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Palm kernel shell activated carbon: circular zinc chloride activation and batch adsorption of methylene blue

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Published/Copyright: April 7, 2026
Pure and Applied Chemistry
From the journal Pure and Applied Chemistry

Abstract

This study was aimed to investigate the effectiveness of recycled activator solutions to produce activated carbons. The activated carbons were evaluated for physicochemical characteristics and methylene blue adsorption. Activated carbon with fresh ZnCl2 solution and palm kernel shell char were prepared for comparison. The fresh activated carbon (AC1) exhibits higher surface area (891 m2/g), followed by the ones produced using the recycled activator solutions from the first (AC2, 681 m2/g) and second (AC3, 602 m2/g) activations. The former exhibits a higher methylene blue capacity of 379 mg/g. Although AC3 exhibits a lower adsorption capacity (204 mg/g), it shows a slightly higher Langmuir b constant, indicating stronger adsorbate–adsorbent interactions at individual sites. The performance of recycled-activator carbons positions them among advanced composite adsorbents recently reported for efficient cationic pollutant removal with excellent recyclability, demonstrating that activator recycling does not compromise functional performance. The equilibrium and kinetics data obeyed the Redlich–Peterson and pseudo-second-order models, respectively, while the thermodynamic parameters suggest that the process is endothermic, feasible and spontaneous. Water is more effective to regenerate the spent activated carbon with desorption efficiency of 98.3 %. To conclude, the use of recycled activator solutions is viable to produce activated carbons with considerable performance for dye wastewater treatment.

Keywords: Activated carbon; adsorption; methylene blue; palm kernel shell; recycled activator solution; zinc chloride
Corresponding author: Muhammad Abbas Ahmad Zaini, Faculty of Chemical & Energy Engineering, Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia; and Centre of Lipids Engineering and Applied Research (CLEAR), Ibnu-Sina Institute for Scientific and Industrial Research (ISI-SIR), Universiti Teknologi Malaysia, 81310 UTM Johor Bahru, Johor, Malaysia, e-mail:
Novelty statement: This study presents a novel and sustainable approach to valorize recycled ZnCl2 solutions in the production of activated carbons. The recycled solution was collected from the washing step of activated carbon to assess its effectiveness for subsequent activation. Remarkably, the activated carbons produced by recycled solutions exhibit high surface area and excellent dye adsorption capacity. The resultant materials also demonstrate enhanced affinity toward dyes due to their rich microporosity, underscoring their potential for wastewater treatment applications.

Funding source: Land & survey Department of Sarawak

Award Identifier / Grant number: Kursi Premier Sarawak Grant No. 1R037

Acknowledgments

We gratefully acknowledged Land & Survey Department (JTS) Sarawak for the award of Kursi Premier Sarawak Grant No. 1R037.

  1. Research ethics: Not applicable.

  2. Informed consent: Not applicable.

  3. Author contributions: Batrisyia Aliah Muhamad Amin: Conceptualization, methodology, experimental work, analysis, first draft. Fadina Amran: Methodology, analysis, first draft. Ahmad Syahmi Zaini: Conceptualization, analysis, review, first draft. Nicky Rahmana Putra: Analysis, validation. Azrul Nurfaiz Mohd Faizal: Analysis, validation, review. Ahmad Hazim Abdul Aziz: Conceptualization, analysis. Muhammad Abbas Ahmad Zaini: Funding, resources, supervision, conceptualization, analysis, validation, review.

  4. Use of Large Language Models, AI and Machine Learning Tools: Large Language Models, AI and Machine Learning Tools were not used during the preparation of the manuscript.

  5. Conflict of interest: The authors state no conflict of interest.

  6. Research funding: This work was partly funded by Sarawak Premier Research Grant No. 1R037. We gratefully acknowledged Sarawak State Government and Land and Survey Department of Sarawak for the financial support.

  7. Data availability: Not applicable.

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Received: 2025-09-23
Accepted: 2026-02-21
Published Online: 2026-04-07

© 2026 IUPAC & De Gruyter

https://doi.org/10.1515/pac-2025-0621
Keywords for this article
Activated carbon; adsorption; methylene blue; palm kernel shell; recycled activator solution; zinc chloride
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