Experimental and Theoretical Investigation of Gadolinium Oxyhydride (GdHO) Thin Films: Optical, Photocatalytic, and Electronic Properties.

Oxyhydrides of rare-earth metals (REMOHs) exhibit notable photochromic behaviors. Among these, yttrium oxyhydride (YHO) stands out for its impressive transparency and swift UV-responsive color change, positioning it as an optimal material for self-cleaning window applications. Although semiconductor photocatalysis holds potential solutions for critical environmental issues, optimizing the photocatalytic efficacy of photochromic substances has not been adequately addressed. This research advances the study of REMOHs, focusing on the properties of gadolinium oxyhydride (GdHO) both theoretically and experimentally. The electronic and structural characteristics of GdHO, vital for ceramic technology, are thoroughly examined. Explicitly determined work functions for GdH2, GdHO, and Gd2O3 stand at 3.4 eV, 3.0 eV, and 4.3 eV, respectively. Bader charge analysis showcases GdHO's intricate bonding attributes, whereas its electron localization function majorly presents an ionic nature. The charge neutrality level is situated about 0.33 eV below the top valence band, highlighting these materials' inclination for acceptor-dominant electrical conductivity. Remarkably, this research unveils GdHO films' photocatalytic capabilities for the first time. Even with their restricted surface due to thinness, these films follow the Langmuir-Hinshelwood degradation kinetics, ensuring total degradation of methylene blue in a day. It was observed that GdHO's work function diminishes with reduced deposition pressure, and UV exposure further decreases it by 0.2 eV-a change that reverts post-UV exposure. The persistent stability of GdHO films, hinting at feasible recyclability, enhances their potential efficiency, underlining their viability in practical applications. Overall, this study accentuates GdHO's pivotal role in electronics and photocatalysis, representing a landmark advancement in the domain.

Cerium oxide thin films: synthesis, characterization, photocatalytic activity and influence on microbial growth.

The resistance of surfaces to biofouling remains a significant advantage for optical devices working in natural conditions, increasing their lifetime and reducing maintenance costs. This paper reports on the functionalities of transparent CeO2 thin films with thicknesses between 25 and 600 nm deposited by reactive magnetron sputtering on the glass substrate. The CeO2 photocatalytic performance exhibited an efficiency of 30% on imidacloprid degradation under 6 h of UV radiation and increased linearly with the irradiation time, suggesting a complete degradation within 48 h. The films did not alter the growth rate of the green algae Chlorella vulgaris after 72 h short-term exposure. The tested CeO2 films proved to efficiently inhibit with high efficiency the Staphylococcus aureus biofilms and planktonic growth (reducing the counts of bacterial cells by 2 to 8 logs), demonstrating the promising potential of these materials for obtaining antimicrobial and antibiofilm surfaces, with broad applications for the biomedical, ecological and industrial fields.

UV-Vis Activated Cu2O/SnO2/WO3 Heterostructure for Photocatalytic Removal of Pesticides.

A three-steps sol-gel method was used to obtain a Cu2O/SnO2/WO3 heterostructure powder, deposited as film by spray pyrolysis. The porous morphology of the final heterostructure was constructed starting with fiber-like WO3 acting as substrate for SnO2 development. The SnO2/WO3 sample provide nucleation and grew sites for Cu2O formation. Diffraction evaluation indicated that all samples contained crystalline structures with crystallite size varying from 42.4 Å (Cu2O) to 81.8 Å (WO3). Elemental analysis confirmed that the samples were homogeneous in composition and had an oxygen excess due to the annealing treatments. Photocatalytic properties were tested in the presence of three pesticides-pirimicarb, S-metolachlor (S-MCh), and metalaxyl (MET)-chosen based on their resilience and toxicity. The photocatalytic activity of the Cu2O/SnO2/WO3 heterostructure was compared with WO3, SnO2, Cu2O, Cu2O/SnO2, Cu2O/WO3, and SnO2/WO3 samples. The results indicated that the three-component heterostructure had the highest photocatalytic efficiency toward all pesticides. The highest photocatalytic efficiency was obtained toward S-MCh (86%) using a Cu2O/SnO2/WO3 sample and the lowest correspond to MET (8.2%) removal using a Cu2O monocomponent sample. TOC analysis indicated that not all the removal efficiency could be attributed to mineralization, and by-product formation is possible. Cu2O/SnO2/WO3 is able to induce 81.3% mineralization of S-MCh, while Cu2O exhibited 5.7% mineralization of S-MCh. The three-run cyclic tests showed that Cu2O/SnO2/WO3, WO3, and SnO2/WO3 exhibited good photocatalytic stability without requiring additional procedures. The photocatalytic mechanism corresponds to a Z-scheme charge transfer based on a three-component structure, where Cu2O exhibits reduction potential responsible for O2 production and WO3 has oxidation potential responsible for HO· generation.

