Composition Of Mixed Oxides Research Articles

Wet-chemical preparation and physicochemical characterization of nanostructured Zn-Bi2O3/CeO2 composite: A visible-light-driven catalyst for the annihilation of pharmaceutical pollutant

A modified co-precipitation technique assisted with cetyltrimethylammonium bromide (CTAB) surfactant was used to synthesize a nanostructured and zinc-doped mixed metal oxide (Zn-Bi2O3/CeO2) composite. Using X-ray diffraction (XRD), the synthesized nanocomposite was studied in terms of its crystal structure, grain size, percentage crystallinity, and percentage porosity. Energy dispersive X-ray elemental analysis (EDX) was used to ascertain the chemical composition, SEM to confirm the creation of nanostructure material, and Fourier transform infrared spectroscopy (FTIR) to extract the existing functional groups. Investigation of light harvesting properties (UV/Vis) and thermogravimetric analysis (TGA) reveals that the doped composite exhibits a band gap driven by visible light and remarkable thermal stability at high temperatures. The pH value at which a material's net charge is zero, known as pHpzc, is 7.93 for the doped mixed metal oxide composite. The Zn-Bi2O3/CeO2 nanocomposite effectively eliminates 98.4 percent of the quinolone antibiotic (levofloxacin) via a mechanism that integrates sorption and photocatalytic degradation induced by visible light. To determine the optimal circumstances for the efficient operation of a photocatalyst, we experimented with different time intervals, beginning drug concentrations, catalyst dosages, operating temperatures, and pH levels. Reusability tests and post-activity FTIR analysis were used to investigate the long-term usability and structural stability of the newly developed doped composite photocatalyst. The scavenging tests revealed a potential photocatalytic mechanism to explain the annihilation of the levofloxacin drug on the synthesized catalyst. The physicochemical and photocatalytic evaluations recommend that the assembled integrated material has excellent potential for mineralizing medicinal products in pharmaceutical wastes.

Performance evaluation and mechanism of Al2O3/TiO2 sorbents for fluoride remediation in groundwater

Excessive fluoride levels in drinking water are problematic in several countries, particularly those which are relatively poor. Thus, there is a need to create cost effective sorbents which can easily be applied to make the water safe to use. Therefore, this study focussed on Al2O3/TiO2 sorbents which appear to address issues with commercially available alumina such as aluminium dissolution. Adjusting the alumina/titania ratio significantly influenced not only the fluoride uptake capacity but also the uptake of a wide range of contaminants found in groundwater. The exchange kinetics were relatively fast regardless of mixed oxide composition with equilibrium obtained within 6 h. Equilibrium isotherms were unfavourable for fluoride removal where titania compositions were dominant. In contrast, favourable isotherms were noted when alumina was the dominant oxide present. Barium, calcium, strontium, boron, iron, manganese, zinc, potassium, lithium, and silica were all substantially removed by varying the alumina/silica ratio in the sorbent. This behaviour may be valuable for broader remediation of dissolved species in groundwater (not just fluoride). Based upon the tests data a 70% Al2O3 – 30% TiO2 material was recommended to be the preferred composition for comprehensive treatment of groundwater. The sorbents appeared to comprise of alumina and titania with surface areas between 129 and 255 m2/g. There was no evidence for new oxide phases nor for a relationship between surface area and performance. Mechanistically both ion exchange and surface complexation may occur when treating groundwater.

Soft sol–gel combustion synthesis: A potential route for functional nanocomposites of copper-based mixed valent oxides and cermet

