Flocculation of kaolin particles by two typical polyelectrolytes: A comparative study on the kinetics and floc structures

The flocculation kinetics of kaolin particles induced by two polyelectrolytes is studied by using small-angle laser light scattering (SALLS). Two different methods, image analysis and SALLS, are used to calculated the fractal dimensions of flocs formed under different flocculation mechanisms. For a high charge density of polydiallyldimethylammonium chloride (PDADMAC), the initially flocculation rates are slow due to the quite low molecular weight. Smaller and more compact flocs are in the particle–particle connections, and restructuring of the flocs occurs in the flocculation process. With cationic polyacrylamide C498 of very high molecular weight and low charge density, however, the initially flocculation rates are much higher due to its rapid adsorption on kaolin particles, but it will take the adsorbed polymer a much longer time to reach equilibrium due to re-conformation. High potentialities of adsorption prevent the particles from entering the interior of the floc structure or rearrangement, which results in a more open floc structure. Different underlying flocculation mechanisms are evident for these two kinds of polyelectrolytes, in which charge neutralization is mainly involved for the low molecular weight and high charge density polymer of PDADMAC while polymer bridging is suggested to be the dominant mechanism for the high molecular weight polyelectrolyte of C498.     

Hydrolysis of poly(l-lactic acid) using microwave irradiation

Poly(l-lactic acid) (PLLA) was hydrolyzed using microwave irradiation, and yields of the resultant lactic acid and reaction time were compared with those obtained by conventional heating. In both cases, the reaction temperature was maintained at 170 °C and the weight ratio of PLLA:H₂O was 3:1. Under conventional heating, the lactic acid yield reached saturation after 800 min at 45%, whereas only 120 min was required to reach the same yield level under microwave irradiation. The optical purity under conventional heating decreased with hydrolysis of the PLLA and dropped to 94%ee when the lactic acid yield reached at 45%. Under microwave irradiation, however, the optical purity decreased only after the equilibrium state of hydrolysis was attained. Therefore, to maintain the optical purity at 98%ee, it was necessary to stop microwave irradiation when the lactic acid yield reached 45%.     

Influence of humic acid on the flocculation of clay

The aim of this study was to improve the flocculation of wastewater from gravel pits, especially the separation of the finely dispersed inorganic particles and the removing of humic acid. Clay was used as a model to investigate the influence of humic acid on the flocculation with two different types of polycation. The dependence of the sedimentation behaviour on time was investigated as well as the turbidity of the supernatant and the light absorption as a measure for humic acid removal. Bridging of particles remained the dominant mechanism of particle destabilisation by treating the clay in water with cationic polyacrylamides of very high molecular mass (CPAM). Poly(diallyldimethylammonium chloride) (PDADMAC) of lower molar mass (35 000 g/mol) was found to act by charge neutralisation. In this case the so-called flocculation window was very small. This behaviour is the same for systems containing humic acid. However, the need for cationic flocculant increases because humic acid as a weak polyanion can interact with the polycation. By using CPAMs with low charge this interaction does not play a significant role. The optimum flocculation concentration is relatively high. The flocs are larger and the velocity of sedimentation is higher than for the short-chain and highly charged polycation PDADMAC. However, because the latter is more effective in removal of humic acid at the point of optimum flocculation it is more advantageous to combine the highly charged polycation with a high molecular weight polyanion (dual system).     

QbD approached comparison of reaction mechanism in microwave synthesized gold nanoparticles and their superior catalytic role against hazardous nirto‐dye

