Electrosorption performance on graphene-based materials: a review.

Due to its unique advantages such as flexible planar structure, ultrahigh specific surface area, superior electrical conductivity and electrical double-layer capacitance in theory, graphene has unparalleled virtues compared with other carbon materials. This review summarizes the recent research progress of various graphene-based electrodes on ion electrosorption fields, especially for water desalination utilizing capacitive deionization (CDI) technology. We present the latest advances of graphene-based electrodes, such as 3D graphene, graphene/metal oxide (MO) composites, graphene/carbon composites, heteroatom-doped graphene and graphene/polymer composites. Furthermore, a brief outlook on the challenges and future possible developments in the electrosorption area are also addressed for researchers to design graphene-based electrodes towards practical application.

Highly Efficient Removal of Uranium from an Aqueous Solution by a Novel Phosphonic Acid-Functionalized Magnetic Microsphere Adsorbent.

The development of adsorption materials which can efficiently isolate and enrich uranium is of great scientific significance to sustainable development and environmental protection. In this work, a novel phosphonic acid-functionalized magnetic microsphere adsorbent Fe3O4/P (GMA-MBA)-PO4 was developed by functionalized Fe3O4/P (GMA-MBA) prepared by distill-precipitation polymerization with O-phosphoethanolamine. The adsorption process was endothermic, spontaneous and kinetically followed the pseudo second-order model. The maximum uranium adsorption capacity obtained from the Langmuir model was 333.33 mg g-1 at 298 K. In addition, the adsorbent also had good acid resistance and superparamagnetic properties, which could be quickly separated by a magnetic field. XPS analysis showed that the adsorption of adsorbent mainly depended on the complexation of phosphonic acid group with uranium. This work offers a promising candidate for the application of magnetic adsorbents in the field of uranium separation and enrichment.

Synergistic removal of U(VI) from aqueous solution by TAC material: Adsorption behavior and mechanism.

The adsorption and recovery of uranium from wastewater is of positive significance to the development of nuclear industry and environmental remediation. The ternary polymer (PZS-co-TA) was prepared from hexachlorocyclotriphosphazene (HCCP), 4,4-sulfonyldiphenol (BPS) and tannic acid (TA) under ultrasonic. TAC was then obtained after carbonization under high temperature from PZS-co-TA. The structure and performance of TAC were analyzed using SEM, EDS, FT-IR, XRD, Raman, BET and TG. The adsorption capacity of TAC for uranium under different static adsorption conditions was investigated. The adsorption process was more consistent with pseudo-second-order model. The maximum adsorption capacity calculated by non-linear Langmuir model was 492.5 mg/g at pH 5.5. The thermodynamic values suggested that the adsorption process was spontaneous and endothermic. Moreover, after five cycles of adsorption-desorption tests, TAC remained effective at adsorbing uranium, implying the introducing of TA to the precursor (PZS-co-TA) could enhance the adsorption capacity for uranium.

Highly Efficient Organic Dyes Capture Using Thiol-Functionalized Porous Organic Polymer.

It is of great significance to develop new materials for efficient capture cationic dyes methylene blue (MB) and malachite green (MG). In this work, a novel triptycene-based porous organic polymer with abundant thiol groups (TPP-SH) was prepared successfully by postmodification with a high surface area and robust triptycene-based porous organic polymer (TPP). The obtained TPP-SH exhibited a high surface area, good porosity, and good thermal stability. In addition, TPP-SH was highly effective at capturing MB and MG from aqueous solution because of the abundant thiols in its hierarchical structure. Under optimal adsorption conditions, the maximum adsorption capacities of MB and MG calculated by the Langmuir model at room temperature were 1146.3 and 689.6 mg g-1, respectively. These values are higher than those of many reported materials. The MB and MG adsorption rates were 0.0154 and 6.69 × 10-4 mg g-1 min-1, respectively. Furthermore, the polymer TPP-SH had a good recycling performance after adsorption-desorption at least five times. Therefore, the TPP-SH exhibited a high adsorption capacity, fast adsorption kinetics, and easy-recycling behavior, providing a new avenue for the preparation of green functionalized adsorbents with good performance for water decontamination.

Efficient adsorption of methyl orange and methyl blue dyes by a novel triptycene-based hyper-crosslinked porous polymer.

It is still a great challenge to develop new materials for the highly efficient entrapment of organic dyes from aqueous solution. Herein, a novel triptycene-based hyper-crosslinked porous polymer (TPP-PP) was designed and synthesized by a simple Friedel-Crafts reaction. The obtained polymer TPP-PP has a high surface area, abundant pore structure and stable thermal performance. Due to the above characteristics, TPP-PP has good adsorption performance for anionic methyl orange solution (MO) and cationic methyl blue solution (MB). Under the optimal experiment conditions, the TPP-PP showed an excellent adsorption capacity for MO (220.82 mg g-1) and MB (159.80 mg g-1), respectively. The adsorption kinetics fitted the pseudo-second-order model. The adsorption of MO by TPP-PP reaches equilibrium within 180 minutes, and the adsorption of MB reaches equilibrium within 150 minutes. The adsorption behavior was not only spontaneous but also endothermic in reality. At the same time, TPP-PP also has good reusability. After 5 cycles of experiments, the removal rate of MO and MB by TPP-PP can still reach more than 80%. Thus, the Friedel-Crafts reaction crosslinked method might be a promising approach for the synthesis of novel material for the highly efficient extraction of dye wastewater.

