Grafting of β-cyclodextrin to magnetic graphene oxide via ethylenediamine and application for Cr(VI) removal

Maltodextrin-modified graphene oxide composite membrane applied to the enantioseparation of amino acids

The separation of enantiomers using chiral membranes has garnered much research interest. In this study, the enantioseparation of amino acids using chiral membranes, namely graphene oxide-ethylenediamine-maltodextrin (GO-EDA-MD) and GO-EDA-hydroxypropyl-MD (GO-EDA-HP-MD), was evaluated. HP-MD and MD were investigated as chiral selectors due to their inherent chirality. Various characterization techniques, including atomic force microscopy, Fourier transform infrared spectrometry, field emission scanning electron microscopy, water contact angle analysis, tensile properties, and thermal gravimetric analysis were employed to analyze the membrane structures. The evaluation of enantioseparation performance was conducted by employing tryptophan, phenylalanine, and tyrosine enantiomers. Optimal conditions for enantiomer separation were achived using a GO-EDA-HP-MD chiral composite (1.75 wt%), a feed concentration of 10 mg/L for each enantiomer, a separation time of 15 min, and a membrane effective surface area of 1.0 cm2. Also, the bovine serum albumin rejection was 90.0 %, and the water flux reached 37.1 L m-2 h-1. The highest enantiomeric excess (ee.%) values were 46.33 %, 76.97 %, and 73.04 % for tryptophan, phenylalanine, and tyrosine, respectively. The impact of voltage on ee.% and substance flux was also explored. This membrane was able to separate enantiomers successfully.

Sustainable approach for the expulsion of metaldehyde: risk, interactions, and mitigation: a review

All pests can be eliminated with the help of pesticides, which can be either natural or synthetic. Because of the excessive use of pesticides, it is harmful to both ecology and people's health. Pesticides are categorised according to several criteria: their chemical composition, method of action, effects, timing of use, source of manufacture, and formulations. Many aquatic animals, birds, and critters live in danger owing to hazardous pesticides. Metaldehyde is available in various forms and causes significant impact even when small amounts are ingested. Metaldehyde can harm wildlife, including dogs, cats, and birds. This review discusses pesticides, their types and potential environmental issues, and metaldehyde's long-term effects. In addition, it examines ways to eliminate metaldehyde from the aquatic ecosystem before concluding by anticipating how pesticides may affect society. The metal-organic framework and other biosorbents have been appropriately synthesized and subsequently represent the amazing removal of pesticides from effluent as an enhanced adsorbent, such as magnetic nano adsorbents. A revision of the risk assessment for metaldehyde residuals in aqueous sources is also attempted.

Cu-nanoparticles@ graphene nanocomposite: A robust and efficient nanocomposite for micro-solid phase extraction of trace aflatoxins in different foodstuffs

Cu-nanoparticles-immobilized graphene (Cu@G) nanocomposite was fabricated in this study by reducing Cu(II) ions in the presence of graphene oxide using a simple chemical reduction step. Cu@G nanocomposite was applied as a sorbent for the SPE of four aflatoxins (AFs). A reusable syringe was filled with the fabricated nanocomposite and used as a sorbent for the micro-solid phase extraction of four AFs (AFB1, AFB2, AFG1, AFG2). The impact of different analytical factors was fully investigated and optimized. Excellent recoveries, ranging from 92.0 to 108.5 %, were detected when evaluating target AFs in samples of rice, maize, and pistachio. The LOD, LOQ, and linear ranges were attained under optimal circumstances in the ranges of 0.0062 µg kg-1, 0.0192 µg kg-1, and 0.0-20 µg kg-1, respectively. The discovered approach provided the dual benefits of a high enrichment capability of Cu-nanoparticles via AFs complexation and a huge porosity of graphene sheets.

Novel mixed heterovalent (Mo/Co)Ox-zerovalent Cu system as bi-functional electrocatalyst for overall water splitting

A novel hybrid ternary metallic electrocatalyst of amorphous Mo/Co oxides and crystallized Cu metal was deposited over Ni foam using a one-pot, simple, and scalable solvothermal technique. The chemical structure of the prepared ternary electrocatalyst was systematically characterized and confirmed via XRD, FTIR, EDS, and XPS analysis techniques. FESEM images of (Mo/Co)Ox-Cu@NF display the formation of 3D hierarchical structure with a particle size range of 3-5 µm. The developed (Mo/Co)Ox-Cu@NF ternary electrocatalyst exhibits the maximum activity with 188 mV and 410 mV overpotentials at 50 mA cm-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Electrochemical impedance spectroscopy (EIS) results for the (Mo/Co)Ox-Cu@NF sample demonstrate the minimum charge transfer resistance (Rct) and maximum constant phase element (CPE) values. A two-electrode cell based on the ternary electrocatalyst just needs a voltage of about 1.86 V at 50 mA cm-2 for overall water splitting (OWS). The electrocatalyst shows satisfactory durability during the OWS for 24 h at 10 mA cm-2 with an increase of only 33 mV in the cell potential.

