Nanostructured Oxides in Chemistry: Characterization and Properties

Atomic and Electronic Structures of Co-Doped In2O3 from Experiment and Theory

The synthesis and properties of stoichiometric, reduced, and Co-doped In2O3 are described in the light of several experimental techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)-visible spectroscopy, porosimetry, and density functional theory (DFT) methods on appropriate models. DFT-based calculations provide an accurate prediction of the atomic and electronic structure of these systems. The computed lattice parameter is linearly correlated with the experimental result in the Co concentration ranging from 1.0 to 5.0%. For higher Co concentrations, the theoretical-experimental analysis of the results indicates that the dopant is likely to be preferentially present at surface sites. The analysis of the electronic structure supports the experimental assignment of Co2+ for the doped material. Experiments and theory find that the presence of Co has a limited effect on the material band gap.

Nanoscale Chemical Probing of Metal-Supported Ultrathin Ferrous Oxide via Tip-Enhanced Raman Spectroscopy and Scanning Tunneling Microscopy

Metal-supported ultrathin ferrous oxide (FeO) has attracted immense interest in academia and industry due to its widespread applications in heterogeneous catalysis. However, chemical insight into the local structural characteristics of FeO, despite its critical importance in elucidating structure-property relationships, remains elusive. In this work, we report the nanoscale chemical probing of gold (Au)-supported ultrathin FeO via ultrahigh-vacuum tip-enhanced Raman spectroscopy (UHV-TERS) and scanning tunneling microscopy (STM). For comparative analysis, single-crystal Au(111) and Au(100) substrates are used to tune the interfacial properties of FeO. Although STM images show distinctly different moiré superstructures on FeO nanoislands on Au(111) and Au(100), TERS demonstrates the same chemical nature of FeO by comparable vibrational features. In addition, combined TERS and STM measurements identify a unique wrinkled FeO structure on Au(100), which is correlated to the reassembly of the intrinsic Au(100) surface reconstruction due to FeO deposition. Beyond revealing the morphologies of ultrathin FeO on Au substrates, our study provides a thorough understanding of the local interfacial properties and interactions of FeO on Au, which could shed light on the rational design of metal-supported FeO catalysts. Furthermore, this work demonstrates the promising utility of combined TERS and STM in chemically probing the structural properties of metal-supported ultrathin oxides on the nanoscale.

Glutathione-Mediated Synthesis of WO3 Nanostructures with Controllable Morphology/Phase for Energy Storage, Photoconductivity, and Photocatalytic Applications

Developing an improved synthesis method that controls the morphology and crystal phase remains a substantial challenge. Herein, we report phase and morphology-controlled hydrothermal synthesis of tungsten oxides by varying acid concentration and utilizing glutathione (GSH) as a structural directing agent, together with the exploration of their applications in supercapacitors, photoconductivity, and photocatalysis. Orthorhombic hydrated tungsten oxide (WO3·0.33H2O) with nonuniform block and plate-like morphology was obtained at 3 M hydrochloric acid (HCl). In contrast, nonhydrated monoclinic tungsten oxide (WO3) with smaller rectangular blocks was obtained at 6 M HCl. Further, the addition of GSH results in an increase in the surface area of the materials along with a narrowing of the band gap. Moreover, it plays a pivotal role in regulating the morphology through oriented attachments, Ostwald ripening, and the self-assembly of WO3 nuclei. GHTO and GTO polymorphs showed pseudocapacitive behavior with the highest specific capacitances of 450 and 300 F g-1 at 0.5 A g-1, maintaining 94 and 92% retention stability, respectively, over 1000 cycles at 2 A g-1. Also, the synthesized materials displayed favorable photoconductivity under light irradiation, implying potential utilization in photovoltaic applications. Moreover, these materials exhibited remarkable photocatalytic performance in the degradation of methylene blue (MB) dye, establishing themselves as highly effective photocatalysts. Therefore, nanostructured tungsten oxide showcases its versatility, rendering it an appealing candidate for energy storage, photovoltaic systems, and photocatalysis.

Phytosynthesis via wasted onion peel extract of samarium oxide/silver core/shell nanoparticles for excellent inhibition of microbes

The aqueous onion peel extract (OPE) was used to synthesize silver nanoparticles (Ag-onion), samarium oxide nanoparticles (Sm2O3-onion), and silver/samarium oxide core/shell nanoparticles (Ag@Sm2O3-onion). The produced nanoparticles were characterized by thermal gravimetric analysis (TGA), infrared spectra (FT-IR), absorption spectra (UV-Vis), energy band gap, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), zeta potential, and transmission electron microscopy (TEM). OPE and NPs were tested for the disinfection of some water microbes. XRD analysis exhibited an amorphous structure of samarium oxide in both Sm2O3-onion and Ag@ Sm2O3-onion. The isolated bacteria from the water sample were Bacillus subtilis (OQ073500) and Escherichia coli (MW534699), while the isolated fungi were Alternaria brassicae (MZ266540), Aspergillus flavus (MT550030), Aspergillus penicillioides (MW957971), Pythium ultimum (MW830915), Verticillium dahlia (MW830379), Fusarium acuminatum (MZ266538), Candida albicans (MW534712), and Candida parapsilosis (MW960416). High levels of antimicrobial activity were seen in both the nanoparticles and the aqueous onion peel extract. Based on experimental results, Ag@Sm2O3 demonstrated the highest activity as an effective disinfectant, indicating the effectiveness of the modification process.

