Carbyne with finite length: The one-dimensional sp carbon

Laser synthesis of nanoparticles in organic solvents - products, reactions, and perspectives

Laser synthesis and processing of colloids (LSPC) is an established method for producing functional and durable nanomaterials and catalysts in virtually any liquid of choice. While the redox reactions during laser synthesis in water are fairly well understood, the corresponding reactions in organic liquids remain elusive, particularly because of the much greater complexity of carbon chemistry. To this end, this article first reviews the knowledge base of chemical reactions during LSPC and then deduces identifiable reaction pathways and mechanisms. This review also includes findings that are specific to the LSPC method variants laser ablation (LAL), fragmentation (LFL), melting (LML), and reduction (LRL) in organic liquids. A particular focus will be set on permanent gases, liquid hydrocarbons, and solid, carbonaceous species generated, including the formation of doped, compounded, and encapsulated nanoparticles. It will be shown how the choice of solvent, synthesis method, and laser parameters influence the nanostructure formation as well as the amount and chain length of the generated polyyne by-products. Finally, theoretical approaches to address the mechanisms of organic liquid decomposition and carbon shell formation are highlighted and discussed regarding current challenges and future perspectives of LSPC using organic liquids instead of water.

Reactions of Platinum Terminal Polyynyl Complexes trans-(C6F5)(p-tol3P)2Pt(C≡C)nH (n = 2-4) and n-BuLi, Generation of Functional Equivalents of Pt(C≡C)nLi Species, and Derivatization with Organic and Inorganic Electrophiles

Reactions of the title complexes and n-BuLi (1.5 equiv, -45 °C) afford functional equivalents of the deprotonated species trans-(C6F5)(p-tol3P)2Pt(C≡C)nLi (n = 2-4), as assayed by subsequent additions of MeI or Me3SiCl to give trans-(C6F5)(p-tol3P)2Pt(C≡C)nMe (66-52%) or trans-(C6F5)(p-tol3P)2Pt(C≡C)nSiMe3 (63-49%). However, 31P NMR data suggest more complicated mechanistic scenarios, and small amounts of the hydride complex trans-(C6F5)(p-tol3P)2PtH (independently synthesized from the chloride complex, AgClO4, and NaBH4) are detected in most cases. Analogous sequences involving trans-(C6F5)(p-tol3P)2Pt(C≡C)2H and benzyl bromide, D2O, or W(CO)6/Me3O+ BF4- similarly afford products with Pt(C≡C)2Bn, Pt(C≡C)2D, or Pt(C≡C)2C(OCH3)=W(CO)5 linkages. The crystal structures of the tungsten and corresponding SiMe3 adduct, the three Pt(C≡C)nMe species, and hydride complex are determined.

Unravelling the formation of carbyne nanocrystals from graphene nanoconstrictions through the hydrothermal treatment of agro-industrial waste molasses

The delicate synthesis of one-dimensional (1D) carbon nanostructures from two-dimensional (2D) graphene moiré layers holds tremendous interest in materials science owing to its unique physiochemical properties exhibited during the formation of hybrid configurations with sp-sp2 hybridization. However, the controlled synthesis of such hybrid sp-sp2 configurations remains highly challenging. Therefore, we employed a simple hydrothermal technique using agro-industrial waste as the carbon source to synthesize 1D carbyne nanocrystals from the nanoconstricted zones of 2D graphene moiré layers. By employing suite of characterization techniques, we delineated the mechanism of carbyne nanocrystal formation, wherein the origin of carbyne nanochains was deciphered from graphene intermediates due to the presence of a hydrothermally cut nanoconstriction regime engendered over well-oriented graphene moiré patterns. The autogenous hydrothermal pressurization of agro-industrial waste under controlled conditions led to the generation of epoxy-rich graphene intermediates, which concomitantly gave rise to carbyne nanocrystal formation in oriented moiré layers with nanogaps. The unique growth of carbyne nanocrystals over a few layers of holey graphene exhibits excellent paramagnetic properties, the predominant localization of electrons and interfacial polarization effects. Further, we extended the application of the as-synthesized carbyne product (Cp) for real-time electrochemical-based toxic metal (As3+) sensing in groundwater samples (from riverbanks), which depicted superior sensitivity (0.22 mA μM-1) even at extremely lower concentrations (0.0001 μM), corroborating the impedance spectroscopy analysis.

