Heavy metals adsorption by novel EDTA-modified chitosan–silica hybrid materials

Preparation and characterization of cellulose-chitosan/β-FeOOH composite hydrogels for adsorption and photocatalytic degradation of methyl orange

Biopolymer-based hydrogels have received great attention in wastewater treatment due to their excellent properties, e.g., high adsorption capacity, fast kinetics, reusability and ease of operation. In the present work, cellulose-chitosan/β-FeOOH composite hydrogels were prepared via co-dissolution and regeneration process as well as hydrothermal in situ synthesis of β-FeOOH. Effect of β-FeOOH loading on the properties of the composite hydrogels and the removal efficiency of methyl orange (MO) was investigated. Results showed that β-FeOOH was uniformly loaded onto the hydrogel framework, and the nanoporous structure of composite hydrogels could increase not only the effective contact area between β-FeOOH and the pollutants but also the active sites. Moreover, the increased β-FeOOH loading led to the enhanced MO removal rate under light conditions. When the loading time was extended from 6 h to 9 h, the MO removal rate increased by 21%, which can be mainly due to the photocatalytic degradation. In addition, MO removal rate reached 97.75% within 40 min under optimal conditions and attained 80.81% after five repetitions. The trapping experiment and EPR results indicated that the main active species were hydrogel radicals and holes. Consequently, this work provides an effective preparation approach for cellulose-chitosan/β-FeOOH composite hydrogel with high adsorption and photocatalytic degradation, which would hold great promise for wastewater treatment applications.

Preparation, characterization, and adsorption kinetics of graphene oxide/chitosan/carboxymethyl cellulose composites for the removal of environmentally relevant toxic metals

This study attempted to develop a low-cost and eco-friendly bio-based composite adsorbent that is highly efficient in capturing potential toxic metals. The bio-composite adsorbent was prepared using graphene oxide (GO), carboxymethyl cellulose (CMC) and chitosan (CS); and characterized using FTIR, SEM-EDX and WAXD techniques. Metal-ion concentration in an aqueous solution was measured by ICP-OES. This article reveals that the adsorption of heavy metal ions varied according to the adsorbent quantity, initial metal concentration, pH, and interaction time. The metal ions' adsorption capacity (mg/g) was observed to increase when the interaction time and metal concentration increased. Conversely, metal ions adsorption was decreased with an increase in adsorbent dosages. The effect of pH on metal ions' adsorption was ion-specific. The substantial adsorption by GO/CMC/CS composite for Co2+, CrO42-, Mn2+ and Cd2+, had the respective values of 43.55, 77.70, 57.78, and 91.38 mg/g under acidic conditions. The metal ions experimental data were best fitted with pseudo-second-order (PSO) kinetics, and Freundlich isotherm model (except Co2+). The separation factors (RL) value in the present investigation were found between 0 and 1, meaning that the metal ions adsorption onto GO/CS/CMC composite is favorable. The RL and sorption intensity (1/n) values fitted well to the adsorption isotherm.

Green conversion of waste PET into magnetic Ni0·4Fe2·6O4/(Fe,Ni)@carbon nanostructure for adsorption and separation of dyes from aqueous media

A nanostructured core-shell composite (Ni0·4Fe2·6O4/(Fe,Ni)@carbon, NFC) comprising magnetic nano-cores encapsulated with graphitic shells (≈80 wt%) is prepared by facile and clean mechanochemical-molten salt processing approach using waste PET; providing a specific surface area of 201.9 m2 g-1, well-developed mesopores, and ferromagnetic behavior characterized by the coercivity value of 149 Oe. NFC is utilized as a high-performance adsorbent for the removal of organic dyes from their aqueous solutions. Moreover, the magnetic performance of NFC enables the facile collection of the exhausted adsorbent out of the purified water. Performances of NFC for the removal of crystal violet dye (CV), methyl orange (MO) and rhodamine B (Rh B) from their aqueous solutions are systematically investigated under different environmental conditions including the adsorbent dosage and dye concentration, as well as the solution pH and temperature, where an impressive CV removal capacity of 201.6-243.8 mg g-1 is recorded for a wide pH range of 2-10. Mechanism and kinetics involved in the adsorption process are investigated by studying the adsorption isotherms and thermodynamics. The dye adsorption of the nanocomposite material is confirmed to follow the pseudo-second-order kinetic model combined with the Langmuir isotherm model, exhibiting an excellent spontaneous and exothermic monolayer adsorption capacity of around 153 mg g-1 (for MO) for the fresh adsorbent and around 89 mg g-1 after three adsorption-regeneration cycles.

Synthesis & fabrication of O-linked polymeric hybrids for recovery of textile dyes: Closed loop economy

Dyes are an important resource employed for the production systems in textile, paper, paint and leather industry. An estimate of 200,000 tons of dyes are discharged as textile effluent each year worldwide. It becomes imperative to recover these dyes by treating the effluents using economically viable routes. The present research was undertaken with the objective to attain zero emission and zero waste through development of novel polymeric hybrids as adsorbents. For this purpose, metal moieties (Al3+, Si4+, Ti4+ and Zr4+) were hybridized with polyacrylic acid, and cellulose acetate for the uptake of selected dyes under optimized parameters. The structural elucidation of four synthesized hybrids (MP-Al, MP-Si, MP-Ti and MP-Zr) by FTIR, EDX and TGA confirmed O-linked grafting of metal moieties with polymers and thermally stable porous materials. SEM micrographic images displayed void spaces providing channels for effective adsorption. The batch experiments demonstrated removal of malachite green (77-96%) and congo red (70-82%) upon contact of initial 45 min on polymeric hybrids On the other hand, pristine polyacrylic acid and cellulose acetate showed remarkably low removal of dyes. The adsorption mechanism is proposed as physical in nature following type II isotherm. Further, Langmuir and Ho's pseudo second order fitness was evaluated. In order to determine the economic viability of the present research, the real textile dyes were recovered in three consecutive cycles of adsorption and chemical treatment of hybrids. The results propose a system with positive impact on economy by maximum utilization of hybrids as adsorbents and recovery of textile dyes for reuse in textile processing.

