In situ synthesis of hierarchical platinum nanosheets-polyaniline array on carbon cloth for electrochemical detection of ammonia

Electroactive RuPt NPs programmed dual-channel electrochemical sensor for methyl mercaptan monitoring

The accurate and sensitive detection of methyl mercaptan (CH3SH) was of great significance for food corruption monitoring. Electroactive labels engineered electrochemical sensors possessed tailorable electrochemical responses, and showed potential prospects for CH3SH monitoring. In comparison to a single electrochemical signal, electroactive nanocomposites with multiple electrochemical responses not only provided multi-channel sensing signals for accurate detection, but also increased the peak intensity for sensitive detection. Herein, RuPt NPs were designed and explored to possess two independent and non-interfering electrochemical oxidation peaks at 0.75 V and -0.73 V. The formation of metal-SH covalent bonds between electroactive sites of RuPt NPs and CH3SH induced the changes of two electrochemical oxidation peaks. By utilizing the sum intensity of two electrochemical peaks as detection signal, a dual-channel electrochemical sensor was established for CH3SH detection in the range of 1 μM-1 mM, and had a low limit of detection (LOD) of 300 nM. This work gave a new insight into promoting more electroactive nanocomposites with multiple signals for accurate and sensitive electrochemical detection applications.

Development of Betalain-immobilized polylactic acid nanofibers as a green and sustainable sensor for toxic ammonia

Ammonia has been an important industrial colorless agent. Exposure to gaseous ammonia results in organ damage or even death. Herein, an environmentally friendly colorimetric detector for aqueous and gaseous ammonia was prepared utilizing vapochromic polylactic acid nanofibers. Betalain (BTN) has been reported as a natural probe that can be extracted from the beetroot plant (Beta vulgaris L.). Mordant (M)/BTN coordinating complex nanoparticles were produced in situ by depositing the Betalain probe onto polylactic acid (PLA) nanofibers. The colorimetric change of the Betalain-dyed PLA nanofibers from red to yellow when exposed to ammonia was examined using both absorbance spectra and coloration parameters. The PLA membrane displayed a detection limit of 5-400 ppm. Upon exposure to ammonia, the absorbance spectra of the nanofibrous membrane showed a hypsochromic shift, moving from 572 nm to 402 nm with an isosbestic wavelength of 466 nm. Scanning electron microscopy (SEM) analysis demonstrated that the nanofibrous membrane had diameters of 100-350 nm. Transmission electron microscopy (TEM) analysis of the M/BTN particles revealed diameters of 10-13 nm. After immobilizing the M/BTN nanoparticles onto the nanofibrous membrane, no substantial variations in the bend length and air permeability were observed. The colorfastness of the Betalain-dyed nanofibrous membrane showed satisfactory results.

A Highly Selective Ammonia Ratiometric Fluorescence Sensor Based on Multifunctional Metal-Organic Framework Platform with Rich Brønsted Acidic Metal Clusters

Ammonia is a critical chemical in industry and our daily life, but its corrosiveness and toxicity also require enough attention. With the increasing pursuit of beauty, the safety of cosmetics has aroused widespread concern. Aqueous ammonia has been widely used as a universal additive in cosmetics, especially in different types of hair dye products. However, a high concentration of ammonia is toxic to human beings. In addition, improper treatment and discharge of substances with high ammonia content can also cause pollution of human domestic water. Therefore, it is of great significance to accurately monitor the level of aqueous ammonia in relative cosmetics for safe beauty and in our domestic water for daily health. In this work, a highly selective and sensitive ratiometric fluorescent sensor UiO-66-NH2@O170 was carefully designed to quickly and accurately detect the concentration of aqueous ammonia in different brands of hair dyes and human domestic water. The detection limit was as low as 83.5 nM, and the recovery rate ranged from 98.2 to 102.9%. In addition, while evaluating the actual application performance of the sensor, a novel detection mechanism based on the rich Brønsted acidic response sites on the metal clusters of the fluorescent MOF materials was demonstrated here.

