Fluidization is known to minimize the adverse effects of mass-transfer, poor radiation distributi... more Fluidization is known to minimize the adverse effects of mass-transfer, poor radiation distribution, parasitic back-reactions and photocatalyst handling, which limit the scalability of immobilized-film and suspended slurry photocatalysts.
A sensitive 1D single crystal ZnO nanostructure gas sensor decorated with Pt nanoparticles was pr... more A sensitive 1D single crystal ZnO nanostructure gas sensor decorated with Pt nanoparticles was prepared to detect low concentrations of toxic gases at room temperature under UV-LED irradiation. The developed UV-LED activated sensors have a variety of advantages, compared to the traditional high temperature chemi-resistive metal oxide semiconductor (MOS) sensors, such as higher stability, smaller size, lower preparation time, and the ability to safely detect flammable gases. The developed sensing materials were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analyses. To obtain a visual evidence of Pt nanoparticles on the surface of ZnO nanowires, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field (HAADF) STEM were employed. The gas sensing results indicated a significant increase (an order of magnitude) in sensor response toward NO2 as a model gas, compared to pristine ZnO sample mainly due to ...
Abstract Light-driven CO2 conversion into valuable chemicals is the most promising pathway for mi... more Abstract Light-driven CO2 conversion into valuable chemicals is the most promising pathway for minimizing the greenhouse effect and producing alternative energies. A wide variety of photocatalyst, cocatalyst, and Z-scheme component compositions for CO2 photoreduction (CO2PR) have been extensively studied. However, research focusing on microporous zeolite-based photocatalysts for CO2PR is scarce, compared to that of semiconductor-based photocatalysts. This review article is a comprehensive guide of the most recent developments and future prospects of microporous zeolite-based photocatalysts with respect to CO2PR. Apart from photoreduction, this article also briefly discusses studies on thermal reduction for the comprehensive understanding of CO2 reduction over zeolites, with the aim of introducing new ideas for future zeolite-based photocatalyst designs. Herein, we briefly review the fundamentals of CO2PR mechanisms and zeolite crystallography. We then discuss the seven major configurations of zeolite-based photocatalysts applied to CO2PR, namely (i) single heterocation species on and (ii) single heteroatom substitutions in the zeolite framework, (iii) metal and (iv) metal oxide clusters embedded in zeolite caves, dispersion of (v) metal and (vi) metal oxide nanoparticles on the zeolite surface, and (vii) integration with polymeric semiconductors. Most of these materials are naturally photocatalytically active, owing to the unavoidable presence of trace amounts of heteroatoms in zeolites. Reported strategies that further improve their photocatalytic performance for CO2 conversion are also discussed in this article. The introduction of some specific configurations on microporous zeolite-based photocatalysts results in a synergistic effect on CO2PR. Zeolite nanosheets improve the reactant/product mass transfer in CO2PR, while zeolite-based Z-scheme photocatalysts enhance visible light absorption, charge transfer, and separation. Throughout the article, we offer a rich description of these techniques by providing mechanistic insights, application areas, and possible potentials for the development of innovative zeolite-based photocatalysts.
Synthesis of nanoporous GaZnON-RGO composite photocatalyst with enhanced capacity for HER active ... more Synthesis of nanoporous GaZnON-RGO composite photocatalyst with enhanced capacity for HER active site and improved visible light hydrogen evolution performance is reported.
Binary and ternary oxynitride solid alloys were studied extensively in the past decade due to the... more Binary and ternary oxynitride solid alloys were studied extensively in the past decade due to their wide spectrum of applications, as well as their peculiar characteristics when compared to their bulk counterparts. Direct bottom-up synthesis of one-dimensional oxynitrides through solution-based routes cannot be realized because nitridation strategies are limited to high-temperature solid-state ammonolysis. Further, the facile fabrication of oxynitride thin films through vapor phase strategies has remained extremely challenging due to the low vapor pressure of gaseous building blocks at atmospheric pressure. Here, we present a direct and scalable catalytic vapor–liquid–solid epitaxy (VLSE) route for the fabrication of oxynitride solid solution nanowires from their oxide precursors through enhancing the local mass transfer flux of vapor deposition. For the model oxynitride material, we investigated the fabrication of gallium nitride and zinc oxide oxynitride solid solution (GaN:ZnO) t...