Tuneable-by-design copper oxide nanoparticles in ionic liquid nanofluids

In this study, copper oxide nanoparticles (CuO-NPs) were synthesised in an ionic liquid, [C2MIm][CnHnCO2], and the respective copper(II) carboxylate precursors. Heating the solution to 120 °C caused a colour change from blue to red, indicating a change in copper salt coordination and nanoparticle formation. Crystallography and UV-Vis spectroscopy were used to monitor the transition upon temperature changes. The particle formation was characterised using TEM and SWAXS analyses. The results showed that different anion chain lengths led to different particle sizes. When using copper(II) acetate precursors, the transformation resulted in CuO(I,II) clusters (<1 nm), depending on the imidazolium-based cation used. However, using a copper(II) octanoate precursor, small CuO-NPs in the range of 10-25 nm were formed, while larger CuO-NPs were obtained using a copper(II) butanoate precursor in the range of 10-61 nm.

Surface ligand length influences kinetics of H-atom uptake in polyoxovanadate-alkoxide clusters

The uptake of hydrogen atoms (H-atoms) at reducible metal oxide nanocrystal surfaces has implications in catalysis and energy storage. However, it is often difficult to gain insight into the physicochemical factors that dictate the thermodynamics and kinetics of H-atom transfer to the surface of these assemblies. Recently, our research group has demonstrated the formation of oxygen-atom (O-atom) defects in polyoxovanadate-alkoxide (POV-alkoxide) clusters via conversion of surface oxido moieties to aquo ligands, which can be accomplished via addition of two H-atom equivalents. Here, we present the dependence of O-atom defect formation via H-atom transfer at the surface of vanadium oxide clusters on the length of surface alkoxide ligands. Analysis of H-atom transfer reactions to low-valent POV-alkoxide clusters [V6O7(OR)12]1- (R = Me, Et, nPr, nBu) reveals that the length of primary alkoxide surface ligands does not significantly influence the thermodynamics of these processes. However, surface ligand length has a significant impact on the kinetics of these PCET reactions. Indeed, the methoxide-bridged cluster, [V6O7(OMe)12]1- reacts ∼20 times faster than the other derivatives evaluated. Interestingly, as the aliphatic linkages are increased in size from -C2H5 to -C4H9, reaction rates remain consistent, suggesting restricted access to available ligand conformers as a result of the incompatibility of the aliphatic ligands and acetonitrile may buffer further changes to the rate of reaction.

Selective and Robust Ru Catalyst for the Aqueous Phase Aerobic Oxidation of Furfural to 2-Furoic Acid

Synthesis of 2-furoic acid (FURA) via oxidation of furfural (FAL) is vital in evolving the biorefinery concept as FURA has numerous important applications in the pharmaceuticals and optic areas. Though few works on this reaction are done, those are marred with shortcomings such as the nonrecyclability of catalyst, dilute solutions, lower yields, or use of H2O2 as an oxidizing agent. Herein, we report catalytic aqueous phase oxidation of FAL to FURA using molecular oxygen as an oxidizing agent. For the synthesis of FURA, various catalysts with a combination of metal (Pt, Pd, Ru) and supports (carbon, Al2O3) were prepared and characterized by multiple techniques (X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS)). Oxidation of FAL carried out over 5 wt % Ru/C catalyst in the presence of Na2CO3 yielded 83% of FURA at 120 °C and 15 bar oxygen pressure. The catalyst could show potential for reusability as similar activity was achieved after subjecting the spent catalyst to mild reduction treatment (150 °C). Studies on the effects of temperature, pressure, and time could help accomplish enhanced yields of FURA. Additionally, learning about the effect of base (weak/strong/solid) revealed that due to the weak basicity of Na2CO3, higher yields could be achieved by maintaining approximately a pH of 11, which is optimal for suppressing side reactions. Under the given conditions, FURA is stable (>90%) and also adsorption studies divulge that it is immediately removed from the catalyst surface, and hence higher yields could be achieved in our catalytic system. Using the initial rates methodology, an activation energy of 21.91 kJ mol-1 was derived and also a high turn over frequency (TOF) (85.9 h-1) was observed under optimized conditions.