Adsorption of Cd(II) ions on magnetic graphene oxide/cellulose modified with β-cyclodextrin: Analytical interpretation via statistical physics modeling and fractal like kinetic approach

In the present study, β-cyclodextrin modified magnetic graphene oxide/cellulose (CN/IGO/Cel) was fabricated for removal of Cd(II) ions. The material was characterized through various analytical techniques like FTIR, XRD, TGA/DTA, SEM, TEM, and XPS. The point of zero charge of the material was obtained as 5.38. The controllable factors were optimized by Taguchi design and optimum values were: adsorbent dose-16 mg, equilibrium time-40 min, and initial concentration of Cd(II) ions-40 mg/L. The material shows high adsorption capacity (303.98 mg/g). The good fitting of Langmuir model to adsorption data (R2 = 0.9918-0.9936) revealed the monolayer coverage on adsorbent surface. Statistical physics model M 2 showed best fitting to adsorption data (R2 > 0.997), suggesting the binding of Cd(II) ions occurred on two different receptor sites (n). Stereographically n > 1 confirming vertical multi-molecular mechanisms of Cd(II) ions adsorption on CN/IGO/Cel surface. The adsorption energies (E1 = 23.71-28.95 kJ/mol; E2 = 22.69-29.38 kJ/mol) concluded the involvement of physical forces for Cd(II) ions adsorption. Kinetic data fitted well to fractal-like pseudo first-order model (R2 > 0.9952), concluding the adsorption of Cd(II) ions occurred on energetically heterogeneous surface. The kinetic analysis shows that both the film-diffusion and pore-diffusion were responsible for Cd(II) ions uptake. XPS analysis was utilized to explain the adsorption mechanism of Cd(II) ions onto CN/IGO/Cel.

How β-Cyclodextrin-Functionalized Biochar Enhanced Biodenitrification in Low C/N Conditions via Regulating Substrate Metabolism and Electron Utilization

Biodenitrification plays a vital role in the remediation of nitrogen-contaminated water. However, influent with a low C/N ratio limits the efficiency of denitrification and causes the accumulation/emission of noxious intermediates. In this study, β-cyclodextrin-functionalized biochar (BC@β-CD) was synthesized and applied to promote the denitrification performance of Paracoccus denitrificans when the C/N was only 4, accompanied by increased nitrate reduction efficiency and lower nitrite accumulation and nitrous oxide emission. Transcriptomic and enzymatic activity analyses showed BC@β-CD enhanced glucose degradation by promoting the activities of glycolysis (EMP), the pentose phosphate pathway (PPP), and the tricarboxylic acid (TCA) cycle. Notably, BC@β-CD drove a great generation of electron donors by stimulating the TCA cycle, causing a greater supply of substrate metabolism to denitrification. Meanwhile, the promotional effect of BC@β-CD on oxidative phosphorylation accelerates electron transfer and ATP synthesis. Moreover, the presence of BC@β-CD increased the intracellular iron level, causing further improved electron utilization in denitrification. BC@β-CD helped to remove metabolites and induced positive feedback on the metabolism of P. denitrificans. Collectively, these effects elevated the glucose utilization for supporting denitrification from 36.37% to 51.19%. This study reveals the great potential of BC@β-CD for enhancing denitrification under low C/N conditions and illustrates a potential application approach for β-CD in wastewater bioremediation.

Intrinsic mechanisms for the inhibition effect of graphene oxide on the catalysis activity of alpha amylase

Comprehending the interactions between graphene oxide (GO) and enzymes is critical for understanding the toxicities of GO. In this study, the inherent interactions of GO with α-amylase as a typical enzyme, and the impacts of GO on the conformation and biological activities of α-amylase were systematically investigated. The results reveal that GO formed ground-state complex with α-amylase primarily via hydrogen bonding and van der Waals interactions, thus quenching the intrinsic fluorescence of the protein statically. Particularly, the strong interactions altered the microenvironment of tyrosine and tryptophan residues, caused rearrangement of polypeptide structure, and reduced the contents of α-helices and β-sheets, thus changing the conformational structure of α-amylase. According to molecular docking results, GO binds with the amino acid residues (i.e., His299, Asp300, and His305) of α-amylase mainly through hydrogen bonding, which is in accordance with in vitro incubation experiments. As a consequence, the ability of α-amylase to catalyze starch hydrolysis into glucose was depressed by GO, suggesting that GO might cause dysfunction of α-amylase. This study discloses the intrinsic binding mechanisms of GO with α-amylase and provides novel insights into the adverse effects of GO as it enters organisms.

Single/co-adsorption and mechanism of methylene blue and lead by β-cyclodextrin modified magnetic alginate/biochar

Due to the high biological toxicity, the concurrent elimination of lead (Pb (II)) and methylene blue (MB) has become a challenging problem. Therefore, a newly β-cyclodextrin (β-CD) modified magnetic alginate/biochar (β-CD@MBC_P) material was developed. Comprehensive characterizations proved the successful coating of β-CD onto MBC_P surface by microwave-aided fabrication. The β-CD@MBC_P achieved high-efficiency uptake for contaminants under a wide pH scope. In the dual system, Pb (II) elimination was facilitated with the presence of MB, due to the active sites provided by MB. In the presence of Pb (II), MB uptake was inhibited due to the electrostatic repulsion between positively charged MB and Pb (II). Electrostatic attraction and complexation contributed to capturing Pb (II), while π-π interactions, host-guest effect, and H-bonding were important in MB elimination. After four cycles, β-CD@MBC_P maintained comparatively good renewability. Findings demonstrated that β-CD@MBC_P could be an effective remediation material for Pb (II)/MB adsorption from aqueous environments.

Recent advances in application of metal-organic frameworks (MOFs) as adsorbent and catalyst in removal of persistent organic pollutants (POPs)

The presence of persistent organic pollutants (POPs) in the aquatic environment is causing widespread concern due to their bioaccumulation, toxicity, and possible environmental risk. These contaminants are produced daily in large quantities and released into water bodies. Traditional wastewater treatment plants are ineffective at degrading these pollutants. As a result, the development of long-term and effective POP removal techniques is critical. In water, adsorption removal and photocatalytic degradation of POPs have been identified as energy and cost-efficient solutions. Both technologies have received a lot of attention for their efforts to treat the world's wastewater. Photocatalytic removal of POPs is a promising, effective, and long-lasting method, while adsorption removal of persistent POPs represents a simple, practical method, particularly in decentralized systems and isolated areas. It is critical to develop new adsorbents/photocatalysts with the desired structure, tunable chemistry, and maximum adsorption sites for highly efficient removal of POPs. As a class of recently created multifunctional porous materials, Metal-organic frameworks (MOFs) offer tremendous prospects in adsorptive removal and photocatalytic degradation of POPs for water remediation. This review defines POPs and discusses current research on adsorptive and photocatalytic POP removal using emerging MOFs for each type of POPs.

