Nitroaromatic Compounds In Water Research Articles

Two Stable Pillar-Layered Zn-LMOFs for Highly Fluorescence Sensing of Inorganic Pollutants and Nitro Aromatic Compounds in Water.

Luminescent metal-organic frameworks (LMOFs) are a potential class of functional materials for the photoluminescent detection of a wide range of analytes as well as for the detection of pollutants in wastewater. Herein, by using the pillar-layered strategy, two new luminescence Zn-LMOFs (JLU-MOF222 and JLU-MOF223) were successfully solvothermal synthesized. The 2D layers are both consisting of Zn2+ and TPHC [TPHC = (1,1':2',1″-terphenyl)-3,3″,4,4',4″,5'-hexacarboxylic acid] ligands and then pillared by the different N-donor ligands to form the 3D Zn-LMOFs with fsh topology. Benefiting from the uncoordinated carboxylate sites, uncoordinated N atom, or -NH2 group in the pillaring ligands and excellent stability in pH = 2-13 aqueous phase, JLU-MOF222 and JLU-MOF223 not only can sensitively detect trace amounts of inorganic pollutants (Fe3+, Cr2O72-) and nitro aromatic compounds TNP and 2,4-DNP (TNP = 2,4,6- trinitrophenol, 2,4-DNP = 2,4-dinitrophenol) through luminescence quenching but also exhibit high selectivity of other anti-interference competing analytes. The two new Zn-LMOFs can be used as potential luminescent sensors for pollutant detection in water due to their high KSV and low limit of detection (LOD).

Bifunctional In-MOFs for Selective and Sensitive Detection of Trace Nitrobenzene Compounds in Water and Possessing High Proton Conductivity.

With the escalating prevalence of terrorism and global environmental pollution, nitroaromatic compounds (NACs) have increasingly come into focus as the primary culprit. To counter these challenges, it is imperative to develop simple and efficient methods for detecting NACs. Considering the electron-deficient structure of NAC molecules, this paper constructed a novel three-dimensional In-MOF with permanent porosity using electron-rich organic molecules 4'-[1,2,2-tris(3',5'-dicarboxy[1,1'-biphenyl]-4-yl)ethenyl]-[1,1'-biphenyl]-3,5-dicarboxylic acid (H8ETTB) for fluorescence detection by photoinduced electron transfer. The results indicated that In-ETTB can sensitively detect trace NACs in water. In-ETTB exhibited the best detection performance for 3-NP, achieving a Ksv value of 8.75 × 104 M-1 with a limit of detection of 0.27 μΜ in aqueous solution; this belongs to a relatively high level among the reported metal organic framework (MOF) materials. Subsequently, anti-interference experiments revealed that In-ETTB exhibits strong specificity fluorescence recognition of NACs, and it could still maintain its structural integrity and fluorescence emission intensity even after 7 cycles of testing. We confirmed that the fluorescence detection of NACs was due to a combined effect of competitive absorption and photoinduced electron transfer through experimental collaboration DFT calculations in detail. Meanwhile, the proton conductivity reached 2.45 × 10-2 S·cm-1 at 98% relative humidity and 90 °C, which is also a high level in MOFs. This work provides a universal method theoretical basis for designing NAC detectors with practical application prospects.

Ionothermal synthesis of magnetic N-doped porous carbon to immobilize Pd nanoparticles as an efficient nanocatalyst for the reduction of nitroaromatic compounds

Carbon materials play important roles as catalysts or catalyst supports for reduction reactions owing to their high porosity, large specific surface area, great electron conductivity, and excellent chemical stability. In this paper, a mesoporous N-doped carbon substrate (exhibited as N–C) has been synthesized by ionothermal carbonization of glucose in the presence of histidine. The N–C substrate was modified by Fe3O4 nanoparticles (N–C/Fe3O4), and then Pd nanoparticles were stabilized on the magnetic substrate to synthesize an eco-friendly Pd catalyst with high efficiency, magnetic, reusability, recoverability, and great stability. To characterize the Pd/Fe3O4–N–C nanocatalyst, different microscopic and spectroscopic methods such as FT-IR, XRD, SEM/EDX, and TEM were applied. Moreover, Pd/Fe3O4–N–C showed high catalytic activity in reducing nitroaromatic compounds in water at ambient temperatures when NaBH4 was used as a reducing agent. The provided nanocatalyst's great catalytic durability and power can be attributed to the synergetic interaction among well-dispersed Pd nanoparticles and N-doped carbonaceous support.

