A review on the recent advances in the use of hydrochar for adsorption of methylene blue dye from aqueous systems

Onyango, Collins; Nyairo, Wilfrida; Shikuku, Victor

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dc.contributor.author	Onyango, Collins
dc.contributor.author	Nyairo, Wilfrida
dc.contributor.author	Shikuku, Victor
dc.date.accessioned	2026-02-23T08:45:51Z
dc.date.available	2026-02-23T08:45:51Z
dc.date.issued	2026
dc.identifier.citation	1. Elsayed I, Madduri S, El-Giar EM, El Barbary H. Effective removal of anionic dyes from aqueous solutions by novel polyethylenimine-ozone oxidized hydrochar (PEI-OzHC) adsorbent. Arab J Chem. 2022;15(5):103757. https://doi.org/10.1016/j.arabj c.2022.103757. 2. Lellis B, Fávaro-Polonio CZ, Pamphile JA, Polonio JC. Effects of textile dyes on health and the environment and bioremediation potential of living organisms. Biotechnol Res Innov. 2019;3(2):275–90. https://doi.org/10.1016/j.biori.2019.09.001. 3. Al-Tohamy R, Ali SS, Li F, Okasha KM, Mahmoud YAG, Elsamahy T, et al. A critical review on the treatment of dye-containing wastewater: ecotoxicological and health concerns of textile dyes and possible remediation approaches for environmental safety. Ecotoxicol Environ Saf. 2022;231:113160. https://doi.org/10.1016/j.ecoenv.2021.113160. 4. Bhatia D, Sharma NR, Singh J, Kanwar RS. Biological methods for textile dye removal from wastewater: a review. Crit Rev Environ Sci Technol. 2017;47(19):1836–76. https://doi.org/10.1080/10643389.2017.1393263. 5. ChemicalResearch. Methylene Blue Market, Global Outlook & Forecast 2025–2032. 2025. https://www.24chemicalresearch. com/reports/283427/methylene-blue-market 5th September 2025. 6. Sahu S, Pahi S, Sahu JK, Sahu UK, Patel RK. Kendu (Diospyros melanoxylon Roxb) fruit Peel activated carbon—an efficient bioadsorbent for methylene blue dye: equilibrium, kinetic, and thermodynamic study. Environ Sci Pollut Res. 2020;27(18):22579–92. https://doi.org/10.1007/s11356-020-08561-2. 7. Sabar S, Abdul Aziz H, Yusof NH, Subramaniam S, Foo KY, Wilson LD, et al. Preparation of sulfonated Chitosan for enhanced adsorption of methylene blue from aqueous solution. Reactive Funct Polym. 2020;151:104584. https://doi.org/10.1016/j.re actfunctpolym.2020.104584. 8. Wei X, Wang Y, Feng Y, Xie X, Li X, Yang S. Different adsorption-degradation behavior of methylene blue and congo red in nanoceria/H2O2 system under alkaline conditions. Sci Rep. 2019;9(1):4964. https://doi.org/10.1038/s41598-018-36794-2. 9. Mahmoud MS, Farah JY, Farrag TE. Enhanced removal of methylene blue by electrocoagulation using iron electrodes. Egyptian J Petroleum. 2013;22(1):211–6. https://doi.org/10.1016/j.ejpe.2012.09.013. 10. Uddin MK, Nasar A. Decolorization of basic dyes solution by utilizing fruit seed powder. KSCE J Civ Eng. 2020;24(2):345–55. https://doi.org/10.1007/s12205-020-0523-2. 11. Nedu M-E, Tertis M, Cristea C, Georgescu AV. Comparative Study Regarding the Properties of Methylene Blue and Proflavine and Their Optimal Concentrations for In Vitro and In Vivo Applications. Diagnostics. 2020;10(4):223. https://www.mdpi .com/2075-4418/10/4/223#. 12. Mijinyawa AH, Geeta D, Mishra A. A sustainable process for adsorptive removal of methylene blue onto a food grade mucilage: kinetics, thermodynamics, and equilibrium evaluation. Int J Phytoremediation. 2019;21(11):1122–9. https://doi.o rg/10.1080/15226514.2019.1606785. 