Copper NPs decorated titania: A novel synthesis by high energy US with a study of the photocatalytic activity under visible light

Visible-light-activated antibacterial and antipollutant properties of biocompatible Cu-doped and Ag-decorated TiO2 nanoparticles

Optical and photocatalytic restrictions of anatase TiO2 nanoparticles (Nps) limit their potential applications, as antipollutant and antibacterial agents for sanitary applications, to the UV spectral region. While modification with transition metals extends the absorption capacity to the visible light spectrum, often undermines the photocatalysts' biocompatibility due to toxic ion leaching. In this study, we synthesized Cu-doped and Ag-decorated TiO2 photocatalysts by employing solvothermal (ATiO2:Cu) and sol-gel synthetic procedures (BTiO2:Ag), respectively. We acquired TiO2 Nps modified with three percentages of either Cu or Ag content, to examine the potential differentiation of their structural, photocatalytic, and biological impact. Comprehensive structural characterization supports the prevailing anatase crystalline structure of bare and modified titania nanostructures, while morphological differences are demonstrated among the different samples. Optical response in the visible region of ATiO2:Cu Nps stems from band gap narrowing and lattice-defect generation, while plasmonic effects are at play for BTiO2:Ag Nps. Their photocatalytic potential under visible light irradiation, originated from low-energy LED lamps commonly found in indoor spaces, was verified after monitoring the successful enhancement of methylene blue (MB) degradation rate. Safety assessment on immortalized healthy human keratinocyte cell line (HaCaT) revealed their biocompatibility up to a certain concentration, while reactive oxygen species (ROS) production was intensified after light irradiation. The visible-light-induced photocatalytic-driven antibacterial activity was confirmed against both gram-positive Staphylococcus aureus and gram-negative Escherichia coli.

Hierarchical Phonon Scattering from Nano to Macro Scale in Ag-Nano/TiO2-Micro Particle-Decorated p-type Bismuth Telluride Bulk Composites

We study the thermoelectric properties of a p-type Bi0.4Sb1.6Te3.4 (BST) composite with Ag nanoparticle-decorated TiO2 microparticles (US-Ag/TiO2). The dispersion of US-Ag/TiO2 particles, synthesized by an ultrasonication (US) method, into the matrix effectively decreases lattice and bipolar thermal conductivity, attributed to the scattering centers formed at nano and micro scales. The electron backscattering diffraction (EBSD) measurements revealed smaller grain sizes within the BST composite when paired with the US-Ag/TiO2 particle dispersion. These reduced grain sizes, alongside nanoparticle-decorated microparticles dispersed throughout the matrix, scatter phonons effectively from long- to short-wavelength phonons and subsequently decrease lattice thermal conductivity. While the power factors of the composites are reduced, significant suppression of lattice and bipolar thermal conductivity has led to an increase in the maximum zT value (1.4 at 325 K) for a 0.9 wt % US-Ag/TiO2 particle dispersion within the BST matrix. This particle dispersion in the BST composite consistently demonstrates a high zT value across an extensive temperature spectrum, leading to an exceptionally high average zTavg value (1.38 up to 400 K), which is superior to the other values from reported BST composites. Thus, this research indicates that the dispersion of nanoparticle-decorated microparticles within a thermoelectric material matrix can significantly improve thermoelectric performance, which has promising implications for practical applications in thermoelectric cooling and sustainable and economical energy harvesting technologies.

Key Points of Advanced Oxidation Processes (AOPs) for Wastewater, Organic Pollutants and Pharmaceutical Waste Treatment: A Mini Review

Advanced oxidation procedures (AOPs) refer to a variety of technical procedures that produce OH radicals to sufficiently oxidize wastewater, organic pollutant streams, and toxic effluents from industrial, hospital, pharmaceutical and municipal wastes. Through the implementation of such procedures, the (post) treatment of such waste effluents leads to products that are more susceptible to bioremediation, are less toxic and possess less pollutant load. The basic mechanism produces free OH radicals and other reactive species such as superoxide anions, hydrogen peroxide, etc. A basic classification of AOPs is presented in this short review, analyzing the processes of UV/H2O2, Fenton and photo-Fenton, ozone-based (O3) processes, photocatalysis and sonolysis from chemical and equipment points of view to clarify the nature of the reactive species in each AOP and their advantages. Finally, combined AOP implementations are favored through the literature as an efficient solution in addressing the issue of global environmental waste management.

