Metal Oxide Nanostructures (MONs) as Photocatalysts for Ciprofloxacin Degradation.

In recent years, organic pollutants have become a global problem due to their negative impact on human health and the environment. Photocatalysis is one of the most promising methods for the removal of organic pollutants from wastewater, and oxide semiconductor materials have proven to be among the best in this regard. This paper presents the evolution of the development of metal oxide nanostructures (MONs) as photocatalysts for ciprofloxacin degradation. It begins with an overview of the role of these materials in photocatalysis; then, it discusses methods of obtaining them. Then, a detailed review of the most important oxide semiconductors (ZnO, TiO2, CuO, etc.) and alternatives for improving their photocatalytic performance is provided. Finally, a study of the degradation of ciprofloxacin in the presence of oxide semiconductor materials and the main factors affecting photocatalytic degradation is carried out. It is well known that antibiotics (in this case, ciprofloxacin) are toxic and non-biodegradable, which can pose a threat to the environment and human health. Antibiotic residues have several negative impacts, including antibiotic resistance and disruption of photosynthetic processes.

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 (τ1/2 = ln2/k) was evaluated to be about τ1/2 =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.

Application of Surface-Modified Nanoclay in a Hybrid Adsorption-Ultrafiltration Process for Enhanced Nitrite Ions Removal: Chemometric Approach vs. Machine Learning.

Herein, we report the results of a study on combining adsorption and ultrafiltration in a single-stage process to remove nitrite ions from contaminated water. As adsorbent, a surface-modified nanoclay was employed (i.e., Nanomer® I.28E, containing 25-30 wt. % trimethyl stearyl ammonium). Ultrafiltration experiments were conducted using porous polymeric membranes (Ultracel® 10 kDa). The hybrid process of adsorption-ultrafiltration was modeled and optimized using three computational tools: (1) response surface methodology (RSM), (2) artificial neural network (ANN), and (3) support vector machine (SVM). The optimal conditions provided by machine learning (SVM) were found to be the best, revealing a rejection efficiency of 86.3% and an initial flux of permeate of 185 LMH for a moderate dose of the nanoclay (0.674% w/v). Likewise, a new and more retentive membrane (based on PVDF-HFP copolymer and halloysite (HS) inorganic nanotubes) was produced by the phase-inversion method, characterized by SEM, EDX, AFM, and FTIR techniques, and then tested under optimal conditions. This new composite membrane (PVDF-HFP/HS) with a thickness of 112 µm and a porosity of 75.32% unveiled an enhanced rejection efficiency (95.0%) and a lower initial flux of permeate (28 LMH). Moreover, molecular docking simulations disclosed the intermolecular interactions between nitrite ions and the functional moiety of the organonanoclay.

Multi-Functional Materials Based on Cu-Doped TiO2 Ceramic Fibers with Enhanced Pseudocapacitive Performances and Their Dielectric Characteristics.

In this work, pure TiO2 and Cu (0.5, 1, 2%)-doped TiO2 composites prepared by electrospinning technique followed by calcination at 900 °C, and having high pseudocapacitive and dielectric characteristics were reported. These nanocomposites were characterized by scanning electron microscopy, X-ray diffraction, and dynamic water sorption vapor measurements. The structural characterization of these nanostructures highlighted good crystallinity including only the rutile phase. The electrochemical characteristics were investigated by cyclic voltammetry and galvanostatic charge-discharge measurements, which were performed in a KOH electrolyte solution. Among the Cu-doped TiO2 nanostructures that were prepared, the one containing 0.5% Cu exhibited superior electrochemical properties, including high specific gravimetric capacitance of 1183 F·g-1, specific capacitance of 664 F·g-1, energy density of 45.20 Wh·kg-1, high power density of 723.14 W·kg-1, and capacitance retention of about 94% after 100 cycles. The dielectric investigation shows good dielectric properties for all materials, where the dielectric constant and the dielectric loss decreased with the frequency increase. Thus, all the interconnected studies proved that these new materials show manifold ability and real applicative potential as pseudocapacitors and high-performance dielectrics. Future work and perspectives are anticipated for characterizing electrochemical and dielectric properties for materials including larger amounts of Cu dopant.

