Porous TiO2 Research Articles

From bio-inertness to osseointegration and antibacterial activity: A one-step micro-arc oxidation approach for multifunctional Ti implants fabricated by additive manufacturing

Infectious bone defects (IBD) remain a major problem in orthopedics in clinical settings. For IBD repair, implants possessing multiple functions such as osseointegration and antibacterial activity are in demand. This study aims to develop a surface-modified titanium (Ti) implant (MTi/Ag/CaP) with osseointegration and antibacterial functions for IBD repair. The pure Ti implant is printed using a selective laser melting technique, and a two-layer hierarchical structure is formed on its surface using a one-step micro-arc oxidation (MAO) approach. The outer layer is an apatite-like material decorated with Ag nanoparticles, whereas the inner layer is porous TiO2. In vitro experiments show that the MTi/Ag/CaP implant can effectively eliminate and inhibit the adhesion and proliferation of bacteria over a long period time while promoting MG-63 cell adhesion, proliferation, and osteogenic differentiation. In vivo experiments further reveal that the MTi/Ag/CaP implant produces more mineralized bone tissue than non-treated samples and interlocks closely with the bone tissue after 8 weeks. The one-step MAO modification developed in this study is simple, efficient, and environment-friendly, which demonstrates great potential as a promising approach for providing advanced biomedical materials in orthopedic applications, including for the prevention and treatment of IBDs.

Porous vs. Nanotubular Anodic TiO2: Does the Morphology Really Matters for the Photodegradation of Caffeine?

Herein, the preparation of nanotubular and porous TiO2 structures (TNS) is presented for photocatalytic applications. Different TNS were prepared in three different types of glycerol- and ethylene glycol-based electrolytes on a large area (approx. 20 cm2) via anodization using different conditions (applied potential, fluoride concentration). Morphology, structure, and optical properties of TNS were characterized by Scanning Electron Microscopy (SEM), X-ray Diffractometry (XRD), and Diffuse Reflectance Spectroscopy (DRS), respectively. All TNS possess optical band-gap energy (EBG) in the range from 3.1 eV to 3.2 eV. Photocatalytic degradation of caffeine was conducted to evaluate the efficiency of TNS. Overall, nanotubular TiO2 possessed enhanced degradation efficiencies (up to 50% degradation) compared to those of porous TiO2 (up to 30% degradation). This is due to the unique properties of nanotubular TiO2, e.g., improved incident light utilization. As the anodization of large areas is, nowadays, becoming a trend, we show that both nanotubular and porous TiO2 are promising for their use in photocatalysis and could be potentially applicable in photoreactors for wastewater treatment. We believe this present work can be the foundation for future development of efficient TiO2 nanostructures for industrial applications.

A New TiO with in-Situ Transformed Rutile TiO2 Nanothorns As a Superb Anode Material for Lithium-Ion Battery

Developing high-performance anodes is highly desired to meet the recent ever-increasing demands for lithium-ion battery (LIB). Herein we report a uniquely integrated hybrid structure of rutile TiO2 (r-TiO2) nanothorns in situ grown over a new porous and conductive TiO core, which is generated from pyrolysis of anatase TiO2 with Mg metal at 650℃. The new hybrid exhibits superb LIB performance as an anode with high reversible capacity and almost no capacity decay during 1000 cycles at a high current density of 20 C (4000 mA g-1). Two independent reactions of intercalation and pseudocapacitive interaction are confirmed to occur in the composite of the r-TiO2 and TiO, respectively. In particular, the excellent rate capability along with long cycle life enables the new hybrid to have ultrafast charging of the system. Furthermore, the hybrid with the job-sharing property exhibits stable charge-discharge performance over a wider potential window range of 0.01 to 3.0 V, particularly even in the low potential range of 0.01~1.0 V, which usually causes irreversible Li-intercalation and rapid capacity decay for pristine TiO2. All the properties including the wider potential window allows the hybrid to realize the highest electrochemical performance that titanium oxides have ever achieved so far.

