Tuning the physicochemical features of titanium oxide nanomaterials by ultrasound: Elevating photocatalytic selective partial oxidation of lignin-inspired aromatic alcohols

The research for “green” and economically feasible approaches such as (photo)catalysis especially for biomass valorization such as selective oxidation of biomass derived compounds like aromatic alcohols to corresponding aldehyde by avoiding the harsh reaction conditions and the addition of reagents concentrate the focus of attention the last years. Hence, design and development of novel photocatalyst for the partial selective oxidation is highly desirable. In this research work, ultrasonication of different frequencies (22, 40, 80 kHz) and different amplitudes was utilized as synthesis tool in order to obtain novel materials by precipitation method. The synthesized samples were characterized by using different techniques such as N₂ sorption, TEM, XPS, XRD, thermal analysis, and diffuse reflectance spectroscopy. The synthesized sample by using low ultrasound frequency (22 kHz) and amplitude showed a mixed morphological and structural nature consisting of asymmetric 1-dimensional (nanorods-like), layered nano-structures and not well-defined areas, leading to elevate for metal oxide specific surface areas up to 155 m²/g. The observed 1-D nanostructures have diamentions in the range of 20–60 nm. This sample revealed the highest photo-oxidation efficiency for the selective conversion of two biomass-derived, and more specifically lignin-inspired model compounds, benzyl alcohol and cinnamyl alcohol to benzaldehyde and cinnamyl aldehyde, respectively, and hence the highest yield towards the desired aldehydes. The selective photo-oxidation activity was retained even after 5 photocatalytic cycles, while no leaching of Ti was recorded.     

Pt nanoparticles supported over Ce–Ti–O: the solvothermal and photochemical approaches for the preparation of catalytic materials

Ce–Ti–O supports with different Ce/Ti molar ratios were synthesized by the solvothermal method using hexadecyltrimethylammonium bromide. Pt nanoparticles were then supported by photochemical deposition. The shape, size, and structure of these materials were analyzed by high-resolution transmission electron microscopy. The single CeO₂ support was also prepared, consisting of agglomerated cubic particles ranging from ~3 to 8 nm. When titania was combined with ceria, a nanostructured architecture was produced, evidencing the strong influence of Ti in the support structure. Photodeposition of Pt nanoparticles is more efficient on Ce–Ti–O supports than in pristine CeO₂. Crystalline Pt nanoparticles (mainly of ~2 to 4 nm) were detected. The catalytic properties of the materials were tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. It was observed that Pt supported on Ce–Ti–O is more active and selective than Pt on CeO₂ or TiO₂ separately. The catalyst with 40 mol% Ce leads to total conversion of cinnamaldehyde in a few minutes; however, higher selectivity toward the desired product (cinnamyl alcohol) was obtained with higher amounts of Ce (50 mol%).     

Carbon nanotubes supported Cu-Ni bimetallic catalysts and their properties for the direct synthesis of dimethyl carbonate from methanol and carbon dioxide

Multi-walled carbon nanotubes (MWCNTs) supported Cu-Ni bimetallic catalysts for the direct synthesis of dimethyl carbonate (DMC) from CH₃OH and CO₂ were synthesized and investigated. The supporting materials and the synthesized catalysts were fully characterized using FTIR, scanning electron microscopy (SEM), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) techniques. The catalytic activities were investigated by performing micro-reactions. The experimental results showed that the metal phase and Cu-Ni alloy phase in the catalyst were partially formed during the calcination and activation step. Active metal particles were dispersed homogeneously on the surface of the MWCNTs. Cu-Ni/MWCNTs catalysts were efficient for the direct synthesis of DMC. The highest conversion of CH₃OH was higher than 4.3% and the selectivity of DMC was higher than 85.0% under the optimal catalytic conditions of 120 °C and around 1.2 MPa. The high catalytic activity of Cu-Ni/MWCNTs in DMC synthesis can be attributed to the synergetic effects of metal Cu, Ni and Cu-Ni alloy in the activation of CH₃OH and CO₂, the unique structure of MWCNTs and the interaction between the metal particles and the supports.     

