Mesoporous TiO2 Research Articles

Study of chlorophyll dye from peppermint (mentha spicata) used as a sensitizer in TiO2 solar cells

Abstract Chlorophyll from peppermint (mentha spicata) was evaluated as a natural dye sensitizer in TiO2 solar cells. The final photoconversion efficiency depended on the solvent used as chlorophyll dispersant and the technique used to sensitize the mesoporous TiO2 film. Evaluated sensitization techniques included pipetting, immersion, and electrophoresis. Best solar cell performance was obtained using methanol as solvent simultaneously with electrophoresis. A short circuit current density (J sc) of 0.174 mA/cm2 and an open circuit voltage (V oc) of 0.508 V were obtained. The photoconversion efficiency reached 0.39 %. However, sensitizing by the pipetting technique allowed a photoconversion efficiency of 0.35 % with better reproducibility.

Solar-powered commercial diesel fuel desulfurization: Exploring the factors affecting and recyclability of mesoporous Tl-doped TiO2 nanofiber photocatalysts

The study aims to fabricate mesoporous TiO2 nanofibers (NFs) with different thallium (Tl) doping ratios (1–2 wt%) using the solution electrospinning method and examine their photocatalytic oxidation activity in the desulfurization of commercial diesel fuel. The results show that the Tl doping restricted the transition of the anatase to rutile fraction, shifting it from an initial composition of 58.3% rutile and 41.7% anatase to a significantly altered state with only 2.4% rutile and 97.6% anatase. Additionally, Tl-doping resulted in a decrease in crystalline size (from 55.4 to 9.5 nm), a reduction in the band gap from 3.2 to 2.93 eV, and a decrease in the diameter of the nanofibers from 200 nm to 100 nm, compared to pristine TiO2 NFs. The most efficient photocatalyst, 1 wt% Tl-doped TiO2 NFs, demonstrated remarkable performance with 98.74% sulphur removal under Xenon lamp irradiation (450 nm, 500 Watts) for 90 min. Under sunlight, the photocatalytic oxidation activity in the desulfurization process resulted in a remarkable reduction of 99.2% in sulphur content, decreasing from 11500 ppm to 98 ppm. Notably, this photocatalyst demonstrated efficient oxidative photocatalytic desulfurization and maintained the recyclability of the solvent over eight cycles without any loss.

Designed Mesoporous Architecture by 10–100 nm TiO2 as Electron Transport Materials in Carbon-Based Multiporous-Layered-Electrode Perovskite Solar Cells

Fully printable carbon-based multiporous-layered-electrode perovskite solar cells (MPLE-PSCs) are easy to fabricate and have excellent durability. In this study, the porosity of the mesoporous TiO2 layer as the electron transport layer in MPLE-PSCs was controlled by varying the particle diameter of TiO2 nanoparticles from 14 nm to 98 nm. Furthermore, the results of absorbed photon-to-current conversion efficiency, visible light reflectance spectroscopy, pore-size distribution, X-ray diffraction, field emission scanning electron microscopy, and photovoltaic parameters of MPLE-PSCs are discussed. Although the porous TiO2 layer with smaller nanoparticles showed higher photoabsorption, it was found that the more voids of perovskite crystals created in the TiO2 porous layer, the smaller the particle size (<18 nm). The porous TiO2 layers with particles over 26 nm are well filled with perovskite crystals, resulting in a higher photovoltaic capacity with TiO2 particles over 26 nm. As a result, the short-circuit current density (JSC) showed a maximum value using 43 nm TiO2 particles, with an average power conversion efficiency (PCE) of 10.56 ± 1.42%. Moreover, the PCE showed a maximum value of 12.20% by using 26 nm TiO2 nanoparticles.