Tuning of Sm3+ and Er3+-doped TiO2 nanofibers for enhancement of the photocatalytic performance: Optimization of the photodegradation conditions.

Titanium dioxide (TiO2)-based nanofibers doped with samarium (Sm3+) and erbium (Er3+) at doping levels tuned in the range of 0.05-1.0% were prepared by the electrospinning-calcination method. The produced materials were well characterized by X-ray diffraction, SEM, EDX, and UV-vis diffuse reflectance spectroscopy. These one-dimensional nanostructures showed a crystalline structure with values of fiber diameters values between 60 and 100 nm. The best catalyst sample of this study was formulated as TiO2:Sm (0.1%) and sintered at 600 °C. And, it was employed to intensify the photocatalytic process under visible-light irradiation. Likewise, the chemometric approach was applied to optimize the process. The results revealed that the rate constant for the photo-degradation of a cationic organic pollutant was significantly improved (k = 3.496 × 10-1 min-1). In terms of the reaction half-life, the intensification and optimization of the process led to a decrease in the half-life of the reaction from 68 to 2 min. And, these are outstanding findings for the photo-degradation process under visible-light irradiation. In addition, the total organic carbon (TOC) removal efficiencies were found to be 69.95% and 72.30% for the mineralization of MB and CIP, respectively, after a 360 min reaction time, which are significant results. Moreover, this material demonstrated remarkable photocatalytic activity for the degradation of ciprofloxacin (CIP) with a 99.6% removal efficiency and a rate constant of 4.292 × 10-1 min-1. Finally, the stability and reusability of this catalyst were demonstrated during five repetitive cycles of the CIP photodegradation.

High-performance photocatalytic membranes for water purification in relation to environmental and operational parameters.

Growing technologies, increasing population and environmental pollution lead to severe contamination of water and require advanced water treatment technologies. These aspects lead to the need to purify water with advanced smart materials. This paper reviews the recent advances (during the last 5 years) in photocatalytic composite membranes used for water treatment. For this purpose, the authors have reviewed the main materials used in the development of (photocatalytic membranes) PMs, environmental and operational factors affecting the performance of photocatalytic membranes, and the latest developments and applications of PMs in water purifications. The composite photocatalytic membranes show good performance in the removal and degradation of pollutants from water.

Obtaining Nanostructured ZnO onto Si Coatings for Optoelectronic Applications via Eco-Friendly Chemical Preparation Routes.

Although the research on zinc oxide (ZnO) has a very long history and its applications are almost countless as the publications on this subject are extensive, this semiconductor is still full of resources and continues to offer very interesting results worth publishing or warrants further investigation. The recent years are marked by the development of novel green chemical synthesis routes for semiconductor fabrication in order to reduce the environmental impacts associated with synthesis on one hand and to inhibit/suppress the toxicity and hazards at the end of their lifecycle on the other hand. In this context, this study focused on the development of various kinds of nanostructured ZnO onto Si substrates via chemical route synthesis using both classic solvents and some usual non-toxic beverages to substitute the expensive high purity reagents acquired from specialized providers. To our knowledge, this represents the first systematic study involving common beverages as reagents in order to obtain ZnO coatings onto Si for optoelectronic applications by the Aqueous Chemical Growth (ACG) technique. Moreover, the present study offers comparative information on obtaining nanostructured ZnO coatings with a large variety of bulk and surface morphologies consisting of crystalline nanostructures. It was revealed from X-ray diffraction analysis via Williamson-Hall plots that the resulting wurtzite ZnO has a large crystallite size and small lattice strain. These morphological features resulted in good optical properties, as proved by photoluminescence (PL) measurements even at room temperature (295 K). Good optical properties could be ascribed to complex surface structuring and large surface-to-volume ratios.

Phyto-Functionalized Silver Nanoparticles Derived from Conifer Bark Extracts and Evaluation of Their Antimicrobial and Cytogenotoxic Effects.

