离子液体在大气压等离子体中稳定性研究

The Stability of Ionic Liquids in DBD Plasma under Atmospheric Pressure

采用发射光谱、紫外可见吸收光谱、红外吸收光谱和核磁共振技术分析1-丁基-3-甲基咪唑硫酸氢盐([Bmim]HSO_4), 1-丁基吡啶硫酸氢盐([BPy]HSO_4)和1-丁基-3-甲基咪唑四氟化硼([Bmim]BF_4)三种离子液体在大气压介质阻挡放电氩等离子体体系中的稳定性,并分别以上述三种离子液体为辅助液采用大气压介质阻挡放电等离子体技术制备TiO_2,进一步研究三种离子液体在等离子体中的稳定性对所制备的TiO_2晶相结构的影响。结果表明:向大气压介质阻挡放电氩等离子体中分别引入[Bmim]HSO_4,[BPy]HSO_4和[Bmim]BF_4离子液体后并未改变氩等离子体放电光谱谱峰的位置和数量且没有新的谱峰生成,但谱峰强度都明显降低,说明上述三种离子液体没有在等离子体区蒸发形成激发态物种;[Bmim]HSO_4和[BPy]HSO_4放电前后的红外吸收光谱基本一致,表明离子液体在放电后的化学键未发生改变;[Bmim]HSO_4和[BPy]HSO_4的紫外可见吸收光谱显示其吸收峰的位置和强度未发生改变,说明两种离子液体在等离子体作用后的结构是稳定的;[Bmim]BF_4放电前后的红外吸收光谱各个特征峰并无明显差异,但其紫外可见吸收光谱图谱吸收峰的位置却发生较大的偏移,进一步对放电前后的[Bmim]BF_4离子液体进行核磁共振分析,两者的~1H NMR峰数相同,但放电后的离子液体化学位移向高位偏移大约0.2单位,说明其化学环境发生了变化,表明有部分[Bmim]BF_4结构发生改变。光谱和核磁共振技术分析表明离子液体[Bmim]BF_4在等离子体作用后结构发生了改变。采用三种离子液体辅助大气压介质阻挡放电等离子体技术制备TiO_2样品的X-射线衍射分析结果表明[Bmim]HSO_4和[BPy]HSO_4辅助制备的[BPy]HSO_4-TiO_2和[Bmim]HSO_4-TiO_2,谱图与锐钛矿相TiO_2标准谱图基本一致,表明所制备的TiO_2为纯锐钛矿型。而[Bmim]BF_4辅助制备的[Bmim]BF_4-TiO_2在2θ=24.1°处的衍射峰向小角度偏移, 2θ=48°处的衍射峰向大角度偏移,说明[Bmim]BF_4在辅助制备TiO_2过程中, F进入TiO_2的晶格,破坏了TiO_2原子间的平衡状态,生成了F掺杂TiO_2光催化材料。F掺杂TiO_2光催化材料的形成也间接证明了离子液体[Bmim]BF_4在大气压等离子体中的不稳定性,此结果与核磁共振及紫外可见光的检测结果相一致。同时说明离子液体在等离子体的作用下对于纯锐钛矿晶格的形成和促进高活性掺杂型的光催化材料具有重要作用。为等离子体辅助离子液体制备高性能纳米材料提供重要的实验和理论依据。

The stability of three Ionic liquids ([Bmim]HSO 4,[ BPy]HSO 4 and [Bmim]BF 4) in DBD (Dielectric Barrier Discharge) Plasma under atmospheric pressure was investigated by using the OES (Optical Emission Spectrometer), UV-Vis (Ultraviolet and Visible Spectrophotometer), FTIR(Fourier Transform Infrared Spectroscopy) and NMR (Nuclear Magnetic Resonance) techniques. The influences of the stability of three Ionic liquids on the crystal phase structure of TiO 2 were also studied by preparation of TiO 2 with DBD plasma under atmospheric pressure using three kinds of Ionic liquids as assistant, respectively. The results showed that the position and quantity of argon argon plasma emission spectra peak did not change when three kinds of ionic liquid were introduced in DBD plasma. This indicated that the three ionic liquids of above did not evaporate in the plasma area and form excited species. However, the intensity argon emission peak decreased obviously. Both FTIR and UV-Vis spectrospecy of [Bmim] HSO 4 and [BPy]HSO 4 showed no difference before and after plasma discharge. This indicated that the [Bmim]HSO 4 and [BPy ]HSO 4 were stable in plasma. There was no significant difference in the infrared spectra of [Bmim]BF 4 before and after plasma treatment. However, the position of the absorption peak in the UV-Vis spectra of [Bmim]BF 4 before and after plasma treatment had a large shift, and the analysis of 1H NMR showed that all the peaks shifted to right 0.2 units approximately. That indicated that the structure of some [Bmim]BF 4 changed in plasma. The XRD spectra of [BPy]HSO 4-TiO 2 and [Bmim]HSO 4-TiO 2, which were prepared by DBD plasma under atmospheric pressure using [Bmim] HSO 4 and [BPy]HSO 4 as assistant respectively, showed that all the diffraction peaks were the same as the standard spectra of anatase TiO 2, and this indicated that [BPy]HSO 4-TiO 2 and [Bmim]HSO 4-TiO 2 were pure anatase. However, The XRD spectra of [Bmim]BF 4-TiO 2, which were prepared by DBD plasma under atmospheric pressure using [Bmim]BF 4 as assistant, showed that the diffraction peaks at round 24.1° shifted to lower 2 θ values, while the diffraction peaks at around 48.0° shifted toward higher 2 θ values. The shift of the diffraction peak for [Bmim]BF 4-TiO 2 samples indicated that lattice imperfection was formed due to F doping. The fluorine atoms entered into the lattice of TiO 2, therefore breaking the equilibrium of original TiO 2 atoms and varying the inter planar crystal spacing of anatase TiO 2. This revealed that same of [Bmim]BF 4 were broken down in plasma. The formation of F doped TiO 2 photocatalyst also indirectly proved the instability of ionic liquid [Bmim]BF 4 in atmospheric pressure plasma, and this results were the same with the analysis of UV-Vis and 1H NMR. The formation of F-doped TiO 2 photocatalytic materials also indirectly proved the instability of ionic liquid [Bmim]BF 4 in atmospheric pressure plasma, which was consistent with the results of NMR and UV-Vis. It was also proved that ionic liquids play an important role in the formation of pure anatase crystals and the promotion of highly reactive photocatalysis materials under the action of plasma. It provides an important experimental and theoretical basis for the preparation of high performance nano-materials by plasma-assisted ionic liquids.