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Article

Comparative Thermal and Supramolecular Hydrothermal Synthesis of g-C3N4 Toward Efficient Photocatalytic Degradation of Gallic Acid

by
Fernando Cantor Pérez
1,
Julia Liliana Rodríguez Santillán
1,*,
Ricardo Santillán Peréz
2,*,
Iliana Fuentes Camargo
1,
Issis C. Romero Ibarra
3,
Jesús I. Guzmán Castañeda
4,
Jorge L. Vazquez-Arce
5,
Hugo Tiznado
6 and
Hugo Martínez Gutiérrez
7
1
Laboratorio de Investigación en Ingeniería Química Ambiental, ESIQIE-Instituto Politécnico Nacional, Zacatenco, Ciudad de Mexico 07738, Mexico
2
Laboratorio de Polímeros, Escuela Superior de Ingeniería Química e Industrias Extractivas-Instituto Politécnico Nacional, Zacatenco, Ciudad de Mexico 07738, Mexico
3
Unidad Profesional Interdisciplinaria en Ingeniería y Tecnologías Avanzadas, Instituto Politécnico Nacional, Av. IPN No. 2580, Gustavo A. Madero, Ciudad de Mexico 07340, Mexico
4
Unidad Profesional Adolfo López Mateos, Instituto Politécnico Nacional, Escuela Superior de Ingeniería Química e Industrias Extractivas, Edificio 6, Ciudad de Mexico 07738, Mexico
5
Leibniz Institute for Solid State and Materials Research, Helmholtzstraße 20, 01069 Dresden, Germany
6
Centro de Nanociencias y Nanotecnología, Universidad Nacional Autónoma de Mexico, Km 107 Carretera Tijuana-Ensenada s/n, Ensenada 22860, BC, Mexico
7
Centro de Nanociencias y Micro y Nanotecnologías, Instituto Politécnico Nacional, Zacatenco, Ciudad de Mexico 07738, Mexico
*
Authors to whom correspondence should be addressed.
Catalysts 2025, 15(9), 858; https://doi.org/10.3390/catal15090858
Submission received: 14 August 2025 / Revised: 28 August 2025 / Accepted: 3 September 2025 / Published: 5 September 2025
(This article belongs to the Special Issue Environmentally Friendly Catalytic Nanomaterials for Advanced Oxidation and Reduction Technology)
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Abstract

Gallic acid (GA), a polyphenol extensively used in the food, wine, and pharmaceutical industries, is known for its inhibitory effects on soil microbial activity. Photocatalytic degradation offers an environmentally friendly solution for GA removal from water. In this work, graphitic carbon nitride (g-C3N4) photocatalysts were synthesized by two methods: thermal exfoliation (CN-E) and supramolecular assembly via hydrothermal processing (HCN-II). Structural analyses by XRD, FTIR, and XPS confirmed the formation of the g-C3N4 framework, while SEM revealed that CN-E consisted of folded and curled nanosheets, whereas HCN-II displayed a polyhedral–nanosheet hybrid architecture with internal channels. Both materials achieved approximately 80% GA degradation within 180 min under visible-light irradiation, yet HCN-II exhibited a superior apparent rate constant (k = 0.01156 min−1) compared with CN-E. Radical trapping experiments demonstrated that O2•− and h+ were the primary reactive oxygen species involved, with OH• making a minor contribution. The enhanced performance of HCN-II is attributed to its higher surface area, improved light harvesting, and efficient charge separation derived from supramolecular assembly. These findings highlight the potential of engineered g-C3N4 nanostructures as efficient, metal-free photocatalysts for the degradation of recalcitrant organic pollutants in water treatment applications.

