Solution pH Conditions Research Articles

Synthesis of polyoxometalate-based complexes and photocatalytic degradation of metronidazole

A new complex, [Cu2(1,10-phenanthroline-5,6-dione)3(PMo12O40)]2·3H2O (1), was prepared via solvothermal method. A one-dimensional structure was formed by the bonding of ligand and metal. Then, a two-dimensional layered structure was constructed by hydrogen bonding. The structures were characterized using X-ray powder diffraction, Fourier transform infrared spectroscopy, differential thermal analysis and thermogravimetric analysis, X-ray photoelectron spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy. The degradation of metronidazole under UV light was studied under varying ionic strength and solution pH conditions. Compared with original conditions, the addition of sodium chloride significantly increased the degradation rate of metronidazole to 80.2%.

Study on optimal adsorption conditions of norfloxacin in water based on response surface methodology

Abstract The waste pomelo peel was pyrolyzed at 400 °C to prepare biochar and used as adsorbent to remove norfloxacin (NOR) from simulated wastewater. The adsorption conditions of norfloxacin by biochar were optimized by response surface methodology (RSM). On the basis of single-factor experiment, the adsorption conditions of biochar dosage, solution pH and reaction temperature were optimized by Box-Behnken Design (BBD), and the quadratic polynomial regression model of response value Y1 (NOR removal efficiency) and Y2 (NOR adsorption capacity) were obtained respectively. The results show that the two models are reasonable and reliable. The influence of single factor was as follows: solution pH > biochar dosage > reaction temperature. The interaction between biochar dosage and solution pH was very significant. The optimal adsorption conditions after optimization were as follows: biochar dosage = 0.5 g/L, solution pH = 3, and reaction temperature = 45 °C. The Y1 and Y2 obtained in the verification experiment were 75.68% and 3.0272 mg/g, respectively, which were only 2.38% and 0.0242 mg/g different from the theoretical predicted values of the model. Therefore, the theoretical model constructed by response surface methodology can be used to optimize the adsorption conditions of norfloxacin in water.

Investigation of Operation Strategy Based on Solution pH for Improving the Crystal Quality Formed during Reactive Crystallization of l-Aspartic Acid.

The production of crystalline particles with a thick and low degree of agglomeration is required because the agglomerated crystals with thin primary particles, which are frequently formed during reactive crystallization, deteriorate the crystal size distribution (CSD) of the final product due to their fragile morphology. This study aimed to develop an operation strategy for improving the degree of agglomeration and thickness of crystalline particles in the reactive crystallization considering the effect of the solution pH using l-aspartic acid as an experimental system. The scanning electron microscopy observations showed that the thickness of primary particles which form agglomerated crystals could be increased by operating the crystallization under low solution pH conditions. In contrast, it was found that operating the crystallization under high solution pH led to a decrease in the nucleation rate of crystalline particles, which resulted in a decrease in the degree of agglomeration. Then, an operation method, that is, changing the addition method of feed solutions to overcome the trade-off between the thickness and degree of agglomeration, was proposed by considering the effect of solution pH. Consequently, crystalline particles with a narrow CSD could be successfully obtained using the proposed method due to the suppression of the agglomeration and increase of the thickness. Therefore, the development of the operation strategy based on the effect of the solution pH on the degree of agglomeration and thickness is important to produce crystalline particles with improved CSD in reactive crystallization.

