About

Zahra Fakhraai is a Professor of Chemistry at the University of Pennsylvania, with a background in Physics from Sharif University of Technology, Iran, and a Ph.D. from the University of Waterloo. Her research group studies the effect of nano-confinement and interfacial interactions on the structure, dynamics, and properties of nanostructured materials. Her work focuses on understanding how materials behave differently on surfaces, interfaces, or at small length scales compared to their bulk properties, which is crucial for technological applications such as organic electronics, polymer nanocomposites, and biomolecular drugs. Her research includes investigating glass physics at the nanoscale, where she explores how confinement and interfaces influence glass dynamics, phase transitions, and stability. She has developed methods to produce near-equilibrium and exceptionally stable glasses through physical vapor deposition, studying their structure, properties, and aging mechanisms. Additionally, her group examines novel optical properties in disordered nanoparticle clusters, utilizing synthetic routes to create nanoparticle assemblies with unique optical behaviors such as higher-order scattering and magnetic dipole plasmons. Fakhraai also studies surface-mediated self-assembly processes of amyloid aggregates, employing high-resolution imaging techniques to understand peptide adhesion, diffusion, and fibril formation on various surfaces. Her work aims to elucidate fundamental physics of nanoscale phenomena and leverage this knowledge to design advanced materials.

Research topics

• Materials science
• Chemistry
• Organic chemistry
• Nanotechnology
• Chemical engineering
• Composite material
• Optoelectronics
• Physics
• Metallurgy
• Optics
• Condensed matter physics
• Physical chemistry

Selected publications

• Precision Molecular Sieving Enabled by Tunable Slit-like Nanochannels in Anodic Aluminum Oxide-Supported MXene/GO Composite Membranes

  ACS Applied Materials & Interfaces · 2026-04-14

  articleOpen access

  Overcoming the permeance-selectivity trade-off in membrane-based separations requires materials with precisely defined nanochannels and robust molecular sieving capabilities. Two-dimensional nanomaterials offer such control; however, random stacking of nanosheets often produces disordered transport pathways that limit separation performance. Here, we report anodic aluminum oxide-supported Ti3C2Tx MXene/graphene oxide (GO) composite membranes with tunable interlayer spacing and enhanced sheet alignment for ultrahigh molecular sieving. Large-area GO flakes seal structural defects within the MXene scaffold while inducing well-aligned, slit-like nanochannels. At an optimized MXene/GO weight ratio of 1:1, the composite membranes achieve a H2 permeance of 2681.6 GPU (2011.2 GPU under mixed-gas conditions) with a H2/CO2 selectivity of 536.3 (457.1 under mixed-gas conditions), substantially surpassing the performance of state-of-the-art membranes. Molecular simulations reveal that ordered interlayer galleries and tailored slit pores underpin this exceptional molecular sieving behavior. This scalable composite platform enables high-precision separations for applications such as gas purification, advanced water treatment, and organic solvent nanofiltration.

  PublisherDOI

• Band-like Optical Signatures of Ti ₃ C ₂ T <i> _x </i> MXenes

  The Journal of Physical Chemistry C · 2026-01-27 · 4 citations

  articleSenior authorCorresponding

  MXenes have shown great potential in electronic and optoelectronic applications. However, the optical properties of these highly conductive two-dimensional materials are not fully understood. The broad near-infrared (IR) optical extinction (∼1.5 eV) in Ti3C2Tx with mixed terminations (Tx: ═O, −OH, −F, −Cl) has been widely attributed to a localized surface plasmon resonance (LSPR). However, previous simulations suggest this peak may be due to an interband transition (IBT). Here, we show that the real component of the dielectric constant of Ti3C2Tx at this peak is positive (ε1 > 0), as measured by spectroscopic ellipsometry (SE), ruling out the possibility of LSPR. Moreover, this band nearly vanishes for experimentally synthesized chlorine-terminated Ti3C2Cl2. Density functional theory (DFT) calculations confirm an IBT origin for this band, specifically due to the oxygen terminations (Ti3C2O2). Metallic behavior is only experimentally observed below 1 eV (ε1 < 0), and DFT calculations predict surface plasmon polaritons (SPPs) in the mid-IR (∼0.5 eV, outside the optical domain) and only for Ti3C2O2, but not for Ti3C2Cl2 or other terminations. Additionally, we demonstrate that making thicker Ti3C2Tx MXene films and/or removing the intercalated water can induce a blue shift in this IBT due to the influence of water in facilitating the out-of-plane conductivity. The IBT assignment is critical because its light-matter interaction is fundamentally different from that of an LSPR, providing a new foundation for designing innovative MXene-based optoelectronic materials, which can be tailored through their termination states, while an LSPR would be insensitive to such synthetic variations.

