Enhanced Photoelectrochemical Water-Splitting Property on TiO2 Nanotubes by Surface Chemical Modification and Wettability Control

Molecular Mechanisms of the Generation and Accumulation of Gas at the Interface

Gas-evolving reactions are widespread in chemical and energy fields. However, the generated gas will accumulate at the interface, which reduces the rate of gas generation. Understanding the microscopic processes of the generation and accumulation of gas at the interface is crucial for improving the efficiency of gas generation. Here, we develop an algorithm to reproduce the process of catalytic gas generation at the molecular scale based on the all-atom molecular dynamics simulations and obtain the quantitative evolution of the gas generation, which agrees well with the experimental results. In addition, we demonstrate that under an external electric field, the generated gas molecules do not accumulate at the electrode surface, which implies that the electric field can significantly increase the rate of the gas generation. The results suggest that the external electric field changes the structure of the water molecules near the electrode surface, making it difficult for gas molecules to accumulate on the electrode surface. Furthermore, it is found that gas desorption from the electrode surface is an entropy-driven process, and its accumulation at the electrode surface depends mainly on the competition between the entropy and the enthalpy of the water molecules under the influence of the electric field. These results provide deep insight into gas generation and inhibition of gas accumulation.

Superomniphobic and Photoactive Surface Presents Antimicrobial Properties by Repelling and Killing Pathogens

Healthcare-acquired infections place a significant burden on the cost and quality of patient care in hospitals. Reducing contamination on surfaces within healthcare environments is critical for halting the spread of these infections. Herein, we report a bifunctional─repel and kill─surface developed using photoactive TiO2 nanoparticles integrated into a hierarchical scaffold (OmniKill). To quantify the repellency of OmniKill, we developed a touch-based assay, capable of simulating the transfer of individual pathogens, multiple pathogens, or pathogen-latent fecal matter from hands to surfaces. OmniKill repels bacterial pathogens by at least 2.77-log (99.8%). The photoactive material within OmniKill further reduces the viability of transferred pathogens on the surface by an additional 2.43-log (99.6%) after 1 h of light exposure. The antipathogenic effects─repel and kill─remain robust under complex biological contaminates such as feces. These findings show the potential use of OmniKill in reducing the physical transmission of bacterial pathogens in healthcare settings.

Anchoring Bi2S3 quantum dots on flower-like TiO2 nanostructures to boost photoredox coupling of H2 evolution and oxidative organic transformation

The rational integration of semiconductor quantum dots (QDs) with anatase TiO2 nanostructures is a promising strategy to develop efficient photocatalysts. Herein, Bi2S3QD/TiO2 photocatalyst was constructed by controllably depositing Bi2S3 QDs on flower-like TiO2 nanostructures and used for the photocatalytic redox-coupling reaction of H2 evolution and oxidative transformation of benzyl alcohol. The abundant amino groups in TiO2 nanostructures served as the anchoring sites for uniform growth of Bi2S3 QDs. The anchoring of Bi2S3 QDs onto TiO2 nanostructures not only enhanced the photoabsorption ability and the photogenerated charge separation efficiency but also afforded powerful photogenerated charge carriers and abundant active sites for the photocatalytic reaction. As a result, the Bi2S3QD/TiO2 photocatalyst exhibited a favorable performance in the redox-coupling reaction, providing the high production rates of H2 up to 4.75 mmol·gcat-1·h-1 and benzaldehyde up to 6.12 mmol·gcat-1·h-1, respectively, as well as an excellent stability in the long-term photocatalytic reaction. Meanwhile, a trace amount of water in the reaction system could act as a promoter to accelerate the photocatalytic redox-coupling reaction. The photocatalytic mechanism following S-scheme heterojunction was proposed according to the systematic characterizations and experimental results. This work offers some insight into the rational construction of efficient and cost-effective photocatalysts for the conversion of solar to chemical energy.

LDPE/M-TiO2 composite films for modified atmosphere packaging to realize comprehensive preservation of strawberry (Fragaria × ananassa Duch.)

BACKGROUND

A shelf-life that is too short is the main problem with strawberries. Nano-TiO₂ can catalyze and oxidize ethylene under ultraviolet (UV) light irradiation to eliminate its ripening effect on fruits and prolong the freshness period.

RESULTS

In this work, nano-TiO₂ modified by methacryloxy propyl trimethoxyl silane (KH570) was blended with low-density polyethylene (LDPE) to prepare modified atmosphere packaging (MAP), and the influence of TiO₂ content on films was analyzed before and after UV treatment. The results show that the modified nano-TiO₂ (M-TiO₂ ) can be uniformly distributed in LDPE, improving its mechanical strength, hydrophobicity, oxygen barrier and UV shielding properties. A modified atmosphere with low ethylene, low O₂ and high CO₂ can be created to inhibit the ripening and spoilage of strawberries. The weight loss rate of fruit can be effectively reduced. The tendency of fruit firmness decline and nutrient loss can be slowed and stabilized, contributing to controllable shelf-life. Excellent freshness preservation function can be realized without special UV treatment.

