HNO3 Oxidation Research Articles

Effect of biochar structure on the selective adsorption of heavy components in bio‐oil

AbstractIn this study, biochars with different structures were prepared through HNO3 oxidation and secondary pyrolysis to study the relationship between the structure of biochar and its selectivity for the adsorption of light and heavy aromatics in bio‐oil. The results showed that the adsorption rates of biochar with different structures ranged from 2.90 to 4.00 g bio‐oil per g biochar. The influence of pore structure was dominant, followed by the influence of O‐containing functional groups and the degree of graphitization. The higher the adsorption capacity of biochar for bio‐oil, the smaller the concentrations of the light aromatic model compounds in the absorbed bio‐oil (ABO). Among the five light aromatics, biochar has the best adsorption selectivity for dihydroxybiphenyl and the worst for eugenol and propyl phenol. This is attributed to the diphenyl ring structure of dihydroxybiphenyl, which makes it more susceptible to adsorption, and other light model compounds only have one benzene ring. In summary, biochar demonstrates better adsorption selectivity for heavy aromatics than light aromatics. The more developed the pore structure is, the more enriched O‐containing functional groups are, and the higher the graphitization degree of biochar is, the better the selective adsorption of aromatic compounds in bio‐oil.

Preparation of N and O doped coal tar pitch based porous carbon for supercapacitor electrode

Coal tar pitch (CTP) is mainly composed of a mixture of polycyclic aromatic hydrocarbons, is almost hydrophobic, and has a low heteroatom content, which limits its surface function. During carbonization, it is prone to condensation and difficult to form pore structures, resulting in poor electrochemical performance for carbon electrode materials. Herein, nitrogen (N) and oxygen (O) doped hierarchical porous carbon (C-ANOCTP) was prepared by HNO3 oxidation and KOH activation using CTP as carbon precursor. The oxidation of HNO3 remarkably increases the hydrophilic functional groups containing N and O on the surface of CTP, improves the hydrophilicity of CTP surface, facilitates the activation process of KOH, promotes the development of carbon material pore structure and the generation of active sites, as well as the formation of defect structures. The specific surface area of C-ANOCTP obtained is 1130 m2/g, with O content of 10.29 at% and N content of 2.37 at%. The specific capacitance of C-ANOCTP in a three-electrode system with 6 M KOH electrolyte is as high as 410.51 F/g at 0.5 A/g. A symmetric supercapacitor is assembled in a 6 M KOH electrolyte using C-ANOCTP as electrode. When the power density is 25 W/kg, the energy density is 10.24 Wh/kg. After 10,000 cycles, the capacitance retention rate is still 90.03% and the coulomb efficiency is 100%. The high N and O content of porous carbon is prepared by simple HNO3 oxidation synergistic KOH activation and low temperature carbonization, which shows excellent electrochemical properties in supercapacitors, making CTP an ideal candidate material for high energy density supercapacitors.

Preparation and evaluation of petroleum pitch-based carbon materials with three-dimensional structure containing micron-scale carbon sheets for capacitive deionization anode material

Pitch-based carbon materials have long-term market potential as capacitive deionization (CDI) materials owing to their low cost. In this study, micron-scale carbon sheets with superior electrosorption performance and a large Specific surface area (2400 m2 g−1) was successfully prepared by oxidizing pitch with HNO3 combined with the modification of different crosslinking agents. Characterization results show that HNO3 oxidation promote moderate dissociation of pitch, the addition of a crosslinking agent promote the formation of C-O-C as well as pyrrole nitrogen and improve the degree of disorder of the materials, which are key to forming a micron-scale carbon sheet structure and improved electrosorption capacity. In addition, with a 1 mol L−1 NaCl electrolyte and a scan speed of 2 mv s−1, BTP-3 had a large specific capacitance of 328 F g−1. The desalination absorption capacity was 40.2 mg g−1 (500 mg L−1 NaCl, 1.2 V). The NaNO3 absorption capacity was 30 mg g−1 (500 mg L−1 NaNO3, 1.2 V). Furthermore, DFT calculation results showed that ether bonds and pyrrole nitrogen act as double reaction centers to promote the ability of Cl− to lose electrons.