1. Introduction

The rapid growth of the global population and accelerated industrialization have intensified the water contamination crisis worldwide. Significant amounts of hazardous substances are continuously introduced into aquatic environments through industrial effluents, agricultural runoff, domestic and restaurant wastewater, automotive manufacturing, and oil refinery processes [1]. In recent years, a broad spectrum of micropollutants, commonly referred to as emerging contaminants (ECs), has drawn considerable attention due to their adverse impacts on ecosystems and human health. These ECs encompass perfluorinated compounds, disinfection byproducts, personal care products, pesticides, illicit drugs, UV filters, pharmaceuticals, hormones, and various industrial chemicals, all frequently detected in wastewater, groundwater, and surface water [2]. Among these, pharmaceutical compounds, particularly antibiotics characterized by mutagenic and carcinogenic potential, present significant environmental challenges due to their persistence, low biodegradability, and toxicity to both human health and aquatic ecosystems. Consequently, developing effective strategies for the removal of antibiotics from wastewater is imperative [3].
Considering these challenges, innovative water purification technologies are essential for the effective removal of toxic organic pollutants. Advanced oxidation processes (AOPs) have emerged as promising methods for the treatment of organic contaminants in wastewater, offering superior removal efficiencies compared to conventional physicochemical techniques such as adsorption, precipitation, reverse osmosis, anaerobic oxidation, flocculation, and coagulation. The efficacy of AOPs is primarily attributed to the generation of reactive oxidizing species, including hydroxyl radical (OH•), peroxide ion (O2−2), singlet oxygen (1O2), superoxide anion radical (O2•−), and sulfate radicals (SO4•−), which efficiently oxidize hazardous chemicals in wastewater [4,5]. Among AOPs, heterogeneous photocatalysis (HP) stands out for its operational simplicity and environmental compatibility. HP relies on the photogeneration of electron–hole pairs (e−/h+), which drive the degradation of toxic organic compounds into smaller fragments, ultimately achieving high degrees of mineralization to water and carbon dioxide [6].
In recent decades, significant advances have been made in the development of inorganic semiconductor catalysts for photocatalytic pollutant removal. However, many of these semiconductors depend on expensive or scarce metal elements, limiting their large-scale application [7]. Graphitic carbon nitride (g-C3N4), a metal-free polymer n-type semiconductor, has garnered widespread attention due to its low cost, visible light responsiveness, non-toxicity, and excellent chemical and thermal stability [8]. Typically, bulk g-C3N4 is synthesized via thermal polymerization, which results in low surface area materials with limited active sites caused by the formation of disordered agglomerates. This structural limitation promotes significant recombination of photogenerated electron–hole pairs and reduces the number of available active sites [9].
To address these limitations, several strategies have been developed to enhance the photocatalytic performance of g-C3N4, including morphology control, element doping [10,11], heterojunction construction [12], porous structure design [13], metal loading [14] and defect engineering [15,16,17,18,19]. Among these approaches, morphology control, particularly the synthesis of g-C3N4 nanosheets, has proven highly effective in increasing the density of reactive sites for pollutant degradation while simultaneously suppressing the recombination of photogenerated charge carriers. Supramolecular assembly stands out as a promising route to obtain well-defined architectures without the need for additional templates, relying instead on molecular self-assembly driven by non-covalent interactions [7,20,21]. In such processes, hydrogen bonding plays a key role in the formation of supramolecular aggregates, with well-documented systems including melamine-cyanuric acid (MC), dicyandiamide-cyanuric acid, and melamine-cyanuric chloride complexes [22]. For instance, Chen et al. [7] employed acetic acid in the MC assembly to synthesize porous g-C3N4 hexagonal prisms with a tightly packed structure and a surface area nearly eight times greater than that of bulk g-C3N4. Likewise, Li et al. [23] fine-tuned the acid environment by introducing varying amounts of HCl during hydrothermal reaction, producing g-C3N4 nanotubes or nanosheets with significantly enhanced photocatalytic activity under visible light.
In addition to supramolecular-based strategies, g-C3N4 can be further modified through thermal exfoliation, a process in which the multilayer structure of bulk g-C3N4 is subjected to pyrolysis to produce thinner layers with enhanced physicochemical properties, such as increased specific surface area. Studies have demonstrated that single- or few-layer g-C3N4 exhibits superior photocatalytic performance compared to its bulk counterpart, primarily due to more efficient charge carrier transfer and separation [24,25,26].
Although several strategies have been reported to modify g-C3N4, most studies investigate either thermal exfoliation or supramolecular hydrothermal synthesis independently. A direct and systematic comparison between these two widely used approaches is still lacking. Such a comparison is relevant since the thermal route typically produces ultrathin nanosheets with enlarged surface areas, while the supramolecular hydrothermal method can generate porous and defect-rich frameworks. Establishing how these structural differences influence photocatalytic performance toward gallic acid degradation will provide valuable insights for the rational design of g-C3N4-based photocatalysts.
In this work, g-C3N4 was synthesized by three distinct routes: bulk thermal polycondensation (reference), thermal exfoliation, and supramolecular hydrothermal synthesis. The impact of synthesis conditions on structural, morphological, and surface properties of the catalysts was elucidated by comprehensive physicochemical characterization. The most active catalyst was further evaluated in terms of optimal dosage and reactive oxygen species (ROS) generation, which are critical parameters for water pollutant degradation. Gallic acid (GA), a polyphenol widely employed in the olive oil and wine industries, was selected as the model contaminant owing to its inhibitory effects on soil microbial activity, which can significantly compromise soil fertility [27]. The development of efficient photocatalysts for GA degradation is therefore of considerable environmental significance.

