Sitthisuntorn Supothina

Efficacy of photocatalytic HEPA filter on microorganism removal

UNLABELLED This study assessed the application of photocatalytic oxidation (PCO) to the high efficiency particulate air (HEPA) filter for disinfection of airborne microorganisms. Experiments were conducted at two TiO2 loadings (1870 +/- 169 and 3140 +/- 67 mg/m(2)) on the HEPA filter irradiated with UV-A at the intensity of 0.85 +/- 0.18 or 4.85 +/- 0.09 mW/cm(2) under two relative humidity conditions (45 +/- 5% and 75 +/- 5%). Inactivation and penetration of four microorganisms were tested, including Aspergillus niger, Penicillium citrinum, Staphylococcus epidermidis, and Bacillus subtilis. It was found that microorganisms retained on a photocatalytic filter were inactivated around 60-80% and even 100% for S. epidermidis when the PCO reactions occurred. Lower penetration was also found from the photocatalytic filter for all airborne microorganisms. High humidity decreased photocatalysis efficacy. Increasing TiO2 loading or irradiance intensity did not substantially affect its disinfection capability. PRACTICAL IMPLICATIONS The high efficiency particulate air filter is used widely to remove particulates and microorganisms from the air stream. However, the filter may become a source of microbes if those retained microorganisms proliferate and re-entrain back into the filtered air. This study demonstrates that such a problem can be handled effectively by using photocatalytic reactions to inactivate those confined microorganisms. A 60-100% microbe reduction can be achieved for a wide variety of microorganisms to provide better indoor air quality for hospitals, offices, and domestic applications.

Performance of photocatalytic lamps on reduction of culturable airborne microorganism concentration.

Reduction of viable airborne Staphylococcus epidermidis and Aspergillus niger spore concentrations using two types of photocatalytic fluorescent lamps under controlled environmental conditions (25 vs. 35°C and 55 vs. 75% relative humidity) were investigated. Visible white-light and UVA black light were in-house spray-coated with TiO(2) and then compared with a commercially coated visible white-light for microbial concentration reduction. The white-light photocatalytic lamps reduced the concentration of culturable S. epidermidis up to 92% independent of temperature or humidity change, while the black light photocatalytic lamps completely inactivated the culturable bacteria at 25°C, 55% relative humidity. Humidity seemed to alleviate UVA damage since better bacteria survival was found. For A. niger spores, rising humidity or temperature could lower their concentration or drop their culturabilities so that a difference between the natural decay and photocatalytic disinfection could not be distinguished. Reductions of total bacteria and total fungi concentrations using these lamps were also examined under uncontrolled environmental conditions in an office and a waste-storage room. It was found that photocatalytic lamps could reduce total culturable bacteria concentration from 9 to 97% and total culturable fungi concentration from 3 to 95% within irradiation time of 30-480 min, respectively. Insignificant difference in concentration reduction among these photocatalytic lamps was pronounced.

Effect of binders on airborne microorganism inactivation using TiO2 photocatalytic fluorescent lamps

5% Degussa P25 TiO2 was spray-coated onto black-light and white-light fluorescent lamps, using five different binders, namely DURAMAX B-1000, DURAMAX D-3005, silane-69, and two polyethylene glycols with molecular weight 1000 (PEG-1000) and 700 (PEG-700). The coated lamps were tested with Staphylococcus epidermidis, Escherichia coli, spores of Bacillus subtilis and spores of Aspergillus niger. It was found that 0.5% B-1000 and 1% PEG-1000 gave the highest inactivation rates: 93-96% from coated black-light lamps and 85-88% from coated white-light lamps for bacteria. In the case of spores, 70-72% and 55-57% inactivation rates were recorded from coated black-light and coated white-light lamps, respectively. The effects of UVA irradiance and face velocity were also examined. Significant improvement was observed from coated white-light lamps when the UVA irradiance increased. High face velocity adversely affected microorganism inactivation.

