Initial Solution pH Value Research Articles

Lanthanide doped Y6O5F8/YF3 microcrystals: phase-tunable synthesis and bright white upconversion photoluminescence properties

High-quality Y(6)O(5)F(8)/YF(3) microcrystals have been synthesised by using a hydrothermal and subsequent calcination route. Upon changing the initial solution pH value, the as-prepared microcrystal can be well tuned from YF(3) octahedron microcrystals to YF(3) hollow spheres and finally to Y(6)O(5)F(8) microtubes. The as-obtained microcrystals have been characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL) spectra. When the Y(6)O(5)F(8):Ln(3+) microtubes are excited by a 980 nm continual wave laser diode, bright red, green, and blue room temperature upconversion PL emissions have been observed. A series of white light emissions have been obtained by precisely adjusting dopants concentration in Y(6)O(5)F(8) microtubes.

Optimization for decolorization of azo dye acid green 20 by ultrasound and H 2O 2 using response surface methodology

Response surface methodology (RSM) based on Box-Behnken design was successfully applied to the optimization of the operating conditions in decolorization of acid green 20 (AG 20) by ultrasonic irradiation in the presence of H 2O 2. The effects of three operating variables, ultrasonic power density, initial pH value of dye solution and H 2O 2 concentration on the decolorization efficiency of AG 20 were evaluated. A quadratic model for AG 20 decolorization was proposed. Analysis of variance (ANOVA) indicated that the proposed quadratic model could be used to navigate the design space. The proposed model was approximately in accordance with the experimental case with correlation coefficients R 2 and R adj 2 of 0.9995 and 0.9984, respectively. The optimum operating conditions for AG 20 decolorization were found to be 1.08 W/mL of ultrasonic power density, 4.85 of initial pH and 1.94 mM of H 2O 2 concentration, respectively. The predicted decolorization rate under the optimum conditions determined by RSM was 96.8%. Confirmatory tests were carried out under the optimum conditions and the decolorization rate of 96.3% was observed, which closely agreed with the predicted value. The results confirmed that RSM based on Box-Behnken design was an accurate and reliable method to optimize the operating conditions of AG 20 decolorization.

Treatment of winery wastewater by UV-A radiation

Winery wastewater typically has a pH of 3-4, with COD (chemical oxygen demand) of 800-12800 mg/L, and Biochemical Oxygen Demand (BOD) 1500-6000 mg/L depending on the vintage cycle. To date, there has been no general agreement on the most suitable method for the treatment of winery wastewater. On the other hand, Advanced Oxidation Processes (AOPs) based on various techniques offer a promising alternative method for its treatment. The principal mechanism of AOPs function is the production of highly reactive free radicals. Ultraviolet (UV)-A radiation as one of the UV-driven AOPs was applied in the present work. The photodegradation of winery wastewater was studied by using UV-A radiation at different initial solution pH values using different number of UV lamps. The highest conversion of the pollutants removal was found under alkaline conditions. The average reaction rate increases with increasing number of lamps.

Model for Predicting the Initial Solution pH at Pre-Assumed Final pH and Concentration of Dissolved Zinc during Leaching of Galena in Butanoic Acid Solution

Model for predicting the initial solution pH at pre-assumed final pH and concentration of dissolved zinc, during leaching of galena in butanoic acid solution has been derived. The model; α = 1.4γ/ln[(Zn) 1/3shows that the initial pH of the leaching is dependent on the values of the pre-assumed final solution pH and concentration of dissolved zinc. The validity of the model was rooted in the expression eN(γ/α) = 3√Zn where both sides of the expression were approximately equal to 4. The respective deviation of the model-predicted initial solution pH value from that of the corresponding experimental value was less than 2% which is quite within the acceptable deviation limit of experimental results.

