Self-assembly formation of Co quantum dot loaded N-doped porous carbon cathode for quinoline degradation in the electro-Fenton system.

Quinoline is high toxicity and difficult biodegradation in oil washing wastewater. Therefore, efficient removal of quinoline contaminant from water bodies poses a major challenge. Hence, Co quantum dot loaded N-doped porous carbon (CoNC) nanosheets grown in situ on carbon cloth were fabricated as cathode for the degradation of quinoline in electro-Fenton system. Under optimal conditions (c(Fe2+) = 0.5 mM, U = -0.3 V, pH = 3), quinoline was completely degraded within 15 min with superior apparent rate constant of 0.385 min-1, which was 19.6 times higher than that of the ZIF-L precursor, due to the abundance of Co QDs active sites and hydrophilicity and electrical conductivity of N-doped porous carbon. In addition, three reaction pathways for quinoline were deduced by combining Density Functional Theory (DFT) calculation and Liquid Chromatography-Mass Spectrometry (LC-MS). More importantly, in situ FTIR and free energy calculations were analyzed to reveal that pathway Ⅰ as spontaneous reaction was the main reaction pathway. Finally, the toxicity of the intermediates was assessed with ECOSAR software and E. coli experiments, and the overall toxicity decreased during the degradation reactions. This work provides novel perspectives on environmental protection by designing in-situ grown cathodes through self-assembly method, thereby effectively purifying pollutants from wastewater.

Antimony(III) removal by biogenic manganese oxides formed by Pseudomonas aeruginosa PA-1: kinetics and mechanisms.

In this study, Pseudomonas aeruginosa PA-1, a manganese-oxidizing bacterium screened from the soil at a manganese mining area, was found to be tolerated to Sb(III) stress during the Mn(II) oxidation, and the generated biological manganese oxide (BMO) outperformed the identical type of Abiotic-MnOX in terms of oxidation and adsorption of Sb(III). Adsorption kinetics and isotherm experiments indicated that Sb(III) was primarily adsorbed through chemisorption and multilayer adsorption on BMO; the maximum adsorption capacity of BMO was 143.15 mg·g-1. Removal kinetic studies showed that the Sb(III) removal efficiency by BMO was 72.38-95.71% after 15 min, and it could be up to 96.32-98.31% after 480 min. The removal procedure could be divided into two stages, fast (within 15 min) and slow (15 ~ 480 min), both of which exhibited first-order kinetic behavior. Dynamic fitting in two steps revealed that the removal speed correlated to the level of dissolved Sb(III) with low Sb(III) concentrations, but with the initial concentration being high, the removal speed rate was independent of dissolved Sb(III). During the whole process, the Sb(III) removal speed by BMO was also higher than that by the Abiotic-MnOX. Combining multiple spectroscopic techniques revealed that Sb(V) was generated through the Sb(III) oxidation by BMO and replacing surface metal hydroxyl groups to form the complex internal Mn-O(H)-Sb(V) or generating stable Mn(II)-antimonate precipitates on the surface. In addition, microbial metabolites, including tryptophan and humus, in BMO may be complex with Sb(III) and Sb(V) to achieve the treatment of Sb(III). This research investigates the factors and mechanisms influencing the adsorption and removal of Sb(III) by BMO, which could aid in its future engineering applications for the BMO.

Heterostructured Co/Co3O4 anchored on N-doped carbon nanotubes as a highly efficient electrocatalyst for nitrate reduction to ammonia.

The electrochemical reduction of nitrate (NO3-) to ammonia (NH3) has emerged as an attractive approach for selectively reducing NO3- to highly value-added NH3 and removing NO3- pollutants simultaneously. In this work, a heterostructured Co/Co3O4 electrocatalyst anchored on N-doped carbon nanotubes was prepared and applied for the NO3- reduction towards NH3 under alkaline conditions. The catalyst achieves outstanding performance with up to 67% NH3 faradaic efficiency at -1.2 V vs. Hg/HgO and 8.319 mg h-1 mgcat-1 yield at -1.7 V vs. Hg/HgO. In addition, it also exhibits good long-term stability. 15N isotopic labelling experiments prove that the yielded NH3 is derived from NO3- species. In situ electrochemical Raman spectra revealed that the structure of the as-prepared catalyst showed outstanding stability and identified possible intermediates during the electrocatalytic NO3- reduction reaction (NO3RR).

In situ interface engineered Co/NC derived from ZIF-67 as an efficient electrocatalyst for nitrate reduction to ammonia.

