Different Amounts Of Citric Acid Research Articles

Effect of Heating and Citric Acid on the Performance of Cellulose Nanocrystal Thin Films

Cellulose nanocrystals (CNCs) were extracted from bleached cotton by sulfuric acid hydrolysis. Thin films were prepared from the aqueous suspension of CNCs by casting and evaporation with 15% glycerol as a plasticizer. Our research aimed to create stable films resistant to water. The structure and the interactions of the films were modified by short (10 min) heating at different temperatures (100, 140, and 160 °C) and by adding different amounts of citric acid (0, 10, 20, and 30%). Various analytical methods were used to determine the structure, surface properties, and mechanical properties. The interaction of composite films with water and water vapor was also investigated. Heat treatment did not significantly affect the film properties. Citric acid, without heat treatment, acted as a plasticizer. It promoted the disintegration of films in water, increased water vapor sorption, and reduced tensile strength, resulting in flexible and easy-to-handle films. The combination of heat treatment and citric acid resulted in stable liquid-water-resistant films with excellent mechanical properties. A minimum heating temperature of 120 °C and a citric acid concentration of 20% were required to obtain a stable CNC film structure resistant to liquid water.

Phytoremediation of uranium-contaminated soil by perennial ryegrass (Lolium perenne L.) enhanced with citric acid application.

Perennial ryegrass (Lolium perenne L.) was planted in uranium-contaminated soil mixtures supplemented with different amounts of citric acid to investigate the defense strategies of perennial ryegrass against U and the enhanced mechanism of citric acid on the remediation efficiency in the laboratory. The uranium content in the plant tissues showed that the roots were the predominant tissue for uranium accumulation. In both root and shoot cells, the majority of U was located in the cell wall fraction. Furthermore, antioxidant enzymes were also stimulated when exposed to U stress. These results suggested that perennial ryegrass had evolved defense strategies, such as U sequestration in root tissue, compartmentalization in the cell wall, and antioxidant enzyme systems, to minimize uranium stress. For an enhanced mechanism, the optimal concentration of citric acid was 5mmol/kg, and the removal efficiency of U in the shoots and roots increased by 47.37% and 30.10%, respectively. The treatment with 5mmol/kg citric acid had the highest contents of photosynthetic pigment and soluble protein, the highest activity of antioxidant enzymes, and the lowest content of MDA (malondialdehyde) and relative electrical conductivity. Moreover, the TEM (transmission electron microscope) results revealed that after 5mmol/kg citric acid was added, the cell structure of plant branches partially returned to normal, the number of mitochondria increased, chloroplast surfaces seemed normal, and the cell wall became visible. The damage to the cell ultrastructure of perennial ryegrass was significantly alleviated by treatment with 5mmol/kg citric acid. All the results above indicated that perennial ryegrass could accumulate uranium with elevated uranium tolerance and enrichment ability with 5mmol/kg citric acid.

Synthesis of WO3 nanorods through anodization in the presence of citric acid: Formation mechanism, properties and photoelectrocatalytic performance

In this study, WO 3 nanorods have been fabricated by simple anodization in the presence of different amounts of citric acid and at different anodization times. A comprehensive morphological, structural, electrochemical and photoelectrochemical characterization of different samples has been carried out. Moreover, a formation mechanism for WO 3 nanorods has been proposed. Finally, these nanostructures have been proven to be excellent visible-light photoelectrocatalysts to remove persistent organic pollutants present in wastewaters, such as fenamiphos. Almost the 80% of this molecule was eliminated from the test solution after 180 min of irradiation, indicating the great potential of these WO 3 nanorods, fabricated following a very simple and unexpensive procedure, in the energy and environmental fields as photoelectrocatalysts. • Citric acid influences the type and size of WO 3 nanostructures formed by anodization. • Large nanoplatelets were obtained in the absence of citric acid. • Nanorods formed with citric acid whose size decreased with increasing concentration. • WO 3 nanorods were used as photoelectrocatalysts for the degradation of fenamiphos. • After 180 min, almost the 80% of initial fenamiphos was degraded.

