The influence of crystallite size and crystallinity of anatase nanoparticles on the photo-degradation of phenol

Accelerated mineralization of textile wastewater under 222 nm irradiation from Kr/Cl2 excilamp: an environmentally friendly and energy efficient approach

The textile dyeing and manufacturing industry is the major producer of significant amounts of wastewater that contain persistent substances such as azo dyes that require adequate remediation measures. Far ultraviolet at 222 nm light may provide an advantage for contaminants degradation as compared to conventional UV sources (254 nm). In this paper, the degradation of reactive black 5 (RB5) in artificial wastewater has been performed using a 222 nm Kr/Cl2 excimer source under direct photolysis and an advanced oxidation process using TiO2/H2O2. The solution pH, catalyst concentration, 222 nm intensity, initial concentration of dye, and addition of H2O2 influence the degradation rate constant. The molar absorption coefficient, quantum yield of RB5 at 222 nm and the electrical energy per order (EEO) from different treatment methods have been reported. RB5 shows 1.26 times higher molar absorption at 222 nm than at 254 nm. The EEO for excimer-222/H2O2 ( ∼ 13 kWh/m3) is five times lower than that of the excimer-222/TiO2 process, which makes the process energy efficient. The degradation of wastewater has been carried out at three distinct pH values (2, 6, and 10), and the pH level of 10 exhibited the highest degree of degradation. The degradation rate in the alkaline medium is 8.27 and 2.05 times higher than in the acidic or ambient medium. Since textile effluent is highly alkaline, this result is significant, as no neutralization of the wastewater is required, and direct treatment is possible. A possible degradation pathway has been established based on Fourier transform infrared spectroscopy (FTIR) and high resolution mass spectroscopy (HRMS) analysis. The phytotoxicity of the treated wastewater has also been evaluated for its suitability for reuse in agriculture. The study reveals that the excimer-222/H2O2 treated wastewater significantly enhanced the germination percentage of Raphanus sativus seed (97%) compared to dye wastewater-grown seeds (75%). This work offers crucial information for future studies on the direct and indirect photolysis of azo dyes, as well as insight into the process of RB5 degradation under Kr/Cl2 excimer radiation.

Environmentally Friendly UV-C Excimer Light Source with Advanced Oxidation Process for Rapid Mineralization of Azo Dye in Wastewater

Wastewater discharged from the textile industry contains approximately 15% unfixed dyes, predominantly 60-70% azo dyes. These unfixed dyes are a major environmental concern due to their persistence and potential toxicity. In this paper, an environmentally friendly mercury-free XeI* excilamp emitting 253 nm UV light is reported, and the same has been utilized for the degradation of azo dyes using the advanced oxidation process (AOP) with TiO2/H2O2. A new process is developed in which one electrode of excilamp is coated with TiO2 nanoparticles that improves the efficiency of the dye degradation. Additionally, the effects of varying TiO2 loading concentrations, XeI*-excimer light intensity, starting dye concentration, suspension pH, and H2O2 addition are examined. The outcomes of this study confirm 13 times faster degradation in XeI*-excimer/H2O2 than in XeI*-excimer/TiO2, attributed to an abundance of hydroxyl radicals generated by the modified XeI*-excimer/H2O2. Also, the degradation of RB5 in the modified XeI*-excimer/H2O2 is 2.3 times faster as compared to that of the bare electrode XeI*-excimer/H2O2. A more than 95% reduction in chemical oxygen demand has been achieved in 40 min in the case of XeI*-excimer/H2O2. In this study, a maximum energy yield of 5712 mg/kWh is reported. Furthermore, a high degree of degradation is found in the alkaline medium (pH 10). Because textile effluent is highly alkaline, this result is significant, and direct treatment of azo dyes is possible. The use of the developed source in industrial applications appears to be highly promising based on testing on a real wastewater matrix. The treated effluent has been utilized to study its reusability for agricultural purposes on the germination of radish seeds in soil, and ∼26% enhanced germination has been observed compared to dye wastewater.

Copper Modulated Lead-Free Cs4 MnSb2 Cl12 Double Perovskite Microcrystals for Photocatalytic Reduction of CO2

In order to deal with the global energy crisis and environmental problems, reducing carbon dioxide through artificial photosynthesis has become a hot topic. Lead halide perovskite is attracted people's attention because of its excellent photoelectric properties, but the toxicity and long-term instability prompt people to search for new photocatalysts. Herein, a series of <111> inorganic double perovskites Cs4 Mn1-x Cux Sb2 Cl12 microcrystals (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) are synthesized and characterized. Among them, Cs4 Mn0.7 Cu0.3 Sb2 Cl12 microcrystals have the best photocatalytic performance, and the yields of CO and CH4 are 503.86 and 68.35 µmol g-1 , respectively, after 3 h irradiation, which are the highest among pure phase perovskites reported so far. In addition, in situ Fourier transform infrared (FT-IR) spectroscopy and electron spin resonance (ESR) spectroscopy are used to explore the mechanism of the photocatalytic reaction. The results highlight the potential of this class of materials for photocatalytic reduction reactions.

