Silica Based Superhydrophobic Nanocoatings for Natural Rubber Surfaces

Silica based nonfluorinated superhydrophobic coatings for natural rubber surfaces have been developed. The coating was synthesized using nanosilica dispersion and a polychloroprene type binder as a compatibilizer. This nanocoating of silica was applied on to the surface of finished natural rubber gloves, by spray coating or dipped coating methods. The nanocoating demonstrates a water contact angle of more than 150° and sliding angle of 7°. The morphological features of the coating have been studied using scanning electron microscopy and atomic force microscopy while Fourier transform infrared spectroscopy was used to understand the nature of surface functional groups. Both imaging techniques provided evidence for the presence of nanosized particles in the coating. Coated gloves demonstrated comparable mechanical properties and significantly better alcohol resistivity when compared to those of the uncoated gloves

Oxidative Esterification of 5-Hydroxymethylfurfural into Dimethyl 2,5-Furandicarboxylate Using Gamma Alumina-Supported Gold Nanoparticles

Gold nanoparticles (Au NPs) supported on a nanostructured gamma alumina (γ-Al2O3) fiber can exhibit excellent catalytic activity for the conversion of 5-hydroxymethylfurfural to produce its ester derivative, dimethyl 2,5-furandicarboxylate (FDMC). γ-Al2O3 was synthesized using a PEG surfactant to generate oxide fibers that randomly stack together into irregular shapes. The average particle sizes of the Au NPs are 1-6 nm, where the catalytically active Au (111) surface is the exposed facet. This 3D nanocatalyst architecture enhances the 5-hydroxymethylfurfural (HMF) oxidative esterification because HMF reactant molecules can readily diffuse into this fibrous structure and adsorb to active catalytic sites, while ester product molecules can diffuse out. Up to 99% HMF conversion and 90% FDMC selectivity can be obtained at a low reaction temperature of 45 °C, and the catalyst shows excellent recyclability. Increasing the Au content in the catalyst minimizes the requirement of a base for HMF conversion. Thus, the Au NPs supported on γ-Al2O3 can drive HMF esterification to FDMC efficiently with high product selectivity under very mild reaction conditions, omitting the need for an additional esterification step of the HMF acid.</p

Washable and Flexible All Carbon Electrothermal Joule Heater for Electric Vehicles

Amid the rapid development of electric vehicles, a flexible and waterproof radiant heater that can withstand repeated bending and washing is highly desirable. Herein, a freestanding, ultra-flexible, and washable joule heater is constructed using a biocompatible poly(styrene-isoprene-styrene) (SIBS) polymer as binder and carbon black (CB) as heating material. By controlling the amount of CB and the thickness of the film, a minimum resistivity, and conductivity of 26 mΩ cm and 7.4 S cm−1, respectively, is achieved. Remarkably, the 28% CB/SIBS film can reach a maximum temperature of 201 °C while maintaining a stable temperature at 130 °C for repeated ON/OFF cycles. Time-of-flight secondary ion mass spectrometry of post-mortem material analysis shows that a 1 h stability test at 130 °C has no sign of degradation and the films remain extremely stable. The films also show exceptional electrothermal heater performance after carrying out mechanical property tests such as bending (over 30°), repetitive bending (1000 cycles), twisting (two turns), and washing (soaked in distilled water for over 12 h). These outstanding heater performances incorporate extreme chemical stability and mechanical flexibility proposing that the CB/SIBS-based electrothermal elements hold great potential for numerous practical applications, such as heating systems in electric vehicles and wearable electronics.</p

AuCu/ZnO heterogeneous photocatalysts: Photodeposited AuCu alloy effect on product selectivity in alkene epoxidation

AuCu metal alloy nanoparticles were photodeposited on ZnO nanorods (ZnO_NRs) which proved to be effective photocatalysts for alkene epoxidation. The alloy nanoparticles were photodeposited onto ZnO nanorods with controlled ratios of gold and copper, with the deposition monitored in situ by UV-Vis spectroscopy. The alloy catalyst hybrids were tested for activity toward styrene epoxidation and HMF oxidative esterification, where the photoreactions were both optimized for time, temperature, and metal ratio content of the catalyst. The Au0.54Cu1/ZnO_NR alloy catalysts showed excellent photocatalytic activity and were most effective for conversion of styrene to styrene epoxide, where the product selectivity could be controlled by varying the metal ratio. Cu content in the alloy NP was essential to this process, as shown by the extrema in terms of metal content, using Au/ZnO only, where 100% benzaldehyde was obtained as the product. Au/ZnO evidenced best photocatalytic activity for HMF esterification, with conversion rapidly diminishing upon alloying of Au with Cu. A detailed XPS study was carried out to investigate reaction mechanism based on these studies, in particular, mechanisms are proposed for styrene epoxidation and oxidation cycles using the AuCu/ZnO_NR photocatalysts.</p

