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Open research questions in Adsorption and biosorption for pollutant removal

36 unresolved questions extracted from the limitations and future-work sections of 1,284 Adsorption and biosorption for pollutant removal papers in our library. Each links back to the study that raised it.

What the literature leaves open

  • While the MBC-40 composite demonstrates high effi- cacy for arsenic immobilization in the tested environments, several limitations of the current study should be noted: Mechanistic uncertainty: The proposed immobiliza- tion mechanisms are interpreted as plausible based on macroscopic adsorption data rather than direct speciation measurements. This study did not utilize advanced spectro- scopic tools such as X-ray absorption spectroscopy (XAS) or XPS to definitively distinguish between surface adsorp- tion, inner-sphere complexation, and the formation of spe- cific surface precipitates. Aqueous matrix simplification: Experimental evalua- tions, including the SMW tests, were conducted in the ab- sence of DOM or NOM. Because DOM can compete for reactive sites or alter arsenic mobility, these findings pri- marily reflect material performance in simplified inorganic matrices rather than complex natural or field conditions. Geochemical ageing and passivation: The study fo- cused on short-term performance and did not account for time-dependent geochemical ageing or the long-term passi- vation of the nZVI core under oxic or anoxic environmental conditions. Assessing the long-term stability and reductive 13 lifespan of the Fe(0)@Fe3O4 architecture remains a priority for future field-oriented research. Kinetic and structural interpretations: The application of PSO kinetic models serves as a macroscopic compari- son of uptake behavior across different conditions but does not uniquely diagnose a specific rate-limiting step or pro- vide definitive proof of chemisorption. Additionally, the I(D)/I(G) ratio obtained via Raman spectroscopy is a mea- sure of relative disorder and should not be interpreted as a definitive quantification of true graphitization within the biochar matrix. Loss of reductive capacity: Reusability experiments showed a moderate decline in arsenic removal efficiency after five cycles (from 98.5% to 81.3%), which is likely at- tributed to the progressive consumption of the Fe(0) core’s reductive capacity and the irreversible binding of arsenic to certain reactive sites.

    Magnetic Biochar–Nanoscale Zero-Valent Iron Composites for Arsenic Immobilization and Magnetically Assisted Separation From Aqueous Matrices in Mining-Impacted Environments · 2026 · DOI

  • Additionally, long-term material stability under continuous flow systems, mechanical stress, variable temperatures, and extreme pH conditions has not yet been established. The adsorption performance was evaluated using synthetic aqueous solutions; therefore, the selectivity and efficiency of CS@NCs/ALG in real industrial wastewa- ter containing competing ions, mixed heavy metals, organic pollutants, and fluctuating physicochemical conditions remain uncertain.

    Mercury (II) and Zinc (II) Detoxification from Aqueous Systems using Chitosan/Nanocellulose-based Biocomposite Hydrogel · 2026 · DOI

  • Rifampicin (RIF), a chemically stable and biologically active antibiotic, is increasingly detected in wastewater streams and remains insufficiently removed by conventional treatment processes.

    Upcycling Cellulosic Waste into Reduced Graphene Oxide Nanostructures for Antibiotic Removal and Sustainable Water Purification · 2026 · DOI

  • The present findings therefore position BM-ECB as a promising, sustainable, and scalable material for hexavalent chromium removal, while future studies should focus on the application of advanced three-parameter isotherm models, column breakthrough flow conditions, regeneration and reusability assessment, and pilot-scale evaluation to further advance the practical deployment of ball-milled E.

    Valorization of Invasive Water Hyacinth (Eichhornia crassipes) into Ball-Milled Biochar for Hexavalent Chromium Remediation from Industrial Wastewater: A Kinetic, Equilibrium, and Thermodynamic Study · 2026 · DOI

  • Future work should focus on enhancing membrane durability through material modification, improving zeolite dispersion, optimizing membrane thickness, reducing mechanical-property loss, evaluating lower-impact regeneration agents, and integrating the membrane with biological or physicochemical treatment methods to improve reusability, operational lifespan, and regulatory compliance. A notable limitation is the decline in adsorption performance over successive regeneration cycles, suggesting limited long-term stability.

