Multifunctional Binding Chemistry on Modified Graphene Composite for Selective and Highly Efficient Adsorption of Mercury

Hierarchical V2O3 spiny hollow nanosphere for efficient adsorption of precious metal ions in complicated matrices

Treatment of precious metals in electronic waste has attracted tremendous attention and is essential for both environmental protection and resource sustainable development. In this study, a novel adsorbent for precious metal ions, V2O3 spiny hollow nanospheres (p-V2O3 SHN), was synthesized through a one-step hydrothermal-assisted methodology for the adsorption of Au(III), Ag(I), Pd(II), and Pt(IV) from the leaching solution of electronic waste. The results reveal that the p-V2O3 SHN hierarchy was successfully constructed with a hollow structure and dense spiny morphology. The prepared p-V2O3 SHN can effectively remove precious metal ions such as Au(III), Ag(I), Pd(II), and Pt(IV), with the selective capture order being Au(III) > Ag(I) > Pt(IV) > Pd(II) > other metal ions. This superior adsorption capability can be attributed to the multi-diffusible, intermingled composition, and numerous active sites decorating the p-V2O3 SHN hierarchy, facilitating the uptake of Au(III), Ag(I), Pd(II), and Pt(IV) ions from electronic waste. The Langmuir model provided a better fit for the uptake process, revealing maximum uptake capacities of 833.33 mg/g for Au(III), 370.37 mg/g for Ag(I), 42.01 mg/g for Pd(II), and 77.51 mg/g for Pt(IV) on p-V2O3 SHN. Remarkably, p-V2O3 SHN exhibited a robust affinity for the adsorbate due to the presence of surface defects and reduction reactions. The new p-V2O3 SHN also demonstrated good reusability for three sorption cycles, highlighting its potential for electronic waste treatment. Due to its facile synthesis and excellent efficiency, hierarchical p-V2O3 SHN presents itself as a promising candidate for the selective uptake of Au(III), Ag(I), Pt(IV), and Pd(II) from electronic waste.

Advances in graphene-based nanomaterials for heavy metal removal from water: Mini review

The environment and public health are seriously at risk from the increasing levels of heavy metal (HM) pollution in water bodies, hence efficient remediation techniques must be developed. Unique physicochemical properties of graphene (Gn) such as its enormous surface area, chemical stability, and extraordinary adsorption capabilities have made it a promising candidate for application in various adsorption processes. Recent studies indicate the heavy metal removal capabilities of Gn-based materials such as Gn oxide (GO) and reduced GO (rGO) reach 99% efficiency rates for lead (Pb2+), cadmium (Cd2+), and mercury (Hg2+) through strong electrostatic bonds and metal coordination along with π-π stacking interactions. In addition, the selective nature of Gn-based adsorbents grows better through functionalization because it incorporates thiol, amine, and sulfonic acid groups. The integration of Gn-based materials with metal-organic frameworks (MOFs) combined with magnetic nanoparticles along with bio-based polymers enhances adsorption efficiency and increases stability while offering recyclability features. The conclusion of this study discusses the current obstacles such as cost, scalability, environmental impact, and selectivity and potential future developments for the widespread use of Gn-based adsorbents in water treatment, highlighting the significance of continued research to improve these substances for useful environmental applications. PRACTITIONER POINTS: Graphene-based materials exhibit high capacity for adsorbing various heavy metals, enhancing water purification. Functionalization of graphene improves its ability to selectively target and remove specific heavy metals like mercury and lead. Graphene derivatives can achieve heavy metal removal within minutes, making them efficient for water treatment. Despite high synthesis costs, graphene's superior performance may lower long-term operational costs in wastewater treatment.

Quantifying the Epoxide Group and Epoxide Index in Graphene Oxide by Catalyst-Assisted Acid Titration

Graphene oxide (GO), having diverse oxygen functional groups, including carboxyl, hydroxyl, carbonyl, and epoxy groups, is a significant graphene-related 2D material (GR2M) essential for various applications. The quantification of these functional groups traditionally utilizes Boehm acid titration, which, however, does not account for epoxy groups crucial for these applications. Presently, there exists no analytical method enabling quantitative assessment of the concentration of epoxy groups in GO available in the market in different forms such as powders, pastes, and dispersions. This paper presents a new approach employing catalyst-assisted acid-water-based titration to quantify epoxy groups in GO materials. The method's efficacy was validated using a well-characterized reference GO sample and tested on commercially produced GO powders, yielding epoxy group concentrations ranging from 1.15 ± 0.047 to 1.37 ± 0.051 mmol/g with high precision and reproducibility. The method introduces two new quality parameters, including the epoxide index (EI) and the equivalent epoxide weight (EEW) not implemented for GO before. Control measurements with a commercial epoxide material of known epoxide content demonstrated excellent agreement by using the proposed approach. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used for comparative characterizations of epoxide groups in GO samples during titrations.

Carbonized Apples and Quinces Stillage for Electromagnetic Shielding

Electromagnetic waves (EMWs) have become an integral part of our daily lives, but they are causing a new form of environmental pollution, manifesting as electromagnetic interference (EMI) and radio frequency signal leakage. As a result, the demand for innovative, eco-friendly materials capable of blocking EMWs has escalated in the past decade, underscoring the significance of our research. In the realm of modern science, the creation of new materials must consider the starting materials, production costs, energy usage, and the potential for air, water, and soil pollution. Herein, we utilized biowaste materials generated during the distillation of fruit schnapps. The biowaste from apple and quince schnapps distillation was used as starting material, mixed with KOH, and carbonized at 850 °C, in a nitrogen atmosphere. The structure of samples was investigated using various techniques (infrared, Raman, energy-dispersive X-ray, X-ray photoelectron spectroscopies, thermogravimetric analysis, BET surface area analyzer). Encouragingly, these materials demonstrated the ability to block EMWs within a frequency range of 8 to 12 GHz. Shielding efficiency was measured using waveguide adapters connected to ports (1 and 2) of the vector network analyzer using radio-frequency coaxial cables. At a frequency of 10 GHz, carbonized biowaste blocks 78.5% of the incident electromagnetic wave.

Synthesis of chiral graphene structures and their comprehensive applications: a critical review

From a molecular viewpoint, chirality is a crucial factor in biological processes. Enantiomers of a molecule have identical chemical and physical properties, but chiral molecules found in species exist in one enantiomer form throughout life, growth, and evolution. Chiral graphene materials have considerable potential for application in various domains because of their unique structural framework, properties, and controlled synthesis, including chiral creation, segregation, and transmission. This review article provides an in-depth analysis of the synthesis of chiral graphene materials reported over the past decade, including chiral nanoribbons, chiral tunneling, chiral dichroism, chiral recognition, and chiral transfer. The second segment focuses on the diverse applications of chiral graphene in biological engineering, electrochemical sensors, and photodetectors. Finally, we discuss research challenges and potential future uses, along with probable outcomes.

Advancing Albumin Isolation from Human Serum with Graphene Oxide and Derivatives: A Novel Approach for Clinical Applications

This study introduces a novel, environmentally friendly albumin isolation method using graphene oxide (GO). GO selectively extracts albumin from serum samples, leveraging the unique interactions between GO's oxygen-containing functional groups and serum proteins. This method achieves high purification efficiency without the need for hazardous chemicals. Comprehensive characterization of GO and reduced graphene oxide (rGO) through techniques such as X-ray diffraction (XRD) analysis, Raman spectroscopy, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) confirmed the structural and functional group transformations crucial for protein binding. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometry analyses demonstrated over 95% purity of isolated albumin, with minimal contamination from other serum proteins. The developed method, optimized for pH and incubation conditions, showcases a green, cost-effective, and simple alternative for albumin purification, promising broad applicability in biomedical research and clinical applications.