CONCLUSION

Since UV treatment is rare in actual storage and transportation, LDPE/M-TiO₂ composite film has practical value as MAP for strawberry and similar non-climacteric fruits. © 2022 Society of Chemical Industry.

Role of chemistry in bio-inspired liquid wettability

Chemistry and topography are the two distinct available tools for customizing different bio-inspired liquid wettability including superhydrophobicity, superamphiphobicity, underwater superoleophobicity, underwater superoleophilicity, and liquid infused slippery property. In nature, various living species possessing super and special liquid wettability inherently comprises of distinctly patterned surface topography decorated with low/high surface energy. Inspired from the topographically diverse natural species, the variation in surface topography has been the dominant approach for constructing bio-inspired antiwetting interfaces. However, recently, the modulation of chemistry has emerged as a facile route for the controlled tailoring of a wide range of bio-inspired liquid wettability. This review article aims to summarize the various reports published over the years that has elaborated the distinctive importance of both chemistry and topography in imparting and modulating various bio-inspired wettability. Moreover, this article outlines some obvious advantages of chemical modulation approach over topographical variation. For example, the strategic use of the chemical approach has allowed the facile, simultaneous, and independent tailoring of both liquid wettability and other relevant physical properties. We have also discussed the design of different antiwetting patterned and stimuli-responsive interfaces following the strategic and precise alteration of chemistry for various prospective applications.

Always-on photocatalytic antibacterial facemask with mini UV-LED array

The facemask is a device to protect yourself and others against pandemics, such as coronavirus disease 2019 (COVID-19), and adding a functional filter to the facemask could offer extra protection against infectious microbes (such as bacteria and viruses) to the wearer. Here, we designed and fabricated an always-on photocatalytic antibacterial facemask, which comprised a reusable polypropylene filter layer coated with the photocatalytic laminated ZnO/TiO₂ bilayer and a separate UV-LEDs layer to supply UV whenever necessary. The fabricated photocatalytic filter was able to be directly inserted into the reusable facemask together with the UV-LEDs layer. This facemask could be used repeatedly and sustainably anytime and anywhere regardless of solar illumination. The photocatalytic filter exhibited an excellent photocatalytic antibacterial effect likely due to recombination suppression of electrons and holes of ZnO/TiO₂ bilayer and wetting transition from hydrophilic to superhydrophilic state on the surface of the filter. Thanks to the kirigami pattern in both photocatalytic filter and UV-LEDs layer, full-face covering, breathability, flexibility, and the snug fit are believed to be improved. Although further in-depth studies are still needed and there is a long way to go, we expect our design idea on the facemask to be considered in various fields.

Wetting-regulated gas-involving (photo)electrocatalysis: biomimetics in energy conversion

(Photo)electrolysis of water or gases with water to species serving as industrial feedstocks and energy carriers, such as hydrogen, ammonia, ethylene, propanol, etc., has drawn tremendous attention. Moreover, these processes can often be driven by renewable energy under ambient conditions as a sustainable alternative to traditional high-temperature and high-pressure synthesis methods. In addition to the extensive studies on catalyst development, increasing attention has been paid to the regulation of gas transport/diffusion behaviors during gas-involving (photo)electrocatalytic reactions towards the goal of creating industrially viable catalytic systems with high reaction rates, excellent long-term stabilities and near-unity selectivities. Biomimetic surfaces and systems with special wetting capabilities and structural advantages can shed light on the future design of (photo)electrodes and address long-standing challenges. This article is dedicated to bridging the fields of wetting and catalysis by reviewing the cutting-edge design methodologies of both gas-evolving and gas-consuming (photo)electrocatalytic systems. We first introduce the fundamentals of various in-air/underwater wetting states and their corresponding bioinspired structural properties. The relationship amongst the bubble transport behavior, wettability, and porosity/tortuosity is also discussed. Next, the latest implementations of wetting-related design principles for gas-evolving reactions (i.e. the hydrogen evolution reaction and oxygen evolution reaction) and gas-consuming reactions (i.e. the oxygen reduction reaction and CO2 reduction reaction) are summarized. For photoelectrode designs, additional factors are taken into account, such as light absorption and the separation, transport and recombination of photoinduced electrons and holes. The influences of wettability and 3D structuring of (photo)electrodes on the catalytic activity, stability and selectivity are analyzed to reveal the underlying mechanisms. Finally, remaining questions and related future perspectives are outlined.