Effects of oxidation degree of support and phosphorus modification on the catalytic cracking of coal pyrolysis tar by char-supported nickel catalysts

The low rank coal can be converted efficiently when it undergoes the pyrolysis process. The utilization of tar is modified and the problems such as pipeline blockage are solved by cracking and lightning heavy components in tar. In this study, the char-supported nickel (Ni) catalysts were prepared by different Ni loading methods, and the cracking of coal pyrolysis tar was improved by the coal char support with different oxidation degrees. The catalysts prepared by ion exchange method showed better performance for the tar cracking than other methods, which is related to their smaller Ni crystallite size (NCS). The oxidation of H2O2 and HNO3 significantly increased the number of oxygen-containing groups. The intrinsic correlation between oxidation degree of support and catalytic property indicated that the XH2O2-Ni/C (ZD coal pretreated by H2O2) series catalysts had better tar cracking activity than XHNO3-Ni/C (ZD coal pretreated by HNO3) series catalysts, which did not only depend on the increase of Ni loading amounts but also related to the smaller NCS and higher dispersion. Moreover, the non-metallic additive phosphorus (P) was added to modify the catalysts. It was found that the addition of P significantly improved the tar cracking performance of the 30%H2O2 P-Ni/C catalyst. The amounts of active components loaded and NCS contributed to the production of light tar.

Improvement of Carbonyl Groups and Surface Defects in Carbon Nanotubes to Activate Peroxydisulfate for Tetracycline Degradation.

Carbon nanotubes (CNTs) were considered a promising activator for persulfates due to their high electrical conductivity, large specific surface area and low toxicity. The functional groups and surface defects of CNTs could significantly affect their activation performance. In this study, CNTs with high C=O ratio and defect density (CNT-O-H) were prepared through a facile treatment of raw CNTs with HNO3 oxidation followed by calcination at 800 °C under an argon atmosphere. X-ray photoelectron spectroscopy (XPS) and Raman results showed that the C=O proportion and defect degree (ID/IG) rose to 75% and 1.53, respectively. The obtained CNT-O-H possessed a superior performance towards peroxydisulfate (PDS) activation, and the degradation efficiency of tetracycline (TC) in the CNT-O-H/PDS system was increased to 75.2% from 56.2% of the raw CNTs/PDS system within 40 min. Moreover, the activity of CNT-O-H after use could be easily recovered with re-calcination. In addition, the CNT-O-H/PDS system exhibited high adaptabilities towards wide solution pH (2-10), common coexisting substances and diverse organic pollutants. Singlet oxygen (1O2) was confirmed to be the dominant reactive oxygen species (ROS) generated in the CNT-O-H/PDS system. It was inferred that surface C=O groups and defects of CNTs were the key site to activate PDS for TC degradation.

Regulating nitrogen vacancies within graphitic carbon nitride to boost photocatalytic hydrogen peroxide production

AbstractIntroducing nitrogen vacancies is an effective method to improve the catalytic performance of g‐C3N4‐based photocatalysts, whereas understanding how nitrogen vacancies types affect the catalytic performance remains unclear. Herein, two different types of nitrogen vacancies were successfully introduced into g‐C3N4 by pyrolysis of melamine under argon and ammonia atmosphere with subsequent HNO3 oxidation. The pyrolysis atmosphere is found to have a significant influence on the introduced nitrogen vacancies type, where tertiary nitrogen groups (N3C) and sp2‐hybridized nitrogen atoms (N2C) were the preferred sites for the formation of nitrogen vacancies under ammonia and argon pyrolysis, respectively. Moreover, nitrogen vacancies from N3C are experimentally and theoretically demonstrated to facilitate the narrowed band gap and the improved oxygen absorption capability. As expected, the optimal catalyst exhibits high H2O2 yield of 451.8 µM, which is 3.8 times higher than the pristine g‐C3N4 (119.0 µM) after 4 h and good stability after10 photocatalytic runs.

