Chitosan/UiO-66 composites as high-performance adsorbents for the removal of methyl orange in aqueous solution

UiO-66 and chitosan/UiO-66 composites were successfully synthesized by varying the mass addition of chitosan which were 0%, 2.5%, 5%, 10%, and 20% of the mass of UiO-66, denoted as UiO-66, Cs(2.5)/UiO-66, Cs(5)/UiO-66, Cs(10)/UiO-66, and Cs(20)/UiO-66, respectively. UiO-66 was modified with chitosan using the impregnation process. The X-ray diffraction patterns of the synthesized materials showed characteristic peaks at 2θ of 7.25° and 8.39°, which matched to that of the reported UiO-66. In addition, the Fourier transform infrared spectroscopy spectra of the materials showed absorption bands at the same wavenumber as UiO-66 and chitosan previously reported. The surface morphology of UiO-66 observed from scanning electron microscopy images was in the form of agglomerated small cube particles, where the smaller particles were observed for Cs(10)/UiO-66. From the N₂ adsorption isotherms, it was found that the Brunauer-Emmett-Teller surface areas of UiO-66, Cs(5)/UiO-66, and Cs(10)/UiO-66 materials were 825.7 m²/g, 835.4 m²/g, and 882.2 m²/g, respectively. The results of the study on adsorption of methyl orange in aqueous solutions showed that Cs(5)/UiO-66 had the highest adsorption capacity of 370.37 mg/g and followed the pseudo–second-order adsorption kinetic with a Langmuir isotherm model.     

Preparation and photocatalytic performance research of Bi2WO6/UiO-66-NH2 composite

Bi₂WO₆/UiO-66-NH₂ photocatalysts were fabricated through solvothermal method using acetic acid as template. The photocatalytic performance of as-fabricated composites was highly improved under simulated visible light due to the addition of UiO-66-NH₂. The structural and chemical properties of the composites were characterized through FTIR, XRD, XPS, SEM, BET, UV–vis DRS and PL. After 90 min of visible light irradiation, the RhB at an initial concentration of 10 mg·L^?1 in the solution was degraded by 99.4% due to the addition of 10 mg of the composite. There was no significant decrease in the photocatalytic activity even after four rounds of cycles. The free radical capture experiments indicate that the photogenerated holes (h⁺) were the main active sites. The possible photocatalytic degradation mechanism was proposed as the specific surface area of the composite was enlarged due to the uniform distribution of UiO-66-NH₂ on the surface of Bi₂WO₆. The electron–hole pairs recombination rate was decreased due to the photogenerated electrons (e^?) on the CB of Bi₂WO₆ which can be rapidly transferred to the CB of UiO-66-NH₂ and the photogenerated holes of UiO-66-NH₂ transferred to the VB of Bi₂WO₆. Meanwhile, the RhB was directly oxidized to H₂O and CO₂ by h⁺ to achieve the purification effect.

     

Determination of 4-nonylphenol and 4-tert.-octylphenol in water samples by stir bar sorptive extraction and thermal desorption-gas chromatography-mass spectrometry

A simple and highly sensitive method called thermal desorption (TD)-gas chromatography-mass spectrometry (GC-MS), which is used for the determination of trace amounts of 4-nonylphenol (NP) and 4-tert.-octylphenol (OP) in water samples, is described. NP and OP in samples are extracted from water samples and concentrated by the stir bar sorptive extraction (SBSE) technique. A stir bar coated with polydimethylsiloxane (PDMS) is added to a 2.0 ml water sample and stirring is carried out for 60 min at room temperature (25 °C) in a headspace vial. Then the extract is high sensitively analyzed by TD-GC-MS without any derivatization step. The optimum SBSE conditions are realized at an extraction time of 60 min. The detection limits are 0.02 ng ml⁻¹ for NP and 0.002 ng ml⁻¹ for OP. The method shows good linearity over the concentration range of 0.1-10 ng ml⁻¹ for NP and 0.01-10 ng ml⁻¹ for OP, and the correlation coefficients are higher than 0.999. The average recoveries of NP and OP are higher than 97% (R.S.D.: 3.6-6.2%) with correction using the added surrogate standards, 4-(1-methyl) octylphenol-d₅ and deuterium 4-tert.-octylphenol. This simple, accurate, sensitive and selective analytical method may be used in the determination of trace amounts of NP and OP in tap and river water samples.     