Remediation of heavy metal polluted waters using activated carbon from lignocellulosic biomass: An update of recent trends

The use of a cheap and effective adsorption approach based on biomass-activated carbon (AC) to remediate heavy metal contamination is clearly desirable for developing countries that are economically disadvantaged yet have abundant biomass. Therefore, this review provides an update of recent works utilizing biomass waste-AC to adsorb commonly-encountered adsorbates like Cr, Pb, Cu, Cd, Hg, and As. Various biomass wastes were employed in synthesizing AC via two-steps processing; oxygen-free carbonization followed by activation. In recent works related to the activation step, the microwave technique is growing in popularity compared to the more conventional physical/chemical activation method because the microwave technique can ensure a more uniform energy distribution in the solid adsorbent, resulting in enhanced surface area. Nonetheless, chemical activation is still generally preferred for its ease of operation, lower cost, and shorter preparation time. Several mechanisms related to heavy metal adsorption on biomass wastes-AC were also discussed in detail, such as (i) - physical adsorption/deposition of metals, (ii) - ion-exchange between protonated oxygen-containing functional groups (-OH, -COOH) and divalent metal cations (M²⁺), (iii) - electrostatic interaction between oppositely-charged ions, (iv) - surface complexation between functional groups (-OH, O^2-, -CO-NH-, and -COOH) and heavy metal ions/complexes, and (v) - precipitation/co-precipitation technique. Additionally, key parameters affecting the adsorption performance were scrutinized. In general, this review offers a comprehensive insight into the production of AC from lignocellulosic biomass and its application in treating heavy metals-polluted water, showing that biomass-originated AC could bring great benefits to the environment, economy, and sustainability.

Graphene-based nanomaterials in the electroplating industry: A suitable choice for heavy metal removal from wastewater

The presence of various heavy metal ions in the industrial waste waters has recently been a challenging issue for human health. Since heavy metals are highly soluble in the aquatic environments and they can be absorbed easily by living organisms, their removal is essential from the environmental point of view. Many studies have been devoted to investigating the environmental behaviour of graphene-based nanomaterials as sorbent agents to remove metals from wastewaters arising by galvanic industries. Among the graphene derivates, especially graphene oxide (GO), due to its abundant oxygen functional groups, high specific area and hydrophilicity, is a high-efficient adsorbent for the removal of heavy and precious metals in aquatic environment. This paper reviews the main graphene, GO, functionalized GO and their composites and its applications in the metals removal process. The influencing factors, adsorption capacities and reuse capability are highlighted for the most extensively used heavy metals, including copper, zinc, nickel, chromium, cobalt and precious metals (i.e., gold, silver, platinum, palladium, rhodium, and ruthenium) in the electroplating process.

Heavy metal removal by biomass-derived carbon nanotubes as a greener environmental remediation: A comprehensive review

The concentrations of heavy metal ions found in waterways near industrial zones are often exceed the prescribed limits, posing a continued danger to the environment and public health. Therefore, greater attention has been devoted into finding the efficient solutions for adsorbing heavy metal ions. This review paper focuses on the synthesis of carbon nanotubes (CNTs) from biomass and their application in the removal of heavy metals from aqueous solutions. Techniques to produce CNTs, benefits of modification with various functional groups to enhance sorption uptake, effects of operating parameters, and adsorption mechanisms are reviewed. Adsorption occurs via physical adsorption, electrostatic interaction, surface complexation, and interaction between functional groups and heavy metal ions. Moreover, factors such as pH level, CNTs dosage, duration, temperature, ionic strength, and surface property of adsorbents have been identified as the common factors influencing the adsorption of heavy metals. The oxygenated functional groups initially present on the surface of the modified CNTs are responsible towards the adsorption enhancement of commonly-encountered heavy metals such as Pb²⁺, Cu²⁺, Cd²⁺, Co²⁺, Zn²⁺, Ni²⁺, Hg²⁺, and Cr⁶⁺. Despite the recent advances in the application of CNTs in environmental clean-up and pollution treatment have been demonstrated, major obstacles of CNTs such as high synthesis cost, the agglomeration in the post-treated solutions and the secondary pollution from chemicals in the surface modification, should be critically addressed in the future studies for successful large-scale applications of CNTs.

Nanocarbon hybrid for simultaneous removal of arsenic, iron and manganese ions from aqueous solutions

Heavy metal contamination is a severe problem with serious ecological and human health effects due to its toxic effect and tendency to accumulate throughout the food chain. Batch experiments were conducted to investigate the simultaneous removal of arsenic, iron and manganese ions from aqueous solutions using Nanocarbon hybrid (NCH). Nanocarbon hybrid (NCH) of carbon xerogel decorated with 1wt% multi-walled carbon nanotubes was prepared by carbonization at 850 °C for 2 h. The TEM, SEM, EDX, FTIR, and N₂ adsorption-desorption measurements were used to characterize the prepared NCH. NCH is enriched with surface oxygen functional groups and micropores as well as it have total surface area of 162 m²/g and total pore volume of 0.129 cm³/g. The adsorption of metal ions onto NCH, which confirmed by EDX, happened quickly, with 30%, 97%, and 41% of As, Fe, and Mn adsorbed in less than 10 min, however the equilibrium time was achieved in less than 30 min. The maximum adsorption capacities for As, Fe, and Mn ions onto NCH were 20, 48, and 21 mg/g, respectively. The experimental adsorption results of the three metal ions showed linearly fitting with Freundlich isotherms. In addition, the computed adsorption energies for Fe, Mn, and As ions were 4.08, 1.95, and 2.42 kJ/mol, indicating physical adsorption. NCH are easily regenerated and reusable sorbent owing to the adsorption–desorption studies. Conclusively, NCH is promising material for removing mixture of metal ions from aqueous media.