The Synergistic Effect of Graphene Oxide in Epoxy Resin on Photocured Coating Films with Anticorrosion and Antibacterial Properties

In this work, graphene oxide (GO) and epoxy-functionalized graphene oxide (GOSi) are chosen as additives and incorporated into epoxy resin (EP) for nanocomposite photo-coating films (GO/EP and GOSi/EP series). Compared to GO/EP, the GOSi/EP nanocomposite demonstrates strong binding and excellent dispersibility, highlighting covalent bonding between GOSi and the epoxy coating. Furthermore, GOSi/EP-based films demonstrated superior thermal stability and adhesion performance on galvanized steel plates. The corrosion performance of the coated galvanized steel is investigated using electrochemical impedance spectroscopy (EIS) and polarization curve analysis (Tafel). The effectiveness of corrosion protection is evaluated based on a combination of photoreactivity, crosslinking density, dispersity, and adhesion properties. Out of all the treated films, the film based on 0.1GOSi/EP exhibited the highest percentage of inhibition (98.89%) and demonstrated superior long-term anticorrosion stability. In addition, the 0.1GOSi/EP based formulation showed remarkable antibacterial activity against S. aureus, resulting in a 92% reduction. This work demonstrates the development of a facile, environmentally friendly functionalized graphene oxide/epoxy photocured film with superior dual functionalities in both anticorrosion and antibacterial properties. These advancements hold promising potential for impactful practical applications.

Ultrasound-Based Micro-/Nanosystems for Biomedical Applications

Due to the intrinsic non-invasive nature, cost-effectiveness, high safety, and real-time capabilities, besides diagnostic imaging, ultrasound as a typical mechanical wave has been extensively developed as a physical tool for versatile biomedical applications. Especially, the prosperity of nanotechnology and nanomedicine invigorates the landscape of ultrasound-based medicine. The unprecedented surge in research enthusiasm and dedicated efforts have led to a mass of multifunctional micro-/nanosystems being applied in ultrasound biomedicine, facilitating precise diagnosis, effective treatment, and personalized theranostics. The effective deployment of versatile ultrasound-based micro-/nanosystems in biomedical applications is rooted in a profound understanding of the relationship among composition, structure, property, bioactivity, application, and performance. In this comprehensive review, we elaborate on the general principles regarding the design, synthesis, functionalization, and optimization of ultrasound-based micro-/nanosystems for abundant biomedical applications. In particular, recent advancements in ultrasound-based micro-/nanosystems for diagnostic imaging are meticulously summarized. Furthermore, we systematically elucidate state-of-the-art studies concerning recent progress in ultrasound-based micro-/nanosystems for therapeutic applications targeting various pathological abnormalities including cancer, bacterial infection, brain diseases, cardiovascular diseases, and metabolic diseases. Finally, we conclude and provide an outlook on this research field with an in-depth discussion of the challenges faced and future developments for further extensive clinical translation and application.

A novel functionalized graphdiyne oxide membrane for efficient removal and rapid detection of mercury in water

In practice, efficient, rapid and simple removal of Hg(II) from water using nano adsorbents remains an extreme challenge at present. In this work, a novel Hg(II) adsorbent based on functionalized graphdiyne oxide (GDYO-3M) membrane was designed for the purpose of effective and prompt removal of Hg(II) from environmental water for the first time. Through filtration, the proposed GDYO-3M membrane (4 cm diameter size) fulfilled an exceeding 97% removal efficiency in > 10 L water containing 0.1 mg/L Hg(II) within 1 h. Due to the presence of -SH groups, the GDYO-3M membrane demonstrates an excellent selectivity for Hg(II) vs. 14 co-existing metal ions. In the meantime, the GDYO-3M membrane represents a favorable reproducibility (above 95% Hg(II) removal) after 9 successive adsorption-desorption cycles. For the mechanism, it is believed that the active sites in the adsorption process mainly include -SH groups, oxygen-containing functional groups, and alkyne bonds. Further, the GDYO-3M membrane can be utilized as an enrichment approach for sensitive analysis of Hg(II) in water based on energy dispersion X-ray fluorescence spectrometry (ED-XRF), whose detection limit (LOD) reaches 0.2 μg/L within 15 min. This work not only provides a green and efficient method for removing Hg(II), but also renders an approach for rapid, sensitive and portable Hg(II) detection in water.

Cysteamine Chemisorption at Mercury-Solution Interfaces in the Context of Redox and Microdissociation Equilibria

The redox behavior and chemisorption of cysteamine (CA) at a charged mercury surface are described, with an emphasis on its acid-base properties supported by molecular dynamics and quantum mechanical calculations. It was found that CA forms chemisorbed layers on the surface of the mercury electrode. The formation of Hg-CA complexes is connected to mercury disproportionation, as reflected in peaks SII and SI at potentials higher than the electrode potential of zero charge (p.z.c.). Both the process of chemisorption of CA and its consequent redox transformation are proton-dependent. Also, depending on the protonation of CA, the formation of typical populations of chemisorbed conformers can be observed. In addition, cystamine (CA disulfide dimer) can be reduced on the mercury surface. Between the potentials of this reduction and peak SI, the p.z.c. of the electrode used can be found. Furthermore, CA can serve as an LMW catalyst for hydrogen evolution. The mechanistic insights presented here can be used for follow-up research on CA chemisorption and targeted modification of other metallic surfaces.

Mercury remediation from wastewater through its spontaneous adsorption on non-functionalized inverse spinel magnetic ferrite nanoparticles

In this study, inverse spinel cubic ferrites MFe2O4 (M = Fe2+, and Co2+) have been fabricated for the high-capacity adsorptive removal of Hg(II) ions. The PXRD analysis confirmed ferrites with the presence of residual NaCl. The surface area of Fe3O4 (Fe-F) and CoFe2O4 (Co-F) material was 69.1 and 45.2 m2 g-1, respectively. The Co-F and Fe-F showed the maximum Hg(II) adsorption capacity of 459 and 436 mg g-1 at pH 6. The kinetic and isotherms models suggested a spontaneous adsorption process involving chemical forces over the ferrite adsorbents. The Hg(II) adsorption process, probed by X-ray photoelectron spectroscopy (XPS), confirmed the interaction of Hg(II) ions with the surface hydroxyl groups via a complexation mechanism instead of proton exchange at pH 6 with the involvement of chloride ions. Thus, this study demonstrates a viable and cost-effective solution for the efficient remediation of Hg ions from wastewater using non-functionalized ferrite adsorbents. This study also systematically investigates the kinetics and isotherm mechanism of Hg(II) adsorption onto ferrites and reports one of the highest Hg(II) adsorption capacities among other ferrite-based adsorbents.

