1. Introduction

The growing emphasis on sustainability in environmental processes has highlighted adsorption techniques as a key approach for contaminant removal in water treatment. Adsorption is a separation process where molecules from a fluid phase (liquid or gas) adhere to the external and internal surfaces of a solid material known as the adsorbent [1]. This process plays a crucial role in environmental protection, pollutant removal, gas purification, and industrial separation processes, making it an essential tool for sustainable development [2]. Adsorption occurs through a mass transfer mechanism, where substances migrate from the liquid phase and bind to a solid surface via physical or chemical interactions [3]. The choice of a suitable adsorbent depends on its application, with key factors such as cost, kinetics, compatibility, selectivity, capacity, and regenerability influencing its effectiveness [4]. Lignocellulosic biomass has been identified as a promising precursor for carbon adsorbents.[5] noted that global lignocellulosic fiber production is estimated at 10–50 billion tons annually, offering vast potential for alternative environmental remediation methods. Biomass-derived carbon adsorbents from agricultural and household residues have been widely used in pollutant removal due to their large internal surface area, mechanical integrity, and regenerability [6]. For low-cost activated carbon, the preferred precursors should be freely available, inexpensive, and environmentally safe [7].

Crustacean shells have emerged as effective and sustainable adsorbents for pollutant removal due to their natural abundance and cost-effectiveness [8]. The key component responsible for their versatility is chitin, the second most abundant biopolymer after cellulose, with approximately 80% of chitin production derived from crustacean shells [9]. Chitin’s nitrogen-rich polysaccharide structure provides chemical resistance and mechanical strength, making it suitable for conversion into activated carbon through pyrolysis [10]. Chitin-derived biochar has shown promising applications in water treatment and gas adsorption, further reinforcing its potential as a sustainable adsorbent [11]. To enhance adsorption efficiency, various activation techniques have been developed to modify surface properties and improve adsorption capacity.

This study explores the use of crustacean shell-derived carbons in sustainable water treatment by employing different activation methods and conducting a comparative analysis of their effectiveness in pollutant removal through adsorption studies.

1.       Materials and Methods

Preparation of the adsorbent: Periwinkle shells (Tympanotamus fuscatus), West African clam shells (Galatea paradoxa), and whelk shells (Buccinum undatum) were sourced from a local market in Borokiri, Port Harcourt. The shells were soaked in warm water with detergent for four days to remove dust, residual organic matter, and soluble impurities. They were then thoroughly rinsed with tap water under continuous agitation to dislodge any remaining contaminants.

Afterward, the shells were sun-dried for three days and stored in plastic containers before laboratory processing.

To enhance surface properties, the shells were subjected to carbonization in a muffle furnace at 450°C for three hours. The resulting carbonized materials were pulverized into fine powder, sieved through a 75 μm mesh to eliminate larger particles, and stored in plastic containers. The prepared samples were then divided into two equal portions for chemical activation using acidic and basic treatments.

Chemical activation

Acid Activation: The powdered samples were individually mixed with 0.5 M H₂SO₄ to form a paste, then heated in a muffle furnace at 750°C for two hours. The activated samples were allowed to cool, thoroughly washed with deionized water until the pH reached approximately 6, and then dried in an oven at 105°C for six hours before being stored in airtight containers.

Base Activation: The second portion of the samples was soaked in 0.5 M KOH and mixed to form a paste, followed by heating in a muffle furnace at 650°C for two hours. After cooling, the samples were washed with deionized water, dried in an oven at 105°C for six hours, and stored in airtight containers.

Characterization of Adsorbents: Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) was performed using AGILENT TECHNOLOGIES CARY 630 FTIR CARY630 ZnSe. PART NO: – G8043 64002, MODEL NO: – MY19322004.A baseline correction

is first performed by measuring the spectrum of the Attenuated Total Reflectance (ATR) crystal without a sample to eliminate background interference. The activated carbon samples are then placed on the ATR crystal, aligned with the infrared beam, and pressed for optimal contact before spectra are recorded by measuring the reflected infrared light. The collected spectra are processed to remove noise and baseline drift, allowing for qualitative and quantitative analysis of the sample’s composition and structure. Carbon yield was determined using [12] method by measuring the sample weight before and after carbonization and calculating the yield. The specific surface area was estimated using the Sear method [13]. Bulk density was measured following [14] by filling a 10 cm³ centrifuge tube with a known weight of lump-free activated carbon while tapping to eliminate voids. The final weight was recorded, and bulk density was calculated using Equation

