Hexavalent Chromium Reduction Mediated by Interfacial Electron Transfer over the Co@NC Nanosheet-Assembled Microflowers

The reductive transformation of Cr(VI) into Cr(III) mediated by formic acid with efficient, stable, and cost-effective catalysts is a promising strategy for remediating Cr(VI) contamination. Herein, we report the facile construction of uniform Co@NC nanosheet-assembled microflowers for the reduction of Cr(VI). Both experimental results and density functional theory (DFT) calculations reveal the vital role of the intensive interfacial electronic interaction between Co nanoparticles and the N-doped carbon layer in facilitating the anchoring and dispersion of Co nanoparticles within the carbon framework. The interfacial electron transfer from Co to NC contributes to the interaction with Cr2O72- ions, promoting the subsequent H-transfer reaction. A Langmuir-Hinshelwood kinetic model has been established for the Cr(VI) reduction catalyzed by the CNCF2 (pyrolyzed at 700 °C), which shows a superior reaction performance. This study provides a facile strategy to delicately design well-assembled heterostructures with rich interfaces and strong interfacial interactions for a series of applications in environmental/thermal catalysis.

Metallic nanoparticles for catalytic reduction of toxic hexavalent chromium from aqueous medium: A state-of-the-art review

The ever increasing concentration of toxic and carcinogenic hexavalent chromium (Cr (VI)) in various environmental mediums including water-bodies due to anthropogenic activities with rapid civilization and industrialization have become the major issue throughout the globe during last few decades. Therefore, developing new strategies for the treatment of Cr(VI) contaminated wastewaters are in great demand and have become a topical issue in academia and industry. To date, various techniques have been used for the remediation of Cr(VI) contaminated wastewaters including solvent extraction, adsorption, catalytic reduction, membrane filtration, biological treatment, coagulation, ion exchange and photo-catalytic reduction. Among these methods, the transformation of highly toxic Cr(VI) to benign Cr(III) catalyzed by metallic nanoparticles (M-NPs) with reductant has gained increasing attention in the past few years, and is considered to be an effective approach due to the superior catalytic performance of M-NPs. Thus, it is a timely topic to review this emerging technique for Cr(VI) reduction. Herein, recent development in synthesis of M-NPs based non-supported, supported, mono-, bi- and ternary M-NPs catalysts, their characterization and performance for the reduction of Cr(VI) to Cr(III) are reviewed. The role of supporting host to stabilize the M-NPs and leading to enhance the reduction of Cr(VI) are discussed. The Cr(VI) reduction mechanism, kinetics, and factors affecting the kinetics are overviewed to collect the wealthy kinetics data. Finally, the challenges and perspective in Cr(VI) reduction catalyzed by M-NPs are proposed. We believe that this review will assist the researchers who are working to develop novel M-NPs catalysts for the reduction of Cr(VI).

One-Pot Aqueous Synthesis of Porous Hollow PdCu Alloy Nanoparticles for Enhanced Ethanol Electrooxidation

Bimetallic PdCu porous hollow nanoparticles (PHNs) with hierarchical nanostructures and well-alloyed compositions were precisely synthesized through a one-pot aqueous synthetic route. Bimetallic PdCu PHNs exhibited multiple enhancement synergies and thus performed well in ethanol oxidation electrocatalysis with remarkable activity and stability. This work expedites rational design and synthesis of the high-hierarchy alloy electrocatalysts for fuel cell electrocatalysis.

Application of polymer-coated Macadamia integrifolia nutshell biomass impregnated with palladium for chromium(VI) remediation

Freely suspended and porous basket restrained granules of palladium nanoparticles supported on polymer-grafted Macadamia nutshell biomass (Pd@Polym-MNS) composite were used for the treatment chromium(VI)-containing water. In the presence of formic acid, the Pd@Polym-MNS demonstrated its activity in the adsorption-reduction-based conversion of noxious chromium(VI) to less toxic chromium(III) with a low activation energy of 13.4 kJ mol-1, ΔH0 (+ 10.8 kJ mol-1), ΔS0 (-270.0 J mol-1 K-1), and ΔG0 (+ 91.3 to + 98.0 kJ mol-1) indicated the exothermic, endergonic and non-spontaneous nature of the catalytic redox reaction. In addition to facilitating easy recovery, rinsing, and reuse, restraining the Pd@Polym-MNS in the basket reactor helped maintain the integrity of the catalysts by preventing violent collisions of suspended granules with the mixing apparatus and the walls of the reaction vessel. Whereas the pseudo-first-order rate constant was recorded as 0.157 min-1 upon initial use, values of the mean and relative standard deviation for the second, third and fourth consecutive uses were found to be 0.219 min-1 and 1.3%, respectively. According to a response surface methodological approach to batch experimentation, the initial concentration of chromium(VI) and catalyst dosage had the greatest impact on the redox reaction rate, accounting for 85.7% and 11.6% of the variability in the value of the pseudo-first-order rate constant, respectively. Mutually beneficial effects of the combinations of high formic acid and low chromium(VI) concentration, high temperature and catalyst dosage as well as high formic acid and catalyst dosage were recorded.