Optimization of Fabrication Parameters To Produce Chitosan−Tripolyphosphate Nanoparticles for Delivery of Tea Catechins

This work investigated the polyanion-initiated gelation process in fabricating chitosan-tripolyphosphate (CS-TPP) nanoparticles intended to be used as carriers for delivering tea catechins. The results demonstrated that the particle size and surface charge of CS-TPP nanoparticles could be controlled by fabrication conditions. For preparation of CS-TPP nanoparticles loaded with tea catechins, the effects of modulating conditions including contact time between CS and tea catechins, CS molecular mass, CS concentration, CS-TPP mass ratio, initial pH value of CS solution, and concentration of tea catechins on encapsulation efficiency and the release profile of tea catechins in vitro were examined systematically. The study found that the encapsulation efficiency of tea catechins in CS-TPP nanoparticles ranged from 24 to 53%. In addition, FT-IR analysis showed that the covalent bonding and hydrogen bonding between tea catechins and CS occurred during the formation of CS-TPP nanoparticles loaded with tea catechins. Furthermore, studies on the release profile of tea catechins in vitro demonstrated that the controlled release of tea catechins using CS-TPP nanoparticles was achievable.

Point of Zero Charge and Isoelectric Point of Alumina

The point of zero charge, pHpzc, and the isoelectric point, pHiep, of a commercial alumina sample was investigated in KNO3 solutions. The influence of the concentration and the initial pH value of KNO3 solution used for preparation and equilibration of the alumina suspension, as well as of the alumina/solution ratio on pHpzc and pHiep were investigated. The obtained results indicate that pHiep values are dependent on initial pH values of KNO3 solutions used for equilibration of alumina suspensions. Simultaneously with isoelectric point determination, the particle size of alumina was also measured. It was shown that the particle size of alumina increases with increasing suspension pH due to agglomeration, reaching the maximum value at pHiep.

Removal of methylene blue from aqueous solution using chitosan-g-poly(acrylic acid)/montmorillonite superadsorbent nanocomposite

Batch adsorption experiments were carried out for the removal of methylene blue (MB) cationic dye from its aqueous solution using chitosan-g-poly(acrylic acid)/montmorillonite (CTS-g-PAA/MMT) nanocomposites as adsorbent. The factors influencing adsorption capacity of the nanocomposite such as initial pH value (pH0) of the dye solution, MMT content (wt%), weight ratio (wr) of AA to CTS and adsorption temperature (T) were investigated. The results showed that the wr of AA to CTS of the nanocomposites have great influence on adsorption capacities and introducing a small amount of MMT could improve adsorption ability of the CTS-g-PAA. The adsorption behaviors of the nanocomposite showed that the adsorption kinetics and isotherms were in good agreement with pseudo-second-order equation and the Langmuir equation, respectively, and the maximum adsorption capacity is 1859mg/g for CTS-g-PAA/MMT with wt% of 30% and wr of 7.2:1. The desorption studies revealed that the nanocomposite provided the potential for regeneration and reuse after MB dye adsorption.

Adsorption behaviors of Congo red on the N,O-carboxymethyl-chitosan/montmorillonite nanocomposite

Abstract A series of N , O -carboxymethyl-chitosan/montmorillonite ( N , O- CMC–MMT) nanocomposites were prepared by controlling the molar ratios of N , O -carboxymethyl-chitosan ( N , O- CMC) and montmorillonite (MMT). The nanocomposites were characterized by FTIR, XRD and SEM. Adsorption of Congo red (CR) anionic dye from aqueous solution onto N , O- CMC–MMT was studied. The results showed that the nanocomposite with the molar ratio of N , O- CMC to MMT of 5:1 exhibited the higher adsorption capacity. This may be attributed to the fact that the introduction of N , O- CMC in the galleries of MMT may have different influences on physico-chemical properties of MMT and in turn result in different influences on adsorption capacity of N , O- CMC–MMT for CR. The effects of different molar ratios of N , O- CMC and MMT, initial pH value of the dye solution and temperature on adsorption capacities of samples for CR dye have been investigated. The results of adsorption behaviors of CR on N , O- CMC–MMT indicated that all the adsorption processes followed the pseudo-second-order and the Langmuir isotherm, respectively.

Adsorption of phenol with modified rectorite from aqueous solution

Abstract The natural rectorite (REC) was modified with surfactant of dodecyl benzyl dimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide and octadecyl trimethyl ammonium bromide, respectively, to form three kinds of organic-modified rectorite (OREC), termed OREC1, OREC2 and OREC3. Three kinds of ORECs were used as adsorbents for phenol in aqueous solution. Through FTIR and XRD analysis, it confirmed the cation exchange reaction between REC and surfactant. The amount of surfactant exchanged in OREC1, OREC2 and OREC3 were determined as 0.27, 0.51 and 0.62 mmol/g, respectively, through incineration method. Through the research of phenol adsorption, it was found that the removal percentage (%) of phenol increased with the increase in adsorbents dose, whereas the adsorption amount q e (mg/g) decreased. The adsorption efficiency of OREC adsorbents was greatly affected by the initial phenol solution pH value. The thermodynamics study of adsorption process showed that the adsorption of phenol with three adsorbents was carried out spontaneously, and that the process was exothermic in nature. The adsorption kinetic data of phenol with OREC adsorbents were well fitted to the Lagergren rate equation. The Freundlich isotherm model was employed and well represented in the experimental data.

