Adsorption of Nitrogen Dioxide on Nitrogen-Enriched Activated Carbons.

The aim of this study was to obtain nitrogen-enriched activated carbons from orthocoking coal. The initial material was subjected to a demineralisation process. The demineralised precursor was pyrolysed at 500 °C and then activated with sodium hydroxide at 800 °C. Activated carbon adsorbents were subjected to the process of ammoxidation using a mixture of ammonia and air at two different temperature variants (300 and 350 °C). Nitrogen introduction was carried out on stages of demineralised precursor, pyrolysis product, and oxidising activator. The elemental composition, acid-base properties, and textural parameters of the obtained carbon adsorbents were determined. The activated carbons were investigated for their ability to remove nitrogen dioxide. The results demonstrated that the ammoxidation process incorporates new nitrogen-based functional groups into the activated carbon structure. Simultaneously, the ammoxidation process modified the acid-base characteristics of the surface and negatively affected the textural parameters of the resulting adsorbents. Furthermore, the study showed that all of the obtained carbon adsorbents exhibited a distinct microporous texture. Adsorption tests were carried out against NO2 and showed that the carbon adsorbents obtained were highly effective in removing this gaseous pollutant. The best sorption capacity towards NO2 was 23.5 mg/g under dry conditions and 75.0 mg/g under wet conditions.

A {Ni12 }-Wheel-Based Metal-Organic Framework for Coordinative Binding of Sulphur Dioxide and Nitrogen Dioxide.

Air pollution by SO2 and NO2 has caused significant risks on the environment and human health. Understanding the mechanism of active sites within capture materials is of fundamental importance to the development of new clean-up technologies. Here we report the crystallographic observation of reversible coordinative binding of SO2 and NO2 on open NiII sites in a metal-organic framework (NKU-100) incorporating unprecedented {Ni12 }-wheels; each wheel exhibits six open NiII sites on desolvation. Immobilised gas molecules are further stabilised by cooperative host-guest interactions comprised of hydrogen bonds, π⋅⋅⋅π interactions and dipole interactions. At 298 K and 1.0 bar, NKU-100 shows adsorption uptakes of 6.21 and 5.80 mmol g-1 for SO2 and NO2 , respectively. Dynamic breakthrough experiments have confirmed the selective retention of SO2 and NO2 at low concentrations under dry conditions. This work will inspire the future design of efficient sorbents for the capture of SO2 and NO2 .

Transition-Metal-Containing Porphyrin Metal-Organic Frameworks as π-Backbonding Adsorbents for NO2 Removal.

Mitigating ambient nitrogen dioxide (NO2 ) pollution via selective adsorption on porous materials is a promising approach to tackle such an increasingly pressing environmental health issue. However, very few porous adsorbents have sufficiently high NO2 adsorption capacity and good regenerability simultaneously. Here we attempt to address this challenge by developing π-backbonding adsorbents in the transition metal (TM) incorporated porphyrin metal-organic frameworks (PMOFs). Breakthrough experiments show that PMOFs with inserted TMs achieve appreciable NO2 capacity and good regenerability. Combined in situ DRIFTS, synchrotron powder XRD, and DFT calculations reveal the adsorption mechanism: NO2 partially transforms to N2 O4 and interacts with transition metal via π-backbonding and Al-node via hydrogen bonding. This work affords new insights for designing next-generation adsorbents for ambient NO2 removal and presents PMOFs as a platform to tailor π-backbonding adsorbents.

Production of new activated bio-carbons by chemical activation of residue left after supercritical extraction of hops.

A technology of activated bio-carbons production from the residue left after supercritical extraction of hops is described. The effect of the variant of chemical activation and impregnation ratio on the physicochemical properties as well as sorption capacity towards toxic gas of acidic character (nitrogen dioxide), basic organic dye (aqueous solution of methylene blue - MB) and iodine was investigated. The materials obtained were activated bio-carbons of well-developed surface area ranging between 897 and 1095m2/g, showing clearly acidic character of the surface. The sorption tests results proved that chemical activation of the residue left after supercritical extraction of hops allows obtaining activated bio-carbons with very high sorption capacity towards nitrogen dioxide, reaching to 77.2 and 155.3mg/g in dry and wet conditions, respectively. The maximum sorption capacity of the adsorbents towards methylene blue was 328.75mg/g, while towards iodine 1815mg/g. The equilibrium data for aqueous solution of MB were analyzed by the Langmuir and Freundlich models, whereas the kinetics of the adsorption process was studied using pseudo-first and second-order models. According to the obtained data, the adsorption of MB from aqueous solution is better described by Langmuir model and pseudo-second order kinetic model.

Analysis of a Cu-Doped Metal-Organic Framework, MFM-520(Zn1-x Cux ), for NO2 Adsorption.

