Hierarchical flower-like ZnO–Ag@Cellulose composite with antifouling and antibacterial properties for efficient recovery of tellurium (IV) from wastewater

Recovery of the tellurium from wastewater is significant for both industrial applications and sustainable development due to the adverse impacts emanating from environmental pollution and strategic values in the photovoltaic industry. Herein, this study presents the recovery of tellurium from wastewater by flower-like structure ZnO−Ag@cellulose (ZAC) composite. Cellulose was first extracted from waste wood debris by an alkaline extraction process. Then, the flower-like structure of ZAC composite was synthesized by a facile one-step hydrothermal method. The obtained materials were conducted under different parameters to investigate tellurium adsorption properties. Thermodynamic and kinetic results indicate that the adsorption process of tellurium is dominated by monolayer exothermic chemisorption. Besides, as-prepared ZAC exhibited excellent performance for tellurium elimination from wastewater with superior removal efficiency of 98.86%. ZAC also shows outstanding antifouling performance in polluted environments, and still achieves 94.23% adsorption efficiency for tellurium. Moreover, the ZAC composite reveals high reusability and stability after six desorption-regeneration cycles. Importantly, the ZAC composite exhibits disinfection performance against E. coli and S. aureus. Therefore, this work not only demonstrates that ZAC composite is an efficient adsorbent with antifouling and antibacterial ability, but also provides an effective channel for wastewater decontamination and practical application as a promising candidate.

Besides, as-prepared ZAC exhibited excellent performance for tellurium elimination from wastewater with superior removal efficiency of 98.86%. ZAC also shows outstanding antifouling performance in polluted environments, and still achieves 94.23% adsorption efficiency for tellurium. Moreover, the ZAC composite reveals high reusability and stability after six desorption-regeneration cycles. Importantly, the ZAC composite exhibits disinfection performance against E. coli and S. aureus. Therefore, this work not only demonstrates that ZAC composite is an efficient adsorbent with antifouling and antibacterial ability, but also provides an effective channel for wastewater decontamination and practical application as a promising candidate.