Effect of citric acid on the morpho-structural and magnetic properties of ultrasmall iron oxide nanoparticles

The structural and magnetic properties of iron oxide nanoparticles obtained by the precipitation of iron ions in the presence of different amounts of citric acid were studied. The citric acid acts as a capping agent and provides control of the particle size to be obtained. The size dependence of the magnetic properties was investigated by comparing the results for ~2, 4, 6, and 8 nm particles. With decreasing the particle size, a reduction of the saturation magnetization (from ~84 to 33 Am2/kg) and an increase of coercivity (from ~32 to ~100 mT) were observed, due to the increasing role of the disordered surface. The behaviour of the zero-field cooled/field cooled magnetization curves indicates a superspin-glass freezing for 2 nm and 4 nm particle samples. Memory experiments below the freezing temperature on the 2 nm particle sample provide further evidence of a glassy magnetic state. The observation of exchange bias, due to core/shell interface exchange coupling, for 2 nm and 4 nm particle samples provides evidence of a surface spin-glass type freezing, which contributes to the observed glassy properties.

Crystal phase, morphology evolution and luminescence properties of Eu3+ -doped BiPO4 phosphor prepared using the hydrothermal method.

A series of Bi1-x Eux PO4 phosphors was successfully prepared using an easy citric acid- assisted hydrothermal method. The effects of synthesis temperature, amount of citric acid, and Eu3+ concentration on the crystal phase, morphology, and luminescence properties were investigated. X-ray diffraction results revealed that BiPO4 :Eu3+ formed a hexagonal phase at 80°C, although it transformed to a monoclinic phase when the hydrothermal temperature was increased to 160°C. Moreover, it was found that a small amount of Eu3+ doping and the addition of citric acid introduced no secondary or related phases. The morphologies of the samples varied from nanoparticles to spherical microparticles to polyhedrons after the synthesis temperature was adjusted. Particle size was controlled by adding different amounts of citric acid. Under 394 nm excitation, the Bi0.95 Eu0.05 PO4 phosphor prepared at 160°C with 0.3 g of citric acid had excellent luminescence properties. A possible crystal growth mechanism during this reaction is proposed.

Mosaic structure ZnO formed by secondary crystallization with enhanced photocatalytic performance

Zinc acetate is used as a raw material to synthesize the desired ZnO in hot solvent by controlling the amount of citric acid (CA) added. Notably, the amount of CA added has a significant relationship with the control of the morphology of ZnO. Spherical ZnO wrapped in nanosheets is synthesized through the secondary crystallization of Zn2+. The optical properties of the ZnO sample are tested through the degradation of organic pollutants. Notably, the photocatalytic properties of ZnO vary with the different amounts of CA added. Exposure of the active crystal face increases the photocatalytic activity of ZnO. In addition, the number of defects on the surface of the ZnO sample increases because of its large specific surface area, thus changing the bandgap of ZnO. Therefore, the resulting sample can respond under visible light.

Sustainable production of value-added chemicals and fuels by using a citric acid-modified carbon nitride optical semiconductor

Citric acid-modified graphite-like carbon nitride materials (GCN-zCA) were synthetized by thermal co-polymerization of dicyandiamide with different amounts of citric acid (z = between 5 and 25 mg). The resulting materials presented surface porosity, defective polymeric structure, and enhanced visible light absorption in the 450−700 nm range, attributed to the existence of mid-gap states and n-π* electronic transitions. All the modified catalysts presented high selectivity (>99 %) towards the conversion of p-anisyl alcohol into p-anisaldehyde under visible-LED irradiation, the best performing photocatalyst (GCN-20CA) reaching 63 % yield (contrasting with 22 % obtained with bulk GCN) after 240 min reaction. GCN-20CA was also applied for hydrogen generation from water splitting. The modified material practically duplicated the hydrogen production when compared to bulk GCN (75 and 44 μmol H2 evolved in three hours, respectively), by using platinum nanoparticles as co-catalyst and EDTA as sacrificial electron donor. Moreover, p-anisyl alcohol was successfully used as sacrificial agent for water splitting, with simultaneous production of p-anisaldehyde and H2. Reusability tests showed that GCN-20CA remained stable in a series of consecutive runs both for p-anisaldehyde synthesis and hydrogen production.

