Microwave-Driven Hexagonal-to-Monoclinic Transition in BiPO₄: An In-Depth Experimental Investigation and First-Principles Study

Abstract

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.

Efficient Ni and Fe doping process in ZnO with enhanced photocatalytic activity: A theoretical and experimental investigation

“…The photocatalysts were irradiated under ultraviolet light, followed by UV-vis analysis to estimate the concentration of remaining RhB. It could be observed that the characteristic absorption band of RhB (at 554 nm) decreases as a result of the gradual de-ethylation of the functional groups N,N'-diethylammonium, causing the color to change from pink to transparent [63].…”

Temporal interaction of hybrid signals in various phases of Eu3+: BiPO4 through photon–phonon dressing

“…The phase transition of BiPO 4 from low-or-high temperature monoclinic phase (LTMP-or-HTMP) to hexagonal phase (HP) occurs through continuously doping trivalent Ln 3+ /Eu 3+ ions. Their different samples composition proportions i.e., 6:1 (half HP + half LTMP), 1:1 (more HP + less LTMP), 0.5:1 (pure HP), 7:1 (pure LTMP) and 20:1 (less HP + more LTMP), exhibits different phonon detuning [11]. Different crystals structure determines different lattice vibration frequencies of phase transition phonon.…”

The Relationship between Photoluminescence Emissions and Photocatalytic Activity of CeO2 Nanocrystals

“…V O present in the clusters can become V O • and V O •• depending on how photogenerated e – –h + pairs shift on the CeO 2 surface by cluster–cluster charge transfer (Figure e; steps I and II). According to Tello et al, V O • /V O •• formation in the clusters favors the processes that lead to H 2 O oxidation/O 2 reduction (Figure e; steps IV and V), resulting in the formation of ·OH and ·O 2 – radicals. After the redox processes, the clusters regenerate, continuing the oxidation processes (Figure e; steps III–V).…”