A versatile method to fabricate self-supported aerogels of nanoparticle (NP) building blocks is presented. This approach is based on freezing colloidal NPs and subsequent freeze drying. This means that the colloidal NPs are directly transferred into dry aerogel-like monolithic superstructures without previous lyogelation as would be the case for conventional aerogel and cryogel fabrication methods. The assembly process, based on a physical concept, is highly versatile: cryogelation is applicable for noble metal, metal oxide, and semiconductor NPs, and no impact of the surface chemistry or NP shape on the resulting morphology is observed. Under optimized conditions the shape and volume of the liquid equal those of the resulting aerogels. Also, we show that thin and homogeneous films of the material can be obtained. Furthermore, the physical properties of the aerogels are discussed.

The surface modification of semiconductor photoelectrodes with passivation overlayers has recently attracted great attention as an effective strategy to improve the charge-separation and charge-transfer processes across semiconductor-liquid interfaces. It is usually carried out by employing the sophisticated atomic layer deposition technique, which relies on reactive and expensive metalorganic compounds and vacuum processing, both of which are significant obstacles toward large-scale applications. In this paper, a facile water-based solution method has been developed for the modification of nanostructured hematite photoanode with TiO2 overlayers using a water-soluble titanium complex (i.e., titanium bis(ammonium lactate) dihydroxide, TALH). The thus-fabricated nanostructured hematite photoanodes have been characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Photoelectrochemical measurements indicated that a nanostructured hematite photoanodes modified with a TiO2 overlayer exhibited a photocurrent response ca. 4.5 times higher (i.e., 1.2 mA cm(-2) vs RHE) than that obtained on the bare hematite photoanode (i.e., 0.27 mA cm(-2) vs RHE) measured under standard illumination conditions. Moreover, a cathodic shift of ca. 190 mV in the water oxidation onset potential was achieved. These results are discussed and explored on the basis of steady-state polarization, transient photocurrent response, open-circuit potential, intensity-modulated photocurrent spectroscopy, and impedance spectroscopy measurements. It is concluded that the TiO2 overlayer passivates the surface states and suppresses the surface electron-hole recombination, thus increasing the generated photovoltage and the band bending. The present method for the hematite electrode modification with a TiO2 overlayer is effective and simple and might find broad applications in the development of stable and high-performance photoelectrodes.

In this paper, hematite p-CaFe 2 O 4 /n-Fe 2 O 3 heterojunction photoanode has been fabricated employing a facile template-less film processing technique by controlling the chemical bath. Anisotropic growth of β-FeOOH akaganeite film on FTO conductive glass from an aqueous FeCl3 solution containing CaCl 2 followed by two-step thermal annealing at 550 and 800 °C, induces the formation of p-CaFe 2 O 4 /n-Fe 2 O 3 heterojunction.The structural, morphological, electronic states and electrochemical characteristics of the films have been investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and impedance spectroscopy, respectively. The heterojunction photoanode showed 100 % higher photocurrent response than that is obtained using bare hematite electrode under simulated 1-sun (100 mW/cm 2 ). The photocurrent enhancement is attributed to the enhanced charge carrier separation and the reduced resistance in the charge transfer across the electrode and electrolyte as revealed by electrochemical impedance spectroscopy analysis. The modification of the p-CaFe 2 O 4 /n-Fe 2 O 3 heterojunction photoanode with CoPi cocatalyst further facilitate the electron transfer at the electrode/electrolyte interface and thus enhance the photoelectrochemical water oxidation. Since cheap and abundant materials have been employed for the synthesis of the heterojunction photoanode via a simple route, the current results have great importance from scientific and economical point of view.

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In this work, a very simple one-pot synthetic approach was developed to generate aqueous CdTe/CdS/ZnS type-II/type-I red-emitting nanocrystals (NCs). Strain-induced optical properties of CdTe/CdS particles having core (small) /shell (thick) structure with a maximum quantum yield (QY max ) $ 57% were further improved with the overgrowth of a ZnS shell, resulting in a core (small) /shell (thick) /shell (small) structure (QY max $ 64%). The spectral properties were tuned further to the near-infrared region as the ZnS shell grew in thickness. X-ray powder diffraction (XRD) analysis and high-resolution transmission electron microscope (HRTEM) images showed the crystalline structure of NCs proving the epitaxial growth of ZnS without crystalline defects. Under continuous UV-irradiation for 5 h, the NCs did not exhibit any photodegradation but instead displayed a photo-annealing process. These extremely photostable NCs were further characterized in terms of their cytotoxicity and their cell labeling performances. The presence of a ZnS shell was found to reduce the toxicity of the CdTe/CdS NCs. Furthermore, aptamer-conjugated NCs were successfully utilized in targeted cell imaging. Promisingly, the aptamer-NCs bioconjugates were internalized by A549 cells within 2 hours of incubation and retained their fluorescence even after 24 hours of internalization.