Thermodynamics of the adsorption of nickel ions from aqueous phase using graphene oxide and glycine functionalized graphene oxide

Kinetic and equilibrium study of graphene and copper oxides modified nanocomposites for metal ions adsorption from binary metal aqueous solution

Presently, the main cause of pollution of natural water resources is heavy metal ions. The removal of metal ions such as nickel (Ni2+) and cadmium (Cd2+) has been given considerable attention due to their health and environmental risks. In this regard, for wastewater treatment containing heavy metal ions, graphene oxide (GO) nanocomposites with metal oxide nanoparticles (NPs) attained significant importance. In this study, graphene oxide stacked with copper oxide nanocomposites (GO/CuO-NCs) were synthesized and characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and atomic force microscopy (AFM) analytical procedures. The prepared GO/CuO-NCs were applied for the removal of Ni2+ and Cd2+ ions from a binary metal ion system in batch and continuous experiments. The obtained results revealed that GO/CuO-NCs exhibited the highest removal efficiencies of Ni2+ (89.60% ± 2.12%) and Cd2+ (97.10% ± 1.91%) at the optimum values of pH: 8, dose: 0.25 g, contact time: 60 min, and at 50 ppm initial metal ion concentration in a batch study. However, 4 mL/min flow rate, 50 ppm initial concentration, and 2 cm bed height were proved to be the suitable conditions for metal ion adsorption in the column study. The kinetic adsorption data exhibited the best fitting with the pseudo-second-order model. The adsorption isotherm provided the best-fitting data in the Langmuir isotherm model. This study suggested that the GO/CuO nanocomposites have proved to be efficient adsorbents for Ni2+ and Cd2+ ions from a binary metal system.

Highly effective removal of nickel ions from wastewater by calcium-iron layered double hydroxide

Water pollution due to heavy metals has become a universal environmental problem. Ni(II) is a common heavy metal ion in polluted wastewater, which has high toxicity and carcinogenicity. In this study, the structure of a calcium-iron layered double hydroxide (Ca-Fe-LDHs) was synthesized and characterized by FTIR, XRD, SEM and XPS. Then, Ni(II) ion was effectively removed by Ca-Fe-LDHs and its mechanism for this materials was described. The maximum adsorption capacity of Ni(II) for Ca-Fe-LDHs was 418.9 mg‧g^-1 when the initial concentration of Ni(II) was 1 g/L. The adsorption and removal of Ni(II) by Ca-Fe-LDHs was attributed to the action of hydroxyl groups on the hydrotalcite, generating surface capture. Ni(OH)₂)0.75(H₂O)0.16(NiCO₃)0.09, Ni(OH)₂, NiO, NiSO₄ and other precipitates were generated on its surface. And a small amount of Ni-Fe-LDHs was generated through isomorphic transition before hydrolysis. Therefore, surface capture and isomorphic transition enhanced the removal efficiency of Ni(II) with Ca-Fe-LDHs, making Ca-Fe-LDHs as a potential material for effective removal of Ni(II).

Eco-friendly Synthesis of Carbon Quantum Dots as an Effective Adsorbent

Fluorescent carbon quantum dots (CQDs) were prepared by an economical, green, and single-step procedure with the assistance of microwave heating of urea with bagasse (SCB), cellulose (C), or carboxymethyl cellulose (CMC). The prepared CQDs were characterized using a series of spectroscopic techniques, and they had petite size, intense absorption in the UV, and excitation wavelength-dependent fluorescence. The prepared CQDs were used for Pb(II) adsorption from an aqueous solution. The removal efficiency percentages (R %) were 99.16, 96.36, and 98.48% for QCMC, QC, and QSCB, respectively. The findings validated the efficiency of CQDs synthesized from CMC, cellulose, and SCB as excellent materials for further utilization in the environmental fields of wastewater pollution detection, adsorption, and chemical sensing applications. The kinetics and isotherms studied found that all CQDs isotherms fit well with the Langmuir model than Freundlich and Temkin models. According to R², the pseudo-second-order fits the adsorption of QCMC, while the first-order one fits with QC and QSCB.

