Preparation of Carbon nitride/Carbon dots/4A molecular sieve composite and evaluation of adsorption performance for Methylene Blue

doi:10.21203/rs.3.rs-3887556/v1

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Preparation of Carbon nitride/Carbon dots/4A molecular sieve composite and evaluation of adsorption performance for Methylene Blue

https://doi.org/10.21203/rs.3.rs-3887556/v1

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The discharge of dye wastewater poses significant hazards to the ecological environment and human health. In this paper, a new composite material carbon nitride/carbon dots/4A molecular sieve (C₃N₄/CDs/4A) was prepared by using urea, citric acid and 4A molecular sieve to remove dyes from wastewater. The material was characterized by SEM, FTIR and XRD tests to prove the successful preparation of C₃N₄/CDs/4A. Compared with 4A molecular sieve, the C₃N₄/CDs/4A had a larger specific surface area of 164.54 m²/g. The C₃N₄/CDs/4A had great adsorption performance for methylene blue (MB), with the adsorption capacity of up to 44.34 mg/g. Adsorption isotherm and kinetic studies showed that the adsorption of MB on C₃N₄/CDs/4A followed Langmuir isotherm (R² = 0.999) and pseudo-second-order kinetic model (R² = 1). In addition, the C₃N₄/CDs/4A maintained almost the same adsorption amount for MB in the pH range of 5–11 and was less affected by temperature. Furthermore, the excellent thermal regeneration performance of C₃N₄/CDs/4A laid a foundation for its industrial application. This study provided a new method for treating refractory dye wastewater.

4A molecular sieve

Carbon nitride

Carbon dots

Methylene Blue

Adsorption

Regeneration

With the continuous advancement of industrial modernization, the demand for dyes in the entire industrial system has steadily increased. However, the discharge of dye wastewater is also on the rise (Wang D Y et al. 2022). The composition of dye wastewater is complex and there are many harmful substances (Zhang H B et al. 2022). It poses a threat to aquatic ecosystems and affects human health (Malakootian et al. 2018). Therefore, effective treatment of dye wastewater is not only a challenge for the industrial sector but also for the whole society (Yeow P K et al. 2021). Currently, the methods used for treating dye wastewater include coagulation (Long Y et al. 2020), photocatalytic degradation (Bahmani M et al. 2020), adsorption (Puga F et al. 2021), and advanced oxidation technology (Liang Q H et al. 2021; Shao et al. 2020 and 2021), among which adsorption stands out for its simple operation and cost-effectiveness (Hassan et al. 2021 and Uddin et al. 2021).

The selection of adsorbent is the key to the application of adsorption method (MashkooR et al. 2020). 4A molecular sieve is an alkali metal silicate that has a simple preparation method and good adsorption ability, which has been widely used in laboratories and industrial environment (Parinyakit et al. 2021 and Xiong Y H et al. 2019). Hendriyana et al. (2017) found that 4A molecular sieve had a stronger ability to adsorb water in methanol solution than sodium sulfate and magnesium sulfate through batch experiments. Tomadakis et al. (2018) reported that 4A molecular sieve could significantly increase the concentration of sulfur dioxide in the adsorbed product with high recovery rate when used for pressure swing adsorption of carbon dioxide and methane mixed with a small amount of hydrogen sulfide. However, it should be noted that the adsorption capacity of 4A molecular sieve alone is not always satisfactory (Alver et al. 2012). Therefore, the development of modified materials based on 4A molecular sieve had attracted great attention. Liu et al. (2022) designed a new composite material based on graphene oxide and 4A zeolite (GO/4A) for efficient removal of rhodamine B in aqueous solutions. Under optimized experimental conditions, GO/4A-3 showed a high RB adsorption capacity of 62.81 mg/g. Chao et al. (2022) synthesized a 4A molecular sieve/carbon composite material using waste bleaching earth as raw material, which effectively improved the adsorption performance of volatile organic compounds and had an equilibrium adsorption capacity of 209.57 mg/g for xylene. Although these experiments had problems such as complex synthesis steps and poor cycling performance of the composite materials, they all indicated that 4A molecular sieve can be modified to expand the adsorption range and enhance the adsorption capacity.

