Coordination Environment Engineering to Regulate the Adsorption Strength of Intermediates in Single Atom Catalysts for High-performance CO2 Reaction Reduction.

The modulation of the coordination environment of single atom catalysts (SACs) plays a vital role in promoting CO2 reduction reaction (CO2RR). Herein, N or B doped Fe-embedded graphyne (Fe-GY), Fe-nXGYm (n = 1, 2, 3; X = N, B; m = 1, 2, 3), are employed as probes to reveal the effect of the coordination environment engineering on CO2RR performance via heteroatom doping in SACs. The results show that the doping position and number of N or B in Fe-GY significantly affects catalyst activity and CO2RR product selectivity. In comparison, Fe-1NGY exhibits high-performance CO2RR to CH4 with a low limiting potential of -0.17 V, and Fe-2NGY3 is demonstrated as an excellent CO2RR electrocatalyst for producing HCOOH with a low limiting potential of -0.16 V. With applied potential, Fe-GY, Fe-1NGY, and Fe-2NGY3 exhibit significant advantages in CO2RR to CH4 while hydrogen evolution reaction is inhibited. The intrinsic essence analysis illustrates that heteroatom doping modulates the electronic structure of active sites and regulates the adsorption strength of the intermediates, thereby rendering a favorable coordination environment for CO2RR. This work highlights Fe-nXGYm as outstanding SACs for CO2RR, and provides an in-depth insight into the intrinsic essence of the promotion effect from heteroatom doping.

Surface Engineering of Flower-Like Ionic Liquid-Functionalized Graphene Anchoring Palladium Nanocrystals for a Boosted Ethanol Oxidation Reaction.

The development of low-cost and high-performance electrocatalyst-supporting materials is desirable and necessary for the ethanol oxidation reaction (EOR). Here, we report a facile and universal template-free approach for the first time to synthesize three-dimensional (3D) flower-like ionic liquid-functionalized graphene (IL-RGO). Then, the crystalline Pd nanoparticles were anchored on IL-RGO by a simple wet chemical growth method without a surfactant (denoted as Pd/IL-RGO). In particular, the IL is conducive to form a 3D flower-like structure. The optimized Pd/IL-RGO-2 presents a much-promoted electrocatalytic performance toward the EOR compared with commercial Pd/C catalysts, which is mainly derived from the grafted IL on RGO and the unique 3D flower-like structure. In detail, the IL can control, stabilize, and disperse the Pd nanocrystals as well as serving as the solvent and electrolyte in the microenvironment of the EOR, and the 3D flower-like structure endows the Pd/IL-RGO with high surface areas and rich opened channels, thereby kinetically accelerating the charge/mass transfers. Furthermore, density functional theory calculations reveal that the strong electronic interaction between Pd and IL-RGO generates a downshift of dcenter for Pd and thereby enhances the durability toward CO-like intermediates and electrocatalytic reaction kinetics.

Label-Free LSPR Detection of Trace Lead(II) Ions in Drinking Water by Synthetic Poly(mPD-co-ASA) Nanoparticles on Gold Nanoislands.

Using self-assembly gold nanoislands (SAM-AuNIs) functionalized by poly(m-phenylenediamine-co-aniline-2-sulfonic acid) (poly(mPD-co-ASA)) copolymer nanoparticles as specific receptors, a highly sensitive localized surface plasmon resonance (LSPR) optochemical sensor is demonstrated for detection of trace lead cation (Pb(II)) in drinking water. The copolymer receptor is optimized in three aspects: (1) mole ratio of mPD:ASA monomers, (2) size of copolymer nanoparticles, and (3) surface density of the copolymer. It is shown that the 95:5 (mPD:ASA mole ratio) copolymer with size less than 100 nm exhibits the best Pb(II)-sensing performance, and the 200 times diluted standard copolymer solution contributes to the most effective functionalization protocol. The resulting poly(mPD-co-ASA)-functionalized LSPR sensor attains the detection limit to 0.011 ppb toward Pb(II) in drinking water, and the linear dynamic range covers 0.011 to 5000 ppb (i.e., 6 orders of magnitude). In addition, the sensing system exhibits robust selectivity to Pb(II) in the presence of other metallic cations as well as common anions. The proposed functional copolymer functionalized on AuNIs is found to provide excellent Pb(II)-sensing performance using simple LSPR instrumentation for rapid drinking-water inspection.