The Effect of Surface Coating Treatment on the Properties of Carbon Nanotube Reinforced Copper Matrix Composites

Herein, the surface of multi‐walled carbon nanotubes (MWCNTs) is treated with HNO3 oxidation to carry on oxygen‐containing functional groups. Then, the pretreatment surface of MWCNTs are plated with copper to improve the low wettability of carbon nanotubes (CNTs). Finally, metal matrix composite blocks with excellent properties are prepared by spark plasma sintering (SPS). When the content of the reinforcing phase is 0.25 wt%, the tensile strength and hardness of Cu‐MWCNTs/Cu composite compared with pure copper are increased by 34.6% and 136.1%, respectively.

Stab-resistance improvement of short carbon fiber reinforced UHMWPE knitted composites with plasma/oxidation treatment

Two modification methods, including low temperature plasma treatment and HNO3 oxidation, used to modify double-layer knitted fabric (DLKF) with UHMWPE yarn and CFs respectively. Contact angle, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) are used to evaluate the modification effect of the fabric or CFs. Epoxy resin (ER) is used as adhesive to prepare composite, and the effect of modification on the stab resistance is further studied through the test of stab resistance. In addition, the damage mechanism of DLKF and R-DLKF are analyzed. The results showed that the plasma treatment has a great effect on the modification of DLKF. After 15–20min of modification, the stab resistance of the composite is the best. The peak load and energy can be increased by about 19.1% and 23.1%. HNO3 oxidation has a great effect on the modification of CFs, the stab-resistance of CFs reinforced DLKF (R-DLKF) can be improved by about 17.3% after being treated with 60% HNO3 for 24h. DLKF fails mainly due to the stretching and cutting action of the yarn. Fabric as matrix can prevent crack propagation further, and the shear force, yarn cutting and pullout action within the composite is the key to improve the stab resistance. This work opens up the possibilities for the industrial production of personal protection products and devices, which is expected to provides a reference for the modification of fabrics and fibers in the production of composite.

Tailoring surface carboxyl groups of mesoporous carbon boosts electrochemical H2O2 production

Oxygen-doped porous carbon materials have been shown promising performance for electrochemical two-electron oxygen reduction reaction (2e− ORR), an efficient approach for the safe and continuous on-site generation of H2O2. The regulation and mechanism understanding of active oxygen-containing functional groups (OFGs) remain great challenges. Here, OFGs modified porous carbon were prepared by thermal oxidation (MC-12-Air), HNO3 oxidation (MC-12-HNO3) and H2O2 solution hydrothermal treatment (MC-12-H2O2), respectively. Structural characterization showed that the oxygen doping content of three catalysts reached about 20%, with the almost completely maintained specific surface area (exception of MC-12- HNO3). Spectroscopic characterization further revealed that hydroxyl groups are mainly introduced into MC-12-Air, while carboxyl groups are mainly introduced into MC-12- HNO3 and MC-12- H2O2. Compared with the pristine catalyst, three oxygen-functionalized catalysts showed enhanced activity and H2O2 selectivity in 2e− ORR. Among them, MC-12-H2O2 exhibited the highest catalytic activity and selectivity of 94 %, as well as a considerable HO2− accumulation of 46.2 mmol L-1 and excellent stability in an extended test over 36 h in a H-cell. Electrochemical characterization demonstrated the promotion of OFGs on ORR kinetics and the greater contribution of carboxyl groups to the intrinsically catalytic activity. DFT calculations confirmed that the electrons are transferred from carboxyl groups to adjacent carbon and the enhanced adsorption strength toward *OOH intermediate, leading to a lower energy barrier for forming *OOH on carboxyl terminated carbon atoms.

