Maintenance-free antifouling polymeric membrane potentiometric sensors based on self-polishing coatings.

Polymeric membrane ion-selective electrodes (ISEs) have been widely used in environmental monitoring. However, in complicated marine environments, marine biofouling usually becomes a sticky problem for these electrodes. Herein, for the first time, a novel maintenance-free antifouling potentiometric marine sensor based on a self-polishing coating (SPC) is proposed. The SPC is synthesized by using the seeded emulsion polymerization method based on the triisopropylsilyl methacrylate monomer as the regulator of the self-renewal rate. This coating can be simply modified onto the electrode surface by drop-casting. The silyl acrylate side groups of the obtained SPC on the sensor surface can be hydrolyzed in the marine alkaline medium. The shear movement of seawater driven by sea waves, wind, gravity, or vibration removes the leftover (fouled) brittle polymer backbone and thus the fouling marine microorganisms. As a proof-of-concept experiment, a polymeric membrane Ca2+-ISE is chosen as a model. Compared to the unmodified electrode, the SPC-coated Ca2+-ISE exhibits remarkable improved antifouling properties in terms of superior anti-adhesive abilities towards marine microorganisms, such as bacterial cells and algae and excellent long-term stability even in the presence of high levels of marine microorganisms. Since no additional manual maintenance is required for maintaining the antifouling abilities of the sensor, the proposed self-polishing sensor may lay an important foundation for construction of unattended long-term potentiometric monitoring systems in real marine environments.

Achieving health-oriented air pollution control requires integrating unequal toxicities of industrial particles.

Protecting human health from fine particulate matter (PM) pollution is the ambitious goal of clean air actions, but current control strategies  largely ignore the role of source-specific PM toxicity. Here, we proposed health-oriented control strategies by integrating the unequal toxic potencies of the most polluting industrial PMs. Iron and steel industry (ISI)-emitted PM2.5 exhibit about one order of magnitude higher toxic potency than those of cement and power industries. Compared with the current mass-based control strategy (prioritizing implementation of ultralow emission standards in the power sector), the proposed health-oriented control strategy (priority control of the ISI sector) could generate 5.4 times higher reduction in population-weighted toxic potency-adjusted PM2.5 exposure among polluting industries in China. Furthermore, the marginal abatement cost per unit of toxic potency-adjusted mass of ISI-emitted PM2.5 is only a quarter of that of the other two sectors under ultralow emission scenarios. We highlight that a health-oriented air pollution control strategy is urgently required to achieve cost-effective reductions in particulate exposure risks.

Dual-Channel Surface Waves Directional Radiation with Customizable Intensity and Switchable Pattern.

Achieving the conversion from surface waves (SWs) to propagating waves has captivated long-standing interest, and various ingenious metasurfaces benefiting from the powerful control capability for electromagnetic waves are able to realize efficient SWs directional radiation. Nevertheless, most existing schemes still suffer from the bottlenecks of single radiation channel, uncontrollable radiation intensity, and immutable radiation pattern, which immensely hinder their practical application in high-integration intelligent devices. Herein, a series of appealing strategies are proposed to achieve the dual-channel SWs directional radiation with customizable radiation intensity and switchable radiation pattern. The dual-channel SWs radiation metadevice based on the phase modulation metasurface is designed to directionally radiate SWs in left-handed circular polarized channel and right-handed circular polarized channel and possesses the broadband frequency scanning characteristic. More strikingly, the intensity-customizable dual-channel SWs radiation metadevice loaded with lumped resistors can control the realized gain of two circular polarized radiation beams, and the pattern-switchable dual-channel SWs radiation metadevice loaded with PIN diodes can dynamically adjust the radiation direction of the radiation beams. Numerous simulations and experiments of the proof-of-concept prototypes with modular design corroborate the theoretical predictions. Our methodology shows unprecedented flexibility in regulating SWs directional radiation and has enormous potential in engineering applications.

Anti-fouling TiO2-Coated Polymeric Membrane Ion-Selective Electrodes with Photocatalytic Self-Cleaning Properties.

