Improved photocatalytic activity of WO3 through clustered Fe2O3 for organic degradation in the presence of H2O2

Photocatalytic degradation of organic substrates over WO(3) in an aerated aqueous suspension is very slow due to the difficulty of O(2) reduction by the conduction band electron on WO(3). In this work, we report on H(2)O(2) as an electron scavenger significantly accelerating the photodegradation of phenol and azo-dye X3B in water under UV or visible light. More importantly, an iron-containing WO(3) (FeW) synthesized through thermal decomposition of a ferrotungstenic acid displayed a much higher activity than pure WO(3) (HW) prepared in parallel. As the sintering temperature increased, both FeW and HW showed an exponential increase in activity. The maximum rate constant of phenol degradation obtained with FeW at 400 °C was about 2 times larger than that with HW at 600 °C. Sample characterization with electron paramagnetic resonance (EPR) spectroscopy and other techniques revealed that ferric species (0.3 wt % Fe(2)O(3)) were mainly present as clusters on the oxide surface at 120 °C and then they diffused toward the lattice sites of WO(3) at high temperature, which was detrimental to the photocatalytic reaction. 5,5-Dimethyl-1-pyrroline N-oxide spin-trapping EPR showed that the production of hydroxyl radicals was greatly enhanced upon the addition of H(2)O(2), the trend of which among different catalysts was the same as that of the rate of phenol degradation. The catalysts after excitation at 350 nm displayed a blue emission centered at 469 nm, the intensity of which varied with the catalyst activity nearly as expected. A possible mechanism for the improved photoactivity of WO(3) is proposed involving the electron transfer from WO(3) to Fe(2)O(3) and the reaction of the reduced oxide with H(2)O(2) to generate hydroxyl radicals.     

NH3处理温度对N掺杂P25-TiO2的可见光催化活性的影响

研究了NH3处理温度对N掺杂P25-TiO2可见光催化活性的影响以及可见光催化活性与表面组成和结构的关系．实验结果表明：NH3处理温度在600℃时,有最高活性;在700℃,P25-TiO2转变为以金红石相为主,表面未发生N掺杂,这与700℃时NH3分解有关;N掺杂浓度、可见光吸收两者与可见光催化活性之间均不存在顺变关系．讨论揭示：N掺杂P25-TiO2的可见光催化活性是由三个要素协同作用产生：（i）表面生成大量束缚单电子氧空位（Vo）,（ii）表面有N掺入,（iii）晶型以锐态矿为主,三者缺一不可．     

Improved activity of Ni/MgAl_2O_4 for CO_2 methanation by the plasma decomposition

CO2 methanation has been a hot topic because of its important application in the spacecraft and potential utilization of carbon dioxide. Nickel catalyst is active for this reaction. However, its activity still needs to be improved. Dielectric barrier discharge(DBD) plasma, initiated at ambient condition and operated at ~150 °C,has been employed in this work for decomposition of nickel precursor to prepare Ni/Mg Al2O4. The plasma decomposition results in high dispersion, unique structure, enhanced reducibility of Ni particles and promoted catalyst-support interaction. An improved activity of CO2 methanation with a higher yield of methane has been achieved over the plasma decomposed catalyst, compared to the catalyst prepared thermally. For example, the methane yield of the plasma prepared catalyst is 71.8% at 300 °C but it is 62.9% over the thermal prepared catalyst. The catalyst characterization confirmed that CO2 methanation over the DBD plasma prepared catalyst follows pathway of CO methanation.     

燃烧剂和前驱体对TiO_2光催化性能的影响

溶胶-凝胶自蔓燃合成也称低温燃烧合成是二十世纪九十年代发展起来的合成工艺.这种依靠反应自身放热使化学反应继续进行并合成出所需材料的技术有以下优点:它点火温度低(300-500℃),点燃后利用原料自身的燃烧放热即可达到化合反应所需的高温;产生气体使形成的粉末不易团聚生长,能够合成均匀、比表面积高的粉体.     

