Aluminum-based Metal Organic Framework Research Articles

Hydroxyl-functionalized linker endows an ultra-microporous aluminum based metal–organic framework with electronegative site for enhancing ethane/ethylene separation

Efficient purification of ethylene (C2H4) from the cracking gas containing a small amount of ethane (C2H6) by selective adsorption of C2H6 is meaningful but remains challenging. Aluminum-based metal–organic frameworks (Al-MOFs) with ultra-microporous structure show preferential adsorption of C2H6 over C2H4, relying on the existence of multiple hydrogen bonding acceptors (e.g., AlO6 polyhedra) for C2H6 molecule in the confined pores. However, most Al-MOFs exhibit limited C2H6/C2H4 selectivity (<2), which lack other strong preferential binding sites for C2H6. Here we report that a hydroxyl functionalized Al-MOF (i.e., CAU-1-OH) exhibits notably improved C2H6/C2H4 selectivity (2.13) and C2H6 uptake (3.95 mmol g−1) at 298 K and 1 bar compared to its amino-functionalized counterpart, CAU-1-NH2. Prior to experiment, theoretical calculations were performed, revealing that O atom from hydroxyl group in CAU-1-OH acts as a fairly strong hydrogen bond acceptor due to its more negative charge than N atom in CAU-1-NH2. The in-situ infrared experiment further confirmed the formation of multiple hydrogen bonds (C–H⋅⋅⋅O) between CAU-1-OH and C2H6 molecules, which plays vital role for C2H6-selective capture. The actual potential for C2H4 purification was fully demonstrated by dynamic breakthrough experiments, in which CAU-1-OH displayed excellent separative performance from C2H6/C2H4 (1/15, v/v) mixture. Moreover, the structural stability and excellent recyclability suggested and the promise for cost-effective industrial application in C2H6/C2H4 separation.

Investigation on open water adsorption performance of multi-walled carbon nanotubes modified MIL-96(Al)

An aluminum-based metal-organic framework material MIL-96(Al) was prepared by solvent-thermal synthesis method, and by adding multi-walled carbon nanotubes (MWCNTs) in the preparation process, MWCNT/MIL-96(Al) composite adsorbent was synthesized for the first time. The morphology of the adsorbents was discussed by scanning electron microscopy (SEM). In adsorption experiments under different working conditions, MIL-96(Al) exhibited a stable equilibrium adsorption capacity, while the addition of only 0.50% mass fraction of multi-walled carbon nanotubes increased equilibrium adsorption capacity by approximately 30%. The enhancement ratio of six composite adsorbents compared to MIL-96(Al) in equilibrium adsorption capacities was almost constant under different working conditions. The adsorption rate of MIL-96(Al) could reach up to 0.573 g g−1 h, while that of the composite adsorbents under the same conditions was 0.763 g g−1 h. MIL-96(Al) could be completely desorbed within 40 min at 110 °C, and the optimal desorption temperature of MWCNT/MIL-96(Al) was reduced to 100 °C. The cyclic stability of the seven adsorbents was also confirmed through cyclic regeneration experiments. The experimental results indicated that the MWCNT/MIL-96(Al) composite adsorbent was a potential adsorbent for solar-driven atmospheric water harvesting in arid regions.

A Porous Carbazolic Al-MOF for Efficient Aerobic Photo-Oxidation of Sulfides into Sulfoxides under Air.

A robust, microporous, and photoactive aluminum-based metal-organic framework (Al-MOF, LCU-600) has been assembled by an in situ-formed [Al3O(CO2)6] trinuclear building unit and a tritopic carbazole ligand. LCU-600 shows a high water stability and permanent porosity for N2 and CO2 adsorption. Notably, the incorporation of photoresponsive carbazole moieties into LCU-600 makes it a highly efficient and recyclable photocatalyst for aerobic photo-oxidation of sulfides into sulfoxides under an air atmosphere at room temperature. Mechanism investigations unveil that photogenerated holes (h+), superoxide radical anion (O2•-), and singlet oxygen (1O2) are critical active spices for the photo-oxidation reaction performed in an air atmosphere.

Harvesting Water from Air with High-Capacity, Stable Furan-Based Metal-Organic Frameworks.

We synthesized two isoreticular furan-based metal-organic frameworks (MOFs), MOF-LA2-1(furan) and MOF-LA2-2(furan) with rod-like secondary building units (SBUs) featuring 1D channels, as sorbents for atmospheric water harvesting (LA = long arm). These aluminum-based MOFs demonstrated a combination of high water uptake and stability, exhibiting working capacities of 0.41 and 0.48 gwater/gMOF (under isobaric conditions of 1.70 kPa), respectively. Remarkably, both MOFs showed a negligible loss in water uptake after 165 adsorption-desorption cycles. These working capacities rival that of MOF-LA2-1(pyrazole), which has a working capacity of 0.55 gwater/gMOF. The current MOFs stand out for their high water stability, as evidenced by 165 cycles of water uptake and release. MOF-LA2-2(furan) is the first aluminum MOF to employ a double 'long arm' extension strategy, which is confirmed through single-crystal X-ray diffraction (SCXRD). The MOFs were synthesized by using a straightforward synthesis route. This study offers valuable insights into the design of durable, water-stable MOFs and underscores their potential for efficient water harvesting.

Enhancing CO2/N2 and CH4/N2 separation performance by salt-modified aluminum-based metal-organic frameworks.

The energy-saving separation of CO2/N2 and CH4/N2 in the energy industry facilitates the reduction of greenhouse gas emissions and replenishes energy resources, but is a challenging separation process. The trade-off between adsorption capacity and selectivity of the adsorbents is one of the key bottlenecks in adsorption separation technologies' large-scale application in the above separation task. Herein, we introduced a series of fluoroborate or fluorosilicate salts (Cu(BF4)2, Zn(BF4)2 and ZnSiF6) into the open coordination nitrogen sites of aluminum-based metal-organic frameworks (MOF-253) to create multiple binding sites to simultaneously enhance the adsorption capacity and selectivity for the target gas. By the synergistic adsorption effect of metal ions (Cu2+ or Zn2+) and fluorinated anions (BF4- or (SiF6)2-), the single-component adsorption capacity and selectivity of salt-modified MOF-253 (MOF-253@Cu(BF4)2, MOF-253@Zn(BF4)2 and MOF-253@ZnSiF6) for CO2 and CH4 were effectively improved when compared to pristine MOF-253 at 298 K and 1 bar. In addition, the salt-modified MOF-253 has a moderate adsorption heat (<30 kJ mol-1) which could be rapidly regenerated at low energy by evacuation desorption. As confirmed by the ambient breakthrough experiments of MOF-253 and MOF-253@ZnSiF6, the real separation performance for both CO2/N2 (1/4) and CH4/N2 (1/4) was obviously improved. This work provides a feasible post-modification strategy on uncoordinated sites of the framework to improve adsorption separation performance and promote the development of ideal adsorbents with a view to realizing their application in the energy industry.

A robust aluminum-octacarboxylate framework with scu topology for selective capture of sulfur dioxide

A novel 4,8-c scu-type aluminum-based metal–organic framework shows a robust structure, reversible SO2 adsorption with high capacity, and high SO2/N2, SO2/CO2, and SO2/CH4 selectivities.

Separation of High-Purity C2H2 from Binary C2H2/CO2 Using Robust Al-Based MOFs Comprising Nitrogen-Containing Heterocyclic Dicarboxylate.

In this study, three nitrogen-containing aluminum-based metal-organic frameworks (Al-MOFs), namely, CAU-10pydc, MOF-303, and KMF-1, were investigated for the efficient separation of a C2H2/CO2 gas mixture. Among these three Al-MOFs, KMF-1 demonstrated the highest selectivity for C2H2/CO2 separation (6.31), primarily owing to its superior C2H2 uptake (7.90 mmol g-1) and lower CO2 uptake (2.82 mmol g-1) compared to that of the other two Al-MOFs. Dynamic breakthrough experiments, using an equimolar binary C2H2/CO2 gas mixture, demonstrated that KMF-1 achieved the highest separation performance. It yielded 3.42 mmol g-1 of high-purity C2H2 (>99.95%) through a straightforward desorption process under He purging at 298 K and 1 bar. To gain insights into the distinctive characteristics of the pore surfaces of structurally similar CAU-10pydc and KMF-1, we conducted computational simulations using canonical Monte Carlo and dispersion-corrected density functional theory methods. These simulations revealed that the secondary amine (C2N-H) groups in KMF-1 played a more significant role in differentiating between C2H2 and CO2 compared to that of the N atoms in CAU-10pydc and MOF-303. Consequently, KMF-1 emerged as a promising adsorbent for the separation of high-purity C2H2 from binary C2H2/CO2 gas mixtures.

An effective approach for CH4/N2 separation using aluminum-based metal-organic frameworks (MOFs) prepared from coal fly ash

Metal-organic frameworks (MOFs) are considered one of the promising adsorbents for CH4/N2 separation. However, MOFs commercialization is a big challenge since their synthetic materials are expensive and not environmentally friendly. Herein, the dealumination solution obtained from coal fly ash (CFA) using sulfuric acid as an extracting agent through direct leaching and roasting technologies was applied as metal feedstock to prepare CFAx-FumMOF-y and compared to aluminum fumarate MOF (Al-FumMOF) in morphology, surface area, micropore volume, and CH4/N2 selective separation. The results indicated that CFAx-FumMOF-y exhibited closely similar surface area (1164.94–1073.08 m2/g) and micropore volume (0.40–0.36 cm3/g) to Al-FumMOF (1287.55 m2/g, 0.42 cm3/g), even there were no detectable differences in CH4 uptakes (CFAx-FumMOF-y, 21.93–20.69 cm3/g; Al-FumMOF, 22.13 cm3/g) at 298 K and 1.0 bar, suggesting that the impurity metal species in dealumination solution hardly affect textural properties and gas uptakes. Moreover, the isosteric heat of adsorption (Qst) and IAST CH4/N2 selectivity of CFAs-FumMOF-1 (19.25–17.84 kJ/mol) and CFAb-FumMOF-1 (18.83–18.64 kJ/mol) were slightly superior to Al-FumMOF (17.83.64–16.86 kJ/mol, 4.87), suggesting that CFAx-FumMOF-1 played an identical role as Al-FumMOF in gases separation. The cyclic regeneration experiments and binary breakthrough tests further confirmed that CFAx-FumMOF-y was feasible for practical application. This study provides a new perspective for reducing the production cost of MOFs as well as realizing high-value utilization of CFA.

Aluminum-based metal organic frameworks for greenhouse gases CF4 and C2F6 capture with excellent capacity and selectivity

The capture and recovery of perfluorinated greenhouse gases CF4 and C2F6 from industrial exaust can not only mitigate global warming but also produce value-added products. Adsorption technology based on porous materials is promising for such purpose, while adsorbents with high capacity and selectivity are still lacking due to the chemical inertness of CF4 and C2F6. Herein, three ultra-microporous Al-MOFs with multiple electropositive binding sites in 1D channel were synthesized and evaluated for CF4/C2F6 adsorption. Among the synthesized Al-MOFs, Al-Fum displayed the best adsorption performance due to its desirable pore environment. It has a record-breaking C2F6 adsorption capacity (3.30 mmol/g at 1 bar and 298 K) and C2F6/N2 (10/90, v/v) selectivity (299.6 at 1 bar). In addition, it also displays excellent CF4 adsorption performance, exceeding most of the reported adsorbents. Theoretical simulations demonstrate the high CF4/C2F6 affinity towards Al-Fum is resulted from the multiple interactions of F atoms with H atoms of fumarate linkers and corner hydroxyl groups in frameworks. Moreover, dynamic column breakthrough tests confirmed the excellent separation performance of CF4/N2 and C2F6/N2 on Al-Fum with outstanding regenerability. Due to the green and energy-efficient synthesis method and outstanding adsorption performance, Al-Fum is considered to be an ideal porous material for CF4/C2F6 capture under practical conditions.

Nitrogen-modified spherical porous carbon derived from aluminum-based metal-organic frameworks as activation-free materials for supercapacitors

Carbon materials derived from metal-organic frameworks (MOFs) retain the precursor's regular unique morphology and net-like voids, which offers them the advantages of large specific surface area (SSA) and high capacitance for energy storage. In this paper, spherical amorphous porous carbon materials with hierarchical pores (DHTAC-2) were prepared using one-step carbonization of Al-MOF. The carbon has a large SSA (2666 m2 g−1) and a large pore volume (2.35 cm3 g−1). The obtained carbon (DHTAC-2) demonstrates an excellent specific capacitance (298.8 F g−1) at 1 A g−1 and capacitance retentions of 97.3 % and 98.0 % after 120,000 cycles at 50 A g−1 and 100 A g−1, respectively. In addition, Nitrogen-doped carbon (N-DHTAC) has increased pyridine-N, pyrrole-N and graphite-N content. The three types of N significantly improved its wettability, reversible pseudocapacitance and conductivity, respectively, resulting in a superior capacitance (355.0 F g−1@1 A g−1) and enhanced energy density (17.7 Wh kg−1@350 W kg−1) of the assembled electric double layer capacitor (EDLC) device. The device exhibits an extremely low decline rate of 10.12 % over 10,000 cycles at 10 A g−1, verifying N-DHTAC material is a promising active material for supercapacitors.

Metal-organic framework and porous polymer monolith as ion-receptor carrier templates for the solid-state naked-eye sensing of ultra-trace Cr(III) from aqueous medium

We report on an effective onsite optical sensor strategy using probe-decorated porous polymer monolith (PPM) and aluminum-based metal-organic framework (MIL-53 (Al) MOF) as a reliable colorimetric sensor for the detection of ultra-trace levels of Cr3+. MOFs and PPMs have attracted considerable interest in environmental applications due to their high surface area, perpetual porosity, and tunable structural network. Here, Al-MOF and PPM materials were used as porous templates for the uniform infusion of a chromoionophoric probe, i.e., (Z)-1,2-diphenyl-2-((4-(E)-phenyldiazenyl)phenyl)imino)ethan-1-ol (DPPE), for the solid-state colorimetric recognition and capturing of Cr3+ from aqueous medium. The structural morphology and surface topography of the sensor materials have been characterized using the transmission/scanning electron microscopy, optical spectroscopy, X-ray/electron diffraction, elemental mapping, surface area/pore volume and thermal analysis to understand the surface properties and stability features of the long-range ordered porous framework. The sensor's superior structural and surface features tender faster ion diffusion to the anchored probe sites within 60 s. The sensor induces a selective ligand-to-metal charge transfer (LMCT) chelation with Cr3+, resulting in a sequence of color transition from pale orange to sepia-brown, with incremental levels of Cr3+. The significance of physicochemical factors, such as pH, probe content, sensor dose, kinetics, temperature, reusability, selectivity, sensitivity, and stability, has been optimized to maximize the ion-sensing performance. The sensors' reusability has been tested by replicating the ion-sensing performance up to eight cycles. The solid-state sensor exhibited a linear range of 1.0–200 ppb for Cr3+, with a detection limit of 0.44 and 0.53 ppb and a quantification limit of 1.39 and 2.22 ppb for DPPE-loaded PPM and Al-MOF sensors, respectively. The practical utility of the sensor materials with industrial/environmental water samples reveals excellent data reliability/reproducibility (recovery ≥99.1 %; RSD ≤2.5 %) for real-time monitoring.

Bio-Sustainable Alternatives Synthesis of Nanoporous Activated Carbon @Al-MOF for the Adsorption of Hazardous Organic Dyes from Wastewater

The disposal of textile pollutants tainted by soluble organic dyes into the water without proper treatment may adversely impact the aquatic environment, humans, plants, and animals due to their toxic nature. As a result, the goal of this work is to look into the adsorptive removal of Eriochrome Black T (EBT) dye (as a model of soluble anionic organic dyes) from aqueous solution using a green synthesis nanoporous activated carbon @ Aluminum based metal–organic frameworks (AC@Al-MOFs) from a lemon peel waste as an inexpensive biosorbent. The physicochemical properties of Al-MOF and AC@Al-MOF composite were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), and the impact of varied parameters on adsorption efficiency of Eriochrome Black T (EBT) including pH, dye concentrations, contact time and adsorbent dose, was examined. The experimental isotherms data were analyzed using Langmuir and Freundlich isotherm equations. The best fit was obtained by the Langmuir model with high correlation coefficients (R2 = 0.9976) with a maximum monolayer adsorption capacity of 303.0 mg/g. The results suggest that AC@Al-MOF composite is a potential choice for removing EBT dye molecules from aqueous media.Graphical

Synthesis of Aluminum-Based Metal-Organic Framework (MOF)-Derived Carbon Nanomaterials and Their Water Adsorption Isotherm.

The characteristics of water vapor adsorption depend on the structure, porosity, and functional groups of the material. Metal-organic framework (MOF)-derived carbon (MDC) is a novel material that exhibits a high specific area and tunable pore sizes by exploiting the stable structure and porosity of pure MOF materials. Herein, two types of aluminum-based MOFs were used as precursors to synthesize hydrophobic microporous C-MDC and micro-mesoporous A-MDC via carbonization and activation depending on the type of ligands in the precursors. C-MDC and A-MDC have different pore characteristics and exhibit distinct water adsorption properties. C-MDC with hydrophobic properties and micropores exhibited negligible water adsorption (108.54 mgg-1) at relatively low pressures (P/P0~0.3) but showed a rapid increase in water adsorption ability (475.7 mgg-1) at relative pressures of about 0.6. A comparison with the isotherm model indicated that the results were consistent with the theories, which include site filling at low relative pressure and pore filling at high relative pressure. In particular, the Do-Do model specialized for type 5 showed excellent agreement.

Diazotization-coupling reaction on aluminum-based metal–organic framework for efficient purification of wastewater from carbofuran pesticide

A crucial issue is the development of highly and selectively absorbable pesticides. At room temperature, aluminum-based metal–organic frameworks (MIL-53-NH2, MIL-53-AZA, MIL-53-AZA-La, and MIL-53-AZA-Ce) were successfully formed. Using prepared MOFs as sorbents, carbofuran was adsorbed from wastewater. Experimental and spectroscopic studies were used to investigate the elimination mechanisms. The current process can connect a mixture of pi- pi stacking contact, coordination bonding, and hydrogen bond production. The adsorption of carbofuran from wastewater was best described by pseudo-second-order kinetics and Langmuir isothermal models. MIL-53-NH2, MIL-53-AZA, MIL-53-AZA-La, and MIL-53-AZA-Ce had elimination capacities of 367.87, 433.50, 610.23, and 635.05 mg g-1, respectively. The synthesized MOFs are represented as promising materials for the removal of carbofuran.

A robust ultra-microporous cationic aluminum-based metal-organic framework with a flexible tetra-carboxylate linker

Al-based cationic metal-organic frameworks (MOFs) are uncommon. Here, we report a cationic Al-MOF, MIP-213(Al) ([Al18(μ2-OH)24(OH2)12(mdip)6]6Cl·6H2O) constructed from flexible tetra-carboxylate ligand (5,5'-Methylenediisophthalic acid; H4mdip). Its crystal structure was determined by the combination of three-dimensional electron diffraction (3DED) and high-resolution powder X-ray diffraction. The structure is built from infinite corner-sharing chains of AlO4(OH)2 and AlO2(OH)3(H2O) octahedra forming an 18-membered rings honeycomb lattice, similar to that of MIL-96(Al), a scarce Al-polycarboxylate defective MOF. Despite sharing these structural similarities, MIP-213(Al), unlike MIL-96(Al), lacks the isolated μ3-oxo-bridged Al-clusters. This leads to an ordered defective cationic framework whose charge is balanced by Cl- sandwiched between two Al-trimers at the corner of the honeycomb, showing strong interaction with terminal H2O coordinated to the Al-trimers. The overall structure is endowed by a narrow quasi-1D channel of dimension ~4.7 Å. The Cl- in the framework restrains the accessibility of the channels, while the MOF selectively adsorbs CO2 over N2 and possesses high hydrolytic stability.

