Project description:Molecular sieving membranes with sufficient and uniform nanochannels that break the permeability-selectivity trade-off are desirable for energy-efficient gas separation, and the arising two-dimensional (2D) materials provide new routes for membrane development. However, for 2D lamellar membranes, disordered interlayer nanochannels for mass transport are usually formed between randomly stacked neighboring nanosheets, which is obstructive for highly efficient separation. Therefore, manufacturing lamellar membranes with highly ordered nanochannel structures for fast and precise molecular sieving is still challenging. Here, we report on lamellar stacked MXene membranes with aligned and regular subnanometer channels, taking advantage of the abundant surface-terminating groups on the MXene nanosheets, which exhibit excellent gas separation performance with H2 permeability >2200?Barrer and H2/CO2 selectivity >160, superior to the state-of-the-art membranes. The results of molecular dynamics simulations quantitatively support the experiments, confirming the subnanometer interlayer spacing between the neighboring MXene nanosheets as molecular sieving channels for gas separation.
Project description:Oxide materials are important candidates for the next generation of electronics due to a wide array of desired properties, which they can exhibit alone or when combined with other materials. While SrTiO3 (STO) is often considered a prototypical oxide, it, too, hosts a wide array of unusual properties, including a 2-dimensional electron gas (2DEG), which can form at the surface when exposed to ultraviolet (UV) light. Using layer-by-layer growth of high-quality STO films, we show that the 2DEG only forms with the SrO termination and not with the TiO2 termination, contrary to expectation. This dichotomy of the observed angle-resolved photoemission spectroscopy (ARPES) spectra is similarly seen in BaTiO3 (BTO), in which the 2DEG is only observed for BaO-terminated films. These results will allow for a deeper understanding and better control of the electronic structure of titanate films, substrates, and heterostructures.
Project description:As a major contributor to agricultural greenhouse gas (GHG) emissions, it has been suggested that reducing animal agriculture or consumption of animal-derived foods may reduce GHGs and enhance food security. Because the total removal of animals provides the extreme boundary to potential mitigation options and requires the fewest assumptions to model, the yearly nutritional and GHG impacts of eliminating animals from US agriculture were quantified. Animal-derived foods currently provide energy (24% of total), protein (48%), essential fatty acids (23-100%), and essential amino acids (34-67%) available for human consumption in the United States. The US livestock industry employs 1.6 × 106 people and accounts for $31.8 billion in exports. Livestock recycle more than 43.2 × 109 kg of human-inedible food and fiber processing byproducts, converting them into human-edible food, pet food, industrial products, and 4 × 109 kg of N fertilizer. Although modeled plants-only agriculture produced 23% more food, it met fewer of the US population's requirements for essential nutrients. When nutritional adequacy was evaluated by using least-cost diets produced from foods available, more nutrient deficiencies, a greater excess of energy, and a need to consume a greater amount of food solids were encountered in plants-only diets. In the simulated system with no animals, estimated agricultural GHG decreased (28%), but did not fully counterbalance the animal contribution of GHG (49% in this model). This assessment suggests that removing animals from US agriculture would reduce agricultural GHG emissions, but would also create a food supply incapable of supporting the US population's nutritional requirements.
Project description:Environmentally friendly degradable sensors with both hazardous gases and pressure efficient sensing capabilities are highly desired for various promising applications, including environmental pollution monitoring/prevention, wisdom medical, wearable smart devices, and artificial intelligence. However, the transient gas and pressure sensors based on only identical sensing material that concurrently meets the above detection needs have not been reported. Here, we present transient all-MXene NO2 and pressure sensors employing three-dimensional porous crumpled MXene spheres prepared by ultrasonic spray pyrolysis technology as the sensing layer, accompanied with water-soluble polyvinyl alcohol substrates embedded with patterned MXene electrodes. The gas sensor achieves a ppb-level of highly selective NO2 sensing, with a response of up to 12.11% at 5 ppm NO2 and a detection range of 50 ppb-5 ppm, while the pressure sensor has an extremely wide linear pressure detection range of 0.14-22.22 kPa and fast response time of 34 ms. In parallel, all-MXene NO2 and pressure sensors can be rapidly degraded in medical H2O2 within 6 h. This work provides a new avenue toward environmental monitoring, human physiological signal monitoring, and recyclable transient electronics.
Project description:We investigate, and quantify, changes in structure and surface terminations of epitaxial thin films of titanium carbide (Ti3C2) MXene, when treated by sodium hydroxide solution followed by vacuum annealing at 550 °C. Using X-ray photoelectron spectroscopy and scanning transmission electron microscopy, we show that NaOH treatment produce an increase in the c-lattice parameter together with an increase in the O terminations and a decrease in the F terminations. There is also an increase in the percentage of the binding energy of Ti-species in Ti 2p XPS region, which suggests an increase in the overall oxidation state of Ti. After subsequent annealing, the c-lattice parameter is slightly reduced, the overall oxidation state of Ti is decreased, and the F surface terminations are further diminished, leaving a surface with predominantly O as the surface terminating species. It is important to note that NaOH treatment facilitates removal of F at lower annealing temperatures than previously reported, which in turn is important for the range of attainable properties.
