A new triazine functionalized luminescent covalent organic framework for nitroaromatic sensing and CO2 storage

Article abstract of DOI:10.1039/c6ra01717g

A new hexagonally ordered covalent organic framework (COF), TRIPTA has been synthesized using Schiff base condensation reaction between 1,3,5-tris-(4-aminophenyl)triazine (TAPT) and 1,3,5-triformylphloroglucinol (TFP). TRIPTA exhibits high crystallinity, a large BET surface area (609 m² g^-1) and pore volume (0.351 cm³ g^-1) and possesses high nitrogen content (14.97%). TRIPTA was found to be highly luminescent when suspended in polar solvents upon irradiation of UV light and can detect various nitroaromatic compounds with good sensitivity by fluorescence quenching at concentrations as low as in the range of 10^-8 M. The maximum fluorescence quenching was observed for trinitrophenol (61.7% at 5.46 × 10^-7 M) with a Stern-Volmer constant of 2.7 × 10⁶ M^-1. The COF also showed excellent CO₂ uptake capacity of 57.07 wt% at 273 K and 16.02 wt% at 298 K up to 5 bar pressure, with an initial heat of adsorption (Q_st) value 56.77 kJ mol^-1.

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DOI: 10.1039/C6RA01717G
A new triazine functionalized luminescent covalent organic framework for
nitroaromatic sensing and CO2 storage
Ruth Gomes and Asim Bhaumik*
Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur,
Kolkata–700 032, India
Abstract
A new hexagonally ordered covalent organic framework (COF), TRIPTA has been
synthesized using Schiff base condensation reaction between 1,3,5ꢀtrisꢀ(4ꢀ
aminophenyl)triazine (TAPT) and 1,3,5ꢀtriformylphloroglucinol (TFP). TRIPTA exhibit high
crystallinity, large BET surface area (609 m2gꢀ1) and pore volume (0.351 ccgꢀ1) and possess
high nitrogen content (14.97 %). TRIPTA was found to be highly luminescent when
suspended in polar solvents upon irradiation of UV light and can detect various nitroaromatic
compounds with good sensitivity by fluorescence quenching at concentrations as low as in
the range of 10ꢀ8 M. The maximum fluorescence quenching was observed for trinitrophenol
(61.7 % at 5.46 x 10ꢀ7 M) with a SternꢀVolmer constant of 2.7 X 106 Mꢀ1. The COF also
showed excellent CO2 uptake capacity of 57.07 wt % at 273 K and 16.02 wt % at 298 K up to
5 bar pressure, with an initial heat of adsorption (Qst) value 56.77 kJmolꢀ1.
Keywords. Covalent organic framework; luminescent; nitroaromatic sensing; CO2
adsorption.
Introduction:
Porous polymeric materials formed by strong covalent bonds following reversible
condensation strategy e.g. boronic ester formation,1 polymerization of aromatic nitrile,2
Schiff base condensation of aromatic amine and aromatic aldehyde/anhydride3 etc. are
1

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classified as covalent organic frameworks (COFs)4. Since their discovery in 20055 these
COFs have gained much attention as they are highly crystalline, light weight materials
possessing exceptionally high surface area with a definite pore size distribution pattern.
These unique properties make them an emerging and promising candidate in various fields
like gas storage,6 chemical sensing,7 charge transport carrier8 and for heterogeneous catalysis9
etc. Among these, chemical sensing of hazardous –NO2 containing high energy aromatic
compounds such as 2,4,6ꢀtrinitrophenol (TNP)ꢀ commonly known as picric acid, 2,4,6ꢀ
trinitrotoluene (TNT), dinitrophenol (DNP), dinitrotoluene (DNT) etc. is of prior importance,
as these polynitro aromatic compounds (NACs) are highly explosive and toxic in nature, even
present in extremely low concentrations.10 Several fluorescence based chemoꢀsensors, e.g.
metalꢀorganicꢀframeworks (MOF), polymers and hybrid materials are reported for this
purpose, which works upon the simple principle of gradual change in fluorescence intensity
of the sensor with the addition of analyte.10 But, surprisingly enough, till date, there are very
few reports listed on the fluorescent property and sensing behavior of COFs11 and the
ongoing research on covalent organic frameworks is mostly concentrated on improving their
porosity and gas storage capacity.12 As these type of materials contain electron rich aromatic
building blocks and extended πꢀconjugation they can be successfully employed as
fluorescence based chemosensor.
