Amorphous TiO2 Nanoparticles Research Articles

XAS study of sol–gel synthesized amorphous and anatase TiO2 nanoparticles

Amorphous titanium dioxide (TiO2) nanoparticles were obtained by the sol–gel method with subsequent crystallization to anatase by annealing at 350 °C for 4 h. Based on the research results using XANES and EXAFS X-ray absorption spectroscopy, it was determined that the as-prepared amorphous TiO2 contains vacancies in the oxygen and titanium sublattices.

Unraveling the Synergistic Effects of Oxygen Vacancy and Amorphous Structure on TiO2 for High‐Performance Lithium Storage

The improved electronic conductivity and ion diffusion efficiency of TiO2‐based anode materials have been extensively studied by introducing oxygen vacancies or creating amorphous structure. There has been little exploration of the synergistic effects by combining these two modification strategies into one TiO2‐based matrix. In addition, the structure–activity relationship and energy storage mechanism involved remain to be understood. Herein, a facile one‐step coreduction method is reported to successfully produce the oxygen vacancy‐doped amorphous TiO2 nanoparticles. The oxygen vacancy‐doped amorphous TiO2 anode exhibits significantly enhanced electrochemical activity and high‐rate stability (up to 87 mAh g−1 over 10 000 discharge/charge cycles at a current rate of 100 C). This outstanding electrochemical performance is attributable to the synergistic effects of amorphous structure and oxygen vacancies. Density functional theory calculations reveal the enhanced electronic conductivity and thermodynamically favorable lithium insertion architecture due to the introduction of oxygen vacancy and the construction of the amorphous skeleton. Dynamic analysis indicates that the lithium‐storage mechanism is a hybrid of surface capacitive storage and enhanced diffusion‐controlled ion insertion. This work opens up new pathways in developing novel anode materials for efficient energy storage from the wide spectrum of metal oxides.

Controllable and facile one-pot synthesis of high surface area amorphous, crystalline, and triphasic TiO2: catalytic and photocatalytic applications

A simple and controllable synthesis led to both amorphous and crystalline porous TiO2 with remarkably high surface area and pore volume. Their distinctive characteristics influenced their effectiveness in photocatalytic and catalytic processes.

A novel Z-scheme heterojunction Fe-BDC/TiO2 for efficient photocatalytic degradation of acetaldehyde

Constructing heterojunction structures is considered one of the effective methods to improve the activity of photocatalysts. A novel Z-Scheme heterojunction Fe-BDC/TiO2 was designed and synthesized by amorphous gel Fe-BDC and TiO2 nanoparticles with electrostatic self-assembly method. The introduction of Fe-BDC has been proved to expand the light absorption range and promote the separation and transfer of interface photo generated electrons and holes. Thus, the photocatalytic degradation efficiency of acetaldehyde by 5% Fe-BDC/TiO2 sample is 2.3 times than that of pure TiO2 sample. And the reaction rate is 2.5 times than that of pure TiO2 sample. The free radical capture experiment shows that O2− played a more important role in the degradation of acetaldehyde. In addition, in situ infrared analysis further reveals the surface species of the photocatalysts during adsorption and degradation processes. The acetaldehyde degradation route of Fe-BDC/TiO2 has been speculated. ‘1These findings provide valuable references for the design of metal oxide semiconductor/Fe based MOF heterojunctions and the efficient degradation of aldehyde VOCs.

Regulating crystallinity in cellulose substrate to construct highly and homogeneously dispersed TiO2 for tetracycline hydrochloride adsorption

This work developed a simple and mild strategy for controllable synthesis of highly and homogeneously distributed TiO2 nanoparticles on a cellulose template via tuning the cellulose crystallinity. As the crystallinity of cellulose increases, the restriction from crystallinity on nanoparticles increases, leading to homogeneous distribution, a decrease in size, and structural changes of TiO2 from crystalline to amorphous. The carboxyl groups grafted on the periodically arranged hydroxyl groups of crystalline cellulose, which act as anchor sites for metal oxide precursor, restrict the distribution, growth and crystallization of TiO2 nanoparticles. The amorphous TiO2 nanoparticles on the cellulose with the highest degree of crystallinity (72.40 %) give the highest adsorption capacity toward tetracycline hydrochloride (152.89 mg/g), which is the state of art among the supported TiO2. The high adsorption capacity is proposed to be the oxygen defects caused by the Ti3+ species, originating from the amorphous TiO2 nanoparticles.

