Plasma-Activated Solutions Regulate Surface-Terminating Groups Enhancing Pseudocapacitive Ti3 C2 Tx Electrode Performance.

2D transition metal carbides and nitrides (MXenes) are actively pursued as pseudocapacitive materials for supercapacitors owing to their advantages in electronic conductivity and surface reactivity. Increasing the fraction of ─O terminal groups in Ti3 C2 Tx is a promising approach to improve the pseudocapacitive charge storage in H2 SO4 electrolytes, but it suffers from a lack of effective functionalization methods and stability of the groups in practical operation. Here a low-temperature and environment-friendly approach via the interaction of nonequilibrium plasmas with Ti3 C2 Tx dispersion is demonstrated to generate abundant and stable surface-terminating O groups. The impact of the discharge environment (Ar, O2 , and H2 ) on the structural characteristics and electrochemical performance of Ti3 C2 Tx nanosheets is studied. The Ti3 C2 Tx modified in Ar and H2 maintains their original morphology but a significantly lower F content. Consequently, an extraordinarily high content (78.5%) of surface-terminating O groups is revealed by the high-resolution X-ray photoelectron spectroscopy spectra for the Ti3 C2 Tx samples modified in H2 plasma-treated solutions. Additionally, the Ti3 C2 Tx treated using H2 plasmas exhibits the best capacitive performance of 418.3 F g-1 at 2 mV s-1 , which can maintain 95.88% capacity after 10 000 cycles. These results contribute to the development of advanced nanostructured pseudocapacitive electrode materials for renewable energy storage applications.

Binary ionic liquids hybrid electrolyte based supercapacitors with high energy & power density.

Supercapacitors with high energy and power densities have become highly desirable in practical applications. Ionic liquids (ILs) are considered as promising electrolytes of supercapacitors owing to their excellent electrochemical stability window (approx. 4-6 V) and good thermal stability. However, the high viscosity (up to 102 mPa s) and low electric conductivity (<10 mS cm-1) at room-temperature extremely reduce the ion diffusion dynamics in the energy storage process, resulting in the unsatisfactory power density and rate performance of supercapacitors. Herein we propose a novel binary ionic liquids (BILs) hybrid electrolyte composed of two kinds of ILs in an organic solvent. Along with the organic solvent with high dielectric constant and low viscosity, the addition of binary cations effectively improves the electric conductivity and reduces the viscosity of IL electrolytes. By mixing trimethyl propylammonium bis(trifluoromethanesulfonyl)imide ([TMPA][TFSI]) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([Pyr14][TFSI]) with an equal mole ratio in acetonitrile (1 M), the as-prepared BILs electrolyte shows superior electric conductivity (44.3 mS cm-1), low viscosity (0.692 mPa s), and a wide electrochemical stability window (4.82 V). The supercapacitors assembled with activated carbon electrodes (commercial mass loading) and this BILs electrolyte achieve a high working voltage of 3.1 V, leading to a maximum energy density of 28.3 W h kg-1 at 803.35 W kg-1 and a maximum power density of 32.16 kW kg-1 at 21.17 W h kg-1, which are obviously superior to those of commercial supercapacitors based on organic electrolytes (2.7 V).

Unexpected rise of atmospheric secondary aerosols from biomass burning during the COVID-19 lockdown period in Hangzhou, China.

After the global outbreak of COVID-19, the Chinese government took many measures to control the spread of the virus. The measures led to a reduction in anthropogenic emissions nationwide. Data from a single particle aerosol mass spectrometer in an eastern Chinese megacity (Hangzhou) before, during, and after the COVID-19 lockdown (5 January to February 29, 2020) was used to understand the effect lockdown had on atmospheric particles. The collected single particle mass spectra were clustered into eight categories. Before the lockdown, the proportions of particles ranked in order of: EC (57.9%) < K-SN (13.6%) < Fe-rich (10.2%) < ECOC (6.7%) < K-Na (6.6%) < OC (3.4%) < K-Pb (1.0%) < K-Al (0.7%). During the lockdown period, the EC and Fe-rich particles decreased by 42.8% and 93.2% compared to before lockdown due to reduced vehicle exhaust and industrial activity. By contrast, the K-SN and K-Na particles containing biomass burning tracers increased by 155.2% and 45.2% during the same time, respectively. During the lockdown, the proportions of particles ranked in order of: K-SN (39.7%) < EC (38.1%) < K-Na (11.0%) < ECOC (7.7%) < OC (1.2%) < K-Pb (0.9%) < Fe-rich (0.8%) < K-Al (0.6%). Back trajectory analysis indicated that both inland (Anhui and Shandong provinces) and marine transported air masses may have contributed to the increase in K-SN and K-Na particles during the lockdown, and that increased number of fugitive combustion points (i.e., household fuel, biomass combustion) was a contributing factor. Therefore, the results imply that regional synergistic control measures on fugitive combustion emissions are needed to ensure good air quality.

