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Here we demonstrate, chitosan−sodium alginate based bionanomaterial scaffolds (BMS) with in situ functionalized alumina hydroxide forming scaffold like structure and its application in removal of fluoride (F − ), chromium (Cr(VI)), and dye from water. Further, the bionanomaterial scaffold surface was modified with silver nanoparticles (Ag NPs) to enhance the shelf life of the bionanomaterial scaffold (BMS). This Ag NP-coated BMS exhibited as high as ∼168 and ∼60 mg g −1 fluoride uptake efficiency at pH 4 and 7, respectively. Experiments were also carried out to check the chromium removal efficiency, and results showed ∼8.5 mg g −1 of Cr(VI) uptake capacity was achieved from contaminated water at room temperature. Further, over 99% Reactive Black 5 (RB-5) removal was achieved with remarkable surface regeneration properties. To test the end user affordability, the bionanomaterial was packed both in a columnlike filter cake and tea-baglike pouches in a series of experiments. This study demonstrates a viable and sustainable solution for removal of fluoride, chromium, and color contaminants from contaminated water streams.

A sunlight induced simple green route has been developed for the synthesis of polyacrylate functionalized gold nanoparticles (PAA-AuNPs), in which poly(acrylic acid) functions as a reducing as well as stabilizing agent. This material has been characterized on the basis of spectroscopic and microscopic studies; it exhibited selective colorimetric detection of Al in aqueous media, and the Al induced aggregated PAA-AuNPs exhibited detection of F with sharp color change and high selectivity and sensitivity out of a large number of metal ions and anions tested. The mechanistic study revealed that, for Al, the color change is due to a shift of the SPR band because of the Al induced aggregation of PAA-AuNPs, whereas for F, the reverse color change (blue to red) with return of the SPR band to its original position is due to dispersion of aggregated PAA-AuNPs, as F removes Al from the aggregated species by complex formation. Only concentration-dependent fluoride ion can prevent Al from aggregating PAA-AuNPs. The method is successfully used for the detection of F in water collected from various sources by the spiking method, in toothpastes of different brands by the direct method. The solid Al-PAA-AuNPs were isolated, adsorbed on ZIF@8 (zeolitic imidazolate framework) and on a cotton strip, and applied as solid sensing material for detection of F in aqueous media.

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A citrate stabilised silver nanoparticle (Ci-AgNP) based solvatochromic sensor, which functions as a highly selective and sensitive colorimetric probe for 1,4-dioxane in aqueous media is reported. The surfaces of the AgNPs generate reactive oxygen species, which promote the degradation of 1,4-dioxane assembled in the vicinity of the nanoparticle surfaces through charge transfer interactions. During this process, Ag(0) is oxidised to Ag(+) and the yellow colour of the solution turns to colourless. The sensor was used for the estimation of 1,4-dioxane in ground water and also 1,4-dioxane vapour diffused in aqueous media.

An oxacalix[4]arene-Ce(iii) complex viz. L–Ce(III) has been introduced for the selective detection of As(v) and Cr(vi) oxyanions in aqueous medium.

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