Reclined trend of alkyl chain of sodium dodecylbenzenesulfonate molecules induced by friction

Surfactants tend to adsorb on the surface/interface mostly in a directional manner. The alkyl chain orientation and conformation order for molecular monolayers of sodium dodecylbenzenesulfonate (SDBS) at low concentrations are studied by using the sum frequency generation vibrational spectroscopy (SFG-VS). The molecular arrangement of the surfactants adsorbed at the solid/liquid interface is further investigated. It is found that the arrangement of the SDBS at the interface becomes relatively ordered with increasing bulk concentration. Meanwhile, the orientation angle reduces gradually, and the molecules tend to be upright state. In addition, the effect of friction on the conformation order and orientation angle are also analyzed. The intensity of the SDBS vibrational contraction peak becomes lower after friction, which indicates that the anion has a reorientation process at the interface. The arrangement of molecules becomes more disordered due to friction. The orientation angle increases slightly, which indicates the monolayer has an inclined trend relative to the lateral direction on the interface. A modified adsorption model considering friction effect is proposed. This work may provide a reference for the further study of adsorption mechanism and application of surfactants.

Designing Phenyl Porous Organic Polymers with High-Efficiency Tetracycline Adsorption Capacity and Wide pH Adaptability

Adsorption is an effective method to remove tetracycline (TC) from water, and developing efficient and environment-friendly adsorbents is an interesting topic. Herein, a series of novel phenyl porous organic polymers (P-POPs), synthesized by one-pot polymerization of different ratios of biphenyl and triphenylbenzene under AlCl3 catalysis in CH2Cl2, was studied as a highly efficient adsorbent to removal of TC in water. Notably, the obtained POPs possessed abundant phenyl-containing functional groups, large specific surface area (1098 m2/g) with abundant microporous structure, high pore volume (0.579 cm3/g), favoring the removal of TC molecules. The maximum adsorption capacity (fitted by the Sips model) could achieve 581 mg/g, and the adsorption equilibrium is completed quickly within 1 h while obtaining excellent removal efficiency (98%). The TC adsorption process obeyed pseudo-second-order kinetics and fitted the Sips adsorption model well. Moreover, the adsorption of POPs to TC exhibited a wide range of pH (2–10) adaptability and outstanding reusability, which could be reused at least 5 times without significant changes in structure and efficiency. These results lay a theoretical foundation for the application of porous organic polymer adsorbents in antibiotic wastewater treatment.

Influence of Particle Size of River Sand on the Decontamination Process in the Slow Sand Filter Treatment of Micro-Polluted Water

Slow sand filters (SSFs) have been widely used in the construction of water plants in rural areas. It is necessary to find river sand of suitable particle size to improve SSF treatment of micro-polluted water so as to ensure the effective and long-term operation of these plants. In this study, SSF1# (particle size of 0.1–0.5 mm), SSF2# (particle size of 0.5–1 mm), and SSF3# (particle size of 1–1.5 mm) were selected. The physical absorption, CODMn and NH4+-N removal effect, and microbial community were analyzed. According to Langmuir and Freundlich adsorption model fitting, the smaller the particle size of the river sand, the more pollutants are adsorbed under the same conditions. SSF1# has the shortest membrane-forming time, highest CODMn and NH4+-N removal rate, and highest Shannon estimator, indicating that there are more abundant microbial species in the biofilm. Mesorhizobium, Pannonibacter, Pseudoxanthomonas, Aquabacterium, Devosia, and other bacteria have different proportions in each system, each forming its own stable biological chain system. The effluent quality of the three SSFs can meet drinking water standards. However, river sand with a particle size range of 0.1–0.5 mm is easily blocked, and thus the recommended size range for SSF is 0.5–1 mm.

Interfacial properties of chitosan lactate at the liquid/air interface

The interfacial properties (dynamic and equilibrium surface tension, viscosity and elasticity moduli) of chitosan lactate have been studied at the liquid/air interface by the oscillating drop shape method. Isotherms of dynamic surface tension of chitosan lactate are similar to dependences for other polyelectrolyte solutions, in particular for proteins. Chitosan is a weak cationic polyelectrolyte which can change its conformation from a linear rod to a chaotic and compacted coil. Therefore, the experimental dependence of the equilibrium surface tension on concentration of chitosan lactate was analyzed with the adsorption model proposed earlier for proteins. This model accounts the possibility of polyelectrolyte molecules existence in surface layer in n states with different molar surface varying from the maximum value at very low surface coverage by polyelectrolyte molecules to a minimum value at high surface coverage. Good agreement between the calculated and experimental values of surface tension was observed. The dependences of the elasticity and viscosity moduli of chitosan lactate solutions on the drop oscillations frequency are conditioned by the influence of exchange processes both between the surface layer and the bulk solution and in the surface layer itself. An increase of the solution concentration intensifies the exchange processes, and an increase of the oscillation frequency suppresses them. It is shown that the dependence of the surface viscoelasticity modulus of chitosan lactate is extreme in nature with a pronounced maximum. The reason for such behavior is the possibility of changing the molar surface area of the polyelectrolyte at the interface dependent on the amount of adsorption and its structural properties. Attempt of theoretical description of the viscoelasticity modulus within the framework of model accounting mono- or bilayer adsorption did not lead to a satisfactory result, possibly due to barrier adsorption mechanism of chitosan. But bilayer model provide qualitative description of extreme behavior of surface viscoelasticity on concentration. The values of the surface viscoelasticity modulus of chitosan lactate occupy an intermediate position in comparison with the data available in the literature for globular and flexible-chain proteins, that is consistent with their molecular structure. In addition, the work shows the applicability of the adsorption model, developed earlier for proteins in the framework of a nonideal two-dimensional solution theory, for describing the surface properties of other polyelectrolytes. This makes it possible to obtain qualitative and quantitative information about the processes occurring in the systems under study.

