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Article

Synthesis of g-C3N4 Derived from Different Precursors for Photodegradation of Sulfamethazine under Visible Light

by
Ke Li
1,2,
Miaomiao Chen
1,
Lei Chen
1,*,
Songying Zhao
1,
Wencong Xue
1,
Zixuan Han
1 and
Yanchao Han
2
1
Key Laboratory of Song Liao Aquatic Environment, Ministry of Education, Jilin Jianzhu University, Changchun 130118, China
2
State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China
*
Author to whom correspondence should be addressed.
Processes 2023, 11(2), 528; https://doi.org/10.3390/pr11020528
Submission received: 25 January 2023 / Revised: 3 February 2023 / Accepted: 7 February 2023 / Published: 9 February 2023
(This article belongs to the Special Issue Novel Materials/Technologies for the Adsorption and Removal of Antibiotics from Aqueous Solution)
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Abstract

:
In this study, a series of g-C3N4 nanosheets were prepared by various thermal oxidative etching times from four different precursors (urea, melamine, dicyandiamide and thiourea). The physicochemical properties of these g-C3N4 nanosheets were analyzed in detail using scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence emission spectra, Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) analysis and ultraviolet-visible diffuse reflectance. The results revealed that the g-C3N4 nanosheets obtained a thinner layer thickness and larger specific surface area, with an extension of thermal oxidative etching time. Meanwhile, sulfamethazine (SMZ), one of the most widely used sulfonamides, was used to evaluate the photocatalyst activity of the g-C3N4 nanosheets prepared in this study. Compared to other g-C3N4 nanosheets, urea-derived g-C3N4 nanosheets under 330 min thermal oxidative etching showed the highest photocatalytic activity for SMZ under visible light. In conclusion, our study provides detailed insights into the synthesis and characterization of g-C3N4 nanosheets prepared from various precursors and highlights the importance of thermal oxidative etching time in determining the photocatalytic activity of these materials.