Direct laser writing carbonization of polyimide films enabled multilayer structures for the use in interfacial solar-driven water evaporation

Direct laser writing carbonization in conjunction with HNO3 oxidation is used for readily fabricating multi-layer structured interfacial solar-driven water evaporation systems with excellent water evaporation performance and long-term stability.

In situ regulation of microstructure and microwave-absorbing properties of FeSiAl through HNO3 oxidation

Abstract Wrapping insulation of coatings is effective for enhancing the microwave-absorbing properties (MAPs) of ferromagnetic absorbents (FMAs). However, the process is still limited by the low bonding strength with the matrix. Herein, an in situ regulation strategy based on the preparation of thin thickness and strong adhesion insulating layers through HNO3 oxidation was developed to address the limitations. The oxidation process of FeSiAl (FSA) powders was carried out by HNO3 following three main steps. First, the original oxide layer first reacted with HNO3 to form Fe3+ and Al3+. Second, the oxide layer composed of Al2O3 and Fe3O4 was preferentially formed due to the negative change in Gibbs free energy. Finally, the oxide and pigment-deposition layers were subjected to competitive growth and dissolution accompanied by the dissolution of Fe and Al atoms. Oxidation time up to 10 min resulted in the formation of a bilayer structure with a thickness of ∼50 nm on the FSA surface, as well as an outer layer crammed of Al(OH)3 and Fe(OH)3, and an inner layer containing mixed Fe2O3, Fe3O4, Al2O3, and SiO2. The MAPs of as-treated FSA achieved minimum reflection loss (RL) of −25.90 dB at 13.36 GHz, as well as absorption bandwidth of 5.61 GHz (RL < −10 dB) at 10.13–15.74 GHz and thickness of 2.5 mm. In sum, the developed route looks promising for the preparation of high-performance FMAs.

Preparation of a N, S, P co-doped and oxidized porous carbon for the efficient adsorption of uranium(VI)

A N, S, P co-doped and oxidized porous carbon was prepared by the carbonization of poly (cyclotriphosphazene-co-4,4’-sulfonyldiphenol) at 750 °C, followed by KOH activation and HNO3 oxidation. The carbon was used as an adsorbent for uranium(VI) in aqueous solutions. TEM, SEM, XPS and FTIR were used to characterize its microstructure before and after adsorption. Results indicate that there is an optimum pH value of 6 for U(VI) adsorption. The adsorption kinetics and isotherms were fitted well by the pseudo-second-order and the Langmuir models, respectively. The maximum adsorption capacity determined by the Langmuir model at 298 K and a pH value of 6 was 402.9 mg g−1. The carbon has excellent reusability and retains 70% of the capacity of the original value after five adsorption-desorption cycles. The high U(VI) adsorption capacity is mainly attributed to the carboxyl, and P and S groups by the formation of the UO22+(COO−)2 complex, and U―O―P and U―O―S bonds.

Extraction and Chemical Characterization of Humic Acid from Nitric Acid Treated Lignite and Bituminous Coal Samples