Project description:Bioactive gibberellins (GAs or diterpenes) are essential hormones in land plants that control many aspects of plant growth and development. In flowering plants, 13-OH GAs (having low bioactivity-for example, GA1) and 13-H GAs (having high bioactivity-for example, GA4) frequently coexist in the same plant. However, the identity of the native Arabidopsis thaliana 13-hydroxylase GA and its physiological functions remain unknown. Here, we report that cytochrome P450 genes (CYP72A9 and its homologues) encode active GA 13-hydroxylases in Brassicaceae. Plants overexpressing CYP72A9 exhibited semi-dwarfism, which was caused by significant reduction in GA4 levels. Biochemical assays revealed that recombinant CYP72A9 protein catalysed the conversion of 13-H GAs to the corresponding 13-OH GAs. CYP72A9 was expressed predominantly in developing seeds in Arabidopsis. Freshly harvested seeds of cyp72a9 mutants germinated more quickly than the wild type, whereas stratification-treated seeds and seeds from long-term storage did not. The evolutionary origin of GA 13-oxidases from the CYP72A subfamily was also investigated and discussed here.
Project description:A large amount of gas, such as CO, accumulates in a coal mine after an explosion, leading to CO poisoning. In this study, a self-developed platform was used to eliminate CO from coal mines and determine the mass of the rapidly eliminated CO and its concentration in the eliminated gases. Equations were derived to calculate the amount of CO eliminated and the removing rate. The results showed that a rapid removing reagent in the form of nonprecious metal catalysts is useful for removing CO. Removing agents with larger masses facilitated the activation, irrespective of the CO concentration. For removing reagent amounts of 10, 15, 20, 25, and 30 g, the amount of CO eliminated, the removing rate, and the time required to complete catalytic oxidation increased sequentially. The CO removing process could be divided into three stages (I, II, and III) based on the variations in the CO, CO2, and O2 concentrations during CO removing. The removing reagent first chemically adsorbs CO and O2, and then desorbs CO2. The final CO concentration tends to 0, the O2 concentration remains stable, and the CO2 concentration decreases. This shows that the ablation agent has an impact on the changes in the CO and CO2 concentrations.
Project description:BioDeNOx is an integrated physicochemical and biological process for the removal of nitrogen oxides (NOx) from flue gases. In this process, the flue gas is purged through a scrubber containing a solution of Fe(II)EDTA2-, which binds the NOx to form an Fe(II)EDTA.NO2- complex. Subsequently, this complex is reduced in the bioreactor to dinitrogen by microbial denitrification. Fe(II)EDTA2-, which is oxidized to Fe(III)EDTA- by oxygen in the flue gas, is regenerated by microbial iron reduction. In this study, the microbial communities of both lab- and pilot-scale reactors were studied using culture-dependent and -independent approaches. A pure bacterial strain, KT-1, closely affiliated by 16S rRNA analysis to the gram-positive denitrifying bacterium Bacillus azotoformans, was obtained. DNA-DNA homology of the isolate with the type strain was 89%, indicating that strain KT-1 belongs to the species B. azotoformans. Strain KT-1 reduces Fe(II)EDTA.NO2- complex to N2 using ethanol, acetate, and Fe(II)EDTA2- as electron donors. It does not reduce Fe(III)EDTA-. Denaturing gradient gel electrophoresis analysis of PCR-amplified 16S rRNA gene fragments showed the presence of bacteria closely affiliated with members of the phylum Deferribacteres, an Fe(III)-reducing group of bacteria. Fluorescent in situ hybridization with oligonucleotide probes designed for strain KT-1 and members of the phylum Deferribacteres showed that the latter were more dominant in both reactors.
Project description:Water-repellent glass surfaces have become increasingly important to ensure clear visibility in outdoor cameras, sensors, and automotive windows. In this study, we investigated a process for the formation of nanoscale structures on a glass surface using chemical reactions with hydrogen fluoride gas. Using this approach, nanostructures with superhydrophobicity, superhydrophilicity, and antireflective properties were formed on glass surfaces with minimal processing time. This mask-free method, working at atmospheric pressure, can be efficiently integrated within the float process, a mainstream manufacturing technique for flat glass, to introduce nanostructures onto the glass surface. Notably, after treatment with (1-H, 1-H, 2-H, 2-H-tridecafluorooctyl)trimethoxysilane (FAS-13), a typical hydrophobic agent, the resulting surface exhibited a maximum water contact angle of 162°. Owing to its low reflectivity and superhydrophobicity, this surface is anticipated to find applications in not only the design of architectural window glass and vehicle windows but also the development of solar panels and sensor cover glass for autonomous vehicles.
Project description:Convoluted cortical folding and neuronal wiring are 2 prominent attributes of the mammalian brain. However, the macroscale intrinsic relationship between these 2 general cross-species attributes, as well as the underlying principles that sculpt the architecture of the cerebral cortex, remains unclear. Here, we show that the axonal fibers connected to gyri are significantly denser than those connected to sulci. In human, chimpanzee, and macaque brains, a dominant fraction of axonal fibers were found to be connected to the gyri. This finding has been replicated in a range of mammalian brains via diffusion tensor imaging and high-angular resolution diffusion imaging. These results may have shed some lights on fundamental mechanisms for development and organization of the cerebral cortex, suggesting that axonal pushing is a mechanism of cortical folding.