Carbon nitride/Carbon dots (C₃N₄/CDs) is a catalytic material with adsorption ability. After Liu firstly prepared C₃N₄/CDs and efficiently produced hydrogen, numerous researchers probed into this kind of composite material (Wang X Y et al. 2018;Wang W J et al. 2019). Bian J.C. et al. (2017) observed that doping CDs increased the specific surface area of C₃N₄ materials, thereby enhancing the adsorption performance of the materials. Fang et al. (2019) conducted a series of experiments and found that C₃N₄/CDs had a certain adsorption effect on dyes. However, due to the small scale of C₃N₄/CDs materials, they are not suitable for large-scale treatment of dye wastewater in industrial settings. Therefore, the modification of 4A molecular sieve with C₃N₄/CDs allows for the loading of C₃N₄/CDs and enhances the adsorption performance of 4A molecular sieve. This novel composite material exhibits tremendous industrial application potential.

In this study, a novel adsorbent material named C₃N₄/CDs/4A was synthesized via immersion and thermal polymerization methods. C₃N₄/CDs/4A exhibited excellent adsorption capacity for dye wastewater and remarkable stability, offering a potential new solution for treating dye wastewater. Azo dyes are the most commonly used dyes in industry due to their simple coupling reactions and diverse structural variations, meeting complex application needs (Mussa et al. 2023). Methylene blue (MB) is a classic azo dye (Soni et al. 2020). Therefore, it was selected as the target adsorbate in this study.

2.1. Materials

Molecular sieves type 4A (CAS: 70955-01-0), Urea (CAS: 57-13-6), Citric acid monohydrate (CAS: 5949-29-1), Methylene blue (CAS: 7220-79-3) were purchased from Sinopharm Chemical Reagent Co., Ltd (China). All the chemicals were analytically pure and used as received without further purification.

2.2. Preparation of C₃N₄/CDs/4A composites

First, 50 g of urea and 1.5 g citric acid monohydrate were dissolved in 50 mL of deionized water. Then, the molecular sieve type 4A was ground into molecular sieve powders (particle size range:0.10 mm-0.15 mm) and 2 g of molecular sieve powders were added to the solution of urea and citric acid monohydrate. The mixture was magnetically stirred at 293 K for 2 h, and filtered to obtain the residue. The filtrate residue was put into the crucible and heated in the Muffle furnace. According to the heating rate of 2 ℃/min, it was heated to 550 ℃, held for 2 h, cooled to room temperature naturally, and C₃N₄/CDs/4A composites was obtained. Different composites were obtained by changing the particle size, adding mass, and stirring time of molecular sieve powders. The part of experiment about different composites was given in the supporting information and the best preparation method was selected.

2.3. Material characterization

The morphology of C₃N₄/CDs/4A was characterized using the Nova 400 Nano SEM scanning electron microscope, and the functional groups in the C₃N₄/CDs/4A were analyzed by a FT-IR spectrometer (Nicolet 6700, Wavelength range: Mid-infrared region: 4000 − 400 cm^− 1, Fast scanning: 1 scan/second, Highest resolution: 0.019 cm^− 1). The content of MB in the adsorption experiment was determined using a UV visible absorption spectrometer (UV-5500PC, 665 nm). The phase composition was characterized by X-ray powder diffraction analysis (Empyrean, Cu Kα radiation, 60 kV, 60 mA, 5° to 80°). The specific surface area and the pore sizes distribution was characterized by a specific surface area and pore size microanalyzer (BSD-PM2, via N₂ at 77 K and CO₂ at 273 K).

2.4. Adsorption experiment

The adsorption experiments were performed as follows. 100 mL of a specific concentration of MB solution was inject into 150 mL of glass bottles containing 100 mg of adsorbent. In the magnetic stirrer, the solution is stirred at 25°C and a speed of 200 rpm. After adsorption, the mixture was separated with a syringe membrane filter (0.22µm). The resulting concentration of MB after adsorption was determined by a UV-Vis spectrophotometer

The adsorption capacity (q_e, mg/g) and adsorption efficiency (E, %) were calculated using Eqs. (1) and (2)

$${q}_{e}={(C}_{0}-{C}_{e})\text{*}V/m$$

$$E={(C}_{0}-{C}_{e})/{C}_{0}\text{*}100\text{%}$$

where C₀ (mg/L) and C_e (mg/L) are the initial and equilibrium concentrations, m (g) and V (L) are the mass of absorbent and the volume of MB solution, respectively.

