Facile construction of Z-scheme AgCl/Bi3TaO7  photocatalysts for effective removal of tetracycline under visible-light irradiation

doi:10.21203/rs.3.rs-2355049/v1

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Facile construction of Z-scheme AgCl/Bi3TaO7 photocatalysts for effective removal of tetracycline under visible-light irradiation

https://doi.org/10.21203/rs.3.rs-2355049/v1

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published 20 Mar, 2023

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A string of AgCl/Bi₃TaO₇ two-component composite was synthesized by hydrothermal and deposition-precipitation process initially. The photocatalytic activities of mixed-phase AgCl/Bi₃TaO₇ were evaluated toward the decomposition of tetracycline (TC). Among these as-prepared materials, AgCl/Bi₃TaO₇ nanocomposites when the molar ratio of baked materials between AgCl and Bi₃TaO₇ was 1:5 presented the optimal photocatalytic quantum efficiency for TC dissociation (86.82%) with visible light exposure, which was 1.69 and 2.38 folders than that of single Bi₃TaO₇ and AgCl, respectively. What's more, it illustrated that the photogenerated carriers were markedly isolated on account of the formation of heterojunction confirmed by EIS analysis. Meanwhile, radical trapping experiments implied that the photo-induced holes (h⁺), hydroxyl radical (·OH) and superoxide radical (·O-2) were the major active species. The escalated photocatalytic activity could be ascribed to the unique construction of Z-scheme AgCl/Bi₃TaO₇ heterojunction, which could expedite charge separation and transmission, cement light absorption capability and retain the strong redox ability of photogenerated electrons and holes. Our finding suggests that AgCl/Bi₃TaO₇ nanocomposites possess great potential for photocatalytic oxidation of residual TC in the wastewater effluents and the reported strategy can contribute to the development of novel high-performance photocatalyst.

photocatalysts

tetracycline removal

AgCl

Bi3TaO7

Z-sheme

visible-light-driven

Tetracycline (TC), the second most used antibiotic and the most adopted drug for livestock worldwide, has been frequently implemented in medicine, agriculture and animal husbandry to boost the complete community’s healthy level(Phoon et al, 2022, Sharma et al, 2022). Whereas, the indiscriminate overuse and improper disposal of antibiotics would render more resistant mutations of bacteria and genes, further disturb the balance of ecosystem and endanger human health(Liu et al, 2022c, Xu et al, 2021b). Hence, it is essential and urgent to explore efficient methods to degrade sewage containing antibiotics. Currently, numerous methods for the antibiotics decomposition have been employed including adsorption(Xiang et al, 2020), chemical oxidation(Qiu et al, 2022), biological degradation(Joo and Hussein, 2022) and membrane treatment(Iborra-Torres et al, 2020). In comparison with these traditional treatments, the photocatalysis technique has stimulated growing interest in the dissociation of antibiotics in that low price, simple operation, maneuverability and no secondary pollution(Hou et al, 2021). Notably, this strategy alleviates the conflict between energy depletion and sustainable development. Thus, photocatalysis has been recognized as an effective strategy to cope with residual pharmaceuticals.

To date, numerous significant effort has been worked to design and build efficient and speedy photocatalysts to dissociate antibiotics in the aqueous phase. The common materials mainly involved metal-based photocatalysts (such as Ag(Thao et al, 2022), non-noble metal-based photocatalysts (TiO₂(Bai et al, 2022), ZnO(Faisal et al, 2021), MoS₂(Liu et al, 2022a), CdS(Fu et al, 2022), Ta₃N₅(Xiao et al, 2021) etc.), carbon-based photocatalysts (such as g-C₃N₄(Hu et al, 2020), GO(Li et al, 2021a), rGO(Sun et al, 2022) etc.) and MOFs (such as ZIFs(El Ouardi et al, 2022), UIOs(Li et al, 2021b) etc.) based on the ingredients. Nevertheless, the poor quantum efficiency and rapid charge recombination are still the constraints derived from the photocatalysts in the photocatalytic practical reaction. Thus, new emerging photocatalytic materials have evoked growing awareness in recent years. Particularly, the oxidative potential of TC is 2.4 eV, therefore the relative positive valence band and negative conduction band are required for photocatalysts(Zhang et al, 2019). Currently, tantalate photocatalysts have established substantial public attention in that the very positive VB involving tantalum (Ta) 5d orbital(Zhuk et al, 2022). Particularly, such as Bi₃TaO₇, the hybridized VB is priorly composed of O 2p and Bi 6s orbitals, causing a shrank band gap energy and an ultrahigh oxidative activity(Bisht et al, 2021, Geng et al, 2022). Additionally, Bi₃TaO₇ possesses a tuning band gap of 2.76–2.87 eV that makes it absorb visible light(Song et al, 2020). Furthermore, high specific surface area and active sites could be generated due to the unique layered crystal structure of Bi₃TaO₇(Cao et al, 2022a). Besides, it has been discovered metal cations (the Bi ions) could generate a chelation effect with organic molecules like TC with strong coordination bonds(Salavati-Niasari et al, 2005). Nonetheless, Bi₃TaO₇ subjects to the drawbacks of fast recombination and dissatisfied charge separation. To address the constraints, various strategies have been proposed and adopted. Among them, an eminent strategy is the construction of heterostructure by integration Bi₃TaO₇ with other semiconductors.

