RESUMEN
The transport properties of charge carriers in MXene, a promising material, have been studied using terahertz time-domain spectroscopy (THz-TDS) to examine its potential applications in optical and electronic devices. However, previous studies have been limited by narrow frequency ranges, which have hindered the understanding of the intrinsic mechanisms of carrier transport in MXenes. To address this issue, ultrabroadband THz-TDS with frequencies of up to 15 THz to investigate the complex photoconductances of MXene (Ti3C2Tx) films with different thicknesses are employed. The findings indicate that the electronic localization is substrate-dependent, and this effect decreases with an increase in the number of layers. This is attributed to the screening effect of the high carrier density in Ti3C2Tx. Additionally, the layer-independent photocarrier relaxations revealed by optical pump THz probe spectroscopy (OPTP) provide evidence of the carrier heating-induced screening effect. These results are significant for practical applications in both scientific research and various industries.
RESUMEN
Silicon photonic-integrated circuits (PICs) operating in the 2â µm wave band are of great interest for spectroscopic sensing, nonlinear optics, and optical communication applications. However, the performance of silicon PICs in this wave band lags far behind the conventional optical communication band (1310/1550â nm). Here we report the realization of a low-loss waveguide and an ultrahigh-Q microring resonator in the 2â µm wave band on a standard 200â mm silicon photonic platform. The single-mode strip waveguide fabricated on a 220â nm-thick silicon device layer has a record-low propagation loss â¼0.2â dB/cm. Based on the low-loss waveguide, we demonstrate an ultrahigh-Q microring resonator with a measured loaded Q-factor as high as 1.1 × 106 and intrinsic Q-factor of 2 × 106, one order of magnitude higher than prior silicon resonators operating in the same wave band. The extinction ratio of the resonator is higher than 22â dB. These high-performance silicon photonic components pave the way for on-chip sensing applications and nonlinear optics in the 2â µm wave band.
RESUMEN
Ethylene glycol (EG) is one of the most attractive platform molecules derived from biomass and waste plastics. Thus, the selective electrooxidation of ethylene glycol (EGOR) into value-added chemicals (especially glycolic acid (GA)) can promote its recycling and upgrading. However, the understanding of the EG-to-GA process on Pt-group metal (PGM) electrodes is far limited now. It has been shown that the Pt and Pd electrodes could show considerable EGOR activity but not Rh and Ir electrodes. Meanwhile, EGOR mainly produces the glycolate, oxalate, and formate on Pt and Pd electrodes, whereas it can obtain minute amounts of glycolate and oxalate on Rh and Ir electrodes. Impressively, the selectivity of glycolate on Pt and Pd electrodes can be over 85% (apparent Faradaic efficiency) in alkaline media, although the stability should be further improved through interfacial tuning and/or engineering. This work might deepen the fundamental understanding of the EGOR process on the nature of PGM electrodes.
RESUMEN
A tunnel health monitoring (THM) system ensures safe operations and effective maintenance. However, how to effectively process and denoise several data collected by THM remains to be addressed, as well as safety early warning problems. Thus, an integrated method for Savitzky-Golay smoothing (SGS) and Wavelet Transform Denoising (WTD) was used to smooth data and filter noise, and the coefficient of the non-uniform variation method was proposed for early warning. The THM data, including four types of sensors, were attempted using the proposed method. Firstly, missing values, outliers, and detrend in the data were processed, and then the data were smoothed by SGS. Furthermore, data denoising was carried out by selecting wavelet basis functions, decomposition scales, and reconstruction. Finally, the coefficient of non-uniform variation was employed to calculate the yellow and red thresholds. In data smoothing, it was found that the Signal Noise Ratio (SNR) and Root Mean Square Error (RMSE) of SGS smoothing were superior to those of the moving average smoothing and five-point cubic smoothing by approximately 10% and 30%, respectively. An interesting phenomenon was discovered: the maximum and minimum values of the denoising effects with different wavelet basis functions after selection differed significantly, with the SNR differing by 14%, the RMSE by 8%, and the r by up to 80%. It was found that the wavelet basis functions vary, while the decomposition scales are consistently set at three layers. SGS and WTD can effectively reduce the complexity of the data while preserving its key characteristics, which has a good denoising effect. The yellow and red warning thresholds are categorized into conventional and critical controls, respectively. This early warning method dramatically improves the efficiency of tunnel safety control.
