Amine-decorated zirconium-based metal-organic framework for ultrafast detection of 2, 4, 6-trinitrophenol in aqueous medium

doi:10.21203/rs.3.rs-2485049/v1

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Amine-decorated zirconium-based metal-organic framework for ultrafast detection of 2, 4, 6-trinitrophenol in aqueous medium

https://doi.org/10.21203/rs.3.rs-2485049/v1

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An amine-decorated zirconium-based metal–organic framework (MOF, coded as UiO-66-NH₂) with rod shaped morphology has been solvothermally synthesized using low-cost and easily available 2-aminoterephthalic acid as an organic linker. The crystallinity of the synthesized MOF material has been confirmed by sharp PXRD diffraction pattern. Photoluminescent studies showed that the UiO-66-NH₂ features a strong fluorescent behaviour when dispersed in water, which could be used as a highly selective and sensitive sensor for detection of trace amount of 2,4,6-trinitrophenol (TNP), even in coexistence with other potentially competitive nitroaromatic analytes. High value of Stern-Volmer quenching constant K_sv (1.106 x 10⁵M^-1), photoluminescent quenching efficiency (97.8%) and lower detection limit (0.95 μM/217ng mL^-1) ascertained extraordinary sensitivity of developed UiO-66-NH₂ for TNP. Density functional theory (DFT) calculations and electrostatic interactions (i.e. ionic interaction, H-bonding and π-π interaction) indicated that electron and energy transfer processes play a key role in the turn-off quenching response of UiO-66-NH₂ sensor towards TNP.

Metal-organic framework

fluorescent sensor

nitro-aromatic compounds

6-trinitrophenol

density functional theory

photo-induced electron transfer

fluorescence resonance energy transfer

An amine-decorated zirconium-based metal–organic framework (UiO-66-NH₂) was synthesised.
Developed sensor detects 2,4,6-trinitrophenol (TNP) in water.
Detection of TNP was done even in coexistence with other potentially competitive nitroaromatic analytes.
Lower detection limit (0.95 μM/217ng mL^-1) ascertained extraordinary sensitivity of developed UiO-66-NH₂ for TNP.
Electron and energy transfer processes justify the sensitivity of UiO-66-NH₂ sensor for TNP.

Persistent contamination of environmental resources by harmful organic pollutants (OPs) is one of the serious challenges faced by modern society. Nitro-aromatic compounds (NACs), a class of OPs, are used extensively in synthesis of explosives, herbicides, insecticides, medicines, dyes, and other useful industrial chemicals [1]. The utilization of NACs has brought about inevitable environmental contamination. The NACs have shown high toxicity, non-degradability, mutagenicity and carcinogenicity [2]. Toxicity of NACs is determined by their higher hydrophobicity (log Kow) and electronic factors [3]. NACs are broadly classified into two major categories i.e., phenolic and non-phenolic compounds. Among diverse phenolic and non-phenolic NACs, 2,4,6-trinitrophenol (TNP) shows an exceptionally high toxicity [4]. It is utilized in different industries such as dyes, drugs, polymers, rocket fuel, matchbox, electric battery and firecrackers etc. [5]. It is meaningful to be noted that 2,4,6-TNP has more explosive power than TNT [6]. The presence of three electron withdrawing nitro groups and one hydroxyl group in TNP make it highly water soluble and resistive towards environmental degradation which subsequently leads to the soil and water resources contamination [7]. The long term exposure of TNP in humans can cause number of detrimental influences related to skin, eyes, lungs, intestine, liver, and kidney [6, 8]. Thus, development of a selective, sensitive, rapid and precise approach for detection of TNP from water and industrial waste samples is necessitated for public safety and human well-being [6].