Microwave irradiation (MI) process characteristically enables extremely rapid “in‐core” heating of dipoles and ions, in comparison to conventional thermal (conductance) process of heat transfer. During the process of nanoparticles synthesis, MI both modulates functionality behaviors as well as dynamic of reaction in favorable direction. So, MI providing a facile, favorable and alternative approach during nanoparticles synthesis nanoparticles with enhanced catalytic performances. Although, conventionally used reducing and capping reagents of synthetic origin, are usually environmentally hazardous and toxic for living organism. But, in absence of suitable capping agent; stability, shelf life and catalytic activity of metallic nanoparticles adversely affected. However, polymeric templates which emerged as suitable choice of agent for both reducing and capping purposes; bearing additional advantages in terms of catalyst free one step green synthesis process with high degree of biosafety and efficiency. Another aspect of current works was to understand role of process variables in growth mechanism and catalytic performances of microwave processed metallic nanoparticles, as well as comparison of these parameters with conventional heating method. However, due to poor prediction ability with previously published architect OFAT (One factor at a time) design with these nanoparticles as well as random selection of process variables with their different levels, such comparison couldn't be possible. Hence, using gum Ghatti (Anogeissus latifolia) as a model bio‐template and under simulated reaction conditions; architect of QbD design systems were integrated in microwave processed nanoparticles to establish mechanistic role these variables. Furthermore, in comparison to conventional heating; we reported well validated mathematical modeling of process variables on characteristic of nanoparticles as well as synthesized gold nanoparticles of desired and identical dimensions, in both thermal and microwave‐based processes. Interestingly, despite of identical dimension, MI processed gold nanoparticles bearing higher efficiency (kinetic rate) against remediation of hazardous nitro dye (4‐nitrophenol), into safer amino (4‐aminophenol) analogues.     

微波作用下的多肽固相缩合反应及动力学研究

分别在微波作用以及传统加热两种方式下, 研究了Fmoc-Val-OH与NH₂-Tyr(t-Bu)-Wang树脂的固相缩合反应及其动力学. 测定了温度变化对反应速率的影响, 并获得了两种方式下的缩合反应的宏观动力学参数: 300 W微波作用下表观缩合反应级数为2.3, 活化能为104.7 kJ/mol; 传统方法中表观反应级数为2.9, 活化能为142.4 kJ/mol. 微波作用将常规条件下的连接率由68%提高到95%, 而所需时间降为常规条件的1/14.     

微波辐照合成羟基功能化离子液体氯盐中间体

采用微波辐照法合成了4种羟基功能化离子液体中间体氯化1-甲基-3-羟乙基咪唑、氯化N-羟乙基吡啶、氯化1-甲基-3-(2,3-二羟基)丙基咪唑和氯化N-(2,3-二羟基)丙基吡啶,考察了微波功率、辐射方式和辐射时间对反应产率的影响。结果表明,利用常规加热方法合成这4种离子液体中间体耗时长达24～96h,而用微波方法只需110～390s,反应时间大大缩短,同时微波方法较常规加热方法产率也略有提高。     

微波辐射活性炭负载磷钨酸催化合成季戊四醇双缩酮(醛)

在微波辐射下，以活性炭负载磷钨酸为催化剂，不用溶剂，合成了8种季戊四醇双缩酮（醛），以环己酮与季戊四缩的缩合为模型反应进行优化，其优化反应条件为：季戊四醇2．0g，催化剂0．3g，环己酮4．0mL，微波输出功率600W，辐射时间3min，产率达95．4％，该条件下的反应速度是常规加热反应速度的30倍，所得产物经元素分析，IR和1H NMR表征。     

“讲一练二考三”理念在有机化学实验教学中的运用——以苯甲酸的制备为例

采用微波辐射及相转移催化剂改进了高锰酸钾氧化制备苯甲酸实验,系统研究了微波功率、反应温度、反应时间、反应物物质的量比、催化剂用量等因素对产率的影响,并同电热套加热方式进行了比较.结果表明,该反应的最佳条件为:微波辐射时间40 min,微波功率80 W,反应温度80℃,相转移催化剂氯化苄基三乙铵用量为甲苯的0.2当量,高锰酸钾与甲苯的物质的量比为4.5:1.与电热套加热方式相比,微波辐射法缩短了反应时间,并显著提高了反应效率.以苯甲酸制备实验为例介绍了“讲一练二考三”教学新理念及其在有机化学实验教学实践中的运用.     

