CuO Aggregates Research Articles

Catalytic functionalization of MCM-41 and MCM-48 with copper by modified template ion-exchange method for low-temperature NH3-SCR process: the role of complexing agents for copper dispersion

Mesoporous silicas of MCM-41 and MCM-48 types were synthesized and modified with copper by template ion-exchange (TIE) technique. A high dispersion of deposited copper species was managed by subsequent treatment of the samples with ammonia, urea, or acetonitrile solution. Copper-modified silicas were analysed in terms of their chemical composition (ICP-OES), ordering of porous structure (XRD), textural parameters (low-temperature N2 sorption), dispersion and form of introduced copper species (UV–vis-DR, XRD, H2-TPR, NH3-TPD). Mesoporous silicas modified with copper exhibited promising catalytic efficiency in selective catalytic reduction of NO with ammonia (NH3-SCR). The samples containing dispersed copper species (predominantly monomeric copper cations) presented enhanced catalytic activity compared to catalysts containing CuO aggregates. On the other hand, CuO aggregates showed greater catalytic activity in the side process of direct ammonia oxidation by oxygen present in the reaction mixture. It was demonstrated that TIE post-treatment of the samples with urea resulted in most effective improving dispersion of deposited copper and is less destructive for ordered porous structures of mesoporous silica comparing to treatment with ammonia solution.Graphical abstract

Revealing the Roles of Cu/Ba on Ce-Based Passive NOx Adsorbers

At present, passive NOx adsorbers (PNAs) represent one of the most effective technologies for addressing NOx emissions from diesel engines during cold-start periods. Conventional PNAs, which primarily consist of noble metals (such as Pt, Pd, and Ag) loaded on metal oxides or zeolites, share the common drawback of high production costs. Consequently, developing low-cost PNAs with outstanding NOx storage performance remains a significant challenge. In this study, a series of CuxBa5Ce adsorbents were synthesized using the impregnation method, and a monolithic adsorbent was employed to evaluate NOx storage and release performance. Techniques such as XRD, UV-Vis DRs, H2-TPR, XPS, and in situ DRIFTs confirmed the crucial roles of Cu and Ba in NOx storage and release. Specifically, the incorporation of Cu into CeO2 enhanced NOx storage performance. Moreover, in the Cu3Ba5Ce adsorbent, the addition of Ba not only introduced new storage sites and altered the stability of NOx adsorption species but also helped prevent the aggregation of CuO, thereby prolonging the complete NOx storage duration and satisfying desorption temperature requirements. The Cu3Ba5Ce adsorbent exhibited the most favorable NOx storage performance, including a complete NOx storage time of 135 s and a NOx storage efficiency exceeding 50% at 80 °C over a 10 min period. While PNAs loaded with noble metals, such as Pd/CeO2 and Pt/CeO2, exhibited NOx storage efficiencies below 50% after adsorbing for 5 min at 80 °C. Therefore, this research offered a crucial strategy for developing non-noble-metal-loaded, Ce-based PNAs.

Mesoporous silicas of MCM-48 and MCM-41 types doped with copper by modified template ion-exchange method as effective catalysts for low-temperature reduction of nitrogen oxide with ammonia

Mesoporous silica materials of MCM-48 and MCM-41 types were synthetized by surfactant directed methods and modified with copper by template ion-exchange (TIE) protocol and its extended version including post-treatment of modified silicas with ammonia solution. Obtained samples were characterized with respect to their textural parameters (low-temperature N2 sorption), porous structure, chemical composition, surface acidity (NH3-TPD), form and aggregation of deposited copper species (UV–vis-DRS) as well as their reducibility (H2-TPR). It was shown that application of TIE method resulted in deposition of copper into MCM-48 in more dispersed forms comparing to MCM-41. Both, in the case of MCM-41 and MCM-48, treatment of the samples with ammonia directly after copper introduction resulted in deposition mainly monomeric copper cations. The catalysts containing such dispersed copper species were more active in the low-temperature NH3-SCR process. The NO conversion above 90% with selectivity to N2 above 97% was obtained in the temperature range of 225–325 °C. CuO aggregates, deposited on mesoporous silicas, were found to be active in the side process of direct ammonia oxidation at higher temperatures.

