Journal Information
Journal ID (publisher-id): chemical
Title: Journal of the Korean Chemical Society
Translated Title (ko): 대한화학회지
ISSN (print): 1017-2548
ISSN (electronic): 2234-8530
Publisher: Korean Chemical Society대한화학회
Since titanium dioxide (TiO2) was first used in photocatalytic reactions for degrading contaminants in water and air by Fujishima and Honda,1 TiO2 has been extensively studied as a photocatalyst for environmental application.2−7 However, the general use of TiO2 as a photocatalyst has been limited because TiO2 requires ultraviolet (UV) irradiation under the wavelength of 380 nm for its activation due to the wide band gap of 3.2 eV.8 To overcome this limitation, much effort has been devoted to the development of visible-light-induced photocatalysts by doping TiO2 with transition metals such as Cr, Zn, Cu, Mn and Fe.9−14 It has been recently found that visible-light-induced photocatalysts brought out efficient decomposition of organic compounds, and could be anti-bacterial and viral agents.15−18
Hollow sphere nanoparticles have been known as potentially excellent materials for contaminated pollutants removal.19,20 TiO2 hollow nanospheres with chromium ion were shown to improve the photocatalytic activity and photodecompose methylene blue (MB) under visible light irradiation.20 Thus, because photocatalysts of TiO2 hollow nanospheres with Cr3+ are activated by visible-light rather than UV and have more spacious superficies than any flat layer array, they can be used effectively for the decomposition of volatile organic compounds (VOCs) in air. In this work, TiO2 hemisphere nanostructures with Cr3+ were synthesized with polystyrenemethyl acrylic acid (PSA) latex particles as templates and characterized by FESEM (field emission scanning electron microscope). And the reduction extent of VOCs (toluene and trimethylamine) and ammonia by ABS (acrylonitrile butadiene styrene) copolymer coated with the prepared TiO2 hemispheres under fluorescent light irradiation was evaluated.
TiO2 hemisphere nanostructures were obtained by using PSA latex particles as templates. Fig. 1 shows the SEM image of TiO2 hemispheres with 0.5% Cr3+, which were formed by rupture according to abrupt temperature change from RT to 600 °C during calcination. The diameter (~300 nm) of the PSA polymer was smaller than that of the prepared hemispheres. This result revealed that TiO2 spheres were successfully coated on PSA particles and PSA was removed by calcination in air at 600 °C.
Hydroxyl radicals generated from the photocatalytic reactions were considered to be very potent oxidants and non-selective in reactivity for the oxidation of organic substances (Fig. 2).21 The reduction effect of VOCs and ammonia by ABS copolymer coated with 0.5% Cr/Ti hemispheres was assayed with Gastec detector tube method. The extent of photodecomposition of VOCs and ammonia under fluorescent light was shown in Table 1 and Fig. 3.
Table1.
Crystal data and structure refinement for 1
Sample 1 : an ABS coated with only TiO2 hemispheres without any pretreatment
Sample 2 : an ABS coated with TiO2 hemispheres after pretreatment
Figure3.
Difference in the deodorization rates of toluene, trimethylamine and ammonia by TiO2 hemispheres with and without strong acid pretreatment. The values are the averages of three separated experiments.
The concentration of toluene was decreased to 22 ppm by addition of a TiO2 hemisphere-coated ABS copolymer, whose deodorization rate was 45% (denoted as sample 1). A deodorization rate of 62.5% was achieved for toluene by addition of a pretreated and hemisphere-coated ABS, in which an ABS was first pretreated with a corrosive strong acid and dipped in TiO2 hemisphere solution (denoted as sample 2). This value was 17.5% higher than the deodorization rate of 45% of toluene obtained by the use of a hemisphere-coated ABS. The first treatment of an ABS with a strong acid before dipping in a photocatalytic solution improved both the coating efficiency of TiO2 and the deodorization rate of toluene. Corrosive acid pretreatment is thought to activate surface energy state leading to strong binding between TiO2 nanoparticle and ABS surface, and more nanoparticles are coated on ABS surface so that more photocatalytic active sites are made. The photo-catalytic degradation rate of toluene over Ce-TiO2 thin film was 61.9% with illumination using a 254 nm light source for 8 h of irradiation time.22 So our Cr-TiO2 hemisphere is thought to be practically more excellent in eliminating toluene in air because it does not need UV irradiation for its activation.
