Regulating Lewis Acidic Sites of 1T-2H MoS2 Catalysts for Solar-Driven Photothermal Catalytic H2 Production from Lignocellulosic Biomass.

Solar-driven photothermal catalytic H2 production from lignocellulosic biomass was achieved by using 1T-2H MoS2 with tunable Lewis acidic sites as catalysts in an alkaline aqueous solution, in which the number of Lewis acidic sites derived from the exposed Mo edges of MoS2 was successfully regulated by both the formation of an edge-terminated 1T-2H phase structure and tunable layer number. Owing to the abundant Lewis acidic sites for the oxygenolysis of lignocellulosic biomass, the 1T-2H MoS2 catalyst shows high photothermal catalytic lignocellulosic biomass-to-H2 transformation performance in polar wood chips, bamboo, rice straw corncobs, and rice hull aqueous solutions, and the highest H2 generation rate and solar-to-H2 (STH) efficiency respectively achieves 3661 µmol·h-1·g-1 and 0.18% in the polar wood chip system under 300 W Xe lamp illumination. This study provides a sustainable and cost-effective method for the direct transformation of renewable lignocellulosic biomass to H2 fuel driven by solar energy.

Machine Learning for Experimental Reactivity of a Set of Metal Clusters toward C-H Activation.

Understanding the mechanisms of C-H activation of alkanes is a very important research topic. The reactions of metal clusters with alkanes have been extensively studied to reveal the electronic features governing C-H activation, while the experimental cluster reactivity was qualitatively interpreted case by case in the literature. Herein, we prepared and mass-selected over 100 rhodium-based clusters (RhxVyOz- and RhxCoyOz-) to react with light alkanes, enabling the determination of reaction rate constants spanning six orders of magnitude. A satisfactory model being able to quantitatively describe the rate data in terms of multiple cluster electronic features (average electron occupancy of valence s orbitals, the minimum natural charge on the metal atom, cluster polarizability, and energy gap involved in the agostic interaction) has been constructed through a machine learning approach. This study demonstrates that the general mechanisms governing the very important process of C-H activation by diverse metal centers can be discovered by interpreting experimental data with artificial intelligence.

Spectroscopic Characterization of Thermal Methane Activation by Lewis-Acid-Base Pair in a Gas-Phase Metal Nitride Anion Ta2N3.

Activation and transformation of methane is one of the "holy grails" in catalysis. Understanding the nature of active sites and mechanistic details via spectroscopic characterization of the reactive sites and key intermediates is of great challenge but crucial for the development of novel strategies for methane transformation. Herein, by employing photoelectron velocity-map imaging (PEVMI) spectroscopy in conjunction with quantum chemistry calculations, the Lewis acid-base pair (LABP) of [Taδ+-Nδ-] unit in Ta2N3 - acting as an active center to accomplish the heterolytic cleavage of C-H bond in CH4 has been confirmed by direct characterization of the reactant ion Ta2N3 - and the CH4-adduct intermediate Ta2N3CH4 -. Two active vibrational modes for the reactant (Ta2N3 -) and four active vibrational modes for the intermediate (Ta2N3CH4 -) were observed from the vibrationally resolved PEVMI spectra, which unequivocally determined the structure of Ta2N3 - and Ta2N3CH4 -. Upon heating, the LABP intermediate (Ta2N3CH4 -) containing the NH and Ta-CH3 unit can undergo the processes of C-N coupling and dehydrogenation to form the product with an adsorbed HCN molecule.

Size-dependent reactivity of VnO+ (n = 1-9) clusters with ethane.

