Nitric Acid Treatment Research Articles

Expanded titanosilicate MWW-related materials synthesized from a boron-containing precursor as an efficient catalyst for cyclohexene oxidation

Titanosilicate forms of expanded MWW-related materials (Ti-MWW-exp) are synthesized starting from a lamellar boron-containing MWW precursor. The boron expulsion by the nitric acid treatment from the molecular sieve framework left behind the vacancies. By extending the acid treatment time, Si species around the defects is dissolved and is the likely source for the species required to expand the interlayer space. The obtained Ti-MWW-exp material exhibits a superior catalytic activity in cyclohexene oxidation, and a high selectivity for cyclohexene oxide is also achieved. Moreover, this convenient post synthesis was also used in the preparation of interlayer expanded B-MWW and B–Al-MWW materials, giving rise to the design of the other interlayer expanded metallosilicates. A facile strategy is put forward to construct the interlayer expanded MWW-type metallosilicates. The interlayer expanded Ti-MWW-exp zeolite can exhibit the excellent catalytic performance in the epoxidation of bulky cyclohexene. • An interlayer expanded MWW-type metallosilicate is post-synthesized. • Removal of boron can change the stability of the neighboring Si species. • Si species reinserted into the zeolite can serve as pillars in the interlayer space. • The interlayer expanded Ti-MWW-exp is an efficient catalyst for the cyclohexene oxidation. • This strategy is a promising way for designing other interlayer expanded boron-containing zeolites.

Separation and catalytic depolymerization of empty palm fruit bunch lignin

Lignin is a heterogeneous and complex polymer and a potential renewable source of aromatic compounds as precursors to many industrially useful products. Microbial biotransformations for lignin valorization are reported but require not only its separation from biomass matrix but also breakdown into its monomeric components. Abundantly available empty palm fruit bunch was used as the lignin-rich biomass to process it to obtain a mixture of lignin-derived monomeric aliphatic and aromatic compounds. A two-step acid-alkali treatment was deployed to extract lignin and its breakdown into smaller fragments. Dilute nitric acid treatment could extract 80% of the lignin and the hydrolysate was fractionated through a series of nanofiltration membranes. The residual polymeric lignin obtained after monomer separation was catalytically depolymerized using Cu/Al2O3 under optimized conditions i.e., 180 °C, 7 MPa, 60 min, methanol: water ratio as 1:1 to give 80% conversion. Lignin mixture at every step was analyzed by GC-MS and gel permeation chromatography (GPC). The scheme resulted in 37% of the overall lignin being obtained as monomers.

Activation of Porous Pt Electrodes Deposited on YSZ Electrolyte by Nitric Acid Treatment.

The effect of nitric acid treatment on the electrochemical performance of porous Pt electrodes deposited on YSZ (abbreviation from yttria stabilized zirconia) electrolyte was investigated. Two identical symmetrical Pt/YSZ/Pt cells with porous Pt electrodes were fabricated, after which the electrodes of the first cell were kept as sintered, while those of the second cell were impregnated with HNO3 solution. The electrochemical behavior of the prepared electrodes was studied using impedance spectroscopy and cyclic voltammetry. Significant reduction of the polarization resistance of the HNO3-treated electrodes was revealed. The observed enhancement of the electrochemical performance of porous Pt electrodes was assumed to be caused by adsorption of NOx-species on YSZ and Pt surfaces, which promotes oxygen molecules dissociation and transport to the triple phase boundary by the “relay-race” mechanism. The obtained results allow for considering the nitric acid treatment of a porous Pt electrode as an effective way of electrode activation.

