Sorption/Desorption Behavior and Mechanism of NH₄⁺ by Biochar as a Nitrogen Fertilizer Sustained-Release Material

Biochar, the pyrolysis product of biomass material with limited oxygen, has the potential to increase crop production and sustained-release fertilizer, but the understanding of the reason for improving soil fertility is insufficient, especially the behavior and mechanism of ammonium sulfate. In this study, the sorption/desorption effect of NH₄⁺ by biochar deriving from common agricultural wastes under different preparation temperatures from 200 to 500 °C was studied and its mechanism was discussed. The results showed that biochar displayed excellent retention ability in holding NH₄⁺ above 90% after 21 days under 200 °C preparation temperature, and it can be deduced that the oxygen functional groups, such as carboxyl and keto group, played the primary role in adsorbing NH₄⁺ due to hydrogen bonding and electrostatic interaction. The sorption/desorption effect and mechanism were studied for providing an optional way to dispose of agricultural residues into biochar as a nitrogen fertilizer sustained-release material under suitable preparation temperature

Enhanced Single-Photon Emission from Carbon-Nanotube Dopant States Coupled to Silicon Microcavities

Single-walled carbon nanotubes are a promising material as quantum light sources at room temperature and as nanoscale light sources for integrated photonic circuits on silicon. Here, we show that the integration of dopant states in carbon nanotubes and silicon microcavities can provide bright and high-purity single-photon emitters on a silicon photonics platform at room temperature. We perform photoluminescence spectroscopy and observe the enhancement of emission from the dopant states by a factor of ∼50, and cavity-enhanced radiative decay is confirmed using time-resolved measurements, in which a ∼30% decrease of emission lifetime is observed. The statistics of photons emitted from the cavity-coupled dopant states are investigated by photon-correlation measurements, and high-purity single photon generation is observed. The excitation power dependence of photon emission statistics shows that the degree of photon antibunching can be kept high even when the excitation power increases, while the single-photon emission rate can be increased to ∼1.7 × 10⁷ Hz

Volatile Organic Compound Gas-Sensing Properties of Bimodal Porous α‑Fe₂O₃ with Ultrahigh Sensitivity and Fast Response

Porous solid with multimodal pore size distribution provides plenty of advantages including large specific surface area and superior mass transportation to achieve high gas-sensing performances. In this study, α-Fe₂O₃ nanoparticles with bimodal porous structures were prepared successfully through a nanocasting pathway, adopting the bicontinuous 3D cubic symmetry mesoporous silica KIT-6 as the hard template. Its structure and morphology were characterized by X-ray diffraction, nitrogen adsorption–desorption, transmission electron microscopy, and so on. Furthermore, the gas sensor fabricated from this material exhibited excellent gas-sensing performance to several volatile organic compounds (acetone, ethyl acetate, isopropyl alcohol, <i>n</i>-butanol, ethanol, and methanol), such as ultrahigh sensitivity, rapid response speed (less than 10 s) and recovery time, good reproducibility, as well as stability. These would be associated with the desirable pore structure of the material, facilitating the molecules diffusion toward the entire sensing surface, and providing more active sensing sites for analytical gas

Figure of Merit for Carbon Nanotube Photothermoelectric Detectors

Carbon nanotubes (CNTs) have emerged as promising materials for visible, infrared, and terahertz photodetectors. Further development of these photodetectors requires a fundamental understanding of the mechanisms that govern their behavior as well as the establishment of figures of merit for technology applications. Recently, a number of CNT detectors have been shown to operate based on the photothermoelectric effect. Here we present a figure of merit for these detectors, which includes the properties of the material and the device. In addition, we use a suite of experimental characterization methods for the thorough analysis of the electrical, thermoelectric, electrothermal, and photothermal properties of the CNT thin-film devices. Our measurements determine the quantities that enter the figure of merit and allow us to establish a path toward future performance improvements

Photothermoelectric p–n Junction Photodetector with Intrinsic Broadband Polarimetry Based on Macroscopic Carbon Nanotube Films

Light polarization is used in the animal kingdom for communication, navigation, and enhanced scene interpretation and also plays an important role in astronomy, remote sensing, and military applications. To date, there have been few photodetector materials demonstrated to have direct polarization sensitivity, as is usually the case in nature. Here, we report the realization of a carbon-based broadband photodetector, where the polarimetry is intrinsic to the active photodetector material. The detector is based on p–n junctions formed between two macroscopic films of single-wall carbon nanotubes. A responsivity up to ∼1 V/W was observed in these devices, with a broadband spectral response spanning the visible to the mid-infrared. This responsivity is about 35 times larger than previous devices without p–n junctions. A combination of experiment and theory is used to demonstrate the photothermoelectric origin of the responsivity and to discuss the performance attributes of such devices

