Dong Fan

In situ FT-IR investigation on visible light photocatalytic NO oxidation mechanism with (BiO) 2 CO 3 and N-doped (BiO) 2 CO 3 hiararchical microspheres

With the rapid development of industry, air pollution has become a focused issue worldwide. As one of the major air pollutants, nitric oxide (NO) would lead to serious atmospheric problems such as acid rain, haze, and photochemical smog. Photocatalysis, as a green and effective technology, has become one of the most promising technologies for solving air pollution problems. As one of the typical photocatalyst, (BiO)2CO3 consists of alternating layers of [Bi2O2]2+ and CO32− groups and has good optical absorption property, emerging as an attractive photocatalyst. In this work, (BiO)2CO3 and in situ N-doped (BiO)2CO3 hierarchical microspheres were fabricated by a one-pot hydrothermal method and applied to photocatalytic NO removal. The as-prepared samples were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL and ESR. The photocatalytic NO oxidation process was monitored by in situ DRIFTS. The results indicated that the addition of urea has significant impact on (BiO)2CO3. The changed exposed facet influenced the morphological structure, band gap has narrowed and electronic-hole recombination rate of the as-prepared N doped (BiO)2CO3 has decreased. There are a lot of reports on photocatalytic NO oxidation, and the photocatalytic reaction mechanism for NO purification has been proposed for some photocatalysts with ·O2− and ·OH radicals as the main reactive species and nitrates as the final products. However, little is known about the reaction intermediates during photocatalysis. To reveal the reaction mechanism of photocatalytic NO oxidation, in situ DRIFTS investigation was applied to probe the reaction process. The photocatalytic NO oxidation mechanism was revealed based on the in situ DRIFTS and ESR results. With N doping, the reaction process and the free radicals which participated during the photocatalystic reaction process become different from the pure (BiO)2CO3 sample. For BOC, ·O2− is main active radical, but for NBOC, the active radical changed to ·OH. A new intermediate of NO+ was discovered during photocatalysis, which increased the efficiency of the reaction. Because of the N doping, the electronic structure of (BiO)2CO3 has been broken, which leads to the formation of more oxygen vacancy. The present work could provide new perspectives for advancing the photocatalysis efficiency, offer a new insight into the photocatalytic NO oxidation process and promote large-scale environmental applications of high-performance photocatalysts.

The reaction mechanism of plasmonic photocatalytic NO oxidation on Bi-metal/BiPO4

With the rapid development of economy, factories and vehicles make the air pollution became a worldwide focused issue. As one of the major air pollutants, nitric oxide (NO) would lead to serious atmospheric problems such as acid rain, haze, and photochemical smog. However, low concentration nitric oxide is hard to be removed by the way of industrialization. Photocatalysis, as a green and effective technology, has become one of the most promising technologies for solving air pollution problems and that works on low concentration air pollutant. As one of the typical photocatalyst, BiPO4 consists of alternating layers of [Bi2O2]2+ and PO43− groups and has the better UV-light photocatalysis performance when compare with TiO2, emerging as an attractive photocatalyst. At present, the study to enable BiPO4 respond visible light which comes up with many ways, such as element doping, build heterojunction and surface hybridization. The recent investigation shows that metal Bi possess the property of surface plasmon resonance (SPR) as well as noble metal like gold could enhance the photocatalysis activity by increasing light absorption and raising the separation efficiency of photogenerated electron-hole pair. In this study, Bi/BiPO4 composite photocatalyst was synthesized via a two steps method. Firstly, the hexagonal phase BiPO4 was prepared by a precipitation method. And then, the metal Bi was deposited on the surface of BiPO4 in the presence of NaBH4. The as-prepared photocatalyst was applied to the photocatalytic removal of low concentration of NO in air. The microstructures of the catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), UV-visible diffuse-reflectance spectrum (UV-vis DRS) and electron spin-resonance spectroscopy (ESR). The in situ FT-IR was used to analyze the reaction intermediates of photocatalytic NO oxidation under visible light irradiation. On the basis of free radicals capture from ESR, the reaction mechanism was proposed. The results show that the surface plasmon resonance of Bi metal promoted the visible light absorption and separation of photogenerated charge on BiPO4. The DFT calculation results indicated that the presence of oxygen defects induced the formation of the intermediate energy level between the valence band and the conduction band of the bismuth phosphate, which is beneficial to the electron transition from valence band. The results of electronic structure calculations manifest that the metal Bi also plays a role of storing and transferring electrons from the conduction band of BiPO4. The generation and rapid transfer of photogenerated carriers could decrease the photogenerated electron-hole pair recombination rate. As a result, the BiPO4 can be converted into a high performance visible light photocatalyst. The present work could provide new insights into the understanding of the Bi-based plasmonic photocatalyst and the mechanism of gas-phase photocatalytic reaction.

