### Recent Submissions

• #### The elemental analysis and multi-nuclear NMR study of an alkali molten salt used to digest reference and commercial SWCNT powders

(Journal of Analytical Atomic Spectrometry, Royal Society of Chemistry (RSC), 2020-10-09) [Article]
For quite some time, alkaline oxidation (or fusion) has been used to solubilize refractory materials and mineral ores. Recently, its application scope was extended to facilitate batch-scale elemental analysis of nanomaterials such as carbon nanotubes. Here, a sodium tetraborate salt was used to digest four different types of single-walled carbon nanotubes. These samples were produced employing Co–Mo or Fe catalyst systems. Their graphitic matrix was exposed to different melt temperatures for a short period of time, following which the concentration of six transition metals was measured. Recoveries in excess of 80% were obtained, with the melt temperature affecting more the elemental extraction in Fe-catalyzed nanotubes. Together with previous results, the work described allows drawing pertinent conclusions on the advantages and limitations of alkaline oxidation as an alternative sample digestion approach for the routine chemical analysis of nanocarbons.
• #### Cyclized polyacrylonitrile anode for alkali metal ion batteries

(Angewandte Chemie International Edition, Wiley, 2020-10-05) [Article]
Alkali metal (Li, Na, and K) ion batteries are vital in portable and large-scale stationary energy storage. Recently, organic anodes have attracted increasing attention for alkali metal ion batteries due to their chemical diversity and potential high capacity. In this work, we discovered that cyclized polyacrylonitrile (cPAN) can serve as a superior anode for alkali metal ion batteries. Remarkably, upon activation cycling, as an anode of lithium-ion battery, cPAN exhibits a reversible capacity as high as 1238 mAh g-1 under a current density of 50 mA g-1. Based on electrochemical experiments and first-principles calculations, it is demonstrated that the hexagonal carbon ring, piperidine ring, and pyridine nitrogen in ladder cPAN are the main active sites for lithium-ion storage. In addition, we show that cPAN displays a unique potential-dependent solid electrolyte interphase formation from 0.1 to 0.01 V vs. Li/Li+. Furthermore, cPAN displays decent performance as an anode in SIBs and PIBs. The discovery of cPAN anode could pave the way for the future development of organic anodes for alkali metal ion batteries.
• #### Cyclized polyacrylonitrile anode for alkali metal ion batteries

(Angewandte Chemie International Edition, Wiley, 2020-10-05) [Article]
Alkali metal (Li, Na, and K) ion batteries are vital in portable and large-scale stationary energy storage. Recently, organic anodes have attracted increasing attention for alkali metal ion batteries due to their chemical diversity and potential high capacity. In this work, we discovered that cyclized polyacrylonitrile (cPAN) can serve as a superior anode for alkali metal ion batteries. Remarkably, upon activation cycling, as an anode of lithium-ion battery, cPAN exhibits a reversible capacity as high as 1238 mAh g-1 under a current density of 50 mA g-1. Based on electrochemical experiments and first-principles calculations, it is demonstrated that the hexagonal carbon ring, piperidine ring, and pyridine nitrogen in ladder cPAN are the main active sites for lithium-ion storage. In addition, we show that cPAN displays a unique potential-dependent solid electrolyte interphase formation from 0.1 to 0.01 V vs. Li/Li+. Furthermore, cPAN displays decent performance as an anode in SIBs and PIBs. The discovery of cPAN anode could pave the way for the future development of organic anodes for alkali metal ion batteries.
• #### Titanium methyl tamed on silica: synthesis of a well-defined pre-catalyst for hydrogenolysis of n-alkane

(Chemical Communications, Royal Society of Chemistry (RSC), 2020-10-05) [Article]
Alkylation of Ti(CH3)2Cl2 1 by MeLi gives the homoleptic Ti(CH3)42 for the first time in the absence of any coordinating solvent. The reaction of 2 with silica pretreated at 700 8C (SiO2–700) gives two inequivalent silica-supported Ti-methyl species 3. Complex 3 was characterized by IR, microanalysis (ICP-OES, CHNS, and gas quantification), and advanced solid-state NMR spectroscopy (1H, 13C, DQ, TQ, and HETCOR). The catalytic activity of the precatalyst 3 is investigated in low-temperature hydrogenolysis of propane and n-butane with TONs of 419 and 578, respectively
• #### Bending strain tailored exchange bias in epitaxial NiMn/γ′-Fe4N bilayers

