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Synthesis of LDH for Photocatalytic Removal of Toxic Dyes from Aqueous Solution
Published in Satya Bir Singh, Prabhat Ranjan, A. K. Haghi, Materials Modeling for Macro to Micro/Nano Scale Systems, 2022
Rasna Devi, Dipshikha Bharali, Ramesh Chandra Deka
Dyes can be defined as colored substances, which bind to the substrate to which it is being applied. Dyes possess colors because they absorb light in the visible region of the electromagnetic spectrum (400–800 nm). The basic structural component responsible for the color is a chromophore group. A chromophore can be defined as substance that has nearly same absorption wavelength as that of the considering dye or as that of the substructure, which is electronically related to the dye [14]. Chromophores possess conjugated system having alternate double and single bonds. Electrons are delocalized in this conjugated system and therefore resonance of electrons occurs. Generally, chromophores contain heteroatoms like N, O, S that have nonbonding electrons. Some of commonly found chromophores in dyes are shown in Scheme 5.2. Apart from the chromophores, most dyes have another structural group, which is called auxochromes or color helpers. Although auxochromes are not directly responsible for furnishing colors of dyes, their presence can enhance the color of a colorant and influence solubility of the dye. For example, benzene itself does not show any color, but when attached to –NH2 it imparts yellowish color. Some commonly known auxochromes are –NH2, –OH, –NHR, –NR2, –COOH, –HSO3, etc.
Crystal Clear
Published in Sharon Ann Holgate, Understanding Solid State Physics, 2021
Metals are good electrical and thermal conductors because the valence electrons are not bound to the positive ions but are instead free to move around the solid and take part in conduction. (Thermal conduction is explained in Chapter 5, while electrical conduction is discussed in detail in Chapter 6.) Because the electrons in metals do not remain in the local environment of a single bond, or indeed of their parent atom, they are said to be delocalized. However, despite the fact that the electrons in solid metals are not bound to any particular atom, they are bound to the metal as a whole. They can only escape from the metal if they receive enough energy from, for example, a beam of light or X-rays, to overcome their attraction to the metal. (The ejection of electrons from metals by electromagnetic radiation is of course the well-known photoelectric effect.)
Interaction of Nanoparticles with Crop Plants
Published in Ramesh Raliya, Nanoscale Engineering in Agricultural Management, 2019
Samarendra Barik, Saheli Pradhan, Arunava Goswami
Nanotechnology is the new era of science which explores the investigation of materials typically in the size range of 10−9 meter. Property of these nanomaterials is governed by both classical physics/chemistry and quantum mechanics. This new science was pioneered by American physicist Richard Feynman in his famous lecture “There’s Plenty of Room at the Bottom”. Since then, nanotechnology has taken a long stride into the modern research field. Presently, overwhelming applications of nanotechnology have expanded to catalysis, optical communications, sensing, optoelectronics and bio-medical sectors (Klaine et al. 2008, Zhao and Castranova 2011). Normally nanomaterials possess small size, high surface area, porosity and high surface area per volume ratio which results in alterable chemical and physical properties compared to its bulk materials. Surface functionality, magnetic properties, aggregation properties and often unique emission properties contribute to their improved catalytic properties (Salata 2004). Depending upon the localization of the electrons, nanomaterials are classified as: (a) metallic/conductor (have delocalized electrons) or (b) insulator (have localized electrons). In terms of quantum mechanics, often there is a restriction of electronic movement within the system. Considering such restriction of electronic movement, nanomaterials are classified as: (a) zero-dimensional (quantum dots), (b) 1-dimensional (nanowires), (c) 2-dimensional (nanotubes) and (d) 3-dimensional (clusters). Band-gap (a difference between the valence band and conductance band) plays the pivotal role of such electronic movement.
Metal nanoclusters: from fundamental aspects to electronic properties and optical applications
Published in Science and Technology of Advanced Materials, 2023
Rodophe Antoine, Michel Broyer, Philippe Dugourd
The metallic character of small metal clusters may be discussed on a different points of view. The first aspect is to consider the electrons responsible of the bonding. In covalent systems, the electrons roughly localized on the line connecting two atoms. In ionic bonding, the electrons are located on the atoms. In metals, the electrons are delocalized, this means that they are between the atoms. In this respect in Na5 and even in Na3 [40,49], the electrons are already delocalized and the bonding is metallic. It is similar for transition metal clusters even if the bonding is more complicated with both d and s electrons. The only exception is divalent metal clusters which have an ns2 atomic structure. The metallic character comes from the mixing of s and p band which occurs as the size increases from typically 10 or 20 atoms, except for mercury where the gap closure between s and p bands occur around 200 atoms [50]. Therefore, for most divalent metal clusters, the metallic character of the bonding is present for very small sizes even if the progressive building up of the metallic bands needs a given number of atoms depending of studied element.
Monitoring polycyclic aromatic compounds exposure in fish using biliary metabolites
Published in Critical Reviews in Environmental Science and Technology, 2022
Jamie M. Dearnley, Charles Killeen, Rebecca L. Davis, Vince P. Palace, Gregg T. Tomy
Polycyclic aromatic compounds are ring-based aromatic compounds composed primarily of carbon and hydrogen (Figure 1). Those consisting solely of carbon and hydrogen comprise a subset of PACs known as polycyclic aromatic hydrocarbons (PAHs). Other PACs incorporate other elements, referred to as heteroatoms, into their structures while still maintaining aromaticity. Nitrogen, oxygen, and sulfur are the most common heteroatoms to be incorporated (Collier et al., 2013). With only two fused rings, naphthalene is the simplest PAC and PACs containing seven rings and more are commonly documented. PACs can also be substituted by one or more alkyl groups, rendering compounds termed alkyl-PACs. Most PACs are exceedingly non-polar, imparting them with high lipophilicity and low water solubility. This leads to PACs generally being strongly bioaccumulative in fatty tissues, as evidenced by their high octanol-water partition coefficients (KOW; Sette et al., 2013). This tendency to partition into lipids generally increases with the number of constituent rings; two-ringed naphthalene has log KOW = 3.35, while most six-ringed PACs have log KOW >7 (Achten & Andersson, 2015). Aromatic compounds have some unique properties associated with their delocalized electronic structures including unusually high chemical stability and fluorescence (Bandeira & Meneses, 2013). In particular, the environmental persistence of PACs is due to the aromaticity (cyclic delocalized electrons) of their fused ring structures. These compounds are not readily degraded by common processes which destroy other common xenobiotics, such as atmospheric oxidation. Aromaticity is also responsible for the highly fluorescent nature of PACs, which makes fluorescence spectroscopy an ideal method for their analysis and quantitation.