Comparative Study of Graphene Hydrogels and Aerogels Reveals the Important Role of Buried Water in Pollutant Adsorption

High-Level Disordered Metal-Organic Frameworks Synthesized by Interference-Oriented Attachment for Electrochemical Anion Sieve

Disordered MOFs seamlessly amalgamate the robust stability and pore tunability inherent in crystalline MOFs with the advantages derived from abundant defects and active sites present in amorphous structures. This study pioneers the use of the interference-oriented attachment (IOA) mechanism to meticulously craft the morphology and crystal growth of MIL-101(Cr) (Cr-MOF), resulting in the successful synthesis of a high-level disordered Cr-MOF boasting an enhanced array of active sites and exceptional electrochemical properties. The correlation between disordered structures and the electrochemical properties of MOFs are elucidated using the lattice distortion index and fractal dimension. The high-level disordered MOF electrode showcases a remarkable fluoride sieving effect, outperforming conventional fluoride removal materials with a remarkable fluoride adsorption capacity of 41.04 mgNaF gelectrodes -1. First-principles calculations, in conjunction with relevant experiments, provided further validation that the disordered structure significantly enhances the defluorination performance of the material. This study introduces a novel approach for the direct bottom-up synthesis of high-level disordered MOFs, showcasing their potential for applications in electrochemical water treatment.

Evaluation of the difference in adsorption of amphetamine-type drugs on deep eutectic solvent-functionalized graphene oxide/ZIF-67 composite: Experiment and theoretical calculations

Herein, the capture and separation properties of the deep eutectic solvent-functionalized magnetic graphene oxide/ZIF-67 composite (ZMG-DES) towards amphetamine-type drugs (MDMA, MAM and AM) from water were investigated. Kinetic and isotherm models showed that the adsorption behaviors were monolayer chemisorption. Batch experiment results showed that the maximal adsorption of MDMA (933.652 μg⋅g-1) was 2.3 and 2.8 times higher than that of MAM (412.849 μg⋅g-1) and AM (328.652 μg⋅g-1), respectively, and this superiority remained consistent under varied environmental influences (pH, background ion and humic acid). Theoretical calculations and characterization analyses demonstrated the methylenedioxy group of MDMA led to the highly selective adsorption. Electrostatic potential (ESP) distribution indicated that the methylenedioxy added electron-rich areas and provided more adsorption sites. The Independent Gradient Model (IGMH) quantified the adsorption contribution of the functional groups in each system, which the contribution of the methylenedioxy reached 25.23%, significantly exceeding that of -NH- (18.80%) and benzene ring (20.76%), and proved that the H-bonds formed methylenedioxy enhanced adsorption. Furthermore, the Hirshfeld surface analysis proved that the methylenedioxy and -NH- of MDMA acted as H-bond acceptor and donor, respectively, which synergistically promoted the adsorption. The present study will help us to understand the structure-property relationship between amphetamine-type drugs and ZMG-DES.

New Insights into Aggregation Behaviors of the UV-Irradiated Dissolved Biochars (DBioCs) in Aqueous Environments: Effects of Water Chemistries and Variation in the Hamaker Constant

The aggregation behavior of ubiquitous dissolved black carbon (DBC) largely affects the fate and transport of its own contaminants and the attached contaminants. However, the photoaging processes and resulting effects on its colloidal stability remain yet unknown. Herein, dissolved biochars (DBioCs) were extracted from common wheat straw biochar as a proxy for an anthropogenic DBC. The influences of UV radiation on their aggregation kinetics were systematically investigated under various water chemistries (pH, electrolytes, and protein). The environmental stability of the DBioCs before and after radiation was further verified in two natural water samples. Hamaker constants of pristine and photoaged DBioCs were derived according to Derjaguin-Landau-Verwey-Overbeek (DLVO) prediction, and its attenuation (3.19 ± 0.15 × 10-21 J to 1.55 ± 0.07 × 10-21 J after 7 days of radiation) was described with decay kinetic models. Pearson correlation analysis revealed that the surface properties and aggregation behaviors of DBioCs were significantly correlated with radiation time (p < 0.05), indicating its profound effects. Based on characterization and experimental results, we proposed a three-stage mechanism (contended by photodecarboxylation, photo-oxidation, and mineral exposure) that DBioCs might experience under UV radiation. These findings would provide an important reference for potential phototransformation processes and relevant behavioral changes that DBC may encounter.

Applications of hollow nanostructures in water treatment considering organic, inorganic, and bacterial pollutants

One of the major issues of modern society is water contamination with different organic, inorganic, and contaminants bacteria. Finding cost-effective and efficient materials and methods for water treatment and environment remediation is among the scientists' most important considerations. Hollow-structured nanomaterials, including hollow fiber membranes, hollow spheres, hollow nanoboxes, etc., have shown an exciting capability for wastewater refinement approaches, including membrane technology, adsorption, and photocatalytic procedure due to their extremely high specific surface area, high porosity, unique morphology, and low density. Diverse hollow nanostructures could potentially eliminate organic contaminants, including dyes, antibiotics, oil/water emulsions, pesticides, and other phenolic compounds, inorganic pollutants, such as heavy metal ions, salts, phosphate, bromate, and other ions, and bacteria contaminations. Here, a comprehensive overview of hollow nanostructures' fabrication and modification, water contaminant classification, and recent studies in the water treatment field using hollow-structured nanomaterials with a comparative attitude have been provided, indicating the privilege abd detriments of this class of nanomaterials. Eventually, the future outlook of employing hollow nanomaterials in water refinery systems and the upcoming challenges arising in scaling up are also propounded.

In-situ magnetic alginate coated chitosan core@shell beads with excellent performance in simulated and real wastewater treatment: Behavior, mechanisms, and new perspectives

Herein, a new hybrid magnetic core@shell biocomposite was prepared based on an alginate-bentonite core and a chitosan shell layer (mAB@Cs) where magnetic Fe3O4 NPs (50.7 nm) were in-situ generated on the surface via a simple non-thermal co-precipitation approach. The biocomposite has a high ability to magnetically separate and remove organic (ciprofloxacin (CPX)) and seven toxic inorganic (Cu2+, Cd2+, Co2+, Ni2+, Pb2+, Zn2+, and Hg2+) contaminants from simulated wastewater. Experimental results showed a CPX monolayer chemisorption with a Langmuir maximum adsorption capacity of 264.7 mg/g, maintained effectiveness up to the fifth cycle, and high removal rates of heavy metals ranging from 74.89 % to 99.86 % corresponding to adsorption capacities ranging from 12 to 20 mg/g. For a more accurate evaluation, the biocomposite was tested on a real urban wastewater sample (RWW) and it has manifested a noteworthy efficiency in removing a mixture of inorganic pollutants in terms of potassium K+ and orthophosphate phosphorous P-PO43-, and organic matter in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD) with 46 %, 90 %, 84 %, and 64 % removal efficiencies, respectively. On top of this, a high inactivation rate of E. coli of the order of 96 % was recorded, making the prepared magnetic biocomposite adept for the simultaneous removal of emergent wastewater pollutants, from organic, inorganic, to pathogen microorganisms.