Fe-zeolites for the adsorption and oxidative degradation of nitroaromatic compounds in water

Nitroaromatic compounds (NACs) are prominent explosives. In this context, these toxic substances were released into the environment and cause long-lasting groundwater contamination. In preparation of a possible in-situ remediation, colloidal Fe-zeolites were investigated for their capabilities as adsorbents and oxidation catalysts. It was shown that the Fe-zeolites FeBEA35 and FeFAU55 are potent inorganic adsorbents for NACs and simultaneously capable of activating H2O2 as Fenton-like oxidation catalysts. Adsorption isotherms of 15 NACs on both zeolites were measured to evaluate the option of coupling adsorptive contaminant enrichment with oxidative degradation. The faujasite-type zeolite FeFAU55 showed a distinct S-type adsorption behaviour and reached significantly higher NAC loadings of > 20 wt%. For FeBEA35, L-type adsorption isotherms and maximum loadings qmax of about 4 wt% were obtained. Degradation of all NACs, monitored by nitrate formation, was observed. Apparent rate constants of the NACs with hydroxyl radicals in a homogeneous, stoichiometric Fenton reaction were related to the heterogeneous system to examine the role of adsorption on the oxidative degradation. Beneficial influence of the adsorption on the oxidation rates was identified. The results of this work open up promising prospects for future application of Fe-zeolites for the in-situ remediation of NAC-contaminated groundwater.

Metal oxide single-component light-powered micromotors for photocatalytic degradation of nitroaromatic pollutants

Mass transfer is a key parameter in heterogeneous reactions. Micro/nanomachines, a promising technology for environmental applications, significantly enhance the performance of conventional purification treatments because of the active motion ability and thus enhanced diffusion (superdiffusion) of these photocatalysts, which in turn leads to dramatically improved mass transfer and higher degradation capability compared to stationary microparticles. However, the design of micromotors generally involves noble metals, for instance, Au and Pt, to achieve an effective autonomous motion. Considering the expensive fabrication cost and complicated steps, we present Pt-free single-component light-powered WO3 micromotors capable of enhanced diffusion and effective degradation of nitroaromatic compounds in water. These microswimmers, synthesized by a hydrothermal method, which is highly scalable at low cost, followed by calcination, exhibit fuel-free light-driven motion due to asymmetric light irradiation. Picric acid (PA) and 4-nitrophenol (4-NP) were selected as representative nitroaromatic contaminants and photocatalytically decomposed by WO3 micromotors thanks to the close contact with the micromotors promoted by their self-propulsion. This work provides a low-cost, sustainable, scalable method for enhancing mass transfer by creating moving catalysts with broad application potential for water cleanup.

Explicating the recognition phenomenon of hazardous nitro-aromatic compound from contaminated environmental and cellular matrices by rationally designed pyridine-functionalized molecular probes

In the quest of recognizing hazardous nitro-aromatic compounds in water, two pyridine-functionalized Schiff-base chemosensors, DMP ((E)-N-(3,4-dimethoxybenzylidene)(pyridin-2-yl)methanamine)) and MP (4-((E)-((pyridin-2-yl)methylimino)methyl)-2-ethoxyphenol) have been synthesized to detect mutagenic 2,4,6-Trinitrophenol (TNP) in soil, water as well as cellular matrices by producing turn-off emission responses as a combined consequence of PET and RET processes. Several experimental analyses including ESI-MS, FT-IR, photoluminescence, 1H NMR titration, and the theoretical calculations ascertained the formation and sensing efficacies of the chemosensors. The analytical substantiations revealed that structural variation of the chemosensors played a significant role in improving the sensing efficiency, which would certainly be worthwhile in developing small molecular TNP sensors. The present work depicted that the electron density within the MP framework was more than that of DMP due to the intentional incorporation of –OEt and –OH groups. As a result, MP represented a strong interaction mode towards the electron-deficient TNP with a detection limit of 39 μM.

