Publications by authors named "Pulickel M Ajayan"

430 Publications

Corrosion Resistance of Sulfur-Selenium Alloy Coatings.

Adv Mater 2021 Oct 15:e2104467. Epub 2021 Oct 15.

Department of Materials Science and NanoEngineering, Rice University, Houston, TX, 77005, USA.

Despite decades of research, metallic corrosion remains a long-standing challenge in many engineering applications. Specifically, designing a material that can resist corrosion both in abiotic as well as biotic environments remains elusive. Here a lightweight sulfur-selenium (S-Se) alloy is designed with high stiffness and ductility that can serve as an excellent corrosion-resistant coating with protection efficiency of ≈99.9% for steel in a wide range of diverse environments. S-Se coated mild steel shows a corrosion rate that is 6-7 orders of magnitude lower than bare metal in abiotic (simulated seawater and sodium sulfate solution) and biotic (sulfate-reducing bacterial medium) environments. The coating is strongly adhesive, mechanically robust, and demonstrates excellent damage/deformation recovery properties, which provide the added advantage of significantly reducing the probability of a defect being generated and sustained in the coating, thus improving its longevity. The high corrosion resistance of the alloy is attributed in diverse environments to its semicrystalline, nonporous, antimicrobial, and viscoelastic nature with superior mechanical performance, enabling it to successfully block a variety of diffusing species.
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http://dx.doi.org/10.1002/adma.202104467DOI Listing
October 2021

3D-printed silica with nanoscale resolution.

Nat Mater 2021 Oct 14. Epub 2021 Oct 14.

Department of Materials Science and NanoEngineering, Rice University, Houston, TX, USA.

Fabricating inorganic materials with designed three-dimensional nanostructures is an exciting yet challenging area of research and industrial application. Here, we develop an approach to 3D print high-quality nanostructures of silica with sub-200 nm resolution and with the flexible capability of rare-earth element doping. The printed SiO can be either amorphous glass or polycrystalline cristobalite controlled by the sintering process. The 3D-printed nanostructures demonstrate attractive optical properties. For instance, the fabricated micro-toroid optical resonators can reach quality factors (Q) of over 10. Moreover, and importantly for optical applications, doping and codoping of rare-earth salts such as Er, Tm, Yb, Eu and Nd can be directly implemented in the printed SiO structures, showing strong photoluminescence at the desired wavelengths. This technique shows the potential for building integrated microphotonics with silica via 3D printing.
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http://dx.doi.org/10.1038/s41563-021-01111-2DOI Listing
October 2021

Manipulation on active electronic states of metastable phase β-NiMoO for large current density hydrogen evolution.

Nat Commun 2021 Oct 13;12(1):5960. Epub 2021 Oct 13.

Institute of Special Materials and Technology, Fudan University, Shanghai, China.

Non-noble transition metal oxides are abundant in nature. However, they are widely regarded as catalytically inert for hydrogen evolution reaction (HER) due to their scarce active electronic states near the Fermi-level. How to largely improve the HER activity of these kinds of materials remains a great challenge. Herein, as a proof-of-concept, we design a non-solvent strategy to achieve phosphate substitution and the subsequent crystal phase stabilization of metastable β-NiMoO. Phosphate substitution is proved to be imperative for the stabilization and activation of β-NiMoO, which can efficiently generate the active electronic states and promote the intrinsic HER activity. As a result, phosphate substituted β-NiMoO exhibits the optimal hydrogen adsorption free energy (-0.046 eV) and ultralow overpotential of -23 mV at 10 mA cm in 1 M KOH for HER. Especially, it maintains long-term stability for 200 h at the large current density of 1000 mA cm with an overpotential of only -210 mV. This work provides a route for activating transition metal oxides for HER by stabilizing the metastable phase with abundant active electronic states.
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http://dx.doi.org/10.1038/s41467-021-26256-1DOI Listing
October 2021

Amine-Functionalized Carbon Nanodot Electrocatalysts Converting Carbon Dioxide to Methane.

Adv Mater 2021 Oct 11:e2105690. Epub 2021 Oct 11.

Department of Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, OH, 45221, USA.

The electrochemical conversion of carbon dioxide (CO ) to methane (CH ), which can be used not only as fuel but also as a hydrogen carrier, has drawn great attention for use in supporting carbon capture and utilization. The design of active and selective electrocatalysts with exceptional CO -to-CH conversion efficiency is highly desirable; however, it remains a challenge. Here a molecular tuning strategy-in situ amine functionalization of nitrogen-doped graphene quantum dots (GQDs) for highly efficient CO -to-CH conversion is presented. Amine functionalized nitrogen-doped GQDs achieve a CH Faradic efficiency (FE) of 63% and 46%, respectively, at CH partial current densities of 170 and 258 mA cm , approximating to or even outperforming state-of-the-art Cu-based electrocatalysts. These GQDs also convert CO to C products mainly including C H and C H OH with a maximum FE of ≈10%. A systematic analysis reveals that the CH yield varies linearly with amine group content, whereas the C production rate is positively dependent on pyridinic N dopant content. This work provides insight into the rational design of carbon catalysts with CO -to-CH conversion efficiency at the industrially relevant level.
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http://dx.doi.org/10.1002/adma.202105690DOI Listing
October 2021

Gas-Phase Fluorination of Hexagonal Boron Nitride.

