3d transition metal oxides composed of Mn, Fe, Co, and Ni have emerged as promising candidates for supercapacitor electrode materials due to their high theoretical specific capacitance, abundant redox-active sites, variable oxidation states, environmental friendliness, and low cost. Various synthesis strategies have been developed to fabricate these nanostructures, including hydrothermal/solvothermal methods, sol–gel processing, and microwave-assisted synthesis. Among them, microwave irradiation technology, with its rapid heating characteristics and unique thermal/non-thermal effects, offers significant advantages in controlling crystallinity and particle size distribution, suppressing particle agglomeration, and enhancing material purity. Furthermore, microwave effects facilitate the self-assembly and morphological evolution of transition metal oxides, promote the formation of crystal defects, and strengthen interfacial interactions. These effects enable precise microstructural tuning, leading to an increased specific surface area and a higher density of active sites, ultimately enhancing specific capacitance, rate capability, and cycling stability. In recent years, microwave-assisted synthesis has made significant progress in constructing 3d transition metal oxides and their composites, particularly in the development of single-metal and binary-metal oxides, as well as their hybrids with carbon-based materials (e.g., graphene and carbon nanotubes) and other metal oxides. This review systematically summarizes the research progress on microwave-assisted techniques for 3d transition metal oxide-based nanomaterials, with a particular focus on the role of microwave effects in morphology control, interfacial optimization, and electrochemical performance enhancement. Additionally, key challenges in current research are critically analyzed, and potential optimization strategies are proposed. This review aims to provide new insights and perspectives for advancing microwave-assisted synthesis of 3d transition metal oxides in energy storage applications.

$$q$$ q -rung orthopair fuzzy sets ( $$q$$ q -ROFSs), as a generalization of intuitionistic fuzzy sets (IFSs) and Pythagorean fuzzy sets (PFSs), can depict uncertain attitudes more flexibly and bear decision information more extensively. Innumerable fuzzy assessment verdicts that exceed IFSs or PFSs can be captured by $$q$$ q -ROFSs. To make the evaluation process more adaptive, in this article, we explore the application of $$q$$ q -ROFSs to multiattribute group decision making (MAGDM) by employing the technique for order preference by similarity to ideal solution (TOPSIS) approach. In view of the comprehensive tool of projection method for measuring the proximity of decision vectors, we further propose innovative bidirectional normalized projection measures that consider not only distance but also spatial angle to replace traditional distance measures such as Hamming and Euclidean. A new extension of TOPSIS methodology is then addressed in the context of MAGDM with $$q$$ q -ROFSs, which eliminates the transformation and aggregation steps to ensure less information loss. At length, the effectiveness and superiority of the proposed framework are demonstrated by an example of ship equipment reliability evaluation with comparative analysis, and future research directions are also suggested.

This study investigated the temporal appearance of CO₂-derived signals and qualitative spectral differences between rich and lean phases in a diethylenetriamine (DETA)/dimethyl sulfoxide (DMSO)/H₂O (DTSO) biphasic absorbent using FTIR, time-series and phase-separated ¹³C NMR, and DFT calculations. CO₂ reacted mainly with DETA, forming carbamate-related species. The earliest detectable CO₂-derived carbonyl signal appeared at 10 min and was tentatively assigned to a terminal mono-carbamate-related environment. Additional overlapping resonances attributable to candidate carbamate environments appeared as absorption progressed. Phase-separated ¹³C NMR showed carbonyl signals in both phases. Preliminary internal-standard estimates indicated a higher amount associated with the selected DETA-related signal in the analyzed rich-phase aliquot and a slightly higher amount associated with the selected DMSO-related signal in the lean-phase aliquot. However, these estimates do not establish a complete mass balance or quantitative partition coefficients. At the original B3LYP/SMD(H₂O) level, terminal-site candidates had lower calculated relative Gibbs free energies than corresponding central-site candidates. Representative ion-associated structures exhibited N–H···O contacts geometrically consistent with hydrogen bonding, although the relative electronic-energy ordering of the ion-pair models was sensitive to D3(BJ) dispersion treatment. Therefore, the calculations provide a model-dependent comparison of candidate-structure stability, not definitive predictions of solution-phase species populations or ion-pair formation.