Studies of NO Reduction with Ammonia Over Copper Species Deposited on MCM‐41 Nanospheres ‐ Experimental Evidence of Reaction Mechanism

AbstractNanospheres of MCM‐41 were modified with copper by template ion‐exchange (TIE) and cocondensation methods. In the samples modified by TIE, dispersion of copper was significantly improved by their post‐treatment in ammonia solutions. Highly dispersed copper species were significantly more active in low‐temperature NH3‐SCR than CuO aggregates. Copper dispersed on silica MCM‐41 catalytically operated at lower temperatures than copper deposited on silica‐alumina MCM‐41. The studies of reaction mechanism showed that ammonia and NOx species compete for these same adsorption sites (copper cations) and NH3 can remove NOx from such sites. Dispersed copper species are more active in NO to NO2 oxidation than CuO aggregates. Accumulation of oxidised NOx species in the absence of ammonia was more privileged on CuO aggregates. It is postulated that the main reaction pathway in the low‐temperature range is reaction of ammonia bounded to copper with NOx from gas phase or loosely bounded to the catalyst surface.

Enhancing flotation separation of fine copper oxide from silica by microbubble assisted hydrophobic aggregation

One of the main challenges facing the flotation of base metal oxide minerals is their fine sizes of particles as a result of fine grinding to achieve a desired degree of liberation for low-grade and finely disseminated complex ores. This study aims at studying hydrophobic aggregation and in situ gas nucleation of fine copper oxides with sodium dodecyl sulfate (SDS) as a selective collector to enhance CuO recovery. Experimental results by in situ and real time particle size measurement using focused beam reflectance measurement (FBRM) coupled with particle vision measurement (PVM) showed an enhanced aggregation of fine CuO by SDS adsorption. Particle aggregation assisted by gas nuclei which were generated in situ on CuO by high intensity agitation (HIA) was visualized by total internal reflection fluorescence microscopy (TIRFM). It is the enhanced aggregation with nanobubbles as bridges that improved its recovery from fine silica. Coupled with the calculation using the extended DLVO theory, contact angle and zeta potential of fine particles were measured to understand the critical role of hydrophobic forces in aggregation of fine CuO particles. The copper ions dissolved from the fine copper oxide were found to inadvertently activate fine silica flotation which could be effectively depressed by ethylene diamine tetraacetic acid (EDTA). A combination of SDS with EDTA was proposed and demonstrated to achieve selective recovery of fine copper oxide from fine silica gangue. The results from this study provide directions for enhancing copper recovery from low grade and finely disseminated copper oxidize ores, in particular from tenorite ores.

Synthesis of Cu/SiO2(MCM-41) mesostructured catalysts. Effect of the preparation method on the textural properties and chemical structure

Two Cu/SiO2 mesoporous materials (Cu-MCM-41) were synthesized, one by the ion exchange (IE) post-synthesis method and the other, by the sol-gel (SG) method by co-precipitation of copper and silica (Cu-MCM-41) in the cetyltrimethylammonium bromide (CTAB) presence. The effects of the synthesis method on these materials were analyzed. They were characterized by XRD, N2 adsorption-desorption, TEM, DRUV–vis, FTIR, TPR, XPS, and FTIR with both, CO and pyridine adsorbed. Using the SG method, an MCM-41 material with a uniform mesoporous structure (Dp ≈ 35 Å), and a specific surface area (SBET) of 800 m2.g-1, was obtained. With the IE method and due to the partial collapse of the SiO2-MCM-41 mesoporous structure used as support, a material with a lower SBET (560 m2.g-1) was produced. The Cu in the SG synthesized material was mainly constituted by SiO-[CuO]n-CuOSi polymeric species and small CuO agglomerates. On the other hand, in the IE material, the copper was in the form of isolated SiO–Cu–OSi monomers, SiO–Cu–O–Cu–OSi dimers, and only a low proportion of SiO-[CuO]n-CuOSi oligomers. The catalytic activity of both materials was tested against the 2-propanol (2-PrOH) dehydrogenation in the gas phase. The reaction rate of the IE synthesized material was an order of magnitude higher than that prepared by the SG method. This behavior was attributed to the presence of SiO–Cu+ pair formed by the reduction of SiO–Cu–O–Cu–OSi dimmers present in the material prepared by IE; in contrast with the CuO aggregates obtained by the SG method.