Overlooked role of void-nanoconfined effect in emerging pollutant degradation: Modulating the electronic structure of active sites to accelerate catalytic oxidation

The efficient removal of emerging pollutant from water is the ultimate frontiers of advanced oxidation processes (AOPs), yet it is challenging to obtain higher catalytic activity and oxidation rate. Herein, a sustainable solution was proposed by optimizing the curvature of confined structure to modulate the electronic state of the active sites in nanochannels for improving the catalytic activity. In addition, the confined effect can enhance the oxidation rate by shorting the mass transfer of active species and pollutants. A void-nanoconfined nanoreactor was prepared by loading Fe2O3 into the nanochannels (<5 nm) of the hollow carbon sphere. An enhancement of 3 orders of magnitude was obtained in the degradation rate constant of void-nanoconfined catalytic system toward sulfamethoxazole (SMX) (6.25 min-1) compared with the non-confined system. The kinetics enhancement was attributed to the larger electron potential difference between the outer and inner nanochannel caused by the curvature increase of carbon sphere, accelerating the electron transfer, so that the energy barrier of SMX degradation reaction was reduced by 31 kcal/mol with the assistance of confinement energy. Importantly, the NC-IN/PDS system exhibited outstanding removal efficiency for the actual river water using a continuous flow reactor. This work provides a new insight into designing an efficient and stable catalytic nanoreactor, enriching the domain of advanced wastewater treatment strategies.

Coupled Surface-Confinement Effect and Pore Engineering in a Single-Fe-Atom Catalyst for Ultrafast Fenton-like Reaction with High-Valent Iron-Oxo Complex Oxidation

The nanoconfinement effect in Fenton-like reactions shows great potential in environmental remediation, but the construction of confinement structure and the corresponding mechanism are rarely elucidated systematically. Herein, we proposed a novel peroxymonosulfate (PMS) activation system employing the single Fe atom supported on mesoporous N-doped carbon (FeSA-MNC, specific surface area = 1520.9 m2/g), which could accelerate the catalytic oxidation process via the surface-confinement effect. The degradation activity of the confined system was remarkably increased by 34.6 times compared to its analogue unconfined system. The generation of almost 100% high-valent iron-oxo species was identified via 18O isotope-labeled experiments, quenching tests, and probe methods. The density functional theory illustrated that the surface-confinement effect narrows the gap between the d-band center and Fermi level of the single Fe atom, which strengthens the charge transfer rate at the reaction interface and reduces the free energy barrier for PMS activation. The surface-confinement system exhibited excellent pollutant degradation efficiency, robust resistance to coexisting matter, and adaptation of a wide pH range (3.0-11.0) and various temperature environments (5-40 °C). Finally, the FeSA-MNC/PMS system could achieve 100% sulfamethoxazole removal without significant performance decline after 10,000-bed volumes. This work provides novel and significant insights into the surface-confinement effect in Fenton-like chemistry and guides the design of superior oxidation systems for environmental remediation.

Preparation of graphene oxide-doped silica aerogel using supercritical method for efficient removal of emerging pollutants from wastewater

Emerging pollutants and a large volume of unused dyes from the textile industry have been contaminating water bodies. This work introduces a scalable approach to purifying water by the adsorption of Acid green 25 (AG), Crystal Violet (CV), and Sulfamethoxazole (SMA) from an aqueous solution by graphene oxide (GO) doped modified silica aerogel (GO-SA) with supercritical fluid deposition (SFD) method. Characterization of GO-SA using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), high-resolution scanning electron microscopy (HR-SEM), thermogravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) adsorption isotherms revealed the improvement in the adsorbent surface area, and its textural properties. The high removal percentages observed in most of the experimental runs provide evidence of the excellent performance of the adsorbent towards the anionic and cationic dyes along with the antibiotic. The adsorption isotherm and kinetics showed that the Langmuir isotherm and pseudo-second-order kinetic models could explain adsorption. The adsorbent holds a higher adsorption capacity for SMA (67.07 mg g-1) than for CV (41.46 mg g-1) and AG (20.56 mg g-1) due to the higher hydrophobicity that interacts with the hydrophobic adsorbent. The GO-SA successfully removed AG, CV, and SMA with removal percentages of 98.23%, 98.71%, and 94.46%, respectively. The parameters were optimized using Central Composite Design (RSM-CCD). The prepared aerogel showed excellent reusability with a removal efficiency of > 85% even after 5 cycles. This study shows the potential of GO-SA adsorbent in textile and other wastewater purification.

Confined water-encapsulated activated carbon for capturing short-chain perfluoroalkyl and polyfluoroalkyl substances from drinking water

The global ecological crisis of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water has gradually shifted from long-chain to short-chain PFASs; however, the widespread established PFAS adsorption technology cannot cope with the impact of such hydrophilic pollutants given the inherent defects of solid-liquid mass transfer. Herein, we describe a reagent-free and low-cost strategy to reduce the energy state of short-chain PFASs in hydrophobic nanopores by employing an in situ constructed confined water structure in activated carbon (AC). Through direct (driving force) and indirect (assisted slip) effects, the confined water introduced a dual-drive mode in the confined water-encapsulated activated carbon (CW-AC) and completely eliminated the mass transfer barrier (3.27 to 5.66 kcal/mol), which caused the CW-AC to exhibit the highest adsorption capacity for various short-chain PFASs (C-F number: 3-6) among parent AC and other adsorbents reported. Meanwhile, benefiting from the chain length- and functional group-dependent confined water-binding pattern, the affinity of the CW-AC surpassed the traditional hydrophobicity dominance and shifted toward hydrophilic short-chain PFASs that easily escaped treatment. Importantly, the ability of CW-AC functionality to directly transfer to existing adsorption devices was verified, which could treat 21,000 bed volumes of environment-related high-load (~350 ng/L short-chain PFAS each) real drinking water to below the World Health Organization's standard. Overall, our results provide a green and cost-effective in situ upgrade scheme for existing adsorption devices to address the short-chain PFAS crisis.