AgX (X = Cl, Br and I) have been adopted to couple with multiple semiconductors to construct heterojunctions that exhibit preferable quantum yields toward the elimination of organic pollutants. Particularly, AgCl has attracted the attention of scholars in the domain of photocatalysis(Zhang et al, 2022). For instance, AgCl/WO₃ composite microrods was fabricated with p-n junction, which presented promising photocatalytic activity and stability (Yu et al, 2019). Direct Z-scheme Bi₃O₄Cl/AgCl heterojunction expressed 98.5% TOC removal rate of ceftriaxone(Du et al, 2020). S-scheme AgCl/MIL-100(Fe) heterojunction photocatalyst exhibited a complete removal efficiency (99.9%) of sulfamethazine(Ning et al, 2022). Based on the available literature, it’s reasonable and feasible that the integration of AgCl and Bi₃TaO₇ could accelerate the carriers separation effectively on account of the benign band potential matching between AgCl and Bi₃TaO₇ for TC deterioration.

Herein, we prepared a series of AgCl decorated AgCl/Bi₃TaO₇ materials with varying proportions via facile hydrothermal method and deposition–precipitation method. The crystal phases, chemical compositions, morphologies and optical characteristics of the as-obtained samples were investigated. Additionally, the photocatalytic performance of as-prepared binary metarials were accessed by regulating the molar ratio of AgCl and Bi₃TaO₇, solution pH and initial TC concentration in detail. Subsequently, the possible mechanism for decent photocatalytic property was proposed in view of the corresponding testing data.

Materials and reagents

Bismuth nitrate pentahydrate (Bi(NO₃)₃⋅5H₂O), tantalum pentachloride (TaCl₅), potassium hydroxide (KOH), tetracycline hydrochloride (C₂₂H₂₄N₂O₈), were purchased from Aladdin (Shanghai, China). Anhydrous ethanol (C₂H₆O) silver nitrate (AgNO₃, 99.99%), sodium chloride (NaCl) and benzyl alcohol (C₇H₈O), were acquired from the respective suppliers. All reagents were of analytical grade and utilized without further purification.

Preparation of Bi3TaO7 composite

2.2548 g Bi(NO₃)₃⋅5H₂O and 1.0000 g TaCl₅ were separately dispersed into 10 mL of ethanol with ultrasonic stirring for 30 min. Subsequently, TaCl₅ solution was continuously mixed in the Bi(NO₃)₃ solution, stirring for 30 min to gain a suspension. Afterward, KOH aqueous sample (7M) was included into the mixed suspension until the value of pH was regulated to 10.0. Then the resultant mixture was stirred for 30 min to obtain a yellow suspension. Thereafter, the yellow suspension was diverted into a 25 mL autoclave and reacted for 24 h at 200 ℃. Cooling down to ambient temperature, it was separated via centrifugation with distilled water and ethanol 6 times. Finally, pure Bi₃TaO₇ nanoparticles were yielded by air oven drying at 60 ℃ for 12 h, denoted as BTO.

