Emerging Bottom‐Up Strategies for the Synthesis of Graphene Nanoribbons and Related Structures

The solution‐phase synthesis is one of the most promising strategies for the preparation of well‐defined graphene nanoribbons (GNRs) in large scale. To prepare high quality, defect‐free GNRs, cycloaromatization reactions need to be very efficient, proceed without side reaction and mild enough to accommodate the presence of various functional groups. In this Minireview, we present the latest synthetic approaches for the synthesis of GNRs and related structures, including alkyne benzannulation, photochemical cyclodehydrohalogenation, Mallory and Pd‐ and Ni‐catalyzed reactions.     

Sorbents for the Direct Capture of CO2 from Ambient Air

The urgency to address global climate change induced by greenhouse gas emissions is increasing. In particular, the rise in atmospheric CO₂ levels is generating alarm. Technologies to remove CO₂ from ambient air, or “direct air capture” (DAC), have recently demonstrated that they can contribute to “negative carbon emission.” Recent advances in surface chemistry and material synthesis have resulted in new generations of CO₂ sorbents, which may drive the future of DAC and its large‐scale deployment. This Review describes major types of sorbents designed to capture CO₂ from ambient air and they are categorized by the sorption mechanism: physisorption, chemisorption, and moisture‐swing sorption.     

Online Monitoring of Electrochemical Carbon Corrosion in Alkaline Electrolytes by Differential Electrochemical Mass Spectrometry

Carbon corrosion at high anodic potentials is a major source of instability, especially in acidic electrolytes and impairs the long‐term functionality of electrodes. In‐depth investigation of carbon corrosion in alkaline environment by means of differential electrochemical mass spectrometry (DEMS) is prevented by the conversion of CO₂ into CO₃^2?. We report the adaptation of a DEMS system for online CO₂ detection as the product of carbon corrosion in alkaline electrolytes. A new cell design allows for in situ acidification of the electrolyte to release initially dissolved CO₃^2? as CO₂ in front of the DEMS membrane and its subsequent detection by mass spectrometry. DEMS studies of a carbon‐supported nickel boride (Ni_xB/C) catalyst and Vulcan XC 72 at high anodic potentials suggest protection of carbon in the presence of highly active oxygen evolution electrocatalysts. Most importantly, carbon corrosion is decreased in alkaline solution.     

Production of Hydrogen Peroxide by Photocatalytic Processes

Hydrogen peroxide (H₂O₂) has received increasing attention because it is not only a mild and environmentally friendly oxidant for organic synthesis and environmental remediation but also a promising new liquid fuel. The production of H₂O₂ by photocatalysis is a sustainable process, since it uses water and oxygen as the source materials and solar light as the energy. Encouraging processes have been developed in the last decade for the photocatalytic production of H₂O₂. In this Review we summarize research progress in the development of processes for the photocatalytic production of H₂O₂. After a brief introduction emphasizing the superiorities of the photocatalytic generation of H₂O₂, the basic principles of establishing an efficient photocatalytic system for generating H₂O₂ are discussed, highlighting the advanced photocatalysts used. This Review is concluded by a brief summary and outlook for future advances in this emerging research field.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Highly Mesoporous Metal‐Organic Frameworks as Synergistic Multimodal Catalytic Platforms for Divergent Cascade Reactions

Rational engineering and assimilation of diverse chemo‐ and biocatalytic functionalities in a single nanostructure is highly desired for efficient multistep chemical reactions but has so far remained elusive. Here, we design and synthesize multimodal catalytic nanoreactors (MCNRs) based on a mesoporous metal‐organic framework (MOF). The MCNRs consist of customizable metal nanocrystals and stably anchored enzymes in the mesopores, as well as coordinatively unsaturated cationic metal MOF nodes, all within a single nanoreactor space. The highly intimate and diverse catalytic mesoporous microenvironments and facile accessibility to the active site in the MCNR enables the cooperative and synergistic participation from different chemo‐ and biocatalytic components. This was shown by one‐pot multistep cascade reactions involving a heterogeneous catalytic nitroaldol reaction followed by a [Pd/lipase]‐catalyzed chemoenzymatic dynamic kinetic resolution to yield optically pure (>99 % ee) nitroalcohol derivatives in quantitative yields.     