Controllable Synthesis of Flower-Like MoS₂ and Its Quick Photodegradation of Methylene Blue Under Visible Irradiation.

Molybdenum disulfide (MoS₂) was synthesized via hydrothermal process under the assistance of citric acid, which exhibited high photocatalytic property in the application of methylene blue (MB) degradation. The flower ball microstructure of MoS₂ changed with different amounts of citric acid. X-ray diffraction (XRD), Scanning electron microscope (SEM), UV-Vis diffuse reflectance spectra have been employed to characterize the samples. It improved the photocatalytic efficiency nearly 19.77% compared to MoS₂ without citric acid. When H₂O₂ was added, the synergistic effect of MoS₂ and hydrogen peroxide (H₂O₂) was observed in photocatalytic reaction system, which degraded MB completely within 40 min under visible light irradiation.

A High-Performance Ni/SiO2 Prepared by the Complexed-Impregnation Method with Citric Acid for Carbon Dioxide Reforming of Methane

A group of Ni/SiO2 catalysts was prepared via the complexed-impregnation method with different amounts of citric acid (Ni–C/SiO2). The Ni–C/SiO2 and Ni/SiO2 prepared by the conventional impregnatio...

Mechanical and Drug Release Properties of Sponges from Cross-linked Cellulose Nanofibers.

All-organic porous sponges were obtained throughout the direct and solvent-free (oven 105 °C, time>6 h) crosslinking of TEMPO-oxidized cellulose nanofibers (TOCNF) with 25 kDa branched polyethyleneimine (bPEI) in the presence of different amounts of citric acid (CA) as co-crosslinker. The chemical and mechanical stability of these materials was provided by the formation of amide bonds between the carboxylic moieties of TOCNF and CA with the primary amines of bPEI. The mechanical properties were investigated under static and dynamic loads with both dry and wet samples. The materials had the interesting capability to recover their shape with reduced losses in mechanical resistance, while their Young's modulus progressively increased with the content of CA. In work toward developing possible applications of bPEI-TOCNF sponges in drug delivery, amoxicillin (AM) and ibuprofen (IB) were considered as model drugs. All materials showed very good performance in adsorbing both AM and IB (ca. 200 mg g-1 ) from methanol solution. In particular, an increased adsorption of IB was observed in parallel to the increase of citrate moieties in the samples. Moreover, samples crosslinked in presence of CA showed slower kinetic release in aqueous environments than materials obtained without CA.

Development and virucidal activity of a novel alcohol-based hand disinfectant supplemented with urea and citric acid.

BackgroundHand disinfectants are important for the prevention of virus transmission in the health care system and environment. The development of broad antiviral spectrum hand disinfectants with activity against enveloped and non-enveloped viruses is limited due to a small number of permissible active ingredients able to inactivate viruses.MethodsA new hand disinfectant was developed based upon 69.39 % w/w ethanol and 3.69 % w/w 2-propanol. Different amounts of citric acid and urea were added in order to create a virucidal claim against poliovirus (PV), adenovirus type 5 (AdV) and polyomavirus SV40 (SV40) as non-enveloped test viruses in the presence of fetal calf serum (FCS) as soil load. The exposure time was fixed to 60 s.ResultsWith the addition of 2.0 % citric acid and 2.0 % urea an activity against the three test viruses was achieved demonstrating a four log10 reduction of viral titers. Furthermore, this formulation was able to inactivate PV, AdV, SV40 and murine norovirus (MNV) in quantitative suspension assays according to German and European Guidelines within 60 s creating a virucidal claim. For inactivation of vaccinia virus and bovine viral diarrhea virus 15 s exposure time were needed to demonstrate a 4 log10 reduction resulting in a claim against enveloped viruses. Additionally, it is the first hand disinfectant passing a carrier test with AdV and MNV.ConclusionsIn conclusion, this new formulation with a low alcohol content, citric acid and urea is capable of inactivating all enveloped and non-enveloped viruses as indicated in current guidelines and thereby contributing as valuable addition to the hand disinfection portfolio.

