4-nitrophenol Research Articles

Fluorescence and absorbance dual-mode immunoassay for detection of Ochratoxin A based on 2-aminoterephthalic acid and p-nitrophenol

In this work, a dual-mode immunoassay to detect Ochratoxin A (OTA) was developed relied on p-nitrophenyl phosphate (PNPP) and 2-aminoterephthalic acid (PTA-NH2). This proposed immunoassay based on microplate immunoenzyme technique used alkaline phosphatase (ALP) as a label for forming immune complexes. The ALP was used to catalyze the dephosphorization of PNPP to generate yellow p-nitrophenol (PNP). Since the absorption wavelength of PNP overlapped with the fluorescence emission of PTA-NH2, the fluorescence of PTA-NH2 can be quenched by PNP. The color of PNP and the fluorescence of PTA-NH2 were used as double signals to detect OTA. In this dual-mode immunoassay, the limit of detection (LOD) and the linear detection range of fluorescence mode were 0.57 ng/mL (about 0.57 μg/kg) and 1.56–50.00 ng/mL (about 1.56–50.00 μg/kg), respectively. For absorbance mode, the LOD and linear range were 0.07 ng/mL (about 0.07 μg/kg) and 0.39–25.00 ng/mL (about 0.39–25.00 μg/kg), respectively. Both detection modes showed good selectivity for OTA. The recoveries rates of fluorescence mode and absorption mode in maize flours were 91.80–128.85% and 100.10–114.00%, respectively.

New 5,5-(1,4-Phenylenebis(methyleneoxy)diisophthalic Acid Appended Zn(II) and Cd(II) MOFs as Potent Photocatalysts for Nitrophenols.

Metal-organic frameworks (MOFs) are peculiar multimodal materials that find photocatalytic applications for the decomposition of lethal molecules present in the wastewater. In this investigation, two new d10-configuration-based MOFs, [Zn2(L)(H2O)(bbi)] (1) and [Cd2(L)(bbi)] (2) (5,5-(1,4-phenylenebis(methyleneoxy)diisophthalic acid (H2L) and 1,1'-(1,4-butanediyl)bis(imidazole) (bbi)), have been synthesized and characterized. The MOF 1 displayed a (4,6)-connected (3.43.52)(32.44.52.66.7) network topology, while 2 had a (3,10)-connected network with a Schläfli symbol of (410.511.622.72)(43)2. These MOFs have been employed as photocatalysts to photodegrade nitrophenolic compounds, especially p-nitrophenol (PNP). The photocatalysis studies reveal that 1 displayed relatively better photocatalytic performance than 2. Further, the photocatalytic efficacy of 1 has been assessed by altering the initial PNP concentration and photocatalyst dosage, which suggest that at 80 ppm PNP concentration and at its 50 mg concentration the MOF 1 can photo-decompose around 90.01% of PNP in 50 min. Further, radical scavenging experiments reveal that holes present over 1 and ·OH radicals collectively catalyze the photodecomposition of PNP. In addition, utilizing density of states (DOS) calculations and Hirshfeld surface analyses, a plausible photocatalysis mechanism for nitrophenol degradation has been postulated.

Visible light photo-Fenton degradation of p-nitrophenol on Ag/Fe3O4/WO3 nanocomposites: Experimental and molecular dynamics investigations

The present research combines the adsorption behavior of phases in an aqueous medium with their band gap information for constructing a composite photo-Fenton catalyst that degrades para-nitrophenol (PNP). Thus, a series of Ag/ Fe3O4/WO3 Z-scheme photocatalysts were investigated for photo-Fenton PNP degradation. Classical MD simulations predicted effective H2O2 interaction with the photocatalyst's reduction (Fe3O4) part. The decoration of the composite surface by fine Ag nanostructures enhanced the visible light absorption efficiency of the photocatalyst through the localized surface plasmon resonance phenomenon. Photo-Fenton activities of Fe3O4/WO3 composites changed with their Ag loading. The composite with five-weight percent Ag loading demonstrated the best PNP degradation activity. The photoexcitation of Ag/Fe3O4/WO3 photocatalyst results in the accumulation of electrons on the CB of Fe3O4 and holes on the VB of WO3. The H2O2 molecules adsorb on the Fe3O4 part and are reductively cleaved to produce hydroxyl radicals, oxidizing PNP molecules nearby.

