Nothing Special   »   [go: up one dir, main page]
Next Article in Journal
Synthesis of Novel Gefitinib-Conjugated 1,2,3-Triazole Derivatives and Their Effect of Inducing DNA Damage and Apoptosis in Tumor Cells
Previous Article in Journal
Valorisation of Winery By-Products: Revealing the Polyphenolic Profile of Grape Stems and Their Inhibitory Effects on Skin Aging-Enzymes for Cosmetic and Pharmaceutical Applications
You seem to have javascript disabled. Please note that many of the page functionalities won't work as expected without javascript enabled.
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Molecules
Volume 29
Issue 22
10.3390/molecules29225439
molecules-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Carbon Nanotube–Phenyl Modified g-C3N4: A Visible Light Driven Efficient Charge Transfer System for Photocatalytic Degradation of Rhodamine B

by
Sahar Aghapour Ghourichay
1,
Samira Agbolaghi
2,
Riccardo Corpino
1 and
Pier Carlo Ricci
1,*
1
Department of Physics, University of Cagliari, S.P. 8 Km 0.700, 09042 Monserrato, CA, Italy
2
Chemical Engineering Department, Faculty of Engineering, Azarbaijan Shahid Madani University, Tabriz 53714-161, Iran
*
Author to whom correspondence should be addressed.
Molecules 2024, 29(22), 5439; https://doi.org/10.3390/molecules29225439
Submission received: 20 September 2024 / Revised: 31 October 2024 / Accepted: 1 November 2024 / Published: 18 November 2024
(This article belongs to the Section Physical Chemistry)
Browse Figures
Figure 1
<p>Raman spectra of CNT-COOH, f-CNT, and f-CNT/PhCN. The asterisks (*) indicate the Raman peaks of PhCN.</p> "> Figure 2
<p>XRD patterns for (<b>a</b>) PhCN, f-CNT/PhCN, inset normalized area of PhCN diffraction peak and (<b>b</b>) f-CNT, f-CNT/PhCN.</p> "> Figure 3
<p>TEM images of (<b>a</b>) f-CNT, (<b>b</b>) PhCN, and (<b>c</b>) f-CNT/PhCN.</p> "> Figure 4
<p>Absorption spectra of PhCN and f-CNT/PhCN.</p> "> Figure 5
<p>Time-resolved measurement for PhCN and f-CNT/PhCN: ((<b>a</b>,<b>c</b>) 3D profiles for f-CNT/PhCN and PhCN), (<b>b</b>) photoluminescence intensity versus time delay. The blue and red line represent the numerical fit. (<b>d</b>) Photoluminescence intensity versus wavelength.</p> "> Figure 6
<p>Evaluation of the photocatalytic activity. (<b>A</b>) Photocatalytic degradation of pure PhCN, CNT/PhCN and f-CNT/PhCN. (<b>B</b>) Absorption spectrum of RhB solution with f-CNT/PhCN. (<b>C</b>) Repeatability test of f-CNT/PhCN evaluated after four hours.</p> "> Figure 7
<p>Scheme of the mechanism of f-CNT/PhCN for RhB degradation.</p> ">
Versions Notes

Abstract

:
In this study, we report the synthesis and characterization of a novel photocatalyst composite composed of functionalized carbon nanotubes (f-CNT) and phenyl-modified graphitic carbon nitride (PhCN). The incorporation of the phenyl group extends the absorption range into the visible spectrum compared to pure g-C3N4. Additionally, the formation of the heterostructure in the f-CNT/PhCN composite exhibits improved charge transfer efficiency, facilitating the separation and transfer of photogenerated electron-hole pairs and reducing recombination rates. The photocatalytic performance of this composite was evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation. The f-CNT/PhCN composite exhibits remarkable efficiency in degrading RhB, achieving 60% degradation after 4 h, and 100% after 24 h under low-power white LED excitation. This represents a substantial improvement over the non-functionalized CNT/PhCN composite, which shows much lower performance. In contrast, pure PhCN demonstrates very little activity. Structural and optical properties were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, and UV–Vis spectroscopy. Time-resolved photoluminescence measurements were used to study the behavior of photoexcited carriers, confirming that the composite improves charge transfer efficiency for photogenerated carriers by approximately 30%. The results indicate that the functionalization of CNTs significantly enhances the photocatalytic properties of the composite, making f-CNT/PhCN a promising candidate for environmental remediation applications, particularly in the degradation of organic pollutants in wastewater.

1. Introduction

The issue of water pollution—marked by chemical contaminants like dyes, viruses, and heavy metals—is escalating, causing detrimental effects on both the environment and human health [1,2,3]. Photocatalytic technology emerges as a beacon of hope, garnering worldwide attention for its eco-friendly nature and cost-effective capabilities [4]. Enter graphitic carbon nitride (g-C3N4), hailed for its stability, thermal resilience, chemical inertness, non-toxicity, ease of modification, and remarkable electrical properties [5,6]. However, its standalone efficacy in breaking down organic pollutants remains limited due to the high recombination rates of the photogenerated carriers [7]. To enhance its photocatalytic prowess, diverse strategies have been devised, including template utilization, acid treatment to increase surface area, heteroatom doping to narrow the bandgap, and coupling with other semiconductors to create heterojunction photocatalysts, aiming to suppress the recombination of electron-hole pairs [8,9,10]. Recent studies have demonstrated that modifying the surface of carbon nitride materials, such as heterojunction formation or incorporating carbon-based materials like carbon dots, can significantly enhance photocatalytic activity by improving charge separation and exposing additional active sites [11,12,13].
Zhu et al. devised a novel strategy to enhance the optical and electronic attributes of the g-C3N4 semiconductor by incorporating sulfur or phosphorus through using substitutional and interstitial doping models [14]. g-C3N4/ZnO photocatalysts with varied CN loadings were prepared via a simple precipitation–calcination method in the presence of exfoliated C3N4 nanosheets. The resulting CN/ZnO composite, where ZnO nanoparticles were uniformly distributed on CN nanosheets, showed enhanced photocatalytic activity compared to pure ZnO under visible light [15,16]. Similarly, the LaFeO3-coupled graphitic carbon nitride composite exhibited enhanced photocatalytic efficiency in degrading organic pollutants under visible light due to the effective interfacial transfer of photogenerated electrons and holes between LaFeO3 and g-C3N4, which inhibits the recombination [17]. Carbon nanotubes (CNT) have garnered considerable attention as catalyst carriers, thanks to their distinctive one-dimensional structure, expensive specific surface area, robust mechanical attributes, and commendable thermal stability [18,19]. Due to their high current density and substantial specific surface area, these materials can form strong synergies with various semiconductors, including metal sulfides, metal oxides, and other metal substrates. This capability facilitates enhanced performance through collaborative effects, demonstrating their versatility in diverse applications within the realm of materials science and semiconductor technology [20,21,22,23,24,25,26]. In contemporary applications, CNTs have been strategically integrated with g-C3N4 to amplify the photocatalytic prowess of g-C3N4. In this regard, a metal-free photocatalyst was created by synthesizing a composite of mesoporous carbon nitride and carbon nanotubes through a simple polymerization method involving melamine as the precursor in the presence of CNT in methanol. The resulting CNT/mpg-C3N4 composite demonstrated a faster decomposition rate under visible light compared to bulk graphitic carbon nitride and pure mpg-C3N4. The improved photocatalytic performance is attributed to the synergistic effects of combining open-ended carbon nanotubes with mpg-C3N4 in the composite [27,28]. Beyond this, CNTs act as distributed templates and carriers, exerting influence over the morphology of semiconductor materials. Furthermore, CNTs serve as photosensitizers, broadening the absorption range of g-C3N4, thereby enhancing photocatalytic efficiency [29]. However, CNTs exhibit poor dispersibility and are insoluble in solvents, significantly limiting their applications [30]. Various techniques, including mechanical and chemical methods, involve altering their wetting or adhesion properties, facilitating the charge transfer process and improving their dispersion stability [31,32]. In this regard, Agbolaghi et al. enhanced photovoltaic efficiency through the creation of nanohybrids, utilizing chemically surface-modified CNTs paired with regioregular Poly (3-hexylthiophene) and non-regular Poly (3-dodcylthiophene). These unique donor–acceptor nanohybrids proved effective in the active layer of organic electronics [33]. Nova-Fernandez et al. prepared a hybrid system through direct covalent functionalization of SWNT with 10-phenylphenothiazine via diazonium chemistry. This process resulted in an increase in photocatalytic activity due to the formation of a direct covalent bond between the two units [34].
In the present work, we employed a rapid and straightforward method to prepare a composite photocatalyst by functionalizing carbon nanotubes with polythiophenes and phenyl-modified graphitic carbon nitride. The Catalyst’s morphology, structure, and optical properties were characterized, and RhB photodegradation performance was assessed to showcase the activity of the composite catalyst. This study introduces the successful design and synthesis of a hybrid photocatalyst composed of functionalized carbon nanotubes (f-CNT) and phenyl-modified graphitic carbon nitride (PhCN), significantly enhancing visible-light-driven photocatalytic performance. By improving charge separation and reducing recombination rates, this approach outperforms both pure PhCN and the non-functionalized CNT/PhCN composite, distinguishing this work from previous research in photocatalytic materials. In addition to demonstrating the novel design of the f-CNT/PhCN hybrid photocatalyst, this work focuses on the significant enhancements in photocatalytic efficiency under visible light by using a low-power LED source to avoid UV light exposure. This ensures that the observed degradation results from pure visible-light-induced activity, which makes the system highly relevant for sustainable environmental applications. The study not only highlights the importance of charge separation and the reduction recombination but also rules out potential dye sensitization effects, which could skew photocatalytic performance assessments.

