Adsorption isotherms and thermochemical data of FD&C Red n° 40 binding by Chitosan

Sustainable heavy metal (Cr(VI) ion) remediation: Ternary blend approach with chitosan, carboxymethyl cellulose, and bioactive glass

Heavy metal pollution poses a significant environmental challenge to worldwide, especially in developing countries. This study focuses on eliminating the heavy metal chromium (VI) ion from wastewater, employing an eco-friendly and economical ternary blend composed of Chitosan (CS), Carboxymethyl cellulose (CMC), and bioactive glass (BAG). The innovative bioactive glass is crafted from biosilica extracted from biowaste of cow dung ash, calcium oxide from eggshell ash, and phosphorus pentoxide. The CS/CMC/BAG blend is prepared via sol-gel method and characterized using XRD, FT-IR, TGA, BET, TEM and SEM revealing a porous structural morphology during blending. Batch adsorption studies explore various parameters such as pH, adsorbent dose, contact time and initial metal ion concentrations. The results are then evaluated through adsorption kinetics and adsorption isotherms (Langmuir, Freundlich, D-R, and Temkin isotherm modeling). The investigation concludes that the optimal conditions for Cr (VI) removal are pH 3, contact time of 300 min, adsorbent dosage of 0.5 g, and an initial metal ion concentration of 50 ppm. The adsorption isotherm model indicates an excellent fit with the Freundlich isotherm (R2 = 0.9576) and pseudo-second-order kinetics (R2 = 0.981). In summary, the CS/CMC/BAG ternary blend exhibits a remarkable ability to effectively remove heavy metal Cr(VI) ions from industrial wastewater.

Enhancing Zn (II) recovery efficiency: Bi-divalent nickel-cobalt ferrite spinel NiXCo1-xFe2O4 as a Game-changing Adsorbent-an experimental and computational study

This study presents a comprehensive investigation into NiXCo1-xFe2O4 (x = 0.5) spinel nanoparticles synthesized through a one-pot hydrothermal method using Co(NO3)2.6H2O and Ni(NO3)2.6H2O salts. XRD, FTIR, FESEM, and VSM analyses confirmed a cubic structure of NiXCo1-xFe2O4 (x = 0.5) nanoparticles without impurities. These nanoparticles exhibit efficient Zn (II) adsorption characteristics, following Langmuir isotherm and pseudo-second-order kinetics. The maximum adsorption capacity was measured to be 666.67 mg g-1 at pH = 7, with mechanisms involving both electrostatic attraction and cation exchange. Desorption studies indicate more than 75% Zn (II) recovery in an acidic environment (pH = 2) after three cycles. Computational analysis was used to validate the experimental results through Molecular Dynamics simulations, initially focusing on NiXCo1-xFe2O4 (x = 0.5). Further exploration involved variations in x at 0.25 and 0.75 to identify the optimal Ni and Co ratio in this bivalent cation spinel ferrite. Computational analyses reveal the superior performance of NiXCo1-xFe2O4 (x = 0.75) in Zn (II) removal, supported by radial distribution analysis, VdW energy, Coulombic energy, mean square displacement (MSD), root mean square displacement (RMSD), and interaction energy. This comprehensive study provides valuable insights into the adsorption behavior and structural stability of NiXCo1-xFe2O4 nanoparticles, showcasing potential applications in Zn (II) removal.

Highly Efficient Removal of 2,4,5-Trichlorophenoxyacetic Acid by Adsorption and Photocatalysis Using Nanomaterials with Surface Coating by the Cationic Surfactant

Extensive removal of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) using titania (TiO2) nanoparticles by adsorption and photocatalysis with a surface coating by cetyltrimethylammonium bromide (CTAB) is reported. The CTAB-coated TiO2 nanoparticles (CCTN) were characterized by FT-IR, zeta-potential measurements, and UV-vis diffuse reflectance spectroscopy (UV-vis-DRS). 2,4,5-T removal increased significantly after surface modification with CTAB compared with bare TiO2 nanoparticles. Optimal parameters affecting 2,4,5-T removal were found to be pH 4, CCTN dosage 10 mg/mL, and adsorption time 180 min. The maximum adsorptive removal of 2,4,5-T using CCTN reached 96.2% while highest adsorption capacity was 13.4 mg/g. CCTN was also found to be an excellent photocatalyst that achieved degradation efficiency of 99.2% with an initial concentration of 25 mg/L. The removal mechanisms of 2,4,5-T using CCTN by both adsorption and photocatalysis are discussed in detail based on changes in functional group vibrations and surface charge. Our results indicate that CCTN is an excellent material for 2,4,5-T removal in water by both adsorption and photocatalysis.

Nanomaterials for sustainable remediation: efficient removal of Rhodamine B and lead using greenly synthesized novel mesoporous ZnO@CTAB nanocomposite

This study explores the dual applications of a greenly synthesized ZnO@CTAB nanocomposite for the efficient remediation of Rhodamine B (RhB) and lead (Pb). The synthesis method involves a sustainable approach, emphasizing environmentally friendly practices. FT-IR, XRD, FESEM, zeta potential, and particle size analyzer (PSA), BET, and UV-VIS were used to physically characterize the zinc oxide and CTAB nanocomposite (ZnO@CTAB). The size and crystalline index of ZnO@CTAB are 77.941 nm and 63.56% respectively. The Zeta potential of ZnO@CTAB is about - 22.4 mV. The pore diameter of the ZnO@CTAB was 3.216 nm, and its total surface area was 97.42 m2/g. The mechanism of adsorption was investigated through pHZPC measurements. The nanocomposite's adsorption performance was systematically investigated through batch adsorption experiments. At pH 2, adsorbent dose of 0.025 g, and temperature 50 °C, ZnO@CTAB removed the most RhB, while at pH 6, adsorbent dose of 0.11 g, and temperature 60 °C, ZnO@CTAB removed the most Pb. With an adsorption efficiency of 214.59 mg/g and 128.86 mg/g for RhB and Pb, the Langmuir isotherm model outperforms the Freundlich isotherm model in terms of adsorption. The pseudo-2nd-order model with an R2 of 0.99 for both RhB and Pb offers a more convincing explanation of adsorption than the pseudo-1st-order model. The results demonstrated rapid adsorption kinetics and high adsorption capacities for RhB and Pb. Furthermore, there was minimal deterioration and a high reusability of ZnO@CTAB till 4 cycles were observed.

