Enhanced room-temperature HCHO decomposition activity of highly-dispersed Pt/Al2O3 hierarchical microspheres with exposed {110} facets

Solvothermal synthesis of 3D rod-shaped Ti/Al/Cr nano-oxide for photodegradation of wastewater micropollutants under sunlight: a green way to achieve SDG:6

Waterbodies are day-by-day polluted by the various colored micropollutants, e.g., azo dyes enriched (carcinogenic, non-biodegradable) colored wastewater from textile industries. Water pollution has become a serious global issue as ~ 25% of health diseases are prompted by pollution as reported by WHO. Around 1 billion people will face water scarcity by 2025 and this water crisis is also a prime focus to the UNs' sustainable development goal 6 (SDG6: clean water and sanitation). To prevent the water pollution caused by micropollutants, a mesoporous, 3D rod-like nano-oxide Ti/Al/Cr (abbreviated as TAC) has been synthesized via the solvothermal method. TAC degraded all classes of azo dyes (mono, di, tri, etc.) with > 90% efficiency under renewable energy source solar irradiation within the pH range 2-11. The detailed study was done on the photodegradation of carcinogenic di-azo dye Congo red (CR) which is banned in many countries. TAC showed 90.64 ± 2% degradation efficiency for CR at pH 7. The proposed photodegradation mechanism of CR was confirmed by the high-resolution liquid chromatography-mass spectroscopy (HRLC-MS) analysis obeying the Pirkanniemi path. The photodegradation obeyed the pseudo-1st-order kinetics and was reusable up to successive 5 cycles which can be an efficient tool to meet the UNs' SDG:6.

Insight into the effect of exposed crystal facets of anatase TiO2 on HCHO catalytic oxidation of Mn-Ce/TiO2

Indoor formaldehyde pollution seriously jeopardizes human health. The development of efficient and stable non-precious metal catalysts for low-temperature catalytic degradation of formaldehyde is a promising approach. In this study, TiO2 {001} and {101} supports were loaded with different ratios of Mn and Ce active components, and the effects of the ratios of the active components on the catalytic activity were investigated. The elemental oxidation states, redox capacities, active oxygen mobilities and acid site distributions of the catalysts were determined using characterization techniques such as XPS, H2-TPR, O2-TPD, and NH3-TPD. In situ infrared spectroscopy was utilized to reveal the differences in the two-step dehydrogenation reactions of dioxymethylene (DOM) in 5Mn1Ce/Ti-NS and 5Mn1Ce/Ti-NP. Density-functional theory was used to investigate the differences in the catalytic steps and maximum energy barriers of Mn-Ce/Ti-NS and Mn-Ce/Ti-NP for HCHO. The differences in catalytic activity due to the influence of the manganese and cerium active components on the {001} and {101} crystal faces of anatase titanium dioxide are comprehensively revealed. Exposure of the supported crystalline surfaces alters the catalytic activity centers and reaction pathways at the molecular level. This study provides experimental and theoretical guidance for the selection of exposed crystalline surfaces for loaded catalysts.

Effect of preparation method of noble metal supported catalyts on formaldehyde oxidation at room temperature: Gas or liquid phase reduction

Formaldehyde (HCHO) is toxic to the human body and is one of the main threats to the indoor air quality (IAQ). As such, the removal of HCHO is imperative to improving the IAQ, whereby the most useful method to effectively remove HCHO at room temperature is catalytic oxidation. This review discusses catalysts for HCHO room-temperature oxidation, which are categorized according to their preparation methods, i.e., gas-phase reduction and liquid-phase reduction methods. The HCHO oxidation performances, structural features, and reaction mechanisms of the different catalysts are discussed, and directions for future research on catalytic oxidation are reviewed.

Review on Catalytic Oxidation of VOCs at Ambient Temperature

As an important air pollutant, volatile organic compounds (VOCs) pose a serious threat to the ecological environment and human health. To achieve energy saving, carbon reduction, and safe and efficient degradation of VOCs, ambient temperature catalytic oxidation has become a hot topic for researchers. Firstly, this review systematically summarizes recent progress on the catalytic oxidation of VOCs with different types. Secondly, based on nanoparticle catalysts, cluster catalysts, and single-atom catalysts, we discuss the influence of structural regulation, such as adjustment of size and configuration, metal doping, defect engineering, and acid/base modification, on the structure-activity relationship in the process of catalytic oxidation at ambient temperature. Then, the effects of process conditions, such as initial concentration, space velocity, oxidation atmosphere, and humidity adjustment on catalytic activity, are summarized. It is further found that nanoparticle catalysts are most commonly used in ambient temperature catalytic oxidation. Additionally, ambient temperature catalytic oxidation is mainly applied in the removal of easily degradable pollutants, and focuses on ambient temperature catalytic ozonation. The activity, selectivity, and stability of catalysts need to be improved. Finally, according to the existing problems and limitations in the application of ambient temperature catalytic oxidation technology, new prospects and challenges are proposed.