Conversion of benzoic acid during TiO2-mediated photocatalytic degradation in water

Abstract The photocatalytic degradation of benzoic acid in water over Degussa P-25 TiO 2 suspensions was studied. UVA irradiation at 365 nm was supplied by a medium pressure mercury lamp providing 25 mW cm −2 light intensity. Experiments were conducted at benzoic acid initial concentrations between 25 and 150 mg L −1 , catalyst loadings between 0.2 and 1 g L −1 and initial solution pH values between 2 and 10.6. Conversion increased with increasing catalyst loading up to about 0.6 g L −1 and it was favored at alkaline or neutral conditions but impeded at extremely acidic conditions. Increasing initial substrate concentration led to decreased benzoic acid conversion, which was found to follow a Langmuir–Hinshelwood kinetic expression. High performance liquid chromatography (HPLC) was employed to follow benzoic acid concentration profiles as well as to identify reaction by-products, while chemical oxygen demand (COD) and total organic carbon (TOC) analyses were carried out to assess the extent of mineralization. Benzoic acid hydroxylation by-products, namely 2-, 3- and 4-hydroxybenzoic acids as well as phenol were identified as reaction intermediates, although these contributed only a small fraction of the residual organic content. Although benzoic acid at 50 mg L −1 was not ecotoxic to marine photobacteria Vibrio fischeri , its photodegraded solution exhibited substantial toxicity, which, however, proved not to be due to the identified intermediates.

Adsorption behavior of Cr(VI) on organic-modified rectorite

The natural rectorite (REC) was modified with the surfactant of dodecyl benzyl dimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide and octadecyl trimethyl ammonium bromide, respectively. Three kinds of organic-modified rectorite (OREC), termed OREC1, OREC2 and OREC3, respectively, were prepared. Three kinds of OREC were used as adsorbents for Cr(VI) removal in aqueous solution. Through FTIR and X-ray diffraction (XRD) analyses, it was confirmed that they indeed carried out cation exchange reaction between REC and surfactant. Through the research of Cr(VI) adsorption, the removal percentage (%) of Cr(VI) increased with increasing adsorbents dose. The adsorption efficiency of OREC adsorbent was greatly affected by the initial solution pH value. According to thermodynamics study, it can be concluded that the adsorption of Cr(VI) with three adsorbents was carried out spontaneously. The research of adsorption isotherm demonstrated that, adsorption reactions of three prepared OREC adsorbents belonged to Langmuir model. The kinetic data of Cr(VI) with OREC adsorbents were well fitted to the Lagergren rate equation, which indicated that the three adsorption processes belonged to first-order adsorption reaction. Values of coefficients of intra-particle diffusion and mass transfer have been determined for three different OREC adsorbents. Intra-particle diffusion analysis demonstrated that Cr(VI) ions diffused quickly at the beginning of the adsorption process, and then intra-particle diffusion slowed down and stabilized. Mass transfer analysis showed the process of transfer of Cr(VI) removal onto the adsorbents surface was rapid enough.

Morphological evolution of PbS crystals under the control of l-lysine at different pH values: The ionization effect of the amino acid

PbS crystals were synthesized by a simple hydrothermal process with l-lysine as the crystal growth modifier. Depending on the initial pH value of the reaction solution, the morphologies of the PbS crystals varied and the crystals with shapes of truncated nanocube, star-shaped dendrite, comb-like dendrite were obtained. The morphological evolution of the PbS crystals was explained by the different state of the ionization equilibrium of l-lysine in the solution at different pH values. The presence of differently charged l-lysine molecules would influence the crystal growth rates along different directions and result in the final morphologies of PbS crystals. It is proposed that when amino acids are used as crystal growth modifiers, besides the types of amino acids, which have been regarded to influence the crystals' growth, the ionized state of the amino acids at different pH values would play an important role in the morphological control, and this point may have been neglected before.