Effective Removal of Carcinogenic Azo Dye from Water Using Zea mays-Derived Mesoporous Activated Carbon

Addressing industrial wastewater treatment challenges and removing hazardous organic pollutants, such as carcinogenic methyl orange (MO) and azo dyes, is a pressing concern. This study explores the use of the Zea mays envelope, an agricultural waste product, to produce Z. mays activated carbon (ZMAC) through the chemical activation of maize envelopes with phosphoric acid. Various analytical techniques, including FTIR, XRD, TGA, DSC, and SEM, characterize ZMAC. Results show that ZMAC exhibits an impressive monolayer adsorption capacity of 66.2 mg/g for MO. The Langmuir isotherm model fits the experimental data well, indicating monolayer coverage of the MO on the ZMAC surface. The pH-sensitive adsorption process demonstrates an optimal removal efficiency at pH 4. ZMAC follows the pseudo-second-order kinetic model, and diffusion rate constant analysis identifies three consecutive stages in the adsorption process. Moreover, the uptake of MO ions by ZMAC is identified as an exothermic and spontaneous process. Reusability tests demonstrate efficient regeneration of ZMAC up to five times with 1 mL of 2 M HNO3 in each cycle, without sorbent mass loss. Thermodynamic analysis shows an increase in the uptake capacity from 66.2 to 73.2 mg/g with temperature elevation. This study offers practical solutions for industrial wastewater treatment challenges, providing an environmentally sustainable and effective approach to mitigate the risks associated with hazardous organic pollutants.

Imidazolate framework material for crude oil removal in aqueus media: Mechanism insight

Considerable amount of produced water discharged by the oil industry contributes to an environmental imbalance due to the presence of several components potentially harmful to the ecosystem. We investigated the factors influencing the adsorption capacity of Zinc Imidazolate Framework-8 (ZIF-8) in finite bath systems for crude oil removal from petroleum extraction in synthetic produced water. ZIF-8, experimentally obtained by solvothermal method, was characterized by XRD, FTIR, TGA, BET and its point of zero charge (pHpcz) was determined. Synthesized material showed high crystallinity, with surface area equal to 1558 m2 g-1 and thermal stability equivalent to 400 °C. Adsorption tests revealed, based on the Sips model, that the process takes place in a heterogeneous system. Additionally, intraparticle diffusion model exhibited multilinearity characteristics during adsorption process. Thermodynamic investigation demonstrated that adsorption process is spontaneous and exothermic, indicating a physisorption phenomenon. These properties enable the use of ZIF-8 in oil adsorption, which presented an adsorption capacity equal to 452.9 mg g-1. Adsorption mechanism was based on hydrophobic interactions, through apolar groups present on ZIF-8 structure and oil hydrocarbons, and electrostatic interactions, through the difference in charges between positive surface of adsorbent and negatively charged oil droplets.

Adsorptive removal of dissolved Iron from groundwater by brown coal - A low-cost adsorbent

Iron (Fe) contamination in groundwater is a widespread issue, necessitating the implementation of efficient removal methods to ensure the provision of safe drinking water. To contribute to the development of effective and sustainable solutions for addressing Fe contamination problems, this study investigated the potential of natural brown coal (BC) as a cost-effective adsorbent for removing dissolved Fe from groundwater. The study also explored the regeneration and reusability potential, as well as the effects of operational parameters, including pH, temperature, adsorbate concentration, and competitive ions, on the adsorption process. The equilibrium data fitted very well with the Langmuir model (R2 = 0.983), yielding a maximum adsorption capacity of 1.41 mg g-1. The adsorption kinetics were well described by the pseudo-second-order kinetic model. Notably, higher solution pH, Fe concentration, and temperature values led to higher Fe removal. The adsorption process exhibited endothermic behaviour, accompanied by an increase in randomness at the interface between the BC and the Fe. The BC was easily regenerated and maintained good adsorption capacity after four cycles of adsorption and regeneration. However, the presence of high-valent cations could affect its performance. Fourier-transform infrared spectrometry, coupled with structural and aqueous solution elemental analyses, revealed a synergetic adsorption mechanism, comprising ion-exchange with mono and divalent basic cations and complexation with functional groups. Overall, these findings highlight the potential of brown coal as a cost-effective adsorbent for Fe removal from groundwater.

Surface interaction of vancomycin with polystyrene microplastics and its effect on human serum albumin

Microplastics have a well-documented ability to adsorb various chemicals and contaminants found in the environment. By similar mechanisms, when medicines are stored in plastic packaging, the leaching of plastics into the contents poses the risk of possible toxicity and decreased drug efficacy. The work thus examines the presence of two categories of anthropogenic materials - microplastics (MPs) and medications - with their possible combined effects and fate in biological systems. A study on the kinetics and isotherm of the adsorption of vancomycin hydrochloride on the surface of polystyrene microspheres is performed, and the best-fitting models are obtained respectively as the pseudo-second-order model and the Temkin isotherm. Further, the interaction of each of, the drug, MPs and drug-adsorbed MPs with human serum albumin (HSA), the model protein chosen to validate the potential toxicity in humans, is determined by fluorescence spectroscopy. A thermodynamic analysis of this protein-ligand interaction shows that the process is spontaneous, endothermic and entropically favoured, and that hydrophobic forces operate between the interacting species. An unfolding of HSA is observed, disrupting its functions like the esterase activity. Competitive binding experiments with Warfarin and Ibuprofen as specific site markers on HSA reveal that all the studied ligands bind non-specifically to HSA.

Examination of the Factors Inhibiting CO2 Adsorption on Coal: A Case Study from Shallow-Depth Low-Rank Coal Seams

