Surficial engineering of active hydroxyls for ambient formaldehyde oxidation via enhanced Lewis acidity over Zr-doped cryptomelane materials.

Lewis acids of solid catalysts have been featured for a pivotal role in promoting various reactions. Regarding the oxidation protocol to remove formaldehyde, the inherent drawback of the best-studied MnO2 materials in acidic sites has eventually caused deficiency of active hydroxyls to sustain low-temperature activity. Herein, the cryptomelane-type MnO2 was targeted and it was tuned via incorporation of Zr metal, exhibiting great advances in not only the complete HCHO-to-CO2 degradation but also cycling performance. Zr species were existent in doping state in the MnO2 lattice, rendering lower crystallinity and breaking the regular growth of MnO2 crystallites, which thereby tripled surface area and created larger volume of smaller mesopores. Meantime, the local electronic properties of Mn atoms were also changed by Zr doping, i.e., more low-valence Mn species were formed due to the electron transfer from Zr to Mn. The results of infrared studies demonstrate the higher possession of Lewis acid sites on ZrMn, and this high degree of electrophilic agents favored the production of hydroxyl species. Furthermore, the reactivity of surface hydroxyls, as investigated by CO temperature programmed reduction and temperature programmed desorption of adsorbed O2, was obviously improved as well after Zr modification. It is speculated jointly with the characterizations of the post-reaction catalysts that the accelerated production of active hydroxyls helped rapidly convert formaldehyde into key intermediate-formate, which was then degraded into CO2, avoiding the side reaction path with undesired intermediate-hydrocarbonate-over the pristine MnO2, where active sites were blocked and formaldehyde oxidation was inhibited. Additionally, Zr decoration could stabilize Lewis acidity to be more resistant to heat degeneration, and this merit brought about advantageous thermal recyclability for cycled application.

Formulating the Li sites of Li-CoOx composites for achieving high-efficiency oxidation removal of formaldehyde over the Ag/Li-CoOx catalyst under ambient conditions.

Oxide supported noble metals are extensively investigated for ambient formaldehyde oxidation, and the Ag-CoOx complex is one promising combination in terms of cost and activity. Further, we previously observed that cooperating Ag with Li + greatly boosted formaldehyde degradation on CoOx. Yet, there is still room for improvement in removal efficiency, mineralization capacity and resistance to severe conditions. These objectives could be realized via strategically formulating the Li+ sites of Li-CoOx composite in this sister study. Three samples with Li + ---Co3+-O2- connections (L-CO), spinel Li+ (LCO-S) and layered Li+ (LCO-L) were obtained at low (300 °C), moderate (500 °C) and high (700 °C) temperatures, respectively. The specific Li+ positions and componential interaction were demonstrated by Hyperspectral imaging (HSI), XRD, SEM, TEM, HAADF mapping, UV-vis DRS and XPS. Moreover, the effect of reactive oxygen exposure on catalytic oxidation of formaldehyde (330-350 mg/m3) was disclosed through CO-TPR and O2-TPD. Compared with the LCO-S and LCO-L, L-CO exhibited dominant formaldehyde degradation due to the larger content of surface oxygen. After Ag decoration, the Li+---Co3+-O2- connections uniquely caused a strong binding of Ag species with catalyst host, which boosted the amount of reactive oxygen and finally resulted in an even higher elimination of ∼73% (CO2 yield = âˆ¼21%), 47% higher than that of the L-CO (CO2 yield = âˆ¼6%). But in contrast, the Ag@LCO-S only achieved ∼53% removal (CO2 yield = âˆ¼9%) and Ag modification was powerless in altering the inertness of LCO-L, demonstrating that the chemical environment of alkali metal is crucial to effectively tuning the catalyst activity. The advantage of Ag@L-CO in formaldehyde depollution was further reflected from its much better resistance to moisture and aromatic compound omnipresent in indoor air. For the first time, this study extended the understanding of the alkali-metal-promoted formaldehyde oxidation reaction to an in-depth level.

Enhanced oxidative ability, recyclability, water tolerance and aromatic resistance of α-MnO2 catalyst for room-temperature formaldehyde oxidation via simple oxalic acid treatment.