Removal of car battery heavy metals from wastewater by activated carbons: a brief review

Spent automobile batteries are one of the most significant secondary sources of harmful heavy metals for the environment. After being incorporated into the aquatic ecosystems, these metals disseminate to various plants, microorganisms, and the human body and cause multiple adverse effects. Activated carbons (ACs) have long been used as an effective adsorbent for different heavy metals in wastewater treatment processes. Although numerous research works have been published to date on this topic, they are scattered in the literature. In this review, we have assembled these works and provided an extensive overview of the application of ACs for treating spent car battery heavy metals (CBHMs) from aquatic systems. The preparation of ACs from different precursor materials, their application in the adsorption of CBHMs, the adsorption mechanism, kinetics, adsorption isotherms and various parameters that may affect the adsorption processes have been discussed in detail. A brief comparative analysis of the adsorption performances of ACs prepared from different precursor materials is also provided. Finally, recommendations for future research works are also offered.

The impact of co-treatment with graphene oxide and metal mixture on Salmo trutta at early development stages: The sorption capacity and potential toxicity

Graphene oxide (GO) are novel nanomaterials with a wide range of applications due to their high absorption capacity. This study was undertaken with a view to assess the bioaccumulation and acute toxicity of GO used in combination with the heavy metal mixture (Cr, Cu, Ni and Zn) to fish embryos and larvae. For this purpose, Salmo trutta embryos and larvae were subjected to the 4-day long treatment with three different concentrations of GO, the metal mixture, which was prepared of four metals at the concentrations corresponding to the maximum-permissible-concentrations for EU inland waters (Cr-0.01, Cu-0.01, Ni-0.034, and Zn-0.1 mg/L), and with GO in combination with MIX (GO+MIX). When used in combination with the metal mixture, GO exhibited a high metal sorption capacity. The obtained confocal fluorescence microscopy results showed that GO located in the embryo chorion causing its damage; in larvae, however, GO were found only in the gill region. Results of these experiments confirmed the hypothesis that GO affects the accumulation of metals and mitigates their toxic effects on organism. In embryos, the acute toxicity of exposure to GO and co-exposure to MIX+GO was found to manifest itself through the decreased heart rate (HR) and malondialdehyde (MDA) level and through the increased metallothionein (MT) concentration. Meanwhile, in larvae, GO and MIX+GO were found to induce genotoxicity effects. However, changes in HR, MDA, MT, gill ventilation frequency, yolk sack absorption and cytotoxicity compared with those of the control group were not recorded in larvae. The obtained results confirmed our hypothesis: the combined effect of MIX and GO was less toxic to larvae (especially survival) than individual effects of MIX components. However, our results emphasize that fish exposure to GO alone and in combination with heavy metal contaminants (MIX+GO) even at environmentally relevant concentrations causes health risks that cannot be ignored.

Selective removal of some heavy metals from Lanthanide solution by graphene oxide functionalized with sodium citrate

Lanthanides are widely used in several advanced technologies, and the presence of heavy metal ions as traces reduce their efficiencies. Hence, adsorption of some heavy metals from Lanthanides aqueous solution using previously prepared graphene oxide-citrate (GO-C) composite was reported. In this regard, the GO-C was applied to remove various heavy metal ions (Fe, Ni, Mn) through the batch technique. The GO-C after the adsorption process was characterized by various advanced techniques. The results obtained from the experimental investigations revealed that the GO-C showed a rapid equilibrium adsorption time (1.0 min) for all the studied heavy metal ions. Moreover, the adsorption isotherm data for Fe3+, Mn2+, and Ni2+ was fit by the Langmuir isotherm model with excellent adsorption capacity for Fe3+ (535.0 mg/g), Mn2+ (223.22 mg/g), and Ni2+ (174.65 mg/g). Furthermore, the GO-C can be reused over five times to enhance the removal efficiency. Interestingly, the GO-C adsorbent achieved removal performance reached 95.0% for the Fe3+ and ≥ 35.0% for Ni, Mn, Co, and Cu compared to < 1% for lanthanides metal ions.

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.

