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Article

Date Seed-Derived Activated Carbon: A Comparative Study on Heavy Metal Removal from Aqueous Solutions

by
Mohammad Shahedur Rahman
1,*,
Neetu Bansal
2,
Mohammod Hafizur Rahman
3 and
Maruf Mortula
2
1
Civil Engineering Department, College of Engineering, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 13318, Saudi Arabia
2
Department of Civil Engineering, American University of Sharjah, Sharjah P.O. Box 26666, United Arab Emirates
3
Chemical Engineering Department, College of Engineering, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 13318, Saudi Arabia
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(6), 3257; https://doi.org/10.3390/app15063257
Submission received: 12 February 2025 / Revised: 13 March 2025 / Accepted: 14 March 2025 / Published: 17 March 2025
(This article belongs to the Special Issue Wastewater Treatment Technologies—3rd Edition)
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Abstract

:
The presence of heavy metals in groundwater and wastewater has been a concern for health organizations. This study investigated the effectiveness of activated carbon derived from various natural precursors, including acorns from red oak trees (Quercus rubra), date seeds, and peach seeds, employing the thermal activation method for the removal of heavy metals from aqueous solutions. Batch adsorption tests investigated the effects of sorbent quantity, pH levels, disinfectant presence, and dissolved organic matter (DOM) on the removal efficiency of Pb and Cu. Characterization of the prepared activated carbon was conducted using scanning electron microscopy (SEM). Lead removal efficiency diminished at pH 7 relative to pH 3 and 5, but copper exhibited superior removal efficiencies at pH 7 compared to pH 5. The addition of monochloramine at 4 parts per million (ppm) effectively eliminated lead from the solution. A rise in free chlorine concentration from 2 to 4 mg/L led to a reduction in metal removal from water by 20 to 60%. DOM at concentrations of 1 and 6 mg/L reduced metal removal efficacy relative to DOM at 3 mg/L. Date seed-activated carbons underscore their distinctive potential, offering useful insights for the enhancement of water and wastewater treatment systems.