Optical and magnetic properties of small-size core–shell Fe3O4@C nanoparticles

Core–shell Fe3O4@C magnetic nanoparticles which are of great interest for research have a widely applied prospect. However, people know little about the optical and magnetic properties of the small-size Fe3O4@C nanoparticles due to the difficulty of uniformly coating small size Fe3O4 nanoparticles. In this paper, the influence of carbon shell coating on the optical and magnetic properties of small size Fe3O4 nanoparticles was presented. Carbon coating can strengthen the absorption intensity in the UV–visible light region through the introduction of oxygen defects on the surface of the nanoparticles by nitric acid treatment. Fe3O4 and Fe3O4@C nanoparticles both display typical superparamagnetic behavior in the high-temperature regime and a blocked state at low temperature from hysteresis loop, zero-field cooled and field cooled curves. Carbon coating reduce the surface uniaxial anisotropy, thus the average blocking temperature <TB> decreases from 59 K of Fe3O4 nanoparticles to 50 K of Fe3O4@C nanoparticles.

A mechanism study of acid-assisted oxidative stabilization of asphaltene-derived carbon fibers

The development of inexpensive carbon fiber precursors is necessary to meet the future demands of carbon fibers. This work shows how asphaltenes, which are obtained as a by-product in bitumen production, can play an important role as such inexpensive carbon fiber precursors. To synthesize carbon fibers from asphaltene, stabilization by means of oxidizing acids (HNO3 and H2SO4) was developed. Stabilization could not be achieved by a non-oxidizing acid (HCl). The reactions leading to fiber stabilization was investigated for nitric acid treatment, which led to oxidation and the incorporation of nitro-groups. Further thermal treatment caused an increase in C/H ratio that was related to decomposition of nitro-groups, which facilitated air oxidation and other reactions leading to the loss of volatile hydrogen-rich products, such as light hydrocarbons. Additionally, the influence of the acid concentration during treatment on fiber properties, such as fiber diameter, composition, tensile strength and elastic modulus, has been examined. The application of the acid treatment leads to carbon fibers with good tensile properties, with a tensile strength and elastic modulus of 811 MPa and 32.7 GPa, respectively. The overall yield of carbon fibers is 37 – 38 wt.%.

Synergistic effect of UV, thermal, and chemical treatment on biological degradation of low-density polyethylene (LDPE) by Thermomyces lanuginosus.

The present analysis deals with the ability of Thermomyces lanuginosus to degrade pre-treated low-density polyethylene (LDPE). The synergistic effect of UV irradiation, heat, and acid pre-treatments on the biodegradability of the polymer was thoroughly assessed. Oxidative structural modifications such as the appearance of carboxylate and carbonyl groups in LDPE chains were recorded post the UV and heat treatments. Furthermore, the nitric acid treatment incorporated NO2 groups into the polymer matrix. Alterations in the polymer thermal stabilities and surface morphologies after each pre-treatment were analyzed using thermogravimetric analysis and scanning electron microscopy (SEM), respectively. The gravimetric analysis revealed a reduction in the weight of the pre-treated LDPE films by 9.21 ± 0.84% after 1month of the incubation period with Thermomyces lanuginosus. An increase in the thermal stability, disappearance of the incorporated hydrophilic functional groups, and reduction in the carbon content of the polymer samples post the incubation period further justified the biodegradation process. SEM analysis showed modifications in the morphology and texture patterns in pre-treated LDPE after inoculation with Thermomyces lanuginosus. The findings suggest that Thermomyces lanuginosus could be efficient for the decomposition of pre-treated LDPE under laboratory conditions.

Oxidative synthesis of yellow photoluminescent carbon nanoribbons from carbon black

Micrometer long multilayer carbon nanoribbons with high oxygen content and nitrogen doping were obtained from the nitric acid treatment of Black Pearls 2000. The nanoribbons (NRs) exhibited yellow light emission under UV excitation. The oxidation of other grades of carbon black yielded irregular and small graphene oxide fragments or carbon quantum dots instead. Remarkably, the familiar and straightforward treatment of carbon materials with nitric acid reemerges as a powerful tool for the synthesis of technology-relevant carbon nanoribbons, and unlocking the potential of such straighforward oxidation chemistry applied to inexpensive and commercially available carbon black.

