Nitric Acid Treatment Research Articles

Dimethyl ether synthesis from methanol over diatomite catalyst modified using nitric acid treatment

ABSTRACTDimethyl ether synthesis from methanol over diatomite catalysts modified using nitric acid was investigated. The catalytic performance of diatomite was tested in a fixed-bed reactor under atmospheric pressure and within the temperature range of 250–350°C. It was discovered that high acidity of the catalyst yielded a higher methanol conversion rate. Moreover, it was revealed that the acidity of the catalyst surface was controlled by Al(IV) ions whereas basicity of the catalyst surface was determined by Al(V) and Al(VI) ions. From this finding, the authors were able to propose the mechanism of DME synthesis from methanol over treated diatomite.

Enhanced solar evaporation of water from porous media, through capillary mediated forces and surface treatment

The relative influence of the capillary, Marangoni, and hydrophobic forces in mediating the evaporation of water from carbon foam based porous media, in response to incident solar radiation, are investigated. It is indicated that inducing hydrophilic interactions on the surface, through nitric acid treatment of the foams, has a similar effect to reduced pore diameter and the ensuing capillary forces. The efficiency of water evaporation may be parameterized through the Capillary number (Ca), with a lower Ca being preferred. The proposed study is of much relevance to efficient solar energy utilization.

Novel synthesis of holey reduced graphene oxide (HRGO) by microwave irradiation method for anode in lithium-ion batteries.

In this work, holey reduced graphene oxide (HRGO) was synthesized by the deposition of silver (Ag) nanoparticles onto the reduced graphene oxide (RGO) sheets followed by nitric acid treatment to remove Ag nanoparticles by microwave irradiation to form a porous structure. The HRGO were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), ultra violet-visible spectroscopy (UV-Vis), thermogravimetric analysis (TGA), and Raman spectroscopy. These novel HRGO exhibited high rate capability with excellent cycling stability as an anode material for lithium-ion batteries. The results have shown an excellent electrochemical response in terms of charge/discharge capacity (423 mAh/g at 100 mA/g). The cyclic performance was also exceptional as a high reversible capacity (400 mAh/g at 100 mA/g) was retained for 100 charge/discharge cycles. This fascinating electrochemical performance can be ascribed to their specific porous structure (2–5 nm pores) and high surface area (457 m2/g), providing numerous active sites for Li+ insertion, high electrical conductivity, low charge-transfer resistance across the electrolyte–electrode interface, and improved structural stability against the local volume change during Li+ insertion–extraction. Such electrodes are envisioned to be mass scalable with relatively simple and low-cost fabrication procedures, thereby providing a clear pathway toward commercialization.

Electrochemical properties of multi-walled carbon nanotubes treated with nitric acid for a supercapacitor electrode

The capacitances of partially oxidized multi-walled carbon nanotubes (MWNTs) electrodes treated with nitric acid were investigated for use as the electrode materials of electric double-layer capacitors (EDLCs). The oxidized MWNTs had a much higher specific surface area, pore volume and average pore width than those of pristine MWNTs. Moreover, functional groups such as hydroxyl, carbonyl and carboxyl groups were observed on the surfaces of oxidized MWNTs. The specific capacitance of the oxidized MWNTs after 3h a nitric acid treatment was 68.8F/g in the highest oxidized state, more than 7 times greater than that of the pristine MWNTs. Further, the capacitance trends apparently follow the change of the zeta potentials, not the surface areas, indicating that this trend depends on the adsorption of electrolytes as compared to the migration path structure. Further, the oxidized MWNT electrode materials showed good long-term stability during repeated cycles and no decay for more than 1000 cycles.

Systematic comparison of conventional and reductive single-walled carbon nanotube purifications

As-synthesised single-walled carbon nanotubes (SWCNTs) are often contaminated with amorphous carbon and residual catalyst particles. These contaminants have a detrimental effect on the effective mechanical and electronic properties, limiting their performance in many applications. A comparative series of SWCNT purifications including acid treatments, gas phase purifications and recently-developed reductive purifications have been conducted using a single commercial SWCNT type (Tuball™). Each of the purification procedures was selected for its potential scalability to bulk quantities and evaluated for the extent of impurity removal, SWCNT damage, and overall yield. Raman spectra confirmed that reductive purification using sodium naphthalide gave the lowest D/G ratio, suggesting that the sp2 carbon framework was most effectively preserved, whilst removing a large proportion (∼74%) of the metal impurities. Conversely, nitric acid treatment was most effective at removing virtually all the metal impurities, but the sp2 carbon framework was most heavily damaged in the process. The development of scalable, one pot, reductive separations provides a useful new approach to SWCNT purification.