A number of analytical instrumental strategies like ion chromatography-mass spectrometry [9], raman spectroscopy [10], high performance liquid chromatography [11], and electrochemical analysis [12] have been utilized for detection of TNP and other NACs. Sample pre-treatment, expensive instrumentation, complex procedures and skilled workforce requirement are some common drawbacks in above traditional techniques which significantly limit their utilization for detection of NACs. Recently, fluorescence spectroscopy has acquired huge attraction as an alternative approach to traditional techniques on account of its simple and speedy procedure, minimal expense, and high sensitivity. Until now, variety of fluorescent probes viz., metal complexes [13], carbon nitride nano-sheets [14], carbon dots [15], and conjugated network polymers [16] are extensively used for detection of TNP in the aqueous samples. However, these fluorescent probes suffer from major limitations such as large time consumption, multistep or complex synthetic methodology, environmental toxicity, etc. Therefore, an easy, inexpensive and swift fluorescence probe methodology is required to achieve ultrafast detection of TNP.

Metal organic frameworks (MOFs) are crystalline materials made up of organic linkers and metal ions or metal clusters that have gained significant attention as fluorescent sensors. These crystalline materials have applications in emerging research domains such as heterogeneous catalysis [17], gas storage [18], separation [19], and drug delivery structures [20]. Fluorescent MOF sensors possess large number of extraordinary properties such as imbibed high porosity, large surface areas, chemical functionalities, and tuneable structures, which make them excellent material for in-field applications. In order to enhance the selectivity of MOF sensors towards particular analyte the functionalization of organic linkers is regarded an effective option. As well-documented in literature, the amine-decoration of MOF pore cages enhance their selectivity towards highly explosive TNP. The amine groups provide hydrogen bonding sites for interaction with the phenolic proton of TNP. However, the major drawback of MOFs is their moisture sensitivity which limits their usefulness in water. To overcome this limitation, nowadays zirconium based MOFs were synthesized which showed high water stability because the higher valent metal means tetravalent zirconium form strong bond with carboxylate groups of organic linkers commonly utilized in MOF preparation.

Encouraged by above facts, in this research work an amine-decorated zirconium-based metal–organic framework (MOF, coded as UiO-66-NH₂) has been solvothermally synthesized using 2-aminoterephthalic acid as an organic linker. The structure of UiO-66-NH₂ showed that amine groups remain free within pore cages of MOF which enhance its selectivity towards TNP explosive. As expected, TNP showed excellent fluorescence quenching response i.e., 97.86% on the fluorescence intensity of UiO-66-NH₂. The high Stern-Volmer quenching constant value K_sv=1.106 x 10⁵ M^− 1, established that the synthesized MOF is an excellent fluorescent sensing probe for TNP. High water stability and low detection limit (0.95 µM/217ng mL^− 1) of UiO-66-NH₂ towards TNP signifies its high sensitivity, which may make it useful for practical applications.

2.1. Materials and methods

All chemicals were procured from the different commercial sources. Zirconium tetrachloride (ZrCl₄), 2-aminoterephthalic acid (2-ATA or NH₂-BDC), hydrochloric acid (HCl), nitrobenzene (NB), 4-nitrotoluene (4-NT), 1,3-dinitrobenzene (1,3-DNB), 2,4-dinitrotoluene (2,4-DNT), and 4-nitrophenol (4-NP) were supplied by the Sigma Aldrich. N,N-dimethylformamide (DMF), 2,4-dinitrophenol (2,4-DNP) and TNP were supplied by the Avra chemicals. These chemicals were of analytical grade and used without additional refinement. Triply distilled water was prepared in the laboratory for solutions preparation. Fourier transform-infrared (FT-IR) spectra were scanned in the spectral region of 450–4000 cm^-1 on a Perkin Elmer FT-IR spectrometer (RXIFT-IR, Japan). Powder X-ray diffraction (PXRD) data were collected within 2θ range of 2–50⁰ using monochromated Cu-k_α radiation (λ = 1.5406Å) on a Empyrean X-rays Diffractometer at 40 mA (1800 W) current and 45 kV voltage. Scanning electron microscope (SEM) images of gold coated sample were taken by Carl Zeiss Merlin compact SEM equipment. The EDS spectra of gold layered sample firmly fixed on a sample stub were obtained by utilising an EDS spectrometer installed as an extra accessory on SEM instrument for elemental analysis. Ultrasonication was performed on ultrasonic bath (Sarthak Scientific Services, India). UV-Vis absorption spectra were recorded at room temperature using a UV-Vis 1800 spectrophotometer (Shimadzu, Japan). All the fluorescence studies were carried out on a Shimadzu RF-5301PC spectrofluorophotometer. During fluorescence studies, the slit widths of both excitation and emission monochromators were set at 5 nm. The theoretical calculations were done using a Gauss View version 5.08 and Gaussian 09 software.