Effect of the modification of magnetic graphene oxide with ionic liquid on the adsorption of nonionic surfactant NP10EO

The large-scale application of ionic surfactants in industrial and agricultural production has caused great harm to the environment due to by-products. In order to remove this pollutant from the environment, graphene oxide as an adsorption material has received extensive attention. However, practically, it is difficult to separate the GO from aqueous solutions, making water treatment on a large scale challenging. To allow the recycling of GO, as well as enhance its adsorption ability to remove surfactants from water, a composite of magnetic graphene oxide (MGO) and 1-dodecyl-3-methylimidazolium chloride ionic liquid (IL) was synthesized. The MGO was prepared by coprecipitation, and IL-MGO was prepared by ultrasonic impregnation. Nitrogen adsorption-desorption curves show that the specific surface area of the composite was increased by the addition of the IL, from 103.28 to 163.35 m²/g. Finally, the adsorption ability of MGO and IL-MGO for the nonionic surfactant NP10EO was investigated. The results showed that the adsorption of MGO on NP10EO fits the Langmuir isothermal model and the quasi-second-order kinetic model. In addition, the equilibrium adsorption capacity of NP10EO by MGO at 298K, 308K, and 318K can reach 87.03 mg/g, 156.25 mg/g, and 214.13 mg/g. The adsorption is an endothermic reaction that occurs spontaneously and is governed by physical adsorption. The adsorption of IL-MGO on NP10EO conforms to the Langmuir isotherm model and the quasi-second-order kinetic model. At 298K, 308K, and 318K, the equilibrium adsorption capacity of NP10EO by MGO reached 261.02 mg/g, 280.24 mg/g, and 295.03 mg/g, respectively. Compared with the two results, the incorporation of IL greatly improved the adsorption capacity of MGO to NP10EO.

Graphene-Based Materials Immobilized within Chitosan: Applications as Adsorbents for the Removal of Aquatic Pollutants

Graphene and its derivatives, especially graphene oxide (GO), are attracting considerable interest in the fabrication of new adsorbents that have the potential to remove various pollutants that have escaped into the aquatic environment. Herein, the development of GO/chitosan (GO/CS) composites as adsorbent materials is described and reviewed. This combination is interesting as the addition of graphene to chitosan enhances its mechanical properties, while the chitosan hydrogel serves as an immobilization matrix for graphene. Following a brief description of both graphene and chitosan as independent adsorbent materials, the emerging GO/CS composites are introduced. The additional materials that have been added to the GO/CS composites, including magnetic iron oxides, chelating agents, cyclodextrins, additional adsorbents and polymeric blends, are then described and discussed. The performance of these materials in the removal of heavy metal ions, dyes and other organic molecules are discussed followed by the introduction of strategies employed in the regeneration of the GO/CS adsorbents. It is clear that, while some challenges exist, including cost, regeneration and selectivity in the adsorption process, the GO/CS composites are emerging as promising adsorbent materials.

Highly efficient and ultrafast removal of Cr(VI)in aqueous solution to ppb level by poly(allylamine hydrochloride) covalently cross-linked amino-modified graphene oxide

We herein report a facile strategy to prepare poly(allylamine hydrochloride) cross-linked amino-modified graphene oxide (PAH-ASGO) by Schiff-base reactions. The resulting PAH-ASGO exhibited a maximum adsorption capacity of 373.1 mg/g for Cr(VI), which was nearly 9 times higher than that of pure graphene oxide, exceeding that of most GO-based materials previously reported. More significantly, PAH-ASGO can effectively diminish the Cr(VI) concentration from 9.9 mg/L to the extremely low level of 0.004 mg/L within 10 s, far below the maximum allowable level of Cr(VI) (0.05 mg/L) in drinking water. In addition, the adsorbents still displayed excellent removal efficiency of 91.8% after 10 cycles. Considering the broad diversity, we developed also a magnetic PAH-ASGO/Fe₃O₄ adsorbent by a simple cross-linking reaction to achieve rapid separation of PAH-ASGO from their aqueous solution. Finally, the PAH-ASGO was successfully utilized to treat the actual industrial effluent.

Magnetically Recyclable Graphene Oxide Demulsifier Adapting Wide pH Conditions on Detachment of Oil in the Crude Oil-in-Water Emulsion

In the present work, an amphiphilic and magnetically recyclable graphene oxide (MR-GO) demulsifier was devised and synthesized by graft of magnetic nanoparticles (Fe₃O₄@SiO₂-APTES) and ethylenediamine on the GO surface. The wettability and surface charges of MR-GO under various pH conditions can be regulated via adjusting the contents and species of surface functional groups (such as amino, carboxyl, and hydroxyl). In the demulsificaition test, MR-GO displayed favorable demulsification performance for crude oil-in-water (O/W) emulsion under pH of 2.0-10.0, thusly greatly improving the application scope of common demulsifier. The optimal dosage of MR-GO was 200 mg/L and the demulsification efficiency attained a maximum value of 99.7% for crude O/W emulsion with pH of 6.0. What's more, owing to its magnetic response performance, the MR-GO can be reused and the demulsification efficiency remained above 91.0% after six cycles. Based on the strong interfacial activity, MR-GO can arrive to the crude oil-water interface. With the synergy effects of interfacial adsorption (π-π/n-π) interactions and electrostatic attraction of demulsifier and interfacial films, and the aid of external mechanical forces, the interfacial films stabilized the emulsion were disrupted. Therefore, the oil droplets coated on the water droplets were gathered rapidly to form oily flocs and then migrated to the water surface to accomplish the demulsification of crude O/W emulsion.

