Strong Local Heating Research Articles

Plasmonic inhibition of bacterial adhesion on gold-decorated mesoporous zirconium oxide thin films

Preventing bacterial development on surfaces is essential to avoid problems caused by biofouling. Surfaces decorated with gold nanoparticles have been shown to thermally kill bacteria under high-intensity NIR illumination. In this study, we evaluated the colonization by E. coli of nanostructured surfaces composed of mesoporous zirconia thin films, both with and without gold nanoparticles embedded into the pores. We studied the effect of the nanostructure and of low intensity visible light excitation of the gold nanoparticles on the colonization process. We found that neither the zirconia, nor the presence of pores, or even gold nanoparticles affect bacterial adhesion compared to the bare glass substrate. Therefore, mesoporous zirconia thin films are biologically inert scaffolds that enable the construction of robust surfaces containing functional nanoparticles that can affect bacterial growth. When the gold containing surfaces are irradiated with light, bacterial adhesion shows a remarkable 96 ± 4% reduction. Our studies revealed that these surfaces affect early colonization steps, prior to biofilm formation, preventing bacterial adhesion without affecting its viability. In contrast to related systems where plasmonic excitation induces membrane damage due to strong local heating, the membrane integrity is preserved, showing that these surfaces have a different working principle.

Numerical study on spherical flame propagation in dispersed liquid ammonia droplets

Directly using liquid ammonia in combustion devices can simplify the fuel supply system and reduce equipment costs. However, the detailed ignition and propagation mechanisms of liquid ammonia flames have not been fully understood. This study aims to investigate the ignition and propagation of liquid ammonia flames numerically under various conditions. Spherically expanding liquid ammonia flames are studied using detailed chemistry. The effects of initial temperatures, droplet diameters, equivalence ratios, and heat fraction are investigated. The results indicate that the rapid flash boiling of liquid ammonia droplets leads to a strong local heat loss, hindering the ignition and propagation of the flame. Preheating can significantly increase the reaction rate, which compensates for the heat loss caused by phase change, allowing the flame kernel to ignite and propagate outwards. While droplet-flame interaction is present but not significant due to the rapid evaporation of liquid ammonia. The effect of droplet on the flame surface curvature is only distinguishable at conditions of large diameter. Equivalence ratio and ammonia heat fraction ratio change the amount of liquid ammonia. The more liquid ammonia, the more heat is absorbed by the phase change process, making the flame more difficult to be ignited.

Solar-driven strongly coupled plasmonic Au nanoarrays on mesoporous silica nanodisks enable selective fungal and bacterial inactivation in well water

Well water is an important water source in isolated rural areas but easily suffers from microbial contamination. Herein, we anchored periodic Au nanoarrays on mesoporous silica nanodisks (Au-MSN) to fabricate a solar-driven nano-stove for well water disinfection. The solar/Au-MSN process completely inactivated 3.98, 6.55, 7.11 log10 cfu/mL, and 3.37 log10 pfu/mL of Aspergillus niger spores, Escherichia coli, chlorine-resistant Spingopyxis sp. BM1–1, and bacteriophage MS2 within 5 min, respectively. Moreover, the complete inactivation of various microorganisms (even at a viable but nonculturable state) was achieved in the flow-through reactor under natural solar light in real well water matrixes. Thorough characterizations and theoretical simulations verified that the densely anchoring strategy of Au-MSN's nanoarray worked on broadband absorption via the photon confinement effect, and trace amounts of Au can induce strong electromagnetic fields and collective localized heating. The resulting surge of 1O2 and heat synergically destroyed membranes, dysfunction cellular self-defense and metabolic system, induced intracellular oxidative stress, and ultimately inactivated microorganisms. Additionally, the 1O2-dominated oxidation and cell adhesion facilitated the selective disinfection in real well water matrixes. This study provides a cost-effective and practical solution for efficient well water disinfection, which assists isolated rural areas in getting safe drinking water.

