Confined synthesis of g-C3N4 modified porous carbons for efficient removal of Cd ions.

Carbon nitride (C3N4) nanosheets have excellent adsorption capacity, environmental friendliness, and high stability for heavy metal removal. However, its application in Cd-polluted soil is difficult as aggregation induces the specific surface area to substantially decrease. In this study, a series of C3N4 nanosheet-modified porous carbons (C3N4/PC-X) were prepared by a simple one-step calcination of mixed aerogels with different mass ratios (X) of carboxymethyl cellulose (CMC) and melamine. These were based on the confined effect of the CMC aerogel, whose 3D confined region controls the C3N4 morphology and prevents the aggregation of nanosheets. The resulting C3N4/PC-4 exhibited a porous structure with interpenetrating C3N4 nanosheets and carbon rods. C3N4/PC-4 was characterized by SEM, elemental analysis, XRD, FTIR and XPS, and the existence of C3N4 nanosheets was confirmed. Compared with that of unmodified porous carbons, the adsorption capacity of C3N4/PC-4 for Cd ions increased 3.97 times, up to 273.1 mg/g. The adsorption kinetics and adsorption isotherm analyses showed that the adsorption properties were in agreement with the quasi-second-order and Freundlich adsorption models. Moreover, the material had a good passivation effect on the Cd ions in the soil. The confined synthesis of aerogels could be extended to the preparation of other nanostructures.

A sensitive ratiometric fluorescent sensor based on carbon dots and CdTe quantum dots for visual detection of biogenic amines in food samples.

A novel dual-emission ratiometric fluorescent sensor for biogenic amines (BAs) was prepared by simple mixing blue fluorescent carbon dots (CDs) and yellow fluorescent CdTe quantum dots (CdTe QDs). Based on different sensitive properties of pH, CdTe QDs and CDs were used as the response signal and internal reference signal, respectively. The developed ratiometric fluorescent sensor achieved quantitative analysis of eight kinds of BAs with rapid response (30 s) and low limits of detection (1.259-5.428 µM). Furthermore, color-tunable fluorescent test strips were constructed by easily assembling CDs and CdTe QDs onto filter paper. The obtained smart label showed a distinguishable fluorescent color variation from blue to green during the corruption of shrimp samples. The smart label with advantages of convenience and rapidness provided a method for visually monitoring the freshness of food samples.

Colorimetric and ratiometric fluorescent dual-mode sensitive detection of Hg2+ based on UiO-66-NH2@Au composite.

A colorimetric and ratiometric fluorescent dual-mode assay is constructed for sensitive and specific Hg2+ sensing based on UiO-66-NH2 and Au composite (UiO-66-NH2@Au). The addition of Hg2+ stimulates the peroxidase-like activity of UiO-66-NH2@Au by the formation of Au-Hg amalgam, promoting the oxidizing of chromogenic substrate OPD to DAP with the aid of H2O2, which lead to the change of colorimetric and fluorescent signals. The absorbance of the sensing system at 450 nm is linear positive correlation with Hg2+ concentration of 30-1400 nM and the color of the solution under visible light shaded from light yellow to dark yellow. With the increase of Hg2+ concentration, the fluorescence signal at 570 nm (DAP) increased whereas that at 455 nm (intrinsic fluorescence of UiO-66-NH2) decreased due to inner filter effect (IFE), the fluorescence intensity ratio (F455/F570) decreasing linearly with Log [Hg2+] over the range 60-1700 nM; the fluorescence emission of sensing system under UV excitation changed from blue to yellow, which can easily be discerned visually. This assay was successfully applied to the determination of Hg2+ in tap water and river water. The results indicate that the colorimetric and ratiometric fluorescent dual-mode assay based on UiO-66-NH2@Au realized visual determination of Hg2+ rapidly and reliably, revealed application prospect in Hg2+ monitoring.

Regenerable magnetic aminated lignin/Fe3O4/La(OH)3 adsorbents for the effective removal of phosphate and glyphosate.

