Model predictive control of two-step nitrification and its validation via short-cut nitrification tests

<p>Short-cut nitrification (SCN) is shown to be an attractive technology due to its savings in aeration and external carbon source addition cost. However, the shortage of excluding nitrite nitrogen as a model state in an Activated Sludge Model limits the model predictive control of biological nitrogen removal via SCN. In this paper, a two-step kinetic model was developed based on the introduction of pH and temperature as process controller, and it was implemented in an SBR reactor. The simulation results for optimizing operating conditions showed that with increasing of dissolved oxygen (DO) the rate of ammonia oxidation and nitrite accumulation firstly increased in order to achieve a SCN process. By further increasing DO, the SCN process can be transformed into a complete nitrification process. In addition, within a certain range, increasing sludge retention time and aeration time are beneficial to the accumulation of nitrite. The implementation results in the SBR reactor showed that the data predicted by the kinetic model are in agreement with the data obtained, which indicate that the two-step kinetic model is appropriate to simulate the ammonia removal and nitrite production kinetics.</p

Stereoselective Cascade Formal Nucleophilic Substitution and Mannich Reaction of Ethyl 2‑Aroyl-1-chlorocyclopropanecarboxylates

A highly regio- and diastereoselective cascade formal nucleophilic substitution and Mannich reaction of ethyl 2-aroyl-1-chlorocyclopropanecarboxylates with salicylaldimines is described. Under basic conditions, ethyl 2-aroyl-1-chlorocyclopropanecarboxylate is easily converted into a cyclopropene intermediate via simple 1,2-elimination of hydrogen chloride. The highly reactive cyclopropene quickly combines with salicylaldimine through regioselective oxa-addition to the strained CC bond and subsequent diastereoselective addition to CN bond, constructing C–O and C–C bonds at one time. This provides a highly stereoselective novel methodology for synthesis of conformationally constrained <i>cis</i>-tetrahydrocyclopropa­[<i>b</i>]­chromene derivatives

Activation of the Solid Silica Layer of Aerosol-Based C/SiO₂ Particles for Preparation of Various Functional Multishelled Hollow Microspheres

Double-shelled C/SiO₂ hollow microspheres with an outer nanosheet-like silica shell and an inner carbon shell were reported. C/SiO₂ aerosol particles were synthesized first by a one-step rapid aerosol process. Then the solid silica layer of the aerosol particles was dissolved and regrown on the carbon surface to obtain novel C/SiO₂ double-shelled hollow microspheres. The new microspheres prepared by the facile approach possess high surface area and pore volume (226.3 m² g^–1, 0.51 cm³ g^–1) compared with the original aerosol particles (64.3 m² g^–1, 0.176 cm³ g^–1), providing its enhanced enzyme loading capacity. The nanosheet-like silica shell of the hollow microspheres favors the fixation of Au NPs (C/SiO₂/Au) and prevents them from growing and migrating at 500 °C. Novel C/C and C/Au/C (C/Pt/C) hollow microspheres were also prepared based on the hollow nanostructure. C/C microspheres (482.0 m² g^–1, 0.92 cm³ g^–1) were ideal electrode materials. In particular, the Au NPs embedded into the two carbon layers (C/Au/C, 431.2 m² g^–1, 0.774 cm³ g^–1) show a high catalytic activity and extremely chemical stability even at 850 °C. Moreover, C/SiO₂/Au, C/Au/C microspheres can be easily recycled and reused by an external magnetic field because of the presence of Fe₃O₄ species in the inner carbon shell. The synthetic route reported here is expected to simplify the fabrication process of double-shelled or yolk–shell microspheres, which usually entails multiple steps and a previously synthesized hard template. Such a capability can facilitate the preparation of various functional hollow microspheres by interfacial design

Stereoselective Cascade Formal Nucleophilic Substitution and Mannich Reaction of Ethyl 2‑Aroyl-1-chlorocyclopropanecarboxylates