Preparation of AgCl-Bi3TaO7 composite

The deposition of AgCl on Bi₃TaO₇ was obtained via a deposition-precipitation method. Typically, the resultant sample Bi₃TaO₇ was dispersed into the distilled water (50 mL) while being continuously agitated for uniform dispersion. A certain amount of NaCl and AgNO₃ were dissolved into Bi₃TaO₇ solution and stirred vigorously for 120 min. Lastly, the obtained sediment was cleaned with ethanol and deionized water several times and dried at 60 ℃ for 12 h. AgCl/Bi₃TaO₇ nanopaticles were gathered that the molar ratios of AgCl and Bi₃TaO₇ were 3:20, 4:20, 5:20, 6:20 and denoted as AB-1, AB-2, AB-3, AB-4, respectively. The preparation process of AgCl/Bi₃TaO₇ samples was depicted using different amounts as illustrated in Fig. 1.

Characterization of the photocatalysts

The phase composition and crystallinity of the ass–synthesized samples were investigated based on powder X-ray diffraction (XRD, DX-27mini X-ray diffractometer) equipped with Cu-Kα beam source and the 2θ ranging from 5° to 90°, at a scanning speed of 2° per minute. The morphologies and structures of catalysts were detected using field emission scanning electron microscopy (SEM, Philips XL30) and transmission electron microscopy (TEM, JEM–ARM 200F). The surface elemental compositions were recorded by usinga monochrome Al X-ray resource (XPS, ESCALAB 250Xi). The photocatalytic experiments were examined on an XPA-7 photochemical reactor (Xujiang Electromechanical Plant). The specific surface areas were performed on the Brunauer–Emmett–Teller (BET, Micromeritics ASAP 2460). Photo-electrochemical measurements were implemented with electrochemical impendence spectroscopy (EIS, CHI660) in a sodium sulfate electrolyte solution. A standard platinum wire electrode, Ag/AgCl electrode and the as-obtained material act as the auxiliary electrode, the reference electrode and the working electrode, respectively. The working electrode was fabricated on the graphene with a thin film through a manual deposition process.

Assessment of photocatalytic performance

The photocatalytic performance of as-obtained catalysts was accessed for the TC decomposition by a 350 W Xe lamp with a 420 nm cutoff filter. During the experimental process, 15 mg of photocatalysts were put to 20 mg/L TC solution (50 mL). Before the irradiation, the mixture was magnetically stirred in dark for 90 min to assure the absorption-desorption equilibrium between TC and as-obtained photocatalysts. Soon afterwards, at given intervals of illumination, 4 mL of mixture was sampled, coupled with centrifuging at 6000 rpm for 20 min and filtering to wipe off photocatalysts in the TC residual solution. The concentration of TC was defined on a UV-Vis spectrophotometer (UV8800s) at the absorption peak of 356 nm.

Radical-trapping experiment

To verify the pivotal active species during the photo-degrading TC process, radical-trapping experiment was implemented by employing four quenchers, benzoquinone (BQ, a superoxide anion radical scavenger), ammonium oxalate (AO, a hole scavenger), tertiary butyl alcohol (TBA, a hydroxyl radical scavenger) and AgNO₃(an electron scavenger). Different from the above photocatalytic process, 15 mg of AB-2 photocatalyst and 1mmol of distinct radical scavengers were introduced to 20 mg/L of TC solution (50 mL).

Morphologies and structure of as-prepared photocatalysts

The crystalline structure of all as-obtained samples was performed by XRD analysis in the 2θ raging of 5–90°. As shown in Fig. 2, four characteristic peaks of pure Bi₃TaO₇ at 2θ values of 28.32°, 32.27°, 46.93°, 55.67° were obviously observed, which matched with the (111), (200), (220) and (311) planes of Bi₃TaO₇ (JCPDS No. 044–0202)(Xu et al, 2021a). Simultaneously, from the XRD patterns of the AgCl/Bi₃TaO₇ powder, the predominant seven characteristic peaks appeared at 2θ values of 27.82°, 32.24°, 46.24°, 54.83°, 67.46 °, 76.75° and 85.70° that were indexed to the (111), (200), (220), (311), (400), (420) and (422) planes of AgCl (JCPDS No.031-1238)(Panchal et al, 2021). In the AgCl/Bi₃TaO₇ composites, the characteristic peaks of AgCl and Bi₃TaO₇ was found, demonstrating the formation of heterojunction. Meanwhile, the peaks of Bi₃TaO₇ became more non-prominent and the diffraction peaks of AgCl grew stronger gradually as the proportion of AgCl increased. In addition, the peaks of AgCl/Bi₃TaO₇ composites were explicit and without additional diffraction peaks, affirming the fine crystallinity, high purity and interaction occurring at the interface in the binary components.

