Activated carbon/g-C3N4 /H2O2 system with enhanced photocatalytic activity for Rhodamine-B degradation under the visible light

Lan Nguyen Thi; Thi Thuy Trang Phan; Lam Nguyen Tan; Thanh Lieu Thi Le; Le Tuan Nguyen; Nguyen Tien Hoang; Vien Vo; Dinh Quang Khieu

doi:10.4491/eer.2024.121

Environ Eng Res > Volume 30(1); 2025 > Article

Thi, Phan, Tan, Le, Nguyen, Hoang, Vo, and Khieu: Activated carbon/g-C3N4 /H2O2 system with enhanced photocatalytic activity for Rhodamine-B degradation under the visible light

Research

Environmental Engineering Research 2025; 30(1): 240121.

Published online: June 7, 2024

DOI: https://doi.org/10.4491/eer.2024.121

Activated carbon/g-C₃N₄ /H₂O₂ system with enhanced photocatalytic activity for Rhodamine-B degradation under the visible light

Lan Nguyen Thi^1,^†, Thi Thuy Trang Phan^1,^*, Lam Nguyen Tan^1,^*, Thanh Lieu Thi Le^1,^*, Le Tuan Nguyen^1,^*, Nguyen Tien Hoang^2,^*, Vien Vo^1,^†

, Dinh Quang Khieu^3,^†

¹Faculty of Natural Science, Quy Nhon University, 590000, Viet Nam

²University of Science and Education, The University of Da Nang, 550000, Viet Nam

³University of Sciences, Hue University, 530000, Vietnam

^†Corresponding author: E-mail: vovien@qnu.edu.vn (V.V.), dqkhieu@hueuni.edu.vn (D.Q.K.) Tel: +84-914908789 (V.V.), +84-368706850 (D.Q.K.)

* These authors contributed equally to this work.

Received February 28, 2024 Revised June 4, 2024 Accepted June 6, 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

In this study, activated carbon/g-C₃N₄ photocatalyst (BC/CN) was successfully prepared by a facile calcination method from activated carbons derived from banana peels and urea. As a result, the morphology of BC/CN consisted of the activated carbons highly dispersed on the g-C₃N₄ matrix. The advanced oxidation process of BC/CN and hydogen peroxide exhibits a better catalytic activity towards Rhdamine-B degradation in visible-light region than those of the pristine g-C₃N₄ or BC with hydrogen peroxide. The grafting of activated carbon to g-C₃N₄ enhanced the electron transfer efficiency and suppressed the photoinduced electron-hole recombination. Initial TOC was about 650 mg/L; however, it decreased by 93% to 60 mg/L after 60 min treating. After four cycles of experiments, the catalyst BC/CN still presented high activity for the degradation of RhB. In addition, all N-deethylation intermediates and several small molecular products were separated and identified by LC/MS method. Based on the analytical results, a possible mechanism of photocatalytic degradation was proposed. This work demonstrates a facile and efficient approach to improving the performance of g-C₃N₄-based catalysts.

Keywords: Activated carbon, g-C3N4, Photocatalysis, Rhodamine B, Hydrogen peroxide

Graphical Abstract

Keywords: Activated carbon, g-C3N4, Photocatalysis, Rhodamine B, Hydrogen peroxide

