Metal-Free g-C3N4/Nanodiamond Heterostructures for Enhanced Photocatalytic Pollutant Removal and Bacteria Photoinactivation
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-09-14 |
| Journal | Photochem |
| Authors | Natalya Kublik, Luiz E. Gomes, Luiz F. Plaça, Thalita H. N. Lima, Thais Fedatto Abelha |
| Institutions | Centro de Tecnologias Estratégicas do Nordeste, Arizona State University |
| Citations | 9 |
| Analysis | Full AI Review Included |
Metal-Free g-C3N4/Nanodiamond Heterostructures Analysis
Section titled âMetal-Free g-C3N4/Nanodiamond Heterostructures AnalysisâExecutive Summary
Section titled âExecutive SummaryâThis research successfully developed and characterized metal-free g-C3N4/Nanodiamond (DNC) heterostructures for enhanced photocatalysis, focusing on pollutant removal and bacterial inactivation.
- Core Achievement: Synthesis of Type-II g-C3N4/DNC heterojunctions via a simple, cost-effective in situ urea decomposition method.
- Performance Enhancement: The optimal composite (28.3 wt.% DNC) achieved a 76% increase in the Methylene Blue (MB) photodegradation rate (k = 0.0104 min-1) compared to pure g-C3N4 (0.0059 min-1).
- Antibacterial Efficacy: The best heterojunction demonstrated enhanced photoinactivation capability against Staphylococcus aureus under visible LED irradiation.
- Mechanism (Charge Separation): The Type-II heterojunction facilitates electron transfer from the g-C3N4 conduction band (CB) to the DNC CB, significantly reducing electron-hole recombination (confirmed by lowered Photoluminescence intensity).
- Mechanism (Adsorption/Transfer): DNC presence increased the materialâs specific surface area (up to 111.7 m2 g-1) and enhanced adsorption due to highly negative surface charge (-29.5 mV), while Electrochemical Impedance Spectroscopy (EIS) confirmed lower charge transfer resistance.
- Electronic Properties: Both g-C3N4 and DNC exhibited n-type semiconducting features, with DNC possessing an intragap state (2.64 eV) that aids visible light harvesting.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal DNC Loading | 28.3 | wt.% | Best photocatalytic performance (g-C3N4/DNC-28) |
| MB Degradation Rate (k) | 0.0104 | min-1 | Pseudo-first-order kinetic constant for optimal sample |
| Pure g-C3N4 Rate (k) | 0.0059 | min-1 | Baseline performance |
| Total MB Removal | 71 | % | After 120 min simulated solar irradiation |
| g-C3N4 Indirect Bandgap (Eg) | 2.91 | eV | Determined via Tauc plot |
| DNC Intragap Bandgap (Eg) | 2.64 | eV | Component aiding visible light absorption |
| DNC Bulk Bandgap (Eg) | 4.83 | eV | Bulk diamond structure |
| g-C3N4 Flat Band Potential (Vfb) | -0.17 | V | vs. RHE (Conduction Band minimum) |
| DNC Flat Band Potential (Vfb) | -0.01 | V | vs. RHE (Conduction Band minimum) |
| Highest Specific Surface Area (SBET) | 111.7 | m2 g-1 | g-C3N4/DNC-11 composite |
| DNC Mean Particle Diameter | 125.4 ± 48.9 | nm | Determined via DLS |
| g-C3N4 Pyrolysis Temperature | 550 | °C | Synthesis temperature (2 h duration) |
| Bacterial Inactivation Flux | 18 | mW cm-2 | RGB LED visible light irradiation |
Key Methodologies
Section titled âKey MethodologiesâThe g-C3N4/DNC heterostructures were prepared using a modified in situ urea decomposition method, followed by comprehensive structural and electronic characterization.
- Precursor Preparation:
- Urea (calculated based on 4.4% yield to g-C3N4) was dissolved in deionized water.
- Non-detonated DNC powder (purity 99.95%) was added, followed by 30 min sonication (40 kHz, 315 W RMS).
- Thermal Processing (In Situ Synthesis):
- The mixture was dried at 120 °C for 6 h (heating rate 5 °C min-1).
