensional (3D) printing and metal deposition procedure. Through a systematic assessment of the deposition procedure, we confirm the close relationship between extrinsic electrode properties (i.e., wettability, surface roughness, and electrochemically active surface area) and electrochemical performance. Modifying the electrode geometry, size, and electrolyte flow rate results in an overpotential decrease and different bubble diameters and lifetimes for the hydrogen (HER) and oxygen evolution reactions (OER). Hence, we demonstrate the essential role of the electrode architecture and forced electrolyte convection on bubble release. Additionally, we confirm the suitability of ordered, Ni-coated 3D porous structures by evaluating the HER/OER performance, bubble dissipation, and long-term stability. Finally, we utilize the 3D porous electrode as a support for studying a benchmark NiFe electrocatalyst, confirming the robustness and effectiveness of 3D-printed electrodes for testing electrocatalytic materials while extrinsic properties are precisely controlled. Overall, we demonstrate that tailoring electrode architectures and surface properties result in precise tuning of extrinsic electrode properties, providing more reproducible and comparable conditions for testing the efficiency of electrode materials for water electrolysis.

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Heterogeneous bubble nucleation is one of the most fundamental interfacial processes ranging from nature to technology. There is excellent evidence that surface topology is important in directing heterogeneous nucleation; however, deep understanding of the energetics by which nanoscale architectures promote nucleation is still challenging. Herein, we report a direct and quantitative measurement of single-bubble nucleation on a single silica nanoparticle within a microsized droplet using scanning electrochemical cell microscopy. Local gas concentration at nucleation is determined from finite element simulation at the corresponding faradaic current of the peak-featured voltammogram. It is demonstrated that the criteria gas concentration for nucleation first drops and then rises with increasing nanoparticle radius. An optimum nanoparticle radius around 10 nm prominently expedites the nucleation by facilitating the special topological nanoconfinements that consequently catalyze the nucleation. Moreover, the experimental result is corroborated by our theoretical calculations of free energy change based on the classic nucleation theory. This study offers insights into the impact of surface topology on heterogenous nucleation that have not been previously observed.

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Frequency combs (FCs)-spectra containing equidistant coherent peaks-have enabled researchers and engineers to measure the frequencies of complex signals with high precision, thereby revolutionising the areas of sensing, metrology and communications and also benefiting the fundamental science. Although mostly optical FCs have found widespread applications thus far, in general FCs can be generated using waves other than light. Here, we review and summarise recent achievements in the emergent field of acoustic frequency combs (AFCs), including phononic FCs and relevant acousto-optical, Brillouin light scattering and Faraday wave-based techniques that have enabled the development of phonon lasers, quantum computers and advanced vibration sensors. In particular, our discussion is centred around potential applications of AFCs in precision measurements in various physical, chemical and biological systems in conditions where using light, and hence optical FCs, faces technical and fundamental limitations, which is, for example, the case in underwater distance measurements and biomedical imaging applications. This review article will also be of interest to readers seeking a discussion of specific theoretical aspects of different classes of AFCs. To that end, we support the mainstream discussion by the results of our original analysis and numerical simulations that can be used to design the spectra of AFCs generated using oscillations of gas bubbles in liquids, vibrations of liquid drops and plasmonic enhancement of Brillouin light scattering in metal nanostructures. We also discuss the application of non-toxic room-temperature liquid-metal alloys in the field of AFC generation.

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Background: Diving in cold water is thought to increase the risk of decompression sickness (DCS), especially if the diver is cold during decompression. In this study, we investigated hemodynamic function and DCS risk in an animal model, where cold decompression was followed by rewarming at the surface. Methods: Nine female Sprague Dawley rats had pressure-volume catheters inserted into their left heart ventricle and femoral artery before they were exposed to dry air dives in which their core temperature was normothermic during the bottom phase, cold (35°C) during decompression, and normothermic after the dive. Data from an earlier study were used as controls. The rats were compressed in air to 600kPa, maintained at pressure for 45min, and decompressed at 50kPa/min. Hemodynamic data were recorded before, during, and 60min after decompression. Venous gas bubbles were recorded in the right heart ventricle and pulmonary artery for 60min after the dive. Results and Conclusion: During decompression, cardiac output (CO), and stroke volume (SV) decreased equally in cold rats and controls. CO and SV were temporarily re-established at the surface, before falling again in the cold rats. There was no difference in post-dive venous bubble grades. However, as the post-dive fall in CO and SV could be a sign of gas emboli obstructing the pulmonary circulation, we cannot conclude whether the DCS risk was increased. More sensitive bubble detection methods are needed to elucidate this point.

