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Article

Fabrication of Silver-Incorporated Zn-Al Layered Double Hydroxide: Characterization and Bromide-Adsorption Performance

by
Aiman Eid Al-Rawajfeh
1,2,
Albara Ibrahim Alrawashdeh
1,3,*,
Mohammad Taha Etiwi
1,
Bandita Mainali
4,
Muhammad Kashif Shahid
4,5,*,
Hosam Al-Itawi
1,
Ehab Al-Shamaileh
6,
Mariam Al-E’bayat
1 and
Al Al-Sahary
2
1
Chemical Engineering Department, Tafila Technical University, P.O. Box 179, Tafila 66110, Jordan
2
Water Technologies Innovation Institute & Research Advancement (WTIIRA), Saudi Water Authority, P.O. Box 8284, Al-Jubail 31951, Saudi Arabia
3
Department of General Subjects, College of Engineering, University of Business and Technology, Jeddah 21361, Saudi Arabia
4
School of Engineering, Faculty of Science and Engineering, Macquarie University, Sydney, NSW 2109, Australia
5
Faculty of Civil Engineering and Architecture, National Polytechnic Institute of Cambodia (NPIC), Phnom Penh 12409, Cambodia
6
Department of Chemistry, School of Science, The University of Jordan, Amman 11942, Jordan
*
Authors to whom correspondence should be addressed.
Water 2025, 17(11), 1578; https://doi.org/10.3390/w17111578
Submission received: 27 March 2025 / Revised: 4 May 2025 / Accepted: 19 May 2025 / Published: 23 May 2025
(This article belongs to the Special Issue Advanced Adsorbent-Based Technologies for Efficient Wastewater Treatment)
Browse Figures
Versions Notes

Abstract

:
In this study, a novel adsorbent was developed by synthesizing Zn-Al layered double hydroxide (LDH) incorporated with silver nanoparticles (Ag-NPs), and its effectiveness in bromide removal from aqueous solutions was systematically evaluated. The X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) analyses confirmed the integration of Ag-NPs within the LDH, ensuring uniform chemical composition and structural integrity. A series of controlled batch trials, each varying a single parameter (adsorbent dose, contact time, or temperature) confirmed that over 95% of bromide (initially 5320 μg/L) was removed under optimized conditions. LDH/Ag-NPs exhibited superior performance, with kinetics well described by a second-order reaction model. Thermodynamic analysis confirmed the spontaneous and exothermic nature of bromide adsorption, with ΔG° values ranging from −2.03 to −0.73 kJ/mol as the temperature increased from 22 °C to 52 °C. In continuous-flow experiments, packed-bed column tests illustrated that LDH/Ag-NPs maintained more effective bromide removal than LDH alone over extended periods. Conductivity measurements further supported this enhancement, with LDH/Ag-NPs reducing final conductivity to 139 µS/cm, compared to 212 µS/cm for LDH. Furthermore, this study revealed the notable antimicrobial activity of LDH/Ag-NPs, as evidenced by a significant reduction in bacterial growth compared to LDH alone, highlighting its dual functionality for both bromide adsorption and water disinfection. Overall, the incorporation of Ag-NPs into LDH offers a promising strategy for developing multifunctional and sustainable water treatment systems.

1. Introduction

Br− is commonly found in surface waters, particularly in areas with significant human activities, such as hydraulic fracturing operations and power plants that primarily use coal [1]. The presence of Br− in water can result in the generation of regulated disinfection byproducts (DBPs) during water and wastewater treatment, including BrO3−, haloacetic acids (HAAs), and brominated trihalomethanes (THMs) [2]. It is worth emphasizing that brominated DBPs (Br-DBPs) exhibit significantly higher genotoxicity when compared to their chlorinated counterparts [3,4]. Typically, the toxicity of Br-DBPs surpasses that of chlorinated DBPs by one to two orders of magnitude [5]. Moreover, when treating water that contains dissolved bromide, the ozonation process can generate bromate, a substance that is believed to have carcinogenic, toxic, and mutagenic effects on humans. Numerous nations have implemented strict regulations governing the levels of bromide in drinking water as a result [6].
There are three main approaches to eliminate bromate: pre-ozonation bromate removal, control of bromate formation during ozonation, and post-ozonation bromate removal [7]. One of the more prompts and efficient methods involves eliminating bromide from drinking water sources prior to the ozonation disinfection [8]. Although electrochemical treatment can effectively oxidize bromide, it generates hazardous byproducts [9,10]. Several techniques, such as coagulation, nanofiltration, activated carbon, synthetic polymers, and silver-loaded activated carbon, have been employed for bromide removal [11,12,13]. Adsorption proves to be a suitable method for water treatment, given its effective capacity to capture contaminants [14,15].
Layered double hydroxides (LDHs) are materials composed of numerous layers with positively charged layers and interchangeable anions in the interlayer [16]. LDHs exhibit high anion exchange capacities, which improve their potential to eradicate anionic pollutants from aqueous mediums. In recent years, LDHs have garnered substantial attention because of their distinctive layered structures and high anion exchange capabilities, making them valuable as ion exchangers and components in organic-inorganic nanocomposites [17,18]. LDHs typically have a layered structure, with positively charged layers alternating with layers of negatively charged guest ions and water molecules. The distance between the layers in LDHs can change depending on the shape and size of the negatively charged particles that are sandwiched between them. Additionally, LDHs possess moderately enormous surface areas and high capacity for anion exchange. These properties have led to extensive research into LDHs as possible adsorbents for eradicating harmful anionic species from aqueous environments [19].
A previous study reported the utilization of Zn-Al-LDH for heavy metal remediation, specifically targeting the removal of Pb2+ and Cd2+ from aqueous solutions [20]. Yulun and his colleagues investigated the mitigation of bromate formation through catalytic ozonation of organic contaminants using Fe–Al LDH/Al2O3 [21]. LDH was primarily employed to remove BrO3−. Results were promising, as researchers achieved an 81.6% reduction in BrO3− in drinking water by utilizing humic acid (HA) and Fe (II) as part of their treatment process [21].
While LDHs have been widely studied for the removal of various anionic contaminants, limited attention has been given to their application for bromide (Br−) removal, a growing concern in drinking water due to its potential to form harmful disinfection byproducts such as bromate during water treatment processes. Unlike fluoride or chloride, which are more commonly regulated and studied, bromide receives less focus, despite its increasing concentrations in water sources in arid regions such as Jordan. This study addresses this gap by investigating the adsorption behavior of Zn-Al LDHs specifically for bromide ions. Furthermore, although LDHs possess inherent anion exchange capacities, their performance can be significantly enhanced through modification. The incorporation of Ag-NPs into the LDH matrix aims to improve not only bromide adsorption efficiency but also to introduce antimicrobial functionality, offering a dual benefit for water treatment. The synergistic effects of LDH and Ag-NPs in bromide removal and bacterial suppression have not been thoroughly explored, making this study a novel contribution to multifunctional water purification technologies.