13. Parakala S, Moulik S, Sridhar S. Effective separation of methylene blue dye from aqueous solutions by integration of micellar enhanced ultrafiltration with vacuum membrane distillation. Chem Eng J. 2019;375:122015. https://doi.org/10.1016/j.c ej.2019.122015. 14. Sun L, Hu D, Zhang Z, Deng X. Oxidative Degradation of Methylene Blue via PDS-Based Advanced Oxidation Process Using Natural Pyrite. Int J Environ Res Public Health. 2019;16(23):4773. https://www.mdpi.com/1660-4601/16/23/4773#.Onyango et al. Discover Chemistry (2026) 3:20 Page 24 of 27 15. Contreras M, Grande-Tovar CD, Vallejo W, Chaves-López C. Bio-Removal of methylene blue from aqueous solution by galactomyces geotrichum KL20A. Water. 2019;11(2):282. https://doi.org/10.3390/w11020282. 16. Arias Arias F, Guevara M, Tene T, Angamarca P, Molina R, Valarezo A, et al. The adsorption of methylene blue on Eco-Friendly reduced graphene oxide. Nanomaterials. 2020;10(4):681. https://doi.org/10.3390/nano10040681. 17. Tran H, Huang F, Lee C, Chao H. Activated carbon derived from spherical hydrochar functionalized with triethylenetetramine: synthesis, characterizations, and adsorption application. Green Process Synthesis. 2017;6:565–76. https://doi.org/10. 1515/gps-2016-0178. 18. Sadh PK, Chawla P, Kumar S, Das A, Kumar R, Bains A et al. Recovery of agricultural waste biomass: A path for circular bioeconomy. Sci Total Environ. 2023:870161904. https://doi.org/10.1016/j.scitotenv.2023.161904 19. Falco C, Sieben JM, Brun N, Sevilla M, Van der Mauelen T, Morallón E, et al. Hydrothermal carbons from hemicellulosederived aqueous hydrolysis products as electrode materials for supercapacitors. Chemistry-Sustainability-Energy-Materials. 2013;6(2):374–82. https://doi.org/10.1002/cssc.201200817. 20. Masoumi S, Borugadda VB, Nanda S, Dalai AK. Hydrochar: a review on its production technologies and applications. Catalysts. 2021;11(8):939. https://doi.org/10.3390/catal11080939. 21. Chen N, Cao S, Zhang L, Peng X, Wang X, Ai Z, et al. Structural dependent Cr(VI) adsorption and reduction of biochar: hydrochar versus pyrochar. Sci Total Environ. 2021;783:147084. https://doi.org/10.1016/j.scitotenv.2021.147084. 22. Li J, Pan L, Suvarna M, Tong YW, Wang X. Fuel properties of hydrochar and pyrochar: prediction and exploration with machine learning. Appl Energy. 2020;269:115166. https://doi.org/10.1016/j.apenergy.2020.115166. 23. Kozyatnyk I, Yakupova I. Impact of chemical and physical treatments on the structural and surface properties of activated carbon and hydrochar. ACS Sustain Chem Eng. 2025;13(6):2500–7. https://doi.org/10.1021/acssuschemeng.4c09189. 24. Medina-Martos E, Istrate I-R, Villamil JA, Gálvez-Martos J-L, Dufour J, Mohedano ÁF. Techno-economic and life cycle assessment of an integrated hydrothermal carbonization system for sewage sludge. Clean Prod. 2020;277:122930. https://doi.or g/10.1016/j.jclepro.2020.122930. 25. Yahya MA, Al-Qodah Z, Ngah CWZ. Agricultural bio-waste materials as potential sustainable precursors used for activated carbon production: A review. Renew Sustain Energy Rev. 2015;46:218–35. https://doi.org/10.1016/j.rser.2015.02.051. 26. Delgado-Moreno L, Bazhari S, Gasco G, Méndez A, El Azzouzi M, Romero E. New insights into the efficient removal of emerging contaminants by biochars and hydrochars derived from Olive oil wastes. Sci Total Environ. 2021;752:141838. htt ps://doi.org/10.1016/j.scitotenv.2020.141838. 