Novel Synthesis Of Stable Polypyrrole Nanospheres Biology Essay

In this survey, a novel and extremely simple method for the aqueous synthesis of polypyrrole nanospheres was investigated. The method is template and surfactant free utilizing merely pyrrole monomer, H2O, and ozone. By changing the monomer concentration, exposure clip to ozone, and the temperature, it was determined through atom size and transmittal electron microscope ( TEM ) measurings that temperature was the critical factor commanding atom size. From the atom size measurings, a atom size distribution with a figure weighted average diameter of 73 nanometers and a standard divergence of 18 nanometer was achieved. The atoms were besides investigated utilizing zeta possible measurings, UV-Vis spectrometry, FTIR spectrometry, and thermic hydrometric analysis in an attempt to find the individuality of the nanoparticles every bit good as the mechanism by which the nanoparticles are formed and stabilized.

Due to their alone belongingss, there is presently great involvement in polypyrrole nanoparticles and other C based nanoparticles in assorted applications such as chemical & A ; biological detectors, optically crystalline carry oning stuffs, electrochromic devices, actuators, supercapacitor, photovoltaic cell, transistor and informations storage and surface protection. [ 1-5 ] Due to the environmental stableness and high conduction of polypyrrole, it has become one of the most widely studied carry oning polymers. [ 6-14 ] The challenge when synthesising nanosized atoms is to forestall agglomeration. This procedure is more marked with nanosized atoms because of their increased surface country and hence new waves der wall interactions. Many efforts have been made to synthesise polypyrrole nanoparticles utilizing a big figure of different synthesis conditions. [ 15-20 ] From these surveies, two chief schemes have emerged to synthesise non-aggregated polypyrrole. These schemes are known as difficult and soft templet procedures. [ 19, 21-24 ]

Hard templet procedures use pores in “ difficult ” stuffs such as anodized aluminium oxide to direct the growing of polypyrrole atoms and wires and maintain them from agglomerating. [ 25-27 ] After the synthesis the templets must so be etched off normally with strong acids. Another fluctuation of the difficult templet attack is the coating of colloidal atoms, such as Ag or silicon oxide, with polypyrrole. [ 28-32 ] Soft templet methods typically use surfactant micelles as a templet for the formation of nanoparticles. [ 33-37 ] Microemulsion polymerisation and reversed-microemulsion polymerisation are illustrations of soft templet based methods, wherein, construction and concentration of surfactant and monomers are critical factors for commanding morphological parametric quantities of merchandises. [ 21 ] The job with difficult templet procedures is that they are frequently complicated and hence expensive, affecting the really carefully controlled growing of oxide beds or colloidal atoms to give precise and unvarying pore sizes or atom sizes. After synthesis the templets must so be etched off which normally involves the usage of rough chemicals. [ 38 ] Soft templet procedures typically produce merchandises in which the soft templet can ne’er be to the full removed which will impact the belongingss of the merchandise and big sums of wetting agent are typically required which adds to the disbursal of the procedure.

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To besiege these issues, there have been some procedures developed which either do non utilize traditional templet systems or utilize a templet which double as a dopant for the polypyrrole. One such procedure developed by Kim et. Al. uses a surfactant free emulsion system utilizing H2O droplets in octanol as a soft templet and FeCl3 as the oxidizer. [ 39 ] Li et. Al. use a procedure that uses a dilute solution of rhodamine B as a molecular templet that besides acts as a dopant for the polypyrrole. [ 40 ] Henry et. Al. nowadayss production of polypyrrole nanofibers utilizing bipyrrole in oxidative polymerisation of pyrrole. [ 41 ] Catherine Debiemme-Chouvy has obtained nanostructures with diameters in the scope of 40-120 nanometer by electrodepositing polypyrrole in the presence of jointly non-acidic and weak-acidic anions. [ 42 ] In this survey, an even simpler method for the synthesis of unagglomerated polypyrrole nanospheres of a controlled size is outlined that lone utilizations H2O, pyrrole, and ozone in a one pot, one measure, synthesis.