2. Materials and Methods

2.1. Reagents and Chemicals

Analytically graded reagents and chemicals were employed in this investigation, sourced from different companies located in Jordan. Tri-sodium citrate (Na3C6H5O7·2H2O) was supplied by the BDH laboratory (Dubai, UAE), sodium hydroxide (NaOH) was provided by Scharlab (Barcelona, Spain), AgNO3 was provided by AppliChem (Darmstadt, Germany), and KBr was supplied by VWR International (Dubai, UAE). Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was supplied by AZ Chemicals (Amman, Jordan), while aluminum nitrate (Al(NO3)3·9H2O) was sourced from Avonchem (Cheshire, UK).

2.2. Instrumentation

Several advanced analytical techniques were utilized for the characterization and examination of several quality parameters of synthesized material. Conductivity assessments were performed employing the Schott Instruments equipment (Mainz, Germany), spanning a wide spectrum (0–200.0 μS/cm) and benefiting from a 1–4 points auto-calibration capability to confirm precision. A high-precision ion electrode (Model 720) from Metrohm (Herisau, Switzerland) facilitated ion concentration analysis. Fourier Transform Infrared Spectroscopy (FT-IR) analysis was performed using a SHIMADZU instrument (Tokyo, Japan) featuring a single disk, enabling the scanning of a wide wavenumber range (600 to 4000 cm−1) and offering valuable information on the material’s chemical composition and molecular structure. LabX XRD-6100 (Tokyo, Japan) was employed for X-ray diffraction analysis (XRD), providing comprehensive structural details. Ultrasonication was carried out employing a Metrohm SB-5200 DTD device (Scientz, Ningbo, China), while UV–visible spectroscopy was conducted on a Shimadzu UV-1800 double-beam UV–vis spectrophotometer (Tokyo, Japan), capable of scanning a wavelength range of 200–700 nm, providing precise measurements of absorbance and transmittance.

2.3. Preparation of Ag-NPs

The silver NPs were prepared using a chemical reduction process [22,23], and distilled water was used to prepare all the solutions. According to the established method, 50 mL of 0.001 M AgNO3 was heated to boiling. Subsequently, 5 mL of a 1% TSC solution (trisodium citrate), serving as the reducing agent, was gradually added. During this procedure, the solutions underwent robust mixing and heating until an evident alteration in color transpired, leading to a pale-yellow shade. The fundamental mechanism involved in these reactions can be concisely represented in Equation (1) [22].
4 Ag+ + C6H5O7Na3 + 2 H2O → 4 Ago + C6H5O7H3 + 3 Na+ + H+ + O2↑

2.4. Preparation of LDH and LDH/Ag-NPs

Zn–Al LDHs were prepared using zinc nitrate (Zn(NO3)2·6H2O, aluminum nitrate Al(NO3)3·9H2O), NaOH, and distilled water. In a 250 mL volumetric flask, 10.2 g of Al(NO3)3·9H2O and 29.2 g of Zn (NO3)2·6H2O were dissolved in distilled water and diluted to the mark. Then, 250 mL of 0.05 M NaOH solution was added under stirring to induce precipitation. The resulting precipitate was filtered to collect the LDH material. This procedure was repeated seven times. The collected LDH was dried at 40–50 °C and ground into a fine powder.
To prepare the LDH/Ag-NPs composite, the dried and ground LDH powder was dispersed in the freshly synthesized Ag-NPs colloidal solution. The suspension was stirred continuously at room temperature for 12 h to facilitate the adsorption and uniform distribution of Ag-NPs onto the LDH surface. After the mixing period, the resulting material was filtered, thoroughly washed with distilled water to remove unbound nanoparticles, and dried at 60 °C to obtain the final LDH/Ag-NPs composite.

