Facile Preparation of Attapulgite-Supported Ag-AgCl Composite Photocatalysts for Enhanced Degradation of Tetracycline

: In this study, Ag-AgCl/attapulgite (Ag-AgCl/ATP) composites were synthesized via a direct precipitation method using ATP nanorods as a catalyst supporter. ATP nanorods helped to increase the dispersion of Ag-AgCl particles and broaden the light absorption spectrum, which would also help to increase the active site of the catalyst to promote the degradation of tetracycline (TC). The photocatalytic activity of the Ag-AgCl/ATP composites was evaluated through the degradation of TC, identifying the loading amount of Ag-AgCl, the concentration of TC, and the reaction temperature as critical factors influencing activity. Specifically, the optimal conditions were observed when the loading of Ag-AgCl was 75%, resulting in a photocatalytic degradation efficiency of 77.65%. Furthermore, the highest degradation efficiency (85.01%) was achieved with a TC concentration of 20 mg/L at 20 ◦ C. Radical trapping experiments suggested that the superoxide anion radical ( · O 2 − ) was the primary active species in the degradation process, although hydroxyl radicals ( · OH) and holes (h + ) also contributed. Reusability tests confirmed that the Ag-AgCl/ATP composites exhibited excellent stability and could be effectively reused.


Introduction
The country's rapid industrialization has accelerated China's move to the center of the world stage, but at the same time, environmental pollution has become more and more serious [1][2][3][4].In real life, antibiotics are widely used and often treat bacterial infections in humans and animals.Most of the antibiotics are excreted in feces and urine in the form of prototypes or metabolites after use, resulting in generally high concentrations of antibiotics remaining in the feces [5][6][7].It will increase the resistance of bacteria and accelerate the spread of antibiotic-resistant genes, causing different degrees of harm to humans and the ecology.The World Health Organization has listed the problem of antibiotic resistance genes caused by the abuse of antibiotics as one of the major challenges facing human health in this century [8][9][10].It is urgent to find a new technology to remove antibiotics.Photocatalytic technology is considered to be one of the most effective technologies for degrading and removing antibiotics [11][12][13].Photocatalytic technology has been studied by many researchers because of its mild reaction conditions, low price and simple operation [14 -16].Although photocatalysis technology has been fully developed, it has not played a very wide role in practical application because most semiconductor photocatalysts have low surface energy and are prone to agglomeration, resulting which has low photocatalytic activity [17,18].Therefore, it is very important to select a suitable photocatalyst for TC degradation.
Ag-AgCl nanoparticles could possess photocatalytic activity that changes with the crystal face structure, which could be prepared to catalyze the degradation of much pollution, printing dyes and acetaldehyde, etc. [19][20][21][22].However, Ag-AgCl particles are easy to agglomerate, and finding suitable materials that are too dispersive will help to increase the concentration of the active site to achieve efficient TC degradation.Natural one-dimensional nanomaterial attapulgite (Mg 5 Si 8 O 20 (OH) 2 (OH 2 ) 4 •4H 2 O) (ATP) is a kind of water-containing magnesium-rich aluminum silicate clay mineral with a chain layered structure, belonging to the 2:1 type clay mineral, which possesses ultra-high internal and external specific surface area, non-toxic, tasteless, chemical properties stability and other advantages, for instance, high adsorption performance, catalytic, chargeability, and stability [23][24][25][26][27].However, the utilization trend of some ATP is not high, which undoubtedly causes the waste and loss of mineral resources.Accordingly, many researchers have devoted themselves to the development and research of ATP resources as carriers [28][29][30].
In this paper, ATP was used as the basic material, and a simple experimental method was used to pre-treat it.Ag-AgCl is built into the attapulgite structure to synthesize a series of new composite catalysts.The photocatalytic degradation efficiency of TC was used to evaluate the photodegradation performance of the composite catalyst.At the same time, the optimal special-performance materials were used to conduct recycling experiments to investigate the stability of the materials.ATP possesses a high specific surface area, with attapulgite as the basic material; it can effectively prevent the occurrence of agglomeration and improve the performance of the catalyst.The introduction of Ag-AgCl nanoparticles is deposited on the surface of the photocatalyst, and the photogenerated electrons generated by the light excitation will diffusion from the surface of the catalyst to the surface of the metal.This work provides new ideas for the design and preparation of composite photocatalysts based on ATP.Realizing the effective utilization of attapulgite, especially in water treatment, attapulgite has important theoretical and practical significance.

