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Abstract: Nanomaterials with unique electronic, optical and catalytic properties have recently been at the forefront of research due to their tremendous range of applications. Taking gold, silver and titania nanoparticles as examples, we have reviewed the current research works on paper functionalized by these nanoparticles. The functionalization of paper with only a very small concentration of nanoparticles is able to produce devices with excellent photocatalytic, antibacterial, anti-counterfeiting, Surface Enhanced Raman Scattering (SERS) and Surface Plasmon Resonance (SPR) performances. This review presents a brief overview of the properties of gold, silver and titania nanoparticles which contribute to the major applications of nanoparticles-functionalized paper. Different preparation methods of the nanoparticles-functionalized paper are reviewed, focusing on their ability to control the morphology and structure of paper as well as the spatial location and adsorption state of nanoparticles which are critical in achieving their optimum applications. In addition, main applications of the nanoparticles-functionalized papers are highlighted and their critical challenges are discussed, followed by perspectives on the future direction in this research field. Whilst a few studies to date have characterized the distribution of nanoparticles on paper substrates, none have yet optimized paper as a nanoparticles'' substrate. There remains a strong need to improve understanding on the optimum adsorption state of nanoparticles on paper and the heterogeneity effects of paper on the properties of these nanoparticles. [Copyright &y& Elsevier]

Abstract: The mechanism of the retention of TiO2 filler particles on cellulose fibers has been under discussion for several decades; the diverse models, and the properties of the components relevant to retention, are critically reviewed in the first part of this study. In addition, two new quantitative models of detachment of polyelectrolyte-bonded colloidal particles from the fiber are also examined; one of these is based on DLVO theory for description of the influence of particle charge and polyelectrolyte amount, and should hold true at low shear rates and high bond strengths. The other model applies Kolmogorov''s theory of isotropic turbulence in order to relate the work necessary for particle detachment to the turbulent energy of pulp in paper machines, i.e., under high shear rate and low bond-strength conditions. The second model is based on analysis of fluid dynamics in paper machines, and is formulated here for laboratory tests using the Dynamic Drainage Jar (DDJ). A series of laboratory-prepared TiO2 fillers covering a range of isoelectric points (ieps) from pH 4.4 to pH 7.5, additionally with poly-(aminoamide)-epichlorohydrin (PAE) and polyethyleneimine (PEI) as retention aids, and commercially milled cellulose, were used in the experimental part of the study. The retention-aid demand of fillers and cellulose for surface neutralization was determined using electrokinetic methods. Filler retention on cellulose was measured in the DDJ for various stirrer speeds and amounts of retention aid, with the amount of filler not exceeding that for a monolayer on the fiber. Without retention aids, neutral filler particles are accordingly completely retained on the negative fiber, whereas negatively charged particles are not. The retention of the latter can, however, be steadily improved by increasing polyelectrolyte concentration. Retention of colloidal particles in paper manufacturing is therefore determined by a delicate balance between H-bridging and van der Waals forces, on the one hand, and Coulomb forces, on the other, resolving the long-enduring debate concerning the relative influence of bridging and patch-charge mechanisms. Results obtained using PAE also indicate that polyelectrolytes initially spread over the filler surface are redistributed into the gap between the filler particle and the fiber during filler attachment. [Copyright &y& Elsevier]

Abstract: This review paper investigates the synthesis of porous structures with controlled hole pattern and provides an overall view of the various factors involved when synthesizing such porous materials. The following factors are discussed: 1) various methods of synthesis to produce the porous structures; 2) materials which the porous structures are made of; 3) control of the pore structure; 4) various applications of such porous materials. The materials of the porous structures and the control of the pore structure will also be discussed separately under each different method, as these two factors are closely dependent on the method of fabrication. [Copyright &y& Elsevier]