Langmuir Model Research Articles

Size Effects in Climatic Aging of Epoxy Basalt Fiber Reinforcement Bar.

The purpose of this study was to obtain information on the influence of the size factor on the climatic aging of circular fiber plastics produced by pultrusion. The kinetics of moisture transfer was obtained in humidification and drying modes at 60 °C in samples of epoxy basalt fiber reinforcement bars: after 28 months of exposure in the extremely cold climate of Yakutsk and 30 months of exposure in the moderately warm climate of Gelendzhik. It was shown that the 2D Langmuir model adequately describes the kinetics. The diffusion coefficients in the reinforcement direction for bars with diameters of 6, 8, 10, 16 and 20 mm turned out to be significantly higher than in the radial direction. To clarify the aging mechanism of the bars and the tensile, compressive and bending strength, the coefficient of linear thermal expansion and the glass transition temperature of the epoxy matrix of the bars with a diameter of 6, 8 and 10 mm after 51 months of exposure in Yakutsk and 54 months of exposure in Gelendzhik were measured. It was shown that after climatic exposure, the deformability of the bars decreased with increasing diameter of the bar; the glass transition temperature increased more significantly in the bar with a smaller diameter. In 6 mm diameter bars, the compressive and bending strength limits decreased by 10-25 % due to the plasticizing effect of moisture. With the same depth of moisture penetration into the volume of the samples, its effect on the strength of thin bars was significant, and for thick bars, it was insignificant. An increase in the glass transition temperature by 6 °C, associated with the additional curing of the polymer matrix, occurred in the surface layer of the epoxy basalt fiber reinforcement bars and was revealed in bars with a smaller diameter.

KINETIC AND THERMODYNAMIC ADSORPTION STUDIES ON THE REMOVAL AND TREATMENT OF TEXTILES EFFLUENTS USING ACTIVATED CARBON DERIVED FROM DIOSPYROS MESPILLIFORMIS SEEDS.

An agricultural waste Diospyros mespiliformis seeds were treated, and activated with 30% of 0.3M sodium hydroxide base, to obtain an activated carbon employed in an adsorption process. It was utilize to treat effluent textile water sample from African Textile Manufacturers Limited in Dala, Kano State, Nigeria. Various techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and proximate analysis were employed to investigate the adsorption process. The adsorbent was able to remove the dark red color to colorless found in textile effluents and shown a higher removal affinity for zinc ( 99.4%) and least affinity for nickel (0.11%), also Chromium (Cr) reduced by 39.4%, Copper (Cu) reduced by 20.9%, Iron (Fe) reduced by 91.9% , Manganese (Mg) reduced by 79.3%, are reduced significantly, the PH change from acidic PH 6.4 to neutral PH 7.1, turbidity decrease from 131 to 14 NTU , electrical conductivity change from 723 to 110 ?s·cm?1 .Diospyros mespiliformis seeds activated carbon was used for removal of congo red and malachite green from an aqueous solution. The effect of adsorbent dose, adsorbate concentration and contact time on the process of adsorption was investigated. The optimum dosage was found to be 0.5g had a percentage removal of 98.1% for congo red and 94.4% for malachite green. 10mg/l and 80minute was found to optimum concentration and optimum time in adsorption of congo red and malachite green. The equilibrium, kinetic and thermodynamic properties of the dyes removal were also investigated. The experimental data were modeled using linear regression method of analysis. The correlation coefficient was used as a criterion for model adequacy and acceptance. The pseudo second-order kinetic model was found to best correlate the experimental data with R2 of 0.9523 for CR and 0.9297 for MG. The experimental data were investigated at three different temperature, 305k, 325k and 335k were found to follow the Langmuir model with R2 of 0.9679, 0.9662 and 0.989 for CR and 0.9529, 0.9662 and 0.994 for MG. also were found to follow Temkinp model with with R2 of 0.9549, 0.9318 and 0.9952for CR and 0.9885, 0.9443 and 0.9209 for MG. The negative free gribbs energy indicated that the adsorption processes were spontaneously feasible. The positive values of +31.66KJ/mol and +92.3KJ/mol on both CR and MG indicate that adsorption process has been found to be endothermic in nature. The removal of congo red was found to be more spontaneous and feasible than the removal of malachite green on the adsorbent. From the study, it was deduced that the Diospyros mespiliformis seeds activated with sodium hydroxide was found to be a good adsorbent for the treatment of textile wastewater containing Congo red and Malachite green.

