Biosynthesis of zinc oxide nanoparticles using Euphorbia milii leaf constituents: Characterization and improved photocatalytic degradation of methylene blue dye under natural sunlight

A facile biosynthesis route was followed to prepare zinc oxide nanoparticles (ZnO NPs) using Euphorbia milii (E. milii) leaf constituents. The SEM images exhibited presence of spherical ZnO NPs and the corresponding TEM images disclosed monodisperse nature of the ZnO NPs with diameter ranges between 12 and 20 nm. The Brunauer–Emmett–Teller (BET) analysis revealed that the ZnO NPs have specific surface area of 20.46 m²/g with pore diameter of 2 nm–10 nm and pore volume of 0.908 cm³/g. The EDAX spectrum exemplified the existence of Zn and O elements and non-appearance of impurities that confirmed pristine nature of the ZnO NPs. The XRD pattern indicated crystalline peaks corresponding to hexagonal wurtzite structured ZnO with an average crystallite size of 16.11 nm. The FTIR spectrum displayed strong absorption bands at 512 and 534 cm^?1 related to ZnO. The photocatalytic action of ZnO NPs exhibited noteworthy degradation of methylene blue dye under natural sunlight illumination. The maximum degradation efficiency achieved was 98.17% at an illumination period of 50 min. The reusability study proved considerable photostability of the ZnO NPs during photocatalytic experiments. These findings suggest that the E. milii leaf constituents can be utilized as suitable biological source to synthesis ZnO NPs for photocatalytic applications.     

纳米TiO_2用于甲基橙溶液的光催化氧化研究

本实验采用纳米级的二氧化钛,对甲基橙溶液进行了紫外光催化氧化处理,探讨了pH的影响和添加Fe3+的效果及反应动力学方程,结果表明,采用UV/O3/TiO2工艺对其进行处理,pH4-5时,10W紫外灯光照60min,CODcr去除率达84%,脱色率达96%以上。添加Fe3+,对溶液的催化降解速度提高不明显。动力学研究表明,CODcr降解速度对CODcr的浓度为一级反应。     

Photooxidation of aqueous trichloroethylene using a buoyant photocatalyst with reaction progress monitored via micro-headspace GC/MS

Although photooxidation has previously been shown to be successful in removing organic contaminants from water, methods combining the rapid photooxidation of the desired contaminant with easy catalyst manipulation and removal are few and far between. In the absence of an easy means of catalyst removal, the photooxidation process becomes more costly and time consuming, and photocatalysis cannot be employed as an in situ method for the remediation of aqueous organic contaminants. In this study, the photocatalyst was added to an aqueous trichloroethylene (TCE) solution in the form of TiO₂-coated buoyant microspheres. The solution, placed in a flow-cell photoreactor along with the buoyant catalyst, was irradiated with a UV-filtered Xenon light source. Limited sample sizes necessitated the development of a low-cost headspace GC/MS analysis method, utilizing a standard direct-injection autosampler. This analytical technique aptly monitored reaction progress and indicated that aqueous TCE concentration decreases by nearly 90% in the first hour of irradiation. Subsequent solvent extraction GC/MS analysis indicated that the TCE is initially sorbed by the photocatalyst spheres, but as irradiation continued, TCE is removed from the catalyst spheres surfaces. During the course of irradiation, the expected TCE mineralization product hydrochloric acid appeared, as indicated by a decrease in pH and ion chromatography analysis. The microsphere-born catalyst was easily removed from the treated solution by filtration. Thus, it is possible that a method for effective, low-cost in situ photooxidation of aqueous organic contaminants will be realized in the near future.     

X-ray photoelectron spectroscopy characterization of composite TiO2–poly(vinylidenefluoride) films synthesised for applications in pesticide photocatalytic degradation

X-ray photoelectron spectroscopy (XPS) was adopted for the analytical characterization of composite titanium dioxide–poly(vinylidenefluoride) (TiO₂–PVDF) films developed for applications in the photocatalytic degradation of pollutants.

The composites were deposited on glass substrates by casting or spin coating from TiO₂–PVDF suspensions in dimethylformamide (DMF). XPS data on the TiO₂–PVDF surface composition were used to optimize preparation conditions (composition of the TiO₂/PVDF suspension, deposition technique) in terms of titanium dioxide surface amount and film stability.

The use of spin-coating deposition and the increase of TiO₂ amount in the DMF suspensions were found to improve the titanium surface content, although high TiO₂/PVDF ratios led to film instability. PVDF–TiO₂ films were also used in preliminary photocatalytic degradation tests on isoproturon, a phenylurea herbicide, under solar UV irradiation; the results were compared to direct photolysis to evaluate the catalytic efficiency of immobilized TiO₂ and the role played by the PVDF film during the degradation process.     