1. Introduction

The advancement and swift progress of civilization have led to the emission of several undesirable contaminants into the environment [1]. Heavy metal pollutants contamination is a significant issue, according to current data, particularly in water systems. For instance, about 10% of the water sources in underdeveloped rural areas are said to have lead levels greater than 50 µg/L, which is the maximum amount allowed by the WHO guidelines [2]. In industrial areas, heavy metal contamination in water sources frequently surpasses safety thresholds; for example, in specific regions, copper levels have been documented at concentrations markedly above the World Health Organization’s advised limit of 2 mg/L [3]. The introduction of heavy metals, originating from both natural and human activities, has concerned the scientific community in recent decades. These metals have the ability to be adsorbed onto cell membranes, leading to the development of numerous incurable diseases in both humans and aquatic plants and animals. Metals such as lead (Pb) and copper (Cu) are widely present in the environment and pose significant risks [4].
Lead (Pb), listed as a priority pollutant by the Environmental Protection Agency, surpasses other heavy metals in contamination levels in water bodies and poses severe cumulative health risks globally. In Addis Ababa, lead levels in water have been found to average 62.6 μg/L [5], which exceeds the permissible lead concentration of 50 μg/L set by the World Health Organization for drinking water [6]. The exposure to lead (Pb) disrupts physiological functions, damages vital organs, and causes kidney failure. Furthermore, Pb can accumulate in many tissues of fish exposed to it, leading to harm in the liver and kidneys, as well as stunted growth. This accumulation also causes stress, resulting in disrupted cortisol levels and metabolic enzymes [7].
Studies have shown that elevated blood lead levels are associated with cognitive deficits in children [8] and an increased risk of cardiovascular disease mortality [9], hypertension, and renal dysfunction [10]. Lead has been extensively utilized in drinking water distribution systems throughout history due to its corrosion resistance and malleability [11]. Although there have been extensive prohibitions on lead pipes and lead-tin solders, there still exists a residue of plumbing that contains lead [12,13]. Despite the well-known lead-in-water emergencies in Flint, MI, and Washington, D.C., the risk of lead exposure through drinking water remains a persistent danger to public health [14].
Copper is a vital metal in several enzymes for all living organisms; complications arise when there is a deficiency or excess of it [15]. Copper is one of the most widely used heavy metals, with the cupric ion [Cu(II)] being the predominant species in the environment. In this form, copper exhibits toxicity towards numerous living creatures [16]. Individuals are subjected to excessively elevated concentrations of harmful metals in their beverages and meals as a result of some habits, such as preparing food in pots lined or glazed with copper and utilizing copper pipes for water delivery [17,18]. Copper waste originates from several sources, such as drainage discharge, fertilizer companies, mining wastes, electroplating baths, dyes and pigments, as well as electronic waste (e-waste) and discarded electrical equipment, among others [19]. While a small quantity of copper is necessary for living organisms, an overabundance of copper in water can lead to detrimental effects, such as neurotoxicity, depression, brain damage, jaundice, respiratory problems, liver and kidney failure, cardiovascular disease, gastrointestinal problems, and potentially death [20]. The permissible concentration of copper in drinking water is 1.3 mg/L as per the U.S. Environmental Protection Agency (EPA) [21], less than 2 mg/L in Canada [22], and 2.0 mg/L according to the World Health Organization (WHO) [21].
These metals gradually build up in the human nervous system when exposed to polluted water and air sources, leading to lethal disorders even at extremely low levels. Consequently, it is crucial to dispose of them promptly to prevent their concentration from exceeding acceptable thresholds [23].
Numerous physical and chemical methods have been developed to reduce heavy metal concentrations, including membrane separation, accelerated oxidation, and adsorption [24,25,26,27]. However, most of these methods have inherent limitations, such as operational complexity and high costs. In comparison to other technologies, adsorption is a simpler and more convenient approach for successfully removing pollutants [28,29]. However, the cost and regeneration of activated carbon are a major hindrance for its use. Therefore, researchers have focused their attention on waste-based adsorbents for heavy metal removal due to their low cost, renewable nature, and effectiveness. Additionally, by utilizing waste materials such as agricultural by-products and forestry wastes, we can reduce environmental impact and boost the added value of waste materials [30]. This is why, in recent years, adsorbent materials have been prepared from a variety of natural low-cost materials such as coconut shells [31], wood ash [32], sugarcane [33], eggshell [34], rice husk [35], sludge [36], the pedicels of dates [37], sugar beet pulp [38], waste from the pulp and paper industry [39], gulfweed [40], apple pulp [41], palm tree derivatives [42], red oak acorn [43], mushrooms [44] etc. A single low-cost adsorbent will not be able to remove all pollutants adequately [45]. Additionally, a larger quantity of adsorbents is required throughout the removal process, as the majority of low-cost adsorbents have limited adsorption capabilities. As a result, novel, readily available, low-cost, environmentally friendly, and highly effective adsorbents are required.
In addition, most past research has concentrated on heavy metal removal from wastewater, soil, or natural water. In the realm of water purification, the utilization of novel activated carbon for the removal of heavy metals represents a distinctive and innovative approach, particularly in the context of enhancing drinking water quality. While activated carbon has been widely explored for water treatment, the novelty of this study lies in its exclusive focus on addressing heavy metal contamination, specifically in drinking water, diverging from conventional research that often targets wastewater or natural sources. Plant and agricultural waste such as red oak acorns, date seeds, and peach seeds were used in this project for removing heavy metals from drinking water.
Red oak, native to Canada and the US, is cost-effective and abundant. Date palm tree, a cost-effective and abundant plant, is cultivated in arid and semi-arid environments [46]. The global date production is around 9.7 million tons [47], with palm waste generated at a rate of 35 kg per tree [48]. The date palm, a staple crop, generates 750,000 tons of date seeds annually, offering potential for sustainable applications such as water treatment and environmental remediation. Using this agricultural waste for value-added products and responsible waste management is beneficial for date farmers [49,50]. Peaches, renowned for their sweet, vibrant flavor, are celebrated globally, with global production estimated at 24.2 million in 2022–2023 [51].
There are several factors affecting the adsorption capacity of any adsorbents. The most common factors influencing the adsorption process include pH, adsorbent dosage, and the presence of other competing ions in the solution. Disinfection is common in water and wastewater treatment plants. The presence of chlorine may have consequences on the adsorption process. In addition, dissolved organic material is a known adsorbate competing against heavy metal ions.
This research highlights the potential of plant and agricultural waste-derived activated carbon as a sustainable solution for heavy metal adsorption in drinking water purification. By offering an environmentally friendly, cost-effective, and readily available adsorbent, it addresses critical public health concerns while enhancing water safety. The comparative study demonstrates the effectiveness of these novel activated carbons, providing valuable insights that contribute to the advancement of water treatment technologies.
From our initial research, some agricultural tree residues, such as oak and peach tree wastes, were studied with the intent to use them for activated carbon production and to eliminate lead (Pb) and copper (Cu) from water solutions. However, the decision for this study was influenced by the performance and availability of date seed waste and its ability to solve ecological problems. Activated carbon from date seeds has a high adsorption capacity, as well as the desired combination of heavy metal removal and waste utilization. Nowadays, such a strategic move not only utilizes the huge amount of biomass produced annually by the date industry, but it also helps solve important environmental problems. It is therefore safe to assume that the present study expands on this base by dealing with the preparation, characterization, and application of date seed-based activated carbon for Pb and Cu removal from water systems, which is a novel approach to tackling water treatment.

2. Materials and Methods

2.1. Precursor Materials and Preparation of Activated Carbon

The acorns were gathered from the ground beneath the red oak trees located in the Dartmouth district of Atlantic Canada, in Nova Scotia. The fruits underwent a drying process in ambient air conditions for a minimum duration of 24 h, during which they were meticulously cleaned of any foliage or small remnants of branches and trees. Locally grown peaches were purchased from the local market in Halifax, NS, Canada. Dates imported from the Middle East were also purchased from local stores in Halifax, NS. The seeds from the dates and the peaches were extracted, washed, and air-dried (Figure 1). Prior to commencing the studies, the samples underwent a process of drying and grinding using a high-speed rotary cutting mill. Grinded seeds were thermally activated in a muffle furnace under limited oxygen conditions. The temperature increased at a rate of 10 °C per minute and was maintained at 500 °C for one hour during carbonation. After cooling in the oven, the carbonized sample was pulverized into tiny particles using a mortar and pestle. A fraction of 0.5–1.00 mm diameter red oak acorn activated carbon (RAC), date seed activated carbon (DAC), and peach seed activated carbon (PAC) was used in this investigation.

