Crystalline Mesoporous TiO2 Research Articles

Fe-Ni porphyrin/mesoporous titania thin film electrodes: a bioinspired nanoarchitecture for photoelectrocatalysis.

Porphyrin and porphyrinoid derivatives have been extensively studied in the assembly of catalysts and sensors, seeking biomimetic and bioinspired activity. In particular, Fe and Ni porphyrins can be used for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by immobilization of these molecular catalysts on semiconductor materials. In this study, we designed a hybrid material containing a crystalline mesoporous TiO2 thin film in which the catalytic centres are Ni-porphyrin (NiP), Fe-porphyrin (FeP), and a NiP/FeP bimetallic system to assess whether the coexistence of both metalloporphyrins improves the OER activity. The obtained photoelectrodes were physicochemically and morphologically characterized through high-resolution FE-SEM images, UV-vis and Raman spectroscopies, cyclic voltammetry, and impedance measurements. The results show a differential behavior of the mono- and bimetallic porphyrin systems, where the Fe(iii) centre in FeP may increase the acidity and lower the reduction potential of the Ni2+/3+ couple when co-deposited with NiP leading to an improved photoelectrochemical water-oxidation performance. We have validated the cooperative effect of both metal complexes within this novel system, where the μ-peroxo-bridged interaction between Fe and Ni is integrated into a supramolecular heterometallic structure of porphyrins.

Synthesis of recyclable SERS platform based on magnetic Fe3O4/mTiO2/Ag composites for photodegradation and identification of organic pollutants in different water samples

In this study, we coatedmagnetic Fe3O4 nanospheres with a crystalline mesoporous TiO2 (mTiO2) layer with photocatalytic activity, followed by the deposition of Ag nanoparticles as an outer layer through in-situ reduction of AgNO3 to obtain multifunctional Fe3O4/mTiO2/Ag core-shell-shell structured composites. By adjusting the amount of AgNO3, we were able to precisely control the size and coverage of the Ag nanoparticles. To evaluate the surface-enhanced Raman spectroscopy (SERS) activity of the Fe3O4/mTiO2/Ag composites, we employed 4-mercaptobenzoic acid (4-MBA) as a model Raman reporter. The limit of detection (LOD) of 4-MBA was down to 10−10 M. Moreover, for practical applications, we successfully detected methylene blue (MB) in different water samples, such as tap water and industrial wastewater, and both of systems presented an ultralow LOD of 10−9 M. Notably, a strong linear relationship (R2 ≥ 0.95) between the SERS intensities and the logarithmic concentration of MB was observed, highlighting the excellent quantitative sensing capabilities of these substrates. The Fe3O4/mTiO2/Ag composites also exhibited remarkable signal reproducibility and exceptional stability during storage. Additionally, these composites demonstrated promising photocatalytic property. In five consecutive cycles, we were able to efficiently detect MB by utilizing the composites' photocatalytic removal ability under UV irradiation, which was facilitated by simple magnetic separation. These findings hold significant importance for environmental safety and pollutant removal applications.

Mesoporous CuO/TiO2 catalysts prepared by the ammonia driven deposition precipitation method for CO preferential oxidation: Effect of metal loading

Supported CuO catalysts onto a highly crystalline mesoporous TiO2 material are produced via an ammonium driven deposition precipitation method and tested for preferential oxidation of CO in H2-rich gases. The effect of Cu loading on the oxidation activity is investigated by producing samples with final Cu content varying between 2.5 and 10 wt%. According to the analysis results, the chemical nature of the CuO species differs in each sample depending on the Cu loading. All materials tested are highly selective towards CO oxidation up to 160 °C. The 5 wt% Cu loaded material demonstrates the optimum CO-PROX performance, which is ascribed to the formation of finely dispersed and easily reducible copper oxide nanoparticles. Stability and durability of the latter sample are assessed by performing multiple testing cycles corresponding to >100hrs on stream as well as by the separate and combined addition of CO2 and H2O in the feeding stream.

A Polymer-Oriented Self-Assembly Strategy toward Mesoporous Metal Oxides with Ultrahigh Surface Areas.