Dust dynamics in current sheets within protoplanetary disks

Context.Chondrules originate from the reprocessing of dust grains. They are key building blocks of telluric planets, yet their formation, which must happen in strongly localized regions of high temperature, remains poorly understood.Aims.We examine the dust spatial distribution near regions of strong local heating produced by current sheets, as a step toward exploring a potential path for chondrule formation. We further aim to investigate current sheet formation under various conditions in protoplanetary disks in the presence of ambipolar diffusion and Ohmic resistivity and the effect of current sheet morphology on dust dynamics in their vicinity.Methods.We used the RAMSES code including modules for nonideal magnetohydrodynamics and the solution of the dynamics of multiple sizes of dust grains to compute unstratified shearing box simulations of current sheet formation. Through seven models, we investigated the effect of the ambipolar diffusion and Ohmic resistivity strength, the initial density, and magnetic field, as well as the resolution and box size.Results.We find that current sheets form in all our models, with typical widths of 10−3–10−2AU, and that strong dust fraction variations occur for millimeter-sized grains. These variations are typically of an order of magnitude and up to two orders of magnitude for the most favorable cases. We also show that the box size and resolution has a strong impact on the current sheet distribution and intensity.Conclusions.The formation of current sheets that can intensely heat their surroundings near strong dynamical dust fraction variations could have important implications for chondrule formation, as it appears likely to happen in regions with a large dust fraction.

Short-term damage and its mechanism of a CaF2 window for a DUV lithography machine

The CaF2 window is the laser exit of the DUV lithography machine as well as its sealing component. Bearing the irradiation, high pressure, and discharging pollutants, the window is easy to damage and directly deteriorate the performance and reliability of the laser. In this paper, considering the effects of the above factors, two typical short-term damages to the CaF2 window - high energy induced damage and pollutant-induced damage are studied quantitatively. Using an experimental design, theoretical calculation, characterization analysis, and numerical simulation, we found that the damage induced by high-energy irradiation is dominated by defect propagation at the initial stage. At the later stage, it is dominated by heat and thermal stress with thermal melting and evenly distributed microcracks of 1∼10 µm in size. Low-energy irradiation only causes expansion and deformation of the window, but the highly absorbent electrode discharging particles with a diameter of 0.1∼1 µm strongly absorb the laser. Strong local heat is caused during the melting and gasification of the particles, which easily leads to ablation and cracks. The damaged area is proportional to the particle size, and the damaged rate is proportional to the average power density at a high repetition frequency. High energy density and the defects with high absorptivity, the electrode discharging particles, and the heat accumulation effect, are the main factors for the two short-term damage, respectively.

Improving the Performance of Direct Solar Collectors and Stills by Controlling the Morphology and Size of Plasmonic Core–Shell Nanoheaters

Plasmonic nanofluids, based on metal nanoparticles (NPs), has received tremendous attention for its potential to increase the efficiency of solar energy harvesting and harnessing systems. The ability to manage their optical absorption by tuning localized surface plasmon (LSP) bands is the reason why metal NPs are considered excellent nanoheaters with unique thermo-optic properties. In this work, we demostrate the influence of the tuning of plasmonic nanofluid absorption bands in different spectral regions, by modifying the morphology and size of the core–shell NPs, on the efficiency of plasmonic nanoheaters to heat fluids and generate steam. Five plasmonic nanofluids containing spherical Au@SiO2, rodlike Au@SiO2, with three different aspect ratios, and spherical SiO2@Au nanoshells were fabricated and characterized to study the local heating induced by plasmon-enhanced light absorption. Gains of up to 28.3 times in the nanofluid temperature increase in direct absorption solar collectors (DASCs) and 7.5 times in the amount of steam generated in the solar ethanol distillation were measured from control over LSP resonances of spherical and rodlike core–shell NPs. Energy distribution analysis shows that plasmonic nanofluids present an efficient energy transfer management, dedicating ∼72% of the absorbed energy to heating liquids at low levels of solar irradiance. However, at high solar irradiances, the good spectral matching between the plasmonic nanofluid LSP bands and the solar irradiance spectrum promotes strong local heating around the core–shell NPs, allowing local temperatures above the boiling point to be reached. Under these conditions, plasmonic nanofluids spend a small amount of energy to heat liquids and they transfer ∼83% of the absorbed energy to generate steam. Thus, a 7.7-fold increase in solar ethanol vaporization rate was achieved. The experimental results, understood from the optical properties of core–shell plasmonic NPs by using the Maxwell–Garnett theoretical model, corroborate the importance of fabricating nanoheaters with projected geometries to maximize the efficiency of solar collectors and stills.

