Robust Photocatalytic MICROSCAFS® with Interconnected Macropores for Sustainable Solar-Driven Water Purification

Advanced oxidation processes, including photocatalysis, have been proven effective at organic dye degradation. Tailored porous materials with regulated pore size, shape, and morphology offer a sustainable solution to the water pollution problem by acting as support materials to grafted photocatalytic nanoparticles (NPs). This research investigated the influence of pore and particle sizes of photocatalytic MICROSCAFS® on the degradation of methyl orange (MO) in aqueous solution (10 mg/L). Photocatalytic MICROSCAFS® are made of binder-less supported P25 TiO2 NPs within MICROSCAFS®, which are silica-titania microspheres with a controlled size and interconnected macroporosity, synthesized by an adapted sol-gel method that involves a polymerization-induced phase separation process. Photocatalytic experiments were performed both in batch and flow reactors, with this latter one targeting a proof of concept for continuous transformation processes and real-life conditions. Photocatalytic degradation of 87% in 2 h (batch) was achieved, using a calibrated solar light simulator (1 sun) and a photocatalyst/pollutant mass ratio of 23. This study introduces a novel flow kinetic model which provides the modeling and simulation of the photocatalytic MICROSCAFS® performance. A scavenger study was performed, enabling an in-depth mechanistic understanding. Finally, the transformation products resulting from the MO photocatalytic degradation were elucidated by high-resolution mass spectrometry experiments and subjected to an in silico toxicity assessment.

Photocatalytic Oxidation of 5-Hydroxymethylfurfural Over Interfacial-Enhanced Ag/TiO2 Under Visible Light Irradiation

Photocatalytic conversion of biomass-derived 5-hydroxyfurfural (HMF) to value-added 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) is an environmentally friendly process. Here, Ag nanoparticle (NP) supported on TiO₂ (Ag/TiO₂ ) materials with different interfacial structures were fabricated via incipient wetness impregnation. In the photocatalytic oxidation of 5-HMF to HMFCA, low-temperature reduction (473 K) on Ag/TiO₂ could improve the photoinduced charge separation efficiency and promote the reaction due to the "enhanced" localized surface plasmon resonance (LSPR) effects achieved through strong metal-support interaction (SMSI). In particular, 2.5 % Ag/TiO₂ -LTR exhibited superior performance with an HMFCA selectivity of up to 96.7 % under visible-light illumination. In contrast, the photocatalytic efficiency was greatly reduced when the reduction temperature increased to 773 K because of the encapsulation of Ag NPs by a thicker TiO_x overlay, which significantly weakened visible-light harvesting. Overall, these findings offer an efficient methodology for designing interfacial enhanced plasmonic photocatalysts for the valorization of biomass.

Conformal Coating of Freestanding Particles by Vapor-Phase Infiltration

A novel atomic layer method for encapsulating individual micro- and nano-particles with thin (sub-10-nm) dielectric films is presented. This method leverages the diffusion of vapor-phase precursors through an underlying inert polymer film to achieve growth of a metal oxide film on all sides of the particle simultaneously; even on the side that is in contact with the substrate. Crucially, the deposition is performed on stationary particles and does not require an agitation mechanism or a special reaction chamber. Here, conformal coatings of alumina are shown to improve stability in aqueous environments for two optically-relevant particles: compound semiconductor laser microparticles and lead halide perovskite nanocrystals.

Low cycles pulsed chemical vapor deposition of polycrystalline anatase TiO2

In this work, an atomic layer deposition (ALD) system is used to identify deposition conditions resulting in anisotropic growth and the formation of highly defined polycrystalline anatase titanium dioxide. FESEM, Raman Spectroscopy, and XRD were extensively used to characterize the deposited titania. The ALD parameter refinement resulted in the attainment of a polycrystalline anatase phase titania in as low as 30 cycles, although the final parameter resulted in a pulsed-chemical vapor deposition (pulsed-CVD). This work suggests that the anatase crystal phase’s development is more dependent on deposition process parameters such as precursor pulse, waiting time, and vacuum times than on the number of cycles. Moreover, the developed pulsed-CVD procedure to deposit anatase titania was capable of coating rough aluminum and titanium substrates with polycrystalline anatase titania, highly increasing the potential to be used in other biomedical implants made of different metals such as stainless steel or in other applications such as dielectrics

Rate-Limiting Steps of Dye Degradation over Titania-Silica Core-Shell Photocatalysts

