Efficient treatment of palladium from wastewater by acrolein cross-linked chitosan hydrogels: Adsorption, kinetics, and mechanisms.

Herein we present a study on the preparation and properties of a hydrogel adsorbent for treatment of wasted palladium souring from actial petrochemical industrial wastewater. Chitosan was used as the raw material and acrolein as the cross-linking agent for the hydrogel (A/CS). The adsorption behaviors of the hydrogel for Pd(II) ions were characterized and analyzed. The effect of pH, temperature, adsorption kinetics, and thermodynamics were investigated. Langmuir models were employed to describe the adsorption isotherms, while the pseudo-second-order equation was applied to describe the adsorption kinetics. The experimental results demonstrated that the adsorption was a monolayer chemical adsorption, and the adsorption capacity was found to reach 505.05 mg/g under optimal conditions. In addition, FT-IR and XPS analyses, combined with MS calculations confirmed that chelation and electrostatic attraction were dominated in the adsorption process. Overall, the development of this hydrogel adsorbent will provide a practical approach to the treatment of industrial wastewater containing palladium and have great potential for practical applications.

Synthesis and Micellization of Carbosilane Sulfonate Surfactants with Short Alkyl Chains.

Carbosilane surfactants, consisting of carbosilane as a hydrophobic group linked to hydrophilic groups, are one kind of silicone surfactants. In this paper, a series of carbosilane sulfonate surfactants with short alkyl chains (Cn-Si2C-SO3Na (n = 1-6)), Me-Si2C-SO3Na, Et-Si2C-SO3Na, Pr-Si2C-SO3Na, Bu-Si2C-SO3Na, Pen-Si2C-SO3Na, and Hex-Si2C-SO3Na, were prepared and characterized by 29 Si NMR, 1H NMR, and FT-IR spectroscopies. The influence of the alkyl chain length on their micellization was studied using surface tension, dynamic light scattering, conductivity, and transmission electron microscopy. The CMC value decreases with increasing length of the short alkyl group. The γCMC value of Cn-Si2C-SO3Na (n = 1-6) increases as the alkyl chain increases from methyl to propyl, while the γCMC value gradually decreases as the alkyl chain increases from propyl to hexyl. The larger and rigid tetramethyldicarbosilane group functioned synergistically with a short alkyl chain, resulting in carbosilane sulfonate surfactants adsorbing at the air/water interface with a rugby ball shape; accordingly, the Amin values of the investigated carbosilane sulfonate surfactants increase with increasing length of the alkyl chain. The micellization process of carbosilane sulfonate surfactants is enthalpy-driven at lower temperatures and entropy-driven at high temperatures. The ΔHm0 values became more negative and ΔSm0 values more positive as the alkyl chain length increased. Aggregates in the range of 10-800 nm were observed for Cn-Si2C-SO3Na (n = 1-6) in an aqueous solution, and the hydrodynamic diameter (Dh) decreased with increasing length of the short alkyl group.

Nanomechanical Insights into Versatile Polydopamine Wet Adhesive Interacting with Liquid-Infused and Solid Slippery Surfaces.

Mussel-inspired polydopamine (PDA) can be readily deposited on almost all kinds of substrates and possesses versatile wet adhesion. Meanwhile, slippery surfaces have attracted much attention for their self-cleaning capabilities. It remains unclear how the versatile PDA adhesive would interact with slippery surfaces. In this work, both liquid-infused poly(tetrafluoroethylene) (PTFE) (LI-PTFE) and solid slippery surfaces (i.e., self-assembly of small thiol-terminated organosilane, polysiloxane covalently attached to substrates) were fabricated to investigate their capability to prevent PDA deposition. It was found that PDA particles could be easily deposited on a PTFE membrane and the two types of solid slippery surfaces, which resulted in the alternation of their surface wettability and slippery behavior of water droplets. Adhesion was detected between a PDA-coated silica colloidal probe and the PTFE membrane or solid slippery surfaces through quantitative force measurements using an atomic force microscope (AFM), mainly due to van der Waals (vdW) and hydrophobic interactions, which led to the PDA deposition phenomenon. In contrast, LI-PTFE with a thin liquid lubricant film could effectively prevent PDA deposition, with negligible changes in surface morphology, wettability, and slippery characteristics. Although PDA particles could be loosely attached to the lubricant/water interface for LI-PTFE based on the capillary adhesion measured by AFM, they could be readily removed by gentle rinsing with water, as demonstrated by the ultralow friction over LI-PTFE as compared to PTFE using lateral force microscopy (LFM). Our results indicate that LI-PTFE possesses excellent antifouling and self-cleaning properties even when interacting with the versatile PDA wet adhesives. This work provides new insights into the deposition of PDA on slippery surfaces and their interaction mechanism at the nanoscale, with useful implications for the design and development of novel slippery surfaces.