Understanding the inhibitory factors affecting the adsorption of CO2 on low-rank coal from shallow-depth coal seams is essential to identify potential coal seams for CO2 sequestration. The CO2 adsorption capacity of shallow-depth coals was measured at a low pressure on raw and dry coals. The samples were also prepared for organic analyses, scanning electron microscopy analyses, and low-temperature nitrogen adsorption analyses to evaluate the CO2 adsorption and identify the inhibitory factors. An investigation was conducted to determine how CO2 adsorption occurs on coal by fitting experimental data to adsorption isotherm models, followed by analyzing the results based on the statistical analysis. In addition, this study used Henry's law, surface potential, and Gibbs free energy to identify the adsorption inhibitor between CO2 and coal. The CO2 adsorption experiment was conducted on raw coal with a moisture content of 15.18-20.11% and dry coal with no moisture. The experimental data showed that the CO2 adsorption capacity in dry coal was 1.6-1.8 times greater than that in raw coal. A fitting graph between the adsorption data and the isotherm model indicated that CO2 adsorption on coal occurred on monolayers and multilayers under raw and dry conditions. Statistical evaluation of the adsorption isotherm models showed that the Langmuir and Freundlich models aligned more closely to the experimental data. According to this result, low-pressure adsorption of CO2 on coal occurred in monolayers and multilayers under raw and dry conditions. Coal containing a high huminite content had a higher potential for CO2 adsorption, and the drying increased the positive relationship. On the other hand, coal containing high inertinite content inhibited CO2 adsorption onto the coal, but the drying process did not adversely affect CO2 adsorption. Furthermore, coal with high moisture and inertinite content inhibited the affinity, accommodation, and spontaneous CO2 adsorption onto the coal. CO2 adsorption could lead to swelling, but moisture loss opened more sites and micropores, resulting in the swelling effect not closing all micropores in dry coal. Based on these results, coal seams with low moisture and inertinite content are the most promising for CO2 adsorption. Altogether, this study provides an understanding of the percentage of inhibitor factors that affects CO2 adsorption on low-rank coal from shallow depths, which may lead to different CO2 adsorption capacities.

Synthesis, Characterization, and Adsorptive Characteristics of Radiation-Grafted Glycidyl Methacrylate Bamboo Fiber Composites

In the present study, a biosorbent was prepared through the radiation-induced graft polymerization (RIGP) technique by using a glycidyl methacrylate (GMA) monomer. Functionalized bamboo materials were used for grafting. The grafting percentage (G %) of GMA on bamboo fibers was assessed based on the optimization of the absorbed dose and concentration of the monomer. The chemical modification of the polymerized product into the sulfonated form of the grafted biopolymer was carried out by using sodium sulfite solution. The modification of the biopolymer at various stages was analyzed by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques. By performing scanning electron microscopy (SEM), the morphological changes of the prepared biopolymer were analyzed. The temperature stability of the synthesized material was assessed by the thermogravimetric analysis (TGA) technique. The prepared sulfonated biosorbent was used in the batch adsorption study for the uptake of copper. We examined a variety of variables, including pH, adsorbent dosage, and time. The adsorption kinetics were studied using pseudo-first-order (PFO) and pseudo-second-order (PSO) models. Adsorption isotherms and thermodynamic parameters were also applied to study the adsorption capacity of the biosorbent. The maximum copper adsorption capacity was found to be 198 mg g-1 from the Langmuir isotherm. Copper adsorption followed PSO kinetics (R2 = 0.999). This inexpensive and eco-friendly biosorbent removed 96% of copper ions from the solution.

Green wastewater treatment of repurposed COVID-19 therapy (levofloxacin) using synthesized magnetite pectin nanoparticles, comparison with mesoporous silica nanoparticles

RATIONALE

Antibiotics have been detected worldwide in the aquatic environment. Moreover, certain classes of antibiotics have been repurposed for the management of COVID-19, which increased their use and presence in wastewater. Their occurrence even in low concentrations leads to the development of antibiotic resistance.

METHODOLOGY

Magnetite pectin nanoparticles (MPNP) were fabricated and compared to an established model of mesoporous silica nanoparticles (MSNP). Our studied adsorbate is levofloxacin, a fluoroquinolone antibiotic, commonly used in managing COVID-19 cases.

RESULTS

The influence of various factors affecting the adsorption process was studied, such as pH, the type and concentration of the adsorbent, contact time, and drug concentration. The results illustrated that the optimum adsorption capacity for antibiotic clearance from wastewater using MPNP was at pH 4 with a contact time of 4 h; while using MSNP, it was found to be optimum at pH 7 with a contact time of 12 h at concentrations of 10 µg/mL and 16 g/L of the drug and nanoparticles, respectively, showing adsorption percentages of 96.55% and 98.89%. Drug adsorption equilibrium data obeyed the Sips isotherm model.

DISCUSSION AND CONCLUSION

HPLC assay method was developed and validated. The experimental results revealed that the MPNP was as efficient as MSNP for removing the antibacterial agent. Moreover, MPNP is eco-friendly (a natural by-product of citrus fruit) and more economic as it could be recovered and reused. The procedure was evaluated according to the greenness assessment tools: AGREE calculator and Hexagon-CALIFICAMET, showing good green scores, ensuring the process's eco-friendliness.

Conversion of waste biomass to designed and tailored activated chars with valuable properties for adsorption and electrochemical applications

Waste biomass, a renewable energy source, is inexpensive material that has great potential in sorption and electrochemical application. The selected waste materials (corncobs, coconut shells, walnuts, and pistachio husks) allow to close the production cycle and enable material recycling, which are important aspects in the hierarchy of waste management. The proposed methodology for production and activation of biochars can be used industrially due to highly porous structure, developed surface area, and sorption ability of the obtained activated carbons (AC). A significant increase (from 4 up to more than 10 times) in specific surface area (SSA) is observed for all samples after the CO2 activation process (0.5 h at 800 °C) up to 725 m2 g-1 for corncobs, 534.9 m2 g-1 for pistachio husks, 523 m2 g-1 for coconut shells, and 393 m2 g-1 for walnut husks. The highest value of SSA is achieved for the AC derived from corncobs. This material is evaluated for use as an adsorbent, revealing 99% removal of Rhodamine B (dye/AC ratio of 0.0017) and 69% removal of chromium (dye/AC ratio of 0.0028). Based on the adsorption kinetics analysis, it is demonstrated that the Cr(VI) undergoes physical adsorption, while RhB undergoes chemisorption. In addition, corncob-derived AC exhibits superior electrochemical performance in 6 M KOH compared to the nonactivated biochar. A specific capacitance of 70 F g-1 at 5 A g-1 is achieved, along with outstanding rate capability (45 F g-1 at 50 A g-1) and cycling stability (94% at 10 A g-1 after 10,000 cycles). In contrast, the nonactivated sample shows only 34 F g-1 at 5 A g-1 and 13 F g-1 at 50 A g-1, with a stability of 91.4%.

Adsorption of organophosphorus malathion pesticide from aqueous solutions using nano-polypropylene-titanium dioxide composite: Equilibrium, kinetics and Optimization studies

Purpose

The purpose of this study was to investigate the applicability of the adsorption process of a persistent organophosphorus pesticide (malathion) from aqueous solutions by using titanium dioxide- polypropylene nanocomposite (Nano-PP/TiO2).

