Strategically devised multiresponsive porous materials for environmental remediation with mechanistic insights
Creators: name: Goswami, Ranadip
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340203
subject: F-block chemistry
classificationCode: 340305
subject: Physical properties of materials
classificationCode: 340703
subject: Statistical mechanics in chemistry

description: Porous materials are state-of-the-art in the field of assorted potential applications like gas adsorption, separation, molecular recognition, catalysis, chemical sensing, and so forth (Chapter 1.0). Exponential growth in continuous quest to develop mixed-linker metal-organic frameworks (MOFs), a sub-class of porous materials is observed owing to the importance in synergistic improvement in stability as well as structure-property investigation. In this milieu, electronically contrasting dual-functionalized Zn (II) MOF (CSMCRI-1) (Chapter 2.1) was developed for ultrasensitive detection of electron lacking analytes e.g. nitrofurazone (NZF) antibiotic and explosive nitro-aromatic 2,4,6-trinitrophenol (TNP). Impressively, the framework represents the first ever MOF for isomeric speciation of toxic and electron rich 4-aminophenol (4-AP) via significant fluorescence “turn-on” mode. Further the fluorescence intensity of 1′ (activated CSMCRI-1) dramatically quenches by trace amount of Fe3+ ions over other competing metal ions, alongside visible colorimetric change of the framework in solid and solution phase upon Fe3+ encapsulation. In another work, strategically designed, mixed-linker luminescent MOF (LMOF), CSMCRI-2 (Chapter 2.2) manifests first-ever sensor for electron rich antibiotic sulfadiazine (SDZ) with 30 fold emission increment. Moreover, antibiotic-induced fluorescence tuning is endorsed through highly selective quenching by electron deficient drug NZF wherein, reversible turn ‛on–off–on′ luminescence switching by SDZ and/or NZF is demonstrated by paper strip method. Notably, both the noxious antibiotics exhibit ultra-sensitive (SDZ: 65 nM, NZF: 0.7 µM) and quick-responsive detection, with enhancement (7.06 × 105 M–1) and quenching (1.30 × 105 M–1) values ranking top tier among contemporary literature. The LMOF further represents nanomolar (10 nM) detection of adenosine monophosphate (AMP) via massive fluorescence enhancement with admirable selectivity and ultra-fast response. To address the wide-range physicochemical stability lies with MOFs, we have developed CSMCRI-6 (Chapter 2.3), exemplifying contrary combination of hydrophobic-hydrophilic pore functionalization benefitting from both, this chemically robust and microporous framework delineates remarkable 37 wt % (0.36 g/g) water uptake (P/P0 =1.0) with impressive recyclability and trivial hysteresis at 300 K. Highly emissive attribute of the framework renders ultrafast and recyclable detection of four assorted classes of organics in water at nanomolar level along with their triphasic detection. This material also serves as a reliable platform for paper-strip based detection of all these organo-toxins alongwith image reliant monitoring of pesticide contamination over food sample, via reversible fluoro-switching. Depending on protonation/ deprotonation on self-calibrated linker, this MOF exemplifies pH-responsive luminescence defect repair via site-specific emission modulation. Such “encrypted and decrypted” states are used in highly regenerable anti-counterfeiting labels over various platforms and conceptualized as molecular switch.

We have also developed two novel isostructural Ni (II) and Co (II) based MOFs containing cationic [M2(μ2-OH)(CO2)2] SBUs through astute blending of nitrogen-enriched linkers. The robust Ni(II)-framework, CSMCRI-3 (Chapter 3.1) displayed extremely selective CO2 adsorption over N2 (292.5) and CH4 (11.7). Importantly, water vapour exposure does not affect the surface area and/or multiple CO2 uptake-release cycles, signifying potential of the porous structure for long-term use under humid conditions. Aqueous phase sensing studies illustrate ultra-fast and highly sensitive detection of explosive TNP and three noxious oxo-anions (Cr2O72–, CrO42–, MnO4–) via remarkable fluorescence quenching. To extrapolate advanced scavenging applications, in-situ fabricated ionic MOF-sponge (CSMCRI-24) was constructed and used for reversible gas sequestration as well as scavenging of toxic oxo-anions which was further evidenced via battery of experiments including Field-Emission Scanning Electron Microscopy (FE-SEM), X-ray Photoelectron Spectroscopy (XPS), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Energy Dispersive X-Ray Spectroscopy (EDX) analysis. On the other hand, acid-base resistant Co (II) analougue, CSMCRI-18 (Chapter 3.2) shows outstanding oxygen evolution reaction (OER) performance in 1M KOH, requiring only 410 mV overpotential to achieve 10 mA cm-2 anodic current density, and possesses low Tafel slope of 55 mV/dec with 93.1 % Faradaic efficiency. The OER activity overpowers commercial IrO2 and Co3O4, and surpasses most of the reported MOF catalysts. Moreover, admirable turn-over frequency (0.02 s-1) and electrochemical assessable surface area (5.75 cm2) stand among the best values while steady OER performance in potentiodynamic and potentiostatic conditions over 500 successive cycles validates long-term catalyst durability. Highly emissive attribute benefits the MOF in ultra-fast, recyclable and discriminative fluoro-detection of three biothiols (L-cysteine, Homocysteine, L-glutathione) in water at record-low sensitivity by virtue of molecular-dimension-mediated pore diffusion.
 
In an another one-of-a-kind report, a chemo-robust H-bonded luminescent MOF (CSMCRI-14) (Chapter 4.0), simultaneously possessing Lewis-Bronsted acidic functionality within the same structure and acting as ppb level lumino-monitor for reactive oxygen species via fluoroswitchable tweezing approach besides an excellent heterogeneous catalyst for mild-condition alkene epoxidation in presence of green oxidant H2O2 with high recyclability. Further, pore-fitting induced size-selective catalytic activity is achieved in epoxidation where excellent yield is maintained over five consecutive catalytic cycles. Additionally, fabricated MOF-composite exhibits simultaneous detection of ClO- and neutralization of free chlorine and excellent catalytic activity over multiple cycles sets an example of futuristic continuous flow reactor using such economical, biocompatible and flexible catalyst system.

This Ph.D. dissertation focuses on the production of mixed-linker multifunctional new MOFs employing pre-designed building blocks, which transcends the problem of MOF degradation during post-functionalization. Simultaneously, it leads to the formation of a robust structure caused by adequate functionalization or catenation and exhibits two or more contradictory or complimentary features.