Morphology Analysis
To understand and study the morphology of the catalytic materials, we pe SEM and TEM characterizations.Figure 2A is the SEM image of the attapulg processed with a magnification of 25,000 times.In Figure 2A, it can be seen that the clay has an acicular or rod-like structure with a random network of rod crystal fib a length of about 2 um [36,37].Figure 2B shows Ag-AgCl, which is granular with number of agglomerates and a few fine particles on the surface, which is consist the appearance of Ag. Figure 2C is the enlarged SEM images of Ag-AgCl/ATP.F figure, it can be clearly seen that the attapulgite is loaded with a large number particles, and the dispersion is uniform.Attapulgite clay needles or rods can be o in Figure 2D consistent with scanning.Whereas the spherical shape of AgCl is also in Figure 2E, the rod-like structure can be seen interspersed in the spheres in Fi indicating that the two were successfully composite.Elemental mapping (Figur reveals the distribution of oxygen (O), iron (Fe), chlorine (Cl), silver (Ag), sili aluminum (Al), and magnesium (Mg) in the Ag-AgCl/ATP photocatalytic com confirming the complex composition of the material.

Morphology Analysis
To understand and study the morphology of the catalytic materials, we performed SEM and TEM characterizations.Figure 2A is the SEM image of the attapulgite pre-processed with a magnification of 25,000 times.In Figure 2A, it can be seen that the bumpy clay has an acicular or rod-like structure with a random network of rod crystal fibers with a length of about 2 um [36,37].Figure 2B shows Ag-AgCl, which is granular with a small number of agglomerates and a few fine particles on the surface, which is consistent with the appearance of Ag. Figure 2C is the enlarged SEM images of Ag-AgCl/ATP.From the figure, it can be clearly seen that the attapulgite is loaded with a large number of AgCl particles, and the dispersion is uniform.Attapulgite clay needles or rods can be observed in Figure 2D consistent with scanning.Whereas the spherical shape of AgCl is also shown in Figure 2E, the rod-like structure can be seen interspersed in the spheres in Figure 2F, indicating that the two were successfully composite.Elemental mapping (Figure 3A-F) reveals the distribution of oxygen (O), iron (Fe), chlorine (Cl), silver (Ag), silicon (Si), aluminum (Al), and magnesium (Mg) in the Ag-AgCl/ATP photocatalytic composite, confirming the complex composition of the material.

Morphology Analysis
To understand and study the morphology of the catalytic materials, we performed SEM and TEM characterizations.Figure 2A is the SEM image of the attapulgite preprocessed with a magnification of 25,000 times.In Figure 2A, it can be seen that the bumpy clay has an acicular or rod-like structure with a random network of rod crystal fibers with a length of about 2 um [36,37].Figure 2B shows Ag-AgCl, which is granular with a small number of agglomerates and a few fine particles on the surface, which is consistent with the appearance of Ag. Figure 2C is the enlarged SEM images of Ag-AgCl/ATP.From the figure, it can be clearly seen that the attapulgite is loaded with a large number of AgCl particles, and the dispersion is uniform.Attapulgite clay needles or rods can be observed in Figure 2D consistent with scanning.Whereas the spherical shape of AgCl is also shown in Figure 2E, the rod-like structure can be seen interspersed in the spheres in Figure 2F, indicating that the two were successfully composite.Elemental mapping (Figure 3A-F) reveals the distribution of oxygen (O), iron (Fe), chlorine (Cl), silver (Ag), silicon (Si), aluminum (Al), and magnesium (Mg) in the Ag-AgCl/ATP photocatalytic composite, confirming the complex composition of the material.

FT-IR Analysis
Figure 4 shows the FT-IR spectra of ATP, Ag-AgCl, and Ag-AgCl/ATP.ATP primarily consists of palygorskite, characterized by prominent infrared spectral peaks at 510, 980, 1030, 1460, 1640-1660 and 3450-3600 cm −1 .In the mid-wave number region, the peaks at 980 cm −1 and 1030 cm −1 correspond to the stretching vibrations of Si-O-Si bonds within the internal structure of ATP [38][39][40].The peaks observed at 1460 and 1640 cm −1 are attributed to coordinated water (surface-adsorbed water) and zeolite water (pore channel).In the high-wave number region, the peak at 3540 cm −1 reflects the stretching vibration of coordinated water, while the peak at 3600 cm −1 corresponds to bond stretching in ATP.The FT-IR spectra of Ag-AgCl/ATP composites indicate that the fundamental properties of attapulgite remain unchanged throughout the synthesis process.

FT-IR Analysis
Figure 4 shows the FT-IR spectra of ATP, Ag-AgCl, and Ag-AgCl/ATP.ATP primarily consists of palygorskite, characterized by prominent infrared spectral peaks at 510, 980, 1030, 1460, 1640-1660 and 3450-3600 cm −1 .In the mid-wave number region, the peaks at 980 cm −1 and 1030 cm −1 correspond to the stretching vibrations of Si-O-Si bonds within the internal structure of ATP [38][39][40].The peaks observed at 1460 and 1640 cm −1 are attributed to coordinated water (surface-adsorbed water) and zeolite water (pore channel).In the high-wave number region, the peak at 3540 cm −1 reflects the stretching vibration of coordinated water, while the peak at 3600 cm −1 corresponds to bond stretching in ATP.The FT-IR spectra of Ag-AgCl/ATP composites indicate that the fundamental properties of attapulgite remain unchanged throughout the synthesis process.

