Ozone Degradation Research Articles

Data Fusion Approach to Simultaneously Evaluate the Degradation Process Caused by Ozone and Humidity on Modern Paint Materials.

The knowledge of the atmospheric degradation reactions affecting the stability of modern materials is still of current interest. In fact, environmental parameters, such as relative humidity (RH), temperature, and pollutant agents, often fluctuate due to natural or anthropogenic climatic changes. This study focuses on evaluating analytical and statistical strategies to investigate the degradation processes of acrylic and styrene-acrylic paints after exposure to ozone (O3) and RH. A first comparison of FTIR and Py-GC/MS results allowed to obtain qualitative information on the degradation products and the influence of the pigments on the paints’ stability. The combination of these results represents a significant potential for the use of data fusion methods. Specifically, the datasets obtained by FTIR and Py-GC/MS were combined using a low-level data fusion approach and subsequently processed by principal component analysis (PCA). It allowed to evaluate the different chemical impact of the variables for the characterization of unaged and aged samples, understanding which paint is more prone to ozone degradation, and which aging variables most compromise their stability. The advantage of this method consists in simultaneously evaluating all the FTIR and Py-GC/MS variables and describing common degradation patterns. From these combined results, specific information was obtained for further suitable conservation practices for modern and contemporary painted films.

Copper(II)-Doped Carbon Dots as Catalyst for Ozone Degradation of Textile Dyes.

A catalytic ozonation advanced oxidation process (AOP) with a copper(II)-doped carbon dot as catalyst, Cu-CD (using L-cysteine and polyethylene glycol (PEG) as precursors and passivation agents), was developed for textile wastewater treatment (T = 25 °C and pH = 7). Four dyes were analyzed—Methyl Orange (MO), Orange II sodium salt (O-II), Reactive Black 5 (RB-5) and Remazol Brilliant Blue R (RBB-R), as well as a real effluent from the dying and printing industry. The Cu-CD, with marked catalytic ozonation properties, was successfully synthesized by one-pot hydrothermal procedure with a size of 4.0 nm, a charge of −3.7 mV and a fluorescent quantum yield of 31%. The discoloration of the aqueous dye solutions followed an apparent first-order kinetics with the following rate constants (kap in min−1): MO, 0.210; O-II, 0.133; RB-5, 0.177; RBB-R, 0.086. In the presence of Cu-CD, the following apparent first-order rate constants were obtained (kapc in min−1) with the corresponding increase in the rate constant without catalyst (%Inc): MO, 1.184 (464%); O-II, 1.002 (653%); RB-5, 0.709 (301%); RBB-R, 0.230 (167%). The presence of sodium chloride (at a concentration of 50 g/L) resulted in a marked increase of the discoloration rate of the dye solution due to generation of other radicals, such as chlorine and chlorine oxide, resulting from the reaction of ozone and chloride. Taking into consideration that the real textile effluent under research has a high carbonate concentration (>356 mg/L), which inhibits ozone decomposition, the discoloration first-order rate constants without and with Cu-CD (kap = 0.0097 min−1 and kapc = 0.012 min−1 (%Inc = 24%), respectively) were relatively small. Apparently, the Cu-CD, the surface of which is covered by a soft and highly hydrated caramelized PEG coating, accelerates the ozone decomposition and dye adsorption, increasing its degradation.

Mesoporous Fe3O4/graphene oxide nanohybrid for catalytic Ozonation: Preparation, characterization and process modeling by neural network

BackgroundCatalytic activity of graphene and its related compounds have been reported in the ozonation process. In addition, Fe3O4 has a good catalytic activity in the ozonation process. Fabrication of high porosity Fe3O4/graphene oxide nanohybrids can improve the production of reactive oxygen species. MethodsMesoporous Fe3O4/ graphene oxide nanohybrid was prepared by coprecipitation method. The catalytic activity of nanohybrid was investigated in ozonation degradation of acid red88 in the simulated wastewater. The progress of degradation process was determined using reactive oxygen species scavengers. The process was modeled by the artificial neural network. Significant FindingsThe mesoporous nanohybrid has a specific surface area of 252.7 m2/g, total pore volume of 0.353 cm3/g and mean pore diameter of 5.6 nm. Fe3O4/ graphene oxide showed superior catalytic activity compared to Fe3O4 and graphene oxide. Hydroxyl (OH·) and superoxide radicals (O2·−) were identified the main radical reactive species. The influence of ozone dosage, pH, dye and catalyst concentration, on the acid red88 degradation rate was investigated. The degradation process was pH dependent, and acidic condition was more favorable to mineralization of acid red88 than neutral or basic mediums. Chemical oxygen demand removal has reached 69% in the catalytic ozonation process, while it reached only 25% in single ozonation process. A very good agreement (R = 0.99) was observed between the calculated and experimental degradation efficiency. The results demonstrated that mesoporous nanohybrid is a promising catalyst for ozonation process, especially treating water polluted by azo dyes.