Introduction
Tellurium as a strategic resource has become a major public concern due to its high commercial and industrial value (Liu et al. 2021). Simultaneously, tellurium as a p-type semiconductor has remarkable thermal conductivity and exhibits extensive industrial application prospect, especially in photovoltaic (Curtin et al. 2020), metallurgy (Li et al. 2021), electrical , glass (Machado and Pereira da Silva 2020), and ceramic industry. However, the extensive use of tellurium-containing materials has engendered a large amount of toxic tellurium-containing wastewater, resulting in severe environmental pollution and destruction of the ecological balance. The bigger challenge is to address its long-term impact (Missen et al. 2020). With the increase in environmental awareness, how to treat tellurium-containing wastewater is an extensive attention problem in industrial development. For instance, the arbitrary discharge may cause tellurium-containing wastewater to enter the groundwater system and accumulate in the food chain, making it difficult to biodegrade (Bullock et al. 2018). Additionally, metal smelting and coal combustion have resulted in tellurium (IV) levels in industrial wastewater and groundwater exceeding the stipulated standards and posing a severe threat to human life . Therefore, the recovery of tellurium from wastewater is of great importance for both industrial applications and sustainable development owing to the adverse impact of environmental pollution and the strategic value of the photovoltaic industry.
Currently, several separation purification methods have been proposed to treat tellurium in wastewater, such as ion exchange, solvent extraction (Narimani-Sabegh and Noroozian 2019), membrane separation (Mudhoo et al. 2019), adsorption Wu et al 2021), and biological treatment processes (Ramos-Ruiz et al. 2016). Among the above methods, adsorption technology in the removal of tellurium from wastewater exhibits many advantages, including high efficiency, simple operation, versatility, and environmental friendliness ). Thence, a variety of nanomaterials, TiO 2 , ZrO 2 , NZVFe, and MnO 2 , have been prepared and adopted to remove tellurium in wastewater, which have high adsorption activities and large surface functional groups towards the adsorption tellurium processes (Wan et al. 2020).
For instance, Wu et al. fabricated porous 3D zirconia microspheres as an efficient adsorbent for tellurium removal (Wu et al. 2019). NZVFe was utilized to adsorb tellurium and exhibited outstanding adsorption capacity (Yu et al. 2018). However, the aggregation problem of powder materials limits their reusability and removal efficiency in aqueous solutions, and also hinders their practical application and further development in the field of adsorption. To overcome the drawbacks of aggregation, Yu et al. presented strategies in powder materials aggregation problem using CNTs as substrate synthesized NZVI/ACNTs showed excellent promising in the recovery of tellurium (Yu et al. 2019). But it still suffers from some issues such as low stability, complex preparation process, environmental issue, poor antifouling, and antibacterial capability. Therefore, the adsorption performance of composite materials is still a challenge, and it is imperative to develop environmentally friendly, efficient and antibacterial tellurium removal adsorbents.
Recently, ZnO has an excellent performance in purifying organic and inorganic pollutants from wastewater, such as removing arsenic (Sharma et al. 2019b), chromium (Sharma et al. 2019a), and dyes . These behaviors may be derived from the high adsorption efficiency, antimicrobial capacity (Bhutiya et al. 2018), and chemical stability of ZnO, making it exhibit remarkable adsorption capacity for the elimination of various contaminants from wastewater. But it is worth noting that the ZnO is also a powder material, which is difficult to actual production application in wastewater. Meanwhile, support materials have been evaluated as significant components that can avoid the aggregation and improve the dispersion of materials . Cellulose, as a renewable support material with outstanding performance in wastewater treatment, has attracted vast attention because of its distinct physical, chemical properties and being environmentally friendly (Wang et al. 2020b). Additionally, as one of the most abundant substances globally, cellulose has non-toxic, chemical compatibility, low density, superior mechanical properties, and high aspect ratio. To enhance the surface properties of the support materials, many researchers have attempted to develop cellulose composites with relative low cost and high adsorption capacity. For instance, Zhang and coworkers prepared a layered mesoporous nano-TiO 2 /cellulose composite material by microwave-assisted method for rapid adsorption of Pb 2? in wastewater (Zhang et al. 2017), but the application of composite material has been restricted by the inherent interaction of cellulose with proteins, bacteria, and other foulants, which seriously damage the adsorbent and affect the ability of the adsorbent (Fakhre and Ibrahim 2018). Based on the above defects, Phan et al. successfully fabricated ZnO-HT-PAN, indicating that the ZnO nanoparticles attached to nanofibers can improve the antibacterial ability . However, the antibacterial ability of only the ZnO is limited in practical applications. Thence, Huang et al. synthesized Ag@ZnO-OAc NPs, in which Ag@ZnO enhanced the antibacterial performance of composite membranes (Huang et al. 2020). Moreover, Dumée et al. prepared a biofouling membrane material that employed a novel cold spray technique to embed silver nanoparticles in the membrane to reduce biological contamination and bacteria for the purpose of purifying wastewater, indicating that silver nanoparticles are promising for biofouling and antibacterial purposes (Dumée et al. 2015). To our best knowledge, there was little research on ZnO-Ag composite with antifouling and antibacterial capabilities for adsorption tellurium in wastewater. Besides, understanding of interface characteristics between nanomaterials and cellulose is essential to enhance the adsorption properties.
In this work, a cost-effective and eco-friendly composite was prepared by a facile one-step hydrothermal method. To obtain a high-efficiency adsorbent for tellurium with antifouling and antibacterial capabilities, ZnO and Ag were introduced into the surface of cellulose as critical substances for treating wastewater. Furthermore, ZAC has more hydroxyl groups on the surface, which helps achieve the purpose of adsorbing tellurium. This study also discussed the kinetics, interfering ions, and thermodynamics in the tellurium adsorption process to have a deeper understanding of the adsorption mechanism, thermodynamics, and kinetics. Significantly, the antifouling and antibacterial experiments of ZAC were performed with bovine serum albumin, E. coli, and S. aureus, respectively. This work provides a novel orientation for adsorbing tellurium with antifouling and antibacterial capabilities from wastewater, not only for the valorization of waste cellulose resources but also for large-scale elimination of toxic ions in industrial wastewater.

