TiO2 photocatalysis: Design and applications

Nitrogen-containing organic compounds: Origins, toxicity and conditions of their photocatalytic mineralization over TiO2

Sustainable water management remains a global concern to meet the food needs of industrial and agricultural activities. Therefore, pollution abatement techniques, cheap and environmentally, are highly desired and recommended. The present review is devoted to the origin and the toxicity of nitrogen-containing organic compounds in water. The progress made in removing these pollutants, in recent years, is addressed. However, a prominent place is given to the photocatalytic degradation process using the TiO₂ as a semiconductor, the conditions for good mineralization and especially the factors influencing it. The parameters that impact the performance of this method are the pH, the temperature, the reactor used, the light, the concentration of the pollutant, the amount of catalyst, etc. Up to now, the importance of one parameter relative to another has not been established because in the context of the photocatalytic degradation, certain parameters are often tightly coupled. Consequently, the mineralization is dependent on the initial degree of oxidation of nitrogen atom contained in the pollutant to be degraded. The hydroxyl nitrogen is primarily converted into nitrate ions (NO₃^-), while the amides and the primary amines are converted into ammonium ions (NH₄⁺).

Kinetics and degradation pathways of photolytic and photocatalytic oxidation of the anthelmintic drug praziquantel

In this study, an anthelmintic drug, praziquantel(PZQ), was degraded using the direct photolysis, photocatalysis, and oxidation processes including UV radiation, TiO₂ film, and hydrogen peroxide. The photolytic degradation with predominant wavelengths of 185/254nm (UV-C) proved to be more efficient with a half-life of 3.13min compared to the radiation of 365nm (UV-A) where the degradation did not occur. In order to enhance the rate of PZQ photolytic degradation, H₂O₂ was added, which resulted in two to three times higher degradation rates. In the photocatalytic degradation, TiO₂ film was used as catalyst. The degradation was ten times faster in the photocatalytic experiments where UV-C light (k=0.2390min^-1) was used than in those with UV-A (k=0.0201min^-1). Comparing the results from all performed experiments it can be concluded that the UV-C/TiO₂/H₂O₂ process yielded the highest degradation rate and complete degradation of PZQ was obtained in less than 7min. The degradation of PZQ followed the first order kinetics in all the experiments. The photo degradation was inhibited in the presence of methanol. The degradation pathways and the structural formulae of five degradation products (m/z 273, 269, 189, 147, 132) were proposed based on the liquid chromatography tandem mass spectrometry analysis.

Inhibitory effect of TiO2 NPs on symbiotic arbuscular mycorrhizal fungi in plant roots

While nanoparticles (NPs) are known to exhibit antimicrobial properties, their effects on symbiotic arbuscular mycorrhizal fungi (AMF) in plant roots has to be carefully examined as NPs particularly of titanium dioxide (TiO2) reach plant roots through varied sources such as fertilisers, plant protection products and other nanoproducts. The objective of the present study is to assess the effect of TiO2 NPs on the symbiotic behaviour of AMF colonising rice (Oryza sativa L.) plants. Using sol-gel method, TiO2 NPs with three different sizes were successfully synthesised employing doping. Characterisation of the prepared material was done by X-ray powder diffraction and scanning electron microscopy. The synthesised materials were applied at 0, 25, 50 and 100 mg plant-1 to the rhizosphere of mycorrhizal rice plants maintained in pots. The study revealed that the prepared NPs had an inhibitory effect on arbuscular mycorrhizal symbiosis in plant roots. Development of AMF structures such as vesicles and arbuscules was significantly reduced in TiO2-doped NPs with a relatively more inhibition in 2% TiO2-doped NPs. Among the concentrations of TiO2 NPs applied to different treatments, %F was significantly (P < 0.001) affected at medium to higher levels of application.

Photocatalysis applications of some hybrid polymeric composites incorporating TiO2 nanoparticles and their combinations with SiO2/Fe2O3

Polymer nanocomposites containing titanium oxide nanoparticles (TiO₂ NPs) combined with other inorganic components (Si-O-Si or/and γ-Fe₂O₃) were prepared by the dispersion of premade NPs (nanocrystalline TiO₂, TiO₂/SiO₂, TiO₂/Fe₂O₃, TiO₂/SiO₂/Fe₂O₃) within a photopolymerizable urethane dimethacrylate (polytetrahydrofuran-urethane dimethacrylate, PTHF-UDMA). The physicochemical characterization of nanoparticles and hybrid polymeric composites with 10 wt % NPs (S1-S4) was realized through XRD, TEM and FTIR analyses. The mean size (10-30 nm) and the crystallinity of the NPs varied as a function of the inorganic constituent. The catalytic activity of these hybrid films was tested for the photodegradation of phenol, hydroquinone and dopamine in aqueous solution under UV or visible-light irradiation. The best results were obtained for the films with TiO₂/Fe₂O₃ or TiO₂/SiO₂/Fe₂O₃ NPs. The degradation of the mentioned model pollutants varied between 71% and 100% (after 250 min of irradiation) depending on the composition of the hybrid film tested and the light applied (UV-visible light). Also, it was established that such hybrid films can be reused at least for five cycles, without losing too much of the photocatalytic efficiency (ca. 7%). These findings could have implications in the development of new nanocatalysts.