A composite graphene aerogel for real-time degradation of low-concentration ozone: The synergetic effect of defects

A graphene and manganese oxide composite aerogel has been developed for real-time degradation of low concentrated ozone. Being a widely studied catalyst for ozone degradation, manganese oxide is loaded on graphene aerogel via a one-step method to form a freestanding composite aerogel for ozone degradation. A dynamic degradation percentage over 90% at 0.15 lpm with the initial ozone concentration below 100 ppm can be obtained. The nucleation of manganese oxide as well as the uniformity of the composite aerogels have been found very sensitive to the precursory pH value, which would further influence the performance on ozone degradation. The posting thermal treatment has been applied to adjust the chemical components of the composite aerogels, which has inferred that the synergetic and compensating effect of various defects including structural disorder and functional groups, as well as the components of manganese oxide should hold the responsibility for optimizing the performance on ozone degradation.

Numerical investigation of ozone decomposition by self-excited oscillation cavitation jet

Abstract Extreme environmental changes caused by the cavitation bubble collapse, such as high pressure, high temperature and the microjet, will cause pyrolysis reaction at the gas and liquid interface inside the bubble. Self-excited pulsed cavitation jet has an instantaneous strong pulse pressure, which leads to local hot spots surrounding the cavitation bubbles. The generation of strong oxidizing free radicals promotes easy ozone conversion into oxygen. Numerical simulations were conducted for ozone decomposition by cavitation jet. Three groups of different collision angles were applied to compare and analyze the ozone degradation reaction. Results showed that the collision angle has a certain influence on the chemical reaction intensity, the degradation of ozone, and oxygen production. At the collision angle of 180°, the chemical reaction was the most violent, with ozone degradation and oxygen production at the highest level, followed by 120° and lowest at 90°.

Incorporating Catalytic Ceramic Membrane into the Integrated Process of in Situ Ozonation, Membrane Filtration and Biological Degradation: Enhanced Performance and Underlying Mechanisms

Incorporating Catalytic Ceramic Membrane into the Integrated Process of in Situ Ozonation, Membrane Filtration and Biological Degradation: Enhanced Performance and Underlying Mechanisms

The reaction laws and toxicity effects of phthalate acid esters (PAEs) ozonation degradation on the troposphere

Low-molecular-weight (LMW) phthalate acid esters (PAEs) tend to enter the atmosphere, flying for several kilometers, so it is easy to endanger human health. This work is the first to use quantum chemistry calculations (Gaussian 16 program) and computational toxicology (ECOSAR, TEST, and Toxtree software) to comprehensively study the ozonolysis mechanism of six LMW PAEs (dimethyl phthalate (DMP), diethyl phthalate (DEP), dipropyl phthalate (DPP), diisopropyl phthalate (DIP), dibutyl phthalate (DBP), and diisobutyl phthalate (DIBP)) in the atmosphere and the toxicity of DMP (take DMP as an example) in the conversion process. The results show that the electron-donating effect of the ortho position of the LMW PAEs has the most obvious influence on the ozonolysis. We summarized the ozonation reaction law of LMW PAEs at the optimal reaction site. At 298 K, the law of initial ozonolysis total rate constant of the LMW PAEs is kDIP > kDPP > kDIBP > kDMP > kDEP > kDBP, and the range is 9.56 × 10−25 cm3 molecule−1 s−1 — 1.47 × 10−22 cm3 molecule−1 s−1. According to the results of toxicity assessment, the toxicity of products is lower than DMP for aquatic organisms after ozonolysis. But those products have mutagenicity, developmental toxicity, non-genotoxicity, carcinogenicity, and corrosiveness to the skin. The proposed ozonolysis mechanism promotes our understanding of the environmental risks of PAEs and provides new ideas for studying the degradation of PAEs in the tropospheric gas phase.

