Fabrication of Unique Mixed-Valent CoICoII and CuICuII Metal-Organic Frameworks (MOFs) for Desulfurization of Fuels: A Combined Experimental and Theoretical Approach toward Green Fuel.

Herein, metal-organic framework (MOF)-based adsorbents are designed with distinct hard and soft metal building units, namely, [Co2ICoII(PD)2(BP)] (Co_PD-BP) and [Cu2ICuII(PD)2(BP)] (Cu_PD-BP), where H2PD = pyrazine-1,4-diide-2,3-dicarboxylic acid and BP = 4,4'-bipyridine. The designed MOFs were characterized via spectral and SCXRD techniques, which confirm the mixed-valent states (+1 and +2) of the metal ions. Topological analysis revealed the rare ths and gwg topologies for Co MOF, while Cu-MOF exhibits a unique 8T21 topology in the 8-c net (point symbol for net: {424·64}). Moreover, severe environmental issues can be resolved by effectively removing heterocyclic organosulfur compounds from fuels via adsorptive desulfurization. Further, the developed MOFs were investigated for sulfur removal via adsorptive desulfurization from a model fuel consisting of dibenzothiophene (DBT), benzothiophene (BT), and thiophene (T) in the liquid phase using n-octane as a solvent. The findings revealed that Cu_PD-BP effectively removes the DBT with a removal efficiency of 86% at 300 ppm and an operating temperature of 25 °C, with a recyclability of up to four cycles. The adsorption kinetic analysis showed that the pseudo-first-order model could fit better with the experimental data indicating the physisorption process. Further, the studies revealed that adsorption capacity increased with the increasing initial DBT concentration with a remarkable capacity of 70.5 mg/g, and the adsorption process was well described by the Langmuir isotherm. The plausible reason behind the enhanced removal efficiency shown by Cu_PD-BP as compared to Co_PD-BP could be the soft-soft interactions between soft sulfur and soft Cu metal centers. Interestingly, density functional theory (DFT) studies were done in order to predict the mechanism of binding of thiophenic compounds with Cu_PD-BP, which further ascertained that along with other interactions, the S···π and S···Cu interactions predominate, resulting in a high uptake of DBT as compared to others. In essence, Cu_PD-BP turns out to be a promising adsorbent in the field of fuel desulfurization for the benefit of mankind.

Carbon Nanotubes Decorated with Coordination Polymers for Fluorescence Detection of Heavy-Metal Ions and Nitroaromatic Chemicals.

Herein, [Nd(NO3)3(H2pzdca)] n (MA-1) was synthesized from a reaction of 2,3-pyrazinedicarboxylic acid [H2Pzdca] as an organic linker with salt of Nd(III) under solvothermal conditions. The detailed structural analysis for crystals was performed utilizing single-crystal X-ray diffraction (SCXRD). After that, the neodymium-based coordination polymer (MA-1) crystal was directly generated upon the surface of functionalized carbon nanotubes (F-CNTs) through bonds or affinity between F-CNTs and MA-1 via the solvothermal approach. Meanwhile, the existence of F-CNTs does not affect the production of MA-1 crystals. FT-IR, PXRD, SEM, TEM, and SCXRD studies were used to characterize the crystalline material, MA-1 and MA-1@CNT. To investigate the MA-1@CNT sensing properties, Pb(II), As(III), Cr(VI), and nitrobenzene (NB) were utilized as analytes. It is worth mentioning that MA-1@CNT developed as a susceptible sensor exhibits a fluorescence "turn-on" response for Pb(II) and As(III) ions, while a fluorescence "turn-off" response in the case of Cr(VI) and NB with significantly low limit of detection (LOD) values of 15.9 for Pb(II), 16.0 for As(III), 76.9 for Cr(VI), and 21.1 nM for NB, which are comparable with the lowest LOD available in the literature. Furthermore, MA-1@CNT could be conveniently regenerated and reused for at least three cycles by simply filtering and washing with water several times. The sensing mechanism is ascribed to the inner filter effect owing to the overlap between the emission and/or excitation bands of MA-1@CNT with the absorption bands of Cr(VI) and NB. In contrast, the fluorescence enhancement in the case of Pb(II) and As(III) could be correlated to the chelation-enhanced fluorescence phenomenon. These results indicate that MA-1@CNT is an ideal sensor for Pb(II), As(III), Cr(VI), and NB recognition.

Highly efficient iodine capture and ultrafast fluorescent detection of heavy metals using PANI/LDH@CNT nanocomposite.

