Nickel nanoparticles incorporated Co, N co-doped carbon polyhedron derived from core-shell ZIF-8@ZIF-67 for electrochemical sensing of nitrite

Non-enzymatic electrochemical sensor based on ionic liquid [BMIM][PF6] functionalized zirconium‑copper bimetallic MOF composite for the detection of nitrite in food samples

In this study, we developed an electrochemical sensor utilizing a composite material consisting of zirconium‑copper bimetallic metal-organic framework functionalized with ionic liquid [BMIM][PF6]. This composite material was fabricated by simple wet impregnation method, which not only maintains excellent electrocatalytic activity but also enhances electron transfer rate and electroactive surface area. The ZrCu-MOF-818/ILs composite modified electrode has been demonstrated as an effective tool for the detection of nitrite. The electrode exhibited a remarkable limit of detection (LOD) of 0.148 μM and wide linear ranges of 6-3000 μM and 3000-5030 μM. It is worth noting that the sensor displayed excellent reproducibility and repeatability, with relative standard deviation (RSD) values of 1.06% and 1.37%, respectively. Furthermore, the proposed method was successfully applied for the detection of nitrite in tap water and pickle juice.

Decoration of alkalization-intercalated Ti3C2 with ZIF-8@ZIF-67-derived N-doped carbon nanocage for detecting 4-nitrophenol

The highly effective alk-Ti₃C₂/bimetallic Co, Zn embedded N-doped carbon (Co-Zn-NC) composite was fabricated by a convenient self-assembled method strategy and applied to  the reduction of 4-nitrophenol(4-NP). Co-Zn-NC nanocage was synthesized by using designed core-shell ZIF-8@ZIF-67 as sacrificial template. The Co-Zn-NC was prepared by pyrolysis of ZIF-8@ZIF-67 at 900 °C with high-specific surface area and hollow structure, which facilitates the dispersion of Co species and produces abundant Co-Nx active sites. In addition, the electrochemical property and specific surface area of Ti₃C₂ were improved by alkaline treatment. As a result, compared with alk-Ti₃C₂ and Co-Zn-NC, the alk-Ti₃C₂/Co-Zn-NC sensor showed higher activity and stability in detecting 4-NP. The alk-Ti₃C₂/Co-Zn-NC sensor has a wide determination range of 2-500 μM and a low detection limit of 0.23 μM for 4-NP. In addition, the newly developed alk-Ti₃C₂/Co-Zn-NC sensor displayed satisfactory reproducibility and  good stability in detecting 4-NP in aqueous samples.

A sensing platform based on Cu-MOF encapsulated Dawson-type polyoxometalate crystal material for electrochemical detection of xanthine

A promising sensing platform based on polyoxometalate-based metal-organic framework (POMOF) was established for sensitive electrochemical detection of xanthine (XA). In the unique structure of POMOF, the Dawson polyoxoanions P₂W₁₈ were encapsulated into 3D open copper-mixed ligand nanotube framework Cu-MOF, in which the cavity of the metal-organic framework provides a specific shelter to prevent the aggregation and loss of polyoxometalate in electrocatalytic reactions; meanwhile, unsaturated Cu(II) active sites of Cu-MOF can also serve as electrocatalytic active center. The POMOF-based sensor (CuMOFP₂W₁₈/XC-72R) was fabricated by using acetylene black (XC-72R) as a support material to enhance the conductivity of POMOF. The performances of the POMOF-based sensor were studied by using different electrochemical testing methods. The composite displayed remarkable electrocatalytic activity for the oxidation of XA due to the synergistic effect of polyoxometalate (POM) and metal-organic framework (MOF). The electrochemical sensor demonstrated a wide linear range (0.5 μM-240 μM), low detection limit (0.26 μM), and excellent selectivity for detecting XA. Furthermore, the composite further demonstrated excellent reproducibility and great stability. More importantly, the proposed sensor was utilized to detect XA in real samples, which may provide a new way for early disease diagnosis.

Binary organic-inorganic nanocomposite of polyaniline-MnO2 for non-enzymatic electrochemical detection of environmental pollutant nitrite

Due to wide usage as nitrogen fertilizer in agriculture and food additive in industry, nitrite, as one of inorganic environmental pollutants, could cause detrimental effects to the ecological environment. Therefore, accurate, sensitive and rapid detection of nitrite is necessary. In this work, binary hybrid polyaniline-MnO₂ organic-inorganic nanocomposite is prepared chemically and characterized via X-ray diffraction spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Polyaniline-MnO₂ organic-inorganic nanocomposite serves as excellent electrode modifier for electrochemical sensing of nitrite by two modes of cyclic voltammetry and chronoamperometry, achieving broad linear ranges and low limits of detection for both methods. Moreover, the organic-inorganic nanocomposite displays satisfactory sensing performance in real water sample analysis. Amine and imino groups of polyaniline contribute to the better adsorption behavior of nitrite onto the nanocomposite, which improves the nanocomposite's sensing performance. In summary, the synergistic effects between polyaniline and MnO₂ is taken advantaged in the nanocomposite for effective electrochemical sensor development.

Core-shell Cu@C@ZIF-8 composite: a high-performance electrode material for electrochemical sensing of nitrite with high selectivity and sensitivity

Herein, an efficient electrochemical sensing platform is proposed for selective and sensitive detection of nitrite on the basis of Cu@C@Zeolitic imidazolate framework-8 (Cu@C@ZIF-8) heterostructure. core-shell Cu@C@ZIF-8 composite was synthesized by pyrolysis of Cu-metal-organic framework@ZIF-8 (Cu-MOF@ZIF-8) in Ar atmosphere on account of the difference of thermal stability between Cu-MOF and ZIF-8. For the sensing system of Cu@C@ZIF-8, ZIF-8 with proper pore size allows nitrite diffuse through the shell, while big molecules cannot, which ensures high selectivity of the sensor. On the other hand, Cu@C as electrocatalyst promotes the oxidation of nitrite, thereby resulting high sensitivity of the sensor. Accordingly, the Cu@C@ZIF-8 based sensor presents excellent performance for nitrite detection, which achieves a wide linear response range of 0.1-300.0μM, and a low limit of detection of 0.033μM. In addition, the Cu@C@ZIF-8 sensor possesses excellent stability and reproducibility, and was employed to quantify nitrite in sausage samples with recoveries of 95.45%-104.80%.