A New Schiff Base Organically Modified Silica Aerogel-Like Material for Metal Ion Adsorption with Ni Selectivity

Abstract

Nickel has several industrial uses and is a valuable metal, making its selective separation and recycling a priority goal. A novel adsorbent, a Schiff base organically modified silica (ORMOSIL) aerogel, was prepared, for selective nickel removal from wastewater with other metal ions, by including a salen ionophore in the silica-based network. The newly developed adsorbent takes advantage of the salen’s selectivity and of the high porosity of silica aerogels. The aerogel-like adsorbent was prepared via sol-gel chemistry, using a coprecursor approach and ambient pressure drying. The inclusion of the Schiff base in the silica network was accomplished by reacting an amine-containing silica precursor with an aldehyde and confirmed by nuclear magnetic resonance (NMR) analysis. The adsorbent shrunk only 10% after evaporative drying, which resulted in a highly porous material (85% porosity, 4 cm3 g−1 specific pore volume). The low surface area of 28 m2 g-1 was due to the predominantly macroporous structure of the material (mean pore diameter of 563 nm). Adsorption isotherms and kinetic curves with single and binary mixtures of cations at room temperature were used to assess the selectivity of the adsorbent. The adsorption follows a BET (Brunauer-Emmett-Teller) trend. Due to the proximity of the oxygen and nitrogen atoms in the salen and steric hindrance from their neighboring atoms, it is likely that only the smallest hydrated cations can act as a coordination center and interact with both donor atoms. Thus, nickel was fairly removed (50 mg g-1), while other cations barely interacted with the adsorbent (cadmium adsorption maximum of 5 mg g-1). The estimated selectivity coefficient for nickel ranges from 1.8, in relation to copper, to 9.4 relatively to cadmium, which can be relevant for the separation of nickel in several industrial contexts, for instance, from electroplating sludge.

Chitosan–Silica Composite Aerogel for the Adsorption of Cupric Ions

“…The equilibrium values of (39 ± 9) and (32 ± 2) mg g −1 , obtained using Equations (8) and (10) (in Section 4.5 ), respectively, are also similar or better than the equilibrium uptake obtained for copper with different adsorbents, such as natural materials [ 18 ], in particular many chitosan-based sorbents and composites [ 49 ], and activated carbons [ 50 ], carbon nanotubes [ 51 ], some silica-based structures [ 52 , 53 ] and other aerogels [ 20 , 54 ]. On the other hand, the maximum adsorption capacity obtained for the synthesized aerogel is lower than that obtained for reduced chitosan [ 55 ] as well as for other adsorbents, ranging from simple, bio-based materials, to purely synthetic materials of greater structural complexity (see Table 5 ).…”

“…However, in most reported cases, it should be noticed that materials cannot be obtained as monoliths, which limits their potential for recuperation and recycling, and their removal kinetics are often slower, which is not the case with the synthesized chitosan-silica composite aerogel, as it is generally superior regarding the process scalability and quickness. Silica gel/chitosan composite 870 15 [62] Magnetic chitosan-tripolyphosphate@silica-coated composite 73 200 [63] Chitosan-grafted-acrylic acid and modified nanosilica hydrogel 795 120 [64] β-cyclodextrin-grafted-carboxymethylchitosan-modified silica gel 9 120 [65] Carboxymethylchitosan-functionalized colloidal silica particles 172 60 [66] Carboxymethylchitosan@silica-coated magnetic nanoparticles 346 120 [67] Si Reduced salicylaldehyde-modified chitosan polymer 78 840 [55] Schiff base organically modified silica aerogel 14 180 [52] Schiff base-functionalized silica aerogel 244 360 [77] Amino propyl triethoxysilane-modified silica aerogel 48 1440 [43] Mercapto-functionalized silica aerogel 51 120 [78] Amino-mercapto-functionalized silica xerogel 140 30 [79] Amine-modified silica aerogel 130 >1440 [46] Amine-modified silica xerogel 124 160 [80] Amidoxime-functionalized silica aerogel 534 120 [81] Methyl acrylate-modified silica aerogel 219 60 [82] Nano-silica aerogel gelatin 369 300 [83] APTES and EDTA-modified silica aerogel 94 20 [84] Hybrid surfactant-templated mesoporous silica material…”

β-Ketoenamine Covalent Organic Frameworks—Effects of Functionalization on Pollutant Adsorption

“…Removal efficiency and sorption isotherm studies were performed following a procedure similar to those described elsewhere [ 53 , 54 ]. For sorption isotherm studies, small COF samples (ca., 10 mg) were added to 10 mL adsorbate solutions (25 ppm–300 ppm) in ultrapure water.…”

“…Metal ions concentrations were measured by Flame Atomic Absorption Spectroscopy (FAAS) using the procedure described elsewhere [ 53 ].…”