Phosphates and organophosphorus cause environmental pollution, and excessive phosphate leads to water eutrophication. Glyphosate, an organophosphorus herbicide, harms the environment and human health. In this study, regenerable magnetic AL/Fe3O4/La(OH)3 adsorbents were developed by modifying Fe3O4 and La(OH)3 on aminated lignin (AL) for phosphate and glyphosate removal. The adsorption capacity for phosphate and glyphosate reached 60.36 mg g-1 and 83.87 mg g-1 when the initial concentrations were 150 mg L-1 and 250 mg L-1, respectively. The thermodynamic data showed that adsorption is a spontaneous and endothermic process. Adsorption can be applied at pH values ranging from 3 to 11 and is more suitable under acidic conditions. Fe3O4 and La(OH)3 both enhanced the adsorption capacities of phosphate and glyphosate. Phosphate and glyphosate compete slightly when coexisting in the adsorption process at low concentrations. Due to the magnetic properties of Fe3O4, the adsorbents can be separated rapidly and effectively with an external magnetic field. 89% adsorption capacity remained after four adsorption-desorption recycles. Thus, AL/Fe3O4/La(OH)3 shows potential for phosphate and glyphosate removal as an effective and reusable adsorbent.

A simple and sensitive sensor for lactose based on cascade reactions in Au nanoclusters and enzymes co-encapsulated metal-organic frameworks.

In this work, one kind of zeolite imidazole frameworks containing bovine serum albumin stabilized Au nanoclusters (AuNCs), ß-galactosidase (ß-Gal) and glucose oxidase (GOx) (AuNCs/ß-Gal/GOx@ZIF-8) were obtained to detect lactose. Compared with other fluorescent nano-materials, AuNCs show distinct advantages as a guest species in ZIF-8, specifically their extremely small size (<1 nm), simple synthesis, excellent biocompatibility and high stability. Furthermore, the bovine serum albumin on their surfaces can promote the formation of ZIF-8 coating; thus, AuNCs were co-encapsulated in ZIF-8 with the enzymes together. X-ray diffraction (XRD) analysis indicates the composite possesses the similar crystalline structure with pure ZIF-8. Fluorescence microscope images, Fourier transform infrared spectra and energy dispersive X-ray spectroscopy indicate the presence of AuNCs in the composite. Owing to the high local concentrations of the fluorescent probe and the quenching agent in AuNCs/ß-Gal/GOx@ZIF-8, the quenching rate was enhanced 3.4-fold that of free AuNCs and enzymes in solution.

Fluorometric determination of mercury(II) based on dual-emission metal-organic frameworks incorporating carbon dots and gold nanoclusters.

Carbon dots and gold nanoclusters co-encapsulated by zeolitic imidazolate framework-8 (CDs/AuNCs@ZIF-8) have been obtained at room temperature. The composite has been applied to the ratiometric fluorescence determination of mercury(II). The composite shows fluorescence emission maxima at 440 and 640 nm under 360 nm excitation, due to the CDs and AuNCs, respectively (associated quantum yields were 18% and 17%, respectively). In the presence of Hg2+, the fluorescence at about 640 nm is quenched, while the fluorescence at about 440 nm is unaffected. The CDs/AuNCs@ZIF-8 composite allows the sensitive detection of Hg2+, with the fluorescence intensity ratio (I640/I440) decreasing linearly with Hg2+ concentration over the range 3-30 nM. The fluorescence emission of the composite changes color from red to blue with increasing Hg2+ under UV excitation, which can easily be discerned visually. This visual detection of Hg2+ is due to the high fluorescence quantum yields of the CDs and AuNCs and the ~ 200 nm separation between the two emission maxima. Graphical abstract (A) Schematic diagram showing the operating principle of the determination for Hg(II). (B) Digital graph of the solutions in absence and presence of 30 nM Hg(II) under a portable UV lamp.

A simple aptamer-based fluorescent aflatoxin B1 sensor using humic acid as quencher.