High-Selectivity Hydrogen Gas Sensors based on Mesoporous PbOx -ZnO Nanocomposites

Hydrogen heralded as a promising renewable and environmentally friendly energy carrier, carries inherent risks owing to its highly flammable nature. A mere 4 % concentration of hydrogen in the air can trigger an explosion. To counteract this peril, a composite material comprising PbOX -ZnO (2 : 1) was synthesized, characterized, and subsequently employed to fabricate a hydrogen sensing device. Various analytical tools were used to characterize as-deposited materials, including X-ray diffraction, Scanning electron microscopy /Energy Dispersive X-ray Spectroscopy, Transmission electron microscopy UV-Vis Reflectance Spectroscopy and Fourier-transform infrared spectroscopy. The device exhibited favorable properties, such as good selectivity, stability, and a low detection limit for hydrogen. At ambient room temperature, the device demonstrated a sensing signal reaching 468.7, with a response time (T90) of 155 seconds and a recovery time (Tr90) of 69 seconds when exposed to a hydrogen concentration of 5 ppm. This performance underscores the device's rapid and effective response to hydrogen exposure. Moreover, the PbOX-ZnO (2 : 1) composite-based device exhibited a detection limit of 2.4 ppm, functioning accurately within a linear range spanning from 5 ppm to 50 ppm. This capability confirms its precision in accurately detecting hydrogen concentrations within this designated range.

Design of Mixed Ionic-Electronic Materials for Permselective Membranes and Solid Oxide Fuel Cells Based on Their Oxygen and Hydrogen Mobility

Oxygen and hydrogen mobility are among the important characteristics for the operation of solid oxide fuel cells, permselective membranes and many other electrochemical devices. This, along with other characteristics, enables a high-power density in solid oxide fuel cells due to reducing the electrolyte resistance and enabling the electrode processes to not be limited by the electrode-electrolyte-gas phase triple-phase boundary, as well as providing high oxygen or hydrogen permeation fluxes for membranes due to a high ambipolar conductivity. This work focuses on the oxygen and hydrogen diffusion of mixed ionic (oxide ionic or/and protonic)-electronic conducting materials for these devices, and its role in their performance. The main laws of bulk diffusion and surface exchange are highlighted. Isotope exchange techniques allow us to study these processes in detail. Ionic transport properties of conventional and state-of-the-art materials including perovskites, Ruddlesden-Popper phases, fluorites, pyrochlores, composites, etc., are reviewed.

Synthesis and multi-scale properties of PuO2 nanoparticles: recent advances and open questions

Due to the increased attention given to actinide nanomaterials, the question of their structure-property relationship is on the spotlight of recent publications. Plutonium oxide (PuO₂) particularly plays a central role in nuclear energetics and a comprehensive knowledge about its properties when nanosizing is of paramount interest to understand its behaviour in environmental migration schemes but also for the development of advanced nuclear energy systems underway. The element plutonium further stimulates the curiosity of scientists due to the unique physical and chemical properties it exhibits around the periodic table. PuO₂ crystallizes in the fluorite structure of the face-centered cubic system for which the properties can be significantly affected when shrinking. Identifying the formation mechanism of PuO₂ nanoparticles, their related atomic, electronic and crystalline structures, and their reactivity in addition to their nanoscale properties, appears to be a fascinating and challenging ongoing topic, whose recent advances are discussed in this review.

Multifunctional Modulation of High-Performance Znx Fe3-x O4 Nanoparticles by Precisely Tuning the Zinc Doping Content

The possibility to precisely control important properties of nanoparticles (NPs) such as their size, morphology, surface charge, or doping content is crucial for enhancing the performance of existing solutions beyond the state-of-the-art and for enabling novel applications. In this work, custom-tailored Zn_x Fe_{3- x} O₄ NPs are synthesized at different Zn doping concentrations to augment and expand their usefulness for high-performance applications in nanomedicine. By precisely increasing the Zn²⁺ content in the range of 0 ≤ x ≤ 2.0, the discussed NPs can sequentially acquire valuable properties enabling magnetic resonance imaging, near-infrared (NIR) photothermal effects, NIR photocatalytic and photoelectric effects, depending on the variation of substitution position of the Zn²⁺ in the magnetite structure and the emergence of a ZnO/ZnFe₂ O₄ heterostructure at high doping concentrations. The presented work demonstrates and explainsa facile route for the synthesis and modulation of multifunctional nanomaterials with manifold roles in disease diagnostics and therapy, and provides helpful guidance in designing divalent transition metal ion-doped nanomaterials.

Nd2O3, Cr2O3, and V2O3 Nanoparticles via Calcination: Synthesis, Characterization, Antimicrobial and Antioxidant Activities

Nd2O3, Cr2O3, and V2O3 nanoparticles were prepared by calcining the precursor materials that are novel mixed ligand complexes: [Nd(BDC)(ADMPY)(OAc)].H2O, [Cr(BDC)(ADM PY)Cl].H2O, and [V(BDC)(ADMPY)Cl].H2O, where BDC = 1,4-benzenedicarboxylic acid and ADMPY = 2-amino-4,6-dimethyl pyrimidine. The generated compounds were examined through several techniques such as elemental analysis (C.H.N), UV-Vis spectroscopy, thermal analysis (thermogravimetric, differential thermogravimetry, and differential thermal analysis), FT-IR spectra, X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The TEM micrographs showed that neodymium oxide nanoparticles assumed agglomerated platelet-like particles, with particle sizes around 30.16 nm, while chromium oxide NPs showed solid block material with compact density and fewer pores with nearly spherical shape and 56.12 nm size. The vanadium oxide NPs were an agglomeration of small spherical nanoparticles of 28.4 nm size. The antimicrobial properties of the samples were assessed using two strains of Gram-positive bacteria, two strains of Gram-negative bacteria, and one strain of yeast. The antimicrobial results demonstrated that a large spectrum of activity characterizes the tested compounds because they are active on Gram-positive and Gram-negative bacteria, especially on Gram-positive strains. The antioxidant activity of prepared compounds was assessed by scavenging free radicals of DPPH. Metal oxide NPs also showed promising results as antioxidants.