UV-Vis DRS
Figure 6 depicts the characterization of the prepared composite photocatalytic materials using an ultraviolet-visible diffuse reflectance spectrometer.The spectral data demonstrate that these materials exhibit pronounced absorption peaks within the wavelength range of 200-400 nm.Notably, ATP and AgCl display distinct absorption edges at 420 nm and 440 nm, respectively.When compared with the ultraviolet-visible diffuse reflectance spectrum of ATP, AgCl and Ag-AgCl/ATP show variations; particularly, the spectrum of Ag-AgCl/ATP exhibits a noticeable blue shift.This shift indicates an increase in the light absorption capacity of the catalyst and an increase in its efficiency in the presence of light.

UV-Vis DRS
Figure 6 depicts the characterization of the prepared composite photocatalytic materials using an ultraviolet-visible diffuse reflectance spectrometer.The spectral data demonstrate that these materials exhibit pronounced absorption peaks within the wavelength range of 200-400 nm.Notably, ATP and AgCl display distinct absorption edges at 420 nm and 440 nm, respectively.When compared with the ultraviolet-visible diffuse reflectance spectrum of ATP, AgCl and Ag-AgCl/ATP show variations; particularly, the spectrum of Ag-AgCl/ATP exhibits a noticeable blue shift.This shift indicates an increase in the light absorption capacity of the catalyst and an increase in its efficiency in the presence of light.

Photo-Electrochemistry Analysis
To further investigate charge transfer and separation effects, electrochemical tests were conducted.Figure 7a illustrates stable photocurrent density profiles across all samples, with composites exhibiting prominent photocurrent signals compared to bare ATP with AgCl; notably, the 75% loaded sample shows optimal photocurrent intensity.This suggests that AgCl addition effectively enhances hole-electron pair separation [44].Furthermore, impedance spectra (EIS) of composite samples with varying AgCl proportions alongside pure AgCl and ATP are presented in Figure 7b.Results reveal the smallest arc radius for the 75% Ag-AgCl/ATP electrode, indicating lower interfacial resistance conducive to enhanced electron transport [45].Linear sweep voltammetry (LSV) curves in Figure 7c demonstrate that 75% Ag-AgCl/ATP exhibits the lowest overpotential at identical current densities, underscoring the catalysts' synergistic facilitation of photocatalytic degradation processes.In Figure 6b, the band gaps of ATP and AgCl were tested and found to be 3 eV and 3.24 eV, respectively, and the valence bands (VB) of ATP and AgCl were measured in Figure 6c,d using XPS valence band spectroscopy to be 2.56 eV and 2.76 eV, respectively, and through the empirical formula EVB = ECB + Eg, it can be obtained that the conduction bands (CB) for ATP and AgCl were −0.44 eV and −0.48 eV.

Photo-Electrochemistry Analysis
To further investigate charge transfer and separation effects, electrochemical tests were conducted.Figure 7a illustrates stable photocurrent density profiles across all samples, with composites exhibiting prominent photocurrent signals compared to bare ATP with AgCl; notably, the 75% loaded sample shows optimal photocurrent intensity.This suggests that AgCl addition effectively enhances hole-electron pair separation [44].Furthermore, impedance spectra (EIS) of composite samples with varying AgCl proportions alongside pure AgCl and ATP are presented in Figure 7b.Results reveal the smallest arc radius for the 75% Ag-AgCl/ATP electrode, indicating lower interfacial resistance conducive to enhanced electron transport [45].Linear sweep voltammetry (LSV) curves in Figure 7c demonstrate that 75% Ag-AgCl/ATP exhibits the lowest overpotential at identical current densities, underscoring the catalysts' synergistic facilitation of photocatalytic degradation processes.In Figure 6b, the band gaps of ATP and AgCl were tested and found to be 3 eV and 3.24 eV, respectively, and the valence bands (VB) of ATP and AgCl were measured in Figure 6c,d using XPS valence band spectroscopy to be 2.56 eV and 2.76 eV, respectively, and through the empirical formula EVB = ECB + Eg, it can be obtained that the conduction bands (CB) for ATP and AgCl were −0.44 eV and −0.48 eV.