Differential phase-detecting localized surface plasmon resonance sensor with self-assembly gold nano-islands.

Self-assembly (SAM) gold nano-islands are fabricated by two-step thin-film deposition-annealing method. Despite random distribution of the SAM, the p-polarized light after total internal reflection shows significant phase transition at the extinction wavelengths upon refractive index variation due to localized surface plasmon resonance (LSPR) effect. It resembles the sharp phase transition observed in conventional surface plasmon resonance (SPR) biosensors, so that the bulk sensitivity of the SAM-LSPR sensor is improved via the phase interrogation method. In this Letter, we present both computational and experimental investigations to the SAM-LSPR sensor and the results show excellent agreement with each other. With bulk refractive index resolution to 9.75×10(-8) RIU, we believe the phase-detecting SAM-LSPR sensor would be an essential step toward low-cost label-free sensing applications.

The effect of grain boundaries on the mechanical properties and failure behavior of hexagonal boron nitride sheets.

In this work, the effect of grain boundaries (GBs) on the mechanical properties and failure behavior of two-dimensional hexagonal boron nitride (h-BN) sheets are systematically and comprehensively investigated using density functional theory. Results show that the formation of homoelemental bonds on GBs is an important factor, which could affect the atomic structures and stability of the h-BN sheet. The relationship between the formation energy and the misorientation angles is downward opening parabolic. The intrinsic strength shows an obvious decreasing trend with increasing inflection angles, while it shows a periodic dependence on the increase in misorientation angles. Thus, the mechanical properties of h-BN are significantly influenced by GBs. The h-BN sheets with different types of GBs show varied failure behavior, which are caused by the distinct stress distribution on GBs. The information obtained in this study would be useful for the understanding of GBs on the h-BN surface.

Common-path spectral interferometry with temporal carrier for highly sensitive surface plasmon resonance sensing.

Incorporating the temporal carrier technique with common-path spectral interferometry, we have successfully demonstrated an advanced surface plasmon resonance (SPR) biosensing system which achieves refractive index resolution (RIR) up to 2 × 10(-8) refractive index unit (RIU) over a wide dynamic range of 3 × 10(-2) RIU. While this is accomplished by optimizing the SPR differential phase sensing conditions with just a layer of gold, we managed to address the spectral phase discontinuity with a novel spectral-temporal phase measurement scheme. As the new optical setup supersedes its Michelson counterpart in term of simplicity, we believe that it is a significant contribution for practical SPR sensing applications.

Adsorption of nucleobase pairs on hexagonal boron nitride sheet: hydrogen bonding versus stacking.

The adsorption of hydrogen-bonded and stacked nucleobase pairs on the hexagonal boron nitride (h-BN) surface was studied by density functional theory and molecular dynamics methods. Eight types of nucleobase pairs (i.e., GG, AA, TT, CC, UU, AT, GC, and AU) were chosen as the adsorbates. The adsorption configurations, interaction energies, and electronic properties of the nucleobase pair on the h-BN surface were obtained and compared. The density of states analysis result shows that both the hydrogen-bonded and stacked nucleobase pairs were physisorbed on h-BN with minimal charge transfer. The hydrogen-bonded base pairs lying on the h-BN surface are significantly more stable than the stacked forms in both the gas and water phase. The molecular dynamics simulation result indicates that h-BN possessed high sensitivity for the nucleobases and the h-BN surface adsorption could revert the base pair interaction from stacking back to hydrogen bonding in aqueous environment. The h-BN surface could immobilize the nucleobases on its surface, which suggests the use of h-BN has good potential in DNA/RNA detection biosensors and self-assembly nanodevices.

Eco-Friendly Cerium-Cobalt Counter-Doped Bi2Se3 Nanoparticulate Semiconductor: Synergistic Doping Effect for Enhanced Thermoelectric Generation.

