Enhanced Removal of Diclofenac and Lead by Granular Activated Carbon: Optimization and Mechanistic Insights

Since water contaminants harm the environment and people, there has been a lot of research on how to remove them [27]. DCF, a popular medicine, and lead (Pb), a toxic heavy metal, are the most problematic contaminants because they persist in water systems for so long. As a common anti-inflammatory, diclofenac is found in wastewater. Industrial operations and urban runoff cause most lead contamination. While several studies have examined how to remove diclofenac and lead individually, few have examined how to do it simultaneously using granular activated carbon [28].

GAC is noted for its large surface area and capacity to absorb several organic and inorganic contaminants. However, GAC's ability to remove diclofenac and lead simultaneously, and its adsorption mechanisms, are yet unknown. This section reviews the literature on diclofenac and lead adsorption with GAC, concentrating on pH, temperature, adsorbent dosage, and contact duration. We also highlight research gaps, such as the lack of studies that compare the clearance of these two unique pollutants at the same time and investigate their mechanisms.

Espina de Franco et al. [2] represented the most toxic non-steroidal anti-inflammatory drug, diclofenac, which is a common ingredient in wastewater treatment plants and surface waterways. To remove emerging contaminants, such as pharmaceutical compounds, from water sources and wastewaters, adsorption has been widely used. This research looked into diclofenac adsorption in batch operations and fixed-bed columns using activated carbon as the adsorbent. We used batch adsorption experiments to determine adsorption isotherms, and we used a full factorial two-level experimental design with three variables to test fixed-bed adsorption: initial pollutant concentration (20-100 mg/L), adsorbent weight (0.5-1.0 g), and volumetric feed flow rate (3-5 mL min⁻¹). At 298, 308, and 318 K, the Freundlich equation successfully explains the isotherm behaviour, as shown by the adsorption equilibrium at different temperatures. According to the results of the thermodynamic analysis, ΔG0 was negative, whereas ΔH0 and ΔS0 were both positive. The adsorption of diclofenac onto activated carbon is enhanced at higher temperatures and occurs independently, according to this finding. When the starting concentration was higher, and the flow rate was lower, the breakthrough time—the time it takes for the effluent to contain 5% of the original concentration—was shorter. Fractional bed usage increased in tandem with increases in starting concentration and flow rate. However, fractional bed utilisation decreased as activated carbon amounts increased. To fit the experimental data for breakthrough curves, we utilised analytical models developed by Thomas, Bohart-Adams, and Yan. Out of all the experiments, the Yan model exhibited the highest average of the determination coefficients (R² = 0.9842), although the packed column adsorption was better predicted by the Thomas equation.

According to Tünay et al. [29], the goal of this study is to evaluate the efficacy of phosphoric acid-activated hazelnut shell carbon (HSAC) in removing the antibiotics diclofenac (DC), ciprofloxacin (CIP), and sulfamethoxazole (SMX) from various water-based solutions and wastewater. Numerous pits of varied sizes and forms were found on the surface of HSAC through a scanning electron microscopy study. The Brunauer-Emmett-Teller surface area of HSAC was determined to be 1,173 mg g^-1. Concerning the batch adsorption of DC, CIP, and SMX, several factors were examined, such as pH, contact time, initial concentration, dosage, and temperature. We utilized the Freundlich, Dubinin-Radushkevich, Temkin, and Langmuir isotherms to simulate the adsorption equilibrium of DC, CIP, and SMX. Using the Langmuir isotherm, we can confirm that DC, CIP, and SMX were adsorbed onto HSAC. At 125, 95.2, and 285.7 mg g^-1, respectively, DC, CIP, and SMX exhibited the highest adsorption capabilities. The pseudo-second-order model was found to be the most appropriate for describing the adsorption kinetics of DC, CIP, and SMX after extensive deliberation. Endothermic and spontaneous adsorption of DC, CIP, and SMX onto HSAC was shown in thermodynamic investigations. Based on the results, HSAC is a great adsorbent for cleaning wastewater of DC, CIP, and SMX; it's also environmentally friendly and readily available.

Stjepanović et al. [28] reported that drugs in natural waters have been the subject of extensive study over the past decade due to concerns that they pose health risks to humans and ecosystems. It is a fact that drugs make it into municipal sewage due to their excessive use. Wastewater treatment plants do not prioritise drug removal since ongoing drug testing in natural waters and drinking water is not mandated by international and national regulations. When you need pain relief, inflammation reduction, or fever reduction, reach for diclofenac, also known as 2-[2-(2,6-dichloroanilino)phenyl] acetic acid (DCF), a nonsteroidal drug. Due to its characteristics, DCF is able to survive in water and quickly ascend the food chain. Accordingly, DCF should be removed from wastewater before discharging it into aquatic bodies. Eliminating DCF from water using adsorption is a simple and fast process. The potential for DCF removal by adsorption onto activated carbon is investigated in this work. As adsorbents, we tested modified commercial activated carbon Cullar (MC), which is activated carbon derived from commercial Cullar that has been modified for a specific application (e.g., adsorption, catalysis, biofuel production). The modification can be done by chemical activation, surface functionalization, or impregnation with other materials to enhance its performance over the unmodified form. Other materials used are modified hazelnut shell (MHS), and unmodified commercial activated carbon CULLAR (C) in batches. To characterise the adsorbents that were examined, we utilised FTIR, zeta potential, and pHpzc. To further evaluate the adsorbent's performance across a pH range of 2–10, we conducted isothermal tests. The most effective adsorbent that was evaluated was the modified activated carbon Cullar, which had a maximum absorption capacity of 48.7 mg g⁻¹. Freundlich and Langmuir isotherm models were both satisfactorily applied to the data. There was an effective elimination of DCF using modified activated carbon that was generated from hazelnut shells.