(Applied Physics Letters, AIP Publishing, 2020-09-28) [Article]
The strain tunable exchange bias has attracted much attention due to its practical applications in flexible and wearable spintronic devices. Here, the flexible epitaxial NiMn/c0-Fe4N bilayers are deposited by facing-target reactive sputtering. The maximum strain-induced change ratios of exchange bias field HEB and coercivity HC (jDHEB/HEBj and jDHC/HCj) are 51% and 22%, respectively. A large strain-induced jDHEB/HEBj appears in a thicker ferromagnetic layer, but a large jDHC/HCj) appears in a thinner ferromagnetic layer. At a compressive strain, the antiferromagnetic anisotropy of the tetragonal NiMn layer increases, resulting in an increased HC of NiMn/c0-Fe4N bilayers. The bending-strain induced changes of anisotropy magnetoresistance and planar Hall resistance are also observed at low magnetic fields. The bending-strain tailored magnetic properties can be ascribed to the distributions of ferromagnetic and antiferromagnetic anisotropies.
• #### Extension of the Surface Organometallic Chemistry to Metal-Organic Framework: development of well-defined single site [(≡Zr-O-)W(=O)(CH2tBu)3] olefin metathesis catalyst.

(Journal of the American Chemical Society, American Chemical Society (ACS), 2020-09-09) [Article]
We report here the first step by step anchoring of a W(≡CtBu)(CH2 tBu)3 complex on a highly crystalline and mesoporous MOF, namely Zr-NU-1000, using Surface organometallic Chemistry (SOMC) concept and methodology. SOMC allowed us to selectively graft the complex on the Zr6 clusters and characterize the obtained single site material by using state of the art experimental methods including extensive solid-state NMR techniques and HAADF-STEM imaging. Further FT-IR spectroscopy revealed the presence of a W=O moiety arising from the in situ reaction of the W≡CtBu functionality with the coordinated water coming from the 8-connected hexanuclear Zr6 clusters. All the steps leading to the final grafted molecular complex have been identified by DFT. The obtained material was tested for gas phase and liquid phase olefin metathesis and exhibited higher catalytic activity than the corresponding catalysts synthesized by different grafting methods. This contribution establishes the importance of applying SOMC to MOF chemistry to get well defined single site catalyst on MOF inorganic secondary building units, in particular the in situ synthesis of W=O alkyl complexes from their W carbyne analogues.
• #### Impact of p-type doping on charge transport in blade-coated small-molecule:polymer blend transistors

(Journal of Materials Chemistry C, Royal Society of Chemistry (RSC), 2020-09-03) [Article]
Blade-coating is used to fabricate high hole mobility organic transistors based on a p-doped small-molecule:polymer blend semiconductor.
• #### Quantifying the Transverse-Electric-Dominant 260 nm Emission from Molecular Beam Epitaxy-Grown GaN-Quantum-Disks Embedded in AlN Nanowires: A Comprehensive Optical and Morphological Characterization

(ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2020-09-01) [Article]
There has been a relentless pursuit of transverse electric (TE)-dominant deep ultraviolet (UV) optoelectronic devices for efficient surface emitters to replace the environmentally unfriendly mercury lamps. To date, the use of the ternary AlGaN alloy inevitably has led to transverse magnetic (TM)-dominant emission, an approach that is facing a roadblock. Here, we take an entirely different approach of utilizing a binary GaN compound semiconductor in conjunction with ultrathin quantum disks (QDisks) embedded in AlN nanowires (NWs). The growth of GaN QDisks is realized on a scalable and low-cost Si substrate using plasma-assisted molecular beam epitaxy as a highly controllable monolayer growth platform. We estimated an internal quantum efficiency of ∼81% in a wavelength regime of ∼260 nm for these nanostructures. Additionally, strain mapping obtained by high-angle annular dark-field scanning transmission electron microscopy is studied in conjunction with the TE and TM modes of the carrier recombination. Moreover, for the first time, we quantify the TE and TM modes of the PL emitted by GaN QDisks for deep-UV emitters. We observed nearly pure TE-polarized photoluminescence emission at a polarization angle of ∼5°. This work proposes highly quantum-confined ultrathin GaN QDisks as a promising candidate for deep-UV vertical emitters.
• #### Smart covalent organic networks (CONs) with “on-off-on” light-switchable pores for molecular separation

