Krishnaiah Damarla

Diatoms are the most abundant photosynthetic microalgae found in all aquatic habitats. In the extant study, the spent biomass (after lipid extraction) of the centric marine diatom Thalassiosira lundiana CSIRCSMCRI 001 was subjected to acid digestion for the extraction of micro composite inorganic biosilica. Then, the resulting three-dimensional mesoporous biosilica material (diatomite) was used as a filler in polysulfone (PSF) membrane preparation by phase inversion. The fabricated PSF/diatomite composite membranes were characterized by SEM-EDX, TGA, and ATR-IR, and their performances were evaluated. The number of pores and pore size were increased on the membrane surface with increased diatomite in the composite membranes as compared to the control. The diatomite composite membranes had high hydrophilicity and thermal stability, lower surface roughness, and excellent water permeability. Membranes with high % diatomite, i.e., PSF/Dia_0.5, had a maximum water flux of 806.8 LMH (Liter/m²/h) at 20 psi operating pressure. High-diatomite content membranes also exhibited the highest rejection of BSA protein (98.5%) and rhodamine 6G (94.8%). Similarly, in biomedical rejection tests, the PSF/Dia_0.5 membrane exhibited a maximum rejection of ampicillin (75.84%) and neomycin (85.88%) at 20 Psi pressure. In conclusion, the mesoporous inorganic biosilica material was extracted from spent biomass of diatom and successfully used in filtration techniques. The results of this study could enhance the application of natural biogenic porous silica materials in wastewater treatment for water recycling.

Fabrication of lanthanum iron oxide nanosurface by a natural polysaccharide, carrageenan to develop nanocomposite useful for the removal of As³⁺ from water. Eco-friendly, easily separable, low cost CA-LaFeNPs could efficiently remove As³⁺.

Microemulsions (MEs) comprising choline dioctylsulfosuccinate [Cho][AOT], a biobased ionic liquid (IL) surfactant as an emulsifier, (R)-(+)-limonene (RL) as a nonpolar phase, and ethylene glycol (EG)/ethanolammonium formate (EOAF) as an organic solvent/low-viscosity IL polar component were constructed. Spontaneous aggregation of [Cho][AOT] was observed with a negative ΔH form using isothermal titration calorimetry. The aggregates of [Cho][AOT] in RL showed a critical micellar concentration (cmc) of ∼5.49 mM, EG (cmc ∼3.99 mM), and EOAF (cmc ∼1.56 mM), and these are further characterized by various techniques. These novel IL-based MEs have been used as nanoreactors for the sustainable synthesis of uniform nanosized metal–organic frameworks (N-MOFs), such as MIL-53(Al), HKUST-1, UIO-66-NH₂, and ZIF-8, with a precise control over size and morphology at room temperature. Characterization of N-MOFs has been performed using scanning electron microscopy, powder X-ray diffraction, and Fourier transform infrared spectroscopy. The synthesized N-MOFs have been used to prepare stable and uniform thin film nanocomposite nanofiltration membranes, suitable for desalination of brackish water with excellent flux (31.8 LMH/bar) and rejection (99.0%) of divalent salts.

In this study, a water-miscible ‘classic’ ionic liquid (IL), 1-ethyl-3-methylimidazoliumacetate ([EMIM][Ac]), has been used for lipid extraction from marine diatoms Thalassiosira lundiana CSIR-CSMCRI 001 by following a non-polar solvent partition method. The composition of lipid was determined using gas chromatography-mass spectrometry (GC-MS). In total, 91.4 mg g⁻¹ (dry wt) of lipid was produced, out of which the percentage of docosahexaenoic acids (DHA), myristic acid, palmitic acid, and arachidonic acid was 19.6%, 15.1%, 11.2%, and 10.4%, respectively. The IL-inseparable residual waste solution was directly used to generate green fluorescent carbon dots (FCDs) by constructing a colloidal solution with the help of a surface-active IL, choline dioctyl sulfosuccinate ([Cho][AOT]). The stability of colloidal FCDs was examined using FTIR, FT-NMR, and Raman spectroscopy. FCDs were extracted from the colloidal solutions via the demicellization process and characterized using HR-TEM (2 to 5 nm) and PXRD techniques. The optical properties of colloidal FCDs were measured using UV-Vis and fluorescence spectroscopy and showed a wide range of emission (λ_{460 nm} to λ_{590 nm}). Such FCD stabilized colloidal solutions could be effectively used in fluorescence imaging of yeast cells, thus making the biorefinery approach more sustainable.