27. Aktas K, Liu H, Eskicioglu C. Treatment of aqueous phase from hydrothermal liquefaction of municipal sludge by adsorption: comparison of biochar, hydrochar, and granular activated carbon. Environ Manage. 2024;356:120619. https://doi.org/ 10.1016/j.jenvman.2024.120619. 28. Jahin H, Hesham A, Awad Y, El-Korashy S, Khairy G. THMs removal from aqueous solution using hydrochar enhanced by Chitosan nanoparticles: preparation, characterization, kinetics, equilibrium studies. Int J Environ Sci Technol. 2024;21(3):2811–26. https://doi.org/10.1007/s13762-023-05150-x. 29. Nadarajah K, Rodriguez-Narvaez OM, Ramirez J, Bandala ER, Goonetilleke A. Lab-scale engineered hydrochar production and techno-economic scaling-up analysis. Waste Manag. 2024;174:568–74. https://doi.org/10.1016/j.wasman.2023.12.024. 30. Badaruddin M, Hanum L, Melwita E, Wibiyan S, Wijaya A, Ahmad N, et al. Study of selectivity anionic dye removal and sustainable regeneration of hydrochar from Spirogyra Sp. Algae Biomass Trends Sciences. 2025;22(6):9657. https://doi.org/ 10.48048/tis.2025.9657. 31. Saba B, Christy AD, Shah A, Recycling. Hydrochar for pollution remediation: effect of process parameters, adsorption modeling, life cycle assessment and techno-economic evaluation. Resour Conserv Recycl. 2024;202:107359. https://doi.or g/10.1016/j.resconrec.2023.107359. 32. Qian K, Kumar A, Zhang H, Bellmer D, Huhnke R. Recent advances in utilization of Biochar. Renew Sustain Energy Rev. 2015;42:1055–64. https://doi.org/10.1016/j.rser.2014.10.074. 33. Rasaq WA, Okpala COR, Igwegbe CA, Białowiec A. Catalyst-Enhancing hydrothermal carbonization of biomass for hydrochar and liquid fuel Production-A review. Materials. 2024:17, 2579. https://doi.org/10.3390/ma17112579 34. Jalilian M, Bissessur R, Ahmed M, Hsiao A, He QS, Hu Y. A review: hydrochar as potential adsorbents for wastewater treatment and CO 2 adsorption. Sci Total Environ. 2024;914:169823. https://doi.org/10.1016/j.scitotenv.2023.169823. 35. Huang J, Feng Y, Xie H, Wu P, Wang M, Wang B, et al. A bibliographic study reviewing the last decade of hydrochar in environmental application: history, status quo, and trending research paths. Biochar. 2023;5(1):12. https://doi.org/10.1007/ s42773-023-00210-4. 36. Yu K, Huan W-W, Teng H-J, Guo J-Z, Li B. Effect of oxygen-containing functional group contents on sorption of lead ions by acrylate-functionalized hydrochar. Environ Pollut. 2024;349:124921. https://doi.org/10.1016/j.envpol.2024.123921. 37. Li B, Lv J-Q, Guo J-Z, Fu S-Y, Guo M, Yang P. The polyaminocarboxylated modified hydrochar for efficient capturing methylene blue and Cu(II) from water. Bioresour Technol,. 2019:275360–7. https://doi.org/10.1016/j.biortech.2018.12.083 38. Ning Q, Liu Y, Liu S, Jiang L, Zeng G, Zeng Z et al. Fabrication of hydrochar functionalized Fe–Mn binary oxide nanocomposites: characterization and 17β-estradiol removal. RSC Adv. 2017:7, 37122–9. https://doi.org/10.1039/C7RA06065C 39. Amode JO, Santos JH, Md. Alam Z, Mirza AH, Mei CC. Adsorption of methylene blue from aqueous solution using untreated and treated (Metroxylon spp.) waste adsorbent: equilibrium and kinetics studies. Int J Industrial Chem. 2016;7(3):333–45. https://doi.org/10.1007/s40090-016-0085-9. 40. Albayati TM, Sabri AA, Alazawi RA. Separation of methylene blue as pollutant of water by SBA-15 in a Fixed-Bed column. Arab J Sci Eng. 2016;41(7):2409–15. https://doi.org/10.1007/s13369-015-1867-7. 