To obtain a versatile formaldehyde oxidation material, simultaneously increasing the oxidative ability, recyclability and deactivation repellence (e.g., enduring the interference from moisture and aromatic compound omnipresent in indoor air) is of great significance. Herein, the above properties of α-MnO2 were synchronously updated via one step treatment in oxalic acid (H2C2O4), and an in-depth understanding of the surface properties-performance relationship was provided by systematic characterizations and designed experiments. Compared with the pristine sample, XPS, ESR, O2-TPD, CO-TPR and pyridine-IR reveal that H2C2O4 created substantial Mn3+ species on surface, exposing a higher coverage of oxygen vacancies that actively participated in the dissociative activation of gas-phase O2 into reactive chemically adsorbed oxygen (OC), and the abundant Lewis acid sites further enabled the effective O2 activation process. The large amount of oxygen OC promoted the HCHO-to-CO2 conversion and inhibited the accumulation of formate that required a high temperature of 170 °C to be eliminated, thus conspicuously improving the α-MnO2's thermal recovery. The combined H2O-TPD, H2O-preadsorbed CO-TPR, C6H6-TPD and C6H6-preadsorbed CO-TPR investigations shed light on the H2C2O4-induced water and benzene resistance. The notably weakened water and benzene binding strength with the H2C2O4-modified surface together with the unrestrained oxygen OC accounted for the outstanding anti-deactivation performance.

Water durability modification of cerium-manganese oxide by tin shell for efficient airborne benzene oxidation.

Single or cooperative incorporation of Ce and Sn elements into α-MnO2 parent were tried to update the catalytic benzene oxidation performance, and the successive modification via Ce doping and Sn deposition was demonstrated to be a promising methodology to offer high mineralization and avoid moisture-aroused inactivation. Ce doping caused lattice distortion, increased Mn3+ content to 2.7 times that of the pristine MnO2 and weakened Mn-O bonds due to electron transfer from Ce3+ to lattice oxygen, thus facilizing oxygen vacancy formation. Further, Sn deposition on CeMn substrate induced strong metal support interaction (SMSI) due to the core-shell like structure of Sn@CeMn, which promoted the construction of active oxygen vacancies to an even larger extent (1.2 and 2.5 times that of the CeMn and pristine MnO2, respectively). The thus-formed larger amount of reactive oxygen species rendered the Sn@CeMn simultaneously with high CO2 yield and low CO production. Also benefited from the SMSI effect, the Sn@CeMn's ability to continuously activate O2 and H2O into reactive oxygen species (e.g.,·OH radicals) was enhanced, which could offset the negativity caused by water vapor, thereby keeping > 95% removal during 5.5 h water switch on/off investigation at 200 °C. Reaction pathways were uncovered with designed experimentations.

Ultra-light 3D MnO2-agar network with high and longevous performance for catalytic formaldehyde oxidation.

Under the background of indoor air formaldehyde decontamination, a freestanding ultra-light assembly was fabricated via ice-templating approach starting from MnO2 nanoparticles and environmentally benign agar powder. The 3D composite of agar and MnO2 (AM-3D) was comparatively studied with powdered counterparts (including pure MnO2 and mixture of agar and MnO2) and the 3D-structured agar for formaldehyde oxidation, and their physicochemical properties were examined with XRD, ATR, SEM, XPS, isothermal N2 adsorption, ESR, Raman, CO-TPR and O2-TPD. For the single test of formaldehyde oxidation, the AM-3D catalyst exhibited 62.0%-67.0% removal percentage for ~400 mg/m3 formaldehyde, which did not demonstrate significant advantage over the control samples. However, thanks to the porous 3D agar scaffold with large spatial volume that could promote a rapid gas-phase formaldehyde concentration reduction, and the strong interaction between the dispersed MnO2 particles and agar substrate that could afford a large amount of reactive oxygen species to further oxidize the adsorbed formaldehyde, the AM-3D composite was a much better HCHO-to-CO2 converter and possessed much more advantageous stability for repeated cycles of formaldehyde oxidation: even after ten cycles, there was still 41.7% of formaldehyde removed. Furthermore, the viable sunlight irradiation could easily restore the activity of the used AM-3D catalyst back to the level approaching that of the fresh one. Finally, reaction pathways were put forward via the infrared spectroscopic and ion chromatographic investigations on the surface intermediates of the spent materials.

Highly selective colorimetric determination of catechol based on the aggregation-induced oxidase-mimic activity decrease of δ-MnO2.

