Nano-/microstructure improved photocatalytic activities of semiconductors

Design and construction of high strength double network hydrogel with flow-induced orientation

The design and construction of high strength hydrogels is a widely discussed topic in hydrogel research. In this study, we combined three toughening strategies, including dual network, oriented structure construction and nanophase doping, to develop an alginate/polyacrylamide (PAM)/modified titanium dioxide fiber (TiO2 NF@PAM) dual network composite hydrogel prepared via syringe. The effects of different preparation methods, AM/Alginate ratios, inorganic doping phases and TiO2 NF@PAM/AM ratios on the mechanical properties of composite hydrogels were investigated. The study found that the alginate hydrogel prepared by syringe exhibited superior axial orientation and achieved a tensile strength of (1091 ± 46) kPa. And the composite hydrogel doped with 0.2 wt% TiO2 NF@PAM had a tensile strength of (1006 ± 64) kPa, which was higher than that of the composite hydrogel doped with 0.2 wt% TiO2 nanoparticles (976 ± 66) kPa. The highest tensile strength (1120 ± 67) kPa and elongation at break (182 ± 8) % were achieved when the ratio of TiO2 NF@PAM/AM was 0.6 wt%. The force applied to the gel solution in the syringe affects the orientation of the polymer chains and TiO2 NF@PAM within the gel, which subsequently impacts the mechanical properties of the hydrogel. Therefore, we further investigated the mechanical properties of composite hydrogels under varying propulsion speeds, syringe diameters, and syringe lengths. It was observed that the gel solution's shear strength increased as the syringe diameter decreased. The resulting composite hydrogels were better oriented and had improved mechanical properties. The composite hydrogels' tensile strength peaked at (1117 ± 47) kPa when the syringe advance rate was between 1-7 mL/min. The mechanical properties of the hydrogels were optimal when the syringe length was 30 mm, with a maximum tensile strength of (1131 ± 67) kPa and a tensile ratio of (166 ± 5) %. This study demonstrates the viability of integrating three distinct strengthening methodologies to generate hydrogels of considerable strength. Furthermore, the Alginate/PAM/TiO2 NF@PAM composite hydrogels possess remarkable potential as adaptable, wearable sensors due to their exemplary mechanical properties, knittability, and conductivity.

Evaluation of antifungal activity of visible light-activated doped TiO2 nanoparticles

Titanium dioxide (TiO2) is a well-known material for its biomedical applications, among which its implementation as a photosensitizer in photodynamic therapy has attracted considerable interest due to its photocatalytic properties, biocompatibility, high chemical stability, and low toxicity. However, the photoactivation of TiO2 requires ultraviolet light, which may lead to cell mutation and consequently cancer. To address these challenges, recent research has focused on the incorporation of metal dopants into the TiO2 lattice to shift the band gap to lower energies by introducing allowed energy states within the band gap, thus ensuring the harnessing of visible light. This study presents the synthesis, characterization, and application of TiO2 nanoparticles (NPs) in their undoped, doped, and co-doped forms for antimicrobial photodynamic therapy (APDT) against Candida albicans. Blue light with a wavelength of 450 nm was used, with doses ranging from 20 to 60 J/cm2 and an NP concentration of 500 µg/ml. It was observed that doping TiO2 with Cu, Fe, Ag ions, and co-doping Cu:Fe into the TiO2 nanostructure enhanced the visible light photoactivity of TiO2 NPs. Experimental studies were done to investigate the effects of different ions doped into the TiO2 crystal lattice on their structural, optical, morphological, and chemical composition for APDT applications. In particular, Ag-doped TiO2 emerged as the best candidate, achieving 90-100% eradication of C. albicans.

Femtosecond Laser Combined with Hydrothermal Method to Construct Three-Dimensional Spatially Distributed Wurtzite ZnO Micro/Nanostructures to Enhance Photocatalytic Properties

Conventional approaches employing nanopowder particles or deposition photocatalytic nanofilm materials encounter challenges such as performance instability, susceptibility to detachment, and recycling complications in practical photocatalytic scenarios. In this study, a novel fabrication strategy is proposed that uses femtosecond laser direct writing of self-sourced metal to prepare a self-supporting microstructure substrate and combines the hydrothermal method to construct a three-dimensional spatially distributed metal oxide micro/nanostructure. The obtained wurtzite ZnO micro/nanostructure has excellent wetting properties while obtaining a larger specific surface area and can achieve effective adsorption of methyl orange molecules. Moreover, the tight integration of ZnO with the surface interface of the self-sourced metal microstructure substrate will facilitate efficient charge transfer. Simultaneously, it improves the efficiency of light utilization (absorption) and the number of active sites in the photocatalytic process, ultimately leading to excellent photodegradation stability. This result provides an innovative technology solution for achieving efficient semiconductor surface-interface photocatalytic performance and stability.