Recent Advances in Plasmonic Photocatalysis Based on TiO2 and Noble Metal Nanoparticles for Energy Conversion, Environmental Remediation, and Organic Synthesis

Plasmonic photocatalysis has emerged as a prominent and growing field. It enables the efficient use of sunlight as an abundant and renewable energy source to drive a myriad of chemical reactions. For instance, plasmonic photocatalysis in materials comprising TiO₂ and plasmonic nanoparticles (NPs) enables effective charge carrier separation and the tuning of optical response to longer wavelength regions (visible and near infrared). In fact, TiO₂ -based materials and plasmonic effects are at the forefront of heterogeneous photocatalysis, having applications in energy conversion, production of liquid fuels, wastewater treatment, nitrogen fixation, and organic synthesis. This review aims to comprehensively summarize the fundamentals and to provide the guidelines for future work in the field of TiO₂ -based plasmonic photocatalysis comprising the above-mentioned applications. The concepts and state-of-the-art description of important parameters including the formation of Schottky junctions, hot electron generation and transfer, near field electromagnetic enhancement, plasmon resonance energy transfer, scattering, and photothermal heating effects have been covered in this review. Synthetic approaches and the effect of various physicochemical parameters in plasmon-mediated TiO₂ -based materials on performances are discussed. It is envisioned that this review may inspire and provide insights into the rational development of the next generation of TiO₂ -based plasmonic photocatalysts with target performances and enhanced selectivities.

Study on the influence of advanced treatment processes on the surface properties of polylactic acid for a bio-based circular economy for plastics

New biotechnological processes using microorganisms and/or enzymes to convert carbonaceous resources, either biomass or depolymerized plastics into a broad range of different bioproducts are recognized for their high potential for reduced energy consumption and reduced GHG emissions. However, the hydrophobicity, high molecular weight, chemical and structural composition of most of them hinders their biodegradation. A solution to reduce the impact of non-biodegradable polymers spread in the environment would be to make them biodegradable. Different approaches are evaluated for enhancing their biodegradation. The aim of this work is to develop and optimize the ultrasonication (US) and UV photodegradation and their combination as well as dielectric barrier discharge (DBD) plasma as pre-treatment technologies, which change surface properties and enhance the biodegradation of plastic by surface oxidation and thus helping bacteria to dock on them. Polylactic acid (PLA) has been chosen as a model polymer to investigate its surface degradation by US, UV, and DBD plasma using surface characterization methods like X-ray Photoelectron Spectroscopy (XPS) and Confocal Laser Microscopy (CLSM), Atomic Force Microscopy (AFM) as well as FT-IR and drop contour analysis. Both US and UV affect the surface properties substantially by eliminating the oxygen content of the polymer but in a different way, while plasma oxidizes the surface.

Synergetic decolorization of azo dyes using ultrasounds, photocatalysis and photo-fenton reaction

In the present work, ultrasound irradiation, photocatalysis with TiO₂, Fenton/Photo-Fenton reaction, and the combination of those techniques were investigated for the decolorization of industrial dyes in order to study their synergy. Three azo dyes were selected from the weaving industry. Their degradation was examined via UV illumination, Fenton and Photo-Fenton reaction as well as ultrasound irradiation at low (20 kHz) and high frequencies (860 kHz). In these experiments, we investigated the simultaneous action of the ultrasound and UV irradiation by varying parameters like the duration of photocatalysis and ultrasound irradiation frequency. At the same time, US power, temperature, amount of TiO₂ photocatalyst and amount of Fenton reagent remained constant. Due to their diverse structure, each azo dye showed different degradation levels using different combinations of the above-mentioned Advanced Oxidation Processes (AOPs). The Photo-Fenton reagent is more effective with US 20 kHz and US 860 kHz for the azo dyes originated from the weaving industry at pH = 3 as compared to pH = 6.8. The combination of the Photo-Fenton reaction with 860 kHz ultrasound irradiation for the same dye gave an 80% conversion at the same time. Experiments have shown a high activity during the first two hours. After that threshold, the reaction rate is decreased. FT-IR and TOC measurements prove the decolorization due to the destruction of the chromophore groups but not complete mineralization of the dyes.

Rhenium oxide nanoparticles - Sonochemical synthesis and integration on anode powders for solid oxide fuel cells

Rhenium oxide nanoparticles have been prepared using ultrasonication at 20 kHz. Samples characterization was committed via SEM-EDX, TEM, XRD, and Raman spectroscopy. Various experimental parameters were examined, including precursor/substrate amounts, ultrasonication intensity, and type of solvent used. Insights to the agglomeration of the prepared nanoparticles depending on the preparation parameters are given. As ultrasonic source we used either an ultrasonic probe by Sonics & Materials Inc. (20 kHz, 750 W net output) or a Bandelin SONOPULS HD 3200 ultrasound generator (20 kHz, 200 W net output) at intensities between 30 and 100 W/cm². The rhenium oxide nanoparticles haven been decorated on state-of-the-art anode materials (NiO/GDC) for solid oxide fuel cells (SOFCs) in order to prepare catalytically more active anode powders. These experiments revealed that ultrasonication intensity and solvents used are able to affect final nanoparticles size distribution and morphology. At the same time, ratio of precursor and substrate compounds amounts as well as ultrasonication intensity and duration were all found to affect the decoration loading extend of nanoformations on substrate powders. The results showing the influence of the above-mentioned parameters allowed for the quantification of the effects on the loading and the preferable sites of the decoration.