Production of hydrogen from glucose by LaFeO3 based photocatalytic process during water treatment

In this work the hydrogen production from photocatalytic degradation of glucose aqueous solution using LaFeO3 catalysts was investigated under UV or visible light irradiation by light-emitting diodes (LEDs). Different LaFeO3 catalysts were prepared by solution combustion synthesis, starting from lanthanum nitrate and iron nitrate aqueous solution, and different amounts of citric acid as organic fuel. The influence of light irradiation and amount of citric acid was evaluated. The photocatalysts were characterized by different techniques, such as XRD, BET, UV–Vis DRS and Raman spectroscopy. As the amount of citric acid was increased from 0.86 to 2.15 g, the specific surface area of perovskite was increased from 4 to 24 m2/g, with crystallite size of 38 and 6 nm, respectively. Moreover, the different amounts of citric acid induced changes in the crystallinity degree of LaFeO3 perovskite. LaFeO3 catalyst prepared with a double amount of citric acid (1.72 g) compared to the initial content (0.86 g), was the most active in the photocatalytic production of H2 (up to 1.6 mmol/gcat after 4 h of UV irradiation, corresponding to 16% of hydrogen yield). With this photocatalyst the simultaneous degradation of glucose was 73% after 4 h of UV irradiation. These results are encouraging with respect to the possibility to produce hydrogen during photocatalytic treatment of sugar-containing water by using photocatalysts in the absence of noble metals.

Improvement of electrochemical and electrical properties of LiFePO4 coated with citric acid

LiFePO4 was synthesized using hydrothermal method and coated with different amounts of citric acid as carbon source. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), surface area measurement—Brunauer–Emmett–Teller (BET), discharge capability, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The results show that the quality and thickness of the carbon coating on the surface of LiFePO4 particles are very important. The optimum carbon content (about 30 wt%) can lead to a more uniform carbon distribution. Electrochemical results show that the samples containing 20 wt%, 30 wt%, 40 wt%, and 50 wt% carbon deliver a discharge capacity of 105, 167, 151, and 112 mAh·g−1, respectively, at the rate of 0.1C. The increase of carbon content leads to the decrease of discharge capacity of LiFePO4/C, owing to the fact that excess carbon delays the diffusion of Li+ through the carbon layers during charge/discharge procedure. The LiFePO4/C with low carbon content exhibits poor electrochemical performance because of its low electrical conductivity. Therefore, the amount of carbon must be optimized in order to achieve excellent electrochemical performance of LiFePO4/C for its application in a lithium ion battery.

Preparation of NiMo/KIT-6 hydrodesulfurization catalysts with tunable sulfidation and dispersion degrees of active phase by addition of citric acid as chelating agent

A series of NiMo catalysts supported on 3-Dimension cubic Ia3¯d mesoporous KIT-6 silica were prepared by co-impregnation method using citric acid (CA) as chelating agent to adjust the sulfidation and dispersion degrees of active phase. Dried catalysts without calcination were tested in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). Impregnation solutions, supports, and catalysts were characterized by means of UV–Vis, Raman, TEM, XRD, N2-physisorption, H2-TPR, elemental analysis, XPS, and HRTEM. The addition of CA results in the formation of MoO3(H2cit)− and Ni(Hcit)(cit)3− complexes, which favors the formation of well dispersed active NiMoS phase. Sulfidation and dispersion degrees of the active phase (average slab length and stacking number of MoS2 particles) could be modulated by adding different amounts of CA. The addition of CA exhibited a promotion effect on hydrogenation (HYD) route and activities and selectivities to HYD of different catalysts were related to the CA contents. NiMoKC2 catalyst with the molar ratio of CA/Ni=2 exhibited the highest reaction rate of 3.1×10−4molg−1h−1 and the highest HYD selectivity of 86% in the HDS of 4,6-DMDBT.

