Nanoplasmonically Engineered Interfaces on Amorphous TiO2 for Highly Efficient Photocatalysis in Hydrogen Evolution

Flexible Nano-TiO2 Sheets Exhibiting Excellent Photocatalytic and Photovoltaic Properties by Controlled Silane Functionalization-Exploring the New Prospects of Wastewater Treatment and Flexible DSSCs

TiO₂ nanoparticles surface-modified with silane moieties, which can be directly coated on a flexible substrate without the requirement of any binder materials and postsintering processes, are synthesized and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, X-ray photoelectron spectroscopy, Raman spectroscopy, photoluminescence spectroscopy, time-correlated single-photon counting, and transmission electron microscopy. The viability of the prepared surface-modified TiO₂ (M-TiO₂) sheets as a catalyst for the photo-induced degradation of a model dye, methylene blue, was checked using UV-visible absorption spectroscopy. The data suggest that, compared to unmodified TiO₂, M-TiO₂ sheets facilitate better dye-degradation, which leads to a remarkable photocatalytic activity that results in more than 95% degradation of the dye in the first 10 min and more than 99% of the degradation in the first 50 min of the photocatalytic experiments. We also demonstrate that M-TiO₂ can be recycled with negligible reduction in photocatalytic activity. Further, the photovoltaic properties of the developed M-TiO₂ sheets were assessed using UV-visible absorption spectroscopy, electrochemical impedance spectroscopy (EIS), and photochronoamperometry. Dye-sensitized solar cells (DSSC) fabricated using M-TiO₂ as the photoanode exhibited a photoconversion efficiency of 4.1% under direct sunlight. These experiments suggested that M-TiO₂ sheets show enhanced photovoltaic properties compared to unmodified TiO₂ sheets, and that, when N-719 dye is incorporated, the dye-TiO₂ interaction is more favorable for M-TiO₂ than bare TiO₂. The simple solution processing method demonstrated in this paper rendered a highly flexible photoanode made of M-TiO₂ with superior charge-separation efficiency to an electrode made of bare TiO₂. We propose that our findings on the photovoltaic properties of M-TiO₂ open up arenas of further improvement and a wide scope for the large-scale production of flexible DSSCs on plastic substrates at room temperature in a cost-effective way.

Recent Advances in Plasmonic Photocatalysis Based on TiO2 and Noble Metal Nanoparticles for Energy Conversion, Environmental Remediation, and Organic Synthesis

Plasmonic photocatalysis has emerged as a prominent and growing field. It enables the efficient use of sunlight as an abundant and renewable energy source to drive a myriad of chemical reactions. For instance, plasmonic photocatalysis in materials comprising TiO₂ and plasmonic nanoparticles (NPs) enables effective charge carrier separation and the tuning of optical response to longer wavelength regions (visible and near infrared). In fact, TiO₂ -based materials and plasmonic effects are at the forefront of heterogeneous photocatalysis, having applications in energy conversion, production of liquid fuels, wastewater treatment, nitrogen fixation, and organic synthesis. This review aims to comprehensively summarize the fundamentals and to provide the guidelines for future work in the field of TiO₂ -based plasmonic photocatalysis comprising the above-mentioned applications. The concepts and state-of-the-art description of important parameters including the formation of Schottky junctions, hot electron generation and transfer, near field electromagnetic enhancement, plasmon resonance energy transfer, scattering, and photothermal heating effects have been covered in this review. Synthetic approaches and the effect of various physicochemical parameters in plasmon-mediated TiO₂ -based materials on performances are discussed. It is envisioned that this review may inspire and provide insights into the rational development of the next generation of TiO₂ -based plasmonic photocatalysts with target performances and enhanced selectivities.

Size-dependent interaction of plasma with anatase TiO2 nanoparticles

We study the particle size distribution and phase changes of the anatase TiO2 nanopowder samples when they are subject to the plasma treatments of three different kinds of gases as nitrogen (N2), oxygen (O2), and argon (Ar). The plasma gas pressures vary as 0.1, 0.3, and 0.6 Torr. We demonstrate that the plasma treatments have an effect neither on the phase structure nor on the mean nanocrystalline size. The phase and size invariances of the samples are attributed to their nanoscale thermodynamic aspects. We find out that elevating the gas pressure in some cases creates fine-size amorphous nanoparticles with a narrow distribution. Our findings authenticate that plasma treatment affects the amorphous phase with etching particles down to a mean value of ∼3 nm. The small-angle X-ray scattering (SAXS) technique was utilized to obtain the size distribution of the nanoparticles, and the wide-angle X-ray scattering (WAXS) technique was used to probe the phase and size changes of the crystalline structure.

One-Step Hydrothermal Synthesis of P25 @ Few Layered MoS2 Nanosheets toward Enhanced Bi-catalytic Activities: Photocatalysis and Electrocatalysis

P25 loaded few layered molybdenum disulfide (MoS₂) nanosheets (P25@MoS₂) are successfully synthesized through a facile one-step hydrothermal process. The bi-catalytic activities, i.e., photocatalytic and electrocatalytic activities, of the as-prepared nanomaterials have been investigated. For the as-prepared products, the photocatalytic performances were investigated by degrading simulated pollutant under sunlight irradiation, and the hydrogen evolution reaction evaluated the electrocatalytic performances. The results indicate that P25@MoS₂ possesses excellent activities in both photocatalysis and electrocatalysis. The presence of MoS₂ broadens the light absorption range of P25 and improves the separation and transformation efficiency of photogenerated carriers, thus improving its photocatalytic performance. The existence of P25 inhibits the aggregation of MoS₂ to form more dispersed MoS₂ nanosheets with only few layers increasing its active sites. Thereby, the electrocatalytic performance is heightened. The excellent multifunction makes the as-prepared P25@MoS₂ a promising material in the fields of environment and energy.

