Low Water Affinity Research Articles

Confinement Effect in Multilayer Films Made from Semicrystalline and Bio-Based Polyamide and Polylactic Acid.

Bio-based multilayer films were prepared by using the innovative nanolayer coextrusion process to produce films with a number of alternating layers varying from 3 to 2049. For the first time, a semicrystalline polymer was confined by another semicrystalline polymer by nanolayering in order to develop high barrier polyamide (PA11)/polylactic acid (PLA) films without compromising thermal stability and mechanical behavior. This process allows the preparation of nanostratified films with thin layers (down to nanometric thicknesses) in which a confinement effect can be induced. The stratified structure has been investigated, and the layer thicknesses have been measured. Barrier properties were successfully correlated to the microstructure, as well as the thermal behavior, and mechanical properties. The layer continuity was fully achieved for most of the films, but some layer breakups have been observed on the film with the thinnest PLA layer (2049-layers film). Coextruding PLA with PA11 has induced an increase in PLA crystallinity (from 4 to 16%) along with an increase in thermal stability of the multilayer films without impacting PA11 properties. Gas barrier properties were driven by the PLA confined layers due to the microstructural rearrangement by increasing crystallinity, whereas water barrier properties were governed by the PA11 confining layers due to its lower water affinity. As a consequence, a decrease of water permeability (up to 11 times less permeable for the 6M film) but an increase of gas barrier properties (barrier improvement factor (BIF) of 66% for the 0M film for N2 and BIF of 36% for the 6M film for CO2 for instance) were evidenced as the layer number was increased. This study paves the way for the development of ecofriendly materials with outstanding barrier performances and highlights the importance of nonmiscible polymers adhesion at melt state and additives presence.

Functionalized Superhydrophobic Coatings with Electro‐Photothermal Effect for All‐Day Durable Anti‐Icing

AbstractSuperhydrophobic surfaces offer notable advantages, including markedly low water affinity and reduced ice adhesion strength. Nevertheless, their practical utility is impeded by their limited durability and vulnerability to failure in cold and humid environments. In this study, a novel approach for devising an electro‐photothermal superhydrophobic (EPS) nanocomposite coating is presented. The findings indicate that the EPS nanocomposite coating exhibits both physical and chemical self‐cleaning attributes, showcasing a synergistic interplay of superhydrophobicity, electrothermal, and photothermal characteristics. The superhydrophobic coating delays icing about four times longer than the original coating. At ambient temperatures of −20 °C, the coating stacked with an electro‐ and photo‐thermal performance de‐icing layer reduces the de‐icing time by about 5 times more than the purely photo‐thermal performance de‐icing time, and reduces the de‐icing time by about 4 times more than the purely electro‐thermal de‐icing time. Furthermore, the EPS surface demonstrates the capability to sustain temperatures above 0 °C through the photothermal effect on sunny days, utilizing both the electrothermal and photothermal effects on cloudy days, and relying on the electrothermal effect during cold nights. The research introduces a novel method for fabricating functional materials, pertinent to practical anti‐icing and de‐icing applications.

Underground hydrogen storage: A recovery prediction using pore network modeling and machine learning

Understanding the hydrogen-brine transport properties and the hydrogen trapping rate (i.e., ratio of residual hydrogen saturation after recovery to initial hydrogen saturation) is critical to the site selection for underground hydrogen storage (UHS). In this study, a three-dimensional pore network model (PNM) was used to simulate hydrogen-brine two phase flow in various porous media, including sandstone, carbonate, and sand packs. Surface contact angles measured from previous experiments were used to study the influence of the wettability on hydrogen transport in porous media. Many studies have investigated the impact of these factors on carbon dioxide sequestration. However, because of the difference in the thermal dynamic properties of the fluids and the purpose of UHS and carbon dioxide sequestration, it is still essential to analyze the UHS performance under the different rock and fluid properties. PNM simulations showed that a relatively larger contact angle with low water affinity was more suitable for UHS due to its low hydrogen trapping rate. Two machine learning methods, the least square fitting and the support vector machine (SVM), were developed to classify the ability of a rock to trap hydrogen and to predict hydrogen trapping rates. Hydrogen trapping rates simulated using the PNM were used as the training data in the machine learning models. The SVM classified rock samples into two groups which had high hydrogen trapping rates (>50 %) and low hydrogen trapping rates (<50 %). The machine learning results showed that rock samples with a low ratio of pore size to throat size and high pore connectivity (i.e., average number of throats connected to a given pore) were favorable for a low hydrogen trapping rate. This study illustrated that the impact of both rock surface wettability and pore structural geometry should be accounted for when evaluating a hydrogen-brine two-fluid system in porous media. This work is the first study that combined PNM simulation with machine learning to investigate the influence of rock surface wettability and pore structure features on the hydrogen trapping rate, which will provide insights into site selections and decision making in large-scale UHS projects.

