Initial Solution pH Value Research Articles

An ecological new approach for treating Cr(VI)-containing industrial wastewater: Photochemical reduction

An ecological new approach for photochemical reduction of Cr(VI) in aqueous solution by adding into water-soluble copolymer, polyethylene glycol (PEG), was investigated. Various influences including light intensity, initial solution pH value, PEG molecular weight and initial concentration ratio of PEG to Cr(VI) on photochemical reduction of Cr(VI) were discussed, and a possible reaction mechanism was proposed. Experimental results revealed that Cr(VI) could be reduced to Cr(III) by PEG under sunlight irradiation. The photo-reduction rate of Cr(VI) increased with the decrease of solution pH and PEG molecular weight, but increased with the light intensity. The reduction percentage of Cr(VI) increased with the initial concentration ratio of PEG to Cr(VI). When the initial solution pH value was below 3.0, almost all of Cr(VI) was completely reduced to Cr(III) within 20 min of 50 × 103 lux solar irradiation in the presence of PEG. After photo-reduction, PEG and Cr(III) in aqueous solutions could be recovered by adding into a high-concentrated Na2SO4 aqueous solution to induce the formation of a stable PEG-based aqueous biphasic system. By doing so, Na2SO4 in aqueous solution could also be removed. The present work highlights a promising new route for treating the industrial wastewater containing toxic Cr(VI) ions by adding into environmental-friendly PEG for photo-reduction of Cr(VI) to Cr(III), and then salting-out recovery of PEG and removal of Cr(III) in wastewater by adding into another high-salt wastewater, so that the high-salt wastewater could also be treated.

EDTA-modified DR/SiO2 adsorbent: Preparation, characterization, and application in heavy metal adsorption

ABSTRACTA hybrid material of diazoresin (DR) and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) coated onto silica particles were synthesized and applied as adsorbents. The study of UV-vis spectrum revealed that DR and EDTA could be successfully modified onto silica. The effect of initial pH value of aqueous solution and dosage of the adsorbents on the adsorption capability for heavy metal Cu(II) ion were investigated and discussed.

Adsorption of Amido Black 10B from aqueous solutions onto Zr (IV) surface-immobilized cross-linked chitosan/bentonite composite

Zr(IV) surface-immobilized cross-linked chitosan/bentonite composite was synthesized by immersing cross-linked chitosan/bentonite composite in zirconium oxychloride solution, and characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy techniques. The adsorption of an anionic dye, Amido Black 10B, from aqueous solution by Zr(IV) loaded cross-linked chitosan/bentonite composite was investigated as a function of loading amount of Zr(IV), adsorbent dosage, pH value of initial dye solution, and ionic strength. The removal of Amido Black 10B increased with an increase in loading amount of Zr(IV) and adsorbent dosage, but decreased with an increase in pH or ionic strength. The adsorption of AB10B onto Zr(IV) loaded cross-linked chitosan/bentonite composite was favored at lower pH values and higher temperatures. The Langmuir isotherm model fitted well with the equilibrium adsorption isotherm data and the maximum monolayer adsorption capacity was 418.4mg/g at natural pH value and 298K. The pseudo-second-order kinetic model well described the adsorption process of Amido Black 10B onto Zr(IV) loaded cross-linked chitosan/bentonite composite. The possible mechanisms controlling Amido Black 10B adsorption included hydrogen bonding and electrostatic interactions.