Nowadays, using a polymeric membrane ion-selective electrode (ISE) to achieve reliable ion sensing in complex samples remains challenging because of electrode fouling. To address this challenge, we describe a polymeric membrane ISE with excellent anti-fouling and self-cleaning properties based on surface covalent modification of an anatase TiO2 coating. Under ultraviolet illumination, the reactive oxygen species produced by photocatalytic TiO2 can not only kill microorganisms but also degrade organic foulants into carbon dioxide and water, and a formed superhydrophilic film can effectively prevent the adsorption of foulants, thus inhibiting the occurrence of biofouling and organic fouling of the sensors. More importantly, residual foulants could be fully self-cleaned through the flow of water droplets. By using Ca2+-ISE as a model, an anti-fouling polymeric membrane potentiometric sensor has been developed. Compared to the unmodified electrode, the TiO2-coated Ca2+-ISE exhibits remarkably improved anti-biofouling properties with a low bacterial adhesion rate of 4.74% and a high inhibition rate of 96.62%. In addition, the proposed electrode displays unique properties of anti-organic dye fouling and a superior self-cleaning ability even after soaking in a concentrated bacterial suspension of 109 CFU mL-1 for 60 days. The present approach can be extended to improve the fouling resistance of other electrochemical or optical membrane sensors and is promising for the construction of contamination-free sensors.

Intelligent metasurface system for automatic tracking of moving targets and wireless communications based on computer vision.

The fifth-generation (5G) wireless communication has an urgent need for target tracking. Digital programmable metasurface (DPM) may offer an intelligent and efficient solution owing to its powerful and flexible controls of electromagnetic waves and advantages of lower cost, less complexity and smaller size than the traditional antenna array. Here, we report an intelligent metasurface system to perform target tracking and wireless communications, in which computer vision integrated with a convolutional neural network (CNN) is used to automatically detect the locations of moving targets, and the dual-polarized DPM integrated with a pre-trained artificial neural network (ANN) serves to realize the smart beam tracking and wireless communications. Three groups of experiments are conducted for demonstrating the intelligent system: detection and identification of moving targets, detection of radio-frequency signals, and real-time wireless communications. The proposed method sets the stage for an integrated implementation of target identification, radio environment tracking, and wireless communications. This strategy opens up an avenue for intelligent wireless networks and self-adaptive systems.

Deep-Learning-Empowered Holographic Metasurface with Simultaneously Customized Phase and Amplitude.

Metasurfaces with simultaneously and independently controllable amplitude and phase have provided a higher degree of freedom in manipulating electromagnetic (EM) waves. Compared with phase- or amplitude-only modulation, the capability of simultaneously controlling the phase and amplitude of EM waves can enable holography with a higher resolution. However, this drastically increases the design complexity of holographic metasurfaces, and the design process is usually quite time-consuming. In this paper, we propose an inverse design of meta-atoms that can simultaneously and independently tailor the phase and amplitude of transmitted waves using customized deep ResNet while eliminating the coupling of parameters. To demonstrate the design method, two holographic metasurfaces were designed using the trained network without the need for parameter sweeping, which will significantly enhance design efficiency. Prototypes were fabricated and measured. Both the simulated and measured results show that high-resolution holography is obtained, which sufficiently verifies the reliability of the design method. Our work paves the way for the intelligent design of metasurfaces and can also be applied to the design of other artificial materials or surfaces.

Improved atmospheric mercury simulation using updated gas-particle partition and organic aerosol concentrations.

The gaseous or particulate forms of divalent mercury (HgII) significantly impact the spatial distribution of atmospheric mercury concentration and deposition flux (FLX). In the new nested-grid GEOS-Chem model, we try to modify the HgII gas-particle partitioning relationship with synchronous and hourly observations at four sites in China. Observations of gaseous oxidized Hg (GOM), particulate-bound Hg (PBM), and PM2.5 were used to derive an empirical gas-particle partitioning coefficient as a function of temperature (T) and organic aerosol (OA) concentrations under different relative humidity (RH). Results showed that with increasing RH, the dominant process of HgII gas-particle partitioning changed from physical adsorption to chemical desorption. And the dominant factor of HgII gas-particle partitioning changed from T to OA concentrations. We thus improved the simulated OA concentration field by introducing intermediate-volatility and semi-volatile organic compounds (I/SVOCs) emission inventory into the model framework and refining the volatile distributions of I/SVOCs according to new filed tests in the recent literatures. Finally, normalized mean biases (NMBs) of monthly gaseous element mercury (GEM), GOM, PBM, WFLX were reduced from -33%-29%, 95%-300%, 64%-261%, 117%-122% to -13%-0%, -20%-80%, -31%-50%, -17%-23%. The improved model explains 69%-98% of the observed atmospheric Hg decrease during 2013-2020 and can serve as a useful tool to evaluate the effectiveness of the Minamata Convention on Mercury.