Methods

The structure of Nano-PP/TiO2 was specified by field emission scanning electron microscopes (FE-SEM), fourier-transform infrared spectroscopy (FTIR), brunauer-emmett-teller (BET), and transmission electron microscope (TEM) technologies. Response surface methodology (RSM) was applied to optimize the adsorption of malathion onto Nano-PP/TiO2 and investigates the effects of various experimental parameters including contact time (5-60 min), adsorbent dose (0.5-4 g/l) and initial malathion concentration (5-20000 mg/l). Extraction and analysis of malathion were performed by dispersive liquid-liquid microextraction (DLLME) coupled with a gas chromatography, coupled with flame ionization detector (GC/FID).

Results

The isotherms obtained for Nano-PP/TiO2 revealed that it was a mesoporous material with a total pore volume of 2.06 cm3/g, average pore diameters of 2.48 nm and a surface area of 51.52 m2/g. The obtained results showed that the Langmuir type 2 was the best-fitted model for delegating the equilibrium data of isotherm studies with adsorption capacity of 7.43 mg/g, and pseudo-second-order type 1 for kinetic model. The optimized conditions to achieve the maximum removal (96%) were at a malathion concentration of 7.13 mg/L, contact time of 52 min and adsorbent dose of 0.5 g/L.

Conclusion

Due to its efficient and appropriate function in adsorbing malathion from aqueous solutions, it was revealed that Nano-PP/TiO2 can be used as an effective adsorbent as well as in further studies.

Green synthesize of nano-MOF-ethylcellulose composite fibers for efficient adsorption of Congo red from water

Two novel MOF- ethyl cellulose (EC)- based nanocomposites have been designed and synthesized in water by electrospinning and applied for adsorption of congo red (CR) in water. Nano- Zeolitic Imidazolate Framework-67 (ZIF-67), and Materials of Institute Lavoisier (MIL-88A) were synthesized in aqueous solutions by a green method. To enhance the dye adsorption capacity and stability of MOFs, they have been incorporated into EC nanofiber to prepare composite adsorbents. The performance of both composites in the absorption of CR, a common pollutant in some industrial wastewaters, has then been investigated. Various parameters including initial dye concentration, the dosage of the adsorbent, pH, temperature and contact time were optimized. The results indicated 99.8 and 90.9% adsorption of CR by EC/ZIF-67 and EC/MIL-88A, respectively at pH = 7 and temperature at 25 °C after 50 min. Furthermore, the synthesized composites were separated conveniently and successfully reused five times without significant loss of their adsorption activity. For both composites, the adsorption behavior can be explained by pseudo-second-order kinetics, Intraparticular diffiusion and Elovich models demonstrated that the experimental data well matched to the pseudo-second-order kinetics. Intraparticular diffiusion model showed that the adsorption of CR on EC/ZIF-67 and EC/MIL-88a took place in one and two steps, respectively. Freundlich isotherm models and thermodynamic analysis indicated exothermic and spontaneous adsorption.

Effective toluene removal from aqueous solutions using fast pyrolysis-derived activated carbon from agricultural and forest residues: Isotherms and kinetics study

In this study, the production and characterization of activated carbons (ACs) from agricultural and forest residue using physical activation are discussed. Biomass-based biochars produced during fast pyrolysis process is introduced as alternative precursors to produce AC and the integrated process for the co-production of porous adsorbent materials from biochar via the fast pyrolysis process is suggested. Moderate surface areas and good adsorption capacities were obtained from switchgrass (SWG) and pine tops (PT) based AC. The surface areas were 959 and 714 m²/g for SWG- and PT-based AC, respectively. The adsorption capacities using toluene as pollutant for two model systems of 180 and 300 ppm were measured and ranged between 441-711 and 432-716 mg/g for SWG-based and PT-based AC, respectively. The nitrogen adsorptive behavior, Lagergren pseudo-second-order kinetic (PSOK) model and kinetics isotherms studies describe a heterogeneous porous system, including a mesoporous fraction with the existence of a multilayer adsorption performance. The presence of micropores and mesopores in SWG- and PT-based AC suggests potential commercial applications for using pyrolytic biochars for AC production.

Removal of pollutants from aqueous product of Co-hydrothermal liquefaction: Adsorption and isotherm studies

Hydrothermal liquefaction (HTL) is an attractive technology for the conversion of wet waste into biofuel and co-HTL has been touted to increase the quality of products. However, the recovery of energy from wastewater byproduct called aqueous co-product (ACP) is limited due to the presence of toxic inhibitory substances. Adsorption has been countenanced to remove these toxic compounds but there has not been a distinct comprehensive adsorption isotherm study to explain the interaction between the adsorbate molecules and the adsorbent sites. This study investigated the sorption mechanism of oxidizable reducing pollutants measured as chemical oxygen demand (COD); heavy metals (boron and copper); and phenols from ACP samples obtained from co-HTL of brewery trub (BT), and primary sludge (PS) onto granular and powdered activated carbon (GAC and PAC). Conventional isotherm models such as Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich were used for data analysis. Results indicated that the adsorptive capacity (qe) of PAC was greater than GAC in COD adsorption (BT-1947 > 234; BTPS-617 > 245; PS-289 > 207), boron adsorption (BTPS-70 > 7; PS-53 > 49), copper adsorption (BT-5 > 1; BTPS-3 > 2; PS-1.3 > 1.1) and phenol adsorption (BT-1340 > 356; BTPS-1587 > 253; PS-460 > 245) in mg/g, μg/g, μg/g, and μg/g respectively. Comparing the adsorption of pollutants onto PAC and GAC, this study observed that PAC followed the Temkin, and Dubinin-Radushkevich models in the adsorption of the four pollutants while GAC followed the Freundlich and Langmuir models in the adsorption of phenol and copper, and Temkin, and Dubinin-Radushkevich in the adsorption of COD and boron. This study proved that combining feedstock in HTL (co-HTL) does not only change the quality of the ACP but also changes the dynamics of the adsorption isotherms. The Free Energy Change (ΔG⁰) result showed a spontaneous reaction in the adsorption of copper and phenol. This study presents an adsorption equilibrium information for the interpretation of adsorption isotherms for the overall improvement of adsorption mechanism pathways and the effective design of adsorption systems for the treatment of ACP.