Aggregation Behavior and Intermolecular Interaction of Cationic Trisiloxane Surfactants: Effects of Unsaturation.

Imidazolium/pyridinium-based trisiloxane surfactants containing a phenyl or vinyl group in the hydrophobic siloxane chain, bis(vinyldimethylsiloxy)methylsilylpropyl-pyridinium chloride (Vi-Si3pyrCl), bis(vinyldimethylsiloxy)methylsilylpropyl-imidazolium chloride (Vi-Si3minCl), and bis(phenyldimethylsiloxy)methylsilylpropylimidazolium chloride (Ph-Si3minCl), were synthesized and confirmed by nuclear magnetic resonance (NMR) (1H, 13C, and 29Si NMR), mass spectrometry, and Fourier transform infrared spectrometry. The effect of the phenyl/vinyl group on their micellization behavior was studied by surface tension, electric conductivity, dynamic light scattering, 2D nuclear Overhauser effect spectroscopy (NOESY) NMR, and transmission electron microscopy. Owing to the hydrophobicity of the siloxane groups and cationic head groups, the critical micelle concentration (cmc) values follow the order Ph-Si3minCl < Vi-Si3pyrCl < Vi-Si3minCl < Si3pyrCl. Ph-Si3minCl has a larger γcmc value, resulting from the introduction of the phenyldimethylsiloxy unit (π-π stacking interaction). The ß values of Vi-Si3minCl and Ph-Si3minCl increase with the increase in temperature, which is attributed to the intermolecular interaction which hinders the association of Cl- with the imidazolium ring and confirmed by 2D NOESY NMR. In aqueous solutions, the investigated cationic trisiloxane surfactants can self-assemble into spherical aggregates.

Impact of Molecular Architecture on Surface Properties and Aqueous Stabilities of Silicone-Based Carboxylate Surfactants.

Silicone surfactants consist of siloxane or carbosilane hydrophobic groups that possess better surface activity compared with alkane surfactants. The surfactants, containing Si atoms which bring excellent bond flexibility and low cohesive energy properties are a promising class of materials for unique surface working, but there are few studies to elaborate their surface activity mechanism with regard to the molecular architecture. Herein, two novel carboxylate surfactants with different silicone hydrophobic groups (Si-O-Si and Si-C-Si) were synthesized and their surface activities, aggregate behaviors, and solution stabilities were systematically investigated. Results showed that both surfactants had excellent surface activities which are attributed to the hydrophobic structure of silicone. The hydrolysis resistance of the carbosilane-based carboxylate surfactant was better than that of the siloxane-based carboxylate surfactant. The differences in hydrolysis processes for the surfactants were confirmed by the mass spectrum and kinetic analysis. Meanwhile, the aggregation number of Si-C-Si surfactants was also determined by the fluorescence quenching method for the first time.

Aggregation Behavior of "Linear" Trisiloxane Surfactant with Different Terminal Groups (CH3-, ClCH2-, and CF3-) in Aqueous Solution.

