Harnessing the Chemical Functionality of Metal-Organic Frameworks Toward Removal of Aqueous Pollutants.

Wastewater treatment has been bestowed with a plethora of materials; among them, metal-organic frameworks (MOFs) are one such kind with exceptional properties. Besides their application in gas adsorption and storage, they are applied in many fields. In orientation toward wastewater treatment, MOFs have been and are being successfully employed to capture a variety of aqueous pollutants, including both organic and inorganic ones. This review sheds light on the postsynthetic modifications (PSMs) performed over MOFs to adsorb and degrade recalcitrant. Modifications performed on the metal nodes and the linkers have been explained with reference to some widely used chemical modifications like alkylation, amination, thiol addition, tandem modifications, and coordinate modifications. The boost in pollutant removal efficacy, reaction rate, adsorption capacity, and selectivity for the modified MOFs is highlighted. The rationale and the robustness of micromotor MOFs, i.e., MOFs with motor activity, and their potential application in the capture of toxic pollutants are also presented for readers. This review also discusses the challenges and future recommendations to be considered in performing PSM over a MOF concerning wastewater treatment.

Performance analysis of hydrochar derived from catalytic hydrothermal carbonization in the multicomponent emerging contaminant systems: Selectivity and modeling studies.

In this work, as an alternative to pyrochar, catalytic hydrothermal carbonization has been employed to synthesize hydrochar to eliminate emerging contaminants in multicomponent systems. The hydrochar has been synthesized using a single step catalytic hydrothermal carbonization at low temperature (200 °C) without any secondary activation with high specific surface area and very good adsorption efficiency for the removal of emerging contaminants. The synthesized hydrochar (HC200) was characterized using various analytical techniques and found to have porous structure with 114.84 m2.g-1 of specific surface area and also contained various oxygen-containing functionalities. The maximum adsorption efficiencies of 92.4 %, 85.4 %, and 82 % were obtained for ibuprofen, sulfamethoxazole, and bisphenol A, respectively. Humic acid, a naturally occurring organic compound had a negligible effect on the adsorption of the selected contaminants. The hydrochar's selectivity towards the emerging contaminants in binary and ternary multicomponent systems was in the order of ibuprofen > sulfamethoxazole > bisphenol A.

UiO-66 octahedrons for adsorptive removal of direct blue-6: process optimization, interaction mechanism, and phytotoxicity assessment.

The materials for water treatment have been evolving in multitude of dimensions, indicating the importance of water reuse and increasing level of water pollution around the globe. Among the various materials that are utilized in wastewater treatment, the material that has attracted the research community for the past decades is the metal organic framework (MOF). In this work one of the water stable and microporous MOF, UiO-66, and its aminated version has been employed to adsorb an anionic azo dye, direct blue-6 (DB-6), from the aqueous matrix. Performance of both the MOFs was compared to know the efficiency under varying solution conditions. The optimized parameters for DB-6 adsorption by UiO-66 was performed using response surface methodology. This numerical optimization was further extended with canonical and ridge analysis. Under optimal conditions, the materials were exhibiting a good adsorption capacity of 754.4 mg/g. The materials were analyzed in terms of morphology, crystallinity, thermal stability, and surface area using instruments like X-ray diffraction, electron microscopy, thermogravimetric analysis, and BET surface area analysis. The mechanism of interaction between UiO-66 and DB-6 molecule was elucidated with the help of XPS analysis which helps to know the main interacting group of UiO-66. This study was concluded with a phytotoxicity analysis of DB-6 and the antioxidant system of Vigna radiata assessed using pre and post adsorbed water.

Sequestration and toxicological assessment of emerging contaminants with polypyrrole modified carboxymethyl cellulose (CMC/PPY): Case of ibuprofen pharmaceutical drug.

