TEMPO-oxidized cellulose nanofiber-based hydrogels for removal of methyl blue dyes in water

Water contamination caused by industrial and municipal effluents has become global environment concern, especially for dyestuff wastewater. Dyes are extensively utilized in diverse industries such as textile, food, paper, drugs, leather, amongst others and they have ubiquity, toxicity and deleterious effects on photosynthetic activity in aquatic life. Therefore, it is very important to develop efficient methods to remove them from water sources. In this work, a TEMPO-cellulose nanofiber (TEMPO-CNF) and polyethylenimine (PEI) composite hydrogels (TEMPO CNF-PEI) were synthesized by pre-crosslinking TEMPO-CNF by cation ions and combine with physical adsorption of PEI; this composite was further tested its removal ability for methyl blue dyes in aqueous solution. It was found that more than 82.6% of methyl blue dyes were removed by the TEMPO CNF-PEI hydrogels at pH values in the range of 2.7-7.7, showing a maximum removal efficiency of 99.3% at pH 7.7. Interestingly, the TEMPO CNF-PEI hydrogels removed methyl blue dyes by both adsorption and precipitation depending on pH. When the pH is 2.7, 91.1% of methyl blue dye were removed just after 6 h mainly by precipitation while 88.3 % of methyl blue dye was removed mainly by adsorption after 48 h at pH of 4.7. Thus, the TEMPO CNF-PEI hydrogel show great promise as adsorbent materials for water remediation.