Adv Mater 2021 Oct 7:e2106084. Epub 2021 Oct 7.

Department of Materials Science & NanoEngineering, Rice University, Houston, TX, 77005, USA.

Hexagonal boron nitride (hBN) has received much attention in recent years as a 2D dielectric material with potential applications ranging from catalysts to electronics. hBN is a stable covalent compound with a planar hexagonal lattice and is relatively unreactive to most chemical environments, making the chemical functionalization of hBN challenging. Here, a simple, scalable strategy to fluorinate hBN using a direct gas-phase fluorination technique is reported. The nature of fluorine bonding to the hBN lattice and their chemical coordination are described based on various characterization studies and theoretical models. The fluorine functionalized hBN shows a bandgap reduction and displays a semiconducting behavior due to the fluorination process. Additionally, the fluorinated hBN shows significant improvement in its thermal and friction properties, which could be substantial in applications such as lubricants and thermal fluids. Theory and simulations reveal that the enhanced friction properties of fluorinated hBN result from reduced inter-planar interaction energy by electrostatic repulsion of intercalated fluorine atoms between hBN layers without significant disruption of the in-plane lattice. This technique paves the way for the fluorination of several other 2D structures for various applications such as magnetism and functional nanoscale electronic devices.
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http://dx.doi.org/10.1002/adma.202106084DOI Listing
October 2021

Structure, Properties and Applications of Two-Dimensional Hexagonal Boron Nitride.

Adv Mater 2021 Sep 24:e2101589. Epub 2021 Sep 24.

Department of Materials Science and NanoEngineering, Rice University, 6100 Main St., Houston, TX, 77005, USA.

Hexagonal boron nitride (h-BN) has emerged as a strong candidate for two-dimensional (2D) material owing to its exciting optoelectrical properties combined with mechanical robustness, thermal stability, and chemical inertness. Super-thin h-BN layers have gained significant attention from the scientific community for many applications, including nanoelectronics, photonics, biomedical, anti-corrosion, and catalysis, among others. This review provides a systematic elaboration of the structural, electrical, mechanical, optical, and thermal properties of h-BN followed by a comprehensive account of state-of-the-art synthesis strategies for 2D h-BN, including chemical exfoliation, chemical, and physical vapor deposition, and other methods that have been successfully developed in recent years. It further elaborates a wide variety of processing routes developed for doping, substitution, functionalization, and combination with other materials to form heterostructures. Based on the extraordinary properties and thermal-mechanical-chemical stability of 2D h-BN, various potential applications of these structures are described.
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http://dx.doi.org/10.1002/adma.202101589DOI Listing
September 2021

Regulation of functional groups on graphene quantum dots directs selective CO to CH conversion.

Nat Commun 2021 Sep 6;12(1):5265. Epub 2021 Sep 6.

Department of Chemical and Environmental Engineering, University of Cincinnati, Cincinnati, OH, USA.

A catalyst system with dedicated selectivity toward a single hydrocarbon or oxygenate product is essential to enable the industrial application of electrochemical conversion of CO to high-value chemicals. Cu is the only known metal catalyst that can convert CO to high-order hydrocarbons and oxygenates. However, the Cu-based catalysts suffer from diverse selectivity. Here, we report that the functionalized graphene quantum dots can direct CO to CH conversion with simultaneous high selectivity and production rate. The electron-donating groups facilitate the yield of CH from CO electro-reduction while electron-withdrawing groups suppress CO electro-reduction. The yield of CH on electron-donating group functionalized graphene quantum dots is positively correlated to the electron-donating ability and content of electron-donating group. The graphene quantum dots functionalized by either -OH or -NH functional group could achieve Faradaic efficiency of 70.0% for CH at -200 mA cm partial current density of CH. The superior yield of CH on electron-donating group- over the electron-withdrawing group-functionalized graphene quantum dots possibly originates from the maintenance of higher charge density of potential active sites (neighboring C or N) and the interaction between the electron-donating group and key intermediates. This work provides insight into the design of active carbon catalysts at the molecular scale for the CO electro-reduction.
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http://dx.doi.org/10.1038/s41467-021-25640-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8421353PMC
September 2021

Damage-tolerant 3D-printed ceramics via conformal coating.

Sci Adv 2021 Jul 7;7(28). Epub 2021 Jul 7.