2.2. Chemicals Used

All compounds utilized in this study were analytical or trace metal grade reagents. Analytical grade cupric sulfate anhydrous (CuSO4) and trace metal grade lead (II) nitrate [Pb(NO3)2] were purchased from Fisher Scientific, Waltham, MA, USA. Humic acid as a model DOM was obtained from Sigma Corp., Cream Ridge, NJ, USA. In addition, sodium hydroxide (NaOH), hydrochloric acid (HCl), and sodium hypochlorite (NaOCl) were procured from Fisher Scientific, USA. Sodium hypochlorite (NaOCl) stock solution of about 60,000 mg/L was used to make the free chlorine solution used in this project.

2.3. Adsorbate

Stock solutions of heavy metals were prepared by dissolving the accurate amount of CuSO4 and Pb(NO3)2 in distilled water; the other solutions were prepared by dilution. The pH was adjusted with 0.1 M HCl or 0.1 M NaOH.

2.4. Chemical Preparation

The NaOCl stock solution, which had a high concentration, was diluted to achieve a solution with a concentration of 100 mg/L. Throughout this project, only fresh solutions were utilized. The preparation of monochloramine was carried out according to the methodology described by Eisnor [52]. This technique combined sodium hypochlorite and ammonium chloride with phosphate buffer saline (PBS) at a pH of 9.5. PBS consisted of 8.0 g of sodium chloride (NaCl), 0.2 g of potassium dihydrogen phosphate (KH2PO4), 2.9 g of disodium hydrogen phosphate dodecahydrate (Na2HPO4 12H2O), and 0.2 g of potassium chloride (KCl) dissolved in 1 L of deionized water. For the preparation of this solution, 1.85 mL of sodium hypochlorite (at a concentration of 60,000 mg/L) was added to 500 mL of a phosphate-buffered saline (PBS) solution. An amount of 400 mg (0.4 g) of NH4Cl was introduced into a 2 L glass Erlenmeyer flask, which was separate from the one being used. This was achieved by combining it with 500 mL of PBS solution.
The sodium hypochlorite solution was introduced into the NH4Cl solution using a gradual drip process. Throughout this procedure, the mixture was agitated incessantly until the entire sodium hypochlorite solution was included. The pH of the monochloramine solution was adjusted to 9.5 using 0.1 N NaOH and then stored in the refrigerator at 4 °C. Monochloramine was synthesized and kept for a maximum duration of 5 days. A DOM stock solution of 350 mg/L was prepared by dissolving the required amount of humic acid in distilled water and was kept in the refrigerator. The DOM stock solution was diluted to achieve a solution with the desired concentration.

2.5. Adsorption Experiment

Batch adsorption tests for heavy metals (i.e., Cu, Pb) were conducted utilizing VWR® polypropylene tubes with lids. A stock solution of heavy metal was created and subsequently diluted to various quantities, with the pH of the solution adjusted using 0.1 M NaOH or 0.1 M HCl. Following pH correction, the necessary quantity of the prepared activated carbon (RAC, DAC, PAC) was incorporated. The sample was subsequently combined in an orbital shaker (Barnstead/Lab-Line MaxQ™ 2000) at 175, rpm for a duration of 2 h. Following the conclusion of the mixing period, the samples (suspensions) were centrifuged using a centrifuge machine (IEC Centra GP8R, Thermo Electronic Corporation, Waltham, MA, USA) for ten minutes at 25,000 revolutions per minute. Aliquots of the supernatant were taken from the mixture by decantation, acidified using concentrated HNO3 (to a pH less than 2.0), and then stored in the refrigerator. Inductively coupled plasma mass spectrometry (ICP-MS, X Series II, Thermo Scientific, reporting limits: Pb = 0.4 µg/L and Cu = 0.7 µg/L) was utilized to determine the amounts of metals in the samples. The efficiency of metal removal (expressed as a percentage, R%) was estimated using the following equation:
R ( % ) = C i − C f C i × 100
The symbols Ci and Cf represent the starting and final concentrations of the metal, respectively, measured in milligrams per liter (mg/L).

2.6. Statistical Analysis

Paired t-test analysis of the data was performed using Microsoft Excel 2019 to see if there were significant differences between samples. Unless otherwise mentioned, all statistical analyses were conducted at a 95% confidence level.

3. Results

The outcomes of the sample characterization study are presented at the beginning of this section, followed by the findings of several adsorption tests pertaining to all the adsorbents that were chosen for this investigation.

3.1. Sample Characterization

Samples were characterized by (i) SEM, (ii) EDX, (iii) XRD, and (iv) FTIR.

