Facile synthesis of ZnO nanoparticles for the photocatalytic degradation of methylene blue

Journal of Sol-Gel Science and Technology - ZnO nanoparticle photocatalysts with a grain size range of 20–100?nm were prepared via a simple sol–gel method and characterized by...     

Emulsion polymerization of styrene in a single continuous stirred-tank reactor

The effects of mean residence time, initiation rate, and emulsifier concentration on particle formation, particle growth, and polymerization rate are examined for the emulsion polymerization of styrene in a completely mixed continuous stirred-tank reactor. Experimental measurements of number of particles, particle size distribution, polymerization rate, and molecular weights are compared with theoretical predictions. A theoretical model which incorporates Stockmayer's modification of the Smith-Ewart theory into the particle growth equation allows reasonably accurate prediction of polymerization rate, particle formation rate, and particle size distribution. Agreement between experimental measurements of number-average and weight-average molecular weights and a theory based on Smith-Ewart case 2 kinetics is also reasonable.     

可见光光催化降解抗生素研究进展

随着抗生素废水在水体和陆地生态系统的肆意排放,抗生素污染已成为当今世界重要的环境问题。由于抗生素废水具有生物毒性大、含有抑菌物质等特点,传统的物理吸附法、生物处理法在处理这类难降解有毒有机废水,尤其是含残留微量抗生素的废水时效果较差。为了解决抗生素废水所引起的环境危机,人们尝试了许多方法。近年来,光催化技术作为一种适用范围广、反应速率快、氧化能力强、无污染或少污染的处理抗生素废水的方法受到人们广泛关注。半导体材料在太阳光照射下,可产生具有较强氧化作用的羟基或超氧自由基,从而起到降解抗生素分子的作用。然而,传统的光催化处理抗生素废水光催化剂主要局限于 TiO2半导体,它存在太阳光谱吸收范围窄、光生电荷复合率高等问题,严重制约其工业化应用。因此,人们一直致力于开发高效、稳定的可见光响应型光催化剂。本文根据光催化技术的基本原理,综述了目前几种基于不同策略设计开发可见光光催化降解抗生素废水的新型光催化剂的方法。
　　离子掺杂改性宽带隙半导体是开发高效可见光光催化剂的常用方法。通过过渡金属离子或非金属离子掺杂改性,可以使传统的 TiO2和SrTiO3等紫外光催化剂吸收带边发生红移,响应可见光,从而显著提高可见光下光催化剂降解抗生素的效率。然而必须注意的是,掺杂的金属离子本身会成为电子-空穴复合点位,因此,过量的掺杂金属或非金属离子可能会降低其光催化活性。考虑到单一半导体材料在光催化反应中存在的光生载流子容易复合、可见光利用率低等问题,构建异质结构复合光催化体系,通过不同半导体之间的协同作用,促进光生电荷的分离与转移,是获得高效光催化体系的重要策略之一。典型的 II型异质结光催化剂,当不同的半导体紧密接触时,由于异质结两侧能带等性质的不同会形成空间电势差,从而有利于光生载流子的分离,光催化效率提高。作为一种复合光催化体系,表面等离子体共振增强型光催化体系近年来引起了国内外学者的广泛关注。 Ag, Au和Pd金属纳米粒子在吸收光后其表面发生等离共振,随后等离子体发生衰减,把聚集的能量转移到半导体材料的导带。这个过程产生的高能电子(热电子),逃离贵金属纳米粒子而被与其接触的半导体收集,从而形成金属-半导体肖特基接触。形成的肖特基结可以显著提高光催化的光生电荷分离效率,从而提高光催化降解抗生素活性。
　　目前,与传统物化法/生化法相比,光催化技术用于处理抗生素废水具有十分明显的技术优势,在水处理方面有着很好的应用前景。针对目前光催化体系存在的光生载流子容易复合的巨大挑战,今后,构筑高效复合光催化体系(例如石墨烯基二维复合光催化剂在光生电荷分离、太阳光利用率等方面已展现出较好的综合性能)将成为高效光催化降解抗生素催化剂研发的重要方向之一。     

