浮游植物现存量表征指标间相关性研究Ⅰ:叶绿素a与生物量

收集国内、外有关资料,并结合潘家口水库现场围隔实验,主要从实验室内研究水体、野外围隔水体及天然水体三个方面,对浮游植物叶绿素a含量与生物量间的相关性进行探讨。结果表明:在实验室条件下,叶绿素a与生物量一般呈显著正相关关系,但当优势藻种发生明显变更时,二者相关性不明显甚至不相关;现有资料显示,野外围隔实验水中,叶绿素a与生物量一般呈显著正相关。在天然水体中,叶绿素a与生物量可能相关或不相关。叶绿素a与藻密度的关系将在续文中予以讨论。     

Catalytic activity of nickel nanoparticles in hydrogenation of p-nitrophenol to p-aminophenol

Nickel nanoparticles with different sizes and different structures were prepared by reducing nickel oxalate with hydrazine hydrate in the presence of citric acid, sodium dodecyl sulphonate, Tween 80, PEG 6000, and D-sorbitol as organic modifiers. The type of organic modifiers affected the size and the structure of the resultant nickel nanoparticles. The catalytic activities of the nickel nanoparticles increased with decreasing the particle size in the hydrogenation of p-nitrophenol to p-aminophenol. All the as-prepared nickel nanoparticles showed higher catalytic activity and selectivity than conventional Raney Ni catalyst.     

Adsorption of single-ringed N- and S-heterocyclic aromatics on carbon nanotubes

Adsorption of single-ringed N- and S-heterocyclic aromatics on single-walled carbon nanotubes (SWCNTs) was examined to explore the potential of using carbon nanotubes (CNTs) as drug carriers and environmental adsorbents. Adsorbates included pyrimidine, 2-aminopyrimidine, 4,6-diaminopyrimidine, thiophene, benzene and aniline. Adsorbents included pristine SWCNTs, oxidized SWCNTs, and nonporous graphite. Adsorption of N- and S-heterocyclic aromatics was significantly enhanced by non-hydrophobic interactions. Particularly, the -NH₂-substituted compounds exhibited much stronger (up to 2 orders of magnitude) adsorption affinities to oxidized SWCNTs than benzene, even though they are much less hydrophobic. The π-π coupling or electron donor-acceptor (EDA) interactions are likely adsorption-enhancement mechanisms for all six compounds. The lone-pair electrons of the N heteroatoms and the -NH₂ group can enable n-π EDA interactions with SWCNT surfaces. Lewis acid-base interactions are another significant adsorption-enhancement mechanism for the -NH₂-substituted compounds (and possibly for pyrimidine) on SWCNTs. For the N-heterocyclic aromatics, adsorption affinity is highly dependent on the O-functionality of the SWCNT surface and on solution pH, due to the speciation reactions of both adsorbates and SWCNT surface O-functional groups, indicating that selective adsorption of N-heterocyclic aromatics is possible by combining the surface functionality of CNTs and solution chemistry.     

Preparation of magnetic polymeric composite nanoparticles by seeded emulsion polymerization

Seeded emulsion polymerization was used to prepare magnetic polymeric composite nanoparticles (MPCNPs) with the aim to successfully encapsulate magnetite particles and to improve particle size distribution (PSD). Microscopical morphology and number-average diameter of hydrophilic magnetite particles (HMPs), magnetic seed latex nanoparticles (MSLNPs) and MPCNPs were observed and analyzed by transmission electron microscope (TEM). Weight-average diameter and PSD of MSLNPs and MPCNPs were also analyzed by TEM. Magnetic properties of MPCNPs were investigated by Vibrating Sample Magnetometry (VSM). The results showed that the encapsulation of magnetite particles was not complete by conventional emulsion polymerization but very successful by seeded emulsion polymerization, the resulted MPCNPs were nanoparticles with much narrower PSD than that of MSLNPs, and exhibited superparamagnetism and possessed a certain level of magnetic response.     

Adsorption behavior of methylene blue onto titanate nanotubes

Calcined titanate nanotubes were synthesized with hydrothermal treatment of the commercial TiO₂ (Degussa P25) followed by calcination. The morphology and structures of as-prepared samples were investigated by transmission electron microscopy, X-ray diffraction and N₂ adsorption/desorption. The samples exhibited a tubular structure and a high surface area of 157.9 m²/g. The adsorption of methylene blue onto calcined titanate nanotubes was studied. The adsorption kinetics was evaluated by the pseudo-first-order, pseudo-second-order and Weber's intraparticle diffusion model. The pseudo-second-order model was the best to describe the adsorption kinetics, and intraparticle diffusion was not the rate-limiting step. The equilibrium adsorption data were analyzed with three isotherm models (Langmuir model, Freundlich model and Temkin model). The best agreement was achieved by the Langmuir isotherm with correlation coefficient of 0.993, corresponding to maximum adsorption capacity of 133.33 mg/g. The adsorption mechanism was primarily attributed to chemical sorption involving the formation of methylene blue-calcined titanate nanotubes nanocomposite, associated with electrostatic attraction in the initial bulk diffusion.     