41. Saeed M, Jamal MA, Haq A, Younas M, Shahzad MA. Oxidative degradation of methylene blue in aqueous medium catalyzed by lab prepared nickel hydroxide. Int J Chem Reactor Eng. 2016;14(1):45–51. https://doi.org/10.1515/ijcre-2015-0088. 42. Mondal S, De Anda Reyes ME, Pal U. Plasmon induced enhanced photocatalytic activity of gold loaded hydroxyapatite nanoparticles for methylene blue degradation under visible light. RSC Adv. 2017;7(14):8633–45. https://doi.org/10.1039/C 6RA28640B. 43. Hemdan SS. The shift in the behavior of methylene blue toward the sensitivity of medium: Solvatochromism, solvent Parameters, regression analysis and investigation of cosolvent on the acidity constants. J Fluoresc. 2023;33(6):2489–502. https://doi.org/10.1007/s10895-023-03234-y.Onyango et al. Discover Chemistry (2026) 3:20 Page 25 of 27 44. Xia Y, Yao Q, Zhang W, Zhang Y, Zhao M. Comparative adsorption of methylene blue by magnetic baker’s yeast and EDTAD-modified magnetic baker’s yeast: equilibrium and kinetic study. Arab J Chem. 2019;12(8):2448–56. https://doi.org/ 10.1016/j.arabjc.2015.03.010. 45. Teng X, Li J, Wang Z, Wei Z, Chen C, Du K, et al. Performance and mechanism of methylene blue degradation by an electrochemical process. RSC Adv. 2020;10(41):24712–20. https://doi.org/10.1039/D0RA03963B. 46. Rashad M, Shaalan NM, Abd-Elnaiem AM. Degradation enhancement of methylene blue on ZnO nanocombs synthesized by thermal evaporation technique. Desalination Water Treat. 2016;57(54):26267–73. https://doi.org/10.1080/19443994.201 6.1163511. 47. Siong VLE, Lee KM, Juan JC, Lai CW, Tai XH, Khe CS. Removal of methylene blue dye by solvothermally reduced graphene oxide: a metal-free adsorption and photodegradation method. RSC Adv. 2019;9(64):37686–95. https://doi.org/10.1039/C9 RA05793E. 48. León ER, Rodríguez EL, Beas CR, Plascencia-Villa G, Palomares RAI. Study of methylene blue degradation by gold nanoparticles synthesized within natural zeolites. J Nanomaterials. 2016;2016(1):9541683. https://doi.org/10.1155/2016/9541683. 49. Shaban M, Elwahab FA, Ghitas AE, El Zayat MY. Efficient and recyclable photocatalytic degradation of methylene blue dye in aqueous solutions using nanostructured Cd1 – xCoxS films of different doping levels. Int J Chem Reactor Eng. 2020;95(2):276–88. https://doi.org/10.1007/s10971-020-05331-x. 50. Ebi OE, Taiwo AF, Folorunsho AT. Kinetic modelling of the biosorption of methylene blue onto wild melon (Lagenaria sphaerica). Am J Chem Eng. 2018;6(6):126–34. https://doi.org/10.11648/j.ajche.20180606.12. 51. Zhou S, Du Z, Li X, Zhang Y, He Y, Zhang Y. Degradation of methylene blue by natural manganese oxides: kinetics and transformation products. Royal Soc Open Access. 2019;6(7):190351. https://doi.org/10.1098/rsos.190351. 52. Koyuncu H, Kul AR. Removal of methylene blue dye from aqueous solution by nonliving lichen (Pseudevernia furfuracea (L.) Zopf.), as a novel biosorbent. Appl Water Sci. 2020;10(2):72. https://doi.org/10.1007/s13201-020-1156-9. 53. Balarak D, Bazzi M, Shehu Z, Chandrika K. Application of surfactant-modified bentonite for methylene blue adsorption from aqueous solution. Orient J Chem. 2020;36(2):293. https://doi.org/10.13005/ojc/360212. 54. Siddeeg SM, Tahoon MA, Mnif W, Ben Rebah F. Iron Oxide/Chitosan magnetic nanocomposite immobilized manganese peroxidase for decolorization of textile wastewater. Processes. 2020;8(1):5. https://www.mdpi.com/2227-9717/8/1/5#. 55. Funke A, Ziegler F. Hydrothermal carbonization of biomass: a summary and discussion of chemical mechanisms for process engineering. Biofuels Bioproduction Biorefining. 