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Article

G-C3N4 Dots Decorated with Hetaerolite: Visible-Light Photocatalyst for Degradation of Organic Contaminants

by
Zahra Lahootifar
1,
Aziz Habibi-Yangjeh
1,*,
Shima Rahim Pouran
2 and
Alireza Khataee
3,4
1
Department of Chemistry, Faculty of Science, University of Mohaghegh Ardabili, Ardabil 56199-11367, Iran
2
Social Determinants of Health Research Center, Department of Environmental and Occupational Health, Ardabil University of Medical Sciences, Ardabil 85991-56189, Iran
3
Research Laboratory of Advanced Water and Wastewater Treatment Processes, Department of Applied Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz 16471-51666, Iran
4
Department of Environmental Engineering, Faculty of Engineering, Gebze Technical University, Gebze 41400, Turkey
*
Author to whom correspondence should be addressed.
Catalysts 2023, 13(2), 346; https://doi.org/10.3390/catal13020346
Submission received: 5 January 2023 / Revised: 27 January 2023 / Accepted: 27 January 2023 / Published: 3 February 2023
(This article belongs to the Special Issue Advanced Oxidation Catalysts)
Browse Figures
Versions Notes

Abstract

:
In this paper, a facile hydrothermal approach was used to integrate graphitic carbon nitride dots (CNDs) with hetaerolite (ZnMn2O4) at different weight percentages. The morphology, microstructure, texture, electronic, phase composition, and electrochemical properties were identified by field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), ultraviolet-visible diffuse reflectance (UV-vis DR), photoluminescence (PL), electrochemical impedance spectroscopy (EIS), Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH), and photocurrent density. The results of XRD, FT-IR, EDX, and XPS analyses confirmed the synthesis of CNDs/ZnMn2O4 (20%) nanocomposite. As per PL, EIS, and photocurrent outcomes, the binary CNDs/ZnMn2O4 nanocomposite revealed superior features for interfacial transferring of charge carriers. The developed p–n heterojunction at the interface of CNDs and ZnMn2O4 nanoparticles partaken a significant role in the impressive charge segregation and migration. The binary nanocomposites were employed for the photodegradation of several dye pollutants, including rhodamine B (RhB), fuchsin, malachite green (MG), and methylene blue (MB) at visible wavelengths. Amongst the fabricated photocatalysts, the CNDs/ZnMn2O4 (20%) nanocomposite gave rise to about 98% RhB degradation efficiency within 45 min with the rate constant of 747 × 10−4 min−1, which was 66.5-, 3.44-, and 2.72-fold superior to the activities of CN, CNDs, and ZnMn2O4 photocatalysts, respectively. The impressive photodegradation performance of this nanocomposite was not only associated with the capacity for impressive visible-light absorption and boosted separation and transport of charge carriers, but also with its large surface area.

1. Introduction

Over the past few decades, the shortage of energy and water pollution issues raised by organic compounds have become global concerns of the scientific community [1]. Among the primary water pollutants are organic dyes, which have been a considerable part of water pollution due to their high consumption rate in various industries and resistance to biodegradation. To tackle the detrimental effects of these organic molecules on human health and the environment [2], especially on marine life, numerous advanced materials [3] and strategies have been developed and implemented over time. In particular, the focus has been paid to bio-compatible materials and practical strategies, in addition to being effective and efficient from energy and cost perspectives [2,3]. Advanced oxidation processes (AOPs) are on top of the wastewater treatment techniques that can fulfill the effective degradation of various organic pollutants [4]. The visible-light-driven heterogeneous photocatalysis is of particular interest among AOPs, since it uses solar energy to drive oxidation reactions for the degradation of organic molecules and eco-clean energy generation [5]. In this regard, the utilized photocatalyst undertakes the central role because its optical, structural, and surface properties chiefly determine the efficiency of a photocatalytic system [6].
On account of the appropriate energy band edges and band gap, tunable electronic structure, high stability, and biocompatibility, graphitic carbon nitride (CN) quickly became the subject of research for various photocatalytic reactions, including CO2 reduction, synthesis of organic compounds, hydrogen production, removal of pollutants, and nitrogen fixation [7,8,9]. Nonetheless, the solar-light utilization ability of pristine CN is poor and generates an inefficient amount of charge carriers. Moreover, the rapid recombination of electron/hole pairs, insufficient surface-active centers, and low conductivity confine its practical applications [10]. Hence, numerous attempts have been made to improve the activity of CN through some structural/morphological modifications or heterojunction/s development by integration with other semiconductor/s [11]. Recently, dots and quantum dots of CN have received much interest due to their high disperse ability, quantum confinement effect, and improved heterojunction construction, in addition to the intrinsic properties of the bulk CN [12,13]. For example, Ma et al. realized that anchoring CN quantum dots on 2D g-C3N4 improved photocatalytic activity [13]. Moreover, the latest research activities on the improvement of carbon nitride photocatalytic activity have been reviewed [14,15].
Spinel zinc manganese oxide (ZnMn2O4, Eg = 1.70 eV) is a p-type semiconductor active in the visible region. Among spinels, ZnMn2O4 has attracted much attention due to its outstanding technological importance as catalyst, solid electrolyte, etc., [16]. Reduction in CO2 and destruction of pollutants are photocatalytic applications of this spinel [16].
Among water pollutants, rhodamine B (RhB), with carcinogenic and neurotoxic properties, has a high potential to cause diseases in humans [17]. Fushin can affect the central nervous system and cause drowsiness and dizziness in humans [18]. Malachite Green (MG) is a carcinogenic and mutagenic agent in living organisms [19]. Moreover, methylene blue (MB) has a severe impact on human health and the environment, because it is carcinogenic and non-biodegradable in nature. Among the dangers of MB, its effect on the respiratory system, blindness, digestive and mental disorders, shock, gastritis, jaundice, tissue necrosis, and an increase in heart rate has been highlighted [20].
The appealing properties of CN dots (CNDs) and complementary characteristics of ZnMn2O4 brought the idea of designing a binary heterostructure based on these semiconductors. For this purpose, a hydrothermal method was used to deposit various weight percentages of ZnMn2O4 nanoparticles over CNDs. The photocatalytic activities were also determined for the degradation of several organic dye contaminants, including RhB, fuchsin, MG, and MB molecules. Finally, the nanocomposite with the best optical and photocatalytic activity was introduced, and the corresponding degradation mechanism was suggested.

