"Functional connector" strategy on tunable organo-vermiculites: The superb adsorption towards Congo Red.

With the increasingly worldwide concentration of environmental pollution, exploiting cost-effective adsorbents has been a research hotspot. Here we introduce novel "functional connector" amide-containing gemini surfactants (LDAB, LDAPP, LDAMP and LDABP) and apply to modify Na-vermiculite (Na-Vt) for Congo red (CR) removal. Chain amide as the functional connector in the modifier, increases 6.9 times of CR uptake than traditional organo-Vts, which is further enhanced by tunning the functional group of modifier spacers. Superb uptake of CR on organo-Vts reaches 1214.05, 1375.47 and 1449.80 mg/g, and the removal efficiencies achieve 80.94%, 91.70% and 96.65% on LDAB-Vt, LDAPP-Vt and LDAMP-Vt, respectively. Notably, the maximum experimental adsorption capacity of LDAPP-Vt is 1759.64 mg/g. These experimental values are among the highest reported CR adsorbents. A combination experimental and theoretical analysis is conducted to unveil the structure-adsorptivity relationship: (i) Adsorptivity enhancement of organo-Vts is more effectively by regulating functional chains than the functional spacer. (ii) para-substituted aromatic spacers own the best adsorptive configuration and strongest stability for π-π interaction. (iii) π-π interaction provided by isolated aromatic ring is stronger than biphenyl, whose steric hindrance depresses the adsorptivity. Results in this study not only explain a new "functional connector" strategy to Vt-based adsorbents, but also provide a practical designing strategy for organic adsorbents characterized with high uptake capacity.

Efficient removal of mefenamic acid and ibuprofen on organo-Vts with a quinoline-containing gemini surfactant: Adsorption studies and model calculations.

To pursue the adsorptivity of versatile vermiculite (Na-Vt)-based adsorbent targeted at emerging pharmaceuticals (mefenamic acid and ibuprofen, corresponding to MEA and IBP, respectively), a quinoline-based gemini surfactant (DHQU) with multi-functional groups is applied as modifier on Na-Vt. Enhanced hydrophobicity, enlarged interlayer space and decreased surface area of DHQU-Vt are obtained, whose modifier availability (the mole ratio of modifier intercalated to added) reaches up to 84.18% as characterized by FT-IR, XRD, TG-DTG, EA and BET analysis. Efficient adsorption of MEA/IBP (123.71/240.69 mg/g) is achieved under an extremely low DHQU dosage (0.2 CEC lower than the usual saturated dosage of organo-Vts), with all the processes fitting satisfactorily with pseudo-second order and Freundlich isotherm models accompanied by an exothermic nature. Acid pickling testifies a stable and reliable reusability process of DHQU-Vt even after 3 cycles. Multiple interactions (i.e., partition process, XH-π interaction, π-π interaction, π-π stacking and electrostatic interaction) are revealed and compared from not only characterization results, but also simulation of frontier orbital analysis, the adsorption configuration and bonding analysis: (i) The greater molecular flexibility of the adsorbate, the greater intra particle diffusion effect. (ii) π-π stacking between isolated aromatic rings is stronger than that between parallelly connected aromatic rings. (iii) The strength of multiple active sites provided by quinoline (CH-π, NH-π and π-π interactions) are comparable but weaker than electrostatic interaction/intra particle diffusion.

Synergistic construction of bifunctional and stable Pt/HZSM-5-based catalysts for efficient catalytic cracking of n-butane.

Efficient conversion of light alkanes is of essential significance for enhancing the utilization efficiency of resources and exploring the activation and evolution regulation of C-C and C-H bonds in stable molecules. The processes are often executed with catalysts under harsh conditions. The olefin yield and metal stability have been the long-standing concerns. Herein, we report a facile strategy of constructing a bifunctional Pt/HZSM-5-based catalyst by two-step atomic layer deposition (ALD) to achieve a high light olefin formation rate of 0.48 mmol gcat-1·min-1 in the catalytic cracking of n-butane at 600 °C, which is ∼2.2 times higher than that of the conventional Pt/HZSM-5 catalyst (0.22 mmol gcat-1·min-1). Moreover, the bifunctional Pt/HZSM-5-based catalyst exhibited outstanding recyclability and excellent metal stability against sintering in comparison with conventional Pt/HZSM-5. Detailed microscopic and spectroscopic characterization studies demonstrate that the metal oxide (TiO2 or Al2O3) coating not only prevents the metal from high-temperature sintering, but also regulates the proportion of coordinately unsaturated platinum surface atoms. Theoretical calculations further confirm the preference of nucleation of TiO2 or Al2O3 on coordinately unsaturated platinum sites, which in turn modulates the bifunctional dehydrogenation-cracking pathway to improve the olefin formation rate.