  PublisherDOI

• The Effect of Nanoparticle Shape, Orientation, and Heterogeneity on the Optical Birefringence of Polymer Nanocomposites

  The Journal of Physical Chemistry C · 2026-02-16

  articleOpen accessSenior authorCorresponding

  Embedding plasmonic nanoparticles (NPs) into polymer nanocomposites (PNCs) is a facile method for integrating them into functional devices, whose properties are tunable through varying NP size, shape, and loading. Using anisotropic NPs adds an additional degree of tunability to their orientation order in the PNC, as properties such as conductivity and charge transport can be enhanced in specific directions. In thin films, the film thickness and block copolymer self-assembly can affect the degree of NP orientation, which can be used as a method of control over these properties. However, large-scale control of orientation order in randomly distributed NPs, with both anisotropic NP shapes and heterogeneous shape distributions, remains a challenge. This is partly due to the lack of cost-effective, ensemble-level characterization methods that can independently determine the orientation order and degree of aggregation of anisotropic NPs. Here, we model the complex index of refraction of PNCs with plasmonic NP inclusions in the optical frequency domain by using an effective medium approximation. We quantitatively relate the simulated optical birefringence of the medium to the orientation order parameter of plasmonic nanorods and nanodisks in a robust manner insensitive to heterogeneity in simulated NP size and shape. Experimentally, we measure this orientation order parameter through the birefringent index of refraction using variable-angle spectroscopic ellipsometry (VASE). We demonstrate that we can independently determine the orientation order and degree of aggregation for various PNCs with gold nanorods and nanosphere inclusions. This facile technique provides a powerful method to broadly measure the average orientation order of anisotropic particles in PNCs, which can be correlated to their functional properties.

  PublisherDOI

• Tribute to Professor Mark Ediger

  The Journal of Physical Chemistry B · 2025-11-13

  articleCorresponding
  PublisherDOI

• Order-to-disorder transition due to entropy in layered and 2D carbides

  Science · 2025-09-04 · 34 citations

  articleCorresponding

  In compositionally complex materials, there is controversy on the effect of enthalpy versus entropy on the structure and short-range ordering in so-called high-entropy materials. To help address this controversy, we synthesized and probed 40 M 4 AlC 3 layered carbide phases containing two to nine metals and found that short-range ordering from enthalpy was present until the entropy increased enough to achieve complete disordering of the transition metals in their atomic planes. We transformed all of these layered carbide phases into two-dimensional (2D) sheets and showed the effects of the order versus disorder on their surface properties and electronic behavior. This study suggests the key effect that the competition between enthalpy and entropy has on short-range order in multicompositional materials.

  PublisherDOI

• Substantially Improving CO₂ Permeability and CO₂/CH₄ Selectivity of Matrimid Using Functionalized-Ti₃C₂T_<i>x</i>

  ACS Applied Materials & Interfaces · 2025-01-02 · 19 citations

  articleOpen access

  Mixed-matrix membranes (MMMs) with favorable interfacial interactions between dispersed and continuous phases offer a promising approach to overcome the traditional trade-off between permeability and selectivity in membrane-based gas separation. In this study, we developed free-standing MMMs by embedding pristine and surface-modified Ti3C2Tx MXenes into Matrimid 5218 polymer for efficient CO2/CH4 separation. Two-dimensional Ti3C2Tx with adjustable surface terminations provided control over these critical interfacial interactions. Characterization (Raman spectroscopy, XPS, DSC, FTIR) indicated the formation of hydrogen bonds between the termination groups on Ti3C2Tx and the carbonyl groups of Matrimid, promoting enhanced compatibility and dispersion of MXenes within the polymer matrix. The resulting MMMs with 5 wt % Ti3C2Tx showed a 67% increase in CO2 permeability and an 84% enhancement in CO2/CH4 selectivity compared to pristine Matrimid membranes. Surface modification of Ti3C2Tx using [3-(2-aminoethylamino)propyl]trimethoxysilane (AEAPTMS) further enhanced compatibility, leading to MMMs with 140% higher CO2 permeability and 130% greater CO2/CH4 selectivity. Molecular simulations suggested that AEAPTMS functionalization improved interfacial interactions with Matrimid chains, increasing the affinity of MXenes toward CO2 molecules. Additionally, the elongation of gas pathways, polymer chain disruption, and the presence of interlayer nanogalleries contributed positively to the enhanced separation performance. This work provides insights into tailoring nanomaterial–polymer interfaces to address the challenges of gas separation, paving the way for environmentally friendly CO2 separation technologies.