Introduction

The water pollution caused by the contamination of various chemicals from industrial, agricultural, and livestock farming has raised a major concern for governments and the scientific community. Untreated sewage discharged directly into natural water bodies could cause devastation to the ecosystem and then turn back to damage human lives. Therefore, decontaminating the sewage is not only a protective pathway for the environment and public health but also a sustainable strategy for nations’ development. Among various techniques have applied in wastewater purification such as filtration, adsorption, flocculation, sedimentation, and reverse osmosis, the advanced oxidation processes (AOPs) have become a potential strategy because of their function through the usage of highly active oxidants without causing secondary pollution [1]. As one of the AOPs, photocatalysis with oxidative radicals formation using photo-excited electron-hole pairs over semiconductors has gained the great attention of researchers. Traditional semiconductors such as TiO₂ ZnO and SnO₂ have been widely investigated as UV-activated photocatalysts due to their photostability, non-toxicity, and low cost. However, the wide bandgaps allow them only application in UV or blue-light regions which account for 4% of available solar radiation [2]. Therefore, the metal-free polymeric graphitic carbon nitride (g-C₃N₄) with medium bandgaps (2.7 eV) active in the visible-light region has been considered as an alternative photocatalyst for practical application [3], [4]. Besides, the high recombination rate of photo/electron-induced charged carriers is one of the challenging drawbacks of pure semiconductor photocatalysts. Various approaches have been developed to overcome this limitation, including doping modification and composite formation. While the defects caused by impurities doping could suppress recombination rate by charge trapping which is difficult to achieve, coupling semiconductors or non-metals with other materials is a facile way to improve charge separation [5]. Luu et al. [6] reported the synthesis of TiO₂@g-C₃N₄ to decompose NO in visible light through plasma-treated photocatalytic. Chu et al. [7] performed an approach to synthesis of g-C₃N₄ with cobalt single atom for photocatalytic H₂O₂ production. In addition, the S, K modified g-C₃N₄ doping S and K for photocatalytic production of H₂O₂ was reported by Zhang et al [8].

As high electronic conductivity, carbonaceous materials such as graphene, graphite, and carbon nanotubes, have been used as conductive frameworks to accelerate the charge transfer process in various photocatalysts [9], [10], [11], [12]. However, the high cost and complex preparation of these carbon-based materials have limited their application.

In this work, the activated carbons prepared from a local biomass-waste resource (banana peels) was used as a conductive agent to disperse g-C₃N₄ nanosheets. The obtained composite performed significant photocatalytic degradation of Rhodamine B within an additional H₂O₂ oxidant. This enhancement could be attributed to the effectiveness of charge separation via improved electronic conductivity which is further illustrated by a proposed mechanism.

Experimentals and Methods

2.1. Materials

Urea (CH₄N₂O, 99%, Merck), potassium hydroxide (KOH, ≥ 99%, Merck), ethanol (C₂H₆O, ≥ 99%, Merck), hydrogen peroxide (H₂O₂, 35%, Merck), rhodamine B (C₂₈H₃₁ClN₂O₃, ≥ 99%, Merck), tert-butanol (C₄H₁₀O, 99.5%, Merck) and hydrochloric acid (HCl, 35%, Sigma Aldrich), dimethyl sulfoxide (C₂H₆OS, ≥ 99%, Sigma Aldrich), ammonium oxalate (NH₃, ≥ 99%, Sigma Aldrich), 1,4-benzoquinone (C₆H₄O₂, ≥ 99%, Merck) were used as received. The bananas were collected from the local market (Binh Dinh province, Vietnam). Use the peel of a whole bunch of ripe bananas. The banana peels were washed, ground into small pieces, and dried under vacuum at 110 °C for 24 hours. The dried crushed banana peels are ready for use.

2.2. Methods

2.2.1. Preparation of banana peel derived activated carbon (BC)

The activated carbon were prepared following the previous publication [13]. Briefly, the dried crushed banana peels were loaded into a tubular furnace and heated at 800°C for five hours under Ar gas flow with a heating rate of 10°C min⁻¹. The collected solid was stirred in 20%(wt) KOH solution for two hours, followed by 2M HCl for 15 hours, before being washed with deionized (DI) water to neutral pH and dried in a vacuum oven for 24 hours at 110°C. The solid was treated at 300°C for three hours in the air with a ramp rate of 10°C min⁻¹. The re-ground powder was rinsed with 2M HCl and DI water, dried, and denoted as BC.

2.2.2. Preparation of g-C₃N₄

The pure g-C₃N₄ was synthesized from urea [14]. Typically, powder urea was ground and transferred to a ceramic crucible covered by aluminum foil and treated at 550°C for one hour at heating rate of 10°C min⁻¹ to obtain g-C₃N₄ (denoted as CN).