Dual immobilization of magnetite nanoparticles and biosilica within alginate matrix for the adsorption of Cd(II) from aquatic phase

The adsorption of cadmium ions by magnetite (Fe₃O₄)@biosilica/alginate (MBA nano-hybrid) was the main aim of the present investigation. Herein, MBA nano-hybrid was synthesized via chemical precipitation technique. As-synthesized MBA nano-hybrid was characterized using FT-IR, FESEM and XRD analyzes. Based on the results, the maximum adsorption capacity of the adsorbent for the removal of Cd(II) was obtained at the initial pH of 7.0. At the initial Cd(II) concentration of 40 mg/L, increasing the reaction time to 180 min led to the Cd adsorption of 35.36 mg/g. Since the removal of Cd(II) after the reaction time of 60 min was insignificant, the reaction time of 60 min was considered as optimum reaction time for performing the experimental runs. According to the results, Langmuir isotherm and pseudo-second order kinetic models were the best fitted models with high correlation coefficients (R² > 0.99). The results of thermodynamic study indicated exothermic (positive ΔH°) and spontaneous nature (negative ΔG°) of the adsorption of Cd(II) on the surface of MBA nano-hybrid. Negligible reduction in the adsorption capacity of the nano-hybrid was observed (16.57%) after fifth experimental runs, indicating high reusability potential of the as-synthesized nano-hybrid adsorbent.

Review on some metal oxide nanoparticles as effective adsorbent in wastewater treatment

Water contamination has turned into one of the most serious issues in the world. Nanomaterials are proficient to carry away heavy metals, organic and inorganic dyes, pesticides, and small molecules from polluted water. In this regard, nanoparticles have gained much attention due to their extraordinary properties compared to bulk materials. Metal oxide nanoparticles and nanocomposites have several advantages such as elevated surface area, low concentration, easily separable after treatment and so on. Among many feasible techniques, the adsorption process is one of the most useful techniques for removing heavy ions and dyes from wastewater and has gained much attention from researchers. Several studies on metal oxide nanoparticles and their use in wastewater treatment have been published in the literature. This chapter gives an outline about five metal oxide based nanomaterials and nanocomposites as well as their applications in water pollution removal where the efficiency, limits and favourable circumstances are compared and explored. This article surely helps to gather information about some metal oxide nanoparticles and nanocomposites in wastewater treatment by the adsorption technique. In this review article, we primarily focused on five metal oxide nanoparticles and some of their recent applications published in the last two years.

Solvothermal synthesis of CeO2-ZrO2-M2O3 (M = La, Y, Bi) mixed oxide and their soot oxidation activity

CeO₂–ZrO₂-M₂O₃ (M = La, Y, Bi) mixed oxide has been prepared by a solvothermal synthesis method. The physico–chemical properties of the mixed oxide have been studied by X-ray powder diffraction (XRD), Raman spectroscopy, BET, X-ray photoelectron spectroscopy (XPS), TEM and temperature-programmed reduction (TPR), and the catalytic activity for soot oxidation has been studied by thermogravimetry (TG). La³⁺, Y³⁺ and Bi³⁺ exhibit positive effects on lowering the oxidation temperature of the soot. The XRD and Raman results showed formation of mixed oxides and TEM images suggested the nanosized nature of the particles. The benefit of yttrium or lanthana doping on the catalytic activity of ceria can be related to active oxygen formation provoked by the defective structure of ceria due to the presence of La³⁺ and Y³⁺. The benefit of Bi³⁺ doping on catalytic activity can be related to the reduction at low temperature both with Bi₂O₃ and ceria.

Nano CeO₂-based oxides with meso-pores have been synthesized by a solvothermal method.

Potential antimicrobial, antidiabetic, catalytic, antioxidant and ROS/RNS inhibitory activities of Silybum marianum mediated biosynthesized copper oxide nanoparticles