Cost-effective and readily accessible 3d transition metals (TMs) have been considered as promising candidates for alkane activation while 3d TMs especially the early TMs are usually not very reactive with light alkanes. In this study, the reactivity of Vn+ and VnO+ (n = 1-9) cluster cations towards ethane under thermal collision conditions has been investigated using mass spectrometry and density functional theory calculations. Among Vn+ (n = 1-9) clusters, only V3-5+ can react with C2H6 to generate dehydrogenation products and the reaction rate constants are below 10-13 cm3 molecule-1 s-1. In contrast, the reaction rate constants for all VnO+ (n = 1-9) with C2H6 significantly increase by about 2-4 orders of magnitude. Theoretical analysis evidences that the addition of ligand O affects the charge distribution of the metal centers, resulting in a significant increase in the cluster reactivity. The analysis of frontier orbitals indicates that the agostic interaction determines the size-dependent reactivity of VnO+ cluster cations. This study provides a novel approach for improving the reactivity of early 3d TMs.

Experimental Reactivity of (MoO3)NO- (N = 1-21) Cluster Anions with C1-C4 Alkanes: A Simple Model to Predict the Reactivity with Methane.

Metal oxide clusters with atomic oxygen radical anions are important model systems to study the mechanisms of activating and transforming very stable alkane molecules under ambient conditions. It is extremely challenging to characterize the activation and conversion of methane, the most stable alkane molecule, by metal oxide cluster anions due to the low reactivity of the anionic species. In this study, using a ship-lock type reactor that could be run at relatively high pressure conditions to provide a high number of collisions in ion-molecule reactions, the rate constants of the reactions between (MoO3)NO- (N = 1-21) cluster anions and the light alkanes (C1-C4) were measured under thermal collision conditions. The relationships among the reaction rates of different alkanes were obtained to establish a model to predict the low rate constants with methane from the high rate constants with C2-C4 alkanes. The model was tested by using available experimental results in literature. This study provides a new method to estimate the relatively low reactivity of atomic oxygen radical anions with methane on metal oxide clusters.

Difference of carrier dynamics in a semiconductor saturable absorber mirror with and without B+ ion-implantation.

Three samples whose growth temperatures were 450°C, 500°C, and 560°C for S E S A M 1, S E S A M 2, and S E S A M 3, respectively, were tested by femto-second time-resolved transient absorption spectroscopy. The results indicate that the carrier dynamics of excited state absorption were dominant, and the lifetimes of carriers trapped by defect levels were about tens of pico-seconds. To further study the influence of carrier dynamics and recovery time of samples by ion-implantation, B + ions of 80 and 130 KeV were implanted into the samples with dose of 1014/c m 2. The modified samples showed a dominance of ultra-fast carrier dynamics of ground-state bleaching and direct recombination, which lasted for hundreds of femto-seconds, over excited state absorption. Additionally, carrier fast trapping was observed to be competitive with the excited state absorption process. After ion-implantation, the carrier dynamics of carrier trapping were enhanced, which contributed to forming an ultra-short laser, while the carrier dynamics of absorption of the excited state were suppressed. The conclusion that defect levels were partially eliminated by B + ion-implantation can be drawn.

Sequential-Dependent Synthesis of Bimetallic Silver-Chromium Nanoparticles for Multichannel Sensing, Logic Computing, and 3 in 1 Information Protection.

Bimetallic nanomaterials (BNMs) have been used in sensing, biomedicine, and environmental remediation, but their multipurpose and comprehensive applications in molecular logic computing and information security protection have received little attention. Herein, This synthesis method is achieved by sequentially adding reactants under ice bath conditions. Interestingly, Ag-Cr NPs can dynamically selectively sense anions and reductants in multiple channels. Especially, ClO- can be quantitatively detected by oxidizing Ag-Cr NPs with detection limits of 98.37 nM (at 270 nm) and 31.83 nM (at 394 nm). Based on sequential-dependent synthesis process of Ag-Cr NPs, Boolean logic gates and customizable molecular keypad locks are constructed by setting the reactants as the inputs, the states of the resulting solutions as the outputs. Furthermore, dynamically selective response patterns of the Ag-Cr NPs can be converted into binary strings to exploit molecular crypto-steganography to encode, store, and hide information. By integrating the three dimensions of authorization, encryption, and steganography, 3 in 1 advanced information protection based on Ag-Cr nanosensing system can be achieved, which can enhance the anti-cracking ability of information. This research will promote the development and application of nanocomposites in the field of information security and deepen the connection between molecular sensing and the information world.

