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Article

Aqueous Cymbopogon citratus Extract Mediated Silver Nanoparticles: Part II. Dye Degradation Studies

by
Himabindu Kurra
1,2,
Aditya Velidandi
3,
Ninian Prem Prashanth Pabbathi
3 and
Vikram Godishala
1,2,*
1
Department of Biotechnology, Vaagdevi Degree and P.G. College, Warangal 506001, Telangana, India
2
Department of Biotechnology, Bharatiya Engineering Science and Technology Innovation University, Gorantla 515231, Andhra Pradesh, India
3
Department of Biotechnology, National Institute of Technology, Warangal 506004, Telangana, India
*
Author to whom correspondence should be addressed.
Eng 2025, 6(5), 102; https://doi.org/10.3390/eng6050102
Submission received: 20 March 2025 / Revised: 14 May 2025 / Accepted: 15 May 2025 / Published: 19 May 2025
(This article belongs to the Special Issue Emerging Technologies for the Treatment and Reduction of Pollutants in Industrial Processes)
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Abstract

:
This study investigates the catalytic potential of silver nanoparticles (AgNPs) synthesized using aqueous Cymbopogon citratus (lemongrass) extract for the degradation of toxic textile dyes, offering an eco-friendly solution to industrial wastewater treatment. The green-synthesized AgNPs demonstrated remarkable degradation efficiency (>94%) for multiple dyes, such as rhodamine B, methyl red, methyl orange, methylene blue, eosin yellow, and Eriochrome black T, in the presence of sodium borohydride. Optimization studies employing a one-factor-at-a-time approach revealed the critical influence of AgNPs and reductant concentration, temperature, and pH. Kinetic analysis confirmed pseudo-first-order degradation behavior. Reactive species scavenging experiments established that hydroxyl radicals and holes played dominant roles in the degradation mechanism. Notably, the AgNPs retained catalytic activity across eight reuse cycles with negligible performance loss, demonstrating strong potential for repeated application. Comparative analysis with data from the literature highlights the superior performance of C. citratus-derived AgNPs in terms of reaction rate and efficiency. This work underscores the value of plant-extract-mediated AgNPs synthesis not only for its environmental compatibility but also for its catalytic effectiveness. The study advances the practical applicability of green nanotechnology in wastewater remediation and supports its integration into sustainable industrial practices.

1. Introduction

The depletion of freshwater reserves caused by the impacts of global warming has emerged as a major obstacle confronting humanity in recent times [1]. Water pollution is a global concern that poses significant threats to both human health and the environment [2]. Regrettably, various elements contribute to the pollution of water sources, such as chemical residue discharge from dyeing facilities [3]. These chemicals are known for their chemical stability, and they are major contributors to waterborne infections [4]. Specifically, the industrial waste produced during textile manufacturing comprises a blend of diverse dyes, as well as other natural and mineral pollutants [5,6]. The discharge of organic dyes or dye-based effluents into water has become a pervasive issue worldwide, leading to a scarcity of clean and safe water sources due to the inherent toxicity and non-biodegradable nature of most dyes [7,8]. As these dyes find extensive use in industries such as food, textiles, and leather, various methods such as adsorption, electrochemical destruction, ozonation, ion exchange, membrane filtration, biodegradation, solvent extraction, flocculation, coagulation, and chemical precipitation have been developed to mitigate dye pollution and safeguard the environment and aquatic ecosystems [9,10,11]. Unfortunately, these approaches often come with high operational costs and fall short of achieving complete removal of organic dyes from wastewater [12,13].
Extensive research is being conducted on nanoparticles (NPs) because of their size-related benefits, stability, strength, activity, substantial surface area, and distinctive chemical and biological characteristics [14,15]. These attributes offer a broad range of applications in nanomedicine, such as their use as antimicrobial agents, in wound dressing, in the treatment of diabetic wounds, for diagnostic purposes, for targeted drug delivery, and in biomedical applications as biosensors [16,17,18,19,20]. Transitional metal NPs like silver (Ag) [21], gold [22,23,24], zinc [25,26], copper [27,28], iron [29,30], palladium [31,32], and platinum [33,34] are receiving increased attention because of their versatile characteristics and diverse applications, particularly in serving as catalytic and antimicrobial agents [35,36,37]. Silver nanoparticles (AgNPs), in particular, have garnered attention in the field of nanotechnology due to their economical nature, non-toxic attributes, environmental friendliness, and expansive surface area [38,39]. Compared to other noble and transition metals, Ag is a cost-effective choice [40]. The plasmonic impact of Ag finds widespread application in catalyst-related activities [3]. The synthesis process plays a crucial role in determining the size and shape of AgNPs, which subsequently influences their functional properties [41,42]. Furthermore, an examination of the literature reveals that the removal percentage and reaction time in the photocatalytic process are contingent upon the size of the AgNPs utilized [43,44].
Various methods exist for the synthesis of AgNPs, including chemical reduction, mechanical synthesis, and biological approaches [45,46]. The synthesis of AgNPs has been documented using all these techniques. Nevertheless, a recent shift toward environmentally friendly practices in AgNP synthesis has emphasized innovative approaches involving microbes, bacteriophages, and animal extracts [47,48]. These methods leverage synergies to enhance efficacy. Notably, reducing Ag ions to AgNPs using plant extracts has gained prominence, as it seeks to mitigate the adverse effects associated with conventional synthetic methods and aims to establish environmentally benign procedures in this field [49,50,51]. The inherent presence of secondary metabolites, amino acids, proteins, and vitamins in plant extracts has facilitated enhanced control over NP sizes and shapes during the green synthesis process [52,53]. Several crucial factors play a role in achieving the desired nanometric size in this process, including the concentration of the precursor (typically silver nitrate (AgNO3)), the type and concentration of extract used, the temperature, the pH, and the reaction time [54,55,56]. While the optimization of synthesis methods involves complex interrelationships among these factors, the relatively short time scales associated with green synthesis make it an appealing and feasible alternative to traditional chemical synthesis methods [53].
Previously, authors have reported synthesizing AgNPs using aqueous Cymbopogon citratus (lemongrass) extract as a reducing agent [57]. Optimal conditions were 1.50 mM AgNO3, 3.5% (v/v) extract, pH 9, 100 °C, and 60 min reaction time. Characterization confirmed spherical AgNPs with a hydrodynamic diameter of 135.41 ± 49.30 nm, zeta potential of −29.9 ± 1.4 mV, and crystalline structure (peaks at 38.19°, 44.23°, 64.43°, and 77.38°). Field emission scanning electron microscopes and transmission electron microscopes revealed minimal aggregation, with sizes ranging from 40 to 110 nm and 15 to 62.5 nm, respectively. Energy dispersive X-ray spectroscopy confirmed elemental silver. The AgNPs exhibited significant antibacterial, anti-inflammatory, antidiabetic, and antioxidant properties.
Based on the above-stated information, the present work focuses on the potential catalytic application of AgNPs synthesized using aqueous C. citratus extract in the degradation of several textile dyes in the presence of sodium borohydride (SBH). The synthesis and characterization of the reported AgNPs have already been published [57]. The objectives of the present work are: (i) to determine the catalytic potential of AgNPs in the degradation of textile dyes (such as rhodamine B (RhB), methyl red (MR), methyl orange (MO), methylene blue (MB), eosin yellow (EY), and Eriochrome black T (EBT)), (ii) to explore the possible role of scavengers in the degradation process, (iii) to understand the influence of various physicochemical parameters (such as AgNP concentration, SBH concentration, reaction temperature, and reaction pH) in the degradation of dyes via the one-factor-at-a-time (OFAT) approach, (iv) to evaluate the reusability of AgNPs in dye degradation, and lastly, (v) to determine the possible mechanism involved in the dye degradation in presence of AgNPs and SBH.

2. Materials and Methods

2.1. Materials

RhB, MR, MO, MB, EY, EBT, SBH, hydrochloric acid, sodium hydroxide, and 0.22 μm PVDF syringe filters were purchased from HiMedia Laboratories Pvt. Ltd. (Maharashtra, India). Sterile double-distilled water (DW; pH was in the range of 6.6 to 7.4) was used for the work. The pH of solutions was adjusted by using 1 M sodium hydroxide and 1 N hydrochloric acid, accordingly, wherever required. Stock solutions and necessary dilutions were made using DW. Non-ionic detergent was used to wash the glassware, which was later rinsed with DW several times and then dried in a hot air oven before use. An ultraviolet–visible spectrophotometer (UV-Vis spec; Shimadzu UV-1800, Kyoto, Shimadzu, Japan) was used to record the absorbance values for all dye degradation experiments.

2.2. Stock Solutions

The AgNP stock solution was prepared by adding 1 mg of AgNPs to 1 mL of DW. Furthermore, the solution was sonicated (20% amplitude, 10 min, pulse on/off 5 s) for uniform distribution of AgNPs in the solution. The AgNPs were sonicated under the same conditions before use. All stock solutions were freshly prepared and used. All dye stock solutions were prepared by dissolving 100 mg of dye in 100 ml of DW to achieve 1 mg/mL concentration. Absorbance spectra of the dye solutions were recorded to determine maximum absorbance (λmax) after 60× dilution of stock solutions using UV-Vis spec (Figure 1).

2.3. Catalytic Studies

The final reaction volume for the dye degradation experiments was 5 mL, unless specified. At regular intervals, the samples were centrifuged to remove AgNPs at 15,000 rpm for 5 min, followed by dilution, and the degradation of dyes was recorded by UV-Vis spec (300 to 700 nm). The dye degradation was monitored by the drop in the value of the absorbance peak (RhB: 554 nm, MR: 430 nm, MO: 464 nm, MB: 664 nm, EY: 514 nm [58], and EBT: 573 nm [59] (Figure 1)). Furthermore, degradation percentage (%) was calculated by using Equation (1).
D e g r a d a t i o n   % = A 0 − A t A 0 × 100
where ‘A0′ and ‘At’ are the absorbance of dye solution at ‘0’ and ‘time’ (regular intervals) min, respectively.

2.3.1. Dye Degradation

The typical reaction contains 5 mL of dye solution, 3 mg of SBH, and 20 µL (20 µg) of AgNPs. The temperature and pH of the reaction solution were maintained at 37 °C and 7, respectively. Absorbance values were recorded at regular intervals (time = 20 min (RhB and EBT); 15 min (MO and EY); and 10 min (MB and MR)).

2.3.2. Role of Scavengers

The effect of scavengers was studied to determine the possible involvement of reactive species (hydroxyl radicals (•OH), superoxide anions (•O2–), holes (h+), and electrons (e–)) in the degradation of RhB, MR, MO, MB, EY, and EBT dyes in presence of AgNPs and SBH. Scavengers such as isopropyl alcohol (IPA), benzoquinone (BQ), ethylenediaminetetraacetic acid (EDTA), and AgNO3 were used at a concentration of 1 mM to quench •OH, •O2–, h+, and e– reactive species, respectively. A degradation reaction with no scavengers was used as a control.