Characterization and electrochemical properties of CuO–Cu2O@rGO nanocomposite synthesized by a seed-mediated growth process

A CuO–Cu2O@rGO nanocomposite (CuO–Cu2O@rGO NCP) has been successfully prepared through a seed-mediated growth process. X-ray diffraction (XRD) analysis results indicated a monoclinic phase of CuO–Cu2O@rGO NCP with space group C2/c. Transmission electron microscopy (TEM) revealed agglomeration of the CuO and Cu2O nanoparticles in the rGO sheet matrix. The interaction of CuO–Cu2O@rGO NPC resulted from the aggregation and overlapping of CuO and Cu2O nanoparticles owing to the influence of a seed-mediated growth process. The electrochemical properties of the CuO–Cu2O@rGO NPC electrode indicate the storage of energy at the surface through a pseudo-capacitive mechanism. The specific capacitance at a current density of 0.5 A g−1 and the average percentage capacity retention after 1000 cycles of a CuO–Cu2O@rGO electrode at a current density of 10 A g−1 were evaluated as 125.54 F g−1 and 89.87 ± 3.30%, respectively. In the CuO–Cu2O@rGO electrode, the incorporated rGO affects the electrical conductivity and the synergistic interactions in charge–discharge processes. Interestingly, these results showed that the material was synthesized through a seed-mediated growth process and reveal the key factors that determine the combination and volume expansion of the reversible redox transition between Cu+ and Cu2+ during charge–discharge processes.

Electrophoretic Deposition of Nanoporous Oxide Coatings from Concentrated CuO Nanoparticle Dispersions.

Electrophoretic deposition (EPD) of nanoporous oxide coatings is an interesting research avenue owing to the experimental simplicity and broad scope of applications and materials. In this study, the properties of concentrated (up to 5000 mg/L), nonaqueous CuO nanoparticle (NP) dispersions were tailored to produce micrometer-thick, nanoporous CuO films by EPD. In particular, we performed a systematic investigation of the electrophoretic mobilities and size distributions of dispersed CuO aggregates and developing agglomerates in different organic solvents for concentrations ranging from 50 to 5000 mg/L with and without surfactant addition. Time-resolved dynamic light scattering analyses showed that aggregate mobilities and agglomeration rates decrease with increasing hydrocarbon chain length of the organic solvent (from ethanol to hexanol) and thus with increasing viscosity. The highest electrophoretic mobility was obtained for CuO NP aggregates and agglomerates dispersed in ethanol as a solvent. However, the addition of ≥0.5 wt % acetylacetone as a surfactant is required to stabilize these dispersions for subsequent EPD and at the same time introduce a net attractive (electrostatic) interaction between neighboring agglomerates on the substrate to promote layer formation during the EPD step. The produced micrometer-thick nanoporous CuO coatings can serve as high surface area nanostructured materials or nanoporous scaffolds in catalysis, combustion, propellants, and nanojoining.

Discovery of mono(u-oxo)dicopper and bis(u-oxo)dicopper in ordered Cu incorporated in SBA-15 via sol-gel process from silatrane at room temperature: An in situ XAS investigation

Abstract We proposed a synthesis pathway to obtain high-yielding SBA-15 containing copper (Cu-SBA-15) via a sol-gel process from silatrane and discovered that the active copper species had a large pore size and narrow size distribution, where the pore sizes increased with increasing copper content. In addition, the results from UV–Vis–NIR spectroscopy revealed that the active copper species were mono(u-oxo)dicopper [Cu2(μ-OH)2]2+ (21 740 cm−1) and bis(μ- η2: η2 peroxo)dicopper [Cu2(μ- η2: η2-O2]2+ bent (17 850–18 691 cm−1) and planar (24 690 cm−1). Furthermore, the microscopic techniques (scanning (SEM) and transmission (TEM) electron microscopy) showed the characteristic of a long length channel and retained SBA-15 structure after incorporation of Cu, even at high copper loadings, and had a higher copper content loading with a longer length of Cu-SBA-15. In addition, the 9% Cu-SBA-15 was characterized by broad X-ray powder diffraction (XRD) which was used to inspect the aggregation and formation of CuO and no peak was observed. All evidence suggested that the Cu-SBA-15 successfully prepared and discovered the active copper species. In-situ XAS showed that to produce active copper species in Cu-SBA-15, heating under a helium atmosphere at 350 °C for 30 min was sufficient for the formation of bridge oxygen (Cu-Ox-Cu) with the characteristics of mono(u-oxo)dicopper and bis(u-oxo)dicopper.