MFM-520(Zn) confines dimers of NO2 with a high adsorption of 4.52 mmol g-1 at 1 bar at 298 K. The synthesis and the incommensurate structure of Cu-doped MFM-520(Zn) are reported. The introduction of paramagnetic Cu2+ sites allows investigation of the electronic and geometric structure of metal site by in situ electron paramagnetic resonance (EPR) spectroscopy upon adsorption of NO2 . By combining continuous wave and electron-nuclear double resonance spectroscopy, an unusual reverse Berry distorted coordination geometry of the Cu2+ centers is observed. Interestingly, Cu-doped MFM-520(Zn0.95 Cu0.05 ) shows enhanced adsorption of NO2 of 5.02 mmol g-1 at 1 bar at 298 K. Whereas MFM-520(Zn) confines adsorbed NO2 as N2 O4 , the presence of monomeric NO2 at low temperature suggests that doping with Cu2+ centers into the framework plays an important role in tuning the dimerization of NO2 molecules in the pore via the formation of specific host-guest interactions.

Physics and chemistry of nitrogen dioxide (NO2) adsorption on gallium nitride (GaN) surface and its interaction with the yellow-luminescence-associated surface state.

Surface states have been a longstanding and sometimes underestimated problem in gallium nitride (GaN) based devices. The instability caused by surface-charge-trapping in GaN-based transistors is practically the same problem faced by the inventors of the silicon (Si) field effect transistors more than half a century ago. Although in Si this problem was eventually solved by oxygen and hydrogen-based passivation, in GaN, such breakthrough has yet to be made. Apparently, some of this surface charge originates in molecules adsorbed on its surface. Here, it is shown that the charge density associated with the GaN yellow band desorbs upon mild heat treatment in vacuum and re-adsorbs on exposure to the air. Selective exposure of GaN to nitrogen dioxide (NO2) reproduces this surface charge to its original distribution, as does exposure to air. Residual gas analysis of the gases desorbed during heat treatment shows a large concentration of nitric oxide (NO). These observations suggest that selective adsorption of NO2 is responsible for the surface charge that deleteriously affects the electrical properties of GaN. The physics and chemistry of this NO2 adsorption, reported here, may open a new path in the search for passivation to improve GaN device reliability.

Activation of Waste Materials with Carbon(IV) Oxide as an Effective Method of Obtaining Biochars of Attractive Sorption Properties towards Liquid and Gas Pollutants.

Biochars that are the subjects of this report have been obtained from the residue of supercritical extraction of common nettle seeds with CO2. The residue was subjected to direct activation with carbon(IV) oxide as an activator. The obtained biochars were found to have a specific surface area inthe range of 888-1024 m2/g and a basic surface. They were used for the adsorption of a liquid organic pollutant (methylene blue) and a gas inorganic pollutant (NO2). As follows from the test results, the biochars were able to adsorb 150-239 mg of the dye. The Langmuir model was found to better describe the adsorption experimental data, while the kinetics of the process was better described by the pseudo-second-order model. From the thermodynamic analysis, it was inferred that the adsorption of methylene blue from a water solution was an endothermic and spontaneous reaction. It was established that elevated temperature of activation and the presence of air stream during adsorption had a positive impact on the adsorption of NO2 by the biochars studied. The greatest sorption capacity of the biochars towards NO2 was 59.1 mg/g.

Revealing a Highly Sensitive Sub-ppb-Level NO2 Gas-Sensing Capability of Novel Architecture 2D/0D MoS2/SnS Heterostructures with DFT Interpretation.

In this work, we use a chemical method to design novel 2D-material/0D-quantum dot (MoS2/SnS) heterostructures. Furthermore, the unique 2D/0D heterostructure enhanced the NO2 gas-sensing capability 3 times and increased the sensing recoverability by more than 90%. Advanced characterization tools such as SEM, TEM, XRD, and AFM confirm the formation of MoS2/SnS heterojunction nanomaterials. Using AFM data, the average thickness of the MoS2 layer was found to be 5 nm. The highest sensor response of 0.33 with good repeatability was observed at 250 ppb of NO2. Sensing characterization reveals the ultra-fast response time, that is, 74 s, at 50 ppb of NO2. The limit of detection for detecting NO2 was also found to be very low, that is, 0.54 ppb, by using MoS2/SnS heterostructures. The theoretical calculations based on density functional theory well corroborated and quantified the intermolecular interaction and gas adsorption on the surface of MoS2/SnS.

Porous Ceramics Adsorbents Based on Glass Fiber-Reinforced Plastics for NOx and SOx Removal.