    Oil Palm Empty Fruit Bunch-Derived Cellulose Acetate-Zeolite Mixed Matrix Membrane Adsorbers (MMMAs) for Ammonia Removal in Palm Oil Mill Effluent Wastewater Treatment · 2026 · DOI

  • The study optimizes Chi-AgNPs dosage at 0.025 g and sonication time at 5 min for Congo Red removal, but does not systematically investigate the scalability of this ultrasound-assisted adsorption process to larger treatment volumes or evaluate the cost-effectiveness and energy requirements compared to conventional adsorption methods.

    Ultrasound-assisted adsorption of congo red dye using green synthesized silver nanoparticles coated with chitosan · 2026 · DOI

  • The paper reports monolayer chemical adsorption of Congo Red on Chi-AgNPs based on Langmuir isotherm fitting, but does not provide mechanistic evidence or spectroscopic analysis (FTIR, XPS) of the specific functional groups involved in dye-adsorbent interactions or the role of reactive oxygen species (ROS) generation during ultrasound-assisted adsorption.

    Ultrasound-assisted adsorption of congo red dye using green synthesized silver nanoparticles coated with chitosan · 2026 · DOI

  • Although the study uses green synthesis of silver nanoparticles from plant materials, it does not compare the adsorption performance of Chi-AgNPs synthesized using different plant precursors or evaluate how variations in the green synthesis protocol (extraction method, reaction time, temperature) influence the final adsorbent's dye removal capacity.

    Ultrasound-assisted adsorption of congo red dye using green synthesized silver nanoparticles coated with chitosan · 2026 · DOI

  • The paper demonstrates 90.14% Congo Red removal efficiency under specific laboratory conditions but does not assess the performance of Chi-AgNPs adsorbent in real wastewater matrices containing competing ions, organic matter, or multiple dye species simultaneously.

    Ultrasound-assisted adsorption of congo red dye using green synthesized silver nanoparticles coated with chitosan · 2026 · DOI

  • The study validates chitosan encapsulation on silver nanoparticles using SEM-EDX and XRD characterization, but lacks investigation of how the thickness, uniformity, and crystallinity of the chitosan coating layer affect the adsorption kinetics and equilibrium capacity for Congo Red dye removal.

    Ultrasound-assisted adsorption of congo red dye using green synthesized silver nanoparticles coated with chitosan · 2026 · DOI

  • The study demonstrates Chi-AgNPs adsorption of Congo Red at optimal conditions (0.025 g dosage, 5 min sonication), but does not investigate the effect of varying ultrasound frequencies, intensities, or power outputs on adsorption capacity and removal efficiency of the chitosan-coated silver nanoparticles system.

    Ultrasound-assisted adsorption of congo red dye using green synthesized silver nanoparticles coated with chitosan · 2026 · DOI

  • The CuPc dye sorption on Purolite A 500PS is limited by the intraparticle diffusion, whereas sorption on Macronet MN 200 is limited by the intraparticle diffusion depending on pore size distribution and on the boundary layer thickness.

    Removal of the phthalocyanine dye from acidic solutions using resins with the polystyrene divinylbenzene matrix · 2025 · DOI

  • GSCQD-FeFe2O4 displayed excellent potential for Pb(II) removal, but further research on reusability and stability in industrial settings is needed for broader applicability.

    Groundnut shell carbon quantum dot magnetic iron oxide nanocomposite (GSCQD-FeFe2O4) for lead removal from water · 2024 · DOI

  • Based on the above discussion, multiple modifications/engineering strategies have been employed to improve the physicochemical and biological properties of biochar. The multiple-functionalized biochars have been successfully utilized for the remediation of soil and aquatic systems contaminated by various pollutants. The specific attributes of multiple-modified biochar including the appearance of new functional groups, enhanced surface area, and greater electron transport capability are amongst the main factors affecting the remediation efficiency in multifaceted applications.

    Recent trends and economic significance of modified/functionalized biochars for remediation of environmental pollutants · 2024 · DOI

  • Future research should focus on continuous adsorption processes in order to scale-up and use on an industrial level, as well as using actual wastewater rather than synthesized wastewater for adsorption experiments, as well as cost analysis to determine the feasibility of scaling up on an industrial level.

    Recent advances on humic acid removal from wastewater using adsorption process · 2023 · DOI

  • In this study, jute stick (JS), the underexplored by‐product of jute ( Corchorus olitorius ) cultivation system, has been used as a novel low‐cost adsorbent to remove methylene blue (MB), a cationic dye, from an aqueous medium.