Synergy of photocatalytic reduction and adsorption for boosting uranium removal with PMo12/UiO-66 heterojunction

In this work, we proposed a new U(VI) removal strategy combining adsorption and photocatalytic reduction by the PMo₁₂/UiO-66 heterojunctions. The PMo₁₂ has been encapsulated in the cavities of UiO-66 by a one-step hydrothermal method, and the PMo₁₂/UiO-66 exhibited high adsorption capacity and photocatalytic activity. The maximal theoretical sorption capacity of U(VI) on 15% PMo₁₂/UiO-66 reached 225.36 mg/g and the photoreduction rate of 15% PMo₁₂/UiO-66 is about thirty times as much as UiO-66. Under the light irradiation, the photogenerated electrons rapidly transport from UiO-66 to PMo₁₂, and the photo-generated electrons could efficiently reduce the pre-enriched U(VI) to U(IV). This work provides new insights into remediation of the radioactive environment.     

Room-temperature luminescence optosensings based on immobilized active principles actives: Application to nafronyl and naproxen determination in pharmaceutical preparations and biological fluids

This paper presents two easy and selective methods for determining the active principles nafronyl (NFL) and naproxen (NAP), using a flow-through fluorescence optosensor based on the on-line immobilization on a nonionic-exchanger (Silica Gel, Davisil™ and Amberlite XAD 7, respectively) solid support. The determination was performed in 5×10⁻³ M HAc/NaAc buffer solution at pH 5 for NFL and 15×10⁻³ M glycine/HCl buffer solution at pH 2.5 for NAP at a working temperature of 20 °C. The fluorescence intensities were measured at λ_ex/em=294/336 nm and λ_ex/em=332/354 nm for NFL and NAP, respectively. The response time for these optosensors were practically instant, obtaining a linear concentration range between 0 and 700.0 ng ml⁻¹ with a detection limit of 20.8 ng ml⁻¹, an analytical sensitivity of 10.1 ng ml⁻¹ and a standard deviation of 1.27% at a 500 ng ml⁻¹ concentration level for NFL and a linear concentration range between 0 and 200.0 ng ml⁻¹ with the detection limit of 13.3 ng ml⁻¹, an analytical sensitivity of 6.0 ng ml⁻¹ and a standard deviation of 3.52% at a 100 ng ml⁻¹ concentration level for NAP. The proposed methods were satisfactorily applied to real samples (three commercial formulations and urine samples). The effects of the possible interferences were evaluated in all cases.     

Solid-state NMR studies of the acidity of functionalized metal–organic framework UiO-66 materials

The acid strength of metal–organic frameworks plays a key role in their catalytic performance such as activity and selectivity during catalytic reactions. Solid-state nuclear magnetic resonance in combination with probe molecules including 2-¹³C-acetone and pyridine-d₅ was employed to characterize the acid strength of UiO-66-X (X = -H, -2COOH, -SO₃H). It was found that after introduction of the functional groups, the acid strength of UiO-66-2COOH and UiO-66-SO₃H is considerably enhanced compared with that of parent UiO-66, with that of the former being similar to that of zeolite H-ZSM-5, and with that of the latter being slightly stronger than that of the former. Even though the acid density can efficiently be modified through changing the relative ratio in multivariate functionalized UiO-66-X, no significant alternation for the acid strength could be discerned in the MTV-UiO-66-X compared with acidic same-link counterpart. Theoretical calculations were employed to further confirm the acid strength of UiO-66-SO₃H and UiO-66-2COOH.     