Use of medicinal plants for the biosynthesis of nanoparticles offers several advantages over other synthesis approaches. Plants contain a variety of bioactive compounds that can participate in reduction and capping of nanoparticles. Plant mediated synthesis has the leverage of cost effectiveness, eco-friendly approach and sustained availability. In the current study Silybum marianum, a medicinally valuable plant rich in silymarin content, is used as a reducing and stabilizing agent for the fabrication of nanoparticles. Biosynthesized CuO-NPs were characterized using High Performance Liquid Chromatography (HPLC), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Dynamic Light Scattering (DLS) techniques. Characterization revealed that CuO-NPs having a crystalline structure showed spherical morphology with an average size of 15 nm. HPLC analysis demonstrated conjugation of various silymarin components, especially the presence of silybin A (705.06 ± 1.59 mg g^-1 DW). CuO-NPs exhibited strong bactericidal potency against clinically important pathogenic bacterial strains e.g. Enterobacter aerogenes and Salmonella typhi with an inhibition zone of 18 ± 1.3 mm and 17 ± 1.2 mm, respectively. Synthesized nanoparticles indicated a dose dependent cytotoxic effect against fibroblast cells exhibiting a percentage cell viability of 83.60 ± 1.505% and 55.1 ± 1.80% at 25 μg mL^-1 and 100 μg mL^-1 concentration, respectively. Moreover, CuO-NPs displayed higher antioxidant potential in terms of (TAC: 96.9 ± 0.26 μg AAE/mg), (TRP: 68.8 ± 0.35 μg AAE/mg), (DPPH: 55.5 ± 0.62%), (ABTS: 332.34 μM) and a significant value for (FRAP: 215.40 μM). Furthermore, enzyme inhibition assays also exhibited excellent enzyme inhibition potential against α-amylase (35.5 ± 1.54%), urease (78.4 ± 1.26%) and lipase (80.50.91%), respectively. Overall findings indicated that biosynthesized CuO-NPs possess immense in vitro biological and biomedical properties and could be used as a broad-spectrum agent for a wider range of biomedical applications.

Importance of Species Heterogeneity in Supported Metal Catalysts

The structural heterogeneity of surface metal species, which is represented by the distribution in size, morphology, and local coordination environment of the active metal component, is almost inevitable in practical supported metal catalysts. This is often regarded as a major hindrance to the full utilization of metal loading and the high mass-specific catalytic activity. In this work, by quantitative evaluation of the individual reaction steps of a probe reaction, cyclohexanol dehydrogenation (an important reaction for hydrogen storage and transportation as well as high valued chemical production), we demonstrate that the inherent heterogeneity of supported Rhodium catalysts prepared by conventional synthesis has unique advantages in a complex heterogeneous catalytic reaction. The isolated Rh species (Rh₁) is extremely active for the first step of dehydrogenation, the transformation of cyclohexanol to cyclohexanone, while the Rh ensemble sites (Rh_e, including Rh clusters, Rh_n, and Rh nanoparticles, Rh_p) are highly efficient for the successive reaction step, cyclohexanone to phenol, for which the Rh₁ sites are almost inactive. Only with the coexistence of both active structures could the optimal reaction performance be achieved, which ambiguously demonstrates the importance of species heterogeneity in some multistep catalytic reactions. Our study provides a new view of the benefits from structural heterogeneity in practical catalysts and sheds light on the catalyst design strategy for complex catalytic reactions.

Solid-State Preparation of Metal and Metal Oxides Nanostructures and Their Application in Environmental Remediation

Nanomaterials have attracted much attention over the last decades due to their very different properties compared to those of bulk equivalents, such as a large surface-to-volume ratio, the size-dependent optical, physical, and magnetic properties. A number of solution fabrication methods have been developed for the synthesis of metal and metal oxides nanoparticles, but few solid-state methods have been reported. The application of nanostructured materials to electronic solid-state devices or to high-temperature technology requires, however, adequate solid-state methods for obtaining nanostructured materials. In this review, we discuss some of the main current methods of obtaining nanomaterials in solid state, and also we summarize the obtaining of nanomaterials using a new general method in solid state. This new solid-state method to prepare metals and metallic oxides nanostructures start with the preparation of the macromolecular complexes chitosan·Xn and PS-co-4-PVP·MXn as precursors (X = anion accompanying the cationic metal, n = is the subscript, which indicates the number of anions in the formula of the metal salt and PS-co-4-PVP = poly(styrene-co-4-vinylpyridine)). Then, the solid-state pyrolysis under air and at 800 °C affords nanoparticles of M°, M_xO_y depending on the nature of the metal. Metallic nanoparticles are obtained for noble metals such as Au, while the respective metal oxide is obtained for transition, representative, and lanthanide metals. Size and morphology depend on the nature of the polymer as well as on the spacing of the metals within the polymeric chain. Noticeably in the case of TiO₂, anatase or rutile phases can be tuned by the nature of the Ti salts coordinated in the macromolecular polymer. A mechanism for the formation of nanoparticles is outlined on the basis of TG/DSC data. Some applications such as photocatalytic degradation of methylene by different metal oxides obtained by the presented solid-state method are also described. A brief review of the main solid-state methods to prepare nanoparticles is also outlined in the introduction. Some challenges to further development of these materials and methods are finally discussed.