The high reaction rate in the sol–gel combustion synthesis (SCS) often restricts precise control over the composition of mixed valent oxides in a single step. The current study overcomes this limitation by employing melamine—that forms a hydrogel with Cu(II)—as a novel fuel in the combustion synthesis. As opposed to the conventional SCS approach, the current synthesis occurs in a mild and controlled way under oxygen-lean conditions,wherein at and above 300 °C of calcination, a red-hot coke is found to form and persist for hours and hence termed as ‘soft sol–gel combustion synthesis’ (SSCS). Such a controlled synthesis is shown to be pivotal in obtaining a copper-based mixed-valent oxide/cermet nanocomposite system, comprising tunable levels of g-C3N4, in a single step. The phase compositions of the nanocomposites are modulated by varying calcination parameters like temperature and duration. These nanocomposites are thoroughly characterized for their microstructural, morphological, elemental, bandgap, and optical properties.Unique compositions are synthesized from the blend of Cu(II)–melamine complex gel with ZIF-8, in which formulations comprising different proportions of ZnO, CuO, Cu2O, metallic Cu and g-C3N4 have been obtained. Such multicomponent formulations post ball-milling exhibit notable photocatalytic activity in degrading organic pollutants and show high antibacterial efficacy against Escherichia coli under dark-light dual-mode conditions. Additionally, the SSCS approach has also been demonstrated for its versatility by synthesizing nickel-based cermet, which opens up numerous avenues for developing exotic material compositions for diverse applications in the realms of energy and environment.

Oxide Reduction Treatment with a Thermal Plasma Torch: A Case Study

This article presents the findings of a study on oxide reduction utilizing a novel reducing plasma torch, employing greenhouse gases such as CO2 and CH4 as plasma gases. The primary aim of this investigation is to establish the viability of this approach. The innovative plasma torch was employed to reduce various oxides, including aluminum oxide, iron oxide, and titanium oxide, as well as a mixed oxide composition, employing a CO2/CH4 molar ratio of 1:1 within a spouted bed reactor. Following plasma treatment, X-ray diffraction (XRD) analysis was conducted to examine the metallic phases, notably titanium, iron, and aluminum. SEM–EDS observations were carried out to assess microstructural changes and identify elemental compositions pre- and post-plasma treatment. The results demonstrate that within the conical section of the reactor, titanium oxide experiences partial reduction, resulting in limited titanium production, while aluminum oxide and iron oxides (magnetite and hematite) undergo reduction to yield aluminum and iron, respectively. Thermodynamic calculations, performed using Factsage software version 8.3, were utilized to predict stable-phase formations following plasma treatment for each material.

Facile synthesis of cobalt-nickel oxide nanocomposites for trifunctional application towards antioxidant, anticancer and electrochemical performance

Transition metallic mixed oxides have received a lot of curiosity due to their exceptional electrochemical performance and incredibly low cost for hybrid supercapacitors. Herein, we report a facile synthetic approach of cobalt nickel oxide (CNC) composites from Carica papaya leaf extract. The synthesized mixed oxide composite was analyzed by various spectroscopic techniques (IR, UV–Vis, Powder XRD, SEM-EDAX, TEM and XPS). The electrochemical behavior of CNC was investigated by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) method in 2 M KOH solution. The composites exhibit specific capacitance of 289.28 F g−1 at 1 A g−1 demonstrating improved charge storage. The electrode retains 81 % of its specific capacitance from the initial value after repeated charge–discharge processes for 2000 cycles. In addition to the electrochemical studies, biological activities such as anti-oxidant and anti-cancer activities of the CNC were examined. The radical scavenging activity of CNC was assessed with different radicals such as DPPH•, ABTS+., NO–, OH•, O2– and the acquired results showed that the composites possessed substantial activity. Anticancer activity of CNC was studied against HepG2 and MM2 cancer cells and the CNC possessed significant activity with the IC50 value of 45.8 and 38.3 µg/ml respectively compared with the standard drug cisplatin. Further apoptogenic nature of the CNC was confirmed with DAPI staining assay.

Overview of the catalytic properties of bulk unsupported and supported group 4–5-6 oxides

The number of active sites (Ns), surface chemistry (redox, acid, base) and TOF values were compared for bulk one component oxides, bulk mixed metal oxides and supported metal oxides. The number of active sites was based on CH3OH chemisorption. The surface chemistry was based on CH3OH-TPSR and steady state CH3OH oxidation. The specific TOF values were based on the steady state methanol oxidation activity values and Ns values. The Ns values were found to depend on the catalyst morphology (isotropic > anisotropic). The surface chemistry was found to dramatically depend on the specific metal oxide element. For supported bulk mixed metal molybdates, the surfaces were found to be dominated by segregation of MoOx and, consequently, the surface chemistry and TOFredox values were dominated by the characteristics of the bulk one component MoO3. Similarly, for the supported molybdenum oxide catalysts, the surface is dominated by the surface MoOx sites that dictate the surface chemistry and TOFredox values that reflect the surface chemistry and TOFredox of the bulk one component MoO3. Thus, it is possible to predict the surface chemistry and TOF values from knowledge of the surface composition of mixed oxides and the surface chemistry and TOF values of the bulk one component oxides. This conclusion should also hold for other types of mixed oxides such as polyoxometalates (POMs) and supported MOx/silicates and MOx/zeolite catalyst systems.