Adsorption properties of congo red from aqueous solution onto N, O-carboxymethyl-chitosan

N, O-carboxymethyl-chitosans ( N, O-CMC) with different degree of substitution (DS) were synthesized under heterogeneous conditions by controlling the reaction temperature. The factors influencing adsorption capacity of N, O-CMC such as the DS of N, O-CMC, initial pH value of the dye solution and adsorption temperature for anionic dye congo red (CR) were investigated. Compared with chitosan (78.90 mg/g), N, O-CMC with the DS of 0.35 exhibited much higher adsorption capacity (330.62 mg/g) for CR at the same adsorption conditions. The adsorption kinetics and isotherms showed that the sorption processes were better fitted by pseudo-second-order equation and the Langmuir equation, respectively. The adsorption mechanism of N, O-CMC was also discussed by means of IR and XPS spectra. The results in this study indicated that N, O-CMC was an attractive candidate for removing CR from the dye wastewater.

Adsorption characteristics of Congo Red onto the chitosan/montmorillonite nanocomposite

A series of biopolymer chitosan/montmorillonite (CTS/MMT) nanocomposites were prepared by controlling the molar ratio of chitosan (CTS) and montmorillonite (MMT). The nanocomposites were characterized by FTIR and XRD. The effects of different molar ratios of CTS and MMT, initial pH value of the dye solution and temperature on adsorption capacities of samples for Congo Red (CR) dye have been investigated. The adsorption capacities of CTS, MMT and CTS/MMT nanocomposite with CTS to MMT molar ratio of 5:1 for CR were compared. The results indicated that the adsorption capacity of CTS/MMT nanocomposite was higher than the mean values of those of CTS and MMT. The adsorption kinetics and isotherms were also studied. It was shown that all the sorption processes were better fitted by pseudo-second-order equation and the Langmuir equation.

Photocatalytic degradation of methamidophos by UV irradiation in the presence of nano-TiO2

In this paper, photocatalytic degradation of methamidophos (o,s-dimethylphosramidothooate) by nano-TiO2 was studied, and the effect factors (such as the nature and the concentration of the TiO2 photocatalyst, and the environment (pH, oxidant additives) of treatment solution, etc.) of this process were systemically investigated. It was found that nano-TiO2 has higher photocatalytic activity than that of bulk-sized counterparts, and the pretreatment temperature and the concentration of the nano-TiO2 used in photocatalysis both exhibited a direct effect on this process; in addition, in the presence of nano-TiO2, the change of initial pH value of the treatment solution and addition of oxidants (KIO4, K2S2O8, and H2O2) to this solution both showed an obviously positive effect on this degradation process, markedly enhancing the degradation rate of methamidophos. Under optimal condition (such as 0.04% KIO4 to the treatment solution), the degradation rate of methamidophos could reach about 83.55% in the first 5 min, which is obviously faster than the degradation speed reported in the literature. Langmuir-Hinshelowood rate expression was employed for the degradation of methamidophos by the UV/TiO2 system and adsorption equilibrium constant and rate constant were determined to be 2.02 m/M and 0.0027 mM/min, respectively.

Synthesis of hydrogen peroxide from carbon monoxide, water and oxygen catalyzed by amorphous NiP(B)/Al 2O 3

Amorphous NiP(B)/Al 2O 3 catalysts were prepared by a coating method. The factors that influence the preparation of the catalysts, such as plating temperature, the initial pH value of the plating solution, the loadings of NiP and the temperature of heat treatment, were studied in detail. The catalysts were characterized with XRD, SEM and XPS, and were studied in the reaction for the synthesis of hydrogen peroxide from carbon monoxide, water and oxygen. The results showed that the catalysts had amorphous structure with Ni–P–B alloy formed on the surface; that the catalysts had better activity and stability than the catalysts reported previously when the H 2O 2 production rate reached 0.228 mmol/(g h), which is higher than the maximum rate of 0.1 mmol/(g h) over noble catalysts (5% Pd/CaCO 3 and 1% Ru/graphite) and 0.07 mmol/(g h) over Ni–La–B/Al 2O 3 catalyst; and that the preparation conditions significantly influenced the activities of the catalysts. The higher stability values of the catalysts were attributed to the amorphous Ni–P–B structure.