Effect of acid treatment on the characteristics and structures of high-sulfur bituminous coal

In this paper, a series of modern advanced analysis and measurement technologies such as X-ray Fluorescence (XRF), X-ray Diffraction (XRD), 13C Nuclear Magnetic Resonance (13C NMR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) have been used to analyze the sample after acid treatment. The result shows that after hydrochloric acid treatment and combined treatment of hydrochloric acid/nitric acid, the water content of coal sample and fixed carbon increase to some extent while the volatile component and ash content decrease. Acid treatment has reduced the content of carbon, hydrogen and sulfur but increased the oxygen content. In addition, hydrochloric acid treatment has resulted in the increase of chlorine content in coal and nitric acid treatment increase the nitrogen content. Acid treatment will influence the microcrystalline structure of the coal and improve the aromaticity which finally makes the carbon atom arrangement more orderly. After hydrochloric acid treatment, the ratio of methyl carbon, aliphatic carbon attached to oxygen, carboxyl carbon and carbonyl carbon decreases slightly, while that of other carbon functional groups increases correspondingly. The raw coal shows large differences from coal sample after the beneficiation of hydrochloric acid and nitric acid. The content of methyl carbon and the aliphatic carbon attached to oxygen is reduced obviously, while that of methylene and carbonyl carbon is raised dramatically. After acid treatment, the ratio of CC bond and CH bond on the coal surface increases gradually, but carbon in oxidation state decreases step by step which means acid treatment will destroy the active functional groups on coal surface and reduce the ratio of oxygen-containing functional groups such as ether bond and hydroxyl group. Meanwhile, acid treatment will influence the organic sulfur such as mercaptan, thioether, sulfoxide, sulfone, and sulfonate, which will change the component of organic sulfur on coal surface and decrease its content. The coal particles have no obvious change after the beneficiation of hydrochloric acid and nitric acid but their surface morphology has changed. The edges of coal particles turn obscure and their surface becomes blurred. The combined treatment of hydrochloric acid/nitric acid has increased the specific surface area of coal sample, leading to more micropores on coal surface, and thus oxygen molecules are more easily absorbed by the coal. In general, hydrochloric acid treatment has little influence on coal characteristics, chemical construction of the organic matter, inorganic minerals, functional groups on coal surface, microstructure, etc., while nitric acid treatment has significant effect on coal quality. Therefore, the influence must be taken into consideration when using the nitric acid to pretreat the coal sample.

Continuous Carbon Nanotube-Based Fibers and Films for Applications Requiring Enhanced Heat Dissipation.

The production of continuous carbon nanotube (CNT) fibers and films has paved the way to leverage the superior properties of individual carbon nanotubes for novel macroscale applications such as electronic cables and multifunctional composites. In this manuscript, we synthesize fibers and films from CNT aerogels that are continuously grown by floating catalyst chemical vapor deposition (FCCVD) and measure thermal conductivity and natural convective heat transfer coefficient from the fiber and film. To probe the mechanisms of heat transfer, we develop a new, robust, steady-state thermal characterization technique that enables measurement of the intrinsic fiber thermal conductivity and the convective heat transfer coefficient from the fiber to the surrounding air. The thermal conductivity of the as-prepared fiber ranges from 4.7 ± 0.3 to 28.0 ± 2.4 W m(-1) K(-1) and depends on fiber volume fraction and diameter. A simple nitric acid treatment increases the thermal conductivity by as much as a factor of ∼3 for the fibers and ∼6.7 for the thin films. These acid-treated CNT materials demonstrate specific thermal conductivities significantly higher than common metals with the same absolute thermal conductivity, which means they are comparatively lightweight, thermally conductive fibers and films. Beyond thermal conductivity, the acid treatment enhances electrical conductivity by a factor of ∼2.3. Further, the measured convective heat transfer coefficients range from 25 to 200 W m(-2) K(-1) for all fibers, which is higher than expected for macroscale materials and demonstrates the impact of the nanoscale CNT features on convective heat losses from the fibers. The measured thermal and electrical performance demonstrates the promise for using these fibers and films in macroscale applications requiring effective heat dissipation.

