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Article

Fabrication of Silver-Doped UiO-66-NH2 and Characterization of Antibacterial Materials

by
Feng Tian
1,
Rengui Weng
1,*,
Xin Huang
1,
Guohong Chen
1 and
Zhitao Huang
2
1
College of Ecological Environment and Urban Construction, Fujian University of Technology, Fuzhou 350118, China
2
Sunstar Membrane Technology (Xiamen) Co., Ltd., Xiamen 361000, China
*
Author to whom correspondence should be addressed.
Coatings 2022, 12(12), 1939; https://doi.org/10.3390/coatings12121939
Submission received: 21 October 2022 / Revised: 22 November 2022 / Accepted: 8 December 2022 / Published: 9 December 2022
(This article belongs to the Special Issue New Developments of Protective Coatings, Organic Polymers, and Surface Analysis)
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Abstract

:
Metal-organic frameworks (MOFs) are highly crystalline inorganic-organic complexes formed from metal ions or metal clusters and multi-toothed organic ligands. MOFs have great potential for use in antibacterial materials in the biological, environmental, and food antimicrobial fields. They can act as a reservoir of metal ions, releasing them gradually and leading to a sustained antibacterial effect analogous to that proposed for metal oxide nanoparticles (NPs). Herein, UiO-66-NH2 as a type of MOF was first prepared by a facile solvothermal method and then loaded with Ag NPs to form a Ag/UiO-66-NH2 composite and the different materials were synthesized by controlling silver doping amount, which are then applied to an antibacterial test. Works on the synthesis of Ag/UiO-66-NH2 and its antibacterial test were not reported before. The synthesized materials were characterized using the field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), thermal gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) techniques. The antibacterial activity of the Ag/UiO-66-NH2 was then assessed against E. coli (gram-negative bacteria) and Staphylococcus aureus (gram-positive bacteria), using the inhibition zone (ZIO) method and optical density (OD) method. The obtained results have shown that the introduction of Ag does not interfere with the crystallization of UiO-66-NH2. The FT-IR spectral profiles recorded for the UiO-66-NH2 samples fabricated under conditions of varying silver ion doping levels are similar to those recorded for UiO-66-NH2. The thermal stability of UiO-66-NH2 containing varying amounts of silver ions was lower than the thermal stability of UiO-66-NH2. However, under these conditions, the specific surface area and pore volume increased. The antibacterial performance of UiO-66-NH2 improved significantly following the process of silver ion doping. The best antibacterial performance was observed when the silver ion content was 4 wt.%. Overall, we synthesized a new nanocomposite material with broad-spectrum bacterial sterilization, which was easy to manufacture.