Here, the hybrid material of polyaniline/layered double hydroxide@carbonnanotubes (PANI/LDH@CNT) is considered a multifunctional material. Instrumental methods, including FTIR, XRD, TEM, SEM, and TGA/DTA were utilized to characterize PANI/LDH@CNT. The polymerization method created PANI/LDH@CNT as an adsorbent to remove toxic iodine in hexane solution with a capture capacity of 303.20 mg g-1 during 9 h. It is 900 mg g-1 in the vapor phase within 24 h. After three cycles, the PANI/LDH@CNT could be regenerated while maintaining 91.90 % iodine adsorption efficiency. Due to the presence of free amine (-N) groups, OH-, CO2H, and π-π conjugated structures in the PANI/LDH@CNT, it is also explored for efficient iodine uptake. It was demonstrated that the pseudo-first-order (PFO) and Langmuir model had the optimum correlation with the kinetic and isotherm data, respectively. Moreover, the use of PANI/LDH@CNT is not only limited to iodine capture; it can also be utilized as a sensitive sensor that displays a fluorescence "turn-off" response for Mn7+ and Cr6+ ions and a fluorescence "turn-on" response in the case of Al3+ ions. The fluorescence intensity of the PANI/LDH@CNT was turned off in the presence of Mn7+ and Cr6+ because of the fluorescence inner filter effect (IFE) mechanism. In contrast, the fluorescence intensity was turned on in the case of Al3+, relying on the chelation-enhanced fluorescence (CHEF) effect mechanism. Under optimal conditions, the limit of detection (LOD) of 51, 59, and 81 nM for Mn7+, Cr6+, and Al3+, respectively. According to the literature, this is probably the first example based on PANI/LDH@CNT as a multifunctional hybrid material employed as an adsorbent for capturing radioactive iodine and as a chemosensor for detecting heavy metal ions in aqueous solutions.

Nano chromium embedded in f-CNT supported CoBi-LDH nanocomposites for selective adsorption of Pb2+and hazardous organic dyes.

Transition metal-doped carbon-coated layered double hydroxides for the removal of lead (II) and hazardous organic dyes have attracted increasing attention for wastewater treatment in recent years. In this work, nanostructured CoBi-LDH/Cr@CNT composites were successfully synthesized by hydrothermal route. The CoBi-LDH/Cr@CNT was characterized by instrumental techniques such as XRD, FTIR, TEM, SEM, XPS and TGA/DTA. Adsorption of Pb2+ and organic dyes, i.e.,Rose Bengal (RB) and Congo red (CR) by CoBi-LDH/Cr@CNT was performed by batch experiment.The effect of several parameters including contact time, adsorbent dose, pH, temperature, and concentration was also investigated. Under optimum conditions, the adsorption capacity of CoBi-LDH/Cr@CNT for RB, CR and Pb2+ pollutants were (278.4 mg g-1), (164.6 mg g-1) and (503.2 mg g-1) and the removal efficiency achieved is 98.2%, 95.0% and 100% respectively. The selectivity of CoBi-LDH/Cr@CNT nanocomposite towards Pb2+ has been studied using ICP-AES.The isothermal results were analyzed using Freundlich and Langmuir models. Adsorption isotherm for Pb2+(R2 = 0.975), RB (R2 = 0.997) and CR (R2 = 0.992) agrees with the Langmuir model indicating monolayer adsorption. The sorption kinetics data well fitted pseudo-first-order model for Pb2+ (R2 = 0.975), RB (R2 = 0.996), and CR (R2 = 0.995).The results demonstrated that the synthesized CoBi-LDH/Cr@CNT nanocomposite can be used as an effective sorbent for the removal of pollutants from wastewater.

Selective adsorption and ultrafast fluorescent detection of Cr(VI) in wastewater using neodymium doped polyaniline supported layered double hydroxide nanocomposite.

Neodymium-doped polyaniline supported Zn-Al layered double hydroxide (PANI@Nd-LDH) nanocomposite has been prepared via an ex-situ oxidative polymerization process. The as-prepared nanocomposite shows selective fluorescence detection and adsorption of hexavalent chromium Cr(VI) within a short period. The fluorescence intensity of PANI@Nd-LDH decreases linearly with Cr(VI) concentrations ranging from 200 ppb to 1000 ppb with a limit of detection (LOD) of 1.5 nM and a limit of quantification (LOQ) of 96 nM. The sensing mechanism can be ascribed by the inner filter effect of Cr(VI), the intercalation of Cr(VI) within the intergallery region of LDH, and the synergistic affinity of metal ions along with the polymer chain for Cr(VI). The adsorption performance of PANI@Nd-LDH nanocomposite is evaluated for Cr(VI) from wastewaters, which displayed high removal capacity towards Cr(VI) (219 mg/g) as compared on bare Nd-LDH (123 mg/g) and LDH (88 mg/g) respectively. The adsorption of Cr(VI) on PANI@Nd-LDH depends on the pH of the aqueous solution. The adsorption isotherm and kinetics are supported by the Langmuir model and pseudo-second-order model, respectively. Owing to the highly sensitive detection and adsorption of Cr(VI) from aqueous water samples demonstrated the potential application of PANI@Nd-LDH as an excellent environmental probe can be exploited.