The effect of nitric acid (HNO3) treatment on the electrical conductivity and stability of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) thin films

Abstract In this work, the posttreatment of an organic polymer is performed using an inorganic acid, nitric acid (HNO3). We picked poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the base material and improved its electrical conductivity by acid treatment with different concentrations of HNO3. The acid treatment was able to achieve the optimum electrical conductivity of 197 S/cm, which is 115.5 times higher than the base material when treated with an aqueous solution containing 65% of HNO3. Moreover, the films showed higher transparency in the visible range while conducting Fourier transform infrared analysis. In addition, the treated films showed improved stability against outdoor operating conditions in terms of sheet resistance compared with untreated PEDOT:PSS films. We tried to develop a hypothesis to describe the reason behind the electrical conductivity enhancement by studying the thicknesses of all the samples at different acid concentration levels. The results from atomic force microscopy, the Hall effect, and the trend of film thickness suggest that the conformational change, the removal of excess PSS from the polymer, and the increase in carrier concentration are the reasons behind the improvement in electrical conductivity.

Nitric acid functionalization of carbon monoliths for supercapacitors: Effect on the electrochemical properties

Activated carbon monoliths and oxidized carbon monoliths are prepared from Eucalyptus grandis wood by pyrolysis and subsequent activation under CO2 (aCMs) and further functionalization using nitric acid (ox-aCMs). Their textural and chemical properties are compared and the electrochemical characteristics as supercapacitor electrodes are tested. The nitric acid treatment does not produce substantial changes in the textural properties of the monolith obtained. Elemental analysis and X-ray photoelectron spectroscopy (XPS) reveal that the oxidized monolith presents a high content of oxygenated functional groups that can participate in pseudocapacitive reactions. This determines that the oxidized monoliths have higher electrical capacitance (80 F cm−3) at low current densities and higher energy density (up to Wv = 2.7 W h L−1) than the non-oxidized ones. The supercapacitor cell containing the oxidized monoliths presents higher total resistance values and response time compared to the non-oxidized monolith. The non-oxidized monolith showed the highest power density (up to PV = 94.5 W L−1).

Staphylococcus epidermidis adhesion on surface-treated open-cell Ti6Al4V foams.

The effect of alkali and nitric acid surface treatments on the adhesion of Staphylococcus epidermidis to the surface of 60% porous open-cell Ti6Al4V foam was investigated. The resultant surface roughness of foam particles was determined from the ground flat surfaces of thin foam specimens. Alkali treatment formed a porous, rough Na2Ti5O11 surface layer on Ti6Al4V particles, while nitric acid treatment increased the number of undulations on foam flat and particle surfaces, leading to the development of finer surface topographical features. Both surface treatments increased the nanometric-scale surface roughness of particles and the number of bacteria adhering to the surface, while the adhesion was found to be significantly higher in alkali-treated foam sample. The significant increase in the number of bacterial attachment on the alkali-treated sample was attributed to the formation of a highly porous and nanorough Na2Ti5O11 surface layer.

Enzymatic hydrolysis of lignocellulosic materials in aqueous media and the subsequent microbiological synthesis of bioethanol

The enzymatic hydrolysis of lignocellulosic materials (LCMs) from miscanthus and oat husks (OH) in an aqueous medium and the subsequent production of ethanol are studied. LCMs are obtained at a pilot plant of the Institute of Problems of Chemical and Energy Technologies by means of one-stage nitric acid treatment. Enzymatic hydrolysis is conducted in an aqueous medium with a high initial concentration of phosphates (90 g/L) using freely available CelloLux-A and BrewZyme BGX industrial enzymatic preparations. The yields of reducing compounds are found to be 65.4 and 73.3% for miscanthus and oat husk LCM, respectively. The composition of monosaccharides (products of enzymatic LCM destruction) is studied for the first time. It is shown that glucose comprises the largest share of monosaccharides. Ethanol is produced from LCM for the first time. Ethanol yields per metric ton of raw material are 19.4 and 16.2 daL/t for miscanthus biomass and OH, respectively. Ethanol samples are characterized by low methanol contents (0.002 to 0.005 vol %).