2. Results and Discussions

The fabricated CN, CNDs, ZnMn2O4, and CNDs/ZnMn2O4 (20%) materials were characterized by XRD to expose the corresponding crystalline phases (Figure 1a). In the pattern of CN, two sharp peaks appeared at 2ϴ values of 13.1° and 27.4° (JCPDS No. 01-087-1526), corresponding to stacking between the surfaces of the CN layers [21]. The pattern of CNDs shows only one peak at 27.4°, indicating that CNDs has the same intrinsic crystal structure as CN. The peak at 13.1° disappeared and the intensity of the peak at 27.4° diminished compared to CN. This decrease is due to the small size of CNDs particles [22]. On the other hand, the peaks appeared at 2ϴ = 18.62°, 29.47°, 31.42°, 33.22°, 36.47°, 39.27°, 44.77°, 52.22°, 54.42°, 56.87°, 58.98°, 60.92°, and 65.25°, respectively, correspond to the reflections from (101), (112), (200), (103), (211), (004), (220), (105), (312), (303), (321), (224), and (400) planes of ZnMn2O4 (JCPDS file No. 01-077-0470) [23]. The XRD pattern of CNDs/ZnMn2O4 (20%) nanocomposite included all the diffraction peaks relevant to CNDs and the tetragonal phase of ZnMn2O4, indicating the accuracy of the synthesis procedure. According to the correct position of the XRD peaks, it is concluded that the synthesis of the nanocomposite has been correctly performed. The surface functional groups of the CNDs/ZnMn2O4 (20%) sample were recorded by FT-IR spectroscopy and elucidated with respect to CN and CNDs spectra (Figure 1b). The CN and CNDs samples gave rise to similar FT-IR spectra. In both of them, the wide-ranging peaks at 2900–3450 cm−1 assign to the O–H and N–H stretching modes [24]. The peaks that appeared at wavenumbers of 1200–1650 cm−1 are relevant to the C–N and C=N groups [22,25]. Moreover, the bands related to the atmospheric CO2 and C–O stretching modes emerged at 2385 cm−1 and 1060 cm−1, respectively [26]. The peak related to the stretching vibration of heptazine units was also identified at 800 cm−1 [26]. In the case of CNDs/ZnMn2O4 (20%) nanocomposite, not only the peaks attributing to CNDs appeared in the spectrum, but also the peaks assigning to the M–O bonds of the corresponding metal oxides (M = Zn and Mn) showed up at 640 cm−1 and 545 cm−1, respectively [27,28]. Hence, all the functional groups are visible in the figure, which confirmed the synthesis of the binary photocatalyst.
The electronic properties of CN, CNDs, ZnMn2O4, and CNDs/ZnMn2O4 composites were studied through their UV–vis DR spectra (Figure 1c). As per the data, although the CN and CNDs photocatalysts showed absorptions at visible wavelengths, the visible-light absorption capability of CNDs/ZnMn2O4 nanocomposites is highly promoted following the incorporation of the small band gap ZnMn2O4 with medium band gap CNDs. The Eg values were afterward obtained using Tauc᾽s plots [29], which were 2.70, 2.83, 1.70, 2.54, 2.10, and 2.02 eV for CN, CNDs, ZnMn2O4, CNDs/ZnMn2O4 (10%), CNDs/ZnMn2O4 (20%), and CNDs/ZnMn2O4 (30%) photocatalysts, respectively (Figure 1d). Moreover, the flat-band potentials and the type of semiconductors were determined via applying the Mott-Schottky (M-S) analysis [30] as illustrated in Figure 1e,f. As noticed, the CNDs and ZnMn2O4 exhibited n-type and p-type characteristics with a positive and negative slopes, respectively. The calculated ECB and EVB values for CNDs were −1.48 eV and +1.35 eV, and for ZnMn2O4 were −0.90 eV and +0.80 eV, respectively.
The morphological features of the CNDs/ZnMn2O4 (20%) nanocomposite were studied through FESEM, TEM, and HRTEM images. The FESEM and TEM images of the sample present aggregated particles composed of nearly spherical particles (Figure 2a,b). In the HRTEM image of CNDs/ZnMn2O4 (20%) nanocomposite presented in Figure 2c, the lattice fringes of CNDs and ZnMn2O4 were identified with inter-planar distances of 0.340 and 0.490 nm, respectively [22,31]. This figure confirms the combination of CNDs and ZnMn2O4 components to construct a binary p-n heterojunction photocatalyst. The elements of the binary nanocomposite were detected by EDX analyses (Figure 2d). The C, N, O, Mn, and Zn elements were the only elements identified in the CNDs/ZnMn2O4 (20%) nanocomposite. The EDX mapping images of the nanocomposite were also collected, which displayed elements with almost homogeneous dispersion in the nanocomposite structure (Figure 2e).
Figure 3 shows the oxidation states of the elements in the CNDs/ZnMn2O4 (20%) nanocomposite as per XPS analysis. The survey spectrum consisted of the peaks related to C 1s, N 1s, Zn 2p, Mn 2p, and O 1s. The narrow scan of carbon was completed in the 283–292 eV region and produced two dominant peaks, which were deconvoluted into three peak components at binding energies (B.E) of 284.7, 285.5, and 288.5 eV, which were, respectively, associated with the sp2 graphitic carbon (C–C), sp2 aromatic C attached to –NH2, and the carbon corresponded to heptazine/triazine C-N-C coordination (Figure 3b) [24]. The N 1s spectrum generated in the corresponding narrow scan was deconvoluted into four peak components positioned at 398.5, 399.1, and 400.5 eV (Figure 3c), which correspond to the nitrogen as sp2-hybridized (C=N-C), tertiary form (N–(C)3) and hydrogen-bonded (C–N–H), respectively [24]. The Zn 2p high-resolution spectrum produced two peaks at B.E. of 1043.6 eV and 1020.5 eV, respectively, matched with Zn 2p1/2 and Zn 2p3/2 and indicated the existence of Zn element in +2 oxidation state (Figure 3d) [32]. On the other hand, the Mn 2p narrow scan generated two strong peaks, one associated with Mn 2p3/2 centered at binding energy of 641.8 eV and the other one ascribed to Mn 2p1/2 at 653.4 eV (Figure 3e) [32]. The O 1s spectrum deconvolution resulted in three peaks at 530.2, 531.8, and 533 eV, respectively, related to ZnMn2O4 lattice oxygen, surface hydroxyl content, and residual adsorbed H2O, respectively (Figure 3f) [31,33].
The photocatalytic degradation efficiency of the samples was examined for photo-oxidation of RhB under visible light. Figure 4a depicts the changes in the RhB concentration (Ct/C0) within diverse photocatalytic systems per irradiation period. Prior to the experiments, the adsorption capacity of the samples was investigated through the stirring of the dye solution with the photocatalyst under dark conditions for 60 min. As per results, a negligible amount (8%) of RhB was removed through only light illumination, i.e., the absence of photocatalyst, indicating the inefficacy of visible light in breaking the chemical bonds of RhB molecules. The system including the pristine CN resulted in low RhB removal efficiency of about 20%, which can be strongly associated with the poor harvesting of light in visible region and rapid recombination of charges. However, the CNDs photocatalyst showed much higher activity with removal of 73% at the same time. By contrast, almost complete removal of RhB has been achieved over the CNDs/ZnMn2O4 (20%) nanocomposite within 45 min. The order of photoactivity was as CNDs/ZnMn2O4 (20%) > CNDs/ZnMn2O4 (30%) > CNDs/ZnMn2O4 (10%) > CNDs/ZnMn2O4 (40%) > CNDs/ZnMn2O4 (5%) > ZnMn2O4 > CNDs > CN. The plots of ln (C0/C) vs. time for degradation of RhB over the studied samples revealed that the photocatalytic reactions obeyed the pseudo-first-order kinetic model (see Figure 4b). The rate constants for RhB removal using different photocatalysts were calculated to be 11.2 × 10−4 min−1 (CN), 217 × 10−4 min−1 (CNDs), 275 × 10−4 min−1 (ZnMn2O4), 284 × 10−4 min−1 (CNDs/ZnMn2O4 (5%)), 329 × 10−4 min−1 (CNDs/ZnMn2O4 (40%)), 333 × 10−4 min−1 (CNDs/ZnMn2O4 (10%)), 429 × 10−4 min−1 (CNDs/ZnMn2O4 (30%)), and 747 × 10−4 min−1 (CNDs/ZnMn2O4 (20%)) (Figure 4c). As per results, the nanocomposites showed higher photodegradation rates than pristine CN, wherein the activity of CNDs/ZnMn2O4 (20%) nanocomposite was, respectively, 66.5, 3.44, and 2.72-fold superior to the activities of CN, CNDs, and ZnMn2O4 photocatalysts, respectively. The boosted photocatalytic activities of the binary samples implied that the combination of CNDs with ZnMn2O4 was the right action, which should be taken place with optimum weight percentages.
The reactive species produced in a photocatalytic system are the central elements involved in the photodegradation of organic molecules. To estimate the type of the reactive species, a group of experiments using scavengers, including AOX, BQ, and 2-PrOH was performed to, respectively, probe h+, •O2−, and •OH species. Figure 4d depicts the RhB photo-oxidation rate constants using the CNDs/ZnMn2O4 (20%) nanocomposite, without or with the scavengers. The rate constant of 747 × 10−4 min−1, which was obtained in the absence of the scavengers, was significantly dropped to 154 × 10−4, 53.4 × 10−4, and 1.03 × 10−4 min−1 upon 2-PrOH, AOX, and BQ supplementation into the system, respectively. As can be inferred from the result, all three probed species contributed to the RhB photodegradation process and their role are as •O2− > h+ > •OH.
The photocatalytic activities of CN, CNDs, and CNDs/ZnMn2O4 (20%) samples were further examined for degradation of some other dye pollutants, including MG, fuchsin and MB and the outcomes were presented as compared with the RhB results (Figure 4e). As per the results, the highest removal efficiencies of all the studied dyes were achieved over the CNDs/ZnMn2O4 (20%) system. The photoactivity of the binary sample for degradation of RhB, MG, fuchsin, and MB was 66.5, 15.8, 13.2, and 31.2-fold greater than CN, and 3.44, 1.5, 18.1, and 11.5 times premier than CNDs, respectively. Accordingly, the CNDs/ZnMn2O4 (20%) sample showed an outstanding photocatalytic activity for the treatment of various recalcitrant dye wastewater. The binary photocatalyst underwent four consecutive runs under the same operational conditions for RhB removal in order to assess its stability and potential reusability (Figure 4f). As noticed, the CNDs/ZnMn2O4 (20%) nanocomposite demonstrated excellent efficiency for RhB photodegradation under visible light in all the conducted experiments, and the loss of performance was insignificant at the end of the cycle, confirming its significant stability.
The ability for adequate segregation and transfer of the photoinduced charge carriers is among the crucial factors connected with immense photocatalytic activities [34]. On this basis, electrochemical impedance spectroscopy, photoluminescence, and photocurrent spectroscopy analyses were conducted to figure out the characteristics of the CNDs/ZnMn2O4 (20%) nanocomposite with respect to the ZnMn2O4, CNDs, and CN materials. Figure 5a shows the EIS responses of the samples, wherein the least impedance was detected for the CNDs/ZnMn2O4 (20%) sample compared to those of ZnMn2O4, CNDs, and CN photocatalysts. This indicated the notable reduction in the resistance towards charge transfer in the CNDs/ZnMn2O4 (20%) nanocomposite. The PL results were also in line with the EIS response of the binary nanocomposite, wherein the weakest PL belonged to the CNDs/ZnMn2O4 (20%) nanocomposite (Figure 5b). Since the photoluminescence intensity shows the amount of photo energy released from returning the photo-excited material to the ground state, the higher released energy means more recombination of photoinduced charges. As per the results, the CNDs/ZnMn2O4 (20%) sample had a minimal recombination rate or the best performance for transferring the charge carriers compared to the pristine photocatalysts. The best optical performance of the binary sample was further confirmed via photocurrent analyses, as presented in Figure 5c. The stronger photocurrent intensity of the CNDs/ZnMn2O4 (20%) photocatalyst in comparison to the CN, CNDs, and ZnMn2O4 samples indicated its exceptional performance in extending the lifespan of the photoinduced charges. Therefore, the EIS, PL, and photocurrent results confirmed the high potential of the CNDs/ZnMn2O4 (20%) nanocomposite for photocatalytic applications.
The surface properties of a photocatalyst are also influential factors as photocatalytic reactions take place on the surface [35]. Moreover, the charge transfer is also affected by surface characteristics. Therefore, the active sites and pore features of the studied photocatalysts were identified via N2 adsorption–desorption isotherms (Figure 5d,e). From the BET isotherms, the N2 sorption behavior of CNDs, ZnMn2O4, and CNDs/ZnMn2O4 (20%) photocatalysts followed type II with H3 hysteresis loops. As per the outcomes (Table 1), the integration of CNDs (12.03 m2 g−1) and ZnMn2O4 (33.8 m2 g−1) contributed to an expanded active surface of the binary sample (44.6 m2 g−1). The enlarged surface area could play a remarkable role in its promoted photocatalytic activity.
Based on the outcomes, a mechanism was suggested to illustrate the route through which the pollutant molecules undergo a visible-light photodegradation reaction over the binary CNDs/ZnMn2O4 nanocomposites. As a result of the constructed p–n heterojunction between n-type CNDs and p-type ZnMn2O4, the electrons more from the Fermi level of CNDs to that of ZnMn2O4 until the Fermi levels reach an equilibrium state, resulting in, respectively, positive and negative charges on CNDs and ZnMn2O4 in the junction regions [36,37]. Upon the excitation of CNDs and ZnMn2O4 semiconductors by visible light, the electrons on the VBs of both components move to the corresponding CBs, while the holes remain on the VBs (Figure 6). After that, due to the influence of the inner electric field, the electrons on the CBZnMn2O4 rapidly transfer to the CBCNQDs, where they can be trapped by oxygen molecules to produce •O2− and •OH species. Additionally, the contaminants can get oxidized directly by the holes remaining at the VB of ZnMn2O4. The rapid migration of the photo generated charges can be facilitated via the formed p–n heterojunction, leading to extending the lifetime of the charge carriers and diminishing recombination of them, which is highly beneficial for impressive photocatalytic performance [38,39].