Single-Layer Achiral Metasurface with Independent Amplitude-Phase Control for Both Left-Handed and Right-Handed Circular Polarizations.

Amplitude-phase control for circular polarized (CP) waves is experiencing a research upsurge in electromagnetics owing to the kaleidoscopic electromagnetic responses and promising application prospects of circular polarizations, and chiral metasurfaces are more facile to achieve a series of intriguing chiral phenomena than natural materials. However, it is difficult for most existing chiral metasurfaces to independently tailor the amplitude and phase of left-handed circular polarized and right-handed circular polarized waves at the same frequency as they suffer the drawbacks of large thickness, multiple layers, and complex structure. Herein, an innovative strategy of single-layer achiral metasurfaces of thickness 0.13λ0 is proposed to independently and simultaneously manipulate the amplitude and phase of orthogonal CP waves. As a proof of concept, an amplitude and phase controlled dual-channel meta-hologram is designed to reconstruct diverse images with high fidelity under orthogonal CP illumination, and the simulated and experimental results collectively validate the availability of our methodology. Significantly, the meta-hologram is also applicable to full polarization states according to the decomposition of electromagnetic waves. The inspiring design of single-layer achiral metasurfaces provides a simple and effective approach to explore chiral effects, and they possess enormous application potential in multitudinous microwave devices.

Generating diverse functionalities simultaneously and independently for arbitrary linear polarized illumination enabled by a chiral transmission-reflection-selective bifunctional metasurface.

A multifunctional metasurface is capable of manipulating electromagnetic waves and achieving kaleidoscopic functions flexibly, which significantly improves the integration and utilization of a single metasurface and has become one of the hotspots in electromagnetics. However, the majority of designs to date can only operate for limited polarization states in half-space and are difficult to show diverse functions at the same time, which restrict the widespread applications of multifunctional metadevices. Herein, an inspiring strategy of a chiral transmission-reflection-selective bifunctional metasurface is proposed to generate two independent functions in co-polarized reflection channel for left-handed circular polarized (LCP) incidence utilizing rotation-induced geometric phase modulation and in co-polarized transmission channel for right-handed circular polarized (RCP) incidence utilizing scaling-induced propagation phase modulation, and both functions appear concurrently under arbitrary linear polarized (LP) incident waves. To verify the feasibility of this methodology, three proof-of-concept metadevices composed of a dual-mode orbital angular momentum (OAM) generator, a bifocal metalens and an integrated metadevice of OAM generator and metalens are constructed and their performances in simulations and experiments are in good accordance with the theoretical ones. This exotic design of bifunctional metasurface will open up a promising way for multifunctional metadevices in engineering applications.

Broadband surface wave coupler with low infrared emission and microwave reflection.

Metasurfaces possess excellent capabilities to flexibly manipulate electromagnetic waves in multiple frequency domains, which show great potential application in multispectral stealth. Herein, a broadband surface waves coupler based on the design of thin Pancharatnam-Berry (PB) phase gradient metasurfaces (PGMs) of thickness 0.12λ0 is proposed to reduce infrared emission and microwave reflection simultaneously. Low infrared emission results from the high filling ratio of the indium-tin-oxide (ITO) on the surface, and low microwave reflection results from the conversion from propagating waves to surface waves. Intriguingly, this design is also capable of acting as a simple circular polarized (CP) discriminator because orthogonal CP waves are coupled into surface waves propagating along opposite directions. A proof-of-concept prototype is simulated and measured to validate the effectiveness of our methodology. The results indicate that the broadband surface waves coupler shows low infrared emissivity less than 0.28 from 3 to 14 µm and has microwave reflection reduction larger than 10 dB in 7.3-9.5 GHz. The exceptional performances of the proposed broadband surface waves coupler make us believe that our design offers an alternative strategy for multispectral stealth and multifunctional application.