Visible light photocatalytic decomposition of 2-naphthol by anodic-biased alpha-Fe2O3 film

Transparent alpha-Fe2O3 films with varying film thickness were formed on a SnO2 transparent conducting film-coated glass substrate by metal organic deposition. Under anodic-biased conditions, the alpha-Fe2O3 film showed a high photocatalytic activity for the decomposition of 2-NAP with visible light irradiation. The alpha-Fe2O3 is transformed to inactive hydroxide as the reaction proceeds, while the activity of alpha-Fe2O3 is almost maintained in acetonitrile.     

Fe_3O_4@TiO_2光催化剂的制备及其性能研究

采用溶剂热法制备了Fe3O4磁性纳米颗粒,通过溶胶-凝胶法在Fe3O4表面包覆一层Ti O2,并对其进行水热处理,制备了核壳结构光催化剂Fe3O4@Ti O2。利用透射电镜(TEM)分析了其形貌、并用X射线衍射(XRD)分析了其物相组成,利用紫外-可见光谱(UV-Vis)研究了其光谱特征,以罗丹明B(RB)模型污染物,在紫外光照射下评价了纳米Fe3O4@Ti O2的光催化活性,探讨了其重复使用的可能性。结果表明:Ti O2均匀包覆在Fe3O4表面,形成核壳结构,Ti O2转变为锐钛矿型;光催化结果显示Fe3O4@Ti O2在60 min内对RB降解率为97.2%,该材料结合了光催化与可再生的优点,5次循环使用后降解率仍保持在92.3%。     

固相法制备PTh/TiO_2复合纳米粉可见光催化剂

利用Sol-gel法制备了TiO_2纳米颗粒,然后以无水三氯化铁为氧化剂,室温固相氧化聚合噻吩,得到聚噻吩(Polythiophene,PTh)敏化纳米TiO_2形成的PTh/TiO_2复合纳米粉.以XRD、TEM、DRS等方法对其相组成、形貌及其光谱特性进行了研究.结果表明,所得纳米TiO_2为纯锐钛矿晶型,平均颗粒尺寸为18 nm;PTh/TiO_2复合物具有20× 80 nm的棒状形貌;DRS中吸收限在605nm处.以甲基橙作为模型试验了产品的光催化性能,结果表明,在太阳光照射下,120 min时PTh/TiO_2对甲基橙降解率达85.6%,光催化性能优于纯TiO_2、PTh及商品Degussa P25 TiO_2光催化剂.探讨了PTh促进TiO_2光催化性能的机理.     

Preparation and photocatalytic activity of TiO_2-coated granular activated carbon composites by a molecular adsorption-deposition method

TiO2 nanoparticle-coated granular activated carbon (GAC) composite photocatalysts (CPs) were suc-cessfully prepared by a molecular adsorption-deposition (MAD) method. The CPs were detected by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), BET surface area and UV-Vis adsorption spectroscopy, and their photoactivity was evaluated by methyl orange (MO) photodegradation. The results show that small-sized TiO2 nanoparticles were dispersed well, deposited on the surface of GAC, and showed slight blue shift in comparison with pure TiO2. With the increase in TiO2 content, the CPs showed band gaps in lower energy, smaller surface areas and the higher content of Ti3 ions. Compared with pure TiO2 and others CPs samples, CPs-382 sample showed the highest photoactivity due to the optimum TiO2 content and surface area besides the synergic effect of photocatalytic degradation of TiO2 and adsorptive property of GAC. In addition, the CPs could be very easily reclaimed, recycled and reused for methyl orange removal while high photoactivity is pre-served.     

