Tuesday, January 28, 2020

Synthesis of New Coordination Polymers or MOFs

Synthesis of New Coordination Polymers or MOFs 1.1 Design Principles Coordination polymers also known as metal–organic frameworks (MOFs) or metal-coordination networks are compounds constructed from organic ligands and metal ions connected through coordination bonds and other weak chemical bonds which can extend infinitely into one two or three dimensions [1-3]. The arrangement of the components in coordination polymers mostly exists only in solid state which results from coordination interactions and weaker forces forming a smaller molecular units and growth occurs through self-assembly processes to give the final overall structure (Fig. 1) [4]. There are four different kinds of building blocks of which coordination polymers are built; ligands, metal ions or clusters, counter anions and solvent molecules. Metal ions which are called nodes or connectors and ligands which act as linkers are the main components [7]. They are the starting reagents which form the principal framework of the coordination polymer. The important characteristics of connectors and linkers are the number and orientation of their binding sites. Transition-metal ions are the most widely used connectors in the construction of coordination polymers. The choice of the metal and its oxidation state will determine the coordination geometries, which can be linear, T- or Y-shaped, tetrahedral, square-planar, square-pyramidal, trigonal-bipyramidal, octahedral, trigonal-prismatic, pentagonal-bipyramidal, and the corresponding distorted forms. Lanthanide ions are less used because of the high coordination number and variability coordination environment. However, th e large coordination numbers from 7 to 10 and the polyhedral coordination geometry of the lanthanide ions will create new and unusual network topologies. In addition, coordinatively unsaturated lanthanide ion centers can be generated by the removal of coordinated solvent molecules. The vacant sites could be utilized in chemical adsorption, heterogeneous catalysis, and sensors [8,9]. Multidentate carboxylate functionalities provide rigid frameworks due to their ability to chelate metal ions and lock in to M-O-C clusters, which are referred as secondary building units (SBUs). Instead of employing one transition metal ion at a network vertex, SBUs can produce extended frameworks of high structural stability. Metal-complex connectors have the advantage of controlling the bond angles and restricting the number of coordination sites; sites for no use can be blocked by chelating or macrocyclic ligands directly bound to a metal connector, and therefore, leave specific sites free for linkers [25,10,11]. Linkers are categorized in to three: inorganic, organic, and organic-inorganic hybrid types. Halides (F, Cl, Br, and I) are the smallest and simplest of all linkers. CN and SCN have similar bridging ability to halides [12,13]. Typical organic ligands are shown in Fig. 2 consisting of neutral, anionic and cationic organic ligands. The organic ligands act as bridging organic groups between the metal ions. Most famous neutral ligands are pyrazine (pyz) and 4,4’-bpy [15-18]. An example of a coordination polymer with the 4,4’-bpy ligand is illustrated in Fig. 3. Recent efforts have been devoted to utilization of long bridging ligands with appropriate spacers [20-25]. Among the anionic organic ligands di-,[26-28] tri-,[26, 29-32] tetra-,[33,34] and hexacarboxylate [35,36] molecules are representative anionic linkers. Coordination polymers having nonsymmetric anionic ligands described as pyridine-X-COO (X=spacer) have been exhaustively studied [37]. 1,4-Dihydroxy-2,5-benzoquinone and its derivatives provide a variety of frameworks, in which they act as linear linkers [38]. Coordination polymers with cationic organic ligands are very rare, which is naturally a result of their very low coordination power for cationic metal ions [39–43]. Developed were novel cationic ligands based on N-aryl pyridinium and viologen derivatives and were successfully employed [39–41]. Counter ions are present in the coordination frameworks when neutral bridging ligands are used as linkers to keep the neutrality in the overall charge. Furthermore, other roles such as coordination and hydrogen bonding linker, guest for vacant spaces in the solid state are expected, eventually resulting in overall structure regulation. Solvent molecules are used not only for reaction media, but also the regulation of framework topology. It may co-crystallize, increasing the number of possible weak interactions in the final solid state packing, and can also act as guest molecules in the vacant space between polymer construct [7]. Synthesis Many new coordination polymers or MOFs have been synthesized in the last few years; however, their methods of preparation and synthesis were quite similar. Most of them are synthesized by employing a so called â€Å"modular synthesis†, in