Mesoporous metal oxides (MMOs) have attracted comprehensive attention in many fields, including energy storage, catalysis, and separation. Current synthesis of MMOs mainly involve use of surfactants as templates to generate mesopores and organic reagents as solvents to hinder hydrolysis and condensation of inorganic precursors, which is adverse to adjusting the interactions between surfactants and inorganic precursors. The resulting products have uncontrollable pore structure, crystallinity, and relatively lower surface areas. Here, a facile and general polymer‐oriented self‐assembly strategy to synthesize a series of MMOs (e.g., TiO2, ZrO2, NbO5, Al2O3, Ta2O5, HfO2, and SnO2) by using cationic polymers as porogens and metal alkoxides as metal oxide precursors in a robust aqueous synthesis system are reported. Nitrogen adsorption analysis and transmission electron microscopy confirm that the obtained MMOs have ultrahigh specific surface areas and large pore volumes (i.e., 733 m2 g−1 and 0.485 cm3 g−1 for mesoporous TiO2). Moreover, the structural parameters (surface area, pore size, and pore volume) and crystallinity can be readily controlled by tuning the interactions between cationic polymers and precursors. The as‐synthesized crystalline mesoporous TiO2 exhibits promising performance in photocatalytic water splitting of hydrogen production and a high hydrogen production rate of 3.68 mol h−1 g−1.

Plasmochemical Approach to Template‐Free Synthesis of Highly Crystalline Mesoporous TiO2 within Milliseconds

AbstractA plasmochemical synthetic strategy for the template‐free and one‐step preparation of highly crystalline mesoporous TiO2 from oxidation of titanium tetraisopropoxide (TTIP) aerosol by gliding arc plasma in a vortex air flow within milliseconds is reported. The scanning electron microscopy, high‐resolution transmission electron microscopy, and nitrogen sorption characterizations confirm the wormhole‐like mesoporous structures. The highly crystalline mesoporous TiO2 has an optimized anatase/rutile weight ratio of about 80/20 for photocatalytic applications, exhibiting superior thermal stability and good photocatalytic activity.

Mesoporous TiO2 synthesis using a semi-hard biological template

The bacteriophage M13, a rod-shaped virus, was used as a semi-rigid template to synthesize crystalline mesoporous TiO2. This strategy allowed us to modulate sol-gel reactions on the virus surface without the need of chemical or genetic manipulation. Important parameters as pH influence and concentration were investigated. The studies by which the pH was varied were the principal route to obtain materials with pores of around 6.1 and 8.2 nm. When an M13 phage concentration of 0.1 mg/mL was employed, anatase mesopores presented specific surface areas from 80 to 130 m2/g and pore volumes from 0.18 to 0.21 cm3/g. It should be mentioned that surface area is due exclusively to mesopores, and from N2 adsorption/desorption experiments, no evidence of micropores was detected. This absence of micropores results from the stable protein arrangement on M13 phage, which contrasts with the disruption of micellar assemblies of soft templates. These results show that anatase mesophases are obtained in an easy and rapid route at room temperature and could be expanded to synthesize other metal oxide mesostructures tuning M13 phage properties.

Soft-Template Synthesis of Mesoporous Anatase TiO₂ Nanospheres and Its Enhanced Photoactivity.

Highly crystalline mesoporous anatase TiO2 nanospheres with high surface area (higher than P25 and anatase TiO2) are prepared by a soft-template method. Despite the high specific surface area, these samples have three times lower equilibrium adsorption (<2%) than Degussa P25. The rate constant of the mesoporous anatase TiO2 (0.024 min−1) reported here is 364% higher than that of P25 (0.0066 min−1), for the same catalytic loading. The results of oxidation-extraction photometry using several reactive oxygen species (ROS) scavengers indicated that mesoporous anatase TiO2 generates more ROS than P25 under UV-light irradiation. This significant improvement in the photocatalytic performance of mesoporous spherical TiO2 arises from the following synergistic effects in the reported sample: (i) high surface area; (ii) improved crystallinity; (iii) narrow pore wall thicknesses (ensuring the rapid migration of photogenerated carriers to the surface of the material); and (iv) greater ROS generation under UV-light.

Solvent-Free Self-Assembly to the Synthesis of Nitrogen-Doped Ordered Mesoporous Polymers for Highly Selective Capture and Conversion of CO2.