Ag nanoparticles loaded on porous graphitic carbon nitride with enhanced photocatalytic activity for degradation of phenol

Highly efficient photocatalyst of visible-light-driven Ag nanoparticles loaded on porous graphitic carbon nitride (g-C₃N₄) was prepared by the reduction of Ag ions on porous g-C₃N₄. The obtained Ag/porous g-C₃N₄ composite products were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflection spectra (DRS), thermal gravimetric analysis (TGA). The results demonstrated that a homogeneous distribution of Ag NPs of 10 nm was attached onto the surface of the porous g-C₃N₄. The prepared Ag/porous g-C₃N₄ samples were applied for catalyzing the degradation of phenol in water under visible light irradiation. Porous g-C₃N₄ demonstrated an excellent support for the formation and dispersion of small uniform Ag NPs. When the weight percentage of Ag reaches 5%, the nanohybrid exhibits superior photocatalytic activities compared to bulk g-C₃N₄, porous g-C₃N₄, and 2% Ag/porous g-C₃N₄ hybrids. The enhanced photocatalytic performance is due to the synergic effect between Ag and porous g-C₃N₄, which suppressed the recombination of photogenerated electron-hole pairs.     

Design and tailoring of one-dimensional ZnO nanomaterials for photocatalytic degradation of organic dyes: a review

Research on Chemical Intermediates - Photocatalysis using semiconductors has emerged as a promising wastewater treatment process to overcome the major challenges faced by conventional technologies....     

Electrospun Pd-doped ZnO nanofibers for enhanced photocatalytic degradation of methylene blue

Pure and Pd-doped ZnO nanofibers were synthesized via an electrospinning technique, in which polyvinylpyrrolidone was used as the fiber template, zinc acetate/palladium chloride as the precursors, and a mixture of ethanol/acid acetate/water at ratio of 8:5:2 (v/v/v) as the co-solvent. The electrospun fibers were calcined at 600 °C in air for 2 h and characterized by various methods. The photocatalytic activity of the pure and Pd-doped ZnO nanofibers was studied through the photodegradation of methylene blue. Comparing to the pure ZnO nanofibers, the Pd-doped catalysts showed a much enhanced photodegradation efficiency. The possible mechanism was also discussed.     

Etching graphitic carbon nitride by acid for enhanced photocatalytic activity toward degradation of 4-nitrophenol

Graphitic carbon nitride （g-C3N4） with high photocatalytic activity toward degradation of 4-nitrophenol under visible light irradiation was prepared by HCI etching followed by ammonia neutralization. The structure, morphology, surface area, and photocatalytic properties of the prepared samples were studied. After treatment, the size of the g-C3N4 decreased from several micrometers to several hundred nanometers, and the specific area of the g-C3N4 increased from 11.5 m2/g to 115 m2/g. Meanwhile, the photocatalytic activity of g-C3N4 was significantly improved after treatment toward degradation of 4- nitrophenol under visible light irradiation. The degradation rate constant of the small particle g-C3N4 is 5.7 times of that of bulk g-C3N4, which makes it a promising visible light photocatalyst for future applications for water treatment and environmental remediation.     

