Removal of Hg(II) from aqueous solution by resin loaded magnetic β-cyclodextrin bead and graphene oxide sheet: Synthesis, adsorption mechanism and separation properties

Synthesis of salicylaldehyde tailored PAMAM dendrimers/chitosan for adsorption of aqueous Hg(II): Performance and mechanism

Water pollution caused by Hg(II) exerts hazardous effect to environmental safety and human health. Herein, a family of salicylaldehyde tailored poly(amidoamine) (PAMAM) dendrimers/chitosan composites (G0-S/CTS, G1-S/CTS, and G2-S/CTS) were prepared and used for the removal of Hg(II) from water solution. The adsorption performance of the as-prepared composites for Hg(II) was thoroughly demonstrated by determining various influencing factors. G0-S/CTS, G1-S/CTS and G2-S/CTS exhibited competitive adsorption capacity and good adsorption selective property for Hg(II). The maximum adsorption capacity of G0-S/CTS, G1-S/CTS and G2-S/CTS for Hg(II) were 1.86, 2.18 and 4.47 mmol‧g-1, respectively. The adsorption for Hg(II) could be enhanced by raising initial Hg(II) concentration and temperature. The adsorption process was dominated by film diffusion processes with monolayer adsorption behavior. The functional groups of NH2, CONH, CN, OH, CO and CN were mainly responsible for the adsorption of Hg(II). G0-S/CTS, G1-S/CTS and G2-S/CTS displayed good regeneration property and the regenerate rate maintained 95.00 % after five adsorption-desorption cycles. The as-prepared adsorbents could be potentially used for the efficient removal of Hg(II) from aqueous solution.

Nanocomposite with high adsorption activity developed using stabilized silver modified alumina and TiO2-NPs incorporated into β-cyclodextrin-graphene oxide

Multifunctional nanocomposites Ag/Al₂O₃/TiO₂@β-cyclodextrin-graphene oxide (AATG) incorporating graphene oxide sheets, TiO₂, and Ag/Al₂O₃ nanoparticles were prepared in two steps. We benefited from the inherent properties of β-cyclodextrin to create a stable aqueous graphene solution capable of self-assembling in situ grown TiO₂ nanoparticles on graphene nanosheets. Ag/Al₂O₃ catalysts with a high surface-to-volume ratio were prepared by a combustion technique in solution with urea as a new fuel. The synthesized nanoparticles were also characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis, and BJH pore analysis. FE-SEM was used to evaluate the morphology of β-cyclodextrin-graphene oxide, Ag/Al₂O₃ and AATG nanoplatforms. This research examined the use of AATG as a novel nanocomposite for removing methylene blue from water and compared its effectiveness with that of TiO₂@β-cyclodextrin-graphene oxide (TG) as an intermediate material to assess the impact of the final composite and its components on absorption. The effect of pH, temperature, time, and dye concentration on the reaction rate was investigated. The results showed that at pH above 4, the adsorption rate of MB by AATG gradually increased to about 98%. The results also show that methylene blue is more effectively removed at higher temperatures, implying that the adsorption is temperature dependent and the elimination process is endothermic. The adsorption kinetics, isothermal studies, and thermodynamic analysis were also evaluated. The adsorption data showed excellent agreement with pseudo-second order models (R² > 0.99) and the Langmuir isotherm. The AATG nanocomposites showed excellent adsorption activity, making them potential candidates for water treatment.

