Preferential Photocatalytic Degradation Of Methamphetamine In Seizure Samples

Ice drugs,an amphetamine-type stimulant is a commonly consumed drug of abuse.Methamphetamine（MAT）is an active ingredient of ice drugs.Chinese government seized about 67.9 tons of various drugs,including more than 10.5 tons of methamphetamine in 2018.MAT is usually destroyed by incineration.However,the waste gases generated in this process such as carbon monoxide and nitrogen oxides would cause serious pollution to the environment and harm to human health.Besides,MAT can easily transmit through environmental aqueous media and difficult to biodegrade.Researches from several countries and regions demonstrates that MAT can influence and alter the eutrophication.Thus,the treatment of MAT has drawn much attention in recent years.TiO₂ photocatalytic technology has widely used in environmental treatment,including the treatment of waste drugs with low concentration in natural water due to its characteristics of high efficiency,energy saving and no secondary pollution.Currently,there are only a few reports on the use of commercial TiO₂ for the photocatalytic degradation of methamphetamine standard products.The photocatalytic degradation of MAT seizure samples mixed with other additives,such as caffeine these materials was seldom explored.However,the large bandgap of commercial TiO₂ determines that it can only be activated by ultraviolet light,so the efficiency is low in the range of sunlight.In addition,since oxidation is governed by a free radical mechanism,it is expected to operate in a manner that hardly differentiates between different contaminants.Hence the seizure samples of additives in methamphetamine seizure samples may degraded with methamphetamine simultaneously.In summary,it is of great significance to use photocatalytic technology to treat methamphetamine seizure samples mixed caffeine,which can effectively remove methamphetamine while preserving valuable additives such as caffeine.In this paper,tungsten has been introduced into TiO₂ system by in the form of transition metal salts,transition metal oxides and transition metal cations to prepare tungstate doped TiO₂-SiO₂ aerogel,WO₃/TiO₂ composite and sulfur and tungsten co-doped TiO₂.High efficiency and priority oxidation to remove methamphetamine from seized samples,while preserving the additive caffeine.The main contents of this paper as follows:1.TiO₂-SiO₂ aerogels with different Ti/Simolar ratios were prepared by sol-gel method and photocatalytic degradation of methamphetamine was carried out.It was found that the photocatalytic degradation rate of methamphetamine in seizure samples solution reached 75% after 4h under simulated sunlight used TiO₂-SiO₂ aerogels（Ti:Si=3:1）as photocatalysts and the caffeine is retained.Furthermore,tungstate was doped TiO₂-SiO₂ aerogels due to its stability.The obtained samples of tungstate doped TiO₂-SiO₂ aerogels showed enhanced photocatalytic efficiency for the degradation of methamphetamine in seizure samples with 7.0-,4.4-,and 1.9-fold simulated sunlight activities compared to the P25,TiO₂-SiO₂ aerogels and tungstate doped TiO₂.The preferential degradation ability of tungstate doped TiO₂-SiO₂ aerogels for methamphetamine in the seizure samples may be related to the strong absorption in visible region and the selective adsorption caused by surface charge change after tungstate doping.This study provides a simple and feasible method to improve the activity of TiO₂-SiO₂ aerogel.2.WO₃/TiO₂ composites were prepared by two-step method,and it was found that the calcination temperature also had an influence on the photocatalytic degradation of the materials.In general,10wt%-WO₃/TiO₂ after calcination at 700℃ exhibited the photocatalytic efficiency for the degradation of methamphetamine in seizure samples with 66.1-,1.7-1.6-,and 24.7-fold simulated sunlight activities compared to the TiO₂-700,5wt%-WO₃/TiO₂,20wt%-WO₃/TiO₂ and WO₃ after 90 min.Compared with the pure TiO₂ material calcined at same temperature,WO₃/TiO₂ composite material also has the ability of photocatalytic preferential oxidation to degraded methamphetamine in the seizure samples mixed with caffeine.The enhancement of photodegradation efficiency can be attributed to the increase of absorption intensity in visible region and the close contact between TiO₂ and WO₃ lattice.These findings will open an avenue for using transition metal oxides and TiO₂ coupling materials as a photocatalytic degradation of illegal drugs.3.The co-doped SW-TiO₂ with sulfur and tungsten was prepared by two-step method,and the material was directly obtained after hydrothermal reaction without the subsequent annealing at high temperature.The tungsten and sulfur of the prepared SW-TiO₂ materials were characterized as interstitial doping.SW-TiO₂ showed the enhanced photocatalytic efficiency for the degradation of methamphetamine in seizure samples with 25.1-,25.6-,and 59.4-fold simulated sunlight activities compared to the TiO₂,W-TiO₂ and S-TiO₂ after 180 min.The enhancement of photocatalytic degradation may be related to the strong absorption in visible region and the fact that tungsten and sulfur doped can act as both hole and electron trapping agent,thus inhibiting the recombination of photogenic carriers.