Attachment of Fe3O4 nanoparticles on UiO-66: A stable composite for efficient sorption and reduction of selenite from water

In the present work, Fe₃O₄ nanoparticles were attached to the surface of UiO-66, a zirconium-based metal–organic framework material and the composite material formed was used to remove selenite (Se(IV)) in water. The Fe₃O₄/UiO-66 composite were assembled by a facile two-stage strategy. Benefiting from the ultra-high specific surface area of UiO-66, the Fe₃O₄/UiO-66 also had a large specific surface area, which made it easier to expose the active sites of Fe₃O₄ on the surface of UiO-66. The XPS and Mössbauer spectroscopy analysis indicated that there was charge transfer between Fe₃O₄ and UiO-66 in the Fe₃O₄/UiO-66, which made the Fe₃O₄ on the surface of UiO-66 had enhanced reductive activity. The mechanism of Fe₃O₄/UiO-66 to removed Se(IV) from the solution was further investigated by Zeta potential, FT-IR, SEM, TEM, and XPS spectra. The results indicated that the Fe₃O₄ nanoparticles on the surface of UiO-66 not only interacted with selenite through electrostatic action and inner-sphere complex but could also reduce a large amount of selenite to the insoluble Se⁰. The combination of these three actions finally strengthened the removal of selenite. This study cloud promote the practical application of MOF-based composites in removing heavy metal ions.     

Comparison of different extraction methods for the determination of statin drugs in wastewater and river water by HPLC/Q-TOF-MS

Three preconcentration techniques including solid phase extraction (SPE), dispersive liquid-liquid microextraction (DLLME) and stir-bar sorptive extraction (SBSE) have been optimized and compared for the analysis of six hypolipidaemic statin drugs (atorvastatin, fluvastatin, lovastatin, pravastatin, rosuvastatin and simvastatin) in wastewater and river water samples by high performance liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (HPLC/Q-TOF-MS). Parameters that affect the efficiency of the different extraction methods such as solid phase material, sample pH and elution solvent in the case of SPE; the type and volume of the extracting and dispersive solvent, pH of sample, salt addition and number of extraction steps in the case of DLLME; and the stirring time, pH of sample, sample volume and salt addition for SBSE were evaluated. SPE allowed the best recoveries for most of the analytes. Pravastatin was poorly extracted by DLLME and could not be determined. SBSE was only applicable for lovastatin and simvastatin. However, despite the limitations of having poorer recovery than SPE, DLLME and SBSE offered some advantages because they are simple, require low organic solvent volumes and present low matrix effects. DLLME required less time of analysis, and for SBSE the stir-bar was re-usable. SPE, DLLME and SBSE provided method detection limits in the range of 0.04-11.2 ng L⁻¹, 0.10-17.0 ng L⁻¹ for 0.52-2.00 ng L⁻¹, respectively, in real samples. To investigate and compare their applicability, SPE, DLLME and SBSE procedures were applied to the detection of statin drugs in effluent wastewater and river samples.     

Group-specific enzyme-linked immunosorbent assay for fenitrooxon and 3-methyl-4-nitrophenol in water samples based on a polyclonal antibody

Fenitrooxon [O,O-dimethyl-O-(4-nitro-m-tolyl)phosphate] is the major metabolite of the organophosphorus insecticide fenitrothion, and 3-methyl-4-nitrophenol is its major degradation product. In the present study, we describe the development of an indirect competitive enzyme-linked immunosorbent assay (ELISA) for the detection of these compounds in water samples based on a group-specific polyclonal antiserum generated with a “bifunctional hapten”, which has two functions: the conventional function of producing an antibody against an antigen and a unique function of promoting the production of the antibodies in rabbit. For application to water samples, the influence of several factors such as organic solvent, pH, and detergent was studied. Under optimized conditions, the quantitative working range of the fenitrooxon ELISA was 0.71-27 ng ml⁻¹ with a limit of detection (LOD) of 0.32 ng ml⁻¹, and the fenitrooxon concentration giving 50% reduction of the maximum signal (IC₅₀) was 4.2 ng ml⁻¹. The quantitative working range of the 3-methyl-4-nitrophenol ELISA was 0.67-27 ng ml⁻¹ with a LOD of 0.38 ng ml⁻¹ and an IC₅₀ of 3.7 ng ml⁻¹. No significant matrix effect originating from the water sample (river water, tap water, purified water, and bottled water) was shown by addition of Tween 20 to the assay buffer. Water samples spiked with each of these compounds at 1, 5, 10, and 20 ng ml⁻¹ were directly analyzed without extraction and clean-up by the proposed ELISA. The mean recovery was 100.9%, and the mean coefficient of variation (CV) was 7.7% for the fenitrooxon ELISA and for the 3-methyl-4-nitrophenol ELISA, the mean recovery was 97.6%, and the mean CV was 7.2%. The proposed ELISA allows precise and accurate determination of these compounds in water at such low levels.     