A solvent-free induced self-assembly technology for the synthesis of nitrogen-doped ordered mesoporous polymers (N-OMPs) is developed, which is realized by mixing polymer precursors with block copolymer templates, curing at 140-180 °C, and calcination to remove the templates. This synthetic strategy represents a significant advancement in the preparation of functional porous polymers through a fast and scalable yet environmentally friendly route, since no solvents or catalysts are used. The synthesized N-OMPs and their derived catalysts are found to exhibit competitive CO2 capacities (0.67-0.91 mmol g-1 at 25 °C and 0.15 bar), extraordinary CO2 /N2 selectivities (98-205 at 25 °C), and excellent activities for catalyzing conversion of CO2 into cyclic carbonate (conversion >95% at 100 °C and 1.2 MPa for 1.5 h). The solvent-free technology developed in this work can also be extended to the synthesis of N-OMP/SiO2 nanocomposites, mesoporous SiO2 , crystalline mesoporous TiO2 , and TiPO, demonstrating its wide applicability in porous material synthesis.

Preparation of highly crystalline mesoporous TiO2 by sol–gel method combined with two-step calcining process

ABSTRACTMesoporous TiO2 samples, with large specific surface area and high crystallinity, were prepared by a sol–gel method using polyethylene glycol and polyacrylamide (PAM) as composite templates and by two-step calcining process (at 500—700 °C in nitrogen and 500 °C in air). As a comparison, the sample was prepared using same composite templates by one-step calcining process (at 500 °C in air). The samples were characterised by X-ray diffraction, transmission electron microscopy, N2 adsorption–desorption, and diffuse reflectance UV-visible absorption spectra. The results showed that when the samples were fabricated using two-step calcining process, they exhibited typical mesoporous structure, large specific surface area, and high crystallinity. The properties of samples were studied. The results showed that PAM accelerates gel rate. The crystallinity and specific surface areas of samples were increased by using two-step calcining process. Compared with the sample prepared using one-step calcining process, the visible light absorption of samples synthesised by the two-step calcining process was improved.

Effects of pore size on the photocatalytic activity of mesoporous TiO2 prepared by a sol–gel process

Highly crystalline mesoporous TiO2 was prepared by a facile sol–gel process in the presence of poly(oxyethylene-23) lauryl ether (Brij-35) surfactant. The pore size distribution of the samples became wider as the amount of Brij-35 increased. When the sample was prepared with moderate concentration of Brij-35, the sample had a bimodal pore size distribution with the small pores at 7 nm and the large pores at 20 nm. The photocatalytic activity was evaluated by the degradation of methylene blue under UV irradiation. The sample with large pore size and wide pore size distribution showed higher photocatalytic activity. The crystalline mesoporous TiO2 with large pore size and wide pore size distribution showed higher photocatalytic activity.

Carbon-Coated Mesoporous TiO2 Nanocrystals Grown on Graphene for Lithium-Ion Batteries.

Graphene-based hybrids have been well studied as advanced catalysts and high-performance electrode materials. In this Article, we have fabricated a novel graphene@mesoporous TiO2 nanocrystals@carbon nanosheet by a simple one-step solvothermal method. We have found that titanocene dichloride can act as an extraordinary source with multiple roles for forming TiO2 nanocrystals, ultrathin carbon outer shells, and cross-linkers to binding TiO2 nanocrystals on graphene surface. Moreover, it also serves as a controlling agent to produce mesoporous structure on TiO2 nanocrystals. The loading-concentration of mesoporous TiO2 nanocrystals on graphene sheets can be well controlled by adjusting the initial content of titanocene dichloride. The as-obtained graphene@mTiO2@carbon nanosheets possess a uniform sandwich-like structure, highly crystalline mesoporous TiO2 nanocrystals, a high surface area of ∼209 m(2)/g, and a large pore volume of ∼0.68 cm(3) g(-1). When used as anodes for LIBs, the resultant nanosheets show a high reversible capacity (∼145 mAh/g), good rate capability, and long cycling life (capacity remains 110 mAh/g after 100 cycles at a current density of 0.2 A/g). We believe that our method represents a new path way to synthesize novel nanostructured graphene-based hybrids for future applications.

Noble metal free naphthylbisimide/TiO2/graphene: an efficient H2evolution photocatalyst