Photocatalytic Activity
This study investigates the photocatalytic properties of prepared materials using TC as a model pollutant.Figure 8A depicts the photocatalytic efficiencies of various loadings of photocatalytic materials (ATP, 2%Ag-AgCl/ATP, 5%Ag-AgCl/ATP, 10%Ag-AgCl/ATP, 20%Ag-AgCl/ATP, 50%Ag-AgCl/ATP, 75%Ag-AgCl/ATP, 80%Ag-AgCl/ATP and AgCl).Upon exposure to a 300 W xenon lamp for 120 min, the photocatalytic efficiencies of Ag-AgCl/ATP photocatalysts were 35.00%, 20.11%, 37.46%, 44.83%, 64.23%, 77.65%, 71.60%, and 76.10%, respectively.Notably, at 2% AgCl loading, Ag-AgCl/ATP exhibits the lowest photocatalytic efficiency, even lower than pure ATP.As the AgCl loading increases within Ag-AgCl/ATP, the photocatalytic efficiency improves significantly.The peak efficiency is achieved at 75% AgCl loading, after which further increases diminish photocatalytic performance, likely due to surface blockage of attapulgite preventing effective pollutantcatalyst interaction and reducing activity.Figure 8B illustrates the photocatalytic degradation rate curve of the optimized Ag-AgCl/ATP photocatalytic material across different concentrations of TC (10, 20, 30, 50, and 100 mg/L).After 120 min of photocatalytic degradation, the degradation rates for each TC concentration are 81.46%,85.01%, 79.08%, 68.42%, and 35.18%, respectively.Notably, the highest degradation rate is achieved at a TC concentration of 20 mg/L, followed by 10 mg/L, and then 30 mg/L.The lowest degradation rate is observed at 100 mg/L TC concentration.These results indicate that the optimized Ag-AgCl/ATP photocatalytic material exhibits greater efficiency at lower TC concentrations, with degradation rates declining as TC concentration increases.This underscores the importance of considering pollutant concentrations when applying such photocatalytic materials in practical environmental remediation scenarios.

Photocatalytic Activity
This study investigates the photocatalytic properties of prepared materials using TC as a model pollutant.Figure 8A depicts the photocatalytic efficiencies of various loadings of photocatalytic materials (ATP, 2%Ag-AgCl/ATP, 5%Ag-AgCl/ATP, 10%Ag-AgCl/ATP, 20%Ag-AgCl/ATP, 50%Ag-AgCl/ATP, 75%Ag-AgCl/ATP, 80%Ag-AgCl/ATP and AgCl).Upon exposure to a 300 W xenon lamp for 120 min, the photocatalytic efficiencies of Ag-AgCl/ATP photocatalysts were 35.00%, 20.11%, 37.46%, 44.83%, 64.23%, 77.65%, 71.60%, and 76.10%, respectively.Notably, at 2% AgCl loading, Ag-AgCl/ATP exhibits the lowest photocatalytic efficiency, even lower than pure ATP.As the AgCl loading increases within Ag-AgCl/ATP, the photocatalytic efficiency improves significantly.The peak efficiency is achieved at 75% AgCl loading, after which further increases diminish photocatalytic performance, likely due to surface blockage of attapulgite preventing effective pollutant-catalyst interaction and reducing activity.Figure 8B illustrates the photocatalytic degradation rate curve of the optimized Ag-AgCl/ATP photocatalytic material across different concentrations of TC (10, 20, 30, 50, and 100 mg/L).After 120 min of photocatalytic degradation, the degradation rates for each TC concentration are 81.46%,85.01%, 79.08%, 68.42%, and 35.18%, respectively.Notably, the highest degradation rate is achieved at a TC concentration of 20 mg/L, followed by 10 mg/L, and then 30 mg/L.The lowest degradation rate is observed at 100 mg/L TC concentration.These results indicate that the optimized Ag-AgCl/ATP photocatalytic material exhibits greater efficiency at lower TC concentrations, with degradation rates declining as TC concentration increases.This underscores the importance of considering pollutant concentrations when applying such photocatalytic materials in practical environmental remediation scenarios.The rate equation obtained from the Langmuir-Hinshelwood kinetic equation is expressed as the following Equation (1): Among them, C0 and C represent the initial and degraded concentration of TC at time t, kc is the pseudo-first rate constant, and KCIP is the equilibrium constant for the adsorption of TC by the catalyst.According to the above equation expression, in the presence of Fedoped AgCl photocatalyst, the pseudo-first-order kinetic equation of photocatalytic degradation is expressed as the following Equation ( 2): Where kobs is the quasi-first order kinetic rate constant, and the above formula can be transformed into (3).
According to Equation ( 3), the linear relationship between ln(C0/C) and time t is shown in Figure 8D.The linear relationship expression between kobs and C0 can be transformed from Equation (1).
It can be seen from Formula (4) that the reciprocal rate (1/kobs) and the initial concentration of TC show a linear relationship.At the same time, the photocatalytic degradation rate of TC, kobs, changes with the initial concentration, as shown in Figure 9A.According to the slope and intercept of the straight line, the equilibrium adsorption constant of TC KTC = 0.135 L mg −1 , and the pseudo-second rate constant kc = 0.933 mg L −1 min −1 .In Table 1, we also show the effects of different concentrations on the degradation rate.The rate equation obtained from the Langmuir-Hinshelwood kinetic equation is expressed as the following Equation (1): Among them, C 0 and C represent the initial and degraded concentration of TC at time t, k c is the pseudo-first rate constant, and K CIP is the equilibrium constant for the adsorption of TC by the catalyst.According to the above equation expression, in the presence of Fe-doped AgCl photocatalyst, the pseudo-first-order kinetic equation of photocatalytic degradation is expressed as the following Equation ( 2

