Superior removal of Methylene Blue by mesoporous g-C3N4@WO3 nanocomposite: equilibrium and kinetic study
| Meeting | VIWC2026 |
| Topic | OS4: Water quality and Aquaculture |
| Author | Dinh-Trinh Tran | Manh Cuong Le | Van Tiep Hoang | Xuan Khanh Bui | Van Thang Pham | Cong Tu Nguyen | Lan Anh Luu Thi |
| Organization | VNU Key Lab. of Advanced Materials for Green Growth, University of Science, Vietnam National University | Faculty Building Material, Hanoi University of Civil Engineering | School of Engineering Physics, Hanoi University of Science and Technology | Faculty Building Material, Hanoi University of Civil Engineering | School of Engineering Physics, Hanoi University of Science and Technology | School of Engineering Physics, Hanoi University of Science and Technology | School of Engineering Physics, Hanoi University of Science and Technology |
| ID | 2023.1676262756 |
Content
1. Introduction
Water pollution has been a great concern and attracted increasing attention of the society, especially the problems related to heavy metals and pigment pollution. Therefore, researches on the removal of pollutants are of significant importance. Recently, graphite carbon nitride (g-C3N4) has been considered a promising material for environmental remediation because of its chemical stability, high adsorption capacity. g-C3N4 could be also used as a support for adsorbents, especially for those in nanoscales (Modwia et al, 2022). WO3 presents stable physicochemical structure, high surface structure, and could be used to remove organic pollutants from solutions. The combination of g-C3N4 and WO3 could lead to better removal of organic pollutants and more feasible in real applications. In this work, a series of g-C3N4@WO3 nanocomposites were synthesized by hydrothermal process using Na2WO4 and urea as precursors. The as-synthesized materials were then examined by means of various techniques and applied for studying the adsorption process of Methylene Blue (MB) in solutions.
2. Experimental
2.1. Synthesis of g-C3N4, WO3, and g-C3N4@WO3 nanocomposites
All chemicals were of analytical grade provided by Sigma Aldrich, and used without any further purification. g-C3N4 in yellow bulk form was synthesized by pyrolyzing urea in a muffle furnace at 550 ºC for 2.5 h according to our previous study (Nguyen et al, 2019). WO3 nanoparticles were synthesized by hydrothermal method using modified procedure from our previous work (Vu et al, 2021). The g-C3N4@WO3 nanocomposites were synthesized using the same synthesis procedure of WO3 in which g-C3N4 was added to Na2WO4 solution with the content of 0, 0.5, 1, 3, and 5% wt before the mixture was subjected to hydrothermal process. The samples prepared with 0; 0.5; 1; 3; and 5% wt of g-C3N4 were denoted CNW-000; CNW-005; CNW-010; CNW-030; and CNW-050, respectively.
2.2. Characterization of materials
The crystalline structure and phase purity were examined by using X’pert Pro (PANalytical) MPD with CuK-α1 radiation (1.54056 Å) at a scanning rate of 0.03o/2s. Raman spectra were observed using a Renishaw Invia Raman Microscope with a 633 nm laser and 25mW power. FT-IR spectra were analyzed using a FT-IR-4600 type A (JASCO) with wavenumbers ranging from 400 cm-1 to 4000 cm-1. The morphology of materials was studied by a field-emission scanning electron microscopy (FE-SEM, JEOL JSM-7600F). Surface area was tested by a NOVAtouch LX4, Quantachrome Instrument, USA.
2.3. Removal of MB by adsorption process
In a typical experiment, 20 mg of the g-C3N4@WO3 nanocomposites were well-dispersed into 100 mL of MB solutions (10 mg/L) with constant stirring in dark. At each time interval, 5 mL of the mixture was sampled and filtered to remove the adsorbent. The remaining MB concentration was quantified by using an UV-Vis spectrometer at the wavelength of 664 nm.
3. Results and discussion
3.1. Material characterization
The CNW-000 sample (pure WO3) observed at 14.0°, 22.7°, 24.2°, 26.7°, 28.1°, 33.5°, 36.5°, 37.5°, 49.7°, 55.3° and 63.2° respectively, indicating high crystallinity of WO3. g-C3N4 exhibited two fundamental diffraction peaks at around 13.10° and 27.80° (Mamba, G., Mishra, 2016). The characteristic peaks of WO3 and g-C3N4 were observed in almost all C3N4@WO3 composites (Figure 1a and b), confirming successful load of WO3 nanoparticles on the g-C3N4. The crystal size calculated according to Williamson-Hall equation showed the more g-C3N4 content, the larger crystalline size (WO3 had an average diameter of 15.41 nm vs 20.70 nm for CNW-050).
