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Plant diseases result in 20-40% of agricultural loss every year worldwide. Timely detection of plant diseases can effectively prevent the development and spread of diseases and ensure the agricultural yield. High-throughput and rapid methods are in great demand. This review investigates the advanced application of Raman spectroscopy (RS) and surface-enhanced Raman spectroscopy (SERS) in the detection of plant diseases. The determination of bacterial diseases and stress-induced diseases, fungal diseases, viral diseases, pests in beans, and mycotoxins related to plant diseases using RS and SERS are discussed in detail. Then, biomarkers for RS and SERS detection are analyzed with regard to plant disease diagnosis. Finally, the advantages and challenges are further illustrated. Additionally, potential alternatives are proposed for the challenges. The review is expected to provide a reference and guidance for the use of RS and SERS in plant disease diagnostics.

MXene is a growing two-dimensional material family of transition metal carbides and nitrides and showing great promise in various applications, such as energy storage, water treatment, composites, electromagnetic interference shielding, etc. In all these applications, at least one of the MXene flake sides is in contact with a medium of interest. So the wetting behaviors of MXene are critical for the performance of MXene. Although the hydrophilicity of MXene is unquestionable, the reported contact angles of MXene have covered an extensive range. Additionally, the surface energy of MXene flakes is surprisingly poorly known and rarely studied. In this work, the static contact angles of MXene films were studied using water, glycerol, and diiodomethane. The surface energy of MXene films has a range of 49.92 ± 2.01 to 62.44 ± 0.25 mJ m−2, calculated based on the measured contact angles. The loading, drying and storage condition of the MXene films have various impacts on their contact angles and surface energy. The root cause for the wide-range of contact angles is related to the surface chemistry of the MXene films. Organic contamination and surface oxidation are responsible for the scattering water contact angle. The contact angles are mass loading-independent for MXene films with loadings from 0.3 to 2 mg cm−2. The surface energy and its acid–base component are sensitive to the delamination methods and MXene compositions, while the dispersion component of the surface energy is stable. These findings will provide valuable insight and guidance for measuring contact angles of MXene films and the rational design and synthesis of MXene-based films, composites, coatings, and energy storage devices.

Gas hydrates have an important role in environmental and astrochemistry, as well as in energy materials research. Although it is widely accepted that gas accumulation is an important and necessary process during hydrate nucleation, how guest molecules aggregate remains largely unknown. Here, we have performed molecular dynamics simulations to clarify the nucleation path of methane hydrate. We demonstrated that methane gather with a three-body aggregate pattern corresponding to the free energy minimum of three-methane hydrophobic interaction. Methane molecules fluctuate around one methane which later becomes the central gas molecule, and when several methanes move into the region within 0.8 nm of the potential central methane, they act as directional methane molecules. Two neighbor directional methanes and the potential central methane form a three-body aggregate as a regular triangle with a distance of ~6.7 Å which is well within the range of typical methane-methane distances in hydrates or in solution. We further showed that hydrate nucleation and growth is inextricably linked to three-body aggregates. By forming one, two, and three three-body aggregates, the possibility of hydrate nucleation at the aggregate increases from 3/6, 5/6 to 6/6. The results show three-body aggregation of guest molecules is a key step in gas hydrate formation.

Recent studies have shown impressive transport behaviors of water and ions within lamellar MXene membranes, which endows great promise in developing advanced separation application based high performance MXene membranes. However, most of the researches focused on modification of MXene nanoflakes and optimizing interlayer distance, leaving the impact of membrane fabrication process marginal. In this work, we studied the water flux of membranes made by vacuum filtration using delaminated MXene nanoflakes as the building-blocks. Our results show that the water permeability is extremely sensitive to the process, especially at the drying process, loading and deposit rate of nanoflakes (the feeding concentration). We find that the voids from less ordered stack rather than in-plane defects and interlayer galleries contribute to the large water permeability. The voids can be effectively avoided via deposition of MXene nanoflakes at a slow rate. Manipulating the stack of MXene nanoflakes during vacuum filtration and drying are critical for development of MXene membranes with desired performance for water permeation.