EXPERIMENTAL

Pyrrole was obtained from Sigma Aldrich and was newly distilled earlier usage. Millipore 18.2 MI© H2O was the dissolver used for the reaction. Ozone was obtained by running pure dried O supplied by Air Gas through a theoretical account ATLAS 30 C ozone generator supplied by Absolute Ozone. Particle size measurings were carried out utilizing a NICOMP 380 submicron atom sizer supplied by Particle Sizing Systems. A Gaussian analysis was applied to all informations. For the TEM images, 300 mesh Formvar/carbon coated grids were dipped into the solution incorporating the atoms and instantly wicked off utilizing filter paper. After leting the grid to dry, images were obtained utilizing a JEOL JEM-100CX II Transmission Electron Microscope at 80 keV. UV Vis spectra of the polypyrrole nanoparticles in H2O were recorded on Varian-5000 UV-Vis-NIR Spectrophotometer. Thermal debasement analysis of the samples was performed utilizing a thermohydrometric analysis instrument TGA Q 500 supplied by TA Instruments. The samples were heated from room temperature up to 800Es C at a heating rate of 20Es C/min. The obtained consequences were analyzed utilizing the package, Universal Analysis 2000. A Nicolet FT-IR spectrometer was used for the FT-IR word picture. A Veeco Dimension 3100 atomic force microscope ( AFM ) with contact manner and current detection investigation was used for conductive AFM ( C-AFM ) measurings to qualify pressed pellets of the nanoparticles for surface morphology and conduction. Zeta potency was measured utilizing a Zetasizer ( Malvern Instruments, Worcestershire, U.K. ) . All measurings were recorded at 25oC. The reactions that were carried out can be seen in Table 1.

Table 1. A sum-up of the reactions that were carried out.

Chemical reaction

Pyrrole ( M )

Ozone Exposure ( S )

Temperature ( A°C )

1

0.17

60

23

2

0.17

60

4

3

0.17

30

23

4

0.085

60

23

The synthesis process for the first set of reactions was as follows: 100 milliliter of Millipore H2O was placed in a 125 milliliter Erlenmeyer flask followed by 1.35g of pyrrole. In the instance of reaction 4, 0.675g of pyrrole was added. The mixture was so stirred until all of the pyrrole was dissolved. Oxygen was provided to the ozone generator at a force per unit area of 20 pounds per square inchs and a flow rate of 0.2 liters/minute. Harmonizing to the literature provided by Absolute Ozone, this flow rate should be bring forthing an oxygen/ozone mixture that is 18 % ozone by weight. For reactions 1 and 4, the oxygen/ozone mixture was bubbled through the pyrrole solution for 60 seconds. For reaction 3 the oxygen/ozone mixture was bubbled through the pyrrole solution for 30 seconds. After the ozone exposure was complete, any staying ozone in the flask was removed with a gently blowing watercourse of air from a tight air line. The flasks were so sealed with a gum elastic stopper and allowed to sit for 4 yearss.

The process for reaction 2 was similar except that anterior to the pyrrole being added to the Millipore H2O, the flask was placed in an ice bath until the H2O reached a temperature of 4A° C. Pyrrole was so added and stirred until it dissolved. The oxygen/ozone mixture was so bubbled through the pyrrole solution while it remained in the ice bath. After ozone exposure, staying ozone was removed with a watercourse of tight air and the flask was sealed with a stopper and placed in a icebox at a temperature of 4A° C for 4 yearss. The same reaction process was followed for all the reactions in this work ; the discrepancies include temperature, molar concentration and ozone exposure clip. After the consequences from the first set of reactions were obtained, a larger set of reactions was carried out in an attempt to find factors impacting the stableness and formation of the nanoparticles. These reactions can be seen in Table 2. The reactions in Table 2 were carried out utilizing the same force per unit area and flow rate as the old reactions from Table 1. All reactions in Table 2 were carried out at room temperature.

Table 2: Chemical reactions for analyzing zeta possible measuring and atom size behaviour as a map of monomer concentration and ozone exposure.

