Abstract
The role of surface nanoscale roughness on the charging behavior of nanostructuredγ-AlOOH (Boehmite) andβ-FeOOH (Akaganeite)/γ-AlOOH (Boehmite) mesostructures deposited onto siliceous substrates has been investigated. Two-dimensional (2D) quantum-sized and one-dimensional (1D) nanometer sizeγ-AlOOH (Boehmite) structures and 2D atomically-thinβ-FeOOH (Akaganeite) nanobelts with a mean width of approximately 10 nm were deposited onto siliceous substrates in aqueous processes at moderate temperatures. Low cost and large scale manufacturing of siliceous substrates coated with 2D and 1Dγ-AlOOH (Boehmite) crystallites of 2.7 ± 0.5 nm in diameter, with an average length of 2.9 ± 0.9 nm and 250 ± 50 nm, respectively, that were further functionalized with atomically thin 2Dβ-FeOOH (Akaganeite) nanobelts was demonstrated. Zeta potentials of surfaces have been characterized by direct measurement of streaming potentials in NaCl aqueous electrolyte. A model explaining the pH dependent behavior of the zeta potential was proposed. The isoelectric point values of rough nanostructured surfaces are three pH units higher as compare to the flat crystallineγ-AlOOH (Boehmite) andβ-FeOOH (Akaganeite) surfaces, resulting in a high removal efficacy of submicron particles from aqueous suspension by the surfaces with combined microscale and nanoscale structures. This suggests the existence of a coupling electrokinetic effect of the local electrical double layer (EDL) fields with the local flow fields.
Highlights
Coating sand and diatomaceous earth (DE) particles with aluminum and ferrous hydroxides changes the zeta potential of filtration media from negative to positive in the pH range from 3 to 11 and from 3 to 10, respectively
This is consistent with boehmite crystal growth, which occurs mainly along the a–c plane where atomic inplane bonds are stronger than the weak, van der Waals (VDW)-type, interlayer bond along the b-axis [24]
A model explaining the pH dependent behavior of the zeta potential based on contributions from the three morphological planes of different chemical composition existing at siliceous particles coated with 2D and 1D γ-AlOOH crystallites was proposed: γ-AlOOH face and edge layers, and siliceous basal layer which are complex oxides of the two constituents: γ-AlOOH and SiO2
Summary
Coating sand and diatomaceous earth (DE) particles with aluminum and ferrous hydroxides changes the zeta potential of filtration media from negative to positive in the pH range from 3 to 11 and from 3 to 10, respectively. As a result, those surface modified media greatly improve removal efficacy of submicron particles [1,2,3,4,5,6,7,8]. The influence of surface roughness of filter media on streaming potential measurements is well documented [11]. The influence of particle shape and particle size on the zeta potential of colloidal suspensions is well known for the case of ultrapure silica powders where the authors found that the maximum zeta potential occurs for particle size ranging between 0.1 μm and 1 μm [13]
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