Template assisted synthesis and assembly of nanoparticles 2

Chapter Chapter Experimental 2.1 Chemical reagents The following chemicals were used as received unless otherwise stated: (1) Absolute ethanol, (Merck) (2) Toluene, AR (Tedia) (3) N,N-Dimethylformamide, HPLC grade (Fisher) (4) n-Hexane, HPLC grade (Tedia) (5) N-methyl pyrrolidone, 99.5% (Merck) (6) Methyl alcohol, AR (Tedia) (7) Acetone, AR (Tedia) (8) Thiobenzonic acid, 90% (Fluka) (9) Propylamine, 99 % (Aldrich) (10) Silver nitrate, 99% (Merck) (11) Sodium carbonate decahydrate, >99% (Dumont Chemical) (12) Lead (II) acetate trihydrate, 99% (Fluka) (13) Aniline, unknown source, purified by vacuum distillation before use (14) Ammonium persulfate, AR (BDH Laboratory Supplies) (15) Sodium hydroxide, >99% (Dickson Instrument & Reagent) (16) Hydrogen peroxide, 35%, w/w, extra pure (Scharlau H10140) (17) Concentrated sulfuric acid, 96% (Fisher) (18) Mercury nitrate standard solution (EA analytical lab)* 56 Chapter (19) I30 p modified clay (Nanocor Inc) (20) 1-dodecanethiol, 98% (Acros) (21) Multi-wall carbon nanotube (Shenzhen Nanotech Port) (22) Hexadecylamine, 99% (Fluka) (23) Trioctylphosphine, 90% (Fluka) (24) 3-mercaptopropyltrimethoxysilane (Tokyo Kasei Kogyo) (25) polystyrene microbeads, 2.6% aqueous dispersion, 1.053 µm (Polysciences) (26) Copper (II) nitrate hemipentahydrate, 98% (Aldrich) (27) Silicon (100) substrates (Shinetsu) *The Hg(NO3)2 was standardized as follows: 3.0 grams of Hg(NO3)2 (AR, BDH) was weight accurately and dissolved in 500 mL of 0.01 M HNO3. After filtering, the solution was made up to 1750 mL with 0.01 M HNO3 and the pH was adjusted to 2.6 with 1M HNO3. NaCl solution was used to standardize the concentration of Hg(NO3)2 using: bromophenol blue and diphenylcarbazone as indicators. 2.2 Characterization Techniques 2.2.1 Elemental analysis (EA) The microanalysis for C, H and S was conducted on a Perkin Elmer CHNS/O 2400 Analyzer Series II instrument in the Microanalytical Laboratory at the Department of Chemistry, National University of Singapore. 2.2.2 Thermogravimetric analysis (TGA) TGA was recorded on a SDT 2960 Simultaneous DTA-TGA. Approximately 10 mg of sample was put in a ceramic pen for the TGA experiment. TGA of the MTB 57 Chapter precursors was recorded under a flow of inert N2 gas (flow rate 90mL/min) with a heating rate of 10°C/min. 2.2.3 Fourier transform Infrared (IR) spectroscopy FT-IR spectra were recorded using a Bio-Rad FTS 165 FTIR spectrophotometer in the range of 4000-400 cm-1 using KBr pellets. 2.2.4 Ultraviolet/Visible (UV/Vis) spectroscopy A Shimadzu UV-2550 UV/vis recording spectrophotometer was used to carry out the optical measurements. Samples are dispersed as dilute solution in a suitable solvent and contained in a quartz cell. Background spectrum was subtracted from the recorded sample spectrum using solvent as reference. 2.2.5 Powdered X-ray diffraction (XRD) Powdered XRD analysis was carried out on a Siemens D5005 X-ray powder diffractometer with Cu Kα radiation (40 kV, 40 mA), which was calibrated by quartz SiO2 2θ = 26.638°. The powdered sample was mounted onto a sample holder and scanned with a step size of = 0.05o in the range 5−90o. 2.2.6 Transmission electron microscopy (TEM) TEM and selected area electron diffraction (SAED) patterns were obtained on a 100 kV JEM-100CXII TEM or 200KV JEOL 2010F microscope. Samples were prepared by placing a drop of the sample solution dispersed in a certain solvent onto a copper grid coated with carbon film, and was allowed to dry in vacuum desiccators. 58 Chapter 2.2.7 High resolution transmission electron microscopy (HRTEM) HRTEM was performed using a Philips CM300 FEG instrument with an acceleration voltage of 300 kV. One drop of the sample solution or dispersion was placed on a 200 mesh carbon-coated copper grid. Excess liquid was removed with filter paper and the grid was dried in vacuum. 2.2.8 Scanning electron microscopy (SEM) SEM analysis was carried out with FEI XL-30FEG instrument operated at 25 kV. The samples were prepared by sticking the powder or dropping the dispersed solution of the sample onto a clean silicon substrate and dry in desiccators. The cleaning procedure of silicon wafer refers to Section 2.7.1. 2.2.9 X-ray photoelectron spectroscopy (XPS) XPS was performed using a VG Scientific ESCALAB MK II system, with a monochromatic Mg Kα x-ray source (1253.6 V) at 120 W (10 mA, 12 kV). The C 1s peak at 284.7 eV was used as reference for the calibration of the energy scale. 