Modulating the Electronic Structure of Cobalt in Molecular Catalysts via Coordination Environment Regulation for Highly Efficient Heterogeneous Nitrate Reduction.

Ammonia (NH3) is pivotal in modern industry and represents a promising next-generation carbon-free energy carrier. Electrocatalytic nitrate reduction reaction (eNO3RR) presents viable solutions for NH3 production and removal of ambient nitrate pollutants. However, the development of eNO3RR is hindered by lacking the efficient electrocatalysts. To address this challenge, we synthesized a series of macrocyclic molecular catalysts for the heterogeneous eNO3RR. These materials possess different coordination environments around metal centers by surrounding subunits. Consequently, electronic structures of the active centers can be altered, enabling tunable activity towards eNO3RR. Our investigation reveals that metal center with an N2(pyrrole)-N2(pyridine) configuration demonstrates superior activity over the others and achieves a high NH3 Faradaic efficiency (FE) of over 90 % within the tested range, where the highest FE of approximately 94 % is obtained. Furthermore, it achieves a production rate of 11.28 mg mgcat -1 h-1, and a turnover frequency of up to 3.28 s-1. Further tests disclose that these molecular catalysts with diverse coordination environments showed different magnetic moments. Theoretical calculation results indicate that variated coordination environments can result in a d-band center variation which eventually affects rate-determining step energy and calculated magnetic moments, thus establishing a correlation between electronic structure, experimental activity, and computational parameters.

Conjugated Nickel Phthalocyanine Derivatives for Heterogeneous Electrocatalytic H2 O2 Synthesis.

Electrocatalytic hydrogen peroxide (H2 O2 ) production has emerged as a promising alternative to the chemical method currently used in industry, due to its environmentally friendly conditions and potential for higher activity and selectivity. Heterogeneous molecular catalysts are promising in this regard, as their active site configurations can be judiciously designed, modified, and tailored with diverse functional groups, thereby tuning the activity and selectivity of the active sites. In this work, nickel phthalocyanine derivatives with various conjugation degrees are synthesized and identified as effective pH-universal electrocatalysts for H2 O2 production after heterogenized on nitrogen-decorated carbon, with increased conjugation degrees leading to boosted selectivity. This is explained by the regulated d-band center, which optimized the binding energy of the reaction intermediate, reducing the energy barrier for oxygen reduction and leading to optimized H2 O2 selectivity. The best catalyst, NiPyCN/CN, exhibits a high H2 O2  electrosynthesis activity with ≈95% of H2 O2 faradic efficiency in an alkaline medium, demonstrating its potential for H2 O2 production.

Tailoring of Active Sites from Single to Dual Atom Sites for Highly Efficient Electrocatalysis.

Single atom catalysts (SACs) have been attracting extensive attention in electrocatalysis because of their unusual structure and extreme atom utilization, but the low metal loading and unified single site induced scaling relations may limit their activity and practical application. Tailoring of active sites at the atomic level is a sensible approach to break the existing limits in SACs. In this review, SACs were first discussed regarding carbon or non-carbon supports. Then, five tailoring strategies were elaborated toward improving the electrocatalytic activity of SACs, namely strain engineering, spin-state tuning engineering, axial functionalization engineering, ligand engineering, and porosity engineering, so as to optimize the electronic state of active sites, tune d orbitals of transition metals, adjust adsorption strength of intermediates, enhance electron transfer, and elevate mass transport efficiency. Afterward, from the angle of inducing electron redistribution and optimizing the adsorption nature of active centers, the synergistic effect from adjacent atoms and recent advances in tailoring strategies on active sites with binuclear configuration which include simple, homonuclear, and heteronuclear dual atom catalysts (DACs) were summarized. Finally, a summary and some perspectives for achieving efficient and sustainable electrocatalysis were presented based on tailoring strategies, design of active sites, and in situ characterization.

Photocatalytic degradation of norfloxacin using N-doped TiO2: Optimization, mechanism, identification of intermediates and toxicity evaluation.

In this study, the photocatalytic degradation of Norfloxacin (NOR) has been studied using N-doped TiO2 (N-TiO2) under visible light irradiation, which was synthesized from a self-owned patent recipe and procedure. Subsequently, a three-factor five-level model, which was based on the central composite design (CCD), was developed to determine the optimal NOR concentration, N-TiO2 dosage, and initial pH in practical use. Meanwhile, the degradation pathway was identified by high-performance liquid chromatography-mass spectroscopy (HPLC-MS). Moreover, the toxicity of degradation intermediates was determined using the bacterium Escherichia coli so as to evaluate the health risk of the photocatalytic treated influent. The synthesized N-TiO2 nanoparticles were spherical, and the grain sizes were distributed from approximately 12 nm-20 nm, with a specific surface area of 148.52 m2/g. The light absorption is range from the ultraviolet region to the visible light region since the band gap was reduced to 2.92eV. It was demonstrated from the response surface method results that the initial NOR of 6.03 mg/L, N-TiO2 dose of 0.54 g/L, and pH of 6.37 could be the proposed optimal degradation conditions, which resulted in a 99.53% removal of NOR within 30 min under visible light irradiation. Two possible degradation pathways were proposed, including the replacement of F atoms by hydroxyl radicals, piperazinyl ring cleavage, hydroxylation, and decarboxylation. In the acute toxicity test, the toxicity declined 55% after photocatalytic treatment for 60 min. The results show the feasibility and novelty for photocatalytic treatment of antibiotics by N-TiO2 photocatalyst.