Effect of an internal thermal-conductive cylinder on the conjugate conduction-convection in an enclosure

We numerically studied the conjugate conduction-convection in an enclosure with a circular cylinder placed at the center. The enclosure is differentially heated on its lateral sidewalls but keeps adiabatic for the top and bottom sidewalls. The internal cylinder is assumed thermally conductive which is determined by the ratio of thermal conductivity coefficient between solid and fluid medium. The influence of the cylinder is conducted through two mechanisms: the conduction in the cylinder which alters the temperature distribution in the enclosure and thus the buoyancy acting on the fluid, and the confinement on the fluid circulation especially in the region close to the walls of the enclosure. We aim to explore the effects of cylinder diameter and thermal conductivity ratio on the conjugate conduction-convection under two Rayleigh numbers, i.e., Ra = 104 and 106, to consider both weak convection and convection dominant conditions. The effects of the two parameters are analyzed by the thermal and flow distributions, wall heat transfer and the flow behaviors around the cylinder. Numerical results reveal smooth circulation of fluid within the enclosure at Ra = 104 without the formation of local vortices. Since convection is relatively weak at this Rayleigh number, the thermal and flow distributions are roughly skew-symmetric about the center of the geometry, and the variation of thermal characteristics with the cylinder diameter and thermal conductivity ratio is significant for the top-left and bottom-right regions of the enclosure because of strong local heat transfer. However, two local circulating vortices are generated beside the cylinder and move upward with increasing thermal conductivity ratio and are deformed at Ra = 106. The spatial variations of temperature and Nusselt number on the solid walls are relatively small in magnitude compared with the Ra = 104 case, while the variation tendency with respect to the two governing parameters is generally monotonic.

Experimental and numerical analysis of the energy performance of building windows with solar NIR-driven plasmonic photothermal effects

Thin films made of metallic nanoparticles can exhibit strong photothermal effects (PPE) on near-infrared light irradiation, paving a way for new designs of spectrally selective building windows for solar infrared modulation that operates without the need to compensate for visible transmittance. More importantly, the surface plasmon-induced light-to-heat conversion creates strong localized heating effects with a much smaller fraction resulting in the heating of the substrate. Incorporating such nanoscale PPE into the design of complex building fenestrations, this research conducted a comprehensive analysis to better understand the PPE-induced heating effect and conductive, convective, and radiative heat exchanges between windowpane surfaces and the surrounding indoor and outdoor environments. The authors first developed and then validated a numerical analysis method to incorporate spectral features, solar spectral irradiance, and nanoscale PPE. Subsequently, using the established numerical method, two-dimensional windowpane temperature profiles and solar heat gains were yielded under different boundary conditions. To understand the energy performance of windows with solar near-infrared-dependent PPE, a series of parametric energy simulations was employed. The results show the photothermal coating can be used as a new energy-efficient retrofit technology for single-pane windows, with heating energy saving 16.2–20.8%, which performs similar to the double pane windows. Notably, these energy savings were not achieved by increasing the thermal insulation via additional layers or insulating materials, but rather by the spectrally selective design of glazing materials and utilization of solar near-infrared energy. This work presents the energy saving mechanism on an architectural scale due to the nanoscale surface plasmon-induced photothermal effect and associated heat gain coefficient enhancement. It also poses a fundamental reference for the future integration of this novel nanoscale phenomenon into the building envelope systems.

Manipulating the Dynamics of Dark Excited States in Organic Materials for Phototheranostics.