1. These measurements provided key physical characteristics essential for evaluating the adsorbents’ effectiveness.

Collection of PAHs contaminated water: The groundwater study was carried out at Site X in Rumuekpe, Emuoha Local Government Area, Rivers State, Nigeria, positioned at longitude 6°41’25”E and latitude 5°01’41”N. The region is home to multiple oil processing facilities and an extensive crude oil pipeline network. Due to pipeline vandalism, ruptures, and illegal activities, frequent oil spills have been reported. Groundwater samples were collected and analyzed from five wells, each drilled to a depth of 8 meters.

Batch Adsorption studies

Effect of Adsorbent Dosage: Specified adsorbent doses of 0.2, 0.4, 0.6, 0.8, and 1.0 g were added to 50 mL water samples with an initial PAH concentration of 50 mg/L at pH 6. The mixtures were agitated at 150 rpm using a mechanical shaker for optimal contact times of 90 minutes (PSAAC), 60 minutes (CSAAC and CWSAAC), and 120 minutes (WSAAC). Equilibrium studies were conducted at room temperature (25°C). After agitation, the mixtures were filtered using Whatman No. 542 filter paper, and the residual PAH concentrations in the filtrates were analyzed using GC- MS. The equilibrium adsorption capacity (qe) was calculated using Equation (2).

Effect of Contact time: The relationship between contact time and the adsorption capacity of the activated carbon samples was investigated. In this experiment, 1 g of each activated carbon sample was added to 50 mL of a PAH standard solution with an initial concentration of 50 mg/L in a conical flask. The samples were collected at 10-minute intervals from 10 to 120 minutes at room temperature. Residual PAH concentrations in the solution were then extracted and analyzed.

PAHs Extraction Method: The liquid-liquid extraction technique described by [15] was employed to extract PAHs from the sampled solutions. PAHs were extracted from the sampled solutions using analytical-grade dichloromethane (DCM) (99.0% purity, Loba Chemie) as the solvent. A 25 mL volume of DCM was added to the solution and vigorously shaken for approximately 2 minutes to promote phase separation, with intermittent venting to release pressure. The extraction process was repeated twice to enhance PAH recovery. The mixture was then left to evaporate at room temperature for six hours. To remove residual moisture, 1 g of anhydrous sodium sulfate was added before transferring 1 mL of the extract into a vial for analysis using an Agilent 7890N GC/MS gas chromatograph.

Statistical Analysis: Studies of T Test were carried out to perform a comparative analysis of the removal efficiencies of the selected adsorbents

Equilibrium Modeling: The adsorption performance of the activated carbons was assessed using various isotherm models, including Henry, Langmuir, Freundlich, Elovich, and Jovanovic models. The XLSTAT 2014 software was utilized to estimate model coefficients via nonlinear optimization. The Henry isotherm was modelled as a single-parameter system, while the Langmuir, Freundlich, Elovich, and Jovanovic models were treated as two-parameter isotherms. Parameter estimation was performed using an iterative direct optimization method to minimize errors.

2.       Results and Discussion

Results of the Adsorbent Characterization Experiments: The FTIR, and Physicochemical Analysis of the Activated Carbon Prepared: FT-IR analysis was conducted to identify functional groups on the activated carbon surfaces, with spectra data summarized in Tables 1 and 2. Acid-activated samples exhibited O-H, C-H, C=O, and C-O absorption bands, indicating hydroxyl, aliphatic, ester, and carboxyl groups. The spectra of CSAAC showed prominent bands at 3540, 3394, 1797, and 1616 cm⁻¹, attributed to O-H, C-H, esters C=O, and amides C=O, with similar trends observed in PSAAC, WSAAC, and CWSAAC, suggesting comparable surface functionality. Additional bands at 1150, 1398, 873, and 713 cm⁻¹, assigned to C-O, C-O-C, M-O, and aromatic C-H bending,

also appeared across all acid-treated samples, as confirmed in Figure 1, aligning with previous studies [16];[17];[18].