2. Results and Discussion

Characterization of the f-CNT/PhCN Photocatalyst

The analysis of the Raman spectra sheds important indications on the functionalization of the carbon nanotubes and the formation of the hybrid f-CNT/PhCN compound. Two characteristic peaks are typically observed for carbon nanotubes: the D-band at about 1350 cm−1 is representative of the sp3 disorder carbons, while the G-band is associated with the graphitic sp2 carbons. More specifically, the G-band is related to the doubly-degenerate ITO and LO phonon with E2g symmetry at the Brillouin zone center [35,36], while the doubly-resonant second-order D-band involves one ITO phonon and one defect [37]. The strong linear dispersion of the phonon frequency of the D-band (53 cm−1/eV) is related to a resonance process between phonons and an electronic transition between linearly dispersive π and π* states. In this case, the Raman spectra are acquired with a near-infrared excitation (1064 nm), and a shift of the D-band to 1300 cm−1 is observed for CNT. A further shift to 1260 cm−1 with broadening of the Raman band is assigned to the functionalization of the CNT surface, particularly the increased electron doping associated with the thiophene group that enhances π-electron conjugation. A direct observation of the presence of the thiophene is the new band at 1450 cm−1 (A-Band) related to collective mode involving the stretching CC modes of the polythiophene backbone [38,39]. The B-band, related to localized vibrational modes, is not clearly visible (at about 1350 cm−1), as it partially overlaps with the D-band of the CNT [40].
The Raman spectrum of the hybrid system presents several additional bands, indicated in Figure 1 with asterisks, all of them associated with the PhCN vibrational modes. In particular, the most intense peak at 1600 cm−1, generated by the motion of the phenyl group, overlaps with the G-band. Another intense feature is a band at about 1390 cm−1, assigned to conjugated stretching vibration (C-C) between the phenyl ring and the triazine rings [41].
Further peaks at about 1350 and cm−1 and at 1500 cm−1 have been assigned to the bending of CNCN and stretching of NH, respectively [42]. In the hybrid system, we can observe the peak at around 1600 cm−1 which can be attributed to the CNT, but by the presence of PhCN, the intensity of the peak has increased.
The XRD patterns of as-prepared photocatalysts are shown in Figure 2a,b. The XRD pattern of PhCN reveals two peaks, approximately at 27.5°, corresponding to the (001) plane, and a peak at 13°, associated with the reflection from the (100) plane [43]. In the case of f-CNT, a broad peak is observed at 18°, where we would expect to see a peak around 26°, corresponding to the graphite-like SP2 structure of CNT [44]. The diffraction patterns of the f-CNT display characteristics resembling both MWCNT and polythiophenes, marked by a noticeable decrease in peak and shift in peak position [45]. According to the previous studies, the peaks related to the typically multi-walled carbon nanotube are in the range of 26.3, 42.5, and 54.3, but due to the hybridization their intensity is strongly reduced, falling below the observable threshold [46]. The (001) distinctive peak of the PhCN is clearly visible in the XRD of the hybrid system, presenting a shift to 25.7°. Since the peak is related to the distance between planes, a higher diffraction angle indicates a smaller distance between the planes. In pure PhCN, the distance is about 3.26 Å, while in the hybrid f-CNT/PhCN, it is shifted to 3.24 Å. The decrease in the distance can be connected to the role of CNT which acts as a bridge between the PhCN planes, reducing their distance for electrostatic attraction.
The microstructure and morphology of the f-CNT and the hybrid system are illustrated in Figure 3 by TEM images. The f-CNTs have an average diameter of 40 Å with very low dispersion and lengths up to 1 micrometer with a wider distribution, while PhCN agglomerates into micrometer-sized clusters. As depicted in Figure 3, it is evident that f-CNT envelops the PhCN, demonstrating the successful integration of the two materials. The images show a precise overlap of the f-CNTs and the polymer, with no evidence of building block clusters or a spread distribution of the f-CNT component. Due to the composition of the composite materials, functionalized carbon nanotubes (f-CNT) and phenyl-doped graphitic carbon nitride (PhCN), both are predominantly carbon-based—the primary elemental difference is the nitrogen in PhCN. Consequently, elemental analysis yields a high margin of error, particularly in distinguishing between the carbon sources, making precise estimation challenging. The weight percentages provided ensure experimental reproducibility but do not offer a detailed breakdown of the elemental composition in the final composite.
The UV–Vis spectra were employed to examine the optical characteristics of f-CNT, PhCN, and f-CNT/PhCN hybrid systems. As depicted in Figure 4, the absorption spectra of the composites closely resemble the spectral dependence of pure PhCN; however, f-CNT presents a flat absorption in the visible range and does not contribute to the band gap of polymer (2.70 eV) [47], while increasing the absorbance in the near-infrared region. To understand the interaction mechanism between PhCN and f-CNT upon illumination, the kinetics behavior of the photo-excited carriers has been studied by time-resolved measurements.
The comparison of decay profiles, acquired using a 410 nm excitation wavelength and recorded over a 500 ns time window (as illustrated in Figure 5), reveals that the f-CNT/PhCN hybrid system exhibits a considerably swifter decay profile in contrast to the decay observed in the PhCN system alone. PhCN in general possesses a slower decay behavior compared to the pure graphitic carbon nitride, with the phenyl group further slowing its kinetic behavior. This slower decay in PhCN is thought to facilitate charge transfer to materials such as metal oxides [48] or the CNT, compared to the hybrid system with g-C3N4. Figure 5, panels A and C, reports the 3D imaging profile of the recombination kinetics. The horizontal axis reports the spectral dependence, while the vertical axis reports the time delay.
Panel D displays the spectral dependence of photoluminescence for both pure PhCN and the f-CNT/PhCN composite. The luminescence of phenyl-modified graphitic carbon nitride (PhCN) primarily arises from the formation of self-trapped excitons (STEs). Upon photoexcitation, excitons (electron-hole pairs) are generated in PhCN and subsequently localized as STEs due to network distortions. Highly localized STEs emit in the blue spectral region, while less localized excitons result in a red shift. The observed red shift in the f-CNT/PhCN hybrid suggests that the STEs in the composite are less localized than in pure PhCN, likely due to the interaction between f-CNT and PhCN that modify the excitonic behavior. Panel C presents the experimental data and the corresponding fitting procedure, which integrates the entire spectral range (no significant variations were observed in the kinetics as a function of wavelength). The decay time profiles were modeled using a multi-exponential decay function (Equation (1)), capturing the complexity of the recombination dynamics in both the pure and hybrid systems.
y = ∑ i A i e − t τ i
The experimental time-resolved luminescence data are connected to the probability of recombination from the excited states, by Equation (2):
γ t o t = γ r a d + γ N R = 1 τ r a d + 1 τ N R = 1 τ t o t
where i = 1 or 2, γtot is the overall recombination probability from the excited state with γrad and γNR as the probabilities for radiative and non-radiative recombination, respectively. τrad and τNR are the relative time lifetime of the radiative and non-radiative paths, and τtot, the overall decay time, is experimentally found by the fitting procedure. A double exponential curve indicates the presence of two excited levels with different lifetimes. The fast component τ1 decreases from 6.9 ns to 4.8 ns, while the slower component decreases from 75 ns from the pure PhCN to 54 ns in the f-CNT\PhCN system. This faster decay in the hybrid system suggests a new non-radiative decay channel, associated with the transfer of photogenerated electrons from PhCN to f-CNT. The observed 30% increase in the charge transfer efficiency (Eff), calculated as alongside a significant reduction in overall emission intensity, underscores the role of f-CNT as an electron acceptor (Equation (3))