Department of Materials Science and NanoEngineering, Rice University, Houston, TX 77005, USA.

Ceramic materials, despite their high strength and modulus, are limited in many structural applications due to inherent brittleness and low toughness. Nevertheless, ceramic-based structures, in nature, overcome this limitation using bottom-up complex hierarchical assembly of hard ceramic and soft polymer, where ceramics are packaged with tiny fraction of polymers in an internalized fashion. Here, we propose a far simpler approach of entirely externalizing the soft phase via conformal polymer coating over architected ceramic structures, leading to damage tolerance. Architected structures are printed using silica-filled preceramic polymer, pyrolyzed to stabilize the ceramic scaffolds, and then dip-coated conformally with a thin, flexible epoxy polymer. The polymer-coated architected structures show multifold improvement in compressive strength and toughness while resisting catastrophic failure through a considerable delay of the damage propagation. This surface modification approach allows a simple strategy to build complex ceramic parts that are far more damage-tolerant than their traditional counterparts.
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http://dx.doi.org/10.1126/sciadv.abc5028DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8262818PMC
July 2021

Super-elasticity at 4 K of covalently crosslinked polyimide aerogels with negative Poisson's ratio.

Nat Commun 2021 Jul 2;12(1):4092. Epub 2021 Jul 2.

Institute of Special materials and Technology, Fudan University, Shanghai, China.

The deep cryogenic temperatures encountered in aerospace present significant challenges for the performance of elastic materials in spacecraft and related apparatus. Reported elastic carbon or ceramic aerogels overcome the low-temperature brittleness in conventional elastic polymers. However, complicated fabrication process and high costs greatly limited their applications. In this work, super-elasticity at a deep cryogenic temperature of covalently crosslinked polyimide (PI) aerogels is achieved based on scalable and low-cost directional dimethyl sulfoxide crystals assisted freeze gelation and freeze-drying strategy. The covalently crosslinked chemical structure, cellular architecture, negative Poisson's ratio (-0.2), low volume shrinkage (3.1%), and ultralow density (6.1 mg/cm) endow the PI aerogels with an elastic compressive strain up to 99% even in liquid helium (4 K), almost zero loss of resilience after dramatic thermal shocks (∆T = 569 K), and fatigue resistance over 5000 times compressive cycles. This work provides a new pathway for constructing polymer-based materials with super-elasticity at deep cryogenic temperature, demonstrating much promise for extensive applications in ongoing and near-future aerospace exploration.
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http://dx.doi.org/10.1038/s41467-021-24388-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8253740PMC
July 2021

Achieving High-Quality Freshwater from a Self-Sustainable Integrated Solar Redox-Flow Desalination Device.

Small 2021 07 23;17(30):e2100490. Epub 2021 Jun 23.

Department of Materials Science and NanoEngineering, Department Chemical and Biomolecular Engineering, Department of Chemistry, Rice University, Houston, Texas, 77005, USA.

Solar-assisted electrochemical desalination has offered a new energy-water nexus technology for sustainable development in recent studies. However, only a few reports have demonstrated insufficient photocurrent, a low salt removal rate, and poor stability. In this study, a high-quality freshwater level of 5-10 ppm (from an initial feed of 10 000 ppm), an enhanced salt removal rate (217.8 µg cm min of NaCl), and improved cycling and long-term stability are achieved by integrating dye-sensitized solar cells (DSSCs) and redox-flow desalination (RFD) under light irradiation without additional electrical energy consumption. The DSSC redox electrolyte (I /I ) is circulated between the photoanode (N719/TiO ) and intermediate electrode (graphite paper). Two DSSCs in parallel or series connections are directly coupled to the RFD device. Overall, this hybrid system can be used to boost photo electrochemical desalination technology. The energy-water nexus technology will open a new route for dual-role devices with photodesalination functions without energy consumption and solar-to-electricity generation.
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http://dx.doi.org/10.1002/smll.202100490DOI Listing
July 2021

Interferometric 4D-STEM for Lattice Distortion and Interlayer Spacing Measurements of Bilayer and Trilayer 2D Materials.

Small 2021 Jul 3;17(28):e2100388. Epub 2021 Jun 3.

Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.

Van der Waals materials composed of stacks of individual atomic layers have attracted considerable attention due to their exotic electronic properties that can be altered by, e.g., manipulating the twist angle of bilayer materials or the stacking sequence of trilayer materials. To fully understand and control the unique properties of these few-layer materials, a technique that can provide information about their local in-plane structural deformations, twist direction, and out-of-plane structure is needed. In principle, interference in overlap regions of Bragg disks originating from separate layers of a material encodes 3D information about the relative positions of atoms in the corresponding layers. Here, an interferometric 4D scanning transmission electron microscopy technique is described that utilizes this phenomenon to extract precise structural information from few-layer materials with nm-scale resolution. It is demonstrated how this technique enables measurement of local pm-scale in-plane lattice distortions as well as twist direction and average interlayer spacings in bilayer and trilayer graphene, and therefore provides a means to better understand the interplay between electronic properties and precise structural arrangements of few-layer 2D materials.
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http://dx.doi.org/10.1002/smll.202100388DOI Listing
July 2021

HCl-Based Hydrothermal Etching Strategy toward Fluoride-Free MXenes.