Microcrystalline Nanofiber Electrode with Adaptive Intrinsic Structure and Microscopic Interface

A strategy of microcrystalline aggregation is proposed to fabricate energy storage electrode with outstanding capacity and stability. Carbon-rich electrode (BDTG) functionalized with benzo[1,2-b:4,5-b']dithiophene units and butadiyne segments are prepared. The linear conjugate chains pack as microcrystalline nanofibers on nanoscale, which further aggregates to form a porous interpenetrating network. The microcrystalline aggregation feature of BDTG exhibit stable structure during long cycling test, revealing the following advantage in structure and property. The stretchable butadiyne linker facilitates reversible adsorption and desorption of Li with the aid of adjacent sulfur heteroatom. The alkyne-alkene transition exhibits intrinsic structural stability of microcrystalline region in BDTG electrodes. Meanwhile, alkynyl groups and sulfur heteroatoms on the surface of BDTG nanofibers participate in the formation of microscopic interface, providing a stable interfacial contact between BDTG electrodes and adjacent electrolyte. As a proof-of-concept, BDTG-based electrode shows high capacity (1430 mAh g-1 at 50 mA g-1) and excellent cycle performance (8000 cycles under 5 A g-1) in half-cell of lithium-ion batteries, and a reversible capacity of 120 mAh g-1 is obtained under the current density of 2 C in full-cell. This work shows microcrystalline aggregation is beneficial to realize adaptive intrinsic structure and interface contact during the charge-discharge process.

Polarization-Sensitive Photoluminescence from Aligned Carbon Chains Terminated by Gold Clusters

We synthesize a thin film composed of long carbyne chains terminated by gold clusters and study its optical properties. The presence of gold particles stabilizes longer chains and leads to their alignment. We show that the gold clusters also act as a source of electron doping, thus, changing the intensity of photoluminescence from quadratic dependence on the pumping intensity without gold to linear with gold. We also observe that the excitation of the film at the gold plasmon frequency causes the blue shift of photoluminescence and estimate, on the basis of this effect, the minimum length of the carbyne chains. The high degree of alignment of the gold-terminated carbyne chains results in strongly anisotropic light absorption characterized by a distinctive cosine dependence on the angle between the carbyne molecule and polarization plane of the excitation. This paves the way for a new class of ultimately thin polarization sensitive emitters to be used in future integrated quantum photonics devices.

Monodisperse Molecular Models for the sp Carbon Allotrope Carbyne; Syntheses, Structures, and Properties of Diplatinum Polyynediyl Complexes with to Linkages

Extended conjugated polyynes provide models for the elusive sp carbon polymer carbyne, but progress has been hampered by numerous synthetic challenges. Stabilities appear to be enhanced by bulky, electropositive transition-metal endgroups. Reactions of trans-(C6F5)(p-tol3P)2Pt(C≡C)nSiEt3 (n = 4-6, PtCxSi (x = 2n)) with n-Bu4N+F-/Me3SiCl followed by excess tetrayne H(C≡C)4SiEt3 (HC8Si) and then CuCl/TMEDA and O2 give the heterocoupling products PtCx+8Si, PtCx+16Si, and sometimes higher homologues. The PtCx+16Si species presumably arise via protodesilylation of PtCx+8Si under the reaction conditions. Chromatography allows the separation of PtC16Si, PtC24Si, and PtC32Si (from n = 4), PtC18Si and PtC26Si (n = 5), or PtC20Si and PtC28Si (n = 6). These and previously reported species are applied in similar oxidative homocouplings, affording the family of diplatinum polyynediyl complexes PtCxPt (x = 20, 24, 28, 32, 36, 40 in 96-34% yields and x = 44, 48, 52 in 22-7% yields). These are carefully characterized by 13C NMR, UV-visible, and Raman spectroscopy and other techniques, with particular attention to behavior as the Cx chain approaches the macromolecular limit and endgroup effects diminish. The crystal structures of solvates of PtC20Pt, PtC24Pt, and PtC26Si, which feature the longest sp chains structurally characterized to date, are analyzed in detail. All data support a polyyne electronic structure with a nonzero optical band gap and bond length alternation for carbyne.