Polyoxometalate-based graphitic carbon nitride for reduction of toxic nitro aromatic compounds in water

The present study focuses on the development of an impressive way to eliminate toxic nitro aromatic compounds as hazardous industrial pollutants using polyoxometalate-based composites. For this purpose, transition metal substituted Keggin-type polyoxometalates were integrated on modified protonated graphitic carbon nitride (POMs@g-C3N4) via an electrostatic self-assembly strategy. These stable compounds are characterized by different techniques and used in the reduction of toxic nitro aromatic compounds. Among Cr, Mn, Fe, Co, Ni, Cu, and Zn, the composite containing copper substituted Keggin-type polyoxometalate (CuPOM@g-C3N4) presents the most respectable catalytic activity in these reduction reactions. Moreover, this efficient catalytic system is applied in the reduction of different toxic nitro aromatic compounds into the amino aromatic analogues with appropriate conversions and reaction times. Kinetic studies are also used to determine their apparent rate constants. This process is easy, low-cost, non-toxic, high potential catalytic performance, and environmental friendliness that could be accomplished in water as solvent and at room temperature.

New Insights into the Catalytic Activity and Reusability of Water‐Soluble Silver Nanoparticles

AbstractSilver nanoparticles (AgNPs) ‐stabilized by different sulfonated imidazolium salts (Lx)‐ have been synthesized as potential recyclable and reusable catalysts for the reduction of nitroaromatic compounds in water. An exhaustive study of the catalytic activity is presented and kinetic data are explained in terms of the Langmuir–Hinshelwood model. The kinetic parameters and the performance of AgNP as catalysts were determined. The results reveal that catalysis is a superficial process and the reaction rate depends on the type of AgNP:Lx used as catalyst, with the imidazolium salts having the effects on the catalytic activity. The physicochemical and structural characteristics of AgNPs are factors that influence the catalytic efficiency. The fact that these catalysts are recycled, in some cases for more than 6 cycles, opens a way for their recovery and reuse of AgNPs. Finally, a comparative study with gold nanoparticles (AuNP) stabilized by the same salts has been realized.

In Situ Preparation of Gold–Silica Particles from a Mixture of Oil Palm Leaves and Chloroauric Acid for Reduction of Nitroaromatic Compounds in Water

Gold–silica composites were prepared via a simple green approach using oil palm leaves (OPL) as sustainable source of natural silica. The presence of peaks at 2θ = 21.7°, 38.1°, 44.2°, 64.5°, and 77.4° in X-ray diffraction (XRD) analysis indicated that gold metal was incorporated into the solid silica-containing product. The as-prepared solid material, Au–SiO2(OPL), was effective as a heterogeneous catalyst for 4-nitrophenol and 4-nitrobenzaldehyde reduction in the presence of sodium borohydride to give the corresponding amino compounds. The good catalytic activity of Au–SiO2(OPL) for the reduction of nitro compounds can be ascribed to the presence of active sites in the ligand-free gold surface supported by green silica. The catalyst exhibited good stability, as confirmed by the consistency of the XRD pattern of the catalyst before and after being used in the 4-nitrophenol reduction reaction.

Determination of nitroaromatic explosive residues in water by stir bar sorptive extraction-gas chromatography-tandem mass spectrometry.

Nitroaromatic compounds were massively used in the formulation of explosives during both world wars. Even several decades after the end of these wars, their residues are suspected to be widely present in the environment. Their occurrence and effect on ecosystems and human health are still not fully determined. This paper describes the development of a method for the determination of 28 nitroaromatic compounds in water, including isomers of nitrotoluene (NT), dinitrotoluene (DNT), trinitrotoluene (TNT), nitrobenzene (NB), dinitrobenzene (DNB), chloronitrobenzene (ClNB), chlorodinitrobenzene (DNCB), nitronaphthalene (NN), dinitronaphthalene (DNN), nitroaniline (NA), dinitroanisole (DNAN), diphenylamine (DPA), and nitrodiphenylamine (nitro-DPA). In order to separate and individually quantify all the analytes with the best possible sensitivity, stir bar sorptive extraction (SBSE) was chosen as the extraction and pre-concentration step prior to gas chromatography (GC) separation and tandem mass spectrometry detection (MS/MS). Our SBSE optimization efforts focused on parameters such as the type of stir bar, ionic strength, addition of organic solvent, and extraction and desorption times. After these optimizations, the analytical method enabled us to reach limits of quantification (LOQs) between 1 and 50ng/L in tap water, groundwater, and surface water. The method was applied to the determination of targeted nitroaromatic explosive residues in spring and groundwater samples collected in an area where mine warfare had raged during World War I. Up to 16 different nitroaromatic compounds were detected in the same sample. The highest concentrations were recorded for 2,4-DNT and 1,3-DNB (1700 and 2690ng/L respectively).