Adv Mater 2021 Jul 31;33(27):e2101015. Epub 2021 May 31.

National Synchrotron Radiation Laboratory, CAS Center for Excellence in Nanoscience, University of Science and Technology of China, Hefei, Anhui, 230029, P. R. China.

Due to their ultrathin layered structure and rich elemental variety, MXenes are emerging as a promising electrode candidate in energy generation and storage. MXenes are generally synthesized via hazardous fluoride-containing reagents from robust MAX materials, unfortunately resulting in plenty of inert fluoride functional groups on the surface that noticeably decline their performance. Density functional theory calculations are used to show the etching feasibility of hydrochloric acid (HCl) on various MAX phases. Based on this theoretical guidance, fluoride-free Mo C MXenes with high efficiency about 98% are experimentally demonstrated. The Mo C electrodes produced by this process exhibit high electrochemical performance in supercapacitors and sodium-ion batteries owing to the chosen surface functional groups created via the HCl etch process. This strategy enables the development of fluoride-free MXenes and opens a new window to explore their potential in energy-storage applications.
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http://dx.doi.org/10.1002/adma.202101015DOI Listing
July 2021

Mapping Modified Electronic Levels in the Moiré Patterns in MoS/WSe Using Low-Loss EELS.

Nano Lett 2021 May 26;21(9):4071-4077. Epub 2021 Apr 26.

Department of Materials Science and Nanoengineering, Rice University, Houston, Texas 77005, United States.

Hybrid/moiré interlayer and intralayer excitons have been realized in twisted two-dimensional transition metal chalcogenides (2D-TMD) due to variation in local moiré potential within a moiré supercell. Though moiré excitons have been detected in TMD heterostructures by macroscopic spectroscopic techniques, their spatial distribution is experimentally unknown. In the present work, using high-resolution scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS), we explore the effect of the twist angle in MoS/WSe heterostructures. We observe weak interaction between the layers at higher twist angles (>5°) and stronger interaction for lower twist angles. The optical response of the heterostructure varies within the moiré supercell, with a lower energy absorption peak appearing in regions with the stacking.
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http://dx.doi.org/10.1021/acs.nanolett.1c00984DOI Listing
May 2021

Deformation resilient cement structures using 3D-printed molds.

iScience 2021 Mar 12;24(3):102174. Epub 2021 Feb 12.

Department of Materials Science and NanoEngineering, Rice University, Houston, TX 77005, USA.

Cementitious structures exhibit high compression strength but suffer from inherent brittleness. Conversely, nature creates structures using mostly brittle phases that overcome the strength-toughness trade-off, mainly through internalized packaging of brittle phases with soft organic binders. Here, we develop complex architectures of cementitious materials using an inverse replica approach where a soft polymer phase emerges as an external conformal coating. Architected polymer templates are printed, cement pastes are molded into these templates, and cementitious structures with thin polymer surface coating are achieved after the solubilization of sacrificial templates. These polymer-coated architected cementitious structures display unusual mechanical behavior with considerably higher toughness compared to conventional non-porous structures. They resist catastrophic failure through delayed damage propagation. Most interestingly, the architected structures show significant deformation recovery after releasing quasi-static loading, atypical in conventional cementitious structures. This approach allows a simple strategy to build more deformation resilient cementitious structures than their traditional counterparts.
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http://dx.doi.org/10.1016/j.isci.2021.102174DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7921815PMC
March 2021

Highly efficient photoelectric effect in halide perovskites for regenerative electron sources.

Nat Commun 2021 Jan 29;12(1):673. Epub 2021 Jan 29.

Department of Chemical and Biomolecular Engineering Rice University, Houston, TX, USA.

Electron sources are a critical component in a wide range of applications such as electron-beam accelerator facilities, photomultipliers, and image intensifiers for night vision. We report efficient, regenerative and low-cost electron sources based on solution-processed halide perovskites thin films when they are excited with light with energy equal to or above their bandgap. We measure a quantum efficiency up to 2.2% and a lifetime of more than 25 h. Importantly, even after degradation, the electron emission can be completely regenerated to its maximum efficiency by deposition of a monolayer of Cs. The electron emission from halide perovskites can be tuned over the visible and ultraviolet spectrum, and operates at vacuum levels with pressures at least two-orders higher than in state-of-the-art semiconductor electron sources.
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http://dx.doi.org/10.1038/s41467-021-20954-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7846809PMC
January 2021

Structural Defects Modulate Electronic and Nanomechanical Properties of 2D Materials.

