Short communicationTungstate doped TiO2-SiO2 aerogels for preferential photocatalytic degradation of methamphetamine in seizure samples containing caffeine under simulated sunlight
Graphical abstract
Introduction
Methamphetamine (MAT), a non-ecstasy amphetamine-type stimulant is a commonly consumed drug of abuse. Considering the irreversible risks and threat to the human and environment, dozens of tons of MAT samples which contained additives, such as caffeine, were seized every year and usually destroyed by traditional treatments such as incineration, landfill and sea abandon. However, ongoing investigations have shown that these drugs can infiltrate and remain in aquatic environments [1]. Thus, the above common treatment processes which were used to treat MAT seizure samples for many years still regarded with suspicion due to secondary pollutions. Moreover, the additives, such as caffeine in seizure samples which is valuable, may remove with MAT simultaneously in these methods.
For the treatment of MAT seizure samples in green way, some advanced techniques including sonocatalytic degradation [2], ozonation [3], Fenton and Fenton-like reactions [4,5] and biological method [6] has drawn attention in recent years. Particularly, TiO2 has been served as candidates for the photocatalytic degradation of MAT in the water [7,8]. But so far, these efforts were mainly devoted to the degradation of the pure MAT and the concentration in these studies are very low (100 μg L−1). More importantly, the wide bandgap of TiO2 limited its application under nature solar light.
The improvement of light absorption and suppression of aggregation are important approach to expand the application of TiO2. In view of this, preparing TiO2 aerogels and supported on absorbent such as SiO2 may be the effective measure [9]. These materials are of considerable attention in various applications for their high surface area, low-density, highly porous structure and efficient transfer of electron [10].
Transition metals have attracted much attention in catalysis due to its physico–chemical properties [[11], [12], [13]]. Hence, doping with transition metals on TiO2 to improve the performance are common method [14]. Among of these, the presence of tungsten could improve the photocatalytic efficiency of photocatalysts by hinder the recombination of the photo-generated electron–hole pairs and shift the range of adsorption to visible light region [15]. However, the available information about TiO2-SiO2 aerogels modified with tungstate to enhance the photocatalytic efficiency still limited [16], let alone its application on photocatalytic degradation of MAT in seizure samples containing caffeine.
On the other hand, photocatalysis is governed by free radical mechanism and it is difficult to operate in a manner that distinguish different contaminants [17]. Therefore, it is of great significance to decompose MAT in seizure samples while preserving valuable additives such as caffeine. Despite the relatively scarce report on preferential photocatalytic degradation, we are also inspired to recent study. Sharabi and Paz reported a method for obtaining preferential degradation by means of preparation of molecularly imprinted TiO2 [18]. Besides, selective photocatalytic degradation of charged pollutants in water was achieved by the electrostatic attraction [19]. Hence, it will be a good possibility to apply photocatalytic technique in the degradation of MAT seizure samples containing caffeine by adjusting the surface properties of photocatalyst which has not been reported as far as we known.
Herein, we reported a simple method for synthesis of W/TiO2-SiO2. The results of the study proved that the photocatalytic activity could be significantly improved by the doping of tungstate. In particular, in contrast to TiO2 (P25), it exhibited preferential photocatalytic degradation of MAT in the presence of caffeine.
Section snippets
Preparation
W/TiO2-SiO2 were synthesized by sol–gel methods. Tetraethyl orthosilicate (2.48 mL), titanium tetraisopropoxide (9.80 mL) and nitric acid (0.55 mL) was dissolved in ethanol (38.60 mL). Then deionized water (1.80 mL) which is dissolved with sodium tungstate dehydrate (0.37 g) were added to above solution, continuous stirring until obtain the clear gelatin. Transferred gelatin into a standard autoclave and kept at 538 K for 120 min under nitrogen atmosphere. Then cool down the temperature of
Characterization
The crystal phase compositions of W/TiO2, TiO2-SiO2 aerogels and W/TiO2-SiO2 were identified by X-ray diffraction (XRD), as shown in Fig. S2. All the samples showed the characteristic diffraction peaks attributing to the anatase titanium oxide (JCPDS, PDF 21-1272). No signal of tungstate anion is found in any of the prepared samples. This could be also interpreted as that tungsten ions incorporated into the titania lattice or located at interstitial sites [16].
All the adsorption-desorption
Conclusion
We have synthesized tungstate doped TiO2-SiO2 aerogels (W/TiO2-SiO2) with large surface area (197.99 m2 g−1) exhibiting preferential photocatalytic oxidation of methamphetamine (MAT) in seizure samples containing caffeine. MAT in seizure samples was almost removed within 60 min, which contacts with illuminated W/TiO2-SiO2 suspension (0.4 g L−1), while TiO2 (P25) photodegraded both MAT and caffeine simultaneously. The increased photocatalytic degradation of the W/TiO2-SiO2 may be attributed to
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (81860532, 21773204, 21367024) and Key Research and Development Plan of Yunnan Province (2018BA065). The authors thank the Industrialization Cultivation Project (2016CYH04), Scientific Research Fund of Department of Yunnan Education (2017ZZX223), the Program for Innovation Team of Yunnan Province and Key Laboratory of Advanced Materials for Wastewater Treatment of Kunming for financial support.
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