Nitrate (NO3-) removal from wastewater by adsorption using modified kaolin

This study aims to determine the effect of the initial concentration and pH conditions of the nitrate solution on the removal of nitrate in water, which was carried out in batch. The raw material used is kaolin, which is firstly mashed and sieved with a size of 120 mesh, then activated by immersing it in a 0.5 M HCl solution for 24 hours, followed by modification of the surfactant by immersion in a 0.5 M cetyltrimethyllammonium bromide (CTABr) solution for 120 minutes, and accompanied by stirring using a magnetic stirrer at a speed of 150 rpm. Before being used as an adsorbent, kaolin CTABr-modified was analyzed using a scanning electron microscope (SEM) to determine the surface morphology of the material. Batch adsorption test was carried out by adding 1 gram of kaolin CTABr-modified to 100 mL of a solution containing nitrate with various concentrations of 10; 20; 30 mg/L and the pH of the solution is 5; 7; 8. The experiment was carried out for 180 minutes, where every 30 minutes the solution was sampled and analyzed for nitrate content using a spectrophotometer UV-Vis. The conclusion of this study is that kaolin CTABr-modified can be used as an adsorbent, where the SEM test results show that the surface morphology of kaolin CTABr-modified is denser and more compact than the prepared kaolin and kaolin HCl-activated. Based on the experimental results according to the Langmuir isotherm equation, the constant value was 0.78. The mechanism of nitrate removal includes ion exchange, hydrogen bonding, and intermolecular interactions. The maximum adsorption capacity was 0.72 mg/g, found under acidic conditions (pH 5) and with a contact time of 180 minutes.

Water recovery from yarn fabric dyeing wastewater using electrochemical oxidation and membrane processes.

This study intended to evaluate and compare the efficiency of electrochemical oxidation (EO), nanofiltration (NF), and reverse osmosis (RO) membranes processes in the treatment of yarn fabric dyeing wastewater (YFDW) in terms of chemical oxygen demand (COD) removal, color removal, salinity reduction, and conductivity removal. EO tests of the textile effluent were conducted under various current densities and solution pH conditions employing a graphite electrode. Membrane filtration experiments were conducted using two different NF membranes: NP010 and NP030 and two distinct RO membranes: BW30 and SW30 flat-sheet membranes. The experimental results showed that NF membrane process is not suitable for yarn fabric wastewater treatment showing low removal efficiencies for COD, color, and conductivity. However, both EO and RO membranes could reduce COD and color to high removal performances. EO results showed more than 99% of color removal and 80% of COD elimination at pH = 6 and current density of 50 mA/cm2 after 180 min of reaction. Using RO membrane for yarn fabric wastewater treatment demonstrated relatively complete removal of color concentration and 98% of COD elimination. However, EO process showed less performance in conductivity removal efficiency compared to the RO membranes. EO treatment of YFDW decreased conductivity by 31.2%, whereas RO membrane process reduced conductivity to a greater extent and recorded 97.1% of removal elimination percentage. Therefore, the treated water by RO membrane could be recycled back to the process such as washing and dyeing, in that way offering economic profits by decreasing water consumption and wastewater treatment cost. PRACTITIONER POINTS: Electrochemical oxidation and membrane filtration processes were combined for the treatment of yarn fabric dyeing wastewater (YFDW). A 100% color removal of color and 98.5% COD elimination efficiencies were obtained for the electrochemical oxidation (EO) + RO combined process. EO treatment of YFDW decreased conductivity by 32.7%, whereas the RO membrane process reduced conductivity to a greater extent and recorded 97.7% of removal elimination percentage.

Ex situ and in situ Magnetic Phase Synthesised Magneto-Driven Alginate Beads

Biocompatible magnetic hydrogels provide a great source of synthetic materials, which facilitate remote stimuli, enabling safer biological and environmental applications. Prominently, the ex situ and in situ magnetic phase integration is used to fabricate magneto-driven hydrogels, exhibiting varied behaviours in aqueous media. Therefore, it is essential to understand their physicochemical properties to target the best material for each application. In this investigation, three different types of magnetic alginate beads were synthesised. First, by direct, ex situ, calcium chloride gelation of a mixture of Fe3O4 nanoparticles with an alginate solution. Second, by in situ synthesis of Fe3O4 nanoparticles inside of the alginate beads and third, by adding an extra protection alginate layer on the in situ synthesised Fe3O4 nanoparticles alginate beads. The three types of magnetic beads were chemically and magnetically characterised. It was found that they exhibited particular stability to different pH and ionic strength conditions in aqueous solution. These are essential properties to be controlled when used for magneto-driven applications such as targeted drug delivery and water purification. Therefore, this fundamental study will direct the path to the selection of the best magnetic bead synthesis protocol according to the defined magneto-driven application.

