Hydrogen Peroxide In Aqueous Solution Research Articles

ТЕРМИЧЕСКИЙ АНАЛИЗ ПРОДУКТОВ ОКИСЛЕНИЯ АКТИВИРОВАННОГО СПЛАВА АЛЮМИНИЯ RAU-85 В РАЗЛИЧНЫХ ОКИСЛИТЕЛЬНЫХ СРЕДАХ

By methods of differential thermal and thermogravimetric analysis, the composition of the thermally active part of the studied multicomponent samples of the products of the interaction of the activated aluminum alloy with various oxidizers was determined, and their thermal behavior was revealed under conditions of dynamic temperature rise. Thermal analysis was carried out in air environment, in the temperature range from 20 to 1000°C. The heating mode of the furnace was linear (dT/dt = 10 grad/min), the reference substance was calcined Al2 O3 . Water, 3% aqueous solution of hydrogen peroxide, 5% aqueous solution of sulfuric acid were used as oxidizing agents. Establishment of the material composition of the active part of powder samples was carried out according to the morphologies of thermal curves and numerical values of the intensities of endo- and exothermic effects using the thermogravimetric readings of TG-lines associated with them. A series of endo- and exothermic effects revealed during the decomposition of the test samples made it possible to follow the order of the stage of their thermal destruction and quantitatively determine the composition of volatile components. A number of features of sample decomposition were established depending on their composition and weight ratios of thermally active sample components. The obtained data on the thermal analysis of the oxidation products of the activated alloy RAU-85 in various oxidizing environments can be successfully applied to develop a technology for cleaning the bottomhole zone of the well from asphalt resin paraffin deposits, based on the thermal gas-chemical interaction of the activated aluminum alloy and formation water, which results in the formation of a large amount of heat and vapor-gas mixture.

Estimating Inhalation Exposure Resulting from Evaporation of Volatile Multicomponent Mixtures Using Different Modelling Approaches.

In many professional and industrial settings, liquid multicomponent mixtures are used as solvents, additives, coatings, biocidal products, etc. Since, in all of these examples, hazardous liquids can evaporate in the form of vapours, for risk assessments it is important to know the amount of chemicals in the surrounding air. Although several models are available in legal contexts, the current implementations seem to be unable to correctly simulate concentration changes that actually occur in volatile mixtures and in particular in thin films. In this research, the estimation of evaporation rates is based on models that take into account non-ideal behaviour of components in liquids and backpressure effects as well. The corresponding system of differential equations is solved numerically using an extended Euler algorithm that is based on a discretisation of time and space. Regarding air dispersion of volatile components, the model builds upon one-box and two-box mass balance models, because there is some evidence that these models, when selected and applied appropriately, can predict occupational exposures with sufficient precision. That way, numerical solutions for a wide variety of exposure scenarios with instantaneous and continuous/intermittent application, even considering “moving worker situations”, can be obtained. A number of example calculations have been carried out on scenarios where binary aqueous solutions of hydrogen peroxide or glutaraldehyde are applied as a biocidal product to surfaces by wiping. The results reveal that backpressure effects caused by large emission sources as well as deviations from liquid-phase ideality can influence the shape of the concentration time curves significantly. The results also provide some evidence that near-/far-field models should be used to avoid underestimation of exposure in large rooms when small/medium areas are applied. However, the near-field/far-field model should not be used to estimate peak exposure assuming instantaneous application, because then the models tend to overestimate peak exposure significantly. Although the example calculations are restricted to aqueous binary mixtures, the proposed approach is general and can be used for arbitrary liquid multicomponent mixtures, as long as backpressure effects and liquid-phase non-idealities are addressed adequately.

