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Growing efforts have been focused on processing MOF particles into hydrogels. We propose a novel one-step method for the preparation of a novel 3D alginate based MOF hydrogel and use it for tetracycline removal. Rather than the formation of ZIF-67-alginate hydrogel (AM-M) using Co-alginate as the precursor, the Co2+ chelates with alginate and 2-methylimidazolate simultaneously and forms into a different MOF hydrogel (MA-M). The microstructure of the material turns from a smooth surface similar to the alginate hydrogel into a uniform particle-like one, indicating the AM-M has a polymer skeleton while the MA-M has a whole MOF structure. In tetracycline adsorption, the MA-M reaches equilibrium faster than AM-M. The maximum adsorption capacity of tetracycline adsorption on MA-M is 364.89 mg g−1, which is higher than that of AM-M (302.32 mg g−1). The MA-M has good regeneration properties after 10 cycles. The results pave a new way for the preparation of novel polymer based MOF hydrogels with great potential for water treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • A salt-resistant solar evaporator inspired by the mangrove trees was fabricated. • The hierarchical channels of loofah sponge offer abundant escape channels for solar steam. • High chemical potential of contained Na+ in sodium polyacrylate hydrogel leads to Donnan effect. • The mechanism of solar desalination mechanism based Donnan effect was proposed systematically. • Efficient solar evaporation performance is realized even for concentrated brines. Solar desalination is considered an efficient way to alleviate the global shortage of freshwater resources. However, the salt accumulation on the surface of solar absorbers drastically reduces light absorption and steam evaporation efficiency, especially in highly concentrated brines. Herein, inspired by the salt rejection mechanisms of the mangrove trees, a sodium polyacrylate carbonized loofah (PAAS-CLF) was designed using the biomass porous loofah sponge as the matrix, modified with sodium polyacrylate (PAAS) hydrogel coating for solar-driven desalination. The loofah sponge coated PAAS hydrogel as a substrate could obtain a naturally high porosity. Moreover, relying on the negatively charged PAAS hydrogel rich in –COO– groups, it could confine Na+ to induce the Donnan effect, thus reducing the diffusion of salt ions into the water supply layer and avoiding salt accumulation fundamentally. The PAAS-CLF had high water evaporation rates of 1.83 kg m−2h−1 with an efficiency of 94.54% attained under 1 sun. More notably, the evaporator maintained stable water evaporation rates over 1.45 kg m−2h−1 in salt water with a broad range of salinity (35–200 g kg−1), and no salt accumulation was observed during the long-time evaporation. Therefore, this work provides an approach of the flexible application using environmentally friendly biomass sponge composite polyelectrolyte hydrogel for salt-resistant evaporator in solar desalination and concentrated brine treatment. [ABSTRACT FROM AUTHOR]

The stability and activity of the material are promoted by the formation of dual reaction center. • Macroscopic Fe-based graphene catalyst was facile prepared with N doping. • DFT indicated the enhanced formation of dual reaction center by N doping. • MD proved the hydrogen bonding enhanced the electron donor role of pollutant. • The N doping lowered the reduction potential of Fe(II)/Fe(III). A graphene-based hydrogel is prepared by a simple one-step method, establishing a strong dual reaction center and easy separation for efficient pollutant removal from aqueous solution. The FeOOH was grown in situ simultaneously with N doping in a graphene matrix during the self-assembly of graphene hydrogels, resulting in strong interactions in the resulting hydrogel. Density functional theory (DFT) calculation showed that the Fe–π interaction through the Fe–O–C linkage induced the formation of a dual-reaction-center around Fe and C, which was further enhanced by N doping. Furthermore, molecular dynamics (MD) simulations showed that the adsorption process was promoted due to the increase in hydrogen bonding and active sites, further enhancing the electron donor role of pollutant tetracycline for Fe(III) in the Fenton reaction. As revealed by the cyclic voltammetry results, N doping lowered the reduction potential of Fe(II)/Fe(III), which was a key factor in the Fenton reaction. In addition, high stability of the hydrogel was observed after five runs, which suggests promising applications for water treatment. [ABSTRACT FROM AUTHOR]