Porous TiO2 Nanotubes Research Articles

Innovative Nanostructured Fillers for Dental Resins: Nanoporous Alumina and Titania Nanotubes.

The possibility of improving dental restorative materials is investigated through the addition of two different types of fillers to a polymeric resin. These fillers, consisting of porous alumina and TiO2 nanotubes, are compared based on their common physicochemical properties on the nanometric scale. The aim was to characterize and compare the surface morphological properties of composite resins with different types of fillers using analytical techniques. Moreover, ways to optimize the mechanical, surface, and aesthetic properties of reinforced polymer composites are discussed for applications in dental treatments. Filler-reinforced polymer composites are the most widely used materials in curing dental pathologies, although it remains necessary to optimize properties such as mechanical resistance, surface characteristics, and biocompatibility. Anodized porous alumina nanoparticles prepared by electrochemical anodization offer a route to improve mechanical properties and biocompatibility as well as to allow for the controlled release of bioactive molecules that can promote tissue integration and regeneration. The inclusion of TiO2 nanotubes prepared by hydrothermal treatment in the resin matrix promotes the improvement of mechanical and physical properties such as strength, stiffness, and hardness, as well as aesthetic properties such as color stability and translucency. The surface morphological properties of composite resins with anodized porous alumina and TiO2 nanotube fillers were characterized by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and X-ray chemical analysis. In addition, the stress-strain behavior of the two composite resins is examined in comparison with enamel and dentin.

Preparation of TiO2 nanofibers, porous nanotubes, RGO/TiO2 composite by electrospinning and hydrothermal synthesis and their applications in improving the electrochemical hydrogen storage properties of Co2B material

Co2B hydrogen storage material was prepared via a high temperature solid phase process. The TiO2 nanofibers (TiO2–NF) and TiO2 porous nanotubes (TiO2-NT) with different size, structure and morphology were fabricated by electrospinning and hydrothermal synthesis. In order to improve the conductivity, the reduced graphene oxide/TiO2 nanotubes composite (RGO/TiO2-NT) was synthesized by an alkaline hydrothermal process. The three-dimensional porous TiO2 nanotubes were attached to the two-dimensional RGO and formed a uniform dispersion. For the purpose of improving the electrochemical performance of Co2B, composites of Co2B doped with TiO2–NF, TiO2-NT and RGO/TiO2-NT were manufactured by ball milling. Ultimately, all the composite electrodes showed higher discharge capacities than ordinary Co2B. Among them, Co2B modified with RGO/TiO2-NT exhibited the highest discharge capacity (691.4 mAh/g). TiO2-NT with large specific surface area and unique tubular porous structure can offer sufficient electrochemical active sites to anchor hydrogen and improve the electrocatalytic activity of Co2B, meanwhile, the RGO component in RGO/TiO2-NT with excellent electrical conduction can further provide fast channels for charger transfer during the charging/discharging processes. Moreover, the corrosion resistance, HRD and kinetics performance of Co2B were also enhanced after doping of TiO2–NF, TiO2-NT and RGO/TiO2-NT.

One-step synthesis of N-doped porous wall TiO2 nanotube arrays for efficient removal of dibutyl phthalate under visible light

The N-doped porous wall TiO2 nanotube arrays (N@p-TNTAs) was synthesized by one-step anodization method for the first time. The excellent adsorption performance and visible light response of N@p-TNTAs result in significantly superior photocatalytic activity, due to the porous wall nanotube array structure and the successful doping of N element. The photocatalytic activity of catalyst was evaluated by using the refractory organic pollutants dibutyl phthalate (DBP) as target pollutant. >97 % of DBP was degraded after 3 h of irradiation with visible light, and the degradation kinetic constant was nearly 88 and 9 times higher than that of TiO2 nanotube arrays (TNTAs) and TiN, respectively. During the calcination process, due to the N doping, the orbital of N 2p and O 2p were mixed to produce new valence bands, which effectively shortened the bandgap width of N@p-TNTAs to have visible light response. Meanwhile, a part of N escaped in the form of gas, forming the structure of porous wall. In addition, N@p-TNTAs still showed outstanding photocatalytic activity after 6 cycles, which indicated that the structure of material was stable and can be widely used in environmental photocatalysis.