Zeolite-carbon composite synthesis and its adsorption property

In this study, SUZ-4 zeolite-carbon composites were synthesized by a one-step hydrothermal method with solid waste, silica fume (SF), aluminum ash (AA), and chitosan (CS), as raw materials. The composites were analyzed by XRD, SEM, FTIR and BET characterizations. The adsorption capacities of the composites for lead ions (Pb2+) and methyl orange (MO) from aqueous solutions were investigated. Based on the adsorption data, pseudo-second-order model and the Freundlich model were suitable to describe the adsorption process of Pb2+ on the composite, while the pseudo-second-order model and the Langmuir model were preferred to describe the adsorption process of MO on the composite. The maximum adsorption capacity of the composite for Pb2+ was 102.2 mg/g at pH=6, and that for MO was 488.3 mg/g at pH=3. The resulting composites have practical applications as adsorbents for wastewater treatment, thus achieving the goal of “waste for waste”.

Synthesis of composites from coal gasification slag by acid leaching and NaOH activation for efficient adsorption of methylene blue

This study successfully developed a carbon-silicon composite material (C-Si@GS) by acid leaching (HCl) and alkali activation (NaOH) treatments from solid waste CGS and applied to the adsorption of methylene blue (MB). The effects of material dosage, pH, contact time, initial concentration and co-existing ions on the removal of MB were investigated. The results revealed C-Si@GS had good adsorption performance at different pH and cations, suggesting that the material had stable properties. The adsorption of MB by C-Si@GS reached the equilibrium within 12 h, and the removal rate was up to 99 %. The maximum adsorption capacity of C-Si@GS was 456.8 mg/g calculated by Langmuir model (C0 (MB) = 120 mg/L, pH=7 ± 0.2, dosage = 0.6 g/L, and T=298 K). The adsorption process is consistent with Pseudo-secondary and Freundlich models, suggesting that both physical and chemical adsorption processes coexist. Adsorption mechanisms are mainly van der Waals forces, hydrogen bonding, electrostatic attraction and π-π bond interaction, as analyzed by XPS and FT-IR. The composites were regenerated using HCl as desorption agent and the removal rate was about 50 % after 3 cycles. The results illustrated that C-Si@GS can serve as an effective adsorbent for removing MB.

Facile synthesis of ATTM@ZIF-8 modified pullulan hydrogels for enhanced adsorption of Congo red and malachite green

Efficient capture of dyes from wastewater is of great importance for environmental remediation. Yet constructing adsorbents with satisfactory adsorption efficiency and low cost remains a major challenge. This work reports a simple and scalable method for the fabrication of functionalized porous pullulan hydrogel adsorbent decorated with ATTM@ZIF-8 for the adsorption of congo red (CR) and malachite green (MG). The embedding of ammonium tetrathiomolybdate (ATTM) into the ZIF-8 nanoclusters offered additional adsorption sites and enlarged the pore size of the resulting ATTM@ZIF-8. The homogeneous dispersion of the nanoparticles in the three-dimensional network of polysaccharide gels prevents their agglomeration and thus improves the affinity for dye molecules. The resulting adsorbent AZP-20 at optimized composite ratios exhibits high activity, selectivity, interference resistance, reusability and cytocompatibility in dye adsorption applications, and possesses high removal rate of dye in real water systems. Batch experiments demonstrated that the adsorption rate of AZP-20 for MG and CR was 1645.28 mg g−1 and 680.33 mg g−1, and would be influenced by pH conditions. Adsorption kinetics followed pseudo-second-order model. Adsorption isotherms followed Langmuir model for MG and Freundlich model for CR. The adsorption of dye molecules primarily relied on electrostatic interaction (MG) and π-π stacking interaction (CR). Conclusively, the prepared AZPs adsorbent illuminated good application prospects in the treatment of complex component dye wastewater.