Role of Activated Carbon Precursor for Mercury Oxidation and Removal: Oxidized Surface and Carbene Site Interaction

Activated carbon (AC) is widely accepted for the removal of inorganic contaminants like mercury; however, the raw material used in the production of activated carbon is not always taken into consideration when evaluating its efficacy. Mercury oxidation and adsorption mechanisms governed by carbene sites are more likely to occur when graphitic-like activated carbons (such as those produced from high-ranking coals) are employed versus lignocellulosic-based ACs; this is likely due to the differences in carbon structures where lignocellulosic materials are less aromatic. In this research, the team studied bituminous coal-based ACs in comparison to coconut shell and wood-based (both less aromatic) ACs for elemental mercury removal. Nitric acid of 0.5 M, 1 M, and 5 M concentrations along with 10 M hydrogen peroxide were used to oxidize the surface of the ACs. Boehm titrations and FTIR analysis were used to quantify the addition of functional groups on the activated carbons. A trend was observed herein, resulting in increasing nitric acid molarity and an increased quantity of oxygen-containing functional groups. Gas-phase mercury removal mechanisms including physisorption, oxygen functional groups, and carbene sites were evaluated. The results showed significantly better elemental mercury removal in the gas phase with a bituminous coal-based AC embodying similar physical and chemical characteristics to that of its coconut shell-based counterpart. The ACs treated with various oxidizing agents to populate oxygen functional groups on the surface showed increased mercury removal. It is hypothesized that nitric acid treatment creates oxygen functional groups and carbene sites, with carbene sites being more responsible for mercury removal. Heat treatments post-oxidation with nitric acid showed remarkable results in mercury removal. This process created free carbene sites on the surface and shows that carbene sites are more reactive to mercury adsorption than oxygen. Overall, physisorption and oxygen functional groups were also dismissed as mercury removal mechanisms, leaving carbene-free sites as the most compelling mechanism.

Effect of nitric acid treatment on the pitch properties and preparation of activated carbon

Effect of nitric acid treatment on the pitch properties and preparation of activated carbon

Cracking mechanism and degradation performances of HTV silicone rubber with interfacial defects under acid and thermal stress

High temperature vulcanized (HTV) silicone rubber (SIR), as the sheath of composite insulators, is widely used as the insulation device in transmission lines due to their excellent hydrophobicity and pollution flashover resistance. However, the interfacial defects of insulators and severe operating environment will accelerate the aging of HTV SIR sheath, seriously affecting the operation reliability of electrical equipment. Herein, the samples designed with different sizes of interfacial defects are aged under water, sulfuric acid and nitric acid at 80 °C, respectively. The results show that a large number of cracks appear on the surface of HTV SIR samples with interfacial defects after nitric acid treatment at 80 °C for more than 2 days, while samples with no interfacial defects aged under same condition for 8 days maintain unchanged. According to the results of the micro morphology of the sample, the crack is caused by the interfacial stress of the sample. In addition, after nitric acid treatment, the thermal stability, tensile and dielectric properties of HTV SIR with interfacial defects decreased significantly. The initial decomposition temperature decreases by about 30 °C, while the residual weight increases by about 2.5%. Meanwhile, the tensile strength and fracture strain decrease from 4.58 MPa and 470% to 2.07 MPa and 130% respectively, proving that cracks caused by interfacial defects can critically avianize the mechanical properties and thermal stability of HTV SIR. Also, there is an extra dielectric loss peak appearing in the frequency range of 102–104 Hz, which attributed to water invading and the MWS polarization at cracks. By aging HTV SIR with artificial interfacial defects under thermal and acid stress, the HTV SIR cracking phenomenon of composite insulators under severe operating environment is successfully simulated. This work can provide theoretical support ulteriorly for studying the cracking mechanism and the corresponding aging characteristics of HTV SIR used in composite insulators.