which a mixture of metal precursors and appropriate ligands are combined under mild conditions to provide a crystalline porous network [26]. In most of the resulting materials the solvent used during synthesis is removed by applying vacuum, heat, or exchange with volatile molecules, resulting in large pore volume and large surface area accessible to guest molecules. Synthetic methods such as solvothermal synthesis (conventional approach), microwave synthesis [45], sonication synthesis [46], mechanochemical synthesis [47], and solid start synthesis [48] have been developed. Despite the simplicity of the synthesis, there are several challenges in the preparation of new materials related to the optimization of the reaction conditions that lead t o the desired MOF, in high yield and crystallinity. The following parameters can influence MOFs’ optimization and synthesis: temperature, solvent compositions, reaction times, reagent ratios, reagent concentrations, and pH of the co-solvent solution [44]. Accordingly, any change in any of these parameters can result in large number of network connectivities, many of which are nonporous and have adverse effect on the gas storage and separation applications. Therefore, large numbers of reactions trails are required to discover the new desired MOFs in which the reaction parameters are systematically varied. As a result high throughput technologies have been employed for the synthesis of new MOFs in the recent years [49,50]. 1.2.1 Solvothermal Synthesis Solvothermal methods have been confirmed to be among the most effective and convenient routes under relatively mild conditions, in particular for the crystal growth of coordination polymers [50-52]. Solvothermal reactions are carried out in closed vessels under autogenous pressure above the boiling point of the solvent. In most cases, high-boiling organic solvents have been used for solvothermal reactions. The most commonly used being dimethyl formamide, diethyl formamide, acetonitrile, acetone, ethanol, and methanol etc. Mixtures of solvents have also been used to tune the solution polarity and the kinetics of solvent-ligand exchange, effecting enhanced crystal growth. Solvothermal reactions can be carried out in different temperature ranges, depending on the requirement of the reaction [53]. When water is used as the solvent, the reactions are referred to as hydrothermal. The hydrothermal method has been used successfully for the synthesis of an enormous number of inorganic compoun ds and inorganic organic hybrid materials [54]. Due to their unique advantageous properties such as high thermal stability, air and moisture non-sensitivity, non-volatility, low reactivity, and templating and charge balancing ability of ionic liquids, they can be chosen as solvothermal reaction media. Solvothermal synthesis in ionic liquids is specifically referred to as ionothermal synthesis [55]. The coordination polymer [Cu(I)(bpp)]BF4 [bpp = 1,3-bis(4-pyridyl)propane] [56] was prepared by solvothermal reaction using the ionic liquid [bmim][BF4] (bmim = 1-butyl-3-methylimidazolium). The synthesis methods employed for different structures of coordination polymers (MOFs) and their key findings are listed in Table 1. 1.2.2 Microwave-assisted synthesis Microwave-assisted synthesis has attracted much attention as it provides a very rapid method for the synthesis of MOFs and has been used extensively to produce nanosize metal oxides [59]. Such processes involve heating a solution with microwaves for a period of about an hour to produce nanosized crystals. The microwave-assisted synthesis has been termed ‘microwave-assisted solvothermal synthesis’ for the preparation of MOFs. Microwave-assisted processes generally produce the same qualities of crystals as those obtained by the regular solvothermal processes, but much quicker [60-64]. The first coordination polymer reported to be synthesized by microwave synthesis was Cr-MIL-100 [65]. The compound was synthesized in 4 h at 220 oC with 44% yield, which is comparable with that of conventional hydrothermal synthesis (220 oC and 4 days). The author expanded this method to synthesis of Cr-MIL-101 at 210 oC in less than 60 min, and reported similar physicochemical and textural properties compared with the standard material synthesized using the conventional electrical heating method [66]. Another coordination polymer, MOF-5, was also synthesized by applying microwave irradiation: increase in microwave irradiation time, power level, and concentration of the substrates beyond an optimal condition led to a reduction in synthesis time at the expense of crystal quality [67]. Microwave-assisted heating was found to be the method of choice to rapidly synthesize HKUST-1 crystals in the range of 10-20 ÃŽ ¼m in high yields (~90%) within 1 h [68]. Fe-MIL-53 [69], Fe-MIL-101-NH2 [7 0], IRMOF-3 (H2BDC-NH2) [71], and ZIF-8 (HMeIm) [72] were also synthesized using microwave-assisted synthesis method. 