Synthesis of improved upconversion nanoparticles as ultrasensitive fluorescence probe for mycotoxins

Rare earth-doped upconversion nanoparticles (UCNPs) have promising potentials in biodetection due to their unique frequency upconverting capability and high detection sensitivity. This paper reports an improved UCNPs-based fluorescence probe for dual-sensing of Aflatoxin B1 (AFB1) and Deoxynivalenol (DON) using a magnetism-induced separation and the specific formation of antibody-targets complex. Herein, the improved UCNPs, which were namely NaYF₄:Yb/Ho/Gd and NaYF₄:Yb/Tm/Gd, were systematically studied based on the optimization of reaction time, temperature and the concentration of dopant ions with simultaneous phase and size controlled NaYF₄ nanoparticles; and the targets were detected using the pattern of competitive combination assay. Under an optimized condition, the advanced fluorescent probes revealed stronger fluorescent properties, broader biological applications and better storage stabilities compared to traditional UCNPs-based ones; and ultrasensitive determinations of AFB1 and DON were achieved under a wide sensing range of 0.001–0.1 ng ml⁻¹ with the limit of detection (LOD) of 0.001 ng ml⁻¹. Additionally, the applicability of the improved nanosensor for the detection of mycotoxins was also confirmed in adulterated oil samples.     

Exploiting parameter space in MOFs: a 20-fold enhancement of phosphate-ester hydrolysis with UiO-66-NH2

The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO₂ and UiO-66-(OH)₂ showed little to no change in hydrolysis rate. However, UiO-66-NH₂ showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe₂ and UiO-67-NH₂. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH₂ is a faster catalyst than UiO-67 and UiO-67-NMe₂. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.     

Determination of polycyclic and nitro musks in environmental water samples by means of microextraction by packed sorbents coupled to large volume injection-gas chromatography–mass spectrometry analysis

In this work the development and validation of a new procedure for the simultaneous determination of 9 nitro and polycyclic musk compounds: musk ambrette (MA), musk ketone (MK), musk mosken (MM), celestolide (ADBI), phantolide (AHMI), tonalide (AHTN), traseolide (ATII), cashmeran (DPMI) and galaxolide (HHCB) in environmental water samples (estuarine and wastewater) using microextraction by packed sorbent (MEPS) followed by large volume injection-gas chromatography–mass spectrometry (LVI-GC–MS) was carried out. Apart from the optimization of the different variables affecting MEPS (i.e., nature of the sorbent, nature of the solvent elution, sample load, and elution/injection volume) extraction recovery was also evaluated, not only for water samples but also for environmental water matrices such as estuarine and waste water. The use of two deuterated analogs ([²H₃]-AHTN and [²H₁₅]-MX) was successfully evaluated in order to correct matrix effect in complex environmental matrices such as influent samples from wastewater treatment plants. Method detection limits (MDLs) ranged from 5 to 25 ng L⁻¹, 7 to 39 ng L⁻¹ and 8 to 84 ng L⁻¹ for influent, effluent and estuarine samples, respectively. Apparent recoveries were higher than 75% for all target compounds in all the matrices studied (estuarine water and wastewater) and the precision of the method, calculated as relative standard deviation (RSD), was below 13.2% at 200 ng L⁻¹ concentration level and below 14.9% at low level (20 ng L⁻¹ for all the target analytes, except for AHTN which was set at 40 ng L⁻¹ and HHCB at 90 ng L⁻¹, due to the higher MDL values presented by those target compounds). Finally, this MEPS procedure was applied to the determination of the target analytes in water samples, including estuarine and wastewater, from two estuaries, Urdaibai (Spain) and Adour (France) and an established stir-bar sorptive extraction-liquid desorption/large volume injection-gas chromatography–mass spectrometry (SBSE-LD/LVI-GC–MS) method was performed in parallel for comparison. Results were in good agreement for all the analytes determined, except for DPMI.     

