Improvement of self-cleaning waterborne polyurethane-acrylate with cationic TiO2/reduced graphene oxide

Construction of photocatalytic coating for alleviating the shriveling of postharvest fruit cucumber after simulated transportation

The shriveling of fruit cucumber was commonly occurred during supply chain, photocatalyst exposed to UV light can endow the coatings with ethylene removal capacity to reduce the respiration of fruit and water loss. The study developed a novel photodynamic technology responsive photocatalytic coating with exceptional ultraviolet (UV) photocatalytic degradation of ethylene ability to decay the shriveling of postharvest fruit cucumber during supply chain. This coating involved the integration of Carbon dots (CDs)-loaded nano ZnO and the skillful selection of pullulan (Pul) and apple pectin (AP) matrix. The CDs/ZnO coatings boasted an impressive array of photocatalytic degradation of ethylene and adhesion properties, including high ethylene removal rates of 32.04 % in 60 min UV light stimulation. The decrease of cell-wall strength, degradation of the cell wall polysaccharides and water loss resulted in cucumber shriveling. Compared with CK sample, after UV-CDs/ZnO coating treatment, the higher firmness and cell wall polysaccharides were found in cucumbers with lower cell wall degrading enzymes activities, weight loss and water movement, which was associated with the decrease of respiration and ethylene accumulation. The UV-CDs/ZnO coatings possessed promising potential for alleviating the shriveling of postharvest fruit cucumber and applications in fruits preservation in the future.

The Influence of the Flexibility of a Polymeric Adhesive Layer on the Mechanical Response of a Composite Reinforced Concrete Slab and a Reinforced Concrete Beam Girder

This study addresses the challenges of modeling flexible connections in composite structures employing a polymeric adhesive layer. These types of connections provide a more uniform stress distribution compared to conventional rigid connectors. However, they lack standardized design rules and still require much research to sufficiently comprehend their properties. The novelty of this research lies in proposing an analytical solution to address these issues. Its aim is to investigate the influence of the stiffness of the polymer adhesive on the girder's deflection and on the maximum stresses in both the adhesive and concrete. The analyzed composite structure consists of a reinforced concrete (RC) slab and an RC beam connected with a layer of flexible polyurethane (FPU) adhesive. Analytical and numerical approaches for the description of the mechanical response of a composite bridge girder are presented. Another objective is to validate the analytical design formulas using 3D nonlinear numerical analysis, both in the case of uncracked and cracked concrete. Seven types of FPUs are tested in the uniaxial tension test, each examined at five strain rates. The obtained data is used to predict the mechanical response of the considered girder using finite element analysis (FEA) as well as with a simplified one-dimensional composite beam theory. Fair agreement is found between the FEA results and theoretical predictions. A comparison of the results obtained for these two models is performed, and the similarities and discrepancies are highlighted and discussed.

Influence of the Surface Chemistry of Graphene Oxide on the Structure-Property Relationship of Waterborne Poly(urethane urea) Adhesive

Small amounts-0.04 wt.%-graphene oxide derivatives with different surface chemistry (graphene oxide-GO-, amine-functionalized GO-A-GO-, reduced GO-r-GO) were added during prepolymer formation in the synthesis of waterborne poly(urethane urea) dispersions (PUDs). Covalent interactions between the surface groups on the graphene oxide derivatives and the end NCO groups of the prepolymer were created, these interactions differently altered the degree of micro-phase separation of the PUDs and their structure-properties relationships. The amine functional groups on the A-GO surface reacted preferentially with the prepolymer, producing new urea hard domains and higher percentage of soft segments than in the PUD without GO derivative. All GO derivatives were well dispersed into the PU matrix. The PUD without GO derivative showed the most noticeable shear thinning and the addition of the GO derivative reduced the extent of shear thinning differently depending on its functional chemistry. The free urethane groups were dominant in all PUs and the addition of the GO derivative increased the percentage of the associated by hydrogen bond urethane groups. As a consequence, the addition of GO derivative caused a lower degree of micro-phase separation. All PUs containing GO derivatives exhibited an additional thermal decomposition at 190-206 °C which was ascribed to the GO derivative-poly(urethane urea) interactions, the lowest temperature corresponded to PU+A-GO. The PUs exhibited two structural relaxations, their temperatures decreased by adding the GO derivative, and the values of the maximum of tan delta in PU+r-GO and PU+A-GO were significantly higher than in the rest. The addition of the GO derivative increased the elongation-at-break, imparted some toughening, and increased the adhesion of the PUD. The highest T-peel strength values corresponded to the joints made with PUD+GO and PUD+r-GO, and a rupture of the substrate was obtained.