The concentration of trimethylamine (TMA) was decreased to 10 ppm by addition of a TiO2 hemisphere-coated ABS copolymer, whose deodorization rate was 50%. A deodorization rate of 60% was achieved for TMA by addition of a pretreated and hemisphere-coated ABS. This value was 10% higher than the deodorization rate of 50% of TMA obtained by the use of a hemisphere-coated ABS. Like toluene, the first treatment of an ABS with a strong acid before dipping in a photocatalytic solution improved both the coating efficiency of TiO2 and the deodorization rate of TMA.
The concentration of ammonia was decreased to 19 ppm by addition of a TiO2 hemisphere-coated ABS copolymer, whose deodorization rate of 52.5%. On the other hand, the addition of a pretreated and hemisphere-coated ABS resulted in a deodorization rate of 60% of ammonia. This value was 7.5% higher than deodorization rate of 52.5% of ammonia by a hemisphere-coated ABS. Similar to toluene and TMA, the first treatment of an ABS copolymer with a strong acid increased both the coating efficiency of TiO2 and the deodorization rate of ammonia. This more deodorization rate was observed after the pretreatment of an ABC with a corrosive strong acid, followed by coating of the copolymer with the photocatalytic solution. These results suggest that TiO2 hemispheres can be used for effective decomposition of VOCs under fluorescent light inside buildings so that indoor air quality could be improved.
In conclusions, TiO2 hemisphere nanostructures were obtained by using polystyrene-methyl acrylic acid particles as templates and by rupture according to abrupt temperature change during calcination. The reduction of VOCs and ammonia by an ABS copolymer coated with 0.5% Cr/Ti hemispheres was assayed with Gastec detector tube method. Deodorization rate showed 45% for toluene, 50% for TMA and 52.5% for ammonia. An ABS copolymer which was first pretreated with corrosive strong acid and then dipped in the photocatalytic TiO2 solution showed the more deodorization rate of 62.5% for toluene, 60% for TMA and 60% for ammonia than without strong acid pretreatment.
EXPERIMENTAL▼
Preparation of TiO2 Hemisphere Nanostructures with Cr3+
TiO2 hemisphere nanostructures with Cr3+ were prepared as follow: 180 uL of Ti(SO4)2 was added to 32 mL of distilled water and stirred vigorously. 0.07 g of polystyrene (~300 nm) particles, 1.98 mL of CTACl (cetyltrimethylammonium chloride), 800 uL of HCl and 0.36 mg of Cr2(SO4)3×H2O were added under the stirring condition. The mixture was agitated for 20 min and left at 70 °C with stirring overnight, then cooled and centrifuged for 10 min. The supernatant were discarded. And the precipitates were harvested and washed with distilled water and ethanol (1:1, v/v). The resulting solids were collected by centrifugation and dried at 60 °C overnight. The obtained sample was then put into oven and kept at 600 °C for 5 h. 1 g of the baked sample was added to 10 ml of ethanol and the mixture was sonicated for 30 min, followed by the addition of 300 uL of ammonia solution and 500 uL of distilled water. The mixture was then stirred at 300 rpm overnight, collected by centrifugation and dried at 60 °C overnight. 3 mL of methanol was added to 1 g of the resulting, dried sample and the mixture was stirred for 6 hr. Additive agent /leveling agent (0.3 part of the dried sample) was added to the mixture and agitated. ABS copolymer was coated by dipping in the above solution and dried in air.
SEM image was obtained using a field emission scanning electron microscope (ULTRA PLUS, Zeiss).
VOCs Assay
The effect of VOC reduction of the Ti/Cr hemisphere-coated ABS copolymer was tested with Gastec detector tube method. Ti/Cr hemisphere-coated resin and no coated resin were put in each 3L Tedlar bag, respectively and exposed to each VOC (toluene and trimethylamine) and ammonia. After 2 h at (18±2)°C, the extent of VOC reduction was measured with each gas-detecting tube.