Current photocatalytic systems must meet numerous very demanding features such as being non-noble, high-performance, cost-effective and environmentally friendly. Herein, an active and cheap photocatalyst was constructed by combining graphene with a naphthylbisimide-core based organic photosensitizer on TiO2. This synergistic photocatalyst displayed enhanced photocatalytic hydrogen generation by splitting water in the presence of methanol as the electron donor. A one-step soft template directed solvothermal synthesis process has been developed to prepare the crystalline mesoporous TiO2 materials. Electrochemical characterization of the sensitizer showed that naphthyl core has the ability to act as an electron acceptor, which has been further supported by the density functional theory (DFT) calculation. The as-prepared photocatalysts were thoroughly characterized by FESEM, TEM, AFM, XPS, UV-vis DRS, Raman and FTIR spectroscopic techniques. Graphene sheets, with desirable electronic properties, acted as good support for TiO2 to enhance the photocatalytic activity. Surface adsorption of the sensitizer on TiO2 extended the light absorption over the visible region (400–510 nm). High surface area (76.66 m2 g−1) and morphological changes in the as-synthesized TiO2 and graphene reinforcement play a vital role in the enhancement of photocatalytic activity. Hydrogen generation reached up to TON 4790 with the rate of 10 mmol g−1 h−1 after 6 h irradiation with a light intensity of ∼0.2 W cm−2 under the conditions of 10% v/v CH3OH, sensitizer concentration of 2.5 × 10−5 mol g−1, 5 wt% graphene and pH 7.0. The photocatalyst showed remarkable long term stability and reproducibility of H2 evolution without any appreciable deactivation. This study provides an inexpensive means of harnessing solar energy to achieve highly efficient H2 evolution without noble metals.

UV/ozone-assisted low temperature preparation of mesoporous TiO2with tunable phase composition and enhanced solar light photocatalytic activity

In this paper, we report a UV/ozone-assisted method for low temperature preparation of mesoporous TiO2 with controlled crystalline phase. The results showed that the crystallization of mesoporous TiO2 can occur at temperatures as low as 100 °C under UV/ozone irradiation. Highly crystalline mesoporous anatase TiO2 was obtained after UV/ozone treatment at 200 °C. The phase transformation from anatase to rutile occurred during the UV/ozone treatment at 300 °C and mesoporous bicrystalline TiO2 with a controlled mixture of anatase and rutile phases was prepared by adjusting the exposure time. The photocatalytic performance of the mesoporous TiO2 strongly depends on the crystal structures and the bicrystalline mesoporous TiO2 exhibits remarkably enhanced solar light photocatalytic activity. This technique can be useful for low temperature preparation of crystalline mesoporous titania on various substrates and may be generalized to the synthesis of other materials.

Polymeric Micelle Assembly for the Direct Synthesis of Platinum-Decorated Mesoporous TiO2 toward Highly Selective Sensing of Acetaldehyde

Platinum-decorated mesoporous TiO2 is synthesized by the self-assembly of polymeric micelles of an asymmetric triblock copolymer with three chemically distinct units in an acidic tetrahydrofuran solution. The strong hydrophobic interaction of platinum(II) 2,4-pentanedionate with a polystyrene core and electrostatic interaction of titanium tetraisopropoxide with a poly(vinylpyridine) shell enable us to directly synthesize crystalline mesoporous TiO2 with platinum nanoparticles. A thermally stable block copolymer prevents collapse of the ordered mesostructure during the calcination process. The platinum source is in situ reduced to form the platinum nanoparticles on the TiO2 walls. The sensing performance of platinum-decorated mesoporous TiO2 is studied in detail using a quartz crystal microbalance technique, and it is found that it shows excellent sensitivity for acetaldehyde.

Photophysical properties of hybrid complexes of quantum dots and reaction centers of purple photosynthetic bacteria Rhodobacter sphaeroides adsorbed on crystalline mesoporous TiO2 films

Complexes of CdSe/ZnS and CdTe quantum dots (QDs) with proteins of reaction centers (RCs) of purple bacteria Rhodobacter sphaeroides have been obtained. An efficient energy transfer from QDs (a donor of electron excitation energy) to RCs (acceptor) is observed for them both in the solution and in the films of crystalline mesoporous titanium oxide. The design of such hybrid structures allows us to increase the absorptive ability of the RC many times and, respectively, increase the efficiency of the light energy conversion into the electrical potential. Such hybrid structures can be used for the development of high-performance solar cells.

Synthesis and characterisation of mesoporous anatase TiO2 with highly crystalline framework

Highly crystalline mesoporous nano TiO2 (anatase) was achieved from tetrabutyl orthotitanate modified with acethylacetone by surfactant-assisted route in presence of P123. The material was characterised using X-ray diffraction (XRD) (low and wide angle), FTIR spectra, SEM, TEM, N2 adsorption, and UV-DRS. The particle size of the material was calculated from TEM analysis, XRD, as well as BET method. Mesopores of average width ∼7.2nm have been achieved. The material possessed band gap of 3.24eV, and exhibited a significant blue-shift in UV absorption when compared to the bulk material, due to quantum confinement.