The surface composition and chemical states of AgCl, BTO and AB-2 nanocomposite were conducted by XPS for the sake of more structural information. The XPS survey spectrum from Fig. 3 identified that AgCl and BTO were compounded from corresponding elements of Ag, Cl and elements of Bi, Ta and O, respectively. Withal, AB-2 composite was consistent with five elements including Bi, Ta O, Ag and Cl, demonstrating the coexistence in AB-2 powder.

Figure 4a-f displayed the high-resolution XPS spectra of AgCl, BTO and AB-2 composite. Thereinto, the C 1s peak of 284.8 eV was regarded as the calibration value since the XPS instrument itself received the adventitious hydrocarbon(Al-Kandari et al, 2021). As displayed in Fig. 4a, the binding energies at 159.07 and 164.31 eV were are classified as Bi 4f_7/2 and Bi 4f_5/2 for the bulk BTO, suggesting Bi presented as trivalent oxidation state, while it was located at 158.79 eV and 164.09 eV for the AB-2, respectively(Bisht et al., 2021). The individual peaks at 26.06, 27.76 and 29.23 eV were elucidated as Ta 4f_7/2, Ta 4f_5/2 of Ta⁵⁺ and Ta 4f_5/2 of Ta⁴⁺ oxidation state (Fig. 4b), respectively(Xu et al., 2021a). The primary peak of 530.16 eV belonged to the lattice oxygen and another peak of 531.7 eV was correlated with the hydroxy oxygen of the material (Fig. 4c)(He et al, 2020). The peak of C 1s was observed at 284.9 eV (Fig. 4d) which stemmed from accidental carbon-containing compounds and was introduced as the calibrating binding energy of other elements. From the XPS spectra of Ag (Fig. 4e), the peaks located at 368.1 eV and 374.01 eV were in line with Ag 3d_5/2 and Ag 3d_3/2, which originated from Ag⁺ of AgCl and AB-2(Aletayeb et al, 2020). Likewise, Ag presented in the silver ions form with no metallic silver in the AgCl and AB-2 composite. The characteristic peaks around 198.32 and 199.63 eV were associated with Cl 2p_3/2 and Cl 2p_1/2 orbits, respectively(Fan et al, 2021). Compared with pristine AgCl and BTO, the peaks of AB-2 shifted slightly with a certain degree to higher binding energy, implying the strong interactions and the possible electron transfer between AgCl and BTO. In light of the above evidence, the electron transfer in AB-2 contributed to the heterojunction formation with built-in electric field direction between two components.

To observe clearly the morphology and structure of pure BTO, AgCl and AB-2 nanocomposite, SEM, SEM-EDS, TEM and HRTEM were investigated. In Fig. 5a, the pure phase AgCl showed the sphere-like morphology inclined to agglomerate with diameter of about 100 nm and relatively smooth surface. The SEM observation displayed that Bi₃TaO₇ consisted of staggered stacks with rough surface (Fig. 5b). Figure 5c proofed that the AgCl particles deposited on the surface of BTO nanosheets to form a substantial interaction. In addition, the energy dispersive X-ray spectroscopy (EDS) was also utilized to determine the element distributions of AB-2 (Fig. 5d-f). It was evident that each element of BC-2 material was uniformly distributed over the whole surface, identifying the successful synthesis of AgCl/Bi₃TaO₇ heterojunction. The above results were in great agreement with the result of XRD and XPS analysis, which further illustrated that the AB-2 composite was composed of AgCl and BTO.

The morphology of AB-2 was performed by TEM tests to further explore morphological features. As depicted in Fig. 6a-c, it was distinct that AgCl particles were anchored on the surface of BTO in the AB-2 composite through deposition-precipitation route. This implied that they are in intimate contact with each other, which was unanimous in SEM results. The HRTEM image of AB-2 (Fig. 6d) demonstrated the interplanar distance of 0.273 nm and 0.277 nm were gathered for BTO and AgCl, respectively, matching well with (200) plane of Bi₃TaO₇(Wang et al, 2022) and (200) plane of AgCl, separately (Liu et al, 2022b). As a result, it elucidated that the co-existed binary phases of BTO and AgCl formed an intimate interface, indicating a good interaction.

