Sains Malaysiana 47(11)(2018): 2841–2849

http://dx.doi.org/10.17576/jsm-2018-4711-27

 

Kajian terhadap Sifat Optik Titik Kuantum Kadmium Sulfida pada Pelbagai Nilai pH dan Modifikasi Permukaan dengan Asid Tioglikolik

(Study on Optical Properties of Cadmium Sulphide Quantum Dots in Various pH Values and Surface Modification by Thioglycolic Acid)

 

SITI AISYAH SHAMSUDIN^* & JENNIVER JUNAS

 

School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

 

Received: 30 April 2018/Accepted: 2 August 2018

 

ABSTRAK

Pengimejan tradisi mempunyai banyak kekurangan seperti mempunyai jangka hayat yang pendek serta bersaiz besar kerana sifat pendafluornya tidak tahan lama atau berlakunya pelunturanfoto. Melalui kajian ini, nanohablur kadmium sulfida dihasilkan dan berfungsi sebagai pengimejan titik kuantum yang sesuai dengan sifat optiknya yang pelbagai mengikut saiz zarahnya. Sifat optik titik kuantum kadmium sulfida (TK CdS) boleh dipengaruhi oleh saiz dan juga komposisi kimia TK seperti perubahan pH. Dalam kajian ini, sifat optik TK CdS dikaji terhadap perubahan nilai pH dengan menghasilkan TK CdS melalui kaedah koloidal. Kadmium asetat dihidrat (C4H6CdO4.2H2O) dan natrium sulfida (Na2S) digunakan sebagai sebagai bahan pemula bagi menghasilkan TK CdS. Nilai pH diubah suai dengan menitiskan natrium hidroksida (NaOH) ke dalam larutan TK CdS. Lima jenis larutan disediakan iaitu pada nilai pH5, pH7, pH8, pH9 dan pH10. Masalah penggumpalan sering berlaku semasa proses sintesis CdS. Oleh itu, kajian ini menggunakan asid tioglikolik (HSCH2CO2H) sebagai agen penstabil kepada TK CdS. Spektra keserapan UV memberi anjakan biru apabila TK CdS pada pH alkali kerana saiz nanohablur mengecil. Hasil daripada spektroskopi pendarfluor mendapati larutan yang mempunyai nilai pH8 memberi puncak yang tertinggi. Hal ini adalah kerana pada pH ini nanohablur mampu berubah pada posisi yang tepat dan membentuk TK CdS pada kehabluran yang tinggi. Oleh itu, mekanisme ini dapat membentuk perangkap lubang dan seterusnya eksiton terbentuk.

 

Kata kunci: Asid tioglikolik; nilai pH; sifat optik; titik kuantum kadmium sulfide

 

ABSTRACT

Traditional imaging has many drawbacks such as a short lifetime and larger particles’ sizes as the result the fluorescence property does not long lasting due to the photo-bleaching phenomenon. Via this study, nanocrystal cadmium sulphide has been synthesized and functioned as a quantum dot imaging corresponding to optical properties that vary with particle size. Optical properties of the quantum dots of cadmium sulphide (CdS QDs) can be changed by particles’ size and also of the chemical composition while synthesis such as pH values. In this study, the optical properties of CdS QDs were studied against the change in the pH values by preparing CdS QDs via the colloidal method. Cadmium acetate dehydrated (C4H6CdO4.2H2O) and sodium sulphide (Na2S) are used as the precursors for producing CdS QDs. The pH values are modified by titrating sodium hydroxide (NaOH) into CdS QDs’ aqueous solution. Five pH values of aqueous solutions at pH5, pH7, pH8, pH9 and pH10 were prepared however, agglomeration often occurs during the synthesising process. Therefore, thioglycolic acid (HSCH2CO2H) was used as a stabilizer agent for CdS QDs. UV-vis Spectra have shown blue-shifted when CdS QDs on the alkaline medium due to the nanocrystals’ sizes are decreased. The result from fluorescence spectroscopy has given the CdS QDs in pH8 gives the highest peak compared to others pH values. This happened because at this pH value, the nanocrystalline is able to change to the right position and formed the CdS QDs with high crystallization. Thus, this mechanisms of the occurrence of the trap hole obtained and caused the exciton.

 

Keywords: CdS quantum dot; optical properties; pH value; thioglycolic acid

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*Corresponding author; email: aisyah@ukm.edu.my