Nanoencapsulation of Curcuma longa L. extract for the treatment of experimental colitis

Inflammatory bowel diseases (IBDs) are gastrointestinal chronic inflammatory diseases characterized by chronic and recurrent intestinal ulcerations. Curcuminoids are naturally occurring polyphenolic compounds with remarkable bioactivity; however, their low water affinity and bioavailability usually hinder their application. Encapsulation techniques can be coupled with extraction procedures to yield nanoparticles that may have enhanced properties. In this work, curcuminoids were extracted from rhizomes of Curcuma longa L. and simultaneously encapsulated using ultrasound. The characterization of the curcuminoids nanoparticles showed that particles ranging from 124 ± 81 to 252 ± 68 nm were formed, and the main properties of the curcuminoids were maintained after encapsulation. Experimental colitis was induced in rats by 2,4,6-trinitrobenzene sulfonic acid, and they were subsequently treated with 10, 25, or 50 mg kg-1 of nanoencapsulated curcuminoids for 7 days through gavage, during which the disease activity index (DAI) was evaluated. Then the rats were euthanized, and the distal colon was removed for macroscopic analysis and the assessment of the activity of the enzymes myeloperoxidase and N-acetylglucosaminidase. The dose of 25 mg kg-1 of nanoencapsulated curcuminoids reduced the DAI and the activity of inflammatory enzymes compared to the untreated group and was established as the minimum effective dose to be used in the treatment of this model of experimental colitis in rats.

Investigating activated carbons for SO2 adsorption in wet flue gas

The removal of sulfur dioxide from flue gas is an important process for the mitigation of acid rain. Activated carbons have a low affinity for water and a high affinity for polarizable molecules, such as sulfur dioxide, making them good candidates for selective adsorbents for flue gases. This work presents results on the multicomponent adsorption of N2/CO2/SO2 and N2/CO2/SO2/H2O flue gas mixtures on four activated carbons prepared from petroleum coke, and one carbon black. Multicomponent adsorption was measured at T = 30, 60, 90 °C. All five activated carbons had a high affinity and selectivity for SO2 in both the presence and absence of water. The activated carbons prepared with KOH (P_K) and NaOH (P_Na) showed the highest capacity for SO2 under wet conditions with thermal swing regeneration (P_K: nadsSO₂ = 0.148 ± 0.002 mmol g−1, P_Na: nadsSO₂ = 0.13 ± 0.01 mmol g−1). In pressure swing experiments of the wet flue gas mixture, the activated carbon prepared with a K2CO3 and KOH (P_CK) (nadsSO₂ = 0.077 ± 0.002 mmol g−1) and P_K (nadsSO₂ = 0.064 ± 0.005 mmol g−1) activated carbons had the highest SO2 capacities. Of the activated carbon, P_K had the greatest SO2/H2O selectivity for the thermal swing adsorption (T = 30 °C, SSO₂/H₂O = 3.0 ± 0.2) and pressure swing adsorption (T = 90 °C, SSO₂/H₂O = 3.9 ± 0.6) experiments. It was observed that activated carbons with higher carbon fraction were less likely to have a difference in SO2 adsorption from dry versus wet conditions. After the wet SO2 multicomponent adsorption, no change in the adsorption performance of any activated carbons was observed after 10 cycles.