Electrocatalytic nitrate (NO3-) reduction to ammonia (NH3) is a promising alternative approach for simultaneous NH3 green synthesis and NO3- contaminants removal. However, the complex eight-electron reaction requires catalysts with superb performance due to the low NH3 selectivity and yield. In this work, the Co nanoparticles decorated N-doped carbon (NC) by in situ interface engineering were prepared by deriving ZIF-67 at 800 ℃ (Co/NC-800) for the selective NH3 synthesis. This catalyst exhibits a remarkable performance and excellent cycle stability, achieving a great NH3 yield of 1352.5 µg h-1 mgcat-1 at -1.7 V vs Ag/AgCl, with a high NH3 selectivity of up to 98.2 %, and a maximum Faradic efficiency of 81.2 % at -1.2 V vs Ag/AgCl. Moreover, DFT calculation results indicate that the interfacial effect between Co nanoparticle and NC could enhance electron transfer, and the composite Co/NC-800 shows a lower adsorption and conversion free energy, which promotes the production of ammonia.

Active Sites in Single-Atom Fe-Nx-C Nanosheets for Selective Electrochemical Dechlorination of 1,2-Dichloroethane to Ethylene.

Electrochemical dechlorination of 1,2-dichloroethane (DCE) is one of the prospective and economic strategies for the preparation of high-value ethylene. However, the exploration of advanced electrocatalysts with high reactivity and selectivity and the identification of their active sites are still a challenge. Herein, a single-atom (SA) Fe-Nx-C nanosheet with the presence of a highly efficient Fe-N4 coordination pattern is reported. The as-prepared single-atom electrocatalyst exhibits a higher reactivity and ethylene selectivity for DCE dechlorination reaction than those of the commercially adopted 20% Pt-C catalyst. By a combination of experiments and theoretical calculations, the atomically dispersed Fe center in the Fe-N4 structure was unveiled to be the dominating active site for electrochemical production of ethylene. Our work would offer an approach for the rational development of SA materials and supply crucial insight into the mechanism of ethylene production through the DCE dechlorination reaction.

Oxygen Vacancy-rich Porous Co3O4 Nanosheets toward Boosted NO Reduction by CO and CO Oxidation: Insights into the Structure-Activity Relationship and Performance Enhancement Mechanism.

Oxygen vacancy-rich porous Co3O4 nanosheets (OV-Co3O4) with diverse surface oxygen vacancy contents were synthesized via facile surface reduction and applied to NO reduction by CO and CO oxidation. The structure-activity relationship between surface oxygen vacancies and catalytic performance was systematically investigated. By combining Raman, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and O2-temperature programmed desorption, it was found that the efficient surface reduction leads to the presence of more surface oxygen vacancies and thus distinctly enhance the surface oxygen amount and mobility of OV-Co3O4. The electron transfer towards Co sites was promoted by surface oxygen vacancies with higher content. Compared with the pristine porous Co3O4 nanosheets, the presence of more surface oxygen vacancies is beneficial for the catalytic performance enhancement for NO reduction by CO and CO oxidation. The OV-Co3O4 obtained in 0.05 mol L-1 NaBH4 solution (Co3O4-0.05) exhibited the best catalytic activity, achieving 100% NO conversion at 175 °C in NO reduction by CO and 100% CO conversion at 100 °C in CO oxidation, respectively. Co3O4-0.05 exhibited outstanding catalytic stability and resistance to high gas hour space velocity in both reactions. Combining in situ DRIFTS results, the enhanced performance of OV-Co3O4 for NO reduction by CO should be attributed to the promoted formation and transformation of dinitrosyl species and -NCO species at lower and higher temperatures. The enhanced performance of OV-Co3O4 for CO oxidation is due to the promotion of oxygen activation ability, surface oxygen mobility, as well as the enhanced CO2 desorption ability. The results indicate that the direct regulation of surface oxygen vacancies could be an efficient way to evidently enhance the catalytic performance for NO reduction by CO and CO oxidation.

Facile tailoring of Co-based spinel hierarchical hollow microspheres for highly efficient catalytic conversion of CO2.

