Browsing by Author "Nemani, Srinivasa Kartik"

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    2D transition metal carbides (MXenes) in metal and ceramic matrix composites
    (Springer, 2021-06-02) Wyatt, Brian C.; Nemani, Srinivasa Kartik; Anasori, Babak; Mechanical and Energy Engineering, School of Engineering and Technology
    Two-dimensional transition metal carbides, nitrides, and carbonitrides (known as MXenes) have evolved as competitive materials and fillers for developing composites and hybrids for applications ranging from catalysis, energy storage, selective ion filtration, electromagnetic wave attenuation, and electronic/piezoelectric behavior. MXenes’ incorporation into metal matrix and ceramic matrix composites is a growing field with significant potential due to their impressive mechanical, electrical, and chemical behavior. With about 50 synthesized MXene compositions, the degree of control over their composition and structure paired with their high-temperature stability is unique in the field of 2D materials. As a result, MXenes offer a new avenue for application driven design of functional and structural composites with tailorable mechanical, electrical, and thermochemical properties. In this article, we review recent developments for use of MXenes in metal and ceramic composites and provide an outlook for future research in this field.
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    Double transition-metal MXenes: Atomistic design of two-dimensional carbides and nitrides
    (Cambridge UP, 2020-10) Hong, Weichen; Wyatt, Brian C.; Nemani, Srinivasa Kartik; Anasori, Babak; Mechanical Engineering and Energy, School of Engineering and Technology
    MXenes are a large family of two-dimensional (2D) transition-metal carbides, nitrides, and carbonitrides. The MXene family has expanded since their original discovery in 2011, and has grown larger with the discovery of ordered double transition-metal (DTM) MXenes. These DTM MXenes differ from their counterpart mono-transition-metal (mono-M) MXenes, where two transition metals can occupy the metal sites. Ordered DTM MXenes are comprised of transition metals in either an in-plane or out-of-plane ordered structure. Additionally, some DTM MXenes are in the form of random solid solutions, which are defined by two randomly distributed transition metals throughout the 2D structure. Their different structures and array of transition-metal pairs provide the ability to tune DTM MXenes for specific optical, magnetic, electrochemical, thermoelectric, catalytic, or mechanical behavior. This degree of control over their composition and structure is unique in the field of 2D materials and offers a new avenue for application-driven design of functional nanomaterials. In this article, we review the synthesis, structure, and properties of DTM MXenes and provide an outlook for future research in this field.
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    High-Entropy 2D Carbide MXenes: TiVNbMoC3 and TiVCrMoC3
    (ACS, 2021-06) Nemani, Srinivasa Kartik; Zhang, Bowen; Wyatt, Brian C.; Hood, Zachary D.; Manna, Sukrita; Khaledialidusti, Rasoul; Hong, Weichen; Sternberg, Michael G.; Sankaranarayanan, Subramanian K. R. S.; Anasori, Babak; Mechanical and Energy Engineering, School of Engineering and Technology
    Two-dimensional (2D) transition metal carbides and nitrides, known as MXenes, are a fast-growing family of 2D materials. MXenes 2D flakes have n + 1 (n = 1–4) atomic layers of transition metals interleaved by carbon/nitrogen layers, but to-date remain limited in composition to one or two transition metals. In this study, by implementing four transition metals, we report the synthesis of multi-principal-element high-entropy M4C3Tx MXenes. Specifically, we introduce two high-entropy MXenes, TiVNbMoC3Tx and TiVCrMoC3Tx, as well as their precursor TiVNbMoAlC3 and TiVCrMoAlC3 high-entropy MAX phases. We used a combination of real and reciprocal space characterization (X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, and scanning transmission electron microscopy) to establish the structure, phase purity, and equimolar distribution of the four transition metals in high-entropy MAX and MXene phases. We use first-principles calculations to compute the formation energies and explore synthesizability of these high-entropy MAX phases. We also show that when three transition metals are used instead of four, under similar synthesis conditions to those of the four-transition-metal MAX phase, two different MAX phases can be formed (i.e., no pure single-phase forms). This finding indicates the importance of configurational entropy in stabilizing the desired single-phase high-entropy MAX over multiphases of MAX, which is essential for the synthesis of phase-pure high-entropy MXenes. The synthesis of high-entropy MXenes significantly expands the compositional variety of the MXene family to further tune their properties, including electronic, magnetic, electrochemical, catalytic, high temperature stability, and mechanical behavior.