Futalan et al. [4] synthesised activated carbon (RHAC-LJ), and the adsorptive capability of RHAC-LJ in removing Pb(II) from water was investigated. As far as FTIR analysis can tell, RHAC-LJ contains hydroxyl, carboxyl, alkene, and amide groups. SEM micrographs reveal that the material's pore volume and diameter were significantly increased after activation with lemon juice. One method for removing pollutants is to activate the adsorbent surface with acid from lemon juice. The surface area and pore volume of the RHAC-LJ are 112.87 m² g⁻¹ and 0.107 cm³/g, respectively. The kinetics of adsorption were characterised by the pseudo-second-order equation (R² = 0.9941), with a rate constant of 3.3697 mg g^-1 min for Pb (II). This indicates that chemisorption was the most time-consuming step. To discover how pH, stirring speed, adsorbent dosage, and their interactions affected the removal efficiency of RHAC-LJ, the BBD model using RSM was employed. To determine the significance of the model, independent parameters, and interactions between them, we used analysis of variance. Furthermore, a removal efficacy of 98.49% can be achieved under the following optimal conditions: 197 rpm, pH 5.49, and an adsorbent dosage of 0.3487 g. Overall, our research suggests that RHAC-LJ could be an affordable strategy for treating synthetic wastewater with Pb(II) removed.

4.1 The characterization of GAC

4.1.1 XRD analysis of GAC and pollutant-loaded GAC

These X-ray diffraction (XRD) patterns are for granular activated carbon (GAC), a mixture of GAC and diclofenac sodium (Voltaren), and Pb in the presence of GAC. Radiation XRD is one of the most important instruments to investigate material crystal structures. Figure 4 shows the diffraction intensities of the figure’s measurements, which indicate the strength of X-ray scattering, on the y-axis. The diffraction angles (2θ degrees) are presented on the x-axis. These numbers enable us to calculate the spacing between the planes of the material.

For reference, the GAC peak is typically broad and centered at 2θ about 20°-30° in most materials. The broad peak indicates that the structure of GAC contains both microcrystalline and amorphous carbon phases. The peak, although not very sharp, is assigned to activated carbon due to its high intensity and presence of pores. Such a structure allows GAC to treat various parameters of water, which is important for its adsorption capabilities. The absence of a well-defined crystalline structure of the powder reveals that amorphous material is attained. This is a waste product from the activated charcoal industry.

The XRD pattern is altered when GAC is mixed with Voltaren (Diclofenac Sodium). Moving and strengthening of the pattern peaks demonstrate that the GAC surface had been changed by diclofenac sodium. The medicine might have adhered to the carbon or even seeped into it. Depending on the extent to which they broaden or truncate the GAC peak, sodium diclofenac can modify carbon microstructure. The structure of the GAC can be slightly changed by diclofenac sodium (e.g., interplanar distances or crystal lattice), as proved also by a peak shift (Figure 4). The XRD pattern of GAC and diclofenac sodium physically varies in their combination at the peak intensities. As the drug modifies the crystallinity of carbon upon binding to GAC, weak forces or physisorption between the drug and carbon can be expected.

Figure 4. The XRD for the GAC, Voltaren with GAC, and lead with GAC

The XRD pattern experiences much greater change with lead doping for GAC. The GAC peaks are present and have their location and intensity altered differently again, as for the diclofenac sodium peaks. These differences show that in the presence of lead, the activated carbon is attached to the surface. The heavy ion nature of lead may result in more interaction between lead ions and surface functional groups of GAC. This could have a huge impact on the structure of the carbon. Insoluble lead phases (Pb oxide and Pb hydroxide) showed more or less XRD peaks because of the chemical combination. The additional peaks evidence that the lead phase is generated upon lead adsorption on GAC. The intensity of the GAC peak can be enhanced or reduced due to the lead-carbon interaction. It can be inferred that lead can be absorbed by GAC, and the configuration changes according to its XRD pattern. Both lead and diclofenac sodium shift the peaks, indicating that they alter GAC plane spacing. The diffraction peaks of GAC shifted upon interaction with these pollutants as its crystallinity changed. One of the ways that its peak position and intensity can be adjusted is by the adsorption of molecules or ions. This effect modifies the electronic density near the carbon atoms and thus also the X-ray diffraction pattern. The structural changes are due to the existence of diclofenac sodium and lead. Therefore, GAC is obviously an excellent material for removing pollutants from water and adsorption of chemicals.

Finally, XRD patterns made scenarios such as diclofenac sodium + GAC or lead + GAC provide information on the interactions of GAC. It can be seen that diclofenac sodium and lead have an influence on the crystal structure of GAC from the patterns in Figure 5. Such impurities are adsorbed by GAC and also influence the structure of the activated carbon, indicating the intensity degree and position shift of peaks. The outcomes also underscore the great potential of GAC to remove undesired substances from water, such as lead and diclofenac sodium. This interaction is evident, and the contributions to the adsorption mechanism can be realized by observing the XRD patterns.

A wide peak at 2θ = 23° with having intensity of ≈2400 counts is observed in the XRD of GAC with Lead. So GAC is not a crystal. The maximum positions are slightly shifted, and the intensity is largely modified with the addition of diclofenac sodium (Voltaren) (1321 counts at about 2θ = 23°). Further evidence that diclofenac modifies the structure of GAC crystals according to interactions with them. In the same way, in Figure 5, the lead + GAC pattern also shows variable peaks with a more intense peak at about 2θ = 23° and a count of 1131. This indicates that lead ions attach to the carbon surface. The adsorbed pollutants and GAC are interacting, as manifested by variable changes and intensity.

