Engineering of oxygen vacancy defect in CeO2 through Mn doping for toluene catalytic oxidation at low temperature.

Catalytic oxidation is considered a highly effective method for the elimination of volatile organic compounds. Oxygen vacancy defect engineering in a catalyst is considered an effective approach for high-performance catalysts. Herein, a series of doped MnxCe1-xO2 catalysts (x = 0.05-0.2) with oxygen vacancy defects were synthesized by doping low-valent Mn in a CeO2 lattice. Different characterization techniques were utilized to inspect the effect of doping on oxygen vacancy defect generation. The characterization results revealed that the Mn0.15Ce0.85O2 catalyst has the maximum oxygen vacancy concentration, leading to increased active oxygen species and enhanced oxygen mobility. Thus, Mn0.15Ce0.85O2 catalyst showed an excellent toluene oxidation activity with 90% toluene conversion temperature (T90) of 197 °C at a weight hourly space velocity of 40,000 mL g-1 h-1 as compared to undoped CeO2 (T90 = 225 °C) and Ce based oxides in previous reports. In addition, the Mn0.15Ce0.85O2 catalyst displayed strong recyclability, water resistant ability and long-time stability. The in situ DRIFT results showed that the Mn0.15Ce0.85O2 catalyst has a robust oxidation capability as toluene is quickly adsorbed and actuated as compared to CeO2. Thus, the present work lays the foundation for designing a highly active catalyst for toluene elimination from the environment.

Engineering the Defects and Microstructures in Ferroelectrics for Enhanced/Novel Properties: An Emerging Way to Cope with Energy Crisis and Environmental Pollution.

In the past century, ferroelectrics are well known in electroceramics and microelectronics for their unique ferroelectric, piezoelectric, pyroelectric, and photovoltaic effects. Nowadays, the advances in understanding and tuning of these properties have greatly promoted a broader application potential especially in energy and environmental fields, by harvesting solar, mechanical, and heat energies. For example, high piezoelectricity and high pyroelectricity can be designed by defect or microstructure engineering for piezo- and pyro-catalyst, respectively. Moreover, highly piezoelectric and broadband (UV-Vis-NIR) light-responsive ferroelectrics can be designed via defect engineering, giving rise to a new concept of photoferroelectrics for efficient photocatalysis, piezocatalysis, pyrocatalysis, and related cocatalysis. This article first summarizes the recent developments in ferroelectrics in terms of piezoelectricity, pyroelectricity, and photovoltaic effects based on defect and microstructure engineering. Then, the potential applications in energy generation (i.e., photovoltaic effect, H2 generation, and self-powered multisource energy harvesting and signal sensing) and environmental protection (i.e., photo-piezo-pyro- cocatalytic dye degradation and CO2 reduction) are reviewed. Finally, the outlook and challenges are discussed. This article not only covers an overview of the state-of-art advances of ferroelectrics, but also prospects their applications in coping with energy crisis and environmental pollution.

Synthesis of CoCrFeO4-chitosan beads sun-light-driven photocatalyst with well recycling for efficiently degrading high-concentration dyes.

It is highly desired to develop an efficient large surface area CoCrFeO4-based beads sun-light driven photocatalysts with excellent recycling features for degrading high-concentration dyes. Herein, a novel CoCrFeO4 oxide nanoparticles have customarily been synthesized by the combination of three metals (Co, Cr and Fe) via co-precipitation method in aqueous solution and then millimeter-scale CoCrFeO4 oxide chitosan-composite beads (CoCrFeO4-CB) were prepared by incorporating the CoCrFeO4 in chitosan polymer in basic medium, which makes the adsorbent easier to separate. The number of optimized nanocomposite beads used for the removal of high-concentration dyes displays 5-time photoactivity enhancement under sun-light irradiation compared to pristine CoCrFeO4. Based on the fluorescence spectra related to the formed OH amounts, temperature-programmed desorption and electrochemical results, it is deduced that the unprecedented photocatalytic activities are mainly attributed to the large surface area, and enhanced charge separation from the chitosan as well as its promotion effects on O2 activation. Influencing factors that effect the photocatalytic efficiency of dyes, such as catalyst dose, dyes concentration, time, and the light source was also studied. More importantly, after five catalytic cycles, no evident deactivation was observed, suggesting the satisfactory stability of the investigated photocatalyst. Also, large numbers of superoxides radicals form which is the main active species participate in the degradation of acid black were analyzed using a radical trapping experiment. It is expected that our work could render navigated information for steering toward the design and applications of the CoCrFeO4-based photocatalyst with sun-light utilization for environmental remediation.

