Arsenic: Removal from Water
Contamination of arsenic in surface and ground water is a worldwide problem today. Arsenic is widely distributed in nature as a metalloid and as a chemical compound both in organic and inorganic forms. Among all other forms As(III) and As(V) are mostly found in nature and the former is predominantly found in ground waters and pose a serious threat to health. Presence of arsenic, even at low concentrations, in drinking water causes severe health, such as skin damage, heart disease, and respiratory problems. Moreover, because of its mutagenic nature, it can also lead to cancer in the skin, lungs, liver, and kidney. Due to these reason removal of arsenic from water is very important before use it. However, the World Health Organization (WHO) has established a provisional guideline value of 0.01 mg/L for arsenic in drinking water.
Many conventional techniques, such as precipitation, oxidation, membrane technologies, filtration, adsorption, coagulation, flocculation and ion exchange have been applied for the removal of arsenic shows a schematic of different methods for the removal of arsenic from water. Conventional adsorbents used in arsenic removal are activated carbons, soil, alumina and resins. But these methods are having some limitations, such as lower % removal of arsenic, high cost method, pH dependent process, etc. Moreover, these processes produce a high amount of arsenic-concentrated sludge. Management of this sludge again becomes necessary so as to prevent the consequence of secondary pollutants in the environment and this treatment of sludge is costly. In this scenario a simple, inexpensive and highly efficient method is demanding for the removal of arsenic from water. Recent advancement of nanomaterials is showing some alternative path for removing the arsenic from water. Because of high specific surface area, high reactivity and high specificity, nanomaterials have been considered as novel adsorbents for water contaminants. Carbon nanotubes and nanocomposites, titanium, iron and other metal-based nanomaterials are widely investigated for the treatment of arsenic contamination. Literature shows that nanomaterial based adsorbents have good removal efficiency of arsenic from water as well as they have good recycled properties. Overall this technology is quite simple, inexpensive and suitable for the treatment of arsenic contaminated water to bring it arsenic free.
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D.; Rahman, M. M.; Raul, K.; Chowdhyry, U. K.; Sengupta, M. K.; Lodh, D.;
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Production of Biodiesel using
The search for sustainable and renewable energy resources has become the most significant challenge in the present era. Energy crisis, depletion of nonrenewable energy sources, along with considerable increase of environmental pollution due to the use of fossil based fuels might endanger the existence of mankind for the upcoming century. In this scenario biodiesel might be a perfect alternative. Biodiesel is reported to be one of the most renewable fuel sources and possesses nontoxic and biodegradable properties with less emission of greenhouse gases like NOx, SOx, CO, CO2, etc. Biodiesel is nothing but the lower alkyl ester of long chain fatty acids produced due to the transesterification reaction.
Transesterification is the reaction of oil or fat with alcohol to form alkyl esters and glycerol. As the demand of substitute of petroleum based products is increasing day by day more importance should be given for the production of biodiesel. Several research groups have reported for the increase of commodity price of food and animal feed stocks due to the emergence of first generation of biofuels. With this context the advent of the second generation biodiesel production became inevitable. The use of second generation of biodiesel can reduce the price of feedstock by 2 to 3 times. The second-generation biodiesel production utilizes heterogenous catalyst for accelerating the reaction and also to increase the ultimate yield of the biodiesel. Cheap sources of feed stocks, such as waste cooking oil, rubber seed oil, rap sed oil, jatopha oil, etc were used.
The heterogenous catalyst, such as nanomaterials which exhibit extraordinary properties, can be utilized for the production of biodiesel. Properties such as insolubility, recyclability, stability, ability to produce FAME under normal temperatures and atmospheric pressure makes it advantageous over the heterogenous catalyst. Moreover, because of lower particle size and higher surface area, nanaomaterials were reported to be more active in transesterification reaction. TiO2 is reported to have some significant properties compared to other conventional nanomaterials. Significant properties of TiO2 include durability, antifungal, environmental friendly, Copper was reported to possesses some good thermophysical properties, such as thermal conductivity, antifungal properties, etc.
Very few works were done on metal impregnated TiO2 as catalyst for the production of biodiesel. Very recently Li impregnated TiO2 was used as a catalyst for the production of biodiesel and it was reported an product yield of 98%. Impregnation method is effective due to the shift of electronic band structures of the shell metal. The synthesized catalysts can be used for the production of biodiesel from palm oil.
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Catalysis Applications of Semiconductor Nanomaterial
Metal oxide semiconductors play an important role in different areas of science and engineering. The application of this material in the field of catalysis has become a substantial research area. In the past decades, the utilization of transition metal oxide nanoparticle catalysts for industrial application in the synthesis of important chemical intermediates has been investigated by industrial and academic communities. Compared to other catalysts, one of the outstanding properties of metal oxide nanoparticles in catalysis is represented by the high selectivity which allows discrimination within chemical groups and geometrical positions, favoring high yields of the desired product. The metal oxide nanoparticles exhibit unique chemical and physical properties due to their high density and limited size of corner or edge on the surface sites. In order to display mechanical stability, nanoparticles must have a low surface free energy. As a consequence of this requirement, phases that have a low stability in bulk materials can become very stable in nanostructures.
Among several metal oxide semiconductor nanoparticles TiO2 is a promising photo catalyst because of its relatively higher efficiency, low toxicity, long term stability, low cost, photoinduced strong oxidation activity properties. Being used in this manner contributes to the ability of TiO2 to develop Lewis acidity as well as redox properties. TiO2 is considered very close to an ideal semiconductor for photo catalysis because of high stability, low cost, and safety towards both humans and environment. But, photo catalytic activity of TiO2 is limited in visible light because of certain limitations such as poor absorption of visible radiation, rapid recombination of photogenrated electron holes pairs and also its high band gap energy (3.03 eV for rutile and 3.18 eV for anatase).
Because of this reasons
the development of visible light active catalysts are important now.
Significant efforts have been made till now to impregnate different metals into
TiO2. The study of
deposition of metal nanoparticles on TiO2 support is important in
heterogeneous catalysis due to the size and nature of the interaction of a
metal nanoparticle with TiO2. This interaction strongly influences
the determination of catalytic activity and selectivity of the metal
heterogeneous catalyst. Reduction and oxidation at elevated
temperature are compulsory steps in the synthesis of metal supported TiO2
heterogeneous catalyst. Modification of TiO2 by depositing transition
metal like Fe, Mn, Cr, Co, Au, Ag, Pd, Pt, and Cu on the surface of TiO2.
nanoparticles are used in various of industrial applications. TiO2
and modified TiO2 are used in antiseptic and antibacterial
compositions, degrading organic contaminants and germs, UV-resistant material,
manufacturing of printing ink, self-cleaning ceramics and glass, coating,
making of cosmetic products. It is also used in the paper industry for
improving the opacity of the paper.
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