Decorating Mg12O12 Nanocage with Late First-Row Transition Metals To Act as Single-Atom Catalysts for the Hydrogen Evolution Reaction.

In the pursuit of sustainable clean energy sources, the hydrogen evolution reaction (HER) has attained significant interest from the scientific community. Single-atom catalysts (SACs) are among the most promising candidates for future electrocatalysis because they possess high thermal stability, effective electrical conductivity, and excellent percentage atom utilization. In the present study, the applicability of late first-row transition metals (Fe-Zn) decorated on the magnesium oxide nanocage (TM@Mg12O12) as SACs for the HER has been studied, via density functional theory. The late first-row transition metals have been chosen as they have high abundance and are relatively low-cost. Among the studied systems, results show that the Fe@Mg12O12 SAC is the best candidate for catalyzing the HER reaction as it exhibits the lowest activation barrier for HER. Moreover, Fe@Mg12O12 shows high stability (Eint = -1.64 eV), which is essential in designing SACs to prevent aggregation of the metal. Furthermore, the results of the electronic properties' analysis showed that the HOMO-LUMO gap of the nanocage is decreased significantly upon doping of Fe (from 4.81 to 2.28 eV), indicating an increase in the conductivity of the system. This study highlights the potential application of the TM@nanocage SAC systems as effective HER catalysts.

Removal of methylene blue by using sodium alginate-based hydrogel; validation of experimental findings via DFT calculations.

Removal of commonly used dyes from water bodies has recently gained great interest from the scientific community. Presence of the methylene blue (MB) dye in drinking water poses harmful effects on the human health. The large-scale removal of MB is achievable through highly efficient, inexpensive, renewable, and biodegradable adsorbents. Our research group has recently synthesized a sodium alginate-based hydrogel and explored its application towards the removal of MB. Previous results have shown that the synthesized hydrogel exhibits a high adsorption capacity of 51.34 mg/g under basic conditions. Herein, we employed the density functional theory (DFT) calculations to explore the mechanism of MB removal by using sodium alginate hydrogel at various pH levels. Results of this study have shown that under acidic/neutral conditions the removal of MB is endergonic (ΔGint = 6.10 kcal/mol). Whereas under basic conditions it is highly exergonic (ΔGint = -97.58 kcal/mol). Moreover, the QTAIM and NCI analyses have shown that the MB dye is chemisorbed to the absorbent via strong covalent-like interactions between the polymer's carboxylate groups and the hydrogens in MB. Furthermore, preferability of basic conditions have been confirmed by the large charge transfer (0.104 |e|), as compared to no charge being transferred in the acidic/neutral conditions.