Effect of chitosan coating on polypropylene fibers on the deposition of copper ions

AbstractComposites based on chitosan coatings and metal ions are attracting great attention due to their antibacterial properties and biocompatibility. It is known that the presence of chitosan helps to stabilize the growth of metal films or individual nanoparticles during their deposition. In this work chitosan coating obtained from an aqueous carbonic acid solution is applied to fibers of a polypropylene nonwoven membrane. Aqueous carbonic acid solution is a clean and cheap solvent for chitosan that can effectively impregnate a porous polypropylene matrix. Before chitosan deposition, the fibers were pretreated in the presence of peroxycarbonic acid (i.e., in an aqueous hydrogen peroxide solution saturated with pressurized carbon dioxide). Copper ions were then deposited on the chitosan‐coated fibers. It was shown that the presence of a chitosan interlayer can significantly improve adhesion and reduce the aggregation of growing particles, which results in the decoration of the fibers with uniform thin copper‐containing films. The proposed method for creating composite materials can serve as a new approach to antibacterial polymer‐inorganic composites manufacturing.

Properties for the spectral parameters of intermolecular vibrations obtained using Raman scattering of light in dilute aqueous solutions of hydrogen peroxide and in the water

The spectra of Raman scattering (in the region 4-350 cm-1) of dilute aqueous solutions of hydrogen peroxide in a wide range of concentrations (from 3 to 0.024%), were measured. The spectral parameters of the high-frequency band of intermolecular (longitudinal) vibrations, obtained using the previously proposed approximating function, were analyzed. To do this, the spectral parameters of the band (for each experiment) were plotted on a diagram in which the abscissa axis is the square of the band width, and the ordinate axis is the square of the band frequency. Previously, it was shown that in such coordinates the water points are located in two regions separated by an inclined strip, in which spectral points (frequency gap) are practically absent. For points of hydrogen peroxide solutions with a concentration from 3 to 0.33%, all points are grouped near the straight line approximating them and are located below this frequency gap. For a series with extended range of peroxide concentrations from 3 to 0.024%, the scatter of points from the approximating straight line increases, but also most of the points are located below the gap. Of the rest of points, several points are near the edge of the gap, some of them are inside the gap, but the gap remains. It has been suggested that the presence of this gap is due to the fact that in the liquid phase some of the water molecules are bound to four neighbors, while the remaining molecules are bound to a smaller number of neighbors. Keywords: Raman scattering, hydrogen peroxide, water, intermolecular vibrations, high-frequency band, inhomogeneous distribution, frequency gap, destruction of high-frequency states.

An ESIPT-Dependent AIE Fluorophore Based on HBT Derivative: Substituent Positional Impact on Aggregated Luminescence and its Application for Hydrogen Peroxide Detection.

Aiming to develop the facile organic fluorophore possessing excited state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE), we designed and synthesized two isomers with different linkage site between hydroxyl of 2-(2-hydroxyphenyl) benzothiazole (HBT) and a benzothiazole substituent (para position refers to p-BHBT and ortho position refers to o-BHBT). Fluorescence emission properties of p-BHBT and o-BHBT in THF/water mixtures with different water volume fractions indicated an opposite luminescence in aggregates, in which p-BHBT showed an ESIPT-dependent AIE properties while o-BHBT displayed ESIPT effect and aggregation-caused quenching (ACQ) qualities. A possible mechanism for molecular actions to illustrate the aggregating luminescence alteration of these two isomers had been proposed and verified by theoretical and experimental studies. More importantly, Probe-1, generated from dual ESIPT-AIE fluorophore p-BHBT, was successfully used as a ratiometric fluorescent chemosensor for highly selective (above 15-fold over other ROS) and sensitive (69-fold fluorescence enhancement with 0.22 μM of detection limit) detection of hydrogen peroxide in aqueous solution and living cells, respectively.