):
Where k obs is the quasi-first order kinetic rate constant, and the above formula can be transformed into (3).
According to Equation ( 3), the linear relationship between ln(C 0 /C) and time t is shown in Figure 8D.The linear relationship expression between k obs and C 0 can be transformed from Equation (1).
It can be seen from Formula (4) that the reciprocal rate (1/k obs ) and the initial concentration of TC show a linear relationship.At the same time, the photocatalytic degradation rate of TC, k obs , changes with the initial concentration, as shown in Figure 9A.According to the slope and intercept of the straight line, the equilibrium adsorption constant of TC KTC = 0.135 L mg −1 , and the pseudo-second rate constant k c = 0.933 mg L −1 min −1 .In Table 1, we also show the effects of different concentrations on the degradation rate.To assess the impact of temperature on the photocatalytic performance of our prepared samples, we conducted experiments on TC solution degradation using the catalysts under different thermal conditions.Figure 9B presents degradation efficiency curves of the optimized Ag-AgCl/ATP photocatalytic material for degrading a 20 mg/L TC solution at temperatures of 20, 30, 40 and 50 • C. Results show that after 120 min of photocatalytic activity, the degradation efficiencies at these temperatures are 85.01%, 70.18%, 67.49%, and 67.97%, respectively.Notably, the highest degradation rate of 85.01% is achieved at 20 • C, indicating superior TC degradation efficiency of the prepared Ag-AgCl/ATP photocatalytic material at lower temperatures.Conversely, efficiency decreases with increasing temperature.Considering that operational environments for these photocatalytic materials typically involve room temperature conditions, the findings highlight the substantial potential for practical applications in TC degradation scenarios.

Stability
The stability of a material is a crucial metric for assessing its practical applicability.In particular, the stability of photocatalytic materials is indicative of their quality and potential for broader applications.To evaluate the stability of our composite

Stability
The stability of a material is a crucial metric for assessing its practical applicability.In particular, the stability of photocatalytic materials is indicative of their quality and potential for broader applications.To evaluate the stability of our composite photocatalytic material, we conducted five successive cycles of photocatalytic experiments.As illustrated in Figure 9C, the photocatalytic degradation efficiency after 120 min of photoreaction was recorded at 74.24%, 70.70%, 69.19%, 69.56%, and 69.32% for each cycle, respectively.These results indicate a slight initial decrease in efficiency, which subsequently stabilizes around 69%.This consistent performance demonstrates that the Ag-AgCl/ATP photocatalytic composite material we developed maintains substantial degradation capability after repeated use, thereby confirming its excellent stability and reinforcing its suitability for practical applications in pollutant degradation.

Capture Experiment
To ascertain the predominant active species involved in the degradation process, this study conducted trapping experiments targeting key reactive species such as holes (h + ), hydroxyl radicals (•OH), and superoxide anion radicals (•O 2 − ), to elucidate the photocatalytic degradation mechanism of TC (Figure 9D).Triethanolamine, isopropanol (IPA), and p-benzoquinone were utilized as specific scavengers for these active species, respectively.The trapping experiments were integrated into the standard photocatalytic degradation protocol for TC.Specifically, a precise amount of each scavenger was added to the reaction vessel containing the catalyst and 100 mL of TC solution: 0.133 mL of triethanolamine, 0.076 mL of isopropanol, or 0.108 g of p-benzoquinone.Following this, the concentration of TC was monitored by sampling at designated intervals, and the photocatalytic efficiency was quantitatively assessed.This experimental setup was replicated across three separate trials to ensure reproducibility and accuracy in the findings.

Mechanism Analysis
The role of active species in the photodegradation of TC using an Ag-AgCl/ATP composite photocatalyst was elucidated through a series of trapping experiments.Figure 9D illustrates that the addition of isopropanol, a scavenger for •OH, has a minimal effect on the degradation rate of TC, indicating a marginal role of •OH radicals in the degradation process.Conversely, the addition of triethanolamine, a scavenger for h + , significantly impacts the TC degradation rate more than isopropanol, suggesting a predominant role of h + over •OH radicals in the TC degradation mechanism.However, the overall influence of both species is limited, leading to the introduction of p-benzoquinone to further probe the degradation kinetics.In Figure 10, the mechanistic pattern of the reaction can be seen.This addition markedly reduces the photocatalytic degradation efficiency of TC compared to the baseline condition without scavengers, confirming that the•O 2 − is the principal active species in the degradation process.Experimental findings reveal that: (1) the inherent high specific surface area of attapulgite provides numerous active adsorption sites, enhancing the photocatalytic activity of the Ag-AgCl/ATP composite; (2) the presence of silver on the AgCl surface induces plasmon resonance effects upon photolysis, facilitating the generation of active species such as h + and •O 2 − , which substantially improve the photocatalytic efficiency of the composite material.the•O2 − is the principal active species in the degradation process.Experimental findings reveal that: (1) the inherent high specific surface area of attapulgite provides numerous active adsorption sites, enhancing the photocatalytic activity of the Ag-AgCl/ATP composite; (2) the presence of silver on the AgCl surface induces plasmon resonance effects upon photolysis, facilitating the generation of active species such as h + and •O2 − , which substantially improve the photocatalytic efficiency of the composite material.