2.2 Synthesis of UiO-66-NH₂

Amine-decorated UiO-66-NH₂ was prepared according to the procedure reported previously in literature [21]. ZrCl₄ (420 mg, 1.8 mmol) was dissolved in 30 mL DMF in 100 mL round bottom flask and then dropwise addition of 5 mL conc. HCl was done, after that ultrasonication was performed for 20 min for proper dispersion of starting materials. The contents of round bottom flask were magnetically stirred at 100°C for 3 h. The resultant clear solution was cooled down to room temperature. After that, 2-ATA (400 mg, 2.3 mmol) was mixed in 30 mL DMF in a separate beaker and gently added into the ZrCl₄ solution. The resultant mixture was again magnetically stirred for next 24 hours at 80°C. A pale yellow crystalline material formed was separated via vacuum filtration, followed by washing with DMF, and finally dried at 70°C in an electric oven for 18 h. The synthetic scheme of UiO-66-NH₂ is presented in Fig. 1.

2.3 Sample preparation

3.1 Characterization of UiO-66-NH₂

3.1.1 FT-IR

The successful formation of UiO-66-NH₂ was confirmed by the FT-IR analysis, which is presented in Fig. 2a. As clear from this figure, the strong bands detected at 1552 and 1386 cm^− 1 was related to asymmetric and symmetric stretching vibrations of carboxylate group confirmed the formation of UiO-66-NH₂. Additionally, the FT-IR spectrum does not show any peak at 1685 cm^− 1 corresponding to free carboxylic acid group present in 2-ATA ligand also indicated that -COOH group of ligand are coordinated to zirconium metal ions during formation of UiO-66-NH₂. The presence of DMF solvent molecules within pores of UiO-66-NH₂ was confirmed by the appearance of peak at 1652 cm^− 1 corresponding to carbonyl group of DMF. On the other hand, the presence of free amine group within pore cages of UiO-66-NH₂ was verified by the appearance of asymmetric stretching vibration of N-H bond of an 2-ATA linker at 3317 cm^− 1 in UiO-66-NH₂ MOF as well. Two peaks at 1255 and 771 cm^− 1 have been identified as the C-N stretching band and N-H rocking vibration, respectively.

3.1.2 PXRD

The crystallinity and the phase purity of synthesized UiO-66-NH₂ was confirmed by the PXRD. The peaks located at 2θ = 7.13°, 11.7°, and 25.14° corresponding to the Miller indices (111), (022) and (224), respectively in recorded PXRD spectra of UiO-66-NH₂ matched well with the stimulated pattern of UiO-66-NH₂ already reported in literature confirmed the successful formation of UiO-66-NH₂ (Fig. 2b) [22]. The sharp PXRD peaks confirmed the high crystallinity of the synthesized material. The phase purity of the synthesized materials was verified by the absence of extra peaks in the recorded PXRD pattern. Based on PXRD data, the proposed structure of UiO-66-NH₂ is presented as the end product of the reaction in Fig. 1.

3.1.3 SEM

The morphological and topographical analysis of synthesized UiO-66-NH₂ was confirmed by the SEM micrographs. Figure 3a represent the SEM micrographs of UiO-66-NH₂. According to these micrographs, the UiO-66-NH₂ exhibited a flattened sheet like morphology constituted of small flakes and a rod-like morphology.

3.1.4 EDX and Elemental Mapping

The elemental composition of synthesized MOF material was determined by the EDX analyses. The compositional analyses based on the recorded EDX spectra indicated the existence of nitrogen (N), carbon (C), oxygen (O), and zirconium (Zr) with identified atomic weights (%) as 33.78, 6.43, 15.95, and 43.84, respectively in the synthesized UiO-66-NH₂ (Fig. 3b). The existence and distribution of Zr, C, N, and O in UiO-66-NH₂ were also validated by elemental mapping analyses (Fig. 3c). The presence of elements of the ligand and zirconium metal in the final structure of MOF confirmed the successful amine-decorated UiO-66-NH₂.