2.5. Bacterial Growth Test

This study examined how silver nanoparticles influence bacterial growth in the context of drinking water treatment, with a focus on their interaction with materials designed to remove bromide ions from water supplies. The experiment assessed bacterial growth on samples from two sources: LDH and LDH combined with silver nanoparticles (Ag-NPs). The testing media were prepared by dissolving a specified amount in distilled water employing a magnetic stirrer. The non-sterile media were then covered with cotton and aluminum foil and sterilized in an autoclave at 15 psi and 121 °C. Following media preparation in the autoclave, the laminar flow hood was sanitized by exposing the interior to UV light, ensuring a sterile environment for the experiment. The sterilized media and petri dishes were then kept in the cabinet, followed by a precise and careful transfer of media into the dishes. Next, a brief interval was allowed for the media to harden and solidify. After solidification, the dishes were turned upside down and subjected to a 24 h incubation period at 37 °C, with clear labels attached for identification purposes.

2.6. Batch Tests

Four independent trials were carried out, each modifying a single parameter while maintaining other factors at a constant level. In the first experiment, the time, volume, temperature, and mixing rate (500 rpm) remained constant, with only the adsorbent mass being altered. The second experiment maintained the adsorbent mass, volume, temperature, and mixing rate (500 rpm) as constants, with time being the variable. Experiment 3 sustained constant values for adsorbent mass, time, volume, and mixing speed (500 rpm), with temperature being the varied factor. In the fourth experiment, ultrasonication was utilized to stabilize the temperature, adsorbent mass, volume, and mixing rate (500 rpm), whereas time was the variable examined. Across these experiments, this study explored a range of adsorbent masses (0.5, 1.0, 2.0, 4.0, 6.0, and 8.0 g), contact times (5, 10, 15, 30, 40, and 50 min), and temperatures (22, 32, 42, and 52 °C).
Precision preparation of a standard solution at multiple wavelengths was followed by calibration with a specific ion electrode (SIE). This enabled the creation of a reliable reference tool, which was then applied to unknown samples for precise evaluation and analysis.

2.7. Column Experiments

This study utilized a packed column made of acrylic glass, featuring an internal diameter measuring 19 mm and 330 mm height. At the column’s base, a stainless sieve (0.5 mm mesh size) was incorporated, complemented by a layer of glass wool to enhance filtration. To maintain a uniform effluent flow into the packed-bed column reactor, a uniform layer of circular glass beads with a diameter of 1.5 mm was placed 20 mm above the column’s base. The influent was introduced from the top, and the treated water was collected at the bottom of the column. Figure 1 illustrates the schematic design of the packed-bed column.

3. Results and Discussion

3.1. Bromide Adsorption onto LDH

The batch adsorption results, including residual Br− concentrations and removal efficiencies under various conditions, are provided in the Supplementary Materials (Table S1). Table S1a exhibits the effect of the LDH on reducing bromide ions from drinking water, with an initial concentration of 5320 μg/L. This impact was examined through altering the LDH dosage, while keeping the conditions constant in terms of RT (22 °C), mixing speed (500 rpm), and time (5 min). Specifically, with an adsorbent mass of 0.5 g in the solution, around 94.1% of bromide was removed using LDH. However, this removal rate increased to 96.5% when the mass of the adsorbent was elevated to 8 g. Based on these results, it can be stated that an increase in the LDH mass resulted in a proportional decline in the proportion of Br− ions existing in the solution.
Table S1b outlines the effect of the LDH on Br−, changing the contact time while maintaining other parameters unchanged. Particularly, LDH mass (2 g), mixing rate (500 rpm), and RT (22 °C) were consistently applied. Specifically, an increase in the residence time of the LDH resulted in a proportional decline in the concentration of Br− in the drinking water. Specifically, a bromide removal efficiency of approximately 96.1% was achieved at a residence time of 10 min, which slightly increased to 96.5% upon extending the residence time to 50 min.
Table S1c demonstrates the impact of the LDH on Br− by changing the temperature while keeping all other parameters constant. The experiment lasted for 5 min, employing a 2 g of LDH with a mixing rate of 500 rpm. Noticeably, the data showed a pronounced inverse correlation, where higher temperatures led to lower bromide ion concentrations in the drinking water. At 22 °C, approximately 96.1% of the bromide was removed from the solution, and this removal rate increased to 96.5% at 52 °C.
Table S1d outlines the influence of LDH on Br− when employing ultrasonication, specifically focusing on varying the contact time while keeping other parameters constant. The experimental conditions consisted of a 2g LDH sample, a 500 rpm mixing speed, and a RT of 22 °C. The data reveal a strong inverse relationship between LDH contact time and bromide ion concentration, with longer contact times resulting in lower bromide ion levels. In detail, the removal rates were 96.10%, 96.20%, 96.30%, 96.40%, and 96.50% for residence times of 10 min, 15 min, 30 min, 40 min, and 50 min, respectively.