Preliminary Study on the Preparation of Conductive Nanosized Calcium Carbonate Utilizing Biogas Slurry by a Synchronous Double Decomposition Coating Method

Nanosized calcium carbonate (NCC) plays a vital role in the rubber and plastic fields as a filler, but it cannot resolve the electrostatic problem. Humic-acid-based NCC (HA-NCC) was accidentally discovered in the reaction between biogas slurry and calcium chloride (CaCl₂), based on nutrient recovery and gradient treatment technology to solve the biogas slurry problem. A preliminary study on the preparation of conductive nanosized calcium carbonate (CNCC) from the HA-NCC was implemented. Meanwhile, a synchronous double decomposition coating method was proposed to properly explain the formation of HA-NCC in the biogas slurry. The CNCC was further obtained through drying and carbonizing the HA-NCC sample. The morphology of CNCC was a square shape with aggregation, and its crystals were calcite. The C content of CNCC was 5% higher than that of the normal CaCO₃, implying a synchronous coating effect of soluble HA in biogas slurry on NCC. The weight loss of CNCC was about 2.5% at 630 °C, explaining why the HA-NCC remained black at 550 °C for 4 h. The CNCC was partly ordered and graphitized. The resistivity of the CNCC reached 2.62 × 10⁶ Ω·cm. It could be used as a conductive powder. In view of the favorable characteristics described above, CNCC would be expected to be a filler and antistatic agent for plastics and rubbers to enhance the tensile and bending resistance of polymer materials, while eliminating electrostatic hazards. The results are also of great significance for developing high-end products to realize resource utilization of biogas slurry.

Air-enclosed pores in graphene aerogel inhibit the adsorption of bisphenol A but accelerate the adsorption of naphthalene

Graphene hydrogel (GH) and aerogel (GA) have great application potential as highly effective adsorbents, but the accessibility of their adsorption sites have not yet been identified, restricting our understanding on the adsorption mechanisms and manufacturing. This study comparatively studied the adsorption characteristics of bisphenol A (BPA) and naphthalene (NAP) on GH and GA, focussing on the accessibility of the adsorption sites. The adsorption of BPA on GA was much lower but faster than that on GH. NAP adsorption on GA was very close to that on GH but faster than that on the latter. Considering that NAP is volatilisable, we speculate that some unwetted sites in the air-enclosed pores are available to it, but not to BPA. We applied ultrasonic and vacuum treatments to remove the air in GA pores, which was verified using a CO₂ replacement experiment. BPA adsorption was greatly enhanced but slowed, while that of NAP was not enhanced. This phenomenon suggested that some inner pores became accessible in the aqueous phase after air removal from pores. The enhanced accessibility of air-enclosed pores was verified by the increased relaxation rate of surface-bounded water on GA, based on a ¹H NMR relaxation analysis. This study highlights that the accessibility of adsorption site plays a crucial role for the adsorption properties of carbon-based aerogel. The volatile chemicals may be quickly adsorbed in the air-enclosed pores, which be useful for immobilizing volatile contaminants.

Spatial confinement: A green pathway to promote the oxidation processes for organic pollutants removal from water

Organic pollutants removal from water is pressing owing to the great demand for clean water. Oxidation processes (OPs) are the commonly used method. However, the efficiency of most OPs is limited owing to the poor mass transfer process. Spatial confinement is a burgeoning way to solve this limitation by use of nanoreactor. Spatial confinement in OPs would (i) alter the transport characteristics of protons and charges; (ii) bring about molecular orientation and rearrangement; (iii) cause the dynamic redistribution of active sites in catalyst and reduce the entropic barrier that is high in unconfined space. So far, spatial confinement has been utilized for various OPs, such as Fenton, persulfate, and photocatalytic oxidation. A comprehensive summary and discussion on the fundamental mechanisms of spatial confinement mediated OPs is needed. Herein, the application, performance and mechanisms of spatial confinement mediated OPs are overviewed firstly. Subsequently, the features of spatial confinement and their effects on OPs are discussed in detail. Furthermore, environmental influences (including environmental pH, organic matter and inorganic ions) are studied with analyzing their intrinsic connection with the features of spatial confinement in OPs. Lastly, challenges and future development direction of spatial confinement mediated OPs are proposed.

"Blockchain-Like" MIL-101(Cr)/Carbon Black Electrodes for Unprecedented Defluorination by Capacitive Deionization

Metal-organic frameworks (MOF) have attracted extensive attention due to their ultra-high specific surface area and tunable structure, the mechanism of direct utilization for capacitive deionization (CDI) defluorination remains undefined. Here, MIL-101(Cr) with ultra-high specific surface area, high water stability, and open metal sites (OMSs) is prepared by a hydrothermal method for defluorination of CDI. Carbon black is used as a "chain" to connect F-stored in the holes of MIL-101(Cr) (Cr-MOF)as "blocks" to enhance the conductivity and ion storage capacity of MIL-101(Cr)/carbon black electrodes (Cr-MOF electrodes). This simple construction method avoids the process complexity of in situ synthesis and performs better. These easily constructed "blockchain-like" Cr-MOF electrodes exhibit excellent defluorination capacity (39.84 mg_NaF g_electrodes ^-1 ), low energy consumption (1.2 kWh kg_NaF ^-1 ), and good stability. The coupling of the electrochemical redox reaction of Cr³⁺ /Cr⁴⁺ with confined water is investigated using in situ and ex situ analysis methods combined with density functional theory (DFT), resulting in an unprecedented defluorination mechanism for Cr-MOF electrodes. This study opens up new ideas for the application of MOF in CDI, clarifies the removal mechanism of MOF, and lays a foundation for further promoting the application of raw materials with poor conductivity in the field of CDI.

A Review of the Mechanical Properties of Graphene Aerogel Materials: Experimental Measurements and Computer Simulations

Graphene aerogels (GAs) combine the unique properties of two-dimensional graphene with the structural characteristics of microscale porous materials, exhibiting ultralight, ultra-strength, and ultra-tough properties. GAs are a type of promising carbon-based metamaterials suitable for harsh environments in aerospace, military, and energy-related fields. However, there are still some challenges in the application of graphene aerogel (GA) materials, which requires an in-depth understanding of the mechanical properties of GAs and the associated enhancement mechanisms. This review first presents experimental research works related to the mechanical properties of GAs in recent years and identifies the key parameters that dominate the mechanical properties of GAs in different situations. Then, simulation works on the mechanical properties of GAs are reviewed, the deformation mechanisms are discussed, and the advantages and limitations are summarized. Finally, an outlook on the potential directions and main challenges is provided for future studies in the mechanical properties of GA materials.

Adsorption of dyestuff by nano copper oxide coated alkali metakaoline geopolymer in monolith and powder forms: Kinetics, isotherms and microstructural analysis

To remove contaminants and pollutants from wastewater systems, adsorbents are widely used. Geopolymers offer a convenient alternative as adsorbents in the wastewater treatment system as they are low-cost, environmentally friendly, and safer. A new adsorbent material prepared by coating nano copper oxide on the surface of alkali-activated metakaolin showed a higher ability to remove methylene blue (MB) dye from wastewater, thus making them attractive in dye removal applications. First, nano copper oxide was prepared by sol gel method and metakaolin geopolymer was produced using sodium silicate solution having a Ms value of 1.1 (M). Afterwards, nano copper oxide (MC) was coated on the surface of the geopolymer. The ability of MB dye to bind to both pristine (M^p, MC^p) and powder forms (M^pr, MC^pr) of the geopolymer was evaluated. X-ray diffraction revealed that the halo found at 27.40°-31.077° (2θvalue) in both samples related to amorphous gel's composition and the major peaks of copper oxide in MC^pr were sited at a 2θ value of 35.45° and 38.88°.The dye removal efficiency can be inferred from the increased adsorption capacity of 11.9 mg/g (M^p) and 14.4 mg/g (MC^p) for the monolith form and 81.43 mg/g (M^pr) and 87.82 mg/g (MC^pr) for the powder form. The adsorption of reused active sites was 73% for M^pr and 83% for MC^pr up to the fifth cycle after regeneration by heat treatment at 400 °C. The models that best suited the adsorption data were pseudo-second-order and Freundlich isotherms, which indicated possible chemisorption with intra-particle diffusion. Furthermore, the binding energy is shifted to lower value in XPS spectra due to dye adsorption arising from electrostatic attraction. A higher electron density is formed due to interaction with an equal contribution of silanol Si-O-H and Si-O-Na/Cu(O1s). The adsorbents are effective over a wide pH range and their improved recycling capability increases their applications for a wide range of uses.