Pore wettability for enhanced oil recovery, contaminant adsorption and oil/water separation: A review.

Wettability, a fundamental property of porous surface, occupies a pivotal position in the fields of enhanced oil recovery, organic contaminant adsorption and oil/water separation. In this review, wettability and the related applications are systematically expounded from the perspectives of hydrophilicity, hydrophobicity and super-wettability. Four common measurement methods are generalized and categorized into contact angle method and ratio method, and influencing factors (temperature, the type and layer charge of matrix, the species and structure of modifier) as well as their corresponding altering methods (inorganic, organic and thermal modification etc.) of wettability are overviewed. Different roles of wettability alteration in enhanced oil recovery, organic contaminant adsorption as well as oil/water separation are summarized. Among these applications, firstly, the hydrophilic alteration plays a key role in recovery of the oil production process; secondly, hydrophobic circumstance of surface drives the organic pollutant adsorption more effectually; finally, super-wetting property of matrix ensures the high-efficient separation of oil from water. This review also identifies importance, challenges and future prospects of wettability alteration, and as a result, furnishes the essential guidance for selection and design inspiration of the wettability modification, and supports the further development of pore wettability application.

Insights into the efficient adsorption of rhodamine B on tunable organo-vermiculites.

Organo-vermiculites (organo-Vts) were prepared by intercalation of four designed gemini surfactants (BDIN, BDHP, BDPD, BDPB) with different functional groups (imino, hydroxy, phenyl, pyridyl) into vermiculite (Vt). The structures and properties of four obtained organo-Vts were tested by a series of characterization techniques. Rhodamine B (RhB) was chosen as the target contaminant to investigate the impacts of type and location of surfactant functional group on adsorption process. The adsorption of RhB onto organoclays was in the order: BDIN-Vt > BDHP-Vt > BDPD-Vt > BDPB-Vt, especially BDIN-Vt with the maximum adsorption capacity (qmax) of 528 mg g-1, which was much larger than known existing adsorbents. Differentiations of the adsorption capacity verify that (i) the combination of hydrogen bond and XH-π interaction was beyond π-π interactions, (ii) π-π interactions between the benzene rings surpassed the π-π interactions between heteroaromatic ring and benzene ring, (iii) the gemini surfactant with polar spacers in the main chain is more favorable for adsorption than that in the pendant group. The key factors which influence the adsorption process were also explored. Additionally, adsorption kinetics, isotherm and thermodynamic parameters were discussed. The work provides new insight into design of excellent adsorbents with organo-clays to remove organic pollutants.

Organo-vermiculites with biphenyl and dipyridyl gemini surfactants for adsorption of bisphenol A: Structure, mechanism and regeneration.

Two novel biphenyl and dipyridyl gemini surfactants, bis-N, N, N,-hexadecyldimethyl-p-biphenylenediammonium dichloride (BHBP) and 1,1'-dihexadecyl-4,4'-bispyridinium bromide (DHBP) were designed and used to functionalize the high layer charged vermiculite (Vt) for the first time. Key organo-Vt characteristics, such as the modifier loading, arrangement and the stacking unit of platelets were specified by FT-IR, XRD, TG, SEM and Elemental Analysis. The saturated surfactant dosage in the modification process, in reverse relationship with the availability of the modifier, was defined as low as 0.4 CEC of Vt. The adsorption performance of organo-Vts were tested by bisphenol A (BPA), which showed great potential as organic adsorbents (143.5 mg g-1 and 139.7 mg g-1 for BHBP-Vt and DHBP-Vt, respectively). Insights into the adsorption mechanism were discussed through kinetics, isotherms and thermodynamics, as well as characterization of the spent samples. BPA onto orgno-Vts matched well with pseudo-second-order, Freundlich models and an exothermic process in nature. Interestingly, π-π interactions between aromatic rings were stronger than that between heteroaromatic ring and aromatic ring, and π-π stacking between the BPA adsorbed and dissociated in solution turned out to promote the adsorption process. The organo-Vts were sustainable and could reuse by ethanol at least for three cycles. Organo-Vts could not only guide focuses on the high layer charged precursors, but open up a new area for the fabrication of novel materials to serve as tunable and cost-effective adsorbents.