Chemical reaction

0.17 Molar

R – 1

30 Seconds Ozone Exposure

R – 2

60 Seconds Ozone Exposure

R – 3

120 Seconds Ozone Exposure

0.34 Molar

R – 4

30 Seconds Ozone Exposure

R – 5

60 Seconds Ozone Exposure

R – 6

120 Seconds Ozone Exposure

0.51 Molar

R – 7

30 Seconds Ozone Exposure

R – 8

60 Seconds Ozone Exposure

R – 9

120 Seconds Ozone Exposure

0.68 Molar

R – 10

30 Seconds Ozone Exposure

R – 11

60 Seconds Ozone Exposure

R – 12

120 Seconds Ozone Exposure

0.85 Molar

R – 13

30 Seconds Ozone Exposure

R – 14

60 Seconds Ozone Exposure

R – 15

120 Seconds Ozone Exposure

Another set of reactions was performed to look into the consequence of pH in concurrence with ozone exposure on the synthesis reaction. The conditions used for these reactions can be seen in Table 3.

Table 3. Chemical reactions analyzing the consequence of pH and ozone exposure on the synthesis of PPY nanoparticles.

Chemical reaction

Molar Concentration

pH

Ozone Exposure Time ( s )

Temperature ( EsC )

R-16

0.17

2

60

23

R-17

0.17

4

60

23

R-18

0.17

6

60

23

R-19

0.17

8

60

23

R-20

0.17

10

60

23

R-21

0.17

12

60

23

R-22

0.17

2

60

0

R-23

0.17

1.8

60

0

R-24

0.17

1.65

60

0

R-25

0.17

1.5

60

0

R-26

0.17

1.3

60

0

R-27

0.17

1.8

60

0

R-28

0.17

1.6

60

0

R-29

0.17

1.4

60

0

R-30

0.17

1.8

120

0

R-31

0.17

1.6

120

0

R-32

0.17

1.4

120

0

R-33

0.17

1.8

240

0

R-34

0.17

1.6

240

0

R-35

0.17

1.4

240

0

R-36

0.17

1

480

0

A dradendroff reagent was used to prove for the presence of a nonionized wetting agent which could account for steric stabilisation. The Dragendroff reagent was supplied by M/s Sigma-Aldrich. The trial was performed in a little extractor tubing. One millilitre sample solution is diluted to a 4-5ml with 20 % acetic acid, combined with an equal volume of trial solution, and shaken smartly. The present of nonionized wetting agent is shown by precipitation. [ 43 ]

RESULTS AND DISCUSSION

The first group of reactions carried out in this survey was a study to seek to find what factors may hold an consequence on the atom size of the merchandises of the reaction. The consequences from the Gaussian analysis of the atom size distributions from the assorted reactions can be seen in Table 3. It is apparent that the continuance of ozone exposure has a moderate consequence on the average atom size cut downing it by 58 nanometers. However, with this moderate lessening in the average diameter of the atoms there is a big addition in the standard divergence and therefore a lessening in the uniformity of the mensural atom diameter. It is besides apparent that temperature has a big consequence on the atom size. With a figure weighted average atom diameter of 73 nanometers and for reaction 2, a bead in temperature of 19Es C resulted in a bead in average atom size of 251 nanometers and reduced the atom size to a value below 100 nanometer. The curves of the information from which these Numberss were calculated can be seen in Figures 1-4.

Table 3. The figure and volume weighted average atom diameter and their standard divergences for reactions 1-4.

Chemical reaction

Mean Weighting

Average Diameter ( nanometer )

Standard Deviation ( nanometer )

1

Number

324

16

Volume

325

16

2

Number

73

18

Volume

88

22

3

Number

266

78

Volume

373

109

4

Number

288

32

Volume

301

34

Figure 1. The figure weighted atom size distribution for the merchandise of reaction 1.

Figure 2. The figure weighted atom size distribution for the merchandise of reaction 2.

Figure 3. The figure weighted atom size distribution for the merchandise of reaction 3.

Figure 4. The figure weighted atom size distribution for the merchandise of reaction 4.

Figures 1-4 show the atom size distribution for the merchandises of reactions 1-4. It is apparent from these secret plans that particle distributions achieved from these reactions all approximate Gausian behaviour. The fact that these extremums are all Gaussian in nature indicates that there are likely non any big mechanistic differences between the merchandises of the different reactions. A bimodal distribution, for illustration, would bespeak that some consequence that was doing a drastic difference in the merchandises was act uponing the merchandises of the reactions. It is besides apparent that the lessening in temperature in reaction narrowed the distribution every bit good as shifted it to smaller diameters.