Engineering of 3D graphene hydrogel-supported MnO2-FeOOH nanoparticles with synergistic effect of oxidation and adsorption toward highly efficient removal of arsenic

Iron-manganese-based adsorbent has been regarded as a promising candidate for arsenic purification from water, especially the inorganic As(III), due to its inherent advantage of low cost and large-scale producibility. However, the nanoparticle aggregation, metal leaching and insufficient removal efficiency remain the main challenges in the practical applications of the granular adsorbents. In this work, we develop a universal strategy for the fabrication of an active Fe(III) oxyhydroxide-Mn(IV) oxide/3D graphene oxide (GO) gel composite via a simple hydrothermal reaction. The successful immobilization of Fe-Mn oxyhydroxide/oxides on the interconnected GO gels was intuitively confirmed by the transmission electron microscopy and atomic force microscopy. The combinative characterizations of the X-ray absorption near edge structure and X-ray photoelectron spectroscopy clearly reveal the electron transfer from Fe atoms to Mn atoms. The optimized Fe-Mn/GO composites possess the superior performance with the removal efficiency of over 90% for As(III) at pH 7.0 and ∼97% for As(V) at pH 5.0 and the As(III, V) levels (100 μg l^-1) are reduced to below the WHO guideline of 10 μg l^-1. The sorption isotherm and kinetic experiments on the As removal were also carried out. The post characterizations are employed to better unveil the oxidation-adsorption mechanism. Notably, the application of Fe-Mn/GO composites in the treatment of As-simulated natural water demonstrated a stable and continuous operation for over 20 days and an effluent concentration of arsenic as low as the 10 μg l^-1 in a specially designed flow reactor.

Lignin nanoparticles-reduced graphene oxide based hydrogel: A novel strategy for environmental applications

In this work, facile fabrication of lignin nanoparticles (L_NP)-based three-dimensional reduced graphene oxide hydrogel (rGO@L_NP) has been demonstrated as a novel strategy for environmental applications. Herein, L_NP were facilely synthesized from walnut shell waste through a direct chemical route. These L_NP were incorporated into the continuous porous network of rGO network to fabricate rGO@L_NP hydrogel. Characterization studies were carried out using various analytical techniques viz. scanning electron microscopy, Fourier transform IR spectroscopy, X-ray diffraction and thermogravimetric analysis. The efficiency of rGO@L_NP hydrogel as adsorptive platform was evaluated by employing methylene blue and Pb²⁺ as model pollutants, whilst the effect of various experimental parameters was ascertained for optimal performance. Furthermore, Agar well diffusion method was used to check the antibacterial activities of the hydrogel using two bacterial pathogenic strains, i.e. Klebsiella pneumoniae (gram negative) and Enterococcus faecalis (gram positive). Results showed that after the inclusion of L_NP into rGO hydrogel, there was a marked improvement in pollutant's uptake ability and compared to bare L_NP and rGO, the composite hydrogel showed enhanced bactericidal effect. Overall, this approach is outstanding because of the synergy of functional properties of nano-lignin and rGO due to multi-interaction sites in the resulting hydrogel. The results presented herein support the application of rGO@L_NP as innovative water filter material for scavenging broad spectrum pollutants and bactericidal properties.

Synthesis and adsorption performance of three-dimensional gels assembled by carbon nanomaterials for heavy metal removal from water: A review

This review focuses on the removal of heavy metals from water by three-dimensional gels with carbon nanomaterials as the main building units. It highlights the fundamental knowledge, most recent advances, and future prospects of carbon nanomaterial-assembled gels (CNAGs) as effective adsorbents for heavy metals in water. Various synthesis methods of CNAGs including template-assisted, self-assembly and other methods are systematically summarized and evaluated. Adsorption performances of CNAGs to typical cationic and anionic heavy metals, especially lead, cadmium, mercury, chromium, and arsenic, are thoroughly examined and discussed in detail. These analyses bring out that composite CNAGs constructed from carbon nanomaterials with polymers or other engineered nanoparticles are the most promising adsorbents for heavy metal removal from water. Current challenges and future research directions that are critical to the applications of CNAGs in the removal of heavy metals from contaminated water are outlined at the end of the review.

Graphene oxide modified κ-carrageenan/sodium alginate double-network hydrogel for effective adsorption of antibiotics in a batch and fixed-bed column system

The treatment of antibiotic wastewater pollution is imminent, the studies of double-network hydrogels as adsorbents have gradually increased, it is quite important to develop a non-toxic hydrogel with excellent properties as adsorbent. In this study, a graphene oxide modified κ-carrageenan/sodium alginate (GO-κ-car/SA) gel was prepared by calcium hardening. The addition of GO nanosheets enhances the mechanical strength and anti-swelling property of the double-network hydrogel, making it possible for the application in the fixed-bed column system. The elastic modulus is twice as much as the hydrogel without GO. The maximum adsorption capacity in the experiments of the GO-κ-car/SA gel for CIP and OFL can reach 272.18 mg g^-1 and 197.39 mg g^-1, respectively. The GO-κ-car/SA gel always remains negatively charged, which means that the adsorption capacity of the gel is better in an acidic environment. In the fixed-bed column system, through Thomas fitting, the maximum adsorption capacity of the simulated OFL wastewater (200 mg L^-1) is 83.99 mg g^-1. The adsorption mechanism of antibiotics by GO-κ-car/SA gel depends on hydrogen bond, functional groups and electrostatic adsorption. The good hydrophilic properties, excellent adsorption capacity and high mechanical strength, which can ensure that the adsorbent is in full contact with the contaminants without major deformation or damage, makes the study more helpful for the further study on hydrogel in the fixed-bed column system.