Novel "linear" trisiloxane surfactants with different terminal groups (CH3-, ClCH2-, CF3-) and two polyether hydrophilic groups were successfully synthesized and confirmed using 1H NMR, 13C NMR, 29Si NMR, and FT-IR spectroscopy. The aggregation and adsorption behavior of the "linear" trisiloxane surfactants in aqueous solution was studied by surface tension, dynamic light scattering (DLS), transmission electron microscopy (FF-TEM), and TEM. Owing to the introduction of two polyether hydrophilic groups in the terminal positions of the trisiloxane hydrophobic part, "linear" trisiloxane surfactants (Me-Si3-EO8, Cl-Si3-EO8, and F-Si3-EO8) tend to lie flat in the air/water interface and result in an increasing the surface tension at the CMC ( γCMC) and single trisiloxane surfactant molecule at the air/water interface ( A min) values. Following the difference in the intermolecular forces and molecular volumes (CH3- < ClCH2- < CF3-), the γCMC values decrease following the order Me-Si3-EO8 > Cl-Si3-EO8 > F-Si3-EO8, and the adsorption efficiency ( p C20), surface pressure at the CMC ( πCMC), CMC/ C20 , and A min values increase following the order Me-Si3-EO8 < Cl-Si3-EO8 < F-Si3-EO8. As comparison, fluorinated trisiloxane surfactant (F-Si3-EO8) has greater surface activity attributed to the terminal CF3- group. The TEM and FF-TEM results illustrated that all the investigated "linear" trisiloxane surfactants can form nonuniform size spherical aggregates.

Aggregation Behavior of Polyether Based Siloxane Surfactants in Aqueous Solutions: Effect of Alkyl Groups and Steric Hindrance.

A series of polyether based siloxane surfactants with different branched chain and alkyl groups were synthesized by thiol-ene reaction and Piers-Rubinsztajn reaction. The effect of the siloxane structures (alkyl groups and branched chains) on the adsorption and aggregation behavior in aqueous solution was investigated by surface tension, fluorescence, dynamic light scattering (DLS), freeze-fracture transmission electron microscopy (TEM), and TEM. The molecular structures of siloxane can obviously influence their surface activities and thermodynamics. Replacing the methyl of trimethylsiloxyl groups with longer alkyl groups (ethyl, propyl, and butyl) and branching trimethylsiloxyl resulted in an obvious decrease of the values of critical micelle concentration (CMC) and surface tension at CMC (γCMC). Dense surface films packed with CH3 groups result in the lower surface tensions being disordered by longer alkyl groups or branched chains of siloxane hydrophobic groups. And the minimum surface area per surfactant molecule ( Amin) values of Si3-PG, Et-Si3-PG, Pro-Si3-PG, and But-Si3-PG successively decrease about 3.5 Šwith each increasing -CH2- group. All polyether based siloxane surfactants can form nonuniform size spheroidal aggregates in aqueous solution. Concerning the driving force, the micellization process was spontaneous but less spontaneous compared with adsorption.

Pseudopolyrotaxanes based polyhedral oligomeric silsesquioxanes and cucurbit[7]uril.

Pseudopolyrotaxanes (POSS/CB[7]) were synthesized using octaimidazolium-based polyhedral oligomeric silsesquioxanes (POSS) and cucurbit[7]uril (CB[7]) in aqueous solution. The binding interactions were monitored by (1)H NMR. Their regular octahedral morphologies were confirmed by TEM. The POSS/CB[7] was also characterized by FT-IR, thermogravimetric analysis (TGA), and elemental analysis. The TGA results show that the thermal stabilities of POSS/CB[7] can be improved by the threading of CB[7].

Synthesis and characterization of an octaimidazolium-based polyhedral oligomeric silsesquioxanes ionic liquid by an ion-exchange reaction.

Preparation of POSS-min-DS, an octaimidazolium-based polyhedral oligomeric silsesquioxanes (POSS) room temperature ionic liquid, by an ion-exchange reaction between POSS and sodium dodecyl sulfate was reported. Octaimidazolium-based POSS was synthesized with more than 98% yield within 3 h. POSS-min-DS and octaimidazolium-based POSS were confirmed by (1)H, (13)C, and (29)Si NMR, FT-IR and elemental analysis.