微波辅助合成缺陷型氧化钨及其光催化杀菌机理:氧空位的作用

饮用水的微生物污染问题受到越来越多的重视,亟需发展更加安全的饮用水消毒技术.光催化消毒由于其利用取之不尽的太阳光作为能源的特点成为近年来最有潜力的"绿色"杀菌技术,然而传统TiO2光催化只能响应紫外光,并且目前已报道的可见光响应催化剂的杀菌效率仍然较低,不能满足应用需求.表面氧空位修饰是提高光催化剂性能的有效途径,已被证明可提高光催化降解、产氢及CO2还原性能,然而其对于光催化杀菌的增强机制少有研究.WO3由于具备可见光催化性能而受到较多关注,同时研究表明表面氧空位可提高WO3光吸收性能从而增强活性,但氧缺陷型WO3的光催化杀菌性能尚不明确.另一方面,氧缺陷WO3多是通过H2热还原制备或长时间水热反应制备,存在高温易爆、反应时间长等缺点.本文以WO3为例,利用微波辅助溶剂热法合成WO3–x,研究其在可见光下的光催化杀菌性能,探明氧空位对杀菌作用的增强机制,提出针对光催化杀菌的缺陷型催化剂制备策略.研究发现,以乙醇作为溶剂WO3–x可在150 ℃经4 h微波加热成功合成,相对于传统水热合成大幅缩短了制备时间.SEM/TEM表明其为纳米片形貌, UV-Vis DRS结果显示其带隙由2.53 eV增加到2.61 eV,主要是由于量子尺寸效应导致带隙蓝移,同时发现WO3–x在500–800 nm范围内具有强可见光吸收,来源于氧空位导致的LSPR吸收.XPS表明W:O比为1:2.87,说明样品含有大量氧空位,并通过EPR测试进一步证实了氧空位的生成.光催化杀菌实验表明, WO3–x在可见光(λ﹥420nm)照射下可在150 min内实现对6 log大肠杆菌的完全杀灭,其杀菌反应动力学符合Geeraerd模型,最大反应速率常数kmax为18.87 h–1,是无氧空位WO3的15.2倍,充分说明表面氧空位修饰是大幅提高WO3光催化杀菌性能的有效途径.进一步对光催化杀菌机理进行了深入研究,发现草酸钠(空穴湮灭剂)的加入可完全抑制杀菌反应,说明细菌灭活主要是空穴引起的氧化反应,同时利用表面氟化取代表面羟基实验发现经空穴氧化生成的表面羟基自由基·OHads也不是主要的活性物种,从而证实WO3–x体系中光催化杀菌主要是通过空穴直接氧化实现.XPS-VB测试表明合成的WO3–x相对于WO3其价带发生下移,导致光生空穴的氧化能力提高,同时电化学阻抗谱(EIS)及稳态荧光光谱(PL)证实WO3–x具有更高的光生电子-空穴分离率和界面电子传输效率.这些结果表明氧空位修饰不仅可以通过调控能带结构影响光生空穴氧化能力,而且可以提高载流子迁移率从而提高光催化杀菌性能.综上所述,本文提供了一种通过微波辅助调控半导体光催化剂表面氧空位的方法,并以WO3–x为例阐明了氧空位对光催化杀菌的增强机制,为今后定向开发缺陷型光催化剂,实现对病原微生物的高效控制和杀灭提供了新的研究思路.

