Orbital-Resolved DFT+U for Molecules and Solids

We present an orbital-resolved extension of the Hubbard U correction to density-functional theory (DFT). Compared to the conventional shell-averaged approach, the prediction of energetic, electronic and structural properties is strongly improved, particularly for compounds characterized by both localized and hybridized states in the Hubbard manifold. The numerical values of all Hubbard parameters are readily obtained from linear-response calculations. The relevance of this more refined approach is showcased by its application to bulk solids pyrite (FeS2) and pyrolusite (β-MnO2), as well as to six Fe(II) molecular complexes. Our findings indicate that a careful definition of Hubbard manifolds is indispensable for extending the applicability of DFT+U beyond its current boundaries. The present orbital-resolved scheme aims to provide a computationally undemanding yet accurate tool for electronic structure calculations of charge-transfer insulators, transition-metal (TM) complexes and other compounds displaying significant orbital hybridization.

Enhancement of the photocatalytic activity of rGO/NiO/Ag nanocomposite for degradation of methylene blue dye

The current study focuses on boosting the photocatalytic ability of reduced graphene oxide (rGO) by decorating the rGO nano-sheets with nickel oxide (NiOx) and silver (Ag) nanomaterials. The developed ternary nanomaterials were investigated using FTIR, XRD, FESEM, TEM, Raman, and UV-vis to evaluate the photo-degradation process. The rGO/NiOx/Ag ternary system showed promising photocatalytic dye degradation under simulated sunlight irradiance. The addition of NiOx and Ag nanomaterials widened the catalytic activity spectrum from the visible region to the UV-region. Besides, these materials hindered the electron-hole recombination, boosting the catalytic activity. The reusability results also clearly showed that the synthesized ternary nanomaterials have good reproducibility and stability for photocatalytic degradation of industrial wastewater.

Morphological reduction of Fe3O4 by single step hydrothermal synthesis using 1D MnO2 as a template and its supercapacitive behaviour

Nanomaterials have attracted wide attention due to its promising characteristics in contrast to its bulk counterpart. However, its synthesis techniques need to be explored further for its employability in the...

Polymorphic Effects on Electrochemical Performance of Conversion-Based MnO2 Anode Materials for Next-Generation Li Batteries

In this study, four different MnO₂ polymorphs are synthesized with a controlled morphology of hollow porous structures to systematically investigate the influences of polymorphs in conversion-based material. As the structure of these materials transforms into nanosized metal and maintains an extremely low-crystalline phase during cell operation, the effects of polymorphs are overlooked as compared to the case of insertion-based materials. Thus, differences in the ion storage behaviors among various MnO₂ polymorphs are not well identified. Herein, the structural changes, charge storage reaction, and electrochemical performance of the different MnO₂ polymorphs are investigated in detail. The experimental results demonstrate that the charge storage reactions, as part of which spinel-phased MnO₂ formation is observed after lithiation and delithiation instead of recovery of the original phases, are similar for all the samples. However, the electrochemical performance varies depending on the initial crystal structure. Among the four polymorphs, the spinel-type λ-MnO₂ delivers the highest reversible capacity of ≈1270 mAh g^-1 . The structural similarity between the cycled and pristine states of λ-MnO₂ induces faster kinetics, resulting in the better electrochemical performance. These findings suggest that polymorphs are another important factor to consider when designing high-performance materials for next-generation rechargeable batteries.

Structural-Phase Catalytic Redox Reactions in Energy and Environmental Applications

The structure-property engineering of phase-based materials for redox-reactive energy conversion and environmental decontamination nanosystems, which are crucial for achieving feasible and sustainable energy and environment treatment technology, is discussed. An exhaustive overview of redox reaction processes, including electrocatalysis, photocatalysis, and photoelectrocatalysis, is given. Through examples of applications of these redox reactions, how structural phase engineering (SPE) strategies can influence the catalytic activity, selectivity, and stability is constructively reviewed and discussed. As observed, to date, much progress has been made in SPE to improve catalytic redox reactions. However, a number of highly intriguing, unresolved issues remain to be discussed, including solar photon-to-exciton conversion efficiency, exciton dissociation into active reductive/oxidative electrons/holes, dual- and multiphase junctions, selective adsorption/desorption, performance stability, sustainability, etc. To conclude, key challenges and prospects with SPE-assisted redox reaction systems are highlighted, where further development for the advanced engineering of phase-based materials will accelerate the sustainable (active, reliable, and scalable) production of valuable chemicals and energy, as well as facilitate environmental treatment.

