A Luminescent Nanocrystal Metal Organic Framework for Chemosensing of Nitro Group Containing Organophosphate Pesticides

Analytical Methods

Journal: Analytical Methods

Manuscript ID: AY-ART-12-2013-042189.R4

Article Type: Paper

Date Submitted by the Author: 08-Apr-2014

Complete List of Authors: KUMAR, PAWAN; CSIR-CSIO, Chandigarh, Nano Sciences & Technology; CSIR-CSIO, Chandigarh, Nano Sciences & Technology Paul, A.; CSIR-CSIO, Chandigarh, Nano Science and Nano Technology (H- 1), Deep, Akash; CSIR-CSIO, Chandigarh, Nano Sciences & Technology

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 A Luminescent Nanocrystal Metal Organic Framework for 21 22 23 Chemosensing of Nitro Group Containing Organophosphate 24 25 Pesticides 26 27 28 29 Pawan Kumar$#*, A.K. Paul$#, Akash Deep$# 30 31 $ 32 Central Scientific Instruments Organisation (CSIR-CSIO), Sector 30 C, Chandigarh, 33 34 160030, India 35 36 # 37 Academy of Scientific and Innovative Research, CSIR-CSIO, Sector 30 C, Chandigarh, 38 39 160030, India 40 41 42 43 44 *Tel: 0172-2657811 (452-Ext), Fax: 0172-2657287, 45 46 Email: [email protected],[email protected] 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 4 5 6 Abstract. A luminescent nanocrystal metal–organic framework (NMOF1) of 7 8 [Cd(atc)(H2O)2n] has been synthesized by the reaction of Cd(II) ions with the sodium salt of 9 10 11 H2atc (2-aminoterephthalic acid) in aqueous solution. The obtained fluorescent porous 12 13 material has been characterized by X-ray diffraction, transmission electron microscopy, 14 15 confocal microscopy, UV-Vis spectroscopy, photoluminescence spectroscopy and surface 16 17 18 area analysis. The synthesized NMOF1 exhibits reasonably good fluorescence characteristics 19 20 (excitation wavelength = 340nm, emission wavelength = 436 nm). The potential of above 21 22 Cd(II) based nanocrystal metal–organic framework (NMOF1) for the sensing of nitro 23 24 25 aromatic containing organophosphate pesticides (OPs) parathion, methyl parathion, paraoxon 26 27 and fenitrothion is demonstrated. It has been possible to detect the above four OPs separately 28 29 in the concentration range of 1ppb - 500 ppb. The detection limit of the proposed method for 30 31 32 all the said OPs is 1ppb. Interestingly, their mixture also shows the above characteristic data. 33 34 The proposed method for the sensing of nitroaromatic OPs is also selective towards other 35 36 37 OPs such as malathion, dichlorvos and monocrotophos. 38 39 40 41 42 43 44 Keywords: Nanocrystal Metal Organic Framework, Chemosensening, Nitroaromatic 45 46 Compound, Organophosphate Pesticides. 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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1 2 3 Introduction 4 5 6 Organophosphates pesticide (OPs) compounds are highly toxic and affect the neural system 7 8 of the organism, which may lead to several lethal problems to human beings and may cause 9 10 1-2 11 neurological disorders . These compounds disposal in the open environment is regulated 12 13 and their routine monitoring is important for maintaining desired standards of water resources 14 15 and food supplies 3-4. Various OPs e.g. parathion, methyl parathion, paraoxon and 16 17 18 fenitrothion are widely used products by the agriculture industry which have nitroaromatic 19 20 compounds. Parathion is one of the most toxic and widely used insecticides. It converts to 21 22 paraoxon and leaves residues on plant surfaces 5. The resulting residues persist in the 23 24 25 environment and present hazards especially in hot and dry agricultural areas, where the 26 27 agricultural products are not properly washed before storage. The toxicity due to parathion is 28 29 known to affect animal life and is responsible for many illnesses and deaths 6. Fenitrothion is 30 31 32 also one of the most hazardous and broad spectrum insecticide used for pest control in rice, 33 34 vegetables, wheat, cereals, and cotton. Though fenitrothion has low mammalian toxicity, it is 35 36 7 37 known to disrupt endocrine . 38 39 Many analytical methods are available for the detection of OPs, including gas 40 41 chromatography (GC), high-performance liquid chromatography (HPLC) and mass 42 43 10 44 spectroscopy . Most of these methods are very sensitive and reliable, but the requirements 45 46 of large set-ups, expensive instrumentation and highly skilled manpower requirement limit 47 48 their applicability. Currently, enzymatic biosensors have been explored as viable, handy and 49 50 11 51 portable alternative with fair levels of sensitivity and accuracy . The sensitive biosensors 52 53 based on acetylcholinesterase (AChE) / butyryl cholinesterase (BChE) inhibition, or 54 55 organophosphate hydrolase (OPH) induced hydrolysis have been developed for the 56 57 12 58 monitoring of OPs . The limitation of the immunoassays method involves the requirements 59 60 of label process 13. A label-free electrochemical immunosensor with paraoxon antibodies 3