Facile sol-gel preparation of amorphous TiO2 nanoparticles under pH of 8 for synergistic adsorption-photocatalytic degradation of tetracycline

In this work, an amorphous TiO2 nanoparticle (8-AT) was prepared via the sol-gel route in which the pH of sol was facilely adjusted to 8 with ammonia. The characterization results of physicochemical properties revealed that as-prepared 8-AT had the particle size of 20–24 nm and specific surface area of 365.68 m2/g. The degradation of 8-AT for 20 mg·L−1 tetracycline (TC) aqueous solution achieved 93.9% within 30 min dark reaction and 60 min visible light irradiation, which was 1.3 and 2.0 times higher than that of anatase TiO2 and P25. Moreover, 8-AT can maintain a degradation capacity of 82.7% for the concentrations up to 50 mg·L−1 of TC, and the degradation rate decreased slightly by 11.86% after five cycles. Based on the synergistic adsorption-photocatalytic activity of 8-AT catalyst, the possible degradation mechanism of TC was proposed. This work provided a facile method for obtaining amorphous TiO2 through adjustment of pH and a new idea for developing efficient photodegradation catalyst.

Design of Organic-Free Superhydrophobic TiO2 with Ultraviolet Stability or Ultraviolet-Induced Switchable Wettability.

Superhydrophobic TiO2 with great application potential is mainly obtained by surface modification with low surface energy organics, which is easily degraded under sunlight irradiation, which results in the loss of superhydrophobic properties. Herein, we developed a room-temperature pulsed chemical vapor deposition (pulsed CVD) method to develop amorphous TiO2-deposited TiO2 nanoparticles. The ultraviolet stability/ultraviolet-induced reversible wettability switch had been simultaneously realized by different and controllable deposition cycles of amorphous TiO2. The superhydrophobic properties of the organic-free TiO2 were determined by the micrometer-nanometer-sub-nanometer multiscale structure, the multiscale pore structure, and the large Young's contact angle resulting from carboxylic acid adsorption. Also, we found that the adsorption rate and adsorption stability of oxygen and water at the surface oxygen vacancies were the key to facilitate the reversible switching between superhydrophilic and superhydrophobic states, which was well demonstrated by experimental characterization and theoretical simulation. In addition, we also found that the resistance of dense amorphous TiO2 films on the TiO2 surface to the migration of photogenerated electrons and holes was the key to maintain the stable superhydrophobic properties of superhydrophobic TiO2 under ultraviolet illumination. The powders were strongly ground and the coating surface was rubbed on the surface of the sandpaper, which still maintained superhydrophobic properties, providing favorable conditions for the application of superhydrophobic TiO2. This work modulates the ultraviolet stability and dark/ultraviolet-induced switchable superhydrophobicity/superhydrophilicity of coated TiO2 by simply adjusting the number of deposition times in a pulsed CVD process for the first time, thus contributing to the development of organic-free superhydrophobic TiO2.

Electrocatalytic production of glycolic acid via oxalic acid reduction on titania debris supported on a TiO2 nanotube array

Electrodes prepared by anodic oxidation of Ti foils are robust and not toxic materials for the electrocatalytic reduction of oxalic acid to glycolic acid, allowing the development of a renewable energy-driven process for producing an alcoholic compound from an organic acid at low potential and room temperature. Coupled with the electrochemical synthesis of the oxalic acid from CO2, this process represents a new green and low-carbon path to produce added value chemicals from CO2. Various electrodes prepared by anodic oxidation of Ti foils were investigated. They were characterized by the presence of a TiO2 nanotube array together with the presence of small patches, debris, or TiO2 nanoparticles. The concentration of oxygen vacancies, the amount of Ti3+ measured by X-ray photoelectron spectroscopy (XPS) and the intensity of the anodic peak measured by cyclic voltammetry, were positively correlated with the achieved oxalic acid conversion and glycolic acid yield. The analysis of the results indicates the presence of small amorphous TiO2 nanoparticles (or surface patches or debris) interacting with TiO2 nanotubes, the sites responsible for the conversion of oxalic acid and glycolic acid yield. By varying this structural characteristic of the electrodes, it is possible to tune the glycolic acid to glyoxylic acid relative ratio. A best cumulative Faradaic efficiency (FE) of about 84% with FE to glycolic acid around 60% and oxalic conversion about 30% was observed.