Improving Photoelectrochemical Activity of ZnO/TiO2 Core–Shell Nanostructure through Ag Nanoparticle Integration

In solar energy harvesting using solar cells and photocatalysts, the photoexcitation of electrons and holes in semiconductors is the first major step in the solar energy conversion. The lifetime of carriers, a key factor determining the energy conversion and photocatalysis efficiency, is shortened mainly by the recombination of photoexcited carriers. We prepared and tested a series of ZnO/TiO2-based heterostructures in search of designs which can extend the carrier lifetime. Time-resolved photoluminescence tests revealed that, in ZnO/TiO2 core–shell structure the carrier lifetime is extended by over 20 times comparing with the pure ZnO nanorods. The performance improved further when Ag nanoparticles were integrated at the ZnO/TiO2 interface to construct a Z-scheme structure. We utilized these samples as photoanodes in a photoelectrochemical (PEC) cell and analyzed their solar water splitting performances. Our data showed that these modifications significantly enhanced the PEC performance. Especially, under visible light, the Z-scheme structure generated a photocurrent density 100 times higher than from the original ZnO samples. These results reveal the potential of ZnO-Ag-TiO2 nanorod arrays as a long-carrier-lifetime structure for future solar energy harvesting applications.

Fabrication of ZnO and TiO2 Nanotubes via Flexible Electro-Spun Nanofibers for Photocatalytic Applications

Web-like architectures of ZnO and TiO2 nanotubes were fabricated based on a three-step process of templating polymer nanofibers produced by electrospinning (step 1). The electrospun polymer nanofibers were covered by radio-frequency magnetron sputtering with thin layers of semiconducting materials (step 2), with FESEM observations proving uniform deposits over their entire surface. ZnO or TiO2 nanotubes were obtained by subsequent calcination (step 3). XRD measurements proved that the nanotubes were of a single crystalline phase (wurtzite for ZnO and anatase for TiO2) and that no other crystalline phases appeared. No other elements were present in the composition of the nanotubes, confirmed by EDX measurements. Reflectance spectra and Tauc plots of Kubelka-Munk functions revealed that the band gaps of the nanotubes were lower than those of the bulk materials (3.05 eV for ZnO and 3.16 eV for TiO2). Photocatalytic performances for the degradation of Rhodamine B showed a large degradation efficiency, even for small quantities of nanotubes (0.5 mg/10 mL dye solution): ~55% for ZnO, and ~95% for TiO2.

Titanium Dioxide Derived Materials with Superwettability

Titanium dioxide (TiO2) is widely used in various fields both in daily life and industry owing to its excellent photoelectric properties and its induced superwettability. Over the past several decades, various methods have been reported to improve the wettability of TiO2 and plenty of practical applications have been developed. The TiO2-derived materials with different morphologies display a variety of functions including photocatalysis, self-cleaning, oil-water separation, etc. Herein, various functions and applications of TiO2 with superwettability are summarized and described in different sections. First, a brief introduction about the discovery of photoelectrodes made of TiO2 is revealed. The ultra-fast spreading behaviors on TiO2 are shown in the part of ultra-fast spreading with superwettability. The part of controllable wettability introduces the controllable wettability of TiO2-derived materials and their related applications. Recent developments of interfacial photocatalysis and photoelectrochemical reactions with TiO2 are presented in the part of interfacial photocatalysis and photoelectrochemical reactions. The part of nanochannels for ion rectification describes ion transportation in nanochannels based on TiO2-derived materials. In the final section, a brief conclusion and a future outlook based on the superwettability of TiO2 are shown.

Synthesis, Characterization and Photocatalytic Activity of MoS2/ZnSe Heterostructures for the Degradation of Levofloxacin

Antibiotics have been extensively used over the last few decades. Due to their extensive usage and persistence in the environment, they are considered as emergent pollutants. It is, therefore, important to synthesize new materials for efficient antibiotic degradation. Herein, we report the MoS2/ZnSe heterostructures prepared by a simple ultrasonication method. Heterostructures were prepared with different ratios of MoS2 and ZnSe, i.e., 1:3, 1:1 and 3:1. Characterization of the heterostructures was done by UV-vis diffused reflectance spectroscopy (UV-vis-DRS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and photoluminescence (PL) techniques to understand the morphology and surface chemistry. The results show that an efficient interface was formed to harness the visible light and degrade levofloxacin, which was monitored by gradual decreases in the UV-vis absorbance signal of levofloxacin. Among the prepared heterostructures and their pure counter parts, MoS2/ZnSe 3:1 (3:1 MZ) showed a better degradation activity of 73.2% as compared to pure MoS2 (29%) and ZnSe (17.1%) in the presence of visible light in a time span of two hours. The reusability studies showed that the catalytic performance of 3:1 MZ did not decrease significantly after three cycles. Moreover, the morphology and the crystal structure also remained unchanged.