Metal chalcogenides are primarily used for thermoelectric applications due to their enormous potential to convert waste heat into valuable energy. Several studies focused on single or dual aliovalent doping techniques to enhance thermoelectric properties in semiconductor materials; however, these dopants enhance one property while deteriorating others due to the interdependency of these properties or may render the host material toxic. Therefore, a strategic doping approach is vital to harness the full potential of doping to improve the efficiency of thermoelectric generation while restoring the base material eco-friendly. Here, we report a well-designed counter-doped eco-friendly nanomaterial system (~70 nm) using both isovalent (cerium) and aliovalent (cobalt) in a Bi2Se3 system for enhancing energy conversion efficiency. Substituting cerium for bismuth simultaneously enhances the Seebeck coefficient and electrical conductivity via ionized impurity minimization. The boost in the average electronegativity offered by the self-doped transitional metal cobalt leads to an improvement in the degree of delocalization of the valence electrons. Hence, the new energy state around the Fermi energy serving as electron feed to the conduction band coherently improves the density of the state of conducting electrons. The resulting high power factor and low thermal conductivity contributed to the remarkable improvement in the figure of merit (zT = 0.55) at 473 K for an optimized doping concentration of 0.01 at. %. sample, and a significant nanoparticle size reduction from 400 nm to ~70 nm, making the highly performing materials in this study (Bi2-xCexCo2x3Se3) an excellent thermoelectric generator. The results presented here are higher than several Bi2Se3-based materials already reported.

Inducing Fe 3d Electron Delocalization and Spin-State Transition of FeN4 Species Boosts Oxygen Reduction Reaction for Wearable Zinc-Air Battery.

Transition metal-nitrogen-carbon materials (M-N-Cs), particularly Fe-N-Cs, have been found to be electroactive for accelerating oxygen reduction reaction (ORR) kinetics. Although substantial efforts have been devoted to design Fe-N-Cs with increased active species content, surface area, and electronic conductivity, their performance is still far from satisfactory. Hitherto, there is limited research about regulation on the electronic spin states of Fe centers for Fe-N-Cs electrocatalysts to improve their catalytic performance. Here, we introduce Ti3C2 MXene with sulfur terminals to regulate the electronic configuration of FeN4 species and dramatically enhance catalytic activity toward ORR. The MXene with sulfur terminals induce the spin-state transition of FeN4 species and Fe 3d electron delocalization with d band center upshift, enabling the Fe(II) ions to bind oxygen in the end-on adsorption mode favorable to initiate the reduction of oxygen and boosting oxygen-containing groups adsorption on FeN4 species and ORR kinetics. The resulting FeN4-Ti3C2Sx exhibits comparable catalytic performance to those of commercial Pt-C. The developed wearable ZABs using FeN4-Ti3C2Sx also exhibit fast kinetics and excellent stability. This study confirms that regulation of the electronic structure of active species via coupling with their support can be a major contributor to enhance their catalytic activity.

Can Charge-Modulated Metal-Organic Frameworks Achieve High-Performance CO2 Capture and Separation over H2 , N2 , and CH4 ?

CO2 capture and separation by using charge-modulated adsorbent materials is a promising strategy to reduce CO2 emissions. Herein, three TM-HAB (TM=Co, Ni, and Cu; HAB=hexa-aminobenzene) metal-organic frameworks (MOFs) were evaluated as charge-modulated CO2 capture and separation materials by using density functional theory and grand canonical Monte Carlo simulations. The results showed that each TM-HAB presented a high electrical conductivity and structural stability when injecting charges. The CO2 adsorption energy increased from 0.211 to 2.091 eV on Co-HAB, 0.262 to 2.119 eV on Ni-HAB, and 0.904 to 2.803 eV on Cu-HAB, respectively, with the increase in charge state from 0.0 to 3.0 e- . Co-HAB and Ni-HAB were better charge-modulated CO2 capture materials with less structure deformation based on energy decomposition analyses. The kinetic process demonstrated that considerably low energy consumptions of 0.911 and 1.589 GJ ton-1 CO2 were observed for a complete adsorption-desorption cycle on Co-HAB and Ni-HAB. All charged MOFs, especially Co-HAB and Ni-HAB, exhibited higher CO2 adsorption energies and adsorption capacities than those of H2 , N2 , and CH4 , thereby exhibiting high CO2 selectivities. Interaction analysis confirmed that the injecting charges had a more pronounced enhancement in the coulombic interactions between CO2 and MOFs. The results of this work highlight Co-HAB and Ni-HAB as promising charge-modulated CO2 capture and separation materials with controllable CO2 capture, high selectivity, and low energy consumption.

