Recent development and applications of differential electrochemical mass spectrometry in emerging energy conversion and storage solutions.

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal-air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS.

Regio- and stereospecific cis-hydrophenoxylation of ynamides with acidic phenols.

Herein we describe a self-acid-enabled chemo-, regio-, and stereospecific cis-hydrophenoxylation of ynamides under reagent-free conditions. The presence of a non-polar solvent such as toluene was found to be beneficial to facilitate the rate-limiting proton transfer between phenols and ynamides to form an intimate ion pair, which is followed by a swift nucleophilic attack of the phenolate oxygen on keteniminium, fulfilling the overall hydrofunctionalization event. This protocol is operationally simple and easily scalable, tolerates a wide variety of functional groups, and shows good compatibility with the requirements of modern green chemistry.

Green synthesis of carbon dots using the flowers of Osmanthus fragrans (Thunb.) Lour. as precursors: application in Fe3+ and ascorbic acid determination and cell imaging.

In this work, dried flowers of Osmanthus fragrans Lour. were applied as green precursors to synthesize carbon dots (CDs) by a green hydrothermal method for the first time. The CDs showed strong blue fluorescence at 410 nm under 340-nm excitation with a quantum yield of approximately 18.53%. Furthermore, the CDs were applied for the sensitive detection of Fe3+. The linear response of Fe3+ ranged from 10 nM to 50 µM with a limit of detection as low as 5 nM. In addition, other ions were used as competitive substances to explore the selectivity of CDs for Fe3+. The fluorescence quenching effect of Fe3+ was much stronger, which demonstrated that the CDs had high selectivity for Fe3+ and they can be employed for the selective detection of Fe3+. The potential fluorescence quenching mechanism between CDs and Fe3+ was identified as the inner filter effect. The CDs were then used as a fluorescent sensor for the detection of Fe3+ in water samples and human serum; the recovery range was 93.76-113.80% (relative standard deviation less than 0.79%). These results indicate that the CDs can be applied for the sensitive and selective detection of Fe3+ in real samples. Moreover, on the basis of the redox reaction between Fe3+ and ascorbic acid (AA), the CD-Fe3+ system can be used as a fluorescent "off-on" sensor for the detection of AA with a limit of detection of 5 µM. What is more, because of their low toxicity and biocompatibility, the CDs can also be used for cell imaging and acted as a fluorescent probe for fluorescence imaging of Fe3+ and AA in living cells. These results demonstrate that the CDs have great potential for application in the fields of sensing, bioimaging, and even disease diagnosis.

Extraction and determination of bioactive flavonoids from Abelmoschus manihot (Linn.) Medicus flowers using deep eutectic solvents coupled with high-performance liquid chromatography.

A highly efficient and ecofriendly extraction method using deep eutectic solvents was developed to extract bioactive flavonoids from Abelmoschus manihot (Linn.) Medicus flowers. First, a series of deep eutectic solvents using choline chloride as hydrogen bond acceptor with different hydrogen bond donors was successfully synthesized. Then, the types of deep eutectic solvents and the extraction conditions for bioactive flavonoids (hyperoside, isoquercitrin, and myricetin) were optimized based on the flavonoids extraction efficiencies. The optimized deep eutectic solvent for hyperoside and isoquercitrin extraction was composed of choline chloride and acetic acid with a molar ratio of 1:2. The optimized deep eutectic solvent for myricetin extraction was composed of one mole of choline chloride and two moles of methacrylic acid. The optimal extraction conditions were set as: solid to solvent ratio, 35:1 (mg/mL); extraction time, 30 min; extraction temperature, 30°C. Qualitative and quantitative analysis were performed using ultra high performance liquid chromatography with tandem mass spectrometry and high-performance liquid chromatography. And the extraction efficiencies of hyperoside, isoquercitrin, and myricetin under optimal extraction conditions were calculated as 11.57, 5.64, and 1.11 mg/g, much higher than those extracted by traditional extraction solvents. Therefore, the prepared deep eutectic solvents can be selected as alternative solvent to extract bioactive flavonoids.

A magnetic and carbon dot based molecularly imprinted composite for fluorometric detection of 2,4,6-trinitrophenol.

A magnetic molecularly imprinted composite was prepared by reverse microemulsion using carbon dots (CDs), Fe3O4 as the co-nucleus, and a molecularly imprinted polymer (MIP; with 2,4,6-trinitrophenol as the template) acting as recognition sites. The composite of type CD/Fe3O4@MIPs was characterized by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), zeta potentiometric analysis, X-ray diffraction (XRD) and vibrating sample magnetometry (VSM). The results showed that the composite MIP has a spherical shape with average diameter of 200 nm. They also showed that the composite contains core-shell structures with several Fe3O4 nanoparticles and CDs embedded in each of the microsphere. The composite can extract 2,4,6-trinitrophenol (TNP) and has an imprinting factor of 3.6. It has high selectivity and sensitivity for TNP which acts as a quencher of the fluorescence of the CDs (with excitation/emission maxima at 370/470 nm). The limit of detection of this fluorometric TNP assay is 0.5 nM. The method was successfully applied to the determination of TNP in spiked tap water and river water samples, and recoveries ranged from 89.4% to 108.5% (with an RSD of <6%). Graphical abstract Schematic representation of the magnetic molecularly imprinted composite containing fluorescent carbon dots, Fe3O4 and molecularly imprinted polymer (CD/Fe3O4@MIPs). The CD/Fe3O4@MIPs were applied to the selective and sensitive detection of 2,4,6-trinitrophenol (TNP) by fluorometry.

Novel dual functional monomers based molecularly imprinted polymers for selective extraction of myricetin from herbal medicines.

Herein, novel dual functional monomers based molecularly imprinted polymers (MIPs) were successfully prepared and used to extract myricetin from Carthamus tinctorius L., also named safflower (family, Compositae) and the flower of Abelmoschus manihot (Linn.) Medicus (family, Malvaceae). The polymers were prepared using myricetin as template, 4-vinylpyridine (4-VP) and glycidyl methacrylate (GMA) as dual functional monomers, ethylene glycol dimethyl acrylate (EGDMA) as cross-linker and methanol-acetonitrile (1:2, v/v) as solvent, respectively. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were applied to characterize the polymers. Further, the adsorption and selectivity experiments of MIPs were evaluated. The results revealed that MIPs showed high adsorption ability and selectivity toward myricetin. Finally, MIPs were employed as adsorbents for solid phase extraction (SPE) of myricetin from safflower and the flowers of A. manihot (Linn.) Medicus. Further analysis was conducted by using high performance liquid chromatography-diode array detection (HPLC-DAD). The recovery of mrricetin in safflower and in the flowers of A. manihot ranged from 79.82% to 83.91%, 81.50% to 84.32%, respectively. These results indicated that MIPs can be applied to the extraction and separation of myricetin from various complex matrixes.