Manipulating the dynamics of dark excited states (DESs), such as higher excited singlet or excited triplet states with no or small radiative decay, are of both fundamental and practical interests, an important application being photoactivated diagnosis and therapy (phototheranostics), which include photoacoustic (PA) imaging, photodynamic therapy (PDT), and photothermal therapy (PTT). However, the current understanding of DESs in organic structures is rather limited, thus making any rational manipulation of DES in organic materials very challenging.A DES decays primarily by radiationless transition through two pathways: (i) singlet-to-triplet intersystem crossing (ISC) and (ii) internal conversion (IC) relaxation. The deactivation of a DES via ISC can generate cytotoxic reactive oxygen species (ROS) for PDT, while IC could convert photons into heat for PA imaging and PTT. In this Account, we highlight our research on developing a fundamental understanding of structure-property relationships for manipulation of DESs in organic materials in relation to phototheranostic applications. We describe the application of femtosecond transient absorption (fs-TA) spectroscopy for obtaining valuable insights into the DES dynamics. Afterward, we present our work on DESs in nonrigid molecules that revealed greatly enhanced ISC through geometry twisting, which leads to an innovative pathway to develop organic materials exhibiting external stimuli-responsive reversible switching of ISC. We introduce the concept of smart PDT where highly efficient ISC imparted by geometry twisting in the acidic environment specific to tumors leads to very efficient and highly localized PDT, thus leaving surrounding healthy tissues at a different pH unaffected. This insightful understanding of ISC can lead to the development of more advanced photosensitizers for PDT. Two other emergent concepts from our work presented here are (1) significantly enhanced IC producing strong local heating by combining two-photon absorption with excited state absorption for cumulative multiphoton absorption, thus greatly increasing the strength of the PA signal for nonlinear PA imaging, and (2) shown by an example of an organic molecule, BODIPY, nanoscale charge-transfer state mediated strong IC in aggregate nanoparticles resulting in exceptionally high photothermal conversion efficiency of 61% for both PA and PTT. Some in vivo results of the phototheranostic studies using BODIPY are presented, providing an elegant example of nanoscale manipulation of the excited state dynamics.This Account concludes with a summary and discussion of future perspectives. We hope this Account will deepen the understanding of molecular and nanoscale control of excited state dynamics in organic materials, hopefully enticing a broad range of scientists within different disciplinary areas.

An accentuated “hot blob” over Vidarbha, India, during the pre-monsoon season

A “hot blob”, distinct hot region, is identified over Vidarbha in the south-central parts of the Indian subcontinent during the pre-monsoon season from the analysis of gridded surface air maximum temperature data from India Meteorological Department for the period 1951–2019. Spatial distribution and frequencies of temperatures > 40 °C and > 42 °C establish the hot blob over Vidarbha region. A similar analysis of simulated maximum temperatures from the NEX-GDDP substantiates the revelation of the “hot blob” over Vidarbha. Further, analysis of the wind circulation at 850 hPa over South Asia region indicates that the “COL” region between the two seasonal high-pressure systems over the Indian Ocean seas, Bay of Bengal and Arabian Sea promotes accumulation of heat over Vidarbha. Further, horizontal temperature convergence complimented by strong local heating of the black soil aids and abets the sustenance of the “hot blob”. This “hot blob” region is observed to be hotter as well as having higher frequencies of hot days than the north-west desert Rajasthan region and assumes importance as its modulation causes heatwaves over the south-east coastal regions. This study establishes the presence of the hottest region over Vidarbha in south-central parts, paradoxically hotter than the desert north-west region of India.

Importance of Regional‐Scale Auroral Precipitation and Electrical Field Variability to the Storm‐Time Thermospheric Temperature Enhancement and Inversion Layer (TTEIL) in the Antarctic E Region

AbstractA dramatic thermospheric temperature enhancement and inversion layer (TTEIL) was observed by the Fe Boltzmann lidar at McMurdo, Antarctica during a geomagnetic storm (Chu et al. 2011, https://doi.org/10.1029/2011GL050016). The Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) driven by empirical auroral precipitation and background electric fields cannot adequately reproduce the TTEIL. We incorporate the Defense Meteorological Satellite Program (DMSP)/Special Sensor Ultraviolet Spectrographic Imager (SSUSI) auroral precipitation maps, which capture the regional‐scale features into TIEGCM and add subgrid electric field variability in the regions with strong auroral activity. These modifications enable the simulation of neutral temperatures closer to lidar observations and neutral densities closer to GRACE satellite observations (~475 km). The regional scale auroral precipitation and electric field variabilities are both needed to generate strong Joule heating that peaks around 120 km. The resulting temperature increase leads to the change of pressure gradients, thus inducing a horizontal divergence of air flow and large upward winds that increase with altitude. Associated with the upwelling wind is the adiabatic cooling gradually increasing with altitude and peaking at ~200 km. The intense Joule heating around 120 km and strong cooling above result in differential heating that produces a sharp TTEIL. However, vertical heat advection broadens the TTEIL and raises the temperature peak from ~120 to ~150 km, causing simulations deviating from observations. Strong local Joule heating also excites traveling atmospheric disturbances that carry the TTEIL signatures to other regions. Our study suggests the importance of including fine‐structure auroral precipitation and subgrid electric field variability in the modeling of storm‐time ionosphere‐thermosphere responses.