Porous titania nanotube confined ultrafine platinum catalysts synthesized by atomic layer deposition with enhanced hydrolytic dehydrogenation performance

Synthesizing the catalysts with high activity and stability has always been the research hotspot in the field of heterogeneous catalysis, and the confinement provides a promising route to achieve the goal. Herein we report the porous TiO2 nanotube confined Pt catalysts synthesized by the template-assisted atomic layer deposition (ALD) strategy for hydrolytic dehydrogenation of NH3BH3, in which the ultrafine Pt nanoparticles are decorated on the inner surfaces of the nanotubes with increased Pt-TiO2 interfacial sites compared with the supported Pt/TiO2 counterparts. Combined with the porous structures of the nanotubes with suitable thickness and large open ends, these factors synergistically contribute to the excellent catalytic performances of the confined Pt@TiO2 catalysts. The present strategy can be extended to prepare the corresponding PtNi@TiO2 bicomponent catalysts exhibiting the further boosted activity with a TOF value of 1055.2 molH2 molPt−1 min−1. This work offers a reliable and general approach for synthesizing the confined catalysts with high efficiency.

Double-anode anodization of metal Ti in two beakers

Porous anodic TiO2 nanotubes have been widely studied because of their interesting prospects and mysterious mechanism of formation. However, most traditional anodization is done in a single beaker, and few changes have been made to the method by which titanium is anodized. In this study, a double-anode anodizing method involving a wired anode and a wireless anode in two beakers was used for the first time. Nanotubes were found to form at the two anodes. The effect of changing the electrolytes in the two beakers was studied. The current–time curve showed the normal three stages when the electrolytes in both beakers were the same. However, when the electrolytes in the two beakers were different, the time–current curve showed a tendency to decrease, and ginseng-root-shaped nanotubes (where a thick nanotube splits into several thinner nanotubes) appeared at a high voltage (100 V).

Comparison of Formation Mechanism between Porous Anodic Sn Oxide and Anodic TiO2 Nanotubes

Porous anodic Sn oxide (PASO) and other porous anodic oxides have aroused worldwide scientific interest. However, the relationship between the complex porous structure and the current-time curve cannot be interpreted by the traditional dissolution theory. In particular, with the change of anodizing conditions of Sn, the current-time curve sometimes shows three stages, sometimes five stages. In order to study the relationship between current-time curve and the growth model of complex PASO structure during Sn anodization, this study compares the anodizing processes of Sn and Ti. Under normal circumstances, the current-time curve of Ti in anodizing process is three stages, which can be interpreted reasonably by electronic current and oxygen bubble model. By adjusting the anodizing processes of both metals, their current-time curves would be changed into five stages, which means that the formation mechanism of the two metal oxide porous structures may be inherently connected. Here, the current-time curves of three stages and five stages are carefully compared. The internal relationship between the structure of anodic TiO2 nanotubes and the complex porous structure of PASO is found, revealing that the complex porous structure of PASO is caused by excessive gas evolution which is the result of electronic current.