Ultrasound-assisted adsorption of chlorpyrifos from aqueous solutions using magnetic chitosan/graphene quantum dot‑iron oxide nanocomposite hydrogel beads in batch adsorption column and fixed bed

Chlorpyrifos is a hazardous material that pollutes the environment and also poses risks to human health. Thus, it is necessary to remove chlorpyrifos from aqueous media. In this study, chitosan-based hydrogel beads with different content of iron oxide-graphene quantum dots were synthesized and used for the ultrasonic-assisted removal of chlorpyrifos from wastewater. The results of batch adsorption experiments showed that among the hydrogel beads-based nanocomposites, the chitosan/graphene quantum dot‑iron oxide (10) indicated a higher adsorption efficiency of about 99.997 % at optimum conditions of the response surface method. Fitting the experimental equilibrium data to different models shows that the adsorption of chlorpyrifos is well described by the Jossens, Avrami, and double exponential models. Furthermore, for the first time, the study of the ultrasonic effect on the removal performance of chlorpyrifos showed that the ultrasonic-assisted removal of chlorpyrifos significantly reduces the equilibration time. It is expected that the ultrasonic-assisted removal strategy can be a new method to develop highly efficient adsorbents for rapid removal of pollutants in wastewater. Also, the results of the fixed bed adsorption column showed that the breakthrough time and exhausting time of chitosan/graphene quantum dot‑iron oxide (10) were equal to 485 and 1099 min, respectively. And finally, the adsorption-desorption study showed the successful reuse of adsorbent for chlorpyrifos adsorption in seven runs without a significant decrease in adsorption efficiency. Therefore, it can be said that the adsorbent has a high economic and functional potential for industrial applications.

Feasible synthesis of bifunctional polysilsesquioxane microspheres for robust adsorption of Hg(II) and Ag(I): Behavior and mechanism

The pollution of Hg(II) and Ag(I) to water system exerts hazardous effect to aquatic ecosystem and public security. Simple strategy for constructing adsorbents to efficient remove them is greatly desired. Thus, a series of thiol and amino groups containing bifunctional polysilsesquioxanes (ASPSS) microspheres with adjustable porous structure and functional group content were synthesized by one-step feasible sol-gel process. The adsorption behavior and mechanism of ASPSS microspheres toward Hg(II) and Ag(I) was thoroughly determined. The maximum adsorption capacity of ASPSS for Hg(II) and Ag(I) are 4.32 and 3.86 mmol·g^-1 under 25 ℃. The as-prepared ASPSS microspheres can 100% selectively capture Hg(II) with the coexisting of Mn(II), Co(II), Pb(II), Cd(II), Cu(II), Fe(III). And they can 100% adsorb Ag(I) with the presence of Cd(II), Pb(II), Co(II), Ni(II), and Zn(II). Moreover, the ASPSS microspheres exhibit good removal efficiency for Hg(II) and Ag(I) from simulated industrial wastewater with the coexistence of multiple pollutants. Adsorption mechanism suggests the adsorption for Hg(II) and Ag(I) is the synergistic coordination effect of amino and thiol groups. The excellent adsorption selectivity for Hg(II) and Ag(I) is attributed to the super binding ability of these functional group. ASPSS microspheres also exhibit good regeneration ability and could be reused for removing Hg (II) and Ag(I) from aqueous solution with practical value.

Mesoporous Silica Materials Loaded with Gallic Acid with Antimicrobial Potential

This paper aimed to develop two types of support materials with a mesoporous structure of mobile crystalline matter (known in the literature as MCM, namely MCM-41 and MCM-48) and to load them with gallic acid. Soft templating methodology was chosen for the preparation of the mesoporous structures—the cylindrical micelles with certain structural characteristics being formed due to the hydrophilic and hydrophobic intermolecular forces which occur between the molecules of the surfactants (cetyltrimethylammonium bromide—CTAB) when a minimal micellar ionic concentration is reached. These mesoporous supports were loaded with gallic acid using three different types of MCM—gallic acid ratios (1:0.41; 1:0.82 and 1:1.21)—and their characterizations by FTIR, SEM, XRD, BET and drug release were performed. It is worth mentioning that the loading was carried out using a vacuum-assisted methodology: the mesoporous materials are firstly kept under vacuum at ~0.1 barr for 30 min followed by the addition of the polyphenol solutions. The concentration of the solutions was adapted such that the final volume covered the wet mesoporous support and—in this case—upon reaching normal atmospheric pressure, the solution was pushed inside the pores, and thus the polyphenols were mainly loaded inside the pores. Based on the S_BET data, it can be seen that the specific surface area decreased considerably with the increasing ratio of gallic acid; the specific surface area decreased 3.07 and 4.25 times for MCM-41 and MCM-48, respectively. The sample with the highest polyphenol content was further evaluated from a biological point of view, alone or in association with amoxicillin administration. As expected, the MCM-41 and MCM-48 were not protective against infections—but, due to the loading of the gallic acid, a potentiated inhibition was recorded for the tested gram-negative bacterial strains. Moreover, it is important to mention that these systems can be efficient solutions for the recovery of the gut microbiota after exposure to antibiotics, for instance.