Base-activated samples exhibited similar functional groups but with reduced O-H, C-H, and C-O intensities and the absence of amide C=O bands, attributed to potassium hydroxide treatment [19]. These variations suggest that acid activation introduces more oxygen-containing functional groups, which can enhance hydrophilicity and favor the adsorption of polar contaminants. In contrast, base activation alters the surface chemistry, potentially improving selectivity for non- polar pollutants. Furthermore, the disappearance of amide C=O in base-activated samples suggests the breakdown or removal of nitrogen-containing functional groups due to the strong alkaline conditions. Despite these differences, Figure 2 highlights the overall surface chemical similarities among base-treated samples. These observations confirm that the activation method significantly influences surface chemistry, which in turn affects adsorption efficiency and selectivity.

Activated carbon (PAC) has slightly lower values than granular forms. [21] suggested that a bulk density of approximately 0.5 g/cm³ is suitable for adsorption, and the crustacean shell-based carbons in this study ranged from 0.454 to 0.687 g/cm³, consistent with [22]. Higher bulk density enables greater adsorbate retention per unit weight, which is beneficial for PAH adsorption. The activated carbon samples exhibited surface areas between 960 and 1288 m²/g, making them suitable for adsorption applications [23]. Generally, base-activated samples showed slightly higher surface areas than acid-activated ones, with CSBAC and CSAAC recording 1288 and 1277 m²/g, respectively. Larger surface areas enhance adsorption by increasing active sites for adsorbate interaction, and both carbonization and chemical activation improve adsorption capacity by modifying surface properties [24]. Surface area variations in activated carbon depend on factors such as precursor material, activation method, and production conditions [23].

Effect of Adsorbent Dosage on Adsorption Efficiency: Figures 3 and 5 illustrate the effect of adsorbent mass on PAH removal for acid- and base-activated carbons, respectively. As the adsorbent mass increased from 0.2 g to 1 g, the percentage removal also increased for all samples, with CSAAC and CWSAAC achieving up to 98.93% removal, and CSBAC and CWSBAC reaching 98.94%. The initial steep slope (0.2–0.4 g) suggests that adding adsorbent significantly improves removal efficiency due to increased adsorption sites [25]. Beyond 0.4 g, the slope flattens, indicating site saturation and reduced removal efficiency gains [26]. WSAAC and WSBAC consistently exhibited lower adsorption efficiencies, requiring higher masses to achieve similar removal levels as the other adsorbents. Adsorption capacity, as shown in Figures 4.25 and 4.27, followed an inverse trend, decreasing with increasing adsorbent mass due to the dilution effect [27]. CSAAC, CWSAAC, and PSAAC exhibited the highest adsorption capacities at 0.2 g (~10 mg/g), while WSAAC had the lowest (~9.85 mg/g). Similarly, CSBAC, CWSBAC, and PSBAC showed comparable adsorption trends, while WSBAC had the least efficiency. At 1 g, adsorption capacities dropped to ~2.5 mg/g for acid-activated samples and ~3 mg/g for base- activated samples, confirming that increased mass leads to lower adsorption efficiency per gram of adsorbent [28]. The findings highlight the balance between higher removal efficiency and reduced adsorption capacity, emphasizing the need to optimize adsorbent dosage for efficient and cost-effective PAH removal. These results are consistent with previous studies on adsorption performance [29];[30].

Effect of Contact time on adsorption capacity: The adsorption experiment in Figure 7 showed that at 10 minutes, PSAAC, CSAAC, and CWSAAC exhibited higher adsorption capacities than WSAAC, with values of 2.269 mg/g, 2.296 mg/g, and 2.358 mg/g, respectively, while WSAAC had 1.994 mg/g. This suggests that WSAAC adsorbed less PAH per gram of adsorbent, while CSAAC performed the best initially. Adsorption capacities increased over time, with CSAAC, CWSAAC, and PSAAC reaching equilibrium at 60–90 minutes, while WSAAC continued.

Increasing steadily, reaching 2.37 mg/g after 100 minutes. The highest adsorption capacity was observed for CWSAAC (2.473 mg/g), followed by PSAAC (2.469 mg/g) and CSAAC (2.3 mg/g). The ANOVA results in Table 4 confirmed significant differences among the four acid-activated carbons (F(3,31) = 11.667, p < 0.0001). Tukey’s test results in Table 5 grouped CSAAC, PSAAC, and CWSAAC, indicating no significant differences in their adsorption capacities, while WSAAC was in a separate group due to significantly lower performance. This suggests that WSAAC’s activation process or intrinsic properties are less effective.

