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Excessive intake of nitrite is a serious risk to human health. Research on the method of detecting nitrite in food is of great significance to avoid this issue. In this work, we report a colorimetric method based on iodide-mediated etching of gold nanostars (Au NSs) for the determination of nitrite with high selectivity and sensitivity. In the presence of iodide, the strong affinity between iodide and Au NSs results in the rapid etching of Au NSs into spherical gold nanoparticles, resulting in significant changes in the surface plasmon resonance (SPR) spectrum and the solution color. Because nitrite can oxidize iodide under acidic conditions, the etching degree of Au NSs could be controlled by adding different nitrite concentrations to consume iodide, leading to quantitative detection of nitrite. Under the optimal conditions, nitrite exhibits a good linear relationship with the absorption ratio (

Trivalent chromium is generally assumed to form insoluble species, resulting in low mobility of Cr(III) in soils. Here, we report continuous distributions (0-19 m) of a high concentration of Cr(III) in the alkaline soils of a historically industrial site for producing Na

Identification of sulfonamides (SAs) residues in food is vital for human health. A set of 4-channel sensor array was constructed by carbon dots (CDs) embedded in photonic crystal molecularly imprinted (PCMIP@CDs) film which included 3 PCMIP@CDs units and 1 PCNIP@CDs unit to determine typical SAs: sulfadimethoxine, sulfathiazole, sulfaguanidine, sulfamethazine, sulfadiazine. Under the optimal conditions, the response time of the sensor array was only 200 s. Moreover, 300 fluorescence response signals (4 sensor units × 5 sulfonamides × 3 concentrations × 5 repeats) were processed by pattern recognition technique to analyze the ability of the sensor array to recognize 5 kinds of SAs. Subsequently, the linear discrimination analysis (LDA) method was used to identify the five SAs simultaneously with 100 % classification accuracy and the limit of detection was 0.01-0.26 nmol/L. Moreover, the proposed method can effectively identify-five SAs in water and fish samples.

A colorimetric method combining WSe2 nanosheets with peroxidase-like activity and xanthine oxidase (XAO) was developed for xanthine detection. XAO catalyzes xanthine oxidation and thereby induces H2O2 production. WSe2 nanosheets can catalyze the oxidization of 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 and produce a blue oxidation product of TMB (oxTMB). Under optimal conditions, the colorimetric method showed a linear response for xanthine detection in a range of 0.01–0.5 mM. The limit of detection was 4.37 μM. The recovery rate from spiked serum samples was 95.5%–115.5%. Therefore, our strategy provides new opportunities for the detection of xanthine and evaluation of health care.

β-Lactoglobulin (β-Lg), a food allergen, can easily cause allergic reactions in infants and young children. Therefore, it is necessary to develop a rapid, sensitive, and selective detection method to protect individuals prone to allergies. In this paper, a fluorescence assay based on WS

A colorimetric approach is developed for the detection of hydrogen sulfide (H2S) in water samples based on copper-metal–organic frameworks (Cu-MOFs) and a smartphone.

The emerging animal-derived biochar (AB) has shown potential for mitigating the contamination of cationic heavy metals, but has no affinity to oxyanionic metals. In this study, we developed an AB/ferrihydrite composite with a AB/Fe mass ratio of 4.0 (ABF-4) for the simultaneous adsorption of cationic Pb(II)/Cd(II) and anionic As(III). ABF-4 is a type of hydroxyapatite-rich biochar coated with nanoscale iron hydroxide aggregates. The adsorption of Pb(II), Cd(II), and As(III) on ABF-4 were 2.64, 1.55, and 0.48 mmol/g, and were 135%, 150%, and 4500% higher than those of pure AB, respectively. The enhanced adsorption of Pb(II) and Cd(II) by ABF-4 is partially due to the increase in surface area and micropores. The nano-sized ferrihydrite on ABF might help form surface complexation with As(III) and oxidize As(III) to As(V). In multimetal systems, Pb(II) and Cd(II) can promote As(III) adsorption due to the formation of NaPb

In this work, the mechanism of Pb(II)-mediated precipitation transformation to improve the removal of Cr(VI)-oxyanion on biogenic hydroxyapatite (BHAp) were investigated. The Pb(II)-preloading formed pyromorphite [Pb5(PO4)3Cl] precipitate on the BHAp surface (Pb@BHAp), thus causing an increase of 2.2 times in the uptake of Cr(VI) by Pb@BHAp at pH of 2.4. It was primarily due to the dissolution of Pb5(PO4)3Cl accompanied with the release of Pb(II), resulting in the rapid formation of crocoite (PbCrO4). Although the Ksp of Pb5(PO4)3Cl was approximately 23 orders of magnitude lower than that of PbCrO4, Pb(II)-mediated precipitation transformation could still occur. XRD and SEM-EDX analyses demonstrated that the process was a time-dependent that included rapid crystal precipitation in the initial 10 min and subsequent precipitate accumulation for several hours. The Pb(II) released from the dissolution of Pb5(PO4)3Cl was immediately immobilized by Cr(VI); therefore, it did not cause any retention risk of Pb(II) in the solution. Furthermore, a small quantity of Cr(VI) could be reduced to Cr(III) by BHAp, and Cr(III) could enter into the BHAp lattice for the exchange of Ca(II). This study provides a new insight into the resource utilization of Pb-bearing BHAp and a potential method for the successive removal of Pb(II) and Cr(VI).