Pd-based catalysts promoted by hierarchical porous Al2O3 and ZnO microsphere supports/coatings for ethyl acetate highly active and stable destruction

Developing economical and active materials is of great significance for VOC purification. Here, hierarchical porous Al₂O₃ and ZnO microspheres (Al₂O₃-pm and ZnO-pm) were synthesized by a facile hydrothermal strategy. The urchin-like Al₂O₃-pm and flower-like ZnO-pm possess high specific surface area (especially; external surface area) obviously boost the dispersion of Pd with 29.3 % and 30.1 % over Pd/Al₂O₃-pm and Pd/ZnO-pm, respectively, over 3.4 times higher than those of commercial Al₂O₃- and ZnO-supported counterparts. Pd/Al₂O₃-pm possesses excellent activity and CO₂ yield in ethyl acetate (EA) degradation, with TOF reaches 7.76 × 10^-3 s^-1 at 160 °C under GHSV of 50,000 h^-1. Moreover, Pd/Al₂O₃-pm exhibits satisfied performance in EA-contained binary VOCs oxidation and has high long-term stability under both dry and humid conditions. Both Pd sites and Brønsted acid sites participated in reaction process and initially react with EA to form ethylene and ethanol, respectively. Larger amount Brønsted acid sites over Pd/Al₂O₃-pm promote ethanol formation and C-C cleavage, resulting in different CO₂ yields and EA activation mechanisms. The coating greatly enhances Pd dispersion over Pd supported monolithic catalyst, endowing its desired activity and stability even with a much lower Pd loading. This work promotes the potential application of noble-metal-based monolithic materials in VOC degradation.

Highly sensitive and selective detection of 4-nitroaniline in water by a novel fluorescent sensor based on molecularly imprinted poly(ionic liquid)

A novel molecularly imprinted fluorescent sensor for the determination of 4-nitroaniline (4-NA) was synthesized via free radical polymerization with 3-[(7-methoxy-2-oxo-2H-chromen-4-yl)methyl]-1-vinyl-1H-imidazol-3-ium bromide as the fluorescence functional monomer, 4-NA as the template molecule, ethylene glycol dimethacrylate as the cross-linker, and 2,2'-azo(bisisobutyronitrile) as the initiator. The obtained fluorescent poly(ionic liquid) was characterized through Fourier transform infrared, scanning electron microscopy, Brunauer-Emmett-Teller analysis, and fluorescence spectrophotometry. The fluorescent sensor had high fluorescence intensity, short detection time (0.5 min), good selectivity, and excellent sensitivity (limit of detection = 0.8 nM) for 4-NA, with good linear relationships of 2.67-10,000 nM. The practical applicability of the fluorescence sensor in detecting 4-NA in industrial wastewater and spiked environmental water was demonstrated, and a satisfactory result was obtained. Graphical abstract Highly sensitive and selective detection of 4-nitroaniline in water by a novel fluorescent sensor based on molecularly imprinted poly(ionic liquid).

Hierarchical γ-alumina: From Pure Phase to Nanocomposites

Recent advances in nanotechnology make it possible to create nanomaterials based on γ-alumina with novel hierarchical structure and physicochemical properties. Hierarchical γ-alumina can be synthesized using chemical or physical methods. The nanostructures based on γ-alumina exhibit unique properties, which are utilized in the design of efficient applications. These superior properties are often due to their hierarchical organizations from the nanosize scale to the macroscopic level. The present review is devoted to the contemporary state of the studies on the methods to produce hierarchical γ-alumina. We tried to summarize herein the literature data on the methods of synthesis of hierarchical γ-AlOOH and γ-Al2O3 with controlled morphology and the application of these methods for the synthesis of hierarchical γ-AlOOH and γ-Al2O3 nanocomposites.

