Colloids and Surfaces C: Environmental Aspects最新文献

Hydrogels based on hydrophilic, crosslinked polymer networks can reduce surface contamination in aqueous environments and continue attracting research interest due to their low adhesion, biocompatibility and tunable properties. In particular, sub-micron hydrogel films can potentially screen a surface from interaction with foulant colloids and microorganisms without compromising original functions, such as water permeation in membranes. This study focuses on the preparation of thin hydrogel films with the goal of understanding their adhesive and micromechanical properties, as well as factors affecting the dynamics of microparticle deposition on such films, mimicking the initial stages of surface fouling with colloids, microparticles and microorganisms. For this purpose, a simple procedure was developed to simultaneously crosslink and covalently anchor multi-arm-PEG precursors to a surface to form a submicron coating as a representative model. The effects of synthetic parameters and external conditions on adhesion and viscoelasticity were studied by force spectroscopy using polystyrene colloidal probes. The same particles were also employed in macroscopic deposition experiments in a parallel plate flow cell under identical solution conditions. Microscopic adhesion and elasticity were unaffected by the hydrogel crosslinking density and by salinity, but strongly affected by solution pH and dwell time, whereas macroscopic deposition was strongly affected both by salinity and by pH. These differences were ascribed to the effect of long-range double-layer forces, involved in deposition but absent in measurements of adhesion and elasticity. The results highlight the differences and similarities between the two types of measurements and underlying phenomena, as a step towards the understanding and rational design of soft antifouling coatings.

The discharge of wastewater containing toxic and radioactive iodine into water leads to a negative impact on aquatic life, animals and humans. In this work, we synthesized Polythiophene (PTh) and Polythiophene/α-MnO₂ nanocomposite (PTh/α-MnO₂) by the chemical route and used them to remove iodine from aqueous solution. The surface morphology showed presence of rod-shaped α-MnO₂ with a size of 25–200 nm embedded in polythiophene. The interplaner distance was found to be 0.7 nm corresponds to the (211) plane. Specific surface area of PTh and PTh/α-MnO₂ nanocomposite was found to be 22.15 m²/g and 51.98 m²/g respectively and equilibrium I₂ adsorption capacity was found to be (q_e) 266.08 mg/g and 304.21 mg/g respectively. Langmuir isotherm (R² = 0.99) fitted well compared to Freundlich isotherm (R² = 0.84) indicates monolayer adsorption of iodine onto adsorbent surface. The adsorbent is stable, recyclable, high adsorption capacity, and environment friendly so it can be used at large scale for treatment of I₂ contaminated water.

Organic arsenic contamination in groundwater and surface water is one of threats to human beings. In this study, a novel zirconium-based nanoparticle was developed to remove dimethylarenic acid (DMA) from aqueous solution. The adsorption behavior was evaluated by various batch adsorption experiments. The pH effect study revealed that the maximum adsorption was achieved around pH 3.0. The ionic strength did not have significant effect on the uptake of DMA. The adsorption kinetics study showed that the adsorption equilibrium was established within 24 h; an intraparticle kinetics model fit the experimental data well. In the adsorption isotherm study, the Langmuir equation described the adsorption data better than the Freundlich equation; the maximum adsorption capacity of the sorbent was calculated to be 58.82 mg-As/g at the optimal pH. In the natural organic matters and coexisting anions effect studies, the presence of humic acid and coexisting anions have little effect on the uptake of DMA. The performance of the Zr-based NP was not largely inhibited in the presence of NOMs and coexisting anion. The FTIR and XPS spectroscopic analyses demonstrated that DMA was successfully adsorbed onto the sorbent and the adsorption mechanism was proposed to be ions exchange between arsenic and sulfate ions.

Electrocoagulation has emerged as a rapidly advancing area in the field of wastewater treatment due to its capability to eliminate pollutants that are typically resistant to filtration or chemical treatment methods, as well as its overall effectiveness, which is often impeded by the formation and growth of flocs. In this study, simulated photovoltaic wastewater was treated using the electrocoagulation method, with cathodic water reduction employed to induce a highly efficient electrocoagulation rate towards the removal of SiO₂ and F⁻. Our results demonstrate that the optimal conditions for this process involved the use of an Al anode, Nickel foam as cathode, an inter-electrode distance of 1.0 cm, a current density of 30 mA cm⁻², a stirring speed of 300 rpm, sodium chloride as supporting electrolyte, and an initial pH of 7. Our experimental findings indicated satisfactory performance with respect to EC, as evidenced by the reduction of F⁻ content from 25 mg L⁻¹ to 3.68 mg L⁻¹, and the complete removal of SiO₂ from 16 mg L⁻¹. Furthermore, electrochemical analysis and texture characterization revealed that the overall rate of flocculation was dependent on the cathodic material, with in-situ generated OH⁻ in the electrolysis cell influencing the microenvironment of iron hydroxide floc formation and sedimentation. Our study offers conclusive evidence that the optimal cathodic material capable of intensifying OH⁻ concentration from water dissociation is key to achieving superior electrocoagulation performance.