Antibacterial properties of Ag/TiO2/PDA nanofilm on anodized 316L stainless steel substrate under illumination by a normal flashlight.

The demand of medical materials for rapid and efficient elimination of bacteria has seen a dramatic surge over the past few years. In this study, antibacterial nanofilms with reactive oxygen species were generated by photocatalysis. To prepare these nanofilms, Ag and amorphous TiO2 nanoparticles decorated on polydopamine (PDA) were coated on three-dimensional (3D) nanopore arrays, which was fabricated on a substrate of anodized stainless steel. All the antibacterial tests were conducted with a household flashlight, which may be considered as a practical approach for antibacterial materials. The photoelectrochemical property of the 3D Ag/TiO2/PDA nanofilm on 316L stainless steel (Ag/TiO2/PDA SS) was about 15 times higher than that of the annealed Ag/TiO2/PDA SS, and consequently, it exhibited higher antibacterial activity. The enhanced photoelectrochemical property is attributed to the successful separation of electrons (amorphous TiO2) and holes (Ag nanoparticles). Further, when a plate containing 3D Ag/TiO2/PDA SS was irradiated with visible light just for 10 min, it immediately destroyed the bacteria in 106 CFU/mL without any bacterial colony. After five weeks, there were still no bacterial colonies in the plate corresponding to Ag/TiO2/PDA SS under visible light, while Ag/TiO2/PDA SS in dark had a negligible effect on the bacteria, i.e., the antibacterial mechanism through direct contact and ion dissolution was not efficient. The excellent antibacterial properties of 3D Ag/TiO2/PDA SS illuminated by flashlight provides an efficient, facile, and cost-effective technique for the development of antibacterial medical materials to meet the increasing demand of eliminating bacterial infections.Electronic supplementary materialThe online version of this article (10.1007/s10853-020-04610-w) contains supplementary material, which is available to authorized users.

Surface Potential and Interfacial Water Order at the Amorphous TiO2 Nanoparticle/Aqueous Interface.

Colloidal nanoparticles exhibit unique size-dependent properties differing from their bulk counterpart, which can be particularly relevant for catalytic applications. To optimize surface-mediated chemical reactions, the understanding of the microscopic structure of the nanoparticle–liquid interface is of paramount importance. Here we use polarimetric angle-resolved second harmonic scattering (AR-SHS) to determine surface potential values as well as interfacial water orientation of ∼100 nm diameter amorphous TiO2 nanoparticles dispersed in aqueous solutions, without any initial assumption on the distribution of interfacial charges. We find three regions of different behavior with increasing NaCl concentration. At very low ionic strengths (0–10 μM), the Na+ ions are preferentially adsorbed at the TiO2 surface as inner-sphere complexes. At low ionic strengths (10–100 μM), a distribution of counterions equivalent to a diffuse layer is observed, while at higher ionic strengths (>100 μM), an additional layer of hydrated condensed ions is formed. We find a similar behavior for TiO2 nanoparticles in solutions of different basic pH. Compared to identically sized SiO2 nanoparticles, the TiO2 interface has a higher affinity for Na+ ions, which we further confirm with molecular dynamics simulations. With its ability to monitor ion adsorption at the surface with micromolar sensitivity and changes in the surface potential, AR-SHS is a powerful tool to investigate interfacial properties in a variety of catalytic and photocatalytic applications.

Composited micropores constructed by amorphous TiO2 and graphene for degrading volatile organic compounds

The adsorption ability and photoactivity of photocatalysts directly determine the mineralization efficiency of volatile organic compounds. In this study, a 2D–2D microporous structure of amorphous TiO2 nanoparticles and graphene (GR) was constructed to simultaneously enhance the adsorption ability and charge separation efficiency of catalysts. N2 adsorption–desorption, scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction measurements were conducted to investigate the physical properties of the prepared samples. The atmospheric surface photovoltage (SPV) was utilized to study the separation process of the photogenerated charge carriers. Toluene was chosen as the model agent to estimate the adsorption ability and photoactivity of the samples. Results showed that the amorphous TiO2 nanoparticles homogeneously deposited onto the GR surface and hence formed a 2D–2D microporous structure. Although the surface area of the GR–TiO2 compositions increased by only 4–8% relative to that of microporous TiO2 alone, the amount of adsorbed toluene for the GR–TiO2 compositions was 156–193% times higher than that for the microporous TiO2. The SPV result proved that the GR significantly enhanced the intrinsic separation of the photogenerated charge carriers. The contribution of O2 and the GR to the charge separation was dependent on the weight addition ratio of the GR. The GR dominated the charge separation process as its weight addition ratio ≥5%. Given the advantages in adsorption ability and photoactivity, toluene showed mineralization efficiencies for the composite with 5.0 wt% GR of 1.4 and 2.7 folds those of microporous TiO2 and P25, respectively, after 96 min irradiation.