(Invited) Growth of Self-Ordered Porous Anodic Oxide Nanomaterials By Coupled Ion Migration and Viscous Flow

Porous anodic oxide (PAO) films are self-organized porous oxide nanomaterials formed by electrochemical oxidation. PAO includes porous anodic alumina and TiO2 nanotube layers. These films eventually evolve into a hexagonally-ordered array of parallel cylindrical pores or nanotubes of order 100 nm diameter, with a characteristic interpore spacing that scales directly with the cell voltage.We explore the roles of mechanical stress and oxide flow in self-ordering, through a modeling analysis of stress-driven viscous flow of oxide (1). The model is based on coupled viscous flow of oxide and stress- and electric field-driven migration of metal and oxygen ions (2). Stress at the film interfaces is generated by ion-transfer processes and relaxed by viscous flow, resulting in layers with elevated compressive or tensile stress within a few nm of the interfaces (3,4). Experimental evidence for these layers has been found from in situ stress measurements (5,6). We present linear stability analysis incorporating the surface stress boundary conditions in the coupled oxide flow-electrical migration model of Houser and Hebert (2).For porous alumina, the calculations reveal self-organized pattern formation with steady-state pore spacing-voltage scaling ratios that compare favorably to those found experimentally (1). The scaling ratios are independent of oxide viscosity or uncertainties in the values of any other model parameters. The stress driving oxide flow arises at the oxide-solution interface due to strong electrolyte anion adsorption, which blocks direct oxide deposition on the surface itself. New results for TiO2 nanotube layers are presented. Near-surface stress is not present in TiO2 nanotube layers (6); instead, compressive stress driving flow arises at the metal-oxide interface from the volume change upon conversion of metal to oxide.REFERENCES P. Mishra and K. R. Hebert, Electrochim. Acta, 340, 135879 (2020).J. E. Houser and K. R. Hebert, Nature Mater., 8, 415 (2009).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E737 (2018).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E744 (2018).Ö. Ö. Çapraz, P. Shrotriya, P. Skeldon, G. E. Thompson, K. R. Hebert, Electrochim. Acta, 167, 404 (2015).Q. Dou, P. Shrotriya, W. F. Li, K. R. Hebert, Electrochim. Acta, 292, 676 (2018).Q. Dou, P. Shrotriya, W. F. Li, K. R. Hebert, Electrochim. Acta, 295, 418 (2019).

Removal of aqueous triclosan using TiO2 nanotube arrays reactive membrane by sequential adsorption and electrochemical degradation

Removal of triclosan (TCS) in water has attracted increasing attention due to its high detection frequency and potential toxicity. In this study, porous TiO2 nanotube arrays (TiO2 NTA) was prepared as the reactive electrochemical membrane (REM) to adsorb aqueous TCS, and subsequently to degrade TCS in-situ (a regeneration process of TiO2 NTA). Adsorption kinetics and thermodynamic of TCS followed pseudo-second-order model and Langmuir model, respectively. Compared with adsorption at 0 mL min−1 (static adsorption), the initial adsorption rate and the maximum adsorption capacity increased 18.8-fold and 73.8-fold at 300 mL min−1, respectively. The optimal equilibrium absorption capacity (per projected area of TiO2 NTA) and the initial adsorption rate were 2042.92 mg m−2 and 108.51 mg m−2 min−1, respectively. In the subsequently electrochemical oxidation process, 99.8% of the adsorbed TCS was degraded in-situ and TiO2 NTA was regenerated simultaneously. TiO2 NTA electrode maintained the stable removal performance of TCS during four adsorption-degradation cycles. The adsorption process was a complex combination of the hydrophobic interaction and electrostatic interaction with/without applied voltage at different pH value. The electrochemical degradation pathways of TCS on TiO2 NTA were hydroxylation, disproportionation, dichlorination and cleavage of ether bond under the attack of electrochemical generated OH and O2−. The flow-through sequential adsorption and electrochemical degradation (SAED) based on TiO2 NTA REM were proved to be effective method to removal TCS in waters, especially for the water with low conductivity.

