Phosphorylation of graphehe oxide to improve adsorption of U(VI) from aquaeous solutions

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.

Synthesis of phosphorylated hyper-cross-linked polymers and their efficient uranium adsorption in water

Uranium (U) is hazardous and radioactive, wastewater containing U(VI) should be treated before being discharged. Here, two novel uranium adsorbents, phosphorylated hyper-cross-linked bisphenol A (PHCP-1) and fluorene-9-bisphenol (PHCP-2) were separately synthesized via Friedel-Crafts reaction followed by phosphorylation using phosphorus oxychloride. PHCPs had a BET surface area (up to 564 m²/g) with pore sizes of 2.2-2.8 nm. These adsorbents were used for the first time for uranium adsorption from water and demonstrated outstanding adsorption performance. PHCP-2 had a great uranium adsorption capacity (297.14 mg/g) and a very fast sorption rate (85% removal rate within 5 min). The adsorption data were well fitted with Freundlich isotherm and the pseudo-second-order kinetic model. PHCPs displayed selective adsorption capacity for U(VI) from solution that including a variety of competing metal ions. The reusability was confirmed through three regeneration cycles. Based on a series of spectroscopic analyses, the mechanism of action between PHCPs and U(VI) is primarily derived from the complex between phosphate functional groups and U (VI). The sorption performance of PHCPs is attributed to their huge specific surface area and the strong complex between phosphate groups and U(VI). These findings suggest that PHCPs could be useful in the effective adsorption of uranium from water.

Surfactant-assisted adsorption of uranyl ions in aqueous solution on TiO2/polythiophene nanocomposite

In this work, hexadecyltrimethylammonium-bromide (HTAB)-modified polythiophene (PTh)/TiO₂ nanocomposite (HTAB/PTh/TiO₂) was applied to remove uranyl ions (UO₂²⁺). FT-IR, XRD, ζ potential, TGA, SEM, and XPS were utilized to obtain the chemical and physical properties of HTAB/PTh/TiO₂. The effects of HTAB content, preparation temperature, and adsorption conditions on UO₂²⁺ removal were investigated comprehensively. And the UO₂²⁺ adsorption process on HTAB/PTh/TiO₂ was fitted to the Sips model with a saturated adsorption capacity of 234.74 mg/g, which was 6 times over TiO₂. The results suggested that the surfactant of HTAB can significantly improve the adsorption ability of TiO₂ for UO₂²⁺ ions. This work provides a strategy of surfactant modification for enhancing the separation and recovery ability of adsorbent toward UO₂²⁺ in the radioactive wastewater.

Engineering of amine-based binding chemistry on functionalized graphene oxide/alginate hybrids for simultaneous and efficient removal of trace heavy metals: Towards drinking water

Engineering of versatile binding chemistry on graphene oxide surface using nucleophilic substitution/amidation reactions for highly efficient adsorption of Cd (II), Cu (II) and Pb (II) is herein proposed. Graphene oxide (GO) was used as a precursor for covalent bonding of hexamethylenediamine (HMDA) molecules via the nucleophilic substitution/amidation reactions on epoxy (COC) and carboxyl (COOH) groups to yield hexamethylenediamine functionalized graphene oxide (GO-HMDA) with multiple binding chemistries such as oxygen and nitrogen. Afterwards, GO-HMDA was encapsulated in alginate hydrogel beads with different loadings 5, 10, 15 and 20 wt% to produce Alg/GO-HMDA hybrid adsorbents for the removal of trace heavy metal ions from aqueous solution. Batch adsorption studies showed remarkable adsorption rates reaching 100% for Pb (II), 98.18% for Cu (II) and 95.19 for Cd (II) (~1 mg L^-1) with only 15 wt% of GO-HMDA incorporated into the alginate beads. Moreover, Alg/GO-HMDA showed high removal efficiencies of heavy metals from tap water with a removal order of (Pb > Cu > Cd) similar to that observed in single aqueous solution. In Addition, the Alg/GO-HMDA adsorbents displayed excellent regeneration ability for six consecutive adsorption-desorption cycles confirming the high performance and potential of these adsorbents, for real heavy metals remediation in environment and in drinking waters in both single and multiple systems. Finally, the adsorption mechanism of traces heavy metals resulted from several phenomena including the electrostatic interactions occurring between the COOH groups of Alginate and the GO-HMDA surface groups as well as, through chelation interactions occurring between the metal cations and amino-functionalized groups of Alg/GO-HMDA 15 hybrid adsorbent.