The influence of contact time on adsorption capacity was explored by dispersing 0.40 g of 4A molecular sieves and C₃N₄/CDs/4A in 100 mL solutions of 100 mg/L MB. The impact of dosage on adsorption performance was investigated. 0.10 g, 0.20 g, 0.30 g, 0.40 g, 0.45 g, and 0.50 g of C₃N₄/CDs/4A were added to 100 mL solutions of 100 mg/L MB separately. The adsorption efficiency was calculated after adsorption equilibrium. The effect of different pH levels on adsorption performance were examined by dispersing 0.10 g of C₃N₄/CDs/4A in MB solutions with varying pH values. The influence of different temperatures on adsorption performance were explored by dispersing 0.10 g of C₃N₄/CDs/4A materials in MB solutions with varying temperatures (V = 100 mL, [MB] = 50 mg/L). The recyclability was investigated by filtering the C₃N₄/CDs/4A, which was then heated in a muffle furnace at a heating rate of 10°C/min to 400°C, where it was maintained for 60 minutes, cooled to room temperature, and subsequently subjected to five cycles of adsorption experiments.

3.1. Characterization of C₃N₄/CDs/4A

The morphology of the composited was characterized via SEM in Fig. 1. The SEM images revealed the typical cubic morphology of 4A molecular sieve (Fig. 1A-B) with a smooth and flat surface. The average size of the 4A molecular sieve particles was approximately 2 µm. The SEM characterization of the C₃N₄/CDs/4A showed that the C₃N₄ exhibited thin edges and folded layers, tightly wrapped around the surface of the 4A molecular sieve (Li W et al. 2022). Carbon dots were also observed on the surface (Fig. 1C-D). The presence of carbon dots on the surface of 4A molecular sieve significantly increased its specific surface area, enhancing its adsorption capacity. Moreover, even after multiple cycles of thermal regeneration, the adsorption performance remained excellent, indicating the strong anchoring of carbon dots on the crystal surface of 4A molecular sieve.

Further structural characterization was conducted using FTIR spectroscopy in Fig. 2. The FTIR spectra of 4A molecular sieve and C₃N₄/CDs/4A exhibited characteristic absorption peaks (Li W et al. 2022). The absorption peak at 466 cm^− 1 corresponded to the stretching vibration of Si-O bonds (YU J et al. 2021), while the peak at around 551 cm^− 1 indicated the bending vibration of Al-O bonds. The absorption peak at 665 cm^− 1 represented the bending vibration of Si-O bonds, indicating the formation of AlO₄ and SiO₄ tetrahedra. The absorption peak at 1002 cm^− 1 corresponded to the asymmetric stretching vibration of Si-O-Si bonds, indicating the presence of asymmetric Si-O-Si linkages and the formation of the framework structure of the molecular sieve. The absorption peak at 1658 cm^− 1 indicated the bending vibration of H-O-H bonds, and a broad peak at 3432 cm^− 1 suggested the presence of bound water in the product (Goyal et al. 2020). The FTIR spectra of C₃N₄/CDs/4A exhibited a characteristic absorption peak at 812 cm^− 1, corresponding to the tri-s-triazine structure of graphitic carbon nitride, and a new peak at 2341 cm^− 1, attributed to the vibrational mode of the O = C = O bond in carbon dots.

The XRD patterns of 4A molecular sieve and the C₃N₄/CDs/4A were also analyzed, which were shown in Fig. 3. The XRD pattern of 4A molecular sieve exhibited strong diffraction peaks at 2θ angles of 7.22°, 10.19°, 12.48°, 16.13°, 21.70°, 24.02°, 27.14°, 29.97°, and 34.21°, matching the standard card of 4A molecular sieve without any additional peaks, indicating good crystallinity of the unmodified 4A molecular sieve. The XRD pattern of C₃N₄/CDs/4A showed a leftward shift of the peaks, indicating an increase in the lattice parameters and interplanar spacing due to the doping of foreign atoms. Compared to 4A molecular sieve, the new peak observed at 2θ = 27.2° in C₃N₄/CDs/4A corresponded to the (002) crystal plane of carbon nitride (Ma T et al. 2019; Song et al. 2014). The decrease in peak intensity of 4A molecular sieve was attributed to the loading of carbon nitride and carbon dots on the surface, disrupting the crystalline state of the molecular sieve (Fang L J et al. 2019).