Electrocatalytic degradation of p-nitrophenol on metal-free cathode: Superoxide radical (O2•−) production via molecular oxygen activation

Although metal-free electrodes in molecular oxygen-activated Fenton-like wastewater treatment technologies have been developed, the reactive oxygen species (ROS) generation mechanisms are still not sufficiently clear. As a typical example of refractory phenolic wastewater, p-nitrophenol (PNP) has been widely studied. This study demonstrated the critical role of superoxide radicals (O2•−) in PNP degradation by metal-free electrodes through electron spin resonance (ESR), ROS quenching, and density functional theory (DFT) tests. The most superior metal-free electrode exhibited a mass activity of approximately 133.5 h−1 gcatalyst−1. Experimental and theoretical studies revealed the mechanism of O2•− generation via oxygen activation, including one- and three-electron transfer pathways, and found that O2•− mainly attacked the nitro group of PNP to degrade and transform the pollutant. This study enhances the mechanistic understanding of metal-free materials in the electrochemical degradation of refractory pollutants.

New sensitive LC-MS/MS method for the simultaneous determination of 13 phenolic and carboxylic acid pesticide biomarkers in human urine, including dicamba

The commercialization in 2016 of genetically engineered seeds tolerant to dicamba and/or 2,4-dichlorophenoxyacetic acid (2,4-D) has caused a rapid increase in the use of these herbicides. New questions about the reproductive and chronic health effects of long-term exposure to these herbicides have been raised. To assess exposure to dicamba and other pesticides of interest in the Heartland Study, a birth cohort study based in the United States, a new analytical method was needed. The present study describes the development and validation of this new solid phase extraction and liquid chromatography-tandem mass spectrometry method that detects simultaneously 13 pesticides or their metabolites in 250 μL of urine. More specifically, the method allows the analysis of dicamba, 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), which are herbicides, of malathion dicarboxylic acid (MDA), para-nitrophenol (PNP), 3,5,6-trichloro-2-pyridinol (TCPy), 2-diethylamino-6-methylpyrimidin-4-ol (DEAMPY) and 2-isopropyl-6-methyl-4-pyrimidinol (IMPY), which are metabolites of organophosphate insecticides, and finally of cis-3-(2,2-Dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (cis-DCCA), trans-3-(2,2-Dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (trans-DCCA), 3-Phenoxybenzoic acid (3-PBA), 4-Fluoro-3-phenoxybenzoic acid (4-F-3-PBA) and cis-3-(2,2-Dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid (cis-DBCA), which are metabolites of synthetic pyrethroids insecticides. The method was validated under ISO/IEC 17025 guidance. The limit of detection (LOD) in urine samples was 0.10 μg/L for dicamba, while the LOD for other analytes ranged between 0.0038 μg/L and 0.091 μg/L. Accuracy was evaluated by analyzing samples from two External Quality Assessment Schemes, namely G-EQUAS and OSEQAS. Preliminary results obtained following the analysis of 91 urine samples taken from pregnant women enrolled in the Heartland Study are presented here. This method is suitable for human biomonitoring studies.

Characterization and mechanism of p-nitrophenol removal based on modified nanoscale zero-valent iron electrocoagulation

p-Nitrophenol (PNP) is a toxic chemical and is difficult to degrade naturally when it enters the environment. It is of great importance to develop methods to remove PNP efficiently and safely. Electrocoagulation has been widely used for the removal of PNP, but challenges remain in the improvement of anode materials and solid-liquid separation of PNP-containing precipitates. In this work, the characteristics and mechanism of activated biochar (ABC) and sulfide dual-modified nanoscale zero-valent iron (nZVI) electrocoagulation anode for the removal of PNP were systematically investigated. The synergistic effect of magnetic iron oxide generated by zero-valent iron oxidation and electrochemical oxidation technique was used to rapidly reduce the PNP concentration for water purification. The results showed that the modified nZVI anode had higher electrocoagulation activity than the iron sheet anode, and the S-nZNI/ABC anode had the highest PNP removal efficiency. The main component of the precipitate after the reaction was Fe3O4, which facilitated the magnetic solid-liquid separation of the precipitate and scum. The seed germination test confirmed that the electrocoagulation material synthesized in this work had almost no adverse effects on the ecological environment. The electrocoagulation process had good degradation performance for PNP, which could significantly attenuate the ecotoxicity of PNP in the aquatic environment and thus improve the water quality. It is expected that this work may provide design references and ideas for the efficient degradation of PNP and the application of electrocoagulation.