Visible-Light-Active Black TiO2 Nanoparticles with Efficient Photocatalytic Performance for Degradation of Pharmaceuticals.

Special attention has recently been paid to surface-defective titanium dioxide and black TiO2 with advanced optical, electrical, and photocatalytic properties. Synthesis of these materials for photodegradation and mineralization of persistent organic pollutants in water, especially under visible radiation, presents interest from scientific and application points of view. Chemical reduction by heating a TiO2 and NaBH4 mixture at 350 °C successfully introduced Ti3+ defects and oxygen vacancies at the surface of TiO2, with an increase in the photocatalytic degradation of amoxicillin-an antibiotic that is present in wastewater due to its intense use in human and animal medicine. Three TiO2 samples were prepared at different annealing temperatures to control the ratio between anatase and rutile and were subjected to chemical reduction. Electron paramagnetic resonance investigations showed that the formation of surface Ti3+ defects in a high concentration occurred mainly in the anatase sample annealed at 400 °C, contributing to the bandgap reduction from 3.32 eV to 2.92 eV. The reduced band gap enhances visible light absorption and the efficiency of photocatalysis. The nanoparticles of ~90 m2/g specific surface area and 12 nm average size exhibit ~100% efficiency in the degradation of amoxicillin under simulated solar irradiation compared with pristine TiO2. Mineralization of amoxicillin and by-products was over 75% after 48 h irradiation for the anatase sample, where the Ti3+ defects were present in a higher concentration at the catalyst's surface.

Synthesis, Characterisation, Photocatalytic Activity, and Aquatic Toxicity Evaluation of TiO2 Nanoparticles.

Imidacloprid (IMD) is a toxic pesticide, and is one of the eight most widely used pesticides globally. Heterogeneous photocatalysis has often been investigated in recent years and can be successfully applied to remove imidacloprid from water. However, less investigated is the toxic effect of both the photocatalyst and the pesticide on aquatic life. Titanium dioxide (TiO2) remains the most effective photocatalyst, provided it is not toxic to the aquatic environment. This study investigated the TiO2 synthesis, characterisation, and photocatalytic activity on imidacloprid degradation and the toxicity of TiO2 nanoparticles and imidacloprid on the green algae Chlorella vulgaris. In the photodegradation process of IMD (initial concentration of 20 mg/L), electrons play an essential role; the degradation efficiency of IMD after 6 h increased from 69 to 90% under UV irradiation when holes (h+) scavengers were added, which allowed the electrons to react with the pollutant, resulting in lowering the recombination rate of electron-hole charge carriers. Growth inhibition of Chlorella vulgaris and effective concentration (EC50) were determined to study the toxic effect of TiO2 nanoparticles and imidacloprid. The EC50 increased from 289.338 mg/L in the first 24 h to 1126.75 mg/L after 96 h Chlorella vulgaris algal age, when the toxicant was TiO2. When IMD was the aquatic toxicant, a decrease in EC50 was observed from 22.8 mg/L (24 h) to 0.00777 mg/L (120 h), suggesting a long-term high toxicity level when pesticides in low concentrations are present in an aquatic environment.

Toxicity of a Binary Mixture of TiO2 and Imidacloprid Applied to Chlorella vulgaris.