Poly(ionic liquids)-functionalized metal-organic frameworks for sustainable water purification

Ion exchange adsorption has demonstrated great promise for the removal of toxic ion contaminants from wastewater. Here, by combining in situ polymerization and quaternization, we successfully fabricated a series of poly(ionic liquids)/aluminum-based metal-organic framework composites, DUT-5-(X)I. The optimized DUT-5-(60)I possesses relatively large surface area and abundant exchangeable free iodide ions, which endow this composite with highly efficient adsorption of anionic pollutants. Specifically, over 90% of permanganate, methyl blue and methyl orange can be removed within 10 min. In addition, effects of pH and coexisting ions on the removal of adsorbates were examined. Pseudo-second-order kinetics and Langmuir isotherm model can well describe the adsorption results. The Langmuir isotherm model based maximum adsorption capacities of DUT-5-(60)I for permanganate, methyl blue, and methyl orange reached up to 1132, 1548, and 1474 mg/g, respectively. Adsorption mechanism studies suggest that the removal of these adsorbates was mainly controlled by electrostatic adsorption. This study will provide new insights for the development of MOF-based materials for environmental remediation.

A green aluminum-based metal organic framework outperforms its polymorph with MIL-53 type topology in o-xylene purification

Investigation of structure–property relationships for xylene separation using polymorphic metal–organic frameworks (MOFs) as adsorbent is highly desirable but the practice remains a vacancy. Herein, we report a comprehensive performance comparison between two polymorphic aluminum-based MOFs (MIL-53-TDC and CAU-23) for selective adsorption of o-xylene (OX) over m-xylene (MX) and p-xylene (PX) in liquid phase. Although containing the same chemical compositions and similar 1D channels, MIL-53-TDC and CAU-23 exhibit distinct pore geometries (square shape VS pseudo-square shape) and pore sizes (8.5 Å VS 6.8 Å). It was found that CAU-23 exhibited much higher OX uptake (1.90 mmol g−1) and selectivity (αOX/PX: 10.4; αOX/MX: 7.6) in liquid-phase competitive adsorption in comparison to MIL-53-TDC. The enhancement of OX preference by the efficient pore confinement in the narrow channel of CAU-23 was confirmed by the theoretical calculations. By virtue of the multiple hydrogen bonding interactions in the confined environment, CAU-23 exhibited excellent preferential OX uptake over other isomers in liquid phase, outperforming most of the reported sorbents. Further, the continuous adsorption–desorption experiments as well as recycling experiments demonstrated exceptional separation performance of CAU-23 under dynamic conditions. Therefore, the excellent separation performance combined with the facile green low-cost synthesis suggest an impressive potential of CAU-23 for practical application.

Facile fabrication of microstructure-tunable aluminum-based metal–organic frameworks for exceptional phosphorus recovery from water

The recovery of phosphorus from phosphorus-contaminated water is of great significance to prevent the eutrophication of natural water and overcome the shortage of phosphorus resources. To increase the effectiveness of phosphorus removal from water, aluminum metal–organic frameworks (Al-MOFs) with different microstructures were synthesized in this study by varying the ratio of metal centers (Al) to organic ligands (terephthalic acid, BDC) in the precursor solution. For the precursor solution of a 10:1 M ratio of Al3+ to BDC, the synthesized Al-MOF exhibited the maximum phosphorus adsorption capacity (100.37 mg P/g). The pseudo-second-order kinetic model indicated a better fit for the experimental data obtained from the adsorption of phosphorus onto the synthesized Al-MOFs. The synthesized Al-MOFs appeared highly effective in removing phosphorus from water at an initial pH of 3.0 to 9.0. In addition, phosphorus adsorption onto Al-MOFs is not seriously affected by the presence of coexisting ions in water such as Ca2+, Mg2+, CO32–, HCO3–, NO3–, and Cl-. After five cycles of adsorption–desorption, the phosphorus recovery efficiency of the synthesized Al-MOFs decreased by only 15%. The phosphorus adsorption onto synthesized Al-MOFs is mainly governed by electrostatic interaction, complexation, and ligand exchange mechanisms.