Improved photocatalytic performance of gradient reduced TiO2 ceramics with aligned pore channels

Magnéli, a fascinating sub-stoichiometric titanium oxide phase that contains oxygen vacancies of TiO 2 , is proposed as a potential photo-electrode for photocatalysis due to its high conductivity and photoelectric conversion efficiency. In this work, partially reduced porous TiO 2 ceramics with a graded reduction profile and an aligned pore structure were prepared by carbo-thermal reduction of freeze-cast TiO 2 with a range of porosities from 10 to 30 ​vol.%. AC conductivity evaluation revealed that the oxygen vacancies that exist in Magnéli lead to a relatively high AC conductivity of ∼10 ​S/m at 1 ​kHz, as compared to that of the stoichiometric porous TiO 2 . A maximum photocurrent density and incident photon-to-current efficiency (IPCE) of 9.14 ​mA/cm 2 and 40.52% respectively were achieved from the gradient porous Magnéli with a porosity of 30 ​vol.%.

Hybrid porous titania phosphonate networks with different bridging functionalities: Synthesis, characterization, and evaluation as efficient solvent separation materials

Hybrid titania phosphonate materials can demonstrate a high added value as tailored sorption materials. They combine high chemical stability with great structural versatility, given the wide diversity of functional groups that can be incorporated. Hereto, a fundamental understanding of the synthesis strategies influencing the material performance is required. Therefore three porous TiO2 phosphonate hybrid structures with different functional groups (octyl, propyl, and phenyl) were evaluated in a solid-phase extraction application aimed towards solvent separation. The synthesis was performed by mixing bridged diphosphonic acids (DPAs) with Ti(OBu)4 in a water-ethanol mixture at 30 °C, followed by a hydrothermal post-treatment at 120 °C. The materials were characterized by ICP-AES, 31P solid-state CP/MAS NMR, Raman and FTIR spectroscopy, X-ray diffraction, N2-sorption, and transmission electron microscopy. It is shown that the diphosphonic acids are quantitatively incorporated in the hybrid structures, leading to nanosized particles with a complex but uniquely functionalized surface. A study of the pore structure as a function of the incorporated DPA amount showed materials with a maximum BET surface area of 379 m2/g. The alkyl functionalized hybrid titania phosphonates demonstrated excellent and tunable sorption behavior.

CO Oxidation over Pd Catalyst Supported on Porous TiO2 Prepared by Plasma Electrolytic Oxidation (PEO) of a Ti Metallic Carrier.

A porous TiO2 layer was prepared with the plasma electrolytic oxidation (PEO) of Ti. In a further step, Pd was deposited on the TiO2 surface layer using the adsorption method. The activity of the Pd/TiO2/Ti catalyst was investigated during the oxidation of CO to CO2 in a mixture of air with 5% CO. The structure of the catalytic active layer was studied using a scanning electron microscope equipped with an energy dispersive spectrometer (SEM-EDS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), inductively coupled plasma mass spectrometry (ICP-MS), and X-ray diffraction (XRD). The PEO process provided a porous TiO2 layer with a uniform thickness in the range of 5–10 µm, which is desirable for the production of Pd-supported catalysts. A TOF-SIMS analysis showed the formation of Pd nanoparticles after the adsorption treatment. The conversion of CO to CO2 in all samples was achieved at 150–280 °C, depending on the concentration of Pd. The composition of Pd/ TiO2/Ti was determined using ICP-MS. The optimum concentration of Pd on the surface of the catalyst was approximately 0.14% wt. This concentration was obtained when a 0.4% PdCl2 solution was used in the adsorption process. Increasing the concentration of PdCl2 did not lead to a further improvement in the activity of Pd/ TiO2/Ti.

Ni-Doped SnO2 as an Electron Transport Layer by a Low-Temperature Process in Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) based on a planar structure have recently become more attractive due to their simple manufacturing process and relatively low cost, while most perovskite solar cells employ highly porous TiO2 as an electron transport layer in mesoporous devices offering higher energy conversion efficiency (PCE). In planar structural devices, non-radiative recombination effects of the absorber layer and the electron transport layer cause potential loss and lower PCE. We created an efficient electron transport layer by combining low-temperature Ni-doped SnO2 with SDBS as a surfactant (denoted as Ni:SnO2). Doping Ni+ into low-temperature solution-processed SnO2 increased the power conversion efficiency of PSCs from 17.8 to 19.7%.