Ultrasonically assisted surface modified CeO2 nanospindle catalysts for conversion of CO2 and methanol to DMC

This study developed a facile and effective approach to engineer the surface properties of cerium oxide (CeO₂) nanospindle catalysts for the direct synthesis of dimethyl carbonate (DMC) from CO₂ and methanol. CeO₂ nanospindles were first prepared by a simple precipitation method followed by wet chemical redox etching with sodium borohydride (NaBH₄) under high intensity ultrasonication (ultrasonic horn, 20 kHz, 150 W/cm²). The ultrasonically assisted surface modification of the CeO₂ nanospindles in NaBH₄ led to particle collisions and surface reduction that resulted in an increase in the number of surface-active sites of exposed Ce³⁺ and oxygen vacancies. The surface modified CeO₂ nanospindles showed an improvement of catalytic activity for DMC formation, yielding 17.90 mmol·g_cat⁻¹ with 100 % DMC selectivity. This study offers a simple and effective method to modify a CeO₂ surface, and it can further be applied for other chemical activities.     

Very rapid synthesis of highly efficient and biocompatible Ag2Se QD phytocatalysts using ultrasonic irradiation for aqueous/sustainable reduction of toxic nitroarenes to anilines with excellent yield/selectivity at room temperature

There are many problems associated with the synthesis of nanocatalysts and catalytic reduction of nitroarenes - e.g., high temperatures, costs, long reaction/synthesis process times, the toxicity of chemicals/solvents, undesirable byproducts, the toxic/harmful wastes, low efficiency/selectivity, etc. This study represents an attempt to overcome these challenges. To this purpose, biocompatible and highly efficient Ag₂Se quantum dots (QDs) catalysts with antibacterial activity were synthesized in a very rapid (30 sec, rt), simple, inexpensive, sustainable/green, and one-pot strategy in water using ultrasonic irradiation. Characterization of the QDs was performed using different techniques. UV–Vis absorption and fluorescence spectroscopic studies showed an absorption peak at 480–550 nm and a maximum emission peak around 675 nm, which confirmed the successful synthesis of Ag₂Se QDs via the applied biosynthetic method. Subsequently, catalytic reduction of nitroarenes by them was carried out under safe conditions (H₂O, rt, air atmosphere) in ∼ 60 min with excellent yield and selectivity (>99%). Their catalytic activity in the reduction of various toxic nitroarenes to aminoarenes under green conditions was investigated. Thus, a rapid and safe ultrasound-based method was employed to prepare stable and green Ag₂Se QDs phyto-catalysts with unique properties, including exquisite monodispersity in shape (orthorhombic) and size (∼7 nm), air-stability, and good purity and crystallinity. Importantly, instead of various toxic chemicals, the plant extract obtained by rapid ultrasonic method (10 min, rt) was used as natural reducing, capping, and stabilizing agents. Moreover, antibacterial assays results showed that Ag₂Se-QDs catalysts at low concentrations (ppm) have high activity against all tested bacteria, especially E. coli (MIC:31.25 ppm, MBC:125 ppm) which were significantly different from those of Fig extract (MIC = MBC:500 ppm). The data reflect the role of these bio-synthesized Ag₂Se-QDs catalysts in the development of versatile and very safe catalysts with biomedical properties.     

Synthesis of novel amorphous calcium carbonate by sono atomization for reactive mixing

Droplets of several micrometers in size can be formed in aqueous solution by atomization under ultrasonic irradiation at 2 MHz. This phenomenon, known as atomization, is capable of forming fine droplets for use as a reaction field. This synthetic method is called SARM (sono atomization for reactive mixing). This paper reports on the synthesis of a novel amorphous calcium carbonate formed by SARM. The amorphous calcium carbonate, obtained at a solution concentration of 0.8 mol/dm³, had a specific surface area of 65 m²/g and a composition of CaCO₃•0.5H₂O as determined using thermogravimetric/differential thermal analysis (TG-DTA). Because the ACC had a lower hydrate composition than conventional amorphous calcium carbonate (ACC), the ACC synthesized in this paper was very stable at room temperature.     

