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Zinc plant residue (ZPR) is a secondary material generated during hydrometallurgical zinc production that contains considerable contents of valuable elements such as Zn, Cu, Fe, Pb, Cd, Ag, In, Ga, Tl. Zinc, copper and accompanying elements in ZPR are in different minerals, mainly in the ferrites. A promising approach for recycling ZPR is the sulfating roasting using iron sulfates followed by water leaching. In this study, the composition of ZPR and the obtained products were thoroughly investigated by various methods including X-ray diffraction analysis (XRD), chemical phase analysis and Mössbauer spectroscopy. The effect of temperature, amount of iron sulfates and roasting time on the conversion of valuable metals into a water-soluble form was thermodynamically and experimentally studied both using pure ferrites and ZPR. Based on the results of time-resolved XRD analysis and synchronous thermal analysis (STA), a mechanism of the sulfation roasting was elucidated. The rate-controlling step of zinc and copper sulfation process during the ZPR roasting was estimated. The sulfating roasting at 600 °C during 180 min with the optimal Fe2(SO4)3∙9H2O addition followed by water leaching enables to recover 99% Zn and 80.3% Cu, while Fe, Pb, Ag, In, Ga retained almost fully in the residue.

Reactive surface of mesoporous nanocrystalline silicon was used to synthesise noble metal nanoparticles via in situ reduction of the precursor salt solutions. The synthetic methodology for metal nanoparticle formation was systematically developed, and reaction conditions of metal salts reduction were optimised to prepare nanoparticles of controlled size distribution in the order 5–10 nm inside the mesoporous silicon template. CO oxidation was used as a test reaction for the synthesised Pt/porous silicon catalysts. Sharp reaction light-off was observed at about 120 °C on the optimised catalysts. The catalysts were shown to be stable in the extended steady-state runs and in the catalysts re-use experiments. Metal nanoparticles were shown to be stable to sintering at elevated temperatures up to 1000 °C. However, after thermal treatment on air, Pt nanoparticles were covered by a SiOx layer and were less active in CO oxidation.

Reactive surface of mesoporous nanocrystalline silicon was used to synthesise noble metal nanoparticles via in situ reduction of the precursor salt solutions. The synthetic methodology for metal nanoparticle formation was systematically developed, and reaction conditions of metal salts reduction were optimised to prepare nanoparticles of controlled size distribution in the order 5–10 nm inside the mesoporous silicon template. CO oxidation was used as a test reaction for the synthesised Pt/porous silicon catalysts. Sharp reaction light-off was observed at about 120 °C on the optimised catalysts. The catalysts were shown to be stable in the extended steady-state runs and in the catalysts re-use experiments. Metal nanoparticles were shown to be stable to sintering at elevated temperatures up to 1000 °C. However, after thermal treatment on air, Pt nanoparticles were covered by a SiOx layer and were less active in CO oxidation.

The efficiency of singlet oxygen photosensitization by porous silicon is compared with that of a conventional dye photosensitizer tetraphenylporphine by means of singlet oxygen-mediated photooxidation of α-terpinene. Based on photoluminescence measurements it was concluded that the efficiency of porous silicon as a sensitizer is much lower than that of the conventional organic dye. The main reasons for this are the low quantum yield of long living photoinduced electronic excitations (excitones) confined in silicon nanocrystals and deactivation of singlet oxygen by H-terminated internal surface of porous silicon powder. Efficient quenching of excitons in porous silicon by 1,3-diphenylisobenzofuran via the direct energy transfer was demonstrated. This process is believed to be responsible for photobleaching of 1,3-diphenylisobenzofuran at its millimolar concentrations.

In this work we studied the reduction of metal salts and their mixtures on extended hydrogen-terminated porous silicon surfaces. For these experiments we employed salts of Au, Ag, Pt and their mixtures. We show that the size and shape of resulting metal and metal alloy nanoparticles depends on the pore morphology. This has been confirmed by transmission electron microscopy measurements and plasmon resonance experiments. Finally we demonstrate catalytic activity of formed Pt nanoparticles in PSi matrix via monitoring the conversion of carbon monoxide.

We report on spin-flip activation of organic molecules from the ground state to one of the excited states having different electronic spin configurations. Based on photoexcitations in silicon (Si) nanocrystals, stored electronic energy can be transferred to other substances. The huge hydrogen passivated surface being accessible for acceptor molecules, the tunable confinement energy of excitons and their very long radiative lifetime allow Si nanocrystals to act efficiently as photosensitizers. We demonstrate that the energy transfer is governed by electron exchange mechanism. Therefore a good overlap of the electron wave functions, of donor and acceptor, is crucial for the efficiency of this type of interaction.