Enzymatic Activity of Glucose Oxidase on Mesoporous TiO2:Mn Surfaces

Introduction: It is well known, that titanium dioxide (TiO2) nanoparticles can lead to the generation of reactive oxygen species (ROS) upon photoexcitation. Method: In this work, we investigated mesoporous surfaces based on TiO2 nanoparticles doped with 0.6-0.7% manganese (Mn), which showed reduced photoactivity and were based on the more stable rutile polymorph of titania. Result: In particular, we showed spectrophotometrically that the enzyme glucose oxidase (GOD) can be successfully adsorbed up to 80% while retaining its bioactivity in contact with the TiO2:Mn-based surface. Conclusion: We propose that this study could potentially give rise to biocompatible surfaces for biosensing applications.

Insights into the Interfacial Charge Transfer Dynamics in Semiconductor–Molecular Catalyst Assemblies for Photo–Induced CO2 Reduction

AbstractThis mini–review summarises examples of photo and photoelectrochemical CO2 reduction reactions (CO2RR) using semiconductor–molecular catalyst–based hybrid assemblies in which studies of charge transfer dynamics were also performed. In these catalysts, the grand challenges are controlling ultra–fast one–electron charge separation and simultaneously governing its impact on the efficiency and product selectivity in the multielectron and multi–proton–assisted CO2RR. In practice, several unwanted electron recombination processes occur in the femtosecond to millisecond timescale range impacting the overall catalysis efficiency. Titanium di‐oxide (TiO2) nanoparticle, mesoporous TiO2 film, copper indium sulphide (CuInS2) quantum dots were used as semiconductor materials, in turn rhenium (I) bipyridine, cobalt (II) terpyridine, cobaloxamine complex, and iron (III) porphyrins were investigated as molecular catalysts. The results of the charge transfer dynamic studies operating in such hybrid systems shed light on their charge accumulation processes, their rate constants for the intramolecular charge transfer processes and the decay lifetimes of the different excited state species that are produced. Moreover, a comprehensive understanding of the catalysts’ charge transfer dynamics is crucial to identifying detrimental charge recombination pathways. These undesired pathways can be used as rational basis for improving the design of future multi–redox–driven hybrid catalysts.

Preparation of TiO2/Ni‐NG Mesoporous Microspheres and Photocatalytic Hydrogen Evolution Properties

AbstractThe regulation of surface active sites and structures is a key factor affecting the performance of photocatalysts. In order to prepare monodisperse anatase TiO2 mesoporous microspheres with higher specific surface area, smaller pore size and particle size, a dual‐surfactant orientation assembly method was selected. Graphene (NG) was selected as a cocatalyst to compound with mesoporous TiO2 and nickel doping was performed on the cocatalyst to improve the photocatalytic hydrogen production activity of the semiconductor photocatalyst. Through proper regulation and rational design, the semiconductor photocatalyst with desired properties was prepared. SEM characterization of mesoporous titanium dioxide (TiO2/Ni‐NG) with graphene cocatalyst proved that TiO2 nanospheres have good monodispersion, and TiO2 nanospheres are well supported on graphene cocatalyst. The composite material belonged to mesoporous group with the pore size being mainly distributed between 10–20 nm. The loading of graphene and Ni‐NG cocatalyst increased the absorption band edge by 9 nm and 38 nm, respectively, and the band gap decreased by 0.07 eV and 0.16 eV, respectively. The selection of graphene as cocatalyst improved the hydrogen production activity of photocatalyst and nickel doping was very effective in the modification of graphene. For reaction time of 2.5 h, the H2 production of TiO2/Ni‐NG material reached 1.767 mmol/g which was 7.27 times that of TiO2/NG composite material.

Phenol degradation on the surface of mesoporous TiO2 particles via ligand-to-metal charge transfer under visible light irradiation

Degradation behaviors of phenol from aqueous solution under the blue light irradiation were studied using a series of sol–gel prepared TiO2 particles exhibiting different blue light absorbing abilities. The phenol degradation under the blue light irradiation was most pronounced in the presence of TiO2 sample exhibiting the lowest blue light absorbing ability among the samples, showing no correlations between phenol degradation and light absorbing ability of TiO2 particles. UV-DRS analysis and scavenging experiments revealed that phenol degradation under visible light irradiation can be majorly proceed via the light absorption by the ligand-to-metal-charge-transfer (LMCT).