2.3.3. Influence of Parameters

To study the influence of various parameters on the degradation of dyes, four influencing factors were considered, such as AgNPs (as nano-catalyst) concentration, SBH (as reducing agent) concentration, reaction temperature, and reaction pH. The effect of AgNP concentration on the dye degradation was studied by varying the concentrations between 20, 40, 60, 80, 100, 120, and 140 μg. SBH concentration was fixed at 3 mg, whereas the temperature and pH of the reaction solution were maintained at 37 °C and 7, respectively. To determine the effect of SBH concentration on the dye degradation, varying concentrations, such as 3, 6, 9, 12, 15, 18, and 21 mg, were used. The temperature and pH of the reaction solution were maintained at 37 °C and 7, respectively. The observed AgNP concentration from the previous experiment was used. The effect of the temperature on the reduction of dyes was studied by varying the temperature of the reaction solution between 20, 30, 40, 50, 60, 70, and 80 °C. pH was maintained at 7. The observed AgNP and SBH concentrations from previous experiments were used. To study the influence of pH on the degradation of dyes, the pH of the reaction solution was adjusted to 3, 4, 5, 6, 7, 8, 9, and 10. Observed temperature, AgNPs, and SBH concentrations from previous experiments were used.

2.3.4. Reusability

The reusability of the AgNPs as a nano-catalyst was determined by employing the observed conditions from Section 2.3.3. in the degradation of dyes. Reusability experiments were performed with 100 mL dye solution. At the end of each degradation cycle, dye solution was centrifuged for 5 min at 15,000 rpm to remove the AgNPs, then the obtained pellet was re-suspended in 20 mL DW, followed by sonication for 10 min. At the end, the pellet was dried (70 °C) overnight and reused for the dye degradation.

2.3.5. Pseudo-First-Order Kinetics

The dye degradation kinetics were evaluated under the assumption that the SBH concentration remains uniform throughout the dye reduction reaction, as the concentration of reducing agent (SBH) used was much higher than that of the dye employed, and thus, they obey pseudo-first-order reaction kinetics according to the Langmuir–Hinshelwood model [60,61]. The pseudo-first-order reaction was represented by Equation (2) [60,61]. Plotting the graph with ln [At] vs. ‘time’ min gives a straight line going downwards with slope ‘k’, which is the pseudo-first-order rate constant [60,61].
k = 1 t l n A 0 A t
where ‘k’ is the pseudo-first-order rate constant, ‘A0’ is the absorbance of dye solution at ‘0’ min, and ‘At’ is the absorbance at ‘time’ (regular intervals) min.

2.4. Statistical Analysis

All experiments were carried out in triplicate (n = 3). Mean values ± standard deviations were represented as error bars in graphs. The statistical significance of the data was determined by Student’s t-test (p value <0.05). Microsoft Office Excel 2021 was used for graphical representation of results and analysis.

3. Results and Discussion

3.1. Dye Degradation Studies

Table 1 provides data on the degradation of dyes, indicating the percentage degradation, time required for degradation, degradation rate constant (k), and the correlation coefficient (R2), which reflects the fit of the degradation data to the pseudo-first-order kinetic model.
RhB (Figure 2) shows the degradation percentage (97.34 ± 1.12%) over a duration of 120 min. The rate constant (k) is 0.0355 ± 0.0042 min−1, and the R2 value of 0.9366 ± 0.0218 indicates a strong correlation between the observed experimental data points. MR (Figure 3) showed a degradation percentage of 96.89 ± 1.28% under 70 min with a rate constant of 0.0456 ± 0.0043 min−1, indicating a faster degradation rate, though the R2 (0.9288 ± 0.0262) is slightly lower than RhB. MO (Figure 4) degraded by 95.82 ± 2.37% in 90 min, with a rate constant of 0.0413 ± 0.0028 min−1. It had a slightly lower degradation percentage compared to RhB and MR. MB (Figure 5) showed a 95.16 ± 1.77% degradation in 60 min, the shortest time, with a rate constant of 0.0539 ± 0.0036 min−1 and an R2 of 0.9349 ± 0.0308. The combination of a relatively fast rate constant and shorter degradation time suggests efficient degradation. EY (Figure 6) had a degradation percentage of 96.41 ± 1.57%, taking 105 min. Its rate constant is 0.0363 ± 0.0032 min−1, and the R2 of 0.9232 ± 0.0387. EBT (Figure 7) had the lowest degradation percentage (94.36 ± 1.73%) and the slowest rate constant (0.0222 ± 0.0029 min−1), with a degradation time of 140 min. The R2 value (0.8843 ± 0.0165) was also the lowest. In summary, MR and MB degraded more quickly, while RhB and EY required more time. EBT showed the least efficient degradation and the weakest model correlation.

3.2. Role of Scavengers

In dye degradation processes, reactive species such as •OH, •O2–, h+, and e– play crucial roles in breaking down complex dye molecules into simpler, non-toxic compounds. Scavengers are employed to selectively inhibit the activity of these reactive species, allowing researchers to identify the specific contributions of each species to the overall degradation process. By observing the reduction in dye degradation when these scavengers are introduced, the relative importance of each reactive species in the degradation mechanism can be assessed, offering insights into the pathways that govern the dye degradation process.
Table 2 summarizes the degradation percentages of dyes in the presence of different scavengers, providing insight into the contribution of reactive species such as •OH, •O2–, h+, and e– in the dye degradation process. The scavengers used were IPA, scavenger for •OH; BQ, scavenger for •O2–; EDTA, scavenger for h+; and AgNO3, scavenger for e–. The values indicate the degradation percentage observed under control conditions (without scavengers) and in the presence of each scavenger.
For RhB (Figure 8a), control showed 97.37 ± 1.55% degradation. In the presence of IPA, 43.57 ± 2.27% degradation was observed, showing that •OH species play a significant role in RhB degradation (a large decrease compared to control). In the presence of BQ, 71.60 ± 2.72% degradation was observed, indicating •O2– species are less significant than •OH but still contribute substantially. In the presence of EDTA, 87.49 ± 2.64% degradation was observed, suggesting h+ species contribute moderately to degradation. AgNO3 showed 88.31 ± 1.82% degradation, indicating a small role for e–.
For MR (Figure 8b), the control showed 96.44 ± 1.35% degradation. In the presence of IPA, 75.02 ± 1.76% degradation was observed, showing that •OH species have a moderate role in MR degradation. In the presence of BQ, 59.56 ± 2.12% degradation was observed, revealing the more prominent role of •O2–. In the presence of EDTA, 68.80 ± 1.95% degradation was observed, indicating that h+ species play a moderate role. AgNO3 showed 86.26 ± 2.14% degradation, suggesting e– species play a less significant role in MR degradation.
For MO (Figure 8c), the control showed 95.36 ± 2.34% degradation. In the presence of IPA, 83.92 ± 2.53% degradation was observed, indicating that •OH species have a lesser effect on MO degradation. In the presence of BQ, 84.10 ± 2.04% degradation was observed, showing that •O2– species are not crucial in MO degradation. In the presence of EDTA, 54.39 ± 1.92% degradation was observed, highlighting a significant role for h+. AgNO3 showed 63.38 ± 1.76% degradation, indicating e– species are moderately involved in MO degradation.
For MB (Figure 8d), the control showed 95.63 ± 1.36% degradation. In the presence of IPA, 83.53 ± 1.73% degradation was observed, suggesting that •OH species play a less significant role. In the presence of BQ, 61.02 ± 2.67% degradation was observed, indicating that •O2– species have a more significant effect on MB degradation. In the presence of EDTA, 74.99 ± 1.36% degradation was observed, pointing to the importance of h+. AgNO3 showed 67.80 ± 2.33% degradation, suggesting e– species also contribute to the MB degradation process.
For EY (Figure 8e), control showed 95.85 ± 2.14% degradation. In the presence of IPA, 62.64 ± 1.66% degradation was observed, indicating that •OH species play a significant role. In the presence of BQ, 84.10 ± 1.85% degradation was observed, showing •O2– species are less involved. In the presence of EDTA, 74.31 ± 2.61% degradation was observed, indicating that h+ species play a moderate role. AgNO3 showed 66.38 ± 1.48% degradation, suggesting e– species also contribute significantly.
For EBT (Figure 8f), control showed 94.51 ± 1.27% degradation. In the presence of IPA, 53.87± 1.99% degradation was observed, indicating that •OH species have a substantial role. In the presence of BQ, 68.64 ± 1.73% degradation was observed, showing •O2– species are involved, but less so than •OH. In the presence of EDTA, 72.36 ± 2.45% degradation was observed, indicating h+ species contribute moderately. AgNO3 showed 87.30 ± 1.39% degradation, suggesting e– species have a smaller role in EBT degradation.
Control degradation is very high for all dyes, around 94 to 97%, showing that the system (without scavengers) is highly efficient at dye degradation. IPA (•OH scavenger) consistently shows lower degradation percentages across all dyes, indicating that •OH species are crucial for the degradation of RhB and EBT dyes, but less so for MO and MB dyes. BQ (•O2– scavenger) shows varied degradation levels, with RhB and MR dyes being more dependent on •O2–. MO was less dependent. EDTA (h+ scavenger), which suggests that h+ species play a significant role in dye degradation, especially in RhB and MO dyes. AgNO3 (e– scavenger) results show that e– species contribute to degradation, but their significance varies between dyes, with MR and EBT showing higher dependence on e–. The degradation of dyes is dependent on multiple reactive species. The •OH and h+ species seem to play the most dominant roles across different dyes, with •O2– and e– species contributing variably. Different dyes rely on different reactive species, as demonstrated by their varying degradation percentages in the presence of specific scavengers (Figure 8g).
The interaction of reactive species such as •OH, •O2–, h+, and e– with complex dye molecules in the presence of AgNPs and SBH facilitates the degradation of dyes through a series of oxidative and reductive processes. •OH species are highly reactive and can attack dye molecules at various sites, leading to the breakdown of complex structures. For instance, •OH radicals preferentially attack azo bonds in dyes, facilitating their cleavage and subsequent degradation [62]. •O2– species can participate in the degradation process by further oxidizing the dye molecules or by generating additional reactive species through secondary reactions [63]. In photocatalytic systems, the generation of e–-h+ pairs is crucial. The h+ can oxidize water or OH ions to produce •OH radicals, while the e– can reduce oxygen to form •O2–, both contributing to dye degradation [64]. Figure 9 presents a schematic representation of dye degradation in presence of AgNPs and SBH based on the available literature.

3.3. Influence of Parameters

To investigate the degradation of dyes, four parameters were selected for analysis: the concentration of AgNPs, which function as the nano-catalyst, the concentration of SBH acting as the reducing agent, the reaction temperature, and the reaction pH of the solution via the OFAT approach. AgNPs facilitate the catalytic breakdown of dyes by increasing the reaction rate, while the SBH serves as the electron donor to initiate the reduction process. Reaction temperature influences the kinetic energy of reactant molecules, potentially accelerating the degradation reaction. Lastly, the reaction pH of the solution can affect the surface charge and stability of the AgNPs, as well as the protonation state of the dye molecules, further altering the reaction efficiency. By examining these parameters, this study aimed to determine the conditions for maximum dye degradation efficiency.