Nanostructure Shape-Effects in ZnO heterogeneous photocatalysis

Selective oxidation of alcohols is an essential reaction for fine chemical production. Here, the photocatalytic oxidation of benzyl alcohol by zinc oxide (ZnO) nanocrystals was investigated to clarify the mechanism of selective oxidation with this process. Reactivity when in contact with three distinct ZnO nanocrystal shapes: nanocones, nanorods and nanoplates, was studied in order to compare crystal facet-specific effects in the reaction system. The same non-hydrothermal and non-hydrolytic aminolysis method was used to synthesise all three nanocrystal shapes. The ZnO catalysts were characterized using by a range of techniques to establish the key properties of the prominent ZnO crystal facets exposed to the reaction medium. The ZnO nanocrystals photocatalysed the benzyl alcohol oxidation reaction when irradiated by a 370 – 375 nm LED output and each ZnO crystal morphology exhibited different reaction kinetics for the oxidation reaction. ZnO nanocones displayed the highest benzyl alcohol conversion rate while nanorods gave the lowest. This established a facet-dependent kinetic activity for the benzyl alcohol reaction of (101¯1) > (0001) > (101¯0). Experimental and density functional theory computation results confirm that the {101¯1} facet is a surface that exposes undercoordinated O atoms to the reaction medium, which explains why the reactant benzyl alcohol adsorption on this facet is the highest. Light irradiation can excite valence band electrons to the conduction band, which are then captured by O2 molecules to yield superoxide (O2•–). In a non-aqueous solvent, the photogenerated holes oxidise benzyl alcohol to form a radical species, which reacts with O2•– to yield benzaldehyde. This results in 100% product selectivity for benzaldehyde, rather than the carboxylic acid derivative.</p

Sustainable Claisen-Schmidt chalcone synthesis catalysed by plasma-recovered MgO nanosheets from seawater

Chalcones enable the biosynthesis of flavonoids which protect plants from infections and parasites and have emerged as valuable medicines against diverse human diseases. The common way to synthesize chalcones through the homogeneous catalytic Claisen-Schmidt condensation reaction is compromised from difficult catalyst recovery, waste generation, side reactions, and low yield. As a solution, solid base catalysts are developed as a green catalytic process. It is still a major challenge to synthesize highly active heterogeneous catalysts with a quick, simple, sustainable, and economical approach in the chalcone synthesis. To address these issues, a simple and sustainable synthesis of chalcones has been accomplished here by the solvent-free Claisen-Schmidt condensation reaction using magnesium oxide (MgO) nanosheets as the catalyst. The heterogeneous two-dimensional (2D) MgO catalyst was synthesized using salt recovered from inexhaustible seawater, using an atmospheric pressure plasma (APP)-assisted method making the whole method sustainable and potentially economically feasible. The catalytic activity of the 2D nanosheets was compared with irregular MgO nanoparticles. Irregular MgO showed 25% of benzaldehyde and 10% of acetophenone conversion, while 2D MgO showed >99% of conversion of both reactants with a product selectivity of 100%, while no products were formed in the absence of a catalyst. The effect of substituent groups on the benzaldehyde moiety on the catalytic activity was also analysed. The prepared 2D MgO catalyst showed reusability up to three cycles without any significant loss in the catalytic activity.</p

Leveraging doping and defect engineering to modulate exciton dissociation in graphitic carbon nitride for photocatalytic elimination of marine oil spill

Limited light absorption ability and rapid photogenerated electron-hole recombination severely impedes applications of g-C3N4. Herein, highly efficient point-defect engineering including dual dopants as well as vacancy was adopted to modulate the photo-induced exciton dissociation kinetics. Specifically, P, O dopants and carbon vacancy modified 3D honeycomb-like POCVN was fabricated through facile one-pot polymerization with (NH4)3PO4 as P, O precursors. The obtained POCVN catalyst exhibited superior photocatalytic degradation performance for n-tetradecane under visible light illumination (38.1 %), which was 4.6 and 1.8 times higher than that of bulk g-C3N4 (8.2 %) and tubular g-C3N4 (21.1 %), respectively. The suppressed recombination of electrons and holes contributed to the superior catalytic performance compared to pristine g-C3N4, single P and single O doping g-C3N4. Structural analysis demonstrated P atoms may replace C atoms of N-C = N, O atom located at P-O-C and carbon vacancies located at N = C-N2 position at heptazine framework. Based on experimental and theoretical analysis, it was found P, O and Cv defects prefer to accumulate together in 3-trizine ring, which is conductive to the formation of localized defect state in the band gap region. It resulted in high exciton dissociation efficiency, thus, more reactive radicals were generated. Based on this, degradation path, interference parameter, reactive radicals and toxicity evaluation were investigated deeply and systematically. This work shed light on non-metal green ecological remediation material for marine oil spill.</p