1. Introduction

While the discovery and development of antibiotics undoubtedly provides effective ways to combat pathogens, the overuse of antibiotics leads to antimicrobial resistance [1,2,3]. Antibiotic resistance can develop through various mechanisms, including altering an antibiotic’s target site or metabolic pathway, reducing the drug’s accumulation in a cell, or inactivating it [4,5]. To this end, a new approach is required and there is an urgent need to develop effective antimicrobial materials. Both metal oxide nanoparticles (NPs) and metal-organic frameworks (MOFs) have shown remarkable antibacterial activity. Silver NPs (Ag NPs) are the most commonly applied in industry because of their unique biocidal features. The synthesis of Ag NPs is an important aspect of nanotechnology [6,7,8]. There are a wide variety of synthesis approaches because the physical, chemical, and biological properties are intensely dependent on the synthetic method. Generally, there are three different categories on synthesizing Ag NPs, which are chemical, physical, and biological methods. The most common and widely reported synthesis method of Ag NPs is chemical reduction. Physical methods are generally fast and do not contain toxic or harmful chemicals. Nonetheless, the shortcoming of these methods is the high energy consumption required during the synthesis process [6,7,9,10,11,12,13,14,15,16]. Among nanomaterials with porous structures, MOFs appear promising because their active centers are an intrinsic part of the molecular structure, similar to those in NPs. Such centers are stabilized by forming chemical bonds which are extraordinarily strong to stabilize their form, but do not block their activity [17,18,19]. Producing Ag NPs without employing toxic reducing agents require biological methods, which are famous as green synthesis approaches [4,10,14]. Despite the benefits of green biological synthesis, controlling the polydispersity of NPs is a significant challenge. As a result, many strategies have been used to overcome these problems, among which immobilization of Ag NPs on different matrices has proven to be a more desired approach. MOFs as porous inorganic hybrids have usually been applied as models for the immobilization of metal oxide NPs [20,21,22].
MOFs are synthesized following the hydrothermal, solvothermal, solvent-free, and chemical vapor deposition methods, among which the simplest and most widely used method is hydrothermal synthesis [23,24,25]. MOFs are highly crystalline inorganic-organic complexes formed from metal ions or metal clusters and multi-toothed organic ligands [26,27]. MOFs have ultrahigh surface areas, porous structures, and most importantly, easy and uniform metal doping [28,29,30,31]. During the synthesis of MOFs, the site for metals can be replaced according to the need. A variety of metal ions, such as Cu2+, Zn2+, Ag+, and Co2+ are easily loaded on MOFs, and most of them can act as chemical antibacterial agents [32]. Among all of the metal ions, the silver ion exhibits the strongest bactericidal ability. It also exhibits good antibacterial durability. These ions exhibit excellent performance at low dosages. The silver ions are highly stable and non-toxic, and they do not need to be stimulated before action. Therefore, silver ions can be efficiently used to modify MOF-based materials, which perform well in various fields. This method of tuning the characteristics of MOF-based materials can be potentially used for developing various materials in the future [33,34,35,36].
M.D. Firouzjaei et al. [37] reported a novel Ag-based nanocomposite (GO-Ag-MOF). They fabricated the material by modifying a silver (Ag) elemental organic framework (Ag-MOF) with graphene oxide (GO). They analyzed the growth curves and used fluorescence imaging and flow cytometry techniques to evaluate the toxicity of GO-Ag-MOF, Ag-MOF, and GO against E. coli (Gram-negative bacteria) and Bacillus subtilis (Gram-positive bacteria). The results revealed that GO-Ag-MOF exhibited significant antibacterial activity, and its biocidal activity was higher than that of Ag-MOF and GO-based nanomaterials. S.F. Seyedpour et al. [38] fabricated the material with silver as the center. The material was fabricated at room temperature using green solvents, following a simple and environmentally friendly method. Three new Ag-MOFs were fabricated, and the results from the experiments revealed that for silver and imidazole coupling agents under the Ag-MOFs, there was a synergistic action against E. coli in colloid form. Under these conditions, the bacterial death rate increased to 95% within 3 h. Zhang et al. [39] used Ag-Metal-organic framework-loaded chitosan NPs and polyvinyl alcohol/sodium alginate/chitosan as the upper and lower two layers to successfully synthesize a bilayer composite dressing for healing. Liu et al. [40] synthesized visible light-sensitive Ag/AgCl@ZIF-8 catalysts. After a series of characterizations of the material, they reached the results that the composite photo catalyst Ag/AgCl@ZIF-8 sample revealed exceptional photocatalytic antibacterial properties. Under light for 90 min, the composite material could inactivate almost all bacteria.
Consequently, MOFs are appropriate for the preparation of a nanoscale system with chemical antibacterial properties. Inspired by the works above, UiO-66-NH2 as a kind of MOF is first synthesized by a hydrothermal synthesis method and then loaded with Ag NPs to form an Ag/UiO-66-NH2 composite, and the different materials were synthesized by controlling the silver doping amount, which are applied to an antibacterial test. UiO-66-NH2 is a MOF with water stability, high heat resistance, and corrosion resistance. Due to the high specific area, large porosity, and chelation of the N atom and transition metal ions, UiO-66-NH2 and its derivatives are widely used as adsorbents of transition metal ions [41,42,43,44,45,46]. Moreover, as far as we know, works on the synthesis of Ag/UiO-66-NH2 and its antibacterial test were not reported before.