E f f = 1 − τ f − C N T / P h C N τ P h C N
Notably, the excitation wavelength falls within the visible range, indicating that the process under study can resume the behavior of the hybrid sample under visible light excitation and confirms the efficiency of the excitation process for wavelengths above 400 nm. The high-rate transfer process (rapid charge transfer), resulting from efficient charge separation and low-energy optical excitation, enhances the f-CNT/PhCN hybrid system’s performance, highlighting its potential as a photocatalyst under visible excitation.
The hybrid system was utilized to degrade Rhodamine B in an aqueous solution under visible light (Figure 6). To ensure that no UV components interfere with the process, light from a white LED was used to activate the photocatalysis.
The degradation efficiency of Rhodamine B was determined by monitoring changes in the absorption spectrum over time. Variations in the 554 nm absorption peak shape indicate dye degradation, while reductions in absorption without changes to the spectrum suggest adsorption onto the photocatalyst surface. While the adsorption of RhB onto the catalyst surface is a necessary step in the photocatalytic process, the optical absorption spectra indicate that it constitutes only a minor fraction of the overall degradation. The spectral data show a clear shift in the absorption peak during photocatalysis, indicating molecular breakdown rather than mere adsorption, which would result in a reduction in peak intensity without any spectral shift.
By normalizing the absorbance maximum values to the initial dye concentration and using the Beer–Lambert law, we were able to accurately estimate the concentration of the dye and calculate the degradation efficiency over time (Equation (4)).
Degradation   Efficiency = A 0 − A t A 0 × 100 .
where A0 stands for the initial absorbance and At for the absorbance measured at different times.
As observed in previous studies, although phenyl-modified graphitic carbon nitride extends absorption above 450 nm, its photocatalytic activity is significantly inhibited by a fast and efficient radiative recombination process. After one day of illumination, the efficiency remains very poor, below 20%, and functionalized CNTs demonstrate no photocatalytic activity under visible light [49]. The marked enhancement in performance is only observed with the f-CNT/PhCN composite, underscoring the synergistic effect between the two components in improving charge separation and reducing recombination rates.
The enhanced effect attributed to the presence of carbon nanotubes (CNT) or, more precisely, the formation of the heterostructure is evident in the high photodegradation efficiency of CNT/PhCN and functionalized CNT/PhCN, underlining that CNTs increase the charge migration and separation, significantly enhancing the photocatalytic performance. The efficiency reaches 40% and 60% after four hours, respectively, and up to 100% after one day of illumination for the functionalized CNT hybrid system. The result is comparable with the similar recent composite based on graphitic Carbon Nitride (Table 1). The functionalization of the carbon surface facilitates the formation of the hybrid system and enhances the stability of the compound, which shows no reduction in performance after four cycles.
Phenyl-modified graphitic carbon nitride (PhCN) is considered an intrinsic semiconductor, similar to g-C3N4, with its Fermi level positioned approximately in the middle of the bandgap at +0.25 V vs. NHE. Given that the bandgap of PhCN is 2.0 eV, the LUMO (lowest unoccupied molecular orbital) is located at −0.43 V vs. NHE, while the HOMO (highest occupied molecular orbital) is positioned at +1.57 V vs. NHE [63]. The introduction of f-CNT is expected to slightly alter the band edge positions of the nanocomposite, while primarily facilitating electron transport from PhCN. This change is expected to reduce the recombination rate of photogenerated electron-hole pairs.
The mechanism of the hybrid system for RhB degradation is illustrated in Figure 7. The carbon atoms in CNTs are primarily derived from sp2 hybrid orbitals and, to a lesser extent, from sp3 hybrid orbitals. The chemical bonds of carbon atoms in CNTs are a mixture of sp2 and sp3 hybridizations. These p-orbitals overlap to form graphene-like external surfaces of CNTs, resulting in highly delocalized large π bonds. These large π bonds can form conjugated macromolecular composites through noncovalent interactions. Since phenyl-doped carbon nitride has a π-bond-rich conjugated structure, it naturally tends to interact noncovalently with CNTs to form composites.
As is well known, the defects in organic polymers cause free electrons to transfer very slowly on the surfaces and within the volume of carbon nitride. The photocatalytic ability of PhCN is limited by rapid electron-hole recombination and low electron utilization rate. Further, the presence of self-trapped excitons (STE) affects photocatalytic efficiency. STEs are characterized by the localization of electron-hole pairs within the material that reduces the mobility of the charge carriers. As a result, photogenerated electrons and holes are less likely to migrate to the surface of the photocatalyst where they can participate in redox reactions. This diminished mobility can lead to lower photocatalytic efficiency; therefore, fewer charge carriers are available to drive the photocatalytic reactions. The non-covalent interaction causes CNTs to tightly adsorb onto the polymer, forming groups that accelerate electron migration on the surface and within the volume of PhCN, decreasing the effect of STE [64,65,66,67].
Scavenger tests were performed using three different solutions: isopropanol for hydroxyl radicals (•OH), benzoquinone (BQ) for superoxide radicals (O2•−), and ascorbic acid for photogenerated holes (h+). The measurements, conducted over 4 h, revealed distinct reductions in photocatalytic efficiency. The presence of ascorbic acid resulted in a moderate decrease in efficiency (approximately 30%), further dropping to 12% with BQ, and becoming nearly null in the presence of isopropanol. These results indicate that hydroxyl radicals (•OH) are the primary species responsible for oxidative degradation in the photocatalytic system, though superoxide radicals also play a significant role.
As evidenced by the scavenger tests, under light irradiation, the photocatalyst absorbs photons that excite electrons (e−) from the valence band (VB) to the conduction band (CB) of PhCN, leaving behind holes (h+) in the VB. The recombination of these charge carriers is greatly reduced due to the electron transfer process to the f-CNTs (as shown by time-resolved measurements), allowing the positive charge (holes) to remain available for oxidation reactions. The holes (h+) in the VB are highly oxidative and can react with surface-bound water molecules (H2O) or hydroxide ions (OH−), generating hydroxyl radicals (•OH):
h + + H 2 O → ∙ O H + H + h + + O H − → ∙ O H
The hydroxyl radicals (•OH) are responsible for attacking and oxidizing the organic pollutant (e.g., Rhodamine B) during the photocatalytic process. In addition to generating hydroxyl radicals, the electrons (e−) transferred to the f-CNTs can react with dissolved oxygen (O2) in the solution, forming superoxide radicals (O2•−). The synergistic effect of f-CNTs and PhCN significantly enhances degradation efficiency, as demonstrated by the complete photodegradation of RhB after one day of illumination under low-power-density visible light.
In summary, the degradation mechanism of Rhodamine B in the f-CNT/PhCN photocatalytic system is driven by the generation of electron-hole pairs upon visible light irradiation (Figure 7). The phenyl-modified graphitic carbon nitride (PhCN) acts as the primary photocatalyst, transferring photoexcited electrons to the functionalized carbon nanotubes (f-CNTs), improving charge separation and minimizing recombination. The electrons in the f-CNTs facilitate the reduction of RhB, while the holes in PhCN promote oxidative processes, leading to the effective degradation of the dye molecules.

