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1. Highly Selective Room-Temperature Blue LED-Enhanced NO2 Gas Sensors Based on ZnO-MoS2-TiO2 Heterostructures

   https://doi.org/10.3390/s25061781  

   Flores, Soraya Y; Pacheco, Elluz; Malca, Carlos; Peng, Xiaoyan; Chen, Yihua; Zhou, Badi; Pinero, Dalice M; Diaz-Vazquez, Liz M; Zhou, Andrew F; Feng, Peter X (March 2025, Sensors)

   This study presents the fabrication and characterization of highly selective, room-temperature gas sensors based on ternary zinc oxide–molybdenum disulfide–titanium dioxide (ZnO-MoS2-TiO2) nanoheterostructures. Integrating two-dimensional (2D) MoS2 with oxide nano materials synergistically combines their unique properties, significantly enhancing gas sensing performance. Comprehensive structural and chemical analyses, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR), confirmed the successful synthesis and composition of the ternary nanoheterostructures. The sensors demonstrated excellent selectivity in detecting low concentrations of nitrogen dioxide (NO2) among target gases such as ammonia (NH3), methane (CH4), and carbon dioxide (CO2) at room temperature, achieving up to 58% sensitivity at 4 ppm and 6% at 0.1 ppm for NO2. The prototypes demonstrated outstanding selectivity and a short response time of approximately 0.51 min. The impact of light-assisted enhancement was examined under 1 mW/cm2 weak ultraviolet (UV), blue, yellow, and red light-emitting diode (LED) illuminations, with the blue LED proving to deliver the highest sensor responsiveness. These results position ternary ZnO-MoS2-TiO2 nanoheterostructures as highly sensitive and selective room-temperature NO2 gas sensors that are suitable for applications in environmental monitoring, public health, and industrial processes. 

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2. Partitioning of NH3-NH4+ in the Southeastern U.S.

   https://doi.org/10.3390/atmos12121681  

   Cheng, Bin; Wang-Li, Lingjuan; Meskhidze, Nicholas; Classen, John; Bloomfield, Peter (December 2021, Atmosphere)

   The formation of inorganic fine particulate matter (i.e., iPM2.5) is controlled by the thermodynamic equilibrium partitioning of NH3-NH4+. To develop effective control strategies of PM2.5, we aim to understand the impacts of changes in different precursor gases on iPM2.5 concentrations and partitioning of NH3-NH4+. To understand partitioning of NH3-NH4+ in the southeastern U.S., responses of iPM2.5 to precursor gases in four seasons were investigated using field measurements of iPM2.5, precursor gases, and meteorological conditions. The ISORROPIA II model was used to examine the effects of changes in total ammonia (gas + aerosol), total sulfuric acid (aerosol), and total nitric acid (gas + aerosol) on iPM2.5 concentrations and partitioning of NH3-NH4+. The results indicate that reduction in total H2SO4 is more effective than reduction in total HNO3 and total NH3 to reduce iPM2.5 especially under NH3-rich condition. The reduction in total H2SO4 may change partitioning of NH3-NH4+ towards gas-phase and may also lead to an increase in NO3− under NH3-rich conditions, which does not necessarily lead to full neutralization of acidic gases (pH < 7). Thus, future reduction in iPM2.5 may necessitate the coordinated reduction in both H2SO4 and HNO3 in the southeastern U.S. It is also found that the response of iPM2.5 to the change in total H2SO4 is more sensitive in summer than winter due to the dominance of SO42− salts in iPM2.5 and the high temperature in summer. The NH3 emissions from Animal Feeding Operations (AFOs) at an agricultural rural site (YRK) had great impacts on partitioning of NH3-NH4+. The Multiple Linear Regression (MLR) model revealed a strong positive correlation between cation-NH4+ and anions-SO42− and NO3−. This research provides an insight into iPM2.5 formation mechanism for the advancement of PM2.5 control and regulation in the southeastern U.S. 

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3. U-Pb dating of titanite by LA-ICP-QQQ-MS

   Stone, Joshua S; Cruz-Uribe, AM; Brooks, HL (May 2019, North American Workshop on Laser Ablation 2019 Abstracts)

