Life Cycle Payback Estimates of Nanosilver Enabled Textiles under Different Silver Loading, Release, And Laundering Scenarios Informed by Literature Review.

Silver was utilized throughout history to prevent the growth of bacteria in food and wounds. Recently, nanoscale silver has been applied to consumer textiles (nAg-textiles) to eliminate the prevalence of odor-causing bacteria. In turn, it is proposed that consumers will launder these items less frequently thus, reducing the life cycle impacts. While previous studies report that laundering processes are associated with the greatest environmental impacts of these textiles, there is no data available to support the proposed shift in consumer laundering behavior. Here, the results from a comprehensive literature review of nAg-textile life cycle studies are used to inform a cradle-to-grave life cycle impact assessment. Rather than assuming shifts in consumer behavior, the impact assessment is conducted in such a way that considers all laundering scenarios to elucidate the potential for reduced laundering to enable realization of a net life cycle benefit. In addition to identifying the most impactful stages of the life cycle across nine-midpoint categories, a payback period and uncertainty analysis quantifies the reduction in lifetime launderings required to recover the impacts associated with nanoenabling the textile. Reduction of nAg-textile life cycle impacts is not straightforward and depends on the impact category considered.

Multifunctional photoactive and selective adsorbent for arsenite and arsenate: Evaluation of nano titanium dioxide-enabled chitosan cross-linked with copper.

A novel multifunctional sorbent material of nano-titanium dioxide-enabled chitosan beads cross-linked with copper (CuTICB) is capable of photo-oxidation of As(III) to the less-toxic and more easily adsorbed As(V) in UV light and selective adsorption of arsenite (As(III)) and arsenate (As(V)) in the presence of phosphate, a strong adsorptive competitor and inhibitor of arsenic removal performance. CuTICB is an attractive sorbent as simultaneous photo-oxidation and adsorption reduces treatment time and cost while selective adsorption improves removal efficiency of arsenic in typical environmental conditions where competitive ions are predominant. In CuTICB, nano-titanium dioxide (n-TiO2) anatase photo-oxidizes As(III) to As(V) through generation of reactive oxygen species. Additionally, Cu-chitosan bidentate crosslinkers form through Lewis acid-base coordinate bonding between Cu(II) and chitosan amine groups resulting in cationic behavior that electrostatically favors As(V) chelation even when phosphate concentrations are orders of magnitude higher. The influence of copper and n-TiO2 loading on arsenic photo-oxidation and selective removal over phosphate was explored to optimize CuTICB design using batch experiments under varying systems conditions. For a system requiring both photo-oxidation and selective adsorption, it was found that copper and n-TiO2 act non-linearly and synergistically, where maximum loadings of both does not yield the optimal selectivity or removal efficacy.

Towards a selective adsorbent for arsenate and selenite in the presence of phosphate: Assessment of adsorption efficiency, mechanism, and binary separation factors of the chitosan-copper complex.

The potential for a chitosan-copper polymer complex to select for the target contaminants in the presence of their respective competitive ions was evaluated by synthesizing chitosan-copper beads (CCB) for the treatment of (arsenate:phosphate), (selenite:phosphate), and (selenate:sulfate). Based on work by Rhazi et al., copper (II) binds to the amine moiety on the chitosan backbone as a monodentate complex (Type I) and as a bidentate complex crosslinking two polymer chains (Type II), depending on pH and copper loading. In general, the Type I complex exists alone; however, beyond threshold conditions of pH 5.5 during synthesis and a copper loading of 0.25 mol Cu(II)/mol chitosan monomer, the Type I and Type II complexes coexist. Subsequent chelation of this chitosan-copper ligand to oxyanions results in enhanced and selective adsorption of the target contaminants in complex matrices with high background ion concentrations. With differing affinities for arsenate, selenite, and phosphate, the Type I complex favors phosphate chelation while the Type II complex favors arsenate chelation due to electrostatic considerations and selenite chelation due to steric effects. No trend was exhibited for the selenate:sulfate system possibly due to the high Ksp of the corresponding copper salts. Binary separation factors, α12, were calculated for the arsenate-phosphate and selenite-phosphate systems, supporting the mechanistic hypothesis. While, further research is needed to develop a synthesis method for the independent formation of the Type II complexes to select for target contaminants in complex matrices, this work can provide initial steps in the development of a selective adsorbent.

The role of counter ions in nano-hematite synthesis: Implications for surface area and selenium adsorption capacity.

