33 Search Results

In this work, ordered porous thin films of reduced graphene oxide and tin oxide (rGO/SnO₂) were synthesized by a polystyrene sphere monolayer colloidal crystal template method, and their gas-sensing properties were systematically studied. The formed amorphous SnO₂ and partially reduced graphene oxide were analyzed using several complementary material characterization techniques. Further, the results show that the incorporation of rGO significantly improved the humidity sensitivity and the electrical conductivity of the sensor relative to the pristine SnO₂ thin film. Fast response time and excellent selectivity towards humidity were also achieved for the rGO/SnO₂ composite film. The long-term stability of the rGO/SnO₂more » sensor was confirmed by comparing its performance to a commercial humidity sensor. The enhanced sensor performance is attributed to the synergistic effects of the incorporation of rGO and the ordered porous structure of the composite film.« less

This work details the synthesis, materials characterization and absorption capacity of graphene aerogel (GA) loaded with UiO-66-NH₂ metal organic framework (MOF). Throughout the study, a series of density-tunable MOF/GA composites were synthesized by adjusting the MOF/graphene oxide (GO) mass ratio of the precursors before hydrothermal reduction and subsequent critical point drying to achieve MOF-x%/GA composites, with x, ranging from 0 to 100, denoting the weight percent ratio of MOF to GO in the starting solution. Scanning electron microscopy (SEM) images and Barrett-Joyner-Halenda (BJH) pore size calculations supported that MOF loading enlarged the macroporous (>50 nm) structure of the GA frameworkmore » but had no influence on the mesoporous (2–50 nm) structure of GA. The degree of MOF loading first decreased and then increased the density of resulting composites, exhibiting a minimum for the 10–30% samples. Such behavior with respect to MOF loading has not been reported previously. MOF-x%/GA samples were further investigated for absorption capacity using various organic liquids. MOF-30%/GA proved to be the best absorbent sample for all solvents tested, achieving the highest capacity for chloroform at 147.0 ± 10.0 mg/mg. The behavior is attributed to the structural changes induced by the MOF incorporation as well as the interactions between the organic molecules and the MOF.« less

The accumulation of carbon dioxide (CO₂) within enclosed spaces, along with volatile organic compounds, under certain humidity, temperature, and ventilation conditions is associated with detrimental human health symptoms such as fatigue. Color-based chemical sensing is a promising approach to detect CO₂ levels relevant to indoor air quality through producing fast, quantifiable output visible to the naked eye. In a prior work, a colorimetric gas sensor was fabricated through synthesizing the metal-organic framework, ZIF-8, as the adsorbent, followed by post-synthetic mixing with a dye, phenol red (PSP), and primary amine, ethylenediamine (ED). While this sensor (termed PSP-ED/ZIF-8) maintained its structural integritymore » in atmospheric conditions and exhibited an increasing fuchsia-to-yellow color change with increasing CO₂ levels in dry environment, the colorimetric response greatly suffered in the presence of humid CO₂. Here in this work, a significantly improved colorimetric CO₂ sensor (referred to as ED/PSP:ZIF-8) is accomplished through directly incorporating phenol red in the ZIF-8 metal and linker precursor solutions and then blending with ethylenediamine. MATLAB-generated color distributions and in-situ ultraviolet-visible (UV-Vis) spectroscopic studies quantitatively demonstrate an enhanced colorimetric gas response of ED/PSP:ZIF-8 compared to that of PSP-ED/ZIF-8 across an important range of CO₂ for indoor air quality monitoring (500 – 3500 ppm) and across a range of humidity. The new sensor also exhibits high selectivity to CO₂ compared to select volatile organic compounds, such as acetone and ethanol, which contribute to human health symptoms experienced indoors. The enhanced performance is attributed to the proposed incorporation of phenol red within ZIF-8, while maintaining the chemical stability of the MOF.« less

Coenzyme F ₄₂₀ -dependent sulfite reductase (Fsr) protects methanogenic archaea inhabiting deep-sea hydrothermal vents from the inactivation of methyl coenzyme M reductase (Mcr), one of their essential energy production enzymes. Anaerobic methanotrophic archaea (ANME) that oxidize methane and rely on Mcr, carry Fsr homologs that form a distinct clade.

