Water contamination by cationic dyes such as crystal violet (CV) is a significant environmental concern due to their toxicity and persistence. This study investigated and optimized CV adsorption onto Ceratophyllum demersum activated carbon (CDAC) using the Box-Behnken design (BBD) and artificial neural network (ANN) models. CDAC exhibited a specific surface area of 190.56 m2 g-1 and a mesoporous structure containing oxygen- and phosphorus-bearing functional groups. Batch adsorption experiments showed adsorption capacities ranging from 95 to 290 mg g-1, with adsorption following pseudo-second-order kinetics and exhibiting favorable isotherm behavior. Although the ANN model produced lower prediction errors (≤ 8%) than the BBD model (≥ 20%), the BBD model was considered more reliable given the limited experimental dataset. Optimization predicted a maximum adsorption capacity of 258.76 mg g-1 and a removal efficiency of 86% at an initial CV concentration of 150 mg L-1, a CDAC dose of 0.5 g L-1, and a contact time of 10 min. Germination assays using Lens culinaris seeds indicated reduced phytotoxicity after treatment. These results demonstrate that CDAC is an effective and sustainable adsorbent for CV removal from aqueous solutions.

The valorization of agricultural waste into effective adsorbents presents a promising strategy for sustainable wastewater remediation. This study investigates the conversion of lemon peel (LP), a common biowaste, into nano-graphitic biochar (NGB). Evaluating both materials as green adsorbents for the removal of the cationic dye Basic Fuchsin (BF). FTIR, SEM, and XRD were used to characterize the NGB. The obtained data confirm graphitization, high porosity, and exfoliated morphology compared to raw LP. The batch adsorption experiment conditions, pH, adsorbent dose, contact time, initial dye concentration, and temperature, have been optimized. NGB demonstrated exceptional performance, achieving 99.2% removal efficiency within just 5 min at optimal conditions (pH 7, 0.1 g adsorbent dose), significantly outperforming raw LP (86.4%). Isotherm analysis revealed that adsorption onto LP followed the Freundlich model (R[2] = 0.972), indicating heterogeneous, multilayer adsorption. In contrast, NGB adsorption was best described by the Temkin model (R[2] = 0.988), suggesting a uniform distribution of binding energies. Kinetic data were accurately fitted to a pseudo-second-order model, and thermodynamic parameters confirmed a spontaneous exothermic physisorption process. Furthermore, NGB exhibited excellent regeneration, maintaining 97.3% efficiency after five adsorption-desorption cycles. Application to spiked real water samples (groundwater, saline wells) yielded recovery rates up to 96%, underscoring its practical potential.

The aim of this study was to produce biochars and activated biocarbons from corn postharvest residues (stalks and cobs) and to evaluate their physicochemical properties. The carbonaceous materials were prepared via simple thermochemical conversion methods, including microwave-assisted pyrolysis, impregnation with urea or calcium carbonate followed by thermal treatment at 400°C, or direct activation of the precursor with CO2. The resulting materials were characterized in terms of elemental composition, textural properties, surface acid-base characteristics, and thermal stability. Their effectiveness in removing model organic and inorganic contaminants from aqueous solutions was also evaluated. In addition, their usefulness as a soil additive supporting the growth of corn seedlings was tested. The results demonstrated that corn crop residues are a highly promising precursor for low-cost adsorbents. Various thermochemical treatment methods enabled the synthesis of a wide range of carbonaceous materials with favorable physicochemical properties and high sorption capacity. The properties of the adsorbents were influenced not only by the thermochemical treatment method but also by the specific plant fraction used in their production. The study also demonstrated that the resulting biochars can be used as an effective soil amendment in corn cultivation, and calcium carbonate-modified materials exhibiting particularly favorable properties in this regard.