   Titanite has the ability to incorporate significant amounts of common Pb, which leads to uncertainty when applying the U-Pb decay series for geochronology. The isobaric interference of 204Hg on 204Pb poses an additional complexity in applying common Pb corrections. Here we investigate the removal of 204Hg interferences during titanite U-Pb dating using reaction cell gas chemistry via triple quadrupole mass spectrometry. U-Pb dates were determined for the natural titanite reference materials MKED-1 and BLR1 using an ESI NWR193UC excimer laser coupled to an Agilent 8900 ‘triple quad’ mass spectrometer. The 8900 is equipped with an octopole collision/reaction cell, which enables online interference removal. Two experiments were run, one in which we collected data in NoGas mode, and one in which NH3 was used as a reaction cell gas in MS/MS mode, in order to assess the feasibility of determining U/Pb ratios with mass shifted isotopes. In all experiments, a signal smoothing device was placed inline just before the ICP-MS interface, downstream from the addition of the Ar nebulizer gas to the He carrier gas stream. For the NoGas experiment, titanite was ablated using a 25 µm spot, with a beam energy density of 3 J/cm2, and a pulse rate of 4 Hz. In NoGas mode, signal intensities for the isotopes 201Hg, 202Hg, 204Pb, 206Pb, 207Pb, 232Th, 235U, and 238U were counted. In MS/MS mode, titanite was ablated using a 40 µm spot, with a beam energy density of 5 J/cm2, and a pulse rate of 4 Hz. A larger spot size in this experiment was used to counteract the decrease in signal intensity due to use of the reaction cell. In MS/MS mode, NH3 was flowed through the reaction cell in order to enable a charge transfer reaction between NH3 and Hg+, effectively neutralizing Hg. The isotopes 201Hg, 202Hg, 204Pb, 206Pb, and 207Pb were measured on-mass, as the isotopes of Pb are not affected by the NH3 gas. Uranium and Th both exhibit partial reaction with NH3 gas; therefore, the isotopes 232Th, 235U, and 238U were measured mass-shifted up 15 mass units, at masses 247, 250, and 253 respectively. Ratios of 207Pb/235U, 206Pb/238U, and 207Pb/206Pb were determined using the UPbGeochron4 DRS in Iolite (v.3.71) with MKED-1 as the primary reference material. Dates were calculated using IsoplotR by applying the Stacey-Kramers correction for common Pb. All isotopes of Hg were effectively neutralized by the NH3 charge transfer reaction in MS/MS mode; zero counts were detected for Hg isotopes. Dates for the BLR-1 titanite were 1050.55 ± 2.72 (2σ, n=12) Ma in NoGas mode, and 1048 ± 1.88 (2σ, n=15) Ma in MS/MS mode. These dates are in excellent agreement with the TIMS 206Pb/238U date for the BLR-1 titanite of 1047.1 ± 0.4 Ma. This method has the potential to enable measurement of 204Pb without needing to correct for Hg interferences. 

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4. Effect of Tungsten Oxide Nanostructures on Sensitivity and Selectivity of Pollution Gases

   https://doi.org/10.3390/s20174801  

   An, Fenghui; Zhou, Andrew F.; Feng, Peter X. (September 2020, Sensors)

   null (Ed.)

   We report on the different surface structures of tungsten oxides which have been synthesized using a simple post-annealing-free hot-filament CVD technique, including 0D nanoparticles (NPs), 1D nanorods (NRs), and 2D nanosheet assemblies of 3D hierarchical nanoflowers (NFs). The surface morphologies, crystalline structures, and material compositions have been characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy, respectively. The sensor performances based on the synthesized samples of various surface morphologies have been investigated, as well as the influences of operating temperature and applied bias. The sensing property depends closely on the surface morphology, and the 3D hierarchical nanoflowers-based gas sensor offers the best sensitivity and fastest response time to NH3 and CH3 gases when operated at room temperature. 

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5. OPPORTUNITIES FOR USING NUCLEAR MICROREACTORS FOR WASTEWATER TREATMENT, HYDROGEN PRODUCTION, AND AMMONIA PRODUCTION

   https://doi.org/10.1615/TFEC2024.icc.050659  

   Strine, Bailey; Pakkebier, Jack; Parameswaran, Prathap; Derby, Melanie M (January 2024, Begellhouse)

   In 2021, the White House proposed a 50-52% reduction in greenhouse gas emissions by the year 2030; therefore, there is significant interest in energy sources and processes that reduce carbon dioxide emissions. This paper presents a sensitivity analysis of a nuclear microreactor-powered design for concurrent hydrogen (H2) and ammonia (NH3) production, with a focus on wastewater treatment plant applications. Wastewater with organic materials (e.g., municipal wastewater, swine lagoon waste, and food waste) are the analyzed feedstocks. The system integrates the anaerobic digestion of wastewater sludge with a Brayton cycle-based power generation unit heated by the microreactor. Using empirical data and an analytical model, the paper investigates the system's response to variations in key operational parameters. The sensitivity analysis explores the influence of parameters such as the chemical oxygen demand of the feedstock, compressor isentropic efficiency, and reactor temperature and pressure on H2 and NH3 production rates, Brayton cycle efficiency, and carbon dioxide emissions. Highlights from this analysis show a nonlinear dependence for Brayton efficiency on reactor temperature, the proportionality of ammonia and hydrogen production on chemical oxygen demand values, the major impact of compressor isentropic efficiency, and the minimal response from changing the pressure of steam methane reforming. These results signify opportunities to improve the system and ultimately lead to lowered greenhouse gas emissions. 

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