Microstructure of titania aerogels by reverse Monte Carlo simulations

The local atomic structure of TiO2 aerogels calcinated at 450 °C and 550 °C has been studied in comparison with that of well-crystallized TiO2 anatase by the X-ray diffraction (XRD) method and Reverse Monte Carlo (RMC) simulations. The influence of calcination temperature on the crystallographic properties and microstructure of TiO2 aerogels was discussed. The large X-ray line broadening of TiO2 aerogels was due to the small crystallite size and lattice strain. From the traditional Williamson-Hall (W–H) analysis results, it was observed that the strain value decreased but the particle size increased as calcination temperature was increased. The TiO2 anatase sample revealed an average particle size of about 62 nm and a very low strain in the nano-crystallite. The experimental X-ray structure factor was derived from the wide-angle X-ray scattering (WAXS) pattern after suitable data reduction. The partial atomic pair correlation functions gij(r), like the gTiO(r), gOO(r) and gTiTi(r) have been revealed from RMC simulation with a fairly good stability and acceptable statistics. The structure model that best describes both the WAXS data consists of nano-crystalline TiO2 with a highly distorted shell and a strained anatase-like crystalline core. The pre-existence of the anatase like core may be critical to the formation of single-phase nano-crystalline TiO2 anatase in crystallization of highly porous TiO2 aerogels upon heating.

Oxidation and hot corrosion behaviors of MAX-phase Ti3SiC2, Ti2AlC, Cr2AlC

Oxidation and hot corrosion behaviours of Ti3SiC2, Ti2AlC and Cr2AlC at 750 °C were investigated in this work. Ti3SiC2 and Ti2AlC showed a linear increase in mass gain and a relatively poor oxidation resistance. This might be attributed to the porous TiO2 scale. A dense α-Al2O3 layer was formed during the oxidation test. Cr2AlC exhibited the best oxidation resistance. This dense oxide scale can effectively isolate the substrate from contact with oxygen leading to excellent oxidation resistance. In contrast to the oxidation test, Ti3SiC2 and Ti2AlC showed relatively better resistance to hot corrosion, while Cr2AlC showed inferior resistance to NaCl introduced hot corrosion. The hot corrosion mechanism of the MAX phases was analyzed. Due to the formation of Na2TiO3, Ti containing MAX phases showed a continuous increase in the mass gain. The corrosion products of Cr2AlC were Al2O3, Cr2O3 and Na2CrO4. However, due to the volatilization of Na2CrO4, Cr2AlC showed a mass loss during the hot corrosion test. The chemical reaction process of the MAX phase was also analyzed.

New Mechanism for Long Photo-Induced Enhanced Raman Spectroscopy in Au Nanoparticles Embedded in TiO2.

The photo-induced enhanced Raman spectroscopy (PIERS) effect is a phenomenon taking place when plasmonic nanoparticles deposited on a semiconductor are illuminated by UV light prior to Raman measurement. Results from the literature show that the PIERS effect lasts for about an hour. The proposed mechanism for this effect is the creation of oxygen vacancies in the semiconductor that would create a path for charge transfer between the analyte and the nanoparticles. However, this hypothesis has never been confirmed experimentally. Furthermore, the tested structure of the PIERS substrate has always been composed of plasmonic nanoparticles deposited on top of the semiconductor. Here, gold nanoparticles co-deposited with porous TiO2 are used as a PIERS substrate. The deposition process confers the nanoparticles a unique position half buried in the nanoporous semiconductor. The resulting PIERS intensity is among the highest measured until now but most importantly the duration of the effect is significantly longer (at least 8 days). Cathodoluminescence measurements on these samples show that two distinct mechanisms are at stake for co-deposited and drop-casted gold nanoparticles. The oxygen vacancies hypothesis tends to be confirmed for the latter, but the narrowing of the depletion zone explains the long PIERS effect.

Surface Structuring and Reverse Deposition of Nanoporous Titanium Oxides by Laser Ablation of Titanium in Air

The deposition of titanium oxides during titanium laser ablation in air has been experimentally and numerically investigated. A titanium sample was irradiated by nanosecond pulses from an Yb-fiber laser with a beam scanned across the sample surface for its texturing. As a result, the hierarchical structure was observed consisting of a microrelief formed by the laser ablation and a nanoporous coating formed by the reverse deposition from the laser induced plasma plume. The chemical and phase composition of the nanoporous coating, as well as the morphology and structure of the surface, were studied using scanning electron microscopy, atomic force microscopy, and X-ray microanalysis. It was found that the deposit consists mostly of porous TiO2 with 26% porosity and inclusions of TiO, Ti2O3, and Ti2O3N. Optical emission spectroscopy was used to control the plasma composition and estimate the effective temperature of plasma plume. The chemical-hydrodynamic model of laser induced plasma was developed to get a deeper insight into the deposition process. The model predicts that condensed titanium oxides, formed in peripheral plasma zones, gradually accumulate on the surface during the plasma plume evolution. A satisfactory agreement between the experimental and calculated chemical composition of the plasma plume as well as between the experimental and calculated composition and thickness of the deposited film was demonstrated. This allows a cautious conclusion that the formation of condensed oxides in the plasma and their consequent deposition onto the ablation surface are among the key mechanisms of formation of porous surface films.

