Low Impurity Levels Research Articles

Luminescence and Faraday rotation properties of Tb2O3 and Tb:Y2O3 single crystals

Heavily-doped and fully concentrated 2.78% Tb:Y2O3 and Tb2O3 single crystals with high optical quality and very low levels of impurities have been grown and studied for their luminescence and Faraday rotation properties. Absorption, emission and fluorescence decay measurements performed vs excitation wavelength and temperature and their confrontation with Judd-Ofelt and crystal-field calculations show the contributions of two types of luminescent centers: dominant ones with a 5D4 emission lifetime of 23 μs corresponding to coupled near-neighbor Tb3+ ions, all in C2 symmetry sites, and minority ones with a 5D4 emission lifetime of about 2 ms corresponding to coupled Tb3+ ions in C2 and C3i near-neighbor symmetry sites. Faraday rotation measurements confirm Tb2O3 as the Tb-based Faraday crystalline material with the largest ever measured Verdet constant, at all temperatures and from the visible to the near-infrared. They also show that the dominant luminescent centers contribute more particularly to this large Verdet constant thanks to a favorable crystal-field splitting of their 7F6 ground multiplet and also to the contributions of both types of spin-allowed and spin-forbidden 4f-5d absorption bands.

A new approach for extracellular RNA recovery from Rhodovulum sulfidophilum

The development of RNA-based drugs is highly pursued due to the possibility of creating viable and effective therapies. However, their translation to clinical practice strongly depends on efficient technologies to produce substantial levels of these biomolecules, with high purity and high quality. RNAs are commonly produced by chemical or enzymatic methods, displaying these limitations. In this sense, recombinant production arises as a promising, cost-effective method, allowing large-scale production of RNA. Rhodovulum sulfidophilum (R. sulfidophilum), a marine purple bacterium, offers the advantage of RNA secretion into the extracellular medium, which contains low levels of RNases and other impurities. Therefore, RNA recovery can be simplified compared to standard extraction protocols involving cell lysis, resulting in a more clarified sample and an improved downstream process. In this work, R. sulfidophilum was transformed with a plasmid DNA encoding pre-miR-29b-1, which is known to be involved in the Alzheimer's disease pathway. After production, the pre-miR-29b-1 was recovered through different extraction methods to verify the most advantageous one. A protocol for extracellular RNA recovery was then established, revealing to be a simpler and less time-consuming method, reducing around 16 h in execution time and the quantity of reagents needed when compared to other established methods. The new strategy brings the additional advantage of eliminating the toxic organic compounds routinely used in intracellular RNA extractions. Overall, the optimized process described here, using isopropanol as the precipitation agent, offers a greener, safer, and faster alternative for recombinant RNA recovery and concentration, with an extracellular RNA recovery of 7 μg/mL and target pre-miRNA-29b-1 recovery of 0.7 μg/L of medium.

Structure-optical properties of CdO glass matrix with low levels of cobalt impurities

The impacted role of cadmium oxide (CdO) on the structure-optical properties of current borate glasses with low cobalt oxide impurities was studied. The study was performed on a glass system of the formula [x CdO – (80-x) B2O3 – 0.4 CoO – 19.6 Na2O]; x = 0, 6, 12, 18 and 24 mol%, and produced by melt quenching method. Structure and optical absorption spectroscopy were done to explore the electronic transitions of Co cations inside the glass matrix. The obtained data indicated that structure and optical properties were significantly changed following CdO additives. Bands of optical absorption within both visible and near-infrared ranges showed signatures from Co2+ cations in the tetrahedral and octahedral sites, while Co3+ cations in the octahedral sites within the glass network. Optical absorption also changed significantly for the CdO-doped glasses which exhibited red shifts in visible absorption bands and blue shifts in the NIR absorption bands. The obtained absorption bands in both visible and NIR were employed to obtain the crystal field splitting parameter (Δt) showing augmented records from 3364 cm−1 to 3377 cm−1 with more CdO addition. The Tauc gap energy values were then attained showing decreased values from 3.50 to 3.27 eV when further CdO is added. Further, the impacted role of CdO addition on the nonlinearity optical properties of the present glasses was finally estimated. Potential increases in the linear and nonlinear optical are discussed based on polarizability and basicity increments inside the glass matrix.