Sensitive Electrochemical Detection of Ammonia Nitrogen via a Platinum-Zinc Alloy Nanoflower-Modified Carbon Cloth Electrode

As a common water pollutant, ammonia nitrogen poses a serious risk to human health and the ecological environment. Therefore, it is important to develop a simple and efficient sensing scheme to achieve accurate detection of ammonia nitrogen. Here, we report a simple fabrication electrode for the electrochemical synthesis of platinum-zinc alloy nanoflowers (PtZn NFs) on the surface of carbon cloth. The obtained PtZn NFs/CC electrode was applied to the electrochemical detection of ammonia nitrogen by differential pulse voltammetry (DPV). The enhanced electrocatalytic activity of PtZn NFs and the larger electrochemical active area of the self-supported PtZn NFs/CC electrode are conducive to improving the ammonia nitrogen detection performance of the sensitive electrode. Under optimized conditions, the PtZn NFs/CC electrode exhibits excellent electrochemical performance with a wide linear range from 1 to 1000 µM, a sensitivity of 21.5 μA μM-1 (from 1 μM to 100 μM) and a lower detection limit of 27.81 nM, respectively. PtZn NFs/CC electrodes show excellent stability and anti-interference. In addition, the fabricated electrochemical sensor can be used to detect ammonia nitrogen in tap water and lake water samples.

Electrochemically Grown Ultrathin Platinum Nanosheet Electrodes with Ultralow Loadings for Energy-Saving and Industrial-Level Hydrogen Evolution

Nanostructured catalyst-integrated electrodes with remarkably reduced catalyst loadings, high catalyst utilization and facile fabrication are urgently needed to enable cost-effective, green hydrogen production via proton exchange membrane electrolyzer cells (PEMECs). Herein, benefitting from a thin seeding layer, bottom-up grown ultrathin Pt nanosheets (Pt-NSs) were first deposited on thin Ti substrates for PEMECs via a fast, template- and surfactant-free electrochemical growth process at room temperature, showing highly uniform Pt surface coverage with ultralow loadings and vertically well-aligned nanosheet morphologies. Combined with an anode-only Nafion 117 catalyst-coated membrane (CCM), the Pt-NS electrode with an ultralow loading of 0.015 mgPt cm-2 demonstrates superior cell performance to the commercial CCM (3.0 mgPt cm-2), achieving 99.5% catalyst savings and more than 237-fold higher catalyst utilization. The remarkable performance with high catalyst utilization is mainly due to the vertically well-aligned ultrathin nanosheets with good surface coverage exposing abundant active sites for the electrochemical reaction. Overall, this study not only paves a new way for optimizing the catalyst uniformity and surface coverage with ultralow loadings but also provides new insights into nanostructured electrode design and facile fabrication for highly efficient and low-cost PEMECs and other energy storage/conversion devices.

Detection and removal technologies for ammonium and antibiotics in agricultural wastewater: Recent advances and prospective

With the extensive development of industrial livestock and poultry production, a considerable part of agricultural wastewater containing tremendous ammonium and antibiotics have been indiscriminately released into the aquatic systems, causing serious harms to ecosystem and human health. In this review, ammonium detection technologies, including spectroscopy and fluorescence methods, and sensors were systematically summarized. Antibiotics analysis methodologies were critically reviewed, including chromatographic methods coupled with mass spectrometry, electrochemical sensors, fluorescence sensors, and biosensors. Current progress in remediation methods for ammonium removal were discussed and analyzed, including chemical precipitation, breakpoint chlorination, air stripping, reverse osmosis, adsorption, advanced oxidation processes (AOPs), and biological methods. Antibiotics removal approaches were comprehensively reviewed, including physical, AOPs, and biological processes. Furthermore, the simultaneous removal strategies for ammonium and antibiotics were reviewed and discussed, including physical adsorption processes, AOPs, biological processes. Finally, research gaps and the future perspectives were discussed. Through conducting comprehensive review, future research priorities include: (1) to improve the stabilities and adaptabilities of detection and analysis techniques for ammonium and antibiotics, (2) to develop innovative, efficient, and low cost approaches for simultaneous removal of ammonium and antibiotics, and (3) to explore the underlying mechanisms that governs the simultaneous removal of ammonium and antibiotics. This review could facilitate the evolution of innovative and efficient technologies for ammonium and antibiotics treatment in agricultural wastewater.