Photonic Band Gap and Bactericide Performance of Amorphous Sol-Gel Titania: An Alternative to Crystalline TiO₂.

In addition to its traditional application in white pigments, nanocrystalline titania (TiO2) has optoelectronic and photocatalytic properties (strongly dependent on crystallinity, particle size, and surface structure) that grant this naturally occurring oxide new technological applications. Sol-gel is one of the most widely used methods to synthesize TiO2 films and NPs, but the products obtained (mostly oxy-hydrated amorphous phases) require severe heat-treatments to promote crystallization, in which control over size and shape is difficult to achieve. In this work, we obtained new photocatalytic materials based on amorphous titania and measured their electronic band gap. Two case studies are reported that show the enormous potential of amorphous titania as bactericide or photocatalyst. In the first, amorphous sol-gel TiO2 thin films doped with N (TiO2−xNx, x = 0.75) were designed to exhibit a photonic band gap in the visible region. The identification of Ti-O-N and N-Ti-O bindings was achieved by XPS. The photonic band gaps were found to be 3.18 eV for a-TiO2 and 2.99 eV for N-doped a-TiO2. In the second study, amorphous titania and amine-functionalized amorphous titania nanoparticles were synthetized using a novel base-catalysed sol-gel methodology. All the synthesized amorphous TiO2 nanoparticles exhibit bactericide performance (E. coli, ASTME 2149-13).

CO2 Adsorption Property of Amine-Modified Amorphous TiO2 Nanoparticles with a High Surface Area

Carbon dioxide capture and storage (CCS) technologies have attracted a great deal of attention as effective measures to prevent global warming. Adsorption methods using porous materials seem to have several advantages over the liquid absorption methods. In this study, we have developed a synthesis method of new amorphous titanium dioxide (TiO2) nanoparticles with a diameter of 3 nm, a high surface area of 617 m2/g and a large amount of OH groups. Next, the surface of the amorphous TiO2 nanoparticles was modified using ethylenediamine to examine whether CO2 adsorption increases. Amorphous TiO2 nanoparticles were successfully modified with ethylenediamine, which was used in excess due to the presence of a large amount of hydroxyl groups. The amorphous TiO2 nanoparticles modified with ethylenediamine show a higher CO2 adsorption capacity (65 cm3/g at 0 °C, 100 kPa) than conventional TiO2 and mesoporous SiO2. We discuss the origin of the higher CO2 adsorption capacity in terms of the high specific surface area of the amorphous TiO2 nanoparticles and the modification with ethylenediamine on the surface of the amorphous TiO2 nanoparticles. The optimization of the amount of ethylenediamine bound on the particles increased the CO2 adsorption capacity without pore blocking.

Synthesis of titania nanoparticle-dispersed hybrid membranes from allyloxytitanium and phosphonic acid derivatives for fuel cell

Inorganic-organic hybrid membranes consisting of an aliphatic backbone and amorphous TiO2 nanoparticles (NPs) were synthesized from tetraallyloxytitanium and phosphonic acid methacrylate via a simple copolymerization-hydrolysis method. Tetraallyoxytitanium (TAT) was copolymerized with 2-hydroxyethyl methacrylate acid phosphate (HEMAP), and then hydrolyzed, yielding inorganic-organic hybrid composites. IR and 13C NMR spectroscopy confirmed the formation of the inorganic-organic hybrid structure. TEM and SAXS showed that amorphous TiO2 NPs were dispersed in the polymer matrix. The membranes exhibited good thermal stability up to 180 °C. The aliphatic chains of the methacrylate derivative dispersed with TiO2 NPs improved the mechanical properties of the membranes. The tensile modulus of the HEMAP/TAT membrane with a composition of 95:5 was 505 MPa. The conductivity of the 95:5 membranes was 4.1 × 10-2 S cm-1 at 130 °C and 100% relative humidity (RH), while it was 4.7 × 10-4 S cm-1 at 130 °C and 19.3% RH. The peak power of the 95:5 membrane was 4.8 mW/cm2 at 140 °C and 30% RH. The cell utilizing the hybrid membrane was operated at 140 °C and 30% RH for 72 h without any drop in cell voltage.