Numerical Study on Flow and Heat Transfer Characteristics of Trapezoidal Printed Circuit Heat Exchanger.

Printed circuit heat exchanger (PCHE) is a promising regenerative device in the sCO2 power cycle, with the advantages of a large specific surface area and compact structure. Its tiny and complex flow channel structure brings enhanced heat transfer performance, while increasing pressure drop losses. It is, thus, important to balance heat transfer and flow resistance performances with the consideration of sCO2 as the working agent. Herein, three-dimensional models are built with a full consideration of fluid flow and heat transfer fields. A trapezoidal channel is developed and its thermal-hydraulic performances are compared with the straight, the S-shape, and the zigzag structures. Nusselt numbers and the Fanning friction factors are analyzed with respect to the changes in Reynolds numbers and structure geometric parameters. A sandwiched structure that couples two hot channels with one cold channel is further designed to match the heat transfer capacity and the velocity of sCO2 flows between different sides. Through this novel design, we can reduce the pressure drop by 75% and increase the regenerative efficiency by 5%. This work can serve as a solid reference for the design and applications of PCHEs.

Generalized prediction and optimal operating parameters of PCDD/F emissions by explainable Bayesian support vector regression.

The current derived models for predicting polychlorinated dibenzo-p-dioxins and -furans (PCDD/F) emissions from incineration can only be applied to a specific incinerator due to high deviation or systematic errors. And the models fail to provide quantized guidance for the operation of full-scale municipal solid waste incinerators. To address the problem, explainable Bayesian support vector regression (E-BSVR) has been established to generalized predict and maximumly reduce the PCDD/F emissions. First, forty-two PCDD/F samples were determined from a whole year experiment in a full-scale incinerator. Meanwhile, 1,2,4-trichlorobenzene(1,2,4-TrCBz), carbon monoxide, sulfur dioxide, oxynitride, particulate matter, fluoride, and hydrogen chloride were measured, as input features. Second, after box-cox transformation normalization, and hyperparameters tuning, the R-Squared and root mean square error (RMSE) of the proposed method are 0.983 and 0.044, exhibiting high accuracy. The high accuracy (R-Squared = 0.992) and generalization are also proven on the dataset with high PCDD/F emissions. Then, the performances of BSVR are compared with kernel ridge regression, multiple linear regression, and unary linear regression, indicating afar smaller RMSE of BSVR. Finally, the optimal operating parameters are calculated through local interpretable model-agnostic explanations and the partial dependence plot. Results indicate that reducing the content of organic chlorine in municipal solid waste and inhibiting the deacon reaction are important methods for reducing PCDD/F emissions. The optimal operating parameters for the maximal reduction of PCDD/F emissions are 1,2,4-TrCBz < 0.098 ug/m3, fluoride > 0.452 mg/m3. As a whole, the E-BSVR method can be used as a reliable and accurate approach for the prediction and reduction of PCDD/F emissions.

Regulating thermochemical redox temperature via oxygen defect engineering for protection of solar molten salt receivers.

An active coating based on thermochemical redox reactions is proposed to protect molten salt receivers from solar flux fluctuation. However, appropriate metal oxides working in the temperature range of 530 and 850°C are still missing. Herein, we put forward an oxygen defect engineering strategy to regulate the thermochemical redox temperatures of perovskites. A tunable temperature range of 426-702°C is obtained by BaCo1-x Mn x O3-δ (x = 0-0.4). It is found that a raised redox temperature can be obtained with the increase of the oxygen vacancy formation energy. For application, BaCo0.8Mn0.2O3-δ is designed as the active protective coating of a lab-scale receiver, which has a thermal capacity of 82.95 kJ kg-1. The smart coating can slow down the temperature rising rate from 8.5°C min-1 to 3°C min-1 in the first 2 min under strong solar radiation, effectively relieving the thermal shock of the receiver.