Ultramicro Interdigitated Array Electrode Chip with Optimized Construction for Detection of Ammonia Nitrogen in Water

Ammonia nitrogen is a common contaminant in water and its determination is important for environmental protection. In this paper, an electrochemical sensor based on an ultramicro interdigitated array electrode (UIAE) chip with optimized construction was fabricated with Micro-Electro-Mechanical System (MEMS) technology and developed to realize the detection of ammonia nitrogen in water. The effects of spacing-to-width ratio and width of the working electrode on UIAE's electrochemical characteristics and its ammonia nitrogen detection performance were studied by finite element simulation and experiment. The results demonstrated that the smaller the spacing-to-width ratio, the stronger generation-collection effect, and the smaller the electrode width, the stronger the edge effect, which led to an easier steady-state reach, a higher response current, and better ammonia nitrogen determination performance. The fabricated UIAE chip with optimized construction showed the linear detection range of 0.15 mg/L~2.0 mg/L (calculated as N), the sensitivity of 0.4181 μA·L·mg^-1, and good anti-interference performance, as well as a long lifetime. UIAE based on bare Pt was successfully applied to ammonia nitrogen detection in water by optimizing structure, which might broaden the methods of ammonia nitrogen detection in water.

Electrochemical sensing mechanism of ammonium ions over an Ag/TiO2 composite electrode modified by hematite

Here, we demonstrate a new electrochemical sensing mechanism of ammonium ions (NH₄⁺) involving a two-electron oxygen reduction reaction (ORR) and a hydrazine reaction. The NH₄⁺ are electrooxidized to hydrazine by H₂O₂ derived from the ORR over a self-supporting Ag/TiO₂ nanotube array composite electrode modified by hematite (Ag/Fe₂O₃/TNTs). The Ag/Fe₂O₃/TNT sensor exhibits a high sensitivity of 1876 µA mM^-1 cm^-2 with a detection limit of 0.18 µM under non-alkaline conditions, a short response time of 3 s, good reproducibility, and fine selectivity among various interferents, and is also successfully used in real water bodies to display high accuracy. Furthermore, this new mechanism has a certain universality in a range of Ag (main catalyst)/transition metal oxide (cocatalyst)/TNT sensing systems. This work offers a new design basis for the urgently needed electrochemical ammonia nitrogen sensors.

A High-Performance Self-Supporting Electrochemical Biosensor to Detect Aflatoxin B1

High-performance electrochemical biosensors for the rapid detection of aflatoxin B1 (AFB₁) are urgently required in the food industry. Herein, a multi-scaled electrochemical biosensor was fabricated by assembling carboxylated polystyrene nanospheres, an aptamer and horseradish peroxidase into a free-standing carbon nanofiber/carbon felt support. The resulting electrochemical biosensor possessed an exceptional performance, owing to the unique structures as well as the synergistic effects of the components. The 3D porous carbon nanofiber/carbon felt support served as an ideal substrate, owing to the excellent conductivity and facile diffusion of the reactants. The integration of carboxylated polystyrene nanospheres with horseradish peroxidase was employed as a signal amplification probe to enhance the electrochemical responses via catalyzing the decomposition of hydrogen peroxide. With the aid of the aptamer, the prepared sensors could quantitatively detect AFB₁ in wine and soy sauce samples via differential pulse voltammetry. The recovery rates of AFB₁ in the samples were between 87.53% and 106.71%. The limit of detection of the biosensors was 0.016 pg mL^-1. The electrochemical biosensors also had excellent sensitivity, reproducibility, specificity and stability. The synthetic strategy reported in this work could pave a new route to fabricate high-performance electrochemical biosensors for the detection of mycotoxins.

Wireless Volatile Organic Compound Detection for Restricted Internet of Things Environments Based on Cataluminescence Sensors

Cataluminescence-based sensors do not require external light sources and complex circuitry, which enables them to avoid light scattering with high sensitivity, selectivity, and widely linear range. In this study, a wireless sensor system based on hierarchical CuO microspheres assembled from nano-sheets was constructed for Volatile Organic Compound (VOC) online detection. Through sensor characteristics and data process analysis, the results showed that the luminous sensor system has good luminous characteristics, including the intensity of visible light, high signal/noise (S/N) values, and very short response and recovery times. Different VOC concentration values can be detected on multiple wavelength channels and different Cataluminescence signal spectra separations can process multiple sets of Cataluminescence data combinations concurrently. This study also briefly studied the mechanism action of the Cataluminescence sensor, which can specifically be used for VOC detecting.