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1 2 3 loaded on the gold nanoparticles has been reported for the monitoring of paraoxon in aqueous 4 5 14 6 samples, but it has poor selectivity and specificity . Recently, solid phase extraction (SPE) 7 8 of OPs combined with square-wave voltammetric analysis, and electrochemical sensing with 9 10 11 zirconia nanoparticles-decorated graphene hybrid nanosheets have been highlighted for 12 15-17 13 convenient and cost-effective enzyme-less sensing . A highly sensitive fluorescent 14 15 chemosensor for fenitrothion has been reported using per-6-amino--cyclodextrin:Eu(III) 16 17 18 18 complex . The sensor system showed sensitivity response in the order, fenitrothion > 19 20 quinalphos > methylparathion > parathion > methylparaoxon > paraoxon > fenchlorphos > 21 22 23 profenofos >malathion. The comparison studies really important and very help to assess the 24 25 environmental quality, protection of water resources, food supplies, and monitoring of the 26 27 detoxification processes. 28 29 30 Recently, the luminescent MOFs have been found new and interesting applications in the 31 32 sensing of small molecules, solvents and explosives 19-20. The detectable changes in 33 34 luminescence of MOFs by tuning the host–guest chemistry along with the tunable porosity 35 36 37 and high surface area makes MOFs the excellent candidates in sensing applications. The 38 39 pioneering work of Wang et al.22 sparked research activities towards exploiting the potential 40 41 of luminescent MOFs in explosives detection and small molecules sensing 23-24. However the 42 43 44 bulky MOFs have limited interaction between MOFs and analytes in solvent, lower solubility 45 46 nature in well known solvents 25-26. In other hand, nanocrystal metal–organic frameworks 47 48 49 (NMOFs) attracted due to better dispersive nature which makes them easily contact with 50 51 small molecules with no loss in their intrigue framework architectures and topologies. In 52 53 addition, high luminescence of NMOFs provides opportunity to implement them for the 54 55 28-30 56 development of unique sensing materials . Basically, NMOFs are new class of hybrid 57 58 materials built from metal ions with well- defined coordination geometry and organic 59 60 bridging ligands and already explored a number of promising and potential applications in 4