Bimetallic nickel molybdate supported Pt catalyst for efficient removal of formaldehyde at low temperature

Efficient removal of formaldehyde from indoor environments is of significance for human health. In this work, a typical binary transition metal oxide that could provide various oxidation states, β-NiMoO₄, was employed as a support to immobilize the active Pt component (Pt/NiMoO₄) for catalytic formaldehyde elimination at low ambient temperature (15°C). The results showed that the hydrothermal preparation temperature and time had a noticeable impact on the morphology and catalytic activity of the samples. The catalyst prepared with hydrothermal temperature of 150°C for 4 hr (Pt-150-4) exhibited superior catalytic activity and stability mainly due to its distinctly porous structure, relative abundance of adsorbed surface hydroxyls/water, and high oxidation ability, which resulted from the interaction of Pt with Ni and Mo of the bimetallic NiMoO₄ support. Our results might shed light on the rational design of multifunctional catalysts for removal of indoor air pollutants at low ambient temperature.

Hydroxyapatite-Supported Low-Content Pt Catalysts for Efficient Removal of Formaldehyde at Room Temperature

Indoor environmental quality directly affects the life quality and health of human beings, and therefore, it is highly vital to eliminate the volatile organic compounds especially formaldehyde (HCHO), which is regarded as one of the most common harmful pollutants in indoor air. Hydroxyapatite (HAP)-supported Pt (Pt/HAP) catalysts with a low content of Pt (0.2 wt %) obtained via hydrothermal and chemical reduction processes could effectively remove gaseous HCHO from the indoor environment at room temperature. The influence of modifier in the preparation on the catalyst activity was investigated. The HAP and HAP modified by sodium citrate and hexamethylenetetramine-supported 0.2 wt % Pt could completely decompose HCHO into CO2 and water, while HAP modified by sodium dodecyl-sulfate-supported Pt removed HCHO primarily via adsorption. The HAP modified by the sodium citrate catalyst exhibited superior catalytic performance of HCHO compared to the HAP and HAP modified by hexamethylenetetramine and sodium dodecyl-sulfate-supported Pt catalysts, which was mainly because of its higher surface Ca/P ratio providing more Lewis acidic sites (Ca2+) for co-operational capture of HCHO molecules and a larger amount of active oxygen species. Our results indicate that an optimized combination of functional supports and low-content noble metal nanoparticles could be a route to fabricate effective room-temperature catalysts for potential application in indoor air purification.

A Hybrid Reactor System Comprised of Non-Thermal Plasma and Mn/Natural Zeolite for the Removal of Acetaldehyde from Food Waste

The degradation of low concentrations of acetaldehyde while using a non-thermal plasma (NTP)/catalyst hybrid reactor system was investigated while using humidified air at ambient temperature. A series of highly active manganese-impregnated natural zeolite (Mn/NZ) catalysts were synthesized by the incipient wetness method using sonication. The Mn/NZ catalysts were analyzed by Brunauer-Emmett-Teller surface area measurements and X-ray photoelectron spectroscopy. The Mn/NZ catalyst located at the downstream of a dc corona was used for the decomposition of ozone and acetaldehyde. The decomposition efficiency of ozone and acetaldehyde was increased significantly using the Mn/NZ catalyst with NTP. Among the various types of Mn/NZ catalysts with different Mn contents, the 10 wt.% Mn/NZ catalyst under the NTP resulted the highest ozone and acetaldehyde removal efficiency, almost 100% within 5 min. Moreover, this high efficiency was maintained for 15 h. The main reason for the high catalytic activity and stability was attributed to the high dispersion of Mn on the NZ made by the appropriate impregnation method using sonication. This system is expected to be efficient to decompose a wide range of volatile organic compounds with low concentrations.

Effective Formaldehyde Capture by Green Cyclodextrin-Based Metal-Organic Framework

A kind of metal-organic framework made from γ-cyclodextrin (γ-CD) and potassium ions were explored as excellent formaldehyde (HCHO) absorbents. The adsorption capacity and speed of γ-CD-MOF-K are both about 9 times higher than those of activated carbon, which are attributed to the porous structure and synergistic effect of hydrogen bonding and host-guest interactions.

Catalytic decomposition and mechanism of formaldehyde over Pt–Al2O3 molecular sieves at room temperature

Al₂O₃ molecular sieve supported Pt was prepared for catalytic formaldehyde oxidation at room temperature.

Preparation of a Pt/TiO2/cotton fiber composite catalyst with low air resistance for efficient formaldehyde oxidation at room temperature

Pt/TiO₂/cotton fiber catalyst was successfully prepared with much lower air resistance than powder-like sample. It can catalyze oxidation of HCHO into CO₂ and H₂O with an optimum Pt loading of 0.75 wt%. It also exhibited good catalytic stability.