الفهرس 
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Abstract
Metal oxides play a very important role in many areas of chemistry, physics and materials science [Manoj et al, 2012; Dong and Bok, 2014; Marcos and José, 2007; Fernández-García et al, 2004].
The metal elements are able to form a large diversity of oxide compounds [Steurer, 2014].
These can adopt a vast number of structural geometries with an electronic structure that can exhibit metallic, semiconductor or insulator character.
In technological applications, oxides are used in the fabrication of microelectronic circuits, sensors, piezoelectric devices, fuel cells, coatings for the passivation of surfaces against corrosion, and as catalysts [Marcos and José, 2007].
I.2. Synthesis of Nanopartical Oxides.
I.2.1. Sol-gel processing.
The method prepares metal oxides via hydrolysis of precursors, usually alcoxides in alcoholic solution, resulting in the corresponding oxo-hydroxide. Condensation of molecules
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by giving off water leads to the formation of a network of the metal hydroxide: Hydroxyl-species undergo polymerization by condensation and form a dense porous gel. Appropriate drying and calcinations lead to ultrafine porous oxides [John and Nico, 2000].
I.2.2. Microemulsion technique.
Microemulsion or direct/inverse micelles represent an approach based on the formation of micro/nano-reaction vessels under a ternary mixture containing water, a surfactant and oil.
Metal precursors on water will precede precipitation as oxo-hydroxides within the aqueous droplets, typically leading to mono dispersed materials with size limited by the surfactant-hydroxide contact [Uskokovick and Drofenik, 2005].
I.2.3. Solvo-thermal methods.
In this case, metal complexes are decomposed thermally either by boiling in an inert atmosphere or using an autoclave with the help of pressure. A suitable surfactant agent is usually added to the reaction media to control particle size growth and limit agglomeration [Marcos and José, 2007].
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I.2.4. Template/Surface derivatives methods.
Template techniques are common to some of the previous mentioned methods and use two types of tools; soft-templates (surfactants) and hard-templates (porous solids as carbon or silica). Template- mediated and surface-mediated nanoparticles precursors have been used to synthesize self-assembly systems [D´Souza and Richards, 2007].
I.2.5. Multiple-pulsed laser deposition.
Multiple-pulsed laser deposition heats a target sample (4000 K) and leads to instantaneous evaporation, ionization, and decomposition, with subsequent mixing of desired atoms [Marcos and José, 2007].
I.2.6. Co-precipitation methods.
This involves dissolving a salt precursor (chloride, nitrate, etc.) in water (or other solvent) to precipitate the oxo-hydroxide form with the help of a base. Very often, control of size and chemical homogeneity in the case of mixed-metal oxides are difficult to achieve. However, the use of surfactants, sonochemical methods, and high-gravity reactive precipitation appear as novel and viable alternatives to optimize the resulting
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solid morphological characteristics [D´Souza and Richards, 2007; Suslick et al, 1991; Chen et al, 2002].
I.2.7. Organic solvent method.
Nanocrystalline metal oxide powder was prepared by the reaction between metal nitrate and oxalic acid in ethanol solvent. Calcination gives narrow distribution, weak agglomeration and small particle size [Guo-Jun Li et al, 2001].
I.2.8. Microwave irradiation method.
Microwave processing of materials has attracted the growing interest of researchers worldwide. The benefits of microwave processing are mostly associated with the possibility of volumetric heating and some peculiar features [Akrati et al, 2013].
Microwave irradiation using metal nitrate and sodium hydroxide solutions as the starting materials. The precipitation of metal hydroxide after dry was irradiated by microwave radiation for short time [Mohammadyani et al, 2012].
I.3. Applications of Metal Oxides in Removal of Heavy Metals.
Nowadays, numerous methods have been proposed for efficient heavy metal removal from water, including but not limited to adsorption.
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Among the available adsorbents, nanosized metal oxides (NMOs), including nanosized ferric oxides, manganese oxides, aluminum oxides, titanium oxides, magnesium oxides and cerium oxides, are classified as the promising ones for heavy metals removal from aqueous systems [Ming, et al, 2012; Tiwari, et al, 2014; Agrawal and Sahu, 2006].
I.4. Pollution of Water.
