Dispersed copper nanoparticles promote the electron mobility of nitrogen-rich graphitized carbon aerogel for electrochemical determination of 4-nitrophenol

Nitrophenols in the environment: An update on pretreatment and analysis techniques since 2017

Nitrophenols, a versatile intermediate, have been widely used in leather, medicine, chemical synthesis, and other fields. Because these components are widely applied, they can enter the environment through various routes, leading to many hazards and toxicities. There has been a recent surge in the development of simple, rapid, environmentally friendly, and effective techniques for determining these environmental pollutants. This review provides a comprehensive overview of the latest research progress on the pretreatment and analysis methods of nitrophenols since 2017, with a focus on environmental samples. Pretreatment methods include liquid-liquid extraction, solid-phase extraction, dispersive extraction, and microextraction methods. Analysis methods mainly include liquid chromatography-based methods, gas chromatography-based methods, supercritical fluid chromatography. In addition, this review also discusses and compares the advantages/disadvantages and development prospects of different pretreatment and analysis methods to provide a reference for further research.

A novel core-shell composite of PCN-222@MIPIL for ultrasensitive electrochemical sensing 4-nonylphenol

A novel core-shell composite of PCN-222 and molecularly imprinted poly (ionic liquid) (PCN-222@MIPIL) with high conductivity and selectivity was prepared for electrochemical sensing 4-nonylphenol (4-NP). The electrical conductivities of some MOFs including PCN-222, ZIF-8, NH₂-UIO-66, ZIF-67, and HKUST-1 were explored. The results indicated that PCN-222 had the highest conductivity and was then used as a novel imprinted support. PCN-222@MIPIL with core-shell and porous structure was synthesized using PCN-222 as support and 4-NP as template. The average pore volume of PCN-222@MIPIL was 0.085 m³ g^-1. In addition, the average pore width of PCN-222@MIPIL was from 1.1 to 2.7 nm. The electrochemical response for PCN-222@MIPIL sensor for 4-NP was 2.54, 2.14, and 4.24 times that of non-molecularly imprinted poly (ionic liquid) (PCN-222@NIPIL), PCN-222, and MIPIL sensors, respectively, which result from superior conductivity and imprinted recognition sites of PCN-222@MIPIL. The current response of PCN-222@MIPIL sensor to 4-NP concentration from 1 × 10^-4 to 10 μM presented an excellent linear relationship. The detection limit of 4-NP was 0.03 nM. The synergistic effect between the PCN-222 supporter with high conductivity, specific surface area and shell layer of surface MIPIL results in the outstanding performance of PCN-222@MIPIL. PCN-222@MIPIL sensor was adopted for detecting 4-NP in real samples and presented to be a reliable approach for determining 4-NP.

Preparation of Copper Nanoplates in Aqueous Phase and Electrochemical Detection of Dopamine

Compared with gold and silver, cheap copper has attracted more attention and can potentially be applied in non-enzymatic electrochemical sensors due to its excellent conductivity and catalytic activity. In this paper, copper nanoplates were rapidly synthesized using copper bromide as the copper precursor, polyethyleneimine as the stabilizer, and ascorbic acid as a reducing agent in the presence of silver nanoparticles at a reaction temperature of 90 °C. The Cu nanoplates with an average side length of 10.97 ± 3.45 μm were obtained after a short reaction time of 2 h, demonstrating the promoting effect of an appropriate amount of silver nanoparticle on the synthesis of Cu nanoplates. Then, the electrochemical dopamine sensor was constructed by modifying a glass carbon electrode (GCE) with the Cu nanoplates. The results obtained from the test of cyclic voltammetry and chronoamperometry indicated that the Cu-GCE showed a significant electrochemical response for the measurement of dopamine. The oxidation peak current increased linearly with the concentration of dopamine in the range of 200 µmol/L to 2.21 mmol/L, and the corresponding detection limit was calculated to be 62.4 μmol/L (S/N = 3). Furthermore, the anti-interference test showed that the dopamine sensor was not affected by a high concentration of ascorbic acid, glucose, uric acid, etc. Therefore, the constructed Cu-GCE with good selectivity, sensitivity, and stability possesses a high application value in the detection of dopamine.