Highly efficient Cd(II) removal from groundwater utilizing layered mixed metal oxides-graphitic carbon nitride composite with improved cycling stability

Graphitic carbon nitride (GCN) and its mixed metal oxide (MMO) composites are synthesized via co-precipitation followed by the pyrolysis method using various ratios of calcium aluminium (Ca:Al) with GCN, to enhance the adsorption ability towards Cd(ii) present in wastewater. Synthesized composite materials were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface analysis, Fourier transforms infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses. Due to its higher specific surface area (218.65 m2/g), the produced GCN and CaAl mixed metal oxide composite (GCN-MMO) exhibits improved adsorption ability towards Cd(II) ions. Approximately >99 % were adsorbed with Langmuir qmax of 131.57 mg/g. An overall pseudo-second-order (PSO) model fitted the kinetics data well. The possible mechanisms were surface complexation and precipitation, outer-sphere complexation, and acid-base mechanism. Further, the groundwater application was studied, and it achieved adsorption below the maximum permissible limit of USEPA with excellent cycling stability. The findings of this study showed that GCN-MMO composite material may be useful for the adsorption of Cd(II) heavy metal from an aqueous solution.

Hydrothermal Synthesis of Mixed Oxide Compositions of Cobalt‐Zirconium and their Catalytic Activity in the Decomposition of Hydrogen Peroxide

AbstractThe article presents the results of research on the hydrothermal synthesis of nanoscale oxide of cobalt and zirconium and their mixed oxide compositions. The synthesized samples have been characterized by the X‐ray phase, scanning electron microscopy and nitrogen adsorption‐desorption methods; the composition of the samples has been determined by chemical analysis methods, and their catalytic activity in the decomposition of hydrogen peroxide has been studied. It has been shown that during synthesis, highly dispersed cobalt and zirconium oxide are formed, and the sample of the composition (mol %): Co3O4(88)−ZrO2(12) has the highest specific surface area (181.2 m2/g) and the highest activity (K=6.18 ⋅ 10−2 s−1) against the decomposition of hydrogen peroxide. The increasing of the ZrO2 content in oxide compositions reduces their catalytic activity. The particle size in the synthesized samples is 7–38 nm.

Hydrothermally synthesized mixed metal oxide nanocomposites for electrochemical water splitting and photocatalytic hydrogen production

Here, mixed metal oxide composites CuO/NiO/ZrO2 (CNZr) were fabricated by a facile hydrothermal route, and their electrochemical water splitting, and photocatalytic hydrogen production were further investigated. The CNZr600 composite exhibited the H2 generation rate of 14.27 mmol g−1 h−1, which is greater than that of the CNZr400, CNZr500 composites. The mixed metal oxide composite of CNZr600/NF with numerous catalytically active centers and charge transfer ability furnished minor overpotentials of 218 mV and 372 mV for HER and 400 mV and 540 mV for OER at 10 and 50 mA cm−2, respectively, in potassium hydroxide electrolyte. The alkaline electrolyzer designed by CNZr600/NF requires an appealing operating potential of 1.69 V for efficient H2 production. In addition, electrochemical impedance spectroscopy measurements showed a reduced impedance response for the composites, which was dominated by the relaxation of the intermediate frequency connected with the adsorption of the intermediate. Furthermore, the superior catalytic activities of the mixed metal oxide composites were attributed to their structural properties, high electroactive surface areas, fast electron transport kinetics, and good chemo-electrical bonding between CuO, NiO, and ZrO2. These consequences provide a new vision for the design of mixed metal oxide composite catalysts for low-cost H2 production.