Tin Lodide Thin Films Growth via Plasma Enhanced Chemical Vapor Deposition and its Optimization Using V–I Probe Impedance Analyser for Optoelectronic Applications

AbstractTin(ii) iodide (SnI2) faces significant challenges in photodetector applications, primarily due to its sensitivity to moisture and degradation over time. Achieving uniform, high‐quality films with low impurity and defect levels is also a challenge. Potential solutions include advanced deposition techniques to improve film quality and stability, surface passivation and encapsulation, doping and alloying. In this study, SnI2 thin films have been deposited for the first time using plasma enhanced chemical vapour deposition (PECVD) technique to the best of our knowledge. Process parameters like deposition pressure and RF‐power have been optimised via non‐intrusive in‐situ V−I probe impedance analyser. SnI2 thin films have been deposited on glass & transparent conducting oxide (TCO) and p‐Si wafer at various RF‐power to make SnI2/p‐Si heterojunction followed by metallization to make Ag/SnI2/p‐Si/Ag heterojunction photodetector. Characterization techniques like thin film thickness measurement, UV‐Vis‐NIR spectroscopy, Photoluminescence spectroscopy, glancing incidence x‐ray diffraction (GIXRD), SEM and I−V measurements were carried out to study its optical, structural and electronic properties. Fabricated devices, Ag/SnI2/p‐Si/Ag heterojunction photodiode exhibits best critical performance for the film deposited at 150 W having rectifying ratio of 6.9×104 at 1.0 V and photo‐sensitivity of 1.6×104 at 100 mW/cm2 light intensity.

Coal and Coal By-Products as Unconventional Lithium Sources: A Review of Occurrence Modes and Hydrometallurgical Strategies for Metal Recovery

Lithium, a critical material for the global development of green energy sources, is anomalously enriched in some coal deposits and coal by-products to levels that may be considered economically viable. Recovering lithium from coal, particularly from coal gangue or coal ashes, offers a promising alternative for extracting this element. This process could potentially lead to economic gains and positive environmental impacts by more efficiently utilizing coal-based waste materials. This review focuses on lithium concentrations in coal and coal by-products, modes of lithium occurrence, methods used to identify lithium-enriched phases, and currently available hydrometallurgical recovery methods, correlated with pretreatment procedures that enable lithium release from inert aluminosilicate minerals. Leaching of raw coal appears inefficient, whereas coal gangue and fly ash are more feasible due to their simpler composition and higher lithium contents. Lithium extraction can achieve recovery rates of over 90%, but low lithium concentrations and high impurity levels in the leachates require advanced selective separation techniques. Bottom ash has not yet been evaluated for lithium recovery, despite its higher lithium content compared to feed coal.

Nanocrystalline copper for direct copper-to-copper bonding with improved cross-interface formation at low thermal budget

Direct copper-to-copper (Cu-Cu) bonding is a promising technology for advanced electronic packaging. Nanocrystalline (NC) Cu receives increasing attention due to its unique ability to promote grain growth across the bonding interface. However, achieving sufficient grain growth still requires a high thermal budget. This study explores how reducing grain size and controlling impurity concentration in NC Cu leads to substantial grain growth at low temperatures. The fabricated NC Cu has a uniform nanograin size of around 50 nm and a low impurity level of 300 ppm. To prevent ungrown NC and void formation caused by impurity aggregation, we propose a double-layer (DL) structure comprising a normal coarse-grained (CG) layer underneath the NC layer. The CG layer, with a grain size of 1 μm and an impurity level of 3 ppm, acts as a sink, facilitating impurity diffusion from the NC layer to the CG layer. Thanks to sufficient grain growth throughout the entire NC layer, cross-interface Cu-Cu bonding becomes possible under a low thermal budget, either at 100 °C for 60 min or at 200 °C for only 5 min.

Assessment of adeno-associated virus purity by capillary electrophoresis-based western

A rigorous analytical assessment of recombinant adeno-associated virus (rAAV)-based drug products is critical for their successful development as clinical candidates. It is especially important to ascertain high purity while simultaneously ensuring low levels of impurities in the final drug product. One approach to evaluate the purity of rAAV drug products is to determine the relative stoichiometry of the three viral proteins (VPs) that comprise an rAAV capsid, and the levels of impurities in the final drug product. Here we present two capillary electrophoresis-western (CE-western) assays for quantifying (1) the relative stoichiometry of VP using the anti-AAV B1 antibody, and (2) residual levels of a baculovirus protein impurity, GP64, using the anti-GP64 antibody. In each assay, various purified samples from diverse AAV serotypes were analyzed to determine their VP ratio or GP64 levels. The ratio of VP3/VP1 in rAAV samples was correlated with biological activity, and the clearance of GP64 from the manufacturing process was demonstrated. The results obtained from both assays were further supported by liquid chromatography-mass spectrometry analyses. Overall, we report that CE-western is a high-throughput platform that utilizes low sample volumes for a rapid, sensitive, and robust assessment of the identity, composition, and purity of rAAV drug products.

