Biosynthesis of silver nanoparticles using Onosma sericeum Willd. and evaluation of their catalytic properties and antibacterial and cytotoxic activity

In this study, silver nanoparticle (AgNP) synthesis was carried out using Onosma sericeum Willd. aqueous extract for the first time, with a simple, economical, and green method without the need for any other organic solvent or external reducing or stabilizing agent. A variety of AgNPs, all of different particle sizes, were synthesized by controlling the silver ion concentration, extract volume, temperature, and pH. It was determined that the optimum conditions for AgNP synthesis were 1 mM AgNO3, pH 8, 25 °C, 20 g/200 mL extract, silver nitrate, and extract ratio 5:1 (v/v). The AgNPs were defined using UV-Vis spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The particle size distribution and zeta potential measurements of the AgNPs were measured using the dynamic light scattering (DLS) technique. It was determined that the AgNPs with a particle size of less than 10 nm showed a higher catalytic effect in the reduction of 2-nitrobenzenamine. It was also found that these nanoparticles had a cytotoxic effect on the MCF-7 breast cancer cell line depending on dosage and time. The resulting IC50 values were between 76.63 µg/mL and 169.77 µg/mL. Furthermore, the biosynthesized AgNPs showed effective antibacterial activity against the Acinetobacter baumannii bacteria. The results of the study showed that synthesized AgNPs can have a promising role in biomedical and nanobiotechnology applications.     

Nanoporous Palladium Hydride for Electrocatalytic N2 Reduction under Ambient Conditions

The electrocatalytic nitrogen reduction reaction (NRR) is an alternative eco‐friendly strategy for sustainable N₂ fixation with renewable energy. However, NRR suffers from sluggish kinetics owing to difficult N₂ adsorption and N≡N cleavage. Now, nanoporous palladium hydride is reported as electrocatalyst for electrochemical N₂ reduction under ambient conditions, achieving a high ammonia yield rate of 20.4 μg h^?1 mg^?1 with a Faradaic efficiency of 43.6 % at low overpotential of 150 mV. Isotopic hydrogen labeling studies suggest the involvement of lattice hydrogen atoms in the hydride as active hydrogen source. In situ Raman analysis and density functional theory (DFT) calculations further reveal the reduction of energy barrier for the rate‐limiting *N₂H formation step. The unique protonation mode of palladium hydride would provide a new insight on designing efficient and robust electrocatalysts for nitrogen fixation.     

Underestimated Color Centers: Defects as Useful Reducing Agents in Lanthanide‐Activated Luminescent Materials

Inorganic hosts, such as SrB₄O₇ or certain nitrides, intrinsically stabilize Eu²⁺ even when the dopant is an Eu³⁺‐based precursor and reducing conditions are not employed in the synthesis. Although this concept is well known in the synthesis of phosphorescent materials, the mechanistic details are scarcely understood. Herein, we demonstrate that trapped charge carriers, such as color centers, can also act as redox partners to stabilize certain oxidation states of activators. Eu‐activated CsMgCl₃ and CsMgBr₃ are used as examples. Upon doping with EuCl₃ and in the absence of reducing conditions during the synthesis, dominant cyan or green luminescence from Eu²⁺ ions was observed. Photoluminescence spectroscopy at 10 K revealed that the reduction is correlated to color centers localized at defects. Although defects are typically undesired in phosphors, we have shown that their role may be underestimated and they could be used on purpose in the preparation of selected inorganic phosphors.     

Electroreductive Cobalt‐Catalyzed Carboxylation: Cross‐Electrophile Electrocoupling with Atmospheric CO2

The chemical use of CO₂ as an inexpensive, nontoxic C1 synthon is of utmost topical interest in the context of carbon capture and utilization (CCU). We present the merger of cobalt catalysis and electrochemical synthesis for mild catalytic carboxylations of allylic chlorides with CO₂. Styrylacetic acid derivatives were obtained with moderate to good yields and good functional group tolerance. The thus‐obtained products are useful as versatile synthons of γ‐arylbutyrolactones. Cyclic voltammetry and in operando kinetic analysis were performed to provide mechanistic insights into the electrocatalytic carboxylation with CO₂.     