A novel synthesis of porous TiO2 nanotubes and sequential application to dye contaminant removal and Cr(VI) visible light catalytic reduction

Abstract Porous TiO2 nanotubes (PTNTs) were successfully prepared by a versatile sepiolite-sacrificed template method. The PTNTs possess a unique porous structure and a high specific surface area (120 m2 g−1). It exhibits significantly enhanced adsorption performance for azo dye Congo Red (CR, model dye pollutant) with maximum adsorption capacity of 540 mg g−1, which is much better than common TiO2-based materials, as well as some other semiconductor adsorbents. The dye-impregnated PTNTs (CR-PTNTs) were re-utilized as a photocatalyst for the visible light-induced reduction of Cr(VI). The results show that the CR-PTNTs exhibit significantly superior photocatalytic reduction ability to Cr(VI), and such performance can be attributed to the huge adsorption of CR molecules on the PTNTs and the unique porous structure of PTNTs. Current work not only reports an effective adsorbent for dye CR removal, but also put forward a reutilization strategy of the spent adsorbent for efficient visible-light photocatalytic reduction of Cr(VI), applicable to the other non-coexisting dyes and Cr(VI) pollutant scenarios.

Model for Formation of Self-Ordered Anodic Oxide Nanomaterials

Porous anodic films are self-organized porous oxides nanomaterials formed by electrochemical oxidation. Pores in porous alumina and nanotubes in TiO2nanotube layers initiate after an initial stage of barrier oxide growth. The porous film eventually evolves into a hexagonally-ordered array of parallel cylindrical pores or nanotubes of order 10-100 nm diameter with a characteristic spacing that scales directly with the cell voltage. We explore the roles of mechanical stress and oxide flow in self-ordering, through a modeling analysis of stress-driven viscous flow of oxide (1-3). The model is based on coupled viscous flow of oxide and stress- and electric field-driven migration of metal and oxygen ions (1). Stress at the film interfaces is generated by ion-transfer processes and relaxed by viscous flow, resulting in layers with elevated compressive or tensile stress within a few nm of the interfaces (2,3). Experimental evidence for these layers has been found from in situ stress measurements (2-4). We present linear stability analysis incorporating the surface stress boundary conditions in the coupled oxide flow-electrical migration model of Houser and Hebert (1). The calculations reveal self-organized pattern formation with steady-state pore spacing-voltage scaling ratios that compare favorably to those found experimentally, for both porous alumina and TiO2nanotube layers. The scaling ratios are independent of oxide viscosity or uncertainties in the values of any other model parameters. In the case of Al anodization, oxide flow resulting in pore patterns is driven by elevated stress near the oxide-solution interface, through a mechanism that has common features with the Marangoni instability in thin liquid films. Stress near the oxide surface is produced because strong electrolyte anion adsorption suppresses oxide growth on the surface. Such near-surface stress is not present in TiO2nanotube layers (5). Instead, compressive stress driving flow arises at the metal-oxide interface from the volume change upon conversion of metal to oxide. REFERENCES J. E. Houser and K. R. Hebert, Nature Mater., 8, 415 (2009).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E737 (2018).K. R. Hebert, P. Mishra, J. Electrochem. Soc., 165, E744 (2018).Ö. Ö. Çapraz, P. Shrotriya, P. Skeldon, G. E. Thompson, K. R. Hebert, Electrochim. Acta, 167, 404 (2015). Q. Dou, P. Shrotriya, W. F. Li, K. R. Hebert, Electrochim. Acta, 295, 418 (2019).

Providing significantly enhanced photocatalytic H2 generation using porous PtPdAg alloy nanoparticles on spaced TiO2 nanotubes

In the present work we introduce a simple approach to produce porous PtPdAg alloy nanoparticles on TiO2 nanotubes by a simple combined sputtering-dewetting-dealloying process. In a first step, three individual metals (Pt, Pd and Ag) were sequentially sputter-deposited on spaced TiO2 nanotubes, followed by a thermal dewetting treatment in Ar to convert these metal layers into ternary PtPdAg alloyed particles. Dealloying was carried out by a selective chemical dissolution of Ag in piranha solution that finally generated porous alloyed nanoparticles located on the TiO2 nanotube walls. The porous PtPdAg-decorated TiO2 nanotubes show enhanced photocatalytic H2 generation in comparison with porous Pt (67% increase) or any monometallic decoration (>120% increase). The photocatalytic enhancement is not only due to the increased number of active sites (larger surface area) of the porous particles but also due to the synergistic effects of the different alloying elements.