Improved dynamic performance of turbocharged SI engine power trains using clutch actuation

This article proposes a new model-based optimal control strategy that is able to substantially reduce the torque lag present in spark-ignited turbocharged engine systems. The key idea is to utilize an automated wet clutch as an additional control actuator.The optimal control signals are obtained using a mean value model of the combined engine-power-train system and numerical optimization methods. The optimization problem is defined by choosing a representative test case and an objective function that parametrizes the trade-off between fast torque dynamics and comfort.The proposed control strategy achieves a reduction of the time lag to reach 90% of full load torque by up to 70%. These results are experimentally confirmed on an engine dynamometer for a downsized and turbocharged SI engine.     

A review of material aspects in developing direct Z-scheme photocatalysts

Photocatalysis utilizes solar energy to produce clean fuels such as hydrogen or generate highly reactive species to subsequently break the organic pollutants into clean end products. Direct Z-scheme heterostructured photocatalysts can overcome the fundamental shortcomings in conventional photocatalysts and thus enable this green technology in tackling the energy crisis and environmental problems at the same time. Various approaches and numerous materials have been attempted in the hope of achieving high efficiency and broad effectiveness for practical applications. This work intends to provide a comprehensive and timely review on direct Z-scheme photocatalysts from the material’s point of view. The formation mechanisms based on the driving forces of the charge transfer are firstly discussed to guide the material design. Three mechanisms, namely internal electric field, interfacial defect-induced charge transfer, and facet-induced charge transfer, are identified and summarized. Various material systems are then extensively discussed and compared according to their applications, followed by the emerging material modification strategies for performance improvement. Lastly, the review provides the perspectives for future development. It is expected that the insights of this up-to-date review could guide the material design and performance improvement of the direct Z-scheme systems to achieve their maximum potentials.     

Controlled Experimental Study on Removing Diesel Oil Spillages Using Agricultural Waste Products

Diesel oil was used as adsorbate, while corn stalk, wheat straw and sawdust were used as natural sorbents for adsorbing and absorbing pure oil and oil in water. The results showed that all three agricultural wastes absorbed diesel. The corresponding saturated sorption amounts of wheat straw, corn stalk and sawdust were 8.54 g g^–1, 7.03 g g^–1 and 8.2 g g^–1. The optimum conditions found were: corn stalk particle size between 830 and 1700 μm, oscillation frequency of 0 r min^–1, i.e., no wave movement, oil film thickness of 0.55 mm and adsorbent dosage of 0.29 g; sawdust particle size between 830 and 1700 μm, oscillation frequency of 0 r min^–1, oil film thickness of 0.55 mm and adsorbent dosage of 0.25 g; wheat straw particle size between 500 and 830 μm, oscillation frequency of 0 r min^–1, oil film thickness of 0.55 mm and adsorbent dosage of 0.24 g.     

Equilibrium theory revisited. Isothermal fixed-bed sorption of binary systems-II. Non-Langmuir solutes with type I parent isotherms: Azeotropic systems

The preceding analysis of the equilibrium percolation of binary Langmuir solutes (Part I) is extended to systems with arbitrary equilibrium relations and parent isotherms of Type I. The use of “extended” binary Langmuir isotherms is proposed as the best means for providing some analytical insight while satisfying important thermodynamic and mathematical requirements.We show that the simple method for locating the watershed point given in Part I can be extended to broad classes of parent solute isotherms. It consists of determining, analytically or graphically, the intersection of the light component Henry's line with the heavy component isotherms. This opens up a rapid path for assessing the effectiveness of displacement agents in purging a loaded bed and achieving high levels of desorbate enrichment (see Part III).The behaviour of binary non-Langmuir solutes, both with and without selectivity reversal is addressed. The latter case yields solute trajectories and other properties which resemble, in all major aspects, those established for Langmuir solutes (Part I). It is shown that under certain conditions minor changes in the equilibrium parameters can lead to serious aberrations in the predicted solute trajectories. The use, in particular, of single component isotherms to represent strongly sorbed solutes yields highly erroneous predictions of binary desorption and displacement processes.The effect of selectivity reversal is expressed through azeotropic loci, incorporated in the hodograph diagrams. These curves constitute deflecting barriers in some cases and can be traversed by the solute trajectories in others. The distinguishing feature of the hodographs is the shape of the negative characteristics in q-Y space which inflect across a diagonal in much the same way as binary vapour-liquid azeotropes. The resulting solute fronts still follow the binary Langmuir pattern in most instances, except in certain displacement operations and in cases of simultaneous azeotropic propagation. The inflecting form of the Γ⁻ characteristics also gives rise to the interesting possibility of isolating pure gaseous solute fractions from a binary feed through the use of dual column systems operated at different total pressures.Various solute pathways, created by the presence of the azeotropic curves are analyzed, and compared with experimental column breakthrough curves. The extreme sensitivity of certain azeotropic pathways to the precise form of the equilibrium relation is discussed.