Effect of cleaning procedures on the electrical properties of carbon nanotube transistors—A statistical study

The interface between a carbon nanotube (CNT) and its environment can dramatically affect the electrical properties of CNT-based field-effect transistors (FETs). For such devices, the channel environment plays a significant role inducing doping or charge traps giving rise to hysteresis in the transistor characteristics. Thereby the fabrication process strongly determines the extent of those effects and the final device performance. In CNT-based devices obtained from dispersions, a proper individualization of the nanotubes is mandatory. This is generally realized by an ultrasonic treatment combined with surfactant molecules, which enwrap nanotubes forming micelle aggregates. To minimize impact on device performance, it is of vital importance to consider post-deposition treatments for removal of surfactant molecules and other impurities. In this context, we investigated the effect of several wet chemical cleaning and thermal post treatments on the electrical characteristics as well as physical properties of more than 600 devices fabricated only by wafer-level compatible technologies. We observed that nitric acid and water treatments improved the maximum-current of devices. Additionally, we found that the ethanol treatment successfully lowered hysteresis in the transfer characteristics. The effect of the chemical cleaning procedures was found to be more significant on CNT-metal contacts than for the FET channels. Moreover, we investigated the effect of an additional thermal cleaning step under vacuum after the chemical cleaning, which had an exceptional impact on the hysteresis behavior including hysteresis reversal. The presence of surfactant molecules on CNT was evidenced by X-ray photoelectron and Raman spectroscopies. By identifying the role of surfactant molecules and assessing the enhancement of device performance as a direct consequence of several cleaning procedures, these results are important for the development of CNT-based electronics at the wafer-level.

Physicochemical characterization of a diatomaceous upon an acid treatment: a focus on surface properties by inverse gas chromatography

Natural diatomite from Sig/Algeria was treated with 0.5, 1.0, 3.0 and 5.0M nitric acid solutions for 2h under reflux at 333K in order to improve its performance as support of catalyst. The purified silica powders obtained from frustules can also be used to reinforce composites. The solids obtained were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy, thermal analyses, and nitrogen adsorption–desorption at 77K. Treatment of diatomite earth with nitric acid reduced mineral impurities, such as Fe2O3 and alkali metal oxides (CaO, MgO), eliminated carbonates and increased SiO2 ratio from 88% to 98%. The SEM micrographs showed the original geometry of the pores to be preserved. The surface properties were also evaluated using inverse gas chromatography at infinite dilution (IGC-ID) and finite concentration (IGC-FC). The interest here was to establish whether the technique is sufficiently sensitive to detect variations in the surface properties of the diatomite due to this chemical treatment. The IGC analysis permitted to reach several surface energy components with organic probes. Between them, the distribution function of the adsorption energy sites obtained with the isopropanol probe revealed a silica structure after the 5M nitric acid treatment.

Highly active carbon supported Pd cathode catalysts for direct formic acid fuel cells

One of the drawbacks of low-temperature fuel cells is high price of platinum-based catalysts used for the electroreduction of oxygen at the cathode of the fuel cell. The aim of this work is to develop the palladium catalyst that will replace commonly used platinum cathode catalysts. A series of palladium catalysts for oxygen reduction reaction (ORR) were prepared and tested on the cathode of Direct Formic Acid Fuel Cell (DFAFC). Palladium nanoparticles were deposited on the carbon black (Vulcan) and on multiwall carbon nanotubes (MWCNTs) surface by reduction of palladium(II) acetate dissolved in ethanol. Hydrazine was used as a reducing agent. The effect of functionalization of the carbon supports on the catalysts physicochemical properties and the ORR catalytic activity on the cathode of DFAFC was studied. The supports were functionalized by treatment in nitric acid for 4h at 80°C. The structure of the prepared catalysts has been characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscope (TEM) and cyclic voltammetry (CV). Hydrophilicity of the catalytic layers was determined by measuring contact angles of water droplets. The performance of the prepared catalysts has been compared with that of the commercial 20wt.% Pt/C (Premetek) catalyst. The maximum power density obtained for the best palladium catalyst, deposited on the surface of functionalized carbon black, is the same as that for the commercial Pt/C (Premetek). Palladium is cheaper than platinum, therefore the developed cathode catalyst is promising for future applications.