CONSTRUCTIVE-FUNCTIONAL ANALYSIS AND SIZING OF HYDRAULIC FILTERS

The reliability of hydrostatic installations depends on the low level of impurities in an environment with pressure at an allowable value, which avoids an accentuated wear of the individual elements of the installations. Hydraulic filters are elements that have a role in protecting the hydrostatic installations from the particles that are found in the hydraulic oil. The paper aims to present some of the elements underlying the construction of hydraulic environment filtration equipment, certain conditions that are imposed on them, as well as the main problems related to the calculation and sizing of filters.

Silane functionalized cardanol/calcium carbonate epoxy‐reinforced polymer nanocomposites for sustainable microwave absorption applications

AbstractMicrowave absorption properties of epoxy resin/cardanol (ER/C) and epoxy resin/silane functionalized cardanol (ER/SFC) nanocomposites with various percentages of calcium carbonate nanoplatelets (CCNPs) studied in the frequency range of 8–18 GHz. The CCNPs obtained from the mussel shell were reinforced into a cardanol‐toughened ER matrix to mimic the composite structure of the abalone shell. The phase separation between ER, SFC, and CCNPs encapsulated in a polymer matrix was analyzed with SEM, and the presence of a low level of Fe3O4 magnetic impurities of 0.007 emu/g present as shown and verified by XRD and VSM analyses. The nanocomposites with ER/SFC/CCNPs 3 wt.% demonstrate a high surface roughness of 3.467 nm and an enhanced hydrophobicity, as indicated by a high contact angle of 102°. The silanization‐induced localization of CCNPs facilitates a mutually conducive morphology for excellent viscoelastic and microwave absorption properties. The increase in damping factor ratio of approximately 0.85 augments the microwave absorption property and it observed that ER/SFC/CCNPs 3 wt.% nanocomposites show higher reflection loss (RL) of more than 99.9% with RL of −43 dB at 12 GHz. The research aims to fabricate cost‐effective and multifunctional nanocomposites for microwave absorption applications.Highlights Excellent hydrophobicity owing to the surface roughness of 3.467 nm. Maximum contact angle of 102.1° due to the reinforcement of CCNPs and SFC to the epoxy matrix. Efficient microwave attenuation due to the reflection loss of −43 dB. Excellent microwave absorption of 99.99% with a damping factor of 0.85. Higher storage modulus due to the strong inter‐penetrating network of the composite.

Characterization of Sapropterin Dihydrochloride Tablet

Characterization of Kuvan tablets involved thorough analysis of physical, chemical, and dissolution properties. Formulation development encompassed pre-formulation studies, feasibility trials, and process optimization. Kuvan tablets demonstrated variability in sapropterin dihydrochloride concentration but rapid dissolution across different media. Consistent mechanical strength, low impurity levels, and appropriate pH values were observed, ensuring efficacy, safety, and reliability. Keywords: Sapropterin dihydrochloride, Hyperphenylalaninemia, Kuvan tablets

Gelation and large thermoresponse of cranberry-based xyloglucan

Cranberry waste contains potentially valuable components, such as proanthocyanidins, flavanols, and xyloglucan. Highly-purified xyloglucan (XG) from cranberries were studied through steady and oscillatory shear rheology at various concentrations and temperatures. At room temperature, an apparent yield stress is observed and the storage modulus exceeds the loss modulus (G′>G′′) for concentrations of 0.5 wt% and higher, indicating that the XG solution has formed a physical hydrogel. Thermoresponsive gelation is observed with a five-order of magnitude increase in shear moduli as it undergoes a weak to strong gel transition around 52 °C. The gelation time was 5 min with an observed storage moduli up to 3500 Pa. Cranberry-based XG exhibits thermoresponsive behavior at concentrations as low as 0.1 wt% (w/v), which is significantly lower than prior gelation studies of XG from other sources. The formation of a weak gel at room temperature and large storage moduli observed at room temperature is likely associated with the low level of impurities and small amount of galactose present in the XG chains.