A review on heavy metal biosorption utilizing modified chitosan

Heavy metal pollution in water bodies is a global concern. The prominent source of metal contamination in aqueous streams and groundwater is wastewater containing heavy metal ions. Elevated concentrations of heavy metals in water bodies can have a negative impact on water quality and public health. The most effective way to remove metal contaminants from drinking water is thought to be adsorption. A deacetylated derivative of chitin, chitosan, has a wide range of commercial uses since it is biocompatible, nontoxic, and biodegradable. Due to its exceptional adsorption behavior toward numerous hazardous heavy metals from aqueous solutions, chitosan and its modifications have drawn a lot of interest in recent years. Due to its remarkable adsorption behavior toward a range of dangerous heavy metals, chitosan is a possible agent for eliminating metals from aqueous solutions. The review has focused on the ideas of biosorption, its kinds, architectures, and characteristics, as well as using modified (physically and chemically modified) chitosan, blends, and composites to remove heavy metals from water. The main objective of the review is to describe the most important aspects of chitosan-based adsorbents that might be beneficial for enhancing the adsorption capabilities of modified chitosan and promoting the usage of this material in the removal of heavy metal pollutants.

Effective Removal of Fe (III) from Strongly Acidic Wastewater by Pyridine-Modified Chitosan: Synthesis, Efficiency, and Mechanism

A novel pyridine-modified chitosan (PYCS) adsorbent was prepared in a multistep procedure including the successive grafting of 2-(chloromethyl) pyridine hydrochloride and crosslinking with glutaraldehyde. Then, the as-prepared materials were used as adsorbents for the removal of metal ions from acidic wastewater. Batch adsorption experiments were carried out to study the impact of various factors such as solution pH value, contact time, temperature, and Fe (III) concentration. The results showed that the absorbent exhibited a high capacity of Fe (III) and the maximum adsorption capacity was up to 66.20 mg/g under optimal experimental conditions (the adsorption time = 12 h, pH = 2.5, and T = 303 K). Adsorption kinetics and isotherm data were accurately described by the pseudo-second-order kinetic model and Sips model, respectively. Thermodynamic studies confirmed that the adsorption was a spontaneous endothermic process. Moreover, the adsorption mechanism was investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results revealed the pyridine group forms a stable chelate with iron (III) ions. Therefore, this acid-resistant adsorbent exhibited excellent adsorption performance for heavy metal ions from acidic wastewater compared to the conventional adsorbents, helping realize direct decontamination and secondary utilization.

A Laser-Induced Graphene-Titanium(IV) Oxide Composite for Adsorption Enhanced Photodegradation of Methyl Orange

Numerous treatment methods such as biological digestion, chemical oxidation, and coagulation have been used to treat organic micropollutants. However, such wastewater treatment methods can be either inefficient, expensive, or environmentally unsound. Here, we embedded TiO₂ nanoparticles in laser-induced graphene (LIG) and obtained a highly efficient photocatalyst composite with pollutant adsorption properties. TiO₂ was added to LIG and lased to form a mixture of rutile and anatase TiO₂ with a decreased band gap (2.90 ± 0.06 eV). The LIG/TiO₂ composite adsorption and photodegradation properties were tested in solutions of a model pollutant, methyl orange (MO), and compared to the individual and mixed components. The adsorption capacity of the LIG/TiO₂ composite was 92 mg/g using 80 mg/L MO, and together the adsorption and photocatalytic degradation resulted in 92.8% MO removal in 10 min. Adsorption enhanced photodegradation, and a synergy factor of 2.57 was seen. Understanding how LIG can modify metal oxide catalysts and how adsorption can enhance photocatalysis might lead to more effective pollutant removal and offer alternative treatment methods for polluted water.

Contribution of halloysite as nanotubular clay mineral on mechanism and adsorption rate of Cd(II) onto nanocomposites alginate-halloysite

In this work nanocomposites based on alginate (Alg) and halloysite as a nanotubular clay (Hy) were developed. Characterization techniques reveal that Hy/Alg nanocomposites are cation exchangers with predominantly negative charge density and good thermal stability. The adsorption equilibrium of Cd(II) in aqueous solution onto Hy/Alg nanocomposites revealed that by increasing the mass of halloysite in the nanocomposite, the adsorption capacity diminished significantly due to the halloysite-alginate interactions. Maximum adsorption capacities of 8, 65, 88, and 132 mg/g of Cd(II) were obtained for samples Hy, Hy/Alg 50%, Hy/Alg 95%, and Alg, respectively. In addition, the adsorption equilibrium of Cd(II) on the Hy/Alg bionanocomposites was affected by the pH and temperature of the solution, demonstrating the presence of electrostatic interactions during adsorption and that this is an exothermic process. The controlling mechanism of adsorption was cation exchange influenced by electrostatic forces. The Cd(II) adsorption rate studies were interpreted by the diffusion-permeation model and reveal that the presence of Hy in the structure of the nanocomposites enhances the permeation coefficient, that is, the adsorption rate was increased. The values of the permeation coefficient varied from 1.95 × 10^-7 to 8.50 × 10^-7 cm²/s for Hy/Alg 50% and from 1.70 × 10^-7 to 3.55 × 10^-7 cm²/s for Hy/Alg 95%.

Green synthesis of P − ZrO2CeO2ZnO nanoparticles using leaf extracts of Flacourtia indica and their application for the photocatalytic degradation of a model toxic dye, Congo red

In the present work P−ZrO2CeO2ZnO nanoparticles were synthesised for the first time using phytochemical extracts from Flacourtia indica leaves and applied in the photocatalytic degradation of Congo Red in the presence of Light Emitting Diode warm white light. The photocatalytic degradation was optimized with respect to P−ZrO2CeO2ZnO nanoparticle dosage, initial Congo Red concentration, and degradation time. The optimum conditions for P−ZrO2CeO2ZnO nanoparticle synthesis was pH 9, leaves extracts of F. indica dosage 4 g 100 mL⁻¹, Zirconia, Cerium and Zinc metal ion concentration 0.05 mg/L and metal ion to plant volume ratio of 1:4. The leaves extract dosage, pH and metal concentration had the most significant effects on the synthesis of the nanoparticles. The nanoparticles followed type III physisorption adsorption isotherms with surface area of 0.4593 m³g⁻¹, pore size of 6.80 nm, pore volume 0.000734 cmg−13 and average nanoparticle size 0.255 nm. A degradation efficiency of 86% was achieved and the optimum degradation conditions were 0.05 g/L of P−ZrO2CeO2ZnO nanoparticle dosage, 10 mg/L initial Congo red concentration, and 250 minutes irradiation time. Data from kinetic studies showed that the degradation followed pseudo first order kinetics at low concentration, with a rate constant of 0.069 min⁻¹. The superoxide, h+ holes and light were the main determinants of the reaction mechanisms for the degradation of Congo Red. The investigation outcomes demonstrated that P−ZrO2CeO2ZnO nanoparticles offer a high potential for photocatalytic degradation of Congo Red.

