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1. Green Synthesis of Gold Nanoparticles Using Upland Cress and Their Biochemical Characterization and Assessment

   https://doi.org/10.3390/nano12010028  

   Hutchinson, Noah ; Wu, Yuelin ; Wang, Yale ; Kanungo, Muskan ; DeBruine, Anna ; Kroll, Emma ; Gilmore, De’Jorra ; Eckrose, Zachary ; Gaston, Stephanie ; Matel, Phoebe ; et al ( January 2022 , Nanomaterials)

   This article belongs to the Special Issue Synthesis and Applications of Gold Nanoparticles) Rodolphe Antoine (Ed.)

   This research focuses on the plant-mediated green synthesis process to produce gold nanoparticles (Au NPs) using upland cress (Barbarea verna), as various biomolecules within the upland cress act as both reducing and capping agents. The synthesized gold nanoparticles were thoroughly characterized using UV-vis spectroscopy, surface charge (zeta potential) analysis, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), atomic force microscopy (AFM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results indicated the synthesized Au NPs are spherical and well-dispersed with an average diameter ~11 nm and a characteristic absorbance peak at ~529 nm. EDX results showed an 11.13% gold content. Colloidal Au NP stability was confirmed with a zeta potential (ζ) value of −36.8 mV. X-ray diffraction analysis verified the production of crystalline face-centered cubic gold. Moreover, the antimicrobial activity of the Au NPs was evaluated using Gram-negative Escherichiacoli and Gram-positive Bacillus megaterium. Results demonstrated concentration-dependent antimicrobial properties. Lastly, applications of the Au NPs in catalysis and biomedicine were evaluated. The catalytic activity of Au NPs was demonstrated through the conversion of 4-nitrophenol to 4-aminophenol which followed first-order kinetics. Cellular uptake and cytotoxicity were evaluated using both BMSCs (stem) and HeLa (cancer) cells and the results were cell type dependent. The synthesized Au NPs show great potential for various applications such as catalysis, pharmaceutics, and biomedicine.

    

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2. Chelating Agent Functionalized Substrates for the Formation of Thick Films via Electrophoretic Deposition

   https://doi.org/10.3389/fchem.2021.703528  

   Mills, Sara C. ; Starr, Natalie E. ; Bohannon, Nicholas J. ; Andrew, Jennifer S. ( June 2021 , Frontiers in Chemistry)

   null (Ed.)

   Incorporating nanoparticles into devices for a wide range of applications often requires the formation of thick films, which is particularly necessary for improving magnetic power storage, microwave properties, and sensor performance. One approach to assembling nanoparticles into films is the use of electrophoretic deposition (EPD). This work seeks to develop methods to increase film thickness and stability in EPD by increasing film-substrate interactions via functionalizing conductive substrates with various chelating agents. Here, we deposited iron oxide nanoparticles onto conductive substrates functionalized with three chelating agents with different functional moieties and differing chelating strengths. We show that increasing chelating strength can increase film-substrate interactions, resulting in thicker films when compared to traditional EPD. Results will also be presented on how the chelating strength relates to film formation as a function of deposition conditions. Yield for EPD is influenced by deposition conditions including applied electric field, particle concentration, and deposition time. This work shows that the functionalization of substrates with chelating agents that coordinate strongly with nanoparticles (phosphonic acid and dopamine) overcome parameters that traditionally hinder the deposition of thicker and more stable films, such as applied electric field and high particle concentration. We show that functionalizing substrates with chelating agents is a promising method to fabricate thick, stable films of nanoparticles deposited via EPD over a larger processing space by increasing film-substrate interactions. 

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3. A High-Pressure System for Studying Oxygen Reduction During Pt Nanoparticle Collisions

   https://doi.org/10.1149/1945-7111/abcde2  

   Zhang, Yulun ; Robinson, Donald A. ; McKelvey, Kim ; Ren, Hang ; White, Henry S. ; Edwards, Martin A. ( December 2020 , Journal of The Electrochemical Society)

   Here we report measurements of the oxygen reduction reaction (ORR) at single Pt nanoparticles (NPs) through their collision with a Au microdisk electrode of lower electrocatalytic activity. Performing measurements at an elevated pressure (10-atm, pure O₂) raises the O₂concentration ∼50-fold over air-saturated measurements, allowing the ORR activity of smaller Pt NPs to be resolved and quantified, compared to measurements taken at atmospheric pressure. Single-NP ORR current vs potential measurements for 2.6, 16, and 24 nm radius citrate-capped Pt NPs, show the catalytic activity of the smallest Pt NPs to be roughly one order of magnitude greater than the activity of the larger NPs. The particle-by-particle nature of our measurement quantifies the distribution of electrocatalytic activities of individual particles, which we determine to be larger than can be explained by the distribution of particle sizes. Additionally, we report that some of the observed ORR current transients contain multiple sharp peaks per single-NP measurement, indicating multiple collisions of a single Pt NP at the electrode surface.

    

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4. Integration of Sequential Reactions in a Continuous Flow Droplet Reactor: A Route to Architecturally Defined Bimetallic Nanostructures

   https://doi.org/10.1002/ppsc.201900142  

   Santana, Joshua S. ; Gamler, Jocelyn T. L. ; Skrabalak, Sara E. ( August 2019 , Particle & Particle Systems Characterization)

   Microreactors for nanoparticle (NP) synthesis offer advantages over batch reactions in terms of scale‐up and integration with online analyses. Herein, two microreactors (i.e., a duo‐microreactor) are integrated to achieve sequential reactions for the synthesis of bimetallic NPs with architectural control. The generality of the duo‐microreactor is shown with the synthesis of branched Pd‐Pt NPs and core@shell Pd@Au NPs, both achieved by synthesizing Pd nanocubes in the first part of the duo‐microreactor and then using those nanocubes downstream as seeds for Pt or Au deposition. Control of the dimensions of these NPs is further demonstrated and achieved by tailoring metal precursor concentrations inline. This microreactor methodology is anticipated to be applicable to other bimetallic NP systems.

    

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5. Multilayer electrodeposition of Pt onto 1–2 nm Au nanoparticles using a hydride-termination approach

   https://doi.org/10.1039/d0nr02929g  

   Lapp, Aliya S. ; Crooks, Richard M. ( May 2020 , Nanoscale)

   Here we report on hydride-terminated (HT) electrodeposition of Pt multilayers onto ∼1.6 nm Au nanoparticles (NPs). The results build on our earlier findings regarding electrodeposition of a single monolayer of Pt onto Au NPs and reports relating to HT Pt electrodeposition onto bulk Au. In the latter case, it was found that electrodeposition of Pt from a solution containing PtCl 4 2− can be limited to a single monolayer of Pt atoms if it is immediately followed by adsorption of a monolayer of H atoms. The H-atom capping layer prevents deposition of Pt multilayers. In the present report we are interested in comparing the structure of NPs after multiple HT Pt electrodeposition cycles to the bulk analog. The results indicate that a greater number of HT Pt cycles are required to electrodeposit both a single Pt monolayer and Pt multilayers onto these Au NPs compared to bulk Au. Additionally, detailed structural analysis shows that there are fundamental differences in the structures of the AuPt materials depending on whether they are prepared on Au NPs or bulk Au. The resulting structures have a profound impact on formic acid oxidation electrocatalysis. 

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