Analysis of reactions 1 and 2 via a transmittal negatron microscope yielded the images in Figure 5. It is clear in these images that both reactions yielded atoms that were spherical in nature with little sums of agglomeration. The atom size difference seen in Figures 1 and 2 are besides evident in these images with the atoms produced from reaction 2 being much smaller. It is besides of import to observe that the atoms seen in Figure 1 seem to hold a big sum of negatron denseness which could be an indicant that there is a important sum of junction within the atoms. This is apparent because the atoms are wholly opaque under the TEM. Most nanosized polymer atoms such as poly methyl methacrylate appear to be slightly semitransparent under the TEM because they do non hold a high denseness of negatrons. [ 44 ] In contrast to this, carry oning polymers have a high grade of unsaturation taking to much higher negatron densenesss which make carry oning polymer nanoparticles appear opaque. The consequences obtained in this analysis are in good understanding with other TEM consequences for carry oning polymer nanoparticles. [ 45, 46 ]

degree Celsiuss

vitamin D

B

a

Figure 5. The TEM images of the atoms produced from reaction 1 ( a and B ) and reaction 2 ( degree Celsius and vitamin D ) .

After assuring consequences were obtained from reactions 1-4, further survey was carried out to analyze correlativity between the monomer concentration, ozone exposure and atom size at room temperature. These reactions can be seen in Table 2. The TGA consequences for reactions 1-3 can be seen in Figure 6 below. It can be seen that greater sums of ozone exposure increase the thermic stableness of the merchandise. This behaviour could be declarative of a higher molecular weight merchandise indicating that the ozone is originating cationic extremist polymerisation of the polypyrrole similar to other instigators that act as oxidising agents. TEM consequences from these reactions are shown in Figure 7. It is apparent from these consequences that there is a bed that has formed on the exterior of the atoms despite the absence of a wetting agent in the synthesis reaction. It is thought that this bed may be responsible for the stabilisation of the atom scattering. It may be possible that this outer bed is composed of more polar overoxidized polypyrrole which could move as a steric stabilizer. More grounds and treatment on this hypothesis is shown below.

Figure 6. The secret plan of the isothermal TGA informations collected from reactions R-1 through R-3.

Figure 7: TEM Images of the atoms ( a ) & A ; ( B ) : a bed can be seen around the nanoparticles, ( degree Celsius ) & A ; ( vitamin D ) : ideal behaviour of stable nanoparticles in H2O, ( vitamin E ) & A ; ( degree Fahrenheit ) : Agglomerated atoms because of high ozone exposure and really low pH ( Below pH of 1.65 )

The consequence of monomer concentration and ozone exposure can be seen in Figure 7. It is apparent from this secret plan that increased ozone exposure and higher monomer concentration consequences in larger atom sizes at room temperature. It is besides evident that the sum of ozone exposure has a larger affect on atom size at higher monomer concentrations. These consequences may bespeak that it is necessary to oxidise a certain per centum of the monomer in order for the atoms sizes to be kept little. Once that per centum goes down in the instance of the higher monomer concentrations it seems that the atom size additions.

Figure 8: Molar concentration vs. average atom diameter for reactions R-1 through R-15.

In order to assist find the mechanism by which the nanoparticles may be stabilized and whether the bed on the exterior of the atoms may be involved, zeta possible measurings were performed on the scatterings. The zeta possible consequences of all the reactions from Table 2 can be seen in Table 3. For all of the mensural reactions, the zeta potency was really nigh 0 V which indicates that there is non adequate electrostatic activity in the scattering to maintain it stabilised. Therefore it is likely that the stableness of the atoms could be attributed to steric stabilisation. To assist corroborate this, a Dragendroff reagent was added to a sample of the scattering in a extractor tubing. [ 43 ] In this instance precipitation was observed after smartly agitating the extractor tubing for 15-20 proceedingss bespeaking that mode in which the nanoparticles were being stabilized was similar to a nonionized wetting agent. Harmonizing to Cataldo et al. , ozone easy signifiers amide ketones on the I± Cs and hydrated oxide groups on the I? Cs of a polypyrrole concatenation with some pealing scission. [ 47 ] This may be another account for the built-in stableness that seems to be imparted to the nanoparticles.