Absorption process is the most common method that is being applied to sweeten sour gas in the oil and gas industry. However, this process does have several consequences which will trigger the foam formation of foam that will reduce the mass transfer efficiency and absorption capacity as well as amine solutions carryover to the downstream processes. The removal of undesired contaminants in activated methyldiethanolamine (MDEA) was conducted by utilizing magnetic activated carbon (MAC). In this work, MAC was synthesized from coconut husk through chemical activation and co-precipitation methods. The performance of this material as an adsorbent was evaluated based on the foaming behaviour of activated MDEA solvent after being contacted with MAC at different duration and varying amounts. Nitrogen gas was introduced into the solvent through a gas diffuser to create foam. Based on the results, the foam volume generated by activated MDEA solvent was identified to decrease with the increase in both MAC contact time and amount. The highest removal efficiency by MAC was identified to be at 1 h contact time between MAC and activated MDEA solvent where the foam breaking time was reduced to 10–30 min. Meanwhile, the addition of 50 % MAC into the solvent was able to further decrease the foam breaking time to 5–10 min. The characteristics of the prepared MAC were evaluated through various instrumental analyses. This study shows that the MAC synthesized from coconut husk has a good potential as an adsorbent in removing the contaminants in activated MDEA solvent to reduce foam formation.

Rhamnolipids are bacterial amphiphiles. In addition to emulsifying hydrophobic solvents, they affect the phase behaviour of miscible solvents. In mixtures of toluene and water, rhamnolipids mediate the migration of metal ions (e.g., iron and copper) from the water to the toluene phase. Also, rhamnolipids phase separate the miscible solvent tetrahydrofuran (THF) from water, yielding emulsions even in the absence of toluene. This is because they compete with THF for hydrogen (H) bonding with similar water species. Water is an ensemble of species, including single donors (SD) or double (DD) donors, and single acceptors (SA) or double (DA) acceptors. In pure water, SD-SA and DD-DA have similar abundance and are dominant, as shown by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). With 50–200 g/L rhamnolipids, a water species intermediate between SD-SA and DD-DA is dominant, indicating that rhamnolipid-water interactions mainly occur through this species. This same species primarily interacts with THF, at 50–80% THF. At lower THF percentages, a similar (albeit not identical) species dominates, namely DD-DA, explaining separation. Emulsions are THF in water, as demonstrated by synchrotron mid-infrared spectro-microscopy and confocal microscopy using a hydrophobic dye. Synchrotron small angle X-ray scattering (SAXS) showed that rhamnolipids self- assemble into micelles, which contain THF. These findings have potential implications for miscible pollutant migration in groundwater, and their toxicity to rhamnolipid-secreting bacteria.

In this study, we synthesized and characterized a modified polyurethane (PUF) adsorbent using Sodium Dodecyl Sulfate (SDS) and TiO2-PUF nanocomposite. The adsorption performance of these modified PUF adsorbents was evaluated for the removal of Methylene Blue (MB) dye from wastewater. Optimum values and conditions for the adsorption process were determined based on the maximum dye adsorption (temperature 25 ℃, equilibrium contact time 180 min, adsorbent dose 0.2 g, pH 9 and initial concentration 120 mg/L). The surface-modified PUF adsorbent exhibited significantly enhanced adsorption capacity, increasing from 6.25 to 20.12 mg/g compared to the pure PUF. Langmuir and Freundlich adsorption isotherm models were applied, with the Langmuir model providing the best fit (R² = 0.99) and a maximum adsorption capacity of 120.48 mg/g of the adsorbent. Thermodynamic studies indicated an exothermic adsorption process, while the pseudo-second-order kinetic model dominated the adsorption kinetics. Continuous experiments at optimized conditions revealed an optimum flow rate of 15 mL/min and a bed height of 2 cm for efficient dye uptake. The adsorbent demonstrated good regeneration and reusability over more than 3 cycles. The modified PUF adsorbent showed great potential for MB dye adsorption. Surface modification significantly improved the adsorption capacity, and the Langmuir model accurately described the adsorption behavior. These findings contribute to our understanding of PUF adsorbents and their applicability for wastewater treatment.