Photoelectrocatalytic decontamination of oilfield produced wastewater containing refractory organic pollutants in the presence of high concentration of chloride ions

The feasibility study of the application of the photoelectrocatalytic decontamination of high saline produced water containing refractory organic pollutants was investigated in the slurry photoelectrocatalytic reactor with nanometer TiO 2 particle prepared with sol–gel method using the acetic acid as hydrolytic catalyst. The efficiency of the photoelectrocatalytic decontamination of produced water was determined with both COD removal from the tested wastewater and the decrease of mutagenic activity evaluated by Ames tests. The experimental results showed that the photoelectrocatalysis is a quite efficient process for decontaminating the produced water, although there are high concentration of salt existed in oilfield wastewater. We found that the COD removal efficiencies by photoelectrocatalytic process are much higher than that of by photocatalytic or electrochemical oxidation individually in the photoelectrocatalytic reactor. The COD removal can be substantially improved by the added H 2O 2 and the generation of active chlorine from high concentration chlorides in the wastewater. The effects of various operating conditions, such as initial COD concentration, applied cell voltage, catalyst amount and initial pH value of solution, on the photoelectrocatalytic efficiencies, is also investigated in detail. The results showed that when the raw produced wastewater was diluted in a 1:1 (v/v) ratio, there is a highest COD removal efficiency. And the photoelectrocatalytic degradation of organic pollutants in saline water is much favored in acidic solution than that in neutral and/or alkaline solution.

Ultrasonic Degradation of Polysaccharide from a Red Algae (Porphyra yezoensis)

Polysaccharide from Porphyra yezoensis (PYPS) was degraded by ultrasound in this study. The changes of intrinsic viscosity with various conditions, such as ultrasonic power, irradiation time, reaction temperature, initial pH value of solution, and its concentration, were investigated by using Ubbleholde viscometry. It was found that the ultrasonic degradation rate of PYPS solution increases with the increase of ultrasonic power and reaction temperature and the decrease of the initial pH value of the solution. The order of the susceptibility of initial PYPS concentrations on degradation is 0.75 > 0.5 > 1.00 > 2.00 g/dL. The mechanism about the ultrasonic degradation of PYPS may be explained by more for mechanical and less for radical effects. Relationships between degradation rate and ultrasound time are exponential functions. The activation energy of ultrasonic degradation of PYPS solution is 52.13 kJ/mol, which was calculated by the logarithmic form of the Arrhenius equation, and is lower than one for the acid or enzyme catalyzing degradation of similar glycosidic bonds.

Biosorption of copper(II) and cobalt(II) from aqueous solutions by crab shell particles

Biosorption of each of the heavy metals, copper(II) and cobalt(II) by crab shell was investigated in this study. The biosorption capacities of crab shell for copper and cobalt were studied at different particle sizes (0.456–1.117 mm), biosorbent dosages (1–10 g/l), initial metal concentrations (500–2000 mg/l) and solution pH values (3.5–6) in batch mode. At optimum particle size (0.767 mm), biosorbent dosage (5 g/l) and initial solution pH (pH 6); crab shell recorded maximum copper and cobalt uptakes of 243.9 and 322.6 mg/g, respectively, according to Langmuir model. The kinetic data obtained at different initial metal concentrations indicated that biosorption rate was fast and most of the process was completed within 2 h, followed by slow attainment of equilibrium. Pseudo-second order model fitted the data well with very high correlation coefficients (>0.998). The presence of light and heavy metal ions influenced the copper and cobalt uptake potential of crab shell. Among several eluting agents, EDTA (pH 3.5, in HCl) performed well and also caused low biosorbent damage. The biosorbent was successfully regenerated and reused for five cycles.

Specific Influence of the Modifier (1-Decanol) on the Extraction of Tartaric Acid by Different Extractants

The effect of the modifier 1-decanol on the extraction of tartaric acid by the extractants tri-n-octylamine (TOA), quaternary ammonium chloride (Aliquat 336), or their mixture in the diluent n-dodecane was studied at different pH values. The effect of the modifier was examined as a function of the initial pH value of the aqueous solution for the three extractants mentioned above. A positive, negative, or no effect of the modifier on the distribution coefficient of tartaric acid was observed in the different cases.