聚乙烯塑料在连续超临界水反应器中的油化研究

在连续超临界水（SCW）反应器中考察了反应温度、停留时间和反应压力对聚乙烯（PE）降解油化的影响。实验结果表明,在120s、25MPa下,从500℃提高到550℃,液体收率呈现先升后降的趋势,在530℃达到最大值（79%）;在520℃、25MPa下,随停留时间的延长,PE裂解程度加深,产物轻质化程度提高,导致液体收率降低,停留240s时,气体收率达到43%;反应压力对产物收率的影响较小,气、液产物中烯/烷比随反应压力的增加而增大。     

Photocatalytic degradation intrinsic kinetics of gaseous cyclohexane in a fluidized bed photocatalytic reactor

The special photocatalytic degradation intrinsic kinetics of gaseous cyclohexane were investigated in a designed fluidized bed photocatalytic reactor (FBPR). A series of photocatalytic kinetic reaction equations were developed to explore the relationship of degradation efficiency and operating variables based on photocatalytic mechanism and particle fluidization hydrodynamic characteristics. The corresponding results indicated that the initial concentration has influenced the photocatalytic degradation reaction conversion, and having a concentration inflexion point which theoretically divided the photocatalysis into a first-order apparent kinetic rate equation at low concentrations and a zero-order kinetic rate equation at high concentrations. Furthermore, these results were validated theoretically by the intrinsic kinetic models of photocatalytic degradation conversion developed according to variation of cyclohexane concentration and gas velocity. Based on the experimental results, the optimal operating gas velocity range was determined. The multi-factors synergy effect resulting from gas velocity on photocatalytic degradation efficiency was explored and proved by mass transfer, illumination transmission and adsorption models. Finally, the degradation pathways of the cyclohexane and deactivation mechanism of the photocatalyst were studied according to the intermediates degraded on TiO₂ surface, and a feasible method presented for catalyst regeneration.     

Bifunctional copper modified graphitic carbon nitride catalysts for efficient tetracycline removal: Synergy of adsorption and photocatalytic degradation

In order to efficiently remove tetracycline in wastewater through the synergistic effect of adsorption and photocatalytic degradation, a series of novel composite materials (Cu doped g-C₃N₄) were synthesized by two-pot hydrothermal method. It was found that the composite materials with optimized ratio (Cu/CN-1) displayed outstanding adsorption and photocatalytic performance as compared with pure g-C₃N₄ photocatalyst. The removal efficiency of tetracycline (TC, 50 mg/L) reached almost 99% within 30 min by Cu/CN-1 through the synergy of adsorption and photocatalysis under visible-light irradiation, which was the highest removal efficiency ever reported. The adsorption kinetics and isotherms of TC on the Cu/CN-1 were well fitted with the pseudo-second-order kinetic model and Langmuir model, respectively. Moreover, it was confirmed that the main effective reactive groups were O₂⁻ and h⁺ in photocatalytic process. The Cu/CN-1 exhibited high stability and excellent reusability after five cycle experiments. Finally, the mechanism of synergy between Cu and g-C₃N₄ was proposed: on the one hand, the decoration of Cu particles significantly increased the adsorption sites of Cu/CN-1 to tetracycline, on the other hand, the modification of Cu particles effectively inhibits charge recombination and broadens the visible light absorption range of the photocatalyst.This study provided a promising photocatalyst to be used for TC removal in the actual wastewater.     

Kinetics of heterogeneous photocatalytic degradation of reactive dyes in an immobilized TiO2 photocatalytic reactor

The photocatalytic degradation of two reactive dyes has been investigated by UV/TiO2/H2O2 using an immobilized TiO2 photocatalytic reactor. Reactive Blue 8 (RB 8) and Reactive Blue 220 (RB 220) textile dyes were used as model compounds. Photocatalytic degradation processes were performed using a 5-L solution containing dyes. The initial concentrations of dyes were 50 mg/L. The radiation source was two 15 W UV-C lamps. A batch mode immersion photocatalytic reactor was utilized. UV-vis and ion chromatography (IC) analyses were employed to obtain the details of the photodegradation of the selected dyes. Colored synthetic waters were completely decolorized in relatively short time after UV irradiation in the presence of various concentrations of hydrogen peroxide. Formate, acetate, oxalate, and glyoxylate anions were detected as dominant aliphatic intermediates where they were further oxidized slowly to CO2. The UV/TiO2/H2O2 process was able to oxidize the dyes with partial mineralization of carbon, nitrogen, and sulfur heteroatoms into CO2, NO3-, and SO4(2-), respectively. Kinetics analysis indicates that the photocatalytic decolorization rates of the dye can be approximated by a pseudo-first-order model. The UV/TiO2/H2O2 process proved to be capable of decolorization and mineralization of the reactive dyes (RB 8 and RB 220).     