Concentration identification and endpoint-oriented health risk assessments on a broad-spectrum of organic compounds in atmospheric fine particles: A sampling experimental study in Beijing, China

Understanding the complicate chemical components in atmospheric fine particulate matter (PM2.5) helps policy makers for pollutants control track progress and identify disparities in overall health risks. However, till now, information on accurate component detection, source identification, and effect-oriented risk assessment is scarce, especially for the simultaneous analysis of a broad-spectrum of compounds. In this study, a high-throughput target method was employed to distinguish the occurrence and characteristics of 152 chemicals: phthalate esters (PAEs), organophosphate esters (OPEs), carboxylic acid esters (CAEs), nitrophenols (NPs), nitrogen heterocyclic compounds (NHCs), per- and poly-fluoroalkyl substances (PFASs), triclosan and its derivatives (TCSs), and organosulfates (OSs) in ambient PM2.5 collected from Beijing, China. Detection frequencies of 77 targeted compounds were >50 %. Total concentrations of all compounds ranged from 33.1 to 745 ng/m3. The median concentration of ∑PAEs (108 ng/m3) was the highest, followed by ∑CAEs (12.2 ng/m3) and ∑NPs (10.1 ng/m3). Organophosphate diesters (di-OPEs) and TCSs were reported for the first time in ambient PM2.5. The pollutants mainly originated from the local industrial production, release of building materials, and environmental degradation of parent compounds. Based on absorption, distribution, metabolism, excretion, and toxicity (ADMET)-oriented risk evaluations, we found that bis (2-ethylhexyl) phthalate, diisobutyl phthalate, dibutyl phthalate, and di (2-ethylhexyl) adipate have high health risks. Additionally, the high oxidative stress potential of 4-nitrocatechol and the strong blood-brain barrier penetration potential of triclosan cannot be ignored. Our study will facilitate the evaluations of specific health outcomes and mechanisms of pollutants, and suggestion of pollutants priority control to reduce human health hazards caused by atmospheric particles.

Reactivity of aged biochars to the degradation of adsorbed p-nitrophenol: Role of intensity and species of persistent free radicals

Persistent free radicals (PFRs) in biochar have been found to the transformation of organic contaminants in environment. However, there remains insufficient comprehension on the relationship of biochar aging with interfacial reactivity of PFRs to the degradation of phenolic compound in geochemical process. Herein, we studied both sorption and degradation of p-nitrophenol (PNP) on fresh and aged biochars via H2O2 aging under anoxic condition. With increasing aging extent, the enhancive proportion of O-centered radicals was observed progressively as indicated by increased g factors. The aging of PS350 annihilated the presence of PFRs in aged biochars of low-temperature, weakening PFR intensity. But, the aging of PS650 supplied more O-centered radicals for aged biochars of high-temperature, enhancing PFR intensity. This caused the decreased degradation on 5%PS350 and 15%PS350 (37.7–79.6% decline), whereas the increased degradation on 5%PS650 and 15%PS650 (33.3–55.8% increase). At similar intensity and species of PFRs, more adsorbed amount on fresh and aged biochars produced more degradation of PNP. Nevertheless, when PFR intensity of PS650 was much lower than that of PS350, despite high sorption capacity of PS650, the degradation amount of PS350 and PS650 was comparable. The results indicated that the reactivity of C-centered radicals of PS650 was stronger than that of O-centered radicals of PS350 in anoxic system. Overall, the interfacial reactivity of biochars was simultaneously regulated by the sorption capacity of biochars and intensity and species of PFRs. This work provides a deep perspective to the impact of biochar aging on the interfacial reactivity of PRFs to phenolic compound, which will be beneficial to accurately predict the fate of organic contaminant in carbon-rich environment.