3.3.1. Nano-Catalyst (AgNP) Concentration

The concentration of AgNPs plays a crucial role in the catalytic degradation of dyes, as AgNPs are known to exhibit excellent catalytic properties due to their high surface-area-to-volume ratio and unique surface chemistry. AgNPs act as active sites for the electron transfer and breakdown of dye molecules, significantly enhancing the reaction rate. When present in optimal concentrations, AgNPs can accelerate the electron transfer process, facilitating the reduction of dye molecules, particularly in reactions involving reducing agents like SBH. However, concentrations that are too low may lead to insufficient catalytic activity, while excessively high concentrations can cause agglomeration of AgNPs, reducing their available surface area and thus diminishing their catalytic efficiency. Moreover, higher concentrations can introduce issues related to AgNPs’ stability and dispersion, potentially leading to inconsistent reaction kinetics. Therefore, studying the concentration of AgNPs is critical in identifying the balance between efficient catalytic activity and practical limitations, ensuring effective dye degradation.
The concentrations of AgNPs ranged from 20 µg to 140 µg, while the SBH concentration, reaction temperature, reaction pH, reaction volume, and reaction time were constant at 3 mg, 37 °C, pH 7, 5 mL, and 35 min throughout the experiments (Figure 10). The degradation percentage increases as AgNP concentration rises, peaking at 80 µg with a degradation efficiency of 95.69 ± 1.41%. After this concentration, degradation efficiency begins to decrease slightly, with 87.18 ± 1.57% for 100 µg and further declining to 63.67 ± 2.10% for 140 µg.
The rate constant follows a similar trend, increasing from 0.0290 ± 0.0024 min−1 at 20 µg to a maximum of 0.1094 ± 0.0053 min−1 at 80 µg, then gradually decreasing. This indicates that the reaction rate is initially enhanced by increasing AgNP concentration but shows diminishing returns or possible inhibition beyond a certain threshold. The high R2 throughout, ranging between 0.9509 and 0.9825, suggests a strong linear relationship between AgNP concentration and the degradation rate. Maximum degradation time decreases as AgNP concentration increases, but beyond 80 µg, it begins to rise again, signifying a possible limitation in the reaction kinetics at higher concentrations.
The optimal concentration for maximum degradation efficiency and reaction rate occurs at 80 µg AgNPs. Beyond this, higher concentrations lead to reduced degradation efficiency and a slower reaction rate, possibly due to saturation or aggregation effects.

3.3.2. Reducing Agent (SBH) Concentration

The concentration of the reducing agent, SBH, is a vital factor in the degradation of dyes, as it directly drives the reduction reaction. SBH is a strong reductant that provides electrons, enabling the breakdown of dye molecules into less complex, often colorless, compounds. In the presence of a catalyst like AgNPs, SBH facilitates electron transfer to the dye, accelerating the degradation process. An optimal concentration of SBH ensures that sufficient electrons are available for the reaction, promoting rapid and efficient dye breakdown. However, if the concentration of SBH is too low, the electron supply may be insufficient, leading to incomplete or slower degradation. On the other hand, an excessively high concentration of SBH can result in an excess of reducing equivalents, potentially causing side reactions or the destabilization of the catalytic system, such as the agglomeration of AgNPs, which can decrease the overall efficiency. Thus, balancing the concentration of SBH is critical for maximizing dye degradation while maintaining catalyst stability and minimizing unwanted reactions.
The concentrations of SBH ranged from 3 mg to 21 mg, while the AgNP concentration, reaction temperature, reaction pH, reaction volume, and reaction time were constant at 80 µg, 37 °C, pH 7, 5 mL, and 15 min throughout the experiments (Figure 11). As SBH concentration increases, the degradation efficiency initially rises. At 3 mg, the degradation percentage is 46.50 ± 2.07% with a rate constant of 0.0511 ± 0.0035 min−1. As SBH increases to 6 mg and 9 mg, degradation improves to 50.70 ± 2.16% and 60.21 ± 0.68%, respectively, with corresponding rate constants increasing to 0.0541 ± 0.0031 min−1 and 0.0605 ± 0.0042 min−1. This suggests that increasing SBH concentration enhances the reaction rate and degradation efficiency.
The most significant degradation is observed at 15 mg SBH, where the degradation percentage reaches 95.36 ± 1.41%, with a high-rate constant of 0.2433 ± 0.0057 min−1. This indicates a very rapid and efficient degradation at this concentration. Beyond 15 mg, degradation efficiency decreases. At 18 mg, the degradation percentage drops to 70.57 ± 2.16% with a rate constant of 0.0860 ± 0.0036 min−1, while at 21 mg, the degradation efficiency further declines to 44.71 ± 2.80%, with a lower rate constant of 0.0481 ± 0.0028 min−1.
The R2 across the SBH concentrations are high (ranging from 0.9546 to 0.9933), suggesting a strong linear relationship between SBH concentration and degradation rate. However, beyond the optimal concentration of 15 mg SBH, the degradation efficiency and reaction rate decrease, indicating possible saturation effects or an imbalance in the reaction kinetics. The optimal SBH concentration for maximum degradation efficiency and fastest reaction rate was 15 mg. Further increases in SBH concentration led to a reduction in degradation efficiency, likely due to saturation or side reactions interfering with the degradation process.

3.3.3. Reaction Temperature

Reaction temperature is a key factor influencing the rate and efficiency of dye degradation, as it affects both the kinetic energy of molecules and the catalytic activity of AgNPs. Higher temperatures generally increase the rate of chemical reactions by providing more energy for overcoming activation barriers, thereby accelerating the degradation of dye molecules. In catalytic dye degradation processes, increased temperatures can enhance electron transfer, promote the adsorption of dye molecules onto the catalyst surface, and improve the overall reaction kinetics. However, excessively high temperatures may lead to the thermal deactivation of the catalyst, changes in AgNPs’ morphology, or the breakdown of the reducing agent (SBH), all of which can reduce the efficiency of the degradation process. Furthermore, elevated temperatures may also increase the risk of unwanted side reactions. Therefore, optimizing the reaction temperature is essential to achieve a balance between maximizing dye degradation efficiency and maintaining the stability of both the catalyst (AgNPs) and the reducing agent (SBH).
The reaction temperature ranged from 20 °C to 80 °C, while the AgNP concentration, SBH concentration, reaction pH, reaction volume, and reaction time were constant at 80 µg, 15 mg, pH 7, 5 mL, and 10 min throughout the experiments (Figure 12). At lower temperatures, such as 20 °C, the degradation percentage is relatively low at 17.34 ± 0.84% with a corresponding rate constant of 0.0223 ± 0.0018 min−1, indicating a slower reaction. The maximum degradation of 95.86 ± 1.82% is achieved at 70 min, demonstrating that lower temperatures slow both the degradation process and the reaction rate. As the temperature increases to 30 °C, the degradation efficiency rises to 44.45 ± 2.02% with a higher rate constant of 0.0640 ± 0.0029 min−1, and the maximum degradation was observed within 20 min.
At 40 °C, the degradation percentage further increases to 72.89 ± 1.08%, with a substantial rise in the rate constant to 0.1686 ± 0.0032 min−1, and the maximum degradation was achieved within 13 min. The highest degradation efficiency of 95.77 ± 1.21% was observed at 50 °C, with a rapid rate constant of 0.3875 ± 0.0048 min−1 and degradation occurring within 10 min. However, temperatures beyond 50 °C, the degradation efficiency begins to decline. At 60 °C, the degradation percentage drops to 40.52 ± 2.36%, with a lower rate constant of 0.0611 ± 0.0038 min−1, and the time to maximum degradation increases to 35 min. At 70 °C, the efficiency further decreases to 31.40 ± 2.27%, with a rate constant of 0.0429 ± 0.0027 min−1, and the time to maximum degradation extends to 50 min. At 80 °C, the degradation efficiency was the lowest at 16.04 ± 1.18%, with a rate constant of 0.0210 ± 0.0015 min−1 at 10 min, and the maximum degradation occurred at 75 min.
The R2 remain high across all temperatures, ranging from 0.9526 to 0.9948, indicating a strong relationship between temperature and degradation rate. Results show that the degradation process was highly temperature-dependent, with the highest efficiency and fastest rates occurring at 50 °C. Temperatures lower than 50 °C slow the reaction, while temperatures higher than 50 °C lead to decreased degradation efficiency, possibly due to destabilization of the reaction system or increased side reactions, suggesting an optimal temperature range for the reaction.

3.3.4. Reaction pH

Reaction pH of the solution plays a significant role in dye degradation processes, particularly in systems involving catalysts such as AgNPs and reducing agents such as SBH. pH influences several aspects of the reaction, including the charge and stability of both the dye molecules and the AgNPs, as well as the ionization state of the reducing agent (SBH). In acidic or basic environments, the surface charge of AgNPs can change, affecting their ability to transfer electrons and catalyze the degradation process. For instance, at a certain pH, the dye molecules may become protonated or deprotonated, altering their interaction with the AgNPs. Similarly, the reactivity of SBH may vary with pH, which can either enhance or suppress its reducing power. A highly acidic or basic pH can also cause aggregation of AgNPs, reducing their effective surface area and hindering catalytic activity. Additionally, extreme pH conditions may lead to the degradation of the catalyst (AgNPs) or reducing agent (SBH) itself. Therefore, controlling the pH is crucial to maintaining optimal catalyst activity, ensuring dye molecule reactivity, and maximizing degradation efficiency in a balanced reaction environment.
The reaction pH ranged from 3 to 10, while the AgNP concentration, SBH concentration, reaction temperature, reaction volume, and reaction time were constant at 80 µg, 15 mg, 50 °C, 5 mL, and 10 min throughout the experiments (Figure 13). At pH 3, the degradation percentage is low at 6.90 ± 0.69% with a rate constant of 0.0101 ± 0.0022 min−1 and a high R2 (0.9835 ± 0.0047), with maximum degradation (95.53 ± 1.35%) occurring at 105 min. As the pH increases to 4 and 5, the degradation improves to 17.91 ± 2.27% and 42.04 ± 0.82%, with corresponding increases in rate constants to 0.0291 ± 0.0036 min−1 and 0.0839 ± 0.0026 min−1, respectively. At pH 6, the degradation significantly peaks at 97.19 ± 1.16%, with the highest rate constant of 0.5668 ± 0.0067 min−1 and a corresponding R2 of 0.9609 ± 0.0152. Maximum degradation occurs within just 8 min at this pH, indicating optimal reaction conditions.
Beyond pH 6, the degradation efficiency decreases, with pH 7 showing 85.83 ± 1.06% degradation and a lower rate constant of 0.3131 ± 0.0037 min−1, although the R2 remains strong (0.9738 ± 0.0043). As the pH increases further, the degradation percentages drop progressively, with 62.84 ± 1.92% at pH 8, 37.22 ± 2.11% at pH 9, and 9.95 ± 1.86% at pH 10. However, the R2 remains consistently high throughout, indicating strong reliability in the data. pH also played a crucial role, with pH 6 and 7 offering the most optimal conditions for maximum degradation within a shorter time, while extreme pH values (3 and 10) led to slower degradation rates and lower efficiency.
The superior performance of AgNPs synthesized using C. citratus can be attributed to its rich phytochemical profile, including flavonoids and phenolics, which act as effective reducing and capping agents [65]. These compounds likely enhance AgNP stability and surface reactivity. Furthermore, the green synthesis method employed ensures biocompatibility [66] and uniform particle size [57], contributing to efficient dye degradation. The smaller particle size and high surface-area-to-volume ratio of these AgNPs [57] facilitate greater interaction with dye molecules, thereby improving catalytic activity. These factors collectively justify the observed enhanced performance. Table 3 presents the OFAT results. Table 4 presents the comparison of MB dye degradation in the presence of AgNPs and SBH with those reported in the literature after OFAT studies.