Combined quartz crystal microbalance with dissipation (QCM-D) and generalized ellipsometry (GE) to characterize the deposition of titanium dioxide nanoparticles on model rough surfaces

Measuring the interactions between engineered nanoparticles and natural substrates (e.g. soils and sediments) has been very challenging due to highly heterogeneous and rough natural surfaces. In this study, three-dimensional nanostructured slanted columnar thin films (SCTFs), with well-defined roughness height and spacing, have been used to mimic surface roughness. Interactions between titanium dioxide nanoparticles (TiO₂NP), the most extensively manufactured engineered nanomaterials, and SCTF coated surfaces were measured using a quartz crystal microbalance with dissipation monitoring (QCM-D). In parallel, in-situ generalized ellipsometry (GE) was coupled with QCM-D to simultaneously measure the amount of TiO₂NP deposited on the surface of SCTF. While GE is insensitive to effects of mechanical water entrapment variations in roughness spaces, we found that the viscoelastic model, a typical QCM-D model analysis approach, overestimates the mass of deposited TiO₂NP. This overestimation arises from overlaid frequency changes caused by particle deposition as well as additional water entrapment and partial water displacement upon nanoparticle adsorption. Here, we demonstrate a new approach to model QCM-D data, accounting for both viscoelastic effects and the effects of roughness-retained water. Finally, the porosity of attached TiO₂NP layer was determined by coupling the areal mass density determined by QCM-D and independent GE measurements.

Jointed toxicity of TiO2 NPs and Cd to rice seedlings: NPs alleviated Cd toxicity and Cd promoted NPs uptake

Previous studies have reported that nanoparticles (NPs) and heavy metals are toxic to the environment. However, the jointed toxicity is not yet well understood. This study was aimed to investigate the combined toxicity of TiO₂ NPs and the heavy metal cadmium (Cd) to plants. Rice (Oryzasativa L.) was selected as the target plant. The rice seedlings were randomly separated into 12 groups and treated with CdCl₂ (0, 10 and 20 mg/L) and TiO₂ NPs (0, 10, 100 and 1000 mg/L). The plant height, biomass and root length indicated significant toxicity of Cd to the growth, but TiO₂ NPs exhibited the potential ability to alleviate the Cd toxicity. Transmission electron microscopy (TEM) and energy dispersive spectrometer (EDS) confirmed the existence of TiO₂ NPs in plants. Elemental analysis of Ti and Cd suggested that the presences of Cd significantly decreased the Ti accumulation in the rice roots in the co-exposure treatments. Interestingly, TiO₂ NPs could lower the Cd uptake and distribution in rice roots and leaves. The results of antioxidant enzyme activity, lipid peroxide as well as phytohormones varied in the different treatments. Comparing with the Cd alone treatment, the net photosynthetic rate and chlorophyll content were significantly increased in the co-exposure treatments, suggesting that TiO₂ NPs could tremendously reduce the Cd toxicity.

Novel β-Ag2MoO4/g-C3N4 heterojunction catalysts with highly enhanced visible-light-driven photocatalytic activity

The kernel of photocatalysis research is the development of catalysts with remarkable photocatalytic activity.

Highly efficient photocatalytic degradation of methylene blue by P2ABSA-modified TiO2 nanocomposite due to the photosensitization synergetic effect of TiO2 and P2ABSA

A photocatalytic activity enhanced mechanism accounting for the photosensitization synergetic effect is proposed, with MB degradation pathways including chromophoric and auxochrome group degradation.

TiO2-coated window for facilitated gas evolution in PEC solar water splitting

TiO₂ films were prepared for facilitating the evolved gas bubbles to slip over the front window of PEC cells resulting in a transparency improvement of up to 10%.

Effect of post-heat treatment on the photocatalytic activity of titanium dioxide nanowire membranes deposited on a Ti substrate

Titanium dioxide nanowire membranes have been synthesized by a hydrothermal growth on the surfaces of Ti substrates in a 12 M NaOH aqueous solution at 160 °C for 24 h, followed by ion-exchange with 0.5 M HCl aqueous solution and subsequent heat treatment.

Hybrid metal–Cu2S nanostructures as efficient co-catalysts for photocatalytic hydrogen generation

Unique colloidal synthesis of monodispersed dumbbell shaped metal–Cu₂S (M–Cu₂S where M = Pt, FePt) HNs and their utilization in hydrogen production.