Assess the performance of chemical coagulation process for microplastics removal from stormwater

Microplastic (MP) is considered as one of the emerging pollutants in marine environments. Because of low density and small particle size (<5 mm), MPs are easily discharged into open waterways by stormwater runoff. Therefore, the aim of this study was to investigate the effect of coagulation process for the removal of different types of MPs such as low-density polyethylene (LDPE), high-density polyethylene (HDPE) and polypropylene (PP) from synthetic stormwater. The effect of different types of a coagulant such as alum and polyacrylamide (PAM), dosages of coagulants, solution pH and weathering conditions was investigated for the removal of MPs. Results found that a combination of alum and PAM performed better than standalone coagulant for MPs removal. The removal of all three types of MPs was high at low pH (3–5). It is also found that the removal efficiency of LDPE, HDPE and PP was 92 %, 84 % and 96 %, respectively under the weathering conditions. The mechanisms for MP removal were charge neutralization and hydrophobic interaction between MP and coagulant flocs. Overall, this study has confirmed that the coagulation process was very effective for removing MP particles under weathering conditions.

Crown ether functionalized polysulfone membrane coupling with electric field for Li+selective separation

BackgroundIn order to improve the selective separation performance of the membrane for Li+ and enhance the separation efficiency, a crown ether functionalized polysulfone membrane was prepared in this paper, and the Li+ was separated by electrodialysis process. MethodsChloromethylated polysulfone (CMPSf) was used as the base membrane, 4′-aminobenzo-12-crown-4-ether (AB12C4) was in-situ grafted onto the surface of CMPSf membrane to obtain the PSf-sg-AB12C4 membrane. The chemical structure of the membrane surface was characterized by ATR-FTIR and XPS. The surface and cross-sectional morphologies of the membrane were characterized by FESEM. The PSf-sg-AB12C4 membrane was used for selective separation of Li+ by membrane coupling with electric field. FingingsThe results show that the CMPSf membranes and the PSf-sg-AB12C4 porous membrane have almost no selective separation performance for Li+, while the PSf-sg-AB12C4 dense membrane can selectively separate Li+. After optimizing the conditions of voltage, ion concentration and solution pH, the separation factor of the PSf-sg-AB12C4 dense membrane for Mg2+ to Li+ is up to 32.6. In addition, the separation factors of coexisting ions such as Na+, K+, Ca2+ to Li+ are all higher than that of Mg2+ to Li+, suggesting that the PSf-sg-AB12C4 dense membrane is a promising material for selective separation of Li+ from brine.

Tuning Exchange Coupling in NiO-Based Bimagnetic Heterostructured Nanocrystals.

A series of bimagnetic heterostructured nanocrystals having an antiferromagnetic NiO core and a ferrimagnetic MnxNi1-xO and/or FiM Mn3O4 island nanophase overgrowth has been synthesized under varying aqueous solution pH conditions. The two-step self-assembly process employs a thermal decomposition method to synthesize NiO nanoparticles, followed by growth of the MnxNi1-xO and/or Mn3O4 nanophase over the NiO core using hydrothermal synthesis at pH values ranging from 2.4-7.0. The environmentally benign hydrothermal process involves pH control of the protonation vs hydroxylation reactions occurring at the nanoparticle surface. TEM analysis and Rietveld refinement of XRD data show that three distinct types of heterostructured nanocrystals occur: NiO/MnxNi1-xO core-shell-like heterostructures at the pH of 2.4, mixed NiO/MnxNi1-xO and/or/Mn3O4 core-overgrowth structures for 2.4 < pH < 4.5, and predominantly NiO/Mn3O4 core-island structures for pH > 4.5. The magnetic coercivity and exchange bias of the heterostructured nanocrystals vary systematically with the pH of the aqueous solution used to synthesize the samples. The temperature-dependent magnetization and hysteresis loop data are consistent with the nature of overlayer coverage of the NiO core. Our DFT based calculations show that the MnxNi1-xO phase has ferrimagnetic properties with a stable spin orientation along the ⟨111⟩ orientation. Furthermore, the calculations show that the magnetic anisotropy constant (K1) of the Mn3O4 phase is considerably larger than that of the MnxNi1-xO phase, which is confirmed by our experimental results. The coercivity and exchange bias field are the largest for the NiO/Mn3O4 core-island nanocrystals, synthesized at a pH value of 5.0, with robust values of nearly 6 kOe and 3 kOe, respectively. This work demonstrates the tunability of hydrothermal deposition, and concomitant magnetic coercivity and exchange bias properties, of MnxNi1-xO and/or Mn3O4 nanophase overgrowth over a NiO core with pH, that makes these heterostructured nanocrystals potentially useful for magnetic device, biomedical, and other applications.

