Surface-enhanced Raman scattering (SERS) for semiconductor nanomaterial systems is limited due to weak Raman signal intensity and unclear charge-transfer (CT) processes for chemical enhancement. Here, rare-earth element neodymium-doped titanium dioxide (Nd-TiO2) nanoparticles (NPs) were synthesized by the sol–gel method. The characterizations show that the doping of Nd ions causes TiO2NPs to show an increase in the concentration of defects and change in the energy level structure. The CT process between Nd-TiO2NPs substrate and probe molecule 4-Mercaptopyridine (4-Mpy) was innovatively analyzed using the relative energy level location relationship of the Dorenbos model. The SERS signal intensity exhibits an exponential enhancement with increasing Nd doping concentration and reaches its optimum at 2%, which is attributed to two factors: (1) The increase in the defect concentration is beneficial to the CT process between the TiO2and the probe molecule; (2) the introduction of 4felectron orbital energy levels of rare-earth ions created unique CT process between Nd3+and 4-Mpy. Moreover, the Nd-TiO2NPs substrate shows excellent SERS performance in Raman signal reproducibility (RSD = 5.31%), the limit of detection (LOD = 10−6M), and enhancement factor (EF = 3.79 × 104). Our work not only improves the SERS performance of semiconductor substrates but also provides a novel approach to the development of selective detection of probe molecules.
Jinlong Li,Boxin Li,Guozhe Sui,Lijuan Du,Yan Zhuang,Yulin Zhang,Yuanfang Zou
Volatile organic compounds (VOCs) with toxicity properties discharged from industrial emissions and combustion engines threaten human health and cause environmental problems. Therefore, it is important to develop technologies to remove VOCs from air. In this study, the performance of Nd (neodymium) -TiO 2 nanoparticles embedded in a supported ionic liquid membrane (SILM) for removal of VOCs from air was investigated. Aiming at functionalizing the ionic liquid membrane with photocatalytic capability, we developed a facile and effective approach for the removal of VOCs by coupling highly efficient photocatalysts with the SILM. Nd-TiO 2 nanoparticles , which are ultraviolet-visible (UV–Vis) light-driven photocatalysts, were prepared by sol-gel and immersed in the SILM for use as a photocatalytic membrane-based reactor. The gaseous VOCs tested were toluene, acetone, chloroform, benzene, and xylene. We confirmed that at a loading of 50 wt% Nd-TiO 2 nanoparticles (1 wt% Nd content) and 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMI m ]PF 6 ) as SILM ([HMI m ]PF 6 /Nd-TiO 2 SILM), the as-prepared photocatalytic membrane-based reactor exhibited higher removal efficiency of VOCs from air (60~80% removal after 10 h) under UV–Vis light illumination than individual SILM or photocatalytic systems. Effluent gas analysis revealed that 25–55% of VOCs was decomposed and mineralized in the photocatalytic membrane reactor, which exhibited higher VOCs removal efficiency than membrane separation. These results indicate that the photocatalytic membrane-based reactor containing Nd-TiO 2 nanoparticles and SILM designed in this study is highly active and stable. This study on [HMIm]PF 6 /Nd-TiO 2 SILM was initiated to couple membrane separation with photocatalytic degradation of gaseous VOCs and can serve as a promising way for eliminating harmful VOCs with low concentration from air.
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