A highly regio- and diastereoselective cascade formal nucleophilic substitution and Mannich reaction of ethyl 2-aroyl-1-chlorocyclopropanecarboxylates with salicylaldimines is described. Under basic conditions, ethyl 2-aroyl-1-chlorocyclopropanecarboxylate is easily converted into a cyclopropene intermediate via simple 1,2-elimination of hydrogen chloride. The highly reactive cyclopropene quickly combines with salicylaldimine through regioselective oxa-addition to the strained CC bond and subsequent diastereoselective addition to CN bond, constructing C–O and C–C bonds at one time. This provides a highly stereoselective novel methodology for synthesis of conformationally constrained <i>cis</i>-tetrahydrocyclopropa­[<i>b</i>]­chromene derivatives

Enhancement of anaerobic digestive efficiency by the use of exchange resin to remove cations in sewage sludge

<p>Hydrolysis is considered as the rate-limiting stage of anaerobic digestion which is one of the most applied stabilization processes in the disposition of sludge. It is urgent to accelerate the hydrolysis of the sludge particles and improve its biodegradability. This study utilized cation-exchange resin (CER) to adsorb divalent cations in the supernatant of activated sludge with the purpose of making the sludge floc disintegrated. The results showed that the biopolymers incorporated in the tightly bound extracellular polymeric substances can be released to the bulk using CER to remove cations. However, the lack of essential elements led to a much lower methane yield of treated sludge than that of activated sludge. The treated sludge got a higher methane production rate constants after added Fe²⁺. It is necessary to add Fe²⁺ or regenerated liquid of resin-containing essential elements in order to maintain the activities of microbial life.</p

Preparation of Double-Shelled C/SiO₂ Hollow Spheres with Enhanced Adsorption Capacity

In this study, double-shelled C/SiO₂ hollow spheres with an outer hydrophilic silica shell and an inner hydrophobic carbon shell were initially prepared by activating a solid silica layer of C/SiO₂ aerosol particles. This low-cost preparation technique, which can easily be scaled up, includes a rapid aerosol process and a subsequent dissolution–regrowth process. The large surface area (226.3 m²/g), high pore volume (0.51 cm³/g), and high mechanical stability of the spheres benefit their high adsorption capacities for methylene blue (MB) and metal ions. The novel spheres show a high adsorption capacity of 171.2 mg/g for MB, which is higher than the adsorption capacity of single-shelled silica hollow spheres (150.0 mg/g). The adsorption efficiency of the hollow spheres remains higher than 95% after five cycles of regeneration. The saturation adsorption values of Pb²⁺ and Ag⁺ ions on the hollow spheres were found to be 216.5 and 283.1 mg/g, respectively, which are higher than the corresponding values of 189.8 and 213.4 mg/g on the single-shelled SiO₂ spheres. Moreover, the adsorption capacities of the five-times-recycled spheres for Pb²⁺ and Ag⁺ ions reached as high as ∼180 and ∼245 mg/g, respectively. These results reveal that the outer porous silica layer with a ζ-potential of −37.4 mV makes the main contribution to the excellent adsorption performance of the spheres. In addition to the contribution to the adsorption capacity of the double-shelled hollow spheres, the inner carbon layer plays a crucial role in supporting the outer silica shell and in improving the adsorption efficiency, mechanical stability, and recycling properties of the hollow spheres

Shape-Controlled Synthesis of Magnetic Iron Oxide@SiO₂–Au@C Particles with Core–Shell Nanostructures

The preparation of nonspherical magnetic core–shell nanostructures with uniform sizes still remains a challenge. In this study, magnetic iron oxide@SiO₂–Au@C particles with different shapes, such as pseduocube, ellipsoid, and peanut, were synthesized using hematite as templates and precursors of magnetic iron oxide. The as-obtained magnetic particles demonstrated uniform sizes, shapes, and well-designed core–shell nanostructures. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) analysis showed that the Au nanoparticles (AuNPs) of ∼6 nm were uniformly distributed between the silica and carbon layers. The embedding of the metal nanocrystals into the two different layers prevented the aggregation and reduced the loss of the metal nanocrystals during recycling. Catalytic performance of the peanut-like particles kept almost unchanged without a noticeable decrease in the reduction of 4-nitrophenol (4-NP) in 8 min even after 7 cycles, indicating excellent reusability of the particles. Moreover, the catalyst could be readily recycled magnetically after each reduction by an external magnetic field