1. Introduction

Antibiotics have been extensively used to treat infectious diseases in humans and domestic animals since the first antibiotic was deployed in 1910 [1,2,3]. Among these antibiotics, sulfonamide, a class of antibiotics which contains sulfonamide groups, has been one of the most widely used antibiotics in medical and animal livestock since 1968 [4]. Numerous sulfonamides are discharged into the aquatic environment through incomplete metabolism and wastewater treatment each year [5,6]. Sulfonamides may be harmful to the ecosystem and induce an antimicrobial resistance crisis after enough time has passed [7,8]. However, sulfonamides cannot be removed effectively through conventional biological wastewater treatment owing to their antibacterial nature [9]. Six kinds of sulfonamide were detected in the Pearl River Delta, which received effluents from four nearby typical wastewater treatment plants, demonstrating that the wastewater treatment plants cannot completely remove sulfonamides in the influent [10]. García-Galán et al. made use of removal rates and half-lives to study the rate of sulfonamides in the influent and effluent from 22 conventional wastewater treatment plants, 15 of which involved sewage. The results showed that even increasing hydraulic retention time could not increase the removal rate of sulfonamides, while sulfamethoxazole, sulfapyridine and their corresponding acetylated metabolites were detected most frequently and at very high concentrations [11]. Thus, finding an effective way to remove sulfonamides from surface water is essential to protect human health and guarantee ecology security.
Thus far, numerous technologies have been employed to solve sulfonamide contamination, such as adsorption [12,13], electrolysis [14], membrane separation [15], biological treatment [16], chemical catalysts [17,18] and photocatalysis [9]. Azhar et al. successfully synthesized a metal–organic framework adsorptive with high surface area and unsaturated metal sites through a facile method, which could totally remove sulfachloropyridazine from wastewater within 15 min due to its significant adsorption capacity [19]. Zhang et al. constructed an in situ electro-Fenton system to degrade sulfadiazine from simulated livestock and poultry breeding wastewater, and found that 96.5% of sulfadiazine could be removed in 150 min by this system when the pH value equals 3, the Pd/CeO2 catalyst dosage is 0.1 g, the current density is 15 mA/cm2, and the current ratio is 0.15:0.02 [20]. Liang et al. built an integrated membrane filtration consisting of ultrafiltration and two-stage reverse osmosis to remove antibiotic resistance genes mainly induced by sulfonamides from swine wastewater, and discovered that more than 99.79% of antibiotic resistance genes could be reduced by the integrated membrane filtration [21]. Yu et al. constructed an aerobic submerged membrane bioreactor integrating sponge-plastic biocarriers and successfully applied it to the degradation of sulfadiazine and sulfamethoxazole [22]. Li et al. investigated the use of surface molecular imprinting technology to remove sulfonamides, and the result revealed that the catalyst capacity for sulfamethazine (SMZ) and sulfathiazole reached more than 70% and 87%, respectively [23]. Among these technologies, photocatalysis has been revealed to be a promising method of removing sulfonamides and other organic contaminants because it is efficient, costly and environmentally friendly [24,25,26]. The photocatalysis process should be driven by light irradiation, and visible light accounts for 45% of solar sunlight, while only 5% of sunlight is UV light [27]. Therefore, it is very important to determine whether visible light can be utilized for photocatalyst technology. Over past years, graphitic carbon nitride (g-C3N4) has exhibited great potential to be applied in visible light photocatalysis because it can absorb visible light due to its band gap of 2.70 eV [28]. Additionally, g-C3N4 possesses many advantages, such as physicochemical stability, cost-effectiveness, easy synthesis, material abundance and environmental friendliness [29,30,31]. However, it is worth noting that bulk g-C3N4 shows lower catalytic activity due to its fast photogenerated charge recombination, low specific surface area, and weak oxidation-reduction ability. In general, the bands associated with steep edges are caused by electronic excitations from the valence band (VB) to the conduction band (CB), while those associated with weak visible light absorption are caused by incomplete long-range order in the atomic structure caused by tail excitation [32,33]. Hence, to obtain better catalytic performance, it is necessary to optimize the structure of g-C3N4 to improve the quantum size effect [34]. At present, there are many methods of improving the visible light catalytic activity of g-C3N4, including the preparation of surface sensitization, metal or non-metal doping, and heterojunctions with other photocatalysts [24,35,36,37,38]. Putri et al. doped oxygen atoms to bulk g-C3N4 through the hydrothermal method with H2O2 at 120 °C. The result showed that the specific surface area of g-C3N4 increased from 75 to 85 m2·g−1 because of the presence of the O element, which can enhance photocatalyst activity significantly [39]. Yan et al. successfully doped metal elements, such as Mg, K, Ca and Na, to g-C3N4 derived from urea, and found that the doped metal atoms junking with O atoms would change the photocatalyst morphology and electronic structures, which can improve the photocatalyst absorption capacity of visible light and decrease photogenerated charge recombination rate [40]. Li et al. synthesized and charactered g-C3N4/Bi2MoO6 heterojunctions, and the results suggested that the photocatalytic efficiency of g-C3N4/Bi2MoO6 was more than three times that of pristine g-C3N4 or Bi2MoO6 [41].
Many studies have proven that the morphology of g-C3N4 nanostructures is essential for photocatalysis performance [42]. Exfoliating bulk g-C3N4 into nanosheets has been proven to enhance its photocatalytic activity through thermal oxidative etching [43,44]. Meanwhile, the length of thermal oxidative etching time plays a key role in the microstructure and surface chemistries of g-C3N4 [45,46]. Moreover, g-C3N4 synthesized from various precursors also has different photocatalytic activities [30,46]. Therefore, it is also crucial to choose the proper precursor to improve the photocatalytic performance of g-C3N4.
In this study, bulk g-C3N4 was first synthesized by using urea, melamine, dicyandiamide and melamine, respectively, as precursors. Then, g-C3N4 with different surface morphologies and sizes were directly synthesized via thermal oxidative etching of bulk g-C3N4 in air for various periods of time. Next, the physiochemical properties of the different bulk g-C3N4 derived from various precursors, and their corresponding g-C3N4 through thermal oxidative etching, were then analyzed according to the characterization results. SMZ, one of the most widely used sulfonamides, was chosen as a model contaminant substance to evaluate the photocatalytic activities of g-C3N4 derived from various precursors under visible sunlight. This paper focuses on the different precursors, as well as the impact of the thermal oxidative etching time on the structure and photocatalytic performance.