Investigation of water treatment sludge for the treatment of saline water: Batch studies

In this study, water treatment sludge was investigated through batch modes for the treatment of saline water to meet livestock drinking consents. The water quality was assessed using water quality index (WQI).The kinetic data was best described by the Pseudo - Second - Order model and the equilibrium isotherm by the Freundlich model. The maximum removal efficiency was 51.5 ± 0.65%, 22.6 ± 0.5% and 100% for Sulphates (SO4 2-), Chloride (Cl-), and Nitrates (NO3 -), respectively. The maximum removal efficiency of sodium (Na) and nickel (Ni) was 100% each at 0.4g dose and that of manganese (Mn) was 87.5% at 1.2g dose. The effect of temperature revealed that the adsorption capacity for anions, decreased with increasing temperature, whereas for the cations the adsorption capacities increased with increasing temperature. The water treatment sludge reduced the total dissolved solids (TDS) and electrical conductivity (EC) from the initial values of 19600 mgL-1 and 38900 μScm-1 to 98 mgL-1 and 1728 μScm-1,respectively. The Water Quality Indices were 37.35 and 7.57, before and after treatment, respectively. Water treatment sludge can be used for the pre-treatment process before using conventional treatment technologies. Pilot scale investigations should be conducted before field trials.

Graphene-magnetite functionalized diatomite for efficient removal of organochlorine pesticides from aquatic environment

A unique composite based on graphene oxide, magnetite, and diatomite was synthetized by eco-friendly dry coating technique for the removal of four toxic organochlorine pesticides from agricultural drainage. The prepared composite was fully characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), particle size analyzer, Vibrating-sample magnetometer (VSM), magnetic susceptibility meter, zeta potential, scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDS), and Brunauer-Emmett-Teller analysis (BET) techniques. The characterization results confirmed the fabrication of a discrete core/shell structured composite possess both adsorptive and magnetic nature. The surface area, pore volume and pore diameter were 23.4 m²/g, 0.0026 cm³/g, and 4.5 nm, respectively. The amenability to use the fabricated composite as an adsorbent for some organochlorine pesticides was investigated under different conditions of concentration, time, pH, and temperature. Batch adsorption experiment showed that 97% removal efficiency was observed for all the studied pesticides with adsorption capacities of 7.78 mg/g after 2 h contact time and at any pH region. The adsorption was exothermic (ΔH < 0), spontaneous (ΔG° < 0), followed pseudo 2nd order kinetics (R² > 0.998), and fitted well to Langmuir's isotherm pattern for all pesticides (R² > 0.98). It is assumed that organochlorine pesticides were initially physisorbed by the graphene nanoplatelets via hydrophobic and π-π interactions along with chemisorption for forming monolayer. Moreover, the pesticides molecules could diffuse in the DMG composite micropores and be trapped in the structural defects. The regeneration of the composite exhibited over 90% removal efficiency even after seven cycles. The fabricated composite was examined to remove organochlorine from a real water sample, the obtained results suggest the possibility to use this composite as an economical, effective and sustainable adsorbent for the treatment of pesticides contaminating water.

Mussel-inspired polydopamine-modified silk nanofibers as an eco-friendly and highly efficient adsorbent for cationic dyes

Obtaining silk nanofibers by simple swelling and mechanical splitting of fibers.

Regularities of Encapsulation of Tolfenamic Acid and Some Other Non-Steroidal Anti-Inflammatory Drugs in Metal-Organic Framework Based on γ-Cyclodextrin

Metal-organic frameworks based on cyclodextrins (CDs) have been proposed as promising drug delivery systems due to their large surface area, variable pore size, and biocompatibility. In the current work, we investigated an incorporation of tolfenamic acid (TA), a representative of non-steroidal anti-inflammatory drugs (NSAIDs), in a metal-organic framework based on γ-cyclodextrin and potassium cations (γCD-MOF). Composites γCD-MOF/TA obtained by absorption and co-crystallization methods were characterized using powder X-ray diffraction, low temperature nitrogen adsorption/desorption, scanning electron microscopy, and FTIR spectroscopy. It was demonstrated that TA loaded in γCD-MOF has an improved dissolution profile. However, the inclusion of TA in γ-CD reduces the membrane permeability of the drug. A comparative analysis of the encapsulation of different NSAIDs in γCD-MOF was performed. The impact of NSAID structure on the loading capacity was considered for the first time. It was revealed that the presence of heterocycles in the structure and drug lipophilicity influence the loading efficiency of NSAIDs in γCD-MOF.

A review of adsorption techniques for removal of phosphates from wastewater

Phosphate is considered the main cause of eutrophication and has received considerable attention recently. Several methods have been used for removal of phosphates in water and these include biological treatment, membrane filtration processes, chemical precipitation, and adsorption. Adsorption technology is highly effective in the removal of phosphate from wastewater even at low phosphate concentrations. Nanomaterials/nanoparticles, carbon-based materials (activated carbon and biochar), and their composites have been widely employed for the adsorptive removal and recovery of phosphate from wastewater due to their exceptional properties such as high surface area and high phosphate adsorption properties. This article is a review of the recently reported literature in the field of nanotechnology and activated carbon for the adsorption of phosphate from wastewater. Highlights of the adsorption mechanisms, adsorption behaviour, experimental parameters, effects of co-existing ions, and adsorbent modifications are also discussed.

Kinetic and Isothermal Investigations on the Use of Low Cost Coconut Fiber-Polyaniline Composites for the Removal of Chromium from Wastewater

Pollution due to various heavy metals is increasing at an alarming rate. Removal of hexavalent chromium from the environment is a significant and challenging issue due to its toxic effects on the ecosystem. Development of a low-cost adsorbent with better adsorption efficiency is presently required. In this study, waste coconut fibers (CF) were used to prepare its composite with polyaniline (PANI) via in-situ oxidation. The obtained composites with varying loading of PANI (15, 25, 50, and 75% w/w) were characterized by FE-SEM, TGA, and FTIR spectroscopy. The prepared composites were evaluated for their adsorption performance for removal of Cr(VI). It was concluded that the composite with 50% w/w polyaniline loading on coconut fiber exhibited a maximum adsorption efficiency of 93.11% in 30 min. The effect of pH, dosage, and concentration of the aqueous solution of chromium on the Cr(VI) adsorption efficiency of the composite was also studied. From the optimization studies it was observed that the absorbents exhibited the best adsorption response for Cr(VI) removal with 0.25 mg/mL adsorbent at pH 4, in 30 min. The effect of pH, dosage, and concentration of the aqueous solution of chromium on the Cr(VI) adsorption efficiency of the composite was also studied. This study highlights the application of low-cost adsorbent as a potential candidate for the removal of hexavalent chromium. A detailed study on the adsorption kinetics and isothermal analysis was conducted for the removal of Cr(VI) from aqueous solution using coconut fiber-polyaniline composite. From the kinetic investigation, the adsorption was found to follow the pseudo second order model. The data obtained were best fitted to the Elovich model confirming the chemisorption of the Cr(VI) on coconut polymer composites. The analysis of the isothermal models indicated monolayer adsorption based on the Langmuir adsorption model.