Over two-orders of magnitude enhancement of the photocatalytic hydrogen evolution activity of carbon nitride via mediator-free decoration with gold-organic microspheres

A Pt and mediator free route was developed to achieve binary sized AuNPs in g-C₃N₄for enhanced photocatalytic hydrogen generation.

UV and visible light synergetic photodegradation using rutile TiO2 nanorod arrays based on a p–n Junction

The enhanced photocatalytic performance of a TiO₂-based multi-junction device is ascribed to a photovoltage generated in the junction, promoting the carriers separation.

Highly enhanced photocatalytic activity of WO3 thin films loaded with Pt–Ag bimetallic alloy nanoparticles

This study provides a novel approach to design efficient WO₃ photocatalysts decorated by bimetallic Pt–Ag alloy nanoparticles.

Bifunctional property of Pt nanoparticles deposited on TiO2 for the photocatalytic sp3C–sp3C cross-coupling reactions between THF and alkanes

Photocatalytic direct cross-coupling between THF and alkanes was accelerated by Pt nanoparticles on TiO₂, as a receiver for photoexcited electron and a metal catalyst.

Synergistic piezophotocatalytic and photoelectrochemical performance of poly(vinylidene fluoride)–ZnSnO3 and poly(methyl methacrylate)–ZnSnO3 nanocomposites

This study investigated the piezophotocatalytic and photoelectrochemical (PEC) properties of poly(vinylidene fluoride) (PVDF)– and poly(methyl methacrylate) (PMMA)–ZnSnO₃ (ZTO) nanocomposites.

Ag2S quantum dots in situ coupled to hexagonal SnS2 with enhanced photocatalytic activity for MO and Cr(vi) removal

A highly efficient visible-light-driven composite photocatalyst of Ag₂S quantum dots coupled to hexagonal SnS₂ exhibited considerably increased photocatalytic activity for MO and Cr(vi) removal.

Hollow Sr/Rh-codoped TiO2 photocatalyst for efficient sunlight-driven organic compound degradation

Sunlight-driven photocatalysis has emerged as a potential technology to address organic pollutant issues.

Heterostructured TiO2@OC core@shell photocatalysts for highly efficient waste water treatment

Facile, scalable and cost-effective organic layer coating of TiO₂ particles greatly enhances the photocatalytic degradation of dye molecules.

Insights into TiO2 polymorphs: highly selective synthesis, phase transition, and their polymorph-dependent properties

Herein we report the selective synthesis and two kinds of phase transformation of TiO₂ polymorphs under hydrothermal conditions.

Monoclinic Ga2O3 (100) surface as a robust photocatalyst for water-splitting

The β-Ga₂O₃ (100) surface, with or without defects, as a robust photocatalyst for water decomposition was studied on the basis of density functional theory (DFT).

Studies on photodegradation process of psychotropic drugs: a review

Consumption of psychotropic drugs is still increasing, especially in high-income countries. One of the most crucial consequences of this fact is significant release of them to the environment. Considerable amounts of atypical antipsychotics, benzodiazepines, antidepressants, and their metabolites were detected in river, lake, and sea water, as well as in tissues of aquatic organisms. Their ecotoxicity was proved by numerous studies. It should be noticed that interaction between psychotropic pharmaceuticals and radiation may lead to formation of potentially more toxic intermediates. On the other hand, photo-assisted wastewater treatment methods can be used as an efficient way to eliminate them from the environment. Many methods based on photolysis and photocatalysis were proposed and developed recently; nevertheless, the problem is still unsolved. However, according to recent studies, photocatalysis could be considered as the most promising and far more effective than regular photolysis. An overview on photolytic as well as homogenous and heterogeneous photocatalytic degradation methods with the use of various catalysts is presented. The photostability and phototoxicity of pharmaceuticals were also discussed. Various analytical methods were used for the photodegradation research, and this issue was also compared and summarized. Use of high-resolution multistage mass spectrometry (Q-TOF, ion trap, Orbitrap) was suggested. The combined techniques such as LC-MS, GC-MS, and LC-NMR, which enable qualitative and quantitative analyses in one run, proved to be the most valuable in this case. Assembling of MS/MS spectra libraries of drug molecules and their phototransformation products was identified as the future challenge.

A novel composite of W18O49 nanorods on reduced graphene oxide sheets based on in situ synthesis and catalytic performance for oxygen reduction reaction

A novel composite catalyst based on in situ synthesis of W₁₈O₄₉ nanorods on reduced graphene oxide sheets was successfully fabricated through a one-pot solvothermal route.

Tuning the surface structure and conductivity of niobium-doped rutile TiO2 single crystals via thermal reduction

We report on the systematic exploration of electronic and structural changes of Nb-doped rutile TiO₂(110) single crystal surfaces due to the thermoreduction under ultra-high vacuum conditions (without sputtering), with comparison to undoped TiO₂(110) crystals.

Interfacial effects of MnOx-loaded TiO2 with exposed {001} facets and its catalytic activity for the photoreduction of CO2

The percentage of the exposed facets affect the interface connection between the semiconductor and the cocatalysts, leading to different separation rates of carriers.

Design of gold nanoparticles-decorated SiO2@TiO2 core/shell nanostructures for visible light-activated photocatalysis

In this study, we designed core/shell nanostructures (CSNs) of silicon dioxide (SiO₂)/titanium dioxide (TiO₂), which were decorated with gold (Au) nanoparticles (NPs), to activate the visible light-driven photocatalytic reaction.

Synthesis and Characterization of Ag-Modified V2O5Photocatalytic Materials

V2O5powders modified with different theoretical silver contents (1, 5, 10, 15, and 20 wt% as Ag2O) were obtained with acicular morphologies observed by scanning electron microscopy (SEM). Shcherbinaite crystalline phase is transformed into the Ag0.33V2O5crystalline one with the incorporation and increase in silver content as was suggested by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis. With further increase in silver contents the Ag2O phase appears. Catalysts were active in photocatalytic degradation of malachite green dye under simulated solar light, which is one of the most remarkable facts of this work. It was found that V2O5-20Ag was the most active catalytic formulation and its activity was attributed to the mixture of coupled semiconductors that promotes the slight decrease in the rate of the electron-hole pair recombination.

Preparation of Cu(ii) porphyrin–TiO2 composite in one-pot method and research on photocatalytic property

A promising strategy for porphyrin–TiO₂ photocatalyst preparation by using sol–gel process and solvothermal condition showed prospective utilization in the field of dye pollutant photodegradation.

Ultra-high aspect ratio functional nanoporous silicon via nucleated catalysts

Large scale, sub-10 nm high aspect ratio nanoporous silicon is fabricatedviascalable sputtering and a solution-based process.

Novel synthesis of magnetic, porous C/ZnFe2O4 photocatalyst with enhanced activity under visible light based on the Fenton-like reaction

Magnetic, porous C/ZnFe₂O₄ with highly visible-light activity in presence of H₂O₂ was one-pot fabricated through CO₂-mediated route.

Effects of annealing atmosphere and rGO concentration on the optical properties and enhanced photocatalytic performance of SnSe/rGO nanocomposites

The photocatalytic properties of SnSe nanostructures (NSs) and SnSe/graphene nanocomposites with different graphene concentrations (5, 10, and 15 wt%/v) were investigated.

Influence of titanium dioxide modification on the antibacterial properties

Antibacterial properties of 15 titania photocatalysts, mono- and dual-modified with nitrogen and carbon were examined. Amorphous TiO2, supplied by Azoty Group Chemical Factory Police S.A., was used as titania source (Ar-TiO2, C-TiO2, N-TiO2 and N,C-TiO2 calcined at 300°C, 400°C, 500°C, 600°C, 700°C). The disinfection ability was examined against Escherichia coli K12 under irradiation with UV and artificial sunlight and in dark conditions. It has been found the development of new photocatalysts with enhanced interaction ability with microorganisms might be a useful strategy to improve disinfection method conducted under artificial sunlight irradiation. The efficiency of disinfection process conducted under artificial sunlight irradiation with carbon (C-TiO2) and carbon/nitrogen (N,C-TiO2) photocatalysts was similar as obtained under UV irradiation. Furthermore, during dark incubation, any toxicity of the photocatalyst was noted.

Light-Responsive Polymer Micro- and Nano-Capsules

A significant amount of academic and industrial research efforts are devoted to the encapsulation of active substances within micro- or nanocarriers. The ultimate goal of core–shell systems is the protection of the encapsulated substance from the environment, and its controlled and targeted release. This can be accomplished by employing “stimuli-responsive” materials as constituents of the capsule shell. Among a wide range of factors that induce the release of the core material, we focus herein on the light stimulus. In polymers, this feature can be achieved introducing a photo-sensitive segment, whose activation leads to either rupture or modification of the diffusive properties of the capsule shell, allowing the delivery of the encapsulated material. Micro- and nano-encapsulation techniques are constantly spreading towards wider application fields, and many different active molecules have been encapsulated, such as additives for food-packaging, pesticides, dyes, pharmaceutics, fragrances and flavors or cosmetics. Herein, a review on the latest and most challenging polymer-based micro- and nano-sized hollow carriers exhibiting a light-responsive release behavior is presented. A special focus is put on systems activated by wavelengths less harmful for living organisms (mainly in the ultraviolet, visible and infrared range), as well as on different preparation techniques, namely liposomes, self-assembly, layer-by-layer, and interfacial polymerization.