Cellulose extraction
Cellulose was extracted from waste wood debris by an alkaline extraction process. Typically, 30 g of wood debris was washed several times with deionized water, ethanol and dried in an oven at 80°C overnight. Then, 15 g of pre-treated wood debris was dispersed in 100 mL of 5% sodium hydroxide solution and stirred at 80°C for 6 h to remove lignin and hemicellulose of wood debris. The suspension was further filtered and washed through deionized water until the pH reached neutral. Subsequently, the crude cellulose was bleached in a 5 wt% (pH = 4) sodium chlorite under magnetic stirring at 80°C for 6 h. Finally, the cellulose was obtained by filtration and washed several times with deionized water and dried at 80°C for 6 h.

Preparation of ZAC composite
The ZAC with flower-like structures were prepared by a facile one-step hydrothermal method. In a typical experiment, 0.29 g zinc nitrate hexahydrate, 5.5 g cellulose, and 0.167 g silver nitrate were dissolved in 85 mL of deionized water and stirred magnetically at room temperature for 2 h. Then, the reaction system was sonicated at 60 kHz for 30 min. After that, a certain amount of ammonia water was slowly dropped into the above-mixed solution at a rate of 10 drops/min until the pH of the solution was 9, and transferred to a Teflon stainless steel autoclave for hydrothermal synthesis at 130°C for 8 h. Finally, the product obtained was collected by centrifugation and filtration, washed several times with distilled water and ethanol, and then dried at 70°C for 15 h under vacuum condition and sealed. The preparation process of ZAC was illustrated in Scheme 1.

Characterization
The morphology of ZAC was investigated by scanning electron microscopy (SEM FEI, Quanta 200, USA), and the content of elements was measured by energydispersive X-ray spectroscopy (EDS, JEM-2100). The crystal structures of ZAC hybrid nanoparticles were analyzed by X-ray diffraction (XRD, JEOL JDX-3530, Tokyo, Japan) with Cu Ka radiation with a scanning speed of 4°/min in the 2h range from 10°to 80°. The functional groups on the surface of the sample were analyzed by Fourier Transform Infrared (FT-IR) spectrophotometer (Thermo Nicolet, NEXUS, TM) in the range of 400-4000 cm -1 . The surface element composition and chemical valences of ZAC before and after tellurium adsorption were analyzed by X-ray photoelectron spectroscopy (XPS) on Thermo ESCALAB 250 XI. Inductively coupled plasma optical emission spectrometry (ICP-OES, Perkin-Elmer Optima 2100DV) was used to measure the tellurium content in the solution after adsorption.

Batch adsorption experiment
To investigate the tellurium adsorption properties of ZAC composites, the batch experiments were conducted under different conditions. For tellurium adsorption, 1 g/L tellurium solution was prepared as a stock solution for different concentrations of adsorption experiments. In the batch experiment, thermodynamics, kinetics, adsorbent dosage, pH, and interfering ions were also investigated. Moreover, the experiments were carried out under the conditions: adsorption dose of 30 mg, the pH was adjusted with 0.1 mol/L sodium hydroxide and hydrochloric acid, the temperature of 25°C , and the adsorption time was 6 h. After adsorption under certain conditions, centrifuge at 10,000 rpm for 15 min to separate the solid/liquid phase. Finally, the supernatant was filtered, and the concentration of tellurium in the solution was measured by ICP-OES.
where C i and C e represent the initial concentration and equilibrium concentration of TeO 3 2in solution (mg/ L), respectively, V is the volume of solution (mL), and m is the mass of adsorbent (mg).

Antifouling experiment
During the antifouling experiments, bovine serum albumin (BSA) solution was employed to simulate protein contamination of the adsorbent surface. The adsorption capacity of the initial adsorbent was firstly explored. Then the adsorption capacity after BSA fouling was investigated to compare its adsorption capacity for exploring the antifouling performance of the adsorbent. In a typical process, BSA (5.0 g) was dissolved in 50 mL of phosphate-buffered saline (PBS), and then ZAC was added to the BSA/PBS solution and soaked for 24 h to be well contaminated. Thereafter, the adsorbent was washed with distilled water and then applied for tellurium adsorption experiments.

