Membrane based optical chemical sensor (optode) for Cd(II) was developed by the immobilization of a dye 1-(2-Pyridylazo)-2-Napthol (PAN) in the Tri-(2-Ethylhexyl) Phosphate (TEHP) plasticized Cellulose Triacetate (CTA) matrix. Various combinations of PAN immobilized in the cellulose triacetate CTA and Polystyrene (PS) matrices plasticized with Tri-(2-Ethylhexyl) Phosphate TEHP, 2-Nitrophenyl Octyl Ether (NPOE) and Dioctyl Phthalate (DOP) were studied to arrive a suitable composition and found that the optode does not require any extractant to produce a distinct colour change on complexation with Cd(II). On sorption of Cd(II) in the optode matrix, PAN changes color of the optode from golden yellow to violet red having a maximum absorbance (l_max = 553 nm) within 150 min of total equilibration time at pH = 7.5. The optode developed in the present work was studied for its analytical application for Cd(II) in the aqueous samples by spectrophotometry and as well as Flame Atomic Absorption Spectrophotometry (FAAS). This preconcentrated optode showed a linear response by UV-visible spectrophotometry at λ_max = 553 nm over a concentration range of 10 ng/mL^–1 to 500 ng/mL^–1 of Cd(II) ions. Where as the aqueous solutions was also subjected to FAAS before and after equilibration of the optode and found to be linear in the concentration range of 250 ng/mL^–1 to 5000 ng/mL^–1 of Cd(II) ions. The optode found to be reversible and can be desorbed by equilibrating it with 0.01 mol/L^–1 HNO₃. The applicability of the developed optode in real samples was studied by determining cadmium in the natural waters spiked with a known amount of Cd(II) ions

A B S T R A C TBiochars (BWBC 300, BWBC 500 and BWBC 700) derived from buffalo weed (Ambrosia trifida L. var. trifida) at different pyrolysis temperatures of 300, 500 and 700˚C were investigated for the removal of Cd(II) and Pb(II) ions from aqueous solutions. The physicochemical properties of the biochars were studied using FTIR, scanning electron microscopy (SEM), X-ray diffraction, Brunauer, Emmett and Teller surface area, cation exchange capacity and energy dispersive X-ray analysis. The adsorption at solution pH = 5 could be well described by Freundlich model for Cd(II) and Pb(II) in their single and mixed system with R 2 P 0.95. The maximum adsorption capacities of the biochar BWBC 700 from the Langmuir equation were found to be 11.63 and 333.33 mg g À1 for Cd(II) and Pb(II), respectively. Pseudo-second-order kinetic model was fitted well in describing the adsorption kinetics of Cd(II) and Pb(II) onto the biochar BWBC 700. About 0.02 mol L À1 disodium salt of EDTA was able to desorb Cd(II) and Pb(II) from the biochar BWBC 700 with an approximately 63.5% and 96.8% desorption yield, respectively. Ion exchange and surface complexation found to be the main mechanisms involved in the adsorption process. The developed biochar derived from Ambrosia trifida L. var. trifida found to be a low cost adsorbent and could be used for the effective removal of Cd(II) and Pb(II) in waste waters.

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Commonly available herbal leaves powder namely Achyranthes aspera (uthareni) and Phyllanthus niruri (Nela usiri) are used as biosorbents for the removal of malathion in the present investigation. The efficiency of the biosorbents is tested for the determination of malathion using batch experiments under controlled conditions as a function of pH, contact time, initial malation concentration and the optimization amount of biosorbents. The quantification of malathion in aqueous samples, before and after equilibration with biosorbents is carried out by existing spectrophotometric method based on the oxidation of malathion with excess N-bromosuccinimide (NBS) and Rhodamine B at ( max = 550 nm) is used for the unconsumed NBS. The biosorption capacities are found to be pH dependent. The maximum adsorption is noticed at pH = 6 with a contact time of 120 minutes. Biosorption equilibrium isotherms are plotted for malathion uptake capacity (Q e ) against residual malathion concentration (C e ) in solution. The Q e versus C e sorption isotherms relationship is expressed mathematically by Langmuir and Freundlich models. The removal of malathion using biosorbents Achyranthes aspera (uthareni) and Phyllanthus niruri (Nela usiri) from spiked river water samples are found to be 94% and 96% respectively. The developed eco-friendly potential biosorbents indicate that the present method can be successfully applied for the quantitative determination and removal of malathion from real water samples.

Biomimetic potentiometric sensor for the determination of diethyl chlorophosphate was developed using imprinted polymer inclusion membrane strategy. Semi-covalent imprinted and non-imprinted polymer particles were synthesized and found that non-imprinted polymer inclusion membrane was unstable in contrast to imprinted polymer inclusion membrane in determination and quantification of diethyl chlorophosphate. Imprinted polymer inclusion membrane based sensor found to be pH dependant with a 5 min equilibrium response time at pH = 10.5 and linearly responds to diethyl chlorophosphate in the concentration range of 1 × 10 -9 to 1 × 10 -4 and 1 × 10 -4 to 1 × 10 -2 mol·L -1 with a detection limit of 1 × 10 -9 mol·L -1 (0.17 ppb). It was found that diethyl chlorophosphate response was selective against various selected interferents like pinacolyl methylphosphonate, dimethyl methyl phosphonate, methylphosphonic acid, Phorate and 2, 4-D. The developed sensor was found to be stable for 3 months and can be reusable more than 30 times without loosing sensitivity. The developed sensor was successfully applied for the determination of diethyl chlorophosphate in natural waters.