Silver nanoparticles synthesized using plant extracts as reducing and capping agents showed various biological activities. In the present study, colloidal silver nanoparticle solutions were produced from the aqueous extracts of Picea abies and Pinus nigra bark. The phenolic profile of bark extracts was analyzed by liquid chromatography coupled to mass spectrometry. The synthesis of silver nanoparticles was monitored using UV-Vis spectroscopy by measuring the Surface Plasmon Resonance band. Silver nanoparticles were characterized by attenuated total reflection Fourier transform infrared spectroscopy, Raman spectroscopy, dynamic light scattering, scanning electron microscopy, energy dispersive X-ray and transmission electron microscopy analyses. The antimicrobial and cytogenotoxic effects of silver nanoparticles were evaluated by disk diffusion and Allium cepa assays, respectively. Picea abies and Pinus nigra bark extract derived silver nanoparticles were spherical (mean hydrodynamic diameters of 78.48 and 77.66 nm, respectively) and well dispersed, having a narrow particle size distribution (polydispersity index values of 0.334 and 0.224, respectively) and good stability (zeta potential values of -10.8 and -14.6 mV, respectively). Silver nanoparticles showed stronger antibacterial, antifungal, and antimitotic effects than the bark extracts used for their synthesis. Silver nanoparticles obtained in the present study are promising candidates for the development of novel formulations with various therapeutic applications.

Innovative Low-Cost Carbon/ZnO Hybrid Materials with Enhanced Photocatalytic Activity towards Organic Pollutant Dyes' Removal.

A new type of material based on carbon/ZnO nanostructures that possesses both adsorption and photocatalytic properties was obtained in three stages: cellulose acetate butyrate (CAB) microfiber mats prepared by the electrospinning method, ZnO nanostructures growth by dipping and hydrothermal methods, and finally thermal calcination at 600 °C in N2 for 30 min. X-ray diffraction (XRD) confirmed the structural characteristics. It was found that ZnO possesses a hexagonal wurtzite crystalline structure. The ZnO nanocrystals with star-like and nanorod shapes were evidenced by scanning electron microscopy (SEM) measurements. A significant decrease in Eg value was found for carbon/ZnO hybrid materials (2.51 eV) as compared to ZnO nanostructures (3.21 eV). The photocatalytic activity was evaluated by studying the degradation of three dyes, Methylene Blue (MB), Rhodamine B (RhB) and Congo Red (CR) under visible-light irradiation. Therefore, the maximum color removal efficiency (both adsorption and photocatalytic processes) was: 97.97% of MB (C0 = 10 mg/L), 98.34% of RhB (C0 = 5 mg/L), and 91.93% of CR (C0 = 10 mg/L). Moreover, the value of the rate constant (k) was found to be 0.29 × 10-2 min-1. The novelty of this study relies on obtaining new photocatalysts based on carbon/ZnO using cheap and accessible raw materials, and low-cost preparation techniques.

New Electrospun ZnO:MoO3 Nanostructures: Preparation, Characterization and Photocatalytic Performance.

New molybdenum trioxide-incorporated ZnO materials were prepared through the electrospinning method and then calcination at 500 °C, for 2 h. The obtained electrospun ZnO:MoO3 hybrid materials were characterized by X-ray diffraction, scanning and transmission electron microscopies, ultraviolet (UV)-diffuse reflectance, UV-visible (UV-vis) absorption, and photoluminescence techniques. It was observed that the presence of MoO3 as loading material in pure ZnO matrix induces a small blue shift in the absorption band maxima (from 382 to 371 nm) and the emission peaks are shifted to shorter wavelengths, as compared to pure ZnO. Also, a slight decrease in the optical band gap energy of ZnO:MoO3 was registered after MoO3 incorporation. The photocatalytic performance of pure ZnO and ZnO:MoO3 was assessed in the degradation of rhodamine B (RhB) dye with an initial concentration of 5 mg/L, under visible light irradiation. A doubling of the degradation efficiency of the ZnO:MoO3 sample (3.26% of the atomic molar ratio of Mo/Zn) as compared to pure ZnO was obtained. The values of the reaction rate constants were found to be 0.0480 h-1 for ZnO, and 0.1072 h-1 for ZnO:MoO3, respectively.

