Unravelling lewis acidic and reductive characters of normal and inverse nickel-cobalt thiospinels in directing catalytic H2O2 cleavage

Enhanced ability of toluene oxidation by controlling inversion degree of spinel composed of only Co, Mn

Exploring the single relationship between the inversion degree of spinel and its catalytic performance is a great challenge, but has important significance for further structural design and application. A series of CoMn inverse spinels were prepared and the general formula [Formula: see text] was deduced through X-ray diffraction refinement to find a decreased inversion degree x as calcination temperature rose. Catalytic oxidation of toluene showed that higher inversion degree (S-300 with x ≈ 0.95) can reach larger conversion rate (90 % at about 250 °C for 400 ppm toluene) with greater reaction stability (140 h). Density Functional Theory (DFT) calculations on density of states indicated its metallic nature, and found that the strength of O-p and Transition metal-d orbitals at Fermi energy is positively correlated to the inversion degree, meaning stronger electron migration ability. Along with the adsorption calculation analysis that lattice oxygen species are proved to work dominantly (S-300 with lowest adsorption energy but highest performance), this work uncovered a theoretical insight into inverse spinel oxide, to provide the possibility of elevated oxidation ability through structural control.

Boosting the singlet oxygen production from H2O2 activation with highly dispersed Co-N-graphene for pollutant removal

Singlet oxygen (1O2) is a promising reactive species for the selective degradation of organic pollutants. However, it is difficult to generate 1O2 from H2O2 activation with high efficiency and selectivity. In this work, a graphene-supported highly dispersed cobalt catalyst with abundant Co-N x active sites (Co-N-graphene) was synthesized for activating H2O2. The Co-N-graphene catalyzed H2O2 reaction system selectively catalyzed 1O2 production associated with the superoxide radical (O2˙-) as the critical intermediate, as proven by scavenger experiments, electron spin resonance (ESR) spin trapping and a kinetic solvent isotope effect study. This resulted in excellent degradation efficiency towards the model organic pollutant methylene blue (MB), with an outstanding pseudo-first-order kinetic rate constant of 0.432 min-1 (g Lcatalyst -1)-1 under optimal reaction conditions (C H2O2 = 400 mM, initial pH = 9). Furthermore, this Co-N-graphene catalyst enabled strong synergy with HCO3 - in accelerating MB degradation, whereas the scavenger experiment implied that the synergy herein differed significantly from the current Co2+-HCO3 - reaction system, in which contribution of O2˙- was only validated with a Co-N-graphene catalyst. Therefore, this work developed a novel catalyst for boosting 1O2 production from H2O2 activation and will extend the inventory of catalysts for advanced oxidation processes.

Deciphering Evolution Pathway of Supported NO3 • Enabled via Radical Transfer from •OH to Surface NO3 - Functionality for Oxidative Degradation of Aqueous Contaminants

NO₃ ^• can compete with omnipotent ^•OH/SO₄ ^•- in decomposing aqueous pollutants because of its lengthy lifespan and significant tolerance to background scavengers present in H₂O matrices, albeit with moderate oxidizing power. The generation of NO₃ ^•, however, is of grand demand due to the need of NO₂ ^•/O₃, radioactive element, or NaNO₃/HNO₃ in the presence of highly energized electron/light. This study has pioneered a singular pathway used to radicalize surface NO₃ ^- functionalities anchored on polymorphic α-/γ-MnO₂ surfaces (α-/γ-MnO₂-N), in which Lewis acidic Mn^2+/3+ and NO₃ ^- served to form ^•OH via H₂O₂ dissection and NO₃ ^• via radical transfer from ^•OH to NO₃ ^- (^•OH → NO₃ ^•), respectively. The elementary steps proposed for the ^•OH → NO₃ ^• route could be energetically favorable and marginal except for two stages such as endothermic ^•OH desorption and exothermic ^•OH-mediated NO₃ ^- radicalization, as verified by EPR spectroscopy experiments and DFT calculations. The Lewis acidic strength of the Mn^2+/3+ species innate to α-MnO₂-N was the smallest among those inherent to α-/β-/γ-MnO₂ and α-/γ-MnO₂-N. Hence, α-MnO₂-N prompted the rate-determining stage of the ^•OH → NO₃ ^• route (^•OH desorption) in the most efficient manner, as also evidenced by the analysis on the energy barrier required to proceed with the ^•OH → NO₃ ^• route. Meanwhile, XANES and in situ DRIFT spectroscopy experiments corroborated that α-MnO₂-N provided a larger concentration of surface NO₃ ^- species with bi-dentate binding arrays than γ-MnO₂-N. Hence, α-MnO₂-N could outperform γ-MnO₂-N in improving the collision frequency between ^•OH and NO₃ ^- species and in facilitating the exothermic transition of NO₃ ^- functionalities to surface NO₃ ^• analogues per unit time. These were corroborated by a greater efficiency of α-MnO₂-N in decomposing phenol, in addition to scavenging/filtration control runs and DFT calculations. Importantly, supported NO₃ ^• species provided 5-7-fold greater efficiency in degrading textile wastewater than conventional ^•OH and supported SO₄ ^•- analogues we discovered previously.

Novel flexible bifunctional amperometric biosensor based on laser engraved porous graphene array electrodes: Highly sensitive electrochemical determination of hydrogen peroxide and glucose

Polyimide-laser-engraved porous graphene (LEPG) are hopeful electrode modification materials for flexible electrochemical sensing based on its high-efficiency preparation and low cost. Herein, a flexible, multi-patterned, and miniaturized electrode was fabricated via a simple and novel direct laser engraving. 3D LEPG with porous network structure can selective decorated with Pt nanoparticles (Pt NPs) by in situ electrochemical depositions (Pt-LEPG) as sensitively H₂O₂ sensors with a wide range of linear (0.01-29 nM) and high sensitivity (575.75 μA mM^-1 cm^-2). Subsequently, a glucose biosensor was successfully constructed through immobilized glucose oxidases (GOD) onto Pt-LEPG electrode. New-designed GOD/Pt-LEPG glucose sensor exhibited a noteworthy lower limit of detection (0.3 μM, S/N = 3) and high sensitivity (241.82 μA mM^-1 cm^-2), as much a wide-range of linear (0.01-31.5 mM) at near-neutral pH conditions, enabling detect glucose in real human serum specimens with satisfactory results. Predictably, these outstanding performance sensors have great potential in terms of flexible and wearable electronics.