Abstract
The adsorption and separation of hazard metal ions, radioactive nuclides, or minor actinides from wastewater and high-level radioactive waste liquids using functional silica-based nano/micro-particles modified with various inorganic materials or organic groups, has attracted significant attention since the discovery of ordered mesoporous silica-based substrates. Focusing on inorganic and organic modified materials, the synthesis methods and sorption performances for specific ions in aqueous solutions are summarized in this review. Three modification methods for silica-based particles, the direct synthesis method, wetness impregnation method, and layer-by-layer (LBL) deposition, are usually adopted to load inorganic material onto silica-based particles, while the wetness impregnation method is currently used for the preparation of functional silica-based particles modified with organic groups. Generally, the specific synthesis method is employed based on the properties of the loading materials and the silicon-based substrate. Adsorption of specific toxic ions onto modified silica-based particles depends on the properties of the loaded material. The silicon matrix only changes the thermodynamic and mechanical properties of the material, such as the abrasive resistance, dispersibility, and radiation resistance. In this paper, inorganic loads, such as metal phosphates, molybdophosphate, titanate-based materials, and hydrotalcite, in addition to organic loads, such as 1,3-[(2,4-diethylheptylethoxy)oxy]-2,4-crown-6-Calix{4}arene (Calix {4}) arene-R14 and functional 2,6-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-pyridines(BTP) are reviewed. More specifically, we emphasize on the synthesis methods of such materials, their structures in relation to their capacities, their selectivities for trapping specific ions from either single or multi-component aqueous solutions, and the possible retention mechanisms. Potential candidates for remediation uses are selected based on their sorption capacities and distribution coefficients for target cations and the pH window for an optimum cation capture.
Highlights
Functionalized silica-based nanoparticle materials have opened a wide range of opportunities in research fields related to catalysis, separation, and adsorption [1,2] since the discovery of the ordered mesoporous silica-based carriers, such as MCM-41, MCM-48, M41S [3,4,5], SBA-1 [6], SBA-15 [7], FSM-16 [8], and silica spheres [9]
Most silica-based mesoporous materials do not have specific surface properties, which limits their applications in fields such as ion exchange, catalysis, sensing, and adsorption, which require stereochemical configurations or charge densities, specific binding sites, and acidities [14,15]
The adsorption of Cr (III), Mn (II), Fe (III), Co (II), Ni (II), Cu (II), Zn (II), Cd (II), Ba (II), Hg (II), and Pb (II) lanthanum phosphate samples has been studied, and the results show that mercury and nickel ions are highly adsorbed onto lanthanum phosphate compared to other ions
Summary
Functionalized silica-based nanoparticle materials have opened a wide range of opportunities in research fields related to catalysis, separation, and adsorption [1,2] since the discovery of the ordered mesoporous silica-based carriers, such as MCM-41, MCM-48, M41S [3,4,5], SBA-1 [6], SBA-15 [7], FSM-16 [8], and silica spheres [9]. Functional silica nanoparticles are exploited to produce a photoacoustic signal enhancement in the biological window for molecular and cellular characterization of cancer through near-infrared (NIR)-absorbing dyes or organic/inorganic nanoparticles [17] This present review is concerned with synthesis processes of functional silica-based particles modified using various inorganic or organic materials, and their applications in the adsorption of environmental wastewater that contains typical radioactive ions and hazardous heavy metal ions. Mineral adsorption materials with bidimensional-layered structures, such as zirconium and titanium phosphonates, are deposited onto silica-based carriers [21,22] This method has been successfully generalized for complex oxides, such as niobates [23] or perovskites [24].
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