2010;4:160 – 77. https://doi.org/10.1002/bbb.198. 56. Jaruwat D, Udomsap P, Chollacoop N, Fuji M, Eiad-ua A, editors. Effects of hydrothermal temperature and time of hydrochar from Cattail leaves. International Conference on Science and Technology of Emerging Materials; 2018: AIP. https://doi. org/10.1063/1.5053192 57. Fakkaew K, Koottatep T, Polprasert C. Effects of hydrolysis and carbonization reactions on hydrochar production. Bioresour Technol. 2015;192:328–34. https://doi.org/10.1016/j.biortech.2015.05.091. 58. Fang J, Zhan L, Ok YS, Gao B. Minireview of potential applications of hydrochar derived from hydrothermal carbonization of biomass. Ind Eng Chem. 2018;57:15–21. https://doi.org/10.1016/j.jiec.2017.08.026. 59. Tran TH, Le AH, Pham TH, Nguyen DT, Chang SW, Chung WJ, et al. Adsorption isotherms and kinetic modeling of methylene blue dye onto a carbonaceous hydrochar adsorbent derived from coffee husk waste. Sci Total Environ. 2020;725:138325. https://doi.org/10.1016/j.scitotenv.2020.138325. 60. Patrinoiu G, Musuc AM, Calderon-Moreno JM, Florea M, Neatu F, Ionita P. Honey-Derived hydrochar containing 2,2,6,6-tetramethylpiperidine-1-oxyl free radical for degradation of aqueous organic pollutants. Environ Processes. 2024;11(4):60. https://doi.org/10.1007/s40710-024-00731-5. 61. Tabassum M, Bardhan M, Novera TM, Islam MA, Hadi Jawad A, Islam MA. NaOH-Activated betel nut husk hydrochar for efficient adsorption of methylene blue dye. Water Air Soil Pollut. 2020;231(8):398. https://doi.org/10.1007/s11270-020-047 62-0. 62. Afrah Solih F, Buthiyappan A, Hasikin K, Myo Aung K, Abdul Raman AA. Optimization-driven modelling of hydrochar derived from fruit waste for adsorption performance evaluation using response surface methodology and machine learning. J Ind Eng Chem. 2025;141:328–39. https://doi.org/10.1016/j.jiec.2024.06.042. 63. El Ouadrhiri F, Elyemni M, Lahkimi A, Lhassani A, Chaouch M, Taleb M. Mesoporous carbon from optimized date stone hydrochar by catalytic hydrothermal carbonization using response surface methodology: application to dyes adsorption. 2021;2021(1):5555406. https://doi.org/10.1155/2021/5555406 64. Islam MT, Chambers C, Toufiq Reza M. Effects of process liquid recirculation on material properties of hydrochar and corresponding adsorption of cationic dye. J Anal Appl Pyrol. 2022;161:105418. https://doi.org/10.1016/j.jaap.2021.105418. 65. Zhou F, Li K, Hang H, Zhang Z, Chen P, Wei L. Efficient removal of methylene blue by activated hydrochar prepared by hydrothermal carbonization and NaOH activation of sugarcane Bagasse and phosphoric acid. RSC Adv. 2022;12:1885. https://doi.org/10.1039/D1RA08325B. 66. Zhang Y, Wan Y, Zheng Y, Yang Y, Huang J, Chen H, et al. Potassium permanganate modification of hydrochar enhances sorption of Pb(II), Cu(II), and Cd(II). Bioresour Technol. 2023;386:129482. https://doi.org/10.1016/j.biortech.2023.129482. 67. Xu Z-X, Shan Y-O, Zhang Z, Deng X-O, Yang Y, Luque R, et al. Hydrothermal carbonization of sewage sludge: effect of inorganic salts on hydrochar’s physicochemical properties. Green Chem. 2020;22:7010–22. https://doi.org/10.1039/D0GC0 2615H. 68. Wang X, Wu Y, Yue C, Song Y, Shen Z, Zhang Y. Enhanced adsorption of dye wastewater by low-temperature combined NaOH/urea pretreated hydrochar: Fabrication, performance, and mechanism. Environ Sci Pollut Res. 2024;31:32800–12. https://doi.org/10.1007/s11356-024-33230-z. 69. Yan W, Zhang H, Sheng K, Mustafa AM, Yu Y. Evaluation of engineered hydrochar from KMnO4 treated bamboo residues: physicochemical properties, hygroscopic dynamics, and morphology. Bioresour Technol. 