FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
J. Title of the invention
A PROCESS FOR FORMING A RICE HUSK ASH COMPOSITION
2. Applicants)
Name Nationality Address
TATA CHEMICALS LTD. INDIA BOMBAY HOUSE. 24 HOM! MODI STREET.
MUMBAI-400001
J
< z
CD 3. Preamble to the description
X 0 COMPLETE SPECIFICATION
The following specification particularly describes the invention and the manner in which it is
to be performed.

The invention relates to a process for binding metal nanoparticles to rice husk ash. More particularly the invention relates to a process for binding silver nanoparticles to rice husk ash. DESCRIPTION OF RELATED ART
Clean potable water is a basic human requirement. However, a large portion of the world's population, especially those living in developing countries do not have access to clean potable water.
Growing population, lack of sanitary conditions, poverty, poor planning, industrial pollution, over exploitation of natural water and national disasters are the main reasons of contamination of water. This contaminated water is the source of many diseases such as diarrhea, dysentery, fever, abdominal pain, and constipation, caused due to bacterial contamination transmitted through water. In India for example, as per the data collected by the Ministry of Health and Family Welfare, in 2003 there were 10.5 million cases of diarrhea with 4709 deaths resulting majorly due to consumption of contaminated water. According to the World Health Organization, the provision of safe water alone can reduce diarrheal and enteric disease by up to 50%, even in the absence of improved sanitation and other hygiene measures.
Rice husk ash has been used as a water purifier but the results obtained are not
consistent over time, the rice husk ash is not able to remove all bacteria, and the filter devices
required for adequate filtration tend to be bulky. Moreover as the rice husk ash has a potential
to trap water born bacteria due to the small size of its pores, trapped bacteria may survive on
the rice husk ash and may even seep into the water that is filtered through the rice husk ash.
In order to use rice husk ash as an effective water filtration medium, there is a need for a
process that would impart antimicrobial properties to rice husk ash, so that the rice husk ash
is also able to destroy microbes that are present in water. There is also a need for a water
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purification composition that is inexpensive, easy to use and effective in removing bacterial
contamination from drinking water.
SUMMARY
The invention relates to a process comprising binding silver nanoparticles to rice husk ash.by adding to the rice husk ash a silver precursor, and reducing the silver ions bonded to the rice husk ash by a reducing agent to obtain rice husk ash with bonded silver nanoparticles. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS:
The accompanying drawings illustrate the preferred embodiments of the invention and
together with the following detailed description serve to explain the principles of the
invention.
Fig 1: Transmission electron microscopy of dislodged silver nanoparticles from rice husk ash
bonded with silver nanoparticles synthesized using chitosan as a stabilizing agent and sodium
citrate as a reducing agent.
Fig 2: UV-Vis spectra of dislodged silver nanoparticles from rice husk ash bonded with silver
nanoparticles synthesized using chitosan as a stabilizing agent and tri-sodium citrate as a
reducing agent.
Fig 3(A):UV-Vis spectra of dislodged silver nanoparticles from rice husk ash bonded with
silver nanoparticles synthesized using sodium bis(2-ethylhexyl) sulfosuccinate as. a
stabilizing agent and tri-sodium citrate as a reducing agent.
Fig 3(B) UV-Vis spectra of dislodged silver nanoparticles from rice husk ash bonded with
silver nanoparticles synthesized using tri-sodium citrate as a stabilizing agent & ascorbic acid
as a reducing agent.
Fig 3(C) UV-Vis spectra of dislodged silver nanoparticles from rice husk ash bonded with
silver nanoparticles synthesized using and chitosan as a stabilizing agent and ascorbic acid as
a reducing agent.
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Table 1: Silver leaching in ppb, measured using GFAAS technique from the sample wherein silver nanoparticles bonded to rice husk ash using chitosan as a stabilizing agent & tri-sodium citrate as a reducing agent. DETAILED DESCRIPTION
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment described and specific language will be used to describe the same! It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the process, and such further applications of the principles of the invention therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
The following description explains the principles of the invention as applied to the
coating of silver nanoparticles. It is however believed that the teachings of the document may
be equally applied to the other metals such as copper, gold, platinum, magnesium, zinc or
titanium. In particular, a process for treating rice husk ash with a bactericidal agent is
described. The following description also discusses certain specific compounds such as
stabilizing agents and reducing agents to explain the principles of the invention. The
invention however is not restricted to such compounds as equivalent chemical compounds
may be utilized to achieve the desired end result as taught by the invention. Reference
throughout the specification to an embodiment, an aspect or similar language means that a
particular feature, characteristic or step in connection with the embodiment is included in at
least one embodiment of the present invention. References to an aspect or an embodiment
may, but do not necessarily all refer to the same embodiment.
