Novel nanocomposites have been prepared by intercalating TiO2 nanoparticles into talc. The nanocomposites have been verified by X-ray diffraction (XRD) from the appearance of a characteristic diffraction peak of TiO2. Thermal behavior of the prepared samples is examined by thermogravimetric analyzer (TGA), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS), which have shown no TiO2 particles on the surface of the talc. The TiO2 particles are found in the layers of talc by transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller (BET) method, which have shown the increase of specific surface areas and total pore volumes and the decline of average pore diameters. As the strong adsorption ability of talc can intensify the power of photon absorption and capture-recombination carriers, more than 99.5% of 2,4-dichlorophenol can be degraded in 1 h by the nanocomposite under an ultraviolet lamp in neutral solution and room temperature after reaching adsorption equilibrium, and the result of adsorbance is in accord with the first-order kinetic. The degradation rate was maintained at about 99% after 20 times. Therefore, the prepared talc/TiO2 nanocomposite is an efficient, stable, and recyclable material for wastewater treatment.
Phenolic compounds have been widely used in industrial and agricultural manufacture and are ranked as one of the most harmful and extensive organic contaminants [
TiO2 has superior photocatalytic performance due to its strong oxidizing ability, nontoxicity, and long-term stability of photochemistry [
In order to improve the purification efficiency of wastewater and promote the application of the talc in photocatalysis, we prepared TiO2/medical talc nanocomposites under two different temperature conditions through the full-scan UV–Vis absorption spectra and total organic carbon (TOC) analyzer, establishing whether the benzene ring was decomposed and confirming that 2,4-DCP was mineralized into inorganic substances. Finally, the photocatalytic stability of the nanocomposite was verified by repeated trails.
Medical talc obtained from talc powder plant of You County, Hunan Province, China, with a particle size of 38
The medical talc (50 g) was dried at 80°C for 8 h and was marked as MT. TNBT solution was added dropwise into absolute ethanol with stirring for 2 h; distilled water was added into the mixture dropwise until there was no sedimentation. The obtained product was named as HTO.
50 g of TNBT solution was mixed with 10 g of MT in a mortar, and the mixture ground till it became pasty, and dried after cleaning to acquire intercalating composite, T-H. All three samples were calcined at 400°C for 2 h at a heating rate of 2°C min-1. The products were labeled as T-400, H-400, and T-H-400, respectively, [
The list of samples that were prepared during each stage.
Name | Treatment |
---|---|
MT | Medical talc |
HTO | Hydrolyzing TiO2 |
T-H | Intercalation of TNBT into talc |
T-400 | Calcined MT at 400°C |
H-400 | Calcined HTO at 400°C |
T-H-400 | Calcined TH at 400°C |
X-ray diffraction (XRD) spectra of samples were examined by a Rigaku D/Max 2550 X-ray Diffractometer (Japan) using Cu Kα radiation (
For the adsorption experiment, the mixture (50 ppm 2,4-DCP solution and 2 g·L-1 sample) was stirred vigorously in darkness. After 25 min, the platform of 2,4-DCP solution removal was reached indicating that an adsorption/desorption equilibrium has been achieved. The mixture was then irradiated with a 250 W high-pressure mercury ultraviolet (UV) lamp (main emission wavelength: 365 nm, intensity: 327.3 kJ·mol-1, Shenzhen Guyou Special Light Source Co., Ltd., China) for certain times. After the UV irradiation, the mixture was centrifuged, and its absorbance was analyzed by using a UV–Vis spectrophotometer (Shimadzu UV-2550, Japan) at a wavelength of 283 nm [
Figure
XRD spectra of samples ((a) XRD spectra of samples: MT, HTO, and T-H; (b) XRD spectra of samples: T-400, H-400, and T-H-400).
Figure
TG curves of all samples.
The morphology of samples is displayed in Figures
SEM images of (a) medical talc (MT), (b) medical talc after calcining at 400°C (T-400), (c) hydrolyzing TiO2 (HTO), and (d) TiO2 after calcining at 400°C (H-400).