2.2.10 Photoluminescence (PL) PL spectra of organo-clay samples (Chapter 4) were recorded at room temperature with an Accent RPM2000 Photoluminescence Mapping System using a He-Cd laser (325 nm) and a diode laser-pumped solid-state laser (532 nm). Signals were collected by InGaAs detector. The excitation energy was removed from the measured spectrum using long-pass filters following the monochromator (Grating 300g/mm-500). For other samples, Fluorolog fluorescence spectrometer (Jobin Yvon HORIBA) was employed to obtain PL spectrum. iHR 320 was used as detector in NIR region, while PMT was used as detector in UV-vis region. IR glass (for iHR320) and water 59 Chapter (for PMT) was used to calibrate the detectors each time before the sample measurement. For all samples, both the slit width of the emission and excitation are controlled as mm while the integration time was set at 0.1 s. 2.2.11 Gel Permeation Chromatograph (GPC) Gel Permeation Chromatography (GPC) measurements were used to characterize the molecular weight and dispersity of polyaniline (PANi) discussed in Chapter 3. The chromatography column used is Phenogel linear (300×4.6 mm, µm). A series of standard polystyrene were used to calibrate the columns. 2.2.12 Potentiometric/Amperometric measurements Potentiometric/amperometric measurements were performed using a PGSTAT30 Autolab Potentiostat Galvanostat (Eco Chemie). Standard Ag/AgCl electrode (obtained from Metrohm) was used as the reference electrode while PANi/Ag2S films (Chapter 3) or MWCNT/PbS composites (Chapter 5) were used as the working electrode and platinum rod is used as counter electrode. 2.2.13 pH measurements The pH value was measured by a Metrohm 744 pH meter. The pH meter was calibrated with Fisher buffer (pH = 4.00 ± 0.01 and pH= 7.00 ± 0.01, 25°C). 2.2.14 Spin coating Bench top spinner coater WS-400B-6NPP/LITE (Laurell Technologies Corporation) was employed to prepare thin films on the surface of ITO or silicon wafer. Silicon wafer was cleaned according to procedure described in section 2.7.1 while ITO was cleaned by sonication in acetone and ethanol for minutes respectively. 60 Chapter 2.2.15 Atomic Force Microscopy (AFM) Tapping mode AFM was measured with a Digital Instruments Dimension TM3000 (Vecco instruments). The thickness of PANi/Ag2S composites film (Chapter 3) was determined using the section analysis. 2.2.16 Vis-near-IR absorption spectroscopy Visible to near-IR absorption spectra were recorded at room temperature using a Shimadzu UV-3600 UV/vis/near-IR spectrophotometer. Samples were dispersed in dilute solution and contained in a quartz cell. Background spectrum was first recorded and subtracted from the recorded sample spectrum. 2.2.17 Raman Spectroscopy Micro Raman spectrum was obtained by Renishaw Raman Scope 2000 System with an attached Olympus optical microscope. The laser from excitation source (532 nm line of an argon-ion laser) was focused onto substrate (silicon wafer) covered with our sample (MWCNT/PbS, Chapter 5) using a 100× objective lens of the optical microscope. The scattered light was collected using the same objective lens. 2.2.18 Conductivity measurement I-V characteristic curves of MWCNT/PbS and aCNT/PbS composite samples (Chapter 5) were obtained from Keithley 237 Source Measurement Unit. The powder dispersion of those samples (in ethanol) was casted on the surface of quartz and dried under vacuum. Voltages were applied from to V and to -2 V at room temperature while the corresponding current was detected. 61 Chapter 2.3 Synthesis of metal thiobenzoate precursors and metal sulfide nanoparticles 2.3.1 Synthesis of silver (I) thiobenzoate precursor Metal thiobenzoates were prepared according to the literature method9. The synthesis procedure of silver thiobenzoate is given below: Thiobenzoic acid (0.01mol) was added to a stirred solution of Na2CO3⋅10H2O (0.005 mol in 20 mL deionized water) slowly. The mixture was stirred for 30 minutes, then added into a solution of AgNO3 (0.01 mol in 20 mL deionized water). All containers were covered by alumina foil because of the light sensitiveness of silver ions. Creamy precipitate appeared quickly during the process, and the mixture was stirred further for hour at room temperature to ensure complete reaction. After centrifugation, the supernatant was discarded and solid was washed several times with water and ethanol. The greyyellow product was dried under vacuum. Elemental calculation for C7H5OAgS: C 34.31, H 2.28, S 13.08; found: C 34.63, H 2.33, S 13.22. This sample is referred to as the AgTB precursor in Chapter 3. 