Metal Oxide Semiconductor (MOS) gas sensors have been studied for monitoring indoor/outdoor air p... more Metal Oxide Semiconductor (MOS) gas sensors have been studied for monitoring indoor/outdoor air pollutants. A drawback of conventional chemical-resistive gas sensing is the high operating temperature (up to 500°C) that is required for surface reactions. The high temperature operation, however, causes drift problems and makes sensors unsafe for environments containing flammable gases. Ultraviolet light-emitting diode (UV-LED) is a new technological field that has recently seen rapid improvements and novel possible applications. These include the development of UV-LED based gas sensors. UV photons emitted from UV-LED could activate sensors to allow detection of chemicals at ambient temperature. UV irradiation can also improve the sensor performance in harsh environments, where SO2 or NOx gases are present, through desorbing surface contaminants. The state-of-the-art ultraviolet light emitting diode (UV-LED) that emit radiation at a power of a few milli-watts is a promising UV source f...
Recently, ultraviolet light-emitting diodes (UV-LEDs) have emerged as a new UV source, bringing f... more Recently, ultraviolet light-emitting diodes (UV-LEDs) have emerged as a new UV source, bringing flexibility for various UV wavelength combinations due to their unique feature of wavelength diversity. In this study, we investigated inactivation mechanisms of representative microorganisms at different wavelength combinations using UV-LEDs. Two types of indicator microorganisms were examined, namely Escherichia coli (E. coli) as a representative bacteria and bacteriophage MS2 as a representative virus. Different inactivation effects were observed, and the results for UVA pretreatment followed by UVC inactivation were particularly interesting. While a substantial shoulder in the E. coli UVC inactivation curve was observed, this was reduced by UVA pretreatment (365 nm) at 17 J/cm2. Further, 52 J/cm2 UVA eliminated the shoulder in the fluence-response curves, resulting in improved UVC (265 nm) inactivation of E. coli by over two orders of magnitude. No inactivation improvement was observed for MS2. Moreover, UVA pretreatment eliminated photoreactivation of E. coli but did not affect dark repair. Detailed investigation of inactivation mechanisms revealed that hydroxyl radicals (•OH) played a significant role in the effects of UVA pretreatment. This study demonstrated that •OH radicals were generated inside E. coli cells during UVA pretreatment, which accounted for the subsequent effects on E. coli. The impact of UVA pretreatment on E. coli inactivation and reactivation was mainly due to increased levels of •OH radicals in E. coli cells, impairing cell functions such as DNA self-repair.
Fluidization is known to minimize the adverse effects of mass-transfer, poor radiation distributi... more Fluidization is known to minimize the adverse effects of mass-transfer, poor radiation distribution, parasitic back-reactions and photocatalyst handling, which limit the scalability of immobilized-film and suspended slurry photocatalysts.
A sensitive 1D single crystal ZnO nanostructure gas sensor decorated with Pt nanoparticles was pr... more A sensitive 1D single crystal ZnO nanostructure gas sensor decorated with Pt nanoparticles was prepared to detect low concentrations of toxic gases at room temperature under UV-LED irradiation. The developed UV-LED activated sensors have a variety of advantages, compared to the traditional high temperature chemi-resistive metal oxide semiconductor (MOS) sensors, such as higher stability, smaller size, lower preparation time, and the ability to safely detect flammable gases. The developed sensing materials were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analyses. To obtain a visual evidence of Pt nanoparticles on the surface of ZnO nanowires, high-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field (HAADF) STEM were employed. The gas sensing results indicated a significant increase (an order of magnitude) in sensor response toward NO2 as a model gas, compared to pristine ZnO sample mainly due to ...
Abstract Light-driven CO2 conversion into valuable chemicals is the most promising pathway for mi... more Abstract Light-driven CO2 conversion into valuable chemicals is the most promising pathway for minimizing the greenhouse effect and producing alternative energies. A wide variety of photocatalyst, cocatalyst, and Z-scheme component compositions for CO2 photoreduction (CO2PR) have been extensively studied. However, research focusing on microporous zeolite-based photocatalysts for CO2PR is scarce, compared to that of semiconductor-based photocatalysts. This review article is a comprehensive guide of the most recent developments and future prospects of microporous zeolite-based photocatalysts with respect to CO2PR. Apart from photoreduction, this article also briefly discusses studies on thermal reduction for the comprehensive understanding of CO2 reduction over zeolites, with the aim of introducing new ideas for future zeolite-based photocatalyst designs. Herein, we briefly review the fundamentals of CO2PR mechanisms and zeolite crystallography. We then discuss the seven major configurations of zeolite-based photocatalysts applied to CO2PR, namely (i) single heterocation species on and (ii) single heteroatom substitutions in the zeolite framework, (iii) metal and (iv) metal oxide clusters embedded in zeolite caves, dispersion of (v) metal and (vi) metal oxide nanoparticles on the zeolite surface, and (vii) integration with polymeric semiconductors. Most of these materials are naturally photocatalytically active, owing to the unavoidable presence of trace amounts of heteroatoms in zeolites. Reported strategies that further improve their photocatalytic performance for CO2 conversion are also discussed in this article. The introduction of some specific configurations on microporous zeolite-based photocatalysts results in a synergistic effect on CO2PR. Zeolite nanosheets improve the reactant/product mass transfer in CO2PR, while zeolite-based Z-scheme photocatalysts enhance visible light absorption, charge transfer, and separation. Throughout the article, we offer a rich description of these techniques by providing mechanistic insights, application areas, and possible potentials for the development of innovative zeolite-based photocatalysts.