2.2.3. Preparation of BC/CN composite

1 g of BC was added to a mixture of ethanol (300 mL) and DI water (150 mL) containing × g of urea (x = 100, 150, and 200). This mixture was sonicated for 30 minutes, and then completely evaporated at 60°C. The obtained solid was transferred into a ceramic crucible and heated at 550°C for 1 hour under an Ar gas flow at heating rate of 10°C min⁻¹. The resulting powder was denoted as BC/CN-x (x = 100, 150, and 200).

2.2.4. Characterization

X-ray diffraction (XRD) measurements were carried out using a Bruker D8 Advance X-ray diffractometer. Scanning electron microscopy (SEM) images were conducted on a JSM-7600F. Infrared (FTIR) spectra were obtained using an FT-IR – GX – PerkinElmer spectrophotometer. Ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS) measurements were performed on a U4100 UV-Vis-NIR Hitachi. Photoluminescence (PL) spectra were recorded on a Fluorescence spectrophotometer (Hitachi F-7000). Transmission electron microscopy (TEM) was conducted using JEOL JEM-2100F. X-ray electron spectra (XPS) were recorded using (ESCALab 250-Thermo). The intermediates of RhB decomposition are determined by LC/MSD-Trap-SL method in combination with ESI method ionized mass spectrometry on Agilent.

2.2.5. Photocatalytic experiment

The RhB degradation over the BC/CN catalysts was studied. A mixture containing 100 mL (10 mg.L⁻¹ RhB) and 0.05 g of the catalyst was stirred using sonication and placed in dark for 1 h to ensure adsorption/desorption equilibrium. Then the resulting mixture was irradiated with visible light (using a 30 W–220 V LED lamp). Next, V μL H₂O₂ was added to the RhB aqueous solution. After every 10 min, 5 mL of suspension was withdrawn and centrifuged to collect the solution. The concentration of the RhB was determined by spectrophotometry using a UV–Vis spectrophotometer (Jenway 6800) at λ_max of 553 nm. The percentage of degradation for RhB was calculated using the following equation, H (%) = 100×[(C_o−C_t)/C_o], where C_o and C_t are concentrations of RhB at the initial and t times, respectively.

Results and Discussion

3.1. Characterization of Photocatalysts

The XRD patterns of BC, CN and BC/CN are presented in Fig. 2a. For BC, the broad (002) diffraction band (2θ = 15–35º) peaked at 26^o can be assigned to the amorphous carbon structures. The weak and broad (101) diffraction band (2θ = 40–50º) peaked at 44^o is due to the a axis of the graphite structure [15]. The XRD pattern of CN exhibits two characteristic peaks at 2θ = 13.2° and 27.6° corresponding to the stacking structure of (100) and (002) planes of g-C₃N₄ [16]. The XRD patterns of BC/CN-a possess characteristic peaks of g-C₃N₄ while the diffraction of activated carbons peaked at 26^o and 44^o are very weak and disappeared as the large amount of g-C₃N₄ is added. Fig. 2b shows the FT-IR spectra of obtained materials. The CN and BC/CN-a spectra includes various signals of characteristic bonds of g-C₃N₄ such as N-H stretching mode at 3180 cm⁻¹, bending vibration of C-N, and C=N of triazine rings at 1242, 1325, 1408, 1568, and 1640 cm⁻¹ [17]. Additionally, peaks at 809 and 889 cm⁻¹ could be attributed to breathing mode of triazine and heptazine units [18], [19]. The optical properties of single material and composites were evaluated via the UV-Vis DRS spectra (Fig. 2c). Accordingly, BC shows a no-absorption in the UV-Vis region while g-C₃N₄ possess the highest absorption from the ultraviolet region to the visible range up to 430 nm having a bandgap of 2.9 eV. Compared with the CN, the absorption edges of BC/CN-x composites showed almost little change, suggesting that the BC was mainly decorated on the surface of g-C₃N₄ and did not alter the band structure of CN. Ultraviolet -light absorption decreases and visible-light absorption increases slightly as the activated carbon is added. However, this trend seems to be irregular as the added CN amount increases. The reason is not clear. It is possible that the pore volume and surface area of BC/CN-150 are larger than those of others (Table S1 and Fig. S1). This may cause a higher visible absorbance of BC/CN-150 compared to BC/CN-100 and BC/CN-200. The bandgap energy value E_g determined by the Kubelka-Munk function [20, 21] for CN, BC/CN-100, BC/CN-150 and BC/CN-200 composite sample were found as 2.84; 2.82; 2.78 and 2.83 eV, respectively (Fig. 2d). This result suggested that the nanocomposite combines the features of BC and CN and this indicates an interaction between g-C₃N₄ and activated carbon, which may modify photo-induced electron–hole pair formation. The nitrogen adsorption-desorption isothermal curves of the as-prepared samples were shown in Fig. 2e.