Efficient Removal of Methylene Blue by Novel Magnetic Hydrogel Nanocomposites of Poly(acrylic acid)

ABSTRACTIn the current research, the sonochemically prepared magnetite nanoparticles (MNPs) were silylated with triethoxyvinylsilane to produce a core–shell structure containing vinyl moieties on the surface. The radical polymerization of the silylated product with acrylic acid in the presence of N,N‐methylenebisacrylamide, as the cross‐linker, led to the formation of novel magnetic hydrogel nanocomposites (MHNCs) in which some of polyacrylic acid (PAA) chains were chemically grafted onto MNPs (PAA‐grafted MNPs). Vibrating sample magnetometry showed the unique phenomenon of superparamagnetism for the prepared MNPs, silylated MNPs, and PAA‐grafted MNPs. Batch adsorption experiments were carried out for the removal of methylene blue (MB) using pure hydrogel and MHNCs as an adsorbent. The effects of contact time, PAA‐grafted MNP content, adsorbent mass, and initial pH value of the dye solution on adsorption were investigated. Results showed the MHNC containing 10 wt% of PAA‐grafted MNP (MHNC 10 wt%) had the maximum adsorption capacity. It was observed that the adsorption kinetics of MB followed pseudo–second‐order kinetics. The adsorption equilibrium data obeyed Langmuir isotherm, and the maximum adsorption amount of MB reached 507.7 mg g–1 for MHNC 10 wt%. It was shown that the adsorbed MB could be desorbed from the MHNCs by using methanol solution containing acetic acid and the nanoadsorbents could be recycled.

Comparison on Copper (II) Desorption from Loess Soil with and without Biochars Derived from Flax and Rape Straws

It has been reported that biochar is capable of adsorbing and immobilizingheavy metals in soils due to its prominent properties, such as the porous structure,large and charged surface, and functional groups on surface. The desorption of Cu (II)(Cu) from loess soil was studied and compared using batch washing method, with andwithout biochars derived from flax and rape straws. The effects of contact time, initial pHvalue of solution, temperature, initial concentration of Cu in soil, and co-existing Ca2+ ondesorptions were investigated. The pseudo-second-order kinetic model could be usedto describe the desorbing process well. The leaching ability (η) of Cu from solid phaseincreased in overly acidic solutions. Increasing temperature improved desorption of Cufrom loess soil. When the initial concentration of Cu in soil increased, the η values ofCu decreased. Slight effect of Ca2+ on the η value of Cu was found. No significant immobilizationof Cu by biochars was found because loess soil is much capable of holdingCu, possibly due to high content of carbonates. The results could provide references forimmobilization remediation of loess soils contaminated with heavy metals using biocharsas amendment.

UV-Enhanced NaClO Oxidation of Nitric Oxide from Simulated Flue Gas

A wet de-NOxtechnique based on an UV-enhanced NaClO oxidation process was investigated for simulated flue gas of a diesel engine using a bench-scale reaction chamber. The effects of UV irradiation time, initial pH value, and available chlorine concentration of NaClO solution were studied, respectively. The results showed that when the UV irradiation time was 17.5 min and the initial pH value of NaClO solution was 6, NO removal efficiency of UV/NaClO solution was increased by 19.6% compared with that of NaClO solution. Meanwhile, when the available chlorine concentration of NaClO solution decreased from 0.1 wt% to 0.05 wt%, the enhancement in NO removal efficiency of UV/NaClO solution increased from 19.6% to 24%, compared with that of NaClO solution. The reaction pathways of NaClO solution photolysis and NO removal by UV/NaClO process were preliminarily discussed. The results suggested that HOCl might be the most active species that released many UV-induced photooxidants through photolysis reactions, which played an important role in NO removal process.

Effect of pH value and calcination temperature on synthesis and characteristics of Cu–Ni nano-alloys

Cu–Ni nano-alloys were prepared using precursors synthesized by the citrate-gel method. The effects of initial solution pH value and calcination temperature on the composition, crystalline structure, purity, morphology, homogeneity and grain size of Cu–Ni nanoparticles were investigated. Both the parameters significantly affect the crystalline structure, composition and grain size. Cu–Ni alloys prepared at pH value of 1 do not contain impurities, and their compositions are Cu0.42Ni0.58, Cu0.45Ni0.55 and Cu0.52Ni0.48 reduced at 300, 400 and 500 °C, respectively. The grain size grows with the increase of calcination temperature for the precursor prepared at pH values of 1.6 and 3. The Ni content of the alloys gradually increases with the increase of calcination temperature at pH value of 3.