Self-Supported Reduced Graphene Oxide Membrane and Its Cu2+ Adsorption Capability

Graphene stratiform membrane materials have been recently applied to heavy metal removal in aqueous systems via adsorption due to their high mechanical strength, chemical stability, and other properties. We applied reduced graphene oxide (rGO) alone as an adsorbent to remove heavy metal ions from wastewater. Self-supported rGO membrane was prepared using a green reduction method with sodium hydrosulfite. We used the Raman spectra to observe the structure of the rGO membrane. The morphology of the self-supported membrane was measured by a scanning electron microscope. The Cu²⁺ adsorption performance was measured in terms of pH, reaction time, metal ion concentration, and temperature. The maximum Cu²⁺ adsorption capacity of the rGO membrane was found to be 149.25 mg/g. The adsorption process followed a pseudo-second-order kinetic model, and adsorption isotherms were simulated by the Freundlich model.

Efficient Removal 17-Estradiol by Graphene-Like Magnetic Sawdust Biochar: Preparation Condition and Adsorption Mechanism

The occurrence of environmental endocrine disrupting chemicals (EDCs) in aquatic environments has caused extensive concern. Graphene-like magnetic sawdust biochar was synthesized using potassium ferrate (K₂FeO₄) to make activated sawdust biochar and applied for the removal of 17-estradiol (E2). The characterization showed that the surface morphology of five graphene-like magnetic sawdust biochars prepared with different preparation conditions were quite different. The specific surface area and pore structure increased with the increment of K₂FeO₄ addition. The results have shown that graphene-like magnetic sawdust biochar (1:1/900 °C) had the best removal on E2. The experimental results indicated that pseudo-first-order kinetic model and the Langmuir model could describe the adsorption process well, in which the equilibrium adsorption capacity (q_e,1) of 1:1/900 °C were 59.18 mg·g⁻¹ obtained from pseudo-first-order kinetic model and the maximum adsorption capacity (q_max) of 1:1/900 °C were 133.45 mg·g⁻¹ obtained from Langmuir model at 298K. At the same time, lower temperatures, the presence of humic acid (HA), and the presence of NaCl could be regulated to change the adsorption reaction in order to remove E2. Adsorption capacity was decreased with the increase of solution pH because pH value not only changed the surface charge of graphene-like magnetic sawdust biochar, but also affected the E2 in the water. The possible adsorption mechanism for E2 adsorption on graphene-like magnetic sawdust biochar was multifaceted, involving chemical adsorption and physical absorption, such as H-bonding, π-π interactions, micropore filling effects, and electrostatic interaction. To sum up, graphene-like magnetic sawdust biochar was found to be a promising absorbent for E2 removal from water.

Optimization of Cadmium Adsorption by Magnetic Graphene Oxide Using a Fractional Factorial Design

Graphene materials have attracted increasing interest in water remediation. In this study, magnetic graphene oxide (MGO) was prepared through the modified Hummers method and the adsorption behaviors of cadmium were investigated. Firstly, the sorption kinetics, isotherms, as well as the effects of pH were investigated. Then, fractional factorial design (FFD) was used to optimize the effects of pH, temperature, time, initial concentration of cadmium ion and NaCl on cadmium adsorption. The results indicate that MGO could effectively remove cadmium ions from an aqueous solution and the sorption data could be described well by pseudo-second-order and Freundlich models, showing that the adsorption rate of cadmium ions on MGO is multilayer adsorption and dominated by the chemical adsorption. According to the FFD results, the maximum adsorption capacity of cadmium ions was 13.169 mg/g under the optimum condition of pH value 8, 45 °C, contact time 60 min, initial cadmium concentration of 70 mg/L and NaCl concentration of 100 mg/L. Higher levels of the pH value, temperature and initial cadmium concentration are beneficial to the adsorption process. These results are important for estimating and optimizing the removal of metal ions by MGO composite.

Preparation of ternary amino-functionalized magnetic nano-sized illite-smectite clay for adsorption of Pb(II) ions in aqueous solution

Ternary amino-functionalized magnetic illite-smectite (AMNI/S) nanocomposites were prepared via integrating two-dimensional illite-smectite nanoflakes (NI/S), magnetite nanoparticles (Fe₃O₄), and 3-aminopropyltriethoxysilane (APTES). The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and vibrating sample magnetometry (VSM). The results show that Fe₃O₄ nanoparticles can be well dispersed on NI/S flakes and the hydrolyzed APTES molecules can simultaneously bond to the hydroxyl groups of Fe₃O₄ and NI/S. Due to the synergetic effect, magnetic NI/S composite can graft more amount of APTES molecules rather than Fe₃O₄ nanoparticles or NI/S alone. When the mass ratio of NI/S:Fe₃O₄ is 1:1, the saturation magnetization of AMNI/S-1 is 17.4 emu/g, facilitating the efficient magnetic separation in aqueous solution. Also, AMNI/S-1 shows a maximal adsorption amount of Pb(II) ions of 227.8 mg/g calculated by the Langmuir model. The effects of initial concentration of Pb(II) ions, pH value, adsorption time, and temperature on the adsorption amount of Pb(II) ions were investigated. The adsorption kinetic models and isotherm models were applied to analyze the adsorption of Pb(II) ions, respectively. The thermodynamic analysis reveals that the adsorption of Pb(II) onto AMNI/S-1 is spontaneous and endothermic in nature. The mechanism for the adsorption of Pb(II) ions onto AMNI/S-1 is due to the surface complexation of Fe₃O₄ and NI/S, and the chelation of amine groups (-NH₂). AMNI/S-1 can be efficiently reused and the regenerated AMNI/S-1 remains 82.91% of initial adsorption capacity after 6-cycle adsorption/desorption process. Thus, ternary AMNI/S-1 could be used as a prospective effective adsorbent.

