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A dual functional material fulfilling twin objectives; simultaneous sensing and adsorption of Pb2+ ions in an aqueous medium.

An efficient and selective electrochemical sensor for the simultaneous detection of Hg2+ and Cd2+ ions in an aqueous medium is developed using bimetallic CuO@Au composite nanoparticles prepared using a novel graft copolymer, sodium alginate-g-poly(allylamine-co-acrylic acid), as a bio-template. The graft copolymer is synthesized via a solution-phase graft copolymerization technique. The same graft copolymer is also used for the preparation of monometallic Au and CuO composite nanoparticles. The developed polymer and composite nanoparticles are characterized using several characterization techniques. All three composite nanoparticles are globular in shape with an average particle size of 5.5 nm for the CuO NPs, 7.5 nm for the Au NPs and 13 nm for the CuO@Au NPs, and are well polydispersed. Metal ion sensing is carried out electrochemically using the linear sweep voltammetry (LSV) technique. The sensing ability of the bimetallic composite nanoparticles towards Hg2+ and Cd2+ ions is sufficient, with limit of detection values (LODs) of 0.99 nM and 0.78 nM for [Hg2+] and [Cd2+], respectively. The catalytic activities of the three metal NPs are evaluated by the reduction of 4-nitrophenol to 4-aminophenol. Here, the developed bimetallic composite nanoparticles also show excellent results superior to those of the other two monometallic composite nanoparticles, as well as those of some other reported materials, with a Kapp value of 0.556 min−1.

The binding of a small molecule to a protein through non-covalent interactions mainly depends on its size and electronic environment. Such binding can change the stability of the three dimensional protein structure which sometimes may destabilize it to accelerate or to inhibit protein aggregation. Coumarin is a widely used fluorescent dye with several biological applications. Different substituents (electron-donating and electron-withdrawing) at different positions of the coumarin moiety can influence its molecular volume, physical and chemical properties. Here we investigate the effect of such substituents of coumarin on the aggregation of a model protein, beta-lactoglobulin (β-lg) through a multi spectroscopic approach. It was observed that coumarin methyl ester with an 8-hydroxyl group can inhibit the β-lg aggregation. This compound can bind the hydrophobic site of beta-lactoglobulin and stabilize a particular protein conformation through the formation of hydrogen bond and hydrophobic interactions. Thus a properly designed compound can inhibit protein-protein interactions through protein-small molecule interactions. Other coumarinoid compounds also are effective in the prevention of thermal aggregation of β-lg.

A pH sensitive nanocomposite (NC) hydrogel based on katira gum-cl-poly(acrylic acid-co-N, N-dimethylacrylamide) incorporated bentonite (BT) nano clay (KG-cl-poly(AA-co-DMA)@BT abbreviated as KGNCH) is prepared by in-situ crosslinked co-polymerization technique using N, N′-methylene-bis-acrylamide (MBA) as crosslinker and potassium peroxodisulphate (KPS) as a free radical initiator. Various nanocomposite hydrogels (KGNCH-1 to KGNCH-4) are prepared by varying weight percentage of bentonite clay. The best one is selected (KGNCH-3) with respect to their highest swelling percentage in aqueous medium. The prepared KGNCH-3 is characterized by the FTIR, FESEM, XRD and EDS analysis and is used for the removal of cationic dyes [Methylene blue (MB), Crystal violet (CV) and Auramine-O (AO)] from their aqueous solutions. The adsorption of cationic dyes onto the KGNCH-3 is found to be pH dependent, the adsorption isotherm and kinetic data are best fitted with the Freundlich isotherm and pseudo second order kinetic model respectively and maximum adsorption capacity (qmax) is found to be at pH = 8.0 for MB, pH = 7.5 for CV and pH = 10 for AO. Calculation of different thermodynamic parameters shows the spontaneous and endothermic nature of the adsorption. The KGNCH-3 also exhibits excellent regeneration capacity at different pH using five cycle of adsorption-desorption studies. From the selectivity study the order of adsorption capacity of the KGNCH-3 is found to be MB > CV > AO.

A novel, highly anionic hydrogel, sulfated katira gum-crosslinked-poly(acrylic acid) (SKG-cl-PAA) was prepared by sulfation of katira gum-crosslinked-poly(acrylic acid) (KG-cl-PAA) hydrogel using chlorosulfonic acid (ClSO3H) in presence of anhydrous pyridine and formamide. Both the hydrogels KG-cl-PAA and SKG-cl-PAA were characterized by FTIR, XRD, and SEM studies. Swelling characteristics the hydrogels were studied and maximum equilibrium swelling ratio (ESR) was found to be 2376 for the SKG-cl-PAA and 2241 for KG-cl-PAA at pH 8.5 and at 70 °C. The hydrogels were used for the adsorption of V (IV) ions from aqueous solution. Adsorption dynamics, kinetics and isotherms for adsorption were also evaluated. Selectivity of the adsorption of V(IV) ion with other competitive metal ions are evaluated. Equilibrium adsorption data were well fitted with the Langmuir isotherm model and maximum monolayer adsorption capacity was found to be 500 mg g−1 for SKG-cl-PAA and 454 mg g−1 for KG-cl-PAA. Kinetic data were well explained by pseudo second order kinetic model. The negative value of ΔG0 confirmed that adsorption of V (IV) ions onto the SKG-cl-PAA was spontaneous and favourable. The positive value of ΔH0 indicated that the adsorption of V (IV) ion onto SKG-cl-PAA is endothermic in nature. Electrostatic attractions are mainly responsible for the adsorption.