Uranium extraction using hydroxyapatite recovered from phosphorus containing wastewater

A considerable amount of uranium (U(VI))-containing industrial wastewater is generated from both uranium mining and processing, and nuclear electrical power generation. Discharge of U(VI) containing wastewater causes severe damage to the environment and leads to a loss of resources. Uranium sorption on hydroxyapatite (HAP) has been studied extensively to address the abovementioned issues. In the present study, BC-HAP was recovered through phosphate sorption from wastewater, which was first reused as a potential sorbent for extracting uranium from aqueous solutions comparing to commercially available nano-HAP. The sorption behavior of uranium and its transformation on the recovered BC-HAP were investigated by conducting batch experiments as well as Fourier-transform infrared, scanning electron microscopy, and x-ray diffraction analyses. BC-HAP had superior sorption ability for uranium extraction. Autunite precipitant at nano-scale is observed after uranium sorption. Partial desorption of uranium was observed in the presence of Na₂CO₃ and NaHCO₃. Surface complexation and phosphate dissolution precipitation contributed to the favorable uranium sorption. Thus, recovered BC-HAP can be widely used as a promising and cost-effective adsorbent to extract uranium from aqueous solution.

Nano-sized architectural design of multi-activity graphene oxide (GO) by chemical post-decoration for efficient uranium(VI) extraction

The introduction of organic groups onto graphene oxide (GO) platelets can supply additional active sites for adsorption of uranium(VI) (U(VI)) to improve the adsorption capacity. However, as a result of the existence of stabilizing π-conjugation system, a facile and effective modification method remains a challenge. Therefore, a novel strategy is exploited by nano-sized architectural design of multi-activity GO through post-decoration with amidoxime functionalized diaminomaleonitrile (DM-AO). The post-modification of DM-AO successfully activated the inert sites in GO platelets. Meanwhile, the amidoxime group in DM-AO can improve the adsorption selectivity. Adsorption amount of U(VI) on the as prepared GO-DM-AO reached at 935 mg g^-1, which is increased by 209% increment compared with that of pristine GO at the same concentration. The adsorption efficiency of GO-DM-AO is greatly improved, and the time to reach the adsorption equilibrium is half of that of GO. Excitingly, the excellent removal efficiency could still maintained even after 5 cycles of adsorption-desorption. The outstanding adsorption amount, short adsorption equilibrium time, and excellent removal efficiency can provide a theoretical guidance for further immobilization of U(VI) from seawater.

Fully phosphorylated 3D graphene oxide foam for the significantly enhanced U(VI) sequestration

Efficient sequestration of U(VI) from complex aqueous solution is of vital importance for environmental remediation. In this work, the fully phosphorylated graphene oxide foam (phos-GOF) was synthesized via a facile hydrothermal method and the as-prepared 3D phos-GOF was served as an adsorbent to capture U(VI) from aqueous solution. The introduction of abundant phosphorus-containing groups via phytic acid endows phos-GOF good hydrophilia and excellent affinity for U(VI). The adsorption performance of phos-GOF for U(VI) was carefully evaluated under different environments. phos-GOF shows rapid and high efficiency for U(VI) adsorption. The maximum adsorption capacity of phos-GOF for U(VI) is ∼483 mg/g, which is much higher than that of pristine graphene oxide foam (GOF). In addition, the spent 3D phos-GOF can be easily regenerated by a simple and low-cost desorption process using 0.02 mol/L HNO₃. The interaction mechanism between phos-GOF and U(VI) is mainly attributed to the inner-sphere complexation between phosphoric functional groups and U(VI) based on a series of spectroscopic analyses. The 3D phos-GOF exhibits favorable sequestration performance towards U(VI) which can be used as a potential candidate in uranium-bearing wastewater treatment and disposal.