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The most significant factors on P−ZrO2CeO2ZnO nanoparticles synthesis were plant leaves dosage, pH and initial metal concentration.

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The nanoparticles exhibited high catalytic activity towards photocatalytic degradation of Congo red.

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Superoxide, h+ holes and light were the main determinants of the photocatalytic degradation mechanisms.

In situ Functionalized Mesoporous Silicas for Sustainable Remediation Strategies in Removal of Inorganic Pollutants from Contaminated Environmental Water

Low-cost mesoporous silicas of the SBA-15 family were prepared, aimed for removal of a broad spectrum of both cationic and anionic forms of hazardous metal pollutants (Cr(III, VI), Mn(II, VII), Pb(II), Cd(II), and Cu(II)) from environmental water. Series of mono- and bifunctional materials with immobilized ethylenediaminetriacetic acid (EDTA), primary amine (NH₂), and quaternary ammonium (QAS) groups were prepared in a cost-efficient one-step synthesis using two silica sources, low-cost sodium metasilicate (Na₂SiO₃ 9H₂O) and the conventional source-tetraethylorthosilicate (TEOS). The functionalized SBA-15 samples obtained from both silica sources were highly ordered, as evidenced by TEM and SAXS data. All obtained materials were mesoporous with high surface area values of up to 745 m²/g, pore volumes from 0.99 to 1.44 cm³/g, and narrow pore distributions near 7 nm. The adsorption affinity of the EDTA-functionalized samples followed the common order Pb(II)> Cd(II)> Cu(II)> Cr(III)> Mn(II), which could be explained based on the Pearson theory. The highest adsorption capacities were observed for samples functionalized by EDTA groups using TEOS for synthesis (TEOS/EDTA): 195.6 mg/g for Pb(II), 111.2 mg/g for Cd(II), 58.7 mg/g for Cu(II), 57.7 mg/g for Cr(III), and 49.4 mg/g for Mn(II). Moreover, organic matter (humic acid up to 10 mg/L) and inorganic (Na(I), K(I), Mg(II), Ca(II), etc) macrocomponents present in environmental water had almost negligible effect on the removal of these cations. The NaSi/EDTA/NH₂ sample revealed a better selectivity compared to the NaSi_/NH₂ sample towards such species as Cr(III), Mn(II), Cd(II), and Cu(II). The chromate-ions uptake at pH 7.5 by the TEOS/QAS sample turned practically unaffected by the presence of doubly charged anions (CO₃ ^2-, SO₄ ^2-). The content of functional groups on the surface of MS decreased only slightly (∼1-5%) after several regeneration cycles. The complete desorption of all heavy metal ions can be achieved using 1 mol/L EDTA solution. Reusability tests demonstrated the complete stability of the adsorbent for at least five to six consecutive adsorption/desorption cycles with no decrease in its adsorption characteristics compared to those obtained by 0.05 mol/L HNO₃ treatments. The synthesized mesoporous materials were evaluated for removal of the heavy metal ions from drinking and different natural water samples, proving their potential as sustainable, effective, and cost-efficient adsorbents.

Enhanced adsorptive removal of Cr(III) from the complex solution by NTA-modified magnetic mesoporous microspheres

The Fe₃O₄@nSiO₂@mSiO₂/NTA (FNMs-NTA) was prepared by grafting magnetic mesoporous microspheres with nitrilotriacetic acid (NTA) and applied as an adsorbent for the removal of Cr(III) from complex solutions. Some characterization techniques including Brunauer-Emmett-Teller (BET), Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), small-angle X-ray diffraction (SAXS), vibrating sample magnetometer (VSM), and thermal gravimetric analysis (TGA) were used to characterize functional groups and pore structure of FNMs-NTA, which proved that NTA was successfully decorated onto the magnetic Fe₃O₄@nSiO₂@mSiO₂ (FNMs) and FNMs-NTA featured a regular mesoporous structure. The batch adsorption of Cr(III) by FNMs-NTA exhibited high adsorption capacity (16.0 mg·g^-1 at pH 3.0, and 25 °C). Adsorption data followed Freundlich isotherm and adsorption process was a spontaneous adsorption process. Moreover, the kinetics of adsorption were well explained by pseudo-second-order kinetic model. FNMs-NTA showed resistance to interfering inorganic cations (Na⁺, Ca²⁺) and complexing agents (EDTA). Furthermore, FNMs-NTA exhibited remarkable regeneration performance and easy separation under external magnetic field. X-ray photoelectron spectroscopy (XPS) analysis showed the FNMs-NTA had excellent adsorption ability for Cr(III) because of the ion exchange and surface complexation.

Synthesis, characterization and application of new adsorbent composites based on sol-gel/chitosan for the removal of soluble substance in water

In this work, new adsorbent composites from the silica precursor tetraethyl orthosilicate (TEOS) and chitosan have been successfully synthesized, denominated 20%Chi, 30%Chi and 40%Chi. The composites presented enhanced chemical and physical characteristics, with emphasis on the high surface areas between 374.94 m²/g to 886.31 m²/g. The application of the composites in the model system (TY - Tartrazine yellow dye), presented adsorption capacities dependent on the amount of chitosan in the composite (40%Chi > 30%Chi > 20%Chi). However, from the experimental data of the constituent materials, 30%Chi provided the greatest increase in the adsorption capacity in the monolayer, with values of 36%. This demonstrates that the amount of chitosan in the compound alters the arrangement of adsorption sites. The 30%Chi composite presented life cycle superior to 10 reuse cycles.

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The addition of silica provided better physical and chemical properties to the developed composites.

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The synthesis of the 30%Chi composite enabled an increase in the adsorption capacity of the TY dye.

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The 30%Chi composite obtained a surface area of 886.31 m²/g.

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The 30%Chi composite was useful for more than 10 adsorption and desorption cycles.