This work described a fluorometric and aptamer-based assay for aflatoxin B1 (AFB1). Aptamer-modified carbon dots (DNA-CDs) were first synthesized as fluorescence probes, then reacted with humic acid (HAs) which acted as quencher of the blue fluorescence of the CDs. It was found that HAs can readily adsorb ssDNA aptamers due to the presence of a rich surface chemistry (quinoidal units, aromatic rings and sugar moieties). This resulted in quenching of the fluorescence of the CDs (with excitation/emission peaks at 360/450 nm), probably due to π interactions. If the nanoprobe was reacted with AFB1, the DNA-CDs detached from the HAs and fluorescence was restored. Under optimized experimental conditions, the assay had a linear response in the 0.1-0.8 ng mL-1 AFB1 concentration range, with a low limit of detection of 70 pg mL-1.

An electrochemical immunosensor based on an etched zeolitic imidazolate framework for detection of avian leukosis virus subgroup J.

A novel sandwich-type electrochemical immunosensor for avian leukosis virus subgroup J (ALV-J) is described. The immunosensor was prepared by first modifying a glassy carbon electrode (GCE) with reduced graphene oxide that was functionalized with tannic acid and magnetite nanoparticles (rGO-TA-Fe3O4). Primary antibodies (Ab1) were then deposited on the modified GCE. Hollow zeolitic imidazolate framework (eZIF) crystals functionalized with tannic acid and carrying secondary antibodies (Ab2) and horseradish peroxidase (HRP) were used for signal amplification. The hollow eZIF crystals were found to be an excellent carrier for both Ab2 and HRP, prompting the wider use of metal organic frameworks in electrochemical sensing. Under optimal conditions, the immunoassay afforded a detection range from 152 to 10,000 TCID50 mL-1 (where TCID50 is the 50% tissue culture infective dose) and a low detection limit of 140 TCID50 mL-1 (at S/N = 3). The immunoassay is highly selective for ALV-J, and it demonstrates excellent reproducibility and operational stability. The practicability of the immunoassay for the fast detection of ALV-J was confirmed in experiments with spiked avian serum samples. Graphical abstract Schematic of a sandwich-type electrochemical immunosensor for avian leukosis virus subgroup J (ALV-J). It consists of reduced graphene oxide, tannic acid and magnetite as the sensing platform, and an etched zeolitic imidazolate framework carrying horseradish peroxidase for signal amplification.

A novel pH-responsive electrochemiluminescence immunosensor for ALV-J detection based on hollow MnO2 encapsulating Ru(bpy)3Cl2.

A novel pH-responsive sandwich-type electrochemiluminescence immunosensor was successfully developed for the detection of avian leukosis virus subgroup J (ALV-J). The immunosensor consisted of graphene oxide functionalized with tannic acid (rGO-TA) and primary antibodies (Ab1) as the main ALV-J sensing platform. For signal amplification, pH-responsive hollow MnO2 (hMnO2) nanospheres encapsulating Ru(bpy)3Cl2 and carrying secondary antibodies (Ab2) were employed. Under optimal conditions, the immunosensor exhibited a wide ALV-J detection range of 101.80 to 104.30 TCID50/mL (TCID50: 50% tissue culture infective dose) and a low detection limit of 101.71 TCID50/mL (S/N = 3). Importantly, the immunosensor showed high sensitivity, good reproducibility and excellent operational stability. Finally, the immunosensor was evaluated using a real avian serum sample containing ALV-J, with excellent results being achieved.

A sensitive fluorescent sensor for selective determination of dichlorvos based on the recovered fluorescence of carbon dots-Cu(II) system.

