Iron (III) oxyhydroxide powders with TEMPO-oxidized cellulose nanofibrils: effective adsorbents for removal of fluoride ion in water

Fluoride ions are toxic, and F- in groundwater for drinking should be sufficiently reduced to be less than the regulated concentration. In this study, cellulose nanofibril-containing iron oxyhydroxide (FeOOH) powders were synthesized, and their F- adsorption behaviors were studied under various conditions. 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibrils (CNFs) were added to 0.1 M FeCl3, and 1 M NaOH was added to the FeCl3/TEMPO-CNF mixture to prepare FeOOH precipitates at various FeOOH/TEMPO-CNF mass ratios. When TEMPO-CNFs were present in the FeCl3 solution, the FeOOH/TEMPO-CNF precipitates were quantitatively obtained by straightforward filtration with filter paper; enabled by the larger size (> 300 mu m) of the FeOOH/TEMPO-CNF precipitates than the FeOOH precipitates (<100 mu m) prepared without TEMPO-CNFs. The oven-dried FeOOH/TEMPO-CNF powder (87/13 by mass) showed the highest F- adsorption ratio in water compared with the synthesized FeOOH/TEMPO-CNF powders with FeOOH/TEMPO-CNF mass ratios of 100/0, 79/21, and 73/27. The F- adsorption ratios of the FeOOH/TEMPO-CNF powders were stable over the pH range 4-10. Scanning electron microscopy and energy-dispersive spectroscopy analyses of the powder surfaces before and after F- adsorption indicate that the F- in water adsorbed onto the FeOOH/TEMPO-CNF powder (87/13 by mass) and partially replaced the Cl- that was originally present in the powder. Thus, the FeOOH/TEMPO-CNF powder prepared in this study can be used as efficient, cost-effective F- adsorbents for drinking water and industrially polluted wastewater. [GRAPHICS] .

Automated summary

FeOOH/TEMPO-CNF powder prepared with cellulose nanofibrils showed high fluoride ion adsorption rate in water and stable adsorption ratios in the pH range of 4-10. This powder can be used as efficient and cost-effective fluoride adsorbents for drinking water and industrial wastewater.