Antibacterial activity tests
Two classic bacteria, Escherichia coli (E. coli, ATCC 25,922) and Staphylococcus aureus (S. aureus, CMCC(B) 26003), were the representative model microorganisms to investigate the antibacterial performance of ZAC by viable plate counting technique. The E. coli and S. aureus were cultured in a biochemical incubator at 37°C for 24 h, the concentrations of E. coli and S. aureus were adjusted to 10 8 CFU/mL with the PBS solution, and then diluted a certain number of times and transferred to agar culture medium to form approximately 300-500 colonies. Subsequently, the ZAC (20 mg) was mixed with 10 mL of deionized water by ultrasonic dispersion for 30 min, and then took 1 mL of the above solution to add to the agar medium. Finally, the above mixture was placed in an agar medium and incubated in a biochemical incubator for 24 h. The growth of bacteria was observed, and the number of surviving bacteria colonies was counted to explore the antibacterial properties of the samples.
Scheme 1 Schematic diagram of the manufacture of ZAC composite materials and adsorption process

Structure and morphology
The microstructure and surface morphology of ZnO@cellulose (ZC) and ZAC was detected by SEM, and the comparison of ZC can provide a better understanding of the adsorption performance of ZAC. From Fig. 1A, it can be seen that the flower-like structure of zinc oxide has an irregular morphology on the cellulose surface. Meanwhile, the inset of Fig. 1A shows that the flower-like microstructure about 6.0 lm in diameter. Besides, the mapping images confirmed that C, O, and Zn were successfully loaded. Compared with the ZC, when the silver nanoparticles are successfully deposited on the fiber surface, ZAC exhibits fiber morphology with the coarse texture (Fig. 1B). The presence of silver will increase the roughness (inset in Fig. 1B) and antimicrobial capacity of ZAC, which is in agreement with the results of previous works (Trang et al. 2020). Additionally, the mapping research demonstrates that C, O, Zn, and Ag were evenly dispersed on the surface of the biomass fiber. After adsorption of tellurium, the morphology of ZAC was significantly changed from a rough structure to a smooth planar structure (Seen in Fig. S1), and the gaps of the particles were filled, which may be attributed to successful adsorption of tellurium from the wastewater.
To further illustrate the composition, EDS was used to analyze the element distribution onto ZAC. As shown in Fig. 1C, the EDS research reveals that four elements (C, O, Zn, and Ag) are uniformly distributed in the flower-like structure. The C atomic content is calculated to be about 38.25 at%. Ag element is also calculated with the content of 5.92 at%. Besides, the content of O and Zn elements in the composites reached 33.54 and 22.29 at%, respectively, implying that the ZAC surface has abundant hydroxyl functional groups, which are favorable for the adsorption of tellurium in wastewater. Furthermore, after adsorption of tellurium (Seen in Fig. S2), the EDS results indicated that the presence of elemental Te in the ZAC surface, which confirmed that the adsorption of tellurium on the ZAC surface.
Moreover, the crystal structures of ZC and ZAC were analyzed by XRD, and the results are shown in Fig. 1D. Figure 1D(a) exhibits that the intensity of the characteristic peak located at 22.5°(200) reveals that the cellulose is relatively pure and without impurity peaks, consistent with the previously reported results (French. 2014;Tang et al. 2020). As shown in Fig. 1D(b) (111), (200) and (220) planes of Ag (JCPDS Card No.04-0783) (Wei et al. 2018). Importantly, as illustrated in Fig. S3, the intensity of the ZAC peak changed significantly after tellurium adsorption, which might be attributed to the presence of tellurium masking its intensity.

