Adsorption-Oriented Processes Using Conventional and Non-conventional Adsorbents for Wastewater Treatment

Mechanism and application of bacterial exopolysaccharides: An advanced approach for sustainable heavy metal abolition from soil

The escalation of heavy metal pollutants in soils and effluents, driven by industrialization and human activities, poses significant environmental and health risks. Conventional remediation methods are often costly and ineffective, prompting a shift towards sustainable alternatives such as biological treatments. Natural biosorbents, including microbial cells and their byproducts, have emerged as promising solutions. One such approach involves leveraging exopolysaccharides (EPS), complex high-molecular-weight biopolymers synthesized by microbes under environmental stress conditions. EPS are intricate organic macromolecules comprising proteins, polysaccharides, uronic acids, humic compounds, and lipids, either located within microbial cells or secreted into their surroundings. Their anionic functional groups enable efficient electrostatic binding of cationic heavy metals, making EPS effective biosorbents for soil remediation. This review thoroughly explores the pivotal role of bacterial EPS in the removal of heavy metals, focusing on EPS biosynthesis mechanisms, the dynamics of interaction with heavy metals, and case studies that illustrate their effectiveness in practical remediation strategies. By highlighting these aspects, the review underscores the innovation and practical implications of EPS-based bioremediation technologies, demonstrating their potential to address critical environmental challenges effectively while paving the way for sustainable environmental management practices. Key findings reveal that EPS exhibit robust metal-binding capacities, facilitated by their anionic functional groups, thereby offering a promising solution for mitigating metal pollution in diverse environmental matrices.

Methodical study of chromium (VI) ion adsorption from aqueous solution using low-cost agro-waste material: isotherm, kinetic, and thermodynamic studies

This study involved preparation and modification of Saccharum officinarium as adsorbent used for the removal of chromium (VI) ions in a batch process. The adsorbent was modified with oxalic acid for improved performance of the adsorbent by increasing the surface area of the adsorbent. Surface morphology of the adsorbents was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), while Fourier transform infrared (FT-IR) analysis was carried out before and after the adsorption of Cr (VI) ions to determine the participating functional group in the processes. The optimum adsorption was attained at pH 2 and contact time of 180 min with efficiency of adsorption of 56.7 and 92.6% onto RSO and MSO, respectively. The adsorption capacity increases with increase in initial metal ion concentration of the sorption mixture. The isotherms studies indicate that the experimental data were best fitted to Freundlich, Langmuir, and Sips models with R² = 0.999 for adsorption of Cr (VI) ions onto raw S. officinarium (RSO) and modified S. officinarium (MSO). The maximum adsorption capacity obtained were 227.27 and 243.90 mg*g^-1 while the adsorption energy obtained from D-R were found to be 3.460 and 6.325 kJ*mol^-1 onto RSO and MSO, respectively. This revealed that the physiosorption process was favored in interaction of Cr (VI) ions onto both adsorbents. Separation factors obtained showed that the process is favored with increase in initial concentration of the adsorbate. Thermodynamic parameter values obtained showed that the sorption of Cr (VI) ions onto RSO and MSO is feasible, spontaneous, and endothermic in nature. The positive value of ΔS° indicates increase in disorderliness of the adsorption process. Kinetic data achieved at different initial concentrations of adsorbate have been analyzed, and the mechanism of the reaction was also studied by intra-particle and Bangham kinetic model. Each of the models was tested with R² ˃ 0.9, where pseudo-second-order is the best-fitted model and Bangham mechanism only fitted with adsorption of Cr (VI) ions onto RSO. The reusability potential of RSO and MSO contributes to the economic values and reliability of the adsorbents for removal of Cr (VI) ions from aqueous solution.