SEM images of (a, b) medical talc intercalated with TNBT (T-H) and (c, d) medical talc intercalated with TNBT after calcining at 400°C (T-H-400).
Figure
EDS spectrum of the nanocomposites ((a) T-H; (b) T-H-400).
The microstructures of the samples are shown in Figure
TEM images of all samples ((a) MT; (b) T-400; (c) T-H; (d) T-H-400).
Figure
(a) Nitrogen adsorption-desorption isotherms for all samples; (b) pore diameter distribution curves of all samples.
The specific surface areas (
Specific surface area (
Sample | |||
---|---|---|---|
MT | 7.92 | 0.032 | 15.98 |
T-400 | 8.03 | 0.030 | 15.13 |
HTO | 280.69 | 0.36 | 5.16 |
H-400 | 112.06 | 0.31 | 11.04 |
T-H | 244.07 | 0.17 | 2.74 |
T-H-400 | 63.59 | 0.14 | 9.10 |
In order to examine the photocatalytic degradation capacities of the TiO2/medical talc for 2,4-DCP, all samples were tested in the dark to first obtain the adsorption data. The plateau of adsorptions of the 2,4-DCP of all samples was reached after 25 min, indicating that they have reached the adsorption equilibrium. From Figure
The effect of the adsorption on the degradation of 2,4-DCP solution by all samples in the dark.
Figure
Full-scan UV–Vis absorption spectrums of 2,4-DCP solution after treatments by all samples. Initial 2,4-DCP concentration: 50 mg L-1.
From the results shown in Figures
After reaching the adsorption equilibrium, the UV lamp was turned on to examine the photocatalytic performance of the samples. From Figure
Photodegradation rate of 2,4-DCP solution for 1 h by all materials. Total absorption is in accordance with equation (
Figure
The full-scan UV–Vis absorption spectra of 2,4-DCP solutions for all samples after photodegradation by for 1 h.
Apart from the medical talc, which has little or no photocatalytic ability on its own, the time dependence of the removal rates of the 2,4-DCP by T-H-400, T-H, H-400, and HTO are shown in Figure
The change of the removal rate of the 2,4-DCP by T-H, T-H-400, H-400, and HTO.
Figure
Full-scan UV–Vis absorption spectrums of 2,4-DCP solutions after treatments by T-H-400 for 0 min, 40 min, 60 min, and 90 min.
It has been measured for the total oxygen carbon of the initial 2,4-DCP concentration and the 2,4-DCP concentration after treatment by T-H-400 under UV lamp for 2 h. The NPOC declined from 16.04 mg·L-1 to 0.91 mg·L-1 which is positively correlated with the concentration of TOC in the solution, indicating that the benzene rings in the 2,4-DCP have been almost completely broken down. Compared with the result shown in Figure
From the proposed pathway for 2,4-DCP degradation by TiO2/medical talc which has been investigated [
The pathway of decomposition of 2,4-DCP.
In order to establish the stability of photocatalytic degradation, the T-H-400 has been recycled 20 times to photodegrade the initial 2,4-DCP solution under the UV lamp for 1 h after 25 min in the dark, and the result is shown in Figure
The removal rate of the initial 2,4-DCP solution by T-H-400 under the UV lamp for 1 h after 25 min in the dark.
The 99.5% decomposition of the pollutant can be achieved in 1 h. The optimum condition is in neutral aqueous solution at room temperature under a UV lamp. This clearly enhances the photocatalytic capacity of TiO2. The excellent photocatalytic performance can be achieved by a few of nanocomposites. The degree of degradation can be maintained at about 99% after 20 iterations with the same nanocomposite material.
In situ formation of TiO2 nanoparticles in the layers of medical talc thus has marked effect on the purification of the initial solution, indicating that medical talc can significantly enhance the photocatalytic activity of TiO2. This remarkable photocatalytic power will promote the potential applications of medical talc in wastewater treatment.
The data used to support the findings of this study are included within the article.
The authors declare that they have no conflicts of interest.
We thank Professor Benjamin Kneller for polishing the manuscript. This work has been supported by the National Oil and Gas Project 529000-RE1201.