2.3.2 Synthesis of lead (II) thiobenzoate precursor Pb(SOCPh)2 was synthesized similarly as above. Thiobenzoic acid (5.5 mL, 46.8 mmol) was dissolved in 20 mL methanol and was added to a stirred solution of Pb(OAc)2.3H2O (5.17 g or 13.6 mmol in 20 mL methanol) slowly. A thick suspension of cream chocolate-like precipitate appeared immediately. Each time thiobenzoic acid was added below the Pb2+ solution surface using a dropper in order to avoid the formation of dark brown contaminant, presumably PbS. The mixture was stirred for 1.5 hours to ensure complete reaction. The whole suspension was centrifuged, and the 62 Chapter supernatant liquid was removed. The solid was washed three times with methanol until the supernatant liquid was colorless. The creamy chocolate-like product was dried under vacuum. Elemental calculation for C14H10O2PbS2: C 34.92, H 2.09, S 13.31; found: C 34.96, H 2.16, S 14.39. This sample is referred to as the PbTB precursor used in Chapter and 5. 2.3.3 Synthesis of copper (II) thiobenzoate precursor Thiobenzoic acid (0.01 mol) was added slowly to a stirred solution of Na2CO3.10H2O (0.005 mol) in deionized water (10 mL). The mixture was stirred for 30 minutes, and then added into a solution of Cu(NO3)2 (0.01 mol in 20 mL deionized water). Creamy precipitate appeared quickly during the process, and the mixture was stirred for hr to ensure complete reaction. After centrifugation, the supernatant was discarded and solid was washed several times with water and ethanol. The orange product was dried under vacuum. Elemental calculation for C7H5OCuS: C 41.92, H 2.91, S 15.96; found: C 48.18, H 2.93, S 18.95. This sample is the CuTB precursor used in Section 2.3.5 below. 2.3.4 Synthesis of silver sulfide (Ag2S) nanoparticles through hotinjection method Silver sulfide nanoparticles were prepared according to a method developed in our research group1 from the AgTB precursor prepared in Section 2.3.1 above. Hexadecylamine (HDA) (0.30 g) was degassed at 100°C. The liquid was then heated to ~ 120°C under nitrogen. A degassed solution of prepared AgTB (0.025 g) in 0.2 mL trioctylphosphine (TOP) was injected swiftly into the hot liquid of HDA. The pale yellow color of the solution rapidly turned brown and reaction proceeded for 10 63 Chapter minutes. After the reaction mixture was cooled down to room temperature, toluene (ca. mL) was added and particles were precipitated by the addition of excess methanol. The precipitate was centrifuged and dispersed in solution of toluene or hexane with 1-dodecanethiol and sonicated for more than 10 minutes. 2.3.5 Synthesis of copper sulfide (CuxS) nanodisks through hot-injection method Similarly, copper sulfide nanoparticles were also prepared with the injection method similar to the method above1, 2. The capping agent used was 1-dodecanethiol (2.4 mL) instead of HDA and the precursor was a degassed solution of the CuTB precursor (0.026 g) in 0.2 mL TOP. Reaction was carried out at ~ 170°C under nitrogen for 10 minutes. Similarly, toluene (ca. mL) was added and particles were precipitated by the addition of excess methanol. 2.4 Synthesis of PANi/Ag2S nanocomposites 2.4.1 Polymerization of aniline Polyaniline (PANi) was synthesized via oxidative polymerization of aniline at room temperature3. mL of distilled aniline was added to 100 mL M HCl followed by 3.15 g of (NH4)2S2O8 which acts as the oxidizer. The solution was stirred for 13 hours at room temperature. Dark green powder produced was centrifuged and washed with M HCl. The isolated product was dried overnight under vacuum. The dried polyaniline was treated with 100 mL 0.5 M NaOH for hours followed by washing with deionized water in order to obtain the emeraldine (EM) base. The color of the powder changed to dark blue. This was used for the preparation of PANi/Ag2S 64 Chapter nanocomposites and electrodes as follows. 2.4.2 Preparation of PANi/Ag2S nanocomposites For all these experiments, the concentration of PANi dissolved in N-methyl pyrrolidone (NMP) was fixed at 0.01 mol L-1. The amount of reagents added was varied to achieve the desired molar ratios of Ag : PANi according to Table 2.1. The number of moles of propylamine used was kept similar to AgTB. AgTB as prepared in Section 2.3.1 was added to PANi solution and stirred at room temperature for hour. After which, an equimolar amount of propylamine was added to the solution and the solution was stirred further for hour. The color of the solution changed from blue to green then finally to dark green, indicating the protonated PANi was formed accompanying the formation of Ag2S nanoparticles. Ethanol was then added to precipitate the nanoparticles formed and thus terminating