Variation in defects and properties in composite of ZnO and α-Fe2O3 for sustainable wastewater treatment

Defects in nanostructures play a pivotal role in determining their properties and performance in the desired applications. Herein, the defect states and structural properties of the bi-metal oxide composite of ZnO and α-Fe2O3 (ZF-W) are varied by annealing the composite at different temperatures. The changes in defects, structures, and phase are evaluated thoroughly using transmission electron microscopy, x-ray diffraction, photoluminescence, and Mössbauer spectroscopy techniques. The defect-rich ZF-W composite is found to be composed of defect-deficient ZnFe2O4 attaining the equilibrium state when as-synthesized ZF-W is annealed at 500 °C [ZF-W(500)]. Further annealing at 1000 °C, ZF-W(1000), a non-stoichiometric and highly defected ZnFe2O4 is evidenced in the composite. The changes in the composite with the annealing temperature are correlated with the cationic migration and evolution of defect states. Moreover, the transition associated with the vacancy defects, which trapped the excited electron and dispel the free electrons, thereby inhibiting fast electron–hole pair recombination, is corroborated from the photoluminescence spectra. When implemented for methyl blue adsorption/degradation without the assistance of any external sources, the degradation efficiency of ZF-W, ZF-W(300), ZF-W(500), and ZF-W(1000) is found to be 86%, 84%, 68%, and 82%, respectively. The prepared samples are highly stable and can be used repeatedly without losing effectiveness. The simultaneous evolution of defects and structural properties of the composite are attributed for the variation in methyl blue adsorption/degradation. The present study reveals the importance of defects present in the mixed metal oxide composite in obtaining high-performance dye degradation/adsorption properties for sustainable wastewater treatment.

Facile Fabrication of Fe2O3/TiO2 Composite from Titanium Slag as Adsorbent for As(V) Removal from Aqueous Media

Mixed metal oxide composites have been widely used as adsorbents for the removal of heavy metal ions from wastewater. In this work, Fe2O3/TiO2 composite was sustainably prepared via the treatment of titanium slag with a low-concentration sulfuric acid solution (20%) and used for the removal of As(V) from aqueous solutions. The resulting products were characterized by X-ray diffraction (XRD), N2 adsorption−desorption, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The batch adsorption was employed to investigate the removal efficiency of the Fe2O3/TiO2 adsorbent toward As(V). The Langmuir and Freundlich isotherms were plotted in order to study the adsorption process. The adsorption of As(V) on FeO3/TiO2 fitted well with the Freundlich isotherm model, suggesting a multilayer adsorption process with an adsorption capacity of 68.26 mg·g−1. The adsorption kinetics study demonstrated that the adsorption behavior of the Fe2O3/TiO2 composite for the As(V) was pseudo-second-order. With low-cost preparation and high adsorption capacity, the prepared Fe2O3/TiO2 adsorbent could be used as an effective adsorbent for As(V) removal from contaminated water sources. The approach utilized in this research is viewed as a sustainable route for creating a proficient adsorbent for the purification of water.

Green and sustainable recycling of MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4 mixed oxide from of spent Li-ion and Zn–MnO2 batteries and evaluation of its photocatalytic properties

In this study, MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4 spinel-like mixed oxide was synthesized by green recycling of spent Li-ion and Zn–MnO2 batteries. The first step consisted of leaching the cathode of Li-ion batteries and the cathode of Zn–MnO2 batteries with citric acid and glucose. Then, Li-ion cathode leachate was mixed with Zn–MnO2 cathode leachate. Leachate mixture received the addition of oxalic acid, yielding oxalate precursor material, which was calcined at 450 °C for 3 h to afford MnCo2O4/Mn3O4/Li(Mn0.75Ni0.25)2O4. Mixed oxide structure, composition, and morphology were determined by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP OES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic properties of mixed oxide were evaluated in the decolorization of a model dye (methylene blue) under UV radiation. System using UV radiation + H2O2 + catalyst reached decolorization efficiency >93% in 120 min of reaction. This study provides a possible solution for two environmental liabilities (batteries and wastewater), and the results reported here are of scientific, economic, environmental, and social interest.

Mixed valence copper oxide composites derived from metal–organic frameworks for efficient visible light fuel denitrification

CuxO-300 has the best photocatalytic performance, and its denitrification rate reaches 81% after 4 hours of visible light (≥420 nm) irradiation.