Tapping the potential of a glucosamine polysaccharide-diatomaceous earth hybrid adsorbent in the solid phase extraction of a persistent organic pollutant and toxic pesticide 4,4'-DDT from water

A chitosan (a glucosamine polysaccharide)-diatomaceous earth hybrid was studied for the adsorption of 4,4′-dichloro-diphenyl-trichloroethane (4,4′-DDT), a persistent organic pollutant and organochlorine pesticide compound from water. The diverse adsorption process parameters were studied and the modified adsorbent was characterized through XRD, SEM-EDX, FT-IR, XRF, BET and TGA analysis. The concentration of 4,4′-DDT was measured using gas chromatography-tandem mass spectrometry (GC-MS/MS) by adopting a validated analytical procedure. The Langmuir and Freundlich isotherms ascertained the adsorption capacity. The optimum pH and temperature for 4,4′-DDT adsorption were found to be between 5.0 and 7.0 and 20 and 30 °C respectively. Thermodynamic parameters confirmed that the adsorption of DDT on chitosan modified with diatomaceous earth was an exothermic process. The data obtained from kinetics and intra-particle diffusion showed that the composite material is able to sequester 4,4′-DDT and this is reflected in the Langmuir adsorption capacity of 0.968 mg g⁻¹. The adsorbed 4,4′-DDT was successfully eluted with ethyl acetate and recycling studies showed that the modified chitosan can be used for three cycles with significant adsorption performance and this adsorbent proved its efficacy in removing 4,4′-DDT from farm water.

A chitosan (a glucosamine polysaccharide)-diatomaceous earth hybrid was studied for the adsorption of 4,4′-dichloro-diphenyl-trichloroethane (4,4′-DDT), a persistent organic pollutant and organochlorine pesticide compound from water.

Synthesis of glutaraldehyde-modified silica/chitosan composites for the removal of water-soluble diclofenac sodium

Composite materials are effective adsorbents for the removal of various types of contaminants, such as pharmaceutical products. However, they require improvement to achieve a good adsorption capacity. This study presents the development of a promising adsorbent: silica/chitosan modified with different proportions of glutaraldehyde, which involves the D-glucosamine units from chitosan. The developed materials were evaluated for their ability to remove diclofenac sodium. The adsorption data showed that the diclofenac adsorption efficiency increased with increasing degree of glutaraldehyde crosslinking. The equilibrium and kinetic data were well fit by the Liu and Elovich models, respectively, and the maximum adsorption capacity was 237.8 mg/g. Therefore, it can be assumed that the process is predominantly chemical and exothermic, with a high affinity between the adsorbents and diclofenac sodium. The adsorption mechanisms were investigated to better understand the interactions, and the predominance of covalent bonds with the self-polymerized glutaraldehyde was verified.

New rhodium(II)-ED3AP-complex: Crystal structure, characterization and computational chemistry

Only one (trans(O5)-Na[Rh(ed3ap)]?3H2O) of possible two isomers was synthesized and characterized by single crystal X-ray analysis, IR, and UV-Vis spectroscopy. Computational analysis of both isomers was performed with three levels of theory (B3LYP/TZV, BP86/TZV, OPBE/TZV), which gave consistent results. The more stable isomer by total energy and ligand field stabilization energy (LFSE) was trans(O5) which appeared in synthesis. Calculation of excited state energies complied with UV-Vis spectra, especially with OPBE functional. The results of excited state energy pointed out the differences among isomers in means of a splitting pattern of 1T2g excited state term. Both isomers have a strongly delocalized structure according to the natural bonding orbital (NBO) analysis. The trans(O5) geometry has the stabilization of the whole system for roughly 87 kJ/mol and makes this isomer as the only one present in the reaction mixture.

Removal of levofloxacin from aqueous solution by green synthesized magnetite (Fe3O4) nanoparticles using Moringa olifera: Kinetics and reaction mechanism analysis

Levofloxacin antibiotic is frequently being detected in the environment and regarded as an emerging contaminant. The present study was focused on the green synthesis of magnetite (Fe₃O₄ - gINPs) nanoparticles from Moringa olifera and its efficiency for removal of levofloxacin from aqueous solution. The adsorbent magnetite nanoparticles (Fe₃O₄) were prepared by green synthesis using Moringa olifera and coprecipitation method. Characterizations analyses of both chemically and green synthesized nanoparticles were performed by SEM, XRD, and FTIR. The average crystallite size of gINPs was 14.34 nm and chemically synthesized was 18.93 nm. The performance of the synthesized product was evaluated by adsorption capacity and removal efficiency. The parameters considered included adsorbent (gINPs) dosage, initial concentration of adsorbate, pH, contact time, and temperature. The obtained data were fitted to kinetic and isotherm models to determine the mechanism. Adsorption batch experiments were conducted to determine the reaction mechanism by studying kinetics while fitting isotherm models for samples analyzed using HPLC at 280 nm. Results showed that 86.15% removal efficiency of 4 mg L^-1 levofloxacin was achieved by 100 mg L^-1 gINPs in 24 h contact time when all other parameters (pH 7, temperature 25 °C) were kept constant. The maximum adsorption capacity achieved at equilibrium was 22.47 mg/g. Further, it was identified as a pseudo-second-order model with R² = 0.965 for adsorption kinetics while isotherm data better fitted to the Freundlich model compared to Langmuir isotherm with R² = 0.994. The potential pathway determined for levofloxacin removal was chemisorption with minor diffusion, multilayer, spontaneous and exothermic processes on the gINPs (Fe₃O₄). Reusability experiments were conducted in four cycles and removal efficiency varied from 85.35% to 80.47%, indicating very high potential of the adsorbent for re-use.

Diatom microalgae as smart nanocontainers for biosensing wastewater pollutants: recent trends and innovations

Microalgae have been recognized as one of the most efficient microorganisms to remediate industrial effluents. Among microalgae diatoms are silica shelled unicellular eukaryotes, found in all types of water bodies and flourish very well even in wastewater. They have their silica cell wall made up of nano arrayed pores arranged in a uniform fashion. Therefore, they act as smart nanocontainers to adsorb various trace metals, dyes, polymers, and drugs which are hazardous to human as well to aquatic life. The beautiful nanoarchitecture in diatoms allows them to easily bind to ligands of choice to form a nanocomposite structure with the pollutants which can be a chemical or biological component. Such naturally available diatom nanomaterials are economical and highly sensitive compared to manmade artificial silica nanomaterials to help in facile removal of the toxic pollutants from wastewater. This review is thus focused on employing diatoms to remediate various pollutants such as heavy metals, dyes, hydrocarbons detected in the wastewater. It also includes different microalgae as biosensors for determination of pollutants in effluents and the perspectives for nanotechnological applications in the field of remediating pollutants through microalgae. The review also discusses in length the hurdles and perspectives of employing microalgae in wastewater remediation.