3.2. Adsorption of Bromide onto LDH + Ag-NPs

The batch adsorption results, including residual Br− concentrations and removal efficiencies under various conditions, are provided in the Supplementary Materials (Table S2). Table S2a exhibits the effect of LDH + Ag-NPs on Br− removal from drinking water. This phenomenon was examined by changing the LDH/Ag-NPs mass, while keeping conditions consistent, such as a 5 min duration, a mixing rate of 500 rpm, and a temperature of 22 °C. Particularly, as the dosage of LDH + Ag-NPs enhanced, there was a parallel fall in the concentration of Br− ions in the solution. A 0.5 g mass of LDH/Ag-NPs appeared effective in removing up to 95% of bromide from the solution, while this removal rate increased to 97.3% in the presence of 8 g of LDH/Ag-NPs.
Table S2b illustrates the effect of varying residence time on bromide ions using LDH/Ag-NPs under consistent conditions. Employing a 2 g mass of LDH/Ag-NPs, a mixing rate of 500 rpm, and a RT of 22 °C, the findings demonstrate a reduction in bromide ions in drinking water as the contact time of LDH/Ag-NPs increases. Specifically, LDH/Ag-NPs exhibited a 95.20% removal rate of bromide at a residence time of 10 min, which increased to 97.2% with a contact time of 50 min.
In Table S2c, the focus shifts to the impact of LDH/Ag-NPs on Br− ions while changing the temperature under constant conditions. The experiment involved a 5 min duration using a 2 g mass of LDH/Ag-NPs at a mixing rate of 500 rpm. The obtained outcomes indicate that with increased contact time of LDH/Ag-NPs, there is a consequent decrease in the Br− concentration in drinking water. Specifically, LDH/Ag-NPs exhibited bromide removal rates of 94.4%, 95%, 96%, and 96.8% at temperatures of 22, 32, 42, and 52 °C, respectively.
Table S2d demonstrates the influence of LDH/Ag-NPs on the removal of Br− ions, specifically examining the impact of changing residence time while keeping ultrasonication conditions constant. The experimental setup involved a 2 g mass of LDH/Ag-NPs, a room temperature (RT) of 22 °C, and a mixing rate of 500 rpm. Particularly, the results intensely exhibit that with an increase in the contact time of LDH/Ag-NPs, there is a consequent decline in the ionic concentration of bromide in the drinking water. Thorough analysis shows removal rates of 96.30%, 96.42%, 96.46%, 96.50%, and 96.60% for residence times of 10 min, 15 min, 30 min, 40 min, and 50 min, respectively.
Figure 2, Figure 3 and Figure 4 offer a comparative analysis of bromide ion removal from water using LDH and LDH/Ag-NPs under different conditions. Both adsorbents displayed significant removal efficiency, consistently exceeding 94% across various conditions. Noteworthy is the apparent improvement in bromide removal rates observed with LDH/Ag-NPs, emphasizing the superior efficacy of this composite compared to LDH alone. Although LDH/Ag-NPs demonstrated superior overall bromide removal efficiency, the initial adsorption rate was slightly slower than that of LDH (Figure 3). This may be due to transient competition or rearrangement at the surface between Ag-NPs and LDH active sites, temporarily limiting bromide access during the early stages. As the process proceeds, the synergistic interaction between LDH and Ag-NPs enhances the overall removal capacity.
Though the increase in bromide removal efficiency from ~96% to >97% appears modest, the presence of Ag-NPs likely enhances the adsorption mechanism through surface modification and possible changes in surface charge distribution. Ag-NPs may increase the number of reactive sites and alter the electronic properties of the LDH surface, thereby improving ion exchange interactions or facilitating additional adsorption pathways. Such enhancements, though subtle in batch tests, could become more impactful under continuous-flow or real-water conditions.

3.3. Bromide Adsorption Employing Column Reactor

A packed-bed column filled with adsorbent material, made of acrylic glass, was used to purify the water. The conductivity of the water was determined to examine the effect of water circulation on bromide ion removal in the presence of LDH and LDH/Ag-NPs. The water was cycled through the column multiple times, with each cycle indicated by a numerical value ranging from 0 to 4. A steady decrease in bromide ion concentration was observed with each consecutive route, demonstrating the efficacy of the adsorbent material. These results are visualized in Figure 5a,b, which depict the % removal of bromide ions from aqueous solution over multiple operational rounds, highlighting the efficacy and durability of the adsorbent material.
It is apparent that when LDH alone is used, the initial conductivity of 1656 µS/cm decreases to 1289 µS/cm, 875 µS/cm, 430 µS/cm, and finally 212 µS/cm in the first, second, third, and fourth cycles, respectively. Similarly, in the presence of LDH/Ag-NPs, the initial conductivity is reduced to 1120 µS/cm, 731 µS/cm, 310 µS/cm, and 139 µS/cm in the first, second, third, and fourth cycles, respectively.