Oxide of porous graphitized carbon as recoverable functional adsorbent that removes toxic metals from water

The numerous oxygenated functional groups on graphite oxide (GO) make it a promising adsorbent for toxic heavy metals in water. However, the GO prepared from natural graphite is water-soluble after exfoliation, making its recovery for reuse extremely difficult. In this study, porous graphitized carbon (PGC) was oxidized to fabricate a GO-like material, PGCO. The PGCO showed an O/C molar ratio of 0.63, and 8.4% of the surface carbon species were carboxyl, exhibiting enhanced oxidation degree compared to GO. The small PGCO sheets were intensely aggregated chemically, yielding an insoluble solid easily separable from water by sedimentation or filtration. Batch adsorption experiments demonstrated that the PGCO afforded significantly higher removal efficiencies for heavy metals than GO, owing to the former's greater functionalization with oxygenated groups. An isotherm study suggested that the adsorption obeyed the Langmuir model, and the derived maximum adsorption capacities for Cr³⁺, Pb²⁺, Cu²⁺, Cd²⁺, Zn²⁺, and Ni²⁺ were 119.6, 377.1, 99.1, 65.2, 53.0, and 58.1 mg/g, respectively. Furthermore, the spent PGCO was successively regenerated by acid treatment. The results of the study indicate that PGCO could be an alternative adsorbent for remediating toxic metal-contaminated waters.

Synthesis of “(aminomethyl)phosphonic acid-functionalized graphene oxide”, and comparison of its adsorption properties for thorium(IV) ion, with plain graphene oxide

The current study presents a simple and scalable method for the synthesis of (aminomethyl)phosphonic acid-functionalized graphene oxide (AMPA-GO) adsorbent. The chemical structure of the new material was disclosed by different instrumental analyses (e.g. FTIR, Raman, XPS, AFM, TEM, XRD, CHN, and UV), and two pertinent mechanisms namely nucleophilic substitution and condensation were suggested for its formation. Adsorption experiments revealed that both AMPA-GO and plain GO have a high affinity toward Th(IV) ions, but the AMPA-GO is superior in terms of adsorption capacity, rate of adsorption, selectivity, pH effect, etc. Indeed, the AMPA-GO can uptake Th(IV) nearly instantaneously, and coexisting Na+ ions have no effect on its adsorption. Thanks to Langmuir isotherm, the maximum adsorption capacities of the GO and AMPA-GO were obtained 151.06 and 178.67 mg g−1, respectively. Interestingly, GO and AMPA-GO both showed a higher preference for thorium over uranium so that the average “K d (Th)/K d (U)” for them was 52 and 44, respectively. This data suggests that chromatographic separation of thorium and uranium is feasible by these adsorbents.

Adsorptive Removal of Cd, Cu, Ni and Mn from Environmental Samples Using Fe3O4-Zro2@APS Nanocomposite: Kinetic and Equilibrium Isotherm Studies

In this study, Fe₃O₄-ZrO₂ functionalized with 3-aminopropyltriethoxysilane (Fe₃O₄-ZrO₂@APS) nanocomposite was investigated as a nanoadsorbent for the removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions from aqueous solution and real samples in batch mode systems. The prepared magnetic nanomaterials were characterized using X-ray powder diffraction (XRD), scanning electron microscopy/energy dispersion x-ray (SEM/EDX) Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Factors (such as adsorbent dose and sample pH) affecting the adsorption behavior of the removal process were studied using the response surface methodology. Under optimized condition, equilibrium data obtained were fitted into the Langmuir and Freundlich isotherms and the data fitted well with Langmuir isotherms. Langmuir adsorption capacities (mg/g) were found to be 113, 111, 128, and 123 mg/g for Cd, Cu, Ni and Mn, respectively. In addition, the adsorption kinetics was analyzed using five kinetic models, pseudo-first order, pseudo-second order, intraparticle diffusion and Boyd models. The adsorbent was successfully applied for removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions in wastewater samples.

Sustainable Adsorption Removal of Nickel and Chromium on Eco-Friendly Industrial Waste: Equilibrium Study

Adsorption of nickel and chromium was investigated using fuller’s earth. The experimental data were analyzed using five 2-parameter adsorption models and three 3-parameter models. The maximum adsorption capacities for nickel and chromium were 769 and 556 mg/g, respectively. The Langmuir isotherm model was found to have the best fitting indicating monolayer adsorption. The adsorption was found to have an exothermic nature.