Gadolinium based contrast agents (GBCAs): Uniqueness, aquatic toxicity concerns, and prospective remediation

The current toxicity concerns of gadolinium-based contrast agents (GBCAs) have birthed the need to regulate and, sometimes restrict its clinical administration. However, tolerable concentration levels of Gd in the water sector have not been set. Therefore, the detection and speedy increase of the anthropogenic Gd-GBCAs in the various water bodies, including those serving as the primary source of drinking water for adults and children, is perturbing. Nevertheless, the strongly canvassed risk-benefit considerations and superior uniqueness of GBCAs compared to the other ferromagnetic metals guarantees its continuous administration for Magnetic resonance imaging (MRI) investigations regardless of the toxicity concerns. Unfortunately, findings have shown that both the advanced and conventional wastewater treatment processes do not satisfactorily remove GBCAs but rather risk transforming the chelated GBCAs to their free ionic metal (Gd ³⁺) through inadvertent degradation processes. This unintentional water processing-induced GBCA dechelation leads to the intricate  pathway for unintentional human intake of Gd ion. Hence exposure to its probable ecotoxicity and several reported inimical effects on human health such as; digestive symptoms, twitching or weakness, cognitive flu, persistent skin diseases, body pains, acute renal and non-renal adverse reactions, chronic skin, and eyes changes. This work proposed an economical and manageable remediation technique for the potential remediation of Gd-GBCAs in wastewater, while a precautionary limit for Gd in public water and commercial drinks is advocated.

Application of Pistacia atlantica Leaves Powder as Natural Material To Remove Nitrate and Phosphate Ions From Domestic Wastewater by Characterization, Bio-removal, and Phytotoxicity Studies

Application of Pistacia atlantica Leaves Powder as Natural Material To Remove Nitrate and Phosphate Ions From Domestic Wastewater by Characterization, Bio-removal, and Phytotoxicity StudiesObaida Alhajali1* , Adnan Ali-Nizam1 , Rasha Almostafa2 1Damascus University, Department of Plant Biology, Damascus, Syria.2International University for Science and Technology, Department of General and Analytical Chemistry, Syria. Abstract: Description of Pistacia leaves powder using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy (EDX), specific surface area according to nitrogen adsorption (SBET) and methylene Blue (MB), and point of zero charge determination (pHpzc). A series of batch adsorption tests were conducted to study effect of various factors (plant powders dose, contact time, temperature, pH) on the percentage of nitrate and phosphate removal from domestic wastewater. The adsorption kinetics, regeneration ability test of plant powder, and phytotoxicity tests for treated water and spent powder on germination were studied. Results of SBET analysis showed that Pistacia leaves powders have a low surface area and microscopic pores, SEM images revealed rough surfaces with uneven cavities, EDX analysis showed that there are high percentages of carbon and oxygen, good percentages for nitrogen, and few percentages of potassium, calcium, magnesium, phosphorous, sulfur and chlorine, and FTIR analysis showed that there are more than five distinct absorption peaks. The maximum value of nitrate and phosphate removal was 76.47% and 52.20%, respectively, at powder dose of 2 g/L, temperature 25 °C, and pH 5, and the percentage of nitrate and phosphate removal increased with increasing contact time until equilibrium was reached after 120 min for nitrate and 180 min for phosphate, and It was found that adsorption of ions follows kinetics of reaction from pseudo-second-order model, and powders can be Regeneration and used for two successive cycles with a slight decrease in removal efficiency. Germination tests on Lepidium sativum indicate no phytotoxicity. That is, Pistacia leaves powder is one of the natural products that are effective in removing nitrate and phosphate from domestic wastewater.

Hydrothermal Carbonization of Residual Algal Biomass for Production of Hydrochar as a Biobased Metal Adsorbent

Conversion of residual algal biomass to value-added products is essential for enhancing the economics of algae cultivation. Algal hydrochar produced via hydrothermal carbonization of lipid-extracted Picochlorum oculatum is a material rich in oxygen functional groups and carbon (up to 67.3%) and hence a promising candidate for remediation of wastewaters. The hydrothermal carbonization conditions were optimized and the adsorption capacity of the hydrochar was tested for metal removal. By the end of the remediation process, cumulative removal of Al3+, Cu2+, Fe2+, Mg2+, Mn2+, and Pb2+ reached 89, 98, 75, 88, 75, and 100%, respectively. The adsorption of all metals was found to follow pseudo second-order kinetics and the Langmuir isotherm. Overall, when hydrothermal carbonization is applied to lipid-extracted algae, it generates a promising biobased adsorbent with value-added potential in metal remediation.