2. Experimental

2.1. Materials

Experimental instruments. The FA2004B electronic balance was manufactured by the Shanghai Yueping Scientific Instrument Co., Ltd. (Shanghai, China). The TG18G type bench high-speed centrifuge was manufactured by the Gongyi Yuhua Instrument Co., Ltd. (Gongyi, Henan). The D8 X-ray diffractometer (XRD) was manufactured by Bruck AXS (Bruck, Germany). The JSM-7600f field emission scanning electron microscope (FE-SEM) was manufactured by the JEOL Company in Tokyo, Japan. The JEM-1400 transmission electron microscopy (TEM), the QUANTAX 400 element mapping (EDS), and the Nicolet-460 Fourier transform infrared (FT-IR) spectrometer were manufactured by Bruker, Bruker, Germany. The ASAP2020HD88 specific surface area and Brunauer-Emmett-Teller (BET) was manufactured by the Micromeritics Company (Shanghai, China) in the United States. The Q500 thermogravimetric analyzer (TGA) was manufactured by the TA Company (New Castle, DE, USA) in the United States. The AXISUlTRADLD X-ray electron spectrometer (XPS) was manufactured by the Shimadzu Company (Tokyo, Japan ) in Japan. The software for processing images are Adobe Photoshop (PS) and Origin 2021. Data processing was done in Excel.
Reagents. Zirconium tetrachloride (ZrC14; analytically pure), 2-aminoterephthalic acid (2-BDC-NH2; analytically pure), and N,N-dimethylformamide (DMF; analytically pure) were purchased from the Shanghai Aladdin Sublimation Technology Co., Ltd. (Shanghai, China). Methanol (analytically pure) and silver nitrate (AgNO3; analytically pure) were purchased from the Nanjing Chemical Reagent Co., Ltd.. (Nanjing, China). Deionized water was produced in the laboratory.

2.2. Synthesis and Characterization of Ag/UiO-66-NH2-Based Materials

Ag/UiO-66-NH2 was synthesized following the solvothermal method. UiO-66-NH2 was prepared according to a previous report [47,48,49]. Specifically, ZrC14 (0.772 g) and 2-BDC-NH2 (0.556 g) was taken in 80 mL of DMF. Various concentrations of AgNO3 (1%, 2%, 4%, and 6%; mass fraction of AgNO3 calculated with respect to the amount of ZrC14 and 2-BDC-NH2 taken together) were added to the solution successively, and the mixture was transferred to a stainless-steel high-pressure reaction kettle (100 mL) lined with Teflon and heated at 120 °C for 24 h. In the states of high pressure and high temperature, Ag NPs were mixed into a solution containing organic ligands. Afterwards, Ag NPs were absorbed on the MOF crystals. Thus a series of Ag/UiO-66-NH2 compounds were obtained [50]. The product was cooled to room temperature and centrifuged at 4000× g/min for 15 min to obtain the product as a yellow powder. The product was washed thrice with DMF and methanol. Following this, it was immersed in methanol (80 mL) and heated at 120 °C for 12 h. Subsequently, the sample was re-centrifuged, and the Ag/UiO-66-NH2 system was dried in a vacuum oven at 120 °C for 12 h to obtain Ag/UIO-66-NH2. The Ag and Ag/UiO-66-NH2 are stable in water PBS and culture medium [51,52,53,54]. The products were recorded as UiO-66-NH2 (A0) 1 wt.% Ag/UiO-66-NH2 (A1), 2 wt.% Ag/UiO-66-NH2 (A2), 4 wt.% Ag/UiO-66-NH2 (A3), and 6 wt.% Ag/UiO-66-NH2 (AA4). Figure 1 is a flow chart that presents the method of preparation of the materials.
The FE-SEM technique was used to observe the morphology of the samples, and high-resolution images of the sample were recorded. The tungsten filament was used as the light source, and the sample was amplified by 20,000 times under an acceleration voltage of 20 KV. The sample was sprayed with gold for 10 min before conducting the test [43]. The TEM was applied to inspect the surface structure of the samples at an accelerating voltage of 80 kV [50]. The XRD technique was used to analyze the crystal structure of the sample. The X-ray tube voltage was 40 kV, the current was 40 mA, and the Cu Kα ray was used for sample analysis at the scanning speed of 0.02/s. The 2θ test range was 5°–50°. The types, valence states, and composition of elements on the surface of samples were studied using the XPS technique [35,55]. The samples were put into the sample chamber of the XPS instrument. When the pressure in the sample chamber was under 2.0 × 10−7 Mbar, the sample was sent to the analysis chamber (spot size: 400 μm). The operating voltage was 12 kV, and the filament current was 6 mA. Full spectrum scanning energy was 150 eV, the step size was 1 eV, the narrow-spectrum scanning energy was 50 eV, and the step size was 0.1 eV [21].
The FT-IR technique was used to analyze the chemical composition of the sample. The sample was prepared under dry conditions. A small amount of the samples and a moderate amount of dry potassium bromide were placed in a mortar, and ground the sample into a powder. Subsequently, the ground sample was placed inside the tableting machine, and pressure was applied to the transparent slices. The background information was first collected, following which the infrared spectra were recorded (resolution: 4 cm−1). The scanning number was 32, and the spectrum was recorded in the wave number range of 400–4000 cm−1.The specific surface area, pore volume, and pore size distribution of the samples were determined by analyzing the BET isotherms. The BET equation was used to estimate the relative surface area, and the density functional theory (DFT) technique was used to determine the size of the aperture. The TGA technique was used to study the relationship between the mass and temperature of the samples to analyze the thermal stability of the samples. The samples were weighed and placed evenly in an alumina crucible in an atmosphere of nitrogen (nitrogen flow rate: 30 mL/min; heating rate: 10 °C/min). The testing range was in the range of room temperature to 800 °C [49,55,56,57].