High-efficiency degradation of p-arsanilic acid and arsenic immobilization with iron encapsulated B/N-doped carbon nanotubes at natural solution pH

p-arsanilic acid (p-ASA) is still widely applied as feed additive in many countries. Accompanied with chemical reactions in the environment, p-ASA will release more toxic inorganic arsenic. In order to safely and efficiently treat p-ASA flow washing into the environment, iron encapsulated B/N-doped carbon nanotubes (Fe@C-NB) were fabricated and used as the catalyst for the degradation of p-ASA. The calcination temperature and the dose of the iron salt have significant effects on the structure and properties of the catalysts. We have produced a series of catalysts of the same type to facilitate the degradation of p-ASA. Under optimal conditions of material (Fe@C-NB) syntheses, both 95% degradation of p-ASA and 86% total arsenic immobilization can be obtained with oxidant (Peroxymonosulfate, PMS) and catalyst (Fe@C-NB) treatment after 60 min. The effects of oxidant types (peroxydisulfate (PDS), PMS, hydrogen peroxide (H2O2)), amount, initial solution pH, inorganic anion, and other reaction conditions were studied in the p-ASA removal. In this Fenton-like reaction, the Fe@C-NB exhibits high efficiency and excellent stability without complex preparation methods; besides, the advantages of short reaction time and natural reaction conditions in Fe@C-NB/PMS system will promote the practical application of Fenton-like.

Machine learning to determine optimal conditions for controlling the size of elastin-based particles

This paper evaluates the aggregation behavior of a potential drug and gene delivery system that combines branched polyethyleneimine (PEI), a positively-charged polyelectrolyte, and elastin-like polypeptide (ELP), a recombinant polymer that exhibits lower critical solution temperature (LCST). The LCST behavior of ELP has been extensively studied, but there are no quantitative ways to control the size of aggregates formed after the phase transition. The aggregate size cannot be maintained when the temperature is lowered below the LCST, unless the system exhibits hysteresis and forms irreversible aggregates. This study shows that conjugation of ELP with PEI preserves the aggregation behavior that occurs above the LCST and achieves precise aggregate radii when the solution conditions of pH (3, 7, 10), polymer concentration (0.1, 0.15, 0.3 mg/mL), and salt concentration (none, 0.2, 1 M) are carefully controlled. K-means cluster analyses showed that salt concentration was the most critical factor controlling the hydrodynamic radius and LCST. Conjugating ELP to PEI allowed crosslinking the aggregates and achieved stable particles that maintained their size below LCST, even after removal of the harsh (high salt or pH) conditions used to create them. Taken together, the ability to control aggregate sizes and use of crosslinking to maintain stability holds excellent potential for use in biological delivery systems.