3.1.1. SEM Analysis

SEM images are shown in Figure 2, Figure 3 and Figure 4. The SEM micrographs show a significant difference in the surface between before and after adsorption. The scanning electron microscopy (SEM) images of all activated samples exhibited an uneven and well-defined porous structure, suggesting a comparatively large surface area. Upon activation, the outer surface of activated carbon exhibits fissures, crevices, and a range of grain sizes within its macroscopic pores. The porous and defective structure of carbon is attributed to the liberation of non-carbon components, such as hydrogen, oxygen, and nitrogen, from the char’s surface during the pyrolysis process [53]. This liberation leads to the creation of a stiff carbon framework with a rudimentary pore structure. An efficient adsorbent requires the presence of pores and an internal surface area. The formation of pores in activated carbon is crucial, as pores serve as active sites, playing a major part in the process of adsorption [54].
After the adsorption of Cu and Pb, visible modifications in the surface morphology confirm the adsorption of metal ions onto the activated carbon. In the Cu-adsorbed samples, some blocked pores and increased surface roughness are observed, indicating that the copper ions penetrated the more compressed portions of the activated carbon. Copper ions are retained as coordination complexes by the oxygenated functional groups (-OH and -COOH). By contrast, the Pb-adsorbed samples exhibit greater surface aggregation and structural compaction. This behavior can be attributed to the precipitation of lead in the pores or the formation of surface complexes with functional groups. The surface morphology of bioadsorbents RAC, DAC, and PAC significantly differs due to their precursor materials. All three adsorbents exhibit substantial adsorption potential, making them viable candidates for metal removal.

3.1.2. EDX Analysis

The EDX analysis of the adsorbent (date seed activated carbon) before and after Cu and Pb adsorption is shown in Figure 5, Figure 6 and Figure 7. Before adsorption, the activated carbon contains various elements, such as O, Cl, Na, Si, K, Br, and Mg, along with a major peak for C. The presence of trace elements indicates residual components originating from the seed’s inherent mineral content. The EDX analyses of lead- and copper-adsorbed activated carbon confirm a high carbon content, characteristic of activated carbon. After adsorption, distinct Cu and Pb peaks appear, which directly signify metal uptake by activated carbon. At the same time, the oxygen content is decreased, which is indicative of the fact that metal ions interacted with surface functional groups by ion exchange or complexation. The removal of elements such as sodium, silicon, and potassium also provides support to the ion replacement hypothesis for heavy metals. Additionally, the significant loss of oxygen content is indicative of the participation of oxygenated functional groups such as hydroxyl (-OH) and carboxyl (-COOH) in chelating Cu2⁺ and Pb2⁺ ions. In the copper-adsorbed activated carbon samples, copper, oxygen, phosphorus, and silicon were detected, while the lead-adsorbed activated carbon exhibited the presence of lead, oxygen, phosphorus, and iron. These results confirm the potency of activated carbon in adsorbing both copper and lead while maintaining its carbon-rich structure.
In the Pb- and Cu-adsorbed samples, metal ion binding may reduce or displace the various functional groups present in activated carbon, leading to a relative increase in the carbon signal due to the decrease in oxygen and other surface elements.

3.1.3. XRD Analysis

The structural analysis of activated carbon samples after heavy metal adsorption (Figure 8 and Figure 9) provides crucial insights into their effectiveness and interaction mechanisms. X-ray diffraction (XRD) analysis is a commonly employed technique to identify the crystalline phases and structural changes in adsorbents. By analyzing the XRD patterns, it is possible to determine the presence (and crystalline nature) of adsorbed metals. This offers valuable information on the adsorption behavior and material properties.
The XRD pattern of activated carbon with adsorbed copper (Figure 8) exhibits peaks located around 43.8°, 51.31°, and 74°. These peaks closely match the characteristic peaks of copper reported in the literature, corresponding to the (111), (200), and (220) planes of FCC copper [55]. The literature confirmed the use of the standard JCPDS card (No. 04-0836) for copper, indicating that the peaks in the activated carbon sample can also be indexed to these crystal planes of copper [56]. This alignment with the literature confirms the presence of copper in the activated carbon and supports its structure as FCC copper [55,56].
The broad peak between 20° and 30° shows the amorphous nature of the activated carbon. This peak, which can be observed in both activated carbon samples, is due to amorphous carbon. There is no characteristic peak of lead observed in the XRD pattern of Pb-adsorbed activated carbon.