3. Antibacterial Performance of the Ag/UiO-66-NH2 Materials

The inhibition zone (ZIO) method was used to analyze the antibacterial activity of the Ag/UiO-66-NH2. We chose Staphylococcus aureus (gram-positive strains, ATCC 6538) and E. coli (gram-negative, ATCC 25922). Firstly, we plated the bacterial suspension evenly on agar plates (Muller Hinton). In addition, sterile filter paper discs with a diameter of 6 mm were saturated with 35 μL nanocomposites and placed on solid medium. It was then incubated at 37 °C for 24 h and finally the inhibitory zone around each disc was measured in millimeters. At the intervals of 0 h, 1 h, 2 h, 3 h, 4 h, 5 h, and 6 h, 100 µL of the samples was taken out of the petri dishes. The Ultraviolet spectrophotometer was used to measure the optical density (OD) of the samples at a wavelength of 600 nm. The data were recorded, the growth curves corresponding to E. coli and S. aureus were generated, and the influence of different contact time on bacterial growth was observed.

4. Results and Discussion

4.1. SEM Analysis

SEM and TEM images (Figure 2A,C) demonstrated that synthesized UiO-66-NH2 is an octahedral structure with a size of around 35 nm. After Ag NPs were deposited, the morphology of UiO-66-NH2 hardly changed (Figure 2B). However, TEM images showed NPs on UiO-66-NH2 particles (red circles in Figure 2D). EDS analysis revealed that these particles contained Ag (Figure 2E,F). In the EDS spectrum of UiO-66-NH2, the corresponding peaks to the elements of Zr, O, C, and N appeared at 2.040, 0.526, 0.0.390, and 0.279, respectively. In addition, the EDS spectra of Ag/UiO-66-NH2 showed a peak corresponding to Ag element at 3.012 (Figure 2F), which further confirms that Ag had been loaded on UiO-66-NH2 successfully.