Effect of Graphene Oxide-Modified CaAl-Layered Double Hydroxides on the Carbon Dioxide Permeation Properties of Fluoroelastomers

This work aimed to investigate the CO2 gas barrier and mechanical properties of fluorine rubber nanocomposites filled with Ca/Al layered hydroxide (graphene oxide [GO]/LDH-Ca2Al) modified by GO. GO/LDH-Ca2Al nanocomposite fillers were prepared by depositing Ca/Al layered hydroxide (LDH-Ca2Al) into the surface of alkalized GO (Al-GO). The prepared GO/LDH-Ca2Al nanocomposite fillers and complexes were characterized by Fourier infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) for structural and micromorphological characterization. The results showed that GO/LDH-Ca2Al was successfully prepared with strong interactions between Al-GO and LDH, and the compatibility of GO/LDH-Ca2Al nanocomposite fillers with the polymer was significantly improved compared with that of LDH-Ca2Al. Consequently, both the fracture strength (σb) and strain (εb) of GO/LDH-Ca2Al nanocomplexes remarkably increased, and they exhibited excellent mechanical properties. Differential scanning calorimetry and thermogravimetric analysis were used to characterize the thermal stability of GO/LDH-Ca2Al nanocomposite fillers, and GO/LDH-Ca2Al nanocomposite fillers have better thermal stability than LDH-Ca2Al. The reaction products (S-LDH-Ca2Al and S-GO-Ca2Al) of LDH-Ca2Al and GO/LDH-Ca2Al with CO2 were characterized using XRD and TGA, respectively, and the results show that LDH-Ca2Al reacts readily and chemically with CO2, resulting in a lower diffusion coefficient of CO2 in the LDH-Ca2Al nanocomplexes than that of the GO/LDH-Ca2Al nanocomplexes and leading to the destruction of the laminar structure of LDH-Ca2Al, while GO/LDH-Ca2Al has better CO2 resistance stability. GO/LDH-Ca2Al nanocomplexes exhibited a reduced content of hydroxyl groups with pro-CO2 nature exposed on the surface of LDH-Ca2Al, improving the interfacial interaction between the nanofillers and the rubber matrix and enhancing the dispersion of GO/LDH-Ca2Al in the polymers. Moreover, CO2 in the soluble GO/LDH-Ca2Al nanocomposites was significantly reduced, while the diffusion properties demonstrated weak temperature dependence on solubility. The mechanism of the CO2 gas barrier of polymers filled with GO/LDH-Ca2Al was proposed on the basis of the Arrhenius equation.

The "How" and "Where" Behind the Functionalization of Graphene Oxide by Thiol-ene "Click" Chemistry

Graphene oxide (GO) is a 2D nanomaterial with unique chemistry due to the combination of sp2 hybridization and oxygen functional groups (OFGs) even in single layer. OFGs play a fundamental role in the chemical functionalization of GO to produce GO-based materials for diverse applications. However, traditional strategies that employ epoxides, alcohols, and carboxylic acids suffer from low control and undesirable side reactions, including by-product formation and GO reduction. Thiol-ene "click" reaction offers a promising and versatile chemical approach for the alkene functionalization (-C=C-) of GO, providing orthogonality, stereoselectivity, regioselectivity, and high yields while reducing by-products. This review examines the chemical functionalization of GO via thiol-ene "click" reactions, providing insights into the underlying reaction mechanisms, including the role of radical or base catalysts in triggering the reaction. We discuss the "how" and "where" the reaction takes place on GO, the strategies to avoid unwanted side reactions, such as GO reduction and by-product formation. We anticipate that multi-functionalization of GO via the alkene groups will enhance GO physicochemical properties while preserving its intrinsic chemistry.

Large-scale synthesis of 2D-silica (SiOx) nanosheets using graphene oxide (GO) as a template material

Graphene oxide (GO) was used in this study as a template to successfully synthesize silicon oxide (SiOx) based 2D-nanomaterials, adapting the same morphological features as the GO sheets. By performing a controlled condensation reaction using low concentrations of GO (<0.5 wt%), the study shows how to obtain 2D-nanoflakes, consisting of GO-flakes coated with a silica precursor that were ca. 500 nm in lateral diameter and ca. 1.5 nm in thickness. XPS revealed that the silanes had linked covalently with the GO sheets at the expense of the oxygen groups present on the GO surface. The GO template was shown to be fully removable through thermal treatment without affecting the nanoflake morphology of the pure SiOx-material, providing a methodology for large-scale preparation of SiOx-based 2D nanosheets with nearly identical dimensions as the GO template. The formation of SiOx sheets using a GO template was investigated for two different silane precursors, (3-aminopropyl) triethoxysilane (APTES) and tetraethyl orthosilicate (TEOS), showing that both precursors were capable of accurately templating the graphene oxide template. Molecular modeling revealed that the choice of silane affected the number of layers coated on the GO sheets. Furthermore, rheological measurements showed that the relative viscosity was significantly affected by the specific surface area of the synthesized particles. The protocol used showed the ability to synthesize these types of nanoparticles using a common aqueous alcohol solvent, and yield larger amounts (∼1 g) of SiOx-sheets than what has been previously reported.

Postsynthetic Modification of Core-Shell Magnetic Covalent Organic Frameworks for the Selective Removal of Mercury

Core-shell magnetic covalent organic framework (COF) materials were prepared, followed by shell material functionalization with different organic ligands, including thiosemicarbazide, through a postsynthetic modification approach. The structures of the prepared samples were characterized with various techniques, including powder X-ray diffraction (PXRD), Brunauer-Emmett-Teller (BET) method, thermogravimetric analysis (TGA), photoinduced force microscopy (PiFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and solid ¹³C NMR. PXRD and BET studies revealed that the crystalline and porous nature of the functionalized COFs was well maintained after three steps of postsynthetic modification. On the other hand, solid ¹³C NMR, TGA, and PiFM analyses confirmed the successful functionalization of COF materials with good covalent linkage connectivity. The use of the resulting functionalized magnetic COF for selective and ultrafast adsorption of Hg(II) has been investigated. The observations displayed rapid kinetics with adsorption dynamics conforming to the quasi-second-order kinetic model and the Langmuir adsorption model. Furthermore, this prepared crystalline magnetic material demonstrated a high Langmuir Hg(II) uptake capacity, reaching equilibrium in only 5 min. Thermodynamic calculations proved that the adsorption process is endothermic and spontaneous.

Bis-Schiff base cellulosic nanocrystals for Hg (II) removal from aqueous solution with high adsorptive capacity and sensitive fluorescent response

Mercury pollution in aqueous solutions is a severe problem in environmental protection and the contaminated water may cause serious risks to human health. Based on the constant development of adsorptive materials, adsorption technique is widely applied as an efficient and convenient approach to eliminate mercury species from waters. In this work, we report a one-pot procedure to prepare a bis-Schiff base cellulosic adsorbent to integrate the advantages of large adsorptive capacity and excellent fluorescent recognition towards mercury ions. The adsorption experiments demonstrate that sulfydryl-contained cellulosic nanocrystals exhibit specific affinity with mercury species and the adsorption capacity reaches as high as 624.8 mg/g at room temperature. Besides, the introduction of rhodamine moiety endows the material a 19 times enhancement of selective "off-on" fluorescent sensing while exposed to mercury. Additionally, the bifunctional adsorbent material shows high sensitivity towards mercury ions in aqueous solution with detection limits of as low as 8.29 × 10^-8 M for fluorescence and 5.9 × 10^-9 M for UV-vis spectrum, respectively. The fitting results of the adsorption models indicate a monolayer adsorption during the uptake of mercury ions and the removal process follows the pseudo-second order kinetics. Moreover, density functional theory studies are employed to further understand the adsorptive and responsive mechanisms.