3.4. Reusability

The reusability of AgNPs in dye degradation is an important factor for evaluating the practicality and sustainability of using nano-catalysts in environmental remediation. AgNPs exhibit strong catalytic properties due to their large surface area and high electron transfer capacity, making them highly effective for multiple cycles of dye degradation. However, their ability to maintain catalytic activity over repeated use depends on several factors, such as AgNPs’ stability, resistance to aggregation, and retention of surface properties. Over time, AgNPs may undergo surface oxidation, leaching, or morphological changes, leading to a decline in their catalytic efficiency. Additionally, fouling or surface blockage by reaction by-products or residual dye molecules can reduce the availability of active sites, diminishing the AgNPs’ performance in subsequent cycles. Strategies such as surface modification of AgNPs, stabilizers, or regeneration techniques can help improve their reusability. Ensuring effective reusability not only reduces the cost and environmental impact of using AgNPs, but also enhances the overall efficiency and feasibility of catalytic dye degradation systems for industrial and environmental applications.
Table 5 presents data on the degradation efficiency of MB dye across multiple cycles, along with the corresponding rate constants, correlation coefficients, and the time at which maximum degradation was observed. This degradation reaction involves the MB dye using AgNPs as a nano-catalyst in the presence of SBH under controlled experimental conditions (AgNP concentration: 1.6 mg; Dye concentration: 1 mg/mL; SBH concentration: 300 mg; Reaction temperature: 50 °C; Reaction pH: 6; Reaction time: 8 min; and Reaction volume: 100 mL).
The degradation efficiency remains high throughout the cycles, generally fluctuating between 95% and 97%. It shows a slight downward trend as the cycle number increases, indicating a possible decrease in the AgNPs’ catalytic efficiency over time. In the first nine cycles, the rate constant values are fairly consistent, ranging from around 0.5609 ± 0.0053 min−1 to 0.5642 ± 0.0061 min−1. This stability suggests that the reaction kinetics remain unchanged despite multiple cycles.
For the first nine cycles, the degradation percentages remain consistently around 95% to 97%, indicating stability in performance. However, starting from Cycle 10, a noticeable decrease is seen in the degradation percentage. In Cycle 10, the rate constant drops significantly to 0.1524 ± 0.0026 min−1, and by Cycle 12, it reaches 0.0454 ± 0.0027 min−1. This sharp decrease indicates a slower reaction rate in later cycles, suggesting a significant degradation in the catalytic activity of AgNPs. The R2 values, which measure the goodness of fit for the kinetic model, remain relatively high throughout the cycles, mostly above 0.96, indicating a strong correlation between the experimental data. Even though the rate constant dropped sharply after Cycle 9, this implies that, while the reaction slowed down, the process was still well-described by the model.
For the first nine cycles, the maximum degradation occurs consistently at 8 min. However, starting from Cycle 10, the time required for maximum degradation increases dramatically to 15 min in Cycle 10, 27 min in Cycle 11, and 49 min in Cycle 12. This increase in reaction time indicates a substantial reduction in the efficiency of the AgNPs, correlating with the drop in the rate constant. The AgNPs required more time to achieve similar degradation percentages as in earlier cycles (Figure 14).
The data suggest that the AgNPs maintained their catalytic activity with minimal degradation of performance over the first nine cycles. The consistent degradation percentages, rate constants, and reaction times imply a stable catalytic process. However, starting from Cycle 10, the system undergoes a dramatic decrease in its reaction kinetics, with a substantial drop in the rate constant and an increase in the time required for maximum degradation. This could be due to the gradual deactivation of the AgNPs, possibly caused by surface passivation or aggregation of AgNPs, leading to a decline in catalytic efficiency. Table 6 presents the comparison of the reusability of AgNPs with those reported in the literature for MB dye degradation.

4. Conclusions

The work reports the application of AgNPs synthesized using aqueous extract of C. citratus in the degradation of various textile dyes (such as RhB, MR, MO, MB, EY, and EBT) in a laboratory setting. Among the dyes studied, MB showed the maximum degradation (95.16 ± 1.77%) in 60 min. Further, the roles of various reactive species were determined by employing uniform concentrations of scavengers to determine the possible mechanism involved in the dye degradation in the presence of AgNPs and SBH. Through the OFAT studies in the degradation of MB dye, the influence of various physicochemical parameters was determined, which further reduced the time (8 min) taken to achieve total (maximum) degradation. Additionally, the reusability of the AgNPs was determined by using optimized conditions, which show a remarkable degradation efficiency, up to eight cycles, without any loss of activity. This work offers a possible prospective application of AgNPs synthesized via a green synthesis approach in the treatment of dyes present in wastewater.
However, limitations include the need for further validation under real-world wastewater conditions, scalability challenges, and potential environmental impacts of residual AgNPs. Commercialization potential exists due to the method’s cost-effectiveness, reusability of AgNPs (up to eight cycles), and alignment with sustainable practices. Future work should address large-scale production, stability in diverse environments, and regulatory approvals. With refinement, this approach could offer a viable solution for textile industries seeking eco-friendly wastewater treatment, leveraging the catalytic properties of AgNPs for pollution control.

Author Contributions

Conceptualization, H.K. and V.G.; methodology, H.K., A.V. and V.G.; investigation, H.K. and V.G.; data curation, H.K. and V.G.; formal analysis, H.K. and V.G.; resources, H.K. and V.G.; software, A.V. and N.P.P.P.; validation, H.K. and V.G.; visualization, A.V. and N.P.P.P.; writing—original draft preparation, H.K., A.V. and N.P.P.P.; writing—review and editing, A.V. and V.G.; supervision, V.G.; project administration, V.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

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.

Acknowledgments

Authors thank Principal and Management, Vaagdevi Degree and P.G. College, Warangal (Telangana, India) for providing the required laboratory facilities for the work.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

AgSilver
AgNO3Silver nitrate
AgNPsSilver nanoparticles
BQBenzoquinone
DWSterile double-distilled water
e–Electrons
EBTEriochrome Black T
EDTAEthylenediaminetetraacetic acid
EYEosin yellow
h+Holes
IPAIsopropyl alcohol
kPseudo-first-order rate constant
MOMethyl orange
MRMethyl red
NPsNanoparticles
R2Correlation coefficient
OFATOne-factor-at-a-time
•OHHydroxyl radicals
•O2–Superoxide anions
RhBRhodamine B
RTRoom temperature
SBHSodium borohydride
UV-Vis specUltraviolet–visible spectrophotometer