The adsorption-desorption isotherms and particle size distribution of 4A molecular sieve and C₃N₄/CDs/4A were obtained in Fig. 4. CO₂ was used to characterize the microporous structure of 4A molecular sieve, while nitrogen gas was used for the C₃N₄/CDs/4A (Chen Z et al. 2018). The adsorption isotherm of 4A molecular sieve exhibited a type I isotherm, indicating predominant microporous adsorption. The adsorption isotherm of the C₃N₄/CDs/4A belonged to type IV with hysteresis loops, indicating the presence of mesoporous adsorption characteristics. Specific surface area, pore volume, and pore size of the materials were analyzed and presented in Table 1. The C₃N₄/CDs/4A showed increased specific surface area and total pore volume, indicating a structure more favorable for adsorption.

Table 1

Specific surface area, pore volume, and pore size of 4A molecular sieve and C₃N₄/CDs/4A.
Sample	Specific surface area (m²/g)	Pore volume (ml/g)	Pore size (nm)
4A	77.45	0.04	5.42
C₃N₄/CDs/4A	164.54	0.05	2.79

3.2. Adsorption performance of C₃N₄/CDs/4A for MB

3.2.1. dosage effect

The relationship between varying adsorbent dosages and adsorption efficacy, with a constant MB concentration of 100 mg/L and a solution volume of 100 mL, was demonstrated by Fig. 5. Up to an adsorbent mass of 0.40 g, the adsorption efficiency escalated with increasing mass. However, at 0.40 g, the adsorption efficiency peaked at 99.6%, and further increasing the mass to 0.50 g did not yield significant improvements. Therefore, the mass of 4A molecular sieve and C₃N₄/CDs/4A was 0.4 g in the subsequent adsorption kinetics experiments.

3.2.2. kinetics study

The effect of contact time on adsorption efficiency, with a constant MB concentration of 100 mg/L (pH = 5.9) and a solution volume of 100 mL, was illustrated by the Fig. 6. The mass of 4A molecular sieve and C₃N₄/CDs/4A was 0.40 g. During the initial 10 minutes period, the adsorption rate for MB was remarkably high due to the abundant availability of adsorption sites on the surface of the adsorbent and its effective dispersion within the solution. Subsequently, as the adsorption process progressed without reaching equilibrium, the gradual occupation of adsorption sites led to a deceleration in the adsorption rate. Notably, the equilibrium adsorption capacity of the C₃N₄/CDs/4A was 4.34 times than 4A molecular sieve. This remarkable enhancement showed the substantial improvement in adsorption performance following material modification. The adsorption conditions and specific adsorption data at other masses were given by the supporting information.

Kinetic fitting of the adsorption process was carried out. The pseudo-first-order Eq. (3) and the pseudo-second-order Eq. (4) were used to fit the data (Ho Y S. 2004).

$${ln}\left({q}_{e}-{q}_{t}\right)=ln{q}_{e}-{k}_{1}t$$

$$t/{q}_{t}=1/\left({\text{k}}_{2}^{2}{*q}_{e}^{2}\right)+\text{t}/{q}_{e}$$

where q_e (mg/g) is the equilibrium adsorption capacity, q_t (mg/g) is the adsorption capacity at time t, k₁ and k₂ are the rate constants for the first-order and second-order kinetics, which can be calculated from the slope and intercept of the linear plot. The fitting of experimental data to the models was shown in the Fig. 7 and Table 2.