Rare‐Earth Single Erbium Atoms for Enhanced Photocatalytic CO2 Reduction

The solar‐driven photocatalytic reduction of CO₂ (CO₂RR) into chemical fuels is a promising route to enrich energy supplies and mitigate CO₂ emissions. However, low catalytic efficiency and poor selectivity, especially in a pure‐water system, hinder the development of photocatalytic CO₂RR owing to the lack of effective catalysts. Herein, we report a novel atom‐confinement and coordination (ACC) strategy to achieve the synthesis of rare‐earth single erbium (Er) atoms supported on carbon nitride nanotubes (Er₁/CN‐NT) with a tunable dispersion density of single atoms. Er₁/CN‐NT is a highly efficient and robust photocatalyst that exhibits outstanding CO₂RR performance in a pure‐water system. Experimental results and density functional theory calculations reveal the crucial role of single Er atoms in promoting photocatalytic CO₂RR.     

Photo‐excited Oxygen Reduction and Oxygen Evolution Reactions Enable a High‐Performance Zn–Air Battery

The storage of solar energy in battery systems is pivotal for a sustainable society, which faces many challenges. Herein, a Zn–air battery is constructed with two cathodes of poly(1,4‐di(2‐thienyl))benzene (PDTB) and TiO₂ grown on carbon papers to sandwich a Zn anode. The PDTB cathode is illuminated in a discharging process, in which photoelectrons are excited into the conduction band of PDTB to promote oxygen reduction reaction (ORR) and raise the output voltage. In a reverse process, holes in the valence band of the illuminated TiO₂ cathode are driven for the oxygen evolution reaction (OER) by an applied voltage. A record‐high discharge voltage of 1.90 V and an unprecedented low charge voltage of 0.59 V are achieved in the photo‐involved Zn–air battery, regardless of the equilibrium voltage. This work offers an innovative pathway for photo‐energy utilization in rechargeable batteries.     

Bridge Bonded Oxygen Ligands between Approximated FeN4 Sites Confer Catalysts with High ORR Performance

The applications of the most promising Fe—N–C catalysts are prohibited by their limited intrinsic activities. Manipulating the Fe energy level through anchoring electron‐withdrawing ligands is found effective in boosting the catalytic performance. However, such regulation remains elusive as the ligands are only uncontrollably introduced oweing to their energetically unstable nature. Herein, we report a rational manipulation strategy for introducing axial bonded O to the Fe sites, attained through hexa‐coordinating Fe with oxygen functional groups in the precursor. Moreover, the O modifier is stabilized by forming the Fe?O?Fe bridge bond, with the approximation of two FeN₄ sites. The energy level modulation thus created confers the sites with an intrinsic activity that is over 10 times higher than that of the normal FeN₄ site. Our finding opens a novel strategy to manage coordination environments at an atomic level for high activity ORR catalysts.     

A Blinking Mesoporous TiO2−x Composed of Nanosized Anatase with Unusually Long‐Lived Trapped Charge Carriers

A mesoporous TiO_2?x material comprised of small, crystalline, vacancy‐rich anatase nanoparticles (NPs) shows unique optical, thermal, and electronic properties. It is synthesized using polymer‐derived mesoporous carbon (PDMC) as a template. The PDMC pores serve as physical barriers during the condensation and pyrolysis of a titania precursor, preventing the titania NPs from growing beyond 10 nm in size. Unlike most titania nanomaterials, during pyrolysis the NPs undergo no transition from the anatase to rutile phase and they become catalytically active reduced TiO_2?x. When exposed to a slow electron beam, the NPs exhibit a charge/discharge behavior, lighting up and fading away for an average period of 15 s for an extended period of time. The NPs also show a 50 nm red‐shift in their UV/Vis absorption and long‐lived charge carriers (electrons and holes) at room temperature in the dark, even long after UV irradiation. The NPs as photocatalysts show a good activity for CO₂ reduction.