The present paper highlights the synthesis of novel Citric acid functionalized-Nickel-Cobalt-Sulphide nanoparticles, abbreviated as Ni-Co-S@Ct, via simple co-precipitation method. The prepared nanoparticles have been characterized using several analytical techniques, like XRD, HR-TEM, TGA, HR-SEM, FT-IR, XPS and BET and zeta potential measurements. The prepared Ni-Co-S@Ct nanoparticles have been investigated for the adsorptive removal of different types of pollutants, namely, cationic and anionic dyes, and arsenic ions and interestingly all of these pollutants were removed with high efficiency. The equilibrium sorption capacity of Ni-Co-S@Ct has been found 90.91 mg/g for Methylene blue, 232.55 mg/g for Crystal violet, 357.14 mg/g for Nile blue, 142.9 mg/g for Congo red, 1111 mg/g for As(III) and 2000 mg/g for As(V). The sorption data for these pollutants fitted well to Freundlich and Temkin isotherms which showed the attachment of these ions/molecules to the specific sites at Ni-Co-S@Ct heterogeneous surface. The kinetics of sorption process was explained using the pseudo-second order model which suggested pollutant ion attachment at specific sites at the surface of Ni-Co-S@Ct. The FT-IR and Zeta potential analysis led to the conclusion that electrostatic interaction and metal complexation might be the prominent pathways adopted by the Ni-Co-S@Ct for the sorption of dyes and arsenic ions. The nanomaterials was further investigated for the removal of dyes from the mixture of dyes and the results have been quite promising as the material was found effective for elimination of four dyes simultaneously. Therefore, the high adsorption capacity, low-cost and facile synthesis, takes Ni-Co-S@Ct a step ahead in environmental remediation and wastewater treatment technology.

The coal gasification industry generates a large amount of coal gasification ash (CGA) which can contaminate environment by seeping harmful substances into both soil and water. In this study, CGA was used for the preparation of Poly-Aluminum-Ferric-Silicate coagulant (PAFSiC) to treat steel industry wastewater, and the effects of acid leaching, alkaline leaching, and copolymerization stages were investigated. Our results indicated that the dissolution rates of iron and aluminum from CGA were 53.49% and 55.43%, respectively, under leaching temperature at 95 °C, time at 1.4 h, and concentration of HCl at 5.1 mol/L. The dissolution rate of silicon from the residue of CGA leaching by HCl was 41.44% under leaching temperature at 75 °C, time at 0.5 h, and concentration of NaOH at 5 mol/L. The PAFSiC prepared under (Fe+Al)/Si molar ratio at 4.3 indicated the best coagulation performance, and its removal rates for turbidity, color, and chemical oxygen demand (COD) from steel industry wastewater were 93.69%, 36.47%, and 62.66%, respectively. Compared to commercial polysilicate aluminum ferric (PSAF), PAFSiC increased removal rates of for turbidity, color, and COD by 28.67%, 18.21%, and 7.38%, respectively. The coagulation efficiency of PAFSiC was influenced by pH; a removal rate of color of 54.43% was recorded from the steel industry wastewater using PAFSiC prepared at pH of 2. PAFSiC synthesized from CGA under (Fe+Al)/Si molar ratio at 4.3 exhibited a branching amorphous structure with spatial stereoscopic sense, resulting in higher capacity to bind with and remove contaminates. Our results underline the potent performance of PAFSiC as a viable solution to alleviate pollution from the steel industry.

Industrial wastewater contains high concentrations of refractory organic carbons, resulting in a low biodegradability difficult for the following biological treatments. The iron-carbon micro-electrolysis (ICME) was developed to break down the larger organic molecules and enhance the biodegradability. Previous ICME pretreatment coupling studies focused primarily on pharmaceutical, dye, and medical wastewater. In this study, the ICME was applied to treat the electroplating wastewater with surfactants, followed by an anaerobic-anoxic-oxic (A²O) biological process. When the ratio of the ICME-treated wastewater was low (10 %), the strike on nutrient removal efficiency (chemical oxidation demand, ammonia, total nitrogen, and total phosphate) was almost negligible. With the increase of ICME-treated wastewater up to 50 %, the removal efficiency gradually decreased, but the effluent water quality still met the discharge standard. Meanwhile, a shift of microbial communities in the three zones was also observed after the 50-day incubation. The abundance of Hydrogenophaga, Chitinophagaceae, and Lentimicrobiaceae all increased, which may be responsible for the degradation of refractory organics in the oxic and anaerobic zones. The functional gene analysis indicated that the adaptation of microbial communities was probably related to cell-to-cell communications and the transportation of molecules across the cell membrane. The microbial community and functional gene analysis revealed the adaptation of the microorganisms to the industrial wastewater. This study provides new insights into the ICME to enhance the biodegradability of electroplating wastewater for A²O treatment.