3. Experimental Part

3.1. Materials Section

The chemicals utilized in this research are melamine (C3H6N6, 99%, Central Drug House), ethanol (96%, Merck), Zn(NO3)2·6H2O (96%, Loba Chemie), Mn(CH3COO)2·4H2O (99%, Merck), NaOH (98%, Merck), H2O2 (35%, Neutron).

3.2. Photocatalyst Synthesis

The CN was synthesized via the previously reported method [40]. For the synthesis of the CNDs sample, the mixture of CN with 20 mL of ethanol was stirred for half an hour. Then the solution of 25 mL of water and 25 mL of ethanol was added dropwise to the previous mixture. After stirring for half an hour, it was heated at 180 °C for 4 h in an autoclave.
The CNDs/ZnMn2O4 systems were fabricated using a hydrothermal procedure (Scheme 1). For the synthesis of CNDs/ZnMn2O4 (20%) nanocomposite, as the optimal photocatalyst with the best performance, 0.4 g of CNDs was mixed with 100 mL of H2O under sonication for 10 min. Meanwhile, an aqueous solution of zinc nitrate (Zn(NO3)2.6H2O, Loba Chemie, 0.124 g in 10 mL H2O) was mixed with the above-obtained suspension, while stirring for 60 min at 25 °C. On the other hand, an aqueous solution of manganese (II) acetate (Mn (CH3COO)2.4H2O, Merck, 0.205 g in 10 mL H2O) was added to the resultant suspension and stirred for 60 min. At the next step, 20 mL NaOH (Merck, 0.4 M) and 1 mL H2O2 (Neutron, 14.9 M) solutions were combined with the suspension under stirring for more 15 min. In the end, the suspension was heated in a stainless-steel autoclave for 18 h at 160 °C. After cooling and washing, the resultant composite was dried in an oven.