Bisphenol A Adsorption on Silica Particles Modified with Beta-Cyclodextrins

This study presents the synthesis of silica particles bearing two beta-cyclodextrin (BCD) (beta-cyclodextrin-BCD-OH and diamino butane monosubstituted beta-cyclodextrin-BCD-NH2). The successful synthesis of the BCD-modified silica was confirmed by FT-IR and TGA. Using contact angle measurements, BET analysis and SEM characterization, a possible formation mechanism for the generation of silica particles bearing BCD derivatives on their surface was highlighted. The obtained modified silica displayed the capacity to remove bisphenol A (BPA) from wastewater due to the presence of the BCD moieties on the surface of the silica. The kinetic analysis showed that the adsorption reached equilibrium after 180 min for both materials with qe values of 107 mg BPA/g for SiO2-BCD-OH and 112 mg BPA/g for SiO2-BCD-NH2. The process followed Ho’s pseudo-second-order adsorption model sustaining the presence of adsorption sites with different activities. The fitting of the Freundlich isotherm model on the experimental results was also evaluated, confirming the BCD influence on the materials’ adsorption properties.

The performance of calcined serpentine to simultaneously remove fluoride, iron and manganese

To solve the problem of high fluoride, iron and manganese concentrations in groundwater, serpentine (Srp) was modified by metal salt impregnation, acid-base activation and calcination, and the effects of these three modifications on removal performance of Srp were compared. Specifically, the effects of the calcined serpentine (Csrp) dose, reaction time, pH, and temperature on the removal performance of F−, Fe2+ and Mn2+ on Csrp were analysed. An isothermal adsorption model and adsorption kinetic equation were established and confirmed through SEM, EDS, XRD and FTIR spectroscopy to analyse the mechanism of removing F−, Fe2+ and Mn2+ by Csrp. The results show that when 3 g/L Csrp was used to treat water samples with 5 mg/L F−, 20 mg/L Fe2+, and 5 mg/L Mn2+ (pH of 6, reaction temperature of 35 °C, and time of 150 min), the removal rates of F−, Fe2+, and Mn2+ were 94.3%, 99.0%, 98.9%, respectively. The adsorption of F−, Fe2+ and Mn2+ on Csrp follows the quasi-second-order kinetic equation and Langmuir isotherm adsorption model. After 5 cycles of regeneration of Csrp, Csrp can still maintain good properties of fluoride,iron and manganese removal.

Adsorption Study of Soluos Dumpsite Leachate Treatment Using Musa sapientum Peels as Biosorbent

Dumpsite leachate has the potential to pollute ground and surface water as well as vegetation within the vicinity of the dumpsite. Its treatment therefore needs adequate attention. The aim of this work is to study the adsorption of Soluos dumpsite leachate treatment using Musa sapientum peel as biosorbent with a view of establishing the adsorption isotherm model. Musa sapientum peels sourced from Ayetoro market in Epe area of Lagos State, Nigeria were used to prepare the adsorbent. Batch adsorption was carried out with various dosage of the prepared absorbent in leachate collected from Soluos dumpsite in Lagos. The adsorption data obtained were fitted into Linear, Freundlich, Langmuir, Temkin and Hasley isotherm models. The results showed that the concentration of total dissolved solids (TDS) in the dumpsite leachate decreased as the adsorbent dosage increased. At adsorbent dosage of 10 g/L, the concentration of TDS in the leachate was 485.7 mg/L which was less than the 500 mg/L stipulated by National Environmental Standard and Regulatory Agency (NAESRA) for the discharge of wastewater. The coefficient of determination (R2) values for Linear, Freundlich and Hasley, Langmuir and Temkin isotherm models were 0.9944, 0.9936, 0.8562 and 0.9723 respectively. Linear isotherm model was jettisoned because the plot did not pass through the origin and Freundlich isotherm model was ignored as a result of N value which was less than unity hence Hasley isotherm model was adopted in this work. A good correlation existed between the experimental and predicted values, having a R2 value of 0.9965 which further validated the Hasley isotherm model as the best adsorption model for the treatment of Soluos dumpsite leachate using Musa sapientum peel as biosorbent. It was concluded that Musa sapientum peel as biosorbent can be used for treatment of Soluos dumpsite leachate.

Structural Adaptive, Self-Separating Material for Removing Ibuprofen from Waters and Sewage

β-Cyclodextrin nanosponge (β−CD−M) was used for the adsorption of ibuprofen (IBU) from water and sewage. The obtained material was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), Barrett–Joyner–Halenda (BJH), Harkins and Jura t-Plot, zeta potential, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and elementary analysis (EA). Batch adsorption experiments were employed to investigate the effects of the adsorbent dose, initial IBU concentration, contact time, electrolyte ions and humic acids, and sewage over adsorption efficiency. The experimental isotherms were show off using Langmuir, Freundlich, Hill, Halsey and Sips isotherm models and thermodynamic analysis. The fits of the results were estimated according to the Sips isotherm, with a maximum adsorption capacity of 86.21 mg g−1. The experimental kinetics were studied by pseudo-first-order, pseudo-second-order, Elovich, modified Freundlich, Weber Morris, Bangham’s pore diffusion, and liquid film diffusion models. The performed experiments revealed that the adsorption process fits perfectly to the pseudo-second-order model. The Elovich and Freundlich models indicate chemisorption, and the kinetic adsorption model itself is complex. The data obtained throughout the study prove that this nanosponge (NS) is extremely stable, self-separating, and adjusting to the guest structure. It also represents a potential biodegradable adsorbent for the removal IBU from wastewaters.