2. Results and Discussion

2.1. Catalyst Characterization

The crystalline structures of the synthesized g-C3N4 samples were examined by X-ray diffraction (XRD), Figure 1a. All patterns displayed two characteristic diffraction peaks at 2ϴ = 13.1° and 27.4°, assigned to the (100) and (002) planes of g-C3N4, respectively. According to Wu K. et al. [28], the (100) peak corresponds to the interlayer structural packing of tri-s-triazine units, whereas the (002) reflection is related to the interlayer stacking of the π-conjugated aromatic system. Variations in peak intensity and width indicated differences in crystallinity and stacking order. In particular, HCN-I and HCN-II exhibited lower (002) intensities compared to CN-I and CN-E, suggesting that the hydrothermal route disrupts the regular stacking of g-C3N4 layers. The diffraction angle of the (002) plane followed the trend CN-I = HCN-II > CN-E = HCN-I, implying a decrease in interlayer spacing for CN-I and HCN-II, Table 1. The broader (002) peak in HCN-II supports the formation of a more disordered and porous architecture, in agreement with previous reports on porous g-C3N4 [7,29].
Fourier transform infrared (FTIR) spectra (Figure 1b) confirmed that all samples retained the basic tri-s-triazine framework, as evidenced by the characteristic bands between 1000 and 1750 cm−1 (C–N stretching modes), the stretching modes of the triazine ring at 500–900 cm−1, and the N–H stretching vibration at 3000–3300 cm−1. The preservation of these signals, despite changes in XRD patterns, indicates that the hydrothermal and exfoliation treatments modify the long-range order without destroying the fundamental chemical structure.
To assess the impact of these structural modifications on textural properties, N2 adsorption–desorption measurements were carried out (Figure 2a). All samples displayed type III isotherms with H3 hysteresis loops, indicative of layered structures. CN-I exhibited the lowest specific surface area (24.3 m2 g−1), consistent with the stacked flake morphology observed by SEM. In contrast, HCN-II reached 81.7 m2/g, about 3.3 times higher, due to reduced layer thickness and the creation of interconnected pores, Table 1. This enhanced porosity is expected to increase the number of accessible active sites for photocatalytic reactions.
Optical absorption properties were investigated by ultraviolet-visible diffuse reflectance spectroscopy (UV–Vis DRS), Figure 2b. The bandgap energies (Eg), calculated using the Kubelka–Munk method, range from 2.65 to 2.68 eV (Figure 2c), indicating similar intrinsic light absorption thresholds for all samples. However, the presence of structural defects and increased surface area in HCN-II may facilitate charge separation and light harvesting beyond what is predicted solely by the bandgap values.
The surface chemical states and composition were analyzed by X-ray photoelectron spectroscopy (XPS), Figure 3 and Table 2. The survey spectra signals corresponding to N1s, C1s, and O1s regions, Figure S1. Furthermore, all synthesized catalysts exhibit similar C1s and N1s spectra, demonstrating the presence of the basic tri-s-triazine units, which are the elementary building blocks of g-C3N4. High-resolution N1s spectra were deconvoluted into four peaks at 397.9, 399.2, 400.3, and 404.4 eV, attributed to sp2-hybridized nitrogen in C=N-C, tertiary nitrogen N-(C)3, amino groups C-N-H, and π–π * excitations, respectively [30], Figure 3a.
The C=N-C/N-(C)3 ratio decreased in the order HCN-I (3.70) > CN-E (3.57) > CN-I (3.33) > HCN-II (3.22), indicating more structural defects associated with nitrogen deficiency in HCN-II [31]. Such defects, often described in the literature as nitrogen vacancies, may act as electron trapping centers, thereby facilitating charge separation efficiency [32,33,34]. The C1s spectra confirmed the presence of graphitic carbon (C-C, 284.8 eV) and the sp2-hybridized C-N bonds of the triazine rings (288.2 eV), with minor contributions from C-OH species related to oxygen incorporation during synthesis, Figure 3b.
Morphologies and structural features of synthesized catalysts were examined by scanning electron microscopy (SEM), Figure 4. The CN-I sample exhibited large agglomerates of stacked flakes (Figure 4a), whose high-magnification image (Figure 4e) reveals that the basic structural unit is sheets-like layers. This morphology likely explains its lowest specific surface area (24.3 m2/g), in agreement with structures reported by Pattnaik et al. [35]. Thermal exfoliation of CN-I to produce CN-E resulted in thinner, more separated layers, with evident folding and curling of the sheets (Figure 4b,f), consistent with the formation of g-C3N4 nanosheets as described by Jiang X. et al. [36].
Distinct morphological features were also observed in the hydrothermally synthesized samples. HCN-I (Figure 4c) presented a compact solid structure composed of agglomerated nanosheets and well-defined regular shapes. At higher magnification, hexagonal prisms were visible (Figure 4g), possibly formed due to a slower crystallization rate under hydrothermal conditions compared to thermal treatment. In contrast, HCN-II exhibited a loosely packed structure with abundant pores (Figure 4d). High-magnification images revealed a polyhedral structure interlaced with abundant nanosheets forming open channels (Figure 4h). This distinctive morphology arises from the molecular self-assembly of cyanuric acid and melamine via non-covalent interactions, leading to a structurally stable and porous framework.
In summary, the combined structural (XRD, FTIR), textural (BET), optical (UV–Vis), chemical (XPS), and morphological (SEM) analyses reveal that HCN-II possesses a unique combination of high surface area, abundant mesopores, and nitrogen vacancies, while preserving the fundamental g-C3N4 framework. These synergistic features are expected to enhance light absorption, charge separation, and availability of active sites, which should directly improve photocatalytic performance.