Facet-dependent photocatalytic decomposition of N2O on the anatase TiO2: a DFT study.

The photocatalytic N2O dissociation on anatase TiO2 is an attractive reaction and the mechanism of the photocalytic process, the role of excited electrons, and the favorable facet for higher activity need a more detailed study at the molecular level. Using DFT + U calculations, we investigate the dissociation process of N2O into N2 with and without photoexcited electrons on anatase TiO2 (001) and (101) facets to unravel such puzzles. The optical absorption properties of TiO2 (001) and (101) facets are compared in combination with electronic analysis. The localization of excited electrons on the two surfaces with the existence of oxygen vacancies is explored. When there is no photo-excitation, on a perfect TiO2 surface, N2O decomposition is difficult due to the inhibitive high reaction energy. In contrast, the reaction energy decreases dramatically in the presence of photoexcited or excess electrons on the TiO2 surface. The reaction energy is related to the electronic state of dissociated O. The more negative charges make O more stable, and accordingly lead to higher exothermic reaction energy. Based on this point, the influence of surface morphology and excited states can be understood. This is the first theoretical study of the photocatalytic process of N2O elimination, which will guide further experimental study and improve its activity.

A comparative study and evaluation of sulfamethoxazole adsorption onto organo-montmorillonites.

Three organo-montmorillonites were prepared using surfactants, and their adsorption behaviors toward sulfamethoxazole (SMX) were investigated. The surfactants used were cetyltrimethyl ammonium bromide (CTMAB), 3-(N,N-dimethylhexadecylammonio) propane sulfonate (HDAPS) and 1,3-bis(hexadecyldimethylammonio)-propane dibromide (BHDAP). The properties of the organo-montmorillonites were characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption-desorption isotherm measurements. Results showed that the interlayer spacing of montmorillonite was increased and the surface area as well as the morphology were changed. Batch adsorption experiments showed that the surfactant loading amount had a great effect on the adsorption of SMX. The adsorption process was pH dependent and the maximum adsorption capacity was obtained at pH3 for HDAPS-Mt, while CTMAB-Mt and BHDAP-Mt showed a high removal efficiency at 3-11. The adsorption capacity increased with the initial SMX concentration and contact time but decreased with increasing solution ionic strength. Kinetic data were best described by the pseudo second-order model. Equilibrium data were best represented by the Langmuir model, and the Freundlich constant (n) indicated a favorable adsorption process. The maximum adsorption capacity of SMX was 235.29 mg/g for CTMAB-Mt, 155.28 mg/g for HDAPS-Mt and 242.72 mg/g for BHDAP-Mt. Thermodynamic parameters were calculated to evaluate the spontaneity and endothermic or exothermic nature. The adsorption mechanism was found to be dominated by electrostatic interaction, while hydrophobic interaction played a secondary role.

Comparison between the removal of phenol and catechol by modified montmorillonite with two novel hydroxyl-containing Gemini surfactants.

Na-montmorillonites were modified with two novel hydroxyl-containing Gemini surfactants, 1,3-bis(hexadecyldimethylammonio)-2-hydroxypropane dichloride (BHHP) and 1,3-bis(octyldimethylammonio)-2-hydroxypropane dichloride (BOHP), via ion-exchange reaction in this study. The modified samples were characterized by X-ray diffraction (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy. Phenol and catechol were removed from aqueous solution by these two kinds of organo-montmorillonites in a batch system. Important parameters have been investigated, which affect the adsorption efficiency, such as the amount of modifier, temperature, pH and contact time. The adsorption kinetics of phenol and catechol were discussed using pseudo-first-order, pseudo-second-order and intra-particle diffusion model. It indicated that the experimental data fitted very well with the pseudo-second-order kinetic model, and the equilibrium adsorption data was proved in good agreement with the Langmuir isotherm. The result also showed the adsorption capacity of catechol was higher than that of phenol in the same conditions, which might result from the extra hydroxyl in the structure of catechol. Thermodynamic quantities such as Gibbs free energy (ΔG°), the enthalpy (ΔH°), and the entropy change of sorption (ΔS°) were also determined. These parameters suggested the adsorption of phenol was a spontaneous and exothermic process, while the sorption of catechol was endothermic.