3.4. Adsorption Kinetics

The adsorption kinetics study provides key insights into the reaction dynamics and mechanisms for both LDH and LDH/Ag-NPs, facilitating the evaluation of kinetic behavior corresponding to first- and second-order models. This enables a thorough comprehension of the adsorption phenomenon, revealing the intricacies of the reaction mechanisms [24]. Equations (2) and (3) represent the mathematical models corresponding to kinetic behaviors of first and second orders, respectively, offering a quantitative framework to understand the adsorption process.
ln[M] = ln[M]o − kt
Here, [M], [M]o, t, and k, signify the final Br− concentration (mol·L−1), initial Br− concentration (mol·L−1), time (s), and rate constant (s−1), respectively.
1[M] = 1[M]o + kt
where k indicates the rate constant for second-order reaction kinetics, expressed in mol·L−1·s−1.
Figure 6 presents the linear kinetic plots for the pseudo-first-order and pseudo-second-order models describing Br− adsorption onto LDH. The corresponding rate constants were calculated as 2.25 × 10−4 s−1 for the pseudo-first-order model and 1.07 × 10−6 mol·L−1·s−1 for the pseudo-second-order model. The correlation coefficients (R2) were found to be 0.88 and 0.91, respectively, indicating a better fit with the second-order model. This higher R2 value suggests that the adsorption process follows predominantly second-order kinetics. Following ultrasonic treatment, Figure 7 presents the updated linear kinetic plots for both models applied to Br− adsorption onto LDH. The findings under sonication conditions further reinforce the dominance of second-order kinetics. The rate constants were determined as 4.70 × 10−5 s−1 for the pseudo-first-order model and 2.44 × 10−7 mol·L−1·s−1 for the pseudo-second-order model. Interestingly, under these conditions, both models exhibited an R2 value of 0.99, indicating excellent linearity. However, the pseudo-second-order model showed closer agreement with the experimental qe and better reflects the likely chemisorption mechanism, supporting its selection as the more appropriate kinetic model.
Figure 8 shows the linear kinetic plots for the pseudo-first-order and pseudo-second-order models applied to Br− adsorption onto LDH/Ag-NPs. The estimated rate constants were 2.22 × 10−4 s−1 for the pseudo-first-order model and 1.20 × 10−6 mol·L−1·s−1 for the pseudo-second-order model. The corresponding R2 were 0.88 and 0.91, respectively, suggesting a stronger agreement with the second-order kinetic model. The results indicate that Br− adsorption onto LDH/Ag-NPs is best described by second-order kinetics. Previous studies on bromide removal using LDH materials have also reported similar kinetic behavior [25,26]. Comparable trends were observed under ultrasonication. As shown in Figure 9, the linear kinetic plots for both pseudo-first-order and pseudo-second-order models were evaluated for Br− adsorption onto LDH/Ag-NPs under ultrasonicated conditions. The calculated rate constants were 2.67 × 10−5 s−1 for the pseudo-first-order model and 1.43 × 10−7 mol·L−1·s−1 for the pseudo-second-order model. Both models yielded an R2 value of 0.96, indicating good linearity.

3.5. Adsorption Thermodynamics

Thermodynamic factors, including entropy (ΔS), enthalpy (ΔH), and Gibbs free energy (ΔG), can be determined by employing following equations [27]:
Kd = Cs/Ce
ΔG = −RTlnKd
lnKd = ΔSR − ΔHRT
where R specifies a universal gas constant (8.314 J·mol−1). K−1 and Kd represent the thermodynamic equilibrium constant (L/g) or (mol). Cs and Ce indicate the concentration of adsorbate on solid and equilibrium concentration in solution, respectively. Moreover, ΔS and ΔH values are determined employing the Van’t Hoff equation. A linear relationship can be observed in the lnKd versus (1/T) plots, presenting a straight line. The slope of the line provides the value for ΔH, while the intercept corresponds to ΔS.
Table 1 displays the thermodynamic constraints for bromide ion adsorption onto LDH, indicating a spontaneous process. The observed drop in the equilibrium constant with rising temperature, along with the negative ΔH° values, confirms the exothermic nature of the process. Additionally, the negative ΔG° values affirm the spontaneous character of the reaction. Our experimental findings are generally consistent with prior research on the adsorption of bromide ions using natural materials [28]. The Van’t Hoff plot in Figure 10a graphically illustrates the thermodynamic trends, providing a visual representation of the adsorption process.
Table 2 presents the thermodynamic factors for bromide adsorption onto LDH/Ag-NPs. The Van’t Hoff plot in Figure 10b illustrates this adsorption process. ΔG°, ΔH°, and ΔS° values suggest the spontaneous nature of adsorption. The reduction in the equilibrium constant with rising temperature and the negative ΔH° values indicate that bromide ion adsorption is exothermic. Additionally, the negative ΔG° values confirm the spontaneity of the reaction. These findings are consistent with previous studies on bromide ion adsorption on LDH materials [26].

3.6. UV–Visible Spectroscopy

The λ max for LDH/Ag-NPs was observed at 393.5 nm with an absorbance of 3.0261 at the selected Ag-NPs concentration of 100 ppm, as shown in Figure 11a. This concentration was identified as optimal based on preliminary tests evaluating spectral intensity and stability. Figure 11b illustrates the absorbance stability over time at this concentration under continuous stirring.

3.7. Antibacterial Impact of Particles

The addition of Ag-NPs has demonstrated a notable ability to impede the proliferation of microbes in the sample, attributed to its inherent antimicrobial characteristics. Silver, recognized as a selective metal, falls within the category of inorganic antibacterial agents [29]. Expanding on these observations, an experiment was undertaken to evaluate bacterial progression on the samples. The outcomes showed a marked drop in bacterial development on surfaces having Ag-NPs compared to those with only LDH, as shown in Figure 12. These figures clearly illustrate the noticeable effect of bacterial growth inhibition.
This study intended to highlight the strong antibacterial properties of Ag through its interaction with bacterial DNA [30]. Ag-NPs interact with sulfur and phosphorus components present in DNA, proteins, and other subcellular structures, forming bonds that disrupt cellular functions [31]. This binding disrupts metabolic enzymes and bacterial electron transfer, hindering normal bacterial functions [32]. Additionally, Ag-NPs penetrate and gather in the bacterial internal membrane, instigating destabilization and improved permeability [33]. This promotes cellular content leakage and eventually leads to the death of bacterial cells. This positive influence on water purification was consistently observed in the samples even after one month of testing.

