Siti Hajar Othman

Dispersion and stabilization of photocatalytic TiO 2 nanoparticles in aqueous suspension for coatings applications

To produce titanium dioxide (TiO2) nanoparticle coatings, it is desirable that the nanoparticles are dispersed into a liquid solution and remain stable for a certain period of time. Controlling the dispersion and aggregation of the nanoparticles is crucial to exploit the advantages of the nanometer-sized TiO2 particles. In this work, TiO2 nanoparticles were dispersed and stabilized in aqueous suspensions using two common dispersants which were polyacrylic acid (PAA) and ammonium polymethacrylate (Darvan C). The effect of parameters such as ultrasonication amplitude and type and amount of dispersants on the dispersibility and stability of the TiO2 aqueous suspensions were examined. Rupture followed by erosion was determined to be the main break up mechanisms when ultrasonication was employed. The addition of dispersant was found to producemore dispersed andmore stabilized aqueous suspension. 3wt.% of PAA with average molecular weight (Mw) of 2000 g/mol (PAA 2000) was determined to produce the best and most stable dispersion. The suspensions were then coated on quartz glass, whereby the photocatalytic activity of the coatings was studied via the degradation of formaldehyde gas under UV light. The coatings were demonstrated to be photocatalytically active.

Antimicrobial activity of TiO2 nanoparticle-coated film for potential food packaging applications

Recent uses of titanium dioxide (TiO2) have involved various applications which include the food industry. This study aims to develop TiO2 nanoparticle-coated film for potential food packaging applications due to the photocatalytic antimicrobial property of TiO2. The TiO2 nanoparticles with varying concentrations (0–0.11 g/ 100 mL organic solvent) were coated on food packaging film, particularly low density polyethylene (LDPE) film. The antimicrobial activity of the films was investigated by their capability to inactivate Escherichia coli (E. coli) in an actual food packaging application test under various conditions, including types of light (fluorescent and ultraviolet (UV)) and the length of time the film was exposed to light (one–three days). The antimicrobial activity of the TiO2 nanoparticle-coated films exposed under both types of lighting was found to increase with an increase in the TiO2 nanoparticle concentration and the light exposure time. It was also found that the antimicrobial activity of the films exposed under UV light was higher than that under fluorescent light. The developed film has the potential to be used as a food packaging film that can extend the shelf life, maintain the quality, and assure the safety of food.

Fe-Doped TiO 2 nanoparticles produced via MOCVD: synthesis, characterization, and photocatalytic activity

Iron (Fe)-doped titanium dioxide (TiO2) nanoparticles were produced via the metallorganic chemical vapour deposition (MOCVD) method at 700°C. Different amounts of ferrocene as the Fe dopant source (0.001-0.05g) were introduced inside the reactor together with the titanium precursor in order to synthesize different Fe dopant concentrations of TiO2 nanoparticles. Nitrogen (N2) adsorption results showed that increasing the Fe dopant concentration caused a slight increase in the surface area of the nanoparticles due to the decrease in nanoparticle size. The UV-diffuse reflectance spectra demonstrated an absorption shift in Fe-doped TiO2 nanoparticles to longer wavelengths, thus showing an enhancement of the absorption in the visible spectrum. Bandgap energy values determined from the UV-diffuse reflectance spectra data decreased with an increase in the Fe dopant concentrations. The photocatalytic activity of Fe-doped TiO2 nanoparticles was investigated via degradation of methylene blue under UV and fluorescent light. It was found that Fe doping reduced the photocatalytic activity of the samples. Based on X-ray photoelectron spectroscopy (XPS) results, it is believed that this is due to the unfavourable location of Fe3+ inside the interior matrix of the TiO2 nanoparticles rather than on the exterior surface, which would affect photocatalytic behaviour.

Effect of postdeposition heat treatment on the crystallinity, size, and photocatalytic activity of TiO 2 nanoparticles produced via chemical vapour deposition

Titanium dioxide (TiO2) nanoparticles were produced using chemical vapour deposition (CVD) at different deposition temperatures (300-700°C). All the samples were heat treated at their respective deposition temperatures and at a fixed temperature of 400°C. A scanning electron microscope (SEM), a transmission electron microscope (TEM), and X-ray diffraction (XRD) were used to characterize the nanoparticles in terms of size and crystallinity. The photocatalytic activity was investigated via degradation of methylene blue under UV light. The effects of post deposition heat treatment are discussed in terms of crystallinity, nanoparticle size as well as photocatalytic activity. Crystallinity was found to have a much larger impact on photocatalytic activity compared to nanoparticle size. Samples having a higher degree of crystallinity were more photocatalytically active despite being relatively larger in size. Surprisingly, the photocatalytic activity of the samples reduced when heat treated at temperatures lower than the deposition temperature despite showing an improvement in crystallinity.