Selective adsorption of uranyl and potentially toxic metal ions at the core-shell MFe2O4-TiO2 (M=Mn, Fe, Zn, Co, or Ni) nanoparticles

Potentially toxic metal ions (Xⁿ⁺: Rb⁺, Sr²⁺, Cr³⁺, Mn²⁺, Ni²⁺, Zn²⁺, Cd²⁺) usually coexist with uranyl (UO₂⁺), which will have a great influence on the selective adsorption process. Here, the core-shell MFe₂O₄-TiO₂ (M = Mn, Fe, Zn, Co, or Ni) nanoparticles were synthesized and assessed as new selective adsorbents. The results reveal that TiO₂(101) preferentially grows along the MFe₂O₄(311)/(111) orientation. The M²⁺ ions as the mediators transfer the holes from MFe₂O₄ to TiO₂, at the conduction bands. On the TiO₂(101) surfaces and TiO₂(101)-TiO₂(101) gaps, the paired active electrons mainly complex with water molecules as hydroxyl radicals to capture Xⁿ⁺ ions, forming an ion layer to block UO₂²⁺ from being adsorbed. Simultaneously, it should be noted that an interesting adsorption pathway was UO₂²⁺ being horizontally and irreversibly adsorbed in the MFe₂O₄(311)/(111)-TiO₂(101) interface, and therein, the stable adsorption capacity was found to be 66.78 mg g^-1 in the MnFe₂O₄(311)/(111)-TiO₂(101) interface. Finally, a mechanism of hybrid orbitals between MnFe₂O₄-TiO₂ and UO₂⁺-Xⁿ⁺ was proposed.

Recovery of phosphorus rich krill shell biowaste for uranium immobilization: A study of sorption behavior, surface reaction, and phase transformation

Increased generation of shrimp shell from exploitation of krill results in emerging biowaste pollution, in addition, uranium pollution has drawn public concern due to the rapid development of nuclear power, uranium mining, and nuclear fuel processing. In this study, krill shells were recovered and used as a potential natural biosorbent for uranium immobilization, thereby enabling both uranium decontamination and krill shell reutilization. Interaction of uranium with krill shell surface and their transformation were investigated by using batch sorption experiments, scanning electron microscopy, and transmission electron microscopy. Krill shell had high uranium sorption ability. Uranium was transformed into a nano-scale precipitate. The mapping of phosphorus and uranium was related to the nano-scale precipitate, indicating that sorption of uranium was dependent on phosphorus. Surface chemisorption between phosphate in krill shell and uranium as well as the formation of the nano-scale precipitate were interpreted as the mechanism of uranium immobilization. Thus, natural krill shell waste has potential for extensive use as a promising and cost-effective sorbent for uranium immobilization and krill shell reutilization.

Enhanced adsorption of U(VI) and 241Am(III) from wastewater using Ca/Al layered double hydroxide@carbon nanotube composites

Ca/Al layered double hydroxide decorated carbon nanotube (Ca/Al-LDH@CNTs) composites were fabricated by co-precipitation method and hydrothermal aged treatment. The prepared Ca/Al-LDH@CNTs was characterized by SEM, TEM, EDS, XRD, FT-IR, UV-vis and XPS techniques, and applied to remove U(VI) from aqueous solutions under various environmental conditions (i.e., pH, ionic strength, temperature and contact time). The results indicated that the adsorption of U(VI) on Ca/Al-LDH@CNTs was four times higher than that of U(VI) on bare CNTs. The kinetic investigations reflected the chemisorption of U(VI) on Ca/Al-LDH@CNTs through oxygen-containing functional groups. The adsorption isotherms demonstrated that the adsorption of U(VI) was well fitted by Langmuir model and the maximum adsorption capacity of U(VI) on Ca/Al-LDH@CNTs was calculated to be 382.9 mg g^-1 at 289.15 K. The thermodynamic parameters calculated from temperature-dependent isotherms suggested that U(VI) adsorption on Ca/Al-LDH@CNTs were endothermic and spontaneous process. Furthermore, Ca/Al-LDH@CNTs could remove ∼91% of ²⁴¹Am(III) at pH = 8.0, which confirmed Ca/Al-LDH@CNTs as a promising material for multiply low level radionuclides' pollution remediation.