Metal-organic framework on porous TiO2 thin film-coated alumina beads for fractional distillation of plant essential oils.

Fractionation of essential oils is technically challenging due to enormous scaffold diversities and structural complexities as well as difficulties in the implementation of the fractionation in the gas phase. Packing beads with multi-dimensional hierarchical nanostructures have been developed herein to pack fractional columns for atmospheric distillations. Activated alumina beads were coated with a porous TiO2 thin film. Growth of Cu-BTC (benzene-1,3,5-tricarboxylate) crystals in resultant porous surfaces leads to the generation of new nanopores and increased metal centers for differential coordination with diverse components of essential oils. The TiO2 thin film is not only an integral part of the composites but also induces the oriented growth of Cu-BTC metal organic framework (MOF) crystals through coordinative interactions. These Al2O3@TiO2@Cu-BTC MOF beads show very strong absorptive capability for major components of essential oils, except for a single cyclic ether eucalyptol with steric hindrances. The eucalyptol was fractionated by using the column packed with those modified alumina beads from raw materials of Artemisia argyi, and Rosmarinus officinalis with high purities up to 96% and 93%, respectively.

Fabrication of Functional Super-Hydrophilic TiO2 Thin Film for pH Detection

A super-hydrophilic pH-sensitive electrode with a porous TiO2 thin film is proposed in this work and fabricated using the chemical etching method. In total, 30 groups of porous TiO2 thin film were obtained by immersing a Ti sheet in NaOH, with the solution concentration ranging from 0.5–4 M and the reaction time ranging from 15–240 min. SEM, XRD, XPS, and a contact angle meter were used to investigate the influence of the chemical etching parameters on the morphology, composition, and wettability of the fabricated electrodes. The chemical etching parameters were found to have a significant influence on the specific surface area and the component of the films, which strongly affected the wettability and pH sensing characteristics of the electrodes. The electrode obtained with a solution concentration of 1 M and reaction time of 120 min is the ideal product because of its excellent wettability, with a contact angle of 5.46°, and good pH sensing characteristics in pH buffer solutions. The electrode also showed good stability regarding its wettability and pH sensing properties during storage and utilization.

Reversing the Catalytic Selectivity of Single-Atom Ru via Support Amorphization.

Supported single-atom catalysts (SACs), with the extremely homogenized active sites could achieve high hydrogenation selectivity toward one of the functional groups coexisting in the reactant molecule. However, as to the target group, the control of selective recognition and activation by SACs still remains a challenge. Herein, the phase engineering of the support is adopted to control the chemo-recognition behavior of SACs in selective hydrogenation. Single-atom Ru on amorphous porous ultrathin TiO2 nanosheets (Ru1/a-TiO2) is constructed, in which Ru is more positively charged than that in the crystalline counterpart (Ru1/c-TiO2). Moreover, in the nitro/vinyl selective hydrogenation process, Ru1/a-TiO2 shows superior nitro selectivity, opposite to the vinyl selectivity of Ru1/c-TiO2. Density functional theory calculations for single-atom Ru of different charge states show that the reactant adsorption configuration could be inverted in the amorphous TiO2, accounting for the chemo-recognition behavior controlled by the phase of support.

