High electrochemical detection of dopamine based on Cu doped single phase hexagonally ZnO plates

Dopamine is a chemical that plays a key role in various neurological diseases such as Parkinson's, depression, and some types of cancer. Hence, sensitive detection methods of dopamine are necessary for early discernment of diseases related to abnormal levels. In this study, Cu doped ZnO (Cu/ZnO) nanostructures, immobilized onto the surface of glassy carbon electrode (GCE), have been investigated as a highly efficient electrode material for the electrochemical detection of dopamine (DA). A simple hydrothermal process was used for the synthesis of the ZnO and Cu/ZnO nanostructures. Detailed characterization revealed that addition of Cu on the ZnO changed the morphology of ZnO creating a highly microporous nanostructure. The electrochemical response of DA on the Cu/ZnO/GC electrodes, determined using cyclic voltammetry (CV) and differential pulsed voltammetry (DPV), indicated that on these materials it is possible to achieve lower over-potentials for the DA oxidation and higher catalytic activity. Furthermore, the GCE modified with 50 % Cu doped ZnO showed the most promising performance with high stability in wide range of pH values (2–8 pH), and linear response for DA from 0.1–20 μM with high sensitivity of 2630 nA/μM and detection limit as low as 55 nM. The analytical performance of the developed sensor showed its potential capability for the DA quantification in complex biological systems

Stimulus-Responsive Control of Transition States on Nanohybrid Polymer-Metal Catalysts

In designing effective catalysts, one must consider how to control the accessibility and activity of the active sites. Inspired by nature, we have leveraged the chemistry of thermoresponsive poly(N-isopropylacrylamide) (p-NIPAM) to tailor the extent of solvation of the transition state key surface reaction intermediates during the hydrogenation of nitrobenzene to aniline on Pd/SiO2. Detailed reaction kinetics, catalyst characterization, and NMR diffusion-ordered spectroscopy (DOSY)/nuclear Overhauser effect spectroscopy (NOESY) experiments indicate that nitrobenzene reduction is co-limited by both the formation and the hydrodeoxygenation of phenylhydroxylamine (PHA) to aniline (AN) precursor. Transition-state treatment of the kinetic data revealed that when the temperature is below the lower critical solution temperature (LCST) of p-NIPAM (32 °C), the apparent enthalpy of activation decreases 3-fold. This change was attributed to the drop in the apparent enthalpy of activation when the polymer was in a swollen state. A concomitant reduction in the apparent entropy of activation was obtained at these conditions, indicative of losses in the degree of freedom of the kinetically relevant intermediate (i.e., surface hydrogen). At temperatures above the LCST, it was possible to reverse these effects, leading to similar apparent activation energy as that observed in the Pd/SiO2 catalyst. These results establish the foundational work on the development of materials capable of taming the intrinsic activity of the active site in a fast, reversible manner. We envision that these results will facilitate the development of catalysts that can mimic the homeostatic behavior of enzymes, allowing more stable operation even when complex feedstocks are employed (e.g., biomass conversion and pollution control)

Inhibition caused by adsorption of organic micropollutants (MPs) on PES@CoFe2O4 polymeric ultrafiltration membranes and the enhanced MPs degradation by a continuous pH regulation

In this work, catalytic membranes were fabricated by blending CoFe2O4 catalysts into polyethersulfone (PES) and then used to treat naproxen with the addition of peroxymonosulfate (PMS). It was found that the addition of PMS results in a decrease in pH, which increases the adsorption of naproxen. This often overlooked phenomenon is demonstrated here to have an important role since the adsorption of naproxen on the polymeric matrix and catalytic particles decreases the degradation efficiency of naproxen. To verify this hypothesis and rule out the decrease in pH after the addition of pH, two ways of controlling the pH of the naproxen solution were compared: adjusting pH before and after the addition of PMS, respectively. Our results indicate that in the batch experiment, adjusting the pH of naproxen solution after adding PMS led to a dramatic 23-fold increase in the kinetic constant of the naproxen oxidation (0.42/min, pH6) compared to when pH was adjusted before adding PMS (0.018/min, pH 6). This enhancement in the overall kinetics was attributed to the elimination of the inhibition caused by MPs adsorption at low pH. In a dead-end cell, the catalytic membranes with 2.0 % of CoFe2O4 achieved quantitative conversion of naproxen, bisphenol A, and atrazine, with values of 98 %, 97 %, and 74 %, respectively, demonstrating the efficacy of this approach to convert multitype of MPs in wastewater streams. In a reusability study, the naproxen removal of the catalytic membranes with 2.0 % of CoFe2O4 decreased by 81 % and 45 % after 5 rounds in the batch experiment and dead-end cell, respectively. However, with a chemical cleaning process between each round, the degradation efficiency can be effectively recovered, proving the negative effects of the adsorption of MPs or their intermediates during the SR-AOPs. Our work demonstrates that pH in SR-AOP-based catalytic membrane processes determined both the reaction rate and the adsorption of MPs or their intermediates on the membrane and its reactive sites. We envision that these results will be valuable in developing efficient catalytic membranes for the treatment of MPs in wastewater streams