The pollution of water resources due to the indiscriminate disposal of heavy metals has been causing worldwide concern for the last few decades. It is well known that some metals can have toxic or harmful effects on many forms of life. Metals, which are significantly toxic to human beings and ecological environments, include chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), manganese (Mn), cadmium (Cd), nickel (Ni), zinc (Zn) and iron (Fe), etc. [Meena et al, 2005].
This problem has received considerable amount of attention in recent years. One primarily concern is that marine animals which can readily absorb those heavy metals in waste water and directly enter the human food chains present a high health risk to consumers [Mohamed and Youssouf, 2014].
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Waste water from many industries such as metallurgical, tannery, chemical manufacturing, mining, battery manufacturing industries, etc. contains one or more of these toxic heavy metals. Industries carries out operations like electroplating, metal/surface finishing and solid-state wafer processing, generate waste water contaminated with hazardous heavy metals. The concentrations of some of the toxic metals like Cr, Hg, Pb, As, etc. are higher than permissible discharge levels in these effluents. It, therefore, becomes necessary to remove these heavy metals from these waste water by an appropriate treatment before releasing them into the environment [ Meena et al, 2005].
The chemical industry comprises the companies that produce industrial chemicals. Basic chemicals or ‘‘commodity chemicals’’ are abroad chemical category including pharmaceutical products, polymers, bulk petrochemicals and intermediates, other derivatives and basic industrials, inorganic/organic chemicals, and fertilizers. The chemical industry is of importance in terms of its impact on the environment [ Mohamed and Youssouf, 2014].
Chemical industrial waste water usually contains organic and inorganic matter in varying concentrations. Many materials
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in the chemical industry are toxic, mutagenic, carcinogenic or simply almost non-biodegradable. This means that the production waste water also contains a wide range of substances that cannot be easily degraded. For instance, surfactant and petroleum hydrocarbons, among other chemical products that are being used in chemical industry reduce performance efficiency of many treatments unit operations [Fayza et al, 2007].
I.5. Water Pollution in Egypt.
Water pollution is one of the environmental and public health problems in Egypt and the Middle East region are facing [Anwar, 2003]. In Egypt pollution is generally associated with heavy industrialization and dense population and is one of the ecological problems of the river Nile system [Hussein and Raouf, 2002]. The river Nile is the principal fresh water resource for the country, meeting nearly all demands for drinking water, irrigation, and industry [Alaa and Werner, 2010].
The pollution of the river Nile resulted from many sources, e.g. accidental spillage and deficiencies in the treatment of chemical wastes, discharge of industrial or
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sewerage effluents, domestic waste water, the disposal of untreated sewage and gasoline from fishery boats
[Tahlawi and Farrag, 2007; Ali and Soltan, 1996; Mohamed et al, 1998]. Furthermore, modern agricultural activities have introduced several polluting substances such as organic matter, chemical fertilizer, and insecticides into the river Nile and the drainage systems.
I.6. Heavy Metals.
Heavy metals are elements having atomic weights between 63.5 and 200.6, and a specific gravity greater than 5.0 [Srivastava and Majumder, 2008]. With the rapid development of industries such as metal plating facilities, mining operations, fertilizer industries, tanneries, batteries, paper industries and pesticides, etc., heavy metals waste water are directly or indirectly discharged into the environment increasingly, especially in developing countries. Unlike organic contaminants, heavy metals are not biodegradable and tend to accumulate in living organisms and many heavy metal ions are known to be toxic or carcinogenic. Toxic heavy metals of particular concern in treatment of industrial waste water include zinc, copper, nickel, mercury, cadmium, lead and chromium [Fenglian and Qi, 2011].
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There are many heavy metals in our environment both naturally and from pollution. The term “heavy metal” applies to a group of metals with similar chemical properties. Some of these, including copper, iron and zinc, play important roles in our bodies. Others have no known benefit for health. Examples of these are lead, which is found in paint in old homes as well as many other sources; arsenic, which can be found in well water and wood products; and mercury, which can build up in fish that we eat. At very high levels, most heavy metals can cause health problems. Luckily, this is very uncommon. [Bánfalvi, 2001].
The level of heavy metals in the water and in the sediment of some parts of the river Nile is higher than the tolerance levels or limits set by the Egyptian General Authority for Standards and Quality Control [Anwar, 2003].The presence of heavy metals in different kind of food constitutes serious health hazards, depending on their relative levels.
I.6.1. How are people exposed to heavy metals?
People may be exposed to small amounts of heavy metals through food, water, air, and commercial products. People can also be exposed in their workplace, as several industries use or produce these metals. Each metal is different in where it is found and how it behaves in our bodies. Exposure
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alone does not mean that it is causing any disease or harm. [Fulekar, 1999].
I.6.2. What are the symptoms of “chronic” heavy metal poisoning?
There is growing evidence that “chronic” or long-term exposure to lower levels of heavy metals also causes health problems. The symptoms of chronic heavy metal poisoning can be severe, but are often less obvious and develop much more slowly over time than the symptoms caused by acute exposure. This is a topic of growing scientific evidence that still needs more research to clarify all the possible health effects. chronic heavy metal poisoning can be challenging for both health care providers and patients because there are often many more questions than answers.
Many of the symptoms of chronic heavy metal toxicity can include:
1-Headache 2- Constipation
3-Muscle and joint pains 4-Weakness
True chronic heavy metal poisoning is rare. More often, these same symptoms can be caused by other health problems not related to a metal exposure at all. It is important to know
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that it may not be possible to find the true cause [Bánfalvi, 2001].
I.6.3. Lead and its impact on human health.
Lead is one such heavy metal with specific toxicity and cumulative effects. The chief sources of lead in water are the effluents of lead and lead processing industries. Lead is also used in storage batteries, insecticides, plastic water pipes, food, beverages, ointments and medicinal concoctions for flavoring and sweetening [Ponangi et al, 2000].
Lead poisoning causes damage to liver, kidney and reduction in hemoglobin formation, mental retardation, infertility and abnormalities in pregnancy. chronic lead poisoning may cause three general disease syndromes:
(a) Gastrointestinal disorders, constipation, abdominal pain, etc.
(b) Neuromuscular effects (lead lapsy) weakness, fatigue muscular atrophy.
(c) Central nervous system effects or CNS syndrome that may result to coma and death [Manahan, 1984].
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I.6.4. Manganese and its impact on human health.
Chronic manganese poisoning has been reported to affect the central nervous system, and manganese pneumonia has often been reported to be resulting in death [Hanaa et al, 2000]. Manganese toxicity has been found to results in acute effects on lungs, liver, central nerves system and blood system of the body.
Manganese and its salts have been reported to be present in the waste water of the following industries: steel alloy dry cell battery, glass and ceramics, paint and varnish, ink and dyes, match and fireworks [Silvio and Jorge, 2009]. Galvanization plant effluents have also been found to contain Mn(II) at significant levels.
I.6.5. Zinc and its impact on human health.
Due to its remarkable resistant to atmospheric corrosion, zinc is commonly used to protect iron from rusting, in the process called galvanization. Zinc is widely used for the manufacturing of zinc white and several useful alloys such as brass, German silver, delta metal, for the preparation of gold and silver in the cyanide method, for the desilverization of lead in Parks process and as an anode material in galvanic cells.
Various zinc salts are used industrially in wood preservatives, catalysts, photographic paper, accelerators for
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rubber vulcanization, ceramics, textiles, fertilizers, pigments, steel production and batteries [Ananda, 2013]. Zinc toxicity from excessive ingestion is uncommon but causes gastrointestinal distress and diarrhea.
I.6.6. Cadmium and its impact on human health.
Cadmium is an irritant to the respiratory tract and prolonged exposure to this pollutant can cause anemia and a yellow stain that gradually appears on the joints of the teeth.
Cadmium and their salts are used in electroplating, paint pigments, plastics, silver cadmium batteries [Johannes et al, 2006], smelting, cadmium nickel batteries, stabilizer, phosphate fertilizer, mining and alloy industries [Bernard, 2008; Meena et al, 2004].
I.6.7. Copper and its impact on human health.
Environmental contamination due to copper is caused by mining, printed circuits, metallurgical, fiber production, pipe corrosion and metal plating industries [Georgopoulos et al, 2001].
The other major industries discharging copper in their effluents are paper and pulp, petroleum refining and wood preserving. Agricultural sources such as fertilizers, fungicidal sprays and animal wastes, also lead to water pollution due to copper.
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Copper may be found as a contaminant in food, especially shellfish, liver, mushrooms, nuts and chocolates. Any packaging container using copper material may contaminate the product such as food, water and drink.
Copper has been reported to cause neurotoxicity commonly known as “Wilson’s disease” due to deposition of copper in the lenticular nucleus of the brain and kidney failure [Petr et al, 2014]. In some instances, exposure to copper has resulted in jaundice and enlarged liver. It is suspected to be responsible for one form of metal fume fever [Brewer, 2010].
Moreover, continued inhalation of copper-containing sprays is linked to an increase in lung cancer among exposed workers.
I.6.8. Mercury and its impact on human health.
Mercury is generally considered to be one of the most toxic metals found in the environment [Hailemariam and Bolger, 2014].
Once mercury enters the food chain, progressively larger accumulation of mercury compounds takes place in humans and animals.
The major sources of mercury pollution in environment are industries like chlor-alkali, paints, pulp and paper, oil
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refining, rubber processing and fertilizer [Manohar et al, 2002], batteries, thermometers, fluorescent light tubes and high intensity street lamps, pesticides, cosmetics and pharmaceuticals [Krishnan and Anirudhan, 2002].
Methyl mercury causes deformities in the offspring, mainly affecting the nervous system (teratogenic effects). Children suffer from mental retardation, cerebral palsy and convulsions.
Mercury also brings about genetic defects causing chromosome breaking and interference in cell division, resulting in abnormal distribution of chromosome.
Mercury causes impairment of pulmonary function and kidney, chest pain and dyspnoea [María et al, 2007].
The harmful effect of methyl mercury on aquatic life and humans was amply brought out by the Minamata episode in Japan [Ullrich et al, 2001].
I.6.9. Nickel and its impact on human health.
Electroplating is one important process involved in surface finishing and metal deposition for better life of articles and for decoration. Although several metals can be used for electroplating, nickel, copper, zinc and chromium are the most commonly used metals, the choice depending upon the specific requirement of the articles. During washing of the
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electroplating tanks, considerable amounts of the metal ions find their way into the effluent.
Ni(II) is present in the effluents of silver refineries, electroplating, zinc base casting and storage battery industries [Maryam et al, 2014].
Higher concentration of nickel causes cancer of lungs, nose and bone. Dermatitis (Ni itch) is the most frequent effect of exposure to Ni, such as coins and jewellery.
Acute poisoning of Ni(II) causes headache, dizziness, nausea and vomiting, chest pain, tightness of the chest, dry cough and shortness of breath, rapid respiration, cyanosis and extreme weakness [Piyush et al, 2007; Paul et al, 2012].
I.7. Heavy Metal Wastewater Treatment Techniques.
In view of the toxicity and in order to meet regulatory safe discharge standards, it is essential to remove heavy metals from waste water/effluents before it is released into the environment. Conventional methods for the removal of heavy metals include precipitation, coagulation/ flocculation, ion exchange, reverse osmosis, complexation/ sequestration, electrochemical operation and biological treatment [Fenglian and Qi, 2011 ; Barakat, 2011; Akpor and Muchie, 2010].
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I.7.1. Chemical precipitation.
Chemical precipitation is effective and by far the most widely used process in industry [Ku and Jung, 2001] because it is relatively simple and inexpensive to operate. In precipitation processes, chemicals react with heavy metal ions to form insoluble precipitates. The forming precipitates can be separated from the water by sedimentation or filtration. And the treated water is then decanted and appropriately discharged or reused. The conventional chemical precipitation processes include hydroxide precipitation and sulfide precipitation.
I.7.2. Ion-exchange.
Ion-exchange processes have been widely used to remove heavy metals from waste water due to their many advantages, such as high treatment capacity, high removal efficiency and fast kinetics [Kang et al, 2004].
Ion-exchange resin, either synthetic or natural solid resin, has the specific ability to exchange its cations with the metals in the waste water. Among the materials used in ion-exchange processes, synthetic resins are commonly preferred as they are effective to nearly remove the heavy metals from the solution [Alyüz and Veli , 2009]