磁性纳米TiO_2/SiO_2/NiFe_2O_4的制备及其催化性能

采用溶胶凝胶法制备了核壳结构磁性纳米TiO2/SiO2/NiFe2O4催化剂.利用XRD、TEM、VSM等手段对样品的粒径、晶体结构、磁性和光催化性能进行了研究.结果表明:SiO2/NiFe2O4的加入抑制了TiO2纳米粒子的生长,使晶粒尺寸减小,促进了锐钛矿相向金红石相的转变,催化剂的回收率和光催化性能均得到提高.光催化实验结果表明,当SiO2/NiFe2O4的负载量为15%时,焙烧温度为500℃时对亚甲基兰的脱色率最高.     

TiO_2-Supported Binary Metal Oxide Catalysts for Low-temperature Selective Catalytic Reduction of NO_x with NH_3

Binary metal oxide（MnOx-A/TiO2）catalysts were prepared by adding the second metal to manganese oxides supported on titanium dioxide（TiO2）,where,A indicates Fe2O3,WO3,MoO3,and Cr2O3.Their catalytic activity,N2 selectivity,and SO2 poisonous tolerance were investigated.The catalytic performance at low temperatures decreased in the following order：Mn-W/TiO2〉Mn-Fe/TiO2〉Mn-Cr/TiO2〉Mn-Mo/TiO2,whereas the N2 selectivity decreased in the order：Mn-Fe/TiO2〉Mn-W/TiO2〉Mn-Mo/TiO2〉Mn-Cr/TiO2.In the presence of 0.01%SO2 and 6%H2O,the NOx conversions in the presence of Mn-W/TiO2,Mn-Fe/TiO2,or Mn-Mo/TiO2 maintain 98.5%,95.8%and 94.2%, respectively,after 8 h at 120°C at GHSV 12600 h？ 1 .As effective promoters,WO3 and Fe2O3 can increase N2 selectivity and the resistance to SO2 of MnOx/TiO2 significantly.The Fourier transform infrared（FTIR）spectra of NH3 over WO3 show the presence of Lewis acid sites.The results suggest that WO3 is the best promoter of MnOx/TiO2,and Mn-W/TiO2 is one of the most active catalysts for the low temperature selective catalytic reduction of NO with NH3.     

纳米Fe/TiO_2粉体的制备及其光催化性能

光催化法是近年来发展较快的一种环境治理技术,掺杂型TiO_2催化剂是当前研究的焦点之一.以四氯化钛为主要原料,利用简单的溶胶法制备了纳米TiO_2、Fe/TiO_2粉体,研究发现掺杂铁,能够有效地延缓锐钛矿型TiO_2向金红石型TiO_2的转变,提高Fe/TiO_2粉体的光催化活性,并且500℃焙烧后的Fe/TiO_2催化剂,在紫外光下催化活性较好.     

NiFe2O4/g-C3N4 heterojunction composite with enhanced visible-light photocatalytic activity

Spinel structure nickel ferrite (NiFe₂O₄) doped graphitic carbon nitride (g-C₃N₄) photocatalyst NiFe₂O₄/g-C₃N₄ was synthesized by the coprecipitation route to enhance the photocatalytic activity for the visible-light driven degradation of methyl orange. The NiFe₂O₄ doping content is responsible for the microstructure and photocatalytic activity of NiFe₂O₄/g-C₃N₄ samples. Compared with pure NiFe₂O₄ and g-C₃N₄, the 2-NiFe₂O₄/g-C₃N₄ composite with NiFe₂O₄ doping of 2.0 wt% exhibited excellent photocatalytic activity and superior stability after five runs for degrading methyl orange under visible light irradiation. The catalytic activity of 2-NiFe₂O₄/g-C₃N₄ sample produced using the coprecipitation route was higher than those of conventional 2-NiFe₂O₄/g-C₃N₄ bulks prepared by the impregnation approach. The prepared samples for the photocatalytic degradation of methyl orange followed pseudo-first-order reaction kinetics. It’s ascribed to the synergistic effect between NiFe₂O₄ and g-C₃N₄, which can inhibit the recombination of photoexcited electron-hole pairs, accelerate photoproduced charges separation, and enhance the visible light absorption.     