3.1.5 Photoluminescent (PL) properties

3 mg of powdered sample of UiO-66-NH₂ was dispersed in 3 mL water to identify the fluorescent properties of synthesized amine-decorated MOF material. Before recording the fluorescent spectra, the MOF aqueous suspension 3 mg/3 mL was ultra sonicated for 30 min for proper dispersion. The recorded fluorescent spectra showed the emission peak at 455 nm upon excitation at λ_ex 355 nm and keeping the excitation and emission slit widths 5nm. The excellent fluorescent band in the synthesized material indicates that it can be utilized as a sensor for detection of NACs.

3.2 TNP detection by the UiO-66-NH₂ sensor

3.2.1 Solvent effect

UiO-66-NH₂ exhibited high chemical stability in multiple solvents. To examine highest quantum yield (ф), photoluminescence (PL) experiments were performed using polar as well as non-polar solvent such as water, acetone, DMF, acetonitrile, and methanol. Solvent dependent PL spectra of UiO-66-NH₂ were recorded and presented in Fig. 4a and b. It was observed that the MOF suspension in water showed the highest PL intensity compared to suspensions in other solvents. Moreover, UiO-66-NH₂ also showed an excellent dispersion and structural stability in water. Therefore, water was chosen as an acceptable solvent for further studies.

3.2.2 Excitation wavelength

Emission spectrum of aqueous UiO-66-NH2 suspension was noted at different excitation wavelengths extending from 350 nm to 395 nm (Fig. 5a). It was observed that the aqueous UiO-66-NH₂ suspension showed the highest PL emission intensity at excitation wavelength of λ_ex 355 nm. Therefore, this optimized excitation value of 355 nm was selected as an acceptable excitation wavelength for subsequent experiments.

3.2.3 Concentration effect

To study the concentration effect of UiO-66-NH₂, the different aqueous concentrations of synthesized MOF ranging from 0.17mg/mL to 0.8mg/mL were prepared. These suspensions were ultra-sonicated and then immediately recorded their emission spectrum, which are presented in Fig. 5b. As clear from this figure, the maximum fluorescence intensity was observed in case of MOF aqueous suspension of concentration of 0.33 mg/mL. Therefore, 0.33 mg/mL or 1.0 mg/3mL of MOF was selected as an optimized concentration for further PL studies.

3.2.4 Response time

Under optimized conditions, 1 mg of UiO-66-NH₂ was added to 3 mL of 1mM of aqueous TNP solution and PL spectrum was observed successively at 1 minute interval up to 10 minutes. The complete quenching process occurred within 1 min and fluorescence intensity remained constant thereafter (Fig. 5c). This indicated the fast response of the synthesized fluorescent probe.

3.2.5 pH effect

Quenching efficiency of MOF sensors containing amino group decreases with lowering the pH of the solution [23]. This happens due to the protonation of -NH₂ group of MOF sensors which reduces the interactions of amine group with the phenolic group of electron-deficient TNP moiety. Therefore, quenching study was performed without lowering the pH of MOF solution.

3.2.6 Selectivity Studies

For NACs selectivity studies, 3 mL standard aqueous solutions (1.0 mM) of the selected NACs viz., 1, 3-DNB, NB, 2, 4-DNT, 4-NT, 2,4-DNP, 4-NP, and TNP were prepared in the triply distilled water. After that MOF aqueous suspensions were made by dispersing 1.0 mg of UiO-66-NH₂ powders to the above prepared NACs solution via sonication for 30 min and PL spectra recorded immediately. The observed results indicated that all NACs quenched the PL emission intensity of UiO-66-NH₂ but TNP showed an exceptional behaviour with highest quenching impact (Fig. 6a). It was important to mention here that the intensity of aqueous MOF suspension was quenched around ten times in the presence of TNP in comparison to the original blank suspension (Fig. 6b and c). The fluorescence quenching efficiency of the selected NACs was calculated by the following formula

Quenching efficiency = [(I₀ − I)/ I₀] × 100%

where I and I₀ are the luminescence intensities after and before addition of the NACs.