Kinetics of photocatalytic degradation of gaseous p-xylene on UiO-66-NH2 and LaFeO3 thin films under combined illumination of ultraviolet and visible lights

The thin film photocatalysts were prepared from solvothermal UiO-66-NH₂ and sol-gel perovskite LaFeO₃ by a dip-coating technique. The properties of obtained catalysts were investigated by the methods of Brunauer-Emmett-Teller adsorption, XRD, SEM, FT-IR, TGA, and UV-vis spectroscopies. The results proved that the thin film of the thickness of 4.2 and 4.7 µm was successfully prepared from micro-mesoporous UiO-66-NH₂ and LaFeO₃ nanocrystals. Possessing small crystals (9-35 nm) and the band gap energy of 2.83 and 1.92 eV, respectively, UiO-66-NH₂ and LaFeO₃ are shown to be a highly active visible-light photocatalyst for photodegradation of p-xylene-contained gas. The kinetics of photocatalytic degradation of p-xylene under combined illumination of ultraviolet and visible lights over obtained UiO-66-NH₂ and LaFeO₃ thin films were carried out in a gradientless flow circulating system at room temperature and atmospheric pressure. The results showed that the Langmuir-Hinshelwood kinetic model was successfully applied to correlate the obtained data. The kinetics of the reaction on both catalysts were found to be written by the fractional equation, describing the dependence of the reaction rate on the concentration of p-xylene, oxygen molecules, dissociative adsorbed water vapor, the photon flux, and the inhibition of CO₂ product. It implies that the reaction occurred at high surface coverages, molecular p-xylene, and oxygen participated in the reaction in the form of surface molecular; water—in the forms of ^•OH and H⁺. Although there is a general kinetic equation for reaction on various catalysts, the different affinities of the catalysts with the compounds present in the reaction create the kinetic feature of the reaction on each catalyst. Because of the high affinity of catalysts with water vapor, the given reactant increased the rate of p-xylene photocatalytic degradation at low concentration but inhibited it in the high concentration region. The adsorption affinity of LaFeO₃ to oxygen is higher compared to UiO-66-NH₂; then, there was an optimum concentration of oxygen in the photodegradation of p-xylene on the former, whereas in the latter monotonically increasing relationship was found.     

Application of a polysiloxane-based extraction method combined with column liquid chromatography to determine polycyclic aromatic hydrocarbons in environmental samples

Silicone rods with a diameter of 1 mm and 10 mm long were used to extract polycyclic aromatic hydrocarbons (PAHs) from water samples and for the rapid screening of highly contaminated waste material. The rods were placed in a 15 ml glass vial for the extraction of the analytes, which involved shaking (300 min⁻¹) the sample for 3 h. After extraction the rods were placed into 250 μl inserts of 2 ml vials filled with 100 μl of an acetonitrile-water mixture (4:1) and desorption was performed with sonication for 10 min. Then the PAHs were determined using LC and fluorescence detection. Recoveries of the rod extraction ranged between 62 and 97% and the detection limits were between 0.1 and 1.2 ng l⁻¹. These results are comparable with those of stir bar sorptive extraction (SBSE). Although the rods are reusable, their low price means they can be discarded if contaminated, eliminating the need for expensive cleaning. One disadvantage compared to SBSE is the longer extraction time needed to reach equilibrium.     