Biosynthesis of gold nanoparticles by Aspergillum sp. WL-Au for degradation of aromatic pollutants

A simple method for synthesis of gold nanoparticles (AuNPs) using Aspergillum sp. WL-Au was presented in this study. According to UV–vis spectra and transmission electron microscopy images, the shape and size of AuNPs were affected by different parameters, including buffer solution, pH, biomass and HAuCl₄ concentrations. Phosphate sodium buffer was more suitable for extracellular synthesis of AuNPs, and the optimal conditions for AuNPs synthesis were pH 7.0, biomass 100 mg/mL and HAuCl₄ 3 mM, leading to the production of spherical and pseudo-spherical nanoparticles. The biosynthesized AuNPs possessed excellent catalytic activities for the reduction of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, o-nitroaniline and m-nitroaniline in the presence of NaBH₄, and the catalytic rate constants were calculated to be 6.3×10⁻³ s⁻¹, 5.5×10⁻³ s⁻¹, 10.6×10⁻³ s⁻¹, 8.4×10⁻³ s⁻¹ and 13.8×10⁻³ s⁻¹, respectively. The AuNPs were also able to catalyze the decolorization of various azo dyes (e.g. Cationic Red X-GRL, Acid Orange II and Acid scarlet GR) using NaBH₄ as the reductant, and the decolorization rates reached 91.0–96.4% within 7 min. The present study should provide a potential candidate for green synthesis of AuNPs, which could serve as efficient catalysts for aromatic pollutants degradation.     

Synthesis and luminescence of SrZnO2 phosphors

SrZnO₂ phosphors have been synthesized by two new methods viz. carbonate decomposition at 1000 °C and combustion synthesis. Phosphors activated with Pb²⁺, Sm³⁺, Tb³⁺, Bi³⁺ and Pr³⁺ could be prepared in one step using the combustion synthesis. Characteristic emission and excitation were observed for Bi³⁺. For the remaining activators excitation spectra always contained a band at 283 nm. Presence of this band for all these different types of activators was interpreted as host sensitization.     

Effect of growth time of hydrothermally grown cobalt hydroxide carbonate on its supercapacitive performance

We present the time-dependent synthesis of cobalt hydroxide carbonate nanorods by hydrothermal method with a systematic increase of different parameters such as specific surface area and specific capacitance as a function of different synthesis time. Morphological characterization of the cobalt hydroxide carbonate nanorods were carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that variation of the time of reaction plays a crucial role in the transformation of samples’ morphology. Cobalt hydroxide carbonate nanorods synthesized with 12 h reaction time, which is the reaction just before the materials transforms into cobalt oxide under the same synthesis conditions exhibited the highest specific capacitance of 466 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH electrolyte and also showed excellent stability with ∼99% capacitance retention after 2000 cycles at a current density of 10 A g⁻¹. Based on the above results, the cobalt hydroxide carbonate nanorods show a considerable potential as electrodes materials for supercapacitor applications.     

Facile sonochemical synthesis of rutile-type titanium dioxide microspheres decorated graphene oxide composite for efficient electrochemical sensor

In this reports the facile and green synthesis of rutile-type titanium dioxide nanoparticles decorated graphene oxide nanocomposite via the ultrasonication process (frequency: 50 kHz, Power: 100 W/cm² and Ultrasonic type: Ti-horn). Because, the sonochemical synthesis method is simple, non-explosive and harmless method than other conventional technique. Furthermore, the synthesized material was characterized by various analytical techniques including FESEM, EDX, XRD, EIS and electrochemical methods. Then, the synthesized TiO₂ MPs@GOS composite was applied for the electrocatalytic detection of theophylline (TPL) using CV and amperometric (current-time) techniques. Captivatingly, the modified sensor has excellent electrocatalytic performance with the wider linear range from 0.02 to 209.6 µM towards the determination of theophylline and the LOD and sensitivity of the modified sensor was calculated as 13.26 nM and 1.183 μA·µM⁻¹·cm⁻², respectively. In addition, a selectivity, reproducibility and stability of the TiO₂ MPs@GOS modified GCE were analyzed towards the determination of theophylline molecule. Finally, the real time application of TiO₂ MPs@GOS modified theophylline sensor was established in serum and drug samples.     