2.2. Photocatalytic Performance of g-C3N4 Samples for GA Removal

Considering the structural, textural, and optical properties discussed in Section 2.1, the photocatalytic activity of the synthesized g-C3N4 catalysts was evaluated for the degradation of GA under visible light irradiation. As shown in Figure 5a, the adsorption of GA in dark conditions was limited (<15% after 30 min), indicating that surface area alone did not significantly contribute to pollutant removal. Furthermore, a control experiment under light irradiation without a catalyst confirmed that direct photodegradation of GA was negligible (Figure S2). In addition, GA adsorption profiles for the four catalysts (Figure S3) show that only ~10% of the initial GA concentration was adsorbed, indicating minimal contribution from adsorption.
In the presence of both catalyst and light, clear performance differences were observed. HCN-II and CN-E exhibited markedly higher degradation efficiencies compared to CN-I and HCN-I. These results are consistent with the morphological and compositional features described earlier, where HCN-II, with the highest specific surface area (81.7 m2/g), abundant nitrogen vacancies (lowest C=N-C/N-(C)3 ratio in Table 2), and a polyhedral–nanosheet hybrid architecture (Figure 4d,h), demonstrated enhanced light absorption, improved charge separation, and a greater number of active sites. Similarly, CN-E, composed of thinner and more exfoliated nanosheets (Figure 4b,f), allowed for increased light penetration and easier access to reactive sites, contributing to its higher photocatalytic activity compared to CN-I and HCN-I [37].
The degradation kinetics followed a pseudo-first-order model, ln (C/C0) = kt, where k is the rate constant (min−1). As shown in Figure 5b, the rate constants decreased in the order HCN-II > CN-E > CN-I ~ HCN-I, with HCN-II reaching a value 1.8 times higher than CN-I. This superior activity is attributed to the combined effect of large surface area, nitrogen vacancy-induced electron trapping, and supramolecular assembly from cyanuric acid and melamine during synthesis.
The influence of catalyst dosage was further examined using HCN-II (Figure 6a). The degradation efficiency increased with loading up to 0.1 g L−1, reaching 95% removal after 180 min, with a corresponding k value of 0.01446 min−1 (Figure 6b). Further increases in dosage led to decreased efficiency due to light scattering and shielding effects (Figure 6c). This behavior can be explained by three factors: (i) at low loading, insufficient photons are absorbed; (ii) moderate loading maximizes photon–catalyst interactions; and (iii) excessive loading reduces light penetration into the suspension.
To identify the reactive species responsible for GA degradation, radical trapping experiments were conducted using tert-butanol (TBA), benzoquinone (BQ), and ethylenediaminetetraacetic acid (EDTA) as scavengers for OH•, O•2−, and h+, respectively. These assignments are consistent with previous studies in which TBA, p-BQ, and EDTA have been widely employed as selective radical scavengers, with reported reaction rate constants on the order of 108 M−1 s−1 [38,39,40,41,42].
In Figure 7, the most pronounced inhibition was observed with BQ and EDTA, indicating that O2•− and h+ are the dominant species, while •OH radicals play a secondary role. It should be noted that the use of scavengers, while effective for identifying ROS, may also influence photocatalytic efficiency by adsorbing onto the catalyst surface or generating secondary species that can alter the degradation pathway [43]. In this study, scavenger experiments were employed mainly as a qualitative approach to identify the dominant reactive species.
HPLC analysis identified intermediate products formed during GA degradation (Figure S4), indicating that active radicals such as superoxide radicals, hydroxyl radicals, and photoinduced holes played a key role in breaking down the aromatic ring into smaller molecules. Based on these observations, a photocatalytic degradation pathway for GA using HCN-II as the catalyst is proposed (Figure 8).
The catalytic performance of the synthesized g-C3N4 materials was found to be comparable or superior to that of previously reported photocatalysts, Table 3, underscoring the outstanding efficiency of HCN-II. These results confirm that HCN-II is an adequate photocatalyst for the removal of polyphenolic contaminants from water, offering a viable route toward advanced water purification technologies.

3. Materials and Methods

3.1. Chemicals and Reagents

Melamine (C3H6N6) and cyanuric acid (C3H3N3O3) were purchased from Sigma-Aldrich (Mexico City, Mexico). Ethanol (C2H6O) was supplied by Tecsiquim (Iztacalco, Mexico). All chemicals were of analytical-grade purity and used without further purification. Deionized water was employed in all experimental procedures.

3.2. Synthesis of Catalysts

g-C3N4 nanomaterials were synthesized via a hydrothermal method using a 1:1 weight ratio of melamine (4 g) and cyanuric acid (4 g). The powders were dispersed and thoroughly mixed in 80 mL of deionized water, and the resulting suspension was transferred into a Teflon-lined stainless-steel autoclave. The autoclave was heated at 180 °C for 24 h, followed by natural cooling to room temperature. The obtained solids were filtered, washed with deionized water and ethanol to remove residual byproducts, and then dried. The dried material was placed in an alumina crucible, sealed, and calcinated at 550 °C for 4 h in a muffle furnace to obtain yellow g-C3N4, which was subsequently ground into a fine powder. Samples synthesized in the absence of cyanuric acid were designated as HCN-I, while those prepared in its presence were denoted as HCN-II. For comparison, bulk g-C3N4 (CN-I) was prepared by direct thermal polycondensation of melamine (8 g) at 550 °C for 4 h. Thermal exfoliation of bulk g-C3N4 was performed by heating CN-I (2 g) under the same conditions, producing exfoliated nanosheets (CN-E).

3.3. Characterization

The structural properties of the catalysts were analyzed by XRD using a Bruker D8 Advance diffractometer with Cu Kα radiation (λ = 1.5406 Å) at a scan rate of 0.02° s−1 over a 2ϴ range of 10–40°. Functional groups were identified via FTIR on a PerkinElmer spectrum 400 equipped with an attenuated total reflectance (ATR) accessory. UV–Vis DRS was performed on an Agilent Cary 500 spectrophotometer with an integrating sphere. XPS measurements were conducted using a SPECS system with Al Kα radiation (hν  =  1487 eV). Morphologies were examined via scanning electron microscopy (SEM) using a JEOL-JSM-7800F microscope (JEOL Ltd., Tokyo, Japan).