Ultrathin, transparent, and free-standing films assembled from low-dimensional nanomaterials (LDMs) are promising for various applications, including transparent heaters and membranes. However, the intact separation of the assembled films, especially those with controlled ultrathin thickness from deposited substrates, is a tremendous challenge, particularly for fast peeling off via self-detaching. Herein, we propose a versatile method to rapidly peel off ultrathin assembled LDM films, including three types of carbon nanotubes, vermiculite, Ag nanowires, and carbon nanotube@graphene, by dissolving the MXene interlayer from the layer-by-layer filtered MXene/LDM Janus films using diluted H

Theoretically, impurities can be excluded from hydrate structure and pure water can be extracted during hydrate formation. We achieved the heavy metal (Cu2+ in this study) removal from aqueous solution by hydrate process. The hydrate samples were analyzed by X-ray computed tomography (CT). Boundary layer analysis was conducted to reveal the mechanism of ion exclusion. Moreover, the effect of initial concentrations on removal characteristics was analyzed and the solid–liquid separations were optimized. The main findings were as follows: (1) Solution pockets and trapped solution were identified as the limiting and controlling factors for the removal efficiency; (2) nonguest molecule exclusion and directed substance migration occur during hydrate formation; and (3) this method was suitable for relatively high concentration wastewater treatment application, and a removal efficiency of 96.63% could be achieved. We then proposed a theory in regard to the concentration gradient and directed substance migration d...

Desalination via hydrate processes is promising in producing freshwater at low energy cost. However, it is a great challenge to instantaneously produce and form large amount of hydrates in short time, particularly with salts presence. In this study, we used cheap and easily separated graphite particles to promote hydrate based desalination. The added graphite can promote the formation of hydrate, greatly shortening the induction time. The desalination efficiency was also enhanced due to the introduced graphite. Combined graphite and stirring, both the desalination efficiency and water conversion ratio were boosted. The impact of particle sizes of graphite on hydrate formation was found to be different at static state and stirring. The proposed hydrate based desalination is almost independent on treated volume. Additionally, this method can use the nature chilling, which is potential in further reducing the energy cost of desalination via hydrate. The findings in this study would help rationally choose and design promoting agents and hydrate processes for facilitating hydrate formation and desalination via hydrates.

Measuring the changes in tumor cell surface temperature can provide insights into cellular metabolism and pathological features, which is significant for targeted chemotherapy and hyperthermic therapy. However, conventional micro-nano scale methods are invasive and can only measure the temperature of cells across a single plane, which excludes specific organelles. In this study, fluorescence quantum dots (QDs) are functionalized with the membrane transport protein transferrin (Tf) as a thermo-sensor specific for tumor cell membrane. The covalent conjugation is optimized to maintain the relative fluorescence intensity of the Tf-QDs to >90%. In addition, the Tf-QDs undergo changes in the fluorescence spectra as a function of temperature, underscoring its thermo-sensor function. Double helix point spread function imaging optical path is designed to locate the probe at nanoscale, and 3D thermal imaging technology is proposed to measure the local temperature distribution and direction of heat flux on the tumor cell surface. This novel targeted nanoscale 3D thermometry method can be a highly promising tool for measuring the local and global temperature distribution across intracellular organelles.