A novel benzothiazole modified chitosan with excellent adsorption capacity for Au(III) in aqueous solutions

A novel benzothiazole modified chitosan (BCS) with excellent Au(III) adsorption performance and selectivity was prepared as adsorbents. The structure and morphology of the adsorbents were characterized by FTIR, SEM, XRD and XPS. The adsorption property of the adsorbents for Au(III) were investigated under different reaction time, initial concentration of Au(III), temperature, pH and coexisting ions. The maximum adsorption capacity of BCS for Au(III) was 1072.22 mg/g at 298 K and optimal pH = 4, which was better than that of other adsorbents reported in literature. The adsorption kinetics and isotherm models fit the pseudo-second-order and Langmuir equations. This shows that the adsorption process of Au(III) is a monolayer chemical adsorption. The adsorption process can proceed spontaneously and belong to the endothermic reaction according to the thermodynamic results. The excellent adsorption performance is mainly attributed to the ion exchange and chelation of the nitrogen, sulfur and oxygen groups on the adsorbent with gold ions. Significantly, BCS has excellent selectivity toward Au(III) and remarkable recycle performance. With the high adsorption capacity, excellent selectivity and outstanding reusability, the BCS adsorbent could be a promising candidate to adsorb Au(III) from wastewater.

Activated Graphene Oxide-Calcium Alginate Beads for Adsorption of Methylene Blue and Pharmaceuticals

The remarkable adsorption capacity of graphene-derived materials has prompted their examination in composite materials suitable for deployment in treatment of contaminated waters. In this study, crosslinked calcium alginate–graphene oxide beads were prepared and activated by exposure to pH 4 by using 0.1M HCl. The activated beads were investigated as novel adsorbents for the removal of organic pollutants (methylene blue dye and the pharmaceuticals famotidine and diclofenac) with a range of physicochemical properties. The effects of initial pollutant concentration, temperature, pH, and adsorbent dose were investigated, and kinetic models were examined for fit to the data. The maximum adsorption capacities q_max obtained were 1334, 35.50 and 36.35 mg g⁻¹ for the uptake of methylene blue, famotidine and diclofenac, respectively. The equilibrium adsorption had an alignment with Langmuir isotherms, while the kinetics were most accurately modelled using pseudo- first-order and second order models according to the regression analysis. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated and the adsorption process was determined to be exothermic and spontaneous.

Novel amidinothiourea-modified chitosan microparticles for selective removal of Hg(II) in solution

Glutaraldehyde-crosslinked chitosan microparticles (CGP) prepared via the inversed-phase emulsification were successively modified by epichlorohydrin (ECH) and amidinothiourea (AT) as novel adsorbent (CGPET) for selective removal of Hg(II) in solution. FTIR, EA, XPS, SEM-EDX, TG, DTG, and XRD results indicated that CGPET had ample -NH₂ and CS, relative rough surface, mean diameter of ~40 μm, great thermal stability, and crystalline degree of 2.4%, beneficial to the uptake of Hg(II). The optimum parameters (pH 5, dosage 1 g/L, contact time 4 h, and initial concentration 150 mg/L) were acquired via batches of adsorption experiments. Adsorption behavior was well described by the Liu isothermal and pseudo-second-order kinetics models, and the maximum adsorption capacity was 322.51 mg/g, surpassing many reported adsorbents. Regeneration and coexisting-ion tests demonstrated that CGPET had outstanding reusability (R_r > 86.89% at the fifth cycle) and selectivity (R_s > 93%). Besides, its potential adsorption sites and mechanisms were proposed.

Removal of multiple metal ions from wastewater by a multifunctional metal-organic-framework based trap

The design and preparation of multifunctional adsorbent for practical wastewater treatment is still an enormous challenge. To remove multiple metal ions from wastewater, we developed a broad-spectrum metal ions trap named UIO-67-EDTA by incorporation of ethylenediaminetetraacetic acid into robust UIO-67. The adsorption experiments for 15 kinds of heavy metal ions including hard acid (Mn²⁺, Ba²⁺, Al³⁺, Cr³⁺, Fe³⁺), borderline acid (Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Sn²⁺, Bi²⁺), soft acid (Ag⁺, Cd²⁺, Hg²⁺), and two kinds of dissolved minerals (Mg²⁺, Ca²⁺) show that the trap is very effective both in batch adsorption processes and breakthrough processes. At a pH value of 4.0, the removal efficiency for all metal ions was over 98% within 10 min, and the maximum static adsorption capacity for the representative metal ions Cr³⁺, Hg²⁺and Pb²⁺ was up to 416.67, 256.41, and 312.15 mg g^-1, respectively. The adsorption kinetics fitted well with the pseudo-second-order model, indicating that the chemical adsorption was the rate-determining step in the adsorption process. Meanwhile, the material showed high stability and recyclability, the removal efficiency for the three representative metals was still maintained over 93% after five consecutive adsorption cycles.

Polyaniline/Nanomaterial Composites for the Removal of Heavy Metals by Adsorption: A Review

Heavy metals represent one of the most important kinds of pollutants, causing serious threats to the ecological balance. Thus, their removal from aqueous solution is a major environmental concern worldwide. The process of adsorption—being very simple, economical, and effective—is widely applied for the decontamination of wastewaters from heavy metals. In this process, the adsorbent is the key factor affecting the performance; for this reason, significant efforts have been made to develop highly efficient and selective adsorbents with outstanding properties. This paper presents a detailed overview of the research on different methods of synthesis of nanocomposite materials based on the polymer polyaniline combined with nanomaterials, along with the influence of the synthesis method on their size, morphology, and properties. In addition, the study evaluates the adsorption efficiency of various developed nanocomposites for the adsorption of heavy metals from aqueous solution. From an economical and environmental point of view, the regeneration studies of the nanocomposites are also reported.