Cost-effective sol-gel synthesis of porous CuO nanoparticle aggregates with tunable specific surface area

CuO nanoparticles (NPs) are applied in various key technologies, such as catalysis, energy conversion, printable electronics and nanojoining. In this study, an economic, green and easy-scalable sol-gel synthesis method was adopted to produce submicron-sized nanoporous CuO NP aggregates with a specific surface area > 18 m²/g. To this end, a copper-carbonate containing precursor was precipitated from a mixed solution of copper acetate and ammonia carbonate and subsequently calcinated at T ≥ 250 °C. The thus obtained CuO nanopowder is composed of weakly-bounded agglomerates, which are constituted of aggregated CuO NPs with a tunable size in the range of 100–140 nm. The CuO aggregates, in turn, are composed of equi-axed primary crystallites with a tunable crystallite size in the range of 20–40 nm. The size and shape of the primary CuO crystallites, as well as the nanoporosity of their fused CuO aggregates, can be tuned by controlled variation of the degree of supersaturation of the solution via the pH and the carbonate concentration. The synthesized submicron-sized CuO aggregates can be more easily and safely processed in the form of a solution, dispersion or paste than individual NPs, while still offering the same enhanced reactivity due to their nanoporous architecture.

The Influence of Ionic and Nonionic Surfactants on the Colloidal Stability and Removal of CuO Nanoparticles from Water by Chemical Coagulation.

The widespread use of copper oxide nanoparticles (CuO NPs) and surfactants in various consumer products makes it likely that they coexist in aqueous environments, making it important to study the effects of surfactants on the fate and transport behavior of CuO NPs. The present study aims to investigate the influence of anionic sodium lauryl sulfate (SLS) and nonionic nonylphenol ethoxylate (NPEO, Tergitol NP-9), on CuO NPs adsorption, aggregation, and removal from water by the coagulation process. The result of the sorption study indicates that both surfactants could be adsorbed on the surface of CuO NPs, and that SLS remarkably decreases the ζ potential as well as the hydrodynamic diameter (HDD) of CuO as compared to NP-9. The kinetic aggregation study showed that both SLS and NP-9 reduced the HDD of CuO NPs and retarded the settling rates at surfactant concentrations above 0.015% (w:v) over a 24 h-period. Moreover, enhanced aggregation of CuO NPs was observed in two environmental waters as compared to pure water, which could be related to their high ionic strength. The addition of surfactants in natural waters has been shown to reduce the aggregation and sedimentation of CuO; however, the reductive effect of SLS was more pronounced than that of NP-9. Finally, the coagulation results showed that the removal efficiencies of CuO, Cu2+, and the surfactant in all tested waters at optimum ferric chloride dosage reached around 98, 95, and 85%, respectively. Furthermore, the coagulation mechanism revealed that the combination of charge neutralization and adsorptive micellar flocculation (AMF) might be involved in the removal of both pollutants. The results of the present study provide new insight into the environmental behavior of coexisting NPs and surfactants in wastewater treatment processes.

Aggregation, sedimentation, and dissolution of CuO and ZnO nanoparticles in five waters.