Nanocellulose for Sustainable Water Purification

Nanocelluloses (NC) are nature-based sustainable biomaterials, which not only possess cellulosic properties but also have the important hallmarks of nanomaterials, such as large surface area, versatile reactive sites or functionalities, and scaffolding stability to host inorganic nanoparticles. This class of nanomaterials offers new opportunities for a broad spectrum of applications for clean water production that were once thought impractical. This Review covers substantial discussions based on evaluative judgments of the recent literature and technical advancements in the fields of coagulation/flocculation, adsorption, photocatalysis, and membrane filtration for water decontamination through proper understanding of fundamental knowledge of NC, such as purity, crystallinity, surface chemistry and charge, suspension rheology, morphology, mechanical properties, and film stability. To supplement these, discussions on low-cost and scalable NC extraction, new characterizations including solution small-angle X-ray scattering evaluation, and structure-property relationships of NC are also reviewed. Identifying knowledge gaps and drawing perspectives could generate guidance to overcome uncertainties associated with the adaptation of NC-enabled water purification technologies. Furthermore, the topics of simultaneous removal of multipollutants disposal and proper handling of post/spent NC are discussed. We believe NC-enabled remediation nanomaterials can be integrated into a broad range of water treatments, greatly improving the cost-effectiveness and sustainability of water purification.

Efficient removal of U(VI) in acidic environment with spent coffee grounds derived hydrogel

In this study, humic-like substances (HLSs) was extracted from spent coffee grounds (SCGs), and it together with poly acrylic acid (PAA), was used for the first time to synthesize hydrogel material, namely HLSs/PAA gel, by one-step radical polymerization. Its maximum theoretical sorption capacity toward U(VI) at pH 3.00 was 661.01 mg/g, and it could decrease the concentration of U(VI) in acidic actual groundwater from 0.2537 to 0.0003 mg/L, showing that the gel had excellent U(VI) removal efficiency in acidic environment. The SEM characterization of HLSs/PAA gel showed that its macroporous network structure maintained well after the sorption process, indicating that the gel had excellent acid-resistant property. Moreover, the gel exhibited excellent anti-interference performance in the interfering ions effect experiment. The gel integrates the merits of excellent U(VI) sorption properties, stability and anti-interference performance in acidic environment, and has promising application prospects in the remediation of acidic uranium wastewater.

Fast preparation of Fe3O4@polydopamine/Au for highly efficient degradation of tetracycline

This work reported the fast synthesis of magnetic polydopamine Au-Fenton catalyst (Fe₃O₄@PDA/Au) under UV irradiation at 365 nm. The microstructure of prepared nanocomposites was characterized by various techniques. The effects of several key factors (pH values, H₂O₂ content and TC concentration) of tetracycline (TC) degradation were evaluated. The results revealed that the TC and total organic carbon (TOC) removal rate reached up to 98.16% and 93.14% within 300 min under optimal conditions (pH 3, H₂O₂ 80 μL, TC concentration 20 mg/L). Besides, HO radicals were generated during the Fenton-like degradation process and the plausible degradation mechanism was discussed. Moreover, Fe₃O₄@PDA/Au catalyst retained excellent catalytic capacity (TC removal rate 96.94% and TOC removal rate 87.69%) and exhibited fantastic stability after six cycles. Moreover, metal ions leaching was evaluated (0.023 mg/L). Altogether, the novel Fe₃O₄@PDA/Au Fenton-like catalyst is highly promising for wastewater management.

Graphene oxide-chitosan hydrogel for adsorptive removal of diclofenac from aqueous solution: preparation, characterization, kinetic and thermodynamic modelling

This work aimed at developing a natural compound-based hydrogel adsorbent to remove diclofenac as a model pharmaceutical from water. First, graphene oxide-chitosan (GO-CTS) and amine graphene oxide-chitosan (AGO-CTS) hydrogel adsorbents were synthesized via a facile mechanical mixing method. The synthesized materials were characterized through Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning and transmission electron microscopy (SEM and TEM), Raman spectroscopy, and thermogravimetric analysis (TGA) techniques. In the second stage, adsorption experiments were conducted to determine the best GO to CTS ratio and find the optimized adsorption parameters, including the initial drug concentration, adsorbent dosage, pH, and temperature. The results showed that the optimal GO to CTS mass ratio is 2 : 5 and thus the same ratio was selected as the AGO to CTS mass ratio to understand the effect of amine-functionalization on removal efficiency. The optimal adsorption parameters were determined to be pH of 5, C _i of 100 ppm and dosage of 1.5 g L^-1, where 90.42% and 97.06% removal was achieved for optimal GO-CTS and AGO-CTS hydrogel adsorbents, respectively. Langmuir and Freundlich isotherms models were employed to investigate the adsorption behavior of diclofenac onto the synthesized hydrogels. The results revealed that the adsorption tends to be of the monolayer type and homogeneous, as the results were in better accordance with the Langmuir model than the Freundlich model. The thermodynamics of adsorption demonstrated that the adsorption is exothermic, exhibiting higher removal efficiency at lower temperatures. Furthermore, Gibb's free energy change of adsorption (ΔG) suggested that the adsorption is spontaneous, being more spontaneous for AGO-CTS than GO-CTS hydrogels. Finally, the regeneration ability of the hydrogel adsorbents was studied in five consecutive cycles. The adsorbent maintained its efficiency at a relatively high level for three cycles but a considerable decrease was observed between the third and the fourth cycle, indicating that the hydrogels were recoverable for three cycles.

Ultrafast and efficient removal of Pb(II) from acidic aqueous solution using a novel polyvinyl alcohol superabsorbent

The direct removal of heavy metal ions from acidic wastewater is a hard problem. In this study, a novel superabsorbent, polyvinyl alcohol phosphate ester (PVAP), was designed and prepared to remove Pb(II) from acidic wastewater (pH = 3). The PVAP can absorb water and swell to reach equilibrium within 30 s, which provides the conditions for ultrafast kinetic adsorption. For 100 mg/L Pb(II) solution, the adsorption reaches equilibrium within 5 min, and the removal ratio is more than 99.9% over a wide pH range of 3-6. Adsorption kinetics and isotherm data are consistent with pseudo-second-order and Langmuir model, respectively. The calculated maximum adsorption capacity for Pb(II) is 558.66 mg/g. Thermodynamic results show that the adsorption is spontaneous and exothermic process. The removal ratio for Pb(II) of PVAP still maintains above 99% after ten recycles. The PVAP can also simultaneously remove more than 97% of other heavy metal ions (Cu(II), Cd(II), Zn(II), Co(II), and Ni(II)) from an acidic solution. Moreover, the PVAP can efficiently purify simulated acid mine heavy metal wastewater, and the results meet EPA drinking water standards. The studies of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectroscopy prove that the adsorption mechanism involves surface complexation. This new superabsorbent is a promising candidate for acidic heavy metal sewage disposal.