Enhancing OER Activity of Ni/Co Oxides via Fe/Mn Substitution within Tailored Mesoporous Frameworks

Non-noble mixed metal oxides are promising electrocatalysts for water splitting reactions in alkaline media. The synthesis of complex mixed metal oxides with the desired composition is challenging due to the formation of phase impurities when synthesis is performed via classical approaches. In this work, we applied the nanocasting technique combined with low-temperature calcination (200 °C) in a quasi-sealed container to obtain highly ordered mesoporous mixed metal (Mn/Fe/Ni/Co) oxides. This procedure provides electrocatalysts with distinctive physicochemical characteristics and improved electrocatalytic properties. Partial Ni substitution in Ni0.5Co2.5O4 by Fe and Mn in combination with the highly ordered mesostructure offers a large number of active sites and enhances the performance of the catalyst toward the oxygen evolution reaction (OER) in the alkaline electrolyte. The Mn/Fe/Ni/Co oxide calcined at 200 °C outperforms all other synthesized oxides (current density of 262 mA cm–2 at 1.7 V versus RHE and overpotential of 363 mV at 10 mA cm–2) due to synergistic effects. Moreover, this catalyst exhibits significantly higher activity compared to the oxide of identical composition calcined at higher temperature. The results presented in this work show that tuning the synthesis conditions and composition of mixed metal oxides is a simple way to tailor their surface chemistry, mesoporous structure, and catalytic performance for the OER.

Efficient Removal of Eriochrome Black T (EBT) Dye and Chromium (Cr) by Hydrotalcite-Derived Mg-Ca-Al Mixed Metal Oxide Composite

Eriochrome Black T (EBT) and chromium (Cr) are considered to be potential pollutants due to their toxicity and severe impact on the environment. In the current study, hydrotalcite-derived Mg-Ca-Al-LDO mixed metal oxide composite was prepared using a conventional co-precipitation method and explored in terms of the removal of Cr and EBT dye from aqueous solution in a batch mode adsorption process. The prepared Mg-Ca-Al-LDH, Mg-Ca-Al-LDO and spent Mg-Ca-Al-LDO adsorbents were characterized to propose the adsorption mechanism. Different adsorption parameters were examined, such as adsorbent dosage, initial concentration, pH, reaction temperature and contact time. The EBT adsorption kinetic results matched strongly with the pseudo-second-order model for both Cr (R2 = 0.991) and EBT (R2 = 0.999). The Langmuir isotherm model exhibited a maximum adsorption capacity of 65.5 mg/g and 150.3 mg/g for Cr and EBT, respectively. The structure and morphology results obtained after Cr and EBT dye adsorption reveal that the adsorption mechanism is associated with electrostatic interactions and surface complexation of Cr and EBT dye with Mg-Ca-Al-LDO surface functional groups. Moreover, more than 84% of the initial adsorption capacity of EBT and Cr can be achieved on the Mg-Ca-Al-LDO surface after five adsorption/desorption cycles. Finally, the Mg-Ca-Al-LDO mixed metal oxide composite can be potentially used as a cost-effective adsorbent for wastewater treatment processes.

Effect of transformation temperature toward optical properties of derived CuO/ZnO composite from Cu–Zn hydroxide nitrate for photocatalytic ciprofloxacin degradation

In this work, visible light driven CuO/ZnO photocatalyst composite derived from Cu–Zn hydroxide nitrate (CuZn–HN) was fabricated via thermal transformation at varying temperatures. The effect of temperature on their morphology and optical properties was examined. The CuZn–HN calcined at 400 °C (400HN) showed the better performance than 200HN, 800HN and uncalcined CuZn–HN in terms of the photocatalytic oxidation rate for Ciprofloxacin (CIP) degradation under visible light irradiation conditions. The improved photocatalytic performance of 400HN could resulted from the combination of narrow energy band gap, suppressed photogenerated e−-h+ recombination, and strong interactions between CIP and the composite' surface. The finding suggested the transformation temperature of CuZn–HN to CuO/ZnO composite is a key factor to produce the highly effective photocatalyst with the simple protocol as an alternative synthetic method to prepare the mixed metal oxide composites. Moreover, the photocatalytic CIP degradation pathway was elucidated by GC-MS analysis, and the charge transfer mechanism in CuO/ZnO composite was also proposed.