With the accelerated application of copper oxide (CuO) and zinc oxide (ZnO) nanoparticles (NPs) in commercial products, concerns about the potential impacts on the environment have been growing. Environmental behaviors of NPs are expected to significantly influence their fate and ecological risk in the aquatic environment. In this study, the environmental behaviors of two metallic NPs (CuO and ZnO NPs), including aggregation, sedimentation, and dissolution, were systematically evaluated in five representative waters (pool water, lake water, rainwater, tap water, and wastewater) with varying properties. Remarkable aggregation, sedimentation, and dissolution were observed for both metallic NPs, among which ZnO NPs exhibited greater influence. CuO (ZnO) NPs aggregated to 400 (500) nm, 500 (900) nm, and 800 (1500) nm in lake water, wastewater, and tap water, respectively. The sedimentation rates of CuO and ZnO NPs in the five waters were ranked as tap water > wastewater > lake water > pool water > rainwater. The dissolution of CuO and ZnO NPs in waters follows a first-order reaction rate model and is affected by ionic type, ionic strength (IS), and NOM (natural organic matter) concentrations. Redundancy analysis (RDA) indicated that the aggregation and sedimentation of NPs have a strong correlation, insofar as the sedimentation rates increase with increasing aggregation rates. The aggregation and dissolution of NPs have a negative correlation, insofar as the dissolution rates reduce with increasing aggregation rates. The aggregation, sedimentation, and dissolution of NPs can be influenced by ionic types, IS, and TOC in waters, among which, TOC may the dominant factor.

Time-Dependent Toxicity Responses in Daphnia magna Exposed to CuO and ZnO Nanoparticles.

Aggregation and dissolution of CuO and ZnO nanoparticles (NPs) increased with increasing exposure time (24, 48, and 72h). Acute toxicity of CuO NPs to Daphnia magna also increased significantly with increasing exposure time (p < 0.05), whereas exposure time did not significantly affect acute toxicity of ZnO NPs. The dissolved Cu concentration of CuO NPs was much lower than the median effective concentration (EC50) value (44μgL-1 at 72h), implying that the increase in acute toxicity was caused by particles rather than by dissolved ions. However, the dissolved Zn concentration of ZnO NPs was higher than the EC50 value (600μgL-1 at 72h), suggesting this acute toxicity may be caused by dissolved ions. Moreover, CuO NPs induced greater lipid peroxidation than Cu ions did at an exposure time of 72h, whereas converse results were observed for ZnO NPs.

Effect of addition of non ionic surfactant on the gas sensing properties of CuO films

Non ionic surfactant (Poly ethylene glycol (PEG-400)) has been used as dispersing and stabilizing agent along with citric acid in the sol-gel reaction to synthesize nanocrystalline CuO structures The decomposed gel sample calcined at temperature of 400°C has been assembled on glass substrate using an organic binder to form thick film sensor. The X-ray diffraction study of samples shows the formation of CuO as dominant phase in as decomposed gel and calcined CuO powder samples. Surfactant addition in precursor results in the decrease of crystallite size and leads to uniform distribution of CuO aggregates as noticed in the SEM micrographs. The activation energy of charge carrier in thick film samples has been investigated by two probe technique and is found to be of the order of 0.24 eV. Gas sening measurements on the samples performed at room temperature for analyte (ammonia gas) show an increase in response (4 times) as compare to sample formed by same procedure without surfactant.

Heterogeneous activation of peroxymonosulfate by Cu/ZSM5 for decolorization of Rhodamine B

Cu/ZSM5 catalyst was prepared by wet impregnation method and used for the activation of peroxymonosulfate (PMS) and the subsequent decolorization of Rhodamine B (RhB). The as-prepared catalyst was characterized with X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption–desorption. The results showed that ZSM5 could effectively restrain the aggregation of CuO. The catalytic activity of Cu/ZSM5 was significantly higher than that of pure CuO due to its large surface area and uniform micropores. Furthermore, effects of several operational parameters such as pH of solution, PMS amount, Cu loading rate, and initial RhB concentration on the decolorization efficiency were investigated in detail. Finally, the stability of the Cu/ZSM5 was studied and the catalyst maintained high catalytic activity with the color removal more than 95% in 1h after several rounds of regeneration.

Effects of physiochemical properties of test media on nanoparticle toxicity to Daphnia magna Straus.

The physicochemical property of standard test media significantly influenced the aggregation and dissolution of Ag, CuO and ZnO nanoparticles (NPs) and the toxicity of the NPs to Daphnia magna. For all the NPs, the highest amount of metal ions was released from the ISO medium, whereas acute toxicity to D. magna was highest in the moderately hard water medium (EC50 = 4.94, 980, and 1,950 μg L(-1) for Ag, CuO, and ZnO, respectively). By comparing EC50 values based on the total and dissolved concentrations of NPs with those of metal salt solutions, we found that both particulate and dissolved fractions were likely responsible for the toxicity of Ag NPs, whereas the dissolved fraction mostly contributed to the toxicity of CuO and ZnO NPs.