In our previous report we have presented the first oneꢀstep synthesis of 1,3,5ꢀtrisꢀ(4ꢀ
aminophenyl)triazine (TAPT) by trimerization of 4ꢀaminobenzonitrile using
trifluoromethanesulfonic acid as catalyst.13 TAPT was successfully employed to design a new
covalent organic framework TRITERꢀ1 using Schiff base condensation reaction with
terephthaldehyde.13 Banerjee et al. have previously reported a series of COFs, (TpPa),14
where the –OH groups underwent ketoꢀenol tautomerization so that the Hꢀbonded ketoꢀ
enamine form of the material gives highly crystalline and stable framework. Using this
2

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concept, herein we report the synthesis of a new triazine functionalized covalent organic
framework TRIPTA via the Schiff base condensation pathway between 1,3,5ꢀtrisꢀ(4ꢀ
aminophenyl)triazine (TAPT) and 1,3,5ꢀtriformylphloroglucinol (TFP) which is followed by
an irreversible ketoꢀenol tautomerization step, where the reversible condensation reaction
helps to produce highly ordered framework and the final Hꢀbonded ketoꢀenamine form
introduces high thermal and chemical stability. The fluorescence property of TRIPTA with
various nitroaromatic analytes i.e. TNP, DNP, DNT and NP as well as its CO2 storage
capacity has been examined thoroughly.
Experimental Section:
Chemicals:
For the synthesis of 1,3,5ꢀtriformyl phloroglucinol (TFP), phloroglucinol
(MW=126.11) was obtained from Sigma Aldrich, India whereas hexamine (MW=140.19),
trifluoroacetic acid (MW=114.02) and hydrochloric acid were produced by EꢀMerk, India.
For the synthesis of 1,3,5ꢀtrisꢀ(4ꢀaminophenyl)triazine (TAPT), 4ꢀaminobenzonitrile
(MW=118.14) and trifluoromethanesulfonic acid were purchased from Sigma Aldrich, India.
Anhydrous N,Nꢀdimethylformamide was obtained from Spectrochem, India and used without
further purification. The nitroaromatic compounds, 2,4,6ꢀtrinitrophenol (MW=229.1), 2,4ꢀ
dinitrophenol (MW=184.106), 2,4ꢀdinitrotoluene (MW=182.134) and 4ꢀnitrophenol
(MW=139.11), for the sensing experiment were purchased from Sigma Aldrich, India. All
other solvents used were of analytical grade produced by EꢀMerk and were distilled prior use.
Synthesis of covalent organic framework TRIPTA:
1,3,5ꢀtrisꢀ(4ꢀaminophenyl)triazine (TAPT) was synthesized by the trimerization reaction of 4ꢀ
aminobenzonitrile using trifluoromethanesulfonic acid as catalyst following the procedure
1
13
described in our previous report13 and the purified product was characterized by H and C
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NMR (ESI Section S1). The yield of TAPT was found to be 90.6 mol %. 1,3,5ꢀtriformyl
phloroglucinol (TFP) was synthesized via Duff formylation procedure using phloroglucinol
and hexamine.15 The polymer TRIPTA was synthesized by Schiff base condensation reaction
between TAPT and TFP (Scheme 1). For the synthesis 709 mg (2 mmol) of TAPT and 420
mg (2 mmol) TFP were taken in a flameꢀdried twoꢀneck round bottom flask fitted with a
reflux condenser under inert atmosphere. To the reaction flask 15 mL anhydrous DMF was
added and the mixture was refluxed for 12 h. The final solid product obtained was filtered,
washed several times with anhydrous DMF and ethanol to remove any starting material
present. The material thus obtained was further purified by Soxhlet extraction using methanol
as solvent for 48 h. The yield of the final COF was calculated to be 85.41 wt%.