Fixed-bed column studies for the removal of anionic dye from aqueous solution using TiO2@glucose carbon composites and bed regeneration study

Glucose carbon with uniform diameter was successfully anchored by TiO2 nanoparticles via a facile low-temperature hydrothermal process independent of surfactants or external forces. The resultant TiO2@glucose carbon composite (TiO2@GCs) was characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The elimination of direct deep blue (DDB) from aqueous solution by adsorption onto TiO2@GCs was investigated in the up-flow fixed-bed columns. The effects of the influent concentration (10–30 mg L−1), flow rate (3–5 mL min−1), bed depth (1.0–2.0 cm) and pH (1.0–9.0) were investigated. Breakthrough time and adsorption capacity of the fixed-bed increased with increasing bed depth, whereas decreased with the increase in initial concentration, bed depth and solution pH values. The experimental data was in good agreement with both Thomas model and Yoon-Nelson model. The employed bed saturated with DDB was readily regenerated through a simple regeneration process with UV irradiation for 1 h. Furthermore, the adsorption–regeneration process was conducted for six cycles and no major decrease of regeneration efficiency was observed for the first three cycles. One possible mechanism for regenerating dye-loaded TiO2@GCs was proposed. The verifying experiment found that hydroxyl radicals and superoxide ions significantly affected the regeneration of employed TiO2@GCs bed.

Biosynthesis of silver and platinum nanoparticles using orange peel extract: characterisation and applications.

This study focuses on the green synthesis of noble metal nanoparticles (silver (Ag) and platinum (Pt)) and how the size and shape of the nanoparticles produced can be controlled through changes in the initial pH value of the precursor solution. The nanoparticles were characterised by ultra-violet-visible spectroscopy, transmission electron microscopy and X-ray diffraction. This simple and environmentally friendly method allows the synthesis of diverse nanostructures in the absence of a surfactant or polymer to direct nanoparticle growth, and without externally adding seed crystallites. The antibacterial effects of Ag nanoparticles and catalytic properties of Pt nanoparticles were explored for future promising biotechnological approaches in different fields.

Photocatalytic Degradation of Phenol by Impure BiFeO<sub>3</sub> under Visible Light Irradiation

Impure BiFeO3 as a visible light photocatalyst for phenol degradation was synthezied via solid state method. The calcined temperatures of catalysts were studied. The characteristics of the catalysts were determined by XRD, SEM/EDS and BET. The catalysts were mainly composed of rhombohedral distorted perovskite-type BiFeO3 phase with impurity phases (B2Fe4O9, Bi25FeO40 and Bi2O3). Photocatalytic activity of phenol (5 mg/l) was studied in the impure BiFeO3 illuminated with 200 w fluorescence lamps. The catalyst amount and initial pH value of phenol solution on the photocatalytic effiency have been also investigated. In the present experiments, the catalyst calcined at 800°C shows the highest activity. The optimum loading of impure BiFeO3 and pH value were obtained to be 0.5 g/l and 6, respectively.

Enzymatic removal of chlorophenols using horseradish peroxidase immobilized on superparamagnetic Fe3O4/graphene oxide nanocomposite

Magnetic Fe3O4 nanoparticles were successfully deposited on graphene oxide sheets by ultrasound-assisted coprecipitation. The nanoparticles were characterized using transmission electron microscopy, vibrating sample magnetometry, and X-ray photoelectron spectroscopy. The synthesized material was used as a support for the immobilization of horseradish peroxidase (HRP). The removals of 2-chlorophenol, 4-chlorophenol, and 2,4-dichlorophenol using the immobilized HRP were investigated. Batch degradation studies were used to determine the effects of the initial solution pH values, reaction temperature, reaction time, H2O2 and chlorophenol concentrations, and immobilized enzyme dosage on the removal of chlorophenols. The different numbers and positions of electron-withdrawing substituents affected the chlorophenol removal efficiency; the order of the removal efficiencies was 2-chlorophenol < 4-chlorophenol < 2,4-dichlorophenol. The oxidation products formed during chlorophenol degradation were identified using gas chromatography-mass spectrometry. The biochemical properties of the immobilized HRP were investigated; the results indicated that the storage stability and tolerance to changes in pH and temperature of the immobilized HRP were better than those of free HRP. The nanoparticles were recovered using an external magnetic field, and the immobilized HRP retained 66% of its initial activity for the first four cycles, showing that the immobilized HRP had moderate stability. These results suggest that the immobilized enzyme has potential application in wastewater treatment.