High sensitive electrochemical sensor for imatinib based on metal-organic frameworks and multiwall carbon nanotubes nanocomposite

A new sensitive electrochemical sensor has been constructed based on glassy carbon electrode (GCE) modified by nanocomposite of multiwall carbon nanotubes (MWCNTs) and metal–organic frameworks of copper (CuMOFs). The voltammetric response of the offered sensor (CuMOFs-MWCNTs/GCE) exhibited the catalytic effect toward imatinib (IMB). To characterize the structure and morphology of the constructed sensor, the procedures of electrochemical impedance spectroscopy (EIS) and field emission scanning electron microscopy (FE-SEM) were applied. The porosity of CuMOF was described by Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) technique. This sensor depicted an excellent electrocatalytic response for IMB detection under optimized conditions of solution pH, scan rate, accumulation potential, and time. Two linear segments in the calibration plot have been obtained for ranges of 0.01–20 and 20–220 µM with the limit of detection (LOD) 4.1 nM. The prepared sensor results were acceptable for the quantitative measurement of IMB in human blood serum (HBS), urine, and pharmaceutical dosage (Tablet), and it compared well with the reported HPLC method.Finally, the fabricated sensor demonstrated an acceptable accuracy, reproducible behaviour, and also, high stability in all electrochemical evaluations. Besides, analytical parameters were determined, and the results were compared with the reportages of similar methods.

Bacteriophage Capsid Modification by Genetic and Chemical Methods.

Bacteriophages are viruses whose ubiquity in nature and remarkable specificity to their host bacteria enable an impressive and growing field of tunable biotechnologies in agriculture and public health. Bacteriophage capsids, which house and protect their nucleic acids, have been modified with a range of functionalities (e.g., fluorophores, nanoparticles, antigens, drugs) to suit their final application. Functional groups naturally present on bacteriophage capsids can be used for electrostatic adsorption or bioconjugation, but their impermanence and poor specificity can lead to inconsistencies in coverage and function. To overcome these limitations, researchers have explored both genetic and chemical modifications to enable strong, specific bonds between phage capsids and their target conjugates. Genetic modification methods involve introducing genes for alternative amino acids, peptides, or protein sequences into either the bacteriophage genomes or capsid genes on host plasmids to facilitate recombinant phage generation. Chemical modification methods rely on reacting functional groups present on the capsid with activated conjugates under the appropriate solution pH and salt conditions. This review surveys the current state-of-the-art in both genetic and chemical bacteriophage capsid modification methodologies, identifies major strengths and weaknesses of methods, and discusses areas of research needed to propel bacteriophage technology in development of biosensors, vaccines, therapeutics, and nanocarriers.

Modeling of Congo Red Adsorption onto Multi-walled Carbon Nanotubes Using Response Surface Methodology: Kinetic, Isotherm and Thermodynamic Studies

In this present study, an adsorption process was investigated to removal of Congo Red (CR) dye from aqueous solutions by using multi-walled carbon nanotubes (MWCNTs) as an adsorbent. The physico-chemical properties of MWCNTs were characterized by TEM, SEM, Raman spectroscopy and BET surface area. The response surface methodology, which is including central composite design, was used to investigate the effects of four independent parameters (initial pH of solution (5.5–11.5), initial CR concentration (15–75 mg/L), MWCNTs amount (0.05–0.25 g/L) and contact time (20–60 min)). ANOVA evaluated with Design Expert 10.0 showed that a high value of regression coefficient (R2 = 0.988) a good agreement between experimental and model predicted response in addition to significance of the model. The optimum values of the independent variables giving the maximum removal efficiency (78.36%) of CR dye were obtained at the optimum adsorption conditions of initial solution pH: 5.5; initial CR concentration: 15 mg/L; MWCNTs dosage: 0.25 g/L and contact time: 59.62 min. The kinetic study illustrated that the experimental data are well defined with pseudo-second-order adsorption kinetic model. The maximum adsorption capacity (qmax) increased from 115.8 mg/g to 138.3 mg/g with the increase in temperature from 293 to 323 K. Thermodynamic parameters, ΔH (8.56 kJ/mol), ΔG (− 27.08 and − 30.73 kJ/mol) and ΔS (0.1215 kJ/mol K) were determined for the adsorption process.

Study on the fluorescence properties of the interaction between felodipine and bovine serum protein

The interaction between felodipine and bovine serum protein was studied, the optimal experimental conditions were selected, and the fluorescence quenching mechanism was discussed. The interaction between filodipine and bovine serum protein was determined by UV spectrophotometry, and the optimal experimental conditions were selected by control variable method. The mechanism of fluorescence quenching in the system was explored by fluorescence spectrophotometry. The fluorescence intensity of the system between felodipine and bovine serum protein was the most obvious under the experimental conditions of buffer solution pH 7.4, felodipine concentration 8.0*10-4mol/L, reaction time 30min and 25°C. Static fluorescence quenching caused by the formation of complex compounds.