Green synthesis of silver nano-catalyst using ionic liquid and their photocatalytic application to the reduction of p-nitrophenol

Ionic liquids (ILs) carrying special properties can act as electronic as well as steric stabilisers by preventing nanoparticle (NP) growth and NP aggregation. The effect of visible light on the catalytic properties of silver nanoparticles is a hot topic of extensive research nowadays. The present report demonstrates the current developments in the green synthesis of silver nanoparticles in ionic liquids and a detailed study of the room-temperature catalytic and photocatalytic reduction of p-nitrophenol (PNP) to p-aminophenol (AP). The Ag nanoparticles (AgNPs) functionalised by ionic liquids are prepared in the 40-140 nm range and are found to be spherical in shape. The photocatalytic properties of these nanocomposites for the reduction of PNP to AP were studied. Photocatalytic degradation of PNP was also analysed by these composite nanostructures. The plasmonic photocatalytic properties of the synthesised AgNPs revealed activity significantly higher than that of the room-temperature catalysis. Density functional theory calculations showed that strong interactions exist between nanoclusters and ILs. Natural bond orbital analysis showed that IL also activates the nanoparticles for further photocatalytic reduction by transferring electron transfer from the donor (IL) to the acceptor (Ag cluster) and activating the silver NPs for further catalytic reaction. Photocatalytic degradation of PNP (reduction of PNP to AP) using NP in the absence of light follows first-order kinetics, whereas in the presence of light it follows zero-order reaction kinetics.

Synthesis of carbon microsphere-supported nano-zero-valent iron sulfide for enhanced removal of Cr(VI) and p-nitrophenol complex contamination in peroxymonosulfate system

Carbon microspheres supported sulfurized nano zero-valent iron (CMS@S-nFe0) was successfully prepared. The interaction impact of different dosages on the removal of Cr(VI) and p-nitrophenol (PNP) complex contamination was explored by response surface method (RSM). The results showed both the C group and Fe2+ on the surface of carbon microspheres could be used as activators of peroxymonosulfate (PMS) decomposition, and •OH and SO4•- could be produced to promote the oxidative degradation of PNP. Among them, SO4•- was the main reactive oxygen species. The presence of PNP could further promote the reduction of Cr(VI). Besides, loading nFe0 and FeS compounds on the carbon base could significantly reduce the production of free iron ions, which could effectively remove Cr(VI) and PNP from polluted water. In terms of treatment results, CMS@S- nFe0 was a promising material for wastewater treatment because of its excellent performance in adsorption of heavy metals and degradation of organic pollutants.

A fluorescent biomass derived cellulose/PANI/NiFe2O4 composite for the mitigation of toxic pollutants and Cr(VI) sensing from aqueous environment

Targeting routine water pollution due to industries and biowaste management, present work focuses on synthesis of biomass derived photocatalysts for abatement and detection of noxious pollutants. Herein, a series of nickel ferrite/cellulose-polyaniline composites (NF/C-PA) were fabricated via hydrothermal route and were successfully characterized. The comparative analysis of all the synthesized composites was carried out for photo-Fenton degradation of different pollutants, namely, Remazol brilliant yellow (RBY), Safranin O (SO) dyes, Levofloxacin (LVX) and Ofloxacin (OFX) drugs, and para-nitrophenol (PNP). Amongst all composites, NF/C-PA 1.5 bestowed best photocatalytic results with a degradation value of 95.42 % (k1 = 0.0859 min−1), 93.42 % (k1 = 0.0859 min−1), 91.96 % (k1 = 0.0731 min−1), 87.44 % (k1 = 0.1213 min−1), and 90.73 % (k1 = 0.1195 min−1) within 30 min for RBY, SO, LVX, OFX and PNP, respectively. Furthermore, the synthesized NF/C-PA 1.5 composite was successfully employed as fluorescence probe for selective and sensitive detection of Cr(VI) in wastewater with the limit of detection value 4 µM in the linear range of 0 to 200 µM. The sensor demonstrated virtuous pertinency in real water samples. Thus, the synthesized biobased composites exhibited multifunctional platform for the removal and detection of pernicious contaminants from aqueous environment.

Fe2O3/coal fly ash Fenton-like catalyst for the elimination of organic pollutants in wastewater: Kinetic, mechanism, and application feasibility

