Long-range attractive forces extending from the alumina’s nanolayer surface in aqueous solutions

Abstract

Aluminum oxide-hydroxide nanolayer with a thickness of approximately 1.2 nm is electroadhesively deposited onto silicious support material with large surface area of about 50 m 2 /g, forming a highly electropositive composite of boehmite nanolayer in the form of monocrystalline oxide/hydroxide (α-Al 2 O 3 ·H 2 O) on the second electronegative solid. The composite can be viewed as a sphere with a rough surface and charge density of approximately 0.08 C/m 2 . This creates a significant electric field with negligible screening (ka ( 1) in the region close to the surface of the nanocomposite. This field attracts nano-and micron-sized particles from as far as 200 μm in a few seconds, many orders of magnitude greater than conventional Derjaguin-LandauVerwey-Overbeek (DLVO) theory, which predicts only nanometer-scale effects arising from the presence of the surface. The strong electric field on the surface is then able to retain small particles such as viruses, atomically thin sheets of graphene oxide, RNA, DNA, proteins, dyes as well as heavy metals such as cobalt, arsenic, and lead.Alumina's nanolayer surface can be further functionalized by adding other submicron or nano-sized particles to target a specific contaminant. An example is shown where alumina nanolayer is coated with nano-sized iron monohydrate to yield an arsenic sorbent that shows high sorption capacity.

Pristine point of zero charge (p.p.z.c.) and zeta potentials of boehmite’s nanolayer and nanofiber surfaces

“…[11] is boehmite nanolayer in the form of monocrystalline oxide/hydroxide (α-Al 2 O 3 ·H 2 O) with a thickness of approximately 1.2 nm electroadhesively deposited onto siliceous support material with large SSA of about 50 m 2 /g, thereby forming a highly electropositive composite of boehmite nanolayer on the second electronegative solid. The active component can be classified as quantum dots rather than 2D continuous nanocoating (see Table 7 and Equations (14-16)).…”

“…In this paper, we report on the similarity in the surface charges as a function of pH and on differences in geometrical parameters of boehmite's nanofibers either agglomerated into a micron-sized powders with average particle size of~50 μm [9] or grafted onto microglass fibers [10] and boehmite's oxide-hydroxide nanolayer in the form of monocrystalline oxide/hydroxide electroadhesively deposited onto high surface area (from 20 to 200 m 2 /g) siliceous support material [11]. XRD data were supplemented by SEM and TEM microscopy and infrared spectroscopy in order to characterize fully synthetic boehmites and to discern the property variations among them.…”

“…The boehmites that have been produced and studied are probably more chemically pure than most boehmite materials previously studied and which were reported in the literature. In all cases involved in this study, the syntheses involve a reaction of high-purity aluminum metal (purity >99%) with alkaline water, resulting in a pristine boehmite surface [9][10][11].…”