Study on photocatalytic oxidation for determination of chemical oxygen demand using a nano-TiO2-K2Cr2O7 system

A photocatalytic method for the determination of chemical oxygen demand (COD) using a nano-TiO₂-K₂Cr₂O₇ system is described. The measuring principle is based on direct determination of the change of Cr(III) concentration resulting from photocatalytic oxidation of organic compounds and simultaneous photocatalytic reduction of stoichiometrically involved K₂Cr₂O₇ in the solution. The operation conditions were optimized. The determinative COD value using this method was calculated from the absorbance of Cr(III). The operational characteristics of this method were demonstrated by use of a standard glucose solution as substrate. This method was also applied to the determination of the COD of wastewater samples. The results were in good agreement with those from the conventional (i.e., dichromate) COD methods.     

A solid composite electrode for the determination of the electrochemical oxygen demand of aqueous samples

A composite electrode containing graphite, paraffin, AgO and CuO is described for the determination of the electrochemical oxygen demand (EOD) of waste waters. The oxidation of dissolved organic compounds at the electrode is based on a heterogeneous chemical reaction of AgO/CuO with the organic constituents of the waste water. This chemical reaction can be followed by a solid state electrochemical oxidation of the formed Ag₂O/Cu₂O. The method has been tested with various organic compounds and applied to real samples of sewage water. The EOD values correlate well to BOD and COD values.     

Study on photocatalytic oxidation for determination of the low chemical oxygen demand using a nano-TiO2-Ce(SO4)2 coexisted system

A new photocatalytic system, nano-TiO₂-Ce(SO₄)₂ coexisted system, which can be used to determine the low chemical oxygen demand (COD) is described. Nano-TiO₂ powders is used as photocatalyst in this system. The measuring method is based on direct determination of the concentration change of Ce(IV) resulting from photocatalytic oxidation of organic compounds. The mechanism of the photocatalytic oxidation for COD determination was discussed and the optimum experimental conditions were investigated. Under the optimum conditions, a good calibration graph for COD values between 1.0 and 12 mg l⁻¹ was obtained and the LOD value was achieved as low as 0.4 mg l⁻¹. When determining the real samples, the results were in good agreement with those from the conventional methods.     

Preparation of photocatalytic nano-ZnO/TiO2 film and application for determination of chemical oxygen demand

A composite nano-ZnO/TiO₂ film as photocatalyst was fabricated with vacuum vaporized and sol-gel methods. The nano-ZnO/TiO₂ film improved the separate efficiency of the charge and extended the range of spectrum, which showed a higher efficiency of photocatalytic than the pure nano-TiO₂ and nano-ZnO film. The photocatalytic mechanism of nano-ZnO/TiO₂ film was discussed, too. A new method for determination of low chemical oxidation demand (COD) value in ground water based on nano-ZnO/TiO₂ film using the photocatalytic oxidation technology was founded. This method was originated from the direct determination of the Mn(VII) concentration change resulting from photocatalytic oxidation of organic compounds on the nano-ZnO/TiO₂ film, and the COD values were calculated from the absorbance of Mn(VII). Under the optimal operation conditions, the detection limit of 0.1 mg l⁻¹, COD values with the linear range of 0.3-10.0 mg l⁻¹ were achieved. The results were in good agreement with those from the conventional COD methods.     

纳米TiO2膜用于光催化氧化测定化学需氧量的研究

A photocatalytic oxidation method for determination of chemical oxygen demand （COD） using nano-TiO2 film, based on the use of a nano-TiO2-Ce（SO4）2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce（Ⅲ） concentration change resulting from photocatalytic oxidation of organic compounds. Ce（Ⅲ）, which was produced by photocatalytic reduction of Ce（SO4）2, could be measured at a multi-walled carbon nanotubes （MWNT） chemically modified electrode （CME）. The COD values by this method were calculated from the differential pulse voltammetry （DPV） current of Ce（Ⅲ） at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones.     

光催化氧化法测定地表水化学需氧量的研究

用溶胶-凝胶法在石英管上制备了纳米TiO₂膜, 并采用光催化氧化法建立了一种测定地表水化学需氧量(COD)的新方法. 以Ce(IV)作为纳米TiO₂光生电子的接受体, 从而减少了纳米TiO₂光生电子和光生空穴的复合, 提高纳米TiO₂的光催化氧化能力. 以测定Ce(IV)的紫外吸收为手段探讨了光催化氧化测定COD的机理, 考察了测定COD的最佳反应条件. 实验结果表明, 该方法条件温和, 不会造成二次污染, 能够实现地表水等低COD值水样的快速准确测定. 在该实验所选择的条件下, 可准确地测定1.0～12 mg?L^－1之间的COD值, 检测限为0.4 mg?L^－1.     

Dichromate method for the determination of chemical oxygen demand

The oxidizability of organic substances of different classes was studied under the conditions of an official procedure for the determination of chemical oxygen demand (COD) with and without using Ag₂SO₄ as a catalyst. Organic substances can be divided into three groups: easily oxidizable compounds that are oxidized by 80–100% without a catalyst; medium-oxidizable compounds that are oxidized by 40–80% in the absence of a catalyst; and hardly oxidizable compounds that are oxidized by less than 40% without a catalyst. It was shown that, in the presence of a catalyst, not all organic substances are completely oxidized; therefore, the verification of the results of the determination of COD using easily oxidizable potassium hydrophthalate and glucose cannot be reliable in the presence of more hardly oxidizable substances. A standard mixture containing ethylene glycol, acetic acid, dimethylformamide, and nitrobenzene was proposed to verify the results of determining COD in waters of any type. The error in COD values found in a standard mixture varied in the range from 15 to 840 mg O/L. A modified procedure for the determination of COD in pure waters was proposed.     

Amperometric Determination of Chemical Oxygen Demand via the Functional Combination of Three Digestion Types

The study focused on the proposal and experimental validation of an combined photoelectrocatalytic principle for chemical oxygen demand determination (combined PeCOD, PeCOD‐combined), which was functionally comprised of photon‐efficient thin‐film photochemical, photocarrier‐efficient electrochemical and conventional bulk‐phase photochemical digestion types in one single photodigestion process. The combined PeCOD technology was proposed mainly on the basis of the significantly informative work of existing photoelectrocatalytic COD (thin‐layer PeCOD, PeCOD‐thin), and could realize the three different digestion types on one single rotating photoanode. The three important operation conditions of rotating speed, applied bias and pH value were investigated and optimized, and a wide analytical linear range of 2.7–11 500 mg/L was consequently obtained during an approximately 5–110 min determination period, and a real sample analysis further validated the practical feasibility of the proposed PeCOD‐combined. In PeCOD‐combined the main organics digestion and signal generation occurred via PeCOD‐thin due to efficient UV utilization and excellent photodigestion activity.     

一种新的光催化氧化体系用于化学需氧量的测定研究

基于KMnO₄能获得光生电子从而提高半导体光催化氧化能力的原理,建立了一种用纳米ZnO-KMnO₄协同体系光催化测定化学需氧量(COD)的新方法,探讨了催化氧化测定COD的机理,考察了测定COD的最佳反应条件.COD值浓度在1.5～10mg/L范围内与信号呈良好的线性关系,检测限为0.5mg/L.用本方法测定实际水样,结果和标准高锰酸盐指数法(COD_Mn法)相符.     

A new screening procedure for the estimation of oxidizable organic compounds in water samples

Summary Immobilized lead dioxide (supported on SiO₂) has been used as the packing material in a solid phase reactor for the oxidation of organic compounds in water samples by flow injection analysis (FIA). On-line oxidation takes place in a FIA-system; this allows the detection of mobilized Pb²⁺ either photometrically, after complex formation with 4-(2-pyridylazo)-recorcinol (PAR), or directly with flame-AAS. The oxidation yield is quite different (0–100%) for a variety of organic compounds; however, calibration was possible in all cases investigated. Thus the systems can be used for the screening of polluted waters and as a post-column chemical-reaction detector (e.g. after HPLC-separation of organic compounds). After modification the FIA determination of COD equivalent values should be possible.     

Ultrasound-assisted method for determination of chemical oxygen demand

A method for determination chemical oxygen demand (COD) assisted by use of ultrasound has been successfully evaluated for the first time. The method uses instrumentation simpler and cheaper and, in some instances, safer than that used by previous methods for the same purpose. The new device used for sonication is an all-glass cylindrical sonotrode that can be introduced directly into the reaction mixture. Use of this device enables more efficient interaction between sample and ultrasonic energy. The optimized experimental conditions are high ultrasonic power (55% amplitude, 0.9-second pulses each second), high sulfuric acid concentration (>60%), and a sonication time of 2 min. Under these conditions the method has limitations similar to those of the official COD method with regard to the type of organic compound. It works adequately with easily oxidized organic matter (potassium hydrogen phthalate and dextrose) and other organic compounds difficult to oxidize by conventional methods (e.g. phenol and acetic acid) but the COD values obtained with volatile compounds and difficult organic matter are poor. Chloride is tolerated up to a concentration of 7000 mg L(-1) without any masking agent. Gasification of the sample is recommended to improve results; use of air and argon resulted in no significant differences - bubbling with air during sonication resulted in COD values for certified materials and real wastewater samples statistically identical with the certified COD values and those obtained by the classic (open reflux) method. The use of ultrasound energy for COD determination thus seems to be an interesting and promising alternative to conventional oxidation methods used for the same purpose.     

Electrocatalytic Sensor for the Determination of Chemical Oxygen Demand Using a Lead Dioxide Modified Electrode

An amperometric method that makes use of a nano‐PbO₂ modified electrode as an electrocatalytic sensor for the determination of chemical oxygen demand (COD) is described. The sensor signal was observed as a result of the detection of the oxidation current due to electrocatalytic oxidation of organic compounds in the sample solution. This sensor responded linearly to the COD_Cr of standard samples in the range of 5–3 000 ppm and the detection limit was 2.5 ppm. When using the sensor to determine real samples, it displays short analysis time, simplicity and no sample pretreatment. The sensor was stable for over 20 days in real wastewater samples and has successfully been applied to the determination of COD in real wastewater samples.     

Determination of the chemical oxygen demand (COD) using a copper electrode: a clean alternative method

A clean alternative method for the determination of chemical oxygen demand (COD) was developed using a copper electrode as an electrocatalytic sensor. The measuring principle is based on oxidation current of organic compounds in the wastewater. The effects of important experimental conditions, such as electrolytic solution concentration and potential scan rate, on analytical performance have been investigated. Analytical linear range of 53.0–2,801.4 mg l⁻¹ COD with detection limit of 20.3 mg l⁻¹ COD was achieved. The procedure was successfully applied to the COD determination in wastewater from soft industries. The results obtained using the proposed method were in good agreement with those obtained using the conventional (i.e., dichromate) COD method. In this fashion, the COD value of a sample can be determined in a simple, rapid, accurate manner, and the end products do not contain toxic metals.     

Rapid Determination of the Chemical Oxygen Demand in Water with the Use of High-Temperature Solid-Electrolyte Cells

A new procedure is proposed for the determination of the oxidazibility of organic and inorganic matter in water (an analogue of the chemical oxygen demand (COD)). The procedure is based on high-temperature oxidation in a controlled binary oxygen–inert gas mixture and the determination of the amount of oxygen consumed for oxidation in a solid-electrolyte cell. A new design for the setup is presented as a monoblock with a vertical sample introduction into the reactor. A sampler of the immersion type is proposed. It has been found that the detection limit obtained with the use of this setup is 5 mg O₂/L.     

Investigation on the application of titania nanorod arrays to the determination of chemical oxygen demand

In the present paper, the TiO₂ nanorod arrays electrode was developed as a sensor for the determination of chemical oxygen demand (COD) based on a photoelectrochemical degradation principle. Effects of common parameters, such as applied potential, light intensity and pH on its analytical performance were investigated. Under the optimized conditions, the nanorod arrays electrode was successfully applied in the COD determination for both synthetic and real samples. In the COD determination, the proposed method can achieve a practical detection limit of 18.3 mg L⁻¹ and a linear range of 20–280 mg L⁻¹. Furthermore, the results obtained by the proposed method were well correlated with those obtained using the conventional (i.e., dichromate) COD determination method. The main advantages of this COD determination method were its simplicity, long term stability and environmental friendly (corrosive and toxic reagents not consumed). This work would open a new application area (COD determination) of the TiO₂ nanorod arrays.     

Optimization of conditions for the determination of the organic matter content of waters by reagentless oxithermography and its application to the analysis of natural waters

To determine the chemical oxygen demand (COD) of water by oxithermography, we studied a high-temperature reactor with two inputs of the gas flow. Such a design allowed the creation of an internal circuit of the oxygen–inert gas (argon) binary flow in the reactor for the oxidation of organic substances and the determination of COD by the decrease in the concentration of oxygen in the binary mixture. The optimum operation parameters of the instrument, affecting the analytical characteristics of the method, were determined. The detection limit for a water sample of the volume 10 µL was 3.4 mg O/L. It was shown that the oxithermograph and the proposed procedure can be used for the determination of COD in drinking and natural waters of Bryansk oblast. The approach developed has an advantage, consisting in the reagentless rapid determination of the COD of waters without preliminary sample preparation.     