3.4. Photocatalytic Activity

Photocatalytic performance was evaluated using GA as a model pollutant in an open-top glass reactor containing 200 mL of GA solution (50 mg/L). Illumination was provided by a 50 W LED chip lamp (λ = 400 nm). All experiments under light irradiation were conducted at ambient temperature (25 ± 1 °C) with a ventilator and heat dissipator used to prevent any temperature rise. Prior to irradiation, the suspension was stirred in the dark for 30 min to achieve adsorption–desorption equilibrium.
Upon light exposure, aliquots were withdrawn at 30 min intervals, filtered through 0.22 µm membrane filters, and analyzed by high-performance liquid chromatography (HPLC) using a Perkin Elmer Flexar system. The HPLC analysis was carried out with (a) a C18 column (4.6 × 250 mm, 5 µm), (b) a mobile phase of acetonitrile and potassium dihydrogen phosphate solution (pH 2.5) in a 30:70 v/v ratio, (c) a flow rate of 0.6 mL min−1, and (d) detection at 210 nm using a diode array detector.

4. Conclusions

g-C3N4 nanomaterials were successfully synthesized via two distinct approaches: thermal exfoliation (CN-E) and supramolecular assembly through a hydrothermal process (HCN-II). Structural characterization by XRD, FTIR, and XPS not only confirmed the successful formation of g-C3N4 but also revealed that the synthesis route exerted a decisive influence on the resulting morphology. Thermal exfoliation produced folded and curled nanosheets, whereas the hydrothermal route with supramolecular assembly yielded well-defined polyhedral structures with internal channels. These morphologies contrasted sharply with the densely packed agglomerates of stacked flakes observed in bulk g-C3N4 (CN-I) and the hexagonal prisms obtained for hydrothermal synthesis without supramolecular precursors (HCN-I).
Textural analysis showed a progressive increase in specific surface area, following the order CN-I (24.3 m2/g) < CN-E (28.1 m2/g) < HCN-I (36.4 m2/g) < HCN-II (81.7 m2/g). These structural and surface properties directly influenced the photocatalytic degradation of GA, with the apparent rate constant following the trend HCN-II > CN-E > CN-I ~ HCN-I. Catalyst loading optimization for HCN-II indicated that the concentrations above 0.1 g/L induced a light-screening effect, thereby reducing photocatalytic efficiency. Reactive species trapping experiments identified photoinduced h+ and O•2− as the primary oxidizing agents, with OH• contributing to a lesser extent.
Overall, HCN-II demonstrated the highest photocatalytic performance, attributable to its large surface area, tailored polyhedral–nanosheet hybrid morphology, and efficient charge carrier separation. Supramolecular-assisted hydrothermal synthesis emerges as a viable pathway for developing efficient, metal-free photocatalysts for water treatment applications.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal15090858/s1, Figure S1: Survey spectra of prepared catalysts. Figure S2: Photodegradation of GA without a catalyst. Figure S3: GA adsorption profiles for the synthetized catalysts. Figure S4: Chromatogram of identified byproducts during photocatalytic of GA.

Author Contributions

F.C.P.: Conceptualization, methodology, formal analysis, investigation. J.L.R.S.: Formal analysis, writing—original draft, writing—review and editing, supervision. R.S.P.: investigation, writing—review and editing, supervision. I.F.C.: Investigation, resources. I.C.R.I.: Formal analysis. J.I.G.C.: Formal analysis, investigation. J.L.V.-A.: Data curation, writing—original draft. H.T.: Data curation, writing—review and editing, H.M.G.: Formal analysis, investigation. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Instituto Politécnico Nacional (Projects No. 20253497, Innovation No. 20250332), the projects PAPIIT IN119023 and IG100925. Proyecto apoyado por la Secihti en el año 2025 (C-1456).

Data Availability Statement

Data will be made available on request.