4.2. XRD Analysis

Figure 3 presents the XRD patterns of UiO-66-NH2 synthesized under conditions of varying silver doping levels. Typical strong diffraction peaks appear at 7.4°, 8.5°, 12.1°, 25.7°, and 33.1°, which represent the (111), (002), (022), (224), and (137) lattice planes of UiO-66-NH2, respectively. The results agree well with the results reported by Lee D. T. et al. [58]. UiO-66-NH2 was synthesized successfully. The positions of all of the peaks were the same, which indicated that the synthesized materials exhibited the same structure, and no obvious loss in crystal composition was observed. In addition, high intensities of the principal diffraction peaks were recorded. This indicated that the synthesized materials were characterized by good structural integrity and crystal properties. However, none of them showed the Ag-related diffraction peaks. It may be due to the poor crystallinity of Ag NPs [57].

4.3. XPS Analysis

Figure 4 presents the full-spectrum XPS profile of UiO-66-NH2 synthesized under conditions of varying silver doping levels. The peaks corresponding to Zr3d (193.98 eV), C1s (294.11 eV), N1s (399.98 eV), and O1s (544.98 eV) are clearly visible in the spectrograph. Significantly intense magazine peaks were not observed. Results obtained by conducting elemental analysis revealed that following the introduction of Ag, the intensity of the N1s peak associated with the C-NH2 group decreased, indicating that N might react at this site [58]. The decrease in the intensity of the peaks corresponding to Zr3d and O1s indicates that the chemical environment of these two elements has changed. This phenomenon indicates that Zr-O participates in the reaction, and the O atom in the Zr-O-Zr structure potentially bonds with Ag through covalent bonds, resulting in a decrease in the binding energy of the O atom [33].

4.4. FT-IR Analysis

Figure 5 presents the FT-IR profile of the UiO-66-NH2 system synthesized under conditions of varying silver doping levels. Analysis of the figure reveals that the peak at 3344 cm−1 is the characteristic peak of the OH group present on the surface of UiO-66-NH2. The peak at 1655 cm−1 represents the bending vibration of the N-H group present in UiO-66-NH2. The peaks at 1572 and 1386 cm−1 correspond to the symmetric and asymmetric stretching vibrations, respectively, of the COO group connected to Zr4+ in UiO-66-NH2. The peak at 1499 cm−1 represents the stretching vibration of the C=C unit present in the benzene ring. The peak at 1434 cm−1 can be attributed to the shear vibration peak of the N-H unit in UiO-66-NH2. The peak at 1256 cm−1 can be attributed to the unique C-N tensile absorption of aromatic amines. The peaks at 768 and 662 cm−1 represent the stretching vibration of μ3-O in Zr-(OC). The peak at the range 600 to 483 cm−1 is attributed to the metal-oxide bonds in the secondary construction unit [56]. Thus, it could be further inferred that UiO-66-NH2 was successfully synthesized, and the peaks in the infrared spectral profiles recorded for A1, A2, A3, and A4 were similar to those appearing in the profiles recorded for UiO-66-NH2. This validated that the crystal structure of Ag/UiO-66-NH2 was stable.

4.5. BET Analysis

Figure 6 presents the nitrogen adsorption/desorption isotherms of the UiO-66-NH2 system synthesized under conditions of varying silver doping levels. Type Ⅰ isotherms were generated for all the synthesized materials. This indicated that they primarily presented microporous structures. As micropore filling is observed in type Ⅰ isotherms, it is situated at a low relative pressure region. The adsorption capacity increases rapidly and reaches a plateau when the limit is reached. The specific surface area and total pore volume of A0–A4 are shown in Table 1. The specific surface area of UiO-66-NH2 is slightly smaller than that reported [55] previously. This can be attributed to the fact that the amount of DMF used influences the dosage ratio of Zr in the synthesis process. The specific surface area and total pore volume of Ag/UiO-66-NH2 are larger than those of UiO-66-NH2, indicating that the introduction of Ag exerts no adverse effect on the original void structure of UiO-66-NH2. Under these conditions, new pores are generated on the composite interface.