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Rice husk is a perennially renewable agro-waste available at virtually no cost wherever rice paddy is grown. On combustion, the rice husk ash residue contains 85-95% silica, 4-12% carbon and the rest comprises of various metal oxides such as alkali, alkali earth metal and ion oxides. On account of its crypto-crystalline or amorphous and highly porous structure, the BET(Brunauer Emmett Teller) surface area of rice husk ash can be as high as 80-100 square meters per gram, depending on the conditions employed for the combustion of rice husk. Its high surface area and porosity make rice husk ash an effective filtration medium that removes particulate matter as well as color and odor from water.
The rice husk ash used for the process may be any rice husk ash that is produced by burning rice husk. The rice husk ash may be produced by burning rice husk in heaps, in a step grate furnace, fluidized bed furnace or tube-in-basket (TiB) burner. The rice husk ash may also be obtained from boilers and brick kiln, provided it is free of unburned husk and wood tar, grit, stone, and fused lumps of silica. In accordance with an aspect the rice husk ash should have high silica content. Preferably the rice husk ash should have a silica content of 60 to 90%.
Silver is a safe and effective antimicrobial agent that is lethal to single cell microorganism but is harmless to human cells. Silver's antimicrobial property stems from its extremely slow release of silver ions. These silver ions bind to the cellular components of microorganisms, disrupting the normal reproduction and growth cycle resulting in the death of the microbial cell. When made into particles only a few nanometers in size silver releases a lot more ions and therefore becomes an even stronger antimicrobial agent. Moreover unlike silver ions, elemental silver (Ag°) is not deactivated by chloride or organic matter that may be present in water. These qualities make nano silver a suitable anti microbial agent that may be bound to rice husk ash to impart antimicrobial properties to the rice husk ash.
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A process for binding silver nanoparticles to rice husk ash is described. The process effectively binds silver nanoparticles to rice husk ash such that minimum leaching of silver occurs when water is passed through the rice husk ash.
The process involves binding silver nanoparticles to rice husk ash by first binding silver ions to the rice husk ash and then reducing the silver ions bonded to the rice husk ash to obtain silver nanoparticles bound to rice husk ash. More specifically, an in-situ process for binding silver nanoparticles to rice husk ash is described. The process involves adding to the rice husk a silver precursor to obtain rice husk ash bonded with silver ions and reducing the silver ions bound to the rice husk ash by a reducing agent to obtain silver nanoparticles bound to rice husk ash.
The carbonaceous silica present in the rice husk ash carries a negative charge which helps in binding the positively charged silver ions of the silver precursor by forming electrostatic bonds. When these bonded silver ions are reduced to form silver nanoparticles, the particles so formed are also bonded strongly to the rice husk ash.
In accordance with an aspect the rice husk ash is soaked with the silver precursor for effective binding of the silver ions to the rice husk ash for a pre-determined period. The rice husk ash is soaked with the silver precursor for a period of 10 minutes to 2 hours, though longer periods of soaking may be used. Preferably the rice husk ash is soaked for a period of 1 hour.
In accordance with an aspect the reducing agent is added slowly with mild stirring and not as a dumping action. In accordance with an aspect the rice husk ash may be allowed to soak with the reducing agent for a predetermined period. The rice husk ash may be soaked with the reducing agent for a period of 10 minutes to 24 hours and preferably for a period of 1 hour.
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The rice husk ash to which silver nanoparticles are bonded is separated from the reducing agent and washed with water. The rice husk ash with bound silver nanoparticles may be separated by any means including but not limited to filtration or centrifugation, and preferably filtration. The separated rice husk ash to which nano silver is bonded is washed with copious amount of water and the water used for washing the rice husk ash with bound silver nanoparticles may be removed by any method including but not limited to filtration or vacuum filtration, preferably filtration. The rice husk ash to which silver nanoparticles are bound so obtained are dried by any method including but not limited to air drying or drying in a vacuum oven.
In accordance with an aspect the process is carried out in the presence of a stabilizing agent. The stabilizing agent prevents the aggregation of nanoparticles during their formation by capping the silver nanoparticles that are formed. The stabilizing agent also facilitates in binding of silver nanoparticles to rice husk ash due to associated charge.
