Walid A. Daoud

Recent advances in making nano-sized TiO2 visible-light active through rare-earth metal doping

Doping with metals and non-metals is a popular technique that facilitates visible light activity of titanium dioxide. More recently, rare-earth metals have shown tremendous potential as dopants not only in red-shifting the absorption but also in improving the photocatalysis of TiO2. This feature article discusses recent developments in making TiO2 visible-light active through single and co-doping with rare earth metals. An emphasis is placed on wet chemical techniques and their associated effects on the phase, adsorption, surface area, and photocatalytic activity of TiO2. New techniques, such as electrospinning, magnetron sputtering, co-precipitation, and complexation, as well as the use of nanotubes and physical support are also discussed.

Self-cleaning cotton

Nanocrystalline titanium dioxide has been prepared under ambient pressure and at temperatures close to or approaching room temperature using hydrolysis of titanium tetraisopropoxide in an acidic aqueous solution. A transparent thin layer of nanocrystalline titania has been produced on cotton textiles by a dip-pad–dry-cure process. These TiO2 coated cotton textiles possess significant photocatalytic self-cleaning properties, such as bactericidal activity, colorant stain decomposition and degradation of red wine and coffee stains. The UV absorption and tearing strength of the TiO2 coated cotton has also been studied. Self-cleaning cotton may find potential commercialization in the textile industry.

A New Approach to UV-Blocking Treatment for Cotton Fabrics

In this study, a new approach to a uv-blocking treatment for cotton fabrics is developed using the sol-gel method. The treatment forms a thin layer of titania on the surface of cotton fibers, and the treated fabrics show much improved protection against UV radiation. with a UPF factor of 50+ or excellent protection according to the Australian/New Zealand standards. The treated fabrics are also tested for washfastness. The results show that the excellent uv protection rating of the treated fabrics can be maintained even after 55 home launderings, indicating a high level of adhesion between the titania layer and the cotton. A bursting strength test of the treated fabrics shows no adverse effect from the treatment.

Facile preparation of anatase/SiO2 spherical nanocomposites and their application in self-cleaning textiles

Anatase TiO2/SiO2 nanocomposites were prepared by a sol–gel process at a low temperature. The structural properties of these as-prepared nanocomposites were characterized with scanning electron microscopy (SEM) and X-ray diffraction (XRD), showing that TiO2 nanoparticles were deposited on the surface of SiO2 spheres. The spherical TiO2/SiO2 nanocomposites were coated onto cotton fabrics by a simple dip-pad–dry-cure process. The treated cotton fabrics demonstrated higher photocatalytic activity in comparison to pure TiO2 treated cotton fabrics in a typical photocatalytic test using a model compound of Neolan Blue 2G dye. Our results demonstrate that this composite material is a step towards better self-cleaning performance of textile materials.

Recent progress in organic–inorganic halide perovskite solar cells: mechanisms and material design

While energy shortage is always an issue, the impending exhaustion of fossil fuel sources makes it an ever increasingly pressing one. Photovoltaic technology brings hope in the struggle to alleviate this problem, but no solar cell has yet fulfilled the requirements of the viability of large scale production together with high efficiency and low cost. Fortunately, recently reported organic–inorganic halide perovskites, possessing the desirable properties of a high absorption coefficient, a long charge diffusion length, an appropriate band gap, and solution processability, show great potential for photovoltaic applications. Within a few years, the power conversion efficiency of perovskite solar cells has increased from 3.8% to 19.3%. Reports on new preparation methods and materials continue to emerge. While reviews have focused on mechanisms, cell structures, preparation methods and materials applied, it is important to give a combined overview of all these aspects. Furthermore, this review considers the newly reported preparation methods and mechanisms and summarizes the applied materials for each function of these solar cells.