Post-synthetic thiol modification of covalent organic frameworks for mercury(II) removal from water

Various materials have been developed for environmental remediation of mercury ion pollution. Among these materials, covalent organic frameworks (COFs) can efficiently adsorb Hg(II) from water. Herein, two thiol-modified COFs (COF-S-SH and COF-OH-SH) were prepared, through the reaction between 2,5-divinylterephthalaldehyde and 1,3,5-tris-(4-aminophenyl)benzene, followed by post-synthetic modification using bis(2-mercaptoethyl) sulfide and dithiothreitol, respectively. The modified COFs showed excellent Hg(II) adsorption abilities with maximum adsorption capacities of 586.3 and 535.5 mg g^-1 for COF-S-SH and COF-OH-SH, respectively. The prepared materials showed excellent selective absorbability for Hg(II) against multiple cationic metals in water. Unexpectedly, the experimental data showed that both co-existing toxic anionic diclofenac sodium (DCF) and Hg(II) performed positive effect for capturing another pollutant by these two modified COFs. Thus, a synergistic adsorption mechanism between Hg(II) and DCF on COFs was proposed. Moreover, density functional theory calculations revealed that synergistic adsorption occurred between Hg(II) and DCF, which resulted in a significant reduction in the adsorption system's energy. This work highlights a new direction for application of COFs to simultaneous removal of heavy metals and co-existing organic pollutants from water.

Synthesis of graphene derivatives from asphaltenes and effect of carbonization temperature on their structural parameters

A method for synthesizing graphene derivatives from asphaltene is proposed in this work. The graphene derivatives are mainly composed of few-layer graphene-like nano-sheets of randomly distributed heteroatoms; mainly sulfur and nitrogen. The proposed method is based on a thermal treatment in which asphaltene is carbonized in a rotating quartz-tube furnace under an inert atmosphere at a temperature in the range of 400-950 °C. Asphaltenes from different origins were employed to verify the synthesis method. The results indicate that graphene derivatives obtained at high carbonization temperature have similar structural parameters, despite the evident differences in parent asphaltenes structures and compositions. The transformation of asphaltene to graphene derivatives mainly occurred due to three factors: the reduction in the average number of aromatic layers (n), the expansion in aromatic sheet diameter (L _a), and the elimination of alkyl side chains. The reduction in the number of aromatic sheets per stack is primarily ascribed to thermal exfoliation, while the increase in the aromatic sheet diameter is attributed to secondary reactions in the aromatic core of asphaltene. The elimination of side chains, on the other hand, is mainly credited to thermal cracking. The quantification of defect density (L _D) in the graphene derivatives suggests an association between defects and heteroatoms presence.

A Sandwich Structure of Fulvic Acid and PMIDA-Modified LDHs for the Simultaneous Removal of Cu2+ and Aniline in Multicomponent Solutions

The coexistence of organic and inorganic pollutants in industrial wastewater has emerged as a concerning environmental issue worldwide due to the critical levels of biological toxicity of these pollutants. In this context, the present study proposes a sandwich structure of fulvic acid and PMIDA-modified LDHs (FA/PMIDA-LDHs) for the simultaneous removal of Cu²⁺ and aniline from wastewater. The specific structure was synthesized using a combination of coprecipitation and impregnation methods. Abundant benzene rings and oxygen-containing functional groups greatly increased the number of sites for the adsorption of both Cu²⁺ and aniline. The maximum adsorption capacity of Cu²⁺ and aniline in solution with initial pH 5.0 at 25 °C could reach 221.24 and 132.28 mg/g, respectively. Cu²⁺ could be chelated by the functional groups in the FA/PMIDA-LDHs structure, and a coupled reduction-complexation mechanism was proposed for this process. The uptake of aniline on FA/PMIDA-LDHs was demonstrated to be a result of the combination of coordination forces, hydrophobic effects, π-π interactions, and hydrogen bonds. In a multicomponent solution, FA/PMIDA-LDHs exhibited excellent salt tolerance of up to 1000 mg/L of Na⁺ or Ca²⁺. The effects of Fe³⁺, Ni²⁺, Cl^-, Cr₂O₇^2-, SO₄^2-, and H₂PO₄^- on the uptakes of Cu²⁺ and aniline were also investigated.

Self-Assembled Nanofibrous Membranes by Electrospinning as Efficient Dye Photocatalysts for Wastewater Treatment

Water pollution has become a leading problem due to industrial development and the resulting waste, which causes water contamination. Different materials and techniques have been developed to treat wastewater. Due to their self-assembly and photocatalytic behavior, membranes based on graphene oxide (GO) are ideal composite materials for wastewater treatment. We fabricated composite membranes from polylactic acid (PLA) and carboxylic methyl cellulose (CMC)/carboxyl-functionalized graphene oxide (GO-f-COOH) using the electrospinning technique and the thermal method. Then, a nanofibrous membrane (PLA/CMC/GO-f-COOH@Ag) was produced by loading with silver nanoparticles (Ag-NPs) to study its photocatalytic behavior. These membranes were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) in order to investigate the behavior of the fabricated membranes. The degradation kinetics studies were conducted using mathematical models, such as the pseudo first- and second-order models, by calculating their regression coefficients (R²). These membranes exhibited exceptional dye degradation kinetics. The R² values for pseudo first order were PCGC = 0.983581, PCGC@Ag = 0.992917, and the R² values for pseudo second order were PCGC = 0.978329, PCGC@Ag = 0.989839 for methylene blue. The degradation kinetics of Rh-B showed R² values of PCGC = 0.973594, PCGC@Ag = 0.989832 for pseudo first order and R² values of PCGC = 0.994392, PCGC@Ag = 0.998738 for pseudo second order. The fabricated nanofibrous membranes exhibited a strong π-π electrostatic interaction, thus providing a large surface area, and demonstrated efficient photocatalytic behavior for treating organic dyes present in wastewater. The fabricated PLA/CMC/GO-f-COOH@Ag membrane presents exceptional photocatalytic properties for the catalytic degradation of methylene blue (MB) dye. Hence, the fabricated nanofibrous membrane would be an eco-friendly system for wastewater treatment under catalytic reaction.

Selective removal of aqueous Hg2+ by magnetic composites sulfur-containing on the hyper-branched surface: Characterization, performance and mechanism

The adsorbents with recyclable, large adsorption capacity and selective adsorption can effectively remove the pollution and harm of heavy metal ions in water. Therefore, two magnetic composites containing sulfur (MCP-S4 and MCP-S8) on the hyper-branched surface were prepared, furthermore, their structures were characterized and adsorption performance was analyzed by FTIR, XRD, TGA, BET, SEM, TEM, VSM and ICP. The results showed that both MCP-S4 and MCP-S8 had superparamagnetism with saturation susceptibility of 22.10 and 22.26 emu/g, and owned a specific surface area of 11.394 and 11.235 m²/g, respectively. MCP-S4 and MCP-S8 could selectively adsorb Hg²⁺ with the exist of Fe³⁺, Cu²⁺, Co²⁺, Ni²⁺, Mn²⁺, and Al³⁺ in solution. The adsorption kinetics accorded with pseudo-second-order model and Boyd film diffusion model, and the adsorption isotherm was fitted better with Langmuir isotherm model and D-R model, furthermore, the adsorption was an entropic-increasing and endothermic process. The removal rate of Hg²⁺ from simulated sewage by the two materials was more than 91%, and the adsorption retention rate was more than 85% after five adsorption-desorption cycles. The adsorption mechanism was analyzed by comparing the changes of FTIR, EDS and XPS spectra before and after adsorption. It was found that functional groups (C-N, CONH, CS, SH) could form stable chelates with Hg²⁺, which was the main reason why MCP-S4 and MCP-S8 could adsorb Hg²⁺ selectively, furthermore, S atoms of CS and -SH played a leading role in the process of adsorption. In addition, DFT calculation was also used as an auxiliary means to verify the adsorption mechanism.