Enhanced Photocatalytic Degradation of Methyl Orange Using Nitrogen‐Functionalized MesoporousTiO2 Decorated with Au9 Nanoclusters

A novel catalyst for dye degradation is fabricated through attaching Au9 nanoclusters (Au9 NCs) to N functionalized mesoporous TiO2 (NMTiO2). The NMTiO2 is created through chitosan‐assisted soft templating resulting in an N terminated surface preventing the agglomeration of the Au9 NCs adsorbed surface and enhancing the overall loading with Au9. The calcination atmosphere influenced the surface properties of the NMTiO2 and its capability to adsorb the Au9 NCs. The photocatalytic effectiveness of these materials was probed through methyl orange (MO) dye degradation. The black coloured Au9/NMTiO2 catalyst is highly effective to completely degrade MO dyes within 20 min due to its large reaction constant (0.176 min−1). Parameter interactions for the dye degradation process were explored using response surface methodology (RSM) and the dependency of MO degradation on the affecting parameters was evaluated based on the statistical analysis and 3D plots.

Photoanode Modification Based on Lignin Extracted from Rice Husk for Dye-Sensitized Solar Cells

The photoanode optimization of dye-sensitized solar cells (DSSCs) has been developed to create renewable devices based on green chemistry. TiO2 plays a crucial role in light absorption, charge separation, and electron transport within the photoanode of DSSCs. Modifying mesoporous TiO2 photoanode using lignin-template has been considered a viable option for photocatalyst synthesis. Lignin derived from rice husk is a potential material due to its abundant sources in many countries. Therefore, in this work, rice husk lignin was employed for non-toxic and low-cost material performance improvement of TiO2. Experimental results showed that the best efficiency and current density were identified as the effect of adding a 5% concentration of lignin on the TiO2 composite, namely 4.81% PCE.

Au9 clusters deposited as co-catalysts on S-modified mesoporous TiO2 for photocatalytic degradation of methyl orange

Au9 nanoclusters (Au9 NCs) were deposited onto S-functionalized mesoporous TiO2 (SMTiO2) to produce efficient photocatalysts for Methyl Orange (MO) dye degradation with UV light. The morphology, the surface composition and the size of the deposited Au9 NCs of the catalyst was analysed. SMTiO2 could adsorb more clusters with lesser Au9 cluster agglomeration than unmodified MTiO2. This finding is attributed to the capability of the thiol groups to form strong bonds with the Au9 clusters. To study Au9 NCs effect on dye degradation activity, the MO degradation reaction constants under UV-light irradiation for SMTiO2 nanoparticles (NPs) and Au9 NCs decorated SMTiO2 photocatalysts were studied, which were 0.07 min−1 and 0.149 min−1, respectively. Hence, it takes almost half the time to completely degrade MO using Au9 NCs decorated SMTiO2 photocatalysts compared to SMTiO2 substrate. Results were analysed using the response surface methodology (RSM) to study the interaction between the reaction parameters.

Self-templated formation of hierarchically porous TiO2 hollow microspheres with fast lithium-uptake performance

Hollow TiO2 microspheres composed of low-dimensional anisotropic building blocks (such as nanowires or nanosheets) possess a hierarchical porosity and thus favor mass/Li+ transfer. However, developing an easy-control method to synthesize this type of TiO2 is still a challenge. Herein, an aerosol-assisted self-assembly method is developed to construct the nanowire-assembled TiO2 hollow microspheres (NW-TOHMS). The nanowire-intertangle configuration results in forming large surface area (∼207 m2 g−1) and hierarchical porosity with a broad pore-size distribution from 2 to 100 nm. Moreover, finite element analysis suggests that nanowire-constructed open meso-/macro-pores benefit the Li+-transport/storage kinetics. As a consequence, the NW-TOHMS electrode exhibits a high specific capacity of 117 mA h g−1 at 5 A g−1 after 1000 cycles. Excitingly, the activated carbon/NW-TOHMS Li-ion capacitors demonstrate an energy density as high as 37 Wh kg−1 at the maximum power density of 6.1 kW kg−1. This work offers a new pathway for the synthesis of mesoporous TiO2 hollow superstructures used to fast energy storage and conversion.

