γ-MnOOH低温催化降解异味气体正己醛:锰缺陷的影响（英文）

正己醛是室内常见的挥发性有机物,主要由板材类家具等释放,由于其嗅味阈值很低、检出率高,是引起室内异味的主要成分之一,目前对正己醛的催化去除研究很少.γ-MnOOH是常见的羟基锰氧化物,常作为合成其他锰氧化物的前驱体,在超级电容、离子电池、催化等领域有广泛的应用前景,但将其作为气相反应催化剂的研究较少,关于γ-MnOOH中锰缺陷含量对其催化性能的影响未有报道.本文通过两种水热反应体系制备了结晶性良好的γ-MnOOH催化剂,通过在高锰酸钾-乙二醇制备体系中添加一定量的硫酸制备了高锰缺陷含量的γ-MnOOH催化材料,通过正己醛的动态催化氧化反应体系对不同样品的催化性能进行了评价.结果表明,高锰缺陷含量的γ-MnOOH对正己醛具有很高的催化活性,85℃下可以将浓度为15ppm、相对湿度50%、质量空速(GHSV)为240L/(g·h)的正己醛完全去除,在160℃下可将正己醛完全转化为CO2.通过X射线衍射、扫描电镜、透射和高分辨透射电镜、N2吸附-脱附,拉曼光谱(Raman)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)、氧气程序升温脱附(O2-TPD)和电子自旋共振谱(ESR)对材料的结构、形貌及物理化学性质等进行了表征,并通过热脱附-气相色谱/质谱联用(ATD-GC/MS)和原位红外光谱分别对正己醛催化氧化反应中的气相产物、催化剂表面的中间物种进行了鉴别.材料结构和形貌表征结果表明,高锰缺陷含量的γ-MnOOH结晶性相对较差,表面晶格条纹畸变及化学键无序性很大,锰的平均价态较高;H2-TPR和O2-TPD的测试结果表明,添加硫酸制备的催化剂起始还原温度低,还原过程连续性及晶格氧的迁移转化能力增强,表面吸附氧物种含量增大;ESR的测试结果也表明,该材料活化氧气产生超氧自由基(?O2^–)的能力更强,这些都有利于提高催化剂的催化活性.ATD-GC/MS的表征结果表明,当正己醛未完全分解时,正戊醛和正丁醛是最主要的气相产物;通过原位红外对催化过程中催化剂表面的中间物种进行测定,检测到醛类和羧酸类的吸收峰,由此推测正己醛的催化氧化途径为正己醛氧化为己酸,脱羧并氧化生成正戊醛,后者再被氧化脱羧,最终正己醛被逐级完全降解.

Research advances on blockchain-as-a-service:architectures,applications and challenges

Due to the complexity of blockchain technology,it usually costs too much effort to build,maintain and monitor a blockchain system that supports a targeted application.To this end,the emerging“Blockchain as a Service”(BaaS)makes the blockchain and distributed ledgers more accessible,particularly for businesses,by reducing costs and overheads.BaaS combines the high computing power of cloud computing,the pervasiveness of IoT and the decentralization of blockchain,allowing people to build their own applications while ensuring the transparency and openness of the system.This paper surveys the research outputs of both academia and industry.First,it introduces the representative architectures of BaaS systems and then summarizes the research contributions of BaaS from the technologies for service provision,roles,container and virtualization,interfaces,customization and evaluation.The typical applications of BaaS in both academic and practical domains are also introduced.At present,the research on the blockchain is abundant,but research on BaaS is still in its infancy.Six challenges of BaaS are concluded in this paper for further study directions.

Ontology modeling of semantics in social media:Public issue knowledge base (PIKB)of the Weibo

Purpose:This study aims to construct an ontology to model the semantics of social media streams,in particular,trending topics and public issues.Design/methodology/approach:Our knowledge base included 10 public events and topics from Weibo respectively,which were collected through keyword search and a crawler program.We used a semi-automatic approach to model and annotate the semantics in social media,and adapted the multi-layered ontology to refine the design based on previous researches,then we used named entity recognition(NER) to extract entities to instantiate the ontology.Relationships were extracted based on co-occurrence measures.Finally,we manually conducted post-filtering evaluation and edited the extracted entities and relationships.Findings:An initial assessment demonstrated that our multi-layered ontology supports various types of queries and analyses in the public issue knowledge base(PIKB),which can serve as an effective tool to query,understand and trace public issues.Research limitations:Manual involvement cannot meet the requirements for challenges of sustainable developments.Since the relationships extracted are fully based on the co-occurrence of entities,rich semantic relationships,such as how much the key players have been involved,could not be fully reflected.Besides,the user evaluation is necessary for further ontology assessment.Practical implications:The PIKB can be used by regular Web users and policy makers to query,understand,and make sense of public events and topics.The methodology and reusable ontology model are useful for institutions that are interested in making use of the social media data.Originality/value:In this study,a multi-layered ontology is applied to model the evolving semantics of public events and trending topics in social media,and the semi-automatic approach could make it possible to extract entities and relationships from large amount of unstructured short texts of user generated content(UGC) from social media.