The calculated fluorescence quenching efficiencies values indicated that TNP caused the highest fluorescence quenching efficiency (97.86%) compared to other selected NACs such as 4-NP (78.56%), 2,4-DNP (74.74%), 2,4-DNT (46.72%),1,3-DNB (41.13%), NB (28.7%) and 4-NT (18.75%) (Fig. 6c). TNP exhibited the maximum fluorescence quenching efficiency in presence of other NACs. So, presence of other NACs did not pose any interference towards TNP detection. Therefore, synthesized MOF probe clearly demonstrates higher affinity for TNP over other nitroaromatic species. Thus, UiO-66-NH₂ could be used as a "turn-off" fluorescence sensor for TNP.

3.2.7 Sensitivity Studies

1 mg of powdered UiO-66-NH₂ was dispersed to aqueous solutions of TNP having different concentrations ranging from 2–10 µM. After that, the PL emission intensities of prepared suspension were recorded and presented in Fig. 7a. The quenching influence of TNP was quantified by Stern Volmer equation I₀ / I = 1 + K_SV[24], where I and I₀ are the PL emission intensities of UiO-66-NH₂ suspension at 355 nm in absence and presence of TNP, [24] is molar concentration of TNP, and K_SV is the Stern-Volmer constant. There is an excellent linear correlation (R² = 0.9988) between I/I₀ and concentration of TNP (2–10 µM). Obtained K_SV value i.e., 1.203 x 10⁵ M^-1, indicated a substantial quenching impact on MOF PL emission (Fig. 7b). The LOD value was calculated using equation LOD = 3.3 SD/m, where SD is standard deviation and m is slope of the linear curve. As per equation, TNP’s LOD value was calculated to be 217 ng mL^-1. Low detection limit (0.95µM or 217ng mL^-1) and high Ksv proved the effectiveness of UiO-66-NH₂ as an excellent fluorescence sensor for TNP.

3.3 Mechanistic Study for TNP detection

In general, the following processes may explain the sensitive detection of TNP by MOF sensors: (i) Photoelectron transfer (PET), (ii) Resonance energy transfer (RET), and (iii) Electrostatic (H-bonding, ionic interaction) and π-π – interactions.

Usually, LUMOs; the lowest unoccupied molecular orbitals of NACs are typically situated in-between the MOFs conduction and valence bands [25]. As a result, an electron transfer pathway from the conduction band of UiO-66-NH₂ to the LUMO of electron-deficient NACs is rather easy and hence can cause its fluorescence intensity to be quenched. The E_HOMO-E_LUMO energies of the various NACs and 2-ATA ligand were estimated using DFT through B3LYP/6-311G basic set and the Gaussian 09 package to confirm the PET mechanistic studies responsible for this turn-off quenching (Fig. 8). The Frontier Molecular Orbital (FMO) theory reveals the presence of an easy electron transfer between E_HOMO and E_LUMO of reacting species. In accordance with FMO theory, analytes quenching efficiency is determined by their energy gap between E_HOMO and E_LUMO i.e., smaller the gap among HOMO and LUMO, the easier electron transitions will be occurring. It is generally known that molecules with high energy of highest occupied molecular orbitals (HOMO) may transfer electrons more efficiently than those with low energy HOMO. Species with low-lying LUMO, on the other hand, are more proficient for accepting electrons in comparison to higher energetic LUMO and hence have a greater quenching performance. As clearly realised in HOMO-LUMO energy gaps, electron transfer take place from HOMO of UiO-66-NH₂ to the LUMO of TNP easier in comparison to other NACs and is consistent with the experimentally observed highest quenching effectiveness for TNP (Fig. 8). TNP molecules were found to have the bottommost LUMO energy value of all the NACs studied i.e. -4.730 eV. The computed LUMO energy values of the selected NACs are listed in increasing order as follows: TNP < 1,3-DNB < 2,4-DNT < 2,4-DNP < NB < 4-NT < 4-NP. So, ease of electron transfers from the electron-rich UiO-66-NH₂ species toward the electron deficient NACs must occur in the opposite order. However, the experimentally observed order of quenching effectiveness (i.e., 4-NT < NB < 2, 4-DNT < 1, 3-DNB < 4-NP < 2, 4-DNP < TNP) is not completely consistent with the calculated LUMO energy values of NACs studied. Such conceptual findings do not correspond to our experimental findings. These findings imply that PET mechanism alone cannot explain the experimentally observed quenching response.

