The methods utilized in preparations of ceria nanoparticles and its coating on nanotubes is also reviewed.
History of arsenic in field of chemistry, medicine and technology has been completely overshadowed by its role as poison in various homicides. In today's world extension of its similar role has been widely discussed due to world wide ground water contamination and many times referred as 21st century calamity. High concentration of arsenic has been reported from almost 21 countries and among them Bangladesh and West bengal region of India are considered to be the most affected area and significant amount of population are at risk (1). Arsenic is the 20th most abundant material found in earth crust and its concentration in most of rocks ranges between 0.5 to 2.5 mg/kg. Mobilization of arsenic is contributed by various natural phenomenon which include natural weathering reaction, biochemical mobilization, geochemical and volcanic emission etc. but, at many places excessive mining also contributes for the same. Arsenic exist in various oxidation state in natural environment which includes -3,,0.+3. and +5. Figure 1 indicates the Eh-pH diagram of arsenic at 25C.
Long term exposure to arsenic contaminated drinking water have many medical manifestation which includes skin, lungs, bladder and kidney cancer, change in pigmentation, hyperkeratosis, neurological disorders, muscular weakness loss of appetite and nausea etc. As per the WHO guidelines the permissible arsenic concentration in ground water is 10ppb (0.01mg/l).
World wide problem of ground water contamination with arsenic leads to extensive research in area of arsenic remediation in ground water. There are different methodologies developed arsenic removals, which are mainly classified as 1) Chemical processes, 2) Physical processes, 3) Biological processes, and 4) combination of all. Table 1 characterizes the various methodologies applied for arsenic remediation based on their principles.
Arsenic pollution of water occurs due to various reasons like the natural leaching of rocks containing arsenic, mining, processing of mineral deposits and a discharge of industrial pollutants. Many techniques as shown in Table 1 are known for arsenic removal and adsorption is one of the main methods for its treatment. Many adsorbents like carbon, rare earth oxides, lanthanium and yttrium impregnated alumina, ion exchange fiber and lanthanium compounds are being known for the removal of arsenic from water(3). The development of nanotechnology and nanosciences has raised the expectation of its crucial role in environmental issues. A variety of nano-materials have been experimented in treatment of environment pollutants like Photocatalytic TiO2 and ZnS for removal of organics. Zerovalent iron (Fe (0)) and bimetallic Fe (0) as effective redox media for in-situ remediation of organics and inorganic pollutant. Among others Carbon nanotubes (CNTs) emerges as one of the most promising agent to be used with other nanomaterials due to its unique mechanical, electrical, optical and thermal properties which takes it one of the most ideal supporting material for nano coatings.