Biosorption of copper ions from aqueous solution by Codium vermilara: Optimization,kinetic, isotherm and thermodynamic studies

In this investigation, the efficiency of Codium vermilara for copper ions removal from aqueous solution was studied. Central Composite Design has been used for the Response Surface Methodology and has been found to be an effective method for investigating the influences of various variables and their interactions on the efficiency of Cu²⁺ ions removal. The interactive impacts of four variables: algal dose, pH, initial concentrations of copper and contact time on the copper removal efficiency were assessed. Algal dose 0.75 g/L, pH 5.28, contact time 70.51 min, and copper concentration 48.75 mg/L were found to be the conditions of optimum biosorption. The efficiency of copper removal was found to be 85.5% under these optimum conditions. Copper removal on the biomass of C. vermilara followed well the kinetics of pseudo-first-order, Elvoish and Intraparticle diffusion. Compared to the other models, Dubinin-Radushkevich isotherm best suited the experimental data revealing that the adsorption mechanism was physical adsorption. Thermodynamic parameters exhibited non-spontaneous, randomness and endothermic biosorption of Cu²⁺ ions. Additionally, the biosorbent characterization was estimated by scanning electron microscopy and Fourier transform infrared analysis. Thus, C. vermilara could be used as possible biosorbent for removing heavy metals and other pollutants from the environment.     

Biosorption of zinc from aqueous solution using Azadirachta indica bark: equilibrium and kinetic studies

The removal of zinc ions from aqueous solutions on the biomass of Azadirachta indica bark has been studied by using batch adsorption technique. The biosorption studies were determined as a function of contact time, pH, initial metal ion concentration, average biosorbent size and biosorbent dosage. The equilibrium metal uptake was increased and percentage biosorption was decreased with an increase in the initial concentration and particle size of biosorbent. The maximum zinc biosorption occurred at pH 6 and percentage biosorption increases with increase in the biosorbent dosage. Experimental data obtained were tested with the adsorption models like Langmuir, Freundlich and Redlich-Peterson isotherms. Biosorption isothermal data were well interpreted by Langmuir model with maximum biosorption capacity of 33.49mg/g of zinc ions on A. indica bark biomass and kinetic data were properly fitted with the pseudo-second-order kinetic model.     

Constructing MAX dispersed Ni2P/TiO2 nanocomposite with investigating influential effect of parameters through design expert and kinetic study for photocatalytic H2 evolution

Well-designed Ni₂P/TiO₂ nanoparticles dispersed over 2D Ti₃AlC₂ MAX, were investigated for H₂ evolution with parameter optimization and kinetic modelling in a liquid phase slurry photoreactor. The highest H₂ production rate of 1300 µmol was obtained over MAX dispersed Ni₂P/TiO₂ nanocomposite. The H₂ production was observed to be 3.80 times more than the H₂ generated by pristine TiO₂, based on the inhibited charge recombination, improved visible light response, and good redox potential of TiO₂. The sacrificial reagents, catalyst loading, and reaction time were optimized through the design of experiment (DoE). The results revealed 10.5 CH₃OH concentration, 0.11 g loading, and a 3.59 h reaction time as the optimum conditions for maximum H₂ generation. Finally, for investigating the adsorption behaviour, a modified Langmuir-Hinshelwood (L-H) mechanism-based kinetic model was developed. According to the kinetic model, the lower CH₃OH adsorption constant suggested low adsorption at lower concentrations, but the higher CH₃OH value indicated more adsorption at higher reactant concentrations. Thus, structured photocatalysts with enhanced photoactivity and kinetic-model findings should help researchers to comprehend photocatalytic reaction engineering properly for solar energy applications.     

Potential of pomegranate husk carbon for Cr(VI) removal from wastewater: kinetic and isotherm studies

Pomegranate husk was converted into activated carbon and tested for its ability to remove hexavalent chromium from wastewater. The new activated carbon was obtained from pomegranate husk by dehydration process using concentrated sulfuric acid. The important parameters for the adsorption process such as pH, metal concentration and sorbent weight were investigated. Batch equilibrium experiments exhibited that a maximum chromium uptake was obtained at pH 1.0. The maximum adsorption capacity for pomegranate husk activated carbon was 35.2mgg(-1) as calculated by Langmuir model. The ability of activated carbon to remove chromium from synthetic sea water, natural sea water and wastewater was investigated as well. Different isotherm models were used to analyze the experimental data and the models parameters were evaluated. This study showed that the removal of toxic chromium by activated carbon developed from pomegranate husk is a promising technique.     