Formation of Porous Structures and Crystalline Phases in Poly(vinylidene fluoride) Membranes Prepared with Nonsolvent-Induced Phase Separation—Roles of Solvent Polarity

PVDF membranes were prepared with nonsolvent-induced phase separation, using solvents with various dipole moments, including HMPA, NMP, DMAc and TEP. Both the fraction of the polar crystalline phase and the water permeability of the prepared membrane increased monotonously with an increasing solvent dipole moment. FTIR/ATR analyses were conducted at the surfaces of the cast films during membrane formation to provide information on if the solvents were present as the PVDF crystallized. The results reveal that, with HMPA, NMP or DMAc being used to dissolve PVDF, a solvent with a higher dipole moment resulted in a lower solvent removal rate from the cast film, because the viscosity of the casting solution was higher. The lower solvent removal rate allowed a higher solvent concentration on the surface of the cast film, leading to a more porous surface and longer solvent-governed crystallization. Because of its low polarity, TEP induced non-polar crystals and had a low affinity for water, accounting for the low water permeability and the low fraction of polar crystals with TEP as the solvent. The results provide insight into how the membrane structure on a molecular scale (related to the crystalline phase) and nanoscale (related to water permeability) was related to and influenced by solvent polarity and its removal rate during membrane formation.

Influence of ligands within Al-based metal-organic frameworks for selective separation of methane from unconventional natural gas

Efficient CH4/N2 separation from unconventional natural gas is vital for both energy recycling and climate change control. Figuring out the reason for the disparity between ligands in the framework and CH4 is the crucial problem for developing adsorbents in PSA progress. In this study, a series of eco-friendly Al-based MOFs, including Al-CDC, Al-BDC, CAU-10, and MIL-160, were synthesized to investigate the influence of ligands on CH4 separation through experimental and theoretical analyses. The hydrothermal stability and water affinity of synthetic MOFs were explored through experimental characterization. The active adsorption sites and adsorption mechanisms were investigated via quantum calculation. The results manifested that the interactions between CH4 and MOFs materials were affected by the synergetic effects of pore structure and ligand polarities, and the disparities of ligands within MOFs determined the separation efficiency of CH4. Especially, the CH4 separation performance of Al-CDC with high sorbent selection (68.56), moderate isosteric adsorption heat for CH4 (26.3 kJ/mol), and low water affinity (0.1 g/g at 40% RH) was superior to most porous adsorbents, which was attributed to its nanosheet structure, proper polarity, reduced local steric hindrance, and extra functional groups. The analysis of active adsorption sites indicated that hydrophilic carboxyl groups and hydrophobic aromatic ring were the dominant CH4 adsorption sites for liner ligands and bent ligands, respectively. The methylene groups with saturated C–H bonds enhanced the wdV interaction between ligands and CH4, resulting in the highest binding energy of CH4 for Al-CDC. The results provided valuable guidance for the design and optimization of high-performance adsorbents for CH4 separation from unconventional natural gas.

Aspergillus sclerotiorum lipolytic activity and its application in bioremediation of high-fat dairy wastewater environments.

Oils and grease (O&G) have low affinity for water and represent a class of pollutants present in the dairy industry. Enzyme-mediated bioremediation using biocatalysts, such as lipases, has shown promising potential in biotechnology, as they are versatile catalysts with high enantioselectivity and regioselectivity and easy availability, being considered a clean technology (white biotechnology). Specially in the treatment of effluents from dairy industries, these enzymes are of particular importance as they specifically hydrolyze O&G. In this context, the objective of this work is to prospect filamentous fungi with the ability to synthesize lipases for application in a high-fat dairy wastewater environment. We identified and characterized the fungal species Aspergillus sclerotiorum as a good lipase producer. Specifically, we observed highest lipolytic activity (20.72 U g-1) after 96h of fermentation using sunflower seed as substrate. The fungal solid fermented was used in the bioremediation in dairy effluent to reduce O&G. The experiment was done in kinetic from 24 to 168h and reduced over 90% of the O&G present in the sample after 168h. Collectively, our work demonstrated the efficiency and applicability of fungal fermented solids in bioremediation and how this process can contribute to a more sustainable wastewater pretreatment, reducing the generation of effluents produced by dairy industries.

Distribution Characteristics and Influencing Factors of Rural Settlements in Metropolitan Fringe Area: A Case Study of Nanjing, China