Here we demonstrate that H-terminated porous silicon (PSi) powders and layers can be utilized as highly efficient reductive templates for noble metal salts. The metal salt reduction results in a metal nanoparticle (NP) formation in the porous matrix of PSi. Gold NP formation has been monitored in-situ by measuring the plasmon resonance response. Pt NPs, formed in the pores of PSi, were investigated by transmission electron microscopy (TEM) and energy-dispersive X-ray (EDX) analysis. Furthermore, hybrid Pt/PSi nanocomposites exhibit a high catalytic activity for CO oxidation. Some of the samples were oxidized to obtain Pt/PSiOx nanocomposites for comparison of catalytic activity.

Nano-sized silicon crystals have entirely new physical properties which do not occur in its bulk form. Investigation of its photoluminescence properties can explain the mechanism of transferring energy from photoexcited excitons confined in silicon nanocrystals to energy accepting substances via electron exchange mechanism. This excitation process changes the electronic spin structure of the acceptor molecule, which is forbidden in the dipole approximation, and therefore it requires the involvement of photosensitizers.

An annular flow photochemical reactor illuminated by UV and green (524 nm) light emitting diodes (LEDs) was characterised by a chemical actinometer. Very high efficiency of absorption of photons, most likely promoted by the specific orientation of LED elements in the reactor, was calculated based on the measured actinometry results. Generation of singlet oxygen mediated by nanoporous silicon under illumination by Ar+ laser, UV and green LEDs was demonstrated by indirect measurement of suppression of porous Si photoluminescence, and by direct measurements of singlet oxygen luminescence. The efficiency of reactor in singlet oxygen mediated reactions was tested using reaction of decomposition of diphenylbenzofuran. Estimated quantum yield of chemical reaction is about 34%.

We present a detailed study of the anisotropic optical properties of mesoporous silicon layers prepared from substrates having different doping levels under various preparation conditions. It is demonstrated that the morphology of the layers strongly depends on the preparation conditions. The experimental data are explained in the framework of an effective medium model which takes into account different morphologies of the layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this Letter we demonstrate that hydrogen-terminated porous silicon (PSi) layers and powders can serve as highly efficient reductive templates for noble metal salts. The reduction results in metal nanoparticle (NP) formation in the pores of PSi. Gold NP formation has been monitored in-situ by measuring the plasmon resonance response. Pt NPs, formed in the PSi matrix, were investigated by transmission electron microscopy and energy-dispersive X-ray analysis. Furthermore, hybrid Pt/PSi nanocomposites exhibit a high catalytic activity for CO oxidation.

Silicon nanoparticles of three types (oxide-terminated silicon nanospheres, micron-sized hydrogen-terminated porous silicon grains and micron-size oxide-terminated porous silicon grains) were incorporated into silica aerogels at the gel preparation stage. Samples with a wide range of concentrations were prepared, resulting in aerogels that were translucent (but weakly coloured) through to completely opaque for visible light over sample thicknesses of several millimetres. The photoluminescence of these composite materials and of silica aerogel without silicon inclusions was studied in vacuum and in the presence of molecular oxygen in order to determine whether there is any evidence for non-radiative energy transfer from the silicon triplet exciton state to molecular oxygen adsorbed at the silicon surface. No sensitivity to oxygen was observed from the nanoparticles which had partially H-terminated surfaces before incorporation, and so we conclude that the silicon surface has become substantially oxidised. Finally, the FTIR and Raman scattering spectra of the composites were studied in order to establish the presence of crystalline silicon; by taking the ratio of intensities of the silicon and aerogel Raman bands, we were able to obtain a quantitative measure of the silicon nanoparticle concentration independent of the degree of optical attenuation.

Recently, various bio-medical applications of nanoporous silicon (np-Si) have been suggested. This work investigates the biocompatibility of np-Si particles taking into account hazardous residua confined in the pores after preparation. The emphasis is on the potential application of such particles as oxygen photosensitizer for photodynamic therapy of cancer, which requires both negligible toxicity of np-Si particles in darkness and a high photo-cyto-toxic effect due to generation of singlet oxygen under illumination. Considerable amounts of water soluble toxic impurities are found to be present in the nanoporous shell of micrometer-sized np-Si particles immediately after their preparation by chemical etching of bulk silicon powder. The effects of several ordinary cleaning treatments are investigated by using thermal effusion mass-spectroscopy and FTIR spectroscopy. A particular purification procedure is developed, capable to reduce the concentration of residual impurities to levels acceptable for bio-medical applications while preserving the required photo-activity of the np-Si particles.

Periodic solid state structures exhibit transmission stop bands for waves of certain frequencies. We report the realization and direct measurement of acoustic band gaps in porous silicon multilayer structures which exhibit similar to 50 dB stop bands for longitudinal acoustic waves in the gigahertz range. Furthermore, realization of an acoustic microcavity structure in porous silicon is demonstrated.