2. Experimental

2.1. Materials

Urea, melamine, dicyandiamide and thiourea for this experiment were obtained from Tianjin Xintong Fine Chemicals Company Limited, Tianjin, P. R. China. SMZ was obtained from Shanghai McLean Biochemical Technology Co., Ltd., Shanghai, P. R. China. All chemicals used in this study were analytical grade and used without further purification. All solutions were prepared using deionized water.

2.2. Synthesis of g-C3N4 Samples

The g-C3N4 samples were synthesized by a thermal oxidative etching method using urea, melamine, dicyandiamide and thiourea, respectively [43]. Briefly, the bulk g-C3N4 sample prepared from urea was synthesized as follows: 10 g of urea was put into a semi-closed crucible with a cover and calcined at 550 °C for 4 h with a heating rate of 2 °C min−1 in a muffle furnace. After the thermal treatment, the obtained yellow-colored powder was cooled to room temperature naturally, then washed thoroughly with distilled water and ethanol, and then dried at 60 °C for 12 h and denoted as U0. Other precursors (melamine, dicyandiamide and thiourea) were also used to synthesize bulk g-C3N4 samples by a similar method, and the synthesized samples were denoted as M0, D0 and T0, respectively. U0 was calcined at 500 °C for 165 min or 330 min with a heating rate of 5 °C min−1 in a muffle furnace; the resulting products were denoted as U165 and U330, respectively. M0, D0 and T0 were also used to synthesize g-C3N4 samples through a similar thermal oxidative etching method to that mentioned above and denoted as M165, M330, D165, D330, T165 and T330, respectively.

2.3. Characterization of the Synthesized g-C3N4

The surface morphologies and microstructure properties of the g-C3N4 samples were measured by a scanning electron microscope (SEM, FEI Quanta-PEG450, American FEI, USA). X-ray diffraction (XRD) patterns of the g-C3N4 samples were collected by an X-ray diffractometer (Rigaku UltimaIV, Japan), where the 2θ values of the obtained data ranged from 10 to 90◦ with Cu Kα irradiation. The photoluminescence (PL) properties of the g-C3N4 samples were measured using a F-98 system (Shanghai, China). XPS measurements were finished using a Thermo VG ESCALAB-250 (Thermo-VG Scientific, Waltham, MA, USA) under A1Kα (1486.6 eV) radiation. The FTIR spectrum was obtained with a PerkinElmer Spectrum Two spectrometer (PerkinElmer Instruments Co., Ltd., Waltham, MA, USA). The specific surface area was quantified using a multipoint Brunauer–Emmett–Teller (BET, Conta NOVE-1000 e, Quantachrome Instruments, USA). The UV–vis diffuse reflectance spectra (DRS) were obtained by a TU-1901 (Beijing, China) with a wavelength range of from 200 to 800 nm.

2.4. Measurement of Photocatalyst Activity

The photocatalytic performance of g-C3N4 samples was evaluated in terms of degrading the SMZ under a 500 W xenon lamp with a 420 nm cut-off filter to simulate visible light irradiation. The distance between the surface of the reaction liquid and the light source was about 10 cm, and then the photocatalyst (100 mg/L) was added to the SMZ solution (3 mg/L) to make a final volume of 50 mL. After ultrasonic treatment for 5 min, the dispersed solution was subjected to gentle stirring for 30 min under dark conditions to reach adsorption–desorption equilibrium. A 1.5 mL suspension was withdrawn and filtered through a 0.22 μm filter (Millipore) at fixed internal time intervals. The SMZ concentration was measured by HPLC (Agilent Technologies 1200-Series).
The photocatalytic degradation process can be transformed to pseudo-first-order kinetics (Equation (1)) through data fitting; thus, pseudo-first-order reaction kinetics (k) can be used to compare the photodegradation efficiency of photocatalyst samples under the same conditions [47,48]:
ln(C0/Ct) = kt