К вопросу об оптимальной микробиологической деконтаминации воздушной среды и поверхностей

Modern civilization, providing economic and social progress, at the same time objectively creates – sometimes close to ideal – conditions for the spread of various infections. The catastrophic consequences of the SARS-CoV-2 pandemic clearly indicate that homo sapiens appeared to be unable to resist effectively the onslaught of the coronavirus. The purpose of this publication is an attempt to fill the gap in the development of effective methods and means for microbiological decontamination that are optimal in terms of critical parameters. Observational data indicate that a significant number of SARS-CoV-2 coronavirus infections occur by air without a direct contact with the source, including, over a long time interval. Precipitations help to cleanse the air from pollutants and viruses, reducing non-contact contamination, which additionally brings up to date the problem of optimal microbiological decontamination of the air environment and surfaces. A thermodynamic approach has been used to optimize microbiological sterilization. It is shown that irreversible chemical oxidation reactions are the shortest way to achieve sterility, and they are capable of providing high reliability of deconta-mination. It has been established that oxygen is an optimal oxidant, also from the point of view of ecology, since its reactive forms harmoniously fit into natural exchange cycles. The optimal method for obtaining reactive oxygen species for disinfection is the use of low-temperature (“cold”) plasma, which provides energy-efficient generation of oxidative reactive forms – atomic oxygen (O), ozone (O3), hydroxyl radical (·OH), hydrogen peroxide (H2O2), superoxide (O2-), and singlet oxygen O2(a1Δg). Due to a short lifetime for most of the above forms outside the plasma applicator, remote from the plasma generator objects should be sterilized with ozone (O3), the minimum lifetime of which is quite long. It has been substantiated that the microwave method of generating oxygen plasma is optimal for the energy efficient ozone production. A modular principle of generation is proposed for varying the productivity of ozone generating units over a wide range. The module has been developed on the base of an adapted serial microwave oven, in which a non-self-sustaining microwave discharge is maintained thanks to ionizers (igniters), including those based on radiating radionuclides-emitters. In case of massive contamination of surfaces, it is advisable – in addition to ozone (O3) air disinfecting – to use aqueous solutions of hydrogen peroxide (H2O2). It is essential that these reactive oxygen species for disinfecting remote from the plasma generator objects are highly efficient and, at the same time, environmentally neutral. Reliable and affordable personal protective equipment is proposed for activities in zones of increased ozone concentration. The considered optimal means of disinfection can be applicable not only in medicine, but also adapted for numerous practices in agriculture, industry, and in everyday life.

Highly permeable and antioxidative graphene oxide membranes for concentration of hydrogen peroxide aqueous solution

Hydrogen peroxide, as a green oxidant, received broad and increasing applications. Membrane technology affords a promising solution to achieve in-situ production and concentration of hydrogen peroxide. Membrane material selection and structure design remain a grand challenge arising from the strong oxidation property of hydrogen peroxide. Herein, we explored graphene oxide membranes to concentrate hydrogen peroxide for the first time. By manipulating the cross-linking process of thiourea molecules, the interlayer channel size can be tuned in the range of 2.9–3.2 Å, ensuring the distinct molecular sieving between water and hydrogen peroxide. The graphene oxide membranes displayed superior separation performance with separation factor of 22.8 and permeation flux of 18.2 kg m−2 h−1. Compared with conventionally water-permeable membranes, graphene oxide membranes exhibit excellent antioxidative ability and stability in the 168 h operation test.

Reactions in Activated Peroxide Systems and their Influences on Bleaching Performance

Activated peroxide systems are formed by adding so-called bleach activators to an aqueous solution of hydrogen peroxide, developed in the seventies of the last century for use in the domestic laundry for their high energy efficiency and introduced at the beginning of the 21st century to the textile industry as an approach toward overcoming the extensive energy consumption in bleaching. In activated peroxide systems, bleach activators undergo perhydrolysis to generate more kinetically active peracids that enable bleaching under milder conditions while hydrolysis of bleach activators and decomposition of peracids may occur as side reactions to weaken the bleaching efficiency. This mini-review aims to summarize these competitive reactions in activated peroxide systems and their influence on bleaching performance.