Nanoparticles have applications in various fields such as manufacturing and materials synthesis, the environment, electronics, energy harvesting, and medicine. Besides many applications of nanoparticles, further research is required for toxic environmental effect investigation. The toxic effect of titanium dioxide nanoparticles on the physiology of the green alga Chlorella vulgaris was studied with a widely used pesticide, imidacloprid (IMD). Chlorella vulgaris was exposed for 120 h in Bold's basal medium to different toxic compounds, such as (i) a high concentration of TiO2 nanoparticles, 150-2000 mg/L, usually optimised in the photocatalytic degradation of wastewater, (ii) an extremely toxic pesticide for the aquatic environment, imidacloprid, in concentrations ranging from 5 to 40 mg/L, (iii) TiO2 nanoparticles combined with imidacloprid, usually used in a photocatalytic system. The results show that the TiO2 nanoparticles and IMD inhibited Chlorella vulgaris cell growth and decreased the biovolume by approximately 80% when 2 g/L TiO2 was used, meaning that the cells devised a mechanism to cope with a potentially stressful situation; 120 h of Chlorella vulgaris exposure to 40 mg/L of IMD resulted in a 16% decreased cell diameter and a 41% decrease in cell volume relative to the control sample, associated with the toxic effect of pesticides on the cells. Our study confirms the toxicity of nanoparticles through algal growth inhibition with an effective concentration (EC50) value measured after 72 h of 388.14 mg/L for TiO2 and 13 mg/L for IMD in a single-toxic system. The EC50 of TiO2 slowly decreased from 258.42 to 311.11 mg/L when IMD from 5 to 20 mg/L was added to the binary-toxic system. The concentration of TiO2 in the binary-toxic system did not change the EC50 for IMD, and its value was 0.019 g/L. The photodegradation process of imidacloprid (range of 5-40 mg/L) was also investigated in the algal medium incubated with 150-600 mg/L of titanium dioxide.

Synergic Effect of TiO2 Filler on the Mechanical Properties of Polymer Nanocomposites.

Nanocomposites with polymer matrix offer excellent opportunities to explore new functionalities beyond those of conventional materials. TiO2, as a reinforcement agent in polymeric nanocomposites, is a viable strategy that significantly enhanced their mechanical properties. The size of the filler plays an essential role in determining the mechanical properties of the nanocomposite. A defining feature of polymer nanocomposites is that the small size of the fillers leads to an increase in the interfacial area compared to traditional composites. The interfacial area generates a significant volume fraction of interfacial polymer, with properties different from the bulk polymer even at low loadings of the nanofiller. This review aims to provide specific guidelines on the correlations between the structures of TiO2 nanocomposites with polymeric matrix and their mechanical properties. The correlations will be established and explained based on interfaces realized between the polymer matrix and inorganic filler. The paper focuses on the influence of the composition parameters (type of polymeric matrix, TiO2 filler with surface modified/unmodified, additives) and technological parameters (processing methods, temperature, time, pressure) on the mechanical strength of TiO2 nanocomposites with the polymeric matrix.

Photocatalytic Activity of S-Scheme Heterostructure for Hydrogen Production and Organic Pollutant Removal: A Mini-Review.

Finding new technologies and materials that provide real alternatives to the environmental and energy-related issues represents a key point on the future sustainability of the industrial activities and society development. The water contamination represents an important problem considering that the quantity and complexity of organic pollutant (such as dyes, pesticides, pharmaceutical active compounds, etc.) molecules can not be efficiently addressed by the traditional wastewater treatments. The use of fossil fuels presents two major disadvantages: (1) environmental pollution and (2) limited stock, which inevitably causes the energy shortage in various countries. A possible answer to the above issues is represented by the photocatalytic technology based on S-scheme heterostructures characterized by the use of light energy in order to degrade organic pollutants or to split the water molecule into its components. The present mini-review aims to outline the most recent achievements in the production and optimization of S-scheme heterostructures for photocatalytic applications. The paper focuses on the influence of heterostructure components and photocatalytic parameters (photocatalyst dosage, light spectra and intensity, irradiation time) on the pollutant removal efficiency and hydrogen evolution rate. Additionally, based on the systematic evaluation of the reported results, several perspectives regarding the future of S-scheme heterostructures were included.

Black TiO2 Synthesis by Chemical Reduction Methods for Photocatalysis Applications.

Applications of TiO2 nanomaterials in photocatalysis, batteries, supercapacitors and solar cells, have seen widespread development in recent decades. Nowadays, black TiO2 have won attention due to enhancing the solar light absorption by the formation of oxygen vacancies and Ti3+ defects, to promote the separation of photo-generated charge carriers leading to the improvement of the photocatalytic performance in H2 production and pollutants degradation. The enhanced photocatalytic activity of black TiO2 is also due to a lattice disorder on the surface and the presence of oxygen vacancies, Ti3+ ions, Ti-OH and Ti-H groups. Enhancing the optical absorption characteristics of TiO2 and change of energy level and band-gap of materials have been successfully demonstrated to improve their photocatalytic activities, especially for black TiO2 nanoparticles, which promote visible light absorption. The current review focuses on the investigation of the chemical reduction synthetic route for black TiO2 nanomaterials, and their proposed association with green applications such as photodegradation of organic pollutants and photocatalytic water splitting. The synthesis methods of black TiO2 involves the changes from Ti4+ to Ti3+ state, into different strategies: (1) The use of highly active hydrogen species such as H2, H2/Ar or H2/N2 gases, and metal hydrides (NaBH4, CaH2), (2) the reduction by active metals such as aluminum, magnesium and zinc, and (3) organic molecules such as imidazole and ascorbic acid.