C-H Activation by Iron-Vanadium Bimetallic Oxide Cluster Anions FeV3 O10 - and FeV5 O15 - : A Comparison with Scandium-Vanadium Oxide Clusters.

Late transition metal-bonded atomic oxygen radicals (LTM-O⋅- ) have been frequently proposed as important active sites to selectively activate and transform inert alkane molecules. However, it is extremely challenging to characterize the LTM-O⋅- -mediated elementary reactions for clarifying the underlying mechanisms limited by the low activity of LTM-O⋅- radicals that is inaccessible by the traditional experimental methods. Herein, benefiting from our newly-designed ship-lock type reactor, the reactivity of iron-vanadium bimetallic oxide cluster anions FeV3 O10 - and FeV5 O15 - featuring with Fe-O⋅- radicals to abstract a hydrogen atom from C2 -C4 alkanes has been experimentally characterized at 298 K, and the rate constants are determined in the orders of magnitude of 10-14 to 10-16  cm3 molecule-1 s-1 , which are four orders of magnitude slower than the values of counterpart ScV3 O10 - and ScV5 O15 - clusters bearing Sc-O⋅- radicals. Theoretical results reveal that the rearrangements of the electronic and geometric structures during the reaction process function to modulate the activity of Fe-O⋅- . This study not only quantitatively characterizes the elementary reactions of LTM-O⋅- radicals with alkanes, but also provides new insights into structure-activity relationship of M-O⋅- radicals.

Catalytic NO Reduction by NO Pre-Adsorbed RhCeO2 NO- Clusters.

A fundamental understanding on the dynamically structural evolution of catalysts induced by reactant gases under working conditions is challenging but pivotal in catalyst design. Herein, in combination with state-of-the-art mass spectrometry for cluster reactions, cryogenic photoelectron imaging spectroscopy, and quantum-chemical calculations, we identified that NO adsorption on rhodium-cerium bimetallic oxide cluster RhCeO2 - can create a Ce3+ ion in product RhCeO2 NO- that serves as the starting point to trigger the catalysis of NO reduction by CO. Theoretical calculations substantiated that the reduction of another two NO molecules into N2 O takes place exclusively on the Ce3+ ion while Rh behaves like a promoter to buffer electrons and cooperates with Ce3+ to drive NO reduction. Our finding demonstrates the importance of NO in regulating the catalytic behavior of Rh under reaction conditions and provides much-needed insights into the essence of NO reduction over Rh/CeO2 , one of the most efficient components in three-way catalysts for NOx removal.

Visible-Light-Driven Photocatalytic Cellulose-to-H2 Conversion by MoS2 /ZnIn2 S4 Photocatalyst with Cellulase Assistance.

Visible-light-driven photocatalytic cellulose-to-H2 conversion system was successfully designed by using MoS2 /ZnIn2 S4 as the photocatalyst and cellulase as the enzyme catalyst. At first, the cellulose was converted to glucose by cellulase. The generated glucose acted as an efficient hole trapper and electron donor, which was further converted into H2 through photocatalytic reaction over MoS2 /ZnIn2 S4 under visible light irradiation. The optimum H2 generation rate achieved under visible light irradiation (λ>420 nm) was 12.2 µmol ⋅ h-1 ⋅ g-1 in the presence of 100 mg of 3 % MoS2 /ZnIn2 S4 , 100 mg cellulase and 2 g poplar wood chip. These results open up a new possibility for the development of efficient visible-light-responding photocatalytic cellulose to H2 conversion system that combine photocatalysis and enzyme technology.

A comparative study on the reactivity of ditantalum deuteride cluster anions Ta2D2- and Ta2D4- toward N2.