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    High-temperature stability and phase transformations of titanium carbide (Ti3C2Tx) MXene
    (IOP, 2021-06) Wyatt, Brian C.; Nemani, Srinivasa Kartik; Desai, Krishay; Kaur, Harpreet; Zhang, Bowen; Anasori, Babak; Mechanical and Energy Engineering, School of Engineering and Technology
    Two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, known as MXenes, are under increasing pressure to meet technological demands in high-temperature applications, as MXenes can be considered to be one of the few ultra-high temperature 2D materials. Although there are studies on the stability of their surface functionalities, there is currently a gap in the fundamental understanding of their phase stability and transformation of MXenes' metal carbide core at high temperatures (>700 °C) in an inert environment. In this study, we conduct systematic annealing of Ti3C2TxMXene films in which we present the 2D MXene flake phase transformation to ordered vacancy superstructure of a bulk three-dimensional (3D) Ti2C and TiCycrystals at 700 °C ⩽T⩽ 1000 °C with subsequent transformation to disordered carbon vacancy cubic TiCyat higher temperatures (T> 1000 °C). We annealed Ti3C2TxMXene films made from the delaminated MXene single-flakes as well as the multi-layer MXene clay in a controlled environment through the use ofin situhot stage x-ray diffraction (XRD) paired with a 2D detector (XRD2) up to 1000 °C andex situannealing in a tube furnace and spark plasma sintering up to 1500 °C. Our XRD2analysis paired with cross-sectional scanning electron microscope imaging indicated the resulting nano-sized lamellar and micron-sized cubic grain morphology of the 3D crystals depend on the starting Ti3C2Txform. While annealing the multi-layer clay Ti3C2TxMXene creates TiCygrains with cubic and irregular morphology, the grains of 3D Ti2C and TiCyformed by annealing Ti3C2TxMXene single-flake films keep MXenes' lamellar morphology. The ultrathin lamellar nature of the 3D grains formed at temperatures >1000 °C can pave way for applications of MXenes as a stable carbide material 2D additive for high-temperature applications.
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    Rational Design of Two-Dimensional Transition Metal Carbide/Nitride (MXene) Hybrids and Nanocomposites for Catalytic Energy Storage and Conversion
    (ACS, 2020-08) Lim, Kang Rui Garrick; Handoko, Albertus D.; Nemani, Srinivasa Kartik; Wyatt, Brian; Jiang, Hai-Ying; Tang, Junwang; Anasori, Babak; Seh, Zhi Wei; Engineering Technology, School of Engineering and Technology
    Electro-, photo-, and photoelectrocatalysis play a critical role toward the realization of a sustainable energy economy. They facilitate numerous redox reactions in energy storage and conversion systems, enabling the production of chemical feedstock and clean fuels from abundant resources like water, carbon dioxide, and nitrogen. One major obstacle for their large-scale implementation is the scarcity of cost-effective, durable, and efficient catalysts. A family of two-dimensional transition metal carbides, nitrides, and carbonitrides (MXenes) has recently emerged as promising earth-abundant candidates for large-area catalytic energy storage and conversion due to their unique properties of hydrophilicity, high metallic conductivity, and ease of production by solution processing. To take full advantage of these desirable properties, MXenes have been combined with other materials to form MXene hybrids with significantly enhanced catalytic performances beyond the sum of their individual components. MXene hybridization tunes the electronic structure toward optimal binding of redox active species to improve intrinsic activity while increasing the density and accessibility of active sites. This review outlines recent strategies in the design of MXene hybrids for industrially relevant electrocatalytic, photocatalytic, and photoelectrocatalytic applications such as water splitting, metal–air/sulfur batteries, carbon dioxide reduction, and nitrogen reduction. By clarifying the roles of individual material components in the MXene hybrids, we provide design strategies to synergistically couple MXenes with associated materials for highly efficient and durable catalytic applications. We conclude by highlighting key gaps in the current understanding of MXene hybrids to guide future MXene hybrid designs in catalytic energy storage and conversion applications.
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    Ti3C2 MXene–polymer nanocomposites and their applications
    (Royal Society of Chemistry, 2021-04) Riazi, Hossein; Nemani, Srinivasa Kartik; Grady, Michael C.; Anasori, Babak; Soroush, Masoud; Mechanical and Energy Engineering, School of Engineering and Technology
    MXene/polymer nanocomposites simultaneously benefit from the attractive properties of MXenes and the flexibility and facile processability of polymers. These composites have shown superior properties such as high light-to-heat conversion, excellent electromagnetic interference shielding, and high charge storage, compared to other nanocomposites. They have applications in chemical, materials, electrical, environmental, mechanical, and biomedical engineering as well as medicine. This property-based review on MXene/polymer nanocomposites critically describes findings and achievements in these areas and puts future research directions into perspective. It surveys novel reported applications of MXene-based polymeric nanocomposites. It also covers surface modification approaches that expand the applications of MXenes in nanocomposites.