Kinetics and Mechanism for the Reaction of Hexafluoroacetylacetone with CuO in Supercritical Carbon Dioxide

Abstract

A kinetic model and mechanism were developed for the heterogeneous chelation reaction of thin CuO films with hexafluoroacetylacetone (hfacH) in supercritical CO2. This reaction has relevance for processing nanoscale structures and, more importantly, serves as a model system to tune the reaction behavior of solids using supercritical fluids. Precise control over reaction conditions enabled accurate etching rates to be measured as a function of both temperature [(53.5-88.4) +/- 0.5 degrees C] and hfacH concentration (0.3-10.9 mM), yielding an apparent activation energy of 70.2 +/- 4.1 kJ/mol and an order of approximately 0.6 with respect to hfacH. X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the CuO surface, and a maximum etching rate of 24.5 +/- 3.1 A/min was obtained. Solvation forces between hfacH and the dense CO2 permitted material removal at temperatures more than 100 degrees C lower than that of the analogous gas-phase process. In the low concentration regime, the etching reaction was modeled with a three-step Langmuir-Hinshelwood mechanism. Small amounts of excess water nearly doubled the reaction rate through the proposed formation of a hydrogen-bonded hfacH complex in solution. Further increases in the hfacH concentration up to 27.5 mM caused a shift to first-order kinetics and an adsorption-limited or Rideal-Eley mechanism. These results demonstrate that relatively modest increases in concentration can prompt a heterogeneous reaction in supercritical CO2 to switch from a mechanism most commonly associated with a low-flux gas to one emblematic of a high-flux liquid.

Activation pathways taking place at molecular copper precatalysts for the oxygen evolution reaction

“…The signal at 933.3 eV is similar to that of CuO for which we find a binding energy of 933.4 eV (slightly higher values have been reported in literature: i.e. 933.9 eV [34], 933.7 eV [43], 933.8 eV [44]). The shake-up structure is mostly characteristic of CuO, except for the small but visible feature on the high binding energy side (about 942 eV), which is also present in the Apparently [Cu II (bdmpza) 2 ] slowly converts to CuO at 2.0 V versus RHE.…”

Green synthesis of copper oxide nanoparticles using gum karaya as a biotemplate and their antibacterial application

“…As shown in Figure 5B, the O 1s core-level spectrum is broad, and two O 1s peaks, at a lower energy of 529.5 eV, is in agreement with O 2− in CuO, while the other peak, at a higher energy of 531.6 eV, is attributed to O adsorbed on the surface of the CuO particles. 37 Thus, the XPS results indicate that the nanoparticles are composed of CuO. The strong shake-up satellites recorded in the CuO sample confirm the Cu 2+ oxidation state, and rule out the possibility of the existence of a Cu 2 O phase.…”

Synthesis of Novel CuO Nanosheets and Their Non-Enzymatic Glucose Sensing Applications

“…Figure 3(a) shows the combined XPS spectrum for the elements present in the prepared sample and it can be inferred those three distinct peaks at 284.00 and 531.00 eV are observed for C 1s, and O 1s respectively [53]. Moreover, the measured peaks at 933.30, 121.10 and 77.00 eV could be assigned to the Cu 2p, Cu 3s and Cu 3p respectively [54].…”