Surrounded catalysts prepared by ion-exchange inverse loading

Sheet-Like Morphology CuO/Co3O4 Nanocomposites for Enhanced Catalysis in Hydrogenation of CO2 to Methanol

The selective hydrogenation of CO2 into high-value chemicals is an effective approach to address environmental issues. Cobalt-based catalysts have significant potential in CO2 hydrogenation reaction systems; however, there is a need to control their selectivity better. In this study, copper is introduced onto Co3O4 nanosheets using the ion exchange reverse loading method. The unique interaction of these materials significantly alters the selectivity of the cobalt-based catalyst. Results from scanning transmission electron microscopy and scanning electron microscopy indicate that this catalyst enables a more even dispersion of copper species in the Co3O4 nanosheets. Temperature-programmed reduction and X-ray photoelectron spectroscopy reveal that the catalyst facilitates the metal-metal interaction between Co and Cu. Temperature-programmed desorption experiments for CO2 and H2 demonstrate that the close interaction between Co and Cu modifies CO2 adsorption, leading to differences in catalytic activity. Moreover, the catalyst effectively suppresses CO2 methanation and promotes methanol formation by altering the alkalinity of the catalyst surface and weakening the hydrogen dissociation ability.

Green calcium-based photocatalyst derived from waste marble powder for environmental sustainability: A review on synthesis and application in photocatalysis

Calcium, with its excellent adsorptive property and higher permissible limits in the environment, emerges as an effective wastewater treatment earth metal. Most of the catalysts, photocatalysts, and adsorbents reported in the literature have heavy metal complex, which creates a leaching problem. Majorly, precursors used for the synthesis of heterogeneous catalysts for wastewater treatment are costly. Therefore, the use of such precursors would be not suitable and feasible approach from an economic point of view. This review work is focused on giving an overview of the utilisation of calcium-based catalysts (adsorbents and photocatalyst) for the removal/degradation of various types of dye water pollutants and summarises the reported effects of calcium as a base on the removal efficiency of dopants. In this article, an extensive literature survey is presented on the various photocatalysts developed and the different syntheses involved in their preparation. As the utilisation of marble powder is a green sustainable approach, the scope of various calcium-based photocatalysts and their application is presented. This article also aims for the elementary and inclusive determination of the effect of introducing calcium as a base for different catalysts and adsorbents.

NiCoP-CeO2 composites for efficient electrochemical oxygen evolution

In this study, a novel NiCoP-CeO2 composite was constructed on a Ni foam by a simple hydrothermal method and thermal phosphating strategy. In the OER test, NiCoP-CeO2 exhibited a low overpotential of 217 mV at 10 mA cm-2, 45 mV dec-1 of Tafel slopes. With the help of theoretical calculations and experimental characterization, the reason for performance improvement was analyzed in depth. The results show that CeO2 leads to a confinement effect, maintaining the nanosheet morphology of NiCo-LDHs, which contributes to sustaining the catalyst in favourable contact with H2O and minimizing the OER potential. Furthermore, by loading CeO2 onto NiCoP, the hydrophilicity of the catalyst is significantly enhanced. Our work provides an ingenious synthesis strategy for the preparation of efficient and inexpensive electrocatalytic materials.

Overturned Loading of Inert CeO2 to Active Co3 O4 for Unusually Improved Catalytic Activity in Fenton-Like Reactions

In the past decades, numerous efforts have been devoted to improving the catalytic activity of nanocomposites by either exposing more active sites or regulating the interaction between the support and nanoparticles while keeping the structure of the active sites unchanged. Here, we report the fabrication of a Co₃ O₄ -CeO₂ nanocomposite via overturning the loading direction, i.e., loading an inert CeO₂ support onto active Co₃ O₄ nanoparticles. The resultant catalyst exhibits unexpectedly higher activity and stability in peroxymonosulfate-based Fenton-like reactions than its analog prepared by the traditional impregnation method. Abundant oxygen vacancies (O_v with a Co⋅⋅⋅O_v ⋅⋅⋅Ce structure instead of Co⋅⋅⋅O_v ) are generated as new active sites to facilitate the cleavage of the peroxide bond to produce SO₄ ^.- and accelerate the rate-limiting step, i.e., the desorption of SO₄ ^.- , affording improved activity. This strategy is a new direction for boosting the catalytic activity of nanocomposite catalysts in various scenarios, including environmental remediation and energy applications.