Integration of electron beam technology into fresh produce wash water line: Effect of inoculum suspension medium and water quality parameters on the radioresistance of Salmonella Typhimurium ATCC 13311

AbstractElectron beam technology may be integrated into the fresh produce wash water line, as an advanced oxidation process (AOP). However, prior to implementation, effectiveness of the technology must be assessed. Hydroxyl radical scavengers were used to quantify the role of yield of hydroxyl radicals in inactivation of the selected pathogen in aqueous solution. The combined lethal effect of e‐beam treatment with aqueous hydrogen peroxide (H2O2) solution was also investigated. The radioresistance of Salmonella Typhimurium ATCC 13311 in deionized (DI) water, that is radiation D10 values, increased (p < .05) from 0.15 ± 0.00 kGy to 0.18 ± 0.00 kGy and to 0.19 ± 0.06 kGy when peptone water (PW) and phosphate buffered saline (PBS) was dissolved into DI water, respectively. Membrane‐permeable ethanol provided better protection for this pathogen than nonpermeable PEG. Results suggest that to minimize the protective effects of inoculating suspending media used for the preparation of Salmonella suspension, 1.0 mM phosphate buffer (PB) should be used in microbial studies of irradiated foods. Nitrate and dissolved organic carbon (DOC) reacting with hydrated electrons (eaq−) and hydroxyl radicals (·OH), respectively, induced more sequestering of ·OH. E‐beam treatment with 0.60 kGy dose in aqueous solution with H2O2 led to a reduction of 6.44 ± 0.03 log CFU/mL f S. Typhimurium ATCC 13311.

Structure of bimetallic tartrate complexes for the rapid formation of new non-enzymatic bimetallic sensors of glucose and hydrogen peroxide in aqueous solutions using laser synthesis

The use of laser methods for synthesizing new materials for non-enzymatic electrochemical microsensors for express analysis of biological fluids is a promising scientific question.Laser-induced chemical liquid phase deposition is the laser deposition of invisible miniature bimetallic deposits from aqueous solutions of salts and complexes of transition metals. Bimetallic complexes containing two transition metal cations in the shell of one ligand are of increased interest. There is an information gap in this area even for ligands such as tartrate. The studies carried out make it possible to obtain new information on the structure of bimetallic tartaric complexes in solutions containing simultaneously copper, nickel, silver, iron, and cobalt.

Experimental Investigation on the Cleaning Effect and Influence Rule of Hydrogen Peroxide–Acetic Acid on Lead–Bismuth Eutectic Alloy

During the refueling process of lead–bismuth eutectic (LBE)–cooled fast reactors, lead–bismuth alloy can easily adhere to the surface of the fuel rod clads when spent fuel assemblies are unloaded from the reactor core. For some designs, the lead–bismuth alloy attached on the spent fuel rods will be cleaned via physical or/and chemical methods prior to their transportation, storage, and reprocessing. In this article, the cleaning effect of a washing lotion composed of hydrogen peroxide (H2O2) aqueous solution and concentrated acetic acid (CH3COOH) as the main components on LBE was experimentally investigated. By adjusting the composition ratio of the washing lotion and the reaction temperature, the law of their influence on the cleaning effect of LBE was determined. The optimal washing lotion composed of 30 Vol% hydrogen peroxide aqueous solution as oxidant, 40 Vol% concentrated acetic acid as acid, and 30 Vol% ultrapure water as the solvent was proposed based on experimental investigations. The optimal working temperature range was also obtained. The reaction intermediate product was characterized with the XRD analysis in order to understand the reaction mechanism. The composition of the released gas (even in a slight amount) was also analyzed with gas chromatography. The hydrogen concentration in the released gas was found to be lower than the detection limit of gas chromatography (10 ppm). Since the explosion limits of hydrogen at atmospheric pressure are between 3.95 and 75.73 Vol%, the risk of possible hydrogen explosion is concluded to be extremely low. Therefore, no special treatment of the released gas is required even in a large-scale industrial platform. Furthermore, corrosion effect of the washing lotion on austenitic stainless steel components was tested as well and found to be negligibly small. The relative mass loss of the thin-walled stainless steel samples immersed in the washing lotion was found to be less than 0.5% after an experimental duration of 144 h, which facilitates sufficient cleaning time in future industrial applications.

