Synthesis of Photoactive Materials by Sonication: Application in Photocatalysis and Solar Cells

Synthetic approaches for perovskite thin films and single-crystals

Halide perovskites are compelling candidates for the next generation of photovoltaic technologies owing to an unprecedented increase in power conversion efficiency and their low cost, facile fabrication and outstanding semiconductor properties.

A correlation between cavitation bubble temperature, sonoluminescence and interfacial chemistry - A minireview

Ultrasound induced cavitation (acoustic cavitation) process is found useful in various applications. Scientists from various disciplines have been exploring the fundamental aspects of acoustic cavitation processes over several decades. It is well documented that extreme localised temperature and pressure conditions are generated when a cavitation bubble collapses. Several experimental techniques have also been developed to estimate cavitation bubble temperatures. Depending upon specific experimental conditions, light emission from cavitation bubbles is observed, referred to as sonoluminescence. Sonoluminescence studies have been used to develop a fundamental understanding of cavitation processes in single and multibubble systems. This minireview aims to provide some highlights on the development of basic understandings of acoustic cavitation processes using cavitation bubble temperature, sonoluminescence and interfacial chemistry over the past 2-3 decades.

Effect of switching ultrasonic amplitude in preparing a hybrid of fullerene (C60) and gallium oxide (Ga2O3)

In this study, we proposed 'switching ultrasonic amplitude' as a new strategy of applying ultrasonic energy to prepare a hybrid of buckminsterfullerene (C₆₀) and gallium oxide (Ga₂O₃), C₆₀/Ga₂O₃. In the proposed method, we switched the ultrasonic amplitude from 25% to 50% (by 5% amplitude per 10 min, within 1 h of ultrasonic irradiation) for the sonochemical treatment of a heterogeneous aqueous mixture of C₆₀ and Ga₂O₃ by a probe-type ultrasonic horn operating at 20 kHz. We found that compared to the conventional techniques associated with high amplitude oriented ultrasonic preparation of functional materials, switching ultrasonic amplitude can better perform in preparing C₆₀/Ga₂O₃ with respect to avoiding titanium (Ti) as an impurity generating from the tip erosion of a probe-type ultrasonic horn during high amplitude ultrasonic irradiation in an aqueous medium. Based on SEM/EDX analysis, the quantity of Ti (wt.%) in C₆₀/Ga₂O₃ prepared by the proposed technique of switching ultrasonic amplitude was found to be 1.7% less than that prepared at 50% amplitude of ultrasonic irradiation. The particles of C₆₀/Ga₂O₃ prepared by different modes of amplitude formed large (2-12 μm) aggregates in their solid phase.Whereas, in the aqueous medium, they were found to disperse in their nano sizes. The minimum particle size of the as-synthesized C₆₀/Ga₂O₃ in an aqueous medium prepared by the proposed method of switching ultrasonic amplitude reached to approximately 467 nm. Comparatively, the minimum particle sizes were approximately 658 nm and 144 nm, using 25% and 50% amplitude, respectively. Additionally, Ga₂O₃ went under hydration during ultrasonic irradiation. Moreover, due to the electron cloud interference from C₆₀ in the hybrid structure of C₆₀/Ga₂O₃, the vibrational modes of Ga₂O₃ were Raman inactive in C₆₀/Ga₂O₃.

Improvements in Catalyst Synthesis and Photocatalytic Oxidation Processing Based on the Use of Ultrasound

The efficacy of photocatalysis strongly depends on the activity of the catalysts and the operational factors, especially factors associated with mass transfer and the possibility of catalyst deactivation. The use of ultrasound has great potential to enhance catalyst activity, during both the synthesis and actual oxidation processes due to the cavitational effects of turbulence and liquid streaming. This article presents an overview of the application aspects of ultrasound, both in the synthesis of the photocatalyst and applications for wastewater treatment. A review of the literature revealed that the use of ultrasound in the synthesis processes can result in a catalyst with a lower mean size and higher surface area as well as uniform size distribution. The application of ultrasound in the actual photocatalytic oxidation facilitates enhancement of the oxidation capacity, leading to higher degradation rates, sometimes synergistic results and definitely lower treatment times. This article also presents guidelines for the selection of the best operating conditions for the use of ultrasound in photocatalytic systems and includes a discussion on the possible reactor configurations suitable for large-scale operations. Overall, a combination of ultrasound with photocatalytic oxidation or the optimized application of ultrasound in catalyst synthesis can yield significant benefits.

Ultrasound-Assisted Synthesis of Nanostructured Oxide Materials

This chapter is focused on the use of high intensity ultrasound for the preparation of nanostructured materials with an emphasis on recent prominent examples of the production of dense or porous metal oxides through sonochemical and ultrasonic spray pyrolysis routes. Sonochemistry enables the synthesis of oxides that are often unachievable by traditional methods or affords known materials with shape, size, and nano/microstructure control under fast reaction conditions. The fundamental principles of acoustic cavitation, as well as the main ultrasonic parameters affecting the cavitation phenomenon, are first summarized. Next, the applications of ultrasound in the synthesis of nanostructured oxide materials following both preparation methods are reviewed. Particular focus is given to the ultrasound-assisted synthesis of metal oxide nanoparticles for energy applications.

Photoactive Hybrid Catalysts Based on Natural and Synthetic Polymers: A Comparative Overview

In the present review, we would like to draw the reader's attention to the polymer-based hybrid materials used in photocatalytic processes for efficient degradation of organic pollutants in water. These inorganic-organic materials exhibit unique physicochemical properties due to the synergistic effect originating from the combination of individual elements, i.e., photosensitive metal oxides and polymeric supports. The possibility of merging the structural elements of hybrid materials allows for improving photocatalytic performance through (1) an increase in the light-harvesting ability; (2) a reduction in charge carrier recombination; and (3) prolongation of the photoelectron lifetime. Additionally, the great majority of polymer materials exhibit a high level of resistance against ultraviolet irradiation and improved corrosion resistance. Taking into account that the chemical and environmental stability of the hybrid catalyst depends, to a great extent, on the functional support, we highlight benefits and drawbacks of natural and synthetic polymer-based photocatalytic materials and pay special attention to the fact that the accessibility of synthetic polymeric materials derived from petroleum may be impeded due to decreasing amounts of crude oil. Thus, it is necessary to look for cheap and easily available raw materials like natural polymers that come from, for instance, lignocellulosic wastes or crustacean residues to meet the demand of the "plastic" market.