Simultaneous reduction of microwave reflection and infrared emission enabled by a phase gradient metasurface.

Metasurfaces have shown promising applications in radar-infrared compatible stealth because of its superior electromagnetic wave control capabilities, but, to date, the majority of designs still suffer from the defects of large thickness, limited working bandwidth, relatively high infrared emissivity and so on. Here, an exotic phase gradient metasurface (PGM) is proposed to achieve low microwave reflection and low infrared emission concurrently, which has a small thickness of about 0.10λ0. The microwave reflection reduction larger than 10 dB in 14-20 GHz is attributed to the anomalous reflection for arbitrary LP incident waves, and the infrared emissivity less than 0.28 from 3 to 14 µm is due to the indium-tin-oxide (ITO) with low infrared emissivity and high filling ratio. Also, the designed PGM can also realize beam deflection for orthogonal CP waves because of the meta-atoms' isotropic characteristics. Our methodology is fully verified by numerous simulations and experiments and may open a new avenue for radar-infrared compatible stealth research.

Effect of the Coal Preparation Process on Mercury Flows and Emissions in Coal Combustion Systems.

Coal preparation is effective in controlling primary mercury emissions in coal combustion systems; however, the combustion of coal preparation byproducts may cause secondary emissions. The inconsistent coal preparation statistics, unclear mercury distribution characteristics during coal preparation, and limited information regarding the byproduct utilization pathways lead to great uncertainty in the evaluation of the effect of coal preparation in China. This study elucidated the mercury distribution in coal preparation based on the activity levels of 2886 coal preparation plants, coal mercury content database, tested mercury distribution factors of typical plants, and then traced the mercury flows and emissions in the downstream sectors using a cross-industry mercury flow model. We found that coal preparation altered the mercury flows by reducing 68 tonnes of mercury to sectors such as coking and increasing the flows to byproduct utilization sectors. Combusting cleaned coal rather than raw coal reduced the mercury emissions by 47 tonnes; however, this was offset by secondary mercury emissions. Coal gangue spontaneous combustion and the cement kiln coprocessing process were dominant secondary emitters. Our results highlight the necessity of whole-process emission control of atmospheric mercury based on flow maps. Future comprehensive utilization of wastes in China should fully evaluate the potential secondary mercury emissions.

Highly Resolved Inventory of Mercury Release to Water from Anthropogenic Sources in China.

This study developed an up-to-date and point-source-based inventory of mercury (Hg) releases to water in China by applying probabilistic release factors that combined industry removal efficiencies, reuse of reclaimed water, and receiving water types. In 2017, the national mercury release to water was estimated to be 50 (35-66) tons, in which 47%, 8%, 7%, and 25% were from nonferrous metal smelting, vinyl chloride monomer (VCM) production, coal-fired boilers, and domestic sewage, respectively. Approximately 95% of mercury was released to inland rivers, and the rest was discharged to lakes or coastal water. The significant sources were identified based on their mercury releases to water. The control of mercury release to water in China shall focus on zinc smelting plants, municipal sewage treatment plants, and the VCM production process. For zinc smelting plants, China can tighten the limit of mercury concentration in discharged wastewater and combine Hg-catcher device in traditional integrated treatment. For municipal sewage treatment plants and the VCM production process, promoting processes of Hg-free production can reduce mercury inputs at the source. Our study provides insights for other parties to identify the relevant sources of mercury release to water and to conduct control measures, so as to promote the global convention implementation.

Genetic-algorithm-empowered metasurface design: simultaneous realization of high microwave frequency-selection and low infrared surface-emissivity.