The isothermal curves of all samples are classified to the IV type according to IUPAC and characteristic of mesoporous structure. All the composites perform the hysteresis in relative pressure of 0.8–1.0 while the BC extended this phenomenon in 0.4–1.0. The specific surface areas of CN, BC, BC/CN-100, BC/CN-150 and BC/CN-200 were found as 61.4; 861.6; 73.9; 90.9 and 66.3, respectively. The surface area of activated carbon derived from banana peel (BC) is higher than those of carbon materials prepared from several biomasses such as micronsized commercial wood-derived activated carbon (428.7 m².g⁻¹) [22], sugarcane bagasse (425.1 m².g⁻¹) [23], raw P. australis (22.8 m².g⁻¹) [24] but lower than some activated carbons (1272 and 1597 m².g⁻¹) prepared by from Kanlow Switchgrass and Public Miscanthus, respectively [25]. The BC/CN composites all have a specific surface area larger than that of CN but much smaller compared to BC. This is because g-C₃N₄ has been dispersed, covering the pores of activated carbons, greatly reducing the specific surface area of activated carbons. The PL spectroscopy is a useful tool to estimate the recombination of photo-induced electron-hole pair. Fig. 2f shows the intensity of the PL emission of g-C₃N₄ was significantly reduced by the addition of activated carbons, which could be derived from the suppression in the recombination rate of photo-induced electron-hole pairs [26], [27].

The morphology of as-prepared samples was elucidated using SEM and TEM images, as shown in Fig. 3. The SEM image of BC (Fig. 3a) exhibits the porous structure of activated carbons while the flake morphology of CN (Fig. 3b) is present for the stacking structure of g-C₃N₄ nanosheets. The composite is observed as coverage of the g-C₃N₄ flake on a porous carbon (Fig. 3c). For further structural observations, TEM image of a representative composite (Fig. 3d) was presented, which shows the BC/CN composite consisting of g-C₃N₄ nanosheets dispersed in the carbon matrix.

The surficial chemical state of CN, BC, and BC/CN-150 was analyzed via the XPS technique. The survey spectrum of BC/CN-150 possess the nitrogen and carbon elements as expected (Fig. 3e). The C1s XPS spectrum of BC exhibited a peak at 284.4 eV corresponding to the C=C bonds while the relevant spectra of CN and composite performed signals at binding energies of 285.0 and 288.1 eV corresponding to graphitic C=C and sp²-hybridized carbon C(N)₃ [28] (Fig. 3f). In addition, the N1s spectra were deconvoluted into three signals at 398.5, 399.7, and 401.2 eV attributed to pyridinic (C-N=C), ternary (C)₃N, and boundary amino −NH₂ of g-C₃N₄ [29] (Fig. 3g). The results further confirmed the interaction of g-C₃N₄ and activated carbons.