RESUMEN
The severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) is highly contagious, and the coronavirus disease 2019 (COVID-19) pandemic caused by it has forced many countries to adopt 'lockdown' measures to prevent the spread of the epidemic through social isolation of citizens. Some countries proposed universal mask wearing as a protection measure of public health to strengthen national prevention efforts and to limit the wider spread of the epidemic. In order to reveal the epidemic prevention efficacy of masks, this paper systematically evaluates the experimental studies of various masks and filter materials, summarises the general characteristics of the filtration efficiency of isolation masks with particle size, and reveals the actual efficacy of masks by combining the volume distribution characteristics of human exhaled droplets with different particle sizes and the SARS-CoV-2 virus load of nasopharynx and throat swabs from patients. The existing measured data show that the filtration efficiency of all kinds of masks for large particles and extra-large droplets is close to 100%. From the perspective of filtering the total number of pathogens discharged in the environment and protecting vulnerable individuals from breathing live viruses, the mask has a higher protective effect. If considering the weighted average filtration efficiency with different particle sizes, the filtration efficiencies of the N95 mask and the ordinary mask are 99.4% and 98.5%, respectively. The mask can avoid releasing active viruses to the environment from the source of infection, thus maximising the protection of vulnerable individuals by reducing the probability of inhaling a virus. Therefore, if the whole society strictly implements the policy of publicly wearing masks, the risk of large-scale spread of the epidemic can be greatly reduced. Compared with the overall cost of social isolation, limited personal freedoms and forced suspension of economic activities, the inconvenience for citizens caused by wearing masks is perfectly acceptable.
Asunto(s)
COVID-19/epidemiología , COVID-19/prevención & control , Máscaras/normas , Aerosoles , COVID-19/transmisión , Humanos , Nasofaringe/virología , Orofaringe/virología , Tamaño de la Partícula , Carga ViralRESUMEN
A Q-switched Er:ZBLAN fiber laser operating at 2.8 µm was realized by employing Sb as the saturable material. The Sb material was deposited on a gold mirror by the magnetron-sputtering deposition method to develop a saturable absorber mirror (SAM). By employing the Sb-SAM in an Er:ZBLAN fiber laser, stable Q-switching operation was achieved at central wavelength of 2799.7 nm with the repetition rates ranging from 33.3 to 58.8 kHz and the pulse duration ranging from 5.7 to 1.7 µs. The Sb-SAM still works stably under the maximum pump power of 5.6 W, with an output power of 59 mW corresponding to the pulse energy of 1.03 µJ. To our knowledge, this was the first demonstration of Sb-based saturable material in Er:ZBLAN fiber laser for mid-infrared Q-switched pulse generation operating in the 2.8 µm regime, indicating its potential applications in the mid-infrared waveband.
RESUMEN
A ternary composite (SA/GE@BC) for cadmium removal from wastewater was successfully prepared. The alginate and gelatin were successfully impregnated with biochar (derived from water caltrop shell) to improve the recyclability and adsorption capacity. The prepared SA/GE@BC demonstrated a good removal for cadmium at pH 4.0-7.0 conditions. The cadmium removal increased with increasing SA/GE@BC dosage. The adsorption kinetics process was well consistent with the pseudo-second order model. And the Langmuir model (R2 > 0.99) best described the isotherm data. The calculated adsorption capacity reached a maximum of 86.25 mg/g. The adsorption was a spontaneous and endothermic process, and elevating temperature favored the removal of cadmium. The alginate-gelatin composition enhanced the number of oxygenated functional groups and exchangeable ions. This enhanced the removal of cadmium by complexation and cation ion exchange. Also, the removal mechanism of cadmium on SA/GE@BC involved electrostatic attraction and π-bond coordination. The saturated SA/GE@BC could be well regenerated by 0.1 M HNO3. All these results suggested the preparation of SA/GE@BC could effectively use waste resources to produce highly effective adsorbents for removing cadmium from contaminated water.
