Design of nanoscaled heterojunctions in precursor-derived t-ZrO2/SiOC(N) nanocomposites: Transgressing the boundaries of catalytic activity from UV to visible light

Abstract

in this work, nanocomposites made of nanosized zirconia crystallized in situ in an amorphous silicon oxycarbo(nitride) (Sioc(n)) matrix have been designed through a precursor route for visible light photocatalytic applications. the relative volume fraction of the starting precursors and the pyrolysis temperatures not only influences the phase fraction of zirconia crystallites but also stabilizes the tetragonal crystal structure of zirconia (t-Zro 2) at room temperature. the presence of carbon in interstitial sites of zirconia and oxygen vacancy defects led to drastic reduction in the band gap (2.2 eV) of the nanocomposite. Apart from being a perfect host avoiding sintering of the active phase and providing mechanical stability, the amorphous matrix also reduces the recombination rate by forming heterojunctions with t-Zro 2. the reduction in band gap as well as the formation of heterojunctions aids in harnessing the visible light for photocatalytic activity. Large scale industrialization and urbanization has led to extensive pollution and contamination of rivers and water bodies, posing a threat to future generations and sustainable development 1. Chemical industries, leather factories, paint manufactures, dyeing and plating units release harmful untreated waste directly into our water bodies 2-4. These are non-biodegradable and toxic to humans as well as flora and fauna. Filtration with activated carbon, coagulation using chemical agents, ozonization, flocculation and reverse osmosis are some of the techniques that are frequently used to remove these harmful substances 5-8. However, these techniques are not effective in complete removal and merely result in the transfer of chemicals from one source to another. The photocatalytic phenomenon is capable of converting these toxic substances (EDTA, Cr(VI), nitrite) to harmless counterparts such as hydrogen, Cr(III) and nitrates 9-11. This is achieved via a catalyst that upon subsequent excitation produces electrons and holes. These electrons and holes produce superoxide and hydroxyl radicals that are responsible for the oxidation and reduction processes 12-15. But the efficiency of photocatalyst is largely dependent on the recombination rate of these electrons and holes. This drives the need for developing suitable catalysts which could be eventually scaled up for a large-scale clean-up drive 16-19. The wide band gap (3.25-5.1 eV) combined with a negative conduction band potential (−1.0 V vs. NHE at pH 0) 11 has recently spurred a lot of research on zirconia as a photocatalyst 20-23. It is important to note that the band gap value depends on the crystal structure (3.84 eV for cubic, 4.11 eV for tetragonal and 4.51 eV for monoclinic) 24 , defects and processing route of the ceramics 25. From the available limited literature, it is known that the presence of both monoclinic and tetragonal phases of zirconia 26-28 is beneficial for photocatalysis. The high temperature tetragonal phase of zirconia namely t-ZrO 2 can be stabilized at room temperature by using suitable

Metal-doped mesoporous ZrO2catalyzed chemoselective synthesis of allylic alcohols from Meerwein–Ponndorf–Verley reduction of α,β-unsaturated aldehydes

“…47 Upon doping, the peak intensity at 3435 cm À1 decreased, indicating a decline in hydroxy groups and hydrophilic property of ZrO 2 . 48 Like pXRD patterns (Fig. 1), the peak intensity at 500-823 cm À1 representing the t-ZrO 2 decreased upon the substitution of M n+ into ZrO 2 .…”

Detection and photothermal inactivation of Gram-positive and Gram-negative bloodstream bacteria using photonic crystal biosensor and plasmonic core–shell

“…ZrO 2 is chosen for its outstanding optical properties, including transparency to visible light, excellent optical clarity, relatively low thermal conductivity, and thermal stability. 44 These qualities make it ideal for use in high-temperature environments without compromising its optical performance. 19 In addition, GaN has been chosen for its unique optical properties (including a wide bandgap, allowing efficient operation in the ultraviolet and visible light spectrum; a high refractive index, enabling effective light confinement and manipulation crucial for enhancing biosensor sensitivity and selectivity; low optical losses essential for maintaining a high signal-to-noise ratio; and chemical stability and resistance to corrosion, making it suitable for long-term and reliable operation in biological sensing environments), 45,46 making it an ideal dielectric layer for PCB.…”

One-pot Hydrothermal Synthesis and Characterization of Zirconium Oxide Nanoparticles

“…Thus, the observation of absorption maxima for ZrO 2 samples in the range of 250 to 350 nm can be linked to the charge transfer transitions from O 2 →Zr 4+ with Zr being in a low coordination state (mostly six) either in an isolated or available in the small Zr x Oy clusters (Azdad et al, 2018) . The plotting of a graph between (𝛼h𝜐) 2 and h𝜐, and then extrapolating the line drawn tangent to the resulting curve gives the value of band gap energy, as shown in Similarly, Figure 8 provides the FL spectrum of ZrO 2 NPs where the graph summarizes the main photoluminescence (PL) transitions and are appearing due to some intrinsic defects discussed in the literature, i.e., based on the calculation of oxygen vacancies (Vo) energy level above the valence band (VB) (Bhaskar et al, 2020;Horti et al, 2020). In that way, the observation of an emission band for the ZrO 2 sample around 473 nm can be attributed to the transition of electrons among the two energy levels (oxygen vacancies and VB) and thereby suggesting a possible origin for the observation of blue emission.…”