(Science Advances, American Association for the Advancement of Science (AAAS), 2020-08-19) [Article]
Development of the new-generation membranes for tunable molecular separation requires materials with abilities beyond strict separation. Stimuli response could remotely adjust the membrane selectivity. Azobenzene derivatives can be photo-switched between trans and cis isomers under ultraviolet or visible light. Here, the azobenzenes were implanted as light switches to bridge the flexible cyclen building blocks. The smart covalent organic network membranes fold and unfold as origami that can be photo-switched between on-state (large) and off-state (small) pores. The cis membranes with off state under ultraviolet (UV) light have higher dye rejection than trans membranes with on-state channels. By controlling the trans-to-cis azobenzene isomerization via UV/Vis light, the pore size can be remotely controlled at the molecular level and the solvent permeance and dye rejection can be dynamically tuned.
• #### Evidence for Silica Surface Three- and Five-Membered Metallacycle Intermediates in the Catalytic Cycle of Hydroaminoalkylation of Olefins Using Single-Ti-Metal Catalysts

(Organometallics, American Chemical Society (ACS), 2020-06-30) [Article]
The single-site silica-supported group IV metal amido complex [Ti(NMe2)4] gives the tris(amido)-supported fragment [(=Si−O−)Ti(−NMe2)3], which transforms into a three-membered metallacycle (called a metallaaziridine) by an αH transfer between two amido ligands. When the three-membered metallacycle reacts with 1-octene, it gives a five-membered metallacycle by insertion of the double bond into the M−C bond of the metallaziridine. These two metallacycles, key intermediates in the catalytic cycle of the hydroaminoalkylation of terminal olefins, were isolated and fully characterized following the surface organometallic chemistry (SOMC) concept and procedures. This paper shows that surface organometallic chemistry can be used to identify and fully characterize three- and five-membered metallacycles of Ti in the hydroaminoalkylation of olefins.
• #### Capacity Retention Analysis in Aluminum-Sulfur Batteries

(ACS Applied Energy Materials, American Chemical Society (ACS), 2020-06-15) [Article]
The electrochemical performance of aluminum-sulfur batteries is beset by poor stability and sluggish charge-storage properties. To address these issues, carbon allotropes have been used as electrode fillers, but successful outcomes remain inexplicably elusive. Here, a composite of sulfur and small-diameter single-walled carbon nanotubes was studied as a cathode for AlCl3:[EMIM]-based aluminum batteries. The presence of carbon nanotubes, while enabling a high capacity (1024 mAh g-1) with slower decay and reducing the electrolyte-to-sulfur ratio, is insufficient to fully stabilize the cell's performance. In fact, the main obstacle is in the interaction between sulfur and chloroaluminate ions. As we show, there is a gradual buildup of insoluble and poorly conductive discharge products that inhibit the diffusion of electroactive ions and, ultimately, cause capacity decay. Overall, this work sheds light on the carbon-sulfur-electrolyte interactions and their role on the underlying charge-storage mechanism of aluminum-sulfur batteries.
• #### Phenanthroline Covalent Organic Framework Electrodes for High-Performance Zinc-Ion Supercapattery

(ACS Energy Letters, American Chemical Society (ACS), 2020-06-08) [Article]
Aqueous zinc-ion batteries and capacitors are potentially competitive grid-scale energy storage devices because of their great features such as safety, environmental friendliness, and low cost. Herein, a completely new phenanthroline covalent organic framework (PA-COF) was synthesized and introduced in zinc-ion supercapatteries (ZISs) for the first time. Our as-synthesized PA-COF shows a high capacity of 247 mAh g-1 at a current density of 0.1 A g-1, with only 0.38% capacity decay per cycle during 10â€»000 cycles at a current density of 1.0 A g-1. Although covalent organic frameworks (COFs) are attracting great attention in many fields, our PA-COF has been synthesized using a new strategy involving the condensation reaction of hexaketocyclohexanone and 2,3,7,8-phenazinetetramine. Detailed mechanistic investigations, through experimental and theoretical methods, reveal that the phenanthroline functional groups in PA-COF are the active zinc ion storage sites. Furthermore, we provide evidence for the cointercalation of Zn2+ (60%) and H+ (40%) into PA-COF using inductively coupled plasma atomic emission spectroscopy and deuterium solid-state nuclear magnetic resonance (NMR). We believe that this study opens a new avenue for COF material design for zinc-ion storage in aqueous ZISs.
• #### Lattice deformation in epitaxial Fe3O4 films on MgO substrate studied by polarized Raman spectroscopy∗