3.2. Photocatalytic Degradation of RhB over BC/CN

The photocatalytic activity of CN and BC/CN was investigated via RhB decomposition under the visible light of an LED using H₂O₂ as an oxidant. As shown in Fig. 4a, without the addition of H₂O₂, the RhB degradation efficiencies over CN and BC/CN-150 were low. The addition of H₂O₂ enhanced significantly the efficiency of RhB degradation for the BC/CN-150 catalyst. Herein, the degradation efficiency of BC/CN-150 exhibited a highest value of 95.67% after 60 minutes of reaction. The rate constants of RhB decomposition over BC/CN catalysts within additional H₂O₂ were significantly higher than those of CN without hydrogen peroxide, in which the highest value of rate constants for BC/CN-150 catalyst is 0.053 min⁻¹, almost five times higher than CN (Fig. 4b). Comparing the catalytic activity of this material with previous studies is misleading because the reaction conditions are different. A comparison of the rate constant of the present work with the previous works is listed in Table S2. To some extent, it shows that in the the catalytic activity of BC/CN-150 reaction system is ten times higher than those of catalytic systems that do not use H₂O₂ [30], [31], [32], [33]. This improvement is consistent with the aforementioned discussion on improved electronic conductivity and suppression in charge carriers’ recombination. Due to its highest degradation efficiency, BC/CN-150 was used as a photocatalyst for the next experiments. The photocatalytic activity of BC/CN-150 material for degradation of the different colorants such as rhodamine B (RhB), methylene blue (MB) and tetracycline (TC) antibiotic. The results in Fig. S2 show that the photodegradation efficiency of RhB, MB and TC are 95.67%, 73.6%, and 50.63% respectively after 60 minutes under visible light illumination. These results confirm that BC/CN-150 can photo-catalytically degrade various dyes.

The effect of initial RhB concentration on photocatalytic degradation (10 to 50 mg L⁻¹) is presented in Fig. 4c. The decrease of RhB degradation efficiency decreases with increasing initial concentration. This could be assigned to three main reasons: (i) an increase in the initial concentration leads to a larger amount of adsorbed pollutant molecules on the catalyst surface, preventing the photon-absorbability of the catalyst; (ii) the competitive adsorption of organic molecules prohibits the mas transport toward active sites on the catalyst surface [34], [35]; and (iii) the high concentration of colored pollutant could hinder the penetration of photons into bulk solution and catalytic surface due to the photon absorption of RhB molecules [36]. The effect of the light sources on the degradation efficiency of the RhB was examined under the irradiation of the natural solar light and 30 W LED lamp induced visble-light. As shown in Fig. S3, the efficiency of RhB degradation after 30 minutes under lighting of the LED lamp is 74.5%, while 96.1% for the solar light. This can be explained by the fact that the BC/CN material can absorb light photons in whole ultraviolet-visible region as shown in its UV-Vis DRS spectrum, and the light intensity of sunlight is much higher than that of the LED lamp as mentioned above.

The pH of pigment wastewater could be varied in a wide range and affect the performance of photocatalysts. Therefore this effect has been examined for BC/CN-150 with various initial pH values of 2.20, 4.09, 5.17, 8.06, and 10.15, adjusted using 0.1 M HCl and NaOH solution. As shown in Fig. 4d, in acidic environment, the degradation efficiencies remain higher than 95% while the basic medium significantly reduced photocatalytic decomposition of RhB to 73 % and 66.7% at pH value of 8.06 and 10.15. This could be explained by the effect of pH on the charge on the surface of the catalyst and the forms of target molecules. To clarify this issue, the point of zero charges (pH_pzc) of the catalyst was determined as 5.12 (Fig. S4). According to pH_pzc, a lower pH could raise a positively charged surface, and a higher pH could induce a negatively charged surface. Meanwhile, the pKa of RhB is 3.17 which means RhB molecule should be in cationic form at pH < 3.17 and zwitterionic form at pH > 3.17. In the strongly acidic solution, the protonation of RhB increases its hydrophobicity due to transforming to neutral molecules. This drives target molecules reach to the gas-liquid boundary wherein hydroxyl radicals are highly concentrated, accelerating the photocatalytic process. When increasing the pH value, the dimerization of zwitterionic ions of RhB and the negatively charged surface of a catalyst prohibit adsorbability of pollutants leading to a decrease in photocatalytic performance.

The photocatalytic performance of BC/CN-150 was further studied in variation of catalyst dosage. According to Fig. 4e, when the amount of catalyst increases, the degradation proportion of RhB increases and reaches the highest point at a dosage of 0.05 g, then reduces at higher doses. Larger amounts of heterogeneous catalysts could lower the penetration of light radiation and inhibit the photocatalytic performance.

