A comparative study on the preparation methods and properties of coal-based fluorescent carbon nanoparticles

Fluorescent carbon nanoparticles (FCNPs) have broad application prospects in the fields of bioimaging, ion detection, and photocatalysis. In this paper, coal-based FCNPs were prepared by using mixed acid oxidation, hydrogen peroxide etching, and organic solvent extraction methods (marked as FCNPs-AO, FCNPs-HE, and FCNPs-OS, respectively), and the structures and properties of the as-prepared products were compared. It was found that the coal-based FCNPs obtained by three kinds of methods are all aromatic structural nanomaterials linked with oxygen-containing groups. Among them, FCNPs-AO is a kind of hollow annular spherical particles and FCNPs-HE and FCNPs-OS are solid spherical particles. These FCNPs not only have similar fluorescence properties as traditional quantum dots, but also can be photoexcited to generate photogenerated electrons and holes, and it can also suppress the recombination of photogenerated electrons and holes by using its own surface defects. In particular, the electron transport capability of the FCNPs-AO is stronger than that of FCNPs-HE and FCNPs-OS because of its lower charge transfer impedance, so it can be excited to generate more photogenerated electrons and has the best photogenerated carrier separation efficiency.     

Analysis of steady viscous flow in slender tubes

The computer extended perturbation series method is used to analyze the problem of steady viscous flow in slender tubes. The objective is to obtain an expansion in a power series of λ (= ɛ R, ɛ is a small parameter and R = \fracMLnR = \frac{M}{{L\nu }} is a streamwise Reynolds number) and look for its analytic continuation. Such an expansion was usually terminated at the second or third order term and consequently they have a very limited utility. Sufficiently large number of terms in the series, representing physical quantities are, generated for the detail analysis which enables to get converging Pade’ sums for large λ. Domb-Sykes plot enables in finding singularity restricting the convergence of the series. Useful results valid up to λ = 15 are obtained for different derived quantities whereas in earlier findings [6], analysis could be done only up to λ = 10 resulting into a substantial improvement in the present study.     

Boundary Value Problems for Third-Order Nonlinear Ordinary Differential Equations

In this paper, we describe how to analyze boundary value problems for third-order nonlinear ordinary differential equations over an infinite interval. Several physical problems of interest are governed by such systems. The seminumerical schemes described here offer some advantages over solutions obtained by using traditional methods such as finite differences, shooting method, etc. These techniques also reveal the analytic structure of the solution function. For illustrative purposes, several physical problems, mainly drawn from fluid mechanics, are considered; they clearly demonstrate the efficiency of the techniques presented here.     

Analysis of steady viscous flow in slender tubes

The computer extended perturbation series method is used to analyze the problem of steady viscous flow in slender tubes. The objective is to obtain an expansion in a power series of λ (= ɛ R, ɛ is a small parameter and is a streamwise Reynolds number) and look for its analytic continuation. Such an expansion was usually terminated at the second or third order term and consequently they have a very limited utility. Sufficiently large number of terms in the series, representing physical quantities are, generated for the detail analysis which enables to get converging Pade’ sums for large λ. Domb-Sykes plot enables in finding singularity restricting the convergence of the series. Useful results valid up to λ = 15 are obtained for different derived quantities whereas in earlier findings [6], analysis could be done only up to λ = 10 resulting into a substantial improvement in the present study.Received: September 17, 2003; revised: July 5, 2004     

基于氨基化煤基碳点的复合光催化剂的制备及对CO2还原的催化性能

采用过氧化氢氧化法剥离出煤炭结构中的晶体碳[煤基碳点(CDs)], 并通过亚硫酰氯氯化及乙二胺钝化等步骤对其进行氨基化修饰, 制得N, S共掺杂的氨基化煤基碳点(NH₂-CDs), 再利用其表面的氨基和含氧基等官能团的配位及分散作用, 将由氯化铜原位还原得到的氧化亚铜(Cu₂O)纳米粒子包覆于其中, 制备了复合催化剂Cu₂O/NH₂-CDs, 表征了其结构和形貌, 并考察了其可见光催化还原CO₂/H₂O的性能. 结果发现, NH₂-CDs的存在使复合催化剂不仅具备了较强的CO₂吸附性能, 而且还具有了高效的电子-空穴对分离和电子转移能力, 从而表现出优异的光催化还原CO₂制备HCOOH的性能. 反应6 h时, 产物HCOOH的量为2582.4 μmol/g cat, 约为同条件下纯Cu₂O作为光催化剂时产物HCOOH产率的7.3倍.     

Approximate elongation flow properties utilising the opposed orifice technique – Correction for shear and inertia

Mackay et al. (1995) have presented an approximate technique to determine the elongation viscosity from pressure drop measurements in a simple stagnation flow device. In the present paper we describe experiments using a high viscosity Newtonian oil, aimed at probing some of the assumptions made by Mackay et al. We find that Trouton ratios calculated using the original analysis are well above the value of three expected for Newtonian fluids. Finite element simulations of the flow field show this is due to the net pressure drop having a substantial shear contribution, which should be corrected for before the Trouton ratios are evaluated. Interestingly, most of the shear correction is due to shear on the inside of the orifice near the exit from the central flow region. The shear contribution to the pressure drop occurs for all flow rates, however, at large flow rates there is also an inertial correction to the pressure drop. In this paper we describe an approximate method that corrects for both shear and inertial effects. With these effects recognised and corrected for, the measured Trouton ratios are reduced to around three. Received: 15 December 1997 Accepted: 16 March 1998