Synergy of production of value-added bioplastic, astaxanthin and phycobilin co-products and Direct Green 6 textile dye remediation in Spirulina platensis

Phyco-remediation of dyestuffs in textile wastewaters is of economic, industrial, and environmental importance. We evaluated the remediation of the textile dye, Direct Green 6 (DG6), by Spirulina platensis, and investigated the novel possibility that DG6 treatment enhances production of the biopolymer, polyhydroxybutyrate (PHB). We showed that both live and dead cells of Spirulina were capable of DG6 remediation, but live cells could be re-used with no loss of remediation efficiency. Furthermore, DG6 remediation by live cells resulted in increased algal biomass and trichome lengths, and stimulated production of valuable metabolites, including PHB, antioxidants, carbohydrates and pigments (phycobilins and astaxanthin). We determined the optimal conditions for DG6 remediation and an artificial neural network (ANN) accurately modeled the experimental data and predicted the concentration of dye as the most and algal turbidity as the least important parameters for DG6 removal efficiency. A DG6 concentration of 60 mg L^-1 resulted in the highest simultaneous co-production of PHB (12.7 ± 1.7% DW) and increase of astaxanthin (194%), carotenoids (50%), phenol (51%), carbohydrates (27%) total phycobilin (43%), together with the enhancement of biomass and trichome lengths (95%). Oxidative stress indices and enzyme activities such as peroxidases and laccase (involved in dye removal/antioxidant functions) were also increased by dye dosage. On the basis of our results, we propose that S. platensis may use DG6 dye as a nitrogen/carbon source for co-accumulation of valuable bioplastic and metabolites.

Enhanced Performance of Chitosan via a Novel Quaternary Magnetic Nanocomposite Chitosan/Grafted Halloysitenanotubes@ZnγFe3O4 for Uptake of Cr (III), Fe (III), and Mn (II) from Wastewater

A novel chitosan/grafted halloysitenanotubes@Znγmagnetite quaternary nanocomposite (Ch/g-HNTs@ZnγM) was fabricated using the chemical co-precipitation method to remove the ions of Cr (III), Fe (III), and Mn (II) from wastewater. The characteristics of the synthesized Ch/g-HNTs@ZnγM quaternary nanocomposite were investigated using FTIR, SEM, XRD, GPC, TGA, TEM, and surface zeta potential. The characterization analysis proved that the mentioned nanocomposite structure contains multiple functional groups with variable efficiencies. Additionally, they proved the existence of magnetic iron in the nanocomposite internal structure with the clarity of presentation of gaps and holes of high electron density on its surface. The results showed that the pH and time to reach an equilibrium system for all the studied metal ions were obtained at 9.0 and 60 min, respectively. The synthesized Ch/g-HNTs@ZnγM nanocomposite exhibited maximum adsorption removal of 95.2%, 99.06%, and 87.1% for Cr (III), Fe (III), and Mn (II) ions, respectively. The pseudo-second-order kinetic model and, for isotherm, the Langmuir model were best fitted with the experimental data. The thermodynamic parameters indicated the exothermic and spontaneous nature of the adsorption reaction as proven by the ΔH° and ΔG° values. Additionally, chemical adsorption by the coordination bond is supposed as the main mechanism of adsorption of the mentioned metal ions on the nanocomposite. Finally, Ch/g-HNTs@ZnγM displays prospected advantages, such as a low-expense adsorbent, high efficiency and availability, and an eco-friendly source, that will reduce the environmental load via an environmentally friendly method.

