Enhanced Photocatalytic Properties of g-C3N4/ZnO/Attapulgite (CNZATP) Composite Nano-Mineral Materials on Methylene Blue Dye Degradation

A nano-ZnO semiconductor material loaded with mineral attapulgite (ATP) photocatalyst has been investigated. Using ATP as a carrier, a variety of various mixtures of ZnO/ATP composites was synthesized. A scanning electron microscope (SEM), X-ray diffractometry (XRD), and UV-Vis spectrophotometer (UV-Vis) were used to examine the morphology, synergistic effects, and photocatalytic properties of ZnO/ATP nanocomposites. The target pollutant for photocatalytic degradation is methylene blue solution. When ATP is mixed with pure ZnO, the degrading performance of composite nanomaterials in methylene blue solution is considerably enhanced. The degree of methylene blue degradation increases as the amount of ATP in the composite grows, and the degradation rate of ZnO/40% ATP can reach 96% in 45 min under solar light illumination. The amount of ATP in the system is excessive, and the adsorption effect is visible. The optimal composite ratio was determined to be ZnO/30% ATP. After discovering the ideal composite ratio and synergy of ZnO/ATP, g-C3N4 was compounded in the aforesaid system, dramatically increasing the composite’s photocatalytic activity. At 45 min, the degradation rate of methylene blue reaches 97%. The absorption range and intensity of ternary composites increased, and the photogenerated electron-hole recombination rate decreases significantly. The reaction rate constant increases from 0.033 to 0.069 min−1. SEM revealed rod-like attapulgite particles packed with tiny zinc oxide particles and a moderate layered structure of C3N4. The XRD pattern indicated that C3N4’s crystallinity is poor and ZnO’s peak intensity is excessively high, masking the composite material’s distinctive peaks. The degradation rate of g-C3N4/ZnO/30% ATP to methylene blue was found to be 91.5% after 5 cycles.


