Amorphous TiO2 Layer Research Articles

Synthesis of 1D-Anisotropic Particles Consisting of TiO2 Nanorods and SnO2 with Heteroepitaxial Junctions and Self-Assembled 3D-Microspheres.

Anisotropic one-dimensional (1D)-particles with a SnO2 "head", a TiO2 "tail", and self-assembled three-dimensional (3D)-microspheres were synthesized by a hydrothermal method. At the first stage of the reaction, an amorphous TiO2 layer is deposited on the SnO2 surface. At the second stage, rutile nuclei are generated in the amorphous TiO2 layer. At the third stage, a single TiO2 nanorod grows from a SnO2 particle with a heteroepitaxial relation of TiO2(001)//SnO2(001). Finally, the resulting 1D-anisotropic hybrid particles are self-assembled to form a radial 3D-microsphere with the SnO2 head oriented in the central direction.

Z-scheme Bi2O2.33/Bi2S3 heterojunction nanostructures for photocatalytic overall water splitting

Photocatalysts with a wide response to solar spectrum especially to visible light are supposed to have a high energy conversion efficiency in solar water splitting. Heterogeneous binary composite photocatalysts exhibit outstanding performance in solar light absorption and photocarrier transfer/transport. In this work, a Z-scheme photocatalyst based on Bi2O2.33/Bi2S3 heterojunction is successfully designed and fabricated by assembling Bi2S3 nanoneedles on Bi2O2.33 nanosheets. Benefiting from the effective light absorption of Bi2S3 to solar light and the facilitated charge transfer by the Z-scheme band structure of Bi2O2.33/Bi2S3, the composite photocatalyst exhibits a fascinating photocatalytic performance in water splitting. With the help of Pt as a co-catalyst and sacrificial agent, the production rate of H2 can reach 62.61 μmol·h−1 (sample area 2 cm2). The direct Z-scheme junction also exhibits the capacity of overall water splitting. Moreover, the stability of the heterojunction photocatalyst is optimized by depositing an ultra-thin amorphous TiO2 layer (about 3 nm) to avoid photocorrosion of Bi2S3. This work will provide a new insight into the design and development of efficient and long-life photocatalysts.

(Invited) Element-Specific Measurement of Hole Transport in a Photoanode By Transient Extreme Ultraviolet Spectroscopy

A passivating oxide layer is critical for the performance and stability of solar-fuel photoelectrodes. While the semiconductor surface can be passivated by a few nanometer oxide film, the best performance often correlates with a thicker and defect-rich amorphous TiO2 layer. The defect states are suggested to facilitate hole transport between the semiconductor and metal catalyst. In this presentation, transient extreme ultraviolet (XUV) absorption spectroscopy is used to measure the electron and hole transport between each element of a photoexcited Ni-TiO2-Si junction. The transient changes in the Ni M2,3 edge, Si L2,3­ edge, and Ti M2,3 edge are quantified using a broad-band, high harmonic XUV continuum that spans 30 to 120 eV. Hole tunneling from the p-type Si to the Ni metal is measured immediately following 800 nm optical excitation. The measured transport time and electric field indicate a ballistic tunneling through the TiO2 that originates from a Si hole with a mobility of ~400 cm2/Vs. An appreciable transfer of photoexcited electrons is not measured. The quantum yield of the hole tunneling is calculated to be ~50% percent by using the photoexcited carrier density in Si and the measured shift in the Ni M2,3 edge Fermi energy. On a picoseconds time scale, the holes are measured to back-transfer from the Ni to the Si through the mid-gap states in the TiO2. The extracted kinetics suggest a hole diffusion constant of ~1 cm2/s. The surface recombination velocity of electrons and holes at the Si-TiO2 interface is also quantified as ~200 cm/s. These results suggest that transient XUV spectroscopy can be used to quantitatively measure electron and hole transport in solar-fuel relevant nanoscale junctions.