From Khoi-San indigenous knowledge to bioengineered CeO2 nanocrystals to exceptional UV-blocking green nanocosmetics

Single phase CeO₂ nanocrystals were bio-synthesized using Hoodia gordonii natural extract as an effective chelating agent. The nanocrystals with an average diameter of 〈Ø〉 ~ 5-26 nm with 4⁺ electronic valence of Ce displayed a remarkable UV selectivity and an exceptional photostability. The diffuse reflectivity profile of such CeO₂ exhibited a unique UV selectivity, in a form of a Heaviside function-like type profile in the solar spectrum. While the UV reflectivity is significantly low; within the range of 0.7%, it reaches 63% in the VIS and NIR. Their relative Reactive Oxygen Species (ROS) production was found to be < 1 within a wide range of concentration (0.5-1000 μg/ml). This exceptional photostability conjugated to a sound UV selectivity opens a potential horizon to a novel family of green nano-cosmetics by green nano-processing.

A Review of Preparation Methods for Heterogeneous Catalysts

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Catalysts contribute significantly to the industrial revolution in terms of reaction rates and reduction in production costs. Extensive research has been documented on various industrial catalysis in the last few decades. The performance of catalysts is influenced by many parameters, including synthesis methods. The current work overviews the most common methods applied for the synthesis of supported catalysts. This review presents the detailed background, principles, and mechanism of each preparation method. The advantages and limitations of each method have also been elaborated in detail. In addition, the applications of each method in terms of catalyst synthesis have been documented in the present review paper.

Strategic Structure Tuning of Yolk-Shell Microcages for Efficient Nitrogen Fixation

The electrocatalytic nitrogen reduction reaction (ENRR) under ambient conditions is considered as a promising process to produce ammonia. Towards highly efficient catalysts, here an optimized one-step pyrolysis strategy was tailored to design yolk-shell microcages (YS Co@C/BLCNTs), consisting of Co nanocrystals encapsulated in N-doped carbon framework and bridged by bamboo-like carbon nanotubes (BLCNTs). The cavity created between yolk and shell not only served as a "micro-bag" to store the reactant N₂ and enhance its dissolution, but also induced a "cage effect" to confine the diffusion of reaction intermediate, hence making the reaction proceed in the direction of producing NH₃ . This catalyst displayed excellent catalytic activities for ENRR: a high NH₃ yield of 12.87 μg mg_cat ^-1  h^-1 at a high faradaic efficiency of 20.7 % at -0.45 V (vs. reversible hydrogen electrode, RHE). After 5 cycles of consecutive ENRR process, the NH₃ yield rate was 11.29 μg mg_cat ^-1  h^-1 , indicating the excellent electrocatalytic stability. These results provide a structural engineering for ENRR catalyst with doped N, cooperating with non-precious metal to activate the inert triple bond of N₂ and achieve NH₃ fixation.

Metal Cation Valency Dependence in Morphology Evolution of Cu2-x S Nanodisk Seeds and Their Pseudomorphic Cation Exchanges

A crucial parameter in the design of semiconductor nanoparticles (NPs) with controllable optical, magnetic, electronic, and catalytic properties is the morphology. Herein, we demonstrate the potential of additive metal cations with variable valency to direct the morphology evolution of copper-deficient Cu_2-x S nanoparticles in the process of seed-mediated growth. In particular, the djurleite Cu_1.94 S seed could evolve from disk into tetradecahedron in the presence of tin(IV) cations, whereas they merely formed sharp hexagonal nanodisks with tin(II) cations. In addition to djurleite Cu_1.94 S, the tin(IV) cations could be generalized to direct the growth of roxbyite Cu_1.8 S and covellite CuS nanodisk seeds into tetradecahedra. We further perform pseudomorphic cation exchanges of Cu_1.94 S tetradecahedra with Zn²⁺ and Cd²⁺ to produce polyhedral zinc sulfide (ZnS) and cadmium sulfide (CdS) NPs. Moreover, we achieve Cu_1.8 S/ZnS and Cu_1.94 S/CdS tetradecahedral heterostructures via partial cation exchange, which are otherwise inaccessible by traditional synthetic approaches.