Synthesis of N-Aryl-N′- (5-aryloxymethyl-1,3,4-thiadiazol-2-yl) ureas under Microwave Irradiation

The rapid heating effect of microwave irradiation has caught the attention of synthetic chemists in the recent times due to the remarkable reduction of reaction time. It is an efficient method because of its virtue of rapid heating capability, high yield and simple procedure. The superiority of these virtues goes beyond of traditional heating reaction.     

以水作溶剂微波法合成1,4-二氢苯并咪唑并[1,2-a]嘧啶类衍生物

以芳香醛、2-氨基苯并咪唑和丙二腈为原料,用传统法和微波辐射法三组分一锅煮法合成1,4-二氢苯并咪唑并[1,2-a]嘧啶类化合物。反应均在无催化剂条件下以水作反应溶剂进行。结果表明,采用微波辐射优于常规方法,三组分摩尔比n(2-氨基苯并咪唑)∶n(丙二腈)∶n(取代苯甲醛)=1∶1.1∶1,辐射功率400 W,时间为6～8 min时,1,4-二氢苯并咪唑并[1,2-a]嘧啶的收率在85%以上,反应速率比常规加热条件下提高70倍。通过荧光发射光谱研究证实,该系列化合物具有明显的荧光性质,其荧光发射峰位于480～550 nm。     

微波固相法制备ZnCl2/NaY催化剂ZnCl2/NaY在月桂烯Diels-Alder反应中的催化性能

比较了微波固相法、普通加热法和简单混合法制备的ZnCl2/NaY及溶液离子交换法制备的ZnNaY在月桂烯与丙烯醛Diels-Alder反应中的催化性能,发现微波固相法制备的催化剂表现出最高的环加成选择性和区域选择性.通过对微波固相法制备的催化剂中ZnCl2负载量的考察,揭示了微波诱导ZnCl2在NaY分子筛表面形成了不同催化活性中心的特点,分散在分子筛表面的ZnCl2具有更高的催化活性和区域选择性.微波辐射可成功地将ZnCl2固载于NaY分子筛中,当ZnCl2负载量为6.3%时,ZnCl2与NaY分子筛主要发生固态离子交换反应;当ZnCl2负载量达25%时,催化活性提高了3倍,区域选择性提高了1倍以上.而且,以微波固相法制备的ZnCl2/NaY催化剂,其环加成选择性和区域选择性随反应温度的升高而下降.     

Microwave-assisted synthesis of 1,3-dialkyl ethers of calix[4]arenes: application to the synthesis of cesium selective calix[4]crown-6 ionophores

Partial etherification of phenolic-OH groups of calix[4]arenes with various alkyl halides/tosylates and K₂CO₃ under microwave irradiation afforded 1,3-dialkoxycalix[4]arenes in their cone conformation only as predominant/sole product in good yields (71–85%). The protocol was found to be much superior to conventional heating both in terms of yield and reaction time. Some of the 1,3-dialkoxycalix[4]arenes were elaborated further to the syntheses of cesium selective calix[4]crown-6 ionophores.     

微波辐射用于聚酰亚胺的研究进展

聚酰亚胺因具有优良的综合性能而得到广泛的研究.微波辐射在高分子化学研究领域中的应用越来越广泛,效果也十分明显.与常规加热方式相比,微波辐射具有内部加热、缩短反应时间、提高反应产率、节省能耗、无温度梯度、制得产物性能好等优点.近年来,微波辐射用于聚酰亚胺的研究越来越多.因此本文对微波辐射在聚酰亚胺的合成、三阶非线性光学、聚酰亚胺复合材料以及稀土-聚酰亚胺配合物等方面的应用进行了综述.     