Luminescent Lanthanide-Based Probes for the Detection of Nitroaromatic Compounds in Water.

A new mixed pyridyl–carboxylate ligand with two picolinate chromophores and a flexible linear spacer, potassium 2,2′-(butane-1,4-diylbis((pyridin-2-ylmethyl)azanediyl))diacetate (K2bpbd), which is obtained in high yield and spectroscopically characterized, has been utilized to make new lanthanide complexes, namely, [Ln(bpbd) (H2O)2(NO3)]·xH2O, where Ln = Tb (1) and x = 6, Ln = Sm (2) and x = 7, and Ln = Dy (3) and x = 7. These complexes have been extensively characterized by various spectroscopic techniques (UV–vis and Fourier transform infrared spectroscopy), elemental analyses, thermogravimetric analysis, field emission scanning electron microscopy, and powder X-ray diffraction. These show very intense characteristic luminescence features that confirm the antenna effect of the ligand on the metal center. These complexes have been utilized for the detection of various nitroaromatic compounds. Among these three complexes, 1 is found to be the best for the selective sensing of 2,4,6-trinitrophenol in water with a detection limit of (0.35 ± 0.05) ppm. Its Stern–Volmer constant, KSV [(5.48 ± 0.1) × 104 M–1], is one of the highest among similar sensors reported so far.

Degradation of nitroaromatic compounds: a novel approach using iron from laterite soil

The Fenton’s oxidation process has been found to be a simple and economical method for the treatment of nitroaromatic compounds in water. In the present study, the iron extracted from the laterite soil was used as a catalyst and optimization of pH, hydrogen peroxide concentration and iron concentration was studied for different initial concentrations of 2-nitroaniline (2-NA), 3-nitroaniline (3-NA) and 4-nitroaniline (4-NA). The optimum pH obtained was 2.5 for 2-NA and 3-NA and 3 for 4-NA. The maximum removal efficiency obtained was 85.3%, 84.3% and 98.7% for 0.5 mM initial concentration at a hydrogen peroxide concentration of 3.5 mM, 4.5 mM and 5 mM for 2-NA, 3-NA and 4-NA, respectively, with a constant iron concentration of 0.05 mM.

Neutral Luminescent Metal-Organic Frameworks: Structural Diversification, Photophysical Properties, and Sensing Applications.