White-light spectral interferometry for surface plasmon resonance sensing applications.

A novel differential phase detecting surface plasmon resonance (SPR) sensor based on white-light spectral interferometry is presented. Our proposed scheme employs a white-light source for SPR excitation and measures the corresponding SPR phase change at the optimized coupling wavelength with fixed angle of incidence across the visible spectrum. Compared to existing laser based phase detecting schemes, this system offers optimal sensitivity and extended dynamic range of measurement without any compromise in phase detection resolution. Results obtained from sodium chloride solutions indicate that the detection limit is 2.6×10⁻7 RIU over a refractive index range of 10⁻² RIU, which is considerably wider than that achievable by existing laser based approach, thus making our scheme very attractive for practical SPR sensing applications.

Rational Design and Effective Control of Gold-Based Bimetallic Electrocatalyst for Boosting CO2 Reduction Reaction: A First-Principles Study.

Electrochemical CO2 reduction reaction (CO2 RR) is an effective strategy converting CO2 to value-added products. Au is regarded as an efficient catalyst for electrochemical reduction of CO2 to CO, and the introduction of Pd can tune CO2 RR properties due to its strong affinity to CO. Herein, Au-Pd bimetallic electrocatalysts with different metal ratio were firstly investigated on CO2 RR mechanism by using density functional theory. The Au monolayer over Pd substrate and single Pd atom on Au(111) were found to show better CO2 RR selectivity against hydrogen evolution reaction (HER). Based on this, various single-atom catalysts on Au(111) and core-shell models with top Au monolayer were designed to study their CO2 RR performance. The results indicated that Pt, Cu, and Rh substrates below Au monolayer could enhance the activity and selectivity for CO production compared to pure Au, in which the limiting potential reduced from -0.74 to -0.63, -0.69, and -0.71 V, respectively. The single Pd embedded on Au(111) could adjust the adsorption strength, which provided an effective site to receive and further reduce CO to CH3 OH and CH4 at a low limiting potential of -0.61 V, and also avoided catalyst poisoning due to the over-strengthened CO adsorption caused by high Pd proportion on the surface. In addition, the adsorption energy of COOH was observed as a better CO2 RR reactivity descriptor than the common CO adsorption when establishing scaling relationship, which could avoid the fitting error caused by intermediate physisorption of CO.

In vivo liquid biopsy for glioblastoma malignancy by the AFM and LSPR based sensing of exosomal CD44 and CD133 in a mouse model.

Glioblastoma (GBM) is the fatal brain tumor in which secreted lactate enhances the expression of cluster of differentiation 44 (CD44) and the release of exosomes, cell-derived nanovesicles (30-200 nm), and therefore promotes tumor malignant progression. This study found that lactate-driven upregulated CD44 in malignant Glioblastoma cells (GMs) enhanced the release of CD44-enriched exosomes which increased GMs' migration and endothelial cells' tube formation, and CD44 in the secreted exosomes was sensitively detected by "capture and sensing" Titanium Nitride (TiN) - Nanoholes (NH) - discs immunocapture (TIC) - atomic force microscopy (AFM) and ultrasensitive TiN-NH-localized surface plasmon resonance (LSPR) biosensors. The limit of detection for exosomal CD44 with TIC-AFM- and TiN-NH-LSPR-biosensors was 5.29 × 10-1 µg/ml and 3.46 × 10-3 µg/ml in exosome concentration, respectively. Importantly, this work first found that label-free sensitive TiN-NH-LSPR biosensor could detect and quantify enhanced CD44 and CD133 levels in immunocaptured GMs-derived exosomes in the blood and the cerebrospinal fluid of a mouse model of GBM, supporting its potential application in a minimally invasive molecular diagnostic for GBM progression as liquid biopsy.

Mechanistic insight into the gas-phase reactions of methylamine with ground state Co+(3F) and Ni+(2D).