Multi-functional amorphous TiO2 layer on ZIF-67 for enhanced CO2 photoreduction performances under visible light

Multi-functional amorphous TiO2 (a-TiO2) layer is uniformly decorated on ZIF-67 through a simple hydrothermal and low temperature calcination methods, which promotes the conversion efficiency and selectivity in the photoreduction of CO2 under visible light. The optimized ZIF-67@a-TiO2 demonstrates high CO production of 43.8 μmol after 4 h irradiation with high CO selectivity of 67.2%, which are substantially enhanced compared with that of pristine ZIF-67. State and transient optical and electrochemical tests indicate that the multi-functional a-TiO2 layer not only leads to enhanced utilization of incident light by the effective light scattering effect, but also serves as blocking layer to suppress the charge recombination by restraining the backwards photoelectron flow without interrupting the photoelectron transfer from the photosensitizer to ZIF-67. In addition, the a-TiO2 layer introduces abundant mesoporous characteristics in the catalyst, which facilitates the mass diffusion without scarifying the overall CO2 absorption capacity. Meanwhile, it is tentatively believed that the H3O+ is more likely adsorbed on the hydrophilic a-TiO2 with highly polarized surface, which inhibits the H2 generation and results in the pleasant CO selectivity. Furthermore, the a-TiO2 shell effectively suppresses the photo-corrosion of ZIF-67, which finally leads to the superior photocatalytic performances along with the high stability.

(Invited) Element-Specific Measurement of Hole Transport and Kinetics in a Ni-TiO2-Si Photolectrode Using Transient Extreme Ultraviolet Spectroscopy

A passivating oxide layer is critical for the stability and the performance of solar-fuel photoelectrodes. While the semiconductor surface can be passivated by a few nanometer oxide film, the best performance often correlates with a thicker and defect-rich amorphous TiO2 layer. The defect states are suggested to facilitate hole transport between the semiconductor and metal catalyst. In this presentation, transient extreme ultraviolet (XUV) absorption spectroscopy measures the electron and hole transport between each element of a photoexcited Ni-TiO2-Si photoelectrode. The transient changes in the Ni M2,3 edge, Si L2,3­ edge, and Ti M2,3 edge are quantified using a broad-band, high harmonic XUV continuum that spans 30 to 120 eV. Photoexcitation with a 30 fs, 800 nm optical pulse leads to hole tunneling from the p-type Si to the Ni metal. The transport time and electric field indicate a ballistic tunneling through the TiO2 that originates from a Si hole with mobility of ~400 cm2/Vs. An appreciable transfer of photoexcited electrons is not measured. The quantum yield of the hole tunneling is calculated to be ~50% percent by using the photoexcited carrier density in Si and the measured shift in the Ni M2.3 edge Fermi energy. The holes are measured to back-transfer from the Ni to the Si through the mid-gap states in the TiO2 on a picoseconds time scale. The measured kinetics suggest a hole diffusion constant of ~1 cm2/s. The surface recombination velocity of electrons and holes at the Si-TiO2 interface is also quantified as ~200 cm/s. These results suggest that transient XUV spectroscopy can be used to quantitatively measure electron and hole transport in solar-fuel relevant nanoscale junctions.

Engineering an ultrathin amorphous TiO2 layer for boosting the weatherability of TiO2 pigment with high lightening power

TiO2 pigments are typically coated with inert layers to suppress the photocatalytic activity and improve the weatherability. However, the traditional inert layers have a lower refractive index compared to TiO2, and therefore reduce the lightening power of TiO2. In the present work, a uniform, amorphous, 2.9-nm-thick TiO2 protective layer was deposited onto the surface of anatase TiO2 pigments according to pulsed chemical vapor deposition at room temperature, with TiCl4 as titanium precursor. Amorphous TiO2 coating layers exhibited poor photocatalytic activity, leading to a boosted weatherability. Similarly, this coating method is also effective for TiO2 coating with amorphous SiO2 and SnO2 layers. However, the lightening power of amorphous TiO2 layer is higher than those of amorphous SiO2 and SnO2 layers. According to the measurements of photoluminescence lifetime, surface photocurrent density, charge-transfer resistance, and electron spin resonance spectroscopy, it is revealed that the amorphous layer can prevent the migration of photogenerated electrons and holes onto the surface, decreasing the densities of surface electron and hole, and thereby suppress the photocatalytic activity.

Photocatalytic properties of TiO2@polymer and TiO2@carbon aerogel composites prepared by atomic layer deposition

Monolithic structured TiO2/aerogel composites were prepared from resorcinol-formaldehyde polymer aerogel (RFA) and its carbon aerogel (RFCA) derivative. A resorcinol-formaldehyde hydrogel was synthesized in a sol-gel reaction and transformed into polymer aerogel by supercritical drying. The RFA was converted to carbon aerogel by pyrolysis at 900 °C in dry N2. Amorphous and crystalline TiO2 layers were grown from TiCl4 and H2O precursors by atomic layer deposition (ALD) at 80 °C and 250 °C, respectively, on both RFA and RFCA. The substrates and the composites were studied by N2 adsorption, TG/DTA-MS, Raman, SEM-EDX and TEM techniques. Their photocatalytic activity was compared in the UV catalyzed decomposition reaction of methyl orange dye.

