Search

Pb contamination in aquatic environments causes severe pollution; therefore, harmless absorbents are required. In this study, we report a novel synthesis of whitlockite (WH, Ca18Mg2(HPO4)2(PO4)12), which is the second most abundant biomineral in human bone, and its application as a high‐performing Pb2+ absorbent. Hydroxyapatite (HAP) and WH are prepared via a simple precipitation method. The Pb2+ absorption performance and mechanism of the synthesized biominerals are investigated in aqueous solutions at neutral pH. The results demonstrate that WH exhibits an excellent Pb2+ absorption capacity of 2339 mg g−1, which is 1.68 times higher than the recorded value for HAP. Furthermore, the absorbed Pb2+ ions are recycled into high‐purity PbI2. This is employed as a precursor for the fabrication of perovskite solar cells (PSCs), resulting in a conversion efficiency of 19.00% comparable to that of commercial PbI2 powder (99.99% purity). Our approach provides an efficient way to remove Pb2+ ions from water and reuse them in the recycling of PSCs. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is a promising means to produce eco‐friendly hydrogen fuels. Inspired by the Mn4CaO5 cluster in nature, substantial works have been performed to develop efficient manganese (Mn)‐based heterogeneous catalysts. Despite improvements in catalytic activity, the underlying mechanism of the oxygen evolution reaction (OER) is not completely elucidated owing to the lack of direct spectroscopic evidence for the active Mn‐oxo moieties. We identify water oxidation intermediates on the surface of Mn3O4 nanoparticles (NPs) in the OER at neutral pH by in situ Raman spectroscopy. A potential‐dependent Raman peak was detected at 760 cm−1 and assigned to the active MnIV=O species generated during water oxidation. Isotope‐labeling experiments combined with scavenger experiments confirmed the generation of surface terminal MnIV=O intermediates in the Mn‐oxide NPs. This study provides an insight into the design of systems for the observation of reaction intermediates. [ABSTRACT FROM AUTHOR]

As the demand for energy has dramatically increased in the past decade, electrochemical water splitting has been regarded as an attractive approach to produce renewable hydrogen energy. However, large overpotentials of oxygen‐evolving reaction (OER) is a key bottleneck for practical application. Thus, water‐oxidizing electrocatalysts with low cost and high efficiency should be developed. Here, 5 nm‐sized Mn3O4 nanoparticles (NPs) are synthesized by a hydrothermal method, which is appropriate for large‐scale production. To further improve their performance, various 3d transition metal elements are successfully doped in Mn3O4 NPs. Ni‐doped Mn3O4 NPs exhibit the highest efficiency among the Mn3O4 NPs doped with various elements. Based on structural analysis, the Ni‐doping process leads to the lattice distortion of their tetragonal spinel structure and it strongly correlates with the enhancement of OER activity. The overpotential at the current density of 10 mA cm–2 is 524 and 458 mV for pristine and 5 at% doped Mn3O4 NPs under neutral condition. The heteroatom‐doping process in sub‐10 nm‐sized nanocatalysts is expected to be a promising methodology to induce distorted structure related to active species. Thus, it can be effective to improve catalytic performance of various heterogeneous nano‐catalysts. [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is one of the ways to produce environmentally‐friendly hydrogen energy. Transition‐metal (TM)‐based catalysts have been attracting attention due to their low cost and abundance, but their insufficient activity still remains a challenge. Here, 4 nm Mn3O4 nanoparticles (NPs) are successfully synthesized and their electrochemical behavior is investigated. Using electrokinetic analyses, an identical water oxidizing mechanism is demonstrated between the 4 and 8 nm Mn3O4 NPs. In addition, it is confirmed that the overall increase in the active surface area is strongly correlated with the superb catalytic activity of the 4 nm Mn3O4 NPs. To further enhance the oxygen evolution reaction (OER) performance, Ni foam substrate is introduced to maximize the entire number of the NPs participating in OER. The 4 nm Mn3O4/Ni foam electrode exhibits outstanding electrocatalytic activity for OER with overpotential of 395 mV at a current density of 10 mA cm−2 under neutral conditions (0.5 m PBS, pH 7). [ABSTRACT FROM AUTHOR]

Electrochemical water splitting is one of the most important ways to produce hydrogen fuel for an environmentally friendly energy system. Low‐cost and efficient electrocatalysts for oxygen evolution reaction (OER) have been studied to overcome the sluggish kinetics of OER, which is considered to be a bottleneck that affects the overall efficiency of water splitting. However, the atomic‐level understanding and control of the catalyst surface still remains elusive. Here, we show that methylamine treatment of manganese oxide nanoparticles can effectively control their surface charge and enhance their OER catalytic activity under neutral condition. Methylamine treatment can reduce the overpotential for OER by nearly 100 mV at the current density 5 mA cm−2. Through spectroscopic studies, potentiometric titration, and zeta potential analysis, we discovered that methylamine does not exist on the surface after methylamine treatment but deprotonates the surface of nanoparticles and induce additional negative charge on the surface. Surprisingly, treatment with not only methylamine but other amines can also improve the OER performance and the catalytic activity of the amine treated nanoparticles is influenced by the pKa values of amines. Underwater stars: After methylamine treatment of OH− ligand exchanged Mn3O4 nanoparticles, oxygen evolving reaction performance is significantly enhanced. Detailed mechanistic study reveals that methylamine deprotonates the surface and generates additional negative charges on the surface. The catalytic performance could also be enhanced with different amines and the decrease in overpotential is associated with pKa of amines. [ABSTRACT FROM AUTHOR]