Interaction of Nitric Acid and Zn Intermetallides of Fe, Cr, Ni Obtained after Stripping Zn from EP823 Steel Solutions in Zinc

Two samples of the steel EP823 solution in zinc were prepared. The samples were undergone to zinc vacuum distillation. X-ray analysis showed that the residue particles have a different structure and ratio of elements, depending on zinc residual content. Needle-type particles consist mainly of iron (over 60 wt%) and 9-12% of zinc. Sponge-type particles consist mainly of zinc (over 70%). Chromium localize in zinc-rich particles.In the nitric acid treatment (4 and 8 mole/l) and 6 hours boiling, from 60 wt% to 70 wt% of the sample passed into solution. X-ray spectrum analysis shows that the main phase of the insoluble residue is a solid solution of (Cr,Zn,Fe)O4.

Modification of abandoned fine blue-coke: optimization study on removal of p-nitrophenol using response surface methodology

Abandoned fine blue-coke was modified with a physicochemical method including nitric acid (HNO3) treatment and nitrogen gas (N2) calcination, and used as an adsorbent for p-nitrophenol (PNP) removal.

The effects of liquid-phase oxidation of multiwall carbon nanotubes on their surface characteristics

The development of new sorbents based on nanostructured carbon materials recently became a perspective field of research. Main topic of current study is to investigate the effect of different regimes of multiwall carbon nanotubes (MWCNT) surface modification process on their structural characteristics. MWCNT samples were treated with nitric acid at high temperature. Structural properties were studied using low temperature nitrogen adsorption and acid-base back titration methods. The study showed that diluted nitric acid does not affect MWCNT structure. Concentrated nitric acid treatment leads to formation of 2.8 carboxylic groups per 1 nm2 of the sample surface.

Promotional effect of nitric acid treatment on co sensing properties of SnO2/MWCNT nanocomposites

In this paper, SnO2/MWCNT nanocomposites with different types of MWCNTs, namely as-received, acid treated and Ag-decorated, were synthesized via a facile method and their CO gas sensing properties were investigated. Microstructure and phase formation of the synthesized composites were studied using FE-SEM and XRD, respectively. Fourier transform infrared spectroscopy (FTIR) was employed to study the functional groups on the surface of MWCNTs after acid treatment. CO gas sensing results showed that the samples containing 0.8 wt.% MWCNT with 2 h acid treatment by HNO3 have the best response to CO gas.

Electrodeposition of three-dimensional Ni(OH)2 nanoflakes on partially crystallized activated carbon for high-performance supercapacitors

Three-dimensional Ni(OH)2 nanoflakes were prepared via a facile and cost-effective electrodeposition method using commercial activated carbon (AC) as substrate. Nitric acid treatment (NT) and partial crystallization (PC) by metal nickel catalysis were applied for AC. The effects of the oxygen-containing functional groups and the degree of crystallization on the electrochemical performance of the electrode were investigated. The resulting Ni(OH)2/PC–NT–AC/nickel foam electrode exhibits distinct performance with a specific capacitance of 2971 F/g (scaled to the mass of active Ni(OH)2) at a current density of 6 A/g. A high capacitance of 1919 F/g was still achieved even at 40 A/g, which is much higher than Ni(OH)2/AC/nickel foam electrode and Ni(OH)2/NT–AC/nickel foam electrode. The excellent performance of Ni(OH)2/PC–NT–AC/nickel foam electrode can be attributed to the presence of large surface area and highly conductive PC–NT–AC network on nickel foam. This study presents an effective method to improve the dispersion and rate capability of Ni(OH)2 nanostructure electrodes.

Selective Production of Light Olefins from Catalytic Cracking of n-Hexane over OSDA-Free Beta Zeolites

The catalytic cracking of n-hexane for producing light olefins on Beta zeolite synthesized under organic structure-directing agent free conditions (OFB) was carried out as a model reaction of naphtha cracking. The Al-rich H-form OFB (HOFB) catalyst exhibited a short catalytic life and a low selectivity to propylene even at the lower reaction temperature of 773 K, due to its high acid amount. Dealumination of HOFB by ammonium hexafluorosilicate (AHFS) treatment and followed by nitric acid treatment resulted in the increase in the catalytic life and propylene selectivity, regardless of the reaction temperatures ranging from 773 to 923 K. This could be attributed to the lower amount of the acid sites especially the Lewis acid sites, which suppressed the secondary reactions of propylene and butenes and the hydride transfer to form coke. For example, the HOFB-AHFS(0.5 M)-HNO3(6 h) catalyst showed a very high selectivity of ca. 41 C-% to propylene even at nearly 100 % n-hexane conversion, at the higher reaction temperature of 923 K.