A facile method for preparing the CeMnO3 catalyst with high activity and stability of toluene oxidation: The critical role of small crystal size and Mn3+-Ov-Ce4+ sites.

Volatile organic compounds (VOCs) cause severe environmental pollution and are potentially toxic to humans who have no defense against exposure. Catalytic oxidation of these compounds has thus become an interesting research topic. In this study, microcrystalline CeMnO3 catalysts were prepared by a precipitant-concentration-induced strategy and evaluated for the catalytic oxidation of toluene/benzene. The effect of crystal size on catalytic performance was confirmed by XRD, TEM, N2 adsorption-desorption, XPS, Raman, H2-TPR, and TPSR. The CeMnO3 catalyst with more Mn3+-Ov-Ce4+ active sites exhibited enhanced VOCs catalytic oxidation performance, lowest active energy, and highest turnover frequency, which was attributed to its larger surface area, lower crystal size, higher low-temperature reducibility, and presence of more oxygen defects. In-situ FTIR results suggested more oxygen vacancies can profoundly promote the conversion of benzoate to maleate species, the rate-determining step of toluene oxidation. The work provides a convenient and efficient strategy to prepare single-metal or multi-metal oxide catalysts with smaller crystal sizes for VOC oxidation or other oxidation reactions.

Structural and compositional analysis of MOF-derived carbon nanomaterials for the oxygen reduction reaction.

The development of low-cost and efficient cathode catalysts is crucial for the advancement of fuel cells, as the oxygen reduction reaction (ORR) on the cathode is constrained by expensive commercial Pt/C catalysts and a significant energy barrier. Metal-organic frameworks (MOFs) are considered excellent precursors for synthesizing carbon nanomaterials due to their simple synthesis, rich structure and composition. MOF-derived carbon nanomaterials (MDCNM) inherit the morphology of their precursors at low dimensional scales, providing abundant edge defects, larger specific surface area, and excellent electron transport paths. Furthermore, the rich composition of MOFs enables the carbon nanomaterials derived from them to exhibit various physicochemical properties, including stronger electron gaining ability, oxygen affinity, and a higher degree of graphitization, resulting in excellent ORR activity. However, a more detailed analysis is necessary to understand the advantages and mechanisms of MDCNM in the field of the ORR. This review classifies and summarizes the structure and different chemical compositions of MDCNM in low dimensions, and provides an in-depth analysis of the reasons for their improved ORR activity. Additionally, the recent practical applications of MDCNM as cathode material in fuel cells are introduced and analyzed in detail, with a focus on the enhanced electrochemical performance.

Mn3O4/CuOx heterostructure for nitrate electroreduction to ammonia.

Here, we designed a Mn3O4/CuOx heterostructure supported on copper foil (CF) for electrocatalytic nitrate reduction to ammonia. The selectivity and Faraday efficiency of ammonia were 96.79% and 86.55%, respectively. Multiple characterizations revealed that Mn3O4/CuOx/CF showed faster charge transfer and created more electron-deficient Mn sites, electron-rich Cu sites and large numbers of oxygen vacancies, which were conducive to improving the catalytic activity. This work may open an avenue for the construction of heterostructures as an electrocatalyst for the reduction of nitrate to ammonia.

Cobalt oxide/copper bismuth oxide/samarium vanadate (Co3O4/CuBi2O4/SmVO4) dual Z-scheme heterostructured photocatalyst with high charge-transfer efficiency: Enhanced carbamazepine degradation under visible light irradiation.

Herein, a dual Z-scheme heterojunction photocatalyst consisting of Co3O4, CuBi2O4, and SmVO4 for carbamazepine (CBZ) degradation was synthesised and characterised by XRD, FTIR, UV-Vis DRS, XPS, FE-SEM, and TEM. The reduction in electron-hole recombination was evaluated by PL, LSV, and EIS analysis. The heterojunction, Co3O4/CuBi2O4/SmVO4 (CCBSV) showed enhanced photocatalytic activity of 76.1% ± 3.81 CBZ degradation under visible light irradiation, ascribed to the improved interfacial contact, visible light capturing ability, and enhanced electron-hole separation and transportation through the formation of Z-scheme heterojunction. The formation of dual Z-scheme was confirmed by active radical experiments and XPS analysis that helped to prose the mechanism of degradation. The catalyst showed sustained stability after 4 cycles of reuse. Ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS) was employed to identify the degradation by-products of CBZ, and a possible mechanistic degradation pathway was proposed. This study provided an insight into the development of efficient dual Z-scheme heterojunction photocatalyst for remediation of CBZ which can be extended to other organic pollutants.

Protic/aprotic ionic liquids for effective CO2 separation using supported ionic liquid membrane.