Low-Cost and Eco-Friendly Hydroxyapatite Nanoparticles Derived from Eggshell Waste for Cephalexin Removal

This work describes the hydroxyapatite nanoparticle (HAP) preparation from eggshell waste and their application as an adsorbent for Cephalexin (Ceph) antibiotic removal from aqueous solutions. Chemical precipitation with phosphoric acid was used to evaluate the feasibility of calcium oxide for HAP preparation. The structural properties of HAP were characterized by X-ray diffraction, which revealed the formation of the hydroxyapatite crystalline phase formation. In addition, transmitting electron spectroscopy showed an irregular shape with a variation in size. The impact of various experimental conditions on the removal efficiency such as the solution’s pH, contact time, HAP mass, solution temperature, and Ceph concentration were studied. Experimental data showed that HAP could remove most Ceph species from aqueous solutions within 1 h at pH = 7 with 70.70% adsorption efficiency utilizing 50 mg of the HAP. The removal process of Ceph species by HAP was kinetically investigated using various kinetic models, and the results showed the suitability of the pseudo-second-order kinetic model for the adsorption process description. Moreover, the removal process was thermodynamically investigated; the results showed that the removal was spontaneous endothermic and related to the randomness increase. The data confirmed that HAP had high efficiency in removing Ceph antibiotics from an aqueous solution.

Determination of acid structures on the surface of sulfated monoclinic and tetragonal zirconia through experimental and theoretical approaches

The acid structures on both tetragonal and monoclinic sulfated zirconia were studied and successfully proposed through experimental and theoretical approaches.

Nanostructured Manganese Oxides within a Ring-Shaped Polyoxometalate Exhibiting Unusual Oxidation Catalysis

Nanosized manganese oxides have recently received considerable attention for their synthesis, structures, and potential applications. Although various synthetic methods have been developed, precise synthesis of novel nanostructured manganese oxides are still challenging. In this study, using a structurally defined nanosized cavity inside a ring-shaped polyoxometalate, we succeeded in synthesizing two types of discrete 18 and 20 nuclear nanostructured manganese oxides, Mn18 and Mn20, respectively. In particular, Mn18 showed much higher catalytic activity than other manganese oxides for the oxygenation of alkylarenes including electron-deficient ones, and the reaction proceeded through a unique reaction mechanism due to its unusual manganese oxide structure.

Structural, optical and photocatalytic properties of mesoporous CuO nanoparticles with tunable size and different morphologies

Nanomaterials with controllable particle size and shape have fascinating properties. Herein, CuO nanoparticles (NPs) with controlled particle size and morphology are obtained via a simple co-precipitation approach. Variation of the reaction medium composition steers the variation of both particle size and morphology of the CuO NPs. The reaction was performed in ethanol–water solutions with different volume to volume ratios (v/v%) i.e. 0, 25, 50, and 100%. XRD of the obtained samples revealed a drop in their particle size from ∼13 to ∼7 nm when the aqueous medium is entirely replaced by the ethanolic medium. TEM and HR-TEM investigations have pointed to the formation of CuO NPs with rod-like shapes in water (diameter = 15 nm and length = 200 nm). Whereas, spherical NPs with a diameter of 7.2 nm are obtained in ethanol. Structural analysis of CuO samples obtained in different media was done applying the Rietveld method. The volume of the monoclinic unit cell of CuO is increased to 81.869 ų when water (81.207 ų) is completely substituted by ethanol. Moreover, the internal local strain (ε) and the dislocation density (δ) values increase from 2.78 × 10⁻³ to 4.64 × 10⁻³ and 0.592 × 10⁶ to 1.93 × 10⁶ line per m², respectively by changing from aqueous to ethanolic medium. The optical band gap (E_g) determined using Tauc's equation for the direct transition is increased from 2.2 to 2.65 eV when water is totally replaced by ethanol. The feasibility of both CuO samples as photocatalysts for the degradation of Congo red was tested. CuO prepared in pure water showed remarkably high efficiency during the first 25 min of illumination. Both samples showed complete dye removal after 35 min. Ultimately, this work presents a simple and green approach for the preparation of CuO NPs with tunable particle size, varied morphological shapes, high surface area, and different structural and optical properties merely through controlling the ethanol content in water.

Ethanol/water percentage plays a crucial role in tuning of the particle size and morphology, hence the structural, optical and photocatalytic properties of the synthesized CuO nanomaterials.

The Effect of Pristine and Hydroxylated Oxide Surfaces on the Guaiacol HDO Process: A DFT Study

The acid‐base character of oxide supports is crucial for catalytic reactions. In this work, the acid‐base properties of five oxide surfaces common in heterogeneous catalysis were investigated and related to their interaction with monolignol compounds derived from lignin. We have used density functional theory simulations also to understand the role of the surfaces’ hydroxylation state. The results show that moderate hydroxyl coverage on the amphoteric γ‐Al₂O₃ (110) slightly strengthens the oxy‐compounds’ adsorption due to an increase in Lewis acidity. Similarly, low hydroxyl coverage on the reducible TiO₂ (101) enlarges its adsorption capacity by up to 42 % compared with its clean surface. The higher affinity is attributed to the more favourable interaction between the surface‐OH groups and the aromatic rings. Overall, the results indicate that hydroxyl coverage enhances the amphoteric and reducible adsorption capacity towards aromatic species.

