Cellulose-Based Metallogels—Part 1: Raw Materials and Preparation

Abstract

Metallogels are a class of materials produced by the complexation of polymer gels with metal ions that can form coordination bonds with the functional groups of the gel. Hydrogels with metal phases attract special attention due to the numerous possibilities for functionalization. Cellulose is preferable for the production of hydrogels from economic, ecological, physical, chemical, and biological points of view since it is inexpensive, renewable, versatile, non-toxic, reveals high mechanical and thermal stability, has a porous structure, an imposing number of reactive OH groups, and good biocompatibility. Due to the poor solubility of natural cellulose, the hydrogels are commonly produced from cellulose derivatives that require multiple chemical manipulations. However, there is a number of techniques of hydrogel preparation via dissolution and regeneration of non-derivatized cellulose of various origins. Thus, hydrogels can be produced from plant-derived cellulose, lignocellulose and cellulose wastes, including agricultural, food and paper wastes. The advantages and limitations of using solvents are discussed in this review with regard to the possibility of industrial scaling up. Metallogels are often formed on the basis of ready-made hydrogels, which is why the choice of an adequate solvent is important for obtaining desirable results. The methods of the preparation of cellulose metallogels with d-transition metals in the present state of the art are reviewed.

Cellulose-Based Metallogels—Part 2: Physico-Chemical Properties and Biological Stability

“…Table 1 presents the properties of non-derivatized cellulose hydrogels obtained by dissolving in organic solvents or in the alkali/urea/water systems. A detailed analysis of the cellulose-based hydrogel preparation using these solvents is provided in the first part of the review [ 57 ]. Swelling in water is usually calculated according to Formula (1) and is given in the articles as a percentage or in grams of water per gram of dry hydrogel (g/g).…”

“…Cellulose hydrogels that were regenerated from the solutions of organic solvents (DMSO, DMAc, etc.) with water rinsing [ 57 ] may contain solvent residues in the inner layers because the completeness of the solvent removal is quite difficult to control during the experiment. Elemental analysis and IR spectroscopy make it possible to verify the absence of solvent traces in the ready hydrogels.…”

“…However, there are much fewer publications about unmodified cellulose hydrogels and metallogels on their basis. The methods of fabrication of the cellulose-based metallogels and the raw cellulosic materials for that purpose were reviewed by the authors in Part 1 of the series of publications [ 57 ]. There can be several approaches for obtaining a natural cellulose metallogel.…”

Cellulose-Based Metallogels—Part 3: Multifunctional Materials

“…However, the limited solubility of cellulose restricts the choice of suitable solvents for hydrogel production. A comprehensive assessment of cellulose sources and preparation techniques, involving such solvents as N,N-dimethylacetamide (DMAc)/LiCl, dimethyl sulfoxide (DMSO)/LiCl, N-methylmorpholine-N-oxide (NNMO), and NaOH-aqueous solutions, was undertaken by the authors in the first part of the review series "Cellulose-Based Metallogels" [21]. The analysis revealed that DMAc/LiCl and NaOH are the more prevalent solvents, whereas two others are employed by researchers less frequently.…”

“…Metallogels can be derived from ready-made cellulose hydrogels using the diffusionreduction technique [21,24,28]. This convenient and cost-effective approach involves the use of chemical or phyto-chemical reducing agents for the nanoparticles' formation from the precursor salt solutions.…”