3. Experimental Section

3.1. Materials and Methods

3.1.1. Materials

Ph-Triazine (99%), Rhodamine B (95%), Carbon Nanotube Multi-walled, and L-ascorbic acid (99%) were procured from Merck/Sigma Aldrich (Darmstadt, Germany), with absolute methanol (94–96%) sourced from Alfa Aesar (Haverhill, MA, USA). The preparation of the Rhodamine Aqueous solution utilized deionized water. Sulfuric acid (95–97%), nitric acid (65%), and anhydrous dimethyl sulfoxide were acquired from Merck/Sigma Aldrich (Darmstadt, Germany). Additionally, 2-hydroxymethyl thiophene and p-toluensulfonic acid (p-TSA) were purchased from Merck/Sigma Aldrich.

3.1.2. Preparation of Phenyl-Modified Carbon Nitride (PhCN)

The fabrication of phenyl-modified carbon nitride involved meticulously placing 1 g of 6-phenyl-1,3,5-triazine-2,4-diamine powder within a quartz tube, carefully positioned in a tubular furnace. The synthesis process commenced by subjecting the arrangement to a controlled heating regime, gradually elevating the temperature to 400 degrees Celsius over 1 h. This procedure facilitated the development of the desired material with improved phenyl modification [63].

3.1.3. Preparation of Thiophene Functionalized Carbon Nanotubes (f-CNT)

The functionalization process of multi-walled carbon nanotubes involved an oxidation method accompanied by sonication with sulfuric acid and nitric acid. After undergoing five cycles of stirring and decantation, the resultant precipitate underwent drying in a vacuum oven maintained at 60 degrees Celsius. Following this step, the synthesis of the 2-hydroxymethyl thiophene macroinitiator commenced through the esterification of CNT-COOH with 2-hydroxymethyl thiophene. p-toluensulfonic acid was employed as a dehydrating agent. In a reaction flask, a well-balanced combination of CNT-COOH (0.5 g), 2-hydroxymethyl thiophene (1 g), and anhydrous dimethyl sulfoxide (50 mL) underwent sonication for 40 min, resulting in a homogenous suspension. The introduction of a catalytic quantity of p-TSA into the flask was followed by placing it in a silicon oil bath at 140 degrees Celsius, where the reaction mixture was stirred for 6 h under an argon atmosphere. The suspension underwent centrifugation and subsequent washes with methanol to thoroughly remove any residual 2-hydroxymethyl thiophene. The final powder was obtained by drying under reduced pressure at 60 degrees Celsius [33].

3.1.4. Preparation of f-CNT/PhCN Nanocomposite

We incorporated 0.066 g of PhCN into 20 mL of methanol and subjected it to sonication for 30 min. Concurrently, 0.002 g of f-CNT was introduced into 20 mL of methanol and sonicated for the same duration. Subsequently, the two solutions were combined drop by drop while continuous stirring. The resulting mixture was stirred for nearly 2 h, transferred into a 250 mL flask, and heated at 70 degrees Celsius in a water bath for 5 h. The final step involved drying the samples in an oven set at 60 degrees Celsius.

3.2. Structural Characterization

X-ray diffraction patterns were operated at room temperature using a Rigaku Miniflex II diffractometer with θ–2θ Bragg–Brentano geometry with Cu K α   ( λ = 1.54118   Å ) , radiation at room temperature.
Raman Spectra were recorded using a Sol Instruments, MS750 series Monochromator-spectrograph (Sol-Instrument, Augsburg, Germany), excitation wavelengths at 785 nm with a resolution of about 1 cm−1. Time-resolved photoluminescence measurements were captured by stimulating the samples using 200 fs pulses generated from an optical parametric amplifier (light conversion TOPAS-C, Coherent Saxonburg, PA, USA), which was pumped by a regenerative Ti: Sapphire amplifier (Libra-HE Coherent). The repetition frequency was set at 1 kHz, and the signal was registered using a streak camera (C10910, Hamamatsu, Hizuoka Prefecture, Japan) equipped with a grating spectrometer (Acton Spectra Pro SP-2300, Princeton instrument, Trenton, NJ, USA). To mitigate inner filter effects, all measurements were conducted in the front-face configuration. Additionally, appropriate emission filters were employed to eliminate the reflected contribution of the excitation light.
Transmission electron microscopy (TEM) images were recorded on a Hitachi H-7000 equipped with a thermionic tungsten filament running at 100 kV. Images were collected by a CCD camera (2048 × 2048 pixel) AMT DVC (Woburn, MA, USA). Absorption measurements were acquired through diffuse reflectance spectroscopy employing UV–Vis-NIR JASCO FP-8550ST (Jasco, Easton, MD, USA). The measurements were executed utilizing a PbS solid-state photodetector. In reflection configuration, the diffuse reflection of the sample was assessed in comparison to a BaSO4 reference. The application of the Kubelka–Munk equation facilitated the extraction of absorption features.

3.3. Photodegradation of RhB

The evaluation of photocatalytic performance entailed monitoring variations in the concentration of RhB within an aqueous solution under visible light irradiation. A white LED, specifically a Philips 13 W light source with an optical power of 100 mW, was employed for this assessment. To establish absorption–desorption equilibrium between the catalyst and the dye, both the catalyst suspension (4 mg) and RhB solution (20 mL of a 10 mg/L solution) underwent a 30 min stirring process in complete darkness before light exposure. Throughout the photodegradation process, 1.5 mL portions were systematically collected at regular 60 min intervals. Subsequently, these portions underwent centrifugation, and the residual concentrations of RhB were analyzed using the advanced UV–Vis Technologies Cary 5000 Spectrophotometer (Agilent, Santa Clara, CA, USA). The concentration of RhB before and after the reaction was investigated by the UV–Vis spectrophotometer at the wavelength of 554 nm. The degradation kinetics of the catalyst were obtained by the first-order kinetics Equation (5):
− l n ⁡ ( c t / c 0 ) = k t .  
where c 0   (mg L−1) was the initial concentration of RhB, c t (mg L−1) was the concentration at time t (min), and k was the rate constant (min−1).
For the scavenger test, a 1 mM concentration of each scavenger was prepared. We mixed 20 mL of the scavenger solution with 20 mL of Rhodamine B solution. Isopropanol was used as the scavenger for hydroxyl radicals, while benzoquinone and ascorbic acid were used for superoxide radicals and holes, respectively. Subsequently, 4 mg of the nanocomposite was added to the mixture. The solutions were stirred in the dark for 30 min before being exposed to visible light for photocatalytic testing.

4. Conclusions

In this paper, the successful synthesis of f-CNT/PhCN nanocomposites using a simple water-bath method is reported, achieving significant enhancement in photocatalytic activity for Rhodamine B degradation. The integration of functionalized carbon nanotubes at an optimal content of 3% with phenyl-modified graphitic carbon nitride resulted in a marked improvement in visible light absorption and efficient photogenerated electron-hole separation. This synergistic effect contributed to the superior photocatalytic performance of the nanocomposites, highlighting their potential as efficient catalysts for environmental applications, particularly in wastewater purification. Despite the use of a low-power LED source, the photocatalyst exhibited remarkable activity, with the functionalization of CNTs playing a fundamental role in enhancing electron transport and reducing recombination rates. This demonstrated improvement, even without UV light, reinforces the applicability of this system for sustainable photocatalytic applications. These results highlight the innovative combination of phenyl-modified g-C3N4 and thiophene-functionalized CNTs, offering a promising direction for future enhanced sustainable environmental remediation technologies. This study opens new avenues for the development of advanced photocatalytic materials with enhanced performance, underscoring the importance of functionalization and composite formation in optimizing photocatalytic efficiencies.
Future work will focus on exploring the scalability of this synthesis method and the applicability of these nanocomposites to other organic pollutants, aiming to further contribute to sustainable environmental remediation technologies.