Furthermore, the RET mechanism may be outlined for the quenching procedure. RET requires a significant spectral overlap amid the emission spectrum of the MOF sensor and the absorption spectrum of the specific analyte. To justify whether, RET is operative in present case or not, the UV-vis spectrum of selected NACs were recorded. It was found that only TNP absorption overlap with the emission of UiO-66-NH₂. The TNP has absorption band at 354 nm, while NH₂-UIO-66 has a strong fluorescence emission band at 445 nm (Fig. 9). The significant overlap between emission spectrum of UiO-66-NH₂ and absorption spectra of TNP is in good agreement to the experimentally observed maximum results of TNP analyte. However, other NACs have nearly little or no such spectral overlap also support the experimental results. Therefore, we can say that spectral overlap reinforces the idea that TNP quenches fluorescence of UiO-66-NH₂ sensor via an energy transfer process as well along with PET mechanism.

Moreover, some molecular interactions, such as; π-π interactions among the aromatic benzene rings of electron rich moieties of UiO-66-NH₂ and benzene rings of electron deficient TNP analyte may play an important role for quenching (Fig. 10). Similarly, electrostatic interactions, like ionic interaction between the picrate anion (as TNP/Picric acid persists in ionic state in aqueous solution as picrate anion) and protonated amino group of UiO-66-NH₂ in aqueous suspension, may be responsible for the fluorescence quenching. One more interaction like H-bonding between the polar group present in luminescent UiO-66-NH₂ and TNP may also occur. It has been observed that quenching efficiencies of nitro phenols (TNP, 2, 4-DNP and 4-NP) were inspected more than that of other studied NACs because of strong H-bonding interactions involved in the hydroxyl group present in these nitro phenols with UiO-66-NH₂, which is lacking in other NACs. Thus, the presence of these molecular interactions increases the e⁻-transfer rate amongst host (UiO-66-NH₂) and guest (picrate anion). Thus, all of the above explanation leads to the conclusion that PET, RET, H-bonding, ionic and π-π-interactions cohesively explain the fluorescence quenching response of UiO-66-NH₂ towards TNP.

3.4 Comparative study with previously reported sensors

The sensitivity of developed UiO-66-NH₂ MOF was compared with other fluorescent sensors reported earlier for TNP sensing (Table 1). UiO-66-NH₂ achieved lower detection limit (0.95 µM) and higher Ksv value (1.106 x 10⁵ M^− 1) compared to other fluorophore materials (Table 1). Developed method can be applied exclusively for analysis of aqueous matrix while other methods lack this advantage. In other methods, aqueous and organic phase mixtures are incorporated for analysis.

Table 1

A comparative performance of different sensors for TNP detection.
Order	Fluorescent sensors	Solvent	LOD (µM)	K_sv (M^− 1)	Ref.
1	Quinoline derivatives	MeOH/H₂O (v/v = 9:1)	4.7 & 3.6	2.38 × 10⁴ & 1.08 × 10⁴	[26]
2	Phenanthroimidazole derivatives	EtOH	2.3–4.6	1.4–8.6 × 10⁴	[27]
3	Cysteamine-capped CdSe quantum dots	DMSO	2.2	4.3 × 10⁴	[28]
4	Fe₃O₄@Au@Tb-BTC, MOF	EtOH	3.14	5.08×10⁴	[29]
5	Anthracene-bridged Poly(N-vinylpyrrolidone)	H₂O	6.0	-	[30]
6	Lanthanide based coordination polymer	CHCl₃	98	8.951 × 10²	[31]
7	[Cu(L)(I)]_2n	CH₃CN	6.6	9.5 × 10³	[32]
8	UiO-66-NH₂	H₂O	0.95	1.106 x 10⁵	This work