Ibuprofen (IBU) is a non-steroidal anti-inflammatory drug released into water bodies causing toxic biological effects on living organisms. The current study aims to eliminate IBU from aqueous solutions by a novel carboxymethylcellulose/polypyrrole (CMC/PPY) composite with high removal efficiency. Pyrrole was polymerized to polypyrrole whose average size was about 20 nm on the CMC surface. The maximum removal percentage of IBU by CMC/PPY composite was optimized at initial concentration 10 mg/L, dosage 0.02 g, and pH 7 with adsorption capacity of 72.30 (mg/g) and removal of 83.17 %. IBU adsorption onto CMC/PPY theoretically fits into the Langmuir isotherm and Elovich-kinetic models. Fish and Phytotoxicity assessment were performed with zebrafish and seeds of Vigna mungo (VM) and Vigna radiata (VR). The toxicity study reveals that before adsorption, IBU shows high toxicity towards the zebrafish mortality (33 %), growth inhibition (58.52 % for VM, 60.84 % for VR), and germination (86.66 % for VM and 90 % for VR). As CMC/PPY adsorbs IBU, toxicity drastically decreases. Before adsorption, LC50 was 233.02 mg/L. After adsorption, the LC50 increases to 2325.07 mg/L as IBU molecules get adsorbed by CMC/PPY. These findings show the feasibility of preparing CMC/PPY composite to effectively remove pharmaceutical pollutant IBU from aqueous solutions with their toxicological assessment.

Activated carbon-chitosan based adsorbent for the efficient removal of the emerging contaminant diclofenac: Synthesis, characterization and phytotoxicity studies.

The rise in pharmaceutical pollutants due to their unregulated discharge in pharmaceutical wastewater has landed them as emerging contaminants that would gradually affect the aquatic ecosystem and human life. The current study emphasizes the adsorptive elimination of one such emerging pharmaceutical pollutant, i.e., Diclofenac (DIF), using a synthesized adsorbent vis. Activated carbon-chitosan beads (ACCB). The morphological and physicochemical properties of the prepared adsorbent, ACCB and its interaction with the DIF species were investigated. Process parameters influencing the adsorptive interactions between ACCB and DIF were optimised. DIF was efficiently adsorbed at optimised initial DIF pH of 6.0 and ACCB dosage of 1.5 mg/mL at an incubation temperature of 40 °C. Freundlich isotherm model showed the best fit (R2 = 0.98) with the experimental data to conclude that the adsorbent surface is heterogenous, promoting multilayer adsorption. As depicted from the Langmuir isotherm model, the maximum theoretical adsorption capacity was 99.29 mg/g. The seed toxicity assay confirmed the efficacy of ACCB in the adsorptive removal of DIF species from aqueous setups, making the post-treated solution fit enough for seed germination.

Effective removal of pharmaceutical contaminants ibuprofen and sulfamethoxazole from water by Corn starch nanoparticles: An ecotoxicological assessment.

Pharmaceutical pollutants, a vital type of emerging contaminants, have attracted researchers to study their removal from water. In this research, Corn starch nanoparticles (CSNP) have been synthesized and characterized using various analytical techniques. The synthesized CSNP was used for the biosorption of two pharmaceutical drugs, ibuprofen (IBU) and sulfamethoxazole (SUL). The influence of various experimental conditions was optimized through batch study with the removal efficiency of 86.33 % (IBU) and 85.80 % (SUL) at pH 2 and 3, initial concentration of 10 mg/L, 0.01 g of CSNP dosage. The biosorption of IBU follows Temkin, and SUL follows Langmuir isotherm models. The toxicological assessment was performed using the seeds of Vigna mungo (VM) and Vigna radiata (VR) and zebrafish to evaluate the toxic effects of pollutants on these organisms. The LC50 of IBU and SUL on zebrafish before the biosorption process was 209.50 mg/L and 338.84 mg/L. After biosorption, the LC50 values increase to 1435.82 mg/L for IBU and 1317.04 mg/L for SUL. Thus, CSNP is an efficient biosorbent for removing the pharmaceutical pollutants to protect ecological systems.

