Controlling Intermolecular H-atom Abstraction with Ultrafast Pump-Push-Probe Spectroscopy

We utilize ultrafast multi-pulse pump-push-probe transient absorption spectroscopy and time-resolved photoluminescence to monitor excited-state H-atom transfer from hydroxylic compounds to the heptazine derivative 2,5,8-tris(4-methoxyphenyl)-1,3,5,6,7,9,9b-heptaazaphenalene (TAHz). The heptazine moiety is structurally related to the monomer unit of the ubiquitous organic polymeric photocatalyst, carbon nitride. We show that TAHz can photochemically abstract an H-atom from water, in addition to generating H2 in aqueous suspensions with photocatalytic activity matching that of carbon nitride. In our multi-pulse experiment, we use resonant pump pulse to photoexcite TAHz to a bright high-lying excited state, and after a relaxation period of roughly 6 ps, we use a NIR (1150 nm) pulse to “push” the chromophore to a higher-lying excited state. When phenol is present, the push induces a persistent decrease (ΔΔOD) in the initial excited-state absorption, indicating the push pulse engenders a divergence in the photochemical branching ratios. In the presence of electron-donating substituted phenols, the magnitude of ΔΔOD diminishes markedly due to the increased excited-state reactivity of the complex accompanied by the cathodic shift in the phenol oxidation potential. Thus, the H-atom abstraction appears to proceed without aid from the additional energy of the push pulse. These results reveal new insight into the branching ratio among unreactive localized heptazine excited states and reactive intermolecular charge transfer states of H-bonded heptazine chromophores. More generally, this work provides new insight into molecular design strategies to control the excited-state photochemistry of aza-aromatic materials toward important reactions such as H-atom abstraction from water.

Theoretical Investigation of Thermal Expansion Coefficients of SiC Reinforced Copper Matrix Composites

The thermal expansion coefficient (CTE) of the copper element, which is widely used in the electronics industry, is quite high. It is of great importance to decrease the CTE value in order not to deform against the heat it is exposed to. In this study, it is aimed to theoretically examine the changes in CTE value when SiC supplement is applied to pure copper. For this purpose, CTE value calculations were made according to Kerner and Turner's models for composites that were reinforced at different rates by volume. Sample studies in the literature have been utilized for percent component ratios. In this context, the amount of reinforcement was adjusted to be 5, 10, 15, and 20vol.% by volume. According to the findings, it was observed that there was ̴ %4-17 decrease in CTE value based on the Kerner model and ̴ %7-26 decrease based on the Turner model.

A Novel Microwave Treatment to Augment the Mechanical Properties of Polymeric Materials

The present study portrays a novel post-processing treatment by using microwave radiations for enhancing the mechanical properties of five commonly used engineering polymers, Poly-amide (PA), Poly-butylene-terephthalate (PBT), Poly-propylene (PP), Poly-carbonate (PC), Acrylonitrile-butadiene-styrene (ABS). The analysis revealed that the crystal structures of the polymers improved after the treatment due to a more favorable rearrangement of crystalline segments within the polymers. Furthermore, tensile properties and tribological performance of microwave treated polymers were found to be significantly better when compared to those of untreated counterparts. The tensile strength, elongation, and wear performance of PA increased by 51%, 286%, and 45%, respectively, only after a treatment of 20 seconds. A similar response was also exhibited by other polymers as well. It was noted that the optimum time for microwave treatment could vary depending on the different crystalline nature of the polymers. The degree of randomness in the molecular chains of semi-crystalline polymers is less; thus, it requires less treatment time. However, for amorphous polymers, as randomness increases, more time is needed. As such, post-processing microwave treatment of polymers has proven beneficial as a cost-effective, time-saving, and environment-friendly technique for enhancing material properties significantly.

Scaling-up Nanoparticle Beam Deposition for Green Synthesis of Advanced Materials

The deposition of size-controlled nanoparticles (atomic clusters) onto supports from the beam is a solvent-free, green route to small-scale manufacturing of functional nanomaterials. To translate the beautiful physics and chemistry of clusters into practical applications, e.g., coatings, catalysts, biochips, biomaterials, and photonic materials, significant scale-up of the rate of deposition is needed [1,2], while reducing the loss of material in the process (to say 1-10%). For example, the deposition rate needed for industrial catalyst R&D is 10mg/hour of clusters, while for bespoke pharmaceutical manufacturing, 1-10g/hour is required. In this talk, I will discuss both the fundamental aspects of deposited clusters at the atomic-scale – as revealed by aberration-corrected scanning transmission electron microscopy [3,4] – and the status of efforts to meet the scale-up challenge, with emphasis on our “Matrix Assembly Cluster Source” (MACS) [5]. Some first practical demonstrations [6-10] of deposited clusters in heterogeneous and electrocatalysis will be presented, showing attractive activities and selectivities [1, 6-10], as an illustration of what might be done in fields as diverse as surface engineering, theranostics, photonics, and neuromorphic.