Eco-friendly non-conjugated polymer dots for chemiluminometric determination of 4-nitrophenol

Polymer dots (PDs) are a new family of quantum dots which their behavior and potential applications have not yet been completely explored. In this study, non-conjugated PDs were synthesized via a simple pyrolysis method and used for the chemiluminescence (CL) assay of 4-nitrophenol (4-NP). PDs increase the CL signal of the Ce (IV)-Na₂ SO₃ reaction 39-fold. Using the CL spectrum, it was concluded that the emission at 434 nm was generated by the excited PDs (PDs^* ), which are produced via energy transfer from SO₂ ^* to PDs. Our experiments showed that 4-NP enhanced the CL signal of the Ce (IV)-Na₂ SO₃ -PDs reaction. The mechanism of this effect was explored by obtaining CL, UV-Vis and FT-IR spectra. Due to the high sensitivity and selectivity of the CL system to 4-NP, a probe was designed to determine 4-NP in the linear range of 1.0-500 nmol/L with a detection limit of 0.33 nmol/L. Different spiked real samples were successfully analyzed by this probe.

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.

Silk fibroin-derived carbon aerogels embedded with copper nanoparticles for efficient electrocatalytic CO2-to-CO conversion

Metal-carbon matrix catalyst has attracted a great deal of interest in electrochemical carbon dioxide reduction reaction (CO₂RR) due to its excellent electrocatalytic performance. However, the design of highly active metal-carbon matrix catalyst towards CO₂RR using natural biomass and cheap chemical precursors is still under challenge. Herein, a self-assembly strategy, along with CO₂ gas as acidifying agent, to fabricate silk fibroin (SF) derived carbon aerogels (CA) combining trace copper nanoparticles (SF-Cu/CA) is developed. Zinc nitrate was introduced as a pore-forming agent to further optimize the pore structure of the as-prepared catalysts to form SF-Cu/CA-1. The rich mesoporous structure and unique constitute of SF-Cu/CA-1 is conducive to exposed numerous active sites, fast electron transfer rate, and the desorption of *CO intermediate, thus leading to the electrocatalytic CO₂RR of SF-Cu/CA-1 catalyst with an excellent current density of 29.4 mA cm^-2, Faraday efficiency of 83.06% towards carbon monoxide (CO), high the ratio value of CO/H₂ (19.58), and a long-term stability over a 10-hour period. This performance is superior to that of SF-Cu/CA catalyst (13.0 mA cm^-2, FE_CO=58.43%, CO/H₂ = 2.16). This work not only offers a novel strategy using natural biomass and cheap chemicals to build metal-carbon matrix catalyst for electrocatalytic CO₂-to-CO conversion, but also is expected to promote the industrial-scale implementations of CO₂ electroreduction.

Facile in situ redox synthesis of Au@Fe2O3 nanocomposites with multifunctional catalytic activity

Using freshly synthesized Fe(OH)2 matrix and HAuCl4 as precursor, l-lysine as stabilizer and linker, Au nanoparticles coated onto γ-Fe2O3 substrate were in-situ synthesized at room temperature. The Au@Fe2O3 hybrid composites with small highly dispersed gold particles (∼3 nm) exhibited high catalytic activity towards 4-nitrophenol reduction and the oxidation of benzyl alcohol. The results indicated the rate constant for 4-nitrophenol reduction was 5.3 × 10−2 s−1, and displayed efficient catalytic performance in terms of turnover number (TOF) of 134.8 h−1 for the oxidation of benzyl alcohol at 90 ± 1 °C. Furthermore, the facial electrode potential-driven in situ synthesis method paved the way of other metal nanoparticles over Fe2O3.

Selective C–C coupling of terminal alkynes under an air atmosphere without base over Cu–NX–C catalysts

Highly dispersed copper nanoparticles supported on mesoporous nitrogenated carbon were synthesized and exhibited superior catalytic activity towards aerobic oxidative coupling of terminal alkynes.