Coconut shell carbon via phosphoric acid activation for rhodamine B, malachite green, and methylene blue adsorption – equilibrium and kinetics

This study was aimed at evaluating the removal of different cationic dyes onto phosphoric acid-activated coconut shell carbon. The activated carbon was characterized for surface functional groups, thermal decomposition profiles, surface morphology, and textural properties. The specific area was recorded as 1,221 m2/g with 100% mesoporosity. On molecular basis, the activated carbon adsorbs malachite green, methylene blue, and rhodamine B at maximum capacities of 1.52 mmol/g, 0.80 mmol/g, and 0.58 mmol/g, respectively. It indirectly implies the selectivity of activated carbon toward malachite green, and behaves differently due to steric hindrance of dye molecules. All equilibrium data obeyed Langmuir model, while the kinetic data are closely fitted to pseudo-second order model as concentration increases. To conclude, coconut shell activated carbon is more effective to remove malachite green compared to methylene blue and rhodamine B.

Magnetic iron-based waterworks sludge modified by chitosan and FeS for aqueous Cr(vi) adsorption and reduction.

Heavy metals have been considered an evolving environmental concern due to their harmful and long-lasting impacts. We synthesized a composite of FeS/CS@MIBWS for aqueous Cr(vi) adsorption and reduction utilizing the iron-based waterworks sludge modified by chitosan and FeS. After determining the optimal conditions for the FeS/CS@MIBWS preparation, its Cr(vi) removal capability was evaluated using material characterisation and static Cr(vi) adsorption assays. Cr(vi) elimination by the composite was a pH-dependent process, with pH 2 being the optimum in the range of 2-10. The adsorption process was befitted a pseudo-second-order model, and the equilibrium results agreed well with the Langmuir model. The thermodynamics investigation showed that Cr(vi) removal by the composite has both spontaneous and endothermic nature. Considering the ionic effects, Cl-, SO4 2- and PO4 3- decreased Cr(vi) elimination in the sequence of Cl- < SO4 2- < PO4 3-. The key mechanisms for Cr(vi) elimination were physical and chemical adsorption, chelation, and Cr(vi) reduction into Cr(iii). Furthermore, FeS/CS@MIBWS demonstrated steady reusability (removal effectiveness of 70% after 5 cycles). FeS/CS@MIBWS's rapid, high-performance, reusable, and easily separable adsorption properties make it a promising choice for heavy metal environmental cleaning.

Removal of Moxifloxacin from Aqueous Solutions Using GO/Cr-MOFs.

The composite material, consisting of graphene oxide (GO) and chromium metal-organic frameworks (Cr-MOFs), was successfully synthesized by using a solvothermal method. The organic ligand employed was 2,5-dihydroxyterephthalic acid, while chromium acetate served as the source of the metal. The resulting material underwent characterization through Fourier transform infrared, scanning electron microscopy, and X-ray diffraction techniques. Subsequently, the adsorption capacity of the composite material toward moxifloxacin was evaluated. The results indicated a gradual increase in the moxifloxacin removal rate from GO/Cr-MOFs over time until reaching an equilibrium with a maximum removal rate of 90.4%. Additionally, it was observed that higher temperatures led to a decrease in the adsorption capacity. By incorporating 30 mg of GO/Cr-MOFs into a solution containing 40 ppm of moxifloxacin, the adsorption capacity could be maximized at 222.25 mg/g. Experimental data on MOF adsorption of moxifloxacin were analyzed using pseudo-first-order kinetics (PFO), pseudo-second-order kinetics (PSO), and Langmuir, Freundlich, and Temkin isotherm models for theoretical research purposes. Results showed that the PSO model exhibited a better correlation than the PFO model did. Furthermore, experimental data demonstrated good agreement with the Freundlich isothermal model, suggesting its effectiveness in accurately describing the adsorption process. Henceforth, it can be concluded that chemisorption plays a significant role in removing moxifloxacin by GO/Cr-MOFs. The van't Hoff equation analysis revealed an exothermic and spontaneous nature of moxifloxacin adsorption onto GO/Cr-MOFs. Compared to other materials, the GO/Cr-MOF composite exhibited high potential for applications such as drug removal or related fields.