Assembly of three-dimensional ultralight poly(amidoxime)/graphene oxide nanoribbons aerogel for efficient removal of uranium(VI) from water samples.

Assembling graphene oxide nanoribbons (GONRs) into three-dimensional (3D) materials with controllable and desired structure is an effective way to expand their structural features and enable their practical applications. In this work, an ultralight 3D porous amidoxime functionalized graphene oxide nanoribbons aerogel (PAO/GONRs-A) was prepared via solvothermal polymerization method using acrylonitrile as monomer and GONRs as solid matrices for selective separation of uranium(VI) from water samples. The PAO/GONRs-A possessed a high nitrogen content (13.5%), low density (8.5 mg cm-3), and large specific surface area (494.9 m2 g-1), and presented an excellent high adsorption capacity of uranium, with a maximum capacity of 2.475 mmol g-1 at a pH of 4.5, and maximum uranium-selectivity of 65.23% at a pH of 3.0. The results of adsorption experiments showed that U(VI) adsorption on PAO/GONRs-A was a pH-dependent, spontaneous and endothermic process, which was better fitted to the pseudo-second-order kinetic model and Langmuir isotherm model. Both X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations revealed that U(VI) adsorption on PAO/GONRs-A mainly did rely on the amidoxime groups anchored on the aerogel while UO2(PAO)2(H2O)3 was dominant after interaction of uranyl with PAO/GONRs-A. Therefore, as a candidate adsorbent, PAO/GONRs-A has a high potential for the removal of uranium from aqueous solutions.

N, P and S co-doped carbon materials derived from polyphosphazene for enhanced selective U(VI) adsorption.

Herein, the precursor polyphosphazene was synthesized by the polymerization of hexachlorocyclotriphosphazene (HCCP) and bis(4-hydroxyphenyl) sulfone (BPS). The adsorbent which was codoped with N, P and S (amidate-CS) was developed from the precursor by using the carbonization method. The images of Scanning electron microscope (SEM) and Transmission electron microscope (TEM) indicate that the amidate-CS possessed porous graphene-like carbon lamellar structure. The excellent behaviors with respect to kinetics (120 min for equilibrium) and thermodynamics (maximum removal of 290 mg/g when pH was at 6.0) revealed the outstanding performance of amidate-CS in removing U(VI), which is due to the functional groups and strong covalent bonds between heteroatoms and uranyl ions. The adsorption of amidate-CS followed the pseudo-second-order kinetic and Langmuir adsorption model. The thermodynamic parameters indicate that the process was spontaneous and endothermic. The adsorption and desorption efficiency of amidate-CS had a slight decrease after five cycles, indicating excellent regeneration performance. Overall, the amidate-CS is a prospective candidate for highly selective U(VI) removing.

Highly Efficient Removal of Thorium in Strong HNO3 Media Using a Novel Polymer Adsorbent Bearing a Phosphonic Acid Ligand: A Combined Experimental and Density Functional Theory Study.

It is an important task to develop the technologies for the extraction of thorium from strong HNO3 media with high efficiency. In this work, solvothermal polymerization of trimethylolpropane trimethacrylate (TRIM) and vinylphosphonic acid (VPA) has been used to synthesize a novel polymer material P (TRIM-VPA) bearing a phosphonic acid ligand for thorium entrapment in strong HNO3 media. Under the current experiment condition, the polymer adsorbents showed a record-breaking maximum adsorption capacity for thorium (403.2 mg g-1) with an excellent selectivity for thorium over Gd(III), Nd(III), Ce(III), Sr(III), Sm(III), and La(III) in 4 mol L-1 HNO3 media at 298 K. The content of P═O ligands existing on P (TRIM-VPA) has an obvious influence on the adsorption capacities for thorium. Increasing the content of P═O ligands would result in higher adsorption capacity of thorium. The isothermal data fitted well the Langmuir model, and the sorption kinetics fitted the pseudo-second-order model. The adsorption behavior was not only spontaneous but also endothermic in reality. Both XPS and FTIR studies revealed that the adsorption interaction for thorium extraction was acquired only via the coordination of P═O groups anchored on P (TRIM-VPA) with thorium. Moreover, P (TRIM-VPA) still had high adsorption capacity after five sorption-desorption cycles in 4 M HNO3 media. DFT calculation suggested that a 1:2 ratio of Th(IV) with the P═O group on the same graft chain validated the experimental findings. Thus, the solvothermal polymerization method might be a promising way for the synthesis of the adsorbents for the highly efficient extraction of thorium from strong HNO3 media.