the reaction. The solution was centrifuged and the powder was washed with ethanol for three times. Table 2.1. The feed amount of PANi (in NMP 0.01 mol L-1) and AgTB used to prepare PANi/Ag2S nanocomposites in Chapter 3. Sample ID Sample Sample Sample Sample Amount of AgTB (mg) 24.5 24.5 36.5 61.1 Volume of PANi/NMP (mL) 10 5 Volume of propylamine (µL) 8.5 8.5 17.0 34.0 2.4.3 Preparation of PANi/Ag2S nanocomposites film In order to form the composite film for ion selective electrode (ISE, discussed in Chapter 3), freshly prepared wet PANi/Ag2S precipitate (Sample in Table 2.1) was 65 Chapter dissolved in mL NMP. The clear blue solution was spin-coated onto an ITO glass (cleaned by sonication in acetone and ethanol) using spinner coater at a spin speed of 600 rpm/s for mins followed by 5000 rpm/s for mins. Each time droplets of Sample solution was placed on the ITO glass. The thickness of the ISE film was controlled by the number of spin-coating times and was later determined by AFM (Section 2.2.15). ISE films were also prepared by coating different sample solutions (Samples 1, and 4) at fixed spin-coating times to produce films of different Ag content. The coated PANi/Ag2S film was used as the working electrode in our potentiometric measurements after drying in vacuum. For all re-used ISE films, the PANi/Ag2S composite films were immersed in deionized water for at least 24 hours to ensure all absorbed silver ions can be released. The soaking deionized water was changed every 3−4 hours. 2.5 Synthesis of organo-clay/PbS nanocomposites The preparation of clay/PbS nanocomposites were developed in the laboratory as there was no literature report to follow. The optimized procedure and conditions were given below: 48 mg of PbTB precursor (prepared in Section 2.3.2) was dissolved in mL DMF followed by the addition of 50 mg organo-clay I30p. After stirring for 10 minutes, 10 µL propylamine was added. The color of the solution changed to reddish brown and deepened gradually. After some time (this period is denoted as Reaction Time I, varied from 10 minutes to hours), 240 µL DDT was added. The solution was further stirred at room temperature (this period is denoted as Reaction Time II, varied from 30 minutes to 20 hours) before ethanol was added and the whole solution 66 Chapter was centrifuged at 1500 rpm for minutes followed by washing with ethanol. Finally, the precipitates were dried in vacuum. The final organo-clay/PbS products are slightly brown or deep-brown in color, depending on the loading percentage of PbS. The various samples studied in Chapter were prepared according to different feed ratios and Reaction Time I/II as given in Tables 2.2 - 2.9 below. Table 2.2. Feed ratios and reaction conditions of organo-clay/PbS nanocomposites Samples to discussed in Section 4.2. Sample is a control preparation without clay. organoReaction PbTB propylamine DDT clay Time I* (mg) (µL) (µL) (mg) (hours) 3:1:10 108.2 16 80 2 2:1:10 108.3 24.7 8.5 120 1:1:10 107.9 48.4 8.5 240 1:2:20 54.1 48.2 17.0 240 1:5:50 26.9 60.4 34.0 300 0:1:10 40.2 8.5 200 * Reaction Time I is the interval time between the addition of propylamine and DDT; # Reaction Time II is the reaction time after the addition of DDT. Sample ID [clay]/[PbTB]/[DDT] Reaction Time II# (hours) 20 20 20 20 20 20 Table 2.3. Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different amount of DDT (Series I, using longer Reaction Time I). Sample is a control preparation without DDT. Sample ID [clay]/[PbTB]/[DDT] 10 11 12 13 14 15 16 1:5:0 1:5:1 1:5:2 1:5:5 1:5:8 1:5:20 1:5:40 1:5:80 1:5:120 1:5:160 organoclay (mg) 27.5 27.4 26.9 27.0 27.2 27.5 27.0 27.0 27.0 26.8 PbTB (mg) propylamine (µL) DDT (µL) 59.9 60.2 59.9 60.1 60.5 60.3 60.2 60.9 60.2 60.1 20 20 20 20 20 20 20 20 20 20 12 30 50 125 250 500 750 1000 Reaction Time I (hours) 2 2 2 2 2 Reaction Time II (hours) 20 20 20 20 20 20 20 20 20 20 67 Chapter Table 2.4. Feed ratios and reaction conditions and of organo-clay/PbS nanocomposites prepared with different amount of DDT (Series II, using shorter Reaction Time I). Sample ID [clay]/[PbTB]/[DDT] 17 18 19 20 21 22 1:5:2 1:5:5 1:5:10 1:5:50 1:5:100 1:5:250 organoclay (mg) 27.0 27.0 27.3 27.0 27.3 27.1 PbTB (mg) propylamine (µL) DDT (µL) 60.6 60.1 60.3 60.1 60.5 60.5 20 20 20 20 20 20 12 30 60 300 600 1500 Reaction Time I (hours) 0.5 0.5 0.5 0.5 0.5 0.5 Reaction Time II (hours) 20 20 20 20 20 20 Table 2.5. Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared different Reaction Time I (Series I). Sample ID [clay]/[PbTB]/[DDT] 23 24 25 26 27 1:5:40 1:5:40 1:5:40 1:5:40 1:5:40 organoclay (mg) 26.8 27.0 27.1 27.2 27.3 PbTB (mg) propylamine (µL) DDT (µL) 60.0 60.3 60.5 60.0 60.0 20 20 20 20 20 250 250 250 250 250 Reaction Time I (mins) 10 30 45 60 120 Reaction TimeII (hours) 2 2 Table 2.6. Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different Reaction Time I (Series II). Sample ID [clay]/[PbTB]/[DDT] 28 29 30 1:5:10 1:5:10 1:5:10 organoclay (mg) 27.3 27.3 27.2 PbTB (mg) propylamine (µL) DDT (µL) 60.3 60.4 60.5 20 20 20 60 60 60 Reaction Time I (mins) 30 90 120 Reaction Time II (hours) 20 20 20 Table 2.7. Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different Reaction Time I (series III). Sample ID [clay]/[PbTB]/[DDT] 31 32 33 1:5:50 1:5:50 1:5:50 organoclay (mg) 27.0 27.6 26.9 PbTB (mg) propylamine (µL) DDT (µL) 60.1 60.4 60.4 20 20 20 300 300 300 Reaction Time I (mins) 30 90 120 Reaction Time II (hours) 20 20 20 68 Chapter Table 2.8. Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different Reaction Time II. Sample ID [clay]/[PbTB]/[DDT] 34 35 36 37 38 39 1:5:40 1:5:40 1:5:40 1:5:40 1:5:40 1:5:40 organoclay (mg) 27.0 27.2 27.0 27.0 27.4 27.6 PbTB (mg) propylamine (µL) DDT (µL) 60.2 60.3 60.8 60.1 60.2 60.4 20 20 20 20 20 20 250 250 250 250 250 250 Reaction Time I (mins) 90 90 90 90 90 90 Reaction Time II 5mins 30mins 1hr 2hrs 10hrs 20hrs Table 2.9. Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different amount of propylamine. Sample ID [clay]/[PbTB]/[DDT] 40 41 1:5:10 1:5:10 organoclay (mg) 26.8 27.3 PbTB (mg) propylamine (µL) DDT (µL) 60.0 60.3 40 20 60 60 Reaction Time I (mins) 30 30 Reaction Time II (hours) 20hrs 20hrs 2.6 Synthesis of MWCNT/PbS and aligned MWCNT/PbS nanocomposites 2.6.1 Preparation of MWCNT/PbS composites In this preparation, a commercial multi-wall carbon nanotube (MWCNT) was used. A typical procedure is as follows: 48mg PbTB was dispersed in mL DMF followed by the addition of 12 mg MWCNT powder. After stirring at room temperature for 30 minutes, µL propylamine was added and the mixture was stirred for hours. After centrifugation, the supernatant was discarded and the residue solid was washed several times with DMF and ethanol. The dark product was dried under vacuum. By varying the molar ratio of MWCNT to PbTB, a series of MWCNT/PbS nanocomposites have been prepared and the feed ratios of the various reagents used are listed in Table 2.10. 69 Chapter Table 2.10. Feed ratios of PbTB, MWCNT, DMF and propylamine in the preparation of samples of MWCNT/PbS nanocomposites. Sample ID [MWCNT]/[PbTB] 4:1 2:1 1:1 1:2 MWCNT (mg) 12.1 11.9 11.7 6.0 PbTB (mg) 12.4 24.1 47.9 48.1 DMF (mL) 5.0 5.0 5.0 5.0 propylamine (µL) 4.3 4.3 8.5 8.5 Reaction time (hours) 3 3 2.6.2 Synthesis of aligned MWCNT/PbS nanocomposites In this preparation, aligned MWCNT (denoted as aCNT hereafter) was grown on a silicon wafer using plasma enhance chemical vapor deposition (PECVD) method from a mixture of C2H2/H2 according to literature4, 5. Briefly, iron nanoparticles were first deposited onto the silicon substrate by means of radio frequency (rf) magnetron sputtering. The iron nanoparticles were then reduced by hydrogen plasma to metallic iron particles, which served as catalyst in the formation of CNT. A mixture of C2H2 and H2, with a flow rate at 15 sccm (standard cm3/minute) was then flown into the chamber at a pressure of 1200 mtorr and an rf plasma of 100W. The substrate was maintained at 450°C throughout the deposition, of which the duration was varied at 10 minutes, 30 minutes and hour to control the length of the grown aCNT. Next, 12 mg PbTB was added into mL DMF in a beaker. The pieces of aCNT films on Si substrate were placed inside the solution. Equal molar of propylamine was then added to initiate the decomposition of the precursor. The reaction was allowed to carry out for 12 hours without stirring nor shaking. The substrates were finally taken out carefully using a forcep and washed with DMF followed by toluene for several times. Finally, the samples were dried under vacuum. A series of samples were prepared according to the feed ratios of the various reagents listed in Table 2.11. 