Synthesis,structural and optical properties of Eu3+–doped Ca2V2O7 nanophosphors

Europium doped calcium pyrovanadate nanoparticles Ca₂V₂O₇:Eu³⁺, having a size of 57–63 nm, were synthesized using combustion process. Structure, morphological and optical properties of nanophosphors have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fluorescence spectrometry (PL) and Fourier transform infra-red (FT-IR) spectroscopy. X-ray studies shows that a pure triclinic Ca₂V₂O₇ phase was obtained at 900 °C temperature. The red emission observed at 620 nm upon excitation at 305 nm is due to hypersensitive transition ⁵D₀ → ⁷F₂ of luminescent activator Eu³⁺ location at a site with no inversion symmetry in Ca₂V₂O₇ crystal lattice. High luminescent intensity and easy synthesis technique make this red phosphor a promising candidate for application as luminescent materials.     

Nano ZSM-5 type ferrisilicates as novel catalysts for ethylbenzene dehydrogenation in the presence of N2O

Nanosized ZSM-5 type ferrisilicates were successfully prepared using hydrothermal process. Several parameters including gel initiative compositions (Na⁺ or K⁺ alkali system), SiO₂/Fe₂O₃ molar ratios and hydrothermal temperature were systematically investigated. The samples were characterized by XRD, TEM, SEM-EDS, BET surface area and ICP techniques. It was found that surface areas and the total pore volume increase with increasing in the SiO₂/Fe₂O₃ molar ratio at Na-FZ ferrisilicates. The catalytic performance of the synthesized catalysts was evaluated in ethylbenzene dehydrogenation to styrene in the presence of N₂O or steam at temperatures ranging from 400 °C to 660 °C under atmospheric pressure. The effects of gel initiative compositions, SiO₂/Fe₂O₃ molar ratio as well as the hydrothermal synthesis temperature on the catalytic performance of these catalysts have been addressed. It was shown that styrene yield significantly influenced by altering in the SiO₂/Fe₂O₃ ratio but was not greatly influenced by changes in hydrothermal synthesis temperatures. The comparison between performance of potassium and sodium containing catalysts was shown that the one with potassium has higher yield and selectivity toward styrene production at an optimum temperature of 610 °C.     

Enhancement of catalytic activity in NH3-SCR reaction by promoting dispersibility of CuCe/TiO2-ZrO2 with ultrasonic treatment

A series of CuCe-modified TiO₂-ZrO₂ catalysts synthesized by stepwise impregnation method and ultrasonic-assisted impregnation method were investigated to research the removal of NO in the simulated flue gas. Results showed that the CuCe/TiO₂-ZrO₂ catalyst prepared by ultrasonic-assisted impregnation method exhibited the superior NO conversion, in which higher than 85% NO was degraded at the temperature range of 250–400 °C and the highest NO conversion of 94% at 350 °C. It proves that ultrasonic treatment can markedly improve the performance of catalysts. The effect of ultrasonic enhancement on CuCe/TiO₂-ZrO₂ was comprehensively studied through being characterized by physicochemical characterization. Results reveal that the ultrasonic cavitation effect improves the distribution of active species and the synergistic interaction between Cu with Ce components (Cu⁺ + Ce⁴⁺ ↔ Cu²⁺ + Ce³⁺) on the catalysts significantly, thus resulting in better dispersibility as well as a higher ratio of Cu²⁺ and Ce³⁺ of the catalysts. Moreover, it was found that the CuCe/TiO₂-ZrO₂ catalyst prepared by the ultrasonic-assisted impregnation method represented a higher degree of ultrafine metal particles and evenness. The above results were described with the generalized dimension and singularity spectra in multifractal analysis and validated by the comparative test. Therefore, it can be concluded that ultrasonic treatment facilitates the particle size and distribution of active sites on the catalysts.     