Kinetic and equilibrium studies of the removal of Pb from aqueous solutions using Na2SO4-EVA/Cloisite 20A composite

The present work describes the suitability of Na₂SO₄ to improve the wetability of a hydrophobic composite, ethylene vinyl acetate/Cloisite^® 20A, to remove Pb²⁺ ions from aqueous solutions through adsorption. The composite was synthesized via melt-blending method. Scanning electron microscopy showed that suspending the composite in de-ionized water improved porosity resulting from the removal of Na₂SO₄. X-ray diffraction showed that the use of Na₂SO₄ improved the amorphous nature of the composites and hence increased wetability. The holes on the composite improved the contact area between Cloisite^® 20A particles and Pb²⁺ ions. Equilibrium adsorption was achieved in 8 h with a 90% Pb²⁺ ion removal from synthetic wastewater. Kinetic and equilibrium models were applied to determine the type of adsorption mechanism involved. The results showed that the sorption of Pb²⁺ was found to be mainly based on physical interactions and ion-exchange mechanisms. It was established that the adsorption follow pseudo second-order rate equation and intraparticle diffusion was the rate determining step. The results showed that sorption mechanism assumed intraparticle diffusion implying that porous structure of the adsorbent influenced diffusion.     

Synthesis of acetone reduced graphene oxide/Fe3O4 composite through simple and efficient chemical reduction of exfoliated graphene oxide for removal of dye from aqueous solution

A simple and effective technique for reduction of graphene oxide at low temperature (70 °C) using acetone was reported for the first time. Magnetically recoverable acetone reduced graphene oxide (ARGO)/Fe₃O₄ composite was synthesized by uniformly decorating Fe₃O₄ on ARGO. The synthesized ARGO/Fe₃O₄ composite was characterized by the powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform-infrared spectroscopy and thermogravimetric analysis. An organic dye rhodamine 6G was used as an adsorbate for investigating the adsorption characteristics of the composite. The adsorption kinetic data were best described by the pseudo-second-order model, and equilibrium was achieved within 2 h. Dye adsorption was favored in basic conditions (pH 9–11) and governed by intraparticle diffusion process. The maximum dye adsorption on the composite was 93.37 mg/g at 293 K, and it followed the Langmuir–Freundlich model. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the dye adsorption onto composite was feasible, spontaneous and exothermic. The ARGO/Fe₃O₄ composite was easily controlled in magnetic field for desired separation, leading to an easy removal of the dye from wastewater, which holds great potential for dye decontamination.     

Graphene oxide-sulfated lanthanum oxy-carbonate nanocomposite as an adsorbent for the removal of malachite green from water samples with application of statistical optimization and machine learning computations

Sulfated lanthanum oxy-carbonate nanorods (S-La₂O₂(CO₃) NRs) was synthesized by the reverse micelle microemulsion method and then used to modify graphene oxide nanosheets to synthesize of graphene oxide-sulfated lanthanum oxy-carbonate (GO-S-La₂O₂(CO₃)) nanocomposite. By characterization of S-La₂O₂(CO₃) NRs and GO-S-La₂O₂(CO₃) nanocomposite by the Fourier Transform-Infrared (FT-IR) Spectrophotometry, Field Emission-Scanning Electron Microscopy (FE-SEM), Energy-dispersive X-ray spectroscopy (EDS), Transmission Electron Microscopy (TEM) and X-ray diffraction analysis (XRD), GO-S-La₂O₂(CO₃) was used for treatment of malachite green (MG). To find the optimum removal percentage (RP), influencing parameters were investigated by the response surface methodology based on central composite design (RSM-CCD). Adsorption mechanism was evaluated by Dubinin–Radushkevich (D-R), Langmuir, Temkin, Freundlich (two parameter equations) and Sips (Three parameter equations) isotherms and based on the results the adsorption of MG into the GO-S-La₂O₂(CO₃) nanocomposite obeyed by the Freundlich isotherm with the maximum adsorption capacity of 555.5 mg g^?1. Also, the results of kinetic analysis show that the adsorption of MG onto the GO-S-La₂O₂(CO₃) nanocomposite followed by the pseudo second order kinetic model. For estimation of adsorption behavior, different machine learning techniques are used and based on the results; ANFIS model has the confidential operation because of fuzzy procedure and flexibility of data mining in distributed adsorption data.     

