Patent Application
20180186667
The present disclosure relates to the field of water purification and specifically to compositions and methods related to sustained silver release for water purification.
Contamination of drinking water is a major health concern across the world, especially in the developing and under-developed countries. A number of contaminants affect the water quality including biological (e.g. bacteria and virus), inorganic (e.g. fluoride, arsenic, iron) and organic (e.g. pesticides, volatile organics) species. These contaminants in water are a source of a number of diseases for a large population of the world. A significant cost burden associated with health effects of the contaminated water still rests on the shoulders of the poor. This problem can be addressed by developing affordable and effective solutions for removal of these contaminants.
Silver is widely known for its antibacterial property and has been employed as an inorganic silver salt, as an organic silver salt and as colloids of its salt, oxide, and in metallic states for treatment of contaminated water. Although it is well known that silver is a good antibacterial agent, the nature of silver present in the water determines its antibacterial efficiency. Recently, silver has been extensively used in the form of metallic nanoparticles. The antibacterial property of silver nanoparticles emerges either from nanoparticle-bacteria surface interaction or from released silver ions from nanoparticles or both.
Antibacterial property of silver nanoparticles has been discussed in a number of patent applications, wherein improvements to method of synthesis of silver nanoparticles have been disclosed (Pal et. al. in Appl Environ Microbiol., 2007, 73(6), 1712; De Windt et. al. in United States Patent Application 20100272770; Sastry et. al. in 936/MUM/2008), methods for their synthesis in media other than water have been used (Chen et. al. in U.S. Pat. No. 7,329,301), and methods for loading silver nanoparticles on various substrates have been discussed (Rautaray et. al. in Indian patent application 1571/MUM/2008). The enhanced antibacterial property of silver nanoparticles is due to size confinement of silver metal. Although a number of methods have been developed for the synthesis of silver nanoparticles, keeping reactive particles in nanometer size for a long time in real water composed of various species is very difficult. This is due to ion induced aggregation, surface modification, salt deposition and so forth. Therefore, an important requirement while employing reactive silver nanoparticles in water purification is size stabilization and preventing surface modification over extended periods.
Another important aspect of use of silver nanoparticles for anti-bacterial performance is the fraction of silver ions released (quantity of silver ions released/quantity of silver nanoparticle used). It is known that although significant quantities of silver nanoparticles are used, a small amount of silver ions are released into the contaminated water. For example, Hoek et al. (Environ. Sci. Technol. 2010, 44, 7321) reported that in reproduced real water having total dissolved solids (TDS) of around 340 parts per million (ppm), the fraction of dissolved silver is less than 0.1% of the total mass of silver added, regardless of the initial source, i.e., AgNO3 or silver nanoparticles. This phenomenon is attributed to the presence of various anions in water, such as chlorides (many silver salts have very low solubility). Hence, the quantity of silver nanoparticles used in water filters is more than the optimum and results in an increase in the filter size and the cost of the device.
The release rate of silver ion from the nanoparticles determines how long the nanoparticles can be used as an antimicrobial agent. Constant release of silver ions from silver nanoparticles for longer time is essential for effective use in water filters. This ensures consistent anti-microbial performance and release of silver ions below permissible limit as prescribed by the World Health Organization (WHO). The rate of silver ion release has been discussed in the literature. For example, Epple et al. (Chem. Mater. 2010, 22, 4548 and Hurt et al. Environ. Sci. Technol. 2010, 44, 2169) demonstrated that the release of silver ions from silver nanoparticles in distilled water depends on temperature, incubation days, and species present in the water such as dissolved oxygen level, salt, and organic matter. The rate of dissolution is not constant with time and attains saturation in a short period.
Hence, stability of reactive nanoparticles for prolonged periods in water is essential for controlled release of silver ions. Metal oxides have been widely considered as good substrates. Silver nanoparticles have been ex-situ and in-situ loaded in/on metal oxides. In-situ loading in metal oxide has shown promising stability even at high loading percentage. For example, in-situ syntheses of silver nanoparticles in metal oxide matrices have been reported earlier. Chen et al. Environ. Sci. Technol. 2009, 43, 2905 demonstrated the sol-gel synthesis of silver nanoparticles (<5 nm) loaded onto TiO2 nanocomposite where TiO2 particles act as anti-aggregation support and showed that 7.4 wt % Ag loading in TiO2 had highly potent antibacterial properties against E. coli. Similar results were obtained by the use of rice husk ash (Rautaray et. al. 1571/MUM/2008). Results obtained by this group indicates that the leached silver concentration varied in a wide range of 1.3 ppb-65 ppb (measured over a volume of 3000 L).