Pre-Treatment of the ATP
Initially, ATP was subjected to pre-treatment by dispersing it into an ample volume of deionized water, followed by stirring at a speed of 500 rpm using a magnetic stirrer for 1 h.Subsequently, the mixture was transferred to a filter for filtration.The filtration was rapidly conducted, and the residue was washed thrice.The reagents were obtained from Sinopharm Chemical Reagent Co., Ltd.(Shanghai, China).The deionized water used throughout the experiments was obtained from locally purified water.All analytical grade reagents are used directly without further purification.

Preparation of Ag-AgCl/ATP Materials
Initially, 1 g of pre-treated ATP was added to a 100 mL beaker containing 15 mL of deionized water.The mixture was stirred at a speed of 500 r/min for 30 min to ensure complete dispersion of the ATP in the solution.Subsequently, the AgNO3 solution, previously prepared to the required concentration, was added dropwise to the suspension over 5 min.After the addition, stirring was continued for an additional 30 min.Following this, the required amount of NaCl solution was gradually introduced into the beaker over 5 min, using titration for precise control.Upon completion of the titration, the mixture

Pre-Treatment of the ATP
Initially, ATP was subjected to pre-treatment by dispersing it into an ample volume of deionized water, followed by stirring at a speed of 500 rpm using a magnetic stirrer for 1 h.Subsequently, the mixture was transferred to a filter for filtration.The filtration was rapidly conducted, and the residue was washed thrice.The reagents were obtained from Sinopharm Chemical Reagent Co., Ltd.(Shanghai, China).The deionized water used throughout the experiments was obtained from locally purified water.All analytical grade reagents are used directly without further purification.

Preparation of Ag-AgCl/ATP Materials
Initially, 1 g of pre-treated ATP was added to a 100 mL beaker containing 15 mL of deionized water.The mixture was stirred at a speed of 500 r/min for 30 min to ensure complete dispersion of the ATP in the solution.Subsequently, the AgNO 3 solution, previously prepared to the required concentration, was added dropwise to the suspension over 5 min.After the addition, stirring was continued for an additional 30 min.Following this, the required amount of NaCl solution was gradually introduced into the beaker over 5 min, using titration for precise control.Upon completion of the titration, the mixture was stirred at 600 r/min for 60 min.The resultant suspension was then filtered, and the retained solid was washed three times with deionized water and three times with ethanol.The washed solid was dried in a blowing drying oven at 60 • C for 10 h.The resulting AgCl/ATP composite with different loading (2%, 5%, 10%, 20%, 50%, 75% and 80%) was ground into a fine powder and stored in a dark place to prevent photodegradation.For subsequent experiments, the AgCl/ATP was exposed to light for 10 min to prepare the Ag-AgCl/ATP composite.

Photocatalytic Degradation of Tetracycline
To evaluate the photocatalytic activity of the composites, degradation experiments of TC were conducted under various temperatures and concentrations.The experimental procedure is detailed as follows: Initially, 25 mg of the catalyst was suspended in 100 mL of a 20 mg/L TC solution to conduct the photocatalytic degradation tests.The mixture was stirred magnetically in the dark for 30 min to establish adsorption-desorption equilibrium.During this period, aliquots of 10 mL were sampled every 10 min using a centrifuge tube, collecting three samples in total.Subsequently, a xenon lamp was activated to initiate the photocatalytic reaction, which was continued under illumination for 60 min.Samples were taken every 20 min, resulting in six additional samples.Including the initial sample, ten samples were analyzed in total.These ten samples were then centrifuged at 6000 r/min for 3 min to separate the supernatants for photometric analysis.The absorbance of each sample was recorded to calculate the photocatalytic degradation efficiency.This procedure was repeated using AgCl/ATP composites with varying loadings to identify the composite with the highest photocatalytic activity.The optimal composite was then used to degrade tetracycline at different temperatures (20,30,40 and 50 • C) and concentrations (10,20,30,50, and 100 mg/L).For each condition, the procedure mirrored that of the optimal loading tests, and the temperature was strictly controlled during the reaction.The absorbance values were measured, and the corresponding photocatalytic efficiencies were calculated for each set of experimental conditions.In addition, the stirrer was an H01-1A Intelligent Digital Magnetic Stirrer, while the xenon lamp used a power of 300 W (300 mW cm −2 ; full spectrum) (Please refer to Supplementary Information for details).