To reuse waste glass fiber-reinforced plastics (GFRPs), porous ceramics (i.e., GFRP/clay ceramics) were produced by mixing crushed GFRP with clay followed by firing the resulting mixture under different conditions. The possibility of using ceramics fired under a reducing atmosphere as adsorbent materials to remove NOx and SOx from combustion gases of fossil fuels was investigated because of the high porosity, specific surface area, and contents of glass fibers and plastic carbides of the ceramics. NO2 and SO2 adsorption tests were conducted on several types of GFRP/clay ceramic samples, and the gas concentration reduction rates were compared to those of a clay ceramic and a volcanic pumice with high NO2 adsorption. In addition, to clarify the primary factor affecting gas adsorption, adsorption tests were conducted on the glass fibers in the GFRP and GFRP carbides. The reductively fired GFRP/clay ceramics exhibited high adsorption performance for both NO2 and SO2. The primary factor affecting the NO2 adsorption of the ceramics was the plastic carbide content in the clay structure, while that affecting the SO2 adsorption of the ceramics was the glass fiber content.

Surface acid etching for efficient anchoring of potassium on 3DOM La0.8Sr0.2MnO3 catalyst: An integration strategy for boosting soot and NOx simultaneous elimination.

The emission of soot and NOx is one of the most severe environmental issues, and the key factor is the development of catalysts in after-treatment systems. In this study, an innovative non-noble metal catalyst, named HKLSM, was fabricated by etching 3DOM La0.8Sr0.2MnO3 with citric acid and synchronously anchoring potassium salt, for soot and NOx simultaneous removal. The citric acid could not only slightly erode the 3DOM skeleton, thereby beneficial to the dispersion of potassium, but also react with high-valence state Mn to generate abundant coordination unsaturated Mn3+ sites, which could produce more active oxygen species. Moreover, HKLSM showed a higher NOx adsorption capability than the samples that were not subjected to acid etching. This adsorbed NOx could be stored as NO3- species, which could facilitate soot combustion. Among all the as-prepared catalysts, HKLSM demonstrated a competitive soot combustion activity with a T50 value of 368 °C, a TOF value of 3.24 × 10-4 s-1, a reaction rate of 1.87 × 10-7 molg-1s-1, a total NOx to N2 yield of 42.0% and favorable reusability and water-resistance. This integration strategy can rationalize an alternative protocol to soot and NOx simultaneous elimination or even other catalysis systems.

The low-temperature NO2 removal by tailoring metal node in porphyrin-based metal-organic frameworks.

Nitrogen dioxide (NO2) is the most toxic and prevalent form of nitrogen oxides (NOx) pollutant and its removal from ambient air is a pressing challenge. The state-of-the-art deNOx technologies such as selective catalytic reduction (SCR) can only work at elevated temperatures (>250-300 °C), but ineffective for the NOx removal under ambient conditions. The adsorptive removal of NO2 is an alternative approach to SCR, whose success depends on the design of stable adsorbents capable of selectively capturing NO2 with a highly reversible capacity. Here we synthesized and developed five porphyrin-based metal-organic frameworks (PMOFs) as robust ambient NO2 adsorbents, including three aluminum-based (Al-PMOF) isostructures, and two zirconium-based (Zr-PMOFs) isostructures. Of them, Al-PMOF stands out to be the most promising candidate by showing the highest NO2 adsorption capacity (1.85 mmol/g), high stability, and good regenerability (retaining 87% capacity after five cycles of adsorption) at dry conditions. The NO2 adsorption capacity of Al-PMOF was approximately doubled (3.61 mmol/g) at wet conditions. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed the NO2 adsorption mechanism - the hydrogen bonding occurs between bridging hydroxyl (-OH) (attached to the metal node) and NO2 molecules. Our work demonstrates that PMOFs are promising NO2 adsorbents and will provide guidance for designing robust and reusable adsorbents for efficiently removing NO2 at ambient temperature.

Factors Influencing NO2 Adsorption/Reduction on Microporous Activated Carbon: Porosity vs. Surface Chemistry.

The textural properties and surface chemistry of different activated carbons, prepared by the chemical activation of olive stones, have been investigated in order to gain insight on the NO2 adsorption mechanism. The parent chemical activated carbon was prepared by the impregnation of olive stones in phosphoric acid followed by thermal carbonization. Then, the textural properties and surface chemistry were modified by chemical treatments including nitric acid, sodium hydroxide and/or a thermal treatment at 900 °C. The main properties of the parent and modified activated carbons were analyzed by N2-adsorption, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to enlighten the modifications issued from the chemical and thermal treatments. The NO2 adsorption capacities of the different activated carbons were measured in fixed bed experiments under 500 ppmv NO2 concentrations at room temperature. Temperature programmed desorption (TPD) was applied after adsorption tests in order to quantify the amount of the physisorbed and chemisorbed NO2. The obtained results showed that the development of microporosity, the presence of oxygen-free sites, and the presence of basic surface groups are key factors for the efficient adsorption of NO2.