Author Contributions

S.A.G., Writing—original draft, Methodology, Investigation, Data Curation. S.A. and R.C., Investigation, Data curation. P.C.R., Project Administration, Investigation, Methodology, Review and Editing. All authors have read and agreed to the published version of the manuscript.

Funding

This work was developed within the framework of the project e.INS- Ecosystem of Innovation for Next Generation Sardinia (cod. ECS 00000038) funded by the Italian Ministry for Research and Education (MUR) under the National Recovery and Resilience Plan (NRRP)-MISSION 4 COMPONENT 2, “From research to business” INVESTMENT 1.5, “Creation and strengthening of Ecosystems of innovation” and construction of “Territorial R&D Leaders”.

Data Availability Statement

Raw data are available upon request.

Acknowledgments

We acknowledge the CeSAR (Centro Servizi d’Ateneo per la Ricerca) of the University of Cagliari, Italy for access to a JEM 1400 Plus TEM microscope (Joel, Akishima, Japan).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Sanganyado, E.; Gwenzi, W. Antibiotic resistance in drinking water systems: Occurrence, removal, and human health risks. Sci. Total Environ. 2019, 669, 785–797. [Google Scholar] [CrossRef] [PubMed]
  2. Alharbi, O.M.L.; Basheer, A.A.; Khattab, R.A.; Ali, I. Health and environmental effects of persistent organic pollutants. J. Mol. Liq. 2018, 263, 442–453. [Google Scholar] [CrossRef]
  3. Porcu, S.; Maloccu, S.; Corona, A.; Hazra, M.; David, T.C.; Chiriu, D.; Carbonaro, C.M.; Tramontano, E.; Ricci, P.C. Visible Light-Mediated Inactivation of H1N1 Virus UsingPolymer-Based Heterojunction Photocatalyst. Polymers 2023, 15, 2536. [Google Scholar] [CrossRef]
  4. Kayalvizhi, S.; Sengottaiyan, A.; Selvankumar, T.; Senthilkumar, B.; Sudhakar, C.; Selvam, K. Eco-friendly cost-effective approach for synthesis of copper oxide nanoparticles for enhanced photocatalytic performance. Optik 2020, 202, 163507. [Google Scholar] [CrossRef]
  5. Kang, S.; Zhang, L.; Yin, C.; Li, Y.; Cui, L.; Wang, Y. Fast flash frozen synthesis of holey few-layer g-C3N4 with high enhancement of photocatalytic reactive oxygen species evolution under visible light irradiation. Appl. Catal. B Environ. 2017, 211, 266–274. [Google Scholar] [CrossRef]
  6. Li, P.; Zhang, W.; Zhang, Y.; Sun, Y.; Dong, F. (NH4)2SO4-assisted polycondensation of dicyandiamide for porous g-C3N4 with enhanced photocatalytic NO removal. RSC Adv. 2016, 6, 96334–96338. [Google Scholar] [CrossRef]
  7. Huang, Z.; Li, F.; Chen, B.; Lu, T.; Yuan, Y.; Yuan, G. Well-dispersed g-C3N4 nanophases in mesoporous silica channels and their catalytic activity for carbon dioxide activation and conversion. Appl. Catal. B Environ. 2013, 136–137, 269–277. [Google Scholar] [CrossRef]
  8. Li, F.B.; Li, X.Z.; Hou, M.F. Photocatalytic degradation of 2-mercaptobenzothiazole in aqueous La3+-TiO2 suspension for odor control. Appl. Catal. B Environ. 2004, 48, 185–194. [Google Scholar] [CrossRef]
  9. Bakre, P.V.; Tilve, S.G. Dicarboxylic Acids as Soft Templates for the Sol-Gel Synthesis of Mesoporous Nano TiO2 with Enhanced Photocatalytic Activity. Chem. Select 2017, 2, 7063–7072. [Google Scholar] [CrossRef]
  10. Cheng, G.; Zhang, M.; Han, C.; Liang, Y.; Zhao, K. Achieving solar-to-hydrogen evolution promotion using TiO2 nanoparticles and an unanchored Cu co-catalyst. Mater. Res. Bull. 2020, 129, 110891. [Google Scholar] [CrossRef]
  11. Wang, N.; Cheng, L.; Liao, Y.; Xiang, Q. Effect of Functional Group Modifications on the Photocatalytic Performance of g-C3N4. Small 2023, 19, 2300109. [Google Scholar] [CrossRef]
  12. Yu, Z.; Li, F.; Xiang, Q. Carbon dots-based nanocomposites for heterogeneous photocatalysis. J. Mater. Sci. Technol. 2024, 175, 244–257. [Google Scholar] [CrossRef]
  13. Ohemeng, P.O.; Godin, R. Surface properties of carbon nitride materials used in photocatalytic systems for energy and environmental applications. Chem. Commun. 2024, 60, 12034–12061. [Google Scholar] [CrossRef]
  14. Zhu, Y.; Lv, C.; Yin, Z.; Ren, J.; Yang, X.; Dong, C.L.; Liu, H.; Cai, R.; Huang, Y.C.; Theis, W.; et al. A [001]-Oriented Hittorf’s Phosphorus Nanorods/Polymeric Carbon Nitride Heterostructure for Boosting Wide-Spectrum-Responsive Photocatalytic Hydrogen Evolution from Pure Water. Angew. Chem. Int. Ed. 2020, 59, 868–873. [Google Scholar] [CrossRef] [PubMed]
  15. Yuan, X.; Zhou, C.; Jing, Q.; Tang, Q.; Mu, Y.; Du, A.K. Facile synthesis of g-C3N4 nanosheets/ZnO nanocomposites with enhanced photocatalytic activity in reduction of aqueous chromium(VI) under visible light. Nanomaterials 2016, 6, 173. [Google Scholar] [CrossRef] [PubMed]
  16. Porcu, S.; Secci, F.; Ricci, P.C. Advances in Hybrid Composites for Photocatalytic Applications: A Review. Molecules 2022, 27, 6828. [Google Scholar] [CrossRef]
  17. Ismael, M.; Wu, Y. A facile synthesis method for fabrication of LaFeO3/g-C3N4 nanocomposite as efficient visible-light-driven photocatalyst for photodegradation of RhB and 4-CP. New J. Chem. 2019, 43, 13783–13793. [Google Scholar] [CrossRef]
  18. Vijayan, B.K.; Dimitrijevic, N.M.; Finkelstein-Shapiro, D.; Wu, J.; Gray, K.A. Coupling titania nanotubes and carbon nanotubes to create photocatalytic nanocomposites. ACS Catal. 2012, 2, 223–229. [Google Scholar] [CrossRef]
  19. Yan, Y.; Miao, J.; Yang, Z.; Xiao, F.X.; Yang, H.B.; Liu, B.; Yang, Y. Carbon nanotube catalysts: Recent advances in synthesis, characterization and applications. Chem. Soc. Rev. 2015, 44, 3295–3346. [Google Scholar] [CrossRef]
  20. Liu, Y.; Huang, D.; Cheng, M.; Liu, Z.; Lai, C.; Zhang, C.; Zhou, C.; Xiong, W.; Qin, L.; Shao, B.; et al. Metal sulfide/MOF-based composites as visible-light-driven photocatalysts for enhanced hydrogen production from water splitting. Coord. Chem. Rev. 2020, 409, 213220. [Google Scholar] [CrossRef]
  21. Nasir, J.A.; Rehman, Z.U.; Shah, S.N.A.; Khan, A.; Butler, I.S.; Catlow, C.R.A. Recent developments and perspectives in CdS-based photocatalysts for water splitting. J. Mater. Chem. A 2020, 8, 20752–20780. [Google Scholar] [CrossRef]