Backscattering light detection of nucleic acids with tetraphenylporphyrin-Al(III)-nucleic acids at liquid/liquid interface

A backscattering light (BSL) detection assembly is constructed and applied to the determination of nucleic acids with high sensitivity and selectivity based on the measurements of BSL signals at water/tetrachloromethane (H₂O/CCl₄) interface. In aqueous medium of pH 3, the binary complex of of Al(III)-DNAs could be formed by the interaction of Al(III) with the phosphate group of DNAs, which then could interact with tetraphenylporphyrin (TPP) in tetrachloromethane through liquid/liquid interaction, forming a ternary complex of TPP-Al(III)-DNAs at the interface. It was observed that greatly enhanced BSL signals occurred with maximum peak at 469 nm when the ternary complex of TPP-Al(III)-DNAs were absorbed to the liquid/liquid interface. The enhanced backscattering light intensity (I_BSL) is in proportion to the concentration of calf thymus DNA (ctDNA) and fish sperm DNA (fsDNA) in the range of 0.6-1200 ng ml⁻¹ and 1.1-1200 ng ml⁻¹, respectively. The limits of determination (3σ) are 60 pg ml⁻¹ and 110 pg ml⁻¹, correspondingly. Artificial samples with highly interference backgrounds were determined with the recovery ranging from 94.5 to 106.7%, and relative standard deviation (R.S.D.) less than 2.40%.     

An immunoassay for bisphenol A based on direct hapten conjugation to the polystyrene surface of microtiter plates

Based on direct hapten coated format a competitive indirect enzyme-linked immunosorbent assay (ciELISA) for bisphenol A (BPA) was developed. Polystyrene surface was modified by 3-Aminopropyltriethoxysilane (APTES) to produce amino groups after H₂SO₄/HNO₃-pre-treatment. 4,4-bis (4-hydroxyphenyl) valeric acid (BVA) which is analogue of BPA, was successfully immobilized on the surface of microtiter plates by N,N′-dicyclohexylcarbodiimide (DCC) method. The essential steps of the assay were optimized, especially blocking procedure which is key step to prevent unspecific binding of antibody. The results indicated that compared with hapten-protein coated format (IC₅₀ = 176.67 ng ml⁻¹, LOD = 15.90 ng ml⁻¹), the direct hapten coated format (IC₅₀ = 23.50 ng ml⁻¹, LOD = 0.27 ng ml⁻¹) could improve assay sensitivity and the detection ranges were 2.30 ng∼157.60 ng ml⁻¹ with good signal reproducibility (P value > 0.05) after careful optimization of assay conditions. Tap water samples and seawater samples were spiked with a known amount of BPA and measured by ciELISA. The average recoveries were between 70 and 142%. As far as we are aware this is the most sensitive ELISA for BPA yet reported.     

Potassium permanganate-glyoxal chemiluminescence system for flow injection analysis of cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium in pharmaceutical preparations

A sensitive flow injection chemiluminescence (FL-CL) method for the determination of cephalosporin antibiotics, was developed. The method was based on that cephalosporin antibiotics could enhance the CL reaction of glyoxal and KMnO₄ in sulfuric acid. Method development included the optimization of reagent concentrations and flow-rate. Under the optimized conditions, three cephalosporin antibiotics: cefalexin, cefadroxil, and cefazolin sodium, were determined. The detection limits of the method are 10 ng ml⁻¹ cefalexin, 2 ng ml⁻¹ cefadroxil, and 2 ng ml⁻¹ cefazolin sodium. The method was successfully applied to the determination of three cephalosporin antibiotics in pharmaceutical preparations.     

Biomethylation and biotransformation of arsenic in a freshwater food chain: Green alga (chlorella vulgaris)→shrimp (neocaridina denticulata)→killifish (oryzias iatipes)

