A Diamond/Graphene/Diamond Electrode for Waste Water Treatment

At a Glance

Metadata	Details
Publication Date	2023-11-29
Journal	Nanomaterials
Authors	Yibao Wang, Zhigang Gai, Fengxiang Guo, Mei Zhang, Lili Zhang
Institutions	Qilu University of Technology, Shandong Academy of Sciences
Citations	5
Analysis	Full AI Review Included

Executive Summary

This research details the development and performance of a novel Boron-Doped Diamond/Graphene/BDD (DGD) sandwich electrode designed to enhance the efficiency of electrochemical advanced oxidation processes (EAOPs) for wastewater treatment.

Core Innovation: The DGD sandwich structure incorporates a multilayer graphene interlayer, effectively improving electrode conductivity and carrier transfer rate, addressing the high resistance limitation of conventional BDD electrodes.
Performance Enhancement: The optimal DG₂₀D electrode (20 min graphene annealing) demonstrated superior water treatment capability compared to single-layer BDD, achieving approximately 80% TOC removal for Citric Acid (CA) in 20 minutes, versus 50% for BDD.
Energy Efficiency: The DG₂₀D electrode significantly reduced energy consumption per unit TOC removal (E_CTOC). For Catechol degradation, E_CTOC was reduced to 66.9% of the BDD value.
Electrochemical Kinetics: The step current density of DG₂₀D during CA degradation was 1.35 times that of BDD, and its energy utilization ratio was 2.4 times higher (57.34% vs. 23.72%).
Structural Integrity: The sandwich design successfully retains the wide electrochemical window (OEP of DG₂₀D was 2.37 V, higher than BDD’s 2.1 V) and physicochemical stability intrinsic to BDD, avoiding degradation caused by heavy doping or non-diamond carbon introduction.
Material Composition: The optimal graphene interlayer thickness was determined to be 21.2 nm, characterized by lamellar graphite structure parallel to the BDD layer.

Technical Specifications

Parameter	Value	Unit	Context
Bottom BDD Film Thickness	500	µm	HFCVD deposition
Upper BDD Film Thickness	800	nm	HFCVD deposition
BDD Doping Concentration	4000	ppm	Boron doping
HFCVD Base Temperature	850	°C	BDD growth
HFCVD Hot Wire Temperature	2400-2500	°C	BDD growth
Optimal Graphene Annealing Time	20	min	Yields DG₂₀D electrode
Optimal Graphene Interlayer Thickness (DG₂₀D)	21.2	nm	Measured via TEM
DG₂₀D Oxygen Evolution Potential (OEP)	2.37	V	High electrochemical window
BDD Oxygen Evolution Potential (OEP)	2.1	V	Reference electrode
DG₂₀D Step Current Density (CA)	7.7	mA cm^-2	Highest among tested electrodes
Electrolysis Current Density	200	mA/cm²	Water treatment experiment
Electrolysis Voltage Range	6.5 to 7.5	V	Varies based on electrode structure
DG₂₀D Energy Efficiency (q)	57.34	%	CA degradation (2.4x BDD efficiency)
E_CTOC Reduction (Catechol)	66.9	%	Relative to BDD electrode
Graphite (002) Interplanar Distance	0.38	nm	TEM analysis of DG₂₀D interlayer
Raman 2D Peak FWHM (DG₂₀D)	45	cm^-1	Characteristic of multilayer graphene

Key Methodologies

The DGD sandwich electrode was prepared using a combination of Hot Filament Chemical Vapor Deposition (HFCVD) and Cu-metal-assisted vacuum annealing.