3.8. Characterization of Materials Pre- and Post-Adsorption of Br−

Figure 13a and Table 3 offer a comparative study of the FT-IR pattern for LDH, bromide-ion-loaded LDH, LDH/Ag-NPs, and bromide-ion-loaded-LDH/Ag-NPs. The broadband in the range of approximately (3460–3578) cm−1 is attributed to the hydroxyl (–OH) groups, which are associated with the interlayer water molecules, hydroxide layers, and ambient moisture, indicating the existence of these functional groups in the material [34,35]. A distinct band within the range of 1584–1633 cm−1 is attributed to the overlapping vibrational modes of C=O and N=O functional groups, likely originating from the presence of interlayer CO32− and NO3−, respectively. The prominent band at 1384 cm−1, attributed to carbonate anions within the interlayer gallery, aligns closely with spectra reported in previous studies [36]. The overlap of C–O (associated with the host CO32−) and N–O (from the host NO3−) vibrations is clearly recognized at about 1383–1384 cm−1. Two bands related to metal vibrations (M=Al) are found at about 784–835 cm−1 (O–M–O) and 555 cm−1 (MOH). Earlier studies have reported that bands below 900 cm−1 are associated with the M-O vibration and M-O-H bending modes [35]. The results suggest that LDH has a high abundance of host anions (CO32− and NO3−) in its interlayer region, and its external surface is likely to be positively charged due to the prevalence of hydroxyl (–OH) groups, originating mainly from Al-OH and Mg-OH sites on its surface, indicating a positively charged surface chemistry.
An XRD analysis was employed to examine the crystallographic properties of LDH, LDH with bromide ions, LDH/Ag-NPs, and LDH/Ag-NPs with Br− ions. Figure 13b highlights the X-ray patterns of all the samples. These XRD patterns underwent refinement using the Rietveld method for determining phase composition, providing unit cell parameters for the LDH phase. The XRD pattern revealed a composition including pure LDH and LDH/Ag-NPs. The LDH phase was identified as a low-crystalline, smaller phase with broad and low-intensity peaks at 10.7° and 20.9°. Conversely, the LDH phase emerged as the main phase with the prominent peaks at 29.7°, 32.6°, 34.9°, 37.1°, 47.4°, and 62.9°. Additionally, Ag-NPs were recognized as another minority phase, characterized by a slender peak at 2θ = 21.8°, along with peaks at 37.4°, 31.8°, and 43.9°. The newly observed reflections corresponding to Ag-NPs showed similarities to previously reported XRD patterns associated with the incorporation of silver particles in ZnAl LDH materials [37,38].
The XRD analyses revealed that the LDH crystal structure adopts a rhombohedral system with an R-3m space group, indicating a highly symmetrical and ordered arrangement of the unit cell parameters, consistent with the typical crystal structure of LDH. The adsorption of bromide ions indicated LDH as the main phase, but with the formation of new lines. Given the results demonstrating the efficiency of the catalytic scheme based on LDH/Ag-NPs and bromide under ligand-free conditions, we explored the effect of electron-withdrawing/donating functional groups exchanged within aromatic core. In general, this study revealed a noticeable impact of the electron-withdrawing/donating competences of the substitutional functional groups. It became clear that the highly electron-donating amine group did not facilitate the reaction in these instances, and overall, the lack of a substituent resulted in low yields. Based on the XRD data and the application of the Debye–Scherer equation, the average particle size was determined, using the higher intensity peak. This calculation was performed using Equation (7) [39,40].
d = k λ β c o s θ
where λ indicates the wavelength of X-ray, β specifies the FWHM (full width at half-maximum), θ denotes the Bragg angle, and K represents the Scherrer constant (0.94).
The determined size of the Ag-NPs was around 20 ± 3.5 nm. The adsorption of Br− ions to the material’s surface did not cause any change in the crystal structure, affirming the strength of the material. In summary, this research introduces LDH/Ag-NPs as an effective and versatile solution for sustainable water treatment applications. Compared to other bromide-removal materials, such as activated carbon and ion exchange resins, LDH/Ag-NPs exhibit competitive removal efficiency, with added benefits of tunable composition, surface modification through Ag-NPs, and potential antimicrobial properties.
Future studies may explore long-term adsorption performance in various reactor systems such as plug flow reactors and sequencing batch reactors. Integration with other advanced materials such as metal–organic frameworks (MOFs) could further enhance performance [41,42]. Additionally, the material’s potential for removing other contaminants, such as fluoride, as demonstrated in Zn–Al LDHs on aluminum foams [43], needs investigation. The risk of Ag-NPs leaching and the subsequent persistence of Ag NPs in water [44] remains unaddressed in this study and should be considered in future assessments. Furthermore, incorporating zirconium-based supports or palladium nanoparticles may offer added benefits in complex decontamination applications, as these materials have been explored for pollutant degradation and general decontamination [45,46].
In contrast to the current study using LDH/Ag-NPs under controlled conditions, previous research has demonstrated that Ag-impregnated activated carbon can effectively remove bromide from surface waters, with its performance significantly influenced by factors such as surface area, chloride ions, and natural organic matter [47]. Building on this, future investigations should explore the behavior of LDH/Ag-NPs in more complex water matrices, particularly considering the potential impact of co-existing anions and organic matter on bromide adsorption efficiency.