Evolution of the earthworm (Eisenia fetida) microbial community in vitro and in vivo under tetracycline stress

Bioremediation of contaminated soil has received increasing attention, and the effects of antibiotic residues on the soil ecological environment are a current research hotspot. Earthworms are the first choice of soil organisms to indicate the degree of soil pollution, and their detoxification mechanism after antibiotic stress must be further explored. Taking Eisenia fetida as the research object, an antibiotic (tetracycline) stress test was carried out in sterile artificial soil. The stress concentrations were set at 0, 0.3, 3, 30, 300 and 600 mg/kg. The ECO method was used to cultivate microbes in earthworms and soil. The carbon source utilization intensity algorithm developed by our team was used for data statistics, and a factor analysis model was constructed to explore the succession process of microbes of earthworms in vivo and in vitro under tetracycline stress. The results showed that there were four processes in the evolution of microbes under short-term tetracycline stress: at 1-3 days, the microbes in worms played a leading role; at 4-5 days, the microbes in the worms and the soil microbes jointly resisted TET stress; after 6-8 days of stress, the microbes in worms still played the main role, but their role was weakened; and after 9-10 days, soil microbes played a leading role, and tolerant microbes appeared. Under long-term stress, the microbes of earthworms in vivo and in vitro were obvious different, and there may be no regulatory relationship. And the factor analysis model is suitable for the analyse of the changes in microbial communities in vivo and in vitro under TET stress. The research results provide a reference method and model basis for the bioremediation of antibiotic-contaminated soil and the study of earthworm detoxification mechanisms, and help agricultural development.

An environmentally benign synthesis of Fe3O4 nanoparticles to Fe3O4 nanoclusters: Rapid separation and removal of Hg(II) from an aqueous medium

In the field of nanotechnology, nanoadsorbents have emerged as a powerful tool for the purification of contaminated aqueous environments. Among the variety of nanoadsorbents developed so far, magnetite (Fe₃O₄) nanoparticles have drawn particular interest because of their quick separation, low cost, flexibility, reproducibility, and environmentally benign nature. Herein, we describe a new strategy for the synthesis of Fe₃O₄ nanoclusters, which is based on the use of naturally available edible mushrooms (Pleurotus eryngii) and environmentally benign propylene glycol as a solvent medium. By tuning the temperature, we successfully convert Fe₃O₄ nanoparticles into Fe₃O₄ nanoclusters via hydrothermal treatment, as evidenced by transmission electron microscopy. The Fe₃O₄ nanoclusters are functionalized with an organic molecule linker (dihydrolipoic acid, DHLA) to remove hazardous Hg(II) ions selectively. Batch adsorption experiments demonstrate that Hg(II) ions are strongly adsorbed on the material surface, and X-ray photoelectron and Fourier transform infrared spectroscopy techniques reveal the Hg(II) removal mechanism. The DHLA@Fe₃O₄ nanoclusters show a high removal efficiency of 99.2 % with a maximum Hg(II) removal capacity of 140.84 mg g^-1. A kinetic study shows that the adsorption equilibrium is rapidly reached within 60 min and follows a pseudo second-order kinetic model. The adsorption and separation system can be readily recycled using an external magnet when the separation occurs within 10 s. We have studied the effect of various factors on the adsorption process, including pH, concentration, dosage, and temperature. The newly synthesized superparamagnetic DHLA@Fe₃O₄ nanoclusters open a new path for further development of the medical, catalysis, and environmental fields.