Modelization and implementation of free adsorption and electrosorption of Cr (VI) from wastewater using Al2O3 nanoparticles: assessment and comparison of the two processes

The objective of this study was to apply the technique of electrosorption in order to assess the capacity of heterogeneous adsorption under an electric field. This was to enhance the adsorption capacity of the nanoparticles, to shorten the adsorption time, and to reduce the cost of the purification of contaminated waters. A final objective of this study was to compare the free adsorption (FA) and the electrosorption (ES) to understand the interface adsorbent/adsorbate at different contact conditions. For these purposes, a potentially efficient, environment-friendly absorbent was synthesized for dechromation purposes. The experimental design method generated optimum conditions as t_c = 123 min, T = 318°K, and C₀ = 100 mg/L. Freundlich's well-fitted modeling proved that the adsorption of chromate (VI) on nano-Al₂O₃ occurred on a homogenous surface. In addition, the adsorption coefficient intensity n did not only confirm monolayer adsorption but also indicated a favorable adsorption process. Thermodynamic studies confirmed the reaction spontaneity and the physisorption of the process. The electrosorption process was also tested using 20mA/cm² as applied current density. Free-adsorption (FA) and electrosorption (ES) processes were compared. The maximum recorded yield was 99% for (EA) against 87% for (FA). EDS analysis recorded 11.3% of chromate adsorbate with free adsorption. The amount of Cr (VI) on nano-Al₂O₃ was 42.5 %. Nevertheless, the Al₂O₃ nanoparticles lost their crystallinity and exploded after the ES process. Mechanisms of both (FA) and (ES) were proposed.

A Stochastic Model for Adsorption Kinetics

A novel stochastic model is proposed to characterize the adsorption kinetics of pollutants including dyes (direct red 80 and direct blue 1), fluoride ions, and cadmium ions removed by calcium pectinate (Pec-Ca), aluminum xanthanate (Xant-Al), and reed leaves, respectively. The model is based on a transformation over time following the Ornstein–Uhlenbeck stochastic process, which explicitly includes the uncertainty involved in the adsorption process. The model includes stochastic versions of the pseudo-first-order (PFO), pseudo-second-order (PSO), and pseudo- $n$ -order (PNO) models. It also allows the estimation of the adsorption parameters, including the maximum removal capacity ( $q_e$ ), the adsorption rate constant ( $k_n$ ), the reaction pseudoorder ( $n$ ), and the variability $\left({\sigma }^2\right)$ . The model fitted produced $R^2$ values similar to those of the nonstochastic versions of the PFO, PSO, and PNO models; however, the obtained values for each parameter indicate that the stochastic model better reproduces the experimental data. The $q_e$ values of the Pec-Ca-dye, Xant-Al-fluoride, and reed leaf-Cd+2 systems ranged from 2.0 to 9.7, 0.41 to 1.9, and 0.04 and 0.29 mg/g, respectively, whereas the values of $k_n$ ranged from 0.051 to 0.286, 0.743 to 75.73, and 0.756 to 8.861 (mg/g)1-n/min, respectively. These results suggest a variability in the parameters $q_e$ and $k_n$ inherent to the natures of the adsorbate and adsorbent. The obtained $n$ values ranged from 1.13 to 2.02 for the Pec-Ca-dye system, 1.0–3.5 for the Xant-Al-fluoride system, and 1.8–3.8 for the reed leaf-Cd+2 system. These ranges indicate the flexibility of the stochastic model to obtain fractional $n$ values, resulting in high $R^2$ values. The variability in each system was evaluated based on ${\sigma }^2$ . The developed model is the first to describe pollutant removal kinetics based on a stochastic differential equation.

Mesoporous Carbons of Well-Organized Structure in the Removal of Dyes from Aqueous Solutions

Mesoporous carbons with differentiated properties were synthesized by using the method of impregnation of mesoporous well-organized silicas. The obtained carbonaceous materials and microporous activated carbon were investigated by applying different methods in order to determine their structural, surface and adsorption properties towards selected dyes from aqueous solutions. In order to verify applicability of adsorbents for removing dyes the equilibrium and kinetic experimental data were measured and analyzed by applying various equations and models. The structural and acid-base properties of the investigated carbons were evaluated by Small-Angle X-ray Scattering (SAXS) technique, adsorption/desorption of nitrogen, potentiometric titration, and Transmission Electron Microscopy (TEM). The results of these techniques are complementary, indicating the type of porosity and structural ordering, e.g., the pore sizes determined from the SAXS data are in good agreement with those obtained from nitrogen sorption data. The SAXS and TEM data confirm the regularity of mesoporous carbon structure. The adsorption experiment, especially kinetic measurements, reveals the utility of mesoporous carbons in dye removing, taking into account not only the adsorption uptake but also the adsorption rate.