Novel GdTaO4 phase for efficient photocatalytic degradation of organic dye under visible light irradiation: An X-ray spectroscopic investigation

The novel GdTaO4 phase exhibits good photocatalytic activity under visible light irradiation and holds great promise for the removal of organic dyes from industrial wastes. The GdTaO4 samples were synthesized using the hydrothermal and calcination process with different weight ratios of gadolinium nitrate hydrate (G) and tantalum pentachloride (T), and their structural studies confirmed the formation of the GdTaO4 (GT) phase. Among the samples, GT-4 (with a weight ratio of 4:1) exhibited the highest photocatalytic activity for the degradation of Methyl Orange (MO) dye under visible light irradiation. To enhance the photocatalytic performance, H2O2 was used as a green additive, and the photocatalytic abilities were examined by varying dye types and concentrations. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) revealed the local atomic and electronic structures around Ta and Gd and highlighted the contribution of Gd3+ to the GT system, which is a crucial factor in supporting the enhanced photocatalytic performance. Moreover, in-situ XAS at Gd M5-edge and O K-edge were examined under illumination/dark conditions to explore the electronic structures of photo-excited electron transition in the photocatalytic process. The analytical results provided strong evidence correlating the electronic structure and photocatalytic property of the GT. This study demonstrates that GdTaO4 exhibits good photocatalytic activity under visible light irradiation, making it a promising new Ta-based photocatalyst for the effective removal of organic dyes from industrial wastes.

Improvement of the photocatalytic activity of ZnO thin films doped with manganese

In the herein report, we synthesized ZnO thin films doped with manganese (Mn). We studied the impact of Mn doping loads (1 %, 3 %, 5 % wt.) on physicochemical properties of the compounds. Furthermore, we presented the photocatalytic efficiency in removal of methylene blue dye. The structural assay indicated ZnO conserve the wurtzite crystalline structure after dopant insertion. Furthermore, the crystalline size of catalysts was reduced after dopant incorporation. The SEM analysis showed a change in surface morphology after modification of ZnO thin films. Furthermore, Raman spectroscopy verified the Mn insertion inside the ZnO lattice. After the doping process, band gap was reduced by 16 %, in comparison to bare ZnO. After the photocatalytic test, the doped catalysts showed better performance than bare ZnO in removing MB. The best test showed a kinetics constant value of 2.9 × 10-3 min-1 after 120 min of visible irradiation. Finally, the Mn(5 %):ZnO thin film was suitable after five degradation cycles, and the degradation process efficiency was reduced by 32%.

Bismuth Tungstate Nanoplates-Vis Responsive Photocatalyst for Water Oxidation

The development of visible-light-responsive (VLR) semiconductor materials for effective water oxidation is significant for a sustainable and better future. Among various candidates, bismuth tungstate (Bi2WO6; BWO) has attracted extensive attention because of many advantages, including efficient light-absorption ability, appropriate redox properties (for O2 generation), adjustable morphology, low cost, and profitable chemical and optical characteristics. Accordingly, a facile solvothermal method has been proposed in this study to synthesize two-dimensional (2D) BWO nanoplates after considering the optimal preparation conditions (solvothermal reaction time: 10-40 h). To find the key factors of photocatalytic performance, various methods and techniques were used for samples' characterization, including XRD, FE-SEM, STEM, TEM, HRTEM, BET-specific surface area measurements, UV/vis DRS, and PL spectroscopy, and photocatalytic activity was examined for water oxidation under UV and/or visible-light (vis) irradiation. Famous commercial photocatalyst-P25 was used as a reference sample. It was found that BWO crystals grew anisotropically along the {001} basal plane to form nanoplates, and all properties were controlled simultaneously by tuning the synthesis time. Interestingly, the most active sample (under both UV and vis), prepared during the 30 h solvothermal reaction at 433 K (BWO-30), was characterized by the smallest specific surface area and the largest crystals. Accordingly, it is proposed that improved crystallinity (which hindered charge carriers' recombination, as confirmed by PL), efficient photoabsorption (using the smallest bandgap), and 2D mesoporous structure are responsible for the best photocatalytic performance of the BWO-30 sample. This report shows for the first time that 2D mesoporous BWO nanoplates might be successfully prepared through a facile template-free solvothermal approach. All the above-mentioned advantages suggest that nanostructured BWO is a prospective candidate for photocatalytic applications under natural solar irradiation.

