The development of a reagentless electrode system for the determination of nitrate is presented. The approach is based upon the deposition of a macroporous copper deposit which shows marked selectivity for nitrate ion under mildly acidic conditions (pH 3) with a linear range extending from 10 to 200 μM nitrate. Fabrication of the layer is both inexpensive and simple and is relatively substrate independent (Cu, Au, glassy carbon) as the response is attributed to the electrodeposited support. The influence of potential interferents such as chloride, nitrite and complexing agents such as citric acid were examined. In particular, the reduction of nitrite was found to occur at potentials significantly less negative than those required for nitrate reduction and as a result clear resolution of both voltammetric peaks is obtainable. The lack of direct interference between the two ions combined with wide peak separation (200 mV) provides a system that may offer some potential in speciation studies. The analytical applicability of the proposed system was demonstrated through the standard addition determination of nitrate in a number of authentic samples with the nitrate concentrations independently corroborated using established Griess assay spectroscopic protocols.

The development of suitable approaches for the synthesis of ultrathin transition-metal dichalcogenide (TMD) catalysts is required to engineer phases, intercoupling between different phases, in-plane defects, and edges and hence maximize their catalytic performance for hydrogen production. In this work, we report a simple one-step hydrothermal approach for the synthesis of a three-dimensional (3D) network of self-assembled metallic MoS₂/MoO₃ nanosheets, using α-MoO₃ and thiourea (TU) as the Mo and S precursors, respectively. A systematic structural/property relationship study, while varying the precursors’ molar concentration ratios (TU/MoO₃) and reaction temperatures (T_R), revealed a kinetically controlled regime, in hydrothermal synthesis, that enabled the formation of ultrathin branched MoS₂/MoO₃ nanosheets with the highest metallic content of ∼47 % in a reproducible manner. Importantly, the work established that in addition to the rich metallic MoS₂ phase (1T), the electronically coupled interfaces between MoO₃ and MoS₂ nanodomains, profusion of active sites, and tuned electrical conductivity significantly contributed to hydrogen evolution reaction (HER)-catalytic activity, affording a low overpotential of 210 mV (with respect to the reversible hydrogen electrode) at a current density of 10 mA/cm², a small Tafel slope of ∼50 mV/dec, and high stability. Overall, this work demonstrated a controllable one-step hydrothermal method for the rational design and synthesis of a 3D network of MoS₂/MoO₃ nanosheets with high 1T-MoS₂ metallic yield, simultaneous incorporation of MoO₃/MoS₂ heterointerfaces, sulfur vacancies, and tuned electrical conductivity, which are highly beneficial for clean energy conversion applications that can potentially be expanded to other two-dimensional TMD materials.