Various attempts have been made to synthesize silver nanoparticles on low-cost substrates. For example, Shankar et al. (J Chem Technol Biotechnol. 2008, 83, 1177) loaded silver on activated carbon at high silver loading percentage. An optimum of 9-10.5 wt % of Ag loaded in activated carbon (5 g) is necessary to have effective anti-bacterial properties against E. coli (concentration: 103 CFU/ml) in the contact-mode for up to 350 L of flowing water (flow rate: 50 mL/min). Accordingly, ˜0.5 g of silver for 350 L of bacteria free water should be used which has a cost of 10 paise/liter (US$0.0088/gallon) water.
As described above, current systems fail to address the problem of stabilization of silver nanoparticles on a supporting matrix. Further, the surface chemistry is altered in controlled silver ion release systems over extended periods, thereby requiring the use of large quantities of silver. Controlled constant silver release determines the long term use, effectiveness, and the life time of a device and low cost.
The above referenced shortcomings are resolved by the compositions and methods described herein.
The compositions and methods described herein, in one aspect, relates to water purification. Particularly, the disclosure compositions and methods described herein relates to a sustained silver release composition for water purification.
An object of the compositions and methods described herein is to provide dissolution of silver ions from silver nanoparticles in water, for prolonged use (composition for a sustained silver ion release).
Another object of the compositions and methods described herein is to increase the volume of water that can be treated with silver nanoparticles while maintaining a substantially constant concentration of silver ions in the water derived from the silver nanoparticles. The silver nanoparticles can be loaded on organic polymer-metal oxide/hydroxide composite such as an organic-templated-boehmite nanoarchitecture (OTBN).
Yet another object of the compositions and methods described herein is to use organic polymer-metal oxide/hydroxide composites as a dual stabilizing agent for the synthesis of highly dispersed and stable silver nanoparticles. The silver nanoparticles can be antimicrobial, for example antibacterial, at a loading of about 0.1-1 wt %.
The compositions and methods described herein release at least 10% of the silver present in nanoparticles into the water with moderately high TDS from silver nanoparticles loaded OTBN over an extended period. An aspect of the compositions and methods described herein includes the volume of water treated and time independent constant release of silver ion from a Ag-OTBN matrix.
In one aspect, a method is disclosed for preparing an adsorbent composition. The method comprises impregnating silver nanoparticles on an organic-templated-nanometal oxyhydroxide. Particle size of the silver nanoparticles can be less than about 50 nm. The adsorbent composition has antimicrobial properties in water. In an aspect, the organic-templated-nanometal oxyhydroxide can be organic-templated-boehmite nanoarchitecture (OTBN).
In the compositions and methods described herein, the potent antibacterial material for long term use is obtained when silver nanoparticles are synthesized in organic-templated metal oxide/hydroxide nanoarchitecture. Stability of silver nanoparticles in water for longer time determines its antibacterial properties over time. Stable silver nanoparticles can be achieved via a in-situ syntheses of the nanoparticles in the OTBN matrix. Disclosed herein is an OTBN matrix that enhances the antimicrobial (i.e. antibacterial) property of silver nanoparticles in water. The matrix controls the size and stabilizes the particles from aggregation, and prevents the adsorption/deposition/scaling of soluble ligands, organic matters and dissolved solids on the silver nanoparticles.
The surface reactivity of silver nanoparticles can be maintained by both chitosan and metal oxide/hydroxide. Silver nanoparticles encapsulated by chitosan, can be dispersed in metal oxide support and vice-versa. The dual stabilization prevents the surface modification and also salt deposition over a period of time. This is further explained through the material characterization studies.
In one aspect, the compositions disclosed herein can contain 0.5 wt % Ag loaded in OTBN with antimicrobial properties. For example the compositions and methods can kill 105 CFU/mL of E. coli in the contact-mode using several hundred liters, for example 100, 200, 300, 400, 500, 600 or 700 liters, of flowing water at very high flow rate. This is achieved through controlled constant release of silver ion for long time, for example 50 mL/min, 100 mL/min, 200 ml/min, 300 ml/min, 400 ml/min, 500 ml/min or 1000 ml/min.