Synergistic effect in concurrent removal of toxic methylene blue and acid red-1 dyes from aqueous solution by durian rind: kinetics, isotherm, thermodynamics, and mechanism

In the present study, a synergistic effect between cationic methylene blue (MB) and anionic acid red 1 (AR1) on their concurrent adsorptive removal from aqueous binary solution onto durian rind (DR) was systematically investigated in batch mode across different parameters. The concurrent adsorption was pseudo-second-order kinetics and followed the Langmuir isotherm model, similar to their respective single component. The kinetics and intraparticle diffusion analyses demonstrated that the adsorption rate of MB was a 15-fold faster than AR1, and mass transports were governed by a combination of intraparticle and film diffusion. The synergistic effect was evidenced by an enhanced adsorption efficiency of AR1 from 27 to 42%, while that of MB was almost unchanged (97-98%). By changing the molar ratios of MB and AR1, it was found that the maximum adsorption capacity of MB and AR1 was 249 and 200 mg g^-1, respectively, in the binary system higher compared with those in their respective single system (108 and 16 mg g^-1). Overall data indicated that the synergistic effect was due to electrostatic interactions between cationic and anionic synthetic dyes, supported by negatively charged DR surface, leading to the formation of their stacking layers on the adsorbent surface. Novelty statement: A synergistic effect in concurrent adsorptive removal of synthetic dyes from multicomponent wastewater remains a critical research challenge. We believed that electrostatic interaction between ionic dyes could be explored to enhance their removal efficiency. This report is the first time that such a synergistic effect between cationic methylene blue (MB) and anionic acid red 1 (AR1) on their concurrent adsorption from aqueous binary system is systematically investigated. The kinetics, isotherm, thermodynamics, and mechanism of the concurrent adsorption of MB and AR1 attributed to the synergistic effect are elucidated in detail.

Engineered biochar from wood apple shell waste for high-efficient removal of toxic phenolic compounds in wastewater

This study investigated a novel agricultural low-cost bio-waste biochar derived from wood apple fruit shell waste via the pyrolysis method, which is modified by ball milling and utilized to remove toxic phenol and chlorophenols (4-CPh and 2,4-DCPh) from contaminated aqueous media. The ball-milled wood apple fruit shell waste biochar (WAS-BC) sorbent was systematically analyzed by BET, CHN, and FTIR as well as particle size, SEM-EDS, XPS and TGA studies. The sorption equilibrium and kinetic studies exhibit that the sorption capacity was greater than 75% within the first 45 min of agitation at pH 6.0. The uptake capacity of 2,4-DCPh onto WAS-BC was greater than those of 4-CPh and phenol. Equilibrium results were consistent with the Langmuir isotherm model, while the kinetic data were best represented by the Elovich and pseudo-second-order model. The maximum uptake of phenol, 4-CPh, and 2,4-DCPh was 102.71, 172.24, and 226.55 mg/g, respectively, at 30 ± 1 °C. Thus, this study demonstrates that WAS-BC is an efficient, low-cost sorbent that can be used for the elimination of phenol and chlorophenol compounds from polluted wastewater.

