Mahesh Padaki

Preparation and Characterization of Chitosan Thin Films on Mixed-Matrix Membranes for Complete Removal of Chromium.

Herein we present a new approach for the complete removal of CrVI species, through reduction of CrVI to CrIII, followed by adsorption of CrIII. Reduction of chromium from water is an important challenge, as CrIV is one of the most toxic substances emitted from industrial processes. Chitosan (CS) thin films were developed on plain polysulfone (PSf) and PSf/TiO2 membrane substrates by a temperature-induced technique using polyvinyl alcohol as a binder. Structure property elucidation was carried out by X-ray diffraction, microscopy, spectroscopy, contact angle measurement, and water uptake studies. The increase in hydrophilicity followed the order: PSf < PSf/TiO2 < PSf/TiO2/CS membranes. Use of this thin-film composite membrane for chromium removal was investigated with regards to the effects of light and pH. The observations reveal 100 % reduction of CrVI to CrIII through electrons and protons donated from OH and NH2 groups of the CS layer; the reduced CrIII species are adsorbed onto the CS layer via complexation to give chromium-free water.

Novel modified poly vinyl chloride blend membranes for removal of heavy metals from mixed ion feed sample

Herein, an attempt has been made to prepare a novel membrane with good efficiency for removal of heavy metal ions namely lead (Pb), cadmium (Cd) and chromium (Cr). 4-amino benzoic acid (ABA) was covalently grafted onto the poly vinyl chloride (PVC) backbone by CN bond to enhance the hydrophilicity. 1H NMR and ATR-IR spectroscopy analysis confirmed the chemical modification of PVC. Further the modified polymer was blended in different compositions with polysulfone (PSf) for optimization. Morphological changes that occurred in blend membranes, due to the incorporation of modified PVC was studied by AFM and SEM techniques. The effect on hydrophilicity and performance of blends owing to incorporation of modified PVC was evaluated by water uptake, contact angle and flux studies. The density of functional groups in blends was analyzed by its ion-exchange capacity. Batch wise filtration of metal ions was carried out and the effect of pressure, feed pH and interference of ions was thoroughly investigated. Essentially, 100% rejection was obtained for all the metal ions in acidic pH with a productivity of 2.56l/m2h. The results were correlated with the results of commercially available NF 270 membrane under the same operating conditions.

Synthesis and characterization of novel sulfanilic acid–polyvinyl chloride–polysulfone blend membranes for metal ion rejection

Near-complete removal of heavy metals, namely Cd(II), Cr(VI) and Pb(II), has been attempted by a membrane purification process using a blend of modified polyvinyl chloride (PVC) and polysulfone (PSf), prepared by the diffusion induced phase separation (DIPS) method. The prepared novel material was characterized by NMR, ATR-IR spectroscopy and DSC. The sulphonyl groups incorporated into PVC enhance the hydrophilicity and are substantiated by water uptake, contact angle (CA) and flux studies. The obtained properties of the blend membrane like increased surface roughness and porosity are observed from AFM and SEM analysis. An enhanced rejection of ∼95% which is about 1.15, 1.41 and 1.37 times better than the commercially available NF 270 membrane was observed, for Cd(II), Cr(VI) and Pb(II) respectively. The work was further extended to study the antifouling property and the interference of other existing metal ions on the performance. An improved antifouling property with 98.5% rejection for bovine serum albumin (BSA) and a 75.6% flux recovery ratio (FRR) was achieved. The study gains significance in exploring the incorporation of sulphonyl groups in to polymers, to enhance membrane performance.

Eco-friendly membrane process and product development for complete elimination of chromium toxicity in wastewater

Hydrophobic polysulphone (PSf) was reformed into a hydrophilic polymer by sulphonation (via electrophilic substitution) and was subsequently made into a composite by incorporating nano titania to reduce Cr (VI) in the concentrated feed to Cr (III), thus eliminating the hazards of Cr (VI). The modified polymer and its composites were characterized by spectroscopic and microscopic techniques. The composite membranes exhibited enhanced hydrophilicity and flux and were evaluated for the rejection of chromium. The effect of pH and interference of counter ions towards rejection was studied. The charges fixed on the surface of the membrane due to titania, support ionic interactions and facilitated the rejection process. Essentially, rejection of up to 98% was achieved. The innovation of using a bifunctional membrane for the rejection of Cr (VI) together with the removal of its toxicity by photocatalytic reduction, leading to the potential recovery of Cr (III), highlight the uniqueness of this work.

(E)-1-(4-Fluorophenyl)ethan-1-one semicarbazone

In the title compound, C9H10FN3O, the semicarbazone group is nearly planar, with the maximum deviation of 0.044 (1) Å for one of the N atoms. The mean plane of semicarbazone group forms a dihedral angle of 30.94 (4)° with the benzene ring. The molecules are linked into a supramolecular chain by N—H⋯O hydrogen bonds formed along the c axis. The crystal structure is further stabilized by weak intermolucular C—H⋯π interactions; the closest C⋯Cg contact is 3.6505 (11) Å.

6-(4-Bromophenyl)-2-ethoxy-4-(2,4,5-trimethoxyphenyl)nicotinonitrile

In the asymmetric unit of the title nicotinonitrile derivative, C23H21BrN2O4, there are two non-planar independent molecules. The central pyridine ring makes dihedral angles of 9.05 (7) and 77.06 (7)°, respectively, with the 4-bromophenyl and 2,4,6-trimethoxyphenyl rings in one molecule, whereas the corresponding values are 5.96 (7) and 82.37 (7)° in the other. All the three methoxy groups are essentially in the plane of the attached benzene ring [C—O—C—C angles = 2.99 (19), 4.8 (2) and −6.2 (2)° in one molecule, and 2.69 (18), 176.73 (15) and 1.3 (2)° in the other]. The ethoxy group is slightly twisted in one molecule [C—C—O—C = 173.84 (12)°], whereas it is coplanar with the pyridine ring in the other [C—C—O—C = −177.23 (13)°]. Weak intramolecular C—H⋯N interactions generate S(5) ring motifs. In the crystal structure, the molecules are linked by weak intermolecular C—H⋯N and C—H⋯O interactions into a supramolecular three-dimensional network in such a way that the nicotinonitrile units of neighboring molecules are stacked in an antiparallel manner along the c axis. The crystal is further stabilized by C—H⋯π interactions.