Ethyl 6‑Hydroxyfulvene-1-Carboxylate: A Reagent Discriminating Primary Amines from Secondary Amines

A highly chemo-selective reaction was observed when ethyl 6-hydroxyfulvene-1-carboxylate <b>1</b> was treated with different nucleophiles such as primary amines, secondary amines, alcohols, and thiols. Among them, only primary amines are reactive toward <b>1</b> to afford the condensation products <b>3</b>, which exhibit good stability under both weakly acidic and basic conditions. The condensation process proved to be reversible between different primary amines. On the basis of this observation, the chemical selectivity of typical primary aromatic amines was evaluated quantitatively by determining equilibrium constants of the condensation reactions with aniline as a reference. Moreover, the primary amines of <b>3</b> can be readily released upon treatment with aqueous ammonia, making 6-hydroxyfulvene-1-carboxylate <b>1</b> a promising protecting reagent for primary amines

Full-Color Fluorescence of Carbonization-Triggered Carbon Dots for Multifunctional Light Module: Implications for Plant Lighting

Carbon dots (CDs) are widely used in the field of optoelectronics due to their excellent luminescent properties. However, CDs have difficulty achieving long-wavelength modulation due to their complex structure and unclear luminescence mechanism, which limit their application and development in real-life situations. In this work, we explored the effect of the degree of carbonization on the long-wavelength emission of CDs. In this work, blue, green, and red fluorescent CDs were prepared by a hydrothermal carbonization method using sodium lignosulfonate as a carbon source. The experimental results show that the size and graphitization degree of CDs increase gradually with increasing carbonization time, and the sp2 structure and graphite N atoms also increase gradually, which causes the fluorescence red shift of CDs, which is verified by chemical simulation calculations. The starch was embedded in CDs to prepare tricolor phosphors, which were applied to full-color light-emitting diodes (LEDs). Finally, the combination of CDs and modules extends the range of applications for which CDs can be used. The prepared multifunctional modules that can be used for multicolor switching can be used not only for plant lighting to promote plant growth but also for indoor lighting. This work has implications for the modulation of long-wavelength emission of CD fluorescence, expanding the practical applications of LEDs prepared from CDs and promoting the development of CDs in the field of optoelectronics

Tin and Silicon Binary Oxide on the Carbon Support of a Pt Electrocatalyst with Enhanced Activity and Durability

Poor durability is one of the two major problems hindering the commercialization of proton exchange membrane fuel cells, due to Pt nanoparticle aggregation in the electrocatalyst and corrosion of its carbon support. In this paper, we report a Pt electrocatalyst in which carbon black decorated with a tin and silicon binary oxide layer was used as the support, with SnO₂ as a promoter and SiO₂ as a stabilizer. Transmission electron microscopy revealed that the binary oxide formed a thin layer on the surface of the carbon support particles. The catalyst exhibited significantly enhanced performance toward the oxygen reduction reaction (ORR): at 0.9 V (vs RHE), the ORR current density was ∼1.5 times higher than that of a commercial JM Pt/C catalyst with the same Pt loading. Furthermore, it showed excellent durability, again better than that of JM Pt/C: after 8000 cyclic voltammetry cycles in 0.5 M H₂SO₄ solution, the electrochemically active surface area was almost unchanged and the ORR half-wave potential shifted by only 10 mV. We attribute the catalyst’s high activity and durability to the binary oxide coating the surface of the carbon nanoparticles. We suggest it may play two roles: (1) promoted by tin oxide and thereby enhancing the catalytic activity and (2) preventing the Pt nanoparticles from aggregating and carbon support from corrosion. The high ORR performance and excellent stability of this catalyst make it promising for use in practical fuel cell applications