Understanding Coke Deposition Vis-à-Vis DRM Activity over Magnesia-Alumina Supported Ni-Fe, Ni-Co, Ni-Ce, and Ni-Sr Catalysts

The catalytic conversion of CH4 and CO2 into H2-rich syngas is known as the dry reforming of methane (DRM). The dissociation of CH4 over active sites, coupled with the oxidation or polymerization of CH4-x (x = 1-4), plays a crucial role in determining in determining the DRM product yield and coke deposition. Herein, a series of bimetallic-supported catalysts are prepared by the dispersion of Ni-M (M = Ce, Co, Fe, and Sr) over 60 wt% MgO-40 wt% Al2O3 (60Mg40Al) support. Catalysts are tested for DRM and characterized with XRD, surface area and porosity, temperature-programmed reduction/desorption, UV-VIS-Raman spectroscopy, and thermogravimetry. 2.5Ni2.5Sr/60Mg40Al and 2.5Ni2.5Fe/60Mg40Al, and 2.5Ni2.5Ce/60Mg40Al and 2.5Ni2.5Co/60Mg40Al have similar CO2 interaction profiles. The 2.5Ni2.5Sr/60Mg40Al catalyst nurtures inert-type coke, whereas 2.5Ni2.5Fe/60Mg40Al accelerates the deposition of huge coke, which results in catalytic inferiority. The higher activity over 2.5Ni2.5Ce/60Mg40Al is due to the instant lattice oxygen-endowing capacity for oxidizing coke. Retaining a high DRM activity (54% H2-yield) up to 24 h even against a huge coke deposition (weight loss 46%) over 2.5Ni2.5Co/60Mg40Al is due to the timely diffusion of coke far from the active sites or the mounting of active sites over the carbon nanotube.

Overview of the Metallization Approaches for Carbyne-Based Devices

Metallization for contacts in organic electronic nanodevices is of great importance for their performance. A lot of effects can appear at the contact/organic interface and modify the contact parameters, such as contact resistance, adhesive strength, and bonding ability. For novel materials, it is important to study the interactions with metal atoms to develop a suitable technology for contacts, fulfilling to the greatest extent the above-mentioned parameters. A novel material is carbyne, which is still under intensive research because of its great potential in electronics, especially for sensing applications. However, the most appropriate metallization strategy for carbyne-based devices is still unknown, so the interactions between carbyne and metal films should be studied to more precisely direct the development of the metallization technology, and to form contacts that are not limiting factors for device performance.

Enhanced electromagnetic wave absorption of Fe3O4@MnO2@Ni-Co/C composites derived from Prussian blue analogues

Herein, Fe₃O₄@MnO₂@Ni-Co/C composites derived from PBAs were successfully fabricated. Firstly, Ni-Co Prussian blue analogues (Ni-Co PBAs) were used as precursors to derive a carbon layer on their surface by annealing treatment and subsequently translated into MnO₂@Ni-Co/C nanocubes after hydrothermal reactions. Fe₃O₄@MnO₂@Ni-Co/C composites were finally obtained after depositing Fe₃O₄ nanoparticles through the annealing process. Their electromagnetic wave (EMW) absorption performance apparently enhanced, thanks to the excellent impedance matching and strong attenuation derived from the synergy between the dielectric loss and the magnetic loss. In particular, the minimum reflection loss (RL_min) of Fe₃O₄@MnO₂@Ni-Co/C reached -41.2 dB with a thickness of 4.0 mm and the effective absorption bandwidth (EAB) reached 7.1 GHz with a thickness of 2.0 mm. Therefore, the results could be significant for synthesizing EMW absorbers with excellent performance, a broad bandwidth, strong absorption, thin thickness and light weight.

