Monolayer Adsorption Research Articles

Microwave assisted activation of silkworm excrement for fast adsorption of methylene blue and high performance supercapacitor

The activated carbon (AC) with an exceptionally high surface area was made of silkworm excrement (SE) by microwave-assisted KOH activation (MAKA). It was investigated for the potential applications in methylene blue (MB) adsorption and a supercapacitor electrode. The effect of activation time on the AC properties and performance was studied. The physical and chemical properties of the as-prepared samples were analyzed by FE-SEM, TEM, N2 adsorption, and Raman spectroscopy. Remarkably, the AC with the largest specific surface area (SAs) of 2530.3 m2g−1 was produced by partial carbonization of SE at 400 °C (SE400-5) and then activated for only 5 min. The large SAs is attributed to the abundance of micro-pores, leading to the enhanced MB absorption performance, as equilibrium was reached within 10 min at 25 ppm of MB concentration. The maximum MB adsorption capacity for SE400-5 was 902.56 mg g−1. The adsorption isotherms revealed that the Langmuir model best fits the empirical data (R2 ≥ 0.9813), indicating monolayer adsorption. The kinetic model fitted well to the Pseudo-second-order (PSO) (R2 ≥ 0.9691). CV, GCD, and EIS measurements also evaluated the electrochemical properties of all samples. The electrodes were made without the addition of conductive material. The SE400-5 also had the lowest total resistance and highest total effective capacitance, which resulted in its highest specific capacitance (Cs) of 322 F g−1 at 0.5 A g−1. The capacitive retention of SE400-5 remained as high as 98% even after 10,000 cycles at 10 A g−1. These results demonstrate that SE is a viable source of AC for MB adsorption and a supercapacitor electrode.Graphical abstract

Exploring the Potential of Recycled Polyethylene Terephthalate—Lignocellulose/Carbon Nanotube–Graphene Nanosheets an Efficient Extractor for Oil Spill

The global challenge of oil spill treatment has been addressed using nanocomposite-based natural fibers. These materials offer great potential in oil spill cleanup and are considered due to their environmental friendliness, high efficiency, and low cost. Thus, the current study reports a novel composite fabricated from date palm fiber (DPF) and recycled polyethylene terephthalate (rPET) with a proper combination of a mixture of carbon nanotubes (CNTs) and graphene nanosheets (GNSs) for oil removal. The established nanocomposite (DPF-rPET/CNT/GNS) was fabricated via physical mixing of various quantities (0.9, 0.8, and 0.7 g) of PET, along with varying loads of DPF at different proportions of CNT:GNS. The prepared nanocomposite (DPF-rPET/CNT/GNS) was fully characterized using scanning electron microscopy–energy dispersive X-ray (SEM-EDX) analysis, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) analysis. In static experiments and under the optimal parameters of pH, sorbent doze, shaking time, and quantity of diesel oil), the established sorbent (DPF-rPET/CNT-GNS nanocomposite) displayed excellent adsorption capacity (98 mg/g). This study also expands the utility of the sorbent for the reusability of the oil adsorption, maintaining performance after five cycles. The adsorption data fitted well with the Langmuir isotherm model with a correlation coefficient (R2) of 0.99 and maximum adsorption capacity of 99.7 mg/g, indicating monolayer adsorption. Additionally, the adsorption kinetics followed a pseudo-second-order model, with an R2 near unity and an adsorption capacity of 99.09 mg/g. This study highlights the promising potential of the DPF-rPET/CNT-GNS composite as an effective adsorbent for treating oily water.