Catalytic degradation of ranitidine using novel magnetic Ti3C2-based MXene nanosheets modified with nanoscale zero-valent iron particles

Magnetic nanoscale zero-valent iron (nZVI)@Ti3C2-based MXene nanosheets were synthesized via an in-situ reductive deposition method, and were characterized as a novel Fenton-like catalyst for ranitidine degradation. The vast majority of ranitidine was found to be mineralized after 30 min of reaction time with 91.1 % of removal efficiency and the removal of 63.3 % of total organic carbon (TOC). Results showed that the nZVI@Ti3C2-based MXene nanosheets had a synergistic effect enhancing the catalyst chemical reactivity and stability. In particular, Ti3C2-based MXene was found to restrain the agglomeration of nZVI particles (nZVIPs) and promote electron transfer between magnetic particles with a diameter of approximately 10−40 nm. Ranitidine molecules were decomposed mainly by hydroxyl radicals (∙OH) attack especially the surface-bound ∙OHads. This study provided a completely new insight into the mode of surface inactivation of nZVIPs under different solution pH conditions, establishing that this novel catalyst was suitable for use under a wide pH range.

Assessment of sulfamethoxazole removal by nanoscale zerovalent iron

Removal of pharmaceutical compounds, such as sulfamethoxazole (SMX) from the aquatic environments, is critical in order to mitigate their adverse environmental and human health effects. In this study, the effectiveness of nanoscale zerovalent iron (nZVI) particles for the removal of SMX was investigated under varying conditions of initial solution pH (3, 5, 7 and 11) and nZVI to SMX mass ratios (1:1, 5:1, 10:1, 13:1, 25:1). Batch kinetic studies, which were well represented using both pseudo-first-order and pseudo-second-order kinetic models (R2 > 0.98), showed that both solution pH and mass ratios strongly influenced SMX removal. At a fixed mass ratio of 10:1, removal efficiencies were higher in acidic conditions (83% to 91%) compared to neutral (29%) and alkaline (6%) conditions. A similar trend was observed for removal rates and removal amounts. For mass ratios between 1:1 and 10:1, an optimum pH existed (pH 5) wherein highest removal efficiencies were attained. Increasing the mass ratio above 10:1 resulted in virtually complete removal efficiencies at pH 3 and 5, and 70% at pH 7. Analysis of SMX speciation and zeta potential of nZVI particles provided insights into the role of pH on the efficiencies, rates and extents of SMX removal. Total organic carbon analysis and mass spectrometry measurements of SMX solution before and after exposure to nZVI particles suggested the transformation of SMX via redox reactions, which are likely the dominant process compared to adsorption. Five transformation products were observed at m/z 156 (TP1), 192 (TP2), 256 (TP3), 294 (TP4) and 296 (TP5). TP1, TP2 and TP3 were further identified using ion fragment analysis. Overall, results from this study indicate a strong potential for SMX removal by nZVI particles, and could be useful towards identifying reaction conditions for optimum SMX transformation.

Dosage and pH dependence of coagulation with polytitanium salts for the treatment of Microcystis aeruginosa-laden and Microcystis wesenbergii-laden surface water: The influence of basicity