  22. Chava, R.K.; Do, J.Y.; Kang, M. Strategy for improving the visible photocatalytic H2 evolution activity of 2D graphitic carbon nitride nanosheets through the modification with metal and metal oxide nanocomponents. Appl. Catal. B Environ. 2019, 248, 538–551. [Google Scholar] [CrossRef]
  23. Gong, S.; Fan, J.; Cecen, V.; Huang, C.; Min, Y.; Xu, Q.; Li, H. Noble-metal and cocatalyst free W2N/C/TiO photocatalysts for efficient photocatalytic overall water splitting in visible and near-infrared light regions. Chem. Eng. J. 2021, 405, 126913. [Google Scholar] [CrossRef]
  24. Lei, W.; Zhou, T.; Pang, X.; Xue, S.; Xu, Q. Low-dimensional MXenes as noble metal-free co-catalyst for solar-to-fuel production: Progress and prospects. J. Mater. Sci. Technol. 2022, 114, 143–164. [Google Scholar] [CrossRef]
  25. Yang, Y.; Zhou, C.; Wang, W.; Xiong, W.; Zeng, G.; Huang, D.; Zhang, C.; Song, B.; Xue, W.; Li, X.; et al. Recent advances in application of transition metal phosphides for photocatalytic hydrogen production. Chem. Eng. J. 2021, 405, 126547. [Google Scholar] [CrossRef]
  26. Zhang, J.; Fu, J.; Dai, K. Graphitic carbon nitride/antimonene van der Waals heterostructure with enhanced photocatalytic CO2 reduction activity. J. Mater. Sci. Technol. 2022, 116, 192–198. [Google Scholar] [CrossRef]
  27. Chen, Y.; Tan, L.; Zhang, H.; Zhang, X.; Chen, Q.; Jiang, H.; Ge, F.; Wei, S.; Gao, X.; Wang, P. Metal-free in situ carbon-nanotube-modified mesoporous graphitic carbon nitride nanocomposite with enhanced visible light photocatalytic performance. Res. Chem. Intermed. 2021, 47, 3349–3362. [Google Scholar] [CrossRef]
  28. Sharma, N.; Pap, Z.; Székely, I.; Focsan, M.; Karacs, G.; Nemeth, Z.; Garg, S.; Hernadi, K. Combination of iodine-deficient BiOI phases in the presence of CNT to enhance photocatalytic activity towards phenol decomposition under visible light. Appl. Surf. Sci. 2021, 565, 150605. [Google Scholar] [CrossRef]
  29. Chaudhary, D.; Vankar, V.D.; Khare, N. Noble metal-free g-C3N4/TiO2/CNT ternary nanocomposite with enhanced photocatalytic performance under visible-light irradiation via multi-step charge transfer process. Sol. Energy 2017, 158, 132–139. [Google Scholar] [CrossRef]
  30. Mallakpour, S.; Soltanian, S. Surface functionalization of carbon nanotubes: Fabrication and applications. RSC Adv. 2016, 6, 109916–109935. [Google Scholar] [CrossRef]
  31. Andrews, R.; Jacques, D.; Minot, M.; Rantell, T. Fabrication of carbon multiwall nanotube/polymer composites by shear mixing. Macromol. Mater. Eng. 2002, 287, 395–403. [Google Scholar] [CrossRef]
  32. Meng, L.; Fu, C.; Lu, Q. Advanced technology for functionalization of carbon nanotubes. Prog. Nat. Sci. 2009, 19, 801–810. [Google Scholar] [CrossRef]
  33. Agbolaghi, S.; Charoughchi, S.; Aghapour, S.; Abbasi, F.; Bahadori, A.; Sarvari, R. Bulk heterojunction photovoltaics with improved efficiencies using stem-leaf, shish-kebab and double-fibrillar nano-hybrids based on modified carbon nanotubes and poly(3-hexylthiophene). Sol. Energy 2018, 170, 138–150. [Google Scholar] [CrossRef]
  34. Nova-Fernández, J.L.; González-Muñoz, D.; Pascual-Coca, G.; Cattelan, M.; Agnoli, S.; Pérez-Ruiz, R.; Alemán, J.; Cabrera, S.; Blanco, M. Enhancing the Photocatalytic Activity via Direct Covalent Functionalization in Single-Walled Carbon Nanotubes. Adv. Funct. Mater. 2024, 34, 2313102. [Google Scholar] [CrossRef]
  35. Pimenta, M.A.; Dresselhaus, G.; Dresselhaus, M.S.; Cançado, L.G.; Jorio, A.; Saito, R. Studying disorder in graphite-based systems by Raman spectroscopy. Phys. Chem. Chem. Phys. 2007, 9, 1276–1290. [Google Scholar] [CrossRef]
  36. Li, Z.; Deng, L.; Kinloch, I.A.; Young, R.J. Raman spectroscopy of carbon materials and their composites: Graphene, nanotubes and fibres. Prog. Mater. Sci. 2023, 135, 101089. [Google Scholar] [CrossRef]
  37. Ramos, S.L.L.M.; Pimenta, M.A.; Champi, A. Multiple-excitation study of the double-resonance Raman bands in rhombohedral graphite. Carbon 2021, 179, 683–691. [Google Scholar] [CrossRef]
  38. Shi, G.; Xu, J.; Fu, M. Raman spectroscopic and electrochemical studies on the doping level changes of polythiophene films during their electrochemical growth processes. J. Phys. Chem. B 2002, 106, 288–292. [Google Scholar] [CrossRef]
  39. Vu, Q.T.; Pavlik, M.; Hebestreit, N.; Rammelt, U.; Plieth, W.; Pfleger, J. Nanocomposites based on titanium dioxide and polythiophene: Structure and properties. React. Funct. Polym. 2005, 65, 69–77. [Google Scholar] [CrossRef]
  40. Mosca, S.; Milani, A.; Castiglioni, C.; Hernández Jolín, V.; Meseguer, C.; López Navarrete, J.T.; Zhao, C.; Sugiyasu, K.; Ruiz Delgado, M.C. Raman Fingerprints of π-Electron Delocalization in Polythiophene-Based Insulated Molecular Wires. Macromolecules 2022, 55, 3458–3468. [Google Scholar] [CrossRef]
  41. Stagi, L.; Chiriu, D.; Carbonaro, C.M.; Corpino, R.; Ricci, P.C. Structural and optical properties of carbon nitride polymorphs. Diam. Relat. Mater. 2016, 68, 84–92. [Google Scholar] [CrossRef]
  42. Porcu, S.; Roppolo, I.; Salaun, M.; Sarais, G.; Barbarossa, S.; Casula, M.F.; Carbonaro, C.M.; Ricci, P.C. Come to light: Detailed analysis of thermally treated Phenyl modified Carbon Nitride Polymorphs for bright phosphors in lighting applications. Appl. Surf. Sci. 2020, 504, 144330. [Google Scholar] [CrossRef]
  43. Liu, G.; Liao, M.; Zhang, Z.; Wang, H.; Chen, D.; Feng, Y. Enhanced photodegradation performance of Rhodamine B with g-C3N4 modified by carbon nanotubes. Sep. Purif. Technol. 2020, 244, 116618. [Google Scholar] [CrossRef]
  44. Guo, Z.; Cao, H.; Wang, Y.; Xie, Y.; Xiao, J.; Yang, J.; Zhang, Y. High activity of g-C3N4/multiwall carbon nanotube in catalytic ozonation promotes electro-peroxone process. Chemosphere 2018, 201, 206–213. [Google Scholar] [CrossRef]
  45. Raju, V.; Rani, J.V.; Basak, P. One-dimensional polythiophene/multi-walled carbon nanotube composite cathodes for rechargeable magnesium battery: Evidence of improved stability and electrochemically induced rearrangement in electrode morphology. Electrochim. Acta 2022, 404, 139707. [Google Scholar] [CrossRef]