The organization of nanoparticles (NPs) with controlled chemical composition and size distribution into well-defined sheets will find many practical applications, but the chemistry remains problematic. Therefore, we report a facile method to assemble NPs to free-floating two-dimensional (2D) nanosheets with a superlattice and thicknesses reaching 22.8 nm. The ligand oleic acid is critical in the formation of nanosheets. As assembled, these free-floating 2D nanosheets remain intact in both polar and nonpolar solvents, e.g., deionized water, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, toluene, hexane, and chloroform, without any disassembly. Compared to Fe(3)O(4) NP building blocks, these 2D nanosheets show more favorable catalytic properties and enhanced catalytic reactivity, which can be exploited to mimic natural enzymes. Our work is expected to open up a new avenue for synthesizing free-floating 2D supersheets by NP assembly, leading to a new generation of materials with enriched functions and broader applications.

In this study, the adsorption behaviors and mechanisms of Pb(II) and Zn(II) by animal-derived biochar (ADB) in single and binary metal systems were comparatively investigated. ADB contains considerable amounts of Ca/P components and is mainly composed of hydroxyapatite (HAP), which plays an important role in the adsorption of Pb(II) and Zn(II). The maximum adsorption capacities of Pb(II) and Zn(II) on ADB were in the order of Zn(II)-single (3.23 mmol g−1) > Pb(II)-single (2.74 mmol g−1) ≈ Pb(II)-binary (2.71 mmol g−1) > Zn(II)-binary (2.31 mmol g−1). In the single metal system, approximately 99.9% of the adsorbed Pb(II) existed as Pb5(PO4)3Cl, while the dominant adsorption mechanism of Zn(II) was cation exchange, followed by precipitation, accounting for 78.0%–80.6% and 19.4%–21.5% of the adsorption capacity, respectively. These findings were verified by X-ray diffraction refinement, X-ray photoelectron spectroscopy, metal speciation modeling, and Ca(II) exchange experiment. In the binary metal system, the proportion and form of Pb(II) precipitate remained unchanged. However, the binding of Zn(II) to ADB was completely dependent on the cation exchange with Ca(II), and no remarkable Zn(II) precipitation was observed. Phosphate released from HAP preferentially precipitated with Pb(II) than with Zn(II) when they coexisted. Consequently, Pb(II) competition may alter the Zn(II) adsorption mechanism on ADB. Nonetheless, ADB could serve as an efficient biochar for the simultaneous immobilization of Pb(II) and Zn(II) via different mechanisms.

Lead ion (Pb(II)) has emerged as a major mussel pollutant in recent decades, thus the development of sensors capable of detecting Pb(II) is of considerable interest. In this work, a novel, rapid, and “turn-on” phosphorescent sensor was developed to monitor Pb(II) using metal-organic framework-5 (MOF-5, Zn4O(TPA)3, TPA: terephthalic acid) as a highly selective and sensitive luminescent probe. A mechanism describing the leaching of Zn(II) from Zn4O complexes and self-assembly of TPA after Pb(II) coordination is proposed for the MOF-5-Pb(II) system. Using enhanced phosphorescence, the sensor displays a wide linear detection range of 0.01−10 μmol/L and a low detection limit of 2 nmol/L for the determination of Pb(II). Moreover, it is noteworthy that when immobilized in a polyethylene glycol (PEG) film, the MOF-5 probe exhibited a visually distinct color change at 1.0 μmol/L Pb(II) under 365 nm UV light. From these results, a test strip was prepared for semi-quantitative analysis of Pb(II) content. Finally, the proposed phosphorescent sensor was successfully utilized to detect Pb(II) content in mussel. This study demonstrates the first MOF-based “turn-on” phosphorescent sensor for monitoring Pb(II), from which future high-performance phosphorescent sensors to determine food pollutants may be developed.

In this work, a traditional and natural polymer, chitosan (CS) is reported as an efficient hole-scavenger that enhances the photoelectrochemical (PEC) properties of tungsten trioxide (WO3) for Co2+ detection in water. Decoration of WO3/fluorine-doped tin oxide (FTO) electrodes with CS remarkably improves the visible-light absorption and enhances the photo electron–hole separation efficiency of WO3, giving rise to significant photocurrent enhancement. Moreover, by taking the advantage of the strong chelating ability of CS, Co2+ can be extracted effectively from water by using the CS/WO3/FTO material. The introduction of Co2+ prevents CS from consuming the oxidative holes, resulting in a decrease of the photocurrent. Enlightened by this, we developed a sensitive and selective PEC method for tracing of Co2+ in the range of 1.0 to 60.0 μmol L−1, with a detection limit of 0.3 μmol L−1 (S/N = 3). In addition, based on a systematic study, we proposed a possible mechanism for the PEC process on CS/WO3/FTO. This work may provide new insight into the use of natural polymers as electron donors and specific chelating agents in PEC sensors, in addition to expanding the application of the PEC approach in the field of environmental and biological analysis.