Methenamine Hippurate

This paper presents the synthesis of a novel corn-stalk-like MnO₂/CoNi oxide composite using an in situ epitaxial attachment growth strategy, in which CoNi oxide nanosheets are anchored onto MnO₂ nanowires. The one-dimensional MnO₂ nanowires, with their large specific surface area, serve as a support to enhance the electronic conductivity of the CoNi oxides. Hexamethylenetetramine (HMTA) is employed as an alkaline linking agent, playing a key role in shaping the CoNi oxide nanosheets and ensuring their successful growth on the MnO₂ nanowires. The MnO₂/CoNi oxide composite-based electrochemical sensor exhibits excellent synergistic and interfacial effects, promoting electron transfer and charge migration. This composite material shows outstanding electrocatalytic performance for hydrazine detection, with a broad linear range (0.48-6106.58 μM), low detection limit (0.286 μM, S/N = 3), and high sensitivity (0.037 μA μM⁻¹). Moreover, when tested for hydrazine detection in water samples, the sensor achieved a recovery rate of 95.7-105 %, highlighting its high sensitivity and rapid response in practical applications.

Ammonia nitrogen is one of the most important indicators for evaluating the quality of water bodies. It is very difficult to determine ammonia nitrogen directly by Surface-enhanced Raman spectroscopy (SERS) in practice. In order to realize SERS determination of ammonia nitrogen, in this paper, SERS combined with density functional theory (DFT) was used to investigate why ammonia nitrogen needs to be derivatized to hexamethylenetetramine (HMTA) and why HMTA can be determined using SERS. The molecular electrostatic potential (MEP) results exhibit that there was no adsorption site on the surface of ammonia nitrogen, whereas its derivate HMTA had four available adsorption sites. This provides a basic guarantee for the SERS detection of HMTA. The molecular adsorption state of HMTA on the gold nanoparticles surface was concluded from the binding energies, the bond length, and the Raman activity spectra. Among them, the HMTA-Au₄ complex has the lowest bond energy (-586.873 Kcal/mol) and the shortest bond length (2.161 Å), which is the most stable state and its Raman activity spectrum is the closest to the experimental data. Calculations results of frontier molecular orbital (FMO) demonstrate that the energy gap of HMTA and HMTA-Au₄ complex are 0.30258 eV and 0.10947 eV, respectively, with a really obvious difference between them, which indicates that the HMAT-Au₄ complex possessed higher chemical reactivity. In addition, charge transfer phenomenon on the MEP of HMTA-Au₄ complex was deduced due to the change in the symmetry of its charge distribution, which can be explained the mechanism of chemical enhancement in the detection of HMTA by SERS. The selective enhancement at 1048 cm^-1 peaks in theoretical spectrum and at 1044 peaks cm^-1 in experimental spectrum provided theoretical and practical basis for indirect determination of ammonia nitrogen by SERS. The obtained results will help to better understand the reasons why some components are difficult to be directly determined by SERS, and why these components need to be derivatized. It provides a new method for components that are difficult to detect by SERS.