Preparation of Halloysite/Ag2O Nanomaterials and Their Performance for Iodide Adsorption

Abstract

Halloysite/Ag2O (Hal/Ag2O) nanomaterials were prepared by growing Ag2O nanoparticles on the surface of nanotubular halloysite using silver nitrate solution under alkaline conditions. The nanomaterials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption. Good dispersion of Ag2O nanoparticles with average sizes of 6.07 ± 2.5 nm and 8.04 ± 3.8 nm was achieved in the nanomaterials when using different concentrations of alkali. The nanomaterial with 6.36% Ag2O (Hal/Ag2O-2) exhibited rapid adsorption to iodide (I−); adsorption equilibrium can be reached within 100 min. The adsorption capacity of I− on Hal/Ag2O-2 is 57.5 mg/g, which is more than 143 times higher than that of halloysite. The nanomaterial also showed a better adsorption capacity per unit mass of Ag2O due to the better dispersion and less coaggregation of Ag2O in the nanomaterial than in the pure Ag2O nanoparticles. Importantly, Hal/Ag2O-2 exhibited high selectivity for I−, and its I− removal efficiency was hardly affected by the coexistence of Cl−, Br−, or SO42−, as well as the initial pH of the solution. With an excellent adsorption performance, the prepared Hal/Ag2O nanomaterial could be a new and efficient adsorbent capable of the adsorption of radioactive I− from aqueous solution.

Facile Preparation of MCM-41/Ag2O Nanomaterials with High Iodide-Removal Efficiency

“…For the sample 12.5-Ag 2 O@MCM-41, an appreciable number of Ag 2 O nanoparticles could be found at the surface of MCM-41 ( Figure 2 d). Although the size of the Ag 2 O nanoparticles increased with its amount, it seemed that the size of Ag 2 O was smaller than that of the composites in which Ag 2 O nanoparticles were only at the surface of the supports [ 6 , 16 ]. For example, in the reported nanofibrillated chitin/Ag 2 O aerogels, the size of Ag 2 O could easily reach a diameter of more than 15 nm [ 6 ].…”

“…The PSD curve of MCM-41 revealed that the pore size of its mesoporous channel was 3.8 nm ( Figure 3 b). The BET-specific surface area of MCM-41 was 951.0 m 2 /g, which is significantly larger than that of other carriers used to prepare Ag 2 O-based nanocomposites (such as TiO 2 spheres [ 7 ], chitin nanofibers [ 6 ], titanate nanolamina [ 15 ], and halloysite nanotubes [ 16 ]). The total pore volume of MCM-41 was 0.7568 cm 3 /g ( Table 1 ).…”

“…However, directly applying Ag 2 O nanoparticles for the adsorption of radioactive iodine is unfeasible because of problems with the separation and recovery of nanoparticles, and more importantly, because of the coaggregation problem, which decreases the effective surface area of nanoparticles, and thus, reduces their reaction activities. Supporting Ag 2 O nanoparticles on porous carriers, such as TiO 2 spheres [ 7 ], chitin nanofibers [ 6 ], titanate nanolamina [ 15 ], and halloysite nanotubes [ 16 , 17 ] has been found to be effective in preventing coaggregation. The resulting Ag 2 O nanocomposites showed better performance in the capture of iodide or iodine vapor than the pure Ag 2 O nanoparticles.…”

“…For the reported Ag 2 O nanocomposites, the particle dimension of Ag 2 O nanoparticles and the specific surface area of the nanocomposites are two important factors affecting the adsorption performance. However, the classical method for the preparation of supported Ag 2 O is the direct precipitation of Ag 2 O particles on the surface of carriers through the mixing of silver nitrate and hydroxides [ 16 , 18 ]. Although this method is simple, it is very difficult to control the size of Ag 2 O nanoparticles due to the too-fast reaction speed [ 19 ].…”

Iodide Removal by Resorcinol-Formaldehyde Carbon Aerogels

“…Adsorption is widely used in water purification in combination with other technologies, such as flocculation, coagulation, biological oxidation, sedimentation, oxidation/degradation processes and membrane processes [ 15 , 16 , 17 , 18 ]. Porous materials, including carbons, have been extensively used in water treatment [ 19 , 20 , 21 , 22 ]. For instance, zeolites which are very common materials used for water purification, are not suitable for the removal of iodide without modification as they are cation exchangers.…”