Highly efficient composite photocatalysts were prepared through annealing partially oxidized Ti3C2 MXene with melamine under N2 flow. The two-dimensional Ti3C2 MXene was aforehand partially oxidized to form TiO2-Ti3C2 nanosheet by precisely controlling the oxidation conditions. Ternary g-C3N4/TiO2/Ti3C2 MXene photocatalyst was constructed by coating melamine derived g-C3N4 on TiO2-Ti3C2 nanosheet. The photogenerated electron-hole separation was significantly enhanced by the S-scheme heterojunction. Ti3C2 tightly bonded with TiO2 benefits transfer and aggregation of photo-induced holes. The composite material has an interconnected nanosheet structure, which increases the absorption of light and the reaction interface between gaseous reactant and photocatalysts. When evaluated as NOx purification photocatalysts, the fabricated composites get the high NO removal efficiency and low NO2 generation. Under visible light, NO removal efficiency of the composite photocatalyst can reach up to 66.3%, which is significantly better than the g-C3N4 or TiO2-Ti3C2. This work demonstrates that moderately oxidized Ti3C2 MXene is a good candidate for the construction of high-performance air purification photocatalysts.

Significant solvent effects on enantioselection exist in the reaction of Cu-catalyzed asymmetric conjugate addition of alkylzinc reagents to α,β-unsaturated carbonyl compounds. Results of our DFT study suggest that solvent effects on enantioselection can be caused by structural changes in the stereodetermining Transition States (TS). We have seen how unconventional hydrogen bonding of the nucleophilic solvent results in a change of the computed optical yield comparable to that caused by well-known coordination of the solvent to the electrophilic metal center.

A Cu-catalyzed asymmetric alkynylation of cyclic N-sulfonyl ketimines was developed, providing the corresponding chiral α-tertiary amines with up to 98% ee. The method tolerates some variations in cyclic N-sulfonyl ketimine and alkyne scope. These products could be used in several transformations, in particular, the products of 6-membered cyclic N-sulfonyl ketimines could be easily converted to linear chiral α-tertiary amines. This asymmetric alkynylation provides an efficient, gram-scale, low-cost transition-metal catalyzed synthesis of chiral α-tetrasubstituted propargylamines.

Graphene has excellent potential as a sulfur host in a lithium–sulfur (Li–S) battery owing to its outstanding electrical conductivity and robust mechanical properties. However, graphene itself cannot effectively confine sulfur and suppress polysulfide diffusion, leading to severely fast capacity decay. Herein, nitrogen-doped tubular/porous carbon channels were implanted on graphene sheets (NTPC–G) via a double-template method, with graphene sheets as the shape-directed agents and NiCo–carbonate hydroxide nanowires as the guides of tubular channels. The resultant one-dimensional hollow tubular carbon and two-dimensional graphene nanosheets were wrapped by nitrogen-doped porous carbon layers to construct the unique three-dimensional sandwich-type architectures. The adopted graphene sheets functioned as conductive networks and robust frameworks; moreover, the nitrogen-doped tubular/porous carbon channels comprising hollow tubular carbon and porous carbon coating layers implanted on graphene frameworks served as the sulfur-confined space and polysulfide reservoirs. On integrating these fascinating benefits into one electrode material, sulfur and NTPC–G composites (S@NTPC–G) delivered high rate capability (563 mA h g−1 at 6 C) and good cycle stability up to 600 cycles. This rational construction of tubular/porous carbon channels on nanosheet materials with comprehensive advantages could be promising and applicable in rechargeable Li–S batteries and other advanced energy storage devices.

A regio- and enantioselective copper-catalyzed 1,4-conjugate addition of trimethylaluminium to linear δ-aryl-substituted α,β,γ,δ-unsaturated alkyl ketones was developed. A series of γ,δ-unsaturated alkyl ketones were obtained in good yields with high regio- and enantioselectivity (up to 88% ee and 96:4 dr). Expansion of the reaction scope to substrates containing aromatic heterocycles also afforded good yields and enantioselectivities (up to 91% ee) with very high regioselectivities, exclusively providing the single 1,4-products.

