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An Approach for Development of Materials for Green Chemical Catalytic Processes: Green Catalysis
Published in Neha Kanwar Rawat, Iuliana Stoica, A. K. Haghi, Green Polymer Chemistry and Composites, 2021
Rimzhim Gupta, Akanksha Adaval, Sushant Kumar
Photocatalysis drives the chemical reaction by activation of catalysts via absorption of photons.84 Photocatalysts are the substances that facilitate the active surface sites for pollutants or reactant molecules to adsorb/adhere at its surface. The photocatalysts are the photoactive materials/semiconductors that absorb in UV/visible or infrared wavelengths. Absorption of photons of energy equal to its bandgap facilitates the excitation of electrons from valence band to the empty conduction band, leaving behind a vacancy of opposite charge, that is, holes. These bands are the filled or unfilled orbitals of the elements of the respective semiconductor. Based on the location of maxima of valence and minima of the conduction band, band gaps are classified into two categories, that is, direct and indirect band gaps. The species adsorbed at the surface of catalysts are hydroxyl ion and dissolved oxygen.85 The following schematic shows the photon absorption, recombination, and surface reactions in a semiconductor (Fig. 8.8).
Tunneling Field Effect Transistors
Published in Krzysztof Iniewski, Santosh K. Kurinec, Sumeet Walia, Energy Efficient Computing & Electronics, 2019
Amir N. Hanna, Muhammad Mustafa Hussain
Figure 3.8a shows direct tunneling case where electrons tunnel from the vicinity of the conduction-band minimum to the vicinity of the valence-band maximum, without a change of momentum, ki = kf. In other words, for direct tunneling to occur, the conduction-band minimum and the valence-band maximum must have the same momentum. This is typically fulfilled by direct bandgap semiconductors, such as InAs and GaAs [23]. Figure 3.8b shows the indirect tunneling case, where the conduction band minimum does not align with valence band maximum in the E-K diagram. This is the case for indirect band gap materials, such as Si and Ge, shown schematically in Figure 3.8b as a π/a difference between the direct and indirect band gaps [23].
Natural sensitizers-mesoporous TiO2 hybrid nanomaterial for future optoelectronic applications
Published in Journal of Experimental Nanoscience, 2023
Nitasha Chaudhari, Swapnali Walake, Yogesh Hase, Paresh Nasikkar, Sandesh Jadkar, Yogesh Jadhav, Atul Kulkarni
UV–Visible absorption spectra of both the natural dyes are shown in Figure 3a. Figure 3a shows that the Manjishtha dye absorbs the visible wavelength that is 414 nm [42] and Banyan dye shows a prominent absorbance peak at 280 nm assigned to the absorption of light by aromatic amino acids like tyrosine, tryptophan or phenylalanine residues in the proteins. The presence of chlorophyll in the leaf extract of Banyan gives the absorbance at 419 nm. As shown in Figure 3b the absorption wavelength of pure TiO2 is in the UV region (∼300nm) and gives the direct band gap of 3.13 eV. The absorbance of dyes plays a very important role in the present study whereas loading of natural dyes on pure TiO2 has significantly enhanced absorption of light into the visible region. Direct and indirect band gaps were evaluated using the Kubelca–Munk function from the DRS spectra with direct band gap of 3.13 eV, 3.04 eV and 3.01 eV of TiO2, M-TiO2 and B-TiO2, respectively, and indirect band gaps of 1.55 eV and 1.75 eV for B-TiO2 and M-TiO2, respectively. The decrease in the indirect band gap values after the dye loading results in the increased in number of electron-hole pair generation and hence an increase in photocurrent.
Pressure effect on mechanical stability and ground state optoelectronic properties of Li2S2 produced by Lithium−Sulfur batteries discharge: GGA-PBE, GLLB-SC and mBJ investigation
Published in Philosophical Magazine, 2019
H. Bouafia, B. Sahli, Ş. Uğur, S. Akbudak, G. Uğur
Figure 9 shows the electronic band structure of P42/mnm-Li2S2 from which we note that the valence band top coincides with Fermi level but it is not at the same point of high symmetry (k-vector) with the conduction band bottom, which indicates that the band-gap is of an indirect nature. To give more details on the values of the band-gap energy, we grouped in Table 4 all the obtained values of the direct and indirect band-gaps that are respectively obtained by GGA-PBE, optPBE-vdW, PBE-D3(BJ), mBJ and GLLB-SC and which are compared with the available value from Guochun Yang et al. [19]. Using the different potentials and functional, we note that the small found band-gap value is that between RV and ΣC, which indicates that the fundamental band-gap of P42/mnm-Li2S2 is indirect, which confirms the previous results. On the other hand, the small value of the direct band-gap is that of ΣV−ΣC.