Binding and stability of MgO monomers on anatase TiO2(101)

In catalysis, MgO is often used to modify the acid-base properties of support oxides and to stabilize supported metal atoms and particles on oxides. In this study, we show how the sublimation of MgO powder can be used to deposit MgO monomers, hither on anatase TiO₂(101). A combination of x-ray electron spectroscopy, high-resolution scanning tunneling microscopy, and density functional theory is employed to gain insight into the MgO monomer binding, electronic and vibrational properties, and thermal stability. In the most stable configuration, the Mg and O of the MgO monomer bind to two surface oxygens and one undercoordinated surface titanium, respectively. The additional binding weakens the Mg-O monomer bond and makes Mg more ionic. The monomers are thermally stable up to 600 K, where the onset of diffusion into the TiO₂ bulk is observed. The monomeric MgO species on TiO₂(101) represent an ideal atomically precise system with modified acid-base properties and will be employed in our future catalytic studies.

Dispersions of Zirconia Nanoparticles Close to the Phase Boundary of Surfactant-Free Ternary Mixtures

The achievement of a homogeneous dispersion of nanoparticles is of paramount importance in supporting their technological application. In wet processing, stable dispersions were largely obtained via surfactant or surface functionalization: although effective, the use of dispersant can alter, or even impair, the functional properties of the resulting nanostructured systems. Herein, we report a novel integrated modeling and experimental approach to obtain stable ZrO₂ nanoparticle (NP) dispersions at native dimensions (about 5 nm) in homogeneous ternary mixtures of solvents (i.e., water, ethanol, and 1,2-dichlorobenzene) without any further surface functionalization. A miscibility ternary diagram was computed exploiting the universal quasi-chemical functional-group activity coefficient (UNIFAC) model, which was then experimentally validated. Dynamic light scattering (DLS) on these mixtures highlights that nanometric structures, resembling nanoemulsion droplets, form close to the mixture two-phase boundary, with a size that depends on the ternary mixture composition. ZrO₂-NPs were then synthesized following a classic sol-gel approach and characterized by XRD and Raman spectroscopy. ZrO₂-NPs were dispersed in HCl and mixed with different mixtures of ethanol and 1,2-dichlorobenzene (DCB), obtaining homogeneous and stable dispersions. These dispersions were then studied by means of DLS as a function of DCB concentration, observing that the nanoparticles can be dispersed at their native dimensions when the mass fraction of DCB was lower than 60%, whereas the increase of the hydrophobic solvent leads to the NPs' agglomeration and sedimentation. The proposed approach not only offers specific guidelines for the design of ZrO₂-NPs dispersions in a ternary solvent mixture but can also be extended to other complex solvent mixtures in order to achieve stable dispersions of nanoparticles with no functionalization.

Tunable metal–organic framework nanoarrays on carbon cloth constructed by a rational self-sacrificing template for efficient and robust oxygen evolution reactions

The morphology and electronic structure of MOF-74 nanoarrays on carbon cloth were modulated for oxygen evolution reactions with self-sacrificing templates of Co/Ni(OH)2 nanosheets.

Invisible Surface Oxygen Vacancies in a Thin MgO Film: Impacts on the Chemical Activity and Secondary Electron Emission

Today, Fs defects in MgO as isolated surface neutral oxygen vacancies are in the focus of surface science, catalysis research, and emission coating of microchannel plates. With the 10^-4 atom % content at 750 K and under p_O2 = 10^-9 Torr, estimated by us from the known equilibrium T-x and p-T-x diagrams of MgO, Fs defects remain invisible or difficult-to-detect objects. The MgO(100) → MgO(100) + Fs + ¹/₂O₂ phase transition was studied in MgO films deposited by the metal-organic chemical vapor deposition (MOCVD) procedure from the mixed-ligand Mg precursor on Si substrates at 725 K in the O₂ flow where the nonstoichiometric phase (MgO/Fs) is formed in the gas medium containing simultaneous H₂, CO, H₂O, CO, and O₂ species in unbalanced concentrations. Realization of the above transition was proven theoretically and experimentally through kinetic-thermodynamic analysis of the nonequilibrium system with revealing thermodynamic motive forces, i.e., the positive enthalpy and entropy, as well as through a new combination of diagnostic methods including the original differential dissolution method, due to which separate determination of the point and morphological defects was achieved. It was found that Fs defects occur when oxygen in the immediate vicinity to the substrate surface is replaced practically completely by the oxidized products of the precursor and the resulting oxygen pressure becomes enough for this process. The 90 mass % of the as-deposited MgO-film-involved (MgO/Fs) phase; its chemical activity is demonstrated through dissolution in hot water, while the electron donor activity is through 9 at 750 eV secondary electron yield. A good understanding of gas-phase reactions between the precursors and oxygen provides the fundamental basis of the MOCVD process to deposit MgO films that are dense, free from carbon, and of homogeneous texture. This makes the MOCVD process suitable also for use as coatings of microchannel plates.

