Synthesis of hierarchical structured NiCo₂S₄/NSC composites via willow-catkin biotemplate for trace and highly sensitive electrochemical detection of hydroxylamine hydrochloride.

The extensive use of hydroxylamine hydrochloride (HH) in pharmaceutical, agricultural, and chemical industries has led to increasing environmental residues, posing a potential threat to public health and ecological safety. To address this issue, we developed a high-performance electrochemical sensor based on a willow-catkin-derived hierarchical hollow tubular NiCo₂S₄/NSC composite for highly sensitive detection of HH. Using willow catkins as a biomass template, the hierarchical hollow tubular NiCo₂S₄/NSC composite was synthesized through a hydrothermal-assisted bio-templated method. The material integrates the high electrical conductivity of the N, S co-doped carbon (NSC) framework, the large specific surface area offered by the biomass template, and the abundant active sites and excellent catalytic properties of the bimetallic spinel NiCo₂S₄. The electrochemical sensor constructed with this composite demonstrates outstanding performance toward HH detection, achieving a low detection limit of 2.24 nM, a wide linear range from 60 nM to 5 mM, and excellent selectivity, anti-interference capability, and stability. In real river water analysis, the sensor exhibits recoveries of 99.12%-100.4% with relative standard deviations (RSD) below 2%, indicating good practical applicability. The superior performance of the sensor is attributed to the synergistic effect between the abundant redox-active sites provided by NiCo₂S₄ and the enhanced electron-transfer capability of the NSC framework, which significantly improves interfacial reaction kinetics and reduces charge-transfer resistance. This study not only offers a highly sensitive approach for trace detection of HH, but also provides a feasible strategy for developing eco-friendly electrochemical sensors using low-cost biomass materials, showing promising potential in environmental monitoring.