In accordance with an aspect trie process comprises first binding silver ions to rice husk ash in the presence of a stabilizing agent by adding to the rice husk ash a silver precursor along with a stabilizing agent and then reducing the silver ions bound to the rice husk ash by using a reducing agent. Particularly the process comprises adding a solution of a stabilizing agent to a solution of a silver precursor to obtain a silver precursor-stabilizing agent solution; adding rice husk ash to the silver precursor_stabilizing agent solution to obtain a solution of rice husk ash bonded to silver ions in the presence of the stabilizing agent and reducing the silver ions bonded to the rice husk ash by adding a reducing agent to the rice husk ash-silver ion-stabilizing agent solution to obtain silver ions bound to rice husk ash.
By way of a specific example, the process combrises mixing a solution of silver
nitrate with a solution of chitosan in 5% citric acid to obtain a silver nitrate-chitosan solution,
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adding rice husk ash to silver nitrate chitosan solution to obtain rice husk ash-silver ions-chitosan solution and; reducing the silver ions bonded to the rice husk ash by adding tri-sodium citrate dihydrate to the rice husk ash with silver ions to obtain rice husk ash bonded with silver nanoparticles.
In accordance with an embodiment the solution of rice husk ash silver nitrate chitosan solution is heated to a boiling temperature while stirring. A solution of tri-sodium citrate is added to the boiling rice husk ash-silver nitrate-chitosan solution. In accordance with a preferred embodiment the solution of tri-sodium citrate is not added as a dumping action but added slowly. In accordance with a preferred embodiment the rice husk ash-silver nitrate-chitosan solution is boiled further after the addition of the reducing agent. Boiling assists in reducing the silver nitrate to silver nanoparticles.
In accordance with an aspect transmission electron microscopy and UV-Visible spectroscopy of dislodged silver nanoparticles from the bonded silver nanoparticles was carried out. Figure 1 shows Transmission electron microscopy of dislodged silver nanoparticles that was bonded to rice husk ash. Figure 2 shows UV-Visible spectroscopy of dislodged silver nanoparticles that were bonded to rice husk ash.
In accordance with an aspect the process comprises first binding silver ions to rice
husk ash by adding to the rice husk ash a silver precursor and then reducing the silver ions
bound to the rice husk ash in the presence of a stabilizing agent by adding a reducing agent
along with a stabilizing agent. Particularly the process comprises adding rice husk ash to a
solution of a silver precursor to obtain a solution of silver ions bonded to rice husk ash;
mixing a solution of stabilizing agent with a solution of reducing agent to form a reducing
agent-stabilizing agent solution; and reducing the silver ions bonded to the rice husk by
adding the reducing agent-stabilizing agent solution to the solution of silver ions bonded to
rice husk ash to obtain silver ions bound to rice husk ash.
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By way of a specific example the process comprises adding rice husk ash to a solution of silver nitrate to obtain a solution of silver ions bonded to rice husk ash; adding a solution of ascorbic acid to a solution of chitosan to obtain a ascorbic acid-chitosan solution and reducing the silver ions bonded to the rice husk by adding the ascorbic acid-chitosan solution to the solution of silver ions bonded to rice husk ash to obtain rice husk ash bonded with silver nanoparticles.
In accordance with a preferred embodiment the ascorbic acid-chitosan solution is not added as a dumping action but added slowly with constant stirring and the stirring is continued for a predetermined period of time after the entire ascorbic acid-chitosan solution is added.
In accordance with .an aspect UV-Visible spectroscopy of dislodged silver nanoparticles from the bonded silver nanoparticles was carried out. Figure (3) shows a Transmission electron microscopy of dislodged silver nanoparticles that were bound to rice husk ash.
In accordance with an aspect the process comprises first binding silver ions to rice
husk ash by adding to rice husk ash a silver precursor along with a stabilizing agent and then
reducing the silver ions bound to the rice husk ash by using a reducing agent along with a
stabilizing agent. Particularly the process comprises adding a solution of a stabilizing agent
to a solution of a silver precursor to obtain a silver precursor-stabilizing agent solution;
adding rice husk ash to the silver precursor-stabilizing agent solution to obtain a solution of
rice husk ash bonded to silver ions in the presence of the stabilizing agent; mixing a solution
of stabilizing agent with a solution of reducing agent to form a reducing agent-stabilizing
agent solution; and reducing the silver ions bonded to the rice husk ash by adding the
reducing agent-stabilizing agent solution to the solution of silver ions bonded to rice husk ash
to obtain silver ions bound to rice husk ash.
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The silver precursor may be any base metal salts including but not limited to AgNC>3, AgBF4, AgPF6, Ag20, CH3COOAg, AgCF3S03, AgC104, AgCl, Ag2S04- Preferably the silver precursor is silver nitrate (AgN03).