CATALYTIC PROPERTIES OF POLYMER-STABILIZED COLLOIDAL METAL NANOPARTICLES SYNTHESIZED BY MICROWAVE IRRADIATION

Catalytic properties of polymer-stabilized colloidal metal nanoparticles synthesized by microwave irradiation were studied in the selective hydrogenation of unsaturated aldehydes, o-chloronitrobenzene and the hydrogenation of alkenes. The results show that nanosized metal particles synthesized by microwave irradiation have similar catalytic performance in selective hydrogenation of unsaturated aldehydes, better selectivity to o-chloroaniline in hydrogenation of o-chloronitrobenzene and higher catalytic activities in hydrogenation of alkenes, compared with metal clusters prepared by conventional heating. The same apparent activation energy (Ea = 29 kJ mol^-1) for hydrogenation of 1-heptene catalyzed with platinum nanoparticles prepared by both heating modes implied that the reaction followed the same mechanism.     

微波辐射下固相反应合成二苯基甲基醚

在常压下用微波辐射固相反应的方法合成了二苯基甲基醚,与用有机溶剂为介质及传统的热固相反应方法相比,其反应速率快,产率高。     

Microwave-prompted rapid and efficient synthesis of 3-alkyl substituted imidazo[1,5-a]pyridines

Under regular heating and microwave irradiation, 3-alkyl substituted imidazo[1,5-a] pyridines were synthesized from 2,2＇- pyridil, di-2-pyridyl ketone and aliphatic aldehydes in the presence of ammonium acetate and acetic acid. Compared to the traditional heating condition, the reaction time under microwave irradiation was shorter and 3-alkyl imidazo[1,5-a]pyddines were given in higher yield.     

微波辐射下5-取代-2-硫代海因衍生物的合成

微波辐射下, 由硫氰酸铵与α-氨基酸通过两步反应合成了11种5-取代-2-硫代海因衍生物, 并用¹H NMR, IR和元素分析确证了中间产物和终产物的结构. 对比常规加热方法, 微波辐射具有反应时间短(4 min), 每步反应产率高(85%～93%)的优点. 同时对合成化合物2h的反应历程进行了讨论.     

Influence of drying processes on oxidative stability of ethyl corn biodiesel by differential scanning calorimetry

The influence of drying processes in the biodiesel oxidation was investigated by means of the oxidative induction time obtained from differential scanning calorimetry data. For this purpose, corn biodiesel was dried by different methods including: chemical (anhydrous sodium sulfate) and thermal (induction heating, heating under vacuum and with microwave irradiation). The drying efficiency was evaluated by monitoring IR absorption in the 3,500–3,200 cm⁻¹ range and by the AOCS Bc 2-49 method. In general, the oxidative induction times increased inversely to the heating degree, except that of microwave irradiation, which was selective to water evaporation and caused low impact over the unsaturation of biodiesel. The DSC technique was shown to be a powerful tool to evaluate with high level of differentiation the influence of the drying process on the oxidative stability of biodiesel.     

新型含吡唑基3,4-二氢嘧啶类化合物的一锅合成研究

以FeCl3•6H2O为催化剂,无水乙醇为溶剂,按取代-4-甲酰基吡唑：乙酰乙酸乙酯：（硫）脲：FeCl3•6H2O =1：3：3：1的比例,采取微波辐射和常规加热回流的方法通过Biginelli缩合反应一锅合成了6种新型含吡唑基的3,4-二氢嘧啶类化合物,并进行了元素分析、IR、1H-NMR和13C-NMR表征。     

新型氨基甲酸含氮杂环甲基酯的合成及生物活性研究

常规加热或微波照射下, 含氮杂环1与多聚甲醛反应以良好的产率生成含氮杂环基甲醇3, 反应物物质的量的比、反应温度等对反应产率有影响, 微波条件下的反应时间比常规加热下大大缩短. 化合物3和异氰酸酯4在常规加热或微波照射下生成相应的氨基甲酸含氮杂环甲基酯5a～5m. 反应温度、反应物物质的量的比、反应时间、微波辐射功率等对反应产率都有一定的影响, 与常规加热相比微波条件下的反应时间大大缩短. 化合物5的结构经过IR, ¹H NMR, MS, 元素分析测定, 部分化合物经过¹³C NMR测定. 测定了化合物5的杀虫和除草活性, 结果表明其杀虫活性较低, 除草活性高于杀虫活性, 5a, 5d, 5e和5m对苋菜和黄瓜的防除率高达100%.