ZnO超微粒子光催化氧化降解n-C7H16的研究

利用ZnO光催化氧化技术对气相n-C7H16进行了降解研究，考察了氧气、水燕气体积分数等因素对n-C7H16光催化氧化的影响，利用气相色谱－质谱联用仪和气相色谱仪对气相光催化反应过程中的气体组成进行了定性分析，并对主要中间产物丙醛进行了定量分析，结果发现，ZnO超微粒子光催化氧化n-C7H16的降解率较高，n-C7H16绝大部分被完全氧化成CO2，探讨了n-C7H16光催化氧化反尖的动力学行为及机理。     

Characterization of mesoporous nanocrystalline TiO2 photocatalysts synthesized via a sol-solvothermal process at a low temperature

Nanocrystalline TiO₂ samples with mesoporous structure were prepared via a solvothermal treatment of surfactant-stabilized TiO₂ sols. The samples were obtained from media of different acidities including nitric acid, deionized water, and ammonia (denoted as HT-1, HT-2 and HT-3, respectively). These samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N₂-sorption (BET surface area), micro-Raman spectroscopy, infrared absorption spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples were tested by the self-photosensitized degradation of an azo dye, Mordant Yellow 10 (MY), in aqueous solution under visible light irradiation. The results reveal that all three samples have high surface area and are pure anatase phase. The sample prepared in nitric acid medium possesses the most ideal mesoporous structure and also exhibits a blue shift in the Raman spectrum. All three samples show much higher photocatalytic activity than the commercial P-25. The activity order of the three samples is HT-1>HT-2>HT-3.     

微波辅助快速制备2D/1D ZnIn2S4/TiO2 S型异质结及其光催化制氢性能

The threat and global concern of energy crises have significantly increased over the last two decades. Because solar light and water are abundant on earth, photocatalytic hydrogen evolution through water splitting has been considered as a promising route to produce green energy. Therefore, semiconductor photocatalysts play a key role in transforming sunlight and water to hydrogen energy. To date, various photocatalysts have been studied. Among them, TiO₂ has been extensively investigated because of its non-toxicity, high chemical stability, controllable morphology, and high photocatalytic activity. In particular, 1D TiO₂ nanofibers (NFs) have attracted increasing attention as effective photocatalysts because of their unique 1D electron transfer pathway, high adsorption capacity, and high photoinduced electron–hole pair transfer capability. However, TiO₂ NFs are considered as an inefficient photocatalyst for the hydrogen evolution reaction (HER) because of their disadvantages such as a large band gap (~3.2 eV) and fast recombination of photoinduced electron–hole pairs. Therefore, the development of a high-performance TiO₂ NF photocatalyst is required for efficient solar light conversion. In recent years, several strategies have been explored to improve the photocatalytic activity of TiO₂ NFs, including coupling with narrow-bandgap semiconductors (such as ZnIn₂S₄). Recently, microwave (MW)-assisted synthesis has been considered as an important strategy for the preparation of photocatalyst semiconductors because of its low cost, environment-friendliness, simplicity, and high reaction rate. Herein, to overcome the above-mentioned limiting properties of TiO₂ NFs, we report a 2D/1D ZnIn₂S₄/TiO₂ S-scheme heterojunction synthesized through a microwave (MW)-assisted process. Herein, the 2D/1D ZnIn₂S₄/TiO₂ S-scheme heterojunction was constructed rapidly by using in situ 2D ZnIn₂S₄nanosheets decorated on 1D TiO₂ NFs. The loading of ZnIn₂S₄ nanoplates on the TiO₂ NFs could be easily controlled by adjusting the molar ratios of ZnIn₂S₄ precursors to TiO₂ NFs. The photocatalytic activity of the as-prepared samples for water splitting under simulated solar light irradiation was assessed. The experimental results showed that the photocatalytic performance of the ZnIn₂S₄/TiO₂ composites was significantly improved, and the obtained ZnIn₂S₄/TiO₂ composites showed increased optical absorption. Under optimal conditions, the highest HER rate of the ZT-0.5 (molar ratio of ZnIn₂S₄/TiO₂= 0.5) sample was 8774 μmol·g^-1·h^-1, which is considerably higher than those of pure TiO₂ NFs (3312 μmol·g^-1·h^-1) and ZnIn₂S₄nanoplates (3114 μmol·g^-1·h^-1) by factors of 2.7 and 2.8, respectively. Based on the experimental data and Mott-Schottky analysis, a possible mechanism for the formation of the S-scheme heterojunction between ZnIn₂S₄ and TiO₂ was proposed to interpret the enhanced HER activity of the ZnIn₂S₄/TiO₂heterojunctionphotocatalysts.      

芥子气模拟剂2-氯乙基乙基硫醚的光催化降解

利用连续流动微反、原位红外和GC/MS等手段考察了芥子气模拟剂2-氯乙基乙基硫醚（2-CEES）在P25 TiO2上的光催化降解反应,证实CO2和H2O是这个反应的最终产物.详细的跟踪分析表明,除了CO2和H2O外,在反应的气相混合物中可检测到C2H4、CH3CHO、CH4、CO、HCl和H2S；少量小分子的羧酸、醚和砜；微量C2H5SC2H5、C2H5S2C2H5、C2H5SC2H4Cl和CH2ClCH2Cl等中间产物;在反应后的催化剂表面可检测到C2H5S2C2H5、C2H5SC2H4OH、C4H9S2C2H5和C2H5S2C2H4OH、等物.根据这些结果提出了2-CEES光催化降解的反应机理,推断2-CEES的光催化降解涉及脱氯、C－S键断裂、有机硫化物光聚合和裂解等复杂过程最终转化为CO2和H2O.认为各种硫物种在表面的积聚引起了催化剂的缓慢失活.