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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. 

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.

 

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. 

Laser photoreduction of metal ions onto graphene oxide (GO) is a facile, environmentally friendly method to produce functional metal–GO nanocomposites for a variety of applications. This work compares Au–GO nanocomposites prepared by photoreduction of [AuCl 4 ] − in aqueous GO solution using laser pulses of nanosecond (ns) and femtosecond (fs) duration. The presence of GO significantly accelerates the [AuCl 4 ] − photoreduction rate, with a more pronounced effect using ns laser pulses. This difference is rationalized in terms of the stronger interaction of the 532 nm laser wavelength and long pulse duration with the GO. Both the ns and fs lasers produce significant yields of sub-4 nm Au nanoparticles attached to GO, albeit with different size distributions: a broad 5.8 ± 1.9 nm distribution for the ns laser and two distinct distributions of 3.5 ± 0.8 and 10.1 ± 1.4 nm for the fs laser. Despite these differences, both Au–GO nanocomposites had the same high catalytic activity towards p -nitrophenol reduction as compared to unsupported 4–5 nm Au nanoparticles. These results point to the key role of GO photoexcitation in catalyzing metal ion reduction and indicate that both ns and fs lasers are suitable for producing functional metal–GO nanocomposites. 

Heavy metal ions are highly toxic and widely spread as environmental pollutants. This work reports the development of two novel chelating adsorbents, based on the chemical modifications of graphene oxide and zirconium phosphate by functionalization with melamine-based chelating ligands for the effective and selective extraction of Hg( ii ) and Pb( ii ) from contaminated water sources. The first adsorbent melamine, thiourea-partially reduced graphene oxide (MT-PRGO) combines the heavier donor atom sulfur with the amine and triazine nitrogen's functional groups attached to the partially reduced GO nanosheets to effectively capture Hg( ii ) ions from water. The MT-PRGO adsorbent shows high efficiency for the extraction of Hg( ii ) with a capacity of 651 mg g −1 and very fast kinetics resulting in a 100% removal of Hg( ii ) from 500 ppb and 50 ppm concentrations in 15 second and 30 min, respectively. The second adsorbent, melamine zirconium phosphate (M-ZrP), is designed to combine the amine and triazine nitrogen's functional groups of melamine with the hydroxyl active sites of zirconium phosphate to effectively capture Pb( ii ) ions from water. The M-ZrP adsorbent shows exceptionally high adsorption affinity for Pb( ii ) with a capacity of 681 mg g −1 and 1000 mg g −1 using an adsorbent dose of 1 g L −1 and 2 g L −1 , respectively. The high adsorption capacity is also coupled with fast kinetics where the equilibrium time required for the 100% removal of Pb( ii ) from 1 ppm, 100 ppm and 1000 ppm concentrations is 40 seconds, 5 min and 30 min, respectively using an adsorbent dose of 1 g L −1 . In a mixture of six heavy metal ions at a concentration of 10 ppm, the removal efficiency is 100% for Pb( ii ), 99% for Hg( ii ), Cd( ii ) and Zn( ii ), 94% for Cu( ii ), and 90% for Ni( ii ) while at a higher concentration of 250 ppm the removal efficiency for Pb( ii ) is 95% compared to 23% for Hg( ii ) and less than 10% for the other ions. Because of the fast adsorption kinetics, high removal capacity, excellent regeneration, stability and reusability, the MT-PRGO and M-ZrP are proposed as top performing remediation adsorbents for the solid phase extraction of Hg( ii ) and Pb( ii ), respectively from contaminated water.