Efficient heavy metal removal from water by alginate-based porous nanocomposite hydrogels: The enhanced removal mechanism and influencing factor insight

Novel porous alginate-based nanocomposite hydrogels were prepared by incorporating polyaniline-polypyrrole modified graphene oxide (GO@PAN-PPy) as reinforcing fillers into the alginate matrix (GO@PAN-PPy/SA) for Cr(VI) and Cu(II) removal from water. Different in-situ co-polymerization functionalized GO with Py-to-An mass ratios of monomers (from nil to 1:1) and contents of GO@PAN-PPy (from nil to 2.0%(w/v)) were embedded into the alginate backbone to improve the sorption performance. Key factors, such as pH, coexisting metal ions, and swelling states were investigated in batch adsorption modes. The synergistic effect combined from polymer backbone and fillers could lower the impact of the pH-dependent adsorption reaction. With an adsorption ability superior to that of plain SA and GO/SA, the optimized GO@PAN-PPy-2(1)/SA exhibited good experimental maximum adsorption capacities for Cr(VI) (~133.7 mg/g) and Cu(II) (~87.2 mg/g) at pH 3.0, which were better than those of many other similar sorbents. The sorbents possessed excellent adaptability for 0.2 M salt for Cr(VI) removal but poor for Cu(II) removal. Pre-swelling treatment and co-adsorption could enhance the adsorption performance. The excellent reusability of hydrogel was demonstrated after five cycles in single/binary system. Overall, this work reveals that the resultant hydrogel holds potential as candidate sorbent to remove anionic-cationic heavy metal ions from water.

Wastewater treatment nexus: Carbon nanomaterials towards potential aquatic ecotoxicity

Carbon nanomaterials (CNMs) provide an effective solution and a novel advancement for wastewater treatment. In this review, a total of 3823 bibliographic records derived from recent 10 years are visualized based on scientometric analysis. The results indicate metal-free CNMs-mediated advanced oxidation processes (AOPs) might be a motive force to develop CNMs application for wastewater treatment; however, corresponding evaluations of aquatic toxicity still lack sufficient attention. Therefore, recent breakthroughs and topical innovations related to prevalent wastewater treatment technologies (i.e., adsorption, catalysis and membrane separation) using three typical dimensional CNMs (nanodiamonds, carbon nanotubes, and graphene-based nanomaterials) are comprehensively summarized in-depth, along with a compendious introduction to some novel techniques (e.g., computational simulation) for identifying reaction mechanisms. Then, current research focusing on CNMs-associated aquatic toxicity is discussed thoroughly, mainly demonstrating: (1) the adverse effects on aquatic organisms should not be overlooked prior to large-scale CNMs application; (2) divergent consequences can be further reduced if the ecological niche of aquatic organisms is emphasized; and (3) further investigations on joint toxicity can provide greater beneficial insight into realistic exposure scenarios. Finally, ongoing challenges and developmental directions of CNMs-based wastewater treatment and evaluation of its aquatic toxicity are pinpointed and shaped in terms of future research.

Multiple adsorption systems and electron-scale insights into the high efficiency coadsorption of a novel assembled cellulose via experiments and DFT calculations

In view of the characteristics of heavy metal and antibiotic compound pollution in the Pearl River Basin in Guangzhou. More scientifically modified cellulose, named HVUC, is characterized by multiple hydrophilic groups, long chains and large space and displays highly efficient adsorption of both Cd and sulfamethoxazole (SMZ) and good adaptability in a wide pH range and at high ion strength. Furthermore, the coadsorption mechanism was elaborated from multiple angles. Multiple adsorption experiments explained the competition and synergy effect in the adsorption process. The electrostatic potential maps indicated that HVUC had advantageous adsorption sites for both Cd and SMZ and that electrostatic interactions had the greatest impact on the adsorption of Cd and SMZ. The electron density and differential charge density images proved that Cd more easily overlapped electron clouds and transferred electrons with HVUC and that SMZ^- and could act as a bridge for SMZ^-. The equilibrium configuration indicated that the formation of Cd-SMZ^- complexes led to the bending and folding of SMZ^-, which was not conducive to overall adsorption when SMZ^- was close to HVUC and could lead to the release of SMZ^- when Cd was close to HVUC, which confirmed the proposed mechanism of complexation-decomplexation-complexation.

Progress in modifications of 3D graphene-based adsorbents for environmental applications

3D graphene-based materials are promising adsorbents for environmental applications. Furthermore, increasing attention has been paid to the improvement of 3D graphene adsorbents for removing pollutants. In this article, the progress in the modification of 3D graphene materials and their performance for removing pollutants were reviewed. The modification strategies, which were classified as (1) the activation with CO₂ (steam and other oxidants) and (2) the surface functionalization with polymers (metals, and metal oxides), were evaluated. The performances of modified 3D graphene materials were assessed for the removal of waste gases (such as CO₂), refractory organics, and heavy metals. The challenges and future research directions were discussed for the environmental applications of 3D graphene materials.

Insights into the structure-performance relationships of extraction materials in sample preparation for chromatography

Sample preparation is one of the most crucial steps in analytical processes. Commonly used methods, including solid-phase extraction, dispersive solid-phase extraction, dispersive magnetic solid-phase extraction, and solid-phase microextraction, greatly depend on the extraction materials. In recent decades, a vast number of materials have been studied and used in sample preparation for chromatography. Due to the unique structural properties, extraction materials significantly improve the performance of extraction devices. Endowing extraction materials with suitable structural properties can shorten the pretreatment process and improve the extraction efficiency and selectivity. To understand the structure-performance relationships of extraction materials, this review systematically summarizes the structural properties, including the pore size, pore shape, pore volume, accessibility of active sites, specific surface area, functional groups and physicochemical properties. The mechanisms by which the structural properties influence the extraction performance are also elucidated in detail. Finally, three principles for the design and synthesis of extraction materials are summarized. This review can provide systematic guidelines for synthesizing extraction materials and preparing extraction devices.

Preparation of a Three-Dimensional Porous Graphene Oxide-Kaolinite-Poly(vinyl alcohol) Composite for Efficient Adsorption and Removal of Ciprofloxacin

Because of the widespread presence of antibiotics in water, soil, and other environments, they pose great potential risks to the environment, threatening human and animal health. In this study, graphene oxide-kaolinite homogeneous dispersion was prepared by simple liquid phase exfoliation. The three-dimensional (3D) porous graphene oxide-kaolinite-poly(vinyl alcohol) composites were prepared by the cross-linking of poly(vinyl alcohol) and the formation of ice crystals during the freezing-drying process. Three influencing factors [adsorbent dosage, ciprofloxacin (CIP) initial concentration, and time] of CIP adsorption and removal were systematically analyzed by the response surface method. The order of significance for response values (CIP removal rate) was adsorbent dosage > CIP initial concentration > time. The 3D porous material showed good adsorption capacity of CIP, the theoretical maximum adsorption capacity was 408.16 mg/g, and it had good recyclability. By Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy analysis, it was found the composite adsorbs CIP by hydrogen bonding and π-π interaction. In conclusion, the graphene oxide-kaolinite-poly(vinyl alcohol) porous composite is a good candidate for efficient antibiotic wastewater treatment.