2018:250, 806 – 11. https://doi.or g/10.1016/j.biortech.2017.11.052 70. Zheng Y, Wang J, Li D, Liu C, Lu Y, Lin X et al. Insight into the KOH/KMnO4 activation mechanism of oxygen-enriched hierarchical porous Biochar derived from biomass waste by in-situ pyrolysis for methylene blue enhanced adsorption. J Anal Appl Pyrol. 2021:158, 105269. https://doi.org/10.1016/j.jaap.2021.105269 71. Yang X, Wang B, Song X, Yang F, Cheng F. Co-hydrothermal carbonization of sewage sludge and coal slime with sulfuric acid for N, S doped hydrochar. J Clean Prod. 2022;354:131615. https://doi.org/10.1016/j.jclepro.2022.131615.Onyango et al. Discover Chemistry (2026) 3:20 Page 26 of 27 72. Lin Z, Wang R, Tan S, Zhang K, Yin Q, Zhao Z, et al. Nitrogen-doped hydrochar prepared by biomass and nitrogen-containing wastewater for dye adsorption: effect of nitrogen source in wastewater on the adsorption performance of hydrochar. J Environ Manage. 2023;334:117503. https://doi.org/10.1016/j.jenvman.2023.117503. 73. Cavali M, Hennig TB, Libardi Junior N, Kim B, Garnier V, Benbelkacem H, et al. Co-Hydrothermal carbonization of sawdust and sewage sludge: assessing the potential of the hydrochar as an adsorbent and the ecotoxicity of the process water. Appl Sci. 2025;15(3):1052. https://www.mdpi.com/2076-3417/15/3/1052#. 74. Ahmed Alshareef S, Abdullah Alqadami A, Ali Khan M, Alanazi HS, Raza Siddiqui M, Jeon B-H. Simultaneous co-hydrothermal carbonization and chemical activation of food wastes to develop hydrochar for aquatic environmental remediation. Bioresour Technol. 2022;347:126363. https://doi.org/10.1016/j.biortech.2021.126363. 75. Diaz E, Sanchis I, Coronella CJ, Mohedano AF. Activated carbons from hydrothermal carbonization and chemical activation of Olive stones: application in sulfamethoxazole adsorption. Resources. 2022;11(5):43. https://www.mdpi.com/2079-9276/ 11/5/43#. 76. Tu W, Liu Y, Xie Z, Chen M, Ma L, Du G, et al. A novel activation-hydrochar via hydrothermal carbonization and KOH activation of sewage sludge and coconut shell for biomass wastes: Preparation, characterization and adsorption properties. J Colloid Interface Sci. 2021;593:390–407. https://doi.org/10.1016/j.jcis.2021.02.133. 77. Ischia G, Fiori L. Hydrothermal carbonization of organic waste and biomass: A review on Process, Reactor, and plant modeling. Waste Biomass Valoriz. 2021;12(6):2797–824. https://doi.org/10.1007/s12649-020-01255-3. 78. Farru G, Scheufele FB, Moloeznik Paniagua D, Keller F, Jeong C, Basso D. Business and market analysis of hydrothermal carbonization process: roadmap toward implementation. Agronomy. 2024;14(3):541. https://www.mdpi.com/2073-4395/1 4/3/541#. 79. Yan S, Qu J, Bi F, Wei S, Wang S, Jiang Z, et al. One-pot synthesis of porous N-doped hydrochar for atrazine removal from aqueous phase: Co-activation and adsorption mechanisms. Bioresour Technol. 2022;364:128056. https://doi.org/10.1016/j. biortech.2022.128056. 80. Lan Y, Luo Y, Yu S, Ye H, Zhang Y, Xue M, et al. Cornstalk hydrochar produced by phosphoric acid-assisted hydrothermal carbonization for effective adsorption and photodegradation of Norfloxacin. Sep Purif Technol. 2024;330:125543. https://d oi.org/10.1016/j.seppur.2023.125543. 