Spin coating is an out-of-equilibrium technique for producing polymer films and colloidal crystals quickly and reproducibly. In this review, we present an overview of theoretical and experimental studies of the spin coating of colloidal suspensions. The dynamics of the spin coating process is discussed first, and we present insights from both theory and experiment. A key difference between spin coating with polymer solutions and with monodisperse colloidal suspensions is the emergence of long range (centimeter scale) orientational correlations in the latter. We discuss experiments in different physical regimes that shed light on the many unusual partially ordered structures that have long-range orientational order, but no long-range translational order. The nature of these structures can be tailored by adding electric or magnetic fields during the spin coating procedure. These partially ordered structures can be considered as model systems for studying the fundamentals of poorly crystalline and defect-rich solids, and they can also serve as templates for patterned and/or porous optical and magnetic materials.

The simultaneous presence of hazardous chemicals and pathogenic microorganisms in wastewater is tremendously endangering the environment and human health. Therefore, developing a mitigation strategy for adequately degrading toxic compounds and inactivating/killing microorganisms is urgently needed to protect ecosystems. In this paper, the synergetic effects of the photocatalytic activity of TiO₂ and Cu–TiO₂ nanoparticles (NPs) and the oxidation processes of non-thermal atmospheric pressure plasma (NTAPP) were comprehensively investigated for both the inactivation/killing of common water contaminating bacteria (Escherichia coli (E. coli)) and the degradation of direct textile wastewater (DTW). The photocatalytic NPs were synthesized using the hydrothermal method and further characterized employing field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), ultraviolet-visible diffuse reflection spectroscopy (UV-Vis DRS) and photoluminescence (PL). Results revealed the predominant presence of the typical anatase phase for both the flower-like TiO₂ and the multipod-like Cu–TiO₂ structures. UV-Vis DRS and PL analyses showed that the addition of Cu dopants reduced the bandgap and increased oxygen defect vacancies of TiO₂. The inactivation of E. coli in suspension and degradation of DTW were then examined upon treating the aqueous media with various plasma alone and plasma/NPs conditions (Ar plasma, Ar + O₂ plasma and Ar + N₂ plasma, Ar plasma + TiO₂ NPs and Ar plasma + Cu–TiO₂ NPs). Primary and secondary excited species such as OH˙, O, H and N₂* generated in plasma during the processes were recognized by in situ optical emission spectrometry (OES) measurements. Several other spectroscopic analyses were further employed to quantify some reactive oxygen species (ROS) such as OH, H₂O₂ and O₃ generated during the processes. Moreover, the changes in the pH and electrical conductivity (EC) of the solutions were also assessed. The inactivation of bacteria was examined by the colony-forming unit (CFU) method after plating the treated suspensions on agar, and the degradation of organic compounds in DTW was further validated by measuring the total organic carbon (TOC) removal efficiency. All results collectively revealed that the combinatorial plasma-photocatalysis strategy involving Cu–TiO₂ NPs and argon plasma jet produced higher concentrations of ROS and proved to be a promising one-step wastewater treatment effectively killing microorganisms and degrading toxic organic compounds.

A schematic representation of amino acid-functionalized graphene quantum dots.