Mild nitric acid treatments to improve multi-walled carbon nanotubes dispersity and solubility in dielectrophoresis mediums

The major limitation of carbon nanotubes (CNTs) is their poor solubility in the common solvents. Solving the solubility issue of CNTs is comprehended either by functionalizing the CNTs or using a dispersity agent. Agents such as ionic surfactant dramatically alter the suspension conductivity causing undesirable thermal flow in dielectrophoresis (DEP) mediums. In this study, the lack of CNTs solubility in common solvents was resolved by functionalizing multi-wall carbon nanotubes (MWCNTs) using a mild regulated procedure. The mild treatment was used to maintain the electrical conductivity of MWCNTs, since its essential for their dielectrophoretic response. Fourier-transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy were used to investigate the treatment quality. The ability of different solvents to dissolve MWCNT agglomerates after treatment was analyzed using ultraviolet-visible (UV-Vis) spectroscopy and dynamic light scattering (DLS) analysis. The characterization results indicate that the treated MWCNTs by the presented procedure contain hydroxylic and carboxylic functional groups and showed strong solubility in water, dimethylformamide (DMF) and acetone. This study provides a better solution to improve the processability of MWCNTs in common solvents without degrading their electrical conductivity.

Enhanced electrokinetic remediation for Cd-contaminated clay soil by addition of nitric acid, acetic acid, and EDTA: Effects on soil micro-ecology

Enhanced electrokinetic remediation (EKR) allows the rapid remediation of heavy metal-contaminated clay, but the impacts of this process on soil micro-ecology have rarely been evaluated. In this study, nitric acid, acetic acid, and EDTA were applied for enhancement of EKR and the effects on Cd removal, soil enzyme activity, and soil bacterial communities (SBCs) were determined. Nitric acid and acetic acid allowed 93.2% and 91.8% Cd removal, respectively, and EDTA treatment resulted in 40.4% removal due to the formation of negatively charged EDTA-Cd complexes, resulting in opposing directions of Cd electromigration and electroosmosis flow and slow electromigration rate caused by low voltage drop. Activities of soil beta-glucosidase, acid phosphatase, and urease, were all reduced by enhanced EKR treatment, especially nitric acid treatment, by 46.2%, 58.8% and 57.7%, respectively. The SBCs were analyzed by high-throughput sequencing and revealed significantly increased diversity for acetic acid treatment, no effect for EDTA treatment, and reduced diversity for nitric acid treatment. Compared with nitric acid and EDTA, acetic acid treatment enhanced EKR for higher Cd removal and improved biodiversity.

Lignin-based activated carbon-supported metal oxide catalysts in lactic acid production from glucose

In this study, heterogeneous biomass-based activated carbon-supported metal oxide catalysts were prepared and tested for lactic acid production from glucose in aqueous solution. Activated carbons were produced from hydrolysis lignin by chemical (ZnCl2) or steam activation and modified with a nitric acid treatment and Sn, Al, and Cr chlorides to obtain carbon-based metal oxide catalysts. The modification of the carbon support by nitric acid treatment together with Sn and Al oxides led to an increase in lactic acid yield. The highest lactic acid yield (42 %) was obtained after 20 min at 180 °C with the Sn/Al (5/2.5 wt.%) catalyst on steam-activated carbon treated by nitric acid. Reusability of the catalyst was also studied with the conclusion that the deposition of carbonaceous byproducts and leaching of Al oxides led to a decrease in catalyst selectivity to lactic acid.

Agricultural by-products and oyster shell as alternative nutrient sources for microbial sealing of early age cracks in mortar