Tuning Polymorphs and Morphology of Microbially Induced Calcium Carbonate: Controlling Factors and Underlying Mechanisms

Microbially precipitated calcium carbonate (CaCO₃) has drawn broad attention due to its potential applications in various areas, for example, biocementation, medicine, and soil reinforcement. Sporosarcina pasteurii (S. pasteurii), formerly known as Bacillus pasteurii, has been investigated for CaCO₃ biomineralization due to its high ureolytic activity. A high degree of supersaturation with respect to the presence of bacterial cell wall, extracellular polymeric substances, and organic byproducts of bacterial activity plays an important role in the formation and stabilization of CaCO₃ polymorphs. Although microbially induced CaCO₃ and its polymorphs have been investigated broadly, the mechanisms of polymorph selection and morphological evolution are not well understood. This study employs ex situ approaches to address the complication of biomineralization in the presence of living organisms and to elucidate how solution chemistry, bacterial activity, and precipitation kinetics alter the polymorphism and morphology of CaCO₃ induced by S. pasteurii. The results indicate that in the presence of enough calcium ions and urea (as a carbonate source), the bacterial activity favors the formation and stabilization of vaterite. The morphological observations also provide valuable information on the particles' microstructure. The morphology of calcite evolves from single crystal to polycrystalline structures, and the morphology of vaterite evolved from spherical to oval-shaped structures on increasing the organic material concentration. Specific functional groups also exert morphological control on CaCO₃ polymorphs. However, the sensitivity of the calcite polymorph to the composition and orientation of these functional groups is higher compared to that of the vaterite polymorph. These findings offer important insights that can be used to constrain a set of experimental conditions for synthesizing a certain polymorph ratio for vaterite/calcite or a particular morphology of each polymorph and shed light on the crystallization and phase transformation mechanisms in such complicated bioenvironments.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.

Mesoporous silica adsorbents modified with amino polycarboxylate ligands - functional characteristics, health and environmental effects

A series of hybrid adsorbents were produced by surface modification with amino polycarboxylate ligands of industrially available microparticles (MP) of Kromasil® mesoporous nanostructured silica beads, bearing grafted amino propyl ligands. Produced materials, bearing covalently bonded functions as EDTA and TTHA, original Kromasil®, bearing amino propyl ligands, and bare particles, obtained by thermal treatment of Kromasil® in air, were characterized by SEM-EDS, AFM, FTIR, TGA and gas sorption techniques. Adsorption kinetics and capacity of surface-modified particles to adsorb Rare Earth Elements (REE), crucial for extraction in recycling processes, were evaluated under dynamic conditions, revealing specificity matching the ligand nature and the size of REE cations. A detailed comparison with earlier reported adsorbents for REE extraction was presented. The cytotoxicity was assessed using four different types of healthy cells, human skeletal muscles derived cells (SKMDC), fibroblast cells, macrophage cells (RAW264.7), and human umbilical vein endothelial cells (HUVECs), indicating lower toxicity of ligand-free MP than MP bearing amino poly-carboxylate functions. Internalization of the MP inside the cells and release of nitric oxide were observed. In addition, zebrafish embryos were exposed to high concentrations of MP and did not show any pronounced toxicity.

Recent Developments in Chitosan-Based Adsorbents for the Removal of Pollutants from Aqueous Environments

The quality of water is continuously under threat as increasing concentrations of pollutants escape into the aquatic environment. However, these issues can be alleviated by adsorbing pollutants onto adsorbents. Chitosan and its composites are attracting considerable interest as environmentally acceptable adsorbents and have the potential to remove many of these contaminants. In this review the development of chitosan-based adsorbents is described and discussed. Following a short introduction to the extraction of chitin from seafood wastes, followed by its conversion to chitosan, the properties of chitosan are described. Then, the emerging chitosan/carbon-based materials, including magnetic chitosan and chitosan combined with graphene oxide, carbon nanotubes, biochar, and activated carbon and also chitosan-silica composites are introduced. The applications of these materials in the removal of various heavy metal ions, including Cr(VI), Pb(II), Cd(II), Cu(II), and different cationic and anionic dyes, phenol and other organic molecules, such as antibiotics, are reviewed, compared and discussed. Adsorption isotherms and adsorption kinetics are then highlighted and followed by details on the mechanisms of adsorption and the role of the chitosan and the carbon or silica supports. Based on the reviewed papers, it is clear, that while some challenges remain, chitosan-based materials are emerging as promising adsorbents.

Predicted structure and selectivity of 3d transition metal complexes with glutamic N,N-bis(carboxymethyl) acid

Structure and selectivity of 3d transition metal complexes with glutamic N,N-bis(carboxymethyl) acid are analyzed and predicted from DFT calculations.

Generation-3 Polyamidoamine Dendrimer-Silica Composite: Preparation and Cd(II) Removal Capacity

Generation-3 polyamidoamine (PAMAM) dendrimer was implanted on silica to produce a very good adsorbent (G-3 PAMAM-SGA). The composite was characterized and used for the removal of Cd(II) ions from aqueous solution. Kinetic data fit the Lagergren pseudo-second-order model and also follow the intraparticle diffusion kinetic model to an extent, which is an indication that the sorption process is controlled by both mechanisms: intraparticle/film layer and adsorption inside the pores/crevices of the composite. Equilibrium sorption data of Cd(II) on G-3 PAMAM-SGA fit the Freundlich isotherm (R2 = 0.9993) which is indicative of multilayered adsorption that occurred on heterogeneous surfaces. The ΔG° values for all temperatures studied were negative, which indicated a spontaneous and feasible process. The result implies that G-3 PAMAM-SGA is a promising adsorbent for microscale scavenging of Cd(II) ions in aqueous solutions.