In one aspect the silver nanoparticles described herein can kill 105 CFU/mL of E. coli in tap water. In another aspect, killing microorganism with the disclosed compositions and methods does not require contact between the microorganisms and the nanoparticles.
In another aspect, a water purification device that includes a water filter is disclosed. The water filter can be made of an adsorbent composition prepared by impregnating silver nanoparticles on an organic-templated-nanometal oxyhydroxide, wherein a particle size of the silver nanoparticles is less than about 50 nm. The adsorbent composition can kill microorganisms, i.e have antimicrobial properties, in water. The water filter can be in the form of a candle, a molded porous block, a filter bed and a column. In another aspect, the water filter can be in the form of a sachet or porous bag.
Additional aspects and advantages of the invention will be set forth, in part, in the detailed description and any claims which follow, and in part will be derived from the detailed description or can be learned by practice of the invention. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as disclosed.
The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects and together with the description serve to explain the principles of the invention.
The present invention can be understood more readily by reference to the following detailed description of the invention and the examples included therein.
Before the present compounds, compositions, articles, systems, devices, and/or methods are disclosed and described, it is to be understood that they are not limited to specific synthetic methods unless otherwise specified, or to particular reagents unless otherwise specified, as such can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.
All publications mentioned herein are incorporated by reference to disclose and describe the methods and/or materials in connection with which the publications are cited.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, example methods and materials are now described.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a metal” includes mixtures of two or more metals.
Ranges can be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.
As used herein, the terms “optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.
Disclosed are the components to be used to prepare the compositions of the invention as well as the compositions themselves to be used within the methods disclosed herein. These and other materials are disclosed herein, and it is understood that when combinations, subsets, interactions, groups, etc. of these materials are disclosed that while specific reference of each various individual and collective combinations and permutation of these compounds cannot be explicitly disclosed, each is specifically contemplated and described herein. For example, if a particular compound is disclosed and discussed and a number of modifications that can be made to a number of molecules including the compounds are discussed, specifically contemplated is each and every combination and permutation of the compound and the modifications that are possible unless specifically indicated to the contrary. Thus, if a class of molecules A, B, and C are disclosed as well as a class of molecules D, E, and F and an example of a combination molecule, A-D is disclosed, then even if each is not individually recited each is individually and collectively contemplated meaning combinations, A-E, A-F, B-D, B-E, B-F, C-D, C-E, and C-F are considered disclosed. Likewise, any subset or combination of these is also disclosed. Thus, for example, the sub-group of A-E, B-F, and C-E would be considered disclosed. This concept applies to all aspects of this application including, but not limited to, steps in methods of making and using the compositions of the invention. Thus, if there are a variety of additional steps that can be performed it is understood that each of these additional steps can be performed with any specific embodiment or combination of embodiments of the methods of the invention.
Each of the materials disclosed herein is either commercially available and/or the methods for the production thereof are known to those of skill in the art.
It is understood that the compositions disclosed herein have certain functions. Disclosed herein are certain structural requirements for performing the disclosed functions and it is understood that there are a variety of structures that can perform the same function that are related to the disclosed structures, and that these structures will typically achieve the same result.
In one aspect, synthesis, characterization and application of silver nanoparticles impregnated organic-templated-boehmite-nanoarchitecture (Ag-OTBN) are described. Impregnation of silver nanoparticles in OTBN is demonstrated using a number of procedures. The as-synthesized Ag-OTBN composition is characterized by a number of spectroscopic and microscopic techniques. The capability of Ag-OTBN to remove microorganisms from drinking water is demonstrated through the use of E. coli and MS2 bacteriophage as model organisms for bacteria and virus, respectively.
The silver nanoparticles can be impregnated in p-block, transition and rare-earth metal doped organic template metal oxyhydroxide compositions. It should also be noted that it can be of mixed metal oxide/hydroxide/oxyhydroxide nanoarchitecture. The mixture can be binary or a mixture of all the above mentioned metal oxide/hydroxide/oxyhydroxide.
In an aspect, the Ag-OTBN defined in the present invention can have chitosan polymer to metal oxide/hydroxide weight ratio between 5% and 50%. In another aspect, Ag to OTBN weight ratio can be between 0.1 to 10%.
In another aspect, the silver nanoparticles can be synthesized in OTBN using any reducing agent at any temperature for any application. In one aspect, the reducing agent can be ascorbic acid, tri sodium citrate, dextrose, hydrazine, etc., and at a temperature between 40 to 200° C.
