Dually crosslinked graphene oxide reinforced alginate/polyvinyl alcohol (PVA) double network (DN) hydrogels were prepared via a facile freeze/thaw method followed by soaking in a Ca²⁺ solution. The morphology and structure of the hydrogels were systematically examined by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The effects of pH, dosage of hydrogel, adsorption time, and temperature on the adsorptive property of DN hydrogels towards methylene blue (MB) were also studied. Results indicated that the hydrogels exhibited typical 3D porous structures and had an efficient adsorption effect towards MB due to strong interactions between DN hydrogels and MB molecules. The adsorption isotherm was found to coincide with the Langmuir model with a monolayer adsorption. The highest adsorption capacity of DN hydrogels for MB was examined as 480.76 mg·g⁻¹.

Cellulose is the most abundant natural biopolymer, with unique properties such as biodegradability, biocompability, nontoxicity, and so on. However, its extensive application has actually been hindered, because of its insolubility in water and most solvents. Herein, highly efficient cellulose solvents were developed by coupling diallylimidazolium methoxyacetate ([A₂im][CH₃OCH₂COO]) with polar aprotic solvents dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMA). Attractively, these solvents showed extraordinarily powerful dissolution performance for cellulose (e.g., 26.1 g·100g⁻¹) in [A₂im][CH₃OCH₂COO]/DMSO(R_DMSO = 1.01 solvent even at 25 °C), which is much more advantageous over previously reported solvents. To our knowledge, such powerful cellulose solvents have not been reported before. The cellulose dissolution mechanism is proposed to be of three combined factors: (1) The hydrogen bond interactions of the H2, H4 and H6 in [A₂im]⁺ and the carboxyl O atom in [CH₃OCH₂COO]⁻, along with the hydroxyl H atom and O atom in cellulose, are main driving force for cellulose dissolution; (2) the dissociation of [A₂im][CH₃OCH₂COO] by DMF increases the anion and cation concentrations and thus promotes cellulose dissolution; (3) at the same time, DMF also stabilizes the dissolved cellulose chains. Meanwhile, the porous cellulose material with a varying morphologic structure could be facially fabricated by modulating the cellulose solution concentration. Additionally, the dissolution of cellulose in the solvents is only a physical process, and the regenerated cellulose from the solvents retains sufficient thermostability and a chemical structure similar to the original cellulose. Thus, this work will provide great possibility for developing cellulose-based products at ambient temperatures or under no extra heating/freezing conditions.

Developing sustainable, low viscous and efficient solvents are always advantageous to the processing/fabricating of cellulose materials in practical applications. To this end, in this work novel solvents were developed; ([Amim][CH₃COO]/PEG) by dissolving polyethylene glycol 200 (PEG-200) in 1-allyl-3-methylimidazolium acetate ([Amim][CH₃COO]). The solubilities of cellulose in [Amim][CH₃COO]/PEG solvents were determined as a function of temperature, and the possible dissolution mechanism of cellulose in [Amim][CH₃COO]/PEG solvent was investigated. The novel solvent exhibits outstanding advantages for good dissolution capacity of cellulose, such as low viscosity, negligible vapor pressure, and recycling capability. The [CH₃COO]⁻ anion and the [Amim]⁺ cation of [Amim][CH₃COO] in [Amim][CH₃COO]/PEG-10 are the driving force for cellulose dissolution verified by the ¹³C NMR spectra. In addition, the regenerated cellulose films from [Amim][CH₃COO]/PEG solvent were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetric analysis (TGA) to estimate their morphologies and structures.

Four novel choline carboxylate aqueous solution systems were developed by mixing H₂O with choline nicotinate [Ch][Na], choline ferulate [Ch][Fa], choline vanillate [Ch][Va] and choline syringate [Ch][Sa]. The solubility of lignin in the four solvents was determined at 25 °C. The influence of the molar ratio of H₂O to [Ch][Na] ([Ch][Fa], [Ch][Va] and [Ch][Sa]) and the anionic structure on lignin solubility were systematically investigated. It was found that, the anionic structure and H₂O content significantly affected lignin dissolution. Interestingly, H₂O/[Ch][Na] and H₂O/[Ch][Fa] solvents show efficient capacity for lignin dissolution even at room temperatures. The dissolution of lignin in H₂O/[Ch][Na] and H₂O/[Ch][Fa] solvents is mainly ascribed to the interaction of lignin with the alkyl chain in the anion and cation dissociated from [Ch][Na]([Ch][Fa]) by H₂O. In addition, the recycling of the lignin solvent was examined, and the structure and thermostability of the lignin regenerated from the solvent were also estimated.