4.6. TGA Analysis

Figure 7 presents the TGA profile of UiO-66-NH2 synthesized under conditions of varying silver doping levels. As shown in the figure, the weight loss process associated with A0–A4 is divided into three stages. The first stage of weight loss, associated with A0–A4, occurs below 160 °C, and the mass losses for A0–A4 at this stage are 8.55%, 9.39%, 9.97%, 9.98%, and 11.10%, respectively. This can be primarily attributed to the evaporation of the gaseous products. The process is mediated through the physical adsorption of water molecules, DMF, and other solvents. The second stage of weight loss occurred in the range of 160 °C–580 °C, and the mass loss percentages were 31.12%, 31.88%, 31.93%, 32.32%, and 32.81%. This can be primarily attributed to the fact that as the amino terbenzoic acid ligand starts to decompose, the coordination bond with Zr breaks, and the skeleton structure gradually collapses under these conditions. In the third stage of weight loss, beyond 580 °C, the mass loss is approximately 8.3%. At this point, complete decomposition occurs, and the rate of decomposition decreases and gradually reaches a constant value. A similar extent of mass loss was observed for these materials. This indicated that the introduction of the Ag ions on UiO-66-NH2 does not affect the thermal stability of the system. Good thermal stability could be achieved [47,49,59].

5. Evaluation of the Antibacterial Performance

5.1. Inhibition Zone (ZOI)

The bacteriostatic zone method is one of the important methods that can be used to study the antibacterial properties of materials. The larger the diameter of the bacteriostatic zone is, the better the antibacterial effect and antibacterial performance of the material is.
We weighed 100 mg of the composite materials and pressed them into discs with molds. Subsequently, we placed the discs gently into a solid culture medium coated with bacterial suspension. The samples were then sealed with paraffin wax and incubated in a constant temperature oscillation chamber for 24 h under appropriate conditions. The diameter D of the circle was measured using a measuring scale. The results are presented in Figure 8 and Figure 9, and Table 2.
Sample A0 presented in Figure 8 exhibits almost no antibacterial properties, while A1–A4 exhibit different degrees of antibacterial properties. Analysis of the antibacterial zone diameter presented in Histogram Figure 8, Table 1, and other experimental data reveal that the degree of antibacterial effect that Ag/UiO-66-NH2 exerted on Staphylococcus aureus is higher than the degree of the antibacterial effect exerted on Escherichia coli. It was also observed that the antibacterial zone diameter of 4 wt.% Ag/UiO-66-NH2 for Escherichia coli was 7.452 mm. The antibacterial zone diameter corresponding to Staphylococcus aureus was 9.013 mm. These were the maximum diameters that were recorded under the same experimental conditions. Therefore, 4 wt.% Ag/UiO-66-NH2 exhibited the best antibacterial effect. The antibacterial effect decreased with an increase in the silver doping amount. The generation of the change can be attributed to the gradual increase in the amount of Ag, which coalesce to form large silver particles. These are characterized by poor dispersion ability and low activity. A slow release of silver ions is achieved under the reaction conditions, resulting in the deterioration in the antibacterial performance of the sample [21,60,61,62]. It can be seen from the figure that the material exhibits good antibacterial activity against two representative bacteria, namely, E. coli (gram-negative bacteria) and Staphylococcus aureus (gram-positive bacteria), indicating that the material is a broad-spectrum antibacterial material.

5.2. Determination of the Bacterial Growth Curve

The growth curves of two kinds of bacteria were generated following the addition of antibacterial materials to better understand the antibacterial performance of Ag/UiO-66-NH2 under conditions of varying silver doping levels. Results obtained by conducting preliminary experiments revealed that at the Ag/UiO-66-NH2 concentrations of 0.33 mg/L (50 mg/150 mL) and 0.27 mg/L (40 mg/150 mL), bacteria did not grow. The growth inhibition effect of different silver dosage levels of Ag/UiO-66-NH2 on the growth properties of Escherichia coli and Staphylococcus aureus were studied. The optimized conditions have been reported: The Ag/UiO-66-NH2 composites (30 mg) containing different silver dosage levels were dissolved in 150 mL of the fresh LB liquid medium to prepare the liquid medium (0.2 mg/L) containing antibacterial materials.
Figure 10 presents the curves corresponding to the growth of Escherichia coli and Staphylococcus aureus. The curves were generated following the addition of the antibacterial materials into the bacterial culture medium. The silver doping levels were varied to study the inhibition effect. Silver NPs can damage the phospholipid bilayer and permeability of cell membranes, causing the leakage of sugars and proteins in bacterial cells. Thus, cell death was induced [61,62]. As can be seen from Figure 10 and Figure 11, 4 wt.% Ag/UiO-66-NH2 exerts the strongest inhibitory effect on the growth of the two kinds of bacteria, and the OD values measured at the sixth hour are the lowest. This is consistent with the experimental results obtained by analyzing the bacteriostatic zone.

