Ritesh Haldar

Metal–organic frameworks (MOFs) offer tunable reaction space, and using them as porous photocatalysts also allows the catalyst to be recovered and reused. In practice, though, performance is often constrained by how quickly reactants diffuse through the porous material and how well light reaches the active sites. In this work, we present an approach that pairs a MOF thin-film photocatalyst with a cross-flow microfluidic reactor. The thin film sets a well-defined diffusion length, the transparent thin film let light reach the active layer, and crossflow microfluidics allow diffusion control. Together, these features give control over reactant transport and improve illumination of the photocatalyst. To build the photocatalyst, we noncovalently load Ru(bpy)3(PF6)2 (bpy = 2,2′-bipyridine) into mesopores created by defects in a hierarchically porous Zr-based UiO-66 thin film. The well-established aerobic oxidation of ethyl 2-bromo-2-phenylacetate to ethyl 2-oxo-2-phenylacetate serves as a benchmark reaction; it is a test case rather than the main finding of the study. Under cross-flow conditions, the photocatalyst reaches a turnover frequency about ten times that of the equivalent MOF powder system, and it also outperforms the homogeneous benchmark. These findings highlight cross-flow microfluidics as a promising strategy for managing both mass transport and light delivery in MOF-based photocatalysis.

Metal–organic frameworks (MOFs) and covalent organic frameworks (COFs) offer chemically and geometrically programmable pore environments that have been exploited as coatings for capillary- and fiber-based microextraction. However, most formats still rely on discrete adsorbent handling or external fluid actuation, poorly suited to the microliter sample volumes typical of biological specimens. Here we report glass microcapillaries bearing a spatially programmed, nanometer-thick MOF film that simultaneously drives fluid uptake by capillary action and performs localized analyte enrichment within a single, self-contained channel. Retaining the adsorbent as a conformal film rather than a particulate phase removes the need for separate adsorbent handling. It also concentrates chemical functionality at the fluid-contacting surface, enabling efficient enrichment from a few microliters without external pumps. We demonstrate this approach by enriching and quantifying the inflammation-associated metabolites kynurenine and quinolinic acid from microliter volumes of mouse blood serum, achieving clear discrimination between inflammatory and control conditions. These MOF-coated microcapillaries offer an integrated route to low-volume biofluid analysis in settings where sample availability and external fluid handling are limiting.

Biological ion channels achieve highly selective, ultrafast ion transport through stimulus-responsive gating, in which conformational changes triggered by chemical cues such as pH that modulate channel permeability with exquisite precision. Replicating this coupled chemical-structural functionality in synthetic membranes remains a fundamental challenge, particularly for scalable platforms relevant to energy harvesting, desalination, and chemical sensing. Here, we report a bioinspired polymer-metal-organic framework (MOF) composite membrane in which an amino acid (histidine) functionalized MOF nanopores serve as synthetic proton-gated anion channel. The histidine modified, spatially confined ion transport pathway exhibited selective Cl- diffusion at pH 4, enabling pH programmable control of transmembrane potential. Micrometer-scale percolated transport networks within the composite membrane, architecturally inspired by ion channels embedded in lipid bilayers, translate localized αNH2(histidine)-anion specific interaction into macroscopic, anion selective transmembrane potential output. This work establishes a generalizable design strategy for coupling chemical gating with macroscopic ion transport in synthetic membrane systems, with direct implications for ion separations, sensing and osmotic energy generation.

The void space of a metal–organic framework (MOF) can, in principle, be chemically programmed to engage selectively with guest molecules through geometric complementarity or specific non‐covalent interactions. In this work, we have demonstrated that such molecular recognition can be turned on in an otherwise nonselective porous MOF thin film by the deliberate installation of a charge trap chromophore. The chromophore, naphthaleneimide, formed a donor–acceptor complex with the MOF linker 4,4'‐anthracene‐9,10‐diylbis(ethyne‐2,1‐diyl))dibenzoic acid (AEBA) when positioned at the nanopore surface. This spatial design rendered nanochannels with high sensitivity to the polarity of adsorbed guest molecules. Photoexcitation of this engineered MOF film on a patterned Au‐electrode device promoted efficient exciton dissociation, yielding enhanced photocurrents whose magnitude, dark‐to‐light switching ratio, and rise dynamics depend decisively on the adsorbed molecules. Notably, these distinct electrical signatures disappeared in the unmodified MOF film, underscoring the essential role of charge‐trap design. This strategy provides a generalizable route to activate molecular recognition in nonspecific MOF platforms and heralds new opportunities for sensitive, programmable chemical sensing.

Grafting a redox-active chromophore into a Zr-based metal–organic framework, MOF-808, yields a fluorescent porous solid capable of discriminating aromatic amine isomers.

