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One-step synthesis of carbonate-free nitrate containing LDHs was achieved using hexamine hydrolysis at low temperature and the products were delaminated successfully in water; materials showed total delamination in formamide while restacking behavior depended critically on the medium.

Borate uptake studies were carried out over both as-synthesized and calcined ZnAl layered double hydroxides (LDHs) containing carbonate or chloride as interlayer anions, with different Zn/Al atomic ratios (2, 3, and 4). Chloride-containing materials in both as-synthesized and calcined forms showed higher borate uptake than carbonate-containing forms. A maximum borate uptake of 31 mgB/g was achieved for the 400 °C heat-treated Zn2Al–Cl LDH material (referred here as Zn2Al–Cl–CLDH). The mechanism of borate uptake for heat-treated materials involves reconstruction as elucidated from PXRD, FT-IR, and SEM measurements. Interestingly, solid state transformation of tetraborate to monoborate anion occurred in the interlayer on drying for longer time. At a ratio of 4 g Zn2Al–Cl–CLDH per liter of 100 mgB/L solution, the uptake of borate reached 97% further, and at 5 mgB/L solution the borate concentration reduced below the value of 0.5 mgB/L recommended by the World Health Organization (WHO), using 1 g/L ratio of sorbent. The borate uptake adsorption isotherm fitted well to a monolayer Langmuir adsorption model. The influence of various parameters such as the mass of adsorbent, reaction time, borate concentration, temperature, and pH of the medium was studied. Constant borate uptake was observed over the pH range 3–7 owing to the buffering nature of LDH. The influence of the copresence of other anions on borate uptake by Zn2Al–Cl–CLDH depended on the charge to radius ratio of the anion. Cyclic adsorption–desorption studies revealed that the material was recyclable. High uptake capacity along with recyclability of this material suggests the promise as a sorbent for wastewater remediation of borate.

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A powdery lithium ion sieve (HMO) derived from biogenic birnessite was homogeneously integrated in sodium alginate (AL) beads. The composite beads were then characterized and their Li + adsorption properties were investigated. Scanning electron microscopy-energy dispersive spectroscopy analysis showed that the HMO particles were homogeneously dispersed in the AL beads even after drying. The adsorption isotherm of Li + adsorption to HMO encapsulated in AL beads (HMO-AL) was well fitted by the linear Langmuir model, and the beads showed a maximum adsorption capacity of 3.61 mmol/g based on HMO, which is comparable with the value of the original powdery HMO. Kinetic studies revealed that adsorption of Li + follows a pseudo-second-order model with rate constant k 2 = 2.8-11.9 × 10 −3 g/(mmol min) for the initial Li + concentration range 2.56-4.23 mM. Diffusion of Li + from aqueous solution to the HMO particle through the Ca-AL network is the rate-limiting step for Li + adsorption to HMO-AL beads. The HMO-AL beads enhanced the handling efficiency for Li + adsorption and reused without significant reduction of Li + adsorption efficacy.

Co-immobilization of cationic and anionic radionuclides is highly desirable for total remediation of radioactive wastewater. Carbonaceous nanomaterials have received much attention in the field of water remediation and pollution control in recent years. However, the handling of these nanomaterials is challenging due to increased bioavailability and toxicity. In this work, MgAl-NO3 layered double hydroxide (LDH) was synthesized and modified using carbon nanodots (C-dot). The prepared materials were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR), zeta potential, and transmission electron microscopy (TEM) observation. Adsorption of SeO4 2– and Sr2+ on MgAl-NO3-LDH/C-dot composites showed that the Sr2+ immobilization capacities increased with an increase in the amount of C-dot. The mechanism of Sr2+ adsorption on these composites occurs via coordination with the −COO– group of C-dot, whereas that of SeO4 2– occurs through ion exchange with NO3 – in the interlayer galleries of LDH. The adsorption of Sr2+ and SeO4 2– was enhanced in both bicomponent (Sr2+ + SeO4 2–) and tricomponent systems (Sr2+ + SeO4 2– + M+/M2+ = coexisting cations or A n– = coexisting anions) with the presence of other anion and cations. The MgAl-NO3-LDH/C-dot composites demonstrated that the high adsorption efficiency of Sr2+ and SeO4 2– than most of other materials reported. These results demonstrate that MgAl-NO3-LDH/C-dot composites are an effective adsorbent for total remediation of anionic and cationic radioactive nuclides from wastewater.