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Zinc and magnesium oxide nanoparticles were fabricated using green synthesis method for the sequestration of hexavalent chromium Cr(VI) from the aqueous medium. The biogenically prepared ZnO@EC and MgO@EC nanoparticles were successfully loaded on the Eucalyptus. The prepared nanomaterials were characterized using various techniques such as FESEM, TGA, XRD, EDX, FTIR, BET, and elemental mapping. FE-SEM analysis has revealed the surface morphology of ZnO nanoparticles, which were rod-like and spherical in shape, whereas MgO nanoparticles were of irregular shape. Batch mode was selected to remove the hexavalent chromium from aqueous solution using the prepared nanomaterials. The Cr(VI) adsorption was carried out under optimized conditions, viz., pH (3.0), adsorbent dose (0.05 g), contact time (150 min), temperature (25 ± 2 °C), and initial concentration (50 mg/L). The experimental results were compared using the different isotherm models; The observations have indicated that experimental data fit better with Freundlich (R 2  = 0.99) and Langmuir (R 2  = 0.99) isotherms, respectively. The maximum adsorption capacity of ZnO@EC and MgO@EC for Cr(VI) was found to be 49.3 and 17.4 mg/g, respectively. The regeneration study of the adsorbents was conducted using different desorbing agents viz., ethanol, NaOH, and NaCl. The desorbing agent NaOH performed better and showed removal percentage of 34.24% and 20.18% for ZnO@EC and MgO@EC, respectively, after the three reusability cycles. The kinetics of reaction was assessed using the pseudo-first-order and pseudo-second-order kinetic models. The experimental data of both the nanomaterials ZnO@EC and MgO@EC obeyed pseudo-second-order model with correlation coefficient values 0.999 and 0.983, respectively. The thermodynamic study confirmed that adsorption was feasible, spontaneous, and endothermic. The adsorbents were tested for spiked real water which confirms their applicability and potential in real water systems also. The results indicated fair removal of chromium suggesting applicability of both adsorbents., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

This study deals with heavy metal ions removal from simulated water using biosynthesized silica-supported iron oxide nanocomposites (nano-IOS). Agricultural and garden wastes have been utilized to prepare nano-IOS through a green synthesis process. Nano-IOS was characterized by XRD, SEM, FTIR, and zeta potential analysis. The nanocomposites were used to remove five heavy metals, viz., Pb 2+ , Cd 2+ , Ni 2+ , Cu 2+ , and Zn 2+ , with optimization of reaction parameters including pH, the concentration of heavy metals, adsorbent dosage, and contact time in batch mode experiments. The optimized dose of nano-IOS was 0.75 g/L for the adsorption of Pb 2+ , Cd 2+ , Ni 2+ , Cu 2+ , and Zn 2+ (10.0 mg/L) with a contact duration of 70 min at pH 5.0 for Pb 2+ , Cd 2+ , and Cu 2+ and 6.0 for Ni 2+ and Zn 2+ . The adsorption behavior of the nano-adsorbent was well described by Langmuir adsorption isotherm and pseudo-second-order kinetic model indicating chemisorption on the surface of nano-IOS. The adsorption was also found spontaneous and endothermic. Thus, the environmentally benign and bio-synthesized nano-IOS can be utilized as an effective nano-adsorbent for the rapid sequestration of heavy metal ions from water and wastewater., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Herein, for the adsorption and detection of As (III), multifunctional nanohybrid have been synthesized using a solvothermal approach. Structural and functional characterizations confirmed the impregnation of the ZnO over graphene oxide. Nanohybrid exhibits a remarkable q max (maximum adsorption capacity) of 8.17 mg/g, at an adsorbent dose of 3 g/L and pH of 8.23. Higher adsorption with nanohybrid was attributed to a large BET surface area of 32.950 m 2 /g. The chemical nature and adsorption behaviour of As(III) on ZnO-GO were studied by fitting the data with various adsorption isotherms (Langmuir & Freundlich) and kinetics models (six models). It is observed from the findings that removal of As(III) with ZnO-GO nanocomposite appears to be technically feasible with high removal efficiency. The feasibility of the nanocomposite to function as a sensor for the detection of As(III) was also evaluated. The fabricated sensor could detect As(III) with a lower limit of detection of 0.24 μM and linear range up to 80 μM. Overall, this study is significant in nanohybrid as a multifunctional composite for the adsorption and detection of As (III) from wastewater., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