ACS Nano 2021 Feb 25;15(2):2520-2531. Epub 2021 Jan 25.

Department of Physics and Astronomy, University of Sussex, Brighton BN1 9RH, United Kingdom.

Two-dimensional materials such as graphene and molybdenum disulfide are often subject to out-of-plane deformation, but its influence on electronic and nanomechanical properties remains poorly understood. These physical distortions modulate important properties which can be studied by atomic force microscopy and Raman spectroscopic mapping. Herein, we have identified and investigated different geometries of line defects in graphene and molybdenum disulfide such as standing collapsed wrinkles, folded wrinkles, and grain boundaries that exhibit distinct strain and doping. In addition, we apply nanomechanical atomic force microscopy to determine the influence of these defects on local stiffness. For wrinkles of similar height, the stiffness of graphene was found to be higher than that of molybdenum disulfide by 10-15% due to stronger in-plane covalent bonding. Interestingly, deflated graphene nanobubbles exhibited entirely different characteristics from wrinkles and exhibit the lowest stiffness of all graphene defects. Density functional theory reveals alteration of the bandstructures of graphene and MoS due to the wrinkled structure; such modulation is higher in MoS compared to graphene. Using this approach, we can ascertain that wrinkles are subject to significant strain but minimal doping, while edges show significant doping and minimal strain. Furthermore, defects in graphene predominantly show compressive strain and increased carrier density. Defects in molybdenum disulfide predominantly show tensile strain and reduced carrier density, with increasing tensile strain minimizing doping across all defects in both materials. The present work provides critical fundamental insights into the electronic and nanomechanical influence of intrinsic structural defects at the nanoscale, which will be valuable in straintronic device engineering.
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http://dx.doi.org/10.1021/acsnano.0c06701DOI Listing
February 2021

Free-standing SnS/carbonized cellulose film as durable anode for lithium-ion batteries.

Carbohydr Polym 2021 Mar 16;255:117400. Epub 2020 Nov 16.

Institute of Chemicobiology and Functional Materials, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China. Electronic address:

Metal sulfides have recently attracted broad attention for lithium-ion batteries (LIB) owing to their high theoretical capacity and long lifetime. However, the inferior structural integrity and low electron conductivity of metal sulfides limit their practical applications. A feasible strategy is to distribute these materials in conductive carbonaceous substrates with shapeable morphology. Here we report the design of free-standing films of tin sulfide (SnS) nanosheets distributed uniformly on carbonized bacterial cellulose (CBC) nanofibers. The SnS/CBC composites possess three dimensional interconnected nanostructures, which is crucial for the high conductivity and high lithium storage capacity. LIB using SnS/CBC as anode exhibits a reversible capacity of 872 mA h g at 100 mA g after 100 cycles, and the capacity remains as high as 527 mA h g at 2000 mA g after 1000 cycles. The free-standing sulfide-based nanocomposites with unique nanostructure composition and flexibility could be utilized as promising electrode materials for future LIB systems.
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http://dx.doi.org/10.1016/j.carbpol.2020.117400DOI Listing
March 2021

Light-Assisted Rechargeable Lithium Batteries: Organic Molecules for Simultaneous Energy Harvesting and Storage.

Nano Lett 2021 Jan 8;21(2):907-913. Epub 2021 Jan 8.

Department of Materials Science and Nano-engineering, Rice University, Houston, Texas 77005, United States.

Lithium batteries that could be charged on exposure to sunlight will bring exciting new energy storage technologies. Here, we report a photorechargeable lithium battery employing nature-derived organic molecules as a photoactive and lithium storage electrode material. By absorbing sunlight of a desired frequency, lithiated tetrakislawsone electrodes generate electron-hole pairs. The holes oxidize the lithiated tetrakislawsone to tetrakislawsone while the generated electrons flow from the tetrakislawsone cathode to the Li metal anode. During electrochemical operation, the observed rise in charging current, specific capacity, and Coulombic efficiency under light irradiation in contrast to the absence of light indicates that the quinone-based organic electrode is acting as both photoactive and lithium storage material. Careful selection of electrode materials with optimal bandgap to absorb the intended frequency of sunlight and functional groups to accept Li-ions reversibly is a key to the progress of solar rechargeable batteries.
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http://dx.doi.org/10.1021/acs.nanolett.0c03311DOI Listing
January 2021

Determining Quasiparticle Bandgap of Two-Dimensional Transition Metal Dichalcogenides by Observation of Hot Carrier Relaxation Dynamics.

J Phys Chem Lett 2021 Jan 31;12(1):585-591. Epub 2020 Dec 31.

The Laboratory of Soft Matter Physics, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.