Nanoconfinement-Mediated Water Treatment: From Fundamental to Application

Safe and clean water is of pivotal importance to all living species and the ecosystem on earth. However, the accelerating economy and industrialization of mankind generate water pollutants with much larger quantity and higher complexity than ever before, challenging the efficacy of traditional water treatment technologies. The flourishing researches on nanomaterials and nanotechnologies in the past decade have generated new understandings on many fundamental processes and brought revolutionary upgrades to various traditional technologies in almost all areas, including water treatment. An indispensable step toward the real application of nanomaterials in water treatment is to confine them in large processable substrate to address various inherent issues, such as spontaneous aggregation, difficult operation and potential environmental risks. Strikingly, when the size of the spatial restriction provided by the substrate is on the order of only one or several nanometers, referred to as nanoconfinement, the phase behavior of matter and the energy diagram of a chemical reaction could be utterly changed. Nevertheless, the relationship between such changes under nanoconfinement and their implications for water treatment is rarely elucidated systematically. In this Critical Review, we will briefly summarize the current state-of-the-art of the nanomaterials, as well as the nanoconfined analogues (i.e., nanocomposites) developed for water treatment. Afterward, we will put emphasis on the effects of nanoconfinement from three aspects, that is, on the structure and behavior of water molecules, on the formation (e.g., crystallization) of confined nanomaterials, and on the nanoenabled chemical reactions. For each aspect, we will build the correlation between the nanoconfinement effects and the current studies for water treatment. More importantly, we will make proposals for future studies based on the missing links between some of the nanoconfinement effects and the water treatment technologies. Through this Critical Review, we aim to raise the research attention on using nanoconfinement as a fundamental guide or even tool to advance water treatment technologies.

Study on Cost-Efficient Carbon Aerogel to Remove Antibiotics from Water Resources

Because of pharmaceutical-emerging contaminants in water resources, there has been a significant increase in the antibiotic resistance in bacteria. Therefore, the removal of antibiotics from water resources is essential. Various antibiotics have been greatly studied using many different carbon-based materials including graphene-based hydrogels and aerogels. In this study, carbon aerogels (CAs) were synthesized from waste paper sources and their adsorption behaviors toward three antibiotics (hygromycin B, gentamicin, and vancomycin) were investigated, for which there exist a limited number of reports in the literature. The prepared CAs were characterized with scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and micro-computerized tomography (μ-CT). According to the μ-CT results, total porosity and open porosity were calculated as 90.80 and 90.76%, respectively. The surface area and surface-to-volume ratio were found as 795.15 mm² and 16.79 mm^-1, respectively. The specific surface area of the CAs was found as 104.2 m²/g. A detailed adsorption study was carried out based on different pH values, times, and analyte concentrations. The adsorption capacities were found as 104.16, 81.30, and 107.52 mg/g for Hyg B, Gen, and Van, respectively. For all three antibiotics, the adsorption behavior fits the Langmuir model. The kinetic studies showed that the system fits the pseudo-second-order kinetic model. The production of CAs, within the scope of this study, is safe, facile, and cost-efficient, which makes these green adsorbents a good candidate for the removal of antibiotics from water resources. This study represents the first antibiotic adsorption study based on CAs obtained from waste paper.

The mechanisms and environmental implications of engineered nanoparticles dispersion

Dispersion of engineered nanoparticles (ENPs) has drawn special research attentions because the environmental behavior, risks, and applications of ENPs are greatly dependent on their dispersing status. This review summarizes the latest research progress of dispersion mechanisms, environmental applications in contaminants adsorption, and toxicity of ENPs dispersed in liquid and in solid matrix (3D-ENPs). Dispersion mechanisms of ENPs, including steric hindrance, electrostatic repulsion and "micelle wrapping" are well understood in single dispersing agent, however, the prediction of ENPs dispersion in real environments is not straightforward because of the diversity of structures, components, and properties of natural organic molecule mixtures. The adsorption characteristics, depending on the exposed surface areas in liquid, are significantly different between dispersed and aggregated ENPs. Comparing with the aggregated ENPs, the toxicity of dispersed ENPs is generally enhanced due to the increased uptake, released metal ions, carried contaminants, and induced ROS. 3D-ENPs not only inherit the excellent adsorption performance of ENPs dispersed in liquid, but also are beneficial to the separation and recycle from aqueous solutions due to their 3D rigid structures. However, the adsorption mechanisms as affected by environmental conditions are still unclear. Additionally, the potential risks of 3D-ENPs should be paid more attentions, with an emphasis on free radicals and stability of 3D structure.

Reply to the 'Comment on "Hierarchically porous, ultra-strong reduced graphene oxide-cellulose nanocrystal sponges for exceptional adsorption of water contaminants"' by J. Ma, Y. Xiong and F. Yu, Nanoscale, 2019, 11, DOI: 10.1039/C8NR08780F

We respond to the comments of Ma et al. and clarify the rationale behind our methodology and why it is suitable for our work.

Mechanistic insights into heavy metals affinity in magnetic MnO2@Fe3O4/poly(m-phenylenediamine) core-shell adsorbent

Adsorption represents an attractive mean to remediate polluted water. Unfortunately, the surface positive charges, low surface area and complicated separation procedures inhibit the usability of poly (m-phenylenediamine) (PmPD) as an adsorbent for heavy metal removing. To overcome these drawbacks, a magnetic MnO₂@Fe₃O₄/PmPD core-shell adsorbent was designed to remove heavy metals from water. The MnO₂ shell, came from the redox reaction between KMnO₄ and PmPD, increased the surface area and changed the surface electronegativity. MnO₂@Fe₃O₄/PmPD could be easily separated from water. It showed a significant increase in heavy metals removal efficiency, with maximum capacities of 438.6 mg/g for Pb(II) and 121.5 mg/g for Cd(II), respectively. The affinity between heavy metals and MnO₂@Fe₃O₄/PmPD were mainly due to electrostatic attraction, ion exchanges and coordinated interaction. Density functional theory (DFT) calculations further confirmed that Pb and Cd were bonded with O atoms. The calculated adsorption energy indicated that the (111) MnO₂ facet presented stronger adsorption affinity toward Pb(II) than Cd(II). Additionally, FM150 (150 mg) could regenerate 22 L Pb(II) wastewater upon single passage through the filterable column with a flux of 20 mL/min. Thus, the present work demonstrates the promising potential of using MnO₂@Fe₃O₄/PmPD for efficiently removing heavy metals from wastewater.