Effect of Heavy Metal Ions on Steroid Estrogen Removal and Transport in SAT Using DLLME as a Detection Method of Steroid Estrogen

Environmental endocrine-disrupting chemicals have become a global environmental problem, and the distribution, transport, and fate of estrogens in soil and water environments closely relate to human and ecological health as well as to the remediation scheme design. A new micro-extraction technique termed dispersive liquid–liquid micro-extraction (DLLME) combined with high-performance liquid chromatography with fluorescence detector (HPLC-FLD) was developed for the determination of the concentration of steroid estrogens in water samples. The detection limits of HPLC-FLD and DLLME-HPLC/FLD were 0.68–1.73 μg L−1 and 7.16–69.22 ng L−1, respectively. Based on this method, the isothermal adsorption of 17β-E2 on sand and a breakthrough experiment of 17β-E2 and Cu2+ in a soil aquifer treatment (SAT) system were studied. The 17β-E2 adsorption capacity of sand in 17β-E2 solution was detected to be larger than that in a mixed solution of 17β-E2 and Cu(NO3)2 solution, and the breakthrough curves of 17β-E2 and Cu2+ in the mixed solution shifted forward in sand column experiments. Both suggested that the competitive adsorption of 17β-E2 and Cu2+ in the mixed solution might occur on the surface of the sand. In the process of the removal of 17β-E2 in wastewater by SAT, the existence of Cu2+ slightly inhibited the adsorption of 17β-E2 and accelerated the breakthrough of 17β-E2. These results ought to be a warning for SAT application for 17β-E2 removal in water where heavy metals coexist.

Coupling of kenaf Biochar and Magnetic BiFeO3 onto Cross-linked Chitosan for Enhancing Separation Performance and Cr(VI) Ions Removal Efficiency

Cr(VI) contamination has posed great threat to both the ecosystem and human health for its carcinogenic and mutagenic nature. A highly effective adsorbent for the removal of Cr(VI) was prepared and its adsorption mechanism was thoroughly discussed in this study. In detail, magnetic BiFeO₃ and kenaf biochar were loaded on cross-linked chitosan to obtain chitosan-kenaf biochar@BiFeO₃ (CKB) for improving adsorption capacity towards Cr(VI). The adsorption process of Cr(VI) onto CKB was evaluated as a function of the pH, the existence of competing ions, the initial concentration of Cr(VI) and contact time. The results show that CKB exhibits the highest adsorption capacity under the optimal pH 2.0. The presence of competing ions such as Ca²⁺, NO₃⁻, SO₄²⁻, and Cl⁻ decreases the adsorption capacity; among them, Ca²⁺ and NO₃⁻ show the greatest hindrance. By studying the effect of initial Cr(VI) concentration on the adsorption capacity, it was found that CKB in the solution was enough to remove Cr(VI) for all treatments (10–200 mg/L). The adsorption experimental data were well fitted with pseudo-first-order model, suggesting that chemisorption is not the dominant rate-limiting step. Freundlich isotherm model can better explain the adsorption process, indicating a non-ideal adsorption towards Cr(VI) on a heterogeneous surface of CKB. A 2^5-1 Fractional Factorial Design (FFD) showed that pH and initial concentration of Cr(VI) have significant influence on Cr(VI) adsorption in our reaction system. In general, excellent adsorption efficiency of CKB indicates that it may be a good candidate for the remediation of Cr(VI)-contaminating wastewater.

Removal of heavy metals in aquatic environment by graphene oxide composites: a review

As the most important graphene derivate, graphene oxide (GO) is a high-efficient adsorbent for the removal of heavy metals in aquatic environment due to its abundant oxygen functional groups, enormous specific area, and strong hydrophilia. However, there are some drawbacks, such as easily aggregating and difficult separation, restricting the environmental application of GO. GO is not a suitable adsorbent by itself. Hence, some materials were used to synthesize GO composites, and GO composites are commonly characterized by high adsorption capacity to overcome the above drawbacks. This review discusses five main GO composites-GO-chitosan, GO-alginate, GO-SiO₂, NZVI-rGO, and magnetic GO composites-and summarizes the synthesis methods of GO composites and its application for the removal of heavy metals in aquatic environments. The influencing factors, adsorption capacities, and mechanisms related to the removal of heavy metals by GO composites are highlighted. Lastly, the application potentials and challenges of GO composites for aqueous environmental remediation are discussed. Graphical abstract.