Polytitanium coagulants have been recently developed and have received wide attention due to both strong coagulation capability and sludge recycling to produce valuable by-products, titanium dioxide (TiO2). This study reports the performance of coagulation with emerging polytitanium salts, polytitanium chloride (PTC) and polytitanium sulfate (PTS), for the treatment of two common cyanobacteria (Microcystis aeruginosa, MA and Microcystis wesenbergii, MW)-laden surface water, which has been barely reported. Of particular concern is the coagulant dosage and solution pH dependence of polytitanium coagulation, which are the main parameters influencing coagulation efficiency. The influence of basicity (B) of PTC and PTS on coagulation performance was simultaneously included. Results show the optimized B value of 1.5 with coagulant dosage of 30 mg/L and initial solution pH between 7–9 for both PTC and PTS coagulation, wherein obvious advantage of PTC was observed over PTS regardless of MA- or MW-laden surface water treatment. The PTC coagulation could achieve almost complete removal of algae (about 99.0 %) with synergic removal of organic matter with high-efficiency. Both PTC and PTS were more capable at alkaline solution pH conditions for turbidity and algae removal through sweep flocculation, while satisfied removal of the humic acid-representative organic matters was observed at acidic to neutral pH conditions by charge neutralization. Satisfied flocculation zones were determined according to synergic removal of algae, turbidity and organic matters, with most of the satisfied points distributed at solution pH 7–9 conditions. This study will provide theoretical basis and facilitate wide application of the polytitanium coagulation for algae-loaded surface water treatment.

Simulate permeable reactive barrier by using a COMSOL model and comparison with the Thomas, Yoon–Nelson and Clark models for CR dye remediation by composite adsorbent (sewage and waterworks sludge)

The remediation of Congo Red (CR) dye by the synthetic sorbent composited from sewage and waterworks sludge was studied in batch and continuous experiments. The continuous experiments studied the composite synthetic after mixing with composite synthetic sorbent filter (CSF) glass waste to increase the hydraulic conductivity of the permeable reactive barrier (PRB). The synthetic composite sorbent was characterised by the nitrogen adsorption-desorption tests, field emission-scanning electron microscopy and X-ray diffraction. For evaluating the batch tests, the variable conditions of initial concentration, solution pH, agitation time and agitation speed were studied. The synthetic sorbent showed a high ability to remove the CR from a contaminated water, with maximum sorbent uptake equal to 9,469.211 mg/g and composite adsorbent-filter CSF equal to 4,415.946 mg/g. Pseudo-second-order kinetic model and Langmuir isotherm model governed the adsorption process. The column tests showed the highest reactivity, with 50:50 weight ratios of the adsorbent to filter glass waste. The experiments were done with different concentrations of CR and different bed heights of CSF as the PRB for 90 days. There was a delay in the breakthrough time when decreasing the contaminant concentrations and when increasing the composite adsorbent-filter CSF bed height. The breakthrough curves were well represented by the COMSOL model.

Colloid retention and mobilization mechanisms under different physicochemical conditions in porous media: A micromodel study

Clear understanding of pore-scale mechanisms that control transport and retention of colloids in porous media at different physicochemical conditions is critical to improve design and efficient cleanup methodologies of filter beds. The objective of this work was to investigate the impact of hydrophobicity, solution ionic strength, and pH on colloid retention mechanisms in single-phase and two-phase flow in porous media systems. A series of experiments were conducted using a geometrically representative micromodel. Hydrophilic and hydrophobic colloids were dispersed in water at different solution ionic strength and pH conditions. Findings indicate that hydrophilic colloids exhibit high filtration efficiency as the colloids interact attractively with other colloids and solid-water-interface irrespective of the solution chemistry. However, for hydrophobic colloids, changes in solution chemistry significantly increase colloid retention where the colloid interaction become attractive with the increase in ionic strength and decrease in pH values. Colloids attached to the collector surfaces mobilized by the strong capillary forces induced by the moving gas-water interface and transported along with the interface. However, hydrophilic colloids redeposited on gas-water-solid interfaces or thin water films because of their greater capillary potential. Therefore, greater filtration efficiency is achieved with the hydrophilic colloids compared to the hydrophobic colloids for which the efficiency can be improved by changing the solution chemistry. Moreover, the removal efficiency by the moving gas-water interface was observed to be more for hydrophobic colloids compared to hydrophilic colloids for which the efficiency can be improved by lowering the ionic strength or increasing the pH value. This study indicates that the coupled effects of solution chemistry and colloid hydrophobicity should be taken into account while investigating efficient filtration and cleaning practices for the filter beds.