(Chinese Physics B, IOP Publishing, 2020-05-25) [Article]
The lattice structures of epitaxial Fe3O4 films deposited on MgO were studied systematically using polarized Raman spectroscopy as a function of film thickness, where interesting phenomena were observed. Firstly, the spectral conflict to the Raman selection rules (RSRs) was observed under cross sectional configuration, which can be attributed to the tetragonal deformation in the growth direction due to the lattice mismatch between Fe3O4 and MgO. Secondly, the blue-shift and broadening of Raman peaks evidenced the decrease of the tensile strain in Fe3O4 film with decreased thickness. Thirdly, distinct from the other Raman modes, the lowest T 2g mode exhibited asymmetric lineshape, which can be interpreted using the spatial correlation model. The increased correlation length introduced in the model can well explain the enhanced peak asymmetry feature with decreasing thickness. These results provide useful information for understanding the lattice structure of epitaxial Fe3O4 film.
• #### Impact of small promoter amounts on coke structure in dry reforming of methane over Ni/ZrO2

(Catalysis Science & Technology, Royal Society of Chemistry (RSC), 2020-05-22) [Article]
Coke deposition is one of the main challenges in the commercialisation of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of Na, K, and Cs promoters on both these variables over Ni/ZrO2 catalysts. Besides blocking the most active coke-forming sites already at low loading, the promoting effect of the alkali metals is also contributed to by their coke gasification activity. To evaluate the additional impact of the latter, the behaviour of alkali-doped catalysts was compared to that for Mn-doped catalysts, exclusively featuring the site-blocking promotion mechanism. While the conversion is barely affected by the type of promoter, it has a profound effect on the amount and the composition of carbon deposits formed during the reaction. Promoting with K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. The promotion by Cs and Na results in the lowest coke content. The superior performance of Cs and Na-doped Ni/ZrO2 catalysts is attributed to the enhanced coke gasification via carbonate species on top of the site blocking effects.
• #### Piezotronic AlGaN nanowire Schottky junctions grown on a metal substrate

(AIP Advances, AIP Publishing, 2020-05-11) [Article]
The non-centrosymmetric crystal structures of polar-semiconductors comprising GaN, InN, AlN, and ZnO intrigued the scientific community in investigating their potential for a strain-induced nano-energy generation. The coupled semiconducting and piezoelectric properties produce a piezo-potential that modulates the charge transport across their heterostructure interfaces. By using conductive-atomic force microscopy, we investigate the mechanism that gives rise to the piezotronic effect in AlGaN nanowires (NWs) grown on a molybdenum (Mo) substrate. By applying external bias and force on the NWs/Mo structure using a Pt–Ir probe, the charge transport across the two adjoining Schottky junctions is modulated due to the change in the apparent Schottky barrier heights (SBHs) that result from the strain-induced piezo-potential. We measured an increase in the SBH of 98.12 meV with respect to the background force, which corresponds to an SBH variation $\textstyle\frac{\partial\phi}{\partial F}$ of 6.24 meV/nN for the semiconductor/Ti/Mo interface. The SBH modulation, which is responsible for the piezotronic effect, is further studied by measuring the temperature-dependent I–V curves from room temperature to 398 K. The insights gained from the unique structure of AlGaN NWs/Mo shed light on the electronic properties of the metal-semiconductor interfaces, as well as on the potential application of AlGaN NW piezoelectric nanomaterials in optoelectronics, sensors, and energy generation applications.
• #### Impact of Small Promoter Amounts on Coke Structure in Dry Reforming over Ni/ ZrO2

(American Chemical Society (ACS), 2020-04-23) [Preprint]
Coke deposition is one of the main challenges in the commercialization of dry reforming of methane over supported Ni catalysts. Besides the coke quantity, the structure of the deposits is also essential for the catalyst lifetime. Accordingly, in this study, we analysed the effect of different metal promoters on both these variables over Ni/ ZrO$_{2}$ catalysts. Alkali metals are known to block the most active coke forming sites already at low loading, leading to an investigation of Na, K and Cs. To analyse the possible contributions of coke gasification activity of the alkali metals, Mn was additionally used as a comparison. While the conversion is barely affected by the type of promoter, it has profound effect on the amount and the composition of carbon deposits formed during reaction: Addition of K or Mn reduces the coke content to a similar degree but with less carbon fibres observed in the case of K. Promotion by Cs and Na results in the lowest coke content, which is attributed to enhanced coke gasification via carbonate species
• #### [Cu81(PhS)46(tBuNH2)10(H)32]3+ Reveals the Coexistence of Large Planar Cores and Hemispherical Shells in High-Nuclearity Copper Nanoclusters

