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Published in Eli Ruckenstein, Hangquan Li, Chong Cheng, Concentrated Emulsion Polymerization, 2019
Eli Ruckenstein, Xiao-Bai Wang
Styrene (ST; 99%; Aldrich) and divinylbenzene (DVB; 55%; Aldrich) were distilled to remove the polymerization inhibitor (4-tert-butylcatechol), azobisisobutyronitrile (AIBN; Alfa) was recrystallized from methanol, and veratryl alcohol (96%, Aldrich) was purified by distillation. The dispersant Span-80 (Fluka), potassium dihydrogen phosphate (99%; Aldrich), magnesium sulfate heptahydrate (98+%; Aldrich), calcium chloride dihydrate (98+%; Aldrich), ammonium chloride (ACS reagent; Aldrich), thiamine (Sigma), 2-chlorophenol (99+%; Aldrich), hydrogen peroxide (30 wt% solution in water; ACS reagent; Aldrich), sodium tartrate (99.8%; Sigma), Tween-80 (enzyme grade; Fisher), and glucose (≥99.8%; Fisher) were used as received. Water was deionized and distilled.
Covalent Organic Frameworks-Based Nanomaterials for Hydrogen Evolution Reactions
Published in Tuan Anh Nguyen, Ram K. Gupta, Covalent Organic Frameworks, 2023
Felipe M. de Souza, Ram K. Gupta
However, the long time required for proper crystallization to occur makes it necessary to optimize the process. Some of the strategies for that consists of modulation and seed approach. The modulation approach consists of adding a terminating monofunctionalized ligand that disputes with the monomer to promote a slower but more organized growth. In that sense, it was observed that the rate of monomer addition influences the formation of COF in terms of growth and nucleation, at which the growth has a first-order and the nucleation has a second-order dependence over monomer concentration, which means that growth dominates nucleation over the early stages whereas nucleation dominates over the late stages of reaction [9]. Dichtel et al. [10] performed a growth-dominated process for the synthesis of a boronate COF by slowly adding the monomer, which yielded 2D single crystals of the order of micrometers. The solvent aid in the stabilization of the crystal growth of 2D boronate COF as it was observed that the mixture of 1,4-dioxane and mesitylene prevented aggregation. Yet, the process was optimized by further adding CH3CN . In another case also based on the modulation approach, Ditchel et al. [11] used a terminal monofunctional monomer, 4-tert-butylcatechol (TCAT), which served as a competitor during the synthesis of COF-5. Even though the formation of COF was slowed there was an increase in crystalline size domain from 23 to 32 nm. The process was further optimized by adding an excess of TCAT which yielded crystals with an average size of 450 nm. That effect was observed because TCAT acted as a nucleation inhibitor whereas inducing the anisotropic growth. On top of that, the authors observed only traces of TCAT into the COF-5, which suggested that modulation accompanied to seed growth can be a feasible procedure to induce crystallinity without incorporating undesired reagents.
Engineered Pseudomonas putida for biosynthesis of catechol from lignin-derived model compounds and biomass hydrolysate
Published in Preparative Biochemistry & Biotechnology, 2022
Catechol and its derivatives are important chemical precursors for several applications such as carbamate insectidices (carbofuran and propoxur), polymerization inhibitors (4-tert-butylcatechol), photographic developers, tanning agents, perfumes, cosmetics, biomaterial and therapeutic agents.[1,2] Annually, 2.5 × 107 kg of catechol is produced commercially by synthetic/chemical routes.[3] The various chemical routes for catechol production include hydrolysis of 2-chloro phenol with copper as a catalyst at elevated temperature; hydroxylation of phenol in presence of peroxide along with catalyst; dehydrogenation of 1,2-cyclohexanediol with palladium as a catalyst at 300 °C; and oxidation of salicylic aldehyde and demethylation of guaiacol.[1,4,5] Chemical synthesis of catechol is a catalyst-based energy intensive process, resulting in the co-production of compounds such as hydroquinone and resorcinol. This compound along with un-reacted phenol mixtures makes separation and scale up a tedious job.[1,6,7] Moreover, catechol is derived from petroleum-based feedstock leading to several environmental issues thereby necessitating focusing our attention toward catechol synthesis from sustainable and renewable starting material using microbes.[3,8] Lignocellulosic biomass is one such sustainable and renewable feedstock giving rise to bio-refinery concept.