Biomaterials cross-linked graphene oxide composite aerogel with a macro-nanoporous network structure for efficient Cr (VI) removal

Chitosan (CS) is an attractive bio-adsorbent in pollutant removal due to its environment-friendly properties and abundant adsorption sites. However, the weak mechanical properties and strong dissolubility in acidic conditions of CS hinder its wide application. Herein, a facile method was proposed to fabricate polydopamine (PDA) and CS cross-linked graphene oxide (GO) (GO/CS/PDA) composite aerogel for Cr (VI) removal. GO was cross-linked with CS, forming a reinforced and three-dimensional macroporous structure; the introduced PDA was simultaneously cross-linked with CS and GO, providing more abundant nanopores and active sites for Cr(VI) removal. Based on the batch experiment results, GO/CS/PDA exhibited an optimized mass ratio (1:20:2) of GO, CS, and PDA for the most effective Cr(VI) adsorption; the adsorption removal rate of Cr(VI) was pH dependent, with the highest removal rate at pH = 3.0. The pseudo-second-order kinetic and Freundlich models were more suitable for fitting the adsorption kinetics and adsorption isotherms, respectively, and the maximum adsorption capacity for GO/CS/PDA was 312.05 mg/g at 298 K. Thermodynamics parameters indicated that the adsorption was a spontaneous and exothermic process. The excellent mechanical integrity and reusable adsorption performance of GO/CS/PDA promise the adsorbent with satisfactory reusability.

Cyclodextrin functionalized 3D-graphene for the removal of Cr(VI) with the easy and rapid separation strategy

As a useful heavy metal ion, chromium has seen its applications in various fields. While it is also a toxic contaminant in water and may cause serious threats to the environment and human health. To develop a novel material with good adsorption capacity and easy solid-liquid separation strategy was necessary and significant. In this paper, the β-cyclodextrin (β-CD) functionalized three-dimensional structured graphene foam (CDGF) was successfully synthesized with the facile and one-step hydrothermal method. The SEM, BET, XRD, FT-IR and XPS analysis were carried out and the results confirmed the successfully grafting of β-CD onto GF. The batch adsorption of Cr(VI) was also taken out and the CDGF possessed good selectivity compared with other metal ions at pH = 3. The adsorption capacity reduced gradually as the initial pH of the Cr(VI) solution grew higher, which was because the anionic species of Cr(VI) were partial to the positively charged surface of CDGF. The easy separation strategy of the CDGF was also demonstrated and the CDGF could be taken out easily with a tweezer after the adsorption of Cr(VI), which significantly simplified the separation procedure and reduced time. By comparing the FT-IR and XPD analysis results, the adsorption mechanism was explored and the hydroxyl groups on CDGF played the main role in the adsorption process. This work brings a novel material for the adsorption of Cr(VI) from water and provides an innovative direction for the easy and fast solid-liquid separation strategy in the adsorption and other application fields.

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.

A facile one-pot green synthesis of β-cyclodextrin decorated porous graphene nanohybrid as a highly efficient adsorbent for extracting aflatoxins from maize and animal feeds

In this paper, β-cyclodextrin (β-CD) supported on porous graphene nanohybrid (β-CDPG) was obtained by self-assembly of functionalized graphene nanosheets into a three-dimensional network in the presence of ascorbic acid via an in situ graphene oxide reduction and β-CD functionalization process during a hydrothermal reaction. The prepared supramolecular nanohybrid was further packed into a reusable syringe filter holder and applied as an adsorbent for solid phase extraction of four aflatoxins (B1, B2, G1, G2). Under optimal conditions, the detection limits and linear dynamic ranges were achieved in the range of 0.0075-0.030 μg kg^-1 and 0.025-100 μg kg^-1, respectively and the relative standard deviations were less than 6.1%. Good recoveries were observed for analyzing target AFs in maize and cereal-based chicken feed samples ranged from 90.5 to 105%. The method offered simultaneous advantages of high supramolecular recognition and enrichment capability of β-CD and the high specific surface area of the porous graphene.

Ternary assembly of g-C3N4/graphene oxide sheets /BiFeO3 heterojunction with enhanced photoreduction of Cr(VI) under visible-light irradiation

A novel ternary composite of graphitic carbon nitride (g-C₃N₄)/graphene oxide (GO) sheets/BiFeO₃ (CNGB) with highly enhanced visible-light photocatalytic activity toward Cr(VI) photoreduction is prepared and characterized. The characterization and photocatalysis experiments corroborate its reasonable band gap, efficient charge separation and transfer, widened visible-light adsorption, easy solid-liquid separation, good stability and superior catalytic activity of CNGB. Three CNGB samples with different ratios of g-C₃N₄ and BiFeO₃ (CNGB-1, -2, -3 with 2:4, 3:3, and 4:2, respectively), though possessing different adsorption ability, eventually remove all Cr(VI) ions via photocatalysis within 90 min. The catalytic efficiency of the composite is the highest at pH 2; increases in pH decrease the catalytic ability. The inorganic anions such as SO₄^-, Cl^-, and NO₃^- only slightly affects the photocatalytic process. The matching of the band structure between BiFeO₃ and g-C₃N₄ generates efficient photogenerated electron migration from the conduction band of g-C₃N₄ to that of BiFeO₃, which is also facilitated by the electron bridging and collecting effects of GO, and holes transfer from the valence band of BiFeO₃ to that of g-C₃N₄, yielding the efficient separation of photogenerated electron-hole pairs and the subsequent enhancement of photocatalytic activity. The research provides a theoretical basis and technical support for the development of photocatalytic technologies for effective application in wastewater treatment and Cr-contaminated water restoration.