Methylene blue adsorption from aqueous solutions using undoped and silver-doped nanotubes of anatase-titania synthesized via modified hydrothermal method

The nanotubes of undoped and silver (Ag)-doped anatase-titania (TiO2) have been synthesized via the modified hydrothermal method involving the use of acetic acid-modified sol–gel processed nanocrystalline undoped and Ag-doped anatase-TiO2 as precursors. Their dye adsorption characteristics have been investigated using a cationic dye such as the methylene blue (MB). For the undoped nanotubes of anatase-TiO2, the MB dye adsorption measurements have been obtained in the aqueous solutions by varying both the initial dye concentration (~7.5–250 μM) and initial solution pH (~2.5–11). The dye adsorption capacity of undoped nanotubes of anatase-TiO2 has been determined to be 32 mg g−1 at the initial solution pH of ~10. Similar measurements have been obtained for the varying amount of Ag doping (Ag/Ti ratio of 0.01 and 0.05) at the initial solution pH of ~10. The Ag-doped nanotubes of anatase-TiO2 having the Ag/Ti ratio of 0.01 exhibit the highest dye adsorption capacity (39 mg g−1) within the investigated range of Ag/Ti ratio. Hence, controlling the initial solution pH and the amount of Ag doping appear to be two effective approaches for enhancing the amount of dye adsorbed on the surface of hydrothermally synthesized nanotubes of anatase-TiO2. Further analyses reveal that the kinetics of MB adsorption on the surface of nanotubes of undoped anatase-TiO2 follows the pseudo-second-order model and the Langmuir isotherm model shows the best fit to the equilibrium adsorption data typically for higher initial solution pH values (≥10), both of which are not affected by the amount of Ag doping.

Polydopamine-mediated surface functionalization of electrospun nanofibrous membranes: Preparation, characterization and their adsorption properties towards heavy metal ions

In this paper, a simple and versatile approach for the fabrication of a polyethyleneimine (PEI)-functionalized nanofibrous membrane utilizing polydopamine (PDA) as a mediator is proposed. The morphology and structure of the PDA-coated and PEI-grafted nanofibrous membranes were confirmed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Due to a large specific surface area and long fibrous morphology, the synthesized membranes were used as novel adsorbents for copper ion (Cu2+) removal from aqueous solutions. The adsorption of Cu2+ was investigated on the synthesized membranes regarding the membrane dosages, initial solution pH values, initial solution concentrations, contact times and temperatures. In addition, the adsorption equilibrium data of PEI-grafted membranes were well fitted with the Langmuir adsorption isotherm, and a maximum adsorption capacity value of 33.59mgg−1 was determined (while it was 21.94mgg−1 for the PDA-coated membranes). The thermodynamic parameters indicated that Cu2+ absorption was a spontaneous and exothermic adsorption process. In addition, XPS peak differentiation imitating analysis permitted the proposal of a copper-amine coordination adsorption mechanism that can be used to explain changes in the adsorption properties compared to PDA coating nanofibrous membranes.

Ammonia recovery from high concentration wastewater of soda ash industry with membrane distillation process

Vacuum membrane distillation was applied in the treatment of high ammonia content wastewater for the recovery of ammonia. Hydrophobic poly(vinylidene fluoride) hollow fiber membranes were used as the separation media. The initial ammonia concentration and pH value of the feed solution were destined owing to the composition of the wastewater. The effects of feed temperature, velocity, and operation time on the ammonia removal efficiency, separation factor, and water content in produced ammonia vapor were studied. The results showed that feed temperature was the most important factor affecting ammonia removal efficiency, which was improved from 78 to 99% as the temperature enhanced from 30 to 60°C. The feed velocity and operation time also affected the ammonia removal efficiency and separation factor obviously. A pilot-scale experiment was carried out using a membrane module of 20 m2 membrane area. Preliminary results showed that proper ammonia removal efficiency and product property were obtained.