Sulfide modifies physicochemical properties and mercury adsorption of microplastics

Microplastics (MPs) tend to accumulate and undergo a sulfur weathering process that leads to significant surface changes in sulfur-rich anaerobic environments, such as sewage and wastewater treatment plants. Aged MPs can have a profound impact on environmental behaviors of various toxic pollutants, especially heavy metals. Although previous studies have investigated the adsorption characteristics of metal ions on MPs that are aged in aerobic environments, the sorptive interactions of sulfur-aged MPs in anaerobic environments with mercury, i.e., Hg(II), are largely unknown. In this study, laboratory investigations were conducted to study the sorptive behaviors of Hg(II) by six common MPs treated anaerobically in the presence of sulfide. Adsorption isotherms show that the sulfur aging process greatly enhances the MP sorption capacity of Hg(II). The mechanisms including changes in the specific surface area, electrostatic interactions, surface precipitation, and surface functional groups are responsible for the enhanced adsorption capacities of sulfur-aged MPs. The thiol group that forms on the MP surface plays a dominant role in enhancing the MP adsorption capacity of Hg(II), which is determined by the formation of unsaturated bonds in the molecular chains of MPs. Furthermore, the pathways of surface chemical transformation of MPs during sulfur aging have been proposed. This study promotes our understanding of the potential hazard of MPs as well as the fate and transport of heavy metals in the presence of aged MPs.

New insights on energetic properties of graphene oxide (GO) materials and their safety and environmental risks

Graphene oxide (GO) has been recognized as a thermally unstable and energetic material, but surprisingly its environmental and safety risks were not fully explored, defined, and regulated. In this study, systematic explosivity and flammability characterizations of commercial GO materials were conducted to evaluate the influence of key parameters such as physical forms (paste, powders, films, and aerogels), temperature, heating rate, mass, and heating environment, as well as their potential safety and environmental impacts. Results based on thermogravimetric analysis (TGA) showed that GO in paste and powder forms have lower temperature thresholds (>180-192 °C) to initiate micro-explosions compared to GO film and aerogels (> 205 °C and 213 °C) regardless of the environment (inert, air, or oxygen). The observed explosive behavior can be explained by thermal runaway reactions as a result of thermal deoxygenation and decomposition of oxygen functional groups. Flammability rating and limiting oxygen index (LOI) results confirmed that GO films are flammable materials that can spontaneously propagate flame in a low oxygen environment (~11 %). These results provided new insights about potential safety and environmental risks of GO materials, which somehow were not considered, suggesting urgent actions to improve current safety protocols for labeling, handling, transporting, and storage practices from manufacturers to the end-users.

Highly Efficient Elimination of Pb+2 and Al+3 Metal Ions from Wastewater Using Graphene Oxide/3,5-Diaminobenzoic Acid Composites: Selective Removal of Pb2+ from Real Industrial Wastewater

In this study, graphene oxide (GO) was functionalized with 3,5-diaminobenzoic acid (DABA) by a one-step method to produce functionalized graphene oxide (FGO). FGO is a new type of absorbent crystalline substance that has a high surface area and a large porosity site as well as a large number of dentate functional groups which lead to enhanced adsorption performance for heavy metal ions. The adsorption efficiency of FGO for Pb⁺² and Al⁺³ metal ions was extra satisfactory when compared with GO due to the ease of design and the homogeneous structure of FGO. The structure of synthesized GO and FGO was confirmed by different techniques such as FTIR, XRD, TGA, BET nitrogen adsorption-desorption methods, and TEM analyses. The mass of utilized adsorbents, the pH of the medium, the concentration of ionic species in the medium, temperature, and process time were all investigated as variables in the adsorbent procedure. The experimental data recorded that the maximum adsorption efficiency of the 0.5 g/L FGO composite was 99.7 and 99.8% for Pb⁺² and Al⁺³ metal ions, respectively, while in the case of using GO, the maximum adsorption efficiency was 92.6 and 91.9% at ambient temperature in a semineutral medium at pH 6 after 4 h. The adsorption results were in good conformity with the Freundlich model and pseudo-second-order kinetics for Pb⁺² and Al⁺³ metal ions. Also, the reusability study indicates that FGO can be used repeatedly at least for five cycles with a slight significant loss in its efficiency.

Carbon-based adsorbents as proficient tools for the removal of heavy metals from aqueous solution: A state of art-review emphasizing recent progress and prospects

Carbon-centric adsorbents (CCA) are diverse forms, from simple biochar (BC) to graphene derivatives, carbon nanotubes (CNTs), and activated carbon (AC), which have been vastly explored for their removal of a plethora of pollutants, including heavy metals (HM). The prominent features of CCA are their operational attributes like extensive surface area, the occurrence of flexible surface functional groups, etc. This work offers a comprehensive examination of contemporary research on CCA for their superior metal removal aptitude and performances in simulated solutions and wastewater flows; via portraying the recent research advances as an outlook on the appliances of CACs for heavy metal adsorption for removal via distinct forms like AC, BC, Graphene oxide (GO), and CNTs. The bibliometric analysis tool was employed to highlight the number of documents, country-wise contribution, and co-occurrence mapping based on the Scopus database. The coverage of research works in this review is limited to the last 5 years (2017-2021) to highlight recent progress and prospects in using CCAs such as AC, BC, GO, and CNTs to remove HM from aqueous media, which makes the review unique. Besides an overview of the common mechanisms of CACs, the future scope of CAC, especially towards HM mitigation, is also discussed in this review. This review endorses that further efforts should be commenced to enhance the repertory of CCAs that effectively eliminate multiple targeted metals in both simulated and real wastewater.

Engineered Geomedia Kaolin Clay-Reduced Graphene Oxide-Polymer Composite for the Remediation of Olaquindox from Water

Globally, there is an upsurge in the use of unregulated veterinary pharmaceuticals with enhanced release into the environment, resulting in water pollution, which is difficult to remediate. To address this issue, we synthesized and characterized highly hydrophobic three-dimensional ordered engineered geomedia with multiple channels. Kaolin clay (K) was functionalized with either graphene oxide (GO) synthesized via Tour's method or reduced GO in situ with covalently linked methoxyether polyethylene glycol (GO-PEG) using a simple and easily scalable amidation reaction. This was done to enhance the adsorption of olaquindox, a veterinary antibiotic. The X-ray diffraction profile confirmed the grafting of GO and GO-PEG to kaolin. Morphological analysis revealed the architecture of thin films of GO/GO-PEG grafted on the kaolin surface with extensive porosity. Energy-dispersive X-ray mapping, infra-red spectra, and elemental analysis confirmed the successful synthesis of the engineered geomedia composite of K, GO/rGO, and PEG (KrGO-PEG). Due to multiple surface functional groups of polyamide and amido-carbonic groups on the KrGO-PEG composite, it was suitable for olaquindox adsorption. In batch sorption studies of 0.5XKrO-PEG, the effect of pH (2-10) was negligible but with fast equilibrium time (2-1440 min) at 30 min, while the kinetics and equilibrium data suited the pseudo-second order and Langmuir models, respectively. The maximum adsorption value obtained for the composite was 59.5 mg/g; the higher the GO content, the higher the adsorption. The sorption mechanism was majorly through hydrophobic and π-π interactions. Regenerated/reused adsorbents after 4 cycles had the same efficacy in remediating olaquindox from simulated/real water.