Fabrication of ordered layered SnO2/TiO2 heterostructures and their photocatalytic performance for methyl blue degradation

The rapid growth in population and industrialization has given rise to serious environmental issues, especially the water pollution. Photocatalysis with the assist of semiconductor photocatalysts has been considered as an advanced oxidation technique for degrading a variety of pollutants under solar irradiation. In this work, we have fabricated SnO2-TiO2 heterostructures with different ordered layers of SnO2 and TiO2 via the sol-gel dip-coating technique and utilized in photocatalysis for degradation of methyl blue dye under UV irradiation. The influence of the layer's position on SnO2 and TiO2 properties is investigated via the various techniques. The grazing incidence X-ray diffraction (GIXRD) analysis reveals that the as-prepared films exhibit pure anatase TiO2 and kesterite SnO2 phases. The 2SnO2/2TiO2 heterostructure exhibit the maximum crystallite size and smallest deviation from the ideal structure. Scanning electron microscopy cross-section images manifest good adhesion of the layers to each other and to the substrate. Fourier transform infrared spectroscopy reveals the characteristic vibration modes of SnO2 and TiO2 phases. UV-visible spectroscopy measurements indicate that all films exhibit high transparency (T = 80%) and the SnO2 film reveals a direct band gap of 3.6 eV, while the TiO2 film exhibits an indirect band gap of 2.9 eV. The optimal 2SnO2/2TiO2 heterostructure film revealed best photocatalytic degradation performance and the reaction rate constant for methylene blue solution under UV irradiation. This work will trigger the development of highly efficient heterostructure photocatalysts for environmental remediation.

Nd-Doped ZnO Nanostructures with Enhanced Photocatalytic Performance for Environmental Protection

Neodymium (Nd)-doped ZnO nanostructures with different amounts of Nd were obtained by the electrospinning-calcination method. X-ray diffraction measurements indicated that the prepared nanostructures have a wurtzite structure without undesirable impurities. Nd doping changes the mean crystallite size as well the lattice strain, as proved by Williamson-Hall plots. The ZnO-based nanostructures were tested as photocatalysts for methylene blue (MB) dye and ciprofloxacin (CIP) drug pollutant degradations under visible light irradiation. Corroborating the obtained results, it was found that the reaction rate constant increased almost linearly with the mean crystallite size (from 2.235 × 10^-2 to 3.482 × 10^-2 min^-1) with a variation in the mean crystallite size from 24.2 to 42.1 nm. Furthermore, the best catalyst sample (0.1% Nd-doped ZnO) was used to optimize the photodegradation process of ciprofloxacin, taking into account the pollutant concentration as well as the catalyst dose. The removal efficiency after 120 min was about 100%, with the rate constant of k = 5.291·10^-2 min^-1 (CIP) and k = 4.780·10^-2 min^-1 (MB) for the established optimal conditions. Considering the value of the rate constant, the half-life of the reaction (τ_1/2 = ln2/k) was evaluated to be about τ_1/2 =13 min for CIP and 14.5 min corresponding to MB. Several catalytic cycles were successfully performed without any loss of photocatalytic activity using these nanostructures, demonstrating that the obtained nanostructures have good stability in the leaching processes.

Photocatalytic Performances and Antifouling Efficacies of Alternative Marine Coatings Derived from Polymer/Metal Oxides (WO3@TiO2)-Based Composites

This work concerns development of alternative antifouling paints for marine applications using composite metal oxides derived from TiO2 and WO3. Composite metal oxides with a variety of tungsten content were prepared via a sol–gel process using titanium isopropoxide and sodium tungstate dihydrate as the precursors. The crystalline phase, bandgap energy, morphology, surface structure, and electronic states of the synthesized products were then characterized and confirmed by XPS, XRD, UV/Vis spectroscopy, SEM-EDX, and TEM techniques. Photocatalytic performance polymer film loaded with composite metal oxides containing 10% by mole of WO3 (10%WO3@TiO2) was confirmed both under UV irradiation and in the dark. The results are discussed in light of oxygen vacancies and the presence of heterojunctions between the TiO2 and WO3 domains in the composites, which eventually lead to suppression of charges recombination. Finally, antifouling and the antimicrobial efficacy of the polymer film loaded with composite metal oxide particles (10%WO3@TiO2) were evaluated under static marine immersion conditions using Zobell Marine agar. After 30 days, the percentage fouling coverage (16.35%), colonies number (CFU value 12 × 103), and percentage reduction of colonies (92.94%), were obtained, which significantly outperformed those of the control (the bare substrate).