Similarly, the adsorption experiment in Figure 8 showed that at 10 minutes, CSBAC, CWSBAC, and PSBAC exhibited higher adsorption capacities than WSBAC, with values of 2.315 mg/g, 2.295 mg/g, and 2.256 mg/g, respectively, while WSBAC had 1.96 mg/g. Adsorption capacities increased with time, with CSBAC, CWSBAC, and PSBAC reaching equilibrium around 60–90 minutes, whereas WSBAC continued increasing to 2.362 mg/g at 100 minutes. The highest adsorption capacity was observed for CSBAC (2.49 mg/g), followed by CWSBAC (2.473 mg/g) and PSBAC (2.263 mg/g). The ANOVA results in Table 6 confirmed significant differences among the four base-activated carbons (F(3,31) = 9.408, p < 0.0001). Tukey’s test results in Table 7 placed CSBAC, CWSBAC, and PSBAC in the same group, while WSBAC was separate due to lower adsorption performance. These findings highlight the importance of activation methods in determining adsorption efficiency, with CSBAC, CWSBAC, and PSBAC performing better than WSBAC.

Comparative Analysis: Figure 9 illustrates that CSAAC and CSBAC exhibited increasing adsorption capacities with increasing equilibrium concentrations, with CSBAC performing better at lower concentrations and CSAAC excelling at higher concentrations. Similarly, Figure 10 illustrates that PSAAC consistently outperformed PSBAC across all equilibrium concentrations, with both.

Adsorbents reaching approximately 10 mg/g at 8 mg/L, demonstrating strong PAH removal efficiency. Figure 11 shows that WSAAC and WSBAC followed similar adsorption trends, although WSBAC exhibits a slightly higher adsorption capacity at higher equilibrium concentrations (6 mg/g at 9 mg/L vs. 5 mg/g for WSAAC). In Figure 12, CWSAAC marginally outperformed CWSBAC at higher equilibrium concentrations, achieving 9 mg/g at 7 mg/L, while CWSBAC reaches 8.6 mg/g. T-test results in Tables 8 to 11 indicate no significant difference in adsorption capacities between acid- and base-activated carbons, confirming their comparable effectiveness. A comparative analysis of the effect of time was carried out. Figure 13 displays adsorption over time for CSAAC and CSBAC, showing rapid uptake in the first 50–60 minutes, after which CSAAC declines while CSBAC stabilizes. This trend is noted in the comparative analysis in Figures 14 and 15, which depict adsorption trends over time for WSAAC and WSBAC; CWSAAC and CWSBAC, respectively, with adsorption peaking at 60–100 minutes before stabilizing or declining. T-test results in Tables 12 to 14 indicate no statistically significant differences in adsorption performance between acid- and base-activated carbons, suggesting similar efficiency. Across all cases, the rapid initial adsorption is attributed to active site availability, followed by equilibrium or decline due to site saturation, confirming that both activation methods yield effective adsorbents for PAH removal with minimal differences in performance [31];[32].

Adsorption Isotherm Models: The result from the isotherm models for Henry, Langmuir, Freundlich, Elovich and Janovich constants for PAH adsorption in Table 15 indicated that the equilibrium data fitted the Freundlich isotherm better for PSAAC, CSAAC, CWSAAC, PSBAC, CSBAC and CWSBAC with the highest coefficient of determination while Henry Isotherm was a better fit for WSAAC and WSBAC. The resultant Freundlich exponent values n for PSAAC, CSAAC, CWSAAC, PSBAC, CSBAC and CWSBAC were noted as 1.528,1.503, 1.632, 1.329,