Currently, conversion of coal into alternative fuel and non-fuel valuable products is in demand and growing interest. In the present study, humic acid was extracted from two different ranks of coal, i.e., low rank and high rank (lignite and bituminous), through chemical pretreatment by nitric acid. Samples of lignite and bituminous coal were subjected to nitric acid oxidation followed by extraction using KOH and NaOH gravimetric techniques. The chemical pretreatment of both types of coal led to enhanced yields of humic acid from 21.15% to 57.8% for lignite low-rank coal and 11.6% to 49.6% bituminous high rank coal. The derived humic acid from native coal and nitric acid treated coal was analyzed using elemental analysis, E4/E6 ratio of absorbance at 465 nm and 665 nm using UV-Visible spectrophotometry and Fourier transformed infrared spectroscopy FTIR. The chemical characteristics of coal treated with nitric acid have shown increased molecular weight and improved aromaticity with more oxygen and nitrogen and lower C, H, and sulphur content. The E4/E6 ratio of nitric acid-treated low and high ranks of coal was high. The FTIR spectroscopic data of nitric acid-treated lignite coal indicates an intensive peak of carboxyl group at 2981.84 cm−1, while bituminous coal was shown in cooperation with the N-H group at 2923.04 cm−1. SEM was performed to detect the morphological changes that happen after producing humic acid from HNO3 treatment and native coal. The humic acid produced from HNO3 treated coal had shown clear morphological changes and some deformations on the surface. SEM-EDS detected the major elements, such as nitrogen, in treated humic acid that were absent in raw coal humic acid. Hence, the produced humic acid through HNO3 oxidation showed a more significant number of humic materials with improved efficiency as compared to native coal. This obtained humic acid can be made bioactive for agriculture purposes, i.e., for soil enrichment and improvement in growth conditions of plants and development of green energy solutions.

Co-presence of hydrophilic and hydrophobic sites in Ni/biochar catalyst for enhancing the hydrogenation activity

Hydrophilicity/hydrophobicity is one of the most important parameters in heterogenous catalysts, as it significantly impacts the adsorption and activation of the reaction substrate. In this study, we have demonstrated that the treatment of the biochar derived from the pyrolysis of rice husks with HNO3 oxidation and subsequent thermal treatment could remarkably increase the overall hydrophobicity of the Ni catalyst termed as Ni/biochar (treated). However, owing to the un-uniform surface of the biochar, some hydrophilic sites also exist. The co-presence of the hydrophobic and hydrophilic sites in the Ni/biochar (treated) facilitates the adsorption/activation of the CO functionality in vanillin and the aliphatic CC in eugenol. This renders the Ni/biochar (treated) catalyst with the much higher activity for hydrogenation of the unsaturated bonds than the Ni/biochar (un-treated) catalyst with mainly the hydrophilic sites. The reaction substrate like 1-chloro-2-nitrobenzene that could not form strong hydrogen bond with the biochar was less sensitive to the hydrophilicity/hydrophobicity of the catalyst. The results herein provide some reference information for optimizing catalytic performance via tailoring surface properties.

Hydrothermal method oxidized carbon nanotube: Properties and performances in epoxy composite

Further modifications to carbon nanotube (CNT) are often necessary in various application scenarios, however, polluting oxidation processes are typically difficult to be avoided. Efforts were devoted to developing green and facile methods to oxidize CNT. Herein, A hydrothermal process for efficient and eco-friendly oxidization of CNT was explored. The oxidized CNTs were carefully characterized to get clear the transformation in both chemical and physical properties. By comparing both the strength and the toughness of the composites obtained after introducing the oxidized CNTs into epoxy matrices, the oxidation effect was further verified. The strengthening and toughening mechanisms were then studied and attributed to the nicely built chemical and physical interactions. Compared with the concentrated HNO3 oxidized CNT, the hydrothermal method oxidized CNT performed much better reinforcing ability to epoxy, which suggested great potentials for the green hydrothermal method to replace the polluting concentrated HNO3 oxidation method to fabricate high-performance CNT/epoxy composites.

High permeability and low core loss nanocrystalline soft magnetic composites based on FeSiBNbCu@Fe3O4 powders prepared by HNO3 oxidation