3. Results and Discussion

3.1. Characterization

The morphologies and microstructures of the g-C3N4 samples were investigated by SEM, as shown in Figure 1. It can be seen from Figure 1a–c that the surface of g-C3N4 samples exfoliated by the thermal oxidative method had a large number of irregular blocky agglomerates, and the size distribution was mainly in the range of several micrometers, owing to the existence of the O element, which will produce H2O gas during the high-temperature calcination process. Then, the escaping H2O gas acts as soft templates to help inorganic nanocrystals form porous micro-structures [30,31,42,44]. As thiourea were used as precursors, H2S gas was produced and acted as soft templates to change the microstructure, resulting in the g-C3N4 sample microstructure being different, as shown in Figure 1j–l [42]. When melamine and dicyandiamide were used as precursors, there was no obvious pore structure on the surface of the g-C3N4 samples (Figure 1d–i), which may be attributed to the NH3 generated during the high-temperature calcination not reacting with other gases. It revealed that the release of NH3remained constant, resulting in a better quality of the produced g-C3N4 samples. Specifically, these samples had a higher degree of polymerization and crystallinity. As shown in Figure 1, it was found that the bulk g-C3N4 samples were exfoliated more intensively with the increase of thermal oxidative etching time, and the surfaces demonstrated more wrinkles and irregular shapes. At the same time, with the increase of thermal oxidative etching time, the g-C3N4 nanosheets became very thin, and some of the nanosheets tended to break, in that many smaller nanosheets were produced, and the agglomeration phenomenon was improved.
The XRD patterns of g-C3N4 samples synthesized from the four different precursors are shown in Figure 2. Two typical diffraction peaks were observed in the XRD patterns for all samples, indicating the successful synthesis of g-C3N4 by thermal oxidative etching of the four different precursors. A minor angle diffraction peak at 13.0° can be attributed to an in-planar structural packing, which corresponded to (100) crystal planes of g-C3N4, and the strong peak at 27.4° accorded with the repeated the inter-layer stacking of conjugated aromatic systems, which was indexed for graphitic materials as the (002) peak [49,50,51]. The XRD patterns of all samples did not have significant difference at 13.0°, corresponding to diffraction from (100) planes. Meanwhile, the interplane distance of all samples was around 0.68 nm, which is consistent with the other literature [52,53]. The XRD patterns of U0, M0, D0 and T0 showed diffraction peak intensity around 27.4°: M0 > D0 > T0 > U0, indicating the presence of smaller crystalline domains in U0, in line with the SEM observation. In addition, at the same peak positions, these patterns displayed a slight broadening width of the overall peaks following longer thermal oxidative etching time, indicating that the crystallinity of the g-C3N4 decreased at prolonging thermal oxidative etching time and more edge defects were thereupon made. Hence, the interlayer spacing of g-C3N4 material became larger, which is in good agreement with the phenomenon observed by SEM. The average crystallite size of all samples is shown in Table 1. The crystalline size of g-C3N4 that used urea as a precursor was the smallest, and the thermal oxidation etching time had no obvious effect on the crystalline size.
The FTIR spectra indicates the functional groups of the g-C3N4 samples presented in Figure 3. Similar FTIR spectral vibration modes of g-C3N4 samples from different precursors display a similar characteristic IR absorption spectrum. They show several major bands centered at about 810, 1200–1700 and 3200–3400 cm−1. The sharp peak at 810 cm−1 originates from the characteristic breathing mode of s-triazine [54,55,56]. The peaks in the region from 1200 to 1700 cm−1 are the typical stretching vibrations of trigonal C–N(–C)–C or bridging C–N(–H)–C heterocycles associated with skeletal stretching vibrations of aromatic rings [57]. The broad peaks between 3200 and 3400 cm−1 are assigned to the O–H stretches, indicating that there are adsorbed hydroxyl groups on the g-C3N4 sample surfaces [58,59]. The similarity among all the bands suggests that the thermal treatment of the g-C3N4 samples does not bring about significant changes in the structure of the g-C3N4 nanosheets.
