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In this work, gamma–MnO2 nanostructure was used as a sorbent to remove Zn (II) ion from aqueous solution. The influence of pH, sorption time and Zn (II) ion initial concentration were examined. The results showed that equilibrium adsorption was obtained after 60 minutes with 240 rpm of shaking speed at pH = 4.0. The experimental data were analyzed using five non-linear isotherm models: Langmuir, Freundlich, Sips, Tempkin and Dubinin – Radushkevich. The adsorption capacity (qm) from the Langmuir isotherm model for Zn (II) is founded as 55.23 mg/g. The heat of sorption process and the mean free energy were estimated from Temkin and Dubinin – Redushkevich isotherm models to be less than 8 kj/mol which vividly proved that the adsorption experiment followed a physical process. Kinetic studies have shown that although the adsorption data partially followed pseudo-first-order and pseudo-second-order equation for different time, it was well expressed by pseudo-second-order model.

Manganese dioxide nanomaterials have wide applications in many areas from catalysis and Li–ion batteries to gas sensing. Understanding the crystallization pathways, morphologies, and formation of defects in their structure is particularly important but still a challenging issue. Herein, we employed an arsenal of X-ray diffraction (XRD), scanning electron microscopy (SEM), neutron diffraction, positron annihilation spectroscopies, and ab initiocalculations to investigate the evolution of the morphology and structure of α-MnO2nanomaterials prepared via reduction of KMnO4solution with C2H5OH prior to being annealed in air at 200–600 °C. We explored a novel evolution that α-MnO2nucleation can be formed even at room temperature and gradually developed to α-MnO2nanorods at above 500 °C. We also found the existence of H+or K+ions in the [1 × 1] tunnels of α-MnO2and observed the simultaneous presence of Mn and O vacancies in α-MnO2crystals at low temperatures. Increasing the temperature removed these O vacancies, leaving only the Mn vacancies in the samples.

α-MnO2 nanostructure was successfully synthesized via hydrothermal treatment of a precursor γ-MnO2. Structure, morphology, and BET surface area were characterized using X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), and Brunauer-Emmett-Teller nitrogen adsorption (BET-N2 adsorption). Thermal analysis result showed that α-MnO2 nanorods were formed from γ-MnO2 at 600°C. In addition, Pb(II) and Fe(III) adsorptive properties were investigated in an optimal condition. Results showed that equilibrium adsorption was obtained after 60 minutes for Pb(II) at pH = 4.0 and 80 minutes for Fe(III) at pH = 3.5 with 240 rpm of shaking speed overall. Experimental data was analyzed using three models: Langmuir, Freundlich, and Sips. Adsorption capacities (qm) from the Langmuir isotherm models are 124.87 mg/g for Pb(II) and 30.83 mg/g for Fe(III). Along with the highest corelation coefficients, it is clear that the adsorption of Pb(II) and Fe(III) ions on α-MnO2 surface followed Sips model. Kinetic studies indicated that the uptake of Pb(II) and Fe(III) occurred in the pseudo-second-order model with two stages for Pb(II) and three stages for Fe(III).

Manganese dioxide ?-MnO2was synthesized via the reduction-oxidation reaction between KMnO4and C2H5OH at room temperature and characterized with x-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmet-Teller nitrogen adsorption (BET-N2adsorption). The results showed that ?-MnO2was about 10-18 nm in size and the BET surface area was about 65 m2g?1. The feasibility of ?-MnO2used as a low cost adsorbent for the adsorption of Pb(II), Co(II) and Cu(II) from aqueous solutions was explored. During the adsorption process, batch technique was used, and the effects of contact time and pH on adsorption efficiency under room temperature were studied. The adsorption data showed that the Freundlich, Langmuir and Redlich-Peterson isotherms are a good model for the sorption of Co(II) and Cu(II), while the Langmuir and Redlich-Peterson isotherms provide a reasonable fit to the experimental data for Pb(II). By using the Langmuir isotherm, the adsorption capacities for Pb(II), Co(II) and Cu(II) are found to be 200 mg g?1, 90.91 mg g?1and 83.33 mg g?1, respectively. The effectiveness of ?-MnO2in the sorption of the three metal ions from aqueous system has the order Pb(II) > Co(II) > Cu(II). Kinetic studies showed that a pseudo-second-order model was more suitable than the pseudo-first-order model. Also, the intra-particle diffusion models were used to ascertain the mechanism of the sorption process. It is concluded that ?-MnO2can be used as an effective adsorbent for removing Pb(II), Co(II) and Cu(II) from aqueous solutions.