Effects of electrodeposition time on a manganese dioxide supercapacitor

As is well known that the specific capacitance of supercapacitors cannot be improved by increasing the mass of the deposited MnO₂ films, which means an appropriate deposition duration is important. In this study, nanobelt-structured MnO₂ films were prepared by the electrochemical deposition method under different deposition time to explore the effects of electrodeposition time change on the microstructure and electrochemical properties of this material. Benefiting from the microstructure of the MnO₂ films, the transfer properties of the charged electrons and ions were promoted. Meanwhile, a 3D porous nickel foam was chosen as the deposition substrate, which rendered an enhancement of the MnO₂ conductivity and the mass of the active material. The enhanced specific capacitance and specific surface area attributed to synergistic reactions. Subsequently, the electrochemical performances of the as-prepared materials were analyzed via cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) tests. Results show that the optimum sample deposited for 50 s has a specific capacitance of 291.9 F g⁻¹ at the current density of 1 A g⁻¹ and lowest R_ct. However, its electrochemical stability cannot come up to the level of the 300 s sample due to the microstructure change.

As is well known that the specific capacitance of supercapacitors cannot be improved by increasing the mass of the deposited MnO₂ films, which means an appropriate deposition duration is important.

Incorporating Pb2+ Templates into the Crystalline Structure of MnO2 Catalyst Supported on Monolith Applications in H2O2 Decomposition

Several MnO₂ catalysts, promoted with Pb²⁺ ions and supported on a wash-coated monolith (WMon), briefly, xPbyMn-WMon (x = 0, 0.5, 1.0, 1.5, 2, and 2.5 and y = 8 wt %), were prepared. The presence of Pb²⁺ affects the manganese oxidation state, crystalline phase, thermal resistance, metal dispersion, and catalytic performance. According to XPS spectra, XRD patterns and HRTEM images, manganese was dispersed on the monolith surface as Mn³⁺ and Mn⁴⁺ species in both α and β crystalline phases. The ratios of Mn⁴⁺/Mn³⁺ states and α/β phases were highly enhanced, and the desired Pb _x Mn₈O₁₆ phase (coronadite) was formed. Concentrations of the defect oxygen (Mn-O-H) and oxygen vacancies, which improve the catalyst reducibility and the MnO₂ reduction temperature, were also increased. Further, based on the H₂ chemisorption analysis, the Pb²⁺ template would increase the manganese dispersion and the reaction sites. Meanwhile, the average MnO₂ crystallite size was decreased from 13.26 to 8.15 nm. The optimum catalyst 1.5Pb8Mn-WMon exhibited an activity 149% more than the manganese-only catalyst in decomposition of H₂O₂. Evaluation of catalyst stability in the presence of Pb²⁺ after 10 recycles showed only a 6.8% decrease. The catalytic reaction was evaluated based on different criteria.

Multi-functional MnO2 nanomaterials for photo-activated applications by a plasma-assisted fabrication route

Supported MnO2-based nanomaterials were fabricated on fluorine-doped tin oxide substrates using plasma enhanced-chemical vapor deposition (PE-CVD) between 100 °C and 400 °C, starting from a fluorinated Mn(ii) diamine diketonate precursor. Growth experiments yielded β-MnO2 with a hierarchical morphology tuneable from dendritic structures to quasi-1D nanosystems as a function of growth temperature, whose variation also enabled a concomitant tailoring of the system fluorine content, and of the optical absorption and band gap. Preliminary photocatalytic tests were aimed at the investigation of photoinduced hydrophilic (PH) and solid phase photocatalytic (PC) performances of the present nanomaterials, as well as at the photodegradation of Plasmocorinth B azo-dye aqueous solutions. The obtained findings highlighted an attractive system photoactivity even under visible light, finely tailored by fluorine content, morphological organization and optical properties of the prepared nanostructures. The results indicate that the synthesized MnO2 nanosystems have potential applications as advanced smart materials for anti-fogging/self-cleaning end uses and water purification.