Preparation of photocatalytic ZnO nanoparticles and application in photochemical degradation of betamethasone sodium phosphate using taguchi approach

In this study, ZnO nanoparticles were prepared by a sol-gel method for the first time. Taguchi method was used to identify the several factors that may affect degradation percentage of betamethasone sodium phosphate in wastewater in UV/K₂S₂O₈/nano-ZnO system. Our experimental design consisted of testing five factors, i.e., dosage of K₂S₂O₈, concentration of betamethasone sodium phosphate, amount of ZnO, irradiation time and initial pH. With four levels of each factor tested. It was found that, optimum parameters are irradiation time, 180 min; pH 9.0; betamethasone sodium phosphate, 30 mg/L; amount of ZnO, 13 mg; K₂S₂O₈, 1 mM. The percentage contribution of each factor was determined by the analysis of variance (ANOVA). The results showed that irradiation time; pH; amount of ZnO; drug concentration and dosage of K₂S₂O₈ contributed by 46.73, 28.56, 11.56, 6.70, and 6.44%, respectively. Finally, the kinetics process was studied and the photodegradation rate of betamethasone sodium phosphate was found to obey pseudo-first-order kinetics equation represented by the Langmuir-Hinshelwood model.     

Effect of the oxygen transfer coefficient on xylitol production from sugarcane bagasse hydrolysate by continuous stirred-tank reactor fermentation

The effect of the oxygen transfer coefficient on the production of xylitol by biocon version of xylose present in sugarcane bagasse hemicellulosic hydrolysate using the yeast Candiada guilliermondii was investigated. Continuous cultivation was carried out in a 1.25-L fermentor at 30°C, pH 5.5, 300 rpm, and a dilution rate of 0.03/h, using oxygen transfer coefficients of 10,20, and 30/h. The results showed that the microbial xylitol production (11 g/L) increased by 108% with the decrease in the oxygen volumetric transfer coefficient from 30 to 20/h. The maximum values of xylitol productivity (0.7g/[L…h]) and yield (0.58 g/g) were obtained at k _L a 20/h.     

A new optical fiber reactor for the photocatalytic degradation of gaseous organic contaminants

The main objective of this study was to develop a simple, energy-efficient photoreactor for operating at room temperature. In this work, the design of a new gas-phase optical fiber photoreactor (OFP) was introduced which operated under various parameters, such as the UV light intensity and the initial concentration for the photocatalytic decomposition of acetone. Experimental results indicated that increasing the UV light intensity or decreasing the initial concentrations of acetone by a UV/TiO₂ process would result in improving the decomposition and mineralization efficiencies. The apparent quantum yield of the novel optical fiber reactor is about 2 to 3 times greater than that of the traditional annular reactor.     

Facile fabrication of ZnO/N‐doped helical carbon nanotubes composites with enhanced photocatalytic activity toward organic pollutant degradation

Novel ZnO/N‐doped helical carbon nanotubes (ZnO/N‐HCNTs) composites were successfully synthesized via a facile chemical precipitation approach at room temperature. The sample was well characterized by X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDS), transmission electron microscopy (TEM) and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). The photocatalytic activity was evaluated in the degradation of methylene blue (MB) aqueous solution under UV light irradiation. It is found that ZnO nanoparticles were highly and uniformly anchored on the surface and inner tubes of the N‐HCNTs with size of about 5 nm, and significantly enhanced the photocatalytic activity compared to pure ZnO. The enhanced photocatalytic activity of ZnO/N‐HCNTs composites can be ascribed to the integrative synergistic effect of effective interfacial hybridization between N‐HCNTs and ZnO nanoparticles and the prolonged lifetime of photogenerated electron–hole pairs. Moreover, the ZnO/N‐HCNTs could be easily recycled without any obvious decrease in photocatalytic activity and could be promote their application in the area of environmental remediation.     