Table 3. Zeta possible and output informations for reactions R-1 through R-15.

Chemical reaction

Zeta potency ( millivolt )

Output ( gram )

0.17 Molar

R – 1

30 Seconds Ozone Exposure

0.0688

0.01

R – 2

60 Seconds Ozone Exposure

-0.075

0.03

R – 3

120 Seconds Ozone Exposure

0.5038

0.02

0.34 Molar

R – 4

30 Seconds Ozone Exposure

-0.0767

0.02

R – 5

60 Seconds Ozone Exposure

-0.128

0.03

R – 6

120 Seconds Ozone Exposure

0.27256

0.02

0.51 Molar

R – 7

30 Seconds Ozone Exposure

-0.07708

0.03

R – 8

60 Seconds Ozone Exposure

-0.00432

0.04

R – 9

120 Seconds Ozone Exposure

-0.23866

0.04

0.68 Molar

R – 10

30 Seconds Ozone Exposure

0.0602

0.03

R – 11

60 Seconds Ozone Exposure

0.045

0.03

R – 12

120 Seconds Ozone Exposure

-0.29964

0.04

0.85 Molar

R – 13

30 Seconds Ozone Exposure

0.105056

0.03

R – 14

60 Seconds Ozone Exposure

0.12702

0.02

R – 15

120 Seconds Ozone Exposure

-0.14228

0.03

If the bed environing the nanoparticles was made up of overoxidized polypyrrole, it could perchance move as a sterically stabilising bed. The ketone and hydroxyl functional groups that would be added onto the polypyrrole ironss as a consequence of overoxidation would do them more polar and hence more hydrophilic. This hydrophilicity would let the ironss to loosen up in the encompassing H2O. Aggregation would so necessitate these environing ironss to take on less relaxed conformations which would ensue in a lessening in information. Aggregation would hence be entropically unfavourable. This hypothesis is farther supported by the presence of a carbonyl extremum and a hydroxyl extremum in the FTIR consequences in Figure 9.

Figure 9: FTIR Spectra: consequence of increased reaction clip and decreased pH. ( R-24, R-34 and R-36 )

FTIR spectra of reactions performed at 0Es C with different ozone exposure times are shown in Figure 8. The sets at 1563 ( 2,5-substituted pyrrole ) and 1436 cm-1 may be assigned to polypyrrole pealing quivers. [ 48-50 ] The sets at 1345, and 1074 cm-1 may be matching to =C-H in plane quivers while the set at 885 cm-1 may match to out of plane quivers bespeaking polymerisation of pyrrole. [ 49, 50 ] The soaking up extremum at 1658 cm-1 likely correspond to a -C=O linkage. [ 51 ] The C=O construction at the I?-C of pyrrole ring is typically due to the overoxidation of polypyrrole. [ 52 ]

The presence of overoxidized polypyrrole could besides be an account for the consequences of conduction measurings that were performed utilizing the conductive AFM technique. In all of the 15 reactions in Table 2, the synthesized merchandise does non exhibit mensurable conduction. A typical set of images collected from each of the samples can be seen in Figure 10. It is the far right image that would demo mensurable current as white countries in the image. If overoxidized oligomers are organizing an insulating bed around the atoms with more conductive polypyrrole at the centre, it could interrupt conductivity through a pressed pellet of the merchandise and hence prevent conduction in the sample. This insulating behaviour is due to the presence of the Carbonyl functional groups which disrupt the junction of polypyrrole ironss and hence cut down the conduction of polypyrrole.

Figure 10. C-AFM images collected from a pressed pellet of the PPY nanoparticles.