Preparation of graphene oxide-modified palygorskite nanocomposites for high-efficient removal of Co(II) from wastewater

Removing Co(II) from wastewater is urgent due to the threat to the environment and human health. In the work, the nanocomposite of graphene oxide-modified palygorskite (mPal-GO) is synthesized by cross-linking one-dimensional palygorskite (Pal) with two-dimensional material graphene oxide (GO), and used to remove Co(II) from wastewater. Its structure is characterized by Fourier transformed infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area measurement. The parameters, such as mass ratio (GO:mPal), temperature, pH, and contact time, are carefully investigated. The results indicate that pseudo-second-order equation and Langmuir isotherm model are the best fitting one in the adsorption process of Co(II) onto mPal-GO. The maximum adsorption capacity achieves 16.9 mg/g at pH = 6.0 and T = 298 K according to the Langmuir model analysis. Furthermore, mPal-GO can be reused more than 5 times with a slight decrease according to the adsorption-desorption cycle experiments. Finally, mPal-GO with the low-cost and easy separation is a promising candidate for removing of Co(II) from wastewater.

Fabrication and Adsorption Optimization of Novel Magnetic Core-shell Chitosan/Graphene Oxide/β-cyclodextrin Composite Materials for Bisphenols in Aqueous Solutions

A novel magnetic composite material, Fe3O4@SiO2/chitosan/graphene oxide/β-cyclodextrin (MCGC), was prepared by multi-step methods. Various methods were used to systematically characterize the morphology, composition, structure, and magnetic properties of MCGC. The results obtained show that the composite material has good morphology and crystal structure and can be separated quickly by an external magnetic field. The operation is relatively easy, and the raw materials used to prepare this material are economical, easy to obtain, and environmentally friendly. The performance and adsorption mechanism for using this material as an adsorbent to remove bisphenol A (BPA) and bisphenol F (BPF) from water were studied. The adsorption parameters were optimized. Under optimal conditions, MCGC was found to remove more than 90% of BPA and BPF in a mixed solution (20 mg/L, 50 mL); the adsorption process for BPA and BPF on MCGC was found to follow a Redlich-Peterson isotherm model and Pseudo-second-order kinetic model. The adsorption mechanism for MCGC may involve a combination of various forces. Recycling experiments showed that after five uses, MCGC retained a more than 80% removal effect for BPA and BPF, and through real sample verification, MCGC can be used for wastewater treatment. Therefore, MCGC is economical, environmentally friendly, and easy to separate and collect, and has suitable stability and broad application prospects.

Adsorption of Cu(II) and Ni(II) ions from wastewater onto bentonite and bentonite/GO composite

Two superior adsorbents, namely bentonite and graphene oxide (GO), were hybridised to study the removal of copper and nickel ions from synthetic and industrial wastewater. The as-synthesised GO, bentonite/GO and bentonite were characterised by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and N₂ adsorption-desorption analysis. The factors influencing the adsorption behaviours including contact time, initial solution pH, ionic strength, initial concentration of metal ions, temperature and adsorbent dosage were systematically investigated by batch equilibrium method. The adsorption equilibrium for copper and nickel onto bentonite was attained in 90 min while equilibrium was reached in 60 min on bentonite/GO. The adsorption of copper and nickel was pH-dependent in the range from pH 2 to pH 7 and from pH 2 to pH 8. Pseudo-first-order kinetic model excellently described the adsorption of copper and nickel onto bentonite and bentonite/GO. The equilibrium adsorption data was well described by the Langmuir isotherm model and the maximum adsorption capacity was 248.9 mg/g, 558.4 mg/g, 215.8 mg/g and 402.5 mg/g for bentonite-copper, bentonite/GO-copper, bentonite-nickel and bentonite/GO-nickel adsorption systems, respectively. The bentonite/GO composite exhibited a higher adsorption capacity of both cations from synthetic wastewater than pure bentonite owning to the synergistic effect between bentonite and GO. In all adsorption studies, copper was more efficiently removed than nickel due to its higher tendency to form bond with adsorbent surfaces. The adsorption of copper and nickel on bentonite/GO was mainly due to cation exchange, intermolecular and electrostatic interactions and physisorption dominated the adsorption processes. The practical application of bentonite/GO on adsorption of copper was investigated using real wastewater and its removal efficiency was beyond 98%. The excellent adsorption performances of composites for the copper and nickel removal from wastewater demonstrated its significant potential for pollution mitigations.