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Excellent efficiency of combinational therapy of chemotherapy and photodynamic therapy (PDT) highly depends on the amounts of drug and oxygen in tumor tissue. However, how to cleverly promote drug release accompanied with improving oxygen concentration remains a challenge. Herein, we proposed a gas-generator that realized a high drug loading and integrated facilitation of drug release with oxygen replenishment into a single and simple system, utilizing huge cavities and mesoporous channels of hollow mesoporous silica nanoparticles (HMSNs) for encapsulating oxygen (O2) saturated perfluoropentane (PFP) droplets, indocyanine green (ICG) and doxorubicin (DOX), biocompatible polydopamine (PDA) as the gatekeepers. Under irradiation of 808 nm laser, the thermal effect of PDA caused PFP droplets occur liquid-gas phase transition that triggered the burst release of DOX and O2, finally amplifying the synergetic effects of PDT and chemotherapy both in vitro and in vivo. The influence of PFP, GSH and laser on drug release kinetic was explored through mathematical models. Notably, the mechanism of gas-generator on accelerating drug release under irradiation based on doing volume work and enhancing diffusion coefficient was clarified by researching the relation between DOX release, PFP release and temperature change. Additionally, the way of replenishing O2 did not rely on intracellular components but timely offered abundant "fuels" for producing reactive oxygen species (ROS) when compared with traditional manners. This work provides a new research strategy for boosting drug release and opens an avenue for constructing multifunctional controlled delivery systems.

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The use of reactive electrochemical membranes (REM) in flow-through mode during the anodic oxidation of organic compounds makes it possible to overcome the limitations of plate anodes: in the case of REM, the area of the electrochemically active surface is several orders of magnitude larger, and the delivery of organic compounds to the reaction zone is controlled by convective flow rather than diffusion. The main problem with REM is the formation of fouling and gas bubbles in the pores, which leads to a decrease in the efficiency of the process because the hydraulic resistance increases and the electrochemically active surface is shielded. This work aims to study the processes underlying the reduction in the efficiency of anodic oxidation, and in particular the formation of gas bubbles and the recharge of the REM pore surface at a current density exceeding the limiting kinetic value. We propose a simple one-dimensional non-stationary model of the transport of diluted species during the anodic oxidation of paracetamol using REM to describe the above effects. The processing of the experimental data was carried out. It was found that the absolute value of the zeta potential of the pore surface decreases with time, which leads to a decrease in the permeate flux due to a reduction in the electroosmotic flow. It was shown that in the solution that does not contain organic components, gas bubbles form faster and occupy a larger pore fraction than in the case of the presence of paracetamol; with an increase in the paracetamol concentration, the gas fraction decreases. This behavior is due to a decrease in the generation of oxygen during the recombination reaction of the hydroxyl radicals, which are consumed in the oxidation reaction of the organic compounds. Because the presence of bubbles increases the hydraulic resistance, the residence time of paracetamol-and consequently its degradation degree-increases, but the productivity goes down. The model has predictive power and, after simple calibration, can be used to predict the performance of REM anodic oxidation systems.

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The dynamic actions of cavitation bubbles in ultrasonic fields can clean surfaces. Gas and vapor cavitation bubbles exhibit different dynamic behaviors in ultrasonic fields, yet little attention has been given to the distinctive cleaning effects of gas and vapor bubbles. We present an experimental investigation of surface cleaning by gas and vapor bubbles in an ultrasonic field. Using high-speed videography, we found that the primary motions of gas and vapor bubbles responsible for surface cleaning differ. Our cleaning tests under different contamination conditions in terms of contaminant adhesion strength and surface wettability reveal that vapor and gas bubbles are more effective at removing contaminants with strong and weak adhesion, respectively, and furthermore that hydrophobic substrates are better cleaned by vapor bubbles. Our study not only provides a better physical understanding of the ultrasonic cleaning process, but also proposes novel techniques to improve ultrasonic cleaning by selectively employing gas and vapor bubbles depending on the characteristics of the surface to be cleaned.

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Exposure to a reduction in ambient pressure such as in high-altitude climbing, flying in aircrafts, and decompression from underwater diving results in circulating vascular gas bubbles (i.e., venous gas emboli [VGE]). Incidence and severity of VGE, in part, can objectively quantify decompression stress and risk of decompression sickness (DCS) which is typically mitigated by adherence to decompression schedules. However, dives conducted at altitude challenge recommendations for decompression schedules which are limited to exposures of 10,000 feet in the U.S. Navy Diving Manual (Rev. 7). Therefore, in an ancillary analysis within a larger study, we assessed the evolution of VGE for two hours post-dive using echocardiography following simulated altitude dives at 12,000 feet. Ten divers completed two dives to 66 fsw (equivalent to 110 fsw at sea level by the Cross correction method) for 30 minutes in a hyperbaric chamber. All dives were completed following a 60-minute exposure at 12,000 feet. Following the dive, the chamber was decompressed back to altitude for two hours. Echocardiograph measurements were performed every 20 minutes post-dive. Bubbles were counted and graded using the Germonpré and Eftedal and Brubakk method, respectively. No diver presented with symptoms of DCS following the dive or two hours post-dive at altitude. Despite inter- and intra-diver variability of VGE grade following the dives, the majority (11/20 dives) presented a peak VGE Grade 0, three VGE Grade 1, one VGE Grade 2, four VGE Grade 3, and one VGE Grade 4. Using the Cross correction method for a 66-fsw dive at 12,000 feet of altitude resulted in a relatively low decompression stress and no cases of DCS.