High-performance and low-cost photocatalysts are of significance to artificial photosynthetic systems for converting of CO2 into CO and other value-added products. In this work, we developed a controllable and scalable self-templated approach to fabricate hierarchical Co-base spinel hollow microspheres for visible light-driven CO2 reduction with a Ru-based sensitizer. The hollow microspheres are assembled by ultrathin nanosheets using Ni-Co-hydroxides as the morphology-conserved precursor. A series of characterization techniques were conducted to investigate structural features of the prepared Co-base spinel hollow spheres. Owing to the integration of the specific microstructure, functional Ni/Co species and oxygen vacancies, Co-base spinel hollow spheres possess enhanced CO2 adsorption ability, more active sites, and efficient transfer and separation of photoexcited electrons. The high CO-evolving rate (27.7 µmol h-1) and selectivity (84.4%) manifest desirable performance of Co-base spinel hollow spheres for CO2 photocatalytic reduction. The findings suggest that such spinel-structured bimetallic oxides hierarchical hollow spheres, facilely synthesized via the proposed self-templated method, are efficient for photocatalytic CO2 reduction.

The bioelectrochemical synthesis of high-quality carbon dots with strengthened electricity output and excellent catalytic performance.

The emergence of microbial fuel cell (MFC) technology that can effectively recycle renewable energy from organic pollutants has been regarded as a promising and environmentally friendly route that could be widely used in numerous fields. Here, a novel sustainable self-energy conversion system was successfully constructed to renewably synthesize carbon dots (CDs) via in situ coupling with a MFC system. Interestingly, the generation of CDs was found to largely enhance the electricity production performance of the MFC. Low-temperature electron paramagnetic resonance (EPR) spectroscopic measurements and electrochemical characterization analysis results confirmed that the as-prepared CDs exhibited wide-conversion fluorescence properties and exposed carbon-rich active oxygen sites, and demonstrated a suitable band gap as well as excellent electrocatalytic performance. As a result, the prepared CDs possess high photo-bioelectrocatalytic activity for efficient H2 production, reaching 9.58 µmol h-1. Remarkably, CD-derived photocatalytic ink presented excellent contaminant elimination activity at the solid-solid interface. Thus, this work will provide a new platform for catalyst construction via a bio-assisted method towards the next generation of nano-photocatalytic inks for indoor contaminant removal.

Triple-shelled NiMn2O4 hollow spheres as an efficient catalyst for low-temperature selective catalytic reduction of NOx with NH3.

Unique triple-shelled NiMn2O4 hollow spheres are fabricated by a facile solvothermal method. Owing to its particular triple shell structure, the as prepared NiMn2O4 catalyst exhibits superior low-temperature NH3-SCR catalytic performance, achieving above 90% NOx conversion in the temperature range from 100 °C to 225 °C.

Improvement of catalytic activity over Mn-modified CeZrOx catalysts for the selective catalytic reduction of NO with NH3.

A series of MnCeZrOx mixed oxide catalysts were facilely synthesized using the impregnation-NH3·H2O coprecipitation method and tested for selective catalytic reduction (SCR) of NO with NH3. Doping manganese significantly improved the catalytic activity and the best performing SCR catalyst, Mn0.25Ce0.5Zr0.25Ox, was shown to achieve NO conversion > 80% in the temperature range (60-350 °C), with the denitration effect up to 50% at room temperature (conditions: [NO] = [NH3] = 500 ppm, [O2] = 5 vol%, He as balance, flow rate  =  100 mL/min, GHSV  =  40, 000 h-1). Characterization of the catalyst using BET, XRD, XPS, H2-TPR, and in-situ FTIR proved that the improved SCR activity may be attributed to the large surface area, great reduction ability and increased amount of surface adsorbed oxygen afforded by the introduction of manganese. The SCR reaction mechanisms were also investigated by analyzing in-situ FTIR spectra and the SCR reaction pathway over the Mn0.25Ce0.5Zr0.25Ox catalyst was shown to mostly follow the E-R mechanism.

2D, 3D mesostructured silicas templated mesoporous manganese dioxide for selective catalytic reduction of NOx with NH3.

Employing nanocasting method, mesoporous MnO2 catalysts with large specific surface area and regular pore structure were synthesized by using three different types of mesostructure silicas (KIT-6, SBA-15, MCM-41) as hard templates. The physical and chemical properties of the three different mesostructured manganese oxide materials were comparatively and systematically characterized by using XRD, FT-IR, N2 adsorption-desorption, TEM, NH3-TPD, H2-TPR, XPS. The NH3-SCR performance of the mesoporous MnO2 was also evaluated on SCR self-assembly device. It was discovered that the mesostructure of the template would influence the amount and the kind of acid site, the reduction ability and then influence the catalytic performance of the materials. Mesoporous MnO2 templated from KIT-6 exhibited better catalytic performance than other mesoporous MnO2, indicating that the mesostructure of the materials has significant influence on the NH3-SCR performance. The KIT-6 templated MnO2 could induce 100% NOx conservation ratio range from 75 °C to 275 °C and exhibit good resistance of SO2 and H2O.