Characteristics and Quality of Oleoresin Based On Different Stimulant Treatments

AbstractThe quality of oleoresin determines the sale value of exports and imports. The quality of pine resin is determined by its color, moisture content, and impurities. The research method used a T-tes Independent to compare organic stimulants and sulfuric acid stimulants in tapping pine resin and referred to SNI 7837: 2016 to determine the quality of oleoresin. The results showed that trees treated with organic stimulants produced bright white oleoresin compared to trees treated with sulfuric acid stimulants which produced cloudy white oleoresin. However, both of them produce low levels of impurities and moisture content <5% so it is included in the super-premium quality class.

Rancang Bangun Vertical Clarifier Tank Mini dengan Adjusment Variasi Kedalaman Pipa Inlet untuk Melihat Pengaruh Tingkat Kadar Kotoran pada Minyak Overflow Crude Palm Oil

Vertical Clarifier Tank (VCT) has a very crucial role to separate oil, water and sludge by gravity, where oil with a smaller specific gravity of 0.8 grams / cm3 will be in the uppermost layer, while water whose specific gravity is 1 gram / cm3 will be in the middle layer, and sludge with a density of 1.3 grams / cm3 from the Vertical Clarifier Tank (VCT). The experimental design of this study was to determine the appropriate depth of the inlet pipe to obtain low levels of impurities during oil extraction. The results of the study obtained from variations in the depth of 25 cm, 40 cm, 55 cm, and 70 cm inlet pipes used as the inflow of crude oil from Crude Palm Oil with variations in sedimentation time of 100 minutes, 120 minutes, 140 minutes, 160 minutes, 180 minutes, and 200 minutes, obtained the least level of impurities in the Inlet Pipe which has a length of 55 cm with a variable sedimentation time of 200 minutes.

Impurity reduction in lightly doped n-type gallium nitride layer grown via halogen-free vapor-phase epitaxy

The development of gallium nitride (GaN) vertical-type metal-oxide-semiconductor field-effect transistors and p–i–n diode devices has gathered increasing attention. These devices require an n-type drift layer with a low doping level of 1016 cm−3 or less, minimized point defects inhibiting electron conduction, and a layer approximately 10 μm thick. Therefore, a practical method with a growth rate of at least several tens of μm/h and impurity concentrations of less than 1015 cm−3, except for that of dopants, is necessary. Halogen-free vapor-phase epitaxy (HF-VPE) has a high growth rate suitable for fabricating thick drift layers and utilizes a simple reaction between Ga vapor and ammonia gas (without a corrosive halogen gas), resulting in lower impurity levels. Herein, we eliminated the quartz content from the high-temperature zone to reduce the excess unintentional Si doping and identified that the nitrile gloves used for the growth preparation are other impurity contamination sources. We obtained a lightly n-type ([Si]=∼1016 cm−3) GaN layer, in which C, O, B, Fe, Mg, Al, Ca, Cr, Zn, Ni, Mn, and Ti impurity contents were below the detection limits of secondary ion mass spectrometry. Deep-level transient spectroscopy revealed that electron traps at EC − 0.26 and at EC − 0.59 eV were 2.7 × 1013 and 5.2 × 1014 cm−3, respectively. Moreover, the Hall effect analysis showed the acceptor-type defect-compensating donor content as approximately 2.7 × 1015 cm−3, resulting in a high electron mobility of HF-VPE GaN in the 30–710 K temperature range. Furthermore, we identified the Ca impurity as a deep acceptor, another killer defect leading to mobility collapse.

(Invited) Gallium Nitride for Vertical Power Devices: Improving Morphology and Unintentional Impurities for Better Devices