Nano-Hybrid Ag@LCCs Systems with Potential Wound-Healing Properties

The synthesis of contaminant-free silver@linear carbon chains (Ag@LCCs) nanohybrid systems, at different Ag/LCCs ratios, by pulsed laser ablation was studied. The ablation products were first characterized by several diagnostic techniques: conventional UV-Vis optical absorption and micro-Raman spectroscopies, as well as scanning electron microscopy, operating in transmission mode. The experimental evidence was confirmed by the theoretical simulations' data. Furthermore, to gain a deeper insight into the factors influencing metal@LCCs biological responses in relation to their physical properties, in this work, we investigated the bioproperties of the Ag@LCCs nanosystems towards a wound-healing activity. We found that Ag@LCC nanohybrids maintain good antibacterial properties and possess a better capability, in comparison with Ag NPs, of interacting with mammalian cells, allowing us to hypothesize that mainly the Ag@LCCs 3:1 might be suitable for topical application in wound healing, independent of (or in addition to) the antibacterial effect.

The kinked structure and interchain van der Waals interaction of carbyne nanocrystals

Carbyne with one-dimensional sp-hybridized carbon atoms is the third form of carbon following diamond and graphite. Although carbyne nanocrystals have been synthesized, little is known about its structural details. Here, we report experimental evidence of the kinked structure of carbon chains and interchain van der Waals interaction of carbyne nanocrystals by near edge X-ray absorption fine structure (NEXAFS) spectroscopy. We measure the resonance and the feature peaks of the kinked configuration of carbon chains and the van der Waals interaction between chains of carbyne nanocrystals using NEXAFS spectroscopy. We also perform theoretical calculations of density functional theory and simulations based on the super-cell core-hole method for carbon K-edge NEXAFS. The theoretical results are in good agreement with the experimental measurements, which demonstrates that carbyne nanocrystals are van der Waals crystals with kinked chains as structural units. Note that the peak at 288.5 eV in the simulated NEXAFS spectrum implies the possible presence of hydrogen-terminated kinks or hydrogen-terminated chains in carbyne nanocrystals, which clarifies the understanding of the C-H bond in carbyne nanocrystals. These findings are enlightening and significant for pursuing physics and potential applications of carbyne.

Revisiting Polytetrafluorethylene Binder for Solvent-Free Lithium-Ion Battery Anode Fabrication

Solvent-free (SF) anodes with different carbon materials (graphite, hard carbon, and soft carbon) were fabricated to investigate the stability of different anodes with polytetrafluorethylene (PTFE) degradation. The graphite anode with large volume variation during the charge/discharge process showed poor cycle life performance, while hard carbon and soft carbon with low-volume expansion showed good cycle life. The SF hard carbon electrodes with a high loading of 10.7 mg/cm2 revealed good long-term cycling performance similar to conventional slurry-casting (CSC) electrodes. It demonstrated nearly 90% capacity retention after 120 cycles under a current of 1/3 C with LiNi0.5Co0.2Mn0.3O2 (NCM523) as cathode in coin cell. The rate capability of the high-loading SF electrodes also is comparable to the CSC electrodes. The high stability of SF hard carbon and soft carbon anodes was attributed to its low-volume variation, which could maintain their integrity even though PTFE was defluorinated to amorphous carbon irreversibly. However, the reduced amorphous carbon cannot tolerate huge volume variation of graphite during cycling, resulting in poor stability.

Nano-Hybrid Au@LCCs Systems Displaying Anti-Inflammatory Activity

Gold nanoparticles (Au NPs) have received great attention owing to their biocompatible nature, environmental, and widespread biomedical applications. Au NPs are known as capable to regulate inflammatory responses in several tissues and organs; interestingly, lower toxicity in conjunction with anti-inflammatory effects was reported to occur with Au NPs treatment. Several variables drive this benefit-risk balance, including Au NPs physicochemical properties such as their morphology, surface chemistry, and charge. In our research we prepared hybrid Au@LCC nanocolloids by the Pulsed Laser Ablation, which emerged as a suitable chemically clean technique to produce ligand-free or functionalized nanomaterials, with tight control on their properties (product purity, crystal structure selectivity, particle size distribution). Here, for the first time to our knowledge, we have investigated the bioproperties of Au@LCCs. When tested in vitro on intestinal epithelial cells exposed to TNF-α, Au@LCCs sample at the ratio of 2.6:1 showed a significantly reduced TNF gene expression and induced antioxidant heme oxygenase-1 gene expression better than the 1:1 dispersion. Although deeper investigations are needed, these findings indicate that the functionalization with LCCs allows a better interaction of Au NPs with targets involved in the cell redox status and inflammatory signaling.