Stability Test
The recyclability of photocatalysts is critical for the practical application of photocatalytic technologies.To assess whether a photocatalytic material warrants recycling, it is imperative to conduct thorough recycling experiments.These experiments not only evaluate the recyclability of the photocatalyst but also its stability over multiple cycles.The protocol for the recycling experiments mirrors that of the tetracycline photocatalytic degradation tests.Specifically, after each cycle, the nine samples collected are centrifuged to separate the supernatants for photometric analysis to measure their luminosity values.Post-measurement, the supernatants are carefully filtered, and the results are documented.The remaining solution in the centrifuge tubes, along with the sample solution from the degradation container, is recovered.This mixture is then washed and dried to retrieve the catalyst.Subsequently, the recovered catalyst is ground, and its mass is measured.Should there be a shortfall in the catalyst weight, an additional quantity of the original sample is supplemented to match the prescribed mass.This preparation then undergoes another cycle of the tetracycline degradation experiment.This procedure is repeated for a total of five cycles to comprehensively assess the photocatalyst's performance and stability over repeated use.

Conclusions
The direct precipitation method and the oxidation method were used to successfully prepare the Ag-AgCl/ATP composite photocatalytic material.Through photocatalytic degradation experiments under different conditions and detailed analysis of various characteristics of the composite photocatalytic material, we have drawn a series of conclusions: (1) ATP not only enhances the dispersion of Ag-AgCl nanospheres but also ATP aids in the adsorption of TC molecules, thereby synergistically promoting the degradation of TC with Ag-AgCl nanoparticles.(2) Through the test in the photocatalytic degradation of TC solutions of different concentrations, it was found that when the concentration of TC solution is 20 mg/L, the composite photocatalytic material has the highest photocatalytic degradation efficiency of 85.01%.(3) From the photocatalytic degradation test at different temperatures, we found that the photocatalytic composite material has the highest photocatalytic degradation efficiency at a temperature of 20 • C.

Figure 5
Figure 5 presents the compositional analysis and surface chemical states of t optimized photocatalyst, 75% Ag-AgCl/ATP, as determined by X-ray photoelectr spectroscopy (XPS).The full spectrum shown in Figure 5A revealed more pronounc and intense peaks at 532.69 eV, 367.81 eV, 198.22 eV, and 102.49eV, which correspond the presence of oxygen (O), silver (Ag), chlorine (CI), and silicon (Si), respective corroborating the findings from X-ray diffraction (XRD) and elemental mapping analys Figure 5B-E detail the XPS spectra for Ag 3d, Cl 2p, Si 2p, and O 1s, respectively.Amo them, the composite of Figure 5B shows peaks at 533.64 eV, 532.29 eV, and 531.21 e corresponding to the three partial compositions of Si-O-Si, Si-O-H, and Si-O-M respectively.Figure 5D, on the other hand, shows the fitted high-resolution spectrum AgMN1, which can be divided into two different peaks, Ag and AgCl. Figure illustrates the characteristic peak of Si at 102.84 eV in a two-dimensional orbital profi After compounding, the binding energy of Si moves in a large direction, showing blueshift.The binding energies at 199.41 eV and 197.96 eV, shown in Figure 5 correspond to the Cl 2p3/2 and Cl 2p1/2 states, respectively.It can be seen that the bindi energy of Cl in the composite is shifted in a smaller direction than that of Cl in t monomer, showing a redshift.Lastly, the binding energies of 373.91 eV and 367.92 eV Figure 5E are assigned to Ag 3d3/2 and Ag 3d5/2, indicating the presence of these elemen within the composite [41-43].These spectral results provide comprehensive insights in the chemical states at the catalyst surface, further substantiating the successful synthe of the composite catalyst.

Figure 5
Figure5presents the compositional analysis and surface chemical states of the optimized photocatalyst, 75% Ag-AgCl/ATP, as determined by X-ray photoelectron spectroscopy (XPS).The full spectrum shown in Figure5Arevealed more pronounced and intense peaks at 532.69 eV, 367.81 eV, 198.22 eV, and 102.49eV, which correspond to the presence of oxygen (O), silver (Ag), chlorine (CI), and silicon (Si), respectively, corroborating the findings from X-ray diffraction (XRD) and elemental mapping analyses.Figure5B-Edetail the XPS spectra for Ag 3d, Cl 2p, Si 2p, and O 1s, respectively.Among them, the composite of Figure5Bshows peaks at 533.64 eV, 532.29 eV, and 531.21 eV, corresponding to the three partial compositions of Si-O-Si, Si-O-H, and Si-O-Mg, respectively.Figure5D, on the other hand, shows the fitted high-resolution spectrum of AgMN1, which can be divided into two different peaks, Ag and AgCl.Figure5Cillustrates the characteristic peak of Si at 102.84 eV in a two-dimensional orbital profile.After compounding, the binding energy of Si moves in a large direction, showing a blueshift.The binding energies at 199.41 eV and 197.96 eV, shown in Figure5D, correspond to the Cl 2p 3/2 and Cl 2p 1/2 states, respectively.It can be seen that the binding energy of Cl in the composite is shifted in a smaller direction than that of Cl in the monomer, showing a redshift.Lastly, the binding energies of 373.91 eV and 367.92 eV in Figure5Eare assigned to Ag 3d 3/2 and Ag 3d 5/2 , indicating the presence of these elements within the composite[41][42][43].These spectral results provide comprehensive insights into the chemical states at the catalyst surface, further substantiating the successful synthesis of the composite catalyst.