The potential of Gd doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

The study shows that the addition of gadolinium ions has a significant impact on the structure, morphology, and adsorption properties of Ni-Co spinel ferrite that was synthesized by the sol-gel auto-combustion method. The research also indicates that the higher the Gd content, the greater the increase in the lattice parameter, which suggests that Gd3+ ions uniformly replaced the octahedral Fe3+ ions. The morphology and chemical composition of Gd-doped Ni-Co ferrites have been studied using SEM and EDS. Gd adding to the NiCoFe matrix increases the BET surface area by 50% (from 48 to 72 m2/g) and promotes the formation of mesopores with an average radius from 3.9 to 4.9nm. The pHPZC values of Gd-doped ferrites are in the range of 7.22-7.39, which means that the ferrite surface will acquire a positive charge at natural pH, so this will promote the adsorption of Congo red anionic dye through electrostatic interaction forces. Langmuir, Freundlich, and Dubinin-Radushkevich models were used to explain the mechanism of CR adsorption on the Ni0.5Co0.5GdxFe2-xO4 adsorbent surface. The ionic-covalent parameter has been estimated to describe the surface acid-base properties. Overall, this study highlights the potential of Gd3+ doping as a promising approach for enhancing the adsorption properties of nickel-cobalt ferrites.

Response surface methodology-based optimisation of adsorption of diclofenac and treatment of pharmaceutical effluent using combined coagulation-adsorption onto nFe2O3 decorated water chestnut shells biochar.

This work involved the preparation of pristine and iron nanoparticle-loaded biochar from a water chestnut shell to remove diclofenac sodium (DCF) containing effluent of pharmaceutical origin. To create suitable forecasting equations for the modelling of the DCF adsorption onto the adsorbent, response surface methodology (RSM) was used. The parameters, e.g. pH, adsorbent mass, DCF concentration and contact time, were used for the modeling of adsorption. The RSM model predicts that for 98.0% DCF removal, the ideal conditions are pH 6, an adsorbent dose of 0.5 g L-1, and a contact time of 60 min with an initial adsorbate concentration of 25 mg L-1 at 303 K. The maximum capacity deduced from the Langmuir model was 75.9 mg g-1 for pristine water chestnut shell biochar (pWCBC) and 122.3 mg g-1 for magnetically modified nano-Fe2O3 biochar (mWCBC). Under equilibrium conditions, the Langmuir model was the best-suited model compared to the Temkin and Freundlich models. The adsorption data in this investigation efficiently fitted the pseudo-second-order model, emphasizing that chemisorption or ion exchange processes may be involved in the process. The WCBC demonstrated recyclability after 10 cycles of repeated adsorption and desorption of DCF. A combined coagulation adsorption process removed COD, NH3-N, NO3-, PO43-, and DCF by 92.50%, 86.41%, 77.57%, 84.54%, and 97.25%, respectively. This study therefore shows that coagulation followed by adsorption onto biochar can be a cost-effective substitute for conventional pharmaceutical wastewater treatment.