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1 2 3 catalysis, nonlinear optics, and small molecules sensing 31-32. However, capability of NMOFs 4 5 6 for the solid phase extraction of pesticides has not been proposed by some other researchers. 7 8 Conjugated NMOFs with high dimensionality may also be beneficial as sorbents for the solid 9 10 11 phase extraction of nitroaromatic OPs by direct physical adsorption. The mixing of OPs with 12 13 NMOF is characterized with synergetic effects of weak interactions (e.g. hydrogen bond) and 14 15 π----π stacking. In light of the above discussion, MOFs may be envisaged as very useful 16 17 18 compounds for the simultaneous extraction and sensing of OPs in different environmental 19 20 samples. 21 22 The present work explores the utility of a luminescent NMOF1 for the direct chemosensing 23 24 25 of nitro OPs, including parathion, methyl parathion, paraoxon and fenitrothion. The 26 27 Cd(atc)(H2O)2n (ATC : 2-aminoterephthalic acid) has been synthesized via coprecipitation 28 29 method. The synthesized product has been characterized with help of different instrumental 30 31 32 techniques. The NMOF1 was incubated with different concentrations of nitro aromatic OPs 33 34 and the change in the fluorescence intensity recorded which may due to strong electron 35 36 37 withdrawing –NO2 group. The electrostatic interaction between the photoexcited 38 39 Cd(atc)(H2O)2n and electron withdrawing –NO2 moiety has led to a pesticide concentration 40 41 dependent change in the fluorescence intensity. In addition, the proposed method is also 42 43 44 selective with respect to malathion, dichlorvos and monocrotophos due to absence of –NO2 45 46 moiety. 47 48 Experimental Section 49 50 51 Materials. Cd(NO3)2, 2-aminoterephthalic acid, distilled water, parathion, methyl parathion, 52 53 paraoxon,fenitrothion, malathion, dichlorvos and monocrotophoswere high purity grade 54 55 chemicals from Sigma-Aldrich / Merck / Fisher Scientific. All other chemicals and solvents 56 57 58 were A.R / G.R grade products from Sigma-Aldrich. 59 60

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1 2 3 Synthesis of NMOF1. 1.10ml of 0.05M Cd (NO ) and 10ml of 0.5M of sodium salt of H atc 4 3 2 2 5 6 (2-aminoterephthalic acid) were taken in aqueous solution. A large amount of white 7 8 precipitate was generated immediately. After vigorous stirring of one hour at room 9 10 11 temperature precipitate was collected by centrifugation and washed with water and ethanol (2 12 13 x10ml). For the NMOF1 photoluminescence (PL) and pesticide sensing experiments, the 14 15 ethanolic suspensions of NMOF1 (2mg/mL) were prepared by sonication for 5 min. The 16 17 18 homogenous suspensions were transferred in 1 mm optical cells for further measurements. 19 20 Characterization/ equipment. X-ray Diffraction (XRD, Shimadzu 6000), Field-Emission 21 22 Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (FE- 23 24 25 SEM – EDX, Hitachi 4300/SN), Confocal Laser Scanning Microscopy (CLSM, Zeiss LSM 26 27 510) and Transmission Electron Microscopy (TEM, Hitachi H-7500) were used to confirm 28 29 the crystal phase, lattice pattern and morphology of the prepared MOF-5 particles.Nitrogen 30 31 32 isotherm analysis was done with Micromeritics ASAP- 2020 sorptometer. Thermal stability 33 34 was tested using a thermogravimetric analyzer (TGA, SDT Q600 thermal gravimeter). UV- 35 36 37 visible absorption and photoluminescence spectra were measured by UV-visible-NIR 38 39 spectrophotometer (Varian Cary 5000) and PL spectrophotometer (Varian). Fourier transform 40 41 infrared (FTIR) spectra were recorded on a Nicolet iS10 spectrophotometer equipped with an 42 43 44 attenuated total reflectance (ATR) accessory. 45 46 Nitro OPs sensing. Stock solution of the nitro OPs (parathion, methylparathion, paraoxon, 47 48 fenitrothion) was diluted / prepared in ethanol. Known diluted volumes of the stock solutions 49 50 51 were prepared and mixed with the ethanolic suspension of NMOF1 (2 mg/mL). The contents 52 53 were thoroughly mixed and then incubated at 250C for 5 min. The PL intensity of the reaction 54 55 mixture was measured and correlated with OPs concentration. The selectivity experiments 56 57 58 with respect to malathion, dichlorvos and monocrotophos were also carried out in similar 59 60 fashion. 6