Cadmium and copper heavy metal treatment from water resources by high-performance folic acid-graphene oxide nanocomposite adsorbent and evaluation of adsorptive mechanism using computational intelligence, isotherm, kinetic, and thermodynamic analyses

In this paper, folic acid-coated graphene oxide nanocomposite (FA-GO) is used as an adsorbent for the treatment of heavy metals including cadmium (Cd²⁺) and copper (Cu²⁺) ions. As such, graphene oxide (GO) is modified by folic acid (FA) to synthesize FA-GO nanocomposite and characterized by the atomic force microscopy (AFM), Fourier transform-infrared (FT-IR) spectrophotometry, scanning electron microscopy (SEM), and C/H/N elemental analyses. Also, computational intelligence tests are used to study the mechanism of the interaction of FA molecules with GO. Based on the results, FA molecules formed a strong π-π stacking, chemical, and hydrogen bond interactions with functional groups of GO. Main parameters including pH of the sample solution, amounts of adsorbent, and contact time are studied and optimized by the Response Surface Methodology Based on Central Composite Design (RSM-CCD). In this study, the equilibrium of adsorption is appraised by two (Langmuir and Freundlich and Temkin and D-R models) and three parameter (Sips, Toth, and Khan models) isotherms. Based on the two parameter evaluations, Langmuir and Freundlich models have high accuracy according to the R² coefficient (more than 0.9) in experimental curve fittings of each pollutant adsorption. But, multilayer adsorption of each contaminant onto the FA-GO adsorbent (Freundlich equation) is demonstrated by three parameter isotherm analysis. Also, isotherm calculations express maximum computational adsorption capacities of 103.1 and 116.3 mg g^-1 for Cd²⁺ and Cu²⁺ ions, correspondingly. Kinetic models are scrutinized and the outcomes depict the adsorption of both Cd²⁺ and Cu²⁺ followed by the pseudo-second-order equation. Meanwhile, the results of the geometric model illustrate that the variation of adsorption and desorption rates do not have any interfering during the adsorption process. Finally, thermodynamic studies show that the adsorption of Cu²⁺ and Cd²⁺ onto the FA-GO nanocomposite is an endothermic and spontaneous process.

Effects of EDTA on adsorption of Cd(II) and Pb(II) by soil minerals in low-permeability layers: batch experiments and microscopic characterization

Ethylenediaminetetraacetic acid (EDTA) can serve as a washing agent in the remediation of low-permeability layers contaminated by heavy metals (HMs). Therefore, batch adsorption experiments, where pure quartz (SM1) and mineral mixtures (SM2) were used as typical soil minerals (SMs) in low-permeability layers, were implemented to explore the effects of different EDTA concentrations, pH, and exogenous chemicals on the HM-SM-EDTA adsorption system. As the EDTA concentration increased, it gradually cut down the maximum Cd adsorption capacities of SM1 and SM2 from approximately 135 to 55 mg/kg and 2660 to 1453 mg/kg; and the maximum Pb adsorption capacities of SM1 and SM2 were reduced from 660 to 306 mg/kg and 19,677 to 19,262 mg/kg, respectively. When the initial mole ratio (MR = moles of HM ions/sum of moles of HM ions and EDTA) was closer to 0.5, the effect of EDTA was more effective. Additionally, EDTA worked well at pH below 7.0 and 4.0 for Cd and Pb, respectively. Low-molecular-weight organic acids (LMWOAs) affected the system mainly by bridging, complexation, adsorption site competition, and reductive dissolution. Cu²⁺, Fe²⁺ ions could significantly increase the Cd and Pb adsorption onto SM2. Notably, there were characteristic changes in mineral particles, including attachment of EDTA and microparticles, agglomeration, connection, and smoother surfaces, making the specific surface area (SSA) decrease from 16.73 to 12.59 m²/g. All findings indicated that EDTA could effectively and economically reduce the HM adsorption capacity of SMs at the reasonable MR value, contact time, and pH; EDTA reduced the HM adsorption capacity of SMs not only by complexation with HM ions but also by decreasing SSA and blocking active sites. Hence, the acquired insight from the presented study can help to promote the remediation of contaminated low-permeability layers in groundwater.

Removal of Chromium(VI) by Chitosan Beads Modified with Sodium Dodecyl Sulfate (SDS)

In this study, chitosan beads modified with sodium dodecyl sulfate (SDS) were successfully synthesized and employed for the removal of chromium(VI) (Cr(VI)). The adsorption performance of the adsorbent (SDS-chitosan beads) was examined by batch experiments. The partition coefficient (PC) as well as the adsorption capacity were evaluated to assess the true performance of the adsorbent in this work. The adsorbent (SDS-chitosan beads) showed a maximum Cr(VI) adsorption capacity of 3.23 mg·g−1 and PC of 9.5 mg·g−1·mM−1 for Cr(VI). The prepared adsorbent was characterized by different techniques such as scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS) and Fourier transform-infrared spectroscopy (FT-IR). We used inductively coupled plasma mass spectrometry (ICP-MS) for the determination of Cr(VI) in solution. The experimental data could be well-fitted by pseudo-second-order kinetic and Langmuir isotherm models. The thermodynamic studies indicated that the adsorption process was favorable under the higher temperature condition. The SDS-modified chitosan beads synthesized in this work represent a promising adsorbent for removing Cr(VI).

Enhanced immobilization of mercury (II) from desulphurization wastewater by EDTA functionalized graphene oxide nanoparticles

Graphene oxide (GO) is a new promising nanometer material in a superconductor and wastewater heavy metal ions removal for its functionalized groups. Ethylenediaminetetraacetic acid functionalized graphene oxide complexes (EDTA-GO) was produced by a realizable silanization chemical reaction. Characteristics of Hg(II) removal in desulphurization wastewater was also under investigation. The chemical composition and microstructures of the EDTA-GO adsorbents were characterized by X-ray photoelectron spectroscopy (XPS), Transmission electron microscope (TEM), Scanning Electron Microscopy (SEM) analyses. To investigate the performance of EDTA-GO adsorbents on adsorption of Hg(II) in wastewater of wet flue gas desulphurization (WFGD), experiments were performed to optimize the main influence factors such as reaction temperatures (35-70°C), pH values(2-13), contact time (0-120 min), initial Hg(II) concentrations(800 ug/L) and adsorbent doses (20-50 mg/L). The maximum uptake removal efficiency (97.14%) was achieved under the optimal conditions at the pH of 7, the temperature of 70°C, the Hg(II) concentration of 1200 μg/L and the EDTA-GO dose of 40 mg/L. The kinetic data fitting results were well consistent with the pseudo-second-order model (R²= 0.99997) and a spontaneous and endothermic adsorption reaction was elaborated by thermodynamics studies (ΔG < 0, ΔH > 0, ΔS > 0). The experiments of recycled adsorbents by HCl generation were carried out to obtain the performance of the reused EDTA-GO adsorbent, the fourth regenerative adsorption efficiency still maintained 80.4%, which indicated that excellent potential application in desulphurization wastewater treatment.