A generalized adsorption model of CO2-CH4 in shale based on the improved Langmuir model

CO2 enhanced shale gas recovery (CO2-ESGR), as one of the most promising carbon capture, utilization and storage (CCUS) technologies, can both improve the shale gas production for clean energy supply and mitigate greenhouse gas emissions for the goal of carbon neutrality. The adsorption characteristics of CO2 and CH4 in shale play a key role in the reserve assessment of shale gas and the implementation of CO2-ESGR. The problem of accurate prediction of the adsorption and competitive adsorption characteristics of CO2 and CH4 in shale is still one of the main challenges for CO2-ESGR. To bridge the gap, this work developed a generalized prediction model for the adsorption properties of CH4, CO2, and their mixed gas in shale by improving the Langmuir model, covering a large range of temperature, pressure, and total organic carbon content (TOC). The mathematical models for the key parameters of the Langmuir model, the saturated adsorption capacity Q0 and Langmuir pressure PL, were built for the single-component gas based on their functional relationship with temperature and TOC, and for the mixed gas based on their relationship with Q0 and PL of the single-component gas and CO2 content. Then an improved Langmuir model for the adsorption properties of CO2-CH4 in shale was established. The accuracy of the improved model was verified with a relative deviation below 5 % in a large range of temperature (303–363 K), pressure (0–15 MPa) and TOC (1.06 %-3.83 %) by comparing the calculated adsorption with the experimental data. This generalized adsorption model not only ensures the prediction accuracy of CO2-CH4 adsorption characteristics in shale but also expands its application convenience in a large range of temperatures, pressures and TOC, providing a certain theoretical basis for CO2-ESGR technology.

Boron-doping tunes nitrogen species to abundant edge-N and B-N matrix for efficient phosphate removal in capacitive deionization: Additional accessible sites and defective centers

The elimination of eutrophication necessitates the implement of a clean and efficient phosphate removal strategy. Capacitive deionization (CDI) is recently regarded a promising approach for removing pollutants from aqueous environment with high-efficiency, facile operation, and low-energy consumption. Development of electrode materials with good properties is crucial for CDI. In this study, novel edge-N-modified boron-doped hierarchical carbon composites (MBCNs) were prepared via a hard template strategy for phosphate electrosorption. According to the pseudo-second-order kinetic, the MBCN2 electrode exhibited a dynamic capacity of 196.02 mg PO43− g−1 in 150 min with an initial concentration of 100 mg PO43− L−1 at 1.2 V. And it also demonstrated an exceptional saturation capacity of 399.70 mg PO43− g−1 under the Langmuir model. Based on theoretical analysis and experimental results, the incorporation of boron atoms in the carbon framework indicated a dual reinforcement. This included an enhanced proportion of edge-N modifications for defective centers and sufficient high-polarity B-N matrix for additional available active sites. The joint contribution of edge-N and B-N matrix revealed favorable electrical double layer capacitance, which resulted in good phosphate removal performance. This work disclosed the synergistic impact of dual nonmetallic atom doping, providing insights into the efficient phosphate removal anode for CDI.

Sustainable application of modified Luffa cylindrica biomass for removal of trimethoprim in water by adsorption with process optimization.

The present study describes a set of methodological procedures (seldom applied together), including (i) development of an alternative adsorbent derived from abundant low-cost plant biomass; (ii) use of simple low-cost biomass modification techniques based on physical processing and chemical activation; (iii) design of experiments (DoE) applied to optimize the removal of a pharmaceutical contaminant from water; (iv) at environmentally relevant concentrations, (v) that due to initial low concentrations required determination by ultra-performance liquid phase chromatography coupled to mass spectrometry (UPLC-MS/MS). A central composite rotational design (CCRD) was employed to investigate the performance of vegetable sponge biomass (Luffa cylindrica), physically processed (crushing and sieving) and chemically activated with phosphoric acid, in the adsorption of the antibiotic trimethoprim (TMP) from water. The optimized model identified pH as the most significant variable, with maximum drug removal (91.1 ± 5.7%) achieved at pH 7.5, a temperature of 22.5°C, and an adsorbent/adsorbate ratio of 18.6mgµg-1. The adsorption mechanisms and surface properties of the adsorbent were examined through characterization techniques such as scanning electron microscopy (SEM), point of zero charge (pHpzc) measurement, thermogravimetric analysis (TGA), specific surface area, and Fourier-transform infrared spectroscopy (FTIR). The best kinetic fit was obtained by the Avrami fractional-order model. The hypothesis of a hybrid behavior of the adsorbent was suggested by the equilibrium results presented by the Langmuir and Freundlich models and reinforced by the Redlich-Peterson model, which achieved the best fit (R2 = 0.982). The thermodynamic study indicated an exothermic, spontaneous, and favorable process. The maximum adsorption capacity of the material was 2.32 × 102µgg-1 at an equilibrium time of 120min. Finally, a sustainable and promising adsorbent for the polishing of aqueous matrices contaminated by contaminants of emerging concern (CECs) at environmentally relevant concentrations is available for future investigations.