Nature of large (Ti, Nb)(C, N) particles precipitated during the solidification of Ti, Nb HSLA steel

To investigate the microsegregation phenomena and complex （Ti, Nb）（C, N） precipitation behavior during continuous casting, a unidirectional solidification unit was employed to simulate the solidification process. The samples of Ti, Nb-addition steels after unidirectional solidification were examined using field emission scanning electron microscope （FE-SEM） and electron probe X-ray microanalyzer （EPMA）. In such specimens, dendrite structure and mushy zone can be detected along the solidification direction. It shows that the addition of titanium, niobium to high-strength low-alloyed （HSLA） steel results in undesirable （Ti, Nb）（C, N） precipitation because of microsegregation. The effect of cooling rate on （Ti, Nb）（C, N） precipitation was investigated. The composition of large precipitates was determined using FE-SEM with EDS. Large （Ti, Nb）（C, N） precipitates could be divided into three kinds according to the composition and morphology. With the cooling rate increasing, Ti-rich （Ti, Nb）（C, N） precipitates are transformed to Nb-rich （Ti, Nb）（C, N） precipitates.

Thermodynamic calculations and experiments on inclusions to be nucleation sites for intragranular ferrite in Si-Mn-Ti deoxidized steel

Microstructures and inclusions in the Si-Mn-Ti deoxidized steels after cooling in the furnace were investigated. The composition and morphology of the inclusions were analyzed using a field emission scanning electron microscope （FE-SEM） with energy dispersive X-ray spectrometry （EDS）. The kind and composition of the inclusions calculated from the thermodynamic database were in good agreement with the experimental results. There were two main kinds of inclusions formed in the Si-Mn-Ti deoxidized steels. One kind of inclusion was the manganese titanium oxide （Mn-Ti oxide）. Another kind of inclusion was the MnS inclusion with segregation points containing Ti and N. According to the thermodynamic calculation, those segregation points were TiN precipitates. The formation of intragranular ferrite （IGF） microstructures refined the grain size during the austenite-ferrite transformation. The mechanisms of IGF formation were discussed. Mn-Ti oxide inclusions with Mn-depleted zone （MDZ） were effective to be nucleation sites for IGF formation, because the MDZ increased the austenite-ferrite transformation temperature. TiN had the low misfit ratio with IGF, so the TiN precipitated on the MnS surface also promoted the formation of IGF because of decreasing interfacial energies.

Investigation of the solute transportation coupled with heat transfer and fluid flow during twin-roll strip casting process

Mathematical model of solute [C] distribution in twin-roll strip casting process has been setup successfully with Calcosoft for the first time. Simulation result shows that in the center of the molten steel pool between the two rolls there is a vortex flow, which is a solute enriched area. But the highest solute concentration position is at the solidification front of the columnar grain zone near the cooling roll surface. Another solute enriched position is in the back flow above the nip point. Combined with the formation mechanism of microstruoture in final as cast strip, analysis shows that solute enriched area is in the transitional area between columnar and equiaxed grain zone.

Effect of Gas Injection on Fluid Flow in Mold

A mathematical and physical model was adopted to compute the fluid flow distribution in case of localgas holdup in mold. The photography was used to show the fluid field. The predicted flow patterns show. reasonableagreement with experiment observations using actual water model.

Application of Potentiostats Using PC in the Phase Analysis of Galvano-Chemis-try

A set of device is designed based on PC to realize the functions of traditional potentiostats in the phase ana1ysis of galvanochemistry. In the device, A/D and D/A conversion is used to measure the electrode potential and convert the voltage for outPut; specific program runs in the PC to regulate and control the system. The effect of the proportion factor Kp on the control variation is researched through certain experiment. Two experiments, the control of electrolysis in constant poteniial and the determination of polarization curves, are designed to test and evaluate the effectiveness of the device. The experimemel results show that the variation between the actualanode potential and the target potential could be controlled to below 1 mV if Kp is set to an appropriate value.

Experiment Study on Castex Process of AS Wire

In order to optimize the Castex process of AS wire, the systematic experiments have been done for different process parameters with self-made DZJ-II 350 Castex machine. The parameters, such as casting temperature of aluminum, flow of cooling water, extrusion ratio and the gap between the surface of wheel and that of the mould, have been mainly studied. The results show that with the increase of casting temperature or rotating speed of wheel the measured length of liquid metal zone increases too. However, the length of liquid metal zone decreases with the increase of the flow of cooling water. Moreover, the relationship between the extrusion ratio and the extrusion power is studied.