Carbon nanostructures: a comprehensive review of potential applications and toxic effects

There is no doubt that nanotechnology has revolutionized our life since the 1970s when it was first introduced. Nanomaterials have helped us to improve the current products and services we use. Among the different types of nanomaterials, the application of carbon-based nanomaterials in every aspect of our lives has rapidly grown over recent decades. This review discusses recent advances of those applications in distinct categories, including medical, industrial, and environmental applications. The first main section introduces nanomaterials, especially carbon-based nanomaterials. In the first section, we discussed medical applications, including medical biosensors, drug and gene delivery, cell and tissue labeling and imaging, tissue engineering, and the fight against bacterial and fungal infections. The next section discusses industrial applications, including agriculture, plastic, electronic, energy, and food industries. In addition, the environmental applications, including detection of air and water pollutions and removal of environmental pollutants, were vastly reviewed in the last section. In the conclusion section, we discussed challenges and future perspectives.

Effective and reusable 3D CuxS nanocluster structured magnetic adsorbent for mercury extraction from wastewater

The elimination of mercury from polluted water using an effective, cost-economic, and sustainable method was investigated in this work. A modulated multilayer magnetic Hg²⁺ extractor was prepared with a self-assembly engineering that permitting robust anchoring and uniform distribution of the negatively charged 3D Cu_xS nanocluster onto a polydopamine (PDA) covered positively strengthened Fe₃O₄ surface. The developed PAD@Fe₃O₄ supported copper sulfide composite (Cu_xS/PAD@Fe₃O₄) presented an unparalleled Hg²⁺ uptake performance with adsorption capacity of 1394.61 mg/g (without saturation), and extraordinary selectivity with distribution coefficient value K_d of 17419.2 mL/g. A complexation reaction during Hg²⁺ affinity was taken place on Cu_xS/PAD@Fe₃O₄ surface, and almost no components losses occurring during the adsorption. Furthermore, the as-prepared Cu_xS/PAD@Fe₃O₄ micron-adsorbent can be easily magnetic recovery and recycled with hydrochloric acid elution. The purification of 50 L Hg²⁺ containing wastewater, initial concentration of 20 μg/L can be achieved with Cu_xS/PAD@Fe₃O₄ dosage of 0.1 g and treatment cost of 0.077 US $. The outlet Hg²⁺ concentration met drinking water standard of the United States Environmental Protection Agency. The Cu_xS/PAD@Fe₃O₄ magnetic adsorbent can be fabricated cheaply and holds promise for scale-up applications.

Tetrahedral DNA-directed core-satellite assembly as SERS sensor for mercury ions at the single-particle level

To monitor the deteriorating mercury emissions, it is imperative to propose methods for detecting mercury ions (Hg²⁺) with sensitivity and selectivity. The SERS spectral-resolved single-particle detection approach can be carried out using dark-field optical microscopy (DFM) combined with Raman spectroscopy. Herein, we have designed a novel yet convenient single-particle detection assay for quantifying Hg²⁺ using DFM-correlated Raman spectroscopy. In the assay, a tetrahedral DNA-directed core-satellite nanostructure is used as the SERS probe. Especially, one edge of the tetrahedron is made up of a single-stranded DNA containing a Hg²⁺ aptamer, which reconfigures upon the specific recognition of Hg²⁺. As a result, the interparticle distance reduces from 4.5 to 1.2 nm, thus generating Raman signal enhancement. As a proof of concept, Hg²⁺ was detected in a linear range from 1 to 100 nM based on the variation in SERS intensity. Furthermore, the experimental results were supported by the finite difference time domain (FDTD) calculations. Owing to its high sensitivity and selectivity, this method was further employed to detect Hg²⁺ in practical tap water and lake water samples, revealing that the single-particle detection strategy holds great promise for Hg²⁺ analysis in real environment analysis.

Polypyrrole-Bentonite composite as a highly efficient and low cost anionic adsorbent for removing hexavalent molybdenum from wastewater

The aim of current study was to develop a new material for the fast and efficient removal of hexavalent molybdenum (Mo(VI)) from contaminated water. In this work, a novel adsorbent was synthesized through the polypyrrole intercalation modification of bentonite (PPy-BT) via in-situ chemical polymerization method for effectively removal of Mo(VI) from aqueous solution. The surface morphology and chemical composition of PPy-BT composites were investigated by X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectrometer, scanning electron microscopy techniques and X-ray photoelectron spectroscopy. PPy and BT could well resist the aggregation of each other, and therefore resulted in a loose-packed structure and good exposure of active sites. Using materials for the adsorption of Mo(VI) revealed has a maximum adsorption capacity of 100.17 mg/g at 25 °C and pH 4.0 by the Langmuir model. The adsorption kinetics and isotherm data are found to be well elucidated through pseudo-second-order and Langmuir models. Moreover, high regeneration ability (>89.3%) of PPy-BT was noted for five consecutive adsorption-desorption cycles. These findings highlight the potential of PPy-BT for practical water treatment applications. The intercalation material of PPy-BT could provide a new strategy to develop cost-effective clay-based nanomaterials for wastewater treatment.

Sustainable hydrophilic ultrasmall carbonaceous spheres modified by click reaction for high-performance polymeric ion chromatographic stationary phase

Novel poly(ethylvinylbenzene-divinylbenzene) (EVB-DVB) agglomerated with ultrasmall carbonaceous spheres (UCSs) anion-exchange packings for ion chromatography (IC) were constructed. Hydrophilic UCSs with mean sizes of 62-98 nm were synthesized in quantity by the polydiallyl dimethyl ammonium chloride aided hydrothermal carbonization of fructose. The green strategy based on the thiol-ene click reaction with cysteamine in aqueous system was first designed for the hyperbranched polyquaternary amine (HPA) grafting of UCSs with negligible damage on their monodispersity. The HPA modified UCSs were evenly distributed on sulfonated EVB-DVB substrate to form one uniform layer of functional nanospheres without observable coagulum. Seven typical anions (F^-, Cl^-, NO₂^-, Br^-, NO₃^-, SO₄^2- and PO₄^3-) were baseline separated on constructed packing in 5 min with high efficiencies in the range of 44,800-71,100 plates m ^- 1. The rapid separation of polarizable anions, small organic acids and saccharides could be also accomplished under isocratic elution with competitive peak symmetry and efficiency. Good reproducibility was demonstrated by consecutive injection. Thiosulfate in water reducer was further detected on prepared packing in 4 min with detection limit of 0.04 mg L ^- 1 (S/N = 3) and good repeatability.