Study of phosphate removal from aqueous solution by zinc oxide.

Zinc oxide (ZnO) was synthesized and used to investigate the mechanism of phosphate removal from aqueous solution. ZnO particles were characterized by X-ray diffraction, scanning electron microscope and Fourier transform infrared spectroscopy before and after adsorption. Batch experiments were carried out to investigate the kinetics, isotherms, effects of initial pH and co-existing anions. The adsorption process was rapid and equilibrium was almost reached within 150 min. The adsorption kinetics were described well by a pseudo-second-order equation, and the maximum phosphate adsorption capacity was 163.4 mg/g at 298 K and pH ∼6.2±0.1. Thermodynamic analysis indicated the phosphate adsorption onto ZnO was endothermic and spontaneous. The point of zero charge of ZnO was around 8.4 according to the pH-drift method. Phosphate adsorption capacity reduced with the increasing initial solution pH values. The ligand exchange and Lewis acid-base interaction dominated the adsorption process in the lower and the higher pH range, respectively. Nitrate, sulfate and chloride ions had a negligible effect on phosphate removal, while carbonate displayed significant inhibition behavior.

Reaction Kinetics of Oxidative Absorption of Nitric oxide into Sodium Hypochlorite Solution

Absorption of nitric oxide into aqueous sodium hypochlorite solution was studied in a stirred tank reactor. The effect of various operation variables such as nitric oxide (NO) and sodium hypochlorite concentration, initial pH value, and reaction temperature etc. was critically examined. It was observed that the absorption process followed first-order kinetics with respect to both nitric oxide as well as sodium hypochlorite. Nitric oxide absorption reached to maxima when the initial pH value of aqueous sodium hypochlorite solution was taken 5.5 and thereafter absorption decreased slowly. The pre-exponential frequency factor and activation energy of absorption of nitric oxide into aqueous sodium hypochlorite solution were investigated and found to 7.96×108 m3/(mol s) and 28.15 kJ/mol respectively

The effect of salinity on the sorption of cadmium ions from aqueous medium on Fe(III)-sepiolite

In this study, the sorption of cadmium ions onto sepiolite modified with hydrated iron(III) oxide, Fe(III)-sepiolite, has been investigated in natural seawater, artificial seawater, aqueous solution of NaCl of the same ionic strength as the seawater and distilled water. The sorption experiments were performed as a function of the initial solution pH value, the initial metal concentration and the equilibration time, using the batch method. The equilibrium sorption data were analyzed by the Langmuir, Freundlich and Sips isotherm models and the kinetics of sorption was analyzed using the pseudo-first-order and the pseudo-second-order kinetic models. The maximum sorption capacity and the strength of the sorbate-sorbent bonds at initial pH = 7 were found to decrease in the following order: distilled water &gt; NaCl solution &gt; artificial seawater &gt; natural seawater. The values of parameter nS in the Sips model, which fitted the equilibrium sorption results best, showed that heterogeneity of the sorbent surface was the highest in distilled water and the lowest in natural seawater. The sorption kinetic data fitted well with the pseudo-second-order kinetic model, which suggests that the rate-limiting step in Cd2+ sorption onto Fe(III)-sepiolite could be chemisorption. The low desorption percentage in both distilled water and 0.001 M HNO3 indicated that sorption occurred mainly by chemisorption mechanisms.