The largest sources of hydrocarbons worldwide are distributed in the permafrost and submarine sediments in the form of methane hydrates, but exploitation of these hydrocarbons is still years away from being economical, safe, and commercially viable; thus, further research is needed. To analyze the characteristics of methane hydrate (MH) dissociation and evaluate the gas production during the application of different MH decomposition methods, this study firstly compared MH dissociation during depressurization, thermal stimulation, and combined method (depressurization + thermal stimulation) treatments using magnetic resonance imaging (MRI) in situ observation. In particular, the influences of back-pressure and temperature on hydrate dissociation, the hydrate saturation, the rate of hydrate dissociation and MRI images from each of the three methods were investigated. The results proved that during application of the depressurization and combined methods at different back-pressures (2.2–2.6 MPa), the MH dissociation proceeded via radial dissociation rather than axial dissociation; moreover, during the application of the thermal stimulation method at different dissociation temperatures (278.15–288.15 K), the MH dissociated uniformly. Overall, a combination of depressurization and thermal stimulation at the initial stage of hydrate decomposition was proposed and comparison of the three methods demonstrated that the combined method had obvious advantages for methane treatment. Specifically, the combined method was capable of solving the problems related to low gas production and poor energy efficiency that were encountered when using either the depressurization or thermal stimulation method alone.

Herein, we describe a high yielding and switchable synthesis of a range of functionalized pyridines and pyrroles via Cu-catalyzed cascade reactions with alkynes and N-sulfonyl azadienes which are readily available from saccharin. Both unsymmetrical 2,4,6-trisubstituted pyridines and multi-substituted pyrroles could be transformed into some bioactive compounds and chiral ligands.

Pseudocapacitors, which store charge through fast reversible redox reactions occuring at the surface of the electrode, could offer higher specific capacitance than electrochemical double-layer capacitors (EDLCs). However, the prime pseudocapacitive phase, transition metal oxides usually have poor electronic conductivity, limiting their practical application. Here, we fabricated highly conductive HxMoO3−y nanobelts as electrode materials for pseudocapacitors. This electrode has demonstrated great electrochemical activity in various aqueous cation solutions with the highest volumetric capacitance of over 350 F cm−3. Significantly, this electrode has high specific capacitance as well as excellent cycling stability in sea water. Moreover, this hybrid composite also exhibits remarkable ion electrosorptive capacity (4 mg g−1) as a desalination electrode.

The trace SO2 in the atmosphere can cause serious degradation in performance of proton exchange membrane fuel cells. To mitigate this problem, calcium oxide/carbon foam composites were designed and fabricated via a facile one-pot method using phenol formaldehyde resin as the carbon precursor, with polyurethane foam as the template and nano-sized CaCO3 as the precursor of CaO. The composite shows a promising retention capacity for trace SO2 and enhanced cycle stability due to the combined effect of well-distributed CaO particles, the hierarchical porous structure and the anchoring effect of the carbon foam matrix. It has been demonstrated that the as-made composite is a promising adsorbent for the efficient removal of the trace SO2 from air, suggesting this composite can be a potential candidate for desulfurization of the air entering proton exchange membrane fuel cells.

A three-dimensional (3D) structure carbon foam for microwave absorption is synthesized by a facile template method using coal liquefaction residue (CLR) as carbon source. The results have shown that the sample made under optimized conditions has exhibited a broad effective absorption bandwidth up to 5.8 GHz in a range of 2–18 GHz with a reflection loss ≤ −10 dB. The magnetic Fe species derived from CLR are homogeneously dispersed in the 3D scaffold of carbon foam, which increase the magnetic loss, interface polarization relaxation and the synergetic effect between the magnetic Fe species and the dielectric carbon foam matrix.

A direct enantioselective C-acylation of 3-substituted benzofuran-2(3H)-ones (with up to 97% ee) was developed using a chiral bicyclic imidazole catalyst OAc-DPI and an achiral tertiary amine additive DIPEA. The reaction mechanism for the direct C-acylation has been investigated using both experimental and theoretical studies.