Deep eutectic solvent-impregnated activated carbon (AC-DES) is developed as a selective adsorbent for lithium recovery from complex aqueous streams relevant to spent lithium-ion battery recycling. By immobilizing a functional DES phase onto a porous carbon support, the AC-DES creates a tunable coordination environment that enables preferential Li[+] binding in multicomponent systems. AC-DES (1:1 w/w) achieved up to 99% lithium removal under optimized conditions (pH 12, 75 mg, 2 h), with high selectivity over coexisting transition-metal ions. The adsorbent exhibited good stability and reusability, with negligible performance loss (≤1.5%) over four cycles, and allowed efficient lithium recovery using a mild acid solution (0.7 M HCl). Importantly, the AC-DES was successfully applied to selective lithium extraction from ethylenediaminetetraacetic acid (EDTA) leachates of spent NMC532 cathodes obtained via ultrasonic-assisted leaching, where Li[+] coexists with Mn, Co, and Ni. Combined kinetic, isotherm, and pH-dependent analyses, supported by material characterization and density functional theory (DFT) calculations, reveal that lithium uptake is governed by preferential Li-DES coordination interactions. This work demonstrates a DES-functionalized solid platform for selective lithium recovery from complex leachates, offering an effective alternative to conventional solvent-based extraction systems.

Effective removal of per- and polyfluoroalkyl substances (PFAS) form contaminated waters remains a significant treatment challenge in remediation facilities due to their structural heterogenicity, high aqueous mobility, and frequent occurrence as complex multi-component mixtures. Although granular activated carbon (GAC) and ion exchange resins (IER) are widely used for PFAS treatment, their performance is strongly influenced by water-matrix composition and competitive adsorption among PFAS, which can accelerate breakthrough and reduce adsorption capacity. Consequently, treatment performance assessments and capacity estimates may remain uncertain under multi-component conditions. Accordingly, this study evaluates how structurally diverse PFAS compete during adsorption and displacement in single- and multi-solute systems. This unified comparison clarifies how GAC and IER chemistry influence PFAS competitive behavior. Coexisting organic and inorganic constituents, dissolved organic matter (DOM) and phosphate, were incorporated to simulate realistic water matrices and to quantify their influence on PFAS competition and displacement. Results revealed that PFAS chain length and functional group chemistry governed the competitive hierarchy, with sulfonates generally exhibiting greater surface stability and removal efficiency than carboxylates. In addition, the results demonstrated distinct surface-dependent competitive behavior across the studied sorbents. GAC exhibited pronounced inhibition and displacement of PFAS in the presence of dissolved organic matter, whereas IER maintained relatively higher selectivity toward PFAS but was more susceptible to phosphate-induced displacement, highlighting the distinct matrix sensitivities of the two sorbents. These findings provide critical insight into PFAS treatment in multi-component systems and emphasize the importance of water-matrix specific design considerations to improve treatment efficiency, particularly for short-chain PFAS.

Marginal water sources have become increasingly important in fulfilling human and environmental needs. In situ contaminant removal is frequently used as a low-cost method of improving water quality in areas impacted by industries such as mining, which can cause complex adverse effects in surrounding watersheds. Biochar has been used as a soil amendment and considered as a sorbent for aqueous contaminants at a benchtop scale, but studies examining its use to improve surface waters at the field scale have been limited. This study observed the effects of manure-based biochar on two mining-influenced water bodies. Lead and zinc concentrations in an intermittent stream were minimally affected, and exchangeable ions from the biochar increased electrical conductivity and nutrient concentrations to undesirable levels in water downstream from the installation. Lead and zinc concentrations decreased downstream from biochar installed at a small seep in a mine waste repository, but further analysis of the solids showed that lead and zinc were sorbed to iron (oxyhydr)oxide solids precipitating from this water before encountering the biochar. When compared with optimal controlled conditions observed in benchtop studies, field conditions, such as contact time, did not allow for effective use of biochar and resulted in substantial environmental degradation of downstream waters.