While GaN has been researched for many years as a material for light emitting diodes, lasers, high electron mobility transistors, and other devices, further improvements to material purity are still needed to realize the full potential of this material for vertical device applications. To achieve high quality, high purity GaN for power devices, our research employs ammonia-assisted molecular beam epitaxy (NH3-MBE) and plasma-assisted molecular beam epitaxy (PA-MBE). Past studies of fast growth rates (more than 1 μm/hr) and ultra-low impurity incorporation revealed that both PAMBE and NH3-MBE can achieve low net doping levels, and NH3-MBE as low as 1x1015 cm-3.1 However, This work also indicated that impurity incorporation increased with increasing growth rate.Recent research efforts have focused on further improvements to morphology and unintentional dopants in NH3-MBE-grown homoepitaxial layers with fast growth rates. By optimizing growth conditions for faster growth rates and using indium as a surfactant, devices with drift layers up to 10 μm thick were grown. These layers exhibited smooth surface morphology as seen in AFM scans with RMS surface roughness as low as 0.21 nm for a 2x2 μm2 scan area.2 Adding the In surfactant also led to reduced incorporation of unintentional Si impurities in UID films as shown by SIMS depth profiles for GaN films grown with and without In. The extremely low impurity levels were further confirmed by CV measurements which indicated that the net doping density in the UID GaN layers decreased from 2x1016 cm-3 to 5x1015 cm-3 with the addition of the In surfactant.2 Based on these UID levels and the theoretical critical electric field of GaN (3 MV/cm), drift layers up to 29.5 μm and 7.4 μm can be depleted with a triangular electric field profile for net donor concentrations of 5x1015 cm-3 and 2x1016 cm-3, respectively. Devices with the same net concentrations with drift regions 3 μm thick can hold voltages of 854 V and 717 V, respectively.Based on the previously described studies of low-impurity GaN at different growth rates, we developed vertical p-n GaN power devices grown by NH3 MBE.3 These p-n diodes contained a 0.25 µm n+ region, 4 µm n- region with 3x1015 cm-3 unintentional carriers, 0.4 µm p+ region and 10nm p++ capping layer to improve the ohmic anode contact. The circular diodes were fabricated with Pd/Pt anode contacts and Ti/Au cathode contacts. Device diameters were between 80 and 100 µm. The devices featured a 15 µm field plate made from Ti/Au contacts on top of an Al2O3/Si3N4 dielectric stack.The diodes exhibited outstanding forward J-V behavior with a low specific on-resistance (Ron,sp) of 0.28 mΩ-cm2 and a minimum ideality factor of 1.36, which are among the best achieved among similar homoepitaxial GaN p-n diodes.3-5 The best diodes also exhibited a breakdown voltage of > 1 kV (equipment limit 1 kV). The reverse-voltage properties indicate that punch-through was achieved with a peak electric field (EC) >2.6 MV/cm, as confirmed by Silvaco simulations (Fig. 7). The combination of >1 kV breakdown voltage and on-resistance of 0.28 mΩ-cm2 represents one of the best performances of the p-n GaN diodes, achieved with a significantly thinner drift layer compared to comparable MOCVD GaN p-n diodes with drift layers more than 8 µm. Work is ongoing to develop NH3-MBE p-n diodes with indium surfactant-assisted drift layer growth which shows promise to further improve the surface morphology, reduce leakage, and enhance breakdown performance of the vertical devices.

Development and implementation of grade 62PP steel production with special requirements for non‑metallic inclusions content

OJSC “BSW – Management Company of Holding “BMC” produces high‑quality steel used in the automotive, railway, and oil and gas industries. The production of these steel grades involves controlling a range of quality parameters for both continuous cast and hot‑rolled steel billets to ensure the required mechanical, technological, and operational properties of the finished products. The steelmaking process aims to obtain high‑quality steel with the desired microstructure – low levels of harmful impurities and non‑metallic inclusions (hereinafter referred to as NV). This article describes the work and results obtained in the development of the technology for producing hot‑rolled grade 62PP steel, using the example of low‑hardenability carbon steel intended for the production of springs used in vehicle suspension.

Perilla-Leaf-Derived Extracellular Vesicles Selectively Inhibit Breast Cancer Cell Proliferation and Invasion.

Breast cancer is a common type of cancer characterized by high mortality rates. However, chemotherapy is not selective and often leads to side-effects. Therefore, there is a need for the development of highly efficient drugs. Recent studies have shown that some extracellular vesicles (EVs) derived from cell cultures possess anti-cancer activity and hold great potential as cancer therapeutics. However, the use of mammalian cell cultures for EV production results in low productivity and high costs. To address this issue, extracellular vesicles derived from perilla leaves (Perex) were isolated and investigated for their anti-cancer activity in various cancer cells. Initially, a high concentration of Perex with a low level of impurities was successfully purified through a combination of ultrafiltration and size-exclusion chromatography. Perex exhibited potent anti-cancer activities, inhibiting the proliferation, migration, and invasion of MDA-MB-231 cancer cells, which have high levels of caveolin-1 compared to other cancer and normal cells. This selective attack on cancer cells with high levels of caveolin-1 reduces unwanted side-effects on normal cells. Considering its high productivity, low production cost, selective anti-cancer activity, and minimal side-effects, Perex represents a promising candidate for the therapeutic treatment of breast cancer.