Adsorption of rare earth metals from wastewater by nanomaterials: A review

Rare earth elements are widely used in chemical engineering, the nuclear industry, metallurgy, medicine, electronics, and computer technology because of their unique properties. To fulfil ever increasing demands for these elements, recycling of rare-earth-element-containing products as well as their recovery from wastewater is quite important. In order to recover rare earth elements from wastewater, their adsorption from low-concentration aqueous solutions, by using nanomaterials, is investigated due to technological simplicity and high efficiency. This paper is a review of the state-of-the-art adsorption technologies of rare earth elements from diluted aqueous solutions by using various nanomaterials. Furthermore, desorption and reusability of rare earth metals and nanomaterials are discussed. On the basis of this review it can be concluded that laboratory testing indicates promising adsorption capacities, which depend significantly on nanomaterial type and adsorption conditions. The adsorption process, which mostly follows the Langmuir, Freundlich, Sips, and Temkin isotherms, is typically endothermic and spontaneous. Furthermore, pseudo-second order, pseudo-first order, and intra-particle diffusion models are the best models to describe the kinetics of adsorption. The dominant adsorption mechanisms are surface complexation and ion exchange. More investigation, however, will be required in order to synthesize appropriate, environmentally friendly, and efficient nanomaterials for adsorption of rare earth elements from real wastewater.

Acceleration and centralization of a back-diffusion process: Effects of EDTA-2Na on cadmium migration in high- and low-permeability systems

Pollutant accumulation in the low-permeability zones (LPZs) in groundwater systems is regarded as a secondary source, and its consequent back-diffusion can extend the timeframe of pump-and-treat remediation. However, the bioavailability and mobility of heavy metals and the medium characteristics can be changed during the process. This study investigated the accumulation and back-diffusion law of toxic metals and the effects of ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) on them by implementing a series of tank experiments. In these experiments, a cadmium solution was injected first, and deionized water or EDTA-2Na constantly washed the system consisting of different medium layers. The experimental results showed that the cadmium breakthrough curves had some concentration gradient reverse points where the curves fluctuated with elution by deionized water, which did not exist when EDTA-2Na was the eluent. In these scenarios, the mass of accumulated cadmium in the media before elution was large, with a value of 931 mg (153 mg/kg), when the low-permeability medium was clay. However, when EDTA-2Na was injected together with cadmium, the value dropped to 319 mg (52.3 mg/kg), greatly reducing the cadmium accumulation. Additionally, the use of EDTA-2Na as an eluent resulted in the appearance of a secondary peak in the breakthrough curve, showing that EDTA-2Na accelerated and centralized the back-diffusion. Notably, the reduced cadmium accumulation in LPZs with the elution by EDTA-2Na was partly due to a reduced adsorption capacity of the clay minerals. The above results can advance the technology related to pump-and-treat remediation.

Synthesis and Characterization of New Schiff Base/Thiol-Functionalized Mesoporous Silica: An Efficient Sorbent for the Removal of Pb(II) from Aqueous Solutions

A new type of silica hybrid material functionalized with Schiff base-propyl-thiol and propyl-thiol groups (adsorbents 1 and 2, respectively) was synthesized using a co-condensation method. The synthesized materials and their starting materials were successfully characterized using a variety of techniques such as Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption–desorption isotherms, the Brunauer–Emmett–Teller (BET) surface area calculation method, the Barrett, Joyner, and Halenda (BJH) pore size calculation method, thermogravimetry analysis (TGA), and 1H and 13C nuclear magnetic resonance (NMR) spectra. The results indicate that the new material (adsorbent 1) has a large surface and possesses different functional groups (-SH, -OH, -C=O and –N=C). The newly synthesized hybrid materials (1 and 2) were investigated as potential adsorbents for removal of toxic heavy metals, such as Pb(II) from aqueous solutions. The adsorption results show that materials 1 and 2 have different sorption properties and were found to be effective adsorbents for Pb(II) removal from aqueous solutions. In addition, compound 1 exhibited a higher adsorption capacity for Pb(II) compared to compound 2. The results showed that the optimum pH for Pb(II) sorption was 6.5. Contact time was observed to occur after 30 min for 25 mg L−1 Pb(II) concentration and adsorbent dose of 0.4 g L−1 at 25 °C.

Luminescence properties of the Ln-EDTA complexes covalently linked to the chitosan biopolymers containing β-diketonate as antenna ligands

This paper reports on the preparation, characterization, and photoluminescence properties of novel hybrid materials, in which the EDTA-Ln-L complexes (where L: H₂ O, acac, bzac, dbm, and tta ligands, and Ln: Eu, Gd, and Tb) were covalently linked to the precursor medium molecular weight chitosan surface (CS) matrices or on the chitosan surfaces previously crosslinked with epichlorohydrin (CSech). The emission spectra of these materials were characterized by intraconfigurational-4fN transitions centred on the Eu³⁺ and Tb³⁺ ions. Some broad bands from the polymeric matrix were also observed in the emission spectra, however the relative intensities of the intraconfigurational bands increased significantly for systems containing diketonate ligands when the antenna effect became more efficient. The values of the radiative rates (A_rad ) were higher for crosslinked hybrid systems with epichlorohydrin, while nonradiative rates (A_nrad ) presented the opposite behaviour. These data contributed to an increase in the values of emission quantum efficiency (η) for crosslinked materials. The effect of the modification process and antenna ligand on the values of intensities, intensity parameters Ω₂ e Ω₄ of the Eu³⁺ complexes were also investigated. The results showed that the crosslinked biopolymer surfaces have great potential for applications in molecular devices light converters.

Preparation of multifunctional nanocomposites Fe3O4@SiO2-EDTA and its adsorption of heavy metal ions in water solution

Novel magnetic Fe₃O₄@SiO₂-ethylenediamine tetraacetic acid (adsorbent) CMS-COOH-modified magnetic materials, CMS was prepared by surface modification of amino-functionalized Fe₃O₄@SiO₂ (-NH₂-modified magnetic materials, NMS) with EDTA using water-soluble carbodiimide as the cross-linker in deionized water solution. The phase structure, infrared spectra, thermal analysis and magnetic properties of were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and vibrating sample magnetometry and its properties for removal of heavy metal ions under varied experimental conditions were also investigated. The results revealed that CMS had good tolerance to low pH and exhibited good removal efficiency for the metal ions. The maximum adsorption capacities of CMS were found to be 0.11 mmol g^-1 for Cu(II) at pH5.0 (30 °C) and 0.14 mmol g^-1 for Pb(II) ions at pH2.0 (30 °C).