  46. Karim, M.R.; Lee, C.J.; Lee, M.S. Synthesis and characterization of conducting polythiophene/carbon nanotubes composites. J. Polym. Sci. Part A Polym. Chem. 2006, 44, 5283–5290. [Google Scholar] [CrossRef]
  47. Porcu, S.; Secci, F.; Abdullah, Q.A.; Ricci, P.C. 4-nitrophenol efficient photoreduction from exfoliated and protonated phenyl-doped graphitic carbon nitride nanosheets. Polymers 2021, 13, 3752. [Google Scholar] [CrossRef]
  48. Dai, A.; Huang, Z.; Tian, L.; Zhang, Z.; Guan, X.; Guo, L. Phenyl-incorporated carbon nitride photocatalyst with extended visible-light-absorption for enhanced hydrogen production from water splitting. J. Colloid Interface Sci. 2022, 622, 494–502. [Google Scholar] [CrossRef] [PubMed]
  49. Zhang, J.; Dai, M.; Zhang, S.; Dai, M.; Zhang, P.; Wang, S.; He, Z. Recent Progress on Carbon-Nanotube-Based Materials for Photocatalytic Applications: A Review. Sol. RRL 2022, 6, 2200243. [Google Scholar] [CrossRef]
  50. Luo, J.; Dai, Z.; Feng, M.; Gu, M.; Xie, Y. Graphitic carbon nitride/ferroferric oxide/reduced graphene oxide nanocomposite as highly active visible light photocatalyst. Nano Res. 2023, 16, 371–376. [Google Scholar] [CrossRef]
  51. Elhaddad, E.; Al-fawwaz, A.T.; Rehan, M. An effective stannic oxide/graphitic carbon nitride (SnO2 NPs@g-C3N4) nanocomposite photocatalyst for organic pollutants degradation under visible-light. J. Saudi Chem. Soc. 2023, 27, 101677. [Google Scholar] [CrossRef]
  52. Vattikuti, S.V.P.; Nam, N.D.; Shim, J. Graphitic carbon nitride/Na2Ti3O7/V2O5 nanocomposite as a visible light active photocatalyst. Ceram. Int. 2020, 46, 18287–18296. [Google Scholar] [CrossRef]
  53. Razali, M.H.; Md Fauzi, M.A.F.; Mohd Azam, B.; Yusoff, M. g-C3N4/TiO2 nanocomposite photocatalyst for methylene blue photodegradation under visible light. Appl. Nanosci. 2022, 12, 3197–3206. [Google Scholar] [CrossRef]
  54. Jilani, A.; Rehman, G.U.; Ansari, M.O.; Othman, M.H.D.; Hussain, S.Z.; Dustgeer, M.R.; Darwesh, R. Sulfonated polyaniline-encapsulated graphene@graphitic carbon nitride nanocomposites for significantly enhanced photocatalytic degradation of phenol: A mechanistic study. New J. Chem. 2020, 44, 19570–19580. [Google Scholar] [CrossRef]
  55. Jiang, D.; Ma, W.; Xiao, P.; Shao, L.; Li, D.; Chen, M. Enhanced photocatalytic activity of graphitic carbon nitride/carbon nanotube/Bi2WO6 ternary Z-scheme heterojunction with carbon nanotube as efficient electron mediator. J. Colloid Interface Sci. 2018, 512, 693–700. [Google Scholar] [CrossRef]
  56. Ji, H.; Du, P.; Zhao, D.; Li, S.; Sun, F.; Duin, E.C.; Liu, W. 2D/1D graphitic carbon nitride/titanate nanotubes heterostructure for efficient photocatalysis of sulfamethazine under solar light: Catalytic “hot spots” at the rutile–anatase–titanate interfaces. Appl. Catal. B Environ. 2020, 263, 118357. [Google Scholar] [CrossRef]
  57. Dangwang Dikdim, J.M.; Gong, Y.; Noumi, G.B.; Sieliechi, J.M.; Zhao, X.; Ma, N.; Yang, M.; Tchatchueng, J.B. Peroxymonosulfate improved photocatalytic degradation of atrazine by activated carbon/graphitic carbon nitride composite under visible light irradiation. Chemosphere 2019, 217, 833–842. [Google Scholar] [CrossRef]
  58. Mao, S.; Bao, R.; Fang, D.; Yi, J. Fabrication of sliver/graphitic carbon nitride photocatalyst with enhanced visible-light photocatalytic efficiency through ultrasonic spray atomization. J. Colloid Interface Sci. 2019, 538, 15–24. [Google Scholar] [CrossRef] [PubMed]
  59. Liu, S.; Jiang, X.; Waterhouse, G.I.N.; Zhang, Z.M.; Yu, L. min Protonated graphitic carbon nitride/polypyrrole/reduced graphene oxide composites as efficient visible light driven photocatalysts for dye degradation and E. coli disinfection. J. Alloys Compd. 2021, 873, 159750. [Google Scholar] [CrossRef]
  60. Xu, W.; Lai, S.; Pillai, S.C.; Chu, W.; Hu, Y.; Jiang, X.; Fu, M.; Wu, X.; Li, F.; Wang, H. Visible light photocatalytic degradation of tetracycline with porous Ag/graphite carbon nitride plasmonic composite: Degradation pathways and mechanism. J. Colloid Interface Sci. 2020, 574, 110–121. [Google Scholar] [CrossRef]
  61. Dharani, S.; Gnanasekaran, L.; Arunachalam, S.V.; Zielińska-Jure, A.; Almoallim, H.S.; Soto-Moscoso, M. Photodegrading rhodamine B dye with cobalt ferrite-graphitic carbon nitride (CoFe2O4/g-C3N4) composite. Environ. Res. 2024, 258, 119484. [Google Scholar] [CrossRef] [PubMed]
  62. Huy, B.T.; Paeng, D.S.; Thi Bich Thao, C.; Kim Phuong, N.T.; Lee, Y.I. ZnO-Bi2O3/graphitic carbon nitride photocatalytic system with H2O2-assisted enhanced degradation of Indigo carmine under visible light. Arab. J. Chem. 2020, 13, 3790–3800. [Google Scholar] [CrossRef]
  63. Porcu, S.; Castellino, M.; Roppolo, I.; Carbonaro, C.M.; Palmas, S.; Mais, L.; Casula, M.F.; Neretina, S.; Hughes, R.A.; Secci, F.; et al. Highly efficient visible light phenyl modified carbon nitride/TiO2 photocatalyst for environmental applications. Appl. Surf. Sci. 2020, 531, 147394. [Google Scholar] [CrossRef]
  64. Liu, J.; Song, Y.; Xu, H.; Zhu, X.; Lian, J.; Xu, Y.; Zhao, Y.; Huang, L.; Ji, H.; Li, H. Non-metal photocatalyst nitrogen-doped carbon nanotubes modified mpg-C3N4: Facile synthesis and the enhanced visible-light photocatalytic activity. J. Colloid Interface Sci. 2017, 494, 38–46. [Google Scholar] [CrossRef] [PubMed]
  65. Zheng, D.; Zhang, G.; Wang, X. Integrating CdS quantum dots on hollow graphitic carbon nitride nanospheres for hydrogen evolution photocatalysis. Appl. Catal. B Environ. 2015, 179, 479–488. [Google Scholar] [CrossRef]
  66. She, X.; Liu, L.; Ji, H.; Mo, Z.; Li, Y.; Huang, L.; Du, D.; Xu, H.; Li, H. Template-free synthesis of 2D porous ultrathin nonmetal-doped g-C3N4 nanosheets with highly efficient photocatalytic H2 evolution from water under visible light. Appl. Catal. B Environ. 2016, 187, 144–153. [Google Scholar] [CrossRef]