Leaching of microplastic-associated additives in aquatic environments: A critical review

Microplastic pollution has attracted significant attention as an emerging global environmental problem. One of the most important issues with microplastics is the leaching of harmful additives. This review summarizes the recent advances in the understanding of the leaching phenomena in the context of the phase equilibrium between microplastics and water, and the release kinetics. Organic additives, which are widely used in plastic products, have been introduced because they have diverse physicochemical properties and mass fractions in plastics. Many theoretical and empirical models have been utilized in laboratory and field studies. However, the partition or distribution constant between microplastics and water (K_p) and the diffusivity of an additive in microplastics (D) are the two key properties explaining the leaching equilibrium and kinetics of hydrophobic organic additives. Because microplastics in aquatic environments undergo dynamic weathering, leaching of organic additives with high K_p and/or low D cannot be described by a leaching model that only considers microplastic and water phases with a fixed boundary. Surface modifications of microplastics as well as biofilms colonizing microplastic surfaces can alter the leaching equilibrium and kinetics and transform additives. Further studies on the release of hydrophobic organic additives and their transformation products under various conditions are required to extend our understanding of the environmental fate and transport of these additives in aquatic environments.

Do Red Seaweed Nanoparticles Enhance Bioremediation Capacity of Toxic Dyes from Aqueous Solution?

Based on their functional groups, the use of various seaweed forms in phytoremediation has recently gained significant eco-friendly importance. The objective of this study was to determine whether a novel, sustainable, and ecologically acceptable adsorbent could be employed to remove toxic textile dye (Ismate Violet 2R (IV2R)) from an aqueous solution. The low-cost adsorbent was prepared from the nanoparticles form of the native red seaweed species, Pterocladia capillacea. Before and after the adsorption procedure, comprehensive characterization experiments on the bio-adsorbent were carried out, including BET, SEM, FTIR, UV, and dynamic light scattering (DLS) examination. The adsorption performance of the prepared nano-Pterocladia capillacea was optimized by adjusting operating parameters such as the initial dye concentration of 60 mg L⁻¹, pH of 2, and contact time of 15 min, all of which were obtained by batch experiments in the lab. At the optimum conditions, the prepared adsorbent had maximum removal effectiveness of 87.2%. Most typical kinetics and isotherm models were used to test the experimental results. The equilibrium data fit well with the Langmuir isotherm model, with comparatively higher R² values and fewer standard errors, while the pseudo-second-order kinetic model fits better with a decent correlation coefficient. Thermodynamic parameters revealed that the sorption process on nano-alga was exothermic and spontaneous.

Development and Characterization of Bioadsorbents Derived from Different Agricultural Wastes for Water Reclamation: A Review

The presence of dangerous pollutants in different water sources has restricted the availability of this natural resource. Thus, the development of new low-cost and environmentally-friendly technologies is currently required to ensure access to clean water. Various approaches to the recovery of contaminated water have been considered, including the generation of biomaterials with adsorption capacity for dangerous compounds. Research on bioadsorbents has boomed in recent years, as they constitute one of the most sustainable options for water treatment thanks to their abundance and high cellulose content. Thanks to the vast amount of information published to date, the present review addresses the current status of different biosorbents and the principal processes and characterization methods involved, focusing on base biomaterials such as fruits and vegetables, grains and seeds, and herbage and forage. In comparison to other reviews, this work reports more than 60 adsorbents obtained from agricultural wastes. The removal efficiencies and/or maximum adsorption capacities for heavy metals, industrial contaminants, nutrients and pharmaceuticals are presented as well. In addition to the valuable information provided in the literature investigation, challenges and perspectives concerning the implementation of bioadsorbents are discussed in order to comprehensively guide selection of the most suitable biomaterials according to the target contaminant and the available biowastes.

Adsorption of CO2 on In Situ Functionalized Straw Burning Ashes. An Innovative, Circular Economy-Based Concept for Limitation of Industrial-Scale Greenhouse Gas Emission

A new, innovative approach in the search for an effective and cheap carbon dioxide sorbent, in line with the circular economy and sustainable development principles, directs the attention of researchers to various types of waste ashes generated as a result of biomass combustion. In addition to the use of environmentally safe materials that have been experimentally identified, and that, in some way, have adjustable sorption capacity, it is also possible to rationally develop a widely applicable, simple, and inexpensive technology based on large amounts of this type of post-industrial waste, which is also an equally important issue for the natural environment (reducing the need for ash storage and accumulation). Even the lower sorption capacity can be successfully compensated for by their common availability and very low cost. Thus, the CO2 adsorption capability of the ashes from the combustion of straw biomass was experimentally investigated with the use of a high-pressure adsorption stand. The presented original technological concept has been positively verified on a laboratory scale, thus a functionalization-based approach to the combustion of substrate mixtures with nano-structural additives (raw, dried, calcined halloysite, kaolinite), introduced to improve the performance of straw biomass combustion and bottom ash formation in power boilers, clearly increased the CO2 adsorption capacity of the modified ashes. This allows for an advantageous synergy effect in the extra side-production of useful adsorbents in the closed-loop “cascade” scheme of the CE process. The addition of 4 wt.% kaolinite to straw biomass caused an over 2.5-fold increase in the CO2 adsorption capacity in relation to ash from the combustion of pure straw biomass (with a CO2 adsorption capacity of 0.132 mmol/g). In the case of addition of 4 wt.% nano-structured species to the straw combustion process, the best effects (ash adsorption capacity) were obtained in the following order: kaolinite (0.321 mmol/g), raw halloysite (0.310 mmol/g), calcined halloysite (0.298 mmol/g), and dried halloysite (0.288 mmol/g). Increasing the dose (in relation to all four tested substances) of the straw biomass additive from 2 to 4 wt.%, not only increase the adsorption capacity of the obtained ash, thus enriched with nano-structural additives, but also a showed a significant reduction in the differences between the maximum adsorption capacity of each ash is observed. The experimental results were analyzed using five models of adsorption isotherms: Freundlich, Langmuir, Jovanović, Temkin, and Hill. Moreover, selected samples of each ash were subjected to porosimetry tests and identification of the surface morphology (SEM). The obtained results can be used in the design of PSA processes or as permanent CO2 adsorbents, based on the environmentally beneficial option of using ashes from biomass combustion with appropriately selected additives.

