Performance improvement in chemical oxygen demand determination using carbon fiber felt/CeO2-β-PbO2 electrode deposited by cyclic voltammetry method

An integrated smartphone-based electrochemical detection system for highly sensitive and on-site detection of chemical oxygen demand by copper-cobalt bimetallic oxide-modified electrode

A portable and integrated electrochemical detection system has been constructed for on-site and real-time detection of chemical oxygen demand (COD). The system mainly consists of four parts: (i) sensing electrode with a copper-cobalt bimetallic oxide (CuCoOx)-modified screen-printed electrode; (ii) an integrated electrochemical detector for the conversion, amplification, and transmission of weak signals; (iii) a smartphone installed with a self-developed Android application (APP) for issuing commands, receiving, and displaying detection results; and (iv) a 3D-printed microfluidic cell for the continuous input of water samples. Benefiting from the superior catalytic capability of CuCoOx, the developed system shows a high detection sensitivity with 0.335 μA/(mg/L) and a low detection limit of 5.957 mg/L for COD determination and possessing high anti-interference ability to chloride ions. Moreover, this system presents good consistency with the traditional dichromate method in COD detection of actual water samples. Due to the advantages of cost effectiveness, portability, and point-of-care testing, the system shows great potential for water quality monitoring, especially in resource-limited remote areas.

PbO2 materials for electrochemical environmental engineering: A review on synthesis and applications

Lead dioxide (PbO₂) materials have been widely employed in various fields such as batteries, electrochemical engineering, and more recently environmental engineering as anode materials, due to their unique physicochemical properties. Key performances of PbO₂ electrodes, such as energy efficiency and space-time yield, are influenced by morphological as well as compositional factors. Micro-nano structure regulation and decoration of metal/non-metal on PbO₂ is an outstanding technique to revamp its electrocatalytic activities and enhance environmental engineering efficiency. The aim of this review is to comprehensively summarize the recent research progress in the morphology control, the structure constructions, and the element doping of PbO₂ materials, further with many environmental application cases evaluated. Concerning electrochemical environmental engineering, the lead dioxide employed in chemical oxygen demand detection, ozone generators, and wastewater treatment has been comprehensively reviewed. In addition, the future research perspectives, challenges and the opportunities on PbO₂ materials for environmental applications are proposed.

Two-step facile synthesis of Co3O4@C reinforced PbO2 coated electrode to promote efficient oxygen evolution reaction for zinc electrowinning

The conventional Pb-Ag alloy possesses a high oxygen evolution reaction overpotential, poor stability, and short service life in acidic solutions, making it an unsuitable sort of anode material for the zinc electrowinning process. Therefore, a layered carbon-covered cobalt tetroxide (Co3O4@C)-reinforced PbO2-coated electrode is fabricated via a facile two-step pyrolysis-oxidation and subsequent electrodeposition process. As a result, the reinforced PbO2-coated electrode exhibits a low OER overpotential of 517 mV at 500 A m-2 and a Tafel slope of 0.152 V per decade in a zinc electrowinning simulation solution (0.3 M ZnSO4 and 1.53 M H2SO4). The reduced overpotential of 431 mV at 500 A m-2 compared to traditional Pb-0.76%Ag alloy leads to improved energy savings, which is attributable to the presence of Co3O4@C to refine the grain size and thus increase the effective contact area. Moreover, the reinforced PbO2-coated electrode has a prolonged service life of 93 h at 20 000 A m-2 in 1.53 M H2SO4. Therefore, an accessible and efficient strategy for preparing a coated electrode to improve OER performance for zinc electrowinning is presented in this research.

Fabrication of a multi-layer CNT-PbO2 anode for the degradation of isoniazid: Kinetics and mechanism

In this study, the CNTs were successfully compounded in PbO₂ electrode through composite electrodeposition technology to obtain multi-layer CNT-PbO₂ electrode. Scanning electron microscope, X-ray diffraction and X-ray Photoelectron Spectroscopy were comprehensively used to characterize the lead dioxide electrode and the electrochemical performance were also tested by cyclic voltammetry, and electrochemical impedance spectroscopy. Results showed that CNT-PbO₂ significantly improved the electrochemical performance, which was attributed to that the compound of CNTs in PbO₂ improved the active sites on the surface, with higher oxidation peaks, smaller particle size, larger specific surface area, and lower charge transfer resistance. In the degradation experiment, the chemical oxygen demand removal efficiency of isoniazid by CNT-PbO₂ electrode were 1.37 times of that by pure PbO₂ electrode. The main influence factors on the degradation of ISN, such as initial ISN concentration, Na₂SO₄ concentration, current density and initial pH value was analyzed in detail. Considered comprehensively the effects of ISN removal efficiency, COD and average current efficiency, the degradation of ISN and COD reached 99.4% and 86.8%, respectively, after the electrode was degraded by electrochemical oxidation for 120 min under the best conditions. In addition, the degradation mechanism of ISN in electrochemical oxidation was studied. According to the intermediate products detected by GC-MS, the possible degradation pathway of ISN in electrochemical oxidation system were proposed.

A Self-Supported CuO/Cu Nanowire Electrode as Highly Efficient Sensor for COD Measurement

A self-supported CuO/Cu nanowire electrode (CuO/CuNWE), which was prepared by annealing Cu nanowires to form a porous Cu nanowire electrode (CuNWE) and then anodizing the as-prepared CuNWE in alkaline medium to generate Cu(OH)₂ nanowires followed by calcination, was employed for chemical oxygen demand (COD) determination using cyclic voltammetry (CV). The structure and electrochemical behavior of the CuO/CuNWE were investigated by scanning electron microscopy, X-ray diffraction, and CV. The results indicated that the as-synthesized CuO/CuNWE, in which CuO nanowires with a length of several micrometers and a diameter of 100 to 300 nm could be found, was stable in alkaline medium and more electrocatalytically active for oxidizing a wide range of organic compounds in comparison with the CuNWE. Under optimized alkaline concentration and scan rate, the CuO/CuNWE exhibited a good performance for COD measurement, with a linear range of 5 to 1153 mg L⁻¹, a sensitivity of 2.46× 10⁻² mA /(mg L⁻¹), and a detection limit of about 2.3 mg L⁻¹. In addition, an excellent correlation was observed in COD values obtained by our method and the classic dichromate method (r = 0.9995, p < 0.01, n = 11). Finally, our method was successfully used to measure the COD values in real water samples, showing great potential for practical application in water pollution control.