A review on remediation technologies using functionalized Cyclodextrin

Modern lifestyle and alleviated anthropogenic activities have increased the pollutant load, ultimately causing stress on the environment. In industrialization, many harmful compounds are released into the environment polluting air, water, and soil, triggering adverse impacts on the ecosystem and human beings. Therefore, the development of advanced remediation technologies turns out as a significant environmental priority. Less polar cyclic oligosaccharide Cyclodextrin (CD) with cavity binding organic compounds attracted attention by helping effectively as environmental application. The formation of inclusion complexes and modified Cyclodextrin by cross-linking or surface modification enhances their capacity to abate pollutant effectively from the environment. Modification results in the formation of several novel materials such as CD-based composites, nanocomposites, crosslinked polymer or hydrogels, potent cross-linkers, CD-based membranes, and CD immobilized supports. Several environmental remediation technologies based on Cyclodextrin and modified Cyclodextrin have been discussed in detail in this review. Various environmental applications of Cyclodextrin and its derivatives have been discussed, along with their formation, properties, and characterization. Effective removal of organic pollutants, inorganic pollutants, micropollutants, volatile compounds etc., has been explained using several remediation technologies. Based on CD innocuity, this is referred to as the green process. The reversible equilibrium corresponded by the inclusion phenomenon sets a significant trend in the field of CD environmental application to develop techniques by incorporating supramolecular chemistry as well as irreversible methods such as biodegradation and advanced oxidation. It helps in the complete removal of pollutants and ultimately recycling the CD.

Synthesis of nano-scale zero-valent iron-reduced graphene oxide-silica nano-composites for the efficient removal of arsenic from aqueous solutions

Design and synthesis of arsenic adsorbents with high performance and excellent stability has been still a significant challenge. In this study, we anchored nano-zero-valent iron (NZVI) on the surface of graphene-silica composites (GS) with high specific surface area, forming the NZVI/GS nano-composite. The prepared nano-materials were used to remove As(III) and As(V) through adsorption from aqueous solutions. The results indicated that NZVI particles were dispersed well on the surface of GS, and the NZVI/GS showed great potential to remove As(III) and As(V). Adsorption performance of NZVI/GS for As(III) and As(V) highly depended on the pH of solutions. The experimental data fitted well with the pseudo-second-order kinetic model and the Langmuir isotherm model. The calculated maximum adsorption capacities of NZVI/GS for As(III) and As(V) were up to 45.57 mg/g and 45.12 mg/g at 298 K, respectively, and the adsorption equilibrium could be reached within 60 min. The residual concentrations of As(III) and As(V) after treatment with 0.4 g/L NZVI/GS can meet with the drinking water standard of WHO when the initial concentrations were below 4 mg/L and 3 mg/L, respectively. Moreover, the as-prepared NZVI/GS had excellent anti-interference ability during the process of As removal in the presence of foreign ions. During the As removal process, As(III) was oxidized to As(V), which could be removed through adsorption by electrostatic attraction and complexation. These results indicated that the as-synthesized NZVI/GS composite is a promising adsorbent for the removal of arsenic from aqueous solutions.

Enhanced photocatalytic response of ZnO embedded chitosan/β-cyclodextrin towards the detoxification of Cr(VI) under visible light

The present work focused on the assessment of heterogenous photocatalytic efficacy of ZnO@CS-β-CD towards the degradation of hexavalent chromium under visible light illumination. The prepared ZnO@CS-β-CD was extensively characterized using XRD, FTIR, SEM, EDX with mapping, TGA, DSC and UV/vis DRS techniques and the photoreduction of Cr(VI) to Cr(III) was confirmed by X-ray photoelectron spectroscopy. The DRS results revealed that the band gap of ZnO@CS-β-CD was narrowed than ZnO from 3.23 to 2.01 eV. The photocatalyst hold excellent reusability up to seven cycles and the field trail results demonstrated for the practical application for the treatment of wastewater.