4.1.2 SEM analysis of GAC before and after Voltaren adsorption

Figure 5 displays the SEM images at different magnification factors of the surface of GAC doped with diclofenac sodium (Voltaren).

Figure 5. The SEM for Voltaren with GAC (A, B) before adsorption, (C, D) after adsorption

The GAC surface coated by Voltaren has a rough and grainy morphology at this magnification (Figure 5(A)). The surface is rough, and the particles seem to be non-uniformly distributed because of the rough surface. This is why the GAC might be having an interaction with the diclofenac molecules, or could be, in fact, beginning to start bonding up somewhere.

This is a slightly flatter and a bit less rough surface in Figure 5(B) than that of Figure 5(A); perhaps it occurs because the Voltaren molecules that are in the GAC on average keep more separated from each other. It still has some pits and bumps, suggesting that the adsorption process may still continue.

From the side, it looks a bit smoother with less grain showing (Figure 5(C)). This could mean that the surface is either more homogeneous than the adsorption at certain stages of adsorption. If things are humming along as they should, it could mean that GAC and Voltaren are collaborating smoothly.

Because the surface texture is more uniform and smoother in Figure 5(D), it appears less pronounced. There are no densely packed features to give us the sensation that it is rougher or structured. This might suggest that the GAC polymer absorbed the drug better. They show the change of the surface form due to the interaction between Voltaren and GAC. From this morphological study, we can have a better understanding of the adsorption of Voltaren with GAC. It has important medical and environmental consequences, such as the removal of controlled-release systems or drugs.

4.1.3 SEM analysis of GAC before and after lead adsorption

This scanning electron micrograph represents the combination of granular activated carbon (GAC) with lead, as shown in Figure 6. Figures 6 (A, B, C, and D) are offered in four sizes. The surface of the GAC is observed with different levels of roughness and graining at this magnification. The GAC possibly dos not yet reached the lead adsorption on its upper side since it possesses larger channels and holes. The rough surface of the texture has multiple sites for lead ion interaction. In Figure 6(B), the evidence presented in this photo shows that lead particles may be more evenly distributed on the GAC surface. Although the texture is not yet perfect (some 'lumps' and 'bumps'), it looks better in comparison to Figure 6(A). The growth of a more refined structure suggests that lead ions start to move into the GAC matrix, i.e. clear indication of an adsorption process pronounced.

Figure 6. The SEM for lead with GAC (A, B) before adsorption, (C, D) after adsorption

The surface is even smoother and uniform, with fewer visible grains in Figure 6(C). There appears to be a little more bonding or absorption between the lead itself and the GAC, as evidenced by the smoother surface. As the pores got larger, the lead may have begun to close some of them up, and as the surfaces at this point changed from gritty to smooth, it would have been more secure to the GAC.

Under the microscope, the surface texture in Figure 6(D) looks a lot smoother, and fewer pores are visible. A full, smooth surface can also indicate that the GAC has taken up all the lead ions and is near capacity. This illustration has used up our lead count for the current GAC.

These scanning electron micrographs show the process by which GAC absorbs and reacts with lead. Surface morphology variations from rough to smooth textures provide valuable insights into the lead-activated carbon interaction at different time points. In order to clean the air or water, this is essential.

4.1.4 Physicochemical properties of GAC

In contrast, the SEM analysis indicates a highly porous and rough surface with the presence of mesopores and macropores in the range of 2-50 nm, which is a characteristic pattern for GAC.

The XRD results indicate the amorphous character of the GAC, with a broad peak at approximately 22°, indicating that it is crystalline in structure. GAC usually has pore volume between about 0.4-0.8 cm³/g and surface area from 800 to 1200 m²/g, depending on the source and activation procedure used. Due to the literature information and properties of GAC, such particles are expected to have surface oxygen-containing groups, such as –COOH or –OH, providing their acidic surface chemistry.

4.2 Adsorption performance of GAC: Experimental parameters

The amount of lead (Pb) ions was tested at the Environmental Engineering Laboratory using an atomic absorption spectrometer (AAS). The concentration of diclofenac sodium was determined using a UV-Vis spectrophotometer that operates at a wavelength of 276 nm. We measured the pH with a digital meter. For each experiment, we utilised one of two sizes of carbon:

1. Activated carbon in a granular form, with a size range of 1-2 mm.

2. Activated carbon in granular form that has been passed through a fine-mesh screen measuring 150 µm after being processed in a ball mill.

4.2.1 Effect of contact time on adsorption efficiency

Lead and diclofenac sodium were absorbed in increasing amounts within 120 minutes. Powdered activated carbon samples exhibited peak lead adsorption in the initial half an hour. That the GAC sites absorbed the lead so rapidly is demonstrated by this. Adsorption of the granular activated carbon was sluggish at 120 minutes but quickened to 180 minutes. That the granular carbon that isn't powdered is more effective is demonstrated here. More time to make contact is required to accelerate the removal rate.

Figure 7. Effect of contact time on the removal efficiency (%) of Voltaren and lead using 0.5 g GAC at 150 rpm and 25℃ (contact time: 120 min)

Figure 7 illustrates the process of removing lead and diclofenac sodium (Voltaren) from water by use of granular activated carbon (GAC). The absorbance of the two substances was plotted against time from 5 minutes to 180 minutes. The slight decrease in lead uptake during an experiment would appear to show that this metal is also being eliminated very slowly. Since the absorbance decreases to 0.0147 after 5 min, this indicates the presence of lead in the solution. In contrast, this value also decreases with time, and the absorbance at the end of 180 min. increases to 0.0101. The lead is scavenged from the slurry by GAC. Lead may not easily or rapidly adsorb to GAC's surface because of lead's bigger molecular size and/or stronger interaction with water. Children might play a role due to other compounds. Adsorption might also be slower in the case of GC because of the lower number of active sites for lead, or it may be more difficult to access (hence the slow removal).