КОНЦЕНТРАЦИЯ ТЕМПЕРАТУРНЫХ НАПРЯЖЕНИЙ В МЕТАЛЛИЧЕСКИХ МАТЕРИАЛАХ И КОНСТРУКЦИЯХ ПРИ ЛОКАЛЬНОМ НАГРЕВЕ

significant thermal stresses arising in thin-walled metal materials and structures loaded with tensile stresses can lead either to their complete destruction or to the appearance of discontinuity zones in them. The equations for calculation of temperature stresses in flat thin-walled structures at their localized thermal heating caused by the action of concentrated energy flows are analyzed. As an example, a thin-walled stretched plate subjected to strong local heating in a circular spot is considered. The developed model takes into account the change of elastic characteristics under strong local heating and the change in the thickness of the material in the heating spot. As an example, the diagram of the distribution of tangential stresses for a stretched plate in the area of a circular heating spot is given. Thus, the results of the study show that there is a rupture and concentration of stresses along the contour of the heating spot from the cold zone.

Stratocumulus in the Cold and Warm Sides of the Spring Kuroshio Sea Surface Temperature Front in the East China Sea

AbstractThe characteristics and formation mechanisms of stratocumulus (Sc) clouds were investigated in this study based on satellite and sounding data from March and April 2007–2010. The effects of the intensity of the Kuroshio sea surface temperature (SST) front on the amount and height of Sc clouds were also assessed by composite analysis. Sc clouds mainly occurred lower than 3 km as single‐layer clouds, and there was a larger amount of clouds in the warm side than in the cold side of the Kuroshio area. This difference occurred because the Kuroshio SST front produced different dynamics and thermal structures in the planetary boundary layer (PBL) of the warm and cold sides. Both the strong local sensible heat flux forced by strong northwesterly winds and the large relative humidity in the PBL favored the formation of Sc clouds in the warm side. In the cold side, both the strong temperature inversion caused by downdrafts and the PBL top height hindered cloud development, similar to the cloud formation conditions in the subtropical oceans near California. Furthermore, the amount and height of clouds were influenced by the Kuroshio SST front intensity. In the warm side, more abundant clouds and a higher cloud height were associated with a strong SST front background than with a weak SST front background.

Microfluidics control the ballistic energy of thermocavitation liquid jets for needle-free injections

Illuminating a water solution with a focused continuous wave laser produces a strong local heating of the liquid that leads to the nucleation of bubbles, also known as thermocavitation. During the growth of the bubble, the surrounding liquid is expelled from the constraining microfluidic channel through a nozzle, creating a jet. The characteristics of the resulting liquid jet were imaged using ultra-fast imaging techniques. Here, we provide a phenomenological description of the jet shapes and velocities and compare them with a boundary integral numerical model. We define the parameter regime, varying jet speed, taper geometry, and liquid volume for optimal printing, injection, and spray applications. These results are important for the design of energy-efficient needle-free jet injectors based on microfluidic thermocavitation.