Adsorption of low-concentration mercury in water by 3D cyclodextrin/graphene composites: Synergistic effect and enhancement mechanism

The efficient removal of mercury from aqueous media remains a severe challenge in ensuring environmental safety, especially for low-concentration mercury, which requires adsorbents with high mercury affinity. In this work, we reported a nanocomposite of β-cyclodextrin and three-dimensional graphene (3D CD@RGO) to enhance the adsorption affinity and capacity for mercury with low concentrations. Characterization of the nanocomposite revealed that cyclodextrin was well dispersed on the 3D graphene support structure to provide highly exposed hydroxyl groups. Adsorption experiments showed that CD@RGO exhibited different adsorption behaviors for mercury within different concentration ranges of 0.2-4.0 mg/L and 4.0-10.0 mg/L, and the adsorption affinity for the former range (K_L = 10.05 L/mg) was 1.5 times higher than that for the latter range (K_L = 6.69 L/mg). Moreover, CD@RGO had a high adsorption efficiency of 96.6% with a superb adsorption affinity (172.09 L/g) at C_e = 0.01 mg/L, which is 6.70 and 41.25 times higher than that of RGO and RCD (physical mixture of RGO and cyclodextrin), respectively, indicating a synergistic effect of CD@RGO for mercury adsorption. This enhancement can be attributed to the transformation of the adsorption mechanism from the outer-sphere force of electrostatic interaction in RGO to the inner-sphere surface complexation in CD@RGO.

Maleic Anhydride Cross-Linked β-Cyclodextrin-Conjugated Magnetic Nanoadsorbent: An Ecofriendly Approach for Simultaneous Adsorption of Hydrophilic and Hydrophobic Dyes

A magnetic nanoadsorbent with a cross-linked β-Cyclodextrin maleic anhydride polymer capable of simultaneous removal of hydrophilic and hydrophobic dyes was developed with high efficacy and desorption/recycling efficiency. The effect of various parameters (concentration, adsorbent dosage, contact time, pH, and temperature) was evaluated to assess the optimum adsorption conditions. The superparamagnetic nanoadsorbent (SPNA) could be easily separated by magnetic decantation and showed maximum removal of malachite green with 97.2% adsorption efficiency. Studies on simultaneous adsorption of dyes from a mixture were performed and the adsorption capacity was calculated. Interestingly, the phenomenon of competitive adsorption was observed. The adsorption process can be fitted well into the Langmuir isotherm model and follows pseudo-second-order kinetics. SPNA could be effectively regenerated and recycled at least five times without any significant loss in removal efficiency. SPNA could be an ideal adsorbent for water remediation because of excellent dye removal efficiency in addition to chemical stability, ease of synthesis, and better reusability.

Qualitative and Quantitative Analysis of Graphene-Based Adsorbents in Wastewater Treatment

Nowadays water bodies across the world are heavily polluted due to uncontrollable contamination of heavy metal particles, toxic dyes, and other harmful wastes discharged by emerging industries other than normal domestic wastages. This contamination needs sufficient control to protect the natural water bodies. There are various methodologies to be followed to perform wastewater treatment, in which the adsorption method of filtration is found to be efficient. The adsorption method is a high priority and preferable filtration method compared to other waste water treatment methods due to its peculiar characteristics. Considering the adsorption method, there are multiple options available in selecting material and methodology for the filtration process. In selecting the filtering material, there is much attraction towards graphene and its oxides, which have widespread range of differential applications in commercial industries because of their eco-friendly characteristic features. The importance of various graphene composites and their chemical properties is found to be significant in various fields. Analyzing the adsorbing properties of graphene widely, this article deeply reviews about the improvements and the technologies identified for using graphene and (GO) graphene oxide in wastewater treatment taken into discussion elaborately. Therefore, in this hard review, the advantages and demerits of using graphene for wastewater treatment as well as improving its properties to make it more suitable for wastewater treatment are detailed.

