Manganese dioxide-coated biocarbon for integrated adsorption-photocatalytic degradation of formaldehyde in indoor conditions

Formaldehyde is a common indoor air pollutant with hazardous effects on human health. This study investigated the efficiency of biocarbon (BC) functionalized with variable contents of MnO2 for formaldehyde removal in ambient conditions via integrated adsorption-photocatalytic degradation technology. The sample with the highest formaldehyde removal potential was used to prepare a functional coating made of acrylic binder mixed with 20 wt% of the particles and applied on beech (Fagus sylvatica L) substrate. SEM images showed that MnO2 was deposited around and inside the pores of the BC. EDX spectra indicated the presence of Mn peaks and increased content of oxygen in the doped BC compared to pure BC, which indicated the successful formation of MnO2. Raman spectra revealed that the disorder in the BC's structure increased with increasing MnO2 loadings. FTIR spectra of BC-MnO2 samples displayed additional peaks compared to the BC spectrum, which were attributed to MnO vibrations. Moreover, the deposition of increased MnO2 loadings decreased the porosity of the BC due to pores blockage. The BC sample containing 8 % Mn exhibited the highest formaldehyde removal efficiency in 8 h, which was 91 %. A synergetic effect between BC and MnO2 was observed. The formaldehyde removal efficiency and capacity of the coating reached 43 % and 6.1 mg/m2, respectively, suggesting that the developed coating can be potentially used to improve air quality in the built environment.

Electronic transport in a controllably grown carbon nanotube-silicon heterojunction array

A uniform array of a new type of heterojunction formed between carbon nanotubes and silicon is studied. The heterojunction array was controllably grown with parallel and uniform nanotubes vertically aligned to the silicon substrate using a self-organized nanopore array template. The pronounced rectifying characteristics of the heterojunction were measured with an on/off ratio as high as 10(5) at 4 V. The analysis shows a large and type-I band offset at the heterojunction. The charge transport in the nanotubes is found to be strongly coupled to and limited by the dielectric charging and polarization in the hosting alumina matrix surrounding the nanotubes.

Optical control over photoconductivity in polyferrocenylsilane films

We report the study and elucidate the origin of the photoconductivity of polyferrocenylsilanes achieved through photooxidation performed by ultraviolet irradiation in the presence of chloroform. The persistence over months of the changes in the optoelectronic properties allowed more detailed studies of the charge photogeneration process. The photocurrent spectrum mimics that of the absorption indicating that the photooxidized material is not a mechanical mixture of oxidized and unoxidized polymer units. Photomodulation spectroscopy revealed the existence of long-lived photoexcited states with a lifetime in the millisecond range. They have been interpreted as trapped excitons at the oxidized sites where the polymer is deformed due to the presence of the chloroform derived counter ions. Because of the relatively long lifetime of the trapped excitons they can dissociate and the formed charge carriers can be separated in an externally applied electric field. The effect of the polymer chain deformation around the oxidized unit extends over the neighboring polymer units. In light of the potential applications of this class of polymers in various electronic and photonic devices, the clarification of such a basic process as the photocurrent generation will be a key factor for further technological development.

An investigation of the photoinduced changes of absorption of high-performance photoaddressable polymers

Recently, a novel class of photoaddressable polymers (PAPs) has been reported, which allows for reversible photorecording with values of the photoinduced birefringence in excess of 0.2. These polymers are copolymers of methacrylate-type monomers with a mesogenic and a nonmesogEnic photoactive azobenzene in the side chain. This report presents a detailed analysis of the three-dimensional photoinduced reorientation of side chains within thin layers of PAP materials, utilizing polarized UV/Visible spectroscopy, infrared, and photothermal deflection spectroscopy (PDS). The three-dimensional orientation distribution before and after illumination with 514 nm polarized light was investigated by angle-dependent UV/Vis absorption spectroscopy. As-prepared samples possess an uniaxial orientation with the photoactive units being preferentially aligned within the plane of the substrate layer. These films become biaxial upon photoalignment with polarized light incident normal to the substrate plane. For PAP materials containing mesogenic side chains, the out-of-plane absorption stays nearly unchanged, proving that the photoinduced reorientation occurs mainly within the layer plane. For a homopolymer bearing only a nonmesogenic azobenzene in the side chain, photobleaching is observed, associated with a disease in absorption in all three principle directions. This finding can be understood in terms of an orientational coupling between the photodegradation product and the active azobenzene units. Photodegradation was well established by infrared spectroscopy. Photothermal deflection spectroscopy has been performed to manifest photoinduced changes in the transparent wavelength region of the PAP material, below the absorption edge. In contrast to the pronounced optical changes in the UV/Vis and IR spectra, the absorption in this range remains nearly unchanged. This result provides evidence that the polymers can be well applied for holographic storage in thick-layer devices.