Simultaneous co-Photocatalytic CO2 Reduction and Ethanol Oxidation towards Synergistic Acetaldehyde Synthesis

Photocatalytic conversion of CO₂ is of great interest but it often suffers sluggish oxidation half reaction and undesired by-products. Here, we report for the first the simultaneous co-photocatalytic CO₂ reduction and ethanol oxidation towards one identical value-added CH₃CHO product on a rubidium and potassium co-modified carbon nitride (CN-KRb). The CN-KRb offers a record photocatalytic activity of 1212.3 μmol h⁻¹g⁻¹ with a high selectivity of 93.3 % for CH₃CHO production, outperforming all the state-of-art CO₂ photocatalysts. It is disclosed that the introduced Rb boosts the *OHCCHO fromation and facilitates the CH₃CHO desorption, while K promotes ethanol adsorption and activation. Moreover, the H⁺ stemming from ethanol oxidation is confirmed to participate in the CO₂ reduction process, endowing near ideal overall atomic economy. This work provides a new strategy for effective use of the photoexcited electron and hole for high selective and sustainable conversion of CO₂ paired with oxidation reaction into identical product.     

纸质包装材料中甲醛、乙醛向食品模拟物改性聚苯醚的迁移行为

为了解纸质包装材料中甲醛、乙醛向食品模拟物改性聚苯醚( Tenax)中的迁移行为,建立了一步提取衍生化、超高效液相色谱测定纸质包装材料和Tenax中的甲醛和乙醛的方法。本方法在甲醛和乙醛的测定范围内,线性相关系数R2>0.9999,甲醛检出限为0.03 mg/m2,乙醛检出限为0.04 mg/m2,测定纸样和Tenax的加标回收率为90.1%~108.6%。采用本方法研究不同温度和时间下两种纸质包装材料中甲醛、乙醛向Tenax中的迁移规律。研究表明,甲醛、乙醛迁移行为随时间变化趋势大致相同,均呈现迁移率随迁移时间延长先迅速增大,后又减小达到一个常数;甲醛和乙醛迁移率受温度的影响不同,达到平衡后,甲醛在30℃下迁移率最高,乙醛在70℃和50℃下迁移率高;甲醛和乙醛向Tenax中的迁移率差异较大,达到平衡后,乙醛的迁移率远高于甲醛。     

气相色谱-质谱法测定聚对苯二甲酸乙二醇酯瓶装水中乙醛的迁移量

提出了测定聚对苯二甲酸乙二醇酯(PEGTP)瓶装纯水中乙醛迁移量的气相色谱质谱法。水样(100mL)中乙醛用2,4-二硝基苯肼在pH 3柠檬酸盐缓冲溶液10mL中,于40℃水浴上振荡1h加热使之衍生化。冷却后用二氯甲烷萃取3次,每次10mL。萃取液于40℃旋转蒸发至1.0mL,分取1分L进样分析。采用DB-5MS毛细管柱及在70℃～280℃范围内程序升温进行分离。线性范围在300μg·L~(-1)以内,检出限(3S/N)为1μg·L~(-1),加入50μg·L~(-1)及100μg·L~(-1)标准溶液做回收试验及精密度试验,测得平均回收率为88%,相对标准偏差(n=5)依次为5.4%及4.5%。     

Kinetic Study of the Electro‐Catalytic Oxidation of Acetaldehyde on Copper Electrode

Electrocatalytic oxidation of acetaldehyde was investigated on a copper electrode in alkaline solution. The process of oxidation involved and its kinetics were established by using cyclic voltammetry and chronoamperometry techniques as well as steady state polarization measurements. It has been found that in the course of an anodic potential sweep the electro‐oxidation of acetaldehyde follows the formation of Cu(III) and is catalysed by this species through a mediated electron transfer mechanism. A mechanism based on the electrochemical generation of Cu(III) active sites and their subsequent consumption by the acetaldehyde in question was also investigated.     

AlOOH结构对甲醇和一氧化碳反应性能的影响

利用水热法制备了3种AlOOH催化剂,对其进行了表征,并用于催化甲醇和一氧化碳反应.结果表明,适宜的AlOOH结构有利于催化甲醇和一氧化碳反应生成高选择性(≥97.28%)的乙醛,且AlOOH结构的差异会导致反应产物分布出现明显区别.其中,结晶度高、孔径较大、能提供CO解离吸附中心且表面具有适宜酸碱性的AlOOH催化剂表现出高的乙醛选择性,推测乙醛的生成是通过中间体CH_3与HCO的偶联实现的.     