A novel colloidal system comprising choline oleate in deep eutectic solvent (DES: choline chloride–ethylene glycol) is developed and utilized for in situ generation and stabilization of nanosized (1 to 3 nm) N-doped oxygenated, crystalline CDs via dissolution of gelatin. Self-assembly of choline oleate in DES has been characterized using surface tension, DLS and 2D NMR NOESY methods. The stability of colloidal CDs was examined using FTIR and Raman spectroscopy. TEM, HR-TEM, and PXRD techniques have been used to characterize CDs. Optical properties have been investigated using UV, fluorescence and time-resolved photoluminescence (TrPL) spectroscopy. Colloidal CDs possess bright blue to red luminescence and short fluorescence lifetime with exceptionally high quantum yield (ca. 82%), and exhibited excellent biocompatibility as bioimaging agents towards labeling of bacterial cells (both Gram positive and Gram negative), thus indicating a potential benign system for disease detection, drug delivery and light harvesting applications.

This article outlines a sustainable method towards the synthesis of advanced materials such as core/shell Quantum Dots (QDs) and their in situ stabilization using microemulsions (MEs). QDs are versatile materials which show unusual optical properties. We have constructed MEs consisting of an Ionic Liquid (IL) based surfactant i.e. choline dioctylsulfosuccinate, [Cho][AOT] as an emulsifier, toluene as a nonpolar phase and water as a polar phase. The system forms a large single-phase region in the phase diagram without any co-surfactant. Spontaneous formation of micelles has been observed and studied through tensiometry and fluorescence and isothermal titration calorimetry (ITC). The exceptional swelling behaviour of the MEs was studied using Dynamic Light Scattering (DLS) and small angle neutron scattering (SANS). In ME droplets, i.e. Reverse Micelles (RMs), we successfully synthesized spherical core/shell QDs (size ∼3 to ∼6 nm) with precise control over the size and morphology. The QDs have been characterized using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Powder X-ray Diffraction (PXRD). QDs stabilized in MEs exhibited excellent optical properties and can be suitably used as light harvesting materials for diverse applications.

An efficient and novel protocol for pyrazole synthesis has been developed by using fluoroboric acid as the acid catalyst. Simple and easily available 1,3-diketone and hydrazine derivatives are taken as the substrates for this purpose. The reaction entails mild reaction conditions and produces desired pyrazoles in good to excellent yields. Easy accessibility, easy handling, broad substrate scope, evading metal catalyst and economic viability make this protocol advantageous to most of the previously reported literature.

Surface active ionic liquid (SAIL) induced hydrogelation, in the absence of additives, is important considering the properties of soft-hydrogels that can be utilized in different applications. The present study is concerned with the phase behavior and hydrogelation of a SAIL, 1-hexadecyl-3-methylimidazolium p-toluenesulfonate, [C₁₆mim][PTS]. The obtained information about the phase behavior along with the surfactant like behavior of the SAIL was exploited for effective exfoliation of graphene-flakes from graphite in aqueous medium that remain stable for at least one month. Thus the obtained dispersion of graphene-flakes was subsequently hydrogelated exploiting the observations made from the phase behavior of the SAIL, via entanglement of long worm-like micelles of the SAIL formed at higher concentration. The obtained graphene-flake based hydrogels were found to be equally stable as compared to the blank hydrogel as well as against centrifugation. The low melting point of hydrogel facilitates the extraction of graphene-flakes from the hydrogel matrix by heating and diluting the gel and there is no sign of agglomeration in the extracted graphene-flakes even if the extraction is carried out after a period of three months. The present work is an exemplary study on exfoliation, hydrogelation and extraction of graphene-flakes from a hydrogel, when required, using a SAIL and is expected to provide a new platform for utilization of SAILs for efficient graphene exfoliation and subsequent preparation of functional materials.

Here an environmentally friendly process has been developed for the synthesis of pyrazole and its derivatives through cycloaddition‐iodination‐Suzuki type reaction by the use of lithium perchlorate as a Lewis acid catalyst. The synthetic pathway involves the synthesis of pyrazoles with various electron donating and electron withdrawing functional groups containing hydrazines and 1,3‐diketones (70‐95% yields); then one step formation of 4‐iodo‐pyrazoles (59% yield) followed by modification via palladium catalyzed Suzuki‐Miyaura cross coupling reaction to obtain the desired biaryls substituted pyrazoles under mild reaction conditions with high efficiency and product purity (53‐70% yields). The biological activity was evaluated through in vitro analysis towards the antimicrobial activities against the growth of Staphylococcus Aureus (for Gram positive) and Pseudomonas Aeruginosa (for Gram negative) with minimum inhibitory concentration (MIC) values ranging from 225 to 850 μg/ml. Molecular docking studies of the compounds into the active site of thymidylate kinase receptor of Pseudomonas Aeruginosa PAO1 revealed notable information on the probable binding interaction.