Atmospheric VOCs in an industrial coking facility and the surrounding area:Characteristics,spatial distribution and source apportionment

Industrial coking facilities are an important emission source for volatile organic compounds(VOCs).This study analyzed the atmospheric VOC characteristics within an industrial coking facility and its surrounding environment.Average concentrations of total VOCs(TVOCs)in the surrounding residential activity areas(R1 and R2),the coking facility(CF)and the control area(CA)were determined to be 138.5,47.8,550.0,and 15.0μg/m^(3),respectively.The cold drum process and coking and quenching areas within the coking facility were identified as the main polluting processes.The spatial variation in VOCs composition was analyzed,showing that VOCs in the coking facility and surrounding areas were mainly dominated by aromatic compounds such as BTX(benzene,toluene,and xylenes)and naphthalene,with concentrations being negatively correlated with the distance from the coking facility(p<0.01).The sources of VOCs in different functional areas across the monitoring area were analyzed,finding that coking emissions accounted for 73.5%,33.3% and 27.7% of TVOCs in CF,R1 and R2,respectively.These results demonstrated that coking emissions had a significant impact on VOC concentrations in the areas surrounding coking facility.This study evaluates the spatial variation in exposure to VOCs,providing important information for the influence of VOCs concentration posed by coking facility to surrounding residents and the development of strategies for VOC abatement.

Spatiotemporal dynamics of city-level WEEE generation from different sources in China

China stands as one of the leading producers of waste electrical and electronic equipment(WEEE),facing significant challenges in managing the substantial volumes generated.Despite existing regulations,the informal treatment of WEEE persists in some areas due to inadequate recycling networks at the city level.Consequently,there is a critical need for a detailed geographical mapping of WEEE generation to address improper disposal practices effectively.This study introduces the cMAC–EEEs(city Material Cycles and Manufactured Capital–EEEs)database,providing estimates of WEEE generation across approximately 300 prefecture-level cities from 1978 to 2017.It focuses on five commonly used types of electrical and electronic equipment(refrigerators,air conditioners,washing machines,computers,TVs)originating from three key sources(urban residents,rural residents,enterprises).The findings reveal(1)significant spatial variation in WEEE generation within China,with eastern and central city clusters identified as hotspots,particularly for urban residents and enterprises,while the western region exhibits the highest growth rate in WEEE generation,notably among rural residents.(2)The growth in obsolete computers and air conditioners is prominent,especially in rural areas and among enterprises,whereas the generation of obsolete TVs,washing machines,and refrigerators is leveling off and expected to decrease in some urban areas.(3)Enterprises account for a substantial portion of WEEE generation,though uncertainties exist,necessitating further refinement.The study highlights that less developed regions lack adequate recycling facilities,with specific limitations in refrigerators and air conditioners recycling capabilities.To enhance WEEE management,it advocates for increased interregional collaboration and capacity building in less developed areas.Additionally,the regulation of WEEE from private enterprises requires improvement.At the product level,a greater focus on recycling practices for refrigerators and air conditioners is recommended.

Novel Ag-bridged dual Z-scheme g-C_(3)N_(4)/BiOI/AgI plasmonic heterojunction: Exceptional photocatalytic activity towards tetracycline and the mechanism insight

