Formats for submission of projects

(c)
Figure 5. (a) Schematic of the citrate reduction method for synthesizing Ag nanoparticle. (b) Photograph showing Ag nanoparticle dispersion synthesized by us via citrate reduction. (c) TEM image Ag nanoparticles from above, typical particle size is 20-25 nm.

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224. Review of expertise available with proposed investigating group/institution in the subject of the project

The principal investigator, Rajdip Bandyopadhyaya, has considerable experience in experiments and modeling of colloids and nanomaterials. Several PhD and M. Tech. students are working with the PI on various problems in the area of nanoparticles, porous materials, thin films, composites, modeling and simulation.

In addition, other analytical facilities for measurement and characterization are already available in the IIT Bombay campus which would be utilized on a prior booking basis. Some of these are: TEM, SEM, BET, XRD, FTIR, Laser Raman spectrometer etc.

Co-investigator, Prof. K. V. Venkatesh, is an expert in Biosystems Engg. and leads a large research group. Their in-house developed methylene blue reduction test (MBRT) would be utilized to assess the kinetics of E. coli death by quantifying the death rate through spectroscopic measurements. In addition, the usual plate assay and shake flask tests would also give complementary information on the antibacterial properties of Ag-GC.

Dr. V. Shankar (Filtrex Technologies Pvt. Ltd., Bangalore) has extensive experience in working with activated carbon (AC) based water filters and purification systems. In fact, the PI has already published some of their joint research results.⁴⁰ Further innovation and optimization in both nanoparticle synthesis and its impregnation is required in order to improve the performance and make Ag-GC composite a viable alternative.

225. Patent details (domestic and international) No patents on Ag-GC composites in water treatment.
230. Work plan
231. Methodology

1. 
   Nanoparticles would be first formed in a bulk medium like aqueous solution, without the use of any template. For this, we will synthesize Ag nanoparticles in an aqueous medium by reducing AgNO₃ with tri-sodium citrate at near boiling temperature or by reduction via UV-visible radiation. Subsequently, we would prepare Ag embedded AC samples by adsorption of these Ag nanoparticles from its aqueous dispersion. By varying the reactant concentrations, time and reaction temperature one can change the particle size.
   

2. 
   Next, we will use carboxylate terminated PAMAM dendrimers and emulsions to synthesize Ag nanoparticles in an aqueous medium. This Ag dispersion will also be used to prepare Ag-AC composite. This will be compared in its properties and applications with the citrate stabilized Ag nanoparticle dispersion.
   

3. 
   In contrast to methods 1 and 2, where externally prepared Ag dispersion is adsorbed into AC granules, in this step, we will generate Ag nanoparticles in-situ in AC. For this, we will impregnate the AC pores with aqueous AgNO₃ salt solutions by soaking the powder overnight. This will be followed by in-situ reduction (either thermally or by chemically, via NaBH₄) to Ag nanoparticles in the granule itself. Thermal reduction of AgNO₃ will be done by heating the soaked AC at 300 C, whereas, for in-situ chemical reduction, aqueous NaBH₄ solution will be added at room temperature.
   

We will employ variation of pore size, reactant concentration, rate of addition of reactants to vary relative rates of reaction, nucleation, diffusion in pores and particle growth rate, to obtain either spherical nanoparticles or nanorods of Ag in the pores. For in-situ Ag formation, the reactant solutions have to diffuse inside the pores and capillary forces would play a determining role. Conditions of shape transition and shape control will be elucidated in this part of the research.

4. 
   Next, we will compare the antibacterial properties of externally embedded (methods 1 and 2) and in-situ impregnated (method 3) Ag-AC composites.
   

5. 
   In another direction, we will perform surface modification of AC by each of the following techniques separately – by plasma treatment or exposure to UV-visible light. Subsequently, we will embed Ag into these surface modified AC samples by each of the methods 1, 2 and 3, and assess improvement of antibacterial properties.
   

6. 
   Force of adhesion of nanoparticles to the carbon surface, as a function of time will be evaluated, while being exposed to a continuous flow of water, as is the situation during regular use of the Ag-AC composite as a water filter for disinfection purposes.
   

7. 
   One also needs to establish the mechanism of antibacterial properties; is it a contact-kill or leach-kill scenario?
   

8. 
   Evaluation of the loss in activity of Ag particles over time and development of ways to prevent it will also be an important step.
   