3.3. Characterization Techniques

The EDX analyses and FESEM images were obtained by a Tescan Mira3 instrument. The XRD analyses were carried out on a Philips Xpert X-ray instrument with a Cu Kα source. A Scinco 4100 spectrophotometer was employed to record the UV-vis DR spectra. The FT-IR spectra were collected on a PerkinElmer Spectrum RX I apparatus. A PerkinElmer LS 55 fluorescence spectrophotometer was employed to record the PL spectra. The concentration of the dye pollutants was determined by UV-vis spectrophotometer (Cecile 9000). The TEM and HRTEM images were photographed using a HighTech HT7700 (Tokyo, Japan) instrument. The XPS analyses were conducted by a Specs-Flex XPS (Berlin, Germany). A BELSORP mini II (York, PA, USA) instrument was applied to fulfill the N2 adsorption-desorption measurements. A μAutolabIII/FRA2 EIS (Utrecht, The Netherlands) was employed to accomplish the electrochemical analyses. The results of photocurrent data were also obtained with μAutolabIII/FRA2.

3.4. Photodegradation Tests

The photodegradation experiments were conducted in a photoreactor including a glass reactor furnished with a water-circulating device, a magnetic bar, and an air-purging system. An installed LED lamp (50 W, λ = 450–650 nm) on the top of the reactor supplied the visible light. For the experiments, the photocatalyst powder (0.1 g) was supplemented into 250 mL of the aqueous suspensions of the pollutant (RhB: 1.0 × 10−5 M, MB: 1.0 × 10−5 M, MG: 1.0 × 10−5 M, or fuchsin: 1.0 × 10−5 M), and vigorously stirred for 60 min in the absence of light to accomplish the adsorption–desorption equilibrium. Next, the lamp was switched on for a predetermined time and almost 4 mL of the suspension was sampled at fixed time pauses, and photocatalyst particles were separated using a centrifuge (at 4000 rpm). The concentrations of RhB, fuchsin, MG, and MB were monitored by a UV–vis spectrophotometer, respectively, at 553, 540, 610 and 664 nm. To show the stability of the nanocomposite, we performed the recycling tests for four times consecutively. After each photocatalysis experiment, the photocatalyst was removed and utilized in the next test. Furthermore, to identify the reactive species generated during the degradation of RhB, ammonium oxalate (AOX, h+ quencher, 0.035 g), benzoquinone (BQ, •O2− quencher, 0.027 g), and 2-propanol (2-PrOH, •OH quencher, 20 μL) were added to the system to capture, respectively, h+, •O2−, and •OH species.

4. Conclusions

In brief, CNDs/ZnMn2O4 nanocomposites were synthesized via a facile hydrothermal route. The successful integration of ZnMn2O4 nanoparticles over the CNDs was confirmed by various analyses. The photodegradation experiments revealed that the prepared binary nanocomposites had higher efficiencies for degradations of the selected pollutants under visible light compared to the efficiencies of ZnMn2O4, CNDs, and bulk CN photocatalysts. Amongst the binary photocatalysts, the nanocomposite with 20 wt.% of ZnMn2O4 had admirable activity in the removal of RhB with degradation constant of 747 × 10−4 min−1, mainly resulting from the enhanced specific surface area, significant absorption of visible light, and premiere segregation and transfer of the photoinduced charge carriers through developed p-n heterojunction. Moreover, the activity of the binary sample for degradation of RhB, MG, fuchsin, and MB was 66.5, 15.8, 13.2, and 31.2-fold greater than CN, and 3.44, 1.5, 18.1, and 11.5 times premier than CNDs, respectively. As per radical trapping experiments, the •O2−, h+, and •OH radicals were recognized as the core reactive species involved in the photocatalytic processes. The outcomes of this work disclosed that the combination of ZnMn2O4 and CNDs components through p–n heterojunction not only provoked better absorption efficiencies at visible-light region but also improved the lifespan of the photoinduced charges and their movement on the surface of the photocatalyst for promoted degradation of various organic contaminants.

Author Contributions

Z.L.: Validation; Formal analysis; Investigation; Resources; Writing—Original Draft. A.H.-Y.: Conceptualization; Methodology; Writing—Review & Editing; Supervision; Project administration. S.R.P.: Writing—Review & Editing. A.K.: Formal analysis; Review & Editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by University of Mohaghegh Ardabili.

Data Availability Statement

The data will be available on request.

Acknowledgments

We are grateful to the University of Mohaghegh Ardabili for supporting this work.

Conflicts of Interest

Authors stated that there is no conflict of interest.