Four ionic liquids (ILs) namely, 1-butylsulfonate-3-methylimidazolium P-toluene sulfonate ([BSmim][tos]), 1-butylsulfonate pyridine P-toluene sulfonate ([BSmpy][tos]), 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-butylpyridine chloride ([Bpy][Cl]) were synthesized for the effective separation of gases CO2/N2 and CO2/CH4 through supported ionic liquid membranes (SILMs). ILs were confirmed by NMR and FTIR spectroscopy, and their characteristics and physical properties were studied. The ILs were immobilized on the porous hydrophobic 200 µm thick polyvinylidene difluoride (PVDF) support. Pure and mixed gas separation performances of the prepared SILMs were analyzed in a custom-built gas permeation unit. The SILMs were stable up to 0.6 MPa at room temperature without leaching the ionic liquid. [BSmim][tos] was recorded to have the highest solubility coefficient and permeability for CO2, among other ILs. At 0.5 MPa, for pure CO2/N2 and CO2/CH4, IL [BSmim][tos] was observed with selectivities of 56.2 and 47.5, respectively. Based on the SILMs separation performance, the ILs synthesized for this work can be ranked as [BSmim][tos] > [BSmpy][tos] > [Bmim][Cl] > [Bpy][Cl]. Moreover, the exceptionally high selectivity values of [BSmim][tos] and [BSmpy][tos] confirms the potential use of ILs for CO2 separation through SILMs.

Towards understanding corrosion inhibition of sulfonate/carboxylate functionalized ionic liquids: An experimental and theoretical study.

The inhibition performance of ionic liquids, abbreviated as [(CH2)COOHMIm][HSO4], [(CH2)2COOHMIm][HSO4], and [(CH2)3SO3HMIm][HSO4] was investigated for carbon steel in 0.5 M HCl solution. Results indicated that these ionic liquids could act as effective inhibitors by adsorption onto the steel surface, and the inhibition efficiency increases with cation alkyl chain length and concentration up to a limit. The inhibition efficiency of a sulfonate-type ionic liquid with a longer alkyl chain is higher than those of the carboxylate-type ionic liquids. Besides, the order of inhibition efficiency was verified by both computational calculation and electrochemical experimental observations.

Preparation of carbon-coated brookite@anatase TiO2 heterophase junction nanocables with enhanced photocatalytic performance.

One-dimensional TiO2@C nanocables with a heterophase junction have been successfully prepared by coating brookite@anatase TiO2 with a thin layer of hydrothermal carbon (HTC). Compared with anatase TiO2, the biphase brookite@anatase structure can reduce the recombination rate of the excited electron/hole pairs of TiO2. The HTC coating not only enhances the adsorption capability of the TiO2 catalyst for organic pollutants but also facilitates photogenerated electron transfer to further increase its photocatalytic activity. Therefore, compared with anatase TiO2, brookite@anatase TiO2, and TiO2@C, the brookite@anatase TiO2@C shows the highest photocatalytic activity for the photodegradation of tetracycline (TC) under the irradiation of UV-visible light. Moreover, ˙O2 has been proved to be the predominant active species for the photodegradation of TC, and the photocatalytic mechanism of brookite@anatase TiO2@C nanocables has also been proposed.

A polar-hydrophobic ionic liquid induces grain growth and stabilization in halide perovskites.

The addition of a polar-hydrophobic methylammonium trifluoroacetate ionic liquid tailors the hydrophobicity of halide-perovskite precursor solutions and assists in grain growth. This unique additive also functionalizes the grain boundaries via polar-polar interactions, thereby enhancing the optoelectronic properties and chemical stability of perovskites. This study opens the door to the solution hydrophobicity control towards high-performance perovskite devices.

Diethylenediamine-assisted template-free synthesis of a hierarchical TiO2 sphere-in-sphere with enhanced photocatalytic performance.

With the assistance of diethylenediamine (DETA), a template-free solvothermal approach is employed to one-step synthesize a hierarchical TiO2 sphere-in-sphere, which has a unique structure: an interior nanosized sphere is contained in the cavity of another hollow microsphere, and numerous nanosheets of width ca. 20-26 nm vertically distribute on the surface. It is proved that DETA added in solution plays an important inducing role in the formation of both the hollow sphere-in-sphere structure and surface sheet-assembled network. Therefore, a DETA-assisted formation mechanism of the hierarchical TiO2 sphere-in-sphere has been described in detail. The unique hierarchical sphere-in-sphere structure endows the TiO2 product with increasing light-harvesting efficiency and specific surface area, resulting in its enhanced photocatalytic activity for the degradation of various organic pollutants under the illumination of UV light.

Insights into catalytic roles of noble-metal-free catalysts CoxSy for reduction of 4-nitrophenol.

To develop noble-metal-free catalysts, three CoxSy samples, i.e. Co9S8, CoS and CoS2, have been prepared and investigated for the reduction of 4-nitrophenol. Co9S8 has the best surface electron immigration efficiency and the highest H2-adsorption capability, which make it the most promising catalyst. On the other hand, CoS has higher electron transfer efficiency than CoS2, leading to stronger H absorption capability. As a result, the catalytic activity of the three catalysts shows the following trend: Co9S8 > CoS > CoS2 under the same reaction conditions. Finally, a plausible catalytic mechanism has also been proposed, which is helpful in acquiring an in-depth insight into the catalytic role of CoxSy.

