Simultaneous electrochemical determination of nitrophenol isomers based on macroporous carbon functionalized with amino-bridged covalent organic polycalix[4]arenes

A voltammetric sensor based on a reduced graphene oxide/β-cyclodextrin/silver nanoparticle/polyoxometalate nanocomposite for detecting uric acid and tyrosine

In the present work, an electrochemical sensor based on reduced graphene oxide/β-cyclodextrin/silver nanoparticle/polyoxometalate (RGO-CD-AgNP-POM) was developed for the simultaneous detection of uric acid (UA) and L-tyrosine (L-Tyr). First, an RGO-CD-AgNP-POM nanocomposite was synthesized via a simple photoreduction method and characterized by transmission electron microscopy (TEM), energy dispersive X-ray imaging (EDS), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). As an electrode material, RGO-CD-AgNP-POM showed wide linear ranges (0.5-500 μM for UA, and 1-400 μM for L-Tyr) and relatively low detection limits (0.11 μM for UA, and 0.23 μM for L-Tyr). In addition, the combination of supramolecular recognition from CD and excellent electrochemical performances from RGO, AgNPs and POM was expected to enhance the sensing performances toward UA and L-Tyr in real samples with favorable recovery ranges (99%-104%). This nanocomposite provides a new platform for developing the family of electrode materials.

Facile synthesis of yellow-green fluorescent silicon nanoparticles and their application in detection of nitrophenol isomers

A clear formation mechanism is essential for the controllable synthesis of nanomaterials with different optical properties, which is also one of the challenges facing the preparation of fluorescent silicon nanomaterials. In this work, a one-step room temperature synthesis method was established to prepare yellow-green fluorescent silicon nanoparticles (SiNPs). The obtained SiNPs exhibited excellent pH stability, salt tolerance, anti-photobleaching ability and biocompatibility. Based on X-ray photoelectron spectroscopy, transmission electron microscopy, ultra high performance liquid chromatography tandem mass spectrometry and other characterization data, the formation mechanism of the SiNPs was proposed, which provided a theoretical basis and important reference for the controllable preparation of SiNPs and other fluorescent nanomaterials. In addition, the obtained SiNPs illustrated excellent sensitivity for nitrophenol isomers, the linear range of o-nitrophenol, m-nitrophenol, p-nitrophenol was 0.05-600 μM, 20-600 μM and 0.01-600 μM under the λ_ex and λ_em were set as 440 nm and 549 nm, and related limit detection was 16.7 nM, 6.7 μM and 3.3 nM, respectively. The developed SiNP-based sensor achieved satisfactory recoveries in detecting nitrophenol isomers in a river water sample, showing great promise in practical applications.

Tungstic acid-functionalized polycalix[4]resorcinarene as a cavity-containing hyper-branched supramolecular and recoverable acidic catalyst in 4H-pyran synthesis

In this study, tungstic acid immobilized on polycalix[4]resorcinarene, PC4RA@SiPr-OWO₃H, as a mesoporous acidic solid catalyst was synthesized and investigated for its catalytic activity. Polycalix[4]resorcinarene was prepared via a reaction between formaldehyde and calix[4]resorcinarene, and then the resulting polycalix[4]resorcinarene was modified using (3-chloropropyl)trimethoxysilane (CPTMS) to obtain polycalix[4]resorcinarene@(CH₂)₃Cl that was finally functionalized with tungstic acid. The designed acidic catalyst was characterized by various methods including FT-IR spectroscopy, energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), elemental mapping analysis and transmission electron microscopy (TEM). The catalyst efficiency was evaluated via the preparation of 4H-pyran derivatives using dimethyl/diethyl acetylenedicarboxylate, malononitrile, and beta-carbonyl compounds, confirmed by FT-IR spectroscopy and ¹H and ¹³C NMR spectroscopy. The synthetic catalyst was introduced as a suitable catalyst with high recycling power in 4H-pyran synthesis.

Pre-Anodized Graphite Pencil Electrode Coated with a Poly(Thionine) Film for Simultaneous Sensing of 3-Nitrophenol and 4-Nitrophenol in Environmental Water Samples

A very simple, as well as sensitive and selective, sensing protocol was developed on a pre-anodized graphite pencil electrode surface coated using poly(thionine) (APGE/PTH). The poly(thionine) coated graphite pencil was then used for simultaneous sensing of 3-nitrophenol (3-NP) and 4-nitrophenol (4-NP). The poly(thionine) coated electrode exhibited an enhanced electrocatalytic property towards nitrophenol (3-NP and 4-NP) reduction. Redox peak potential and current of both nitrophenols were found well resolved and their simultaneous analysis was studied. Under optimized experimental conditions, APGE/PTH showed a long linear concentration range from 20 to 230 nM and 15 nM to 280 nM with a calculated limit of detection (LOD) of 4.5 and 4 nM and a sensitivity of 22.45 µA/nM and 27.12 µA/nM for 3-NP and 4-NP, respectively. Real sample analysis using the prepared sensor was tested with different environmental water samples and the sensors exhibited excellent recovery results in the range from 98.16 to 103.43%. Finally, the sensor exposed an promising selectivity, stability, and reproducibility towards sensing of 3-NP and 4-NP.