Photochemiresistor Sensor Development Based on a Bismuth Vanadate Type Semiconductor for Determination of Chemical Oxygen Demand

Heating and ultraviolet irradiation: Gas pressure meter-based analytical system for on-site and rapid monitoring of permanganate index (CODMn)

Permanganate index (CODMn) is one of the important indicators of surface water quality measurement. Herein, a portable analytical system was developed for on-site and rapid analysis of CODMn, organic substances in water were oxidized and transformed into gases, so that CODMn concentration was converted into a change of gas pressure signal, the pressure signal change was further detected by a gas pressure meter. Heating method and ultraviolet (UV) irradiation method were used as assisting technologies for oxidization of organic substances by acidic KMnO4, a linear range of 2-150 mg l-1 and a detectable limit of 2 mg l-1 were obtained. Those methods were further applied to the detection of CODMn in various water samples (lake waters and domestic sewage) and certified reference water samples (BWZ 6974-2016C and BWZ 7617-2016), with recoveries of 89-111 %. Among them, a portable analytical system based on UV irradiation gas pressure meter was further established and used for the analysis of CODMn in field. It is a promising analytical system/device for CODMn monitoring in field, offering advantages of low-cost, easy-operation, portability and rapidness.

Spectrophotometric determination of COD based on synergistic photocatalysis redox reaction using titanium dioxide nanoparticles and phosphomolybdic heteropoly acid

Chemical oxygen demand (COD) is one of the important indicators to measure the degree of organic pollution in water. In this work, a rapid spectrophotometric method for detection of COD was achieved based on the oxidation of organics in water by photogenerated holes or free radicals and the reduction of phosphomolybdic heteropolyacid by photogenerated electrons by using TiO2 nanoparticles as a photocatalyst. Taking potassium hydrogen phthalate as the COD standard, under the optimal conditions, the absorbance of reduced phosphomolybdic heteropoly acid was linear with COD in the range of 0.50-100 mg L -1. The detection limit for was COD detection was 0.171 mg L -1. The proposed methods was used for the determination of COD in real water samples, and the results were in general agreement with the national standard method. Compared with the direct photo initiated reduction of phosphomolybdic heteropoly acid without TiO2 nanoparticles, the photocatalytic reaction has better stability and higher efficiency.

Relationship, importance, and development of analytical techniques: COD, BOD, and, TOC in water—An overview through time

Analytical techniques to measure organic matter in water, such as Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD5), and Total Organic Carbon (TOC) are widely used. Modifications have been proposed to make them faster, more sensitive, and more environmentally friendly. The purpose of producing a review over some time is to show the changes made on the standardized methods of each of these techniques, and to highlight the relationship between them in the process of ascertaining organic matter in water. Modifications to techniques COD and BOD entail several factors that need to be considered, namely: time, miniaturization, sensitivity, use of environmentally friendly reagents. Changes to TOC are focused on detection systems. Despite the advantages obtained by the modified techniques, traditional methods continue to be widely used, in most cases due to the lack of standardization of the new methods.

Graphic Abstract

Developing the sensing features of copper electrodes as an environmental friendly detection tool for chemical oxygen demand

The chemical oxygen demand (COD) of water bodies is an essential indicator of organic contaminants. The majority of current testing methods have the drawbacks of requiring multiple processes, being time-consuming, and requiring the use of harmful and hazardous reagents. In this work, a low-cost copper wire (Cu-wire) electrode was designed and fabricated to be used as a sensing electrode for the detection of chemical oxygen demand in water. The sensing features were developed by electrodeposition of copper nanoparticles (nano-Cu) that were prepared by fast-scan cyclic voltammetry (FSCV) deposition at the optimum preparation conditions. For improving the adherence and stability of the deposited nano-Cu thin layer, the Cu-wire electrode was scratched to increase the surface roughness. The surface morphology of the prepared nano-Cu/Cu-wire electrode was investigated by scanning electron microscope (SEM). Energy-dispersive X-ray spectrometer (EDX) was used for elemental analysis characterization. The non-modified and the nano-copper modified electrode were utilized and optimized for electrochemical assay of COD using glycine as a standard in 0.075 M NaOH as an electrolyte solution. The calibration curves (COD, mg L-1 vs. I, mA) were plotted from linear sweep voltammetry (LSV) and chronoamperometry (I-t) curves for a wide range of COD under the optimized conditions. It shows that the electroanalytical features of the proposed nano-Cu-based COD sensor exhibit a linear range from 2 to 595 mg L-1 and a lower limit of detection (LOD) of 2.6 mg L-1 (S/N = 3). The established electrochemical method demonstrated a high tolerance level to Cl- ions where 1.0 M Cl- exhibited a negligible influence. The sensor was employed for detecting the COD in diverse real water samples and the attained results were validated using the standard dichromate method. The obtained results could open the window toward using simple and cost effective tools in order to monitor the water quality.

Rapid Potentiometric Detection of Chemical Oxygen Demand Using a Portable Self-Powered Sensor Chip

Chemical oxygen demand (COD) is an important indicator of organic pollutants in water bodies. Most of the present testing methods have the disadvantages of having complicated steps, being time-consuming, and using toxic and hazardous substances. In this work, rapid potentiometric detection of chemical oxygen demand (COD) using a portable self-powered sensor chip was successfully developed. The indium tin oxide (ITO) electrode was etched by laser, and the photocatalytic materials TiO₂/CuS and Pt were modified onto the photoanode and the cathode to prepare the sensor chip. Based on the principle of photocatalytic degradation, organic pollutants can be oxidized by TiO₂/CuS, and the concentration will affect the generated voltage. The quantitative detection of COD in the range of 0.05-50 mg/L can be rapidly achieved within 5 min by a miniature device. Besides good portability and sensitivity, the proposed sensor also has the advantages of environmental friendliness and ease of use, which is an ideal choice for the on-site detection of water pollution.

Determination of Chemical Oxygen Demand (COD) Using Nanoparticle-Modified Voltammetric Sensors and Electronic Tongue Principles

This manuscript reports the use of nanoparticle-modified voltammetric sensors for the rapid and green determination of chemical oxygen demand in river waters and waters from agricultural waste. Four different variants of modified electrodes have been prepared: CuO nanoparticles electrogenerated over Cu and covered with Nafion film (CuO/Cu-Nf), and graphite–epoxy composites modified with Cu, CuO, and Cu–Ni alloy nanoparticles. The response features of these electrodes were assessed by calibrating them vs. glucose, glycine, ethyleneglycol, and hydrogenphtalate in alkaline media, as samples providing different difficulty in their (bio)degradation characteristics. The most sensitive electrode was demonstrated to be the (CuO/Cu-Nf) electrode, with an LOD of 12.3 mg O2·L−1. The joint information provided by the sensor array showed the ability of estimating both the organic load and the type of sample in terms of difficulty of degradation, in what can be named an intelligent sensor assembly.