Improved photocatalytic efficiency of a WO3 system by an efficient visible-light induced hole transfer

Amorphous Cu(II) nanoclusters grafted WO(3) particles were coated on a smooth TiO(2) film, and site selective depositions of PbO(2) and metal Ag particles by photocatalytic processes were observed on TiO(2) and WO(3) due to transfer of holes to TiO(2), and accumulation of electrons in WO(3) respectively. As a result, the photocatalytic activity of TiO(2) modified Cu(II)-WO(3) increased ~3.5 fold higher than that of Cu(II)-WO(3).     

Pt/TiO_2光催化降解3-甲基吲哚的研究

Pt/TiO_2 was prepared by impregnation method and characterized with XRD、 BET and XRD results showed TiO_2 as prepared was anatase and the average particle sizewas about17 nm.The results of the photocatalytic degradation of 3- methyl indole suggested that the influences of Pt amount and loading amount of catalytics have obvious effect to catalyst activity.The concentration of flow rate and consistence obviously influenced the 3- methyl indole photocatalytic degradation.     

Improved photocatalytic performance of anatase TiO2 synthesized through ethanol supercritical drying technique

Anatase titania (TiO₂) nanoparticles were synthesized via a self‐developed ethanol vapor‐thermal method at 240°C (T240) and 250°C (T250), i.e. at temperatures lower and higher, respectively, than the supercritical temperature (243.5°C, 7.0 MPa) of ethanol. Compared to T240, T250 exhibited a higher ratio of exposed (001) facets, oxygen vacancies, and concomitant TiO_x. The specific surface area of T250 was 119.0 m² g^?1, smaller than that of T240 (144.2 m² g^?1). During the degradation of methylene blue, T250 exhibited a high apparent rate constant (K_app) of 14.5 × 10^?2 min^?1, which was 6.3 times larger than that for T240. Furthermore, compared to T240, T250 exhibited better performance toward degradation of phenol. Results of electron spin resonance spectroscopy and photoluminescence indicated that the photogenerated electron–hole pairs possessed higher separation efficiency for T250 than for T240. In summary, the excellent photocatalytic performance of T250 originates from the higher ratios of exposed (001) facets, oxygen vacancies or TiO_x, C═O groups adsorbed at the surface of particles, and higher separation efficiency of photogenerated electron–hole pairs. By employing this self‐developed vapor‐thermal method, a variety of catalysts and their composites can be synthesized, which may exhibit novel morphological characteristics and properties as well as excellent photocatalytic performance.     

Influence of MnO_2 on the photocatalytic activity of P-25 TiO_2 in the degradation of methyl orange

Influences of α-MnO2, β-MnO2, and δ-MnO2 on the photocatalytic activity of Degussa P-25 TiO2 have been investigated through the photocatalytic degradation of methyl orange. The TiO2 photocatalyst, before and after being contaminated by MnO2, was characterized by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). The results showed that photocatalytic activity of TiO2 could be inhibited significantly or completely deactivated due to the presence of even a small amount of MnO2 particles. It was found that the poisoning effect varied with the crystal phases of MnO2 and the effect was in the order δ-MnO2 >α-MnO2 >β-MnO2. The poisoning effect was attributed to the formation of heterojunctions between MnO2 and TiO2 particles. The heterojunctions changed the chemical state of Ti4 and O2 sites in the crystalline phase of TiO2. MnO2 in contact with TiO2 particles also broadens the band-gap of TiO2, which decreases UV absorption of TiO2. It can also create some deep impurity energy levels serving as photoelec-tron-photohole recombination center, which accelerates the electron-hole recombination.     