Asunto(s)
Contaminantes Químicos del Agua , Purificación del Agua , Cadmio/química , Gelatina , Alginatos , Agua , Contaminantes Químicos del Agua/química , Purificación del Agua/métodos , Carbón Orgánico/química , Adsorción , CinéticaRESUMEN
Temperature segregation during the paving of asphalt pavements is one of the causes of asphalt pavement distress. Therefore, controlling the paving temperature is crucial in the construction of asphalt pavements. To quickly evaluate the road performance of asphalt mixtures during paving, in this work, we used unmanned aerial vehicle infrared thermal imaging technology to monitor the construction work. By analyzing the temperature distribution at the paving site, and conducting laboratory tests, the relationship between the melt temperature, high-temperature stability, and water stability of the asphalt mix was assessed. The results showed that the optimal temperature measurement height for an unmanned aerial vehicle (UAV) with an infrared thermal imager was 7-8 m. By coring the representative temperature points on the construction site and then conducting a Hamburg wheel tracking (HWT) test, the test results were verified through the laboratory test results in order to establish a prediction model for the melt temperature and high-temperature stability of y = 10.73e0.03x + 1415.78, where the predictive model for the melt temperature and water was y = -19.18e-0.02x + 98.03. The results showed that using laboratory tests combined with UAV infrared thermography could quickly and accurately predict the road performance of asphalt mixtures during paving. We hope that more extensive evaluations of the roadworthiness of asphalt mixtures using paving temperatures will provide reference recommendations in the future.
RESUMEN
A bioelectrochemical system (BES) can be operated in both "microbial fuel cell" (MFC) and "microbial electrolysis cell" (MEC) modes, in which power is delivered and invested respectively. To enhance the electric current production, a BES was operated in MFC mode first and a capacitor was used to collect power from the system. Then the charged capacitor discharged electrons to the system itself, switching into MEC mode. This alternate charging and discharging (ACD) mode helped the system produce 22-32% higher average current compared to an intermittent charging (IC) mode, in which the capacitor was first charged from an MFC and then discharged to a resistor, at 21.6 Ω external resistance, 3.3 F capacitance and 300 mV charging voltage. The effects of external resistance, capacitance and charging voltage on average current were studied. The average current reduced as the external resistance and charging voltage increased and was slightly affected by the capacitance. Acquisition of higher average current in the ACD mode was attributed to the shorter discharging time compared to the charging time, as well as a higher anode potential caused by discharging the capacitor. Results from circuit analysis and quantitatively calculation were consistent with the experimental observations.
Asunto(s)
Fuentes de Energía Bioeléctrica , Capacidad Eléctrica , Electrones , Análisis de la Demanda Biológica de Oxígeno , Impedancia Eléctrica , Electrodos , Factores de TiempoRESUMEN
Three polyferric-cationic polymer dual-coagulants were comparatively evaluated in terms of coagulation behavior and floc structure characteristic in the coagulation of humic acid (HA) solution. The first dual-coagulant, PFC-PDADMAC, was prepared by premixing of polyferric chloride (PFC) and polydiallyldimethylammonium (PDADMAC) before dosing. The other two were achieved by dosing PFC and PDADMAC in different order. For the given neutral condition, all three dual-coagulants gave similar HA removal before reaching optimal dosage. The strongest charge neutralization and narrowest effective coagulation dosage range were obtained when PFC was dosed firstly. While the weakest charge neutralization and the broadest effective coagulation dosage were obtained when PDADMAC was used as the primary coagulant. The HA removal of all three dual-coagulants was slightly pH dependent for optimum coagulant doses. Fe(III) hydrolysis species distributions of the dual-coagulants in coagulation process were measured by ferron method. PFC-PDADMAC gave the highest content of active Fe(III) coagulating species which is responsible for the coagulation performance of ferric coagulant. The evolution of floc size and floc fractal dimension (Df) in coagulation process was measured under optimum dose and neutral condition by laser diffraction instrument and small-angle laser light scattering (SALLS), respectively. All three dual-coagulants gave similar final floc size but different floc growth rate and floc structure. Both the growth rate and Df were in the same order: PFC dosed firstly>PDADMAC dosed firstly>PFC-PDADMAC.