Cubic Octa-Carbon: Quantum-Chemical Design of Molecular Structure and Potential Way of Its Synthesis from Cubane

Quantum-chemical calculation of most important parameters of molecular and electronic structures of octa-carbon C₈ having cubic form (bond lengths, bond and torsion angles) using CCSD(T)/QZVP and DFT B3PW91/QZVP methods, has been carried out. NBO analysis data and HOMO/LUMO images for this compound are presented, too. Good agreement was found between the structural data obtained using the above two quantum-chemical methods and, also, with corresponding experimental data. Also, the standard thermodynamic parameters of formation of cubic C₈ considered here, and namely standard enthalpy Δ_fH⁰(298K), entropy S_f⁰(298K) and Gibbs’ energy Δ_fG⁰(298K) of formation for this compound were calculated. By using this data, a theoretically possible variant of the synthesis of this compound by dehydrogenation of cubane C₈H₈ is considered, and the thermodynamic characteristics of each of the four stages of this process have been calculated. It is noted that each of the four stages of this process is characterized by a very high (about 500 kJ/mol) enthalpy of activation, as a result of that, for their realization within a sufficiently short time, the use of appropriate catalysts is necessary.

Carbyne Nanocrystal: One-Dimensional van der Waals Crystal

In terms of carbon-atom hybridization, well-established forms of carbon are the first carbon diamond with three-dimensional sp³-hybridized carbon atoms and the second carbon graphite with two-dimensional sp²-hybridized carbon atoms which have been known and utilized for millennia. Sequentially, there is the third carbon, i.e., carbyne with one-dimensional (1D) sp-hybridized carbon atoms, which would result in an allotrope of carbon. Here, we demonstrate that carbyne nanocrystals (CNCs) are 1D van der Waals crystals (1D-vdWCs) composed of 1D carbon chains with sp-hybridized carbon atoms, and van der Waals action occurs between carbon chains based on an atomic insight into 1D sp-carbon chains. CNCs are synthesized by laser ablation in liquids, and the relevant spectroscopic analyses confirm that CNCs are composed of 1D carbon chains with the alternating carbon-carbon single and triple bonds. The crystal structure of CNCs is determined by X-ray diffraction, transmission electron microscopy (TEM), including selective electron diffraction (SAED), high-resolution TEM (HRTEM), and scanning TEM (STEM) and the corresponding simulations. SAED and HRTEM images reveal the translational symmetry of CNCs, and STEM images show the specific position of the carbon chain in CNCs and the arrangement of atoms on the carbon chain. Experimental data are in good agreement with the simulations, which demonstrate that CNCs are 1D-vdWCs with a hexagonal lattice in which the 1D carbon chain has a kinked structure consisting of an alternating carbon-carbon single bond and a triple bond of eight carbon atoms in a cycle. These findings bring out an emerging era of the third carbon carbyne.

On the Stabilization of Carbynes Encapsulated in Penta-Graphene Nanotubes: a DFT Study

We carried out density functional theory calculations to investigate the electronic and structural properties of linear carbon chains (carbynes) encapsulated in armchair and zigzag penta-graphene (PGNT) nanotubes. Results showed that PGNTs-wrapped carbyne can present negative formation energies that tend to stabilize that encapsulated carbon chains. These chains were stabilized in their cumulene and polyyne forms, with slight dependence on tube diameter. As a general trend, the PGNT band structures are kept almost unchanged upon carbyne encapsulation. This finding indicates weak orbital interactions between the PGNT and the carbyne. No net charge was found in chains encapsulated on zigzag PGNTs. Schematic representation of a carbyne encapsulated in a pentagraphene nanotube.