The activation and transformation of molecular nitrogen (N2) by metal hydride species has attracted widespread attention due to its critical role in nitrogen fixation. Herein, the reactions between tantalum deuteride cluster anions Ta2D2,4- and N2 were investigated experimentally and theoretically. An unprecedented reaction channel of the liberation of a single D atom was observed and much superior reactivity was identified for Ta2D4-. Theoretical investigations indicate that the releasing of D atoms benefits from the completely dissociative adsorption of N2 on the dinuclear metal centres. The extra D atoms in Ta2D4- compared to Ta2D2- are helpful to create sufficient electron density at the adsorption site and modify the symmetry of active orbitals to facilitate a further reduction of N2. This comparative study provides a molecular-level insight to understand the high structure-modulating capability of the additional hydride ligands in polyhydride species in the adsorption and activation of nitrogen molecules.

Reverse water-gas shift reaction catalyzed by diatomic rhodium anions.

The reverse water-gas shift (RWGS, CO2 + H2 → CO + H2O, ΔH298 = +0.44 eV) reaction mediated by the diatomic anion Rh2- was successfully constructed. The generation of a gas-phase H2O molecule and ion product [Rh2(CO)ads]- was identified unambiguously at room temperature and the only elementary step that requires extra energy to complete the catalysis is the desorption of CO from [Rh2(CO)ads]-. This experimentally identified Rh2- anion represents the first gas-phase species that can drive the RWGS reaction because it is challenging to design effective routes to yield H2O from CO2 and H2. The reactions were performed by using our newly developed double ion trap reactors and characterized by mass spectrometry, photoelectron spectroscopy, and high-level quantum-chemical calculations. We found that the order that the reactants (CO2 or D2) were fed into the reactor did not have a pronounced impact on the reactivity and the final product distribution (D2O and Rh2CO-). The atomically precise insights into the key steps to guide the reaction toward the RWGS direction were provided.

Size-dependent reactivity of rhodium deuteride cluster anions Rh3Dn - (n = 0-3) toward dinitrogen: The prominent role of σ donation.

Nitrogen (N2) fixation is a challenging task for chemists. Adsorption of N2 on transition metal (TM) sites has been identified as a prerequisite for activating the very stable N≡N triple bond in both industrial and biological processes. The importance of π back-donation (filled orbitals of TM → π* orbitals of N2) between metal sites and N2 has been well elucidated while the role of another classic orbital interaction, namely σ donation (σ orbitals of N2 → empty orbitals of TM), remains ambiguous. Herein, the size-dependent reactivity of trinuclear rhodium deuteride cluster anions Rh3Dn - (n = 0-3) toward N2 adsorption in the gas phase was investigated experimentally and theoretically. A reverse relationship that higher electron-donating ability of clusters corresponds to lower N2 adsorption reactivity was experimentally observed, which is uncommon in N2 activation by gas-phase species. Theoretical analysis revealed that the σ donation rather than the π back-donation plays a predominant role in the adsorption complexes Rh3DnN2 - and the enhanced reactivity upon D addition is ascribed to the lowered energy levels of active orbitals in Rh3Dn - as n increases. This study provides the first experimental evidence to declare the important role of σ donation and new clues for the design of reactive metal species in nitrogen fixation.

Pyrolysis of mass-selected (V2O5)NO- (N = 1-6) clusters in a high-temperature linear ion trap reactor.

A high-temperature linear ion trap that can stably run up to 873 K was newly designed and installed into a homemade reflectron time-of-flight mass spectrometer coupled with a laser ablation cluster source and a quadrupole mass filter. The instrument was used to study the pyrolysis behavior of mass-selected (V2O5)NO- (N = 1-6) cluster anions and the dissociation channels were clarified with atomistic precision. Similar to the dissociation behavior of the heated metal oxide cluster cations reported in literature, the desorption of either atomic oxygen atom or molecular O2 prevailed for the (V2O5)NO- clusters with N = 2-5 at 873 K. However, novel dissociation channels involving fragmentation of (V2O5)NO- to small-sized VxOy - anions concurrent with the release of neutral vanadium oxide species were identified for the clusters with N = 3-6. Significant variations in branching ratios for different dissociation channels were observed as a function of cluster size. Kinetic studies indicated that the dissociation rates of (V2O5)NO- monotonically increased with the increase in cluster size. The internal energies carried by the (V2O5)NO- clusters at 873 K as well as the energetics data for dissociation channels have been theoretically calculated to rationalize the experimental observations. The decomposition behavior of vanadium oxide clusters from this study can provide new insights into the pyrolysis mechanism of metal oxide nanoparticles that are widely used in high temperature catalysis.