Enhanced adsorption for the removal of antibiotics by carbon nanotubes/graphene oxide/sodium alginate triple-network nanocomposite hydrogels in aqueous solutions

Large-scale abuse of antibiotics has led to serious environmental problems. Some conventional adsorbents such as several biopolymer gels have poor adsorption performance and inadequate mechanical properties. In this paper, carbon nanotubes (CNTs) and graphene oxide (GO), were combined with sodium alginate (SA) to improve the adsorption performance and other properties of traditional adsorbents. With the help of hydrogen peroxide and l-cysteine (L-cys), carbon nanotubes/l-cysteine@graphene oxide/sodium alginate (CNTs/L-cys@GO/SA) triple-network composite hydrogels were prepared. Compared with traditional hydrogels and the double-network hydrogels that are currently being developed, these triple-network composite hydrogels can exploit their three-dimensional structure to improve their adsorption capacity. The independent triple-network structure increases the three-dimensional space, so there are more pores and pollutant adsorption sites to achieve the high-efficient removal of ciprofloxacin. And the adsorption capacity of CNTs/L-cys@GO/SA hydrogels can reach 181 mg g^-1 and 200 mg g^-1 at 25 °C and 15 °C respectively in weak acidity environment. In fact, CNTs/L-cys@GO/SA hydrogels show better property at low temperature. In addition, the thermal stability, mechanical properties and swelling ability of the triple-network hydrogels have also been improved. The independent multilayer network can retain the excellent properties of the original materials and make the internal space of hydrogels larger. These multinetwork hydrogels have great potential for removing pollutants from wastewater. In addition, the CNTs/L-cys@GO/SA hydrogels show the higher adsorption capacity of ciprofloxacin under the conditions of weak acidity, low temperature and low inorganic salt concentration, so the removal of ciprofloxacin by hydrogels can also be promoted by changing environmental conditions.

Amino-functionalized alginate/graphene double-network hydrogel beads for emerging contaminant removal from aqueous solution

Inorganic-organic composite hydrogels have attracted much attention in recent years. In this study, an amino-functionalized graphene/alginate double-network hydrogel (NH₂-DN) with excellent mechanical and adsorption properties was successfully prepared. Triethylenetetramine (TETA) was used as a crosslinker which promotes random few-layer graphene sheets stacking and resulted in a reduced graphene oxide (rGO) network, containing mesopore and macropore structures on the hydrogel surface. Compared to single network hydrogel, enhanced thermal stability and mechanical properties were achieved in NH₂-DN. The elasticity modulus was improved by approximately 3 times due to the formation of the double-network. More importantly, NH₂-DN exhibited excellent adsorption properties for typical emerging contaminants (Cu²⁺ and ciprofloxacin (CIP)). Compared with that of an ordinary graphene/alginate single-network hydrogel (SN), the adsorption capacity of the NH₂-DN for Cu²⁺ and CIP reached 153.91 mg g^-1 and 301.36 mg g^-1, respectively, which was increased by 130% and 182%, respectively. Adsorption isotherm and kinetic analyses reveal that the adsorption process of CIP onto the NH₂-DN was dominated by chemical affinity. Adsorption properties were comprehensively examined, including the effects of the solid-liquid ratios, pH, and ionic strength. NH₂-DN retained 94% of its adsorption capacity when the ionic strength was 0.5 mol L^-1 and maintained at least 87% of its adsorption capacity in weak acidic and alkaline solutions. This novel amino-functionalized organic-inorganic hydrogel has great potential in environmental applications owing to its outstanding physicochemical, mechanical, and adsorption properties for emerging contaminants in wastewater.

Recent Advances in Water Treatment Using Graphene-based Materials

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A variety of processes were reported for efficient removing of heavy metal from wastewater, including but not limited to ion exchange, reverse osmosis, membrane filtration, flotation, coagulation, chemical precipitation, solvent extraction, electrochemical treatments, evaporation, oxidation, adsorption, and biosorption. Among the aforementioned techniques, adsorption/ion exchange has been known as a most important method for removing heavy metal ions and organic pollutants due to great removal performance, simple and easy process, cost-effectiveness and the considerable choice of adsorbent materials.

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Nanotechnology and its applications have been developed in most branches of science and technology. Extensive studies have been conducted to remove heavy metal ions from wastewater by preparation and applications of various nanomaterials. Nanomaterials offer advantages in comparison to other materials including an extremely high specific surface area, low-temperature modification, short intraparticle diffusion distance, numerous associated sorption sites, tunable surface chemistry, and pore size. In order to evaluate an adsorbent, two key parameters are: the adsorption capacity and the desorption property. The adsorption parameters including the absorbent loading, pH and temperature, concentration of heavy metal ion, ionic strength, and competition among metal ions are often studied and optimized.

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Several reviews have been published on the application of Graphene (G), Graphene Oxide (GO) in water treatment. In this minireview, we attempted to summarize the recent research advances in water treatment and remediation process by graphene-based materials and provide intensive knowledge of the removal of pollutants in batch and flow systems. Finally, future applicability perspectives are offered to encourage more interesting developments in this promising field. This minireview does not include patent literature.

Simultaneous in situ nutrient recovery and sustainable wastewater purification based on metal anion- and cation-targeted selective adsorbents

The recovery of nitrogen (N) and phosphorus (P) from wastewater is of great importance in addressing the global nutrient crisis. The limitations of existing methods require the development of effective technology. Here, two different hydrogel adsorbents were fabricated with good separation ability for metal cation (M⁺) and metal anion (M^-) but showed little removal of nutrients. Based on the materials, a novel three-stage operation system combining adsorption and capacitive deionization (CDI) technology was presented for nutrient recovery and wastewater treatment. In the first two stages, mixed metals in wastewater were successfully separated (Cu²⁺: 144.6 mg/g; Cr₂O₇^2-: 167.0 mg/g), and nutrients were retained (N and P < 1 mg/g). In the third stage, the residual trace metal ions in the solution were removed (2.0 mg/L to N/A), and the nutrients were enriched through electroadsorption and desorption processes by CDI. Plants using recovered liquid fertilizers revealed similar values for height, root length, and chlorophyll compared with those obtained using actual fertilizers. The results indicated that this novel three-stage operation system (3S A-C system) combining adsorption and CDI is efficient in recovering liquid fertilizers from wastewater and is a promising technology for simultaneously addressing nutrient crises and environmental pollution.

Mussel-inspired anti-biofouling and robust hybrid nanocomposite hydrogel for uranium extraction from seawater

A major challenge of uranium extraction from seawater (UES) is to effectively block the biofouling without destroying the ecological balance, especially prevent the attachment of macroalgae on the surface of the adsorbent. Herein, a robust montmorillonite-polydopamine/polyacrylamide nanocomposite hydrogel is reported by a two-step method, including PDA intercalation MMT and further free radical polymerization with AM monomers. The interpenetrating structure of hydrogel lead to high water permeability with the swelling ratio of 51, which could fully facilitate the internal accessible sites exposure and increase the uranium diffusion. As a result, a high adsorption capacity of 44 mg g^-1 was achieved in lab-scale dynamic adsorption. Most importantly, the prepared anti-biofouling hydrogel adsorbents display excellent anti-adhesion ability towards Nitzschia after 8 days contact. The adsorption capacity of uranium can reach 2130 μg g^-1 in algae-contained simulated seawater. This hydrogel also exhibited a long service life of acceptable mechanical strength and adsorption capacity after at least 6 adsorption-desorption cycles. This new anti-biofouling nanocomposite hydrogel shows great potential as a new generation adsorbent for UES.