Using excitation-energy-scanning ultrafast infrared microspectroscopy, the excess energy-dependent hot carrier relaxation dynamics in atomically thin two-dimensional transition metal dichalcogenides (2D TMDs) after femtosecond photoexcitation was directly monitored. A good linear relationship between the carrier relaxation time and the excitation wavelength is observed for all measured monolayer (ML) and bilayer (BL) TMD samples, which allows us to determine their quasiparticle bandgaps as well as corresponding exciton binding energies. A carrier-optical-phonon scattering-mediated cascading-relaxation model is proposed, which can perfectly describe all the measured dynamics. As a consequence, the quasiparticle bandgaps of ML MoSe, ML MoS, BL MoSe, and BL WSe are determined to be 2.07, 2.11, 1.67, and 1.81 eV, respectively. Our work reveals a general picture for the hot carrier relaxation dynamics in atomically thin TMDs and offers an effective experimental approach in probing the bandgaps of TMDs under ambient conditions.
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http://dx.doi.org/10.1021/acs.jpclett.0c03414DOI Listing
January 2021

Atomic Layers of Graphene for Microbial Corrosion Prevention.

ACS Nano 2021 01 31;15(1):447-454. Epub 2020 Dec 31.

Department Civil and Environmental Engineering, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701, United States.

Graphene is a promising material for many biointerface applications in engineering, medical, and life-science domains. Here, we explore the protection ability of graphene atomic layers to metals exposed to aggressive sulfate-reducing bacteria implicated in corrosion. Although the graphene layers on copper (Cu) surfaces did not prevent the bacterial attachment and biofilm growth, they effectively restricted the biogenic sulfide attack. Interestingly, single-layered graphene (SLG) worsened the biogenic sulfide attack by 5-fold compared to bare Cu. In contrast, multilayered graphene (MLG) on Cu restricted the attack by 10-fold and 1.4-fold compared to SLG-Cu and bare Cu, respectively. We combined experimental and computational studies to discern the anomalous behavior of SLG-Cu compared to MLG-Cu. We also report that MLG on Ni offers superior protection ability compared to SLG. Finally, we demonstrate the effect of defects, including double vacancy defects and grain boundaries on the protection ability of atomic graphene layers.
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http://dx.doi.org/10.1021/acsnano.0c03987DOI Listing
January 2021

3D-Bioprinted Inflammation Modulating Polymer Scaffolds for Soft Tissue Repair.

Adv Mater 2021 Jan 16;33(4):e2003778. Epub 2020 Dec 16.

Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX, 77030, USA.

Development of inflammation modulating polymer scaffolds for soft tissue repair with minimal postsurgical complications is a compelling clinical need. However, the current standard of care soft tissue repair meshes for hernia repair is highly inflammatory and initiates a dysregulated inflammatory process causing visceral adhesions and postsurgical complications. Herein, the development of an inflammation modulating biomaterial scaffold (bioscaffold) for soft tissue repair is presented. The bioscaffold design is based on the idea that, if the excess proinflammatory cytokines are sequestered from the site of injury by the surgical implantation of a bioscaffold, the inflammatory response can be modulated, and the visceral adhesion formations and postsurgical complications can be minimized. The bioscaffold is fabricated by 3D-bioprinting of an in situ phosphate crosslinked poly(vinyl alcohol) polymer. In vivo efficacy of the bioscaffold is evaluated in a rat ventral hernia model. In vivo proinflammatory cytokine expression analysis and histopathological analysis of the tissues have confirmed that the bioscaffold acts as an inflammation trap and captures the proinflammatory cytokines secreted at the implant site and effectively modulates the local inflammation without the need for exogenous anti-inflammatory agents. The bioscaffold is very effective in inhibiting visceral adhesions formation and minimizing postsurgical complications.
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http://dx.doi.org/10.1002/adma.202003778DOI Listing
January 2021

Immunogenicity of Externally Activated Nanoparticles for Cancer Therapy.

Cancers (Basel) 2020 Nov 28;12(12). Epub 2020 Nov 28.

Department of Radiation Oncology, Mayo Clinic Florida, 4500 San Pablo Road S, Mayo 1N, Jacksonville, FL 32224, USA.

Nanoparticles activated by external beams, such as ionizing radiation, laser light, or magnetic fields, have attracted significant research interest as a possible modality for treating solid tumors. From producing hyperthermic conditions to generating reactive oxygen species, a wide range of externally activated mechanisms have been explored for producing cytotoxicity within tumors with high spatiotemporal control. To further improve tumoricidal effects, recent trends in the literature have focused on stimulating the immune system through externally activated treatment strategies that result in immunogenic cell death. By releasing inflammatory compounds known to initiate an immune response, treatment methods can take advantage of immune system pathways for a durable and robust systemic anti-tumor response. In this review, we discuss recent advancements in radiosensitizing and hyperthermic nanoparticles that have been tuned for promoting immunogenic cell death. Our review covers both preclinical and clinical results, as well as an overview of possible future work.
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http://dx.doi.org/10.3390/cancers12123559DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7760497PMC
November 2020

Publisher Correction: Multifunctional nanocoated membranes for high-rate electrothermal desalination of hypersaline waters.