Effect of the amount of citric acid used in the preparation of NiMo/SBA-15 catalysts on their performance in HDS of dibenzothiophene-type compounds

In the present work, NiMo catalysts supported on SBA-15 were prepared with the addition of different amounts of citric acid (CA) in the impregnation solutions. The aim of this study was to inquire into the effect of the amount of citric acid on the activity and selectivity of the NiMo/SBA-15 catalysts in deep hydrodesulfurization (HDS). Catalysts were prepared by coimpregnation of Ni and Mo species from acidic aqueous solutions containing citric acid without further adjusting the solution's pH. The amount of citric acid used in the catalyst preparation was varied from CA:Mo molar ratio 0.5 to 2.0. In addition, a reference NiMo/SBA-15 catalyst was prepared without citric acid. After the impregnation, catalysts were dried (100°C, 6h) and calcined (500°C, 4h). The prepared catalysts were characterized by nitrogen physisorption, small-angle and powder X-ray diffraction (XRD), UV–vis diffuse reflectance spectroscopy (DRS), temperature-programmed reduction (TPR), high resolution transmission electron microscopy (HRTEM) and tested in simultaneous HDS of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in a batch reactor at 300°C for 8h. XRD, DRS and TPR characterizations showed that Ni and Mo oxide species were well dispersed in all catalysts prepared with CA. In contrast, a NiMoO4 crystalline phase was detected by XRD in the reference NiMo/SBA-15 catalyst prepared without citric acid. Addition of citric acid to the impregnation solutions used for the catalyst preparation also resulted in an increase in the degree of sulfidation and in the dispersion of catalytically active MoS2 phase (elemental analysis, HRTEM). In accordance with this, HDS activity of the NiMo catalysts prepared with the addition of citric acid resulted to be significantly higher than that of the reference NiMo/SBA-15 sample for both sulfur-containing compounds tested (DBT and 4,6-DMDBT). It was found that the optimum amount of citric acid, which allows achieving the highest catalytic activity, corresponds to CA:Mo molar ratio equal to 1. Further increase in the amount of citric acid resulted in a slight decrease in the HDS activity. Regarding selectivity, addition of small amounts of CA, in general, resulted in an increase of the hydrogenation ability of the NiMo/SBA-15 catalysts. However, some differences in the selectivity of the catalysts were observed with different amounts of citric acid used.

Influence of citric acid and curing on moisture sorption, diffusion and permeability of starch films

Starch films with different amounts of citric acid produced by solution casting were subjected to different curing temperatures and compared with films plasticized with glycerol. The films were tested in a controlled moisture generator, which enabled the moisture sorption to be measured and the diffusion coefficient and water vapor permeability to be calculated. It was shown that increasing the amount of citric acid added led to a reduction in the equilibrium moisture content, diffusion coefficient and water vapor permeability of the films, the values of which were all considerably lower than the values obtained for the films plasticized by glycerol. It was also seen that curing the film with 30pph citric acid at 150°C led to a significant reduction in the equilibrium moisture content, the diffusion coefficient and the water vapor permeability at high relative humidity which suggests that crosslinking occurred. The calculated water vapor permeability data were comparable with the value obtained with direct measurements.

A novel approach to enhance protein adsorption and cell proliferation on hydroxyapatite: citric acid treatment

Hydroxyapatite (HA) is a promising carrier for delivery of therapeutic proteins, especially bone morphogenetic proteins (BMPs), due to the affinity between the amino and carboxyl groups of proteins and the calcium and phosphate of HA. The main challenge of employing HA as a protein carrier is the burst release profile of protein. In this study, we developed a strategy to improve the protein loading capacity of HA and to sustain protein release from HA by immobilizing COO− groups onto the HA surface. HA particles were precipitated in presence of different amounts of citric acid (CA). The physico-chemical properties (crystallinity, surface area and surface charge) of CA-treated HA (CA–HA) were significantly changed compared to those of the unmodified HA. CA–HA demonstrated significantly higher affinity towards lysozyme, in which the lysozyme adsorption increased by increasing the concentration of CA during the HA preparation. Using the optimized parameters obtained from lysozyme adsorption, the results demonstrated that functionalizing HA with CA significantly increased the amount of BMP-2 loaded onto HA and prolonged its release profile. The in vitro results showed that the CA–HA is not toxic and indeed citric ions on HA shift the surface charge towards negative value, which promoted osteoblast-like cell proliferation on HA.

