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Oxygen evolution reaction (OER) electrocatalysts generally experience structural and electronic modifications during electrocatalysis. This phenomenon, referred to as surface reconstruction, results in the formation of catalytically active species that act as real OER sites. Controlling surface reconstruction therefore is vital for enhancing the OER performance of electrocatalysts. In this study, a new approach is introduced of heterostructure engineering to facilitate the surface reconstruction of target catalysts. Using MnCo carbonate hydroxide (MnCo─CH)@Co3N as a demonstration, it is discovered that the surface reconstruction occurs more readily and rapidly on MnCo─CH@Co3N than on Co3N. More interestingly, during the reconstruction process, Mn species migrate to the surface, enabling the in situ formation of highly active Mn-doped CoOOH. Consequently, the MnCo─CH@Co3N catalyst after reconstruction exhibits a low overpotential of 257 mV at 10 mA cm-2, compared to 379 mV of individual Co3N. This work offers fresh perspectives on understanding the enhanced OER performance of heterostructure electrocatalysts and the role of heterostructure in promoting surface reconstruction.

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Heterostructured nanomaterials exhibit pronounced potential in environmental science, including the water purification, pollutant monitoring, and environmental remediation. Especially, their application through advanced oxidation processes has been found capable and adaptable in waste water treatment. In semiconductor photocatalysts, metal sulfides are the leading materials. However, for further modifications, the progresses on specific materials need to be overviewed. Among metal sulfides, nickel sulfides are the emerging semiconductors due to relatively narrow band gaps, high thermal and chemical stability, and cost effectiveness. The aim of the present review is to conduct a thorough analysis and summary of recent progress in the application of nickel sulfide-based heterostructures in water decontamination. Initially, the review introduces the emerging needs of the materials for environment following the characteristics features of metal sulfides with emphasis on nickel sulfides. Subsequently, synthesis strategies and structural properties of nickel sulfide (NiS and NiS2)-based photocatalysts are discussed. Herein, controlled synthesis procedures to influence their active structure, compositions, shape, and size for the enhanced photocatalytic performances are also considered. Furthermore, there is discussion on heterostructures formed by metal modification, metal oxides, and carbon hybridized nanocomposites. In the continuation, the modified characteristics are investigated which favors the photocatalytic processes for degradation of organic contaminations in water. The overall study highlights significant improvements in degradation efficiency of hetero-interfaced NiS and NiS2 photocatalysts towards organics that are comparable to expensive noble-metal photocatalysts. Finally, we also added a little on prospects for future advancement of nickel sulfide-based photocatalysts for applications in sustainable environmental remediation.

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Herein, we report the enhanced photocatalytic activity of heterostructured CeO2 nanocatalysts interfaced with Cu, Co, Ni, Mn, and Fe metal oxides. The CeO2 catalysts exhibited an enhanced red shift in the visible-light response compared to CeO2. This improved absorption range effectively suppressed electron (e-)/hole (+h) recombination by forming localized energy bands associated with defect oxygen vacancies (V o) induced by the Mn+ ions incorporated in CeO2. Under visible-light irradiation, CeO2 catalysts are active for α-pinene oxidation to the aroma oxygenates, pinene oxide, verbenol, and verbenone. Both Fe2O3-CeO2 and NiO-CeO2 gave the highest pinene conversions of 71.3 and 53.1%, respectively, with corresponding pinene oxide selectivities of 57.3 and 58.2%. The enhanced photocatalytic performance of the heterostructured CeO2 catalysts compared to CeO2 is attributed to their enhanced visible-light absorption range and efficient suppression of e-/+h recombination. The Fe2O3-CeO2 catalyst was highly recyclable and did not show any significant loss of its photoactivity.

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This study report on the synthesis of spinel CuFe2O4 nanostructures by surfactant-assisted method. The catalysts were characterized by X-ray diffraction (XRD), laser Raman, transition electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), hydrogen temperature programmed reduction (H2-TPR), and Brunauer-Teller-Emmett-Teller (BET) surface area techniques. CuFe2O4 was active for pinene oxidation using tertiary butyl hydroperoxide (TBHP) to pinene oxide, verbenol, and verbenone aroma oxygenates. Under optimized reaction conditions, the spinel CuFe2O4 catalyst could afford 80% pinene conversion at a combined verbenol/verbenone selectivity of 76% within the reaction time of 20 h. The changes in catalyst synthesis solvent composition ratios induced significantly varying redox, phases, and textural structure features, which resulted in various catalytic enhancement effect. Characterization results showed the spinel CuFe2O4 catalyst possessing less than 5 wt% impurity phases, Cu(OH)2, and CuO to afford the best catalytic performance. The CuFe2O4 catalyst was recyclable to up to five reaction cycles without loss of its activity. The recyclability of the bimetal CuFe2O4 oxide catalyst was simply rendered by use of an external magnet to separate it from the liquid solution.

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The promotional effect of nanosized Ru, Fe, Au, and Mn particles on VOHPO4 x 0.5H2O (VHP) catalytic properties was investigated in benzene hydroxylation reaction using hydrogen hydroperoxide (H2O2) as oxidant. Catalytic results indicated a profound effect of the nanoparticle dopants on VHP catalyst activity and products distribution. Amongst the promoted VHP catalysts, Au/VHP exhibited high catalytic effect with benzene conversion of 76% at a combined 85.5% selectivity toward the formation of phenol and hydroquinone achieved in 6 h under optimised reaction conditions. The extended scope application of nanosized doped Au-VHP showed to provide an effective catalyst for activation of the aromatic hydrocarbons C-H bonds into oxygenate derivatives. The catalyst could be re-used for several cycles with insignificant loss of activity. The doped nanosized Au-VHP catalyst provide a clean promising catalytic route based on heterogeneous catalysis for transformation of aromatics into value-added oxygenates.

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A porous layer open tubular (PLOT) silica gel column was used together with subcritical CO2 as the mobile phase to effect the group separation of polar oxygenated compounds. Aliphatic and aromatic compounds were shown to elute together. This group was followed by ethers and aldehydes, which were separated from compounds containing an alcohol functional group. Compounds with a carboxylic acid moiety could also be eluted from the silica gel. The group separation obtained when a silica gel PLOT column is used together with subcritical CO2 was also demonstrated to be valuable as the first dimension of a comprehensive two-dimensional SFCxGC analysis where the GC analysis in the second dimension is performed with a fast and independently heated temperature programmed gas chromatograph. With this combination of SFC and GC, many of the oxygenated compounds, routinely found in petroleum samples, could successfully be separated and identified.

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