Impacts of paste preparation methods on the porous TiO2 nanostructure properties and naturally dye-sensitized solar cells performance

In the last two decades, researchers have attempted to use environmentally friendly pigments and porous nanostructures as sensitizers and semiconductors in dye-sensitized solar cells (DSSCs), respectively. In this study, the pigments were extracted from black plums (Syzygium cumini) to increase the biocompatibility of the DSSCs. The UV–vis spectroscopy of the extracted solution revealed the existence of anthocyanin pigments. The cyclic voltammetry measurement showed that the pigment energy levels were suitable for electron transfer to the TiO2 semiconductor, and the pigment electrochemical properties were also comparable with the commercial synthetic pigments. The dynamic light scattering experiment and zeta potential measurement illustrated that the size and electrostatic potential of the pigments were 0.3 nm and ±5 mV, respectively. These data confirmed the potential of the pigments for the diffusion into the porous structure of the TiO2 semiconductor and attraction as a shell layer on its surfaces. Besides, the TiO2 pastes were produced with seven different methods and characterized using XRD, SEM, and BET experiments. The results showed that the morphology, particle size, porosity, and surface area of the produced nanostructures were different in each method. Finally, the pastes were coated on the glass, sensitized with the extracted natural pigments, and used in the fabricated DSSCs. The efficiency of the cells was evaluated in the range of 0.027%–0.256% using the sun simulator technique. The results showed that the optimum particle size of the TiO2 semiconductor was around 25.6 nm which had been formed in the sixth method of the paste preparation.

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.

Synthesis of carbon-encapsulated metal-based nanoparticles by gas/liquid interfacial plasma under high pressure

Carbon-encapsulated TiO2, Ag and Fe3O4 NPs are synthesized by pulse arc discharge plasma over glycine aqueous solution under high pressures, which is a novel plasma technique to fabricate metal-based NPs/C nanocomposites in one step. The carbon coatings are formed by utilizing glycine as a carbon precursor and confirmed to be amorphous carbon. While TiO2, Ag and Fe3O4 NPs are generated instantaneously via the erosion of the metal electrodes and reaction with the active oxidation radicals and molecular produced during the plasma generation over gas/liquid interface. It was found that the NPs are produced in the uniform size only under high operating pressure and the average size of the TiO2, Ag and Fe3O4 NPs were around 10.2 nm, 6.6 nm and 9.6 nm, respectively. The pulse arc discharge plasma was performed in different pressures, glycine concentrations and pulse times to investigate the effect of the influential factors on the formation of the carbon-encapsulated NPs in this plasma system. The carbon-encapsulated NPs are later annealed at 800 °C under Ar gas to construct the porous structure. In the MB degradation test, the porous carbon-encapsulated TiO2 NPs exhibit good adsorption capacity and improved photocatalytic activity.

Fabrication of fractal structured soot templated titania-silver nano-surfaces for photocatalysis and SERS sensing

A novel approach of candle soot templated TiO2/Ag nanostructures to fabricate highly active photocatalyst and self-cleaning Surface-Enhanced Raman Scattering (SERS) substrates is demonstrated. A three-stage synthetic approach involves the replication of the fractal structure of candle soot in forming a high surface area porous TiO2 nanostructure using chemical vapour deposition and subsequent electroless deposition of silver nanoparticles on the high surface area fractal network that resulted in the formation of TiO2/Ag nanostructures. The unique morphology of TiO2/Ag renders these materials to exhibit photocatalytic and SERS activity. These surfaces showed an enhanced photocatalytic effect due to the Schottky junction which increases the recombination time of the charge carriers. The size and the coverage of the silver nanoparticles were optimized to obtain high conversion towards photocatalytic degradation of a model dye molecule such as Rhodamine B (RhB). The same substrate was also shown to enhance the Raman scattering spectra of RhB. The SERS activity of the substrate can be regenerated by photocatalytic cleaning the substrates. Overall, this present work demonstrated that fractal structured TiO2/Ag materials can be synthesized using fractal soot structures and this multi-functional material offers good potential in those applications, where photo-catalysis, SERS sensing, and self-cleaning sensing multifunctionality are required.

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.

Complementary Powerful Techniques for Investigating the Interactions of Proteins with Porous TiO2 and Its Hybrid Materials: A Tutorial Review.

Understanding the adsorption and interaction between porous materials and protein is of great importance in biomedical and interface sciences. Among the studied porous materials, TiO2 and its hybrid materials, featuring distinct, well-defined pore sizes, structural stability and excellent biocompatibility, are widely used. In this review, the use of four powerful, synergetic and complementary techniques to study protein-TiO2-based porous materials interactions at different scales is summarized, including high-performance liquid chromatography (HPLC), atomic force microscopy (AFM), surface-enhanced Raman scattering (SERS), and Molecular Dynamics (MD) simulations. We expect that this review could be helpful in optimizing the commonly used techniques to characterize the interfacial behavior of protein on porous TiO2 materials in different applications.