Nat Nanotechnol 2020 Dec;15(12):1065

Department of Civil and Environmental Engineering, Rice University, Houston, TX, USA.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.
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http://dx.doi.org/10.1038/s41565-020-00806-yDOI Listing
December 2020

Multifunctional nanocoated membranes for high-rate electrothermal desalination of hypersaline waters.

Nat Nanotechnol 2020 12 26;15(12):1025-1032. Epub 2020 Oct 26.

Department of Civil and Environmental Engineering, Rice University, Houston, TX, USA.

Surface heating membrane distillation overcomes several limitations inherent in conventional membrane distillation technology. Here we report a successful effort to grow in situ a hexagonal boron nitride (hBN) nanocoating on a stainless-steel wire cloth (hBN-SSWC), and its application as a scalable electrothermal heating material in surface heating membrane distillation. The novel hBN-SSWC provides superior vapour permeability, thermal conductivity, electrical insulation and anticorrosion properties, all of which are critical for the long-term surface heating membrane distillation performance, particularly with hypersaline solutions. By simply attaching hBN-SSWC to a commercial membrane and providing power with an a.c. supply at household frequency, we demonstrate that hBN-SSWC is able to support an ultrahigh power intensity (50 kW m) to desalinate hypersaline solutions with exceptionally high water flux (and throughput), single-pass water recovery and heat utilization efficiency while maintaining excellent material stability. We also demonstrate the exceptional performance of hBN-SSWC in a scalable and compact spiral-wound electrothermal membrane distillation module.
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http://dx.doi.org/10.1038/s41565-020-00777-0DOI Listing
December 2020

Hexagonal Boron Nitride for Sulfur Corrosion Inhibition.

ACS Nano 2020 11 26;14(11):14809-14819. Epub 2020 Oct 26.

Department of Civil and Environmental Engineering, 2-Dimensional Materials for Biofilm Engineering Science and Technology (2DBEST) Center, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701, United States.

Corrosion by sulfur compounds is a long-standing challenge in many engineering applications. Specifically, designing a coating that protects metals from both abiotic and biotic forms of sulfur corrosion remains an elusive goal. Here we report that atomically thin layers (∼4) of hexagonal boron nitride (hBN) act as a protective coating to inhibit corrosion of the underlying copper (Cu) surfaces (∼6-7-fold lower corrosion than bare Cu) in abiotic (sulfuric acid and sodium sulfide) and biotic (sulfate-reducing bacteria medium) environments. The corrosion resistance of hBN is attributed to its outstanding barrier properties to the corrosive species in diverse environments of sulfur compounds. Increasing the number of atomic layers did not necessarily improve the corrosion protection mechanisms. Instead, multilayers of hBN were found to upregulate the adhesion genes in G20 cells, promote cell adhesion and biofilm growth, and lower the protection against biogenic sulfide attack when compared to the few layers of hBN. Our findings confirm hBN as the thinnest coating to resist diverse forms of sulfur corrosion.
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http://dx.doi.org/10.1021/acsnano.0c03625DOI Listing
November 2020

Scale-Enhanced Magnetism in Exfoliated Atomically Thin Magnetite Sheets.

Small 2020 Nov 20;16(45):e2004208. Epub 2020 Oct 20.

Department of Materials Science and NanoEngineering, Rice University, Houston, TX, 77005, USA.

The discovery of ferromagnetism in atomically thin layers at room temperature widens the prospects of 2D materials for device applications. Recently, two independent experiments demonstrated magnetic ordering in two dissimilar 2D systems, CrI and Cr Ge Te , at low temperatures and in VSe at room temperature, but observation of intrinsic room-temperature magnetism in 2D materials is still a challenge. Here a transition at room temperature that increases the magnetization in magnetite while thinning down the bulk material to a few atom-thick sheets is reported. DC magnetization measurements prove ferrimagnetic ordering with increased magnetization and density functional theory calculations ascribe their origin to the low dimensionality of the magnetite layers. In addition, surface energy calculations for different cleavage planes in passivated magnetite crystal agree with the experimental observations of obtaining 2D sheets from non-van der Waals crystals.
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http://dx.doi.org/10.1002/smll.202004208DOI Listing
November 2020

Full-color fluorescent carbon quantum dots.

Sci Adv 2020 Oct 2;6(40). Epub 2020 Oct 2.

Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, P. R. China.