Copper released from industrial activities and urban surfaces poses persistent risks to aquatic systems, highlighting the need for scalable and deployable materials for the harvesting of copper from water for practical recovery and removal applications. In this study, biochar-encapsulated, calcium-crosslinked alginate (BECA) hydrogels are developed as a composite platform for Cu[2+] removal from aqueous media. The system integrates the well-established ion-binding properties of alginate with the heterogeneous surface chemistry of algae-derived biochar within a mechanically stable hydrogel matrix, enabling a functional and deployable sorbent architecture rather than a standalone adsorbent. Batch adsorption experiments were conducted to evaluate Cu[2+] uptake under varying initial concentrations and to assess the influence of hydrogel crosslinking conditions. The BECA system achieved removal efficiencies exceeding 98% at low Cu[2+] loading and maintained removal above 87% at higher concentrations (up to 12.5 mM), with adsorption capacities reaching 69 ± 1 mg g[-1]. FTIR analysis confirmed interactions between Cu[2+] and carboxylate-functional groups within the composite structure. Density functional theory (DFT) calculations further supported favorable Cu[2+] coordination within the alginate egg-box structure and stable binding at the alginate-biochar interface. Overall, the results demonstrate that BECA hydrogels function as scalable composite platforms for the harvesting of copper from water, combining adsorption functionality with structural stability and practical deployability. The novelty of this work lies in the integration of biochar into a hydrogel matrix to enable practical Cu[2+] harvesting systems. Future work will further evaluate performance at environmentally relevant trace Cu concentrations and under dynamic flow conditions to extend applicability to real-world stormwater systems.

Heavy metal pollution from industrial activities poses severe threats to aquatic ecosystems and human health, urging the development of low-cost, high-efficiency adsorbents via resource reuse. Herein, a silico-manganese heterojunction adsorbent (RHB&MS) was fabricated by plasma ball milling (PBM) using manganese slag (MS) and rice husk biochar (RHB) as raw materials. The synthesis mechanism, structural characteristics, and adsorption performance of RHB&MS for Cu(II) and Ni(II) were systematically investigated via multiple characterizations and batch adsorption experiments. The results indicated that PBM induced the formation of stable Si-O-Mn covalent bonds at the interface, constructing a "crystalline silica framework-amorphous carbon matrix-nano manganese oxide active site" heterojunction structure. The specific surface area of RHB&MS reached 108.30 m[2]/g, which was 7 times higher than that of pristine RHB. Under optimal conditions, the maximum adsorption capacities of RHB&MS for Cu(II) and Ni(II) calculated by Langmuir model were 235.51 mg/g and 170.68 mg/g, respectively, outperforming most reported solid waste-based adsorbents. The adsorption process followed the pseudo-second-order kinetic model and Langmuir isotherm model, indicating that chemical adsorption dominated the monolayer adsorption. The adsorption mechanism involved synergistic effects of coordination complexation, electron transfer mediated by Mn valence evolution, and electrostatic attraction. Moreover, RHB&MS exhibited excellent cyclic stability (adsorption capacity retention rate >87% after 10 cycles) and environmental safety (leaching toxicity met GB5085.3-2007 standard). This study provides a novel strategy for the high-value utilization of industrial and agricultural wastes, and offers a promising adsorbent for heavy metal-contaminated wastewater treatment.

The presence of estrogenic compounds in aqueous environments has raised significant environmental and public health concerns due to their endocrine-disrupting effects. These compounds, both natural (estrone: E1, 17β-estradiol: E2, and estriol: E3) and synthetic (17α-ethinylestradiol: EE2), are frequently detected in wastewater and surface waters, where conventional treatment processes often fail to remove them successfully. Adsorption has been regarded as a promising, low-cost solution for removing these compounds, especially when coupled with activated carbon made from agro-industrial waste. This is considered an environmentally friendly solution, as it reuses waste materials and adds value to them. This review presents a comprehensive analysis of 28 studies published from 2011 to 2026 on the use of activated carbon for the removal of estrogens. It discusses the properties of estrogens, their environmental impact, and the health risks of long-term exposure. It also explains the physicochemical mechanisms behind estrogen adsorption and highlights the main adsorption and kinetic models used, with a reflective discussion on the results. Although results are promising, most studies only performed their assays under ideal matrices or monocomponent systems. Future research should include multicomponent systems, simulated wastewater matrices, and initial estrogen concentrations closer to those found in nature. Challenges remain in improving adsorbent efficiency, regeneration, and overall sustainability.