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1 2 3 All the above experiments were done in triplicate and the average data value have been 4 5 6 reported. 7 8 Results and Discussion 9 10 33 11 X-ray Diffraction Analysis. Wang et al. have reported powder PXRD measurement for 12 13 crystal structure and chemical composition of bulky [Cd(atc)(H2O)2n]. Thus NMOF1 has 14 15 monoclinic crystal structure with space group C2/C. The sodium salt of H2atc and self- 16 17 18 assembling of Cd(II) ions may be attributed to formation of NMOF1 architectures. The Cd 19 20 (II) ion is six coordinated with a greatly distorted octahedral geometry and consists of 1D 21 22 zigzag motifs with non-covalent interactions. These 1D zigzag motifs chain leads to 23 24 25 formation of 3D network structure. The PXRD [Fig. 1 (I)] peak positions of the herein 26 27 synthesized NMOF1 product matches with the reported NMOF1 materials [Fig. 1 (II)] 33, 34. 28 29 The sharpness and high intensity indicate high crystallinity of the NMOF1, which is also 30 31 32 supported by FESEM data [Fig. 1 (I)]. The NMOF1 is stable and easily dispersed in common 33 34 solvent ethanol, benzene, and nitrobenzene. The peak at 19.60 is reasonably high, and 35 36 37 corresponds to the reflections of octahedral geometry structure. 38 39 Fig.1 [a & b] shows the FE-SEM images of the synthesized NMOF1 samples. FE-SEM 40 41 scanning at a comparatively lower magnification to cover large sample area indicates towards 42 43 44 the formation of nanocrystals. Higher resolution FE-SEM imaging suggests the formation of 45 46 single phase octahedral crystals Fig.1 (b). Nanocrystals was also evidenced in the FE-SEM 47 48 investigations; however, we could also obtain some scans of isolated octahedral crystals. 49 50 51 Typical diameter of the product was estimated to be around 100 – 500 nm. 52 34-36 53 To study the thermal stability of NMOF1 , the thermo gravimetric analysis (TGA) was 54 55 performed under a nitrogen atmosphere in presence of N gas with a heating rate of 10 0C 56 2 57 -1 0 58 min in the temperature range 25–900 C. The TGA curve of the NMOF1 is divided into two 59 60 stages where the first weight loss 19.1% occurs in the temperature range 41–265 0C, which 7

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1 2 3 can be attributed to the loss of both lattice structure and coordinated water molecules 4 5 6 (calculated value 19.6%). Subsequent, there is an individual weight loss stage in the 7 8 temperature range of 311–497 0C, corresponding to the loss of the organic ligand due to the 9 10 11 formation of CdO. The residual weight of 34.9% may correspond to the final product of CdO 12 13 (calculated value 36.1%). 14 15 The FTIR spectrum (Fig. 2) of the synthesized NMOF1 has been characteristics bands of 16 17 -1 18 1610, 1507, 1570, 1457 and 1358 cm . The fundamental vibrations have assigned to 19 20 stretching vibrations at higher energy and bending vibrations at lower energy of C-O in 21 22 carboxylate groups respectively 34. The bands at 3500 – 3200 cm-1 accounts for the adsorbed 23 24 25 water. 26 27 The excitation and emission spectra of NMOF1 are already reported in literature 33, 34. In our 28 29 study, a strong blue emission at around 436 nm was observed by excitation at 349 nm for [Cd 30 31