References

  1. Ramalingam, G.; Perumal, N.; Priya, A.; Rajendran, S. A review of graphene-based semiconductors for photocatalytic degradation of pollutants in wastewater. Chemosphere 2022, 300, 134391. [Google Scholar] [CrossRef]
  2. Solangi, N.H.; Karri, R.R.; Mazari, S.A.; Mubarak, N.M.; Jatoi, A.S.; Malafaia, G.; Azad, A.K. MXene as emerging material for photocatalytic degradation of environmental pollutants. Coord. Chem. Rev. 2023, 477, 214965. [Google Scholar] [CrossRef]
  3. He, J.; Han, L.; Wang, F.; Ma, C.; Cai, Y.; Ma, W.; Xu, E.G.; Xing, B.; Yang, Z. Photocatalytic strategy to mitigate microplastic pollution in aquatic environments: Promising catalysts, efficiencies, mechanisms, and ecological risks. Crit. Rev. Environ. Sci. Technol. 2022, 53, 504–526. [Google Scholar] [CrossRef]
  4. Brillas, E. A critical review on ibuprofen removal from synthetic waters, natural waters, and real wastewaters by advanced oxidation processes. Chemosphere 2021, 286, 131849. [Google Scholar] [CrossRef] [PubMed]
  5. Ganiyu, S.O.; Sable, S.; El-Din, M.G. Advanced oxidation processes for the degradation of dissolved organics in produced water: A review of process performance, degradation kinetics and pathway. Chem. Eng. J. 2021, 429, 132492. [Google Scholar] [CrossRef]
  6. Ch-Th, T.; Manisekaran, R.; Santoyo-Salazar, J.; Schoefs, B.; Velumani, S.; Castaneda, H.; Jantrania, A. Graphene oxide decorated TiO2 and BiVO4 nanocatalysts for enhanced visible-light-driven photocatalytic bacterial inactivation. J. Photochem. Photobiol. A Chem. 2021, 418, 113374. [Google Scholar] [CrossRef]
  7. Lin, J.; Tian, W.; Zhang, H.; Duan, X.; Sun, H.; Wang, H.; Fang, Y.; Huang, Y.; Wang, S. Carbon nitride-based Z-scheme heterojunctions for solar-driven advanced oxidation processes. J. Hazard. Mater. 2022, 434, 128866. [Google Scholar] [CrossRef] [PubMed]
  8. Bai, L.; Huang, H.; Yu, S.; Zhang, D.; Huang, H.; Zhang, Y. Role of transition metal oxides in g-C3N4-based heterojunctions for photocatalysis and supercapacitors. J. Energy Chem. 2021, 64, 214–235. [Google Scholar] [CrossRef]
  9. Huang, H.; Jiang, L.; Yang, J.; Zhou, S.; Yuan, X.; Liang, J.; Wang, H.; Wang, H.; Bu, Y.; Li, H. Synthesis and modification of ultrathin g-C3N4 for photocatalytic energy and environmental applications. Renew. Sustain. Energy Rev. 2023, 173, 113110. [Google Scholar] [CrossRef]
  10. Balakrishnan, A.; Chinthala, M. Comprehensive review on advanced reusability of g-C3N4 based photocatalysts for the removal of organic pollutants. Chemosphere 2022, 297, 134190. [Google Scholar] [CrossRef]
  11. Guo, R.T.; Wang, J.; Bi, Z.X.; Chen, X.; Hu, X.; Pan, W.G. Recent advances and perspectives of g-C3N4–based materials for photocatalytic dyes degradation. Chemosphere 2022, 295, 133834. [Google Scholar] [CrossRef] [PubMed]
  12. Wang, T.; Nie, C.; Ao, Z.; Wang, S.; An, T. Recent progress in g-C3N4 quantum dots: Synthesis, properties and applications in photocatalytic degradation of organic pollutants. J. Mater. Chem. A 2019, 8, 485–502. [Google Scholar] [CrossRef]
  13. Ma, P.; Zhang, X.; Wang, C.; Wang, Z.; Wang, K.; Feng, Y.; Wang, J.; Zhai, Y.; Deng, J.; Wang, L.; et al. Band alignment of homojunction by anchoring CN quantum dots on g-C3N4 (0D/2D) enhance photocatalytic hydrogen peroxide evolution. Appl. Catal. B Environ. 2021, 300, 120736. [Google Scholar] [CrossRef]
  14. Xing, Y.; Wang, X.; Hao, S.; Zhang, X.; Ma, W.; Zhao, G.; Xu, X. Recent advances in the improvement of g-C3N4 based photocatalytic materials. Chin. Chem. Lett. 2021, 32, 13–20. [Google Scholar] [CrossRef]
  15. Huang, R.; Wu, J.; Zhang, M.; Liu, B.; Zheng, Z.; Luo, D. Strategies to enhance photocatalytic activity of graphite carbon nitride-based photocatalysts. Mater. Des. 2021, 210, 110040. [Google Scholar] [CrossRef]
  16. Zhu, F.; Ma, J.; Ji, Q.; Cheng, H.; Komarneni, S. Visible-light-driven activation of sodium persulfate for accelerating orange II degradation using ZnMn2O4 photocatalyst. Chemosphere 2021, 278, 130404. [Google Scholar] [CrossRef]
  17. Al-Buriahi, A.K.; Al-Gheethi, A.A.; Kumar, P.S.; Mohamed, R.M.S.R.; Yusof, H.; Alshalif, A.F.; Khalifa, N.A. Elimination of rhodamine B from textile wastewater using nanoparticle photocatalysts: A review for sustainable approaches. Chemosphere 2022, 287, 132162. [Google Scholar] [CrossRef]
  18. Li, S.-S.; Liu, M.; Wen, L.; Xu, Z.; Cheng, Y.-H.; Chen, M.-L. Exploration of long afterglow luminescent materials composited with graphitized carbon nitride for photocatalytic degradation of basic fuchsin. Environ. Sci. Pollut. Res. 2023, 30, 322–336. [Google Scholar] [CrossRef]
  19. Tsvetkov, M.; Zaharieva, J. Milanova, Ferrites, modified with silver nanoparticles, for photocatalytic degradation of malachite green in aqueous solutions. Catal. Today 2020, 357, 453–459. [Google Scholar] [CrossRef]
  20. Khan, I.; Saeed, K.; Zekker, I.; Zhang, B.; Hendi, A.H.; Ahmad, A.; Ahmad, S.; Zada, N.; Ahmad, H.; Shah, L.A.; et al. Review on Methylene Blue: Its Properties, Uses, Toxicity and Photodegradation. Water 2022, 14, 242. [Google Scholar] [CrossRef]
  21. Li, Y.; Shu, S.; Huang, L.; Liu, J.; Liu, J.; Yao, J.; Liu, S.; Zhu, M.; Huang, L. Construction of a novel double S-scheme structure WO3/g-C3N4/BiOI: Enhanced photocatalytic performance for antibacterial activity. J. Colloid Interface Sci. 2023, 633, 60–71. [Google Scholar] [CrossRef] [PubMed]
  22. Jing, Y.; Chen, Z.; Ding, E.; Yuan, R.; Liu, B.; Xu, B.; Zhang, P. High-yield production of g-C3N4 quantum dots as photocatalysts for the degradation of organic pollutants and fluorescent probes for detection of Fe3+ ions with live cell application. Appl. Surf. Sci. 2022, 586, 152812. [Google Scholar] [CrossRef]
  23. Basaleh, A.S.; Mohamed, R.M. Influence of doped silver nanoparticles on the photocatalytic performance of ZnMn2O4 in the production of methanol from CO2 photocatalytic reduction. Appl. Nanosci. 2020, 10, 3865–3874. [Google Scholar] [CrossRef]
  24. Wei, Y.; Li, X.; Zhang, Y.; Yan, Y.; Huo, P.; Wang, H. G-C3N4 quantum dots and Au nano particles co-modified CeO2/Fe3O4 micro-flowers photocatalyst for enhanced CO2 photoreduction. Renew. Energy 2021, 179, 756–765. [Google Scholar] [CrossRef]
  25. Preeyanghaa, M.; Vinesh, V.; Sabarikirishwaran, P.; Rajkamal, A.; Ashokkumar, M.; Neppolian, B. Investigating the role of ultrasound in improving the photocatalytic ability of CQD decorated boron-doped g-C3N4 for tetracycline degradation and first-principles study of nitrogen-vacancy formation. Carbon 2022, 192, 405–417. [Google Scholar] [CrossRef]
  26. He, L.; Fei, M.; Chen, J.; Tian, Y.; Jiang, Y.; Huang, Y.; Xu, K.; Hu, J.; Zhao, Z.; Zhang, Q.; et al. Graphitic C3N4 quantum dots for next-generation QLED displays. Mater. Today 2018, 22, 76–84. [Google Scholar] [CrossRef]
