Browsing by Author "Hossain, M. S. A."
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Item Open Access Continuous mesoporous pd films by electrochemical deposition in nonionic micellar solution(American Chemical Society, 2017) Iqbal, M.; Li C.; Wood, K.; Jiang B.; Takei, T.; Dag, Ö.; Baba, D.; Nugraha, A. S.; Asahi, T.; Whitten, A. E.; Hossain, M. S. A.; Malgras, V.; Yamauchi, Y.Mesoporous metals that combine catalytic activity and high surface area can provide more opportunities for electrochemical applications. Various synthetic methods, including hard and soft templating, have been developed to prepare mesoporous/nanoporous metals. Micelle assembly, typically involved in soft-templates, is flexible and convenient for such purposes. It is, however, difficult to control, and the ordering is significantly destroyed during the metal deposition process, which is detrimental when it comes to designing precisely mesostructured materials. In the present work, mesoporous Pd films were uniformly electrodeposited using a nonionic surfactant, triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide), as a pore-directing agent. The interaction between micelles and metal precursors greatly influences the metal growth and determines the final structure. The water-coordinated species interact with the ethylene oxide moiety of the micelles to effectively drive the Pd(II) species toward the working electrode surface. From small-angle neutron scattering data, it is found that spherical P123 micelles, with an average diameter of ∼14 nm, are formed in the electrolyte, and the addition of Pd ions does not significantly modify their structure, which is the essence of the micelle assembly approach. The uniformly sized mesopores are formed over the entire mesoporous Pd film and have an average pore diameter of 10.9 nm. Cross-sectional observation of the film also shows mesopores spanning continuously from the bottom to the top of the film. The crystallinity, crystal phase, and electronic coordination state of the Pd film are also confirmed. Through this study, it is found that the optimized surfactant concentration and applied deposition potential are the key factors to govern the formation of homogeneous and well-distributed pores over the entire film. Interestingly, the as-prepared mesoporous Pd films exhibit superior electrocatalytic activity toward the ethanol oxidation reaction by fully utilizing the accessible active surface area. Our approach combines electrochemistry with colloidal and coordination chemistry and is widely applicable to other promising metals and alloy electrocatalysts.Item Open Access Electrochemical synthesis of mesoporous architectured Ru films using supramolecular templates(Wiley-VCH Verlag, 2020) Kani, K.; Henzie, J.; Dağ, Ömer; Wood, K.; Iqbal, M.; Lim, H.; Jiang, B.; Salomon, C.; Rowan, A. E.; Hossain, M. S. A.; Na, J.; Yamauchi, Y.The electrochemical synthesis of mesoporous ruthenium (Ru) films using sacrificial self‐assembled block polymer micelles templates, and its electrochemical surface oxidation to RuOx is described. Unlike standard methods such as thermal oxidation, the electrochemical oxidation method described here retains the mesoporous structure. Ru oxide materials serve as high‐performance supercapacitor electrodes due to their excellent pseudocapacitive behavior. The mesoporous architectured film shows superior specific capacitance (467 F g−1 Ru) versus a nonporous Ru/RuOx electrode (28 F g−1 Ru) that is prepared via the same method but omitting the pore‐directing polymer. Ultrahigh surface area materials will play an essential role in increasing the capacitance of this class of energy storage devices because the pseudocapacitive redox reaction occurs on the surface of electrodes.Item Open Access First synthesis of continuous mesoporous copper films with uniformly sized pores by electrochemical soft templating(Wiley-VCH Verlag, 2016) Li C.; Jiang B.; Wang, Z.; Li Y.; Hossain, M. S. A.; Kim, J. H.; Takei, T.; Henzie, J.; Dag, Ö.; Bando, Y.; Yamauchi, Y.Although mesoporous metals have been synthesized by electrochemical methods, the possible compositions have been limited to noble metals (e.g., palladium, platinum, gold) and their alloys. Herein we describe the first fabrication of continuously mesoporous Cu films using polymeric micelles as soft templates to control the growth of Cu under sophisticated electrochemical conditions. Uniformly sized mesopores are evenly distributed over the entire film, and the pore walls are composed of highly crystalized Cu.Item Open Access Mesoporous metallic rhodium nanoparticles(Nature Publishing Group, 2017) Jiang B.; Li C.; Dag, Ö.; Abe, H.; Takei, T.; Imai, T.; Hossain, M. S. A.; Islam, M. T.; Wood, K.; Henzie, J.; Yamauchi, Y.Mesoporous noble metals are an emerging class of cutting-edge nanostructured catalysts due to their abundant exposed active sites and highly accessible surfaces. Although various noble metal (e.g. Pt, Pd and Au) structures have been synthesized by hard- and soft-templating methods, mesoporous rhodium (Rh) nanoparticles have never been generated via chemical reduction, in part due to the relatively high surface energy of rhodium (Rh) metal. Here we describe a simple, scalable route to generate mesoporous Rh by chemical reduction on polymeric micelle templates [poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA)]. The mesoporous Rh nanoparticles exhibited a ∼1/42.6 times enhancement for the electrocatalytic oxidation of methanol compared to commercially available Rh catalyst. Surprisingly, the high surface area mesoporous structure of the Rh catalyst was thermally stable up to 400 °C. The combination of high surface area and thermal stability also enables superior catalytic activity for the remediation of nitric oxide (NO) in lean-burn exhaust containing high concentrations of O 2.Item Open Access Symmetry-Breaking Plasmonic Mesoporous Gold Nanoparticles with Large Pores(American Chemical Society, 2022-08-23) Nugraha, A. S.; Guselnikova, O.; Henzie, J.; Na, J.; Hossain, M. S. A.; Dag, Ömer; Rowan, A.; Yamauchi, Y.Creating free-standing gold nanoparticles (Au NPs) with large pores is desirable because the exterior and interior voids can enhance electrocatalytic activity, mass transport, and optical extinction properties. However, the high mobility and significant positive reduction potential of Au precursors make it challenging to create Au NPs with pores of sufficient size to strongly interact with light. We demonstrate a method to synthesize mesoporous Au NPs with large, tunable pores. l-Cysteine acts as a metallogelator to form a dense, less mobile Au(I)-thiolate precursor that traps aggregated block copolymer micelles and facilitates the reduction of mesoporous Au NPs. Electron tomography measurements showed that the pores were distributed throughout the interior and exterior of the particle. Electrochemical methods were used to estimate the chemical reactivity of the surface active sites and estimate the accessible surface area of the pores to ensure that the metal surfaces were maximally accessible to the environment. The 3D models generated by tomography were then used to simulate their optical properties. Mesoporous Au NPs support multipolar plasmon resonances that penetrate deep into the interior pores of the NP. A simple model indicates that porosity affects the local optical conductivity of the NP by subdividing it into tiny nanoscale junctions that redshift the plasmon modes without changing the overall size or shape of the NPs. Large pores promote symmetry breaking, causing the quadrupolar and dipolar modes to overlap and form strongly hybridized plasmon modes. In the context of photocatalysis, porosity-induced symmetry breaking is advantageous because strong electric fields of the plasmon are colocalized along concave/convex features where step-edges and kinks in the atomic structure generate numerous catalytic active sites. Plasmon-enhanced photodegradation of metanil yellow was used to demonstrate the superior photocatalytic properties of meso Au NPs versus nonporous Au NPs.