Photocatalytic activity of P-doped TiO2 photocatalyst

In this study, P-doped TiO₂ photocatalysts with different molar percentages (in the range 0.071-1.25 mol %) of the non-metallic element were prepared and their photocatalytic activity under visible light irradiation was tested. All achieved samples were characterized by XRD, Raman, UV-Vis DRS and SEM-EDX techniques. XRD and Raman analysis showed that all doped photocatalysts were in anatase phase and evidenced that P ions were successfully incorporated into the TiO₂ crystal lattice, affecting also the crystallinity degree of the P-doped TiO₂ photocatalysts. Noticeably, the UV-Vis DRS spectra evidenced that the highest redshift in absorption edge was observed for the photocatalyst with the lowest P content (0.071PT), which showed also the lowest bandgap (2.9 eV). The photocatalytic performances of all P-doped TiO₂ samples were compared with that of commercial TiO₂ by evaluating the decolorization of methylene blue (MB) dye under visible light irradiation. Results showed that phosphorus doping strongly promoted photocatalytic activity in the presence of visible light. Furthermore, the most active photocatalyst in visible light tests (0.071PT) also showed better photocatalytic activity than commercial TiO₂ in the decolorization of MB under simulated sunlight irradiation. Finally, 0.071PT photocatalyst was preliminarily tested against Escherichia coli (E. coli) under simulated solar light, showing an inactivation efficiency of 90% after 2 h of treatment time.

Phytochemical-assisted Synthesis of Titania Nanoparticles using Azadirachta indica Leaf Extract as Photocatalyst in the Photodegradation of Methyl Orange

The biosynthesis procedure for nanomaterial preparation is a promising alternative due to its simplicity and environmental friendliness. In this work, TiO2 NPs were biosynthesized using the aqueous leaf extract of Azadirachta indica. The influence of the extract volumes, solvents, and acetic acid on the properties of TiO2 NPs was studied. Phytochemical screening and ATR-FTIR spectrum confirmed the presence of phenolic compounds in the leaf extract. XRD patterns showed that the samples were mainly in the anatase phase. However, for the water-based samples and when 1 and 2 mL of extract volumes were used, anatase/brookite mixture was observed. FESEM images displayed almost spherical and agglomerated NPs. UV-Vis-NIR studies showed that the samples’ bandgaps values are within the range of anatase TiO2. The photocatalytic activity of the TiO2 NPs was evaluated in the photodegradation of methyl orange (MO) under UV light irradiation. The water-based sample synthesized using 2 mL of the extract achieved 98.62% of MO degradation within 270 min and demonstrated the highest pseudo-first-order photodegradation kinetic constant of 0.0147 min-1. These results indicate that the use of the plant-based biosynthesis method with water as the solvent successfully produced TiO2 NPs with good physicochemical properties and photocatalytic activity in the photodegradation of organic dye. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Magnetic Zinc Oxide/Manganese Ferrite Composite for Photodegradation of the Antibiotic Rifampicin

In this study, a composite of zinc oxide and manganese ferrite was synthesized using co-precipitation and hydrothermal routes, to be used as photocatalysts in reactions with UV/Vis light source. The synthesized materials were characterized by FTIR, XRD, and SEM, where it was possible to verify the efficiency of the syntheses performed, through the identification of the resulting phases, the evaluation of the structural morphology of the particles, and the analysis of the detachments of the main vibration bonds present in these materials. The composite ZnO/MnFe₂O₄ was used in photodegradation reactions of the antibiotic rifampicin, with catalyst dosage of 0.20; 0.40, and 0.60 g and 10 ppm of rifampicin, reactions using pure ZnO as a catalyst were also performed as a comparative parameter of the influence of MnFe₂O₄ in this system. The composite ZnO/MnFe₂O₄ showed a maximum percentage of rifampicin decontamination of 94.72% and ZnO, 74.20%using 0.20 g of photocatalyst after 90 min, which indicates a positive influence on this process. The solution treated with ZnO/MnFe₂O₄ was subjected to magnetic field induction for attraction and consequently accelerated removal of the solids present, successfully, compacting for the application of ZnO/MnFe₂O₄ to be presented as a promising material for decontamination of emerging pollutants through photocatalytic reactions.

Mesoporous BiVO4/TiO2 heterojunction: enhanced photoabsorption and photocatalytic ability through promoted charge transfer