To investigate the surface composition and chemical state of U330, XPS was carried out, and the results are shown in Figure 4. For the sake of brevity, only carbon, nitrogen, oxygen and sodium were detected in the XPS spectra. The strength of the N1s intensity was strongest owing to its highest proportion in U330. The O1s peak can be attributed to the adsorbed H2O on the sample surface, which appeared at about 532.3 eV. To further observe the chemical bonding among nitrogen, carbon and oxygen atoms in U330, the high-definition C1s, N1s and O1s spectra were further deconvoluted into Gaussian–Lorentzian peaks, respectively. As shown in Figure 4b, the C1s spectra show three peaks, in which the peak centered at 284.8 eV is attributed to the sp2 hybridized C atoms C-C [30,60], at 286.2 eV is identified as C=O [61,62] and at 288.2 eV originated from the sp2 bonded C in N=C(-N)2 [63,64]. The high-definition N1s spectra can also be deconvoluted into three Gaussian–Lorentzian peaks (Figure 4c) centered at about 398.8, 400.1 and 401.2 eV, respectively. The peak at 398.8 eV is assigned to aromatic N bonded to two C (C=N–C) sp2 bonded C=N-C involved in the triazine rings or heptazine rings [65,66,67]. The peak 400.1 eV is typically attributed to the graphite-like N in the form of the sp2 hybridized N bonded to three atoms (C–N(–C)–C or C–N(–H)–C [30]. Additionally, the peak 401.2 eV is ascribed to the sp3 hybridized terminal N (N–H2 or N–O) of the heptazine rings [30,68]. In addition, the spectrum of O1s in Figure 4d can be deconvoluted into two single peaks with binding energies of 531.3 and 533.6 eV, which ascribed to carbonyl C=O group and adsorbed water [66], respectively. This was also confirmed by FTIR.
The obtained specific BET surface areas of all g-C3N4 samples are summarized in Table 2. From Table 2, the results indicate that the specific BET surface area increased with prolonging thermal oxidative etching time. Additionally, the larger surface area could provide more reactive sites and adsorb more reactants, which can enhance the photocatalyst activity of samples. Furthermore, the average pore volume also increased with the extension of thermal oxidative etching time, which can be attributed to the mesopores originating from the stacking of g-C3N4 nanosheets. These variation tendencies further confirm that the bulk g-C3N4 can be effectively exfoliated by extension of thermal oxidative etching time, which is also consistent with SEM. Meanwhile, urea-derived g-C3N4 nanosheets had the largest specific surface area compared to g-C3N4 derived from other precursors under the same experimental conditions. Elemental analysis results of the prepared samples are given in Table 3. The molar ratios of C to N of all the g-C3N4 are around 0.60 (theoretical value of g-C3N4 = 0.75), implying incomplete crystallization.
The PL emission spectra of g-C3N4 samples that used urea as a precursor were recorded in Figure 5. PL were used to understand the efficiency of trapping, migration, transfer and separation of charge carriers, and to investigate their lifetime in semiconductors, since PL emission results from the recombination of electron/hole pairs [69,70]. In general, a lower PL intensity suggests a lower recombination rate of the electron–hole pairs under light irradiation [71,72,73]. It can be seen from Figure 5 that all the samples show a broad PL emission spectra in the 500–580 nm region. In comparison, it can be observed that U330 exhibits the lowest emission intensity, which means that U330 is more efficient at promoting the separation of electron–hole pairs. This indicates that U330 is preferable in the case of utilizing the materials as catalysts in the photoreactions, and also suggests that the separation efficiency of photogenerated electrons and holes in urea-derived g-C3N4 samples increases with the extension of thermal etching time.
From Figure 6, which shows the UV–vis of U330, it can be seen that the absorption edge of U330 is about 438 nm, indicating that U330 is responsive in the visible light range and can be activated by visible light, which may be attributed to the bulk g-C3N4 nanosheets with different structures and morphology after thermal etching. At the same time, the thickness and size decrease, and the corresponding band gap changes from 2.7 eV to 2.96 eV. Due to the influence of quantum confinement, the red shift of the spectrum is caused and the conduction band and valence band positions move in the opposite direction, which increases the band gap, enhances the redox ability of photogenerated electron hole pairs, and improves the photocatalytic activity of the synthesized samples.