Cumulene Wires Display Increasing Conductance with Increasing Length

One-dimensional sp-hybridized carbon wires, including cumulenes and polyynes, can be regarded as finite versions of carbynes. They are likely to be good candidates for molecular-scale conducting wires as they are predicted to have a high-conductance. In this study, we first characterize the single-molecule conductance of a series of cumulenes and polyynes with a backbone ranging in length from 4 to 8 carbon atoms, including [7]cumulene, the longest cumulenic carbon wire studied to date for molecular electronics. We observe different length dependence of conductance when comparing these two forms of carbon wires. Polyynes exhibit conductance decays with increasing molecular length, while cumulenes show a conductance increase with increasing molecular length. Their distinct conducting behaviors are attributed to their different bond length alternation, which is supported by theoretical calculations. This study confirms the long-standing theoretical predictions on sp-hybridized carbon wires and demonstrates that cumulenes can form highly conducting molecular wires.

Excitonic Fine Structure in Emission of Linear Carbon Chains

We studied monatomic linear carbon chains stabilized by gold nanoparticles attached to their ends and deposited on a solid substrate. We observe spectral features of straight chains containing from 8 to 24 atoms. Low-temperature PL spectra reveal characteristic triplet fine structures that repeat themselves for carbon chains of different lengths. The triplet is invariably composed of a sharp intense peak accompanied by two broader satellites situated 15 and 40 meV below the main peak. We interpret these resonances as an edge-state neutral exciton and positively and negatively charged trions, respectively. The time-resolved PL shows that the radiative lifetime of the observed quasiparticles is about 1 ns, and it increases with the increase of the length of the chain. At high temperatures a nonradiative exciton decay channel appears due to the thermal hopping of carriers between parallel carbon chains. Excitons in carbon chains possess large oscillator strengths and extremely low inhomogeneous broadenings.

Fundamental Understanding of the Formation Mechanism for Graphene Quantum Dots Fabricated by Pulsed Laser Fragmentation in Liquid: Experimental and Theoretical Insight

The pulsed laser fragmentation in liquid (PLFL) process is a promising technique for the synthesis of carbon-based functional materials. In particular, there has been considerable attention on graphene quantum dots (GQDs) derived from multiwalled carbon nanotubes (MWCNTs) by the PLFL process, owing to the low cost and rapid processing time involved. However, a fundamental deep understanding of the formation of GQDs from MWCNTs by PLFL has still not been achieved despite the high demand. In this work, a mechanism for the formation of GQDs from MWCNTs by the PLFL process is reported, through the combination of experimental and theoretical studies. Both the experimental and computational results demonstrate that the formation of GQDs strongly depends on the pulse laser energy. Both methods demonstrate that the critical energy point, where a plasma plume is generated on the surface of the MWCNTs, should be precisely maintained to produce GQDs; otherwise, an amorphous carbon structure is favorably formed from the scattered carbons.

Electric field assisted alignment of monoatomic carbon chains

We stabilize monoatomic carbon chains in water by attaching them to gold nanoparticles (NPs) by means of the laser ablation process. Resulting nanoobjects represent pairs of NPs connected by multiple straight carbon chains of several nanometer lengths. If NPs at the opposite ends of a chain differ in size, the structure acquires a dipole moment due to the difference in work functions of the two NPs. We take advantage of the dipole polarisation of carbon chains for ordering them by the external electric field. We deposit them on a glass substrate by the sputtering method in the presence of static electric fields of magnitudes up to 10⁵ V/m. The formation of one-dimensional carbyne quasi-crystals deposited on a substrate is evidenced by high-resolution TEM and X-ray diffraction measurements. The original kinetic model describing the dynamics of ballistically flowing nano-dipoles reproduces the experimental diagram of orientation of the deposited chains.

Carbyne-enriched carbon anchored on nickel foam: A novel binder-free electrode for supercapacitor application

