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Gold (Au)- and ceria (CeO₂)-based catalysts are amongst the most active catalysts for the gas phase CO oxidation reaction. Nevertheless, nanosized Au and CeO₂catalysts may encounter heat-induced sintering in thermochemical catalytic reactions. Herein, we report on the rational one-pot synthesis of ceria-reduced graphene oxide (CeO₂-RGO) using a facile ethylenediamine (EDA)-assisted solvothermal method. Standalone RGO and free-standing CeO₂were also prepared using the same EDA-assisted method for comparison. We then incorporated Au into the prepared samples by colloidal reduction and evaluated the catalytic activity of the different catalysts for CO oxidation. The RGO-supported CeO₂surpassed the free-standing CeO₂, exhibiting a 100% CO conversion at 285^oC compared to 340^oC in the case of CeO₂. Interestingly, the RGO-supported Au/CeO₂catalysts outperformed the Au/CeO₂catalysts and achieved a 100% CO conversion at 76^oC compared to 113^oC in the case of Au/CeO₂. Additionally, the Au/CeO₂-RGO catalyst demonstrated remarkable room-temperature activity with simultaneous 72% CO conversion. This outstanding performance was attributed to the unique dispersion and size characteristics of the RGO-supported CeO₂and Au catalysts in the ternary Au/CeO₂-RGO nanocomposite, as revealed by TEM and XPS, among other techniques.

 

Herein, we report on the synthesis of ultrasmall Pd nanoclusters (∼2 nm) protected by L‐cysteine [HOCOCH(NH₂)CH₂SH] ligands (Pd_n(L‐Cys)_m) and supported on the surfaces of CeO₂, TiO₂, Fe₃O₄, and ZnO nanoparticles for CO catalytic oxidation. The Pd_n(L‐Cys)_mnanoclusters supported on the reducible metal oxides CeO₂, TiO₂and Fe₃O₄exhibit a remarkable catalytic activity towards CO oxidation, significantly higher than the reported Pd nanoparticle catalysts. The high catalytic activity of the ligand‐protected clusters Pd_n(L‐Cys)_mis observed on the three reducible oxides where 100 % CO conversion occurs at 93–110 °C. The high activity is attributed to the ligand‐protected Pd nanoclusters where the L‐cysteine ligands aid in achieving monodispersity of the Pd clusters by limiting the cluster size to the active sub‐2‐nm region and decreasing the tendency of the clusters for agglomeration. In the case of the ceria support, a complete removal of the L‐cysteine ligands results in connected agglomerated Pd clusters which are less reactive than the ligand‐protected clusters. However, for the TiO₂and Fe₃O₄supports, complete removal of the ligands from the Pd_n(L‐Cys)_mclusters leads to a slight decrease in activity where the T_100%CO conversion occurs at 99 °C and 107 °C, respectively. The high porosity of the TiO₂and Fe₃O₄supports appears to aid in efficient encapsulation of the bare Pd_nnanoclusters within the mesoporous pores of the support.

 

Laser-induced reduction of metal ions is attracting increasing attention as a sustainable route to ligand-free metal nanoparticles. In this work, we investigate the photochemical reactions involved in reduction of Ag + and [AuCl 4 ] − upon interaction with lasers with nanosecond and femtosecond pulse duration, using strong-field ionization mass spectrometry and spectroscopic assays to identify stable molecular byproducts. Whereas Ag + in aqueous isopropyl alcohol (IPA) is reduced through plasma-mediated mechanisms upon femtosecond laser excitation, low-fluence nanosecond laser excitation induces electron transfer from IPA to Ag + . Both nanosecond and femtosecond laser excitation of aqueous [AuCl 4 ] − produce reactive chlorine species by Au–Cl bond homolysis. Formation of numerous volatile products by IPA decomposition during both femtosecond and nanosecond laser excitation of [AuCl 4 ] − is attributed to enhanced optical breakdown by the Au nanoparticle products of [AuCl 4 ] − reduction. These mechanistic insights can inform the design of laser synthesis procedures to improve control over metal nanoparticle properties and enhance byproduct yields. 

A highly porous adsorbent based on a metal–organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal. MIL-125 was densely decorated by 2-imino-4-thiobiuret functional groups, which generated a green, rapid, and efficacious adsorbent for the uptake of Hg( ii ) and Pb( ii ) from aqueous solutions. ITB-MIL-125 showed a high adsorption affinity toward mercury( ii ) ions of 946.0 mg g −1 due to covalent bond formation with accessible sulfur-based functionality. Different factors were studied, such as the initial concentration, pH, contact time, and competitive ions, under same circumstances at the room temperature. Moreover, the experimental adsorption data were in excellent agreement with the Langmuir adsorption isotherm and pseudo-second order kinetics. At a high concentration of 100 ppm mixture of six metals, ITB-MIL-125 exhibited a high adsorption capacity, reaching more than 82% of Hg( ii ) compared to 62%, 30%, 2%, 1.9%, and 1.6% for Pb( ii ), Cu( ii ), Cd( ii ), Ni( ii ), and Zn( ii ), respectively.