Construction of novel Ag/HKUST-1/g-C3N4 towards enhanced photocatalytic activity for the degradation of pollutants under visible light

Engineering the defect distribution in ZnO nanorods through laser irradiation

In recent years, defect engineering has shown great potential to improve the properties of metal oxide nanomaterials for various applications thus received extensive investigations. While traditional techniques mostly focus on controlling the defects during the synthesis of the material, laser irradiation has emerged as a promising post-deposition technique to further modulate the properties of defects yet there is still limited information. In this article, defects such as oxygen vacancies are tailored in ZnO nanorods through nanosecond (ns) laser irradiation. The relation between laser parameters and the temperature rise in the ZnO due to laser heating was established based on the observation in the SEM and the simulation. Raman spectra indicated that the concentration of the oxygen vacancies in the ZnO is temperature-dependent and can be controlled by changing the laser fluence and exposure time. This is also supported by the absorption spectra and the photoluminescence spectra of ZnO NRs irradiated under these conditions. On the other hand, the distribution of the oxygen vacancies was studied by XPS depth profiling, and it was confirmed that the surface-to-bulk ratio of the oxygen vacancies can be modulated by varying the laser fluence and exposure time. Based on these results, four distinctive regimes containing different ratios of surface-to-bulk oxygen vacancies have been identified. Laser-processed ZnO nanorods were also used as the catalyst for the photocatalytic degradation of rhodamine B (RhB) dye to demonstrate the efficacy of this laser engineering technique.

Highly Efficient Oxygen-Activated Self-Cleaning Membranes Prepared by Grafting a Metal-Organic Framework-Derived Catalyst

In this study, an efficient oxygen-activated self-cleaning membrane was successfully prepared by grafting a metal-organic framework-devised catalyst (CuNi-C) onto a membrane surface, resulting in enhanced filtration performance and self-cleaning capability based on oxygen activation under mild conditions. The pore features, surface roughness, and surface hydrophilicity of the prepared membrane were analyzed and used to determine the causes of the enhanced filtration performance; the results showed that an increase in the porosity and surface roughness enhanced the permeate flux, and enhanced adsorption capacity and surface hydrophobicity improved the membrane removal efficiency. The self-cleaning mechanism was elucidated by identifying the reactive oxygen species (ROS) and detecting catalytic element valences. The results revealed that zero-valent Cu embedded into the membrane surface effectively activated natural dissolved oxygen (DO) to generate ROS that degraded organic pollutants. In this study, catalytic oxidation with DO as the oxidant was successively integrated with membrane separation to prevent membrane fouling, providing a novel direction for the development of multifunctional membranes.

Room temperature synthesis of a luminescent crystalline Cu-BTC coordination polymer and metal-organic framework

Synthesis of crystalline materials is elemental in the field of coordination chemistry towards optical applications. In the present work, coordination between copper and benzene-1,3,5-tricarboxylic acid (BTC) is controlled by adjusting the pH scale of the reaction mixture at room temperature to synthesize two crystalline structures: metal-organic framework HKUST-1 and coordination polymer Cu(BTC)·3H2O. The post-synthesis transformation of HKUST-1 into Cu(BTC)·3H2O is further demonstrated. Single crystals of both structures are studied by multi-laser Raman and luminescence spectroscopy. It is found that both crystals exhibit photoluminescence in the range of 700-900 cm-1 within the optical gap of the bulk materials, which can be associated with crystallographic defects. This work gives impetus for the synthesis of large metal-organic crystals based on which optical properties can be studied in depth.

Acid-activated carbon nitrides as photocatalysts for degrading organic pollutants under visible light

Three-dimensional (3D) carbon nitride (C₃N₄) can be used as a promising platform for visible-light-active photocatalysts because of its suitable band positions. This study reports that HNO₃ activation improves the photocatalytic activity of 3D melamine-derived C₃N₄ (MCN) materials, which degrade the organic pollutant rhodamine B (RhB). HNO₃ treatment under reflux removes the carbonaceous impurities in MCN and introduces oxygen-containing functional groups on its surface. Under visible light irradiation, the nitric acid treated MCN (NT-MCN) completely degrades RhB within 30 min. Photophysical characterizations and control experiments with radical scavengers reveal that MCN and NT-MCN follow different reaction mechanisms. Because NT-MCN exhibits a longer photoluminescence lifetime, smaller electrochemical resistance, and larger photocurrent than those of MCN, it enables a better transfer of charge carriers during the catalytic reaction.