Asunto(s)
Cationes/química , Sustancias Húmicas , Hierro/química , Polímeros/química , Floculación , Fractales , Concentración de Iones de Hidrógeno , Luz , Tamaño de la Partícula , Soluciones , Factores de TiempoRESUMEN
In order to study pollution status and distribution characteristics of PAHs in PM10 during the spring in city and suburban Xiamen. A total of 18 PAHs were analyzed in the aerosol samples collected in daytime and nighttime during 11th to 21st of April, 2013 in city and suburban Xiamen. Results showed diurnal variation of Σ PAHs in suburban was weaker than that in city. In the city, the concentration of PAHs during daytimes was higher than that during nighttimes, close to 1.83 times, and it is still under the national environmental standards. In different times and space scales, PAHs were a bimodal distribution, the components of PAHs gave the priority to low and middle rings in urban and suburban during daytimes and nighttimes. PAHs with high molecular weight decreased gradually by the increase of particle size, and the proportion of low molecular weight PAHs increased gradually in the meantime. In the city, the change of size distribution among 2-4 rings PAHs in PM10 during days and nights was bigger than these among 5-7 rings. The main sources of PAHs were estimated by DR, the main contributions included gasoline and diesel combustion, the smelting furnace exhaust emissions. During sampling periods, the relationship between the concentration of PAHs, temperature and WD is negative, PAHs had a positive correlation with the visibility and WS in suburban. And in urban, the relationship with temperature during the day was negative, and with an opposite correlation between other meteorological elements.
Asunto(s)
Contaminantes Atmosféricos/análisis , Monitoreo del Ambiente , Hidrocarburos Policíclicos Aromáticos/análisis , Aerosoles , China , Ciudades , Tamaño de la Partícula , Material Particulado/análisis , Estaciones del Año , Temperatura , Emisiones de Vehículos , Tiempo (Meteorología)RESUMEN
Mixed ion-exchange resins packed microbial desalination cell (R-MDC) could stabilize the internal resistance, however, the impacts of multiple ions on R-MDC performance was unclear. This study investigated the desalination performance, multiple ions migration behaviors and their impacts on R-MDCs fed with salt solution containing multiple anions and cations. Results showed that R-MDC removed multiple anions better than multiple cations with desalination efficiency of 99% (effluent conductivity <0.05 ms/cm) at hydraulic retention time of 50 h. Competitive migration order was SO4(2-)>NO3(-)>Cl(-) for anions and Ca(2+)≈Mg(2+)>NH4(+)>Na(+) for cations, jointly affected by both their molar conductivity and exchange selectivity on resins. After long-term operation, the existence of higher concentration Ca(2+) and Mg(2+) caused the electric conductivity of mixed resins decrease and scaling on the surface of cation-exchange membrane adjoined with cathode chamber, suggesting that R-MDC would be more suitable for desalination of water with lower hardness.
Asunto(s)
Fuentes de Energía Bioeléctrica , Reactores Biológicos , Resinas de Intercambio Iónico , Iones , Purificación del Agua/métodos , Biodegradación Ambiental , Conductividad Eléctrica , Electroquímica/métodos , Electrodos , Concentración de Iones de Hidrógeno , Modelos Estadísticos , Salinidad , Sales (Química)/química , Cloruro de Sodio/química , Soluciones , Factores de Tiempo , Agua/química , Contaminantes Químicos del Agua/análisisRESUMEN
A shorter start-up time and highly negative anode potentials are needed to improve single-chamber air-cathode microbial fuel cells (MFCs). Using a glass fiber separator reduced the start-up time from 10d to 8d at 20°C, and from 4d to 2d at 30°C, and enhanced coulombic efficiency (CE) from <60% to 89% (20°C) and 87% (30°C). Separators also reduced anode potentials by 20-190mV, charge transfer resistances by 76% (20°C) and 19% (30°C), and increased CV peak currents by 24% (20°C) and 8% (30°C) and the potential range for redox activity (-0.55 to 0.10mV vs. -0.49 to -0.24mV at 20°C). Using a glass fiber separator in an air-cathode MFC, combined with inoculation at a mesophilic temperature, are excellent strategies to shorten start-up time and to enhance anode performance and CE.
