Hybrid Hydrogels Of Hyperbranched Poly(erher Amine)s (hPEAs)for Selective Adsorption And Seperation Of Dyes

Recently hydrogels as soft materials are paid more and more attention due to their inherent advantages such as rich sources, excellent biodegradability and renewable capability. Hydrogels are used as efficient adsorbents to absorb guest molecules such as heavy metal ions, proteins and water soluble dyes. The majority of current research on hydrogels is focusing on tissue engineering due to its biocompatibility. The selective adsorption of guest molecules by the hydrogels, however, is really less reported. Very recently, we found that organosilica hybrid nanogel particles of poly(ether amine)s can adsorb the guest dyes selectively. The systematic investigation of the host-guest interaction between the hybrid nanogels of hyperbranched poly(ether amine)(hPEA) and hydrophilic dyes revealed that the selective adsorption is not caused by traditional electrostatic interactions. Actually the hydrophilic and hydrophobic interactions between hyperbranched poly(ether amine)(hPEA) and dyes led to the selective adsorption of the selectivity and it might be from the non-covalent interaction. This work not only opened an new research aspect of poly(ether amine)s, but also helped us better understand the mechanism of the selective adsorption between the host-guest. The selective adsorption of guest molecules gives the hybrid nanogels of hPEAs big potential in the controlled separation. To further put these hPEAs hybrid materials into practical application, we designed and prepared a series of novel hybrid hydrogels (SiO1.5-hPEAs-Gels) with macro-scale based on hyperbranched poly(ether amine)s (hPEAs) with different hydrophobility and charge. SiO1.5-hPEAs-Gels exhibited a quick adsorption to guest dyes such as Ponceau S (PS), Rose Bengal (RB), Neutral Red (NR) and Methyl Orange (MO) with the high adsorption capacity (Qeq), while very slow adsorption to Methylene Blue trihydrate (MB) and Rhodamine6G (R6G) with the low adsorption capacity (Qeq). The big difference in the adsorption behavior of dyes indicated that SiO1.5-hPEAs-Gels can adsorb guest molecules selectively. The negatively charged SiO1.5-hPEA211-SA-Gel adsorbed less amount of the catonic dye MB than the positive charged SiO1.5-hPEA211-Gel, indicating that the electrostatic interaction between host hydrogels and guest dyes is not the predominant factor to Qeq. The adsorption process was found to follow the pseudo-first-order kinetics at the initial stage, but follow the pseudo-second-order kinetics at later stage. Based on the selective adsorption, finally, we demonstrated a method to dynamic separation of mixture of dyes, which can be controlled by the contact time. To obtain the hybrid hydrogel of hPEA with good mechanical performance, we continued to introduce poly (vinyl alcohol)(PVA) into SiO1.5hPEAs-Gels to enhance their mechanical strength by hydrolysis between trimethoxysilane groups of hPEA and hydroxyl groups of PVA and obtained a series of hybrid hydrogel (PVA@SiO1.5-hPEA-Gels) with different charges and content of poly vinyl alcohol. With an increasing of the polyvinyl alcohol content, the mechanical performance has been significantly improved. Compared to previous hybrid hydrogels SiO1.5hPEAs-Gels without enhancement, the compress strain of PVA@SiO1.5-hPEA-Gels increased hundreds of times than that of SiO1.5-hPEAs-Gels, while maintained the unique properties of selective adsorption. Regardless of their charge state, PVA@SiO1.5-hPEA-Gels exhibited the quick adsorption to PS, RB, OG and PSX with a high Qeq, and slow adsorption of BY, MB and R6G with a low Qeq. The big difference in the adsorption to the different dyes suggests the selective adsorption of PVA@SiO1.5-hPEA-Gels to dyes. The detailed investigation of adsorption behaviors of PVA@SiO1.5-hPEA-Gels to ten hydrophilic dyes indicates that the adsorption process follows the pseudo-second-order kinetics. The adsorption experiments of PS onto hybrid hydrogels under different pH indicated that the electrostatic interaction is not the main factor affecting the adsorption kinetics. Based on the selective adsorption, finally, we provided an approach to separate the mixture of dyes. It should be noted that PVA@SiO1.5-hPEA-Gels can keep the original shape after separation and recycling due to their excellent mechanical strength.