81. Rani A, Rongpipi M, Bhardwaj A, Hussain K, Arora M, Babu JN. Improved carboxylate density hydrochar by alkylation of surface phenol for adsorption of cationic dye in aqueous solution. Surf Interfaces. 2025;56:105511. https://doi.org/10.1016 /j.surfin.2024.105511. 82. Zhang S, Pi M, Su Y, Xu D, Xiong Y, Zhang H. Physiochemical properties and pyrolysis behavior evaluations of hydrochar from co-hydrothermal treatment of rice straw and sewage sludge. Biomass Bioenergy. 2020;140:105664. https://doi.org/1 0.1016/j.biombioe.2020.105664. 83. Mumtahina T, Mondira B, Mamun NT, Atikul IM, Ali HJ, Islam MA. NaOH-Activated betel nut husk hydrochar for efficient adsorption of methylene blue dye. Water Air Soil Pollution. 2020;231(8). https://doi.org/10.1007/s11270-020-04762-0. 84. Duarah P, Purkait MK. Fenton oxidation-activated hydrochar derived from factory tea waste with enhanced surface area as a sustainable adsorbent for multiple dyes. Colloids Surf A. 2025;715:136635. https://doi.org/10.1016/j.colsurfa.2025.13663 5. 85. Amer MW, Khdeir EM, Barzagli F, Taha MA, Alsalti HM, Ibrahim EN, et al. Removal of methylene blue by hydrochar modified from hydrothermal carbonization technique. J Environ Progress Sustainable Energy. 2024;43(6):e14469. https://doi.org/10. 1002/ep.14469. 86. Zhang X, Liu S, Qin Q, Chen G, Wang W. Alkali etching Hydrochar-Based adsorbent Preparation using Chinese medicine industry waste and its application in efficient removal of multiple pollutants. Processes. 2023;11(2):412. https://www.mdpi. com/2227-9717/11/2/412#. 87. Liu X, Zhou F, Shi C, Ramirez J, Liu Z, Hang F, et al. Efficient adsorption of methylene blue by polyaminocarboxylated modified hydrochar derived from sugarcane Bagasse. Molecules. 2025;30(7):1536. https://doi.org/10.3390/molecules30071536. 88. Zhang Y, Wan Y, Zheng Y, Yang Y, Huang J, Chen H, et al. Hydrochar loaded with Nitrogen-Containing functional groups for versatile removal of cationic and anionic dyes and aqueous heavy metals. Water. 2024;16(23):3387. https://www.mdpi.co m/2073-4441/16/23/3387#. 89. Chai N, Gao L, Li S, Ma Z, Li L, Hu M. Simple Alkali-Modified Persimmon Peel–Montmorillonite Composite Hydrochar for Rapid and Efficient Removal of Methylene Blue. Appl Sci. 2023:15:11867. 90. Moussaoui F, El Ouadrhiri F, Saleh E-AM, El Bourachdi S, Althomali RH, Kassem AF, et al. Enhancing hydrochar production and proprieties from biogenic waste: merging response surface methodology and machine learning for organic pollutant remediation. J Saudi Chem Soc. 2024;28(5):101920. https://doi.org/10.1016/j.jscs.2024.101920. 91. Soroush S, Ronsse F, Park J, Ghysels S, Wu D, Kim K-W, et al. Microwave assisted and conventional hydrothermal treatment of waste seaweed: comparison of hydrochar properties and energy efficiency. Sci Total Environ. 2023;878:163193. https://d oi.org/10.1016/j.scitotenv.2023.163193. 92. Tóth J. Theory, Modeling, and Analysis. 2001. 93. Cheng L, Ji Y, Liu X. Insights into interfacial interaction mechanism of dyes sorption on a novel hydrochar: experimental and DFT study. Chem Eng Sci. 2021;233:116432. https://doi.org/10.1016/j.ces.2020.116432. 94. Tran HN, You S-J, Chao H-P. Insight into adsorption mechanism of cationic dye onto agricultural residues-derived hydrochars: negligible role of π-π interaction. Korean J Chem Eng. 2017;34(6):1708–20. https://doi.org/10.1007/s11814-017-005 6-7. 95. Kamalanathan S, Amran F, Zaini MAA. Chemistry. Oxidized mangosteen Peel-Derived hydrochar for the removal of methylene blue. Hung J Ind. 2025;53(1):1–7. https://doi.org/10.33927/hjic-2025-01. 