Wideband signal detection in multipath environment affected by impulsive noise.

Detecting the presence or absence of a known signal is an important aspect of underwater acoustic (UWA) communications as it is a vital first step to process the received data. The influence of impulsive noise and multipath propagation on detection are both considered in this paper. Many robust detectors have been designed to cope with impulsive noise, but they tend to ignore the impact of multipath propagation, which may decrease the detection probability. To emphasize the role of multipath channel, we propose two-stage detection methods. In the first stage, the channel is estimated based on robust orthogonal matching pursuit, while in the second stage, detectors that use the channel estimation from the first stage, namely augmented log-likelihood ratio detector and augmented pseudo-correlation detector, are developed. The former detector is parametric and the latter one is non-parametric. The improved performance is demonstrated in simulated multipath channel and actual UWA channel with both simulated noise and recorded snapping shrimp noise, indicating that the proposed detectors are resistant to impulsive noise. It is also shown that the use of multipath information helps to improve the detection performance.

Photooxidation of Isoprene by Titanium Oxide Cluster Anions with Dimensions up to a Nanosize.

Titania (TiO2) nanoparticles are active photocatalysts, and isoprene (C5H8) is a biogenic volatile organic compound that contributes crucially to global particulate matter generation. Herein, the direct photooxidation of isoprene by titanium oxide cluster anions with dimensions up to a nanosize by both ultraviolet (UV) and visible (Vis) light excitations has been successfully identified through mass spectrometric experiments combined with quantum chemistry calculations. The potential role of "dry" titania in atmospheric isoprene oxidation has been revealed, and a clear picture of the photooxidation mechanism on titanium oxide nanoparticles has been provided explicitly at the molecular level. The adsorption of isoprene on the atomic oxygen radicals (O•-) of titanium oxide clusters leads to the formation of the crucial interfacial state (IS) within the band gap of titanium oxides. This IS is demonstrated to be the significant factor in delivering the electron from the π orbital of C5H8 to the Ti3d orbital in the photooxidation process (C5H8 + Ti4+-O•- → C5H8O + Ti3+) and creating photoactivity in the Vis region. It is revealed that after the photogeneration of the O•- radicals by UV excitation on the TiO2 particle surface, the subsequent reactions can be induced by Vis excitation through the IS. This multicolor strategy in both the UV and Vis regions can enhance the efficiency of solar energy harvesting and improve the product yield of the photocatalysis on TiO2 nanoparticles. New insights have been provided into both the atmospheric chemistry of isoprene and the photochemistry of TiO2 nanoparticles.

Dinitrogen Activation by Heteronuclear Metal Carbide Cluster Anions FeTaC2-: A 5d Early and 3d Late Transition Metal Strategy.

Cleavage of the strong N≡N bond has long been a great challenge for energy-efficient dinitrogen (N2) fixation; thus a reasonable design of reactive species to activate N2 under mild conditions is highly desirable and meaningful. Herein a novel N2 activation strategy of combining 5d early (E) and 3d late (L) transition metals (TMs) is proposed, which is verified by the facile and complete N≡N cleavage via the polarized Fe-Ta bond in gas-phase cluster FeTaC2-. The efficient N≡N cleavage benefits from an electronic-level design of highly strengthened donor-acceptor interactions, in which the 5d-ETM (Ta) mainly pushes electrons from occupied 5d-orbitals to N2 π*-orbitals while the 3d-LTM (Fe) simultaneously pulls electrons from N2 σ/π-orbitals to its unoccupied 3d-orbitals. Through employing 5d-ETM and 3d-LTM to play their respective roles, this work provides a new and versatile idea for activating the inert N≡N bond and inspires relevant design of TM-based catalysts.

