Comprehensive interpretation of "BDD electrode electrolytic oxidation method"

01

Concept Overview

BDD electrode electrolytic oxidation is an advanced water treatment technology that uses "boron-doped diamond (BDD) electrode material" (considered to be an ideal electrochemical oxidation anode material - see the following description) to degrade organic pollutants in water. This method has the advantages of high efficiency, environmental protection, and no need to add chemical reagents. During the electrolysis process, the BDD electrode can directly or indirectly oxidize organic matter in water into non-toxic and harmless inorganic substances (such as carbon dioxide and water). This technology is particularly suitable for treating and degrading high-risk organic wastewater, such as industrial wastewater from the pharmaceutical, pesticide, petrochemical, coking, and lithium battery industries. This type of organic wastewater has the characteristics of high concentration, complex composition, high chroma, strong toxicity, stable chemical properties, difficult biodegradation, and long duration.

 

 

(Supplementary explanation):

1. Electrochemical oxidation characteristics of “BDD electrode”

BDD electrode is a new type of efficient multifunctional electrode. The special sp3 bond structure of diamond and its conductivity after doping give BDD electrode excellent electrochemical properties.

① Wide electrochemical potential window and high oxygen evolution potential : The wider the potential window ( the higher the oxygen evolution potential ), the more difficult it is for the oxygen evolution reaction to occur, and the greater the probability that organic pollutants will be oxidized at the anode, which improves the efficiency of sewage treatment and reduces energy consumption;

② Low background current and double-layer capacitance: It is beneficial for diamond electrodes to detect trace pollutants in electrolytes;

③Stable electrochemical performance and corrosion resistance: BDD electrode can still maintain good stability and electrode activity under acidic, neutral and alkaline conditions;

④ Not easy to be polluted, with self-cleaning function: The surface of BDD electrode is not easy to be polluted by "poisoning", and the performance of the electrode is maintained. Because the "reagent" of electrochemical oxidation is electron, which is a clean reactant, and the oxidant does not need to be added in this process, there is no secondary pollution.

It can be said that it is precisely because of these performance characteristics that the BDD electrode is the basis for the selection of ideal electrode materials. In order to ensure the perfect display of the electrochemical properties of the BDD electrode, the material selection and preparation of the BDD electrode are particularly critical, and thus have become a research hotspot in recent years.

 

 

 

2. Preparation of “BDD Electrode”

Chemical vapor deposition (CVD) is one of the common methods for synthesizing diamond. A certain amount of boron source is doped into the gas source, so that boron atoms enter the diamond lattice to replace some carbon atoms and become acceptor centers. At the same time, hole carriers are generated in the lattice, allowing electrons to move freely in the lattice, and diamond will be transformed into a p-type semiconductor. The BDD electrode can be prepared by depositing boron-doped diamond on a substrate of a fixed shape. The CVD method is currently the most mature method for preparing BDD electrodes. Table 3 shows the comparison and application of CVD synthesis methods for common BDD electrodes. As shown in Table 3, the hot wire CVD method is currently the most mature and widely used method for preparing BDD electrodes, and through the reasonable arrangement of the hot wire, large-sized industrial-grade products can be easily obtained, which has the potential for industrial application.

 

 

3. Selection of “BDD electrode”

Selecting a suitable BDD electrode requires comprehensive consideration of factors such as application field, electrode size, electrode material and electrode preparation process.

① Application fields: Different application fields have different requirements for BDD electrodes. For example, in electrochemical water treatment, BDD electrodes need to have stable surface chemical properties, excellent electrochemical catalytic performance, strong corrosion resistance, and a wide potential window.

②Electrode size: Select a BDD electrode of appropriate size according to the application scenario. Generally speaking, the larger the electrode size, the higher its processing capacity will be.

③Electrode material: When selecting electrode materials, factors such as conductivity, chemical stability and corrosion resistance need to be considered, as well as the matching degree between the electrode material and the application scenario.

④Electrode preparation process: Different electrode preparation processes will affect the electrode performance, so it is necessary to select a suitable preparation process to obtain high-quality BDD electrodes.

 

 

02

working principle

Electrochemical oxidation is a process in which an electrochemical reaction occurs by controlling conditions such as voltage or current under an
external low electric field. The result is a decrease in the content of organic pollutants in water, or direct mineralization. From the perspective of the reaction process, the BDD film electrode oxidizes organic matter into CO2 and some simple inorganic substances, thereby reducing the chemical oxygen demand (COD) of organic matter. At the same time, the BDD electrode can form a layer of hydroxyl radicals with strong oxidizing properties on the surface of the electrode, which has a strong oxidizing effect on difficult-to-degrade organic wastewater such as phenols, heterocyclics, dyes, pesticides and surfactants. The current efficiency is >90%, which can completely mineralize organic matter.