Ultrasound-assisted rapid hydrothermal design of efficient nanostructured MFI-Type aluminosilicate catalyst for methanol to propylene reaction

The influence of ultrasound-assisted rapid hydrothermal synthesis of aluminosilicate ZSM-5 catalysts was examined in this work. A series of MFI-type nanostructured materials with sonochemical approach and conventional heating were synthesized and evaluated for conversion of methanol to propylene reaction. The prepared samples were tested by characterization analyses such as XRD, FESEM, BET-BJH, FTIR, TPD-NH₃ and TG/DTG. The obtained results confirmed that ultrasound treatment enhanced the nucleation process and crystal growth for ZSM-5 sample synthesized at moderate temperature of 250 °C. Therefore, it was found the formation of pure MFI zeolite with high crystallinity and improved textural, structural and acidic properties for ZSM-5(UH-250) sample compared with the other zeolites. This observation was attributed to the relationship between the perfect crystallization mechanism and catalytic properties, which led to producing an efficient MFI zeolite toward the optimal catalytic performance. In this manner, the methanol conversion and products selectivity of prepared materials were carried out in MTP reaction at 460 °C and atmospheric pressure. The ZSM-5(UH-250) zeolite with slower deactivation regime exhibited the constant level of methanol conversion (84%) and high propylene selectivity (78%) after 2100 min time on stream. Moreover, the synthesis pathway for MFI zeolite at moderate temperature and also deactivation mechanism of improved sample were proposed.     

Oxidation state of vanadium in amorphous MnV2O6 formed during discharge–charge cycle and the improvement of its synthesis condition

Crystalline powders of anhydrous MnV₂O₆ were successfully synthesized at a temperature below 200 °C under autogenous hydrothermal condition. MnV₂O₆ powders, which were synthesized using high concentration solutions, more than 0.1 mol/L, gave a relatively high reversible capacity of 600 mA h/g and interesting cyclic performance, reversible capacity increasing to more than an initial charge capacity after the 3rd or 4th cycle of charge–discharge. The change in oxidation state of V ion on the course of the 1st discharge–charge process was investigated by different techniques, such as XAFS and XPS. During discharging, V⁵⁺ was found to change gradually to V⁴⁺, but it returned back completely to V⁵⁺ on charging process. The thinner particles of MnV₂O₆ crystals with rod-like morphology were synthesized at 135 °C, and much better anodic performance was achieved, much smaller irreversible capacity as about 300 mA h/g, stable reversible capacity as 600 mA h/g, and 100% Coulombic efficiency.     

Rapid sonochemical synthesis of MCM-41 type benzene-bridged periodic mesoporous organosilicas

Benzene-bridged periodic mesoporous organosilicas (PMOs) with the MCM-41 were synthesized by a rapid sonochemical process via co-condensation of tetraethoxysilane (TEOS) and 1,4-bis(triethoxysilyl) benzene (BTEB) under basic conditions within a few minutes using cetyltrimethylammoniumbromide (CTMABr) as a structure-directing agent. The molar ratio of the silicon precursors and the synthesis time were varied in order to investigate their influence on the structural ordering of the materials. The characteristics of the materials were evaluated by X-ray diffraction (XRD), N₂-sorption, transmission electron microscopy (TEM) and solid-state NMR spectroscopy. The resultant materials exhibited well-ordered hexagonal mesostructures with surface areas in the range of 602–1237 m²/g, pore volumes of 0.37–0.68 cm³/g, and pore diameters in the range of 2.5–3.5 nm. Two dimensional ²⁹Si{¹H} heteronuclear correlation (HETCOR) NMR spectra confirmed the formation of a single mesophase with various Q (from TEOS) and T (from BTEB) silicon species located randomly within the pore walls due to the co-condensation of BTEB and TEOS, which excluded the possibility of formation of island or two separate phases within such a short synthesis time. The prime advantage of the present synthesis route is that it can effectively reduce the total synthesis time from days to a few minutes, much shorter than the conventional benzene-bridged PMOs synthesis methods.     