3.2. Photocatalyst Performance Analysis

The photocatalytic degradation performance of the synthesized samples was evaluated using degradation of SMZ under visible light and recorded by HPLC, as depicted in Figure 7. Among these samples, U330, M330, D330 and T330 exhibited dramatically enhanced visible light photocatalytic activity than the bulk g-C3N4 samples synthesized from different precursors. Kinetic analysis showed that the photodegradation of SMZ followed first-order kinetics, and the kinetic constants (k) were shown as Figure 7b and Table 4. The rate constants of U330, M330, D330 and T330 were 1.57, 2.04, 3.36 and 3.69 times for the corresponding bulk of g-C3N4, respectively. This finding further confirms that the photocatalytic performance could be enhanced by an increase in thermal oxidative etching time. Thermal oxidative etching leads to a significant enhancement of the photocatalytic activity of g-C3N4, mainly due to its thin conjugated structure with a larger surface area and porous structure, which provides the surface with more active sites for promoting adsorption and more channels for mass transfer. Additionally, this is also in line with the BET analysis results. Among these samples, U330 exhibited the most photocatalytic activity for SMZ under the simulated visible sunlight, whose rate constants were 2.14, 1.47 and 1.40 times for M330, D330 and T330, respectively. Among all the photocatalysts from different precursors, U330 was found to be the best one. This might be caused by several factors. Firstly, U330 had enhanced photoactivity due to being less condensed and porous, as confirmed by SEM, leading to a higher BET area and larger proportion of macropores; both allow better mass transport under lower diffusion resistance, enabling molecules to be transferred more easily in the photocatalyst process. Secondly, the urea precursor undergoes a series of gas-releasing stages to form melamine, leading to the formation of a less condensed and porous g-C3N4 with more edge-excited amino groups, compared to other precursors. The substrate could be activated by terminal uncondensed amino groups of the defective U330 structures via O–H bonding and nucleophilic attack [45,74,75]. Hence, U330 is the best choice to be applied to the photodegradation of sulfonamides in water under visible light.

4. Conclusions

In summary, the g-C3N4 nanosheets were synthesized through the thermal oxidative etching method with two different heating times and from four different precursors. The results from characterizations and photocatalytic evaluations showed that thermal oxidative etching time has a significant effect on the properties of g-C3N4, including crystallinity, polymerization degree, surface area and photocatalytic activity. As the heating time increased, the g-C3N4 samples showed lower crystallinity, a higher degree of polymerization, a larger number of macropores and a more enhanced photocatalytic performance. In addition, the type of precursors also significantly affected the photocatalytic performance of the g-C3N4 samples. The kinetic analysis revealed that the photodegradation of SMZ followed first-order kinetics and the rate constant of U330 was 2.14 times that of M330, 1.47 times that of D330 and 1.40 times that of T330. These results indicate that U330 has the potential to be a promising photocatalyst for the degradation of sulfonamides in the aquatic environment due to its superior photodegradation performance and the advantages of its porous and less condensed structure. All these factors prove that U330 is an excellent promising photocatalyst for the degradation of sulfonamides in the aquatic environment.

Author Contributions

Conceptualization, K.L., M.C. and L.C.; methodology, W.X., S.Z. and Y.H.; software, M.C. and W.X.; investigation, M.C., W.X., S.Z. and Z.H.; resources, K.L. and L.C.; data curation, K.L.; writing—original draft preparation, K.L., M.C., and W.X.; writing—review and editing, K.L. and L.C.; visualization, Y.H.; supervision, K.L. and L.C.; funding acquisition, K.L. and L.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (51878316) and the Science and Technology Research Planning Project of Jilin Provincial Department of Education (JJKH20220297KJ, JJKH20220279KJ).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