Stable and Effective Online Monitoring and Feedback Control of PCDD/F during Municipal Waste Incineration.

For the long-term operation of municipal solid waste incineration (MSWI), online monitoring and feedback control of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) can be used to control the emissions to national or regional standards. In this study, 500 PCDD/F samples were determined by thermal desorption gas chromatography coupled to tunable-laser ionization time-of-flight mass spectrometry (TD-GC-TLI-TOFMS) for 168 h. PCDD/F emissions range from 0.01 ng I-TEQ/Nm3 to 2.37 ng I-TEQ/Nm3, with 44% of values below 0.1 ng I-TEQ/Nm3 (the national standard). In addition, the temperature of the furnace outlet, bed pressure, and oxygen content are considered as key operating parameters among the 13 operating parameters comprising four temperature parameters, four pressure parameters, four flow parameters, and oxygen content. More specifically, maintaining the furnace outlet temperature to be higher than 800 °C, or bed pressure higher than 13 kPa, or the oxygen content stably and above 10% are effective methods for reducing PCDD/F emissions. According to the analysis of the Pearson coefficients and maximal information coefficients, there is no significant correlation between operating parameters and PCDD/F I-TEQ. Only when there is a significant change in one of these factors will the PCDD/F emissions also change accordingly. The feedback control of PCDD/F emissions is realized by adjusting the furnace outlet temperature, bed temperature, and bed pressure to control the PCDD/F to be less than 0.1 ng I-TEQ/Nm3.

Sensing mechanism of the nano-confined space constructed by graphene.

Multilayer graphene with dense interlayer space is the most explored two-dimensional material (2DMs) in high performance gas sensor. Herein, the insertion and the diffusion behaviors of NO, NO2, NH3and H2S in the nano-confined space of graphene are investigated using density functional theory calculations. The optimum interlayer distance is found to be 6-7 Å, in which the interaction strength is enhanced by 2 -3 times compared to monolayer graphene. Based on the optimum interlayer spacing, a barrierless diffusion process is observed due to the negligible influence of adsorption sites on the adsorption energy. Besides, an enhanced adsorption of NO2is found at the edge, which leads to a small barrier (<0.15 eV) during the its inserting into graphene layers, while the barrierless process is observed for NO, NH3and H2S. As for sensing performance, an increased sensitivity is observed for NO and NO2at the edge because of the significant energy level shift and charge transfer. Meanwhile, multilayer graphene shows good selectivity towards NO2gas. Therefore, modulating the interlayer spacing of graphene layers is a promising strategy for fabricating practical low-cost gas sensors, which may facilitate future exploration of high performance gas sensor using multilayer 2DMs.

Astigmatic dual-beam interferometric particle imaging for metal droplet 3D position and size measurement.

We propose astigmatic dual-beam interferometric particle imaging (ADIPI) to simultaneously measure the three-dimensional (3D) position and size of spherical metal droplets. A theoretical model reveals that the orientation and spacing of the ADIPI fringes generated from the two reflections propagating through an astigmatic imaging system relate to the depth position and size, respectively. Proof-of-concept experiments on micron-sized gallium droplets are performed, and the tilted fringes in elliptical patterns are observed in the ADIPI interferogram, confirming theoretical predictions. Droplet 3D position and size are determined with ADIPI, and the relative discrepancies are within 5% and 2% compared to those with a dual-view digital inline holography system, demonstrating the feasibility and high accuracy of ADIPI.

Surface tension and viscosity measurement of oscillating droplet using rainbow refractometry.

We extend rainbow refractometry to quantify the oscillations of a droplet in its fundamental mode. The oscillation parameters (frequency and amplitude damping), extracted using the time-resolved rainbow angular shift, are utilized to measure surface tension and viscosity of the liquid. Proof-of-concept experiments on an oscillating droplet stream produced by a monodisperse droplet generator are conducted. Results show that the relative measurement errors of surface tension and viscosity are 1.5% and 8.4% for water and 5.3% and 2.5% for ethanol. This approach provides an alternative mean for characterizing liquid surface properties, e.g., dynamic surface tension and viscosity, especially for liquids with a low Ohnesorge number.

