The pore surface diffusion model as a tool for rapid screening of novel nanomaterial-enhanced hybrid ion-exchange media

Abstract

The primary goal of this study was to examine the feasibility of using Pore Surface Diffusion Model (PSDM) as a rapid screening tool to predict breakthrough curves of short bed columns packed with nanomaterial enhanced hybrid-ion exchange media. A novel hybrid-ion exchange media was fabricated by synthesizing titanium dioxide nanostructured endoskeleton inside nitrate selective strong base ion-exchange resin. The properties of the hybrid media were characterized and batch reactor tests were conducted with arsenate (As) and nitrogen-nitrate IJNO 3 − N) as model contaminants in 5 mM NaHCO 3 buffer ultrapure water at final pH = 7.2 ± 0.3 to assess the contaminant removal capacity and develop sorption isotherms. Freudlich sorption isotherm (q = KC e 1/n ) model was used to provide inputs for the PSDM predictions of the contaminants' breakthrough curves. To validate the PSDM breakthrough curve predictions for both model contaminants, continuous short bed packed column tests were conducted under the modeled conditions. Hybrid media regeneration was also conducted with solution mix of 2% KOH and 1% KCl followed by rinse with 0.1% HCl, and the column was operated under same conditions to assess the regeneration efficiency of the media. The results demonstrated that 100% regeneration efficiency could be achieved for nitrate, while only 75% efficiency could be achieved for arsenate under these regeneration conditions. The PSDM was able to successfully predict the breakthrough curves for arsenic and nitrate with relatively high precision, characterized by R 2 ≈ 0.977 and R 2 ≈ 0.930 for arsenate and nitrate, respectively. 448 | Environ. Sci.: Water Res. Technol., 2015, 1, 448-456 This journal is

The effect of metal (hydr)oxide nano-enabling on intraparticle mass transport of organic contaminants in hybrid granular activated carbon

“…With increase of TiO 2 content, pH PZC decreased to ~ 6.4 for L-Ti-GAC, ~ 6.3 for M-Ti-GAC and ~ 5.1 for H-Ti-GAC. Considering that pH PZC of TiO 2 is around 6 (Kosmulski, 2002), pH PZC for H-Ti-GAC is somewhat lower than expected, but not completely surprising considering the TiO 2 nanoparticle formation process generates sulfates, which could not be completely eliminated from the pores of the hybrid media and contribute to a higher number of negative surface charges (Athanasaki et al, 2015).…”

“…Initial estimates for the external (film) mass transport coefficient (k f ) were calculated using Gnielinski correlation by Eq. 3 - (Sontheimer et al, 1988;Hristovski et al, 2008b;Cooper et al, 2010;Athanasaki et al, 2015):…”

“…The tortuosity (τ) was estimated using the correlation for electrolyte solutions based on particle porosity (ɛ p ) proposed by Mackie and Meares (Eq. 8) (LeVan et al, 1997;Hristovski et al, 2008b;Cooper et al, 2010;Athanasaki et al, 2015):…”

“…The pore surface diffusion model (PSDM) is a dynamic packed-bed model, which has been successfully used to predict the breakthrough curves and quantify mass transport coefficients of both organic and inorganic contaminants in porous media (Crittenden et al, 1986;Hand et al, 1997;Magnuson and Speth, 2005;Hristovski et al, 2008b;Cooper et al, 2010;Yan et al, 2013;Athanasaki et al, 2015). The PSDM simulations were set up for the experimental conditions identical to those used in SBC tests, with elemental mapping revealed that the TiO 2 was distributed throughout the media in a relatively even pattern for all the synthesized media ( Figure S2) although the increase in nanoparticle precursor concentration during synthesis caused TiO 2 content to increase from 0% in pristine GAC to ~ 8% in L-Ti-GAC, ~ 20% in M-Ti-GAC, and ~ 31% in H-Ti-GAC.…”

Iron oxide-modified nanoporous geopolymers for arsenic removal from ground water

“…more available adsorption sites, but not accessible. In contrast, the 3-Fe characterized with gradually increasing breakthrough curve, which is characteristic of pore diffusion dominated intraparticle mass transport, becomes the limiting transport mechanism due to diffusion of arsenic ions deeper into the particle to find available and accessible adsorption sites [38].…”