The effect of solvent in the sol–gel synthesis of visible light-activated, sulfur-doped TiO2 nanostructured porous films for water treatment

Structuring efficient photocatalysts into bespoke fiber shaped systems for applied water treatment

In this study, structured photocatalytic systems were successfully developed by a facile method based on Alginate molds and a wet-spinning/cross-linking technique, yielding commercial photocatalyst (Degussa P25) in the form of all-ceramic hollow fibers (HFs). Taking advantage of alginate's exceptional sorption properties, copper augmented HFs were also developed. The structured photocatalysts were thoroughly characterised by a variety of techniques, including nitrogen adsorption, SEM/EDS, XRD, XPS and Raman. Synthesis and heat treatment parameters were found to affect the fibers' properties, allowing their optimization. Treatment at 600 °C under Ar was found to produce the best performing photocatalysts in terms mechanical stability, resistance to attrition and photocatalytic performance. Ca-Alginate precursors led to structures with increased mechanical stability, while Cu-Alginate decorated the surface of the photocatalyst with highly dispersed copper nanoparticles, in the state of metallic and CuO. The developed materials were photo-catalytically active, while the copper decorated ceramic HFs exhibited the highest MO adsorption and photocatalytic degradation performance, reaching a MO removal of 73.4%. The synergestic effect of adsorption on the MO degradation performance was also noticed. Moreover, the copper addition facilitated the photocatalytic process by improving the electron-hole separation and inhibiting the recombination effects. The presence of carbon residue was also beneficial, enhancing the MO sorption on the photocatalysts. It is noteworthy that the structured photocatalysts retained their efficiency for at least four photocatalytic cycles. The prepared ceramic HFs exhibited enhanced mechanical properties and excellent resistance to attrition after subsequent cycles, rendering them excellent candidates for application in industrial wastewater processes.

In situ construction of sulfated TiO2 nanoparticles with TiOSO4 for enhanced photocatalytic hydrogen production

Photocatalytic hydrogen production from water is a promising method to obtain clean energy in the future. In this work, the sulfated TiO2 photocatalyst is successfully constructed in situ via a soft-templated method for photocatalytic water splitting to produce hydrogen. The content of sulfate species in TiO2 can be tuned by changing the amount of the surfactant. The photocatalyst with the appropriate content of sulfate ions exhibits an apparent quantum efficiency (AQE) of 3.9% at 365 nm and a high hydrogen production rate of 24.32 mmol h-1 g-1, which is 1.65 times that of commercial TiO2 (P25). The optimized photocatalyst has excellent photocatalytic activity for hydrogen evolution benefitting from the presence of sulfate ions on the surface of TiO2, large surface area and oxygen vacancies, which facilitates the rapid migration of photo-generated electrons to its surface and the improvement of the separation efficiency of photo-generated carriers. This work may inspire the rational design and the development of high-efficiency photocatalysts.

Photocatalytic treatment of natural waters. Reality or hype? The case of cyanotoxins remediation

This review compiles recent advances and challenges in the photocatalytic treatment of natural water by analyzing the remediation of cyanotoxins. The review frames the treatment need based on the occurrence, geographical distribution, and legislation of cyanotoxins in drinking water while highlighting the underestimated global risk of cyanotoxins. Next, the fundamental principles of photocatalytic treatment for remediating cyanotoxins and the complex degradation pathway for the most widespread cyanotoxins are presented. The state-of-the-art and recent advances on photocatalytic treatment processes are critically discussed, especially the modification strategies involving TiO₂ and the primary operational conditions that determine the scalability and integration of photocatalytic reactors. The relevance of light sources and light delivery strategies are shown, with emphasis on novel biomimicry materials design. Thereafter, the seldomly-addressed role of water-matrix components is thoroughly and critically explored by including natural organic matter and inorganic species to provide future directions in designing highly efficient strategies and scalable reactors.

Tetracycline hydrochloride degradation by heterogeneous photocatalysis using TiO2(P25) immobilized in biopolymer (chitosan) under UV irradiation

TiO₂(P25) has been widely used to treat wastewater; however, the elimination of TiO₂(P25) suspended in the treated water causes running costs and induces secondary pollution, which greatly restricts its practical applications. Consequently, several methods have been implemented to immobilize TiO₂(P25) on various substrates. This work deals with the immobilization of TiO₂(P25) in chitosan film by using the cross-linking method. The prepared catalyst was characterized using X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), UV-Vis diffuse reflectance spectra (DRS) and scanning electron microscopy (SEM), and its catalytic activity in tetracycline hydrochloride (TC) degradation under UV light was explored. XRD, FTIR, DRS and SEM characterization indicated that TiO₂(P25) was successfully immobilized on chitosan film, the chemical structure of TiO₂(P25) did not change after the immobilization and the TiO₂(P25) was uniformly dispersed in the composite. Chitosan/TiO₂(P25) was used for the removal of TC by photocatalysis under UV irradiation. The effects of operational parameters such as amount of TiO₂(P25), agitation speed and the initial TC concentration were investigated. An 87% removal efficiency of TC was obtained with 0.12 g of TiO₂(P25) and TC removal was significantly enhanced by the agitation of the solution. The TC removal efficiency decreased from 72 to 44% when TC concentration increased from 30 to 40 mg/L after 60 min reaction time, the photocatalytic reactions followed the pseudo-second-order kinetic.

A Facile and Controllable Vapor-Phase Hydrothermal Approach to Anionic S2--doped TiO2 Nanorod Arrays with Enhanced Photoelectrochemical and Photocatalytic Activity

Anionic S^2--doped TiO₂ nanorod arrays (S^2--TiO₂) were synthesized by a facile and controllable vapor-phase hydrothermal (VPH) approach based on the sulfur source of H₂S gas. After the VPH treatment of TiO₂ nanorod arrays (TNA), the isolated O^2- species replaces the S^2- ion in TiO₂ (TiO_2-xS_x). The structural, morphological, optical, compositional, photocatalytic and photoelectrochemical (PEC) properties of the obtained samples were investigated in detail. It was found that S^2--TiO₂ can enhance the separation rate of electron-hole pairs, improve the absorption of visible light, and augment the photocatalytic and photoelectrochemical properties. Anionic S^2- doping can significantly adjust the absorption cut-off wavelength (409.5-542.5 nm) and shorten the bandgap (3.05-2.29 eV) of TNA. For the degradation of methylene orange (MO) under mercury lamp light, the 0.24 At%S^2--TiO₂ (0.24S^2--TiO₂) sample exhibited the best photogradation efficiency of 73% in 180 min compared to bare TiO₂ (46%). The 0.24S^2--TiO₂ showed the highest photocurrent of 10.6 μA/cm², which was 1.73 times higher than that of bare TiO₂ (6.1μA/cm²). The results confirmed that the visible light absorption, photocurrent and photocatalytic activity optimization of TNA are closely related not only to anionic S^2--doped but also different ratios of anionic S^2--doped. It is noteworthy that the VPH approach is very promising for applications in low cost and highly efficient ion doping into nanomaterials for energy devices.

Evolution of large area TiS2-TiO2 heterostructures and S-doped TiO2 nano-sheets on titanium foils

We report a novel and facile method to synthesize sulfur-doped titanium oxide sheets and realize TiS2-TiO2 heterostructures by means of a sequential sulfurization and oxidation step in a dual-zone chemical vapor deposition furnace. The inclusion of chlorine and argon gases during the growth of such titanium-based compounds plays a critical role in the formation of desired geometries and crystalline structures. These heterostructures possess nano-whisker and nanosheet configurations, controlled by adjusting the growth parameters such as temperature, carrier gas and the sequencing between different steps of the growth. The evolution of these complex heterostructures has been investigated using Raman spectroscopy and EDS characterization. The presence of chlorine gas during the growth results in local TiS2 formation as well as faceted growth of TiO2 nanosheets through anatase to rutile phase change prohibition. The electron microscopy (TEM) images and diffraction pattern (SAED) characterization reveal the crystallinity and layered nature of grown structures, further demonstrating the 2D characteristics of S-doped nanosheets. The evolution of TiO2 on TiS2 heterostructures has also has been verified using XPS analysis. These highly featured nanostructures are suitable candidates to enhance the photocatalytic behavior of TiO2 nanostructures.

Constructing a novel three-dimensional scaffold with mesoporous TiO2 nanotubes for potential bone tissue engineering

A novel 3D porous network-structured tissue engineering scaffold built of mesoporous TiO₂ nanotubes has been synthesized via the bacterial cellulose-templated sol–gel route followed by calcination.