Carbon- and carbon derivatives are widely employed as efficient electrode materials for supercapacitor applications. Herein, we demonstrate a cost-effective dip-coating process followed by dehydrohalogenation of PVDF-Ni for the preparation of carbyne enriched carbon anchored on nickel (CEC-Ni) as high-performance electrode material. The removal of halogens in the prepared CEC-Ni were widely characterized using XRD, XPS, Laser Raman, and FT-IR analysis. The occurrence of carbon-carbon vibration in the prepared CEC-Ni foam was confirmed using FT-IR spectroscopy. Laser Raman analysis confirms that the CEC-Ni foam contains both sp and sp² hybridized carbon. The electrochemical properties of prepared carbyne enriched carbon anchored on nickel foam electrode (CEC-NiE) showed an ideal capacitive properties and delivered a maximum specific capacitance of about 106.12 F g^-1 with excellent cyclic retention. Furthermore, the mechanism of charge-storage in the CEC-NiE was analyzed using Dunn's method. In additon, the asymmetric supercapacitor device was fabricated using CEC-NiE as positive and rGO as negative electrode achieved a remarkable energy density of 33.57 Wh Kg^-1 with a maximal power density of 14825.71 W Kg^-1. These results suggested that the facile preparation of CEC-NiE could be a promising and effective electrode material for future energy storage application.

Femtosecond Photon-Mediated Plasma Enhances Photosynthesis of Plasmonic Nanostructures and Their SERS Applications

Laser ablation in liquid has proven to be a universal and green method to synthesize nanocrystals and fabricate functional nanostructures. This study demonstrates the superiority of femtosecond laser-mediated plasma in enhancing photoredox of metal cations for controllable fabrication of plasmonic nanostructures in liquid. Through employing upstream high energetic plasma during laser-induced microexplosions, single/three-electron photoreduction of metallic cations can readily occur without chemical reductants or capping agents. Experimental evidences demonstrate that this process exhibits higher photon utilization efficiency in yield of colloidal metal nanoparticles than direct irradiation of metallic precursors. Photogenerated hydrated electrons derived from strong ionization of silicon and water are responsible for this enhanced consequences. Furthermore, these metallic nanoparticles are accessible to self-assemble into nanoplates for silver and nanospheres for gold, favored by surface-tension gradients between laser irradiated and unirradiated regions. These metallic nanostructures exhibit excellent surface-enhanced Raman spectroscopy performance in trace detection of Rhodamine 6G (R6G), 4-mercaptobenzoic acid (4-MBA), and mercapto-5-nitrobenzimidazole molecules with high sensitivity (down to 10^-12 mol L^-1 , 30 × 10^-15 m for R6G), good reproducibility (relative standard deviation < 7%), and good dual-analyte detection ability with mixture ratios of R6G to 4-MBA ranging from 20 to 0.025. The conceptual importance of this plasma-enhanced-photochemical process may provide exciting opportunities in photochemical reactions, plasmofluidics, and material synthesis.

Room temperature p-orbital magnetism in carbon chains and the role of group IV, V, VI, and VII dopants

The study of magnetism without the involvement of transition metals or rare earth ions is considered the key to the fabrication of next generation spintronic devices. Several recent reports claim that optimizing the occupation number of the mixed p-orbitals is the correct way to reinforce p-orbital magnetism in bulk crystals. We provide experimental evidence that the kinked monoatomic carbon chains, the so-called linear-chained carbon, generate intrinsic ferromagnetism even above room temperature. According to our ab initio calculations, unconventional magnetism has its origin in the p-shells. In contrast, the linear monoatomic carbon chains are non-magnetic. Although the optimized differential spin density of states at the Fermi level (SDOS) of the kinked carbon chains is higher than that of bulk Fe, the magnetic moment is as low as 0.3μB. In order to enhance the magnetic response, we decided to tune the p-orbital magnetism by adding dopants from groups IV to VII of the periodic table. We observed that the strength of the p-orbital magnetism and the sign of the exchange interaction depend not only on the kink angle, but also on the concentration of lone pair electrons, free radical electrons, lateral chain spacing, internal electric dipole, dative covalent bonds and the Bohr radius of the dopants. Surprisingly, the V and VII-doped carbon chains show a strong non-zero SDOS, which has its origin in the p-shells. The VII-doped carbon chains give the SDOS of the opposite sign. Our best system, the arsenic-doped carbon chain, exhibits a strong local magnetic moment of 1.5μB, which is comparable to that of the bulk Fe of 2.2μB, with the mean exchange-correlation energy reaching a 63% ratio relative to that of the bulk Fe.