To develop nanocrystalline soft magnetic composites (NSMCs) with good combination of soft magnetic properties, the core-shell structured FeSiBNbCu@Fe3O4 powders were prepared by nitric acid (HNO3) oxidation of the nanocrystalline FeSiBNbCu alloy. The NSMCs were then fabricated by binding and pressing with resin followed by annealing treatment. The formation mechanism of the Fe3O4 layer on the FeSiBNbCu powders was discussed and the effects of HNO3 concentration and annealing temperature on the magnetic properties of the NSMCs were investigated. It was found that the sharp edges of the initial powders disappeared after the powder was oxidized with 30 wt% HNO3. A complete and uniformly distributed Fe3O4 layer formed on the powder surface. For the NSMCs annealed at 500 °C, the formation of Fe3O4 layer by HNO3 oxidation treatment significantly reduced the core loss but also decreased the permeability. After annealing at 550 °C and 600 °C, the permeability of the NSMCs can be greatly improved. The formed Fe3O4 layer can resist the high annealing temperature up to 600 °C, which is beneficial to effectively releasing the residual stress. The core loss shows a significant increase as the annealing temperature over 600 °C, which is mainly attributed to the decomposition of resin binders. The excellent magnetic properties with permeability μe = 80 and core loss Ps = 269 kW/m3 at 50 mT and 100 kHz have been achieved in the present work.

Enrichment of the surface functional groups of activated carbon by modification method

The wastes formed from various industries' activities draw attention to their ability to be used as a natural adsorbent or as a source for activated carbon production. In this study, we aimed to produce activated carbon rich in surface functional groups from biomass. Surface functional groups of activated carbons (AC) were enriched by HNO3 oxidation. The activated carbons were synthesized with H3PO4 using peach stones (PSs), fruit juice industrial wastes, and can be found in abundance in the World and Turkey. The activated carbons' surface properties, such as BET surface area, micro-mesopore volume, and average pore diameter, were determined. The activated carbon with the highest surface area was produced with the impregnation ratio of 3/1 at 400 °C (3AC400) as 1399 m2/g. The microporous structures of the 3AC400 synthesized were determined to be more than the mesopore structures. The effects of acid modification on the surface of 3AC400, whose surface characterization was completed, were investigated using HNO3 at different concentrations (15, 30, 45, and 69% (v/v) HNO3). When the nitric acid concentration used in the modification was increased from 15% to 69%, the BET surface area of pure activated carbon (3AC400) decreased from 1399 m2/g to 15.44 m2/g. Besides, the micropores were wholly clogged, and the mesopore volume decreased from 0.127 cm3/g to 0.042 cm3/g. Vmic/Vtop of 3AC400 was reduced from 0.813 to 0.008. Modification using in this study was found to have a significant effect on the surface area of 3AC400. Nitric acid led micropores to collapse. So the structure of the surface of modified activated carbons has become more mesopores. The surface properties and surface functional group diversity of the synthesized modified activated carbons by various methods were investigated. With 69% nitric acid modification, the amount of carboxyl, lactone, and phenyl groups on the activated carbon surface was increased by 5.3, 9.75, and 9.00, respectively. The nitric acid modification affected the diversity of surface functional groups such as lactone> phenol> carboxyl. As the nitric acid concentration increased, the modified samples' total surface acidity increased, and IEP values shifted from 3.6 to the left. The total acidity value for the 69NAC/90/2 sample has increased approximately seven times that of the total acidity value of 3AC400.

Mechanisms for sulfide-induced nitrobenzene reduction mediated by a variety of different carbonaceous materials: Graphitized carbon-facilitated electron transfer versus quinone-facilitated formation of reactive sulfur species.