Carbon Dot Loading and TiO2 Nanorod Length Dependence of Photoelectrochemical Properties in Carbon Dot/TiO2 Nanorod Array Nanocomposites

Photoelectrochemcial (PEC) properties of TiO2 nanorod arrays (TNRA) have been extensively investigated as they are photostable and cost-effective. However, due to the wide band gap, only the UV part of solar light can be employed by TiO2. To enhance the photoresponse of TNRA in the visible range, carbon dots (C dots) were applied as green sensitizer in this work by investigating the effects of C dot loading and length of TiO2 nanorod on the PEC properties of TNRA/C dot nanocomposites. As the C dot loading increases, the photocurrent density of the nanocomposites was enhanced and reached a maximum when the concentration of the C dots was 0.4 mg/mL. A further increase in the C dot concentration decreased the photocurrent, which might be caused by the surface aggregation of C dots. A compromise existed between charge transport and charge collection as the length of TiO2 nanorod increased. The incident photon to current conversion efficiency (IPCE) of the TNRA/C dot nanocomposites in the visible range was up to 1.2-3.4%. This work can serve as guidance for fabrication of highly efficient photoanode for PEC cells based on C dots.

Self-cleaning fibers via nanotechnology: a virtual reality

With the fast-growing demand toward innovative functional and intelligent fibrous materials, the self-cleaning functionalization treatment of fibers via nanotechnology has attracted tremendous technological attention over the past four years. This contribution provides a review of the latest developments of contemporary technologies.

Photostable self-cleaning cotton by a copper(II) porphyrin/TiO2 visible-light photocatalytic system.

Thin films of meso-tetra(4-carboxyphenyl)porphyrinato copper(II) (CuTCPP) in conjunction with anatase TiO2 have been formed on cotton fabric. Their self-cleaning properties have been investigated by conducting photocatalytic degradation of methylene blue, coffee and wine stains under visible-light irradiation. CuTCPP/TiO2-coated cotton fabrics showed superior self-cleaning performance when compared to bare TiO2-coated cotton. Furthermore, CuTCPP/TiO2-coated fabrics showed significant photostability under visible-light as compared to free base TCPP/TiO2-coated fabrics. The fabrics were characterized by FESEM, XRD and UV-vis spectroscopy. An insight into the mechanistic aspects of the CuTCPP/TiO2 photocatalysis is also discussed. Visible-light driven self-cleaning cotton based on copper(II) porphyrin/TiO2 catalyst exhibits significant potential in terms of stability and reproducibility for self-cleaning applications.

Photocatalytic self-cleaning keratins: A feasibility study

Anatase nanocrystals were successfully synthesized and deposited on protein keratin-type wool fibers with good compatibility and significant photocatalytic self-cleaning activity using the sol-gel process. Due to the low chemical resistance and liability to photo-degradation of protein materials, the effect of the acid catalyst used in the sol synthesis was studied. The sols were prepared using oxidizing and non-oxidizing catalysts, nitric acid and hydrochloric acid, respectively, for the hydrolysis and condensation reactions of the titanium dioxide precursor. The size distribution and crystallinity of the sols were characterized by X-ray diffraction spectroscopy and photon correlation spectroscopy. The compatibility of sol formulations and wool is thoroughly compared and discussed by analyzing fibers photo-degradation, surface morphology and self-cleaning properties including stain degradation and colorant decomposition. The UV absorption and mechanical properties of wool fibers before and after coating are also discussed.

Achieving selectivity in TiO2-based photocatalysis

Nanocrystalline titanium dioxide (NTO) mediated photocatalysis is a powerful tool for the total mineralization of a wide range of organic compounds caused by the in situ generation of hydroxyl radicals upon ultraviolet/visible light irradiation. NTO is well known for its non-selective catalysis, especially in aqueous media. However, making NTO into a selective photocatalyst enables selective degradation of compounds as well as selective formation of valuable organic products. Both selective degradation and selective formation using NTO are based on the same principles of photocatalysis. Selectivity in degradation is achieved in the attraction, adsorption, and mineralization stages of photocatalysis whereas desorption of the oxygenated products, moderate crystallinity of NTO and doping are responsible for selective formation. Recent reports on NTO selective photocatalysis are reviewed in this article according to the chemistry used to achieve selectivity.