Modified dry bean pod waste (Phaseolus vulgaris) as a biosorbent for fluorescein removal from aqueous media: Batch and fixed bed studies

Clay-moringa seedcake composite for removal of cationic and anionic dyes

The present study investigated the potential of a composite prepared from kaolinite clay and moringa seedcake in removing methylene blue (MB) and acid orange-7 (AO-7) dyes from aqueous solutions using batch and column tests. The composite was modified using different chemicals during the synthesis process, and the composites were characterised using different techniques such as FTIR, SEM-EDS and XRD. Characterisation showed the presence of actively charged functional groups and porous structure on the composites prepared. Batch tests were performed to assess the effect of operating conditions such as adsorbent dosage, pH, initial dye concentration and contact time. NaOH-modified and H2SO4/NaOH-modified composites demonstrated the highest adsorption capacities for AO-7 and MB, respectively, and were selected for subsequent studies. The adsorption process of dye was best fitted by the Freundlich isotherm and pseudo-second-order kinetic models suggesting that the sorption of MB and AO-7 onto the composites is a heterogeneous, multilayer chemical adsorption process. Long-term fixed-column tests were conducted with the composites to assess the impact of flow rate, bed depth and initial dye concentration on the dye removal efficiency. Optimum removals of 86 and 94%, respectively at pH 2 and pH 10 were obtained for AO-7 and MB in batch tests, along with adsorption capacities of 205.65 and 230.49 mg/g for AO-7 and MB. Results from the column tests were best explained by the Clark model and the Bed Depth-Service Time model. Competing ions impacted the removal of AO-7, while no significant effect was found for MB. The composites could be reused up to four cycles without significantly affecting the adsorption capacity. The present study thus shows the potential of the composite for removal of both the dyes.

Sustainable functionalized smectitic clay-based nano hydrated zirconium oxides for enhanced levofloxacin sorption from aqueous medium

In this study, the functionalized smectitic clay (SC)-based nanoscale hydrated zirconium oxide (ZrO-SC) was successfully synthesized and utilized for the adsorptive removal of levofloxacin (LVN) from an aqueous medium. The synthesized ZrO-SC and its precursors (SC and hydrated zirconium oxide (ZrO(OH)₂)) were extensively characterized using various analytical methods to get insight into their physicochemical properties. The results of stability investigation confirmed that ZrO-SC composite is chemically stable in strongly acidic medium. The surface measurements revealed that ZrO impregnation to SC resulted in an increased surface area (six-fold higher than SC). The maximum sorption capacity of ZrO-SC for LVN was 356.98 and 68.87 mg g^-1 during batch and continuous flow mode studies, respectively. The mechanistic studies of LVN sorption onto ZrO-SC revealed that various sorption mechanisms, such as interlayer complexation, π-π interaction, electrostatic interaction, and surface complexation were involved. The kinetic studies of ZrO-SC in the continuous-flow mode indicated the better applicability of Thomas model. However, the good fitting of Clark model suggested the multi-layer sorption of LVN. The cost estimation of the studied sorbents was also assessed. The obtained results indicate that ZrO-SC is capable of removing LVN and other emergent pollutants from water at a reasonable cost.

Enhancement of Fluorescence Mediated by Silver Nanoparticles: Implications for Cell Imaging

In this study, we report the surface enhanced fluorescence (SEF) of a biologically important organic dye, fluorescein (FL), by silver nanoparticles (Ag NPs) in an aqueous medium and its implications for human cell imaging. The as-synthesized Ag NPs were characterized by dynamic light scattering (DLS), zeta potential, transmission electron microscopy (TEM), and UV-vis absorption spectroscopic studies. The interaction and aggregation of FL dye with Ag NPs and a cationic surfactant, namely, cetyltrimethylammonium bromide (CTAB), were explored by UV-vis absorption and steady-state and time-resolved fluorescence spectroscopic methods. The distance-dependent fluorescence enhancement of FL due to Ag NPs in the solution was also theoretically correlated by three-dimensional finite-difference time-domain (3D-FDTD) simulation. The plasmonic coupling between neighboring NPs facilitated the augmentation of the local electric field, thereby producing various "hotspots" that influence the overall fluorescence of the emitter. J-type aggregates of FL in the presence of the CTAB micelles and Ag NP mixed solution were confirmed by electronic spectroscopy. The density functional theoretical (DFT) study revealed the electronic energy levels associated with different forms of FL dye in the aqueous solution. Most interestingly, the Ag NP/FL mixed system used in fluorescence imaging of human lung fibroblast cells (WI 38 cell line) showed a significantly stronger green fluorescence signal compared to that of FL after an incubation period of only 3 h. This study confirms that the Ag NP mediated SEF phenomenon of the FL dye is also manifested in the intracellular medium of human cells giving a brighter and more intense fluorescence image. The cell viability test after exposure to the Ag NP/FL mixed system was confirmed by the MTT assay method. The proposed study may have an implication as an alternate approach for human cell imaging with higher resolution and more contrast.

Efficient and selective removal of Pb2+ from aqueous solution by using an O- functionalized metal-organic framework

Lead (Pb) is one of the most widespread and highly toxic heavy metals in the environment. The design and synthesis of adsorbent materials for the selective and efficient removal of Pb²⁺ from aqueous solution has received much attention. Herein, the ligand 4,4'-azoxydibenzoic acid with the O^- group was elaborately selected to construct a novel Pr-based MOF for Pb²⁺ removal. The as-prepared MOF adsorbents with high stability exhibited ultra-high selectivity for Pb²⁺, even in the presence of various highly concentrated competitive ions (with the ratios from 1 : 5 to 1 : 50). Also, a high uptake capacity (560.26 mg g^-1) can be achieved for the MOF material, due to the availability of sufficient adsorption sites. The strong electrostatic attraction and coordination interaction between the numerous active O^- sites on MOF adsorbents and Pb²⁺ can account for the good adsorption performance for Pb²⁺, which was systematically verified by zeta potential, FT-IR and XPS studies.