Table 2

Kinetic parameters of 4A and C₃N₄/CDs/4A.
Sample	q_{e, exp} (mg/g)	Pseudo-first-order model			Pseudo-second-order model
Sample	q_{e, exp} (mg/g)	k₁(min^− 1)	q_e,cal (mg/g)	R²	k₂[g/(mg*min)]	q_e,cal (mg/g)	R²
4A	5.75	0.206	3.59	0.946	0.172	5.88	0.999
C₃N₄/CDs/4A	24.95	0.232	12.50	0.924	0.065	25.25	1

From the correlation coefficients, it could be observed that the R² values of the Pseudo-second-order equation were higher than that of the Pseudo-first-order equation. The results suggested that the adsorption process better fit the Pseudo-second-order kinetic equation, indicating a chemisorption process where MB molecules shared exchangeable electrons with the functional groups on the surface and within the pores of the C₃N₄/CDs/4A. When comparing the adsorption rate constants with 4A molecular sieves, the C₃N₄/CDs/4A. exhibited significantly lower adsorption rate constants. This was attributed to the increased carbon dot carbon content on the surface of 4A molecular sieves, hindering the transfer of MB to 4A, resulting in slower adsorption kinetics (Khan T A et al. 2012 ). However, C₃N₄/CDs/4A exhibited a much higher adsorption capacity compared to 4A molecular sieves.

3.2.3. pH effect

Figure 8a highlighted the distinctive adsorption of C₃N₄/CDs/4A attributes under varying pH conditions. The optimal adsorption effectiveness of C₃N₄/CDs/4A was observed when the solution pH remained unchanged, achieving a 74.79% adsorption efficiency for a 50 mg/L MB solution. However, significantly lower adsorption was seen in more acidic conditions, with a mere 33.94% adsorption efficiency. This decline was due to the instability of 4A molecular sieve in acidic environments, coupled with electrostatic repulsion between the cationic MB dye and protonated molecular sieve under acidic conditions. C₃N₄/CDs/4A exhibited robust adsorption performance at pH = 5 7, 9, and 11, with slight reductions.

3.2.4. isotherm study

The relationship between equilibrium concentration and adsorption capacity at 0.40 g of C₃N₄/CDs/4A and 4A molecular sieve at different MB concentrations (50 ~ 250 mg/L and a solution volume of 100 mL under 25℃ was shown in Fig. 9. With the increase of the initial concentration, the adsorption capacity gradually increased, and then tended to a constant value. The adsorption capacity of C₃N₄/CDs/4A was much higher than that of 4A molecular sieve. Then, the adsorption isotherm was fitted to the adsorption process. Langmuir (Kraus et al.2009), Freundlich (Wang J L et al. 2020), and Tempkin (Ma J et al.2012) models are commonly used to describe the characteristic parameters of adsorption at interfaces. The Langmuir adsorption equation assumes a uniform surface, single-layer adsorption, and no interaction between adsorbed molecules. The Freundlich and Tempkin equations are empirical equations applicable to heterogeneous surface adsorption. The former relates adsorption enthalpy to coverage in a logarithmic relationship, while the latter shows a linear relationship. The Freundlich equation is suitable for low coverage, while the Tempkin equation is suitable for moderate coverage. By comparing the linearity coefficient or the proximity of experimental points to the model, the adsorption isotherm that best fits the actual data can be determined.

Langmuir adsorption isotherms can be expressed as:

$${C}_{e}/{q}_{e}=1/{q}_{m}b+{C}_{e}/{q}_{m}$$

In the Langmuir equation, q_e (mg/g) is the equilibrium adsorption capacity, C_e (mg/L) is the equilibrium concentration of MB, q_m (mg/g) is the maximum adsorption capacity, and b (L/mg) is the Langmuir constant related to adsorption energy. According to Eq. (5), q_m and b can be calculated from the slopes of 1/q_m and the intercepts of 1/q_mb.

The Freundlich isotherm, based on adsorption on energetically heterogeneous surfaces with no restrictions on monolayer formation, can be expressed as:

$$ln{q}_{e}=ln{K}_{f}+(1/\text{n})ln{C}_{e}$$

where K_f is the Freundlich constant, and 1/n is the heterogeneity factor related to the adsorption capacity and intensity. According to Eq. (6), K_f and n can be calculated from the slope of 1/n and the intercept of lnK_f.