Fullerene as a Photoelectron Transfer Promoter Enabling Stable TiO2‐Protected Sb2Se3 Photocathodes for Photo‐Electrochemical Water Splitting

AbstractUnderstanding the degradation mechanisms of photoelectrodes and improving their stability are essential for fully realizing solar‐to‐hydrogen conversion via photo‐electrochemical (PEC) devices. Although amorphous TiO2 layers have been widely employed as a protective layer on top of p‐type semiconductors to implement durable photocathodes, gradual photocurrent degradation is still unavoidable. This study elucidates the photocurrent degradation mechanisms of TiO2‐protected Sb2Se3 photocathodes and proposes a novel interface‐modification methodology in which fullerene (C60) is introduced as a photoelectron transfer promoter for significantly enhancing long‐term stability. It is demonstrated that the accumulation of photogenerated electrons at the surface of the TiO2 layer induces the reductive dissolution of TiO2, accompanied by photocurrent degradation. In addition, the insertion of the C60 photoelectron transfer promoter at the Pt/TiO2 interface facilitates the rapid transfer of photogenerated electrons out of the TiO2 layer, thereby yielding enhanced stability. The Pt/C60/TiO2/Sb2Se3 device exhibits a high photocurrent density of 17 mA cm−2 and outstanding stability over 10 h of operation, representing the best PEC performance and long‐term stability compared with previously reported Sb2Se3‐based photocathodes. This research not only provides in‐depth understanding of the degradation mechanisms of TiO2‐protected photocathodes, but also suggests a new direction to achieve durable photocathodes for photo‐electrochemical water splitting.

Amorphous TiO2 layer on silicon monoxide nanoparticles as stable and scalable core-shell anode materials for high performance lithium ion batteries

SiOx (0 < x < 2) based materials are attractive for developing high-capacity and durable anodes toward superior lithium storage. Herein, low cost and tailorable core-shell SiO@TiO2 nanocomposites have been synthesized via simple ball milling and sol-gel process. The designed nanocomposite is composed of nano-sized SiO as the inner core and amorphous TiO2 layer as the shell. Remarkably, when used as anode material for lithium-ion batteries, the SiO@TiO2 exhibits greatly enhanced capacity performance and cycling stability due to its rational core-shell structure. The optimal nanocomposite delivers a high initial specific capacity of 1920 mA h g−1 with high initial coulombic efficiency of 79.4%, along with a stable reversible capacity of 901 mA h g−1 after 200 cycles at 200 mA g−1 and impressive high-rate capacity of 272 mA h g−1 at 3000 mA g−1. The excellent electrochemical performance of the nanocomposite is contributed by the synergetic core-shell structure, in which the amorphous TiO2 shell can not only act as protective/elastic buffer layer to accommodate the volume change of the SiO nanoparticles upon cycling, but also largely favor the Li+ diffusion in the nanocomposite toward highly reversible lithium storage. In virtue of the simple, green and scalable fabrication process, these robust and efficient nanocomposites are promising to realize inexpensive and high-performance lithium ion batteries anodes and related energy storage applications.

Titanium dioxide protection against Al4C3 formation during fabrication of aluminum-TiO2 coated MWCNT composite

Aluminum and aluminum alloys have been very useful in the industry, mainly in the transport sector. So, is important to improve their mechanical properties to increase their applications. Carbon nanotubes (CNTs) could be an excellent reinforcing phase for metal matrix composites, specifically for composites with aluminum or aluminum alloy matrix. However, CNTs dispersion, wettability, and interaction with the matrix must be improved, without damaging their structure. In this work, multi-walled CNTs (MWCNTs) were coated by the sol-gel process with a titanium oxide (TiO2) layer with three different thickness and calcined at two different temperatures: 500 °C and 750 °C. The resultant powder was mixed by electrostatic adsorption method with aluminum powder and cold compacted. To simulate high temperature processing, the compacted disks were pressureless heated at 850 °C, aiming to check the effect of TiO2 in protecting the MWCNT when in contact with melted Al. The TiO2 coated MWCNT samples were characterized by a range of analytical techniques including Field-Emission Gun Scanning Electron Microscopy (FEG-SEM), X-ray diffraction (XRD), Z-Potential, Brunauer–Emmett–Teller (BET), Energy Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy (RS). The effect of the TiO2 layer as a protective barrier on the MWCNT against the Al4C3 formation during the heating process and the hardness of the Al/MWCNT (coated and uncoated) composite were studied. The results show that the MWCNT were successful coverage by a uniform amorphous TiO2 layer. After calcination at 500 °C and 750 °C, the layer was completely crystallized into a TiO2 film, with reduced surface area and pore volume. Electrostatic adsorption between TiO2 covered MWCNT and Al powders in aqueous suspension was found to disperse the reinforcing phase prior to consolidation. On the heat-treated discs, the formation of Al4C3 phase was observed to occur only for uncoated MWCNT samples, showing that the TiO2 layer effectively protected the nanotubes in presence of melted Al. The microhardness of the heated samples was increased up to 26% when reinforced with MWCNT and up to 46% when reinforced with TiO2 coated MWCNT, compared with pure aluminum.