Adsorption of heavy metals on silica-supported hydrophilic carbonaceous nanoparticles (SHNPs)

This paper reports experimental results on the removal of Cd(II), Ni(II) and Pb(II) ions using hydrophilic carbon nanoparticles (HNPs) supported over silica beads to enhance their separation from treated water. The supported HNPs (SHNPs) exhibit high removal efficiencies especially at neutral pH and low temperature (10 °C), conditions that commonly occur for natural water remediation and for some types of industrial wastewater. The maximum adsorption capacity of the SHNPs at a reference concentration of 0.2 mM is 0.042 mmol g^-1, 0.027 mmol g^-1 and 0.055 mmol g^-1 for Cd(II), Pb(II) and Ni(II) ions, respectively. Modelling analysis on the adsorption isotherms revealed that the free Gibbs' energy of interactions between the sorbent and Ni(II) and Pb(II) ions is higher than that of Cd(II) ions indicating that the sorbents are more affine to intermediate acids, as Ni(II) and Pb(II) ions, than to soft acids, as Cd(II) ions. The sorbents exhibit appreciable adsorption capacities per gram of active phase (0.54 mg g^-1 for Cd(II) ions, 13.48 mg g^-1 for Ni(II) ions and 8.87 mg g^-1 for Pb(II) ions) at the corresponding quality limit admitted by Italian regulations on wastewater, suggesting their possible use in water treatment plants.

Functional rGO aerogel as a potential adsorbent for removing hazardous hexavalent chromium: adsorption performance and mechanism

A novel functional rGO aerogel was synthesized by a facile hydrothermal method. In this process, graphene oxide (GO) was used as the precursor and oxidant to synthesize the aerogels. Ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and pyrrole monomer (reducing agent) were selected to use as hole scavenger and nitrogen sources. The obtained EDTA-2Na/polypyrrole (Ppy)/rGO aerogel (EPGA) has a high adsorption capacity for Cr(VI) anions, and the maximum adsorption capacity reached 361 mg/g at 298 K at pH of 2. In addition, EPGA exhibited a good ability to selectively remove Cr(VI) anions under the effect of coexisting ions (Cl^-, NO₃^-, SO₄^2-, PO₄^3-, Ni⁺, Cu²⁺, Zn²⁺, and Cd²⁺) and good regeneration ability. The kinetics process and adsorption isotherm can be fitted well with the pseudo-second-order kinetic model and Freundlich isotherm model, respectively. The removal mechanism involved electrostatic interaction, reduction, ion exchange, and chelation process. This work provides a simple and environmentally friendly synthetic route for EPGA, which will be a potential candidate for efficient removal Cr(VI) anions from industrial wastewater.

Theoretical study of glycine amino acid adsorption on graphene oxide

The non-dissociative and dissociative adsorptions of zwitterionic Gly on graphene oxide (GO) was studied in the framework of DFT using a cluster model approach. In this work, the interaction with an epoxy group of GO basal plane was mainly considered. As a comparison, the non-dissociative and dissociative adsorptions of neutral Gly were also taken into account. The non-dissociative adsorption modes for zwitterionic and neutral Gly conformers show binding energies of 12.2 and 14.4 kcal mol^-1, respectively. These molecules are thought to remain over the GO surface due to attractive noncovalent interactions. Two dissociative adsorption modes, for Z-Gly and N-Gly, show smaller binding energies of 7.2 and 8.4 kcal mol^-1, where the deprotonated species links strongly through a C-O or C-N covalent bond to the GO surface. The results obtained in the present theoretical approach to the glycine/graphene oxide system support the fact that glycine can be attached to epoxy groups of graphene oxide basal planes in addition to the anchoring on edge oxidation groups. In summary, we conclude that glycine can be used as a reducing agent as well as a functionalizer of GO sheets.

Nickel ion removal from aqueous solutions through the adsorption process: a review

Recently, removal of nickel ions has been gaining a lot of attention because of the negative impact of nickel ions on the environment. The aim of this review paper is to organize the scattered available information on removal of nickel ions from aqueous solutions through the adsorption process. Survey on investigated materials suggests that composite- and polymer-based adsorbents have the most effective capability for nickel adsorption. The composite material class, i.e. CaCO3-maltose, followed by biopolymer-based material showed the highest Ni(II) adsorption capacity of 769.23 and 500 mg/g, respectively. The importance of treatment parameters (i.e. pH, temperature, contact time, and metal ion concentration) is discussed, together with their effect on the underlying physicochemical phenomena, giving particular attention to the adsorption/desorption mechanism. It was ascertained that adsorption of nickel ions is pH dependent and the optimal pH range for adsorption of Ni(II) ions was in range of 6–8. In general, nickel adsorption is an endothermic and spontaneous process that mainly occurs by forming a monolayer on the adsorbent (experimental data are often fitted by Langmuir isotherms and pseudo-second-order kinetics). Regeneration (i.e. desorption) is also reviewed, suggesting that acidic eluents (e.g. HCl and HNO3) allow, in most of the cases, an efficacious spent adsorbent recovery. The percentage use of desorption agents followed the order of acids (77%) > chelators (8.5%) > alkalis (8%) > salts (4.5%) > water (2%). Helpful information about adsorption and desorption of nickel ions from aqueous solutions is provided.