Tempkin isotherms equation:

$${q}_{e}=RT/{A}_{T}\text{*}(ln{K}_{T}+ln{C}_{e})$$

where R is the ideal gas constant (8.314 J/(mol·K)); A_T is the adsorption constant of the Tempkin model (J/mol); T is the absolute temperature (K); K_T is the equilibrium binding constant (L/g).

The adsorption isotherms for MB on the C₃N₄/CDs/4A and 4A molecular sieve, as described by Langmuir, Freundlich, and Tempkin equations, were shown in the Fig. 10 and the calculated parameters and R² values were presented in Table 3. The R² values served as indicators of the degree of fit between the experimental data and the model. As shown in Table 3, the Langmuir model exhibited the highest regression coefficient (R² = 0.999), indicating its superior suitability in describing the adsorption behavior of the C₃N₄/CDs/4A. Consequently, it could be inferred that adsorption took place at uniformly binding sites on the surface of the adsorbent until a monolayer was formed. The adsorption process was classified as chemisorption, which was commonly regarded as a spontaneous phenomenon. Based on the Langmuir model, the maximum adsorption capacity of the C₃N₄/CDs/4A for MB was determined to be 44.34 mg/L. The incorporation of C₃N₄/CDs onto the surface of 4A molecular sieves increased the specific surface area of the C₃N₄/CDs/4A, enhancing its adsorption performance. Additionally, the electrostatic interaction between oxygen-containing functional groups on the carbon dots and positively charged MB molecules also contributed to the adsorption process.

Table 3

Langmuir, Freundlich and Tempkin isotherm parameters of 4A molecular sieve and C₃N₄/CDs/4A.
		4A	C₃N₄/CDs/4A
Langmuir	b (L/mg)	0.056	1.776
	q_max (mg/g)	19.810	44.343
	R²	0.972	0.999
Freundlich	K_f (L/mg)	3.669	27.539
	n	2.828	8.635
	R²	0.781	0.990
Tempkin	A_T (J/mol)	551.200	691.891
	K_T (L/g)	0.522	3133.795
	R²	0.829	0.973

3.2.4. Thermodynamics study

Figure 8b presented the temperature-dependent adsorption behavior of the composites towards MB solutions of a 50 mg/L concentration. As the temperature rose, the diffusion rate of MB molecules within the external boundary layer and internal pores of C₃N₄/CDs/4A accelerated, promoting the achievement of adsorption equilibrium. Equilibrium was achieved within 60 minutes at varying temperatures. Notably, 87% of the adsorption efficiency persisted even at 47°C, showcasing the applicability of C₃N₄/CDs/4A across a wide temperature range. A decline in equilibrium adsorption capacity with rising temperature implied an exothermic adsorption process. Given that the treatment of dye wastewater typically occurs at room temperature, conducting adsorption experiments under these conditions was appropriate. The adsorption mechanism of C₃N₄/CDs/4A for MB can be determined using thermodynamic values. The standard free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) are calculated using the following formulas (Khatibi et al. 2021):

$$\varDelta G=-RTlnK$$

$$lnK=\varDelta S/R-\varDelta H/RT$$

where K is the adsorption equilibrium constant, which can be calculated from the following equation:

$$K={q}_{e}/{C}_{e}$$

The thermodynamic parameters for MB adsorption on the C₃N₄/CDs/4A at different temperatures were shown in Fig. 11 and Table 4. Among these parameters, ΔG was negative at all temperatures, indicating a spontaneous process. ΔG increased with increasing temperature, suggesting that lower temperatures were favorable for this process. ΔH was negative and relatively large, indicating that the adsorption of MB was exothermic and tended to be a chemisorption process. This could be attributed to the electrostatic interaction between the C₃N₄/CDs/4A and MB. The change in entropy, ΔS, was negative, indicating a decrease in system disorder after adsorption. Combining the adsorption isotherm and adsorption rate, it was determined that the adsorption of MB on the C₃N₄/CDs/4A was a spontaneous, exothermic, and entropy-decreasing chemical adsorption process.