Introduction
Population growth and industrialization are driving environmental degradation (Bouziani et al. 2022;Hsini et al. 2021). The consequences of diverse wastewater treatment plant (WWTP) effluents on river ecosystems and prospective recovery for miscellaneous water supply have drawn attention. Among the various issues faced by WWTPs, color is standard in those that process wastewater from the textile, paper mill, and tannery sectors (Dey and Islam 2015;Islam et al. 2021Islam et al. , 2022Islam and Guha 2013). Hence, finding innovative, effective ways to reverse pollution and solve this situation is vital. Photocatalysis, adsorption, and piezocatalysis have been used in recent decades to produce sustainable wastewater treatment solutions (Jaramillo-Páez et al. 2017;Y. Naciri et al. 2022a).
Photocatalysis is an intriguing technology for water treatment since it harnesses solar energy, making high-efficiency, low-cost water remediation possible (Chen, Dai, et al. 2021a;Chen, Zhang, et al. 2021b;). This method uses highly reactive, non-selective oxidizing species (Cl 2 , O 3 , H 2 O 2 , etc.) (Y Naciri et al. 2019;Tanji et al. 2022) and gained interest after Fujishima and Honda reported water splitting by photochemical electrode employing titanium dioxide (TiO 2 ) (Fujishima and Honda 1972). Many nano-composite materials with photocatalytic activity are being developed to address existing water pollution and hydrological environmental challenges by using more cost-effective and efficient water purification procedures (Islam et al. 2022;Rehman et al. 2021). However, the use of ultraviolet (UV) light is a significant barrier to moving from theoretical research to actual applications (Akhsassi et al. 2021; Barebita et al. 2020). As a result, several solutions have been devised to counteract this issue (Mahesh and Kuo 2015;Yassine Naciri et al. 2022b).
Nano photocatalytic materials have a geometry of 1-100 nm in photocatalytic research (Liu et al. 2010). Achieving such dimensions substantially changes its electrical, magnetic, optical, and chemical properties and boosts its photocatalytic activity. Photocatalysis is primarily described by semiconductor band theory and consists of a valence band (VB), a conduction band (CB), and a forbidden band (Eg) (Han and Zhao 1999;Jing and Dai 2017;Kibria and Mi 2016). The forbidden bandwidth Eg(eV) of a semiconductor material has the following relationship with its maximum absorption wavelength λ max (nm): In Eq. 2, the semiconductor's forbidden bandwidth is inversely related to its maximum absorption wavelength. It implies a large forbidden bandwidth only reacts to UV light and not visible light, reducing its sunlight use rate.
Numerous nanocomposite photocatalysts have previously been tried in the fight against wastewater pollution. Such as, nanocomposite photocatalyst based on graphene oxide (GO) and zinc oxide (ZnO) could be a versatile photocatalyst for the photodegradation of phenanthrene in wastewater treatment (Chauhan et al. 2022). The combination of metals or amalgamation of bimetallic oxides as an efficient photocatalyst demonstrated its propitiousness for the degradation of phenanthrene from aqueous solutions (Chauhan et al. 2021). Non-spherical semiconductors are used in the photocatalytic destruction of organic pollutants due to their structure and physicochemical qualities (Zare et al. 2021). PANI@Fe 2 O 3 @TiO 2 (PANI@TF) composite showed enhanced visible-light photocatalytic activity for methylene blue (MB) dye degradation compared to pure Fe 2 O 3 @TiO 2 . The highest degradation efficiency for MB via 1% PANI@TF ternary catalyst reached 96% after 2 h under sun-like illumination, which was 4.3 higher than TF (Bouziani et al. 2022).
Recently, photocatalysis examinations have been held on graphite phase carbonitride g-C 3 N 4 , the most stable carbon compound. As a photocatalytic material, C 3 N 4 provides the following benefits: (1) non-toxic and easy-to-produce raw materials, (2) chemical stability and a unique semiconductor band structure, and (3) non-metallic photocatalyst (Ma et al. 2014). Although g-C 3 N 4 possesses good chemical stability and photocatalytic properties, it has some limitations when employed directly as a photocatalyst, including a poor photoelectron-hole pair separation rate, a small specific surface area, and a low quantum efficiency (Fang et al. 2011). Due to these traits, its photocatalytic use is restricted. The difference between the energy band structure and band position of various semiconductor materials is employed to build a heterostructure, which allows photogenerated electron-hole pairs to be better separated and expands the method. The composite material's broad spectrum response range optimizes (1) λmax(nm) = 1240∕Eg(eV) sunlight usage, improving its photocatalytic efficacy. On the other hand, nano-minerals are used as photocatalytic support materials. These are porous in structure and have a high specific surface area, stable chemical characteristics, and good adsorption capacity. They act as a fixed carrier for nano-semiconductor materials that do more than keep particles in place. For the manufacture of nanocomposite photocatalysts, natural attapulgite as a zinc oxide carrier is appropriate (Li et al. 2022).
Here, we evaluated the photocatalytic activity of modified mineral nanomaterials and the subsequent modifications that occurred. The nano-zinc oxide (ZnO) was first loaded on porous attapulgite (ATP). Then, various ZnO/ATP composites with various composite ratios were studied to find the optimal ratio for enhanced material's catalytic performance. The impact of attapulgite on nano-zinc oxide was studied using the photocatalytic degradation rate of methylene blue. To improve the composite's (ZnO/ATP) photocatalytic performance, g-C 3 N 4 was doped with the optimal composite ratio of ZnO/ATP and changed to g-C 3 N 4 /ZnO/ATP nano-composites. It was further studied using the photocatalytic degradation rate of methylene blue. By recombining g-C 3 N 4 into the system at the ideal compounding ratio, g-C 3 N 4 increased the electron-hole separation efficiency of the composite while also expanding the spectrum response range and improving the solar light use efficiency. The modification of metallic nanomaterial was investigated using the ultraviolet-visible spectrophotometer (UV-Vis) to assess the photocatalytic performance of methylene blue dye degradation, the scanning electron microscope (SEM) to examine morphology, the X-ray diffraction (XRD) to examine the relative changes in chemical composition as a result of modifications, and UV-visible diffuse reflectance spectroscopy (DRS), which was used to examine the absorption characteristics of materials for UV-visible light. Additionally, the kinetics and reusability of the modified composite nano photocatalyst were examined.