32 (atc) (H2O)]n in ethanol. The observed blue emission which can be assigned to the 33 34 luminescence from intra-ligand emission excited state 34. The emission from [Cd (atc) 35 36 37 (H2O)]n primarily originates from surface defects, such as ionizable oxygen vacancies or cd 38 39 (II) ions vacancies on the surface. Broad absorption and emission spectra of in NMOF1 40 41 crystals suggests that the transition responsible for the photoluminescence takes place 42 43 44 between deeply trapped charges (localized donor and acceptor levels). Most of the defects in 45 46 the NMOFI crystals exist inside. 47 48 The above studies have verified the synthesis of porous NMOF1 crystals with their particle 49 50 51 size in the range of 100 – 500 nm. The blue emission of these NMOF1 crystals and their 52 53 porous structures has further been utilized for convenient, label free and sensitive 54 55 chemosensing of –NO group containing OPs. 56 2 57 58 Chemosensing of –NO2 OPs. Fig. 1(C) shows the photoluminescence spectra of NMOF1 in 59 60 the presence of different concentrations (1 ppb – 1 ppm) of parathion. Methyl parathion, 8

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1 2 3 paraoxon and fenitrothion also exhibited similar effect on the PL of NMOF1.Their data are 4 5 6 not shown in order to avoid repeatability. There is a loss observed in the NMOF1 7 8 photoluminescence (PL) upon interaction with the above OPs solutions. The concentration of 9 10 11 the pesticides plays an important role in deciding the degree of PL quenching. Interestingly, 12 13 all the four tested OPs quench the PL of NMOF1 to similar degree. Consequently, a mixture 14 15 of all the above four pesticides was prepared having equal fractions to prepare 1 ppb – 1 ppm 16 17 18 solutions. The mixing of this mixture of nitro OPs with NMOF1 also resulted in to the 19 20 quenching of PL [Fig. 1(D)]. In all the above cases, a linear trend was observed from 1 ppb – 21 22 500 ppb concentration. The detection limit of the sensing was 1 ppb, below which the 23 24 25 changes in the NMOF1 PL were miniscule and unstable. The stability and reproducibility of 26 27 the measurements was checked by recording the change of PL intensity of different sets of 28 29 NMOF1 suspensions (2 mg/mL) in the presence of 1 ppb, 5 ppb, 100 ppb and 500 ppb nitro 30 31 32 OPs mixture. The results are shown in different sets of NMOF1 provided similar degrees of 33 34 PL quenching and their measurements were stable for a minimum of 48hr. 35 36 37 The selectivity of the above sensing of nitro OPs with NMOF1 with respect to some other 38 39 OPs such as malathion, dichlorvos and monocrotophos was also investigated [Fig. 3(a & b)]. 40 41 A 10 ppb mixture of nitro OPs was incubated with NMOF1 suspension in the presence of 10 42 43 44 and 100 fold concentration (100 ppb and 1 ppm) of malathion, dichlorvos and 45 46 monocrotophos. Similarly, the test was also undertaken in the combined presence of 1 ppm of 47 48 malathion, dichlorvos and monocrotophos. In both the investigations, the degree of PL 49 50 51 quenching corresponded to the presence of 500 ppb of nitro OPs. Separate experiments only 52 53 with the solutions of malathion, dichlorvos and monocrotophos suggested no significant of 54 55 PL quenching which is due to absence of strong electron withdrawing group [Fig. 3 (b)]. 56 57 58 The dominant mechanism of luminescence attenuation of NMOF1 in the presence of nitro 59 60 aromatic OPs can be attributed to the interactions of the analytes with the ligand molecule. 9