Composition control is also of interest in this research project. This will be accomplished by studying multicomponent particles (two materials in a single particle) in either core-shell or homogeneous form. For the former, spherical Ag nanoparticles will be formed as usual. Subsequently aqueous Cu salt solution will be added, which will react with excess reducing agent to form a metallic Cu layer on Ag nanoparticle, forming a core-shell structure. Shell thickness will be estimated from DLS measurements, which can be controlled by the method of addition and relative rates of reaction. In contrast, starting with the pre-dissolved metal salt solutions in water will finally result in a homogeneous (Ag-Cu) nanoparticle. Such compositional heterogeneity can therefore be controlled at a very precise nanometer length scale.

In all experiments, the nanoparticle size distribution will be obtained from dynamic light scattering (DLS) as a function of time. Final particle size and shape will also be obtained from transmission electron microscopy (TEM) with composition from energy dispersive X-Ray (EDAX). UV-Visible spectrophotometer will be used to monitor Ag formation by its absorption peak at 420 nm. Pore size distribution of the AC granules and its specific surface area and specific pore volume would be obtained from BET and BJH gas adsorption experiments.
The experimental results will be compared with modeling of particle size in bulk solution, emulsion and dendrimers. Population balance equation and Monte Carlo simulation would be used as the modeling framework. Existing models and codes of the PI will be extended further and modified for taking account of bigger dendrimer templates, particle shape anisotropy, core-shell morphology for multicomponent systems and concentration based diffusion mechanisms inside a dendrimer. Location of nanoparticle formation – either inside or on the external surface of a dendrimer molecule, achievable by manipulation of surface groups of the dendrimer – is also a key variable of interest, and worthy of investigation. Mechanistic understanding gained from modeling particle formation would help us in selecting and optimizing experimental conditions.
Such general strategies will form guidelines for optimum synthesis strategies for Ag nanoparticles and Ag-AC composite formulations. These will be used for antibacterial tests by plate test, shake flask test and flow tests. A case-control based study will then be carried out to find the potential of the nanoparticle impregnated AC in producing pathogen-free water, compared to the currently used AC filter, having no nanoparticles.

232. Organization of work elements

Figure 6. Fundamental scientific issues related to controlled nanoparticle synthesis and impregnation in porous solid adsorbent.

233. Time schedule of activities giving milestones (bar diagram in Section 410)
1. (0-6 months)

Literature review, obtaining quotations, purchase and installation of equipments, recruitment of personnel to work in the project.

2. (4-9 months)

In-situ synthesis of Ag nanoparticle in activated carbon (AC) by chemical and thermal reduction of impregnated AgNO₃. Testing of antimicrobial properties of Ag embedded AC (Ag-AC).

3. (4-12 months)

Preparation of citrate stabilized Ag nanoparticle dispersion - both with and without UV-visible light - its impregnation in activated carbon (AC) and testing of antimicrobial properties.

4. (7- 15 months)

Preparation of dendrimer and emulsion templated Ag nanoparticle dispersion, different impregnation strategies in activated carbon (AC) and testing of antimicrobial properties.

5. (10-24 months)

Plasma and/or UV exposure of AC for surface modification, with subsequent Ag impregnation (in surface modified AC) by all forms of coated Ag particles. Investigation of enhancement of E. coli removal due to surface modification.

6. (4-24 months)

Modeling and simulation of particle size distribution. Comparison of model predictions with experimental measurement of size, shape and composition for nanoparticles.

7. (25-30 months)

Further tuning and optimization of experimental conditions to be undertaken for different Ag-AC composites by comparison with model predictions. Simultaneous testing to be done for biocompatibility, minimization of leaching-loss of Ag by enhancing adhesion with carbon bed, extent of water disinfection and elucidation of the bacteria-kill mechanism.

8. (25- 33 months)

Implementation of the optimized (obtained by synergistic experimental and modeling studies) routes of Ag-AC formation in a small water disinfection unit, for testing and standardization of engineering issues – like minimizing pressure drop and sustaining high filtration rate of potable water from filter-bed, maximum continuous usage of Ag without drop in disinfection activity.

9. (31 – 36 months)

Exploring the scientific insight gained in biotic-abiotic interaction of the three-way metal, bacteria, carbon contacting mechanism in doing exploratory studies in other systems of interest, wherever living and non-living matter interact.

234. Suggested plan of action for utilization of research outcome expected from the project