The Influence of Photoactive Heterostructures on the Photocatalytic Removal of Dyes and Pharmaceutical Active Compounds: A Mini-Review.

The diversification of pollutants type and concentration in wastewater has underlined the importance of finding new alternatives to traditional treatment methods. Advanced oxidation processes (AOPs), among others, are considered as promising candidate to efficiently remove organic pollutants such as dyes or pharmaceutical active compounds (PhACs). The present minireview resumes several recent achievements on the implementation and optimization of photoactive heterostructures used as photocatalysts for dyes and PhACs removal. The paper is focused on various methods of enhancing the heterostructure photocatalytic properties by optimizing parameters such as synthesis methods, composition, crystallinity, morphology, pollutant concentration and light irradiation.

Copper Sulfide Based Heterojunctions as Photocatalysts for Dyes Photodegradation.

The presence of toxic, non-biodegradable and harmful organic pollutants in soils, wastewater, and atmosphere has become an indisputable, and global fact as a significant environmental problem. The heterogeneous photocatalysis, an advanced oxidation process (AOP) using semiconductor materials as catalysts, is a topic of great interest considering the possibility of the pollutants removal from water. The photocatalytic degradation of organic contaminants (i.e., dyes, pesticides, phenolic compounds) present in water using semiconductor materials depends on a number of parameters such as: the bandgap energy, phase composition, crystallinity, morphology and surface area of catalyst, electron-hole recombination rate, intensity of light, and adsorption capacity of the dye on the photocatalyst surface. One of the important constraints related to the catalyst photocatalytic efficiency is the fast recombination of the photogenerated electrons and holes. Therefore, various strategies have been involved in promoting the charge separation, including the development of heterojunction between two semiconductor materials, by tailoring the photocatalysts properties. This mini-review deals with the recent developments on dyes photodegradation using as catalysts various heterojunctions based on copper sulfide nanostructures, such as copper sulfide/metal oxide, copper sulfide/metal sulfide, copper sulfide/graphene, copper sulfide/organic semiconductors etc. The effects of different parameters, such as synthesis parameters, particle size, bandgap energy, surface area, and morphology on the photocatalytic activity of copper sulfide heterojunctions for dyes degradation is also highlighted.

Pilot-plant evaluation of TiO2 and TiO2-based hybrid photocatalysts for solar treatment of polluted water.

Materials with photocatalytic and adsorption properties for advanced wastewater treatment targeting reuse were studied. Making use of TiO2 as a well-known photocatalyst, Cu2S as a Vis-active semiconductor, and fly ash as a good adsorbent, dispersed mixtures/composites were prepared to remove pollutants from wastewater. X-ray diffraction, scanning electron microscopy, energy-dispersive X-Ray spectroscopy, atomic force microscopy, band gap energy, point of zero charge (pHpzc) and BET porosity were used to characterize the substrates. Phenol, imidacloprid and dichloroacetic acid were used as pollutants for photocatalytic activity of the new photocatalysts. Experiments using the new dispersed powders were carried out at laboratory scale in two solar simulators and under natural solar irradiation at the Plataforma Solar de Almería, in a Compound Parabolic Collector (CPC) for a comparative analysis of pollutants removal and mineralization efficiencies, and to identify features that could facilitate photocatalyst separation and reuse. The results show that radiation intensity significantly affects the phenol degradation rate. The composite mixture of TiO2 and fly ash is 2-3 times less active than sol-gel TiO2. Photodegradation kinetic data on the highly active TiO2 are compared for pollutants elimination. Photodegradation of dichloroacetic acid was fast and complete after 90min in the CPC, while after 150min imidacloprid and phenol removal was 90% and 56% respectively.

Fly ash-TiO2 nanocomposite material for multi-pollutants wastewater treatment.