A graft copolymer/nanosilica composite based on partially hydrolyzed dextrin-g-polymethyl acrylate and tetraethylorthosilicate was developed as an efficient adsorbent for the removal of toxic cationic and anionic dyes (methylene blue (MB), crystal violet (CV) and methyl orange (MO)) from their aqueous solutions. The biopolymer matrix acts as a novel template for nanosilica formation. The synthesized nanocomposite was characterized using FT-IR, 13C NMR, SEM, EDAX and XRD studies. The detail investigation of the adsorption dynamics, isotherms, kinetics and thermodynamics were studied for all the three dyes. The dye adsorption process onto the nanocomposite surface was controlled together by both pseudo-second-order and intraparticle diffusion model. Langmuir isotherm correlates well with adsorption equilibrium data. The adsorption capacity of cationic dyes onto the nanocomposite (qmax = 515.4 mg g−1 for MB and 383.1 mg g−1 for CV) was rationalized on the basis of strong electrostatic attraction and H-bonding. The spontaneous nature of adsorption was confirmed by the negative value of ΔGo. The preferential dye adsorption onto the nanocomposite was followed in the order MB > CV > MO. Further, desorption study affirmed that the synthesized nanocomposite has excellent regeneration capacity also.

A pH responsive hydrogel was prepared by grafting of a mixture of acrylic acid (AA) and N-vinyl imidazole (NVI) onto the katira gum (KG) by free radical co-polymerization technique using KPS as initiator and N,N′-methylene-bis-acrylamide (MBA) as a cross-linking agent in water medium. The pH sensitive hydrogel was characterized by FTIR, XRD and SEM analysis. Swelling studies with water were carried out at different pH in which hydrogel showed two maxima at pH = 4.5 and at pH = 9. The hydrogel containing poly-ampholytic network intelligently responds in the swelling behaviour at different pH. The so prepared hydrogel was used as an adsorbent for the removal of cationic [methylene blue (MB), methyl violet (MV)] and anionic [Tartrazine (TA), Carmoisine-A (CR-A)] dyes from their aqueous solutions. The adsorption showed pH dependence. The cationic dyes were adsorbed at pH = 7 and anionic dyes were adsorbed at pH = 2 for TA and pH = 3 for CR-A. The adsorption followed pseudo second order kinetics and Langmuir isotherm model. The amount of interaction between the hydrogel (adsorbent) and dye molecules (adsorbate) was studied using Gile’s model. The maximum adsorption capacity was found to be 331.5, 286.01, 273.5 and 201.53 mg/g for the MB, MV, CR-A and TA respectively. The cationic dyes were adsorbed strongly than anionic dyes by hydrogel. Various thermodynamics parameters such as Gibbs free energy change (ΔG°), enthalpy change (ΔH°), and entropy change (ΔS°) were also investigated. The removal of dyes by the hydrogel followed in the order MB > MV > CR-A > TA.

Herein, we report for the first time the highly sensitive and selective sensing of Th4+ in aqueous solution, using mushroom polysaccharide-based graft copolymer–CuO composite nanoparticles (TMP–CuO NPs), by optical, colorimetric and electrochemical methods. The graft copolymer was prepared in water by a solution phase radical polymerization technique using Tricholoma mushroom polysaccharide (TMP) with a mixture of N,N-dimethyl acrylamide (DMA) and acrylic acid (AA) in the presence of potassium peroxydisulphate (K2S2O8) as the radical initiator. The graft copolymer was characterized by 1H NMR and FTIR spectroscopy, and FESEM analysis. The TMP–CuO NPs were characterized by UV-visible and FTIR spectroscopy, XRD, EDAX, HRTEM, FESEM, and DLS analyses. The prepared TMP–CuO NPs have unique properties for the sensing of Th4+ in water medium, which were investigated by optical, colorimetric and electrochemical methods. The UV-absorption spectra showed a significant redshift of the localized surface plasmon (LSPR) band (λmax) with a gradual decrease in the absorption intensity upon each addition of Th4+ into the TMP–CuO NPs medium. Also, the reddish brown colour of the TMP–CuO NPs solution changed to colourless after the addition of a certain concentration of Th4+ ions. Electrochemical studies for the sensing of Th4+ by cyclic voltammetry showed a clear reduction peak at 1.009 V. The selective detection of Th4+ in water medium was also investigated in the presence of some environmentally relevant metal ions by using optical and colorimetric analysis. The morphological changes of TMP–CuO NPs in the presence of trace amounts of Th4+via the formation of the CuO–Th amalgam was confirmed by XPS, XRD, FTIR, FESEM, and EDAX analysis.

An eco-friendly synthetic procedure was used to prepare silver-gold bimetallic composite nanoparticles (Ag@AuCNPs)by using a mixture of aqueous solutions of silver nitrate, chloroauric acid and Ramaria botrytis mushroom polysaccharide (RBPS) at 80−85 °C in water medium. The synthesized Ag@AuCNPs were characterised by using UV–vis spectroscopy, X-ray diffraction (XRD) analysis, high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDAX) and X-ray photoelectron spectroscopy (XPS). The synthesized Ag@AuCNPs showed potential antioxidant activities towards DPPH radical, NO radical, hydrogen peroxide scavenging assays and ferric ion reducing assay. Besides that Ag@AuCNPs showed powerful antibacterial activity towards a gram negative bacterium Pseudo monasaeruginosa (MTCC No.-424). Catalytic activity of Ag@AuCNPs was tested by considering, 4-nitrophenol reduction as a model reaction in aqueous medium at room temperature using UV–vis spectroscopy. The catalyst concentration was varied to find out the optimum conditions. The rate constant was evaluated by using pseudo first order kinetic model. The prepared nanoparticles showed a good catalyst towards p-nitrophenol reduction, a good antioxidant and a moderate antibacterial agent towards Pseudomonas aeruginosa. These observations signify that such green method opens up new avenues in nano biotechnology for the synthesis of nanoparticles with intensive industrial and biomedical applications.