Catalytic Performance of MnO_x-WO_3/TiO_2 Catalyst for Selective Catalytic Reduction of NO_x with NH_3 and Its Tolerance Towards SO_2

The performance of Mn-W/TiO₂ for selective catalytic reduction(SCR) of NO_x with NH₃ and its resistance to different concentrations of SO₂ at various temperatures were investigated. The results show that WO₃ increased the active sites and enhanced the strength of acid, so it was an effective promoter of MnO_x/TiO₂. The NO_x conversion on Mn-W/TiO₂ ranges from 80.3% to 99.6% between 100 °C to 350 °C at GHSV=18900 h^–1, while N₂ product selectivity changes from 100% to 98.7%. In the presence of 0.01% SO₂ and 6% H₂O, NO_x conversion maintained 98.5% at 120 °C. The influence of more than 0.01% SO₂ on the activity of MnO_x-WO₃/TiO₂ will disappear if the temperature rises above 250 °C. By means of heating and sweeping with He, the activity of the catalysts can be recovered. At 300 °C, NO_x conversion yielded 99% with 0.07% SO₂ and reached the level of commercial V-W/TiO₂ catalysts. The Mn-W/TiO₂ catalyst showed excellent performance for SCR of NO_x with NH₃ in a wider range of temperature with strong tolerance to SO₂.     

Controlled synthesis of olive-shaped Bi2S3/BiVO4 microspheres through a limited chemical conversion route and enhanced visible-light-responding photocatalytic activity

Well-defined olive-shaped Bi(2)S(3)/BiVO(4) microspheres were synthesized through a limited chemical conversion route (LCCR), where olive-shaped BiVO(4) microspheres and thioacetamide (TAA) were used as precursors and sulfur source, respectively. The as-synthesized products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission microscope (HRTEM), X-ray photoelectron spectra (XPS), UV-visible diffuse-reflectance spectroscopy (UV-vis DRS), and photoluminescence (PL) spectra in detail. Compared with pure BiVO(4) microspheres and Bi(2)S(3) nanorods, the Bi(2)S(3)/BiVO(4) products showed obviously enhanced photocatalytic activity for the degradation of rhodamine B (Rh B) in aqueous solution under visible-light irradiation (λ > 400 nm). In addition, the Bi(2)S(3)/BiVO(4) composite microspheres showed good visible-light-driven photocatalytic activity for the degradation of refractory oxytetracycline (OTC) as well. On the basis of UV-vis DRS, the calculated energy band positions, and PL spectra, the mechanism of enhanced photocatalytic activity of Bi(2)S(3)/BiVO(4) was proposed. The present study provides a new strategy to design composite materials with enhanced photocatalytic performance.     

Facile preparation of MgAl2O4/CeO2/Mn3O4 heterojunction photocatalyst and enhanced photocatalytic activity

Novel Mn₃O₄-promoted double p?n junction MgAl₂O₄/CeO₂/Mn₃O₄ heterojunction photocatalyst was constructed by one-step synthesis method and two-step synthesis method. The X-ray powder diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, optical and photoluminescence demonstrated that the MgAl₂O₄/CeO₂/Mn₃O₄ heterojunction photocatalyst was synthesized by the two-step synthesis method comprehends a high crystallinity, charge carrier migration and separation efficiency, and relatively low optical absorption coefficient. The MgAl₂O₄/CeO₂/Mn₃O₄ heterojunction photocatalysts were efficiently used as simulated sunlight-driven n-n and p-n double junction photocatalyst for the simultaneous degradation of methylene blue (MB) dye. The continuous double p?n junction MgAl₂O₄/CeO₂/Mn₃O₄ heterojunctions strengthened the function of single n-n or p-n junction and guided the charge carrier migration and separation direction; thus, the oxidation and reduction reactions occur at the active site of spatial separation and prevent the recombination of electrons and holes. The results suggest that the continuous double p?n junction MgAl₂O₄/CeO₂/Mn₃O₄ heterojunctions are very promising candidate material for enhancing the photocatalytic activity in the photocatalytic degradation of MB dye.