Porous TiO₂ Nanotube Arrays for Drug Loading and Their Elution Sensing.

Porous TiO₂ nanotube arrays have been attracting much attention as optical sensing layers and surface layers of dental implants because they are stable in acid and biocompatible. To use them as the optical sensing layers, TiO₂ nanotube arrays with various structures were fabricated and obtained an optimized microstructure at 50 V, 50 min and 0.5 wt% of NH4F, 7.4 vol% deionized water in ethylene glycol. TiO₂ nanotube arrays which had diameters of ~73.54 nm and lengths of ~3.39 μm showed the best sensing performance. A Ti implant was also anodized at 60 V for 4 hr in an ethylene glycol electrolyte and TiO₂ nanotube arrays showed the pore diameter of 156.01 nm and the thickness of 6.87 μm. Recombinant human bone morphogenetic protein-2 (rhBMP-2), isobutylphenyl propionic acid, and sodium alendronate were loaded into the TiO₂ nanotube arrays on the surface of the Ti implant. For elution of these drugs, optical thickness changes of 2.4 nm, 3.5 nm and 3.1 nm were respectively observed for about 2.2 hr, 3.6 hr and 3.1 hr. The TiO₂ nanotube arrays were useful for drug loading and their elution interferometric sensing.

Morphology evolution of TiO2 nanotubes with additional reducing agent: Evidence of oxygen release

In order to explore wider application of porous anodic alumina and anodic TiO2 nanotubes (ATNTs), the formation mechanism research of porous anodic materials plays a more significant role. Traditional field-assisted dissolution theory has been put into question and oxygen bubble mold has been accepted gradually. However, it is difficult to prove oxygen release. In this work, we present a method to demonstrate the presence of oxygen in the pores of nanotubes. A kind of water soluble reducing agent (NH4H2PO2) was added into electrolyte containing NH4F. Cavities exists not only between the double walls of nanotubes but also in the inner walls, which are different from normal nanotubes. The morphology evolution of nanotubes results from the reaction between NH4H2PO2 and oxygen. Therefore, the release of oxygen during the formation of ATNTs was further proved.

Rational design of TiO2@ nitrogen-doped carbon coaxial nanotubes as anode for advanced lithium ion batteries

To improve the lithium storage capacity, electrochemical kinetics and stability of TiO2 nanostructured electrode, a hybrid electrode of TiO2 nanotubes coated with nitrogen-doped carbon (TiO2@NC) was rationally designed and prepared. With the unique coaxial nanotube structure, the porous TiO2 nanotubes would offer short paths for Li+ diffusion and numerous active sites, while the N-doped carbon matrix would prefer fast charge transportation and buffer the volume change of TiO2 during lithiation/delithiation processes. In particular, a high reversible specific capacity of 480 mA h g−1 at a current density of 100 mA g−1 was achieved when evaluated as anodes for lithium ion batteries. The high capacity, outstanding cycling stability, and remarkable rate performance may attributed to its unique morphology and the synergetic effect of porous TiO2 nanotube and conductive N-doped carbon nanoshell on the basis of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).

In situ formation of porous TiO2 nanotube array with MgTiO3 nanoparticles for enhanced photocatalytic activity

Heterostructured semiconductor photocatalysts are desirable for applications such as purification of pollutants and water splitting due to the enhanced charge separation. In this work, porous TiO2 nanotube arrays loaded with MgTiO3 nanoparticles (MgTiO3/P-TiO2 NTAs) are prepared hydrothermally by anodization of TiO2 NTAs in the magnesium acetate (Mg(AC)2) solution. The photocatalytic (PC) activity of MgTiO3/P-TiO2 NTAs evaluated by monitoring the degradation of methyl blue (MB) reveals that the effectiveness is related to the thickness of MgTiO3 layer on TiO2. The best PC activity is observed from the MgTiO3/P-TiO2 NTAs hydrothermally treated at 200 °C for 1 h, the degradation rate is twice that of pristine anatase TiO2 NTAs and the transient photocurrent is three times higher. The heterostructured MgTiO3/P-TiO2 NTAs with good PC characteristics have large potential in photoelectrochemical (PEC) water decomposition and solar cell applications.