A sustainable framework that emphasizes circular economy is essential to combat water contamination. This work presents a sustainable and multifunctional adsorbent derived from oil palm frond biochar (OPFB), engineered with nano-Fe2O3 which effectively removes methyl orange (MO), amoxicillin (AMX), and nitrate from aqueous solutions. Through optimization of pyrolysis and modification parameters, 2-h pyrolysis time, 500 °C pyrolysis temperature, and 0.25 M FeCl3 concentration, the nanobiochar achieved particle size of 82.65 nm with enhanced surface properties. Comprehensive characterization via FTIR, XRD, BET, TEM, and SEM-EDX confirmed the physicochemical modifications. ICP MS confirm no leaching occurred during MO, AMX, and nitrate removal. Response surface methodology (RSM) was employed to optimize the removal efficiency, yielding maximum removal of 100% for MO, 82.13% for AMX, and 75.26% for nitrate under specific adsorption conditions. The maximum adsorption capacity for MO is obtained at 41.0662 mg/g, AMX at 77.9870 mg/g, and nitrate at 105.4387 mg/g. Structure-property-performance relationships were assessed in this study to elucidate the correlation between physicochemical properties and adsorption efficiency while offering mechanistic insight via kinetic and isotherm studies, zeta potential, and spectroscopic analyses (FTIR, 2DIR, and XPS).

This paper examined the removal of Acid Yellow 36 (AY36), Methyl Red (MR), and Methylene Blue (MB) dyes using a novel Ammonia-decorated Red Algae Biochar (RAB-A) synthesized from red algae (Pterocladia capillacea) via a reflux technique in the presence of 25% ammonium hydroxide (NH4OH). The physicochemical properties of the synthesized RAB-A, including its surface area, morphology, functional groups, elemental composition, and thermal stability, were comprehensively characterized through Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) integrated with energy-dispersive X-ray (EDX) analysis, and thermogravimetric analysis (TGA). RAB-A demonstrated a low specific surface area (3.262 m[2]/g) and a monolayer adsorption capacity of 0.7495 cm[3] (STP)/g. The adsorbent demonstrated an overall pore volume of 0.011 cm[3]/g, accompanied by an average pore diameter of 13.648 nm. Thermogravimetric analysis revealed an overall mass loss of 40.84% for RAB-A, demonstrating enhanced thermal stability relative to RAB, which showed a weight loss of 51.05%. FTIR analysis confirmed the presence of diverse functional moieties on the surface of RAB-A. Adsorption experiments targeting Acid Yellow 36 (AY36), Methyl Red (MR), and Methylene Blue (MB) were conducted in batch mode by independently adjusting the initial dye concentration (100-200 mg/L), contact time (5-180 min), solution pH (2-12), and adsorbent dosage (0.5-1.5 g/L). The adsorption equilibrium behavior was best described by the Langmuir isotherm, which indicated maximum uptake capacities of 222.22 mg/g for AY36, 192.31 mg/g for MR dye, and 833.33 mg/g for MB dye. Kinetic analyses revealed that the adsorption of all examined dyes was best described by a pseudo-second-order model, thereby demonstrating the high suitability of the synthesized RAB-A for the efficient elimination of dyes from aqueous solutions. Additionally, adsorption was predicted and adjusted utilizing artificial neural networks (ANN).

