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Dye-related water pollution is a worldwide problem. This work describes a facile fabrication of the super-absorbent sodium alginate hydrogel (SA-Ca hydrogel) with improved chemical stability and biocompatibility. By combining the freeze–thaw process with calcium crosslinking, hydrogel with nanopores ranging from 10 to 200 nm was prepared. The SA-Ca hydrogel presents a swelling ratio of 90.6 g·g−1. The effects of pH, initial concentration of the methylene blue (MB) concentration, amounts of absorbents, and temperature on adsorption capacity are investigated. At optimized conditions, the maximum adsorption capacity can reach 2986 mg·g−1. The adsorption kinetics are analyzed using different models, and the pseudo-second-order model can be used to describe the kinetic profile. According to the thermodynamic parameters, the MB adsorption processes using SA-Ca hydrogel are favorable, spontaneous, and endothermic. The proposed SA-Ca hydrogel is expected to be an effective absorbent for water treatment without extra pollution. [ABSTRACT FROM AUTHOR]

Metal–organic framework materials(ZIF-9) were loaded on Sodium alginate/polyvinyl(PVA/SA) hydrogel by in situ growth method for adsorption of heavy metal Cu (II). The structure of hydrogels composited with MOFs and polymers was designed to improve the poor mechanical properties of natural polymer gel materials and the inconvenience of powdered MOFs materials in practical applications. The adsorption results showed that the optimum adsorption process of Cu (II) pH was 5.0. The adsorption kinetics and isotherm suggest that the adsorption process follows the Freundlich isotherm and the pseudo-second-order models. The experimental maximum adsorption capacity was 98.98 mg/g, 2.6 times and 1.5 times higher than ordinary SA and PVA/SA hydrogel spheres. Synthesized hydrogel spheres were characterized by FT-IR, SEM, XRD, and XPS, which confirmed that MOF materials have grown in situ on PVA/SA hydrogel spheres. More importantly, PVA/SA@ZIF-9 exhibited exceptional mechanical stability and showed excellent recycling capability in the cyclic adsorption process. [ABSTRACT FROM AUTHOR]

In this paper, an environmentally friendly, visible and easy-to-recycle spherical adsorbent (SA@PEI-CDs, SA: sodium alginate, PEI: polyethyleneimine, CDs: carbon dots) has been prepared from functionalized positively charged biomass carbons dots (PEI-CDs) and anionic polyelectrolyte sodium alginate (SA) through electrostatic self-assembly. SA@PEI-CDs can efficiently and preferentially adsorb Pb2+. Compared to bare SA, the adsorption capacity of SA@PEI-CDs increased from 206.93 mg/g to 380.39 mg/g (at pH=4), which enhanced 83.82%. It can still maintain 85.67% of the original adsorption capacity after five cycles. The quenching of the blue fluorescence of the adsorbent derived from carbon dots indicates that the adsorption process has reached saturation. The investigation about the adsorption isotherm models, kinetics and thermodynamic parameters reveals that the adsorption process follows Freundlich isotherm model based on chemical adsorption, which is an endothermic spontaneous reaction with an increase in entropy. The possible adsorption mechanism is electrostatic attraction, ion exchange, and together with the coordination of -NH 2 , -OH, -COOH with Pb2+. In addition, the extremely easy-to-recycle spherical adsorbent is also used in the multi-layer adsorption and separation of simulated sewage samples in the water purifier model. For simulated water samples whose concentration of five/three types of heavy metal ions exceeds 100 times the standard, after using adsorbent SA@PEI-CDs for two or three consecutive adsorptions, the content of heavy metals decreases rapidly, which is far below the limit value of high-quality water. The Pb2+ ion concentration decreased from 1.0 mg/L to 0.002540 mg/L and 0.003611 mg/L, respectively. [Display omitted] ● SA@PEI-CDs is derived from functional biomass CDs and sodium alginate hydrogel. ● SA@PEI-CDs can preferentially and selectively adsorb heavy metal Pb2+. ● The blue fluorescence of PEI-CDs can indicate the progress of adsorption. ● SA@PEI-CDs is easy to separate and will not cause secondary pollution. ● The process is chemical adsorption, assisted by intra-particle diffusion. [ABSTRACT FROM AUTHOR]