Effect of Firing Temperature and Mo Doping on the Synthesis of Solar-Reflective Sm2Ce2O7 Yellow Pigment

Solar-reflective yellow pigment was synthesized by a solid-state reaction of the Sm2O3 and CeO2 in the presence of the (NH4)6Mo7O24 employed for the Mo doping. The raw materials were wet milled in acetone for 6 h to acheive a homogeneous slurry followed by calcination at 1100, 1300 and 1500 °C for 6 h. The effect of the Mo doping was investigated by adding 10, 15, 20, 25 and 30 wt.% (NH4)6Mo7O24. XRD analysis of the undoped product revealed the formation of Sm2Ce2O7 at 1300 °C along with the unreacted Sm2O3 and CeO2, and revealed the completed reaction at 1500 °C. The addition of (NH4)6Mo7O24 resulted in the formation of Sm2Ce2-xMoxO7+δ, where x = 0.02, 0.03, 0.04 and 0.05 depending on the amount of the Mo dopant employed. The doping also significantly affected the product’s color; it turned from ivory white to yellow with the increase of dopant content up to 20 wt.% and became dark green afterward. Increasing firing temperature from 1100 to 1500 °C led to brighter yellow due to the substitution of Mo6+ for Ce4+. At the optimum synthesis condition, i.e. 20 wt.% doping and 1500 °C firing temperature, the product was most yellowish and had 69.2 % near-infrared reflectance.

Effect of different oxide fillers on superhydrophobicity of water-repellent organic-inorganic hybrid films

Water-repellent polydimethylsiloxane-based film containing SiO2 or TiO2 filler was deposited onto glass substrate by dip coating method. Different surface roughness and chemistry was created by incorporating various types of filler having different particle size, composition and surface functionality, i.e., Aerosil® SiO2 (~15 nm, hydrophilic), Aeroperl® SiO2 (~30 μ, either hydrophilic or hydrophobic) and P25 TiO2 (~30 nm, hydrophilic). Effect of filler characteristics on the films water-repellency was extensively discussed based on its dispersing ability and effective particle size in the PDMS solution, as well as on its photocatalytic effect (in case of the TiO2).

Nanocrystalline TiO2 Coated-Fabric for UV Shielding and Anti-Bacterial Functions

Due to excellent photocatalytic and optical properties of titanium dioxide (TiO2), it has been applied in several products such as food packaging plastics, materials for vehicles or for buildings and sunscreen-protecting cosmetics. In this present work, the synthesized as well as commercial TiO2 was coated onto a household curtain fabric for anti-microbial and ultraviolet (UV) shielding functions. The coating was performed by inducing the deposition of TiO2 layer from the Ti precursor onto the fabric surface pre-treated with silane adhesive agent so as to improve the adhesion. Ag nanoparticles were also incorporated in some samples to further improve the antibacterial function. Anti-bacterial activities of the coated fabric were evaluated by standard qualitative test (the Kirby-Bauer test (AATCC 147)). Efficiency for UV shielding was evaluated by measuring a UV-Vis reflection of the coated fabrics both before and after subjecting to several washing cycles. The result showed that the TiO2-coated fabrics developed had potential as antibacterial and UV shielding for the curtain industry.

Assessment of Hydrophilic Biochar Effect on Sandy Soil Water Retention

This paper reports studies to investigate the relationships between hydrophobicity of biochar surface and soil water retention. The studied biochars were produced from acacia wood, cashew wood and bamboo. The resulting materials were oxidized via liquid oxidation to generate hydrophilic biochars containing oxygenated functional groups on the surface. All biochars were characterized and their ability as soil additives to enhance water retention was assessed. Our results suggest that hydrophobicity/hydrophilicity of biochars is not the major factor governing water retention ability of this particular soil. However, hydrophilicity of biochar helps improve soil permeability by providing better wettability to the soil.