The performance enhancement of HTM-free ZnO nanowire-based perovskite solar cells via low-temperature TiCl4 treatment

Charge carrier transport layer made of aligned ZnO nanowires (NW) coated with TiO2 layer via low-temperature hydrolysis process for perovskite solar cells (PSC) applications. Aligned ZnO NWs were grown by solution approach onto transparent conducting oxide substrates and treated with 25 mM of titanium tetrachloride (TiCl4). TiO2 layered ZnO NWs were composed of single crystalline, uniformly covered with amorphous TiO2 nanoparticles was characterized by scanning and transmission electron microscopy. Such TiO2 layered ZnO NW architecture, with the unique combination of high surface-area and infiltration of perovskite more into the electrode and a maximum photocurrent density (JSC) of 14.30 mA cm−2 and a power conversion efficiency (η) of 7.05% are demonstrated, which is higher than the ZnO NWs. Dark current density is decreased for TiO2 layered ZnO NW-based PSCs, due to the good interface formation between the electrode/sensitizer and it has higher energy barrier to overcome required high onset potential. TiO2 layered ZnO NWs architecture opens up a novel configuration for high-performance optoelectronic devices.

Cd2+-Doped Amorphous TiO2 Hollow Spheres for Robust and Ultrasensitive Photoelectrochemical Sensing of Hydrogen Sulfide.

Hydrogen sulfide is a highly toxic molecule to human health, but high-performance detection of it remains a challenge. Herein, we report an ultrasensitive photoelectrochemical (PEC) sensor for H2S by modifying indium tin oxide (ITO) electrodes with Cd2+-doped amorphous TiO2 hollow spheres, which are prepared by templating against colloidal silica particles followed by a cadmium-sodium cation exchange reaction. The amorphous TiO2 hollow spheres act as both the probing cation carrier and the photoelectric beacon. Upon exposure to sulfide ions, the photocurrent of the functionalized photoanode proportionately decreases in response to the formation of CdS nanoparticles. The decreased photocurrent could be attributed to the mismatching bandgap between the amorphous TiO2 and CdS nanoparticles: the photoexcited electrons and holes from amorphous TiO2 are transferred to the conduction band and valence band of CdS, respectively, and then recombined. The decrease in photocurrent is linear with the concentration of sulfide ions in the range from 1 to 10 000 pmol L-1 with a detection limit of 0.36 pmol L-1. Enabled by a unique sensitization mechanism, this PEC sensor features excellent performance in a wide linear range, high selectivity and sensitivity, high stability, and low fabrication cost.

Bulk-Direct Synthesis of TiO2 Nanoparticles by Plasma-Assisted Electrolysis with Enhanced Photocatalytic Performance

A new plasma-assisted electrolysis method has been developed to synthesize amorphous TiO2 nanoparticles and exploited for the enhanced photocatalytic performance. The method is simple, environmentally friendly, produces nanoparticles directly from bulk metal, and is suitable for mass production. The process was conducted in low-concentration nitric acid electrolyte under a voltage of 450 V, the minimum necessary to produce plasma on the anode surface. The average nanoparticle size was tuned between 16 and 28 nm by controlling electrolyte concentration within the range of 5 to 15 mM. The production rate increased with time, with the maximum of 11.27 g/h. The amorphous TiO2 nanoparticles were calcined at various temperatures to determine the crystalline structures and to compare their photocatalytic effects. The structure ranged from pure anatase to rutile under various calcination temperatures; the anatase–rutile mixed phase produced at 600°C showed the highest catalytic performance, with 94% degradation of methylene blue within 30 min owing to a synergetic effect between the phases. This liquid-phase plasma-assisted electrolysis method can pave the way for large-scale synthesis of highly pure metal-based ceramic nanoparticles with narrow size distributions.