Bio-concrete using bacterially produced calcium carbonate can repair microcracks but is still relatively expensive due to the addition of bacteria, nutrients, and calcium sources. Agricultural by-products and oyster shells were used to produce economical bio-concrete. Sesame meal was the optimal agricultural by-product for low-cost spore production of the alkaliphilic Bacillus miscanthi strain AK13. Transcriptomic dataset was utilized to compare the gene expressions of AK13 strain under neutral and alkaline conditions, which suggested that NaCl and riboflavin could be chosen as growth-promoting factors at alkaline pH. The optimal levels of sesame meal, NaCl, and riboflavin were induced with the central composite design to create an economical medium, in which AK13 strain formed more spores with less price than in commercial sporulation medium. Calcium nitrate obtained from nitric acid treatment of oyster shell powder increased the initial compressive strength of cement mortar. Non-ureolytic calcium carbonate precipitation by AK13 using oyster shell-derived calcium ions was verified by energy-dispersive X-ray spectroscopy and X-ray diffraction analysis. Stereomicroscope and field emission scanning electron microscopy confirmed that oyster shell-derived calcium ions, along with soybean meal-solution, increased the bacterial survival and calcium carbonate precipitation inside mortar cracks. These data suggest the possibility of commercializing bacterial self-healing concrete with economical substitutes for culture medium, growth nutrient, and calcium sources.

Effect of nitric acid treatment on the final low-frequency microwave absorption performance of TiO2/ZnFe2O4/ZnTiO3 nanocomposite

Effect of nitric acid treatment on the final low-frequency microwave absorption performance of TiO2/ZnFe2O4/ZnTiO3 nanocomposite

Lead poisoning and regeneration of Mn-Ce/TiO2 catalysts for NH3-SCR of NOx at low temperature

The effect of lead on the catalytic performance of Mn-Ce/TiO2 catalysts in the selective catalytic reduction (SCR) of NOx with ammonia at low temperature was investigated; with the help of nitrogen sorption, XRD, FT-IR spectroscopy, H2-TPR and NH3-TPD characterization, the causes of lead poisoning and acid regeneration were clarified. The results indicate that the doping of Pb in Mn-Ce/TiO2 leads to a significant decrease of the low-temperature SCR activity; with a Pb loading of 11%, the conversion of NO over Mn-Ce/TiO2 at 180°C decreases from original 100% on the fresh catalyst to 44% on the Pd-poisoned catalyst. The presence of Pb may reduce the content of active Mn4+ and Ce3+ species on the Mn-Ce/TiO2 catalyst, which suppresses the redox cycle of Mn4+ + Ce3+ ↔ Mn3+ + Ce4+; moreover, the decrease of surface acidity on the Mn-Ce/TiO2 catalyst by the doping of Pb is also disadvantageous to the adsorption and activation of NH3. The Pd-poisoned Mn-Ce/TiO2 can be regenerated by nitric acid treatment; after the regeneration, the catalytic activity of Mn-Ce/TiO2 in NH3-SCR of NO is almost completely recovered and even exceeds that of the fresh catalyst at 80–150°C. The nitric acid treatment can restore the redox capacity of Mn-Ce/TiO2, increase the surface area, and create new acid sites, which contribute to recovery of the activity of Pb-poisoned Mn-Ce/TiO2 catalyst in NH3-SCR.

Experimental and Numerical Study of Carbonation Mechanism of Concrete Exposed to Bending Stress and Nitric Acid Treatment

Experimental and Numerical Study of Carbonation Mechanism of Concrete Exposed to Bending Stress and Nitric Acid Treatment

Health Risk Assessment and Determination of Some Heavy Metals in Commonly Consumed Traditional Herbal Preparations in Northeast Ethiopia