Asunto(s)
Fuentes de Energía Bioeléctrica , Vidrio , Espectroscopía Dieléctrica , Difusión , Electrodos , Oxígeno/química , TemperaturaRESUMEN
Catalysts and catalyst binders are significant portions of the cost of microbial fuel cell (MFC) cathodes. Many materials have been tested as aqueous cathodes, but air-cathodes are needed to avoid energy demands for water aeration. Packed-bed air-cathodes were constructed without expensive binders or diffusion layers using four inexpensive carbon-based materials. Cathodes made from activated carbon produced the largest maximum power density of 676 ± 93 mW/m(2), followed by semi-coke (376 ± 47 mW/m(2)), graphite (122 ± 14 mW/m(2)) and carbon felt (60 ± 43 mW/m(2)). Increasing the mass of activated carbon and semi-coke from 5 to ≥ 15 g significantly reduced power generation because of a reduction in oxygen transfer due to a thicker water layer in the cathode (â¼3 or â¼6 cm). These results indicate that a thin packed layer of activated carbon or semi-coke can be used to make inexpensive air-cathodes for MFCs.
Asunto(s)
Fuentes de Energía Bioeléctrica , Suministros de Energía Eléctrica , Electrodos , CatálisisRESUMEN
Biocathode MFCs using microorganisms as catalysts have important advantages in lowering cost and improving sustainability. Electrode materials and microbial synergy determines biocathode MFCs performance. In this study, four materials, granular activated carbon (GAC), granular semicoke (GS), granular graphite (GG) and carbon felt cube (CFC) were used as packed cathodic materials. The microbial composition on each material and its correlation with the electricity generation performance of MFCs were investigated. Results showed that different biocathode materials had an important effect on the type of microbial species in biocathode MFCs. The microbes belonging to Bacteroidetes and Proteobacteria were the dominant phyla in the four materials packed biocathode MFCs. Comamonas of Betaproteobacteria might play significant roles in electron transfer process of GAC, GS and CFC packed biocathode MFCs, while in GG packed MFC Acidovorax may be correlated with power generation. The biocathode materials also had influence on the microbial diversity and evenness, but the differences in them were not positively related to the power production.
RESUMEN
A simple and low-cost modification method was developed to improve the power generation performance of inexpensive semicoke electrode in microbial fuel cells (MFCs). After carbonization and activation with water vapor at 800-850 °C, the MFC with the activated coke (modified semicoke) anode produced a maximum power density of 74 Wm(-3) , 17 Wm(-3) , and 681 mWm(-2) (normalized to anodic liquid volume, total reactor volume, and projected membrane surface area, respectively), which was 124 % higher than MFCs using a semicoke anode (33 Wm(-3) , 8 Wm(-3) , and 304 mWm(-2) ). When they were used as biocathode materials, activated coke produced a maximum power density of 177 Wm(-3) , 41 Wm(-3) , and 1628 mWm(-2) (normalized to cathodic liquid volume, total reactor volume, and projected membrane surface area, respectively), which was 211 % higher than that achieved by MFCs using a semicoke cathode (57 Wm(-3) , 13 Wm(-3) , and 524 mWm(-2) ). A substantial increase was also noted in the conductivity, C/O mass ratio, and specific area for activated coke, which reduced the ohmic resistance, increased biomass density, and promoted electron transfer between bacteria and electrode surface. The activated coke anode also produced a higher Coulombic efficiency and chemical oxygen demand removal rate than the semicoke anode.
