Dissolution of kaolinite induced by citric, oxalic, and malic acids

Kaolinite is a dominant clay mineral in the soils in tropical and subtropical regions, and its dissolution has an influence on a variety of soil properties. In this work, kaolinite dissolution induced by three kinds of low-molecular-weight organic acid, i.e., citric, oxalic, and malic acids, was evaluated under far-from-equilibrium conditions. The rates of kaolinite dissolution depended on the kind and concentration of organic acids, with the sequence R(oxalate)>R(citrate)>R(malate). Chemical calculation showed the change in concentration of organic ligand relative to change in concentration of organic acid in suspensions of kaolinite and organic acid. The effect of organic acid on kaolinite dissolution was modeled by species of organic anionic ligand. For oxalic acid, L(2-)(oxalic) and HL(-)(oxalic) jointly enhanced the dissolution of kaolinite, but for malic and citric acids, HL(-)(malic) and H2L-(citric) made a higher contribution to the total dissolution rate of kaolinite than L(2-)(malic) and L(3-)(citric), respectively. For oxalic acid, the proposed model was R(Si)=1.89x10(-12)x[(25x)/(1+25x)]+1.93x10(-12)x[(1990x1)/(1+1990x1)] (R2=0.9763), where x and x1 denote the concentrations of HL(oxalic) and L(oxalic), respectively, and x1=10(-3.81)xx/[H+]. For malic acid, the model was R(Si)=4.79x10(-12)x[(328x)/(1+328x)]+1.67x10(-13)x[(1149x1)/(1+1149x1)] (R2=0.9452), where x and x1 denote the concentrations of HL(malic) and L(malic), respectively, and x1=10(-5.11)xx/[H+], and for citric acid, the model was R(Si)=4.73x10(-12)x[(845x)/(1+845x)]+4.68x10(-12)x[(2855x1)/(1+2855x1)] (R2=0.9682), where x and x1 denote the concentrations of H2L(citric) and L(citric), respectively, and [Formula: see text] .     

Synthesis of α-di or trisubstituted (tetrahydrofuran-2-yl)methanols via photoinduced additive-free intermolecular addition of THF to aromatic aldehydes or ketones

THF is found to react with aromatic aldehydes or ketones highly chemoselectively under the irradiation of ultraviolet without any additives, which provides a new protocol to access α-di or trisubstituted (tetrahydrofuran-2-yl)methanols. The scope of this reaction is well studied.     

Unsaturation Characterization of Polyolefins by NMR and Thermal Gradient NMR (TGNMR) with a High Temperature Cryoprobe

Summary: It is important to identify the types of unsaturation and to quantify the amount of unsaturation in polyolefins for understanding chain termination mechanisms of polymerization with different catalysts. Unsaturation is also closely related to processibility, weatherability of polyolefin products and the level of antioxidants to be added for stabilizing purposes. However, it can be very challenging to accurately measure samples with a low level of the unsaturation within a reasonable amount of NMR acquisition time, along with some challenging technical issues, such as dynamic range with ¹H NMR. This paper reports a new method to accurately quantify unsaturation by using multi peak presaturation ¹H NMR with a high temperature NMR cryoprobe. The limit of quantification can be less than 1 unsaturation/1,000,000 carbons with about 30 min NMR acquisition. This paper also introduces a new technique, temperature gradient NMR (TGNMR) with or without substrates, to characterize unsaturation distribution directly in NMR tube upon temperature change.     

Ultrathin Metal–Organic Framework Nanosheets with Ultrahigh Loading of Single Pt Atoms for Efficient Visible‐Light‐Driven Photocatalytic H2 Evolution

A surfactant‐stabilized coordination strategy is used to make two‐dimensional (2D) single‐atom catalysts (SACs) with an ultrahigh Pt loading of 12.0 wt %, by assembly of pre‐formed single Pt atom coordinated porphyrin precursors into free‐standing metal–organic framework (MOF) nanosheets with an ultrathin thickness of 2.4±0.9 nm. This is the first example of 2D MOF‐based SACs. Remarkably, the 2D SACs exhibit a record‐high photocatalytic H₂ evolution rate of 11 320 μmol g^?1 h^?1 via water splitting under visible light irradiation (λ>420 nm) compared with those of reported MOF‐based photocatalysts. Moreover, the MOF nanosheets can be readily drop‐casted onto solid substrates, forming thin films while still retaining their photocatalytic activity, which is highly desirable for practical solar H₂ production.     

N-甲基-2-硫-咪唑树脂对钯吸附的研究

测定了N-甲基-2-硫-咪唑树脂对钯Pd(Ⅱ)吸附的容量,Pd(Ⅱ)与Fe~(3+)、Cu~(2+)、Ni~(2+)、Mn~(2+)的分离系数、吸附Pd(Ⅱ)的速率常数、Freundlich吸附常数。通过化学法、红外光谱等方法,分别确定树脂功能基对钯吸附的络合比,及吸附过程功能基与钯发生了配位键合.选用混合洗脱剂可定量洗脱钯,并证明此法在实际应用中,可富集、回收钯。     

Self-assembly of block copolymers

Block copolymer (BCP) self-assembly has attracted considerable attention for many decades because it can yield ordered structures in a wide range of morphologies, including spheres, cylinders, bicontinuous structures, lamellae, vesicles, and many other complex or hierarchical assemblies. These aggregates provide potential or practical applications in many fields. The present tutorial review introduces the primary principles of BCP self-assembly in bulk and in solution, by describing experiments, theories, accessible morphologies and morphological transitions, factors affecting the morphology, thermodynamics and kinetics, among others. As one specific example at a more advanced level, BCP vesicles (polymersomes) and their potential applications are discussed in some detail.     

Fourier–Bessel theory on flow acoustics in inviscid shear pipeline fluid flow

Flow acoustics in pipeline is of considerable interest in both industrial application and scientific research. While well-known analytical solutions exist for stationary and uniform mean flow, only numerical solutions exist for shear mean flow. Based on potential theory, a general mathematical formulation of flow acoustics in inviscid fluid with shear mean flow is deduced, resulting in a set of two second-order differential equations. According to Fourier–Bessel theory which is orthogonal and complete in Lebesgue Space, a solution is proposed to transform the differential equations to linear homogeneous algebraic equations. Consequently, the axial wave number is numerically calculated due to the existence condition of non-trivial solution to homogeneous linear algebraic equations, leading to the vanishment of the corresponding determinant. Based on the proposed method, wave propagation in laminar and turbulent flow is numerically analyzed.     

A reduced variable neighborhood search algorithm for uncapacitated multilevel lot-sizing problems

Multilevel lot-sizing (MLLS) problems, which involve complicated product structures with interdependence among the items, play an important role in the material requirement planning (MRP) system of modern manufacturing/assembling lines. In this paper, we present a reduced variable neighborhood search (RVNS) algorithm and several implemental techniques for solving uncapacitated MLLS problems. Computational experiments are carried out on three classes of benchmark instances under different scales (small, medium, and large). Compared with the existing literature, RVNS shows good performance and robustness on a total of 176 tested instances. For the 96 small-sized instances, the RVNS algorithm can find 100% of the optimal solutions in less computational time; for the 40 medium-sized and the 40 large-sized instances, the RVNS algorithm is competitive against other methods, enjoying good effectiveness as well as high computational efficiency. In the calculations, RVNS updated 7 (17.5%) best known solutions for the medium-sized instances and 16 (40%) best known solutions for the large-sized instances.