Valorization of sawdust by mineral acid assisted hydrothermal carbonization for the adsorptive removal of bisphenol A: A greener approach.

sawdust was valorized using acid-assisted hydrothermal carbonization and used in the removal of endocrine disruptor bisphenol A (BPA). The effect of acid addition on the hydrothermal carbonization of sawdust and removal of BPA was studied. Two different hydrochars were prepared using deionized water (HCD) and hydrochloric acid solution (HCAH) as feed water. The prepared hydrochars were characterized using FESEM, EDS, XRD, Raman spectroscopy, FTIR, TGA, and surface area analysis to study the structural and functional changes. Then they were compared in the removal of bisphenol A. Out of the two hydrochars prepared, acid-assisted hydrothermal carbonized hydrochar (HCAH) showed better removal efficiency. Hence, HCAH was used to study the influence of different parameters like pH, adsorbent dosage, and initial bisphenol A concentration by one variable at a time approach. Further, the study of interactive effects and optimization of adsorption of bisphenol A onto HCAH was carried out using RSM-CCD. The isotherm, kinetics, and thermodynamic studies revealed that the adsorption of bisphenol A could be explained by the Freundlich isotherm, pseudo-second-order kinetics fitted well in all the initial BPA concentrations, and the adsorption of bisphenol A onto HCAH was exothermic and spontaneous.

Toxicological assessment and adsorptive removal of lead (Pb) and Congo red (CR) from water by synthesized iron oxide/activated carbon (Fe3O4/AC) nanocomposite.

Heavy metals and dyes are the persistent pollutants causing harmful effects on living organisms in different ecosystems. In current study, removal of Lead (Pb) and Congo Red (CR) from water was performed using Iron oxide/Activated Carbon (Fe3O4/AC) nanocomposite. Ferromagnetic behavior of the nanocomposite is the crucial advantage in separation of nanocomposite after biosorption process. The biosorbent was thermally stable till 800 °C of temperature. The synthesized biosorbent was polycrystalline in nature comprising of elements like C, O, Fe. The influence of various experimental conditions was optimized through batch study with the biosorption capacity of 144.92 mg/g (Pb) and 122.22 mg/g (CR) at pH 5-6, Fe3O4/AC dosage (0.04 g) for 40 mg/L of Pb and CR. Toxicological assessment was performed using Danio rerio and seeds to evaluate the harmful effects of pollutants on these organisms. The phytotoxicity results revealed that growth inhibition of seeds lies between 85.64% and 55.92% (Pb) and 77.94%-51.85% (CR). The LC50 value of Pb on the Danio rerio was found to be 20.98 mg/L. In contrast, we observed significant increase in LC50 value about 86.82 mg/L after biosorption of Pb onto biosorbent.

Investigation of the adsorptive removal of methylene blue using modified nanocellulose.

In this study, Ethylenediamine tetraacetic acid (EDTA) embedded nanocellulose (NCED) has been used to study the adsorptive removal of methylene blue (MB) from simulated wastewater. The morphological characterizations have been checked with FESEM, FETEM, AFM, and BET pore analysis, while the fingerprinting of the material has been analyzed with the help of FTIR, Raman spectroscopy, EDS, XRD and TGA. For the experimental designing involving four parameters that affect the removal efficiency of MB, the layout has been prepared with the help of Central Composite Design (CCD). For the correlation among the parameters and their subsequent impact on the removal percentage, response surface methodology (RSM) has been employed. Maximum removal percentage of MB using NCED was found out to be 91.14%. The adsorption process was found to be good fit with the Langmuir isotherm and Elovich kinetics model. From the thermodynamics study, the spontaneity and the endothermic nature of the process was confirmed. With the help of all the obtained data and the associated removal efficiency, NCED could play a role of cost-effective and eco-friendly alternative to the expensive methods of toxic dye removal from wastewater.

Effect of magnetization on the adsorptive removal of an emerging contaminant ciprofloxacin by magnetic acid activated carbon.