Fast removal of heavy metals from water and soil samples using magnetic Fe3O4 nanoparticles

Heavy metal discharge from anthropogenic sources on open soil surfaces and in natural water bodies poses serious environmental and health concerns. In addition to the contamination reduction of metals at the source, post-discharge removal of metals using nanoparticles is one of the remediation technologies being explored nowadays due to its cost-effectiveness, being environment-friendly, and easy application as a technique. In this work, magnetic iron oxide (Fe₃O₄) nanoparticles were synthesized chemically and then used for the removal of heavy metals (Cd, Cr, Cu, Fe, Ni, Pb, and Zn) from water and soil samples. The heavy metal removal efficiency of these iron oxide nanoparticles for different metals in water was best observed at a pH of 4.5 and varied between 63.5 and 98.3%. However, the removal efficiency of these nanoparticles from the soil sample was only measured at a pH of 0.7, and heavy metal removal efficiency varied between 69.6 and 99.6%. In both soil and water samples, the most efficient remediation time was less than 20 min, after which desorption and even dissolution of the nanoparticles can occur at a highly acidic pH. Among all selected metals for removal, lead showed the best adsorption and hence removal efficiency. The nanoparticles were characterized using the TEM, XRD, and FTIR techniques. The adsorption efficiency of various metals was estimated by using atomic absorption spectroscopy. The results suggest that the removal efficiency and stability of adsorbed products can further be improved by adjusting the pH higher towards 7 and also perhaps by modifying the nanoparticles with functional groups. The primary advantage of the magnetic un-coated nanoparticles is easy and efficient removal of the nanoparticles from the treated solutions by using an ordinary magnet.

Modified Spruce Sawdust for Sorption of Hexavalent Chromium in Batch Systems and Fixed-Bed Columns

This study investigated the potential use of spruce sawdust that was pretreated with diethylene glycol and sulfuric acid for the removal of hexavalent chromium from wastewater. The sawdust pretreatment process was conducted at different temperatures and times. The adsorbent was characterized by quantitative saccharification, scanning electron microscopy, and Brunauer-Emmet-Teller surface area analysis. Adsorption capacity was studied for both batch and column processes. The experimental adsorption isotherms were simulated using seven isotherm models, including Freundlich and Langmuir models. By using the Langmuir isotherm model, the maximal Cr(VI) adsorption capacity of organosolv-pretreated spruce sawdust (qm) was 318.3 mg g-1. Furthermore, the kinetic data were fitted to Lagergren, pseudo-second-order, and intraparticle diffusion models, revealing that the adsorption of Cr(VI) onto spruce sawdust pretreated with diethylene glycol and sulfuric acid is best represented by the pseudo-second-order kinetic model. Three kinetic models, namely, the Bohart-Adams model, Thomas model, and modified dose-response (MDR) model, were used to fit the experimental data obtained from the column experiments and to resolve the characteristic parameters. The Thomas adsorption column capacity of the sawdust was increased from 2.44 to 31.1 mg g-1 upon pretreatment, thus, demonstrating that organosolv treatment enhances the adsorption capability of the material.

Bioremediation of water contaminated with uranium using Penicillium piscarium

Penicillium piscarium can be indicated as promising in the treatment of sites contaminated with uranium. Thus, this research aimed to analyze the P. piscarium dead biomass in uranium biosorption. This fungus was previously isolated from a highly contaminated uranium mine located in Brazil. Biosorption tests were carried out at pH 3.5 and 5.5 in solutions contaminated with concentrations of 1 to 100 mg/L of uranium nitrate. Our results showed that the dead biomass of P. piscarium was able to remove between 93.2 and 97.5% uranium from solutions at pH 3.5, at the end of the experiment, the pH of the solution increased to values above 5.6. Regarding the experiments carried out in solutions with pH 5.5, the dead biomass of the fungus was also able to remove between 38 and 92% uranium from the solution, at the end of the experiment, the pH of the solution increased to levels above 6.5. The analysis of electron microscopy, Energy-dispersive spectroscopy, and X-ray fluorescence demonstrated the high concentration of uranium precipitated on the surface of the fungal biomass. These results were impressive and demonstrate that the dead biomass of P. piscarium can be an important alternative to conventional processes for treating water contaminated with heavy metals, and we hope that these ecofriendly, inexpensive, and effective technologies be encouraged for the safe discharge of water from industrial activities.

