Origins of non-ideal behaviour in voltammetric analysis of redox-active monolayers.

Disorder in redox-active monolayers convolutes electrochemical characterization. This disorder can come from pinhole defects, loose packing, heterogeneous distribution of redox-active headgroups, and lateral interactions between immobilized redox-active molecules. Identifying the source of non-ideal behaviour in cyclic voltammograms can be challenging as different types of disorder often cause similar non-ideal cyclic voltammetry behaviour such as peak broadening, large peak-to-peak separation, peak asymmetry and multiple peaks for single redox processes. This Review provides an overview of ideal voltammetric behaviour for redox-active monolayers, common manifestations of disorder on voltammetric responses, common experimental parameters that can be varied to interrogate sources of disorder, and finally, examples of different types of disorder and how they impact electrochemical responses.

Proton-Coupled Electron Transfer at the Pu5+/4+ Couple.

The synthesis and solution and solid-state characterization of [Pu4+(NPC)4], 1-Pu, (NPC = [NPtBu(pyrr)2]-; tBu = C(CH3)3; pyrr = pyrrolidinyl) and [Pu3+(NPC)4][K(2.2.2.-cryptand)], 2-Pu, is described. Cyclic voltammetry studies of 1-Pu reveal a quasi-reversible Pu4+/3+ couple, an irreversible Pu5+/4+ couple, and a third couple evincing a rapid proton-coupled electron transfer (PCET) reaction occurring after the electrochemical formation of Pu5+. The chemical identity of the product of the PCET reaction was confirmed by independent chemical synthesis to be [Pu4+(NPC)3(HNPC)][B(ArF5)4], 3-Pu, (B(ArF5)4 = tetrakis(2,3,4,5,6-pentafluourophenyl)borate) via two mechanistically distinct transformations of 1-Pu: protonation and oxidation. The kinetics and thermodynamics of this PCET reaction are determined via electrochemical analysis, simulation, and density functional theory. The computational studies demonstrate a direct correlation between the changing nature of 5f and 6d orbital participation in metal-ligand bonding and the electron density on the Nim atom with the thermodynamics of the PCET reaction from Np to Pu, and an indirect correlation with the roughly 5-orders of magnitude faster Pu PCET compared to Np for the An5+ species.

Group 13 Lewis acid catalyzed synthesis of metal oxide nanocrystals via hydroxide transmetallation.

A new transmetallation approach is described for the synthesis of metal oxide nanocrystals (NCs). Typically, the synthesis of metal oxide NCs in oleyl alcohol is driven by metal-based esterification catalysis with oleic acid to produce oleyl oleate ester and M-OH monomers, which then condense to form MxOy solids. Here we show that the synthesis of Cu2O NCs by this method is limited by the catalytic ability of copper to drive esterification and thus produce Cu+-OH monomers. However, inclusion of 1-15 mol% of a group 13 cation (Al3+, Ga3+, or In3+) results in efficient synthesis of Cu2O NCs and exhibits size/morphology control based on the nature of M3+. Using a continuous-injection procedure where the copper precursor (Cu2+-oleate) and catalyst (M3+-oleate) are injected into oleyl alcohol at a controlled rate, we are able to monitor the reactivity of the precursor and M3+ catalyst using UV-visible and FTIR absorbance spectroscopies. These time-dependent measurements clearly show that M3+ catalysts drive esterification to produce M3+-OH species, which then undergo transmetallation of hydroxide ligands to generate Cu+-OH monomers required for Cu2O condensation. Ga3+ is found to be the "goldilocks" catalyst, producing NCs with the smallest size and a distinct cubic morphology not observed for any other group 13 metal. This is believed to be due to rapid transmetallation kinetics between Ga3+-OH and Cu+-oleate. These studies introduce a new mechanism for the synthesis of metal oxides where inherent catalysis by the parent metal (i.e. copper) can be circumvented with the use of a secondary catalyst to generate hydroxide ligands.

Simultaneous control of soil erosion and arsenic leaching at disturbed land using polyacrylamide modified magnetite nanoparticles.

Rapid urbanization and human disturbance of land often results in serious soil erosion and releases of fine sediments and soil-bound toxic metals/metalloids. Yet, technologies for simultaneously controlling soil erosion and metals/metalloids leaching have been lacking. This study developed a new class of polyacrylamide-dispersed magnetite (PAM-MAG) nanoparticles and tested the effectiveness for simultaneous control of soil erosion and arsenic leaching from a model soil. Two parallel box test setups (L × W × H: 91.4 × 30.5 × 7.6 cm) were constructed to test the releases of sediments and soluble pollutants from the surface soil under simulated rainfall conditions (intensity = 11.15 cm/hr). A sandy loam soil from a local quarry mining site was used as the model soil, and arsenate As(V) as a prototype leachable metalloid. A stable dispersion of PAM-MAG was prepared with 0.3 wt% of PAM and 0.1 g/L as Fe of magnetite. The results indicated that treating the soil with 5.985 g/m2 of PAM-MAG was able to decrease cumulative soil mass loss in the runoff by 90.8% (from 254.50 ±â€¯0.10 g to 23.35 ±â€¯3.19 g), or turbidity of the runoff by 79.9% (from 244.5 ±â€¯27.5 NTU to 49.2 ±â€¯22.5 NTU). Compared to PAM only, the PAM-MAG suspension showed a 30% reduction of viscosity, allowing for easier application and transport of the nanoparticles in soil. Concurrently, the PAM-MAG treatment also immobilized 82.5% of water-leachable arsenate compared to untreated controls. Fourier-transform infrared (FTIR) spectroscopy analyses revealed that arsenate was immobilized by magnetite nanoparticles through inner sphere surface complexation (Fe-O-As). Overall, the PAM-MAG based technology holds the promise for simultaneously controlling soil erosion and metal/metalloid releases from disturbed land.