This review discusses a fresh pool of research findings reported on the multiple roles played by metal-based, magnetic, graphene-type, chitosan-derived, and sonicated nanoparticles in the treatment of pharmaceutical- and agrochemical-contaminated waters. Some main points from this review are as follows: (i) there is an extensive number of nanoparticles with diverse physicochemical and morphological properties which have been synthesized and then assessed in their respective roles in the degradation and mineralization of many pharmaceuticals and agrochemicals, (ii) the exceptional removal efficiencies of graphene-based nanomaterials for different pharmaceuticals and agrochemicals molecules support arguably well a high potential of these nanomaterials for futuristic applications in remediating water pollution issues, (iii) the need for specific surface modifications and functionalization of parent nanostructures and the design of economically feasible production methods of such tunable nanomaterials tend to hinder their widespread applicability at this stage, (iv) supplementary research is also required to comprehensively elucidate the life cycle ecotoxicity characteristics and behaviors of each type of engineered nanostructures seeded for remediation of pharmaceuticals and agrochemicals in real contaminated media, and last but not the least, (v) real wastewaters are extremely complex in composition due to the mix of inorganic and organic species in different concentrations, and the presence of such mixed species have different radical scavenging effects on the sonocatalytic degradation and mineralization of pharmaceuticals and agrochemicals. Moreover, the formulation of viable full-scale implementation strategies and reactor configurations which can use multifunctional nanostructures for the effective remediation of pharmaceuticals and agrochemicals remains a major area of further research.

The present study explored removal of carcinogenic cationic and anionic dyes from aqueous medium using green fabricated zinc oxide nanoparticles (ZnO-NPs). The ZnO-NPs were synthesized employing biogenic green reduction and precipitation approach. The characterization of ZnO NPs was done using various techniques such as FESEM, XRD, BET, TGA, HRTEM, EDX, and FTIR. All experiments were conducted in batch mode. Maximum removal was achieved at pH 6.0 and pH 8.0 for Congo Red (CR) and Malachite Green (MG) dyes respectively. Dye adsorption process showed better fit with Langmuir and Temkin isotherm models for CR dye and MG dye respectively. Maximum adsorption capacity of ZnO NPs was 48.3 mg/g for CR dye and 169.5 mg/g for MG dye. The dye adsorption followed pseudo-second order model and values of thermodynamic parameters confirmed that the adsorption process was spontaneous and favourable. Reusability efficiency of the nanoparticle was explored using ethanol and water and based on results it was inferred that ZnO-NPs can be reused for dye removal. Effect of salinity on the removal of CR and MG dyes was also explored and found that presence of salinity in aqueous medium have adverse impact on the dye removal efficiency of ZnO-NPs., Competing Interests: Declaration of competing interest There are no conflicts to declare., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This work explored the potential of magnetic sawdust carbon nanocomposites for cationic dyes removal from aqueous medium. EDTA modified magnetic sawdust carbon nanocomposites (EDTA@Fe 3 O 4 /SC ncs) were prepared by biogenic green reduction and precipitation approach. The surface properties, structure and composition of nanocomposites were characterized by HRTEM, FESEM, XRD, EDX, BET, FTIR etc. The Fe 3 O 4 nanoparticles were 10-20 nm in diameters and having 14 m 2 /g surface area. Removal of Methylene blue (MB) and Brilliant green (BG) dyes from aqueous medium was studied in batch mode experiments. The maximum removal was achieved at neutral pH 7.0 with in 30 min. Adsorption capacity of EDTA@Fe 3 O 4 /SC for MB and BG dyes was 227.3 mg/g and 285.7 mg/g, respectively. Dye adsorption behaviour is well explained by Freundlich model. The rate of cationic dye adsorption is explained by pseudo-second order model. The value of thermodynamic parameters confirmed that adsorption process was spontaneous and favourable. Desorption and reusable efficiency of nanocomposites was also evaluated., (Copyright © 2019 Elsevier Inc. All rights reserved.)