Magnetic acid activated carbons (MAAC) were prepared from the shells of Sterculia villosa Roxb by activating the biomass and magnetizing it using the co-precipitation technique. Characterization of MAAC prior and post adsorption was performed using various microscopic and spectroscopic analytical techniques, and they verified the formation of magnetic aggregates over porous activated carbon surface. Vibrating Sample Magnetometer (VSM) analysis confirmed the superparamagnetic behaviour of the adsorbent with saturation magnetization (Ms) value of 18.2 emu/g, causing an easy and rapid recovery from the adsorption setup in the presence of an external magnetic field. Langmuir isotherm and pseudo-second-order kinetic model best fit the experimental data with theoretical Langmuir maximum adsorption capacity as 81.97 mg/g and verifying chemisorption type of adsorption process, respectively. Thermodynamic analysis verified the interaction among adsorbate and adsorbent as endothermic, spontaneous, and thermodynamically favourable. Co-existing metal cations showed a significant reduction in ciprofloxacin removal efficiency; co-existing anions, though, showed a negligible influence on the adsorption efficiency of MAAC. Recyclability studies verified that the adsorption efficiency fell from 98% in the first cycle to 43% in the fifth cycle. The Ms value fell to 7.6 emu/g (after five adsorption cycles), affecting the adsorbent's recovery. The Phyto-toxicological assessment was performed to evaluate the environmental risk to human and aquatic life using Vigna mungo seeds. MAAC proved to be an effective and magnetically separable adsorbent for removing antibiotics.

Magnetic activated charcoal/Fe2O3 nanocomposite for the adsorptive removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous solutions: Synthesis, characterization, optimization, kinetic and isotherm studies.

Magnetic activated charcoal/Fe2O3 nanocomposite (AC/Fe2O3NC) was fabricated using Spondias dulcis leaf extract by a facile method and used for the adsorptive removal of 2,4-Dichlorophenoxyacetic acid (2,4-D) from aqueous solutions for the first time. The nanocomposite was characterized by methods such as FE-SEM, EDS, XRD, FTIR, TGA, VSM, and BET to identify and confirm the surface morphology, elemental composition, crystalline nature, functional groups, thermal stability, magnetic behavior, and surface area respectively. Box-Behnken Design (BBD) - an optimization method, which belongs to the Response surface methodology (RSM) and a modeling tool - Artificial Neural Network (ANN) were employed to design, optimize and predict the relationship between the input parameters (pH, initial concentration of 2,4-D, time and agitation speed) versus the output parameter (adsorption efficiency of 2,4-D). Adsorption efficiency of 98.12% was obtained at optimum conditions (pH: 2.05, initial concentration: 32 ppm, contact time: 100 min, agitation speed: 130 rpm, temperature: 30 °C, and dosage: 0.2 g/L). The predictive ability of the ANN was superior (R2 = 0.99) than the quadratic model, given by the RSM (R2 = 0.93). The equilibrium data were best-fitted to Langmuir isotherm (R2 = 0.9944) and the kinetics obeyed pseudo-second-order model (R2 = 0.9993) satisfactorily. Thermodynamic studies revealed the spontaneity and exothermic nature of adsorption. The maximum adsorption capacity, qm was found to be 255.10 mg/g, substantially larger than the reported values for 2,4-D adsorption by other magnetic nanoadsorbents. Therefore, this nanoadsorbent may be utilized as an excellent alternative for the elimination of 2,4-D from the waterbodies.

Magnetic nanocellulose from Cyperus rotundas grass in the absorptive removal of rare earth element cerium (III): Toxicity studies and interpretation.

In this study a very common grass named Cyperus rotundas was used to extract cellulose which was converted to magnetic grass nano cellulose (MGNC) to adsorb rare earth element Cerium (Ce (III)). The prepared MGNC was analyzed with sophisticated technique to determine the alteration in physical and chemical properties before and after adsorption with the pollutant Cerium. Parameters like pH, temperature, MGNC dosage and initial concentration of Ce were optimized to check parameters influencing the adsorption of Ce (III). The optimized experimental data were perfectly modelled into Langmuir model with adsorption capacity of 353.04 mg g -1 for Ce (III). For kinetics the data fitted into pseudo second order model. To check the efficacy of MGNC in real scenario, untreated and treated Ce was used for phototoxicity studies with 4 different plant seeds. Apart from this, model fish, Danio rerio was used to check the toxicity level on aquatic organism before and after adsorption of Ce (III) with MGNC. This study showed the efficient use of MGNC and maximum removal of Cerium from wastewater and the magnetic behavior incorporated adds advantage of easy retrieval.

