Construction Of Konjac Glucomannan/FeOOH Hydrogels And The Enrichment And Separation Of Uranium

The most traditional application of edible gelatin in the food industry is based on its functional properties.The formation of a hydrogel occurs above the critical polymer concentration,where the entanglement between molecular chains gives rise to a porous framework structure.This hydrogel network effectively restricts the leakage of nanophotocatalysts into the reaction medium,be it air or water,while facilitating the loading of a substantial quantity of these catalysts.By capitalizing on the mutual promotion and synergy between hydrogel and nano photocatalyst,the photocatalyst hydrogel demonstrates remarkable efficacy and stability in the treatment of heavy metal ions,such as uranium(U(Ⅵ)),which is among the most hazardous radionuclides found in radioactive water.To tackle the detrimental effects of free U(Ⅵ)ions on organisms and the ecological environment,this study focuses on the modification of konjac glucomannan(KGM),a food gum,to prepare a porous KGM/γ-FeOOH hydrogel and a KGM/γ-FeOOH/poly-N-isopropylacrylamide composite thermosensitive system.The enrichment and separation capacity of the developed materials for UO22+through photocatalysis in a uranium wastewater system were thoroughly investigated.The key findings are summarized as follows:1.Addressing the challenges related to the recycling and potential pollution associated with small-sized photocatalysts in the photocatalytic reduction of uranyl ions,the study employed in situ growth of the nano-photocatalyst γ-FeOOH within the network structure of KGM hydrogel.Moreover,a pore-making treatment was performed,resulting in a highly stable KGM/γ-FeOOH hydrogel.The synthesized material exhibited an interconnected threedimensional porous network structure,thereby enhancing the contact area between the KGM/γ-FeOOH hydrogel and uranyl ions to a considerable extent.Notably,the tensile,compressive,and swelling properties of the KGM/γ-FeOOH hydrogel surpassed those of the KGM hydrogel.Regarding uranium removal performance,the porous KGM/γ-FeOOH hydrogel achieved an impressive uranium removal rate of 79%,compared to 30%for the nonporous KGM/γ-FeOOH hydrogel.Moreover,the porous KGM/γ-FeOOH hydrogel displayed stable removal performance even after five consecutive cycles,underscoring the superior recycling capability of the bulk hydrogel.2.To address the limited contact area between the bulky porous KGM/γ-FeOOH hydrogel,established in the previous chapter,and uranyl ions,the study proposed the concept of a microgel and a thermosensitive conversion system.A temperature-sensitive material,poly-Nisopropylacrylamide(PNIPAM),was compounded onto the surface of the gel,resulting in the construction of a KGM/γ-FeOOH/PNIPAM composite thermosensitive system capable of reversible transition from a dispersed state to a condensed state.This system aimed to achieve highly efficient enrichment and removal of uranyl ions.The results revealed the presence of a PNIPAM film structure on the surface of the KGM/γ-FeOOH microgel,which accounted for the system’s high-temperature self-condensation behavior.The KGM/γ-FeOOH/PNIPAM composite thermal system exhibited a lower critical solution temperature(LCST)of 41.6℃,indicating a reversible phase transition(dispersed state-condensed state)at this temperature.During the enrichment and removal process of uranium,heat-sensitive materials were introduced under low-temperature conditions to achieve a uniformly dispersed state,ensuring a high contact area between the dispersed state and uranyl ions for the reaction.Subsequently,by increasing the temperature of the system phase,the temperature-sensitive system transformed into a gel,capitalizing on its stable recycling performance in the condensed state.Remarkably,the KGM/γ-FeOOH/PNIPAM thermosensitive system exhibited a significantly higher uranium removal rate compared to the porous KGM/γ-FeOOH hydrogel,with a maximum removal rate of 92.3%.This system also displayed exceptional cycling stability after five cycles.Furthermore,the removal mechanism of uranium elucidated that the KGM/γFeOOH/PNIPAM thermosensitive system primarily relied on adsorption,complemented by photocatalytic reduction,as evidenced by the comparison of removal rates under XPS and light/dark conditions.In conclusion,this study successfully developed a KGM/γ-FeOOH hydrogel and a KGM/γ-FeOOH/PNIPAM composite thermosensitive system,both based on a food additivebased hydrogel loaded with a y-FeOOH photocatalyst,which exhibited exceptional efficiency in uranium enrichment and rapid separation under light exposure.The method of preparation holds great potential for extending similar hydrogel-based research endeavors and realizing the comprehensive utilization of raw materials for food additives.