Present theoretical and experimental work provides an in-depth understanding of the morphological, structural, electronic, and optical properties of hexagonal and monoclinic polymorphs of BiPO 4 . Herein, we demonstrate how microwave irradiation induces the transformation of the hexagonal to a monoclinic phase one in a short period of time and thus, the photocatalytic performance of BiPO 4 . To complement and rationalize the experimental results, first-principle calculations have been performed within the framework of the density functional theory. This was aimed at obtaining the geometric, energetic and structural parameters as well as vibrational frequencies; further, electronic properties (band structure diagram and density of states) of the bulk and the corresponding surfaces of both hexagonal and monoclinic surfaces of BiPO 4 were also acquired. A detailed characterization of the low vibrational modes of both hexagonal and monoclinic polymorphs is key in explaining the irreversible phase transformation from hexagonal to monoclinic. Based on the calculated values of the surface energies, a map of the available morphologies of both phases was obtained by using the Wulff construction and compared with the observed SEM images. The BiPO 4 crystals obtained after 16-32 min of microwave irradiation provided excellent photodegradation of Rhodamine B under visible light irradiation. This enhancement was found to be related to the surface energy and the types of clusters formed on the exposed surfaces of the morphology. These findings provide details of the 3 hexagonal to monoclinic phase transition in BiPO 4 during microwave irradiation; further, the results will assist in designing electronic devices with higher efficiency and reliability.
In this paper, we report the synthesis
of silver selenite (Ag2SeO3) by different methods
[sonochemistry, ultrasonic
probe, coprecipitation, and microwave-assisted hydrothermal methods].
These microcrystals presented a structural long-range order as confirmed
by X-ray diffraction (XRD) and Rietveld refinements and a structural
short-range order as confirmed by Fourier transform infrared (FTIR)
and Raman spectroscopies. X-ray photoelectron spectroscopy (XPS) provided
information about the surface of the samples indicating that they
were pure. The microcrystals presented different morphologies and
sizes due to the synthesis method as observed by field emission scanning
electron microscopy (FE-SEM). The optical properties of these microcrystals
were evaluated by ultraviolet–visible (UV–vis) spectroscopy
and photoluminescence (PL) measurements. Thermal analysis confirmed
the temperature stability of the as-synthetized samples. Further trapping
experiments prove that the holes and hydroxyl radicals, to a minor
extent, are responsible for the photocatalytic reactions. The experimental
results are sustained by first-principles calculations, at the density
functional theory (DFT) level, to decipher the structural parameters,
electronic properties of the bulk, and surfaces of Ag2SeO3. By matching the experimental FE-SEM images and theoretical
morphologies, we are capable of finding a correlation between the
morphology and photocatalytic activity, along with photodegradation
of the Rhodamine B dye under UV light, based on the different numbers
of unsaturated superficial Ag and Se cations (local coordination,
i.e., clusters) of each surface.
In this study, we report the potential of ethylenediamine (En) in the modification of the morphological, structural, optical and catalytic properties of α-Ag2WO4 crystals decorated with Ag nanoparticles (Ag NP)....
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