Insights into the Plasma-Assisted Fabrication and Nanoscopic Investigation of Tailored MnO2 Nanomaterials

Among transition metal oxides, MnO₂ is of considerable importance for various technological end-uses, from heterogeneous catalysis to gas sensing, owing to its structural flexibility and unique properties at the nanoscale. In this work, we demonstrate the successful fabrication of supported MnO₂ nanomaterials by a catalyst-free, plasma-assisted process starting from a fluorinated manganese(II) molecular source in Ar/O₂ plasmas. A thorough multitechnique characterization aimed at the systematic investigation of material structure, chemical composition, and morphology revealed the formation of F-doped, oxygen-deficient, MnO₂-based nanomaterials, with a fluorine content tunable as a function of growth temperature ( T_G). Whereas phase-pure β-MnO₂ was obtained for 100 °C ≤ T_G ≤ 300 °C, the formation of mixed phase MnO₂ + Mn₂O₃ nanosystems took place at 400 °C. In addition, the system nano-organization could be finely tailored, resulting in a controllable evolution from wheat-ear columnar arrays to high aspect ratio pointed-tip nanorod assemblies. Concomitantly, magnetic force microscopy analyses suggested the formation of spin domains with features dependent on material morphology. Preliminary tests in Vis-light activated photocatalytic degradation of rhodamine B aqueous solutions pave the way to possible applications of the target materials in wastewater purification.

Polyethylene glycol-doped BiZn2VO6 as a high-efficiency solar-light-activated photocatalyst with substantial durability toward photodegradation of organic contaminations

In this study, we focus on a simple, low-priced, and mild condition hydrothermal route to construct BiZn₂VO₆ nanocompounds (NCs) as a novel photocatalyst with strong solar light absorption ability for environmental purification using solar energy. NCs were further doped with polyethylene glycol (PEG) to improve their photocatalytic efficiency for photodegradation processes through inhibition of fast charge carrier recombination rates and higher charge separation efficiency. Surface morphology, phase structure, optical characteristics, and band structure of the as-prepared samples were analyzed using XRD, EDX, XPS, SEM, UV-vis spectroscopy, CL, and BET techniques. PEG-doped BiZn₂VO₆ NCs were applied as effective materials to degrade various kinds of organic pollutants including cationic and anionic types, and these NCs exhibited excellent photocatalytic efficiency as compared to traditional photocatalysts. In particular, the PEG-doped BiZn₂VO₆ (0.10% w/v) photocatalyst exhibited highly enhanced photocatalytic performance with improvements of about 46.4, 28.3, and 7.23 folds compared with PEG-doped ZnO nanorods (NRs), pristine BiVO₄, and BiZn₂VO₆ samples, respectively, for the decomposition of congo red (CR) dye. After 40 minutes of sunlight irradiation, 97.4% of CR was decomposed. In this study, scavenging experiments indicated that both hydroxyl radicals and holes play dominant roles in CR photodegradation under simulated solar light irradiation. Meanwhile, the optimal photocatalyst demonstrated good reproducibility and stability for successive cycles of photocatalysis.

Precise control of morphology of ultrafine LiMn2O4 nanorods as a supercapacitor electrode via a two-step hydrothermal method

Ultrafine 1D LiMn₂O₄ and its promising galvanostatic charge/discharge profiles in KOH/K₃Fe(CN)₆ electrolyte.

One-pot synthesis and first-principles elasticity analysis of polymorphic MnO2 nanorods for tribological assessment as friction modifiers

XRD analysis of hydrothermally synthesized polymorphic MnO₂ nanorods and their frictional torque when added with palm oil as against pure palm oil.

Prepared MnO2 with different crystal forms as electrode materials for supercapacitors: experimental research from hydrothermal crystallization process to electrochemical performances

The aim of this study was to prepare manganese dioxide with different crystal forms through hydrothermal treatment of MnSO₄·H₂O–KMnO₄ precursors at various precursor ratios, temperatures, time periods, and pH values.