Versatile silicate-modified hydrochar based on Scutellaria baicalensis-residue for efficiently removing heavy metal-antibiotic co-contamination and relevant bio-contaminants from wastewater

In this study, we utilized typical Chinese medicine herbal residues (CMHRs)－Scutellaria baicalensis (Scutellaria baicalensis Georgi) residue (SR), as the raw material and employed Na2SiO3 and Fe2(SO4)3 as modifying agents to fabricate a novel and multifunctional hydrochar (FeSi-SRHC), which was designed for comprehensive removal of typical contaminants such as Cu2+, Zn2+, tetracycline (TC), and ciprofloxacin (CIP), along with relevant bio-contaminants (resistant bacteria (RBs) and resistance genes (RGs)) present in wastewater. Based on the analysis of adsorption kinetics and Freundlich isotherm, it was found that FeSi-SRHC exhibited physical monolayer adsorption for Cu2+/Zn2+ while mainly chemical multilayer adsorption for TC/CIP in single-contamination system. Furthermore, Langmuir isotherm demonstrated excellent adsorption capacity of FeSi-SRHC towards Cu2+/Zn2+/TC/CIP with maximum capacities of 255.75, 265.26, 425.53, and 404.86 mg/g, respectively. In the co-contamination system, the presence of Cu2+, Zn2+, TC, and CIP exhibited varying degrees of inhibitory or promotive effects on the mutual adsorption by FeSi-SRHC. This divergence stemmed from differences in complexation intensities and concentration ratios among diverse co-existing contaminants. Based on XPS and Density Functional Theory (DFT) analyses, the adsorption process for Cu2+, Zn2+, TC, and CIP by FeSi-SRHC primarily involves pore fill, complexation reactions, ion exchange, hydrogen bonding, π-π stacking interactions, and electrostatic interactions. Bio-contaminant removal experiments revealed that the release of baicalin and wogonoside from FeSi-SRHC disrupts the structure of RBs cells and compromises the integrity of resistance plasmids. The practical application experiment showed that FeSi-SRHC displayed favorable performance for removing heavy metals, antibiotics, and bio-contaminants in actual wastewater. This study presented a “Treating waste with waste” strategy, which provided a method with low carbon, eco-friendly, and inexpensive for CMHRs resources and turning waste into treasure while proposing a idea to address the challenges associated with treating heavy metal, antibiotic, and bio-contaminant contamination in wastewater.

Polymeric Adsorbent for the Effective Removal of Toxic Dyes from Aqueous Solutions: Equilibrium, Kinetic, and Thermodynamic Modeling

AbstractThis study investigates the adsorption behavior of anionic (Congo red, Eosin yellow) and cationic (Malachite green) dyes on synthesized TD polymer particles, highlighting the material's potential as an effective adsorbent for industrial wastewater treatment. Key operational parameters, including initial solution's pH, contact time, initial dye concentration, and temperature, were systematically evaluated to determine their influence on adsorption efficiency. The experimental data demonstrated that the Langmuir isotherm provided the best fit for all three dyes, indicating monolayer adsorption with maximum adsorption capacities of 153.8 mg/g for Malachite green, 49.36 mg/g for Congo red, and 227.9 mg/g for Eosin yellow. Kinetic analysis revealed that the adsorption of Malachite green and Congo red followed pseudo‐second‐order kinetics, while Eosin yellow adsorption was better described by the intra‐particle diffusion model. Thermodynamic assessments, including Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°), confirmed the spontaneous and endothermic nature of the adsorption processes for Malachite green and Eosin yellow, contrasting with the exothermic behavior observed for Congo red. These findings underscore the versatility and effectiveness of TD polymer particles in removing both anionic and cationic dyes from aqueous solutions. Further research could explore material optimization and real‐world applications to broaden their utility in sustainable water treatment strategies.