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1 2 3 NMOF1 generates a valence band hole (h +) and a conduction band electron (e -) during 4 VB CB 5 + - 6 the band gap excitation. These photogenerated (htr ) or trapped (etr ) carriers participate in the 7 8 redox processes with the nitro OPs at the surface or inside the NMOF1 particle. The 9 10 11 quenching of NMOF1 emission can be analyzed by considering equilibrium between the 12 13 uncomplexed and complexed NMOF1 particles with the analyte moieties. It may be assumed 14 15 that the quenching of NMOF1 emission occurs only in the associated complex between 16 17 18 NMOF1 and nitro OPs; and therefore, the association constant Ka may be given as 19 20 I0/(I0 – I) = I0/(I0 – I’) + I0/{Ka × (I0 – I’) × [OP]} eq [1] 21 22 Where I is the initial emission intensity of the NMOF1 particle, I is the emission intensity 23 0 24 25 after adding the OP of concentration [OP] and I’ is the emission intensity of the OP used. 26 27 Fig. 4 shows the straight-line plot of I0/(I0 - I)vs.1/[OP], which confirms the validity of the 28 29 equilibrium model. The K values for various nitroaromatic OPs are computed and given in 30 a 31 32 Fig 5. Stern-Volmer relationship has been utilized to assess the quantitative characteristics of 33 34 the PL quenching process. These experiments have been conducted using the PL quenching 35 36 37 data with various concentrations of the OPs. Stern-Volmer constant (KSV) can be calculated 38 39 according to the following equation 40 41 (I0/I) – 1 = KSV [OP] eq [2] 42 43 44 A plot of I0/Ivs. [OP] gives progressive linear relationship for all the nitro OPs, whereas 45 46 saturation behaviour was observed in case of malathion, dichlorvos and monocrotophos (Fig. 47 48 6). Since K =  ; the average quenching rate constant can also be computed keeping 49 SV 0 50 36 51 the value of 0(lifetime of NMOF1 PL) as 0.66 µs . In the different PL quenching 52 53 54 experiments with nitro OPs, the values (Fig. 6) are comparable or higher than the typical 55 56 diffusion-controlled rate constants, ∼1010M-1s-1 in the bulk solution 36. These parameters 57 58 confirm the diffusion of the nitro OPs molecules on to the surface as well in to the porous 59 60

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1 2 3 structure of the NMOF1. The diffusion process may be correlated with the level of detection 4 5

6 sensitivity offered by the NMOF1. The computed values (Fig. 6) for malathion, 7 8 dichlorvos and monocrotophos are indicative of the non-diffusion process and absence of 9 10 11 nitro group or strong electron withdrawing group, which might be linked with the inability of 12

13 these OPs to quench the PL of NMOF1. The different values may also be correlated with 14 15 16 the oxidation potential Eox of the related OPs. The Eox values of parathion (-0.02 V), methyl 17 18 parathion (0.05 V), paraoxon (0.5 V) and fenitrothion (-0.95 V) are much lower than those of 19 20 malathion (0.6 V) and monocrotophos (0.87 V) 37-42. The decreasing values of with the 21 22 23 increasing Eoxindicate that the process of PL quenching is also governed by the hole transfer 24 25 process from the photoexcited NMOF1 to the OPs. Therefore, it can be proposed that the 26 27 28 selectivity in the PL quenching by the tested OPs may also depend upon their redox 29 30 potentials and presence of electron withdrawing group. The involved donor–acceptor 31 32 electron-transfer is obviously dominant in presence of –NO2 aromatic compounds. Therefore 33 34 35 we can say that stronger quenching effect due to the presence of strong electron withdrawing 36 37 nitroaromatic compounds on OPs offer on-off response for the proposed optical sensors. 38 39 Conclusions. The synthesis of luminescent NMOF1 is presented and the product has been 40 41 42 exploited for the sensitive sensing of -NO2 aromatic OPs namely, parathion, methyl 43 44 parathion, paraoxon and fenitrothion. The formation of NMOF1 particles has been verified 45 46 47 with different analytical techniques. The PL of the dispersed NMOF1 results from the 48 49 photoinduced intra-ligand electron transfer from. The presence of –NO2 aromatic OPs is 50 51 detected through the PL quenching due to strong electron withdrawing group and donor– 52 53 54 acceptor electron-transfer mechanism, which, in turn, is also related to the oxidation 55 56 potentials of the pesticides. The linear range of detection is 5 ppb - 600 ppb with detection 57 58 limit of the proposed method being 5 ppb. The above data remain valid for the mixture of – 59 60 NO2/OPs. The proposed method was also investigated for other OPs, e.g. malathion, 11

