Mechanistic study of visible light driven photocatalytic degradation of clofibric acid using Fe-based metal organic frameworks (MOFs).

Although a series of past studies proved the potential usage of Fe-based metal-organic frameworks (MOFs) as photocatalysts, there remains a knowledge gap of the photocatalytic mechanism stemming from the challenge to separate the simultaneous sorption and photocatalytic degradation. Thus, this article aimed to suggest a novel approach by desorbing target molecules during photocatalysis to excavate the underlying mechanisms of sorption and photocatalytic degradation. In this study, two Fe-based MOFs, MIL-101(Fe) and MIL-101(Fe)-NH2, were selected to remove clofibric acid under visible light irradiation. Prior to photocatalysis, sorption mechanism was uncovered based on the sorption kinetic, isotherm, thermodynamic interpretation, and of its dependence on solution pH. The results inferred that the primary sorption mechanism was through the π-π interaction between the benzene ring of clofibric acid and the organic ligand of Fe-based MOFs. Based on these results, photocatalytic mechanism could be independently or jointly assessed during the photocatalytic degradation of clofibric acid. Subsequently, the application of the Tauc method and XPS spectra revealed that the bandgap structure of Fe-based MOFs had the potential to oxidize clofibric acid by producing ROS through the electron excitation upon visible-light illumination. On top of that, the amine functionalization of Fe-based MOF altered the structural moiety that led to an additional strong acid-base interaction with clofibric acid but a decrease in the bandgap limiting the ROS production during photocatalytic activity.

Nanobubble Reactivity: Evaluating Hydroxyl Radical Generation (or Lack Thereof) under Ambient Conditions.

Nanobubble (NB) generation of reactive oxygen species (ROS), especially hydroxyl radical (·OH), has been controversial. In this work, we extensively characterize NBs in solution, with a focus on ROS generation (as ·OH), through a number of methods including degradation of ·OH-specific target compounds, electron paramagnetic resonance (EPR), and a fluorescence-based indicator. Generated NBs exhibit consistent physical characteristics (size, surface potential, and concentration) when compared with previous studies. For conditions described, which are considered as high O2 NB concentrations, no degradation of benzoic acid (BA), a well-studied ·OH scavenger, was observed in the presence of NBs (over 24 h) and no EPR signal for ·OH was detected. While a positive fluorescence response was measured when using a fluorescence probe for ·OH, aminophenyl fluorescein (APF), we provide an alternate explanation for the result. Gas/liquid interfacial characterization indicates that the surface of a NB is proton-rich and capable of inducing acid-catalyzed hydrolysis of APF, which results in a false (positive) fluorescence response. Given these negative results, we conclude that NB-induced ·OH generation is minimal, if at all, for conditions evaluated.

Effects of MoS2 Layer Thickness on Its Photochemically Driven Oxidative Dissolution.

The distinctive optical and electronic properties of two-dimensional (2D) molybdenum disulfide (MoS2) make it a promising photocatalyst and photothermal agent in aqueous applications. In terms of environmental stability, MoS2 has been considered insoluble, but 2D MoS2 nanosheets can be susceptible to dissolution, owing to their large surface areas and highly accessible reactive sites, including defects at the basal plane and edge sites. Under light illumination, the dissolution of 2D MoS2 nanosheets can be further accelerated by their photochemical reactivity. To elucidate MoS2 reactivity in the environment, here we investigated the thickness-dependent dissolution of MoS2 under illumination. To synthesize nanoscale thicknesses of MoS2, we exfoliated bulk MoS2 by ultrasonication and controlled the layer thickness by iterative cascade centrifugation, producing MoS2 nanosheets averaging either ∼18 nm or ∼46 nm thick, depending on the centrifugation rate. Under simulated sunlight, MoS2 dissolution was accelerated, the Mo6+ composition increased, and the solution pH decreased compared to those in the dark. These results suggest that light exposure promotes the oxidation of MoS2, causing faster dissolution. Importantly, 18 nm thick MoS2 exhibited faster dissolution than either 46 nm or bulk MoS2, driven by the superoxide radical (O2•-) generation promoted by its relative thinness. These findings highlight the important role of the thickness-dependent photochemistry of MoS2 nanosheets in their dissolution, which is directly linked to their environmental behavior and stability.

Distribution and in situ proliferation patterns of intravenously injected immortalized human neural stem-like cells in rats with focal cerebral ischemia.

Neural stem cells are considered as a candidate for cell replacement therapy in various neurological diseases. To investigate whether human neural stem cells can migrate into the adult ischemic rat brain, we transplanted immortalized human neural 'tem-like' cells intravenously 24 h after focal cerebral ischemia. The intravenously injected human neural stem-like cells were found around the infarcted area, differentiated into neurons and astrocytes in the lesioned areas, and survive up to 56 days after transplantation. The number of the injected cells increased between 7 and 14 days after transplantation with incorporating BrdU. Our findings show that intravenously injected human neural stem-like cells may incorporate into the ischemic brain, and undergo proliferation responding to the endogenous mitotic signal during the acute period of focal ischemia.