Research on the microscopic mechanism and model applicability differences of CH4 and CO2 adsorption based on molecular dynamics

To verify the accuracy and rationality of the molecular simulation model, the microscopic mechanism of gas adsorption was analyzed and clarified from a microscopic perspective. The effect of molecular models created by direct construction and supercell expansion on the adsorption capacities of CH4 and CO2 has been analyzed. Eight coal-based molecular configurations were created to simulate the isothermal adsorption process of CH4 and CO2 using various coal-based molecular configurations. Using physical experiments, the validity of different construction methods for coal-based molecular structures was verified. The direct construction method was chosen to simulate the effect of various coal-based molecular numbers on the adsorption capacity of CH4 and CO2. The results show that the adsorption capacity of CO2 on coal is greater than that of CH4. The isothermal adsorption curves of CH4 and CO2 in coal-based molecular systems constructed using different methods reveal that the adsorption of methane on coal molecules adheres to the Langmuir monolayer adsorption theory. The adsorption sites for methane increase with the rise in free volume. The structure directly constructed and the supercell expansion directly determines the amount of methane adsorbed by each coal based molecule. The adsorption constants of CH4 and CO2 on the supercell extended structure are more volatile than those on the directly constructed structure, and the structure constructed directly for different coal based molecules is better than the supercell extended structure. The simulation using the direct construction method shows that as the number of coal-based molecules in the molecular configuration increases, The isothermal adsorption quantities of CH4 and CO2 increase linearly. The molecular configuration is not affected by the number of anthracite molecules. Molecular configuration is not affected by the number of anthracite molecules. The rationality of model construction has no obvious relationship with the number of coal based molecules.

A sustainable approach for the corrosion control of mild steel using Cocous nucifera gum: An electrochemical investigation

The study of corrosion inhibition on mild steel (MS) in an acid medium (1 M HCl) solution was performed using a crude extract of Cocousnucifera gum (CNG). Cocousnucifera develops gum exudates on its palm, the exudate process occurs mainly after some physical or microbiological injuries and is formed on the fruit of the palm. The gum was utilized to study the corrosion inhibition of MS by electrochemical and surface studies. The characterization of the crude gum was done by Fourier transform infrared spectroscopy (FT-IR) which revealed the presence of several active components (aromatic and oxygen-containing functional groups) in its structure. The electrochemical studies resulted in the maximum inhibition efficiency value of 75.64 % at the highest inhibitor concentration of 4000 ppm at 308 K. It was inferred that both the anodic dissolution of the metal and cathodic hydrogen evolution were effectively decreased in the presence of Cocous nucifera gum extract, revealing that inhibitor is of mixed type. From the adsorption studies, it was found that the best fit with R2 ∼ 0.9 followed Langmuir adsorption isotherm indicating the monolayer adsorption of the inhibitor on the metal surface. Gibb’s free energy of adsorption values was found <−20 kJ/mol, a characteristic of predominant physical adsorption. To support the electrochemical data SEM (scanning electron microscopy), AFM (Atomic force microscopy), and X-ray diffraction analysis were performed and these are in good agreement.

Effect of the Total Saponins of Bupleurum chinense DC. Water Extracts Following Ultrafiltration Pretreatment on Macroporous Resin Adsorption

Macroporous resin is an efficient separation technology that plays a crucial role in the separation and purification of traditional Chinese medicine (TCM). However, the application of macroporous resins in TCM pharmaceuticals is hindered by serious fouling caused by the complex materials used in TCM. This study examines the impact of ultrafiltration (UF) membrane technology on the macroporous resin adsorption behavior of TCM extracts. In this paper, Bupleurum chinense DC. (B. chinense) water extracts were included as an example to study the effect of UF pretreatment on the macroporous resin adsorption of total saponins. The study results indicated that the adsorption of total saponins constituents from the water extracts of B. chinense on the macroporous resin followed the pseudo-second-order kinetic model and the Langmuir model. The thermodynamic parameters of adsorption, including enthalpy changes and Gibbs free energies, were negative, while entropy changes were positive. These results demonstrated that the total saponin components form a monolayer adsorption layer by spontaneous thermal adsorption on the macroporous resin, and that the adsorption rate is not determined by the rate of intraparticle diffusion. Following treatment with a UF membrane with an average molecular weight cut-off of 50 kDa, the protein, starch, pectin, tannin, and other impurities in the water extracts of B. chinense were reduced, while the total saponin content was retained at 82.32%. The adsorption kinetic model of the saponin constituents on the macroporous resin remained unchanged and was consistent with both the second-order kinetic model and the Langmuir model; the adsorption rate of the second-order kinetic model increased by 1.3 times and in the Langmuir model at 25 °C, the adsorption performance improved by 1.16 times compared to the original extracts. This study revealed that UF technology as a pretreatment method can reduce the fouling of macroporous resin by TCM extracts and improve the adsorption performance of macroporous resin.