One of the biggest challenges of the 21st century is to provide clean and affordable water through protecting source and purifying polluted waters. This review presents advances made in the synthesis of carbon- and iron-based nanomaterials, graphene-carbon nanotubes-iron oxides, which can remove pollutants and inactivate virus and bacteria efficiently in water. The three-dimensional graphene and graphene oxide based nanostructures exhibit large surface area and sorption sites that provide higher adsorption capacity to remove pollutants than two-dimensional graphene-based adsorbents and other conventional adsorbents. Examples are presented to demonstrate removal of metals (e.g., Cu, Pb, Cr(VI), and As) and organics (e.g., dyes and oil) by grapheme-based nanostructures. Inactivation of Gram-positive and Gram-negative bacterial species (e.g., Escherichia coli and Staphylococcus aureus) is also shown. A mechanism involving the interaction of adsorbents and pollutants is briefly discussed. Magnetic graphene-based nanomaterials can easily be separated from the treated water using an external magnet; however, there are challenges in implementing the graphene-based nanotechnology in treating real water., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The present study reports the use of sunflower waste carbon calcium-alginate beads (SWC-CAB) for cadmium removal from wastewater in continuous flow fixed bed columns. The experiments were conducted as a function of bed height, flow rate and initial Cd(II) concentration. The maximum biosorption capacity (23.6 mg/g) was attained at 30 cm bed height, 1.0 mL/min flow rate and 10 mg/L initial Cd(II) concentration. The Bohart-Adams model constants (N0 and K) were 7.7 mg/L and 1×10(-4) L/mgh with 0.999 R2 value at 50% breakthrough time. The column regeneration efficiency after third cycle was 58.6% for cadmium., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

This paper reports the adsorption of Cr(VI) ions from aqueous solution by sulphuric acid treated sunflower waste. Two adsorbents, namely SHC and SSC, were prepared from sunflower plant head and stem waste. The adsorbents were characterized by FT-IR, SEM and EDX. The surface areas of SHC and SSC were 1.17 and 1.28 m(2)g(-1), respectively. The effect of various process parameters namely pH, temperature, initial metal ion concentration, adsorbent dosage and contact time has been studied. The optimum conditions for removal of Cr (VI) were found to be pH=2, contact time=2h, adsorbent dosage=4.0 g/L, concentration=250 mg/L, temperature=25+/-1 degrees C, rpm=180. The percent removal at these optimum conditions was found to be 75.7% and 85.4% for SHC and SSC respectively. The Freundlich, Langmuir and D-R models were applied for mathematical description of adsorption equilibrium. Adsorption data were well described by the Langmuir isotherm with maximum adsorption capacities of 53.76 mg/g and 56.49 mg/g for SHC and SSC, respectively. Overall, the experimental results suggest that SHC and SSC could be used as low cost alternative adsorbents for the treatment of Cr(VI) containing wastewater. A comparison of different kinetic models showed that our data fitted well to the pseudo-second order model., (Copyright 2009 Elsevier Ltd. All rights reserved.)

In the present work, potential of sunflower head (BSH) [an agricultural waste biomass] to remove Cr(VI) from simulated wastewater has been evaluated under different process conditions such as pH, metal concentration, adsorbent dose and contact time. A contact time of 120 min and pH 2.0 were found to be optimum. Chromium removal decreased from 90.0 to 45.2% as its concentration increased from 10 to 70 mg/L. The Cr(VI) removal increased from 31.4 to 52.4% as adsorbent dose increased from 4.0 to 20.0 g/L using a test solution having 100mg/L Cr(VI) concentration. Adsorption isotherms were employed to evaluate the maximum adsorption capacity. Adsorption data fitted well to Langmuir isotherm and pseudo-second order model as indicated by high values of correlation coefficient (0.9882 and 0.999) respectively. The adsorption capacity calculated from Langmuir isotherm was 8.177 mg/g.