Sensitive detection of NO using a compact portable CW DFB-QCL-based WMS sensor.

This paper introduces a compact and portable sensor based on mid-infrared absorption spectroscopy for NO detection employing a room-temperature continuous wave (CW) distributed feedback quantum cascade laser (DFB-QCL) emitting at 1900.08cm-1. A software-based digital signal generator and lock-in amplifier, in combination with the wavelength modulation spectroscopy (WMS) technique, were used for the concentration measurement of NO. In addition, a Gabor filter denoising method was developed to improve the performance of the measurement system. As a result, a minimum detection limit of 42 ppbv can be achieved at 3 s integration time, and a measurement precision of 450 ppbv can be reached with a time resolution of 0.1 s. The performance of the compact portable sensor was verified by a series of experiments, denoting great potential of field application for sensitive NO sensing.

Multi-linear antenna microwave plasma assisted large-area growth of 6 × 6 in.2 vertically oriented graphenes with high growth rate.

Vertically oriented graphenes (VGs) are promising for many emerging energy and environmental applications, while their mass production still remains a critical challenge. This note reports a multi-linear antenna microwave plasma device for fabricating VGs on a large-scale. Eight coaxial linear plasma antennas are parallelly arrayed to produce large-area plasma, depositing 6 × 6 in.2 VGs on nickel foil at a high rate of 160 nm min-1. In supercapacitor applications, the potential of VGs for AC line filtering (an RC time of 0.43 ms) and decreasing the interfacial contact resistance within commercial activated carbon supercapacitors is demonstrated.

Plasma-Made Graphene Nanostructures with Molecularly Dispersed F and Na Sites for Solar Desalination of Oil-Contaminated Seawater with Complete In-Water and In-Air Oil Rejection.

Solar desalination that exploits interfacial evaporation represents a promising solution to global water scarcity. Real-world feedstocks (e.g., natural seawater and contaminated water) include oil contamination issues, raising a compelling need for desalination systems that offer anti-oil-fouling capability; however, it is still challenging to prepare oil-repellent and meanwhile water-attracting surfaces. This work demonstrates a concept of molecularly dispersing functional F and Na sites on plasma-made vertically oriented graphene nanosheets to achieve an in-air and in-water oleophobic, hydrophilic surface. The graphene architecture presents high in-air (138°) and in-water (145°) oil contact angles, with simultaneously high water affinity (0°). Such surface wettability is enabled by oleophobic, hydrophobic -CFx, and hydrophilic -COONa groups of the molecules that disperse on graphene surfaces; low-dispersion (0.439 mJ m-2) and high-polarity (95.199 mJ m-2) components of the solid surface tension; and increased surface roughness produced by graphene edges. The graphene nanostructures pump water upward by capillary action but repel oil from the surface, leading to complete in-water and in-air oil rejection and universal anti-oil-fouling capability for solar desalination. Consequently, stable solar-vapor energy efficiency of more than 85% is achieved regardless of whether the feedstock is pure or oil-contaminated water (e.g., a mixture of oil floating on water, an oil-in-water emulsion), resulting in the efficient production of clean water over several days. This outstanding performance is attributed to the universal (both in-water and in-air) oleophobic wettability, together with high light absorptance contributed by nanotraps, fast interfacial heat transfer enhanced by finlike nanostructures, and accelerated evaporation enabled by sharp graphene edges.

The effects of humidity and ammonia on the chemical composition of secondary aerosols from toluene/NOx photo-oxidation.

The secondary aerosol formation mechanism in the presence of ammonia (NH3), is poorly understood, especially under high relative humidity (RH) conditions. In this study, a total of seven experiments were conducted from toluene/NOx photo-oxidation in the presence/absence of NH3 under dry (~7% RH) and wet (>60% RH) conditions in a ~3 m3 smog chamber. A series of instruments including gas analysers, scanning mobility particle sizer (SMPS), aerosol mass spectrometry (HR-ToF-AMS) etc. were applied to measure the NOx and O3 concentrations, the mass concentration and chemical composition of secondary aerosol. It was found that NH3 could enhance the mass loading of secondary aerosol, especially under wet condition. However, the presence of NH3 or increasing RH did not have a significant influence on SOA yield. The organic aerosol mass spectrum from AMS showed that the most abundant fragment was at m/z = 44, which was mainly from the fragmentation of carboxylic acids. Compared to the absence of NH3, the fraction of fragment at m/z = 44 and O:C was higher in the presence of NH3, regardless of dry or wet conditions. The highest O:C value of 0.71-0.75 was observed in the presence of NH3 under wet condition, suggesting there could be a synergetic effect between the high RH and the presence of NH3, which jointly contributed to the photochemical aging process of SOA. The N:C increased in the presence of NH3 under both dry and wet conditions, which might be attributed to the carboxylates and organic nitrates formed from the reaction between NH3 and carboxylic acids. The results implied that SOA modelling should consider the role of NH3 and water vapour, which might fill the gap of O:C between laboratory studies and field measurements.