6. Conclusions

In this paper, UiO-66-NH2, 1 wt.% Ag/UiO-66-NH2, 2 wt.% Ag/UiO-66-NH2, 4 wt.% Ag/UiO-66-NH2, and 6 wt.% Ag/UiO-66-NH2 were synthesized following the thermal solvent method. FE-SEM, XRD, FT-IR, BET, TGA, and XPS techniques were used to characterize the synthesized materials. The antibacterial properties were tested by analyzing ZIO and the OD values. The conclusions drawn follow:
(1)
The introduction of Ag does not interfere with the crystallization of UiO-66-NH2. The morphology and crystal structure of the UiO-66-NH2 samples fabricated under conditions of varying silver ion doping levels amount are similar to those of UiO-66-NH2.
(2)
The FT-IR spectral profiles recorded for the UiO-66-NH2 samples fabricated under conditions of varying silver ion doping levels are similar to those recorded for UiO-66-NH2. Stray peaks were not observed, and the peak intensity decreased slightly.
(3)
The thermal stability of UiO-66-NH2, containing varying amounts of silver ions, was lower than the thermal stability of UiO-66-NH2. The higher the silver ion content, the lower the thermal stability. Under these conditions, the specific surface area and pore volume increased.
(4)
The antibacterial performance of UiO-66-NH2 improved significantly following the process of silver ion doping. As the silver ion content increased, the antibacterial performance improved initially and then deteriorated. The best antibacterial performance was observed when the silver ion content was 4 wt.%.
Overall, Ag loading improves the antibacterial properties of UiO-66-NH2. The preparation process of this material is simple, which provides the idea for the preparation of other composite materials. This research also contributes to the understanding of the role of loaded metal NPs and provides new strategies for broad-spectrum bacterial sterilization in many biological applications.

Author Contributions

F.T.: Methodology, Investigation, Writing—Original draft, Data curation, Visualization, and Supervision. R.W.: Supervision, Writing—Reviewing and Editing, Project administration, and Funding acquisition. X.H. and G.C.: Investigation and Data curation. Z.H.: Supervision and Writing-Reviewing. All authors have read and agreed to the published version of the manuscript.

Funding

This research is financially supported by the General project of Fujian Provincial Natural Science Foundation (2022J01922), the National Key Research and Development Program of China in 2019 (No. 2019YFC1904101), the Initial Scientific Research Foundation of Fujian University of Technology (GY-Z20014), and the Research Development Foundation of Fujian University of Technology (GY-Z18186).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