1.2.3 Sonochemical Synthesis Sonochemical methods can also achieve a reduction in crystallization time and significantly smaller particles size than those by the conventional solvothermal synthesis by homogeneous and accelerated nucleation [73,74]. A substrate solution mixture for a given MOF structure is introduced to a horn-type Pyrex reactor fitted to a sonicator bar with an adjustable power output without external cooling. After sonication, formation and collapse of bubbles will be formed in the solution which produces very high local temperatures (~5,000 K) and pressures (~1,000 bar) [74,75], and results in extremely fast heating and cooling rates (>1010 K/s) producing fine crystallites [76]. High-quality MOF-5 crystals in the 5-25ÃŽ ¼m range were obtained within 30min by sonochemical synthesis using NMP (1-methyl-2-pyrrolidone) as the solvent [77]. Detailed characterization and comparison with a conventionally synthesized sample showed almost identical physical properties. HKUST-1 was also prepared using DMF/EtOH/H2O mixed-solution in an ultrasonic bath [78]. High-quality Mg-MOF-74 crystals (1,640m2/g BET surface area) with particle size of ca. 0.6 ÃŽ ¼m were successfully synthesized in 1 h by a sonochemical method after triethylamine (TEA) was added as a deprotonating agent. Interestingly, mesopores were formed, probably due to the competitive binding of TEA to Mg2+ ions [79]. ZIF-8 was prepared recently by a sonochemical method under the pH-adjusted synthesis conditions using NaOH and TEA [80]. Inexpensive industrial grade DMF was employed as a solvent. A small amount of TEA as a deprotonating agent was necessary to obtain ZIF-8 crystals when the resulting solution was subjected to an ultrasonic treatment for 1 h at a 60% power level. 1.2.4 Electrochemical Synthesis The electrochemical synthesis is based on metal ions continuously supplied through anodic dissolution as a metal source instead of metal salts, which react with the dissolved linker molecules and a conducting salt in the reaction medium. The metal deposition on the cathode is avoided by employing protic solvents, but in the process H2 is generated [81]. The electrochemical route is also possible to run a continuous process to obtain a higher solids content compared to normal batch reactions [76]. The first electrochemical synthesis of MOFs was reported in 2005 by researchers at BASF [82] for HKUST-1. Bulk copper plates are used as the anodes in an electrochemical cell with the H3BTC dissolved in methanol as solvent and a copper cathode. During a period of 150 min at a voltage of 12-19V and a currency of 1.3 A, a greenish blue precipitate was formed. After activation, a dark blue colored powder having surface area of 1,820m2/g was obtained. This work was further used in the ZIFs syntheses [81,83]. Recently, HKUST-1, ZIF-8, Al-MIL-100, Al-MIL-53, and Al- MIL-53-NH2 were synthesized via anodic dissolution in an electrochemical cell [84]. The synthesis parameters such as solvent, electrolyte, voltage-current density, and temperature on the synthesis yield and textural properties of the MOFs obtained, was investigated and the produced MOF structures were characterized by X-ray diffraction, gas adsorption, atomic force microscopy, diffuse reflectance infrared Fourier transform spectroscopy, and scanning electron microscopy. 1.2.5 Mechanochemical Synthesis Mechanochemical synthesis involves breakage of intramolecular bonds mechanically followed by a chemical transformation [80]. Synthesis of porous MOF by mechanochemical reaction was reported first in 2006 [89]. Mechanochemical reactions can occur at room temperature under solvent-free conditions, which has an advantage in avoiding organic solvents [90]. Quantitative yields of small MOF particles can be obtained in short reaction times, normally in the range of 10-60min. Mostly, metal oxides were found to be preferred than metal salts as a starting material, which results in water as the only side product [80]. The critical contribution of moisture in mechanochemical synthesis of pillared type MOFs was recently reported by Kitagawa group [91]. Liquid-assisted grinding (LAG) involves addition of small amounts of solvents which can lead to acceleration of mechanochemical reactions due to an increase of mobility of the reactants on the molecular level [92,93]. The liquid can also work as a structure-directing agent. However, mechanochemical synthesis is limited to specific MOF types only and large amount of product is difficult to obtain. While a mechanochemical reaction between H3BTC and copper acetate produces HKUST-1, reaction using copper formate resulted in a previously unknown phase, potentially due to templating effects of the different acid byproducts formed [93]. Recently, a mechanochemical approach was also applied for ZIF synthesis using combinations of ZnO and imidazole (HIm), 2-methylimidazole (HMeIm), and 2-ethylimidazole (HEtIm) as the starting material within 30-60min reaction time [94].