An effective method for TNP sensing was designed by using fluorescence quenching of MOF probes. The UiO-66-NH₂ MOF probe proved to be proficient sensor for TNP detection, with detection limit lower than 1 µM concentration and 98% quenching efficiency. Various processes such as PET, RET, H-bonding, ionic interaction and π-π-interactions are proposed as possible explanations for the sensing potential of the synthesised MOF probe. Comparison study demonstrated that the developed method is superior to the earlier reports in terms of sensitivity and matrix selection. Rapidness, low cost, and high sensitivity of synthesized MOF make it an imminent candidate for quick detection of TNP. Developed UiO-66-NH₂ can be applied to real aqueous sample obtained from explosive manufacturing and testing sites for the analysis of TNP residues. These promising results will aid in the future exploration of new materials for selective and sensitive detection of NACs in the environmental sample.

Acknowledgements

The authors are grateful to the Chemistry Department, Punjabi University, Patiala, for providing lab and instrument facilities.

Funding: Not applicable.

Conflicts of interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Availability of data and material: All the data associated with this research has been presented in this paper.

Code availability: Not applicable.

Authors’ contributions.

Rajpal Verma and Gaurav Dhingra: Conceptualization, Methodology, Data curation, Writing - original draft, Visualization, Validation. Manpreet Kaur, Deepika Garg, and Irshad Mohiuddin: Project administration, Investigation, Writing - original draft, reviewing and editing. Ashok Kumar Malik: Investigation, Project administration, Supervision, Formal analysis, Writing - review and editing.

Ethics Approval: Not applicable.

Consent to participate: Not applicable.

Consent for publication: Not applicable.

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No competing interests reported.

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Amine-decorated zirconium-based metal-organic framework for ultrafast detection of 2, 4, 6-trinitrophenol in aqueous medium

Status:

Version 1

Abstract

Figures

Highlights

1. Introduction

2. Experimental

2.1. Materials and methods

2.2 Synthesis of UiO-66-NH₂

2.3 Sample preparation

3. Results And Discussion

3.1 Characterization of UiO-66-NH₂

3.1.1 FT-IR

3.1.2 PXRD

3.1.3 SEM

3.1.4 EDX and Elemental Mapping

3.1.5 Photoluminescent (PL) properties

3.2 TNP detection by the UiO-66-NH₂ sensor

3.2.1 Solvent effect

3.2.2 Excitation wavelength

3.2.3 Concentration effect

3.2.4 Response time

3.2.5 pH effect

3.2.6 Selectivity Studies

3.2.7 Sensitivity Studies

3.3 Mechanistic Study for TNP detection

3.4 Comparative study with previously reported sensors

4. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

Amine-decorated zirconium-based metal-organic framework for ultrafast detection of 2, 4, 6-trinitrophenol in aqueous medium

Status:

Version 1

Abstract

Figures

Highlights

1. Introduction

2. Experimental

2.1. Materials and methods

2.2 Synthesis of UiO-66-NH2

2.3 Sample preparation

3. Results And Discussion

3.1 Characterization of UiO-66-NH2

3.1.1 FT-IR

3.1.2 PXRD

3.1.3 SEM

3.1.4 EDX and Elemental Mapping

3.1.5 Photoluminescent (PL) properties

3.2 TNP detection by the UiO-66-NH2 sensor

3.2.1 Solvent effect

3.2.2 Excitation wavelength

3.2.3 Concentration effect

3.2.4 Response time

3.2.5 pH effect

3.2.6 Selectivity Studies

3.2.7 Sensitivity Studies

3.3 Mechanistic Study for TNP detection

3.4 Comparative study with previously reported sensors

4. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

2.2 Synthesis of UiO-66-NH₂

3.1 Characterization of UiO-66-NH₂

3.2 TNP detection by the UiO-66-NH₂ sensor