Influence of admixed citric acid and physiological variables on the vinpocetine release from sodium alginate compressed matrix tablets

In this study, the controlled release matrix tablets of vinpocetine were prepared by direct compression using sodium alginate (SAL) as hydrophilic polymer and different amounts of citric acid as hydrosoluble acidic excipient to set up a system bringing about zero-order release of this drug in distilled water containing 0.5% sodium dodecyl sulfate. At the critical content of admixed citric acid (60 mg/tab.), the lowest drug-release rate was observed. In order to explain the effect of this critical content on drug-release rate from SAL matrices, investigation of the possibility of interaction of citric acid with SAL was performed using differential scanning calorimetric analysis and infrared analysis, which confirmed the existence of direct citric acid-SAL interaction when these two excipients came in contact with water. A zero-order drug-release system could be obtained by regulating the ratio of citric acid-to-SAL and the capacity of this system in controlling drug-release rate depended on the extent of interaction between citric acid and SAL. It is worth noticing that pH and the ionic strength of the dissolution medium were found to exert an influence on the drug-release performance of SAL tablets.

Effect of citric acid on photoelectrochemical properties of tungsten trioxide films prepared by the polymeric precursor method

Effect of citric acid (CA) on microstructure and photoelectrochemical properties of WO 3 films prepared by the polymeric precursor method was investigated. The obtained materials were characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The results showed that samples prepared with adding different amounts of citric acid had a pure phase of cubic. The addition of citric acid could significantly increase the particle size and change the surface of WO 3 films. The photoelectrochemical measurements were performed using a standard three-electrode system cell. The films prepared from mass ratios of CA/PEG ( R = 0, 0.2, 0.4, 0.6 and 1) showed 1.0, 1.4, 1.7, 2.1 and 0.9 mA cm −2 at 1.2 V under illumination with a 500 W xenon lamp ( I 0 = 100 mW/cm 2), respectively.

Sweet and sour preferences in young children and adults: role of repeated exposure

We investigated the influence of repeated exposure to orangeades with added sucrose and different concentrations of citric acid, on the taste preferences of 6- to-11-year-old children and young adults. During an intervention study of 8 days, 59 children (9.2±0.9 years) and 46 young adults (22±2.0 years) received, each day, either an orangeade with a sweet taste, a sour taste, or no orangeade (control). Before (baseline) and after the intervention, preferences for a series of orangeades and yoghurt, which varied in balance of sweet and sour tastes, were measured by means of a rank-ordering procedure. The variation in balance of sweet and sour taste was established by adding different amounts of citric acid (orangeade: 0.009, 0.013, 0.020, 0.029, 0.043, and 0.065 M added citric acid; yoghurt: 0.027, 0.038, 0.056, 0.081, 0.12, and 0.17 M added citric acid) to a stock orangeade and yoghurt with 0.42 M sucrose. The sweet and sour tasting orangeade that were consumed during the intervention were equally preferred at baseline. After an 8-day exposure to the sweet orangeade, children's preferences for this orangeade (0.42 M sucrose) significantly increased ( p<0.05). A similar trend was observed for the yoghurt with 0.42 M sucrose ( p=0.09). An 8-day exposure to the sour orangeade did not have a significant effect on children's preference for this orangeade. The taste preferences of adults did not change after the intervention. The control group of children and adults did not show any change in preferences for sweet and sour tastes. Future research is needed to investigate whether the changed preferences for sweet taste are stable over time and how these changed taste preferences are related to a change in the consumption of sugar rich foods.