Design of a new low cost natural phosphate doped by nickel oxide nanoparticles for capacitive adsorption of reactive red 141 azo dye

Nickel oxide doped natural phosphate (NP/NiO) nanoparticles were thermally synthesized for effective adsorption of Reactive Red 141 (RR141) as toxic dye model, characterization methods such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy combined with energy dispersive X-ray analysis(SEM-EDAX)and have been employed to identify the adsorbent. Surface area and pore size volume were determined by the Brunauer, Emmett and Teller (BET) method. Environmental factors such as pH, time of contact, initial RR141 concentration, the dose of adsorbent and solution temperature have been all put to the test to evaluate optimum adsorption activity. Thermal processing NP/NiO at 1% NiO doping percentage was effectual for exhibiting best adsorption behavior at an annealing temperature of 600 °C. Furthermore, batch experiments revealed significant adsorption activity reaching 96%. The maximal adsorption capacity was found to be 38.91 mg of RR 141 per 0.1 g of the adsorbent in only 40min of contact, at an initial colorant concentration of 20 mg L^-1, pH 6 at ambient temperature and a volume of 100 ml. Langmuir isotherm model was more adequate to describe the adsorption process than the Freundlich model. The rate mechanism of the adsorption process was determined from the intraparticle diffusion model, Boyd plot revealed that the adsorption of the dye on the NP/NiO was mainly governed by film diffusion. Moreover, the dye adsorption was spontaneous and exothermic. The mechanism of adsorption may involve chemical adsorption through hydrogen bonding mechanism and electrostatic interactions between the dye molecules and the adsorbent. Thermal regeneration was feasible only for three cycles, the adsorbent also showed great potential for real textile wastewater treatment.

Hydration and Sorption Properties of Raw and Milled Flax Fibers

The physicochemical and hydration properties of mechanically modified flax fibers (FFs) were investigated herein. Raw flax fibers (FF-R) were ball-milled and sieved through mesh with various aperture sizes (420, 210, and 125 μm) to achieve modified samples, denoted as FF-420, FF-210, and FF-125, respectively. The physicochemical and hydration properties of FF-R with variable particle sizes were characterized using several complementary techniques: microscopy (SEM), spectroscopy (FT-IR, XRD, and XPS), thermoanalytical methods (DSC and TGA), adsorption isotherms using gas/dye probes, and solvent swelling studies in liquid H2O. The hydration of FF biomass is governed by the micropore structure and availability of active surface sites, as revealed by the adsorption isotherm results and the TGA/DSC profiles of the hydrated samples. Gravimetric water swelling, water retention values, and vapor adsorption results provide further support that particle size reduction of FF-R upon milling parallels the changes in surface chemical and physicochemical properties relevant to adsorption/hydration in the modified FF materials. This study outlines a facile strategy for the valorization and tuning of the physicochemical properties of agricultural FF biomass via mechanical treatment for diverse applications in biomedicine, energy recovery, food, and biosorbents for environmental remediation.

Magnetic nanosorbents with siliceous hybrid shells of alginic acid and carrageenan for removal of ciprofloxacin

Water contamination with antibiotics is a serious environmental threat. Ciprofloxacin (CIP) is one of the most frequently detected antibiotics in water. Herein, silica-based magnetic nanosorbents prepared using three seaweed polysaccharides, alginic acid, κ- and λ-carrageenan, were developed and evaluated in the uptake of ciprofloxacin. The sorbents were firstly characterized in detail to assess their morphology and composition. A systematic investigation was conducted to study the adsorption performance towards CIP, by varying the initial pH, contact time and initial CIP concentration. The maximum adsorption capacity was 464, 423 and 1350 mg/g for particles prepared from alginic acid, κ- and λ-carrageenan respectively. These high values indicate that these materials are among the most effective sorbents reported so far for the removal of CIP from water. The kinetic data were consistent with the pseudo-second-order model. The CIP adsorption on λ-carrageenan particles followed a cooperative process with sigmoidal isotherm that was described by the Dubinin-Radushkevich model. The high charge density of λ-carrageenan and the propensity of CIP molecules to self-aggregate may explain the cooperative nature of CIP adsorption. The sorbents were easily regenerated in mild conditions and could be reused in CIP removal up to 4 times without a significant loss of adsorptive properties.