Under test, Voltaren (diclofenac sodium) shows a much more dramatic and rapid reduction in absorbance. High concentration of Voltaren in the solution is confirmed by the highest relief reading of 0.385 at 5 min. A rapid decline of the absorbance to a minimum value of 0.12 is evident in the first half an hour. From there, it diminishes slightly until the end of the time and is found to be 0.180. First, this rapid decrease shows the speed with which Voltaren interacts with the GAC. It could also be the reason is that it has more time to get trapped in the pores of activated carbon because its molecular size is smaller. The initial, more rapid adsorption of this is apparent. The rate of absorbance drops after 30 min, but not as fast as that in lead. The system is almost saturated, where uptake of the compound becomes more time-consuming owing to a reduction in the available active sites, although GACs are really very efficient at removing Voltaren.

Granular activated carbon is an effective adsorbent for both contaminants, as seen in Figure 7. However, it does demonstrate a significant disparity in the elimination rates: GAC rapidly gets rid of Voltaren, while lead adsorbs at a much slower rate. The distinction arises from the fact that GAC and the two substances exhibit distinct chemical properties and engage in distinct molecular interactions. Both substances are removed from the water according to the findings, but Voltaren is far more effectively adsorbed, particularly in the first stages of the experiment. It is possible that other factors, including the physical or chemical properties of lead, influence its adsorption kinetics, or that GAC needs more time or a larger surface area to effectively adsorb lead, as its removal is slower than expected.

4.2.2 Effect of initial concentration

When arsenic concentration was between 10 to 50 mg/L, the adsorption rate increased with the lower concentration, and the clearance rate decreased with higher concentrations. Significant removal of material was attributable to active sites, with both powdered and non-powdered granular GAC. Lead is adsorbed to GAC, followed by its absorbance determination. Figure 8 shows the optical adsorption of lead from 0.05 g/L to 10 g/L. The results show the correlation between lead quantity and GAC sorption rate. The absorbance values are very low and slowly increase when the lead concentration is lowered from 0.05 g/L to 1 g/L. This indicates the fact GAC is unable to adsorb any lead ions from solution despite having enough active sites to adsorb the same. At high concentrations, increasingly more lead comes into contact with the GAC surface, causing an increase in adsorption as indicated by linearly increasing absorbance. The adsorption process still proceeds smoothly without reaching the limit level, such that the GAC surface is not overloaded, as indicated by no excessive increase in absorbance with increasing concentration.

At this concentration level, the absorbance increases sharply (0.042), and hence it can be seen that the GAC is approaching its highest ability, where a large part of the lead is held by it. A rapid spike in GAC rapid absorbance flow charts causes a highly intensive absorption rate; thus, the total absorption capacity increases with increasing lead ion concentration. Since these interactions are known to be based on pH, it may be that lead ion adsorption at the GAC surface is stronger for this higher concentration.

Such absorbance falls below 5 g/L at 10 g/L, which is now 0.0097. At the highest concentration, the absorbance decreases due to saturation of adsorption.

Lead causes the GAC surface active sites to load up to capacity. Lead ions can no longer be adsorbed effectively after the surface is saturated. As a result, the absorbance value becomes flat or even decreases. After a certain concentration, the GAC isn't very effective in adsorbing new lead ions, and adding more lead to the solution may prevent it from being adsorbed.

There appears to be a sweet spot for lead adsorption concentrations, according to the trend. At low to moderate concentrations, GAC works effectively; however, once the concentration reaches a specific point, it reaches its adsorption capacity, and further addition of GAC has little effect on its adsorption efficiency. The ability of adsorbent materials, such as GAC, to efficiently remove contaminants is crucial in real-world applications like water treatment.

Figure 8. Effect of lead concentration on removal efficiency (%)

Figure 9. Effect of Voltaren concentration on removal efficiency (%)

Figure 9 depicts how the concentration of a solution of Voltaren changes as a function of its concentration in water, as measured using a spectrophotometer. Based on the findings, it appears that the absorbance increases in direct proportion to the concentration of Voltaren. Absorbance readings of 0.039 at 10 g/L show that the solution contains a negligible amount of Voltaren, since just a tiny fraction of the light reaching the sensor is absorbed. At 50 g/L, the absorbance reaches 0.06, which is a steady increase with increasing concentration. The absorption principle, which states that more molecules in a solution mean more opportunities for molecules to interact with the light travelling through it, is reflected in the fact that absorbance increases as concentration does. As the absorbance typically varies with the solute concentration in accordance with Beer-Lambert Law, this pattern is common for many compounds in solution. Assuming a constant light path length and molar absorption coefficient, the law states that absorbance is directly proportional to concentration. This is what the results demonstrate: that if we increase the concentration of Voltaren, the total absorbance increases, because then, there are more absorbing molecules in solution. The experiment is performed at a temperature of 25℃, 150 rpm, contact time 120 min, and GAC of 0.5 g, pH of lead is 6, and the pH level for Voltaren reaches 5, respectively.

According to the figure, Voltaren exhibits predictable absorbance behaviour across a variety of concentrations, and within the concentration range under study, the correlation between concentration and absorbance is linear. This finding is significant because it sheds light on the light-solvent interaction of Voltaren, which has practical uses such as sample concentration determination and the creation of spectrophotometric methods for Voltaren quantification.