Tuning and monitoring of nitrogen dioxide fixation on Cu decorated graphene: a density functional theory study.

The recycling utilization of harmful nitrogen dioxide (NO2) is of great significance in pollutant control, agriculture and chemical industry. Herein, NO2 fixation using Cu decorated graphene (Cu/G) as an efficient adsorption platform is investigated through density functional theory calculations. Cu atom serves as the active site for NO2 adsorption due to the location of highest occupied molecular orbitals of Cu/G. Consequently, electrons are transferred from Cu atom to NO2, resulting in NO2 chemisorption with the large exothermicity of 3.210 eV. Electronic structure analysis further reveals the strong hybridization of NO2 with Cu is attributed to the formation of co-valence bond. Cu decorated site can adsorb up to 4 NO2 molecules, while more NO2 molecules are thermodynamically and kinetically favorable to form N2O4. Moreover, the fast release of NO2 molecules is achieved when 2.0 hole is applied to Cu/G as evidenced by the ab initio molecular dynamic simulation. Importantly, the adsorption of NO2 can be monitored real-time based on the conductivity change induced by the charge transfer and orbital hybridization. The behaviors and electronic monitoring of NO2 adsorption provide valuable guidance for future application of Cu/G as a potential material for NO2 fixation.

Solar-Enhanced Plasma-Catalytic Oxidation of Toluene over a Bifunctional Graphene Fin Foam Decorated with Nanofin-like MnO2.

In this work, we propose a hybrid and unique process combining solar irradiation and post-plasma catalysis (PPC) for the effective oxidation of toluene over a highly active and stable MnO2/GFF (bifunctional graphene fin foam) catalyst. The bifunctional GFF, serving as both the catalyst support and light absorber, is decorated with MnO2 nanofins, forming a hierarchical fin-on-fin structure. The results show that the MnO2/GFF catalyst can effectively capture and convert renewable solar energy into heat (absorption of >95%), leading to a temperature rise (55.6 °C) of the catalyst bed under solar irradiation (1 sun, light intensity 1000 W m-2). The catalyst weight (9.8 mg) used in this work was significantly lower (10-100 times lower) than that used in previous studies (usually 100-1000 mg). Introducing solar energy into the typical PPC process via solar thermal conversion significantly enhances the conversion of toluene and CO2 selectivity by 36-63%, reaching ∼93% for toluene conversion and ∼83% for CO2 selectivity at a specific input energy of ∼350 J L-1, thus remarkably reducing the energy consumption of the plasma-catalytic gas cleaning process. The energy efficiency for toluene conversion in the solar-enhanced post-plasma catalytic (SEPPC) process reaches up to 12.7 g kWh-1, ∼57% higher than that using the PPC process without solar irradiation (8.1 g kWh-1), whereas the energy consumption of the SEPPC process is reduced by 35-52%. Moreover, the MnO2/GFF catalyst exhibits an excellent self-cleaning capability induced by solar irradiation, demonstrating a superior long-term catalytic stability of 72 h at 1 sun, significantly better than that reported in previous works. The prominent synergistic effect of solar irradiation and PPC with a synergistic capacity of ∼42% can be mainly attributed to the solar-induced thermal effect on the catalyst bed, boosting ozone decomposition (an almost triple enhancement from ∼0.18 gO3 g-1 h-1 for PPC to ∼0.52 gO3 g-1 h-1 for SEPPC) to generate more oxidative species (e.g., O radicals) and enhancing the catalytic oxidation on the catalyst surfaces, as well as the self-cleaning capacity of the catalyst at elevated temperatures driven by solar irradiation. This work opens a rational route to use abundant, renewable solar power to achieve high-performance and energy-efficient removal of volatile organic compounds.