Enantioselective Catalytic Aldehyde α‐Alkylation/Semipinacol Rearrangement: Construction of α‐Quaternary‐δ‐Carbonyl Cycloketones and Total Synthesis of (+)‐Cerapicol

An enantioselective aldehyde α‐alkylation/semipinacol rearrangement was achieved through organo‐SOMO catalysis. The catalytically generated enamine radical cation serves as a carbon radical electrophile that can stereoselectively add to the alkene of an allylic alcohol and initiate ensuing ring‐expansion of cyclopropanol or cyclobutanol. This tandem reaction enables the production of a wide range of nonracemic functionalizable α‐quaternary‐δ‐carbonyl cycloketones in high yields and excellent enantioselectivity from simple aldehydes and allylic alcohols. As a key step, the intramolecular reaction was also successfully applied in the asymmetric total synthesis of (+)‐cerapicol.     

Cu‐Catalyzed Diastereo‐ and Enantioselective Reactions of γ,γ‐Disubstituted Allyldiboron Compounds with Ketones

A catalytic diastereo‐ and enantioselective method for the preparation of complex tertiary homoallylic alcohols containing a vicinal quaternary carbon stereogenic center and a versatile alkenylboronic ester is disclosed. Transformations are promoted by 5 mol % of a readily available copper catalyst bearing a bulky monodentate phosphoramidite ligand, which is essential for attaining both high dr and er. Reactions proceed with a wide variety of ketones and allylic 1,1‐diboronate reagents, which enables the efficient preparation of diverse array of molecular scaffolds.     

Study on structure and performance of surface‐metallized carbon fibers reinforced rigid polyurethane composites

The simultaneous promotion in mechanical and electrical properties of rigid polyurethane (RPU) is an important task for expanding potential application. In this work, carbon fibers (CFs) reinforced RPU composites were prepared with the goal of improving mechanical and electrical properties. Metallized CFs meet our performance requirements and can be easily achieved via electrodeposition. However, the weak bonding strength in fiber‐metal‐RPU interface restricts their application. Inspired by the reducibility and wonderful adhesion of dopamine (DA), we proposed a new and efficient electrochemical method to fabricate metallized CFs, where DA polymerization was simultaneously integrated coupled with the reduction of metal ions (Ni²⁺). The characterization results helped us to gain insight about the reaction mechanism, which was never reported as far as we know. Compared with pure RPU, the tensile, interlaminar shear and impact strength of polydopamine (PDA)‐nickel (Ni) modified CFs/RPU composites were improved by 11.2%, 21.0%, and 78.0%, respectively, which attributed to the strong interfacial adhesion, including mechanical interlocking and chemical crosslinking between treated CFs and RPU. In addition, the PDA‐Ni surface treatment method also affected the dispersion of short CFs in the RPU, which increased the possibility of conductor contact and reduced insulator between fibers networks, resulting in higher electrical conductivity.     

Effect of Ionic Liquid Structure on the Electrochemical Response of Dopamine at Room Temperature Ionic Liquid‐modified Carbon Paste Electrodes (IL–CPE)

In this work 12 different ionic liquids (ILs) have been used added as co‐binders in the preparation of modified carbon paste electrodes (IL–CPEs) used for the voltammetric analysis of dopamine in Britton‐Robinson buffer. The ionic liquids studied were selected based on three main criteria: (1) increasing chain length of alkyl substituents (studying 1‐ethylimidazolium and ethyl, propyl, butyl, hexyl and decylmethylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids); (2) nature of the counter ion (dicyanamide, bis(trifluoromethylsulfonyl)imide and hexafluorophosphate) in 1‐butyl‐3‐methylimidazolium ionic liquids; and (3) cation ring structures (1‐butyl‐3‐methylimidazolium, 1‐butyl‐1‐methylpiperidinium, 1‐butyl‐1‐methylpyrrolidinium and 1‐butyl‐3‐methylpyridinium) in bis(trifluoromethylsulfonyl)imide or hexafluorophosphate (1‐butyl‐3‐methylimidazolium or 1‐butyl‐3‐methylpyridinium as cations) ionic liquids. The use of IL as co‐binders in IL–CPE results in a general enhancement of both the sensitivity and the reversibility of dopamine oxidation. In square wave voltammetry experiments, the peak current increased up to a 400 % when 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was used as co‐binder, as compared to the response found with the unmodified CPE. Experimental data provide evidence that electrostatic and steric effects are the most important ones vis‐à‐vis these electrocatalytic effects on the anodic oxidation of dopamine on IL–CPE. The relative hydrophilicity of dicyanamide anions reduced the electrocatalytic effects of the corresponding ionic liquids, while the use of 1‐ethyl‐3‐methylimidazolium hexafluorophosphate or 1‐ethyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (two relatively small and highly hydrophobic ionic liquids) as co‐binders in IL–CPE resulted in the highest electrocatalytic activity among all of the IL–CPE studied.