In this study, three-dimensional bismutite Bi 2O 2CO 3 nanoparticels (BSC NPs) have been synthesized through a facile hydrothermal treatment under mild conditions. The reaction temperatures and NaOH concentration have a vital influence on the physical and photocatalytic properties of the obtained BSC NPs. The crystal structure, morphology, chemical composition, specific surface area and photoresponse of as-obtained catalysts were characterized by X-ray diffraction, Scanning electron microsprctrosopy, Energy-dispersive spectroscopy, N 2 adsorption/desorption isotherms and UV-Vis spectra, respectively. Furthermore, Rhodamine 6G was used as model reaction to evaluate the photocatalytic activity of BSC NPs. As a result, there was no obvious effect of hydrothermal reaction temperature and NaOH concentration on phase structure and UV-visible light response; while the morphology, BET surface area and photoactivity were affected by hydrothermal reaction temperature and NaOH concentration.
With the increasingly serious environmental problems and dispassion of fossil fuels, the elimination of hazardous chemicals through photochemical degradation technology has attracted enormous research interest [
In recent years, the bismuth-based compounds have attracted much research interest and show excellent performance in a variety of fields such as biomedical fields, solid oxide fuel cells, oxygen sensors, varistors or electrochromic devices as well as environmental science [
About 1% - 20% of the total world textile dyes and other industrial dyes are released to waste water [
Bismuth nitrate (Bi(NO3)3), urea (CO(NH2)2) and sodium hydroxide (NaOH) were of analytical grade and used without any further purification. Deionized water was used in the whole fabricating process. Three-dimensional bismutite Bi2O2CO3 (BSC) was synthesized by a hydrothermal reaction under mild conditions. 10 mmol of bismuth nitrate and 40 mmol of urea were dissolved in 30 ml of 0.5 - 2 M sodium hydroxide solution. The mud mixture was stirred for 2 h at room temperature with a stirring rate of 600 rpm, and then poured into a Teflon autoclave. The autoclave was put in an oven and allowed to be heated at 120˚C - 160˚C for 6 h under autogenous pressure, and then cooled to room temperature. The precipitates were collected and washed with deionized water and absolute ethanol for 3 times each to remove any residual ions. The final product was dried at 80˚C for 6 - 12 h for further use. The BSC samples synthesized using 0.1 M NaOH and at 120˚C, 140˚C, and 160˚C were noted BSC1, BSC2, BSC3, respectively; and BSC4, BSC5, BSC6 were prepared at hydrothermal temperature of 120˚C using 0.5, 1, 2 M NaOH respectively.
X-ray diffraction (XRD, D8 ADVANCE) with Cu Kα radiation (25 mA and 40 kV) was used to investigate the structure of the BSC samples. The morphology and composition of the samples were characterized by a scanning electron microscope (SEM, JEOL JSM-7001F) and Energy dispersive spectrometer (EDS) that is attached to JEOL JSM-7001F. UV-Vis absorption spectra of BSC were scanned by a spectrophotometer in the range of 200 - 800 nm (UV-VIS, SHIMADZU UV-2600). The specific surface area, pore size distribution and pore volume were measured by Tristar II3020 and the specific surface area was calculated with the Brunauer-Emmett-Teller (BET) method (Analysis Adsorptive: liquid N2). The adsorbed amount at a P/P0 value of 0.99 was used to estimate the total pore volume. The Barrett-Joyner-Halenda (BJH) method was utilized to calculate the average pore diameter from desorption branch of the isotherm. The as-obtained catalysts were used for photodegradation of R6G and the corresponding photocatalytic activity was investigated by UV-vis spectroscopy.
change can be observed for 6 BSC samples, further illustrating ignorable effect of hydrothermal temperature on the morphology. However, it can be seen that the crystallite size gradually becomes non-uniform with the increase of thermal treatment temperature. As a consequence, the optimal temperature is 120˚C. However, the NaOH concentration shows significant effect on the morphology of the BSC samples. It can be clearly seen that, the BSC particles change into square plates leading to larger sizes with the increase of NaOH concentration. In the hydrothermal reaction, [OH]− ions affects the nucleation and growth of oxide crystals. It has been inferred that [OH]− ions attach on (110) and (110) facets of oxide crystals, which may hinder the growth of these facets. Therefore, the morphology of BSC crystals gradually changes into square plates. On the other hand, [OH]− ions reacts with Bi(NO3)3 to produce Bi(OH)3 or [Bi(OH)4]−, which are then dehydrated to BiOOH. Meanwhile, NaOH reacts with urea generate sodium carbonate, which speeds up the hydrolysis of urea [
BET surface area, pore size distribution and pore volume of all as-obtained sample are listed in
Samples | BSC1 | BSC2 | BSC3 | BSC4 | BSC5 | BSC6 |
---|---|---|---|---|---|---|
SBET (m2/g) | 6.27 | 5.59 | 2.91 | 6.54 | 5.58 | 1.06 |
Pore volume (cm3/g)a | 0.038 | 0.021 | 0.012 | 0.032 | 0.018 | 0.0036 |
Average pore size (nm) | 25.3 | 16.3 | 16.9 | 20.6 | 13.4 | 42.8 |
aVolume of pores between 1.7 nm and 300 nm.
However, the BET surface area decreases sharply when NaOH concentration increases to 1 and 2 M, which attributes to the particle aggregation along with NaOH concentration increasing. This further confirms that NaOH plays dual function. The average pore diameter, calculated by the BJH method based on the desorption branch, shows that the BSC samples have a very clear mesoporous structure with pore size centered at 13.4 and 42.8 nm.
The photodegration reaction was carried out at room temperature and the pH was adjusted by adding 0.1 M HCl. As reported in our previous work [
Three-dimensional bismutite BSC were prepared through a hydrothermal synthesis with bismuth nitrate, urea and sodium hydroxide under mild conditions. There are no obvious effects of hydrothermal reaction temperature and NaOH concentration on the structure and light response of BSC. However, the particle size, BET surface area, pore volume and photoactivity decrease with the increase of hydrothermal reaction temperature and NaOH concentration. It suggestes that the concentration of NaOH plays dual role in the fabrication of BSC.
Hong Hu is grateful to the Department of Education of Jiangsu Province China for sponsoring her visiting research at Monash University through “Jiangsu Overseas Research & Training Program for University Prominent Young & Middle- aged Teachers and Presidents”.
Hu, H. and Xiao, C.L. (2017) The Effect of Fabrication Conditions on the Morphology and Photocatalytic Activity of Bismutite Bi2O2CO3 Particles. Open Journal of Physical Chemistry, 7, 1-8. http://dx.doi.org/10.4236/ojpc.2017.71001