A Facile Synthesis of RGO-Ag2MoO4 Nanocomposites for Efficient Lead Removal from Aqueous Solution

Efficiently treating wastewater, particularly the elimination of heavy metal ions from water systems, continues to be one of the most pressing and complex challenges in modern environmental management. In this work, reduced graphene oxide coupled silver molybdate binary nanocomposites (RGO-Ag2MoO4 NCs) have been prepared via hydrothermal method. The crystalline nature and surface properties of the developed RGO-Ag2MoO4 NCs were proved by XRD, FTIR, SEM, and EDS techniques. Adsorption experiments demonstrated that the nanocomposites (NCs) effectively removed Pb(II) ions within 120 min, achieving a maximum removal efficiency ranging from 94.96% to 86.37% for Pb(II) concentrations between 20 and 100 mg/L at pH 6. Kinetic studies showed that the adsorption process followed a pseudo-second order model. Isotherm analysis presented that the Langmuir model provided the greatest fit for the equilibrium data, with a monolayer adsorption capacity of 128.94 mg/g. Thermodynamic analysis revealed that the adsorption process was spontaneous and endothermic. The results of this study highlight RGO-Ag2MoO4 NCs as a highly promising and eco-friendly material for the effective elimination of Pb(II) ions from wastewater. Their strong adsorption capacity, coupled with sustainable properties, makes them an efficient solution for addressing lead contamination, offering significant potential for practical applications in water treatment systems.

Efficient removal of basic yellow 28 dye from water using facilely synthesized ZnO and Mg3B2O6 nanostructures

Basic yellow 28 dye, used extensively in the textile and leather industries, poses significant environmental and health risks, including allergic reactions, skin irritation, and respiratory problems. This study reports the Pechini sol-gel synthesis of novel ZnO/Mg3B2O6 nanostructures for the decontamination of basic yellow 28 dye from aqueous solutions. The nanostructures were synthesized by calcining at 650 and 850 °C for 5 h, producing ZM650 and ZM850, respectively. The average crystallite sizes were 39.28 nm for ZM650 and 51.03 nm for ZM850. BET surface areas were 70.71 m2/g for ZM650 and 48.13 m2/g for ZM850. FE-SEM and HR-TEM analyses revealed distinct morphological structures, with ZM650 exhibiting a dense aggregation of rod-like particles and ZM850 showing larger clusters. The maximum adsorption capacities were 381.68 mg/g for ZM650 and 303.03 mg/g for ZM850. The optimum adsorption was observed at a pH of 10, a contact time of 70 min, and a temperature of 298 K. Regeneration using a 6 M HCl solution demonstrated efficient reusability over five cycles. The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm, indicating monolayer adsorption. Also, the adsorption process was found to be physical and exothermic.

A modified dubinin-radushkevich model describing the cryogenic adsorption of 4He on carbon materials

The 4He and 3He adsorption characteristics of porous materials serve as important references for designing and optimizing cryogenic components or systems, including adsorption pumps, helium adsorption refrigerators, and gas-gap heat switches. In this study, various types of activated carbon and carbon nanotubes were measured for their 4He adsorption characteristics in the range of 3–20 K and 1–18000 Pa. Parameters such as micropore volume and adsorption potential energy of porous materials were analyzed through Dubinin-Radushkevich (DR) model. A modified DR model describing the monolayer adsorption of 4He on different carbon-based adsorbents was developed in this study, greatly facilitating the design of adsorption systems. Further, the 4He adsorption model was applied to gas-gap heat switches, and a numerical model of the 4He gas-gap heat switch was established, which accurately predicts the actuation characteristics of several heat switches.