Research Progress in the Odorants and Their Emissions from Indoor Building Decoration Materials

The emission of pollutants from building decoration and furbishing materials associated with unpleasant odors is the main reason for complaints relating to poor quality indoor air. Currently, few studies have focused on the identification of odorants and the quantification of emissions from these building materials. Here, we summarize the analytical methods available for the study of indoor odorants and evaluate existing understanding of odorants from nine kinds of building materials, namely plaster board, wood-based materials, linoleum, carpets, plastics, rubber, artificial leather, paints, and adhesives. The possible odor-causing compounds emitted by these different materials and their odor threshold values are identified. Finally, suggestions are proposed for future research and control measures to minimize indoor odor pollution. Overall, olfactometry is the most important tool for odor analysis desite the non-standardized application of the technique when used in the assessment of odor emissions from building materials. In addition, there are large differences in the reported patterns of odorant emissions from building materials, although oxidized substances such as aldehydes, ketones, and acids are frequently identified in association with the aging of the materials via processes such as oxidation and ozone degradation over time.

Influence of anions on ozonation of bisphenol AF: Kinetics, reaction pathways, and toxicity assessment

In this article, the degradation of 4, 4’-(hexafluoroisopropylidene) diphenol (bisphenol AF, BPAF) by ozone was studied and toxicity of the degradation products was evaluated. Kinetic studies showed that acidic conditions were more conducive to the ozone degradation of BPAF than alkaline conditions. In the presence of common anions, Br− and SO42− promoted the degradation of BPAF, whereas NO2−, NO3−, HSO3− inhibited the degradation, and the other anions and cations had no significant effect. The degradation products were analyzed by mass spectrometry, and were mainly manifested in hydroxylation, carboxylation and cleavage of benzene ring. The addition of NO2−, HSO3− and Br−produced the corresponding free radicals, resulting in the parent compound being attacked and affecting the degradation efficiency and pathways. The theoretical calculated results showed that the ortho-site of the BPAF phenolic hydroxyl group was more active than the meta-position, and it's more likely for free radicals to attack ortho-sites and initiate substitution reactions. Toxicity assessment of the products in the process of ozone degradation showed that toxicity of the products was reduced by benzene ring cleavage and a reduction in the F atomic number. However, the toxicity of nitro and brominated products of BPAF was increased. These findings provide some new insights into the role of common ions in ozonation process and product formation, and supplement the existing conclusions. The results of this study remind future researchers to concern that inorganic ions in real water may be converted into corresponding free radicals that affect the formation of ozone oxidation products.

Unraveling the multiple roles of Ag species incorporation into OMS-2 for efficient catalytic ozonation: Structural properties and mechanism investigation

Silver incorporated manganese oxide octahedral molecular sieves (Ag-OMSX-T) were successfully synthesized via a hydrothermal-calcination method. Due to the multiple roles of Ag species doping, the optimal Ag-OMS0.2-180 nanocatalyst with the Ag/Mn molar ratio of 0.2 had the highest TOF value (2.94 × 10−5 mol g−1 h−1), which could completely degrade 50 mg L−1 OA at pH 5.0 in 30 min much higher than those of OMS-2 (22.3%) in catalytic ozonation system. The results of systematic characterization (such as XRD, XPS, Py-IR, and O2-TPD) and catalytic performance tests of Ag-OMS0.2-180 clearly demonstrated that the proper amount of Ag incorporation not only facilitated the electron transfer but also induced more formation of Lewis acid sites in Ag-OMS0.2-180 as well as metals (Ag and Mn) as activation sites to collectively favor the catalytic ozonation degradation of OA. In addition, the higher mineralization rate has been achieved (79.6%) and the Ag-OMS0.2-180 exhibited the satisfactory stability and reusability with low metal release during multiple consecutive cycles (≥ 5). Meanwhile, the electron spin resonance spectra and radical scavenger tests confirmed that superoxide radical and singlet oxygen were the main reactive oxygen species in catalytic process. The mechanism of solid-liquid interface reaction and the pathway of cycling of oxygen vacancies were also elaborated, which present a new insight for water decontamination.