  27. Xu, C.; Li, D.; Liu, X.; Ma, R.; Sakai, N.; Yang, Y.; Lin, S.; Yang, J.; Pan, H.; Huang, J.; et al. Direct Z-scheme construction of g-C3N4 quantum dots/TiO2 nanoflakes for efficient photocatalysis. Chem. Eng. J. 2021, 430, 132861. [Google Scholar] [CrossRef]
  28. Yan, S.; Yanlong, Y.; Cao, Y. Synthesis of porous ZnMn2O4 flower-like microspheres by using MOF as precursors and its application on photoreduction of CO2 into CO. Appl. Surf. Sci. 2019, 465, 383–388. [Google Scholar] [CrossRef]
  29. Olusegun, S.J.; Larrea, G.; Osial, M.; Jackowska, K.; Krysinski, P. Photocatalytic Degradation of Antibiotics by Superparamagnetic Iron Oxide Nanoparticles. Tetracycline Case. Catalysts 2021, 11, 1243. [Google Scholar] [CrossRef]
  30. Papadas, I.T.; Galatopoulos, F.; Armatas, G.S.; Tessler, N.; Choulis, S.A. Nanoparticulate Metal Oxide Top Electrode Interface Modification Improves the Thermal Stability of Inverted Perovskite Photovoltaics. Nanomaterials 2019, 9, 1616. [Google Scholar] [CrossRef] [Green Version]
  31. Alhaddad, M.; Mohamed, R.M. Synthesis and characterizations of ZnMn2O4-ZnO nanocomposite photocatalyst for enlarged photocatalytic oxidation of ciprofloxacin using visible light irradiation. Appl. Nanosci. 2020, 10, 2269–2278. [Google Scholar] [CrossRef]
  32. Wu, X.; Xiang, Y.; Peng, Q.; Wu, X.; Li, Y.; Tang, F.; Song, R.; Liu, Z.; He, Z.; Wu, X. Green-low-cost rechargeable aqueous zinc-ion batteries using hollow porous spinel ZnMn2O4 as the cathode material. J. Mater. Chem. A 2017, 5, 17990–17997. [Google Scholar] [CrossRef]
  33. Ni, Q.; Cheng, H.; Ma, J.; Kong, Y.; Komarneni, S. Efficient degradation of orange II by ZnMn2O4 in a novel photo-chemical catalysis system. Front. Chem. Sci. Eng. 2020, 14, 956–966. [Google Scholar] [CrossRef]
  34. Iurilli, P.; Brivio, C.; Wood, V. On the use of electrochemical impedance spectroscopy to characterize and model the aging phenomena of lithium-ion batteries: A critical review. J. Power Sources 2021, 505, 229860. [Google Scholar] [CrossRef]
  35. Schlumberger, C.; Thommes, M. Characterization of Hierarchically Ordered Porous Materials by Physisorption and Mercury Porosimetry—A Tutorial Review. Adv. Mater. Interfaces 2021, 8, 2002181. [Google Scholar] [CrossRef]
  36. Deng, H.; Fei, X.; Yang, Y.; Fan, J.; Yu, J.; Cheng, B.; Zhang, L. S-scheme heterojunction based on p-type ZnMn2O4 and n-type ZnO with improved photocatalytic CO2 reduction activity. Chem. Eng. J. 2020, 409, 127377. [Google Scholar] [CrossRef]
  37. Wang, A.; Guo, S.; Zheng, Z.; Wang, H.; Song, X.; Zhu, H.; Zeng, Y.; Lam, J.; Qiu, R.; Yan, K. Highly dispersed Ag and g-C3N4 quantum dots co-decorated 3D hierarchical Fe3O4 hollow microspheres for solar-light-driven pharmaceutical pollutants degradation in natural water matrix. J. Hazard. Mater. 2022, 434, 128905. [Google Scholar] [CrossRef]
  38. Khan, I.; Saeed, K.; Ali, N.; Khan, I.; Zhang, B.; Sadiq, M. Heterogeneous photodegradation of industrial dyes: An insight to different mechanisms and rate affecting parameters. J. Environ. Chem. Eng. 2020, 8, 104364. [Google Scholar] [CrossRef]
  39. Ahmad, S.; Almehmadi, M.; Janjuhah, H.T.; Kontakiotis, G.; Abdulaziz, O.; Saeed, K.; Ahmad, H.; Allahyani, M.; Aljuaid, A.; Alsaiari, A.A.; et al. The Effect of Mineral Ions Present in Tap Water on Photodegradation of Organic Pollutants: Future Perspectives. Water 2023, 15, 175. [Google Scholar] [CrossRef]
  40. Yin, Y.; Liu, M.; Shi, L.; Zhang, S.; Hirani, R.A.K.; Zhu, C.; Chen, C.; Yuan, A.; Duan, X.; Wang, S.; et al. Highly dispersive Ru confined in porous ultrathin g-C3N4 nanosheets as an efficient peroxymonosulfate activator for removal of organic pollutants. J. Hazard. Mater. 2022, 435, 128939. [Google Scholar] [CrossRef]
Catalysts 13 00346 g001 550
Figure 1. (a) XRD, (b) FT-IR, (c) Optical absorbance, (d) Tauc plots, and (e,f) Mott-Schottky plots of the specified samples.
Figure 1. (a) XRD, (b) FT-IR, (c) Optical absorbance, (d) Tauc plots, and (e,f) Mott-Schottky plots of the specified samples.
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Catalysts 13 00346 g002 550
Figure 2. (a) SEM, (b) TEM, and (c) HRTEM images. (d) EDX spectrum and (e) EDX mapping of CNDs/ZnMn2O4 (20%) nanocomposite.
Figure 2. (a) SEM, (b) TEM, and (c) HRTEM images. (d) EDX spectrum and (e) EDX mapping of CNDs/ZnMn2O4 (20%) nanocomposite.
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Figure 3. XPS spectra of CNDs/ZnMn2O4 (20%) photocatalyst: (a) Survey, (b) C1s, (c) N1s, (d) Zn 2p, (e) Mn 2p, and (f) O1s spectra.
Figure 3. XPS spectra of CNDs/ZnMn2O4 (20%) photocatalyst: (a) Survey, (b) C1s, (c) N1s, (d) Zn 2p, (e) Mn 2p, and (f) O1s spectra.
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Figure 4. (a) RhB photodegradation, (b) First-order-kinetic plots for the degradation rates of RhB, (c) degradation rate constants of RhB, (d) Effect of trapping agents on the degradation of RhB, (e) Degradation constants of MB, MG, and fuchsin, and (f) the results of recycling experiments of CNDs/ZnMn2O4 (20%) system for degradation of RhB.
Figure 4. (a) RhB photodegradation, (b) First-order-kinetic plots for the degradation rates of RhB, (c) degradation rate constants of RhB, (d) Effect of trapping agents on the degradation of RhB, (e) Degradation constants of MB, MG, and fuchsin, and (f) the results of recycling experiments of CNDs/ZnMn2O4 (20%) system for degradation of RhB.
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Figure 5. (a) EIS, (b) PL, and (c) Photocurrent of CN, CNDs, ZnMn2O4, and CNDs/ZnMn2O4 (20%) photocatalysts. (d) N2 sorption data and (e) pore-size distributions for CNDs, ZnMn2O4, and CNQDs/ZnMn2O4 (20%) photocatalysts.
Figure 5. (a) EIS, (b) PL, and (c) Photocurrent of CN, CNDs, ZnMn2O4, and CNDs/ZnMn2O4 (20%) photocatalysts. (d) N2 sorption data and (e) pore-size distributions for CNDs, ZnMn2O4, and CNQDs/ZnMn2O4 (20%) photocatalysts.
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Figure 6. Photocatalytic mechanism for improved activity of CNDs/ZnMn2O4 nanocomposites: (a) Conventional and (b) p-n Heterojunction.
Figure 6. Photocatalytic mechanism for improved activity of CNDs/ZnMn2O4 nanocomposites: (a) Conventional and (b) p-n Heterojunction.
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Scheme 1. Schematic illustration for the synthesis of CNDs/ZnMn2O4 photocatalysts.
Scheme 1. Schematic illustration for the synthesis of CNDs/ZnMn2O4 photocatalysts.
Catalysts 13 00346 sch001
Table
Table 1. Textural properties of the CNDs, ZnMn2O4, and CNDs/ZnMn2O4 (20%) photocatalysts.
Table 1. Textural properties of the CNDs, ZnMn2O4, and CNDs/ZnMn2O4 (20%) photocatalysts.
SampleSurface Area
(m2 g−1)		Mean Pore Diameter (nm)Total Pore Volume
(cm3 g−1)
CNDs12.0327.730.08
ZnMn2O433.89.090.08
CNDs/ZnMn2O4 (20%)44.627.50.31
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MDPI and ACS Style