References

  1. Basalius, H.; Mani, A.; Michael, A.; Mary, S.M.; Lenin, M.; Chelliah, P.; Siddiqui, M.R.; Wabaidur, S.M.; Islam, M.A. Green synthesis of nano-silver using Syzygium samarangense flower extract for multifaceted applications in biomedical and photocatalytic degradation of methylene blue. Appl. Nanosci. 2023, 13, 3735–3747. [Google Scholar] [CrossRef]
  2. Varol, M.; Tokatlı, C. Evaluation of the water quality of a highly polluted stream with water quality indices and health risk assessment methods. Chemosphere 2023, 311, 137096. [Google Scholar] [CrossRef] [PubMed]
  3. Aravind, M.; Ahmad, A.; Ahmad, I.; Amalanathan, M.; Naseem, K.; Mary, S.M.M.; Parvathiraja, C.; Hussain, S.; Algarni, T.S.; Pervaiz, M.; et al. Critical green routing synthesis of silver NPs using jasmine flower extract for biological activities and photocatalytical degradation of methylene blue. J. Environ. Chem. Eng. 2021, 9, 104877. [Google Scholar] [CrossRef]
  4. Joseph, T.M.; Al-Hazmi, H.E.; Śniatała, B.; Esmaeili, A.; Habibzadeh, S. Nanoparticles and nanofiltration for wastewater treatment: From polluted to fresh water. Environ. Res. 2023, 238, 117114. [Google Scholar] [CrossRef] [PubMed]
  5. Abdullahi, S.S.; Mohammad, R.E.A.; Jagaba, A.H.; Musa, H.; Birniwa, A.H. Natural, synthetic, and composite materials for industrial effluents treatment: A mini review on current practices, cost-effectiveness, and sustainability. Case Stud. Chem. Environ. Eng. 2024, 9, 100570. [Google Scholar] [CrossRef]
  6. Islam, T.; Repon, M.R.; Islam, T.; Sarwar, Z.; Rahman, M.M. Impact of textile dyes on health and ecosystem: A review of structure, causes, and potential solutions. Environ. Sci. Pollut. Res. 2022, 30, 9207–9242. [Google Scholar] [CrossRef]
  7. Bilal, M.; Adeel, M.; Rasheed, T.; Zhao, Y.; Iqbal, H.M.N. Emerging contaminants of high concern and their enzyme-assisted biodegradation—A review. Environ. Int. 2019, 124, 336–353. [Google Scholar] [CrossRef]
  8. de Jesus, R.A.; de Assis, G.C.; de Oliveira, R.J.; Costa, J.A.S.; da Silva, C.M.P.; Bilal, M.; Iqbal, H.M.N.; Ferreira, L.F.R.; Figueiredo, R.T. Environmental remediation potentialities of metal and metal oxide nanoparticles: Mechanistic biosynthesis, influencing factors, and application standpoint. Environ. Technol. Innov. 2021, 24, 101851. [Google Scholar] [CrossRef]
  9. Muduli, M.; Choudhary, M.; Sonpal, V.; Ray, S. Recent advancements and approaches towards dye industries effluent treatment. Sustain. Water Resour. Manag. 2023, 9, 186. [Google Scholar] [CrossRef]
  10. Nachiyar, C.V.; Rakshi, A.D.; Sandhya, S.; Jebasta, N.B.D.; Nellore, J. Developments in treatment technologies of dye-containing effluent: A review. Case Stud. Chem. Environ. Eng. 2023, 7, 100339. [Google Scholar] [CrossRef]
  11. Solayman, H.M.; Hossen, M.A.; Aziz, A.A.; Yahya, N.Y.; Leong, K.H.; Sim, L.C.; Monir, M.U.; Zoh, K.-D. Performance evaluation of dye wastewater treatment technologies: A review. J. Environ. Chem. Eng. 2023, 11, 109610. [Google Scholar] [CrossRef]
  12. Jagaba, A.H.; Birniwa, A.H.; Usman, A.K.; Mu’azu, N.D.; Yaro, N.S.A.; Soja, U.B.; Abioye, K.J.; Almahbashi, N.M.Y.; Al-dhawi, B.N.S.; Noor, A.; et al. Trend and current practices of coagulation-based hybrid systems for pulp and paper mill effluent treatment: Mechanisms, optimization techniques and performance evaluation. J. Clean. Prod. 2023, 429, 139543. [Google Scholar] [CrossRef]
  13. Suhan, M.B.K.; Al-Mamun, M.R.; Farzana, N.; Aishee, S.M.; Islam, M.S.; Marwani, H.M.; Hasan, M.M.; Asiri, A.M.; Rahman, M.M.; Islam, A.; et al. Sustainable pollutant removal and wastewater remediation using TiO2-based nanocomposites: A critical review. Nano-Struct. Nano-Objects 2023, 36, 101050. [Google Scholar] [CrossRef]
  14. Chandhru, M.; Logesh, R.; Rani, S.K.; Ahmed, N.; Vasimalai, N. Green synthesis of silver nanoparticles from plant latex and their antibacterial and photocatalytic studies. Environ. Technol. 2022, 43, 3064–3074. [Google Scholar] [CrossRef]
  15. Nguyen Thi Anh Nga, V.B.; Raghavendra, R.; Sindhu, M.; Alshiekheid, A.; Sabour, R.; Krishnan, N.T.; Lan Chi, A. Pugazhendhi, Green fabrication of silver nanoparticles using Chloroxylon swietenia leaves and their application towards dye degradation and food borne pathogens. Food Chem. Toxicol. 2022, 165, 113192. [Google Scholar] [CrossRef]
  16. Vidyasagar; Patel, R.R.; Singh, S.K.; Singh, M. Green synthesis of silver nanoparticles: Methods, biological applications, delivery and toxicity. Mater. Adv. 2023, 4, 1831–1849. [Google Scholar] [CrossRef]
  17. Naysmith, A.; Mian, N.S.; Rana, S. Development of conductive textile fabric using Plackett–Burman optimized green synthesized silver nanoparticles and in situ polymerized polypyrrole. Green Chem. Lett. Rev. 2023, 16, 2158690. [Google Scholar] [CrossRef]
  18. Wasilewska, A.; Klekotka, U.; Zambrzycka, M.; Zambrowski, G.; Święcicka, I.; Kalska-Szostko, B. Physico-chemical properties and antimicrobial activity of silver nanoparticles fabricated by green synthesis. Food Chem. 2023, 400, 133960. [Google Scholar] [CrossRef]
  19. Amin, H.M.A.; Baltruschat, H.; Wittmaier, D.; Friedrich, K.A. A Highly Efficient Bifunctional Catalyst for Alkaline Air-Electrodes Based on a Ag and Co3O4 Hybrid: RRDE and Online DEMS Insights. Electrochim. Acta 2015, 151, 332–339. [Google Scholar] [CrossRef]
  20. Wittmaier, D.; Wagner, N.; Friedrich, K.A.; Amin, H.M.A.; Baltruschat, H. Modified carbon-free silver electrodes for the use as cathodes in lithium–air batteries with an aqueous alkaline electrolyte. J. Power Sources 2014, 265, 299–308. [Google Scholar] [CrossRef]
  21. Jabbar, A.; Abbas, A.; Assad, N.; Naeem-ul-Hassan, M.; Alhazmi, H.A.; Najmi, A.; Zoghebi, K.; Al Bratty, M.; Hanbashi, A.; Amin, H.M.A. A highly selective Hg2+ colorimetric sensor and antimicrobial agent based on green synthesized silver nanoparticles using Equisetum diffusum extract. RSC Adv. 2023, 13, 28666–28675. [Google Scholar] [CrossRef]
  22. Rizki, I.N.; Klaypradit, W.; Patmawati. Utilization of marine organisms for the green synthesis of silver and gold nanoparticles and their applications: A review. Sustain. Chem. Pharm. 2023, 31, 100888. [Google Scholar] [CrossRef]
  23. Abed, A.S.; Khalaf, Y.H.; Mohammed, A.M. Green synthesis of gold nanoparticles as an effective opportunity for cancer treatment. Results Chem. 2023, 5, 100848. [Google Scholar] [CrossRef]
  24. Suherman, A.L.; Zampardi, G.; Amin, H.M.A.; Young, N.P.; Compton, R.G. Tannic acid capped gold nanoparticles: Capping agent chemistry controls the redox activity. Phys. Chem. Chem. Phys. 2019, 21, 4444–4451. [Google Scholar] [CrossRef]
  25. MuthuKathija, M.; Badhusha, M.S.M.; Rama, V. Green synthesis of zinc oxide nanoparticles using Pisonia Alba leaf extract and its antibacterial activity. Appl. Surf. Sci. Adv. 2023, 15, 100400. [Google Scholar] [CrossRef]
  26. Alprol, A.E.; Mansour, A.T.; El-Beltagi, H.S.; Ashour, M. Algal Extracts for Green Synthesis of Zinc Oxide Nanoparticles: Promising Approach for Algae Bioremediation. Materials 2023, 16, 2819. [Google Scholar] [CrossRef]
  27. Alahdal, F.A.M.; Qashqoosh, M.T.A.; Manea, Y.K.; Mohammed, R.K.A.; Naqvi, S. Green synthesis and characterization of copper nanoparticles using Phragmanthera austroarabica extract and their biological/environmental applications. Sustain. Mater. Technol. 2023, 35, e00540. [Google Scholar] [CrossRef]
  28. Mali, S.C.; Dhaka, A.; Sharma, S.; Trivedi, R. Review on biogenic synthesis of copper nanoparticles and its potential applications. Inorg. Chem. Commun. 2023, 149, 110448. [Google Scholar] [CrossRef]
  29. Mbachu, C.A.; Babayemi, A.K.; Egbosiuba, T.C.; Ike, J.I.; Ani, I.J.; Mustapha, S. Green synthesis of iron oxide nanoparticles by Taguchi design of experiment method for effective adsorption of methylene blue and methyl orange from textile wastewater. Results Eng. 2023, 19, 101198. [Google Scholar] [CrossRef]
  30. Suppiah, D.D.; Julkapli, N.M.; Sagadevan, S.; Johan, M.R. Eco-friendly green synthesis approach and evaluation of environmental and biological applications of iron oxide nanoparticles. Inorg. Chem. Commun. 2023, 152, 110700. [Google Scholar] [CrossRef]
  31. Naveenkumar, S.; Kamaraj, C.; Prem, P.; Raja, R.K.; Priyadharsan, A.; Alrefaei, A.F.; Govindarajan, R.K.; Thamarai, R.; Subramaniyan, V. Eco-friendly synthesis of palladium nanoparticles using Zaleya decandra: Assessing mosquito larvicidal activity, zebrafish embryo developmental toxicity, and impacts on freshwater sludge worm Tubifex tubifex. J. Environ. Chem. Eng. 2024, 12, 111912. [Google Scholar] [CrossRef]
  32. MubarakAli, D.; Kim, H.; Venkatesh, P.S.; Kim, J.-W.; Lee, S.-Y. A Systemic Review on the Synthesis, Characterization, and Applications of Palladium Nanoparticles in Biomedicine. Appl. Biochem. Biotechnol. 2023, 195, 3699–3718. [Google Scholar] [CrossRef] [PubMed]
  33. Ishak, N.A.I.M.; Kamarudin, S.K.; Timmiati, S.N.; Sauid, S.M.; Karim, N.A.; Basri, S. Green synthesis of platinum nanoparticles as a robust electrocatalyst for methanol oxidation reaction: Metabolite profiling and antioxidant evaluation. J. Clean. Prod. 2023, 382, 135111. [Google Scholar] [CrossRef]
  34. Gholami-Shabani, M.; Sotoodehnejadnematalahi, F.; Shams-Ghahfarokhi, M.; Eslamifar, A.; Razzaghi-Abyaneh, M. Platinum Nanoparticles as Potent Anticancer and Antimicrobial Agent: Green Synthesis, Physical Characterization, and In-Vitro Biological Activity. J. Clust. Sci. 2023, 34, 501–516. [Google Scholar] [CrossRef]