4.2.3 Effect of GAC dosage on adsorption

Raising the carbon dosage from 0.1 to 1.5 grams considerably enhanced the removal of both contaminants. There was a maximum clearance rate of 1 g for diclofenac sodium and 0.8 g for lead. Specifically, the surface area and number of active sites both grew in direct proportion to the adsorbent's mass. No more than 1.5 g of carbon powder could be extracted.

Figure 9 illustrates the correlation between the levels of granular activated carbon (GAC) and the absorbance of Voltaren and lead in a water solution. The fact that the absorbances of Voltaren and lead decrease when the dosage of GAC is increased indicates that GAC is effectively removing those compounds from solution.

The adsorption amount of Voltaren and lead is still high even at a low potential dosage (0.1 mg/L) of GAC. It thus appears that fewer active sites are available for adsorption and, as a result, lower removal of both chemicals from solution can be obtained with a lower dosage of GAC. The absorbance of both GJ2C and RV decreased gradually with increasing amount of GAC dose, which implied that more adsorbates were extracted from the solution. The absorption of the proposed sorbents can be seen in the reduction of absorbance A with time, as Voltaren and lead are absorbed by GAC, showing a diminution in their concentration in the solution.

After the GAC dose approaches 1.5 mg/L, the absorbances of Voltaren and lead decrease significantly, indicating that the higher concentration of GAC has led to more active sites and more effective adsorption. We may conclude that GAC is more successful than lead at eliminating Voltaren since the absorbance of Voltaren decreases more dramatically with larger dosages of GAC.

Because a larger amount allows for more interaction with contaminants, it is normal for adsorbents like GAC to have an increasing removal efficiency with increasing doses. Voltaren and lead concentrations are reduced as the concentration of GAC is increased due to its adsorption capabilities. Findings highlight the requirement of optimizing GAC dosage to ensure effective adsorption and demonstrate that, with increasing doses, GAC can successfully remove these contaminants.

The experiment has occurred at a temperature of 25℃, rpm is 150, contact time is 120 min, GAC is 0.5 g, pH is 6 for lead, pH of Voltaren is 5, and concentration of Voltaren and lead is 10 mg/L, respectively.

As illustrated in Figure 10, the removal effectiveness of Voltaren goes up quickly when the GAC dose goes up. It starts at about 90% at a dose of 0 mg/L and goes up significantly to about 96–97% when the GAC dose reaches 0.2 mg/L. After this first spike, the removal efficiency for Voltaren levels off, with only a small rise, while the GAC dose keeps going up. This means that after a given amount of GAC, the removal efficiency for Voltaren doesn't get any better. The elimination efficiency for lead is comparable, but it starts at a higher value of about 91% and goes up more slowly than for Voltaren. At greater GAC dosages, it works at 98–99% efficiency, and after roughly 1 mg/L of GAC dose, it doesn't vary much. The lead curve demonstrates that the removal efficiency rises more slowly and steadily as the GAC dose goes higher.

Figure 10. Effect of GAC dose on the removal efficiency (%) of Voltaren and lead

4.2.4 Influence of pH on adsorption behavior

The degree to which substances adhered to it was significantly influenced by the solution's pH. Lead had an optimal pH of 5, while diclofenac sodium had an optimal pH of 6 (a high pH removes the proton from diclofenac). The increased interaction between the GAC surface and powdered carbon is due to the electrostatic forces that attract the two. Granular carbon's removal rate increased with decreasing pH, with 3 and 4 yielding the highest rates for the two contaminants, respectively.

Figure 11 illustrates how the adsorption of lead and Voltaren onto granular activated carbon (GAC) is affected by the pH of a water solution. From 4 to 12, the graph displays the changes in the absorbance (Abs) values of lead and voltaren as a function of pH. Lead absorption gradually increases as pH rises. The absorbance begins at 0.0016 at pH 4 and rises steadily with increasing pH up to 0.00664 at pH 12. Lead is more effectively adsorbed to GAC at higher pH values. One possible explanation for the increase in absorbance at higher pH levels is a change in the chemical form of lead in solution. There are a couple of possible explanations for why lead ions are more amenable to adsorption at higher pH levels: either the GAC's surface charge interacts better with the lead ions, or both are true. Voltaren is more complex, however. Here, the absorbance is 0.073 at a pH of 4, and then it increases rapidly to 0.71 at a pH of 6. This sudden increase may indicate that GAC can adsorb more Voltaren under this pH. It falls to 0.098 only at pH 12, and decreases further up the scale of pH. Due to this decrease, the synergistic effect between Voltaren and GAC at higher pH disappears. This may be due to alteration of the surface characters of GAC, or in the solubility or charge of Voltaren moieties.

Figure 11. The effect of pH on the removal of lead and Voltaren

The difference between lead and Voltaren shows the importance of pH in the adsorption performance of GAC to different chemicals. Although adsorption of Voltaren is promoted in a slightly acidic to neutral pH range, higher values offer better channelling for lead adsorption. The adsorption decreases with increasing pH, up to a certain point at basic pH. These results underscore the importance of pH in the adsorption model for chemical compounds on waterborne surfaces. Moreover, they argue that a pH higher than X may work better in removing lead, while perhaps less so for Voltaren, and that a lower pH value might be the preferred condition for the removal of Voltaren.