3.1.4. FTIR Analysis

Functional groups significantly influence the surface adsorption capabilities of activated carbon. The FTIR diagram (Figure 10) shows the spectra of activated carbon (AC) and AC after adsorption of Pb and Cu ions. In the pure AC, the broad peak is observed around 3400 cm−1, which is assigned to -OH stretching vibrations, which proves the presence of hydroxyl groups on the surface [57]. The peak around 1600 cm−1 is the C=C stretching peak, which is characteristic of graphitic carbon [58], while the other smaller peak around 1000 cm−1 is due to C-O stretching, which may include carboxyl or hydroxyl groups [59,60].
In the case of Pb-adsorbed AC, the broad peak observed around 3400 cm−1 wavenumber shifts, which may suggest that the hydroxyl groups on the carbon surface are engaged in a bond with Pb ions, which may lead to the formation of surface complexes. Additionally, new absorption bands in the 500–600 cm−1 region are attributed to Pb-O stretching absorptions, suggesting the formation of lead oxides or other lead-containing species on the surface [59,61]. Likewise, in the Cu-adsorbed AC spectrum, the shift of the 3400 cm−1 peak implies the bonding between Cu ions and the surface hydroxyl groups. The new absorption bands appearing at 600–700 cm−1 are attributed to Cu-O stretching, and this may be due to the formation of copper oxides or complexes on the surface [62,63,64].
These shifts and new peaks in the spectra show that both Pb and Cu ions interact with functional groups on the activated carbon, mostly hydroxyl (-OH) and carbonyl (C=O). This leads to the formation of metal–oxygen bonds, hence suggesting the formation of metal complexes or oxides on the carbon surface after ion adsorption.
The adsorbent’s surface contains pores that serve as sites for the adsorption of metals. Due to the presence of substantial pores, there is a high likelihood that the heavy metal ions will become trapped and adsorbed within them. Koseoglu and Akmil-Başar [65] observed a similar phenomenon regarding the adsorptive characteristics of activated carbon generated from orange peel. Upon the adsorption of heavy metals, it is seen that the surfaces of activated carbon undergo a smoothing effect as a result of the filling of pores by ions.

3.2. Selection of Adsorbent

Based on superior experimental performance and existing research data, date seed activated carbon (DAC) was chosen over the peach- and acorn-based activated carbons The preliminary adsorption experiments revealed significantly higher removal efficiencies of DAC for both lead and copper in the same experimental conditions. Hence, it was concluded that DAC possesses an enhanced capacity for binding heavy metals, which is likely due to a greater surface area, higher pore volume, and more favorable surface chemistry compared to the materials tested. Studies reveal that the carbon produced from date seeds is characterized by high thermal stability, possesses abundant micropores, and has a distribution of hydroxyl and carboxyl groups, which are functional groups that improve the adsorption of metal ions. Furthermore, given that date seeds have vast availability as agricultural byproducts, DAC is considered more sustainable and cost-effective in comparison with other methods for waste valorization and environmental remediation.

3.3. Effect of pH and Adsorbent Dose

The availability and accessibility of adsorption sites were significantly influenced by the adsorbent dose [66,67,68]. The concentration of hydrogen ions is considered to be an important factor in adsorption operations, which can have a significant effect on how heavy metals behave in aqueous solutions. One of the deciding elements is the concentration of hydrogen ions, which affects the solubility of heavy metal ions in a solution [17]. Throughout the process, it also influences the extent of ionization of the adsorbate and replaces certain positive ions that may exist in the active sites of the adsorbent [54].
An investigation was conducted to examine the effect of different dosages of DAC (10–100 g/L for the Cu solution and 5–50 g/L for the Pb solution) on two metals (Cu and Pb), with an initial concentration of 50 mg/L. The impact of varying amounts of adsorbent on the removal of Cu and Pb ions is illustrated in Figure 11 and Figure 12 at various pH levels.
The removal efficiencies of Cu2⁺ and Pb2⁺ by date seed activated carbon (DAC) are highly affected by adsorbent dose and pH, as illustrated in Figure 11 and Figure 12. A strong adsorption potential of DAC was reported, which is driven by its surface chemistry and active functional groups. The results indicate a positive correlation between the dosage of adsorbent and the percentage of lead and copper removal efficiency. It is anticipated that the adsorption will rise as the dose of adsorbent increases, as a result of the expansion in the surface area of the adsorbent and the greater number of available adsorption sites [54,66]. The Cu removal efficiency for DAC was investigated at pH 5 and pH 7, with varying adsorbent doses in g/L. At pH 7 (Figure 11) pH 7, DAC demonstrated consistent performance, achieving high Cu removal percentages, between 95% and 99%. This implies that a neutral pH is the key parameter for the adsorption of Cu ions. Paired t-test analysis showed that the Cu removal rates at pH 5 and 7 are significantly different (p = 1.67 × 10−6 < 0.05).
The copper removal efficiency is consistently high at pH 7, surpassing 95% for all adsorbent concentrations. This suggests that the neutral pH promotes the optimal adsorption of copper ions, presumably as a result of the reduced competition between H⁺ ions and Cu2⁺ ions for active adsorption sites, as observed in previous studies [69,70]. At pH 5, however, the removal rate is comparatively lower, around 32% at the highest adsorbent concentration of 100 g/L. The inferior performance at lower pH is due to the protonation of the DAC active sites, which in turn results in the reduction of the active sites and is responsible for lower Cu removal [71].
The trend, on the other hand, shows that the increase in the adsorbent dose from 10 g/L to 100 g/L results in a better removal efficiency at both pH levels. This is due to the increased availability of surface area and active adsorption sites with the higher adsorbent doses, which aligns with findings in other previous adsorption studies [72].
The efficacy of Pb removal by DAC was evaluated at several pH values (3, 5, and 7), with varied adsorbent dosages in g/L (Figure 12). The results demonstrate that the efficacy of lead adsorbent is superior at low pH levels (pH 3 and 5), achieving around 99% to 100% effectiveness. This phenomenon may be attributed to the prevalence of Pb2⁺ ions available for adsorption and to reduced competition for adsorption in an acidic pH environment. At pH 3 and 5, the surface charge of DAC may be more conducive to electrostatic attraction to Pb2⁺ ions. Similar findings were observed in a prior study, indicating that pH 5 settings facilitate lead adsorption due to increased electrostatic interactions [73]. The decrease in lead adsorption efficiency at higher pH levels can be attributed to the formation of soluble hydroxylated species, such as Pb(OH)⁺ and Pb(OH)2, which remain in the solution rather than binding to the adsorbent surface [74]. The paired t-test analysis indicated a significant difference in Pb removal rates at pH 3, 5, and 7 (p = 1.04 × 10−5 to 0.02 < 0.05).
The extent of Pb removal was found to be significantly dependent on the adsorbent dose, with all pH levels displaying a positive correlation in terms of performance at higher doses. This enhancement is due to the higher dosages resulting in a greater surface area and more active adsorption sites. However, for adsorbent dosages in the range of 40–50 g/L, the removal efficiency becomes relatively constant, indicating the saturation of active sites on the DAC surface. This plateau is consistent with the Langmuir isotherm formulation, which explains the limited adsorption capacity of adsorbents. Therefore, optimizing the adsorbent dose is crucial to maximizing the efficiency of the adsorbent [75].