A versatile β-cyclodextrin and polyethyleneimine bi-functionalized magnetic nanoadsorbent for simultaneous capture of methyl orange and Pb(II) from complex wastewater

Ascribing to their significant differences in physicochemical properties, it is extremely challenging to treat complex wastewater containing more than one class of pollutants via one-step treatment. Here, we focused on disposal of complex wastewater bearing organic dye and heavy metal by using adsorptive method. Thus, by combining the advantages of polyethyleneimine (PEI), β-cyclodextrin (β-CD) as well as Fe₃O₄ magnetic nanoparticles, a versatile β-CD and PEI bi-functionalized magnetic nanoadsorbent (Fe₃O₄-PEI/β-CD) with spatially separated sorption sites was successfully constructed for simultaneous capture of methyl orange (MO) and Pb(II) in complex wastewater. In this setting, β-CD cavities and positively charged N-containing groups of PEI were mainly responsible for removal of MO via host-guest inclusion and electrostatic attraction, respectively, and oxygen-bearing groups on the edge of β-CD as well as the free amino moieties in PEI acted as the active sites for Pb(II) uptake. In their individual mono-pollutant system, the adsorption processes can be better described via applying pseudo-second-order kinetic and Langmuir isotherm models. Interestingly, presence of MO in Pb(II)-MO binary system significantly promoted the uptake of Pb(II). But the coexisting Pb(II) had almost no effects on MO uptake. Such results demonstrated that both MO and Pb(II) could be simultaneously and synergistically removed by Fe₃O₄-PEI/β-CD through multiple mechanisms (such as electrostatic attraction, host-guest inclusion, chelating, etc.). Particularly, the excellent regeneration and stability make Fe₃O₄-PEI/β-CD an ideal integrative adsorbent for purification of actual wastewater contaminated by MO and Pb(II). Thus, this study provides some insights into designing a well-performed and easily recyclable adsorbent for simultaneous and synergetic capture of both organic and inorganic contaminants in complex wastewater.

A high efficient adsorbent for plant growth regulators based on ionic liquid and β-cyclodextrin functionalized magnetic graphene oxide

Four types of ionic liquids which composed of cation with imidazole ring and anion with benzene, naphthalene, anthraquinone and naphthoquinone ring were prepared and named VOIm⁺BenSO₃^-, VOIm⁺NapSO₃^-, VOIm⁺AQSO₃^- and VOIm⁺NQSO₃^-, respectively. Then, ionic liquids and β-cyclodextrin functionalized magnetic graphene oxide materials were firstly synthesized for the extraction of 23 plant growth regulators in vegetable samples. The synthesized materials anticipated the unique properties of ionic liquids, β-cyclodextrin, graphene oxide and Fe₃O₄@SiO₂, including high surface area, high supramolecular recognition capability, superparamagnetism and large delocalized π-electron system, which were successfully characterized. Among four kinds of ionic liquids functionalized adsorbents, the VOIm⁺AQSO₃^- modified material exhibited high adsorption capability to 7 plant growth regulators compared with Fe₃O₄@SiO₂/GO/β-CD, Fe₃O₄@SiO₂/GO and other three types of ionic liquids based adsorbents. Parameters that could affect the recoveries of 7 plant growth regulators were investigated, such as mass ratio of Fe₃O₄@SiO₂/GO/β-CD to ionic liquids, salt concentration, pH, amount of adsorbent, extraction time and desorption solvent. Under the optimal condition, the magnetic solid phase extraction method using VOIm⁺AQSO₃^- and β-cyclodextrin functionalized magnetic graphene oxide material (Fe₃O₄@SiO₂/GO/β-CD/IL) as adsorbent was developed and coupled with ultra-high performance liquid chromatography-triple quadrupole linear ion trap mass spectrometry for the determination of 7 plant growth regulators in vegetable samples. Validation results showed that the limit of detection and limit of quantitation were in the range of 0.01-0.18 μg/kg and 0.03-0.58 μg/kg, respectively. The satisfactory linearities were acquired in the concentration of 2-50 μg/kg with the correlation coefficients higher than 0.9982. Taken together, the synthesized Fe₃O₄@SiO₂/GO/β-CD/IL was a highly effective magnetic solid phase extraction adsorbent for the enrichment of trace level of plant growth regulators in vegetable samples.

Electrostatically in situ binding of zwitterionic glycine on the surface of MGO for determination of nitrite in various real samples

Zwitterionic dispersive magnetic solid phase extraction (ZI-DMSPE) was developed through in situ binding of glycine on the magnetic graphene oxide, electrostatically. This highly selective sorbent was applied for the determination and preconcentration of trace levels of nitrite in soil, sausage, water samples (tap, mineral, and rain), and vegetables (potato, onion, spinach, radish, and lettuce) prior to its determination by UV-Vis spectrophotometry. The major advantage of the method is the analyte adsorption in both acidic and basic media. The sorbent was characterized by SEM, XRD, EDS, and FT-IR. Several parameters affecting ZI-DMSPE were optimized. Under the optimal conditions, LOD and RSD were obtained 17 ng L^-1 and 1.3% respectively. Preconcentration factor and sorption capacity of the proposed method were 666 and 238 mg g^-1 respectively. Accuracy was assessed by comparing results with those obtained by direct determination using ion chromatography and spiked real samples.

Design of an enhanced SAT using the graphene-MAR mixture for the removal of 17β-E2 at a demonstration site of Qianjin farm in China

An adsorption-enhanced soil aquifer treatment (SAT) system was designed to reduce the level of estrogens below the threshold stipulated by the standards. The 17β-E2 adsorption by graphene and MARs (H103) was investigated and an optimum amount of graphene and MARs in the mixture was determined using the linear programming. The kinetics and isotherm characteristics of both adsorbents were well described by the Lagergren pseudo-second order and the Freundlich model, respectively. The 17β-E2 adsorption on graphene and H103 was 88% and 70.37%, and the high temperature was beneficial to the 17β-E2 adsorption on graphene while the thermodynamic behaviors of H103 were in direct contrast to that of graphene. The study found that the maximum economic benefits could be achieved when the mass of graphene and H103 in the mixture is 2.79 g and 13.20 kg, respectively.

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.