Incorporation of NiO into SiO2, TiO2, Al2O3, and Na4.2Ca2.8(Si6O18) Matrices: Medium Effect on the Optical Properties and Catalytic Degradation of Methylene Blue

The medium effect of the optical and catalytic degradation of methylene blue was studied in the NiO/SiO₂, NiO/TiO₂, NiO/Al₂O₃, and NiO/Na_4.2Ca_2.8(Si₆O₁₈) composites, which were prepared by a solid-state method. The new composites were characterized by XRD (X-ray diffraction of powder), SEM/EDS, TEM, and HR-TEM. The size of the NiO nanoparticles obtained from the PSP-4-PVP (polyvinylpyrrolidone) precursors inside the different matrices follow the order of SiO₂ > TiO₂ > Al₂O₃. However, NiO nanoparticles obtained from the chitosan precursor does not present an effect on the particle size. It was found that the medium effect of the matrices (SiO₂, TiO₂, Al₂O₃, and Na_4.2Ca_2.8(Si₆O₁₈)) on the photocatalytic methylene blue degradation, can be described as a specific interaction of the NiO material acting as a semiconductor with the M_xO_y materials through a possible p-n junction. The highest catalytic activity was found for the TiO₂ and glass composites where a favorable p-n junction was formed. The isolating character of Al₂O₃ and SiO₂ and their non-semiconductor behavior preclude this interaction to form a p-n junction, and thus a lower catalytic activity. NiO/SiO₂ and NiO/Na_4.2Ca_2.8(Si₆O₁₈) showed a similar photocatalytic behavior. On the other hand, the effect of the matrix on the optical properties for the NiO/SiO₂, NiO/TiO₂, NiO/Al₂O₃, and NiO/Na_4.2Ca_2.8(Si₆O₁₈) composites can be described by the different dielectric constants of the SiO₂, TiO₂, Al₂O₃, Na_4.2Ca_2.8(Si₆O₁₈) matrices. The maxima absorption of the composites (λ_max) exhibit a direct relationship with the dielectric constants, while their semiconductor bandgap (E_g) present an inverse relationship with the dielectric constants. A direct relationship between λ_max and E_g was found from these correlations. The effect of the polymer precursor on the particle size can explain some deviations from this relationship, as the correlation between the particle size and absorption is well known. Finally, the NiO/Na_4.2Ca_2.8(Si₆O₁₈) composite was reported in this work for the first time.

Sonochemical dissolution of nanoscale ThO2 and partial conversion into a thorium peroxo sulfate

The influence of the sample morphology and experimental conditions towards the sonochemical dissolution of nanoscale ThO₂ samples in sulfuric acid media is described. Significant sonochemical dissolution rates and yields are observed at 20 kHz under Ar/O₂ atmosphere in dilute 0.5 M H₂SO₄ at room temperature, contrasting with the generally-reported high refractory behavior for ThO₂. The dissolution of ThO₂ combines the physical effects driven by acoustic cavitation phenomenon, the complexing affinity of Th(IV) in sulfuric medium and the sonochemical generation of H₂O₂. These sonochemical conditions further allow the observation of the partial conversion of ThO₂ into a scarce Th(IV) peroxo sulfate with 1D morphology resulting from one or both following processes: dissolution/reprecipitation or formation of an intermediate Th(IV) surface complex.

Flame-made Particles for Sensors, Catalysis, and Energy Storage Applications

Flame spray pyrolysis of precursor-solvent combinations with high enthalpy density allows the design of functional nanoscale materials. Within the last two decades, flame spray pyrolysis was utilized to produce more than 500 metal oxide particulate materials for R&D and commercial applications. In this short review, the particle formation mechanism is described based on the micro-explosions observed in single droplet experiments for various precursor-solvent combinations. While layer fabrication is a key to successful industrial applications toward gas sensors, catalysis, and energy storage, the state-of-the-art technology of innovative in situ thermophoretic particle production and deposition technology is described. In addition, noble metal stabilized oxide matrices with tight chemical contact catalyze surface reactions for enhanced catalytic performance. The metal-support interaction that is vital for redox catalytic performance for various surface reactions is presented.

Solar oxidation of toluene over Co doped nano-catalyst

Cobalt (Co) co-doped TiO₂ photo-catalysis were synthesized, characterized and tested toward solar photocatalytic oxidation of toluene (TOL). A multi-technique approach was used to characterize and relate the photo-catalytic property to photo-oxidation performance. Adding Co to TiO₂ significantly changed crystal size and surface morphology (surface area, pore-volume, and pore size), reduced the bandgap energy of TiO₂ and improved the solar photo-oxidation of TOL. Up to 96.5% of TOL conversion (%TN_conv) was achieved by using Co-TiO₂ compared with 28.5% with naked TiO₂. The maximum %TN_conv was achieved at high hydraulic retention time (HRT) ≥ 100 s, Co content in the photo-catalyst of 5 wt% and relative humidity (%RH) of 50%. The mechanism of TOL solar oxidation was related to the concentration of OH• and •O₂^-. radicals produced from the generated electrons and holes on the surface of Co-TiO₂. The products formed during the photo-catalytic oxidation of TOL were mainly CO₂ and water, and minor concentration of benzene and benzaldehyde. Overall, the Co-TiO₂ could be used as a potential photo-catalyst for the oxidation of toluene in gas-phase streams on an industrial scale.