The surface charge on GAC depends on pH, being positive at low pH and negative at high pH. This influences the adsorption, making electrostatic interactions more prevalent. Diclofenac is an acidic organic compound that is protonated and un-ionized at low pH. This is believed to cause the FiCAM solution to adhere to a positively charged GAC surface. But at a higher pH, diclofenac sheds its protons and takes on a negative charge. This means it is less likely to stick to your stuff due to electrostatic repulsion. Lead (Pb²⁺), however, is a cation at low pH and adheres well to the negative surface of GAC. As the pH increases, lead forms hydroxy complexes (PbOH⁺). They are unlikely to adhere to surfaces as electrostatic attraction is weaker. So these two adsorbents, one for diclofenac and lead, would be different. The adsorption of diclofenac is mainly governed by its protonation state, while the ionic form and pH value of lead are predominantly responsible for its adsorption.

The result is utilized to identify that the optimal pH with the end goal to remove the pollutants is as follows: for Voltaren, it is at values higher than 7 and lower than 5, but optimal efficiency is in the alkaline zone from 8 to 12. The level of lead removal is constant around 100% through the whole pH level range from 2 to 12, from which it is visible that pH has the least effect on lead removal level. For Voltaren, the optimal pH is sub-alkaline—from 8 to 12—while for lead, it is neutral to alkaline because removal remains over 90% effective at all pH values.

4.2.5 Effect of shaking speed on adsorption efficiency

It was found that shaking speed was a key aspect in the adsorption process. The optimal removal speed was determined to be 150 rpm. The faster the speed, the less effective the removal. This is because the boundary layer of the adsorbed particles gets thicker when the agitation level goes up. The best results were at 100 and 200 rpm. For powdered carbon, the faster the speed, the less efficient it was. The opposite happened with granular activated carbon, though. The faster the pace, the faster the removal rate. At 250 rpm, granular carbon had the highest removal rate.

Figure 12. Effect of agitation speed on the removal efficiency of Voltaren and lead using 0.5 g GAC at 25℃ (contact time: 120 min)

Figure 12 represents the impact of rotational speed (rpm) on lead and Voltaren removal efficiency in a solution. The absorbance of Volteran decreases as the rpm increases from 100 to 250, but the absorbance of lead first decreases before increasing at higher rpm values.

As the rpm increases, the residual concentration of lead in solution decreased, reaching 0.188 mg/L at 250 rpm, from 0.42 mg/L at 100 rpm. Because of this, the faster the mixing, the less lead there will be in the solution because the material can absorb it better. The decrease in absorbance indicates that the adsorbent is more effective at removing lead from the solution when the rpm is increased. The increased contact between the adsorbent and the lead ions is likely to be to blame. At 100 rpm, the absorbance is 0.083, and at 200 rpm, it drops to 0.063, indicating that the concentration of Voltaren in the solution decreases with increasing rpm. However, the absorbance increases to 0.137mg/L at 250 rpm. This means that at extremely high rpms, the effectiveness of Voltaren's adsorption can decrease or perhaps reach a point where it becomes ineffective at removing the drug. Possible causes include excessive mixing, which impedes the adsorption process or prevents the adsorbent from achieving greater rates of Voltaren attachment.

Based on the results, the maximum for efficient lead adsorption was obtained at a larger rpm, with the absorbance decreasing steadily. The rpm-versus-adsorption efficiency relationship of Voltaren is more complicated. At 200 rpm, absorbances decrease and then increase at higher speeds (250 rpm).

The efficiency of light-absorbing lead and Voltaren dictates the best adsorption %.

The minimal value of the lead absorption is achieved at 250 rpm (0.188), while it decreases with increasing rpm. Being that higher rpms enhance lead removal from solutions, 250 rpm is a suitable speed for lead adsorption. Improved removal of lead by the adsorbent is achieved with increasing mixing speed, as shown by the decrease in absorbance over time.

As its absorbance, diminished from 0.083 at 100 rpm to 0.063 at 200 rpm, is increased to 0.137 at 250 rpm by Voltaren. Because Voltaren absorbs the most at 200 rpm, that’s probably when its performance is optimal. At 200 rpm, the maximum Voltaren can be taken up by the system. Subsequently, the adsorption exhibits a weak impact as rpms increase.

For depuration at both tide speeds, pollutant loads and temperatures, no less than 97% and up to more than 100% of Voltaren were detected. As a result, Voltaren is rapidly removed in the material used to remove it, independent of stirring velocity and initial pollutant concentration. Temperature and agitation speed snap do not affect removal much. Voltaren is desorbed from the solution upon contacting the adsorbent. Another evidence is that the efficiency does not depend on concentration.

But speed, movement, and temperature have a greater effect on lead expulsion. Lead is initially removed at an efficiency of 60–70% and the process improves with GI rate and concentration. The efficiency of removal is 80% even at high agitation speeds and temperatures. Stirring can remove some lead, but not completely, in the experimental conditions. Lead adsorption is highly dependent on adsorbent dosage and temperature. The time and agitation enhance the lead removal percentages, but more efficient work is achieved at higher adsorbent dosage and temperatures.

4.2.6 Temperature dependence of adsorption

Experiments have shown that increasing temperature does not affect the adsorption process for powdered activated carbon, but it does increase the adsorption capacity for granular activated carbon.

Figure 13. The relation between temperature and removal efficiency (%) for Voltaren and lead at GAC is 0.5 g, 150 rpm, contact time is 120 min, respectively

Figure 13 illustrates the relationship between temperature and the change in absorbance of lead and Voltaren. It achieves this by taking readings of the absorbance at four different temperatures: 25, 30, 35, and 40 degrees Celsius. Both compounds adsorb differently depending on the temperature. Because lead is less soluble in water at higher temperatures, the concentration of lead in the solution increases. However, a significant increase to 0.184 is observed at 40℃. This further evidence indicates that high temperature could enhance lead adsorption as a··result of higher activity or availability of the adsorption sites. This trend suggests that the lead-adsorbent interaction becomes stronger at a temperature of ~ 40℃, which is considered as optimum temperature for the adsorption of lead.