All authors thank the editor and anonymous reviewers for their constructive comments and suggestions to improve the quality of this paper.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Processes 11 00528 g001 550
Figure 1. SEM images of all g-C3N4 samples: (a) U0, (b) U165, (c) U330, (d) M0, (e) M165, (f) M330, (g) D0, (h) D165, (i) D330, (j) T0, (k) T165 and (l) T330.
Figure 1. SEM images of all g-C3N4 samples: (a) U0, (b) U165, (c) U330, (d) M0, (e) M165, (f) M330, (g) D0, (h) D165, (i) D330, (j) T0, (k) T165 and (l) T330.
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Figure 2. XRD pattens of all g-C3N4 samples.
Figure 2. XRD pattens of all g-C3N4 samples.
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Figure 3. FT-IR spectra of all g-C3N4 samples.
Figure 3. FT-IR spectra of all g-C3N4 samples.
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Figure 4. XPS spectra of U330: (a) full spectrum of U330, (b) C1s, (c) N1s and (d) O1s.
Figure 4. XPS spectra of U330: (a) full spectrum of U330, (b) C1s, (c) N1s and (d) O1s.
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Figure 5. PL spectra of U0, U165 and U330.
Figure 5. PL spectra of U0, U165 and U330.
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Figure 6. UV–vis diffuse reflectance absorption spectrum of U330: (a) ultraviolet diffuse reflectance spectrum of U330 and (b) energy band spectrum of U330.
Figure 6. UV–vis diffuse reflectance absorption spectrum of U330: (a) ultraviolet diffuse reflectance spectrum of U330 and (b) energy band spectrum of U330.
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Figure 7. Photocatalytic efficiencies of SMZ by different g-C3N4 under visible light: (a) t degradation curve; (b) degradation kinetics.
Figure 7. Photocatalytic efficiencies of SMZ by different g-C3N4 under visible light: (a) t degradation curve; (b) degradation kinetics.
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Table
Table 1. The average crystallite size of 12 kinds of g-C3N4.
Table 1. The average crystallite size of 12 kinds of g-C3N4.
SampleSize (nm)
U03.1
U1652
U3303.9
M05.6
M1655.1
M3304.5
D05.8
D1655
D3307.5
T06.5
T1653.9
T3303.4
Table
Table 2. BET analysis of 12 kinds of g-C3N4.
Table 2. BET analysis of 12 kinds of g-C3N4.
SamplesSpecific Surface Area (m2/g)Average Pore Size (nm)Pore Volume (cm3/g)
U063.4643.8450.333
U165112.5963.8660.385
U330160.7353.8220.794
M010.5853.8500.067
M16546.1793.8530.191
M33075.6103.8540.300
D06.0503.7750.028
D16537.1163.8210.145
D33096.9313.8570.395
T013.3813.7690.066
T16533.3663.7890.179
T33079.7593.7730.379
Table
Table 3. Elemental analysis of 12 kinds of g-C3N4.
Table 3. Elemental analysis of 12 kinds of g-C3N4.
SampleC (wt.%)N (wt.%)C/N Molar Ratio
U037.07661.6340.602
U16537.26661.1530.609
U33037.55761.5470.610
M036.89663.4430.582
M16536.68462.0810.591
M33036.24261.7080.587
D037.25863.0820.591
D16536.10961.4820.587
D33036.07360.7110.594
T036.46261.7660.590
T16536.68560.6030.605
T33036.25661.3660.591
Table
Table 4. Kinetic fitting parameters of photodegradation kinetics of SMZ by g-C3N4 prepared from different precursors under visible light.
Table 4. Kinetic fitting parameters of photodegradation kinetics of SMZ by g-C3N4 prepared from different precursors under visible light.
SamplesK (min−1)
U00.01296
U1650.01592
U3300.02039
M00.00465
M1650.00665
M3300.00953
D00.00414
D1650.00951
D3300.0139
T00.00394
T1650.01355
T3300.01455
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Li, K.; Chen, M.; Chen, L.; Zhao, S.; Xue, W.; Han, Z.; Han, Y. Synthesis of g-C3N4 Derived from Different Precursors for Photodegradation of Sulfamethazine under Visible Light. Processes 2023, 11, 528. https://doi.org/10.3390/pr11020528

AMA Style

Li K, Chen M, Chen L, Zhao S, Xue W, Han Z, Han Y. Synthesis of g-C3N4 Derived from Different Precursors for Photodegradation of Sulfamethazine under Visible Light. Processes. 2023; 11(2):528. https://doi.org/10.3390/pr11020528

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Li, Ke, Miaomiao Chen, Lei Chen, Songying Zhao, Wencong Xue, Zixuan Han, and Yanchao Han. 2023. "Synthesis of g-C3N4 Derived from Different Precursors for Photodegradation of Sulfamethazine under Visible Light" Processes 11, no. 2: 528. https://doi.org/10.3390/pr11020528

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