(Journal of the American Chemical Society, American Chemical Society (ACS), 2020-04-21) [Article]
Copper-based nanomaterials have attracted tremendous interest due to their unique properties in the fields of photoluminescence and catalysis. As a result, studies on the correlation between their molecular structure and their properties are of great importance. Copper nanoclusters are a new class of nanomaterials that can provide an atomic-level view of the crystal structure of copper nanoparticles. Herein, a high-nuclearity copper nanocluster with 81 copper atoms, formulated as [Cu81(PhS)46(tBuNH2)10(H)32]3+ (Cu81), was successfully synthesized and fully studied by X-ray crystallography, X-ray photoelectron spectroscopy, hydrogen evolution experiments, electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and density functional theory calculations. Cu81 exhibits extraordinary structural characteristics, including (i) three types of novel epitaxial surface-protecting motifs; (ii) an unusual planar Cu17 core; (iii) a hemispherical shell, comprised of a curved surface layer and a planar surface layer; and (iv) two distinct, self-organized arrangements of protective ligands on the curved and planar surfaces. The present study sheds light on structurally unexplored copper nanomaterials and paves the way for the synthesis of high-nuclearity copper nanoclusters.
• #### Effect of surface roughness on the anomalous Hall effect in Fe thin films

(Physical Review B, American Physical Societyrevtex@aps.org, 2020-04-01) [Article]
Surface roughness plays an important role on the magnetotransport properties of thin films, especially in ultrathin films. In this work, we prepared Fe thin films with various surface roughness by using different seed layers and studied the electrical transport and anomalous Hall effect. By tuning surface roughness scattering, the longitudinal resistivity (ρxx) measured at 5 K increases by one order of magnitude and the corresponding anomalous Hall resistivity (ρAHE) increases by three times with increasing roughness. The intrinsic, skew-scattering, and side-jump contributions to ρAHE were separated from our data. The anomalous Hall angle depends on the surface roughness, which may be of importance to the material engineering for achieving large spin Hall angle.
• #### Ligand-free gold nanoclusters confined in mesoporous silica nanoparticles for styrene epoxidation

(Nanoscale Advances, Royal Society of Chemistry (RSC), 2020-03-18) [Article]
We present a novel approach to produce gold nanoclusters (Au NCs) in the pores of mesoporous silica nanoparticles (MSNs) by sequential and controlled addition of metal ions and reducing agents. This impregnation technique was followed to confine Au NCs inside the pores of MSNs without adding external ligands or stabilizing agents. TEM images show a uniform distribution of monodisperse NCs with an average size of 1.37 ± 0.4 nm. Since the NCs are grown in situ in MSN pores, additional support and high temperature calcination are not required to use them as catalysts. The use of Au NC/MSNs as a catalyst for the epoxidation of styrene in the presence of tert-butyl hydroperoxide (TBHP) as a terminal oxidant resulted in an 88% conversion of styrene in 12 h with a 74% selectivity towards styrene epoxide. Our observations suggest that this remarkable catalytic performance is due to the small size of Au NCs and the strong interaction between gold and the MSNs. This catalytic conversion is environmentally friendly as it is solvent free. We believe our synthetic approach can be extended to other metal NCs offering a wide range of applications.
• #### Spray-coated graphene oxide hollow fibers for nanofiltration

(Journal of Membrane Science, Elsevier BV, 2020-03-09) [Article]
Advances in process intensification in the chemical and pharmaceutical industry depends on the availability of more sustainable separation methods. For this progress, membranes with high stability in organic solvents are needed. GO-coated membranes could be advantageous in these applications, being chemically, thermally and mechanically stable. However, simple, scalable, low-cost fabrication methods, particularly for GO deposition on hollow fibers are still in an early phase. We propose here a simple spray-coating method for deposition of GO sheets on crosslinked hollow fiber supports. We first fabricated polyetherimide hollow fiber membranes and crosslinked them with hexamethylene diamine. These supports have strong tolerance to various organic solvents. The amide reaction arising between the imide groups of polyetherimide and the amine groups of hexamethylene diamine provide even higher chemical and mechanical stability. Thereafter, the spray-coating of GO dispersions led to the formation of a stable selective layer on the hollow fibers. An excellent adhesion between GO and the substrate was achieved. The chemical reasons for that were investigated by solid state NMR. Overall, this simple method enables the application of GO hollow fiber membranes in organic solvent nanofiltration, with high performance demonstrated in water and acetone.