Rural settlement is the core content of rural geography research. Exploring the spatial distribution characteristics and influencing factors of rural settlements can provide reference for the optimization of rural settlements. This paper selected Nanjing as a typical case, based on remote sensing image, using R statistics, kernel density analysis, hot spot detection analysis and semi variogram function; the paper analyzed the spatial, scale and morphological distribution characteristics of rural settlements; and preliminarily analyzed the influencing factors of rural settlements distribution in the metropolitan fringe area. The results showed that: (1) The spatial distribution of rural settlements generally presented a “multi-core” center, and a spatial distribution trend of stepwise decline from the core to the periphery, showing a typical “core-edge” structure. (2) There was a significant spatial difference in the scale distribution of rural settlements, which was characterized by a gradual decrease in the scale of rural settlements with the increase in the distance from the central urban area. (3) The morphological distribution of rural settlements showed spatial differentiation, and the morphological types of settlements mainly included strip, arcbelt, cluster and scatter. (4) The distribution of rural settlements was affected by such factors as terrain, river system, traffic, economic and social development, cultural and policy. The distribution of rural settlements had the location orientation of “low altitude, water affinity and road affinity”. The increase in agricultural population, rural economic development, cultural and policy factors played an important role in the distribution of rural settlements in the metropolitan fringe area.

CO2 outperforms KOH as an activator for high-rate supercapacitors in aqueous electrolyte

Although high-surface area activated carbons used as supercapacitor (SC) electrodes are frequently produced by KOH activation, this study shows that, when aqueous electrolytes are used, CO2 activation is a better choice from the point of view of SC performance, environment and economy. Ordered mesoporous carbons (OMCs) produced by a mechanochemical synthesis method from mimosa tannin are activated with KOH to use these materials as electrodes for SCs. A comparative analysis of the same OMCs but activated with CO2 is presented to examine the effect of the activation process on materials performance. KOH-activated materials exhibit good electrochemical performance at low charging rates, reaching specific cell capacitance values of 49 F g−1 at 0.5 Ag−1, however, restricted access to microporosity and low water affinity water reduces their performance at high charging rates. In contrast, the best performing CO2-activated material can retain 81% of capacitance at 20 A g−1, compared to 25% for a KOH-activated OMC with similar properties and tested under the same conditions. A thorough review of the open literature suggests that CO2 activation would produce materials with a suitable combination of pore network connectivity and water affinity, resulting in SCs with high rate capability in an aqueous electrolyte. These conclusions were drawn by judiciously integrating the analysis of: (i) the hysteresis loop scanning of N2 adsorption-desorption isotherms; and (ii) water adsorption isotherms as tools to more accurately assess the pore network connectivity and water affinity of the materials, which are not generally considered when studying SC performance.

Plasticity characterization of certain Nigeria clay minerals for their application in ceramic water filters.

Plasticity is an essential property of clay that determines its suitability for water filtration. There are no published works on the plastic behavior of clays from the study locations. The plastic behavior of seven Nigerian clays was examined using plasticity indices and compressive stress parameters in relation to chemical compositions and moisture content. The objective is to determine plastic behavior of some Nigerian clays and their suitability in production of Expanded Clay Aggregates (ECA) for water filters. Compressive stresses and deformation parameters were determined experimentally and compared theoretically. Atterberg limits (D 4318) were used to determine the plasticity indices. Chemical compositions of the samples were examined with XRF and correlated with plasticity and mineral contents of the clays. The clays are aluminosilicates with SiO2/Al2O3 ratio of 1.61 to 3.03 and plastic indices of 8 to 49. Low plastic indices (8-11) and low compressive stresses parameters were observed for kaolinite clays (0.002 MPa) due to their low affinity for water while zeolite rich clays showed high plastic indices (46 and 49) for Obowo and Minna and sharp difference in their compressive stresses parameters (0.15 and 0.03 MPa) at optimum moisture contents of 57% and 53%, respectively. Despite varying moisture content, chemical and mineral compositions, all curves showed similar trends apart from kaolinites at 40% moisture content. Relationships exist among microstructural properties, chemical composition, moisture content, compressive strength, and plasticity indices of the clays. The plastic behaviors show they are suitable for development of ECA for water filters.

Incorporation of N-phenyl in poly(benzimidazole imide)s and improvement in H2O-absorbtion and transparency.

5-Amine-2-(4-amino-benzene)-1-phenyl-benzimidazole (N-PhPABZ) was successfully synthesized and polymerized with 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA) to obtain a novel N-phenyl-poly(benzimidazole imide) (N-Ph-PBII). The successful incorporation of N-phenyl addressed the issue of high H2O-absorption of traditional PBIIs while retained the superheat resistance property. The resulting N-Ph-PBII possessed a high glass-transition temperature (Tg) up to 425 °C and a low affinity for water of 1.4%. Furthermore, the loose molecular packing and noncoplanar structures led to an increase in optical transparency for the modified PBII.