  35. Chelliah, P.; Wabaidur, S.M.; Sharma, H.P.; Jweeg, M.J.; Majdi, H.S.; Kubaisy, M.M.R.A.L.; Iqbal, A.; Lai, W.-C. Green Synthesis and Characterizations of Cobalt Oxide Nanoparticles and Their Coherent Photocatalytic and Antibacterial Investigations. Water 2023, 15, 910. [Google Scholar] [CrossRef]
  36. Meera, K.; Ramesan, M.T. Tailoring the performance of boehmite nanoparticles reinforced carboxymethyl chitosan/cashew gum blend nanocomposites via green synthesis. Polymer 2023, 268, 125706. [Google Scholar] [CrossRef]
  37. Jaiswal, M.; Srivastava, G.; Mishra, S.; Singh, P.K.; Dhar, R.; Dabrowski, R. Synthesis and characterization of semiconducting copper oxide nanoparticles and their impact on the physical properties of a nematic liquid crystalline material 4-pentyl-4′-cyanobiphenyl. J. Mol. Liq. 2023, 383, 122032. [Google Scholar] [CrossRef]
  38. Alzubaidi, A.K.; Al-Kaabi, W.J.; Al Ali, A.; Albukhaty, S.; Al-Karagoly, H.; Sulaiman, G.M.; Asiri, M.; Khane, Y. Green Synthesis and Characterization of Silver Nanoparticles Using Flaxseed Extract and Evaluation of Their Antibacterial and Antioxidant Activities. Appl. Sci. 2023, 13, 2182. [Google Scholar] [CrossRef]
  39. Baran, M.F.; Keskin, C.; Baran, A.; Hatipoğlu, A.; Yildiztekin, M.; Küçükaydin, S.; Kurt, K.; Hoşgören, H.; Sarker, M.M.R.; Sufianov, A.; et al. Green Synthesis of Silver Nanoparticles from Allium cepa L. Peel Extract, Their Antioxidant, Antipathogenic, and Anticholinesterase Activity. Molecules 2023, 28, 2310. [Google Scholar] [CrossRef]
  40. Mihailović, V.; Srećković, N.; Nedić, Z.P.; Dimitrijević, S.; Matić, M.; Obradović, A.; Selaković, D.; Rosić, G.; Stanković, J.S.K. Green Synthesis of Silver Nanoparticles Using Salvia verticillata and Filipendula ulmaria Extracts: Optimization of Synthesis, Biological Activities, and Catalytic Properties. Molecules 2023, 28, 808. [Google Scholar] [CrossRef]
  41. Ibrahim, N.; Zubir, S.A.; Manaf, A.A.; Mustapha, M. Stability and conductivity of water-based colloidal silver nanoparticles conductive inks for sustainable printed electronics. J. Taiwan Inst. Chem. Eng. 2023, 153, 105202. [Google Scholar] [CrossRef]
  42. Menichetti, A.; Mavridi-Printezi, A.; Mordini, D.; Montalti, M.; Size, E.O. Shape and Surface Functionalization on the Antibacterial Activity of Silver Nanoparticles. J. Funct. Biomater. 2023, 14, 244. [Google Scholar] [CrossRef] [PubMed]
  43. Meydan, I.; Aygun, A.; Tiri, R.N.E.; Gur, T.; Kocak, Y.; Seckin, H.; Sen, F. Chitosan/PVA-supported silver nanoparticles for azo dyes removal: Fabrication, characterization, and assessment of antioxidant activity. Environ. Sci. Adv. 2024, 3, 28–35. [Google Scholar] [CrossRef]
  44. Elbadawy, H.A.; Elhusseiny, A.F.; Hussein, S.M.; Sadik, W.A. Sustainable and energy-efficient photocatalytic degradation of textile dye assisted by ecofriendly synthesized silver nanoparticles. Sci. Rep. 2023, 13, 2302. [Google Scholar] [CrossRef]
  45. Nguyen, N.P.U.; Dang, N.T.; Doan, L.; Nguyen, T.T.H. Synthesis of Silver Nanoparticles: From Conventional to ‘Modern’ Methods—A Review. Processes 2023, 11, 2617. [Google Scholar] [CrossRef]
  46. Hai, N.D.; Dat, N.M.; Nam, N.T.H.; An, H.; Tai, L.T.; Huong, L.M.; Cong, C.Q.; Giang, N.T.H.; Tinh, N.T.; Hieu, N.H. A review on the chemical and biological synthesis of silver nanoparticles@graphene oxide nanocomposites: A comparison. Mater. Today Sustain. 2023, 24, 100544. [Google Scholar] [CrossRef]
  47. Luceri, A.; Francese, R.; Lembo, D.; Ferraris, M.; Balagna, C. Silver Nanoparticles: Review of Antiviral Properties, Mechanism of Action and Applications. Microorganisms 2023, 11, 629. [Google Scholar] [CrossRef]
  48. Alsaiari, N.S.; Alzahrani, F.M.; Amari, A.; Osman, H.; Harharah, H.N.; Elboughdiri, N.; Tahoon, M.A. Plant and Microbial Approaches as Green Methods for the Synthesis of Nanomaterials: Synthesis, Applications, and Future Perspectives. Molecules 2023, 28, 463. [Google Scholar] [CrossRef]
  49. Hussain, Z.; Raza, M.A.; Jahangeer, M.; Sarwar, A.; Nadeem, A.A.; Naz, S.; Aziz, T.; Alharbi, M.; Alshammari, A.; Alasmari, A.F. Green synthesis of silver nanoparticles prepared by leaves extract of Trigonila foenum-graecum and its antibacterial potential against Escherichia coli and Pseudomonas aeruginosa. Biomass Convers. Biorefinery 2023, 14, 31431–31438. [Google Scholar] [CrossRef]
  50. Wirwis, A.; Sadowski, Z. Green Synthesis of Silver Nanoparticles: Optimizing Green Tea Leaf Extraction for Enhanced Physicochemical Properties. ACS Omega 2023, 8, 30532–30549. [Google Scholar] [CrossRef]
  51. Keskin, M.; Kaya, G.; Bayram, S.; Kurek-Górecka, A.; Olczyk, P. Green Synthesis, Characterization, Antioxidant, Antibacterial and Enzyme Inhibition Effects of Chestnut (Castanea sativa) Honey-Mediated Silver Nanoparticles. Molecules 2023, 28, 2762. [Google Scholar] [CrossRef] [PubMed]
  52. Kumari, M.; Pandey, S.; Giri, V.P.; Nautiyal, C.S.; Mishra, A. A critical review on green approaches in shape and size evolution of metal nanoparticles and their environmental applications. Environ. Nanotechnol. Monit. Manag. 2023, 20, 100895. [Google Scholar] [CrossRef]
  53. Herrera-Marín, P.; Fernández, L.; Pilaquinga, F.F.; Debut, A.; Rodríguez, A.; Espinoza-Montero, P. Green synthesis of silver nanoparticles using aqueous extract of the leaves of fine aroma cocoa Theobroma cacao linneu (Malvaceae): Optimization by electrochemical techniques. Electrochim. Acta 2023, 447, 142122. [Google Scholar] [CrossRef]
  54. Wen, J.; Gao, F.; Liu, H.; Wang, J.; Xiong, T.; Yi, H.; Zhou, Y.; Yu, Q.; Zhao, S.; Tang, X. Metallic nanoparticles synthesized by algae: Synthetic route, action mechanism, and the environmental catalytic applications. J. Environ. Chem. Eng. 2023, 12, 111742. [Google Scholar] [CrossRef]
  55. Ahmad, N.M.; Mohamed, A.H.; Hasan, N.; Abidin, N.Z.; Nawahwi, M.Z.; Azzeme, A.B.M. Effect of optimisation variable and the role of plant extract in the synthesis of nanoparticles using plant-mediated synthesis approaches. Inorg. Chem. Commun. 2023, 161, 111839. [Google Scholar] [CrossRef]
  56. Velidandi, A.; Pabbathi, N.P.P.; Dahariya, S.; Kagithoju, S.; Baadhe, R.R. Bio-fabrication of silver-silver chloride nanoparticles using Annona muricata leaf extract: Characterization, biological, dye degradation and eco-toxicity studies. Int. J. Environ. Sci. Technol. 2022, 19, 6555–6572. [Google Scholar] [CrossRef]
  57. Kurra, H.; Velidandi, A.; Sarvepalli, M.; Prem, N.; Pabbathi, P.; Godishala, V. Aqueous Cymbopogon citratus Extract Mediated Silver Nanoparticles: Part I. Influence of Synthesis Parameters, Characterization, and Biomedical Studies. Nanomaterials 2025, 15, 328. [Google Scholar] [CrossRef]
  58. Mansour, M.S.; Farid, Y.; Nosier, S.A.; Adli, O.; Abdel-Aziz, M.H. Removal of Eosin Yellow dye from industrial wastewater using UV/H2O2 and photoelectro-Fenton techniques. J. Photochem. Photobiol. A Chem. 2023, 436, 114411. [Google Scholar] [CrossRef]
  59. Shaikh, A.A.; Patil, M.R.; Jagdale, B.S.; Adole, V.A. Synthesis and characterization of Ag doped ZnO nanomaterial as an effective photocatalyst for photocatalytic degradation of Eriochrome Black T dye and antimicrobial agent. Inorg. Chem. Commun. 2023, 151, 110570. [Google Scholar] [CrossRef]
  60. Vijayan, R.; Joseph, S.; Mathew, B. Eco-friendly synthesis of silver and gold nanoparticles with enhanced antimicrobial, antioxidant, and catalytic activities. IET Nanobiotechnol. 2018, 12, 850–856. [Google Scholar] [CrossRef]
  61. El-Bindary, A.A.; El-Marsafy, S.M.; El-Maddah, A.A. Enhancement of the photocatalytic activity of ZnO nanoparticles by silver doping for the degradation of AY99 contaminants. J. Mol. Struct. 2019, 1191, 76–84. [Google Scholar] [CrossRef]
  62. Wahab, O.O.; Olasunkanmi, L.O.; Govender, K.K.; Govender, P.P. Computational Study of the Mechanistic Pathway of Hydroxyl Radical-Initiated Degradation of Disperse Red 73 Dye. Chem. Afr. 2022, 5, 135–148. [Google Scholar] [CrossRef]
  63. Kumar, J.; Justa, P.; Jaswal, N.; Kumar, H.; Pani, B.; Kumar, P. Peroxidase like activity of Prussian blue nanoparticles and visible light mediated catalytic degradation of methylene blue dye. Chem. Phys. Impact 2024, 8, 100575. [Google Scholar] [CrossRef]
  64. Kanchana, S.; Vijayalakshmi, R. Photocatalytic degradation of organic dyes by peg and pvp cappcu, ni and ag nanoparticles in the presence of nabh4 in aqueous medium. J. Water Environ. Nanotechnol. 2020, 5, 294–306. [Google Scholar] [CrossRef]
  65. Oladeji, O.S.; Adelowo, F.E.; Ayodele, D.T.; Odelade, K.A. Phytochemistry and pharmacological activities of Cymbopogon citratus: A review. Sci. Afr. 2019, 6, e00137. [Google Scholar] [CrossRef]
  66. Kurra, H.; Velidandi, A.; Sarvepalli, M.; Godishala, V. Green-synthesized Silver Nanoparticles from Cymbopogon citratus: Synergistic Antibacterial Effects and Food Safety Potential. J. Food Chem. Nanotechnol. 2025, 11, 15–24. [Google Scholar] [CrossRef]
  67. Rajasekar, R.; Samuel, M.; Edison, T.N.J.I.; Raman, N. Sustainable synthesis of silver nanoparticles using Alstonia scholaris for enhanced catalytic degradation of methylene blue. J. Mol. Struct. 2021, 1246, 131208. [Google Scholar] [CrossRef]
  68. Ogundare, S.A.; Adesetan, T.O.; Muungani, G.; Moodley, V.; Amaku, J.F.; Atewolara-Odule, O.C.; Yussuf, S.T.; Sanyaolu, N.O.; Ibikunle, A.A.; Balogun, M.-S.; et al. Catalytic degradation of methylene blue dye and antibacterial activity of biosynthesized silver nanoparticles using Peltophorum pterocarpum (DC.) leaves. Environ. Sci. Adv. 2023, 2, 247–256. [Google Scholar] [CrossRef]
  69. Varadavenkatesan, T.; Vinayagam, R.; Selvaraj, R. Green synthesis and structural characterization of silver nanoparticles synthesized using the pod extract of Clitoria ternatea and its application towards dye degradation. Mater. Today Proc. 2020, 23, 27–29. [Google Scholar] [CrossRef]