Formation of carbyne-like materials during low temperature pyrolysis of lignocellulosic biomass: A natural resource of linear sp carbons

The exploration, understanding and potential applications of ‘Carbyne’, the one-dimensional sp allotrope of carbon, have been severely limited due to its extreme reactivity and a tendency for highly exothermic cross-linking. Due to ill-defined materials, limited characterization and a lack of compelling definitive evidence, even the existence of linear carbons has been questioned. We report a first-ever investigation on the formation of carbyne-like materials during low temperature pyrolysis of biobased lignin, a natural bioresource. The presence of carbyne was confirmed by detecting acetylenic –C≡C– bonds in lignin chars using NMR, Raman and FTIR spectroscopies. The crystallographic structure of this phase was determined as hexagonal: a = 6.052 Å, c = 6.96 Å from x-ray diffraction results. HRSEM images on lignin chars showed that the carbyne phase was present as nanoscale flakes/fibers (~10 nm thick) dispersed in an organic matrix and showed no sign of overlapping or physical contact. These nanostructures did not show any tendency towards cross-linking, but preferred to branch out instead. Overcoming key issues/challenges associated with their formation and stability, this study presents a novel approach for producing a stable condensed phase of sp-bonded linear carbons from a low-cost, naturally abundant, and renewable bioresource.

Twisting of Alkynes towards a Carbon Double Helix

The carbon allotrope exhibiting only one-dimensional sp-hybridized carbon atoms is called carbyne. However, its existence is very controversial. Studies on model compounds for carbyne revealed that many oligoalkynes show not a straight, but a bent structure of the carbon chain. Here, we question whether it would also be possible to obtain a more complex structure from carbyne, such as a dimeric double helix. Based on quantum chemical calculations, we show that only a small energetic expense is needed for the formation of a double helix starting from oligoalkyne chains. In some cases, the double helix-like conformation is more stable than the corresponding conformation with a parallel arrangement of the acetylene chains. Furthermore, model systems were synthesized in which two diphenyl oligoalkyne chains are fixed and twisted by a chiral imidazole-containing clamp. A structural investigation of these model systems was performed based on UV and CD spectroscopy and quantum chemical calculations. The observed twisting in these model systems can be regarded as the first small step towards an imaginable carbon double helix.

Molecular Luminescence of White Carbon

Four-color emission modulated by the molecular chain length from white carbon (carbyne crystals) is observed. It is also established that a carbyne molecule with four carbon atoms is the basic unit or building block to construct carbyne crystals, where the chain length of the carbyne molecule in the synthesized carbyne crystals follows the rule of 4n (n = 1, 2, 3, …).

Mechanical and Electronic Properties of XC₆ and XC12

A series of carbon-based superconductors XC₆ with high T_c were reported recently. In this paper, based on the first-principles calculations, we studied the mechanical properties of these structures, and further explored the XC₁₂ phases, where the X atoms are from elemental hydrogen to calcium, except noble gas atoms. The mechanically- and dynamically-stable structures include HC₆, NC₆, and SC₆ in XC₆ phases, and BC₁₂, CC₁₂, PC₁₂, SC₁₂, ClC₁₂, and KC₁₂ in XC₁₂ phases. The doping leads to a weakening in mechanical properties and an increase in the elastic anisotropy. C₆ has the lowest elastic anisotropy, and the anisotropy increases with the atomic number of doping atoms for both XC₆ and XC₁₂. Furthermore, the acoustic velocities, Debye temperatures, and the electronic properties are also studied.

Pseudocarbynes: Charge-Stabilized Carbon Chains

Carbyne is the long-sought linear allotrope of carbon. Despite many reports of solid carbyne, the evidence is unconvincing. A recent report of supposed carbyne shows gold clusters in transmission electron microscopy (TEM) images. In order to determine the effects of such clusters, we performed ab initio calculations of uncapped and capped linear carbon chains and their complexes with gold clusters. The results indicate that gold dramatically alters the electron densities of the C≡C bonds. The resulting charge-stabilization of the carbon chains leads to pseudocarbynes. These findings are corroborated in calculations of the structures of crystals containing isolated carbon chains and those intercalated with gold clusters. Calculated Raman spectra of these pseudocarbynes with gold clusters are in better agreement with experiment than calculated spectra of isolated carbon chains. The current work opens the way toward the design and development of a new class of metal-intercalated carbon compounds.