Multifunctional Carbon Nanocomposites as Nanoneurons from Multimode and Multianalyte Sensing to Molecular Logic Computing, Steganography, and Cryptography.

Inspired by information exchange and logic functions of life based on molecular recognition and interaction networks, ongoing efforts are directed toward development of molecular or nanosystems for multiplexed chem/biosensing and advanced information processing. However, because of their preparation shortcomings, poor functionality, and limited paradigms, it is still a big challenge to develop advanced nanomaterials-based systems and comprehensively realize neuron-like functions from multimode sensing to molecular information processing and safety. Herein, using fish scales derived carbon nanoparticles (FSCN) as a reducing agent and stabilizer, a simple one-step synthesis method of multifunctional silver-carbon nanocomposites (AgNPs-FSCN) is developed. The prepared AgNPs-FSCN own wide antibacterial and multisignal response abilities in five channels (including color, Tyndall, absorption and fluorescence intensities, and absorption wavelength) for quantitative colorimetric and fluorescence sensing of H2 O2 , ascorbic acid, and dopamine. Benefiting from its multicoding stimuli-responsive ability, molecular concealment, and programmability, AgNPs-FSCN can be abstracted as nanoneurons for implementing batch and parallel molecular logic computing, steganography, and cryptography. This research will promote the preparation of advanced multifunctional nanocomposites and the development of their multipurpose applications, including the multireadout-guided multianalyte intelligent sensing and sophisticated molecular computing, communication, and security.

A Facile N≡N Bond Cleavage by the Trinuclear Metal Center in Vanadium Carbide Cluster Anions V3C4.

Cleavage of the triple N≡N bond by metal clusters is of fundamental interest and practical importance in nitrogen fixation. Previous studies of N≡N bond cleavage by gas-phase metal clusters emphasized the importance of the dinuclear metal centers. Herein, the dissociative adsorption of N2 and subsequent C-N coupling on trinuclear carbide cluster anions V3C4- under thermal collision conditions have been characterized by employing mass spectrometry (collision induced dissociation), cryogenic photoelectron imaging spectroscopy, and quantum chemistry calculations. A theoretical analysis identified a crucial adsorption intermediate with N2 bonded with the V3 metal core in the end-on/side-on/side-on (ESS) mode, which most likely enables the facile cleavage of the N≡N bond. Such a vital N2 coordination in the ESS mode is a result of symmetry-matched interactions between the occupied orbitals of the metal core and both of the two empty π* orbitals of N2. Furthermore, carbon ligands also play a considerable role in enhancing the reactivity of the metal core toward N2. This study strongly suggests a new mechanism of N≡N bond cleavage by gas-phase metal clusters.

Oxidation of isoprene by titanium oxide cluster cations in the gas phase.

The heterogeneous oxidation of isoprene (C5H8) by metal-oxide particles, such as the typical mineral aerosols TiO2, plays an important role in the isoprene atmospheric chemistry. However, the underlying mechanism of C5H8 oxidation remains elusive owing to the complexities of aerosol surfaces and reaction channels. Herein, we report the gas-phase reactions of TixOy+ (x = 1-7, y = 1-14) cations with isoprene by using mass spectrometry and density functional theory (DFT) calculations. Five types of reaction channels were observed: association, hydrogen atom transfer (HAT), C-C bond cleavage, combined oxygen atom transfer (OAT) and HAT and combined OAT and C-C bond cleavage. It is noteworthy that formaldehyde is known as the major oxidation product of isoprene/hydroxyl radicals in the atmosphere. In addition, CO has not been observed in the reactions of isoprene with gas-phase ions. Therefore, the reaction mechanisms of CH2O and CO generation observed in Ti2O5+/C5H8 and Ti4O8+/C5H8 systems were further investigated by DFT calculations, and the calculated results are in agreement with the experimental observations. In these two reactions, both Ti and O atoms can be the adsorption sites for C5H8. The reaction channels and mechanistic information gained in these gas-phase model reactions may offer fundamental insights relevant to the corresponding oxidation processes over titanium oxide aerosols in the atmosphere.