Probing the impact of energetic argon ions on the structural properties of ZnO:Al/TiO2 heterostructures

The efficacy of 50 keV Ar+-ion irradiation toward the interfacial and stoichiometric engineering of strained Al-doped ZnO (AZO)/TiO2 heterostructure is systematically investigated using a variety of experimental techniques, notably by cross-sectional transmission electron microscopy. Glancing-angle X-ray diffraction evidences the release of in-plane compressive stress from the as-grown AZO/TiO2 bilayer structure at a critical fluence of 1 × 1016 ions/cm2, and we discuss in the light of microcracks and voids formation combined with the dewetting phenomenon. Ion irradiation also leads to an improvement of stoichiometry in both top AZO and underneath amorphous TiO2 layers, as manifested by depth-dependent energy dispersive X-ray spectroscopy owing to the large diffusion of oxygen toward the AZO/TiO2 interfacial region through the AZO defect sites. Such ion beam induced self-healing in stoichiometry of AZO/TiO2 heterostructure has been attributed to a conjunction of sputtering and diffusion phenomena involving the constituent elements (Zn, Ti, and O). Further increase in ion fluence up to 5 × 1016 ions/cm2 causes a complete deterioration of the heterostructure with the formation of a graded layer via intermixing of these elements, followed by the evolution of voids.

Promoted Fixation of Molecular Nitrogen with Surface Oxygen Vacancies on Plasmon‐Enhanced TiO2 Photoelectrodes

AbstractA hundred years on, the energy‐intensive Haber–Bosch process continues to turn the N2 in air into fertilizer, nourishing billions of people while causing pollution and greenhouse gas emissions. The urgency of mitigating climate change motivates society to progress toward a more sustainable method for fixing N2 that is based on clean energy. Surface oxygen vacancies (surface Ovac) hold great potential for N2 adsorption and activation, but introducing Ovac on the very surface without affecting bulk properties remains a great challenge. Fine tuning of the surface Ovac by atomic layer deposition is described, forming a thin amorphous TiO2 layer on plasmon‐enhanced rutile TiO2/Au nanorods. Surface Ovac in the outer amorphous TiO2 thin layer promote the adsorption and activation of N2, which facilitates N2 reduction to ammonia by excited electrons from ultraviolet‐light‐driven TiO2 and visible‐light‐driven Au surface plasmons. The findings offer a new approach to N2 photofixation under ambient conditions (that is, room temperature and atmospheric pressure).

Promoted Fixation of Molecular Nitrogen with Surface Oxygen Vacancies on Plasmon-Enhanced TiO2 Photoelectrodes.

A hundred years on, the energy-intensive Haber-Bosch process continues to turn the N2 in air into fertilizer, nourishing billions of people while causing pollution and greenhouse gas emissions. The urgency of mitigating climate change motivates society to progress toward a more sustainable method for fixing N2 that is based on clean energy. Surface oxygen vacancies (surface Ovac ) hold great potential for N2 adsorption and activation, but introducing Ovac on the very surface without affecting bulk properties remains a great challenge. Fine tuning of the surface Ovac by atomic layer deposition is described, forming a thin amorphous TiO2 layer on plasmon-enhanced rutile TiO2 /Au nanorods. Surface Ovac in the outer amorphous TiO2 thin layer promote the adsorption and activation of N2 , which facilitates N2 reduction to ammonia by excited electrons from ultraviolet-light-driven TiO2 and visible-light-driven Au surface plasmons. The findings offer a new approach to N2 photofixation under ambient conditions (that is, room temperature and atmospheric pressure).