Adsorption mechanism
To understand the adsorption mechanism, the FT-IR of ZAC before and after adsorption of tellurium was carried out, and the results are shown in Fig. 2A. Figure 2A(a) displays that the peaks at about 500 cm -1 correspond to the bonds of Zn-O and Ag-O, demonstrating that the ZAC composite was successfully prepared (Zare et al. 2019). Moreover, the peak at 1350 cm -1 was attributed to the bending vibration of Zn-OH and the peak at 3370 cm -1 was consistent with the stretching vibration of -OH on the surface of ZAC . This result indicates that the surface of ZAC is rich in a hydroxyl group, which may contribute to enhance the tellurium adsorption capacity. Compared with the spectrum in Fig. 2A(a), (b) shows that the FT-IR spectrum has significantly changed with a new peak appear near 480 cm -1 , which is attributed to the vibration of the Te-O bond, confirming that the tellurium was successfully adsorbed on ZAC surface (Pang et al. 2020). Most importantly, the peak of the hydroxyl group is decreased significantly after the adsorption of tellurium, revealing that the hydroxyl group on ZAC surface participated in tellurium adsorption. Therefore, the possible mechanism for ZAC to adsorb tellurium is by ligand exchange between the hydroxyl groups and tellurium ions. Furthermore, the adsorption mechanism can be further confirmed by XPS.
To better investigate the adsorption mechanism between the ZAC and tellurium, XPS was performed on the ZAC before and after tellurium adsorption. Figure 2B(a) reveals the XPS full survey spectrum of O1s, Zn2p, and Ag3d about ZAC composite material before adsorption tellurium, indicating the required composite material has been prepared. Compared with the virgin ZAC, the Te3d peak appeared (Fig. 2B(b)) at a binding energy of 576.18 eV and 586.25 eV after adsorption tellurium; these peaks demonstrate that ZAC can adsorb tellurium from wastewater (Yue et al. 2019). Besides, the spectrum of O1s was divided into two peaks at binding energy of 530.55 eV and 532.61 eV ( Fig. 2C(a)), which were ascribed to the oxygen bonded to metal (Zn-O) and hydroxyl bonded to metal (Zn-OH), respectively (Bhattacharyya and Gedanken 2008). This result shows that the surface of ZAC is rich in -OH, which is consistent with infrared spectroscopy analysis results. It is notable that the peak area changed significantly before and after the adsorption of tellurium, and the peak area ratio of Zn-O increased ( Fig. 2C(b)), while the peak area ratio of Zn-OH decreased significantly, which is probably due to the formation of new bonds such as the Te-O bond, indicating the participation of the -OH group in the adsorption process of tellurium. It indicates that the adsorption of tellurium by ZAC may be attributed to the ion exchange between TeO 3 2and -OH, which is in agreement with the FT-IR results. From Fig. 2D(a), the spectrum of Zn2p before adsorption tellurium, the binding energies of 1044.72 eV and 1021.39 eV were assigned to the Zn2p 1/2 and Zn2p 3/2 , respectively (Wang et al. 2020a). The difference in binding energy between them is 23 eV, indicating that this is the standard reference value for ZnO (He et al. 2019). Besides, the peak area ratio of Zn2p decreased ( Fig. 2D(b)), further confirmed the Zn2p participated in the tellurium adsorption process. In Fig. 2E(a), the two peaks of binding energies at 367.61 eV and 373.52 eV, which are attributed to Ag3d 5/2 and Ag3d 3/2 , respectively (Liao et al. 2018). By comparing the Ag peak area ratio of ZAC before adsorption of tellurium, there is a very distinct decrease in Fig. 2E(b), which may be attributed to the formation of chelate between Ag and tellurium, resulting in a decrease in its intensity. Figure 2F shows the spectrum of Te3d after adsorption tellurium, the peaks appeared at 576.18 eV and 586.25 eV corresponded to Te3d 5/2 and Te3d 3/2 , which further demonstrates the successful adsorption of tellurium by ZAC (Trawiński et al. 2020). Therefore, the above results are consistent with FT-IR results, confirming that the contaminant tellurium elimination is ascribed to the -OH, which reveals the domination of adsorption mechanism is ion exchange between TeO 3 2and the -OH on ZAC. Meanwhile, a schematic illustration of the adsorption process was provided in Scheme 2.