Graphene-incorporated nitrogen-rich carbon composite with nitrogen content of ca. 10 wt.% has been synthesized by an effective yet simple hydrothermal reaction of glucosamine in the presence of graphene oxide (GO). The nitrogen content of carbon composite is nearly twice as high as that of hydrothermal carbon without graphene. GO is favorable for the high nitrogen doping in the carbon composite by the reaction between the glucosamine-released ammonia and GO. The hydrothermal carbon composite is further activated by KOH, and graphene in the activated carbon composite demonstrates a positive effect of increasing specific surface area, pore volume and electrical conductivity, resulting in superior electrochemical performance. The activated carbon composite with higher specific surface area and micropore volume possesses higher specific capacitance with a value of 300 F g−1 at 0.1 A g−1 in 6 M KOH aqueous solution in the two electrode cell. Larger mesopore volume and higher conductivity of the activated carbon composite will provide fast ion and electron transfer, thus leading to higher rate capacity with a capacitance retention of 76% at 8 A g−1 in comparison to the activated hydrothermal carbon without graphene.

Two-dimensional carbon belts (CBs) made of carbon nanofibers (CNFs) supported on a carbon foam (CFoam) substrate have been synthesized by a procedure involving carbonization of polyamic acid (PAA)/Ni(NO3)2 solution impregnated polyurethane foam in flowing H2 at 700 °C and catalytic chemical vapor deposition (CCVD) using C2H4 as a carbon source and SO2 as a promoter. The CBs, which are hundreds of micrometers in length, several micrometers in width and tens of nanometers in thickness, are made of CNFs with a low degree of graphitization that array with an orientation roughly parallel to the longitudinal axis of the CBs. The results show that the mass ratio of Ni to PAA, a H2 atmosphere in carbonization and SO2 in CCVD process are the three key factors governing the growth of the CBs.

Carbon foams (CFoams) were made by combining a hard template with a catalytic graphitization method, in which polyurethane foam is used as a sacrificial template, polyamic acid is used as carbon source and Ni is used as catalyst. The cell walls of CFoams are made of in situ self-assembled carbon nanocapsules (CNCs) with diameters of 30–80 nm. The open cells of the CFoams are, on average, 500 μm in diameter, and the cell walls are mesoporous. Thermogravimetric analysis reveals that CNCs account for about 85 wt.% of the CFoams (exclusive of the Ni). The CFoams show high activity and selectivity in the reaction of oxidative dehydrogenation of ethylbenzene to styrene.

A carbon nanofiber (CNF)/carbon foam composite was fabricated from coal liquefaction residue (CLR) through a procedure involving template synthesis of carbon foam and catalytic chemical vapor deposition (CCVD) treatment. The high solubility and high pyrolysis yield make CLR a promising carbon precursor for the synthesis of carbon materials using the template method. The carbon foam has cell size of about 500 μm and a porosity as high as 95 vol.%. Fe species naturally present in the CLR disperse homogeneously on the surface of the carbon foam acting as a catalyst in the CCVD process. After the CCVD treatment, the whole surface of the carbon foam is covered by entangled CNFs with external diameters of 20–100 nm and lengths of several tens of micrometers. The obtained CNF/carbon foam composites are effective selective adsorbents in the separation of oil and water, through a combination of hydrophobicity and capillary action.

Ternary-component NiCoAl-layered double hydroxide nanosheets (NiCoAl-LDH) and multiwall carbon nanotube (MWCNT) nanohybrids (NiCoAl-LDH–MWCNT) have been successfully fabricated by a facile yet simple urea precipitation method. The MWCNTs are well incorporated into the network of NiCoAl-LDH nanosheets to form homogeneous nanohybrid materials. The electrochemical performances of nanohybrids as pseudocapacitor electrode materials were measured and investigated by cyclic voltammetry (CV) and galvanostatic charge and discharge techniques. It was found that the electrochemical performances of NiCoAl-LDH nanosheets are enhanced by the incorporation of MWCNTs into the sheet-shaped NiCoAl-LDH network. The specific capacitance of NiCoAl-LDH–MWCNT nanohybrids reaches 1035 F g−1 at a current density of 1 A g−1, and keeps a value of 597 F g−1 with a 57.7% capacitance retention rate even at a current density of 10 A g−1, which increases by 33.3% in comparison to that of the pristine NiCoAl-LDH nanosheets.