Identification and Analysis of Multi-tasking Product Information Search Sessions with Query Logs

Purpose： This research aims to identify product search tasks in online shopplng ana analyze the characteristics of consumer multi-tasking search sessions. Design/methodology/approach： The experimental dataset contains 8,949 queries of 582 users from 3,483 search sessions. A sequential comparison of the Jaccard similarity coefficient between two adjacent search queries and hierarchical clustering of queries is used to identify search tasks. Findings： （1） Users issued a similar number of queries （1.43 to 1.47） with similar lengths （7.3-7.6 characters） per task in mono-tasking and multi-tasking sessions, and （2） Users spent more time on average in sessions with more tasks, but spent less time for each task when the number of tasks increased in a session. Research limitations： The task identification method that relies only on query terms does not completely reflect the complex nature of consumer shopping behavior.Practical implications： These results provide an exploratory understanding of the relationships among multiple shopping tasks, and can be useful for product recommendation and shopping task prediction. Originality/value： The originality of this research is its use of query clustering with online shopping task identification and analysis, and the analysis of product search session characteristics.

Highly active copper-intercalated weakly crystallizedδ-MnO2 for low-temperature oxidation of CO in dry and humid air

Copper intercalated birnessite MnO2(δ-MnO2)with weak crystallinity and high specific surface area(421 m2/g)was synthesized by a one-pot redox method and investigated for low-temperature CO oxidation.The molar ratio of Cu/Mn was as high as 0.37,which greatly weakened the Mn-O bond and created a lot of low-temperature active oxygen species.In situ DRIFTS revealed strong bonding of copper ions with CO.As-synthesized MnO2-150Cu achieved 100%conversion of 250 ppm CO in normal air(3.1 ppm H2O)even at−10°C under the weight-hourly space velocity(WHSV)of 150 L/(g·h).In addition,it showed high oxygen storage capacity to oxidize CO in inert atmosphere.Though the concurrent moisture in air significantly inhibited CO adsorption and its conversion at ambient temperature,MnO2-150Cu could stably convert CO in 1.3%moisture air at 70°C owing to its great low-temperature activity and reduced competitive adsorption of water with increased temperature.This study discovers the excellent low-temperature activity of weakly crystallizedδ-MnO2 induced by high content intercalated copper ions.

Fabrication of MnO2 coating on aluminum honeycomb for fast catalytic decomposition of ozone at room temperature

Herein, the coating of MnO2nanomaterials on the surface of aluminum honeycomb was carried out to meet the requirements of high air velocity, low pressure drop and high activity in ozone removal scenarios. A commercially readily available waterborne silica sol mixed with waterborne acrylate latex was creatively utilized as the binder. A series of coating samples were prepared by spray coating method and evaluated focusing on their adhesion strength and catalytic activity towards ozone decomposition in an air duct at room temperature, by varying MnO2/binder mass ratio and number of sprayings. It was found that the adhesion strength of the catalytic coatings on the aluminum honeycomb increased with the increase of binder mass ratio, but the increased binder made the catalyst particles closely packed,resulting in reduced exposure of active sites and decrease of ozone conversion. Accordingly,catalyst slurry with 81.8 wt.% MnO2in dry coating and spraying times of two were determined as the optimal process parameters. As-prepared aluminum honeycomb filter with MnO2layer of 50 μm thickness achieved ozone conversion of 29.3%±1.7% under conditions of air velocity 3.0 m/sec, relative humidity50%, room temperature(26°C) and initial ozone concentration of 200 ppbV. This filter can be well adaptable to indoor air purification equipment operating at high air velocity with low wind resistance.

Review on design and evaluation of environmental photocatalysts

Heterogeneous photocatalysis has long been considered to be one of the most promising approaches to tackling the myriad environmental issues.However,there are still many challenges for designing efficient and cost-effective photocatalysts and photocatalytic degradation systems for application in practical environmental remediation.In this review,we first systematically introduced the fundamental principles on the photocatalytic pollutant degradation.Then,the important considerations in the design of photocatalytic degradation systems are carefully addressed,including charge carrier dynamics,catalytic selectivity,photocatalyst stability,pollutant adsorption and photodegradation kinetics.Especially,the underlying mechanisms are thoroughly reviewed,including investigation of oxygen reduction properties and identification of reactive oxygen species and key intermediates.This review in environmental photocatalysis may inspire exciting new directions and methods for designing,fabricating and evaluating photocatalytic degradation systems for better environmental remediation and possibly other relevant fields,such as photocatalytic disinfection,water oxidation,and selective organic transformations.