Applications of Graphene and Its Derivatives in Chemical Analysis

In this review, the applications of graphene and its derivatives in the chemical analysis have been described. The properties of graphene materials which are essential for their use in chemical and biochemical analysis are characterized. The materials are used in sensors and biosensors, in electrochemistry, in chromatography and in the sample preparation techniques. Chemical and electrochemical sensors containing graphene materials are useful devices for detecting some chemical and biochemical compounds. Chromatographic columns for HPLC with graphene containing stationary phases may be used for separation of polar and nonpolar components of some specific mixtures. Graphene materials could be successfully employed during sample preparation for analysis with SPE, magnetic SPE, and SPME techniques. HighlightsThe review of the applications of graphene (G) and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), in chemical and biochemical analysis is proposed.The electron donor-acceptor and proton donor-acceptor interactions for the graphene based materials - analytes systems and their impact on the analysis results are discussed, particularly:    i) in electrochemistry,ii) in chromatography,iii) in modern sample preparation techniquesiv) in sensors of different types.The essence of the thermal stability and the nomenclature of the graphene based materials in their different applications in chemical systems of different classes was discussed (and suggested).The benefits of using SPME fibers with immobilized graphene materials have been presented in detail.

Studying Ni(II) Adsorption of Magnetite/Graphene Oxide/Chitosan Nanocomposite

In this paper, Fe3O4/graphene oxide/chitosan (FGC) nanocomposite was synthesized using coprecipitation method for application to removal of nickel ion (Ni(II)) from aqueous solution by adsorption process. To determine residue Ni(II) ions concentration in aqueous solution after adsorption process, we have used UV-Vis spectrophotometric method, which is an effective and exact method for Ni(II) monitoring at low level by using dimethylglyoxime (DMG) as a complex reagent with Ni(II), which has a specific adsorption peak at the wavelength of 550 nm on UV-Vis spectra. A number of factors that influence Ni(II) ions adsorption capacity of FGC nanocomposite such as contact time, adsorption temperature, and adsorbent dosage were investigated. Results showed that the adsorption equilibrium is established after 70 minutes with the adsorbent dosage of 0.01 g.mL−1 at 30°C (the room temperature). The thermodynamic and kinetic parameters of this adsorption including free enthalpy change (∆G0), enthalpy change (∆H0), entropy change (∆S0), and reaction order with respect to Ni(II) ions were also determined. The Ni(II) ions adsorption equilibrium data are fitted well to the Langmuir isotherm and the maximum monolayer capacity (qmax) is 12.24 mg.g−1. Moreover, the FGC adsorbent can be recovered by an external magnet; in addition, it can be regenerated. The reusability of FGC was tested and results showed that 83.08% of removal efficiency was obtained after 3 cycles. The synthesized FGC nanocomposite with many advantages is a promising material for removal of heavy metal ions from aqueous solution to clean up the environment.

A comprehensive review of applications of magnetic graphene oxide based nanocomposites for sustainable water purification

With the rapid growth of industrialization, water bodies are polluted with heavy metals and toxic pollutants. In pursuit of removal of toxic pollutants from the aqueous environment, researchers have been developed many techniques. Among these techniques, magnetic separation has caught research attention, as this approach has shown excellent performance in the removal of toxic pollutants from aqueous solutions. However, magnetic graphene oxide based nanocomposites (MGO) possess unique physicochemical properties including excellent magnetic characteristics, high specific surface area, surface active sites, high chemical stability, tunable shape and size, and the ease with which they can be modified or functionalized. As results of their multi-functional properties, affordability, and magnetic separation capability, MGO's have been widely used in the removal of heavy metals, radionuclides and organic dyes from the aqueous environment, and are currently attracting much attention. This paper provides insights into preparation strategies and approaches of MGO's utilization for the removal of pollutants for sustainable water purification. It also reviews the preparation of magnetic graphene oxide nanocomposites and primary characterization instruments required for the evaluation of structural, chemical and physical functionalities of synthesized magnetic graphene oxide nanocomposites. Finally, we summarized some research challenges to accelerate the synthesized MGO's as adsorbents for the treatment of water pollutants such as toxic and radioactive metal ions and organic and agricultural pollutants.