Utilizing flexible bis(tridentate)polypyridyl ligands, the two new luminescent 2D metal organic frameworks {Zn2(tpbn)(2,6-NDC)2}n (1) and {[Zn2(tphn)(2,6-NDC)2]·4H2O}n (2), where tpbn = N,N',N″,N‴-tetrakis(2-pyridylmethyl)-1,4-diaminobutane, tphn = N,N',N″,N‴-tetrakis(2-pyridylmethyl)-1,6-diaminohexane, and 2,6-H2NDC = 2,6-naphthalenedicarboxylic acid, have been isolated in good yields under solvothermal conditions. Their solid-state molecular structures have been determined by single-crystal X-ray diffractometry. Both 1 and 2 have pentacoordinated Zn(II) centers with an N3O2 environment from three nitrogen atoms of the tpbn or tphn ligand and two carboxylate oxygen atoms from two different 2,6-NDC linkers. However, the binding modes of the tridentate part of polypyridyl ligands to the Zn(II) center are different in 1 and 2-meridional (tpbn) vs facial (tphn) due to an increase (1.5 times) in the methylene chain length. Thus, the binding mode of 2,6-NDC to the Zn(II) center differs: bis(monodentate) syn-anti in 1 and bis(monodentate) syn-syn in 2. This difference in binding modes of the components has a profound effect on the conformation of the six-membered ring (metal centers are considered as the vertices in it) within the 2D framework: honeycomb vs chair form for 1 and 2, respectively. In addition to further characterization by elemental analysis and UV-vis and FT-IR spectroscopy, their framework stabilities in water and thermal properties have been studied by powder X-ray diffraction and thermogravimetric analysis, respectively. On the basis of thermodiffractometry, 1 and 2 retain their crystallinity and overall structure up to 350 and 325 °C, respectively. Their luminescent properties have been utilized to demonstrate sensing of various solvents as well as nitro-aromatic compounds in water, which correlate well with their structural differences. Through the spectral overlap, lifetime measurements, and nature of the Stern-Volmer plots, the fluorescence quenching pathway for the nitro-analytes, particularly 2,4,6-trinitrophenol (TNP), is established for 1 and 2. Their recyclability and stability after sensing experiments are found to be excellent.

Array-Based Sensing of Explosives by Water-Soluble Poly(p-phenyleneethynylene)s

We have prepared four water-soluble poly(p-phenyleneethynylene)s, two of which are novel and carry benzylic side chains that are negatively charged. All of the four PPEs were employed to detect nitroaromatic compounds in water. The two novel PPEs with the benzylic side chains react fairly sensitive toward DNT and TNT in water. If the benzylic side groups are alkoxy-substituted, TNT is detected at concentrations down to 0.27 μM. 12 different nitroaromatics were successfully discriminated by a small array consisting of either two or four of the PPEs and employing linear discriminant analysis.

Anchoring Semiconductor and Metal Nanoparticle on Graphene Oxide for Simultaneous Sensing and Degradation of Contaminants

Manipulation of photoinduced charge transfer processes on a graphene based catalyst mat has allowed us to tailor the properties for photocatalytic and sensing applications. We have deposited luminescent CdSe quantum dots and SERS active silver nanoparticles to introduce photocatalytic and sensing properties. The role of the GO sheet is to establish electronic communication between semiconductor and metal NPs and promote adsorption of molecules near the silver nanoparticle surface. The GO-assisted communication between semiconductor and metal NPs in particular has enabled us to enhance the detection limit for low level nitroaromatic compounds in water. For example, CdSe emission is quenched upon adsorption of nitrobenzene. Following excitation with visible light the reduction of nitro group to amine proceeds at the CdSe surface and restores the emission. Thus the multifunctional hybrid assemblies designed in this study enable us to achieve greater detection sensitivity as well as capability to degrade the organic contaminants from water.

Luminescent Two-Dimensional Coordination Polymer for Selective and Recyclable Sensing of Nitroaromatic Compounds with High Sensitivity in Water

A stable two-dimensional (2D) coordination Cd(II) polymer [Cd(ppvppa)(1,4-NDC)]n (1) (ppvppa = N-(pyridin-2-yl)-N-(4-(2-(pyridin-4-yl)vinyl)phenyl)pyridin-2-amine; 1,4-H2NDC = 1,4-naphthalenedicarboxylic acid) was prepared by the solvothermal reactions of Cd(NO3)2·4H2O with ppvppa and 1,4-H2NDC in H2O and MeCN at 150 °C. Compound 1 was characterized by elemental analysis, IR, powder X-ray diffraction (PXRD), and single crystal X-ray diffraction and thermogravimetric analysis (TGA). Compound 1 consists of dimeric [Cd2(μ-ppvppa)2] fragments linked by 1,4-NDC bridges to generate a 2D honeycomb network. Complex 1 strongly emits blue light in the solid state when excited at 419 nm at ambient temperature. This emission is selectively quenched by nitro aromatic compounds in water with good sensitivity. Compound 1 also displays recyclable detection of nitro aromatic compounds.

Sensitive surface-enhanced Raman scattering (SERS) detection of nitroaromatic pollutants in water.