Novel fluorescent carbon dots derived from shikimic acid for ultra-high sensitive detection and efficient removal of sulfasalazine

The extensive use of sulfasalazine (SSZ) poses potential threats to human health and ecosystems. Therefore, sensitive detection and simultaneous efficient removal of sulfasalazine is greatly desirable. Meanwhile, shikimic acid, a natural product obtained from Chinese star anise is a promising precursor for carbon dots construction due to its unique structure. Taking the above into account, in this work, novel fluorescent carbon dots (SA-CDs) for sensitive detection and highly efficient removal of sulfasalazine have been developed. SA-CDs were facilely obtained from shikimic acid by using one-pot hydrothermal synthesis. The structure and composition of SA-CDs were fully characterized with TEM, PXRD, FT-IR, DLS and XPS tests. Strong fluorescent emission centered at 428 nm was recorded for SA-CDs, enabling the detection of SSZ. Quantitatively speaking, SA-CDs can selectively detection SSZ amount 17 antibiotics with an experimental limit of detection (LOD) of 100 nM and a calculated LOD of 60 pM. Adsorption experiments suggested that chemical monolayer adsorption predominates in the adsorption process, with a maximum adsorption capacity of 22.67 mg/g. Aggregations formed during detection enable the simultaneous removal of SSZ upon centrifugation. Moreover, SA-CDs have been successfully applied to the detection of SSZ in real samples, including river water, soil, tea and eggs.

Adsorption Thermodynamics for Process Simulation.

Adsorption has rapidly evolved in recent decades and is an established separation technology extensively practiced in gas separation industries and others. However, rigorous thermodynamic modeling of multicomponent adsorption equilibrium remains elusive, and industrial practitioners rely heavily on expensive and time-consuming trial-and-error pilot studies to develop adsorption units. This article highlights the need for rigorous adsorption thermodynamic models and the limitations and deficiencies of existing models such as the extended Langmuir isotherm, dual-process Langmuir isotherm, and adsorbed solution theory. It further presents a series of recent advances in the generalization of the classical Langmuir isotherm of single-component adsorption by deriving an activity coefficient model to account for the adsorbed phase adsorbate-adsorbent interactions, substituting adsorbed phase adsorbate and vacant site concentrations with activities, and extending to multicomponent competitive adsorption equilibrium, both monolayer and multilayer. Requiring a minimum set of physically meaningful model parameters, the generalized Langmuir isotherm for monolayer adsorption and the generalized Brunauer-Emmett-Teller isotherm for multilayer adsorption address various thermodynamic modeling challenges including adsorbent surface heterogeneity, isosteric enthalpies of adsorption, BET surface areas, adsorbed phase nonideality, adsorption azeotrope formation, and multilayer adsorption. Also discussed is the importance of quality adsorption data that cover sufficient temperature, pressure, and composition ranges for reliable determination of the model parameters to support adsorption process simulation, design, and optimization.

Regulation of Adsorption Properties of Whey Protein Isolate Fibril-Calcium Alginate Aerogels by Controlling Protein Fibrillation Time.

Amyloid-like fibrils have a relatively high specific surface area, which makes them suitable as absorbents. In this study, we prepared absorbent composite aerogels from whey protein isolate fibril (WPIF) and calcium alginate (CA). The impact of protein fibrillation time (4-24 h) on the adsorption properties of these aerogels was assessed, as this influences the nature of the WPIFs formed. Fourier transform infrared spectroscopy analysis indicated that hydrogen bonding, hydrophobic interactions, and electrostatic interactions were the main molecular interactions in the composite aerogels. Then, the adsorption properties of the aerogels were investigated using crystal violet as a model compound. The adsorption properties of all composite aerogels were significantly improved compared to CA aerogels, which was mainly attributed to the numerous functional groups of the surfaces of the WPIFs, as well as the rougher surface topology of the composite aerogels. The adsorption capacity of the composite aerogels first increased and then decreased with increasing fibrillation time, with 8 h fibrillation leading to the largest adsorption capacity (1886.11 mg/g). Thioflavin T fluorescence, atomic force microscopy, light extinction, average particle size, and zeta potential analysis indicated that the high fibril content, mature fibril morphology, large number of available functional groups on the surface, and relatively low zeta potential of WPIF8 might be the main reasons. Adsorption kinetics and isothermal adsorption profile analysis suggested that monolayer adsorption occurred through chemical adsorption processes. The edible aerogel with high adsorption properties developed in this work has potential application in food and biomedical fields.