4. Conclusions

This investigation included the synthesis, characterization, and comparative assessment of LDH and LDH/Ag-NPs, revealing their effectiveness in bromide removal from drinking water and highlighting their potential for water treatment applications. Our evaluation included both batch test and packed-bed column operations to provide a comprehensive understanding of their performance. Furthermore, we explored the kinetics and thermodynamics of the adsorption processes to unravel their nature and undelaying pathways. The thermodynamic studies yielded decisive understanding of the adsorptive removal of bromide ions from water. The equilibrium constant decreases as temperature rises, and the negative ΔH° values confirm that bromide ion adsorption is an exothermic process. Simultaneously, the negative ΔG° values signified the spontaneity of the reaction. These thermodynamic properties are pivotal for comprehending the energetics of the adsorption progression. Furthermore, this research investigated the antibacterial impacts of the adsorbent materials, specifically those having Ag-NPs. The outcomes showed a significant drop in bacterial development on the Ag-NPs-containing adsorbent compared to LDH. This highlights the dual potential of these materials for both water disinfection and bromide removal, adding a valuable dimension to their applications.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w17111578/s1, Table S1: The results obtained during adsorption of Br– ion onto LDH under (a) persistent temperature and time, (b) persistent temperature and mass, (c) constant time and mass, and (d) persistent temperatures and mass employing ultrasonication.; Table S2: The results obtained during adsorption of bromide onto LDH + Ag-NPs at (a) persistent temperature and time, (b) persistent temperature and mass, (c) persistent time and mass, and (d) constant temperatures and mass employing ultrasonication.

Author Contributions

Conceptualization, A.E.A.-R., A.I.A. and M.K.S.; methodology, A.E.A.-R., A.I.A. and M.T.E.; software, M.T.E. and H.A.-I.; validation, A.E.A.-R. and B.M.; formal analysis, E.A.-S. and M.A.-E.; investigation, A.E.A.-R. and M.T.E.; writing—original draft preparation, A.E.A.-R. and M.T.E.; writing—review and editing, A.I.A., B.M. and M.K.S.; visualization, E.A.-S., M.A.-E. and A.A.-S.; supervision, A.E.A.-R., A.I.A. and M.K.S.; project administration, A.E.A.-R. and M.K.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All data are included in the manuscript.

Acknowledgments

This research was supported by Tafila Technical University.

Conflicts of Interest

The authors declare no conflicts of interest.