3.4. Effect of Disinfectants

Disinfectants are a significant element of water and wastewater treatment. To investigate the impact of disinfectant presence during heavy metal adsorption, a chlorine dose of 2 and 4 ppm and a monochloramine dose of 4 ppm were used during the adsorption of lead with DAC. The metal removal rates for these tests are shown in Figure 13. The results indicate that increasing the chlorine concentration generally led to lower lead removal efficiency for DAC across different doses. Specifically, at elevated chlorine concentrations, both adsorbents exhibited substantial deterioration, achieving lower levels of lead removal efficiency. This highlights the negative correlation between disinfectant concentration and the efficiency levels of DAC in removing lead from water. It was also observed that the addition of monochloramine resulted in 99% lead removal by DAC. The paired t-test analysis revealed a significant variation in Pb removal rates across different disinfectants (p = 4.80 × 10−6 to 0.002 < 0.05).
At 2 ppm Cl2, DAC shows a consistent and high lead removal efficiency, exceeding 90% across all adsorbent doses. The intense oxidative environment generated by chlorine is responsible for the superior performance, as it facilitates the breakdown of lead-containing complexes and increases the interaction of Pb2⁺ ions with the active sites on the DAC surface. Additionally, a previous study corroborated the enhanced removal of lead from water through the use of activated carbon in oxidative environments [76]. At 4 ppm Cl2, a slight decrease in removal efficiency can be observed in comparison to 2 ppm Cl2, mainly in the case of lower adsorbent dosages. The explanation for this decline in efficiency may come from the changes brought about in surface chemistry as a result of chlorination. For instance, chlorination can change the functional groups existing on the DAC surface, such as -OH and -COOH groups [77], which is expected to decrease the number of active sites available for lead binding. Previous studies have indicated that chlorination enhances the surface acidity and changes the amount of surface oxide present [77], which means that the adsorption process can be modified. In addition, the attachment of Cl− to the carbon surface may result in altered structure of the adsorbent surface, which could affect the surface interaction of the adsorbent with lead ions. These changes are known to reduce adsorption efficiency, particularly at higher levels of chlorine than were reported in previous studies [76].
At a concentration of 4 ppm NH2Cl, the efficiency of lead removal was maintained at a level that was either comparable to or exceeded the outcomes achieved with 2 ppm Cl2. Monochloramine appeared to operate as a milder oxidant compared to chlorine, preserving the integrity of the functional groups on the surface of DAC while still facilitating the adsorption of lead. The stability of NH2Cl in aqueous environments ensures that it does not undergo excessive oxidation, thereby preserving its adsorption efficiency even at elevated concentrations [78].