The gas-phase reaction mechanisms of methylamine (MA) with the ground-state Co(+)((3)F) and Ni(+)((2)D) are theoretically investigated using density functional theory at both the B3LYP/6-311++G(d,p) and B3LYP/6-311++G(3df,2p) levels. The reactions for hydride abstraction and dehydrogenation are analyzed in terms of the topology of potential energy surfaces (PESs). Co(+) and Ni(+) perform similar roles along the isomerization processes to the final products. Hydride abstraction takes place via the key species of metal cation-methyl-H intermediate, followed by a charge transfer process before the direct dissociation of CH(2)NH(2)(+)···MH (M = Co, Ni). The enthalpies of reaction, stability of metal cation-methyl-H species, and competition between different channels account for the sequence of the hydride abstraction products: CoH < NiH < CuH. The most competitive dehydrogenation route occurs through a stepwise reaction, consisting of initial C-H activation, amino-H shift, and direct dissociation of the precursor CH(2)NHM(+)···H(2). This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanisms of amine prototype with late first-row transition metal cations.

DFT/TD-DFT investigation of electronic structures and spectra properties of Cu-based dye sensitizers.

Molecular geometries, electronic structures, and optical absorption spectra were investigated using density functional theory (DFT) at the B3LYP/6-31G(d) and B3LYP/DZVP levels for [CuL(2)](+) and [CuL(2)][PF(6)] (L = 6,6'-dimethyl-2,2'-bipyridine-4,4'-dimethylformate), both in the gas phase and in methyl cyanide (MeCN) solution. The vertical excitation energies were calculated within the framework of the time-dependent DFT (TD-DFT) approach, whereas the solvent effects were taken into account using the polarizable continuum model (C-PCM). Our results show that the five highest occupied molecular orbitals (HOMOs) are composed of a set of distorted degenerate Cu 3d orbitals, whereas the four lowest unoccupied molecular orbitals (LUMOs) are the bipyridine ligand pi*(C horizontal lineN) orbitals. The spectra in the range of 400-600 nm were found to originate from metal-to-ligand charge-transfer (MLCT) transitions, whereas the spectra in the range of 350-400 nm are excitations mainly from the metal Cu 3d orbitals to the carboxyl pi* orbitals. The solvent effects lead to changes in both the geometries and the absorption spectra. The results of this work suggest that copper-based complexes might be effective sensitizers for next-generation dye-sensitized solar cells.

Electrochemical CO2 Reduction to C1 Products on Single Nickel/Cobalt/Iron-Doped Graphitic Carbon Nitride: A DFT Study.

Electrocatalytic CO2 reduction reaction (CRR) is one of the most promising strategies to convert greenhouse gases to energy sources. Herein, the CRR was applied towards making C1 products (CO, HCOOH, CH3 OH, and CH4 ) on g-C3 N4 frameworks with single Ni, Co, and Fe introduction; this process was investigated by density functional theory. The structures of the electrocatalysts, CO2 adsorption configurations, and CO2 reduction mechanisms were systematically studied. Results showed that the single Ni, Co, and Fe located from the corner of the g-C3 N4 cavity to the center. Analyses of the adsorption configurations and electronic structures suggested that CO2 could be chemically adsorbed on Co-C3 N4 and Fe-C3 N4 , but physically adsorbed on Ni-C3 N4 . The H2 evolution reaction (HER), as a suppression of CRR, was investigated, and results showed that Ni-C3 N4 , Co-C3 N4 , and Fe-C3 N4 exhibited more CRR selectivity than HER. CRR proceeded via COOH and OCHO as initial protonation intermediates on Ni-C3 N4 and Co/Fe-C3 N4 , respectively, which resulted in different C1 products along quite different reaction pathways. Compared with Ni-C3 N4 and Fe-C3 N4 , Co-C3 N4 had more favorable CRR activity and selectivity for CH3 OH production with unique rate-limiting steps and lower limiting potential.

Simultaneous Enhancement of Thermopower and Electrical Conductivity through Isovalent Substitution of Cerium in Bismuth Selenide Thermoelectric Materials.

It is challenging to achieve highly efficient thermoelectric materials due to the conflicts between thermopower (Seebeck coefficient) and electrical conductivity. These parameters are the core factors defining the thermoelectric property of any material. Here, we report the use of isovalent substitution as a tool to decouple the interdependency of the Seebeck coefficient and the electrical properties of cerium-doped bismuth selenide thermoelectric material. With this strategy, we can achieve a simultaneous increase in both the electrical conductivity and the Seebeck coefficient of the material by tuning the concentration of cerium doping, due to formation of neutral impurities and consequently the improvement of carrier mobility. Our theoretical calculation reveals a downward shift of the valence band with cerium concentration, which influences the thermoelectric enhancement of the synthesized materials. Finally, an order of magnitude enhancement of the figure of merit is obtained due to isovalent substitution, thus providing a new avenue for enhancing the thermoelectric performance of materials.