Experimental study on supersonic plate boundary layer transition under pulsed arc plasma excitation control

Pulsed arc plasma excitation is characterized by strong local heating effect and wide disturbance range, and it has a broad application prospect in supersonic flow control. In this paper, by using electrical parameter measurement system and high speed schlieren technique, we study the electrical and flow field characteristics of pulsed arc plasma excitation under the condition of <i>Ma</i> = 3 incoming flow. The nano-particle planar laser scattering (NPLS) is used to investigate the flow structure of the supersonic flat boundary layer, and the transition characteristics of the boundary layer at different plasma excitation frequencies are studied. The experimental results show that in the flow field with <i>Ma</i> = 3 and the total incoming pressure <i>P</i><sub>0</sub> = 1 atm (1 atm = 1.01 × 10<sup>5</sup> Pa), the peak voltage of the pulsed arc plasma actuator discharge is 6 kV, the peak current is 70 A, the time scale of the discharge is about 300 ns, the single discharge energy is 70 mJ; the pulsed arc discharge will produce the precursor shock wave with higher velocity and the thermal deposition zone with higher temperature, which will exert continuously disturbance on the boundary layer. The pulsed arc plasma excitation with perturbation can promote the transition of supersonic plate boundary layer. Moreover, the high-frequency impact effect of pulsed discharge can promote the transition to occur ahead of time, and the higher the frequency, the better the effect is. As the excitation frequency increases, the transition position of the boundary layer of the supersonic flat plate moves forward, and the length of the transition area of the boundary layer becomes shorter as the excitation frequency increases. When the excitation frequency is 60 kHz, the length of transition zone is 0 and the thickness of turbulent boundary layer is 25 mm. When a high frequency is applied (<i>f</i> = 40, 60 kHz), the transition path of the boundary layer is that the shock wave generated by the plasma excitation triggers the unstable wave, and the development of unstable waves directly skips the linear growth stage, passes through the bypass and transitions into turbulent flow. The pulsed arc plasma excitation can be used to promote supersonic boundary layer transition.

Magnetic Photoluminescent Nanoplatform Built from Large-Pore Mesoporous Silica

Integrating multiple components to realize cancer diagnosis and therapy in a single theranostic nanoplatform has drawn considerable attention. Herein, a multifunctional theranostic nanoplatform (mSiO2@PbS/CdS-Fe3O4) was successfully fabricated by carefully designing thiol-modified large-pore mesoporous silica nanospheres (mSiO2), followed by coordination-driven embedding of Fe3O4 nanoparticles (NPs) and PbS/CdS quantum dots (QDs) inside. The excellent feature of near-infrared (NIR) excitation and NIR emission of PbS/CdS QDs enables deep-tissue photoluminescence imaging, which was demonstrated ex vivo with tissue as thick as 14 mm. Meanwhile, owing to the presence of superparamagnetic Fe3O4 NPs, mSiO2@PbS/CdS-Fe3O4 can be rapidly confined under an external magnetic field (MF), and exhibit a significantly high T2 relaxivity in T2-weighted magnetic resonance (MR) images in vivo. When mSiO2@PbS/CdS-Fe3O4 was exposed to external physical stimuli of MF and/or NIR laser, they produced strong local heating throug...

The Influence of Superflares of Host Stars on the Dynamics of the Envelopes of Hot Jupiters

Results of a study of the influence of solar-type host stars superflares on the gas dynamics of the extended envelopes of giant exoplanets are presented. During flare events, the radiation intensity of the host star in the extreme ultraviolet and soft X-ray can increase by several orders of magnitude for a short time, leading to strong local heating of the exoplanet atmosphere on the side facing the star, with the formation of shocks in the atmosphere. Computations of the gas-dynamical response of the atmosphere of the hot Jupiter HD 209458b to characteristic superflares of solar-like stars were carried out earlier in [1] using a one-dimensional aeronomical model correctly taking into account heating and chemical processes in the atmosphere. To investigate the outflow of atmospheric gas, the results obtained with this onedimensional model were used as simple boundary conditions for computations of the three-dimensional flow structure after a flare. The results of these three-dimensional gas-dynamical computations show that the mass ejection of the flare increases the size of the envelope over several hours, which could be detected with existing observing facilities. It is shown that the mass-loss rates for the most powerful superflare considered could be enhanced by an order of magnitude over several tens of hours after the flare.

Enhanced Photothermal Effect in Ultralow-Density Carbon Aerogels with Microporous Structures for Facile Optical Ignition Applications.