70 Chapter Table 2.11. The thickness and diameter of aCNT film and the various feed amounts of PbTB, DMF and propylamine used in the preparation of aCNT/PbS nanocomposites. aCNT aCNT PbTB DMF propylamine Reaction time thickness diameter (mg) (mL) (L) (hours) (µm) (nm) 12 50 6.1 2.0 4.0 24 12 50 12.1 2.0 8.0 24 12 50 24.1 2.0 10.0 24 12 50 0.24* 2.0 4.0 24 10 30 6.3 2.0 4.0 24 10 10 30 3.0 2.0 4.0 24 11 10 30 12.0 2.0 8.0 24 12 10 30 24.1 2.0 10.0 24 * A mother solution of PbTB/DMF was prepared by 24.2 mg PbTB dissolved in mL DMF and 20 µL of them was withdrawn then diluted to mL. Sample ID Another series of samples have been prepared in ethanol through similar steps. Detailed feed amount of used reagents and parameter of AMWCNT are listed in Table 2.12. Because the decomposition of PbTB in ethanol is much faster than in DMF, reaction time was controlled at 1hour. Table 2.12. Parameters of AMWCNT film and feed amount of PbTB, ethanol and propylamine. Sample ID 13 14 15 16 AMWCNT thickness (µm) 12 12 12 12 AMWCNT diameter (nm) 50 50 50 50 PbTB (mg) Ethanol (mL) propylamine (µL) 3.4 6.1 12.3 24.6 2.0 2.0 2.0 2.0 4.0 4.0 8.0 10.0 Reaction time (hours) 1 1 2.6.3 Field emission measurement of MWCNT/PbS and aCNT/PbS nanocomposites In this type of measurements, the MWCNT/PbS or aCNT/PbS nanocomposites on silicon wafer were used as the emitter cathode. These were first mounted onto a 71 Chapter sample mount and the total emission area was defined by a circular hole with an area of ~0.23 cm2 fashioned on the polymeric spacer. ITO glass plate, which has been coated with a layer of phosphor material (ZnO:Zn), was employed as the anode. The emitter-to-anode distance was maintained using some 100 µm glass spacers. The setup (as shown in Figure 2.1) was then placed in a main chamber connected to Keithley 237 high voltage source measurement unit. Voltage could be tuned from V to 1100 V in this system. After the pressure of the chamber dropped down to × 10-7 torr, the FE current-voltage (I-V) relationship was obtained by applying a d.c. field. Pre-testing treatment on the emitters was performed by continuous voltage sweeps until an exactly superimposed I-V curves were obtained from subsequent sweeps. Viewing window Pressure gauge Sample ITO glass plate Glass spacers Keithley 237 high voltage source measurement unit Polymeric spacer stand Sample mount Computer Vacuum Pump Figure 2.1. Field emission measurement setup and chamber. 2.6.4 Photocurrent measurement of aCNT/PbS nanocomposites In this measurement, we employed the aCNT/PbS nanocomposite on silicon wafer as working electrode in a photoelectrochemical cell containing acetonitrile solution 72 Chapter with 0.1% triethanolamine as a sacrificial donor. The area of working electrode was set as mm × 10 mm and the electrode was connected to the Autolab Potentiostat through a crocodile clip (as shown in Figure 2.2). A laser source (Shanghai Uniwave Technology Co. Ltd; 532 nm, 250 mW max power, current: 1.2-1.8 A) was used as the excitation source. Photocurrent which generated by the aCNT/PbS composite film was recorded by a PGSTAT30 Autolab Potentiostat as described in Section 2.2.12. c b a Figure 2.2. Setup for photocurrent measurement: (a) Pt counter electrode, (b) Ag/AgCl reference electrode, and (c) aCNT/PbS on p-type silicon wafer as the working electrode. 2.7 Assembly of nanoparticles onto Si wafer, patterned polystyrene beads and line-patterned polystyrene templates 2.7.1 Surface cleaning of silicon wafer Silicon (100) was used as substrate for all the assembly study in this report. The surface of the substrates was cleaned with piranha etching solution before templating. The piranha solution was prepared by mixing hydrogen peroxide and concentrated 73 Chapter sulfuric acid (v/v: 75:25). The Si (100) substrates were immersed in the freshly prepared piranha solution for 1.5 hours. After that, the substrates were washed many times with deionised water, followed by boiling deionised water to rinse off the acid. Nitrogen was used to blow the cleaned surface dry and the Si (100) was used as soon as it was cleaned for better results of assembly. The surface of silicon wafer after cleaning is hydrophilic. 2.7.2 Assembly of Ag2S nanoparticles on silicon wafer via solvent evaporation method Solvent evaporation method was carried out by placing a drop of Ag2S dispersion onto the substrate at 0° and allowed it to dry in a covered Petri dish. Assembly must be done in a covered Petri dish to prevent the system from any kind of disturbance (i.e. wind, vibrations, dust, etc.). Figure 2.3 illustrates the process of solvent evaporation method. A drop of Ag2S dispersion Petri-dish Solvent (toluene) allowed to evaporate to dryness A layer of Ag2S nanoparticles Silicon wafer Figure 2.3. Schematic diagram illustrating the solvent evaporation method. 