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Sains Malaysiana 48(2)(2019): 435–442
http://dx.doi.org/10.17576/jsm-2019-4802-22
Aggregation and Stability of Iron Oxide and
Alumina Nanoparticles: Influences of pH and Humic Acid Concentration
(Pengagregatan dan Kestabilan Oksida Besi dan Zarah
Nano Alumina: Pengaruh pH dan Kepekatan Asid Humik)
NUR SURAYA AHMAD1*, SHAHIDAN RADIMAN1 & WAN ZUHAIRI WAN YAACOB2
1School of Applied Physics, Faculty of
Science and Technology, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia
2School of Environmental and Natural
Sources Sciences, Faculty of Science and Technology, 43600 UKM Bangi, Selangor
Darul Ehsan, Malaysia
Received: 2
May 2018/Accepted: 19 October 2018
ABSTRACT
The scenario of released
nanoparticles from consumer products into the environment especially natural
waters has become a great concern nowadays. Assessing their aggregation and
stability under environmental conditions is important in determining their fate
and behavior in natural waters. The aggregation behavior of selected
nanoparticles (iron oxide and alumina) was investigated at variable
concentrations of humic acid (5, 10, 50 mg/L), and pH variation in solution.
Dynamic light scattering was used to measure their z-average hydrodynamic
diameter and zeta potential. Derjaguin-Landau-Verwey-Overbeak (DLVO)
theory was used to explain the thermodynamic interactions between two
particles. Then, the stability was evaluated by assessing their aggregation.
The increasing of humic acid concentrations enhanced aggregation of iron oxide
and alumina nanoparticles, particularly at low pH levels. The maximum
aggregation was found in pH below the point of zero charge (PZC)
due to electrostatic destabilization and electrostatic stabilization that took
place at pH above the point of zero charge. Meanwhile, at pH point of zero
charge, nanoparticles were coated with negative humic acid charged. From this
study, properties of nanoparticles (size, surface charge, Hamaker constant) and
environmental condition (humic acid concentration, pH) have their specific
roles to control the fate and behavior of nanoparticles in environmental media.
Keywords: Aggregation; DLVO;
nanoparticles; stability
ABSTRAK
Pada masa ini, peningkatan senario
pelepasan zarah nano daripada produk pengguna ke persekitaran terutamanya ke
dalam air semula jadi amatlah membimbangkan. Penilaian agregasi dan kestabilan
zarah nano adalah penting untuk menentukan keadaan dan tingkah lakunya di dalam
kandungan air semula jadi. Kajian mengenai tingkah laku agregasi zarah nano
(oksida besi dan alumina) pada pelbagai kepekatan asid humik (5,10,50 mg/L) dan
pH yang berlainan dijalankan. Penyerakan cahaya dinamik digunakan untuk
mengukur purata diameter hidrodinamik dan nilai keupayaan zeta. Teori
Derjaguin-Landau-Verwey-Overbeak (DLVO) digunakan untuk
menerangkan tindak balas termodinamik antara dua zarah. Kemudian, kestabilan
dinilai berdasarkan tingkah laku agregasi. Peningkatan kepekatan asid humik
telah menggalakkan/meningkatkan tingkah laku agregasi zarah nano oksida besi
dan alumina pada pH yang rendah. Agregasi maksimum dijumpai pada pH di bawah
caj titik sifar yang disebabkan oleh ketidakstabilan elektrostatik dan
kestabilan elektrostatik dilihat berlaku pada pH di atas pH caj titik sifar.
Manakala, pada caj titik sifar, zarah nano disaluti dengan caj asid humik yang
bersifat negatif. Keputusan daripada kajian ini mendapati sifat zarah nano
(saiz, caj permukaan, pemalar Hamaker) dan keadaan persekitaran (kepekatan asid
humik dan pH) memainkan peranan yang penting dalam mengawal keadaan dan tingkah
laku zarah nano pada medium sekitaran.
Kata
kunci: Agregasi; DLVO; kestabilan;
zarah nano
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*Corresponding author; email:
nursuraya_ahmad@siswa.ukm.edu.my
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