Supramolecular Cu(ii) nanoparticles supported on a functionalized chitosan containing urea and thiourea bridges as a recoverable nanocatalyst for efficient synthesis of 1H-tetrazoles

A cost-effective and convenient method for supporting of Cu(ii) nanoparticles on a modified chitosan backbone containing urea and thiourea bridges using thiosemicarbazide (TS), pyromellitic dianhydride (PMDA) and toluene-2,4-diisocyanate (TDI) linkers was designed. The prepared supramolecular (CS-TDI-PMDA-TS-Cu(ii)) nanocomposite was characterized by using Fourier-transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), thermogravimetry/differential thermogravimetry analysis (TGA/DTA), energy-dispersive X-ray spectroscopy (EDS), EDS elemental mapping and X-ray diffraction (XRD). The obtained supramolecular CS-TDI-PMDA-TS-Cu(ii) nanomaterial was demonstrated to act as a multifunctional nanocatalyst for promoting of multicomponent cascade Knoevenagel condensation/click 1,3-dipolar azide-nitrile cycloaddition reactions very efficiently between aromatic aldehydes, sodium azide and malononitrile under solvent-free conditions and affording the corresponding (E)-2-(1H-tetrazole-5-yl)-3-arylacrylenenitrile derivatives. Low catalyst loading, working under solvent-free conditions and short reaction time as well as easy preparation and recycling, and reuse of the catalyst for five consecutive cycles without considerable decrease in its catalytic efficiency make it a suitable candidate for the catalytic reactions promoted by Cu species.

Nano-Silica Modified with Diamine for Capturing Azo Dye from Aqueous Solutions

Nano-silica particles decorated with amine groups (S-DA) were prepared via a simple, one-pot method, and under very mild conditions in an attempt to improve the affinity of the silica nanoparticles toward capturing anionic organic dye, namely, methyl orange (MO). The prepared sample was characterized by different techniques such as XRD for crystallinity, SEM for morphological structure, TGA for thermal stability, BET surface area, and FTIR for surface functional groups. The prepared sample was tested for the removal of MO under different conditions including the mass of adsorbent, pH, initial concentration, and time. Results showed that the adsorption of MO was very fast with equilibrium achieved in less than 30 min and a maximum removal efficiency of 100% for a mass to volume ratio of 10 g/3 L, a pH of 2.5, initial concentration of 10 mgL⁻¹, and under stagnant conditions. These results were compared with a bare nano-silica, which was not able to adsorb more than 3% after 24 h, indicating the important effect of amine groups. Furthermore, recycling the adsorbent was achieved by rinsing the MO-loaded adsorbent with a dilute solution of KOH. The adsorbent maintained 50% of its initial removal efficiency after four adsorption–desorption cycles.

Persimmon tannin functionalized polyacrylonitrile fiber for highly efficient and selective recovery of Au(III) from aqueous solution

An efficient fibrous adsorbent (PANF-TETA-PT) was prepared via grafting triethylenetetramine (TETA) on polyacrylonitrile fiber (PANF), followed by persimmon tannin (PT) immobilizing. Detailed characterization certified that plenty amounts of amino and phenolic hydroxyl groups existed on the surface of PANF-TETA-PT, which would provide excellent active sites for Au(III) adsorption. The batch characteristic results found that the adsorption equilibrium data could be fitted well with Langmuir equation, while the obtained kinetic data were consistent with the Pseudo-second-order equation. The maximum equilibrium adsorption capacity of PANF-TETA-PT towards Au(III) (801.2 mg/g) was apparently superior than that of the reported adsorbents, and the competitive adsorption showed that PANF-TETA-PT had a good preference to adsorption Au(III) in spite of some coexisting pollutants. The characterization analysis of Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffractometer spectrum (XRD) revealed that the electrostatic attraction and chelation dominated the uptake of Au(III) on PANF-TETA-PT, in which a part of loaded Au(III) was reduced to Au particles with the help of reductive functional groups. Thus, this adsorbent could be as a promising candidate to separation and preconcentration of Au(III) from wastewater.

