Melamine (MA) and polyurethane (PU) foams, including both commercial sponges for daily use as well as newly synthesized foams are known for their high sorption ability of both polar and unipolar liquids. From this reason, commercial sponges are widely used for cleaning as they absorb a large amount of water, oil as well as their mixtures. These sponges do not preferentially absorb any of those components due to their balanced wettability. On the other hand, chemical and physical modifications of outer surfaces or in the bulk of the foams can significantly change their original wettability. These treatments ensure a suitable wettability of foams needed for an efficient water/oil or oil/water separation. MA and PU foams, dependently on the treatment, can be designed for both types of separations. The particular focus of this review is dealt with the separation of oil contaminants dispersed in water of various composition, however, an opposite case, namely a separation of water content from continuous oily phase is also discussed in some extent. In the former case, water is dominant, continuous phase and oil is dispersed within it at various concentrations, dependently on the source of polluted water. For example, waste waters associated with a crude oil, gas, shale gas extraction and oil refineries consist of oily impurities in the range from tens to thousands ppm [mg/L]. The efficient materials for preferential oil sorption should display significantly high hydrophobicity and oleophilicity and vice versa. This review is dealt with the various modifications of MA and PU foams for separating both oil in water and water in oil mixtures by identifying the chemical composition, porosity, morphology, and crosslinking parameters of the materials. Different functionalization strategies and modifications including the surface grafting with various functional species or by adding various nanomaterials in manipulating the surface properties and wettability are thoroughly reviewed. Despite the laboratory tests proved a multiply reuse of the foams, industrial applications are limited due to fouling problems, longer cleaning protocols and mechanical damages during performance cycles. Various strategies were proposed to resolve those bottlenecks, and they are also reviewed in this study.

Graphitic carbon nitrides (gCNs) are promising materials for multidisciplinary catalytic applications due to their inimitable physicochemical merits, thermal-physical-chemical stability, and rich electron density. The catalytic properties of gCNs are determined by their structure and composition; therefore, various methods have been developed for the rational synthesis of gCNs with different morphologies and compositions. Unlike other gCN nanostructures, one-dimensional (1D) nanostructures possess an outstanding accessible surface area, multiple adsorption sites, active catalytic sites, aspect ratio, and short electron-diffusion that enable their utilization in various gas conversion reactions. The thermal CO oxidation reaction (CO OR) on either gCNs or other catalysts is important in industrial, fundamental, and environmental issues; however, the reviews on 1D gCNs for CO oxidation is not yet reported. This chapter highlights the fabrication methods of 1D gCN nanostructures (i.e., nanotubes, nanorods, nanofibers, and needles) and their mechanisms and utilization in thermal CO ORs. Lastly, the current challenges and future prospects on gCNs for CO ORs are also discussed.