The as-synthesized OTBN shows peaks corresponding to (120), (013), (051), (151), (200), (231) and (251) planes (refer to curve (a)). These peaks can be indexed as orthorhombic-AlOOH (JCPDS 21-1307). The broadened XRD peaks imply that the crystallite size of OTBN particles is very small. The mean crystallite size calculated from the Scherrer formula shows that nanocrystals have an average size of 3.5 nm. The presence of organic template (i.e., chitosan) can also been seen in the XRD data. The peaks marked by * in
Upon impregnation of silver nanoparticles in the OTBN, there are no new peaks observed in the diffraction pattern (refer to curve (b)). This is attributed to the low loading percentage of silver nanoparticles and homogeneous distribution of silver nanoparticles in OTBN. Comparing the diffraction peaks of OTBN and silver nanoparticles impregnated OTBN, a negative shift in the 20 value is observed. The interplanar distance of OTBN increases after loading of silver nanoparticles. This is a clear evidence of the loading of an external material which increases the interplanar spacing.
In order to determine the interaction between OTBN and silver nanoparticles, silver nanoparticles impregnated OTBN matrix was analyzed under transmission electron microscope. The TEM image shows the three components i.e., silver nanoparticles, organic polymers and metal oxide/hydroxide nanoparticles in the Ag-OTBN. The OTBN matrix stabilizes the silver nanoparticles from aggregation, which results in the homogenous distribution of silver nanoparticles in the matrix. It is clear from the TEM images that homogenously sized silver nanoparticles are anchored in the organic polymer-metal oxide/hydroxide nanoparticle matrix (pictures (b) and (c)) and the silver nanoparticles are of 5-10 nm in size (picture (c)). The sheet-like organic polymer chitosan is seen clearly (
This HRTEM of the composition also shows that silver nanoparticles are trapped in the biopolymer-metal oxyhydroxide cages. This allows nanoparticles to be preserved by reducing contact with the scale forming chemical species while allowing sufficient interaction with water, which results in sustained release of Ag+ions.
Graph (d) shows the EDAX spectrum measured from the area shown in picture (b). From this, the presence of silver is confirmed.
EDAX coupled with TEM was used to image the elemental mapping of Ag loaded OTBN. Elements present in the Ag-OTBN such as C, N, O, Al and Ag were mapped. The presence of three components i.e., chitosan (C, N and O), boehmite (Al and O) and silver nanoparticles (Ag) was confirmed.
The Ag-OTBN material as explained in example 1 was used for batch study. As explained in the example 7, the antibacterial activity was tested for batch mode.
The material was also tested for antibacterial study without contact mode. The 100 mL of the shaken water was filtered and 1×105 CFU/mL of bacterial load was added to the water. It was plated as described in the foregoing specification. The performance of the material tested without contact mode is similar to the material tested with contact mode (data not shown). It showed that the antibacterial property is due to the released silver ions from silver nanoparticles.
The Ag-OTBN material as explained in example 1 was used for column study. As explained in the example 8, the antibacterial activity was tested for Ag-OTBN in column mode. E. coli concentration of 1×105 CFU/mL was periodically spiked in challenge water at the passage of 0, 250, 500, 750, 1000, 1250 and 1500 L. Contaminated water was passed at a flow rate of 10-2000 mL/min, preferably at 1000 mL/min. At regular intervals, the microbial de-contaminated output water was collected. Quantitative detection of concentration of silver ions released from the Ag-OTBN material was performed using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES).
In an aspect of the present invention, a method for preparing an antimicrobial composition for water purification is provided. Silver nanoparticles are impregnated on an organic-templated-nanometal oxyhydroxide, such as OTBN. The particle size of the silver nanoparticles is preferably less than about 50 nm. Sizes include, but are not limited to, less than 50 nm, 40 nm, 30 nm, 20 nm, 10 nm, and 5 nm. The antimicrobial composition is used for killing microorganisms in water as explained in the foregoing specification. The silver ions are impregnated with OTBN in gel or solid states. The method also includes reduction of the silver ions to a zerovalent state by using a reducing agent, such as sodium borohydride, ascorbic acid, tri-sodium citrate, hydrazine hydrate or combinations thereof. In an aspect, the concentration of the reducing agent is kept in the range of about 0.001 M to about 1 M. In a preferred aspect, the concentration of the reducing agent is kept at 0.001 M to 0.05 M. Further, organic templates such as chitosan, banana silk and cellulose can be used. The invention supports following precursors: silver nitrate, silver fluoride, silver acetate, silver sulfate, silver nitrite and combinations thereof.