Understanding the Anomalous J–V Curves in Carbon‐Based Perovskite Solar Cells as a Structural Transition Induced by Ion Diffusion

The investigation of hole transport layer‐free mesoporous carbon perovskite solar cells by analyzing current–voltage (J–V) curves under different scan rates, light intensities, and temperatures is presented. A distinctive bump in the curves is identified, previously reported in the literature. The voltage at the inflection point of this transition shows a linear correlation with the scan rate, directly yielding a characteristic relaxation time. Increasing temperature demonstrates a reduction in the magnitude and characteristic time of the bump. It also indicates an activation energy of 0.8 eV, suggesting a diffusion mechanism. Importantly, the intensity of the illumination has no influence on the overall behavior, indicating that the phenomenon is not a photovoltaic processes. It is proposed that the bump originates from transition between a metastable state at high scan rates and a stable one reached after relaxation. To accurately replicate the measured J–V curves, a novel lumped circuit model is introduced and validated. A schematic microstructural model depicts the reversible reduction in photocurrent as a decline in charge transfer capacity caused by the diffusion of large ions at the mesoporous titanuim dioxyde interface. Ultimately, this study also suggests a plausible reason for the well‐known hysteresis commonly observed with perovskite solar cells.

Study on the photovoltaic characteristics of solar cells based on PbS quantum dots and carbon counter electrode

Lead sulfide (PbS) quantum dots (QDs) with their customizable and precise energy levels, have emerged as highly promising photosensitizers in quantum dots sensitized solar cells (QDSSCs). This research focuses on fabricating high-performance QDSSCs anchored on PbS QDs sensitized mesoporous titania coated FTO electrodes. The PbS QDs were grown on mesoporous TiO2 through the Successive Ionic Layer Absorption and Reaction (SILAR) method. The optical properties were analyzed using UV–visible absorption spectroscopy, revealing that the SILAR cycles impacted the size and band gap of the PbS QDs. By analyzing the absorption data and the hyperbolic band model (HBM), the size of the PbS QDs were estimated to be 1.65 nm, 2.126 nm, 2.326 nm, 2.5692 nm, and 3.048 nm for 1 to 5 SILAR cycles, respectively. The effect of SILAR cycles was investigated, demonstrating a direct correlation between the number of SILAR cycles and the photovoltaic performance of the device. The maximum power conversion efficiency of 2.07 % was attained using 2 SILAR cycles, in contrast to 1.33 % and 1.63 % obtained with one and three SILAR cycles, respectively. Furthermore, impedance spectroscopy (IS), (Cs-V) (Rs-V) was employed at different frequencies, highlighting lowest series resistance for 2 SILAR cycles confirming its highest photovoltaic performance. Moreover, The utilization of a low-cost polysulfide electrolyte and carbon electrode has yielded superior or comparable outcomes compared to previously reported data.

Red mud accommodated mesoporous black TiO2 framework with enhanced organic pollutant photodegradation.

In this work, black TiO2 (BTiO2) loaded on black red mud (BRM) was successfully prepared with the conversion of Fe2O3 into magnetic Fe3O4 in red mud and the reduction of partial Ti4+ to Ti3+ in TiO2 via the facile sol-gel method and H2 reduction treatment. The obtained low-cost BRM/BTiO2 composites exhibit remarkable photocatalytic degradation toward rhodamine B (91.2%) and tetracycline (83.6%) under visible light irradiation, much better than pristine TiO2. This enhancement is attributed to the narrow bandgap with the desired solar-light excitation, the black color with good solar-light absorption, and the heterojunctions with the efficient separation of photogenerated electron-hole pairs. Moreover, the desired magnetic separation of BRM/BTiO2 composites realizes the recycle and recovery of photocatalysts, favoring practical applications in environment. This work provides a cost-efficiency way to prepare RM-supported TiO2 composites for treating organic pollutants in the wastewater, which is of great significance to the comprehensive utilization of RM waste, the cost saving of the photocatalyst, and the visible-light active enhancement of TiO2.