Acknowledgments

The authors acknowledge to Centro de Nanociencias y Micro y Nanotecnologías, Instituto Politécnico Nacional. The authors also thank David Domínguez for his valuable technical assistance.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00858 g001
Figure 1. (a) XRD patterns and (b) FTIR spectra of CN-I, CN-E, HCN-I, and HCN-II samples.
Figure 1. (a) XRD patterns and (b) FTIR spectra of CN-I, CN-E, HCN-I, and HCN-II samples.
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Catalysts 15 00858 g002
Figure 2. (a) N2 adsorption–desorption isotherms of the as-prepared catalysts (closed symbols: adsorption; open symbols: desorption), (b) UV–Vis diffuse reflectance spectra, and (c) Tauc plots of (αhν)1/2 versus hν.
Figure 2. (a) N2 adsorption–desorption isotherms of the as-prepared catalysts (closed symbols: adsorption; open symbols: desorption), (b) UV–Vis diffuse reflectance spectra, and (c) Tauc plots of (αhν)1/2 versus hν.
Catalysts 15 00858 g002
Catalysts 15 00858 g003
Figure 3. High resolution XPS spectra of (a) N 1s and (b) C 1s for CN-I, CN-E, HCN-I, and HCN-II samples.
Figure 3. High resolution XPS spectra of (a) N 1s and (b) C 1s for CN-I, CN-E, HCN-I, and HCN-II samples.
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Catalysts 15 00858 g004
Figure 4. SEM images of (a,e) CN-I, (b,f) CN-E, (c,g) HCN-I, and (d,h) HCN-II. Images acquired at (a–d) 1000× and (e–h) 5000×.
Figure 4. SEM images of (a,e) CN-I, (b,f) CN-E, (c,g) HCN-I, and (d,h) HCN-II. Images acquired at (a–d) 1000× and (e–h) 5000×.
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Catalysts 15 00858 g005
Figure 5. (a) Photocatalytic activity for GA degradation of as-prepared samples and (b) their kinetics curves. Experimental conditions: [GA] = 50 mg/L, [catalyst] = 0.5 g/L, LED Chip lamp (50 W, 400 nm).
Figure 5. (a) Photocatalytic activity for GA degradation of as-prepared samples and (b) their kinetics curves. Experimental conditions: [GA] = 50 mg/L, [catalyst] = 0.5 g/L, LED Chip lamp (50 W, 400 nm).
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Catalysts 15 00858 g006
Figure 6. (a) Photocatalytic activity of HCN-II for GA degradation: (b) their kinetics curves at several catalyst doses, (c) plot of rate constants versus catalyst dose. Experimental conditions: [GA] = 50 mg/L, LED Chip lamp (50 W, 400 nm).
Figure 6. (a) Photocatalytic activity of HCN-II for GA degradation: (b) their kinetics curves at several catalyst doses, (c) plot of rate constants versus catalyst dose. Experimental conditions: [GA] = 50 mg/L, LED Chip lamp (50 W, 400 nm).
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Catalysts 15 00858 g007
Figure 7. Comparison of the photocatalytic performances of HCN-II for the degradation of GA without or with the addition of TBA, EDTA, and BQ. Experimental conditions: [GA] = 50 mg/L.