The effect of H₂O₂ dosage (varying from 0.005 to 0.025 M) on the photocatalytic efficiency was conducted. As shown in Fig. 4f, the variation of H₂O₂ addition performs the highest result of 95.7% efficiency at 0.02 M H₂O₂. The higher concentration of oxidant leads to the self-exclusion of free radicals and prohibits the adsorption of RhB [37], [38].

The stability of carbon-based materials for photocatalytic usage is essential for its application. Self-destruction of reduced graphene oxide due to radical production during photocatalysis was reported in which the OH• radicals induced at the TiO₂ surface lead to mineralize reduce graphene oxide [39]. The recyclability of BC/CN-150 photocatalyst was examined after five cycles of reactions. After each cycle of reaction, the catalyst was collected by centrifugation, rinsed with DI water, and dried before the next reaction. According to Fig. 5a, after a series of reactions, the decrease in photo-degradation efficiency is only 5.4% compared to the first use, demonstrating the photostability and high recovery ability of this photocatalyst. The decay in photocatalytic performance could be attributed to the destruction of catalytic active sites on g-C₃N₄. The structural stability of the catalyst after reuse was tested by XRD (Fig. 5b). As shown in Fig. 5b, there was almost no significant change in the diffraction, indicating a negligible variation in the phase structure of the BC/CN-150 composite after a long period of reuse and according to Fig. S5. the structure of the BC/CN material itself does not change its elemental composition after the photocatalytic process. This proves that the reusability of BC/CN-150 is high and stable.

To study the photocatalytic mechanism, quenching experiments were carried out using tert-butanol (TB), 1,4-benzoquinone (BQ), ammonium oxalate (AO) and dimethyl sulfoxide (DMSO) as scavengers of hydroxyl radicals (^•OH), superoxide anion radicals (^•O₂ ⁻), photo-generated holes and electrons, respectively. Fig. 5c shows reduction in RhB degradation efficiency within TB and DMSO demonstrating the major contribution of the ^•OH and photo-induced electrons in photocatalytic process. This is compatible to the activation of H₂O₂ via electron reduction. Meanwhile, the presence of AO and BQ impact less reduction in RhB degradation, which could imply that the photo-induced holes and ^•O₂ ⁻ give minor effect to the total process. The mechanism of photocatalytic activity over BC/CN composite using H₂O₂ was illustrated by following equations [40], [41]:

(1)

BC / CN- 150 + h υ \to BC / CN- 150 (e -) + BC / CN- 150 (h^{+})

(2)

H_{2} O_{2} + e - \to {OH}^{-} + {}^{\cdot}O H

(3)

e^{-} + O_{2} \to {{}^{\cdot}O}_{2^{-}}

(4)

{OH}^{-} + h^{+} \to {}^{\cdot}O H

(5)

e^{-} + O_{2} \to {{}^{\cdot}O}_{2^{-}}

(6)

{}^{\cdot}O H + RhB \to degradation product

(7)

{{}^{\cdot}O}_{2^{-}} + RhB \to degradation product

When the catalyst is exposed in the visible-light region the electrons and holes are formed Eq. (1). the electrons transfer to adjacent carbons as electron acceptors. The free electrons will reduce H₂O₂ to form ^•OH Eq. (2). or react with oxygen to form peroxoanion (^•O₂⁻_, Eq. (3).) or decompose directly dyes. The free hole reacts with OH- to form ^•OH (Eq. (4).). These free radicals could decompose RhB (Eq. (6 –7)). This process is illustrated as Fig. 6.

To find out the intermediate products in the RhB photocatalytic process, the research solution after illumination time of 30 minutes and 60 minutes. was analyzed by high resolution LC-MS/MS. The results are presented in Fig. S6–9. It was found that after 30 minutes and up to 60 minutes of illumination, RhB content decreased significantly, and many new peaks appeared on the LC spectrum at different retention times. This can infer the formation of intermediates due to RhB decomposition.