SO2 Electrocatalytic Oxidation Properties of Pt-Ru/C Bimetallic Catalysts with Different Nanostructures.

Electrocatalytic oxidation of SO2 has been applied in many fields, and electrocatalyst is the focus of the research. Platinum-based electrocatalysts are the hot spot in this reaction. Although the properties of these materials have been optimized to a certain extent, there is still room for improvement in activity and long-term durability. In light of this, two kinds of carbon-supported Pt-Ru bimetallic electrocatalysts (PtRu/C alloy catalyst and Ru@Pt/C core-shell catalyst) were prepared by the microwave reduction method. The experiments demonstrate that the enhancement in the activity of bimetallic catalysts originates from the electronic effect and bifunctional effect between Pt and Ru. Bimetallic catalyst contains a large number of RuOxHy, which promotes the reaction. Because of the high Pt utilization, Ru@Pt/C catalyst with the Pt shell has a higher performance than alloy catalyst. The unit Pt mass activity of PtRu/C and Ru@Pt/C is 1.73 and 2.43 times that of Pt/C, respectively. Ru@Pt/C exhibits excellent stability in the high acid environment and is a promising SO2 electrocatalyst.

Highly Thermo-Conductive Three-Dimensional Graphene Aqueous Medium.

Highly thermo-conductive aqueous medium is a crucial premise to demonstrate high-performance thermal-related applications. Graphene has the diamond comparable thermal conductivity, while the intrinsic two-dimensional reality will result in strong anisotropic thermal conductivity and wrinkles or even crumples that significantly sacrifices its inherent properties in practical applications. One strategy to overcome this is to use three-dimensional (3D) architecture of graphene. Herein, 3D graphene structure with covalent-bonding nanofins (3D-GS-CBF) is proposed, which is then used as the filler to demonstrate effective aqueous medium. The thermal conductivity and thermal conductivity enhancement efficiency of 3D-GS-CBF (0.26 vol%) aqueous medium can be as high as 2.61 W m-1 K-1 and 1300%, respectively, around six times larger than highest value of the existed aqueous mediums. Meanwhile, 3D-GS-CBF can be stable in the solution even after 6 months, addressing the instability issues of conventional graphene networks. A multiscale modeling including non-equilibrium molecular dynamics simulations and heat conduction model is applied to interpret experimental results. 3D-GS-CBF aqueous medium can largely improve the solar vapor evaporation rate (by 1.5 times) that are even comparable to the interfacial heating system; meanwhile, its cooling performance is also superior to commercial coolant in thermal management applications.

High-Performance Pt Catalyst with Graphene/Carbon Black as a Hybrid Support for SO2 Electrocatalytic Oxidation.

In the electrochemical Bunsen reaction, which is the key reaction of the sulfur-iodide cycle, the main overpotential corresponds to the oxidation of SO2. The catalysts currently used for the liquid phase electrocatalytic oxidation of SO2 are mainly based on noble metals, which have excellent corrosion resistance and catalytic activity in an acidic environment. To improve the performance of the commercial Pt catalyst, a Pt catalyst with reduced graphene oxide (RGO) and carbon black as a hybrid support was synthesized by the microwave-assisted polyol reduction process. The large two-dimensional planar structure of RGO was a better anchor for Pt nanoparticles, and a catalyst with fine and uniform distribution of Pt particles was obtained. The carbon black interior prevented the agglomeration of RGO, forming a stereoscopic catalyst structure. The electrochemical test results showed that the RGO/carbon black hybrid support catalyst possessed a higher electrocatalytic activity than the single support catalysts and could be used as an efficient and stable catalyst for the SO2 electrolyzer.

Accurate detection of small particles in digital holography using fully convolutional networks.

Particle detection is a key procedure in particle field characterization with digital holography. Due to various background noises, spurious small particles might be generated and real small particles might be lost during particle detection. Therefore, accurate small particle detection remains a challenge in the research of energy and combustion. A deep learning method based on modified fully convolutional networks is proposed to detect small opaque particles (e.g., coal particles) on extended focus images. The model is tested by several experiments and proved to have good small particle detection accuracy.