Study on the microbial community in earthworm and soil under cadmium stress based on contour line analysis

Cadmium (Cd) contamination in soil has become the focus of widespread concern in society today. In this paper, with Eisenia fetida as research subjects, an indoor simulation experiment was conducted. A BIOLOG microplate technique was used to determine the carbon source (single-carbon) utilization of the microbial communities in the contaminated soil and earthworms under Cd stress. Contour line analysis was used for the first time to study the difference of carbon source metabolism in microbial communities. And the effects of Cd stress on the functional diversity of the microbial communities and the detoxification mechanism in earthworms were researched. With two test groups, a short-term test and the long-term test were performed. The former test lasted for 10 days, with the removal of an earthworm every day for analysis; the latter test lasted for 30 days, with the removal of an earthworm every 10 days. The Cd²⁺ concentration was set at 0, 50, 100, 125, 250, or 500 mg kg^-1 dry weight, and 10 earthworms were inoculated in each concentration treatment. The earthworm homogenate and soil extracts were used to determine the carbon source utilization of the microbial communities. The results show that Cd stress changed the functional diversity of the microbial communities in the soil and earthworms. With the extension of stress time and the increase of stress concentration, earthworms will adjust their own physiological functions (including the microbial community structure and stress mechanism in the body) and regulate the microbial community structure in the external environment to obtain the necessary substances for growth. In addition, 2-hydroxybenzoic acid, γ-hydroxybutyric acid, glutamyl-L-glutamic acid, α-butyric acid, threonine, and α-cyclodextrin were important carbon sources for the earthworms to maintain their normal physiological metabolism under Cd stress. This study confirms that changes in microbial communities can be used to reveal the detoxification mechanisms of earthworm under heavy metal stress.

Application of Iron-Based Materials for Remediation of Mercury in Water and Soil

Mercury contamination in soil and water has become a major concern to environmental quality and human health. Among the existing remediation technologies for mercury pollution control, sorption via iron-based materials has received wide attention as they are environmental friendly and economic, and their reactivity is high and controllable through modulating the morphology and surface properties of particulate materials. This paper aimed to provide a comprehensive overview on environmental application of a variety of iron-based sorbents, namely, zero valent iron, iron oxides, and iron sulfides, for mercury remediation. Techniques to improve the stability of these materials while enhancing mercury sequestration, such as nano-scale size control, surface functionalization, and mechanical support, were summarized. Mechanisms and factors affecting the interaction between mercury and iron-based materials were also discussed. Current knowledge gaps and future research needs are identified to facilitate a better understanding of molecular-level reaction mechanisms between iron-based materials and mercury and the long-term stability of the immobilized mercury.

Treatment of wastewater containing Reactive Brilliant Blue KN-R using TiO2/BC composite as heterogeneous photocatalyst and adsorbent

Heterogeneous photocatalysis namely titanium dioxide (TiO₂) supported on coconut shell biochar (BC) was synthesized by sol-gel method (calcined at 450 °C) in the paper, which was innovatively applied to the decolorization of Reactive Brilliant Blue KN-R. The transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD) results demonstrated that anatase TiO₂ film was firmly immobilized on the surface and pores of BC. The photocatalysis tests under UV high pressure xenon lamp (300 W) showed highest decolorization efficiency occurred at strong acid and alkali conditions (pH = 1 and 11) reached as 99.71% and 96.99% respectively within 60 min. Therefore, the TiO₂/BC composites demonstrated both photocatalytic and adsorption capacity on KN-R decolorized, and presented quite durable and reusable in regeneration cycles, indicating a widely application possibility in anthraquinones dyeing wastewater treatment.