Chemiresistive CO₂ sensing is attractive due to low cost and ease of chip-level integration. Our previous studies (Yong Xia, 2021) showed the well-developed ZnO material fabricated by in-situ annealing exhibited good CO₂ sensing performance. Here, we have expanded on those studies, including CO₂ cyclic tests under both dry air and N₂ background whereby a much higher response to CO₂ in N₂ background was observed. In this study, detailed density functional theory calculations were conducted to understand the behavior. The results indicated nitrogen doping is mainly responsible for the observed response. In the presence of pre-adsorbed O₂, N-doped ZnO can nomore » longer interact with CO₂, which agrees well with the observation of higher response in N₂ background. Furthermore, density of states analysis showed N sp² hybridized orbital and N 2p orbital of the N dopant mixed with sp² hybridized orbital of C atom and 2p orbitals of C/O atoms in CO₂ to form σ and π bonds, respectively. However, they mixed with O 2s/2p orbitals of O atom in O₂ when pre-adsorbed O₂ was present, hindering CO₂ interaction with N-doped ZnO, and resulting in limited response in air. The illustrated mechanism does not only further the understanding of metal oxide-based CO₂ sensing, but also guide the design of new functional materials for CO₂ sensing or capture.« less

Marine dissolved organic matter, which originates from phytoplankton, holds as much carbon as Earth’s atmosphere; yet, the biological processes governing its fate are primarily studied under idealized laboratory conditions or through indirect measures such as genome sequencing. In this work, we used isotope labeling to directly quantify uptake of complex carbon pools from the two primary sources of marine organic carbon (diatoms and cyanobacteria) by a natural microbial community. Furthermore, our data show that carbon pools are partitioned into distinct microbial lineages whose physiological properties and resource acquisition strategies match the chemical nature of their preferred substrates. Our results providemore » ecological and functional insights into the patterns of microbial community structure changes that occur during marine phytoplankton blooms.« less

Abstract Background Total DNA (intracellular, iDNA and extracellular, eDNA) from ancient permafrost records the mixed genetic repository of the past and present microbial populations through geological time. Given the exceptional preservation of eDNA under perennial frozen conditions, typical metagenomic sequencing of total DNA precludes the discrimination between fossil and living microorganisms in ancient cryogenic environments. DNA repair protocols were combined with high throughput sequencing (HTS) of separate iDNA and eDNA fraction to reconstruct metagenome-assembled genomes (MAGs) from ancient microbial DNA entrapped in Siberian coastal permafrost. Results Despite the severe DNA damage in ancient permafrost, the coupling of DNA repair andmore » HTS resulted in a total of 52 MAGs from sediments across a chronosequence (26–120 kyr). These MAGs were compared with those derived from the same samples but without utilizing DNA repair protocols. The MAGs from the youngest stratum showed minimal DNA damage and thus likely originated from viable, active microbial species. Many MAGs from the older and deeper sediment appear related to past aerobic microbial populations that had died upon freezing. MAGs from anaerobic lineages, including Asgard archaea, however exhibited minimal DNA damage and likely represent extant living microorganisms that have become adapted to the cryogenic and anoxic environments. The integration of aspartic acid racemization modeling and metaproteomics further constrained the metabolic status of the living microbial populations. Collectively, combining DNA repair protocols with HTS unveiled the adaptive strategies of microbes to long-term survivability in ancient permafrost. Conclusions Our results indicated that coupling of DNA repair protocols with simultaneous sequencing of iDNA and eDNA fractions enabled the assembly of MAGs from past and living microorganisms in ancient permafrost. The genomic reconstruction from the past and extant microbial populations expanded our understanding about the microbial successions and biogeochemical alterations from the past paleoenvironment to the present-day frozen state. Furthermore, we provided genomic insights into long-term survival mechanisms of microorganisms under cryogenic conditions through geological time. The combined strategies in this study can be extrapolated to examine other ancient non-permafrost environments and constrain the search for past and extant extraterrestrial life in permafrost and ice deposits on Mars.« less

Carbon dioxide (CO₂) has been shown to contribute to human health consequences indoors, such as shortness of breath, nasal and optic irritation, dizziness, and nausea. Here in this work, we explore the potential of metal–organic frameworks (MOFs) as highly-porous, crystalline sorbents for sensitive colorimetric CO₂ detection. In particular, the zeolitic imidazolate framework (ZIF-8) is chosen as the sorptive material due to its chemical stability and tunable CO₂ affinity. The colorimetric gas sensor is developed in methanol with three components: (i) MOF ZIF-8 as a high surface area adsorbent; (ii) ethylenediamine (ED) as the CO₂-affinitive basic function; and (iii) phenolsulfonpthalein (PSP)more » as the pH indicator. Colorimetric assays and ratiometric analysis confirm a colorimetric response to variable CO₂ concentrations of relevance to indoor air quality. The color response is attributed to a zwitterion mechanism whereby ED reacts with CO₂ to form a zwitterionic intermediate. This intermediate is then deprotonated by the pH indicator, shifting the pH and inducing a color change. Given its simple fabrication, rapid and obvious response, and stability in ambient environment, the ZIF-8-based colorimetric sensor provides a promising route for an improved indoor air quality monitoring.« less