Band 34, Heft 4

Composite membranes based on porous support membranes filled with a proton-conducting polymer appear to be a promising approach to develop novel proton exchange membranes (PEMs). It allows optimization of the properties of the filler and the matrix separately, e.g. for maximal conductivity of the former and maximal physical strength of the latter. In addition, the confinement itself can alter the properties of the filling ionomer, e.g. toward higher conductivity and selectivity due to alignment and restricted swelling. This article reviews the literature on PEMs prepared by filling of submicron and nanometric size pores with Nafion and other proton-conductive polymers. PEMs based on alternating perfluorinated and non-perfluorinated polymer systems and incorporation of fillers are briefly discussed too, as they share some structure/transport relationships with the pore-filling PEMs. We also review here the background knowledge on structural and transport properties of Nafion and proton-conducting polymers in general, as well as experimental methods concerned with preparation and characterization of pore-filling membranes. Such information will be useful for preparing next-generation composite membranes, which will allow maximal utilization of beneficial characteristics of polymeric proton conductors and understanding the complicated structure/transport relationships in the pore-filling composite PEMs.

This paper reviews the research undertaken to study the design criteria that address the monolithic support structure requirements in steam reforming operation for the effective mass transfer of process gases to the active sites and effective conductive heat transfer through tube wall to the active catalytic areas, as well as low pressure drop operation. Design considerations include selection of substrate materials that possess good mechanical strength to withstand the severe reaction conditions and prevent catalyst crushing that would lead to carbon formation and catalyst deactivation, and excessive heating of the tube that results in hot spots which is fatal to tube lifetime. The support’s mechanical properties are listed for the purpose of providing guidelines on verifying the structure durability. The practical aspect of packaging and stacking the monolith structures in the reformer tube for ease of loading and discharge is discussed to understand its readiness in industrial application.

The heavy reliance on fossil fuels, given their inevitable depletion and serious negative impact on the environment, has led to intensive scientific research to produce solutions which will ensure sustainable supply of energy based on renewable sources. Solar radiation is one of the major sources of clean and renewable energy with the potential to provide ample power for the growing human population in the long term. The current energy crisis is aggravated by the escalating concerns over the water quality especially in developing countries. There is great potential for utilisation of solar energy through solar photovoltaic systems throughout the world for electricity generation as well as water and wastewater treatment. Innovations in this area have opened new prospects to improve the quality of life for people as a whole. Hence, the focus of this review paper is to provide the reader with a brief history of solar photovoltaic systems, the various types of solar photovoltaic materials available and the solar cell efficiencies attained with the current solar photovoltaic technologies. Furthermore, applications of photovoltaic systems are discussed in terms of their societal economic and environmental effects.

Metal nanoparticles are being extensively used in a variety of sectors, including drug delivery, cancer treatment, wastewater treatment, DNA analysis, antibacterial agents, biosensors and catalysts. Unlike chemically produced nanoparticles, biosynthesized metal nanoparticles based on green chemistry perspectives impose limited hazards to the environment and are relatively biocompatible. This review is therefore focused on green methods for nanoparticle synthesis by emphasizing on microbial synthesis using bacteria, fungi, algae, and yeasts, as well as phytosynthesis using plant extracts. Furthermore, a detailed description of bioreducing and capping/stabilizing agents involved in the biosynthesis mechanism using these green sources is presented.

Population balance equations (PBE) are widely applied to describe many physicochemical processes such as nanoparticle synthesis, chemical processes for particulates, colloid gel, aerosol dynamics, and disease progression. The numerical study for solving the PBE, i.e. population balance modeling, is undergoing rapid development. In this review, the application of the Taylor series expansion scheme in solving the PBE was discussed. The theories, implement criteria, and applications are presented here in a universal form for ease of use. The aforementioned method is mathematically economical and applicable to the combination of fine-particle physicochemical processes and can be used to numerically and pseudo-analytically describe the time evolution of statistical parameters governed by the PBE. This article summarizes the principal details of the method and discusses its application to engineering problems. Four key issues relevant to this method, namely, the optimization of type of moment sequence, selection of Taylor series expansion point, optimization of an order of Taylor series expansion, and selection of terms for Taylor series expansion, are emphasized. The possible direction for the development of this method and its advantages and shortcomings are also discussed.