Engineering of Interfacial Energy Bands for Synthesis of Photoluminescent 0D/2D Coupled MOF Heterostructure with Enhanced Selectivity toward the Proton-Exchange Membrane

Abstract

Engineering of the interface for tuning the structural, functional, and electronic properties of materials via the formation of heterostructure composites exhibits immense potential in the current research scenario. This study reports a novel ternary composite synthesized by decoration of zero-dimensional Pd nanoparticles (NPs) and two-dimensional (2D) graphite oxide (GO) sheets in the UiO-66 metal−organic framework (MOF). A mixed matrix membrane was fabricated by incorporating this composite in the SPEEK polymer matrix, which exhibited higher selectivity compared to commercial Nafion 117. The synthesized composite and fabricated membranes were thoroughly characterized in terms of their chemical structures, microstructural morphologies, physicochemical, thermal, photo-electrochemical, and optical properties, ion-exchange capacity, proton conductivity, and methanol permeability. As per our knowledge, this is the first study which explores the effect of noble metal NPs and carbon 2D material simultaneously on the electronic structure of the MOF, resulting in improved selectivity. The electron-accepting nature of GO and surface plasmon resonance effect of Pd alter the energy band positions and scavenge the electrons, improving the proton conduction of the composite. The introduction of oxygen vacancies in lattice leads to efficient charge separation. The formation of a Schottky junction results in the localized electric field effect due to electron density fluctuation which aids in ion transport. The current study opens up a new route to overcome the major challenge associated with direct methanol fuel cells (DMFCs), that is, high/low methanol crossover by improving the proton conduction.

Recent advances of metal–organic frameworks‐based proton exchange membranes in fuel cell applications

“…Influencing properties by tuning the interfacial structures of composites is a promising strategy. In 2021, Mandal et al 143 modified GO and Pd nanoparticles onto UiO-66 to form a composite material, which was then used as a filler to composite with SPEEK to synthesize a hybrid membrane. GO contains a variety of hydrophilic functional groups (carboxyl, hydroxyl, epoxy, etc.…”

“…(C) Possible interaction between SPEEK and UiO‐66/Pd‐ graphite oxide (GO). Reproduced with permission from Das et al 143 . Copyright 2021, American Chemical Society…”

Recent Progress in 2D Metal‐Organic Framework‐Related Materials

“…Das et al dispersed GO in DMF by ultrasonic wave to obtain uniform and stable slurry, then introduced UiO-66 framework, added ZrCl 4 and ultrasonic treatment, acidified with HCl, and added BDC. [157] The film was cast on a flat glass plate, dried and annealed, then cooled and immersed in deionized water. Morphological analysis of the composite membrane showed that a uniform and defect-free membrane was formed on the sulfonated poly ether ketone ether (SPEEK) membrane substrate, and the composite was uniformly distributed.…”

Emerging Pristine MOF‐Based Heterostructured Nanoarchitectures: Advances in Structure Evolution, Controlled Synthesis, and Future Perspectives

“…[27][28][29][30][31][32][33][34] However, research on the construction of these materials is still in its infancy and needs to be further expanded and improved. [35][36][37][38][39][40] Constructing well-defined MOF/MOF heterointerfaces using traditional synthetic methods, such as solvothermal, hydrothermal and one-pot method, is challenging, as precise control at the atomic and molecular levels is difficult to achieve. However, it is feasible to achieve controllable fabrication of MOF heterostructures through hierarchical assembly on a host substrate or seed crystal, [41] which allows for customization of components and structures at both the micro and macro levels.…”

“…[27–34] However, research on the construction of these materials is still in its infancy and needs to be further expanded and improved. [ 35–40 ]…”