Development of Fe3O4/CAC nanocomposite for the effective removal of contaminants of emerging concerns (Ce3+) from water: An ecotoxicological assessment.

Contaminants of emerging concerns present in the ecosystems causes various adverse effects on all living organisms. In current study, removal of Ce3+ from water was performed using Fe3O4/CAC nanocomposite (MCAC) synthesized by co-precipitation technique. The synthesized MCAC was characterized using various analytical techniques. The magnetic behavior of the nanocomposite which is a crucial advantage in separation of MCAC after adsorption of Ce3+ from water was determined using vibrating sample magnetometer. MCAC was polycrystalline comprising both amorphous and crystalline regions with elements like C, O, Fe and N. The influence of process parameters was optimized through batch mode with the adsorption capacity of 86.206 mg/g. Ecotoxicological studies were performed using Danio rerio (Zebra fish) and seeds of Vigna mungo and Vigna radiata to assess the harmful effects of Ce3+ before and after adsorption process. The phytotoxicity studies on seeds revealed that inhibition of growth ranges from 50.39% to 12.55% (before adsorption) and 28.57%-3.89% (after adsorption). After 96 h the LC50 value of Ce3+ on the Danio rerio before and after adsorption was 2.44 and 77.85 mg/L. Thus, the current study investigated the effective removal of Ce3+ by MCAC and evaluates its ecotoxicological effects.

A detailed insight on fabricated porous chitosan in eliminating synthetic anionic dyes from single and multi-adsorptive systems with related studies.

Chitosan was fabricated via gelation method using CaBr2.xH2O/methanol solution and was studied as a potential adsorbent (MCh) in adsorbing anionic synthetic dyes like Bromophenol blue (BB), Direct blue 6 (DB) and Congo red (CR) from single (one dye species at a time) and multi (having two dyes; binary and all three dyes; tertiary) adsorptive systems. Physico-chemical modifications of MCh surface prior and post modification and dye adsorption were evaluated using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, powder X-ray diffraction analysis, surface area analysis and Fourier-transformed infrared spectroscopy. Influential parameters influencing the adsorption process viz. initial pH of dye solution, MCh dosage, adsorption temperature and initial concentration of dye species were optimised. Adsorptive studies involving single adsorptive setups verified formation of sorbate's (dye species) monolayer over the sorbent's (MCh) surface via chemisorption; as established by Langmuir isotherm and pseudo-second order kinetics model analysis. Theoretical maximum adsorption capacities of MCh for BB, DB and CR was found to be 81.301 mg/g, 163.934 mg/g and 75.758 mg/g, respectively. Meanwhile, for all multi-adsorptive systems, competitive Langmuir isotherm model verified antagonistic behaviour of an individual dye over other dye adsorption over MCh surface in their respective adsorptive systems. Thermodynamics of the sorbate-sorbent interaction was exothermic, spontaneous, with elevated degree of disorderedness; concluding the interaction as thermodynamically favourable. Co-existing metal cations and anionic salts had minimal effect on MCh's adsorption efficiency. Phytotoxicity assay via germination of Vigna mungo seeds verified the efficacy of the adsorbent in eliminating the dye species from single and multi-adsorptive systems.

Nanotechnology-based approaches for emerging and re-emerging viruses: Special emphasis on COVID-19.

In recent decades, the major concern of emerging and re-emerging viral diseases has become an increasingly important area of public health concern, and it is of significance to anticipate future pandemic that would inevitably threaten human lives. The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a newly emerged virus that causes mild to severe pneumonia. Coronavirus disease (COVID-19) became a very much concerned issue worldwide after its super-spread across the globe and emerging viral diseases have not got specific and reliable diagnostic and treatments. As the COVID-19 pandemic brings about a massive life-loss across the globe, there is an unmet need to discover a promising and typically effective diagnosis and treatment to prevent super-spreading and mortality from being decreased or even eliminated. This study was carried out to overview nanotechnology-based diagnostic and treatment approaches for emerging and re-emerging viruses with the current treatment of the disease and shed light on nanotechnology's remarkable potential to provide more effective treatment and prevention to a special focus on recently emerged coronavirus.