Tolerance, bioaccumulation, biotransformation and excretion of arsenic compounds by the fresh–water shrimp (Neocaridina denticulata) and the killifish (Oryzias latipes) (collected from the natural environment) were investigated. Tolerances (LC₅₀) of the shrimp against disodium arsenate [abbreviated as As(V)], methylarsonic acid (MAA), dimethylarsinic acid (DMAA), and arsenobetaine (AB) were 1.5, 10, 40, and 150μg As ml^?1, respectively. N. denticulata accumulated arsenic from an aqueous phase containing 1 μg As ml^?1 of As(V), 10 μg As ml^?1 of MAA, 30 μg As ml^?1 of DMAA or 150 μg As ml^?1 of AB, and biotransformed and excreted part of these species. Both methylation and demethylation of the arsenicals were observed in vivo. When living N. denticulata accumulating arsenic was transferred into an arsenic–free medium, a part of the accumulated arsenic was excreted. The concentration of methylated arsenicals relative to total arsenic was higher in the excrement than in the organism. Total arsenic accumulation in each species via food in the food chain Green algae (Chlorella vulgaris) → shrimp (N. denticulata) → killifish (O. latipes) decreased by one order of magnitude or more, and the concentration of methylated arsenic relative to total arsenic accumulated increased successively with elevation in the trophic level. Only trace amounts of monomethylarsenic species were detected in the shrimp and fish tested. Dimethylarsenic species in alga and shrimp, and trimethylarsenic species in killifish, were the predominant methylated arsenic species, respectively.     

Post-Synthetic Modification of Zr-based Metal-Organic Frameworks with Imidazole: Variable Optical Behavior and Sensing

UiO-66-NH₂-IM, a fluorescent metal-organic framework (MOF), was synthesized by post-synthetic modification of UiO-66-NH₂ with 2-imidazole carboxaldehyde via a Schiff base reaction. It was examined using various characterization techniques (PXRD, FTIR, NMR, SEM, TGA, UV-Vis DRS, and photoluminescence spectroscopy). The emissive feature of UiO-66-NH₂-IM was utilized to detect volatile organic compounds (VOCs), metal ions, and anions, such as acetone, Fe³⁺, and carbonate (CO₃²⁻). Acetone turns off the high luminescence of UiO-66-NH₂-IM in DMSO, with the limit of detection (LOD) being 3.6 ppm. Similarly, Fe³⁺ in an aqueous medium is detected at LOD=0.67 μM (0.04 ppm) via quenching. On the contrary, CO₃²⁻ in an aqueous medium significantly enhances the luminescence of UiO-66-NH₂-IM, which is detected with extremely high sensitivity (LOD=1.16 μM, i. e., 0.07 ppm). Large Stern-Volmer constant, K_sv, and low LOD values indicate excellent sensitivity of the post-synthetic MOF. Experimental data supported by density functional theory (DFT) calculations discern photo-induced electron transfer (PET), resonance energy transfer (RET), inner filter effect (IFE), or proton abstraction as putative sensing mechanisms. NMR and computational studies propose a proton abstraction mechanism for luminescence enhancement with CO₃²⁻. Moreover, the optical behavior of the post-synthetic material toward analytes is recyclable.     

Synergetic effect of ZnIn2S4 nanosheets with metal-organic framework molding heterostructure for efficient visible- light driven photocatalytic reduction of Cr(VI)

The photocatalytic reduction of toxic Cr(VI), to green Cr(III) by visible light, is highly required. Metal-organic frameworks have been waged more and more devotion in the field of environmental remediation. Diversification along with functionalization is still thought-provoking and crucial for the progress of metal-organic framework (MOF)-based high activity materials. Herein, a succession of UiO-66-NH₂@ZnIn₂S₄ composites with varying amount of UiO-66-NH₂ is prepared by the facile solvothermal technique. Synergetic effect for Cr(VI) reduction is assessed under the influence of visible light (λ > 420 nm). UiO-66-NH₂ octahedron is detained by ZnIn₂S₄ nanoflakes. The obvious enhancement in activity is observed which is credited to the well-suited energy band construction and close interaction between the interface of ZnIn₂S₄ and UiO-66-NH₂, which leads to effective transfer and separation of photogenerated carriers. Synergistic effect could be evidently understood from the PL and UV -spectroscopy, after molding into heterostructure of UiO-66-NH₂@ZnIn₂S₄. In addition, UiO-66-NH₂@ZnIn₂S₄ composites exhibited good stability in photocatalytic reduction. Consequently, this UiO-66-NH₂ constructed composite has high potential in the field of environmental remediation.