  PublisherDOI

• Electrically Tunable Excitonic-Hyperbolicity in Chirality-Pure Carbon Nanotubes

  ArXiv.org · 2025-09-29

  preprintOpen access

  Metamaterials exhibiting hyperbolic dispersion enable unprecedented control over light-matter interactions, from sub-diffraction imaging to enhanced spontaneous emission. However, conventional plasmonic hyperbolic metamaterials suffer from limited tunability and lack intrinsic emission capabilities, constraining their utility for active photonic devices. Here, we demonstrate the first room-temperature, electrically tunable, excitonic hyperbolic metamaterial using aligned films of chirality-pure semiconducting carbon nanotubes. Unlike plasmonic systems, these excitonic metamaterials of aligned nanotubes combine strong optical anisotropy with dynamic electrostatic tunability. Spectroscopic ellipsometry reveals that the hyperbolic dispersion window can be electrically shifted by 53 meV, enabling real-time switching between hyperbolic and elliptical regimes. Theory predicts that this tunability translates to the propagation angle being modulated by 34°, driven by a momentum enhancement 3.11 times that of free space, limited primarily by material losses that can be mitigated through improved alignment. In addition, simulations of the system exhibit a high Purcell factor of 1550 and a modulation of 37 % without an optical cavity for a dipole placed 5 nm above the aligned nanotubes. These findings establish excitonic carbon nanotubes as a versatile platform for dynamically reconfigurable photonic metamaterials, opening pathways for adaptive optical devices, electrically-controlled spontaneous emission, and tunable hyper-lenses operating at room temperature.

  PublisherOA PDFDOI

• High-temperature-resilient hyperbolicity in a mixed-dimensional superlattice

  Matter · 2025-07-21 · 1 citations

  article
  PublisherDOI

• Order to disorder transition due to entropy in layered and 2D carbides

  ChemRxiv · 2025-01-06 · 1 citations

  preprintOpen access

  There is controversy surrounding the moniker “high-entropy” materials due to the unclear effect of entropy and enthalpy. The unique nanolayered structure of MAX phases, with its structural covalent-metallic-covalent carbide interfaces, allowed us to address this controversy systematically. Here, we synthesized nearly 40 known and novel MAX phases containing 2 to 9 metals and found that their enthalpic preference for short-range order remains until entropy increases enough to achieve all configurations of the transition metals in their atomic planes. In addition, we transformed all these MAX phases into two-dimensional (2D) MXenes and showed the effects of the order vs. disorder on their surface properties and electronic behavior. This study indicates that short-range ordering in high-entropy materials determines the impact of entropy vs. enthalpy on their structures and properties.

  PublisherOA PDFDOI

• Tuning Water Transport through Nanochannels of Robust Cation‐Intercalated Ti₃C₂T_<i>x</i> MXene Membranes

  ChemSusChem · 2025-08-13 · 3 citations

  article

  Ti 3 C 2 T x MXene membranes have attracted considerable interest due to their exceptional water transport properties, yet the role of cation intercalation on governing transport remains poorly understood. In this experimental and theoretical study, it shows how intercalation with K + , Na + , Li + , Ca 2+ , and Mg 2+ modulates both the nanochannel architecture and water flux of Ti 3 C 2 T x membranes. Unlike in graphene oxide analogs, cations with larger hydration diameters in Ti 3 C 2 T x expand the interlayer spacing, widening flow channels, enhancing slip length of these nanochannels, and boosting water flux from 31.45 to 61.86 L m −2 h −1 . To overcome intrinsically poor adhesion of Ti 3 C 2 T x to polymeric supports, this study incorporates a thin polyvinyl‐alcohol interlayer, which substantially enhances mechanical robustness and structural integrity. Together, these findings elucidate how cation hydration controls water transport and offer a flexible strategy for tailoring MXene membrane performance.

  PublisherDOI

Recent grants

• CAREER: Free Surface Mobility and its Role in the Formation of Exceptionally Stable Glasses

  NSF · $575k · 2014–2019

• Engineering Stable Glass Films Using Molecular Design and Surface-Mediated Equilibration

  NSF · $1.2M · 2016–2020

Frequent coauthors

• Haonan Wang

  39 shared

• Yi‐Chih Lin

  The University of Texas at Austin

  22 shared

• Yi Jin

  Xi'an Jiaotong University

  22 shared

• Ethan C. Glor

  20 shared

• James A. Forrest

  Centre National de la Recherche Scientifique

  19 shared

• Tianyi Liu

  Shanghai University

  18 shared

• Sarah Wolf

  SUNY Cortland

  16 shared

• Robert A. Riggleman

  University of Pennsylvania

  16 shared

Labs

• Fakhraai GroupPI