Porous N-doped TiO2 nanotubes arrays by reverse oxidation of TiN and their visible-light photocatalytic activity

Highly ordered porous N-doped TiO2 nanotubes arrays (N-TiO2 NTAs) are produced via reverse oxidation of porous TiN NTAs in air atmosphere. The band gap of produced porous N-TiO2 NTAs was reduced from 3.04 eV for TiO2 NTAs to 2.94 eV. Photocatalytic (PC) investigations indicate that the porous N-TiO2 NTAs exhibit three times larger visible light PC kinetic rate constant than that of anatase TiO2 NTAs as a result of the enhanced visible light activity and the large surface area. The results demonstrate that reverse oxidation of nitride is an applicable method for the preparation of nitrogen doping oxide and could be potential using for the fabrication of other carbon or sulfur doped oxide by oxidation of corresponding carbide and sulfide for high efficient visible light photocatalyst.

Cavities between the double walls of nanotubes: Evidence of oxygen evolution beneath an anion-contaminated layer

The mechanisms of formation of porous anodic alumina and anodic TiO2 nanotubes (ATNTs) have attracted increasing attention due to the wide range of application of these materials. The field-assisted dissolution and field-assisted ejection theories are widely supported, despite the fact that many experimental results raise difficult questions. The oxygen bubble mould theory can explain experimental phenomena that contradict the field-assisted dissolution theory, but is controversial as there is a lack of evidence of oxygen evolution. In this work, cavities between the double walls of ATNTs obtained in electrolytes containing NH4F and H3PO4 provide direct evidence of oxygen bubbles resulting in pore formation. Oxygen evolution proceeds at the interface between the anion-contaminated layer and the barrier oxide layer. Small oxygen bubbles that cannot rupture the anion-contaminated layer flow upward with the barrier oxide, resulting in cavities between the double walls of the nanotubes.

Chemically Deposited Sol–Gel Film on Porous TiO2 Nanotube Arrays as an Efficient and Unbreakable Solid-Phase Microextraction Fiber

In the present study, a novel technique was proposed to improve the performance of solid-phase microextraction fibers through the chemical deposition of polydimethylsiloxane/divinylbenzene film on modified TiO2 nanotube arrays substrate. Two different techniques, including the self-assembled monolayer of 3-mercaptopropyl trimethoxysilane and NaOH treatment, were examined to modify the surface of TiO2 nanotube arrays. The morphology of the prepared fibers was studied by scanning electron microscopy. The applicability of the novel fiber was evaluated through the headspace solid-phase microextraction of some polycyclic aromatic hydrocarbons as the model compounds followed by GC–MS determination. Influencing parameters on the extraction efficiency such as extraction time, temperature and salt content were studied and optimized. The thermal stability experiments demonstrated that the novel fiber was stable at 280 °C and reusable for more than 80 times without an obvious decrease in the extraction performance. The proposed method was successfully applied to the determination of PAHs in river water samples with good relative recoveries from 75.8 to 104.5% and the relative standard deviation values for all analytes were below 12%. Finally, the extraction performance of the prepared fiber was compared with those of commercially available fibers and similar previously reported fibers.