Synthesis of ZnO nanoparticles and its application in photocatalytic degradation of LABS by the trial-and-error and Taguchi methods

In the work ZnO nanoparticles were prepared by sol-gel method. The catalyst was characterized by X-ray powder diffractometer (XRD), scanning electron microscopy (SEM). The photocatalytic oxidation of anionic surfactant in detergent industries was studied using ZnO nanoparticles with diameter size 20 nm as catalyst on irradiation with UV light. Analysis of kinetic showed that the amount of surfactant photocatalytic degradation can be fitted with pseudo-first-order model and studied photochemical elimination of Linear alkyl benzene sulfonates by the trial-and-error and Taguchi methods. Our experimental design consisted of testing five factors, i.e. dosage of K₂S₂O₈, concentration of surfactant, amount of ZnO, irradiation time, and initial pH. The results showed that photocatalytic degradation of linear alkyl benzene sulfonates was strongly influenced by these parameters.     

Microwave-assisted synthesis of ZnO and its photocatalytic activity in degradation of CTAB

Nanosized zinc oxide (nano-ZnO) was prepared by a microwave irradiation method using zinc nitrate and triethanolamine as starting materials and distilled water as a solvent. The as-prepared powder was characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photocatalytic degradation of cetyltrimethylammonium bromide (CTAB) using the prepared material under UV irradiation was studied.The effects of ZnO dosage and initial pH on the photodegradation of CTAB were investigated. As the ZnO load increased, the CTAB degradation first increased and then decreased. The optimum ZnO dosage was 3 g L^–1. Photodegradation of CTAB is more efficient in slightly alkaline media (pH 9).     

Fabrication and characterization of ZnO particles with different morphologies for photocatalytic degradation of pentachlorophenol

In this work, ZnO particles with different morphologies were successfully prepared by a simple solution route at low temperature. The products were characterized by SEM, EDS, XRD, TEM, HRTEM, SAED, TG–DTA and UV–Vis DRS. To further understand the formation processes of these ZnO particles, XRD analyses of the intermediates and concentration measurements of Zn(II) remaining in the reaction solution were made at regular intervals throughout the reactions. A possible formation mechanism is discussed. Photocatalytic activity of the as-prepared ZnO powders, evaluated by degradation of pentachlorophenol under UV irradiation, is found to be closely related to the particle morphology.     

Preparation of Mn-doped ZnO nanostructured for photocatalytic degradation of Orange G under solar light

Research on Chemical Intermediates - In this study, undoped ZnO and Mn-doped ZnO nanostructured with different doping concentrations were prepared through a facile chemical method. Then, X-ray...     

Comparison between the performance of an immobilized impinging jet stream reactor and a slurry impinging jet stream reactor for photocatalytic phenol degradation

A new immobilized photocatalytic impinging jet stream reactor was designed, and the influences of the effective parameters like jet flow rate, TiO₂ coating disc diameter, nozzle-to-disc distance, and initial concentration on phenol removal were investigated. The reactor was also used as a slurry reactor, and degradation efficiencies in both reactors were compared based on their catalyst loading. The results indicated that the slurry reactor has a higher degradation efficiency than the immobilized reactor at the same TiO₂ loading and other operational conditions. The slurry reactor needs to separate and recover the TiO₂ nanoparticles from the reaction medium which increases the overall process complexity and cost, while the immobilized reactor could be reused at least 4times without any significant decrease in removal efficiency. RTD result indicates that the tank in series model (N?=?5) could properly predict the reactors hydrodynamic behavior.