Fast formation of amorphous titanium dioxide thin films using a liquid-assisted plasma-enhanced deposition process in open air

In this work, the deposition of titanium oxide thin films at atmospheric pressure via an open-air liquid-assisted plasma-enhanced method has been studied. Morphology, chemical composition, crystal structure as well as optical properties of the deposited thin films were investigated. The method successfully enabled the formation of compact and transparent amorphous TiO2 layers with a high deposition rate of 1.2 μm per minute. The atmospheric pressure method reported here appears to be a promising up-scalable method for the high rate and large scale deposition of amorphous titanium dioxide thin films.

A highly efficient nanoporous BiVO4 photoelectrode with enhanced interface charge transfer Co-catalyzed by molecular catalyst

A highly efficient nanoporous non-doped BiVO4 photoelectrode with high photocurrent and low onset potential for photoelectrochemical water splitting was achieved by using molecular catalyst and amorphous TiO2 stabilization layer. This BiVO4 photoelectrode co-catalyzed by molecular catalyst of Ir-COOH exhibits the photoelectrochemical performance comparable to the limitation values obtained in Na2SO3 sacrifice agent. Interestingly, the BiVO4/Ir-COOH exhibits more efficient interface charge transfer than BiVO4/IrOx as measured by intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) although the Ir-COOH molecular catalyst shows much lower electrochemically catalytic activities than the state-of-the-art IrOx nanoparticles for water splitting. The Ir-COOH/BiVO4 was further stabilized by double amorphous TiO2 layers with little impact on charge transfer. In all, it is promising to achieve high efficiency water splitting by using molecular catalysts to co-catalyze nanostructure photoelectrodes with short diffusion length and such system can be stabilized by amorphous TiO2 layer.

Photodegradation of Rhodamine 6G by Amorphous TiO2 Films Grown on Polymethylmethacrylate by Magnetron Sputtering

Titanium dioxide (TiO2) was deposited on polymethylmethacrylate (PMMA) substrates by magnetron sputtering using a Compact Planar Magnetron sputtering device at different flow rate ratios of O2/Ar. The deposited TiO2 on PMMA substrates were characterized using X-ray Diffraction analysis, X-ray Photoelectron Spectroscopy, Fourier Transform Infrared Spectroscopy, UV-Visible Spectroscopy, and Scanning Electron Microscopy (SEM). These techniques confirm the deposition of a chemically stable amorphous TiO2 layer on the PMMA surface. Photocatalytic activity of the amorphous TiO2 layers were tested via photodegradation of Rhodamine 6G (Rh6G) dye solution. The samples were able to degrade 18–27% of the Rh6G solution after the initial 25 minutes of UV irradiation and complete degradation of Rh6G was observed after 7 hours of UV irradiation.

Atomic layer deposition of TiO2 on nitrogen-doped carbon nanofibers supported Ru nanoparticles for flexible Li-O2 battery: A combined DFT and experimental study

Flexible Li-O2 batteries have attracted worldwide research interests and been considered to be potential alternatives for the next-generation flexible devices. Nitrogen-doped carbon nanofibers (N-CNFs) prepared by electrospinning are used as flexible substrate and an amorphous TiO2 layer is coated by atomic layer deposition (ALD) and then decorated with Ru nanoparticles. The Ru/N-CNFs@TiO2 composite is directly used as a free-standing electrode for Li-O2 batteries and the electrode delivers a high specific capacity, improved round-trip efficiency and good cycling ability. The superior electrochemical performance can be attributed to the amorphous TiO2 protecting layer and superior catalytic activity of Ru nanoparticles. Based on density functional theory (DFT) calculations from first principles, the carbon electrode after coating with TiO2 is more stable during discharge/charge process. The analysis of Li2O2 on three different interfaces (Li2O2/N-CNFs, Li2O2/TiO2, and Li2O2/Ru) indicates that the electron transport capacity was higher on Ru and TiO2 compared with N-CNFs, therefore, Li2O2 could be formed and decomposed more easily on the Ru/N-CNFs@TiO2 cathode. This work paves a way to develop the free-standing cathode materials for the future development of high-performance flexible energy storage systems.

