Explore chapters and articles related to this topic
Functional Nanomaterials
Published in Yasser Shahzad, Syed A.A. Rizvi, Abid Mehmood Yousaf, Talib Hussain, Drug Delivery Using Nanomaterials, 2022
Imran Saleem, Yousef Rasmi, Leyla Fath-Bayati, Zohreh Arabpour
Excitation Bohr radius is the gap between electron and hole in valence band. Decrease in size of semiconductor materials to nanoscale range results in increased surface-to-volume ratio and quantum size effect. If the dimension of the semiconductor materials is decreased to nanometer scales less than Bohr radius (a few nanometers), these nanoscale size materials are termed semiconductor quantum dots (QDs) (Pawar et al. 2018). Semiconductor materials encompass chemical elements near the commonly named “metalloid staircase” on the periodic table of elements gallium arsenide, silicon, and germanium (Saleh 2020). Generally, these semiconductor nanomaterials consist of various components from periodic table groups, including II–VI, III–V, and IV (GaAs) (Saleh 2020).
Advanced Sputtering Technologies of Flexible Hard Nanocoatings
Published in Sam Zhang, Jyh-Ming Ting, Wan-Yu Wu, Protective Thin Coatings Technology, 2021
In this section, a possibility of the formation of hard and simultaneously tough alloy films is demonstrated on metal + metalloid (Me, Met) alloy films. The metalloid is a chemical element with properties between those of typical metals and non-metals. The metalloid elements are found in the middle of the main group of the periodic table at the point where the metals and non-metals meet; see Figure 1.12. Typical metalloids have a metallic appearance, but they are brittle and only fair conductors of electricity. Chemically, they behave mostly as non-metals. Despite the fact that the metalloid elements are brittle they can form flexible hard materials in a combination with TM elements, that is, in (TM, Met) alloys. It is demonstrated for the (Zr,Si) alloy films with a high Si content [70].
Heavy Metals
Published in Abhik Gupta, Heavy Metal and Metalloid Contamination of Surface and Underground Water, 2020
The chemical elements are classified into three broad classes: metals, metalloids, and non-metals. Metals have been defined as “elements which conduct electricity, have a metallic luster, are malleable and ductile, form cations, and have basic oxides” (Atkins and Jones 1997—cited in Duffus 2002). Most metals remain solid at room temperature except mercury (Hg), which is a liquid at room temperature. Another property of metals is their relatively high density. The metalloids share properties of metals and non-metals. Some of the metalloids can conduct electricity under certain conditions, which makes them excellent semiconductors. Metalloids can be either shiny like metals, or dull and lacking in luster like the non-metals. There are differences of opinion about the list of elements in the metalloid category. Arsenic (As), antimony (Sb), boron (B), germanium (Ge), silicon (Si), and tellurium (Te) are commonly designated as metalloids. Selenium (Se), polonium (Po), and astatine (At) are also sometimes designated as metalloids. However, according to the three-criteria description of metalloids (Masterton and Slowinski 1977—cited in Vernon 2013), selenium is better classified as a non-metal, and polonium as a metal. Astatine, although often classified as a non-metal, could be considered as a metalloid based on more recent assessments (Vernon 2013).
Statistical optimization of arsenic biosorption by microbial enzyme via Ca-alginate beads
Published in Journal of Environmental Science and Health, Part A, 2018
Suchetana Banerjee, Anindita Banerjee, Priyabrata Sarkar
The colossal industrial and population growth is leading to continuous disintegration of the environment. Environmental pollutants like heavy metals, toxic industrial effluents cause serious health problems in humans. Among these pollutants, the toxic metalloid arsenic poses serious hazardous effect on human health like skin pigmentations, various neurological and carcinogenic disorders like bladder, kidney, liver cancer.[1] Contamination of drinking water by arsenic (As), is a worldwide major concern in urban water supply system. World health organization (WHO) provided the guideline for arsenic level in drinking water at 10 µg mL−1.[2] The utmost importance should be given to removal of arsenic from drinking water. Arsenic occurs in various oxidation states, the inorganic form of arsenic being arsenite [As(III)] and arsenate [As (V)] abundantly found in water. The most available form present in the oxygenated environments is As(VI).[3,4]
The fate of selected heavy metals and arsenic in a constructed wetland
Published in Journal of Environmental Science and Health, Part A, 2019
Jan Šíma, Lubomír Svoboda, Martin Šeda, Jiří Krejsa, Jana Jahodová
Cadmium is a highly toxic heavy metal with serious effects on organisms. It has no known nutritional consequence for biota. Its concentrations in wastewater should be controlled and if they are increased the wastewater should be appropriately treated. Gao et al.[10] measured the high removal efficiency of Cd (91.8%) in the constructed wetland. Their study was conducted at the microcosmic subsurface vertical flow treatment system planted with Iris sibirica. On the other hand, Březinová and Vymazal[11] observed only the 10% efficiency of Cd removal from wastewater in a treatment wetland planted with Phalaris arundinacea. Lead is a serious pollutant of diverse kinds of wastewater. It is a cumulative poison. It acts as a physiological and neurological toxin to humans. Březinová and Vymazal[11] reported the low Pb removal efficiency (29%) in the case of a constructed wetland planted with Phalaris arundinacea. Gill et al.[12] tested the long-term performance of a constructed wetland treating highway runoff. The removal efficiency of Pb over a 6-year period was 20% only. Copper is an essential microelement for plant and animal organisms.[13] However, its storage in constructed wetland sediments brings a potential risk of creating a hazardous material. Morari et al.[14] obtained the removal efficiency of 91% in the case of Cu. However, Arroyo et al.[15] observed a poorer removal efficiency of this metal in the treatment wetland (52%). Zinc is essential for both animals and plants. However, it is toxic for water organisms at high concentrations.[16] Arroyo et al.[15] observed poor removal efficiency (18%) for Zn in the constructed wetland, whereas Morari et al.[14] reported a high efficiency of 85%. Nickel is toxic even at low concentrations. It is not a cumulative poison, but its elevated concentrations or chronic exposures have toxic and carcinogenic effects. Kumari and Tripathi[17] observed the 58% efficiency of Ni removal in a treatment system planted with Phragmites australis. Březinová and Vymazal[11] reported the efficiency of Ni removal of 25% for the treatment wetland planted with Phalaris arundinacea. Chromium typically occurs in the trivalent form in diverse kinds of waters. Freshwater biota are sensitive to elevated Cr concentrations. Hexavalent chromium (CrVI) is much more toxic compared to CrIII. Cabezas and Cedeno[18] reported high Cr removal efficiencies (88–92%) in a horizontal subsurface flow-constructed wetland. Kadlec and Zmarthie[19] studied in detail a surface flow treatment wetland system. They obtained the removal efficiency of 67% for Cr. Arsenic is a naturally occurring element in all kinds of surface waters. It is considered as a metalloid as it has both metallic and nonmetallic properties. Arsenic is a known human carcinogen. It is acutely and chronically toxic to aquatic organisms. Trivalent arsenic (AsIII) compounds are more toxic than AsV.[13] Kadlec and Zmarthie[19] observed a modest removal efficiency of As (29%) in the case of a leachate treatment wetland system.