3.5. Effect of DOM

The relationship between heavy metals and dissolved organic matter (DOM) is complex and multifaceted [79,80]. The interaction between soluble organic molecules and metals occurs through processes such as anion exchange, ligand exchange, cationic overlapping, Van der Waals forces, and adsorption [81]. Numerous heavy metals exhibit a pronounced attraction for dissolved organic matter (DOM) and form metal complexes, potentially disrupting the adsorption process. The mobility of metals, their elimination rate, and their ability to adhere to adsorption sites are directly affected by the concentration of dissolved organic matter (DOM) [80]. In order to examine the influence of DOM on the process of lead removal, humic acid doses of 1, 3 and 6 ppm, were employed during the adsorption of lead using DAC. The metal removal rates for these experiments are depicted in Figure 14.
The examination of dissolved organic matter (DOM) concentration on lead removal efficiency by DAC reveals noteworthy patterns. Generally, as the DOM concentration increases, there is a corresponding rise in lead removal efficiency, especially evident at higher adsorbent doses. Strikingly, the 3 ppm level of DOM consistently yields the highest lead removal efficiency across various doses of DAC. Ninety percent removal was observed across all adsorbent doses considered. Moderate DOM levels enhance the adsorption of lead by forming stable complexes with the lead ions [82], which are subsequently adsorbed onto the surface of the DAC. The DOM levels within this limit could also help remove interfering hydroxylated lead species; thus, more Pb2⁺ adsorption sites are available. The paired t-test analysis revealed no significant variation in Pb removal rates between 1 and 6 ppm of DOM (p = 0.96 > 0.05). However, the removal rate at 3 ppm of DOM was significantly different from that at 1 and 3 ppm DOM (p = 5.23 × 10−6 to 0.0003 < 0.05).
At a concentration of 1 ppm DOM, removal efficiency was below average and less competitive. It was also anticipated that the DOM concentration at this level would not be sufficient to create stronger complexes with Pb2⁺ ions, as there seems to be reduced occupancy in the active sites on the DAC. This is the same phenomenon exhibited at 6 ppm DOM, where the % removal was lower than that of the 3 ppm adsorbent dose. This decline may be attributed to DOM oversaturation, which hinders adsorption and competes for the active adsorbent surfaces, thereby limiting the adsorption of Pb ions. Increasing the adsorbent dose from the range of 50–60 g/L proved to be effective at all concentrations of DOM, indicating an increased availability of active sites and an enhanced surface area. This observation underscores the significance of the 3 ppm DOM concentration in optimizing the effectiveness of these activated carbons for lead removal.

4. Conclusions

Cost-effective and innovative adsorbents derived from date seeds (DAC) were effectively employed for the removal of heavy metals from aqueous solutions. This investigation explored the impact of factors such as adsorbent dose, pH, the presence and type of disinfectant, as well as the influence of dissolved organic matter (DOM), on the adsorption process. Scanning electron microscopy (SEM) images highlighted substantial changes in surface morphology pre- and post-adsorption. Key findings include the superior performance of date seed activated carbon (DAC) in removing heavy metals, notably Pb(II) and Cu(II). This study revealed a positive correlation between metal removal and increased adsorbent dosage for all three materials. Noteworthy trends emerged, such as higher copper ion removal at neutral pH (7) and lower removal under acidic conditions, while lead ions exhibited higher removal at acidic pH and reduced efficiency at pH 7. In the presence of monochloramine, both DACs exhibited exceptional Pb removal efficiency, nearing 100%. However, increasing the chlorine concentration from 2 to 4 ppm resulted in decreased Pb removal efficiency for DAC. Maximum lead removal was observed in the presence of 3 ppm of DOM by DAC with lower removal rates at 1 and 6 ppm DOM. SEM images further illustrated distinct morphological changes in the activated carbons before and after the adsorption process, providing visual insights into their structural transformations. Therefore, the findings of this study will be utilized in a wide variety of applications, including the purification of drinking water, the treatment of ground and municipal water, the reduction of gas emissions from power plants and landfills, and the recovery of precious metals. Even though the use of waste materials resolves concerns related to disposal, there may be concerns about the cost benefit of such a technology. The performance of date seed-derived activated carbon as an adsorbent is far superior to that of date seed in general. For this reason, the additional cost is justified by the benefits. The use of HCl and NaOH was minimal, indicating insignificant cost implications. In addition, there were no requirements for the removal of residual chloride or sodium. Previous studies suggested that AC can be regenerated and can be reused in a cost-effective way [83,84]. Overall, even with the constraint of additional requirements, it still appears to be a cost-effective option. Future studies should also focus on optimizing the different factors affecting the activated carbon production from date seeds.

Author Contributions

Conceptualization, M.S.R. and M.M.; methodology, M.S.R. and N.B.; validation, M.S.R., M.H.R. and M.M.; formal analysis, M.S.R., M.H.R. and N.B.; investigation, M.S.R. and N.B.; writing—original draft preparation, M.S.R., M.H.R. and N.B.; writing—review and editing, M.S.R., M.H.R. and M.M.; visualization, M.S.R. and N.B.; supervision, M.S.R. and M.M.; project administration, M.M.; funding acquisition, M.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Sharjah National Oil Corporation grants for the American University of Sharjah, grant number 223215. The work in this paper was supported, in part, by the Open Access Program from the American University of Sharjah.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data used and/or analyzed during the current study are available from the corresponding author upon reasonable request.