Recent developments in the synthesis and applications of graphene-family materials functionalized with cyclodextrins

The introduction of cyclodextrin species to graphene-family materials (GFMs) constitutes an important area of research, especially in terms of the development of applied nanoscience. The chemistry of cyclodextrins is the so-called host-guest chemistry, which has impacted on many fields of research, including catalysis, electrochemistry and nanomedicine. Cyclodextrins are water-soluble and biocompatible supramolecules, and therefore they may introduce new interesting properties to GFMs and may enhance the physicochemical/biological features of native GFMs. The reported methods for the conjugation of cyclodextrins to GFMs utilize either covalent or non-covalent approaches. The recent progress in the applications of GFMs functionalized with cyclodextrins, with the respect to the chemistry and features of these conjugates, is discussed. Special consideration is also given to the recent developments in (i) nanomedicine, (ii) electrochemistry, (iii) adsorption and (iv) catalysis. Examples of these materials are discussed in this work, together with the future outlook on the impact of GFM-cyclodextrin conjugates in the development of applied nanoscience.

Removal of tetracycline from aqueous solution by MCM-41-zeolite A loaded nano zero valent iron: Synthesis, characteristic, adsorption performance and mechanism

In this study, nano zero valent iron (NZVI) modified MCM-41-zeolite A (Fe-MCM-41-A) composite as a novel adsorbent was prepared by precipitation method and applied for tetracycline (TC) removal from aqueous solution. The adsorbent was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and N₂-BET analysis. Hysteresis loops indicated that the sample has a desirable magnetic property and can be separated quickly. Adsorption studies were carried out to evaluate its potential for TC removal. Results showed that the optimal Fe-MCM-41-A dosage, initial pH and reaction time at initial TC concentration of 100mgL^-1 solution are 1gL^-1, pH=5, and 60 min respectively, at which the removal efficiency of TC was 98.7%. The TC adsorption results fitted the Langmuir isotherm model very well and the adsorption process could be described by a pseudo-second-order kinetic model. A maximum TC adsorption capacity of 526.32mgg^-1 was achieved. This study demonstrates that Fe-MCM-41-A is a promising and efficient material for TC adsorption from aqueous solution.

Adsorption of Hg(II) from aqueous solution using functionalized hydrogel loaded with hydrous manganese dioxide particles

In this paper, a high performance adsorbent (hydrous manganese oxides onto acylamino and hydroxyl functionalized hydrogel) containing manganese oxide was prepared by the cross-linking polymer; the novel composite adsorbent has an excellent adsorption for Hg(II) removal. The adsorbent was characterized by scanning electron microscopy and Fourier transform infrared analysis, the hydrogel adsorbent had a typical three-dimensional network structure, and manganese oxides particles were dispersed into the channel and pores structure. The adsorption of Hg²⁺ in water was tested by using the adsorbent. The results show that the adsorption isotherms were fitted well with Langmuir model, and the maximum Hg²⁺ adsorption capacity was 0.654 mmol g^-1 (131.2 mg g^-1). The adsorption kinetics followed a pseudo-second-order equation, and the adsorption equilibrium can be reached in the first 120 min. The optimum pH of adsorption was determined to be 8.0. The desorption efficiency of 94% can be reached using 0.7 mol L^-1 HCl as the regeneration agent. The results suggest that this material can be a promising adsorbent for Hg²⁺ removal in several industrial processes.

