研究目的
To develop a mass spectrometric approach for investigating interfacial photoelectron transfer and hydroxyl radical abstraction on semiconductor nanoparticles to identify degradation intermediates of aromatic organochlorines, which is difficult with current spectroscopic techniques.
研究成果
The mass spectrometry-based approach effectively identifies degradation intermediates of aromatic organochlorines through photoelectron capture dissociation and hydroxyl radical abstraction. ZnO showed the highest activity due to its high electron mobility. The method provides insights into site selectivity and bond cleavage mechanisms, aiding in the design of efficient photocatalysts. Mass spectrometric imaging reveals heterogeneous activities across different semiconductor nanoparticles.
研究不足
The experiments were conducted under high vacuum conditions (1x10-3 mbar), which may not fully replicate atmospheric conditions where oxygen presence could alter degradation pathways. The approach is limited to in situ analysis and may not capture all intermediates in real environmental scenarios. Steric effects and electron density variations could affect generalizability to other compounds.
1：Experimental Design and Method Selection:
A mass spectrometry-based approach using a Q-TOF mass spectrometer in negative ion mode with in situ ultraviolet irradiation (355 nm laser) to detect photo-generated negatively charged ions. The design includes a static electric field, high vacuum system, and controllable bias voltage to inhibit electron-hole recombination and facilitate electron transfer and capture.
2：Sample Selection and Data Sources:
Samples include hexachlorobenzene (HCB) and chlorothalonil (CT) adsorbed on semiconductor nanoparticles (ZnO, TiO2, AlN). Nanoparticles were thermally treated to remove contaminants. Solutions were prepared in n-hexane and acetone.
3：List of Experimental Equipment and Materials:
MALDI Synapt G2 HDMS mass spectrometry system (Waters, USA), Nd:YAG laser (355 nm), free fatty acids for calibration, semiconductors (TiO2, ZnO, AlN from Sigma-Aldrich), HCB and CT from Dr. Ehrenstorfer GmbH, solvents (LC-MS grade water, isopropanol, acetone from Fisher Scientific, n-hexane from Guoyao), muffle furnace for thermal treatment, compressor for film preparation, Gaussian software for DFT calculations.
4：Experimental Procedures and Operational Workflow:
Nanoparticles were suspended and deposited on sample plates; HCB or CT solutions were added; sample plate was placed in mass spectrometer under high vacuum; laser irradiation excited electrons; bias voltages (20-100 V) were adjusted; ions were pulled out and analyzed. For imaging, nanoparticles were adsorbed with HCB/CT, compressed into films, and imaged with step size 30 μm x 30 μm.
5：Data Analysis Methods:
Mass spectra were analyzed for ion identification; DFT calculations at B3LYP/6-31G+(d) level for charge distribution; HDI software for imaging analysis; statistical analysis of ion intensities.
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