Effect of salinity on acute copper and zinc toxicity to Tigriopus japonicus: The difference between metal ions and nanoparticles

We investigated the effects of salinity (5‰, 15‰, 25‰ and 35‰) on metal ion (Cu and Zn) and nanoparticle (NP) CuO and ZnO toxicity to Tigriopus japonicus. Increasing the test media volume without renewal increased the 96-h LC50 for Cu (32.75mgL−1) compared to the reported value (3.9mgL−1). There was no significant difference in acute toxicity at different salinities between acclimated and unacclimated T. japonicus (p>0.05). Increasing salinity decreased the dissolved concentrations of Cu and Zn ions due to the precipitation of the metal ions, consequently reducing the acute toxicity to T. japonicus. The effect of salinity on acute CuO and ZnO NP toxicity was similar to that on metal ion toxicity. Since the aggregation of NPs generally enhanced at higher salinities, both the dissolution and aggregation of CuO and ZnO NPs may control the effect of salinity on acute toxicity to T. japonicus.

A plasma-assisted approach for the controlled dispersion of CuO aggregates into β iron(iii) oxide matrices

High-purity supported β-Fe2O3/CuO nanosystems with tailored morphology and tuneable copper content were fabricated by a two-step plasma-assisted process.

Ordered mesostructured Cu-doped TiO2 spheres as active visible-light-driven photocatalysts for degradation of paracetamol

We combined the wet chemical route with an aerosol-assisted self-assembly (AASA) process to prepare ordered mesostructured Cu-doped TiO2 spheres (Cu–TS) with high surface area and crystallinity for the visible-light photocatalytic degradation of paracetamol. The obtained photocatalysts were characterized by scanning electron microscopy, transmission electron microscopy, ultraviolet–visible spectroscopy, N2 adsorption isotherms, X-ray diffraction, and X-ray photoelectron spectroscopy. Cu–TS exhibits a shift in the absorption threshold toward the visible spectrum. No measurable CuO diffraction peaks were detected in the anatase Cu–TS, indicating the Cu2+ ions were homogeneously introduced into crystalline TiO2 frameworks. This result was also confirmed by the similarity of the Cu/Ti ratio in the bulk and on the surface. As the Cu concentration increased, CuO aggregates appeared and favorably affected the crystallization of TiO2 into the rutile structure. Under visible light irradiation, Cu–TS exhibited a much higher photocatalytic activity for the degradation of paracetamol compared with that of undoped TiO2. For the Cu–TS photocatalytic system, the aromatic by-products did not accumulate, and oxamic acid and ammonium were the predominant end products. Even after 10 repeated runs, the recycled Cu–TS showed good photodegradation activity.

Adsorptive Desulfurization by Copper Species within Confined Space

Copper species were incorporated into SBA-15 by solid-state grinding precursor with as-prepared mesoporous silica (SPA). The obtained materials (CuAS) were well-characterized by XRD, TEM, N(2) adsorption, H(2)-TPR, IR, and TG and compared with the material derived from calcined SBA-15 (CuCS). Surprisingly, CuO up to 6.7 mmol·g(-1) can be highly dispersed on SBA-15 by use of SPA strategy. Such CuO forms a smooth layer coated on the internal walls of SBA-15, which contributes to the spatial order and results in less-blocked mesopores. However, the aggregation of CuO takes place in CuCS material containing 6.7 mmol·g(-1) copper, which generates large CuO particles of 21.4 nm outside the mesopores. We reveal that the high dispersion extent of CuO is ascribed to the abundant silanols, as well as the confined space between template and silica walls provided by as-prepared SBA-15. The SPA strategy allows template removal and precursor conversion in one step, avoids the repeated calcination in conventional modification process, and saves time and energy. We also demonstrate that the CuAS material after autoreduction exhibits much better adsorptive desulfurization capacity than CuCS. Moreover, the adsorption capacity of regenerated adsorbent can be recovered completely.