Spectroscopic characterization, X-ray molecular structures and cyclic voltammetry study of two (piperazine) cobalt(II) meso-arylporphyin complexes. Application as a catalyst for the degradation of 4-nitrophenol

Two new cobaltous-porphyrin complexes, namely (μ-piperazine)-bis[(meso-tetra(para-methoxyphenyl)porphyrinato)]cobalt(II) and (piperazine)[meso-tetra(para-chlorophenyl)porphyrin]cobalt(II) dichloromethane disolvate, with the formulas [{CoII(TMPP)}2(μ2-pipz)] (complex 1) and [CoII(TClPP)(pipz)]·2CH2Cl2 (complex 2), were used efficiently as catalysts in the degradation of 4-nitrophenol (4-NP) in an aqueous hydrogen peroxide solution. These cobalt(II)-pipz porphyrin complexes were characterized by a variety of spectroscopic methods including infrared, UV–visible, fluorescence, proton nuclear magnetic resonance, electron paramagnetic resonance (EPR) as well as mass spectrometry. A cyclic voltammetry investigation was also carried out on these two Co(II) metalloporphyrins. The EPR results indicate that both complexes 1 and 2 are paramagnetic low-spin (S = 1/2) cobalt(II) porphyrin complexes. Furthermore, the X-ray diffraction crystal structures of 1 and 2 were determined, and the intermolecular interactions were investigated by Hirshfeld surface analysis.

Effective Epoxidation of Fatty Acid Methyl Esters with Hydrogen Peroxide by the Catalytic System H3PW12O40/Quaternary Phosphonium Salts

Six quaternary phosphonium salts (QPSs) in combination with phosphotungstic heteropolyacid, H3PW12O40, were tested in the epoxidation of rapeseed oil fatty acid methyl esters with a hydrogen peroxide aqueous solution. The QPSs consisted of trihexyl(tetradecyl)phosphonium [P6], tributyl-tetradecylphosphonium [P4] or tetraoctylphosphonium [P8] cation and different anions—chloride (Cl−), bromide (Br−), tetrafluoroborate (BF4−), bis(trifluoromethylsulfonyl)amide (NTf2−), bis(2,4,4-trimethyl-pentyl)phosphinate (Phosf−). The influence of the kind of QPS and temperature on the epoxy number, iodine number, glycol content has been determined. The epoxidation was confirmed using Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR) and elemental analysis CHO. Two QPSs with a trihexyltetradecyphosphonium cation—[P6][Fosf] and [P6][Cl]—were selected as the most effective in the studied epoxidation process. The proposed kinetic model takes into consideration the two reactions, namely, epoxidation and epoxy ring opening involving the formation of hydroxyl groups. The rate constants and activation energies for epoxidation fatty acid methyl esters were determined.

Role of an Inorganic Phosphate in the Photogeneration of Hydrogen Peroxide in Aqueous Solutions of Adenine Derivatives at 77 K

Role of an Inorganic Phosphate in the Photogeneration of Hydrogen Peroxide in Aqueous Solutions of Adenine Derivatives at 77 K