The exact mechanism responsible for the phenomenon known as photoignition with an enhanced photothermal effect in high-surface-area carbon with the addition of a metal catalyst is an open issue. Here, we report the first successful flash ignition of a pure carbon material in ambient air microporous carbon aerogels (CAs) with ultralow density and high surface area. Under flash exposure, the CAs show a strong local heat confinement effect near microporous structures (0.6-2 nm), and the graphite crystallite structures existing in single carbon nanoparticles (∼15 nm) are damaged. The local heat confinement effects are mainly derived from the low gaseous thermal conductivity in micropores and low solid thermal conductivity in low-density CAs. In addition, the limiting effects of the microporous structure on the vibration amplitude of free-state electrons in low-density CAs result in a dramatic increase in optical absorption. Numerical simulations of unsteady temperature fields of CAs with different densities and thicknesses are also performed, and the calculated maximum temperature of a 17 μm-thick 20 mg/cm3 CA bed is 1782 °C. CAs with higher density can also give rise to enhanced photothermal response and ignition with the addition of metal Fe nanoparticles. The metal catalyst increases both the light absorption capacity in the visible-light range and the heat accumulation capacity. These results are important for understanding the mechanism of flash ignition, especially the local high temperature and effects of metal catalyst in carbon materials during the photothermal process.

Single Ag atom engineered 3D-MnO2 porous hollow microspheres for rapid photothermocatalytic inactivation of E. coli under solar light

Atomic level Ag loaded MnO2 porous hollow microspheres (Ag/MnO2 PHMs) were prepared by redox precipitation method, and utilized for E. coli inactivation under solar light irradiation. Ag nanoparticles (NPs) can be downsized into single atoms, thereby realizing highly utilization of Ag element as well as achieving superior photothermocatalytic E. coli inactivation for Ag/MnO2 than MnO2 PHMs. Under attack by the optimal 0.3%Ag/MnO2 PHMs with atomic Ag, 7.11 log10 cfu/mL cells can be completely inactivated within 10 min, much faster than the 0.3%Ag/MnO2 PHMs with Ag cluster (3.3 log10 cfu/mL) prepared by photodeposition method, demonstrating the feasibility of redox precipitation to prepare efficient catalyst for water disinfection. Three effects are believed to contribute to this bacterial inactivation enhancement: (1) atomic Ag with high conductivity induces more formation of Mn3+ and oxygen vacancies in MnO2, which can efficiently accelerate the separation of hot electrons and holes generated by MnO2, collectively work with itself generated hot electrons to form into reactive species for photocatalysis; (2) atomic Ag exhibits strong local heating effect and induces higher reducibility for MnO2, considerably enhances the photothermal conversion and lattice oxygen activity of MnO2, thus promoting the thermocatalysis; and (3) the synergism of solar light driven photocatalysis and thermocatalysis through the activated OL. The highly efficient photothermocatalysis make the designed 3D atomic Ag/MnO2 PHMs have a promising antibacterial ability for cleaning the microbial contaminated water environment.

Light absorption by marine cyanobacteria affects tropical climate mean state and variability

Abstract. Observations indicate that positively buoyant marine cyanobacteria, which are abundant throughout the tropical and subtropical ocean, have a strong local heating effect due to light absorption at the ocean surface. How these local changes in radiative heating affect the climate system on the large scale is unclear. We use the Max Planck Institute Earth System Model (MPI-ESM), include light absorption by cyanobacteria, and find a considerable cooling effect on tropical sea surface temperature (SST) in the order of 0.5 K on a climatological timescale. This cooling is caused by local shading of subtropical subsurface water by cyanobacteria that is upwelled at the Equator and in eastern boundary upwelling systems. Implications for the climate system include a westward shift of the Walker circulation and a weakening of the Hadley circulation. The amplitude of the seasonal cycle of SST is increased in large parts of the tropical ocean by up to 25 %, and the tropical Pacific interannual variability is enhanced by approx. 20 %. This study emphasizes the sensitivity of the tropical climate system to light absorption by cyanobacteria due to its regulative effect on tropical SST. Generally, including phytoplankton-dependent light attenuation instead of a globally uniform attenuation depth improves some of the major model temperature biases, indicating the relevance of taking this biophysical feedback into account in climate models.