Photoinduced in Situ Deposition of Uniform and Well-Dispersed PtO2 Nanoparticles on ZnO Nanorods for Efficient Catalytic Reduction of 4-Nitrophenol.

Based on the photochemical property of semiconductors, a light irradiation-assisted strategy has been designed using one-dimensional ZnO nanorods as carriers to synthesize the rod-type PtO2/ZnO catalyst with a well-defined structure. The high crystallinity and uniform crystal structure of the ZnO matrix conduct the in situ deposition of PtO2 nanoparticles with 1.1-2.1 nm, which are evenly and densely anchored on the surface. Those small-sized and well-dispersed PtO2 nanoparticles endow the PtO2/ZnO catalyst a superior catalytic performance for the reduction of 4-nitrophenol to 4-aminophenol, which can convert all the substrates within 6.25 min. It is demonstrated that the catalytic activity of the PtO2/ZnO catalyst is 2.3 times as high as that of the sample obtained by traditional wet-oxidation method under the same reaction conditions. Moreover, the light-irradiation time has been found to greatly affect the structure and activity of PtO2/ZnO catalysts, and the product with 30 min exhibits the best catalytic performance in this work, as well as the good stability for ten runs. In terms of the photoexcited process of ZnO and reactive species-trapped experiments, the formation mechanism of PtO2/ZnO catalysts has been explored in detail, which will probably stimulate the design and study of other metal-supported catalysts.

Green Brönsted acid ionic liquids as novel corrosion inhibitors for carbon steel in acidic medium.

New ionic liquids with multiple Brönsted acid sites were synthesized in ≥98% yield, and their inhibiting properties for the corrosion of carbon steel in 0.5 M HCl solution had been evaluated using electrochemical impedance spectroscopy, potentiodynamic polarization and weight loss method, finally the possible inhibiting mechanism was proposed according to UV-visible spectroscopic measurements and surface analysis including SEM and XPS techniques. The designed cation structure of Brönsted acid ionic liquids (BAILs), with one phenyl and two imidazolium rings, makes them good mixed-type inhibitors via the adsorption of BAILs on the steel surface to suppress both anodic and cathodic processes, obeying Langmuir adsorption isotherm. As potential acid catalysts, BAILs show nice corrosion inhibiting performance in acidic medium regardless of their Brönsted acidity, which is of great significance to enlarge the industry applications of BAILs.

Controlled synthesis of hierarchically crossed metal oxide nanosheet arrays for diesel soot elimination.

We propose a facile and versatile strategy for the fabrication of a hierarchically crossed metal oxide nanosheet array on a monolithic FeOx substrate. This strategy can also be extended to synthesize a composite metal oxide nanosheet array, in which the composition can be easily modulated. The as-obtained hierarchically crossed metal oxide nanosheet array exhibited high catalytic activities for diesel soot elimination owing to the enhanced contact efficiency between soot particulates and macroporous catalysts.

Pt/ZnO@C Nanocable with Dual-Enhanced Photocatalytic Performance and Superior Photostability.

To improve the photocatalytic activity and photostability of ZnO, a novel cable-like Pt/ZnO@C composite is successfully fabricated by coating a 3-5 nm hydrothermal carbon (HTC) layer on the surface of the Pt nanoparticle-modified ZnO nanowire. After investigating the optical and photoelectrochemical performance in detail, it is found that the Pt/ZnO@C nanocable shows a dual-enhanced migration efficiency for the photoinduced surface electrons, distributing to the modified Pt nanoparticles and the coated HTC layer. Consequently, the Pt/ZnO@C nanocable exhibits a dual-enhanced photocatalytic activity for the degradation of various organic pollutants under the UV light irradiation. The coated HTC layer can also play a role in suspending the ZnO photocorrosion and significantly improves the photostability of the Pt/ZnO@C nanocable. Furthermore, the photocatalysis and photocorrosion mechanism of the Pt/ZnO@C nanocable is proposed and discussed in terms of its structural feature and photoelectrochemical property. The resultant Pt/ZnO@C nanocable with the unique HTC layer-coated structure will probably stimulate to design and synthesize more HTC-hybridized composites with a superior photocatalytic or photoelectrocatalytic performance.

Subcritical ethanol extraction of flavonoids from Moringa oleifera leaf and evaluation of antioxidant activity.

A large-scale process to extract flavonoids from Moringa oleifera leaf by subcritical ethanol was developed and HPLC-MS analysis was conducted to qualitatively identify the compounds in the extracts. To optimize the effects of process parameters on the yield of flavonoids, a Box-Behnken design combined with response surface methodology was conducted in the present work. The results indicated that the highest extraction yield of flavonoids by subcritical ethanol extraction could reach 2.60% using 70% ethanol at 126.6°C for 2.05h extraction. Under the optimized conditions, flavonoids yield was substantially improved by 26.7% compared with the traditional ethanol reflux method while the extraction time was only 2h, and obvious energy saving was observed. FRAP and DPPH assays showed that the extracts had strong antioxidant and free radical scavenging activities.