As(III) removal from aqueous solutions using simultaneous oxidation and adsorption process by hierarchically magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite.

In the present study, a magnetic flower-like Fe3O4@C-dot@MnO2 nanocomposite was synthesized by hydrothermal method and applied for As(III) removal by oxidation and adsorption process. Individual property of the entire material (i.e. magnetic property of Fe3O4, mesoporous surface property of C-dot and oxidation property of MnO2) make the composite efficient with good adsorption capacity for As(III) adsorption. The Fe3O4@C-dot@MnO2 nanocomposite had a saturation magnetization of 26.37 emu/g and it magnetically separated within 40 s. The Fe3O4@C-dot@MnO2 nanocomposite was able to reduce the 0.5 mg/L concentration of As(III) to 0.001 mg/L in just 150 min at pH 3. Pseudo-second-order kinetic and Langmuir isotherm model agreed with experimental data. The uptake capacity of Fe3O4@C-dot@MnO2 nanocomposite was 42.68 mg/g. The anions like chloride, sulphate and nitrate did not show any effect on removal but carbonate and phosphate influenced the As(III) removal rate. Regeneration was studied with NaOH and NaClO solution and the adsorbent was used for repeated five cycles above 80% removal capacity. The XPS studies proposed that As(III) first oxidized to As(V) then adsorb on the composite surface. This study shows the potential applicability of Fe3O4@C-dot@MnO2 nanocomposite to high extent and gives a suitable path for the proficient removal of As(III) from wastewater.

Fruit peel-based mesoporous activated carbon via microwave assisted K2CO3 activation: Box Behnken design and desirability function for methylene blue dye adsorption.

A low-cost fruit waste namely watermelon peel (WMP) was utilized as a promising precursor for the preparation of mesoporous activated carbon (WMP-AC) via microwave assisted-K2CO3 activation. The WMP-AC was applied as an adsorbent for methylene blue dye (MB) removal. Several types of characterizations, such as specific surface area (BET), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX), Elemental Analysis (CHNS/O), and Fourier Transform Infrared Spectroscopy (FTIR) were used to identify the physicochemical properties of WMP-AC. Furthermore, Box-Behnken design (BBD) was applied to optimize the influence of the adsorption operational variables (contact time, adsorbent dose, working temperature, and solution pH) on MB dye adsorption. Thus, based on significant interactions, the optimum BBD output shows the best removal of 50 mg·L-1 MB (92%) was recorded at an adsorbent dose of 0.056 g, contact time of 4.4 min, working temperature of 39 °C, and solution pH 8.4. The Langmuir uptake capacity of WMP-AC was found to be 312.8 mg·g-1, with the best fitness to the pseudo-second-order kinetics model and an endothermic adsorption process. The adsorption mechanisms of MB by WMP-AC can be assigned to the hydrogen bonding, electrostatic attraction, and π-π stacking. The findings of this study indicate that WMP is a promising precursor for producing porous activated carbon for MB dye removal.

The novelty of this research work comes from the conversion of the domestic fruit waste namely watermelon peels into mesoporous activated carbon by the fast and convenient activation method of microwave-assisted chemical activation. The produced activated carbon was applied for the removal of a toxic organic dye. Furthermore, the statistical optimization by using response surface methodology was applied to optimize the adsorption key parameters.

Kendu (Diospyros melanoxylon Roxb) fruit peel activated carbon-an efficient bioadsorbent for methylene blue dye: equilibrium, kinetic, and thermodynamic study.

In this work, activated carbon was synthesized by the carbonization of kendu fruit peel followed by chemical activation using ammonium carbonate as an activating agent to get modified kendu fruit peel (MKFP). The SEM and FESEM images of the biomaterial illustrated a highly porous honeycomb-like structure, further supported by the N2 sorption isotherm analysis. The FTIR spectra specified the presence of oxygen-containing functional groups such as carboxyl, carbonyl, and hydroxyl on the adsorbent surface. Batch experiments were performed for the optimization of methylene blue (MB) dye removal. The adsorption process followed pseudo-second-order kinetic model and Langmuir isotherm model with a maximum adsorption capacity of 144.9 mg g-1. No desorption was found because the adsorbent surface was bonded with the chromophoric group of the MB dye by means of strong chemical interaction evident from the high adsorption energy (E = 10.42 kJ mol-1) and enthalpy change (∆H = 42.7 kJ mol-1). Hence, the MKFP has the potential to act as an efficient bioadsorbent for MB dye removal. Graphical abstract.

Facile synthesis of poly o-toluidine modified lanthanum phosphate nanocomposite as a superior adsorbent for selective fluoride removal: A mechanistic and kinetic study.

This work reports the synthesis of a new adsorbent material (LaP-POT), synthesised by sol-gel polymerisation method from lanthanum phosphate (LaP) and poly o-toluidine (POT). The sustainability and selectivity of the material as a potential adsorbent is evaluated for the removal of fluoride from aqueous as well as real water samples using batch experimental techniques. FESEM and TEM images showed the successful incorporation of rod-shaped lanthanum phosphate into the poly o-toluidine polymer matrix. The increased degradation temperature of LaP-POT from TGA curve inferred a definite interaction between two. XPS study revealed the successful binding of fluoride onto LaP-POT. The selectivity of fluoride ion onto LaP-POT material was ascertained by the distribution coefficient value. The co-anions showed little effect on fluoride removal. Kinetic study suggested that intraparticle diffusion is not the only rate controlling step; the external mass transfer or chemical interaction also impacts the fluoride adsorption. The maximum adsorption was observed at room temperature with a maximum Langmuir uptake capacity of 10.94 mg g-1. The reusability of the material is tested up to 5 successive cycles for a workable commercial application purpose. The results showed that LaP-POT provides more active sites, thus making it a promising adsorbent for the removal of fluoride.

Synthesis and characterization of magnetic bio-adsorbent developed from Aegle marmelos leaves for removal of As(V) from aqueous solutions.

A novel magnetic bio-adsorbent was prepared from the leaves of Aegle marmelos tree (Indian bael) and Fe2O3 nanoparticles. The AMP@Fe2O3 nanocomposite (Aegle marmelos leaf powder) was synthesized by pyrolysis process and applied for As(V) removal through batch adsorption process. The synthesized AMP@Fe2O3 nanocomposite was analyzed by several instrumental techniques like XRD, FESEM, TEM, HRTEM, FTIR, BET, and VSM studies. Maximum amount of As(V) was removed at pH 3, contact time of 250 min, adsorbent dose of 0.1 g/L, and initial concentration of 0.5 mg/L at room temperature. The model study revealed that the pseudo-second-order kinetics and Langmuir isotherm models were best fitted with the experimental data. The nanocomposite showed a maximum adsorption capacity of 69.65 mg/g. The endothermic nature of the adsorption process was ascertained from the thermodynamics studies. The zeta potential and FTIR analysis before and after adsorption demonstrated two types of adsorption mechanism. The first one was the electrostatic attraction between negatively charged As(V) ions (H2AsO4-) and protonated -OH group present on the Fe2O3 surface and the second one was ligand exchange between the surface hydroxyl groups and As(V) ions. The AMP@Fe2O3 nanocomposite was desorbed with 0.5 M NaOH solutions and also used up to four cycles without any major decrease in removal efficiency. Thus, AMP@Fe2O3 nanocomposite can be applied as a potential adsorbent for As(V) removal from wastewater.