Effect of TiO2 structure on hysteretic behaviors in CH3NH3PbI3 perovskite solar cells

This work explores a mechanism behind hysteresis in CH3NH3PbI3 perovskite solar cells. The solar cells in this work employed either compact TiO2, mesoporous TiO2, or a combination of compact and mesoporous TiO2 as an electron transport layer. The solar cells using compact TiO2 layer displayed the most pronounced hysteresis compared to those which made use of mesoporous TiO2. Different hysteretic behavior is attributed to difference in the built-in electric fields present in the architecture of perovskite solar cell. The solar cells with a compact TiO2 layer have a built-in field which allows for iodide ions to migrate and accumulate near to the interface of indium-tin-oxide electrode, ultimately causing a reduction in the measured power conversion efficiency for forward bias scans. In case of the cells with a mesoporous TiO2 layer, they have the built-in fields configured in such a way that iodide ions are blocked from migrating on a large scale to the vicinity of the ITO electrode. This results in the reduced hysteresis in perovskite solar cells when a mesoporous TiO2 electron transport layer is employed.

Enhancing the stability and efficiency of carbon-based perovskite solar cell performance with ZrO2-decorated rGO nanosheets in a mesoporous TiO2 electron-transport layer.

Improving the role of electron-transport layers (ETLs) in carbon-based perovskite solar cells (CPSCs) is a promising method to increase their photovoltaic efficiency. Herein, we employed rGO sheets decorated with ZrO2 nanoparticles to increase the electron transport capability of mesoporous TiO2 ETLs. We found that the rGO/ZrO2 dopant enhanced the conductivity of the ETL, reducing the charge-transfer resistance at the ETL/perovskite interface and reducing charge recombination in the corresponding CPSCs. Notably, this dopant did not effectively change the transparency of ETLs, while increasing the light-harvesting ability of their own top perovskite layer by improving the crystallinity of the perovskite layer. The rGO/ZrO2-containing ETLs produced a champion efficiency of 15.21%, while devices with a net ETL recorded a maximum efficiency of 11.88%. In addition, the modified devices showed a higher stability behavior against ambient air than the net devices, which was linked to the passivated grain boundaries of the modified perovskite layers along with the improved hydrophobicity.

Construction of oxygen-rich vacancies and heterojunctions coupled with different morphologies of CeO2/mesoporous TiO2 framework structures for efficient photocatalytic CO2 reduction performance.

The coupling of efficient adsorption and effective charge separation with photocatalysts enables the use of sunlight for photocatalytic reduction of carbon dioxide (CO2) into high-value-added products. In this work, we used a straightforward solid-phase hydrothermal technique to build an oxygen-vacancy-rich, heterogeneous interface-coupled CeO2/mesoporous TiO2 framework structural system. The heterogeneous structure was constructed by introducing oxygen-vacancy-rich CeO2 into mesoporous TiO2, which may encourage the transfer of charges and increase the number of active sites and CO2 adsorption by utilizing the coupled synergistic effect of oxygen vacancies and heterogeneous interfaces, and it can also regulate the pathway of the photocatalytic reaction and the selectivity of the products. The composite of CeO2 with different morphologies and oxygen-rich vacancies regulated the system's active sites and degree of exposure and enhanced photocatalytic CO2 reduction. The highest CO yield of 6.25 mmol gcat-1 was obtained by use of the rod CeO2/mesoporous TiO2 composite photocatalyst (R-CeO2/TiO2), and this yield was 1.6 times higher than that of pure mesoporous TiO2 and 1.84 times higher than that of pure R-CeO2. Also, the product selectivity increased by 4.3% compared to a single sample. Combining the Mott-Schottky plot results and the energy-barrier perspective to further explore the photocatalytic reduction of the CO2 reaction mechanism as well as the product selectivity, it appears that the construction of the composite system of oxygen-rich vacancies and heterogeneous boundary-coupled photocatalysis provides a practical pathway for the photocatalytic reaction, which may contribute to the photocatalytic reaction's high efficiency and yield selectivity.