  70. Kahraman, H.T. Synthesis of silver nanoparticles using Alchemilla vulgaris and Helichrysum arenarium for methylene blue and 4-nitrophenol degradation and antibacterial applications. Biomass Convers. Biorefinery 2024, 14, 13479–13490. [Google Scholar] [CrossRef]
  71. Erenler, R.; Hosaflioglu, I. Green synthesis of silver nanoparticles using Onobrychis sativa L.: Characterization, catalytic degradation of methylene blue, antioxidant activity, and quantitative analysis of bioactive compounds. Mater. Today Commun. 2023, 35, 105863. [Google Scholar] [CrossRef]
  72. Konduri, V.V.; Kalagatur, N.K.; Gunti, L.; Mangamuri, U.K.; Kalagadda, V.R.; Poda, S.; Krishna, S.B.N. Green synthesis of silver nanoparticles from Hibiscus tiliaceus L. Leaves and their applications in dye degradation, antioxidant, antimicrobial, and anticancer activities. S. Afr. J. Bot. 2024, 168, 476–487. [Google Scholar] [CrossRef]
  73. Mahiuddin, M.; Saha, P.; Ochiai, B. Green Synthesis and Catalytic Activity of Silver Nanoparticles Based on Piper chaba Stem Extracts. Nanomaterials 2020, 10, 1777. [Google Scholar] [CrossRef]
  74. Moond, M.; Singh, S.; Sangwan, S.; Devi, P.; Beniwal, A.; Rani, J.; Kumari, A.; Rani, S. Biosynthesis of Silver Nanoparticles Utilizing Leaf Extract of Trigonella foenum-graecum L. for Catalytic Dyes Degradation and Colorimetric Sensing of Fe3+/Hg2+. Molecules 2023, 28, 951. [Google Scholar] [CrossRef]
  75. Thangamani, N.; Bhuvaneshwari, N. Synthesis, characterization of Ag nanoparticles using the green approach towards degradation of environmental pollutant. J. Mater. Sci. Mater. Electron. 2022, 33, 9155–9162. [Google Scholar] [CrossRef]
  76. Anjana, V.N.; Joseph, M.; Francis, S.; Joseph, A.; Koshy, E.P.; Mathew, B. Microwave assisted green synthesis of silver nanoparticles for optical, catalytic, biological and electrochemical applications. Artif. Cells Nanomed. Biotechnol. 2021, 49, 438–449. [Google Scholar] [CrossRef] [PubMed]
  77. Panneerselvi, V.; Shankar, K.; Muthukrishnan, P.; Prabhu, A. Mangifera indica Resin Assisted Synthesis of Nano Silver: Assessing their Photocatalytic Degradation of Methylene Blue, Anticorrosive and Antioxidant Activity. J. Clust. Sci. 2022, 33, 123–133. [Google Scholar] [CrossRef]
  78. Veisi, H.; Azizi, S.; Mohammadi, P. Green synthesis of the silver nanoparticles mediated by Thymbra spicata extract and its application as a heterogeneous and recyclable nanocatalyst for catalytic reduction of a variety of dyes in water. J. Clean. Prod. 2018, 170, 1536–1543. [Google Scholar] [CrossRef]
  79. Gangarapu, M.; Sarangapany, S.; Veerabhali, K.K.; Devipriya, S.P.; Arava, V.B.R. A High-Performance Catalytic and Recyclability of Phyto-Synthesized Silver Nanoparticles Embedded in Natural Polymer. J. Clust. Sci. 2017, 28, 3127–3138. [Google Scholar] [CrossRef]
  80. Rostami-Vartooni, A.; Nasrollahzadeh, M.; Alizadeh, M. Green synthesis of seashell supported silver nanoparticles using Bunium persicum seeds extract: Application of the particles for catalytic reduction of organic dyes. J. Colloid Interface Sci. 2016, 470, 268–275. [Google Scholar] [CrossRef]
  81. Siddique, A.B.; Amr, D.; Abbas, A.; Zohra, L.; Irfan, M.I.; Alhoshani, A.; Ashraf, S.; Amin, H.M.A. Synthesis of hydroxyethylcellulose phthalate-modified silver nanoparticles and their multifunctional applications as an efficient antibacterial, photocatalytic and mercury-selective sensing agent. Int. J. Biol. Macromol. 2024, 256, 128009. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Maximum absorbance (λmax) of the dyes used in the dye degradation studies.
Figure 1. Maximum absorbance (λmax) of the dyes used in the dye degradation studies.
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Figure 2. RhB dye degradation in presence of AgNPs and SBH. (a) Absorbance values; (b) Degradation percentage; (c) Pseudo-first-order rate constant; (d) Picture showing RhB dye degradation in presence of AgNPs and SBH.
Figure 2. RhB dye degradation in presence of AgNPs and SBH. (a) Absorbance values; (b) Degradation percentage; (c) Pseudo-first-order rate constant; (d) Picture showing RhB dye degradation in presence of AgNPs and SBH.
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Figure 3. MR dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing MR dye degradation in presence of AgNPs and SBH.
Figure 3. MR dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing MR dye degradation in presence of AgNPs and SBH.
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Figure 4. MO dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing MO dye degradation in presence of AgNPs and SBH.
Figure 4. MO dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing MO dye degradation in presence of AgNPs and SBH.
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Figure 5. MB dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing MB dye degradation in presence of AgNPs and SBH.
Figure 5. MB dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing MB dye degradation in presence of AgNPs and SBH.
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Figure 6. EY dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing EY dye degradation in presence of AgNPs and SBH.
Figure 6. EY dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing EY dye degradation in presence of AgNPs and SBH.
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Figure 7. EBT dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing EBT dye degradation in presence of AgNPs and SBH.
Figure 7. EBT dye degradation in presence of AgNPs and SBH. (a) Absorbance values, (b) Degradation percentage, (c) Pseudo-first-order rate constant, and (d) Picture showing EBT dye degradation in presence of AgNPs and SBH.
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Figure 8. Bar graph showing degradation percentages observed for 1 mg/mL of (a) RhB, (b) MR, (c) MO, (d) MB, (e) EY, and (f) EBT in presence of various scavengers (1 mM), AgNPs (20 µg), and SBH (3 mg) at 37 °C and pH 7 in 5 mL reaction volume. (g) Combined representation of reactive species’ roles in dye degradation.
Figure 8. Bar graph showing degradation percentages observed for 1 mg/mL of (a) RhB, (b) MR, (c) MO, (d) MB, (e) EY, and (f) EBT in presence of various scavengers (1 mM), AgNPs (20 µg), and SBH (3 mg) at 37 °C and pH 7 in 5 mL reaction volume. (g) Combined representation of reactive species’ roles in dye degradation.
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Figure 9. Schematic representation of the possible mechanism involved in the degradation of dyes in the presence of AgNPs and SBH based on the literature.
Figure 9. Schematic representation of the possible mechanism involved in the degradation of dyes in the presence of AgNPs and SBH based on the literature.
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Figure 10. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 35 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 35 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye at various concentrations of AgNPs (20, 40, 60, 80, 100, 120, and 140 µg) in presence of SBH (3 mg) at 37 °C and pH 7 in 5 mL reaction volume.
Figure 10. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 35 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 35 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye at various concentrations of AgNPs (20, 40, 60, 80, 100, 120, and 140 µg) in presence of SBH (3 mg) at 37 °C and pH 7 in 5 mL reaction volume.
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Figure 11. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 15 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 15 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye at various concentrations of SBH (3, 6, 9, 12, 15, 18, and 21 mg) in the presence of AgNPs (80 µg) at 37 °C and pH 7 in 5 mL reaction volume.
Figure 11. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 15 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 15 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye at various concentrations of SBH (3, 6, 9, 12, 15, 18, and 21 mg) in the presence of AgNPs (80 µg) at 37 °C and pH 7 in 5 mL reaction volume.
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Figure 12. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 10 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 10 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye in presence of AgNPs (80 µg) and SBH (15 mg) at various temperatures (20, 30, 40, 50, 60, 70, and 80 °C) and pH 7 in 5 mL reaction volume.
Figure 12. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 10 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 10 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye in presence of AgNPs (80 µg) and SBH (15 mg) at various temperatures (20, 30, 40, 50, 60, 70, and 80 °C) and pH 7 in 5 mL reaction volume.
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Figure 13. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 8 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 8 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye in presence of AgNPs (80 µg) and SBH (15 mg) at 50 °C and various pH (3, 4, 5, 6, 7, 8, 9, and 10) in 5 mL reaction volume.