Asunto(s)
Fuentes de Energía Bioeléctrica , Carbono/química , Coque , Análisis de la Demanda Biológica de Oxígeno , ElectrodosRESUMEN
A novel configuration of microbial desalination cell (MDC) packed with ion-exchange resin (R-MDC) was proposed to enhance water desalination rate. Compared with classic MDC (C-MDC), an obvious increase in desalination rate (DR) was obtained by R-MDC. With relatively low concentration (10-2 g/L NaCl) influents, the DR values of R-MDC were about 1.5-8 times those of C-MDC. Ion-exchange resins packed in the desalination chamber worked as conductor and thus counteracted the increase in ohmic resistance during treatment of low concentration salt water. Ohmic resistances of R-MDC stabilized at 3.0-4.7 Ω. By contrast, the ohmic resistances of C-MDC ranged from 5.5 to 12.7 Ω, which were 55-272% higher than those of R-MDC. Remarkable improvement in desalination rate helped improve charge efficiency for desalination in R-MDC. The results first showed the potential of R-MDC in the desalination of water with low salinity.
Asunto(s)
Fuentes de Energía Bioeléctrica , Resinas de Intercambio Iónico/química , Salinidad , Cloruro de Sodio/aislamiento & purificación , Purificación del Agua/instrumentación , Purificación del Agua/métodos , Agua/química , Fuentes de Energía Bioeléctrica/microbiología , Impedancia Eléctrica , Cinética , ReologíaRESUMEN
A new technology (CDI-MFC) that combined capacitive deionization (CDI) and microbial fuel cell (MFC) was developed to treat low-concentration salt water with NaCl concentration of 60mg/L. The water desalination rate was 35.6mg/(Lh), meanwhile the charge efficiency was 21.8%. Two desorption modes were investigated: discharging (DC) mode and short circuit (SC) mode. The desalination rate in the DC mode was 200.6±3.1mg/(Lh), 47.8% higher than that in the SC mode [135.7±15.3mg/(Lh)]. The average current in the DC mode was also much higher than that of the SC mode. The energy stored in the CDI cell has been reused to enhance the electron production of MFC by the discharging desorption mode (DC mode), which offers an approach to recover the electrostatic energy in the CDI cell.
Asunto(s)
Fuentes de Energía Bioeléctrica , Agua de Mar , Cloruro de Sodio/análisisRESUMEN
The performance and cost of electrodes are the most important aspects in the design of microbial fuel cell (MFC) reactors. A wide range of electrode materials and configurations have been tested and developed in recent years to improve MFC performance and lower material cost. As well, anodic electrode surface modifications have been widely used to improve bacterial adhesion and electron transfer from bacteria to the electrode surface. In this paper, a review of recent advances in electrode material and a configuration of both the anode and cathode in MFCs are provided. The advantages and drawbacks of these electrodes, in terms of their conductivity, surface properties, biocompatibility, and cost are analyzed, and the modification methods for the anodic electrode are summarized. Finally, to achieve improvements and the commercial use of MFCs, the challenges and prospects of future electrode development are briefly discussed.
Asunto(s)
Fuentes de Energía Bioeléctrica , Electrodos , Adhesión Bacteriana , Propiedades de SuperficieRESUMEN
Four materials, carbon felt cube (CFC), granular graphite (GG), granular activated carbon (GAC) and granular semicoke (GS) were tested as packed anodic materials to seek a potentially practical material for microbial fuel cells (MFCs). The microbial community and its correlation with the electricity generation performance of MFCs were explored. The maximum power density was found in GAC, followed by CFC, GG and GS. In GAC and CFC packed MFCs, Geobacter was the dominating genus, while Azospira was the most populous group in GG. Results further indicated that GAC was the most favorable for Geobacter adherence and growth, and the maximum power densities had positive correlation with the total biomass and the relative abundance of Geobacter, but without apparent correlation with the microbial diversity. Due to the low content of Geobacter in GS, power generated in this system may be attributed to other microorganisms such as Synergistes, Bacteroidetes and Castellaniella.