3D CFD simulations of MOCVD synthesis system of titanium dioxide nanoparticles

This paper presents the 3-dimensional (3D) computational fluid dynamics (CFD) simulation study of metal organic chemical vapor deposition (MOCVD) producing photocatalytic titanium dioxide (TiO2) nanoparticles. It aims to provide better understanding of the MOCVD synthesis systeme specially of deposition process of TiO2 nanoparticles as well as fluid dynamics inside the reactor. The simulated model predicts temperature, velocity, gas streamline, mass fraction of reactants and products, kinetic rate of reaction, and surface deposition rate profiles. It was found that temperature distribution, flow pattern, and thermophoretic force considerably affected the deposition behavior of TiO2 nanoparticles. Good mixing of nitrogen (N2) carrier gas and oxygen (O2) feed gas is important to ensure uniformdeposition and the quality of the nanoparticles produced. Simulation results are verified by experiment where possible due to limited available experimental data. Good agreement between experimental and simulation results supports the reliability of simulation work.

Effect of halloysite nanoclay concentration and addition of glycerol on mechanical properties of bionanocomposite films

Conventional plastic made from petrochemical based polymer which is non-degradable is not environmentally friendly. Thus, there is a need to develop bionanocomposite films to replace the non-degradable plastic. Bionanocomposite films were produced by the casting method using polylactic acid (PLA) biopolymer with the incorporation of nanoclay, particularly halloysite. The effect of the halloysite nanoclay concentration (0, 2, 4, 6 and 8 wt.%) as well as the addition of a plasticiser, particularly glycerol, on the mechanical properties (tensile stress, elongation at break and tensile strength) of bionanocomposite films was investigated. It was found that without the addition of glycerol, 2 wt.% concentration of halloysite nanoclay film resulted in the maximum tensile strength and elongation at break due to the interaction of the PLA and the nanoclay which is known for interfacial adhesion. The interaction was confirmed by FTIR spectrum. When more than 2 wt.% of nanoclay clay was added, both the tensile strength and the elongation at break reduced due to the agglomeration of the nanoclay. However, when glycerol was added, the film without the addition of halloysite nanoclay exhibited the maximum tensile strength and the film with 8 wt.% halloysite nanoclay exhibited the maximum elongation at break. The addition of glycerol lowered the mechanical properties of the films because the intercalation of the glycerol into the clays prevented the entry of PLA into the interlamellar of the nanoclay.

Detection of Lard in Ink Extracted from Printed Food Packaging Using Fourier Transform Infrared Spectroscopy and Multivariate Analysis

Fourier transform infrared (FTIR) spectroscopy combined with chemometrics was utilised to discriminate the presence of lard in extracted ink of printed food packaging. Two spectral regions (full spectra, 3999–649 cm−1, and combination of two regions, 3110–2630 cm−1 and 1940–649 cm−1) of lard, commercial gravure ink, and the blends of both were selected and used to develop a Soft Independent Modelling of Class Analogy (SIMCA) model. The score plots obtained from the Principal Component Analysis (PCA) revealed that the maximum number of factors (7 factors) was needed to explain 84% of the total variance. SIMCA was employed as the method to classify the samples into their specific groups. Si versus Hi plots showed that the calibration standards can be classified as lard-containing standards. Sample 2 was deduced to have the highest possibility of containing lard, while only samples 5 and 7 cannot be classified as lard-containing samples. These results demonstrated that FTIR spectroscopy, when combined with multivariate analysis, can provide a rapid method with no excessive sample preparation to detect the presence of lard in ink of foodstuff packaging.

Mechanical and thermal properties of PLA/halloysite bio-nanocomposite films: effect of halloysite nanoclay concentration and addition of glycerol

Abstract The usage of biopolymers in developing biodegradable materials for applications that meet demands in society for sustainability and environmental safety has been limited due to the poor mechanical and thermal properties of biopolymers. This study aimed to improve the limited properties of biopolymers, particularly polylactic acid (PLA) films, by investigating the effect of incorporating different concentrations (0–5 wt.%) of halloysite nanoclay and by adding glycerol plasticiser on the mechanical properties (tensile strength, elongation at break, Young’s modulus, and toughness) and thermal properties (glass temperature (Tg), melting temperature (Tm), and crystalline temperature (Tc)) of the produced bio-nanocomposite films. It was found that the addition of halloysite nanoclay and glycerol improved the mechanical and thermal properties of the films. PLA films incorporated with 3 wt.% concentration of halloysite nanoclay resulted in optimum mechanical properties due to the uniform distribution or dispersion of halloysite nanoclay. The addition of halloysite nanoclay and glycerol reduced the Tg, Tm, and Tc of the films, suggesting that they can improve the processability of the biopolymer. The bio-nanocomposite films produced in this work have the potential to replace non-biodegradable films due to the improved properties of the films.