From the MS spectrum (Fig. S8), combined with literature research [42], [43], [44], [45], we propose the RhB decomposition mechanism as follows: RhB (m /z=443.12, RT=13.16 min, still after 30 min) is first N-deethylated (cleaving the ethyl groups in the −N(C₂H₅)₂ group to intermediates with m/z=415.1594 (RT=12.41 min), m/z=413.2230 (RT=21.76 min), m/z=387.1300 (RT=11.50 min), m/z=383.1433 (RT=12.42 min), then the intermediates continue to be oxidized and cut chain and ring opening to allow intermediates with smaller molecular weights. At the same time, the results of LC-ESIMS analysis and the TOC measurement were subjected to reaction solution. Initial TOC was about 650 mg/L; however, it decreased 93% to 60 mg/L after 60 min treating, indicating complete mineralization. It is concluded from LC-MS and TOC analysis that RhB degradation over BC/CN-150 catalyst proceeds via many different intermediates, and they can eventually be converted into CO₂ and H₂O (Fig. 7).

Conclusions

In this study, the composite of g-C₃N₄ and banana-peel derived activated carbons were synthesized successfully using a facile calcination method. The obtained composites performed excellent photocatalytic performance under visible irradiation compared to the single components. With 95.67% decolorization, BC/CN-150 achieved the highest performanc of RhB degradation after 60 min irradiation. The kinetic and thermodynamic factors as well as the optimized conditions for the photocatalytic activity of the BC/CN-150 composite have been investigated. pH value is an important factor that significantly affects photocatalytic activity, BC/CN-150 material works well in strong acid regions. The mechanism of RhB decomposition reaction and photocatalytic degradation pathways on BC/CN-150 were proposed.

Supplementary Information

eer-2024-121-supplementary.pdf

Acknowledgements

This research is funded by Vietnamese Ministry of Education and Training under the Grant B2023-DQN-02.

Notes

Author contributions

V.V. (Professor) and D.Q.K. (Professor) conceived and planned the experiments. N.T.L. (PhD), T.T.T.P. (PhD), L.N. T. (PhD), T.L.T.L. (PhD), T.T.N. (PhD), N.T.H. (PhD) carried out the experiments. V.V. (Prof) and N.T.L. (PhD) contributed to the interpretation of the results. D.Q.K. (Prof) and N.T.L. (PhD) took the lead in writing the manuscript. All authors provided critical feedback and helped shape the research, analysis and manuscript.

Conflict-of-Interest Statement

The authors declare no competing interests.

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Fig. 1

The schematic representation of BC/CN-x composite.

Fig. 2

(a) XRD patterns; (b) FT-IR spectra; (c) UV-Vis DRS; (d) Kubelka Munk plot derived from UV-Vis DRS spectra; (e) N₂ adsorption/desorption isotherms of BC, CN and BC/CN-x ; (f) PL spectra of CN and BC/CN-x.

Fig. 3

SEM of (a) BC; (b) CN and (c) the BC/CN-150; (d) TEM of BC/CN-150 and XPS spectra of (e) BC/CN-150 survey; (f) C of pure BC, g-C3N4, BC/CN-150; (g) N of g-C3N4, BC/CN-150.

Fig. 4

(a) Photocatalytic activity, and (b) kinetic models fitting plot using pseudo-first-order model of (1) H₂O₂ + Vis; (2) CN + Vis; (3) BC/CN-150 + Vis; (4) CN + H₂O₂ + Vis; (5) BC/CN-200 + H₂O₂ + Vis; (6) BC/CN-100 + H₂O₂ + Vis; (7) BC/CN-150 + H₂O₂ + Vis; (c) effect of initial concentration of RhB and (d) effect of pH; (e) effect of catalyst dosage; (f) effect of H₂O₂ concentration on catalytic activity of BC/CN-150 (V = 100 mL; m = 0.05 g).

Fig. 5

(a) RhB degradation efficiency after five reuse cycles of BC/CN-150 (conditions: pH= 5.12; m_catalyst = 0.05 g; concentration of RhB = 10 mg/L; adsorption time = 1 hour); (b) XRD patterns of reused BC/CN-150; (c) Kinetics of RhB degradation on BC/CN-150 in the presence of different scavengers.