Although it has long been known that carbonaceous materials (CMs) can facilitate the reduction of organic contaminants by sulfide, the underlying mechanisms and controlling factors, particularly the surface property dependence, are not well understood. Here, sulfide-induced nitrobenzene reduction was explored as a model reaction to compare the mediation efficiency of a variety of CMs, including rice straw-derived black carbon (R-BC) and pine wood-derived black carbon (P-BC), a commercial activated carbon (AC), multi-walled carbon nanotube (MCNT), and graphite. Given the same load (250mg L-1 ), the observed pseudo-first-order rate constant (kobs ) of nitrobenzene reduction was ordered as AC>R-BC>MCNT>P-BC>graphite. The surface area-normalized rate constant (kSN ) was ordered as R-BC>graphite>MCNT>AC>P-BC. Neither the kobs nor the kSN followed the order of mediator's electron conductivity (graphite>MCNT>AC>P-BC>R-BC). For the low-graphitized R-BC and P-BC, increasing surface oxygen content by HNO3 oxidation enhanced nitrobenzene reduction, whereas decreasing the content by NaBH4 reduction impeded the reaction. Opposite trends were observed with the high-graphitized AC, MCNT, and graphite. The quinone moieties of low-graphitized CMs were found to facilitate nitrobenzene reduction by serving as one-electron acceptors to generate reactive reducing sulfur species (polysulfides and polysulfide free radicals) from sulfide. In contrast, the surface oxygen groups of high-graphitized CMs suppressed the reaction by lowering the electron conductivity. These results demonstrate that the types of CMs and their surface chemistry properties are key determinants in mediating redox transformation of organic contaminants.

Extensive incorporation of carboxyl groups into g-C3N4 by integrated oxygen doping and HNO3 oxidation for enhanced catalytic ozonation of para-chlorobenzoic acid and atrazine

Carbon nitride (CN), oxygen-doped carbon nitride (CNO), HNO3 oxidized CN (CN-10) and CNO (CNO-10), were synthesized and used to catalyze ozonation of para-chlorobenzoic acid (p-CBA) and atrazine in aqueous solution. Pre-doping oxygen atom into CN could create extra defects for grafting more carboxyl groups during HNO3 oxidation, which was verified by much lower formation energy of CNO-10 than that of CN-10. Density functional theory and room temperature electron paramagnetic resonance (EPR) analysis signified the changes of electronic structure afforded by extensively grafted carboxyl groups. The incorporation of carboxyl groups distorted the carbon nitride framework and changed the spatial dimensions of CN and CNO, which attenuated the characters of delocalized π-electrons in conjugated structure. Moreover, the introduction of carboxyl groups reduced the pore diameter and nano-size distributed in aqueous solution for CN-10 and CNO-10 relative to those of CN and CNO. Results showed that the elimination efficiency of p-CBA by catalytic ozonation and Rct (standard reactivity metric for catalytic ozonation process) with CNO-10 improved 1.12- and 1.48-fold relative to those with CN-10, respectively, far surpassing non-catalytic ozonation. The removal of ozone-resisted compounds by CNO-10 catalyzed ozonation was not significantly affected by bicarbonate and NOM, and it was promoted by natural surface water resulting in 87.4% p-CBA removal in 30 min. Mechanistic evaluation demonstrated that carboxyl groups were the main active sites, catalyzing ozone decomposition into hydroxyl radical through radical chain reaction. This work provides fundamental supportive of pre-doping oxygen atom into CN before HNO3 functionalization, which could incorporate more carboxyl groups on surface compared to conventional strategy, further enhancing catalytic activity in ozonation.

Selective Digital Etching of Silicon-Germanium Using Nitric and Hydrofluoric Acids.

A digital etching method was proposed to achieve excellent control of etching depth. The digital etching characteristics of p+-Si and Si0.7Ge0.3 using a combination of HNO3 oxidation and buffered oxide etching oxide removal processes were investigated. Experimental results showed that oxidation saturates as time goes on because of low activation energy and its diffusion-limited characteristic. An oxidation model was developed to describe the wet oxidation process with nitric acid. The model was calibrated with experimental data, and the oxidation saturation time, final oxide thickness, and selectivity between Si0.7Ge0.3 and p+-Si were obtained. In Si0.7Ge0.3/p+-Si stacks, the saturated relative etched depth per cycle was 0.5 nm (four monolayers), and variation between experiments was about 4% after saturation. A corrected selectivity calculation formula was also proposed, and the calculated selectivity was 3.7-7.7 for different oxidation times, which was the same as the selectivity obtained from our oxidation model. The proposed model can be used to analyze process variations and repeatability, and it can provide credible guidance for the design of other wet digital etching experiments.