Figure 1: XRD pattern of samples (a) within 10 – 70° and (b) within 20 – 30°. (c) Raman spectra, and (d) FT-IR spectra of the samples.
Raman spectra of CNW-000 showed two peaks at around 807 cm-1 and 680 cm-1 corresponding to the O-W6+-O stretching modes (Figure 1 c). In the CNW-050 sample, different scattering signals were observed at 982 cm-1, 939 cm-1, 690 cm-1, 629 cm-1 and 337 cm-1, respectively, probably due to the formation of C-O-W bonds between the g-C3N4 and WO3. FT-IR spectra revealed pristine g-C3N4 presented several characteristic peaks ranging from 1630 cm-1 to 811 cm-1, being assigned to aromatic C-N elongation modes, to aromatic C-N stretching vibration of heptazine- derived repeating units, and to vibrations of triazine ring unit. The nanorods were attributed to g-C3N4 while spheric shape was due to WO3 nanoparticles (Figure 2). Both adsorption and desorption isotherms of g-C3N4/WO3 and g-C3N4 samples shared a common characteristic, presenting type IV isotherms with H3 hysteresis loop, which represented for mesoporous materials (Figure 3). The specific surface area calculated by the BET method for g-C3N4 and g-C3N4/WO3 samples were 35.4 m2/g and 68.6 m2/g, respectively, implying an enhancement of surface area. The pore-size distribution of g-C3N4 processed a typical peak with pore diameter < 20 nm while those values for g-C3N4/WO3 was below 10 nm.
Figure 2: FE-SEM images of (a) CNW-000; (b) CNW-010; (c) CNW-005 nanocomposites.
Figure 3: Nitrogen adsorption–desorption isotherms and pore distribution of (a) g-C3N4/WO3 (0.5%) and (b) g-C3N4 samples.
3.2. The adsorption process of MB on the g-C3N4@WO3 nanocomposites
The MB adsorption process occurred very quickly, reaching equilibrium at about 8 min, suggesting a potential adsorbent for real application. The g-C3N4@WO3 nanocomposites presented better MB adsorption capacity than pristine WO3, implying a promising adsorbent for dyes removal. The CNW-005 nanocomposites showed the best adsorption efficiency than the other. The results indicated the second-order kinetics models described the best experimental data with correlation coefficients (R2) higher than 0.9 in all cases compared to R2<0.9 for the first-order kinetics model (Figure 4).
Figure 4: (a) the adsorption capacity/efficiency of the samples, and (b) first order and (c) second-order kinetics of the MB adsorption process.
The equilibrium adsorption isotherm model of the adsorption process was analyzed using the Langmuir isotherm, Freundlich isotherm, and Temkin isotherm models. The validity of the isotherm models can be estimated by using their linearized plots (Figure 5). The regression coefficient (R2) is used as a criterion to compare between models. Freundlich isotherm model described the best the MB adsorption (R2=1), implying monolayer adsorption with uniform adsorption energies. The Temkin model showed adsorption was an exothermic process.
Figure 5: (a) Langmuir, (b) Freundlich, (c) Temkin, and (d) Dubinin–Radushkevich model plots.
4. Conclusion
A series of g-C3N4@WO3 nanocomposites were successfully produced from Na2WO4 and g-C3N4 precursors using the hydrothermal method. The g-C3N4 content affected structure, morphology and properties of g-C3N4@WO3 nanocomposites. The results showed the CNW materials exhibited a better MB adsorption capacity than WO3. The CNW-005 sample showed the highest MB adsorption efficiency (85.10%), with an adsorption capacity of 39.55 mg/g. The Freundlich isotherm model fitted the best the adsorption data. The adsorption was best described by the second-order kinetics model.
5. Reference
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- Modwia, A., Khezami, L., Ghoniem, M.G. et al, 2022. Superior removal of dyes by mesoporous MgO/g-C3N4 fabricated through ultrasound method: Adsorption mechanism and process modeling. Environ. Res. 205, 112543.
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