A chitosan (CS) based nitrogen doped carbon cryogel with a high specific surface area (SSA) has been directly synthesized via a combined process of freeze-drying and high-temperature carbonization without adding any activation agents. The as-made carbon cryogel demonstrates an SSA up to 1025 m(2) g(-1) and a high nitrogen content of 5.98 wt%, while its counterpart derived from CS powder only shows an SSA of 26 m(2) g(-1). Freeze-drying is a determining factor for the formation of carbon cryogel with a high SSA, where the CS powder with a size of ca. 200 μm is transformed into the sheet-shaped cryogel with a thickness of 5-8 μm. The as-made carbon cryogel keeps the sheet-shaped structure and the abundant pores are formed in situ and decorated inside the sheets during carbonization. The carbon cryogel shows significantly enhanced performance as supercapacitor and lithium ion battery electrodes in terms of capacity and rate capability due to its quasi two-dimensional (2D) structure with reduced thickness. The proposed method may provide a simple approach to configure 2D biomass-derived advanced carbon materials for energy storage devices.

International audience; Herein we electrochemically and selectively extract Ti from the MAX phase Ti2SC to form carbon/sulfur (C/S) nanolaminates at room temperature. The products are composed of multi-layers of C/S flakes, with predominantly amorphous and some graphene-like structures. Covalent bonding between C and S is observed in the nanolaminates, which render the latter promising candidates as electrode materials for Li-S batteries. We also show that it is possible to extract Ti from other MAX phases, such as Ti3AlC2, Ti3SnC2, and Ti2GeC, suggesting that electrochemical etching can be a powerful method to selectively extract the M elements from the MAX phases, to produce AX layered structures, that cannot be made otherwise. The latter hold promise for a variety of applications, such as energy storage, catalysis, etc.

Porous anodic alumina (PAA) membranes with highly ordered hexagonal cells and a novel pore structure have been fabricated by two-step hard anodization in a H(2)SO(4)-Al(2)(SO(4))(3)-H(2)O system at 40 and 50 V, giving average cell diameters of 77 and 96 nm, respectively. There are several tiny pores embedded in each big shallow pore on the top of the membranes, and there is only one pore in one cell at their bottom. The cells on both sides of the membranes present almost the same periodic arrangement. In order to explore the formation of the novel pore structure, PAA membranes fabricated at different current densities (30-200 mA cm(-2)) are obtained by maintaining a constant voltage at 40 V. The experimental results show that the interpore distance is not only dependent on the anodization voltage, but is also influenced by the current density, which means that the pore structure of PAA membranes fabricated by hard anodization can be accurately designed and controlled by adjusting the anodization voltage and current density simultaneously.

Graphene–carbon xerogel composites with tailored pore structure and morphology are synthesized by a facile yet effective method with ionic liquids as templates, showing improved supercapacitor performance.

Free-standing, hierarchically porous carbon nanotube film is successfully fabricated by colloidal template-assisted vacuum filtration and post annealing. It can be directly used as a binder-free air electrode in Li–O2 batteries and exhibits excellent electrochemical performance by virtue of the unique bimodal design for porosity.

Novel hierarchical activated carbon nanofiber (ACF) webs with tuned structure have been fabricated by incorporating carbon black (CB) into an electrospun polymer solution, followed by heat treatment. The as-made electrospun ACF webs show superior capacities as electrode materials in capacitive deionization (CDI) for desalination due to their advantageous hierarchical structures.