Efficient and selective removal of Pb(ii) from aqueous solution by a thioether-functionalized lignin-based magnetic adsorbent

The effective and selective removal of heavy metal ions from sewage is a major challenge and is of great significance to the treatment and recovery of metal waste. Herein, a novel magnetic lignin-based adsorbent L@MNP was synthesized by a thiol-ene click reaction under ultraviolet (UV) light irradiation. Multiple characterization techniques, including Fourier transform infrared (FT-IR) spectrometry, X-ray diffraction (XRD), elemental analysis, vibrating sample magnetometry (VSM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirmed the formed nano-morphology and structure of L@MNP. The effects of pH, contact time, initial metal concentration and temperature on the batch adsorption of Pb(ii) by L@MNP were investigated. Due to the existence of sulfur and oxygen-containing sites, the maximum adsorption capacity of L@MNP for Pb(ii) could reach 97.38 mg g^-1, while the adsorption equilibrium was achieved within 30 min. The adsorption kinetics and isotherms were well described by the pseudo-second-order model and Langmuir model, respectively, suggesting a chemical and monolayer adsorption process. In addition, L@MNP showed a high adsorption selectivity (k _Pb = 0.903) toward Pb(ii) in the presence of other co-existing metal ions. The experimental results also revealed that L@MNP displayed structural stability, ease of recovery under an external magnetic field, and acceptable recyclability after the fifth cycle. Considering its facile preparation, low cost and high adsorption efficiency, the developed L@MNP adsorbent demonstrated great potential in removing heavy metal ions from wastewater.

l-Cysteine-Modified Graphene Oxide-Based Membrane for Chiral Selective Separation

A novel chiral separation membrane was fabricated by assembling l-cysteine (l-Cys)-modified graphene oxide sheets. l-Cys modification leads to an enantiomer separation membrane with an accessible interlayer spacing of 8 Å, which allows high solvent permeability. In the racemate separation experiments under isobaric conditions, the enantiomeric excess (ee) values of alanine (Ala), threonine (Thr), tyrosine (Tyr), and penicillamine (Pen) racemates in the permeation solution were 43.60, 44.11, 27.43, and 46.44%, respectively. In the racemate separation experiments under negative pressure, the separation performances of Ala, Thr, and Tyr were still maintained, and the enantiomeric excess (ee) values of the filtrate after separation were 56.80, 54.57, and 32.34%, respectively. These results indicate that the as-prepared GO-Cys membrane has a great practical value in the field of enantiomer separation.

Thiol/methylthio-functionalized porous aromatic frameworks for simultaneous capture of aromatic pollutants and Hg(II) from water

Simultaneously capturing organic pollutants and heavy metal can greatly reduce the water remediation time and cost, however it is still a great challenge presently. Herein, two novel thiol/methylthio-functionalized porous aromatic frameworks were synthesized as sorbents via the Sonogashira-Hagihara reaction of 1,3,5-triethynylbenzene and 1,3,5-tris(4-bromophenyl) benzene, the subsequent chloromethylation of the phenyl rings, and the final nucleophile substitution of -Cl groups by NaSH/NaSMe. These two sorbents were characterized by FT-IR spectra, energy dispersive X-ray spectra, scanning electron microscope, nitrogen adsorption analysis, thermo-gravimetric analysis, and elemental analyses. Adsorption experiments displayed that new sorbents had high uptake abilities and fast adsorption kinetics for aromatic pollutants and mercury (II) (Hg(II)). The maximum adsorption capacity (Q_max) of toluene and m-xylene on both new sorbents were 531.9-571.4 mg/g with the kinetic binding rate constants (k_obs) of 0.00276-0.02422 g/mg/min, and the Q_max values of Hg(II) were 148.1-180.3 mg/g with k_obs of 0.00592-0.01573 g/mg/min. Moreover, new sorbents indicated high simultaneous uptake abilities for these pollutants with good reusability, and finally they were successfully applied to the simultaneous remediation of these pollutants in two simulated sewages with high and low concentration, indicating their great practical application potential in wastewater remediation.

Bi-layered hollow amphoteric composites: Rational construction and ultra-efficient sorption performance for anionic Cr(VI) and cationic Cu(II) ions

Here, we have developed a novel bilayer hollow amphiphilic biosorbent (BHAB-3) with large adsorption capacity, rapid adsorption kinetics, and cost-effective for the removal of Cr(VI) and Cu(II) from aqueous solutions. The synthesis was based on the clever use of freeze-drying to fix the structure, secondary modification of the carboxymethyl cellulose microspheres with polyethyleneimine and cross-linking by glutaraldehyde. The consequences of pH, initial concentration, contact time and temperature on adsorption were investigated. The Langmuir model fits showed that the maximum adsorption capacities of the two target heavy metal ions reached 835.91 and 294.79 mg/g, respectively. Moreover, BHAB-3 was characterized by SEM, FT-IR, TGA, and XPS synergistically, showing that it exhibits a strong complexation ability for Cu(II) and a strong electrostatic effect for Cr(VI). Adsorption and desorption experiments showed only a slight decrease in the adsorption capacity of the BHAB-3 for Cr(VI) and Cu(II) ions after 5 and 26 cycles, respectively. Given the excellent properties of this adsorbent, it is a promising candidate for heavy metal ion removal.

The amino - functionalized magnetic graphene oxide combined with graphite furnace atomic absorption spectrometry for determination of trace inorganic arsenic species in water samples

A novel adsorbent of magnetic graphene oxide (GO) chemically modified by cysteamine hydrochloride (Fe₃O₄@SiO₂/GO-NH₂) through thiol-ene click chemistry reaction was synthesized. The prepared Fe₃O₄@SiO₂/GO-NH₂ exhibit selective adsorption to As(V) with high adsorption capacity (52.66 mg g^-1). Taking Fe₃O₄@SiO₂/GO-NH₂ as the adsorbents, a new method of magnetic solid phase extraction (MSPE) combined with graphite furnace atomic absorption spectrometry (GFAAS) was developed in determining trace-level inorganic arsenic species (As(III) and As(V)) in environmental water and bottled water samples. Various experimental parameters affecting the MSPE have been optimized. Under the optimal experimental parameters, the limit of detection of the established method for As(V) was 1.02 ng L^-1, the relative standard deviations were 7.9% (intra-day, c = 50 ng L^-1, n = 5) and 4.6% (inter-day, c = 50 ng L^-1, n = 7), respectively, and the enrichment factor of the method was 392. GBW08666 and GBW08667 (certified reference material) were analyzed to confirm the accuracy of the method, and the results were matched well with the certified values. The established MSPE-GFAAS method was successfully applied in analyzing trace/ultratrace As(III) and As(V) in real water samples.

Amino-assisted AHMT anchored on graphene oxide as high performance adsorbent for efficient removal of Cr(VI) and Hg(II) from aqueous solutions under wide pH range

The adsorbents with high adsorption capacity for simultaneously removing Cr(VI) and Hg(II) from aqueous solutions under broad working pH range are highly desirable but still extremely scarce. Here, a novel adsorbent with multidentate ligands was facilely fabricated by covalently bonding 4-amino-3-hydrazino-5-mercapto- 1,2,4-triazole on graphene oxide via the Schiff's base reaction. The maximum adsorption capacities of Cr(VI) and Hg(II) on the current adsorbent were 734.2 and 1091.1 mg/g, which were 14.36 and 5.61 times higher than that of the pure graphene oxide, respectively, exceeding those of most adsorbents previously reported. More interestingly, Cr(VI) and Hg(II) concentrations were decreased from 2 mg/L to 0.0001 mg/L for Hg(II) and 0.004 mg/L for Cr(VI), far below the WHO recommended threshold for drinking water. Moreover, the adsorbent shows an excellent performance for simultaneous removal of Cr(VI) and Hg(II) with more than 99.9% and 98.6% removal efficiencies in aqueous solutions. Finally, the adsorbent was successfully applied in dealing with the real industrial effluent, implying huge potential in industrial application. This work offers a new possibility for the removal of the metallic contaminants by rational designing target groups and ligands.