Attapulgite Pretreatment
Unpolished attapulgite was fed into a three-head grinder and whirred around for 30 min. After being refined, attapulgite powder was sieved through a 200 mesh before being packed and stored. The appropriate quantity of attapulgite from storage was added to a 200 mL beaker with the needed amount of deionized water to form a slurry with a mass ratio of 5%. The mixture was stirred for 2 h on a magnetic stirrer. After an hour in the ultrasonic cleaner, it was set aside for 24 h. Following the addition of 2% sodium hexametaphosphate, the slurry was stirred evenly for 1 h on a magnetic stirrer before being left to stand for 0.5 h to separate the slurry and collect the top liquid for centrifugation. After being centrifuged, the sediment is mixed with deionized water in a separate slurry, given a good stir, and added slowly to the existing slurry while continuing to stir. In addition, the slurry was stirred for 1 h while the NaOH solution was added until the pH reached 10 and then centrifuged. After being dried in an oven at 100 °C for a whole night, the attapulgite powder was finally processed.

Preparation of ZnO/ATP Photocatalyst
At first, in a beaker, 1.6463 g of Zn(CH 3 COO) 2 •2H 2 O was weighted, and then 150 ml of 100% ethanol was added to completely dissolve the Zn(CH 3 COO) 2 •2H 2 O while keeping the temperature of the water bath at 80 °C. Once it had cooled to room temperature, a 0.05 mol/l solution (solution A) was ready for use. The second step in making solution B was to combine 150 mL of 100% ethanol with 1.200 g of sodium hydroxide in an ultrasonic cleaner at room temperature until the two components were utterly dissolved and evenly dispersed. After 20 min of stirring at 900 r/min with a magnetic stirrer, solution A had PVP added to it in the same amount as the zinc acetate dihydrate. Then, different amounts of Vol:. (1234567890) attapulgite powder (5%, 0.03213 g; 10%, 0.06782 g; 15%, 0.1077 g; 20%, 0.1526 g; 30%, 0.2616 g; 40%, 0.4069 g) were added simultaneously, creating solution C. Solution B was then transferred to a separatory funnel and added dropwise to the solution C while being agitated at a speed of 1100 revolutions per minute for 30 min. The mixture was then permitted to stand for an additional hour. The resulting sludge was spun out of the mixture after it had been transferred to a centrifuge tube. The silt was centrifuged one more after being washed twice with deionized water to remove any lingering Zn + ions, Na + ions, or acetate ions. Two changes of n-heptane were used to clean the residue before it was placed in a tiny beaker filled with 100% ethanol and stirred for 20 min with a magnetic stirrer to achieve even distribution. After being vacuum filtered using a suction pump, the product was dried in an oven at 100 °C for 6 h. After the dry precursor was finely powdered, it was calcined in a muffle furnace for 30 min at 500 °C at a heating rate of 10 °C per minute. Finally, ZnO/ATP composite samples with different mass ratios were made by grinding.

Composite Modification of g-C 3 N 4
Here, C 3 N 4 is produced by calcining urea for 3 h at 500 °C. We used a three-head mill to combine 5 grams of urea and 0.12 grams of ZnO/30% ATP composite material for an hour. After grinding the sample, it was calcined in a muffle furnace for 3 h at 500 °C at a heating rate of 10 °C per minute. Finally, the product is ground before being packed, labeled, and ready for use.

Characterizations
A JSM 7600F field-emission scanning electron microscope (FESEM) was used to record the morphology of materials (JEOL, Japan). The catalysts' X-ray diffraction (XRD) patterns were determined using a Panalytical X'pert PRO MRD (Holland) and Cu K radiation. A PerkinElmer Lambda 35 UV-Vis spectrophotometer was used to get the UV absorption spectra of the dye concentration. UV-visible diffuse reflectance spectroscopy (DRS) was used to determine the UV-visible diffuse reflectance spectra of materials.