Sensing experiment:
1 mg TRIPTA was suspended in 2 mL acetonitrile and sonicated in an ultrasonic bath for 10
min to get uniform dispersion of 0.5 mg mLꢀ1. To the suspension increasing concentration
[5.2 x 10ꢀ8 (M) to 5.46 x 10ꢀ7 (M)] of analytes (TNP, DNP, DNT and NP) were added and the
fluorescence decay profile was studied upon excitation at 365 nm.
Characterization technique:
Powder XꢀRay diffraction patterns of the COF TRIPTA was obtained in a Bruker AXS Dꢀ8
Advanced SWAX diffractometer using CuꢀKα (0.15406 nm) radiation. N2
adsorption/desorption isotherm of the material was recorded using Quantachrome Autosorb
1C at 77 K. CO2 adsorption isotherm of the material was recorded using a Bel Japan Inc.
BelsorpꢀHP at 273 K and 298 K. The isosteric heat of adsorption was obtained using the
software BELMasterTM version 5.3.3.0. Prior to all the adsorption study, the sample was
degassed at 393 K for 12 h under high vacuum conditions. NLDFT poreꢀsize distribution was
obtained using N2 at 77 K carbon on the slit pore model of the Autosorbꢀ1 software. 13C CP
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MAS NMR spectrum of TRIPTA was recorded using Bruker Advance 500 MHz NMR
spectrometer using a 4 nm MAS probe under static condition (spinning rate 5000 Hz, with
sideband suppression).High resolution transmission electron microscopic (HRꢀTEM) image
of the material was obtained using a JEOL JEM 2010 transmission electron microscope
operated at 200 kV. Sample was prepared by dropping a sonicated ethanol solution of the
TRIPTA over a carbonꢀcoated copper grid. Scanning electron microscopic image was
obtained with a JEOL JEM 6700F fieldꢀemission scanning electron microscope (FEꢀSEM).
FT–IR spectrum of TAPT, TFP and TRIPTA were recorded using a Nicolet MAGNAꢀFT IR
750 Spectrometer Series II. The UVꢀVisible diffuse reflectance spectrum of the solid sample
was recorded in a UV 2401PC with an integrating sphere attachment. BaSO4 was used as the
background standard. The 1H and 13C NMR spectra of the amine TAPT and the aldehyde TFP
were recorded in a Bruker Advance 500 MHz NMR spectrometer. Mass spectrometric data of
TAPT was acquired using the electron spray ionization (ESI) technique at 25–70 eV in a
Micromass QꢀtofꢀMicro Quadruple mass spectrophotometer. Thermogravimetric analysis
(TGA and DTA) of the COF was carried out between the temperature ranges from 308 to
1073 K with a temperature ramp of 10 ºC/min in a TGA instrument thermal analyzer TAꢀ
SDT Qꢀ600 under N2 flow. Elemental analysis of the material was carried out using a Perkin
Elmer 2400 Series II CHN analyzer. The fluorescence spectra were recorded using Horiba
Jobin Yvon Fluorimeter (slit width 5 nm, excitation wavelength 365 nm). TimeꢀCorrelated
Single Photon Counting (TCSPC) measurements were performed using a Horiba Jobin Yvon
IBH instrument attached with a MCP PMT Hamamatsu R3809 detector. NANOꢀLED source
was used for excitation of samples at 375 nm. All data were fitted using Data Station v2.3
software.