1.633 and 1.621, respectively. This signifies a high adsorption rate as the ideal values for the exponent n lying between 0 and 10 suggest favorable adsorption [33];[34];[35]. This implies that the activated samples are heterogeneous with sites of varying affinities and have a varied surface with multiple adsorption sites, each with different adsorption energies, which is better captured by the Freundlich model than by other models [36]. The Freundlich constant KL indicates the adsorption capacity, and it is noted that CSBAC presented the maximum adsorption capacity for the isotherm at a value of 2.770mg/g. The Henry isotherm model best described the adsorption behaviour of WSAAC and WSBAC with R² values of 0.816 and 0.835 and a Henry constant (KHE) of 0.800 and 0.871, respectively. This suggests that the adsorption process for WSAAC and WSBAC follows a linear isotherm, indicative of low-concentration adsorption states or infinite dilution, where the adsorbate molecules do not interact with each other, and the surface sites are uniformly available [37];[38];[39]. The results also indicated that the Coefficient of determination (R²) for Freundlich isotherm for PSAAC, CSAAC, CWSAAC, PSBAC, CSBAC and CWSBAC was   0.970,   0.952,0.971,0.966,0.940   and   0.956;   Langmuir   Isotherm   was

0.941,0.923,0.937,0.9510.898 and 0.917 while Janovich was 0.939,0922, 0.934,0.951,0.897 and

0.915 respectively. The results indicate that the adsorption patterns for PAHs followed the Langmuir and Freundlich isotherms (as Janovich isotherm is established on the assumptions

contained in the Langmuir model). According to [40] and [41], any adsorption system which obeys both the Freundlich and Langmuir isotherms shows that the solute forms a homogenous monolayer on the adsorbate. This implies that the adsorption of PAHs onto PSAAC, CSAAC, CWSAAC, PSBAC, CSBAC and CWSBAC obeyed both Freundlich and Langmuir isotherms, signifying that the PAHs formed a monolayer on the surfaces of the adsorbents. The maximum adsorption capacity for monolayer Qm from Table 4.33 was compared between Langmuir and Janovich isotherms and it was noted that Langmuir Isotherm presented the highest adsorption capacities for PSAAC, CSAAC, CWSAAC, PSBAC, CSBAC and CWSBAC with values of 21.247, 23.995,

18.719, 31.688, 18.335 and 18.743 mg/g respectively while Janovich Isotherm presented a higher maximum capacity for WSAAC and WSBAC at 10.970 and 10.362 mg/g respectively.

Qm = Maximum monolayer adsorption capacity (mg/g), KHE = Henry’s adsorption constant, b = Langmuir constant (L/mg), R² = Coefficient of determinants, KF = Affinity factor (mg/g)*(L/mg)^1/n, n = Freundlich exponent, α =initial rate constant (mg/g * min), β=desorption constant (mg/g)

Adsorption Summary: The levels of Polycyclic Aromatic Hydrocarbons (PAHs) in contaminated groundwater before and after treatment with different activated carbon samples are shown in Table

16. The results demonstrated the robust adsorptive performance of the produced carbons by yielding a significant drop in PAH concentrations after adsorption, with many components reduced to non-detectable levels (N.D.). The samples of activated carbon successfully eliminated a variety of PAH components, indicating their potential for thorough groundwater purification. The adsorption process’s effectiveness was further supported by the fact that measurable PAH residual concentrations were much lower than starting levels. These results highlighted how well-suited the produced activated carbon composites are for the removal of PAHs from contaminated water sources.

3.       Conclusion

This study demonstrated the potential of marine shell wastes—periwinkle, clam, whelk, and clam-whelk composites—as effective raw materials for producing activated carbon for PAH removal from contaminated water. High removal efficiencies were produced by both base and acid activation techniques. Also, CSBAC proved to be the most successful in the removal of PAHs with an efficiency of 98.94%. The characterization results showed notable differences in functional groups and surface area, affecting adsorption effectiveness. Most samples’ adsorption data suited the Freundlich and Langmuir isotherms well, but the Henry model provided a more accurate description of the carbons obtained from whelk. Significantly, statistical analysis showed no discernible difference between base and acid activation techniques, indicating that either approach is feasible based on application objectives and resource availability. These findings highlighted the value of sustainable waste valorization for environmental remediation and offer a promising approach for low-cost, efficient treatment of PAH-contaminated water systems.

Disclaimer (Artificial Intelligence)

Author(s) hereby declare that NO generative AI technologies such as Large Language Models (Chatgpt, COPILOT, etc) and text-to-image generators were used during the writing or editing of this manuscript.

Competing Interests

The authors have declared that no competing interests exist.