We report on the synthesis of freestanding silicon spheres having sizes in the range of 3–10 nm. As-prepared luminescent silicon nanocrystals have H-passivated surface. Therefore, energy transfer from excitons confined in Si nanocrystals to oxygen molecules is found to be efficient. It is demonstrated that a termination of silicon nanocrystal H-passivated hydrophobic surface by lipids provides their water solubility. We found that this procedure preserves photosensitizing ability of silicon nanocrystals. Therefore, this material system can potentially be employed for a variety of biomedical applications.

This special issue of physica status solidi features the papers presented at Symposium J of the 2010 Spring Meeting of the European Materials Research Society (E-MRS) entitled Silicon based Nanophotonics, held in Strasbourg (France) on June 7–11, 2010. These Proceedings address several issues in silicon based nanophotonic materials and devices, from materials growth of nanosized structures to devices. The focus is on the use of silicon as a substrate material to utilize the infrastructure of the silicon microelectronics industry. Over the last few years there has been a strong emphasis to develop photonic devices based on silicon, driven by the prospect of integration into the inexpensive silicon electronics platform. More recently, apparent limitations in heat dissipation and the interconnect bottleneck in microprocessors has fueled the research into monolithically integrated photonic devices to alleviate these limitations. A large number of Si compatible devices have been developed; however, the size of these devices often limits their usefulness for integration into microprocessors. Therefore, these Proceedings focus on the properties of nano scale photonic devices, with the expectations that it will stimulate the development of novel devices and functionalities. This issues features 25 peer reviewed articles that were organized into 7 topics: (1) Nonlinear optical properties of Si nanocrystals; (2) Radiative and non-radiative recombination in Si-based materials; (3) Silicon nanowires and nanorods; (4) Er-doped nanostructures; (5) Silicon-germanium nanostructures; (6) Photonic structures: Microcavities, photonic crystals and waveguides; (7) Si nanostructures for light detection and sensing. We would like to thank all authors for their contributions and the reviewers for their prompt response and comments that have improved the quality of the Proceedings and were instrumental in finalizing the Proceedings in a timely manner. We would also like to thank the scientific advisory committee, Prof. Minoru Fujii, Prof. Yasuhiko Ishikawa, Prof. Wolfgang Jantsch, Prof. Jan Linnros, Dr. Michael Morse, Prof. Stefano Ossicini, Prof. Tony Peaker, Dr. Richard Rizk, Prof. Margit Zacharias, and Prof. Zhiping (James) Zhou for their significant contributions through all stages of the Symposium organization and Proceedings preparation (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Can silicon ever be a true direct-bandgap semiconductor? The first observation of a new, short-lived photoluminescence band from silicon nanocrystals offers fresh hope.

We report on the interaction of silicon nanocrystals with water/alcohol solutions which results in their complete oxidation, the hydrolysis of water and hydrogen generation in amounts close to the ideal scenario. Water acts as an oxidizer while alcohol is required for efficient wetting of nanosilicon. This process results in the formation of silicon-based alcogel which can be further transferred to aerogel.

We present a method for the formation of noble metal nanoparticle ensembles in nanostructured silicon. The key idea is based on the unique property of the large reduction potential of extended internal hydrogen-terminated porous silicon surfaces. The process of metal nanoparticle formation in porous silicon was experimentally traced using their optical plasmon resonance response. We also demonstrate that bimetallic compounds can be formed in porous silicon and that their composition can be controlled using this technique. Experimental results were found to contradict partially with considerations based on Mie theory.

We report on the light emitting properties of freestanding hydrogen-terminated spherical silicon nanocrystals. The nanocrystals exhibit size-dependent tunable light emission properties. Many light emission properties of this system are found to be very similar to those known for other systems containing silicon nanocrystals. However, we found specific emission properties of this system ascribed to the spherical shape of silicon nanocrystals and their spatial separation. We attributed all observations to the spatial confinement of excitons within the crystalline core of the indirect band gap silicon nanocrystals.

Generation of singlet oxygen due to energy transfer from photoexcited silicon nanocrystals in D2O is demonstrated. It is shown that the singlet oxygen generation efficiency, i.e., the intensity of near-infrared emission from singlet oxygen gradually decreases when Si nanocrystals are continuously irradiated in O2-saturated D2O. The mechanism of the photodegradation of the photosensitizing efficiency is studied using photoluminescence and infrared absorption techniques. Experimental results suggest that the interaction of photogenerated singlet oxygen with the hydrogen-terminated surface of silicon nanocrystals results in photo-oxidation of silicon nanocrystals, and the surface oxides reduce the photosensitizing efficiency. It is also demonstrated that photo-oxidation of porous silicon in O2-saturated water results in a strong enhancement of the photoluminescence quantum yield of porous Si.