Its absorbance increases directly proportional to temperature for Voltaren. It starts at 0.063 when you reach 25℃ and goes up to 0.079 when reaching 30℃, then it increases again to arrive at 0.217 going to 35℃, and it peaks at a value of 0.339 with temperature around the number of Celsius degrees equal to that between zero and forty. Since more medicament binds to a certain material as this has its higher temperature, we can conclude that higher temperatures favor the adhesion process of Voltaren gel on any solid surface. Adsorption of Voltaren is best at 40℃, hence it is the optimum temperature for this mechanism.

Lead and Voltaren both absorb most effectively around 40℃. The particular temperature at which adsorption becomes more effective can vary for different compounds, although generally speaking, higher temperatures improve its performance.

The adsorption of diclofenac and lead onto GAC exhibited temperature dependence, with adsorption increasing concomitantly with rising temperature. This means that the process is affected by more than one thing. There are several ways that diclofenac and lead might stick to GAC. GAC has functional groups like -OH and -COOH that interact with diclofenac by hydrogen bonding and electrostatic interactions, especially at lower pH levels. Lead, on the other hand, is coordinated with oxygen-containing groups on GAC. Also, pore filling happens in GAC's micropores and mesopores, where lead is physically confined, and diclofenac mostly sticks to the surface or inside the micropores. The π-π interactions between the aromatic rings of diclofenac and the GAC surface make adsorption even better.

The maximal efficiency toward Voltaren and lead is 95% and 85%, respectively. This demonstrates that agitation, adsorbent dosage, and temperature all contribute, but efficacy plateaus. Granular activated carbon is great for Voltaren, but a bit too wide-strung for lead. It had an adsorption efficiency of 1.9 mg/g for Voltaren (diclofenac), with a removal rate of 95%, proving to be quite effective. It revealed a percentage of 85% of leads were removed, which is the adsorption capacity of 1.7 mg/g. This is slightly less efficient because it was pointed to take off.

Our results represent the removal efficiency of both Voltaren and lead. Our results are in line with Antunes et al. [1], Espina de Franco et al. [2], and Thi Minh Tam et al. [3], who found that the Voltaren removal is affected using adsorbents such as GAC and others. Our results demonstrate the removal of lead, and it is in line with Jaber et al. [30].

4.2.7 The Langmuir and the Freundlich isotherms

Figure 14 shows how the amount of lead adsorbed per unit of adsorbent (Ce/qe) in g/L relates to the equilibrium concentration (Ce) of lead in mg/L. The dots on the graph show the results of an experiment that tests how well a certain adsorbent material can hold lead at varying concentrations.

The fitted line, which is a dotted line, shows the linear equation: y = 337.88 X - 0.9542. Where y is the lead adsorption capacity (Ce/qe), and x is the equilibrium concentration (Ce) of lead in mg/L. The equation shows that the amount of lead adsorbed by the material goes up in a straight line as the equilibrium concentration of lead goes up.

The coefficient R² = 0.9619 indicates that the plot of experimental data and the linear regression model are well-fitted. That’s the data being very well fit to the model.

Finally, it can be seen from the figure that at a lower concentration of lead (Ce), the adsorption capacity increases slowly, but when the level of lead gets higher, the adsorption capacity increases rapidly. This graph is typical of an adsorption isotherm, which illustrates how the concentration of the pollutant in solution influences a material’s capacity to adsorb it.

Figure 14. The relation between Ce/qe (L/g) and the Ce (mg/L) for lead

4.2.8 Langmuir isotherm for Voltaren adsorption on GAC

The Langmuir Isotherm describing how Voltaren (a pharmaceutical pollutant) adheres to GAC is illustrated in Figure 15. The model demonstrates how molecules (Voltaren) compete with each other and adsorbents (GAC), which have a finite amount of uniform binding sites. This ratio is a retrofit to the Langmuir equation that converts the data linearity. How well the data fits the Langmuir model can be determined by plotting this ratio against Ce and obtaining a line. Straight is good, and it looks like the Langmuir Isotherm works nicely for how Voltaren adheres to GAC. From this linear fit, we obtain essential Langmuir constants (qmax and KL).

Figure 15. The relation between Ce/qe (L/g) and Ce (mg/L) for Voltaren

The qmax is the maximum concentration of Voltaren that can be adsorbed on a unit mass of GAC. The adsorption increases as Ce increases, but it decreases when the GAC surface becomes full of Voltaren. The red line hits the y-axis at that point, which corresponds to GAC's maximum capacity, meaning how much it can hold here.

KL is the Langmuir constant that indicates the degree of adsorption. These higher values of KL indicate that not only is there a better interaction between Voltaren and GAC, but also that the adsorption capacity for Voltaren is higher at low concentrations of it.

The solid lines demonstrate that the Langmuir model fits the data well. The latter model assumes adsorption in one layer on the activated carbon, i.e., at any given point, there is no other adsorbate molecule other than a single Voltaren molecule occupying an available active site on the GAC. This is a very significant aspect of Langmuir adsorption. With an increasing Ce, additional Voltaren molecules occupy the adsorption sites of GAC. But eventually, the surface gets congested and adsorption attains a maximum. This is indicated by the plateau in the curve.

The adsorption isotherm can be well fitted to a linear curve, as shown in Figure 15. It can be seen from the high R² value (close to 1) that the data fit to Langmuir model quite well. It implies that adsorption occurs in the manner of monolayer adsorption on a completely smooth surface. The better fit of the Langmuir isotherm to data will be obtained when R² approaches 1.