References

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Water 17 01578 g001
Figure 1. The schematic illustration of column operation.
Figure 1. The schematic illustration of column operation.
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Figure 2. Bromide removal effectiveness as a function of adsorbent dosage for LDH and LDH + Ag-NPs, with temperature and time maintained at constant values.
Figure 2. Bromide removal effectiveness as a function of adsorbent dosage for LDH and LDH + Ag-NPs, with temperature and time maintained at constant values.
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Figure 3. The effect of contact time on bromide removal efficiency by LDH and LDH + Ag-NPs at fixed adsorbent mass and temperature.
Figure 3. The effect of contact time on bromide removal efficiency by LDH and LDH + Ag-NPs at fixed adsorbent mass and temperature.
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Figure 4. The effect of temperature on bromide removal efficiency by LDH and LDH + Ag-NPs at fixed adsorbent mass and residence time.
Figure 4. The effect of temperature on bromide removal efficiency by LDH and LDH + Ag-NPs at fixed adsorbent mass and residence time.
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Figure 5. Variation in conductivity trend with each filtration round for (a) LDH and (b) LDH/Ag-NPs.
Figure 5. Variation in conductivity trend with each filtration round for (a) LDH and (b) LDH/Ag-NPs.
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Figure 6. Kinetic modeling of bromide adsorption onto LDH, with panel (a) illustrating the first-order kinetic profile and panel (b) showing the second-order kinetic profile.
Figure 6. Kinetic modeling of bromide adsorption onto LDH, with panel (a) illustrating the first-order kinetic profile and panel (b) showing the second-order kinetic profile.
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Figure 7. Linear kinetic plots illustrating the adsorption of bromide by LDH under ultrasonication, with (a) showing the pseudo-first-order model and (b) showing the pseudo-second-order model.
Figure 7. Linear kinetic plots illustrating the adsorption of bromide by LDH under ultrasonication, with (a) showing the pseudo-first-order model and (b) showing the pseudo-second-order model.
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Figure 8. Comparative kinetic analysis of Br− adsorption onto LDH with Ag-NPs, featuring (a) pseudo-first-order and (b) pseudo-second-order kinetic models, highlighting the effect of Ag-NPs on adsorption kinetics.
Figure 8. Comparative kinetic analysis of Br− adsorption onto LDH with Ag-NPs, featuring (a) pseudo-first-order and (b) pseudo-second-order kinetic models, highlighting the effect of Ag-NPs on adsorption kinetics.
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Figure 9. Ultrasonication-enhanced Br− adsorption onto LDH with Ag-NPs: (a) pseudo-first-order and (b) pseudo-second-order kinetic models, illustrating the synergistic effects of Ag-NPs and ultrasonication on adsorption kinetics.
Figure 9. Ultrasonication-enhanced Br− adsorption onto LDH with Ag-NPs: (a) pseudo-first-order and (b) pseudo-second-order kinetic models, illustrating the synergistic effects of Ag-NPs and ultrasonication on adsorption kinetics.
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Figure 10. Van’t Hoff plot for adsorption of Br− ions onto (a) LDH and (b) LDH/Ag-NPs.
Figure 10. Van’t Hoff plot for adsorption of Br− ions onto (a) LDH and (b) LDH/Ag-NPs.
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Figure 11. (a) λ max of LDH with Ag-NPs and (b) absorbance of LDH with Ag-NPs at 100 ppm concentration.
Figure 11. (a) λ max of LDH with Ag-NPs and (b) absorbance of LDH with Ag-NPs at 100 ppm concentration.
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Figure 12. Bacterial growth assay for (a) LDH and (b) LDH combined with Ag-NPs.
Figure 12. Bacterial growth assay for (a) LDH and (b) LDH combined with Ag-NPs.
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Figure 13. (a) FTIR pattern and (b) XRD spectra of LDH, bromide-ion-loaded LDH, LDH/Ag-NPs, and bromide-ion-loaded LDH/Ag-NPs.
Figure 13. (a) FTIR pattern and (b) XRD spectra of LDH, bromide-ion-loaded LDH, LDH/Ag-NPs, and bromide-ion-loaded LDH/Ag-NPs.
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Table 1. Thermodynamic parameters for bromide ion adsorption onto LDH.
Table 1. Thermodynamic parameters for bromide ion adsorption onto LDH.
Temperature (°C)103/TKdlnKdΔG° (kJ/mol)ΔS° (J/mol/K)ΔH° (kJ/mol)
223.3902.0000.693−1.700−39.235−13.354
323.2791.8100.591−1.500
423.1751.4800.392−1.027
523.0771.2200.199−0.537
Table 2. Thermodynamic factors for bromide ion adsorption onto LDH + Ag-NPs.
Table 2. Thermodynamic factors for bromide ion adsorption onto LDH + Ag-NPs.
Temperature (°C)103/TKdlnKdΔG° (kJ/mol)ΔS° (J/mol/K)ΔH° (kJ/mol)
223.3902.2850.826−2.026−43.747−15.011
323.2792.0150.701−1.777
423.1751.6230.484−1.268
523.0771.3080.268−0.725
Table 3. FTIR peaks assigned for LDH, LDH loaded with Br− ions, LDH/Ag-NPs, and LDH/Ag-NPs loaded with Br− ions.
Table 3. FTIR peaks assigned for LDH, LDH loaded with Br− ions, LDH/Ag-NPs, and LDH/Ag-NPs loaded with Br− ions.
FunctionalitiesLDHLDH/Br−LDH + Ag-NPsLDH + Ag-NPs/Br−
Al–OH555555555555
O–Al–O835805786784
C–O/N–O1383138313841384
C=O/N=O1633163316031584
–OH3460357835603464
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Al-Rawajfeh, A.E.; Alrawashdeh, A.I.; Etiwi, M.T.; Mainali, B.; Shahid, M.K.; Al-Itawi, H.; Al-Shamaileh, E.; Al-E’bayat, M.; Al-Sahary, A. Fabrication of Silver-Incorporated Zn-Al Layered Double Hydroxide: Characterization and Bromide-Adsorption Performance. Water 2025, 17, 1578. https://doi.org/10.3390/w17111578

AMA Style

Al-Rawajfeh AE, Alrawashdeh AI, Etiwi MT, Mainali B, Shahid MK, Al-Itawi H, Al-Shamaileh E, Al-E’bayat M, Al-Sahary A. Fabrication of Silver-Incorporated Zn-Al Layered Double Hydroxide: Characterization and Bromide-Adsorption Performance. Water. 2025; 17(11):1578. https://doi.org/10.3390/w17111578

Chicago/Turabian Style

Al-Rawajfeh, Aiman Eid, Albara Ibrahim Alrawashdeh, Mohammad Taha Etiwi, Bandita Mainali, Muhammad Kashif Shahid, Hosam Al-Itawi, Ehab Al-Shamaileh, Mariam Al-E’bayat, and Al Al-Sahary. 2025. "Fabrication of Silver-Incorporated Zn-Al Layered Double Hydroxide: Characterization and Bromide-Adsorption Performance" Water 17, no. 11: 1578. https://doi.org/10.3390/w17111578

APA Style

Al-Rawajfeh, A. E., Alrawashdeh, A. I., Etiwi, M. T., Mainali, B., Shahid, M. K., Al-Itawi, H., Al-Shamaileh, E., Al-E’bayat, M., & Al-Sahary, A. (2025). Fabrication of Silver-Incorporated Zn-Al Layered Double Hydroxide: Characterization and Bromide-Adsorption Performance. Water, 17(11), 1578. https://doi.org/10.3390/w17111578

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