Accounting Carbonaceous Counterfeits in Graphene Materials Using the Thermogravimetric Analysis (TGA) Approach

Counterfeits in the supply chain of high-value advanced materials such as graphene and their derivatives have become a concerning problem with a potential negative impact on this growing and emerging industry. Recent studies have revealed alarming facts that a large percentage of manufactured graphene materials on market are not graphene, raising considerable concerns for the end users. The common and recommended methods for the characterization of graphene materials, such as transmission electron microscopy (TEM), atomic force microscopy (AFM), and Raman spectroscopy based on spot analysis and probing properties of individual graphene particles, are limited to provide the determination of the properties of "bulk" graphene powders at a large scale and the identification of non-graphene components or purposely included additives. These limitations are creating counterfeit opportunities by adding low-cost black carbonaceous materials into manufactured graphene powders. To address this problem, it is critical to have reliable characterization methods, which can probe the specific properties of graphene powders at bulk scale, confirm their typical graphene signature, and detect the presence of unwanted additional compounds, where the thermogravimetric analysis (TGA) method is one of the most promising methods to perform this challenging task. This paper presents the evaluation of the TGA method and its ability to detect low-cost carbon additives such as graphite, carbon black, biochar, and activated carbon as potential counterfeiting materials to graphene materials and their derivatives such as graphene oxide (GO) and reduced GO. The superior performance of the TGA method is demonstrated here, showing its excellent capability to successfully detect these additives when mixed with graphene materials, which is not possible by two other comparative methods (Raman spectroscopy and powder X-ray diffraction (XRD)), which are used as the common characterization methods for graphene materials.

In situ remediation efficacy of hybrid aerogel adsorbent in model aquatic culture of Paramecium caudatum exposed to Hg(II)

Silica-gelatin hybrid aerogel of 24 wt% gelatin content is an advanced functional material suitable for the high performance selective adsorption of aqueous Hg(II). The remediation efficacy of this adsorbent was tested under realistic aquatic conditions by exposing cultures of Paramecium caudatum to Hg(II) and monitoring the model cultures by time-lapse video microscopy. The viability of Paramecium was quantified by analyzing the pixel differences of the sequential images caused by the persistent movement (motility) of the cells. The viability of Paramecium displays a clear exposure-response relationship with Hg(II) concentration. Viability decreases with increasing Hg(II) concentration when the latter is higher than 125 μg L^-1. In the presence of 0.1 mg mL^-1 aerogel adsorbent, the viability of the cells decreases only at Hg(II) concentrations higher than 500 μg L^-1, and 220 min survival time was measured even at 1000 μg L^-1 Hg(II). The effective toxicity of Hg(II) is lower in the presence of the aerogel, because the equilibrium concentration of aqueous Hg(II) is low due to adsorption, thus Paramecium cells do not uptake as much Hg(II) as in the un-remediated cultures. Video imaging of Paramecium cultures offers a simple, robust and flexible method for providing quantitative information on the effectiveness of advanced materials used in adsorption processes for water treatment.

Antibacterial chitosan composite films with food-inspired carbon spheres immobilized AgNPs

The cumulative toxicity of AgNPs has limited their application in food packaging. As such, the quest for AgNPs should focus on controlling their release to reduce the cumulative toxicity. Here, two kinds of green hydrothermal carbonized methods were used to treat sulfhydryl-modified chitosan to obtain two kinds of carbon spheres/AgNPs (Glutinous rice sesameballs-like AgNPs-SMCS and dragon fruit-like SMCS-Ag), which exhibited good stability and high immobilization efficiency for AgNPs, and the release of total Ag from AgNPs-SMCS and SMCS-Ag were only about 5.63% and 3.59% after 14 days, respectively. Subsequently, they were added into chitosan separately to prepare chitosan-based films. Two carbon spheres/AgNPs regulated the microstructure of chitosan-based films because of the electrostatic interaction and the micro-nanometer filling behavior, thus further immobilized the AgNPs. Importantly, the films presented good antibacterial activity and excellent safety. These results will provide a theoretical basis for the green and safe design of AgNPs antibacterial agent.

In situ formation of Hg2+-coordinated fluorescent nanoparticles through a supramolecular polymer network used for efficient Hg2+ sensing and separation

There have been many new methods for synthesizing novel nanomaterials with unique functions. Herein, a novel strategy to form fluorescent nanoparticles in situ has been developed, and it can be applied to efficiently sense Hg2+ in living cells and also separate Hg2+ from water.

Highly Water Dispersible Functionalized Graphene by Thermal Thiol-Ene Click Chemistry

Functionalization of pristine graphene to achieve high water dispersibility remains as a key obstacle owing to the high hydrophobicity and absence of reactive functional groups on the graphene surface. Herein, a green and simple modification approach to prepare highly dispersible functionalized graphene via thermal thiol-ene click reaction was successfully demonstrated on pristine graphene. Specific chemical functionalities (–COO, –NH₂ and –S) on the thiol precursor (L-cysteine ethyl ester) were clicked directly on the sp² carbon of graphene framework with grafting density of 1 unit L-cysteine per 113 carbon atoms on graphene. This functionalized graphene was confirmed with high atomic content of S (4.79 at % S) as well as the presence of C–S–C and N–H species on the L-cysteine functionalized graphene (FG-CYS). Raman spectroscopy evidently corroborated the modification of graphene to FG-CYS with an increased intensity ratio of D and G band, I_D/I_G ratio (0.3 to 0.7), full-width at half-maximum of G band, FWHM [G] (20.3 to 35.5) and FWHM [2D] (64.8 to 90.1). The use of ethanol as the reaction solvent instead of common organic solvents minimizes the chemical hazards exposure to humans and the environment. This direct attachment of multifunctional groups on the surface of pristine graphene is highly demanded for graphene ink formulations, coatings, adsorbents, sensors and supercapacitor applications.

Thermogravimetric Analysis (TGA) of Graphene Materials: Effect of Particle Size of Graphene, Graphene Oxide and Graphite on Thermal Parameters

Thermogravimetric analysis (TGA) has been recognized as a simple and reliable analytical tool for characterization of industrially manufactured graphene powders. Thermal properties of graphene are dependent on many parameters such as particle size, number of layers, defects and presence of oxygen groups to improve the reliability of this method for quality control of graphene materials, therefore it is important to explore the influence of these parameters. This paper presents a comprehensive TGA study to determine the influence of different particle size of the three key materials including graphene, graphene oxide and graphite on their thermal parameters such as carbon decomposition range and its temperature of maximum mass change rate (Tmax). Results showed that Tmax values derived from the TGA-DTG carbon combustion peaks of these materials increasing from GO (558–616 °C), to graphene (659–713 °C) and followed by graphite (841–949 °C) The Tmax values derived from their respective DTG carbon combustion peaks increased as their particle size increased (28.6–120.2 µm for GO, 7.6–73.4 for graphene and 24.2–148.8 µm for graphite). The linear relationship between the Tmax values and the particle size of graphene and their key impurities (graphite and GO) confirmed in this study endows the use of TGA technique with more confidence to evaluate bulk graphene-related materials (GRMs) at low-cost, rapid, reliable and simple diagnostic tool for improved quality control of industrially manufactured GRMs including detection of “fake” graphene.