Results and discussion:
Ordered hexagonal phase and nanostructure:
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The PXRD spectrum (Fig. 1) of TRIPTA reveals highly crystalline nature of the COF
material with periodic hexagonal framework possessing the first sharp peak at a 2θ value 5.8,
which can be attributed to the 100 reflection plane. This peak is accompanied with two minor
peaks at 2θ values 10.0 and 15.1 corresponding to the 110 and 210 reflection planes
respectively. The broad peak at higher 2θ value (26.5) could be originated via πꢀπ stalking
between the 2D sheets and was designated as the 001 reflection plane.14a Using Bragg’s
equation (nλ = 2d sin θ, where n = 1 for the 100 plane and λ = 0.15406 nm) the average d
spacing between the 100 planes (d100) was obtained to be 1.52 nm, whereas the interꢀlayer
distance between the 2D sheets (001 plane) was calculated to be 3.36 Å. The experimental
PXRD values were further matched with the theoretical data obtained using REFLEX
software (unit cell parameters a=b=17.55 Å, c=3.36 Å, α=β=90º, γ=120º) and the result is
summarized in Table 1. The energy minimized hexagonal structural unit of TRIPTA has been
analyzed in section S2 of the ESI.
Porosity and BET surface area:
N2 adsorption/desorption study at 77 K were performed to investigate the surface area
and porosity of the material. The N2 adsorption/desorption isotherm of TRIPTA is shown in
Fig. 2 which exhibits mainly the type I pattern associated with some features of type IV
pattern. Large amount of N2 uptake in the initial pressure range (0ꢀ0.1 bar) suggests
micropores being present in the framework. From the isotherm the Brunauer–Emmett–Teller
(BET) surface area and pore volume of TRIPTA were found to be 609 m2gꢀ1 and 0.351 ccgꢀ1.
Nonlocal density functional theory (NLDFT) using N2 at 77 K, carbon on the slit pore model
was employed on the N2 adsorption/desorption isotherm to investigate the materials pore size
distribution pattern and the result suggests presence of uniform supermicropores of
dimensions ca. 1.68 nm (inset of Fig. 2). The HRꢀTEM image (ESI, Fig. S1) also shows
micropores arranged throughout the matrix. The external morphology of TRIPTA was
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studied employing FEꢀSEM analysis which showed aggregation of small crystalline particles
(ESI, Fig. S2).
Framework and bonding:
The FTꢀIR spectra (Fig. 3) for TRIPTA shows a distinct peak at 1620 cmꢀ1 for
carbonyl group (ꢀC=O) associated with a sharp peak at 1576 cmꢀ1 arising due to the –C=Cꢀ
stretching. The absorption peak at 1255 cmꢀ1 originates from the –CꢀNꢀ stretching vibration.
These peaks indicates that the –OH group of the phloroglucinol entity is present in the keto
form and the imine bond formed via Schiff base condensation reaction is tautomerized to give
enamine group. This phenomenon occurs as the keto form is stabilized by the strong
hydrogen bonding between the ꢀNH and the carbonyl carbon. Also the absence of the
absorption band for C=N stretching at 1700 cmꢀ1 and 1202 cmꢀ1 supports the existence of
ketoꢀenamine form.14 Two strong absorption peak at 1503 cmꢀ1 and 1360 cmꢀ1 (aromatic –
C=Nꢀ) indicates the presence of the triazine ring in both the spectra of TAPT and TRIPTA.
Further the aromatic –C=Cꢀ stretching frequency of the benzene ring appears at 1450 cmꢀ1.
The absorption peak for carbonyl stretching of TFP comes at 1641 cmꢀ1.