Figure 7. Comparison of the photocatalytic performances of HCN-II for the degradation of GA without or with the addition of TBA, EDTA, and BQ. Experimental conditions: [GA] = 50 mg/L.
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Catalysts 15 00858 g008
Figure 8. A proposed photocatalytic degradation pathway of GA, showing its stepwise conversion from GA to maleic acid, then to oxalic/formic acids, and finally to complete mineralization (CO2 and H2O).
Figure 8. A proposed photocatalytic degradation pathway of GA, showing its stepwise conversion from GA to maleic acid, then to oxalic/formic acids, and finally to complete mineralization (CO2 and H2O).
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Table 1. Chemical properties of synthesized catalysts.
Table 1. Chemical properties of synthesized catalysts.
Catalyst2ϴ, °d002, nm *BET, m2/gPore Diameter, nmBand Gap, eV
CN-I27.400.324824.33.902.68
CN-E27.270.326828.13.892.66
HCN-I27.240.327236.43.882.64
HCN-II27.480.324381.73.912.67
* d002 denotes the interlayer spacing calculated from the 002 reflection.
Table 2. XPS N 1s spectra results of all synthesized catalysts.
Table 2. XPS N 1s spectra results of all synthesized catalysts.
SampleC=N-C, %N-(C)3, %C=N-C/N-(C)3
CN-I57.2917.193.33
CN-E58.0516.253.57
HCN-I56.9215.373.70
HCN-II58.5818.163.22
Table 3. A comparison study of present work with previously reported work using photocatalysts by GA removal.
Table 3. A comparison study of present work with previously reported work using photocatalysts by GA removal.
PhotocatalystExperimental ConditionsIrradiation Source and Exposure Time% DegradationReference
g-C3N4
(Thermal exfoliation and hydrothermal synthesis)		V = 200 mL
[GA] = 50 mg/L
[g-C3N4] = 0.1 g/L		A LED Chip lamp (50 W)
180 min		82This work
LaNiSbWO4-G-PANI
(Sonochemical process)		V = 100 mL
[GA] = 17 mg/L
[LaNiSbWO4-G-PANI] =1 g/L		Xe lamp (500 W)
180 min		90[44]
BiOI microspheres
(Solvothermal synthesis)		V = 250 mL
[GA] = 20 mg/L
[BiOI]= 0.2–0.6 g/L		Xe lamp (12 W)
5 min		82[45]
TiO2
(P25, Degussa)		V = 250 mL
[GA] = 10 mg/L
[TiO2] = 0.2 g/L		Solar simulator
(300 W)
60 min		70[46]
40%wt CuO–TiO2
(Impregnation method followed by calcination at 400 °C in air)		V = 150 mL
[GA] = 50 mg/L
[40%wt CuO–TiO2] = 0.5 g/L		LEDs
(λ = 375 nm and λ = 470 nm)
150 min		70[47]
r-GO-Cu/Bi-NRs
(Co-precipitation)		V = 250 mL
[GA] = 1–20 mg/L
[catalyst] = 100–600 mg/L		Xe lamp (12 W)
60 min		96[48]
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Cantor Pérez, F.; Rodríguez Santillán, J.L.; Santillán Peréz, R.; Fuentes Camargo, I.; Romero Ibarra, I.C.; Guzmán Castañeda, J.I.; Vazquez-Arce, J.L.; Tiznado, H.; Martínez Gutiérrez, H. Comparative Thermal and Supramolecular Hydrothermal Synthesis of g-C3N4 Toward Efficient Photocatalytic Degradation of Gallic Acid. Catalysts 2025, 15, 858. https://doi.org/10.3390/catal15090858