乙醛光解动力学的离子速度成像

利用时间切片离子速度成像技术在275～321 nm能量范围内重新研究了乙醛自由基通道CH₃+HCO的光解动力学. 通过共振增强多光子电离的方法探测甲基碎片. 对甲基的伞形振动基态和激发态(v₂=0和1)进行了影像探测. 乙醛通过T₁电子态系间窜越到S₁电子态的解离产物具有很高的动能释放和很低的内能激发,碎片的振动能和转动能随激发能量的增加而增加. 乙醛T₁电子态的势垒高度经测量高于基电子态3.881±0.006 eV.     

Photocatalysis of sprayed nitrogen-containing Fe2O3–ZnO and WO3–ZnO composite powders in gas-phase acetaldehyde decomposition

Two series of nano-sized N-containing MO_x–ZnO (M: Fe, W) composite powders were synthesized by spray pyrolysis. The nitrogen content was controlled from 500 to 2100 ppm by changing the powder ingredients and spray pyrolysis temperature. Ultraviolet-visible (UV-Vis) spectra indicated that the N-containing MO_x–ZnO powders absorbed not only ultraviolet light (λ<387 nm) like pure ZnO powder, but also part of visible light (λ<650 nm). Acetaldehyde decomposition was used as a probe reaction to evaluate the photocatalysis of these composite powders. The photocatalytic activity of the N-containing ZnO powder was pronouncedly enhanced by the WO₃ addition under both UV and visible-light irradiation. However, that of the N-containing ZnO powder was suppressed by the Fe₂O₃ addition. A model of the semiconductor energy-band structure is proposed to explain the enhancement and suppression of photocatalytic activity.     

Thermal decomposition of surface compounds for the generation of small quantities of acetaldehyde: Calibration of a thermal desorption-gas chromatography-flame ionization detection

The paper presents a new method for the generation of acetaldehyde in the amounts that allow to calibrate the measuring system. The method is based on thermal decomposition of surface compounds at the range 130-190 °C, in which an acetaldehyde as the decomposition product is released. The synthetic pathway leading to the desired surface compounds is described. Investigations demonstrated that the synthesis of the compounds on the surface of the support material (silica gel) was carried out homogeneously. The technique proposed was used for the generation of gaseous standard mixtures containing acetaldehyde for the calibration of a thermal desorber-gas chromatograph-flame ionization detector system.     

广州市住宅室内外大气羰基化合物的监测分析

选择代表性住宅,在其室内、外同步开展大气羰基化合物的监测分析,准确评价大气羰基化合物的污染状况,揭示其来源。用涂覆2,4-硝基苯肼(DNPH)的硅胶采样管收集羰基化合物,借助高效液相色谱完成样品分析,共检测了13种羰基化合物,其中甲醛、乙醛两种物质的平均浓度最高,占被测物质总浓度的30%~67%。甲醛、乙醛的浓度,夏季室内平均为53.47μg/m3、17.81μg/m3,室外平均为15.00μg/m3、10.97μg/m3;冬季室内平均为37.97μg/m3、11.49μg/m3,室外平均为10.44μg/m3、8.15μg/m3。大气羰基化合物呈现夏季高于冬季、室内大于室外的浓度变化规律。甲醛/乙醛和乙醛/丙醛比值结果反映城市大气羰基化合物的人为污染。     

Hydrogen-atom production channels of acetaldehyde photodissociation: Direct DFT molecular dynamics study

Direct density-functional (DFT) molecular dynamics (MD) calculations have been carried out for the following two hydrogen-atom production channels in acetaldehyde photodissociation on the lowest triplet-state (T₁) potential energy surface (PES): CD₃CHO → CD₂CHO + D (1) and CD₃CHO → CD₃CO + H (2). The employed DFT method was B3LYP with the cc-pVDZ basis set. The average product hydrogen kinetic energies estimated from the results of the direct DFT MD calculations were 18.3 and 16.6 kcal mol⁻¹ for reactions 1 and 2, respectively, and these were half – two thirds of the previously measured values [T.Y. Kang, S.W. Kang, H.L. Kim, Chem. Phys. Lett. 434 (2007) 6]. This is because of the low reverse barrier heights predicted at the B3LYP/cc-pVDZ level. The present results for the product hydrogen kinetic energies, however, agree qualitatively with the experimental measurements and strongly supports the mechanisms taking place on the T₁ PES.