Sunday, January 19, 2020

First Date in A Bad Restaurant :: essays papers

First Date in A Bad Resteraunt It was a beautiful fall evening. The sun was just beginning to give way to incoming twilight. I could smell winter in the air, even through my closed window. Soon there'd be snow on the ground. Matchbox Twenty was playing on my clock radio." I want to push you around...† The mood was set for a soft autumn night. However the mood inside my room was quite different. I was running around trying to do a million things a one time. My makeup was all wrong for my outfit. My hair was too big, no, now too flat. My stomach was rolling inside itself. My poor tummy was on tumble dry and I couldn't quite get it to stop. I couldn't find my shoes; my shirt had foundation on the side. What I really wanted to do was to sit on my bed and cry. Brian had called twenty minutes before the chaos. I could not believe he had called me. He probably thought I was stupid because I was so tongue-tied. He asked me if I would mind coming to dinner with him and a few of his friends. Would I mind? Do cows moo? The horn honked. My frustration grew. If this was a real date, my first one ever, shouldn't he come to the door and pick me up? Maybe take my arm in his and lead me to the car? I had envisioned my first date to at least start off right. This must be an omen. I walked out the door. The moment I heard the click of the lock I knew I looked horrible. A million thoughts raced through my mind, among these were the fact that I should have worn the blue shirt, my hair looks horrible, and oh God everyone is watching me. I tried to hide the sheer gut-retching fear that was boiling in my stomach. I had to do this. I was in too deep to turn and run now. My sweet chariot of the night was a 1988 van. Rust covered the bumper and half of the door. The color of had once been maroon, however had now faded to a slight orange color. Alternative rock boomed from the less then quality speakers. There were at least 6 people in the car, and it was rocking from side to side, in time to the beat.

Saturday, January 11, 2020

Marketing and Product Development

The question in the case is whether Kim should spend the fresh (2nd round) VC financing in Marketing and scale up the business or should focus the resources on fine tuning the existing product. Our recommendation is that the company should allocate around 70% of $4mn in marketing spend and 30% in product development and fine tuning the existing one.This recommendation is primarily based on the fact that the company should maximize the first mover advantage and develop barriers to entry by reducing the cost of goods sold with the help of economies of scale and ventually reducing the sales price so as to be competitive and not let others to enter the space. This is mainly because the business model is very easily replicable and thus create the risk of being thrown out of business in the long run.Moreover, the product development and fine tuning is largely replicable irrespective of the number of customers and each customer could be segmented based on the 4 bins Kim and Nolan came up wi th. With reference to the spend, the company should focus on Email marketing, Sophisticated social media, developing sophisticated search echanics, promoting the deals websites advertising and also advertising through blogs.However, it is worthwhile a mention that though emails and network affiliates program involves huge spends, they are directly proportional to the amount of business the firm does or the customer acquisition. The company may run the risk of: 1. Exposing the activities and products in addition to the business model by scaling up the marketing spends and bringing unprecedented levels of transparency to customers along with the firms competitors and potential competitors 2. Exponentially increase the customer retention and acquisition costs by developing ultiple layers of acquisition costs 3.May negatively affect the performance and reputation of the firm if the customers have complaints about the product However the firm may mitigate these risks by: 1. Acquiring max imum amount of market share and create growth in the market size. Thus, creating barrier to entry as a result of low selling price and variety of product match. This is mainly because the idea is substantially untapped and the product is simultaneously acceptable. The firm must target to tap as much market as possible before any new or existing player takes it over. Marketing and Product Development The question in the case is whether Kim should spend the fresh (2nd round) VC financing in Marketing and scale up the business or should focus the resources on fine tuning the existing product. Our recommendation is that the company should allocate around 70% of $4mn in marketing spend and 30% in product development and fine tuning the existing one. This recommendation is primarily based on the fact that the company should maximize the first mover advantage and develop barriers to entry by reducing the cost of goods sold with the help of economies of scale and eventually reducing the sales price so as to be competitive and not let others to enter the space.This is mainly because the business model is very easily replicable and thus create the risk of being thrown out of business in the long run. Moreover, the product development and fine tuning is largely replicable irrespective of the number of customers and each customer could be segmented based on the 4 bins Kim and Nolan came up with. With reference to the spend, the company should focus on Email marketing, Sophisticated social media, developing sophisticated search mechanics, promoting the deals websites advertising and also advertising through blogs.However, it is worthwhile a mention that though emails and network affiliates program involves huge spends, they are directly proportional to the amount of business the firm does or the customer acquisition. The company may run the risk of:1.Exposing the activities and products in addition to the business model by scaling up the marketing spends and bringing unprecedented levels of transparency to customers along with the firms competitors and potential competitors2.Exponentially increase the customer retention and acquisition costs by developing multiple layers of acquisition costs3.May negatively affect the performance and reputation of the firm if the customers have complaints about the product However the firm may mitigate these risks by:1.Acquiring maximu m amount of market share and create growth in the market size. Thus, creating barrier to entry as a result of low selling price and variety of product match. This is mainly because the idea is substantially untapped and the product is simultaneously acceptable. The firm must target to tap as much market as possible before any new or existing player takes it over.2.The increasing customer retention and acquisition costs could also  be countered by lowing the COGS as a result of economies of scale and effecting the retention by further lowering the selling price without affecting the margins much.3.Negative reputation due to customer complaints could be countered with the help of product development and fine tuning the existing products and ideas based on customer needs and value system. This could be done by implementing the CRM with the help of 30% of the additional funds raised in the 2nd round.