Principles of Photocatalysis Experiment
A spectrophotometer was used to conduct a photocatalytic experiment on a composite material containing varying concentrations of ZnO/ATP and C 3 N 4 doped. First, an ultraviolet-visible spectrophotometer was used to measure the absorption spectra of the methylene blue solution in the range of 200-700 nm, and the absorption spectrum revealed the maximum absorption wavelength of methylene blue. The methylene blue solution tested in this experiment had a maximum absorption wavelength of 665 nm. Lambert Beer's law describes the link between the absorbance of the methylene blue solution at its maximum absorption wavelength and its concentration, and the expression of Lambert-Beer law is as follows (Eq 2): where A is the absorbance, T is the transmitted light intensity ratio of the incident light intensity, k is the molar absorption coefficient, which is related to the nature of the absorbing material and the wavelength λ of the incident light, b is the absorbent layer thickness, and c is the concentration of the light-absorbing substance.
The degradation rate of the solution can be calculated at different times by measuring the absorbance of the methylene blue solution at the maximum absorption wavelength at different photocatalytic reaction times, and the degradation rate X of the solution can be calculated by the following Eq 3.
where A 0 is the initial absorbance of methylene blue, and A is the absorbance of methylene blue at t time. The degradation properties of the composite material to methylene blue can be visually demonstrated by the degradation curves of methylene blue at different times.

Photocatalytic Degradation Experimental Steps
In a 200 ml beaker, 0.05 g of photocatalytic material and 150 ml of a 10 mg/l methylene blue solution were combined, an electromagnet was added, and the solution was placed in the simulated daylight illumination box with continual stirring. To do a dark reaction experiment, stir the liquid for 30 min without turning on the light. Then put on the light source, collect a sample, centrifuge, and take the supernatant after 5, 10, 15, 30, or 40 min of illumination time. To evaluate its degrading performance, an ultraviolet-visible spectrophotometer was used to detect the absorbance at 665 nm.