The increasing and urgent demand for clean water requires new approaches for identifying possible contaminants. In the present study, polymer substrates with embedded silver nanoparticles are employed to reveal the presence of traces of nitroaromatic compounds in water on the basis of the surface-enhanced Raman scattering (SERS) effect. These platforms provide an easy and sensitive method of detecting of low concentrations of these organic pollutants in contaminated water.

Improving the Visible Light Photoactivity of In2S3–Graphene Nanocomposite via a Simple Surface Charge Modification Approach

We report an efficient and easily accessible self-assembly route to synthesize In2S3-GR nanocomposites via electrostatic interaction of positively charged In2S3 nanoparticles with negatively charged graphene oxide (GO) followed by a hydrothermal process for reduction of GO to graphene (GR). The as-synthesized In2S3-GR nanocomposites exhibit much higher visible light photocatalytic activity toward selective reduction of nitroaromatic compounds in water than bare In2S3 nanoparticles and In2S3-GR-H that is obtained from the simple "hard" integration of GR nanosheets with solid In2S3 nanoparticles without modification of surface charge. On the basis of the joint characterizations and structure-photoactivity correlation it is disclosed that the enhanced photocatalytic performance of In2S3-GR is mainly ascribed to the more efficient interfacial contact between In2S3 and the GR nanosheets than In2S3-GR-H, which would amplify the use of electron conductivity and mobility of GR to improve the lifetime and transfer of photogenerated charge carriers more efficiently and thus boost the photoactivity more effectively. This work highlights the significant effect of preparation methods on the photoactivity of GR-semiconductor nanocomposites. It is expected that such a simple electrostatic self-assembly strategy could aid to rationally fabricate more efficient GR-semiconductor nanocomposites with improved interfacial contact and photocatalytic performance toward various photocatalytic selective transformations.

Effervescence-assisted dispersive micro-solid phase extraction

Extraction techniques are surface dependent processes since their kinetic directly depends on the contact area between the sample and the extractant phase. The dispersion of the extractant (liquid or solid) increases this area improving the extraction efficiency. In this article, the dispersion of the sorbent at the very low milligram level is achieved by effervescence thanks to the in situ generation of carbon dioxide. For this purpose a special tablet containing the effervescence precursors (sodium carbonate as carbon dioxide source and sodium dihydrogen phosphate as proton donor) and the sorbent (OASIS-HLB) is fabricated. All the microextraction process takes place in a 10 mL-glass syringe and the solid, enriched with the extracted analytes, is recovered by filtration. Acetonitrile was selected to elute the retained analytes. The extraction mode is characterized and optimized using the determination of five nitroaromatic compounds in water. The absolute recoveries of the analytes were in the range 61-85% while relative recoveries close to 100% in all cases, which demonstrates the absence of matrix effect on the extraction. These values permit the determination of these analytes at the microgram per liter range with good precision (relative standard deviations lower than 6.1%) using ultra performance liquid chromatography (UPLC) combined with ultraviolet (UV) detection as instrumental technique.

Reduction Rate Constants for Nitroaromatic Compounds Estimated from Adiabatic Electron Affinities

Nitroaromatic compounds (NACs) are ubiquitous environmental contaminants and predicting their environmental fate is important. Linear free energy relationships (LFERs) have been reported relating one-electron reduction potentials (E(o)(H)) of NACs in water to their reduction rate constants (k) measured under various conditions. In a recent effort to calculate E(o)(H), we found that E(o)(H) values of NACs are also linearly correlated with their adiabatic electron affinities (EA). This suggests that the reactivity of NACs--and hence their half-lives--can be predicted based on their EA values. We report here a new set of LFERs relating EA and k for NACs. Reduction of substituted nitrobenzenes mediated by quinones, natural organic matter, Fe(II) complexes, and the (CH(3))(2)COH radical was examined using EA values calculated from quantum mechanics. For monosubstituted nitrobenzenes without ortho substituents, strong linear correlations were found between EA and log k, leading to accurate estimates of k. Deviations between measured and estimated k values for most ortho-substituted and/or polysubstituted compounds were somewhat higher, but were accurate to within approximately an order of magnitude using the same LFER for all compounds. We report estimates of 169 reduction rate constants for 23 compounds in nine reducing systems for which no measured values are available.