Diamond-doped silica aerogel for solar geoengineering

Even though aerosol injection into stratosphere is one of the most promising solar geoengineering techniques, sulfate aerosols, which are suggested for such an application, show significant drawbacks such as infra-red (IR) absorption and ozone degradation. The development of new materials for such application that would exhibit substantial up-scattering, with non-IR absorption to allow a cooling effect are needed. Here, a novel composite material comprised of diamonds dispersed in a silica aerogel network is investigated and compared to pure silica aerogel. Silica aerogels are ultralight, highly porous, transparent and can host particles, while fulfilling particle size limitation in terms of potential health risks for humans during respiration. Morphology of both the diamonds and the silica aerogels composites has been studied. The diffuse reflectance of the diamond powders, pure silica aerogels, and the diamond-doped silica aerogels have been measured for comparison. Our experimental work assesses the proposed concept of materials, including discussion and recommendations for the improvements of the synthetized materials. The obtained results are promising and could stimulate further in-depth studies in similar materials with a potential for applications in solar geoengineering.

Ozonation, a novel bio-preservation technique for food processing in food industries

Application of ozone as a replacement to traditional sanitizers requires thorough understanding of its benefits and limitations; in some food a lesser log reduction rate is observable virtually less than the required 5log reduction rate. Ozone’s ability to destroy microorganisms is through the oxidation of some important cellular components, specifically the bacterial cell surface being the major target, ozone does not significantly affect the nutrients contents or sensory qualities in food; it has lesser effect on increasing temperature of food during processing, ozonation is an effective technology in extending the shelf-life of fruit and vegetables, rinsing or dipping vegetables in water saturated with ozone is a positive method. Onions treated with ozone during storage was positive, mold and bacterial populations was greatly decreased and no any sign of change in chemical composition and sensory quality of the product. Ozone has great advantage in the food industry; it is sufficiently soluble and stable in water with high antimicrobial activity, no need for storage of hazardous substances when used it, has low running cost with no residual problems after treatment and it autodecomposes and its stable end-product is oxygen so the by product is virtually oxygen. However, ozone’s limitation is still a threat in the food industry, it has the ability to desolubilize or decompose, or react with food constituents and targeted microorganisms. The reaction and the degradation of ozone diminish the residuals of this sanitizer during processing and subsequently lack of residuals could limit the ability of the processor’s for in-line testing of effectiveness. This paper reviewed the different application of ozone in the food industry.

Simulation and optimization of the removal of toluene in air by ozonation with a catalytic open-cell foam

A heterogeneous catalyst, composed of an open-cell glass foam support impregnated with zerovalent ruthenium nanoparticles (loading around 0.1 wt.%), was used to remove toluene in air by catalytic ozonation. Experiments with lab-designed 2−6 cm length and 1.6 cm diameter catalysts were performed. A model based on the Langmuir–Hinshelwood mechanism, coupled with mass transfer limitations and including competitive effects between toluene and ozone, was designed. It accurately fits experimental data gathered at various temperatures (30−90 °C), gas velocities (0.0025−0.017 m s−1) and inlet ozone concentrations (6.4–11.2 g m−3). The removal of ozone and toluene was mainly ruled by the ozone concentration at low concentrations while the adsorption competition becomes significant at high ozone concentrations.Predictive simulations, at 1.0 g m−3 inlet toluene concentration, were compared in terms of investment cost, operating cost and process performances. The results highlighted the complexity of the process, which involves antagonist aims between toluene removal and the design of a compact and energy-efficient reactor. With the best operating conditions (90 °C and 46 g m−3 ozone inlet concentration), the removal of toluene reached 88% (removal rate of 0.25 g m−3 s−1) with a high ozone degradation (97%) in a moderate reactor length of 0.11 m. These good performances associated to the low cost of the catalyst’s synthesis make it an efficient alternative for the removal of pollutants from air.

Oxidation of aqueous N-nitrosodiethylamine: Experimental comparison of pulsed corona discharge with H2O2-assisted ozonation

Hazardous nitrosamines formed in drinking water disinfection present serious public health and environmental concerns. Pulsed corona discharge (PCD) known for its unequaled energy efficiency in aqueous pollutants oxidation was experimentally compared with ozonation in degradation of N-nitrosodiethylamine (NDEA). Both methods were combined with H2O2 for advancement testing. In neutral media, PCD surpassed conventional ozonation for about twenty-nine times in energy efficiency; ozonation efficiency was substantially improved with H2O2 addition, whereas PCD did not benefit from it still surpassing O3/H2O2 combination for about 20% at pH 7.0. The Fenton-mediated oxidation was noticed in PCD accelerating oxidation of NDEA. The increase of pH to 12.0 predictably accelerated ozonation whereas PCD demonstrated the opposite outcome resulting in higher oxidation efficiency at pH 3.0.