Characterization of CNZATP Through Microscopic Morphology Analysis
SEM pictures of pure phase ZnO (a), ZnO/30% ATP (b), g-C 3 N 4 (c), and g-C 3 N 4 /ZnO/ATP (d), respectively, are shown in Fig. 1. The zinc oxide particles generated in this experiment are tiny, with a particle size of around 50 nm, as seen by the SEM picture (Fig. 1a). Many large rod-like formations can be seen in the SEM picture (Fig. 1b) when zinc oxide is loaded onto the attapulgite (ATP). These rod-shaped particles are attapulgite. Zinc oxide particles are loaded extremely evenly on the surface of the attapulgite, showing that the zinc oxide and attapulgite composite effect is flawless. However, although the pure g-C 3 N 4 SEM (Fig. 1c) reveals an uneven condition, the accumulation of some layered structures can still be seen, which is consistent with the graphite-like phase g-C 3 N 4 structure. Finally, in the SEM image of g-C 3 N 4 /ZnO/ATP (Fig. 1d), many attapulgite rod-like particles were observed, which were loaded with fine particles of zinc oxide, but only a small layered structure of C 3 N 4 was observed around the picture, which is consistent with the XRD pattern, indicating that the content of C 3 N 4 in the sample is small.
3.2 X-ray Diffraction Pattern Analysis on the Modification of ATP on ZnO and g-C 3 N 4 Loaded Composite The X-ray diffraction pattern of pure ZnO prepared by the experimental synthesis method and the pretreated attapulgite is presented in Fig. S1. For the XRD pattern of pure ZnO samples, it can be seen that the purity of the nano-ZnO prepared by the experimental method is very high, and no diffraction peaks of other substances appear.  (110), (103), and (112) crystal faces, and it was confirmed that the ZnO prepared by the experiment has a hexagonal Wurtzite structure. Moreover, the half-width of the diffraction peak is narrow, indicating that the crystallinity of ZnO is good. The crystal lattice parameters of the crystal structure are a = b = 3.25 Å, c = 5.21 Å. For the XRD pattern of the pretreated  (221) crystal faces (corresponding PDF standard card number: No. 31-0783). There are several tiny peaks in other locations, which may be some impurities in the natural attapulgite ore, which cannot be completely cleaned during the pretreatment process and remain in the sample, but the content is minimal, indicating the pretreatment method used in the experiment was effective. From Fig. 2a, it can be seen that the characteristic peak of ZnO is gradually reduced. The reason is that, in the sample of 5% and 10%, the content of ATP is too small so that the load of ATP is too much and is surrounded by zinc oxide particles, so the characteristic peak intensity of ZnO is too large to cover the characteristic peak of ATP. When the content of ATP is increased, the characteristic peaks gradually appear, and the characteristic peaks of ZnO gradually decrease. Figure 2b shows the X-ray diffraction patterns of pure C 3 N 4 , ZnO/30% ATP, and C 3 N 4 /ZnO/ATP materials prepared in this experiment. For pure C 3 N 4 , it can be seen from the spectrum that there is a distinct diffraction peak at 2θ of 27.4 o , which is the characteristic diffraction peak of g-C 3 N 4 , which is the interlayer deposition of the g-C 3 N 4 aromatic structure.
There are no peaks in other locations, indicating that the prepared samples are of higher purity. However, the characteristic peak intensity of g-C 3 N 4 is not high, and the peak width is significant, indicating that the prepared g-C 3 N 4 is not sufficiently crystalline. Comparing the map of C 3 N 4 /ZnO/ATP composite with ZnO/30% ATP, it can be found that the characteristic diffraction peak of C 3 N 4 does not appear in the map of ATP-ZnO-C 3 N 4 composite, and the two maps are very close. This may be because the content of C 3 N 4 is small in the composite material, the crystallinity of C 3 N 4 is weak, and the characteristic peak intensity of ZnO is too high so the characteristic peaks in the composite material are masked. Figure 3 shows that ZnO/ATP nano-composites with varying composite ratios degrade methylene blue at varying rates (5, 10, 15, 30, and 45 min) due to their photocatalytic capabilities. While pure ZnO shows nearly negligible adsorption in the dark for 30 min, the photocatalytic degradation effect is inadequate, leading to a degradation rate of around 70% after 45 min. Combining ZnO Fig. 2 Comparative analysis among different photocatalytic composite through X-ray diffraction patterns of a ZnO/x% ATP composite samples with different ratios of ATP and b ZnO/30% ATP, g-C 3 N 4 , and g-C 3 N 4 /ZnO/30% ATP with attapulgite enhanced its photocatalytic degradation performance over pure ZnO. There was a positive correlation between attapulgite concentration and methylene blue degradation rate. The degradation rate increased to 92.0% and 96.4% after 45 min with increasing amounts of attapulgite, particularly at the 30% and 40% composite ratios, respectively. Furthermore, the degrading efficiency curves show that samples with a composite ratio of 5%, 10%, and 15% are all very near to that of pure ZnO, while each shows some improvement over pure ZnO. The total catalytic degrading impact may not have been much enhanced because of the sample's low attapulgite concentration. The attapulgite adsorption action is also clearly visible in the dark condition. Adsorption is more noticeable at greater concentrations of ATP. Here, 55% of methylene blue dye was absorbed by the ZnO/40% ATP nanocomposites and therefore eliminated. However, if the attapulgite concentration is too high, the ZnO concentration and the photocatalytic action of the ZnO may be diminished. For this experiment, a composite ratio of 30% attapulgite to ZnO was used since there was little difference in removal effectiveness between ZnO/30% ATP (92.0%) and ZnO/40%ATP (96.4%). After that, we experimented with C3N4 doping using a ZnO/30% ATP substrate as a base for the modifications. Figure 4 illustrates experimental results comparing methylene blue degradation rates before and after g-C 3 N 4 doping with composite materials. Adsorption is also present for the first 30 min in the dark for the pure g-C 3 N 4 synthesized in the experiment. After 45 min, the photocatalytic degradation rate is only up to 60%, which is insignificant compared to pure ZnO. However, its photocatalytic activity is drastically enhanced after being doped with g-C 3 N 4 on ZnO/30% ATP material. After 45 min, 97% of the methylene blue has been destroyed, and the solution is clear and colorless, a total and utter deterioration.