Red currant pectin: The physicochemical characteristic of pectin solutions in dilute and semi dilute regimes

In this study red currant was used as a source of pectin. The aim of this study was to investigate the physicochemical properties of obtained polysaccharide, with an emphasis on behaviour in aqueous solutions. Pectin was obtained using water extraction, then the basic characteristics of the obtained polysaccharide was performed (FT-IR-ATR, molar mass distribution, sugar composition, DE). An applied extraction method resulted in a water-soluble pectin fraction with Mw=1020 kg ⋅ mol-1 and DE=57.1%. To study the behaviour of pectins in aqueous solutions various methods were used: membrane osmometry, viscosity measurements, rheology, NMR and DLS. The obtained results allowed to describe pectin chains properties in both dilute and semi-dilute regimes, including c∗ value determination. Osmotic tests indicated low water affinity and strong intermolecular interactions for red currant pectin. Viscosity measurements revealed strong polyelectrolyte behaviour, initially the reduced viscosity of the solutions decreased, until the overlap concentration (c∗=0.78 g ⋅ dL-1) was reached and then increased sharply. Comprehensive interpretation of the results obtained by means of used methods allowed to conclude that red currant pectin takes the form of tightly wound coils in dilute solutions, with increasing concentration chains tending to expand and intermolecular interactions are being enhanced, which result in the formation of complex structures.

Water-based hybrid coatings toward mechanically flexible, super-hydrophobic and flame-retardant polyurethane foam nanocomposites with high-efficiency and reliable fire alarm response

Flammability feature of combustible polymer foam materials often causes massive casualties and property loss, and it is therefore urgent to develop a green and high-efficiency strategy that can reduce or avoid the fire blaze disasters. Here, an extremely simple water-based coating approach is proposed to prepare mechanically flexible, super-hydrophobic and flame-retardant polyurethane (PU) foam nanocomposites with high-efficiency fire warning response. The hybrid ammonium polyphosphate (APP)/graphene oxide (GO) is decorated onto the PU foam surface via electrostatic interactions followed by surface silane functionalization. Interestingly, the silane and APP molecules present selective distributions on the GO and thus form micro-/nano- rough surface with low water affinity to achieve super-hydrophobicity (e.g. water contact angle of ~158.4°). Meanwhile, such hybrid APP/GO/silane coatings produce synergistic flame resistance for the PU foam materials, which is attributed to the formation of compact and uniform P-Si elements co-covered rGO layer on the foam surface. Further, the hybrid coatings can provide high-efficiency fire warning response under complicated conditions, e.g. flame detection response time of only ~2.0 s and excellent fire early warning time in pre-combustion (e.g. 11.2 s at 300 °C). Therefore, this work provides new perspectives to design and develop multi-functional coatings for fire safety and prevention applications.

Stable metal-organic frameworks with low water affinity built from methyl-siloxane linkers.

A tetracarboxylic acid with a methyl-substituted siloxane core (L-H4) has been prepared and applied in the construction of water stable MOFs with low water affinity. L-H4 itself crystallizes as an interpenetrated 3D hydrogen-bonded network. Reaction of L-H4 with ZrIV/HfIV gave IMP-32-Zr/Hf - both 3D MOFs of scu topology.

Trace CO2 capture by an ultramicroporous physisorbent with low water affinity.

CO2 accumulation in confined spaces represents an increasing environmental and health problem. Trace CO2 capture remains an unmet challenge because human health risks can occur at 1000 parts per million (ppm), a level that challenges current generations of chemisorbents (high energy footprint and slow kinetics) and physisorbents (poor selectivity for CO2, especially versus water vapor, and/or poor hydrolytic stability). Here, dynamic breakthrough gas experiments conducted upon the ultramicroporous material SIFSIX-18-Ni-β reveal trace (1000 to 10,000 ppm) CO2 removal from humid air. We attribute the performance of SIFSIX-18-Ni-β to two factors that are usually mutually exclusive: a new type of strong CO2 binding site and hydrophobicity similar to ZIF-8. SIFSIX-18-Ni-β also offers fast sorption kinetics to enable selective capture of CO2 over both N2 (S CN) and H2O (S CW), making it prototypal for a previously unknown class of physisorbents that exhibit effective trace CO2 capture under both dry and humid conditions.