Ecotoxicological assessment of micropollutant Diclofenac biosorption on magnetic sawdust: Phyto, Microbial and Fish toxicity studies.

Diclofenac (DCF), a persistent pharmaceutical micropollutant which occurs in the ecosystems causing adverse effects on aquatic as well as terrestrial organisms. In this study, magnetic sawdust (MSD) was prepared using co-precipitation method for biosorptive removal of DCF from water. The MSD was characterized using various analytical techniques like microscopic and spectroscopic analysis. Magnetometer study confirms the ferromagnetic behavior of the biosorbent which is a key advantage in the separation of MSD after biosorption. The effect of experimental parameters was optimized in batch mode with evaluated maximum efficiency of 86.12 % at pH 6, biosorbent dosage 25 mg for 50 mg/L of DCF. Ecotoxicological assessment has been performed for the treated and untreated sample using plant seeds, microbes and zebra fish to check the adverse effects of DCF on these organisms. Evaluation of toxicity studies revealed that inhibition concentration of DCF for various seeds (60.91 mg/L to 43.11 mg/L), E. coli (48.82 µg/mL) and B. subtilis (31.55 µg/mL). The lethal concentration of DCF on the Danio rerio was found to be 156.99 mg/L. In contrast, significant increase in both the concentration measures of DCF after biosorption was observed making this biosorbent a potent alternative to other available treatment measures.

Use of Nanocellulose extracted from grass for adsorption abatement of Ciprofloxacin and Diclofenac removal with phyto, and fish toxicity studies.

The present study deals with the adsorption of antibiotic Ciprofloxacin (CPXO) and anti-inflammatory agent Diclofenac (DCF) on Grass nanocellulose (GNC) extracted from Cyprus rotundas grass. The adsorbent GNC was characterised using various microscopic, elemental and spectroscopic analysis to monitor the physicochemical alterations of the surface before and after adsorption. The size of the converted nanocellulose was found to be 40-50 nm. The experimental measures influencing the adsorption of CPXO and DCF that were optimised are initial solution pH, GNC dosage, temperature and initial concentration of the adsorbate. Halsey isotherm model and pseudo-second order kinetic model agreed best with the experimental outcome for both the adsorbate. The maximum adsorption capacity of GNC were 227.223 and 192.307 mg/g for CPXO and DCF respectively. Phytotoxicity studies were performed using 6 different types of seeds to evaluate the effect of GNC treated effluent on plants. Similarly, acute fish toxicity on zebra fish analysis showed to have lesser mortality rate of the effluent after adsorption of CPXO and DCF on GNC.

Adsorptive removal of Ciprofloxacin and Amoxicillin from single and binary aqueous systems using acid-activated carbon from Prosopis juliflora.

Adsorptive removal of emerging contaminants like antibiotics from aqueous systems having one or more antibiotics using acid activated carbon have rarely been studied and reported. Current study deals with the adsorptive removal of individual antibiotic species i.e. Ciprofloxacin (CIP) and Amoxicillin (AMX) from single (CIP and AMX) and binary (CIP + AMX) adsorption systems using acid activated carbon prepared from Prosopis juliflora wood (PPJ). Binary adsorption system involved the synergistic and antagonistic influence of one antibiotic over the adsorption of other antibiotic. Physico-chemical alterations of PPJ surface due to acid activation and after adsorption were characterized for any surface modification. Parameters influencing the efficient adsorption of CIP and AMX viz. Initial pH of antibiotic solution, dosage of PPJ, sorbent-sorbate incubation temperature and initial concentration of antibiotic species were optimized. Sorbate-sorbent interaction studies for single system revealed sorbate's monolayer formation over adsorbent's surface and the involvement of chemisorption as verified by Langmuir isotherm model and pseudo-second order model respectively. For single system, Langmuir maximum adsorption capacity of PPJ was 250 mg/g for CIP and 714.29 mg/g for AMX. Meanwhile, competitive Langmuir model was used to investigate adsorption capacity of individual antibiotics in binary system i.e. 370.37 mg/g for CIP and 482.14 mg/g for AMX thus verifying CIP has antagonistic effect on AMX adsorption and AMX has synergistic effect on CIP adsorption on PPJ surface. Recyclability studies verified the PPJ can be used up to 4 cycles and co-existing cationic and anionic salts had minimal effect on the adsorption of antibiotics over PPJ surface. Conclusively PPJ proved efficient in eliminating emerging contaminants like that of antibiotics and thus it can be exploited for other grades of pollutants.

Surface treated acid-activated carbon for adsorption of anionic azo dyes from single and binary adsorptive systems: A detail insight.

Current study deals with the surface modification of acid activated carbon (prepared from Pongamia pinnata shells) with Cetyltrimethylammonium bromide (CTAB) and its role as an adsorbent in eliminating anionic azo dyes viz. Congo red (CR) and Direct blue 6 (DB) from single and binary adsorptive systems. Binary adsorptive system involved the synergistic and antagonistic influence of one dye over the adsorption of other dye. Physico-chemical alterations due to surfactant modification and post adsorption were studied using atomic force microscopy (AFM), Zeta Potential, scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), surface area analysis and Fourier-transformed infrared spectroscopy (FTIR). Process parameters influencing efficient adsorption of CR and DB species viz. initial pH of dye solution, adsorbent dosage, incubation temperature and initial concentration of dye species were optimised. Sorbate-sorbent interaction studies for single adsorptive system revealed sorbate's monolayer formation over adsorbent's surface and the involvement of chemisorption, as verified by Langmuir isotherm model and pseudo-second order model, respectively. Langmuir maximum adsorption capacity of the adsorbent was 555.56 mg/g for CR and 625.00 mg/g for DB. Meanwhile, for binary adsorptive system, competitive Langmuir model verified both CR and DB had antagonistic/competitive effect over each other's adsorption. Thermodynamic analysis revealed the adsorptive process as exothermic, spontaneous and thermodynamically favourable with an elevated degree of dis-orderedness. Co-existing cations and anions has nominal effect on the adsorption capacity of dyes. Recyclability studies verified a modest efficiency of 62.52% for CR and 50.47% for DB species after the end of 4th adsorption-desorption cycle; thus affirming its recyclability potential. Phytotoxic assay affirmed the effectivity of the adsorbent in adsorbing dye species from aqueous solutions using Vigna mungo seeds as the model.

Performance of acid-activated water caltrop (Trapa natans) shell in fixed bed column for hexavalent chromium removal from simulated wastewater.

The current study deals with the adsorption of hexavalent chromium using acid (H3PO4)-activated water caltrop (Trapa natans) shell (PWCS) using an up-flow packed bed column. Characteristics of breakthrough curve was obtained by investigating the effect of several operating parameters viz. inlet flow rate (2-6 mL/min), initial metal ion concentration (50-150 mg/L), and adsorbent's column bed height (1-3 cm). Elevated time of breakthrough curve was reported with elevated adsorbent bed height and vice versa with enhanced initial metal concentration and inlet flow rate of sorbate solution. Process design and breakthrough curves under varying conditions were predicted by applying column models like Thomas model, Adams-Bohart model, Yoon Nelson model, and bed depth service Time (BDST). Column behavior was better described by the BDST and Thomas model and simultaneously gave a good fit with the experimental data of breakthrough curves. The percentage removal for Cr(VI) from aqueous solution having pH 2 and temperature 303.15 K was observed to be 52.46%. The maximum adsorption capacity was found to be 87.31 mg/g according to the Thomas model. Conclusively, phosphoric acid-modified T. natans shell (PWCS) showed better sorption potential for of Cr(VI) species from simulated wastewater.