Kinetic Study
Kinetics models were used to analyze the photocatalytic characteristics of each type of material (i.e., pure phase ZnO, pure phase g-C 3 N 4 , ZnO/30%ATP, and g-C 3 N 4 /ZnO/30%ATP) in a way that is more easily understood. The curve was fitted after determining the composite material's degradation rate. The reaction rate curve for the photocatalytic degradation of the methylene blue solution agrees well with the firstorder reaction rate curve (shown in Fig. 5), suggesting that the process is a first-order chemical reaction. The following (Eq 4) is the first-order kinetic reaction. The magnitude of k in the formula may directly reflect the catalytic rate of each sample; k reflects the first-order reaction rate in units of min-1. The concentration of methylene blue solution at time t (under lighting) is denoted by C, where C 0 is the concentration of the solution immediately after the dark state and C is the concentration of the solution at time t (under illumination), both in mg/L. Lambert-Beer's law states that the concentration of a methylene blue solution is directly proportional to its absorbance at its highest absorption wavelength. The determined (4) ln C o C = kt photocatalytic degradation rates k of pure g-C 3 N 4 , ZnO, ZnO-30% ATP, and g-C 3 N 4 /ZnO/ATP composites are 0.014 min −1 , 0.033 min −1 , 0.035 min −1 , and 0.06 min −1 , respectively. The photocatalytic degradation rate of ZnO/ATP composites rises marginally with ATP loading. In contrast, the photocatalytic degradation rate of g-C 3 N 4 /ZnO/ATP composites is shown to grow linearly to double upon doping with g-C 3 N 4 . This demonstrates that g-modifying C 3 N 4 's influence on ZnO/ATP is substantial.

UV-Visible Diffuse Reflectance Spectroscopy
The absorption characteristics of materials for UVvisible light can be analyzed by UV-visible diffuse reflectance spectroscopy (DRS). Diffuse reflectance spectra of pure ZnO and ZnO/30% ATP are shown in Fig. 6a. As can be observed in the image, the pure ZnO generated in experiments has a very narrow visible-light absorption band, with an absorption edge at about 410 nm. The absorption limit of the composite did not alter much compared to pure ZnO after ATP was loaded into the ZnO. This indicates that ATP is required to improve photocatalytic activity and the uniform dispersion of ZnO semiconductor material by preventing agglomeration. However, it cannot improve the ZnO pair in essence. For the composite material's photocatalytic performance to advance, sunlight must be used as effectively as possible, expanding its light absorption spectrum and bolstering its overall strength. The diffuse reflectance spectra of g-C 3 N 4 in its pure phase and g-C 3 N 4 /ZnO/ATP composite are shown in Fig. 6b. The absorption edge for the  6 Diffuse reflectance spectra of a pure ZnO and ZnO/30% ATP sample and b g-C 3 N 4 and g-C 3 N 4 / ZnO/30% ATP experimentally prepared pure phase C 3 N 4 is located at about 450 nm. Using the formula (5), we can calculate the maximum absorption wavelength max (nm) for a given bandgap energy E g (eV) of the semiconductor material and vice versa.
The experimentally determined prohibited bandwidth of g-C 3 N 4 is 2.76 eV. ZnO/30% ATP, g-C 3 N 4 , and g-C 3 N 4 /ZnO/30% ATP were all compared to one another in terms of their diffuse reflectance spectra, and it was discovered that upon compounding with g-C 3 N 4 , the absorption edge of ZnO/30% ATP shifted significantly to 465 nm, and the absorption intensity was significantly increased. Because of this, the photocatalytic activity of materials may be enhanced by doping with g-C 3 N 4 in order to increase the number of photogenerated carriers generated.