What are the Reaction Laws and Toxicity Effects of Phthalate Acid Esters (PAEs) Ozonation Degradation in the Troposphere?

What are the Reaction Laws and Toxicity Effects of Phthalate Acid Esters (PAEs) Ozonation Degradation in the Troposphere?

Treatment of Landfill Leachate by Heterogeneous Catalytic Ozonation with Granular Faujasite Zeolite

Ozonation, combined with suitable catalyst represents an interesting option in removing poorly degraded pollutants from stabilized landfill leachate. Therefore, this study aimed to eliminate chemical oxygen demand (COD), color, and ammoniacal nitrogen, and to improve the biodegradability of stabilized landfill leachate using the heterogeneous catalytic ozonation with natural zeolite (Faujasite) in comparison with solo ozone or adsorption treatment. First, Faujasite was characterized and used in batch studies to find the optimum removal, followed by isotherm and kinetic studies to understand the mechanism. Next, ozonation as sole treatment under different operating conditions of pH and reaction time was applied. Subsequently, Faujasite was combined in the same reactor with the ozone in heterogeneous catalytic ozonation to enhance the treatment performance. Removal for ammonia, COD, and color by ozone as sole treatment were 29%, 47%, and 90%, respectively, compared with 63%, 66%, and 60% reductions by Faujasite as adsorbent. Heterogeneous catalytic ozonation with Faujasite shows ∼64% and 93% of the COD and color removal at pH 11. At this pH, Faujasite promoted ozone degradation, whereas 35% of ammonia was removed at pH 5 because of the interaction between direct ozone and pollutants on the Faujasite surface. Leachate biodegradability also improved from 0.016 to 0.1 after the combined treatment. Faujasite augmented in the ozonation improved the removal of pollutants and simultaneously enhanced the biodegradability of the stabilized landfill leachate.

Floral Pigmentation Has Responded Rapidly to Global Change in Ozone and Temperature

Across kingdoms, organisms ameliorate UV stress by increasing UV-absorbing pigmentation. Rapid ozone degradation during the 20th century resulted in elevated UV incidence, but pigmentation responses to this aspect of global change have yet to be demonstrated. In flowering plants, UV exposure favors larger areas of UV-absorbing pigmentation on petals, which protects pollen from UV-damage. Pigmentation also affects floral thermoregulation, suggesting climate warming may additionally impact pigmentation. We used 1,238 herbarium specimens collected from 1941 to 2017 to test whether change in UV floral pigmentation was associated with altered ozone and temperature in 42 species spanning three continents. We tested three predictions: first, UV-absorbing pigmentation will increase temporally and be correlated with reduced ozone (higher UV) when accounting for effects of temperature; second, taxa that experienced larger ozone declines will display larger increases in pigmentation; and third, taxa with anthers exposed to ambient UV will respond more strongly than those with anthers protected by petals. Globally, the extent of petal UV pigmentation increased significantly across taxa by ∼2% per year. However, temporal change was species specific-increasing in some taxa but declining in others. Species with exposed anthers experiencing larger declines in ozone displayed more dramatic pigmentation increases. For taxa with anthers enclosed within petals, pigmentation declined with increases in temperature, supporting a thermoregulatory role of UV pigmentation. Results document a rapid phenotypic response of floral pigmentation to anthropogenic climatic change, suggesting that global change may alter pollination through its impact on floral color, with repercussions for plant reproductive fitness.