 

 

 

03

chemical reaction

The reactions in the electrolytic oxidation method mainly include electrolytic reaction and redox reaction. In the electrolytic reaction, the BDD electrode generates oxidative groups on the electrode surface by applying a certain potential, such as hydroxyl radicals (OH-), sulfate radicals, superoxide radicals, etc. These ions convert organic matter into harmless substances such as carbon dioxide and water through redox reactions. The specific reaction process includes steps such as adsorption of organic matter, electron transfer and redox, and ultimately achieves the degradation and removal of organic matter.

 

 

 

 

(Supplementary explanation):

1. Effect of reaction time on the oxidation capacity of BDD electrode

In the BDD electrode electrolytic oxidation method, the length of the reaction time affects the oxidation reaction process and product generation on the electrode surface. A longer reaction time may allow the reactants on the electrode surface to be more fully oxidized, thereby improving the oxidation capacity. However, too long a reaction time may also lead to the occurrence of side reactions, consume too much electricity, and reduce efficiency.

Therefore, it is necessary to determine the most suitable reaction time according to the specific reaction system and target substance. Usually, experimental research can be used to evaluate the effect of different reaction times on oxidation capacity and determine the optimal reaction time range.

 

 

Figure 7 BDD electrode in 1 mol/L H2SO4 solution for different electrolysis times

Effect of RB-19 degradation and change of surface wetting angle

 

 

2. If the electrolytic oxidation reaction of the BDD electrode is carried out for too long, possible side reactions may occur.

① Oxygen precipitation: During the electrolysis process, excessively long reaction time may cause oxygen to precipitate on the electrode surface, reducing the electrolysis efficiency and possibly having an adverse effect on the electrode surface.

② Product decomposition: Some electrolysis products may decompose or transform within an excessively long reaction time, resulting in product instability or reduced effectiveness.

③ Increased energy consumption: Excessively long reaction time will lead to energy waste and increase the cost of the electrolysis process.

The specific side reactions depend on factors such as the reaction system, electrolyte composition and operating conditions. In order to avoid these side reactions, the efficiency and stability of electrolytic oxidation can be improved by optimizing the reaction conditions, controlling the reaction time and selecting appropriate electrode materials.

 

 

04

Process composition

The process structure of BDD electrode electrolytic oxidation method mainly includes: power supply, electrolytic cell, BDD electrode, cathode and exhaust gas treatment device.

The power supply is the key part of providing electrical energy, providing the required voltage and current for the electrodes in the electrolyzer. According to different processing requirements and application scenarios, the appropriate power supply and voltage and current values can be selected.

The electrolytic cell is a container for electrolytic reaction, usually made of corrosion-resistant and good insulating materials. The electrolytic cell is equipped with an anode and a cathode. The BDD electrode is used as the anode and is connected to the cathode through a power supply. During the electrolysis process, an electric field is generated between the anode and the cathode, promoting ion migration and redox reaction.

The tail gas treatment device is a device for treating the tail gas generated during the electrolysis process, which usually includes absorption, adsorption, combustion and other methods. According to different tail gas components and emission standards, select the appropriate tail gas treatment method.

 

(Supplementary explanation: The power supply requirements of the "electrolyzer" )

An electrolytic cell usually consists of electrode plates, electrolyte, and liquid inlets and outlets .

The construction of the electrolytic cell needs to consider the equipment's corrosion resistance, conductivity, safety, energy saving and environmental protection. The material of the electrolytic cell has good corrosion resistance and a compact design. At the same time, it uses an efficient and energy-saving power supply and control system to reduce energy consumption and emissions, meeting environmental protection requirements.

The BDD electrode electrolytic oxidation method has high requirements for power supply, mainly including: the voltage range should be able to meet the needs of the electrolysis process; the stability of the power supply should be good to ensure the stability of the electrolysis process; the efficiency of the power supply should be high to reduce energy consumption and emissions; the safety of the power supply should meet relevant standards, etc. All-round guarantee of treatment effect and stability of equipment operation.

 

05

Electrolyte Type

Acidic electrolytes usually use strong acid solutions such as sulfuric acid and perchloric acid, which have good conductivity and oxidizability, but will cause corrosion to electrodes and equipment.

Neutral electrolytes can be solutions such as sodium chloride and sulfate, which have a pH value close to neutral and can reduce corrosion to electrodes and equipment, but have relatively poor conductivity.

Alkaline electrolytes can be strong alkaline solutions such as potassium hydroxide and sodium hydroxide, which have good conductivity but will cause corrosion to electrodes and equipment.

According to the specific application requirements, other types of electrolytes can also be selected, such as fluorine-containing electrolytes, chlorine-containing electrolytes, etc. In short, the selection of electrolytes should comprehensively consider factors such as specific application scenarios, processing requirements and economic costs.

 

 

 

06

Process steps

1. Prepare a mixed solution: First, prepare a mixed solution containing the target pollutant.

2. Adjust pH value: Use acid or alkali to adjust the pH value of the solution to the optimal range to optimize the electrolysis process and improve treatment efficiency.

3. Electrolysis: Place the BDD electrode in the solution and perform electrolysis through a DC power supply. During the electrolysis process, the BDD electrode oxidizes organic matter into harmless substances through direct oxidation on the surface of the electrode plate or produces intermediate products with strong oxidation ability, such as superoxide, hydroxyl radical, hypochlorite, etc.

4. Tail gas treatment: Some tail gas, such as chlorine and sulfur dioxide, will be produced during the electrolysis process, which needs to be properly treated to avoid harm to the environment and operators.

5. Cleaning and maintenance: After electrolysis, it is necessary to clean the sediment and impurities on the electrode surface to maintain the activity and stability of the electrode.

6. Record and process data: Record relevant data during the treatment process, such as current, voltage, treatment time, pH value, etc., and analyze and process them as needed.

 

(Supplementary explanation: BDD electrode electrolytic oxidation method can be matched with the process)

① Coagulation and sedimentation method: by adding coagulants, the suspended matter and colloidal substances in the wastewater form floccules, which are then separated by sedimentation in the sedimentation tank. This method can effectively remove suspended matter and colloidal substances in the wastewater and reduce the difficulty of subsequent treatment.

② Advanced oxidation method: BDD electrode electrolytic oxidation method can be used in combination with other advanced oxidation technologies, such as ozone oxidation , Fenton oxidation , etc. By generating hydroxyl radicals (·OH) with strong oxidizing ability, organic matter can be converted into harmless substances, thus improving the treatment effect.

③ Activated carbon adsorption method: Activated carbon has a high specific surface area and porous structure, which can adsorb organic matter and harmful substances in wastewater. When used in combination with the BDD electrode electrolytic oxidation method, the removal effect of organic matter can be further improved.

④ Biological treatment method: Through the metabolism of microorganisms, the organic matter in the wastewater is converted into harmless substances. Common biological treatment methods include activated sludge method, biofilm method, etc. Combined with BDD electrode electrolytic oxidation method, it can improve the removal effect of organic matter and the efficiency of biological treatment.

⑤ Membrane separation technology: Through membrane filtration technology, macromolecular substances, ions and organic matter in wastewater are separated and removed. Commonly used membrane separation technologies include ultrafiltration, nanofiltration, reverse osmosis, etc. Combined with BDD electrode electrolytic oxidation method, it can improve the removal effect of organic matter and the efficiency of membrane separation.

These matching processes can be selected and optimized according to specific application scenarios and treatment requirements to improve wastewater treatment effects and reduce treatment costs.

 

07

COD removal rate

The COD removal rate is calculated by calculating the difference between the inlet COD concentration and the outlet COD concentration, dividing the difference by the inlet COD concentration, and then multiplying by 100%. The specific formula is: COD removal rate (%) = (COD inlet - COD outlet) / COD inlet × 100%. The higher this ratio is, the better the treatment effect.

COD removal rate is affected by many factors, including wastewater characteristics, electrolysis conditions and electrode materials. Generally speaking, BDD electrode electrolytic oxidation method can achieve a higher COD removal rate for certain types of wastewater. Studies have shown that this method can achieve a COD removal rate of more than 95% for most organic wastewater.

 

Fig COD removal rate of BDD electrode (after 40 min reaction) and corresponding EEO

 

08

effect evaluation

 

1. Target pollutant removal rate: Calculate the removal rate by measuring the concentration of target pollutants before and after treatment. This is the most direct way to evaluate the effect and can intuitively reflect the treatment effect.

2. COD removal rate: COD is a commonly used water quality indicator. By measuring the concentration of COD before and after treatment, the removal effect of BDD electrode electrolytic oxidation method on organic matter can be evaluated.

3. Suspended solids (SS) removal rate: Calculate the removal rate by measuring the concentration of SS before and after treatment. The higher the SS removal rate, the better the treatment effect.

4. Color removal rate: For some colored wastewater, the color removal effect of BDD electrode electrolytic oxidation method can be evaluated by measuring the color concentration or chromaticity before and after treatment.

5. Turbidity removal rate: Calculate the removal rate by measuring the turbidity concentration before and after treatment. The higher the turbidity removal rate, the better the treatment effect.

6. B/C: The ratio of biochemical oxygen demand to chemical oxygen demand. By comparing B/C before and after wastewater treatment, the effect of electrochemical oxidation on the ring-opening and chain-breaking of difficult-to-degrade organic matter in wastewater and the effect of improving the biodegradability of wastewater are characterized.

7. Ecotoxicity reduction rate: By measuring the ecotoxicity index of water samples before and after treatment, the toxic effect of BDD electrode electrolytic oxidation method on aquatic organisms can be evaluated.

The specific evaluation method needs to be selected and adjusted according to the actual application situation and processing requirements.

 

09

Pros and cons analysis

1. Advantages:

① High degradation rate : BDD electrodes can efficiently remove harmful substances from wastewater. Experimental studies have shown that when the current density is 20mA/cm², the pH value is 7.0, and the reaction time is 120 min, the treatment effect of BDD electrodes is the best, and the COD and dye removal rates can reach more than 90%;

②Wide scope of application: It is suitable for the treatment of wastewater from printing and dyeing, medicine, pesticides, fine chemicals, petrochemicals, coal chemical industry, etc., and can effectively remove harmful substances such as difficult-to-degrade organic matter and ammonia nitrogen in wastewater;

③ Strong corrosion resistance: The high chemical stability and high corrosion resistance of BDD electrodes can ensure the long-term stable operation of the electrodes and will not be affected by impurities in wastewater;

④ High environmental compatibility: It can be combined with other water treatment technologies such as Fenton, photocatalysis and persulfate to construct a binary or ternary coupling system to degrade organic pollutants.

2. Disadvantages:

① High preparation cost: BDD electrodes are usually prepared using CVD technology, and the equipment is expensive;

②High energy consumption: BDD electrode electrolytic oxidation method requires consumption of electrical energy.

At present, Hunan Xinfeng Technology Co., Ltd. in China has achieved obvious cost advantages through continuous technology iteration! In the future, this technology will be more competitive.

 

10

Application

Due to its unique physical and chemical properties, BDD electrodes have been widely used in many fields, mainly including: electrochemical synthesis and resource regeneration, detectors and sensors, environmental monitoring, biosensing and electrochemical water treatment.

1. High-risk wastewater treatment: BDD electrodes perform well in treating industrial wastewater containing high concentrations of difficult-to-degrade organic matter, especially those wastewaters that are potentially harmful to the environment and human health, such as wastewater generated by petrochemicals, textile printing and dyeing, pharmaceutical factories, tanneries, paper mills, etc.

2. Biosensing: In the field of biosensing, BDD electrodes are used in bioanalysis and preparation of biosensors, such as DNA detection, protein determination, etc.

3. Electrochemical water treatment: In water treatment and wastewater treatment, BDD electrodes are used for electrochemical oxidation and reduction reactions to help remove pollutants from water.

These applications demonstrate the importance of BDD electrodes in modern industry and environmental protection, especially in providing clean and sustainable water treatment solutions. With the advancement of technology, the application areas of BDD electrodes are expected to expand further.

 

 

(Supplementary explanation):

1. Pretreatment of wastewater by BDD electrode electrolytic oxidation method

①Remove suspended matter and particulate matter: Suspended matter and particulate matter in wastewater may hinder the electrolysis reaction and reduce the COD removal rate.

② Adjust pH value: BDD is suitable for a wide pH range, but the pH value of wastewater will affect the rate and effect of electrolytic oxidation reaction. By properly adjusting the pH value range of wastewater through pretreatment, the electrolytic reaction conditions can be optimized and the COD removal rate can be improved.

③Remove organic matter: If there are a large number of easily degradable organic matter in the wastewater, it will also consume the free radicals produced by electrolysis and increase unnecessary electrolysis energy consumption. Some of the organic matter can be removed through methods such as biological treatment or chemical oxidation to improve the efficiency of BDD use.

④Remove heavy metal ions: Some heavy metal ions may poison the BDD electrode and reduce its catalytic activity. Or it may precipitate at the cathode, affecting the electrolysis efficiency.