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Manipulation of gas bubbles in an aqueous ambient environment is fundamental to both academic research and industrial settings. Present bubble manipulation strategies mainly rely on buoyancy or Laplace gradient forces arising from the sophisticated terrain of substrates. However, these strategies suffer from limited manipulation flexibility such as slow horizontal motion and unidirectional transport. In this paper, a high performance manipulation strategy for gas bubbles is proposed by utilizing ferrofluid-infused laser-ablated microstructured surfaces (FLAMS). A typical gas bubble (<2 µL) can be accelerated at >150 mm/s2 and reach an ultrafast velocity over 25 mm/s on horizontal FLAMS. In addition, diverse powerful manipulation capabilities are demonstrated including antibuoyancy motion, "freestyle writing", bubble programmable coalescence, three-dimensional (3-D) controllable motion and high towing capacity of steering macroscopic object (>500 own mass) on the air-water interface. This strategy shows terrain compatibility, programmable design, and fast response, which will find potential applications in water treatment, electrochemistry, and so on.

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Minimally invasive therapies avoiding surgical complexities evoke great interest in developing injectable biomedical devices. Herein, a versatile approach is reported for engineering injectable and biomimetic nanofiber microspheres (NMs) with tunable sizes, predesigned structures, and desired compositions via gas bubble-mediated coaxial electrospraying. The sizes and structures of NMs are controlled by adjusting processing parameters including air flow rate, applied voltage, distance, and spinneret configuration in the coaxial setup. Importantly, unlike the self-assembly method, this technique can be used to fabricate NMs from any material feasible for electrospinning or other nanofiber fabrication techniques. To demonstrate the versatility, open porous NMs are successfully fabricated that consist of various short nanofibers made of poly(ε-caprolactone), poly(lactic-co-glycolic acid), gelatin, methacrylated gelatin, bioglass, and magneto-responsive polymer composites. Open porous NMs support human neural progenitor cell growth in 3D with a larger number and more neurites than nonporous NMs. Additionally, highly open porous NMs show faster cell infiltration and host tissue integration than nonporous NMs after subcutaneous injection to rats. Such a novel class of NMs holds great potential for many biomedical applications such as tissue filling, cell and drug delivery, and minimally invasive tissue regeneration.

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Two types of Zr⁻0.8Sn⁻1Nb⁻0.3Fe Zr alloys were irradiated by krypton ions in the temperature range from 320 to 400 °C. The microstructure of the as-received alloys showed that the sizes of Zr crystals and (Zr, Nb)2Fe particles with face-centered cubic (FCC) structure increased from 3.9 µm to 6.0 µm and from 74.6 nm to 89.6 nm, respectively, after cold rolling and subsequent annealing. Kr⁺ irradiation-induced bubble formation in the Zr matrix was observed. The size of the gas bubbles increased with increasing ion fluence and irradiation temperature. An equation that related the bubble size, ion fluence, and temperature were established. Irradiation-induced amorphization of particles was observed and found to be related to the fabrication process and irradiation parameters. The particles in alloy #1 showed a higher irradiation tolerance than those in alloy #2. The threshold damage dose for the amorphization of particles in alloy #2 was 3.5 dpa at 320 °C and 4.9 dpa at 360 °C. The mechanisms for bubble growth and particle amorphization are also discussed.

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Mixed ionic-electronic conducting (MIEC) membranes attract the attention because of their high potential for oxygen separation and energy conversion applications. The different fabrication methods of asymmetric membranes consisting of a thin MIEC layer on porous support were developed. The basically dense but not completely hermetic thin layers were achieved. To overcome this problem, we suggest a new concept of bilayer MIEC-Redox membrane. This solid/liquid composite membrane consists of a gastight MIEC thin external layer and a thick internal layer in which the redox reactions and oxygen bubbling occur. Here, we report the transport properties of a copper oxide-based MIEC-Redox membrane.

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The challenge of identifying cause of death in discarded bycaught marine mammals stems from a combination of the non-specific nature of the lesions of drowning, the complex physiologic adaptations unique to breath-holding marine mammals, lack of case histories, and the diverse nature of fishing gear. While no pathognomonic lesions are recognized, signs of acute external entanglement, bulging or reddened eyes, recently ingested gastric contents, pulmonary changes, and decompression-associated gas bubbles have been identified in the condition of peracute underwater entrapment (PUE) syndrome in previous studies of marine mammals. We reviewed the gross necropsy and histopathology reports of 36 cetaceans and pinnipeds including 20 directly observed bycaught and 16 live stranded animals that were euthanized between 2005 and 2011 for lesions consistent with PUE. We identified 5 criteria which present at significantly higher rates in bycaught marine mammals: external signs of acute entanglement, red or bulging eyes, recently ingested gastric contents, multi-organ congestion, and disseminated gas bubbles detected grossly during the necropsy and histologically. In contrast, froth in the trachea or primary bronchi, and lung changes (i.e. wet, heavy, froth, edema, congestion, and hemorrhage) were poor indicators of PUE. This is the first study that provides insight into the different published parameters for PUE in bycatch. For regions frequently confronted by stranded marine mammals with non-specific lesions, this could potentially aid in the investigation and quantification of marine fisheries interactions.

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