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1 2 3 dichlorvos and monocrotophos which make more selective due to absence of strong electron 4 5 6 withdrawing group. Finally, the –NO2 aromatic OPs exhibited stronger quenching effect 7 8 which can be attributed to the strong electron withdrawing group which work as on-off 9 10 11 response for the proposed optical sensor. 12 13 In addition, this type of utility of luminescent NMOF1 has offered the label-free and direct 14 15 chemosensing of the –NO2 aromatic OPs. The NMOF1 have great potential in the solid-phase 16 17 18 extraction and enrichment of the pesticide residues also. We are continuing our investigations 19 20 towards the simultaneous enrichment and quantitative detection of pesticides using 21 22 luminescent NMOFs so as to obtain ultra-sensitive and label-free quantifications. The 23 24 25 regeneration of NMOF1 PL is also a part of the on-going / future research. 26 27 28 29 30 Funding Sources 31 32 33 The reported work has been funded through CSIR, India grant (OMEGA/PSC0202/2.2.5) 34 35 from CSIR, India. One of the authors (Pawan Kumar) also acknowledges CSIR for his Senior 36 37 Research Fellowship. 38 39 40 41 42 ACKNOWLEDGEMENTS 43 44 Authors thank Mr. Parveen Kumar & Vasudha Bansal for his help in conducting the 45 46 47 experimental works. We are also grateful to the Director, CSIR-CSIO, Chandigarh for 48 49 providing facilities. 50 51 52 53 54 Reference 55 56 1. Eddleston, M.; Buckley, N. A.; Eyer, P.; Dawson, A. H. Management of acute 57 organophosphorus pesticide poisoning. The Lancet 2008, 371 (9612), 597. 58 59 2. Soltaninejad, K.; Abdollahi, M. Current opinion on the science of 60 organophosphate pesticides and toxic stress: a systematic review. Medical

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 186x141mm (96 x 96 DPI) 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 17 of 19 Analytical Methods

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 Fig.1. (A): (I) X-ray diffraction spectra of synthesized NMOF1 & correlated with reference 32 33 X-ray diffraction spectra of NMOF1, (B) FE-SEM images of NMOF1, (C) Effect of the 34 35 addition of different concentrations of Parathion on the PL intensity of NMOF1. Separately 36 investigated, other nitro OPs (methyl parathion, paraoxon, fenitrothion) also yielded similar 37 38 pattern of PL quenching and (D) Effect of the addition of different concentrations of mixed – 39 40 NO 2 OPs mixture on the PL intensity of NMOF1 (Inset image reveals the measurements at 41 low concentrations). 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 Fig. 2 . FTIR spectra of NMOF 1. 58 59 60 Analytical Methods Page 18 of 19

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Fig. 3 (A) Selectivity of PL quenching by –NO 2 OPs in the presence of other OPs (OP= – 22 23 NO 2 OPs; M = malathion, D = dichlorvos; MC = monocrotophos; 10 = 10 ppb; 100 = 100 24 ppb, 1000 = 1000 ppb) and (B) Effect on the PL intensity of NMOF 1 in the presence of 25 26 malathion (M), dichlorvos (D) and monocrotophos (MC); 1000 = 1000 ppb, (ppb = part per 27 28 billion). 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 Fig.4 .Stern – Volmer (reciprocal) plot for the PL quenching experiments with parathion (a); 53 methyl parathion (b); paraoxon (c); fenitrothion (d), [OP] concentration unit is in mol/L. 54 55 56 57 58 59 60 Page 19 of 19 Analytical Methods

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Fig.5. Stern – Volmer plot for the PL quenching experiments with parathion (a); methyl 27 parathion (b); paraoxon (c); fenitrothion (d), [OP] concentration unit is in mol/L. 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 Fig.6. Stern – Volmer plot for the PL quenching experiments with malathion, dichlorvos and 49 monocrotophos, [OP] concentration unit is in mol/L. 50 51 52 53 54 55 56 57 58 59 60