Super-adsorbent poly(acrylic acid)/laponite hydrogel with ultrahigh mechanical property for adsorption of methylene blue

Dye pollution has become a serious threat to environment and human health. Although versatile hydrogels have attracted intensive attentions due to their outstanding adsorption properties, the ultrahigh adsorption capacity and mechanical property are still two critical challenges for the practical applications. Herein, a super-adsorbent poly(acrylic acid)/laponite (PAAc/Lap) nanocomposite hydrogel with ultrahigh mechanical property and adsorption capacity of methylene blue (MB) is prepared by incorporating physical cross-linking with sparse chemical cross-linking. The hydrogel possesses porous 3D network structures and a fairly high water penetration with 1360 times of swelling ratio, which can allow the internal adsorption sites to be fully exposed and facilitate the adsorption. The adsorption capacity of MB can reach up to 3846 mg/g, which is almost the first time that a PAAc-based adsorbent could display superior adsorption capacity of more than 3800 mg/g towards MB. Important factors affecting the adsorption are also investigated, and the adsorption behavior is well fitted by the pseudo-second-order model and Langmuir isotherm model. More importantly, the appropriate physical cross-linking and sparse chemical cross-linking in the polymeric network endows hydrogel with superior mechanical properties. The tensile stress and strain are as high as 1.18 MPa and 2192%, which can facilitate the expansive applications and practical treatment. Mechanism analyses illustrate that the electrostatic interactions and cation-exchange between the functional groups of hydrogel and MB molecules contribute to the extraordinary adsorption ability. The proposed PAAc/Lap hydrogel with ultrahigh adsorption capacity and mechanical property is highly promising as an efficient super adsorbent for water treatment.