BiVO₄ has been constructed into heterojunctions with TiO₂ to boost the photocatalytic ability under visible illumination. Here, mesoporous BiVO₄/TiO₂ nanocomposites have been fabricated by a facile sol-gel approach utilizing nonionic surfactant and addressed for morphological, optical, structural, and degradation of ciprofloxacin (CIP) in water under visible illumination as an antibiotic pollutant model. The TEM images demonstrated that the TiO₂ NPs are homogenous in terms of shape and size (15 ± 5 nm). The introduction of BiVO₄ into mesoporous TiO₂ could effectively enhance the rapid separation efficiency of the photoinduced carriers and optical absorption. The 3%BiVO₄/TiO₂ photocatalyst possessed the best degradation efficiency (100%) within 60 min which was promoted 20-folds larger than TiO₂ NPs (5%). 3%BiVO₄/TiO₂ nanocomposite exhibited the fastest degradation rate (2.15 × 10^-2 min^-1), which was 40 times faster than bare TiO₂ photocatalyst (0.05 × 10^-2 min^-1). The enhanced photocatalytic ability originated from superior charge separation characteristics and high solar energy absorption in mesopore structures. The recombination rate and mobility of charge carriers were characterized utilizing photoluminescence (PL) and photoelectrochemical measurements. This work highlights the advantages of mesoporous heterojunction BiVO₄/TiO₂ nanocomposites for photocatalytic performances and provides a multilateral route to design an effective wide-spectrum response photocatalyst for the development of comparable materials. The photocatalytic mechanism for degradation CIP over BiVO₄/TiO₂ was discussed in detail..

Shape Engineering of TiO2 Microrobots for "On-the-Fly" Optical Brake

Hybrid microrobots have recently attracted attention due to their ability to combine different energy sources and/or external stimuli for propulsion and performing desired tasks. Despite progresses in the past, on-demand speed modulation for hybrid microrobots has not been analyzed in detail. Herein, the influence of surface properties and crystallite size on the propulsion mechanism of Pt/TiO₂ chemical/light-driven hybrid microrobots is investigated. The morphology of urchin-like Pt/TiO₂ microrobots leads to "on-the-fly" optical brake behavior under UV irradiation. In contrast, smooth Pt/TiO₂ microrobots demonstrate accelerated motion in the same conditions. The comparison between two types of microrobots also indicates the significance of a high surface area and a high crystallite size to increase their speed. The results demonstrate the profound impact of surface features for next-generation smart micro/nanorobots with on-demand reaction capability in dynamically changing environments.

Synthesis and Characterization of an α-Fe2O3-Decorated g-C3N4 Heterostructure for the Photocatalytic Removal of MO

This study describes the preparation of graphitic carbon nitride (g-C3N4), hematite (α-Fe2O3), and their g-C3N4/α-Fe2O3 heterostructure for the photocatalytic removal of methyl orange (MO) under visible light illumination. The facile hydrothermal approach was utilized for the preparation of the nanomaterials. Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), and Brunauer-Emmett-Teller (BET) were carried out to study the physiochemical and optoelectronic properties of all the synthesized photocatalysts. Based on the X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance (DRS) results, an energy level diagram vs. SHE was established. The acquired results indicated that the nanocomposite exhibited a type-II heterojunction and degraded the MO dye by 97%. The degradation ability of the nanocomposite was higher than that of pristine g-C3N4 (41%) and α-Fe2O3 (30%) photocatalysts under 300 min of light irradiation. The formation of a type-II heterostructure with desirable band alignment and band edge positions for efficient interfacial charge carrier separation along with a larger specific surface area was collectively responsible for the higher photocatalytic efficiency of the g-C3N4/α-Fe2O3 nanocomposite. The mechanism of the nanocomposite was also studied through results obtained from UV-vis and XPS analyses. A reactive species trapping experiment confirmed the involvement of the superoxide radical anion (O2•-) as the key reactive oxygen species for MO removal. The degradation kinetics were also monitored, and the reaction was observed to be pseudo-first order. Moreover, the sustainability of the photocatalyst was also investigated.

Mechanistic insight of structural and optical properties of BiOCl in the presence of CNTs and investigating photodegradation of phenol by BiOCl/CNT composites

In this work, we have synthesized composites of BiOCl with carbon nanotubes (CNTs) via a hydrothermal method. Different compositions of CNTs were used to study their influence on the physicochemical properties of BiOCl. Based on the interesting results obtained, various significant correlations were made. This study explored how use of CNTs and different hydrothermal crystallization conditions can influence the photocatalytic activity of composites. The CNTs have an impact on the primary crystallite size and morphology of BiOCl. Also, a higher degree of crystallization was obtained in the case of samples containing CNTs. However, in some cases, the synthesis parameters such as high temperature and longer duration also promoted crystallinity in BiOCl/CNT samples. Further, the samples were investigated for their photocatalytic activity to study the photodegradation of RhB and phenol, as model pollutants, under visible and UV light, respectively. The maximum degradation efficiency of 83% for RhB under visible light and almost 40% for phenol under UV light was obtained using BiOCl/CNT composites. Surprisingly, pure BiOCl showed higher performance for the removal of both the pollutants. This is why some comparisons and correlations between the structural and optical properties of BiOCl and CNTs were made. Finally, this study illustrates how a nanostructure like conductive multiwalled carbon nanotubes can sometimes have detrimental effects on the overall photocatalytic properties of a photocatalyst like BiOCl under certain conditions. Therefore, understanding the synergy between physico-chemical properties of BiOCl and nanostructured-modifiers like CNTs could help in designing a photocatalyst system which could benefit wastewater treatment.