In one aspect, the compositions and methods release for silver ion into water for a prolonged period of time. For example, the compositions and methods can release a silver ions at a constant or substantially constant rate for at least 1 day, 1 week, 1 month, 3 months, 6 months, 1 year or 3 years.
In another aspect, a water purification system that includes a filter prepared by the method described herein is provided. The filter can be realized in the form of a candle, a molded porous block, a filter bed and a column. In another aspect, a water purification system can comprise the compositions described herein, for example, a silver impregnated boehmite structure, disposed in a sachet or porous bag, such that the sachet can be placed in contaminated water and the water allowed to flow through the sachet to contact the composition. A skilled artisan will appreciate that such forms of filters are well known in the art and their description has been omitted so as not to obfuscate the present disclosure.
The described aspects are illustrative of the compositions and methods and are not restrictive. Modifications of design, methods, structure, sequence, materials and the like that are apparent to those skilled in the art, also fall within the scope of the compositions and methods described herein.
The identification of the phase(s) of the as-prepared sample was carried out by X-ray powder diffraction (using D8 Discover of Bruker AXS, USA) using Cu-Kα radiation at λ=1.5418 Å. Surface examination was carried out using Field Emission Scanning Electron Microscope (using FEI Nova NanoSEM 600 instrument). For this, the sample was re-suspended in water by sonication for 10 minutes and drop-casted on an indium tin oxide (ITO) conducting glass. The sample was subsequently dried. Surface morphology, elemental analysis and elemental mapping studies were carried out using a Scanning Electron Microscope (SEM) equipped with Energy Dispersive Analysis of X-rays (EDAX) (using FEI Quanta 200 scanning electron microscope). Granular composition was imaged by attaching it on a conducting carbon tape. High resolution Transmission Electron Microscopy (HRTEM) images of the sample were obtained with JEM 3010 (JEOL, Japan). The samples prepared as above were spotted on amorphous carbon films supported on copper grids and dried at room temperature. X-ray Photoelectron Spectroscopic (XPS) analysis was performed using ESCA Probe TPD of Omicron Nanotechnology. Polychromatic Mg Kα was used as the X-ray source (hv=1253.6 eV). Spectra in the required binding energy range were collected and an average was taken. Beam induced damage of the sample was reduced by adjusting the X-ray flux. Binding energy was calibrated with respect to C 1s at 284.5 eV. Silver ion concentration in the water was detected using inductively coupled plasma optical emission spectrometry (ICP-OES).
The following are a few examples that illustrate the methods and compositions described herein. The examples should not be construed as limiting the scope of the methods and compositions described herein.
This example describes the in-situ impregnation of silver nanoparticles on OTBN. In an aspect, OTBN was prepared as reported in the previous Indian patent application 1529/CHE/2010, entire contents of which are herein incorporated by reference. The OTBN gel obtained after washing the salt content was used for the formation of silver nanoparticles. The OTBN gel was again re-dispersed in water, to which 1 mM silver precursor (silver nitrate, silver fluoride, silver acetate, silver permanganate, silver sulfate, silver nitrite, silver bromate, silver salicylate or any combination of the above) was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, 10 mM sodium borohydride was added to the solution drop wise (in ice-cold condition, temperature <5° C.). Thereafter, the solution was allowed to stir for half an hour, filtered and washed with copious amount of water. The obtained gel was then dried at room temperature.
This example describes the in-situ impregnation of silver nanoparticles on OTBN powder. In an aspect, the dried OTBN powder was crushed to a particle size of 100-150 micron. The powder was stirred in water, using an appropriate shaker. 1 mM silver precursor solution was then slowly added. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the mixture overnight, 10 mM sodium borohydride was added to the mixture drop-wise (in ice-cold condition, temperature <5° C.). Thereafter, the mixture was allowed to stir for half an hour, filtered and washed with copious amount of water. The obtained powder is then dried at room temperature.
This example describes the ex-situ impregnation of silver nanoparticles on OTBN. In an aspect, the OTBN gel obtained after washing the salt content was used for the impregnation of silver nanoparticles. The OTBN gel was again re-dispersed in water, to which 1 mM silver nanoparticles solution (prepared by any route reported in the literature) was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, it was filtered and washed with copious amount of water. The obtained gel is then dried at room temperature.