Table 4

Thermodynamic parameters for adsorption of MB.
ΔH(J/mol)	ΔS(J/mol/K)	ΔG(J/mol)
-14419.802	-40.795	298 K	303 K	313 K	320 K
-14419.802	-40.795	-2179.998	-2127.270	-1763.273	-1268.607

3.2.3. Recycling properties of C₃N₄/CDs/4A

The conventional method for material regeneration involves the addition of chemical regenerants, which can cause certain damage to the adsorbent material (Sivalingam et al. 2019). In this study, however, regeneration was achieved through pyrolysis, which resulted in excellent regeneration performance without causing any damage to the material. The recyclability of C₃N₄/CDs/4A held paramount significance as a key metric for their practical utility. In this investigation, thermal regeneration was employed as the methodology for material regeneration. Figure 12 encapsulated the outcomes of subjecting the composite to five consecutive cycles of adsorbing MB solutions. The observed adsorption efficiency for these successive cycles were 99.6%, 98.7%, 98.4%, 98.1%, and 98.6%, respectively. The adsorption efficiency was almost not reduced. Some of the sorbents in the other literature were given by the supporting information. These findings affirmed the exceptional cyclic stability and thermal endurance of C₃N₄/CDs/4A. With its consistent and high adsorption efficiency across multiple cycles, the material demonstrated its robust potential for industrial application. This showed the composite's suitability for sustained use and its promising viability within real-world scenarios.

C₃N₄/CDs/4A were prepared via impregnation and thermal polymerization methods. The adsorption performance towards the MB of C₃N₄/CDs/4A was tested and analyzed. The results showed that the introduction of C₃N₄/CDs significantly enhanced the adsorption performance of 4A molecular sieve. Compared with 4A molecular sieve, the adsorption capacity of the composite was increased by 4.3 times. The adsorption process was abided by Langmuir model and the maximum adsorption capacity of C₃N₄/CDs/4A for MB was 44.34 mg/g. The broad applicability in varying pH conditions and excellent renewability make C₃N₄/CDs/4A have greater potential in industrial treatment of dye wastewater in the future.

Funding and Competing Interests

This work was supported by National Natural Science Foundation of China (Grant number [217071108]). The authors have no relevant financial or non-financial interests to disclose.

Ethical Approval

Not applicable

Consent to Participate

Not applicable

Consent to Publish

Not applicable

Author Contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Bohan Jia, Dan Liu and Junhui He. The first draft of the manuscript was written by Bohan Jia and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Acknowledgments

The authors gratefully acknowledge support from National Natural Science Foundation of China (Grant number [217071108]).

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Preparation of Carbon nitride/Carbon dots/4A molecular sieve composite and evaluation of adsorption performance for Methylene Blue

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Materials

2.2. Preparation of C₃N₄/CDs/4A composites

2.3. Material characterization

2.4. Adsorption experiment

3. Results and discussion

3.1. Characterization of C₃N₄/CDs/4A

3.2. Adsorption performance of C₃N₄/CDs/4A for MB

3.2.1. dosage effect

3.2.2. kinetics study

3.2.3. pH effect

3.2.4. isotherm study

3.2.4. Thermodynamics study

3.2.3. Recycling properties of C₃N₄/CDs/4A

4. Conclusion

Declarations

Ethical Approval

Author Contributions

Acknowledgments

References

Status:

Version 1

Preparation of Carbon nitride/Carbon dots/4A molecular sieve composite and evaluation of adsorption performance for Methylene Blue

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Materials

2.2. Preparation of C3N4/CDs/4A composites

2.3. Material characterization

2.4. Adsorption experiment

3. Results and discussion

3.1. Characterization of C3N4/CDs/4A

3.2. Adsorption performance of C3N4/CDs/4A for MB

3.2.1. dosage effect

3.2.2. kinetics study

3.2.3. pH effect

3.2.4. isotherm study

3.2.4. Thermodynamics study

3.2.3. Recycling properties of C3N4/CDs/4A

4. Conclusion

Declarations

Ethical Approval

Author Contributions

Acknowledgments

References

Status:

Version 1

2.2. Preparation of C₃N₄/CDs/4A composites

3.1. Characterization of C₃N₄/CDs/4A

3.2. Adsorption performance of C₃N₄/CDs/4A for MB

3.2.3. Recycling properties of C₃N₄/CDs/4A