Part of this job may be due to utilizing H2O as a dissolver. Peter Novak has suggested in his work that carbonyl linkages form due to the reaction of pyrrole with H2O and hydroxy groups which are in copiousness when ozone is dissolved in H2O. [ 53 ] This phenomenon is pH dependent nevertheless. Overoxidation is thermodynamically more favourable at basic pH ‘s so, by adjust the pH with hydrochloric acid, it was thought that a conductive merchandise could be obtained. [ 53 ] An extra benefit that lower pH degrees could hold on this reaction would be to diminish the rate of decomposition for ozone. Ozone dissociation in H2O is initiated by negatively charged OH ions, by diminishing the pH of the reaction solution, this reaction can be slowed which may ensue in less overoxidation of the polypyrrole every bit good. [ 54 ] Low temperatures during the reaction could besides assist in cut downing the interior infinite of micelles by virtuousness of deactivating the concatenation mobility of the sterically stabilising beds on the exterior of the atoms and by forestalling overoxidation. [ 4 ]

Therefore it was necessary to look into the consequence that pH had on this synthesis reaction. The consequence of pH was studied utilizing HCl and NaOH to set the pH of the synthesis solutions prior to ozone exposure. The scatterings produced from these reactions were observed visually for colloidal stableness and with UV Vis spectrometry to observe the presence of bipolarons which would bespeak conduction. For this survey we prepared solutions of pyrrole in H2O at different pH concentrations of, 2, 4, 6, 8, 10, and 12. It was observed in Figure 11 that increasing pH reduces stableness of the nanoparticles ; the nanoparticles were most stable at pH 2. By analysing the UV Vis spectra of these reactions in Figure 12, it could be concluded from the extremums at about 294 nanometers that the scatterings of nano-particles contain big sums of terpyrrole oligomers. [ 55 ] By cut downing the Ph of the reaction, it could be observed that the extremum for terpyrrole oligomers became less intense and it shifted towards larger wavelengths which may bespeak an addition in the molecular weight of the polypyrrole. [ 55 ]

Figure 11: The stableness of polypyrrole nanoparticles scatterings 20 yearss after synthesis. ( R-22 to R – 26 )

Figure 12: UV Vis spectrometry of reactions R-24 and R-17 ( pH of 4 and 1.6 ) .

After the above consequences were observed for the reactions at different pH degrees, five more reactions were carried out from a pH of 2 to a pH of 1.3 to find if the stableness or conduction of the nanoparticles could be improved. The sum of ozone exposure was besides increased for these reactions in an attempt to increase the molecular weight of the polypyrrole. The images of the scatterings produced from these reactions can be seen in Figure 13. It was apparent from ocular appraisal that the scatterings were non stable below a pH of 1.65. It may be good to execute the synthesis reaction at the lowest pH possible as this would supply the largest figure of chloride ions from the hydrochloric acid to move as dopant ions if bipolarons were formed on the polypyrrole ironss. UV-Vis spectrometry was used to find if there was a difference between the different merchandises of the reactions.

Figure 13: Optimizing stabilisation for lowest pH ( R-22 to R-26 ) ( Observed that lowest possible pH we could travel is 1.65 )

Figure 14 shows consequence of increased reaction clip and decreased pH on the UV-Vis spectra of the merchandises. It can be observed that with decrease in pH ; the terpyrrole extremums at about 300nm were reduced which suggests a lessening in the sum of terpyrrole in the concluding merchandise. [ 55 ] The wide set at 475 nanometer, which has been assigned to the pi-pi* passage of polypyrrole, indicates that higher molecular weight polypyrrole is produced. [ 55-57 ] The extremums at 475 nanometers besides show bipolaron soaking up due to Cl- ion doping. [ 58, 59 ] However, as before reported, the addition in reaction clip is prone to bring forthing agglomeration of nanoparticles.

Figure 14: UV-Vis spectra consequences at increased reaction clip, and reduced pH. ( R-33 to R-36 )

Decision

This survey investigated the templet free synthesis of polypyrrole nanoparticles via chemical oxidative polymerisation utilizing ozone as the oxidizing agent. It was found that reaction temperature was the factor that had the largest consequence on atom size with colder temperatures bring forthing smaller atoms. It was observed that there is layer environing the atoms that may be lending to the stableness of the nanoparticles. FTIR and UV-Vis consequences indicated that this bed is likely to be overoxidized pyrrole monomers. Zeta possible measurings indicated that the manner by which the atoms were stabilized was steric stabilisation. Future work will look into the usage of colder temperatures by presenting co-solvents such as methyl alcohol into the synthesis reaction to maintain the reaction from stop deading. Extra oxidizing agents will besides be investigated to increase the output of the reaction.

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