Facile synthesis of ZnO/RGO/Fe2O3 using macroalgae Caulerpa taxifolia as green reductor and its application as malachite green removal

This study presents the synthesis of a novel ZnO/rGO/Fe₂O₃ composite using Caulerpa taxifolia as a green reductant for the effective removal of Malachite Green from aqueous solutions. Characterization techniques, including FTIR, SEM, and XRD, confirmed the successful incorporation of ZnO and Fe₂O₃ onto the rGO matrix, enhancing its adsorption properties. The composite achieved an exceptional maximum adsorption capacity of 454.5 mg/g at pH 9, significantly outperforming rGO alone and other adsorbents. The adsorption kinetics followed a pseudo-second-order model, indicating chemisorption as the dominant mechanism, with a high correlation coefficient (R² = 0.999). The adsorption isotherms were best described by the Langmuir model, suggesting monolayer adsorption. Thermodynamic parameters revealed that the process was spontaneous and exothermic, with a Gibbs free energy (ΔGo) of -10.93 kJ/mol at 25 °C. The composite's high adsorption capacity, rapid kinetics, and favorable thermodynamics highlight its potential as an efficient and sustainable adsorbent for dye removal. This research offers a promising approach to water treatment, aligning with environmentally friendly practices and providing a viable solution for mitigating water pollution caused by organic dyes. KEY WORDS: Reduced graphene oxide, Water treatment, Caulerpa taxifolia, Isothermal and kinetic studies, Malachite Green Bull. Chem. Soc. Ethiop. 2025, 39(1), 29-47. DOI: https://dx.doi.org/10.4314/bcse.v39i1.3

Effects of Spontaneous Curvature on Interfacial Adsorption and Collapse of Phospholipid Monolayers.

To function effectively, pulmonary surfactant must adsorb rapidly to the alveolar air/water interface, but avoid collapse from the interface when compressed to low surface tensions. Prior studies show that phospholipids in the cylindrical monolayers of the inverse hexagonal (HII) phase adsorb quickly. The monolayers have negative curvature, defined by the concave shape of the hydrophilic face. Formation of the HII structures, however, involves significant disruption of optimal chain-packing. Samples with significant spontaneous curvature, formed in the absence of applied force, may nonetheless have lamellar structures. The experiments here tested whether planar lamellar bilayers formed by phospholipids with negative spontaneous curvature might adsorb rapidly but collapse slowly. Prior studies have shown that binary mixtures of dioleoyl phosphatidylcholine-dioleoyl phosphatidylethanolamine (DOPC-DOPE) with higher mol fractions of DOPE (XPE) have more negative spontaneous curvature. Samples with higher XPE adsorbed more rapidly but also collapsed more quickly. Over that range of XPE, small angle X-ray scattering showed only lamellar structures. The HII phase was undetectable. The results suggest that the innate tendency of the phospholipids to form curved structures has primary importance for adsorption rather than the presence of HII structures. Planar structures are insufficient to minimize the tendency of spontaneous curvature to promote collapse. These findings are consistent with adsorption and collapse that occur via rate-limiting structures with significant negative curvature.