In this work, we have synthesized composites of BiOCl with carbon nanotubes (CNTs) via a hydrothermal method.

Photocatalytic Inactivation of Plant Pathogenic Bacteria Using TiO2 Nanoparticles Prepared Hydrothermally

Exploitation of engineered nanomaterials with unique properties has been dynamically growing in numerous fields, including the agricultural sector. Due to the increasing resistance of phytopathogenic microbes, human control over various plant pathogens in crop production is a big challenge and requires the development of novel antimicrobial materials. Photocatalytic active nanomaterials could offer an alternative solution to suppress the plant pathogens. In this work, titanium dioxide nanoparticles (TiO₂ NPs) with high photocatalytic activity were synthesized by hydrothermal post-treatment of amorphous titania at different temperatures (250 °C or 310 °C) without using any additives or doping agents. The obtained samples were investigated through X-ray diffraction, N₂-sorption measurements, diffuse reflectance UV-Vis spectroscopy, transmission electron microscopy, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy. The applied hydrothermal treatment led to the formation of TiO₂ nanocrystallites with a predominant anatase crystal phase, with increasing crystallinity and crystallite size by prolonging treatment time. The photocatalytic activity of the TiO₂ NPs was tested for the photo-degradation of phenol and applied for the inactivation of various plant pathogens such as Erwinia amylovora, Xanthomonas arboricola pv. juglandis, Pseudomonas syringae pv. tomato and Allorhizobium vitis. The studied bacteria showed different susceptibilities; their living cell numbers were quickly and remarkably reduced by UV-A-irradiated TiO₂ NPs. The effectiveness of the most active sample prepared at 310 °C was much higher than that of commercial P25 TiO₂. We found that fine-tuning of the structural properties by modulating the time and temperature of the hydrothermal treatment influenced the photocatalytic properties of the TiO₂ NPs considerably. This work provides valuable information to the development of TiO₂-based antimicrobial photocatalysts.

Comparative Study of ZnO Thin Films Doped with Transition Metals (Cu and Co) for Methylene Blue Photodegradation under Visible Irradiation

We synthesized and characterized both Co-doped ZnO (ZnO:Co) and Cu-doped ZnO (ZnO:Cu) thin films. The catalysts’ synthesis was carried out by the sol–gel method while the doctor blade technique was used for thin film deposition. The physicochemical characterization of the catalysts was carried out by Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction, and diffuse reflectance measurements. The photocatalytic activity was studied under visible irradiation in aqueous solution, and kinetic parameters were determined by pseudo-first-order fitting. The Raman spectra results evinced the doping process and suggested the formation of heterojunctions for both dopants. The structural diffraction patterns indicated that the catalysts were polycrystalline and demonstrated the presence of a ZnO wurtzite crystalline phase. The SEM analysis showed that the morphological properties changed significantly, the micro-aggregates disappeared, and agglomeration was reduced after modification of ZnO. The ZnO optical bandgap (3.22 eV) reduced after the doping process, these being ZnO:Co (2.39 eV) and ZnO:Co (3.01 eV). Finally, the kinetic results of methylene blue photodegradation reached 62.6% for ZnO:Co thin films and 42.5% for ZnO:Cu thin films.

Continuous flow hydrothermal synthesis of phase pure rutile TiO2 nanoparticles with a rod-like morphology

Titania nanocrystals are used in numerous applications but specific polymorphs (anatase, rutile, brookite) are typically required in specific applications making synthesis control over the crystal phase essential. Supercritical continuous flow reactors constitute fast, scalable alternatives to conventional autoclave hydrothermal synthesis. They provide outstanding control over nanoparticle characteristics such as size, crystallinity, and morphology but previous studies have always resulted in anatase products. Here we report, for the first time, a continuous hydrothermal flow method for obtaining phase pure rutile nanoparticles thereby significantly broadening the crystal design space for large scale titania applications. Through variation of the reactor temperature, the dimensions of the rod-like rutile crystallites are tunable in a range of 35 to 60 nm in length and 10 to 35 nm in width (maximum aspect ratio of ∼3.5) leading to a tunable band gap (3.2-3.5 eV) and high specific surface areas exceeding 200 m² g^-1.

Boosting Photocatalytic Hydrogen Production by Modulating Recombination Modes and Proton Adsorption Energy

Solar-driven production of renewable energy (e.g., H₂) has been investigated for decades. To date, the applications are limited by low efficiency due to rapid charge recombination (both radiative and nonradiative modes) and slow reaction rates. Tremendous efforts have been focused on reducing the radiative recombination and enhancing the interfacial charge transfer by engineering the geometric and electronic structure of the photocatalysts. However, fine-tuning of nonradiative recombination processes and optimization of target reaction paths still lack effective control. Here we show that minimizing the nonradiative relaxation and the adsorption energy of photogenerated surface-adsorbed hydrogen atoms are essential to achieve a longer lifetime of the charge carriers and a faster reaction rate, respectively. Such control results in a 16-fold enhancement in photocatalytic H₂ evolution and a 15-fold increase in photocurrent of the crystalline g-C₃N₄ compared to that of the amorphous g-C₃N₄.