Novel rare earth (RE-La, Er, Sm) metal doped ZnO photocatalysts for degradation of Congo-Red dye: Synthesis, characterization and kinetic studies.

Synthesis and characterization of novel ZnO:RE nanostructured materials doped with 1% rare-earth elements (RE = La, Er, Sm) and their testing for photocatalytic applications were reported. The materials were obtained via electrospining, followed by calcination at 700 °C. The samples were characterized in terms of surface morphology (SEM, TEM), crystalline structure (XRD) and band gap energies. TEM results showed the formation of a unidimensional structure (ZnO) with an average fiber diameter of 600 nm and a morphology consisting of interconnected nanoparticles having dimensions in the range 25-134 nm (ZnO doped with RE). Optical properties were explored by using UV-VIS reflectance spectra and the band gap values were determined with the Kubelka-Munk function (KM) by plotting [F(R∞)hν]2vs. hʋ. The photocatalytic activity was assessed by studying the degradation of a water-soluble anionic dye (Congo-Red) under UV-light irradiation. The data related to photodegradation kinetics were reasonably fitted to the pseudo-first-order kinetic model. Results revealed that the values of the rate constants ranged from 10-3 to 10-2 min-1, depending on the material type and initial dye concentration. In addition, Langmuir-Hinshelwood (LH) model was utilized to explain the kinetics of photodegradation reactions of CR in the presence of (ZnO:Sm) sample. The LH approach suggested that both adsorption and photocatalysis phenomena prevailed in the process of dye removal. Optimal conditions of experiments were determined empirically by employing the gradient method. Thus, a maximal value of color removal efficiency (95.8%) was observed experimentally for the initial dye concentration of 10.7 mg/L and 0.236 g/L catalyst dosage (ZnO:Sm). Furthermore, a successful recovery of the spent catalyst was accomplished by thermal activation.

Chitosan-based magnetic adsorbent for removal of water-soluble anionic dye: Artificial neural network modeling and molecular docking insights.

Herein, we report a new composite magnetic-adsorbent made of doped spinel ferrite (15%) dispersed throughout a matrix of chitosan (CS) cross-linked with glutaraldehyde (GA). The composite material was well characterized by using instrumental methods of physical-chemical analysis (SEM, EDX, FTIR and VSM). The produced adsorbent was applied for the removal of Acid Orange 7 (AO7) dye from aqueous solutions. Aspects of adsorption kinetics, isotherms and thermodynamics were detailed. According to the Dubinin-Radushkevich (D-R) isotherm, the mean free energy of adsorption ranged from 14.37 to 16.59 (kJ/mol), suggesting ion-exchange dominating phenomena. In addition, we developed an artificial neural network (ANN) model to explore extensively the effects of factors on the adsorption performance. The coupling of ANN model with a genetic algorithm provided optimal conditions of adsorption. A maximal color removal efficiency of 98.01% was observed experimentally under optimal conditions (pH 2.51, sorbent dosage 3.88 g/L, initial dye concentration 25.3 mg/L, contact time 204 min). To unveil interaction mechanism, we employed molecular docking simulations. Computational outcomes suggested the formation of hydrophobic contacts and hydrogen bonds between AO7 dye molecule and CS-GA receptor. Molecular docking results agreed with the D-R isotherm findings, highlighting that electrostatic forces were greater than Van-der-Waals interactions.

Surface Morphology Effects on Photocatalytic Activity of Metal Oxides Nanostructured Materials Immobilized onto Substrates.

Structure, shape and surface morphology of the material are directly determined by the substrate and growth method used for material fabrication of nanostructured metal oxides. Those characteristics play a crucial role in the photocatalytic activity of the material. This paper presents a short review of some of the most recent relevant publications regarding pure and doped nanostructured metal oxides used for photocatalytic applications focusing on the structure, shape and surface morphology of the material effects on photocatalytic activity. The cases of TiO2, ZnO and CuO metal oxides as well as various semiconductors and metal doping were reviewed. It was concluded that, according to the reviewed communications, the most important surface parameters affecting photocatalytic activity are surface area, surface to volume ratio, nanocrystallites size and crystallinity regardless the material. In particular, for each material, more surface parameters may be of significance.