The light absorption properties of AgCl, BTO and AB composites were performed with UV–vis DRS. The band-gap energy (Eg) was measured using the following equation(Chen et al, 2022):

αhv = A(hv-Eg)^n/2 (1)

where α, hv, A, and Eg referred to the optical absorption, the photonic energy, the proportionality coefficient constant and the band gap energy of various catalysts, respectively. Thereinto, r = 2 or 1/2 for a direct or indirect band gap material(Panchal et al., 2021, Zhu et al, 2019). From Fig. 7a, BTO distinctly absorbed with wavelengths less than 400 nm in UV region, conversely, the opposite was the case with AgCl. In comparison with their composites, a stronger absorption capacity of visible light could be observed. Figure 7b depicted that the absorption edge of BTO, AgCl and AB-2 were around 2.8 eV, 3.02 eV and 2.83 eV, respectively. With the decoration of AgCl, the band gap energy of AgCl/Bi₃TaO₇ composites became gradually shrunken by compositing with pristine AgCl and BTO. Summarily, the phenomenon ravealed that the modification of AgCl extended the light absorption region by forming a binary phase heterojunction and further developed the visible light photocatalytic capacity.

It was well known that specific surface area was a momentous factor to finetune the physicochemical properties and escalate the photocatalytic performance with the modification of single material. N₂ adsorption–desorption isotherm and the pore distribution of AgCl, BTO and AB-2 composite were carried out. As illustrated in Fig. 8, BTO and AB-2 corresponded to a type IV isotherm and a type H₃ hysteresis loop, while the bulk AgCl belonged to a type of V isotherm and a type H₁ hysteresis loop, coupling with the mesoporous structure(Zhao et al, 2022). The specific surface area of AB-2 was 43.3249 m²·g^− 1, which sharply augmented by comparison with baked AgCl (1.3993 m²·g^− 1) and raw BTO (28.0337 m²·g^− 1), respectively. In addition, the pore size of AB-2 was bigger than the sole component, manifesting the superior active sites. Decent surface area and pore structure were capable to photo-degrade efficiently which donated more active sites to the target pollutant.

Photocatalytic activity for TC removal

The photocatalytic activity of resultant samples was elucidated toward TC dissociation in aqueous medium under visible light illumination with 15 mg of AgCl, BTO and AB composites, severally. On the other hand, several vital affecting factors in the photocatalytic degradation including pH and initial concentration were also investigated. Prior to the photoreaction, the adsorption-desorption equilibrium was achieved with magnetic stirring in darkness. The controlling trial was allotted to rule out the weak impact of self-degradation in TC solution simultaneously. From Fig. 9a, the TC decomposition ratio was only 36.5% and 51.4% for baked AgCl and pristine Bi₃TaO₇ under 3 h of visible-light exposure, respectively. Above all, the TC degradation rate of AgCl/Bi₃TaO₇ composites dramatically improved relative to that of raw AgCl and BTO. Among them, the optimized AgCl-Bi₃TaO₇ sample with a molar ratio of 1:5 exhibited superior degradation of TC, coming up to 86.8%, which was 1.67 and 2.38 times higher than the level of pure Bi₃TaO₇ and original AgCl. Noticeably, the photocatalytic efficiency was substantially developed with growing the content of AgCl. The eminent photocatalytic ability of AB-2 composite could be credited with the construction of heterojunction, which sped up charge separation and transportation. Whereas the excessive AgCl was loaded, the TC removal efficiency decreased marginally, resulting from the shading effect as excessive AgCl nanoparticles heaped on BTO and inhibited the absorption of light by the AB-2 composites.

As shown in Fig. 9b, the kinetic curves of TC removal over AgCl-Bi₃TaO₇ samples were simulated for further insight into the photocatalytic oxidation process. The pseudo-first-order models was employed to analyze the kinetics of TC decomposition (Cao et al, 2022b):

-ln (C_t/C₀) = kt (2)

where k was the apparent rate constants of pseudo-first-order. C₀ and C_t represented pollutant concentrations at reaction times 0 and t min. The apparent rate constants for TC degradation with AgCl, BTO, AB-1, AB-2, AB-3 and AB-4 were 0.00197, 0.00348, 0.00887, 0.00903, 0.00901 and 0.00869 min^− 1, respectively. The optimal rate constant over AB-2 was 2.59 and 4.58 times as high as relative to sole BTO and AgCl.