Adsorption decolorization of phenolphthalein indicator in aqueous media using natural clay and the activated carbono

Natural clay and activated carbon are extremely encouraging for the removal of colored indicators in an aqueous solution. The natural clay and activated carbon were analyzed by X-ray diffraction (XRD) and Fourier transformation (FTIR) and the colored indicator was characterized by UV-Visible. The effects of various experiments, such as initial phenolphthalein concentration, contact time, temperature, pH and decolorization were studied. Dye removal increases with the decrease in the initial concentration of phenolphthalein and the contact time of the solution. The phenolphthalein removal percentage increases accordingly, reaching 99% for activated carbon and 98% for natural clay. The Langmuir and Freundlich adsorption models were used for descriptions of the adsorption equilibrium. The data was very well corrected with these models. Monolayer adsorption capacities were equal to 35 mgg-1 at pH 8.0 and temperature 27°C. Adsorption Measurements show that the adsorption process is very rapid and physical in nature. The results explain that the adsorption process is an exothermic and spontaneous physisorption.

Development of modified MgO/biochar composite for chemical adsorption enhancement to cleanup fluoride-contaminated groundwater

Fluoride contamination in groundwater has become a global environmental issue. Magnesium oxide (MgO) has demonstrated effectiveness as an adsorbent in treating fluoride pollution in groundwater. However, its use in powder and fine granular form often results in losses during the adsorption process, posing challenges for post-treatment recovery and potentially causing secondary environmental pollution. In this study, two novel fluoride adsorbents [rice husk (RH) and spent coffee grounds (SCG)-based magnesium oxide (MgO) biochar composites (MgO/RH and MgO/SCG)] were developed to cleanup fluoride-polluted groundwater. During the adsorbent synthesis process, RH and SCG biochar were pyrolyzed at 500 °C and modified by calcination using MgO. Both MgO/RH and MgO/SCG surfaces exhibited abundant pore structures and formed MgO crystal phases. Batch experiments results show that when the MgO/RH and MgO/SCG material dosages were 1 g/L, fluoride removal rates reached 80% and 86% respectively. The isotherms and kinetics of fluoride adsorption with MgO/RH and MgO/SCG followed the Langmuir isotherm equation and pseudo-second-order kinetic model. The maximum fluoride adsorption capacities of MgO/RH and MgO/SCG were 63.47 mg/g and 141.98 mg/g, respectively, indicating these materials used mono-layer adsorption mechanism for fluoride adsorption. The addition of MgO into the pores of porous adsorbent materials effectively increased their reactive sites and enhanced the adsorption performance of carbon materials. Particularly, SCG biochar had a richer pore structure than RH biochar, providing a larger contact surface area, facilitating the effective dispersion and doping of MgO into the pores. Therefore, MgO/SCG composite exhibited excellent fluoride adsorption properties in water, indicating the potential for developing a new type of MgO-modified SCG adsorbent material with green prospects. This composite effectively mitigated fluoride contamination, reducing the fluoride concentration in groundwater. Both RH and SCG are agricultural and food waste by-products, thus offering the opportunity to significantly reduce production, operation, and maintenance costs.

The potential application of agroforestry residues in the adsorption of aniline

A low-cost activated carbon based on agroforestry residues (AAC) was synthesized and characterized to remove aniline (AN), a healthy and environmentally toxic substance. The batch adsorption assays were used to assess the effect of contact time (1, 2, 6, 12, and 24 h), pH (2, 4, 6, and 8), and with 1, 5, and 10 mg/L AN concentration. The adsorption mechanism of AN on ACC and commercial carbons (GAP and PAC) was evaluated and compared through Langmuir, Freundlich, and Temkin isotherms. The results show that AN removal increases with decreasing pH, reaching a maximum removal capacity of AAC of 90 %. AAC resulted in similar efficiency to GAC &gt; 90 % to 1 and 5 mg/L. Langmuir shows the best-fit model reaching an R2 of 0.98. These models explain that the adsorption mechanism of AN on ACC is homogeneous, and monolayer adsorption occurs, achieving a maximum capacity of 1.20 and 1.16 mg/g for ACC and PAC, respectively, with a possible endothermic mechanism suggested by Temkin. The results showed that AAC could be considered an effective and economical adsorbent in removing the AN.