Fe2O3/CFA was prepared by loading Fe2O3 on the surface of raw coal fly ash (RCFA), and then used as a Fenton-like catalyst to treat refractory organic wastewater. The characterization results of SEM-EDX, XRD, XPS, XRF, and BET test indicate that Fe2O3 is successfully loaded on the surface of RCFA, while the adsorption performance is not significantly affected. Under optimal treatment conditions of p-nitrophenol (PNP) simulated wastewater (H2O2 dosage = 8 mmol/L, Fe2O3/CFA loading = 6 g/L, pH = 3, and T = 303 K), the removal rate of PNP reaches 97.7 % at 50 min. There exist hydroxyl radicals (·OH), superoxide radicals (∙O2−) and singlet oxygen (1O2) in the Fenton-like system, and ·OH is the primary reactive oxygen species in the removal of PNP·H2O2 dosage, Fe2O3/CFA loading, and pH (i.e., [H+]) show different effects on the generation rate constant of hydroxyl radicals (k·OH), and the corresponding mathematic equation is k∙OH=6.51∙e−640.0T∙[H2O2]1.313∙[Fe2O3/CFA]1.093∙[H+]0.815. The Fenton-like process includes heterogeneous and homogeneous catalytic processes, and it is driven by the synergistic catalysis of multiple metallic elements; Fe and other metallic elements play major and auxiliary roles, respectively. In the advanced treatment of real coking wastewater, the catalytic capacity of Fe2O3/CFA can maintain 91.7 % in its 4th use, and the treatment cost is ¥4.15/ton, which can be decreased by further optimizing the preparation process of Fe2O3/CFA.

Cobalt-aluminum spinel supported on modified γ-alumina for peroxymonosulfate activation: Si–Al ratio of support to optimize performance and reusability

The development of cobalt-based supported catalysts with high PMS catalytic activity and stability by adjusting the composition of the support is highly desirable yet remains scarce. In the work, a series of catalysts (Co2AlO4/Al2O3-xSiO2) were prepared by impregnation and high-temperature calcination using Al2O3-xSiO2 with a low Si–Al ratio as the support. Measurement techniques such as XRD, XPS, UV-DRS, FTIR, BET, SEM and HRTEM were used to characterize textural and chemical properties (ratio of Co3+/Co2+, specific surface area, pore size, pore volume, etc.). The ratio of Co3+/Co2+ and pore volume of Co2AlO4/Al2O3-xSiO2 can be turned by controlling the ratio of Si to Al, which are closely related to the catalytic performance and reusability of the catalysts. The optimized catalyst (Co2AlO4/Al2O3-0.25SiO2) can completely degrade 10 mg/L p-nitrophenol (PNP) in 40 min in the pH range of 3–9 with excellent reusability. The effects of several reaction parameters (i.e., PMS dosage, Co2AlO4/Al2O3-0.25SiO2 dosage, reaction temperature, initial pH value, and inorganic ions) on PNP removal were comprehensively investigated. Sulfate radical (SO4•−) and singlet oxygen (1O2) are making a major contribution to the degradation of PNP. Moreover, a millimeter-scale catalyst (CoSiAl-0.25/Al2O3 pellet) was prepared by sol adsorption and high-temperature calcination method, which maintained high oxidation activity after treatment of 18 L wastewater (PNP of 10 mg/L) in a continuous flow process. The method is simple and easy to operate on a large scale, providing a new perspective on the design and preparation of cobalt-aluminum spinel catalysts for activated PMS.

Ag‐based bimetallic clusters as catalysts for p‐nitrophenol reduction by glycerol: A DFT investigation

AbstractReducing p‐nitrophenol (PNP) to p‐aminophenol is an industrially relevant synthesis. Nevertheless, only a few heterogeneous catalysts have been evaluated for the reduction of PNP by glycerol. Appropriate quantum computational studies can screen potential catalysts for this crucial green reaction. The present research investigates the catalytic activities of Pd@Ag and Ni@Ag core‐shell nanogeometries toward PNP reduction by glycerol through density functional theory (DFT) calculations. The central atom of a geometry‐optimized 13‐atom Ag cluster was replaced by Pd and Ni atoms to create the core‐shell morphologies. The interaction energies of PNP and glycerol with each of the (metal/bimetallic) clusters were evaluated by DFT calculations to find the best PNP and glycerol molecule orientation with the respective bimetallic cluster. Electrostatic potential surface and natural bond orbital analyses were performed to study the charge distribution and transfer between atomic orbitals. The frequencies of vibrational modes in isolated PNP/glycerol structures were compared to those when these molecules were in the presence of the different metal clusters to infer the effect of the interactions. All performed analyses indicated improved catalytic activity toward PNP reduction by glycerol upon Ni‐doping of the Ag13 cluster.