  67. Liu, G.; Wang, H.; Chen, D.; Dai, C.; Zhang, Z.; Feng, Y. Photodegradation performances and transformation mechanism of sulfamethoxazole with CeO2/CN heterojunction as photocatalyst. Sep. Purif. Technol. 2020, 237, 116329. [Google Scholar] [CrossRef]
Molecules 29 05439 g001
Figure 1. Raman spectra of CNT-COOH, f-CNT, and f-CNT/PhCN. The asterisks (*) indicate the Raman peaks of PhCN.
Figure 1. Raman spectra of CNT-COOH, f-CNT, and f-CNT/PhCN. The asterisks (*) indicate the Raman peaks of PhCN.
Molecules 29 05439 g001
Molecules 29 05439 g002
Figure 2. XRD patterns for (a) PhCN, f-CNT/PhCN, inset normalized area of PhCN diffraction peak and (b) f-CNT, f-CNT/PhCN.
Figure 2. XRD patterns for (a) PhCN, f-CNT/PhCN, inset normalized area of PhCN diffraction peak and (b) f-CNT, f-CNT/PhCN.
Molecules 29 05439 g002
Molecules 29 05439 g003
Figure 3. TEM images of (a) f-CNT, (b) PhCN, and (c) f-CNT/PhCN.
Figure 3. TEM images of (a) f-CNT, (b) PhCN, and (c) f-CNT/PhCN.
Molecules 29 05439 g003
Molecules 29 05439 g004
Figure 4. Absorption spectra of PhCN and f-CNT/PhCN.
Figure 4. Absorption spectra of PhCN and f-CNT/PhCN.
Molecules 29 05439 g004
Molecules 29 05439 g005
Figure 5. Time-resolved measurement for PhCN and f-CNT/PhCN: ((a,c) 3D profiles for f-CNT/PhCN and PhCN), (b) photoluminescence intensity versus time delay. The blue and red line represent the numerical fit. (d) Photoluminescence intensity versus wavelength.
Figure 5. Time-resolved measurement for PhCN and f-CNT/PhCN: ((a,c) 3D profiles for f-CNT/PhCN and PhCN), (b) photoluminescence intensity versus time delay. The blue and red line represent the numerical fit. (d) Photoluminescence intensity versus wavelength.
Molecules 29 05439 g005
Molecules 29 05439 g006
Figure 6. Evaluation of the photocatalytic activity. (A) Photocatalytic degradation of pure PhCN, CNT/PhCN and f-CNT/PhCN. (B) Absorption spectrum of RhB solution with f-CNT/PhCN. (C) Repeatability test of f-CNT/PhCN evaluated after four hours.
Figure 6. Evaluation of the photocatalytic activity. (A) Photocatalytic degradation of pure PhCN, CNT/PhCN and f-CNT/PhCN. (B) Absorption spectrum of RhB solution with f-CNT/PhCN. (C) Repeatability test of f-CNT/PhCN evaluated after four hours.
Molecules 29 05439 g006
Molecules 29 05439 g007
Figure 7. Scheme of the mechanism of f-CNT/PhCN for RhB degradation.
Figure 7. Scheme of the mechanism of f-CNT/PhCN for RhB degradation.
Molecules 29 05439 g007
Table 1. Comparison of the results of the present work with some recent literature.
Table 1. Comparison of the results of the present work with some recent literature.
MaterialsSynthesis Method UsedExperimental ConditionsLight SourceType of DyeDegradation TimePhotodegradationReference
1g-C3N4/Fe3O4/rGOPrecipitation methodDifferent ratios of photocatalysts dispersed in RhB solutionVisible lightRhB75 min100%[50]
2SnO2@g-C3N4Solid-state reactionConcentration of dye: 10−5 M
0.2 of nanocomposite concentration: 10, 20, 30%		Visible lightMethyl orange6 h85%[51]
3g-C3N4/Na2Ti3O7/V2O5Hydrothermal methodphotocatalysts (0.05 g) dispersed in an aqueous solution (50 mL) containing 0.25 mmol of Na2SO3 and Na2S Visible lightRhB60 min90%[52]
4CNT/mp-g-C3N4Refluxing/thermal polymerization0.03 g of sample powder was added to the solution of RhB (50 mL)Visible lightRhB5 h90%[27]
5g-C3N4/TiO2Hydrothermal method10 mg powder of photocatalyst dispersed in 60 mL dye aqueous solution concentration of (5 ppm)Visible lightMethylene Blue2 h100%[53]
6s-PANI@g-C3N4In-situ oxidative polymerization0.2 g of nanocomposite added into the 300 mL aqueous solution that comprised 50 ppm
phenol		UVPhenol7 h100% by addition of 1%w GN[54]
7g-C3N4/CNT/Bi2WO6Hydrothermal method40 mg photocatalyst added into 40 mL of TC solutionVisible lightTC aqueous solution90 min87.65%[55]
82D/1D g-C3N4/TNTHydrothermal methodSMT concentration was 5 mg/L and material dosage was 0.2 g/L, PH = 7Solar lightSMT5 h100%[56]
9Activated carbon/g-C3N4By mixing melamine and ACATZ = 5 mg/L
pH = 5.56
Catalyst = 1 g/L		Visible lightAtrazine with PMS2 h78.76%[57]
10Ag/g-C3N4/t-CFPThermal polymerization with IEP methodAs-prepared sample was hung in 20 mL mixed solution containing 20 mg/L MBVisible lightMethylene Blue40 min72%[58]
11PPy/P-C3N4/rGOIn-situ chemical polymerization50 mg of sample dispersed in 125 mg/L of X3B solutionVisible lightX3B (Brilliant red dye)1 h98%[59]
12Ag/graphite carbon nitrideThermal exfoliation and photo-reduction method50 mg of photocatalyst dispersed in 20 mg/L of TC solutionVisible lightTetracycline (TC)2 h83%[60]
13CoFe2O4/g-C3N4Sol-gel and Ultrasonic treatment 30 mg of catalyst dropped into 50 mL of RhBVisible lightRhB2 h57%[61]
14ZnO-Bi2O3/g-C3N4Hydrothermal method50 mg of catalyst added in a 100 mL of Indigo carmine solution (50 mg/L)Visible lightIndigo Carmine3 h68.8%[62]
15f-CNT/PhCNWater-bath method4 mg of sample added into 20 mL of RhB solutionVisible lightRhB4 h60%This work
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Ghourichay, S.A.; Agbolaghi, S.; Corpino, R.; Ricci, P.C. Carbon Nanotube–Phenyl Modified g-C3N4: A Visible Light Driven Efficient Charge Transfer System for Photocatalytic Degradation of Rhodamine B. Molecules 2024, 29, 5439. https://doi.org/10.3390/molecules29225439

AMA Style

Ghourichay SA, Agbolaghi S, Corpino R, Ricci PC. Carbon Nanotube–Phenyl Modified g-C3N4: A Visible Light Driven Efficient Charge Transfer System for Photocatalytic Degradation of Rhodamine B. Molecules. 2024; 29(22):5439. https://doi.org/10.3390/molecules29225439

Chicago/Turabian Style

Ghourichay, Sahar Aghapour, Samira Agbolaghi, Riccardo Corpino, and Pier Carlo Ricci. 2024. "Carbon Nanotube–Phenyl Modified g-C3N4: A Visible Light Driven Efficient Charge Transfer System for Photocatalytic Degradation of Rhodamine B" Molecules 29, no. 22: 5439. https://doi.org/10.3390/molecules29225439

APA Style

Ghourichay, S. A., Agbolaghi, S., Corpino, R., & Ricci, P. C. (2024). Carbon Nanotube–Phenyl Modified g-C3N4: A Visible Light Driven Efficient Charge Transfer System for Photocatalytic Degradation of Rhodamine B. Molecules, 29(22), 5439. https://doi.org/10.3390/molecules29225439

Article Metrics

Back to TopTop