Effect of H2O2 Antiseptic on Dispersal of Cavitation-Induced Microdroplets

The persisting outbreak of SARS-CoV-2 has posed an enormous threat to global health. The sustained human-to-human transmission of SARS-CoV-2 via respiratory droplets makes the medical procedures around the perioral area vulnerable to the spread of the disease. Such procedures include the ultrasonic dental cleaning method, which occurs within the oral cavity and involves cavitation-induced sprays, thus increasing the risk of pathogen transmission via advection. To understand the associated health and safety risks for patients and clinicians, it is critical to understand the flow pattern of the spray cloud around the operating region, the size and velocity distribution of the emitted droplets, and the extent of fluid dispersion until ultimate deposit on surfaces or escape through air vents. In this work, the droplet size and velocity distributions of the spray emerging from the tip of a free-standing common ultrasonic dental cleaning device were characterized via high-speed imaging. Deionized water and 1.5% and 3% aqueous hydrogen peroxide (H2O2) solutions were used as working fluids, with the H2O2—an established oxidizing agent—intended to curb the survival of virus released in aerosols generated from dental procedures. The measurements reveal that the presence of H2O2 in the working fluid increases the mean droplet size and ejection velocity. Detailed computational fluid dynamic simulations with multiphase flow models reveal benefits of adding small amounts of H2O2 in the feed stream of the ultrasonic cleaner; this practice causes larger droplets with shorter residence times inside the clinic before settling down or escaping through air vents. The results suggest optimal benefits (in terms of fluid spread) of adding 1.5% H2O2 in the feed stream during dental procedures involving ultrasonic tools. The present findings are not specific to the COVID-19 pandemic but should also apply to future outbreaks caused by airborne droplet transmission.

Report of the Scientific Committee of the Spanish Agency for Food Safety and Nutrition (AESAN) on the safe use of two aqueous solutions of hydrogen peroxide, acetic acid and peracetic acid as processing aids for the bacterial disinfection of apples and peaches washing water

Report of the Scientific Committee of the Spanish Agency for Food Safety and Nutrition (AESAN) on the safe use of two aqueous solutions of hydrogen peroxide, acetic acid and peracetic acid as processing aids for the bacterial disinfection of apples and peaches washing water

Treatment of the railway freight wagon wash effluents by coagulation methods on accelator reactor

This paper presents results of the research carried out on a system made to pretreat the effluents produced in water treatment of dirty surfaces of railway transportation means (RTMs) mainly G, H, T and incidental F classes of rolling stock according to the International Union of Railways (IURs). The installation was designed for coagulation–flocculation pretreatment of wastewater with flow accelator reactor (AR) in total amount of up to 75.0 m3 day−1. The raw wastewater (RW) was characterized by a significant diversity of loads: TSS (total suspended solids), TDS (total dissolved solids), COD & BOD5 (chemical & biochemical oxygen demand) and periodically it had extremely different colors, Ta (turbidity) and EE (etheric extract). The application of two-stage, coupled acid-alkali or alkaline-acid coagulation using aluminum coagulants with final flocculation and phase separation in the system implemented in practice to treat the wastewater of statistically typical composition, usually allowed to removal, accordingly: EE & TSS > 99% and to eliminate completely color and Ta. However, COD and BOD5 were removal at different levels, depending on both initial concentrations and chemical composition of load pools registered in the RW, and a type of coagulation used. The use of pre-oxidation with aqueous solutions of hydrogen peroxide or peracetic acid coupled with coagulation based only on aluminum coagulants helps to achieve equal levels of removal of the basic indicator values and a sanitary clean stream of pretreated wastewater (PW) with a colony forming unit (CFU) of <100 ml−1.