Preparation of highly ordered mesoporous AlSBA-15-SO3H hybrid material for the catalytic synthesis of chalcone under solvent-free condition

Single-step preparation of SBA-15 materials functionalized with both propylsulfonic acid groups and aluminum species (AlSBA-15-SO₃H) was carried out by hydrothermal treatment of a mixture of aluminum isopropoxide, 3-mercaptopropyltriethoxysilane, tetraethoxysilane, and triblock copolymer surfactant. At Si/Al molar ratio of 11-96, the materials exhibited well-ordered hexagonally arranged mesopores with pore diameter of ca. 9 nm, BET surface area of 546.9-666.0 m² g⁻¹, and pore volume of 0.82-1.03 cm³ g⁻¹. As-prepared AlSBA-15-SO₃H was successfully used in the Claisen-Schmidt condensation reaction of benzaldehyde with acetophenone to produce chalcone under solvent-free condition, and the influence of the reaction parameters including temperatures, molar ratios of BZD to APN, and aluminum loadings were considered during the chalcone synthesis procedure. It showed that AlSBA-15-SO₃H exhibited significantly high catalytic activity and selectivity, outperforming the reference catalysts such as sulfuric acid, ZSM-5, and acidic MCM-49. In addition, the catalytic stability and regeneration of AlSBA-15-SO₃H was studied.     

VPO catalysts synthesized on substrates with modified activated carbons

VPO catalysts were prepared on oxidized and unoxidized activated carbons differing in initial porous structure. Carbons were oxidized under relatively soft (30% H₂O₂, 200 °C) and hard (50% H₂O₂, 350 °C) conditions. Carbon modification was carried out hydrothermally in a traditional autoclave (HTT) or a microwave reactor (MWT). The synthesis was also carried out under hydrothermal (HTS or MWS) conditions. V₂O₅ and NH₄VO₃ were used as precursors. The samples are characterized by diversified porous structure at S_BET = 732-1617 m²/g and V_por = 0.44-0.90 cm³/g, as well as various degree of VPO crystallinity. Possibility of preparation of the VPO catalysts under ecologically appropriate conditions, i.e. in aqueous solutions, was shown.     

Synthesis of LiFePO4-C cathode materials using a green and low-cost method

LiFePO₄-C was prepared by the solid-state reaction using LiH₂PO₄, Fe₂O₃, and glucose as raw materials, which is a green and low-cost method. Thermogravimetry, differential scanning calorimetry, X-ray diffraction, and element analyzer were used to study the phase and carbon content of the synthesized samples. The optimum conditions for synthesizing LiFePO₄ are identified. The discharge capacity of 120 mAh g⁻¹ was achieved at a current density of 100 mA g⁻¹ between 2.5 and 4.2 V during the first 50 cycles.     

Defect Structure and Up-conversion Luminescence Properties of ZrO<Subscript>2</Subscript>:Yb<Superscript>3+</Superscript>,Er<Superscript>3+</Superscript> Nanomaterials

The up-converting ZrO₂:Yb³⁺,Er³⁺ nanomaterials were prepared with the combustion and sol–gel methods. FT-IR spectroscopy was used for analyzing the impurities. The crystal structures were characterized with X-ray powder diffraction and the mean crystallite sizes were estimated with the Scherrer formula. Up-conversion luminescence measurements were made at room temperature with IR-laser excitation at 977 nm. The IR spectra revealed the conventional and OH⁻ impurities for the combustion synthesis products. The structure of the ZrO₂:Yb³⁺, Er³⁺ nanomaterials was cubic except for the minor monoclinic and tetragonal impurities obtained with the sol–gel method. The materials showed red (650–700 nm) and green (520–560 nm) up-conversion luminescence due to the ⁴F_9/2→⁴I_15/2 and (²H_11/2, ⁴S_3/2)→⁴I_15/2 transitions of Er³⁺, respectively. The products obtained with the combustion synthesis exhibited the most intense luminescence intensity and showed considerable afterglow.