References

1. Crini G, Lichtfouse E, Wilson L. D & Crini N.M (2018) Adsorption-Oriented Processes Using Conventional & Non-conventional Adsorbents for Wastewater Treatment. https://doi.org/10.1007/978-3-319-92111-2_2
2. Azizian S & Eris S. (2020). Adsorption isotherms and kinetics. Interface Science & Technology, 33, 445-509. https://doi.org/10.1016/B978-0-12-818805-7.00011-4
3. Khulbe K. C & Matsuura T (2018) Removal of heavy metals & pollutants by membrane adsorption techniques. https://doi.org/10.1007/s13201-018-0661-6
4. Akomah U, Nwaogazie I. L & Akaranta O (2021) A Review on Current Trends in Heavy Metal Removal from Water between 2000-2021. International Journal of Environment            and            Climate            Change                                11(12):      67-90.

https://doi.org/10.9734/ijecc/2021/v11i1230557

• Othmani, A., John, J., Rajendran, H., Mansouri, A., Sillanpää, M. & Velayudhaperumal C.P. (2021). Biochar & activated carbon derivatives of lignocellulosic fibers towards adsorptive removal of pollutants from aqueous systems: Critical study & future insight. Separation & Purification Technology, 274, 119062. https://doi.org/10.1016/j.seppur.2021.119062
• Ani, J.U., Akpomie, K.G., Okoro, U.C., Aneke L.E, Onukwuli O.D & Ujam O.T (2020). Potentials of activated carbon produced from biomass materials for

sequestration of dyes, heavy metals, and crude oil components from aqueous environment. Appl Water Sci 10, 69 . https://doi.org/10.1007/s13201-020-1149-8

• González-García, P. (2018). Activated carbon from lignocellulosics precursors: A review of the synthesis methods, characterization techniques & applications. Renewable & Sustainable Energy Reviews, 82, 1393-1414. https://doi.org/10.1016/j.rser.2017.04.117
• Salleh, M. A. M., Mahmoud, D. K., Karim, W. A. W. A., & Idris, A. (2011). Cationic & anionic dye adsorption by agricultural solid wastes: A comprehensive review. Desalination, 280(1-3), 1-13. https://doi.org/10.1016/j.desal.2011.07.019
• Foong, S. Y., Liew, R. K., Yek, P. N., Chan, Y. H. & Lam, S. S. (2024). A Review in Production of Nitrogen-Enriched Carbon Materials via Chitin Pyrolysis & Activation for Enhanced Wastewater Remediation. Current Opinion in Green and Sustainable Chemistry, 100920. https://doi.org/10.1016/j.cogsc.2024.100920
• Kumari, R., Kumar, M., Vivekanand, V., & Pareek, N. (2023). Chitin biorefinery: A narrative & prophecy of crustacean shell waste sustainable transformation into bioactives & renewable energy. Renewable & Sustainable Energy Reviews, 184, 113595. https://doi.org/10.1016/j.rser.2023.113595
• Magnacca, G., Guerretta, F., Vizintin, A., Benzi, P., Valsania, M. C. & Nisticò, R. (2017). Preparation, characterization and environmental/electrochemical energy storage testing of low-cost biochar from natural chitin obtained via pyrolysis at mild conditions.           Applied           Surface           Science,                             427,   883-893.

https://doi.org/10.1016/j.apsusc.2017.07.277

1. Fapetu, O. P. (2000). Production of charcoal from tropical biomass for industrial and metallurgical process. Nigerian Journal of Engineering Management, 1(2), 34- 37.
2. Abate G. Y , Adugna N.A, Adere T. H & Desiew M.G (2020) Adsorptive removal of malachite green dye from aqueous solution onto activated carbon of Catha edulis stem as a low cost bio-adsorbent. https://doi.org/10.1186/s40068-020-00191-4
3. Efeovbokhan V.E , Alagbe E.E, Odika B, Babalola R,Oladimeji T.E, Abatan O.G. & Yusuf E.O. (2019) Preparation & characterization of activated carbon from plantain peel & coconut shell using biological activators. doi:10.1088/1742- 6596/1378/3/032035
4. Assad A. A, Gaber S. E & Jahin H. S (2019) Removal of Polycyclic Aromatic Hydrocarbons from Water Utilizing Activated Carbons. World Journal of Chemistry 14 (1): 22-32. DOI: 10.5829/idosi.wjc.2019.22.32
5. Akpan, E. I., Gbenebor, O. P., & Adeosun, S. O. (2018). Synthesis and characterisation of chitin from periwinkle (Tympanotonus fusatus (L.)) and snail (Lissachatina fulica (Bowdich)) shells. International journal of biological macromolecules, 106, 1080-1088.
6. Kunusa, W. R., Iyabu, H., & Abdullah, R. (2021). FTIR, SEM, & XRD analysis of activated carbon from sago wastes using acid modification. In Journal of Physics: Conference Series 1968 (1) 012014.