Synthesis of nanoporous GaZnON-RGO composite photocatalyst with enhanced capacity for HER active ... more Synthesis of nanoporous GaZnON-RGO composite photocatalyst with enhanced capacity for HER active site and improved visible light hydrogen evolution performance is reported.
Binary and ternary oxynitride solid alloys were studied extensively in the past decade due to the... more Binary and ternary oxynitride solid alloys were studied extensively in the past decade due to their wide spectrum of applications, as well as their peculiar characteristics when compared to their bulk counterparts. Direct bottom-up synthesis of one-dimensional oxynitrides through solution-based routes cannot be realized because nitridation strategies are limited to high-temperature solid-state ammonolysis. Further, the facile fabrication of oxynitride thin films through vapor phase strategies has remained extremely challenging due to the low vapor pressure of gaseous building blocks at atmospheric pressure. Here, we present a direct and scalable catalytic vapor–liquid–solid epitaxy (VLSE) route for the fabrication of oxynitride solid solution nanowires from their oxide precursors through enhancing the local mass transfer flux of vapor deposition. For the model oxynitride material, we investigated the fabrication of gallium nitride and zinc oxide oxynitride solid solution (GaN:ZnO) t...
Metal Oxide Semiconductor (MOS) gas sensors have been studied for monitoring indoor/outdoor air p... more Metal Oxide Semiconductor (MOS) gas sensors have been studied for monitoring indoor/outdoor air pollutants. A drawback of conventional chemical-resistive gas sensing is the high operating temperature (up to 500°C) that is required for surface reactions. The high temperature operation, however, causes drift problems and makes sensors unsafe for environments containing flammable gases. Ultraviolet light-emitting diode (UV-LED) is a new technological field that has recently seen rapid improvements and novel possible applications. These include the development of UV-LED based gas sensors. UV photons emitted from UV-LED could activate sensors to allow detection of chemicals at ambient temperature. UV irradiation can also improve the sensor performance in harsh environments, where SO2 or NOx gases are present, through desorbing surface contaminants. The state-of-the-art ultraviolet light emitting diode (UV-LED) that emit radiation at a power of a few milli-watts is a promising UV source f...
Recently, ultraviolet light-emitting diodes (UV-LEDs) have emerged as a new UV source, bringing f... more Recently, ultraviolet light-emitting diodes (UV-LEDs) have emerged as a new UV source, bringing flexibility for various UV wavelength combinations due to their unique feature of wavelength diversity. In this study, we investigated inactivation mechanisms of representative microorganisms at different wavelength combinations using UV-LEDs. Two types of indicator microorganisms were examined, namely Escherichia coli (E. coli) as a representative bacteria and bacteriophage MS2 as a representative virus. Different inactivation effects were observed, and the results for UVA pretreatment followed by UVC inactivation were particularly interesting. While a substantial shoulder in the E. coli UVC inactivation curve was observed, this was reduced by UVA pretreatment (365 nm) at 17 J/cm2. Further, 52 J/cm2 UVA eliminated the shoulder in the fluence-response curves, resulting in improved UVC (265 nm) inactivation of E. coli by over two orders of magnitude. No inactivation improvement was observed for MS2. Moreover, UVA pretreatment eliminated photoreactivation of E. coli but did not affect dark repair. Detailed investigation of inactivation mechanisms revealed that hydroxyl radicals (•OH) played a significant role in the effects of UVA pretreatment. This study demonstrated that •OH radicals were generated inside E. coli cells during UVA pretreatment, which accounted for the subsequent effects on E. coli. The impact of UVA pretreatment on E. coli inactivation and reactivation was mainly due to increased levels of •OH radicals in E. coli cells, impairing cell functions such as DNA self-repair.
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