Crystallization and pyrolysis of nitric acid pressure leach liquor of limonitic laterite and separation of valuable metals

Based on the advantages of nitric acid pressure process (NAPL) for laterite nickel ores, this study innovatively proposes nitric acid pressure leach liquor crystallization pyrolysis-mixed metal oxides separation process. Firstly, the feasibility and the possible reactions of mixed nitrate pyrolysis were confirmed by thermodynamic analysis. Subsequently, the optimal pyrolysis temperature was experimentally investigated. Then, the pyrolysis process of combined nitrate was thermodynamically analyzed, and the phase composition of mixed metal oxides was determined by X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS). The Pourbaix diagram shows that using NaOH as leaching agent can selectively separate aluminum from mixed metal oxides, and the variables influencing aluminum's leaching rate are investigated. The experimental results are as follows: the optimal pyrolysis temperature of mixed nitrate crystals is 600 °C; the pyrolysis products are mainly oxides with the formation of NiAl2O4 and MgAl2O4 spinel phases; the aluminum leaching rate is 81.9% under the optimal alkali leaching conditions. The presence of spinel phase is not favorable for aluminum leaching. After leaching, an enriched residue of 15.8% Ni, 1.9% Co and 0.19% Sc was obtained.

Cd2V2O7–ZnO mixed oxide for extended wavelength absorption with suppressed charge carrier recombination: A photocatalytic material

A type-II mixed oxide Cd2V2O7–ZnO was prepared by hydrothermal method and its morphological and optical properties were analysed with various scientific techniques. FESEM and AFM images showed the aggregated porous morphology by the individual spherical particles. The X-ray diffraction studies confirmed its formation, crystallinity and size of the particles as 47 nm. The UV–visible DRS spectrum showed its visible light-responsive nature and the optical band gap of bare ZnO and Cd2V2O7–ZnO mixed oxide to be 3.3 and 3.0 eV respectively. The mixed oxide also revealed the extended lifetime of the charge carriers by means of decreased excitonic emission intensity from the conduction band to valence band. The prepared mixed oxide was employed as photocatalyst in the degradation of methylene blue dye under solar radiation, the results indicated that the mixed oxide degraded the dye to an extent of 90% in just 30 min of light reaction in comparison to bare ZnO which degraded the dye to an extent of 69% in the same period. The degradation reaction followed pseudo-first-order reaction kinetics with the rate constant of 4.097 × 10−2 min−1 for ZnO and 6.665 × 10−2 min−1 for Cd2V2O7–ZnO mixed oxide composite.

Comparative Study of Polyethylene Films Embedded with Oxide Nanoparticles of Granulated and Free-Standing Nature

Nanocomposite polymer films are a very diverse research field due to their many applications. The search for low-cost, versatile methods, producing regulated properties of the final products, has thus become extremely relevant. We have previously reported a bulk-scale process, dispersing granulated metal oxide nanoparticles, of both unary and multi-component nature, in a low-density polyethylene (LDPE) polymer matrix, establishing a reference in the produced films’ optical properties, due to the high degree of homogeneity and preservation of the primary particle size allowed by this method. In this work, unmodified, free-standing particles, namely zinc oxide (), titanium dioxide (), aluminum oxide (), and silicon dioxide () are blended directly with LDPE, and the optical properties of the fabricated films are compared to those of films made using the granulation process. The direct blending process evidently allows for control of the secondary particle size and ensures a homogeneous dispersion of the particles, albeit to a lesser extent than the granulation process. Despite the secondary particle size being comparatively larger than its granulated counterpart, the process still provides a regulated degree of deagglomeration of the free-standing oxide particles, so it can be used as a low-cost alternative. The regulation of the secondary particle size tunes the transmission and reflection spectra, in both unary and mixed oxide compositions. Finally, the direct blending process exhibits a clear ability to tune the energy band gap in mixed oxides.

Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co3O4 and 30 wt.% CeO2. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co3O4-CeO2 mixed metal oxides with preset ratio, γ-Al2O3 intentionally containing 33% boehmite and shortly named Al2O3-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co3O4-CeO2-Al2O3-b (50 wt.% Al2O3-b) exhibited superior activity owing to high Ce3+ and Co3+ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO2 and H2O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification.