Single Adsorption Research Articles

Locating the cocktail and scaling-relation breaking effects of high-entropy alloy catalysts on the electrocatalytic volcano plot

High entropy alloys (HEAs) have been the star materials in electrocatalysis research in recent years. One of their key features is the greatly increased multiplicity of active sites compared to conventional catalytic materials. This increased multiplicity stimulates a cocktail effect and a scaling-relation breaking effect, and results in improved activity. However, the multiplicity of active sites in HEAs also poses new problems for mechanistic studies. One apparent problem is the inapplicability to HEA catalysts of the currently most popular mechanistic study method, which uses the electrocatalytic theoretical framework (ETF) based on the computational hydrogen electrode (CHE). The ETF uses a single adsorption energy to represent the catalyst, i.e., a catalyst is represented by a ‘point’ in the volcanic relationship. It naturally does not involve the multiplicity of active sites of a catalyst, and hence loses brevity in expressing the cocktail effect and scaling-relation breaking effect in HEA catalysis. This paper attempts to solve this inapplicability. Based on the fact that the adsorption energy distribution of HEAs is close to a normal distribution, the mean and variance of the adsorption energy distribution are introduced as descriptors of the ETF, replacing the original single adsorption energy. A quantitative relationship between the variance and the cocktail and scaling-relation braking effects is established. We believe the method described in this work will make the ETF more effective in mechanistic studies of HEA electrocatalysis.

Dense packing of xenon in an ultra-microporous metal–organic framework for benchmark xenon capture and separation

For adsorptive separation of xenon/krypton mixture, it still remains a daunting challenge to target both high Xe adsorption and selectivity in a single adsorbent because of their close size and inert nature. Herein, we report an ultra-microporous alkyl Cu-based MOF-11 with suitable pore architecture for benchmark Xe capture and separation. MOF-11 features small pore channels (4.4 Å) close to the kinetic diameter of Xe, in which a large number of alkyl cavities and oppositely adjacent open Cu-metal sites are densely arranged along the pore channels in staggered mode. Such unique pore system can not only introduce strong binding affinity with Xe, but also enable the dense packing of Xe inside the pores. This material shows the highest Xe storage density of 2826 g/L at ambient conditions, record-high Xe uptake (4.0 mmol g−1at 0.2 bar and 298 K) and one of the highest Xe/Kr selectivity (19.1). The Xe locations within MOF-11 were visually identified by single-crystal X-ray diffraction experiment, which unveils the dense packing mechanism of Xe within the pores accountable for the record Xe capture capacity. The breakthrough experiments confirm that MOF-11 exhibits the exceptional separation performance for 20/80Xe/Kr mixture with both record-high Xe uptake capacity (3.46 mmol g−1) and Kr productivity (350 cm3 g−1).

Enhanced removal of heavy metals by α-FeOOH incorporated carboxylated cellulose nanocrystal: synergistic effect and removal mechanism.

Simultaneous and highly efficient removal of heavy metal cations and oxyanions is significant for both water and soil remediation, but it remains a major challenge due to the complexity. In this work, a novel hybrid of α-FeOOH incorporated carboxylated cellulose nanocrystal (Fe/CNC) is synthesized via a hydrothermal process, which shows improved α-FeOOH dispersion and heavy metal removal capacity. In single adsorbate system, maximum adsorption capacities toward Pb(II), Cd(II), and As(V) by Fe/CNC reach 126.06, 53.07, and 15.80mgg-1, respectively, and the Fe leaching is much lower than that of α-FeOOH. In binary and ternary adsorption systems, simultaneous removal of Pb(II), Cd(II), and As(V) is proved, and the competition and synergy coexist among heavy metals. FTIR and XPS spectra have revealed the synergistic removal mechanism: Pb(II) and Cd(II) are mainly removed by surface complexation with oxygen-containing functional groups on C-CNC and α-FeOOH, and precipitation on the surface of α-FeOOH, while ligand exchange with Fe-OH is responsible for As(V) removal. The soil incubation experiments show that exchangeable and carbonate-bound Pb, Cd, and As are transformed into more stable forms in contaminated soil containing Fe/CNC composites. This work provides a novel composite material for remediation of heavy metal-contaminated environments.

Synthesis and CO2 adsorption kinetics of Aluminum Fumarate MOFs pellet with high recovery

As a promising CO2 adsorbent, Aluminum Fumarate (AlFu) metal organic frameworks (MOFs) were explored for pelletizing technology and CO2 adsorption characteristics. The effects of binder type (sodium carboxymethylcellulose (CMC), aluminum sol (AS)) and content (2.5 wt%-20 wt%), CO2 partial pressure (0.3 bar–1 bar) and temperature (35 °C–65 °C) on the mechanical performance and adsorption process were investigated. The results revealed that with the increase of binder mass, the pellet mechanical strength rose while the CO2 adsorption amount decreased. The AlFu pellet with 2.5 wt% CMC could retain the powder porosity and adsorption capacity. The mechanical strength of AlFu@CMC-2.5 wt% achieved 1.486 MPa, and the maximum adsorption capacity was 1.26 mmol/g at 35 °C and 1.0 bar. The CO2 adsorption capacity was increased with lower adsorption temperature and higher CO2 partial pressure. Compared with pseudo second order model and pseudo first order kinetic model, Avrami kinetic model could better describe the CO2 adsorption behavior of AlFu pellet. It indicated that the adsorption process was not a single physical or chemical adsorption. The rate-limiting kinetic analysis showed that the CO2 adsorption rate was determined by film diffusion and intraparticle diffusion rather than inter-particle diffusion.

Selective gradient separation of aminophenol isomers by cucurbit[6]uril

Separation of aminophenol isomers from their mixture is dominantly crucial in chemical industries. Herein, the selective adsorption of Para-Aminophenol (PAP), Meta-Aminophenol (MAP) and Ortho-Aminophenol (OAP) has been executed by using cucurbit[6]uril (Q[6]). The Q[6] has adsorbed PAP from aminophenol isomers mixture with remarkably high selectivity, resulting in the separation of PAP from PAP:MAP:OAP mixture (v/v/v = 1:1:1) at 25 °C, and yielding in a single adsorption cycle PAP with the purity of > 96.70%. Again, Q[6] has been utilized to isolate MAP from MAP:OAP mixture (v/v = 1:1) at 60 °C, yielding in a single adsorption cycle MAP and OAP with > 94.16% and 91.46% purities, respectively. Single-crystal structures, powder X-ray diffraction patterns, and molecular simulations have suggested that such selectivity has not only originated from guest-induced structural changes in Q[6], but also has been attributed to the simple cavity/ pore size effect. The isolated PAP and MAP and Q[6] can be quickly resolved in organic solvents and recovered, suggesting reusability of the as-synthesized material towards selective isolation of isomers for multiple cycles without any significant loss in performance.

Removal of Cr(VI) and Ag(I) by grafted magnetic zeolite/chitosan for water purification: Synthesis and adsorption mechanism

In this paper, a novel grafted zeolite/Fe3O4/chitosan (ZMC-MAH-TEPA) adsorbent was greenly synthesized and evaluated for the removal of Cr(VI) and Ag(I) in single and bi-component solutions. The characterization data of XRF, XRD, FT-IR, VSM, TGA, BET and SEM showed the successful fabrication of the adsorbent with abundant -NH2 and -NH- as well as great recovery properties (11.70 emu/g). The effects of experimental parameters, including pH value, initial concentration, temperature, time, and coexisting ions on single and bi-component adsorption, were investigated. The results demonstrated that the adsorption capacities increased with the enhanced shaking time and concentration until equilibrium was reached. The optimum pH value was 3 for Cr(VI) adsorption and 5 for Ag(I) adsorption. The maximum adsorption capacities for Cr(VI) and Ag(I) ions, obtained by the Langmuir model, were 50.75 and 70.12 mg·g−1 in single metal solutions and 45.45 and 58.94 mg·g−1 in bi-component metal solutions (Cr(VI)/Ag(I) = 1:1), respectively. Additionally, the adsorption mechanism of Cr(VI) and Ag(I) was explained in terms of electrostatic interaction and hydrogen bonding between metal ions and -NH2 and -NH- in ZMC-MAH-TEPA. Taken together, this study provides a clean approach to synthesizing chitosan-based adsorbents for the efficient removal of Cr(VI) and Ag(I) ions.

Effect of silicon on the mathematical model prediction and adsorption mechanism of boron removal by a fixed-bed column

To promote the practical application of a novel resin (tiron-modified resin) in the removal of toxic element boron from actual water, the dynamic adsorption of boron was investigated in the presence of silicon by a fixed-bed column. The breakthrough time, exhaustion time and adsorption capacity of the column bed decreased in the presence of silicon due to competitive adsorption. The boron adsorption capacity decreased from 5.01 mg/g to 2.91 mg/g in the mixed solution compared with the single solution containing the same initial concentration. However, the total adsorption capacity (the sum of boron and silicon) was close to that of single boron. The Thomas and Yoon-Nelson models can appropriately predict the whole breakthrough curves (BTCs) of boron and the sum of both elements during the column bed adsorption process despite the coexistence of silicon. This result will have great reference value in related fields. The mixed adsorption mechanism of boron and silicon varied from single adsorption. For boron, besides the formation of triangular and tetrahedral complexes, the B-O-Si chemical bonds were also formed. However, the silicon was mainly adsorbed via monomers, with the addition of one-dimensional linear polymer and two-dimensional sheet polymers. The presence of silicon reduced the life factor of the column bed's capability to avoid breakthrough time from 6.8 to 5.5 cycles at t = 0, but prolonged the completely exhausting time from 7.8 to 11.7 cycles. T-resin manifests itself in preferential and continuous adsorption of boron, showing enormous potentialities for controlling boron pollution in actual waters.

Effects of synthesis temperature on ε-MnO2 microstructures and performance: Selective adsorption of heavy metals and the mechanism onto (100) facet compared with (001)

The heavy-metal adsorbent ε-MnO2 was produced through a simple, one-step oxidation-reduction reaction at three different synthesis temperatures (25 °C, 50 °C and 75 °C) and their morphology and chemical-physical properties were compared. Of the three materials, MnO2-25 had the largest specific surface area and the highest surface hydroxyl concentration. Its optimal performance was demonstrated by batch adsorption experiments with Pb2+, Cd2+ and Cu2+. Of the three metals, Pb2+ was adsorbed best (339.15 mg/g), followed by Cd2+ (107.50 mg/g) and Cu2+ (86.30 mg/g). When all three metals were present, Pb2+ was still absorbed best but now more Cu2+ was adsorbed than Cd2+. In order to explore the mechanism for the inconsistent adsorption order of Cd2+ and Cu2+ in single and competitive adsorption, we combined experimental data with density functional theory (DFT) calculations to elucidate the distinct adsorption nature of MnO2-25 towards these three metals. This revealed that the adsorption affinity of the (100) facet was superior to (001), and since the surface complexes were also more stable on (100), this facet was most likely determining the adsorption order for the single metals. When the metals were present in combination, Pb2+ preferentially occupied the active adsorption sites of (100), forcing Cu2+ to be adsorbed on the (001) facet where Cd2+ was only poorly bound. Thus, the adsorption behavior was affected by MnO2-25 surface chemistry at a molecular scale. This study provides an in-depth understanding of the adsorption mechanisms of the heavy metals on this adsorbent and offers theoretical guidance for production of adsorbent with improved removal efficiency.

Desolvation-Degree-Induced Structural Dynamics in a Rigid Cerium-Organic Framework Exhibiting Tandem Purification of Ethylene from Acetylene and Ethane.

Due to the industrial requirements for high production and high quality of ethylene, efficient purification of ethylene from acetylene and ethane is of prime importance but challenging. Dynamic metal-organic frameworks (MOFs) have demonstrated intriguing structural dynamics and diverse applications recently. Among them, although a few flexible ones have exhibited interesting ethylene purification capability, rigid ones were yet barely investigated for such purpose. In this regard, a cerium(III)-based MOF was solvothermally synthesized, which is rigid and assembled from rod molecular building blocks associated with coordinative N,N-dimethylformamide (DMF) molecules. After liberating different degrees of DMF ligands via heating under vacuum or acetone exchange, both partially desolvated compounds of Ce-MOF-1 and Ce-MOF-2 were concertedly isolated in a fashion of single-crystal to single-crystal transformation. Although both newly generated materials crystallize in the same space group, they exhibit dissimilar unit cell parameters and slightly distinct ultramicropore sizes and pore microenvironments, thanks to the discrepancy in the desolvation degree. Consequently, Ce-MOF-1 and Ce-MOF-2 individually demonstrate C2H2- and C2H6-selective adsorption behavior, resulting in the potential tandem separation of C2H4 from C2H2 and C2H6 mixtures. The above results were successfully supported by not only single gas adsorption isotherms but also grand canonical Monte Carlo (GCMC) calculation studies and dynamic breakthrough experiments. The present work may pave the way for rigid MOFs aiming at advancing applications via solid-state structural dynamics.

Improved sono-assisted adsorption of a binary dye mixture using bis(2-ethylhexyl) phosphate modified Amberlite XAD-2 resin and response optimization

Methylene blue (MB) and crystal violet (CV) was simultaneously adsorbed ultrasonically on bis (2-ethylhexyl) phosphate (D2EHPA) modified Amberlite XAD-2 resin. The prepared resin was characterized by FESEM, SEM with EDS, FTIR, and point of zero charge. Preliminary studies for the removal of MB and CV dye in the mixture was done by using different ratio of D2EHPA impregnated XAD-2 resin and at different pH. Central Composite Design (CCD) of response surface methodology (RSM) was used to design and optimize the removal process. The effective parameters chosen for this study were: ultrasonication time (tus: 3–15 min), adsorbent dosage (m: 0.3–1.5 g), and initial concentration of MB (Cmbin) and CV (Ccvin) dye in solution (5–25 mg L−1). At optimized condition (tus = 10.5 min, m = 1.16 g, and concentration of Cmbin = 16 mg.L−1and Ccvin = 16 mg L−1), the maximum percentage removal for MB and CV dye was 93.38% (Qt = 1.29 mg g−1) and 97.80% (Qt = 1.32 mg g−1), respectively. pH study was performed at optimized condition by varying the pH of the dye solution from 3 to 12. At optimized condition, kinetic and equilibrium studies were performed. For single dye adsorption study, Freundlich model and for binary dye adsorption study extended Freundlich model was best fitted. The pseudo-second-order model best fitted the kinetic data for both the dyes with R2 = 0.998 for MB dye and R2 = 0.999 for CV dye which indicated the chemisorption nature of adsorbent. The possible interaction mechanism between D2EHPA and MB/CV dye was proposed. The continuous study was performed by varying flow rates using a recirculating flow vessel and found to be 12.5% more energy efficient than the batch mode. Regeneration of the adsorbent was done successfully using ethanol-water solution up to five cycles.

Effective single and contest carcinogenic dyes adsorption onto A-zeolite/bacterial cellulose composite membrane: Adsorption isotherms, kinetics, and thermodynamics

This study reports loading of A-zeolite particles on the bacterial cellulose membrane for single and binary carcinogenic dye uptake from the aqueous solution. The bio based membrane was obtained using Gluconobacter Oxydans NRRL 759 in liquid culture medium. Meanwhile, the incorporation of zeolite particles within the bacterial cellulose matrix and on its surface was implemented via in-situ synthesis. The crystallite structure and the morphology of obtained composite membrane were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM) hyphenated with energy dispersive X-ray (EDX). The surface characteristics were intensively investigated by N2 adsorption/desorption isotherm, SBET, pore size distribution, and zeta potential. The results indicate that the treatment of bacterial cellulose with zeolite particles reflected two folds in surface area and three folds in the point of zero charge (pHzpc 6.7) compared with un-modified one. The produced composite membrane was also examined against removal of sole cationic methylene blue "MB", and anionic Congo-Red "CR" or in binary solutions included "MB" with Malachite green "MG" or "CR" with different percentages through batch adsorption technique. Different parameters affecting the adsorption process, such as dye concentration, adsorbent type, contact time, temperature, and pH, were optimized. The highest removal was recorded at optimum conditions for sole "MB" dye (99.2%), "CR" dye (81%), binary mixed "2MB/1CR" (96% after 15 min, 91% after 12 h, respectively), and "2MB/1MG" (98.6% after 30 min). Moreover, linear and nonlinear adsorption isotherm models confirmed that MB adsorption and CR obeys Freundlich isotherm model. Also, the kinetic studies revealed that the dyes' adsorption on the composite membrane could be clarified using linear and nonlinear forms of pseudo-first order, pseudo-second order, and intra-particle diffusion models. Thermodynamic findings emphasized the endothermic and spontaneous adsorption process as the adsorbent/ adsorbate physical interaction decreased the entropy. Eventually, the recyclability test revealed that the composite matrix exhibits excellent removal efficiency up to 5 recycles. The primary adsorption mechanism was proposed and confirmed with Fourier transform infrared (FTIR). Finally, the unprecedented composite membrane can be considered as an economically distinguished adsorbent for the removal of not only sol dyes but also mixtures of anionic and cationic dyes.

Sulfur-modified Pleurotus ostreatus spent substrate biochar enhances the removal of cadmium in aqueous solution: Characterization, performance, mechanism

Cadmium (Cd) is a toxic metal element that adversely affects water bodies and poses a threat to the ecological environment and human health. In this experiment, Pleurotus ostreatus spent substrate (P) was used as the initial material to prepare Pleurotus ostreatus spent substrate biochar (PB) at a high temperature of 500 °C, and then modified with CS2 and NaOH to obtain sulfur-modified Pleurotus ostreatus spent substrate (SP) and sulfur-modified Pleurotus ostreatus spent substrate biochar (SPB) to remove Cd(II) in aqueous solution. The adsorption of Cd(II) on the four materials follows the Langmuir isotherm model and the pseudo-second-order kinetic model. After modification with sulfur, the specific surface area and pore volume of both modified materials were significantly increased, and the adsorption capacity for cadmium was enhanced. The equilibrium adsorption capacity of SPB was 55.9636 mg g−1, and the maximum adsorption capacity of SPB was 443%, 369% and 229% of that of P, SP and PB, respectively. Single factor batch adsorption experiments and characterization results showed that the adsorption of cadmium on SPB was mainly due to the interaction of cadmium and organic sulfides, the precipitation of cadmium hydroxide and carbonate, and the formation of Cd-Cπ bonds.

Effect of cationic, anionic and non-ionic surfactants on transport of microplastics: Role of adhesion of surfactants on the polyethylene surface

• Anionic, cationic, and nonionic surfactants all promote PE transport. • The greater adhesion of surfactants on the PE surface cause stronger PE transport. • Adhesion of surfactant on PE is related to the minimum single molecule adsorption area. In view of the amphiphilicity of surfactants, which can improve the hydrophilicity of polyethylene (PE) microplastics and increase the mobility of PE microplastics, the research on the transport behavior of PE microplastics under the coexistence of surfactants is still lacking and necessary. In this work, column experiments were carried out on the suspensions made of 15 surfactants mixed and dispersed with PE microplastics to explore the promoting effect of various surfactants on the transport of PE in saturated porous media. The dynamic contact angle of surfactant on PE surface and the surface tension and zeta potential of PE / surfactant dispersion system were measured. The interaction energy between PE / surfactant and medium, the adhesion of surfactant on PE surface were calculated respectively according to DLVO theory and Young's equation. The experimental results showed that different surfactants promoted the transportation of PE in the column to different degrees. The promotion degree of cationic, anionic and nonionic surfactants on PE transport from large to small were BG > PQ28 > CTAB > BLB > TLB, SDS > SLDED > DSS > SL > SDBS, POES > T40 > T80 > X100 > TX20, respectively. The recovery of PE in the column ranged from 17% to 99.93% under the surfactants. The calculation results of the adhesion of surfactant on PE surface also showed the same law. The minimum single molecule adsorption area (A sL ) of surfactant on PE surface was negatively correlated with the recovery of PE in the column under the same type of surfactant. The high adhesion of surfactant on PE surface was caused by the small adsorption area of single molecule, which finally made PE obtain higher stability and penetration. These findings provide new insights and methods for the fate and transport of microplastic and surfactant coexisting systems in soil and the prediction of their potential risk of groundwater pollution.

Characterization of unconventional sand-based substrates for adsorption of micropollutants in nature-based systems.

The focus of this study is the characterization of unconventional sand-based substrates used in our previous project EmiSûre, (Interreg Greater Region (German federal states Rhineland-Palatinate and Saarland, the Grand Duchy of Luxembourg, regions Wallonia and Lorraine from Belgium and France, respectively), 2017-2021). The project aimed to develop and test alternative, nature-based technologies for the elimination of micropollutants (MPs) from municipal wastewater. For the characterization, two approaches were chosen. In the first approach, adsorption kinetics with a single compound allowed a perception of the adsorption capacity of the studied substrates compared to conventional substrates (granular activated carbons). This knowledge was completed by the second approach: an implementation of the studied substrates in packed-bed columns, which treated a mixture of 27MPs in tap water for 10 months. Additionally, all three substrates (bentonite sand, sand with 15% activated biochar and sand with 15% zeolite) were characterized for physical and chemical properties, and the microbial potential of the activated and non-activated biochar was examined. From the studies, it is clear that the sand with an admixture of activated biochar is the most efficient sorbent in terms of single compound adsorption in batch (dye) and adsorption of 27MPs on packed-bed columns. In contrast to the two other substrates, it shows long-term stable removal efficiencies. In the packed-bed columns, 18 out of 27 compounds were removed on average with high efficiency (80-99%), which is impressive, if we consider the variety of the compounds examined (pharmaceuticals, herbicides, pesticides, etc.) and their removal in conventional treatments. Additionally, adsorption models were created for the experimental data of all compounds adsorbed on the substrate with an admixture of activated biochar resulting in the best fit with the combined Langmuir-Freundlich model. These satisfying results suggest the application of the sand-based substrate with an admixture of activated biochar for further research and possibly upscale installations with the aim to offer and prove a reasonable and efficient alternative for MPs elimination from municipal wastewater.

Semi-interpenetrating network based on xanthan gum-cl-2-(N-morpholinoethyl methacrylate)/titanium oxide for the single and binary removal of cationic dyes from water

In the present study, semi-interpenetrating polymer networks (semi-IPNs) were synthesized based on xanthan gum (XG)-cl-2-(N-morpholinoethyl methacrylate) (MEMA)/titanium dioxide (TiO2) in the presence of N, N` methylene bisacrylamide (MBAAm), as the cross-linking agent. After that, the semi-IPN hydrogel was used to adsorb Methylene Blue (MB+) and Crystal Violet (CV+) from single and two-component adsorption systems. The optimal pH for efficient dye adsorption in aqueous solutions has been determined to be 8 for CV+ and 11 for MB+, respectively. The presence of polar oxygen-containing functional groups such as OH, CO, C-O-C, COOH, and others has been noticed to be the primary driving force in dye adsorption.Equilibrium data from a single process fitted very well to the Freundlich and Dubinin–Radushkevich models (R2 = 0.997 and 0.99) for MB+ and CV+, respectively. In a binary system, CV+ removed more than MB+, and both dyes demonstrated synergism during the adsorption of CV+/MB+ solutions. The dye removal efficiency of the adsorbent was found to be quite good even after the fourth adsorption-desorption cycle. In the treatment of multi-component contaminated water, XG-cl-poly (MEMA)/TiO2 might be a beneficial and reusable adsorbent.

Low-temperature hydrothermal modification of waste paper fiber adsorbent to enhance removal benzothiophene sulfide efficiency from oil: kinetics and equilibrium study

Thiophene sulfide is difficult to be removed by hydrodesulfurization. In this study, ZnCl2-waste paper fiber activated carbon was used as adsorbent to remove thiophene sulfide from simulated oil by hydrothermal modification. Under the optimum condition of ammonia modification, the adsorption capacity of modified adsorbent to BT is 14.8 mg S/g, 2.98 times that of unmodified. BET, FTIR and Boehm analysis showed that the mesopore volume of ammonia modified adsorbent increased by 96.62% and the mesopore ratio increased from 12.58% to 43.40%, which was conducive to improving the adsorption rate. After modification, the basic groups on the surface of the adsorbent increased by 44.3 times, and –NH3+, –OH and –NH2 enhanced the electron attraction and hydrogen bonding force between the adsorbent and BT molecule. Adsorption isotherms, adsorption kinetics and adsorption thermodynamics show that the adsorption process is spontaneous, entropic and exothermic. The pseudo-second-order kinetic rate constant increases with the increase of adsorption temperature, indicating that the increase of temperature is beneficial to accelerate the adsorption rate. The adsorption desulfurization process follows the mechanism of single and multilayer adsorption mixing. The results of this study can help to reveal more clearly that biobased activated carbon can be modified to adsorb thiophene sulfide.

Preparation of novel bifunctionalized magnetic nanoparticles for sequential speciation analysis of inorganic arsenic

An amino- and mercapto-bifunctionalized magnetic nanocomposite (SMNPs-(NH2 + SH)) was synthesized by modification of silica-coated magnetic nanoparticles (SMNPs) via one-pot co-condensation of 3-aminopropyltriethoxysilane (APTES) and 3-mercaptopropyltrimethoxysilane (MPTMS) for the first time. The bifunctional magnetic nanomaterial was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectrometry, X-ray photoelectric spectroscopy, elemental analysis, thermogravimetric analysis and vibrating sample magnetometry, etc. The prepared SMNPs-(NH2 + SH) nanocomposite was employed as magnetic solid-phase extraction (MSPE) sorbent for speciation of inorganic arsenic without any pre-oxidation or pre-reduction process. Different optimal conditions for the MSPE including sample solution pH and volume, adsorbent amount, loading time, eluent composition and volume, and elution time were investigated systematically. As(V) and As(III) were adsorbed simultaneously at pH 4.0, and then desorbed sequentially by 3 % (v/v) HNO3 and 3 % (v/v) HNO3 with 4 % (m/v) mercaptosuccinic acid followed by inductively coupled plasma-mass spectrometry (ICP-MS) analysis with the limits of detection of 15.2 and 24.5 ng/L respectively at an enrichment factor of 10 fold. The reliability of the stepwise speciation strategy based on SMNPs-(NH2 + SH) was validated by analyzing inorganic arsenic species in certified reference material of environmental water as well as mixed standard solutions of As(V) and As(III), and the results were in good accordance with the certified or standard values. The applicability of the SMNPs-(NH2 + SH)-MSPE-ICP-MS method for speciation analysis of inorganic arsenic was evaluated in spiked tap, rain, lake and river water samples at the recoveries of 92 %–102 % and 92 %–100 % with the relative standard deviations of 3.6 %–7.4 % and 2.3 %–8.2 % for As(V) and As(III) respectively. In consideration of the merits of single adsorbent, facile preparation, easy operation and no invasion to labile inorganic arsenic, the bifunctional material based MSPE protocol is attractive for speciation analysis of arsenic in real environmental samples.

A straightforward optical alignment protocol for STM-based single molecule spectroscopy

A light-accessed scanning tunneling microscope (STM) is a powerful spectroscopic tool that enables chemical analysis at the single molecular level, but it requires highly precise optical alignments to pinpoint the nano-scale tunneling gap, leaving experimental challenges. Here we present straightforward procedures to align the optical setup for STM-luminescence and STM-based tip-enhanced Raman spectroscopy (TERS) performed with a reflection geometry in an ultrahigh vacuum chamber. Observing real-space images of the metal tip apex through a spectrograph set to the zeroth-order diffraction enables “in situ” optimization of the detection path and introduction of the excitation light of TERS to the nanogap. The best spatial overlap with the nanogap can be achieved by monitoring plasmon-enhanced, low-frequency inelastic scattering of the metal. This protocol allows us to overcome such difficulties in STM-based spectroscopy and facilitates physicochemical study of single adsorbates on nontransparent substrates.

Selective adsorption desulfurization by single Al atom anchoring on the surface of hexagonal boron nitride through S[sbnd]Al coordination

A concept of single atom adsorbents (SAAs) is proposed to the fields of highly selective adsorption desulfurization from diesel. Here, SAAs with the Al atom anchoring on the surface of hexagonal boron nitride have been systematically explored by density functional theory. Firstly, all the possible doping sites have been considered and their stabilities have been discussed by the doped energy. Additionally, the activity and selectivity for the adsorptive desulfurization of these Al-based SAAs have been predicted. Results show that all the Al-based SAAs can enhance the activity and selectivity of adsorptive desulfurization due to the newly formed S-Al coordination bond. We hope this work can provide a reliable theoretical foundation for the design of SAAs with higher adsorptive activity and superior selectivity.

Adsorption‐hydration hybrid process for CO2 capture in a fixed bed of activated carbons

AbstractThis work reports an investigation of using a fixed bed of activated carbons (ACs) to capture CO2 at hydrate formation conditions. The experiments were conducted at 277.15 K and 3.5 MPa. The water saturation (WS) of the fixed bed of ACs varies from 0% to 100%. The results indicate that an adsorption‐hydration hybrid process occurred in the fixed bed of wet ACs while a single adsorption process occurred in the fixed bed of dry ACs. The adsorption‐hydration hybrid process performs better than the single adsorption process for CO2 capture. Gas consumption at 100% WS is 3.18 times greater than that obtained using dry ACs (single adsorption process). It is found that 40% WS is an optimal value, and the gas consumption obtained at this WS is larger than that obtained at 0%, 70%, and 100% WS. This gas consumption is also greater than that obtained using stirred reactors at the same temperature and pressure conditions, so the adsorption‐hydration hybrid process achieved in the fixed bed of wet ACs has a greater potential to capture CO2 in comparison with the single adsorption or hydrate formation process.