This example describes the ex-situ impregnation of silver nanoparticles on OTBN powder. In an aspect, the dried OTBN powder was crushed to a particle size of 100-150 μm. The powder was stirred in water, using a shaker. 1 mM silver nanoparticles solution (prepared by any route reported in the literature) was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, it was filtered and washed with copious amount of water. The obtained powder was then dried at room temperature.
The organic templated metal oxyhydroxide/oxide/hydroxide matrix defined in the methods and compositions described herein. is such that the metal is chosen from amongst p-block, transition and rare-earth metal series. The metal precursor can be Fe(II), Fe(III), Al(III), Si(IV), Ti(IV), Ce(IV), Zn(II), La(III), Mn(II), Mn(III), Mn(IV), Cu(II) or a combination thereof. And the metal oxide/hydroxide/oxyhydroxide nanoparticle may serve as an inert filler material or an active filtration medium.
This example describes the silver nanoparticles impregnation in p-block, transition and rare-earth metal doped organic templated metal oxyhydroxide composition (as disclosed in the previous Indian patent application 1529/CHE/2010, entire contents of which are herein incorporated by reference). P-block, transition and rare-earth metals were chosen from the following: aluminum, manganese, iron, titanium, zinc, zirconium, lanthanum, cerium, silicon. The synthesis procedure for composition is as follows: the chosen metal (eg: La) salt was mixed with the ferric nitrate salt solution in an appropriate ratio, preferably 1:9 (wt/wt). The salt solution was added slowly to the chitosan solution (dissolved in 1-5% glacial acetic acid or HCl or combination thereof) with vigorous stirring for 60 minutes and was kept overnight. Aqueous ammonia or NaOH solution was slowly added into the La—Fe-chitosan solution with vigorous stirring to facilitate the precipitation of the metal-chitosan composites. Stirring was continued for two hours. The precipitate was filtered, washed to remove any unwanted impurities and dried.
The as-synthesized precipitate gel was again re-dispersed in water, to which 1 mM silver precursor was added drop-wise. The weight ratio of Ag to OTBN can be varied anywhere between 0.1-1.5%. After stirring the solution overnight, 10 mM sodium borohydride was added to the solution drop-wise (in ice-cold condition). Thereafter, the solution was allowed to stir for half an hour, filtered and washed with copious amount of water. The obtained gel was then dried at room temperature.
This example describes the doping of p-block, transition and rare-earth metal precursor in the composition. The procedure is similar to that described in example 5, with a change that gel or dried powder obtained after silver nanoparticles impregnation is soaked with metal precursor chosen from p-block, transition and rare-earth metal series.
This example describes the testing protocol in batch for antibacterial activity of silver nanoparticles impregnated OTBN composition. In an aspect, 100 mL of water was shaken with the material and 1×105 CFU/mL of bacterial load was added to the water. Challenge water having the specific ions concentration similar to prescribed by US NSF for contaminant removal claim was used in the study. After one hour of shaking, 1 mL of the sample along with nutrient agar was plated on sterile petridish using the pour plate method. After 48 hours of incubation at 37° C., the colonies were counted and recorded. This procedure was repeated 25 to 30 times.
This example describes the testing protocol for antibacterial activity of silver nanoparticles impregnated OTBN powder packed in a column. In an aspect, the column in which a known quantity of the material is packed has a diameter between about 35 mm to about 55 mm. The feed water was passed at a flow rate in the range of 10 mL/min to 2000 mL/min. The challenge water was periodically subjected to an E. coli load of 1×105 CFU/mL. The output water collected from the column was screened for bacterial presence by pour plate method. The bacterial colonies were counted and recorded after 48 hours of incubation at 37° C.
This example describes the testing protocol in batch for antiviral activity of silver nanoparticles impregnated OTBN composition. In an aspect, 100 mL of water was shaken with the material and 1×103 PFU/mL of MS2 coliphage load was added to the water. The challenge water having specific ions concentration similar to prescribed by US NSF for contaminant removal claim was used in the study. After one hour of shaking, virus count was obtained by plaque assay method. After 24 hours of incubation at 37° C., the plaques were counted and recorded. This procedure was repeated for 35 to 40 times.
| Number | Date | Country | Kind |
|---|---|---|---|
| 947/CHE/2011 | Mar 2011 | IN | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14007295 | Mar 2014 | US |
| Child | 15677618 | US |