Appropriate pretreatment methods need to be selected based on specific wastewater characteristics and treatment requirements. Pretreatment can help improve the electrolyzability of wastewater, increase COD removal rate, and ensure the effective operation of the BDD electrode electrolytic oxidation method.

 

2. Example: "High-salt" wastewater treatment (BDD electrode electrolytic oxidation method)

BDD electrode electrolytic oxidation method has significant effect in treating high-salt wastewater. BDD electrodes have excellent corrosion resistance, which can effectively prevent the high concentration of salt in high-salt wastewater from corroding the electrodes, ensuring the stability and long service life of the electrodes.

When treating high-salt wastewater, the BDD electrode electrolytic oxidation method can oxidize the organic matter in the wastewater into harmless substances through electrochemical oxidation, effectively degrade the organic matter, and improve the purity of the salt. At the same time, it can also convert part of the chloride ions in the wastewater into chlorine gas, etc., thereby reducing the salt content in the wastewater.

It provides convenience for subsequent treatment and discharge. In summary, the BDD electrode electrolytic oxidation method has a wide range of application scenarios for the treatment of high-salt organic wastewater. In practical applications, it is necessary to adjust the process parameters according to the specific composition and treatment requirements of the wastewater to obtain the best treatment effect.

 

Figure  Degradation effect of high-salinity (sodium sulfate) wastewater and high-salinity (sodium chloride) internal wastewater

 

 

3. Key factors to ensure the best treatment effect of BDD electrode electrolytic oxidation method

① High-efficiency electrode materials: Selecting high-efficiency and stable electrode materials is the prerequisite for ensuring the treatment effect. The electrochemical properties, corrosion resistance, conductivity, etc. of the electrode materials will affect the reaction rate and efficiency during the electrolysis process.

② Suitable electrolyte: According to the different treatment objects, choose the appropriate electrolyte formula and concentration. The composition and concentration of the electrolyte have an important influence on the electrode reaction rate, the generation of oxidants and the treatment effect.

③ Reasonable electrolysis conditions: Control the current density, potential, temperature, pressure and other parameters during the electrolysis process to make the electrolysis conditions reach the optimal state and improve the treatment effect.

④ Appropriate oxidants: During the electrolysis process, by adding appropriate amounts of oxidants, such as chlorine, oxygen, etc., the oxidation capacity can be enhanced and the removal efficiency of harmful substances can be improved.

⑤ Reasonable process design: According to the characteristics and requirements of the treatment object, reasonable process design is carried out, including the structure of the electrolytic cell, the arrangement of electrodes, the water inlet and outlet methods , etc., to improve the treatment effect and reduce energy consumption.

⑥Automatic control: Adopt automatic control system to realize real-time monitoring and automatic adjustment of electrolysis process, ensuring stable operation of electrolysis process and reliability of treatment effect.

⑦ Operator training: Strengthen operator training and management, improve their professional skills and quality, ensure the standardization and accuracy of operations, and avoid the decline of treatment effects due to human factors.

 

 

 

11

Application prospects

1. Industrial wastewater treatment: BDD electrode electrolytic oxidation method can effectively treat various industrial wastewaters, such as printing and dyeing wastewater, papermaking wastewater, coking wastewater, etc., improve water quality and reduce pollutant concentrations to meet emission standards. It not only converts difficult-to-degrade organic matter into easily degradable substances through strong oxidation, but also removes heavy metal ions such as chromium, lead, and mercury, and can also treat high-salt wastewater and reduce salt concentration.

2. Application in the energy field: The high electrocatalytic activity of BDD electrode makes it have application prospects in energy fields such as water electrolysis to produce hydrogen and redox battery catalysts. It is expected to solve key problems in renewable energy conversion and storage and promote the development of clean energy.

3. Organic synthesis: BDD electrode electrolytic oxidation method can be used for organic synthesis reactions, such as oxidation, reduction, nitration and esterification. This technology has the advantages of high selectivity, mild reaction conditions and high product purity, which can improve the efficiency and quality of organic synthesis.

4. Environmental remediation: BDD electrode electrolytic oxidation can be used for soil and groundwater remediation, such as removing pollutants, remediating contaminated soil and groundwater, etc. This technology has the advantages of being environmentally friendly, having good treatment effects and a wide range of applications.
5. Materials science: BDD electrodes themselves have excellent physical and chemical properties and can be used as the basis for new materials, such as catalysts, sensors and biomedical materials.

In short, the BDD electrode electrolytic oxidation method has broad application prospects and development potential. With the continuous advancement of technology and the expansion of application fields, this technology will play an important role in more fields.