Nano metal oxides are of interest for aqueous selenium (Se) remediation, and as such, nano-hematite (nα-Fe2O3) was examined for use as a Se adsorbent. The effect of surface area on adsorption was also studied. nα-Fe2O3 particles were synthesized from Fe(NO3)3 and FeCl3 via forced hydrolysis. The resulting particles have similar sizes, morphologies, aggregate size, pore size, and PZC. The nα-Fe2O3 from FeCl3 (nα-Fe2O3-C) differs from the nα-Fe2O3 from Fe(NO3)3 (nα-Fe2O3-N) with a ∼25±2m(2)/g greater surface area. Selenite Se(IV) adsorption capacity on nα-Fe2O3 has a qmax ∼17mg/g for the freeze-dried and re-suspended nα-Fe2O3. The Δqmax for nα-Fe2O3 from Fe(NO3)3 and FeCl3 that remained in suspension was 4.6mg/g. For selenate Se(VI), the freeze-dried and re-suspended particles realize a Δqmax= 1.5mg/g for nα-Fe2O3 from Fe(NO3)3 and FeCl3. The nα-Fe2O3 from Fe(NO3)3 and FeCl3 that remained in suspension demonstrated Se(VI) Δqmax=5.4mg/g. In situ ATR-FTIR isotherm measurements completed for Se(VI) at a pH 6 suggest that Se(VI) forms primarily outer-sphere complexes with nα-Fe2O3 synthesized from both salts.

Adsorption of selenite and selenate by nanocrystalline aluminum oxide, neat and impregnated in chitosan beads.

Nanocrystalline metal oxide impregnated chitosan beads (MICB) were successfully developed with nanocrystalline aluminum oxide (n-Al2O3) to form n-Al2O3 impregnated chitosan beads (AICB). AICB were able to simultaneously adsorb inorganic aqueous selenite and selenate more effectively than n-Al2O3 or chitosan alone. For completeness, adsorption performance was also compared to n-TiO2, a widely studied adsorbent for selenium, and n-TiO2 impregnated chitosan beads (TICB). For the selenite system, n-Al2O3 was the primary active adsorbent responsible for removal as chitosan has a low affinity for selenite. For selenate, however, chitosan was the primary active adsorbent. The association constants for the adsorbent/adsorbate complexes and the relative amounts in which they are present supported this hypothesis. The association constants for selenate binding on n-Al2O3 and chitosan were 1.215 × 10(-2) and 3.048 × 10(-3), respectively, and the association constants for selenite binding on n-Al2O3 and chitosan were 1.349 × 10(-2) and 1.990 × 10(-4), respectively. For systems with coexisting selenite and selenate, AICB is potentially the most robust option as it maintained the most consistent performance regardless of fractionation of the selenium species. Kinetic studies and equilibrium isotherms were completed and effectively modeled using pseudo-second order kinetics and Langmuir adsorption theory, making it the first comprehensive systematic study of neat n-Al2O3 and AICB for selenium adsorption. pH significantly impacted adsorption due to changes in the adsorbent surface charge; increasing pH corresponded with decreasing adsorbent performance, beginning at approximately pH 6.5-7 for AICB. The trend in performance due to the effect of pH indicated that selenate binds to the amine group in chitosan, as suggested by other studies. In addition, increasing background sulfate concentration was found to negatively impact adsorption efficacy for both selenite, and more significantly, selenate, as sulfate is known to compete with selenium oxyanions due to their similar structures. The results indicate that, in order to maintain consistent removal in more realistic systems, a pre-treatment process to manage sulfate will be necessary as indicated for other adsorbents implemented for selenium adsorption in aqueous systems.

Enhanced arsenic removal using mixed metal oxide impregnated chitosan beads.

Mixed metal oxide impregnated chitosan beads (MICB) containing nanocrystalline Al2O3 and nanocrystalline TiO2 were successfully developed. This adsorbent exploits the high capacity of Al2O3 for arsenate and the photocatalytic activity of TiO2 to oxidize arsenite to arsenate, resulting in a removal capacity higher than that of either metal oxide alone. The composition of the beads was optimized for maximum arsenite removal in the presence of UV light. The mechanism of removal was investigated and a mode of action was proposed wherein TiO2 oxidizes arsenite to arsenate which is then removed from solution by Al2O3. Pseudo-second order kinetics were used to validate the proposed mechanism. MICB is a more efficient and effective adsorbent for arsenic than TiO2-impregnated chitosan beads (TICB), previously reported on, yet maintains a desirable life cycle, free of complex synthesis processes, toxic materials, and energy inputs.