Figure 13. (a) Absorbance values, (b) Degradation percentages, (c) Degradation percentage observed at ‘time’ 8 min, (d) Ln(At) vs. time (min) plot to determine pseudo-first-order rate constant, (e) Pseudo-first-order rate constant observed at ‘time’ 8 min, (f) Time required to observe total (maximum) degradation, and (g) Picture showing degradation of MB (1 mg/mL) dye in presence of AgNPs (80 µg) and SBH (15 mg) at 50 °C and various pH (3, 4, 5, 6, 7, 8, 9, and 10) in 5 mL reaction volume.
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Figure 14. Recyclability studies showing (a) Degradation observed at ‘time’ 8 min, (b) Pseudo-first-order rate constant observed at ‘time’ 8 min, and (c) Time required to observe total (maximum) degradation of MB (1 mg/mL) dye in presence of AgNPs (1.6 mg) and SBH (300 mg) at 50 °C) and pH 6 in 100 mL reaction volume.
Figure 14. Recyclability studies showing (a) Degradation observed at ‘time’ 8 min, (b) Pseudo-first-order rate constant observed at ‘time’ 8 min, and (c) Time required to observe total (maximum) degradation of MB (1 mg/mL) dye in presence of AgNPs (1.6 mg) and SBH (300 mg) at 50 °C) and pH 6 in 100 mL reaction volume.
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Table 1. Details of dye degradation studies in presence of AgNPs and SBH.
Table 1. Details of dye degradation studies in presence of AgNPs and SBH.
DyeλmaxDegradationCorrelation
Coefficient
PercentageTimeRate
nm%mink, min−1R2
RhB55497.34 ± 1.121200.0355 ± 0.00420.9366 ± 0.0218
MR43096.89 ± 1.28700.0456 ± 0.00430.9288 ± 0.0262
MO46495.82 ± 2.37900.0413 ± 0.00280.9467 ± 0.0369
MB66495.16 ± 1.77600.0539 ± 0.00360.9349 ± 0.0308
EY51496.41 ± 1.571050.0363 ± 0.00320.9232 ± 0.0387
EBT57394.36 ± 1.731400.0222 ± 0.00290.8843 ± 0.0165
Experimental conditions: AgNP concentration: 20 µg; Dye concentration: 1 mg/mL; SBH concentration: 3 mg; Reaction temperature: 37 °C; Reaction pH: 7; Reaction volume: 5 mL.
Table 2. Details of scavenger studies to determine the role of various reactive species in the degradation of dyes in presence of AgNPs and SBH. a p < 0.05; b p < 0.005; and c p < 0.0005.
Table 2. Details of scavenger studies to determine the role of various reactive species in the degradation of dyes in presence of AgNPs and SBH. a p < 0.05; b p < 0.005; and c p < 0.0005.
Dye(s)Degradation Percentage Observed in Scavenger(s)
ControlIPA (•OH)BQ (–•O2–)EDTA (h+)AgNO3 (e−)
RhB97.37 ± 1.5543.57 ± 2.27 c71.60 ± 2.72 b87.49 ± 2.64 a88.31 ± 1.82 a
MR96.44 ± 1.3575.02 ± 1.76 b59.56 ± 2.12 c68.80 ± 1.95 c86.26 ± 2.14 a
MO95.36 ± 2.3483.92 ± 2.53 a84.10 ± 2.04 a54.39 ± 1.92 c63.38 ± 1.76 c
MB95.63 ± 1.3683.53 ± 1.73 a61.02 ± 2.67 c74.99 ± 1.36 b67.80 ± 2.33 c
EY95.85 ± 2.1462.64 ± 1.66 b84.10 ± 1.85 a74.31 ± 2.61 b66.38 ± 1.48 c
EBT94.51 ± 1.2753.87 ± 1.99 c68.64 ± 1.73 c72.36 ± 2.45 b87.30 ± 1.39 b
Experimental conditions: AgNP concentration: 20 µg; Dye concentration: 1 mg/mL; SBH concentration: 3 mg; Scavenger(s) conc.: 1 mM each; Reaction temperature: 37 °C; Reaction pH: 7; Reaction volume: 5 mL; and Reaction time: 120 min (RhB), 70 min (MR), 90 min (MO), 60 min (MB), 105 min (EY), and 140 min (EBT).
Table 3. Degradation percentage, pseudo-first-order rate constant, and correlation coefficient values calculated during the OFAT studies of MB dye degradation. Reaction volume was 5 mL for all OFAT experiments.
Table 3. Degradation percentage, pseudo-first-order rate constant, and correlation coefficient values calculated during the OFAT studies of MB dye degradation. Reaction volume was 5 mL for all OFAT experiments.
AgNP Conc.SBH Conc.ReactionDegradation
Percentage		Rate ConstantCorrelation
Coefficient		Time for Maximum Degradation
Temp.pHTime
μgmg°C-min%k, min−1R2‘%’ at ‘min’
2033773556.55 ± 1.970.0290 ± 0.00240.9714 ± 0.019895.55 ± 1.49 at 60
4062.71 ± 1.770.0342 ± 0.00270.9825 ± 0.002895.88 ± 1.22 at 52
6069.69 ± 1.850.0397 ± 0.00310.9699 ± 0.010095.87 ± 1.26 at 46
8095.69 ± 1.410.1094 ± 0.00530.9665 ± 0.012095.69 ± 1.41 at 35
10087.18 ± 1.570.0675 ± 0.00440.9509 ± 0.010495.64 ± 1.47 at 40
12079.46 ± 2.280.0514 ± 0.00380.9660 ± 0.012895.27 ± 1.75 at 42
14063.67 ± 2.100.0345 ± 0.00210.9727 ± 0.011295.86 ± 1.96 at 48
8033771546.50 ± 2.070.0511 ± 0.00350.9647 ± 0.011695.91 ± 1.18 at 35
650.70 ± 2.160.0541 ± 0.00310.9686 ± 0.008296.14 ± 2.38 at 28
960.21 ± 0.680.0605 ± 0.00420.9772 ± 0.012695.93 ± 1.38 at 24
1273.84 ± 1.340.0917 ± 0.00460.9933 ± 0.003295.84 ± 2.13 at 20
1595.36 ± 1.410.2433 ± 0.00570.9732 ± 0.012895.36 ± 1.41 at 15
1870.57 ± 2.160.0860 ± 0.00360.9872 ± 0.003796.10 ± 1.34 at 22
2144.71 ± 2.800.0481 ± 0.00280.9546 ± 0.005795.99 ± 1.27 at 33
80152071017.34 ± 0.840.0223 ± 0.00180.9778 ± 0.010895.86 ± 1.82 at 70
3044.45 ± 2.020.0640 ± 0.00290.9572 ± 0.014295.82 ± 1.81 at 20
4072.89 ± 1.080.1686 ± 0.00320.9555 ± 0.012795.90 ± 1.83 at 13
5095.77 ± 1.210.3875 ± 0.00480.9600 ± 0.011995.77 ± 1.21 at 10
6040.52 ± 2.360.0611 ± 0.00380.9526 ± 0.012296.04 ± 1.53 at 35
7031.40 ± 2.270.0429 ± 0.00270.9948 ± 0.011696.14 ± 1.66 at 50
8016.04 ± 1.180.0210 ± 0.00150.9534 ± 0.016094.98 ± 1.46 at 75
801550386.90 ± 0.690.0101 ± 0.00220.9835 ± 0.004795.53 ± 1.35 at 105
417.91 ± 2.270.0291 ± 0.00360.9617 ± 0.012495.87 ± 1.45 at 60
542.04 ± 0.820.0839 ± 0.00260.9262 ± 0.020195.82 ± 1.44 at 30
697.19 ± 1.160.5668 ± 0.00670.9609 ± 0.015297.19 ± 1.16 at 8
785.83 ± 1.060.3131 ± 0.00370.9738 ± 0.004396.25 ± 1.48 at 10
862.84 ± 1.920.1468 ± 0.00330.9603 ± 0.017695.69 ± 1.41 at 24
937.22 ± 2.110.0726 ± 0.00320.9639 ± 0.001795.33 ± 1.45 at 32
109.95 ± 1.860.0140 ± 0.00250.9926 ± 0.006895.75 ± 2.40 at 97
Table 4. Comparison of AgNPs’ MB dye degradation activity in presence of SBH with those reported in the literature.
Table 4. Comparison of AgNPs’ MB dye degradation activity in presence of SBH with those reported in the literature.
PlantReactionDegradationRef.
NPDyeSBHVol.PercentageTimeRate
Conc.Conc.Conc.mL%Mink, min−1
C. citratus0.08 mg1 mg/mL 15 mg597.1980.5668Present work
Alstonia scholaris0.05 mL100 µM100 mM397270.7 × 10–3 s−1[67]
Peltophorum pterocarpum71 nmol of Ag10–4 M10–2 M3.58260.3378[68]
Clitoria ternatea100 µl12 ppm100 mM2.2Complete180.1448[69]
Alchemilla vulgaris5 mg0.002 M0.01 M2967-[70]
Onobrychis sativa50 ppm2 ppm600 ppm3.66830-[71]
Hibiscus tiliaceus1 mg/ml1 mM10 mM12~98350.101[72]
Piper chaba53.9 mg/L2 ppm600 ppm3.6Complete8-[73]
Trigonella foenum-graecum0.5 ml4 × 10–5 M0.05 M1196.57200.1665[74]
Simarouba glauca81 mM0.01 mM50Complete808.5 × 10–4 s−1[75]
Cyanthillium cinereum0.02 mg/L0.08 × 10–3 M0.06 M3Complete100.0682[76]
Table 5. Details of reusability of AgNPs in MB dye degradation in presence of SBH.
Table 5. Details of reusability of AgNPs in MB dye degradation in presence of SBH.
CycleDegradation PercentageRate ConstantCorrelation CoefficientTime for Maximum Degradation
No.%k, min−1R2‘%’ at ‘min’
Cycle 096.97 ± 1.07 0.5618 ± 0.00380.9670 ± 0.012096.97 ± 1.07 at 8
Cycle 197.39 ± 1.050.5612 ± 0.00440.9567 ± 0.011697.39 ± 1.05 at 8
Cycle 296.53 ± 1.210.5609 ± 0.00530.9557 ± 0.009596.53 ± 1.21 at 8
Cycle 395.46 ± 2.170.5633 ± 0.00390.9707 ± 0.015795.46 ± 2.17 at 8
Cycle 496.50 ± 1.730.5628 ± 0.00630.9649 ± 0.012196.50 ± 1.73 at 8
Cycle 596.79 ± 1.820.5621 ± 0.00460.9618 ± 0.009196.79 ± 1.82 at 8
Cycle 695.97 ± 1.540.5609 ± 0.00510.9723 ± 0.012695.97 ± 1.54 at 8
Cycle 795.89 ± 1.790.5631 ± 0.00470.9629 ± 0.010895.89 ± 1.79 at 8
Cycle 895.75 ± 2.020.5625 ± 0.00520.9665 ± 0.013395.75 ± 2.02 at 8
Cycle 996.46 ± 2.160.5642 ± 0.00610.9630 ± 0.020596.46 ± 2.16 at 8
Cycle 1056.87 ± 1.750.1524 ± 0.00260.9778 ± 0.0144 97.19 ± 1.86 at 15
Cycle 1142.83 ± 1.860.0817 ± 0.00380.9733 ± 0.011296.57 ± 1.92 at 27
Cycle 1228.21 ± 2.170.0454 ± 0.00270.9631 ± 0.006095.37 ± 1.31 at 49
Experimental conditions: AgNP concentration: 1.6 mg; Dye concentration: 1 mg/mL; SBH concentration: 300 mg; Reaction temperature: 50 °C; Reaction pH: 6; Reaction time: 8 min; and Reaction volume: 100 mL.
Table 6. Comparison of reusability of AgNPs with those reported in the literature for MB dye degradation.
Table 6. Comparison of reusability of AgNPs with those reported in the literature for MB dye degradation.
PlantDye Degradation ConditionsCycleOutcome(s)Ref.
NPDyeSBHVol.TimeTotalFirstLast
Conc.Conc.Conc.mLminNo.D%D%
C. citratus1.6 mg1 mg/mL300 mg10081296.9728.21Good stability for 9 cyclesPresent work
A. vulgaris5 mg0.002 M0.01 M-759694Good stability for 5 cycles[70]
Mangifera indica40 mg10 mg/L-757559389No clear decrease in activity after 5 cycles[77]
Thymbra spicata2 mg3 × 10−5 M4 × 10−3 M3518~97~93No appreciable activity loss[78]
Aglaia elaeagnoidea144.8 mg10−4 M10−2 M245 s10~99~96No significant loss of activity[79]
Bunium persicum5 mg3.1 × 10−5 M5.3 × 10−3 M502.55100100No reduction in activity[80]
Hydroxyethylcellulose phthalate300 mg20 mg/L-208057965Slight decrease[81]
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Kurra, H.; Velidandi, A.; Pabbathi, N.P.P.; Godishala, V. Aqueous Cymbopogon citratus Extract Mediated Silver Nanoparticles: Part II. Dye Degradation Studies. Eng 2025, 6, 102. https://doi.org/10.3390/eng6050102

AMA Style

Kurra H, Velidandi A, Pabbathi NPP, Godishala V. Aqueous Cymbopogon citratus Extract Mediated Silver Nanoparticles: Part II. Dye Degradation Studies. Eng. 2025; 6(5):102. https://doi.org/10.3390/eng6050102

Chicago/Turabian Style

Kurra, Himabindu, Aditya Velidandi, Ninian Prem Prashanth Pabbathi, and Vikram Godishala. 2025. "Aqueous Cymbopogon citratus Extract Mediated Silver Nanoparticles: Part II. Dye Degradation Studies" Eng 6, no. 5: 102. https://doi.org/10.3390/eng6050102

APA Style

Kurra, H., Velidandi, A., Pabbathi, N. P. P., & Godishala, V. (2025). Aqueous Cymbopogon citratus Extract Mediated Silver Nanoparticles: Part II. Dye Degradation Studies. Eng, 6(5), 102. https://doi.org/10.3390/eng6050102

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