- The dried precursor was heated in a muffle furnace at 550 °C for 2 h (heating rate 3 °C min-1) under an air atmosphere, promoting urea decomposition and g-C3N4 formation around the DNC.
- Structural and Electronic Characterization:
- TGA/DSC: Used to determine the experimental DNC content (up to 28.3 wt.%) and confirm thermal stability.
- Microscopy (SEM/TEM): Confirmed g-C3N4 nanosheets supporting dispersed DNC nanoparticles (100-200 nm).
- Spectroscopy (DRS-UV-Vis & Tauc): Determined bandgaps and confirmed DNC intragap states (2.64 eV).
- Photoelectrochemistry (EIS & M-S): EIS confirmed reduced charge transfer resistance with DNC inclusion. M-S analysis confirmed n-type conductivity and determined flat band potentials (Vfb) used for Type-II heterojunction modeling.
- Photocatalytic Testing (MB Degradation):
- MB solution (30 mg L-1) was treated with catalyst (1 mg mL-1) under 40 min dark adsorption equilibrium.
- Irradiation used a solar simulator (150 W Xe lamp) calibrated to 200 mW cm-2.
- Bacterial Photoinactivation Testing:
- Staphylococcus aureus (ATCC 25923) was used as the model bacterium.
- Samples were exposed to visible light (RGB LEDs, 18 mW cm-2) for 1 h, followed by CFU counting after 24 h incubation.
Commercial Applications
Section titled âCommercial ApplicationsâThe development of highly efficient, metal-free g-C3N4/DNC heterostructures is relevant for several environmental and biomedical engineering sectors.
- Wastewater Treatment: High-efficiency degradation of Persistent Organic Pollutants (POPs) and micropollutants (e.g., dyes, pharmaceuticals) using simulated solar light.
- Water Disinfection Systems: Utilization of the enhanced photoinactivation capability for sterilizing water sources and controlling microbial growth, particularly against Gram-positive bacteria like S. aureus.
- Metal-Free Catalysis: Provides a low-cost, non-toxic alternative to traditional noble-metal or heavy-metal-based photocatalysts, simplifying regulatory compliance and reducing environmental impact.
- Hydrogen Production: While the study focused on degradation, the Type-II heterojunction mechanism (efficient charge separation) is directly applicable to enhanced photocatalytic H2 evolution, as noted in related literature.
- Nanodiamond-Enhanced Composites: Integration of DNCs to improve the mechanical, thermal, and electronic properties of 2D materials like g-C3N4 for various composite applications.
View Original Abstract
Heterogeneous photocatalysis has emerged as a promising alternative for both micropollutant removal and bacterial inactivation under solar irradiation. Among a variety of photocatalysts explored in the literature, graphite carbon nitride (g-C3N4) is a metal-free semiconductor with acceptable chemical stability, low toxicity, and excellent cost-effectiveness. To minimize its high charge recombination rate and increase the photocatalyst adsorption capacity whilst keeping the metal-free photocatalyst system idea, we proposed the heterojunction formation of g-C3N4 with diamond nanocrystals (DNCs), also known as nanodiamonds. Samples containing different amounts of DNCs were assessed as photocatalysts for pollutant removal from water and as light-activated antibacterial agents against Staphylococcus sureus. The sample containing 28.3 wt.% of DNCs presented the best photocatalytic efficiency against methylene blue, removing 71% of the initial dye concentration after 120 min, with a pseudo-first-order kinetic and a constant rate of 0.0104 minâ1, which is nearly twice the value of pure g-C3N4 (0.0059 minâ1). The best metal-free photocatalyst was able to promote an enhanced reduction in bacterial growth under illumination, demonstrating its capability of photocatalytic inactivation of Staphylococcus aureus. The enhanced photocatalytic activity was discussed and attributed to (i) the increased adsorption capacity promoted by the presence of DNCs; (ii) the reduced charge recombination rate due to a type-II heterojunction formation; (iii) the enhanced light absorption effectiveness; and (iv) the better charge transfer resistance. These results show that g-C3N4/DNC are low-cost and metal-free photoactive catalysts for wastewater treatment and inactivation of bacteria.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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