Bottom BDD Layer Deposition:
- BDD film (500 µm thick) was grown on a Si (100) substrate using HFCVD.
- Conditions: Chamber pressure 3-5 kPa, hot wire temperature 2400-2500 °C, base temperature 850 °C, and 4000 ppm doping concentration.
Copper Catalyst Deposition:
- A copper layer (300 nm thick) was deposited onto the BDD surface using Physical Vapor Deposition (PVD).
Graphene Interlayer Formation:
- The Cu-coated BDD was subjected to metal-assisted vacuum annealing at 1000 °C.
- Annealing times were varied (10, 20, 30, 40 min) to control graphene layer thickness and quality. The 20 min sample (DG₂₀D) was found to be optimal, yielding multilayer graphene (21.2 nm thick).
Upper BDD Layer Deposition:
- A second BDD layer (800 nm thick) was grown on the graphene interlayer using HFCVD under the same conditions as the bottom layer, completing the DGD sandwich structure.
Electrochemical Testing:
- Electrochemical performance was assessed using Cyclic Voltammetry (CV) to determine the Oxygen Evolution Potential (OEP) and Electrochemical Impedance Spectroscopy (EIS).
Electrocatalytic Degradation:
- Degradation tests were performed on 100 mg/L solutions of Citric Acid (CA), Catechol, and Tetracycline Hydrochloride (TCH) in 0.1 M Na₂SO₄ electrolyte.
- A constant current density of 200 mA/cm² was applied, with the DGD electrode as the anode and Ti as the cathode.
- Performance was quantified by Total Organic Carbon (TOC) removal and Energy Consumption per unit TOC removal (E_CTOC).

Commercial Applications

The DGD sandwich electrode technology is highly relevant for industries requiring robust, high-efficiency electrochemical processes, particularly those dealing with complex organic waste streams.

Wastewater Treatment: High-efficiency removal of persistent organic pollutants (POPs), including pharmaceuticals (e.g., Tetracycline Hydrochloride), industrial intermediates (e.g., Catechol), and high-COD waste streams.
Electrochemical Advanced Oxidation Processes (EAOPs): Serving as a novel, low-energy BDD anode material for generating hydroxyl radicals (•OH) and other strong oxidants for mineralization.
Industrial Water Recycling: Applications in food processing waste (Citric Acid) and chemical manufacturing where high stability and long electrode service life are critical.
Electrocatalysis: Use in various electrocatalytic processes requiring a wide potential window and high corrosion resistance, potentially extending beyond water treatment.
Sensor Technology: The stable BDD structure combined with enhanced conductivity could be leveraged for high-sensitivity electrochemical sensing and detection applications.

View Original Abstract

Boron-doped diamond (BDD) thin film electrodes have great application potential in water treatment. However, the high electrode energy consumption due to high resistance directly limits the application range of existing BDD electrodes. In this paper, the BDD/graphene/BDD (DGD) sandwich structure electrode was prepared, which effectively improved the conductivity of the electrode. Meanwhile, the sandwich electrode can effectively avoid the degradation of electrode performance caused by the large amount of non-diamond carbon introduced by heavy doping, such as the reduction of the electrochemical window and the decrease of physical and chemical stability. The microstructure and composition of the film were characterized by scanning electron microscope (SEM), atomic force microscopy (AFM), Raman spectroscopy, and transmission electron microscopy (TEM). Then, the degradation performance of citric acid (CA), catechol, and tetracycline hydrochloride (TCH) by DGD electrodes was systematically studied by total organic carbon (TOC) and Energy consumption per unit TOC removal (ECTOC). Compared with the single BDD electrode, the new DGD electrode improves the mobility of the electrode and reduces the mass transfer resistance by 1/3, showing better water treatment performance. In the process of dealing with Citric acid, the step current of the DGD electrode was 1.35 times that of the BDD electrode, and the energy utilization ratio of the DGD electrode was 2.4 times that of the BDD electrode. The energy consumption per unit TOC removal (ECTOC) of the DGD electrode was lower than that of BDD, especially Catechol, which was reduced to 66.9% of BDD. The DGD sandwich electrode, as a new electrode material, has good electrochemical degradation performance and can be used for high-efficiency electrocatalytic degradation of organic pollutants.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano13233043

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