In this work, we employed a step-by-step sol-gel process to controllably deposit ultra-thin layers of SiO2 on anatase nanoparticles in the range between 0 and 1 nm. The deposition was confirmed by TEM, EDX, and ATR-FTIR (e.g., Ti-O-Si band at 960 cm-1). Zeta potential measurements unravelled a continuous change in surface charge density with increasing silica shell thickness. The photocatalysts were evaluated towards adsorption and degradation of positively-charged and negatively-charged dyes (methylene blue, methyl orange) under UV illumination. The growth mechanism follows the Stranski–Krastanov model with three thickness regimes: (a) Flat islands (first step), (b) mono/bilayers (second/third step), and (c) regular thick films (fourth/fifth step). The results suggest different rate limiting processes for these regimes: (a) For the thinnest scenario, acidic triple-phase boundaries (TPBs) increase the activity for both dyes with their accessibility being the rate limiting step; (b) for continuous mono/bilayers, dye adsorption on the negatively-charged SiO2 shells becomes the rate liming step, which leads to a stark increase in activity for the positively-charged MB and a decrease for MO; (c) for thicker shells, the activity decreases for both dyes and is limited by the charge transport through the isolating shells.

Construction of Indium and Cerium Codoped Ordered Mesoporous TiO2 Aerogel Composite Material and Its High Photocatalytic Activity

In this study, ordered mesoporous In2O3-CeO2/TiO2 aerogel composite material is fabricated via a sol-gel method. According to the preparation process of the aerogel, different weight percentages Ce(NO3)3 and In(NO3)3 are dissolved in the solvent, which would be completely dispersed in the porous gel when the system completely becomes gel. The prepared materials are used to degrade the Rhodamine B (Rh B) under visible light irradiation. 0.2 wt% In2O3-0.2 wt% CeO2/TiO2 (In0.2-Ce0.2/TiO2) sample has the highest degradation rate which reaches to 96.20%. When degradation time is continuously increased to 110 min, the degradation efficiency of In0.2-Ce0.2/TiO2 sample is basically retained. The prepared In0.2-Ce0.2/TiO2 sample has much better stability and reproducibility under visible light irradiation, the photocatalytic degradation efficiency of In0.2-Ce0.2/TiO2 sample is still stable at more than 90% after the five times cycle.

Nanostructured Silica-Titania Hybrid using Dendritic Fibrous Nanosilica as a Photocatalyst

A new method has been developed to fabricate active TiO₂ photocatalysts by tuning the morphology of the catalyst support. A sustainable solution-phase TiO₂ deposition on dendritic fibrous nanosilica (DFNS) protocol is developed, which is better than the complex and expensive atomic layer deposition technique. In general, catalytic activity decreases with an increased TiO₂ loading on conventional mesoporous silica because of the loss of the surface area caused by the blocking of pores. Notably, in the case of the dendritic fibrous nanosilica KCC-1 as a support, because of its open fibrous morphology, even at the highest TiO₂ loading, a relatively large amount of surface area remained intact. This improved the accessibility of active sites, which increased the catalytic performance of the KCC-1/TiO₂ photocatalyst. KCC-1-supported TiO₂ is a superior photocatalyst in terms of H₂ generation (26.4 mmol gTiO2 ^-1  h^-1 ) under UV light. This study may provide a new direction for photocatalyst development through the morphology control of the support.

Performance improvement by alumina coatings on Y3Al5O12:Ce3+ phosphor powder deposited using atomic layer deposition in a fluidized bed reactor

To improve the thermal stability, Al₂O₃ has been successfully coated on a Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce) phosphor powder host by using the Atomic Layer Deposition (ALD) approach in a fluidized bed reactor.

Synthesis of uniformly dispersed anatase nanoparticles inside mesoporous silica thin films via controlled breakup and crystallization of amorphous TiO2 deposited using atomic layer deposition

Amorphous titanium dioxide was introduced into the pores of mesoporous silica thin films with 75% porosity and 12 nm average pore diameter via Atomic Layer Deposition (ALD) using alternating pulses of tetrakis(dimethylamino)titanium and water. Calcination provoked fragmentation of the deposited amorphous TiO2 phase and its crystallization into anatase nanoparticles inside the nanoporous film. The narrow particle size distribution of 4 ± 2 nm and the uniform dispersion of the particles over the mesoporous silica support were uniquely revealed using electron tomography. These anatase nanoparticle bearing films showed photocatalytic activity in methylene blue degradation. This new synthesis procedure of the anatase nanophase in mesoporous silica films using ALD is a convenient fabrication method of photocatalytic coatings amenable to application on very small as well as very large surfaces.