Figure 8 .
Figure 8. (A) Different loading amounts of Ag-AgCl/ATP; (B) optimal Ag-AgCl/ATP degradation of different concentrations of TC; (C) degradation efficiency of different concentrations of TC; (D) quasi-first kinetic curve, the trend of ln(C0/C) with time under different starting concentrations.The initial concentration of TC in this experiment is in the range of 10-100 mg L −1 .The experimental results are shown in Figure 8B,C.The photocatalytic degradation efficiency and rate of TC are negatively correlated with the initial concentration of TC.As the concentration of TC in the solution increases, the total amount of TC also increases.Under the condition of loading with the same AgCl catalyst quality, the degradation rate of high-concentration TC decreases slightly compared with other concentrations.High concentrations of TC cannot absorb photons well and cannot effectively separate photogenerated electrons and holes, which will affect the degradation rate.The rate equation obtained from the Langmuir-Hinshelwood kinetic equation is expressed as the following Equation (1):Among them, C0 and C represent the initial and degraded concentration of TC at time t, kc is the pseudo-first rate constant, and KCIP is the equilibrium constant for the adsorption of TC by the catalyst.According to the above equation expression, in the presence of Fedoped AgCl photocatalyst, the pseudo-first-order kinetic equation of photocatalytic degradation is expressed as the following Equation (2):Where kobs is the quasi-first order kinetic rate constant, and the above formula can be transformed into (3).According to Equation (3), the linear relationship between ln(C0/C) and time t is shown in Figure8D.The linear relationship expression between kobs and C0 can be transformed from Equation(1).It can be seen from Formula (4) that the reciprocal rate (1/kobs) and the initial concentration of TC show a linear relationship.At the same time, the photocatalytic degradation rate of TC, kobs, changes with the initial concentration, as shown in Figure9A.According to the slope and intercept of the straight line, the equilibrium adsorption constant of TC KTC = 0.135 L mg −1 , and the pseudo-second rate constant kc = 0.933 mg L −1 min −1 .In Table1, we also show the effects of different concentrations on the degradation rate.

Figure 8 .
Figure 8. (A) Different loading amounts of Ag-AgCl/ATP; (B) optimal Ag-AgCl/ATP degradation of different concentrations of TC; (C) degradation efficiency of different concentrations of TC; (D) quasifirst kinetic curve, the trend of ln(C 0 /C) with time under different starting concentrations.The initial concentration of TC in this experiment is in the range of 10-100 mg L −1 .The experimental results are shown in Figure 8B,C.The photocatalytic degradation efficiency and rate of TC are negatively correlated with the initial concentration of TC.As the concentration of TC in the solution increases, the total amount of TC also increases.Under the condition of loading with the same AgCl catalyst quality, the degradation rate of high-concentration TC decreases slightly compared with other concentrations.High concentrations of TC cannot absorb photons well and cannot effectively separate photogenerated electrons and holes, which will affect the degradation rate.The rate equation obtained from the Langmuir-Hinshelwood kinetic equation is expressed as the following Equation (1):Among them, C 0 and C represent the initial and degraded concentration of TC at time t, k c is the pseudo-first rate constant, and K CIP is the equilibrium constant for the adsorption of TC by the catalyst.According to the above equation expression, in the presence of Fe-doped AgCl photocatalyst, the pseudo-first-order kinetic equation of photocatalytic degradation is expressed as the following Equation (2):Where k obs is the quasi-first order kinetic rate constant, and the above formula can be transformed into (3).According to Equation (3), the linear relationship between ln(C 0 /C) and time t is shown in Figure8D.The linear relationship expression between k obs and C 0 can be transformed from Equation(1).It can be seen from Formula (4) that the reciprocal rate (1/k obs ) and the initial concentration of TC show a linear relationship.At the same time, the photocatalytic degradation rate of TC, k obs , changes with the initial concentration, as shown in Figure9A.According to the slope and intercept of the straight line, the equilibrium adsorption constant of TC KTC = 0.135 L mg −1 , and the pseudo-second rate constant k c = 0.933 mg L −1 min −1 .In Table1, we also show the effects of different concentrations on the degradation rate.

Catalysts 2024 , 16 Figure 9 .
Figure 9. (A) The linear relationship between the reciprocal of the pseudo-first kinetic rate and the initial concentration of TC; (B) optimal Ag-AgCl/ATP degradation of TC at different temperatures; (C) Ag-AgCl/ATP cycle degradation of TC; (D) Ag-AgCl/ATP photocatalytic degradation of TC capture experiment.

Figure 9 .
Figure 9. (A) The linear relationship between the reciprocal of the pseudo-first kinetic rate and the initial concentration of TC; (B) optimal Ag-AgCl/ATP degradation of TC at different temperatures; (C) Ag-AgCl/ATP cycle degradation of TC; (D) Ag-AgCl/ATP photocatalytic degradation of TC capture experiment.

Table 1 .
Effect of TC initial concentration on the degradation rate.