    Optimization of process parameters for methylene blue removal by jute stick using response surface methodology · 2019 · DOI

  • Furthermore, the potential of predictive modeling and machine learning is noted, but a standardized dataset for training these models is currently lacking, necessitating immediate devel- opment to enhance predictive design capabilities in the field.

    Ecofriendly bionanomaterials for dye laden wastewater treatment through synthesis characterization adsorption and photocatalysis · 2026 · DOI

  • Future research should focus on scaling up production, optimizing functionalization processes, and evaluating the long-term environmental stability of nanobiochar under real- istic conditions.

    Mechanisms of mercury (Hg) and methylmercury (CH3Hg+) removal by pristine and thiol-modified açaí waste nanobiochar · 2026 · DOI

  • The papers in this Research Topic point to several shared messages. First, feedstock selection and modification methods are central to biochar performance. Cotton straw, invasive plant biomass, and traditional Chinese medicine residues can all be converted into valuable remediation materials; however, their properties depend on the production and treatment processes. Second, biochar performance should be interpreted through mechanisms rather than only through removal efficiency. The pore structure, surface chemistry, ion exchange, redox activity, dissolved organic matter release, and soil solution chemistry all affect remediation outcomes. Third, the field is becoming increasingly interdisciplinary. It now connects soil science, environmental chemistry, materials engineer- ing, spectroscopy, agronomy, and artificial intelligence. Despite these advances, several challenges remain. More long- term field studies are needed to test whether promising laboratory results can be maintained under real soil conditions. Biochar aging, wet-dry cycles, plant root activity, microbial processes, and coex- isting ions may alter the behavior of biochar after application. Standardized characterization and testing methods are also needed to compare biochars prepared from different feedstocks and at different pyrolysis temperatures. Future studies should also consider both the benefits and possible risks, including contaminant immo- bilization, nutrient cycling, dissolved organic matter release, green- house gas emissions, crop response, and life-cycle impacts. Overall, this Research Topic shows that biochar-based remedi- ation is becoming more precise and application-oriented. The collected studies move the field toward engineered, mechanism- guided, and context-specific solutions for contaminated and de- graded soils. By linking material design with soil processes and environmental safety, they provide useful guidance for future research and practical remediation. We thank all contributing authors, reviewers, and the Frontiers editorial team for their valuable support in developing this Research Topic.

    Editorial: Recent advances in biochar synthesis for remediation of soil contamination · 2026 · DOI

  • The work was conducted in a controlled laboratory environment; further research is required to evaluate large-scale reproducibility, continu- ous-flow system performance, adsorbent regeneration efficiency, long-term physicochemical stability, and techno-economic feasibil- ity.

    Multi-Feedstock Biochar from Lignocellulosic Biomass: Synthesis and Dye Adsorption Performance · 2026 · DOI

  • The biosorption behavior of fungal biomass presents numerous advantages, warranting further research to fully exploit its potential in wastewater treatment endeavors.

    Unveiling the promise of biosorption for heavy metal removal from water sources · 2024 · DOI

  • However, the key structural factors influencing the adsorption of tetracycline by biochar remain unclear at present, hindering the effective guidance for modification strategies.

    Standardization and micromechanistic study of tetracycline adsorption by biochar · 2024 · DOI

  • The study is described as 'preliminary,' suggesting limited scope regarding adsorbent types tested, solution conditions evaluated, and experimental replicates.

    Preliminary studies regarding the adsorption of phenazone and cadmium ions on commercial zeolite · 2022 · DOI

  • The reasons for the slight decrease in phenazone adsorption capacity and insignificant increase in cadmium adsorption capacity when adsorbates are present in mixture versus individual solutions require further mechanistic investigation.

    Preliminary studies regarding the adsorption of phenazone and cadmium ions on commercial zeolite · 2022 · DOI

  • The mechanisms underlying the observed decrease in phenazone and cadmium adsorption capacity with increasing pH are not explicitly explained or theoretically discussed.

    Preliminary studies regarding the adsorption of phenazone and cadmium ions on commercial zeolite · 2022 · DOI

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36 open questions have been extracted from the limitations and future-work passages of 1,284 Adsorption and biosorption for pollutant removal papers in our library. Each one below links back to the study that raised it, so you can read the original claim in context.

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