The value of pH were affect to TC molecules on account of the protonation-deprotonation change. Thus, the pH of TC solution made a momentous difference on the adsorption and photocatalytic capability. Typically, HNO₃ or KOH (1 M ) were added to monitor the initial pH in the TC solution. As depicted in Fig. 9c, it should be noted that there was an eminent photocatalytic performance at pH = 7, 9 and 11 as the value of pH accelerated TC molecules to adhere on the surface of AB-2. Nevertheless, the initial pH was at 3 and 5 in acidic media, the TC adsorption was restricted remarkably. Furthermore, the activity was the highest at pH = 9, resulting in a 90% TC removal efficiency with visible light.

TC initial concentration was a crucial factor to research deeply the photocatalytic performance of AB-2 as well. The degradation experiments with diverse initial concentrations of TC were conducted. From Fig. 9d, the degradation rate tend to descende gradually from 95.3–44.12% during the TC degradation process with the concentration of TC monitored in thr ranging of 10 mg L^− 1 to 50 mg L^− 1. There were a couple of factors for the decreased photocatalytic property with the increased TC concentration. On the one hand, higher initial TC concentrations made it more difficult that photons reached and acted on the surface of the catalyst and further distinctly diminished the photocatalytic efficiency. Beside that, the increase of TC concentration could inescapably cause more intermediate products, which enhanced adsorption competition between TC molecules and the intermediates(Li et al, 2022). As a consequence, lower TC concentration was more favourable to reaching a higher TC removal rate.

possible photocatalytic mechanism of TC degradation

Electrochemical impedance (EIS) was performed to validate the charge separation and migration rate of BTO, AgCl and AgCl-Bi₃TaO₇ nanoparticles. The arc radius was in accordance with the charge transfer resistance and the smaller arc radius could own higher charge transfer resistance, resulting in better separation of carriers. As illustrated in Fig. 10, AgCl/Bi₃TaO₇ composites presented much smaller radiuses of semicircle arc relating to single AgCl and BTO and the molar ratio of 1:5 exhibited the minimum radius of semicircle arc among them, confirming the highest charge separation capacity. The phenomenon was owing to the heterojunction between BTO and AgCl, which impelled the charge carriers to migrate in opposite directions and further dedicate to the photocatalytic process.

The dominant active species were ascertained through radical capture experiments for the photocatalytic reaction process that various scavengers added into the TC solution with AB-2 sample. In detail, 1 mM isopropyl alcohol (TBA) was employed for quenching ·OH, p-benzoquinone (BQ) for ·O-2, AgNO₃ for e^- and Na₂C₂O₄ (AO) for h⁺. Figure 11 explained the inhibitory effect of distinct scavengers for TC degradation over AB-2. In the existence of AgCl, TC removal was slightly declined from 86.8–81.4%, indicating that e^- produced a weak effect negligibly. Comparatively, the photo-degrading efficiency of TC prominently decreased by introducing TBA into the solution, demonstrating that ·OH impelled the action of TC degradation. Moreover, h⁺ caused the prior inhibition of TC degradation with efficiency from 86.8–44.4%, when AO was added. Furthermore, the photocatalytic performance of TC was heavily inactivated while BQ was integrated upon AB-2, hinting at the remarkedly negative effect. As a result, ·OH, ·O-2 and h⁺ had a leading effect on TC decomposition inordinately.

Additionally, the VB-XPS spectra were detected to explore the interaction between multivariant semiconductors. As displayed in Fig. 12, the VB potentials of AgCl, BTO and AB-2 were calculated as 2.94, 2.05 and 1.83 eV, separately.

The standard hydrogen electrode potential (E_VB-NHE) could be counted up by underneath formula:

E_VB-NHE = ψ + E_VB-XPS − 4.44 (3)

E_VB= E_CB + Eg (4)

where ψ represented the electron work function of the XPS analyzer, and E_VB-XPS was VB value, which was determined by VB-XPS plots(Chen et al, 2020, Li et al, 2020, Zhong et al, 2022). According to Eq. (3), the E_VB-NHE potentials of AgCl and BTO were 3.47 and 2.58 eV. Conmbining with UV-vis DRS analysis, the band gap energy (Eg) of pure AgCl and BTO were 3.02 and 2.80 eV, respectively. According to Eq. (4), the E_CB positions of baked AgCl and BTO were 0.45 and − 0.22 eV, respectively.