Interconnected hierarchical nickel-carbon hybrids assembled by porous nanosheets for Cr(VI) reduction with formic acid

Magnetic carbon materials promise distinct advantages in the decontamination of heavy metal ions. In this work, a novel interconnected hierarchical nickel-carbon (Ni@IHC) hybrid was synthesized by combining the solvothermal method with a one-step pyrolysis under argon atmosphere. Benefitting from 3D flower-like morphology, interconnected porous nanosheets, large surface area, and abundant Ni nanoparticles, Ni@IHC hybrids can remove Cr(VI) within 25 min by using formic acid (FA) as a reductant at 25 ℃. Furthermore, the experimental parameters that can affect the material catalytic performance such as initial Cr(VI) concentration, catalyst dosage, FA concentration, and temperature were also investigated in detail. It was found that highly dispersed Ni nanoparticles contributed significantly to the reduction process. More importantly, the embedded Ni nanoparticles favor fast separation by a magnet and were helpful for the recycles use. This Ni@IHC hybrid was obtained by a facile and easy scale-up method, resulting in the fast transformation of Cr(VI) into Cr(III).

Highly Active Hollow RhCu Nanoboxes toward Ethylene Glycol Electrooxidation

The efficient electrocatalysts toward the ethylene glycol oxidation reaction (EGOR) are highly desirable for direct ethylene glycol fuel cells because of the sluggish kinetics of anodic EGOR. Herein, porous RhCu nanoboxes are successfully prepared through facile galvanic replacement reaction and succedent sodium borohydride reduction strategy. Benefiting from hierarchical pore structure, RhCu nanoboxes display excellent electrocatalytic performance toward the EGOR in alkaline medium with a mass activity of 775.1 A g_Rh ^-1 , which is 2.8 times as large as that of commercial Rh nanocrystals. Moreover, the long-term stability of RhCu nanoboxes is better than that of commercial Rh nanocrystals. Furthermore, the theoretical calculations demonstrate that RhCu nanoboxes possess lower adsorption energy of CO and lower reaction barrier (0.27 eV) for the CO_ads oxidation with aid of the adsorbed OH_ads species, resulting in the outstanding electrocatalytic performance toward the EGOR. This work provides a meaningful reference for developing highly effective electrocatalysts toward the EGOR.

An overview of palladium supported on carbon-based materials: Synthesis, characterization, and its catalytic activity for reduction of hexavalent chromium

Palladium plays a pivotal role in most of the industrial heterogeneous catalysts, because of its unique properties such as well-defined structure, great intrinsic carrier, outstanding electronic, mechanical and thermal stability. The combination of palladium and various porous carbons (PCs) can widen the use of heterogeneous catalysts. This review highlights the advantages and limitations of carbon supported palladium-based heterogeneous catalyst in reduction of toxic hexavalent chromium (Cr^(VI)). In addition, we address recent progress on synthesis routes for mono and bimetallic palladium nanoparticles supported by various carbon composites including graphene-based materials, carbon nanotubes, mesoporous carbons, and activated carbons. The related reaction mechanisms for the Cr^(VI) reduction are also suggested. Finally, the challenge and perspective are proposed.

Agar-induced hollow porous carbon nanospheres anchored platinum for high-performance hydrogenation

Hollow porous carbon has attracted a great deal of interest as catalyst-support because of its high surface area, low density and large pore volume. Herein, we develop a layer-by-layer assembly method to effectively load Pt nanoparticles on hollow porous carbon nanospheres (Pt/HPC) through using modified-SiO₂ nanospheres as the template and agar as the carbon resource. The gel properties of agar (e.g., sensitivity to temperature and high mechanical strength) makes the Pt nanoparticles well crosslink with carbon, as well as endows the carbon nanospheres with robust stability. The synthesized Pt/HPC was employed as a catalyst in the hydrogenation reduction of rhodamine B (RhB). The catalytic results demonstrate that Pt/HPC is very promising for RhB hydrogenation as compared to commercial Pt/C catalyst. It is proven that such excellent activity of Pt/HPC can be attributed to the combined merits of hollow porous architecture and well combination between HPC and Pt nanoparticles.

Concave PtCo nanooctahedra with high-energy {110} facets for the oxygen reduction reaction

For the first time, iminodiacetic acid serves as a morphology control agent for the synthesis of concave PtCo nanooctahedra.