The higher the dose of Voltaren (Ce), the more Voltaren is bound to GAC, but as soon as the sitting capacity of GAC had been reached, this increase flattened. This is a typical mode for saturation in adsorption. At low concentration, the increase in adsorption is significant because there are still plenty of places where it can occur. But when there are many Voltaren molecules, there is not as much room for them to bond with, which slows adsorption, and the pace of healing speeds up. The Langmuir isotherm is a mathematical model that describes the adsorption of systems, and this can be confirmed from the above plot that the settlement of Voltaren on GAC follows the Langmuir model quite efficiently.

The Langmuir qmax, and when the graph is constructed (qe versus Ce), the slope from which the Langmuir constant KL can be calculated. These data give us an indication of how much Voltaren can be eliminated from the solution by GAC and what is the intensity of adsorption.

It can have a practical value in the design of water treatment/fluxion systems or GAC-based adsorption processes for pollutant removal, such as Voltaren from aqueous solutions.

The linear fit of the plot and the high R² value indicate that adsorption of Voltaren by GAC is very effective and it closely follows the Langmuir model, which implies monolayer adsorption. This renders GAC an excellent material for the removal of Voltaren from wastewaters and solutions.

Freundlich isotherm model for Voltaren adsorption

Figure 16 shows the log-log plot for the Freundlich Isotherm of Voltaren's adsorption onto GAC. The figure shows the logarithm of the equilibrium concentration of Voltaren in the solution (Ce), and the figure shows the logarithm of the amount of GAC that is adsorbed per unit mass at equilibrium. We linearize the Freundlich model, which explains how things stick to a surface that isn't smooth, by showing these logarithmic numbers. The red dotted line on the plot is a linear fit to the data that follows the Freundlich equation. The slope of the line is -0.87, which shows how strong the adsorption process is. The equation for the line is ln (qe) = −0.87ln (Ce) +8.76. A slope less than 1 suggests that the adsorption process is good but not straight, which is how many real-world adsorption processes work. The intercept of 8.76 shows how much Voltaren can be adsorbed per unit mass of GAC under the specified conditions. This is the adsorption capacity.

The R² value of 0.93 reveals that there is a strong linear relationship between ln (qe) and ln (Ce), which means that the Freundlich model fits the data well. This means that the GAC is good at adsorbing Voltaren, but as the concentration goes up, the adsorption efficiency goes down a little, which is what the Freundlich Isotherm says should happen.

Figure 16 shows that Voltaren adsorption on GAC follows a heterogeneous surface adsorption model. This means that the process gets less effective at increasing concentrations, but it still favors adsorption because of the surface's properties and the strength of the adsorption sites.

Figure 16. The Freundlich isotherm of Voltaren adsorption onto GAC

Freundlich isotherm model for lead adsorption

The effect of the quantity of lead (Pb) in a solution on the quantity of lead adsorbed by granular activated carbon (GAC), during the process of adsorption, is demonstrated in Figure 17. The logarithm of the lead adsorbed per unit mass of GAC at equilibrium (qe) is plotted against the logarithm of equilibrium lead concentration in solution (Ce) on the y-axis and x-axis, respectively. This experimental result is represented in the figure that demonstrates how much lead has been removed from the solution as a function of the GAC loaded. The red dashed line is a best-fit relation as a function of the logarithm of qe and Ce. This line was calculated through linear regression, indicating that if the data is converted to a log-log scale, it behaves according to some kind of linear relation. That is the equation of the line that best fits:

$\log \left(q_e\right)=-3.20 \log \left(C_e\right)-19.73$

The negative slope of the line indicates that as more lead is in the solution, less lead sticks to GAC, but at a diminishing rate. This is how adsorption processes look when they are according to the Freundlich isotherm. This is the description of how objects stick to surfaces with different species of adsorption sites that have not only different sites, but also different energies. It fit the data very well with an R² value of 0.985 for the Freundlich model. This, in its turn, suggests that the relationship between the quantity of lead in solution and the area on which this is adsorbed can be correctly described by a logarithmic equation. In summary, the data indicate that lead adsorption on GAC occurs in terms of the Freundlich Isotherm. This implies that with increasing concentration, the lead adsorbed decreases. The log Ce and Δx have a linear relationship.

Figure 17. The Freundlich isotherm of lead adsorption onto GAC

6.1 Limitations

The following limitations were noted during the conduction of the research, such as pollutant interactions. Since lead and diclofenac were adsorbed simultaneously, it was challenging to complete this task. Lead can occupy the GAC adsorption sites, meaning that other substances cannot be removed. Therefore, it is evident that more complicated systems are required to address multiple pollutants simultaneously. The complexity in the adsorption at high rpm should also be considered since the adsorption in the case of diclofenac began decreasing at rates higher than 200 rpm. Since the tendency is not linear, it can be considered that the GAC may operate differently depending on the operational speed above a certain limit. Lead removal is another major issue since GAC demonstrated relatively poor efficiency in removing this metal. Since the washing procedure was difficult, the regeneration method needed to be improved.

6.2 Recommendations and future work

Granular activated carbon (GAC) can be effectively used to remove diclofenac sodium and lead from water. Further enhancement of this process involves investigation of less expensive GAC regeneration technologies, performance comparisons between different types of GAC, and the potential influence of actual water quality conditions on adsorption efficiency. Performance review over a long period of time and testing strategy for bigger systems are important. It may well be that, from a cost-benefit perspective, such comparisons should consider a combination of GAC with other substances to reduce costs as an alternative. Research on the environmental impacts of GAC and other substitutes is needed in order to improve their water filtration effectiveness.