High-temperature hydrothermal synthesis of crystalline mesoporous TiO2 with superior photo catalytic activities

Mesoporous titanium dioxide with crystalline mesopore walls (M-TiO2-ns) have been successfully synthesized through the self-assembly of poly 4-Vinylpyridine template and tetrabutyl titanate precursor based on their complex bond interaction under high temperature (180°C) hydrothermal conditions. X-ray diffraction shows that M-TiO2-ns have highly crystalline mesopore walls with anatase phase characters; N2 sorption–desorption isotherms, SEM and TEM images show that M-TiO2-ns have high BET surface areas (85 and 120m2/g, respectively), large pore volumes (0.32 and 0.34cm3/g, respectively) and crystalline mesopore walls, which exhibit monolithic morphology with crystal sizes around 3–5μm. Interestingly, M-TiO2-ns exhibit much higher catalytic activities and good recyclability in both induced reduction of decabromodiphenyl and oxidation of Rhodamine B under UV light than those of nonporous crystalline TiO2 and M-TiO2 templated by hydrocarbon surfactant of F127, which is even comparable with that of commercial P25. Combination of the unique characters such as crystallinity, stable mesostructure, large BET surface areas and superior photo catalytic activities make M-TiO2-ns a kind of potentially important material for removing of organic pollutions in environment through green photo irradiation processes.

One-pot synthesis of highly crystalline mesoporous TiO2 nanoparticle assemblies with enhanced photocatalytic activity

We report an unprecedented formation of mesoporous titania via a surfactant-assisted aggregating assembly of TiO(2) nanoparticles. These mesostructures possess a highly crystalline anatase phase, large and accessible pore surface area, and exhibit superior photocatalytic performance.

Mesophase ordering and structuring of porous titanium dioxide with high surface area and strong light harvesting matrix for dye-sensitized solar cell

ABSTRACTDye sensitized solar cells (DSSC) are attractive because they hold promise for devices that are easy to fabricate and inexpensive. In the present work, highly crystalline mesoporous TiO2 has been synthesized by evaporation induced self assembly (EISA) method using triblock copolymer Pluronic P123 as the organic template. The synthesized TiO2 is anatase in nature with a pore size of 10-15 nm. DSSC made from mesoporous TiO2 demonstrated solar conversion efficiency of ∼7%. This comes from the benefits of increased surface roughness, surface area and uniform porosity. In addition, well ordered and crystalline pores provided good sunlight absorption and low recombination path for charge carriers. To further enhance the efficiency of the DSSCs, light scattering centers were introduced in the mesoporous TiO2 film. Nanoparticles light scatterers are introduced to scatter the incoming light and hence to increase the light harvesting capability of the device. A 26 % increase in DSSC efficiency was observed with the implementation of scattering centers.

Fabrication and characterization of plastic-based flexible dye-sensitized solar cells consisting of crystalline mesoporous titania nanoparticles as photoanodes

We fabricated a highly efficient (with a solar-to-electricity conversion efficiency (η) of 5.51%), plastic-based, flexible dye-sensitized solar cell (DSSC). The photoanode was made of a crystalline mesoporous TiO2 film using a low-temperature electrophoretic deposition (EPD) process and compression treatment. The crystalline mesoporous TiO2 film was composed of secondary mesoporous TiO2 nanoparticles (MTNs, ca. 260 nm in size), synthesized by an aggregation of primary TiO2 nanocrystallites. In contrast to commercial TiO2 nanoparticles (i.e., P90, ca. 15.9 nm in size) that are widely used in DSSCs, the synthesized MTN-based film exhibited a higher surface area and porosity that increased dye adsorption, promoted effective electron transport, and enhanced light scattering, as evidenced by analysis of reflectance and absorbance spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). We also optimized the compression pressure for MTN- and P90-based DSSCs in order to achieve maximum efficiency. We further systematically investigated the cause for the enhanced conversion efficiency of MTN-based DSSCs by measuring incident photon-to-electron conversion efficiency (IPCE) curves and electrochemical impedance spectra (EIS). IPCE results explained the increase in the short-circuit photocurrent density (JSC) for MTN-based DSSCs, and EIS results indicated that MTN-based DSSCs exhibited a larger diffusion coefficient (Deff), longer effective diffusion length (Ln), longer electron lifetime (τe), and lower charge transfer resistance (Rk), resulting in a higher power conversion efficiency. The MTN-based DSSC fabricated in the study showed great potential for application in plastic-based DSSCs using room temperature procedures.