In this paper, a simple and sensitive fluorescent sensor for dichlorvos was first constructed based on carbon dots-Cu(II) system. These carbon dots were obtained by simple hydrothermal reaction of feather. The fluorescence of these carbon dots can be selectively quenched by Cu(2+) ion. When acetylcholinesterase and acetylthiocholine were introduced into the system, thiocholine came into being, which can react with Cu(2+) ion and restore the fluorescence of the system. The reaction mechanism between Cu(2+) ion and thiocholine was confirmed by X-ray photoelectron spectroscopy. As one kind of acetylcholinesterase inhibitor, organophosphorus pesticides can be detected based on this sensing system. As an example of organophosphorus pesticides, dichlorvos was detected with a linear range of 6.0×10(-9)-6.0×10(-8)M. This sensing system has been successfully used for the analysis of cabbage and fruit juice samples.

Innovative approach for the electrochemical detection of non-electroactive organophosphorus pesticides using oxime as electroactive probe.

An innovative approach for sensitive and simple electrochemical detection of non-electroactive organophosphorus pesticides (OPs) was described in this report. The novel strategy emphasized the fabrication of an oxime-based sensor via attaching pralidoxime (PAM) on graphene quantum dots (GQDs) modified glassy carbon electrode. The introduction of GQDs significantly increased the effective electrode area, and then enlarged the immobilization quantity of PAM. Thus, the oxidation current of PAM was obviously increased. Relying on the nucleophilic substitution reaction between oxime and OPs, fenthion was detected using PAM as the electroactive probe. Under optimum conditions, the difference of oxidation current of PAM was proportional to fenthion concentration over the range from 1.0×10(-11)M to 5.0×10(-7)M with a detection limit of 6.8×10(-12)M (S/N=3). Moreover, the favorable detection performance in water and soil samples heralded the promising applications in on-site OPs detection.

A simple and sensitive fluorescent sensor for methyl parathion based on L-tyrosine methyl ester functionalized carbon dots.

In this paper, a simple and sensitive fluorescent sensor for methyl parathion is developed based on L-tyrosine methyl ester functionalized carbon dots (Tyr-CDs) and tyrosinase system. The carbon dots are obtained by simple hydrothermal reaction using citric acid as carbon resource and L-tyrosine methyl ester as modification reagent. The carbon dots are characterized by transmission electron microscope, high resolution transmission electron microscopy, X-ray diffraction spectrum, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The carbon dots show strong and stable photoluminescence with a quantum yield of 3.8%. Tyrosinase can catalyze the oxidation of tyrosine methyl ester on the surface of carbon dots to corresponding quinone products, which can quench the fluorescence of carbon dots. When organophosphorus pesticides (OPs) are introduced in system, they can decrease the enzyme activity, thus decrease the fluorescence quenching rate. Methyl parathion, as a model of OPs, was detected. Experimental results show that the enzyme inhibition rate is proportional to the logarithm of the methyl parathion concentration in the range 1.0×10(-10)-1.0×10(-4) M with the detection limit (S/N=3) of 4.8×10(-11) M. This determination method shows a low detection limit, wide linear range, good selectivity and high reproducibility. This sensing system has been successfully used for the analysis of cabbage, milk and fruit juice samples.

Electroenzymatic oxidation of bisphenol A (BPA) based on the hemoglobin (Hb) film in a membraneless electrochemical reactor.

This paper presents a novel electroenzymatic method for the treatment of bisphenol A (BPA) in a membraneless electrochemical reactor. The electrochemical reactor was arranged with a stainless steel and an enzymatic film as anode and cathode, respectively. The enzymatic film was formed by immobilizing hemoglobin (Hb) on carbon fiber. In the membraneless electrochemical reactor, hydrogen peroxide (H(2)O(2)) was generated in situ in cathode and BPA was oxidated and removed by the combining Hb with H(2)O(2). The experimental conditions for electrogeneration of H(2)O(2) and electroremoval of BPA were optimized. Experimental results showed that in supplied voltage 2.4 V, pH 5.0 and oxygen flow rate 25 mL/min, the electrogeneration of H(2)O(2) and the electroenzymatic removal of BPA were highest. Under optimal operation conditions, the removal efficiency of BPA reached 50.7% in 120 min and then kept constant when further prolonging the period of reaction. Compared with electrochemical and biochemical methods, the removal of BPA through electroenzymatic method was comparatively favorable.