Synthesis of Holey Graphene Nanoparticle Compounds

Polyurethane-grafted graphene oxide from repurposed foam mattress waste

Polyurethanes (PU) make up a large portion of commodity plastics appearing in applications including insulation, footwear, and memory foam mattresses. Unfortunately, as thermoset polymers, polyurethanes lack a clear path for recycling and repurposing, creating a sustainability issue. Herein, using dynamic depolymerization, we demonstrate a simple one-pot synthesis for preparation of an upcycled polyurethane grafted graphene material (PU-GO). Through this dynamic depolymerization using green conditions, PU-GO nanofillers with tunable PU to GO ratios were synthesized. Chemical analysis revealed that the polyurethane graphenic materials primarily contained the polycarbamate hard-segment of polyurethane while the soft polyol component was removed in washes. PU-GOs were incorporated into bulk polyurethane foam to create composites as a filler at 0.25, 0.5, 1.0, and 2.0 weight percent filler and the thermal and mechanical properties of the resulting foams were analyzed. All PU-GO fillers were shown to improve thermal insulation up to a filler content of 0.5%, with all but 2 of the fillers demonstrating improvements up to 2% of filler content. The greatest decrease in thermal conductivity was 38.5% compared to neat PU foam, observed with the composites containing 0.5% of PU10-GO1 and 1.0% of PU3-GO1. Mechanical performance was tested for each foam and showed that lower polyurethane content graphenic composites produced foams that were less susceptible to fatiguing and more durable over cyclic loading, while higher polyurethane content graphenic composites had mechanical stability similar to neat PU but initially had greater impact resistance. Taken together, these novel PU-GO fillers prepared from repurposed PU mattress show promise as a sustainable additive to improve PU performance.

Flat bands without twists: periodic holey graphene

Holey Graphene(HG) is a widely used graphene material for the synthesis of high-purity and highly crystalline materials. The electronic properties of a periodic distribution of lattice holes are explored here, demonstrating the emergence of flat bands. It is established that such flat bands arise as a consequence of an induced sublattice site imbalance, i.e. by having more sites in one of the graphene's bipartite sublattice than in the other. This is equivalent to the breaking of a path-exchange symmetry. By further breaking the inversion symmetry, gaps and a nonzero Berry curvature are induced, leading to topological bands. In particular, the folding of the Dirac cones from the hexagonal Brillouin zone (BZ) to the holey superlattice rectangular BZ of HG, with sizes proportional to an integerntimes the graphene's lattice parameter, leads to a periodicity in the gap formation such thatn≡0(mod 3). A low-energy hamiltonian for the three central bands is also obtained revealing that the system behaves as an effectiveα-T3graphene material. Therefore, a simple protocol is presented here that allows for obtaining flat bands at will. Such bands are known to increase electron-electron correlation effects. Therefore, the present work provides an alternative system that is much easier to build than twisted systems, allowing for the production of flat bands and potentially highly correlated quantum phases.

Environmental and health impacts of functional graphenic materials and their ultrasonically altered products

Graphenic materials have excited the scientific community due to their exciting mechanical, thermal, and optoelectronic properties for a potential range of applications. Graphene and graphene derivatives have demonstrated application in areas stretching from composites to medicine; however, the environmental and health impacts of these materials have not been sufficiently characterized. Graphene oxide (GO) is one of the most widely used graphenic derivatives due to a relatively easy and scalable synthesis, and the ability to tailor the oxygen containing functional groups through further chemical modification. In this paper, ecological and health impacts of fresh and ultrasonically altered functional graphenic materials (FGMs) were investigated. Model organisms, specifically Escherichia coli, Bacillus subtilis, and Caenorhabditis elegans, were used to assess the consequences of environmental exposure to fresh and ultrasonically altered FGMs. FGMs were selected to evaluate the environmental effects of aggregation state, degree of oxidation, charge, and ultrasonication. The major findings indicate that bacterial cell viability, nematode fertility, and nematode movement were largely unaffected, suggesting that a wide variety of FGMs may not pose significant health and environmental risks.

A Review on Silver Nanoparticles: Classification, Various Methods of Synthesis, and Their Potential Roles in Biomedical Applications and Water Treatment

Recent developments in nanoscience have appreciably modified how diseases are prevented, diagnosed, and treated. Metal nanoparticles, specifically silver nanoparticles (AgNPs), are widely used in bioscience. From time to time, various synthetic methods for the synthesis of AgNPs are reported, i.e., physical, chemical, and photochemical ones. However, among these, most are expensive and not eco-friendly. The physicochemical parameters such as temperature, use of a dispersing agent, surfactant, and others greatly influence the quality and quantity of the synthesized NPs and ultimately affect the material’s properties. Scientists worldwide are trying to synthesize NPs and are devising methods that are easy to apply, eco-friendly, and economical. Among such strategies is the biogenic method, where plants are used as the source of reducing and capping agents. In this review, we intend to debate different strategies of AgNP synthesis. Although, different preparation strategies are in use to synthesize AgNPs such as electron irradiation, optical device ablation, chemical reduction, organic procedures, and photochemical methods. However, biogenic processes are preferably used, as they are environment-friendly and economical. The review covers a comprehensive discussion on the biological activities of AgNPs, such as antimicrobial, anticancer anti-inflammatory, and anti-angiogenic potentials of AgNPs. The use of AgNPs in water treatment and disinfection has also been discussed in detail.

Selectively coupled small Pd nanoparticles on sp2-hybridized domain of graphene-based aerogel with enhanced catalytic activity and stability

The precisely coupling of metal nanoparticles with support domain are crucial to enhance the catalytic activity and stability of supported metal nanoparticle catalysts (MNPs). Here we selectively anchor Pd nanoparticles to the sp² domain in graphene-based aerogel constructed with base-washed graphene oxide (BGO) by removing oxidative debris (OD). The effects of OD on the size and chemical composition of Pd nanoparticles in aerogels are initially unveiled. The removal of OD nanoparticles prompt selective coupling of Pd nanoparticles to the exposed sp²-hybridized domain on BGO nanosheets, and then prevent it from agglomeration. As a result, the Pd nanoparticle size of self-assembled Pd/BGA is 4.67 times smaller than that of traditional Pd/graphene oxide aerogel (Pd/GA). The optimal catalytic activity of Pd/BGA for the model catalytic reduction of 4-nitrophenol is 15 times higher than that of Pd/GA. Pd/BGA could maintain its superior catalytic activity and achieves 98.72% conversion in the fifth cycle. The superior catalytic performance could be ascribed to the small Pd nanoparticles and high percentage of Pd(0) in Pd/BGA, and the enhanced electronic conductivity of Pd/BGA. These integrated merits of Pd/BGA as heterogeneous catalysts are attributed to selectively anchor Pd nanoparticles on sp²-hybridized domain of graphene-based aerogel, and strongly coupled interaction of MNPs with support. The structure-regulated BGO nanosheets could serve as versatile building blocks for fabricating MNPs/graphene aerogels with superior performance for catalytic transformation of water pollutants.