1. Okoya, A. A., & Diisu, D. (2021). Research Article Adsorption of Indigo-dye from Textile Wastewater onto Activated Carbon Prepared from Sawdust & Periwinkle Shell. http://dx.doi.org/10.3923/tasr.2021.1.9
2. Eke-emezie, N., Etuk, B.R., Akpan, O.P & Okechukwu C.C (2022) Cyanide removal from cassava wastewater onto H3PO4 activated periwinkle shell carbon. Appl Water Sci 12, 157. https://doi.org/10.1007/s13201-022-01679-3
3. Oyedoh E.A & Ekesiobi U. U. (2023). Effects of Preparation Conditions on Surface Properties & Yields of Periwinkle Shell Activated Carbon. J. Appl. Sci. Environ. Manage. 27 (6) 1083-1091. https://dx.doi.org/10.4314/jasem.v27i6.6
4. Okieimen F.E., Okiemen, C.O. & Wuana, R.A. (2007): Preparation & Characterization of Activated Carbon from Rice Husks, J. of Chem. Soc., Vol. 32: 126-

136.https://www.researchgate.net/publication/288024125_Preparation_&_charact erization_of_activated_carbon_from_rice_husks/citations

• Madojemu, G., Eze, C. B., & Okieimen, F. (2020). OPTIMIZATION OF SURFACE AREA OF ACTIVATED CARBONS PREPARED FROM COCONUT SHELLS BY RESPONSE SURFACE METHODOLOGY. Journal of

Chemical                          Society                           of                          Nigeria, 45(2). https://journals.chemsociety.org.ng/index.php/jcsn/article/view/460

• Ngu, L. H. (2023). Carbon Capture Technologies. Encyclopedia of Sustainable Technologies (Second Edition), 358-377. https://doi.org/10.1016/B978-0-323- 90386-8.00028-0
• Mopoung S. & Nogklai, W.(2008)Chemical and surface properties of longan seed activated charcoal. https://doi.org/10.5897/IJPS.9000116
• Hedayati, M. S. & Li, L. Y. (2020). Removal of polycyclic aromatic hydrocarbons from aqueous media using modified clinoptilolite. Journal of Environmental Management, 273, 111113. https://doi.org/10.1016/j.jenvman.2020.111113
• Huang, Y., Fulton, A. N. & Keller, A. A. (2016). Simultaneous removal of PAHs and metal contaminants from water using magnetic nanoparticle adsorbents. Science    of    The    Total    Environment,    571,    1029-1036.

https://doi.org/10.1016/j.scitotenv.2016.07.093

• Alomar, T.S., Habila, M.A., AlMasoud, N., Alothman, Z.A., Sheikh, M. & Soylak,

M. (2021) Biomass‐Derived Adsorbent for Dispersive Solid‐Phase Extraction of Cr (III), Fe (III), Co (II) and Ni (II) from Food Samples Prior to ICP‐MS.Detection. Appl. Sci. 2021, 11, 7792. https://doi.org/10.3390/app11177792

• Patrulea. V, Anamaria N, Manuela M. M, Laura D. P, Otilia B. S, & Vasile O (2013) Optimization of the Removal of Copper (II) Ions from Aqueous Solution on Chitosan & Cross-Linked Chitosan Beads. DOI: 10.15376/biores.8.1.1147- 1165
• Wang Z., Zheng X., Wang, Y., Lin, H., & Zhang, H. (2022). Evaluation of phenanthrene removal from soil washing effluent by activated carbon adsorption using response surface methodology. Chinese Journal of Chemical Engineering, 42, 399-405. https://doi.org/10.1016/j.cjche.2021.02.027