Screening the Specific Surface Area for Metal-Organic Frameworks by Cataluminescence

Metal-organic frameworks (MOFs) are famous for their large surface area, which is responsible for the dispersed active sites and decent behaviors in gas adsorption, storage, and catalytic reactions. However, it remains a great challenge to acquire a cost-effective and accurate evaluation on the surface area for the MOFs. In this work, we have proposed cataluminescence (CTL) to evaluate the specific surface area for the MOFs, based on the adsorption–desorption and the catalytic reaction of ethanol. Aluminum-based MOFs with large-pore (lp), narrow-pore (np), and medium-pore (mp-130, mp-140, and mp-150 synthesized under 130, 140, and 150 °C) have been prepared. Distinguished CTL signals were acquired from ethanol in the presence of these MOFs: lp &gt; mp-150 &gt; mp-130 &gt; mp-140 &gt; np. Note that the CTL intensities were positively correlated with the specific surface areas of these MOFs acquired by the Brunauer–Emmett–Teller (BET) method. The distinct specific surface area of MOFs determined the capacity to accommodate and activate ethanol, leading to the varied CTL intensity signals. Therefore, the proposed CTL could be utilized for the rapid and accurate evaluation of the specific surface area for MOFs. It is believed that this CTL strategy showed great possibilities in the structural evaluation for various porous materials.

Adsorption performance and mechanism of mesoporous carbon-doped Al2O3 adsorbent derived from NH2-MIL-53 (Al) for removing Cr(Ⅵ) and methyl orange from aqueous solution

A new porous carbon-doped Al2O3 adsorption material was prepared by calcination at 600 °C with the use of aluminum-based metal–organic framework synthesized by hydrothermal method with aluminum as the metal source to solve the problem of instability of MIL-53 in aqueous solution. It was used to remove methyl orange (MO) from single system and aqueous solution with Cr(Ⅵ). The microstructure of the material was characterized by modern analytical techniques, and its adsorption capacity and mechanism were explored. PXRD, SEM, BET and other characterization methods show successfully synthesized NH2-MIL-53(Al) with porous carbon-doped Al2O3 structure. The precursor NH2-MIL-53(Al) and the calcined derivative porous carbon-doped Al2O3 are similar in morphology, and the specific surface area of porous carbon-doped Al2O3 (180.24 m2/g) is larger than that of NH2-MIL-53(Al) (116.73 m2/g). The maximum equilibrium adsorption capacity of Cr(Ⅵ) and MO by porous carbon-doped Al2O3 material could reach 671.56 and 612.09 mg/g, respectively. The fitting results of the adsorption kinetic model show that the adsorption behavior of porous carbon-doped Al2O3 material for Cr(Ⅵ) is more suitable to Langmuir isotherm model, whereas that of MO is more suitable to Freundlich isotherm model. Both are suitable to pseudo-second-order kinetic model. According to XPS analysis, the contents of Cr(III) and Cr(VI) calculated by C600-6 after adsorption are 56.1 % and 44.9 %, indicating that electrostatic interaction and redox action still play a leading role in the adsorption of Cr(VI), while electrostatic interaction and chelation play a leading role in the adsorption of MO. Studies show that the porous carbon-doped Al2O3 material could be used as a Cr(Ⅵ) and MO removal material to achieve efficient removal of Cr(Ⅵ) and MO. The alumina synthesized by MOF is more stable than the traditional industrial alumina, and its acid and alkaline resistance is more excellent. This material not only solves the problem of instability and uneven distribution of MIL-53 crystal and common alumina materials but also provides more adsorption sites.