Cobalt-based conjugated coordination polymers with tunable dimensions for electrochemical sensing of p-nitrophenol

Using planar π-conjugated 2,5-diamino-1,4-benzenedithiol as organic ligand, Co-based conjugated coordination polymers (CoCCPs) with different morphology were prepared through controlling the injection rate of Co2+. When the injection rate decreases from 1.00 to 0.25 mL min−1, the obtained CoCCPs change from 2D nanosheets to quasi-1D nanorods. It is found that the different-shaped CoCCPs exhibit varying electrochemical sensing performance. The prepared CoCCPs-1 with quasi-1D nanowires and porous network structure possesses larger active area, faster electron transfer and higher accumulation ability. Moreover, the CoCCPs-1 is more active for the oxidation of p-nitrophenol (PNP), and greatly enhances its oxidation signal. Based on the morphology-tuned sensing performance of CoCCPs, a highly-sensitive electrochemical sensor has been developed for PNP, with detection limit of 0.00986 μM (9.86 nM). It was used in the analysis of wastewater samples, and the results is validated by other instrumental method.

Solid regulating the electron transfer of ZVAl by ball milling for enhanced para-nitrophenol reduction: Necessity of iron sources

Para-nitrophenol (PNP) exhibits high toxicity, carcinogenicity, accumulation capacity and the existence of an electron-absorbing nitro group makes it hard to oxidize but can be reduced easily. Zero-valent aluminum (ZVAl) is an excellent reductant, while its insulation film limits its electron transfer. The oxide film needs to be broken to release the electrons inside ZVAl, and the electron transfer rate after the electron release needs to be controlled to avoid the rapid reaction that leads to the loss of ZVAl activity. Therefore, Fe-ZVAlbm was synthesized by directly one-pot ball milling solid ZVAl, FeSO4·7H2O and Fe3O4 to promote the electron release and regulate the electron transfer. FeSO4·7H2O and Fe3O4 showed splendid synergy for effectively removing 95.6% of PNP unaffected by co-existing ions in a broad pH range (3–11). FeSO4·7H2O with crystal structure could effectively cut the pristine insulation oxide film of ZVAl in the milling process, thus promoting electrons inside the ZVAl release. The conductive Fe3O4 particles embedded onto the surface of ZVAl and the surface-bound Fe(II) contained in Fe3O4 could mediate electron transfer to PNP and regulate the electron transfer rate. The superior electron transfer capacity of Fe-ZVAlbm was presented by the smallest radius of the Nyquist curve. In conclusion, Fe-ZVAlbm is of considerable potential for efficiently reducing nitro-substituted organic compounds, with broader prospects for wastewater treatment.

Synthesis and evaluation of phosphonato-triphenylamine fluorophore as a highly sensitive chemosensor for nitroaromatics

A sodium (nitrilotris(benzene-4,1-diyl))tris(phosphonic acid) (TPAP) molecular architecture has been synthesized and characterized by modern spectroscopic techniques. The photophysical behaviour of TPAP has been examined using UV–Vis absorption, fluorescence spectra, and time-resolved emission techniques. TPAP showed absorption maxima at 312 nm and strong emission peak at 392 nm with quantum yield 23.55%. Further, TPAP is employed for the nitroaromatics (NACs) detection in H2O media. TPAP exhibited more pronounced sensitivity towards trinitrophenol, i.e., picric acid (PA) over nitrophenol (NP) and dinitrophenol (DNP). The sensor TPAP shows turn-off fluorescence behavior upon interaction with PA with a lower limit of detection to be 5.35×10−8 M. Theoretical studies such as DFT calculations were employed to establish the sensing mechanism of TPAP. The molecular recognition of TPAP with PA is attributed to cooperative H-bonding, resulting in superior detection of PA. Thus, the developed TPAP sensor provides an appropriate method for PA detection and could be explored for environmental samples.

Two-Dimensional Lanthanide Metal-Organic Frameworks as a Platform for Sensing Pollutant and Nitrophenols Reduction.

