Modern trends in the greener synthesis and fabrication of inorganic, organic and coordination compounds, materials, nanomaterials, hybrids and nanocomposites are discussed. Green chemistry deals with synthesis procedures according to its classic 12 principles, contributing to the sustainability of chemical processes, energy savings, lesser toxicity of reagents and final products, lesser damage to the environment and human health, decreasing the risk of global overheating, and more rational use of natural resources and agricultural wastes. Greener techniques have been applied to synthesize both well-known chemical compounds by more sustainable routes and completely new materials. A range of nanosized materials and composites can be produced by greener routes, including nanoparticles of metals, non-metals, their oxides and salts, aerogels or quantum dots. At the same time, such classic materials as cement, ceramics, adsorbents, polymers, bioplastics and biocomposites can be improved or obtained by cleaner processes. Several non-contaminating physical methods, such as microwave heating, ultrasound-assisted and hydrothermal processes or ball milling, frequently in combination with the use of natural precursors, are of major importance in the greener synthesis, as well as solventless and biosynthesis techniques. Non-hazardous solvents including ionic liquids, use of plant extracts, fungi, yeasts, bacteria and viruses are also discussed in relation with materials fabrication. Availability, necessity and profitability of scaling up green processes are discussed.

Contemporary methods for dispersion of carbon nanotubes in water and non-aqueous media are discussed. Most attention is paid to ultrasonic and plasma techniques and other physical techniques, as well as to the use of surfactants, functionalizing and debundling agents of distinct nature (elemental substances, metal and organic salts, mineral and organic acids, oxides, inorganic and organic peroxides, organic sulfonates, polymers, dyes, natural products, biomolecules, and coordination compounds). Special studies on CNTs solubilization are examined.

The analysis of previous classic and recent reports on the interlayer distances in MWCNTs is described in this review.

Recent achievements in the solubilization and stabilization of magnetic nanoparticles (MNPs) are reviewed. The majority of reported MNPs correspond to iron-based {nZVI, superparamagnetic iron oxides (SPIONs), core–shell Fe/Au or Fe_xO_y/Au nanoparticles and ferrites} nanoparticles, with a few numbers corresponding to MnO and cobalt nanoparticles. Magnetic nanoparticles can be solubilized in water or non-aqueous solvents for short or long time periods. The main approaches for MNP solubilization are discussed, namely, suitable choice of precursors, pH, surfactants/coating agents, and solvents, as well as functionalizing agents. MNPs are generally solubilized by functionalization with water-soluble compounds/moieties (in particular, sulfonic acid disodium salts, soluble polymers, porphyrins and calixarenes), under conditions of the thermal decomposition of low stability metal complexes, coprecipitation, microwave heating, and by ultrasonication. The polyol strategy is frequently applied to increase MNP solubility. The stabilization of MNPs in solutions could be achieved with the help of inorganic, monomeric and polymeric compounds.

Micro- and nano-sized magnetic adsorbents based on elemental metals, iron oxides, and ferrites and supported by inorganic (carbon, graphene, silica, and zeolites) or organic (macromolecules, polysaccharides, polymers, and biomolecules) compounds are reviewed. The main focus is on magnetic hydrogels, xerogels, and aerogels due to their high number of environmental and biomedical applications. The roles of carbohydrates and polysaccharides (starch, alginic acid, chitosan, etc.) in the stabilisation of magnetic nanoparticles and the use of the formed composites for adsorption purposes are described. Magnetic adsorbents are mainly used for heavy metal removal, for the separation, destruction and adsorption of oil, dyes, toxic organic compounds, several biomolecules and drugs, as well as in a wide variety of catalytic processes. These last applications of magnetic adsorbents, particularly ferrites, are emphasised. The main advantage of magnetic absorbents for these or other possible applications is that the adsorbent or catalyst can be easily removed from the reaction medium after adsorption or reaction completion via a simple magnet. Magnetic behaviour studies of magnetic adsorbents are also discussed.