With the improvement of equipment integration, it is difficult to meet the increasing functional requirements with the function of a single spectrum. In this work, a multispectral functional metasurface (MFM) is designed to achieve multispectral compatibility between microwave and infrared using multi-optimization. For microwaves, a frequency selective surface (FSS) is designed to achieve frequency selectivity. And for infrared, a twice genetic algorithm (GA) is employed to further increase the metallic filling ratio, thus reducing the infrared emissivity while maintaining the performance of microwave FSS. In order to verify our design and method, the MFM is fabricated and measured, and all the results are consistent with the theoretical design. The performance of FSS can achieve 3dB bandwidth in 7.2-11.2GHz with low insertion losses and stability, and meanwhile the mean infrared emissivity has been reduced to 0.24 in 3-14µm. In summary, the designed multispectral compatible metasurface has wide application value in radome. What's more, the multi-optimization method for designing the multispectral metasurface can also be extended to other fields.

Phase-to-pattern inverse design paradigm for fast realization of functional metasurfaces via transfer learning.

Metasurfaces have provided unprecedented freedom for manipulating electromagnetic waves. In metasurface design, massive meta-atoms have to be optimized to produce the desired phase profiles, which is time-consuming and sometimes prohibitive. In this paper, we propose a fast accurate inverse method of designing functional metasurfaces based on transfer learning, which can generate metasurface patterns monolithically from input phase profiles for specific functions. A transfer learning network based on GoogLeNet-Inception-V3 can predict the phases of 28×8 meta-atoms with an accuracy of around 90%. This method is validated via functional metasurface design using the trained network. Metasurface patterns are generated monolithically for achieving two typical functionals, 2D focusing and abnormal reflection. Both simulation and experiment verify the high design accuracy. This method provides an inverse design paradigm for fast functional metasurface design, and can be readily used to establish a meta-atom library with full phase span.

Quasi-continuous linear phase-gradient metamaterial based on conformal spoof surface plasmon polaritons.

In this work, we propose a method of achieving quasi-continuous linear phase gradient for transmitted waves based on conformal spoof surface plasmon polariton (SSPP). To this end, a SSPP structure with high transmission is firstly designed as the unit cell of the metamaterial. To obtain the phase gradient, SSPP structures are arranged delicately in a way that they are conformal to the brachistochrone curve. In this way, quasi-continuous linear Pancharatnam-Berry (PB) phase profile can be realized strictly along one of the two transverse directions. To verify this idea, a dual-band transmissive metamaterial operating in X and Ku band was designed, fabricated and measured. Due to the phase gradient imparted by the conformal SSPP structures, high-efficiency anomalous refraction can be realized within the two bands. Different from the general PGM, the phase gradient of the conformal SSPP structure allows us to achieve the desired anomalous refraction angle without reconstructing the PB phase. Both the simulation and measurement results are well consistent with theoretical predictions. This work provides another strategy of achieving anomalous refraction and may find applications in beam steering, digital beam forming, etc.

Multifunctional full-space metasurface controlled by frequency, polarization and incidence angle.

Multifunctional metasurfaces have exhibited considerable abilities of manipulating electromagnetic (EM) waves, especially in full-space manipulation. However, most works are implemented with functions controlled by polarization or frequency and seldom involve the incidence angle. Herein, we propose a multifunctional full-space metasurface controlled by frequency, polarization and incidence angle. A meta-atom is firstly designed. When EM waves illumine normally in the C-band, it possesses the characteristic of asymmetric transmission with high-efficient polarization conversion. In the Ku-band, both x- and y-polarized EM waves along both sides will be reflected and achieve broadband and high-efficient cross-polarization conversion. Also, when illumined obliquely, both sides can achieve efficient retroreflection at a certain frequency. As a proof of concept, a metasurface consisting of the above meta-atoms is configured as a dual orbital angular momentum (OAM) vortex beam generator and different beam deflector when illumined normally. Meanwhile, it acts as a multi-channel retroreflector when illumined obliquely. Both the simulated and measured results show excellent performances. Our findings provide a new degree of freedom to design multifunctional metasurfaces that can further promote applications.

Impact of ultra-low emission technology retrofit on the mercury emissions and cross-media transfer in coal-fired power plants.