Performance and mechanism of visible-light-inducedplasmonic photocatalytic purification of NO with Ag/AgX

Photocatalysis technology could utilize solar energy for pollutantsndegradation and water splitting, displaying great potential in environmetnalnremidiation and clean enerfy development. Significant progresses havenbeen made on promoting photocatalysis efficiency and extending lightnabsorption range. Specific semiconductors and plasmonic metals cannbehave photocatalysts. Recently, the plasmonic photocatalysis withnAg/AgX (X=Cl, Br, I) has been received increasing research interests.nThe preparation and application of Ag/AgX plasmonic photocatalystsnhave extensively explored. However, the Ag/AgX plasmonic photocatalystsnwere mainly applied in water splitting and degradation of aquous pollutants.nThe application of Ag/AgX in air purification has been rarely reported.nAlso, the mechanism of photocatalytic NO purification with Ag/AgXnhas never been revealed.

In situ synthesis, bandstructure analysis and of visible light photocatalysis enhancementmechanism of K-doped C 3 N 4

For the past few years, air quality has surged to worldwide attention. nFor NO x purification, semiconductor photocatlysis nas a green technology that could use sunlight to purify air pollutants, nprovides an attractive alternative to decrease pollution. Recently, npolymeric graphitic carbon nitride (g-C 3 N 4 ) nmaterials have drawn intensive attention because of its metal-free nand high-hardness features, reliable chemical inertness, thermal stability, nas well as its versatile optical, electrochemical, and efficient photocatalytic nproperties. But pure g-C 3 N 4 suffers from rapid nrecombination of photo- generated electron-hole pairs resulting in nlow photocatalytic activity. Thus, several coping modifying methods nwere employed to improve the photocatalytic performance of g-C 3 N 4 . The present work developed a facile in situ method to construct novel k-doped g-C 3 N 4 (CN-K) structure with molecular composite precursors. nIn this work, the samples were prepared via pyrolysis of thiourea nand a certain amount of KI as the potassium source in a muffle furnace. nDifferent mass ratio (1%, 3%, 5%, 10%) of K-doping g-C 3 N 4 samples were prepared by changing the amount of KI. nThe as-prepared samples were systematically characterized by XRD, nSEM, TEM, XPS, BET, UV-vis DRS and PL. Material studio was used to nsimulated the crystalline structure of potassium doped g-C 3 N 4 . The bond structure of as-prepared samples can be theoretical ncalculation by DFT theoretical calculation. Both the experimental nand theoretical calculation results indicated that potassium ion which nwere formed chemical bond with nitrogen existed in the interlayer nof g-C 3 N 4 . The modified catalyst exhibited outstanding nphotocatalytic activity and photochemical stability towards degradation nof NO at ppb-level under visible light irradiation. The superior activity ncan be ascribed to the significant function of potassium ion worked non morphological structure, band gap and electronic-hole recombination nof as prepared samples. Firstly, evidenced by valence band XPS and nDFT theoretical calculation, potassium doping has the function of nmodifying band-gap, making for down-shift both conduction band and nvalence band, however, The extent of the conduction band down shifting nmore than the valence band, shortening down the optical band gap more nwhile making a significant enhancement of the solar light response nrange, thus the absorption capacity of as prepared samples strengthen nsignificantly. Secondly, the separation efficiency of photon-generated ncarriers increased with potassium doped in the interlayer of g-C 3 N 4 verified by room temperature PL spectra. Thirdly, nthe in situ K-doped g-C 3 N 4 showed nhigher oxidation capacity of photo-induced holes for degradating NO, nascribed to a more positive valence band. Integrated three factors, npurification efficiency of NO has been significantly improved. This nwork could provide a new perspective for modification of photocatalyst nwith alkali metals and mechanism understanding of NO degradation.