Controllable synthesis of MoS2@MoO2 nanonetworks for enhanced NO2 room temperature sensing in air.

MoS2 nanosheets (NSs) are a promising gas sensing material at room temperature (RT) due to their unique properties and structures. Unfortunately, the activity of pure MoS2 NSs is highly affected by the adsorption of atmospheric oxygen, which strongly influences the stability of MoS2 sensing devices and significantly hinders the practical applications of these sensors in air. Heterostructure formation may be an effective approach to modulate the intrinsic electronic properties of MoS2 NSs. In this study, thin MoO2 nanoplates (NPs) were decorated with multilayer MoS2 NSs via one-step controllable sulfurization to fabricate MoS2@MoO2 nanonetworks, and remarkable gas sensing performance was achieved with high stability in air at RT. In particular, the MSO-2 (1 h sulfurization of the MoO2 NPs) nanonetworks with n-p heterojunctions demonstrated a high response of 19.4 to 100 ppm NO2 in a short period of time (1.06 s) with rapid recovery (22.9 s) to the baseline. The excellent gas sensing performance of the MSO-2 sensor is attributed to the synergistic effect of the MoS2 NSs and thin MoO2 NPs, which created heterojunctions/defects to easily transfer electrons and provide more active sites for NO2 gas. This simple synthetic method to design and fabricate n-p heterojunction sensors will be effective in commercial gas sensing applications.

Synthesis of sub-micrometric SAPO-34 by a morpholine assisted two-step hydrothermal route and its excellent MTO catalytic performance.

SAPO-34 with a sub-micrometer crystal size was synthesized by a double hydrothermal treatment employing cost-effective morpholine as a structure directing agent, which presented an enhanced catalytic lifetime (nearly 3 times the conventional one) in the reaction of methanol to olefins with a higher light olefin selectivity (total selectivity of 97.1%). Detailed studies of the sample after different time intervals in the second crystallization with and without additional morpholine were carried out, which offered insight into crystal degradation and re-crystallization phenomena. The samples with different morpholine concentrations during the second hydrothermal treatment were also prepared, in which the sample with 80% MOR aqueous solution exhibited the smallest crystal size and the longest MTO lifetime. Furthermore, the investigation on the additional amount of mother liquor (from the first crystallization) required for the second crystallization showed that the presence of half the amount of the mother liquor (nutrients) could give us the required results effectively.

CTAB-assisted size controlled synthesis of SAPO-34 and its contribution toward MTO performance.

SAPO-34 shows higher light olefin selectivity in the reaction of methanol to olefin (MTO), but its small pore system implies diffusion limitations to bigger molecular products and results in coking too. To inhibit these limitations, sub-micrometric sized SAPO-34 crystallites were successfully synthesized by a facile surfactant-assisted hydrothermal synthesis route, in which cetyltrimethylammonium bromide (CTAB) was used as a crystal growth inhibitor (CGI). It was found that the crystal size changes in the V shape with the increase in the amount of CTAB. The sub-micrometric sized sample (SP-0.02CTAB) was obtained when the molar ratio of CTAB to Al2O3 was 0.02 in a precursor gel. The SP-0.02CTAB catalyst presents excellent performance for the MTO reaction with 97.8% C2-C4 selectivity and 3 times longer lifetime than the conventional SAPO-34 sample (SP-Conv), which is attributed to its much higher surface area and enhanced acidity derived from the formation of the sub-micrometric sized crystallites. Further study about the appropriate time of CTAB addition demonstrates that CTAB can play its role as a crystal growth inhibitor effectively, only when it is added at the very initial stage of the crystallization process.