Heat and pH stable curcumin-based hydrophilic colorants obtained by the solid dispersion technology assisted by spray-drying

Natural food colorants are on demand due to food safety concerns related with some synthetic counterparts. Health-friendly alternatives can be available from plant sources, which include curcumin extracted from Curcuma longa L. However, its industrial use is difficult to achieve due to the low water affinity, pH and thermal instability, which is particularly challenging, e.g. for baked foods. In this work, the solid dispersion technique followed by spray-drying, an emergent approach in the context of colorants, was applied to curcumin using k-carrageenan, poly(vinyl alcohol) and polyvinylpyrrolidone, as the encapsulant materials. An orthogonal central composite design with dummy-variables was applied, and principal component analysis (PCA) and hierarchical cluster analysis (HCA) carried out to identify the experimental conditions leading to the most effective formulations. In general, particles with a wide range of pH and heat stability have been produced depending on the chosen encapsulant material, used formulation (curcumin, surfactant and polymer contents), and synthesis conditions (pH). Moreover, the used mathematical approach showed to be a valuable tool to support the development of tailor-made formulations directed to specific applications where pH and temperature are relevant processing parameters.

A molecular-scale study on the hydration of sulfuric acid-amide complexes and the atmospheric implication

Amides are ubiquitous in atmosphere. However, the role of amides in new particle formation (NPF) is poorly understood. Herein, the interaction of urea and formamide with sulfuric acid (SA) and up to four water (W) molecules has been studied at the M06-2X/6-311++G(3df,3pd) level of theory. The structures and properties of (Formamide)(SA)(W)n (n = 0–4) and (Urea)(SA)(W)n (n = 0–4) clusters were investigated. Results show that the interaction of SA with the CO group of amides plays a more important role in amide clusters compared with the NH2 group. Proton transfer to water molecule become dominant in highly hydrated amide clusters at lower temperatures. There is no proton transfer to CO group in formamide clusters. The Rayleigh light scattering intensities of amide clusters are comparable to that of amine and oxalic acid clusters reported previously. Moreover, unhydrated (Amide)(SA) clusters have similar or even higher ability than hydrated SA clusters to participate in ion-induced nucleation. In comparison with formamide, urea has more interacting sites and its clusters have higher Rayleigh light scattering intensities, larger dipole moment, stronger interaction with SA and lower water affinity. The intermolecular interaction in (Formamide)(SA) is slightly weaker than that of SA dimer, which may be compensated by the high concentration of formamide, thus enabling formamide to participate in initial steps of NPF. This study may bring new insight into the role of amides in initial steps of NPF from molecular scale and could help better understand the properties of amide-containing organic aerosol.

Fabrication of robust and scalable superhydrophobic surfaces and investigation of their anti-icing properties

Superhydrophobic surface (SHS) has attracted tremendous scientific interests in anti/de-icing due to its extremely low water affinity. However, poor durability and scalability have greatly hindered its applications; besides, study of the ice adhesion on SHS is not sufficient. Here, robust SHS with various surface structures and chemical components were obtained via a facile process: a suspension containing ultra-high molecular weight polyethylene (UHMWPE) and multi-scale silica nanoparticles (SNs) was poured on steel substrate and followed with desiccation. The surface could withstand severe abrasion without losing superhydrophobicity, and showed possibility to be scaled up. The ice adhesion tests showed that: 1) the surface structures played more important role in reducing ice adhesion than the surface chemical components; 2) the ice adhesion tended to be minimized on the SHS with multi-scale nanoparticles. The low ice adhesion could be ascribed to the following two aspects: the air pockets that greatly reduced the contact between ice and the resultant surface, and the lubrication of overcooled water in the surface asperities.

Selective Etching of Nitrogen‐Doped Carbon by Steam for Enhanced Electrochemical CO2 Reduction

AbstractNitrogen‐doped carbon structures have recently been demonstrated as a promising candidate for electrocatalytic CO2 reduction, while in the meantime the pyridinic and graphitic nitrogen atoms also present high activities for electroreduction of water. Here, an etching strategy that uses hot water steam to preferentially bind to pyridinic and graphitic nitrogen atoms and subsequently etch them in carbon frameworks is reported. As a result, pyrrolic nitrogen atoms with low water affinity are retained after the steam etching, with a much increased level of among all nitrogen species from 22.1 to 55.9%. The steam‐etched nitrogen‐doped carbon catalyst enables excellent electrocatalytic CO2 reduction performance but low hydrogen evolution reaction activity, suggesting a new approach for tuning electrocatalyst activity.