Sustainable ecofriendly recruitment of bioethanol fermentation lignocellulosic spent waste biomass for the safe reuse and discharge of petroleum production produced water via biosorption and solid biofuel production

Sustainable lignocellulosic spent waste rice straw (SWRS) from bioethanol production inventively applied in this study to valorize petroleum production produced water (PPPW). SWRS expressed efficient pollutant removal over a wide range of petroleum concentration, temperature, pH, salinity, and mixing rate reaching approximately 217 mg/g, within four hours contact time. Kinetic studies revealed a pseudo-second-order chemisorption process with a boundary layer control and 16.97 kJ/mol activation energy where the intra-particle diffusion was not the only rate regulatory step. Thermodynamic studies revealed spontaneous, favorable, and endothermic adsorption, with a strong affinity between the SWRS and oil molecules. Biosorption mechanism studies proved the enrollment of SWRS components' lignin, cellulose, and hemicellulose in the oil uptake with the predominance of chemisorption over physisorption onto the rough and highly porous SWRS surface. A single-stage batch biosorption process was designed based on the best fitted Langmuir adsorption isotherm and applied on a real PPPW sample. The Egyptian standard limits for safe industrial effluents discharge into marine environment with a concomitant decrease in scale formation precursors were achieved recommending its safe reuse for enhanced oil recovery. Finally, for accomplishing zero-waste, SWRS disposed of PPPW treatment substantiated valorized solid biofuel with a sufficient calorific value 38.56 MJ/kg.

Application of random forest for modeling batch and continuous fixed-bed removal of crystal violet from aqueous solutions using Gypsophila aretioides stem-based biosorbent

In this work, the Gypsophila aretioides (GYP-A) stem is used as a biosorbent to remove crystal violet (CV) by the static and dynamic systems from aqueous solutions; the biosorbent is interesting in green chemistry and, on the other hand, cheaper than activated carbon and does not have the limitation of industrialization. The effects of different operating parameters such as pH(3-9), biosorbent dosage(0.4-1.8 mg/L), and initial concentration of CV(100-250 mg/L) and time for the batch method and the bed height, inlet CV concentration(75-250 mg/L), and flow rate(3-8) on the breakthrough curves for the continuous method is investigated. The result of CV adsorption onto GYP-A using the batch method indicates that the model fits Freundlich > Temkin > Langmuir > R-D, and R² equal 0.9953, 0.9847, 0.9161, 0.7909 were obtained for isotherm model, respectively. A pseudo-second-order model (R² = 0.9995-0.9997) is recommended to describe the adsorption kinetics. The Thomas and Yoon-Nelson models were analyzed to study the adsorption kinetics. The random forest model shows an excellent ability to predict the parameters involved in the CV adsorption process with appropriate accuracy and useable for large data, robust against noise; it can be very effective in selecting important variables.

Use of Thermally Modified Jarosite for the Removal of Hexavalent Chromium by Adsorption

Jarosites are residues generated during the purification of zinc and are composed mainly of iron sulfates ((Na, K)Fe3(SO4)2(OH)6). Due to the large volume of jarosite generated during the process, these residues tend to be deposited in large land areas and are not used. In the present work, jarosite was used without heat treatment (JST) as an adsorbent of hexavalent chromium contained in a sample of wastewater from a chrome plating industry under the following conditions: C0 = 200 mg/L of Cr, T = 25 °C, and pH = 3. It was only possible to remove 34% of Cr (VI). Subsequently, a thermal treatment of a jarosite sample (JTT) was carried out at 600 °C. The heat-treated sample was later used as an adsorbent in the same conditions as those for JST. The maximum chromium removal was 53%, and the adsorption capacity was 10.99 mg/g. The experimental data were fitted to the Langmuir model and to the pseudo-second-order kinetic model. It was determined that the adsorption process involved electrostatic attractions between the surface of the positively charged adsorbent and the chromium anions contained in industrial wastewater.

Photophysical study and in vitro approach against Leishmania panamensis of dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV)

Background: Photodynamic therapy activity against different biological systems has been reported for porphyrins. Porphyrin modifications through peripheral groups and/or by metal insertion inside the ring are main alternatives for the improvement of its photo-physical properties. In this study, we synthesized and characterized 5,10,15,20-tetrakis(4-bromophenyl)porphyrin and the dicloro-5,10,15,20-tetrakis(4-bromophenyl)porphyrinato Sn(IV).

Methods: Metal-free porphyrin was synthesized using the Alder method, while the Sn(IV)-porphyrin complex was prepared by combining metal-free porphyrin with stannous chloride in DMF; the reaction yields were 47% and 64% respectively. Metal-free porphyrin was characterized by UV-Vis, FT-IR, ESI-mass spectrometry and ¹³C-NMR. Additionally, the Sn(IV) -porphyrin complex was characterized using UV-Vis and FT-IR. Cyclic voltammetry tests in four different solvents. The fluorescence quantum yield (Φ _f) was measured using fluorescein as a standard, the singlet oxygen quantum yield (Φ _D) was estimated using the standard 5,10,15,20-(tetraphenyl)porphyrin (H2TPP) and the quencher of singlet oxygen 1,3-diphenylisobenzofuran (DPBF).

Results: UV-Vis assay showed typical Q and Soret bands for porphyrin and its metallo-porphyrin complex. Compounds showed photoluminescence at the visible range of electromagnetic spectrum. The inclusion of the metal in the porphyrin core changed the Φ _f from 0.15 to 0.05 and the Φ _D increased from 0.55 to 0.59. Finally, the effect of the compounds on the viability of L. panamensis was evaluated by means of the MTT test. The results showed that both compounds decreased the viability of the parasite; this inhibitory activity was greater under light irradiation; the porphyrin compound had IC ₅₀ of 16.5 μM and the Sn(IV)-porphyrin complex had IC ₅₀ of 19.2 μM.

Conclusion: The compounds were synthesized efficiently, their characterization was carried out by different spectroscopy techniques and their own signals were evidenced for both structures, both compounds decreased the cell viability of L. panamensis.