Advances in Semiconductor-Based Nanocomposite Photo(electro)catalysts for Nitrogen Reduction to Ammonia

Photo(electro)catalytic nitrogen fixation technology is a promising ammonia synthesis technology using clean solar and electric energy as the driving energy. Abundant nitrogen and water as raw materials uphold the principle of green and sustainable development. However, the generally low efficiency of the nitrogen reduction reaction has seriously restricted the application and development of this technology. The paper introduces the nitrogen reduction process and discusses the main challenges and differences in the current photo(electro)catalytic nitrogen fixation systems. It focuses on promoting the adsorption and activation of N2 and the resolution and diffusion of NH3 generated. In recent years, reviews of the modification strategies of semiconductor materials in light of the typical cases of nitrogen fixation have been reported in the literature. Finally, the future development trend of this field is analyzed and prospected.

Phase-Selective and Localized TiO2 Coating on Additive and Wrought Titanium by a Direct Laser Surface Modification Approach

Titanium has been the material of interest in biological implant applications due to its unique mechanical properties and biocompatibility. Their design is now growing rapidly due to the advent of additive manufacturing technology that enables the fabrication of complex and patient-customized parts. Titanium dioxides (TiO2) coatings with different phases (e.g., anatase, rutile) and morphologies have shown to be effective in enhancing osteointegration and antibacterial behavior. This enhanced antibacterial behavior stems from the photocatalytic activity generated from crystalline TiO2 coatings. Anatase has commonly been shown to be a more photocatalytic oxide phase compared to rutile despite its larger band gap. However, more recent studies have suggested that a synergistic effect leading to increased photocatalytic activity may be produced with a combination of oxides containing both anatase and rutile phases. Here, we demonstrate the selective and localized formation of TiO2 nanostructures on additive and wrought titanium parts with anatase, rutile, and mixed phases by a laser-induced transformation approach. Compared to conventional coating processes, this technique produces desired TiO2 phases simply by controlled laser irradiation of titanium parts in an oxygen environment, where needed. The effects of processing conditions such as laser power, scanning speed, laser pulse duration, frequency, and gas flow on the selective transformation were studied. The morphological and structural evolutions were investigated using various characterization techniques. This method is specifically of significant interest in creating phase-selective TiO2 surfaces on titanium-based bioimplants, including those fabricated by additive manufacturing technologies.

Femtosecond Laser Fabrication of Anatase TiO2 Micro-nanostructures with Chemical Oxidation and Annealing

The fabrication of nanoporous anatase TiO₂ on a microstructured Ti base is achieved through an innovative hybrid fabrication method involving femtosecond laser ablation coupled with H₂O₂ oxidation and annealing. The anatase TiO₂ micro-nanostructures have superior photocatalytic degradation of methyl orange due to enhanced light harvesting capacity and surface area. The photodegradation efficiency increases by a maximum of 80% compared to the nanoporous anatase TiO₂ fabricated through H₂O₂ oxidation and annealing only (without femtosecond laser ablation). Meanwhile, The anatase TiO₂ micro-nanostructures show good cyclic performance, indicating a great potential for practical application. The proposed hybrid method can easily tune the morphology and size of microstructure by simply adjusting the femtosecond laser parameters, showing advantage in fabricating of micro-nanostructures with a rich variety of morphologies.

Comparison of photocatalytic and transport properties of TiO2 and ZnO nanostructures for solar-driven water splitting

Water splitting interfacial reaction kinetics and charge transport of four TiO₂- and ZnO-based nanostructures with similar thickness are investigated.

A template-free facile approach for the synthesis of CuS–rGO nanocomposites towards enhanced photocatalytic reduction of organic contaminants and textile effluents

Copper sulfide–reduced graphene oxide nanocomposites were synthesized hydrothermally from copper nitrate and thiourea as precursor materials.