Lahootifar, Z.; Habibi-Yangjeh, A.; Rahim Pouran, S.; Khataee, A. G-C3N4 Dots Decorated with Hetaerolite: Visible-Light Photocatalyst for Degradation of Organic Contaminants. Catalysts 2023, 13, 346. https://doi.org/10.3390/catal13020346

AMA Style

Lahootifar Z, Habibi-Yangjeh A, Rahim Pouran S, Khataee A. G-C3N4 Dots Decorated with Hetaerolite: Visible-Light Photocatalyst for Degradation of Organic Contaminants. Catalysts. 2023; 13(2):346. https://doi.org/10.3390/catal13020346

Chicago/Turabian Style

Lahootifar, Zahra, Aziz Habibi-Yangjeh, Shima Rahim Pouran, and Alireza Khataee. 2023. "G-C3N4 Dots Decorated with Hetaerolite: Visible-Light Photocatalyst for Degradation of Organic Contaminants" Catalysts 13, no. 2: 346. https://doi.org/10.3390/catal13020346

APA Style

Lahootifar, Z., Habibi-Yangjeh, A., Rahim Pouran, S., & Khataee, A. (2023). G-C3N4 Dots Decorated with Hetaerolite: Visible-Light Photocatalyst for Degradation of Organic Contaminants. Catalysts, 13(2), 346. https://doi.org/10.3390/catal13020346

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