Photocatalytic CO2 Reduction and Thermal Properties of Alumina/Silica Coated TiO2 Nanoparticles

In this study, the surface of TiO2 was coated with SiO2 and Al2O3 layers by sol-gel and chemical deposition methods. Firstly, the TiCl4 was magnetically stirred for 1 h in deionized water, and then the NaOH solution was drop wised to the solution and stirred 2h. Finally, the obtained TiO2 was washed, filtered, and dried in a vacuum oven. The surface of TiO2 was coated with SiO2 and Al2O3 layers subsequently by chemical deposition methods. The morphological, thermal, and crystal properties of products were determined via SEM, TGA, and XRD machines. The X-ray diffraction peaks displayed that the TiO2 nanoparticles were synthesized without any extra peaks. Moreover, the SiO2 and Al2O3 coated TiO2 particles contain extra SiO2 and Al2O3 peaks, indicating that the surface of TiO2 was coated via SiO2 and Al2O3. The SEM results displayed that TiO2 and SiO2 and Al2O3 coated TiO2 were spherical in shape, and the size distribution was found to be around 20-50 nm and 200-300 nm, respectively. The photocatalytic and UV–vis analyses were used to determine the CO2 reduction and optical properties of particles. The results showed that the absorption peaks were broad to longer wavelength with a coating of SiO2 and Al2O3. The CO2 reduction performance of TiO2 has been enhanced via coating SiO2 and Al2O3 layer.

Hydrophobic Waxes in Ivory Nuts Affect Surface Modification by Atmospheric Air Plasma Jet

Ivory nuts, produced by palms from the genus Phytelephas, possess a hard and microporous endosperm with a strong resemblance to elephant ivory. The nuts sustainable appeal made them popular as eco-friendly substitutes to ivory since they promote the development of forest communities without contributing to deforestation and animal poaching. In addition, they have been commercialized as microbeads to replace microplastics in cosmetic applications. However, this material is vulnerable to deterioration by micro-organisms and insects, as they are predominantly constituted by β-1,4-mannan, a hydrophilic polysaccharide similar to cellulose. In this context, seed endosperm was treated for 80 s by an atmospheric air plasma jet so as to modify its wettability, as plasma has been widely studied recently for seed disinfection and surface modification. Plasma treated samples were characterized by the water contact angle, AFM, and Raman imaging. Water contact angle results showed an increase from (31.5 ± 8.7)º to (78.9 ± 5.4)º, indicating incorporation of hydrophobic moieties to the sample surface. In turn, AFM images demonstrate the formation of a rough and heterogeneous coating that resembles epicuticular wax layers. Furthermore, principal component analysis of Raman imaging results evidenced contributions from wax (1156, 1170 and 1410 cm-1), carbohydrates (1020, 1080 and 1106 cm-1), and lignin (1573, 1635 and 1662 cm-1). These results indicate that plasma treatment promoted the migration of hydrophobic waxes to the surface and their crosslinking with fragmented cell wall material such as mannan, xylan, and lignin, promoting seed hydrophobization with no need for additional precursors or generation of side products.

Light-Responsive Porous Aromatic Frameworks: Generation of Photon Upconverted Emission and Modulation of Porosity by Bulk Photoisomerization

Porous aromatic frameworks (PAFs) were engineered to generate solid-state upconverting materials that emit higher energy photons under a suitable light stimulus [1]. Fluorescent PAFs were generated by the inclusion of diphenylanthracene moieties in a low-density 3D porous frameworks that maintained the optical properties of the emitting chromophores in the solid-state. Upon inclusion of a suitable sensitizer (a metallo-porphyrin) inside the nanometer-sized pores, the copolymer displayed sensitized photon upconversion with a quantum yield as high as 15%, a record value for solid-state materials. Moreover, it was possible to tether the sensitizer to the porous matrix through a stable covalent bond, generating self-standing upconverting nanoparticles that can be possibly applied in photovoltaics and bio-imaging. PAFs can also be engineered as light-responsive materials. The co-polymerization of a photoswitch with tetraphenylmethane generated porous networks that provided the free volume for the photoisomerization of the overcrowded alkene [2]. Under UV light irradiation, the quantitative photoisomerization led to structural changes and modulated the CO2 adsorptive properties of the material. The process is reversible by irradiation or heating leading to a cyclable material.