Room Temperature Synthesis of V-Doped TiO₂ and Its Photocatalytic Activity in the Removal of Caffeine under UV Irradiation

In this work, the influence of simple acids in the room temperature sol-gel synthesis of TiO₂ was investigated and the efficiency of prepared photocatalysts was evaluated in the removal of caffeine. To improve the photoactivity of TiO₂, vanadium-doped TiO₂ (VTiO₂) samples were obtained starting from different amount of vanadyl sulphate as a dopant source. The samples were centrifuged, washed and finally dried at room temperature, and no calcination step was carried out. The prepared photocatalysts were characterized by different techniques (X-ray powder diffraction (XRD), specific surface area (SSA), ultraviolet-visible diffuse reflectance spectra (UV-vis DRS) and Raman). VTiO₂ photocatalysts were tested in the photocatalytic removal of aqueous solutions containing caffeine. The photocatalytic tests were carried out in a recirculating batch cylindrical photoreactor irradiated by a UV LEDs strip (nominal power of 12 W and wavelength emission peak at about 365 nm) surrounding the external surface of the reactor. The optimized VTiO₂ photocatalyst was able to reach a caffeine degradation of about 96% after 360 min of UV light irradiation with a total organic carbon (TOC) removal of 72%.

Deciphering Z-scheme Charge Transfer Dynamics in Heterostructure NiFe-LDH/N-rGO/g-C3N4 Nanocomposite for Photocatalytic Pollutant Removal and Water Splitting Reactions

A series of heterostructure NiFe LDH/N-rGO/g-C3N4 nanocomposite were fabricated by combining calcinations-electrostatic self-assembly and hydrothermal steps. In this method, negatively charged N-rGO was electrostaticaly bonded to the self-assembled interface of n-n type g-C3N4/NiFe LDH hybrid. XRD and AFM results revealed successful formation of heterostructure nanocomposite due to the coupling effect of exfoliated NiFe LDH nanosheets with N-rGO and g-C3N4. Among the as synthesized heterostructure, CNNG3LDH performed superior photocatalytic activities towards 95 and 72% mineralization of RhB and phenol. Furthermore, CNNG3LDH could achieve the highest photocatalytic H2 evolution rate of 2508 μmolg-12h-1 and O2 evolution rate of 1280 μmolg-12h-1 under visible light irradiation. The CNNG3LDH possess lowest PL intensity, reduced arc of the Nyquist plot (43.8 Ώ) and highest photocurrent density (-0.97 mA cm-2) which revealed effective charge separation for superior photocatalytic activities. TRPL spectral results reveal the synergistic effect of layered component in CNNG3LDH for achievable higher life time of excitons of ~16.52 ns. In addition, N-rGO mediator based Z-scheme charge transfer mechanisms in CNNG3LDH were verified by the ESR and TA-PL studies. Enriched oxygen vacancy type defects in NiFe LDH and N-rGO mediated Z-scheme charge transfer mechanistic path strongly manifest the superior photocatalytic activities of the heterostructure materials.

Effect of the Preparation Method (Sol-Gel or Hydrothermal) and Conditions on the TiO₂ Properties and Activity for Propene Oxidation

Since the two most commonly used methods for TiO₂ preparation are sol-gel (SG) and hydrothermal (HT) synthesis, this study attempts to compare both methods in order to determine which one is the most suitable to prepare photocatalysts for propene oxidation. In addition, this work studies how the concentration of the HCl used for hydrolysis of the TiO₂ precursor affects the properties of the obtained materials. Also, the effect of avoiding the post-synthesis heat-treatment in a selection of samples is investigated. The photocatalysts are characterized by XRD, N₂ adsorption-desorption isotherms and UV-vis spectroscopy, and the study tries to correlate the properties with the photocatalytic performance of the prepared TiO₂ samples in propene oxidation. TiO₂ materials with high crystallinity, between 67% and 81%, and surface area (up to 134 m²/g) have been obtained both by SG and HT methods. In general, the surface area and pore volume of the TiO₂-HT samples are larger than those of TiO₂-SG ones. The TiO₂-HT catalysts are, in general, more active than TiO₂-SG materials or P25 in the photo-oxidation of propene. The effect of HCl presence during the TiO₂ synthesis and of the post synthesis heat treatment are much more marked in the case of the SG materials.

