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.

Available methods for solubilization and dispersion of several carbon allotropes (with the exception of dispersions in polymers) in organic solvents and water are reviewed. Main attention is paid to graphite, graphene, fullerenes, nanoonions, nanodiamonds, carbon nanotubes, and carbon nanodots. The techniques to increase the "solubility" of carbon allotropes include chemical functionalization of the carbon surface (covalent and non-covalent functionalization, oxidation via ozonation, insertion of electron-withdrawing atoms (fluorination), polymer grafting, swelling and biomolecule treatments, use of molecular "wedges" for intercalation, thermal reduction, etc.). The combination of functionalization with the use of surfactants, ultrasound, laser ablation, milling, microwave expansion, hydrothermal methods, and other treatments leads to better results. The possibility of dispersion and the size of the formed particles depend on a series of factors, in particular the nature of the solvent, its viscosity and hydrogen-bond donation ability, dispersion interactions, π−π stacking between the carbon surface and reagents, and the nature of the surfactants, among others.

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Carbon−carbon allotropic hybrids and their composites are reviewed. Carbon−carbon hybrids are mainly composed of graphene, graphite, graphene oxide, reduced graphene oxide, carbon nanotubes, carbyne chains, fullerenes and more complex spherical and ring-ike carbon forms, graphene quantum dots, and carbon nanodots. Aerogels and xerogels on their basis are also discussed. Most of these hybrides consist of 3D architectures with either covalent or van der Waals interactions between carbon atoms, possessing unusual properties as compared to their counterparts, because of the simultaneous presence of carbon structures of distinct dimensionality and reactivity. These composites can be prepared by a variety of methods starting from already existing allotropes, or by their synthesis in situ, such as chemical vapor deposition, solvothermal techniques, pyrolysis, ultrasonication in solution, and other liquidphase methods, frequently including redox steps. Current and potential applications of hybrids and their metal-doped composites as supercapacitors, sensors, catalysts, and environmental remediation reactants are described.

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