Adsorption isotherms and adsorption kinetics
The equilibrium concentration can well describe the relationship between adsorbent and the concentration of tellurium in wastewater at different temperatures. Hence, the static adsorption experiments of ZAC and ZC at different concentrations (the initial concentrations were 10-100 mg/L, the temperature were at 298.15 K, 308.15 K, and 333.15 K, respectively) were carried out, and fitting results were fitted by Langmuir isotherm and Freundlich isotherm (The form of these models is shown Table S1), which are shown in Fig. 3. Figure 3a shows that ZC is better fitted by Langmuir isotherm (R 2 = 0.996, 0.995, and 0.993) compared to Freundlich isotherm (R 2 = 0.937, 0.958, and 0.947), indicating that the process of adsorbing tellurium is dominated by monolayer adsorption. The removal efficiency of ZC decreases with increasing temperature, suggesting that this adsorption process is an exothermic reaction (Jin et al. 2020). Moreover, compared to the adsorbents of ZC, Fig. 3d reveals that ZAC has outstanding adsorption capacity for tellurium with good Langmuir linear fit coefficients (R 2 = 0.997, 0.998, and 0.995), implying that ZAC has superior potential for tellurium adsorption, which may be ascribed to the formation of chelates that enhance the adsorption performance of ZAC. Another interesting result indicates that the adsorption capacity of ZAC increases with decreasing temperature (from 333.15 k to 298.15 k), which suggests that ZAC adsorbents may be more suitable for operation and application under relatively low temperatures.
To further investigate the performance of tellurium and the rate-limiting step in the adsorption process, pseudo-first-order and pseudo-second-order simulations were performed (kinetic model is shown in Fig. 2 The FT-IR spectra of ZAC composites A; XPS spectra of ZAC before and after adsorption tellurium: B ZAC composites, C O1s, D Zn2p, E Ag3d, F Te3d (a before adsorption, b after adsorption) Table S1). Figure 3B illustrates the pseudo-first-order results for ZC with correlation coefficients (R 2 ) of only 0.817, 0.878 and 0.782, respectively. The pseudosecond-order of ZC (Fig. 3C) with a high correlation coefficient (R 2 = 0.994, 0.986, and 0.996) at three different temperatures (298.15 K, 308.15 K, and 333.15 K), illustrating that the interaction of tellurium and adsorption sites is chemical action. Figure 3E reveals the pseudo-first-order mode results of ZAC with correlation coefficients of 0.967, 0.878, and 0.782 for 298.15, 308.15, and 333.15 K, which suggest that the process of adsorption tellurium is not proper for the physical adsorption process on the ZAC surface. Furthermore, compare with Fig. 3E, the pseudosecond-order model (Fig. 3F) describes the kinetics of tellurium adsorption onto ZAC gave a higher correlation coefficient (R 2 = 0.997, 0.999, and 0.998), demonstrating that the adsorption of tellurium is mostly governed by chemical adsorption in wastewater.
To further investigate the thermodynamic properties of the adsorption process, the adsorption of Scheme 2 Schematic diagram of tellurium adsorption process  Table S2 revealed that DG \ 0 at three different temperatures, indicating that the adsorption process is a spontaneous process and without the need to obtain energy from the outside. Meanwhile, the absolute value of DG decreased as the temperature increased, suggesting that the adsorption process is an exothermic process and can be completed spontaneously at low temperatures, which contributes to the application of ZAC adsorbent at room temperature.