Synergistic effect of the activated carbon addition from leather wastes in chitosan/alginate-based composites

In this work, chitosan/alginate composites were developed by the gelation method with the addition of different amounts of activated carbon produced from tannery waste (ACTW). The performance of these composites was verified through the adsorption of the textile dye Remazol Brilliant Blue R (RBBR). A synergistic effect was observed by the addition of ACTW; with a specific surface area up to 45.584 m²/g, the maximum adsorption capacity was 300.96 mg/g. The synergy was due to the reduction in steric hindrance, with the adsorption capacity 1.2 times higher than expected. The material was regenerated with sodium hydroxide for 10 cycles. The composite containing 30% ACTW (AC30) was applied in the treatment of real textile effluent, with 30% reductions in the biochemical oxygen demand (BOD), 39% in the chemical oxygen demand (COD), 78% in turbidity, and 67% in color.

A kinetic and thermodynamic investigation into the removal of methyl orange from wastewater utilizing fly ash in different process configurations

The removal of methyl orange using coal fly ash, which is a widely available low-cost adsorbent, has been investigated. Adsorption studies for dye removal were conducted using various configurations such as batch, column and heap adsorption at various temperatures and adsorbent dosages at neutral pH. The Langmuir, Freundlich and Tempkin isotherm models were used to describe the process. The Freundlich model best represented the adsorption. Kinetic studies show the adsorption followed pseudo-second-order kinetics. Thermodynamic studies show that the process is spontaneous, endothermic and random. Column configuration was found to be the most efficient with a dye removal percentage of 99.95%, followed by heap adsorption at 99.25% removal and lastly batch configuration with 96.68% removal. Economic analysis shows that column operation would be the most effective for practical implementation.

Exhaustive valorization of cashew nut shell waste as a potential bioresource material

In this paper, we report extraction of cashew nut shell liquid (CNSL) from cashew nut shell waste (CNSW) and further use of residues for generation of activated carbon for removal of heavy metals and methylene blue (MB). Solvent extraction yielded 24.6 ± 0.4%, 38.2 ± 0.4% and 40.1 ± 0.9% for petroleum ether, hexane and ethanol respectively. Phytochemical screening showed presence of alkaloids, carbohydrates, saponins, phenols, tannins, flavonoids, amino acids, terpenoids, proteins, steroids, glycosides and carboxylic acids. The CNSL had a pH of 3.2, viscosity (104.6 ± 1.8 mPa s), moisture (6.5%), ash (1.6 ± 0.1%), refractive index (1.52 ± 0.001), specific density (0.9561 ± 0.0002 g/cm³), acid value (118.7 ± 9.2 mg KOH/g), free fatty acid value (60.1 ± 4.7%), saponification number (138.1 ± 3.2 mg KOH/g) and iodine value (188.1 ± 2.3 mgI 2/100 g). The average percentage removal of Cu (II), Pb (II), Cd (II) and Zn (II) was 99.4 ± 0.5, 95.4 ± 1.5, 99.5 ± 0.1, 98.4 ± 0.1%, and removal efficiency of MB at 50, 150, 250 and 350 mg/L was 99.63, 97.66, 96.48 and 94.81%, respectively. Equilibrium data were best described by the Freundlich isotherm model. The maximum monolayer adsorption capacity was 12.1 mg/g. The adsorption kinetics conformed to pseudo-second-order model. ∆G° was negative and a ∆H° of + 22.76 kJ/mol indicated that adsorption was endothermic. The ΔS° (+ 0.086 kJ/mol/K) showed that there was spontaneous interaction of the solution and adsorbate. These results show that CNSW is a potential bioresource for CNSL production for use in the paints, varnishes, surface coatings, agrochemicals and ethnomedicine industries. Residual shells can be exploited as fuels or converted to activated carbon for use as low-cost filters in water purification.

Removal of per- and polyfluoroalkyl substances from aqueous media using synthesized silver nanocomposite-activated carbons

PURPOSE

Per- and polyfluoroalkyl substances (PFAS) have been found to be widespread, extremely persistent and bioaccumulative with toxicity tendencies. Pre-synthesized nanocomposite-activated carbons, referred to, as physically activated maize tassel silver (PAMTAg) and chemically activated maize tassel silver (CAMTAg) were utilized in the present study. They were used for the removal of 10 PFAS from aqueous solutions.

METHODS

The nanocomposite-activated carbons were characterized via scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer Emmett Teller (BET) and other techniques. Batch equilibrium experiments were conducted in order to investigate the effects of solution pH, adsorbent dosage, initial PFAS concentration and temperature on the removal of PFAS using PAMTAg and CAMTAg. Langmuir and Freundlich adsorption isotherm models were used to analyse the equilibrium data obtained.

RESULTS

Maximum adsorption capacities of 454.1 mg/g (0.91 mmol/g) and 321.2 mg/g (0.78 mmol/g) were recorded for perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA), respectively using CAMTAg. The values recorded for the Gibbs' free energy (ΔG°) for the adsorption of PFOS and PFOA onto PAMTAg and CAMTAg were negative; PFOS (-9.61, -9.99 and - 10.39), PFOA (-8.77, -9.76 and - 10.21) using PAMTAg; and PFOS (-13.70, -12.70 and - 12.37), PFOA (-12.86, -12.21 and - 11.17) using CAMTAg. Therefore, the adsorption processes were spontaneous and feasible. The values recorded for enthalpy (ΔH°) (kJ/mol) for the adsorption of PFOS (-26.15) and PFOA (-35.86) onto CAMTAg were negative, indicating that the adsorption mechanism is exothermic in nature. Positive values were recorded for ΔH° for the adsorption of PFOS (2.32) and PFOA (12.69) onto PAMTAg, indicative of an endothermic adsorption mechanism. Positive entropy (ΔS°) values (0.04 and 0.07) were recorded for PFOS and PFOA using PAMTAg; whereas negative values (-0.04 and - 0.08) were recorded for ΔS° using CAMTAg. A positive ΔS° indicates an increase in randomness of the adsorbate at the solid-solution interface and the reverse is the case for a negative ΔS°.

CONCLUSION

The interplay of electrostatic attraction and hydrophobic interactions enabled the removal of PFAS using PAMTAg and CAMTAg. Findings suggest that PAMTAg and CAMTAg are effective for the removal of PFAS from aqueous media and are good alternatives to commercially available activated carbons.

GRAPHICAL ABSTRACT

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40201-020-00597-3.