Proton shuttling flattens the energy landscape of nitrite catalytic reduction

Water molecules can enhance or inhibit hydrogenation reactions depending on the nature of the reactive species and active sites. In metal-catalyzed nitrite (NO2–) reduction the presence of protons is essential to complete the reaction in the aqueous phase. By coupling rigorous kinetics studies of nitrite hydrogenation on Pd with kinetic isotope studies and theoretical calculations we have shown that, contrary to previously proposed mechanisms of surface H-insertion on NO*, in aqueous environments the reaction proceeds via H-shuttling in which protons move via the aqueous environment while the electrons reach the NO* through the metal in a concerted fashion. This unique mechanism flattens the energy landscape, which leads to the same apparent activation energy barrier (0.6 eV) for the formation of HNO* and HNOH*. These results are consistent with the hydrogen reaction orders, kinetic isotopic experiments, and micro-kinetic modeling including co-limiting reaction steps for NO* hydrogenation to HNO* and HNOH*. This work provides new insights that will be key in developing more efficient catalysts and processes for catalytic removal of micro-pollutants, such as nitrate and nitrite, in drinking water and more broadly to hydrogenation reactions in aqueous phase

Stimulus-Responsive Control of Transition States on Nanohybrid Polymer–Metal Catalysts

In designing effective catalysts, one must consider how to control the accessibility and activity of the active sites. Inspired by nature, we have leveraged the chemistry of thermoresponsive poly(N-isopropylacrylamide) (p-NIPAM) to tailor the extent of solvation of the transition state key surface reaction intermediates during the hydrogenation of nitrobenzene to aniline on Pd/SiO2. Detailed reaction kinetics, catalyst characterization, and NMR diffusion-ordered spectroscopy (DOSY)/nuclear Overhauser effect spectroscopy (NOESY) experiments indicate that nitrobenzene reduction is co-limited by both the formation and the hydrodeoxygenation of phenylhydroxylamine (PHA) to aniline (AN) precursor. Transition-state treatment of the kinetic data revealed that when the temperature is below the lower critical solution temperature (LCST) of p-NIPAM (32 °C), the apparent enthalpy of activation decreases 3-fold. This change was attributed to the drop in the apparent enthalpy of activation when the polymer was in a swollen state. A concomitant reduction in the apparent entropy of activation was obtained at these conditions, indicative of losses in the degree of freedom of the kinetically relevant intermediate (i.e., surface hydrogen). At temperatures above the LCST, it was possible to reverse these effects, leading to similar apparent activation energy as that observed in the Pd/SiO2 catalyst. These results establish the foundational work on the development of materials capable of taming the intrinsic activity of the active site in a fast, reversible manner. We envision that these results will facilitate the development of catalysts that can mimic the homeostatic behavior of enzymes, allowing more stable operation even when complex feedstocks are employed (e.g., biomass conversion and pollution control)

Stimulus-Responsive Control of Transition States on Nanohybrid Polymer–Metal Catalysts

In designing effective catalysts, one must consider how to control the accessibility and activity of the active sites. Inspired by nature, we have leveraged the chemistry of thermoresponsive poly(N-isopropylacrylamide) (p-NIPAM) to tailor the extent of solvation of the transition state key surface reaction intermediates during the hydrogenation of nitrobenzene to aniline on Pd/SiO2. Detailed reaction kinetics, catalyst characterization, and NMR diffusion-ordered spectroscopy (DOSY)/nuclear Overhauser effect spectroscopy (NOESY) experiments indicate that nitrobenzene reduction is co-limited by both the formation and the hydrodeoxygenation of phenylhydroxylamine (PHA) to aniline (AN) precursor. Transition-state treatment of the kinetic data revealed that when the temperature is below the lower critical solution temperature (LCST) of p-NIPAM (32 °C), the apparent enthalpy of activation decreases 3-fold. This change was attributed to the drop in the apparent enthalpy of activation when the polymer was in a swollen state. A concomitant reduction in the apparent entropy of activation was obtained at these conditions, indicative of losses in the degree of freedom of the kinetically relevant intermediate (i.e., surface hydrogen). At temperatures above the LCST, it was possible to reverse these effects, leading to similar apparent activation energy as that observed in the Pd/SiO2 catalyst. These results establish the foundational work on the development of materials capable of taming the intrinsic activity of the active site in a fast, reversible manner. We envision that these results will facilitate the development of catalysts that can mimic the homeostatic behavior of enzymes, allowing more stable operation even when complex feedstocks are employed (e.g., biomass conversion and pollution control)