Catalytic decomposition of low level ozone with gold nanoparticles supported on activated carbon

Highly dispersed gold nanoparticles were supported on coal-based activated carbon(AC)by a sol immobilization method and were used to investigate their catalytic activity for low-level ozone decomposition at ambient temperature.Nitrogen adsorption-desorption,scanning electron microscope(SEM),and X-ray photoelectron spectroscopy(XPS)were used to characterize the catalysts before and after ozone decomposition.The results showed that the supported gold nanoparticles prepared with microwave heating were much smaller and more uniformly dispersed on the activated carbon than those prepared with traditional conduction heating,exhibiting higher catalytic activity for ozone decomposition.The pH values of gold precursor solution significantly influenced the catalytic activity of supported gold for ozone decomposition,and the best pH value was 8.In the case of space velocity of 120000 h–1,inlet ozone concentration of 50 mg/m3,and relative humidity of 45%,the Au/AC catalyst maintained the ozone removal ratio at 90.7%after 2500 min.After being used for ozone decomposition,the surface carbon of the catalyst was partly oxidized and the oxygen content increased accordingly,while its specific surface area and pore volume only decreased a little.Ozone was mainly catalytically decomposed by the gold nanoparticles supported on the activated carbon.

Effects of pH on photochemical decomposition of perfluorooctanoic acid in different atmospheres by 185 nm vacuum ultraviolet

Perfluorooctanoic acid （PFOA）, a persistent organic pollutant, receives increasing concerns due to its worldwide occurrence and resistance to most conventional treatment processes. The photochemical decomposition by 185 nm vacuum ultraviolet （VUV） is one of the efficient methods for PFOA decomposition. The effects of pH on PFOA decomposition in nitrogen atmosphere or oxygen atmosphere were investigated. At its original pH （4.5） of PFOA aqueous solution, PFOA decomposed efficiently both in nitrogen and in oxygen atmosphere. However, when the pH increased to 12.0, PFOA decomposition was greatly inhibited in oxygen atmosphere, while it was greatly accelerated in nitrogen atmosphere with a very short half-life time （9 rain）. Furthermore, fluorine atoms originally contained in PFOA molecules were almost completely transformed into fluoride ions. Two decomposi- tion pathways have been proposed to explain the PFOA decomposition under different conditions. In acidic and neutral solutions, PFOA predominantly decomposes via the direct photolysis in both atmospheres; while in the alkaline solution and in the absence of oxygen, the decomposition of PFOA is mainly induced by hydrated electrons.

Photochemical decomposition of 1H,1H,2H,2H-perfluorooctane sulfonate(6:2FTS)induced by ferric ions

Perfluorooctane sulfonate（PFOS） had wide applications,such as in the electroplating industry,but its use was restricted in 2009 by the Stockholm Convention,due to its environmental persistence and potential hazards.As the most common PFOS alternative,lH,lH,2H,2H-perfluorooctane sulfonic acid（6：2FTS） and its salts have been increasingly used.However,little is known about its photochemical decomposition.This paper reports the ferric ion-induced efficient decomposition and defluorination of 6：2FTS under 254 nm ultraviolet（UV） irradiation;the underlying mechanisms were also investigated.In the presence of 100 ｜imol/L ferric ion and at pH 3.0,the first-order decomposition rate constant of 6：2FTS（10 mg/L） was 1.59/hr,which was 6 times higher than for direct UV photolysis.The effects of the ferric ion concentration and the solution pH on the 6：2FTS photodecomposition were investigated and the optimal reaction conditions were determined.In addition to fluoride and sulfate ions,shorter-chain PFCAs（C2-C7） were detected as major intermediates.The addition of hydrogen peroxide or oxalic acid accelerated the decomposition of 6：2FTS under UV irradiation,but not its defluorination,indicating that hydroxyl radicals can directly react with 6：2FTS but not with the shorter-chain PFCAs.Accordingly,a mechanism for 6：2FTS photochemical decomposition in the presence of ferric ion was proposed,which comprises two reaction pathways.First,hydroxyl radicals can directly attack 6：2FTS,leading to C- C bond cleavage.Alternatively,6：2FTS coordinates with ferric ion to form Fe（III）-6：2FTS complexes,which can undergo ligand-to-metal charge transfer under UV irradiation,causing C-S bond cleavage.