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

This review focuses on environmental implications and applications of engineered magnetite (Fe3O4) nanoparticles (MNPs) as a single phase or a component of a hybrid nanocomposite that exhibits superparamagnetism and high surface area. MNPs are synthesized via co-precipitation, thermal decomposition and combustion, hydrothermal process, emulsion, microbial process, and green approaches. Aggregation/sedimentation and transport of MNPs depend on surface charge of MNPs and geochemical parameters such as pH, ionic strength, and organic matter. MNPs generally have low toxicity to humans and ecosystem. MNPs are used for constructing chemical/biosensors and for catalyzing a variety of chemical reactions. MNPs are used for air cleanup and carbon sequestration. MNP nanocomposites are designed as antimicrobial agents for water disinfection and flocculants for water treatment. Conjugated MNPs are widely used for adsorptive/separative removal of organics, dyes, oil, arsenic, phosphate, molybdate, fluoride, selenium, Cr(VI), heavy metal cations, radionuclides, and rare earth elements. MNPs can degrade organic/inorganic contaminants via chemical reduction or catalyze chemical oxidation in water, sediment, and soil. Future studies should further explore mechanisms of MNP interactions with other nanomaterials and contaminants, economic and green approaches of MNP synthesis, and field scale demonstration of MNP utilization.

Highly promoted removal of Hg(ii) with magnetic CoFe2O4@SiO2 core–shell nanoparticles modified by thiol groups

A simple and environmentally friendly material, CoFe₂O₄@SiO₂–SH, was prepared successfully with CoFe₂O₄ nanoparticles coated by SiO₂ which was further functionalized with thiol groups (–SH).

Highly efficient ultrasonic-assisted removal of Hg(II) ions on graphene oxide modified with 2-pyridinecarboxaldehyde thiosemicarbazone: Adsorption isotherms and kinetics studies

A novel adsorbent, based on modifying graphene oxide (GO) chemically with 2-pyridinecarboxaldehyde thiosemicarbazone (2-PTSC) as ligand, was designed by facile process for removal of Hg(II) from aqueous solution. Characterization of the adsorbent was performed using various techniques, such as FT-IR, XRD, XPS, SEM and AFM analysis. The adsorption capacity was affected by variables such as adsorbent dosage, pH solution, Hg(2+) initial concentration and sonicating time. These variables were optimized by rotatable central composite design (CCD) under response surface methodology (RSM). The predictive model for Hg(II) adsorption was constructed and applied to find the best conditions at which the responses were maximized. In this conditions, the adsorption capacity of this adsorbent for Hg(2+) ions was calculated to be 309mgg(-1) that was higher than that of GO. Appling the ultrasound power combined with adsorption method was very efficient in shortening the removal time of Hg(2+) ions by enhancing the dispersion of adsorbent and metal ions in solution and effective interactions among them. The adsorption process was well described by second-order kinetic and Langmuir isotherm model in which the maximum adsorption capacity (Qm) was found to be 555mgg(-1) for adsorption of Hg(2+) ions over the obtained adsorbent. The performance of adsorbent was examined on the real wastewaters and confirmed the applicability of adsorbent for practical applications.

Magnetic graphene-carbon nanotube iron nanocomposites as adsorbents and antibacterial agents for water purification

One of the biggest challenges of the 21st century is to provide clean and affordable water through protecting source and purifying polluted waters. This review presents advances made in the synthesis of carbon- and iron-based nanomaterials, graphene-carbon nanotubes-iron oxides, which can remove pollutants and inactivate virus and bacteria efficiently in water. The three-dimensional graphene and graphene oxide based nanostructures exhibit large surface area and sorption sites that provide higher adsorption capacity to remove pollutants than two-dimensional graphene-based adsorbents and other conventional adsorbents. Examples are presented to demonstrate removal of metals (e.g., Cu, Pb, Cr(VI), and As) and organics (e.g., dyes and oil) by grapheme-based nanostructures. Inactivation of Gram-positive and Gram-negative bacterial species (e.g., Escherichia coli and Staphylococcus aureus) is also shown. A mechanism involving the interaction of adsorbents and pollutants is briefly discussed. Magnetic graphene-based nanomaterials can easily be separated from the treated water using an external magnet; however, there are challenges in implementing the graphene-based nanotechnology in treating real water.