Solid state NMR and Chemical environment:
13C cross polarization magic angle spinning NMR spectroscopy was used to find out
the chemical environment of each type of carbon atom present in the framework. As seen in
Fig. 4 the 13C CP MAS NMR spectra of TRIPTA displays resonance signals at 185, 172, 151,
145, 134, 124, 118 and 110 ppm corresponding to different types of carbon atoms indicated
in the structure in inset of Fig. 4. The signal at 185 ppm originates from the carbonyl carbon
whereas the peak at 172 ppm confirms the formation of the triazine ring. The signal at 145
ppm can be assigned as the enamine carbon atom. The benzene ring carbon atom adjacent to
the –NH group appears at 151 ppm and that closer to the triazine ring comes at 124 ppm. The
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other two types of aromatic carbon atoms of the benzene rings resonance at 134 and 118 ppm
and the remaining sp2 carbons of the phloroglucinol moiety appears at 110 ppm. Also the
absence of peak at 192 ppm indicates complete consumption of the starting aldehyde. Thus
the 13C CP MAS NMR spectra of TRIPTA confirm the existence of ketoꢀenamine form.
Thermogravimetric and elemental analysis:
The TGA and DTA profile of TRIPTA is shown in ESI, Fig. S3, indicating high
thermal stability of the material. The TGA plot indicates that the material starts decomposing
after 350 °C giving the major weight loss at around 393 °C as seen from the DTA profile.
The elemental analysis of the COF provides the C, H and N content in the framework as C =
63.93 %, H = 4.05 % and N = 14.97 %. These values closely matches with the theoretically
calculated values obtained from the molar ratio of the starting reactant monomers (ESI, Table
S2).
Photophysical property:
Fig. 5 represented the UVꢀVis diffuse reflectance spectrum of TRIPTA, which
showed absorbance maxima at 408 nm arising due to the π → π* transition of the heteroatom
substituted conjugated system. The band gap energy obtained from the spectrum was 2.0 eV
as shown in the inset of Fig. 5. Interestingly TRIPTA showed highly fluorescent green color
when suspended in different polar aprotic solvents (ESI, Fig. S4), which can be attributed to
the extended πꢀconjugation and acceptorꢀdonor charge transfer in the framework.16 ESI, Fig.
S5 represented the fluorescence spectra of TRIPTA upon excitation at 365 nm in solvents of
varying polarity. The spectra suggested that the fluorescence intensity increases with
increasing polarity of aprotic solvents, whereas in case of polar protic solvents (water,
methanol and ethanol) and nonꢀpolar solvents (cyclohexane and toluene) the COF shows no
significant fluorescence property. The solid state fluorescence spectrum of the COF (λex
=
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325 nm) is shown in ESI, Fig S6, where a broad emission maxima at 608 nm is observed. The
fluorescence spectrum (Fig. 6, black line) of the acetonitrile suspension of TRIPTA exhibited
a strong emission band with emission maxima at 513 nm upon excitation at 365 nm
corresponding to the chromophoric triphenyl triazine moiety. It was observed that the
fluorescence intensity is effectively quenched upon addition of various nitroaromatic
analytes. The fluorescence quenching profile of TRIPTA upon the addition of increasing
concentration of 2,4,6ꢀtrinitrophenol (TNP) from 5.2 x 10ꢀ8 M to 5.46 x 10ꢀ7 M is shown in
Fig. 6. The UVꢀVis diffuse reflectance spectrum of acetonitrile suspension of TRIPTA in
presence of TNP is shown in ESI, Fig. S7. The effect of addition of other nitroaromatic
compound i.e. 2,4ꢀdinitrophenol (DNP), 2,4ꢀdinitrotoluene (DNT) and 4ꢀnitrophenol (NP) on
the fluorescence intensity of TRIPTA and the corresponding SꢀV plots are shown in Fig. 7, 8.