China has applied the ultra-low emission technology in coal-fired power plants to control traditional air pollutants and to reduce Hg emissions synergically. In this study, we applied field experiment, model calculation, and literature review to evaluate the Hg control effect of ultra-low emission technology and the potential cross-media effect comprehensively. The dominant ultra-low emission technology significantly improves the atmospheric Hg removal efficiency from 75% to 87%. Such improvement mainly comes from the effect of dust removal devices. Based on the calculated distribution characteristic of Hg content of wastes, we find out that the improvement of Hg control effect of air pollution control devices significantly increase the Hg content of fly ash, which rises from 0.16 mg/kg to 0.33 mg/kg. However, the Hg content of gypsum decreases from 0.75 mg/kg to 0.51 mg/kg. Whether or not to carry out ultra-low emission retrofits, Hg contents of wastes from coal-fired power plants are overall lower than the limit of 25 mg/kg which is intended to be set as the limit for Hg-containing wastes. However, the embodied more than two hundreds of tons Hg in these wastes still require policies to guide the disposal of these wastes.

Transition in source contributions of PM2.5 exposure and associated premature mortality in China during 2005-2015.

The serious fine particle (PM2.5) pollution in China causes millions of premature deaths. Driven by swift economic growth and stringent control policies, air pollutant emissions in China have changed significantly in the last decade, but the change in the source contribution of PM2.5-related health impacts remains unclear. In this study, we develop a multi-pollutant emission inventory in China for 2005-2015, and combine chemical transport modeling, ambient/household exposure evaluation and health impact assessment to quantify the contribution of eight emission sectors to PM2.5 exposure and associated health risk. From 2005 to 2015, the mortality due to PM2.5 from ambient air pollution (AAP) decreases from 1.04 (95% confidence interval, 0.84-1.25) million to 0.87 (0.70-1.04) million. The agricultural sector contributes 25% and 32% to ambient PM2.5-attributed mortality in 2005 and 2015, respectively, representing the largest contributor during this period. The contribution of power plants drops monotonously from 13% to 6%. The percentage contribution of industrial process drops significantly while the contribution of industrial combustion stays the same level. The overall contribution of industry is still as large as 26% in 2015 in spite of strict control measures. For transportation, despite strict emission standards, its contribution increases remarkably due to the rapid growth of vehicle population. When both ambient and household PM2.5 exposures are taken into account, the mortality due to integrated population-weighted exposure to PM2.5 (IPWE) drops from 1.78 (1.46-2.09) million in 2005 to 1.28 (1.05-1.52) million in 2015. Most of the IPWE reduction comes from domestic combustion as a result of urbanization and improved income, whereas this sector remains the largest contributor (58%) to IPWE-related health risk in 2015. Our results suggest that the government should dynamically adjust the air pollution control strategy according to the change in source contributions. Domestic combustion and agriculture should be prioritized considering their predominant contributions to mortality and the lack of effective control policies. More stringent control measures for industry and transportation are necessary since the existing policies have not adequately reduced their health impacts. Electricity production is no longer the top priority of air pollution control policies given its lower health impact compared with that of other sources.

Measure-Specific Effectiveness of Air Pollution Control on China's Atmospheric Mercury Concentration and Deposition during 2013-2017.

China took aggressive air pollution control measures from 2013 to 2017, leading to the mitigation of atmospheric mercury pollution as a cobenefit. This study is the first to systematically evaluate the effect of five major air pollution control measures in reducing mercury emissions, the total gaseous mercury (TGM) concentration and mercury deposition flux (FLX) for unit emissions reduction. From 2013 to 2017, China's mercury emissions decreased from 571 to 444 tons, resulting in a 0.29 ng m-3 decrease in the TGM concentration, on average, and in a 17 µg m-2 yr-1 decrease in FLX. Ultralow emission renovations of coal-fired power plants are identified as the most effective emission abatement measure. As a result of this successful measure, coal-fired power plants are no longer the main mercury emitters. In 2017, the cement clinker sector became the largest emitter due to the use of less effective mercury removal measures. However, in terms of the mitigated TGM concentration and FLX levels per unit emission abatement, newly built wet flue gas desulfurization (WFGD) systems in coal-fired industrial boilers have become particularly effective in decreasing FLX levels. Therefore, to effectively reduce atmospheric mercury pollution in China, prioritizing mercury emissions control of cement clinkers and coal-fired industrial boilers is recommended.