Industrial modernization causes severe contamination of water resources due to which the presence of organic dyes poses a great threat to human life. To address this, we have synthesized a hydrogel GSCg using graphene oxide (GO), sulphonatocalix[4]arene (SC4a), and l -Cys by heating at 90 °C for 30 min and characterized by analytic, spectroscopy, and microscopy techniques. The GSCg possessing porous structure and adsorbs all three types of dyes, viz., eosin yellow (anionic), neutral red, and methylene blue (cationic), as shown by scanning electron microscopy, and the adsorption kinetics are addressed. The dye adsorbed by the gel (dye@GSCg) has been degraded by the treatment of Cu 2+ /N 2 H 4 , which regenerates the gel. The regenerated gel has been demonstrated for further cycles of adsorption followed by degradation. Alternatively, the degradation of the organic dyes was also demonstrated by an in situ approach by taking GO, SC4a, l -Cys, and the organic dye together and subjecting the mixture to hydrothermal conditions and the process leaves out free gel (GSC g d ). This was proven to be true in the case of each of the 12 dyes studied individually and also for their mixture, supporting that this methodology can be employed for large scale purification of contaminated water with high efficiency. GSC g d was repeatedly used for the adsorption and degradation (with the use of Cu 2+ /N 2 H 4 ) cycles wherein the gel does not lose its adsorption capability even after several cycles. Therefore, {GO···SC4a} hybrid is a smart, sustainable, and reusable material suitable for the purification of water contaminated with industrial organic dye effluents.
A naphthalimide-based fluorophore has been conjugated by an octyl chain on one side and an ethylenediamine ("en") moiety on the other to result in a conjugate (L 1 ) that was adapted to exhibit selective ion sensing. Since L 1 is not a receptor for metal ions in water or in organic solvents, this has been introduced into the self-assembly formed by the surfactant, i.e., sodium dodecyl sulfate (SDS), and its ion sensing was studied by varying the concentration of the SDS since it is known to form premicellar as well as micellar assemblies. Thus, the L 1 was successfully converted to a specific, selective, and sustainable chemo-receptor system for Al 3+ and Zn 2+ with the support of such assemblies of SDS. The selectivity was among three trivalent and eight divalent ions studied. The ion recognition ability was dependent on the nature of the assembly of SDS formed and is efficient in the premicellar media. Both the Al 3+ and Zn 2+ were differentially recognized just by tuning the SDS concentration. The results were ratified by comparing with several control experiments. The excited-state lifetime measurements and the size of these assemblies measured by dynamic light scattering (DLS) reveal that at >4 mM SDS concentration (critical micellar concentration is 8 mM) the probe L 1 is not accessible for any of the metal ions studied. The two other derivatives possessing a shorter (propyl, L 2 ) and a longer (dodecyl, L 3 ) alkyl chain showed that the L 1 with an octyl chain performs much better at all the premicellar SDS concentrations. The Zn 2+ -bound assembly of L 1 in 4 mM SDS was demonstrated for sensing the dipicolinic acid (DPA) which happens to be an endospore component of anthrax bacteria. This study was extended to several other carboxylic acid derivatives which would act as control molecular systems. Even in the DPA sensing, the assemblies possessing an octyl derivative stand out when compared to the propyl or the dodecyl derivatives.
This paper deals with the synthesis of a protein–inorganic hybrid hydrogel and its derived materials, including aerogel and sheet, and the demonstration of their application potentials. For this, a common and abundant protein, bovine serum albumin (BSA), and a copper salt were used in order to prepare a hydrogel by cross-linking the protein molecules using epichlorohydrin and embedding Cu2+ ions to give BSA_Cuhydrogel (1). When this material was lyophilized, it resulted in the product powder BSA_Cuaerogel (2); however, when dried under vacuum, it yielded a blue sheet material, BSA_Cusheet (3). All three of these biomaterials were characterized by spectroscopy and microscopy and further studied for three different applications, and the data were compared in order to establish the material vs property/activity relationship. The applications include (i) adsorption of organic dyes, (ii) reductive degradation of these dyes, and (iii) the reductive transformation of nitroaromatic compounds. The study revealed the efficient adsorption of the anionic and neutral dyes, while the adsorption of the cationic dye was much lower. The adsorption capacities (in mg/g) of Congo red followed the trend BSA_Cuaerogel (367 ± 6) > BSA_Cuhydrogel (274 ± 4) > BSA_Cusheet (204 ± 3). The comparison of the rate of reductive degradation of Congo red and methylene blue follows the same trend as that of the adsorption of the dyes. The reductive degradation was demonstrated for six cycles by reusing the recovered catalyst after every cycle. More than half a dozen nitroaromatics were studied for their reduction using BSA_Cuaerogel. In the case of p-nitrophenol, the rate of reduction follows the trend 2 > 1 > 3. Thus, this paper deals with a methodology to synthesize both a robust hydrogel incorporating metal ions and other derived protein-based biomaterials, viz., an aerogel and sheet, and a comparison of their activity toward the adsorption and degradation of dyes and nitroaromatics.
A fluorescent naphthalimide conjugate of calix[4]arene ( L 1 ) has been synthesized and characterized. The selective and efficient detection of trinitrophenol (TNP) by L 1 among nine other different nitroaromatic compounds was demonstrated using absorption and fluorescence spectroscopy. The minimum detection limit is 29 nM, which is the lowest reported so far by any conjugate of calixarene toward TNP. The fluorescence quenching is associated with a high Stern–Volmer constant of 3.3 ± 0.4 × 10 5 M –1 . The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data revealed a network structure with pores having a weighted average size of 0.66 ± 0.08 μm for L 1 . When incubated with TNP, the pores were filled with fibril structures, as supported by both SEM and TEM data. In order to demonstrate the real time applications, the L 1 has been coated onto a Whatman filter paper and the imprint of TNP contaminated thumb has been detected upon physical contact. The 1 HNMR titration and the studies carried out using the control molecule support the necessity of both the naphthalimide moiety and the calixarene platform for sensing. In order to mend L 1 as a reversible sensor for TNP, the same is incorporated into carrageenan beads ( L 1 @ C b ) and the reversible sensing has been shown for three cycles by reusing the same material upon recovery followed by washing it. The solid-state detection of TNP has also been demonstrated using the lyophilized L 1 @ C b bead powder. The fluorescence intensity of L 1 was quenched upon addition of solid TNP to the lyophilized bead powder of L 1 @ C b as studied by fluorescence microscopy. The computational studies show that one of the arms of the calixarene takes a bent conformation, and the 1:1 TNP complex of L 1 is stabilized by exhibiting differential extents of hydrogen bonding interactions with the two arms owing to their conformational difference. The result of such complexation was already felt through the shifts observed in the experimentally measured 1 HNMR spectra.
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