Carbon Nanotube Terahertz Detector

Terahertz (THz) technologies are promising for diverse areas such as medicine, bioengineering, astronomy, environmental monitoring, and communications. However, despite decades of worldwide efforts, the THz region of the electromagnetic spectrum still continues to be elusive for solid state technology. Here, we report on the development of a powerless, compact, broadband, flexible, large-area, and polarization-sensitive carbon nanotube THz detector that works at room temperature. The detector is sensitive throughout the entire range of the THz technology gap, with responsivities as high as ∼2.5 V/W and polarization ratios as high as ∼5:1. Complete thermoelectric and opto-thermal characterization together unambiguously reveal the photothermoelectric origin of the THz photosignal, triggered by plasmonic absorption and collective antenna effects, and suggest that judicious design of thermal management and quantum engineering of Seebeck coefficients will lead to further enhancement of device performance

Solvent- and Wavelength-Dependent Photoluminescence Relaxation Dynamics of Carbon Nanotube sp³ Defect States

Photoluminescent sp³ defect states introduced to single wall carbon nanotubes (SWCNTs) through low-level covalent functionalization create new photophysical behaviors and functionality as a result of defect sites acting as exciton traps. Evaluation of relaxation dynamics in varying dielectric environments can aid in advancing a more complete description of defect-state relaxation pathways and electronic structure. Here, we exploit helical wrapping polymers as a route to suspending (6,5) SWCNTs covalently functionalized with 4-methoxy­benzene in solvent systems including H₂O, D₂O, methanol, dimethylformamide, tetrahydrofuran, and toluene, spanning a range of dielectric constants from 80 to 3. Defect-state photoluminescence decays were measured as a function of emission wavelength and solvent environment. Emission decays are biexponential, with short lifetime components on the order of 65 ps and long components ranging from around 100 to 350 ps. Both short and long decay components increase as emission wavelength increases, while only the long lifetime component shows a solvent dependence. We demonstrate that the wavelength dependence is a consequence of thermal detrapping of defect-state excitons to produce mobile E₁₁ excitons, providing an important mechanism for loss of defect-state population. Deeper trap states (i.e., those emitting at longer wavelengths) result in a decreased rate for thermal loss. The solvent-independent behavior of the short lifetime component is consistent with its assignment as the characteristic time for redistribution of exciton population between bright and dark defect states. The solvent dependence of the long lifetime component is shown to be consistent with relaxation via an electronic to vibrational energy transfer mechanism, in which energy is resonantly lost to solvent vibrations in a complementary mechanism to multiphonon decay processes

Low-Temperature Single Carbon Nanotube Spectroscopy of sp³ Quantum Defects

Aiming to unravel the relationship between chemical configuration and electronic structure of sp³ defects of aryl-functionalized (6,5) single-walled carbon nanotubes (SWCNTs), we perform low-temperature single nanotube photoluminescence (PL) spectroscopy studies and correlate our observations with quantum chemistry simulations. We observe sharp emission peaks from individual defect sites that are spread over an extremely broad, 1000–1350 nm, spectral range. Our simulations allow us to attribute this spectral diversity to the occurrence of six chemically and energetically distinct defect states resulting from topological variation in the chemical binding configuration of the monovalent aryl groups. Both PL emission efficiency and spectral line width of the defect states are strongly influenced by the local dielectric environment. Wrapping the SWCNT with a polyfluorene polymer provides the best isolation from the environment and yields the brightest emission with near-resolution limited spectral line width of 270 μeV, as well as spectrally resolved emission wings associated with localized acoustic phonons. Pump-dependent studies further revealed that the defect states are capable of emitting single, sharp, isolated PL peaks over 3 orders of magnitude increase in pump power, a key characteristic of two-level systems and an important prerequisite for single-photon emission with high purity. These findings point to the tremendous potential of sp³ defects in development of room temperature quantum light sources capable of operating at telecommunication wavelengths as the emission of the defect states can readily be extended to this range <i>via</i> use of larger diameter SWCNTs

Phylogenetic Trees of Six Representative Isolates Based on Comparison of 16S rDNA and Five Putative Virulence-Associated-Factor Genes with Known Sequences

<p>Swine isolates from Sichuan ( S. suis ZYS3 and S. suis ZYS8) labeled in green, human isolates ( S. suis ZYH13 and S. suis ZYH14) from Sichuan labeled in red, Jiangsu isolates from 1998 ( S. suis 9801 and S. suis Habb) labeled in blue, and the standard highly virulent strain S. suis P1/7 labeled in pink. All representative strains from other streptococcus species or isolates of S. suis 2 are as indicated in the tree. </p

RFLP Analysis of Different S. suis 2 Isolates

<p> S. suis S10: a highly virulent strain from China; <i>S</i>. <i>suis</i> 9801: swine isolate from Jiangsu Province in 1998; S. suis Habb: human isolate from Jiangsu Province in 1998; S. suis ZYS3: swine isolate from Sichuan Province in 2005; S. suis ZYH13: human isolate from Sichuan Province in 2005; M: 1 kb DNA Ladder (MBI Ferments, Gdansk, Poland). </p