In light of the above experimental and theoretical research, the possible mechanism for TC dissociation upon visible light exposure was reasonably constructed and proposed in Fig. 13. Furthermore, the degrading process of TC over AgCl/Bi₃TaO₇ composite was explained in detail as below:

AgCl/Bi₃TaO₇ + hv → AgCl/Bi₃TaO₇ (h⁺) + AgCl/Bi₃TaO₇ (e⁻)

e⁻+ AgCl → AgCl (e⁻)

AgCl (e⁻) + O₂ → ·O- 2

h⁺ + Bi₃TaO₇ → Bi₃TaO₇ (h⁺)

Bi₃TaO₇ (h⁺) + H₂O/OH^- →·OH

Bi₃TaO₇ (h⁺) + ·O- 2+ ·OH →Intermediate products + H₂O + CO₂

The binary photocatalysts were excited to produce photo-generated electrons (e⁻) and holes (h⁺). After that, due to the presence of built-in electric field force, the electrons in the CB of AgCl recombined with the holes in the VB of BTO. Holes in the VB of AgCl could oxidize H₂O or OH^- into ·OH owing to its promising oxidative ability. Apart from that, electrons in the CB of BTO could reduce O₂ into ·O- 2 owing to the more positive CB potential of BTO (-0.22 eV vs. NHE) than O₂/·O- 2 potential (− 0.046 eV vs. NHE)(Guo et al, 2022). In this case, ·O- 2 could be produced during the TC degradation process and along with h⁺ and ·OH react with TC molecules. There was no difference in the analysis of the radical trapping experiments. Therefore, the novel Z-scheme heterojunction photocatalysts possessed a magnetic photocatalytic property.

A novel Z-scheme AgCl/Bi₃TaO₇ photocatalyst was initially fabricated via hydrothermal and deposition-precipitation method. By modulating the molar ratio of AgCl and Bi₃TaO₇, the optimal degradation rate reached up to 86.8% under visible light exposure, when the molar ratio of AgCl to Bi₃TaO₇ composite was 1:5. Moreover, the radical trapping measurements suggested that ·OH, ·O-2 and h⁺ took the positive effects on the photocatalytic process for TC elimination. The advanced property was mainly determined by the formation of heterojunction, which could maintain the high redox potential and impede sharply the charge recombination. This work opened up whole new vistas in the development of Z-scheme photocatalysts for residual TC removal.

Funding

This work was supported by the National Natural Science Foundation of China (51901209) for financial support.

Competing interests

The authors declare no competing interests.

Author contributions Xiaoxin Guo: Conceptualization, Methodology, Investigation, Writing – original draft. Jun Liu：Methodology, Writing – review & editing. Dan Li: Resources, Investigation, Data curation. Hongjun Cheng: Software, Methodology. Kankan Liu: Formal analysis, Supervision, Validation. Xiaoqing Liu: Conceptualization, Writing – review & editing, Supervision, Project administration. Tiansheng Liu: Writing – review & editing, Supervision, Validation.

Ethical approval and consent to participate.

We declare that we do not have human participants, human data, or human tissue involved in the study.

Consent to publish

We do not have any individual person’s data in any form.

Availability of data and materials

The data that support the findings of this study are openly available on request.

Acknowledgments This work was supported by the National Natural Science Foundation of China (51901209) for financial support.

I have not submitted my manuscript to a preprint server before submitting it to Environmental Science and Pollution Research

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Facile construction of Z-scheme AgCl/Bi3TaO7 photocatalysts for effective removal of tetracycline under visible-light irradiation

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Abstract

Figures

Introduction

Experimental

Materials and reagents

Preparation of Bi3TaO7 composite

Preparation of AgCl-Bi3TaO7 composite

Characterization of the photocatalysts

Assessment of photocatalytic performance

Radical-trapping experiment

Results And Discussion

Morphologies and structure of as-prepared photocatalysts

Photocatalytic activity for TC removal

possible photocatalytic mechanism of TC degradation

Conclusions

Declarations

References

Supplementary Files

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Journal Publication

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