Optimization of target system for the production of 99Mo via 100Mo(γ,n)99Mo reaction

With an increase of stopping operation of nuclear reactors worldwide, the supply of medical 99Mo becomes difficult and thus many efforts have been made to find an alternative. A process based on an electron linear accelerator (linac) system and a100Mo target via the 100Mo (γ,n)99Mo reaction receives a lot of attention due to the relatively low level of co-produced impurities. This process has been recently developed at the Institute of Modern Physics (IMP) and the Monte Carlo simulation was used to optimize the target system before operating pilot irradiation experiments. First, tungsten and tantalum, as mostly used converter materials, were tested. The yield of 99Mo was evaluated with respect to the converter thickness and the electron beam energy by means of Geant4 simulations. Besides, the specific activity of 99Mo produced from one-stage approach (100Mo target without a converter) and two-stage approach (100Mo target with a converter) was compared when varying the testing conditions. The two-stage approach was selected for the experiment due to the higher specific activity of produced 99Mo at all tested conditions. A target consisting of a 10 mm thickness of the 100Mo tablets and a 2.4 mm thick Ta converter was irradiated for 40 h (50 MeV with 0.2 μA). The Geant4-calculated specific activity of generated 99Mo at the end of bombardment agreed well with the experimental value, which proved high level of accuracy of the Geant4 simulation. In future studies, the Geant4 simulation will be used to optimize the production process when using high power linac system.

Low-temperature synthesis of high-purity TiB2 via carbothermal reduction of metatitanic acid and H3BO3

The purity of TiB2 is unsatisfactory (<97%) even when synthesized at a high reaction temperature (∼1800 °C) using the carbothermal method. In this work, a thermodynamic investigation with an experimental approach was conducted to optimize the reaction parameters to improve TiB2 purity and confirm the carbothermal reaction mechanism utilizing H3BO3, C, and highly-reactive metatitanic acid as raw materials. High-purity TiB2 a with low level of impurities (0.27% C and 0.56% O) was successfully synthesized at 1550 °C for 60 min with carbon black as the optimal reductant at a molar ratio of 1:2.5:5.25 (Ti:B:C). Based on the thermodynamic and experimental results, the TiB2-synthesis mechanism was confirmed to involve TiC as the precursor for TiB2 formation, which then reacted with liquid B2O3 and C to form TiB2. Additionally, the as-synthesized TiB2 powders were spark-plasma sintered to a relative density of 96.5% with fine grains at 1800 °C for 10 min under a pressure of 50 MPa without additives, mainly owing to the lower O content. This study provides a feasible route for large-scale production of high-purity TiB2.

Identifying and clearing individual oxygen impurities on graphene through the use of NO2 as a radical scavenger

We present a novel method to detect and eliminate oxygen adatoms on a graphene basal plane, which can be observed as individual single-electron transfer (SET) events through graphene Hall measurements. The central idea, supported by first-principles calculations, is to use NO2 as a radical scavenger, effectively targeting and removing oxygen impurities on graphene. The reaction between NO2 and the oxygen adatom produces a negatively charged NO3− species and creates a hole carrier in graphene. Subsequently, NO3− reacts with NO2 to form N2O5, accompanied by an electron back-donation to graphene. The thermal decomposition of N2O5 produces neutral NO3, which can accept an electron from graphene and return to the NO3− state. Under conditions of low oxygen impurity levels and NO2 partial pressures, these SET reactions induce intermittent, step-like changes in the graphene's Hall resistivity ρxy at room temperature. Notably, the simulated ρxy patterns during NO2 adsorption closely resemble previously observed patterns [Schedin et al., Nat. Mater. 6 (2007) 652–655], suggesting a connection to the proposed SET reactions for unintentionally introduced oxygen impurities. Furthermore, we find that NO2 also reacts with hydroxyl and peroxide groups on the graphene basal plane, removing them by forming HNO3 and N2O5, respectively. Our findings offer a promising approach to remove oxygen-containing functional groups from graphene, paving the way for obtaining high-quality graphene from reduced graphene oxide.