Efficient Adsorption and Elimination of Tm3+ for Enhanced Seed Germination Using Pillar[5]Arene Polymer.

While rare earth elements (REEs) are essential for modern technology, their production methods raise concerns for agriculture. Researchers are now exploring ways to control and recycle REEs pollution, aiming to minimize agricultural impacts and potentially even develop methods to utilize these elements for improved crop yields. Regarding this issue, a new type of pillar[5]arene polymer (Pol-P[5]-BTZP) has been designed and synthesized by click reaction to enhance the efficiency of adsorption and recovery of rare earth metals. This polymer incorporates the unique structure of 2,6-di-1,2,3-triazolyl-pyridine. The results of various analyses revealed that Pol-P[5]-BTZP exhibits excellent thermal stability, a high specific surface area, and well-distributed networks of micropores and mesoporous structures. The adsorption capacity of Pol-P[5]-BTZP for Tm3+, a representative REE, was evaluated using the Langmuir and Freundlich isothermal adsorption models with a maximum adsorption capacity (Qmax) of 127.71 mg/g. Furthermore, the versatility of Pol-P[5]-BTZP in adsorption and recovering various REEs was tested. In addition to its adsorption capabilities, the potential of Pol-P[5]-BTZP for rare earth recovery and reuse was assessed through experiments on the impact of Tm3+ and La3+ on seed germination. These experiments demonstrated the wide-ranging applicability of Pol-P[5]-BTZP in recovering and reusing REEs for green agriculture.

A novel hydrogel composite of chitosan-phytic acid complex with PAAm: Characterization and adsorptive properties for UO22+and methylene blue

The composite of a polyelectrolyte combination of chitosan and phytic acid (CsPa) and its entrapped form in polyacrylamide (PAAmCsPa) were synthesized. The composites were characterized by a number of methods including ATR-FTIR, SEM-EDX, XRD and XPS. The adsorptive properties of CsPa and PAAmCsPa were analyzed and modelled for UO22+ and methylene blue (MB+). The results showed that the composites exhibited physico-chemical properties that were both inherited from the components as well as unique to them. The isotherms of UO22+ and MB+ were L-type Giles isotherms. The adsorption kinetics followed the pseudo-second-order model, in contrast to the Langmuir model, which predicts first-order kinetics for both species. According to the Weber-Morris model, the nature of the adsorption process was ion exchange and/or complex formation for both composites and ions. The thermodynamics showed that the adsorption process was endothermic (ΔH > 0), with increasing entropy (ΔS > 0) and spontaneous (ΔG < 0). The reusability tests of the composites for UO22+ adsorption showed that the composites were substantially reusable for 6 cycles. The composites were selective for UO22+ over MB+ ions, and UO22+ adsorption increased significantly when MB+ adsorbed composites were used. Reproducible measurements demonstrating the storability of the composites were obtained over a period of approximately one year.