A symbiotic hetero-nanocomposite that stabilizes unprecedented CaCl2-type TiO2 for enhanced solar-driven hydrogen evolution reaction

Symbiotic hetero-nanocomposites prevail in many classes of minerals, functional substances and/or devices. However, design and development of a symbiotic hetero-nanocomposite that contains unachievable phases remain a significant challenge owing to the tedious formation conditions and the need for precise control over atomic nucleation in synthetic chemistry. Herein, we report a solution chemistry approach for a symbiotic hetero-nanocomposite that contains an unprecedented CaCl2-type titania phase inter-grown with rutile TiO2. CaCl2 structured TiO2, usually occurring when bulk rutile-TiO2 is compressed at an extreme pressure of several GPa, is identified to be a distorted structure with a tilt of adjacent ribbons of the c-axis of rutile. The structural specificity of the symbiotic CaCl2/rutile TiO2 hetero-nanocomposite was confirmed by Rietveld refinement, HRTEM, EXAFS, and Raman spectra, and the formation region (TiCl4 concentration vs. reaction temperature) was obtained by mapping the phase diagram. Due to the symbiotic relationship, this CaCl2-type TiO2 maintained a high stability via tight connection by edge dislocations with rutile TiO2, thus forming a CaCl2/rutile TiO2 heterojunction with a higher reduction capacity and enhanced charge separation efficiency. These merits endow symbiotic CaCl2/rutile TiO2 with a water splitting activity far superior to that of the commercial benchmark photocatalyst, P25 under simulated sunlight without the assistance of a cocatalyst. Our findings reported here may offer several useful understandings of the mechanical intergrowth process in functional symbiotic hetero-nanocomposites for super interfacial charge separation, where interfacial dislocation appears to be a universal cause.

Distorted 1T-ReS2 Nanosheets Anchored on Porous TiO2 Nanofibers for Highly Enhanced Photocatalytic Hydrogen Production

Recently, loading TiO₂ with transition-metal disulfides (TMDs) to construct dual functional heterostructures has been widely researched as an effective strategy to improve the photocatalytic performance of a TiO₂ photocatalyst. For the TMD cocatalysts, the 2H-MoS₂ and 1T-MoS₂ have been widely studied and researched. However, they suffer from poor catalytic activity sites/low charge transfer ability and an unstable structure. In this regard, distorted 1T-phase TMDs with a stable structure are greatly fit for the cocatalyst due to their high charge transfer ability and rich catalytic sites on both the edge and basal plane. Therefore, it is highly desirable to develop distorted 1T-phase TMD/TiO₂ heterostructures with well-identified interfaces for highly enhanced photocatalytic performance. Herein, we first introduce distorted 1T-ReS₂ anchored on porous TiO₂ nanofibers as a promising photocatalyst for achieving an excellent photocatalytic hydrogen production. The excellent performance is attributed to the strong chemical interaction of the Ti-O-Re bond between TiO₂ and ReS₂, the excellent electron mobility of distorted 1T-ReS₂, and the abundant catalytic activity sites on both the plane and edge of the ReS₂ cocatalyst.

TiO2 ALD Coating of Amorphous TiO2 Nanotube Layers: Inhibition of the Structural and Morphological Changes Due to Water Annealing

The present work presents a strategy to stabilize amorphous anodic self-organized TiO₂ nanotube layers against morphological changes and crystallization upon extensive water soaking. The growth of needle-like nanoparticles was observed on the outer and inner walls of amorphous nanotube layers after extensive water soakings, in line with the literature on water annealing. In contrary, when TiO₂ nanotube layers uniformly coated by thin TiO₂ using atomic layer deposition (ALD) were soaked in water, the growth rates of needle-like nanoparticles were substantially reduced. We investigated the soaking effects of ALD TiO₂ coatings with different thicknesses and deposition temperatures. Sufficiently thick TiO₂ coatings (≈8.4 nm) deposited at different ALD process temperatures efficiently hamper the reactions between water and F⁻ ions, maintain the amorphous state, and preserve the original tubular morphology. This work demonstrates the possibility of having robust amorphous 1D TiO₂ nanotube layers that are very stable in water. This is very practical for diverse biomedical applications that are accompanied by extensive contact with an aqueous environment.

Amorphous TiO2 nanostructures: synthesis, fundamental properties and photocatalytic applications

In this review, we mainly highlight the advances made in the development of amorphous TiO₂ nanostructures for photocatalysts. Some perspectives on the challenges and new direction are also discussed.

Facile preparation of Ti3+ self-doped TiO2 nanoparticles and their dramatic visible photocatalytic activity for the fast treatment of highly concentrated Cr(vi) effluent

An efficient visible photocatalyst which is suitable for the rapid removal of highly concentrated Cr(vi) for environmental therapy.