Quantum dots have innate advantages as the key component of optoelectronic devices. For white light-emitting diodes (WLEDs), the modulation of the spectrum and color of the device often involves various quantum dots of different emission wavelengths. Here, we fabricate a series of carbon quantum dots (CQDs) through a scalable acid reagent engineering strategy. The growing electron-withdrawing groups on the surface of CQDs that originated from acid reagents boost their photoluminescence wavelength red shift and raise their particle sizes, elucidating the quantum size effect. These CQDs emit bright and remarkably stable full-color fluorescence ranging from blue to red light and even white light. Full-color emissive polymer films and all types of high-color rendering index WLEDs are synthesized by mixing multiple kinds of CQDs in appropriate ratios. The universal electron-donating/withdrawing group engineering approach for synthesizing tunable emissive CQDs will facilitate the progress of carbon-based luminescent materials for manufacturing forward-looking films and devices.
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http://dx.doi.org/10.1126/sciadv.abb6772DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7852397PMC
October 2020

Directly Exfoliated Ultrathin Silicon Nanosheets for Enhanced Photocatalytic Hydrogen Production.

J Phys Chem Lett 2020 Oct 29;11(20):8668-8674. Epub 2020 Sep 29.

School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China.

Here we present direct exfoliation of ultrathin silicon nanosheets from commercial silicon powders through an improved liquid phase exfoliation procedure. The feasibility of exfoliation was ascribed to the intrinsic anisotropic lattice structure, which allowed the oriented propagations of cryo-mediation-induced quenching cracks with the assistance of sonication. It was also revealed that the solid-solvent interface played a critical role in determining the morphology of exfoliated pieces as well as the exfoliation efficiency. Moreover, due to its superior morphology, enlarged surface area, and improved photon absorption, the resulting ultrathin silicon nanosheets presented enhanced and visible light responsive photocatalytic hydrogen generation performance, even without applying any co-catalyst.
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http://dx.doi.org/10.1021/acs.jpclett.0c02049DOI Listing
October 2020

Lithium, sodium and magnesium ion conduction in solid state mixed polymer electrolytes.

Phys Chem Chem Phys 2020 Sep 18;22(34):19108-19119. Epub 2020 Aug 18.

Department of Materials Science and NanoEngineering, Rice University, Houston, USA.

Alkali and alkaline earth metal-ion batteries are currently among the most efficient electrochemical energy storage devices. However, their stability and safety performance are greatly limited when used with volatile organic liquid electrolytes. A solid state polymer electrolyte is a prospective solution even though poor ionic conductivity at room temperature remains a bottleneck. Here we propose the mixing of two similar polymer matrices, poly(dimethyl siloxane) and poly(ethylene oxide), to address this challenge. The resulting electrolyte matrix is denser and significantly improves room-temperature ionic conductivity. Ab initio analyses of the reaction between the cations and the polymers show that oxygen sites act as entrapment sites for the cations and that ionic conduction likely occurs through hopping between adjacent oxygen sites. Molecular dynamics simulations of the dynamics of both polymers and the dynamics of the polymer mix show that the more frequent and more pronounced molecular vibrations of the polymer mix are likely responsible for reducing the time between two consecutive oxygen entrapments, thereby speeding up the conduction process. This hypothesis is experimentally validated by the practically useful ionic conductivity (σ≈ 10 S cm at 25 °C) and the improved safety parameters exhibited by a transparent flexible multi-cation (Li, Na and Mg) conducting solid channel made up of the above mixed polymer system.
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http://dx.doi.org/10.1039/d0cp02609cDOI Listing
September 2020

Lateral Monolayer MoSe -WSe p-n Heterojunctions with Giant Built-In Potentials.

Small 2020 Aug 21;16(34):e2002263. Epub 2020 Jul 21.

Department of Materials Science and NanoEngineering, Rice University, 6100 Main Street, Houston, TX, 77005, USA.

2D transition metal dichalcogenides (TMDs) have exhibited strong application potentials in new emerging electronics because of their atomic thin structure and excellent flexibility, which is out of field of tradition silicon technology. Similar to 3D p-n junctions, 2D p-n heterojunctions by laterally connecting TMDs with different majority charge carriers (electrons and holes), provide ideal platform for current rectifiers, light-emitting diodes, diode lasers and photovoltaic devices. Here, growth and electrical studies of atomic thin high-quality p-n heterojunctions between molybdenum diselenide (MoSe ) and tungsten diselenide (WSe ) by one-step chemical vapor deposition method are reported. These p-n heterojunctions exhibit high built-in potential (≈0.7 eV), resulting in large current rectification ratio without any gate control for diodes, and fast response time (≈6 ms) for self-powered photodetectors. The simple one-step growth and electrical studies of monolayer lateral heterojunctions open up the possibility to use TMD heterojunctions for functional devices.
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http://dx.doi.org/10.1002/smll.202002263DOI Listing
August 2020
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