Rational design and synthesis of highly efficient and robust photocatalysts with positive exciton splitting and interfacial charge transfer for environmental applications is critical.Herein,aiming at overcoming the common shortcomings of traditional photocatalysts such as weak photoresponsivity,rapid combination of photo-generated carriers and unstable structure,a novel Ag-bridged dual Z-scheme g-C_(3)N_(4)/BiOI/AgI plasmonic heterojunction was successfully synthesized using a facile method.Results showed that Ag-AgI nanoparticles and three-dimensional(3D)BiOI microspheres were decorated highly uniformly on the 3D porous g-C_(3)N_(4) nanosheet,resulting in a higher specific surface area and abundant active sites.The optimized 3D porous dual Z-scheme g-C_(3)N_(4)/BiOI/Ag-AgI manifested exceptional photocatalytic degradation efficiency of tetracycline(TC)in water with approximately 91.8%degradation efficiency within 165 min,outperforming majority of the reported g-C_(3)N_(4)-based photocatalysts.Moreover,g-C_(3)N_(4)/BiOI/Ag-AgI exhibited good stability in terms of activity and structure.In-depth radical scavenging and electron paramagnetic resonance(EPR)analyses confirmed the relative contributions of various scavengers.Mechanism analysis indicated that the improved photocatalytic performance and stability were ascribed to the highly ordered 3D porous framework,fast electron transfer of dual Z-scheme heterojunction,desirable photocatalytic performance of BiOI/AgI and synergistic effect of Ag plasmas.Therefore,the 3D porous Z-scheme g-C_(3)N_(4)/BiOI/Ag-AgI heterojunction had a good prospect for applications in water remediation.The current work provides new insight and useful guidance for designing novel structural photocatalysts for environment-related applications.

Photocatalytic defluorination of perfluorooctanoic acid by surface defective BiOCl:Fast microwave solvothermal synthesis and photocatalytic mechanisms

There is an urgent need for developing cost-effective methods for the treatment of perfluorooctanoic acid(PFOA)due to its global emergence and potential risks.In this study,taking surface-defective BiOCl as an example,a strategy of surface oxygen vacancy modulation was used to promote the photocatalytic defluorination efficiency of PFOA under simulated sunlight irradiation.The defective BiOCl was fabricated by a fast microwave solvothermal method,which was found to induce more surface oxygen vacancies than conventional solvothermal and precipitation methods.As a result,the asprepared BiOCl showed significantly enhanced defluorination efficiency,which was 2.7 and33.8 times higher than that of BiOCl fabricated by conventional solvothermal and precipitation methods,respectively.Mechanistic studies indicated that the defluorination of PFOA follows a direct hole(h^+)oxidation pathway with the aid of·OH,while the oxygen vacancies not only promote charge separation but also facilitate the intimate contact between the photocatalyst surface and PFOA by coordinating with its terminal carboxylate group in a bidentate or bridging mode.This work will provide a general strategy of oxygen vacancy modulation by microwave-assisted methods for efficient photocatalytic defluorination of PFOA in the environment using sunlight as the energy source.

Advances in photocatalytic disinfection of bacteria:Development of photocatalysts and mechanisms

Photocatalysis has attracted worldwide attention due to its potential in solar energy conversion.As a ＂green＂ advanced oxidation technology, it has been extensively used for water disinfection and wastewater treatment. This article provides a review of the recent progress in solar energy-induced photocatalytic disinfection of bacteria, focusing on the development of highly efficient photocatalysts and their underlying mechanisms in bacterial inactivation. The photocatalysts are classified into Ti O2-based and non-Ti O2-based systems, as Ti O2 is the most investigated photocatalyst. The synthesis methods, modification strategies, bacterial disinfection activities and mechanisms of different types of photocatalysts are reviewed in detail.Emphasis is given to the modified Ti O2, including noble metal deposition, non-metal doping,dye sensitization and composite Ti O2, along with typical non-Ti O2-based photocatalysts for bacterial disinfection, including metal oxides, sulfides, bismuth metallates, graphene-based photocatalysts, carbon nitride-based photocatalysts and natural photocatalysts. A simple and versatile methodology by using a partition system combined with scavenging study is introduced to study the photocatalytic disinfection mechanisms in different photocatalytic systems. This review summarizes the current state of the work on photocatalytic disinfection of bacteria, and is expected to offer useful insights for the future development in the field.