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Coatings 12 01939 g001 550
Figure 1. Flow chart presenting the method of material preparation.
Figure 1. Flow chart presenting the method of material preparation.
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Figure 2. (A,C) Field emission scanning electron microscope (FE-SEM) and transmission electron microscopy (TEM) images of UiO-66-NH2; (B,D) SEM and TEM images of Ag/UiO-66-NH2; (E,F) Element mapping (EDS) of UiO-66-NH2 and Ag/UiO-66-NH2.
Figure 2. (A,C) Field emission scanning electron microscope (FE-SEM) and transmission electron microscopy (TEM) images of UiO-66-NH2; (B,D) SEM and TEM images of Ag/UiO-66-NH2; (E,F) Element mapping (EDS) of UiO-66-NH2 and Ag/UiO-66-NH2.
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Figure 3. X-ray diffractometer (XRD) patterns of UiO-66-NH2 synthesized under conditions of varying silver doping levels.
Figure 3. X-ray diffractometer (XRD) patterns of UiO-66-NH2 synthesized under conditions of varying silver doping levels.
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Figure 4. X-ray electron spectrometer (XPS) profiles of the UiO-66-NH2 system synthesized under conditions of varying silver doping levels.
Figure 4. X-ray electron spectrometer (XPS) profiles of the UiO-66-NH2 system synthesized under conditions of varying silver doping levels.
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Figure 5. Fourier transform infrared (FT-IR) profiles recorded for UiO-66-NH2 synthesized under conditions of varying silver doping levels.
Figure 5. Fourier transform infrared (FT-IR) profiles recorded for UiO-66-NH2 synthesized under conditions of varying silver doping levels.
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Figure 6. Nitrogen adsorption/desorption isotherms generated for the UiO-66-NH2 system synthesized under conditions of varying silver doping levels.
Figure 6. Nitrogen adsorption/desorption isotherms generated for the UiO-66-NH2 system synthesized under conditions of varying silver doping levels.
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Figure 7. Thermogravimetric analyzer (TGA) profile recorded for the UiO-66-NH2 system synthesized under conditions of varying silver doping levels.
Figure 7. Thermogravimetric analyzer (TGA) profile recorded for the UiO-66-NH2 system synthesized under conditions of varying silver doping levels.
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Figure 8. (A) A0–A4 image of the inhibition zone in Escherichia coli and (B) A0–A4 image of the inhibition zone in Staphylococcus aureus.
Figure 8. (A) A0–A4 image of the inhibition zone in Escherichia coli and (B) A0–A4 image of the inhibition zone in Staphylococcus aureus.
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Figure 9. Diameters of the antibacterial circles corresponding to Escherichia coli and Staphylococcus aureus generated under conditions of varying silver doping levels.
Figure 9. Diameters of the antibacterial circles corresponding to Escherichia coli and Staphylococcus aureus generated under conditions of varying silver doping levels.
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Figure 10. Growth curves for (A) E. coli and (B) S. aureus.
Figure 10. Growth curves for (A) E. coli and (B) S. aureus.
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Figure 11. Final optical density for E. coli and S. aureus.
Figure 11. Final optical density for E. coli and S. aureus.
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Table
Table 1. Porous structure parameters of different samples.
Table 1. Porous structure parameters of different samples.
Sample NameSpecific Surface Area (m2/g)Total Pore Volume (m3/g)
A0462.960.16
A1465.250.16
A2527.740.18
A3574.930.20
A4741.600.27
Table
Table 2. The average and standard Deviation of Diameter of the inhibition zone D (mm) corresponding to Ag/UiO-66-NH2 under conditions of varying silver doping levels.
Table 2. The average and standard Deviation of Diameter of the inhibition zone D (mm) corresponding to Ag/UiO-66-NH2 under conditions of varying silver doping levels.
A0A1A2A3A4
E. coliAverage0.0176.6586.9857.4537.312
Standard Deviation8.16 × 10−46.53 × 10−32.36 × 10−31.41 × 10−39.43 × 10−4
S. aureusAverage0.0257.6748.8929.0138.947
Standard Deviation4.08 × 10−33.27 × 10−31.63 × 10−32.45 × 10−35.72 × 10−3
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Tian, F.; Weng, R.; Huang, X.; Chen, G.; Huang, Z. Fabrication of Silver-Doped UiO-66-NH2 and Characterization of Antibacterial Materials. Coatings 2022, 12, 1939. https://doi.org/10.3390/coatings12121939

AMA Style

Tian F, Weng R, Huang X, Chen G, Huang Z. Fabrication of Silver-Doped UiO-66-NH2 and Characterization of Antibacterial Materials. Coatings. 2022; 12(12):1939. https://doi.org/10.3390/coatings12121939

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Tian, Feng, Rengui Weng, Xin Huang, Guohong Chen, and Zhitao Huang. 2022. "Fabrication of Silver-Doped UiO-66-NH2 and Characterization of Antibacterial Materials" Coatings 12, no. 12: 1939. https://doi.org/10.3390/coatings12121939

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