Friday, January 3, 2020

Kafkas Humor Essay - 1388 Words

Kafkas Humor In Franz Kafkas short fiction, The Metamorphosis, the author was able to skillfully express deep emotions while keeping his readers interested throughout the story. Some may say that the story is sad and horrifying, yet Kafka creatively intertwined humor, which is many times quite ironic, into this seemingly sad story. This gives the reader the opportunity to view the situation from a different angle rather than just to focus on the horrific circumstances that Gregor Samsa, Kafkas protagonist, must go through in The Metamorphosis. Margaret Church, a critic in contemporary studies explains, with Kafka we are in the mind of Gregor and are forced to accept this world of Gregor and to recognize it as our own (189).†¦show more content†¦His many legs, which seemed pathetically thin when compared to the rest of his body, flickered helplessly before his eyes (Kennedy 337). This captures the readers interest immediately. We can all agree that this will probably never happen to us. The fact that Kafka even thought of an event like this is already comical. If we were in Gregors situation, we may feel extremely disturbed or even suicidal. However, Gregor instead thought of how to get out of bed and go to work. Gregor also thought of how to explain his situation to his family and the manager from the office. A conventional person would not even think of explaining the fact that one has been transformed... into a monstrous insect, but would rather be overwhelmed by the fact that his or her life is ruined. Here Kafka made such a disastrous situation into what seems to be a temporary annoyance one may face in daily life. What Gregor awakens to on the morning of his metamorphosis is the truth of his life. His ordinary consciousness has lied to him about himself... (Greenburg 70). Whether symbolic or not, from the very beginning, Kafka creates this terrifying bu t funny plot, something that is very unlikely to happen physically, but gives us an insight to what Kafka himself many have been facing every day. The story moves on explaining the horrified family members trying to deal with Gregor as an insect and rejecting him for beingShow MoreRelatedEssay on Franz Kafkas Use of Humor1619 Words   |  7 PagesFranz Kafkas Use of Humor Franz Kafka, born on July 3, 1883 in Bohemia, in the city of Prague, has been recognized as one of the greatest writers of the twentieth century. His works have been called cloudy, mysterious, inexplicable (Oates ix). Most people hear the term Kafkan or Kafkaesque and think of dark, fantastic tales with almost no basis in our known reality. But what of Kafkas sense of humor? I personally laughed out loud several times while reading Kafkas Amerika. Were these snippetsRead MoreThe Kafka s The Metamorphosis1062 Words   |  5 Pagesinsect. 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