This paper reports the feasibility of using various agricultural residues viz. sugarcane bagasse (SCB), maize corncob (MCC) and Jatropha oil cake (JOC) for the removal of Cd(II) from aqueous solution under different experimental conditions. Effect of various process parameters, viz., initial metal ion concentration, pH, and adsorbent dose has been studied for the removal of cadmium. Batch experiments were carried out at various pH (2-7), adsorbent dose (250-2000 mg), Cd(II) concentration (5-500 mg l(-1)) for a contact time of 60 min. The maximum cadmium removal capacity was shown by JOC (99.5%). The applicability of Langmuir and Freundlich isotherm suggests the formation of monolayer of Cd(II) ions onto the outer surface of the adsorbents. Maximum metal removal was observed at pH 6.0 with a contact time of 60 min at stirring speed of 250 rpm with an adsorbent dose of 20 g l(-1) of the test solution. The maximum adsorption of cadmium (II) metal ions was observed at pH 6 for all the adsorbents viz; 99.5%, 99% and 85% for JOC, MCC, and SCB, respectively. Order of Cd(II) removal by various biosorbents was JOC>MCC>SCB. JOC may be an alternative biosorbent for the removal of Cd(II) ions from the aqueous solution. FT-IR spectra of the adsorbents (before use and after exhaustion) were recorded to explore number and position of the functional groups available for the binding of Cd(II) ions on to studied adsorbents. These results can be helpful in designing a batch mode system for the removal of cadmium from dilute wastewaters.

In the present study adsorption of rhodamine-B from aqueous solution on formaldehyde treated parthenium biomass (WC) and phosphoric acid treated parthenium carbon (PWC) was studied. Aqueous solutions of various concentrations (50-500 mg/l) were shaken with certain amount of adsorbent to determine the adsorption capacity of rhodamine-B on WC and PWC. The effectiveness of formaldehyde treated parthenium biomass (WC) and phosphoric acid treated parthenium carbon (PWC) in adsorbing rhodamine-B from aqueous solution has been studied as a function of agitation time, adsorbent dose, initial dye concentration and pH. The adsorption capacities of the studied adsorbents were in the order PWC>WC. Initial pH had negligible effect on the adsorption capacity. Maximum dye was sequestered from the solution within 60min after the start of every experiment. After that, the concentration of rhodamine-B in the liquid-phase remained constant. The adsorption of rhodamine-B onto PWC and WC followed second-order kinetic model. Adsorption data were modeled using both Langmuir and Freundlich classical adsorption isotherms. The adsorption capacity Q(0) was 59.17 mg/g at initial pH 7.0 for the particle size 0.3-1.0mm for phosphoric acid treated parthenium carbon (PWC). The FT-IR spectra of the adsorbents were recorded to explore number and position of functional groups available for the binding of dye cation onto studied adsorbents. SEMs of the adsorbents were recorded to explore the morphology of the studied adsorbents.

Formaldehyde treated and sulphuric acid treated saw dusts were used to adsorb malachite green at varying dye concentration, adsorbent dose, pH and agitation time. Similar experiments were conducted with laboratory grade activated carbon to compare the results. The adsorption efficiency of sulphuric acid treated sawdust (SD) was higher than formaldehyde treated SD. The adsorption followed first order rate expression and Lagergren equation. An initial pH in the range of 6-9 was favorable for the dye removal by both the adsorbents. Dilute solutions were effectively decolorized by the adsorbents. It is proposed that in batch or stirred tank reactors, both adsorbents can be an attractive option for dye adsorption.