Multiple enzyme-like activities of manganese oxides (MnO2) have been reported and applied in catalysis, biosensors, and cancer therapy. Here, we report that catechol can be determined colorimetrically based on the 3,3',5,5'-tetramethylbenzidine (TMB) oxidase-like activity of δ-MnO2. The detection was based on pre-incubation of catechol containing water samples with δ-MnO2, and then the residual TMB oxidase-like activity of reacted δ-MnO2 was linearly dependent on the catechol concentration in the range of 0.5 to 10 µM. This determination method was stable at pH 3.73-6.00 and was not affected by ion strength up to 200 µM. Common co-solutes in water bodies (50 µM) have negligible effects and excellent selectivity of catechol among various phenolic compounds (15 µM) was facilitated. Both reduction and aggregation of δ-MnO2 were observed during the incubation process with catechol, and aggregation-induced TMB oxidase-mimic activity decrease was the main factor for this colorimetric determination.

Effect of nano zinc oxide on the acute and reproductive toxicity of cadmium and lead to the marine copepod Tigriopus japonicus.

Given the absorbability of nZnO and its inevitable coexistence with trace metals such as Cd and Pb in coastal environment, nZnO can adsorb these pollutants thereby affecting their distribution in different media of marine ecosystem. The marine copepod Tigriopus japonicus was applied in the present study to investigate the combined effect of nZnO and Cd or Pb on mortality and reproduction in marine organisms. For acute exposure, presence of 1.0 mg/L nZnO increased the toxicity of both Cd and Pb, as their LC50 decreased from 5.9 and 75.4 mg/L to 3.95 and 48.0 mg/L, respectively. For 21 d chronic exposure, the reproduction of the copepod was influenced by Cd and Pb at environmental relevant concentrations, and the interaction between nZnO and Cd or Pb appeared to be antagonistic. The waterborne Cd and Pb concentration was affected by nZnO for neither acute nor chronic exposure, indicating no adsorption of these two metals to nZnO at relative low concentration. The overall findings of this study suggested the binary exposure to nZnO/Cd or nZnO/Pb might have potential different toxic mechanisms between acute and chronic exposure.

Characterization of PM2.5-bound phthalic acid esters (PAEs) at regional background site in northern China: Long-range transport and risk assessment.

Eleven major phthalic acid esters (PAEs) congeners were analyzed for PM2.5 samples collected at Mount Tai, a high elevation mountain site in northern China from June to August 2015. The results showed that the average concentration of PAEs in PM2.5 was 19.48ngm-3, and bis(2-Ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP) and diisobutyl phthalate (DIBP) were the predominant species in particle-phase, whereas diethyl phthalate (DEP) and dimethyl phthalate (DMP) were the prevailing PAEs in gas-phase. PAE concentrations decreased at the beginning of cloud/fog events, while they increased after the cloud/fog events since the liquid-phase PAEs could be absorbed by solid-phase PAEs. Potential source contribution function (PSCF) analysis and principal component analysis (PCA) revealed that the highest PSCF value of air masses were mainly sourced from southwest of Mount Tai and multiple sources contributed to PAEs. A Monte Carlo simulation was applied to estimate the incremental lifetime cancer risks (ILCR) from inhalation exposure on the basis of DEHP concentrations. The estimated values of ILCR for the general population were lower than the U.S. Environmental Protection Agency threshold, which is 10-6. However, since the local population was exposed to various local emission sources, the actual health risk is undervalued.

Development of a lipovitellin-based sandwich ELISA for determination of vitellogenin in the marine medaka Oryzias melastigma.

A lipovitellin (Lv) based sandwich enzyme-linked immunosorbent assay (ELISA) was developed to quantify vitellogenin (Vtg) in marine medaka (Oryzias melastigma). Lv and Vtg were purified from the unfertilized eggs and the whole body homogenates (WBH) of estradiol (E2)-exposed fish. The purified Lv sample appeared as three clear bands (118, 112 and 100 kDa) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and was identified as an Lvs mixture from VtgAa and VtgAb by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis. Polyclonal antibody against marine medaka VtgAa was also raised. Compared with Vtg, Lv was more stable to heat stress (37 °C for 8 h or 4 °C for a week) and repeated freeze/thaw stress. In addition, western blot analysis revealed that marine medaka Vtg and Lv had similar immunogenicity. Therefore, in this study, Lv was applied instead of Vtg as the standard to establish an ELISA. The Lv standard curve was parallel to serial WBH dilutions of E2-exposed fish, and the absorbance values were very low in control male samples, suggesting the specificity and feasibility of the method for Vtg quantification. The developed assay was sensitive with the detection limit of 3.1 ng/mL and had a working range between 15.6 and 500 ng/mL. The intra- and inter-assay coefficients of variation were both below 5%. Moreover, the standard curves of Lv antigen treated under different stresses were almost identical, indicating high robustness of the assay. Overall, our study provides an important methodology reference for quantification of marine medaka Vtg.