Copper-based nanomaterials for environmental decontamination - An overview on technical and toxicological aspects

Synthesis of the various types of engineered nanomaterials has gained a huge attention in recent years for various applications. Copper based nanomaterials are a branch of this category seem to be able to provide an efficient and cost-effective way for the treatment of the persistent effluents. The present work aimed to study the various parameters may involve in the overall performance of the copper based nanomaterials for environmental clean-up purposes. To this end, the related characteristics of copper based nanomaterials and their effects on the nanomaterials reactivity and the environmental and operating parameters have been critically reviewed. Toxicological study of the copper based nanomaterials has been also considered as a factor with high importance for the selection of a typical nanomaterial with optimum performance and minimum environmental and health subsequent effects.

Influence of fluorine on the synthesis of anatase TiO2 for photocatalytic partial oxidation: are exposed facets the main actors?

The influence of fluorine on TiO₂ exposed facets and on the physico-chemical properties was evaluated and a synergetic effect of the presence of fluorine and the facets' distribution was observed.

Crystalline phase-dependent eco-toxicity of titania nanoparticles to freshwater biofilms

The potential toxic impacts of different crystal phases of titania nanoparticles (TNPs) on freshwater biofilms, especially under ultraviolet C irradiation (UVC), are unknown. Here, adverse impacts of three phases (anatase, rutile, and P25, 50 mg L^-1 respectively) with UVC irradiation (An-UV, Ru-UV, and P25-UV) on freshwater biofilms were conducted. Characterization experiments revealed that rutile TNPs had a higher water environment stability than anatase and P25 TNPs, possessing a stronger photocatalytic activity under UVC irradiation. Phase-dependent inhibition of cell viability and significant decreases of four- and five-fold in algal biomass at 12 h of exposure were observed compared with unexposed biofilms. Moreover, phase-dependent oxidative stress resulted in remarkably significant reductions (P < 0.01) of the photosynthetic yields of the biofilms, to 40.32% (P25-UV), 48.39% (An-UV), and 46.77% (Ru-UV) of the plateau value obtained in the unexposed biofilms. A shift in community composition that manifested as a strong reduction in diatoms, indicating cyanobacteria and green algae were more tolerant than diatoms when exposed to TNPs. In terms of the toxic mechanisms, rutile TNPs resulted in apoptosis by inducing excessive intracellular reactive oxygen species (ROS) production, whereas P25 and anatase TNPs tended to catalyze enormous acellular ROS lead to cell necrosis under UVC irradiation.

Effect of crystalline phase changes in titania (TiO2) nanotube coatings on platelet adhesion and activation

OBJECTIVE

To explore the relationship between various crystalline phases of titania (TiO₂) nanotube (TNT) coatings and platelet adhesion and activation.

METHODS

TNT coatings were fabricated on pure titanium foils by anodization and then randomly divided into four groups. Three groups were annealed at 350°C, 450°C and 550°C in order to obtain different crystalline phases. The remaining group was not annealed and served as the control group. X-ray diffraction (XRD) was used to define the crystalline phases of different groups. Surface morphology, elemental composition, surface roughness, and contact angles were measured by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), laser scanning confocal microscopy (LSCM) and contact angle analysis, respectively. Platelets were cultured on the TNT coatings for 30min and 60min to assess the number, viability, distribution, and morphology of the adhered platelets. CD62P fluorescence expression and the amount of released platelet-derived growth factor (PDGF) were detected to evaluate platelet activation.

RESULTS

The un-annealed TNT coatings were amorphous and part of TNT converted to anatase after the 350°C annealing treatment. The quantity of anatase increased upon annealing at 450°C and transformed to rutile at 550°C. Nanotubes of all four groups maintained a well-ordered structure, but the wall thickness of the nanotubes increased from (11.874±1.660) nm for the un-annealed TNTs to (26.126±2.130) nm for the 550°C annealed TNTs. The surface roughness of the 550°C annealed TNT coatings was the lowest and the water contact angle was the largest at (28.117±1.182) °. The number and viability of adhered platelets after 30min and 60min were the highest on TNT coatings annealed at 450°C. LSCM and SEM images revealed that the platelets that adhered on the 450°C annealed TNT coatings aggregated, transformed, and spread most obviously. CD62P fluorescence expression results showed that the platelets on the 350°C and 450°C annealed TNT coating groups expressed the strongest fluorescence, followed by platelets on the 550°C annealed group and the un-annealed group. The quantity of released PDGF was highest for the 450°C annealed group at (4719±86) pg/mL, and lowest for the un-annealed group at (4241±74) pg/mL.

CONCLUSION

Crystalline TNT coatings encourage improved platelet adhesion and activation over amprphous analogues. The TNT coatings annealed at 450°C resulted in the most improved platelet behavior. The TNT crystalline phase was the predominant influencing factor in platelet adhesion and activation.