Titanium oxide based photocatalytic materials development and their role of in the air pollutants degradation: Overview and forecast

Due to the anthropogenic pollution, especially the environmental crisis caused by air pollutants, the development of air pollutant degradation photocatalyst has become one of the major directions to the crisis relief. Among them, titania (titanium dioxide, TiO₂) family materials were extensively studied in the past two decades due to their strong activity in the photocatalytic reactions. However, TiO₂ had a drawback of large bandgap which limited its applications, several modification techniques were hence developed to enhance its catalytic activity and light sensitivity. In recent years, other metal oxide based materials have been developed as replacements for TiO₂ photocatalysts. In this review, background information and developments from pure TiO₂ to chemically modified TiO₂-based materials as photocatalysts were discussed in detail, which covered their basic properties and their role in the air pollutant removal. It also proposes to solve the shortcomings of TiO₂ by developing other metal oxide-based materials and predict the future development of TiO₂ materials in future environmental applications.

Ultrasound to improve both synthesis and pollutants degradation based on metal nanoparticles supported on TiO2

Sonochemistry is based on acoustic cavitation, which consist in the formation, growth, and implosive collapse of bubbles within a liquid. Collapsing bubbles generate localized hot spots, characterized by temperatures up to 5000 K and pressures up to 1800 atm. These extreme conditions allow producing a variety of nanostructured and amorphous materials, as well as they are advantageous for chemical processes. Ultrasound requires inexpensive equipment and fewer steps than conventional methods. Combining ultrasound and photocatalysis enhances the performance of the processes, reduces reaction time, avoids the use of extreme physical conditions and improves the photocatalytic materials properties increasing their activity. Here, we reported the positive effect of US in synthesizing Me-modified TiO₂ (Me = Ag, Cu, Mn) for pollutants degradation in gas-phase; also, we proved the advantageous application of ultrasound for the photocatalytic removal of organic compounds in water. Ultrasound produced more efficient Me-doped TiO₂, which showed higher activity in visible light. When combined with photocatalytic water treatment, the organic compounds degradation and mineralization increases.

Nano-MnO₂ Decoration of TiO₂ Microparticles to Promote Gaseous Ethanol Visible Photoremoval

TiO₂-based photocatalysis under visible light is an attractive way to abate air pollutants. Moreover, developing photocatalytic materials on a large-scale requires safe and low-cost precursors. Both high-performance TiO₂ nanopowders and visible-light active noble metals do not match these requirements. Here, we report the design of novel Mn-decorated micrometric TiO₂ particles. Pigmentary TiO₂ replaced unsafe nano-TiO₂ and firmly supported MnO_x particles. Mn replaced noble metals such as Au or Ag, opening the way for the development of lower cost catalysts. Varying Mn loading or pH during the impregnation affected the final activity, thus giving important information to optimize the synthesis. Photocatalytic activity screening occurred on the gas-phase degradation of ethanol as a reference molecule, both under ultraviolet (UV) (6 h) and Light Emitting Diode (LED) (24 h) irradiation. Mn-doped TiO₂ reached a maximum ethanol degradation of 35% under visible light after 24 h for the sample containing 20% of Mn. Also, we found that an acidic pH increased both ethanol degradation and mineralization to CO₂, while an alkaline pH drastically slowed down the reaction. A strict correlation between photocatalytic results and physico-chemical characterizations of the synthesized powders were drawn.

Ultrasound assisted synthesis of Ag-decorated TiO2 active in visible light

Titanium dioxide is the most popular photocatalyst to degrade organic pollutants in air, as well as in water. The principal drawback preventing its commercial application lies in its limited absorption of the visible light (400-700nm), while it is active under UV irradiation (≤387nm). Supporting noble metals in the form of nanoparticles on TiO₂ increases its activity in the visible range. However, both the synthesis of noble metal nanoparticles and their deposition on TiO₂ are multi-step processes that often require organic solvents. Here, we deposit Ag nanoparticles from AgNO₃ on the surface of micrometric TiO₂ with H₂O as a solvent and under ultrasound irradiation at 30Wcm^-2. Ultrasound increases the surface amount of Ag on TiO₂ with heterogeneous size distribution of Ag nanoparticles, which are bigger and overlaid (1-20nm vs. 0.5-3nm) compared to the sample obtained in traditional conditions (TEM images). While this change in morphology had no effect on acetone photodegradation under UV light, the 5%, 10%, and 20% Ag-TiO₂ degraded 17%, 20% and 24% acetone under visible light, respectively. The 10% by weight Ag-TiO₂ sample obtained in absence of ultrasound only degraded 14% acetone in 6h, while the bare TiO₂ was not active.

Aspirin and paracetamol removal using a commercial micro-sized TiO2 catalyst in deionized and tap water

Micro-sized TiO₂ catalyst was employed to degrade pharmaceutical compounds, i.e. aspirin and paracetamol, two of the most widely used drugs, purchasable without prescription. Their active agents, acetylsalicylic acid and acetaminophen, are characterized by different substituent groups, linked to the aromatic ring, which affect both the photodegradation and mineralization processes. The experimental conditions highlight the relationship between the nature of the pristine molecules, their degradation mechanisms, their mutual interference and the water's role. The research started from model systems with a single pollutant to the mixture of them and finally by moving from deionized water to tap water.