Effect of zeolite acidity and structure on ozone oxidation of toluene using Ru-Mn loaded zeolites at ambient temperature

Five different Ru-Mn/zeolites were used to investigate their catalytic efficiencies for removing toluene (100 ppm) with ozone (1000 ppm) at room temperature. In general, most of metal oxide catalysts for removal of organic compounds need higher temperature than the ambient temperature, but Mn-based catalysts shows activity for prevalent organic pollutants even at room temperature with ozone. For the removal of toluene at room temperature without further heating, bimetallic Ru added Mn catalysts were applied in combination with different zeolite supports. The catalytic activity of the Ru-Mn catalysts strongly depended on the zeolite, of which the characteristics such as acidity and adsorption degree of toluene are dependent on the ratio of SiO2/Al2O3. Among the five Ru-Mn catalysts used, Ru-Mn/HY (SiO2/Al2O3 ratio: 80) and Ru-Mn/ZSM-5 (SiO2/Al2O3 ratio: 80) had higher toluene and ozone removal efficiencies. The toluene removal efficiency of Ru-Mn/zeolites was proportional to the pore volume and surface area. In terms of ozone degradation, Ru-Mn/HY(80) and Ru-Mn/HZSM-5(80) had the highest removal efficiencies. Overall, the catalytic ozone oxidation of toluene using Ru-Mn/zeolites seemed to be affected by a combination of the acidic properties of zeolites, Mn3+/Mn4+ ratio, and concentration ratio of oxygen vacancies to oxygen lattices on the catalyst surface.

Ozone Degradation of Prometryn in Ruditapes philippinarum: Response Surface Methodology Optimization and Toxicity Assessment

This study optimized the method for ozone (O3) degradation of prometryn in the clam Ruditapes philippinarum and evaluated toxicity changes during ozone degradation. The gas chromatography method for the detection of prometryn was appropriately improved. The linear range was 5 to 500 ng/mL, with a correlation coefficient of 0.9964. The addition concentration of prometryn was 0.025 to 0.100 mg/kg, the recovery was 77.97 to 85.00%, the relative standard deviation (n = 6) was 2.36 to 7.86%, and the limit of detection was 0.3 μg/kg. Using the central composite design in two experiments, ozone as gas and ozone dissolved in water, the effect of degradation rate was studied on three variables: ozone concentration, temperature, and exposure time. Ozone as gas and ozone dissolved in water have the same degradation effect on prometryn. The O3 concentration was 4.2 mg/L, the temperature was 40°C, the exposure time was 10 min, and the maximum degradation rate was 89.94 and 89.69% for the two experiments, respectively. In addition, the toxicity of ozone degradation products was evaluated using buffalo rat liver cells. After ozone treatment for 30 min, the toxicity of the ozone degradation products was reduced to 52.15% compared with that of prometryn itself. The toxicity of the ozone degradation products increased slightly when the ozonation time was prolonged; the toxicity at 180 min was greater than that of the parent compound prometryn. Overall, the application of ozone degradation of pesticide residues is a promising new technology. This study determined better degradation conditions for prometryn in R. philippinarum and also provided a theoretical basis for the widespread use of ozone technology in the future.

Synthesis and Characterization of Metal Modified Catalysts for Decomposition of Ibuprofen from Aqueous Solutions

The presence of pharmaceuticals in surface water, drinking water, and wastewater has attracted significant concern because of the non-biodegradability, resistance, and toxicity of pharmaceutical compounds. The catalytic ozonation of an anti-inflammatory pharmaceutical, ibuprofen was investigated in this work. The reaction mixture was analyzed and measured by high-performance liquid chromatography (HPLC). Liquid chromatography-mass spectrometry (LC-MS) was used for the quantification of by-products during the catalytic ozonation process. Ibuprofen was degraded by ozonation under optimized conditions within 1 h. However, some intermediate oxidation products were detected during the ibuprofen ozonation process that were more resistant than the parent compound. To optimize the process, nine heterogeneous catalysts were synthesized using different preparation methods and used with ozone to degrade the ibuprofen dissolved in aqueous solution. The aim of using several catalysts was to reveal the effect of various catalyst preparation methods on the degradation of ibuprofen as well as the formation and elimination of by-products. Furthermore, the goal was to reveal the influence of various support structures and different metals such as Pd-, Fe-, Ni-, metal particle size, and metal dispersion in ozone degradation. Most of the catalysts improved the elimination kinetics of the by-products. Among these catalysts, Cu-H-Beta-150-DP synthesized by the deposition–precipitation process showed the highest decomposition rate. The regenerated Cu-H-Beta-150-DP catalyst preserved the catalytic activity to that of the fresh catalyst. The catalyst characterization methods applied in this work included nitrogen adsorption–desorption, scanning electron microscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. The large pore volume and small metal particle size contributed to the improved catalytic activity.