The amount of silver precursor used is such that at least 0.001% by weight of silver is available for bonding with the rice husk ash. By way of a specific example 200 g of rice husk ash is treated with 1400 ml of silver nitrate such that 0.6153 g of silver is available for bonding.
In accordance with an aspect the concentration of silver precursor may range between 0.001 M and 1M.
The reducing agent used may be any reducing agent that is capable of converting Ag+ ions to Ag° including but not limited to tri-sodium citrate, ascorbic acid, tyrosine, sodium borohydride, hydrazine hydrate or D-Glucose and preferably the reducing agent is tri-sodium citrate dihydrate. The amount of reducing agent ranges from 0.1 to 10 wt % and preferably the amount of reducing agent is 2 wt %.■
In accordance with an aspect the stabilizing agent may be any compound that prevents the aggregation of silver nanoparticles that are formed. The stabilizing agent includes but is not limited to chitosan, tri-sodium citrate dihydrate, L-lysine, tyrosine, sodium bis(2-ethylhexyl) sulfosuccinate, sodium dodecyl sulphate, cetyl trimethyl ammonium bromide, polyvinyl pyrrolidone, polyvinyl alcohol or oleylamine used alone or in combination with one another. The preferred stabilizing agent is chitosan. The amount of stabilizing agent ranges from 0.1 to 10 wt % and preferably the amount of stabilizing agent is 1 wt %.
By way of a specific example chitosan is dissolved in 5% citric acid. The citric acid is required to dissolve the chitosan and it also helps in maintaining mild acidic conditions during reduction.
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The size of silver nanoparticles that are obtained by this process are in the range of 5nm to lOOnm and preferably the size of the nanoparticles is in the range of 10 to 50 nm. The silver nanoparticles obtained by this process are spherical, triangular or flat shaped structures. In accordance with an aspect the rice husk ash with bonded silver nanoparticles may be used as a composition for removal of bacterial content from water in a water purification system.
In accordance with the aspect the process as described may also be used to bind other metal nanoparticles to rice husk ash. In accordance with an embodiment the process comprises of binding metal ions to rice husk ash by adding to rice husk ash a metal precursor to obtain metal ions bonded to rice husk ash; and reducing the metal ions bound to the rice husk ash by a reducing agent to obtain rice husk ash with bonded metal nanoparticles.
The metal ion precursor may be a precursor for any metal including copper, silver, gold, platinum, zinc, magnesium and titanium or alloys. Preferably the metal precursor is a bactericidal agent.
The process described by this document results the formation of silver nanoparticles bound to rice husk ash such that the silver nanoparticles are strongly bonded with the rice husk ash and there is minimum leaching of silver on contact with water.
In accordance with an aspect the silver leaching was measured. Bacterial
contaminated water was passes though a bed of rice husk ash coated with silver nanoparticles
and amount of silver present in the output water was measured using graphite furnace atomic
absorption spectrometry (GFAAS). Leaching was measured only after passing 100 to 200
liters of water thought the bed of rice husk ash with bonded silver nanoparticles. The testing
was continued until a total of 3000 liters of water had passed thought the bed, at intervals of
100 or 200 liters. Table 1 tabulates the results of the leaching test conducted on random
samples of output water.
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In accordance with an aspect the UV-Vis spectroscopy of the dislodged silver nanoparticles obtained was carried out. Figure 3(A) is the UV-Visible spectra of the dislodged silver nanoparticles from bonded rice husk ash obtained by using sodium bis(2-ethylhexyl) sulfosuccinate as a stabilizing agent and tri-sodium citrate as a reducing agent. Fig 3(B) UV-Visible spectra of dislodged silver nanoparticles from rice husk ash bonded with silver nanoparticles obtained using tri-sodium citrate as a stabilizing agent and ascorbic acid as a reducing agent.
The following examples are provided to explain and illustrate certain preferred embodiments of the process of the invention. Example 1
0.004 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 1% Chitosan [dissolved in 5% citric acid (C6H807)] aqueous solutions are prepared. The volume of AgNO3 is chosen such that every 200 g of rice husk ash will have 0.6153 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 7 ml of (1%) chitosan solution is added to AgN03 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash-silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 28 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of sodium citrate solution. The in-situ reduction of Ag+ ions to Ag° occurs during the boiling of rice husk ash-silver nitrate-chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with chitosan. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water.
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Example 2
0.002 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 1% Chitosan [dissolved in 5% citric acid (C6H8O7)] aqueous solutions are prepared. The volume of AgN03 is chosen such that every 200 g of rice husk ash will have 0.3076 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 3.5 ml of (1%) chitosan solution is added to AgN03 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash-silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 14 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of sodium citrate solution. The in-situ reduction of Ag+ ions to Ag° occurs during the boiling of rice husk ash-silver nitrate-chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with chitosan. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 3
0.001 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 1% Chitosan [dissolved in 5% citric acid (C6H8O7) aqueous solutions are prepared. The volume of AgN03 is chosen such that every 200 g of rice husk ash will have 0.1538 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 1.75 ml of (1%) chitosan solution is added to AgN03 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash-silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 7 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The
boiling is continued for another 15 mins after addition of sodium citrate solution. The in-situ
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reduction of Ag ions to Ag occurs during the boiling of rice husk ash-silver nitrate-chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with chitosan. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 4
0.0094 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 1% Chitosan [dissolved in 5% citric acid (C6H8O7)] aqueous solutions are prepared. The volume of AgNO3 is chosen such that every 200 g office husk ash will have 1.2307 g of Ag and the total volume of AgNO3 is 1200 ml. In the first step, 14 ml of (1%) chitosan solution is added to AgNO3 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash-silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 56 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of sodium citrate solution. The in-situ reduction of Ag+ ions to Ag occurs during the boiling of rice husk ash-silver nitrate-chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with chitosan. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 5
0.0113 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 1% Chitosan [dissolved in 5% citric acid (C6H8O7)] aqueous solutions are prepared. The volume of AgN03 is chosen such that every 200 g of rice husk ash will have 1.2307 g of Ag and the
total volume of AgNO3 is 1000 ml. In the first step, 14.125 ml of (1%) chitosan solution is
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added to AgN03 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for I hr while mild stirring. Thereafter, the rice husk ash-silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 56.5 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of sodium citrate solution. The in-situ reduction of Ag+ ions to Ag° occurs during the boiling of rice husk ash-silver nitrate-chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with chitosan. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 6
•0.008 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 1% Chitosan [dissolved in 5% citric acid (C6H8O7)] aqueous solutions are prepared. The volume of AgNO3 is chosen such that 130 g of rice husk ash will have 0.80 g of Ag and the total volume of AgN03 is 910 ml. In the first step, 9.1 ml of (1%) chitosan solution is added to AgNO3 solution and stirred for 5mins. 130 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 2 hrs while mild stirring. Thereafter, the rice husk ash—silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 36.4 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of sodium citrate solution. The in-situ reduction of Ag+ ions to Ag occurs during the boiling of rice husk ash-silver nitrate-chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with chitosan. Then, the solution mixture was cooled to room temperature and was kept soaked for 12 hrs. The nano silver coated rice husk ash was filtered
followed by washing with copious amount of water.
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Example 7
0.008 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 1% Chitosan [dissolved in 5% citric acid (C6H8O7)] aqueous solutions are prepared. The volume of AgN03 is chosen such that 200 g of rice husk ash will have 1.2307 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 14 ml of (1%) chitosan solution is added to AgNO3 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash-silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 56 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of sodium citrate. solution. The in-situ reduction of Ag+ ions to Ag° occurs during the boiling of rice husk ash-silver nitrate-chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with chitosan. Then, the solution mixture was cooled to room temperature. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 8
0.008 M silver nitrate (AgN03), 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) and 2% Chitosan [dissolved in 5% citric acid (C6H8O7)] aqueous solutions are prepared. The volume of AgN03 is chosen such that 200 g of rice husk ash will have 1.2307 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 14 ml of (2%) chitosan solution is added to AgN03 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash—silver nitrate-chitosan mixture is heated up to boiling temperature while stirring. 56 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling
is continued for another 15 mins after addition of sodium citrate solution. The in-situ
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reduction of Ag+ ions to Ag occurs during the boiling of rice husk ash-silver nitrate-
chitosan mixture in the presence of tri-sodium citrate followed by instantaneous capping of
silver nanoparticles with chitosan. Then, the solution mixture was cooled to room
temperature and was kept soaked for 12 hrs. The nano silver coated rice husk ash was filtered
followed by washing with copious amount of water.
Example 9
0.008 M silver nitrate (AgN03), 5% trirsodium citrate dihydrate (C6H5Na307.2H20) and 1%
Ascorbic acid (C6H8O6) aqueous solutions are prepared. The volume of AgN03 is chosen
such that 200 g of rice husk ash will have 1.2307 g of Ag and the total volume of AgN03 is
1400 ml. In the first step, 22.4 ml of (5%) tri-sodium citrate dihydrate solution is added to
AgN03 solution and stirred for 5mins. 200 g of rice husk ash is added to the silver nitrate-tri-
sodium citrate dihydrate solution and allowed to soak for 1 hr while mild stirring. Thereafter,
11.2 ml of 1% ascorbic acid solution is added slowly to the above mixture with mild stirring.
The in-situ reduction of Ag+ ions to Ag occurs during the reaction of rice husk ash-silver
nitrate mixture with ascorbic acid in the presence of tri-sodium citrate as a stabilizing agent.
The solution mixture was kept soaked for 1 hrs. The nano silver coated rice husk ash was
filtered followed by washing with copious amount of water.
Example 10
0.008 M silver nitrate (AgN03). 0.001 M sodium bis(2-ethylhexyl) sulfosuccinate (AOT;
C2oH37Na07S) and 1% Ascorbic acid (C6H8O6) aqueous solutions are prepared. The volume
of AgN03 is chosen such that 200 g of rice husk ash will have 1.2307 g of Ag and the total
volume of AgN03 is 1400 ml. In the first step, 0.001 M AOT is dissolved in 1400 ml of
distilled water by stirring for 15 minutes. 1.9357 g of AgN03 is added to the above solution
and stirred for uniform mixing. 200 g of rice husk ash is added to the silver nitrate-AOT
solution and allowed to soak for 2 hrs while mild stirring. Thereafter, ascorbic acid was
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added slowly to above solution while mixing/stirring. Stirring continued for 15 minutes. The
in-situ reduction of Ag+ ions to Ag° occurs during the reaction of rice husk ash-silver nitrate
mixture with ascorbic acid in the presence of AOT as a stabilizing agent. The solution
mixture was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed
by washing with copious amount of water.
Example 11
0.008 M silver nitrate (AgN03), 1% Chitosan and 1% Ascorbic acid (C6H806) aqueous
solutions are prepared. The volume of AgN03 is chosen such that 200 g of rice husk ash will
have 1.2307 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 1.9357 g of
AgNO3 is dissolved in 1200 ml of distilled water. 200 g of rice husk ash is added to the silver
nitrate solution and allowed to soak for 1 hr while mild stirring. Thereafter, 200 ml of
distilled water containing 1% ascorbic acid & 1% chitosan was added slowly to above
solution while mixing/stirring. Stirring continued for 15 minutes. The in-situ reduction of Ag+
ions to Ag° occurs during the reaction of rice husk ash-silver nitrate mixture with ascorbic
acid in the presence of chitosan as a stabilizing agent. The solution mixture was kept soaked
for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious
amount of water.
Example 12
0.008 M silver nitrate (AgN03), 0.001 M sodium bis(2-ethylhexyl) sulfosuccinate (AOT;
C2oH37Na07S) and 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) aqueous solutions are
prepared. The volume of AgN03 is chosen such that 200 g of rice husk ash will have 1.2307
g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 0.001 M AOT is
dissolved in 1400 ml of distilled water by stirring for 15 minutes. 1.9357 g of AgN03 is
added to the above solution and stirred for uniform mixing. 200 g of rice husk ash is added to
the silver nitrate-AOT solution and allowed to soak for 1 hr while mild stirring. Thereafter,
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the rice husk ash-silver nitrate-AOT mixture is heated up to boiling temperature while stirring. 56 ml of 5% tri-sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of tri-sodium citrate solution. The in-situ reduction of Ag+ ions to Ag° occurs during the boiling of rice husk ash-silver nitrate-AOT mixture in the presence of tri-sodium citrate followed by instantaneous capping of silver nanoparticles with AOT. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 13
0.008 M silver nitrate (AgN03) & 0.001 M sodium bis(2-ethylhexyl) sulfosuccinate (AOT; C2oH37Na07S) aqueous solutions are prepared. The volume of AgN03 is chosen such that 200 g of rice husk ash will have 1.2307 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 0.001 M AOT is dissolved in 1400 ml of distilled water by stirring for 15 minutes. 1.9357 g of AgN03 is added to the above solution and stirred for uniform mixing. 200 g of rice husk ash is added to the silver nitrate-AOT solution and allowed to soak for 1 hr while mild stirring. Thereafter, 51.2 ml of freshly prepared 0.01 M sodium borohydride (NaBHL4) solution is added slowly to the above mixture with mild stirring. The in-situ reduction of Ag+ ions to Ag° occurs during the reaction of rice husk ash-silver nitrate-AOT mixture with sodium borohydride in the presence of AOT as a stabilizing agent. The solution mixture was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 14
0.008 M silver nitrate (AgN03) & 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) aqueous solutions are prepared. The volume of AgN03 is chosen such that 200 g of rice husk
ash will have 1.2307 g of Ag and the total volume of AgN03 is 1400 ml. In the first step,
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1.9357 g of AgN03 is dissolved in 1400 ml of distilled water and was mixed with 56 ml of
5% tri-sodium citrate dihydrate. 200 g of rice husk ash is added to the silver nitrate- tri-
sodium citrate dihydrate solution and allowed to soak for 1 hr while mild stirring. Thereafter,
51.2 ml of freshly prepared 0.01 M sodium borohydride (NaBH4) solution is added slowly to
the above mixture with mild stirring. The in-situ reduction of Ag+ ions to Ag occurs during
the reaction of rice husk ash-silver nitrate- tri-sodium citrate dihydrate mixture with sodium
borohydride in the presence of tri-sodium citrate dihydrate as a stabilizing agent. The solution
mixture was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed
by washing with copious amount of water.
Example 15
0.008 M silver nitrate (AgN03) & 1% Chitosan [dissolved in 5% citric acid (C6H807)]
aqueous solutions are prepared. The volume of AgNO3 is chosen such that 200 g of rice husk
ash will have 1.2307 g of Ag and the total volume of AgN03 is 1386 ml. In the first step. 14
ml of (1%) chitosan solution is added to AgN03 solution and stirred for 5mins. 200 g of rice
husk ash is added to the silver nitrate-chitosan solution and allowed to soak for 1 hr while
mild stirring. Thereafter, 51.2 ml of freshly prepared 0.01 M sodium borohydride (NaBH,4)
solution is added slowly to the above mixture with mild stirring. The in-situ reduction of Ag+
ions to Ag° occurs during the reaction of rice husk ash-silver nitrate-chitosan mixture with
sodium borohydride in the presence of chitosan as a stabilizing agent. The solution mixture
was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by
washing with copious amount of water.
Example 16
0.008 M silver nitrate (AgN03), 0.01 M L-lysine (C6H14N2O2) and 5% tri-sodium citrate
dihydrate (C6H5Na307.2H20) aqueous solutions are prepared. The volume of AgN03 is
chosen such that 200 g of rice husk ash will have 1.2307 g of Ag and the total volume of
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AgNO3 is 1400 ml. In the first step. 0.01 M L-lysine is dissolved in 1400 ml of distilled water by stirring for 15 minutes. 1.9357 g of AgNO3 is added to the above solution and stirred for uniform mixing. 200 g of rice husk ash is added to the silver nitrate-Iysine solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash-silver nitrate-Iysine mixture is heated up to boiling temperature while stirring. 56 ml of 5% tri-sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of tri-sodium citrate solution. The in-situ reduction of Ag+ ions to Ag occurs during the boiling of rice husk ash-silver nitrate-Iysine mixture in the presence of tri-sodium citrate. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water. Example 17
0.008 M silver nitrate (AgN03) and 0.01 M L-lysine (C6H14N2O2) aqueous solutions are prepared. The volume of AgNCh is chosen such that 200 g of rice husk ash will have 1.2307 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 0.01 M L-lysine is dissolved in 1400 ml of distilled water by stirring for 15 minutes. 1.9357 g of AgN03 is added to the above solution and stirred for uniform mixing. 200 g of rice husk ash is added to the silver nitrate-Iysine solution and allowed to soak for 1 hr while mild stirring. Thereafter, 51.2 ml of freshly prepared 0.01 M sodium borohydride (NaBH4) solution is added slowly to the above mixture with mild stirring. The in-situ reduction of Ag+ ions to Ag° occurs during the reaction of rice husk ash-silver nitrate-Iysine mixture with sodium borohydride. The solution mixture was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water.
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Example 18
0.008 M silver nitrate (AgN03) and 5% tri-sodium citrate dihydrate (C6H5Na307.2H20) aqueous solutions are prepared. The volume of AgN03 is chosen such that 200 g of rice husk ash will have 1.2307 g of Ag and the total volume of AgN03 is 1400 ml. In the first step, 1.9357 g of AgN03 is dissolved in 1400 ml of distilled water. 200 g of rice husk ash is added to the silver nitrate solution and allowed to soak for 1 hr while mild stirring. Thereafter, the rice husk ash-silver nitrate mixture is heated up to boiling temperature while stirring. 56 ml of 5% sodium citrate solution is added slowly to the above mixture while stirring. The boiling is continued for another 15 mins after addition of sodium citrate solution. The in-situ reduction of Ag+ ions to Ag° occurs during the boiling of rice husk ash-silver nitrate mixture in the presence of tri-sodium citrate. Tri-sodium citrate also acts as a stabilizing agent for silver nanoparticles. Then, the solution mixture was cooled to room temperature and was kept soaked for 1 hr. The nano silver coated rice husk ash was filtered followed by washing with copious amount of water.
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We claim:
1. A process comprising binding silver ions to. rice husk ash by adding to the rice husk ash a silver precursor, and reducing the silver ions bonded to the rice husk ash by a reducing agent to obtain rice husk ash with bonded silver nanoparticles.
2. A process as claimed in claim 1 wherein the binding of silver ions to rice husk ash takes place in the presence of a stabilizing agent.
3. A process as claimed in claim 1 wherein the reduction of silver ions bonded to the rice husk ash takes place in the presence of a stabilizing agent.
4. A process as claimed in claim 1 wherein a stabilizing agent is added along with a silver precursor.
5. A process as claimed on claim 4 wherein the stabilizing agent is chitosan and the silver precursor is silver nitrate.
6. A process as claimed in claim 1 wherein a stabilizing agent is added along with the reducing agent.
7. A process as claimed in claim 6 wherein the stabilizing agent is chitosan and the reducing agent is ascorbic acid.
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8. A process as claimed in claim 6 wherein the reducing agent is ascorbic acid and the chitosan is dissolved in ascorbic acid.
9. A process as claimed in claim 1 wherein the stabilizing agent is added along with the silver precursor and the reducing agent.
10. A process as claimed in claim 1 wherein the rice husk ash is soaked with the silver precursor for a period ranging from 10 minutes to 4 hours and preferably for a period of 1 hour.
11. A process as claimed in claim 1 wherein the rice husk ash is soaked with the reducing
agent for a period ranging from 10 minutes to 12 hours and preferably for a period of
1 hour.
12. A process as claimed in claim 1 wherein the silver precursor is a silver base salt including AgN03, AgBF4, AgPF6, Ag20, CH3COOAg, AgCF3S03, AgC104, AgCl, Ag2SO4 and preferably the silver precursor is AgN03.
13. A process as claimed in claim 1 wherein the molar concentration of silver precursor ranges from 0.001M to 1M.
14. A process as claimed in claim 2, 3 or 9 wherein the stabilizing agent is any one of
chitosan, tri-sodium citrate dihydrate, L-lysine, tyrosine, sodium bis(2-ethylhexyl)
sulfo succinate, sodium dodecyl sulphate, cetyl trimethyl ammonium bromide,
polyvinyl pyrrolidone, polyvinyl alcohol or oleylamine.
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15. A process as claimed in claim 14 wherein the stabilizing agent ranges from 0.1 to 10 wt % and preferably the stabilizing agent is 1 wt %.
16. A process as claimed in claim 1 wherein the reducing agent is any one of tri-sodium citrate dihydrate, ascorbic acid, sodium borohydride, hydrazine hydrate or D-Glucose and preferably the reducing agent is tri-sodium citrate dihydrate.
17. A process as claimed in claim 1 wherein the reducing agent ranges from 0.1 to 10 wt % and preferably the amount of reducing agent is 2 wt %.
18. A process as claimed in claim 2 or 3 wherein the reducing agent, is tri-sodium citrate and the chitosan is dissolved in citric acid.
19. A process as claimed in claim 1. 2, 3 or 9 wherein the reaction mixture is boiled before the addition of the reducing agent.

20. A process comprising binding metal ions to the rice husk ash by adding to the rice husk ash a metal precursor, and reducing the metal ion bonded to the rice husk ash by a reducing agent to obtain rice husk ash with bonded metal nanoparticles.
21. A process as claimed in claim 20 wherein the metal precursor is. a precursor of copper, silver, gold, platinum, zinc, magnesium, titanium or their alloys.
22. A process as claimed in claim 21 wherein the metal precursor is a bactericidal agent.
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23. A process as claimed in any of the preceding claims wherein the size of
nanoparticles obtained is in the range of 5nm to 300nm, and preferably the size of the
nanoparticles is in the range of 10 to 50 nm.
24. A process as claimed in any of the preceding claims wherein the nanoparticles obtained have a spherical, triangular or flat structure.
25. A rice husk ash with silver nanoparticles bonded to it as claimed in any of the preceding claims used in a water purification system.
26. A rice husk ash with silver nanoparticles bonded to it by a process as claimed in any of the preceding claims.
27. A process substantially as herein described with reference to and as illustrated by the accompanying figures.
Dated this 24th day of July 2008
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