Label-free surface plasmon resonance biosensing with titanium nitride thin film.

In this report, titanium nitride thin film synthesized with reactive magneto-sputtering technique is proposed as an alternative surface plasmon resonance sensing material. The physical and chemical natures were initially studied by atomic force microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. In virtue of white-light common-path sensing system, the wavelength modulated TiN films achieved tunable evanescent plasmonic field from 573 nm to 627 nm. The optimized TiN film with 29.8 nm thickness exhibited good differential phase sensitivity (i.e. 1.932 × 10-7 RIU) to refractive index alteration, which is comparable to the performance of gold film. We have also attained direct measurement of biotin adsorption on the TiN and monitored sub-sequential biotin-streptavidin conjugation. It was found that TiN films have significantly higher binding affinity toward biotin than that of gold in experiments, so we are able to detect biotin directly to 0.22 µg/ml (0.90 µM) in label-free manner. The adsorption mechanism of biotin on TiN(200) are also explored with periodic density functional theory (DFT) via computer simulation and it was found that the exceptional biotin-TiN affinity may be due to the stacking formation of both N-Ti and O-Ti bonds. Also, the adsorption energy of biotin-TiN was found to be - 1.85 eV, which was two times higher than that of biotin-gold. Both experimental and computational results indicate, for the first time, that the TiN film can be directly functionalized with biotin molecules, thus it serves as an alternative plasmonic material to existing gold-based SPR biosensors.

Encapsulating Co2 P@C Core-Shell Nanoparticles in a Porous Carbon Sandwich as Dual-Doped Electrocatalyst for Hydrogen Evolution.

A highly efficient and pH-universal hydrogen evolution reaction (HER) electrocatalyst with a sandwich-architecture constructed using zero-dimensional N- and P-dual-doped core-shell Co2 P@C nanoparticles embedded into a 3 D porous carbon sandwich (Co2 P@N,P-C/CG) was synthesized through a facile two-step hydrothermal carbonization and pyrolysis method. The interfacial electron transfer rate and the number of active sites increased owing to the synergistic effect between the N,P-dual-doped Co2 P@C core-shell and sandwich-nanostructured substrates. The presence of a high surface area and large pore sizes improved the mass-transfer dynamics. This nanohybrid showed remarkable electrocatalytic activity toward the HER in a wide pH range with good stability. The computational study and experiments revealed that the carbon atoms close to the N and P dopants on the shell of Co2 P@N,P-C were effective active sites for HER catalysis and that both Co2 P and the N,P dopants gave rise to an optimized binding free energy of H on the active sites.

A redox-controlled electrolyte for plasmonic enhanced dye-sensitized solar cells.

Plasmonic enhanced dye-sensitized solar cells (DSSCs) with metallic nanostructures suffer from corrosion problems, especially with the presence of the iodine/triiodide redox couple in the electrolyte. Herein, we introduce an alternative approach by compensating the corrosion with a modified liquid electrolyte. In contrast to the existing method of surface preservation for plasmonic nanostructures, the redox-controlled electrolyte (RCE) contains iodoaurate intermediates, i.e. gold(i) diiodide (AuI2-) and gold(iii) tetraiodide (AuI4-) with optimal concentrations, such that these intermediates are readily reduced to gold nanoparticles during the operation of DSSCs. As corrosion and redeposition of gold occur simultaneously, it effectively provides corrosion compensation to the plasmonic gold nanostructures embedded in the photoanode. Cycling tests of the specific amount of gold contents in the RCE of DSSCs support the fact that the dissolution and deposition of gold are reversible and repeatable. This gold deposition on the TiO2 photoanode results in forming a Schottky barrier (SB) at the metal-semiconductor interface and effectively inhibits the recombination of electron-hole pairs. Therefore, the RCE increases the short-circuit current, amplifies the open-circuit voltage, and reduces the impedance of the TiO2/dye interface. The power conversion efficiency of DSSCs was improved by 57% after incorporating the RCE.