A surface-fluorinated-TiO2-KMnO4 photocatalytic system for determination of chemical oxygen demand

A new method for chemical oxygen demand (COD) determination has been developed, based on photocatalytic oxidative degradation by using a fluorinated-TiO₂-KMnO₄ system. In such a system, a linear correlation is observed between the amount of oxidizable dissolved organic matter and the amount of MnO₄⁻ consumed by the coupled reduction process. Thus, the COD determination is transformed to a simple and direct determination of the deletion of MnO₄⁻. The surface fluorination of TiO₂ nanoparticles can enhance the rate of photocatalytic oxidation of organic matter and the rate of coupled photocatalytic reduction of MnO₄⁻. This makes the method be rapid, environment friendly and easy for operation. Under optimized conditions, this method can respond linearly to COD of potassium hydrogen phthalate (KHP) in the range of 0.1-280 mg L⁻¹, with a detection limit of 0.02 mg L⁻¹ COD. The COD in samples of tap water, lake water and paper industry sewage has been determined satisfactorily by using this method.     

Determination of chemical oxygen demand in fresh waters using flow injection with on-line UV-photocatalytic oxidation and spectrophotometric detection

A flow injection manifold incorporating UV-photocatalytic oxidation for the determination of chemical oxygen demand (COD) in freshwater is reported. The method utilises the UV-photocatalytic oxidation of organic compounds instead of conventional heating (used in the standard method), with acidified potassium permanganate as the oxidant. Sodium oxalate, d-glucose and potassium hydrogen phthalate were used as COD standards. A 100 microL sample solution was injected into a 0.3 mol L(-1) H2SO4 carrier stream containing 0.1 mol L(-1) (NH4)2SO4, merged with a permanganate solution (8 x 10(-4) mol L(-1)) and passed through a 250 cm FEP (fluoroethylene polymer) photo-reaction coil wound around a 15 W UV lamp. The sample throughput was 30 h(-1), with an LOD (blank plus 3sigma) of 0.5 mg COD L(-1) and a linear range of 0.5-50 mg COD L(-1) (D-glucose, r2 = 0.9966). The method had good precision with relative standard deviations of 2.7% at 5 mg COD L(-1) and 1.2% at 20 mg COD L(-1) (n = 12) for glucose. Results for a COD certified reference material (QC Demand Quality Control Standard) were in good agreement with the certified COD value. Recovery from Tamar River water samples for all three COD standards was 83.0-111.0% and the COD values determined were in good agreement with those of a permanganate index reference method.     

Chemiluminescence system for automatic determination of chemical oxygen demand using flow injection analysis

A novel chemiluminescence (CL) system for automatic determination of chemical oxygen demand (COD) combined with flow injection analysis is proposed in this paper. In this system, potassium permanganate is reduced to Mn²⁺ which is first adsorbed on a strongly acid cation-exchange resin mini-column to be concentrated during chemical oxidation of the organic compounds at room temperature, while the excessive MnO₄⁻ passes through the mini-column to be waste, then the concentrated Mn²⁺ is eluted reversely and measured by the luminol-H₂O₂ CL system. The calibration graph is linear in the range of 4-4000 mg l⁻¹ and the detection limit is 2 mg l⁻¹. A complete analysis could be performed in 1.5 min including washing and sampling, giving a throughout of about 40 h⁻¹. The relative standard deviation was 4.4% for 10 mg l⁻¹ COD (n=11), 4.8% for 100 mg l⁻¹ COD (n=11). This CL flow system for determination of COD is very simple, rapid and suitable for automatic and continuous analysis. The presented system has been applied successfully to the determination of COD of water samples.     

流动注射-电化学氧化法测定水体化学需氧量

采用硼掺杂金刚石(Boron-doped diamond,BDD)薄膜电极为工作电极,利用流动注射分析方法测定水体化学需氧量(COD),根据水样中有机物组分在工作电极表面氧化消耗的电量(Qoxidation)测定样品的COD值。考察了一些基本参数包括载液、工作电位、流速对检测信号的影响并选定了最佳检测条件。在最佳检测条件下,本法检测COD的线性范围为2.5~120 mg/L,检出限为1 mg/L。用该法测定化工厂和食品厂废水的COD值,相对标准偏差和回收率分别在2.4%~4.8%和96%~106%之间,且检测结果与国家标准方法(CODcr法)有良好的一致性。