Adsorption studies
To investigate the surface charge change of ZAC, the zeta potential was measured at different pH values, which have a critical impact on the stability of liquid dispersions. As shown in Fig. 4A, the zeta potential of ZAC decreases with the increase of pH, exhibiting that the surface property of ZAC is negative at pH 2-11. The potential of ZAC was greater than that of ZC over the entire pH range, indicating that the presence of silver contributed to increase its zeta potential. In addition, the pH plays a significant effect on tellurium adsorption performance. Figure 4B shows that the adsorption capacity of ZC and ZAC are firmly dependent on different pH. The removal efficiency of ZC was observed to increase from 78.12% to 82.34% with the increase of pH in the range of 2-6. However, the tellurium adsorption performance of ZAC reached a maximum removal efficiency of 98.86%, which may be due to the protonation and the presence of functional groups on ZAC surface, leading to the improved availability adsorption sites and increased tellurium interactions, resulting in the excellent tellurium adsorption capacity. Moreover, the adsorption capacity of ZC and ZAC decreases sharply with increasing pH (pH value 7-11), which would be attributed to deprotonation and the predominance of negative charges on the ZAC surface. Meanwhile, it should be noted that tellurium mainly exists in the form of TeO 3 2and HTeO 3under acidic and alkaline conditions, respectively. The zeta potential of ZAC is always negative at pH 2-11, making the repulsive force increase between ZAC and the target of tellurium. Therefore, the results indicate that ZAC has outstanding removal efficiency for tellurium under a weak acid environment.
To evaluate the selectivity of ZAC for application in real wastewater, some ions (CO 3 2-, SO 4 2-, Cland NO 3 -) are usually present in tellurium-containing wastewater, which have a significant effect on the adsorption efficiency. As shown in Fig. 5A, similar results were found on ZC and ZAC, that the presence of the NO 3 -, Cland SO 4 2had an unnoticeable effect on the tellurium adsorption, suggesting that the ZAC possess a good selectivity for tellurium in a complex environment. However, when CO 3 2was present, the removal rate of tellurium by ZAC decreased to 72%, indicating that tellurium adsorption on ZAC surface was restrained by CO 3 2-, which can be attributed to the competition with tellurium for the active sites in ZAC, leading to the poor adsorption capability. On the other hand, studies from the effect of pH indicate the alkaline conditions inhibit tellurium adsorption. Another explanation may be associated with the hydrolysis of carbonate, making the solution to be alkaline. This has been reported by other researchers to have a similar suppression effect on the presence of coexisting anions . The regeneration ability of the adsorbent is crucial for evaluating the industrial application and economics; the adsorbent ZAC was investigated by adsorption and desorption processes. In this work, the adsorbed tellurium can be eluted from the ZAC surface with NaOH solution (0.5 M) as the desorption agent. Figure 5B reveals that the regeneration of adsorbent decreased gradually with the cycle time increased. After three regeneration cycles, the removal efficiencies of ZAC and ZC adsorbents were maintained at 88.6% and 73.6%, respectively. The decrease in adsorption efficiency may be due to the destruction of the active sites on the surface of ZAC. Moreover, ZAC exhibits excellent performance than previously reported (Table S3), indicating that ZAC has considerable potential for application in wastewater treatment. Meanwhile, the ZAC can still maintain high adsorption capacity in six desorption-regeneration cycles, and the tellurium removal efficiency was still 72.1%; this phenomenon is because of the reduction of available active sites onto ZAC. In addition, another reason was attributed to the low desorption rate with increase cycles, resulting in lower removal capacities for tellurium. It is also noticeable that the adsorbent has good stability. As seen in Fig. S4, the maximum concentration of zinc was 0.27 mg/L in the 700-min stability experiment, which was much lower than the required 1.0 mg/L in drinking water, and the maximum concentration of silver was 0.24 mg/L, which was probably attributed to the incomplete reaction and partial shedding of silver, but its concentration was in an equilibrium state. The above results demonstrated the excellent cycling stability performance of ZAC and further confirmed that it meets the requirement of adsorption regeneration capacity. Figure 5C exhibits the effect of adsorbent dosage on the tellurium adsorption process. The results revealed that the removal efficiency of tellurium (IV) increased from 71.23% to 83.46% when the ZC dosage was increased from 5 to 35 mg and then maintained at 35-50 mg. Importantly, compared to ZC dosage, the removal efficiency of ZAC reaches a maximum value of 98.86% when the adsorbent dosage increased from 5 to 30 mg and eventually reaches equilibrium. As the amount of adsorbent increased, more active sites were available on the ZAC surface, resulting in more tellurium being adsorbed on the ZAC surface and improving the removal efficiency. However, the adsorbent dosage increased from 30 to 50 mg, while the removal efficiency of tellurium did not change much, which may be limited by the content of tellurium. More importantly, the removal efficiency of ZAC for tellurium was higher than that of ZC over the whole dosage range, implying that the adsorption capacity for tellurium could be improved by introducing Ag on ZC. Therefore, the high removal efficiency of ZAC demonstrated that ZAC could be considered as a promising material for adsorption of telluriumcontaining wastewater and purification of sewage. Figure 5D shows the tellurium removal efficiency of ZC and ZAC at different initial concentrations. The maximum removal efficiency only 78.80% is obtained by ZC at a concentration of 20 mg/L, indicating that ZC has low removal efficiency on tellurium and is not suitable for adsorption application. However, even if the tellurium concentration rises to 40 mg/L, the removal efficiency of tellurium can still maintain a maximum removal efficiency of 98.86%. The outstanding adsorption efficiency of ZAC for tellurium elimination results from the interaction between ZAC and tellurium, which shows the stronger ion exchange capacity of ZAC. In addition, either ZC or ZAC adsorption tellurium, a similar tendency can be observed in the range of 40-100 mg/L, and the value of tellurium adsorption on ZC and ZAC decreased. When the concentration of tellurium is below 40 mg/ L, the removal efficiency of tellurium is dominated by -OH, whereas tellurium plays an increasingly dominant role in the adsorption process when the concentration of tellurium is from 40 to 100 mg/L, which can well explain why the removal efficiency of tellurium decreases as the concentration increases, implying that this is the presence of a trade-off between the removal efficiency and the concentration of tellurium in the adsorption process. Therefore, the above data confirms that the ZAC has excellent adsorption efficiency at a certain tellurium concentration.