2.7.3 Assembly of Ag2S nanoparticles on silicon wafer via dipping & interface method For the dipping & interface method, a toluene/water interface was made up with 74 Chapter about mL water and 0.5 mL toluene in a mL beaker. Six drops of Ag2S or CuxS dispersion was placed into the interface, then a clean silicon wafer was dipped in and pulled out slowly for assembly. Dipping was done manually as shown in Figure 2.4. drops of dispersed nanoparticles 5mL beaker Toluene Water A layer of nanoparticles Modified/ unmodified silicon Toluene A layer of nanoparticles Toluene Water Water A layer of nanoparticles Characterized using SEM Modified silicon wafer Figure 2.4. Schematic diagram illustrating the dipping & interface method. 2.7.4 Assembly of Ag2S and CuxS (x=1.75) nanoparticles on patterned polystyrene beads In this study, pre-assembled polystyrene (PS) beads were used as the base template for the assembly of our prepared nanoparticles. The PS base template was first prepared as follows: a commercial colloidal solution of PS beads (2.6%) was diluted to 0.65%. A drop of PS solution was placed onto a cleaned silicon surface (tilted at 30°) and allowed to dry overnight in a covered Petri plate. Next, the patterned PS beads were used as template to assist the assembly of nanoparticles using dipping & interface method. The speed of pulling the template from the interface was motorized in order to give consistency throughout the experiment. Figure 2.5 showed a computer-controlled pulling stage that we have set 75 Chapter up for the experiments. Optimized pulling speed was determined to be 121.5 µm s-1, for the assembly of Ag2S and CuxS nanoparticles. A hexane/water interface was first set up as in Section 2.7.3. Figure 2.5. Schematic illustration for dipping & interface method using a computercontrolled stage. Assembly by dipping & interface method using computer-controlled stage could be carried out in two ways: (1) by first preparing the hexane/water interface with nanoparticles before the patterned PS template was dipped into the solution, or (2) by dipping the patterned PS template into the solution first, before the nanoparticles were added into the interface. It was found that the second method produce larger area of assembly compared to that of the first method. Varying amount of nanoparticles at the interface was achieved using micropipette in terms of μL volume of a stock solution of the nanoparticles. 76 Chapter 2.7.5 Assembly of CuxS nanoparticles onto ATRP modified polystyrene line pattern prepared by nanoimprint lithography In this attempt, we investigate the assembly of our prepared nanoparticles onto line patterns of PS prepared via nanoimprint lithography (NIL) and further modified by atomic transfer radical polymerization (ATRP) procedure. The line pattern templates were prepared by Li Guangshuo using the facilities at Institute of Materials Research and Engineering (IMRE). The NIL procedure was referred to works done by Low’s group6, using prime Si wafers with thickness of 0.5 mm and Poly(ethylene 2,6- naphthalate) sheets (Goodfellow) with thickness of 0.125 mm as substrates. Precursor include styrene as monomer, divinylbenzene as crosslinker, vinylbenzyl chloride as functional monomer and benzyl peroxide as thermal initiator in the molar ratio of 60 : 12 : 26 : 2. Final imprinting step was carried out on a 4-inch imprinter (Obducat Inc.) at a temperature of 110°C for a period of 10 minutes under a pressure of MPa. ATRP procedure was then carried out to further modify the width of the line patterns. In order to perform the assembly experiments, a piece of PS line pattern without further treatment was put inside a freshly-prepared dispersion of CuxS nanoparticles in toluene. The concentration of CuxS was varied from ~10-3 g/mL to 10-6 g/mL and optimum concentration was found to be 5×10-4 g/mL. The whole solution was left overnight without stirring or shaking. After the PS substrate was taken out and washed with toluene, excess liquid was removed through a flow of N2. 77 Chapter References 1. Lim, W. P.; Zhang, Z.; Low, H. Y.; Chin, W. S. Angewandte ChemieInternational Edition 2004, 43, (42), 5685-5689. 2. Lim, W. P.; Wong, C. T.; Ang, S. L.; Low, H. Y.; Chin, W. S. Chemistry of Materials 2006, 18, (26), 6170-6177. 3. Bhat, N. V.; Seshadri, D. T.; Phadke, R. S. Synthetic Metals 2002, 130, (2), 185-192. 4. Wang, Y. H.; Lin, J.; Huan, C. H. A.; Chen, G. S. Applied Physics Letters 2001, 79, (5), 680-682. 5. Lim, K. Y.; Sow, C. H.; Lin, J. Y.; Cheong, F. C.; Shen, Z. X.; Thong, J. T. L.; Chin, K. C.; Wee, A. T. S. Advanced Materials 2003, 15, (4), 300-303. 6. Zhao, W.; Low, H. Y.; Suresh, P. S. Langmuir 2006, 22, (12), 5520-5524. 7. Zhang, F. X.; Low, H. Y. Nanotechnology 2006, 17, (8), 1884-1890. 78 [...]