Discussion on the Mechanism of Photocatalytic Degradation
According to the experiments mentioned above and sample characterization findings, doping the composite with g-C 3 N 4 significantly improves its photocatalytic activity. Two factors may be used to explain this outcome: (1) the composite sample has a more extensive absorption range, more intense absorption, and boosts its use of sunlight.
(2) At the interface between ZnO and g-C 3 N 4 , the internal electric field is generated, and the electric field drives the effective separation of photogenerated carriers. The forbidden bandwidth of ZnO and after compiling ZnO with ATP is around 3.02 eV, and the absorption edge is 410 nm, according to the findings of the material characterization given above. Furthermore, about 2.76 eV is the prohibited bandwidth of g-C 3 N 4 .
In this case, we may use Eqs. 6 and 7 to determine the valence band and conduction band potential of semiconductor materials, respectively: Here, E VB and E CB are the semiconductor's valence and conduction energy band positions. χ, is the electronegativity value of the semiconductor. Ee is the energy of the free electron. Eg is the forbidden bandwidth of the semiconductor. The literature shows that the values of Eg for ZnO and g-C 3 N 4 are 5.95 eV and 4.72 eV, respectively, and that E e is 4.5 eV (Wang et al. 2015). Through the calculation, we have found that the valence band and the conduction band of ZnO are at 2.96 eV and −0.06 eV, respectively, and that the valence band and the conduction band of g-C 3 N 4 are at 1.6 eV and −1.16 eV, respectively. The results show that both the valence band potential and the conduction band potential of g-C 3 N 4 are more negative than those of ZnO. Figure 7 is a diagram of how the degradation process works. When light hits the surface of the composite, the electrons on the valence band move the energy of the photons to the conduction band while keeping the same number of holes on the conduction band. The way the energy bands are set up in ZnO and g-C 3 N 4 makes an internal electric field. An electric field moves electrons and holes. So, photogenerated electrons move from the conduction band of g-C 3 N 4 to the conduction band of ZnO, and photogenerated holes move from the valence band of ZnO to the valence band of g-C 3 N 4 . This lowers the rate of photogenerated electron-hole recombination, which improves the material's photocatalytic performance.

Stability
Pure ZnO, ZnO/30% ATP, and g-C 3 N 4 /ZnO/30% ATP were all tested for their cycle performances, and the results are shown in Fig. 8. The experiment consisted of five cycles of studies with ZnO, ZnO/30% ATP, and g-C 3 N 4 /ZnO/30% ATP. Based on the findings, it is evident that pure ZnO's photocatalytic performance steadily declined after five cycles as the methylene blue degradation rate dropped from 69.5 to 49.6%. The performance of the composites' was significantly enhanced after adding ATP. Furthermore, the results were comparable to those of the g-C 3 N 4 / ZnO/30% ATP reaction, as the degradation rate of ZnO/30% ATP to methylene blue was maintained at 91.5% and did not drastically diminish for the addition of g-C 3 N 4 .
The outcomes of the experiments match those that were expected. This is because the ZnO particles' agglomeration issue is eliminated, the cycle performance is considerably enhanced once the ATP mineral material is utilized as the carrier, and ZnO is evenly disseminated throughout. Additionally, the photocatalytic degradation performance is considerably enhanced by the enrichment of methylene blue molecules. It is caused by ATP mineral materials' adsorption characteristics and its increased contact area between photocatalysts and organic molecules.

Conclusions
The photocatalytic activity of nano-ZnO enhanced with the addition of ATP, as the ZnO/40% ATP showed around 97% removal efficiency on methylene blue dye. The loading of ATP did not change the crystal structure of ZnO. After loading ATP, the contact area of the molecule, the photocatalytic performance, and the cycle performance of the material are greatly improved. Furthermore, ZnO/30% ATP was the best composite ratio interns of dark reaction adsorption and photocatalytic effect. Incorporating g-C 3 N 4 with ZnO/30% ATP further increases the composite's photocatalytic activity by widening the absorption range from 410 to 465 nm and enhancing the degradation rate to 97%. The reaction rate constant rose from 0.033 to 0.069 min-1 because of the composite construction. Overall, g-C 3 N 4 doping considerably increased the composite's photocatalytic activity. After five cycles, the dye degradation rate remained remarkably steady, reaching 91.5 %.
Acknowledgements The first author (Most Munera Khatun) wishes to express her gratitude to the China Scholarship Council (CSC) for providing her with a scholarship to pursue her Ph.D. studies.

Data availability
The authors confirm that the data supporting the findings of this study are available within the article and its supplementary material. Raw data supporting this study's results are available from the corresponding author upon reasonable request. Fig. 7 Degradation mechanism diagrams of g-C 3 N 4 / ZnO/30% ATP composite photocatalytic Fig. 8 Cyclic experimental results of pure ZnO, ZnO/30% ATP, and g-C 3 N 4 /ZnO/30% ATP composite photocatalytic