In English

Nitrogen-containing carbon nanotubes (CNTs) were synthesized by the CVD method on oxide catalysts of Al-Fe-Mo-O by adding acetonitrile or ethylenediamine to the carbon source (propylene), or completely replacing it, as well as impregnating the original CNTs with urea, followed by heat treatment. The structure of nitrogen-containing CNTs (N-CNT) was characterized by the method of Raman scattering, transmission electron microscopy (TEM), differential thermal and gravimetric analysis (DTA, DTG) and X-ray photoelectron spectroscopy (XPS). The influence of the synthesis method on the number and chemical state of nitrogen heteroatoms in the structure of the carbon matrix is found. According to the TEM, nitrogen-containing CNTs have a characteristic bamboo-like structure, which is less perfect compared to the structure of the original CNTs: the characteristic Raman bands (G and D) are shifted to higher frequencies, their half-width and band D intensity increase relative to G. This is also manifested in the lower thermal stability of nitrogen-containing CNTs. According to the XPS, the direct synthesis of nitrogen-containing CNTs increases the total content of nitrogen atoms and the proportion of pyrrolic and quaternary nitrogen against the background of a significant decrease in the amount of pyridinic form. This can be explained by the fact that nitrogen is evenly distributed throughout the carbon matrix of CNTs, and during nitriding of CNTs with urea, nitrogen is included mainly in the surface layers and defects, because the pyridine form is characteristic of the edge location of the nitrogen atom in the graphene plane.The catalytic effect of multilayer nitrogen-containing carbon nanotubes (N-CNT) on the kinetics of decomposition of hydrogen peroxide in aqueous solutions at different pH values is considered. It is concluded that the method of direct synthesis of nitrogen-containing CNTs allows to obtain more catalytically active carbon nanotubes containing more nitrogen, mainly pyrrolic and quaternary type. It has been found that regardless of the method of synthesis, the maximum catalytic activity in the decomposition of hydrogen peroxide is observed at pH 7.

Dynamics of a bifunctional motor under crowded conditions

A simple and inexpensive fabrication of a polymer based bifunctional motor, containing catalytic palladium nanoparticles (Pd NPs) and luminescent zinc quinolate inorganic complex (Zn-QC), is reported. The motor displayed buoyancy driven self-propulsion in aqueous hydrogen peroxide (H2O2) solution, and could be easily tracked within liquid media using its luminescence under UV light. The propulsion speed and the luminescence of the motor were found to be correlated with the solution viscosity and local concentration of macromolecules within the medium. The bifunctional motor was further used to monitor bacterial concentration in solutions and was found to be an excellent probe for simultaneous characterization of spatio-temporal density and viscosity profiles of inhomogeneous solutions and particle assemblies. The motor fabricated is scalable and offers convenient platform for using self-powered catalytic motors in gleaning comprehensive insights into the rheology and density profiles of complex crowded systems, like the cytosol.

Understanding mechanism of enhanced specific heat of single molten salt-based nanofluids: Comparison with acid-modified salt

This study aimed to identify the mechanisms for enhancing the specific heat of KNO3-SiO2 nanofluids in both solid and liquid phases. The specific heat of the nanofluids was examined by a different scanning calorimetry, by varying the concentration of the nanoparticle (0.1–10 wt%). The specific heat increased with the nanoparticle concentration but decreased beyond the optimal concentration (1 wt%). The specific heat of the nanofluids was enhanced by up to 24.1% and 28.1% in the solid and liquid phases, respectively. In order to account for the reasons for the enhanced specific heat of the molten salt nanofluids, acid-modified salts in which the aqueous hydrogen peroxide (H2O2) solution was added to KNO3 were prepared, and their specific heat was examined by varying the amount of H2O2. The acid-modified salts showed an enhanced specific heat of 21.1% and 29.5% in the solid and liquid phases, respectively, and similar concentration-dependent specific heat as the nanofluids. Fourier transform infrared spectroscopy and energy-dispersive X-ray spectroscopy as well as scanning electron microscopy were used to corroborate the nanoparticle dispersion into the salt. X-ray diffraction analysis was conducted to compare the crystallite sizes of the nanofluids and acid-modified salts to that of pure KNO3. The reduced crystallite size (increased interfacial area between crystallites) accounts for the enhanced specific heat in the solid phase. Based on the zeta potential measurements, the Stern layer and Debye length, which consist of the electric double layer (EDL), were estimated to be 0.45 and 0.97 nm, respectively, for the KNO3-SiO2 nanofluid. Similar features on the Stern layer and Debye length were obtained for the acid-modified salts. The formation of the EDL adjacent to the nanoparticles accounts for the enhanced specific heat of the nanofluids in the liquid phase.