The quenching constant of the sensor was evaluated analyzing the SternꢀVolmer (SꢀV) plot
(Fig. 8A) following the equation I0/I = 1 + KSV[M]. From the plot the quenching constant
(KSV) value was obtained to be 2.7 X 106 Mꢀ1. The KSV values follow the order
TNP>DNP>DNT>NP. Fig. 9 showed a comparative bar diagram of the quenching
efficiencies [I0ꢀI]/I0 of TRIPTA for different nitroaromatic analytes at a concentration 5.46 x
10ꢀ7 M, where the quenching efficiency value for TNP is 61.7 %. Further the Time correlated
single photon counting (TCSPC) studies of acetonitrile suspension of TRIPTA in presence of
various nitroaromatic analytes were performed to measure the change in average fluorescence
lifetime of the COF on addition of the analyte solutions. TRIPTA exhibits a triexponential
decay profile with an average lifetime value 1.49 ns upon excitation at 375 nm and emission
at 513 nm (Figure 10). The average lifetime remains almost unchanged (1.59 ns) after
addition of TNP (5.46 x 10ꢀ7 M), which indicate static quenching via the formation of a
ground state complex. On the other hand, the average lifetime value of TRIPTA on addition
of DNP, DNT and NP decreases to 0.49, 0.36 and 0.35 ns respectively, indicating that
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dynamic quenching mechanism is involved in these cases. ESI, Table S3 represents the
details of TCSPC measurements.7b
CO2 adsorption study:
The CO2 uptake experiment for the COF TRIPTA was conducted at two different
temperatures (273 K and 298 K) up to 5 bar pressure of the adsorbate and the
adsorption/desorption isotherms at these temperatures are presented in Fig. 11. A gradually
increasing uptake was observed in the amount of CO2 adsorbed with increasing pressure, the
value reaching a maximum of 12.97 mmolgꢀ1 (57.07 wt %) and 3.64 mmolgꢀ1 (16.02 wt %) at
273 K and 298 K respectively, at 5 bar pressure. Although the rate of CO2 adsorption is
relatively slower in the high pressure region but the isotherms does not reach any saturation
value, indicating that the material can adsorb some more CO2 if the pressure is further
increased. Moreover, the desorption plot followed a fully reversible pathway, which signifies
that the adsorbed gas can be completely recovered from the adsorbed solid. Fig. 12 represents
the isosteric heat of adsorption (Qst) for TRIPTA as a function of volume of adsorbed CO2, as
obtained using ClausiusꢀClapeyron equation (lnP1/P2 = ꢁH/R[1/T2ꢀ1/T2], at constant V) on
the adsorption isotherms at 273 K and 298 K. The Qst value for the 1st point was found to be
56.77 kJmolꢀ1, which then decreases and becomes almost stable at ~30ꢀ35 kJmolꢀ1. Such high
initial Qst value reflects strong interaction between the adsorbate gas molecules and the
material surface, although the value is considerably lesser than the energy of chemical bond
so that reversible physisorption is feasible. The CO2 adsorption experiment was repeated four
times at both 273 K and 298 K to check the reusability of the material and the results are
summarized in the histogram of ESI, Fig. S8. The CO2 uptake value of TRIPTA was reduced
only by 1.34 wt % at 273 K and 1.14 wt% at 298 K after fourth cycle. The presence of Nꢀrich
functionality (Nꢀcontent 14.97%) in the framework of the material leads to stronger
interaction with the Lewis acidic CO2 molecules.17 Moreover high BET surface area (609
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m2gꢀ1), pore volume (0.351 ccgꢀ1) and sufficient micropore content of the material also
contribute for such high CO2 uptake behavior.
Conclusions
In conclusion, we have successfully synthesized a new crystalline, high surface area
covalent organic framework TRIPTA via Schiff base polycondensation of 1,3,5ꢀtrisꢀ(4ꢀ
aminophenyl)triazine (TAPT) and 1,3,5ꢀtriformylphloroglucinol (TFP). TRIPTA showed
good luminescent property in various polar solvents when irradiated with UV light. The
material was successfully employed for chemical sensing of nitro aromatic compounds at
concentration as low as 5.196 X 10ꢀ8 M. A maximum fluorescence quenching was observed
for TNP (61.7 % at 5.46 x 10ꢀ7 M) with a SternꢀVolmer constant of 2.7 X 106 Mꢀ1. TRIPTA
also showed high CO2 uptake capacity of 57.07 wt% at 273 K and 16.02 wt% at 298 K up to
5 bar pressure with an initial Qst value 56.77 kJmolꢀ1 suggesting its future potential in sensing
and environmental research.