Antifouling property
In general, the presence of macromolecules, biological substances, salts, and particulate substances in wastewater seriously affects the adsorption capacity of adsorbent and limit its practical application in industry. In this work, BSA was selected as the contamination model because of the strong adhesion of proteins on the adsorbent surface. As illustrated in Fig. 6, it is noticeable that the tellurium removal efficiency of ZC maximum is only 77.56% as the adsorbent dosage from 5 to 50 mg, compared to the uncontaminated ZC (83.46%), which gets a low removal efficiency, confirming that the BSA affects the adsorption capacity of ZC. However, ZAC still has Fig. 6 Antifouling performances of ZC and ZAC under different adsorbent dosage strong removal efficiency for tellurium, and the maximum removal efficiency can still reach 94.23%, indicating that ZAC has excellent antifouling properties. BSA can affect the adsorption capacity of adsorbents by destroying the adsorbent surface. Meanwhile, the apparent difference in antifouling performance between ZC and ZAC may be associated with the disparate surface chemical material. These results suggest that the presence of Ag may have a strong hydration capacity, which was attributed to the hydroxyl group that may create a large hydrophilic repulsive force as a barrier between the contaminant and ZAC, contributing to the detachment of the contaminant, revealing that the introduction of Ag improved the antifouling properties of the material. On the other hand, the BSA zeta potential is -3.88 mV (Abdel-Karim et al. 2021); the zeta potential of ZAC is also negative, which will increase the surface of repulsion between the contaminants and ZAC surface and obstruct the contaminants adsorbed on the ZAC surface. Therefore, the antifouling results demonstrate clearly that the ZAC exhibits remarkable removal efficiency for tellurium and can be used in practical applications.

Antibacterial activity
The antibacterial performance of ZC and ZAC was investigated by viable plate counting technique against E. coli and S. aureus, which can be as an intuitive means to detect the antibacterial ability and to obtain the survival from the culture plate . As illustrated in Fig. 7a, the dense bacterial colonies survive as small white dots on the culture plate for the blank control. Compared to blank control, it can be found from Fig. 7B that the reduction in survival colonies in E. coli, suggesting that ZC has a certain sterilization ability. However, in Fig. 7c, the colony count of E. coli decreased sharply, which implies that ZAC has strong bactericidal performance against the same bacteria (E. coli), confirming that the introduction of Ag can improve the antibacterial ability (Umapathi et al. 2019). Figure 7d shows that the S. aureus grows well in the blank control. According to Fig. 7e, the slight inhibition effect suggests that ZC has lower biocide ability. Importantly, in Fig. 7f, few surviving bacterial colonies were found, this result indicates that the excellent antibacterial performance of ZAC is derived from the Fig. 7 Antibacterial properties of adsorbent against E. coli: a blank control, b ZC, c ZAC, Antibacterial properties of adsorbent against S. aureus: d blank control, e ZC, f ZAC introduction of silver on the ZC surface. Therefore, the above results revealed that ZAC not only had good efficiency in removing tellurium from wastewater, but also had powerful antibacterial ability against E. coli and S. aureus.

Conclusions
In this work, flower-like structured ZAC composite has been successfully synthesized by a facile hydrothermal method with outstanding adsorption capacity, reusability, antifouling, and antibacterial ability for tellurium adsorption. The maximum removal efficiency of the fabricated ZAC for tellurium was 98.86%. The antifouling experiment exhibits that ZAC has strong removal efficiency for tellurium and the maximum value can still reach 94.23%. Besides, the ZAC fits well with the Langmuir and Pseudosecond-order kinetic model, revealing that the adsorption process is a monolayer chemisorption process. The coexisting ion adsorption data indicates that ZAC has excellent selectivity for tellurium. Furthermore, ZAC also exhibits excellent reusability, with a removal efficiency of 72.1% after six desorptionregeneration cycles. Importantly, the antibacterial activity demonstrates that ZAC has outstanding antibacterial properties against E. coli and S. aureus, which might be attributed to the introduction of Ag on the ZC surface. Therefore, the above results indicate that ZAC has outstanding adsorption properties, antifouling and antibacterial abilities and is considered as an environmentally friendly and promising adsorbent material for wastewater treatment.