The void space of a metal-organic framework (MOF) can, in principle, be chemically programmed to engage selectively with guest molecules through geometric complementarity or specific non-covalent interactions. In this work we have demonstrated that such molecular recognition can be turned on in an otherwise nonselective porous MOF thin film by the deliberate installation of a charge trap chromophore. The chromophore, naphthaleneimide, formed a donor-acceptor complex with the MOF linker 4,4'-anthracene-9,10-diylbis(ethyne-2,1-diyl))dibenzoic acid (AEBA), when positioned at the nanopore surface. This spatial design rendered nanochannels with high sensitivity to the polarity of adsorbed guest molecules. Photoexcitation of this engineered MOF film on a patterned Au-electrode device promoted efficient exciton dissociation, yielding enhanced photocurrents whose magnitude, dark to light switching ratio and rise dynamics depend decisively on the adsorbed molecules. Notably, these distinct electrical signatures disappeared in the unmodified MOF film, underscoring the essential role of charge-trap design. This strategy provides a generalizable route to activate molecular recognition in nonspecific MOF platforms and heralds new opportunities for sensitive, programmable chemical sensing.

Molecular diffusion in porous solids (metal-organic and covalent organic frameworks, zeolites) can be regulated by engineering the chemical environment of the nanochannels. Selective chemical interactions between the nanochannel surface and diffusing molecules enable discrimination at the molecular level, a feature critical for the development of high-performance chemical separation membranes. A major challenge, however, is to concurrently achieve rapid molecular diffusion and high selectivity, as these attributes exhibit an intrinsic trade-off. In this communication we introduce a de novo methodology exploring the rotational dynamics of the nanochannel chemical components and realize simultaneous enhancement of both diffusion and selectivity for aliphatic chemical isomers (branched hexanes). The methodology utilizes crystalline metal-organic framework thin film architecture akin to membrane structures, supported by a comprehensive experimental and simulation framework to achieve the dual objectives effectively.

Functional, mesoporous UiO-66 (bdc and ndc linkers) MOF thin films are synthesized at ambient condition by exploiting missing-linker and node defects. The resulting mesopores are interconnected through MOF nanochannels and can noncovalently accommodate a bulky Ru2+-complex, as evidenced by Förster resonance energy transfer analysis.

Gas permselective membranes are inherently constrained by a trade‐off between permeability and selectivity. Overcoming this limitation is key to enabling broader industrial adoption, and advanced porous materials—particularly metal‐organic framework (MOF)—has emerged as promising candidate. Yet, to truly rival established separation technologies such as, distillation, pressure swing adsorption and chemisorption, innovative design strategies remain essential. Traditionally, efforts to surpass the trade‐off have focused on regulating porosity, pore architecture, pore surface chemical functionality, and macroscopic transport pathways (particle morphology). These modifications are achieved either through bottom‐up synthetic approaches or by employing external stimuli such as light, pressure, or electric fields. In this work, we introduce a photochargeable membrane that enhances gas permselectivity through precise, molecule‐specific interactions—without altering the underlying porous architecture. This is achieved by incorporating a nanoporous MOF, constructed from redox‐active organic ligands, as filler in a mixed matrix membrane. Upon photoexcitation, ligand–ligand charge separation yields stable pore surface charges, facilitating selective interactions with quadrupolar CO ₂ . This specific interaction enhances CO ₂ /N ₂ and CO ₂ /CH ₄ permselectivity, surpassing the Robeson upper bound. The proof‐of‐concept can be explored for mixed and high purity gas feed preparation.

Gas permselective membranes are inherently constrained by a trade‐off between permeability and selectivity. Overcoming this limitation is key to enabling broader industrial adoption, and advanced porous materials—particularly metal‐organic framework (MOF)—has emerged as promising candidate. Yet, to truly rival established separation technologies such as, distillation, pressure swing adsorption and chemisorption, innovative design strategies remain essential. Traditionally, efforts to surpass the trade‐off have focused on regulating porosity, pore architecture, pore surface chemical functionality, and macroscopic transport pathways (particle morphology). These modifications are achieved either through bottom‐up synthetic approaches or by employing external stimuli such as light, pressure, or electric fields. In this work, we introduce a photochargeable membrane that enhances gas permselectivity through precise, molecule‐specific interactions—without altering the underlying porous architecture. This is achieved by incorporating a nanoporous MOF, constructed from redox‐active organic ligands, as filler in a mixed matrix membrane. Upon photoexcitation, ligand–ligand charge separation yields stable pore surface charges, facilitating selective interactions with quadrupolar CO ₂ . This specific interaction enhances CO ₂ /N ₂ and CO ₂ /CH ₄ permselectivity, surpassing the Robeson upper bound. The proof‐of‐concept can be explored for mixed and high purity gas feed preparation.