• Pathak, S., Sakhiya, A. K., An&, A., Pant, K., & Kaushal, P. (2022). A state-of- the-art review of various adsorption media employed for the removal of toxic Polycyclic aromatic hydrocarbons (PAHs): An approach towards a cleaner environment. Journal of Water Process Engineering, 47, 102674. https://doi.org/10.1016/j.jwpe.2022.102674
• Issabayeva, G., Wong, S.H., Pang, C.Y, Wong M.C & Aroua M.K (2022). Fluoride removal by low-cost palm shell activated carbon modified with prawn shell chitosan adsorbents. Int. J. Environ. Sci. Technol. 19, 3731–3740. https://doi.org/10.1007/s13762-021-03448-2
• Adeleke, A. O., Omar, R., Katibi, K. K., Dele-Afolabi, T. T., Ahmad, A., Quazim,

J. O., Amusa, A. A., & Alshammari, M. B. (2024). Process optimization of superior biosorption capacity of biogenic oyster shells nanoparticles for Congo red & Bromothymol blue dyes removal from aqueous solution: Response surface methodology, equilibrium isotherm, kinetic, and reusability studies. Alexandria Engineering Journal, 92, 11-23. https://doi.org/10.1016/j.aej.2024.02.042

• Tran, H. N., You, S., Hosseini-Bandegharaei, A. & Chao, H. (2017). Mistakes and inconsistencies regarding adsorption of contaminants from aqueous solutions: A critical                        review.             Water             Research,                        120,                  88-116.

https://doi.org/10.1016/j.watres.2017.04.014

• Rolph C.A, Jefferson B, Hassard F & Villa R (2018) Metaldehyde removal from drinking water by adsorption onto filtration media: mechanisms and optimization. http://dx.doi.org/10.1039/C8EW00056E
• Kumar, U. & Bandyopadhyay, M. (2005). Sorption of cadmium from aqueous solution using pretreated rice husk. Bioresource Technology, 97(1), 104-109. https://doi.org/10.1016/j.biortech.2005.02.027
• Kumar, J. A., Amarnath, D. J., Sathish, S., Jabasingh, S. A., Saravanan, A., Hemavathy, R., Anand, K. V., & Yaashikaa, P. (2019). Enhanced PAHs removal using pyrolysis-assisted potassium hydroxide induced palm shell activated carbon: Batch & column investigation. Journal of Molecular Liquids, 279, 77-87. https://doi.org/10.1016/j.molliq.2019.01.121
• Ayawei N, Augustus N. E, & Donbebe W (2017). Modelling and Interpretation of Adsorption Isotherms. https://doi.org/10.1155/2017/3039817
• Deocaris C.C & Osio L.P (2020) Fitting Henry’s Adsorption Isotherm model in R using                                               PUPAIM                                            package. https://www.researchgate.net/publication/342039215_Fitting_Henry%27s_Adsor ption_Isotherm_model_in_R_using_PUPAIM_package?enrichId=rgreq- b9c5374807dae2b2dd2b75647a7fd128- XXX&enrichSource=Y292ZXJQYWdlOzM0MjAzOTIxNTtBUzo5MDA0MjM wMTk5Mzc3OTJAMTU5MTY4ODk4NTEyMg%3D%3D&el=1_x_2
• Ehiomogue, P., Ahuchaogu, I. I., & Ahaneku, I. E. (2021). REVIEW OF ADSORPTION ISOTHERMS MODELS. Acta Technica Corviniensis-Bulletin of Engineering, 14(4). https://acta.fih.upt.ro/pdf/archive/ACTA-2021-4.pdf

• Das, D. D., Mahapatra, R., Pradhan, J., Das, S. N., & Thakur, R. S. (2000). Removal of Cr(VI) from Aqueous Solution Using Activated Cow Dung Carbon. Journal of Colloid             &             Interface             Science,             232(2),             235-240.

https://doi.org/10.1006/jcis.2000.7141

• Sathish, T., Vinithkumar, N.V., Dharani, G.& Kirubagaran R (2015) Efficacy of mangrove leaf powder for bioremediation of chromium (VI) from aqueous solutions: kinetic and thermodynamic evaluation. Appl Water Sci 5, 153–160. https://doi.org/10.1007/s13201-014-0174-x