i have presented this paper in a seminar.Hope you like it.The paper is from JACS

1. SeminarTopic
Sensing and Discrimination of Explosives atVariable
Concentrations with a Large-Pore MOF
• Name – Gaurav Rai Submitted to
Dr. C.M. Nagaraja
Assistant Professor
Department of Chemistry
IIT ROPAR
• Place – IIT Ropar

2. MOF (Metal Organic Framework)
Metal-organic frameworks (MOFs) are made by linking inorganic and organic
units by strong bonds (reticular synthesis). The organic units are ditopic or
polytopic organic carboxylates (and other similar negatively charged
molecules), which, when linked to metal-containing units, yield architecturally
robust crystalline MOF structures with a typical porosity of greater than 50%
of the MOF crystal volume. Crystalline metal-organic frameworks (MOFs) are
formed by reticular synthesis, which creates strong bonds between inorganic
and organic units.

3. Basic Structure
• Metal ions + Organic units (linkers/bridging ligands) Coordination Polymers or MOF materials

4. Isoreticular
This concept has been defined as isoreticular (from the Greek term iso meaning
same and Latin reticulum meaning net), thus giving rise to isoreticular metal
organic frameworks, or IRMOFs. In these compounds, the organic component
can be systematically changed to target a specific size or incorporate a desired
chemical functionality.This method has tremendous utility for control over
pore metrics and organic chemical functionality

7. The flexibility with which the metal and organic linkers can be varied has led to thousands of
compounds being prepared and studied each year.

8.  MOFs are structures made up of inorganic nodes, which can either be single ions or
clusters of ions, and organic linkers. They contain potential voids which can be used
for various application.
 Very low density.
 Crystalline.
 Large voids.
 Significant van der Waals interaction.
Structuralfeatures

9. • Many potential applications of MOFs depends on
the size and nature of the available free volume
or pores within the frameworks structure
• Tuning of the pores is typically achieved by
variation of the metal ions or organic ligands
• Lengthening the organic chains can lead to
increased pore size but is often limited by a
decrease in stability of the framework.
Important of pore size

10. Some Problems
• To prepare MOFs with even higher surface area (ultrahigh porosity) requires
an increase in storage space per weight of the material. Longer organic
linkers provide larger storage space and a greater number of adsorption
sites within a given material. However, the large space within the crystal
framework makes it prone to form interpenetrating structures (two or more
frameworks grow and mutually intertwine together).

11. The most effective way to prevent interpenetration is by making
MOFs whose topology inhibits interpenetration because it would
require the second framework to have a different topology
Chemistry of
MOFs

12. DifferentTypes OF Explosives

13. What we will be studying

14. Sensors
• MOF-based sensors for explosives have seen success in recent years due to
their tunable porosity, variation in the mechanism of interaction with the
explosive (through organic linker or metal center-based quenching), and
hugely customizable structures.

15. Why Fluoroscence Spectroscopy?
The advantages of using fluorescence for detecting explosives include sensitivity, due
to the very electron withdrawing nature of the explosive molecules; the ability to
detect a wide range of different explosives by tuning the fluorescent material in
question; and the simplicity and robustness of the detection method, over techniques
such as mass spectrometry.
MOFs have successfully been used to detect nitroaromatics such as picric acid and
trinitrotoluene (TNT) in solution and vapor phase, respectively, as well as explosive-
related vapors such as taggant 2,3-dimethyl-2,3- dinitrobutane (DMNB), through
“turn-off” luminescent detection.

16. Turn Off
• Turn-off detection is so named because the MOF luminescence is strongly
quenched by the very electron withdrawing materials in nitro-explosives but
not by other common interferants containing other functional groups or
fewer nitro groups.

17. Synthesis of
MOF MJ3
The organic ligand 5,5’,5”,5”’-[1,2,4,5-benzenetetrayltetrakis(methylene-oxy)]
tetra-1,3-benzenedicarboxylic acid

18. • MJ3 unit cell structure showing the two different pore environments (green
and yellow spheres). The smallest portal opening for the largest (yellow)
cavity is 15 Å in diameter, based on van der Waal’s radii and including
hydrogen atoms.