Anodizations of Al and Ti in NH4F or H3PO4 Solutions and Formation of Porous Anodic Alumina with Special Morphology

Porous anodic alumina (PAA) and anodic TiO2 nanotubes (ATNTs) have been widely investigated for decades. However, their formation mechanism and growth kinetics remain unclear. Here two unconventional and two conventional anodizations of aluminum and titanium are contrasted to overcome this challenge. PAA with special morphology was fabricated in NH4F electrolyte for the first time, which cannot be explained by the popular field-assisted theory. Combining the oxygen bubble mold and the oxide flow model with the dissolution model, a new explanation for the special morphology is presented. In addition, anodic titanium oxide films with plenty of cavities were obtained in H3PO4 electrolyte, which absolutely differ from the general compact films. The cavities in anodic titanium oxide films also result from the oxygen bubbles within the oxide films. The anions in electrolyte (e.g., F–, OH–, PO43–) accumulate, and the anion-contaminated layer (ACL) forms due to the electric field. The ACL plays a decisive role in the generation of the electronic current (Je) and the formation of oxygen bubble mold. Regular ATNTs were obtained as titanium was anodized in NH4F electrolyte. The ACL forms and appropriate Je generates because the dissolution from F– on TiO2 is limited. However, PAA with special morphology was obtained as aluminum was anodized in NH4F electrolyte. Thicker ACL results in the impulse peak of the Je because the dissolution and corrosion from F– on alumina is severe.

Design and Properties of Confined Nanocatalysts by Atomic Layer Deposition.

Governing the process and outcome of chemical reactions is the most important aim of catalytic chemistry. The confinement of active sites inside nanosized spaces provides a powerful strategy to achieve this goal. Reacting molecules (reactants, intermediates, and products of a reaction) and nanomaterials (metal/metal-oxide nanoparticles) confined inside nanoreactors have been observed to exhibit modified behaviors and properties with respect to their unconfined counterparts. Typically, catalysts confined in zeolites, mesoporous materials, metal-organic frameworks, and nanotubes are obtained by traditional liquid-phase methods. However, excess metals or undesired solvents and other reagents must be removed. It is also difficult to precisely regulate the confined nanostructures and assemble multifunctional sites in the confined nanospaces. Atomic layer deposition (ALD) provides a controllable method to fabricate confined catalysts due to its outstanding advantages. In this Account, we describe our progress in the design and properties of confined nanocatalysts by ALD. ALD is an elegant method to directly deposit highly dispersed metal or oxide species into porous materials, including zeolites and mesoporous materials. We deposited Pt nanoclusters in the micropores of a KL zeolite with precisely controlled size by ALD. We also introduced CoOx nanoclusters into mesoporous SBA-15. We have reported pioneering works on the synthesis of confined nanoparticles with metal-in-nanotube structures by a template-assisted ALD method. Confined Cu nanoparticles were prepared by reducing CuO nanowires coated with Al2O3, TiO2, or alucone layers by ALD. Confined Cu and Au nanoparticles were also prepared starting from the corresponding metal nanowires with the assistance of sacrificial layers produced by ALD. In a more facile strategy, Au nanoparticles confined in Al2O3 nanotubes were produced using a sacrificial template by ALD. Furthermore, we synthesized a multiply confined Ni-based nanocatalyst through a template-assisted ALD method. We assembled multiple interfaces (Ni/Al2O3 and Pt/TiO2) in a confined nanospace for tandem reactions by template-assisted ALD. The synergistic effect of two interfaces enhanced the tandem reaction, and the confined nanospace favored the instant transfer of intermediates between the two interfaces. In addition, porous TiO2 nanotubes with spatially separated Pt and CoOx cocatalysts were also produced by ALD. The confined catalysts can be further treated by ALD. We used ALD to modify the mesoporous SBA-15 support to precisely tune the active species-support interaction. In addition to the support, the confined metal nanoparticles can also be coated with an ultrathin oxide layer by ALD to further improve their catalytic activities. Moreover, the structure and size of the confined nanospace can be tuned precisely by ALD. Overall, ALD has exhibited noteworthy applications in and will provide new opportunities for the design and synthesis of highly effective confined catalysts.