COVID-19 Global Healthcare System Failures: The Desperate Need for a Paradigm Shift for Better Medical Materials

COVID-19 has highlighted numerous failures in our global healthcare system, from a system focussed on centralized hospitals to a lack of platform technologies to treat viral outbreaks. This presentation will highlight new materials being developed to aid in COVID-19 prevention, detection, and therapy. Rather than waiting for a year or longer for vaccine development, this presentation will highlight how nanomaterials can be a platform technology modified to treat every new virus that comes along. It will also highlight the use of at-home sensors and diagnostic kits that make it easy for patients to determine if they have been exposed to viruses rather than going to a facility (i.e., hospital) in which their infection could spread. Overall, this presentation will demonstrate how new materials will better prepare us for our next viral outbreak and begin to heal our current global healthcare system, which has demonstrated significant failures during the COVID-19 pandemic.

Design, Analysis and Finite Element Modeling of Macro Fiber Composite Piezoelectric Materials

Vibration energy harvester has been paid a lot of attention by many researchers to transforming ambient vibration into electrical energy, which is normally utilized to develop wireless electronic sectors. The paper presents a finite element model (FEM) of a vibration energy harvester consisting of a bimorph electromechanical system (MEMS) generator. The model is used to simulate, and compare, the mechanical characteristics and electrical response of piezoelectric material results between the cantilever beam structure formed by laminating two piezoelectric layers on both sides of a Carbon fiber reinforced polymer (CFRP) substrate and Ti-6Al-4V substrate using ANSYS®19 R1. A set of numerical simulations has been carried out, and the results show that the comparisons of the harmonic response analysis seen change between the different substrates based on the bimorph piezoelectric MEMS generator.

Epoxy Resins and their Zinc Composites as Novel Anti-Corrosive Materials for Copper in 3% Sodium Chloride Solution: Experimental and Computational Studies

The evaluation the anticorrosive performance of two macromolecular aromatic epoxy resins (ERs), namely, tetra glycidyl of ethylene dianiline (TGEDA), hexaglycidyl Tris (p-Ethylene Dianiline) Phosphoric Triamide (HGEDPAT), and their polymer composite reinforced with Zinc for copper corrosion in 3% NaCl by means of computational and experimental analyses. Anticorrosive property of the standards and composites was demonstrated using experimental and computational methods. Electrochemical results showed that HGEDAPT cured with methylene dianiline (MDA) showed better protection efficiency with optimum corrosion current density (icorr) value of 2.0 µcm-2 and the polarization resistance (Rp) value of 17,00 kΩ.cm2 than that of TGEDA-MDA having icorr value of 2.4 µcm-2 and the Rp value of 15.24 kΩ.cm2. The anticorrosive effect of TGEDA-MDA and HGEDAPT-MDA was evaluated in the presence of 5% zinc (Zn). Experimental results demonstrate that the presence of 5% of zinc in TGEDA-MDA and HGEDAPT-MDA formulations significantly enhanced their protection ability. The anticorrosive effect of different formulations followed the order: ER1 (TGEDA-MDA) (potentiodynamic polarization (PDP); 90% and electrochemical impedance spectroscopy (EIS) 92%) < ER2 (HGEDAPT-MDA) (PDP; 92% and EIS 93%) < ER3 (TGEDA-MDA-5%Zn) (PDP; 96% and EIS 97%) < ER4 (HGEDAPT-MDA-5%Zn) (PDP; 97% and EIS 98.5%). Density Functional Theory (DFT) study revealed that ER1 and ER2 interact with the metallic surface using donor-acceptor interactions in which electron-rich centers acted as the most favorable sites for the interactions. Molecular dynamics (MD) simulations studies suggest that ER1 and ER2 acquire flat or horizontal orientations, and their orientations on the metallic surface are largely influenced by the presence of zinc. Different experimental and computational studies are in good agreement.