19. Procedure to get Activated MOF
A four-stage washing procedure was implemented for the removal of coordinating DMF
solvent from the pores of MJ3 to yield the “activated” framework MJ3′ ([Zn4L(H2O)4]n), that
would respond to analytes now able to enter the MOF pores
The powder X-ray diffraction (PXRD)
patterns of the crystalline material
present after each stage of the washing
procedure are shown in Figure .

20. • The excitation spectrum of the MOF MJ3′ suspension in MeCN indicated
that this framework to best excited at wavelength λex = 315 nm ,
therefore, all sensing experiments were conducted at this wavelength.
The fluorescence emission maxima of MOF MJ3′ in MeCN were
observed to be λem = 348 nm, whereas that of the linker H8L (dissolved
in DMF) was 335 nm (λex = 315 nm).

21. Red Shift?
• Observed red-shift in the excitation and emission spectrum of the free linker
and the MOF is very typical of organic ligands being incorporated into MOFs
and is usually ascribed to the electronic coupling of the neighboring organic
ligands in the Ions framework through the metal as well as increased
scattering from the particulate suspension..

22. Testing In Solution Phase
• MOF MJ3′ was tested against known quantities of explosive substances tetryl, TNT, 1,3,5-
trinitroperhydro-1,3,5-triazine (RDX), PETN, and the TNT derivative and contaminant 2,4-DNT
in MeCN solution. Suspensions of MOF MJ3′ in MeCN were used for all solution-phase sensing
experiments .
• It enables the measurement of sensor efficiency and mechanism, the sensitivity of the system,
and performance comparisons to be made with other solution-phase MOF explosives sensors.
In addition, a solution-phase sensing system has the potential to be used as an initial, rapid,
and cheap diagnostic tool for the in-field detection of explosive particles on a surface, or
preconcentrated into a liquid sample, prior to their laboratory identification.

23. A study was performed to investigate whether any of these
particulates settled out of suspension during sensing.
A 6 mg sample of finely ground MJ3′ ultrasonicated for 2 h
gave the most stable suspensions, and the initial fluorescence
intensities (after the implemented settling and vortexing steps
mentioned ) were consistent

24. Experimental Results

25. Greatest quenching of the MOF by the analytes
follows tetryl ≫ 2,4-DNT > PETN >TNT > RDX
Of particular note is the large quenching by PETN,
which is one of the largest achieved to date by a
MOF. We attribute this to the design of the
large-pore system allowing good access to
the analyte.

26. Why tetryl showing high quenching
• Greater spectral overlap
between the emission
spectrum of the MOF and the
absorption spectral of tetryl, in
comparison to the other tested
analytes, it is suggested that
some optical interactions could
be responsible for the
increased sensitivity toward
this analyte with MJ3′

27. Finally, to confirm that organic framework is MJ3’ not being degraded during sensing, a PXRD pattern of
in a sensing solution containing tetryl (62.5 µM) was compared with a PXRD pattern of the MOF in MeCN
solution.The same analysis was also completed on a 2,4-DNT + MOF sample.

28. To investigate whether the
problem of explosive
differentiation at variable
concentration could be
overcome three MOF’s were
designed

30. Conclusion
• MJ3′ showed good sensitivity and quenching constants for this material to a range
of different explosives, and in particular, have shown how a large-pore size allows
interactions with the difficult-to-detect PETN. Limits of detection were in the ppm
range or below, suggesting utility for this material in environmental management
and homeland security.
• Careful selection of MOF constituents can yield crystals of ultrahigh porosity and
high thermal and chemical stability. These characteristics allow the interior of
MOFs to be chemically altered for use in gas separation, gas storage, and catalysis,
among other applications. In particular, applications in energy technologies such as
fuel cells, supercapacitors, and catalytic conversions have made them objects of
extensive study, industrial-scale production, and application.

31. Reference
Sensing and Discrimination of Explosives atVariable Concentrationsith a
Large-Pore MOF as Part of a Luminescent Array
Monika Jurcic,†,⊥William J. Peveler,*,‡,⊥ Christopher N. Savory,† Dejan-
Krešimir Bučar,†Anthony J. Kenyon,David O. Scanlon,†,∥ and Ivan P. Parkin†
ACS Appl. Mater. Interfaces 2019, 11, 11618−11626

32. ThankYou