Background. Most traditional medicines were prepared from plant origins. These plants could be contaminated by heavy metals, pesticides, and/or toxins. Therefore, the aim of the present study was to determine the level of heavy metals such as lead (Pb), cadmium (Cd), chromium (Cr), and copper (Cu) in frequently used traditional herbal preparations sold in Northeast Ethiopia and to estimate their health risks associated with their daily intake. Methods. A total of 6 traditional herbal preparations were randomly collected from local herbal shops of Dessie and Kombolcha town, Northeast Ethiopia. The samples were prepared for analysis by wet digestion method using nitric acid and hydrochloric acid treatment. The accuracy of the method was analyzed by the spike recovery test. Determination of Pb, Cd, Cr, and Cu by microwave plasma atomic emission spectroscopy was made in herbal preparations traditionally used in Dessie and Kombolcha town, Northeast Ethiopia. By calculating estimated daily intake (EDI), hazard quotients (HQ), and Hazard Index (HI) of metals, the health risk associated with the consumption of the analyzed herbal preparations was also evaluated. Results. The levels of heavy metals were in the range of 3.0–3.92 mg/kg for Pb, 5.35–10.7 mg/kg for Cr, and 0.815–12.3 mg/kg for Cu. However, cadmium was not detected in any of the traditional herbal preparations. This study revealed that the level of Pb and Cu in all analyzed samples was within the WHO maximum permissible limit of 10 mg/kg and 40 mg/kg, respectively. The level of Cr in all traditional herbal preparations was beyond the WHO maximum permissible limit (2 mg/kg). From the health point of view, the HQ value of Cr for KD-03 and KD-04 is greater than 1, suggesting potential health risk. Furthermore, the HI value had revealed that the consumption of KD-02, KD-03, and KD-04 samples had the potential of posing health risks to consumers over long-term consumption of herbal preparations. Conclusion. This study showed that most of the metal concentration levels in the herbal products were within the WHO maximum permissible limits. However, all samples had Cr levels above the WHO maximum permissible limit. Based on the results of this study, there would be a noncarcinogenic health risk to the consumer associated with the consumption of some herbal preparations marketed in Northeast Ethiopia.

Influence of nitric acid-assisted hydrothermal conditions on the characteristics of TiO2 catalysts and their activity in the oxidative steam reforming of methanol

Titania (TiO2) nanoparticles (NPs) with different morphologies (spherical, rod-shaped, and mixed) were prepared by hydrothermal treatment of different nitric acid (HNO3)/titanium (IV) isopropoxide (TTIP) molar ratios (0.25, 0.5, 1.0, and 1.7) at different hydrothermal temperatures (90, 150, 200, and 250 °C), hydrothermal times (6, 12, and 24 h), and calcination temperatures (500, 625, and 750 °C). The crystalline structure, morphology, and surface texture of the obtained TiO2 NPs were characterized by X-ray diffraction, nitrogen adsorption–desorption isotherm, field emission-scanning electron microscopy, and high resolution-transmission electron microscopy analyses. Under a larger HNO3: TTIP molar ratio, higher hydrothermal temperature, and higher hydrothermal time, the spherical mixed anatase–rutile phase TiO2 NPs were converted to a nanorod (NR)-shaped rutile phase (TiO2-R). The TiO2-R NRs gave the highest methanol conversion level (65%) and hydrogen yield (45%) in the oxidative steam reforming of methanol at 400 °C.

Investigation on Mechanical, Thermal and Bonding Properties of MWCNTs Reinforced Aramid/Epoxy Composite

The poor ability of bonding performance of aramid fiber with epoxy resin limits its usage for wide range of applications. In this research work, an attempt was made to improve the bonding performance of aramid fiber with polymer matrix by performing nitric acid treatment on fiber. The role of functionalized multi walled carbon nano tubes (F-MWCNTs) reinforced in the base polymer matrix is also studied. Six composite sheets (AF0, AF1, AF2, AF3, AF4, and AF5) with varying content of F-MWCNTs from (0.1wt% to 0.5wt %) are fabricated using hand layup method having dimensions of 25cm x 25 cm x 0.8 cm . AF0 composite sheet is free from presence of F-MWCNTs. The remaining ingredients [80% epoxy resin, 0.2 % rubber powder, 0.2% graphite powder, and 0.2% BaSO4, 0.2% Zirconium Silicate powder and 1.5 % fiber] are kept constant for achieving desirable properties of friction materials. After undergoing, curing process in atmosphere for 72 hrs, the specimens are cut according to ASTM standards to evaluate mechanical, thermal and bonding properties of the composites. Scanning electron microscope images (SEM) are observed for the samples to observe the grain distribution present in the composite. It was observed from results that, AF4 (aramid fiber reinforced composite friction material with 0.4% F-MWCNTs inclusions ) along with remaining ingredients exhibited better mechanical ,thermal and bonding properties compared to remaining formulations of materials.