Green synthesis of nanoscale zero-valent iron impregnated walnut shell biochar as efficient adsorbent for metal(loid)s purification: Performance and mechanism insight

The escalation of metal(loid) contamination in global water poses severe risks to ecological environment safety. Meeting the ‘pollution control with waste’ strategy, we utilized eco-friendly waste tea leaf extract and walnut shell to first fabricate a greenly synthesized nanoscale zero-valent iron impregnated walnut shell biochar (G-nZVI/WSB) for the simultaneous sequestration of cadmium (Cd), lead (Pb), and arsenic (As) from aqueous systems. Since the interactions among these metal(loid)s during adsorption on G-nZVI/WSB and their corresponding mechanisms remain unclear, we conducted a series of batch experiments coupled with characterization techniques. The optimal pyrolysis temperature and Fe/C ratio for G-nZVI/WSB were determined to be 650 °C and 20 %, respectively. Under optimal conditions (contact time = 24 h, pH = 6), G-nZVI/WSB exhibited theoretical maximum adsorption capacities for Cd(II), Pb(II), and As(III) of 52.96, 135.1, and 8.414 mg g−1, respectively, which were significantly higher than those of WSB carrier. In single and combined systems, the monolayer and chemical adsorption of metal(loid)s were predominant, with their competitive affinity for active sites following the order of Pb(II) > Cd(II) > As(III). Characterization analyses using FTIR, SEM, XRD, and XPS confirmed the specific adsorption mechanisms of G-nZVI/WSB for these metal(loid)s, including cation-π interactions, coprecipitation, oxidation, and coordinated complexation. Notably, G-nZVI/WSB exhibited excellent adsorption stability over five cycles of adsorption-desorption, which achieved the efficient purification of multi-contaminated actual wastewaters to meet the standards for wastewater discharge or drinking water. These findings demonstrate the significant potential of G-nZVI/WSB as an eco-friendly and promising nanocomposite for treating metal(loid)-contaminated wastewater.

Synthesis and characterization of guar gum xanthate derivative super adsorbent hydrogel for the capturing of heavy metal ions from wastewater

The Guar Gum Xanthate based hydrogel GGmX-g-poly(AA-co-HEMA) has been successfully synthesized by using the graft copolymerization of two monomers, acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) hydrogel. The synthesis follows the free-radical graft polymerization method. UV-visible spectroscopy (UV), Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Point zero charge (PZC), and field emission scanning electron microscopy (FESEM) were employed for the characterization of the synthesized hydrogel. This hydrogel has shown a high swelling ratio of 430.2 g/g and retention of 75.82% in distilled water which is a notable result. By using GGmX-g-poly(AA-co-HEMA) hydrogel, the maximum percentage of heavy metal ions removal from wastewater was found to be 98.5(±1.5)% and 97.1(±1.5) at optimum pH 6 and 6.5 for Cu2+ and Ni2+ solutions respectively. The Langmuir adsorption isotherm fits best for the adsorption data indicating a monolayer adsorption with maximum adsorption capacity of 423.72 (±26.1) mg/g and 404.85 (±31.4) mg/g for Cu2+ and Ni2+ ions respectively. The pseudo-second-order kinetic model provides the most accurate depiction of adsorption kinetics with rate constant 9.1 × 10−4 (±1.37×10−4)g/(mg.min) for Cu2+ and 8.3 × 10−4 (±1.24×10−4)g/(mg.min) for Ni2+ ions, respectively. The negative ΔG value (-4.75 kJ/mol for Cu2+ and −3.26 kJ/mol for Ni2+ ions) and positive value of ΔH (57.55 (±5.41) kJ/mol for Cu2+ and 40.60(±5.37) kJ/mol for Ni2+ ions) suggested the process to be spontaneous, endothermic, and feasible. It has been found that the hydrogel has excellent regenerative capacity with the % adsorption has been found to be 84.8% for Cu2+ and 82.4% for Ni2+ ions for the fifth cycle.