Acknowledgements. RG wishes to thank CSIR, New Delhi for senior research fellowship.
AB wishes to thank DST, New Delhi for instrumental facilities through DST Unit on
Nanoscience and DSTꢀSERB project grants.
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References and Notes:
*Corresponding author. Eꢀmail: msab@iacs.res.in
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Scheme 1. Schematic representation of synthesis of TRIPTA.
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Figure captions
PXRD pattern of TRIPTA.
Figure 1.
Figure 2.
N2 adsorption/desorption isotherms of TRIPTA at 77 K. Pore size distribution is
shown in the inset.
FTꢀIR spectra of TFP (blue), TAPT (red) and TRIPTA (black).
13C CP MAS NMR spectra of the polymer TRIPTA.
Figure 3.
Figure 4.
Figure 5.
Solid state UVꢀVis absorbance spectrum of TRIPTA (Bandgap of the material is
shown in inset)
Photoluminescence spectra of acetonitrile suspension of TRIPTA upon addition of
increasing concentration [5.2 x 10ꢀ8 (M) to 5.46 x 10ꢀ7 (M)] of 2,4,6ꢀtrinitrophenol
(λex = 365 nm). Photograph of TNP sensing under UV light is shown in inset.
Photoluminescence spectra of acetonitrile suspension of TRIPTA upon addition of
increasing concentration [5.2 x 10ꢀ8 (M) to 5.46 x 10ꢀ7 (M)] of (A) 2,4ꢀ
dinitrophenol, (B) 2,4ꢀdinitrotoluene and (C) 4ꢀnitrophenol (λex = 365 nm)
SternꢀVolmer plots for fluorescence quenching of TRIPTA by (A) 2,4,6ꢀ
trinitrophenol, (B) 2,4ꢀdinitrophenol, (C) 2,4ꢀdinitrotoluene and (D) 4ꢀnitrophenol.
Fluorescence quenching efficiency of TRIPTA towards various nitroaromatic
compounds at concentration 5.46 x 10ꢀ7 (M).
Figure 6.
Figure 7.
Figure 8.
Figure 9.
Figure 10.
TCSPC average fluorescence lifetime decay profile of acetonitrile suspension of
TRIPTA in presence of different nitroaromatic compounds (λex = 375 nm and λem
513 nm).
=
CO2 adsorption/desorption isotherm of TRIPTA at 273K and 298K.
Figure 11.
Figure 12.
Isosteric heat of adsorption (
Qst) of TRIPTA as a function of CO2 adsorbed
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Figure 1 [Gomes and Bhaumik]
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Figure 2 [Gomes and Bhaumik]
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Figure 3 [Gomes and Bhaumik]
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Figure 4 [Gomes and Bhaumik]
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Figure 5 [Gomes and Bhaumik]
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Figure 6 [Gomes and Bhaumik]
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Figure 7 [Gomes and Bhaumik]
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Figure 8 [Gomes and Bhaumik]
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Figure 9 [Gomes and Bhaumik]
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Figure 10 [Gomes and Bhaumik]
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Figure 11 [Gomes and Bhaumik]
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Figure 12 [Gomes and Bhaumik]
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Table 1: Unit cell parameters and indexing of hexagonal planes of TRIPTA:
Symmetry
hexagonal
Lattice parameters
Wavelength (Å)
a = b = 17.55, c = 3.36, α = β = 90º, γ = 120º
1.54056
Range of data collection 0.4≤ 2θ ≤40
h
k
l
Theta (º)
2 Theta (º)
d
1
1
0
1
0
0
2.90502
5.03597
5.81005
10.0719
15.199
8.775
2
0
1
0
0
1
7.70589
13.2529
15.4118
26.5058
5.745
3.360
The experimental small angle PXRD has been matched with the theoretical PXRD pattern
using REFLEX software.
29