Mohamed Esmat

Abstract Single phase TiO2 mesoporous microspheres were synthesized using a facile one step technique from nanotubes. The prepared microspheres were crystallized in an anatase form with a tetragonal symmetry. The results of surface area measurements revealed mesoporous structure of such materials together with uniform pores. The samples possess rough surface and could be exploited in different applications. The methodology is easy, cheap, fast and could be reproduced for morphology tuning and/or transition.

The development of efficient and cost-effective solar photocatalysts capable of producing hydrogen from formic acid as a hydrogen storage medium is still a challenging issue. Herein, we report that iron minerals, ferric iron hydroxy sulfates (FHS), immobilized on a natural layered silicate, magadiite, can be used as a photocatalyst to produce hydrogen from formic acid under irradiation with solar simulator. The material exhibits the hydrogen production rate of 470 μmol g−1 h−1, which is considerably higher than that obtained on other iron minerals and comparable to that obtained on precious metal-based photocatalyst ever reported. The present result may open a way to design efficient photocatalyst for hydrogen production from formic acid in an economically and environmentally friendly way.

Abstract Designing an excellent solar photocatalyst based on TiO2 without an external cocatalyst such as Pt remains unresolved despite its exceptional potential for renewable energy production. Here, we report a state-of-the-art solar-driven photocatalytic Cl-doped rutile TiO2, in nanosheet morphology with (110) facets, for H2 production from water splitting in the absence of any external cocatalyst. The Cl-doped rutile TiO2 nanosheets are easily synthesised via a layered titanate’s interconversion through a simple dilute HCl treatment and thermal heating at a convenient temperature. We demonstrate that engineering the band shape can result in long-lasting photogenerated Ti3+, which subsequently can act as an in situ cocatalysts in rutile TiO2. According to our density functional calculations, the Cl dopant has a pivotal role in improving the band shape of TiO2, i.e., significantly reducing the effective mass of the photogenerated electrons and holes, especially when compared to the effect of oxygen vacancy. Consequently, the boosted carrier mobility, resulting from lighter carriers, photogenerates a significant number of prolonged Ti3+ species that enhance photocatalytic activity in situ (i.e., in situ blue titania). Our results show that despite the considerable efforts that have been directed towards narrowing TiO2’s band gap, band shape engineering offers a more facile and robust solution for photocatalysis.

Abstract Introducing oxygen vacancies (Vo) into TiO2 photocatalyst has been considered an effective strategy for improving co-catalyst-free solar photocatalytic activity. However, the methods used to synthesize it require high pressure/temperature and/or hazardous/costly reagents. Here we propose Vo introduction, concomitant with N-doping in TiO2, as an alternative strategy for achieving efficient co-catalyst-free solar photocatalytic activity under less extreme conditions. After calcination at 450 °C of mesoporous spherical assemblies of a layered titanate nanosheet containing N,N-dimethylformamide as its synthesis solvent in the structure, we successfully synthesized mesoporous spherical assemblies of nanosheets composed of anatase TiO2 nanoparticles with Vo mediated by N doping. This material exhibits good co-catalyst-free solar photocatalytic activity for hydrogen evolution via water splitting under irradiation with simulated solar light, which is considerably higher than that of typical co-catalyst-free defective TiO2 materials. We discuss the possible role of the introduced Vo in facilitating charge separation and raising photocatalytic efficiency.

Abstract Green rust (GR) is a mixed-valent iron mineral and structurally constitutes a family of layered double hydroxides that have attracted widespread attention in environmental and energy applications. However, despite the ubiquity of GR in environments and its potential instrumental role in life’s emergence, its instability against oxidation has limited this material’s applications. Here, we report a new type of GR exhibiting excellent oxidation and chemical stabilities synthesized via a one-pot solvothermal reaction using iron(III) chloride and glycerol. We demonstrate that the GR has a crystallinity and layer charge density considerably higher than that of conventional GR. The high stability of the GR comes from the less defective particle surface and highly-dense interlayer structure that suppress oxygen reaching structural iron(II). This GR can be used as an efficient and durable solar photocatalyst for H2 production from ammonia borane, while other iron minerals and a benchmark TiO2 show little to no activity.

Abstract Management of the solar spectrum by downshifting has been a key theme in broadband solar cell research over the last few years. The absorption of high-energy photons that exceed the bandgap edge of Si causes thermalization of charge carriers, which is a major loss mechanism by which collected energy is underutilized in silicon solar cells. The spectral response of Si also falls in the UV region. Progress in overcoming these effects achieved by modifying the input spectrum will dramatically enhance power conversion efficiency (PCE). Herein we report the application of highly luminescent CdZnS/ZnS and CdZnSe/ZnS quantum dots (QDs) as downshifting materials for nanostructured silicon. The applied QDs show major potential for shifting the high energy in the ultraviolet region to low energy, which is then transferred to the underlying silicon nanostructures via radiative and nonradiative energy transfer. This energy transfer dramatically improves the cell efficiency from 10.4% to 13.5%, showing this approach to be a reliable solution for improving solar cell properties.

Thiourea-bridged organosiloxane is used to synthesize a periodic mesoporous organosilica (PMO). Since this PMO has an S-enriched surface, owing to thiourea functional groups, it exhibits strong coordination toward Pt ions, and it shows a high tunability in the Pt nanoparticles size. This hybrid mesoporous material is employed as a catalyst in the efficient reduction reaction of 4-nitrophenol to 4-aminophenol at room temperature in an aqueous media.