Graphene coupled TiO2 photocatalysts for environmental applications: A review

Nanostructured photocatalysts have always offered opportunities to solve issues concerned with the environmental challenges caused by rapid urbanization and industrialization. These materials, due to their tunable physicochemical characteristics, are capable of providing a clean and sustainable ecosystem to humanity. One of the current thriving research focuses of visible-light-driven photocatalysts is on the nanocomposites of titanium dioxide (TiO₂) with carbon nanostructures, especially graphene. Coupling TiO₂ with graphene has proven more active by photocatalysis than TiO₂ alone. It is generally considered that graphene sheets act as an electron acceptor facilitating the transfer and separation of photogenerated electrons during TiO₂ excitation, thereby reducing electron-hole recombination. This study briefly reviews the fundamental mechanism and interfacial charge-transfer dynamics in TiO₂/graphene nanocomposites. Design strategies of various graphene-based hybrids are highlighted along with some specialized synthetic routes adopted to attain preferred properties. Importantly, the enhancing interfacial charge transfer of photogenerated e¯_CB through the graphene layers by morphology orientation of TiO₂, predominated exposure of their high energy crystal facets, defect engineering, enhancing catalytic sites in graphene, constructing dedicated architectures, tuning the nanomaterial dimensionality at the interface, and employing the synergism adopted through various modifications, are systematically compiled. Portraying the significance of these photocatalytic hybrids in environmental remediation, important applications including air and water purification, self-cleaning surfaces, H₂ production, and CO₂ reduction to desired fuels, are addressed.

Recent Advances in Functional Polyurethane and Its Application in Leather Manufacture: A Review

Over last few years, polyurethane (PU) has been applied in a number of areas because of its remarkable features, such as excellent mechanical strength, good abrasion resistance, toughness, low temperature flexibility, etc. More specifically, PU can be easily "tailor made" to meet specific demands. This structure-property relationship endows great potential for use in wider applications. With the improvement of living standards, ordinary polyurethane products cannot meet people's growing needs for comfort, quality, and novelty. This has recently drawn enormous commercial and academic attention to the development of functional polyurethane. Among the major applications, PU is one of the prominent retanning agents and coating materials in leather manufacturing. This review gives a summary of academic study in the field of functional PU as well as its recent application in leather manufacture.

Facile synthesis of multi-type carbon doped and modified nano-TiO2 for enhanced visible-light photocatalysis

Nano-TiO₂ is a type of environment-friendly and inexpensive substance that could be used for photocatalytic degradation processes. In this study, the multi-type carbon species doped and modified anatase nano-TiO₂ was innovatively synthesized and developed to overcome the deficiency of common nano-TiO₂ photocatalysts. The multi-type carbon species were derived from tetrabutyl titanate and ethanol as the internal and external carbon sources, respectively. Meanwhile, diverse characterization methods were applied to investigate the morphology and surface properties of the photocatalyst. Finally, the visible-light photocatalytic degradation activity of the collected samples was evaluated by using methyl orange as a model pollutant. The promotion mechanism of multi-type carbon species in the photocatalytic process was also discussed and reported. The results in this work show that the doping and modification of multi-type carbon species successfully narrows the bandgap of nano-TiO₂ to expand the light absorption range, reduces the valence band position to improve the oxidation ability of photogenerated holes, and promotes the separation of photogenerated charge carriers to improve quantum efficiency. In addition, the further modification of the external carbon source can promote the surface adsorption of MO and stabilize the multi-type carbon species on the surface of nano-TiO₂.

The synergistic modification of nano-TiO₂ by multi-type carbon species results in excellent and stable visible-light photocatalytic degradation activity.

Effect of heat treatment under vacuum on structure and visible-light photocatalytic activity of nano-TiO2

Nano-TiO2 is known as a photocatalyst with high catalytic activity. However, it should be emphasized that the bandgap of nano-TiO2 is wide, which limits its photocatalytic efficiency in response to visible light and thus hinders its potential application. Improving the photocatalytic activity of nano-TiO2 under visible light by the strategy of heat treatment under vacuum was investigated in this study. The structure and photocatalytic activity of nano-TiO2 before and after heat treatment under vacuum were compared and analyzed by XRD, TEM, HRTEM, XPS and UV-Vis-NIR, respectively. The results show that oxygen vacancies were introduced into the crystal structure of nano-TiO2 to change its inherent energy band structure. Particularly, the samples after heat treatment under vacuum exhibited high photocatalytic activity under visible light. In addition, the formation mechanism of non-stoichiometric compound TiO2-x and the mechanism of oxygen vacancy defects to expand the wavelength of light that nano-TiO2 absorbs to the visible portion of the spectrum have also been addressed in this paper.