The discharge of harmful and toxic pollutants in water is destroying the ecosystem balance and human being health at an alarming rate. Therefore, the detection and removal of water pollutants by using stable and efficient materials are significant but challenging. Herein, three novel lanthanide metal-organic frameworks (Ln-MOFs), [La(L)(DMF)2(H2O)2]·H2O (LCUH-104), [Nd(L)(DMF)2(H2O)2]·H2O (LCUH-105), and [Pr(L)(DMF)2(H2O)2]·H2O (LCUH-106) [H3L = 5-(4-(tetrazol-5-yl)phenyl)isophthalic acid (H3TZI)] were solvothermally constructed and structurally characterized. In the three Ln-MOFs, dinuclear metallic clusters {Ln2} were connected by deprotonated tetrazol-containing dicarboxylate TZI3- to obtain a 2D layered framework with a point symbol of {42·84}·{46}. Their excellent chemical and thermal stabilities were beneficial to carry out fluorescence sensing and achieve the catalytic nitrophenols (NPs) reduction. Especially, the incorporation of the nitrogen-rich tetrazole ring into their 2D layered frameworks enables the fabrication of Pd nanocatalysts (Pd NPs@LCUH-104/105/106) and have dramatically enhanced catalytic activity by using the unique metal-support interactions between three Ln-MOFs and the encapsulating palladium nanoparticles (Pd NPs). Specifically, the reduction of NPs (2-NP, 3-NP, and 4-NP) in aqueous solution by Pd NPs@LCUH-104 exhibits exceptional conversion efficiency, remarkable rate constants (k), and outstanding cycling stability. The catalytic rate of Pd NPs@LCUH-104 for 4-NP is nearly 8.5 times more than that of Pd/C (wt 5%) and its turnover frequency value is 0.051 s-1, which indicate its excellent catalytic activity. Meanwhile, LCUH-105, as a multifunctional fluorescence sensor, exhibited excellent fluorescence detection of norfloxacin (NFX) (turn on) and Cr2O72- (turn off) with high selectivity and sensitivity at a low concentration, and the corresponding fluorescence enhancement/quenching mechanism has also been systematically investigated through various detection means and theoretical calculations.

Effect of tetrachloro cadmium (II)/cobalt (II) ions modulation on organic-macrocyclic adaptive assembly based on cucurbit[6]uril and p-nitrophenol

Adaptive pore channels provide many possibilities for constructing functional supramolecular assemblies, making macrocyclic-based assemblies available for a variety of functions. To investigate the effect of ions modulation on the structure and properties of organic-macrocyclic adaptive assemblies, two supramolecular assemblies based on cucurbit[6]uril (Q[6]) and p-nitrophenol (PNP) are constructed through the outer-surface interactions of cucurbit[n]urils (Q[n]s): assembly 1 (Q[6]-PNP) and assembly 2 (Q[6]-PNP-[CdCl4]2−-[CoCl4]2−). The structural characteristics and the difference in the ability of the two assemblies to capture PNP molecules are investigated by X-ray crystallography, UV–vis spectroscopy, etc. It is found that after [CdCl4]2−, [CoCl4]2− are added as structure-directing agents, many honeycomb-like hexagonal pores are formed in assembly 2, but its ability to capture PNP molecules is only one-third of that of assembly 1. This indicates that ions modulation may reduce the ability of macromolecules to capture organic molecules, but the assembly 2 modulated by tetrachloro cadmium (II) /cobalt (II) ions has many honeycomb-like pores, which also provides new insights for the construction of more supramolecular assemblies with functionality based on Q[n]s.

The degradation of p-nitrophenol by biochar is dominated by its electron donating capacity

The typical aromatic and phenolic pollutant, p-nitrophenol (PNP), is extensively used in the industry and can seriously threaten the environmental health. Biochar, as a solid carbon-rich material, can directly degrade PNP. It has been reported that the PNP degradation by biochar is closely related to the electron exchange capacity of biochar (the sum of electron donating and accepting capacities). However, the roles of electron donating and accepting capacity of biochar in PNP degradation have not been distinguished before. In this study, the biochar samples were chemically modified to manipulate the electron donating and accepting capacities of biochar samples. Compared with pristine biochar (3.67 %), modified biochar had higher degradation efficiencies of PNP (>7.81 %). The strictly positive correlation between the electron donating capacities and the PNP degradation rates of biochar samples (r = 0.98, p < 0.05) indicated that the PNP degradation process by biochar is dominated by the reduction process. Although both the oxidation and reduction degradation products were found in the degradation system, the quenching experiment of OH, a key radical in the process of oxidation degradation, further proved that the oxidation process just played a minor role (<10 %) in the PNP degradation by biochar. This study shed light on the degradation mechanism of PNP by biochar and could promote the application of biochar in the pollution remediation.