96. Qiu C, Jiang L, Gao Y, Sheng L. Effects of oxygen-containing functional groups on carbon materials in supercapacitors: A review. Mater Design. 2023;230:111952. https://doi.org/10.1016/j.matdes.2023.111952. 97. Hamid NA, You JJ. Mangosteen Peel-Derived Hydrochar Prepared via Hydrothermal Carbonization for Methylene Blue Removal. IOP Conference Series: Earth and Environmental Science. 2021;765(1):012114. https://doi.org/10.1088/1755-1315/7 65/1/012114 98. Hidayat ARP, Sulistiono DO, Murwani IK, Endrawati BF, Fansuri H, Zulfa LL, et al. Linear and nonlinear isotherm, kinetic and thermodynamic behavior of Methyl orange adsorption using modulated Al2O3@UiO-66 via acetic acid. J Environ Chem Eng. 2021;9(6):106675. https://doi.org/10.1016/j.jece.2021.106675.Onyango et al. Discover Chemistry (2026) 3:20 Page 27 of 27 99. Elwakeel KZ, Guibal E. Arsenic(V) sorption using chitosan/Cu(OH)2 and chitosan/CuO composite sorbents. Carbohydr Polym. 2015;134:190–204. https://doi.org/10.1016/j.carbpol.2015.07.012. 100. Elovich SY, Larinov OJIANS. Theory of adsorption from solutions of Non electrolytes on solid (I) equation adsorption from solutions and the analysis of its simplest form,(II) verification of the equation of adsorption isotherm from solutions. Otd Khim Nauk. 1962;2(2):209–16. 101. Maimaiti T, Hu R, Yuan H, Liang C, Liu F, Li Q, et al. Magnetic Fe3O4/TiO2/graphene sponge for the adsorption of methylene blue in aqueous solution. Diam Relat Mater. 2022;123:108811. https://doi.org/10.1016/j.diamond.2021.108811. 102. Yildirir E. Performance of vermicompost derived hydrochars for methylene blue removal via ultrasound assisted adsorption. Chem Pap. 2025;79(1):235–45. https://doi.org/10.1007/s11696-024-03777-9.	en_US
dc.identifier.uri	http://erepository.kafuco.ac.ke/123456789/297
dc.description.abstract	This study reviewed the use of hydrochars in the adsorption of methylene blue, a toxic dye, from aqueous phases. Journal articles published predominantly between 2020 and 2025 were assessed. The articles were mainly identified through keyword searches on ScienceDirect, Scopus and Web of Science. The studies reported a high efficacy of hydrochars against the dye. Organic wastes were primarily used as a feedstock in the hydrothermal carbonization processes, aligning to the waste to resource principle, an efficient and cost effective route of synthesis of adsorbents. The pseudo-first order, pseudo-second order and the Elovich model best described the kinetic data while the Freundlich, Sips and Langmuir isotherms best fitted the experimental data, with model predicted adsorption capacities in the range of 30-1060 mg g− 1. All the reviewed studies reported a spontaneous and feasible adsorption process (negative ΔG), while the entropy (ΔS) and enthalpy (ΔH) values varied with feedstock used, the specific modification routes and modification conditions. Several systems retained between 65 and 95% capacity over five cycles with eluents such as HCl, ethanol and methanol. The mechanism of adsorption was reported by most of the studies to be through electrostatic interactions, hydrogen bonding and π-π interactions.	en_US
dc.language.iso	en_US	en_US
dc.subject	Adsorption, Hydrochar, Methylene blue dye, Kinetics, Isotherms and thermodynamics, HTC	en_US
dc.title	A review on the recent advances in the use of hydrochar for adsorption of methylene blue dye from aqueous systems	en_US