Core-shell V2O5- Gum ghatti grafted poly (acrylamide-co-methacrylic acid) adsorbent for the removal of methylene blue dye in water: Kinetic, equilibrium and thermodynamic studies

Herein, vanadium pentoxide (V2O5) encapsulated Gum ghatti grafted poly(acrylamide-co- methacrylic acid) adsorbent was synthesized to remove methylene blue dye from water. The materials were characterized by FTIR, TEM, SEM, Raman and XRD analysis. Batch adsorption studies were performed on the materials. Several variables' effects on methylene blue removal, including pH, contact time, initial dye concentration, and adsorbent dosage, were examined. Kinetics and thermodynamic analysis were also carried out for the adsorbent-adsorbate interaction to determine the maximum adsorption and mechanism for adsorption. By using UV-Vis spectrophotometric analysis, the dye concentration was evaluated both before and after adsorption. Langmuir, Freundlich, and Dubini-Radushkevic's isotherm models were used to analyze the adsorption data. Results showed a maximum adsorption efficiency of 92 % at a pH of 9 and 0.2 g as the maximum adsorbent dosage. The study followed the Langmuir isotherm model with a correlation coefficient (R2) of 0.9995. The results from the kinetic studies show a pseudo-second-order mechanism. The negative values of the Gibbs free energy change ΔG° ranging from −10.57 KJmol−1 to −9.64 Kmol−1 within the temperatures of 298 K to 313 K is an indication of a spontaneous process. A negative enthalpy change (ΔH° = −29.05 KJmol−1) shows an exothermic process and a negative entropy change (ΔS° = −0.06 KJmol−1) represents a highly ordered system. ANOVA in Microsoft Excel and other statistical analyses were used to evaluate the effects of time, pH, concentration, dose, temperature, and other factors on the effectiveness of dye adsorption. Importantly, every parameter that was investigated showed statistically significant impacts on the removal of dye (p < 0.05), revealing their important impact on the adsorption process.

Polycyclic aromatic hydrocarbon derivatives onto polar microplastics of polyurethane: equilibrium, thermodynamics, and kinetics of monolayer-multilayer adsorption.

The study of the adsorption of polycyclic aromatic hydrocarbons on microplastics (MPs) has attracted much attention as to how microplastics can act as carriers of these pollutants. Polyurethane (PU) is one of the MPs found in aquatic environments, containing different functional groups it can interact with polar and nonpolar molecules. PAH derivatives (dPAHs) present different properties and thus can be adsorbed by different interactions; thus, this study investigated the adsorption of fluorene (FLN), dibenzothiophene (DBT), dibenzofuran (DBF), and carbazole (CBZ) onto PU MP. The Langmuir, Freundlich, and BET isotherm models were examined, and the BET model best fitted. The adsorption was a nonspontaneous process, exothermic for mono- and multilayer formation for FLN, DBT, and CBZ, and endothermic for DBF monolayer formation. The adsorption monolayer was formed by van der Waals forces, H─bonding, and π─π interactions, while the formation of the multilayer can be explained by π─π and hydrophobic interactions. The pseudo-second-order model proved to be more consistent for the adsorption of dPAHs. The adsorption in artificial seawater shows no significant differences for the monolayer but favored the adsorption multilayer due to the salting-out effect. Due to the existence of several adsorption mechanisms, PU MP interacts with dPAHs in greater quantities when compared to a MP with a simpler structure.

The Sustainable Remediation of Antimony(III)-Contaminated Water Using Iron and Manganese-Modified Graphene Oxide–Chitosan Composites: A Comparative Study of Kinetic and Isotherm Models

This study introduces a series of Fe/Mn-GOCS composites using high-temperature impregnation with graphene oxide and chitosan as substrates, modified by diverse manganese salts, including MnCl2∙4H2O, KMnO4, and MnSO4. Among these, FeCl2/MnSO4-GOCS demonstrated the highest adsorption capacity for Sb(III), peaking at 57.69 mg/g. The adsorption performance was extensively evaluated under various conditions, such as different initial concentrations, pH levels, solid–liquid ratios, and adsorption durations. It was observed that when the Fe/Mn molar ratio exceeded 4:1, there was a notable decrease in both the adsorption capacity and removal rate. Kinetic analyses using the pseudo-second-order model revealed a better fit (R2 &gt; 0.99) compared to the pseudo-first-order model, indicating that chemisorption dominated the adsorption process. Additionally, isothermal modeling highlighted the efficiency of Fe/Mn-GOCS, particularly in high-concentration environments, with the Sips model demonstrating the best fit, integrating characteristics of both Langmuir and Freundlich models. These results not only offer a robust theoretical and practical basis for efficient Sb(III) removal but also underscore the potential of multi-metal-modified adsorbents as sustainable solutions for environmental remediation.