Efficiency enhancement of organic light-emitting diodes using mesoporous titanium-oxide scattering nanoparticles

In this study, we synthesized mesoporous titanium dioxide (TiO2) nanoparticles and applied them to organic light-emitting diode (OLED) devices to improve the device efficiency by promoting light scattering in the device. Silver nanowire (AgNW) electrode was utilized as transparent anode for the OLEDs, because the AgNW anode integrated with a TiO2 scattering layer can be easily formed using a transfer process. When the mesoporous TiO2 nanoparticles were utilized, the OLED efficiency was improved by about 30% as compared with the case of amorphous TiO2 nanoparticles. This is because the refractive index and surface area of the mesoporous nanoparticles are larger than those of the amorphous ones, thereby further promoting the scattering of the light generated in the OLED device.

Computational study on the structural and surface properties of amorphous hydroxylated TiO2 spherical nanoparticles

Monte Carlo simulations were carried out on amorphous titanium dioxide (TiO2) for both bulk and hydroxylated nanoparticles with particle sizes ranging from 1 to 10 nm. The potential developed by the Matsui and Akaogi (MA) was used to model the interatomic interactions of TiO2 in both cases (bulk and nanoparticles). Besides, Angular and Morse potentials proposed by the Tether, Cormack, Du et. al. (TCD) were introduced to model the interactions of hydroxyl groups on the TiO2 surfaces, i.e., the Ti-O-H groups with an experimental and theoretical angles of 125 o . The bulk system was developed using periodic boundary conditions. The TiO2 nanoparticles were extracted by applying a spherical cut section in the bulk TiO2 melt structure to obtain the required size. Free valences on the nanoparticle surfaces were saturated via additional hydroxyl groups and then quenched to 300 K under free boundary conditions. The bulk and surface properties of the nanoparticles were calculated at 300 K and zero pressure and characterized via radial distribution functions, bond angle distributions, bond distances, coordination numbers, OH group concentrations and radial density profiles. In addition, to understand the difference in properties of amorphous hydroxylated TiO2 nanoparticles and bulk amorphous TiO2, a comparative study was done at the same thermodynamic conditions. The study shows that the bulk properties of amorphous hydroxylated TiO2 nanoparticles are strongly size-dependent and different from those of the bulk TiO2. As expected, increasing the particle size leads to an approach of the particle’s bulk properties to the bulk properties of the (quasi) infinite system. The size effects show that decreasing the particle size results in increasing the surface effects and surface OH group concentrations. Accordingly, small-sized TiO2 nanoparticles have higher surface OH group concentrations and larger surface effects than large-sized TiO2 nanoparticles. Larger surface effects result significant changes in their bond angles, bond distances, and coordination numbers. The simulation results of the surface properties reveal that the surface titanium atoms in the TiO2 nanoparticles have the capability of accommodating up to 5 hydroxyl groups. The mean surface hydroxyl group density of the amorphous TiO2 spherical nanoparticles is estimated to be around 8.1/nm 2, which lies in the range of 8–16/nm 2, found by experimental and other simulation studies. Details of the modelling, simulations results and the study are presented in this paper.

Nonequilibrium Synthesis of TiO2 Nanoparticle "Building Blocks" for Crystal Growth by Sequential Attachment in Pulsed Laser Deposition.

Nonequilibrium growth pathways for crystalline nanostructures with metastable phases are demonstrated through the gas-phase formation, attachment, and crystallization of ultrasmall amorphous nanoparticles as building blocks in pulsed laser deposition (PLD). Temporally and spatially resolved gated-intensified charge couple device (ICCD) imaging and ion probe measurements are employed as in situ diagnostics to understand and control the plume expansion conditions for the synthesis of nearly pure fluxes of ultrasmall (∼3 nm) amorphous TiO2 nanoparticles in background gases and their selective delivery to substrates. These amorphous nanoparticles assemble into loose, mesoporous assemblies on substrates at room temperature but dynamically crystallize by sequential particle attachment at higher substrate temperatures to grow nanostructures with different phases and morphologies. Molecular dynamics calculations are used to simulate and understand the crystallization dynamics. This work demonstrates that nonequilibrium crystallization by particle attachment of metastable ultrasmall nanoscale "building blocks" provides a versatile approach for exploring and controlling the growth of nanoarchitectures with desirable crystalline phases and morphologies.