Preparation and characterization of chitosan/halloysite magnetic microspheres and their application for removal of tetracycline from an aqueous solution

In the work, magnetically separable adsorbent, named chitosan (CTS)/halloysite nanotubes (HNT)HNT-Fe3O4 microspheres are prepared by emulsion cross-linking method and characterized by Fourier transform infrared spectroscopic analysis, vibrating sample magnetometer, X-ray powder diffraction, scanning electron microscope, and transmission electron microscopy. The microspheres are applied as adsorbents for the removal of tetracycline (TC) from aqueous solution. The effects of the initial concentration of TCs solution (C0), temperature, initial pH value (pH0) of TC solution, and the adsorption dose on the adsorption capacity of the microspheres are investigated. The optimum pH value for TC adsorption is found at pH 5.0, and the adsorption capacity increased with the increase in adsorption temperature. The adsorption kinetics is better described by the pseudo-second-order equation, and their adsorption isotherms are better fitted to the Langmuir equation. CTS/HNT-Fe3O4 microspheres could be easily separated from the aqueous solution in a magnetic field. The adsorption–desorption experiments implied that CTS/HNT-Fe3O4 microspheres can be used as promising adsorbents for the removal of TC from wastewater HNT.

Atmospheric Pressure Plasma Jet in Organic Solution: Spectra, Degradation Effects of Solution Flow Rate and Initial pH Value

The organic compounds of p-nitrophenol (PNP) solution was treated by the active species generated in a stirred reactor by an atmospheric pressure plasma jet (APPJ). The emission intensities of hydroxyl (OH), oxygen (O), nitric oxide (NO), hydrogen (H) and molecular (N2) were measured by optical emission spectroscopy (OES). The relations between the flow rates of the PNP solution and degradation, the degradation effects and initial pH value of the solution were also investigated. Experimental results show that there exist intense emissions of O (777.1 nm), N2 (337.1 nm), OH (306–310 nm) and NO band (200–290 nm) in the region of plasma. Given the treatment time and gas flow rate, the degradation increased as a function of discharge energy and solution flow rate, respectively. The solution flow rate for the most efficient degradation ranged from 1.414 m/s to 1.702 m/s, and contributed very little when it exceeded 2.199 m/s. This indicates the existence of diffusion-controlled reactions at a low solution flow rate and activation-controlled reactions at a high solution flow rate. Moreover, increasing or decreasing the initial pH value of neutral PNP solution (pH=5.95) could improve the degradation efficiency. Treated by APPJ, the PNP solutions with different initial pH values of 5.95, 7.47 and 2.78 turned more acidic in the end, while the neutral solution had the lowest degradation efficiency. This work clearly demonstrates the close coupling of active species, photolysis of ultraviolet, the organic solution flow rate and the initial pH value, and thus is helpful in the study of the mechanism and application of plasma in wastewater treatment.

Nitrate removal from aqueous solution using natural zeolite-supported zero-valent iron nanoparticles

A report on the synthesis and characterization of nanoscale zero-valent iron in the presence of natural zeolite as a stabilizer is presented. This novel adsorbent (Ze-nZVI) was synthesized by the sodium borohydride reduction method. The scanning electron microscopy (SEM) images revealed that the stabilized nZVI particles were uniformly dispersed across the zeolite surface without obvious aggregation. The synthesized Ze-nZVI material was then tested for the removal of nitrate from aqueous solution. The effect of various parameters on the removal process, such as initial concentration of nitrate, contact time, initial pH, and Ze-nZVI dosage, was studied. Batch experiments revealed that the supported nZVI materials generally have great flexibility and high activity for nitrate removal from aqueous solution. The nitrogen mass balance calculation showed that ammonium was the major product of nitrate reduction by Ze-nZVI (more than 84% of the nitrate reduced); subsequently the natural zeolite in Ze-nZVI removed it completely via adsorption. The kinetic experiments indicated that the removal of nitrate followed the pseudo-second-order kinetic model. The removal efficiency for nitrate decreased continuously with an increase in the initial solution pH value and Ze-nZVI dosage but increased with the increase in the initial concentration of nitrate. The overall results indicated the potential efficacy of Ze-nZVI for environmental remediation application.