AMA Style

Cantor Pérez F, Rodríguez Santillán JL, Santillán Peréz R, Fuentes Camargo I, Romero Ibarra IC, Guzmán Castañeda JI, Vazquez-Arce JL, Tiznado H, Martínez Gutiérrez H. Comparative Thermal and Supramolecular Hydrothermal Synthesis of g-C3N4 Toward Efficient Photocatalytic Degradation of Gallic Acid. Catalysts. 2025; 15(9):858. https://doi.org/10.3390/catal15090858

Chicago/Turabian Style

Cantor Pérez, Fernando, Julia Liliana Rodríguez Santillán, Ricardo Santillán Peréz, Iliana Fuentes Camargo, Issis C. Romero Ibarra, Jesús I. Guzmán Castañeda, Jorge L. Vazquez-Arce, Hugo Tiznado, and Hugo Martínez Gutiérrez. 2025. "Comparative Thermal and Supramolecular Hydrothermal Synthesis of g-C3N4 Toward Efficient Photocatalytic Degradation of Gallic Acid" Catalysts 15, no. 9: 858. https://doi.org/10.3390/catal15090858

APA Style

Cantor Pérez, F., Rodríguez Santillán, J. L., Santillán Peréz, R., Fuentes Camargo, I., Romero Ibarra, I. C., Guzmán Castañeda, J. I., Vazquez-Arce, J. L., Tiznado, H., & Martínez Gutiérrez, H. (2025). Comparative Thermal and Supramolecular Hydrothermal Synthesis of g-C3N4 Toward Efficient Photocatalytic Degradation of Gallic Acid. Catalysts, 15(9), 858. https://doi.org/10.3390/catal15090858

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