Selective adsorption and photodegradation of residual norfloxacin in water using a mTiO2 based inorganic molecularly imprinted magnetic photocatalyst

In this study, a mesoporous TiO2 (mTiO2) based inorganic molecularly imprinted magnetic photocatalyst was prepared for the selective adsorption and photodegradation of residual antibiotics in water.

Bio-inspired synthesis of N-doped TiO2/C nanocrystals using jellyfish mucus with high visible-light photocatalytic efficiency.

Non-metal doping of titanium dioxide (TiO2) has been widely investigated, because it can facilely improve the optical response of TiO2 under visible light excitation in environmental pollution treatments. In the ongoing efforts, however, little consideration has been given to the use of harmful marine organisms as dopants. Here, we employed the natural mucus proteins of the large harmful jellyfish Aurelia coerulea and Nemopilema nomurai, which have frequently bloomed in East Asian marginal seas in recent decades, to synthesize mesoporous nitrogen-doped TiO2 nanocrystals modified with carbon (N-TiO2/C) by a simple hydrothermal method. These nanocrystals were composed of predominantly anatase phase and a small amount of brookite phase TiO2. Their mesoporous structures changed with the variation of the volume ratio of jellyfish mucus added to tetrabutyl titanate (TBT). At the same ratio, larger surface area and pore volume but smaller pore size were observed in N-TiO2/C nanocrystals from N. nomurai rather than A. coerulea. Nitrogen was determinately doped into the lattice of the prepared nanocrystals and the carbon species were modified on their surfaces, which narrowed the band gap, facilitated the separation of photogenerated electron-hole pairs and favored the absorption of visible light, thus improving their visible light photocatalytic activity. The photocatalytic degradation efficiency of Rhodamine B (RhB) under visible light irradiation first increased and then decreased with the gradual increase of the volume ratio of jellyfish mucus proteins to TBT. The maximum reached 97.52% in 20 min from N-TiO2/C nanocrystals synthesized using N. nomurai mucus at the volume ratio of 4 : 1, which showed a remarkably strong visible light absorption, lower band gap energy and smaller electron transfer resistance. These N-TiO2/C nanocrystals also had a relatively stable crystal structure in multiple degradation reactions. The main active species including superoxide radicals (˙O2 -), photogenerated holes (h+) and hydroxyl radicals (˙OH) were found to play a major role in the degradation process of RhB. This study highlights the potential high-value reapplication of harmful jellyfish mucus as a natural organic matrix in fabricating advanced materials with optimized functional properties.

Au9 nanocluster adsorption and agglomeration control through sulfur modification of mesoporous TiO2.

In the present work phenyl phosphine-protected Au9 nanoclusters were deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS) modified and unmodified mesoporous screen printed TiO2. The removal of the cluster ligands by annealing was applied to enhance the interaction between Au cluster cores and semiconductor surfaces in the creation of efficient photocatalytic systems. The heat treatment could lead to undesired agglomeration of Au clusters, affecting their unique properties as size specific clusters. To address this challenge, the semiconductor surfaces were modified by MPTMS. Characterization techniques confirm the effectiveness of the modification processes, and XPS demonstrates that S functionalized MTiO2 is more efficient than MTiO2 in increasing Au9 NCs adsorption by a factor of 10 and preventing Au cluster agglomeration even after annealing. Overall, this work contributes valuable insights into photocatalytic systems through controlled modification of semiconductor surfaces and Au nanocluster deposition.