Synthesis of NiO-TiO2 hybrids/mSiO2 yolk-shell architectures embedded with ultrasmall gold nanoparticles for enhanced reactivity

Novel NiO-TiO2 hybrids/mSiO2 yolk-shell architectures loaded with ultrasmall Au nanoparticles (STNVS-Au) were developed via the rational synthetic strategy. The hierarchical yolk-shell nanostructures (STNVS) with high surface areas were constructed by a facile “bottom-up” assembly process using SiO2 materials and polymer resins as cores/shells and sacrificial templates, accompanied by a simple hydrothermal incorporation of NiO into uniform amorphous TiO2 layers that were converted to NiO-anatase TiO2 p-n heterojunction hybrids. Then, numerous sub–3nm Au nanoparticles were post encapsulated within STNVS nanostructures through the low-temperature hydrogen reduction based on the unique deposition-precipitation method with Au(en)2Cl3 compounds as gold precursors. The NiO-TiO2 hybrids alloying with Au nanoparticles were effectively protected and entrapped within STNVS architectures, and interacted with outer mSiO2-Au shells, which comprised the powerful STNVS-Au yolk-shell nanoreactors and produced stronger configural synergies in enhancing the heterogeneous catalysis. Into catalyzing the reduction of 4-nitrophenol to 4-aminophenol, the STNVS-Au was shown with outstanding activity and reusability, and its pristine morphology was well retained during the recycling process.

Protecting hydrogenation-generated oxygen vacancies in BiVO4 photoanode for enhanced water oxidation with conformal ultrathin amorphous TiO2 layer

Introducing appropriate amount of oxygen vacancies by hydrogenation treatment is a simple and efficient way to improve the photoelectrochemical performance of nanostructured oxide photoanodes. However, the hydrogenation effect is often not durable due to the gradual healing of oxygen vacancies at or close to surface of photoanodes. Herein, we tackled the problem by conformal coating the hydrogenated nanoporous BiVO4 (H-BiVO4) photoanode with an ultrathin layer of amorphous TiO2. Photoelectrochemical measurements showed that a 4nm-thick TiO2 layer could significantly improve the stability of H-BiVO4 photoanode for repeated working test, with negligible influence on the initial photocurrent compared to the uncoated one. Mott–Schottky and linear sweep voltammetry measurements showed that donor density and photocurrent density of the H-BiVO4 electrode almost decayed to the values of pristine BiVO4 electrode after 3h test, while the amorphous TiO2-coated electrode only degraded by 6% and 5% of the initial values respectively in the same period. The investigation thus suggested that the amorphous TiO2 layer did protect the oxygen vacancies in H-BiVO4 photoanode by isolating these oxygen vacancies from environmental oxygen, while at the same time not impeding the interfacial charge transfer to water molecules due to its leaky nature.

(Invited) Nanostructured Photocatalysts Prepared By Atomic Layer Deposition

Semiconductor oxides are widely used photocatalysts to decompose organic contaminations with solar energy. The activity of these photocatalysts can be further improved by doping them with heteroatoms, by making composites of them with other semiconductor oxide materials, noble metal nanoparticles, organic dyes and other organic absorbers, or by increasing their specific surface using highly structured substrates. Since by ALD uniform thin films with thickness control of sub-nanometer precision can be deposited on nanopatterned surfaces, it is a unique tool for preparing, doping and programming nanoscaled photocatalytic material.In the lecture several examples will be shown about how various nanostructured photocatalysts can be obtained by ALD, based on our own experience. By combining electrospinning and ALD, WO3/TiO2, ZnO/TiO2 and TiO2/ZnO core/shell Vis or UV active nanofiber photocatalysts were prepared. By using sol-gel and ALD, SiO2/TiO2 core/shell photocatalytic nanoparticles were obtained. Photocatalysts based on biological substrates can be also manufactured by ALD, e.g. TiO2 coated lotus leaves with both superhydrophobic and photocatalytic activities. C60/TiO2 (Fig. 1), graphene oxide (GO)/TiO2, CNT/TiO2, carbon aerogel/TiO2 and PMMA/TiO2 composites are examples for ALD prepared carbon and polymer nanostructure based photocatalysts.On the previously mentioned substrates, TiO2 thin films were deposited by ALD using TiCl4 or Ti(OPr)4 and H2O as precursors at various temperatures (80, 160, 250, 300 °C), and therefore nanocomposites containing both crystalline and amorphous TiO2 layers were prepared. While TiO2 is considered to have photocatalytic activity only in the crystalline state; unexpectedly, we observed that when TiO2 was deposited in amorphous form on biological or organic substrates, i.e. lotus leaf, C60-OH, GO or PMMA, the amorphous TiO2 layer clearly exhibited photocatalytic property. Figure 1