One pot green synthesis of m-aminophenol-urea-glyoxal resin as pipette tip solid-phase extraction adsorbent for simultaneous determination of four plant hormones in watermelon juice

Plant hormones (PHs) are a type of pesticide that can potentially affect human health. Therefore, their quantitative detection is particularly important. In this study, a green and economic method for the simultaneous extraction and determination of four PHs, namely thidiazuron, forchlorfenuron, 1-naphthylacetic acid, and 2-naphthoxyacetic acid, in watermelon juice was developed by using m-aminophenol-urea-glyoxal resin as the adsorbent for pipette tip solid phase extraction (PT-SPE) coupled with liquid chromatography. The resin was synthesized via a simple (one pot hydrothermal synthesis) and green (ethanol as the solvent and glyoxal as crosslinking agent) process. The synthesized resin possesses multiple functional groups (hydroxyl, amino, and imino, among others), high adsorption capacity, larger specific surface area than the urea-glyoxal resin and m-aminophenol-glyoxal resin, and can be regenerated easily. The PT-SPE device is simple, cheap, and easy to obtain, and the adsorbent dosage is only 5.0 mg. The proposed method has a wide linear detection range, high recovery, good precision, and high sensitivity, and satisfies the measurement requirements for detecting trace levels of PHs in fruits and vegetables.

Adsorptive recovery of Au(III) from aqueous solution using crosslinked polyethyleneimine resins

Resin adsorption is considered as a promising method to recover gold ions from wastewater, but further reduction reaction is required to convert gold ions into particles. In this study, a crosslinked polyethyleneimine resin (CPEIR) was developed via a suspension polymerization of polyethyleneimine (PEI) and ethylene glycol diglycidyl ether (EGDE) for gold recovery. The Au(III) adsorption capacities of CPEIR were significantly impacted by solution pH and initial Au(III) concentrations but unaffected by co-existing metal ions. Compared with commercial anion-exchange resin IRA400, the CPEIR exhibited higher sorption amount and selectivity for Au(III) due to its high density of amine and hydroxyl groups on the surfaces. The adsorption isotherm of Au(III) on CPEIR was well described by the Langmuir equation, and the maximum uptake amount of Au(III) was high up to 943.5 mg/g, much higher than the reported sorbents. The adsorption kinetic data on the CPEIR were fitted well by the Pseudo-second-order equation, and the intraparticle diffusion was found to be the rate-controlling process of Au(III) adsorption. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis confirmed that Au(III) ions were adsorbed on the CPEIR via electrostatic attraction and chelating interaction, and subsequently the partial loaded Au(III) ions were reduced to elemental gold whereas the hydroxyl groups of CPEIR were oxidized to carbonyl groups.

Fabrication of Triethylenetetramine Terminal Hyperbranched Dendrimer-Like Polymer Modified Silica Gel and Its Prominent Recovery Toward Au (III)

To further increase the quantity and density of functional groups on adsorbent, terminal triethylenetetramine hyperbranched dendrimer-like polymer modified silica-gel (SG-TETA and SG-TETA2) was synthesized. The hyperbranched dendrimer-like polymer was successfully introduced onto silica gel and new cavities were formed, which was demonstrated by FTIR, SEM, and BET. The highest adsorption capacities of SG-TETA and SG-TETA2 obtained from Langmuir model toward Au(III) were 2.11, and 2.27 mmol g⁻¹, respectively, indicating that SG-TETA2 possessing more functional groups had a better adsorption ability. Moreover, the adsorbents combined with Au(III) ion through chelation and electrostatic attraction mechanism, after which reduction reactions for Au(III) ion loaded on adsorbents proceeded. SG-TETA2 had better adsorption selectivity than SG-TETA in removing Au(III) in Au-existed ion solution systems. SG-TETA2 had higher overall adsorption capacities compared to silica-gel-based hyperbranched polymers functionalized by diethylenetriamine. Therefore, the effective recovery makes SG-TETA2 a practical adsorbent in removing Au(III) ion from e-wastes and industrial effluents with much prospect.