Adsorptive, thermodynamic and kinetic performances of Al/Ti and Al/Zr-pillared clays from the Brazilian Amazon region for zinc cation removal

Smectite clay samples from the Amazon region, Brazil, were pillarized by intercalating the species obtained from the chemical reactions: (i) AlCl₃·6H₂O/NaOH, (ii) titanium ethoxide in hydrochloric acid and (iii) direct use of ZrOCl₂·8H₂O solution. The natural matrices and the pillaring solutions were maintained under vigorous stirring at 298 K for 3 h and then subjected to calcination at temperatures of 723 and 873 K. Natural and pillared matrices were characterized by XRD, FTIR, TG–DTG and nitrogen adsorption–desorption isotherms. The resulting materials were used for zinc adsorption from aqueous solution at room temperature. The Langmuir, Freundlich and Temkin adsorption isotherm models have been applied to fit the experimental data and the Freundlich model is limited for higher concentrations. The pillaring process increases the thermal stability, the basal spacing of the natural clay sample (A₁) from 1.55 to 2.06 nm and the surface area from 44.30 to 223.73 m² g⁻¹. Kinetic studies demonstrated an equilibrium time of 180 min for zinc adsorption on the pillared matrices. Pseudo-first-order, Lagergren pseudo-second-order and Elovich equations demonstrated a better agreement with second-order kinetics was obtained with K₂ = 4.17–10.43 × 10⁻³ g mg⁻¹ min⁻¹ for the A₁ sample.     

Computation of stress intensity factors (KI, KII) and T-stress for cracks reinforced by composite patching

To increase the operational life of defected structures, a repairing method using composite patches has been used to reinforce cracked components. Due to various advantages of composite materials, this method has received much attention from researchers and engineers. Considerable investigations have been performed to highlight the effect of bonded composite patches on the fracture parameters such as stress intensity factors (SIF) and J-integral. However the effect of composite patches on the T-stress, the constant stress term acting parallel to the crack, has not been investigated in the past. In this paper, the finite element method is carried out to analyze the effect of bonded composite patches for repairing cracks in pure mode I and also mixed mode I/II conditions, by computing the stress intensity factors and the T-stress, as functions of the crack length, the crack inclination angle and the type of composite material. In pure mode I condition, the finite element analysis is carried out for three different specimens: centre crack, double edge crack and single edge crack specimens. For mixed mode I/II condition the analysis is conducted on an inclined central crack of various slant angles. For both pure mode I and mixed mode I/II, the numerical results show that composite patching has considerable effect on the T-stress.     

Efficient removal of Cr (VI) from aqueous solution by halloysite/poly(amidoamine) dendritic nano-hybrid materials: kinetic,isotherm and thermodynamic studies

This paper demonstrates functionalization of a new hybrid nanoclay for effective adsorption of chromium(VI) ions from wastewater. Halloysite nanotubes (HNTs) were functionalized by poly(amidoamine) dendritic polymers (HNTs-(DEN-NH₂)) via a convergent synthetic route by carboxylic acid as a linkage. Various characterization methods confirm that poly(amidoamine) dendritic groups were effectively grafted onto the surface of HNTs that found a high specific surface area of 75 m²/g, as measured by micrometric BET analyzer. Moreover, the adsorption activity of HNTs-(DEN-NH₂) for Cr(VI) was systematically investigated using a batch solution that reveals the removal efficiency of 98% for HNTs-(DEN-NH₂) comparing to 23% for pristine HNTs, at optimum conditions. The enhancement of Cr(VI) removal for HNTs-(DEN-NH₂) comparing to HNTs was mainly ascribed to be due to the electrostatic interaction, that was confirmed by the results of Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Moreover, regeneration studies display that HNTs-(DEN-NH₂) can maintain removal Cr(VI) with high efficiency after four consecutive cycles.     

Clarified sludge (basic oxygen furnace sludge) – an adsorbent for removal of Pb(II) from aqueous solutions – kinetics, thermodynamics and desorption studies

The basic oxygen furnace waste generated in steel plant has been used as a low cost adsorbent for the removal of Pb(II) from aqueous solution. The effect of pH, adsorbent dosage, initial metal ion concentration, contact time and temperature on adsorption process was studied in batch experiments. Results of the equilibrium experiments showed that the solution pH was the key factor affecting the adsorption characteristics. Optimum pH for the adsorption was found to be 5 with corresponding adsorbent dosage level of 5 g/L. The equilibrium was achieved within 1 h of contact time. Kinetics data were best described by pseudo second order model. The effective particle diffusion coefficient of Pb(II) is the order of 10⁻¹⁰ m²/s. The maximum uptake was 92.5 mg/g. The adsorption data can be well fitted by Freundlich isotherm. The result of the equilibrium studies showed that the solution pH was the key factor affecting the adsorption. External mass transfer analysis was also carried out for the adsorption process. The thermodynamic studies indicated that the adsorption is spontaneous and endothermic. The sorption energy (10.1745 kJ/mol) calculated from Dubinin–Radushkevich isotherm indicated that the adsorption process is chemical in nature. Desorption studies were carried out using dilute mineral acids to elucidate the mechanism of adsorption. Application studies were carried out considering the economic viewpoint of wastewater treatment plant operations.