Removal of Crystal Violet by Using Reduced-Graphene-Oxide-Supported Bimetallic Fe/Ni Nanoparticles (rGO/Fe/Ni): Application of Artificial Intelligence Modeling for the Optimization Process

Reduced-graphene-oxide-supported bimetallic Fe/Ni nanoparticles were synthesized in this study for the removal of crystal violet (CV) dye from aqueous solutions. This material was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), Raman spectroscopy, N₂-sorption, and X-ray photoelectron spectroscopy (XPS). The influence of independent parameters (namely, initial dye concentration, initial pH, contact time, and temperature) on the removal efficiency were investigated via Box⁻Behnken design (BBD). Artificial intelligence (i.e., artificial neural network, genetic algorithm, and particle swarm optimization) was used to optimize and predict the optimum conditions and obtain the maximum removal efficiency. The zero point of charge (pHZPC) of rGO/Fe/Ni composites was determined by using the salt addition method. The experimental equilibrium data were fitted well to the Freundlich model for the evaluation of the actual behavior of CV adsorption, and the maximum adsorption capacity was estimated as 2000.00 mg/g. The kinetic study discloses that the adsorption processes can be satisfactorily described by the pseudo-second-order model. The values of Gibbs free energy change (ΔG⁰), entropy change (ΔS⁰), and enthalpy change (ΔH⁰) demonstrate the spontaneous and endothermic nature of the adsorption of CV onto rGO/Fe/Ni composites.

Development of an auto-phase separable and reusable graphene oxide-potato starch based cross-linked bio-composite adsorbent for removal of methylene blue dye

In this work, we report the development of a cross-linked bio-composite consisting of graphene oxide, potato starch, cross-linker glutaraldehyde and its application to adsorption of the industrial dye, methylene blue, from aqueous solution. The inexpensiveness, non-hazardous nature and easy bio-degradability are the major reasons for the selection of starch material as one of the components of the bio-composite. The bio-composite has been characterized by FTIR, SEM, XRD, particle size and zeta potential analysis. The FTIR analysis reveals the nature of the binding sites and surface morphology of the bio-composite can be understood through SEM. The auto-phase separability of the adsorbent i.e., the precipitation of the adsorbent without any mechanical means is another factor which makes this particular material very attractive as an adsorbent. Parameters like adsorbent dosage, pH, temperature, rotation speed and salt concentration have been varied to find out the suitable dye adsorption conditions. Furthermore, the time dependence of adsorption process has been analyzed using pseudo-first and pseudo-second order kinetics. The adsorption isotherms have been constructed to suggest convincing mechanistic pathway for this adsorption process. Finally, desorption studies have been successfully performed in 3 cycles, establishing the reusability of the material, which should allow the adsorbent to be economically promising for practical application in wastewater treatment.

Removal of emerging contaminants daidzein and coumestrol from water by nanozeolite beta modified with tetrasubstituted ammonium cation

In present research, a simplistic hydrothermal method was adopted for one-step synthesis of nanozeolite beta (NZB) having an average particle size of 18nm with Si/Al ratio 46.67, surface area 328m²/g, pore volume 0.287cm³/g, and pore diameter 3.5nm. The surface of the synthesized NZB was modified with 0.5wt% hexadecyltrimethylammonium bromide (HDTMA-Br) and used as an adsorbent for the removal of two phytoestrogens daidzein and coumestrol from aqueous solutions. The surface properties and surface charge of NZB considerably changed after modification with HDTMA-Br, which resulted in enhanced removal of daidzein (92-98% from 7 to 27%) and coumestrol (93.5-99% from 5 to 9.2%). The surface modified zeolite beta (SMZB) has similar physical characteristics as of NZB with an average particle size of 20nm, surface area 299.8m²/g, pore volume 0.263cm³/g, and pore diameter 3.51nm. The influence of various parameters was examined by conducting a sequence of batch experiments. The adsorption equilibrium was achieved in less than 3h with saturation capacity of 40.74mg/g and 42.87mg/g for daidzein and coumestrol, respectively. The Freundlich isotherm and fractional order kinetic models represented the adsorption data very closely. The thermodynamic parameters indicated that sorption of both phytoestrogens onto SMZB is spontaneous and exothermic.