Organic amines, such as aniline (AN), frequently coexist with dissolved transition metals in mining and industrial wastewater; yet the role of dissolved metal ions in governing adsorption mechanisms remains poorly understood. This study provides evidence that aqueous Mn[2+] can act as a redox-active electron-transfer mediator, thereby altering the adsorption behavior of AN on N-doped biochar (NBC), and offers new insight into pollutant removal under realistic multi-contaminant conditions. NBC synthesized from sawdust biochar (SBC) via urea-assisted pyrolysis exhibited a defect-rich and N-functionalized carbon structure. NBC showed higher AN adsorption than pristine SBC, and this further increased in the presence of Mn[2+] (from 0.35 ± 0.033 to 0.400 ± 0.006 mmol/g; equivalent to ∼32-37 mg/g). ICP-OES, Raman, and XPS analyses, supported by DFT calculations, consistently indicate that Mn[2+] remains predominant in solution and participates in a Mn[2+] ⇌ Mn[3+]/Mn[4+] redox cycling during adsorption. This redox cycling modifies the electronic structure of NBC, reduces defect density, and generates polarized π sites, thereby, strengthening π-π electron donor-acceptor interactions and promoting chemisorption. The effect of competing cations was negligible, while selected anions slightly enhanced adsorption. This indicates that adsorption is governed by specific interfacial interactions rather than simple ionic effects. These findings suggest that naturally occurring or coexisting metal ions in wastewater can be leveraged to enhance adsorption performance without additional material modification, offering a cost-effective strategy for treating complex industrial effluent.

In current years, the elimination of heavy metals from wastewater systems has become a global concern due to persistent adverse effects on ecosystems and human health. Adsorption technique has gained much attention for the removal of heavy metals from aquatic environments because of advantages like great efficiency, cost-effectiveness and simple operation. Biochar, a carbonaceous material, has been extensively applied for removing heavy metals from aqueous systems due to its low cost and eco-friendly nature. However, numerous existing studies are focusing on elimination of heavy metals from wastewater by using biochar as an adsorbent, but very few emphasize on re-utilization of spent biochar, which is a crucial concern. This is because if spent biochar is discharged or landfilled untreated into the environment can increase the risk of secondary pollution thus harming the ecosystem and mankind. Therefore, the present paper critically reviews the recent applications of biochar in removing heavy metals from wastewater along with potential electrochemical applications of metals loaded biochar in developing super-capacitors or other energy storage devices. The review also comprehensively discussed the characteristics of different biomass feedstock, methods used for biochar production and various physical, chemical and biological biochar engineering techniques. The key mechanisms involved in adsorption of heavy metals from aquatic systems through biochar have been reviewed. The paper also highlighted technical barriers, benefits-cost analysis, market status, future directions and scope of biochar as an adsorbent. Hence, the review will assist the successful development of highly efficient biochar-based adsorption techniques for eliminating heavy metals from aqueous environments.

An activated sugarcane bagasse biochar (ASCBB) was used for constructing a filter module to remove p-nitrophenol (PNP) from contaminated water to introduce applicable tools for remediating pollutants. The PNP adsorption on the ASCBB filter was studied at different flow rates, pollutant dose levels, and ASCBB amounts. The PNP adsorption efficiency of ASCBB was evaluated and compared with its raw precursor, sugarcane bagasse (SCB). Furthermore, the reusability and regeneration potential of the ASCBB filter were investigated to ensure its long-term efficacy in removing PNP from aqueous solutions. A one-gram ASCBB filter achieved 94.98% removal of 50 mg/L PNP at a flow rate of 2 mL/min. Increasing the ASCBB adsorbent amount from 1 to 2 g improved the removal of 500 mg/L PNP from 75.96% to 92.84% at 2 mL/min. Furthermore, the two-gram ASCBB filter can remove 85.60% of high tested concentration (1000 mg/L) of PNP when pursuing a flow rate of 2 ml/min. The results indicate that the ASCBB filter (2 gm) demonstrated good reusability by retaining 113 mg out of 150 mg of PNP after five separate cycles without regeneration. The ASCBB filter was restored completely after a simple regeneration process to be capable of retaining 68.2 mg out of 90 mg of PNP after three cycles without any further regeneration. This finding proved that the ASCBB filter can be used as a promising, sustainable, and reusable filter for removing the PNP from contaminated water.