This paper reports on the synthesis, characterization and adsorption properties of a novel nano-composite obtained using the hydrothermal method applied to a fly ash-TiO2 slurry and hexadecyltrimethyl-ammonium bromide, as surface controlling agent. The new adsorbent was investigated in terms of crystallinity (XRD), surface properties (AFM, SEM, and porosity and BET surface) and surface chemistry (EDX, FTIR). The nanocomposite's properties were sequentially tested in adsorption and photocatalysis processes applied to multi-pollutant synthetic wastewaters loaded with copper cations and two industrial dyes: the acid dye Bemacid Blau and the reactive dye Bemacid Rot; the nano-composite substrate allowed reaching high removal efficiencies, above 90%, both in adsorption and in photodegradation experiments, in optimised conditions.

Photocatalytic degradation of methylorange Using TiO2, WO3 and mixed thin films under controlled pH and H2O2.

Wastewaters resulting from textile industry sector have a different chemistry compared with most of the other wastewaters. The different dyes in excess are usually very stable and even small quantities can have a major impact to the effluent. In order to treat these wastewaters, photodegradation is a largely investigated process that can be up-scaled. Photocatalysts based on wide band gap semiconductors can be used in heterogeneous photocatalysis and mostly reported are TiO2 and WO3. Under UV irradiation they form electron-hole pairs that produce active species that can oxidize the dye molecules. The electron-hole recombination represents the main cause for low efficiencies and is limited by the use of oxidant systems like H2O2. Doctor blade technique, a reproducible, up-scalable and low cost technique was used to obtain thin films. The reference dye, used in this experiment is methylorange in solution of 0.0125 mM, corresponding to average polluted water. In order to reduce the recombination in the catalysts, H2O2 is used. Another important aspect of the dye photocatalysis process, investigated in the paper is the adsorption of the dye molecule on the photocatalyst surface, strongly depending on pH which affects the dye's structure and the surface charge. Experiments are conducted at fixed pH values: 3, and respectively 7 covering values below and over the ZPC of the photocatalysts. The results show that TiO2/WO3 films have higher efficiency then the TiO2 and WO3 films, mainly due to the surface morphology of the films. By adding H2O2, higher efficiencies are obtained, confirming that the electron-hole pair recombination is reduced. From the point of view of pH, higher efficiencies are obtained in acidic solutions and the results are comparatively discussed considering the dye's ionic/neutral structure and the photocatalyst surface charge. The efficiency was calculated using UV-VIS spectrophotometer measurements of the solution and the thin films were characterized by AFM and XRD.

Effect of TiO, nanoparticles on the interface in the PET-rubber composites.

Usually, ceramic powders (SiO2, ZnO) are used as fillers for enhancing rubber mechanical strength. Poly-ethylene terephthalate (PET)-rubber nanocomposites were prepared by compression molding using titanium oxide (TiO2) nanoparticles as low content fillers (<2% wt). The interface properties of PET-rubber nanocomposites were studied before and after keeping the samples under UV-radiation for a week. UV-radiation has interesting potential for the photochemical modification of polymers and TiO2. The influence of UV radiation on the properties of the interface polymer-TiO2 nanoparticles was evaluated. The impact of nanoparticle aggregates on the nanometer to micrometer organization of PET-rubber composites was studied with Atomic Force Microscopy (AFM). The interface properties were explained by measuring the contact angles and surface tensions. The interactions between components of nanocomposites were investigated with Fourier Transform-Infrared (FTIR) and the effects of TiO2 nanoparticle on the interfaces and composites crystalline structure were evaluated by X-ray diffraction (XRD). The results proved that the TiO2 nanoparticles, in different weight percentages, did not alter the nanocomposites crystallinity or the average crystallites size, but improve the interface properties.

Photocatalytic degradation of methyl orange: influence of H2O2 in the TiO2-based system.

The purpose of this study was to investigate the photocatalytic oxidation of a reactive azo dye. The photocatalytic activity of the TiO2 was studied using a reactor equipped with UV-A sources, with maximum emission at 365 nm. The photocatalytic activity of the TiO2 powder (99.9% anatase) and thin films has been measured through the decomposition of methyl orange solutions. The thin film was prepared by doctor blade and spray pyrolysis deposition (SPD). The TiO2 suspensions were prepared at 1 g/L concentration, and the initial methyl orange concentration was fixed at 7.8125 mg/L. The influence of the TiO2 (powder or thin films) and/or O2 and H2O2 on the photobleaching rate, was tested under different experiments, at pH = 5. Thin films (doctor blade) of TiO2 formed of mezo-sized aggregates formed of nanosized anatase crystallites show better photobleaching efficiency than thin film (SPD) due to their large internal surface. The rate is even higher in H2O2 compared to oxygen environment.