Application of machine/statistical learning, artificial intelligence and statistical experimental design for the modeling and optimization of methylene blue and Cd(ii) removal from a binary aqueous solution by natural walnut carbon

Analytical chemists apply statistical methods for both the validation and prediction of proposed models. Methods are required that are adequate for finding the typical features of a dataset, such as nonlinearities and interactions. Boosted regression trees (BRTs), as an ensemble technique, are fundamentally different to other conventional techniques, with the aim to fit a single parsimonious model. In this work, BRT, artificial neural network (ANN) and response surface methodology (RSM) models have been used for the optimization and/or modeling of the stirring time (min), pH, adsorbent mass (mg) and concentrations of MB and Cd²⁺ ions (mg L^-1) in order to develop respective predictive equations for simulation of the efficiency of MB and Cd²⁺ adsorption based on the experimental data set. Activated carbon, as an adsorbent, was synthesized from walnut wood waste which is abundant, non-toxic, cheap and locally available. This adsorbent was characterized using different techniques such as FT-IR, BET, SEM, point of zero charge (pH_pzc) and also the determination of oxygen containing functional groups. The influence of various parameters (i.e. pH, stirring time, adsorbent mass and concentrations of MB and Cd²⁺ ions) on the percentage removal was calculated by investigation of sensitive function, variable importance rankings (BRT) and analysis of variance (RSM). Furthermore, a central composite design (CCD) combined with a desirability function approach (DFA) as a global optimization technique was used for the simultaneous optimization of the effective parameters. The applicability of the BRT, ANN and RSM models for the description of experimental data was examined using four statistical criteria (absolute average deviation (AAD), mean absolute error (MAE), root mean square error (RMSE) and coefficient of determination (R²)). All three models demonstrated good predictions in this study. The BRT model was more precise compared to the other models and this showed that BRT could be a powerful tool for the modeling and optimizing of removal of MB and Cd(ii). Sensitivity analysis (calculated from the weight of neurons in ANN) confirmed that the adsorbent mass and pH were the essential factors affecting the removal of MB and Cd(ii), with relative importances of 28.82% and 38.34%, respectively. A good agreement (R² > 0.960) between the predicted and experimental values was obtained. Maximum removal (R% > 99) was achieved at an initial dye concentration of 15 mg L^-1, a Cd²⁺ concentration of 20 mg L^-1, a pH of 5.2, an adsorbent mass of 0.55 g and a time of 35 min.

Effects of ball milling on the physicochemical and sorptive properties of biochar: Experimental observations and governing mechanisms

With the goal of combining the advantages of ball-milling and biochar technologies, a variety of ball-milled biochars (BM-biochars) were synthesized, characterized, and tested for nickel (Ni(II)) removal from aqueous solution. Ball milling increased only the external surface area of low temperature biochars, but still dramatically enhanced their ability to sorb aqueous Ni(II). For higher temperature biochars with relatively low surface area, ball milling increased both external and internal surface area. Measurements of pH, zeta potential, stability, and Boehm titration demonstrated that ball milling also added oxygen-containing functional groups (e.g., carboxyl, lactonic, and hydroxyl) to biochar's surface. With these changed, all the BM-biochars showed much better Ni(II) removal efficiency than unmilled biochars. Ball-milled 600 °C bagasse biochar (BMBG600) showed the greatest Ni(II) adsorption capacity (230-650 compared to 26-110 mmol/kg for unmilled biochar) and the adsorption was dosage and pH dependent. Compared with the unmilled biochar, BMBG600 also displayed faster adsorption kinetics, likely due to an increase in rates of intra-particle diffusion in the latter. Experimental and modeling results suggest that the increase in BM-biochar's external and internal surface areas exposed its graphitic structure, thus enhancing Ni(II) adsorption via strong cation-π interaction. In addition, the increase in acidic surface functional groups enhanced Ni(II) adsorption by BM-biochar via electrostatic interaction and surface complexation. Ball milling thus has great potential to increase the efficiency of environmentally friendly biochar for various environmental applications.

Chemical sensing with 2D materials

During the last decade, two-dimensional materials (2DMs) have attracted great attention due to their unique chemical and physical properties, which make them appealing platforms for diverse applications in sensing of gas, metal ions as well as relevant chemical entities.