... propylamine (µL) DDT (µL) 59.9 60 .2 59.9 60.1 60.5 60.3 60 .2 60.9 60 .2 60.1 20 20 20 20 20 20 20 20 20 20 0 7 12 30 50 125 25 0 500 750 1000 Reaction Time I (hours) 2 2 2 2 2 2 2 2 2 2 Reaction Time II (hours) 20 20 20 20 20 20 20 20 20 20 67 Chapter 2 Table 2. 4 Feed ratios and reaction conditions and of organo-clay/PbS nanocomposites prepared with different amount of DDT (Series II, using shorter Reaction... Time I (Series I) Sample ID [clay]/[PbTB]/[DDT] 23 24 25 26 27 1:5:40 1:5:40 1:5:40 1:5:40 1:5:40 organoclay (mg) 26 .8 27 .0 27 .1 27 .2 27.3 PbTB (mg) propylamine (µL) DDT (µL) 60.0 60.3 60.5 60.0 60.0 20 20 20 20 20 25 0 25 0 25 0 25 0 25 0 Reaction Time I (mins) 10 30 45 60 120 Reaction TimeII (hours) 2 2 2 2 2 Table 2. 6 Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with... 3:1:10 108 .2 16 8 80 2 2 2: 1:10 108.3 24 .7 8.5 120 2 3 1:1:10 107.9 48.4 8.5 24 0 2 4 1 :2: 20 54.1 48 .2 17.0 24 0 2 5 1:5:50 26 .9 60.4 34.0 300 2 6 0:1:10 0 40 .2 8.5 20 0 2 * Reaction Time I is the interval time between the addition of propylamine and DDT; # Reaction Time II is the reaction time after the addition of DDT Sample ID [clay]/[PbTB]/[DDT] Reaction Time II# (hours) 20 20 20 20 20 20 Table 2. 3 Feed... (nm) 5 12 50 6.1 2. 0 4.0 24 6 12 50 12. 1 2. 0 8.0 24 7 12 50 24 .1 2. 0 10.0 24 8 12 50 0 .24 * 2. 0 4.0 24 9 10 30 6.3 2. 0 4.0 24 10 10 30 3.0 2. 0 4.0 24 11 10 30 12. 0 2. 0 8.0 24 12 10 30 24 .1 2. 0 10.0 24 * A mother solution of PbTB/DMF was prepared by 24 .2 mg PbTB dissolved in 5 mL DMF and 20 µL of them was withdrawn then diluted to 2 mL Sample ID Another series of samples have been prepared in ethanol... ID [clay]/[PbTB]/[DDT] 17 18 19 20 21 22 1:5 :2 1:5:5 1:5:10 1:5:50 1:5:100 1:5 :25 0 organoclay (mg) 27 .0 27 .0 27 .3 27 .0 27 .3 27 .1 PbTB (mg) propylamine (µL) DDT (µL) 60.6 60.1 60.3 60.1 60.5 60.5 20 20 20 20 20 20 12 30 60 300 600 1500 Reaction Time I (hours) 0.5 0.5 0.5 0.5 0.5 0.5 Reaction Time II (hours) 20 20 20 20 20 20 Table 2. 5 Feed ratios and reaction conditions of organo-clay/PbS nanocomposites... 1:5:40 1:5:40 organoclay (mg) 27 .0 27 .2 27.0 27 .0 27 .4 27 .6 PbTB (mg) propylamine (µL) DDT (µL) 60 .2 60.3 60.8 60.1 60 .2 60.4 20 20 20 20 20 20 25 0 25 0 25 0 25 0 25 0 25 0 Reaction Time I (mins) 90 90 90 90 90 90 Reaction Time II 5mins 30mins 1hr 2hrs 10hrs 20 hrs Table 2. 9 Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different amount of propylamine Sample ID [clay]/[PbTB]/[DDT]... 2. 3 Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different amount of DDT (Series I, using longer Reaction Time I) Sample 7 is a control preparation without DDT Sample ID [clay]/[PbTB]/[DDT] 7 8 9 10 11 12 13 14 15 16 1:5:0 1:5:1 1:5 :2 1:5:5 1:5:8 1:5 :20 1:5:40 1:5:80 1:5: 120 1:5:160 organoclay (mg) 27 .5 27 .4 26 .9 27 .0 27 .2 27.5 27 .0 27 .0 27 .0 26 .8 PbTB (mg) propylamine... [clay]/[PbTB]/[DDT] 28 29 30 1:5:10 1:5:10 1:5:10 organoclay (mg) 27 .3 27 .3 27 .2 PbTB (mg) propylamine (µL) DDT (µL) 60.3 60.4 60.5 20 20 20 60 60 60 Reaction Time I (mins) 30 90 120 Reaction Time II (hours) 20 20 20 Table 2. 7 Feed ratios and reaction conditions of organo-clay/PbS nanocomposites prepared with different Reaction Time I (series III) Sample ID [clay]/[PbTB]/[DDT] 31 32 33 1:5:50 1:5:50... the formation of CNT A mixture of C2H2 and H2, with a flow rate at 15 sccm (standard cm3/minute) was then flown into the chamber at a pressure of 120 0 mtorr and an rf plasma of 100W The substrate was maintained at 450°C throughout the deposition, of which the duration was varied at 10 minutes, 30 minutes and 1 hour to control the length of the grown aCNT Next, 12 mg PbTB was added into 2 mL DMF in a... of samples were prepared according to the feed ratios of the various reagents listed in Table 2. 11 70 Chapter 2 Table 2. 11 The thickness and diameter of aCNT film and the various feed amounts of PbTB, DMF and propylamine used in the preparation of aCNT/PbS nanocomposites aCNT aCNT PbTB DMF propylamine Reaction time thickness diameter (mg) (mL) (L) (hours) (µm) (nm) 5 12 50 6.1 2. 0 4.0 24 6 12 50 12. 1 . 1:5:0 27 .5 59.9 20 0 2 20 8 1:5:1 27 .4 60 .2 20 7 2 20 9 1:5 :2 26.9 59.9 20 12 2 20 10 1:5:5 27 .0 60.1 20 30 2 20 11 1:5:8 27 .2 60.5 20 50 2 20 12 1:5 :20 27 .5 60.3 20 125 2 20 13 1:5:40 27 .0. (hours) 23 1:5:40 26 .8 60.0 20 25 0 10 2 24 1:5:40 27 .0 60.3 20 25 0 30 2 25 1:5:40 27 .1 60.5 20 25 0 45 2 26 1:5:40 27 .2 60.0 20 25 0 60 2 27 1:5:40 27 .3 60.0 20 25 0 120 2 Table 2. 6. Feed. 3:1:10 108 .2 16 8 80 2 20 2 2:1:10 108.3 24 .7 8.5 120 2 20 3 1:1:10 107.9 48.4 8.5 24 0 2 20 4 1 :2: 20 54.1 48 .2 17.0 24 0 2 20 5 1:5:50 26 .9 60.4 34.0 300 2 20 6 0:1:10 0 40 .2 8.5 20 0 2 20 * Reaction