Top Layer Coating for Improving Superhydrophobic Property of Latex Cup

A latex cup is used to collect latex from a rubber tree which is an economic plant in Thailand. The fresh latex or crude rubber consists of organic compound and water which can wet and adhere to surface of the collecting cup. In this research, surface of the latex cup was treated with polymethylhydrogen siloxane-functionalized silica compound to improve hydrophobicity so that it could repel the dirt and latex, resulting in an anti-adhesion between the latex and the cup. Surface of the latex cup was etched with 10 % v/v hydrofluoric acid for 30 min before application of the siloxane coating which was performed by immersion in the solution, painting and spraying, respectively. The result revealed that the immersion method exhibited optimum property justified by high value of water contact angle, low surface free energy, surface roughness and the field test. At the optimum polymethylhydrogen siloxane : fumed silica ratio of 3 : 1 wt%, the treated sample had water contact angle of 139.24 ± 0.78 degrees and possessed surface energy of 1.07 mJ/m2. The field test conducted in the rubber field in Trang province revealed good durability of the coating. The water contact angles were 132.15 ± 2.05 and 129.20 ± 2.34 degrees after 2 weeks and 1 month, respectively, of the field service.

Influences of Inhibitor and Firing Temperature on Efflorescence Reduction of Clay Products

For ceramic industry, efflorescence is undesirable and cannot be completely eliminated from the finished products. The efflorescence is caused by soluble salts in the raw material and mostly appears as white deposit at the product’s surface. In this research, the removal of sulfate in the raw materials was studied. In addition, the sulfate ions were immobilized by forming a water-insoluble compound. The sulfate ions in the raw materials and fired products were extracted by distilled water, and the concentration was determined by using a UV-visible spectroscopy following the ASTM C1580-09 standard. Three sources of the raw materials from Tambon Suan Phung, Ratchaburi, Tambon Mae Win and Mae Ta, Chiang Mai, were analyzed for sulfate concentrations. The clay from Tambon Suan Phung, Ratchaburi which had the highest sulfate concentration was selected for further study on the effect of inhibitor and firing temperature on efflorescence inhibition. To reduce solubility of the sulfate, three kinds of inhibitor, i.e. barium chloride, barium carbonate and barium hydroxide, were added into the raw material at various concentrations, i.e. 0.5, 1.0, 1.5 and 2.0 wt% and homogeneously mixed by ball milling followed by the addition of distilled water to prepare the clay slip. The clay products were mold casted to 1 x 1 x 3 inch3 in size. Then, they were fired at 800, 900 and 1000 °C. It has been revealed that the addition of barium carbonate at 2 wt%, which is the highest amount employed in this study, and firing temperature of 900 °C resulted in least sulfate leaching due to the formation of water-insoluble barium sulfate. To perform a field test, the fired samples with and without the addition of barium carbonate were immersed in water for 4 months. The efflorescence was observed on the sample without barium carbonate within the 1st month. In contrast, with the addition of barium carbonate, no efflorescence was observed after testing for 4 months.

Synthesis, Characterization and Solar-Reflective Properties of Cr2O3-Based Green Pigment

Solar-reflective green pigment was synthesized from the starting powder consisting of chromium oxide (Cr2O3), aluminum oxide (Al2O3), titanium dioxide (TiO2), and vanadium oxide (V2O5) by high-speed, wet milling at the speed of 300 rpm for 2 h followed by calcination at 1150 or 1200 °C for 0.5-5 h. X-ray diffraction analysis revealed the presence of reduced chromium oxide, Cr2O2.4, which is the major component, and rutile TiO2 phase of which its XRD peak intensities were intensified upon calcination as a result of phase transformation from amorphous portion in the starting TiO2. Microstructural analysis revealed significant particle growth after calcination at 1200 °C for 5 h due to Ostwald ripening. Highest near-infrared reflectance of 70.1% was obtained from the product calcined at 1150 °C for 0.5 h. Higher calcination temperature and/or extended period of calcination time led to a reduced reflection which is ascribed to an increased of particle size of the synthesized pigment.