Acknowledgments

The author wishes to express gratitude to Pat Scallion from the Clean Technologies Research Institute at Dalhousie University for her technical assistance throughout the execution of SEM studies. The authors would like to recognize Daniel Chevalier from the Mineral Resource Engineering Department at Dalhousie University for his contribution in preparing the activated carbon. This paper represents the opinions of the author(s) and does not mean to represent the position or opinions of the American University of Sharjah.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Acorn tree, (b) date seeds, (c) peach seeds, (d) milled acorn, and (e) active carbon from dates.
Figure 1. (a) Acorn tree, (b) date seeds, (c) peach seeds, (d) milled acorn, and (e) active carbon from dates.
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Figure 2. Scanning electron micrographs (SEM) of (a) RAC before adsorption, (b) RAC after Cu adsorption, and (c) RAC after Pb adsorption.
Figure 2. Scanning electron micrographs (SEM) of (a) RAC before adsorption, (b) RAC after Cu adsorption, and (c) RAC after Pb adsorption.
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Figure 3. Scanning electron micrographs (SEM) of (a) DAC before adsorption, (b) DAC after Cu adsorption, and (c) DAC after Pb adsorption.
Figure 3. Scanning electron micrographs (SEM) of (a) DAC before adsorption, (b) DAC after Cu adsorption, and (c) DAC after Pb adsorption.
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Figure 4. Scanning electron micrographs (SEM) of (a) PAC before adsorption, (b) PAC after Cu adsorption, and (c) PAC after Pb adsorption.
Figure 4. Scanning electron micrographs (SEM) of (a) PAC before adsorption, (b) PAC after Cu adsorption, and (c) PAC after Pb adsorption.
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Figure 5. Energy Dispersive X-ray (EDX) spectrum of date seed activated carbon before adsorption.
Figure 5. Energy Dispersive X-ray (EDX) spectrum of date seed activated carbon before adsorption.
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Figure 6. Energy Dispersive X-ray (EDX) spectrum of date seed activated carbon after lead adsorption.
Figure 6. Energy Dispersive X-ray (EDX) spectrum of date seed activated carbon after lead adsorption.
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Figure 7. Energy Dispersive X-ray (EDX) spectrum of date seed activated carbon after copper adsorption.
Figure 7. Energy Dispersive X-ray (EDX) spectrum of date seed activated carbon after copper adsorption.
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Figure 8. XRD pattern of copper-adsorbed activated carbon.
Figure 8. XRD pattern of copper-adsorbed activated carbon.
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Figure 9. XRD pattern of lead-adsorbed activated carbon.
Figure 9. XRD pattern of lead-adsorbed activated carbon.
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Figure 10. FTIR spectra of activated carbon (AC) before and after adsorption of Pb and Cu ions.
Figure 10. FTIR spectra of activated carbon (AC) before and after adsorption of Pb and Cu ions.
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Figure 11. Copper removal efficiency (%) at different pH (5 and 7) levels by DAC at four different doses: 10, 25, 50, and 100 g/L.
Figure 11. Copper removal efficiency (%) at different pH (5 and 7) levels by DAC at four different doses: 10, 25, 50, and 100 g/L.
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Figure 12. Efficiency (%) of lead removal by DAC at different pH levels (3, 5 and 7). Adsorbents are introduced at 5, 10, 25, and 50 g/L.
Figure 12. Efficiency (%) of lead removal by DAC at different pH levels (3, 5 and 7). Adsorbents are introduced at 5, 10, 25, and 50 g/L.
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Figure 13. Lead removal efficiency (%) at 2 and 4 ppm of chlorine and 4 ppm monochloramine dose by DAC (blue bar: DAC+ 2 ppm Cl2; orange bar: DAC+ 4 ppm Cl2; grey bar: DAC + NH2C).
Figure 13. Lead removal efficiency (%) at 2 and 4 ppm of chlorine and 4 ppm monochloramine dose by DAC (blue bar: DAC+ 2 ppm Cl2; orange bar: DAC+ 4 ppm Cl2; grey bar: DAC + NH2C).
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Figure 14. Lead removal efficiency (%) at 1, 3, and 6 ppm of dissolved organic matter by DAC.
Figure 14. Lead removal efficiency (%) at 1, 3, and 6 ppm of dissolved organic matter by DAC.
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MDPI and ACS Style

Rahman, M.S.; Bansal, N.; Rahman, M.H.; Mortula, M. Date Seed-Derived Activated Carbon: A Comparative Study on Heavy Metal Removal from Aqueous Solutions. Appl. Sci. 2025, 15, 3257. https://doi.org/10.3390/app15063257

AMA Style

Rahman MS, Bansal N, Rahman MH, Mortula M. Date Seed-Derived Activated Carbon: A Comparative Study on Heavy Metal Removal from Aqueous Solutions. Applied Sciences. 2025; 15(6):3257. https://doi.org/10.3390/app15063257

Chicago/Turabian Style

Rahman, Mohammad Shahedur, Neetu Bansal, Mohammod Hafizur Rahman, and Maruf Mortula. 2025. "Date Seed-Derived Activated Carbon: A Comparative Study on Heavy Metal Removal from Aqueous Solutions" Applied Sciences 15, no. 6: 3257. https://doi.org/10.3390/app15063257

APA Style

Rahman, M. S., Bansal, N., Rahman, M. H., & Mortula, M. (2025). Date Seed-Derived Activated Carbon: A Comparative Study on Heavy Metal Removal from Aqueous Solutions. Applied Sciences, 15(6), 3257. https://doi.org/10.3390/app15063257

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