A descriptor of active CuO-ZnO(Al₂O₃) methanol-synthesis and water–gas-shift catalysts is the presence of high-temperature carbonates (HT-CO₃) in the oxidic catalyst precursor. Previous reports have shown that such HT-CO₃ lead to an appropriate interaction between the oxides; as a result, a high Cu surface area (or Cu-Zn or Cu/ZnO interphase areas) can be achieved. Yet, their nature is not well understood. In this study, the nature of these carbonates was investigated by experimental and theoretical methods in the oxidic precatalyst. A calcined Cu-Zn-Al hydrotalcite model compound revealed to have well-dispersed ZnO and CuO phases, together with highly stable HT-CO₃. It was hypothesized that these HT-CO₃ groups may be placed at critical locations at nano-scale as a glue, thus avoiding the growth of the oxide crystallites during calcination. This is an excellent pre-condition to achieve a high Cu surface area (or Cu-Zn or Cu/ZnO interphase areas) upon reduction, and therefore a high activity. To prove that, first-principles calculations were carried out based on the density functional theory (DFT); alumina was not considered in the model as the experimental data showed it to be amorphous but it may still have an effect. Comprehensive calculations provided evidence that such carbonate groups favourably bind the CuO and ZnO together at the interface, rather than being isolated on the individual oxide surfaces. The results strongly suggest that the HT-CO₃ groups are part of the structure, in the calcined precatalyst, where they would prevent thermal sintering through a bonding mechanism between CuO and ZnO particles, which is a novel interpretation of this important catalyst descriptor.

The type and loading level of oxygen-containing functional groups on graphene oxide (GO) nanosheets significantly affect the size and alignment of nanochannels formed between the GO nanosheets and the separation performance of laminar GO membranes. Here, we demonstrate how double-oxidation of GO leads to the higher surface charge of GO nanosheets, the formation of highly stable water-based GO solution, more-ordered deposition of GOs on the polyethersulfone membrane through the pressure-assisted self-assembly method, and the formation of highly durable GO membranes possessing smoother surface morphology and higher antifouling properties. A multi-technique investigation was applied to follow the physicochemical difference between GO and double-oxidized GO, and the physical stability and separation performance of the corresponding membranes using experimental and computational studies. The double-oxidized GO-based membranes provided a significantly high water flux of 230 L/(m².h) in 2.5 bar transmembrane pressure, excellent rejection of 99.9% for methylene blue (MB) dye, and outstanding separation performance stability over time. In contrast, GO membranes showed rejection of 81.5% for MB, and their separation performance diminished significantly over time. The antifouling properties of double-oxidized GO membranes were substantially higher (∼ four times) due to their higher negative surface charge and smoother surface morphology. The density functional theory (DFT) was used to gain insight into the interactions between the functional groups and the reasoning for the higher mechanical stability of double-oxidized GO membranes. Results revealed that the formation energy of GO decreases by increasing the number density of functional groups. It was also found that a higher number of carboxyl groups at the edges of the double-oxidized GO leads to higher hydrogen bonding, higher binding energy, and a more stable GO-membrane structure.