Fabrication of nanozeolite-Y/chitosan composite based on rice husks for efficient adsorption of methylene blue dye: kinetic and thermodynamic studies

In this work, three solid adsorbents were synthesized, namely, nanozeolite-Y prepared from rice husks ash by a sol-gel method as a green biosource (ZN), chitosan as a cationic biopolymer (CS), and nanozeolite-Y/chitosan composite (CSZ). An eco-friendly composite that consists of chitosan and nanozeolite-Y was used to combine the advantages of nanoparticles with biopolymers two materials to increase the removal % of methylene blue dye. All the synthetized solid adsorbents were investigated using TGA, nitrogen adsorption, SEM, TEM, FTIR, XRD, and zeta potential. The results showed that CSZ particles had a high specific surface area (432.3 m2/g), mesoporosity (with an average pore diameter of 2.59 nm), a smaller TEM particle size (between 28.6 and 60.7 nm), a lot of chemical functional groups, and high thermal stability. CSZ exhibited the maximum adsorption capacity (141.04 mg/g) towards methylene blue. The adsorption nature of methylene blue onto CS and CSZ is endothermic, spontaneous, and a physical adsorption process, while it is exothermic, nonspontaneous, physical adsorption process in the case of ZN, as confirmed by thermodynamic results. Pseudo-second order, Elovich, Dubinin-Radushkevich, Freundlich, Langmuir, Temkin, and adsorption models all fit the MB adsorption well, with correlation coefficients reaching about 0.9997. Nitric acid was found to be the best desorbing agent, with a desorption efficiency of about 99%.

Selective solid phase extraction of folic acid from tomato as a biological source with a magnetic molecularly imprinted polymer measured by fluorescence spectroscopy

AbstractA novel magnetic molecular-imprinted polymer (MMIP) was used to selectively extract folic acid directly from real samples. Folic acid was used as template molecule, Fe3O4/SiO2-3-triethoxysilyl-propyl-acrylamide as functional monomer, azobisisobutyronitrile as initiation, ethylene glycol dimethacrylate as crosslinker agent, and acrylamide as the secondary monomer in a mixed ethanol-water solvent. The effect of different parameters on the extraction efficiency was studied, and the optimum conditions were established as follows: the concentrations of crosslinking and template were fixed at 0.05 and 0.06 g, absorption percentage was 96.5, pH was adjusted to 8, and extraction time was 8 h with a temperature of 25 °C. By examining the effect of pH, we tried to investigate the effect of the amide groups that present in MMIP and its intermolecular hydrogen interaction with folic acid. After optimising the effective parameters in polymer synthesis and adsorption rate, a magnetic imprinting dispersive solid-phase extraction method combined with fluorescence spectrophotometry at λem = 367 nm (MMIP-DSPE-FL) was constructed for sensitive determination of folic acid in tomato samples. The limit of quantification (LOQ) and limit of detection (LOD) values were 30.00 ± 0.01 μg L−1 and 10.00 ± 0.03 μg L−1, respectively, after the MMIP-DSPE preconcentration. Three tomato samples were analysed to give recoveries in the range of 80.2–81.6%, with relative standard deviation values below 0.6% (n = 3). The prepared MMIP-DSPE showed high selectivity toward folic acid, which could be used six times without changing adsorption capacity. The adsorption isotherm of the folic acid-imprinted polymer pursued the Langmuir model (RL = 0.029), and the kinetics model followed pseudo-first-order (R2 = 0.9974).